source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1744

Last change on this file since 1744 was 1744, checked in by fielding@…, 10 years ago

we know they exist, so reword section on lower-level network intermediaries

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 247.5 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.
605   An implementation is considered conformant if it complies with all of the
606   requirements associated with the roles it partakes in HTTP.
609   Senders &MUST-NOT; generate protocol elements that do not match the grammar
610   defined by the ABNF rules for those protocol elements.
613   Unless noted otherwise, recipients &MUST; be able to parse all protocol
614   elements matching the ABNF rules defined for them and &MAY; attempt to recover a usable
615   protocol element from an invalid construct.  HTTP does not define
616   specific error handling mechanisms except when they have a direct impact
617   on security, since different applications of the protocol require
618   different error handling strategies.  For example, a Web browser might
619   wish to transparently recover from a response where the <x:ref>Location</x:ref>
620   header field doesn't parse according to the ABNF, whereas a systems control
621   client might consider any form of error recovery to be dangerous.
625<section title="Protocol Versioning" anchor="http.version">
626  <x:anchor-alias value="HTTP-version"/>
627  <x:anchor-alias value="HTTP-name"/>
629   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
630   versions of the protocol. This specification defines version "1.1".
631   The protocol version as a whole indicates the sender's conformance
632   with the set of requirements laid out in that version's corresponding
633   specification of HTTP.
636   The version of an HTTP message is indicated by an HTTP-version field
637   in the first line of the message. HTTP-version is case-sensitive.
639<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
640  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
641  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
644   The HTTP version number consists of two decimal digits separated by a "."
645   (period or decimal point).  The first digit ("major version") indicates the
646   HTTP messaging syntax, whereas the second digit ("minor version") indicates
647   the highest minor version to which the sender is
648   conformant and able to understand for future communication.  The minor
649   version advertises the sender's communication capabilities even when the
650   sender is only using a backwards-compatible subset of the protocol,
651   thereby letting the recipient know that more advanced features can
652   be used in response (by servers) or in future requests (by clients).
655   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
656   <xref target="RFC1945"/> or a recipient whose version is unknown,
657   the HTTP/1.1 message is constructed such that it can be interpreted
658   as a valid HTTP/1.0 message if all of the newer features are ignored.
659   This specification places recipient-version requirements on some
660   new features so that a conformant sender will only use compatible
661   features until it has determined, through configuration or the
662   receipt of a message, that the recipient supports HTTP/1.1.
665   The interpretation of a header field does not change between minor
666   versions of the same major HTTP version, though the default
667   behavior of a recipient in the absence of such a field can change.
668   Unless specified otherwise, header fields defined in HTTP/1.1 are
669   defined for all versions of HTTP/1.x.  In particular, the <x:ref>Host</x:ref>
670   and <x:ref>Connection</x:ref> header fields ought to be implemented by all
671   HTTP/1.x implementations whether or not they advertise conformance with
672   HTTP/1.1.
675   New header fields can be defined such that, when they are
676   understood by a recipient, they might override or enhance the
677   interpretation of previously defined header fields.  When an
678   implementation receives an unrecognized header field, the recipient
679   &MUST; ignore that header field for local processing regardless of
680   the message's HTTP version.  An unrecognized header field received
681   by a proxy &MUST; be forwarded downstream unless the header field's
682   field-name is listed in the message's <x:ref>Connection</x:ref> header field
683   (see <xref target="header.connection"/>).
684   These requirements allow HTTP's functionality to be enhanced without
685   requiring prior update of deployed intermediaries.
688   Intermediaries that process HTTP messages (i.e., all intermediaries
689   other than those acting as tunnels) &MUST; send their own HTTP-version
690   in forwarded messages.  In other words, they &MUST-NOT; blindly
691   forward the first line of an HTTP message without ensuring that the
692   protocol version in that message matches a version to which that
693   intermediary is conformant for both the receiving and
694   sending of messages.  Forwarding an HTTP message without rewriting
695   the HTTP-version might result in communication errors when downstream
696   recipients use the message sender's version to determine what features
697   are safe to use for later communication with that sender.
700   An HTTP client &SHOULD; send a request version equal to the highest
701   version to which the client is conformant and
702   whose major version is no higher than the highest version supported
703   by the server, if this is known.  An HTTP client &MUST-NOT; send a
704   version to which it is not conformant.
707   An HTTP client &MAY; send a lower request version if it is known that
708   the server incorrectly implements the HTTP specification, but only
709   after the client has attempted at least one normal request and determined
710   from the response status or header fields (e.g., <x:ref>Server</x:ref>) that
711   the server improperly handles higher request versions.
714   An HTTP server &SHOULD; send a response version equal to the highest
715   version to which the server is conformant and
716   whose major version is less than or equal to the one received in the
717   request.  An HTTP server &MUST-NOT; send a version to which it is not
718   conformant.  A server &MAY; send a <x:ref>505 (HTTP Version Not
719   Supported)</x:ref> response if it cannot send a response using the
720   major version used in the client's request.
723   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
724   if it is known or suspected that the client incorrectly implements the
725   HTTP specification and is incapable of correctly processing later
726   version responses, such as when a client fails to parse the version
727   number correctly or when an intermediary is known to blindly forward
728   the HTTP-version even when it doesn't conform to the given minor
729   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
730   performed unless triggered by specific client attributes, such as when
731   one or more of the request header fields (e.g., <x:ref>User-Agent</x:ref>)
732   uniquely match the values sent by a client known to be in error.
735   The intention of HTTP's versioning design is that the major number
736   will only be incremented if an incompatible message syntax is
737   introduced, and that the minor number will only be incremented when
738   changes made to the protocol have the effect of adding to the message
739   semantics or implying additional capabilities of the sender.  However,
740   the minor version was not incremented for the changes introduced between
741   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
742   is specifically avoiding any such changes to the protocol.
746<section title="Uniform Resource Identifiers" anchor="uri">
747<iref primary="true" item="resource"/>
749   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
750   throughout HTTP as the means for identifying resources. URI references
751   are used to target requests, indicate redirects, and define relationships.
752   HTTP does not limit what a resource might be; it merely defines an interface
753   that can be used to interact with a resource via HTTP. More information on
754   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
756  <x:anchor-alias value="URI-reference"/>
757  <x:anchor-alias value="absolute-URI"/>
758  <x:anchor-alias value="relative-part"/>
759  <x:anchor-alias value="authority"/>
760  <x:anchor-alias value="path-abempty"/>
761  <x:anchor-alias value="path-absolute"/>
762  <x:anchor-alias value="port"/>
763  <x:anchor-alias value="query"/>
764  <x:anchor-alias value="uri-host"/>
765  <x:anchor-alias value="partial-URI"/>
767   This specification adopts the definitions of "URI-reference",
768   "absolute-URI", "relative-part", "port", "host",
769   "path-abempty", "path-absolute", "query", and "authority" from the
770   URI generic syntax <xref target="RFC3986"/>.
771   In addition, we define a partial-URI rule for protocol elements
772   that allow a relative URI but not a fragment.
774<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"/>
775  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
776  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
777  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
778  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
779  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
780  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
781  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
782  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
783  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
785  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
788   Each protocol element in HTTP that allows a URI reference will indicate
789   in its ABNF production whether the element allows any form of reference
790   (URI-reference), only a URI in absolute form (absolute-URI), only the
791   path and optional query components, or some combination of the above.
792   Unless otherwise indicated, URI references are parsed
793   relative to the effective request URI
794   (<xref target="effective.request.uri"/>).
797<section title="http URI scheme" anchor="http.uri">
798  <x:anchor-alias value="http-URI"/>
799  <iref item="http URI scheme" primary="true"/>
800  <iref item="URI scheme" subitem="http" primary="true"/>
802   The "http" URI scheme is hereby defined for the purpose of minting
803   identifiers according to their association with the hierarchical
804   namespace governed by a potential HTTP origin server listening for
805   TCP connections on a given port.
807<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
808  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
811   The HTTP origin server is identified by the generic syntax's
812   <x:ref>authority</x:ref> component, which includes a host identifier
813   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
814   The remainder of the URI, consisting of both the hierarchical path
815   component and optional query component, serves as an identifier for
816   a potential resource within that origin server's name space.
819   If the host identifier is provided as an IP literal or IPv4 address,
820   then the origin server is any listener on the indicated TCP port at
821   that IP address. If host is a registered name, then that name is
822   considered an indirect identifier and the recipient might use a name
823   resolution service, such as DNS, to find the address of a listener
824   for that host.
825   The host &MUST-NOT; be empty; if an "http" URI is received with an
826   empty host, then it &MUST; be rejected as invalid.
827   If the port subcomponent is empty or not given, then TCP port 80 is
828   assumed (the default reserved port for WWW services).
831   Regardless of the form of host identifier, access to that host is not
832   implied by the mere presence of its name or address. The host might or might
833   not exist and, even when it does exist, might or might not be running an
834   HTTP server or listening to the indicated port. The "http" URI scheme
835   makes use of the delegated nature of Internet names and addresses to
836   establish a naming authority (whatever entity has the ability to place
837   an HTTP server at that Internet name or address) and allows that
838   authority to determine which names are valid and how they might be used.
841   When an "http" URI is used within a context that calls for access to the
842   indicated resource, a client &MAY; attempt access by resolving
843   the host to an IP address, establishing a TCP connection to that address
844   on the indicated port, and sending an HTTP request message
845   (<xref target="http.message"/>) containing the URI's identifying data
846   (<xref target="message.routing"/>) to the server.
847   If the server responds to that request with a non-interim HTTP response
848   message, as described in &status-codes;, then that response
849   is considered an authoritative answer to the client's request.
852   Although HTTP is independent of the transport protocol, the "http"
853   scheme is specific to TCP-based services because the name delegation
854   process depends on TCP for establishing authority.
855   An HTTP service based on some other underlying connection protocol
856   would presumably be identified using a different URI scheme, just as
857   the "https" scheme (below) is used for servers that require an SSL/TLS
858   transport layer on a connection. Other protocols might also be used to
859   provide access to "http" identified resources &mdash; it is only the
860   authoritative interface used for mapping the namespace that is
861   specific to TCP.
864   The URI generic syntax for authority also includes a deprecated
865   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
866   for including user authentication information in the URI.  Some
867   implementations make use of the userinfo component for internal
868   configuration of authentication information, such as within command
869   invocation options, configuration files, or bookmark lists, even
870   though such usage might expose a user identifier or password.
871   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
872   delimiter) when transmitting an "http" URI in a message.  Recipients
873   of HTTP messages that contain a URI reference &SHOULD; parse for the
874   existence of userinfo and treat its presence as an error, likely
875   indicating that the deprecated subcomponent is being used to obscure
876   the authority for the sake of phishing attacks.
880<section title="https URI scheme" anchor="https.uri">
881   <x:anchor-alias value="https-URI"/>
882   <iref item="https URI scheme"/>
883   <iref item="URI scheme" subitem="https"/>
885   The "https" URI scheme is hereby defined for the purpose of minting
886   identifiers according to their association with the hierarchical
887   namespace governed by a potential HTTP origin server listening for
888   SSL/TLS-secured connections on a given TCP port.
891   All of the requirements listed above for the "http" scheme are also
892   requirements for the "https" scheme, except that a default TCP port
893   of 443 is assumed if the port subcomponent is empty or not given,
894   and the TCP connection &MUST; be secured for privacy through the
895   use of strong encryption prior to sending the first HTTP request.
897<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
898  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
901   Unlike the "http" scheme, responses to "https" identified requests
902   are never "public" and thus &MUST-NOT; be reused for shared caching.
903   They can, however, be reused in a private cache if the message is
904   cacheable by default in HTTP or specifically indicated as such by
905   the Cache-Control header field (&header-cache-control;).
908   Resources made available via the "https" scheme have no shared
909   identity with the "http" scheme even if their resource identifiers
910   indicate the same authority (the same host listening to the same
911   TCP port).  They are distinct name spaces and are considered to be
912   distinct origin servers.  However, an extension to HTTP that is
913   defined to apply to entire host domains, such as the Cookie protocol
914   <xref target="RFC6265"/>, can allow information
915   set by one service to impact communication with other services
916   within a matching group of host domains.
919   The process for authoritative access to an "https" identified
920   resource is defined in <xref target="RFC2818"/>.
924<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
926   Since the "http" and "https" schemes conform to the URI generic syntax,
927   such URIs are normalized and compared according to the algorithm defined
928   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
929   described above for each scheme.
932   If the port is equal to the default port for a scheme, the normal
933   form is to elide the port subcomponent. Likewise, an empty path
934   component is equivalent to an absolute path of "/", so the normal
935   form is to provide a path of "/" instead. The scheme and host
936   are case-insensitive and normally provided in lowercase; all
937   other components are compared in a case-sensitive manner.
938   Characters other than those in the "reserved" set are equivalent
939   to their percent-encoded octets (see <xref target="RFC3986"
940   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
943   For example, the following three URIs are equivalent:
945<figure><artwork type="example">
954<section title="Message Format" anchor="http.message">
955<x:anchor-alias value="generic-message"/>
956<x:anchor-alias value="message.types"/>
957<x:anchor-alias value="HTTP-message"/>
958<x:anchor-alias value="start-line"/>
959<iref item="header section"/>
960<iref item="headers"/>
961<iref item="header field"/>
963   All HTTP/1.1 messages consist of a start-line followed by a sequence of
964   octets in a format similar to the Internet Message Format
965   <xref target="RFC5322"/>: zero or more header fields (collectively
966   referred to as the "headers" or the "header section"), an empty line
967   indicating the end of the header section, and an optional message body.
969<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
970  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
971                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
972                   <x:ref>CRLF</x:ref>
973                   [ <x:ref>message-body</x:ref> ]
976   The normal procedure for parsing an HTTP message is to read the
977   start-line into a structure, read each header field into a hash
978   table by field name until the empty line, and then use the parsed
979   data to determine if a message body is expected.  If a message body
980   has been indicated, then it is read as a stream until an amount
981   of octets equal to the message body length is read or the connection
982   is closed.
985   Recipients &MUST; parse an HTTP message as a sequence of octets in an
986   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
987   Parsing an HTTP message as a stream of Unicode characters, without regard
988   for the specific encoding, creates security vulnerabilities due to the
989   varying ways that string processing libraries handle invalid multibyte
990   character sequences that contain the octet LF (%x0A).  String-based
991   parsers can only be safely used within protocol elements after the element
992   has been extracted from the message, such as within a header field-value
993   after message parsing has delineated the individual fields.
996   An HTTP message can be parsed as a stream for incremental processing or
997   forwarding downstream.  However, recipients cannot rely on incremental
998   delivery of partial messages, since some implementations will buffer or
999   delay message forwarding for the sake of network efficiency, security
1000   checks, or payload transformations.
1003<section title="Start Line" anchor="start.line">
1004  <x:anchor-alias value="Start-Line"/>
1006   An HTTP message can either be a request from client to server or a
1007   response from server to client.  Syntactically, the two types of message
1008   differ only in the start-line, which is either a request-line (for requests)
1009   or a status-line (for responses), and in the algorithm for determining
1010   the length of the message body (<xref target="message.body"/>).
1011   In theory, a client could receive requests and a server could receive
1012   responses, distinguishing them by their different start-line formats,
1013   but in practice servers are implemented to only expect a request
1014   (a response is interpreted as an unknown or invalid request method)
1015   and clients are implemented to only expect a response.
1017<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1018  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1023   Implementations &MUST-NOT; send whitespace between the start-line and
1024   the first header field. The presence of such whitespace in a request
1025   might be an attempt to trick a server into ignoring that field or
1026   processing the line after it as a new request, either of which might
1027   result in a security vulnerability if other implementations within
1028   the request chain interpret the same message differently.
1029   Likewise, the presence of such whitespace in a response might be
1030   ignored by some clients or cause others to cease parsing.
1033<section title="Request Line" anchor="request.line">
1034  <x:anchor-alias value="Request"/>
1035  <x:anchor-alias value="request-line"/>
1037   A request-line begins with a method token, followed by a single
1038   space (SP), the request-target, another single space (SP), the
1039   protocol version, and ending with CRLF.
1041<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1042  <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>
1044<iref primary="true" item="method"/>
1045<t anchor="method">
1046   The method token indicates the request method to be performed on the
1047   target resource. The request method is case-sensitive.
1049<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1050  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1053   The methods defined by this specification can be found in
1054   &methods;, along with information regarding the HTTP method registry
1055   and considerations for defining new methods.
1057<iref item="request-target"/>
1059   The request-target identifies the target resource upon which to apply
1060   the request, as defined in <xref target="request-target"/>.
1063   No whitespace is allowed inside the method, request-target, and
1064   protocol version.  Hence, recipients typically parse the request-line
1065   into its component parts by splitting on the SP characters.
1068   Unfortunately, some user agents fail to properly encode hypertext
1069   references that have embedded whitespace, sending the characters
1070   directly instead of properly percent-encoding the disallowed characters.
1071   Recipients of an invalid request-line &SHOULD; respond with either a
1072   <x:ref>400 (Bad Request)</x:ref> error or a <x:ref>301 (Moved Permanently)</x:ref>
1073   redirect with the request-target properly encoded.  Recipients &SHOULD-NOT;
1074   attempt to autocorrect and then process the request without a redirect,
1075   since the invalid request-line might be deliberately crafted to bypass
1076   security filters along the request chain.
1079   HTTP does not place a pre-defined limit on the length of a request-line.
1080   A server that receives a method longer than any that it implements
1081   &SHOULD; respond with either a <x:ref>405 (Method Not Allowed)</x:ref>, if it is an origin
1082   server, or a <x:ref>501 (Not Implemented)</x:ref> status code.
1083   A server &MUST; be prepared to receive URIs of unbounded length and
1084   respond with the <x:ref>414 (URI Too Long)</x:ref> status code if the received
1085   request-target would be longer than the server wishes to handle
1086   (see &status-414;).
1089   Various ad-hoc limitations on request-line length are found in practice.
1090   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1091   minimum, request-line lengths of up to 8000 octets.
1095<section title="Status Line" anchor="status.line">
1096  <x:anchor-alias value="response"/>
1097  <x:anchor-alias value="status-line"/>
1099   The first line of a response message is the status-line, consisting
1100   of the protocol version, a space (SP), the status code, another space,
1101   a possibly-empty textual phrase describing the status code, and
1102   ending with CRLF.
1104<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1105  <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>
1108<t anchor="status-code">
1109   The status-code element is a 3-digit integer result code of the attempt to
1110   understand and satisfy the request. See &status-codes; for
1111   further information, such as the list of status codes defined by this
1112   specification, the IANA registry, and considerations for new status codes.
1114<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1115  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1118<t anchor="reason-phrase">  
1119   The reason-phrase element exists for the sole purpose of providing a
1120   textual description associated with the numeric status code, mostly
1121   out of deference to earlier Internet application protocols that were more
1122   frequently used with interactive text clients. A client &SHOULD; ignore
1123   the reason-phrase content.
1125<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1126  <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> )
1131<section title="Header Fields" anchor="header.fields">
1132  <x:anchor-alias value="header-field"/>
1133  <x:anchor-alias value="field-content"/>
1134  <x:anchor-alias value="field-name"/>
1135  <x:anchor-alias value="field-value"/>
1136  <x:anchor-alias value="obs-fold"/>
1138   Each HTTP header field consists of a case-insensitive field name
1139   followed by a colon (":"), optional whitespace, and the field value.
1141<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"/>
1142  <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>
1143  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1144  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1145  <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> )
1146  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1147                 ; obsolete line folding
1148                 ; see <xref target="field.parsing"/>
1151   The field-name token labels the corresponding field-value as having the
1152   semantics defined by that header field.  For example, the <x:ref>Date</x:ref>
1153   header field is defined in &header-date; as containing the origination
1154   timestamp for the message in which it appears.
1157   HTTP header fields are fully extensible: there is no limit on the
1158   introduction of new field names, each presumably defining new semantics,
1159   or on the number of header fields used in a given message.  Existing
1160   fields are defined in each part of this specification and in many other
1161   specifications outside the standards process.
1162   New header fields can be introduced without changing the protocol version
1163   if their defined semantics allow them to be safely ignored by recipients
1164   that do not recognize them.
1167   New HTTP header fields &SHOULD; be registered with IANA according
1168   to the procedures in &cons-new-header-fields;.
1169   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1170   field-name is listed in the <x:ref>Connection</x:ref> header field
1171   (<xref target="header.connection"/>) or the proxy is specifically
1172   configured to block or otherwise transform such fields.
1173   Unrecognized header fields &SHOULD; be ignored by other recipients.
1176   The order in which header fields with differing field names are
1177   received is not significant. However, it is "good practice" to send
1178   header fields that contain control data first, such as <x:ref>Host</x:ref>
1179   on requests and <x:ref>Date</x:ref> on responses, so that implementations
1180   can decide when not to handle a message as early as possible.  A server
1181   &MUST; wait until the entire header section is received before interpreting
1182   a request message, since later header fields might include conditionals,
1183   authentication credentials, or deliberately misleading duplicate
1184   header fields that would impact request processing.
1187   Multiple header fields with the same field name &MUST-NOT; be
1188   sent in a message unless the entire field value for that
1189   header field is defined as a comma-separated list [i.e., #(values)].
1190   Multiple header fields with the same field name can be combined into
1191   one "field-name: field-value" pair, without changing the semantics of the
1192   message, by appending each subsequent field value to the combined
1193   field value in order, separated by a comma. The order in which
1194   header fields with the same field name are received is therefore
1195   significant to the interpretation of the combined field value;
1196   a proxy &MUST-NOT; change the order of these field values when
1197   forwarding a message.
1200  <t>
1201   &Note; The "Set-Cookie" header field as implemented in
1202   practice can occur multiple times, but does not use the list syntax, and
1203   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1204   for details.) Also note that the Set-Cookie2 header field specified in
1205   <xref target="RFC2965"/> does not share this problem.
1206  </t>
1209<section title="Whitespace" anchor="whitespace">
1210<t anchor="rule.LWS">
1211   This specification uses three rules to denote the use of linear
1212   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1213   BWS ("bad" whitespace).
1215<t anchor="rule.OWS">
1216   The OWS rule is used where zero or more linear whitespace octets might
1217   appear. OWS &SHOULD; either not be produced or be produced as a single
1218   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1219   be replaced with a single SP or transformed to all SP octets (each
1220   octet other than SP replaced with SP) before interpreting the field value
1221   or forwarding the message downstream.
1223<t anchor="rule.RWS">
1224   RWS is used when at least one linear whitespace octet is required to
1225   separate field tokens. RWS &SHOULD; be produced as a single SP.
1226   Multiple RWS octets that occur within field-content &SHOULD; either
1227   be replaced with a single SP or transformed to all SP octets before
1228   interpreting the field value or forwarding the message downstream.
1230<t anchor="rule.BWS">
1231   BWS is used where the grammar allows optional whitespace for historical
1232   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1233   recipients &MUST; accept such bad optional whitespace and remove it before
1234   interpreting the field value or forwarding the message downstream.
1236<t anchor="rule.whitespace">
1237  <x:anchor-alias value="BWS"/>
1238  <x:anchor-alias value="OWS"/>
1239  <x:anchor-alias value="RWS"/>
1241<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"/>
1242  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1243                 ; "optional" whitespace
1244  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1245                 ; "required" whitespace
1246  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1247                 ; "bad" whitespace
1251<section title="Field Parsing" anchor="field.parsing">
1253   No whitespace is allowed between the header field-name and colon.
1254   In the past, differences in the handling of such whitespace have led to
1255   security vulnerabilities in request routing and response handling.
1256   Any received request message that contains whitespace between a header
1257   field-name and colon &MUST; be rejected with a response code of 400
1258   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1259   message before forwarding the message downstream.
1262   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1263   preferred. The field value does not include any leading or trailing white
1264   space: OWS occurring before the first non-whitespace octet of the
1265   field value or after the last non-whitespace octet of the field value
1266   is ignored and &SHOULD; be removed before further processing (as this does
1267   not change the meaning of the header field).
1270   Historically, HTTP header field values could be extended over multiple
1271   lines by preceding each extra line with at least one space or horizontal
1272   tab (obs-fold). This specification deprecates such line
1273   folding except within the message/http media type
1274   (<xref target=""/>).
1275   HTTP senders &MUST-NOT; produce messages that include line folding
1276   (i.e., that contain any field-value that matches the obs-fold rule) unless
1277   the message is intended for packaging within the message/http media type.
1278   HTTP recipients &SHOULD; accept line folding and replace any embedded
1279   obs-fold whitespace with either a single SP or a matching number of SP
1280   octets (to avoid buffer copying) prior to interpreting the field value or
1281   forwarding the message downstream.
1284   Historically, HTTP has allowed field content with text in the ISO-8859-1
1285   <xref target="ISO-8859-1"/> character encoding and supported other
1286   character sets only through use of <xref target="RFC2047"/> encoding.
1287   In practice, most HTTP header field values use only a subset of the
1288   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1289   header fields &SHOULD; limit their field values to US-ASCII octets.
1290   Recipients &SHOULD; treat other (obs-text) octets in field content as
1291   opaque data.
1295<section title="Field Length" anchor="field.length">
1297   HTTP does not place a pre-defined limit on the length of header fields,
1298   either in isolation or as a set. A server &MUST; be prepared to receive
1299   request header fields of unbounded length and respond with a <x:ref>4xx
1300   (Client Error)</x:ref> status code if the received header field(s) would be
1301   longer than the server wishes to handle.
1304   A client that receives response headers that are longer than it wishes to
1305   handle can only treat it as a server error.
1308   Various ad-hoc limitations on header length are found in practice. It is
1309   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1310   combined header fields have 4000 or more octets.
1314<section title="Field value components" anchor="field.components">
1315<t anchor="rule.token.separators">
1316  <x:anchor-alias value="tchar"/>
1317  <x:anchor-alias value="token"/>
1318  <x:anchor-alias value="special"/>
1319  <x:anchor-alias value="word"/>
1320   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1321   separated by whitespace or special characters. These special characters
1322   &MUST; be in a quoted string to be used within a parameter value (as defined
1323   in <xref target="transfer.codings"/>).
1325<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"/>
1326  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1328  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1330  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1331 -->
1332  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1333                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1334                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1335                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1337  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1338                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1339                 / "]" / "?" / "=" / "{" / "}"
1341<t anchor="rule.quoted-string">
1342  <x:anchor-alias value="quoted-string"/>
1343  <x:anchor-alias value="qdtext"/>
1344  <x:anchor-alias value="obs-text"/>
1345   A string of text is parsed as a single word if it is quoted using
1346   double-quote marks.
1348<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"/>
1349  <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>
1350  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1351  <x:ref>obs-text</x:ref>       = %x80-FF
1353<t anchor="rule.quoted-pair">
1354  <x:anchor-alias value="quoted-pair"/>
1355   The backslash octet ("\") can be used as a single-octet
1356   quoting mechanism within quoted-string constructs:
1358<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1359  <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> )
1362   Recipients that process the value of the quoted-string &MUST; handle a
1363   quoted-pair as if it were replaced by the octet following the backslash.
1366   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1367   escaping (i.e., other than DQUOTE and the backslash octet).
1369<t anchor="rule.comment">
1370  <x:anchor-alias value="comment"/>
1371  <x:anchor-alias value="ctext"/>
1372   Comments can be included in some HTTP header fields by surrounding
1373   the comment text with parentheses. Comments are only allowed in
1374   fields containing "comment" as part of their field value definition.
1376<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1377  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1378  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1380<t anchor="rule.quoted-cpair">
1381  <x:anchor-alias value="quoted-cpair"/>
1382   The backslash octet ("\") can be used as a single-octet
1383   quoting mechanism within comment constructs:
1385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1386  <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> )
1389   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1390   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1394<section title="ABNF list extension: #rule" anchor="abnf.extension">
1396  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1397  improve readability in the definitions of some header field values.
1400  A construct "#" is defined, similar to "*", for defining comma-delimited
1401  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1402  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1403  comma (",") and optional whitespace (OWS).   
1406  Thus,
1407</preamble><artwork type="example">
1408  1#element =&gt; element *( OWS "," OWS element )
1411  and:
1412</preamble><artwork type="example">
1413  #element =&gt; [ 1#element ]
1416  and for n &gt;= 1 and m &gt; 1:
1417</preamble><artwork type="example">
1418  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1421  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1422  list elements. In other words, consumers would follow the list productions:
1424<figure><artwork type="example">
1425  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1427  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1430  Note that empty elements do not contribute to the count of elements present,
1431  though.
1434  For example, given these ABNF productions:
1436<figure><artwork type="example">
1437  example-list      = 1#example-list-elmt
1438  example-list-elmt = token ; see <xref target="field.components"/>
1441  Then these are valid values for example-list (not including the double
1442  quotes, which are present for delimitation only):
1444<figure><artwork type="example">
1445  "foo,bar"
1446  "foo ,bar,"
1447  "foo , ,bar,charlie   "
1450  But these values would be invalid, as at least one non-empty element is
1451  required:
1453<figure><artwork type="example">
1454  ""
1455  ","
1456  ",   ,"
1459  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1460  expanded as explained above.
1465<section title="Message Body" anchor="message.body">
1466  <x:anchor-alias value="message-body"/>
1468   The message body (if any) of an HTTP message is used to carry the
1469   payload body of that request or response.  The message body is
1470   identical to the payload body unless a transfer coding has been
1471   applied, as described in <xref target="header.transfer-encoding"/>.
1473<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1474  <x:ref>message-body</x:ref> = *OCTET
1477   The rules for when a message body is allowed in a message differ for
1478   requests and responses.
1481   The presence of a message body in a request is signaled by a
1482   a <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1483   field. Request message framing is independent of method semantics,
1484   even if the method does not define any use for a message body.
1487   The presence of a message body in a response depends on both
1488   the request method to which it is responding and the response
1489   status code (<xref target="status-code"/>).
1490   Responses to the HEAD request method never include a message body
1491   because the associated response header fields (e.g.,
1492   <x:ref>Transfer-Encoding</x:ref>, <x:ref>Content-Length</x:ref>, etc.) only
1493   indicate what their values would have been if the request method had been
1494   GET. <x:ref>2xx (Successful)</x:ref> responses to CONNECT switch to tunnel
1495   mode instead of having a message body.
1496   All <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, and
1497   <x:ref>304 (Not Modified)</x:ref> responses &MUST-NOT; include a message body.
1498   All other responses do include a message body, although the body
1499   &MAY; be of zero length. (See &status-codes; and &status-304;.)
1502<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1503  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1504  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1505  <x:anchor-alias value="Transfer-Encoding"/>
1507   When one or more transfer codings are applied to a payload body in order
1508   to form the message body, a Transfer-Encoding header field &MUST; be sent
1509   in the message and &MUST; contain the list of corresponding
1510   transfer-coding names in the same order that they were applied.
1511   Transfer codings are defined in <xref target="transfer.codings"/>.
1513<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1514  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1517   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1518   MIME, which was designed to enable safe transport of binary data over a
1519   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1520   However, safe transport has a different focus for an 8bit-clean transfer
1521   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1522   accurately delimit a dynamically generated payload and to distinguish
1523   payload encodings that are only applied for transport efficiency or
1524   security from those that are characteristics of the target resource.
1527   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1528   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1529   crucial role in delimiting messages when the payload body size is not
1530   known in advance.
1531   When the "chunked" transfer-coding is used, it &MUST; be the last
1532   transfer-coding applied to form the message body and &MUST-NOT;
1533   be applied more than once in a message body.
1534   If any transfer-coding is applied to a request payload body,
1535   the final transfer-coding applied &MUST; be "chunked".
1536   If any transfer-coding is applied to a response payload body, then either
1537   the final transfer-coding applied &MUST; be "chunked" or
1538   the message &MUST; be terminated by closing the connection.
1541   For example,
1542</preamble><artwork type="example">
1543  Transfer-Encoding: gzip, chunked
1545   indicates that the payload body has been compressed using the gzip
1546   coding and then chunked using the chunked coding while forming the
1547   message body.
1550   If more than one Transfer-Encoding header field is present in a message,
1551   the multiple field-values &MUST; be combined into one field-value,
1552   according to the algorithm defined in <xref target="header.fields"/>,
1553   before determining the message body length.
1556   Unlike <x:ref>Content-Encoding</x:ref> (&content-codings;),
1557   Transfer-Encoding is a property of the message, not of the payload, and thus
1558   &MAY; be added or removed by any implementation along the request/response
1559   chain. Additional information about the encoding parameters &MAY; be
1560   provided by other header fields not defined by this specification.
1563   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1564   <x:ref>304 (Not Modified)</x:ref> response (&status-304;) to a GET request,
1565   neither of which includes a message body,
1566   to indicate that the origin server would have applied a transfer coding
1567   to the message body if the request had been an unconditional GET.
1568   This indication is not required, however, because any recipient on
1569   the response chain (including the origin server) can remove transfer
1570   codings when they are not needed.
1573   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1574   implementations advertising only HTTP/1.0 support will not understand
1575   how to process a transfer-encoded payload.
1576   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1577   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1578   might be in the form of specific user configuration or by remembering the
1579   version of a prior received response.
1580   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1581   the corresponding request indicates HTTP/1.1 (or later).
1584   A server that receives a request message with a transfer-coding it does
1585   not understand &SHOULD; respond with <x:ref>501 (Not Implemented)</x:ref> and then
1586   close the connection.
1590<section title="Content-Length" anchor="header.content-length">
1591  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1592  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1593  <x:anchor-alias value="Content-Length"/>
1595   When a message does not have a <x:ref>Transfer-Encoding</x:ref> header field
1596   and the payload body length can be determined prior to being transferred, a
1597   Content-Length header field &SHOULD; be sent to indicate the length of the
1598   payload body that is either present as the message body, for requests
1599   and non-HEAD responses other than <x:ref>304 (Not Modified)</x:ref>, or
1600   would have been present had the request been an unconditional GET.  The
1601   length is expressed as a decimal number of octets.
1603<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1604  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1607   An example is
1609<figure><artwork type="example">
1610  Content-Length: 3495
1613   In the case of a response to a HEAD request, Content-Length indicates
1614   the size of the payload body (without any potential transfer-coding)
1615   that would have been sent had the request been a GET.
1616   In the case of a <x:ref>304 (Not Modified)</x:ref> response (&status-304;)
1617   to a GET request, Content-Length indicates the size of the payload body (without
1618   any potential transfer-coding) that would have been sent in a <x:ref>200 (OK)</x:ref>
1619   response.
1622   HTTP's use of Content-Length is significantly different from how it is
1623   used in MIME, where it is an optional field used only within the
1624   "message/external-body" media-type.
1627   Any Content-Length field value greater than or equal to zero is valid.
1628   Since there is no predefined limit to the length of an HTTP payload,
1629   recipients &SHOULD; anticipate potentially large decimal numerals and
1630   prevent parsing errors due to integer conversion overflows
1631   (<xref target="attack.protocol.element.size.overflows"/>).
1634   If a message is received that has multiple Content-Length header fields
1635   (<xref target="header.content-length"/>) with field-values consisting
1636   of the same decimal value, or a single Content-Length header field with
1637   a field value containing a list of identical decimal values (e.g.,
1638   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1639   header fields have been generated or combined by an upstream message
1640   processor, then the recipient &MUST; either reject the message as invalid
1641   or replace the duplicated field-values with a single valid Content-Length
1642   field containing that decimal value prior to determining the message body
1643   length.
1647<section title="Message Body Length" anchor="message.body.length">
1649   The length of a message body is determined by one of the following
1650   (in order of precedence):
1653  <list style="numbers">
1654    <x:lt><t>
1655     Any response to a HEAD request and any response with a
1656     <x:ref>1xx (Informational)</x:ref>, <x:ref>204 (No Content)</x:ref>, or
1657     <x:ref>304 (Not Modified)</x:ref> status code is always
1658     terminated by the first empty line after the header fields, regardless of
1659     the header fields present in the message, and thus cannot contain a
1660     message body.
1661    </t></x:lt>
1662    <x:lt><t>
1663     Any <x:ref>2xx (Successful)</x:ref> response to a CONNECT request implies that the
1664     connection will become a tunnel immediately after the empty line that
1665     concludes the header fields.  A client &MUST; ignore any
1666     <x:ref>Content-Length</x:ref> or <x:ref>Transfer-Encoding</x:ref> header
1667     fields received in such a message.
1668    </t></x:lt>
1669    <x:lt><t>
1670     If a <x:ref>Transfer-Encoding</x:ref> header field is present
1671     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1672     is the final encoding, the message body length is determined by reading
1673     and decoding the chunked data until the transfer-coding indicates the
1674     data is complete.
1675    </t>
1676    <t>
1677     If a <x:ref>Transfer-Encoding</x:ref> header field is present in a
1678     response and the "chunked" transfer-coding is not the final encoding, the
1679     message body length is determined by reading the connection until it is
1680     closed by the server.
1681     If a Transfer-Encoding header field is present in a request and the
1682     "chunked" transfer-coding is not the final encoding, the message body
1683     length cannot be determined reliably; the server &MUST; respond with
1684     the <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1685    </t>
1686    <t>
1687     If a message is received with both a <x:ref>Transfer-Encoding</x:ref>
1688     and a <x:ref>Content-Length</x:ref> header field, the
1689     Transfer-Encoding overrides the Content-Length.
1690     Such a message might indicate an attempt to perform request or response
1691     smuggling (bypass of security-related checks on message routing or content)
1692     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1693     be removed, prior to forwarding the message downstream, or replaced with
1694     the real message body length after the transfer-coding is decoded.
1695    </t></x:lt>
1696    <x:lt><t>
1697     If a message is received without <x:ref>Transfer-Encoding</x:ref> and with
1698     either multiple <x:ref>Content-Length</x:ref> header fields having
1699     differing field-values or a single Content-Length header field having an
1700     invalid value, then the message framing is invalid and &MUST; be treated
1701     as an error to prevent request or response smuggling.
1702     If this is a request message, the server &MUST; respond with
1703     a <x:ref>400 (Bad Request)</x:ref> status code and then close the connection.
1704     If this is a response message received by a proxy, the proxy
1705     &MUST; discard the received response, send a <x:ref>502 (Bad Gateway)</x:ref>
1706     status code as its downstream response, and then close the connection.
1707     If this is a response message received by a user-agent, it &MUST; be
1708     treated as an error by discarding the message and closing the connection.
1709    </t></x:lt>
1710    <x:lt><t>
1711     If a valid <x:ref>Content-Length</x:ref> header field is present without
1712     <x:ref>Transfer-Encoding</x:ref>, its decimal value defines the
1713     message body length in octets.  If the actual number of octets sent in
1714     the message is less than the indicated Content-Length, the recipient
1715     &MUST; consider the message to be incomplete and treat the connection
1716     as no longer usable.
1717     If the actual number of octets sent in the message is more than the indicated
1718     Content-Length, the recipient &MUST; only process the message body up to the
1719     field value's number of octets; the remainder of the message &MUST; either
1720     be discarded or treated as the next message in a pipeline.  For the sake of
1721     robustness, a user-agent &MAY; attempt to detect and correct such an error
1722     in message framing if it is parsing the response to the last request on
1723     a connection and the connection has been closed by the server.
1724    </t></x:lt>
1725    <x:lt><t>
1726     If this is a request message and none of the above are true, then the
1727     message body length is zero (no message body is present).
1728    </t></x:lt>
1729    <x:lt><t>
1730     Otherwise, this is a response message without a declared message body
1731     length, so the message body length is determined by the number of octets
1732     received prior to the server closing the connection.
1733    </t></x:lt>
1734  </list>
1737   Since there is no way to distinguish a successfully completed,
1738   close-delimited message from a partially-received message interrupted
1739   by network failure, implementations &SHOULD; use encoding or
1740   length-delimited messages whenever possible.  The close-delimiting
1741   feature exists primarily for backwards compatibility with HTTP/1.0.
1744   A server &MAY; reject a request that contains a message body but
1745   not a <x:ref>Content-Length</x:ref> by responding with
1746   <x:ref>411 (Length Required)</x:ref>.
1749   Unless a transfer-coding other than "chunked" has been applied,
1750   a client that sends a request containing a message body &SHOULD;
1751   use a valid <x:ref>Content-Length</x:ref> header field if the message body
1752   length is known in advance, rather than the "chunked" encoding, since some
1753   existing services respond to "chunked" with a <x:ref>411 (Length Required)</x:ref>
1754   status code even though they understand the chunked encoding.  This
1755   is typically because such services are implemented via a gateway that
1756   requires a content-length in advance of being called and the server
1757   is unable or unwilling to buffer the entire request before processing.
1760   A client that sends a request containing a message body &MUST; include a
1761   valid <x:ref>Content-Length</x:ref> header field if it does not know the
1762   server will handle HTTP/1.1 (or later) requests; such knowledge can be in
1763   the form of specific user configuration or by remembering the version of a
1764   prior received response.
1769<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1771   Request messages that are prematurely terminated, possibly due to a
1772   cancelled connection or a server-imposed time-out exception, &MUST;
1773   result in closure of the connection; sending an HTTP/1.1 error response
1774   prior to closing the connection is &OPTIONAL;.
1777   Response messages that are prematurely terminated, usually by closure
1778   of the connection prior to receiving the expected number of octets or by
1779   failure to decode a transfer-encoded message body, &MUST; be recorded
1780   as incomplete.  A response that terminates in the middle of the header
1781   block (before the empty line is received) cannot be assumed to convey the
1782   full semantics of the response and &MUST; be treated as an error.
1785   A message body that uses the chunked transfer encoding is
1786   incomplete if the zero-sized chunk that terminates the encoding has not
1787   been received.  A message that uses a valid <x:ref>Content-Length</x:ref> is
1788   incomplete if the size of the message body received (in octets) is less than
1789   the value given by Content-Length.  A response that has neither chunked
1790   transfer encoding nor Content-Length is terminated by closure of the
1791   connection, and thus is considered complete regardless of the number of
1792   message body octets received, provided that the header block was received
1793   intact.
1796   A user agent &MUST-NOT; render an incomplete response message body as if
1797   it were complete (i.e., some indication needs to be given to the user that an
1798   error occurred).  Cache requirements for incomplete responses are defined
1799   in &cache-incomplete;.
1802   A server &MUST; read the entire request message body or close
1803   the connection after sending its response, since otherwise the
1804   remaining data on a persistent connection would be misinterpreted
1805   as the next request.  Likewise,
1806   a client &MUST; read the entire response message body if it intends
1807   to reuse the same connection for a subsequent request.  Pipelining
1808   multiple requests on a connection is described in <xref target="pipelining"/>.
1812<section title="Message Parsing Robustness" anchor="message.robustness">
1814   Older HTTP/1.0 client implementations might send an extra CRLF
1815   after a POST request as a lame workaround for some early server
1816   applications that failed to read message body content that was
1817   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1818   preface or follow a request with an extra CRLF.  If terminating
1819   the request message body with a line-ending is desired, then the
1820   client &MUST; include the terminating CRLF octets as part of the
1821   message body length.
1824   In the interest of robustness, servers &SHOULD; ignore at least one
1825   empty line received where a request-line is expected. In other words, if
1826   the server is reading the protocol stream at the beginning of a
1827   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1828   Likewise, although the line terminator for the start-line and header
1829   fields is the sequence CRLF, we recommend that recipients recognize a
1830   single LF as a line terminator and ignore any CR.
1833   When a server listening only for HTTP request messages, or processing
1834   what appears from the start-line to be an HTTP request message,
1835   receives a sequence of octets that does not match the HTTP-message
1836   grammar aside from the robustness exceptions listed above, the
1837   server &MUST; respond with an HTTP/1.1 <x:ref>400 (Bad Request)</x:ref> response. 
1842<section title="Transfer Codings" anchor="transfer.codings">
1843  <x:anchor-alias value="transfer-coding"/>
1844  <x:anchor-alias value="transfer-extension"/>
1846   Transfer-coding values are used to indicate an encoding
1847   transformation that has been, can be, or might need to be applied to a
1848   payload body in order to ensure "safe transport" through the network.
1849   This differs from a content coding in that the transfer-coding is a
1850   property of the message rather than a property of the representation
1851   that is being transferred.
1853<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1854  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1855                     / "compress" ; <xref target="compress.coding"/>
1856                     / "deflate" ; <xref target="deflate.coding"/>
1857                     / "gzip" ; <xref target="gzip.coding"/>
1858                     / <x:ref>transfer-extension</x:ref>
1859  <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> )
1861<t anchor="rule.parameter">
1862  <x:anchor-alias value="attribute"/>
1863  <x:anchor-alias value="transfer-parameter"/>
1864  <x:anchor-alias value="value"/>
1865   Parameters are in the form of attribute/value pairs.
1867<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"/>
1868  <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>
1869  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1870  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1873   All transfer-coding values are case-insensitive.
1874   The HTTP Transfer Coding registry is defined in
1875   <xref target="transfer.coding.registry"/>.
1876   HTTP/1.1 uses transfer-coding values in the <x:ref>TE</x:ref> header field
1877   (<xref target="header.te"/>) and in the <x:ref>Transfer-Encoding</x:ref>
1878   header field (<xref target="header.transfer-encoding"/>).
1881<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1882  <iref item="chunked (Coding Format)"/>
1883  <iref item="Coding Format" subitem="chunked"/>
1884  <x:anchor-alias value="chunk"/>
1885  <x:anchor-alias value="chunked-body"/>
1886  <x:anchor-alias value="chunk-data"/>
1887  <x:anchor-alias value="chunk-ext"/>
1888  <x:anchor-alias value="chunk-ext-name"/>
1889  <x:anchor-alias value="chunk-ext-val"/>
1890  <x:anchor-alias value="chunk-size"/>
1891  <x:anchor-alias value="last-chunk"/>
1892  <x:anchor-alias value="trailer-part"/>
1893  <x:anchor-alias value="quoted-str-nf"/>
1894  <x:anchor-alias value="qdtext-nf"/>
1896   The chunked encoding modifies the body of a message in order to
1897   transfer it as a series of chunks, each with its own size indicator,
1898   followed by an &OPTIONAL; trailer containing header fields. This
1899   allows dynamically produced content to be transferred along with the
1900   information necessary for the recipient to verify that it has
1901   received the full message.
1903<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"/>
1904  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1905                   <x:ref>last-chunk</x:ref>
1906                   <x:ref>trailer-part</x:ref>
1907                   <x:ref>CRLF</x:ref>
1909  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1910                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1911  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1912  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1914  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1915  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1916  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1917  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1918  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1920  <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>
1921                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1922  <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>
1925   The chunk-size field is a string of hex digits indicating the size of
1926   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1927   zero, followed by the trailer, which is terminated by an empty line.
1930   The trailer allows the sender to include additional HTTP header
1931   fields at the end of the message. The <x:ref>Trailer</x:ref> header field
1932   can be used to indicate which header fields are included in a trailer (see
1933   <xref target="header.trailer"/>).
1936   A server using chunked transfer-coding in a response &MUST-NOT; use the
1937   trailer for any header fields unless at least one of the following is
1938   true:
1939  <list style="numbers">
1940    <t>the request included a <x:ref>TE</x:ref> header field that indicates
1941    "trailers" is acceptable in the transfer-coding of the response, as
1942    described in <xref target="header.te"/>; or,</t>
1944    <t>the trailer fields consist entirely of optional metadata, and the
1945    recipient could use the message (in a manner acceptable to the server where
1946    the field originated) without receiving it. In other words, the server that
1947    generated the header (often but not always the origin server) is willing to
1948    accept the possibility that the trailer fields might be silently discarded
1949    along the path to the client.</t>
1950  </list>
1953   This requirement prevents an interoperability failure when the
1954   message is being received by an HTTP/1.1 (or later) proxy and
1955   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1956   conformance with the protocol would have necessitated a possibly
1957   infinite buffer on the proxy.
1960   A process for decoding the "chunked" transfer-coding
1961   can be represented in pseudo-code as:
1963<figure><artwork type="code">
1964  length := 0
1965  read chunk-size, chunk-ext (if any) and CRLF
1966  while (chunk-size &gt; 0) {
1967     read chunk-data and CRLF
1968     append chunk-data to decoded-body
1969     length := length + chunk-size
1970     read chunk-size and CRLF
1971  }
1972  read header-field
1973  while (header-field not empty) {
1974     append header-field to existing header fields
1975     read header-field
1976  }
1977  Content-Length := length
1978  Remove "chunked" from Transfer-Encoding
1981   All HTTP/1.1 applications &MUST; be able to receive and decode the
1982   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1983   they do not understand.
1986   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
1987   sent and definition of new chunk-extensions is discouraged.
1991<section title="Compression Codings" anchor="compression.codings">
1993   The codings defined below can be used to compress the payload of a
1994   message.
1997   &Note; Use of program names for the identification of encoding formats
1998   is not desirable and is discouraged for future encodings. Their
1999   use here is representative of historical practice, not good
2000   design.
2003   &Note; For compatibility with previous implementations of HTTP,
2004   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2005   equivalent to "gzip" and "compress" respectively.
2008<section title="Compress Coding" anchor="compress.coding">
2009<iref item="compress (Coding Format)"/>
2010<iref item="Coding Format" subitem="compress"/>
2012   The "compress" format is produced by the common UNIX file compression
2013   program "compress". This format is an adaptive Lempel-Ziv-Welch
2014   coding (LZW).
2018<section title="Deflate Coding" anchor="deflate.coding">
2019<iref item="deflate (Coding Format)"/>
2020<iref item="Coding Format" subitem="deflate"/>
2022   The "deflate" format is defined as the "deflate" compression mechanism
2023   (described in <xref target="RFC1951"/>) used inside the "zlib"
2024   data format (<xref target="RFC1950"/>).
2027  <t>
2028    &Note; Some incorrect implementations send the "deflate"
2029    compressed data without the zlib wrapper.
2030   </t>
2034<section title="Gzip Coding" anchor="gzip.coding">
2035<iref item="gzip (Coding Format)"/>
2036<iref item="Coding Format" subitem="gzip"/>
2038   The "gzip" format is produced by the file compression program
2039   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2040   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2046<section title="TE" anchor="header.te">
2047  <iref primary="true" item="TE header field" x:for-anchor=""/>
2048  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2049  <x:anchor-alias value="TE"/>
2050  <x:anchor-alias value="t-codings"/>
2051  <x:anchor-alias value="te-params"/>
2052  <x:anchor-alias value="te-ext"/>
2054   The "TE" header field indicates what extension transfer-codings
2055   the client is willing to accept in the response, and whether or not it is
2056   willing to accept trailer fields in a chunked transfer-coding.
2059   Its value consists of the keyword "trailers" and/or a comma-separated
2060   list of extension transfer-coding names with optional accept
2061   parameters (as described in <xref target="transfer.codings"/>).
2063<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"/>
2064  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2065  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2066  <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> )
2067  <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> ]
2070   The presence of the keyword "trailers" indicates that the client is
2071   willing to accept trailer fields in a chunked transfer-coding, as
2072   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2073   transfer-coding values even though it does not itself represent a
2074   transfer-coding.
2077   Examples of its use are:
2079<figure><artwork type="example">
2080  TE: deflate
2081  TE:
2082  TE: trailers, deflate;q=0.5
2085   The TE header field only applies to the immediate connection.
2086   Therefore, the keyword &MUST; be supplied within a <x:ref>Connection</x:ref>
2087   header field (<xref target="header.connection"/>) whenever TE is present in
2088   an HTTP/1.1 message.
2091   A server tests whether a transfer-coding is acceptable, according to
2092   a TE field, using these rules:
2093  <list style="numbers">
2094    <x:lt>
2095      <t>The "chunked" transfer-coding is always acceptable. If the
2096         keyword "trailers" is listed, the client indicates that it is
2097         willing to accept trailer fields in the chunked response on
2098         behalf of itself and any downstream clients. The implication is
2099         that, if given, the client is stating that either all
2100         downstream clients are willing to accept trailer fields in the
2101         forwarded response, or that it will attempt to buffer the
2102         response on behalf of downstream recipients.
2103      </t><t>
2104         &Note; HTTP/1.1 does not define any means to limit the size of a
2105         chunked response such that a client can be assured of buffering
2106         the entire response.</t>
2107    </x:lt>
2108    <x:lt>
2109      <t>If the transfer-coding being tested is one of the transfer-codings
2110         listed in the TE field, then it is acceptable unless it
2111         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2112         qvalue of 0 means "not acceptable".)</t>
2113    </x:lt>
2114    <x:lt>
2115      <t>If multiple transfer-codings are acceptable, then the
2116         acceptable transfer-coding with the highest non-zero qvalue is
2117         preferred.  The "chunked" transfer-coding always has a qvalue
2118         of 1.</t>
2119    </x:lt>
2120  </list>
2123   If the TE field-value is empty or if no TE field is present, the only
2124   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2125   always acceptable.
2128<section title="Quality Values" anchor="quality.values">
2129  <x:anchor-alias value="qvalue"/>
2131   Both transfer codings (<x:ref>TE</x:ref> request header field,
2132   <xref target="header.te"/>) and content negotiation (&content.negotiation;)
2133   use short "floating point" numbers to indicate the relative importance
2134   ("weight") of various negotiable parameters.  A weight is normalized to a
2135   real number in the range 0 through 1, where 0 is the minimum and 1 the
2136   maximum value. If a parameter has a quality value of 0, then content with
2137   this parameter is "not acceptable" for the client. HTTP/1.1
2138   applications &MUST-NOT; generate more than three digits after the
2139   decimal point. User configuration of these values &SHOULD; also be
2140   limited in this fashion.
2142<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2143  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2144                 / ( "1" [ "." 0*3("0") ] )
2147  <t>
2148     &Note; "Quality values" is a misnomer, since these values merely represent
2149     relative degradation in desired quality.
2150  </t>
2155<section title="Trailer" anchor="header.trailer">
2156  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2157  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2158  <x:anchor-alias value="Trailer"/>
2160   The "Trailer" header field indicates that the given set of
2161   header fields is present in the trailer of a message encoded with
2162   chunked transfer-coding.
2164<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2165  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2168   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2169   message using chunked transfer-coding with a non-empty trailer. Doing
2170   so allows the recipient to know which header fields to expect in the
2171   trailer.
2174   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2175   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2176   trailer fields in a "chunked" transfer-coding.
2179   Message header fields listed in the Trailer header field &MUST-NOT;
2180   include the following header fields:
2181  <list style="symbols">
2182    <t><x:ref>Transfer-Encoding</x:ref></t>
2183    <t><x:ref>Content-Length</x:ref></t>
2184    <t><x:ref>Trailer</x:ref></t>
2185  </list>
2190<section title="Message Routing" anchor="message.routing">
2192   HTTP request message routing is determined by each client based on the
2193   target resource, the client's proxy configuration, and
2194   establishment or reuse of an inbound connection.  The corresponding
2195   response routing follows the same connection chain back to the client.
2198<section title="Identifying a Target Resource" anchor="target-resource">
2199  <iref primary="true" item="target resource"/>
2200  <iref primary="true" item="target URI"/>
2202   HTTP is used in a wide variety of applications, ranging from
2203   general-purpose computers to home appliances.  In some cases,
2204   communication options are hard-coded in a client's configuration.
2205   However, most HTTP clients rely on the same resource identification
2206   mechanism and configuration techniques as general-purpose Web browsers.
2209   HTTP communication is initiated by a user agent for some purpose.
2210   The purpose is a combination of request semantics, which are defined in
2211   <xref target="Part2"/>, and a target resource upon which to apply those
2212   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2213   an identifier for the "target resource", which a user agent would resolve
2214   to its absolute form in order to obtain the "target URI".  The target URI
2215   excludes the reference's fragment identifier component, if any,
2216   since fragment identifiers are reserved for client-side processing
2217   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2220   HTTP intermediaries obtain the request semantics and target URI
2221   from the request-line of an incoming request message.
2225<section title="Connecting Inbound" anchor="connecting.inbound">
2227   Once the target URI is determined, a client needs to decide whether
2228   a network request is necessary to accomplish the desired semantics and,
2229   if so, where that request is to be directed.
2232   If the client has a response cache and the request semantics can be
2233   satisfied by a cache (<xref target="Part6"/>), then the request is
2234   usually directed to the cache first.
2237   If the request is not satisfied by a cache, then a typical client will
2238   check its configuration to determine whether a proxy is to be used to
2239   satisfy the request.  Proxy configuration is implementation-dependent,
2240   but is often based on URI prefix matching, selective authority matching,
2241   or both, and the proxy itself is usually identified by an "http" or
2242   "https" URI.  If a proxy is applicable, the client connects inbound by
2243   establishing (or reusing) a connection to that proxy.
2246   If no proxy is applicable, a typical client will invoke a handler routine,
2247   usually specific to the target URI's scheme, to connect directly
2248   to an authority for the target resource.  How that is accomplished is
2249   dependent on the target URI scheme and defined by its associated
2250   specification, similar to how this specification defines origin server
2251   access for resolution of the "http" (<xref target="http.uri"/>) and
2252   "https" (<xref target="https.uri"/>) schemes.
2256<section title="Request Target" anchor="request-target">
2258   Once an inbound connection is obtained
2259   (<xref target=""/>),
2260   the client sends an HTTP request message (<xref target="http.message"/>)
2261   with a request-target derived from the target URI.
2262   There are four distinct formats for the request-target, depending on both
2263   the method being requested and whether the request is to a proxy.
2265<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"/>
2266  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2267                 / <x:ref>absolute-form</x:ref>
2268                 / <x:ref>authority-form</x:ref>
2269                 / <x:ref>asterisk-form</x:ref>
2271  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2272  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2273  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2274  <x:ref>asterisk-form</x:ref>  = "*"
2276<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2277   The most common form of request-target is the origin-form.
2278   When making a request directly to an origin server, other than a CONNECT
2279   or server-wide OPTIONS request (as detailed below),
2280   a client &MUST; send only the absolute path and query components of
2281   the target URI as the request-target.
2282   If the target URI's path component is empty, then the client &MUST; send
2283   "/" as the path within the origin-form of request-target.
2284   A <x:ref>Host</x:ref> header field is also sent, as defined in
2285   <xref target=""/>, containing the target URI's
2286   authority component (excluding any userinfo).
2289   For example, a client wishing to retrieve a representation of the resource
2290   identified as
2292<figure><artwork x:indent-with="  " type="example">
2296   directly from the origin server would open (or reuse) a TCP connection
2297   to port 80 of the host "" and send the lines:
2299<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2300GET /where?q=now HTTP/1.1
2304   followed by the remainder of the request message.
2306<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2307   When making a request to a proxy, other than a CONNECT or server-wide
2308   OPTIONS request (as detailed below), a client &MUST; send the target URI
2309   in absolute-form as the request-target.
2310   The proxy is requested to either service that request from a valid cache,
2311   if possible, or make the same request on the client's behalf to either
2312   the next inbound proxy server or directly to the origin server indicated
2313   by the request-target.  Requirements on such "forwarding" of messages are
2314   defined in <xref target="intermediary.forwarding"/>.
2317   An example absolute-form of request-line would be:
2319<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2320GET HTTP/1.1
2323   To allow for transition to the absolute-form for all requests in some
2324   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2325   in requests, even though HTTP/1.1 clients will only send them in requests
2326   to proxies.
2328<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2329   The authority-form of request-target is only used for CONNECT requests
2330   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2331   one or more proxies, a client &MUST; send only the target URI's
2332   authority component (excluding any userinfo) as the request-target.
2333   For example,
2335<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2338<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2339   The asterisk-form of request-target is only used for a server-wide
2340   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2341   for the server as a whole, as opposed to a specific named resource of
2342   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2343   For example,
2345<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2346OPTIONS * HTTP/1.1
2349   If a proxy receives an OPTIONS request with an absolute-form of
2350   request-target in which the URI has an empty path and no query component,
2351   then the last proxy on the request chain &MUST; send a request-target
2352   of "*" when it forwards the request to the indicated origin server.
2355   For example, the request
2356</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2360  would be forwarded by the final proxy as
2361</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2362OPTIONS * HTTP/1.1
2366   after connecting to port 8001 of host "".
2371<section title="Host" anchor="">
2372  <iref primary="true" item="Host header field" x:for-anchor=""/>
2373  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2374  <x:anchor-alias value="Host"/>
2376   The "Host" header field in a request provides the host and port
2377   information from the target URI, enabling the origin
2378   server to distinguish among resources while servicing requests
2379   for multiple host names on a single IP address.  Since the Host
2380   field-value is critical information for handling a request, it
2381   &SHOULD; be sent as the first header field following the request-line.
2383<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2384  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2387   A client &MUST; send a Host header field in all HTTP/1.1 request
2388   messages.  If the target URI includes an authority component, then
2389   the Host field-value &MUST; be identical to that authority component
2390   after excluding any userinfo (<xref target="http.uri"/>).
2391   If the authority component is missing or undefined for the target URI,
2392   then the Host header field &MUST; be sent with an empty field-value.
2395   For example, a GET request to the origin server for
2396   &lt;; would begin with:
2398<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2399GET /pub/WWW/ HTTP/1.1
2403   The Host header field &MUST; be sent in an HTTP/1.1 request even
2404   if the request-target is in the absolute-form, since this
2405   allows the Host information to be forwarded through ancient HTTP/1.0
2406   proxies that might not have implemented Host.
2409   When an HTTP/1.1 proxy receives a request with an absolute-form of
2410   request-target, the proxy &MUST; ignore the received
2411   Host header field (if any) and instead replace it with the host
2412   information of the request-target.  If the proxy forwards the request,
2413   it &MUST; generate a new Host field-value based on the received
2414   request-target rather than forward the received Host field-value.
2417   Since the Host header field acts as an application-level routing
2418   mechanism, it is a frequent target for malware seeking to poison
2419   a shared cache or redirect a request to an unintended server.
2420   An interception proxy is particularly vulnerable if it relies on
2421   the Host field-value for redirecting requests to internal
2422   servers, or for use as a cache key in a shared cache, without
2423   first verifying that the intercepted connection is targeting a
2424   valid IP address for that host.
2427   A server &MUST; respond with a <x:ref>400 (Bad Request)</x:ref> status code
2428   to any HTTP/1.1 request message that lacks a Host header field and
2429   to any request message that contains more than one Host header field
2430   or a Host header field with an invalid field-value.
2434<section title="Effective Request URI" anchor="effective.request.uri">
2435  <iref primary="true" item="effective request URI"/>
2437   A server that receives an HTTP request message &MUST; reconstruct
2438   the user agent's original target URI, based on the pieces of information
2439   learned from the request-target, <x:ref>Host</x:ref> header field, and
2440   connection context, in order to identify the intended target resource and
2441   properly service the request. The URI derived from this reconstruction
2442   process is referred to as the "effective request URI".
2445   For a user agent, the effective request URI is the target URI.
2448   If the request-target is in absolute-form, then the effective request URI
2449   is the same as the request-target.  Otherwise, the effective request URI
2450   is constructed as follows.
2453   If the request is received over an SSL/TLS-secured TCP connection,
2454   then the effective request URI's scheme is "https"; otherwise, the
2455   scheme is "http".
2458   If the request-target is in authority-form, then the effective
2459   request URI's authority component is the same as the request-target.
2460   Otherwise, if a <x:ref>Host</x:ref> header field is supplied with a
2461   non-empty field-value, then the authority component is the same as the
2462   Host field-value. Otherwise, the authority component is the concatenation of
2463   the default host name configured for the server, a colon (":"), and the
2464   connection's incoming TCP port number in decimal form.
2467   If the request-target is in authority-form or asterisk-form, then the
2468   effective request URI's combined path and query component is empty.
2469   Otherwise, the combined path and query component is the same as the
2470   request-target.
2473   The components of the effective request URI, once determined as above,
2474   can be combined into absolute-URI form by concatenating the scheme,
2475   "://", authority, and combined path and query component.
2479   Example 1: the following message received over an insecure TCP connection
2481<artwork type="example" x:indent-with="  ">
2482GET /pub/WWW/TheProject.html HTTP/1.1
2488  has an effective request URI of
2490<artwork type="example" x:indent-with="  ">
2496   Example 2: the following message received over an SSL/TLS-secured TCP
2497   connection
2499<artwork type="example" x:indent-with="  ">
2500OPTIONS * HTTP/1.1
2506  has an effective request URI of
2508<artwork type="example" x:indent-with="  ">
2513   An origin server that does not allow resources to differ by requested
2514   host &MAY; ignore the <x:ref>Host</x:ref> field-value and instead replace it
2515   with a configured server name when constructing the effective request URI.
2518   Recipients of an HTTP/1.0 request that lacks a <x:ref>Host</x:ref> header
2519   field &MAY; attempt to use heuristics (e.g., examination of the URI path for
2520   something unique to a particular host) in order to guess the
2521   effective request URI's authority component.
2525<section title="Intermediary Forwarding" anchor="intermediary.forwarding">
2527   As described in <xref target="intermediaries"/>, intermediaries can serve
2528   a variety of roles in the processing of HTTP requests and responses.
2529   Some intermediaries are used to improve performance or availability.
2530   Others are used for access control or to filter content.
2531   Since an HTTP stream has characteristics similar to a pipe-and-filter
2532   architecture, there are no inherent limits to the extent an intermediary
2533   can enhance (or interfere) with either direction of the stream.
2536   In order to avoid request loops, a proxy that forwards requests to other
2537   proxies &MUST; be able to recognize and exclude all of its own server
2538   names, including any aliases, local variations, or literal IP addresses.
2541   If a proxy receives a request-target with a host name that is not a
2542   fully qualified domain name, it &MAY; add its domain to the host name
2543   it received when forwarding the request.  A proxy &MUST-NOT; change the
2544   host name if it is a fully qualified domain name.
2547   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2548   parts of the received request-target when forwarding it to the next inbound
2549   server, except as noted above to replace an empty path with "/" or "*".
2552   Intermediaries that forward a message &MUST; implement the
2553   <x:ref>Connection</x:ref> header field as specified in
2554   <xref target="header.connection"/>.
2557<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2559  <cref anchor="TODO-end-to-end" source="jre">
2560    Restored from <eref target=""/>.
2561    See also <eref target=""/>.
2562  </cref>
2565   For the purpose of defining the behavior of caches and non-caching
2566   proxies, we divide HTTP header fields into two categories:
2567  <list style="symbols">
2568      <t>End-to-end header fields, which are  transmitted to the ultimate
2569        recipient of a request or response. End-to-end header fields in
2570        responses &MUST; be stored as part of a cache entry and &MUST; be
2571        transmitted in any response formed from a cache entry.</t>
2573      <t>Hop-by-hop header fields, which are meaningful only for a single
2574        transport-level connection, and are not stored by caches or
2575        forwarded by proxies.</t>
2576  </list>
2579   The following HTTP/1.1 header fields are hop-by-hop header fields:
2580  <list style="symbols">
2581      <t><x:ref>Connection</x:ref></t>
2582      <t>Keep-Alive (<xref target="RFC2068" x:fmt="of" x:sec=""/>)</t>
2583      <t><x:ref>Proxy-Authenticate</x:ref> (&header-proxy-authenticate;)</t>
2584      <t><x:ref>Proxy-Authorization</x:ref> (&header-proxy-authorization;)</t>
2585      <t><x:ref>TE</x:ref></t>
2586      <t><x:ref>Trailer</x:ref></t>
2587      <t><x:ref>Transfer-Encoding</x:ref></t>
2588      <t><x:ref>Upgrade</x:ref></t>
2589  </list>
2592   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2595   Other hop-by-hop header fields &MUST; be listed in a
2596   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>).
2600<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2602  <cref anchor="TODO-non-mod-headers" source="jre">
2603    Restored from <eref target=""/>.
2604    See also <eref target=""/>.
2605  </cref>
2608   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2609   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2610   modify an end-to-end header field unless the definition of that header field requires
2611   or specifically allows that.
2614   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2615   request or response, and it &MUST-NOT; add any of these fields if not
2616   already present:
2617  <list style="symbols">
2618    <t>Allow</t>
2619    <t>Content-Location</t>
2620    <t>Content-MD5</t>
2621    <t>ETag</t>
2622    <t>Last-Modified</t>
2623    <t>Server</t>
2624  </list>
2627   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2628   response:
2629  <list style="symbols">
2630    <t><x:ref>Expires</x:ref> (&header-expires;)</t>
2631  </list>
2634   but it &MAY; add any of these fields if not already present. If an
2635   <x:ref>Expires</x:ref> header field is added, it &MUST; be given a
2636   field value identical to that of the <x:ref>Date</x:ref> header field in
2637   that response.
2640   A proxy &MUST-NOT; modify or add any of the following fields in a
2641   message that contains the no-transform cache-control directive, or in
2642   any request:
2643  <list style="symbols">
2644    <t><x:ref>Content-Encoding</x:ref> (&header-content-encoding;)</t>
2645    <t><x:ref>Content-Range</x:ref> (&header-content-range;)</t>
2646    <t><x:ref>Content-Type</x:ref> (&header-content-type;)</t>
2647  </list>
2650   A transforming proxy &MAY; modify or add these fields to a message
2651   that does not include no-transform, but if it does so, it &MUST; add a
2652   Warning 214 (Transformation applied) if one does not already appear
2653   in the message (see &header-warning;).
2656  <t>
2657    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2658    cause authentication failures if stronger authentication
2659    mechanisms are introduced in later versions of HTTP. Such
2660    authentication mechanisms &MAY; rely on the values of header fields
2661    not listed here.
2662  </t>
2665   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2666   though it &MAY; change the message body through application or removal
2667   of a transfer-coding (<xref target="transfer.codings"/>).
2673<section title="Associating a Response to a Request" anchor="">
2675   HTTP does not include a request identifier for associating a given
2676   request message with its corresponding one or more response messages.
2677   Hence, it relies on the order of response arrival to correspond exactly
2678   to the order in which requests are made on the same connection.
2679   More than one response message per request only occurs when one or more
2680   informational responses (<x:ref>1xx</x:ref>, see &status-1xx;) precede a final response
2681   to the same request.
2684   A client that uses persistent connections and sends more than one request
2685   per connection &MUST; maintain a list of outstanding requests in the
2686   order sent on that connection and &MUST; associate each received response
2687   message to the highest ordered request that has not yet received a final
2688   (non-<x:ref>1xx</x:ref>) response.
2693<section title="Connection Management" anchor="">
2695<section title="Connection" anchor="header.connection">
2696  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2697  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2698  <x:anchor-alias value="Connection"/>
2699  <x:anchor-alias value="connection-option"/>
2701   The "Connection" header field allows the sender to specify
2702   options that are desired only for that particular connection.
2703   Such connection options &MUST; be removed or replaced before the
2704   message can be forwarded downstream by a proxy or gateway.
2705   This mechanism also allows the sender to indicate which HTTP
2706   header fields used in the message are only intended for the
2707   immediate recipient ("hop-by-hop"), as opposed to all recipients
2708   on the chain ("end-to-end"), enabling the message to be
2709   self-descriptive and allowing future connection-specific extensions
2710   to be deployed in HTTP without fear that they will be blindly
2711   forwarded by previously deployed intermediaries.
2714   The Connection header field's value has the following grammar:
2716<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-option"/>
2717  <x:ref>Connection</x:ref>        = 1#<x:ref>connection-option</x:ref>
2718  <x:ref>connection-option</x:ref> = <x:ref>token</x:ref>
2721   Connection options are compared case-insensitively.
2724   A proxy or gateway &MUST; parse a received Connection
2725   header field before a message is forwarded and, for each
2726   connection-option in this field, remove any header field(s) from
2727   the message with the same name as the connection-option, and then
2728   remove the Connection header field itself or replace it with the
2729   sender's own connection options for the forwarded message.
2732   A sender &MUST-NOT; include field-names in the Connection header
2733   field-value for fields that are defined as expressing constraints
2734   for all recipients in the request or response chain, such as the
2735   Cache-Control header field (&header-cache-control;).
2738   The connection options do not have to correspond to a header field
2739   present in the message, since a connection-specific header field
2740   might not be needed if there are no parameters associated with that
2741   connection option.  Recipients that trigger certain connection
2742   behavior based on the presence of connection options &MUST; do so
2743   based on the presence of the connection-option rather than only the
2744   presence of the optional header field.  In other words, if the
2745   connection option is received as a header field but not indicated
2746   within the Connection field-value, then the recipient &MUST; ignore
2747   the connection-specific header field because it has likely been
2748   forwarded by an intermediary that is only partially conformant.
2751   When defining new connection options, specifications ought to
2752   carefully consider existing deployed header fields and ensure
2753   that the new connection option does not share the same name as
2754   an unrelated header field that might already be deployed.
2755   Defining a new connection option essentially reserves that potential
2756   field-name for carrying additional information related to the
2757   connection option, since it would be unwise for senders to use
2758   that field-name for anything else.
2761   HTTP/1.1 defines the "close" connection option for the sender to
2762   signal that the connection will be closed after completion of the
2763   response. For example,
2765<figure><artwork type="example">
2766  Connection: close
2769   in either the request or the response header fields indicates that
2770   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2771   after the current request/response is complete.
2774   An HTTP/1.1 client that does not support persistent connections &MUST;
2775   include the "close" connection option in every request message.
2778   An HTTP/1.1 server that does not support persistent connections &MUST;
2779   include the "close" connection option in every response message that
2780   does not have a <x:ref>1xx (Informational)</x:ref> status code.
2784<section title="Via" anchor="header.via">
2785  <iref primary="true" item="Via header field" x:for-anchor=""/>
2786  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2787  <x:anchor-alias value="pseudonym"/>
2788  <x:anchor-alias value="received-by"/>
2789  <x:anchor-alias value="received-protocol"/>
2790  <x:anchor-alias value="Via"/>
2792   The "Via" header field &MUST; be sent by a proxy or gateway to
2793   indicate the intermediate protocols and recipients between the user
2794   agent and the server on requests, and between the origin server and
2795   the client on responses. It is analogous to the "Received" field
2796   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2797   and is intended to be used for tracking message forwards,
2798   avoiding request loops, and identifying the protocol capabilities of
2799   all senders along the request/response chain.
2801<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"/>
2802  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2803                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2804  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2805  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2806  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2809   The received-protocol indicates the protocol version of the message
2810   received by the server or client along each segment of the
2811   request/response chain. The received-protocol version is appended to
2812   the Via field value when the message is forwarded so that information
2813   about the protocol capabilities of upstream applications remains
2814   visible to all recipients.
2817   The protocol-name is excluded if and only if it would be "HTTP". The
2818   received-by field is normally the host and optional port number of a
2819   recipient server or client that subsequently forwarded the message.
2820   However, if the real host is considered to be sensitive information,
2821   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2822   be assumed to be the default port of the received-protocol.
2825   Multiple Via field values represent each proxy or gateway that has
2826   forwarded the message. Each recipient &MUST; append its information
2827   such that the end result is ordered according to the sequence of
2828   forwarding applications.
2831   Comments &MAY; be used in the Via header field to identify the software
2832   of each recipient, analogous to the <x:ref>User-Agent</x:ref> and
2833   <x:ref>Server</x:ref> header fields. However, all comments in the Via field
2834   are optional and &MAY; be removed by any recipient prior to forwarding the
2835   message.
2838   For example, a request message could be sent from an HTTP/1.0 user
2839   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2840   forward the request to a public proxy at, which completes
2841   the request by forwarding it to the origin server at
2842   The request received by would then have the following
2843   Via header field:
2845<figure><artwork type="example">
2846  Via: 1.0 fred, 1.1 (Apache/1.1)
2849   A proxy or gateway used as a portal through a network firewall
2850   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2851   region unless it is explicitly enabled to do so. If not enabled, the
2852   received-by host of any host behind the firewall &SHOULD; be replaced
2853   by an appropriate pseudonym for that host.
2856   For organizations that have strong privacy requirements for hiding
2857   internal structures, a proxy or gateway &MAY; combine an ordered
2858   subsequence of Via header field entries with identical received-protocol
2859   values into a single such entry. For example,
2861<figure><artwork type="example">
2862  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2865  could be collapsed to
2867<figure><artwork type="example">
2868  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2871   Senders &SHOULD-NOT; combine multiple entries unless they are all
2872   under the same organizational control and the hosts have already been
2873   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2874   have different received-protocol values.
2878<section title="Persistent Connections" anchor="persistent.connections">
2880<section title="Purpose" anchor="persistent.purpose">
2882   Prior to persistent connections, a separate TCP connection was
2883   established for each request, increasing the load on HTTP servers
2884   and causing congestion on the Internet. The use of inline images and
2885   other associated data often requires a client to make multiple
2886   requests of the same server in a short amount of time. Analysis of
2887   these performance problems and results from a prototype
2888   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2889   measurements of actual HTTP/1.1 implementations show good
2890   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2891   T/TCP <xref target="Tou1998"/>.
2894   Persistent HTTP connections have a number of advantages:
2895  <list style="symbols">
2896      <t>
2897        By opening and closing fewer TCP connections, CPU time is saved
2898        in routers and hosts (clients, servers, proxies, gateways,
2899        tunnels, or caches), and memory used for TCP protocol control
2900        blocks can be saved in hosts.
2901      </t>
2902      <t>
2903        HTTP requests and responses can be pipelined on a connection.
2904        Pipelining allows a client to make multiple requests without
2905        waiting for each response, allowing a single TCP connection to
2906        be used much more efficiently, with much lower elapsed time.
2907      </t>
2908      <t>
2909        Network congestion is reduced by reducing the number of packets
2910        caused by TCP opens, and by allowing TCP sufficient time to
2911        determine the congestion state of the network.
2912      </t>
2913      <t>
2914        Latency on subsequent requests is reduced since there is no time
2915        spent in TCP's connection opening handshake.
2916      </t>
2917      <t>
2918        HTTP can evolve more gracefully, since errors can be reported
2919        without the penalty of closing the TCP connection. Clients using
2920        future versions of HTTP might optimistically try a new feature,
2921        but if communicating with an older server, retry with old
2922        semantics after an error is reported.
2923      </t>
2924    </list>
2927   HTTP implementations &SHOULD; implement persistent connections.
2931<section title="Overall Operation" anchor="persistent.overall">
2933   A significant difference between HTTP/1.1 and earlier versions of
2934   HTTP is that persistent connections are the default behavior of any
2935   HTTP connection. That is, unless otherwise indicated, the client
2936   &SHOULD; assume that the server will maintain a persistent connection,
2937   even after error responses from the server.
2940   Persistent connections provide a mechanism by which a client and a
2941   server can signal the close of a TCP connection. This signaling takes
2942   place using the <x:ref>Connection</x:ref> header field
2943   (<xref target="header.connection"/>). Once a close has been signaled, the
2944   client &MUST-NOT; send any more requests on that
2945   connection.
2948<section title="Negotiation" anchor="persistent.negotiation">
2950   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2951   maintain a persistent connection unless a <x:ref>Connection</x:ref> header
2952   field including the connection option "close" was sent in the request. If
2953   the server chooses to close the connection immediately after sending the
2954   response, it &SHOULD; send a Connection header field including the
2955   connection option "close".
2958   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2959   decide to keep it open based on whether the response from a server
2960   contains a <x:ref>Connection</x:ref> header field with the connection option
2961   "close". In case the client does not want to maintain a connection for more
2962   than that request, it &SHOULD; send a Connection header field including the
2963   connection option "close".
2966   If either the client or the server sends the "close" option in the
2967   <x:ref>Connection</x:ref> header field, that request becomes the last one
2968   for the connection.
2971   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2972   maintained for HTTP versions less than 1.1 unless it is explicitly
2973   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2974   compatibility with HTTP/1.0 clients.
2977   Each persistent connection applies to only one transport link.
2980   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2981   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2982   for information and discussion of the problems with the Keep-Alive header field
2983   implemented by many HTTP/1.0 clients).
2986   In order to remain persistent, all messages on the connection &MUST;
2987   have a self-defined message length (i.e., one not defined by closure
2988   of the connection), as described in <xref target="message.body"/>.
2992<section title="Pipelining" anchor="pipelining">
2994   A client that supports persistent connections &MAY; "pipeline" its
2995   requests (i.e., send multiple requests without waiting for each
2996   response). A server &MUST; send its responses to those requests in the
2997   same order that the requests were received.
3000   Clients which assume persistent connections and pipeline immediately
3001   after connection establishment &SHOULD; be prepared to retry their
3002   connection if the first pipelined attempt fails. If a client does
3003   such a retry, it &MUST-NOT; pipeline before it knows the connection is
3004   persistent. Clients &MUST; also be prepared to resend their requests if
3005   the server closes the connection before sending all of the
3006   corresponding responses.
3009   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
3010   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
3011   premature termination of the transport connection could lead to
3012   indeterminate results. A client wishing to send a non-idempotent
3013   request &SHOULD; wait to send that request until it has received the
3014   response status line for the previous request.
3019<section title="Practical Considerations" anchor="persistent.practical">
3021   Servers will usually have some time-out value beyond which they will
3022   no longer maintain an inactive connection. Proxy servers might make
3023   this a higher value since it is likely that the client will be making
3024   more connections through the same server. The use of persistent
3025   connections places no requirements on the length (or existence) of
3026   this time-out for either the client or the server.
3029   When a client or server wishes to time-out it &SHOULD; issue a graceful
3030   close on the transport connection. Clients and servers &SHOULD; both
3031   constantly watch for the other side of the transport close, and
3032   respond to it as appropriate. If a client or server does not detect
3033   the other side's close promptly it could cause unnecessary resource
3034   drain on the network.
3037   A client, server, or proxy &MAY; close the transport connection at any
3038   time. For example, a client might have started to send a new request
3039   at the same time that the server has decided to close the "idle"
3040   connection. From the server's point of view, the connection is being
3041   closed while it was idle, but from the client's point of view, a
3042   request is in progress.
3045   Clients (including proxies) &SHOULD; limit the number of simultaneous
3046   connections that they maintain to a given server (including proxies).
3049   Previous revisions of HTTP gave a specific number of connections as a
3050   ceiling, but this was found to be impractical for many applications. As a
3051   result, this specification does not mandate a particular maximum number of
3052   connections, but instead encourages clients to be conservative when opening
3053   multiple connections.
3056   In particular, while using multiple connections avoids the "head-of-line
3057   blocking" problem (whereby a request that takes significant server-side
3058   processing and/or has a large payload can block subsequent requests on the
3059   same connection), each connection used consumes server resources (sometimes
3060   significantly), and furthermore using multiple connections can cause
3061   undesirable side effects in congested networks.
3064   Note that servers might reject traffic that they deem abusive, including an
3065   excessive number of connections from a client.
3069<section title="Retrying Requests" anchor="persistent.retrying.requests">
3071   Senders can close the transport connection at any time. Therefore,
3072   clients, servers, and proxies &MUST; be able to recover
3073   from asynchronous close events. Client software &MAY; reopen the
3074   transport connection and retransmit the aborted sequence of requests
3075   without user interaction so long as the request sequence is
3076   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3077   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3078   human operator the choice of retrying the request(s). Confirmation by
3079   user-agent software with semantic understanding of the application
3080   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
3081   be repeated if the second sequence of requests fails.
3086<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3088<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3090   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3091   flow control mechanisms to resolve temporary overloads, rather than
3092   terminating connections with the expectation that clients will retry.
3093   The latter technique can exacerbate network congestion.
3097<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3099   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3100   the network connection for an error status code while it is transmitting
3101   the request. If the client sees an error status code, it &SHOULD;
3102   immediately cease transmitting the body. If the body is being sent
3103   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3104   empty trailer &MAY; be used to prematurely mark the end of the message.
3105   If the body was preceded by a Content-Length header field, the client &MUST;
3106   close the connection.
3110<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3112   The purpose of the <x:ref>100 (Continue)</x:ref> status code (see &status-100;)
3113   is to allow a client that is sending a request message with a request body
3114   to determine if the origin server is willing to accept the request
3115   (based on the request header fields) before the client sends the request
3116   body. In some cases, it might either be inappropriate or highly
3117   inefficient for the client to send the body if the server will reject
3118   the message without looking at the body.
3121   Requirements for HTTP/1.1 clients:
3122  <list style="symbols">
3123    <t>
3124        If a client will wait for a <x:ref>100 (Continue)</x:ref> response before
3125        sending the request body, it &MUST; send an <x:ref>Expect</x:ref> header
3126        field (&header-expect;) with the "100-continue" expectation.
3127    </t>
3128    <t>
3129        A client &MUST-NOT; send an <x:ref>Expect</x:ref> header field with
3130        the "100-continue" expectation if it does not intend to send a request
3131        body.
3132    </t>
3133  </list>
3136   Because of the presence of older implementations, the protocol allows
3137   ambiguous situations in which a client might send "Expect: 100-continue"
3138   without receiving either a <x:ref>417 (Expectation Failed)</x:ref>
3139   or a <x:ref>100 (Continue)</x:ref> status code. Therefore, when a client sends this
3140   header field to an origin server (possibly via a proxy) from which it
3141   has never seen a <x:ref>100 (Continue)</x:ref> status code, the client &SHOULD-NOT; 
3142   wait for an indefinite period before sending the request body.
3145   Requirements for HTTP/1.1 origin servers:
3146  <list style="symbols">
3147    <t> Upon receiving a request which includes an <x:ref>Expect</x:ref> header
3148        field with the "100-continue" expectation, an origin server &MUST;
3149        either respond with <x:ref>100 (Continue)</x:ref> status code and continue to read
3150        from the input stream, or respond with a final status code. The
3151        origin server &MUST-NOT; wait for the request body before sending
3152        the <x:ref>100 (Continue)</x:ref> response. If it responds with a final status
3153        code, it &MAY; close the transport connection or it &MAY; continue
3154        to read and discard the rest of the request.  It &MUST-NOT;
3155        perform the request method if it returns a final status code.
3156    </t>
3157    <t> An origin server &SHOULD-NOT;  send a <x:ref>100 (Continue)</x:ref> response if
3158        the request message does not include an <x:ref>Expect</x:ref> header
3159        field with the "100-continue" expectation, and &MUST-NOT; send a
3160        <x:ref>100 (Continue)</x:ref> response if such a request comes from an HTTP/1.0
3161        (or earlier) client. There is an exception to this rule: for
3162        compatibility with <xref target="RFC2068"/>, a server &MAY; send a <x:ref>100 (Continue)</x:ref>
3163        status code in response to an HTTP/1.1 PUT or POST request that does
3164        not include an Expect header field with the "100-continue"
3165        expectation. This exception, the purpose of which is
3166        to minimize any client processing delays associated with an
3167        undeclared wait for <x:ref>100 (Continue)</x:ref> status code, applies only to
3168        HTTP/1.1 requests, and not to requests with any other HTTP-version
3169        value.
3170    </t>
3171    <t> An origin server &MAY; omit a <x:ref>100 (Continue)</x:ref> response if it has
3172        already received some or all of the request body for the
3173        corresponding request.
3174    </t>
3175    <t> An origin server that sends a <x:ref>100 (Continue)</x:ref> response &MUST;
3176        ultimately send a final status code, once the request body is
3177        received and processed, unless it terminates the transport
3178        connection prematurely.
3179    </t>
3180    <t> If an origin server receives a request that does not include an
3181        <x:ref>Expect</x:ref> header field with the "100-continue" expectation,
3182        the request includes a request body, and the server responds
3183        with a final status code before reading the entire request body
3184        from the transport connection, then the server &SHOULD-NOT;  close
3185        the transport connection until it has read the entire request,
3186        or until the client closes the connection. Otherwise, the client
3187        might not reliably receive the response message. However, this
3188        requirement ought not be construed as preventing a server from
3189        defending itself against denial-of-service attacks, or from
3190        badly broken client implementations.
3191      </t>
3192    </list>
3195   Requirements for HTTP/1.1 proxies:
3196  <list style="symbols">
3197    <t> If a proxy receives a request that includes an <x:ref>Expect</x:ref>
3198        header field with the "100-continue" expectation, and the proxy
3199        either knows that the next-hop server complies with HTTP/1.1 or
3200        higher, or does not know the HTTP version of the next-hop
3201        server, it &MUST; forward the request, including the Expect header
3202        field.
3203    </t>
3204    <t> If the proxy knows that the version of the next-hop server is
3205        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3206        respond with a <x:ref>417 (Expectation Failed)</x:ref> status code.
3207    </t>
3208    <t> Proxies &SHOULD; maintain a record of the HTTP version
3209        numbers received from recently-referenced next-hop servers.
3210    </t>
3211    <t> A proxy &MUST-NOT; forward a <x:ref>100 (Continue)</x:ref> response if the
3212        request message was received from an HTTP/1.0 (or earlier)
3213        client and did not include an <x:ref>Expect</x:ref> header field with
3214        the "100-continue" expectation. This requirement overrides the
3215        general rule for forwarding of <x:ref>1xx</x:ref> responses (see &status-1xx;).
3216    </t>
3217  </list>
3221<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3223   If the client is sending data, a server implementation using TCP
3224   &SHOULD; be careful to ensure that the client acknowledges receipt of
3225   the packet(s) containing the response, before the server closes the
3226   input connection. If the client continues sending data to the server
3227   after the close, the server's TCP stack will send a reset packet to
3228   the client, which might erase the client's unacknowledged input buffers
3229   before they can be read and interpreted by the HTTP application.
3235<section title="Upgrade" anchor="header.upgrade">
3236  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3237  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3238  <x:anchor-alias value="Upgrade"/>
3239  <x:anchor-alias value="protocol"/>
3240  <x:anchor-alias value="protocol-name"/>
3241  <x:anchor-alias value="protocol-version"/>
3243   The "Upgrade" header field allows the client to specify what
3244   additional communication protocols it would like to use, if the server
3245   chooses to switch protocols. Servers can use it to indicate what protocols
3246   they are willing to switch to.
3248<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3249  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3251  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3252  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3253  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3256   For example,
3258<figure><artwork type="example">
3259  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3262   The Upgrade header field is intended to provide a simple mechanism
3263   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3264   does so by allowing the client to advertise its desire to use another
3265   protocol, such as a later version of HTTP with a higher major version
3266   number, even though the current request has been made using HTTP/1.1.
3267   This eases the difficult transition between incompatible protocols by
3268   allowing the client to initiate a request in the more commonly
3269   supported protocol while indicating to the server that it would like
3270   to use a "better" protocol if available (where "better" is determined
3271   by the server, possibly according to the nature of the request method
3272   or target resource).
3275   The Upgrade header field only applies to switching application-layer
3276   protocols upon the existing transport-layer connection. Upgrade
3277   cannot be used to insist on a protocol change; its acceptance and use
3278   by the server is optional. The capabilities and nature of the
3279   application-layer communication after the protocol change is entirely
3280   dependent upon the new protocol chosen, although the first action
3281   after changing the protocol &MUST; be a response to the initial HTTP
3282   request containing the Upgrade header field.
3285   The Upgrade header field only applies to the immediate connection.
3286   Therefore, the upgrade keyword &MUST; be supplied within a
3287   <x:ref>Connection</x:ref> header field (<xref target="header.connection"/>)
3288   whenever Upgrade is present in an HTTP/1.1 message.
3291   The Upgrade header field cannot be used to indicate a switch to a
3292   protocol on a different connection. For that purpose, it is more
3293   appropriate to use a <x:ref>3xx (Redirection)</x:ref> response (&status-3xx;).
3296   Servers &MUST; include the "Upgrade" header field in <x:ref>101 (Switching
3297   Protocols)</x:ref> responses to indicate which protocol(s) are being switched to,
3298   and &MUST; include it in <x:ref>426 (Upgrade Required)</x:ref> responses to indicate
3299   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3300   response to indicate that they are willing to upgrade to one of the
3301   specified protocols.
3304   This specification only defines the protocol name "HTTP" for use by
3305   the family of Hypertext Transfer Protocols, as defined by the HTTP
3306   version rules of <xref target="http.version"/> and future updates to this
3307   specification. Additional tokens can be registered with IANA using the
3308   registration procedure defined in <xref target="upgrade.token.registry"/>.
3314<section title="IANA Considerations" anchor="IANA.considerations">
3316<section title="Header Field Registration" anchor="header.field.registration">
3318   HTTP header fields are registered within the Message Header Field Registry
3319   <xref target="RFC3864"/> maintained by IANA at
3320   <eref target=""/>.
3323   This document defines the following HTTP header fields, so their
3324   associated registry entries shall be updated according to the permanent
3325   registrations below:
3327<?BEGININC p1-messaging.iana-headers ?>
3328<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3329<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3330   <ttcol>Header Field Name</ttcol>
3331   <ttcol>Protocol</ttcol>
3332   <ttcol>Status</ttcol>
3333   <ttcol>Reference</ttcol>
3335   <c>Connection</c>
3336   <c>http</c>
3337   <c>standard</c>
3338   <c>
3339      <xref target="header.connection"/>
3340   </c>
3341   <c>Content-Length</c>
3342   <c>http</c>
3343   <c>standard</c>
3344   <c>
3345      <xref target="header.content-length"/>
3346   </c>
3347   <c>Host</c>
3348   <c>http</c>
3349   <c>standard</c>
3350   <c>
3351      <xref target=""/>
3352   </c>
3353   <c>TE</c>
3354   <c>http</c>
3355   <c>standard</c>
3356   <c>
3357      <xref target="header.te"/>
3358   </c>
3359   <c>Trailer</c>
3360   <c>http</c>
3361   <c>standard</c>
3362   <c>
3363      <xref target="header.trailer"/>
3364   </c>
3365   <c>Transfer-Encoding</c>
3366   <c>http</c>
3367   <c>standard</c>
3368   <c>
3369      <xref target="header.transfer-encoding"/>
3370   </c>
3371   <c>Upgrade</c>
3372   <c>http</c>
3373   <c>standard</c>
3374   <c>
3375      <xref target="header.upgrade"/>
3376   </c>
3377   <c>Via</c>
3378   <c>http</c>
3379   <c>standard</c>
3380   <c>
3381      <xref target="header.via"/>
3382   </c>
3385<?ENDINC p1-messaging.iana-headers ?>
3387   Furthermore, the header field-name "Close" shall be registered as
3388   "reserved", since using that name as an HTTP header field might
3389   conflict with the "close" connection option of the "<x:ref>Connection</x:ref>"
3390   header field (<xref target="header.connection"/>).
3392<texttable align="left" suppress-title="true">
3393   <ttcol>Header Field Name</ttcol>
3394   <ttcol>Protocol</ttcol>
3395   <ttcol>Status</ttcol>
3396   <ttcol>Reference</ttcol>
3398   <c>Close</c>
3399   <c>http</c>
3400   <c>reserved</c>
3401   <c>
3402      <xref target="header.field.registration"/>
3403   </c>
3406   The change controller is: "IETF ( - Internet Engineering Task Force".
3410<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3412   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3413   <eref target=""/>.
3416   This document defines the following URI schemes, so their
3417   associated registry entries shall be updated according to the permanent
3418   registrations below:
3420<texttable align="left" suppress-title="true">
3421   <ttcol>URI Scheme</ttcol>
3422   <ttcol>Description</ttcol>
3423   <ttcol>Reference</ttcol>
3425   <c>http</c>
3426   <c>Hypertext Transfer Protocol</c>
3427   <c><xref target="http.uri"/></c>
3429   <c>https</c>
3430   <c>Hypertext Transfer Protocol Secure</c>
3431   <c><xref target="https.uri"/></c>
3435<section title="Internet Media Type Registrations" anchor="">
3437   This document serves as the specification for the Internet media types
3438   "message/http" and "application/http". The following is to be registered with
3439   IANA (see <xref target="RFC4288"/>).
3441<section title="Internet Media Type message/http" anchor="">
3442<iref item="Media Type" subitem="message/http" primary="true"/>
3443<iref item="message/http Media Type" primary="true"/>
3445   The message/http type can be used to enclose a single HTTP request or
3446   response message, provided that it obeys the MIME restrictions for all
3447   "message" types regarding line length and encodings.
3450  <list style="hanging" x:indent="12em">
3451    <t hangText="Type name:">
3452      message
3453    </t>
3454    <t hangText="Subtype name:">
3455      http
3456    </t>
3457    <t hangText="Required parameters:">
3458      none
3459    </t>
3460    <t hangText="Optional parameters:">
3461      version, msgtype
3462      <list style="hanging">
3463        <t hangText="version:">
3464          The HTTP-version number of the enclosed message
3465          (e.g., "1.1"). If not present, the version can be
3466          determined from the first line of the body.
3467        </t>
3468        <t hangText="msgtype:">
3469          The message type &mdash; "request" or "response". If not
3470          present, the type can be determined from the first
3471          line of the body.
3472        </t>
3473      </list>
3474    </t>
3475    <t hangText="Encoding considerations:">
3476      only "7bit", "8bit", or "binary" are permitted
3477    </t>
3478    <t hangText="Security considerations:">
3479      none
3480    </t>
3481    <t hangText="Interoperability considerations:">
3482      none
3483    </t>
3484    <t hangText="Published specification:">
3485      This specification (see <xref target=""/>).
3486    </t>
3487    <t hangText="Applications that use this media type:">
3488    </t>
3489    <t hangText="Additional information:">
3490      <list style="hanging">
3491        <t hangText="Magic number(s):">none</t>
3492        <t hangText="File extension(s):">none</t>
3493        <t hangText="Macintosh file type code(s):">none</t>
3494      </list>
3495    </t>
3496    <t hangText="Person and email address to contact for further information:">
3497      See Authors Section.
3498    </t>
3499    <t hangText="Intended usage:">
3500      COMMON
3501    </t>
3502    <t hangText="Restrictions on usage:">
3503      none
3504    </t>
3505    <t hangText="Author/Change controller:">
3506      IESG
3507    </t>
3508  </list>
3511<section title="Internet Media Type application/http" anchor="">
3512<iref item="Media Type" subitem="application/http" primary="true"/>
3513<iref item="application/http Media Type" primary="true"/>
3515   The application/http type can be used to enclose a pipeline of one or more
3516   HTTP request or response messages (not intermixed).
3519  <list style="hanging" x:indent="12em">
3520    <t hangText="Type name:">
3521      application
3522    </t>
3523    <t hangText="Subtype name:">
3524      http
3525    </t>
3526    <t hangText="Required parameters:">
3527      none
3528    </t>
3529    <t hangText="Optional parameters:">
3530      version, msgtype
3531      <list style="hanging">
3532        <t hangText="version:">
3533          The HTTP-version number of the enclosed messages
3534          (e.g., "1.1"). If not present, the version can be
3535          determined from the first line of the body.
3536        </t>
3537        <t hangText="msgtype:">
3538          The message type &mdash; "request" or "response". If not
3539          present, the type can be determined from the first
3540          line of the body.
3541        </t>
3542      </list>
3543    </t>
3544    <t hangText="Encoding considerations:">
3545      HTTP messages enclosed by this type
3546      are in "binary" format; use of an appropriate
3547      Content-Transfer-Encoding is required when
3548      transmitted via E-mail.
3549    </t>
3550    <t hangText="Security considerations:">
3551      none
3552    </t>
3553    <t hangText="Interoperability considerations:">
3554      none
3555    </t>
3556    <t hangText="Published specification:">
3557      This specification (see <xref target=""/>).
3558    </t>
3559    <t hangText="Applications that use this media type:">
3560    </t>
3561    <t hangText="Additional information:">
3562      <list style="hanging">
3563        <t hangText="Magic number(s):">none</t>
3564        <t hangText="File extension(s):">none</t>
3565        <t hangText="Macintosh file type code(s):">none</t>
3566      </list>
3567    </t>
3568    <t hangText="Person and email address to contact for further information:">
3569      See Authors Section.
3570    </t>
3571    <t hangText="Intended usage:">
3572      COMMON
3573    </t>
3574    <t hangText="Restrictions on usage:">
3575      none
3576    </t>
3577    <t hangText="Author/Change controller:">
3578      IESG
3579    </t>
3580  </list>
3585<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3587   The HTTP Transfer Coding Registry defines the name space for transfer
3588   coding names.
3591   Registrations &MUST; include the following fields:
3592   <list style="symbols">
3593     <t>Name</t>
3594     <t>Description</t>
3595     <t>Pointer to specification text</t>
3596   </list>
3599   Names of transfer codings &MUST-NOT; overlap with names of content codings
3600   (&content-codings;) unless the encoding transformation is identical, as it
3601   is the case for the compression codings defined in
3602   <xref target="compression.codings"/>.
3605   Values to be added to this name space require IETF Review (see
3606   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3607   conform to the purpose of transfer coding defined in this section.
3610   The registry itself is maintained at
3611   <eref target=""/>.
3615<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3617   The HTTP Transfer Coding Registry shall be updated with the registrations
3618   below:
3620<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3621   <ttcol>Name</ttcol>
3622   <ttcol>Description</ttcol>
3623   <ttcol>Reference</ttcol>
3624   <c>chunked</c>
3625   <c>Transfer in a series of chunks</c>
3626   <c>
3627      <xref target="chunked.encoding"/>
3628   </c>
3629   <c>compress</c>
3630   <c>UNIX "compress" program method</c>
3631   <c>
3632      <xref target="compress.coding"/>
3633   </c>
3634   <c>deflate</c>
3635   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3636   the "zlib" data format (<xref target="RFC1950"/>)
3637   </c>
3638   <c>
3639      <xref target="deflate.coding"/>
3640   </c>
3641   <c>gzip</c>
3642   <c>Same as GNU zip <xref target="RFC1952"/></c>
3643   <c>
3644      <xref target="gzip.coding"/>
3645   </c>
3649<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3651   The HTTP Upgrade Token Registry defines the name space for protocol-name
3652   tokens used to identify protocols in the <x:ref>Upgrade</x:ref> header
3653   field. Each registered protocol name is associated with contact information
3654   and an optional set of specifications that details how the connection
3655   will be processed after it has been upgraded.
3658   Registrations happen on a "First Come First Served" basis (see
3659   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3660   following rules:
3661  <list style="numbers">
3662    <t>A protocol-name token, once registered, stays registered forever.</t>
3663    <t>The registration &MUST; name a responsible party for the
3664       registration.</t>
3665    <t>The registration &MUST; name a point of contact.</t>
3666    <t>The registration &MAY; name a set of specifications associated with
3667       that token. Such specifications need not be publicly available.</t>
3668    <t>The registration &SHOULD; name a set of expected "protocol-version"
3669       tokens associated with that token at the time of registration.</t>
3670    <t>The responsible party &MAY; change the registration at any time.
3671       The IANA will keep a record of all such changes, and make them
3672       available upon request.</t>
3673    <t>The IESG &MAY; reassign responsibility for a protocol token.
3674       This will normally only be used in the case when a
3675       responsible party cannot be contacted.</t>
3676  </list>
3679   This registration procedure for HTTP Upgrade Tokens replaces that
3680   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3684<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3686   The HTTP Upgrade Token Registry shall be updated with the registration
3687   below:
3689<texttable align="left" suppress-title="true">
3690   <ttcol>Value</ttcol>
3691   <ttcol>Description</ttcol>
3692   <ttcol>Expected Version Tokens</ttcol>
3693   <ttcol>Reference</ttcol>
3695   <c>HTTP</c>
3696   <c>Hypertext Transfer Protocol</c>
3697   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3698   <c><xref target="http.version"/></c>
3701   The responsible party is: "IETF ( - Internet Engineering Task Force".
3707<section title="Security Considerations" anchor="security.considerations">
3709   This section is meant to inform application developers, information
3710   providers, and users of the security limitations in HTTP/1.1 as
3711   described by this document. The discussion does not include
3712   definitive solutions to the problems revealed, though it does make
3713   some suggestions for reducing security risks.
3716<section title="Personal Information" anchor="personal.information">
3718   HTTP clients are often privy to large amounts of personal information
3719   (e.g., the user's name, location, mail address, passwords, encryption
3720   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3721   leakage of this information.
3722   We very strongly recommend that a convenient interface be provided
3723   for the user to control dissemination of such information, and that
3724   designers and implementors be particularly careful in this area.
3725   History shows that errors in this area often create serious security
3726   and/or privacy problems and generate highly adverse publicity for the
3727   implementor's company.
3731<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3733   A server is in the position to save personal data about a user's
3734   requests which might identify their reading patterns or subjects of
3735   interest.  In particular, log information gathered at an intermediary
3736   often contains a history of user agent interaction, across a multitude
3737   of sites, that can be traced to individual users.
3740   HTTP log information is confidential in nature; its handling is often
3741   constrained by laws and regulations.  Log information needs to be securely
3742   stored and appropriate guidelines followed for its analysis.
3743   Anonymization of personal information within individual entries helps,
3744   but is generally not sufficient to prevent real log traces from being
3745   re-identified based on correlation with other access characteristics.
3746   As such, access traces that are keyed to a specific client should not
3747   be published even if the key is pseudonymous.
3750   To minimize the risk of theft or accidental publication, log information
3751   should be purged of personally identifiable information, including
3752   user identifiers, IP addresses, and user-provided query parameters,
3753   as soon as that information is no longer necessary to support operational
3754   needs for security, auditing, or fraud control.
3758<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3760   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3761   the documents returned by HTTP requests to be only those that were
3762   intended by the server administrators. If an HTTP server translates
3763   HTTP URIs directly into file system calls, the server &MUST; take
3764   special care not to serve files that were not intended to be
3765   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3766   other operating systems use ".." as a path component to indicate a
3767   directory level above the current one. On such a system, an HTTP
3768   server &MUST; disallow any such construct in the request-target if it
3769   would otherwise allow access to a resource outside those intended to
3770   be accessible via the HTTP server. Similarly, files intended for
3771   reference only internally to the server (such as access control
3772   files, configuration files, and script code) &MUST; be protected from
3773   inappropriate retrieval, since they might contain sensitive
3774   information. Experience has shown that minor bugs in such HTTP server
3775   implementations have turned into security risks.
3779<section title="DNS-related Attacks" anchor="dns.related.attacks">
3781   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3782   generally prone to security attacks based on the deliberate misassociation
3783   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3784   cautious in assuming the validity of an IP number/DNS name association unless
3785   the response is protected by DNSSec (<xref target="RFC4033"/>).
3789<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3791   By their very nature, HTTP intermediaries are men-in-the-middle, and
3792   represent an opportunity for man-in-the-middle attacks. Compromise of
3793   the systems on which the intermediaries run can result in serious security
3794   and privacy problems. Intermediaries have access to security-related
3795   information, personal information about individual users and
3796   organizations, and proprietary information belonging to users and
3797   content providers. A compromised intermediary, or an intermediary
3798   implemented or configured without regard to security and privacy
3799   considerations, might be used in the commission of a wide range of
3800   potential attacks.
3803   Intermediaries that contain a shared cache are especially vulnerable
3804   to cache poisoning attacks.
3807   Implementors need to consider the privacy and security
3808   implications of their design and coding decisions, and of the
3809   configuration options they provide to operators (especially the
3810   default configuration).
3813   Users need to be aware that intermediaries are no more trustworthy than
3814   the people who run them; HTTP itself cannot solve this problem.
3817   The judicious use of cryptography, when appropriate, might suffice to
3818   protect against a broad range of security and privacy attacks. Such
3819   cryptography is beyond the scope of the HTTP/1.1 specification.
3823<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3825   Because HTTP uses mostly textual, character-delimited fields, attackers can
3826   overflow buffers in implementations, and/or perform a Denial of Service
3827   against implementations that accept fields with unlimited lengths.
3830   To promote interoperability, this specification makes specific
3831   recommendations for minimum size limits on request-line
3832   (<xref target="request.line"/>)
3833   and blocks of header fields (<xref target="header.fields"/>). These are
3834   minimum recommendations, chosen to be supportable even by implementations
3835   with limited resources; it is expected that most implementations will
3836   choose substantially higher limits.
3839   This specification also provides a way for servers to reject messages that
3840   have request-targets that are too long (&status-414;) or request entities
3841   that are too large (&status-4xx;).
3844   Other fields (including but not limited to request methods, response status
3845   phrases, header field-names, and body chunks) &SHOULD; be limited by
3846   implementations carefully, so as to not impede interoperability.
3851<section title="Acknowledgments" anchor="acks">
3853   This edition of HTTP builds on the many contributions that went into
3854   <xref target="RFC1945" format="none">RFC 1945</xref>,
3855   <xref target="RFC2068" format="none">RFC 2068</xref>,
3856   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3857   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3858   substantial contributions made by the previous authors, editors, and
3859   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3860   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3861   Paul J. Leach, and Mark Nottingham.
3862   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3863   acknowledgements from prior revisions.
3866   Since 1999, the following contributors have helped improve the HTTP
3867   specification by reporting bugs, asking smart questions, drafting or
3868   reviewing text, and evaluating open issues:
3870<?BEGININC acks ?>
3871<t>Adam Barth,
3872Adam Roach,
3873Addison Phillips,
3874Adrian Chadd,
3875Adrien W. de Croy,
3876Alan Ford,
3877Alan Ruttenberg,
3878Albert Lunde,
3879Alek Storm,
3880Alex Rousskov,
3881Alexandre Morgaut,
3882Alexey Melnikov,
3883Alisha Smith,
3884Amichai Rothman,
3885Amit Klein,
3886Amos Jeffries,
3887Andreas Maier,
3888Andreas Petersson,
3889Anne van Kesteren,
3890Anthony Bryan,
3891Asbjorn Ulsberg,
3892Balachander Krishnamurthy,
3893Barry Leiba,
3894Ben Laurie,
3895Benjamin Niven-Jenkins,
3896Bil Corry,
3897Bill Burke,
3898Bjoern Hoehrmann,
3899Bob Scheifler,
3900Boris Zbarsky,
3901Brett Slatkin,
3902Brian Kell,
3903Brian McBarron,
3904Brian Pane,
3905Brian Smith,
3906Bryce Nesbitt,
3907Cameron Heavon-Jones,
3908Carl Kugler,
3909Carsten Bormann,
3910Charles Fry,
3911Chris Newman,
3912Cyrus Daboo,
3913Dale Robert Anderson,
3914Dan Winship,
3915Daniel Stenberg,
3916Dave Cridland,
3917Dave Crocker,
3918Dave Kristol,
3919David Booth,
3920David Singer,
3921David W. Morris,
3922Diwakar Shetty,
3923Dmitry Kurochkin,
3924Drummond Reed,
3925Duane Wessels,
3926Edward Lee,
3927Eliot Lear,
3928Eran Hammer-Lahav,
3929Eric D. Williams,
3930Eric J. Bowman,
3931Eric Lawrence,
3932Eric Rescorla,
3933Erik Aronesty,
3934Florian Weimer,
3935Frank Ellermann,
3936Fred Bohle,
3937Geoffrey Sneddon,
3938Gervase Markham,
3939Greg Wilkins,
3940Harald Tveit Alvestrand,
3941Harry Halpin,
3942Helge Hess,
3943Henrik Nordstrom,
3944Henry S. Thompson,
3945Henry Story,
3946Herbert van de Sompel,
3947Howard Melman,
3948Hugo Haas,
3949Ian Hickson,
3950Ingo Struck,
3951J. Ross Nicoll,
3952James H. Manger,
3953James Lacey,
3954James M. Snell,
3955Jamie Lokier,
3956Jan Algermissen,
3957Jeff Hodges (who came up with the term 'effective Request-URI'),
3958Jeff Walden,
3959Jim Luther,
3960Joe D. Williams,
3961Joe Gregorio,
3962Joe Orton,
3963John C. Klensin,
3964John C. Mallery,
3965John Cowan,
3966John Kemp,
3967John Panzer,
3968John Schneider,
3969John Stracke,
3970John Sullivan,
3971Jonas Sicking,
3972Jonathan Billington,
3973Jonathan Moore,
3974Jonathan Rees,
3975Jordi Ros,
3976Joris Dobbelsteen,
3977Josh Cohen,
3978Julien Pierre,
3979Jungshik Shin,
3980Justin Chapweske,
3981Justin Erenkrantz,
3982Justin James,
3983Kalvinder Singh,
3984Karl Dubost,
3985Keith Hoffman,
3986Keith Moore,
3987Koen Holtman,
3988Konstantin Voronkov,
3989Kris Zyp,
3990Lisa Dusseault,
3991Maciej Stachowiak,
3992Marc Schneider,
3993Marc Slemko,
3994Mark Baker,
3995Mark Pauley,
3996Mark Watson,
3997Markus Isomaki,
3998Markus Lanthaler,
3999Martin J. Duerst,
4000Martin Musatov,
4001Martin Nilsson,
4002Martin Thomson,
4003Matt Lynch,
4004Matthew Cox,
4005Max Clark,
4006Michael Burrows,
4007Michael Hausenblas,
4008Mike Amundsen,
4009Mike Belshe,
4010Mike Kelly,
4011Mike Schinkel,
4012Miles Sabin,
4013Murray S. Kucherawy,
4014Mykyta Yevstifeyev,
4015Nathan Rixham,
4016Nicholas Shanks,
4017Nico Williams,
4018Nicolas Alvarez,
4019Nicolas Mailhot,
4020Noah Slater,
4021Pablo Castro,
4022Pat Hayes,
4023Patrick R. McManus,
4024Paul E. Jones,
4025Paul Hoffman,
4026Paul Marquess,
4027Peter Lepeska,
4028Peter Saint-Andre,
4029Peter Watkins,
4030Phil Archer,
4031Phillip Hallam-Baker,
4032Poul-Henning Kamp,
4033Preethi Natarajan,
4034Ray Polk,
4035Reto Bachmann-Gmuer,
4036Richard Cyganiak,
4037Robert Brewer,
4038Robert Collins,
4039Robert O'Callahan,
4040Robert Olofsson,
4041Robert Sayre,
4042Robert Siemer,
4043Robert de Wilde,
4044Roberto Javier Godoy,
4045Roberto Peon,
4046Ronny Widjaja,
4047S. Mike Dierken,
4048Salvatore Loreto,
4049Sam Johnston,
4050Sam Ruby,
4051Scott Lawrence (who maintained the original issues list),
4052Sean B. Palmer,
4053Shane McCarron,
4054Stefan Eissing,
4055Stefan Tilkov,
4056Stefanos Harhalakis,
4057Stephane Bortzmeyer,
4058Stephen Farrell,
4059Stuart Williams,
4060Subbu Allamaraju,
4061Sylvain Hellegouarch,
4062Tapan Divekar,
4063Ted Hardie,
4064Thomas Broyer,
4065Thomas Nordin,
4066Thomas Roessler,
4067Tim Bray,
4068Tim Morgan,
4069Tim Olsen,
4070Tom Zhou,
4071Travis Snoozy,
4072Tyler Close,
4073Vincent Murphy,
4074Wenbo Zhu,
4075Werner Baumann,
4076Wilbur Streett,
4077Wilfredo Sanchez Vega,
4078William A. Rowe Jr.,
4079William Chan,
4080Willy Tarreau,
4081Xiaoshu Wang,
4082Yaron Goland,
4083Yngve Nysaeter Pettersen,
4084Yoav Nir,
4085Yogesh Bang,
4086Yutaka Oiwa,
4087Zed A. Shaw, and
4088Zhong Yu.
4090<?ENDINC acks ?>
4096<references title="Normative References">
4098<reference anchor="ISO-8859-1">
4099  <front>
4100    <title>
4101     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4102    </title>
4103    <author>
4104      <organization>International Organization for Standardization</organization>
4105    </author>
4106    <date year="1998"/>
4107  </front>
4108  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4111<reference anchor="Part2">
4112  <front>
4113    <title>HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation</title>
4114    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4115      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4116      <address><email></email></address>
4117    </author>
4118    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4119      <organization abbrev="W3C">World Wide Web Consortium</organization>
4120      <address><email></email></address>
4121    </author>
4122    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4123      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4124      <address><email></email></address>
4125    </author>
4126    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4127  </front>
4128  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4129  <x:source href="p2-semantics.xml" basename="p2-semantics">
4130    <x:defines>1xx (Informational)</x:defines>
4131    <x:defines>1xx</x:defines>
4132    <x:defines>100 (Continue)</x:defines>
4133    <x:defines>101 (Switching Protocols)</x:defines>
4134    <x:defines>2xx (Successful)</x:defines>
4135    <x:defines>2xx</x:defines>
4136    <x:defines>200 (OK)</x:defines>
4137    <x:defines>204 (No Content)</x:defines>
4138    <x:defines>3xx (Redirection)</x:defines>
4139    <x:defines>3xx</x:defines>
4140    <x:defines>301 (Moved Permanently)</x:defines>
4141    <x:defines>4xx (Client Error)</x:defines>
4142    <x:defines>4xx</x:defines>
4143    <x:defines>400 (Bad Request)</x:defines>
4144    <x:defines>405 (Method Not Allowed)</x:defines>
4145    <x:defines>411 (Length Required)</x:defines>
4146    <x:defines>414 (URI Too Long)</x:defines>
4147    <x:defines>417 (Expectation Failed)</x:defines>
4148    <x:defines>426 (Upgrade Required)</x:defines>
4149    <x:defines>501 (Not Implemented)</x:defines>
4150    <x:defines>502 (Bad Gateway)</x:defines>
4151    <x:defines>505 (HTTP Version Not Supported)</x:defines>
4152    <x:defines>Content-Encoding</x:defines>
4153    <x:defines>Content-Type</x:defines>
4154    <x:defines>Date</x:defines>
4155    <x:defines>Expect</x:defines>
4156    <x:defines>Location</x:defines>
4157    <x:defines>Server</x:defines>
4158    <x:defines>User-Agent</x:defines>
4159  </x:source>
4162<reference anchor="Part4">
4163  <front>
4164    <title>HTTP/1.1, part 4: Conditional Requests</title>
4165    <author fullname="Roy T. Fielding" initials="R." role="editor" surname="Fielding">
4166      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4167      <address><email></email></address>
4168    </author>
4169    <author fullname="Yves Lafon" initials="Y." role="editor" surname="Lafon">
4170      <organization abbrev="W3C">World Wide Web Consortium</organization>
4171      <address><email></email></address>
4172    </author>
4173    <author fullname="Julian F. Reschke" initials="J. F." role="editor" surname="Reschke">
4174      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4175      <address><email></email></address>
4176    </author>
4177    <date month="&ID-MONTH;" year="&ID-YEAR;" />
4178  </front>
4179  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;" />
4180  <x:source basename="p4-conditional" href="p4-conditional.xml">
4181    <x:defines>304 (Not Modified)</x:defines>
4182  </x:source>
4185<reference anchor="Part5">
4186  <front>
4187    <title>HTTP/1.1, part 5: Range Requests and Partial Responses</title>
4188    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4189      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4190      <address><email></email></address>
4191    </author>
4192    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4193      <organization abbrev="W3C">World Wide Web Consortium</organization>
4194      <address><email></email></address>
4195    </author>
4196    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4197      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4198      <address><email></email></address>
4199    </author>
4200    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4201  </front>
4202  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
4203  <x:source href="p5-range.xml" basename="p5-range">
4204    <x:defines>Content-Range</x:defines>
4205  </x:source>
4208<reference anchor="Part6">
4209  <front>
4210    <title>HTTP/1.1, part 6: Caching</title>
4211    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4212      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4213      <address><email></email></address>
4214    </author>
4215    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4216      <organization abbrev="W3C">World Wide Web Consortium</organization>
4217      <address><email></email></address>
4218    </author>
4219    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4220      <organization>Rackspace</organization>
4221      <address><email></email></address>
4222    </author>
4223    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4224      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4225      <address><email></email></address>
4226    </author>
4227    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4228  </front>
4229  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4230  <x:source href="p6-cache.xml" basename="p6-cache">
4231    <x:defines>Expires</x:defines>
4232  </x:source>
4235<reference anchor="Part7">
4236  <front>
4237    <title>HTTP/1.1, part 7: Authentication</title>
4238    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4239      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4240      <address><email></email></address>
4241    </author>
4242    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4243      <organization abbrev="W3C">World Wide Web Consortium</organization>
4244      <address><email></email></address>
4245    </author>
4246    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4247      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4248      <address><email></email></address>
4249    </author>
4250    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4251  </front>
4252  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
4253  <x:source href="p7-auth.xml" basename="p7-auth">
4254    <x:defines>Proxy-Authenticate</x:defines>
4255    <x:defines>Proxy-Authorization</x:defines>
4256  </x:source>
4259<reference anchor="RFC5234">
4260  <front>
4261    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4262    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4263      <organization>Brandenburg InternetWorking</organization>
4264      <address>
4265        <email></email>
4266      </address> 
4267    </author>
4268    <author initials="P." surname="Overell" fullname="Paul Overell">
4269      <organization>THUS plc.</organization>
4270      <address>
4271        <email></email>
4272      </address>
4273    </author>
4274    <date month="January" year="2008"/>
4275  </front>
4276  <seriesInfo name="STD" value="68"/>
4277  <seriesInfo name="RFC" value="5234"/>
4280<reference anchor="RFC2119">
4281  <front>
4282    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4283    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4284      <organization>Harvard University</organization>
4285      <address><email></email></address>
4286    </author>
4287    <date month="March" year="1997"/>
4288  </front>
4289  <seriesInfo name="BCP" value="14"/>
4290  <seriesInfo name="RFC" value="2119"/>
4293<reference anchor="RFC3986">
4294 <front>
4295  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4296  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4297    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4298    <address>
4299       <email></email>
4300       <uri></uri>
4301    </address>
4302  </author>
4303  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4304    <organization abbrev="Day Software">Day Software</organization>
4305    <address>
4306      <email></email>
4307      <uri></uri>
4308    </address>
4309  </author>
4310  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4311    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4312    <address>
4313      <email></email>
4314      <uri></uri>
4315    </address>
4316  </author>
4317  <date month='January' year='2005'></date>
4318 </front>
4319 <seriesInfo name="STD" value="66"/>
4320 <seriesInfo name="RFC" value="3986"/>
4323<reference anchor="USASCII">
4324  <front>
4325    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4326    <author>
4327      <organization>American National Standards Institute</organization>
4328    </author>
4329    <date year="1986"/>
4330  </front>
4331  <seriesInfo name="ANSI" value="X3.4"/>
4334<reference anchor="RFC1950">
4335  <front>
4336    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4337    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4338      <organization>Aladdin Enterprises</organization>
4339      <address><email></email></address>
4340    </author>
4341    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4342    <date month="May" year="1996"/>
4343  </front>
4344  <seriesInfo name="RFC" value="1950"/>
4345  <!--<annotation>
4346    RFC 1950 is an Informational RFC, thus it might be less stable than
4347    this specification. On the other hand, this downward reference was
4348    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4349    therefore it is unlikely to cause problems in practice. See also
4350    <xref target="BCP97"/>.
4351  </annotation>-->
4354<reference anchor="RFC1951">
4355  <front>
4356    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4357    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4358      <organization>Aladdin Enterprises</organization>
4359      <address><email></email></address>
4360    </author>
4361    <date month="May" year="1996"/>
4362  </front>
4363  <seriesInfo name="RFC" value="1951"/>
4364  <!--<annotation>
4365    RFC 1951 is an Informational RFC, thus it might be less stable than
4366    this specification. On the other hand, this downward reference was
4367    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4368    therefore it is unlikely to cause problems in practice. See also
4369    <xref target="BCP97"/>.
4370  </annotation>-->
4373<reference anchor="RFC1952">
4374  <front>
4375    <title>GZIP file format specification version 4.3</title>
4376    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4377      <organization>Aladdin Enterprises</organization>
4378      <address><email></email></address>
4379    </author>
4380    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4381      <address><email></email></address>
4382    </author>
4383    <author initials="M." surname="Adler" fullname="Mark Adler">
4384      <address><email></email></address>
4385    </author>
4386    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4387      <address><email></email></address>
4388    </author>
4389    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4390      <address><email></email></address>
4391    </author>
4392    <date month="May" year="1996"/>
4393  </front>
4394  <seriesInfo name="RFC" value="1952"/>
4395  <!--<annotation>
4396    RFC 1952 is an Informational RFC, thus it might be less stable than
4397    this specification. On the other hand, this downward reference was
4398    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4399    therefore it is unlikely to cause problems in practice. See also
4400    <xref target="BCP97"/>.
4401  </annotation>-->
4406<references title="Informative References">
4408<reference anchor="Nie1997" target="">
4409  <front>
4410    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4411    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4412    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4413    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4414    <author initials="H." surname="Lie" fullname="H. Lie"/>
4415    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4416    <date year="1997" month="September"/>
4417  </front>
4418  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4421<reference anchor="Pad1995" target="">
4422  <front>
4423    <title>Improving HTTP Latency</title>
4424    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4425    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4426    <date year="1995" month="December"/>
4427  </front>
4428  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4431<reference anchor='RFC1919'>
4432  <front>
4433    <title>Classical versus Transparent IP Proxies</title>
4434    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4435      <address><email></email></address>
4436    </author>
4437    <date year='1996' month='March' />
4438  </front>
4439  <seriesInfo name='RFC' value='1919' />
4442<reference anchor="RFC1945">
4443  <front>
4444    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4445    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4446      <organization>MIT, Laboratory for Computer Science</organization>
4447      <address><email></email></address>
4448    </author>
4449    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4450      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4451      <address><email></email></address>
4452    </author>
4453    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4454      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4455      <address><email></email></address>
4456    </author>
4457    <date month="May" year="1996"/>
4458  </front>
4459  <seriesInfo name="RFC" value="1945"/>
4462<reference anchor="RFC2045">
4463  <front>
4464    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4465    <author initials="N." surname="Freed" fullname="Ned Freed">
4466      <organization>Innosoft International, Inc.</organization>
4467      <address><email></email></address>
4468    </author>
4469    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4470      <organization>First Virtual Holdings</organization>
4471      <address><email></email></address>
4472    </author>
4473    <date month="November" year="1996"/>
4474  </front>
4475  <seriesInfo name="RFC" value="2045"/>
4478<reference anchor="RFC2047">
4479  <front>
4480    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4481    <author initials="K." surname="Moore" fullname="Keith Moore">
4482      <organization>University of Tennessee</organization>
4483      <address><email></email></address>
4484    </author>
4485    <date month="November" year="1996"/>
4486  </front>
4487  <seriesInfo name="RFC" value="2047"/>
4490<reference anchor="RFC2068">
4491  <front>
4492    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4493    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4494      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4495      <address><email></email></address>
4496    </author>
4497    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4498      <organization>MIT Laboratory for Computer Science</organization>
4499      <address><email></email></address>
4500    </author>
4501    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4502      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4503      <address><email></email></address>
4504    </author>
4505    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4506      <organization>MIT Laboratory for Computer Science</organization>
4507      <address><email></email></address>
4508    </author>
4509    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4510      <organization>MIT Laboratory for Computer Science</organization>
4511      <address><email></email></address>
4512    </author>
4513    <date month="January" year="1997"/>
4514  </front>
4515  <seriesInfo name="RFC" value="2068"/>
4518<reference anchor="RFC2145">
4519  <front>
4520    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4521    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4522      <organization>Western Research Laboratory</organization>
4523      <address><email></email></address>
4524    </author>
4525    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4526      <organization>Department of Information and Computer Science</organization>
4527      <address><email></email></address>
4528    </author>
4529    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4530      <organization>MIT Laboratory for Computer Science</organization>
4531      <address><email></email></address>
4532    </author>
4533    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4534      <organization>W3 Consortium</organization>
4535      <address><email></email></address>
4536    </author>
4537    <date month="May" year="1997"/>
4538  </front>
4539  <seriesInfo name="RFC" value="2145"/>
4542<reference anchor="RFC2616">
4543  <front>
4544    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4545    <author initials="R." surname="Fielding" fullname="R. Fielding">
4546      <organization>University of California, Irvine</organization>
4547      <address><email></email></address>
4548    </author>
4549    <author initials="J." surname="Gettys" fullname="J. Gettys">
4550      <organization>W3C</organization>
4551      <address><email></email></address>
4552    </author>
4553    <author initials="J." surname="Mogul" fullname="J. Mogul">
4554      <organization>Compaq Computer Corporation</organization>
4555      <address><email></email></address>
4556    </author>
4557    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4558      <organization>MIT Laboratory for Computer Science</organization>
4559      <address><email></email></address>
4560    </author>
4561    <author initials="L." surname="Masinter" fullname="L. Masinter">
4562      <organization>Xerox Corporation</organization>
4563      <address><email></email></address>
4564    </author>
4565    <author initials="P." surname="Leach" fullname="P. Leach">
4566      <organization>Microsoft Corporation</organization>
4567      <address><email></email></address>
4568    </author>
4569    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4570      <organization>W3C</organization>
4571      <address><email></email></address>
4572    </author>
4573    <date month="June" year="1999"/>
4574  </front>
4575  <seriesInfo name="RFC" value="2616"/>
4578<reference anchor='RFC2817'>
4579  <front>
4580    <title>Upgrading to TLS Within HTTP/1.1</title>
4581    <author initials='R.' surname='Khare' fullname='R. Khare'>
4582      <organization>4K Associates / UC Irvine</organization>
4583      <address><email></email></address>
4584    </author>
4585    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4586      <organization>Agranat Systems, Inc.</organization>
4587      <address><email></email></address>
4588    </author>
4589    <date year='2000' month='May' />
4590  </front>
4591  <seriesInfo name='RFC' value='2817' />
4594<reference anchor='RFC2818'>
4595  <front>
4596    <title>HTTP Over TLS</title>
4597    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4598      <organization>RTFM, Inc.</organization>
4599      <address><email></email></address>
4600    </author>
4601    <date year='2000' month='May' />
4602  </front>
4603  <seriesInfo name='RFC' value='2818' />
4606<reference anchor='RFC2965'>
4607  <front>
4608    <title>HTTP State Management Mechanism</title>
4609    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4610      <organization>Bell Laboratories, Lucent Technologies</organization>
4611      <address><email></email></address>
4612    </author>
4613    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4614      <organization>, Inc.</organization>
4615      <address><email></email></address>
4616    </author>
4617    <date year='2000' month='October' />
4618  </front>
4619  <seriesInfo name='RFC' value='2965' />
4622<reference anchor='RFC3040'>
4623  <front>
4624    <title>Internet Web Replication and Caching Taxonomy</title>
4625    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4626      <organization>Equinix, Inc.</organization>
4627    </author>
4628    <author initials='I.' surname='Melve' fullname='I. Melve'>
4629      <organization>UNINETT</organization>
4630    </author>
4631    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4632      <organization>CacheFlow Inc.</organization>
4633    </author>
4634    <date year='2001' month='January' />
4635  </front>
4636  <seriesInfo name='RFC' value='3040' />
4639<reference anchor='RFC3864'>
4640  <front>
4641    <title>Registration Procedures for Message Header Fields</title>
4642    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4643      <organization>Nine by Nine</organization>
4644      <address><email></email></address>
4645    </author>
4646    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4647      <organization>BEA Systems</organization>
4648      <address><email></email></address>
4649    </author>
4650    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4651      <organization>HP Labs</organization>
4652      <address><email></email></address>
4653    </author>
4654    <date year='2004' month='September' />
4655  </front>
4656  <seriesInfo name='BCP' value='90' />
4657  <seriesInfo name='RFC' value='3864' />
4660<reference anchor='RFC4033'>
4661  <front>
4662    <title>DNS Security Introduction and Requirements</title>
4663    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4664    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4665    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4666    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4667    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4668    <date year='2005' month='March' />
4669  </front>
4670  <seriesInfo name='RFC' value='4033' />
4673<reference anchor="RFC4288">
4674  <front>
4675    <title>Media Type Specifications and Registration Procedures</title>
4676    <author initials="N." surname="Freed" fullname="N. Freed">
4677      <organization>Sun Microsystems</organization>
4678      <address>
4679        <email></email>
4680      </address>
4681    </author>
4682    <author initials="J." surname="Klensin" fullname="J. Klensin">
4683      <address>
4684        <email></email>
4685      </address>
4686    </author>
4687    <date year="2005" month="December"/>
4688  </front>
4689  <seriesInfo name="BCP" value="13"/>
4690  <seriesInfo name="RFC" value="4288"/>
4693<reference anchor='RFC4395'>
4694  <front>
4695    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4696    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4697      <organization>AT&amp;T Laboratories</organization>
4698      <address>
4699        <email></email>
4700      </address>
4701    </author>
4702    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4703      <organization>Qualcomm, Inc.</organization>
4704      <address>
4705        <email></email>
4706      </address>
4707    </author>
4708    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4709      <organization>Adobe Systems</organization>
4710      <address>
4711        <email></email>
4712      </address>
4713    </author>
4714    <date year='2006' month='February' />
4715  </front>
4716  <seriesInfo name='BCP' value='115' />
4717  <seriesInfo name='RFC' value='4395' />
4720<reference anchor='RFC4559'>
4721  <front>
4722    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4723    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4724    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4725    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4726    <date year='2006' month='June' />
4727  </front>
4728  <seriesInfo name='RFC' value='4559' />
4731<reference anchor='RFC5226'>
4732  <front>
4733    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4734    <author initials='T.' surname='Narten' fullname='T. Narten'>
4735      <organization>IBM</organization>
4736      <address><email></email></address>
4737    </author>
4738    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4739      <organization>Google</organization>
4740      <address><email></email></address>
4741    </author>
4742    <date year='2008' month='May' />
4743  </front>
4744  <seriesInfo name='BCP' value='26' />
4745  <seriesInfo name='RFC' value='5226' />
4748<reference anchor="RFC5322">
4749  <front>
4750    <title>Internet Message Format</title>
4751    <author initials="P." surname="Resnick" fullname="P. Resnick">
4752      <organization>Qualcomm Incorporated</organization>
4753    </author>
4754    <date year="2008" month="October"/>
4755  </front>
4756  <seriesInfo name="RFC" value="5322"/>
4759<reference anchor="RFC6265">
4760  <front>
4761    <title>HTTP State Management Mechanism</title>
4762    <author initials="A." surname="Barth" fullname="Adam Barth">
4763      <organization abbrev="U.C. Berkeley">
4764        University of California, Berkeley
4765      </organization>
4766      <address><email></email></address>
4767    </author>
4768    <date year="2011" month="April" />
4769  </front>
4770  <seriesInfo name="RFC" value="6265"/>
4773<!--<reference anchor='BCP97'>
4774  <front>
4775    <title>Handling Normative References to Standards-Track Documents</title>
4776    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4777      <address>
4778        <email></email>
4779      </address>
4780    </author>
4781    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4782      <organization>MIT</organization>
4783      <address>
4784        <email></email>
4785      </address>
4786    </author>
4787    <date year='2007' month='June' />
4788  </front>
4789  <seriesInfo name='BCP' value='97' />
4790  <seriesInfo name='RFC' value='4897' />
4793<reference anchor="Kri2001" target="">
4794  <front>
4795    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4796    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4797    <date year="2001" month="November"/>
4798  </front>
4799  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4802<reference anchor="Spe" target="">
4803  <front>
4804    <title>Analysis of HTTP Performance Problems</title>
4805    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4806    <date/>
4807  </front>
4810<reference anchor="Tou1998" target="">
4811  <front>
4812  <title>Analysis of HTTP Performance</title>
4813  <author initials="J." surname="Touch" fullname="Joe Touch">
4814    <organization>USC/Information Sciences Institute</organization>
4815    <address><email></email></address>
4816  </author>
4817  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4818    <organization>USC/Information Sciences Institute</organization>
4819    <address><email></email></address>
4820  </author>
4821  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4822    <organization>USC/Information Sciences Institute</organization>
4823    <address><email></email></address>
4824  </author>
4825  <date year="1998" month="Aug"/>
4826  </front>
4827  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4828  <annotation>(original report dated Aug. 1996)</annotation>
4834<section title="HTTP Version History" anchor="compatibility">
4836   HTTP has been in use by the World-Wide Web global information initiative
4837   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4838   was a simple protocol for hypertext data transfer across the Internet
4839   with only a single request method (GET) and no metadata.
4840   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4841   methods and MIME-like messaging that could include metadata about the data
4842   transferred and modifiers on the request/response semantics. However,
4843   HTTP/1.0 did not sufficiently take into consideration the effects of
4844   hierarchical proxies, caching, the need for persistent connections, or
4845   name-based virtual hosts. The proliferation of incompletely-implemented
4846   applications calling themselves "HTTP/1.0" further necessitated a
4847   protocol version change in order for two communicating applications
4848   to determine each other's true capabilities.
4851   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4852   requirements that enable reliable implementations, adding only
4853   those new features that will either be safely ignored by an HTTP/1.0
4854   recipient or only sent when communicating with a party advertising
4855   conformance with HTTP/1.1.
4858   It is beyond the scope of a protocol specification to mandate
4859   conformance with previous versions. HTTP/1.1 was deliberately
4860   designed, however, to make supporting previous versions easy.
4861   We would expect a general-purpose HTTP/1.1 server to understand
4862   any valid request in the format of HTTP/1.0 and respond appropriately
4863   with an HTTP/1.1 message that only uses features understood (or
4864   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4865   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4868   Since HTTP/0.9 did not support header fields in a request,
4869   there is no mechanism for it to support name-based virtual
4870   hosts (selection of resource by inspection of the <x:ref>Host</x:ref> header
4871   field).  Any server that implements name-based virtual hosts
4872   ought to disable support for HTTP/0.9.  Most requests that
4873   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4874   requests wherein a buggy client failed to properly encode
4875   linear whitespace found in a URI reference and placed in
4876   the request-target.
4879<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4881   This section summarizes major differences between versions HTTP/1.0
4882   and HTTP/1.1.
4885<section title="Multi-homed Web Servers" anchor="">
4887   The requirements that clients and servers support the <x:ref>Host</x:ref>
4888   header field (<xref target=""/>), report an error if it is
4889   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4890   are among the most important changes defined by HTTP/1.1.
4893   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4894   addresses and servers; there was no other established mechanism for
4895   distinguishing the intended server of a request than the IP address
4896   to which that request was directed. The <x:ref>Host</x:ref> header field was
4897   introduced during the development of HTTP/1.1 and, though it was
4898   quickly implemented by most HTTP/1.0 browsers, additional requirements
4899   were placed on all HTTP/1.1 requests in order to ensure complete
4900   adoption.  At the time of this writing, most HTTP-based services
4901   are dependent upon the Host header field for targeting requests.
4905<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4907   In HTTP/1.0, each connection is established by the client prior to the
4908   request and closed by the server after sending the response. However, some
4909   implementations implement the explicitly negotiated ("Keep-Alive") version
4910   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4911   target="RFC2068"/>.
4914   Some clients and servers might wish to be compatible with these previous
4915   approaches to persistent connections, by explicitly negotiating for them
4916   with a "Connection: keep-alive" request header field. However, some
4917   experimental implementations of HTTP/1.0 persistent connections are faulty;
4918   for example, if a HTTP/1.0 proxy server doesn't understand
4919   <x:ref>Connection</x:ref>, it will erroneously forward that header to the
4920   next inbound server, which would result in a hung connection.
4923   One attempted solution was the introduction of a Proxy-Connection header,
4924   targeted specifically at proxies. In practice, this was also unworkable,
4925   because proxies are often deployed in multiple layers, bringing about the
4926   same problem discussed above.
4929   As a result, clients are encouraged not to send the Proxy-Connection header
4930   in any requests.
4933   Clients are also encouraged to consider the use of Connection: keep-alive
4934   in requests carefully; while they can enable persistent connections with
4935   HTTP/1.0 servers, clients using them need will need to monitor the
4936   connection for "hung" requests (which indicate that the client ought stop
4937   sending the header), and this mechanism ought not be used by clients at all
4938   when a proxy is being used.
4942<section title="Introduction of Transfer-Encoding" anchor="introduction.of.transfer-encoding">
4944   HTTP/1.1 introduces the <x:ref>Transfer-Encoding</x:ref> header field
4945   (<xref target="header.transfer-encoding"/>). Proxies/gateways &MUST; remove
4946   any transfer-coding prior to forwarding a message via a MIME-compliant
4947   protocol.
4953<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4955  Clarify that the string "HTTP" in the HTTP-version ABFN production is case
4956  sensitive. Restrict the version numbers to be single digits due to the fact
4957  that implementations are known to handle multi-digit version numbers
4958  incorrectly.
4959  (<xref target="http.version"/>)
4962  Update use of abs_path production from RFC 1808 to the path-absolute + query
4963  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4964  request method only.
4965  (<xref target="request-target"/>)
4968  Require that invalid whitespace around field-names be rejected.
4969  (<xref target="header.fields"/>)
4972  Rules about implicit linear whitespace between certain grammar productions
4973  have been removed; now whitespace is only allowed where specifically
4974  defined in the ABNF.
4975  (<xref target="whitespace"/>)
4978  The NUL octet is no longer allowed in comment and quoted-string
4979  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4980  Non-ASCII content in header fields and reason phrase has been obsoleted and
4981  made opaque (the TEXT rule was removed).
4982  (<xref target="field.components"/>)
4985  Empty list elements in list productions have been deprecated.
4986  (<xref target="abnf.extension"/>)
4989  Require recipients to handle bogus <x:ref>Content-Length</x:ref> header
4990  fields as errors.
4991  (<xref target="message.body"/>)
4994  Remove reference to non-existent identity transfer-coding value tokens.
4995  (Sections <xref format="counter" target="message.body"/> and
4996  <xref format="counter" target="transfer.codings"/>)
4999  Clarification that the chunk length does not include the count of the octets
5000  in the chunk header and trailer. Furthermore disallowed line folding
5001  in chunk extensions, and deprecate their use.
5002  (<xref target="chunked.encoding"/>)
5005  Registration of Transfer Codings now requires IETF Review
5006  (<xref target="transfer.coding.registry"/>)
5009  Remove hard limit of two connections per server.
5010  Remove requirement to retry a sequence of requests as long it was idempotent.
5011  Remove requirements about when servers are allowed to close connections
5012  prematurely.
5013  (<xref target="persistent.practical"/>)
5016  Remove requirement to retry requests under certain cirumstances when the
5017  server prematurely closes the connection.
5018  (<xref target="message.transmission.requirements"/>)
5021  Change ABNF productions for header fields to only define the field value.
5024  Clarify exactly when "close" connection options have to be sent.
5025  (<xref target="header.connection"/>)
5028  Define the semantics of the <x:ref>Upgrade</x:ref> header field in responses
5029  other than 101 (this was incorporated from <xref target="RFC2817"/>).
5030  (<xref target="header.upgrade"/>)
5035<?BEGININC p1-messaging.abnf-appendix ?>
5036<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5038<artwork type="abnf" name="p1-messaging.parsed-abnf">
5039<x:ref>BWS</x:ref> = OWS
5041<x:ref>Connection</x:ref> = *( "," OWS ) connection-option *( OWS "," [ OWS
5042 connection-option ] )
5043<x:ref>Content-Length</x:ref> = 1*DIGIT
5045<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5046 ]
5047<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
5048<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
5049<x:ref>Host</x:ref> = uri-host [ ":" port ]
5051<x:ref>OWS</x:ref> = *( SP / HTAB )
5053<x:ref>RWS</x:ref> = 1*( SP / HTAB )
5055<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5056<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5057<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5058 transfer-coding ] )
5060<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5061<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5063<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
5064 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
5065 comment ] ) ] )
5067<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5068<x:ref>absolute-form</x:ref> = absolute-URI
5069<x:ref>asterisk-form</x:ref> = "*"
5070<x:ref>attribute</x:ref> = token
5071<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5072<x:ref>authority-form</x:ref> = authority
5074<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5075<x:ref>chunk-data</x:ref> = 1*OCTET
5076<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5077<x:ref>chunk-ext-name</x:ref> = token
5078<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5079<x:ref>chunk-size</x:ref> = 1*HEXDIG
5080<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
5081<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5082<x:ref>connection-option</x:ref> = token
5083<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5084 / %x2A-5B ; '*'-'['
5085 / %x5D-7E ; ']'-'~'
5086 / obs-text
5088<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5089<x:ref>field-name</x:ref> = token
5090<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5092<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5093<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5094<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5096<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5098<x:ref>message-body</x:ref> = *OCTET
5099<x:ref>method</x:ref> = token
5101<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5102<x:ref>obs-text</x:ref> = %x80-FF
5103<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
5105<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5106<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5107<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5108<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5109<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5110<x:ref>protocol-name</x:ref> = token
5111<x:ref>protocol-version</x:ref> = token
5112<x:ref>pseudonym</x:ref> = token
5114<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5115 / %x5D-7E ; ']'-'~'
5116 / obs-text
5117<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5118 / %x5D-7E ; ']'-'~'
5119 / obs-text
5120<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5121<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5122<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5123<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5124<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5125<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5127<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5128<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5129<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5130<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5131<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
5132<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
5133 asterisk-form
5135<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5136 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5137<x:ref>start-line</x:ref> = request-line / status-line
5138<x:ref>status-code</x:ref> = 3DIGIT
5139<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5141<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5142<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5143 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5144<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5145<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5146<x:ref>token</x:ref> = 1*tchar
5147<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5148<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5149 transfer-extension
5150<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5151<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5153<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5155<x:ref>value</x:ref> = word
5157<x:ref>word</x:ref> = token / quoted-string
5160<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5161; Connection defined but not used
5162; Content-Length defined but not used
5163; HTTP-message defined but not used
5164; Host defined but not used
5165; TE defined but not used
5166; Trailer defined but not used
5167; Transfer-Encoding defined but not used
5168; URI-reference defined but not used
5169; Upgrade defined but not used
5170; Via defined but not used
5171; chunked-body defined but not used
5172; http-URI defined but not used
5173; https-URI defined but not used
5174; partial-URI defined but not used
5175; special defined but not used
5177<?ENDINC p1-messaging.abnf-appendix ?>
5179<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5181<section title="Since RFC 2616">
5183  Extracted relevant partitions from <xref target="RFC2616"/>.
5187<section title="Since draft-ietf-httpbis-p1-messaging-00">
5189  Closed issues:
5190  <list style="symbols">
5191    <t>
5192      <eref target=""/>:
5193      "HTTP Version should be case sensitive"
5194      (<eref target=""/>)
5195    </t>
5196    <t>
5197      <eref target=""/>:
5198      "'unsafe' characters"
5199      (<eref target=""/>)
5200    </t>
5201    <t>
5202      <eref target=""/>:
5203      "Chunk Size Definition"
5204      (<eref target=""/>)
5205    </t>
5206    <t>
5207      <eref target=""/>:
5208      "Message Length"
5209      (<eref target=""/>)
5210    </t>
5211    <t>
5212      <eref target=""/>:
5213      "Media Type Registrations"
5214      (<eref target=""/>)
5215    </t>
5216    <t>
5217      <eref target=""/>:
5218      "URI includes query"
5219      (<eref target=""/>)
5220    </t>
5221    <t>
5222      <eref target=""/>:
5223      "No close on 1xx responses"
5224      (<eref target=""/>)
5225    </t>
5226    <t>
5227      <eref target=""/>:
5228      "Remove 'identity' token references"
5229      (<eref target=""/>)
5230    </t>
5231    <t>
5232      <eref target=""/>:
5233      "Import query BNF"
5234    </t>
5235    <t>
5236      <eref target=""/>:
5237      "qdtext BNF"
5238    </t>
5239    <t>
5240      <eref target=""/>:
5241      "Normative and Informative references"
5242    </t>
5243    <t>
5244      <eref target=""/>:
5245      "RFC2606 Compliance"
5246    </t>
5247    <t>
5248      <eref target=""/>:
5249      "RFC977 reference"
5250    </t>
5251    <t>
5252      <eref target=""/>:
5253      "RFC1700 references"
5254    </t>
5255    <t>
5256      <eref target=""/>:
5257      "inconsistency in date format explanation"
5258    </t>
5259    <t>
5260      <eref target=""/>:
5261      "Date reference typo"
5262    </t>
5263    <t>
5264      <eref target=""/>:
5265      "Informative references"
5266    </t>
5267    <t>
5268      <eref target=""/>:
5269      "ISO-8859-1 Reference"
5270    </t>
5271    <t>
5272      <eref target=""/>:
5273      "Normative up-to-date references"
5274    </t>
5275  </list>
5278  Other changes:
5279  <list style="symbols">
5280    <t>
5281      Update media type registrations to use RFC4288 template.
5282    </t>
5283    <t>
5284      Use names of RFC4234 core rules DQUOTE and HTAB,
5285      fix broken ABNF for chunk-data
5286      (work in progress on <eref target=""/>)
5287    </t>
5288  </list>
5292<section title="Since draft-ietf-httpbis-p1-messaging-01">
5294  Closed issues:
5295  <list style="symbols">
5296    <t>
5297      <eref target=""/>:
5298      "Bodies on GET (and other) requests"
5299    </t>
5300    <t>
5301      <eref target=""/>:
5302      "Updating to RFC4288"
5303    </t>
5304    <t>
5305      <eref target=""/>:
5306      "Status Code and Reason Phrase"
5307    </t>
5308    <t>
5309      <eref target=""/>:
5310      "rel_path not used"
5311    </t>
5312  </list>
5315  Ongoing work on ABNF conversion (<eref target=""/>):
5316  <list style="symbols">
5317    <t>
5318      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5319      "trailer-part").
5320    </t>
5321    <t>
5322      Avoid underscore character in rule names ("http_URL" ->
5323      "http-URL", "abs_path" -> "path-absolute").
5324    </t>
5325    <t>
5326      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5327      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5328      have to be updated when switching over to RFC3986.
5329    </t>
5330    <t>
5331      Synchronize core rules with RFC5234.
5332    </t>
5333    <t>
5334      Get rid of prose rules that span multiple lines.
5335    </t>
5336    <t>
5337      Get rid of unused rules LOALPHA and UPALPHA.
5338    </t>
5339    <t>
5340      Move "Product Tokens" section (back) into Part 1, as "token" is used
5341      in the definition of the Upgrade header field.
5342    </t>
5343    <t>
5344      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5345    </t>
5346    <t>
5347      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5348    </t>
5349  </list>
5353<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5355  Closed issues:
5356  <list style="symbols">
5357    <t>
5358      <eref target=""/>:
5359      "HTTP-date vs. rfc1123-date"
5360    </t>
5361    <t>
5362      <eref target=""/>:
5363      "WS in quoted-pair"
5364    </t>
5365  </list>
5368  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5369  <list style="symbols">
5370    <t>
5371      Reference RFC 3984, and update header field registrations for headers defined
5372      in this document.
5373    </t>
5374  </list>
5377  Ongoing work on ABNF conversion (<eref target=""/>):
5378  <list style="symbols">
5379    <t>
5380      Replace string literals when the string really is case-sensitive (HTTP-version).
5381    </t>
5382  </list>
5386<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5388  Closed issues:
5389  <list style="symbols">
5390    <t>
5391      <eref target=""/>:
5392      "Connection closing"
5393    </t>
5394    <t>
5395      <eref target=""/>:
5396      "Move registrations and registry information to IANA Considerations"
5397    </t>
5398    <t>
5399      <eref target=""/>:
5400      "need new URL for PAD1995 reference"
5401    </t>
5402    <t>
5403      <eref target=""/>:
5404      "IANA Considerations: update HTTP URI scheme registration"
5405    </t>
5406    <t>
5407      <eref target=""/>:
5408      "Cite HTTPS URI scheme definition"
5409    </t>
5410    <t>
5411      <eref target=""/>:
5412      "List-type headers vs Set-Cookie"
5413    </t>
5414  </list>
5417  Ongoing work on ABNF conversion (<eref target=""/>):
5418  <list style="symbols">
5419    <t>
5420      Replace string literals when the string really is case-sensitive (HTTP-Date).
5421    </t>
5422    <t>
5423      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5424    </t>
5425  </list>
5429<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5431  Closed issues:
5432  <list style="symbols">
5433    <t>
5434      <eref target=""/>:
5435      "Out-of-date reference for URIs"
5436    </t>
5437    <t>
5438      <eref target=""/>:
5439      "RFC 2822 is updated by RFC 5322"
5440    </t>
5441  </list>
5444  Ongoing work on ABNF conversion (<eref target=""/>):
5445  <list style="symbols">
5446    <t>
5447      Use "/" instead of "|" for alternatives.
5448    </t>
5449    <t>
5450      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5451    </t>
5452    <t>
5453      Only reference RFC 5234's core rules.
5454    </t>
5455    <t>
5456      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5457      whitespace ("OWS") and required whitespace ("RWS").
5458    </t>
5459    <t>
5460      Rewrite ABNFs to spell out whitespace rules, factor out
5461      header field value format definitions.
5462    </t>
5463  </list>
5467<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5469  Closed issues:
5470  <list style="symbols">
5471    <t>
5472      <eref target=""/>:
5473      "Header LWS"
5474    </t>
5475    <t>
5476      <eref target=""/>:
5477      "Sort 1.3 Terminology"
5478    </t>
5479    <t>
5480      <eref target=""/>:
5481      "RFC2047 encoded words"
5482    </t>
5483    <t>
5484      <eref target=""/>:
5485      "Character Encodings in TEXT"
5486    </t>
5487    <t>
5488      <eref target=""/>:
5489      "Line Folding"
5490    </t>
5491    <t>
5492      <eref target=""/>:
5493      "OPTIONS * and proxies"
5494    </t>
5495    <t>
5496      <eref target=""/>:
5497      "reason-phrase BNF"
5498    </t>
5499    <t>
5500      <eref target=""/>:
5501      "Use of TEXT"
5502    </t>
5503    <t>
5504      <eref target=""/>:
5505      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5506    </t>
5507    <t>
5508      <eref target=""/>:
5509      "RFC822 reference left in discussion of date formats"
5510    </t>
5511  </list>
5514  Final work on ABNF conversion (<eref target=""/>):
5515  <list style="symbols">
5516    <t>
5517      Rewrite definition of list rules, deprecate empty list elements.
5518    </t>
5519    <t>
5520      Add appendix containing collected and expanded ABNF.
5521    </t>
5522  </list>
5525  Other changes:
5526  <list style="symbols">
5527    <t>
5528      Rewrite introduction; add mostly new Architecture Section.
5529    </t>
5530    <t>
5531      Move definition of quality values from Part 3 into Part 1;
5532      make TE request header field grammar independent of accept-params (defined in Part 3).
5533    </t>
5534  </list>
5538<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5540  Closed issues:
5541  <list style="symbols">
5542    <t>
5543      <eref target=""/>:
5544      "base for numeric protocol elements"
5545    </t>
5546    <t>
5547      <eref target=""/>:
5548      "comment ABNF"
5549    </t>
5550  </list>
5553  Partly resolved issues:
5554  <list style="symbols">
5555    <t>
5556      <eref target=""/>:
5557      "205 Bodies" (took out language that implied that there might be
5558      methods for which a request body MUST NOT be included)
5559    </t>
5560    <t>
5561      <eref target=""/>:
5562      "editorial improvements around HTTP-date"
5563    </t>
5564  </list>
5568<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5570  Closed issues:
5571  <list style="symbols">
5572    <t>
5573      <eref target=""/>:
5574      "Repeating single-value headers"
5575    </t>
5576    <t>
5577      <eref target=""/>:
5578      "increase connection limit"
5579    </t>
5580    <t>
5581      <eref target=""/>:
5582      "IP addresses in URLs"
5583    </t>
5584    <t>
5585      <eref target=""/>:
5586      "take over HTTP Upgrade Token Registry"
5587    </t>
5588    <t>
5589      <eref target=""/>:
5590      "CR and LF in chunk extension values"
5591    </t>
5592    <t>
5593      <eref target=""/>:
5594      "HTTP/0.9 support"
5595    </t>
5596    <t>
5597      <eref target=""/>:
5598      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5599    </t>
5600    <t>
5601      <eref target=""/>:
5602      "move definitions of gzip/deflate/compress to part 1"
5603    </t>
5604    <t>
5605      <eref target=""/>:
5606      "disallow control characters in quoted-pair"
5607    </t>
5608  </list>
5611  Partly resolved issues:
5612  <list style="symbols">
5613    <t>
5614      <eref target=""/>:
5615      "update IANA requirements wrt Transfer-Coding values" (add the
5616      IANA Considerations subsection)
5617    </t>
5618  </list>
5622<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5624  Closed issues:
5625  <list style="symbols">
5626    <t>
5627      <eref target=""/>:
5628      "header parsing, treatment of leading and trailing OWS"
5629    </t>
5630  </list>
5633  Partly resolved issues:
5634  <list style="symbols">
5635    <t>
5636      <eref target=""/>:
5637      "Placement of 13.5.1 and 13.5.2"
5638    </t>
5639    <t>
5640      <eref target=""/>:
5641      "use of term "word" when talking about header structure"
5642    </t>
5643  </list>
5647<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5649  Closed issues:
5650  <list style="symbols">
5651    <t>
5652      <eref target=""/>:
5653      "Clarification of the term 'deflate'"
5654    </t>
5655    <t>
5656      <eref target=""/>:
5657      "OPTIONS * and proxies"
5658    </t>
5659    <t>
5660      <eref target=""/>:
5661      "MIME-Version not listed in P1, general header fields"
5662    </t>
5663    <t>
5664      <eref target=""/>:
5665      "IANA registry for content/transfer encodings"
5666    </t>
5667    <t>
5668      <eref target=""/>:
5669      "Case-sensitivity of HTTP-date"
5670    </t>
5671    <t>
5672      <eref target=""/>:
5673      "use of term "word" when talking about header structure"
5674    </t>
5675  </list>
5678  Partly resolved issues:
5679  <list style="symbols">
5680    <t>
5681      <eref target=""/>:
5682      "Term for the requested resource's URI"
5683    </t>
5684  </list>
5688<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5690  Closed issues:
5691  <list style="symbols">
5692    <t>
5693      <eref target=""/>:
5694      "Connection Closing"
5695    </t>
5696    <t>
5697      <eref target=""/>:
5698      "Delimiting messages with multipart/byteranges"
5699    </t>
5700    <t>
5701      <eref target=""/>:
5702      "Handling multiple Content-Length headers"
5703    </t>
5704    <t>
5705      <eref target=""/>:
5706      "Clarify entity / representation / variant terminology"
5707    </t>
5708    <t>
5709      <eref target=""/>:
5710      "consider removing the 'changes from 2068' sections"
5711    </t>
5712  </list>
5715  Partly resolved issues:
5716  <list style="symbols">
5717    <t>
5718      <eref target=""/>:
5719      "HTTP(s) URI scheme definitions"
5720    </t>
5721  </list>
5725<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5727  Closed issues:
5728  <list style="symbols">
5729    <t>
5730      <eref target=""/>:
5731      "Trailer requirements"
5732    </t>
5733    <t>
5734      <eref target=""/>:
5735      "Text about clock requirement for caches belongs in p6"
5736    </t>
5737    <t>
5738      <eref target=""/>:
5739      "effective request URI: handling of missing host in HTTP/1.0"
5740    </t>
5741    <t>
5742      <eref target=""/>:
5743      "confusing Date requirements for clients"
5744    </t>
5745  </list>
5748  Partly resolved issues:
5749  <list style="symbols">
5750    <t>
5751      <eref target=""/>:
5752      "Handling multiple Content-Length headers"
5753    </t>
5754  </list>
5758<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5760  Closed issues:
5761  <list style="symbols">
5762    <t>
5763      <eref target=""/>:
5764      "RFC2145 Normative"
5765    </t>
5766    <t>
5767      <eref target=""/>:
5768      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5769    </t>
5770    <t>
5771      <eref target=""/>:
5772      "define 'transparent' proxy"
5773    </t>
5774    <t>
5775      <eref target=""/>:
5776      "Header Classification"
5777    </t>
5778    <t>
5779      <eref target=""/>:
5780      "Is * usable as a request-uri for new methods?"
5781    </t>
5782    <t>
5783      <eref target=""/>:
5784      "Migrate Upgrade details from RFC2817"
5785    </t>
5786    <t>
5787      <eref target=""/>:
5788      "untangle ABNFs for header fields"
5789    </t>
5790    <t>
5791      <eref target=""/>:
5792      "update RFC 2109 reference"
5793    </t>
5794  </list>
5798<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5800  Closed issues:
5801  <list style="symbols">
5802    <t>
5803      <eref target=""/>:
5804      "Allow is not in 13.5.2"
5805    </t>
5806    <t>
5807      <eref target=""/>:
5808      "Handling multiple Content-Length headers"
5809    </t>
5810    <t>
5811      <eref target=""/>:
5812      "untangle ABNFs for header fields"
5813    </t>
5814    <t>
5815      <eref target=""/>:
5816      "Content-Length ABNF broken"
5817    </t>
5818  </list>
5822<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5824  Closed issues:
5825  <list style="symbols">
5826    <t>
5827      <eref target=""/>:
5828      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5829    </t>
5830    <t>
5831      <eref target=""/>:
5832      "Recommend minimum sizes for protocol elements"
5833    </t>
5834    <t>
5835      <eref target=""/>:
5836      "Set expectations around buffering"
5837    </t>
5838    <t>
5839      <eref target=""/>:
5840      "Considering messages in isolation"
5841    </t>
5842  </list>
5846<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5848  Closed issues:
5849  <list style="symbols">
5850    <t>
5851      <eref target=""/>:
5852      "DNS Spoofing / DNS Binding advice"
5853    </t>
5854    <t>
5855      <eref target=""/>:
5856      "move RFCs 2145, 2616, 2817 to Historic status"
5857    </t>
5858    <t>
5859      <eref target=""/>:
5860      "\-escaping in quoted strings"
5861    </t>
5862    <t>
5863      <eref target=""/>:
5864      "'Close' should be reserved in the HTTP header field registry"
5865    </t>
5866  </list>
5870<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5872  Closed issues:
5873  <list style="symbols">
5874    <t>
5875      <eref target=""/>:
5876      "Document HTTP's error-handling philosophy"
5877    </t>
5878    <t>
5879      <eref target=""/>:
5880      "Explain header registration"
5881    </t>
5882    <t>
5883      <eref target=""/>:
5884      "Revise Acknowledgements Sections"
5885    </t>
5886    <t>
5887      <eref target=""/>:
5888      "Retrying Requests"
5889    </t>
5890    <t>
5891      <eref target=""/>:
5892      "Closing the connection on server error"
5893    </t>
5894  </list>
5898<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5900  Closed issues:
5901  <list style="symbols">
5902    <t>
5903      <eref target=""/>:
5904      "Proxy-Connection and Keep-Alive"
5905    </t>
5906    <t>
5907      <eref target=""/>:
5908      "Clarify 'User Agent'"
5909    </t>
5910    <t>
5911      <eref target=""/>:
5912      "Define non-final responses"
5913    </t>
5914    <t>
5915      <eref target=""/>:
5916      "intended maturity level vs normative references"
5917    </t>
5918    <t>
5919      <eref target=""/>:
5920      "Intermediary rewriting of queries"
5921    </t>
5922  </list>
5926<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5928  Closed issues:
5929  <list style="symbols">
5930    <t>
5931      <eref target=""/>:
5932      "message-body in CONNECT response"
5933    </t>
5934    <t>
5935      <eref target=""/>:
5936      "Misplaced text on connection handling in p2"
5937    </t>
5938    <t>
5939      <eref target=""/>:
5940      "wording of line folding rule"
5941    </t>
5942    <t>
5943      <eref target=""/>:
5944      "chunk-extensions"
5945    </t>
5946    <t>
5947      <eref target=""/>:
5948      "make IANA policy definitions consistent"
5949    </t>
5950  </list>
5954<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5956  Closed issues:
5957  <list style="symbols">
5958    <t>
5959      <eref target=""/>:
5960      "make IANA policy definitions consistent"
5961    </t>
5962    <t>
5963      <eref target=""/>:
5964      "clarify connection header field values are case-insensitive"
5965    </t>
5966    <t>
5967      <eref target=""/>:
5968      "ABNF requirements for recipients"
5969    </t>
5970  </list>
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