source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1760

Last change on this file since 1760 was 1760, checked in by julian.reschke@…, 10 years ago

Note changes/introductions to IANA registries as changes from RFC 2616 (see #368)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 248.7 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
29  <!ENTITY header-content-encoding    "<xref target='Part2' x:rel='#header.content-encoding' xmlns:x=''/>">
30  <!ENTITY header-content-range   "<xref target='Part5' x:rel='#header.content-range' xmlns:x=''/>">
31  <!ENTITY header-content-type    "<xref target='Part2' x:rel='#header.content-type' xmlns:x=''/>">
32  <!ENTITY header-date            "<xref target='Part2' x:rel='' xmlns:x=''/>">
33  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
34  <!ENTITY header-expires         "<xref target='Part6' x:rel='#header.expires' xmlns:x=''/>">
35  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x=''/>">
36  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
37  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
38  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x=''/>">
39  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x=''/>">
40  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
41  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x=''/>">
42  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x=''/>">
43  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
44  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
45  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
46  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x=''/>">
47  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
48  <!ENTITY status-304             "<xref target='Part4' x:rel='#status.304' xmlns:x=''/>">
49  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x=''/>">
50  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
51  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x=''/>">
53<?rfc toc="yes" ?>
54<?rfc symrefs="yes" ?>
55<?rfc sortrefs="yes" ?>
56<?rfc compact="yes"?>
57<?rfc subcompact="no" ?>
58<?rfc linkmailto="no" ?>
59<?rfc editing="no" ?>
60<?rfc comments="yes"?>
61<?rfc inline="yes"?>
62<?rfc rfcedstyle="yes"?>
63<?rfc-ext allow-markup-in-artwork="yes" ?>
64<?rfc-ext include-references-in-index="yes" ?>
65<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
66     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
67     xmlns:x=''>
68<x:link rel="next" basename="p2-semantics"/>
69<x:feedback template="{docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
72  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
74  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
75    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
76    <address>
77      <postal>
78        <street>345 Park Ave</street>
79        <city>San Jose</city>
80        <region>CA</region>
81        <code>95110</code>
82        <country>USA</country>
83      </postal>
84      <email></email>
85      <uri></uri>
86    </address>
87  </author>
89  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
90    <organization abbrev="W3C">World Wide Web Consortium</organization>
91    <address>
92      <postal>
93        <street>W3C / ERCIM</street>
94        <street>2004, rte des Lucioles</street>
95        <city>Sophia-Antipolis</city>
96        <region>AM</region>
97        <code>06902</code>
98        <country>France</country>
99      </postal>
100      <email></email>
101      <uri></uri>
102    </address>
103  </author>
105  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
106    <organization abbrev="greenbytes">greenbytes GmbH</organization>
107    <address>
108      <postal>
109        <street>Hafenweg 16</street>
110        <city>Muenster</city><region>NW</region><code>48155</code>
111        <country>Germany</country>
112      </postal>
113      <email></email>
114      <uri></uri>
115    </address>
116  </author>
118  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
119  <workgroup>HTTPbis Working Group</workgroup>
123   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
124   distributed, collaborative, hypertext information systems. HTTP has been in
125   use by the World Wide Web global information initiative since 1990. This
126   document is Part 1 of the seven-part specification that defines the protocol
127   referred to as "HTTP/1.1" and, taken together, obsoletes
128   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
129   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
130   2068</xref>.
133   Part 1 provides an overview of HTTP and its associated terminology, defines
134   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
135   the generic message syntax and parsing requirements for HTTP message frames,
136   and describes general security concerns for implementations.
139   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
140   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
141   (on using CONNECT for TLS upgrades) and moves them to historic status.
145<note title="Editorial Note (To be removed by RFC Editor)">
146  <t>
147    Discussion of this draft ought to take place on the HTTPBIS working group
148    mailing list (, which is archived at
149    <eref target=""/>.
150  </t>
151  <t>
152    The current issues list is at
153    <eref target=""/> and related
154    documents (including fancy diffs) can be found at
155    <eref target=""/>.
156  </t>
157  <t>
158    The changes in this draft are summarized in <xref target="changes.since.19"/>.
159  </t>
163<section title="Introduction" anchor="introduction">
165   The Hypertext Transfer Protocol (HTTP) is an application-level
166   request/response protocol that uses extensible semantics and MIME-like
167   message payloads for flexible interaction with network-based hypertext
168   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
169   standard <xref target="RFC3986"/> to indicate the target resource
170   (<xref target="target-resource"/>) and relationships between resources.
171   Messages are passed in a format similar to that used by Internet mail
172   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
173   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
174   between HTTP and MIME messages).
177   HTTP is a generic interface protocol for information systems. It is
178   designed to hide the details of how a service is implemented by presenting
179   a uniform interface to clients that is independent of the types of
180   resources provided. Likewise, servers do not need to be aware of each
181   client's purpose: an HTTP request can be considered in isolation rather
182   than being associated with a specific type of client or a predetermined
183   sequence of application steps. The result is a protocol that can be used
184   effectively in many different contexts and for which implementations can
185   evolve independently over time.
188   HTTP is also designed for use as an intermediation protocol for translating
189   communication to and from non-HTTP information systems.
190   HTTP proxies and gateways can provide access to alternative information
191   services by translating their diverse protocols into a hypertext
192   format that can be viewed and manipulated by clients in the same way
193   as HTTP services.
196   One consequence of HTTP flexibility is that the protocol cannot be
197   defined in terms of what occurs behind the interface. Instead, we
198   are limited to defining the syntax of communication, the intent
199   of received communication, and the expected behavior of recipients.
200   If the communication is considered in isolation, then successful
201   actions ought to be reflected in corresponding changes to the
202   observable interface provided by servers. However, since multiple
203   clients might act in parallel and perhaps at cross-purposes, we
204   cannot require that such changes be observable beyond the scope
205   of a single response.
208   This document is Part 1 of the seven-part specification of HTTP,
209   defining the protocol referred to as "HTTP/1.1", obsoleting
210   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
211   Part 1 describes the architectural elements that are used or
212   referred to in HTTP, defines the "http" and "https" URI schemes,
213   describes overall network operation and connection management,
214   and defines HTTP message framing and forwarding requirements.
215   Our goal is to define all of the mechanisms necessary for HTTP message
216   handling that are independent of message semantics, thereby defining the
217   complete set of requirements for message parsers and
218   message-forwarding intermediaries.
221<section title="Requirement Notation" anchor="intro.requirements">
223   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
224   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
225   document are to be interpreted as described in <xref target="RFC2119"/>.
229<section title="Syntax Notation" anchor="notation">
230<iref primary="true" item="Grammar" subitem="ALPHA"/>
231<iref primary="true" item="Grammar" subitem="CR"/>
232<iref primary="true" item="Grammar" subitem="CRLF"/>
233<iref primary="true" item="Grammar" subitem="CTL"/>
234<iref primary="true" item="Grammar" subitem="DIGIT"/>
235<iref primary="true" item="Grammar" subitem="DQUOTE"/>
236<iref primary="true" item="Grammar" subitem="HEXDIG"/>
237<iref primary="true" item="Grammar" subitem="HTAB"/>
238<iref primary="true" item="Grammar" subitem="LF"/>
239<iref primary="true" item="Grammar" subitem="OCTET"/>
240<iref primary="true" item="Grammar" subitem="SP"/>
241<iref primary="true" item="Grammar" subitem="VCHAR"/>
243   This specification uses the Augmented Backus-Naur Form (ABNF) notation
244   of <xref target="RFC5234"/> with the list rule extension defined in
245   <xref target="abnf.extension"/>.  <xref target="collected.abnf"/> shows
246   the collected ABNF with the list rule expanded.
248<t anchor="core.rules">
249  <x:anchor-alias value="ALPHA"/>
250  <x:anchor-alias value="CTL"/>
251  <x:anchor-alias value="CR"/>
252  <x:anchor-alias value="CRLF"/>
253  <x:anchor-alias value="DIGIT"/>
254  <x:anchor-alias value="DQUOTE"/>
255  <x:anchor-alias value="HEXDIG"/>
256  <x:anchor-alias value="HTAB"/>
257  <x:anchor-alias value="LF"/>
258  <x:anchor-alias value="OCTET"/>
259  <x:anchor-alias value="SP"/>
260  <x:anchor-alias value="VCHAR"/>
261   The following core rules are included by
262   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
263   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
264   DIGIT (decimal 0-9), DQUOTE (double quote),
265   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
266   OCTET (any 8-bit sequence of data), SP (space), and
267   VCHAR (any visible <xref target="USASCII"/> character).
270   As a convention, ABNF rule names prefixed with "obs-" denote
271   "obsolete" grammar rules that appear for historical reasons.
276<section title="Architecture" anchor="architecture">
278   HTTP was created for the World Wide Web architecture
279   and has evolved over time to support the scalability needs of a worldwide
280   hypertext system. Much of that architecture is reflected in the terminology
281   and syntax productions used to define HTTP.
284<section title="Client/Server Messaging" anchor="operation">
285<iref primary="true" item="client"/>
286<iref primary="true" item="server"/>
287<iref primary="true" item="connection"/>
289   HTTP is a stateless request/response protocol that operates by exchanging
290   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
291   transport or session-layer
292   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
293   program that establishes a connection to a server for the purpose of
294   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
295   program that accepts connections in order to service HTTP requests by
296   sending HTTP responses.
298<iref primary="true" item="user agent"/>
299<iref primary="true" item="origin server"/>
300<iref primary="true" item="browser"/>
301<iref primary="true" item="spider"/>
302<iref primary="true" item="sender"/>
303<iref primary="true" item="recipient"/>
305   Note that the terms client and server refer only to the roles that
306   these programs perform for a particular connection.  The same program
307   might act as a client on some connections and a server on others.  We use
308   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
309   such as a WWW browser, editor, or spider (web-traversing robot), and
310   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
311   authoritative responses to a request.  For general requirements, we use
312   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
313   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
314   message.
317  <t>
318    &Note; The term 'user agent' covers both those situations where
319    there is a user (human) interacting with the software agent (and for which
320    user interface or interactive suggestions might be made, e.g., warning the
321    user or given the user an option in the case of security or privacy
322    options) and also those where the software agent can act autonomously.
323  </t>
326   Most HTTP communication consists of a retrieval request (GET) for
327   a representation of some resource identified by a URI.  In the
328   simplest case, this might be accomplished via a single bidirectional
329   connection (===) between the user agent (UA) and the origin server (O).
331<figure><artwork type="drawing">
332         request   &gt;
333    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
334                                &lt;   response
336<iref primary="true" item="message"/>
337<iref primary="true" item="request"/>
338<iref primary="true" item="response"/>
340   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
341   message, beginning with a request-line that includes a method, URI, and
342   protocol version (<xref target="request.line"/>),
343   followed by MIME-like header fields containing
344   request modifiers, client information, and representation metadata
345   (<xref target="header.fields"/>),
346   an empty line to indicate the end of the header section, and finally
347   a message body containing the payload body (if any,
348   <xref target="message.body"/>).
351   A server responds to the client's request by sending one or more HTTP
352   <x:dfn>response</x:dfn>
353   messages, each beginning with a status line that
354   includes the protocol version, a success or error code, and textual
355   reason phrase (<xref target="status.line"/>),
356   possibly followed by MIME-like header fields containing server
357   information, resource metadata, and representation metadata
358   (<xref target="header.fields"/>),
359   an empty line to indicate the end of the header section, and finally
360   a message body containing the payload body (if any,
361   <xref target="message.body"/>).
364   The following example illustrates a typical message exchange for a
365   GET request on the URI "":
368client request:
369</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
370GET /hello.txt HTTP/1.1
371User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
373Accept: */*
377server response:
378</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
379HTTP/1.1 200 OK
380Date: Mon, 27 Jul 2009 12:28:53 GMT
381Server: Apache
382Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
383ETag: "34aa387-d-1568eb00"
384Accept-Ranges: bytes
385Content-Length: <x:length-of target="exbody"/>
386Vary: Accept-Encoding
387Content-Type: text/plain
389<x:span anchor="exbody">Hello World!
393<section title="Connections and Transport Independence" anchor="transport-independence">
395   HTTP messaging is independent of the underlying transport or
396   session-layer connection protocol(s).  HTTP only presumes a reliable
397   transport with in-order delivery of requests and the corresponding
398   in-order delivery of responses.  The mapping of HTTP request and
399   response structures onto the data units of the underlying transport
400   protocol is outside the scope of this specification.
403   The specific connection protocols to be used for an interaction
404   are determined by client configuration and the target URI
405   (<xref target="target-resource"/>).
406   For example, the "http" URI scheme
407   (<xref target="http.uri"/>) indicates a default connection of TCP
408   over IP, with a default TCP port of 80, but the client might be
409   configured to use a proxy via some other connection port or protocol
410   instead of using the defaults.
413   A connection might be used for multiple HTTP request/response exchanges,
414   as defined in <xref target="persistent.connections"/>.
418<section title="Intermediaries" anchor="intermediaries">
419<iref primary="true" item="intermediary"/>
421   HTTP enables the use of intermediaries to satisfy requests through
422   a chain of connections.  There are three common forms of HTTP
423   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
424   a single intermediary might act as an origin server, proxy, gateway,
425   or tunnel, switching behavior based on the nature of each request.
427<figure><artwork type="drawing">
428         &gt;             &gt;             &gt;             &gt;
429    <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>
430               &lt;             &lt;             &lt;             &lt;
433   The figure above shows three intermediaries (A, B, and C) between the
434   user agent and origin server. A request or response message that
435   travels the whole chain will pass through four separate connections.
436   Some HTTP communication options
437   might apply only to the connection with the nearest, non-tunnel
438   neighbor, only to the end-points of the chain, or to all connections
439   along the chain. Although the diagram is linear, each participant might
440   be engaged in multiple, simultaneous communications. For example, B
441   might be receiving requests from many clients other than A, and/or
442   forwarding requests to servers other than C, at the same time that it
443   is handling A's request.
446<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
447<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
448   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
449   to describe various requirements in relation to the directional flow of a
450   message: all messages flow from upstream to downstream.
451   Likewise, we use the terms inbound and outbound to refer to
452   directions in relation to the request path:
453   "<x:dfn>inbound</x:dfn>" means toward the origin server and
454   "<x:dfn>outbound</x:dfn>" means toward the user agent.
456<t><iref primary="true" item="proxy"/>
457   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
458   client, usually via local configuration rules, to receive requests
459   for some type(s) of absolute URI and attempt to satisfy those
460   requests via translation through the HTTP interface.  Some translations
461   are minimal, such as for proxy requests for "http" URIs, whereas
462   other requests might require translation to and from entirely different
463   application-layer protocols. Proxies are often used to group an
464   organization's HTTP requests through a common intermediary for the
465   sake of security, annotation services, or shared caching.
468<iref primary="true" item="transforming proxy"/>
469<iref primary="true" item="non-transforming proxy"/>
470   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
471   or configured to modify request or response messages in a semantically
472   meaningful way (i.e., modifications, beyond those required by normal
473   HTTP processing, that change the message in a way that would be
474   significant to the original sender or potentially significant to
475   downstream recipients).  For example, a transforming proxy might be
476   acting as a shared annotation server (modifying responses to include
477   references to a local annotation database), a malware filter, a
478   format transcoder, or an intranet-to-Internet privacy filter.  Such
479   transformations are presumed to be desired by the client (or client
480   organization) that selected the proxy and are beyond the scope of
481   this specification.  However, when a proxy is not intended to transform
482   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
483   requirements that preserve HTTP message semantics. See &status-203; and
484   &header-warning; for status and warning codes related to transformations.
486<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
487<iref primary="true" item="accelerator"/>
488   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
489   is a receiving agent that acts
490   as a layer above some other server(s) and translates the received
491   requests to the underlying server's protocol.  Gateways are often
492   used to encapsulate legacy or untrusted information services, to
493   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
494   enable partitioning or load-balancing of HTTP services across
495   multiple machines.
498   A gateway behaves as an origin server on its outbound connection and
499   as a user agent on its inbound connection.
500   All HTTP requirements applicable to an origin server
501   also apply to the outbound communication of a gateway.
502   A gateway communicates with inbound servers using any protocol that
503   it desires, including private extensions to HTTP that are outside
504   the scope of this specification.  However, an HTTP-to-HTTP gateway
505   that wishes to interoperate with third-party HTTP servers &MUST;
506   conform to HTTP user agent requirements on the gateway's inbound
507   connection and &MUST; implement the <x:ref>Connection</x:ref>
508   (<xref target="header.connection"/>) and <x:ref>Via</x:ref>
509   (<xref target="header.via"/>) header fields for both connections.
511<t><iref primary="true" item="tunnel"/>
512   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
513   without changing the messages. Once active, a tunnel is not
514   considered a party to the HTTP communication, though the tunnel might
515   have been initiated by an HTTP request. A tunnel ceases to exist when
516   both ends of the relayed connection are closed. Tunnels are used to
517   extend a virtual connection through an intermediary, such as when
518   transport-layer security is used to establish private communication
519   through a shared firewall proxy.
521<t><iref primary="true" item="interception proxy"/>
522<iref primary="true" item="transparent proxy"/>
523<iref primary="true" item="captive portal"/>
524   The above categories for intermediary only consider those acting as
525   participants in the HTTP communication.  There are also intermediaries
526   that can act on lower layers of the network protocol stack, filtering or
527   redirecting HTTP traffic without the knowledge or permission of message
528   senders. Network intermediaries often introduce security flaws or
529   interoperability problems by violating HTTP semantics.  For example, an
530   "<x:dfn>interception proxy</x:dfn>" <xref target="RFC3040"/> (also commonly
531   known as a "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/> or
532   "<x:dfn>captive portal</x:dfn>")
533   differs from an HTTP proxy because it is not selected by the client.
534   Instead, an interception proxy filters or redirects outgoing TCP port 80
535   packets (and occasionally other common port traffic).
536   Interception proxies are commonly found on public network access points,
537   as a means of enforcing account subscription prior to allowing use of
538   non-local Internet services, and within corporate firewalls to enforce
539   network usage policies.
540   They are indistinguishable from a man-in-the-middle attack.
543   HTTP is defined as a stateless protocol, meaning that each request message
544   can be understood in isolation.  Many implementations depend on HTTP's
545   stateless design in order to reuse proxied connections or dynamically
546   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
547   assume that two requests on the same connection are from the same user
548   agent unless the connection is secured and specific to that agent.
549   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
550   been known to violate this requirement, resulting in security and
551   interoperability problems.
555<section title="Caches" anchor="caches">
556<iref primary="true" item="cache"/>
558   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
559   subsystem that controls its message storage, retrieval, and deletion.
560   A cache stores cacheable responses in order to reduce the response
561   time and network bandwidth consumption on future, equivalent
562   requests. Any client or server &MAY; employ a cache, though a cache
563   cannot be used by a server while it is acting as a tunnel.
566   The effect of a cache is that the request/response chain is shortened
567   if one of the participants along the chain has a cached response
568   applicable to that request. The following illustrates the resulting
569   chain if B has a cached copy of an earlier response from O (via C)
570   for a request which has not been cached by UA or A.
572<figure><artwork type="drawing">
573            &gt;             &gt;
574       <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>
575                  &lt;             &lt;
577<t><iref primary="true" item="cacheable"/>
578   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
579   the response message for use in answering subsequent requests.
580   Even when a response is cacheable, there might be additional
581   constraints placed by the client or by the origin server on when
582   that cached response can be used for a particular request. HTTP
583   requirements for cache behavior and cacheable responses are
584   defined in &caching-overview;. 
587   There are a wide variety of architectures and configurations
588   of caches and proxies deployed across the World Wide Web and
589   inside large organizations. These systems include national hierarchies
590   of proxy caches to save transoceanic bandwidth, systems that
591   broadcast or multicast cache entries, organizations that distribute
592   subsets of cached data via optical media, and so on.
596<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
598   This specification targets conformance criteria according to the role of
599   a participant in HTTP communication.  Hence, HTTP requirements are placed
600   on senders, recipients, clients, servers, user agents, intermediaries,
601   origin servers, proxies, gateways, or caches, depending on what behavior
602   is being constrained by the requirement. The verb "generate" is used
603   instead of "send" where a requirement differentiates between creating a
604   protocol element and merely forwarding a received element downstream.
607   An implementation is considered conformant if it complies with all of the
608   requirements associated with the roles it partakes in HTTP.
611   A sender &MUST-NOT; generate protocol elements that do not match
612   the grammar defined by the ABNF rules for those protocol elements that
613   are applicable to the sender's role.
614   If a received protocol element is processed, the recipient &MUST; be able
615   to parse any value that would match the ABNF rules for that protocol
616   element, excluding only those rules not applicable to the recipient's role.
619   Unless noted otherwise, a recipient &MAY; attempt to recover a usable
620   protocol element from an invalid construct.  HTTP does not define
621   specific error handling mechanisms except when they have a direct impact
622   on security, since different applications of the protocol require
623   different error handling strategies.  For example, a Web browser might
624   wish to transparently recover from a response where the <x:ref>Location</x:ref>
625   header field doesn't parse according to the ABNF, whereas a systems control
626   client might consider any form of error recovery to be dangerous.
630<section title="Protocol Versioning" anchor="http.version">
631  <x:anchor-alias value="HTTP-version"/>
632  <x:anchor-alias value="HTTP-name"/>
634   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
635   versions of the protocol. This specification defines version "1.1".
636   The protocol version as a whole indicates the sender's conformance
637   with the set of requirements laid out in that version's corresponding
638   specification of HTTP.
641   The version of an HTTP message is indicated by an HTTP-version field
642   in the first line of the message. HTTP-version is case-sensitive.
644<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
645  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
646  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
649   The HTTP version number consists of two decimal digits separated by a "."
650   (period or decimal point).  The first digit ("major version") indicates the
651   HTTP messaging syntax, whereas the second digit ("minor version") indicates
652   the highest minor version to which the sender is
653   conformant and able to understand for future communication.  The minor
654   version advertises the sender's communication capabilities even when the
655   sender is only using a backwards-compatible subset of the protocol,
656   thereby letting the recipient know that more advanced features can
657   be used in response (by servers) or in future requests (by clients).
660   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
661   <xref target="RFC1945"/> or a recipient whose version is unknown,
662   the HTTP/1.1 message is constructed such that it can be interpreted
663   as a valid HTTP/1.0 message if all of the newer features are ignored.
664   This specification places recipient-version requirements on some
665   new features so that a conformant sender will only use compatible
666   features until it has determined, through configuration or the
667   receipt of a message, that the recipient supports HTTP/1.1.
670   The interpretation of a header field does not change between minor
671   versions of the same major HTTP version, though the default
672   behavior of a recipient in the absence of such a field can change.
673   Unless specified otherwise, header fields defined in HTTP/1.1 are
674   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
675   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
676   HTTP/1.x implementations whether or not they advertise conformance with
677   HTTP/1.1.
680   New header fields can be defined such that, when they are
681   understood by a recipient, they might override or enhance the
682   interpretation of previously defined header fields.  When an
683   implementation receives an unrecognized header field, the recipient
684   &MUST; ignore that header field for local processing regardless of
685   the message's HTTP version.  An unrecognized header field received
686   by a proxy &MUST; be forwarded downstream unless the header field's
687   field-name is listed in the message's <x:ref>Connection</x:ref> header field
688   (see <xref target="header.connection"/>).
689   These requirements allow HTTP's functionality to be enhanced without
690   requiring prior update of deployed intermediaries.
693   Intermediaries that process HTTP messages (i.e., all intermediaries
694   other than those acting as tunnels) &MUST; send their own HTTP-version
695   in forwarded messages.  In other words, they &MUST-NOT; blindly
696   forward the first line of an HTTP message without ensuring that the
697   protocol version in that message matches a version to which that
698   intermediary is conformant for both the receiving and
699   sending of messages.  Forwarding an HTTP message without rewriting
700   the HTTP-version might result in communication errors when downstream
701   recipients use the message sender's version to determine what features
702   are safe to use for later communication with that sender.
705   An HTTP client &SHOULD; send a request version equal to the highest
706   version to which the client is conformant and
707   whose major version is no higher than the highest version supported
708   by the server, if this is known.  An HTTP client &MUST-NOT; send a
709   version to which it is not conformant.
712   An HTTP client &MAY; send a lower request version if it is known that
713   the server incorrectly implements the HTTP specification, but only
714   after the client has attempted at least one normal request and determined
715   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
716   the server improperly handles higher request versions.
719   An HTTP server &SHOULD; send a response version equal to the highest
720   version to which the server is conformant and
721   whose major version is less than or equal to the one received in the
722   request.  An HTTP server &MUST-NOT; send a version to which it is not
723   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
724   Supported)</x:ref> response if it cannot send a response using the
725   major version used in the client's request.
728   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
729   if it is known or suspected that the client incorrectly implements the
730   HTTP specification and is incapable of correctly processing later
731   version responses, such as when a client fails to parse the version
732   number correctly or when an intermediary is known to blindly forward
733   the HTTP-version even when it doesn't conform to the given minor
734   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
735   performed unless triggered by specific client attributes, such as when
736   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
737   uniquely match the values sent by a client known to be in error.
740   The intention of HTTP's versioning design is that the major number
741   will only be incremented if an incompatible message syntax is
742   introduced, and that the minor number will only be incremented when
743   changes made to the protocol have the effect of adding to the message
744   semantics or implying additional capabilities of the sender.  However,
745   the minor version was not incremented for the changes introduced between
746   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
747   is specifically avoiding any such changes to the protocol.
751<section title="Uniform Resource Identifiers" anchor="uri">
752<iref primary="true" item="resource"/>
754   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
755   throughout HTTP as the means for identifying resources. URI references
756   are used to target requests, indicate redirects, and define relationships.
757   HTTP does not limit what a resource might be; it merely defines an interface
758   that can be used to interact with a resource via HTTP. More information on
759   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
761  <x:anchor-alias value="URI-reference"/>
762  <x:anchor-alias value="absolute-URI"/>
763  <x:anchor-alias value="relative-part"/>
764  <x:anchor-alias value="authority"/>
765  <x:anchor-alias value="path-abempty"/>
766  <x:anchor-alias value="path-absolute"/>
767  <x:anchor-alias value="port"/>
768  <x:anchor-alias value="query"/>
769  <x:anchor-alias value="uri-host"/>
770  <x:anchor-alias value="partial-URI"/>
772   This specification adopts the definitions of "URI-reference",
773   "absolute-URI", "relative-part", "port", "host",
774   "path-abempty", "path-absolute", "query", and "authority" from the
775   URI generic syntax <xref target="RFC3986"/>.
776   In addition, we define a partial-URI rule for protocol elements
777   that allow a relative URI but not a fragment.
779<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"/>
780  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
781  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
782  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
783  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
784  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
785  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
786  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
787  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
788  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
790  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
793   Each protocol element in HTTP that allows a URI reference will indicate
794   in its ABNF production whether the element allows any form of reference
795   (URI-reference), only a URI in absolute form (absolute-URI), only the
796   path and optional query components, or some combination of the above.
797   Unless otherwise indicated, URI references are parsed
798   relative to the effective request URI
799   (<xref target="effective.request.uri"/>).
802<section title="http URI scheme" anchor="http.uri">
803  <x:anchor-alias value="http-URI"/>
804  <iref item="http URI scheme" primary="true"/>
805  <iref item="URI scheme" subitem="http" primary="true"/>
807   The "http" URI scheme is hereby defined for the purpose of minting
808   identifiers according to their association with the hierarchical
809   namespace governed by a potential HTTP origin server listening for
810   TCP connections on a given port.
812<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
813  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
816   The HTTP origin server is identified by the generic syntax's
817   <x:ref>authority</x:ref> component, which includes a host identifier
818   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
819   The remainder of the URI, consisting of both the hierarchical path
820   component and optional query component, serves as an identifier for
821   a potential resource within that origin server's name space.
824   If the host identifier is provided as an IP literal or IPv4 address,
825   then the origin server is any listener on the indicated TCP port at
826   that IP address. If host is a registered name, then that name is
827   considered an indirect identifier and the recipient might use a name
828   resolution service, such as DNS, to find the address of a listener
829   for that host.
830   The host &MUST-NOT; be empty; if an "http" URI is received with an
831   empty host, then it &MUST; be rejected as invalid.
832   If the port subcomponent is empty or not given, then TCP port 80 is
833   assumed (the default reserved port for WWW services).
836   Regardless of the form of host identifier, access to that host is not
837   implied by the mere presence of its name or address. The host might or might
838   not exist and, even when it does exist, might or might not be running an
839   HTTP server or listening to the indicated port. The "http" URI scheme
840   makes use of the delegated nature of Internet names and addresses to
841   establish a naming authority (whatever entity has the ability to place
842   an HTTP server at that Internet name or address) and allows that
843   authority to determine which names are valid and how they might be used.
846   When an "http" URI is used within a context that calls for access to the
847   indicated resource, a client &MAY; attempt access by resolving
848   the host to an IP address, establishing a TCP connection to that address
849   on the indicated port, and sending an HTTP request message
850   (<xref target="http.message"/>) containing the URI's identifying data
851   (<xref target="message.routing"/>) to the server.
852   If the server responds to that request with a non-interim HTTP response
853   message, as described in &status-codes;, then that response
854   is considered an authoritative answer to the client's request.
857   Although HTTP is independent of the transport protocol, the "http"
858   scheme is specific to TCP-based services because the name delegation
859   process depends on TCP for establishing authority.
860   An HTTP service based on some other underlying connection protocol
861   would presumably be identified using a different URI scheme, just as
862   the "https" scheme (below) is used for servers that require an SSL/TLS
863   transport layer on a connection. Other protocols might also be used to
864   provide access to "http" identified resources &mdash; it is only the
865   authoritative interface used for mapping the namespace that is
866   specific to TCP.
869   The URI generic syntax for authority also includes a deprecated
870   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
871   for including user authentication information in the URI.  Some
872   implementations make use of the userinfo component for internal
873   configuration of authentication information, such as within command
874   invocation options, configuration files, or bookmark lists, even
875   though such usage might expose a user identifier or password.
876   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
877   delimiter) when transmitting an "http" URI in a message.  Recipients
878   of HTTP messages that contain a URI reference &SHOULD; parse for the
879   existence of userinfo and treat its presence as an error, likely
880   indicating that the deprecated subcomponent is being used to obscure
881   the authority for the sake of phishing attacks.
885<section title="https URI scheme" anchor="https.uri">
886   <x:anchor-alias value="https-URI"/>
887   <iref item="https URI scheme"/>
888   <iref item="URI scheme" subitem="https"/>
890   The "https" URI scheme is hereby defined for the purpose of minting
891   identifiers according to their association with the hierarchical
892   namespace governed by a potential HTTP origin server listening for
893   SSL/TLS-secured connections on a given TCP port.
896   All of the requirements listed above for the "http" scheme are also
897   requirements for the "https" scheme, except that a default TCP port
898   of 443 is assumed if the port subcomponent is empty or not given,
899   and the TCP connection &MUST; be secured for privacy through the
900   use of strong encryption prior to sending the first HTTP request.
902<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
903  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
906   Unlike the "http" scheme, responses to "https" identified requests
907   are never "public" and thus &MUST-NOT; be reused for shared caching.
908   They can, however, be reused in a private cache if the message is
909   cacheable by default in HTTP or specifically indicated as such by
910   the Cache-Control header field (&header-cache-control;).
913   Resources made available via the "https" scheme have no shared
914   identity with the "http" scheme even if their resource identifiers
915   indicate the same authority (the same host listening to the same
916   TCP port).  They are distinct name spaces and are considered to be
917   distinct origin servers.  However, an extension to HTTP that is
918   defined to apply to entire host domains, such as the Cookie protocol
919   <xref target="RFC6265"/>, can allow information
920   set by one service to impact communication with other services
921   within a matching group of host domains.
924   The process for authoritative access to an "https" identified
925   resource is defined in <xref target="RFC2818"/>.
929<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
931   Since the "http" and "https" schemes conform to the URI generic syntax,
932   such URIs are normalized and compared according to the algorithm defined
933   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
934   described above for each scheme.
937   If the port is equal to the default port for a scheme, the normal
938   form is to elide the port subcomponent. Likewise, an empty path
939   component is equivalent to an absolute path of "/", so the normal
940   form is to provide a path of "/" instead. The scheme and host
941   are case-insensitive and normally provided in lowercase; all
942   other components are compared in a case-sensitive manner.
943   Characters other than those in the "reserved" set are equivalent
944   to their percent-encoded octets (see <xref target="RFC3986"
945   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
948   For example, the following three URIs are equivalent:
950<figure><artwork type="example">
959<section title="Message Format" anchor="http.message">
960<x:anchor-alias value="generic-message"/>
961<x:anchor-alias value="message.types"/>
962<x:anchor-alias value="HTTP-message"/>
963<x:anchor-alias value="start-line"/>
964<iref item="header section"/>
965<iref item="headers"/>
966<iref item="header field"/>
968   All HTTP/1.1 messages consist of a start-line followed by a sequence of
969   octets in a format similar to the Internet Message Format
970   <xref target="RFC5322"/>: zero or more header fields (collectively
971   referred to as the "headers" or the "header section"), an empty line
972   indicating the end of the header section, and an optional message body.
974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
975  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
976                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
977                   <x:ref>CRLF</x:ref>
978                   [ <x:ref>message-body</x:ref> ]
981   The normal procedure for parsing an HTTP message is to read the
982   start-line into a structure, read each header field into a hash
983   table by field name until the empty line, and then use the parsed
984   data to determine if a message body is expected.  If a message body
985   has been indicated, then it is read as a stream until an amount
986   of octets equal to the message body length is read or the connection
987   is closed.
990   Recipients &MUST; parse an HTTP message as a sequence of octets in an
991   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
992   Parsing an HTTP message as a stream of Unicode characters, without regard
993   for the specific encoding, creates security vulnerabilities due to the
994   varying ways that string processing libraries handle invalid multibyte
995   character sequences that contain the octet LF (%x0A).  String-based
996   parsers can only be safely used within protocol elements after the element
997   has been extracted from the message, such as within a header field-value
998   after message parsing has delineated the individual fields.
1001   An HTTP message can be parsed as a stream for incremental processing or
1002   forwarding downstream.  However, recipients cannot rely on incremental
1003   delivery of partial messages, since some implementations will buffer or
1004   delay message forwarding for the sake of network efficiency, security
1005   checks, or payload transformations.
1008<section title="Start Line" anchor="start.line">
1009  <x:anchor-alias value="Start-Line"/>
1011   An HTTP message can either be a request from client to server or a
1012   response from server to client.  Syntactically, the two types of message
1013   differ only in the start-line, which is either a request-line (for requests)
1014   or a status-line (for responses), and in the algorithm for determining
1015   the length of the message body (<xref target="message.body"/>).
1016   In theory, a client could receive requests and a server could receive
1017   responses, distinguishing them by their different start-line formats,
1018   but in practice servers are implemented to only expect a request
1019   (a response is interpreted as an unknown or invalid request method)
1020   and clients are implemented to only expect a response.
1022<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1023  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1026   Implementations &MUST-NOT; send whitespace between the start-line and
1027   the first header field. The presence of such whitespace in a request
1028   might be an attempt to trick a server into ignoring that field or
1029   processing the line after it as a new request, either of which might
1030   result in a security vulnerability if other implementations within
1031   the request chain interpret the same message differently.
1032   Likewise, the presence of such whitespace in a response might be
1033   ignored by some clients or cause others to cease parsing.
1036<section title="Request Line" anchor="request.line">
1037  <x:anchor-alias value="Request"/>
1038  <x:anchor-alias value="request-line"/>
1040   A request-line begins with a method token, followed by a single
1041   space (SP), the request-target, another single space (SP), the
1042   protocol version, and ending with CRLF.
1044<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1045  <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>
1048   A server &MUST; be able to parse any received message that begins
1049   with a request-line and matches the ABNF rule for HTTP-message.
1051<iref primary="true" item="method"/>
1052<t anchor="method">
1053   The method token indicates the request method to be performed on the
1054   target resource. The request method is case-sensitive.
1056<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1057  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1060   The methods defined by this specification can be found in
1061   &methods;, along with information regarding the HTTP method registry
1062   and considerations for defining new methods.
1064<iref item="request-target"/>
1066   The request-target identifies the target resource upon which to apply
1067   the request, as defined in <xref target="request-target"/>.
1070   No whitespace is allowed inside the method, request-target, and
1071   protocol version.  Hence, recipients typically parse the request-line
1072   into its component parts by splitting on the SP characters.
1075   Unfortunately, some user agents fail to properly encode hypertext
1076   references that have embedded whitespace, sending the characters
1077   directly instead of properly percent-encoding the disallowed characters.
1078   Recipients of an invalid request-line &SHOULD; respond with either a
1079   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1080   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1081   attempt to autocorrect and then process the request without a redirect,
1082   since the invalid request-line might be deliberately crafted to bypass
1083   security filters along the request chain.
1086   HTTP does not place a pre-defined limit on the length of a request-line.
1087   A server that receives a method longer than any that it implements
1088   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1089   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1090   A server &MUST; be prepared to receive URIs of unbounded length and
1091   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1092   request-target would be longer than the server wishes to handle
1093   (see &status-414;).
1096   Various ad-hoc limitations on request-line length are found in practice.
1097   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1098   minimum, request-line lengths of up to 8000 octets.
1102<section title="Status Line" anchor="status.line">
1103  <x:anchor-alias value="response"/>
1104  <x:anchor-alias value="status-line"/>
1105  <x:anchor-alias value="status-code"/>
1106  <x:anchor-alias value="reason-phrase"/>
1108   The first line of a response message is the status-line, consisting
1109   of the protocol version, a space (SP), the status code, another space,
1110   a possibly-empty textual phrase describing the status code, and
1111   ending with CRLF.
1113<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1114  <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>
1117   A client &MUST; be able to parse any received message that begins
1118   with a status-line and matches the ABNF rule for HTTP-message.
1121   The status-code element is a 3-digit integer code describing the
1122   result of the server's attempt to understand and satisfy the client's
1123   corresponding request. The rest of the response message is to be
1124   interpreted in light of the semantics defined for that status code.
1125   See &status-codes; for information about the semantics of status codes,
1126   including the classes of status code (indicated by the first digit),
1127   the status codes defined by this specification, considerations for the
1128   definition of new status codes, and the IANA registry.
1130<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1131  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1134   The reason-phrase element exists for the sole purpose of providing a
1135   textual description associated with the numeric status code, mostly
1136   out of deference to earlier Internet application protocols that were more
1137   frequently used with interactive text clients. A client &SHOULD; ignore
1138   the reason-phrase content.
1140<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1141  <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> )
1146<section title="Header Fields" anchor="header.fields">
1147  <x:anchor-alias value="header-field"/>
1148  <x:anchor-alias value="field-content"/>
1149  <x:anchor-alias value="field-name"/>
1150  <x:anchor-alias value="field-value"/>
1151  <x:anchor-alias value="obs-fold"/>
1153   Each HTTP header field consists of a case-insensitive field name
1154   followed by a colon (":"), optional whitespace, and the field value.
1156<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"/>
1157  <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>
1158  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1159  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1160  <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> )
1161  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1162                 ; obsolete line folding
1163                 ; see <xref target="field.parsing"/>
1166   The field-name token labels the corresponding field-value as having the
1167   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1168   header field is defined in &header-date; as containing the origination
1169   timestamp for the message in which it appears.
1172   HTTP header fields are fully extensible: there is no limit on the
1173   introduction of new field names, each presumably defining new semantics,
1174   or on the number of header fields used in a given message.  Existing
1175   fields are defined in each part of this specification and in many other
1176   specifications outside the standards process.
1177   New header fields can be introduced without changing the protocol version
1178   if their defined semantics allow them to be safely ignored by recipients
1179   that do not recognize them.
1182   New HTTP header fields &SHOULD; be registered with IANA according
1183   to the procedures in &cons-new-header-fields;.
1184   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1185   field-name is listed in the <x:ref>Connection</x:ref> header field
1186   (<xref target="header.connection"/>) or the proxy is specifically
1187   configured to block or otherwise transform such fields.
1188   Unrecognized header fields &SHOULD; be ignored by other recipients.
1191   The order in which header fields with differing field names are
1192   received is not significant. However, it is "good practice" to send
1193   header fields that contain control data first, such as <x:ref>Host</x:ref>
1194   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1195   can decide when not to handle a message as early as possible.  A server
1196   &MUST; wait until the entire header section is received before interpreting
1197   a request message, since later header fields might include conditionals,
1198   authentication credentials, or deliberately misleading duplicate
1199   header fields that would impact request processing.
1202   Multiple header fields with the same field name &MUST-NOT; be
1203   sent in a message unless the entire field value for that
1204   header field is defined as a comma-separated list [i.e., #(values)].
1205   Multiple header fields with the same field name can be combined into
1206   one "field-name: field-value" pair, without changing the semantics of the
1207   message, by appending each subsequent field value to the combined
1208   field value in order, separated by a comma. The order in which
1209   header fields with the same field name are received is therefore
1210   significant to the interpretation of the combined field value;
1211   a proxy &MUST-NOT; change the order of these field values when
1212   forwarding a message.
1215  <t>
1216   &Note; The "Set-Cookie" header field as implemented in
1217   practice can occur multiple times, but does not use the list syntax, and
1218   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1219   for details.) Also note that the Set-Cookie2 header field specified in
1220   <xref target="RFC2965"/> does not share this problem.
1221  </t>
1224<section title="Whitespace" anchor="whitespace">
1225<t anchor="rule.LWS">
1226   This specification uses three rules to denote the use of linear
1227   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1228   BWS ("bad" whitespace).
1230<t anchor="rule.OWS">
1231   The OWS rule is used where zero or more linear whitespace octets might
1232   appear. OWS &SHOULD; either not be produced or be produced as a single
1233   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1234   be replaced with a single SP or transformed to all SP octets (each
1235   octet other than SP replaced with SP) before interpreting the field value
1236   or forwarding the message downstream.
1238<t anchor="rule.RWS">
1239   RWS is used when at least one linear whitespace octet is required to
1240   separate field tokens. RWS &SHOULD; be produced as a single SP.
1241   Multiple RWS octets that occur within field-content &SHOULD; either
1242   be replaced with a single SP or transformed to all SP octets before
1243   interpreting the field value or forwarding the message downstream.
1245<t anchor="rule.BWS">
1246   BWS is used where the grammar allows optional whitespace for historical
1247   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1248   recipients &MUST; accept such bad optional whitespace and remove it before
1249   interpreting the field value or forwarding the message downstream.
1251<t anchor="rule.whitespace">
1252  <x:anchor-alias value="BWS"/>
1253  <x:anchor-alias value="OWS"/>
1254  <x:anchor-alias value="RWS"/>
1256<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"/>
1257  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1258                 ; "optional" whitespace
1259  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1260                 ; "required" whitespace
1261  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1262                 ; "bad" whitespace
1266<section title="Field Parsing" anchor="field.parsing">
1268   No whitespace is allowed between the header field-name and colon.
1269   In the past, differences in the handling of such whitespace have led to
1270   security vulnerabilities in request routing and response handling.
1271   Any received request message that contains whitespace between a header
1272   field-name and colon &MUST; be rejected with a response code of 400
1273   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1274   message before forwarding the message downstream.
1277   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1278   preferred. The field value does not include any leading or trailing white
1279   space: OWS occurring before the first non-whitespace octet of the
1280   field value or after the last non-whitespace octet of the field value
1281   is ignored and &SHOULD; be removed before further processing (as this does
1282   not change the meaning of the header field).
1285   Historically, HTTP header field values could be extended over multiple
1286   lines by preceding each extra line with at least one space or horizontal
1287   tab (obs-fold). This specification deprecates such line
1288   folding except within the message/http media type
1289   (<xref target=""/>).
1290   HTTP senders &MUST-NOT; produce messages that include line folding
1291   (i.e., that contain any field-value that matches the obs-fold rule) unless
1292   the message is intended for packaging within the message/http media type.
1293   HTTP recipients &SHOULD; accept line folding and replace any embedded
1294   obs-fold whitespace with either a single SP or a matching number of SP
1295   octets (to avoid buffer copying) prior to interpreting the field value or
1296   forwarding the message downstream.
1299   Historically, HTTP has allowed field content with text in the ISO-8859-1
1300   <xref target="ISO-8859-1"/> character encoding and supported other
1301   character sets only through use of <xref target="RFC2047"/> encoding.
1302   In practice, most HTTP header field values use only a subset of the
1303   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1304   header fields &SHOULD; limit their field values to US-ASCII octets.
1305   Recipients &SHOULD; treat other (obs-text) octets in field content as
1306   opaque data.
1310<section title="Field Length" anchor="field.length">
1312   HTTP does not place a pre-defined limit on the length of header fields,
1313   either in isolation or as a set. A server &MUST; be prepared to receive
1314   request header fields of unbounded length and respond with a <x:ref>4xx
1315   (Client Error)</x:ref> status code if the received header field(s) would be
1316   longer than the server wishes to handle.
1319   A client that receives response headers that are longer than it wishes to
1320   handle can only treat it as a server error.
1323   Various ad-hoc limitations on header length are found in practice. It is
1324   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1325   combined header fields have 4000 or more octets.
1329<section title="Field value components" anchor="field.components">
1330<t anchor="rule.token.separators">
1331  <x:anchor-alias value="tchar"/>
1332  <x:anchor-alias value="token"/>
1333  <x:anchor-alias value="special"/>
1334  <x:anchor-alias value="word"/>
1335   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1336   separated by whitespace or special characters. These special characters
1337   &MUST; be in a quoted string to be used within a parameter value (as defined
1338   in <xref target="transfer.codings"/>).
1340<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"/>
1341  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1343  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1345  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1346 -->
1347  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1348                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1349                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1350                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1352  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1353                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1354                 / "]" / "?" / "=" / "{" / "}"
1356<t anchor="rule.quoted-string">
1357  <x:anchor-alias value="quoted-string"/>
1358  <x:anchor-alias value="qdtext"/>
1359  <x:anchor-alias value="obs-text"/>
1360   A string of text is parsed as a single word if it is quoted using
1361   double-quote marks.
1363<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"/>
1364  <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>
1365  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1366  <x:ref>obs-text</x:ref>       = %x80-FF
1368<t anchor="rule.quoted-pair">
1369  <x:anchor-alias value="quoted-pair"/>
1370   The backslash octet ("\") can be used as a single-octet
1371   quoting mechanism within quoted-string constructs:
1373<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1374  <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> )
1377   Recipients that process the value of the quoted-string &MUST; handle a
1378   quoted-pair as if it were replaced by the octet following the backslash.
1381   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1382   escaping (i.e., other than DQUOTE and the backslash octet).
1384<t anchor="rule.comment">
1385  <x:anchor-alias value="comment"/>
1386  <x:anchor-alias value="ctext"/>
1387   Comments can be included in some HTTP header fields by surrounding
1388   the comment text with parentheses. Comments are only allowed in
1389   fields containing "comment" as part of their field value definition.
1391<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1392  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1393  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1395<t anchor="rule.quoted-cpair">
1396  <x:anchor-alias value="quoted-cpair"/>
1397   The backslash octet ("\") can be used as a single-octet
1398   quoting mechanism within comment constructs:
1400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1401  <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> )
1404   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1405   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1409<section title="ABNF list extension: #rule" anchor="abnf.extension">
1411  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1412  improve readability in the definitions of some header field values.
1415  A construct "#" is defined, similar to "*", for defining comma-delimited
1416  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1417  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1418  comma (",") and optional whitespace (OWS).   
1421  Thus,
1422</preamble><artwork type="example">
1423  1#element =&gt; element *( OWS "," OWS element )
1426  and:
1427</preamble><artwork type="example">
1428  #element =&gt; [ 1#element ]
1431  and for n &gt;= 1 and m &gt; 1:
1432</preamble><artwork type="example">
1433  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1436  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1437  list elements. In other words, consumers would follow the list productions:
1439<figure><artwork type="example">
1440  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1442  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1445  Note that empty elements do not contribute to the count of elements present,
1446  though.
1449  For example, given these ABNF productions:
1451<figure><artwork type="example">
1452  example-list      = 1#example-list-elmt
1453  example-list-elmt = token ; see <xref target="field.components"/>
1456  Then these are valid values for example-list (not including the double
1457  quotes, which are present for delimitation only):
1459<figure><artwork type="example">
1460  "foo,bar"
1461  "foo ,bar,"
1462  "foo , ,bar,charlie   "
1465  But these values would be invalid, as at least one non-empty element is
1466  required:
1468<figure><artwork type="example">
1469  ""
1470  ","
1471  ",   ,"
1474  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1475  expanded as explained above.
1480<section title="Message Body" anchor="message.body">
1481  <x:anchor-alias value="message-body"/>
1483   The message body (if any) of an HTTP message is used to carry the
1484   payload body of that request or response.  The message body is
1485   identical to the payload body unless a transfer coding has been
1486   applied, as described in <xref target="header.transfer-encoding"/>.
1488<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1489  <x:ref>message-body</x:ref> = *OCTET
1492   The rules for when a message body is allowed in a message differ for
1493   requests and responses.
1496   The presence of a message body in a request is signaled by a
1497   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1498   field. Request message framing is independent of method semantics,
1499   even if the method does not define any use for a message body.
1502   The presence of a message body in a response depends on both
1503   the request method to which it is responding and the response
1504   status code (<xref target="status.line"/>).
1505   Responses to the HEAD request method never include a message body
1506   because the associated response header fields (e.g.,
1507   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1508   indicate what their values would have been if the request method had been
1509   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1510   mode instead of having a message body.
1511   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1512   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1513   All other responses do include a message body, although the body
1514   &MAY; be of zero length.
1517<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1518  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1519  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1520  <x:anchor-alias value="Transfer-Encoding"/>
1522   When one or more transfer codings are applied to a payload body in order
1523   to form the message body, a Transfer-Encoding header field &MUST; be sent
1524   in the message and &MUST; contain the list of corresponding
1525   transfer-coding names in the same order that they were applied.
1526   Transfer codings are defined in <xref target="transfer.codings"/>.
1528<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1529  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1532   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1533   MIME, which was designed to enable safe transport of binary data over a
1534   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1535   However, safe transport has a different focus for an 8bit-clean transfer
1536   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1537   accurately delimit a dynamically generated payload and to distinguish
1538   payload encodings that are only applied for transport efficiency or
1539   security from those that are characteristics of the target resource.
1542   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1543   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1544   crucial role in delimiting messages when the payload body size is not
1545   known in advance.
1546   When the "chunked" transfer-coding is used, it &MUST; be the last
1547   transfer-coding applied to form the message body and &MUST-NOT;
1548   be applied more than once in a message body.
1549   If any transfer-coding is applied to a request payload body,
1550   the final transfer-coding applied &MUST; be "chunked".
1551   If any transfer-coding is applied to a response payload body, then either
1552   the final transfer-coding applied &MUST; be "chunked" or
1553   the message &MUST; be terminated by closing the connection.
1556   For example,
1557</preamble><artwork type="example">
1558  Transfer-Encoding: gzip, chunked
1560   indicates that the payload body has been compressed using the gzip
1561   coding and then chunked using the chunked coding while forming the
1562   message body.
1565   If more than one Transfer-Encoding header field is present in a message,
1566   the multiple field-values &MUST; be combined into one field-value,
1567   according to the algorithm defined in <xref target="header.fields"/>,
1568   before determining the message body length.
1571   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1572   Transfer-Encoding is a property of the message, not of the payload, and thus
1573   &MAY; be added or removed by any implementation along the request/response
1574   chain. Additional information about the encoding parameters &MAY; be
1575   provided by other header fields not defined by this specification.
1578   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1579   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1580   neither of which includes a message body,
1581   to indicate that the origin server would have applied a transfer coding
1582   to the message body if the request had been an unconditional GET.
1583   This indication is not required, however, because any recipient on
1584   the response chain (including the origin server) can remove transfer
1585   codings when they are not needed.
1588   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1589   implementations advertising only HTTP/1.0 support will not understand
1590   how to process a transfer-encoded payload.
1591   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1592   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1593   might be in the form of specific user configuration or by remembering the
1594   version of a prior received response.
1595   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1596   the corresponding request indicates HTTP/1.1 (or later).
1599   A server that receives a request message with a transfer-coding it does
1600   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1601   close the connection.
1605<section title="Content-Length" anchor="header.content-length">
1606  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1607  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1608  <x:anchor-alias value="Content-Length"/>
1610   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1611   and the payload body length can be determined prior to being transferred, a
1612   Content-Length header field &SHOULD; be sent to indicate the length of the
1613   payload body that is either present as the message body, for requests
1614   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1615   would have been present had the request been an unconditional GET.  The
1616   length is expressed as a decimal number of octets.
1618<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1619  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1622   An example is
1624<figure><artwork type="example">
1625  Content-Length: 3495
1628   In the case of a response to a HEAD request, Content-Length indicates
1629   the size of the payload body (without any potential transfer-coding)
1630   that would have been sent had the request been a GET.
1631   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1632   to a GET request, Content-Length indicates the size of the payload body (without
1633   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1634   response.
1637   HTTP's use of Content-Length is significantly different from how it is
1638   used in MIME, where it is an optional field used only within the
1639   "message/external-body" media-type.
1642   Any Content-Length field value greater than or equal to zero is valid.
1643   Since there is no predefined limit to the length of an HTTP payload,
1644   recipients &SHOULD; anticipate potentially large decimal numerals and
1645   prevent parsing errors due to integer conversion overflows
1646   (<xref target="attack.protocol.element.size.overflows"/>).
1649   If a message is received that has multiple Content-Length header fields
1650   (<xref target="header.content-length"/>) with field-values consisting
1651   of the same decimal value, or a single Content-Length header field with
1652   a field value containing a list of identical decimal values (e.g.,
1653   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1654   header fields have been generated or combined by an upstream message
1655   processor, then the recipient &MUST; either reject the message as invalid
1656   or replace the duplicated field-values with a single valid Content-Length
1657   field containing that decimal value prior to determining the message body
1658   length.
1662<section title="Message Body Length" anchor="message.body.length">
1664   The length of a message body is determined by one of the following
1665   (in order of precedence):
1668  <list style="numbers">
1669    <x:lt><t>
1670     Any response to a HEAD request and any response with a
1671     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1672     <x:ref>304 (Not Modified)</x:ref> status code is always
1673     terminated by the first empty line after the header fields, regardless of
1674     the header fields present in the message, and thus cannot contain a
1675     message body.
1676    </t></x:lt>
1677    <x:lt><t>
1678     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1679     connection will become a tunnel immediately after the empty line that
1680     concludes the header fields.  A client &MUST; ignore any
1681     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1682     fields received in such a message.
1683    </t></x:lt>
1684    <x:lt><t>
1685     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1686     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1687     is the final encoding, the message body length is determined by reading
1688     and decoding the chunked data until the transfer-coding indicates the
1689     data is complete.
1690    </t>
1691    <t>
1692     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1693     response and the "chunked" transfer-coding is not the final encoding, the
1694     message body length is determined by reading the connection until it is
1695     closed by the server.
1696     If a Transfer-Encoding header field is present in a request and the
1697     "chunked" transfer-coding is not the final encoding, the message body
1698     length cannot be determined reliably; the server &MUST; respond with
1699     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1700    </t>
1701    <t>
1702     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1703     and a <x:ref>Content-Length</x:ref> header field, the
1704     Transfer-Encoding overrides the Content-Length.
1705     Such a message might indicate an attempt to perform request or response
1706     smuggling (bypass of security-related checks on message routing or content)
1707     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1708     be removed, prior to forwarding the message downstream, or replaced with
1709     the real message body length after the transfer-coding is decoded.
1710    </t></x:lt>
1711    <x:lt><t>
1712     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1713     either multiple <x:ref>Content-Length</x:ref> header fields having
1714     differing field-values or a single Content-Length header field having an
1715     invalid value, then the message framing is invalid and &MUST; be treated
1716     as an error to prevent request or response smuggling.
1717     If this is a request message, the server &MUST; respond with
1718     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1719     If this is a response message received by a proxy, the proxy
1720     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1721     status code as its downstream response, and then close the connection.
1722     If this is a response message received by a user-agent, it &MUST; be
1723     treated as an error by discarding the message and closing the connection.
1724    </t></x:lt>
1725    <x:lt><t>
1726     If a valid <x:ref>Content-Length</x:ref> header field is present without
1727     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1728     message body length in octets.  If the actual number of octets sent in
1729     the message is less than the indicated Content-Length, the recipient
1730     &MUST; consider the message to be incomplete and treat the connection
1731     as no longer usable.
1732     If the actual number of octets sent in the message is more than the indicated
1733     Content-Length, the recipient &MUST; only process the message body up to the
1734     field value's number of octets; the remainder of the message &MUST; either
1735     be discarded or treated as the next message in a pipeline.  For the sake of
1736     robustness, a user-agent &MAY; attempt to detect and correct such an error
1737     in message framing if it is parsing the response to the last request on
1738     a connection and the connection has been closed by the server.
1739    </t></x:lt>
1740    <x:lt><t>
1741     If this is a request message and none of the above are true, then the
1742     message body length is zero (no message body is present).
1743    </t></x:lt>
1744    <x:lt><t>
1745     Otherwise, this is a response message without a declared message body
1746     length, so the message body length is determined by the number of octets
1747     received prior to the server closing the connection.
1748    </t></x:lt>
1749  </list>
1752   Since there is no way to distinguish a successfully completed,
1753   close-delimited message from a partially-received message interrupted
1754   by network failure, implementations &SHOULD; use encoding or
1755   length-delimited messages whenever possible.  The close-delimiting
1756   feature exists primarily for backwards compatibility with HTTP/1.0.
1759   A server &MAY; reject a request that contains a message body but
1760   not a <x:ref>Content-Length</x:ref> by responding with
1761   <x:ref>411 (Length Required)</x:ref>.
1764   Unless a transfer-coding other than "chunked" has been applied,
1765   a client that sends a request containing a message body &SHOULD;
1766   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1767   length is known in advance, rather than the "chunked" encoding, since some
1768   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1769   status code even though they understand the chunked encoding.  This
1770   is typically because such services are implemented via a gateway that
1771   requires a content-length in advance of being called and the server
1772   is unable or unwilling to buffer the entire request before processing.
1775   A client that sends a request containing a message body &MUST; include a
1776   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1777   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1778   the form of specific user configuration or by remembering the version of a
1779   prior received response.
1784<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1786   Request messages that are prematurely terminated, possibly due to a
1787   cancelled connection or a server-imposed time-out exception, &MUST;
1788   result in closure of the connection; sending an HTTP/1.1 error response
1789   prior to closing the connection is &OPTIONAL;.
1792   Response messages that are prematurely terminated, usually by closure
1793   of the connection prior to receiving the expected number of octets or by
1794   failure to decode a transfer-encoded message body, &MUST; be recorded
1795   as incomplete.  A response that terminates in the middle of the header
1796   block (before the empty line is received) cannot be assumed to convey the
1797   full semantics of the response and &MUST; be treated as an error.
1800   A message body that uses the chunked transfer encoding is
1801   incomplete if the zero-sized chunk that terminates the encoding has not
1802   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1803   incomplete if the size of the message body received (in octets) is less than
1804   the value given by Content-Length.  A response that has neither chunked
1805   transfer encoding nor Content-Length is terminated by closure of the
1806   connection, and thus is considered complete regardless of the number of
1807   message body octets received, provided that the header block was received
1808   intact.
1811   A user agent &MUST-NOT; render an incomplete response message body as if
1812   it were complete (i.e., some indication needs to be given to the user that an
1813   error occurred).  Cache requirements for incomplete responses are defined
1814   in &cache-incomplete;.
1817   A server &MUST; read the entire request message body or close
1818   the connection after sending its response, since otherwise the
1819   remaining data on a persistent connection would be misinterpreted
1820   as the next request.  Likewise,
1821   a client &MUST; read the entire response message body if it intends
1822   to reuse the same connection for a subsequent request.  Pipelining
1823   multiple requests on a connection is described in <xref target="pipelining"/>.
1827<section title="Message Parsing Robustness" anchor="message.robustness">
1829   Older HTTP/1.0 client implementations might send an extra CRLF
1830   after a POST request as a lame workaround for some early server
1831   applications that failed to read message body content that was
1832   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1833   preface or follow a request with an extra CRLF.  If terminating
1834   the request message body with a line-ending is desired, then the
1835   client &MUST; include the terminating CRLF octets as part of the
1836   message body length.
1839   In the interest of robustness, servers &SHOULD; ignore at least one
1840   empty line received where a request-line is expected. In other words, if
1841   the server is reading the protocol stream at the beginning of a
1842   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1843   Likewise, although the line terminator for the start-line and header
1844   fields is the sequence CRLF, we recommend that recipients recognize a
1845   single LF as a line terminator and ignore any CR.
1848   When a server listening only for HTTP request messages, or processing
1849   what appears from the start-line to be an HTTP request message,
1850   receives a sequence of octets that does not match the HTTP-message
1851   grammar aside from the robustness exceptions listed above, the
1852   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1857<section title="Transfer Codings" anchor="transfer.codings">
1858  <x:anchor-alias value="transfer-coding"/>
1859  <x:anchor-alias value="transfer-extension"/>
1861   Transfer-coding values are used to indicate an encoding
1862   transformation that has been, can be, or might need to be applied to a
1863   payload body in order to ensure "safe transport" through the network.
1864   This differs from a content coding in that the transfer-coding is a
1865   property of the message rather than a property of the representation
1866   that is being transferred.
1868<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1869  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1870                     / "compress" ; <xref target="compress.coding"/>
1871                     / "deflate" ; <xref target="deflate.coding"/>
1872                     / "gzip" ; <xref target="gzip.coding"/>
1873                     / <x:ref>transfer-extension</x:ref>
1874  <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> )
1876<t anchor="rule.parameter">
1877  <x:anchor-alias value="attribute"/>
1878  <x:anchor-alias value="transfer-parameter"/>
1879  <x:anchor-alias value="value"/>
1880   Parameters are in the form of attribute/value pairs.
1882<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"/>
1883  <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>
1884  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1885  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1888   All transfer-coding values are case-insensitive.
1889   The HTTP Transfer Coding registry is defined in
1890   <xref target="transfer.coding.registry"/>.
1891   HTTP/1.1 uses transfer-coding values in the <x:ref>TE</x:ref> header field
1892   (<xref target="header.te"/>) and in the <x:ref>Transfer-Encoding</x:ref>
1893   header field (<xref target="header.transfer-encoding"/>).
1896<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1897  <iref item="chunked (Coding Format)"/>
1898  <iref item="Coding Format" subitem="chunked"/>
1899  <x:anchor-alias value="chunk"/>
1900  <x:anchor-alias value="chunked-body"/>
1901  <x:anchor-alias value="chunk-data"/>
1902  <x:anchor-alias value="chunk-ext"/>
1903  <x:anchor-alias value="chunk-ext-name"/>
1904  <x:anchor-alias value="chunk-ext-val"/>
1905  <x:anchor-alias value="chunk-size"/>
1906  <x:anchor-alias value="last-chunk"/>
1907  <x:anchor-alias value="trailer-part"/>
1908  <x:anchor-alias value="quoted-str-nf"/>
1909  <x:anchor-alias value="qdtext-nf"/>
1911   The chunked encoding modifies the body of a message in order to
1912   transfer it as a series of chunks, each with its own size indicator,
1913   followed by an &OPTIONAL; trailer containing header fields. This
1914   allows dynamically produced content to be transferred along with the
1915   information necessary for the recipient to verify that it has
1916   received the full message.
1918<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"/>
1919  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1920                   <x:ref>last-chunk</x:ref>
1921                   <x:ref>trailer-part</x:ref>
1922                   <x:ref>CRLF</x:ref>
1924  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1925                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1926  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1927  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1929  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1930  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1931  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1932  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1933  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1935  <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>
1936                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1937  <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>
1940   The chunk-size field is a string of hex digits indicating the size of
1941   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1942   zero, followed by the trailer, which is terminated by an empty line.
1945   The trailer allows the sender to include additional HTTP header
1946   fields at the end of the message. The <x:ref>Trailer</x:ref> header field
1947   can be used to indicate which header fields are included in a trailer (see
1948   <xref target="header.trailer"/>).
1951   A server using chunked transfer-coding in a response &MUST-NOT; use the
1952   trailer for any header fields unless at least one of the following is
1953   true:
1954  <list style="numbers">
1955    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1956    "trailers" is acceptable in the transfer-coding of the response, as
1957    described in <xref target="header.te"/>; or,</t>
1959    <t>the trailer fields consist entirely of optional metadata, and the
1960    recipient could use the message (in a manner acceptable to the server where
1961    the field originated) without receiving it. In other words, the server that
1962    generated the header (often but not always the origin server) is willing to
1963    accept the possibility that the trailer fields might be silently discarded
1964    along the path to the client.</t>
1965  </list>
1968   This requirement prevents an interoperability failure when the
1969   message is being received by an HTTP/1.1 (or later) proxy and
1970   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1971   conformance with the protocol would have necessitated a possibly
1972   infinite buffer on the proxy.
1975   A process for decoding the "chunked" transfer-coding
1976   can be represented in pseudo-code as:
1978<figure><artwork type="code">
1979  length := 0
1980  read chunk-size, chunk-ext (if any) and CRLF
1981  while (chunk-size &gt; 0) {
1982     read chunk-data and CRLF
1983     append chunk-data to decoded-body
1984     length := length + chunk-size
1985     read chunk-size and CRLF
1986  }
1987  read header-field
1988  while (header-field not empty) {
1989     append header-field to existing header fields
1990     read header-field
1991  }
1992  Content-Length := length
1993  Remove "chunked" from Transfer-Encoding
1996   All HTTP/1.1 applications &MUST; be able to receive and decode the
1997   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1998   they do not understand.
2001   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
2002   sent and definition of new chunk-extensions is discouraged.
2006<section title="Compression Codings" anchor="compression.codings">
2008   The codings defined below can be used to compress the payload of a
2009   message.
2012   &Note; Use of program names for the identification of encoding formats
2013   is not desirable and is discouraged for future encodings. Their
2014   use here is representative of historical practice, not good
2015   design.
2018   &Note; For compatibility with previous implementations of HTTP,
2019   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2020   equivalent to "gzip" and "compress" respectively.
2023<section title="Compress Coding" anchor="compress.coding">
2024<iref item="compress (Coding Format)"/>
2025<iref item="Coding Format" subitem="compress"/>
2027   The "compress" format is produced by the common UNIX file compression
2028   program "compress". This format is an adaptive Lempel-Ziv-Welch
2029   coding (LZW).
2033<section title="Deflate Coding" anchor="deflate.coding">
2034<iref item="deflate (Coding Format)"/>
2035<iref item="Coding Format" subitem="deflate"/>
2037   The "deflate" format is defined as the "deflate" compression mechanism
2038   (described in <xref target="RFC1951"/>) used inside the "zlib"
2039   data format (<xref target="RFC1950"/>).
2042  <t>
2043    &Note; Some incorrect implementations send the "deflate"
2044    compressed data without the zlib wrapper.
2045   </t>
2049<section title="Gzip Coding" anchor="gzip.coding">
2050<iref item="gzip (Coding Format)"/>
2051<iref item="Coding Format" subitem="gzip"/>
2053   The "gzip" format is produced by the file compression program
2054   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2055   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2061<section title="TE" anchor="header.te">
2062  <iref primary="true" item="TE header field" x:for-anchor=""/>
2063  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2064  <x:anchor-alias value="TE"/>
2065  <x:anchor-alias value="t-codings"/>
2066  <x:anchor-alias value="te-params"/>
2067  <x:anchor-alias value="te-ext"/>
2069   The "TE" header field indicates what extension transfer-codings
2070   the client is willing to accept in the response, and whether or not it is
2071   willing to accept trailer fields in a chunked transfer-coding.
2074   Its value consists of the keyword "trailers" and/or a comma-separated
2075   list of extension transfer-coding names with optional accept
2076   parameters (as described in <xref target="transfer.codings"/>).
2078<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"/>
2079  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2080  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2081  <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> )
2082  <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> ]
2085   The presence of the keyword "trailers" indicates that the client is
2086   willing to accept trailer fields in a chunked transfer-coding, as
2087   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2088   transfer-coding values even though it does not itself represent a
2089   transfer-coding.
2092   Examples of its use are:
2094<figure><artwork type="example">
2095  TE: deflate
2096  TE:
2097  TE: trailers, deflate;q=0.5
2100   The TE header field only applies to the immediate connection.
2101   Therefore, the keyword &MUST; be supplied within a <x:ref>Connection</x:ref>
2102   header field (<xref target="header.connection"/>) whenever TE is present in
2103   an HTTP/1.1 message.
2106   A server tests whether a transfer-coding is acceptable, according to
2107   a TE field, using these rules:
2108  <list style="numbers">
2109    <x:lt>
2110      <t>The "chunked" transfer-coding is always acceptable. If the
2111         keyword "trailers" is listed, the client indicates that it is
2112         willing to accept trailer fields in the chunked response on
2113         behalf of itself and any downstream clients. The implication is
2114         that, if given, the client is stating that either all
2115         downstream clients are willing to accept trailer fields in the
2116         forwarded response, or that it will attempt to buffer the
2117         response on behalf of downstream recipients.
2118      </t><t>
2119         &Note; HTTP/1.1 does not define any means to limit the size of a
2120         chunked response such that a client can be assured of buffering
2121         the entire response.</t>
2122    </x:lt>
2123    <x:lt>
2124      <t>If the transfer-coding being tested is one of the transfer-codings
2125         listed in the TE field, then it is acceptable unless it
2126         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2127         qvalue of 0 means "not acceptable".)</t>
2128    </x:lt>
2129    <x:lt>
2130      <t>If multiple transfer-codings are acceptable, then the
2131         acceptable transfer-coding with the highest non-zero qvalue is
2132         preferred.  The "chunked" transfer-coding always has a qvalue
2133         of 1.</t>
2134    </x:lt>
2135  </list>
2138   If the TE field-value is empty or if no TE field is present, the only
2139   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2140   always acceptable.
2143<section title="Quality Values" anchor="quality.values">
2144  <x:anchor-alias value="qvalue"/>
2146   Both transfer codings (<x:ref>TE</x:ref> request header field,
2147   <xref target="header.te"/>) and content negotiation (&content.negotiation;)
2148   use short "floating point" numbers to indicate the relative importance
2149   ("weight") of various negotiable parameters.  A weight is normalized to a
2150   real number in the range 0 through 1, where 0 is the minimum and 1 the
2151   maximum value. If a parameter has a quality value of 0, then content with
2152   this parameter is "not acceptable" for the client. HTTP/1.1
2153   applications &MUST-NOT; generate more than three digits after the
2154   decimal point. User configuration of these values &SHOULD; also be
2155   limited in this fashion.
2157<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2158  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2159                 / ( "1" [ "." 0*3("0") ] )
2162  <t>
2163     &Note; "Quality values" is a misnomer, since these values merely represent
2164     relative degradation in desired quality.
2165  </t>
2170<section title="Trailer" anchor="header.trailer">
2171  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2172  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2173  <x:anchor-alias value="Trailer"/>
2175   The "Trailer" header field indicates that the given set of
2176   header fields is present in the trailer of a message encoded with
2177   chunked transfer-coding.
2179<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2180  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2183   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2184   message using chunked transfer-coding with a non-empty trailer. Doing
2185   so allows the recipient to know which header fields to expect in the
2186   trailer.
2189   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2190   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2191   trailer fields in a "chunked" transfer-coding.
2194   Message header fields listed in the Trailer header field &MUST-NOT;
2195   include the following header fields:
2196  <list style="symbols">
2197    <t><x:ref>Transfer-Encoding</x:ref></t>
2198    <t><x:ref>Content-Length</x:ref></t>
2199    <t><x:ref>Trailer</x:ref></t>
2200  </list>
2205<section title="Message Routing" anchor="message.routing">
2207   HTTP request message routing is determined by each client based on the
2208   target resource, the client's proxy configuration, and
2209   establishment or reuse of an inbound connection.  The corresponding
2210   response routing follows the same connection chain back to the client.
2213<section title="Identifying a Target Resource" anchor="target-resource">
2214  <iref primary="true" item="target resource"/>
2215  <iref primary="true" item="target URI"/>
2217   HTTP is used in a wide variety of applications, ranging from
2218   general-purpose computers to home appliances.  In some cases,
2219   communication options are hard-coded in a client's configuration.
2220   However, most HTTP clients rely on the same resource identification
2221   mechanism and configuration techniques as general-purpose Web browsers.
2224   HTTP communication is initiated by a user agent for some purpose.
2225   The purpose is a combination of request semantics, which are defined in
2226   <xref target="Part2"/>, and a target resource upon which to apply those
2227   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2228   an identifier for the "target resource", which a user agent would resolve
2229   to its absolute form in order to obtain the "target URI".  The target URI
2230   excludes the reference's fragment identifier component, if any,
2231   since fragment identifiers are reserved for client-side processing
2232   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2235   HTTP intermediaries obtain the request semantics and target URI
2236   from the request-line of an incoming request message.
2240<section title="Connecting Inbound" anchor="connecting.inbound">
2242   Once the target URI is determined, a client needs to decide whether
2243   a network request is necessary to accomplish the desired semantics and,
2244   if so, where that request is to be directed.
2247   If the client has a response cache and the request semantics can be
2248   satisfied by a cache (<xref target="Part6"/>), then the request is
2249   usually directed to the cache first.
2252   If the request is not satisfied by a cache, then a typical client will
2253   check its configuration to determine whether a proxy is to be used to
2254   satisfy the request.  Proxy configuration is implementation-dependent,
2255   but is often based on URI prefix matching, selective authority matching,
2256   or both, and the proxy itself is usually identified by an "http" or
2257   "https" URI.  If a proxy is applicable, the client connects inbound by
2258   establishing (or reusing) a connection to that proxy.
2261   If no proxy is applicable, a typical client will invoke a handler routine,
2262   usually specific to the target URI's scheme, to connect directly
2263   to an authority for the target resource.  How that is accomplished is
2264   dependent on the target URI scheme and defined by its associated
2265   specification, similar to how this specification defines origin server
2266   access for resolution of the "http" (<xref target="http.uri"/>) and
2267   "https" (<xref target="https.uri"/>) schemes.
2271<section title="Request Target" anchor="request-target">
2273   Once an inbound connection is obtained
2274   (<xref target=""/>),
2275   the client sends an HTTP request message (<xref target="http.message"/>)
2276   with a request-target derived from the target URI.
2277   There are four distinct formats for the request-target, depending on both
2278   the method being requested and whether the request is to a proxy.
2280<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"/>
2281  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2282                 / <x:ref>absolute-form</x:ref>
2283                 / <x:ref>authority-form</x:ref>
2284                 / <x:ref>asterisk-form</x:ref>
2286  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2287  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2288  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2289  <x:ref>asterisk-form</x:ref>  = "*"
2291<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2292   The most common form of request-target is the origin-form.
2293   When making a request directly to an origin server, other than a CONNECT
2294   or server-wide OPTIONS request (as detailed below),
2295   a client &MUST; send only the absolute path and query components of
2296   the target URI as the request-target.
2297   If the target URI's path component is empty, then the client &MUST; send
2298   "/" as the path within the origin-form of request-target.
2299   A <x:ref>Host</x:ref> header field is also sent, as defined in
2300   <xref target=""/>, containing the target URI's
2301   authority component (excluding any userinfo).
2304   For example, a client wishing to retrieve a representation of the resource
2305   identified as
2307<figure><artwork x:indent-with="  " type="example">
2311   directly from the origin server would open (or reuse) a TCP connection
2312   to port 80 of the host "" and send the lines:
2314<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2315GET /where?q=now HTTP/1.1
2319   followed by the remainder of the request message.
2321<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2322   When making a request to a proxy, other than a CONNECT or server-wide
2323   OPTIONS request (as detailed below), a client &MUST; send the target URI
2324   in absolute-form as the request-target.
2325   The proxy is requested to either service that request from a valid cache,
2326   if possible, or make the same request on the client's behalf to either
2327   the next inbound proxy server or directly to the origin server indicated
2328   by the request-target.  Requirements on such "forwarding" of messages are
2329   defined in <xref target="intermediary.forwarding"/>.
2332   An example absolute-form of request-line would be:
2334<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2335GET HTTP/1.1
2338   To allow for transition to the absolute-form for all requests in some
2339   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2340   in requests, even though HTTP/1.1 clients will only send them in requests
2341   to proxies.
2343<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2344   The authority-form of request-target is only used for CONNECT requests
2345   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2346   one or more proxies, a client &MUST; send only the target URI's
2347   authority component (excluding any userinfo) as the request-target.
2348   For example,
2350<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2353<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2354   The asterisk-form of request-target is only used for a server-wide
2355   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2356   for the server as a whole, as opposed to a specific named resource of
2357   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2358   For example,
2360<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2361OPTIONS * HTTP/1.1
2364   If a proxy receives an OPTIONS request with an absolute-form of
2365   request-target in which the URI has an empty path and no query component,
2366   then the last proxy on the request chain &MUST; send a request-target
2367   of "*" when it forwards the request to the indicated origin server.
2370   For example, the request
2371</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2375  would be forwarded by the final proxy as
2376</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2377OPTIONS * HTTP/1.1
2381   after connecting to port 8001 of host "".
2386<section title="Host" anchor="">
2387  <iref primary="true" item="Host header field" x:for-anchor=""/>
2388  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2389  <x:anchor-alias value="Host"/>
2391   The "Host" header field in a request provides the host and port
2392   information from the target URI, enabling the origin
2393   server to distinguish among resources while servicing requests
2394   for multiple host names on a single IP address.  Since the Host
2395   field-value is critical information for handling a request, it
2396   &SHOULD; be sent as the first header field following the request-line.
2398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2399  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2402   A client &MUST; send a Host header field in all HTTP/1.1 request
2403   messages.  If the target URI includes an authority component, then
2404   the Host field-value &MUST; be identical to that authority component
2405   after excluding any userinfo (<xref target="http.uri"/>).
2406   If the authority component is missing or undefined for the target URI,
2407   then the Host header field &MUST; be sent with an empty field-value.
2410   For example, a GET request to the origin server for
2411   &lt;; would begin with:
2413<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2414GET /pub/WWW/ HTTP/1.1
2418   The Host header field &MUST; be sent in an HTTP/1.1 request even
2419   if the request-target is in the absolute-form, since this
2420   allows the Host information to be forwarded through ancient HTTP/1.0
2421   proxies that might not have implemented Host.
2424   When an HTTP/1.1 proxy receives a request with an absolute-form of
2425   request-target, the proxy &MUST; ignore the received
2426   Host header field (if any) and instead replace it with the host
2427   information of the request-target.  If the proxy forwards the request,
2428   it &MUST; generate a new Host field-value based on the received
2429   request-target rather than forward the received Host field-value.
2432   Since the Host header field acts as an application-level routing
2433   mechanism, it is a frequent target for malware seeking to poison
2434   a shared cache or redirect a request to an unintended server.
2435   An interception proxy is particularly vulnerable if it relies on
2436   the Host field-value for redirecting requests to internal
2437   servers, or for use as a cache key in a shared cache, without
2438   first verifying that the intercepted connection is targeting a
2439   valid IP address for that host.
2442   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2443   to any HTTP/1.1 request message that lacks a Host header field and
2444   to any request message that contains more than one Host header field
2445   or a Host header field with an invalid field-value.
2449<section title="Effective Request URI" anchor="effective.request.uri">
2450  <iref primary="true" item="effective request URI"/>
2452   A server that receives an HTTP request message &MUST; reconstruct
2453   the user agent's original target URI, based on the pieces of information
2454   learned from the request-target, <x:ref>Host</x:ref> header field, and
2455   connection context, in order to identify the intended target resource and
2456   properly service the request. The URI derived from this reconstruction
2457   process is referred to as the "effective request URI".
2460   For a user agent, the effective request URI is the target URI.
2463   If the request-target is in absolute-form, then the effective request URI
2464   is the same as the request-target.  Otherwise, the effective request URI
2465   is constructed as follows.
2468   If the request is received over an SSL/TLS-secured TCP connection,
2469   then the effective request URI's scheme is "https"; otherwise, the
2470   scheme is "http".
2473   If the request-target is in authority-form, then the effective
2474   request URI's authority component is the same as the request-target.
2475   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2476   non-empty field-value, then the authority component is the same as the
2477   Host field-value. Otherwise, the authority component is the concatenation of
2478   the default host name configured for the server, a colon (":"), and the
2479   connection's incoming TCP port number in decimal form.
2482   If the request-target is in authority-form or asterisk-form, then the
2483   effective request URI's combined path and query component is empty.
2484   Otherwise, the combined path and query component is the same as the
2485   request-target.
2488   The components of the effective request URI, once determined as above,
2489   can be combined into absolute-URI form by concatenating the scheme,
2490   "://", authority, and combined path and query component.
2494   Example 1: the following message received over an insecure TCP connection
2496<artwork type="example" x:indent-with="  ">
2497GET /pub/WWW/TheProject.html HTTP/1.1
2503  has an effective request URI of
2505<artwork type="example" x:indent-with="  ">
2511   Example 2: the following message received over an SSL/TLS-secured TCP
2512   connection
2514<artwork type="example" x:indent-with="  ">
2515OPTIONS * HTTP/1.1
2521  has an effective request URI of
2523<artwork type="example" x:indent-with="  ">
2528   An origin server that does not allow resources to differ by requested
2529   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2530   with a configured server name when constructing the effective request URI.
2533   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2534   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2535   something unique to a particular host) in order to guess the
2536   effective request URI's authority component.
2540<section title="Intermediary Forwarding" anchor="intermediary.forwarding">
2542   As described in <xref target="intermediaries"/>, intermediaries can serve
2543   a variety of roles in the processing of HTTP requests and responses.
2544   Some intermediaries are used to improve performance or availability.
2545   Others are used for access control or to filter content.
2546   Since an HTTP stream has characteristics similar to a pipe-and-filter
2547   architecture, there are no inherent limits to the extent an intermediary
2548   can enhance (or interfere) with either direction of the stream.
2551   In order to avoid request loops, a proxy that forwards requests to other
2552   proxies &MUST; be able to recognize and exclude all of its own server
2553   names, including any aliases, local variations, or literal IP addresses.
2556   If a proxy receives a request-target with a host name that is not a
2557   fully qualified domain name, it &MAY; add its domain to the host name
2558   it received when forwarding the request.  A proxy &MUST-NOT; change the
2559   host name if it is a fully qualified domain name.
2562   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2563   parts of the received request-target when forwarding it to the next inbound
2564   server, except as noted above to replace an empty path with "/" or "*".
2567   Intermediaries that forward a message &MUST; implement the
2568   <x:ref>Connection</x:ref> header field as specified in
2569   <xref target="header.connection"/>.
2572<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2574  <cref anchor="TODO-end-to-end" source="jre">
2575    Restored from <eref target=""/>.
2576    See also <eref target=""/>.
2577  </cref>
2580   For the purpose of defining the behavior of caches and non-caching
2581   proxies, we divide HTTP header fields into two categories:
2582  <list style="symbols">
2583      <t>End-to-end header fields, which are  transmitted to the ultimate
2584        recipient of a request or response. End-to-end header fields in
2585        responses &MUST; be stored as part of a cache entry and &MUST; be
2586        transmitted in any response formed from a cache entry.</t>
2588      <t>Hop-by-hop header fields, which are meaningful only for a single
2589        transport-level connection, and are not stored by caches or
2590        forwarded by proxies.</t>
2591  </list>
2594   The following HTTP/1.1 header fields are hop-by-hop header fields:
2595  <list style="symbols">
2596      <t><x:ref>Connection</x:ref></t>
2597      <t>Keep-Alive (<xref target="RFC2068" x:fmt="of" x:sec=""/>)</t>
2598      <t><x:ref>Proxy-Authenticate</x:ref> (&header-proxy-authenticate;)</t>
2599      <t><x:ref>Proxy-Authorization</x:ref> (&header-proxy-authorization;)</t>
2600      <t><x:ref>TE</x:ref></t>
2601      <t><x:ref>Trailer</x:ref></t>
2602      <t><x:ref>Transfer-Encoding</x:ref></t>
2603      <t><x:ref>Upgrade</x:ref></t>
2604  </list>
2607   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2610   Other hop-by-hop header fields &MUST; be listed in a
2611   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>).
2615<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2617  <cref anchor="TODO-non-mod-headers" source="jre">
2618    Restored from <eref target=""/>.
2619    See also <eref target=""/>.
2620  </cref>
2623   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2624   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2625   modify an end-to-end header field unless the definition of that header field requires
2626   or specifically allows that.
2629   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2630   request or response, and it &MUST-NOT; add any of these fields if not
2631   already present:
2632  <list style="symbols">
2633    <t>Allow</t>
2634    <t>Content-Location</t>
2635    <t>Content-MD5</t>
2636    <t>ETag</t>
2637    <t>Last-Modified</t>
2638    <t>Server</t>
2639  </list>
2642   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2643   response:
2644  <list style="symbols">
2645    <t><x:ref>Expires</x:ref> (&header-expires;)</t>
2646  </list>
2649   but it &MAY; add any of these fields if not already present. If an
2650   <x:ref>Expires</x:ref> header field is added, it &MUST; be given a
2651   field value identical to that of the <x:ref>Date</x:ref> header field in
2652   that response.
2655   A proxy &MUST-NOT; modify or add any of the following fields in a
2656   message that contains the no-transform cache-control directive, or in
2657   any request:
2658  <list style="symbols">
2659    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2660    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2661    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2662  </list>
2665   A transforming proxy &MAY; modify or add these fields to a message
2666   that does not include no-transform, but if it does so, it &MUST; add a
2667   Warning 214 (Transformation applied) if one does not already appear
2668   in the message (see &header-warning;).
2671  <t>
2672    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2673    cause authentication failures if stronger authentication
2674    mechanisms are introduced in later versions of HTTP. Such
2675    authentication mechanisms &MAY; rely on the values of header fields
2676    not listed here.
2677  </t>
2680   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2681   though it &MAY; change the message body through application or removal
2682   of a transfer-coding (<xref target="transfer.codings"/>).
2688<section title="Associating a Response to a Request" anchor="">
2690   HTTP does not include a request identifier for associating a given
2691   request message with its corresponding one or more response messages.
2692   Hence, it relies on the order of response arrival to correspond exactly
2693   to the order in which requests are made on the same connection.
2694   More than one response message per request only occurs when one or more
2695   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2696   to the same request.
2699   A client that uses persistent connections and sends more than one request
2700   per connection &MUST; maintain a list of outstanding requests in the
2701   order sent on that connection and &MUST; associate each received response
2702   message to the highest ordered request that has not yet received a final
2703   (non-<x:ref>1xx</x:ref>) response.
2708<section title="Connection Management" anchor="">
2710<section title="Connection" anchor="header.connection">
2711  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2712  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2713  <x:anchor-alias value="Connection"/>
2714  <x:anchor-alias value="connection-option"/>
2716   The "Connection" header field allows the sender to specify
2717   options that are desired only for that particular connection.
2718   Such connection options &MUST; be removed or replaced before the
2719   message can be forwarded downstream by a proxy or gateway.
2720   This mechanism also allows the sender to indicate which HTTP
2721   header fields used in the message are only intended for the
2722   immediate recipient ("hop-by-hop"), as opposed to all recipients
2723   on the chain ("end-to-end"), enabling the message to be
2724   self-descriptive and allowing future connection-specific extensions
2725   to be deployed in HTTP without fear that they will be blindly
2726   forwarded by previously deployed intermediaries.
2729   The Connection header field's value has the following grammar:
2731<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2732  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2733  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2736   Connection options are compared case-insensitively.
2739   A proxy or gateway &MUST; parse a received Connection
2740   header field before a message is forwarded and, for each
2741   connection-option in this field, remove any header field(s) from
2742   the message with the same name as the connection-option, and then
2743   remove the Connection header field itself or replace it with the
2744   sender's own connection options for the forwarded message.
2747   A sender &MUST-NOT; include field-names in the Connection header
2748   field-value for fields that are defined as expressing constraints
2749   for all recipients in the request or response chain, such as the
2750   Cache-Control header field (&header-cache-control;).
2753   The connection options do not have to correspond to a header field
2754   present in the message, since a connection-specific header field
2755   might not be needed if there are no parameters associated with that
2756   connection option.  Recipients that trigger certain connection
2757   behavior based on the presence of connection options &MUST; do so
2758   based on the presence of the connection-option rather than only the
2759   presence of the optional header field.  In other words, if the
2760   connection option is received as a header field but not indicated
2761   within the Connection field-value, then the recipient &MUST; ignore
2762   the connection-specific header field because it has likely been
2763   forwarded by an intermediary that is only partially conformant.
2766   When defining new connection options, specifications ought to
2767   carefully consider existing deployed header fields and ensure
2768   that the new connection option does not share the same name as
2769   an unrelated header field that might already be deployed.
2770   Defining a new connection option essentially reserves that potential
2771   field-name for carrying additional information related to the
2772   connection option, since it would be unwise for senders to use
2773   that field-name for anything else.
2776   HTTP/1.1 defines the "close" connection option for the sender to
2777   signal that the connection will be closed after completion of the
2778   response. For example,
2780<figure><artwork type="example">
2781  Connection: close
2784   in either the request or the response header fields indicates that
2785   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2786   after the current request/response is complete.
2789   An HTTP/1.1 client that does not support persistent connections &MUST;
2790   include the "close" connection option in every request message.
2793   An HTTP/1.1 server that does not support persistent connections &MUST;
2794   include the "close" connection option in every response message that
2795   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2799<section title="Via" anchor="header.via">
2800  <iref primary="true" item="Via header field" x:for-anchor=""/>
2801  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2802  <x:anchor-alias value="pseudonym"/>
2803  <x:anchor-alias value="received-by"/>
2804  <x:anchor-alias value="received-protocol"/>
2805  <x:anchor-alias value="Via"/>
2807   The "Via" header field &MUST; be sent by a proxy or gateway to
2808   indicate the intermediate protocols and recipients between the user
2809   agent and the server on requests, and between the origin server and
2810   the client on responses. It is analogous to the "Received" field
2811   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2812   and is intended to be used for tracking message forwards,
2813   avoiding request loops, and identifying the protocol capabilities of
2814   all senders along the request/response chain.
2816<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"/>
2817  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2818                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2819  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2820  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2821  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2824   The received-protocol indicates the protocol version of the message
2825   received by the server or client along each segment of the
2826   request/response chain. The received-protocol version is appended to
2827   the Via field value when the message is forwarded so that information
2828   about the protocol capabilities of upstream applications remains
2829   visible to all recipients.
2832   The protocol-name is excluded if and only if it would be "HTTP". The
2833   received-by field is normally the host and optional port number of a
2834   recipient server or client that subsequently forwarded the message.
2835   However, if the real host is considered to be sensitive information,
2836   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2837   be assumed to be the default port of the received-protocol.
2840   Multiple Via field values represent each proxy or gateway that has
2841   forwarded the message. Each recipient &MUST; append its information
2842   such that the end result is ordered according to the sequence of
2843   forwarding applications.
2846   Comments &MAY; be used in the Via header field to identify the software
2847   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2848   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2849   are optional and &MAY; be removed by any recipient prior to forwarding the
2850   message.
2853   For example, a request message could be sent from an HTTP/1.0 user
2854   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2855   forward the request to a public proxy at, which completes
2856   the request by forwarding it to the origin server at
2857   The request received by would then have the following
2858   Via header field:
2860<figure><artwork type="example">
2861  Via: 1.0 fred, 1.1 (Apache/1.1)
2864   A proxy or gateway used as a portal through a network firewall
2865   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2866   region unless it is explicitly enabled to do so. If not enabled, the
2867   received-by host of any host behind the firewall &SHOULD; be replaced
2868   by an appropriate pseudonym for that host.
2871   For organizations that have strong privacy requirements for hiding
2872   internal structures, a proxy or gateway &MAY; combine an ordered
2873   subsequence of Via header field entries with identical received-protocol
2874   values into a single such entry. For example,
2876<figure><artwork type="example">
2877  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2880  could be collapsed to
2882<figure><artwork type="example">
2883  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2886   Senders &SHOULD-NOT; combine multiple entries unless they are all
2887   under the same organizational control and the hosts have already been
2888   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2889   have different received-protocol values.
2893<section title="Persistent Connections" anchor="persistent.connections">
2895<section title="Purpose" anchor="persistent.purpose">
2897   Prior to persistent connections, a separate TCP connection was
2898   established for each request, increasing the load on HTTP servers
2899   and causing congestion on the Internet. The use of inline images and
2900   other associated data often requires a client to make multiple
2901   requests of the same server in a short amount of time. Analysis of
2902   these performance problems and results from a prototype
2903   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2904   measurements of actual HTTP/1.1 implementations show good
2905   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2906   T/TCP <xref target="Tou1998"/>.
2909   Persistent HTTP connections have a number of advantages:
2910  <list style="symbols">
2911      <t>
2912        By opening and closing fewer TCP connections, CPU time is saved
2913        in routers and hosts (clients, servers, proxies, gateways,
2914        tunnels, or caches), and memory used for TCP protocol control
2915        blocks can be saved in hosts.
2916      </t>
2917      <t>
2918        HTTP requests and responses can be pipelined on a connection.
2919        Pipelining allows a client to make multiple requests without
2920        waiting for each response, allowing a single TCP connection to
2921        be used much more efficiently, with much lower elapsed time.
2922      </t>
2923      <t>
2924        Network congestion is reduced by reducing the number of packets
2925        caused by TCP opens, and by allowing TCP sufficient time to
2926        determine the congestion state of the network.
2927      </t>
2928      <t>
2929        Latency on subsequent requests is reduced since there is no time
2930        spent in TCP's connection opening handshake.
2931      </t>
2932      <t>
2933        HTTP can evolve more gracefully, since errors can be reported
2934        without the penalty of closing the TCP connection. Clients using
2935        future versions of HTTP might optimistically try a new feature,
2936        but if communicating with an older server, retry with old
2937        semantics after an error is reported.
2938      </t>
2939    </list>
2942   HTTP implementations &SHOULD; implement persistent connections.
2946<section title="Overall Operation" anchor="persistent.overall">
2948   A significant difference between HTTP/1.1 and earlier versions of
2949   HTTP is that persistent connections are the default behavior of any
2950   HTTP connection. That is, unless otherwise indicated, the client
2951   &SHOULD; assume that the server will maintain a persistent connection,
2952   even after error responses from the server.
2955   Persistent connections provide a mechanism by which a client and a
2956   server can signal the close of a TCP connection. This signaling takes
2957   place using the <x:ref>Connection</x:ref> header field
2958   (<xref target="header.connection"/>). Once a close has been signaled, the
2959   client &MUST-NOT; send any more requests on that
2960   connection.
2963<section title="Negotiation" anchor="persistent.negotiation">
2965   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2966   maintain a persistent connection unless a <x:ref>Connection</x:ref> header
2967   field including the connection option "close" was sent in the request. If
2968   the server chooses to close the connection immediately after sending the
2969   response, it &SHOULD; send a Connection header field including the
2970   connection option "close".
2973   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2974   decide to keep it open based on whether the response from a server
2975   contains a <x:ref>Connection</x:ref> header field with the connection option
2976   "close". In case the client does not want to maintain a connection for more
2977   than that request, it &SHOULD; send a Connection header field including the
2978   connection option "close".
2981   If either the client or the server sends the "close" option in the
2982   <x:ref>Connection</x:ref> header field, that request becomes the last one
2983   for the connection.
2986   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2987   maintained for HTTP versions less than 1.1 unless it is explicitly
2988   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2989   compatibility with HTTP/1.0 clients.
2992   Each persistent connection applies to only one transport link.
2995   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2996   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2997   for information and discussion of the problems with the Keep-Alive header field
2998   implemented by many HTTP/1.0 clients).
3001   In order to remain persistent, all messages on the connection &MUST;
3002   have a self-defined message length (i.e., one not defined by closure
3003   of the connection), as described in <xref target="message.body"/>.
3007<section title="Pipelining" anchor="pipelining">
3009   A client that supports persistent connections &MAY; "pipeline" its
3010   requests (i.e., send multiple requests without waiting for each
3011   response). A server &MUST; send its responses to those requests in the
3012   same order that the requests were received.
3015   Clients which assume persistent connections and pipeline immediately
3016   after connection establishment &SHOULD; be prepared to retry their
3017   connection if the first pipelined attempt fails. If a client does
3018   such a retry, it &MUST-NOT; pipeline before it knows the connection is
3019   persistent. Clients &MUST; also be prepared to resend their requests if
3020   the server closes the connection before sending all of the
3021   corresponding responses.
3024   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
3025   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
3026   premature termination of the transport connection could lead to
3027   indeterminate results. A client wishing to send a non-idempotent
3028   request &SHOULD; wait to send that request until it has received the
3029   response status line for the previous request.
3034<section title="Practical Considerations" anchor="persistent.practical">
3036   Servers will usually have some time-out value beyond which they will
3037   no longer maintain an inactive connection. Proxy servers might make
3038   this a higher value since it is likely that the client will be making
3039   more connections through the same server. The use of persistent
3040   connections places no requirements on the length (or existence) of
3041   this time-out for either the client or the server.
3044   When a client or server wishes to time-out it &SHOULD; issue a graceful
3045   close on the transport connection. Clients and servers &SHOULD; both
3046   constantly watch for the other side of the transport close, and
3047   respond to it as appropriate. If a client or server does not detect
3048   the other side's close promptly it could cause unnecessary resource
3049   drain on the network.
3052   A client, server, or proxy &MAY; close the transport connection at any
3053   time. For example, a client might have started to send a new request
3054   at the same time that the server has decided to close the "idle"
3055   connection. From the server's point of view, the connection is being
3056   closed while it was idle, but from the client's point of view, a
3057   request is in progress.
3060   Clients (including proxies) &SHOULD; limit the number of simultaneous
3061   connections that they maintain to a given server (including proxies).
3064   Previous revisions of HTTP gave a specific number of connections as a
3065   ceiling, but this was found to be impractical for many applications. As a
3066   result, this specification does not mandate a particular maximum number of
3067   connections, but instead encourages clients to be conservative when opening
3068   multiple connections.
3071   In particular, while using multiple connections avoids the "head-of-line
3072   blocking" problem (whereby a request that takes significant server-side
3073   processing and/or has a large payload can block subsequent requests on the
3074   same connection), each connection used consumes server resources (sometimes
3075   significantly), and furthermore using multiple connections can cause
3076   undesirable side effects in congested networks.
3079   Note that servers might reject traffic that they deem abusive, including an
3080   excessive number of connections from a client.
3084<section title="Retrying Requests" anchor="persistent.retrying.requests">
3086   Senders can close the transport connection at any time. Therefore,
3087   clients, servers, and proxies &MUST; be able to recover
3088   from asynchronous close events. Client software &MAY; reopen the
3089   transport connection and retransmit the aborted sequence of requests
3090   without user interaction so long as the request sequence is
3091   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3092   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3093   human operator the choice of retrying the request(s). Confirmation by
3094   user-agent software with semantic understanding of the application
3095   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
3096   be repeated if the second sequence of requests fails.
3101<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3103<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3105   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3106   flow control mechanisms to resolve temporary overloads, rather than
3107   terminating connections with the expectation that clients will retry.
3108   The latter technique can exacerbate network congestion.
3112<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3114   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3115   the network connection for an error status code while it is transmitting
3116   the request. If the client sees an error status code, it &SHOULD;
3117   immediately cease transmitting the body. If the body is being sent
3118   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3119   empty trailer &MAY; be used to prematurely mark the end of the message.
3120   If the body was preceded by a Content-Length header field, the client &MUST;
3121   close the connection.
3125<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3127   The purpose of the <x:ref>100 (Continue)</x:ref> status code (see &status-100;)
3128   is to allow a client that is sending a request message with a request body
3129   to determine if the origin server is willing to accept the request
3130   (based on the request header fields) before the client sends the request
3131   body. In some cases, it might either be inappropriate or highly
3132   inefficient for the client to send the body if the server will reject
3133   the message without looking at the body.
3136   Requirements for HTTP/1.1 clients:
3137  <list style="symbols">
3138    <t>
3139        If a client will wait for a <x:ref>100 (Continue)</x:ref> response before
3140        sending the request body, it &MUST; send an <x:ref>Expect</x:ref> header
3141        field (&header-expect;) with the "100-continue" expectation.
3142    </t>
3143    <t>
3144        A client &MUST-NOT; send an <x:ref>Expect</x:ref> header field with
3145        the "100-continue" expectation if it does not intend to send a request
3146        body.
3147    </t>
3148  </list>
3151   Because of the presence of older implementations, the protocol allows
3152   ambiguous situations in which a client might send "Expect: 100-continue"
3153   without receiving either a <x:ref>417 (Expectation Failed)</x:ref>
3154   or a <x:ref>100 (Continue)</x:ref> status code. Therefore, when a client sends this
3155   header field to an origin server (possibly via a proxy) from which it
3156   has never seen a <x:ref>100 (Continue)</x:ref> status code, the client &SHOULD-NOT; 
3157   wait for an indefinite period before sending the request body.
3160   Requirements for HTTP/1.1 origin servers:
3161  <list style="symbols">
3162    <t> Upon receiving a request which includes an <x:ref>Expect</x:ref> header
3163        field with the "100-continue" expectation, an origin server &MUST;
3164        either respond with <x:ref>100 (Continue)</x:ref> status code and continue to read
3165        from the input stream, or respond with a final status code. The
3166        origin server &MUST-NOT; wait for the request body before sending
3167        the <x:ref>100 (Continue)</x:ref> response. If it responds with a final status
3168        code, it &MAY; close the transport connection or it &MAY; continue
3169        to read and discard the rest of the request.  It &MUST-NOT;
3170        perform the request method if it returns a final status code.
3171    </t>
3172    <t> An origin server &SHOULD-NOT;  send a <x:ref>100 (Continue)</x:ref> response if
3173        the request message does not include an <x:ref>Expect</x:ref> header
3174        field with the "100-continue" expectation, and &MUST-NOT; send a
3175        <x:ref>100 (Continue)</x:ref> response if such a request comes from an HTTP/1.0
3176        (or earlier) client. There is an exception to this rule: for
3177        compatibility with <xref target="RFC2068"/>, a server &MAY; send a <x:ref>100 (Continue)</x:ref>
3178        status code in response to an HTTP/1.1 PUT or POST request that does
3179        not include an Expect header field with the "100-continue"
3180        expectation. This exception, the purpose of which is
3181        to minimize any client processing delays associated with an
3182        undeclared wait for <x:ref>100 (Continue)</x:ref> status code, applies only to
3183        HTTP/1.1 requests, and not to requests with any other HTTP-version
3184        value.
3185    </t>
3186    <t> An origin server &MAY; omit a <x:ref>100 (Continue)</x:ref> response if it has
3187        already received some or all of the request body for the
3188        corresponding request.
3189    </t>
3190    <t> An origin server that sends a <x:ref>100 (Continue)</x:ref> response &MUST;
3191        ultimately send a final status code, once the request body is
3192        received and processed, unless it terminates the transport
3193        connection prematurely.
3194    </t>
3195    <t> If an origin server receives a request that does not include an
3196        <x:ref>Expect</x:ref> header field with the "100-continue" expectation,
3197        the request includes a request body, and the server responds
3198        with a final status code before reading the entire request body
3199        from the transport connection, then the server &SHOULD-NOT;  close
3200        the transport connection until it has read the entire request,
3201        or until the client closes the connection. Otherwise, the client
3202        might not reliably receive the response message. However, this
3203        requirement ought not be construed as preventing a server from
3204        defending itself against denial-of-service attacks, or from
3205        badly broken client implementations.
3206      </t>
3207    </list>
3210   Requirements for HTTP/1.1 proxies:
3211  <list style="symbols">
3212    <t> If a proxy receives a request that includes an <x:ref>Expect</x:ref>
3213        header field with the "100-continue" expectation, and the proxy
3214        either knows that the next-hop server complies with HTTP/1.1 or
3215        higher, or does not know the HTTP version of the next-hop
3216        server, it &MUST; forward the request, including the Expect header
3217        field.
3218    </t>
3219    <t> If the proxy knows that the version of the next-hop server is
3220        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3221        respond with a <x:ref>417 (Expectation Failed)</x:ref> status code.
3222    </t>
3223    <t> Proxies &SHOULD; maintain a record of the HTTP version
3224        numbers received from recently-referenced next-hop servers.
3225    </t>
3226    <t> A proxy &MUST-NOT; forward a <x:ref>100 (Continue)</x:ref> response if the
3227        request message was received from an HTTP/1.0 (or earlier)
3228        client and did not include an <x:ref>Expect</x:ref> header field with
3229        the "100-continue" expectation. This requirement overrides the
3230        general rule for forwarding of <x:ref>1xx</x:ref> responses (see &status-1xx;).
3231    </t>
3232  </list>
3236<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3238   If the client is sending data, a server implementation using TCP
3239   &SHOULD; be careful to ensure that the client acknowledges receipt of
3240   the packet(s) containing the response, before the server closes the
3241   input connection. If the client continues sending data to the server
3242   after the close, the server's TCP stack will send a reset packet to
3243   the client, which might erase the client's unacknowledged input buffers
3244   before they can be read and interpreted by the HTTP application.
3250<section title="Upgrade" anchor="header.upgrade">
3251  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3252  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3253  <x:anchor-alias value="Upgrade"/>
3254  <x:anchor-alias value="protocol"/>
3255  <x:anchor-alias value="protocol-name"/>
3256  <x:anchor-alias value="protocol-version"/>
3258   The "Upgrade" header field allows the client to specify what
3259   additional communication protocols it would like to use, if the server
3260   chooses to switch protocols. Servers can use it to indicate what protocols
3261   they are willing to switch to.
3263<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3264  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3266  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3267  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3268  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3271   For example,
3273<figure><artwork type="example">
3274  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3277   The Upgrade header field is intended to provide a simple mechanism
3278   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3279   does so by allowing the client to advertise its desire to use another
3280   protocol, such as a later version of HTTP with a higher major version
3281   number, even though the current request has been made using HTTP/1.1.
3282   This eases the difficult transition between incompatible protocols by
3283   allowing the client to initiate a request in the more commonly
3284   supported protocol while indicating to the server that it would like
3285   to use a "better" protocol if available (where "better" is determined
3286   by the server, possibly according to the nature of the request method
3287   or target resource).
3290   The Upgrade header field only applies to switching application-layer
3291   protocols upon the existing transport-layer connection. Upgrade
3292   cannot be used to insist on a protocol change; its acceptance and use
3293   by the server is optional. The capabilities and nature of the
3294   application-layer communication after the protocol change is entirely
3295   dependent upon the new protocol chosen, although the first action
3296   after changing the protocol &MUST; be a response to the initial HTTP
3297   request containing the Upgrade header field.
3300   The Upgrade header field only applies to the immediate connection.
3301   Therefore, the upgrade keyword &MUST; be supplied within a
3302   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3303   whenever Upgrade is present in an HTTP/1.1 message.
3306   The Upgrade header field cannot be used to indicate a switch to a
3307   protocol on a different connection. For that purpose, it is more
3308   appropriate to use a <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3311   Servers &MUST; include the "Upgrade" header field in <x:ref>101 (Switching
3312   Protocols)</x:ref> responses to indicate which protocol(s) are being switched to,
3313   and &MUST; include it in <x:ref>426 (Upgrade Required)</x:ref> responses to indicate
3314   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3315   response to indicate that they are willing to upgrade to one of the
3316   specified protocols.
3319   This specification only defines the protocol name "HTTP" for use by
3320   the family of Hypertext Transfer Protocols, as defined by the HTTP
3321   version rules of <xref target="http.version"/> and future updates to this
3322   specification. Additional tokens can be registered with IANA using the
3323   registration procedure defined in <xref target="upgrade.token.registry"/>.
3329<section title="IANA Considerations" anchor="IANA.considerations">
3331<section title="Header Field Registration" anchor="header.field.registration">
3333   HTTP header fields are registered within the Message Header Field Registry
3334   <xref target="RFC3864"/> maintained by IANA at
3335   <eref target=""/>.
3338   This document defines the following HTTP header fields, so their
3339   associated registry entries shall be updated according to the permanent
3340   registrations below:
3342<?BEGININC p1-messaging.iana-headers ?>
3343<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3344<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3345   <ttcol>Header Field Name</ttcol>
3346   <ttcol>Protocol</ttcol>
3347   <ttcol>Status</ttcol>
3348   <ttcol>Reference</ttcol>
3350   <c>Connection</c>
3351   <c>http</c>
3352   <c>standard</c>
3353   <c>
3354      <xref target="header.connection"/>
3355   </c>
3356   <c>Content-Length</c>
3357   <c>http</c>
3358   <c>standard</c>
3359   <c>
3360      <xref target="header.content-length"/>
3361   </c>
3362   <c>Host</c>
3363   <c>http</c>
3364   <c>standard</c>
3365   <c>
3366      <xref target=""/>
3367   </c>
3368   <c>TE</c>
3369   <c>http</c>
3370   <c>standard</c>
3371   <c>
3372      <xref target="header.te"/>
3373   </c>
3374   <c>Trailer</c>
3375   <c>http</c>
3376   <c>standard</c>
3377   <c>
3378      <xref target="header.trailer"/>
3379   </c>
3380   <c>Transfer-Encoding</c>
3381   <c>http</c>
3382   <c>standard</c>
3383   <c>
3384      <xref target="header.transfer-encoding"/>
3385   </c>
3386   <c>Upgrade</c>
3387   <c>http</c>
3388   <c>standard</c>
3389   <c>
3390      <xref target="header.upgrade"/>
3391   </c>
3392   <c>Via</c>
3393   <c>http</c>
3394   <c>standard</c>
3395   <c>
3396      <xref target="header.via"/>
3397   </c>
3400<?ENDINC p1-messaging.iana-headers ?>
3402   Furthermore, the header field-name "Close" shall be registered as
3403   "reserved", since using that name as an HTTP header field might
3404   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3405   header field (<xref target="header.connection"/>).
3407<texttable align="left" suppress-title="true">
3408   <ttcol>Header Field Name</ttcol>
3409   <ttcol>Protocol</ttcol>
3410   <ttcol>Status</ttcol>
3411   <ttcol>Reference</ttcol>
3413   <c>Close</c>
3414   <c>http</c>
3415   <c>reserved</c>
3416   <c>
3417      <xref target="header.field.registration"/>
3418   </c>
3421   The change controller is: "IETF ( - Internet Engineering Task Force".
3425<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3427   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3428   <eref target=""/>.
3431   This document defines the following URI schemes, so their
3432   associated registry entries shall be updated according to the permanent
3433   registrations below:
3435<texttable align="left" suppress-title="true">
3436   <ttcol>URI Scheme</ttcol>
3437   <ttcol>Description</ttcol>
3438   <ttcol>Reference</ttcol>
3440   <c>http</c>
3441   <c>Hypertext Transfer Protocol</c>
3442   <c><xref target="http.uri"/></c>
3444   <c>https</c>
3445   <c>Hypertext Transfer Protocol Secure</c>
3446   <c><xref target="https.uri"/></c>
3450<section title="Internet Media Type Registrations" anchor="">
3452   This document serves as the specification for the Internet media types
3453   "message/http" and "application/http". The following is to be registered with
3454   IANA (see <xref target="RFC4288"/>).
3456<section title="Internet Media Type message/http" anchor="">
3457<iref item="Media Type" subitem="message/http" primary="true"/>
3458<iref item="message/http Media Type" primary="true"/>
3460   The message/http type can be used to enclose a single HTTP request or
3461   response message, provided that it obeys the MIME restrictions for all
3462   "message" types regarding line length and encodings.
3465  <list style="hanging" x:indent="12em">
3466    <t hangText="Type name:">
3467      message
3468    </t>
3469    <t hangText="Subtype name:">
3470      http
3471    </t>
3472    <t hangText="Required parameters:">
3473      none
3474    </t>
3475    <t hangText="Optional parameters:">
3476      version, msgtype
3477      <list style="hanging">
3478        <t hangText="version:">
3479          The HTTP-version number of the enclosed message
3480          (e.g., "1.1"). If not present, the version can be
3481          determined from the first line of the body.
3482        </t>
3483        <t hangText="msgtype:">
3484          The message type &mdash; "request" or "response". If not
3485          present, the type can be determined from the first
3486          line of the body.
3487        </t>
3488      </list>
3489    </t>
3490    <t hangText="Encoding considerations:">
3491      only "7bit", "8bit", or "binary" are permitted
3492    </t>
3493    <t hangText="Security considerations:">
3494      none
3495    </t>
3496    <t hangText="Interoperability considerations:">
3497      none
3498    </t>
3499    <t hangText="Published specification:">
3500      This specification (see <xref target=""/>).
3501    </t>
3502    <t hangText="Applications that use this media type:">
3503    </t>
3504    <t hangText="Additional information:">
3505      <list style="hanging">
3506        <t hangText="Magic number(s):">none</t>
3507        <t hangText="File extension(s):">none</t>
3508        <t hangText="Macintosh file type code(s):">none</t>
3509      </list>
3510    </t>
3511    <t hangText="Person and email address to contact for further information:">
3512      See Authors Section.
3513    </t>
3514    <t hangText="Intended usage:">
3515      COMMON
3516    </t>
3517    <t hangText="Restrictions on usage:">
3518      none
3519    </t>
3520    <t hangText="Author/Change controller:">
3521      IESG
3522    </t>
3523  </list>
3526<section title="Internet Media Type application/http" anchor="">
3527<iref item="Media Type" subitem="application/http" primary="true"/>
3528<iref item="application/http Media Type" primary="true"/>
3530   The application/http type can be used to enclose a pipeline of one or more
3531   HTTP request or response messages (not intermixed).
3534  <list style="hanging" x:indent="12em">
3535    <t hangText="Type name:">
3536      application
3537    </t>
3538    <t hangText="Subtype name:">
3539      http
3540    </t>
3541    <t hangText="Required parameters:">
3542      none
3543    </t>
3544    <t hangText="Optional parameters:">
3545      version, msgtype
3546      <list style="hanging">
3547        <t hangText="version:">
3548          The HTTP-version number of the enclosed messages
3549          (e.g., "1.1"). If not present, the version can be
3550          determined from the first line of the body.
3551        </t>
3552        <t hangText="msgtype:">
3553          The message type &mdash; "request" or "response". If not
3554          present, the type can be determined from the first
3555          line of the body.
3556        </t>
3557      </list>
3558    </t>
3559    <t hangText="Encoding considerations:">
3560      HTTP messages enclosed by this type
3561      are in "binary" format; use of an appropriate
3562      Content-Transfer-Encoding is required when
3563      transmitted via E-mail.
3564    </t>
3565    <t hangText="Security considerations:">
3566      none
3567    </t>
3568    <t hangText="Interoperability considerations:">
3569      none
3570    </t>
3571    <t hangText="Published specification:">
3572      This specification (see <xref target=""/>).
3573    </t>
3574    <t hangText="Applications that use this media type:">
3575    </t>
3576    <t hangText="Additional information:">
3577      <list style="hanging">
3578        <t hangText="Magic number(s):">none</t>
3579        <t hangText="File extension(s):">none</t>
3580        <t hangText="Macintosh file type code(s):">none</t>
3581      </list>
3582    </t>
3583    <t hangText="Person and email address to contact for further information:">
3584      See Authors Section.
3585    </t>
3586    <t hangText="Intended usage:">
3587      COMMON
3588    </t>
3589    <t hangText="Restrictions on usage:">
3590      none
3591    </t>
3592    <t hangText="Author/Change controller:">
3593      IESG
3594    </t>
3595  </list>
3600<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3602   The HTTP Transfer Coding Registry defines the name space for transfer
3603   coding names.
3606   Registrations &MUST; include the following fields:
3607   <list style="symbols">
3608     <t>Name</t>
3609     <t>Description</t>
3610     <t>Pointer to specification text</t>
3611   </list>
3614   Names of transfer codings &MUST-NOT; overlap with names of content codings
3615   (&content-codings;) unless the encoding transformation is identical, as it
3616   is the case for the compression codings defined in
3617   <xref target="compression.codings"/>.
3620   Values to be added to this name space require IETF Review (see
3621   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3622   conform to the purpose of transfer coding defined in this section.
3625   The registry itself is maintained at
3626   <eref target=""/>.
3630<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3632   The HTTP Transfer Coding Registry shall be updated with the registrations
3633   below:
3635<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3636   <ttcol>Name</ttcol>
3637   <ttcol>Description</ttcol>
3638   <ttcol>Reference</ttcol>
3639   <c>chunked</c>
3640   <c>Transfer in a series of chunks</c>
3641   <c>
3642      <xref target="chunked.encoding"/>
3643   </c>
3644   <c>compress</c>
3645   <c>UNIX "compress" program method</c>
3646   <c>
3647      <xref target="compress.coding"/>
3648   </c>
3649   <c>deflate</c>
3650   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3651   the "zlib" data format (<xref target="RFC1950"/>)
3652   </c>
3653   <c>
3654      <xref target="deflate.coding"/>
3655   </c>
3656   <c>gzip</c>
3657   <c>Same as GNU zip <xref target="RFC1952"/></c>
3658   <c>
3659      <xref target="gzip.coding"/>
3660   </c>
3664<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3666   The HTTP Upgrade Token Registry defines the name space for protocol-name
3667   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3668   field. Each registered protocol name is associated with contact information
3669   and an optional set of specifications that details how the connection
3670   will be processed after it has been upgraded.
3673   Registrations happen on a "First Come First Served" basis (see
3674   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3675   following rules:
3676  <list style="numbers">
3677    <t>A protocol-name token, once registered, stays registered forever.</t>
3678    <t>The registration &MUST; name a responsible party for the
3679       registration.</t>
3680    <t>The registration &MUST; name a point of contact.</t>
3681    <t>The registration &MAY; name a set of specifications associated with
3682       that token. Such specifications need not be publicly available.</t>
3683    <t>The registration &SHOULD; name a set of expected "protocol-version"
3684       tokens associated with that token at the time of registration.</t>
3685    <t>The responsible party &MAY; change the registration at any time.
3686       The IANA will keep a record of all such changes, and make them
3687       available upon request.</t>
3688    <t>The IESG &MAY; reassign responsibility for a protocol token.
3689       This will normally only be used in the case when a
3690       responsible party cannot be contacted.</t>
3691  </list>
3694   This registration procedure for HTTP Upgrade Tokens replaces that
3695   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3699<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3701   The HTTP Upgrade Token Registry shall be updated with the registration
3702   below:
3704<texttable align="left" suppress-title="true">
3705   <ttcol>Value</ttcol>
3706   <ttcol>Description</ttcol>
3707   <ttcol>Expected Version Tokens</ttcol>
3708   <ttcol>Reference</ttcol>
3710   <c>HTTP</c>
3711   <c>Hypertext Transfer Protocol</c>
3712   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3713   <c><xref target="http.version"/></c>
3716   The responsible party is: "IETF ( - Internet Engineering Task Force".
3722<section title="Security Considerations" anchor="security.considerations">
3724   This section is meant to inform application developers, information
3725   providers, and users of the security limitations in HTTP/1.1 as
3726   described by this document. The discussion does not include
3727   definitive solutions to the problems revealed, though it does make
3728   some suggestions for reducing security risks.
3731<section title="Personal Information" anchor="personal.information">
3733   HTTP clients are often privy to large amounts of personal information
3734   (e.g., the user's name, location, mail address, passwords, encryption
3735   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3736   leakage of this information.
3737   We very strongly recommend that a convenient interface be provided
3738   for the user to control dissemination of such information, and that
3739   designers and implementors be particularly careful in this area.
3740   History shows that errors in this area often create serious security
3741   and/or privacy problems and generate highly adverse publicity for the
3742   implementor's company.
3746<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3748   A server is in the position to save personal data about a user's
3749   requests which might identify their reading patterns or subjects of
3750   interest.  In particular, log information gathered at an intermediary
3751   often contains a history of user agent interaction, across a multitude
3752   of sites, that can be traced to individual users.
3755   HTTP log information is confidential in nature; its handling is often
3756   constrained by laws and regulations.  Log information needs to be securely
3757   stored and appropriate guidelines followed for its analysis.
3758   Anonymization of personal information within individual entries helps,
3759   but is generally not sufficient to prevent real log traces from being
3760   re-identified based on correlation with other access characteristics.
3761   As such, access traces that are keyed to a specific client should not
3762   be published even if the key is pseudonymous.
3765   To minimize the risk of theft or accidental publication, log information
3766   should be purged of personally identifiable information, including
3767   user identifiers, IP addresses, and user-provided query parameters,
3768   as soon as that information is no longer necessary to support operational
3769   needs for security, auditing, or fraud control.
3773<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3775   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3776   the documents returned by HTTP requests to be only those that were
3777   intended by the server administrators. If an HTTP server translates
3778   HTTP URIs directly into file system calls, the server &MUST; take
3779   special care not to serve files that were not intended to be
3780   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3781   other operating systems use ".." as a path component to indicate a
3782   directory level above the current one. On such a system, an HTTP
3783   server &MUST; disallow any such construct in the request-target if it
3784   would otherwise allow access to a resource outside those intended to
3785   be accessible via the HTTP server. Similarly, files intended for
3786   reference only internally to the server (such as access control
3787   files, configuration files, and script code) &MUST; be protected from
3788   inappropriate retrieval, since they might contain sensitive
3789   information. Experience has shown that minor bugs in such HTTP server
3790   implementations have turned into security risks.
3794<section title="DNS-related Attacks" anchor="dns.related.attacks">
3796   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3797   generally prone to security attacks based on the deliberate misassociation
3798   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3799   cautious in assuming the validity of an IP number/DNS name association unless
3800   the response is protected by DNSSec (<xref target="RFC4033"/>).
3804<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3806   By their very nature, HTTP intermediaries are men-in-the-middle, and
3807   represent an opportunity for man-in-the-middle attacks. Compromise of
3808   the systems on which the intermediaries run can result in serious security
3809   and privacy problems. Intermediaries have access to security-related
3810   information, personal information about individual users and
3811   organizations, and proprietary information belonging to users and
3812   content providers. A compromised intermediary, or an intermediary
3813   implemented or configured without regard to security and privacy
3814   considerations, might be used in the commission of a wide range of
3815   potential attacks.
3818   Intermediaries that contain a shared cache are especially vulnerable
3819   to cache poisoning attacks.
3822   Implementors need to consider the privacy and security
3823   implications of their design and coding decisions, and of the
3824   configuration options they provide to operators (especially the
3825   default configuration).
3828   Users need to be aware that intermediaries are no more trustworthy than
3829   the people who run them; HTTP itself cannot solve this problem.
3832   The judicious use of cryptography, when appropriate, might suffice to
3833   protect against a broad range of security and privacy attacks. Such
3834   cryptography is beyond the scope of the HTTP/1.1 specification.
3838<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3840   Because HTTP uses mostly textual, character-delimited fields, attackers can
3841   overflow buffers in implementations, and/or perform a Denial of Service
3842   against implementations that accept fields with unlimited lengths.
3845   To promote interoperability, this specification makes specific
3846   recommendations for minimum size limits on request-line
3847   (<xref target="request.line"/>)
3848   and blocks of header fields (<xref target="header.fields"/>). These are
3849   minimum recommendations, chosen to be supportable even by implementations
3850   with limited resources; it is expected that most implementations will
3851   choose substantially higher limits.
3854   This specification also provides a way for servers to reject messages that
3855   have request-targets that are too long (&status-414;) or request entities
3856   that are too large (&status-4xx;).
3859   Other fields (including but not limited to request methods, response status
3860   phrases, header field-names, and body chunks) &SHOULD; be limited by
3861   implementations carefully, so as to not impede interoperability.
3866<section title="Acknowledgments" anchor="acks">
3868   This edition of HTTP builds on the many contributions that went into
3869   <xref target="RFC1945" format="none">RFC 1945</xref>,
3870   <xref target="RFC2068" format="none">RFC 2068</xref>,
3871   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3872   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3873   substantial contributions made by the previous authors, editors, and
3874   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3875   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3876   Paul J. Leach, and Mark Nottingham.
3877   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3878   acknowledgements from prior revisions.
3881   Since 1999, the following contributors have helped improve the HTTP
3882   specification by reporting bugs, asking smart questions, drafting or
3883   reviewing text, and evaluating open issues:
3885<?BEGININC acks ?>
3886<t>Adam Barth,
3887Adam Roach,
3888Addison Phillips,
3889Adrian Chadd,
3890Adrien W. de Croy,
3891Alan Ford,
3892Alan Ruttenberg,
3893Albert Lunde,
3894Alek Storm,
3895Alex Rousskov,
3896Alexandre Morgaut,
3897Alexey Melnikov,
3898Alisha Smith,
3899Amichai Rothman,
3900Amit Klein,
3901Amos Jeffries,
3902Andreas Maier,
3903Andreas Petersson,
3904Anne van Kesteren,
3905Anthony Bryan,
3906Asbjorn Ulsberg,
3907Balachander Krishnamurthy,
3908Barry Leiba,
3909Ben Laurie,
3910Benjamin Niven-Jenkins,
3911Bil Corry,
3912Bill Burke,
3913Bjoern Hoehrmann,
3914Bob Scheifler,
3915Boris Zbarsky,
3916Brett Slatkin,
3917Brian Kell,
3918Brian McBarron,
3919Brian Pane,
3920Brian Smith,
3921Bryce Nesbitt,
3922Cameron Heavon-Jones,
3923Carl Kugler,
3924Carsten Bormann,
3925Charles Fry,
3926Chris Newman,
3927Cyrus Daboo,
3928Dale Robert Anderson,
3929Dan Winship,
3930Daniel Stenberg,
3931Dave Cridland,
3932Dave Crocker,
3933Dave Kristol,
3934David Booth,
3935David Singer,
3936David W. Morris,
3937Diwakar Shetty,
3938Dmitry Kurochkin,
3939Drummond Reed,
3940Duane Wessels,
3941Edward Lee,
3942Eliot Lear,
3943Eran Hammer-Lahav,
3944Eric D. Williams,
3945Eric J. Bowman,
3946Eric Lawrence,
3947Eric Rescorla,
3948Erik Aronesty,
3949Florian Weimer,
3950Frank Ellermann,
3951Fred Bohle,
3952Geoffrey Sneddon,
3953Gervase Markham,
3954Greg Wilkins,
3955Harald Tveit Alvestrand,
3956Harry Halpin,
3957Helge Hess,
3958Henrik Nordstrom,
3959Henry S. Thompson,
3960Henry Story,
3961Herbert van de Sompel,
3962Howard Melman,
3963Hugo Haas,
3964Ian Hickson,
3965Ingo Struck,
3966J. Ross Nicoll,
3967James H. Manger,
3968James Lacey,
3969James M. Snell,
3970Jamie Lokier,
3971Jan Algermissen,
3972Jeff Hodges (who came up with the term 'effective Request-URI'),
3973Jeff Walden,
3974Jim Luther,
3975Joe D. Williams,
3976Joe Gregorio,
3977Joe Orton,
3978John C. Klensin,
3979John C. Mallery,
3980John Cowan,
3981John Kemp,
3982John Panzer,
3983John Schneider,
3984John Stracke,
3985John Sullivan,
3986Jonas Sicking,
3987Jonathan Billington,
3988Jonathan Moore,
3989Jonathan Rees,
3990Jordi Ros,
3991Joris Dobbelsteen,
3992Josh Cohen,
3993Julien Pierre,
3994Jungshik Shin,
3995Justin Chapweske,
3996Justin Erenkrantz,
3997Justin James,
3998Kalvinder Singh,
3999Karl Dubost,
4000Keith Hoffman,
4001Keith Moore,
4002Koen Holtman,
4003Konstantin Voronkov,
4004Kris Zyp,
4005Lisa Dusseault,
4006Maciej Stachowiak,
4007Marc Schneider,
4008Marc Slemko,
4009Mark Baker,
4010Mark Pauley,
4011Mark Watson,
4012Markus Isomaki,
4013Markus Lanthaler,
4014Martin J. Duerst,
4015Martin Musatov,
4016Martin Nilsson,
4017Martin Thomson,
4018Matt Lynch,
4019Matthew Cox,
4020Max Clark,
4021Michael Burrows,
4022Michael Hausenblas,
4023Mike Amundsen,
4024Mike Belshe,
4025Mike Kelly,
4026Mike Schinkel,
4027Miles Sabin,
4028Murray S. Kucherawy,
4029Mykyta Yevstifeyev,
4030Nathan Rixham,
4031Nicholas Shanks,
4032Nico Williams,
4033Nicolas Alvarez,
4034Nicolas Mailhot,
4035Noah Slater,
4036Pablo Castro,
4037Pat Hayes,
4038Patrick R. McManus,
4039Paul E. Jones,
4040Paul Hoffman,
4041Paul Marquess,
4042Peter Lepeska,
4043Peter Saint-Andre,
4044Peter Watkins,
4045Phil Archer,
4046Phillip Hallam-Baker,
4047Poul-Henning Kamp,
4048Preethi Natarajan,
4049Ray Polk,
4050Reto Bachmann-Gmuer,
4051Richard Cyganiak,
4052Robert Brewer,
4053Robert Collins,
4054Robert O'Callahan,
4055Robert Olofsson,
4056Robert Sayre,
4057Robert Siemer,
4058Robert de Wilde,
4059Roberto Javier Godoy,
4060Roberto Peon,
4061Ronny Widjaja,
4062S. Mike Dierken,
4063Salvatore Loreto,
4064Sam Johnston,
4065Sam Ruby,
4066Scott Lawrence (who maintained the original issues list),
4067Sean B. Palmer,
4068Shane McCarron,
4069Stefan Eissing,
4070Stefan Tilkov,
4071Stefanos Harhalakis,
4072Stephane Bortzmeyer,
4073Stephen Farrell,
4074Stuart Williams,
4075Subbu Allamaraju,
4076Sylvain Hellegouarch,
4077Tapan Divekar,
4078Ted Hardie,
4079Thomas Broyer,
4080Thomas Nordin,
4081Thomas Roessler,
4082Tim Bray,
4083Tim Morgan,
4084Tim Olsen,
4085Tom Zhou,
4086Travis Snoozy,
4087Tyler Close,
4088Vincent Murphy,
4089Wenbo Zhu,
4090Werner Baumann,
4091Wilbur Streett,
4092Wilfredo Sanchez Vega,
4093William A. Rowe Jr.,
4094William Chan,
4095Willy Tarreau,
4096Xiaoshu Wang,
4097Yaron Goland,
4098Yngve Nysaeter Pettersen,
4099Yoav Nir,
4100Yogesh Bang,
4101Yutaka Oiwa,
4102Zed A. Shaw, and
4103Zhong Yu.
4105<?ENDINC acks ?>
4111<references title="Normative References">
4113<reference anchor="ISO-8859-1">
4114  <front>
4115    <title>
4116     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4117    </title>
4118    <author>
4119      <organization>International Organization for Standardization</organization>
4120    </author>
4121    <date year="1998"/>
4122  </front>
4123  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4126<reference anchor="Part2">
4127  <front>
4128    <title>HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation</title>
4129    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4130      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4131      <address><email></email></address>
4132    </author>
4133    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4134      <organization abbrev="W3C">World Wide Web Consortium</organization>
4135      <address><email></email></address>
4136    </author>
4137    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4138      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4139      <address><email></email></address>
4140    </author>
4141    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4142  </front>
4143  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4144  <x:source href="p2-semantics.xml" basename="p2-semantics">
4145    <x:defines>1xx (Informational)</x:defines>
4146    <x:defines>1xx</x:defines>
4147    <x:defines>100 (Continue)</x:defines>
4148    <x:defines>101 (Switching Protocols)</x:defines>
4149    <x:defines>2xx (Successful)</x:defines>
4150    <x:defines>2xx</x:defines>
4151    <x:defines>200 (OK)</x:defines>
4152    <x:defines>204 (No Content)</x:defines>
4153    <x:defines>3xx (Redirection)</x:defines>
4154    <x:defines>3xx</x:defines>
4155    <x:defines>301 (Moved Permanently)</x:defines>
4156    <x:defines>4xx (Client Error)</x:defines>
4157    <x:defines>4xx</x:defines>
4158    <x:defines>400 (Bad Request)</x:defines>
4159    <x:defines>405 (Method Not Allowed)</x:defines>
4160    <x:defines>411 (Length Required)</x:defines>
4161    <x:defines>414 (URI Too Long)</x:defines>
4162    <x:defines>417 (Expectation Failed)</x:defines>
4163    <x:defines>426 (Upgrade Required)</x:defines>
4164    <x:defines>501 (Not Implemented)</x:defines>
4165    <x:defines>502 (Bad Gateway)</x:defines>
4166    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4167    <x:defines>Content-Encoding</x:defines>
4168    <x:defines>Content-Type</x:defines>
4169    <x:defines>Date</x:defines>
4170    <x:defines>Expect</x:defines>
4171    <x:defines>Location</x:defines>
4172    <x:defines>Server</x:defines>
4173    <x:defines>User-Agent</x:defines>
4174  </x:source>
4177<reference anchor="Part4">
4178  <front>
4179    <title>HTTP/1.1, part 4: Conditional Requests</title>
4180    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4181      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4182      <address><email></email></address>
4183    </author>
4184    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
4185      <organization abbrev="W3C">World Wide Web Consortium</organization>
4186      <address><email></email></address>
4187    </author>
4188    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4189      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4190      <address><email></email></address>
4191    </author>
4192    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4193  </front>
4194  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4195  <x:source basename="p4-conditional" href="p4-conditional.xml">
4196    <x:defines>304 (Not Modified)</x:defines>
4197  </x:source>
4200<reference anchor="Part5">
4201  <front>
4202    <title>HTTP/1.1, part 5: Range Requests and Partial Responses</title>
4203    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4204      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4205      <address><email></email></address>
4206    </author>
4207    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4208      <organization abbrev="W3C">World Wide Web Consortium</organization>
4209      <address><email></email></address>
4210    </author>
4211    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4212      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4213      <address><email></email></address>
4214    </author>
4215    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4216  </front>
4217  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4218  <x:source href="p5-range.xml" basename="p5-range">
4219    <x:defines>Content-Range</x:defines>
4220  </x:source>
4223<reference anchor="Part6">
4224  <front>
4225    <title>HTTP/1.1, part 6: Caching</title>
4226    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4227      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4228      <address><email></email></address>
4229    </author>
4230    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4231      <organization abbrev="W3C">World Wide Web Consortium</organization>
4232      <address><email></email></address>
4233    </author>
4234    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4235      <organization>Rackspace</organization>
4236      <address><email></email></address>
4237    </author>
4238    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4239      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4240      <address><email></email></address>
4241    </author>
4242    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4243  </front>
4244  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4245  <x:source href="p6-cache.xml" basename="p6-cache">
4246    <x:defines>Expires</x:defines>
4247  </x:source>
4250<reference anchor="Part7">
4251  <front>
4252    <title>HTTP/1.1, part 7: Authentication</title>
4253    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4254      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4255      <address><email></email></address>
4256    </author>
4257    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4258      <organization abbrev="W3C">World Wide Web Consortium</organization>
4259      <address><email></email></address>
4260    </author>
4261    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4262      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4263      <address><email></email></address>
4264    </author>
4265    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4266  </front>
4267  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4268  <x:source href="p7-auth.xml" basename="p7-auth">
4269    <x:defines>Proxy-Authenticate</x:defines>
4270    <x:defines>Proxy-Authorization</x:defines>
4271  </x:source>
4274<reference anchor="RFC5234">
4275  <front>
4276    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4277    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4278      <organization>Brandenburg InternetWorking</organization>
4279      <address>
4280        <email></email>
4281      </address> 
4282    </author>
4283    <author initials="P." surname="Overell" fullname="Paul Overell">
4284      <organization>THUS plc.</organization>
4285      <address>
4286        <email></email>
4287      </address>
4288    </author>
4289    <date month="January" year="2008"/>
4290  </front>
4291  <seriesInfo name="STD" value="68"/>
4292  <seriesInfo name="RFC" value="5234"/>
4295<reference anchor="RFC2119">
4296  <front>
4297    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4298    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4299      <organization>Harvard University</organization>
4300      <address><email></email></address>
4301    </author>
4302    <date month="March" year="1997"/>
4303  </front>
4304  <seriesInfo name="BCP" value="14"/>
4305  <seriesInfo name="RFC" value="2119"/>
4308<reference anchor="RFC3986">
4309 <front>
4310  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4311  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4312    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4313    <address>
4314       <email></email>
4315       <uri></uri>
4316    </address>
4317  </author>
4318  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4319    <organization abbrev="Day Software">Day Software</organization>
4320    <address>
4321      <email></email>
4322      <uri></uri>
4323    </address>
4324  </author>
4325  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4326    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4327    <address>
4328      <email></email>
4329      <uri></uri>
4330    </address>
4331  </author>
4332  <date month='January' year='2005'></date>
4333 </front>
4334 <seriesInfo name="STD" value="66"/>
4335 <seriesInfo name="RFC" value="3986"/>
4338<reference anchor="USASCII">
4339  <front>
4340    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4341    <author>
4342      <organization>American National Standards Institute</organization>
4343    </author>
4344    <date year="1986"/>
4345  </front>
4346  <seriesInfo name="ANSI" value="X3.4"/>
4349<reference anchor="RFC1950">
4350  <front>
4351    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4352    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4353      <organization>Aladdin Enterprises</organization>
4354      <address><email></email></address>
4355    </author>
4356    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4357    <date month="May" year="1996"/>
4358  </front>
4359  <seriesInfo name="RFC" value="1950"/>
4360  <!--<annotation>
4361    RFC 1950 is an Informational RFC, thus it might be less stable than
4362    this specification. On the other hand, this downward reference was
4363    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4364    therefore it is unlikely to cause problems in practice. See also
4365    <xref target="BCP97"/>.
4366  </annotation>-->
4369<reference anchor="RFC1951">
4370  <front>
4371    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4372    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4373      <organization>Aladdin Enterprises</organization>
4374      <address><email></email></address>
4375    </author>
4376    <date month="May" year="1996"/>
4377  </front>
4378  <seriesInfo name="RFC" value="1951"/>
4379  <!--<annotation>
4380    RFC 1951 is an Informational RFC, thus it might be less stable than
4381    this specification. On the other hand, this downward reference was
4382    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4383    therefore it is unlikely to cause problems in practice. See also
4384    <xref target="BCP97"/>.
4385  </annotation>-->
4388<reference anchor="RFC1952">
4389  <front>
4390    <title>GZIP file format specification version 4.3</title>
4391    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4392      <organization>Aladdin Enterprises</organization>
4393      <address><email></email></address>
4394    </author>
4395    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4396      <address><email></email></address>
4397    </author>
4398    <author initials="M." surname="Adler" fullname="Mark Adler">
4399      <address><email></email></address>
4400    </author>
4401    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4402      <address><email></email></address>
4403    </author>
4404    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4405      <address><email></email></address>
4406    </author>
4407    <date month="May" year="1996"/>
4408  </front>
4409  <seriesInfo name="RFC" value="1952"/>
4410  <!--<annotation>
4411    RFC 1952 is an Informational RFC, thus it might be less stable than
4412    this specification. On the other hand, this downward reference was
4413    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4414    therefore it is unlikely to cause problems in practice. See also
4415    <xref target="BCP97"/>.
4416  </annotation>-->
4421<references title="Informative References">
4423<reference anchor="Nie1997" target="">
4424  <front>
4425    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4426    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4427    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4428    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4429    <author initials="H." surname="Lie" fullname="H. Lie"/>
4430    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4431    <date year="1997" month="September"/>
4432  </front>
4433  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4436<reference anchor="Pad1995" target="">
4437  <front>
4438    <title>Improving HTTP Latency</title>
4439    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4440    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4441    <date year="1995" month="December"/>
4442  </front>
4443  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4446<reference anchor='RFC1919'>
4447  <front>
4448    <title>Classical versus Transparent IP Proxies</title>
4449    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4450      <address><email></email></address>
4451    </author>
4452    <date year='1996' month='March' />
4453  </front>
4454  <seriesInfo name='RFC' value='1919' />
4457<reference anchor="RFC1945">
4458  <front>
4459    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4460    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4461      <organization>MIT, Laboratory for Computer Science</organization>
4462      <address><email></email></address>
4463    </author>
4464    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4465      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4466      <address><email></email></address>
4467    </author>
4468    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4469      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4470      <address><email></email></address>
4471    </author>
4472    <date month="May" year="1996"/>
4473  </front>
4474  <seriesInfo name="RFC" value="1945"/>
4477<reference anchor="RFC2045">
4478  <front>
4479    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4480    <author initials="N." surname="Freed" fullname="Ned Freed">
4481      <organization>Innosoft International, Inc.</organization>
4482      <address><email></email></address>
4483    </author>
4484    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4485      <organization>First Virtual Holdings</organization>
4486      <address><email></email></address>
4487    </author>
4488    <date month="November" year="1996"/>
4489  </front>
4490  <seriesInfo name="RFC" value="2045"/>
4493<reference anchor="RFC2047">
4494  <front>
4495    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4496    <author initials="K." surname="Moore" fullname="Keith Moore">
4497      <organization>University of Tennessee</organization>
4498      <address><email></email></address>
4499    </author>
4500    <date month="November" year="1996"/>
4501  </front>
4502  <seriesInfo name="RFC" value="2047"/>
4505<reference anchor="RFC2068">
4506  <front>
4507    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4508    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4509      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4510      <address><email></email></address>
4511    </author>
4512    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4513      <organization>MIT Laboratory for Computer Science</organization>
4514      <address><email></email></address>
4515    </author>
4516    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4517      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4518      <address><email></email></address>
4519    </author>
4520    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4521      <organization>MIT Laboratory for Computer Science</organization>
4522      <address><email></email></address>
4523    </author>
4524    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4525      <organization>MIT Laboratory for Computer Science</organization>
4526      <address><email></email></address>
4527    </author>
4528    <date month="January" year="1997"/>
4529  </front>
4530  <seriesInfo name="RFC" value="2068"/>
4533<reference anchor="RFC2145">
4534  <front>
4535    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4536    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4537      <organization>Western Research Laboratory</organization>
4538      <address><email></email></address>
4539    </author>
4540    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4541      <organization>Department of Information and Computer Science</organization>
4542      <address><email></email></address>
4543    </author>
4544    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4545      <organization>MIT Laboratory for Computer Science</organization>
4546      <address><email></email></address>
4547    </author>
4548    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4549      <organization>W3 Consortium</organization>
4550      <address><email></email></address>
4551    </author>
4552    <date month="May" year="1997"/>
4553  </front>
4554  <seriesInfo name="RFC" value="2145"/>
4557<reference anchor="RFC2616">
4558  <front>
4559    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4560    <author initials="R." surname="Fielding" fullname="R. Fielding">
4561      <organization>University of California, Irvine</organization>
4562      <address><email></email></address>
4563    </author>
4564    <author initials="J." surname="Gettys" fullname="J. Gettys">
4565      <organization>W3C</organization>
4566      <address><email></email></address>
4567    </author>
4568    <author initials="J." surname="Mogul" fullname="J. Mogul">
4569      <organization>Compaq Computer Corporation</organization>
4570      <address><email></email></address>
4571    </author>
4572    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4573      <organization>MIT Laboratory for Computer Science</organization>
4574      <address><email></email></address>
4575    </author>
4576    <author initials="L." surname="Masinter" fullname="L. Masinter">
4577      <organization>Xerox Corporation</organization>
4578      <address><email></email></address>
4579    </author>
4580    <author initials="P." surname="Leach" fullname="P. Leach">
4581      <organization>Microsoft Corporation</organization>
4582      <address><email></email></address>
4583    </author>
4584    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4585      <organization>W3C</organization>
4586      <address><email></email></address>
4587    </author>
4588    <date month="June" year="1999"/>
4589  </front>
4590  <seriesInfo name="RFC" value="2616"/>
4593<reference anchor='RFC2817'>
4594  <front>
4595    <title>Upgrading to TLS Within HTTP/1.1</title>
4596    <author initials='R.' surname='Khare' fullname='R. Khare'>
4597      <organization>4K Associates / UC Irvine</organization>
4598      <address><email></email></address>
4599    </author>
4600    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4601      <organization>Agranat Systems, Inc.</organization>
4602      <address><email></email></address>
4603    </author>
4604    <date year='2000' month='May' />
4605  </front>
4606  <seriesInfo name='RFC' value='2817' />
4609<reference anchor='RFC2818'>
4610  <front>
4611    <title>HTTP Over TLS</title>
4612    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4613      <organization>RTFM, Inc.</organization>
4614      <address><email></email></address>
4615    </author>
4616    <date year='2000' month='May' />
4617  </front>
4618  <seriesInfo name='RFC' value='2818' />
4621<reference anchor='RFC2965'>
4622  <front>
4623    <title>HTTP State Management Mechanism</title>
4624    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4625      <organization>Bell Laboratories, Lucent Technologies</organization>
4626      <address><email></email></address>
4627    </author>
4628    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4629      <organization>, Inc.</organization>
4630      <address><email></email></address>
4631    </author>
4632    <date year='2000' month='October' />
4633  </front>
4634  <seriesInfo name='RFC' value='2965' />
4637<reference anchor='RFC3040'>
4638  <front>
4639    <title>Internet Web Replication and Caching Taxonomy</title>
4640    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4641      <organization>Equinix, Inc.</organization>
4642    </author>
4643    <author initials='I.' surname='Melve' fullname='I. Melve'>
4644      <organization>UNINETT</organization>
4645    </author>
4646    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4647      <organization>CacheFlow Inc.</organization>
4648    </author>
4649    <date year='2001' month='January' />
4650  </front>
4651  <seriesInfo name='RFC' value='3040' />
4654<reference anchor='RFC3864'>
4655  <front>
4656    <title>Registration Procedures for Message Header Fields</title>
4657    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4658      <organization>Nine by Nine</organization>
4659      <address><email></email></address>
4660    </author>
4661    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4662      <organization>BEA Systems</organization>
4663      <address><email></email></address>
4664    </author>
4665    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4666      <organization>HP Labs</organization>
4667      <address><email></email></address>
4668    </author>
4669    <date year='2004' month='September' />
4670  </front>
4671  <seriesInfo name='BCP' value='90' />
4672  <seriesInfo name='RFC' value='3864' />
4675<reference anchor='RFC4033'>
4676  <front>
4677    <title>DNS Security Introduction and Requirements</title>
4678    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4679    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4680    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4681    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4682    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4683    <date year='2005' month='March' />
4684  </front>
4685  <seriesInfo name='RFC' value='4033' />
4688<reference anchor="RFC4288">
4689  <front>
4690    <title>Media Type Specifications and Registration Procedures</title>
4691    <author initials="N." surname="Freed" fullname="N. Freed">
4692      <organization>Sun Microsystems</organization>
4693      <address>
4694        <email></email>
4695      </address>
4696    </author>
4697    <author initials="J." surname="Klensin" fullname="J. Klensin">
4698      <address>
4699        <email></email>
4700      </address>
4701    </author>
4702    <date year="2005" month="December"/>
4703  </front>
4704  <seriesInfo name="BCP" value="13"/>
4705  <seriesInfo name="RFC" value="4288"/>
4708<reference anchor='RFC4395'>
4709  <front>
4710    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4711    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4712      <organization>AT&amp;T Laboratories</organization>
4713      <address>
4714        <email></email>
4715      </address>
4716    </author>
4717    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4718      <organization>Qualcomm, Inc.</organization>
4719      <address>
4720        <email></email>
4721      </address>
4722    </author>
4723    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4724      <organization>Adobe Systems</organization>
4725      <address>
4726        <email></email>
4727      </address>
4728    </author>
4729    <date year='2006' month='February' />
4730  </front>
4731  <seriesInfo name='BCP' value='115' />
4732  <seriesInfo name='RFC' value='4395' />
4735<reference anchor='RFC4559'>
4736  <front>
4737    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4738    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4739    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4740    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4741    <date year='2006' month='June' />
4742  </front>
4743  <seriesInfo name='RFC' value='4559' />
4746<reference anchor='RFC5226'>
4747  <front>
4748    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4749    <author initials='T.' surname='Narten' fullname='T. Narten'>
4750      <organization>IBM</organization>
4751      <address><email></email></address>
4752    </author>
4753    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4754      <organization>Google</organization>
4755      <address><email></email></address>
4756    </author>
4757    <date year='2008' month='May' />
4758  </front>
4759  <seriesInfo name='BCP' value='26' />
4760  <seriesInfo name='RFC' value='5226' />
4763<reference anchor="RFC5322">
4764  <front>
4765    <title>Internet Message Format</title>
4766    <author initials="P." surname="Resnick" fullname="P. Resnick">
4767      <organization>Qualcomm Incorporated</organization>
4768    </author>
4769    <date year="2008" month="October"/>
4770  </front>
4771  <seriesInfo name="RFC" value="5322"/>
4774<reference anchor="RFC6265">
4775  <front>
4776    <title>HTTP State Management Mechanism</title>
4777    <author initials="A." surname="Barth" fullname="Adam Barth">
4778      <organization abbrev="U.C. Berkeley">
4779        University of California, Berkeley
4780      </organization>
4781      <address><email></email></address>
4782    </author>
4783    <date year="2011" month="April" />
4784  </front>
4785  <seriesInfo name="RFC" value="6265"/>
4788<!--<reference anchor='BCP97'>
4789  <front>
4790    <title>Handling Normative References to Standards-Track Documents</title>
4791    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4792      <address>
4793        <email></email>
4794      </address>
4795    </author>
4796    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4797      <organization>MIT</organization>
4798      <address>
4799        <email></email>
4800      </address>
4801    </author>
4802    <date year='2007' month='June' />
4803  </front>
4804  <seriesInfo name='BCP' value='97' />
4805  <seriesInfo name='RFC' value='4897' />
4808<reference anchor="Kri2001" target="">
4809  <front>
4810    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4811    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4812    <date year="2001" month="November"/>
4813  </front>
4814  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4817<reference anchor="Spe" target="">
4818  <front>
4819    <title>Analysis of HTTP Performance Problems</title>
4820    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4821    <date/>
4822  </front>
4825<reference anchor="Tou1998" target="">
4826  <front>
4827  <title>Analysis of HTTP Performance</title>
4828  <author initials="J." surname="Touch" fullname="Joe Touch">
4829    <organization>USC/Information Sciences Institute</organization>
4830    <address><email></email></address>
4831  </author>
4832  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4833    <organization>USC/Information Sciences Institute</organization>
4834    <address><email></email></address>
4835  </author>
4836  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4837    <organization>USC/Information Sciences Institute</organization>
4838    <address><email></email></address>
4839  </author>
4840  <date year="1998" month="Aug"/>
4841  </front>
4842  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4843  <annotation>(original report dated Aug. 1996)</annotation>
4849<section title="HTTP Version History" anchor="compatibility">
4851   HTTP has been in use by the World-Wide Web global information initiative
4852   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4853   was a simple protocol for hypertext data transfer across the Internet
4854   with only a single request method (GET) and no metadata.
4855   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4856   methods and MIME-like messaging that could include metadata about the data
4857   transferred and modifiers on the request/response semantics. However,
4858   HTTP/1.0 did not sufficiently take into consideration the effects of
4859   hierarchical proxies, caching, the need for persistent connections, or
4860   name-based virtual hosts. The proliferation of incompletely-implemented
4861   applications calling themselves "HTTP/1.0" further necessitated a
4862   protocol version change in order for two communicating applications
4863   to determine each other's true capabilities.
4866   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4867   requirements that enable reliable implementations, adding only
4868   those new features that will either be safely ignored by an HTTP/1.0
4869   recipient or only sent when communicating with a party advertising
4870   conformance with HTTP/1.1.
4873   It is beyond the scope of a protocol specification to mandate
4874   conformance with previous versions. HTTP/1.1 was deliberately
4875   designed, however, to make supporting previous versions easy.
4876   We would expect a general-purpose HTTP/1.1 server to understand
4877   any valid request in the format of HTTP/1.0 and respond appropriately
4878   with an HTTP/1.1 message that only uses features understood (or
4879   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4880   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4883   Since HTTP/0.9 did not support header fields in a request,
4884   there is no mechanism for it to support name-based virtual
4885   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4886   field).  Any server that implements name-based virtual hosts
4887   ought to disable support for HTTP/0.9.  Most requests that
4888   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4889   requests wherein a buggy client failed to properly encode
4890   linear whitespace found in a URI reference and placed in
4891   the request-target.
4894<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4896   This section summarizes major differences between versions HTTP/1.0
4897   and HTTP/1.1.
4900<section title="Multi-homed Web Servers" anchor="">
4902   The requirements that clients and servers support the <x:ref>Host</x:ref>
4903   header field (<xref target=""/>), report an error if it is
4904   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4905   are among the most important changes defined by HTTP/1.1.
4908   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4909   addresses and servers; there was no other established mechanism for
4910   distinguishing the intended server of a request than the IP address
4911   to which that request was directed. The <x:ref>Host</x:ref> header field was
4912   introduced during the development of HTTP/1.1 and, though it was
4913   quickly implemented by most HTTP/1.0 browsers, additional requirements
4914   were placed on all HTTP/1.1 requests in order to ensure complete
4915   adoption.  At the time of this writing, most HTTP-based services
4916   are dependent upon the Host header field for targeting requests.
4920<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4922   In HTTP/1.0, each connection is established by the client prior to the
4923   request and closed by the server after sending the response. However, some
4924   implementations implement the explicitly negotiated ("Keep-Alive") version
4925   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4926   target="RFC2068"/>.
4929   Some clients and servers might wish to be compatible with these previous
4930   approaches to persistent connections, by explicitly negotiating for them
4931   with a "Connection: keep-alive" request header field. However, some
4932   experimental implementations of HTTP/1.0 persistent connections are faulty;
4933   for example, if a HTTP/1.0 proxy server doesn't understand
4934   <x:ref>Connection</x:ref>, it will erroneously forward that header to the
4935   next inbound server, which would result in a hung connection.
4938   One attempted solution was the introduction of a Proxy-Connection header,
4939   targeted specifically at proxies. In practice, this was also unworkable,
4940   because proxies are often deployed in multiple layers, bringing about the
4941   same problem discussed above.
4944   As a result, clients are encouraged not to send the Proxy-Connection header
4945   in any requests.
4948   Clients are also encouraged to consider the use of Connection: keep-alive
4949   in requests carefully; while they can enable persistent connections with
4950   HTTP/1.0 servers, clients using them need will need to monitor the
4951   connection for "hung" requests (which indicate that the client ought stop
4952   sending the header), and this mechanism ought not be used by clients at all
4953   when a proxy is being used.
4957<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4959   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4960   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4961   any transfer-coding prior to forwarding a message via a MIME-compliant
4962   protocol.
4968<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4970  Clarify that the string "HTTP" in the HTTP-version ABFN production is case
4971  sensitive. Restrict the version numbers to be single digits due to the fact
4972  that implementations are known to handle multi-digit version numbers
4973  incorrectly.
4974  (<xref target="http.version"/>)
4977  Update use of abs_path production from RFC 1808 to the path-absolute + query
4978  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4979  request method only.
4980  (<xref target="request-target"/>)
4983  Require that invalid whitespace around field-names be rejected.
4984  (<xref target="header.fields"/>)
4987  Rules about implicit linear whitespace between certain grammar productions
4988  have been removed; now whitespace is only allowed where specifically
4989  defined in the ABNF.
4990  (<xref target="whitespace"/>)
4993  The NUL octet is no longer allowed in comment and quoted-string
4994  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4995  Non-ASCII content in header fields and reason phrase has been obsoleted and
4996  made opaque (the TEXT rule was removed).
4997  (<xref target="field.components"/>)
5000  Empty list elements in list productions have been deprecated.
5001  (<xref target="abnf.extension"/>)
5004  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
5005  fields as errors.
5006  (<xref target="message.body"/>)
5009  Remove reference to non-existent identity transfer-coding value tokens.
5010  (Sections <xref format="counter" target="message.body"/> and
5011  <xref format="counter" target="transfer.codings"/>)
5014  Clarification that the chunk length does not include the count of the octets
5015  in the chunk header and trailer. Furthermore disallowed line folding
5016  in chunk extensions, and deprecate their use.
5017  (<xref target="chunked.encoding"/>)
5020  Registration of Transfer Codings now requires IETF Review
5021  (<xref target="transfer.coding.registry"/>)
5024  Remove hard limit of two connections per server.
5025  Remove requirement to retry a sequence of requests as long it was idempotent.
5026  Remove requirements about when servers are allowed to close connections
5027  prematurely.
5028  (<xref target="persistent.practical"/>)
5031  Remove requirement to retry requests under certain cirumstances when the
5032  server prematurely closes the connection.
5033  (<xref target="message.transmission.requirements"/>)
5036  Change ABNF productions for header fields to only define the field value.
5039  Clarify exactly when "close" connection options have to be sent.
5040  (<xref target="header.connection"/>)
5043  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
5044  other than 101 (this was incorporated from <xref target="RFC2817"/>).
5045  (<xref target="header.upgrade"/>)
5048  Take over the Upgrade Token Registry, previously defined in
5049  <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
5050  (<xref target="upgrade.token.registry"/>)
5055<?BEGININC p1-messaging.abnf-appendix ?>
5056<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5058<artwork type="abnf" name="p1-messaging.parsed-abnf">
5059<x:ref>BWS</x:ref> = OWS
5061<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5062 connection-option ] )
5063<x:ref>Content-Length</x:ref> = 1*DIGIT
5065<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5066 ]
5067<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5068<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5069<x:ref>Host</x:ref> = uri-host [ ":" port ]
5071<x:ref>OWS</x:ref> = *( SP / HTAB )
5073<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5075<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5076<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5077<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5078 transfer-coding ] )
5080<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5081<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5083<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5084 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5085 comment ] ) ] )
5087<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5088<x:ref>absolute-form</x:ref> = absolute-URI
5089<x:ref>asterisk-form</x:ref> = "*"
5090<x:ref>attribute</x:ref> = token
5091<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5092<x:ref>authority-form</x:ref> = authority
5094<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5095<x:ref>chunk-data</x:ref> = 1*OCTET
5096<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5097<x:ref>chunk-ext-name</x:ref> = token
5098<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5099<x:ref>chunk-size</x:ref> = 1*HEXDIG
5100<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5101<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5102<x:ref>connection-option</x:ref> = token
5103<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5104 / %x2A-5B ; '*'-'['
5105 / %x5D-7E ; ']'-'~'
5106 / obs-text
5108<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5109<x:ref>field-name</x:ref> = token
5110<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5112<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5113<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5114<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5116<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5118<x:ref>message-body</x:ref> = *OCTET
5119<x:ref>method</x:ref> = token
5121<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5122<x:ref>obs-text</x:ref> = %x80-FF
5123<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
5125<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5126<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5127<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5128<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5129<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5130<x:ref>protocol-name</x:ref> = token
5131<x:ref>protocol-version</x:ref> = token
5132<x:ref>pseudonym</x:ref> = token
5134<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5135 / %x5D-7E ; ']'-'~'
5136 / obs-text
5137<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5138 / %x5D-7E ; ']'-'~'
5139 / obs-text
5140<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5141<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5142<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5143<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5144<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5145<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5147<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5148<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5149<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5150<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5151<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5152<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5153 asterisk-form
5155<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5156 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5157<x:ref>start-line</x:ref> = request-line / status-line
5158<x:ref>status-code</x:ref> = 3DIGIT
5159<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5161<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5162<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5163 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5164<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5165<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5166<x:ref>token</x:ref> = 1*tchar
5167<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5168<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5169 transfer-extension
5170<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5171<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5173<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5175<x:ref>value</x:ref> = word
5177<x:ref>word</x:ref> = token / quoted-string
5180<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5181; Connection defined but not used
5182; Content-Length defined but not used
5183; HTTP-message defined but not used
5184; Host defined but not used
5185; TE defined but not used
5186; Trailer defined but not used
5187; Transfer-Encoding defined but not used
5188; URI-reference defined but not used
5189; Upgrade defined but not used
5190; Via defined but not used
5191; chunked-body defined but not used
5192; http-URI defined but not used
5193; https-URI defined but not used
5194; partial-URI defined but not used
5195; special defined but not used
5197<?ENDINC p1-messaging.abnf-appendix ?>
5199<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5201<section title="Since RFC 2616">
5203  Extracted relevant partitions from <xref target="RFC2616"/>.
5207<section title="Since draft-ietf-httpbis-p1-messaging-00">
5209  Closed issues:
5210  <list style="symbols">
5211    <t>
5212      <eref target=""/>:
5213      "HTTP Version should be case sensitive"
5214      (<eref target=""/>)
5215    </t>
5216    <t>
5217      <eref target=""/>:
5218      "'unsafe' characters"
5219      (<eref target=""/>)
5220    </t>
5221    <t>
5222      <eref target=""/>:
5223      "Chunk Size Definition"
5224      (<eref target=""/>)
5225    </t>
5226    <t>
5227      <eref target=""/>:
5228      "Message Length"
5229      (<eref target=""/>)
5230    </t>
5231    <t>
5232      <eref target=""/>:
5233      "Media Type Registrations"
5234      (<eref target=""/>)
5235    </t>
5236    <t>
5237      <eref target=""/>:
5238      "URI includes query"
5239      (<eref target=""/>)
5240    </t>
5241    <t>
5242      <eref target=""/>:
5243      "No close on 1xx responses"
5244      (<eref target=""/>)
5245    </t>
5246    <t>
5247      <eref target=""/>:
5248      "Remove 'identity' token references"
5249      (<eref target=""/>)
5250    </t>
5251    <t>
5252      <eref target=""/>:
5253      "Import query BNF"
5254    </t>
5255    <t>
5256      <eref target=""/>:
5257      "qdtext BNF"
5258    </t>
5259    <t>
5260      <eref target=""/>:
5261      "Normative and Informative references"
5262    </t>
5263    <t>
5264      <eref target=""/>:
5265      "RFC2606 Compliance"
5266    </t>
5267    <t>
5268      <eref target=""/>:
5269      "RFC977 reference"
5270    </t>
5271    <t>
5272      <eref target=""/>:
5273      "RFC1700 references"
5274    </t>
5275    <t>
5276      <eref target=""/>:
5277      "inconsistency in date format explanation"
5278    </t>
5279    <t>
5280      <eref target=""/>:
5281      "Date reference typo"
5282    </t>
5283    <t>
5284      <eref target=""/>:
5285      "Informative references"
5286    </t>
5287    <t>
5288      <eref target=""/>:
5289      "ISO-8859-1 Reference"
5290    </t>
5291    <t>
5292      <eref target=""/>:
5293      "Normative up-to-date references"
5294    </t>
5295  </list>
5298  Other changes:
5299  <list style="symbols">
5300    <t>
5301      Update media type registrations to use RFC4288 template.
5302    </t>
5303    <t>
5304      Use names of RFC4234 core rules DQUOTE and HTAB,
5305      fix broken ABNF for chunk-data
5306      (work in progress on <eref target=""/>)
5307    </t>
5308  </list>
5312<section title="Since draft-ietf-httpbis-p1-messaging-01">
5314  Closed issues:
5315  <list style="symbols">
5316    <t>
5317      <eref target=""/>:
5318      "Bodies on GET (and other) requests"
5319    </t>
5320    <t>
5321      <eref target=""/>:
5322      "Updating to RFC4288"
5323    </t>
5324    <t>
5325      <eref target=""/>:
5326      "Status Code and Reason Phrase"
5327    </t>
5328    <t>
5329      <eref target=""/>:
5330      "rel_path not used"
5331    </t>
5332  </list>
5335  Ongoing work on ABNF conversion (<eref target=""/>):
5336  <list style="symbols">
5337    <t>
5338      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5339      "trailer-part").
5340    </t>
5341    <t>
5342      Avoid underscore character in rule names ("http_URL" ->
5343      "http-URL", "abs_path" -> "path-absolute").
5344    </t>
5345    <t>
5346      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5347      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5348      have to be updated when switching over to RFC3986.
5349    </t>
5350    <t>
5351      Synchronize core rules with RFC5234.
5352    </t>
5353    <t>
5354      Get rid of prose rules that span multiple lines.
5355    </t>
5356    <t>
5357      Get rid of unused rules LOALPHA and UPALPHA.
5358    </t>
5359    <t>
5360      Move "Product Tokens" section (back) into Part 1, as "token" is used
5361      in the definition of the Upgrade header field.
5362    </t>
5363    <t>
5364      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5365    </t>
5366    <t>
5367      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5368    </t>
5369  </list>
5373<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5375  Closed issues:
5376  <list style="symbols">
5377    <t>
5378      <eref target=""/>:
5379      "HTTP-date vs. rfc1123-date"
5380    </t>
5381    <t>
5382      <eref target=""/>:
5383      "WS in quoted-pair"
5384    </t>
5385  </list>
5388  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5389  <list style="symbols">
5390    <t>
5391      Reference RFC 3984, and update header field registrations for headers defined
5392      in this document.
5393    </t>
5394  </list>
5397  Ongoing work on ABNF conversion (<eref target=""/>):
5398  <list style="symbols">
5399    <t>
5400      Replace string literals when the string really is case-sensitive (HTTP-version).
5401    </t>
5402  </list>
5406<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5408  Closed issues:
5409  <list style="symbols">
5410    <t>
5411      <eref target=""/>:
5412      "Connection closing"
5413    </t>
5414    <t>
5415      <eref target=""/>:
5416      "Move registrations and registry information to IANA Considerations"
5417    </t>
5418    <t>
5419      <eref target=""/>:
5420      "need new URL for PAD1995 reference"
5421    </t>
5422    <t>
5423      <eref target=""/>:
5424      "IANA Considerations: update HTTP URI scheme registration"
5425    </t>
5426    <t>
5427      <eref target=""/>:
5428      "Cite HTTPS URI scheme definition"
5429    </t>
5430    <t>
5431      <eref target=""/>:
5432      "List-type headers vs Set-Cookie"
5433    </t>
5434  </list>
5437  Ongoing work on ABNF conversion (<eref target=""/>):
5438  <list style="symbols">
5439    <t>
5440      Replace string literals when the string really is case-sensitive (HTTP-Date).
5441    </t>
5442    <t>
5443      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5444    </t>
5445  </list>
5449<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5451  Closed issues:
5452  <list style="symbols">
5453    <t>
5454      <eref target=""/>:
5455      "Out-of-date reference for URIs"
5456    </t>
5457    <t>
5458      <eref target=""/>:
5459      "RFC 2822 is updated by RFC 5322"
5460    </t>
5461  </list>
5464  Ongoing work on ABNF conversion (<eref target=""/>):
5465  <list style="symbols">
5466    <t>
5467      Use "/" instead of "|" for alternatives.
5468    </t>
5469    <t>
5470      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5471    </t>
5472    <t>
5473      Only reference RFC 5234's core rules.
5474    </t>
5475    <t>
5476      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5477      whitespace ("OWS") and required whitespace ("RWS").
5478    </t>
5479    <t>
5480      Rewrite ABNFs to spell out whitespace rules, factor out
5481      header field value format definitions.
5482    </t>
5483  </list>
5487<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5489  Closed issues:
5490  <list style="symbols">
5491    <t>
5492      <eref target=""/>:
5493      "Header LWS"
5494    </t>
5495    <t>
5496      <eref target=""/>:
5497      "Sort 1.3 Terminology"
5498    </t>
5499    <t>
5500      <eref target=""/>:
5501      "RFC2047 encoded words"
5502    </t>
5503    <t>
5504      <eref target=""/>:
5505      "Character Encodings in TEXT"
5506    </t>
5507    <t>
5508      <eref target=""/>:
5509      "Line Folding"
5510    </t>
5511    <t>
5512      <eref target=""/>:
5513      "OPTIONS * and proxies"
5514    </t>
5515    <t>
5516      <eref target=""/>:
5517      "reason-phrase BNF"
5518    </t>
5519    <t>
5520      <eref target=""/>:
5521      "Use of TEXT"
5522    </t>
5523    <t>
5524      <eref target=""/>:
5525      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5526    </t>
5527    <t>
5528      <eref target=""/>:
5529      "RFC822 reference left in discussion of date formats"
5530    </t>
5531  </list>
5534  Final work on ABNF conversion (<eref target=""/>):
5535  <list style="symbols">
5536    <t>
5537      Rewrite definition of list rules, deprecate empty list elements.
5538    </t>
5539    <t>
5540      Add appendix containing collected and expanded ABNF.
5541    </t>
5542  </list>
5545  Other changes:
5546  <list style="symbols">
5547    <t>
5548      Rewrite introduction; add mostly new Architecture Section.
5549    </t>
5550    <t>
5551      Move definition of quality values from Part 3 into Part 1;
5552      make TE request header field grammar independent of accept-params (defined in Part 3).
5553    </t>
5554  </list>
5558<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5560  Closed issues:
5561  <list style="symbols">
5562    <t>
5563      <eref target=""/>:
5564      "base for numeric protocol elements"
5565    </t>
5566    <t>
5567      <eref target=""/>:
5568      "comment ABNF"
5569    </t>
5570  </list>
5573  Partly resolved issues:
5574  <list style="symbols">
5575    <t>
5576      <eref target=""/>:
5577      "205 Bodies" (took out language that implied that there might be
5578      methods for which a request body MUST NOT be included)
5579    </t>
5580    <t>
5581      <eref target=""/>:
5582      "editorial improvements around HTTP-date"
5583    </t>
5584  </list>
5588<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5590  Closed issues:
5591  <list style="symbols">
5592    <t>
5593      <eref target=""/>:
5594      "Repeating single-value headers"
5595    </t>
5596    <t>
5597      <eref target=""/>:
5598      "increase connection limit"
5599    </t>
5600    <t>
5601      <eref target=""/>:
5602      "IP addresses in URLs"
5603    </t>
5604    <t>
5605      <eref target=""/>:
5606      "take over HTTP Upgrade Token Registry"
5607    </t>
5608    <t>
5609      <eref target=""/>:
5610      "CR and LF in chunk extension values"
5611    </t>
5612    <t>
5613      <eref target=""/>:
5614      "HTTP/0.9 support"
5615    </t>
5616    <t>
5617      <eref target=""/>:
5618      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5619    </t>
5620    <t>
5621      <eref target=""/>:
5622      "move definitions of gzip/deflate/compress to part 1"
5623    </t>
5624    <t>
5625      <eref target=""/>:
5626      "disallow control characters in quoted-pair"
5627    </t>
5628  </list>
5631  Partly resolved issues:
5632  <list style="symbols">
5633    <t>
5634      <eref target=""/>:
5635      "update IANA requirements wrt Transfer-Coding values" (add the
5636      IANA Considerations subsection)
5637    </t>
5638  </list>
5642<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5644  Closed issues:
5645  <list style="symbols">
5646    <t>
5647      <eref target=""/>:
5648      "header parsing, treatment of leading and trailing OWS"
5649    </t>
5650  </list>
5653  Partly resolved issues:
5654  <list style="symbols">
5655    <t>
5656      <eref target=""/>:
5657      "Placement of 13.5.1 and 13.5.2"
5658    </t>
5659    <t>
5660      <eref target=""/>:
5661      "use of term "word" when talking about header structure"
5662    </t>
5663  </list>
5667<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5669  Closed issues:
5670  <list style="symbols">
5671    <t>
5672      <eref target=""/>:
5673      "Clarification of the term 'deflate'"
5674    </t>
5675    <t>
5676      <eref target=""/>:
5677      "OPTIONS * and proxies"
5678    </t>
5679    <t>
5680      <eref target=""/>:
5681      "MIME-Version not listed in P1, general header fields"
5682    </t>
5683    <t>
5684      <eref target=""/>:
5685      "IANA registry for content/transfer encodings"
5686    </t>
5687    <t>
5688      <eref target=""/>:
5689      "Case-sensitivity of HTTP-date"
5690    </t>
5691    <t>
5692      <eref target=""/>:
5693      "use of term "word" when talking about header structure"
5694    </t>
5695  </list>
5698  Partly resolved issues:
5699  <list style="symbols">
5700    <t>
5701      <eref target=""/>:
5702      "Term for the requested resource's URI"
5703    </t>
5704  </list>
5708<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5710  Closed issues:
5711  <list style="symbols">
5712    <t>
5713      <eref target=""/>:
5714      "Connection Closing"
5715    </t>
5716    <t>
5717      <eref target=""/>:
5718      "Delimiting messages with multipart/byteranges"
5719    </t>
5720    <t>
5721      <eref target=""/>:
5722      "Handling multiple Content-Length headers"
5723    </t>
5724    <t>
5725      <eref target=""/>:
5726      "Clarify entity / representation / variant terminology"
5727    </t>
5728    <t>
5729      <eref target=""/>:
5730      "consider removing the 'changes from 2068' sections"
5731    </t>
5732  </list>
5735  Partly resolved issues:
5736  <list style="symbols">
5737    <t>
5738      <eref target=""/>:
5739      "HTTP(s) URI scheme definitions"
5740    </t>
5741  </list>
5745<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5747  Closed issues:
5748  <list style="symbols">
5749    <t>
5750      <eref target=""/>:
5751      "Trailer requirements"
5752    </t>
5753    <t>
5754      <eref target=""/>:
5755      "Text about clock requirement for caches belongs in p6"
5756    </t>
5757    <t>
5758      <eref target=""/>:
5759      "effective request URI: handling of missing host in HTTP/1.0"
5760    </t>
5761    <t>
5762      <eref target=""/>:
5763      "confusing Date requirements for clients"
5764    </t>
5765  </list>
5768  Partly resolved issues:
5769  <list style="symbols">
5770    <t>
5771      <eref target=""/>:
5772      "Handling multiple Content-Length headers"
5773    </t>
5774  </list>
5778<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5780  Closed issues:
5781  <list style="symbols">
5782    <t>
5783      <eref target=""/>:
5784      "RFC2145 Normative"
5785    </t>
5786    <t>
5787      <eref target=""/>:
5788      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5789    </t>
5790    <t>
5791      <eref target=""/>:
5792      "define 'transparent' proxy"
5793    </t>
5794    <t>
5795      <eref target=""/>:
5796      "Header Classification"
5797    </t>
5798    <t>
5799      <eref target=""/>:
5800      "Is * usable as a request-uri for new methods?"
5801    </t>
5802    <t>
5803      <eref target=""/>:
5804      "Migrate Upgrade details from RFC2817"
5805    </t>
5806    <t>
5807      <eref target=""/>:
5808      "untangle ABNFs for header fields"
5809    </t>
5810    <t>
5811      <eref target=""/>:
5812      "update RFC 2109 reference"
5813    </t>
5814  </list>
5818<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5820  Closed issues:
5821  <list style="symbols">
5822    <t>
5823      <eref target=""/>:
5824      "Allow is not in 13.5.2"
5825    </t>
5826    <t>
5827      <eref target=""/>:
5828      "Handling multiple Content-Length headers"
5829    </t>
5830    <t>
5831      <eref target=""/>:
5832      "untangle ABNFs for header fields"
5833    </t>
5834    <t>
5835      <eref target=""/>:
5836      "Content-Length ABNF broken"
5837    </t>
5838  </list>
5842<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5844  Closed issues:
5845  <list style="symbols">
5846    <t>
5847      <eref target=""/>:
5848      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5849    </t>
5850    <t>
5851      <eref target=""/>:
5852      "Recommend minimum sizes for protocol elements"
5853    </t>
5854    <t>
5855      <eref target=""/>:
5856      "Set expectations around buffering"
5857    </t>
5858    <t>
5859      <eref target=""/>:
5860      "Considering messages in isolation"
5861    </t>
5862  </list>
5866<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5868  Closed issues:
5869  <list style="symbols">
5870    <t>
5871      <eref target=""/>:
5872      "DNS Spoofing / DNS Binding advice"
5873    </t>
5874    <t>
5875      <eref target=""/>:
5876      "move RFCs 2145, 2616, 2817 to Historic status"
5877    </t>
5878    <t>
5879      <eref target=""/>:
5880      "\-escaping in quoted strings"
5881    </t>
5882    <t>
5883      <eref target=""/>:
5884      "'Close' should be reserved in the HTTP header field registry"
5885    </t>
5886  </list>
5890<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5892  Closed issues:
5893  <list style="symbols">
5894    <t>
5895      <eref target=""/>:
5896      "Document HTTP's error-handling philosophy"
5897    </t>
5898    <t>
5899      <eref target=""/>:
5900      "Explain header registration"
5901    </t>
5902    <t>
5903      <eref target=""/>:
5904      "Revise Acknowledgements Sections"
5905    </t>
5906    <t>
5907      <eref target=""/>:
5908      "Retrying Requests"
5909    </t>
5910    <t>
5911      <eref target=""/>:
5912      "Closing the connection on server error"
5913    </t>
5914  </list>
5918<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5920  Closed issues:
5921  <list style="symbols">
5922    <t>
5923      <eref target=""/>:
5924      "Proxy-Connection and Keep-Alive"
5925    </t>
5926    <t>
5927      <eref target=""/>:
5928      "Clarify 'User Agent'"
5929    </t>
5930    <t>
5931      <eref target=""/>:
5932      "Define non-final responses"
5933    </t>
5934    <t>
5935      <eref target=""/>:
5936      "intended maturity level vs normative references"
5937    </t>
5938    <t>
5939      <eref target=""/>:
5940      "Intermediary rewriting of queries"
5941    </t>
5942  </list>
5946<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5948  Closed issues:
5949  <list style="symbols">
5950    <t>
5951      <eref target=""/>:
5952      "message-body in CONNECT response"
5953    </t>
5954    <t>
5955      <eref target=""/>:
5956      "Misplaced text on connection handling in p2"
5957    </t>
5958    <t>
5959      <eref target=""/>:
5960      "wording of line folding rule"
5961    </t>
5962    <t>
5963      <eref target=""/>:
5964      "chunk-extensions"
5965    </t>
5966    <t>
5967      <eref target=""/>:
5968      "make IANA policy definitions consistent"
5969    </t>
5970  </list>
5974<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5976  Closed issues:
5977  <list style="symbols">
5978    <t>
5979      <eref target=""/>:
5980      "make IANA policy definitions consistent"
5981    </t>
5982    <t>
5983      <eref target=""/>:
5984      "clarify connection header field values are case-insensitive"
5985    </t>
5986    <t>
5987      <eref target=""/>:
5988      "ABNF requirements for recipients"
5989    </t>
5990    <t>
5991      <eref target=""/>:
5992      "note introduction of new IANA registries as normative changes"
5993    </t>
5994  </list>
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