source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1689

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "June">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x=''/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x=''/>">
20  <!ENTITY payload                "<xref target='Part2' xmlns:x=''/>">
21  <!ENTITY media-types            "<xref target='Part2' x:rel='#media.types' xmlns:x=''/>">
22  <!ENTITY content-codings        "<xref target='Part2' x:rel='#content.codings' xmlns:x=''/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
24  <!ENTITY content.negotiation    "<xref target='Part2' x:rel='#content.negotiation' xmlns:x=''/>">
25  <!ENTITY diff-mime              "<xref target='Part2' x:rel='#differences.between.http.and.mime' xmlns:x=''/>">
26  <!ENTITY representation         "<xref target='Part2' x:rel='#representation' xmlns:x=''/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
28  <!ENTITY header-date            "<xref target='Part2' x:rel='' xmlns:x=''/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
30  <!ENTITY header-mime-version    "<xref target='Part2' x:rel='#mime-version' xmlns:x=''/>">
31  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
32  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
33  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
34  <!ENTITY methods                "<xref target='Part2' x:rel='#methods' xmlns:x=''/>">
35  <!ENTITY OPTIONS                "<xref target='Part2' x:rel='#OPTIONS' xmlns:x=''/>">
36  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
37  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
38  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
39  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x=''/>">
40  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
41  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x=''/>">
42  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
43  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x=''/>">
45<?rfc toc="yes" ?>
46<?rfc symrefs="yes" ?>
47<?rfc sortrefs="yes" ?>
48<?rfc compact="yes"?>
49<?rfc subcompact="no" ?>
50<?rfc linkmailto="no" ?>
51<?rfc editing="no" ?>
52<?rfc comments="yes"?>
53<?rfc inline="yes"?>
54<?rfc rfcedstyle="yes"?>
55<?rfc-ext allow-markup-in-artwork="yes" ?>
56<?rfc-ext include-references-in-index="yes" ?>
57<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
58     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
59     xmlns:x=''>
60<x:link rel="next" basename="p2-semantics"/>
61<x:feedback template="{docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
64  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
66  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
67    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
68    <address>
69      <postal>
70        <street>345 Park Ave</street>
71        <city>San Jose</city>
72        <region>CA</region>
73        <code>95110</code>
74        <country>USA</country>
75      </postal>
76      <email></email>
77      <uri></uri>
78    </address>
79  </author>
81  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
82    <organization abbrev="W3C">World Wide Web Consortium</organization>
83    <address>
84      <postal>
85        <street>W3C / ERCIM</street>
86        <street>2004, rte des Lucioles</street>
87        <city>Sophia-Antipolis</city>
88        <region>AM</region>
89        <code>06902</code>
90        <country>France</country>
91      </postal>
92      <email></email>
93      <uri></uri>
94    </address>
95  </author>
97  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
98    <organization abbrev="greenbytes">greenbytes GmbH</organization>
99    <address>
100      <postal>
101        <street>Hafenweg 16</street>
102        <city>Muenster</city><region>NW</region><code>48155</code>
103        <country>Germany</country>
104      </postal>
105      <email></email>
106      <uri></uri>
107    </address>
108  </author>
110  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
111  <workgroup>HTTPbis Working Group</workgroup>
115   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
116   distributed, collaborative, hypertext information systems. HTTP has been in
117   use by the World Wide Web global information initiative since 1990. This
118   document is Part 1 of the seven-part specification that defines the protocol
119   referred to as "HTTP/1.1" and, taken together, obsoletes
120   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
121   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
122   2068</xref>.
125   Part 1 provides an overview of HTTP and its associated terminology, defines
126   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
127   the generic message syntax and parsing requirements for HTTP message frames,
128   and describes general security concerns for implementations.
131   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
132   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
133   (on using CONNECT for TLS upgrades) and moves them to historic status.
137<note title="Editorial Note (To be removed by RFC Editor)">
138  <t>
139    Discussion of this draft ought to take place on the HTTPBIS working group
140    mailing list (, which is archived at
141    <eref target=""/>.
142  </t>
143  <t>
144    The current issues list is at
145    <eref target=""/> and related
146    documents (including fancy diffs) can be found at
147    <eref target=""/>.
148  </t>
149  <t>
150    The changes in this draft are summarized in <xref target="changes.since.19"/>.
151  </t>
155<section title="Introduction" anchor="introduction">
157   The Hypertext Transfer Protocol (HTTP) is an application-level
158   request/response protocol that uses extensible semantics and MIME-like
159   message payloads for flexible interaction with network-based hypertext
160   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
161   standard <xref target="RFC3986"/> to indicate the target resource
162   (<xref target="target-resource"/>) and relationships between resources.
163   Messages are passed in a format similar to that used by Internet mail
164   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
165   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
166   between HTTP and MIME messages).
169   HTTP is a generic interface protocol for information systems. It is
170   designed to hide the details of how a service is implemented by presenting
171   a uniform interface to clients that is independent of the types of
172   resources provided. Likewise, servers do not need to be aware of each
173   client's purpose: an HTTP request can be considered in isolation rather
174   than being associated with a specific type of client or a predetermined
175   sequence of application steps. The result is a protocol that can be used
176   effectively in many different contexts and for which implementations can
177   evolve independently over time.
180   HTTP is also designed for use as an intermediation protocol for translating
181   communication to and from non-HTTP information systems.
182   HTTP proxies and gateways can provide access to alternative information
183   services by translating their diverse protocols into a hypertext
184   format that can be viewed and manipulated by clients in the same way
185   as HTTP services.
188   One consequence of HTTP flexibility is that the protocol cannot be
189   defined in terms of what occurs behind the interface. Instead, we
190   are limited to defining the syntax of communication, the intent
191   of received communication, and the expected behavior of recipients.
192   If the communication is considered in isolation, then successful
193   actions ought to be reflected in corresponding changes to the
194   observable interface provided by servers. However, since multiple
195   clients might act in parallel and perhaps at cross-purposes, we
196   cannot require that such changes be observable beyond the scope
197   of a single response.
200   This document is Part 1 of the seven-part specification of HTTP,
201   defining the protocol referred to as "HTTP/1.1", obsoleting
202   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
203   Part 1 describes the architectural elements that are used or
204   referred to in HTTP, defines the "http" and "https" URI schemes,
205   describes overall network operation and connection management,
206   and defines HTTP message framing and forwarding requirements.
207   Our goal is to define all of the mechanisms necessary for HTTP message
208   handling that are independent of message semantics, thereby defining the
209   complete set of requirements for message parsers and
210   message-forwarding intermediaries.
213<section title="Requirement Notation" anchor="intro.requirements">
215   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
216   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
217   document are to be interpreted as described in <xref target="RFC2119"/>.
221<section title="Syntax Notation" anchor="notation">
222<iref primary="true" item="Grammar" subitem="ALPHA"/>
223<iref primary="true" item="Grammar" subitem="CR"/>
224<iref primary="true" item="Grammar" subitem="CRLF"/>
225<iref primary="true" item="Grammar" subitem="CTL"/>
226<iref primary="true" item="Grammar" subitem="DIGIT"/>
227<iref primary="true" item="Grammar" subitem="DQUOTE"/>
228<iref primary="true" item="Grammar" subitem="HEXDIG"/>
229<iref primary="true" item="Grammar" subitem="HTAB"/>
230<iref primary="true" item="Grammar" subitem="LF"/>
231<iref primary="true" item="Grammar" subitem="OCTET"/>
232<iref primary="true" item="Grammar" subitem="SP"/>
233<iref primary="true" item="Grammar" subitem="VCHAR"/>
235   This specification uses the Augmented Backus-Naur Form (ABNF) notation
236   of <xref target="RFC5234"/> with the list rule extension defined in
237   <xref target="abnf.extension"/>.  <xref target="collected.abnf"/> shows
238   the collected ABNF with the list rule expanded.
240<t anchor="core.rules">
241  <x:anchor-alias value="ALPHA"/>
242  <x:anchor-alias value="CTL"/>
243  <x:anchor-alias value="CR"/>
244  <x:anchor-alias value="CRLF"/>
245  <x:anchor-alias value="DIGIT"/>
246  <x:anchor-alias value="DQUOTE"/>
247  <x:anchor-alias value="HEXDIG"/>
248  <x:anchor-alias value="HTAB"/>
249  <x:anchor-alias value="LF"/>
250  <x:anchor-alias value="OCTET"/>
251  <x:anchor-alias value="SP"/>
252  <x:anchor-alias value="VCHAR"/>
253   The following core rules are included by
254   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
255   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
256   DIGIT (decimal 0-9), DQUOTE (double quote),
257   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
258   OCTET (any 8-bit sequence of data), SP (space), and
259   VCHAR (any visible <xref target="USASCII"/> character).
262   As a convention, ABNF rule names prefixed with "obs-" denote
263   "obsolete" grammar rules that appear for historical reasons.
268<section title="Architecture" anchor="architecture">
270   HTTP was created for the World Wide Web architecture
271   and has evolved over time to support the scalability needs of a worldwide
272   hypertext system. Much of that architecture is reflected in the terminology
273   and syntax productions used to define HTTP.
276<section title="Client/Server Messaging" anchor="operation">
277<iref primary="true" item="client"/>
278<iref primary="true" item="server"/>
279<iref primary="true" item="connection"/>
281   HTTP is a stateless request/response protocol that operates by exchanging
282   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
283   transport or session-layer
284   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
285   program that establishes a connection to a server for the purpose of
286   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
287   program that accepts connections in order to service HTTP requests by
288   sending HTTP responses.
290<iref primary="true" item="user agent"/>
291<iref primary="true" item="origin server"/>
292<iref primary="true" item="browser"/>
293<iref primary="true" item="spider"/>
294<iref primary="true" item="sender"/>
295<iref primary="true" item="recipient"/>
297   Note that the terms client and server refer only to the roles that
298   these programs perform for a particular connection.  The same program
299   might act as a client on some connections and a server on others.  We use
300   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
301   such as a WWW browser, editor, or spider (web-traversing robot), and
302   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
303   authoritative responses to a request.  For general requirements, we use
304   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
305   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
306   message.
309  <t>
310    <x:h>Note:</x:h> The term 'user agent' covers both those situations where
311    there is a user (human) interacting with the software agent (and for which
312    user interface or interactive suggestions might be made, e.g., warning the
313    user or given the user an option in the case of security or privacy
314    options) and also those where the software agent may act autonomously.
315  </t>
318   Most HTTP communication consists of a retrieval request (GET) for
319   a representation of some resource identified by a URI.  In the
320   simplest case, this might be accomplished via a single bidirectional
321   connection (===) between the user agent (UA) and the origin server (O).
323<figure><artwork type="drawing">
324         request   &gt;
325    <x:highlight>UA</x:highlight> ======================================= <x:highlight>O</x:highlight>
326                                &lt;   response
328<iref primary="true" item="message"/>
329<iref primary="true" item="request"/>
330<iref primary="true" item="response"/>
332   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
333   message, beginning with a request-line that includes a method, URI, and
334   protocol version (<xref target="request.line"/>),
335   followed by MIME-like header fields containing
336   request modifiers, client information, and representation metadata
337   (<xref target="header.fields"/>),
338   an empty line to indicate the end of the header section, and finally
339   a message body containing the payload body (if any,
340   <xref target="message.body"/>).
343   A server responds to the client's request by sending one or more HTTP
344   <x:dfn>response</x:dfn>
345   messages, each beginning with a status line that
346   includes the protocol version, a success or error code, and textual
347   reason phrase (<xref target="status.line"/>),
348   possibly followed by MIME-like header fields containing server
349   information, resource metadata, and representation metadata
350   (<xref target="header.fields"/>),
351   an empty line to indicate the end of the header section, and finally
352   a message body containing the payload body (if any,
353   <xref target="message.body"/>).
356   The following example illustrates a typical message exchange for a
357   GET request on the URI "":
360client request:
361</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
362GET /hello.txt HTTP/1.1
363User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
365Accept: */*
369server response:
370</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
371HTTP/1.1 200 OK
372Date: Mon, 27 Jul 2009 12:28:53 GMT
373Server: Apache
374Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
375ETag: "34aa387-d-1568eb00"
376Accept-Ranges: bytes
377Content-Length: <x:length-of target="exbody"/>
378Vary: Accept-Encoding
379Content-Type: text/plain
381<x:span anchor="exbody">Hello World!
385<section title="Connections and Transport Independence" anchor="transport-independence">
387   HTTP messaging is independent of the underlying transport or
388   session-layer connection protocol(s).  HTTP only presumes a reliable
389   transport with in-order delivery of requests and the corresponding
390   in-order delivery of responses.  The mapping of HTTP request and
391   response structures onto the data units of the underlying transport
392   protocol is outside the scope of this specification.
395   The specific connection protocols to be used for an interaction
396   are determined by client configuration and the target URI
397   (<xref target="target-resource"/>).
398   For example, the "http" URI scheme
399   (<xref target="http.uri"/>) indicates a default connection of TCP
400   over IP, with a default TCP port of 80, but the client might be
401   configured to use a proxy via some other connection port or protocol
402   instead of using the defaults.
405   A connection might be used for multiple HTTP request/response exchanges,
406   as defined in <xref target="persistent.connections"/>.
410<section title="Intermediaries" anchor="intermediaries">
411<iref primary="true" item="intermediary"/>
413   HTTP enables the use of intermediaries to satisfy requests through
414   a chain of connections.  There are three common forms of HTTP
415   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
416   a single intermediary might act as an origin server, proxy, gateway,
417   or tunnel, switching behavior based on the nature of each request.
419<figure><artwork type="drawing">
420         &gt;             &gt;             &gt;             &gt;
421    <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>
422               &lt;             &lt;             &lt;             &lt;
425   The figure above shows three intermediaries (A, B, and C) between the
426   user agent and origin server. A request or response message that
427   travels the whole chain will pass through four separate connections.
428   Some HTTP communication options
429   might apply only to the connection with the nearest, non-tunnel
430   neighbor, only to the end-points of the chain, or to all connections
431   along the chain. Although the diagram is linear, each participant might
432   be engaged in multiple, simultaneous communications. For example, B
433   might be receiving requests from many clients other than A, and/or
434   forwarding requests to servers other than C, at the same time that it
435   is handling A's request.
438<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
439<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
440   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
441   to describe various requirements in relation to the directional flow of a
442   message: all messages flow from upstream to downstream.
443   Likewise, we use the terms inbound and outbound to refer to
444   directions in relation to the request path:
445   "<x:dfn>inbound</x:dfn>" means toward the origin server and
446   "<x:dfn>outbound</x:dfn>" means toward the user agent.
448<t><iref primary="true" item="proxy"/>
449   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
450   client, usually via local configuration rules, to receive requests
451   for some type(s) of absolute URI and attempt to satisfy those
452   requests via translation through the HTTP interface.  Some translations
453   are minimal, such as for proxy requests for "http" URIs, whereas
454   other requests might require translation to and from entirely different
455   application-layer protocols. Proxies are often used to group an
456   organization's HTTP requests through a common intermediary for the
457   sake of security, annotation services, or shared caching.
460<iref primary="true" item="transforming proxy"/>
461<iref primary="true" item="non-transforming proxy"/>
462   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
463   or configured to modify request or response messages in a semantically
464   meaningful way (i.e., modifications, beyond those required by normal
465   HTTP processing, that change the message in a way that would be
466   significant to the original sender or potentially significant to
467   downstream recipients).  For example, a transforming proxy might be
468   acting as a shared annotation server (modifying responses to include
469   references to a local annotation database), a malware filter, a
470   format transcoder, or an intranet-to-Internet privacy filter.  Such
471   transformations are presumed to be desired by the client (or client
472   organization) that selected the proxy and are beyond the scope of
473   this specification.  However, when a proxy is not intended to transform
474   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
475   requirements that preserve HTTP message semantics. See &status-203; and
476   &header-warning; for status and warning codes related to transformations.
478<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
479<iref primary="true" item="accelerator"/>
480   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
481   is a receiving agent that acts
482   as a layer above some other server(s) and translates the received
483   requests to the underlying server's protocol.  Gateways are often
484   used to encapsulate legacy or untrusted information services, to
485   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
486   enable partitioning or load-balancing of HTTP services across
487   multiple machines.
490   A gateway behaves as an origin server on its outbound connection and
491   as a user agent on its inbound connection.
492   All HTTP requirements applicable to an origin server
493   also apply to the outbound communication of a gateway.
494   A gateway communicates with inbound servers using any protocol that
495   it desires, including private extensions to HTTP that are outside
496   the scope of this specification.  However, an HTTP-to-HTTP gateway
497   that wishes to interoperate with third-party HTTP servers &MUST;
498   conform to HTTP user agent requirements on the gateway's inbound
499   connection and &MUST; implement the Connection
500   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
501   header fields for both connections.
503<t><iref primary="true" item="tunnel"/>
504   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
505   without changing the messages. Once active, a tunnel is not
506   considered a party to the HTTP communication, though the tunnel might
507   have been initiated by an HTTP request. A tunnel ceases to exist when
508   both ends of the relayed connection are closed. Tunnels are used to
509   extend a virtual connection through an intermediary, such as when
510   transport-layer security is used to establish private communication
511   through a shared firewall proxy.
513<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
514<iref primary="true" item="captive portal"/>
515   In addition, there might exist network intermediaries that are not
516   considered part of the HTTP communication but nevertheless act as
517   filters or redirecting agents (usually violating HTTP semantics,
518   causing security problems, and otherwise making a mess of things).
519   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
520   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
521   or "<x:dfn>captive portal</x:dfn>",
522   differs from an HTTP proxy because it has not been selected by the client.
523   Instead, the network intermediary redirects outgoing TCP port 80 packets
524   (and occasionally other common port traffic) to an internal HTTP server.
525   Interception proxies are commonly found on public network access points,
526   as a means of enforcing account subscription prior to allowing use of
527   non-local Internet services, and within corporate firewalls to enforce
528   network usage policies.
529   They are indistinguishable from a man-in-the-middle attack.
532   HTTP is defined as a stateless protocol, meaning that each request message
533   can be understood in isolation.  Many implementations depend on HTTP's
534   stateless design in order to reuse proxied connections or dynamically
535   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
536   assume that two requests on the same connection are from the same user
537   agent unless the connection is secured and specific to that agent.
538   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
539   been known to violate this requirement, resulting in security and
540   interoperability problems.
544<section title="Caches" anchor="caches">
545<iref primary="true" item="cache"/>
547   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
548   subsystem that controls its message storage, retrieval, and deletion.
549   A cache stores cacheable responses in order to reduce the response
550   time and network bandwidth consumption on future, equivalent
551   requests. Any client or server &MAY; employ a cache, though a cache
552   cannot be used by a server while it is acting as a tunnel.
555   The effect of a cache is that the request/response chain is shortened
556   if one of the participants along the chain has a cached response
557   applicable to that request. The following illustrates the resulting
558   chain if B has a cached copy of an earlier response from O (via C)
559   for a request which has not been cached by UA or A.
561<figure><artwork type="drawing">
562            &gt;             &gt;
563       <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>
564                  &lt;             &lt;
566<t><iref primary="true" item="cacheable"/>
567   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
568   the response message for use in answering subsequent requests.
569   Even when a response is cacheable, there might be additional
570   constraints placed by the client or by the origin server on when
571   that cached response can be used for a particular request. HTTP
572   requirements for cache behavior and cacheable responses are
573   defined in &caching-overview;. 
576   There are a wide variety of architectures and configurations
577   of caches and proxies deployed across the World Wide Web and
578   inside large organizations. These systems include national hierarchies
579   of proxy caches to save transoceanic bandwidth, systems that
580   broadcast or multicast cache entries, organizations that distribute
581   subsets of cached data via optical media, and so on.
585<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
587   This specification targets conformance criteria according to the role of
588   a participant in HTTP communication.  Hence, HTTP requirements are placed
589   on senders, recipients, clients, servers, user agents, intermediaries,
590   origin servers, proxies, gateways, or caches, depending on what behavior
591   is being constrained by the requirement.
594   An implementation is considered conformant if it complies with all of the
595   requirements associated with the roles it partakes in HTTP.
598   Senders &MUST-NOT; generate protocol elements that do not match the grammar
599   defined by the ABNF rules for those protocol elements.
602   Unless noted otherwise, recipients &MUST; be able to parse all protocol
603   elements matching the ABNF rules defined for them and &MAY; attempt to recover a usable
604   protocol element from an invalid construct.  HTTP does not define
605   specific error handling mechanisms except when they have a direct impact
606   on security, since different applications of the protocol require
607   different error handling strategies.  For example, a Web browser might
608   wish to transparently recover from a response where the Location header
609   field doesn't parse according to the ABNF, whereas a systems control
610   client might consider any form of error recovery to be dangerous.
614<section title="Protocol Versioning" anchor="http.version">
615  <x:anchor-alias value="HTTP-version"/>
616  <x:anchor-alias value="HTTP-name"/>
618   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
619   versions of the protocol. This specification defines version "1.1".
620   The protocol version as a whole indicates the sender's conformance
621   with the set of requirements laid out in that version's corresponding
622   specification of HTTP.
625   The version of an HTTP message is indicated by an HTTP-version field
626   in the first line of the message. HTTP-version is case-sensitive.
628<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-version"/><iref primary="true" item="Grammar" subitem="HTTP-name"/>
629  <x:ref>HTTP-version</x:ref>  = <x:ref>HTTP-name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
630  <x:ref>HTTP-name</x:ref>     = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
633   The HTTP version number consists of two decimal digits separated by a "."
634   (period or decimal point).  The first digit ("major version") indicates the
635   HTTP messaging syntax, whereas the second digit ("minor version") indicates
636   the highest minor version to which the sender is
637   conformant and able to understand for future communication.  The minor
638   version advertises the sender's communication capabilities even when the
639   sender is only using a backwards-compatible subset of the protocol,
640   thereby letting the recipient know that more advanced features can
641   be used in response (by servers) or in future requests (by clients).
644   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
645   <xref target="RFC1945"/> or a recipient whose version is unknown,
646   the HTTP/1.1 message is constructed such that it can be interpreted
647   as a valid HTTP/1.0 message if all of the newer features are ignored.
648   This specification places recipient-version requirements on some
649   new features so that a conformant sender will only use compatible
650   features until it has determined, through configuration or the
651   receipt of a message, that the recipient supports HTTP/1.1.
654   The interpretation of a header field does not change between minor
655   versions of the same major HTTP version, though the default
656   behavior of a recipient in the absence of such a field can change.
657   Unless specified otherwise, header fields defined in HTTP/1.1 are
658   defined for all versions of HTTP/1.x.  In particular, the Host and
659   Connection header fields ought to be implemented by all HTTP/1.x
660   implementations whether or not they advertise conformance with HTTP/1.1.
663   New header fields can be defined such that, when they are
664   understood by a recipient, they might override or enhance the
665   interpretation of previously defined header fields.  When an
666   implementation receives an unrecognized header field, the recipient
667   &MUST; ignore that header field for local processing regardless of
668   the message's HTTP version.  An unrecognized header field received
669   by a proxy &MUST; be forwarded downstream unless the header field's
670   field-name is listed in the message's Connection header-field
671   (see <xref target="header.connection"/>).
672   These requirements allow HTTP's functionality to be enhanced without
673   requiring prior update of deployed intermediaries.
676   Intermediaries that process HTTP messages (i.e., all intermediaries
677   other than those acting as tunnels) &MUST; send their own HTTP-version
678   in forwarded messages.  In other words, they &MUST-NOT; blindly
679   forward the first line of an HTTP message without ensuring that the
680   protocol version in that message matches a version to which that
681   intermediary is conformant for both the receiving and
682   sending of messages.  Forwarding an HTTP message without rewriting
683   the HTTP-version might result in communication errors when downstream
684   recipients use the message sender's version to determine what features
685   are safe to use for later communication with that sender.
688   An HTTP client &SHOULD; send a request version equal to the highest
689   version to which the client is conformant and
690   whose major version is no higher than the highest version supported
691   by the server, if this is known.  An HTTP client &MUST-NOT; send a
692   version to which it is not conformant.
695   An HTTP client &MAY; send a lower request version if it is known that
696   the server incorrectly implements the HTTP specification, but only
697   after the client has attempted at least one normal request and determined
698   from the response status or header fields (e.g., Server) that the
699   server improperly handles higher request versions.
702   An HTTP server &SHOULD; send a response version equal to the highest
703   version to which the server is conformant and
704   whose major version is less than or equal to the one received in the
705   request.  An HTTP server &MUST-NOT; send a version to which it is not
706   conformant.  A server &MAY; send a 505 (HTTP
707   Version Not Supported) response if it cannot send a response using the
708   major version used in the client's request.
711   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
712   if it is known or suspected that the client incorrectly implements the
713   HTTP specification and is incapable of correctly processing later
714   version responses, such as when a client fails to parse the version
715   number correctly or when an intermediary is known to blindly forward
716   the HTTP-version even when it doesn't conform to the given minor
717   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
718   performed unless triggered by specific client attributes, such as when
719   one or more of the request header fields (e.g., User-Agent) uniquely
720   match the values sent by a client known to be in error.
723   The intention of HTTP's versioning design is that the major number
724   will only be incremented if an incompatible message syntax is
725   introduced, and that the minor number will only be incremented when
726   changes made to the protocol have the effect of adding to the message
727   semantics or implying additional capabilities of the sender.  However,
728   the minor version was not incremented for the changes introduced between
729   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
730   is specifically avoiding any such changes to the protocol.
734<section title="Uniform Resource Identifiers" anchor="uri">
735<iref primary="true" item="resource"/>
737   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
738   throughout HTTP as the means for identifying resources. URI references
739   are used to target requests, indicate redirects, and define relationships.
740   HTTP does not limit what a resource might be; it merely defines an interface
741   that can be used to interact with a resource via HTTP. More information on
742   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
744  <x:anchor-alias value="URI-reference"/>
745  <x:anchor-alias value="absolute-URI"/>
746  <x:anchor-alias value="relative-part"/>
747  <x:anchor-alias value="authority"/>
748  <x:anchor-alias value="path-abempty"/>
749  <x:anchor-alias value="path-absolute"/>
750  <x:anchor-alias value="port"/>
751  <x:anchor-alias value="query"/>
752  <x:anchor-alias value="uri-host"/>
753  <x:anchor-alias value="partial-URI"/>
755   This specification adopts the definitions of "URI-reference",
756   "absolute-URI", "relative-part", "port", "host",
757   "path-abempty", "path-absolute", "query", and "authority" from the
758   URI generic syntax <xref target="RFC3986"/>.
759   In addition, we define a partial-URI rule for protocol elements
760   that allow a relative URI but not a fragment.
762<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"/>
763  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
764  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
765  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
766  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
767  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
768  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
769  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
770  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
771  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
773  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
776   Each protocol element in HTTP that allows a URI reference will indicate
777   in its ABNF production whether the element allows any form of reference
778   (URI-reference), only a URI in absolute form (absolute-URI), only the
779   path and optional query components, or some combination of the above.
780   Unless otherwise indicated, URI references are parsed
781   relative to the effective request URI
782   (<xref target="effective.request.uri"/>).
785<section title="http URI scheme" anchor="http.uri">
786  <x:anchor-alias value="http-URI"/>
787  <iref item="http URI scheme" primary="true"/>
788  <iref item="URI scheme" subitem="http" primary="true"/>
790   The "http" URI scheme is hereby defined for the purpose of minting
791   identifiers according to their association with the hierarchical
792   namespace governed by a potential HTTP origin server listening for
793   TCP connections on a given port.
795<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
796  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
799   The HTTP origin server is identified by the generic syntax's
800   <x:ref>authority</x:ref> component, which includes a host identifier
801   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
802   The remainder of the URI, consisting of both the hierarchical path
803   component and optional query component, serves as an identifier for
804   a potential resource within that origin server's name space.
807   If the host identifier is provided as an IP literal or IPv4 address,
808   then the origin server is any listener on the indicated TCP port at
809   that IP address. If host is a registered name, then that name is
810   considered an indirect identifier and the recipient might use a name
811   resolution service, such as DNS, to find the address of a listener
812   for that host.
813   The host &MUST-NOT; be empty; if an "http" URI is received with an
814   empty host, then it &MUST; be rejected as invalid.
815   If the port subcomponent is empty or not given, then TCP port 80 is
816   assumed (the default reserved port for WWW services).
819   Regardless of the form of host identifier, access to that host is not
820   implied by the mere presence of its name or address. The host might or might
821   not exist and, even when it does exist, might or might not be running an
822   HTTP server or listening to the indicated port. The "http" URI scheme
823   makes use of the delegated nature of Internet names and addresses to
824   establish a naming authority (whatever entity has the ability to place
825   an HTTP server at that Internet name or address) and allows that
826   authority to determine which names are valid and how they might be used.
829   When an "http" URI is used within a context that calls for access to the
830   indicated resource, a client &MAY; attempt access by resolving
831   the host to an IP address, establishing a TCP connection to that address
832   on the indicated port, and sending an HTTP request message
833   (<xref target="http.message"/>) containing the URI's identifying data
834   (<xref target="message.routing"/>) to the server.
835   If the server responds to that request with a non-interim HTTP response
836   message, as described in &status-codes;, then that response
837   is considered an authoritative answer to the client's request.
840   Although HTTP is independent of the transport protocol, the "http"
841   scheme is specific to TCP-based services because the name delegation
842   process depends on TCP for establishing authority.
843   An HTTP service based on some other underlying connection protocol
844   would presumably be identified using a different URI scheme, just as
845   the "https" scheme (below) is used for servers that require an SSL/TLS
846   transport layer on a connection. Other protocols might also be used to
847   provide access to "http" identified resources &mdash; it is only the
848   authoritative interface used for mapping the namespace that is
849   specific to TCP.
852   The URI generic syntax for authority also includes a deprecated
853   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
854   for including user authentication information in the URI.  Some
855   implementations make use of the userinfo component for internal
856   configuration of authentication information, such as within command
857   invocation options, configuration files, or bookmark lists, even
858   though such usage might expose a user identifier or password.
859   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
860   delimiter) when transmitting an "http" URI in a message.  Recipients
861   of HTTP messages that contain a URI reference &SHOULD; parse for the
862   existence of userinfo and treat its presence as an error, likely
863   indicating that the deprecated subcomponent is being used to obscure
864   the authority for the sake of phishing attacks.
868<section title="https URI scheme" anchor="https.uri">
869   <x:anchor-alias value="https-URI"/>
870   <iref item="https URI scheme"/>
871   <iref item="URI scheme" subitem="https"/>
873   The "https" URI scheme is hereby defined for the purpose of minting
874   identifiers according to their association with the hierarchical
875   namespace governed by a potential HTTP origin server listening for
876   SSL/TLS-secured connections on a given TCP port.
879   All of the requirements listed above for the "http" scheme are also
880   requirements for the "https" scheme, except that a default TCP port
881   of 443 is assumed if the port subcomponent is empty or not given,
882   and the TCP connection &MUST; be secured for privacy through the
883   use of strong encryption prior to sending the first HTTP request.
885<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
886  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
889   Unlike the "http" scheme, responses to "https" identified requests
890   are never "public" and thus &MUST-NOT; be reused for shared caching.
891   They can, however, be reused in a private cache if the message is
892   cacheable by default in HTTP or specifically indicated as such by
893   the Cache-Control header field (&header-cache-control;).
896   Resources made available via the "https" scheme have no shared
897   identity with the "http" scheme even if their resource identifiers
898   indicate the same authority (the same host listening to the same
899   TCP port).  They are distinct name spaces and are considered to be
900   distinct origin servers.  However, an extension to HTTP that is
901   defined to apply to entire host domains, such as the Cookie protocol
902   <xref target="RFC6265"/>, can allow information
903   set by one service to impact communication with other services
904   within a matching group of host domains.
907   The process for authoritative access to an "https" identified
908   resource is defined in <xref target="RFC2818"/>.
912<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
914   Since the "http" and "https" schemes conform to the URI generic syntax,
915   such URIs are normalized and compared according to the algorithm defined
916   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
917   described above for each scheme.
920   If the port is equal to the default port for a scheme, the normal
921   form is to elide the port subcomponent. Likewise, an empty path
922   component is equivalent to an absolute path of "/", so the normal
923   form is to provide a path of "/" instead. The scheme and host
924   are case-insensitive and normally provided in lowercase; all
925   other components are compared in a case-sensitive manner.
926   Characters other than those in the "reserved" set are equivalent
927   to their percent-encoded octets (see <xref target="RFC3986"
928   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
931   For example, the following three URIs are equivalent:
933<figure><artwork type="example">
942<section title="Message Format" anchor="http.message">
943<x:anchor-alias value="generic-message"/>
944<x:anchor-alias value="message.types"/>
945<x:anchor-alias value="HTTP-message"/>
946<x:anchor-alias value="start-line"/>
947<iref item="header section"/>
948<iref item="headers"/>
949<iref item="header field"/>
951   All HTTP/1.1 messages consist of a start-line followed by a sequence of
952   octets in a format similar to the Internet Message Format
953   <xref target="RFC5322"/>: zero or more header fields (collectively
954   referred to as the "headers" or the "header section"), an empty line
955   indicating the end of the header section, and an optional message body.
957<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
958  <x:ref>HTTP-message</x:ref>   = <x:ref>start-line</x:ref>
959                   *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
960                   <x:ref>CRLF</x:ref>
961                   [ <x:ref>message-body</x:ref> ]
964   The normal procedure for parsing an HTTP message is to read the
965   start-line into a structure, read each header field into a hash
966   table by field name until the empty line, and then use the parsed
967   data to determine if a message body is expected.  If a message body
968   has been indicated, then it is read as a stream until an amount
969   of octets equal to the message body length is read or the connection
970   is closed.
973   Recipients &MUST; parse an HTTP message as a sequence of octets in an
974   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
975   Parsing an HTTP message as a stream of Unicode characters, without regard
976   for the specific encoding, creates security vulnerabilities due to the
977   varying ways that string processing libraries handle invalid multibyte
978   character sequences that contain the octet LF (%x0A).  String-based
979   parsers can only be safely used within protocol elements after the element
980   has been extracted from the message, such as within a header field-value
981   after message parsing has delineated the individual fields.
984   An HTTP message can be parsed as a stream for incremental processing or
985   forwarding downstream.  However, recipients cannot rely on incremental
986   delivery of partial messages, since some implementations will buffer or
987   delay message forwarding for the sake of network efficiency, security
988   checks, or payload transformations.
991<section title="Start Line" anchor="start.line">
992  <x:anchor-alias value="Start-Line"/>
994   An HTTP message can either be a request from client to server or a
995   response from server to client.  Syntactically, the two types of message
996   differ only in the start-line, which is either a request-line (for requests)
997   or a status-line (for responses), and in the algorithm for determining
998   the length of the message body (<xref target="message.body"/>).
999   In theory, a client could receive requests and a server could receive
1000   responses, distinguishing them by their different start-line formats,
1001   but in practice servers are implemented to only expect a request
1002   (a response is interpreted as an unknown or invalid request method)
1003   and clients are implemented to only expect a response.
1005<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1006  <x:ref>start-line</x:ref>     = <x:ref>request-line</x:ref> / <x:ref>status-line</x:ref>
1011   Implementations &MUST-NOT; send whitespace between the start-line and
1012   the first header field. The presence of such whitespace in a request
1013   might be an attempt to trick a server into ignoring that field or
1014   processing the line after it as a new request, either of which might
1015   result in a security vulnerability if other implementations within
1016   the request chain interpret the same message differently.
1017   Likewise, the presence of such whitespace in a response might be
1018   ignored by some clients or cause others to cease parsing.
1021<section title="Request Line" anchor="request.line">
1022  <x:anchor-alias value="Request"/>
1023  <x:anchor-alias value="request-line"/>
1025   A request-line begins with a method token, followed by a single
1026   space (SP), the request-target, another single space (SP), the
1027   protocol version, and ending with CRLF.
1029<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-line"/>
1030  <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>
1032<iref primary="true" item="method"/>
1033<t anchor="method">
1034   The method token indicates the request method to be performed on the
1035   target resource. The request method is case-sensitive.
1037<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
1038  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
1041   The methods defined by this specification can be found in
1042   &methods;, along with information regarding the HTTP method registry
1043   and considerations for defining new methods.
1045<iref item="request-target"/>
1047   The request-target identifies the target resource upon which to apply
1048   the request, as defined in <xref target="request-target"/>.
1051   No whitespace is allowed inside the method, request-target, and
1052   protocol version.  Hence, recipients typically parse the request-line
1053   into its component parts by splitting on the SP characters.
1056   Unfortunately, some user agents fail to properly encode hypertext
1057   references that have embedded whitespace, sending the characters
1058   directly instead of properly percent-encoding the disallowed characters.
1059   Recipients of an invalid request-line &SHOULD; respond with either a
1060   400 (Bad Request) error or a 301 (Moved Permanently) redirect with the
1061   request-target properly encoded.  Recipients &SHOULD-NOT; attempt to
1062   autocorrect and then process the request without a redirect, since the
1063   invalid request-line might be deliberately crafted to bypass
1064   security filters along the request chain.
1067   HTTP does not place a pre-defined limit on the length of a request-line.
1068   A server that receives a method longer than any that it implements
1069   &SHOULD; respond with either a 405 (Not Allowed), if it is an origin
1070   server, or a 501 (Not Implemented) status code.
1071   A server &MUST; be prepared to receive URIs of unbounded length and
1072   respond with the 414 (URI Too Long) status code if the received
1073   request-target would be longer than the server wishes to handle
1074   (see &status-414;).
1077   Various ad-hoc limitations on request-line length are found in practice.
1078   It is &RECOMMENDED; that all HTTP senders and recipients support, at a
1079   minimum, request-line lengths of up to 8000 octets.
1083<section title="Status Line" anchor="status.line">
1084  <x:anchor-alias value="response"/>
1085  <x:anchor-alias value="status-line"/>
1087   The first line of a response message is the status-line, consisting
1088   of the protocol version, a space (SP), the status code, another space,
1089   a possibly-empty textual phrase describing the status code, and
1090   ending with CRLF.
1092<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-line"/>
1093  <x:ref>status-line</x:ref> = <x:ref>HTTP-version</x:ref> <x:ref>SP</x:ref> <x:ref>status-code</x:ref> <x:ref>SP</x:ref> <x:ref>reason-phrase</x:ref> <x:ref>CRLF</x:ref>
1096<t anchor="status-code">
1097   The status-code element is a 3-digit integer result code of the attempt to
1098   understand and satisfy the request. See &status-codes; for
1099   further information, such as the list of status codes defined by this
1100   specification, the IANA registry, and considerations for new status codes.
1102<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="status-code"/>
1103  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1106<t anchor="reason-phrase">  
1107   The reason-phrase element exists for the sole purpose of providing a
1108   textual description associated with the numeric status code, mostly
1109   out of deference to earlier Internet application protocols that were more
1110   frequently used with interactive text clients. A client &SHOULD; ignore
1111   the reason-phrase content.
1113<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="reason-phrase"/>
1114  <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> )
1119<section title="Header Fields" anchor="header.fields">
1120  <x:anchor-alias value="header-field"/>
1121  <x:anchor-alias value="field-content"/>
1122  <x:anchor-alias value="field-name"/>
1123  <x:anchor-alias value="field-value"/>
1124  <x:anchor-alias value="obs-fold"/>
1126   Each HTTP header field consists of a case-insensitive field name
1127   followed by a colon (":"), optional whitespace, and the field value.
1129<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"/>
1130  <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>
1131  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1132  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1133  <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> )
1134  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1135                 ; obsolete line folding
1136                 ; see <xref target="field.parsing"/>
1139   The field-name token labels the corresponding field-value as having the
1140   semantics defined by that header field.  For example, the Date header field
1141   is defined in &header-date; as containing the origination
1142   timestamp for the message in which it appears.
1145   HTTP header fields are fully extensible: there is no limit on the
1146   introduction of new field names, each presumably defining new semantics,
1147   or on the number of header fields used in a given message.  Existing
1148   fields are defined in each part of this specification and in many other
1149   specifications outside the standards process.
1150   New header fields can be introduced without changing the protocol version
1151   if their defined semantics allow them to be safely ignored by recipients
1152   that do not recognize them.
1155   New HTTP header fields &SHOULD; be registered with IANA according
1156   to the procedures in &cons-new-header-fields;.
1157   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1158   field-name is listed in the Connection header field
1159   (<xref target="header.connection"/>) or the proxy is specifically
1160   configured to block or otherwise transform such fields.
1161   Unrecognized header fields &SHOULD; be ignored by other recipients.
1164   The order in which header fields with differing field names are
1165   received is not significant. However, it is "good practice" to send
1166   header fields that contain control data first, such as Host on
1167   requests and Date on responses, so that implementations can decide
1168   when not to handle a message as early as possible.  A server &MUST;
1169   wait until the entire header section is received before interpreting
1170   a request message, since later header fields might include conditionals,
1171   authentication credentials, or deliberately misleading duplicate
1172   header fields that would impact request processing.
1175   Multiple header fields with the same field name &MUST-NOT; be
1176   sent in a message unless the entire field value for that
1177   header field is defined as a comma-separated list [i.e., #(values)].
1178   Multiple header fields with the same field name can be combined into
1179   one "field-name: field-value" pair, without changing the semantics of the
1180   message, by appending each subsequent field value to the combined
1181   field value in order, separated by a comma. The order in which
1182   header fields with the same field name are received is therefore
1183   significant to the interpretation of the combined field value;
1184   a proxy &MUST-NOT; change the order of these field values when
1185   forwarding a message.
1188  <t>
1189   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1190   practice can occur multiple times, but does not use the list syntax, and
1191   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1192   for details.) Also note that the Set-Cookie2 header field specified in
1193   <xref target="RFC2965"/> does not share this problem.
1194  </t>
1197<section title="Whitespace" anchor="whitespace">
1198<t anchor="rule.LWS">
1199   This specification uses three rules to denote the use of linear
1200   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1201   BWS ("bad" whitespace).
1203<t anchor="rule.OWS">
1204   The OWS rule is used where zero or more linear whitespace octets might
1205   appear. OWS &SHOULD; either not be produced or be produced as a single
1206   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1207   be replaced with a single SP or transformed to all SP octets (each
1208   octet other than SP replaced with SP) before interpreting the field value
1209   or forwarding the message downstream.
1211<t anchor="rule.RWS">
1212   RWS is used when at least one linear whitespace octet is required to
1213   separate field tokens. RWS &SHOULD; be produced as a single SP.
1214   Multiple RWS octets that occur within field-content &SHOULD; either
1215   be replaced with a single SP or transformed to all SP octets before
1216   interpreting the field value or forwarding the message downstream.
1218<t anchor="rule.BWS">
1219   BWS is used where the grammar allows optional whitespace for historical
1220   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1221   recipients &MUST; accept such bad optional whitespace and remove it before
1222   interpreting the field value or forwarding the message downstream.
1224<t anchor="rule.whitespace">
1225  <x:anchor-alias value="BWS"/>
1226  <x:anchor-alias value="OWS"/>
1227  <x:anchor-alias value="RWS"/>
1229<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"/>
1230  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1231                 ; "optional" whitespace
1232  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1233                 ; "required" whitespace
1234  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1235                 ; "bad" whitespace
1239<section title="Field Parsing" anchor="field.parsing">
1241   No whitespace is allowed between the header field-name and colon.
1242   In the past, differences in the handling of such whitespace have led to
1243   security vulnerabilities in request routing and response handling.
1244   Any received request message that contains whitespace between a header
1245   field-name and colon &MUST; be rejected with a response code of 400
1246   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1247   message before forwarding the message downstream.
1250   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1251   preferred. The field value does not include any leading or trailing white
1252   space: OWS occurring before the first non-whitespace octet of the
1253   field value or after the last non-whitespace octet of the field value
1254   is ignored and &SHOULD; be removed before further processing (as this does
1255   not change the meaning of the header field).
1258   Historically, HTTP header field values could be extended over multiple
1259   lines by preceding each extra line with at least one space or horizontal
1260   tab (obs-fold). This specification deprecates such line
1261   folding except within the message/http media type
1262   (<xref target=""/>).
1263   HTTP senders &MUST-NOT; produce messages that include line folding
1264   (i.e., that contain any field-value that matches the obs-fold rule) unless
1265   the message is intended for packaging within the message/http media type.
1266   HTTP recipients &SHOULD; accept line folding and replace any embedded
1267   obs-fold whitespace with either a single SP or a matching number of SP
1268   octets (to avoid buffer copying) prior to interpreting the field value or
1269   forwarding the message downstream.
1272   Historically, HTTP has allowed field content with text in the ISO-8859-1
1273   <xref target="ISO-8859-1"/> character encoding and supported other
1274   character sets only through use of <xref target="RFC2047"/> encoding.
1275   In practice, most HTTP header field values use only a subset of the
1276   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1277   header fields &SHOULD; limit their field values to US-ASCII octets.
1278   Recipients &SHOULD; treat other (obs-text) octets in field content as
1279   opaque data.
1283<section title="Field Length" anchor="field.length">
1285   HTTP does not place a pre-defined limit on the length of header fields,
1286   either in isolation or as a set. A server &MUST; be prepared to receive
1287   request header fields of unbounded length and respond with a 4xx status
1288   code if the received header field(s) would be longer than the server wishes
1289   to handle.
1292   A client that receives response headers that are longer than it wishes to
1293   handle can only treat it as a server error.
1296   Various ad-hoc limitations on header length are found in practice. It is
1297   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1298   combined header fields have 4000 or more octets.
1302<section title="Field value components" anchor="field.components">
1303<t anchor="rule.token.separators">
1304  <x:anchor-alias value="tchar"/>
1305  <x:anchor-alias value="token"/>
1306  <x:anchor-alias value="special"/>
1307  <x:anchor-alias value="word"/>
1308   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1309   separated by whitespace or special characters. These special characters
1310   &MUST; be in a quoted string to be used within a parameter value (as defined
1311   in <xref target="transfer.codings"/>).
1313<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"/>
1314  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1316  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1318  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1319 -->
1320  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1321                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1322                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1323                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1325  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1326                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1327                 / "]" / "?" / "=" / "{" / "}"
1329<t anchor="rule.quoted-string">
1330  <x:anchor-alias value="quoted-string"/>
1331  <x:anchor-alias value="qdtext"/>
1332  <x:anchor-alias value="obs-text"/>
1333   A string of text is parsed as a single word if it is quoted using
1334   double-quote marks.
1336<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"/>
1337  <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>
1338  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1339  <x:ref>obs-text</x:ref>       = %x80-FF
1341<t anchor="rule.quoted-pair">
1342  <x:anchor-alias value="quoted-pair"/>
1343   The backslash octet ("\") can be used as a single-octet
1344   quoting mechanism within quoted-string constructs:
1346<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1347  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1350   Recipients that process the value of the quoted-string &MUST; handle a
1351   quoted-pair as if it were replaced by the octet following the backslash.
1354   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1355   escaping (i.e., other than DQUOTE and the backslash octet).
1357<t anchor="rule.comment">
1358  <x:anchor-alias value="comment"/>
1359  <x:anchor-alias value="ctext"/>
1360   Comments can be included in some HTTP header fields by surrounding
1361   the comment text with parentheses. Comments are only allowed in
1362   fields containing "comment" as part of their field value definition.
1364<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1365  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1366  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1368<t anchor="rule.quoted-cpair">
1369  <x:anchor-alias value="quoted-cpair"/>
1370   The backslash octet ("\") can be used as a single-octet
1371   quoting mechanism within comment constructs:
1373<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1374  <x:ref>quoted-cpair</x:ref>   = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1377   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1378   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1382<section title="ABNF list extension: #rule" anchor="abnf.extension">
1384  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1385  improve readability in the definitions of some header field values.
1388  A construct "#" is defined, similar to "*", for defining comma-delimited
1389  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1390  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1391  comma (",") and optional whitespace (OWS).   
1394  Thus,
1395</preamble><artwork type="example">
1396  1#element =&gt; element *( OWS "," OWS element )
1399  and:
1400</preamble><artwork type="example">
1401  #element =&gt; [ 1#element ]
1404  and for n &gt;= 1 and m &gt; 1:
1405</preamble><artwork type="example">
1406  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1409  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1410  list elements. In other words, consumers would follow the list productions:
1412<figure><artwork type="example">
1413  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1415  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1418  Note that empty elements do not contribute to the count of elements present,
1419  though.
1422  For example, given these ABNF productions:
1424<figure><artwork type="example">
1425  example-list      = 1#example-list-elmt
1426  example-list-elmt = token ; see <xref target="field.components"/>
1429  Then these are valid values for example-list (not including the double
1430  quotes, which are present for delimitation only):
1432<figure><artwork type="example">
1433  "foo,bar"
1434  "foo ,bar,"
1435  "foo , ,bar,charlie   "
1438  But these values would be invalid, as at least one non-empty element is
1439  required:
1441<figure><artwork type="example">
1442  ""
1443  ","
1444  ",   ,"
1447  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1448  expanded as explained above.
1453<section title="Message Body" anchor="message.body">
1454  <x:anchor-alias value="message-body"/>
1456   The message body (if any) of an HTTP message is used to carry the
1457   payload body of that request or response.  The message body is
1458   identical to the payload body unless a transfer coding has been
1459   applied, as described in <xref target="header.transfer-encoding"/>.
1461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1462  <x:ref>message-body</x:ref> = *OCTET
1465   The rules for when a message body is allowed in a message differ for
1466   requests and responses.
1469   The presence of a message body in a request is signaled by a
1470   a Content-Length or Transfer-Encoding header field.
1471   Request message framing is independent of method semantics,
1472   even if the method does not define any use for a message body.
1475   The presence of a message body in a response depends on both
1476   the request method to which it is responding and the response
1477   status code (<xref target="status-code"/>).
1478   Responses to the HEAD request method never include a message body
1479   because the associated response header fields (e.g., Transfer-Encoding,
1480   Content-Length, etc.) only indicate what their values would have been
1481   if the request method had been GET.
1482   Successful (2xx) responses to CONNECT switch to tunnel mode instead of
1483   having a message body.
1484   All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
1485   responses &MUST-NOT; include a message body.
1486   All other responses do include a message body, although the body
1487   &MAY; be of zero length.
1490<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1491  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1492  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1493  <x:anchor-alias value="Transfer-Encoding"/>
1495   When one or more transfer codings are applied to a payload body in order
1496   to form the message body, a Transfer-Encoding header field &MUST; be sent
1497   in the message and &MUST; contain the list of corresponding
1498   transfer-coding names in the same order that they were applied.
1499   Transfer codings are defined in <xref target="transfer.codings"/>.
1501<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1502  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1505   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1506   MIME, which was designed to enable safe transport of binary data over a
1507   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1508   However, safe transport has a different focus for an 8bit-clean transfer
1509   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1510   accurately delimit a dynamically generated payload and to distinguish
1511   payload encodings that are only applied for transport efficiency or
1512   security from those that are characteristics of the target resource.
1515   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1516   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1517   crucial role in delimiting messages when the payload body size is not
1518   known in advance.
1519   When the "chunked" transfer-coding is used, it &MUST; be the last
1520   transfer-coding applied to form the message body and &MUST-NOT;
1521   be applied more than once in a message body.
1522   If any transfer-coding is applied to a request payload body,
1523   the final transfer-coding applied &MUST; be "chunked".
1524   If any transfer-coding is applied to a response payload body, then either
1525   the final transfer-coding applied &MUST; be "chunked" or
1526   the message &MUST; be terminated by closing the connection.
1529   For example,
1530</preamble><artwork type="example">
1531  Transfer-Encoding: gzip, chunked
1533   indicates that the payload body has been compressed using the gzip
1534   coding and then chunked using the chunked coding while forming the
1535   message body.
1538   If more than one Transfer-Encoding header field is present in a message,
1539   the multiple field-values &MUST; be combined into one field-value,
1540   according to the algorithm defined in <xref target="header.fields"/>,
1541   before determining the message body length.
1544   Unlike Content-Encoding (&content-codings;), Transfer-Encoding is a
1545   property of the message, not of the payload, and thus &MAY; be added or
1546   removed by any implementation along the request/response chain.
1547   Additional information about the encoding parameters &MAY; be provided
1548   by other header fields not defined by this specification.
1551   Transfer-Encoding &MAY; be sent in a response to a HEAD request or in a
1552   304 response to a GET request, neither of which includes a message body,
1553   to indicate that the origin server would have applied a transfer coding
1554   to the message body if the request had been an unconditional GET.
1555   This indication is not required, however, because any recipient on
1556   the response chain (including the origin server) can remove transfer
1557   codings when they are not needed.
1560   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1561   implementations advertising only HTTP/1.0 support will not understand
1562   how to process a transfer-encoded payload.
1563   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1564   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1565   might be in the form of specific user configuration or by remembering the
1566   version of a prior received response.
1567   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1568   the corresponding request indicates HTTP/1.1 (or later).
1571   A server that receives a request message with a transfer-coding it does
1572   not understand &SHOULD; respond with 501 (Not Implemented) and then
1573   close the connection.
1577<section title="Content-Length" anchor="header.content-length">
1578  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1579  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1580  <x:anchor-alias value="Content-Length"/>
1582   When a message does not have a Transfer-Encoding header field and the
1583   payload body length can be determined prior to being transferred, a
1584   Content-Length header field &SHOULD; be sent to indicate the length of the
1585   payload body that is either present as the message body, for requests
1586   and non-HEAD responses other than 304, or would have been present had
1587   the request been an unconditional GET.  The length is expressed as a
1588   decimal number of octets.
1590<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1591  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1594   An example is
1596<figure><artwork type="example">
1597  Content-Length: 3495
1600   In the case of a response to a HEAD request, Content-Length indicates
1601   the size of the payload body (without any potential transfer-coding)
1602   that would have been sent had the request been a GET.
1603   In the case of a 304 (Not Modified) response to a GET request,
1604   Content-Length indicates the size of the payload body (without
1605   any potential transfer-coding) that would have been sent in a 200 (OK)
1606   response.
1609   HTTP's use of Content-Length is significantly different from how it is
1610   used in MIME, where it is an optional field used only within the
1611   "message/external-body" media-type.
1614   Any Content-Length field value greater than or equal to zero is valid.
1615   Since there is no predefined limit to the length of an HTTP payload,
1616   recipients &SHOULD; anticipate potentially large decimal numerals and
1617   prevent parsing errors due to integer conversion overflows
1618   (<xref target="attack.protocol.element.size.overflows"/>).
1621   If a message is received that has multiple Content-Length header fields
1622   (<xref target="header.content-length"/>) with field-values consisting
1623   of the same decimal value, or a single Content-Length header field with
1624   a field value containing a list of identical decimal values (e.g.,
1625   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1626   header fields have been generated or combined by an upstream message
1627   processor, then the recipient &MUST; either reject the message as invalid
1628   or replace the duplicated field-values with a single valid Content-Length
1629   field containing that decimal value prior to determining the message body
1630   length.
1634<section title="Message Body Length" anchor="message.body.length">
1636   The length of a message body is determined by one of the following
1637   (in order of precedence):
1640  <list style="numbers">
1641    <x:lt><t>
1642     Any response to a HEAD request and any response with a status
1643     code of 100-199, 204, or 304 is always terminated by the first
1644     empty line after the header fields, regardless of the header
1645     fields present in the message, and thus cannot contain a message body.
1646    </t></x:lt>
1647    <x:lt><t>
1648     Any successful (2xx) response to a CONNECT request implies that the
1649     connection will become a tunnel immediately after the empty line that
1650     concludes the header fields.  A client &MUST; ignore any Content-Length
1651     or Transfer-Encoding header fields received in such a message.
1652    </t></x:lt>
1653    <x:lt><t>
1654     If a Transfer-Encoding header field is present
1655     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1656     is the final encoding, the message body length is determined by reading
1657     and decoding the chunked data until the transfer-coding indicates the
1658     data is complete.
1659    </t>
1660    <t>
1661     If a Transfer-Encoding header field is present in a response and the
1662     "chunked" transfer-coding is not the final encoding, the message body
1663     length is determined by reading the connection until it is closed by
1664     the server.
1665     If a Transfer-Encoding header field is present in a request and the
1666     "chunked" transfer-coding is not the final encoding, the message body
1667     length cannot be determined reliably; the server &MUST; respond with
1668     the 400 (Bad Request) status code and then close the connection.
1669    </t>
1670    <t>
1671     If a message is received with both a Transfer-Encoding header field
1672     and a Content-Length header field, the Transfer-Encoding overrides
1673     the Content-Length.
1674     Such a message might indicate an attempt to perform request or response
1675     smuggling (bypass of security-related checks on message routing or content)
1676     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1677     be removed, prior to forwarding the message downstream, or replaced with
1678     the real message body length after the transfer-coding is decoded.
1679    </t></x:lt>
1680    <x:lt><t>
1681     If a message is received without Transfer-Encoding and with either
1682     multiple Content-Length header fields having differing field-values or
1683     a single Content-Length header field having an invalid value, then the
1684     message framing is invalid and &MUST; be treated as an error to
1685     prevent request or response smuggling.
1686     If this is a request message, the server &MUST; respond with
1687     a 400 (Bad Request) status code and then close the connection.
1688     If this is a response message received by a proxy, the proxy
1689     &MUST; discard the received response, send a 502 (Bad Gateway)
1690     status code as its downstream response, and then close the connection.
1691     If this is a response message received by a user-agent, it &MUST; be
1692     treated as an error by discarding the message and closing the connection.
1693    </t></x:lt>
1694    <x:lt><t>
1695     If a valid Content-Length header field
1696     is present without Transfer-Encoding, its decimal value defines the
1697     message body length in octets.  If the actual number of octets sent in
1698     the message is less than the indicated Content-Length, the recipient
1699     &MUST; consider the message to be incomplete and treat the connection
1700     as no longer usable.
1701     If the actual number of octets sent in the message is more than the indicated
1702     Content-Length, the recipient &MUST; only process the message body up to the
1703     field value's number of octets; the remainder of the message &MUST; either
1704     be discarded or treated as the next message in a pipeline.  For the sake of
1705     robustness, a user-agent &MAY; attempt to detect and correct such an error
1706     in message framing if it is parsing the response to the last request on
1707     a connection and the connection has been closed by the server.
1708    </t></x:lt>
1709    <x:lt><t>
1710     If this is a request message and none of the above are true, then the
1711     message body length is zero (no message body is present).
1712    </t></x:lt>
1713    <x:lt><t>
1714     Otherwise, this is a response message without a declared message body
1715     length, so the message body length is determined by the number of octets
1716     received prior to the server closing the connection.
1717    </t></x:lt>
1718  </list>
1721   Since there is no way to distinguish a successfully completed,
1722   close-delimited message from a partially-received message interrupted
1723   by network failure, implementations &SHOULD; use encoding or
1724   length-delimited messages whenever possible.  The close-delimiting
1725   feature exists primarily for backwards compatibility with HTTP/1.0.
1728   A server &MAY; reject a request that contains a message body but
1729   not a Content-Length by responding with 411 (Length Required).
1732   Unless a transfer-coding other than "chunked" has been applied,
1733   a client that sends a request containing a message body &SHOULD;
1734   use a valid Content-Length header field if the message body length
1735   is known in advance, rather than the "chunked" encoding, since some
1736   existing services respond to "chunked" with a 411 (Length Required)
1737   status code even though they understand the chunked encoding.  This
1738   is typically because such services are implemented via a gateway that
1739   requires a content-length in advance of being called and the server
1740   is unable or unwilling to buffer the entire request before processing.
1743   A client that sends a request containing a message body &MUST; include a
1744   valid Content-Length header field if it does not know the server will
1745   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1746   of specific user configuration or by remembering the version of a prior
1747   received response.
1752<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1754   Request messages that are prematurely terminated, possibly due to a
1755   cancelled connection or a server-imposed time-out exception, &MUST;
1756   result in closure of the connection; sending an HTTP/1.1 error response
1757   prior to closing the connection is &OPTIONAL;.
1760   Response messages that are prematurely terminated, usually by closure
1761   of the connection prior to receiving the expected number of octets or by
1762   failure to decode a transfer-encoded message body, &MUST; be recorded
1763   as incomplete.  A response that terminates in the middle of the header
1764   block (before the empty line is received) cannot be assumed to convey the
1765   full semantics of the response and &MUST; be treated as an error.
1768   A message body that uses the chunked transfer encoding is
1769   incomplete if the zero-sized chunk that terminates the encoding has not
1770   been received.  A message that uses a valid Content-Length is incomplete
1771   if the size of the message body received (in octets) is less than the
1772   value given by Content-Length.  A response that has neither chunked
1773   transfer encoding nor Content-Length is terminated by closure of the
1774   connection, and thus is considered complete regardless of the number of
1775   message body octets received, provided that the header block was received
1776   intact.
1779   A user agent &MUST-NOT; render an incomplete response message body as if
1780   it were complete (i.e., some indication needs to be given to the user that an
1781   error occurred).  Cache requirements for incomplete responses are defined
1782   in &cache-incomplete;.
1785   A server &MUST; read the entire request message body or close
1786   the connection after sending its response, since otherwise the
1787   remaining data on a persistent connection would be misinterpreted
1788   as the next request.  Likewise,
1789   a client &MUST; read the entire response message body if it intends
1790   to reuse the same connection for a subsequent request.  Pipelining
1791   multiple requests on a connection is described in <xref target="pipelining"/>.
1795<section title="Message Parsing Robustness" anchor="message.robustness">
1797   Older HTTP/1.0 client implementations might send an extra CRLF
1798   after a POST request as a lame workaround for some early server
1799   applications that failed to read message body content that was
1800   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1801   preface or follow a request with an extra CRLF.  If terminating
1802   the request message body with a line-ending is desired, then the
1803   client &MUST; include the terminating CRLF octets as part of the
1804   message body length.
1807   In the interest of robustness, servers &SHOULD; ignore at least one
1808   empty line received where a request-line is expected. In other words, if
1809   the server is reading the protocol stream at the beginning of a
1810   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1811   Likewise, although the line terminator for the start-line and header
1812   fields is the sequence CRLF, we recommend that recipients recognize a
1813   single LF as a line terminator and ignore any CR.
1816   When a server listening only for HTTP request messages, or processing
1817   what appears from the start-line to be an HTTP request message,
1818   receives a sequence of octets that does not match the HTTP-message
1819   grammar aside from the robustness exceptions listed above, the
1820   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1825<section title="Transfer Codings" anchor="transfer.codings">
1826  <x:anchor-alias value="transfer-coding"/>
1827  <x:anchor-alias value="transfer-extension"/>
1829   Transfer-coding values are used to indicate an encoding
1830   transformation that has been, can be, or might need to be applied to a
1831   payload body in order to ensure "safe transport" through the network.
1832   This differs from a content coding in that the transfer-coding is a
1833   property of the message rather than a property of the representation
1834   that is being transferred.
1836<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1837  <x:ref>transfer-coding</x:ref>    = "chunked" ; <xref target="chunked.encoding"/>
1838                     / "compress" ; <xref target="compress.coding"/>
1839                     / "deflate" ; <xref target="deflate.coding"/>
1840                     / "gzip" ; <xref target="gzip.coding"/>
1841                     / <x:ref>transfer-extension</x:ref>
1842  <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> )
1844<t anchor="rule.parameter">
1845  <x:anchor-alias value="attribute"/>
1846  <x:anchor-alias value="transfer-parameter"/>
1847  <x:anchor-alias value="value"/>
1848   Parameters are in the form of attribute/value pairs.
1850<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"/>
1851  <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>
1852  <x:ref>attribute</x:ref>          = <x:ref>token</x:ref>
1853  <x:ref>value</x:ref>              = <x:ref>word</x:ref>
1856   All transfer-coding values are case-insensitive.
1857   The HTTP Transfer Coding registry is defined in
1858   <xref target="transfer.coding.registry"/>.
1859   HTTP/1.1 uses transfer-coding values in the TE header field
1860   (<xref target="header.te"/>) and in the Transfer-Encoding header field
1861   (<xref target="header.transfer-encoding"/>).
1864<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1865  <iref item="chunked (Coding Format)"/>
1866  <iref item="Coding Format" subitem="chunked"/>
1867  <x:anchor-alias value="chunk"/>
1868  <x:anchor-alias value="chunked-body"/>
1869  <x:anchor-alias value="chunk-data"/>
1870  <x:anchor-alias value="chunk-ext"/>
1871  <x:anchor-alias value="chunk-ext-name"/>
1872  <x:anchor-alias value="chunk-ext-val"/>
1873  <x:anchor-alias value="chunk-size"/>
1874  <x:anchor-alias value="last-chunk"/>
1875  <x:anchor-alias value="trailer-part"/>
1876  <x:anchor-alias value="quoted-str-nf"/>
1877  <x:anchor-alias value="qdtext-nf"/>
1879   The chunked encoding modifies the body of a message in order to
1880   transfer it as a series of chunks, each with its own size indicator,
1881   followed by an &OPTIONAL; trailer containing header fields. This
1882   allows dynamically produced content to be transferred along with the
1883   information necessary for the recipient to verify that it has
1884   received the full message.
1886<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"/>
1887  <x:ref>chunked-body</x:ref>   = *<x:ref>chunk</x:ref>
1888                   <x:ref>last-chunk</x:ref>
1889                   <x:ref>trailer-part</x:ref>
1890                   <x:ref>CRLF</x:ref>
1892  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1893                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1894  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1895  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1897  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1898  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1899  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1900  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1901  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1903  <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>
1904                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1905  <x:ref>qdtext-nf</x:ref>      = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1908   The chunk-size field is a string of hex digits indicating the size of
1909   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1910   zero, followed by the trailer, which is terminated by an empty line.
1913   The trailer allows the sender to include additional HTTP header
1914   fields at the end of the message. The Trailer header field can be
1915   used to indicate which header fields are included in a trailer (see
1916   <xref target="header.trailer"/>).
1919   A server using chunked transfer-coding in a response &MUST-NOT; use the
1920   trailer for any header fields unless at least one of the following is
1921   true:
1922  <list style="numbers">
1923    <t>the request included a TE header field that indicates "trailers" is
1924     acceptable in the transfer-coding of the  response, as described in
1925     <xref target="header.te"/>; or,</t>
1927    <t>the trailer fields consist entirely of optional metadata, and the
1928    recipient could use the message (in a manner acceptable to the server where
1929    the field originated) without receiving it. In other words, the server that
1930    generated the header (often but not always the origin server) is willing to
1931    accept the possibility that the trailer fields might be silently discarded
1932    along the path to the client.</t>
1933  </list>
1936   This requirement prevents an interoperability failure when the
1937   message is being received by an HTTP/1.1 (or later) proxy and
1938   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1939   conformance with the protocol would have necessitated a possibly
1940   infinite buffer on the proxy.
1943   A process for decoding the "chunked" transfer-coding
1944   can be represented in pseudo-code as:
1946<figure><artwork type="code">
1947  length := 0
1948  read chunk-size, chunk-ext (if any) and CRLF
1949  while (chunk-size &gt; 0) {
1950     read chunk-data and CRLF
1951     append chunk-data to decoded-body
1952     length := length + chunk-size
1953     read chunk-size and CRLF
1954  }
1955  read header-field
1956  while (header-field not empty) {
1957     append header-field to existing header fields
1958     read header-field
1959  }
1960  Content-Length := length
1961  Remove "chunked" from Transfer-Encoding
1964   All HTTP/1.1 applications &MUST; be able to receive and decode the
1965   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
1966   they do not understand.
1969   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
1970   sent and definition of new chunk-extensions is discouraged.
1974<section title="Compression Codings" anchor="compression.codings">
1976   The codings defined below can be used to compress the payload of a
1977   message.
1980   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1981   is not desirable and is discouraged for future encodings. Their
1982   use here is representative of historical practice, not good
1983   design.
1986   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1987   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1988   equivalent to "gzip" and "compress" respectively.
1991<section title="Compress Coding" anchor="compress.coding">
1992<iref item="compress (Coding Format)"/>
1993<iref item="Coding Format" subitem="compress"/>
1995   The "compress" format is produced by the common UNIX file compression
1996   program "compress". This format is an adaptive Lempel-Ziv-Welch
1997   coding (LZW).
2001<section title="Deflate Coding" anchor="deflate.coding">
2002<iref item="deflate (Coding Format)"/>
2003<iref item="Coding Format" subitem="deflate"/>
2005   The "deflate" format is defined as the "deflate" compression mechanism
2006   (described in <xref target="RFC1951"/>) used inside the "zlib"
2007   data format (<xref target="RFC1950"/>).
2010  <t>
2011    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2012    compressed data without the zlib wrapper.
2013   </t>
2017<section title="Gzip Coding" anchor="gzip.coding">
2018<iref item="gzip (Coding Format)"/>
2019<iref item="Coding Format" subitem="gzip"/>
2021   The "gzip" format is produced by the file compression program
2022   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2023   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2029<section title="TE" anchor="header.te">
2030  <iref primary="true" item="TE header field" x:for-anchor=""/>
2031  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2032  <x:anchor-alias value="TE"/>
2033  <x:anchor-alias value="t-codings"/>
2034  <x:anchor-alias value="te-params"/>
2035  <x:anchor-alias value="te-ext"/>
2037   The "TE" header field indicates what extension transfer-codings
2038   the client is willing to accept in the response, and whether or not it is
2039   willing to accept trailer fields in a chunked transfer-coding.
2042   Its value consists of the keyword "trailers" and/or a comma-separated
2043   list of extension transfer-coding names with optional accept
2044   parameters (as described in <xref target="transfer.codings"/>).
2046<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"/>
2047  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2048  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2049  <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> )
2050  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
2053   The presence of the keyword "trailers" indicates that the client is
2054   willing to accept trailer fields in a chunked transfer-coding, as
2055   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2056   transfer-coding values even though it does not itself represent a
2057   transfer-coding.
2060   Examples of its use are:
2062<figure><artwork type="example">
2063  TE: deflate
2064  TE:
2065  TE: trailers, deflate;q=0.5
2068   The TE header field only applies to the immediate connection.
2069   Therefore, the keyword &MUST; be supplied within a Connection header
2070   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2073   A server tests whether a transfer-coding is acceptable, according to
2074   a TE field, using these rules:
2075  <list style="numbers">
2076    <x:lt>
2077      <t>The "chunked" transfer-coding is always acceptable. If the
2078         keyword "trailers" is listed, the client indicates that it is
2079         willing to accept trailer fields in the chunked response on
2080         behalf of itself and any downstream clients. The implication is
2081         that, if given, the client is stating that either all
2082         downstream clients are willing to accept trailer fields in the
2083         forwarded response, or that it will attempt to buffer the
2084         response on behalf of downstream recipients.
2085      </t><t>
2086         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2087         chunked response such that a client can be assured of buffering
2088         the entire response.</t>
2089    </x:lt>
2090    <x:lt>
2091      <t>If the transfer-coding being tested is one of the transfer-codings
2092         listed in the TE field, then it is acceptable unless it
2093         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2094         qvalue of 0 means "not acceptable".)</t>
2095    </x:lt>
2096    <x:lt>
2097      <t>If multiple transfer-codings are acceptable, then the
2098         acceptable transfer-coding with the highest non-zero qvalue is
2099         preferred.  The "chunked" transfer-coding always has a qvalue
2100         of 1.</t>
2101    </x:lt>
2102  </list>
2105   If the TE field-value is empty or if no TE field is present, the only
2106   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2107   always acceptable.
2110<section title="Quality Values" anchor="quality.values">
2111  <x:anchor-alias value="qvalue"/>
2113   Both transfer codings (TE request header field, <xref target="header.te"/>)
2114   and content negotiation (&content.negotiation;) use short "floating point"
2115   numbers to indicate the relative importance ("weight") of various
2116   negotiable parameters.  A weight is normalized to a real number in
2117   the range 0 through 1, where 0 is the minimum and 1 the maximum
2118   value. If a parameter has a quality value of 0, then content with
2119   this parameter is "not acceptable" for the client. HTTP/1.1
2120   applications &MUST-NOT; generate more than three digits after the
2121   decimal point. User configuration of these values &SHOULD; also be
2122   limited in this fashion.
2124<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2125  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2126                 / ( "1" [ "." 0*3("0") ] )
2129  <t>
2130     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2131     relative degradation in desired quality.
2132  </t>
2137<section title="Trailer" anchor="header.trailer">
2138  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2139  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2140  <x:anchor-alias value="Trailer"/>
2142   The "Trailer" header field indicates that the given set of
2143   header fields is present in the trailer of a message encoded with
2144   chunked transfer-coding.
2146<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2147  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2150   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2151   message using chunked transfer-coding with a non-empty trailer. Doing
2152   so allows the recipient to know which header fields to expect in the
2153   trailer.
2156   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2157   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2158   trailer fields in a "chunked" transfer-coding.
2161   Message header fields listed in the Trailer header field &MUST-NOT;
2162   include the following header fields:
2163  <list style="symbols">
2164    <t>Transfer-Encoding</t>
2165    <t>Content-Length</t>
2166    <t>Trailer</t>
2167  </list>
2172<section title="Message Routing" anchor="message.routing">
2174   HTTP request message routing is determined by each client based on the
2175   target resource, the client's proxy configuration, and
2176   establishment or reuse of an inbound connection.  The corresponding
2177   response routing follows the same connection chain back to the client.
2180<section title="Identifying a Target Resource" anchor="target-resource">
2181  <iref primary="true" item="target resource"/>
2182  <iref primary="true" item="target URI"/>
2184   HTTP is used in a wide variety of applications, ranging from
2185   general-purpose computers to home appliances.  In some cases,
2186   communication options are hard-coded in a client's configuration.
2187   However, most HTTP clients rely on the same resource identification
2188   mechanism and configuration techniques as general-purpose Web browsers.
2191   HTTP communication is initiated by a user agent for some purpose.
2192   The purpose is a combination of request semantics, which are defined in
2193   <xref target="Part2"/>, and a target resource upon which to apply those
2194   semantics.  A URI reference (<xref target="uri"/>) is typically used as
2195   an identifier for the "target resource", which a user agent would resolve
2196   to its absolute form in order to obtain the "target URI".  The target URI
2197   excludes the reference's fragment identifier component, if any,
2198   since fragment identifiers are reserved for client-side processing
2199   (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>).
2202   HTTP intermediaries obtain the request semantics and target URI
2203   from the request-line of an incoming request message.
2207<section title="Connecting Inbound" anchor="connecting.inbound">
2209   Once the target URI is determined, a client needs to decide whether
2210   a network request is necessary to accomplish the desired semantics and,
2211   if so, where that request is to be directed.
2214   If the client has a response cache and the request semantics can be
2215   satisfied by a cache (<xref target="Part6"/>), then the request is
2216   usually directed to the cache first.
2219   If the request is not satisfied by a cache, then a typical client will
2220   check its configuration to determine whether a proxy is to be used to
2221   satisfy the request.  Proxy configuration is implementation-dependent,
2222   but is often based on URI prefix matching, selective authority matching,
2223   or both, and the proxy itself is usually identified by an "http" or
2224   "https" URI.  If a proxy is applicable, the client connects inbound by
2225   establishing (or reusing) a connection to that proxy.
2228   If no proxy is applicable, a typical client will invoke a handler routine,
2229   usually specific to the target URI's scheme, to connect directly
2230   to an authority for the target resource.  How that is accomplished is
2231   dependent on the target URI scheme and defined by its associated
2232   specification, similar to how this specification defines origin server
2233   access for resolution of the "http" (<xref target="http.uri"/>) and
2234   "https" (<xref target="https.uri"/>) schemes.
2238<section title="Request Target" anchor="request-target">
2240   Once an inbound connection is obtained
2241   (<xref target=""/>),
2242   the client sends an HTTP request message (<xref target="http.message"/>)
2243   with a request-target derived from the target URI.
2244   There are four distinct formats for the request-target, depending on both
2245   the method being requested and whether the request is to a proxy.
2247<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"/>
2248  <x:ref>request-target</x:ref> = <x:ref>origin-form</x:ref>
2249                 / <x:ref>absolute-form</x:ref>
2250                 / <x:ref>authority-form</x:ref>
2251                 / <x:ref>asterisk-form</x:ref>
2253  <x:ref>origin-form</x:ref>    = <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ]
2254  <x:ref>absolute-form</x:ref>  = <x:ref>absolute-URI</x:ref>
2255  <x:ref>authority-form</x:ref> = <x:ref>authority</x:ref>
2256  <x:ref>asterisk-form</x:ref>  = "*"
2258<t anchor="origin-form"><iref item="origin-form (of request-target)"/>
2259   The most common form of request-target is the origin-form.
2260   When making a request directly to an origin server, other than a CONNECT
2261   or server-wide OPTIONS request (as detailed below),
2262   a client &MUST; send only the absolute path and query components of
2263   the target URI as the request-target.
2264   If the target URI's path component is empty, then the client &MUST; send
2265   "/" as the path within the origin-form of request-target.
2266   A Host header field is also sent, as defined in
2267   <xref target=""/>, containing the target URI's
2268   authority component (excluding any userinfo).
2271   For example, a client wishing to retrieve a representation of the resource
2272   identified as
2274<figure><artwork x:indent-with="  " type="example">
2278   directly from the origin server would open (or reuse) a TCP connection
2279   to port 80 of the host "" and send the lines:
2281<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2282GET /where?q=now HTTP/1.1
2286   followed by the remainder of the request message.
2288<t anchor="absolute-form"><iref item="absolute-form (of request-target)"/>
2289   When making a request to a proxy, other than a CONNECT or server-wide
2290   OPTIONS request (as detailed below), a client &MUST; send the target URI
2291   in absolute-form as the request-target.
2292   The proxy is requested to either service that request from a valid cache,
2293   if possible, or make the same request on the client's behalf to either
2294   the next inbound proxy server or directly to the origin server indicated
2295   by the request-target.  Requirements on such "forwarding" of messages are
2296   defined in <xref target="intermediary.forwarding"/>.
2299   An example absolute-form of request-line would be:
2301<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2302GET HTTP/1.1
2305   To allow for transition to the absolute-form for all requests in some
2306   future version of HTTP, HTTP/1.1 servers &MUST; accept the absolute-form
2307   in requests, even though HTTP/1.1 clients will only send them in requests
2308   to proxies.
2310<t anchor="authority-form"><iref item="authority-form (of request-target)"/>
2311   The authority-form of request-target is only used for CONNECT requests
2312   (&CONNECT;).  When making a CONNECT request to establish a tunnel through
2313   one or more proxies, a client &MUST; send only the target URI's
2314   authority component (excluding any userinfo) as the request-target.
2315   For example,
2317<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2320<t anchor="asterisk-form"><iref item="asterisk-form (of request-target)"/>
2321   The asterisk-form of request-target is only used for a server-wide
2322   OPTIONS request (&OPTIONS;).  When a client wishes to request OPTIONS
2323   for the server as a whole, as opposed to a specific named resource of
2324   that server, the client &MUST; send only "*" (%x2A) as the request-target.
2325   For example,
2327<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2328OPTIONS * HTTP/1.1
2331   If a proxy receives an OPTIONS request with an absolute-form of
2332   request-target in which the URI has an empty path and no query component,
2333   then the last proxy on the request chain &MUST; send a request-target
2334   of "*" when it forwards the request to the indicated origin server.
2337   For example, the request
2338</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2342  would be forwarded by the final proxy as
2343</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2344OPTIONS * HTTP/1.1
2348   after connecting to port 8001 of host "".
2353<section title="Host" anchor="">
2354  <iref primary="true" item="Host header field" x:for-anchor=""/>
2355  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
2356  <x:anchor-alias value="Host"/>
2358   The "Host" header field in a request provides the host and port
2359   information from the target URI, enabling the origin
2360   server to distinguish among resources while servicing requests
2361   for multiple host names on a single IP address.  Since the Host
2362   field-value is critical information for handling a request, it
2363   &SHOULD; be sent as the first header field following the request-line.
2365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2366  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2369   A client &MUST; send a Host header field in all HTTP/1.1 request
2370   messages.  If the target URI includes an authority component, then
2371   the Host field-value &MUST; be identical to that authority component
2372   after excluding any userinfo (<xref target="http.uri"/>).
2373   If the authority component is missing or undefined for the target URI,
2374   then the Host header field &MUST; be sent with an empty field-value.
2377   For example, a GET request to the origin server for
2378   &lt;; would begin with:
2380<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2381GET /pub/WWW/ HTTP/1.1
2385   The Host header field &MUST; be sent in an HTTP/1.1 request even
2386   if the request-target is in the absolute-form, since this
2387   allows the Host information to be forwarded through ancient HTTP/1.0
2388   proxies that might not have implemented Host.
2391   When an HTTP/1.1 proxy receives a request with an absolute-form of
2392   request-target, the proxy &MUST; ignore the received
2393   Host header field (if any) and instead replace it with the host
2394   information of the request-target.  If the proxy forwards the request,
2395   it &MUST; generate a new Host field-value based on the received
2396   request-target rather than forward the received Host field-value.
2399   Since the Host header field acts as an application-level routing
2400   mechanism, it is a frequent target for malware seeking to poison
2401   a shared cache or redirect a request to an unintended server.
2402   An interception proxy is particularly vulnerable if it relies on
2403   the Host field-value for redirecting requests to internal
2404   servers, or for use as a cache key in a shared cache, without
2405   first verifying that the intercepted connection is targeting a
2406   valid IP address for that host.
2409   A server &MUST; respond with a 400 (Bad Request) status code to
2410   any HTTP/1.1 request message that lacks a Host header field and
2411   to any request message that contains more than one Host header field
2412   or a Host header field with an invalid field-value.
2416<section title="Effective Request URI" anchor="effective.request.uri">
2417  <iref primary="true" item="effective request URI"/>
2419   A server that receives an HTTP request message &MUST; reconstruct
2420   the user agent's original target URI, based on the pieces of information
2421   learned from the request-target, Host, and connection context, in order
2422   to identify the intended target resource and properly service the request.
2423   The URI derived from this reconstruction process is referred to as the
2424   "effective request URI".
2427   For a user agent, the effective request URI is the target URI.
2430   If the request-target is in absolute-form, then the effective request URI
2431   is the same as the request-target.  Otherwise, the effective request URI
2432   is constructed as follows.
2435   If the request is received over an SSL/TLS-secured TCP connection,
2436   then the effective request URI's scheme is "https"; otherwise, the
2437   scheme is "http".
2440   If the request-target is in authority-form, then the effective
2441   request URI's authority component is the same as the request-target.
2442   Otherwise, if a Host header field is supplied with a non-empty field-value,
2443   then the authority component is the same as the Host field-value.
2444   Otherwise, the authority component is the concatenation of the default
2445   host name configured for the server, a colon (":"), and the connection's
2446   incoming TCP port number in decimal form.
2449   If the request-target is in authority-form or asterisk-form, then the
2450   effective request URI's combined path and query component is empty.
2451   Otherwise, the combined path and query component is the same as the
2452   request-target.
2455   The components of the effective request URI, once determined as above,
2456   can be combined into absolute-URI form by concatenating the scheme,
2457   "://", authority, and combined path and query component.
2461   Example 1: the following message received over an insecure TCP connection
2463<artwork type="example" x:indent-with="  ">
2464GET /pub/WWW/TheProject.html HTTP/1.1
2470  has an effective request URI of
2472<artwork type="example" x:indent-with="  ">
2478   Example 2: the following message received over an SSL/TLS-secured TCP
2479   connection
2481<artwork type="example" x:indent-with="  ">
2482OPTIONS * HTTP/1.1
2488  has an effective request URI of
2490<artwork type="example" x:indent-with="  ">
2495   An origin server that does not allow resources to differ by requested
2496   host &MAY; ignore the Host field-value and instead replace it with a
2497   configured server name when constructing the effective request URI.
2500   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
2501   attempt to use heuristics (e.g., examination of the URI path for
2502   something unique to a particular host) in order to guess the
2503   effective request URI's authority component.
2507<section title="Intermediary Forwarding" anchor="intermediary.forwarding">
2509   As described in <xref target="intermediaries"/>, intermediaries can serve
2510   a variety of roles in the processing of HTTP requests and responses.
2511   Some intermediaries are used to improve performance or availability.
2512   Others are used for access control or to filter content.
2513   Since an HTTP stream has characteristics similar to a pipe-and-filter
2514   architecture, there are no inherent limits to the extent an intermediary
2515   can enhance (or interfere) with either direction of the stream.
2518   In order to avoid request loops, a proxy that forwards requests to other
2519   proxies &MUST; be able to recognize and exclude all of its own server
2520   names, including any aliases, local variations, or literal IP addresses.
2523   If a proxy receives a request-target with a host name that is not a
2524   fully qualified domain name, it &MAY; add its domain to the host name
2525   it received when forwarding the request.  A proxy &MUST-NOT; change the
2526   host name if it is a fully qualified domain name.
2529   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2530   parts of the received request-target when forwarding it to the next inbound
2531   server, except as noted above to replace an empty path with "/" or "*".
2534   Intermediaries that forward a message &MUST; implement the
2535   Connection header field as specified in <xref target="header.connection"/>.
2538<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2540  <cref anchor="TODO-end-to-end" source="jre">
2541    Restored from <eref target=""/>.
2542    See also <eref target=""/>.
2543  </cref>
2546   For the purpose of defining the behavior of caches and non-caching
2547   proxies, we divide HTTP header fields into two categories:
2548  <list style="symbols">
2549      <t>End-to-end header fields, which are  transmitted to the ultimate
2550        recipient of a request or response. End-to-end header fields in
2551        responses &MUST; be stored as part of a cache entry and &MUST; be
2552        transmitted in any response formed from a cache entry.</t>
2554      <t>Hop-by-hop header fields, which are meaningful only for a single
2555        transport-level connection, and are not stored by caches or
2556        forwarded by proxies.</t>
2557  </list>
2560   The following HTTP/1.1 header fields are hop-by-hop header fields:
2561  <list style="symbols">
2562      <t>Connection</t>
2563      <t>Keep-Alive</t>
2564      <t>Proxy-Authenticate</t>
2565      <t>Proxy-Authorization</t>
2566      <t>TE</t>
2567      <t>Trailer</t>
2568      <t>Transfer-Encoding</t>
2569      <t>Upgrade</t>
2570  </list>
2573   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2576   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2577   (<xref target="header.connection"/>).
2581<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2583  <cref anchor="TODO-non-mod-headers" source="jre">
2584    Restored from <eref target=""/>.
2585    See also <eref target=""/>.
2586  </cref>
2589   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2590   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2591   modify an end-to-end header field unless the definition of that header field requires
2592   or specifically allows that.
2595   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2596   request or response, and it &MUST-NOT; add any of these fields if not
2597   already present:
2598  <list style="symbols">
2599    <t>Allow</t>
2600    <t>Content-Location</t>
2601    <t>Content-MD5</t>
2602    <t>ETag</t>
2603    <t>Last-Modified</t>
2604    <t>Server</t>
2605  </list>
2608   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2609   response:
2610  <list style="symbols">
2611    <t>Expires</t>
2612  </list>
2615   but it &MAY; add any of these fields if not already present. If an
2616   Expires header field is added, it &MUST; be given a field-value identical to
2617   that of the Date header field in that response.
2620   A proxy &MUST-NOT; modify or add any of the following fields in a
2621   message that contains the no-transform cache-control directive, or in
2622   any request:
2623  <list style="symbols">
2624    <t>Content-Encoding</t>
2625    <t>Content-Range</t>
2626    <t>Content-Type</t>
2627  </list>
2630   A transforming proxy &MAY; modify or add these fields to a message
2631   that does not include no-transform, but if it does so, it &MUST; add a
2632   Warning 214 (Transformation applied) if one does not already appear
2633   in the message (see &header-warning;).
2636  <t>
2637    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2638    cause authentication failures if stronger authentication
2639    mechanisms are introduced in later versions of HTTP. Such
2640    authentication mechanisms &MAY; rely on the values of header fields
2641    not listed here.
2642  </t>
2645   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2646   though it &MAY; change the message body through application or removal
2647   of a transfer-coding (<xref target="transfer.codings"/>).
2653<section title="Associating a Response to a Request" anchor="">
2655   HTTP does not include a request identifier for associating a given
2656   request message with its corresponding one or more response messages.
2657   Hence, it relies on the order of response arrival to correspond exactly
2658   to the order in which requests are made on the same connection.
2659   More than one response message per request only occurs when one or more
2660   informational responses (1xx, see &status-1xx;) precede a final response
2661   to the same request.
2664   A client that uses persistent connections and sends more than one request
2665   per connection &MUST; maintain a list of outstanding requests in the
2666   order sent on that connection and &MUST; associate each received response
2667   message to the highest ordered request that has not yet received a final
2668   (non-1xx) response.
2673<section title="Connection Management" anchor="">
2675<section title="Connection" anchor="header.connection">
2676  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2677  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2678  <x:anchor-alias value="Connection"/>
2679  <x:anchor-alias value="connection-token"/>
2681   The "Connection" header field allows the sender to specify
2682   options that are desired only for that particular connection.
2683   Such connection options &MUST; be removed or replaced before the
2684   message can be forwarded downstream by a proxy or gateway.
2685   This mechanism also allows the sender to indicate which HTTP
2686   header fields used in the message are only intended for the
2687   immediate recipient ("hop-by-hop"), as opposed to all recipients
2688   on the chain ("end-to-end"), enabling the message to be
2689   self-descriptive and allowing future connection-specific extensions
2690   to be deployed in HTTP without fear that they will be blindly
2691   forwarded by previously deployed intermediaries.
2694   The Connection header field's value has the following grammar:
2696<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2697  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2698  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2701   A proxy or gateway &MUST; parse a received Connection
2702   header field before a message is forwarded and, for each
2703   connection-token in this field, remove any header field(s) from
2704   the message with the same name as the connection-token, and then
2705   remove the Connection header field itself or replace it with the
2706   sender's own connection options for the forwarded message.
2709   A sender &MUST-NOT; include field-names in the Connection header
2710   field-value for fields that are defined as expressing constraints
2711   for all recipients in the request or response chain, such as the
2712   Cache-Control header field (&header-cache-control;).
2715   The connection options do not have to correspond to a header field
2716   present in the message, since a connection-specific header field
2717   might not be needed if there are no parameters associated with that
2718   connection option.  Recipients that trigger certain connection
2719   behavior based on the presence of connection options &MUST; do so
2720   based on the presence of the connection-token rather than only the
2721   presence of the optional header field.  In other words, if the
2722   connection option is received as a header field but not indicated
2723   within the Connection field-value, then the recipient &MUST; ignore
2724   the connection-specific header field because it has likely been
2725   forwarded by an intermediary that is only partially conformant.
2728   When defining new connection options, specifications ought to
2729   carefully consider existing deployed header fields and ensure
2730   that the new connection-token does not share the same name as
2731   an unrelated header field that might already be deployed.
2732   Defining a new connection-token essentially reserves that potential
2733   field-name for carrying additional information related to the
2734   connection option, since it would be unwise for senders to use
2735   that field-name for anything else.
2738   HTTP/1.1 defines the "close" connection option for the sender to
2739   signal that the connection will be closed after completion of the
2740   response. For example,
2742<figure><artwork type="example">
2743  Connection: close
2746   in either the request or the response header fields indicates that
2747   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2748   after the current request/response is complete.
2751   An HTTP/1.1 client that does not support persistent connections &MUST;
2752   include the "close" connection option in every request message.
2755   An HTTP/1.1 server that does not support persistent connections &MUST;
2756   include the "close" connection option in every response message that
2757   does not have a 1xx (Informational) status code.
2761<section title="Via" anchor="header.via">
2762  <iref primary="true" item="Via header field" x:for-anchor=""/>
2763  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
2764  <x:anchor-alias value="pseudonym"/>
2765  <x:anchor-alias value="received-by"/>
2766  <x:anchor-alias value="received-protocol"/>
2767  <x:anchor-alias value="Via"/>
2769   The "Via" header field &MUST; be sent by a proxy or gateway to
2770   indicate the intermediate protocols and recipients between the user
2771   agent and the server on requests, and between the origin server and
2772   the client on responses. It is analogous to the "Received" field
2773   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
2774   and is intended to be used for tracking message forwards,
2775   avoiding request loops, and identifying the protocol capabilities of
2776   all senders along the request/response chain.
2778<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"/>
2779  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2780                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2781  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2782  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2783  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2786   The received-protocol indicates the protocol version of the message
2787   received by the server or client along each segment of the
2788   request/response chain. The received-protocol version is appended to
2789   the Via field value when the message is forwarded so that information
2790   about the protocol capabilities of upstream applications remains
2791   visible to all recipients.
2794   The protocol-name is excluded if and only if it would be "HTTP". The
2795   received-by field is normally the host and optional port number of a
2796   recipient server or client that subsequently forwarded the message.
2797   However, if the real host is considered to be sensitive information,
2798   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2799   be assumed to be the default port of the received-protocol.
2802   Multiple Via field values represent each proxy or gateway that has
2803   forwarded the message. Each recipient &MUST; append its information
2804   such that the end result is ordered according to the sequence of
2805   forwarding applications.
2808   Comments &MAY; be used in the Via header field to identify the software
2809   of each recipient, analogous to the User-Agent and Server header fields.
2810   However, all comments in the Via field are optional and &MAY; be removed
2811   by any recipient prior to forwarding the message.
2814   For example, a request message could be sent from an HTTP/1.0 user
2815   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2816   forward the request to a public proxy at, which completes
2817   the request by forwarding it to the origin server at
2818   The request received by would then have the following
2819   Via header field:
2821<figure><artwork type="example">
2822  Via: 1.0 fred, 1.1 (Apache/1.1)
2825   A proxy or gateway used as a portal through a network firewall
2826   &SHOULD-NOT; forward the names and ports of hosts within the firewall
2827   region unless it is explicitly enabled to do so. If not enabled, the
2828   received-by host of any host behind the firewall &SHOULD; be replaced
2829   by an appropriate pseudonym for that host.
2832   For organizations that have strong privacy requirements for hiding
2833   internal structures, a proxy or gateway &MAY; combine an ordered
2834   subsequence of Via header field entries with identical received-protocol
2835   values into a single such entry. For example,
2837<figure><artwork type="example">
2838  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2841  could be collapsed to
2843<figure><artwork type="example">
2844  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2847   Senders &SHOULD-NOT; combine multiple entries unless they are all
2848   under the same organizational control and the hosts have already been
2849   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
2850   have different received-protocol values.
2854<section title="Persistent Connections" anchor="persistent.connections">
2856<section title="Purpose" anchor="persistent.purpose">
2858   Prior to persistent connections, a separate TCP connection was
2859   established for each request, increasing the load on HTTP servers
2860   and causing congestion on the Internet. The use of inline images and
2861   other associated data often requires a client to make multiple
2862   requests of the same server in a short amount of time. Analysis of
2863   these performance problems and results from a prototype
2864   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2865   measurements of actual HTTP/1.1 implementations show good
2866   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2867   T/TCP <xref target="Tou1998"/>.
2870   Persistent HTTP connections have a number of advantages:
2871  <list style="symbols">
2872      <t>
2873        By opening and closing fewer TCP connections, CPU time is saved
2874        in routers and hosts (clients, servers, proxies, gateways,
2875        tunnels, or caches), and memory used for TCP protocol control
2876        blocks can be saved in hosts.
2877      </t>
2878      <t>
2879        HTTP requests and responses can be pipelined on a connection.
2880        Pipelining allows a client to make multiple requests without
2881        waiting for each response, allowing a single TCP connection to
2882        be used much more efficiently, with much lower elapsed time.
2883      </t>
2884      <t>
2885        Network congestion is reduced by reducing the number of packets
2886        caused by TCP opens, and by allowing TCP sufficient time to
2887        determine the congestion state of the network.
2888      </t>
2889      <t>
2890        Latency on subsequent requests is reduced since there is no time
2891        spent in TCP's connection opening handshake.
2892      </t>
2893      <t>
2894        HTTP can evolve more gracefully, since errors can be reported
2895        without the penalty of closing the TCP connection. Clients using
2896        future versions of HTTP might optimistically try a new feature,
2897        but if communicating with an older server, retry with old
2898        semantics after an error is reported.
2899      </t>
2900    </list>
2903   HTTP implementations &SHOULD; implement persistent connections.
2907<section title="Overall Operation" anchor="persistent.overall">
2909   A significant difference between HTTP/1.1 and earlier versions of
2910   HTTP is that persistent connections are the default behavior of any
2911   HTTP connection. That is, unless otherwise indicated, the client
2912   &SHOULD; assume that the server will maintain a persistent connection,
2913   even after error responses from the server.
2916   Persistent connections provide a mechanism by which a client and a
2917   server can signal the close of a TCP connection. This signaling takes
2918   place using the Connection header field (<xref target="header.connection"/>). Once a close
2919   has been signaled, the client &MUST-NOT; send any more requests on that
2920   connection.
2923<section title="Negotiation" anchor="persistent.negotiation">
2925   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2926   maintain a persistent connection unless a Connection header field including
2927   the connection-token "close" was sent in the request. If the server
2928   chooses to close the connection immediately after sending the
2929   response, it &SHOULD; send a Connection header field including the
2930   connection-token "close".
2933   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2934   decide to keep it open based on whether the response from a server
2935   contains a Connection header field with the connection-token close. In case
2936   the client does not want to maintain a connection for more than that
2937   request, it &SHOULD; send a Connection header field including the
2938   connection-token close.
2941   If either the client or the server sends the close token in the
2942   Connection header field, that request becomes the last one for the
2943   connection.
2946   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2947   maintained for HTTP versions less than 1.1 unless it is explicitly
2948   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2949   compatibility with HTTP/1.0 clients.
2952   Each persistent connection applies to only one transport link.
2955   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2956   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2957   for information and discussion of the problems with the Keep-Alive header field
2958   implemented by many HTTP/1.0 clients).
2961   In order to remain persistent, all messages on the connection &MUST;
2962   have a self-defined message length (i.e., one not defined by closure
2963   of the connection), as described in <xref target="message.body"/>.
2967<section title="Pipelining" anchor="pipelining">
2969   A client that supports persistent connections &MAY; "pipeline" its
2970   requests (i.e., send multiple requests without waiting for each
2971   response). A server &MUST; send its responses to those requests in the
2972   same order that the requests were received.
2975   Clients which assume persistent connections and pipeline immediately
2976   after connection establishment &SHOULD; be prepared to retry their
2977   connection if the first pipelined attempt fails. If a client does
2978   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2979   persistent. Clients &MUST; also be prepared to resend their requests if
2980   the server closes the connection before sending all of the
2981   corresponding responses.
2984   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2985   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2986   premature termination of the transport connection could lead to
2987   indeterminate results. A client wishing to send a non-idempotent
2988   request &SHOULD; wait to send that request until it has received the
2989   response status line for the previous request.
2994<section title="Practical Considerations" anchor="persistent.practical">
2996   Servers will usually have some time-out value beyond which they will
2997   no longer maintain an inactive connection. Proxy servers might make
2998   this a higher value since it is likely that the client will be making
2999   more connections through the same server. The use of persistent
3000   connections places no requirements on the length (or existence) of
3001   this time-out for either the client or the server.
3004   When a client or server wishes to time-out it &SHOULD; issue a graceful
3005   close on the transport connection. Clients and servers &SHOULD; both
3006   constantly watch for the other side of the transport close, and
3007   respond to it as appropriate. If a client or server does not detect
3008   the other side's close promptly it could cause unnecessary resource
3009   drain on the network.
3012   A client, server, or proxy &MAY; close the transport connection at any
3013   time. For example, a client might have started to send a new request
3014   at the same time that the server has decided to close the "idle"
3015   connection. From the server's point of view, the connection is being
3016   closed while it was idle, but from the client's point of view, a
3017   request is in progress.
3020   Clients (including proxies) &SHOULD; limit the number of simultaneous
3021   connections that they maintain to a given server (including proxies).
3024   Previous revisions of HTTP gave a specific number of connections as a
3025   ceiling, but this was found to be impractical for many applications. As a
3026   result, this specification does not mandate a particular maximum number of
3027   connections, but instead encourages clients to be conservative when opening
3028   multiple connections.
3031   In particular, while using multiple connections avoids the "head-of-line
3032   blocking" problem (whereby a request that takes significant server-side
3033   processing and/or has a large payload can block subsequent requests on the
3034   same connection), each connection used consumes server resources (sometimes
3035   significantly), and furthermore using multiple connections can cause
3036   undesirable side effects in congested networks.
3039   Note that servers might reject traffic that they deem abusive, including an
3040   excessive number of connections from a client.
3044<section title="Retrying Requests" anchor="persistent.retrying.requests">
3046   Senders can close the transport connection at any time. Therefore,
3047   clients, servers, and proxies &MUST; be able to recover
3048   from asynchronous close events. Client software &MAY; reopen the
3049   transport connection and retransmit the aborted sequence of requests
3050   without user interaction so long as the request sequence is
3051   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
3052   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
3053   human operator the choice of retrying the request(s). Confirmation by
3054   user-agent software with semantic understanding of the application
3055   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
3056   be repeated if the second sequence of requests fails.
3061<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
3063<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
3065   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
3066   flow control mechanisms to resolve temporary overloads, rather than
3067   terminating connections with the expectation that clients will retry.
3068   The latter technique can exacerbate network congestion.
3072<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
3074   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
3075   the network connection for an error status code while it is transmitting
3076   the request. If the client sees an error status code, it &SHOULD;
3077   immediately cease transmitting the body. If the body is being sent
3078   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
3079   empty trailer &MAY; be used to prematurely mark the end of the message.
3080   If the body was preceded by a Content-Length header field, the client &MUST;
3081   close the connection.
3085<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
3087   The purpose of the 100 (Continue) status code (see &status-100;) is to
3088   allow a client that is sending a request message with a request body
3089   to determine if the origin server is willing to accept the request
3090   (based on the request header fields) before the client sends the request
3091   body. In some cases, it might either be inappropriate or highly
3092   inefficient for the client to send the body if the server will reject
3093   the message without looking at the body.
3096   Requirements for HTTP/1.1 clients:
3097  <list style="symbols">
3098    <t>
3099        If a client will wait for a 100 (Continue) response before
3100        sending the request body, it &MUST; send an Expect header
3101        field (&header-expect;) with the "100-continue" expectation.
3102    </t>
3103    <t>
3104        A client &MUST-NOT; send an Expect header field (&header-expect;)
3105        with the "100-continue" expectation if it does not intend
3106        to send a request body.
3107    </t>
3108  </list>
3111   Because of the presence of older implementations, the protocol allows
3112   ambiguous situations in which a client might send "Expect: 100-continue"
3113   without receiving either a 417 (Expectation Failed)
3114   or a 100 (Continue) status code. Therefore, when a client sends this
3115   header field to an origin server (possibly via a proxy) from which it
3116   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
3117   wait for an indefinite period before sending the request body.
3120   Requirements for HTTP/1.1 origin servers:
3121  <list style="symbols">
3122    <t> Upon receiving a request which includes an Expect header
3123        field with the "100-continue" expectation, an origin server &MUST;
3124        either respond with 100 (Continue) status code and continue to read
3125        from the input stream, or respond with a final status code. The
3126        origin server &MUST-NOT; wait for the request body before sending
3127        the 100 (Continue) response. If it responds with a final status
3128        code, it &MAY; close the transport connection or it &MAY; continue
3129        to read and discard the rest of the request.  It &MUST-NOT;
3130        perform the request method if it returns a final status code.
3131    </t>
3132    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
3133        the request message does not include an Expect header
3134        field with the "100-continue" expectation, and &MUST-NOT; send a
3135        100 (Continue) response if such a request comes from an HTTP/1.0
3136        (or earlier) client. There is an exception to this rule: for
3137        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
3138        status code in response to an HTTP/1.1 PUT or POST request that does
3139        not include an Expect header field with the "100-continue"
3140        expectation. This exception, the purpose of which is
3141        to minimize any client processing delays associated with an
3142        undeclared wait for 100 (Continue) status code, applies only to
3143        HTTP/1.1 requests, and not to requests with any other HTTP-version
3144        value.
3145    </t>
3146    <t> An origin server &MAY; omit a 100 (Continue) response if it has
3147        already received some or all of the request body for the
3148        corresponding request.
3149    </t>
3150    <t> An origin server that sends a 100 (Continue) response &MUST;
3151        ultimately send a final status code, once the request body is
3152        received and processed, unless it terminates the transport
3153        connection prematurely.
3154    </t>
3155    <t> If an origin server receives a request that does not include an
3156        Expect header field with the "100-continue" expectation,
3157        the request includes a request body, and the server responds
3158        with a final status code before reading the entire request body
3159        from the transport connection, then the server &SHOULD-NOT;  close
3160        the transport connection until it has read the entire request,
3161        or until the client closes the connection. Otherwise, the client
3162        might not reliably receive the response message. However, this
3163        requirement ought not be construed as preventing a server from
3164        defending itself against denial-of-service attacks, or from
3165        badly broken client implementations.
3166      </t>
3167    </list>
3170   Requirements for HTTP/1.1 proxies:
3171  <list style="symbols">
3172    <t> If a proxy receives a request that includes an Expect header
3173        field with the "100-continue" expectation, and the proxy
3174        either knows that the next-hop server complies with HTTP/1.1 or
3175        higher, or does not know the HTTP version of the next-hop
3176        server, it &MUST; forward the request, including the Expect header
3177        field.
3178    </t>
3179    <t> If the proxy knows that the version of the next-hop server is
3180        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
3181        respond with a 417 (Expectation Failed) status code.
3182    </t>
3183    <t> Proxies &SHOULD; maintain a record of the HTTP version
3184        numbers received from recently-referenced next-hop servers.
3185    </t>
3186    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
3187        request message was received from an HTTP/1.0 (or earlier)
3188        client and did not include an Expect header field with
3189        the "100-continue" expectation. This requirement overrides the
3190        general rule for forwarding of 1xx responses (see &status-1xx;).
3191    </t>
3192  </list>
3196<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3198   If the client is sending data, a server implementation using TCP
3199   &SHOULD; be careful to ensure that the client acknowledges receipt of
3200   the packet(s) containing the response, before the server closes the
3201   input connection. If the client continues sending data to the server
3202   after the close, the server's TCP stack will send a reset packet to
3203   the client, which might erase the client's unacknowledged input buffers
3204   before they can be read and interpreted by the HTTP application.
3210<section title="Upgrade" anchor="header.upgrade">
3211  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3212  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3213  <x:anchor-alias value="Upgrade"/>
3214  <x:anchor-alias value="protocol"/>
3215  <x:anchor-alias value="protocol-name"/>
3216  <x:anchor-alias value="protocol-version"/>
3218   The "Upgrade" header field allows the client to specify what
3219   additional communication protocols it would like to use, if the server
3220   chooses to switch protocols. Servers can use it to indicate what protocols
3221   they are willing to switch to.
3223<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3224  <x:ref>Upgrade</x:ref>          = 1#<x:ref>protocol</x:ref>
3226  <x:ref>protocol</x:ref>         = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3227  <x:ref>protocol-name</x:ref>    = <x:ref>token</x:ref>
3228  <x:ref>protocol-version</x:ref> = <x:ref>token</x:ref>
3231   For example,
3233<figure><artwork type="example">
3234  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3237   The Upgrade header field is intended to provide a simple mechanism
3238   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3239   does so by allowing the client to advertise its desire to use another
3240   protocol, such as a later version of HTTP with a higher major version
3241   number, even though the current request has been made using HTTP/1.1.
3242   This eases the difficult transition between incompatible protocols by
3243   allowing the client to initiate a request in the more commonly
3244   supported protocol while indicating to the server that it would like
3245   to use a "better" protocol if available (where "better" is determined
3246   by the server, possibly according to the nature of the request method
3247   or target resource).
3250   The Upgrade header field only applies to switching application-layer
3251   protocols upon the existing transport-layer connection. Upgrade
3252   cannot be used to insist on a protocol change; its acceptance and use
3253   by the server is optional. The capabilities and nature of the
3254   application-layer communication after the protocol change is entirely
3255   dependent upon the new protocol chosen, although the first action
3256   after changing the protocol &MUST; be a response to the initial HTTP
3257   request containing the Upgrade header field.
3260   The Upgrade header field only applies to the immediate connection.
3261   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3262   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3263   HTTP/1.1 message.
3266   The Upgrade header field cannot be used to indicate a switch to a
3267   protocol on a different connection. For that purpose, it is more
3268   appropriate to use a 3xx redirection response (&status-3xx;).
3271   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3272   Protocols) responses to indicate which protocol(s) are being switched to,
3273   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3274   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3275   response to indicate that they are willing to upgrade to one of the
3276   specified protocols.
3279   This specification only defines the protocol name "HTTP" for use by
3280   the family of Hypertext Transfer Protocols, as defined by the HTTP
3281   version rules of <xref target="http.version"/> and future updates to this
3282   specification. Additional tokens can be registered with IANA using the
3283   registration procedure defined in <xref target="upgrade.token.registry"/>.
3289<section title="IANA Considerations" anchor="IANA.considerations">
3291<section title="Header Field Registration" anchor="header.field.registration">
3293   HTTP header fields are registered within the Message Header Field Registry
3294   <xref target="RFC3864"/> maintained by IANA at
3295   <eref target=""/>.
3298   This document defines the following HTTP header fields, so their
3299   associated registry entries shall be updated according to the permanent
3300   registrations below:
3302<?BEGININC p1-messaging.iana-headers ?>
3303<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3304<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3305   <ttcol>Header Field Name</ttcol>
3306   <ttcol>Protocol</ttcol>
3307   <ttcol>Status</ttcol>
3308   <ttcol>Reference</ttcol>
3310   <c>Connection</c>
3311   <c>http</c>
3312   <c>standard</c>
3313   <c>
3314      <xref target="header.connection"/>
3315   </c>
3316   <c>Content-Length</c>
3317   <c>http</c>
3318   <c>standard</c>
3319   <c>
3320      <xref target="header.content-length"/>
3321   </c>
3322   <c>Host</c>
3323   <c>http</c>
3324   <c>standard</c>
3325   <c>
3326      <xref target=""/>
3327   </c>
3328   <c>TE</c>
3329   <c>http</c>
3330   <c>standard</c>
3331   <c>
3332      <xref target="header.te"/>
3333   </c>
3334   <c>Trailer</c>
3335   <c>http</c>
3336   <c>standard</c>
3337   <c>
3338      <xref target="header.trailer"/>
3339   </c>
3340   <c>Transfer-Encoding</c>
3341   <c>http</c>
3342   <c>standard</c>
3343   <c>
3344      <xref target="header.transfer-encoding"/>
3345   </c>
3346   <c>Upgrade</c>
3347   <c>http</c>
3348   <c>standard</c>
3349   <c>
3350      <xref target="header.upgrade"/>
3351   </c>
3352   <c>Via</c>
3353   <c>http</c>
3354   <c>standard</c>
3355   <c>
3356      <xref target="header.via"/>
3357   </c>
3360<?ENDINC p1-messaging.iana-headers ?>
3362   Furthermore, the header field-name "Close" shall be registered as
3363   "reserved", since using that name as an HTTP header field might
3364   conflict with the "close" connection option of the "Connection"
3365   header field (<xref target="header.connection"/>).
3367<texttable align="left" suppress-title="true">
3368   <ttcol>Header Field Name</ttcol>
3369   <ttcol>Protocol</ttcol>
3370   <ttcol>Status</ttcol>
3371   <ttcol>Reference</ttcol>
3373   <c>Close</c>
3374   <c>http</c>
3375   <c>reserved</c>
3376   <c>
3377      <xref target="header.field.registration"/>
3378   </c>
3381   The change controller is: "IETF ( - Internet Engineering Task Force".
3385<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3387   IANA maintains the registry of URI Schemes <xref target="RFC4395"/> at
3388   <eref target=""/>.
3391   This document defines the following URI schemes, so their
3392   associated registry entries shall be updated according to the permanent
3393   registrations below:
3395<texttable align="left" suppress-title="true">
3396   <ttcol>URI Scheme</ttcol>
3397   <ttcol>Description</ttcol>
3398   <ttcol>Reference</ttcol>
3400   <c>http</c>
3401   <c>Hypertext Transfer Protocol</c>
3402   <c><xref target="http.uri"/></c>
3404   <c>https</c>
3405   <c>Hypertext Transfer Protocol Secure</c>
3406   <c><xref target="https.uri"/></c>
3410<section title="Internet Media Type Registrations" anchor="">
3412   This document serves as the specification for the Internet media types
3413   "message/http" and "application/http". The following is to be registered with
3414   IANA (see <xref target="RFC4288"/>).
3416<section title="Internet Media Type message/http" anchor="">
3417<iref item="Media Type" subitem="message/http" primary="true"/>
3418<iref item="message/http Media Type" primary="true"/>
3420   The message/http type can be used to enclose a single HTTP request or
3421   response message, provided that it obeys the MIME restrictions for all
3422   "message" types regarding line length and encodings.
3425  <list style="hanging" x:indent="12em">
3426    <t hangText="Type name:">
3427      message
3428    </t>
3429    <t hangText="Subtype name:">
3430      http
3431    </t>
3432    <t hangText="Required parameters:">
3433      none
3434    </t>
3435    <t hangText="Optional parameters:">
3436      version, msgtype
3437      <list style="hanging">
3438        <t hangText="version:">
3439          The HTTP-version number of the enclosed message
3440          (e.g., "1.1"). If not present, the version can be
3441          determined from the first line of the body.
3442        </t>
3443        <t hangText="msgtype:">
3444          The message type &mdash; "request" or "response". If not
3445          present, the type can be determined from the first
3446          line of the body.
3447        </t>
3448      </list>
3449    </t>
3450    <t hangText="Encoding considerations:">
3451      only "7bit", "8bit", or "binary" are permitted
3452    </t>
3453    <t hangText="Security considerations:">
3454      none
3455    </t>
3456    <t hangText="Interoperability considerations:">
3457      none
3458    </t>
3459    <t hangText="Published specification:">
3460      This specification (see <xref target=""/>).
3461    </t>
3462    <t hangText="Applications that use this media type:">
3463    </t>
3464    <t hangText="Additional information:">
3465      <list style="hanging">
3466        <t hangText="Magic number(s):">none</t>
3467        <t hangText="File extension(s):">none</t>
3468        <t hangText="Macintosh file type code(s):">none</t>
3469      </list>
3470    </t>
3471    <t hangText="Person and email address to contact for further information:">
3472      See Authors Section.
3473    </t>
3474    <t hangText="Intended usage:">
3475      COMMON
3476    </t>
3477    <t hangText="Restrictions on usage:">
3478      none
3479    </t>
3480    <t hangText="Author/Change controller:">
3481      IESG
3482    </t>
3483  </list>
3486<section title="Internet Media Type application/http" anchor="">
3487<iref item="Media Type" subitem="application/http" primary="true"/>
3488<iref item="application/http Media Type" primary="true"/>
3490   The application/http type can be used to enclose a pipeline of one or more
3491   HTTP request or response messages (not intermixed).
3494  <list style="hanging" x:indent="12em">
3495    <t hangText="Type name:">
3496      application
3497    </t>
3498    <t hangText="Subtype name:">
3499      http
3500    </t>
3501    <t hangText="Required parameters:">
3502      none
3503    </t>
3504    <t hangText="Optional parameters:">
3505      version, msgtype
3506      <list style="hanging">
3507        <t hangText="version:">
3508          The HTTP-version number of the enclosed messages
3509          (e.g., "1.1"). If not present, the version can be
3510          determined from the first line of the body.
3511        </t>
3512        <t hangText="msgtype:">
3513          The message type &mdash; "request" or "response". If not
3514          present, the type can be determined from the first
3515          line of the body.
3516        </t>
3517      </list>
3518    </t>
3519    <t hangText="Encoding considerations:">
3520      HTTP messages enclosed by this type
3521      are in "binary" format; use of an appropriate
3522      Content-Transfer-Encoding is required when
3523      transmitted via E-mail.
3524    </t>
3525    <t hangText="Security considerations:">
3526      none
3527    </t>
3528    <t hangText="Interoperability considerations:">
3529      none
3530    </t>
3531    <t hangText="Published specification:">
3532      This specification (see <xref target=""/>).
3533    </t>
3534    <t hangText="Applications that use this media type:">
3535    </t>
3536    <t hangText="Additional information:">
3537      <list style="hanging">
3538        <t hangText="Magic number(s):">none</t>
3539        <t hangText="File extension(s):">none</t>
3540        <t hangText="Macintosh file type code(s):">none</t>
3541      </list>
3542    </t>
3543    <t hangText="Person and email address to contact for further information:">
3544      See Authors Section.
3545    </t>
3546    <t hangText="Intended usage:">
3547      COMMON
3548    </t>
3549    <t hangText="Restrictions on usage:">
3550      none
3551    </t>
3552    <t hangText="Author/Change controller:">
3553      IESG
3554    </t>
3555  </list>
3560<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
3562   The HTTP Transfer Coding Registry defines the name space for transfer
3563   coding names.
3566   Registrations &MUST; include the following fields:
3567   <list style="symbols">
3568     <t>Name</t>
3569     <t>Description</t>
3570     <t>Pointer to specification text</t>
3571   </list>
3574   Names of transfer codings &MUST-NOT; overlap with names of content codings
3575   (&content-codings;) unless the encoding transformation is identical, as it
3576   is the case for the compression codings defined in
3577   <xref target="compression.codings"/>.
3580   Values to be added to this name space require IETF Review (see
3581   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
3582   conform to the purpose of transfer coding defined in this section.
3585   The registry itself is maintained at
3586   <eref target=""/>.
3590<section title="Transfer Coding Registrations" anchor="transfer.coding.registration">
3592   The HTTP Transfer Coding Registry shall be updated with the registrations
3593   below:
3595<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3596   <ttcol>Name</ttcol>
3597   <ttcol>Description</ttcol>
3598   <ttcol>Reference</ttcol>
3599   <c>chunked</c>
3600   <c>Transfer in a series of chunks</c>
3601   <c>
3602      <xref target="chunked.encoding"/>
3603   </c>
3604   <c>compress</c>
3605   <c>UNIX "compress" program method</c>
3606   <c>
3607      <xref target="compress.coding"/>
3608   </c>
3609   <c>deflate</c>
3610   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3611   the "zlib" data format (<xref target="RFC1950"/>)
3612   </c>
3613   <c>
3614      <xref target="deflate.coding"/>
3615   </c>
3616   <c>gzip</c>
3617   <c>Same as GNU zip <xref target="RFC1952"/></c>
3618   <c>
3619      <xref target="gzip.coding"/>
3620   </c>
3624<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3626   The HTTP Upgrade Token Registry defines the name space for protocol-name
3627   tokens used to identify protocols in the Upgrade header field.
3628   Each registered protocol-name is associated with contact information and
3629   an optional set of specifications that details how the connection
3630   will be processed after it has been upgraded.
3633   Registrations happen on a "First Come First Served" basis (see
3634   <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>) and are subject to the
3635   following rules:
3636  <list style="numbers">
3637    <t>A protocol-name token, once registered, stays registered forever.</t>
3638    <t>The registration &MUST; name a responsible party for the
3639       registration.</t>
3640    <t>The registration &MUST; name a point of contact.</t>
3641    <t>The registration &MAY; name a set of specifications associated with
3642       that token. Such specifications need not be publicly available.</t>
3643    <t>The registration &SHOULD; name a set of expected "protocol-version"
3644       tokens associated with that token at the time of registration.</t>
3645    <t>The responsible party &MAY; change the registration at any time.
3646       The IANA will keep a record of all such changes, and make them
3647       available upon request.</t>
3648    <t>The IESG &MAY; reassign responsibility for a protocol token.
3649       This will normally only be used in the case when a
3650       responsible party cannot be contacted.</t>
3651  </list>
3654   This registration procedure for HTTP Upgrade Tokens replaces that
3655   previously defined in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/>.
3659<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3661   The HTTP Upgrade Token Registry shall be updated with the registration
3662   below:
3664<texttable align="left" suppress-title="true">
3665   <ttcol>Value</ttcol>
3666   <ttcol>Description</ttcol>
3667   <ttcol>Expected Version Tokens</ttcol>
3668   <ttcol>Reference</ttcol>
3670   <c>HTTP</c>
3671   <c>Hypertext Transfer Protocol</c>
3672   <c>any DIGIT.DIGIT (e.g, "2.0")</c>
3673   <c><xref target="http.version"/></c>
3676   The responsible party is: "IETF ( - Internet Engineering Task Force".
3682<section title="Security Considerations" anchor="security.considerations">
3684   This section is meant to inform application developers, information
3685   providers, and users of the security limitations in HTTP/1.1 as
3686   described by this document. The discussion does not include
3687   definitive solutions to the problems revealed, though it does make
3688   some suggestions for reducing security risks.
3691<section title="Personal Information" anchor="personal.information">
3693   HTTP clients are often privy to large amounts of personal information
3694   (e.g., the user's name, location, mail address, passwords, encryption
3695   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3696   leakage of this information.
3697   We very strongly recommend that a convenient interface be provided
3698   for the user to control dissemination of such information, and that
3699   designers and implementors be particularly careful in this area.
3700   History shows that errors in this area often create serious security
3701   and/or privacy problems and generate highly adverse publicity for the
3702   implementor's company.
3706<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3708   A server is in the position to save personal data about a user's
3709   requests which might identify their reading patterns or subjects of
3710   interest.  In particular, log information gathered at an intermediary
3711   often contains a history of user agent interaction, across a multitude
3712   of sites, that can be traced to individual users.
3715   HTTP log information is confidential in nature; its handling is often
3716   constrained by laws and regulations.  Log information needs to be securely
3717   stored and appropriate guidelines followed for its analysis.
3718   Anonymization of personal information within individual entries helps,
3719   but is generally not sufficient to prevent real log traces from being
3720   re-identified based on correlation with other access characteristics.
3721   As such, access traces that are keyed to a specific client should not
3722   be published even if the key is pseudonymous.
3725   To minimize the risk of theft or accidental publication, log information
3726   should be purged of personally identifiable information, including
3727   user identifiers, IP addresses, and user-provided query parameters,
3728   as soon as that information is no longer necessary to support operational
3729   needs for security, auditing, or fraud control.
3733<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3735   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3736   the documents returned by HTTP requests to be only those that were
3737   intended by the server administrators. If an HTTP server translates
3738   HTTP URIs directly into file system calls, the server &MUST; take
3739   special care not to serve files that were not intended to be
3740   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3741   other operating systems use ".." as a path component to indicate a
3742   directory level above the current one. On such a system, an HTTP
3743   server &MUST; disallow any such construct in the request-target if it
3744   would otherwise allow access to a resource outside those intended to
3745   be accessible via the HTTP server. Similarly, files intended for
3746   reference only internally to the server (such as access control
3747   files, configuration files, and script code) &MUST; be protected from
3748   inappropriate retrieval, since they might contain sensitive
3749   information. Experience has shown that minor bugs in such HTTP server
3750   implementations have turned into security risks.
3754<section title="DNS-related Attacks" anchor="dns.related.attacks">
3756   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3757   generally prone to security attacks based on the deliberate misassociation
3758   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3759   cautious in assuming the validity of an IP number/DNS name association unless
3760   the response is protected by DNSSec (<xref target="RFC4033"/>).
3764<section title="Intermediaries and Caching" anchor="attack.intermediaries">
3766   By their very nature, HTTP intermediaries are men-in-the-middle, and
3767   represent an opportunity for man-in-the-middle attacks. Compromise of
3768   the systems on which the intermediaries run can result in serious security
3769   and privacy problems. Intermediaries have access to security-related
3770   information, personal information about individual users and
3771   organizations, and proprietary information belonging to users and
3772   content providers. A compromised intermediary, or an intermediary
3773   implemented or configured without regard to security and privacy
3774   considerations, might be used in the commission of a wide range of
3775   potential attacks.
3778   Intermediaries that contain a shared cache are especially vulnerable
3779   to cache poisoning attacks.
3782   Implementors need to consider the privacy and security
3783   implications of their design and coding decisions, and of the
3784   configuration options they provide to operators (especially the
3785   default configuration).
3788   Users need to be aware that intermediaries are no more trustworthy than
3789   the people who run them; HTTP itself cannot solve this problem.
3792   The judicious use of cryptography, when appropriate, might suffice to
3793   protect against a broad range of security and privacy attacks. Such
3794   cryptography is beyond the scope of the HTTP/1.1 specification.
3798<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3800   Because HTTP uses mostly textual, character-delimited fields, attackers can
3801   overflow buffers in implementations, and/or perform a Denial of Service
3802   against implementations that accept fields with unlimited lengths.
3805   To promote interoperability, this specification makes specific
3806   recommendations for minimum size limits on request-line
3807   (<xref target="request.line"/>)
3808   and blocks of header fields (<xref target="header.fields"/>). These are
3809   minimum recommendations, chosen to be supportable even by implementations
3810   with limited resources; it is expected that most implementations will
3811   choose substantially higher limits.
3814   This specification also provides a way for servers to reject messages that
3815   have request-targets that are too long (&status-414;) or request entities
3816   that are too large (&status-4xx;).
3819   Other fields (including but not limited to request methods, response status
3820   phrases, header field-names, and body chunks) &SHOULD; be limited by
3821   implementations carefully, so as to not impede interoperability.
3826<section title="Acknowledgments" anchor="acks">
3828   This edition of HTTP builds on the many contributions that went into
3829   <xref target="RFC1945" format="none">RFC 1945</xref>,
3830   <xref target="RFC2068" format="none">RFC 2068</xref>,
3831   <xref target="RFC2145" format="none">RFC 2145</xref>, and
3832   <xref target="RFC2616" format="none">RFC 2616</xref>, including
3833   substantial contributions made by the previous authors, editors, and
3834   working group chairs: Tim Berners-Lee, Ari Luotonen, Roy T. Fielding,
3835   Henrik Frystyk Nielsen, Jim Gettys, Jeffrey C. Mogul, Larry Masinter,
3836   Paul J. Leach, and Mark Nottingham.
3837   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for additional
3838   acknowledgements from prior revisions.
3841   Since 1999, the following contributors have helped improve the HTTP
3842   specification by reporting bugs, asking smart questions, drafting or
3843   reviewing text, and evaluating open issues:
3845<?BEGININC acks ?>
3846<t>Adam Barth,
3847Adam Roach,
3848Addison Phillips,
3849Adrian Chadd,
3850Adrien W. de Croy,
3851Alan Ford,
3852Alan Ruttenberg,
3853Albert Lunde,
3854Alek Storm,
3855Alex Rousskov,
3856Alexandre Morgaut,
3857Alexey Melnikov,
3858Alisha Smith,
3859Amichai Rothman,
3860Amit Klein,
3861Amos Jeffries,
3862Andreas Maier,
3863Andreas Petersson,
3864Anne van Kesteren,
3865Anthony Bryan,
3866Asbjorn Ulsberg,
3867Balachander Krishnamurthy,
3868Barry Leiba,
3869Ben Laurie,
3870Benjamin Niven-Jenkins,
3871Bil Corry,
3872Bill Burke,
3873Bjoern Hoehrmann,
3874Bob Scheifler,
3875Boris Zbarsky,
3876Brett Slatkin,
3877Brian Kell,
3878Brian McBarron,
3879Brian Pane,
3880Brian Smith,
3881Bryce Nesbitt,
3882Cameron Heavon-Jones,
3883Carl Kugler,
3884Carsten Bormann,
3885Charles Fry,
3886Chris Newman,
3887Cyrus Daboo,
3888Dale Robert Anderson,
3889Dan Winship,
3890Daniel Stenberg,
3891Dave Cridland,
3892Dave Crocker,
3893Dave Kristol,
3894David Booth,
3895David Singer,
3896David W. Morris,
3897Diwakar Shetty,
3898Dmitry Kurochkin,
3899Drummond Reed,
3900Duane Wessels,
3901Edward Lee,
3902Eliot Lear,
3903Eran Hammer-Lahav,
3904Eric D. Williams,
3905Eric J. Bowman,
3906Eric Lawrence,
3907Eric Rescorla,
3908Erik Aronesty,
3909Florian Weimer,
3910Frank Ellermann,
3911Fred Bohle,
3912Geoffrey Sneddon,
3913Gervase Markham,
3914Greg Wilkins,
3915Harald Tveit Alvestrand,
3916Harry Halpin,
3917Helge Hess,
3918Henrik Nordstrom,
3919Henry S. Thompson,
3920Henry Story,
3921Herbert van de Sompel,
3922Howard Melman,
3923Hugo Haas,
3924Ian Hickson,
3925Ingo Struck,
3926J. Ross Nicoll,
3927James H. Manger,
3928James Lacey,
3929James M. Snell,
3930Jamie Lokier,
3931Jan Algermissen,
3932Jeff Hodges (for coming up with the term 'effective Request-URI'),
3933Jeff Walden,
3934Jim Luther,
3935Joe D. Williams,
3936Joe Gregorio,
3937Joe Orton,
3938John C. Klensin,
3939John C. Mallery,
3940John Cowan,
3941John Kemp,
3942John Panzer,
3943John Schneider,
3944John Stracke,
3945John Sullivan,
3946Jonas Sicking,
3947Jonathan Billington,
3948Jonathan Moore,
3949Jonathan Rees,
3950Jordi Ros,
3951Joris Dobbelsteen,
3952Josh Cohen,
3953Julien Pierre,
3954Jungshik Shin,
3955Justin Chapweske,
3956Justin Erenkrantz,
3957Justin James,
3958Kalvinder Singh,
3959Karl Dubost,
3960Keith Hoffman,
3961Keith Moore,
3962Koen Holtman,
3963Konstantin Voronkov,
3964Kris Zyp,
3965Lisa Dusseault,
3966Maciej Stachowiak,
3967Marc Schneider,
3968Marc Slemko,
3969Mark Baker,
3970Mark Pauley,
3971Mark Watson,
3972Markus Isomaki,
3973Markus Lanthaler,
3974Martin J. Duerst,
3975Martin Musatov,
3976Martin Nilsson,
3977Martin Thomson,
3978Matt Lynch,
3979Matthew Cox,
3980Max Clark,
3981Michael Burrows,
3982Michael Hausenblas,
3983Mike Amundsen,
3984Mike Belshe,
3985Mike Kelly,
3986Mike Schinkel,
3987Miles Sabin,
3988Murray S. Kucherawy,
3989Mykyta Yevstifeyev,
3990Nathan Rixham,
3991Nicholas Shanks,
3992Nico Williams,
3993Nicolas Alvarez,
3994Nicolas Mailhot,
3995Noah Slater,
3996Pablo Castro,
3997Pat Hayes,
3998Patrick R. McManus,
3999Paul E. Jones,
4000Paul Hoffman,
4001Paul Marquess,
4002Peter Lepeska,
4003Peter Saint-Andre,
4004Peter Watkins,
4005Phil Archer,
4006Phillip Hallam-Baker,
4007Poul-Henning Kamp,
4008Preethi Natarajan,
4009Ray Polk,
4010Reto Bachmann-Gmuer,
4011Richard Cyganiak,
4012Robert Brewer,
4013Robert Collins,
4014Robert O'Callahan,
4015Robert Olofsson,
4016Robert Sayre,
4017Robert Siemer,
4018Robert de Wilde,
4019Roberto Javier Godoy,
4020Roberto Peon,
4021Ronny Widjaja,
4022S. Mike Dierken,
4023Salvatore Loreto,
4024Sam Johnston,
4025Sam Ruby,
4026Scott Lawrence (for maintaining the original issues list),
4027Sean B. Palmer,
4028Shane McCarron,
4029Stefan Eissing,
4030Stefan Tilkov,
4031Stefanos Harhalakis,
4032Stephane Bortzmeyer,
4033Stephen Farrell,
4034Stuart Williams,
4035Subbu Allamaraju,
4036Sylvain Hellegouarch,
4037Tapan Divekar,
4038Ted Hardie,
4039Thomas Broyer,
4040Thomas Nordin,
4041Thomas Roessler,
4042Tim Bray,
4043Tim Morgan,
4044Tim Olsen,
4045Tom Zhou,
4046Travis Snoozy,
4047Tyler Close,
4048Vincent Murphy,
4049Wenbo Zhu,
4050Werner Baumann,
4051Wilbur Streett,
4052Wilfredo Sanchez Vega,
4053William A. Rowe Jr.,
4054William Chan,
4055Willy Tarreau,
4056Xiaoshu Wang,
4057Yaron Goland,
4058Yngve Nysaeter Pettersen,
4059Yoav Nir,
4060Yogesh Bang,
4061Yutaka Oiwa,
4062Zed A. Shaw, and
4063Zhong Yu.
4065<?ENDINC acks ?>
4071<references title="Normative References">
4073<reference anchor="ISO-8859-1">
4074  <front>
4075    <title>
4076     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4077    </title>
4078    <author>
4079      <organization>International Organization for Standardization</organization>
4080    </author>
4081    <date year="1998"/>
4082  </front>
4083  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4086<reference anchor="Part2">
4087  <front>
4088    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4089    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4090      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4091      <address><email></email></address>
4092    </author>
4093    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4094      <organization abbrev="W3C">World Wide Web Consortium</organization>
4095      <address><email></email></address>
4096    </author>
4097    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4098      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4099      <address><email></email></address>
4100    </author>
4101    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4102  </front>
4103  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4104  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4107<reference anchor="Part6">
4108  <front>
4109    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4110    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4111      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4112      <address><email></email></address>
4113    </author>
4114    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4115      <organization abbrev="W3C">World Wide Web Consortium</organization>
4116      <address><email></email></address>
4117    </author>
4118    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4119      <organization>Rackspace</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-p6-cache-&ID-VERSION;"/>
4129  <x:source href="p6-cache.xml" basename="p6-cache"/>
4132<reference anchor="RFC5234">
4133  <front>
4134    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4135    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4136      <organization>Brandenburg InternetWorking</organization>
4137      <address>
4138        <email></email>
4139      </address> 
4140    </author>
4141    <author initials="P." surname="Overell" fullname="Paul Overell">
4142      <organization>THUS plc.</organization>
4143      <address>
4144        <email></email>
4145      </address>
4146    </author>
4147    <date month="January" year="2008"/>
4148  </front>
4149  <seriesInfo name="STD" value="68"/>
4150  <seriesInfo name="RFC" value="5234"/>
4153<reference anchor="RFC2119">
4154  <front>
4155    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4156    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4157      <organization>Harvard University</organization>
4158      <address><email></email></address>
4159    </author>
4160    <date month="March" year="1997"/>
4161  </front>
4162  <seriesInfo name="BCP" value="14"/>
4163  <seriesInfo name="RFC" value="2119"/>
4166<reference anchor="RFC3986">
4167 <front>
4168  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4169  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4170    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4171    <address>
4172       <email></email>
4173       <uri></uri>
4174    </address>
4175  </author>
4176  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4177    <organization abbrev="Day Software">Day Software</organization>
4178    <address>
4179      <email></email>
4180      <uri></uri>
4181    </address>
4182  </author>
4183  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4184    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4185    <address>
4186      <email></email>
4187      <uri></uri>
4188    </address>
4189  </author>
4190  <date month='January' year='2005'></date>
4191 </front>
4192 <seriesInfo name="STD" value="66"/>
4193 <seriesInfo name="RFC" value="3986"/>
4196<reference anchor="USASCII">
4197  <front>
4198    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4199    <author>
4200      <organization>American National Standards Institute</organization>
4201    </author>
4202    <date year="1986"/>
4203  </front>
4204  <seriesInfo name="ANSI" value="X3.4"/>
4207<reference anchor="RFC1950">
4208  <front>
4209    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4210    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4211      <organization>Aladdin Enterprises</organization>
4212      <address><email></email></address>
4213    </author>
4214    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4215    <date month="May" year="1996"/>
4216  </front>
4217  <seriesInfo name="RFC" value="1950"/>
4218  <!--<annotation>
4219    RFC 1950 is an Informational RFC, thus it might be less stable than
4220    this specification. On the other hand, this downward reference was
4221    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4222    therefore it is unlikely to cause problems in practice. See also
4223    <xref target="BCP97"/>.
4224  </annotation>-->
4227<reference anchor="RFC1951">
4228  <front>
4229    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4230    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4231      <organization>Aladdin Enterprises</organization>
4232      <address><email></email></address>
4233    </author>
4234    <date month="May" year="1996"/>
4235  </front>
4236  <seriesInfo name="RFC" value="1951"/>
4237  <!--<annotation>
4238    RFC 1951 is an Informational RFC, thus it might be less stable than
4239    this specification. On the other hand, this downward reference was
4240    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4241    therefore it is unlikely to cause problems in practice. See also
4242    <xref target="BCP97"/>.
4243  </annotation>-->
4246<reference anchor="RFC1952">
4247  <front>
4248    <title>GZIP file format specification version 4.3</title>
4249    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4250      <organization>Aladdin Enterprises</organization>
4251      <address><email></email></address>
4252    </author>
4253    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4254      <address><email></email></address>
4255    </author>
4256    <author initials="M." surname="Adler" fullname="Mark Adler">
4257      <address><email></email></address>
4258    </author>
4259    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4260      <address><email></email></address>
4261    </author>
4262    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4263      <address><email></email></address>
4264    </author>
4265    <date month="May" year="1996"/>
4266  </front>
4267  <seriesInfo name="RFC" value="1952"/>
4268  <!--<annotation>
4269    RFC 1952 is an Informational RFC, thus it might be less stable than
4270    this specification. On the other hand, this downward reference was
4271    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4272    therefore it is unlikely to cause problems in practice. See also
4273    <xref target="BCP97"/>.
4274  </annotation>-->
4279<references title="Informative References">
4281<reference anchor="Nie1997" target="">
4282  <front>
4283    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4284    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4285    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4286    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4287    <author initials="H." surname="Lie" fullname="H. Lie"/>
4288    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4289    <date year="1997" month="September"/>
4290  </front>
4291  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4294<reference anchor="Pad1995" target="">
4295  <front>
4296    <title>Improving HTTP Latency</title>
4297    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4298    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4299    <date year="1995" month="December"/>
4300  </front>
4301  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4304<reference anchor='RFC1919'>
4305  <front>
4306    <title>Classical versus Transparent IP Proxies</title>
4307    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4308      <address><email></email></address>
4309    </author>
4310    <date year='1996' month='March' />
4311  </front>
4312  <seriesInfo name='RFC' value='1919' />
4315<reference anchor="RFC1945">
4316  <front>
4317    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4318    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4319      <organization>MIT, Laboratory for Computer Science</organization>
4320      <address><email></email></address>
4321    </author>
4322    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4323      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4324      <address><email></email></address>
4325    </author>
4326    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4327      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4328      <address><email></email></address>
4329    </author>
4330    <date month="May" year="1996"/>
4331  </front>
4332  <seriesInfo name="RFC" value="1945"/>
4335<reference anchor="RFC2045">
4336  <front>
4337    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4338    <author initials="N." surname="Freed" fullname="Ned Freed">
4339      <organization>Innosoft International, Inc.</organization>
4340      <address><email></email></address>
4341    </author>
4342    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4343      <organization>First Virtual Holdings</organization>
4344      <address><email></email></address>
4345    </author>
4346    <date month="November" year="1996"/>
4347  </front>
4348  <seriesInfo name="RFC" value="2045"/>
4351<reference anchor="RFC2047">
4352  <front>
4353    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4354    <author initials="K." surname="Moore" fullname="Keith Moore">
4355      <organization>University of Tennessee</organization>
4356      <address><email></email></address>
4357    </author>
4358    <date month="November" year="1996"/>
4359  </front>
4360  <seriesInfo name="RFC" value="2047"/>
4363<reference anchor="RFC2068">
4364  <front>
4365    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4366    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4367      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4368      <address><email></email></address>
4369    </author>
4370    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4371      <organization>MIT Laboratory for Computer Science</organization>
4372      <address><email></email></address>
4373    </author>
4374    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4375      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4376      <address><email></email></address>
4377    </author>
4378    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4379      <organization>MIT Laboratory for Computer Science</organization>
4380      <address><email></email></address>
4381    </author>
4382    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4383      <organization>MIT Laboratory for Computer Science</organization>
4384      <address><email></email></address>
4385    </author>
4386    <date month="January" year="1997"/>
4387  </front>
4388  <seriesInfo name="RFC" value="2068"/>
4391<reference anchor="RFC2145">
4392  <front>
4393    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4394    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4395      <organization>Western Research Laboratory</organization>
4396      <address><email></email></address>
4397    </author>
4398    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4399      <organization>Department of Information and Computer Science</organization>
4400      <address><email></email></address>
4401    </author>
4402    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4403      <organization>MIT Laboratory for Computer Science</organization>
4404      <address><email></email></address>
4405    </author>
4406    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4407      <organization>W3 Consortium</organization>
4408      <address><email></email></address>
4409    </author>
4410    <date month="May" year="1997"/>
4411  </front>
4412  <seriesInfo name="RFC" value="2145"/>
4415<reference anchor="RFC2616">
4416  <front>
4417    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4418    <author initials="R." surname="Fielding" fullname="R. Fielding">
4419      <organization>University of California, Irvine</organization>
4420      <address><email></email></address>
4421    </author>
4422    <author initials="J." surname="Gettys" fullname="J. Gettys">
4423      <organization>W3C</organization>
4424      <address><email></email></address>
4425    </author>
4426    <author initials="J." surname="Mogul" fullname="J. Mogul">
4427      <organization>Compaq Computer Corporation</organization>
4428      <address><email></email></address>
4429    </author>
4430    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4431      <organization>MIT Laboratory for Computer Science</organization>
4432      <address><email></email></address>
4433    </author>
4434    <author initials="L." surname="Masinter" fullname="L. Masinter">
4435      <organization>Xerox Corporation</organization>
4436      <address><email></email></address>
4437    </author>
4438    <author initials="P." surname="Leach" fullname="P. Leach">
4439      <organization>Microsoft Corporation</organization>
4440      <address><email></email></address>
4441    </author>
4442    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4443      <organization>W3C</organization>
4444      <address><email></email></address>
4445    </author>
4446    <date month="June" year="1999"/>
4447  </front>
4448  <seriesInfo name="RFC" value="2616"/>
4451<reference anchor='RFC2817'>
4452  <front>
4453    <title>Upgrading to TLS Within HTTP/1.1</title>
4454    <author initials='R.' surname='Khare' fullname='R. Khare'>
4455      <organization>4K Associates / UC Irvine</organization>
4456      <address><email></email></address>
4457    </author>
4458    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4459      <organization>Agranat Systems, Inc.</organization>
4460      <address><email></email></address>
4461    </author>
4462    <date year='2000' month='May' />
4463  </front>
4464  <seriesInfo name='RFC' value='2817' />
4467<reference anchor='RFC2818'>
4468  <front>
4469    <title>HTTP Over TLS</title>
4470    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4471      <organization>RTFM, Inc.</organization>
4472      <address><email></email></address>
4473    </author>
4474    <date year='2000' month='May' />
4475  </front>
4476  <seriesInfo name='RFC' value='2818' />
4479<reference anchor='RFC2965'>
4480  <front>
4481    <title>HTTP State Management Mechanism</title>
4482    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4483      <organization>Bell Laboratories, Lucent Technologies</organization>
4484      <address><email></email></address>
4485    </author>
4486    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4487      <organization>, Inc.</organization>
4488      <address><email></email></address>
4489    </author>
4490    <date year='2000' month='October' />
4491  </front>
4492  <seriesInfo name='RFC' value='2965' />
4495<reference anchor='RFC3040'>
4496  <front>
4497    <title>Internet Web Replication and Caching Taxonomy</title>
4498    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4499      <organization>Equinix, Inc.</organization>
4500    </author>
4501    <author initials='I.' surname='Melve' fullname='I. Melve'>
4502      <organization>UNINETT</organization>
4503    </author>
4504    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4505      <organization>CacheFlow Inc.</organization>
4506    </author>
4507    <date year='2001' month='January' />
4508  </front>
4509  <seriesInfo name='RFC' value='3040' />
4512<reference anchor='RFC3864'>
4513  <front>
4514    <title>Registration Procedures for Message Header Fields</title>
4515    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4516      <organization>Nine by Nine</organization>
4517      <address><email></email></address>
4518    </author>
4519    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4520      <organization>BEA Systems</organization>
4521      <address><email></email></address>
4522    </author>
4523    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4524      <organization>HP Labs</organization>
4525      <address><email></email></address>
4526    </author>
4527    <date year='2004' month='September' />
4528  </front>
4529  <seriesInfo name='BCP' value='90' />
4530  <seriesInfo name='RFC' value='3864' />
4533<reference anchor='RFC4033'>
4534  <front>
4535    <title>DNS Security Introduction and Requirements</title>
4536    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4537    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4538    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4539    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4540    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4541    <date year='2005' month='March' />
4542  </front>
4543  <seriesInfo name='RFC' value='4033' />
4546<reference anchor="RFC4288">
4547  <front>
4548    <title>Media Type Specifications and Registration Procedures</title>
4549    <author initials="N." surname="Freed" fullname="N. Freed">
4550      <organization>Sun Microsystems</organization>
4551      <address>
4552        <email></email>
4553      </address>
4554    </author>
4555    <author initials="J." surname="Klensin" fullname="J. Klensin">
4556      <address>
4557        <email></email>
4558      </address>
4559    </author>
4560    <date year="2005" month="December"/>
4561  </front>
4562  <seriesInfo name="BCP" value="13"/>
4563  <seriesInfo name="RFC" value="4288"/>
4566<reference anchor='RFC4395'>
4567  <front>
4568    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4569    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4570      <organization>AT&amp;T Laboratories</organization>
4571      <address>
4572        <email></email>
4573      </address>
4574    </author>
4575    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4576      <organization>Qualcomm, Inc.</organization>
4577      <address>
4578        <email></email>
4579      </address>
4580    </author>
4581    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4582      <organization>Adobe Systems</organization>
4583      <address>
4584        <email></email>
4585      </address>
4586    </author>
4587    <date year='2006' month='February' />
4588  </front>
4589  <seriesInfo name='BCP' value='115' />
4590  <seriesInfo name='RFC' value='4395' />
4593<reference anchor='RFC4559'>
4594  <front>
4595    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4596    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4597    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4598    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4599    <date year='2006' month='June' />
4600  </front>
4601  <seriesInfo name='RFC' value='4559' />
4604<reference anchor='RFC5226'>
4605  <front>
4606    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4607    <author initials='T.' surname='Narten' fullname='T. Narten'>
4608      <organization>IBM</organization>
4609      <address><email></email></address>
4610    </author>
4611    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4612      <organization>Google</organization>
4613      <address><email></email></address>
4614    </author>
4615    <date year='2008' month='May' />
4616  </front>
4617  <seriesInfo name='BCP' value='26' />
4618  <seriesInfo name='RFC' value='5226' />
4621<reference anchor="RFC5322">
4622  <front>
4623    <title>Internet Message Format</title>
4624    <author initials="P." surname="Resnick" fullname="P. Resnick">
4625      <organization>Qualcomm Incorporated</organization>
4626    </author>
4627    <date year="2008" month="October"/>
4628  </front>
4629  <seriesInfo name="RFC" value="5322"/>
4632<reference anchor="RFC6265">
4633  <front>
4634    <title>HTTP State Management Mechanism</title>
4635    <author initials="A." surname="Barth" fullname="Adam Barth">
4636      <organization abbrev="U.C. Berkeley">
4637        University of California, Berkeley
4638      </organization>
4639      <address><email></email></address>
4640    </author>
4641    <date year="2011" month="April" />
4642  </front>
4643  <seriesInfo name="RFC" value="6265"/>
4646<!--<reference anchor='BCP97'>
4647  <front>
4648    <title>Handling Normative References to Standards-Track Documents</title>
4649    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4650      <address>
4651        <email></email>
4652      </address>
4653    </author>
4654    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4655      <organization>MIT</organization>
4656      <address>
4657        <email></email>
4658      </address>
4659    </author>
4660    <date year='2007' month='June' />
4661  </front>
4662  <seriesInfo name='BCP' value='97' />
4663  <seriesInfo name='RFC' value='4897' />
4666<reference anchor="Kri2001" target="">
4667  <front>
4668    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4669    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4670    <date year="2001" month="November"/>
4671  </front>
4672  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4675<reference anchor="Spe" target="">
4676  <front>
4677    <title>Analysis of HTTP Performance Problems</title>
4678    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4679    <date/>
4680  </front>
4683<reference anchor="Tou1998" target="">
4684  <front>
4685  <title>Analysis of HTTP Performance</title>
4686  <author initials="J." surname="Touch" fullname="Joe Touch">
4687    <organization>USC/Information Sciences Institute</organization>
4688    <address><email></email></address>
4689  </author>
4690  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4691    <organization>USC/Information Sciences Institute</organization>
4692    <address><email></email></address>
4693  </author>
4694  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4695    <organization>USC/Information Sciences Institute</organization>
4696    <address><email></email></address>
4697  </author>
4698  <date year="1998" month="Aug"/>
4699  </front>
4700  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4701  <annotation>(original report dated Aug. 1996)</annotation>
4707<section title="HTTP Version History" anchor="compatibility">
4709   HTTP has been in use by the World-Wide Web global information initiative
4710   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4711   was a simple protocol for hypertext data transfer across the Internet
4712   with only a single request method (GET) and no metadata.
4713   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4714   methods and MIME-like messaging that could include metadata about the data
4715   transferred and modifiers on the request/response semantics. However,
4716   HTTP/1.0 did not sufficiently take into consideration the effects of
4717   hierarchical proxies, caching, the need for persistent connections, or
4718   name-based virtual hosts. The proliferation of incompletely-implemented
4719   applications calling themselves "HTTP/1.0" further necessitated a
4720   protocol version change in order for two communicating applications
4721   to determine each other's true capabilities.
4724   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4725   requirements that enable reliable implementations, adding only
4726   those new features that will either be safely ignored by an HTTP/1.0
4727   recipient or only sent when communicating with a party advertising
4728   conformance with HTTP/1.1.
4731   It is beyond the scope of a protocol specification to mandate
4732   conformance with previous versions. HTTP/1.1 was deliberately
4733   designed, however, to make supporting previous versions easy.
4734   We would expect a general-purpose HTTP/1.1 server to understand
4735   any valid request in the format of HTTP/1.0 and respond appropriately
4736   with an HTTP/1.1 message that only uses features understood (or
4737   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4738   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4741   Since HTTP/0.9 did not support header fields in a request,
4742   there is no mechanism for it to support name-based virtual
4743   hosts (selection of resource by inspection of the Host header
4744   field).  Any server that implements name-based virtual hosts
4745   ought to disable support for HTTP/0.9.  Most requests that
4746   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4747   requests wherein a buggy client failed to properly encode
4748   linear whitespace found in a URI reference and placed in
4749   the request-target.
4752<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4754   This section summarizes major differences between versions HTTP/1.0
4755   and HTTP/1.1.
4758<section title="Multi-homed Web Servers" anchor="">
4760   The requirements that clients and servers support the Host header
4761   field (<xref target=""/>), report an error if it is
4762   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4763   are among the most important changes defined by HTTP/1.1.
4766   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4767   addresses and servers; there was no other established mechanism for
4768   distinguishing the intended server of a request than the IP address
4769   to which that request was directed. The Host header field was
4770   introduced during the development of HTTP/1.1 and, though it was
4771   quickly implemented by most HTTP/1.0 browsers, additional requirements
4772   were placed on all HTTP/1.1 requests in order to ensure complete
4773   adoption.  At the time of this writing, most HTTP-based services
4774   are dependent upon the Host header field for targeting requests.
4778<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4780   In HTTP/1.0, each connection is established by the client prior to the
4781   request and closed by the server after sending the response. However, some
4782   implementations implement the explicitly negotiated ("Keep-Alive") version
4783   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4784   target="RFC2068"/>.
4787   Some clients and servers might wish to be compatible with these previous
4788   approaches to persistent connections, by explicitly negotiating for them
4789   with a "Connection: keep-alive" request header field. However, some
4790   experimental implementations of HTTP/1.0 persistent connections are faulty;
4791   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4792   will erroneously forward that header to the next inbound server, which
4793   would result in a hung connection.
4796   One attempted solution was the introduction of a Proxy-Connection header,
4797   targeted specifically at proxies. In practice, this was also unworkable,
4798   because proxies are often deployed in multiple layers, bringing about the
4799   same problem discussed above.
4802   As a result, clients are encouraged not to send the Proxy-Connection header
4803   in any requests.
4806   Clients are also encouraged to consider the use of Connection: keep-alive
4807   in requests carefully; while they can enable persistent connections with
4808   HTTP/1.0 servers, clients using them need will need to monitor the
4809   connection for "hung" requests (which indicate that the client ought stop
4810   sending the header), and this mechanism ought not be used by clients at all
4811   when a proxy is being used.
4816<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4818  Clarify that the string "HTTP" in the HTTP-version ABFN production is case
4819  sensitive. Restrict the version numbers to be single digits due to the fact
4820  that implementations are known to handle multi-digit version numbers
4821  incorrectly.
4822  (<xref target="http.version"/>)
4825  Update use of abs_path production from RFC 1808 to the path-absolute + query
4826  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4827  request method only.
4828  (<xref target="request-target"/>)
4831  Require that invalid whitespace around field-names be rejected.
4832  (<xref target="header.fields"/>)
4835  Rules about implicit linear whitespace between certain grammar productions
4836  have been removed; now whitespace is only allowed where specifically
4837  defined in the ABNF.
4838  (<xref target="whitespace"/>)
4841  The NUL octet is no longer allowed in comment and quoted-string
4842  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4843  Non-ASCII content in header fields and reason phrase has been obsoleted and
4844  made opaque (the TEXT rule was removed).
4845  (<xref target="field.components"/>)
4848  Empty list elements in list productions have been deprecated.
4849  (<xref target="abnf.extension"/>)
4852  Require recipients to handle bogus Content-Length header fields as errors.
4853  (<xref target="message.body"/>)
4856  Remove reference to non-existent identity transfer-coding value tokens.
4857  (Sections <xref format="counter" target="message.body"/> and
4858  <xref format="counter" target="transfer.codings"/>)
4861  Clarification that the chunk length does not include the count of the octets
4862  in the chunk header and trailer. Furthermore disallowed line folding
4863  in chunk extensions, and deprecate their use.
4864  (<xref target="chunked.encoding"/>)
4867  Registration of Transfer Codings now requires IETF Review
4868  (<xref target="transfer.coding.registry"/>)
4871  Remove hard limit of two connections per server.
4872  Remove requirement to retry a sequence of requests as long it was idempotent.
4873  Remove requirements about when servers are allowed to close connections
4874  prematurely.
4875  (<xref target="persistent.practical"/>)
4878  Remove requirement to retry requests under certain cirumstances when the
4879  server prematurely closes the connection.
4880  (<xref target="message.transmission.requirements"/>)
4883  Change ABNF productions for header fields to only define the field value.
4886  Clarify exactly when close connection options have to be sent.
4887  (<xref target="header.connection"/>)
4890  Define the semantics of the "Upgrade" header field in responses other than
4891  101 (this was incorporated from <xref target="RFC2817"/>).
4892  (<xref target="header.upgrade"/>)
4897<?BEGININC p1-messaging.abnf-appendix ?>
4898<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4900<artwork type="abnf" name="p1-messaging.parsed-abnf">
4901<x:ref>BWS</x:ref> = OWS
4903<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4904 connection-token ] )
4905<x:ref>Content-Length</x:ref> = 1*DIGIT
4907<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4908 ]
4909<x:ref>HTTP-name</x:ref> = %x48.54.54.50 ; HTTP
4910<x:ref>HTTP-version</x:ref> = HTTP-name "/" DIGIT "." DIGIT
4911<x:ref>Host</x:ref> = uri-host [ ":" port ]
4913<x:ref>OWS</x:ref> = *( SP / HTAB )
4915<x:ref>RWS</x:ref> = 1*( SP / HTAB )
4917<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4918<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4919<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4920 transfer-coding ] )
4922<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4923<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
4925<x:ref>Via</x:ref> = *( "," OWS ) ( received-protocol RWS received-by [ RWS comment
4926 ] ) *( OWS "," [ OWS ( received-protocol RWS received-by [ RWS
4927 comment ] ) ] )
4929<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4930<x:ref>absolute-form</x:ref> = absolute-URI
4931<x:ref>asterisk-form</x:ref> = "*"
4932<x:ref>attribute</x:ref> = token
4933<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4934<x:ref>authority-form</x:ref> = authority
4936<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4937<x:ref>chunk-data</x:ref> = 1*OCTET
4938<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4939<x:ref>chunk-ext-name</x:ref> = token
4940<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4941<x:ref>chunk-size</x:ref> = 1*HEXDIG
4942<x:ref>chunked-body</x:ref> = *chunk last-chunk trailer-part CRLF
4943<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4944<x:ref>connection-token</x:ref> = token
4945<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4946 / %x2A-5B ; '*'-'['
4947 / %x5D-7E ; ']'-'~'
4948 / obs-text
4950<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4951<x:ref>field-name</x:ref> = token
4952<x:ref>field-value</x:ref> = *( field-content / obs-fold )
4954<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
4955<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4956<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4958<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
4960<x:ref>message-body</x:ref> = *OCTET
4961<x:ref>method</x:ref> = token
4963<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
4964<x:ref>obs-text</x:ref> = %x80-FF
4965<x:ref>origin-form</x:ref> = path-absolute [ "?" query ]
4967<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4968<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4969<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4970<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4971<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
4972<x:ref>protocol-name</x:ref> = token
4973<x:ref>protocol-version</x:ref> = token
4974<x:ref>pseudonym</x:ref> = token
4976<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4977 / %x5D-7E ; ']'-'~'
4978 / obs-text
4979<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
4980 / %x5D-7E ; ']'-'~'
4981 / obs-text
4982<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4983<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4984<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
4985<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4986<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4987<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4989<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
4990<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4991<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4992<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4993<x:ref>request-line</x:ref> = method SP request-target SP HTTP-version CRLF
4994<x:ref>request-target</x:ref> = origin-form / absolute-form / authority-form /
4995 asterisk-form
4997<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
4998 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
4999<x:ref>start-line</x:ref> = request-line / status-line
5000<x:ref>status-code</x:ref> = 3DIGIT
5001<x:ref>status-line</x:ref> = HTTP-version SP status-code SP reason-phrase CRLF
5003<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5004<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5005 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5006<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5007<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5008<x:ref>token</x:ref> = 1*tchar
5009<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5010<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5011 transfer-extension
5012<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5013<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5015<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5017<x:ref>value</x:ref> = word
5019<x:ref>word</x:ref> = token / quoted-string
5022<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5023; Connection defined but not used
5024; Content-Length defined but not used
5025; HTTP-message defined but not used
5026; Host defined but not used
5027; TE defined but not used
5028; Trailer defined but not used
5029; Transfer-Encoding defined but not used
5030; URI-reference defined but not used
5031; Upgrade defined but not used
5032; Via defined but not used
5033; chunked-body defined but not used
5034; http-URI defined but not used
5035; https-URI defined but not used
5036; partial-URI defined but not used
5037; special defined but not used
5039<?ENDINC p1-messaging.abnf-appendix ?>
5041<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5043<section title="Since RFC 2616">
5045  Extracted relevant partitions from <xref target="RFC2616"/>.
5049<section title="Since draft-ietf-httpbis-p1-messaging-00">
5051  Closed issues:
5052  <list style="symbols">
5053    <t>
5054      <eref target=""/>:
5055      "HTTP Version should be case sensitive"
5056      (<eref target=""/>)
5057    </t>
5058    <t>
5059      <eref target=""/>:
5060      "'unsafe' characters"
5061      (<eref target=""/>)
5062    </t>
5063    <t>
5064      <eref target=""/>:
5065      "Chunk Size Definition"
5066      (<eref target=""/>)
5067    </t>
5068    <t>
5069      <eref target=""/>:
5070      "Message Length"
5071      (<eref target=""/>)
5072    </t>
5073    <t>
5074      <eref target=""/>:
5075      "Media Type Registrations"
5076      (<eref target=""/>)
5077    </t>
5078    <t>
5079      <eref target=""/>:
5080      "URI includes query"
5081      (<eref target=""/>)
5082    </t>
5083    <t>
5084      <eref target=""/>:
5085      "No close on 1xx responses"
5086      (<eref target=""/>)
5087    </t>
5088    <t>
5089      <eref target=""/>:
5090      "Remove 'identity' token references"
5091      (<eref target=""/>)
5092    </t>
5093    <t>
5094      <eref target=""/>:
5095      "Import query BNF"
5096    </t>
5097    <t>
5098      <eref target=""/>:
5099      "qdtext BNF"
5100    </t>
5101    <t>
5102      <eref target=""/>:
5103      "Normative and Informative references"
5104    </t>
5105    <t>
5106      <eref target=""/>:
5107      "RFC2606 Compliance"
5108    </t>
5109    <t>
5110      <eref target=""/>:
5111      "RFC977 reference"
5112    </t>
5113    <t>
5114      <eref target=""/>:
5115      "RFC1700 references"
5116    </t>
5117    <t>
5118      <eref target=""/>:
5119      "inconsistency in date format explanation"
5120    </t>
5121    <t>
5122      <eref target=""/>:
5123      "Date reference typo"
5124    </t>
5125    <t>
5126      <eref target=""/>:
5127      "Informative references"
5128    </t>
5129    <t>
5130      <eref target=""/>:
5131      "ISO-8859-1 Reference"
5132    </t>
5133    <t>
5134      <eref target=""/>:
5135      "Normative up-to-date references"
5136    </t>
5137  </list>
5140  Other changes:
5141  <list style="symbols">
5142    <t>
5143      Update media type registrations to use RFC4288 template.
5144    </t>
5145    <t>
5146      Use names of RFC4234 core rules DQUOTE and HTAB,
5147      fix broken ABNF for chunk-data
5148      (work in progress on <eref target=""/>)
5149    </t>
5150  </list>
5154<section title="Since draft-ietf-httpbis-p1-messaging-01">
5156  Closed issues:
5157  <list style="symbols">
5158    <t>
5159      <eref target=""/>:
5160      "Bodies on GET (and other) requests"
5161    </t>
5162    <t>
5163      <eref target=""/>:
5164      "Updating to RFC4288"
5165    </t>
5166    <t>
5167      <eref target=""/>:
5168      "Status Code and Reason Phrase"
5169    </t>
5170    <t>
5171      <eref target=""/>:
5172      "rel_path not used"
5173    </t>
5174  </list>
5177  Ongoing work on ABNF conversion (<eref target=""/>):
5178  <list style="symbols">
5179    <t>
5180      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5181      "trailer-part").
5182    </t>
5183    <t>
5184      Avoid underscore character in rule names ("http_URL" ->
5185      "http-URL", "abs_path" -> "path-absolute").
5186    </t>
5187    <t>
5188      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5189      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5190      have to be updated when switching over to RFC3986.
5191    </t>
5192    <t>
5193      Synchronize core rules with RFC5234.
5194    </t>
5195    <t>
5196      Get rid of prose rules that span multiple lines.
5197    </t>
5198    <t>
5199      Get rid of unused rules LOALPHA and UPALPHA.
5200    </t>
5201    <t>
5202      Move "Product Tokens" section (back) into Part 1, as "token" is used
5203      in the definition of the Upgrade header field.
5204    </t>
5205    <t>
5206      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5207    </t>
5208    <t>
5209      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5210    </t>
5211  </list>
5215<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5217  Closed issues:
5218  <list style="symbols">
5219    <t>
5220      <eref target=""/>:
5221      "HTTP-date vs. rfc1123-date"
5222    </t>
5223    <t>
5224      <eref target=""/>:
5225      "WS in quoted-pair"
5226    </t>
5227  </list>
5230  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5231  <list style="symbols">
5232    <t>
5233      Reference RFC 3984, and update header field registrations for headers defined
5234      in this document.
5235    </t>
5236  </list>
5239  Ongoing work on ABNF conversion (<eref target=""/>):
5240  <list style="symbols">
5241    <t>
5242      Replace string literals when the string really is case-sensitive (HTTP-version).
5243    </t>
5244  </list>
5248<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5250  Closed issues:
5251  <list style="symbols">
5252    <t>
5253      <eref target=""/>:
5254      "Connection closing"
5255    </t>
5256    <t>
5257      <eref target=""/>:
5258      "Move registrations and registry information to IANA Considerations"
5259    </t>
5260    <t>
5261      <eref target=""/>:
5262      "need new URL for PAD1995 reference"
5263    </t>
5264    <t>
5265      <eref target=""/>:
5266      "IANA Considerations: update HTTP URI scheme registration"
5267    </t>
5268    <t>
5269      <eref target=""/>:
5270      "Cite HTTPS URI scheme definition"
5271    </t>
5272    <t>
5273      <eref target=""/>:
5274      "List-type headers vs Set-Cookie"
5275    </t>
5276  </list>
5279  Ongoing work on ABNF conversion (<eref target=""/>):
5280  <list style="symbols">
5281    <t>
5282      Replace string literals when the string really is case-sensitive (HTTP-Date).
5283    </t>
5284    <t>
5285      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5286    </t>
5287  </list>
5291<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5293  Closed issues:
5294  <list style="symbols">
5295    <t>
5296      <eref target=""/>:
5297      "Out-of-date reference for URIs"
5298    </t>
5299    <t>
5300      <eref target=""/>:
5301      "RFC 2822 is updated by RFC 5322"
5302    </t>
5303  </list>
5306  Ongoing work on ABNF conversion (<eref target=""/>):
5307  <list style="symbols">
5308    <t>
5309      Use "/" instead of "|" for alternatives.
5310    </t>
5311    <t>
5312      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5313    </t>
5314    <t>
5315      Only reference RFC 5234's core rules.
5316    </t>
5317    <t>
5318      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5319      whitespace ("OWS") and required whitespace ("RWS").
5320    </t>
5321    <t>
5322      Rewrite ABNFs to spell out whitespace rules, factor out
5323      header field value format definitions.
5324    </t>
5325  </list>
5329<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5331  Closed issues:
5332  <list style="symbols">
5333    <t>
5334      <eref target=""/>:
5335      "Header LWS"
5336    </t>
5337    <t>
5338      <eref target=""/>:
5339      "Sort 1.3 Terminology"
5340    </t>
5341    <t>
5342      <eref target=""/>:
5343      "RFC2047 encoded words"
5344    </t>
5345    <t>
5346      <eref target=""/>:
5347      "Character Encodings in TEXT"
5348    </t>
5349    <t>
5350      <eref target=""/>:
5351      "Line Folding"
5352    </t>
5353    <t>
5354      <eref target=""/>:
5355      "OPTIONS * and proxies"
5356    </t>
5357    <t>
5358      <eref target=""/>:
5359      "reason-phrase BNF"
5360    </t>
5361    <t>
5362      <eref target=""/>:
5363      "Use of TEXT"
5364    </t>
5365    <t>
5366      <eref target=""/>:
5367      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5368    </t>
5369    <t>
5370      <eref target=""/>:
5371      "RFC822 reference left in discussion of date formats"
5372    </t>
5373  </list>
5376  Final work on ABNF conversion (<eref target=""/>):
5377  <list style="symbols">
5378    <t>
5379      Rewrite definition of list rules, deprecate empty list elements.
5380    </t>
5381    <t>
5382      Add appendix containing collected and expanded ABNF.
5383    </t>
5384  </list>
5387  Other changes:
5388  <list style="symbols">
5389    <t>
5390      Rewrite introduction; add mostly new Architecture Section.
5391    </t>
5392    <t>
5393      Move definition of quality values from Part 3 into Part 1;
5394      make TE request header field grammar independent of accept-params (defined in Part 3).
5395    </t>
5396  </list>
5400<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5402  Closed issues:
5403  <list style="symbols">
5404    <t>
5405      <eref target=""/>:
5406      "base for numeric protocol elements"
5407    </t>
5408    <t>
5409      <eref target=""/>:
5410      "comment ABNF"
5411    </t>
5412  </list>
5415  Partly resolved issues:
5416  <list style="symbols">
5417    <t>
5418      <eref target=""/>:
5419      "205 Bodies" (took out language that implied that there might be
5420      methods for which a request body MUST NOT be included)
5421    </t>
5422    <t>
5423      <eref target=""/>:
5424      "editorial improvements around HTTP-date"
5425    </t>
5426  </list>
5430<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5432  Closed issues:
5433  <list style="symbols">
5434    <t>
5435      <eref target=""/>:
5436      "Repeating single-value headers"
5437    </t>
5438    <t>
5439      <eref target=""/>:
5440      "increase connection limit"
5441    </t>
5442    <t>
5443      <eref target=""/>:
5444      "IP addresses in URLs"
5445    </t>
5446    <t>
5447      <eref target=""/>:
5448      "take over HTTP Upgrade Token Registry"
5449    </t>
5450    <t>
5451      <eref target=""/>:
5452      "CR and LF in chunk extension values"
5453    </t>
5454    <t>
5455      <eref target=""/>:
5456      "HTTP/0.9 support"
5457    </t>
5458    <t>
5459      <eref target=""/>:
5460      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5461    </t>
5462    <t>
5463      <eref target=""/>:
5464      "move definitions of gzip/deflate/compress to part 1"
5465    </t>
5466    <t>
5467      <eref target=""/>:
5468      "disallow control characters in quoted-pair"
5469    </t>
5470  </list>
5473  Partly resolved issues:
5474  <list style="symbols">
5475    <t>
5476      <eref target=""/>:
5477      "update IANA requirements wrt Transfer-Coding values" (add the
5478      IANA Considerations subsection)
5479    </t>
5480  </list>
5484<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5486  Closed issues:
5487  <list style="symbols">
5488    <t>
5489      <eref target=""/>:
5490      "header parsing, treatment of leading and trailing OWS"
5491    </t>
5492  </list>
5495  Partly resolved issues:
5496  <list style="symbols">
5497    <t>
5498      <eref target=""/>:
5499      "Placement of 13.5.1 and 13.5.2"
5500    </t>
5501    <t>
5502      <eref target=""/>:
5503      "use of term "word" when talking about header structure"
5504    </t>
5505  </list>
5509<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5511  Closed issues:
5512  <list style="symbols">
5513    <t>
5514      <eref target=""/>:
5515      "Clarification of the term 'deflate'"
5516    </t>
5517    <t>
5518      <eref target=""/>:
5519      "OPTIONS * and proxies"
5520    </t>
5521    <t>
5522      <eref target=""/>:
5523      "MIME-Version not listed in P1, general header fields"
5524    </t>
5525    <t>
5526      <eref target=""/>:
5527      "IANA registry for content/transfer encodings"
5528    </t>
5529    <t>
5530      <eref target=""/>:
5531      "Case-sensitivity of HTTP-date"
5532    </t>
5533    <t>
5534      <eref target=""/>:
5535      "use of term "word" when talking about header structure"
5536    </t>
5537  </list>
5540  Partly resolved issues:
5541  <list style="symbols">
5542    <t>
5543      <eref target=""/>:
5544      "Term for the requested resource's URI"
5545    </t>
5546  </list>
5550<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5552  Closed issues:
5553  <list style="symbols">
5554    <t>
5555      <eref target=""/>:
5556      "Connection Closing"
5557    </t>
5558    <t>
5559      <eref target=""/>:
5560      "Delimiting messages with multipart/byteranges"
5561    </t>
5562    <t>
5563      <eref target=""/>:
5564      "Handling multiple Content-Length headers"
5565    </t>
5566    <t>
5567      <eref target=""/>:
5568      "Clarify entity / representation / variant terminology"
5569    </t>
5570    <t>
5571      <eref target=""/>:
5572      "consider removing the 'changes from 2068' sections"
5573    </t>
5574  </list>
5577  Partly resolved issues:
5578  <list style="symbols">
5579    <t>
5580      <eref target=""/>:
5581      "HTTP(s) URI scheme definitions"
5582    </t>
5583  </list>
5587<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5589  Closed issues:
5590  <list style="symbols">
5591    <t>
5592      <eref target=""/>:
5593      "Trailer requirements"
5594    </t>
5595    <t>
5596      <eref target=""/>:
5597      "Text about clock requirement for caches belongs in p6"
5598    </t>
5599    <t>
5600      <eref target=""/>:
5601      "effective request URI: handling of missing host in HTTP/1.0"
5602    </t>
5603    <t>
5604      <eref target=""/>:
5605      "confusing Date requirements for clients"
5606    </t>
5607  </list>
5610  Partly resolved issues:
5611  <list style="symbols">
5612    <t>
5613      <eref target=""/>:
5614      "Handling multiple Content-Length headers"
5615    </t>
5616  </list>
5620<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5622  Closed issues:
5623  <list style="symbols">
5624    <t>
5625      <eref target=""/>:
5626      "RFC2145 Normative"
5627    </t>
5628    <t>
5629      <eref target=""/>:
5630      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5631    </t>
5632    <t>
5633      <eref target=""/>:
5634      "define 'transparent' proxy"
5635    </t>
5636    <t>
5637      <eref target=""/>:
5638      "Header Classification"
5639    </t>
5640    <t>
5641      <eref target=""/>:
5642      "Is * usable as a request-uri for new methods?"
5643    </t>
5644    <t>
5645      <eref target=""/>:
5646      "Migrate Upgrade details from RFC2817"
5647    </t>
5648    <t>
5649      <eref target=""/>:
5650      "untangle ABNFs for header fields"
5651    </t>
5652    <t>
5653      <eref target=""/>:
5654      "update RFC 2109 reference"
5655    </t>
5656  </list>
5660<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5662  Closed issues:
5663  <list style="symbols">
5664    <t>
5665      <eref target=""/>:
5666      "Allow is not in 13.5.2"
5667    </t>
5668    <t>
5669      <eref target=""/>:
5670      "Handling multiple Content-Length headers"
5671    </t>
5672    <t>
5673      <eref target=""/>:
5674      "untangle ABNFs for header fields"
5675    </t>
5676    <t>
5677      <eref target=""/>:
5678      "Content-Length ABNF broken"
5679    </t>
5680  </list>
5684<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5686  Closed issues:
5687  <list style="symbols">
5688    <t>
5689      <eref target=""/>:
5690      "HTTP-version should be redefined as fixed length pair of DIGIT . DIGIT"
5691    </t>
5692    <t>
5693      <eref target=""/>:
5694      "Recommend minimum sizes for protocol elements"
5695    </t>
5696    <t>
5697      <eref target=""/>:
5698      "Set expectations around buffering"
5699    </t>
5700    <t>
5701      <eref target=""/>:
5702      "Considering messages in isolation"
5703    </t>
5704  </list>
5708<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5710  Closed issues:
5711  <list style="symbols">
5712    <t>
5713      <eref target=""/>:
5714      "DNS Spoofing / DNS Binding advice"
5715    </t>
5716    <t>
5717      <eref target=""/>:
5718      "move RFCs 2145, 2616, 2817 to Historic status"
5719    </t>
5720    <t>
5721      <eref target=""/>:
5722      "\-escaping in quoted strings"
5723    </t>
5724    <t>
5725      <eref target=""/>:
5726      "'Close' should be reserved in the HTTP header field registry"
5727    </t>
5728  </list>
5732<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5734  Closed issues:
5735  <list style="symbols">
5736    <t>
5737      <eref target=""/>:
5738      "Document HTTP's error-handling philosophy"
5739    </t>
5740    <t>
5741      <eref target=""/>:
5742      "Explain header registration"
5743    </t>
5744    <t>
5745      <eref target=""/>:
5746      "Revise Acknowledgements Sections"
5747    </t>
5748    <t>
5749      <eref target=""/>:
5750      "Retrying Requests"
5751    </t>
5752    <t>
5753      <eref target=""/>:
5754      "Closing the connection on server error"
5755    </t>
5756  </list>
5760<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5762  Closed issues:
5763  <list style="symbols">
5764    <t>
5765      <eref target=""/>:
5766      "Proxy-Connection and Keep-Alive"
5767    </t>
5768    <t>
5769      <eref target=""/>:
5770      "Clarify 'User Agent'"
5771    </t>
5772    <t>
5773      <eref target=""/>:
5774      "Define non-final responses"
5775    </t>
5776    <t>
5777      <eref target=""/>:
5778      "intended maturity level vs normative references"
5779    </t>
5780    <t>
5781      <eref target=""/>:
5782      "Intermediary rewriting of queries"
5783    </t>
5784  </list>
5788<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5790  Closed issues:
5791  <list style="symbols">
5792    <t>
5793      <eref target=""/>:
5794      "message-body in CONNECT response"
5795    </t>
5796    <t>
5797      <eref target=""/>:
5798      "Misplaced text on connection handling in p2"
5799    </t>
5800    <t>
5801      <eref target=""/>:
5802      "wording of line folding rule"
5803    </t>
5804    <t>
5805      <eref target=""/>:
5806      "chunk-extensions"
5807    </t>
5808    <t>
5809      <eref target=""/>:
5810      "make IANA policy definitions consistent"
5811    </t>
5812  </list>
5816<section title="Since draft-ietf-httpbis-p1-messaging-19" anchor="changes.since.19">
5818  Closed issues:
5819  <list style="symbols">
5820    <t>
5821      <eref target=""/>:
5822      "make IANA policy definitions consistent"
5823    </t>
5824    <t>
5825      <eref target=""/>:
5826      "ABNF requirements for recipients"
5827    </t>
5828  </list>
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