source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1171

Last change on this file since 1171 was 1171, checked in by fielding@…, 11 years ago

editorial: clean up some of the language surrounding the URI
scheme definitions and request-target.

  • Property svn:eol-style set to native
File size: 247.9 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2011">
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='#errors.or.incomplete.response.cache.behavior' xmlns:x=''/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x=''/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x=''/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
29  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x=''/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
33  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
34  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
35  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
36  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc rfcedstyle="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x=''>
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
60    <address>
61      <postal>
62        <street>345 Park Ave</street>
63        <city>San Jose</city>
64        <region>CA</region>
65        <code>95110</code>
66        <country>USA</country>
67      </postal>
68      <email></email>
69      <uri></uri>
70    </address>
71  </author>
73  <author initials="J." surname="Gettys" fullname="Jim Gettys">
74    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
75    <address>
76      <postal>
77        <street>21 Oak Knoll Road</street>
78        <city>Carlisle</city>
79        <region>MA</region>
80        <code>01741</code>
81        <country>USA</country>
82      </postal>
83      <email></email>
84      <uri></uri>
85    </address>
86  </author>
88  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
89    <organization abbrev="HP">Hewlett-Packard Company</organization>
90    <address>
91      <postal>
92        <street>HP Labs, Large Scale Systems Group</street>
93        <street>1501 Page Mill Road, MS 1177</street>
94        <city>Palo Alto</city>
95        <region>CA</region>
96        <code>94304</code>
97        <country>USA</country>
98      </postal>
99      <email></email>
100    </address>
101  </author>
103  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
104    <organization abbrev="Microsoft">Microsoft Corporation</organization>
105    <address>
106      <postal>
107        <street>1 Microsoft Way</street>
108        <city>Redmond</city>
109        <region>WA</region>
110        <code>98052</code>
111        <country>USA</country>
112      </postal>
113      <email></email>
114    </address>
115  </author>
117  <author initials="L." surname="Masinter" fullname="Larry Masinter">
118    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
119    <address>
120      <postal>
121        <street>345 Park Ave</street>
122        <city>San Jose</city>
123        <region>CA</region>
124        <code>95110</code>
125        <country>USA</country>
126      </postal>
127      <email></email>
128      <uri></uri>
129    </address>
130  </author>
132  <author initials="P." surname="Leach" fullname="Paul J. Leach">
133    <organization abbrev="Microsoft">Microsoft Corporation</organization>
134    <address>
135      <postal>
136        <street>1 Microsoft Way</street>
137        <city>Redmond</city>
138        <region>WA</region>
139        <code>98052</code>
140      </postal>
141      <email></email>
142    </address>
143  </author>
145  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
146    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
147    <address>
148      <postal>
149        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
150        <street>The Stata Center, Building 32</street>
151        <street>32 Vassar Street</street>
152        <city>Cambridge</city>
153        <region>MA</region>
154        <code>02139</code>
155        <country>USA</country>
156      </postal>
157      <email></email>
158      <uri></uri>
159    </address>
160  </author>
162  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
163    <organization abbrev="W3C">World Wide Web Consortium</organization>
164    <address>
165      <postal>
166        <street>W3C / ERCIM</street>
167        <street>2004, rte des Lucioles</street>
168        <city>Sophia-Antipolis</city>
169        <region>AM</region>
170        <code>06902</code>
171        <country>France</country>
172      </postal>
173      <email></email>
174      <uri></uri>
175    </address>
176  </author>
178  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
179    <organization abbrev="greenbytes">greenbytes GmbH</organization>
180    <address>
181      <postal>
182        <street>Hafenweg 16</street>
183        <city>Muenster</city><region>NW</region><code>48155</code>
184        <country>Germany</country>
185      </postal>
186      <phone>+49 251 2807760</phone>
187      <facsimile>+49 251 2807761</facsimile>
188      <email></email>
189      <uri></uri>
190    </address>
191  </author>
193  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
194  <workgroup>HTTPbis Working Group</workgroup>
198   The Hypertext Transfer Protocol (HTTP) is an application-level
199   protocol for distributed, collaborative, hypertext information
200   systems. HTTP has been in use by the World Wide Web global information
201   initiative since 1990. This document is Part 1 of the seven-part specification
202   that defines the protocol referred to as "HTTP/1.1" and, taken together,
203   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
204   its associated terminology, defines the "http" and "https" Uniform
205   Resource Identifier (URI) schemes, defines the generic message syntax
206   and parsing requirements for HTTP message frames, and describes
207   general security concerns for implementations.
211<note title="Editorial Note (To be removed by RFC Editor)">
212  <t>
213    Discussion of this draft should take place on the HTTPBIS working group
214    mailing list ( The current issues list is
215    at <eref target=""/>
216    and related documents (including fancy diffs) can be found at
217    <eref target=""/>.
218  </t>
219  <t>
220    The changes in this draft are summarized in <xref target="changes.since.12"/>.
221  </t>
225<section title="Introduction" anchor="introduction">
227   The Hypertext Transfer Protocol (HTTP) is an application-level
228   request/response protocol that uses extensible semantics and MIME-like
229   message payloads for flexible interaction with network-based hypertext
230   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
231   standard <xref target="RFC3986"/> to indicate the target resource and
232   relationships between resources.
233   Messages are passed in a format similar to that used by Internet mail
234   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
235   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
236   between HTTP and MIME messages).
239   HTTP is a generic interface protocol for information systems. It is
240   designed to hide the details of how a service is implemented by presenting
241   a uniform interface to clients that is independent of the types of
242   resources provided. Likewise, servers do not need to be aware of each
243   client's purpose: an HTTP request can be considered in isolation rather
244   than being associated with a specific type of client or a predetermined
245   sequence of application steps. The result is a protocol that can be used
246   effectively in many different contexts and for which implementations can
247   evolve independently over time.
250   HTTP is also designed for use as an intermediation protocol for translating
251   communication to and from non-HTTP information systems.
252   HTTP proxies and gateways can provide access to alternative information
253   services by translating their diverse protocols into a hypertext
254   format that can be viewed and manipulated by clients in the same way
255   as HTTP services.
258   One consequence of HTTP flexibility is that the protocol cannot be
259   defined in terms of what occurs behind the interface. Instead, we
260   are limited to defining the syntax of communication, the intent
261   of received communication, and the expected behavior of recipients.
262   If the communication is considered in isolation, then successful
263   actions ought to be reflected in corresponding changes to the
264   observable interface provided by servers. However, since multiple
265   clients might act in parallel and perhaps at cross-purposes, we
266   cannot require that such changes be observable beyond the scope
267   of a single response.
270   This document is Part 1 of the seven-part specification of HTTP,
271   defining the protocol referred to as "HTTP/1.1", obsoleting
272   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
273   Part 1 describes the architectural elements that are used or
274   referred to in HTTP, defines the "http" and "https" URI schemes,
275   describes overall network operation and connection management,
276   and defines HTTP message framing and forwarding requirements.
277   Our goal is to define all of the mechanisms necessary for HTTP message
278   handling that are independent of message semantics, thereby defining the
279   complete set of requirements for message parsers and
280   message-forwarding intermediaries.
283<section title="Requirements" anchor="intro.requirements">
285   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
286   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
287   document are to be interpreted as described in <xref target="RFC2119"/>.
290   An implementation is not compliant if it fails to satisfy one or more
291   of the "MUST" or "REQUIRED" level requirements for the protocols it
292   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
293   level and all the "SHOULD" level requirements for its protocols is said
294   to be "unconditionally compliant"; one that satisfies all the "MUST"
295   level requirements but not all the "SHOULD" level requirements for its
296   protocols is said to be "conditionally compliant".
300<section title="Syntax Notation" anchor="notation">
301<iref primary="true" item="Grammar" subitem="ALPHA"/>
302<iref primary="true" item="Grammar" subitem="CR"/>
303<iref primary="true" item="Grammar" subitem="CRLF"/>
304<iref primary="true" item="Grammar" subitem="CTL"/>
305<iref primary="true" item="Grammar" subitem="DIGIT"/>
306<iref primary="true" item="Grammar" subitem="DQUOTE"/>
307<iref primary="true" item="Grammar" subitem="HEXDIG"/>
308<iref primary="true" item="Grammar" subitem="LF"/>
309<iref primary="true" item="Grammar" subitem="OCTET"/>
310<iref primary="true" item="Grammar" subitem="SP"/>
311<iref primary="true" item="Grammar" subitem="VCHAR"/>
312<iref primary="true" item="Grammar" subitem="WSP"/>
314   This specification uses the Augmented Backus-Naur Form (ABNF) notation
315   of <xref target="RFC5234"/>.
317<t anchor="core.rules">
318  <x:anchor-alias value="ALPHA"/>
319  <x:anchor-alias value="CTL"/>
320  <x:anchor-alias value="CR"/>
321  <x:anchor-alias value="CRLF"/>
322  <x:anchor-alias value="DIGIT"/>
323  <x:anchor-alias value="DQUOTE"/>
324  <x:anchor-alias value="HEXDIG"/>
325  <x:anchor-alias value="LF"/>
326  <x:anchor-alias value="OCTET"/>
327  <x:anchor-alias value="SP"/>
328  <x:anchor-alias value="VCHAR"/>
329  <x:anchor-alias value="WSP"/>
330   The following core rules are included by
331   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
332   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
333   DIGIT (decimal 0-9), DQUOTE (double quote),
334   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
335   OCTET (any 8-bit sequence of data), SP (space),
336   VCHAR (any visible <xref target="USASCII"/> character),
337   and WSP (whitespace).
340   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
341   "obsolete" grammar rules that appear for historical reasons.
344<section title="ABNF Extension: #rule" anchor="notation.abnf">
346  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
347  improve readability.
350  A construct "#" is defined, similar to "*", for defining comma-delimited
351  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
352  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
353  comma (",") and optional whitespace (OWS,
354  <xref target="basic.rules"/>).   
357  Thus,
358</preamble><artwork type="example">
359  1#element =&gt; element *( OWS "," OWS element )
362  and:
363</preamble><artwork type="example">
364  #element =&gt; [ 1#element ]
367  and for n &gt;= 1 and m &gt; 1:
368</preamble><artwork type="example">
369  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
372  For compatibility with legacy list rules, recipients &SHOULD; accept empty
373  list elements. In other words, consumers would follow the list productions:
375<figure><artwork type="example">
376  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
378  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
381  Note that empty elements do not contribute to the count of elements present,
382  though.
385  For example, given these ABNF productions:
387<figure><artwork type="example">
388  example-list      = 1#example-list-elmt
389  example-list-elmt = token ; see <xref target="basic.rules"/>
392  Then these are valid values for example-list (not including the double
393  quotes, which are present for delimitation only):
395<figure><artwork type="example">
396  "foo,bar"
397  " foo ,bar,"
398  "  foo , ,bar,charlie   "
399  "foo ,bar,   charlie "
402  But these values would be invalid, as at least one non-empty element is
403  required:
405<figure><artwork type="example">
406  ""
407  ","
408  ",   ,"
411  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
412  expanded as explained above.
416<section title="Basic Rules" anchor="basic.rules">
417<t anchor="rule.CRLF">
418  <x:anchor-alias value="CRLF"/>
419   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
420   protocol elements other than the message-body
421   (see <xref target="tolerant.applications"/> for tolerant applications).
423<t anchor="rule.LWS">
424   This specification uses three rules to denote the use of linear
425   whitespace: OWS (optional whitespace), RWS (required whitespace), and
426   BWS ("bad" whitespace).
429   The OWS rule is used where zero or more linear whitespace characters might
430   appear. OWS &SHOULD; either not be produced or be produced as a single SP
431   character. Multiple OWS characters that occur within field-content &SHOULD;
432   be replaced with a single SP before interpreting the field value or
433   forwarding the message downstream.
436   RWS is used when at least one linear whitespace character is required to
437   separate field tokens. RWS &SHOULD; be produced as a single SP character.
438   Multiple RWS characters that occur within field-content &SHOULD; be
439   replaced with a single SP before interpreting the field value or
440   forwarding the message downstream.
443   BWS is used where the grammar allows optional whitespace for historical
444   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
445   recipients &MUST; accept such bad optional whitespace and remove it before
446   interpreting the field value or forwarding the message downstream.
448<t anchor="rule.whitespace">
449  <x:anchor-alias value="BWS"/>
450  <x:anchor-alias value="OWS"/>
451  <x:anchor-alias value="RWS"/>
452  <x:anchor-alias value="obs-fold"/>
454<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"/>
455  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
456                 ; "optional" whitespace
457  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "required" whitespace
459  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
460                 ; "bad" whitespace
461  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
462                 ; see <xref target="header.fields"/>
464<t anchor="rule.token.separators">
465  <x:anchor-alias value="tchar"/>
466  <x:anchor-alias value="token"/>
467  <x:anchor-alias value="special"/>
468  <x:anchor-alias value="word"/>
469   Many HTTP/1.1 header field values consist of words (token or quoted-string)
470   separated by whitespace or special characters. These special characters
471   &MUST; be in a quoted string to be used within a parameter value (as defined
472   in <xref target="transfer.codings"/>).
474<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"/>
475  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
477  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
479  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
480 -->
481  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
482                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
483                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
484                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
486  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
487                 / ";" / ":" / "\" / DQUOTE / "/" / "["
488                 / "]" / "?" / "=" / "{" / "}"
490<t anchor="rule.quoted-string">
491  <x:anchor-alias value="quoted-string"/>
492  <x:anchor-alias value="qdtext"/>
493  <x:anchor-alias value="obs-text"/>
494   A string of text is parsed as a single word if it is quoted using
495   double-quote marks.
497<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"/>
498  <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>
499  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
500                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
501  <x:ref>obs-text</x:ref>       = %x80-FF
503<t anchor="rule.quoted-pair">
504  <x:anchor-alias value="quoted-pair"/>
505   The backslash character ("\") can be used as a single-character
506   quoting mechanism within quoted-string constructs:
508<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
509  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
512   Producers &SHOULD-NOT; escape characters that do not require escaping
513   (i.e., other than DQUOTE and the backslash character).
520<section title="HTTP-related architecture" anchor="architecture">
522   HTTP was created for the World Wide Web architecture
523   and has evolved over time to support the scalability needs of a worldwide
524   hypertext system. Much of that architecture is reflected in the terminology
525   and syntax productions used to define HTTP.
528<section title="Client/Server Messaging" anchor="operation">
529<iref primary="true" item="client"/>
530<iref primary="true" item="server"/>
531<iref primary="true" item="connection"/>
533   HTTP is a stateless request/response protocol that operates by exchanging
534   messages across a reliable transport or session-layer connection. An HTTP
535   "client" is a program that establishes a connection to a server for the
536   purpose of sending one or more HTTP requests.  An HTTP "server" is a
537   program that accepts connections in order to service HTTP requests by
538   sending HTTP responses.
540<iref primary="true" item="user agent"/>
541<iref primary="true" item="origin server"/>
542<iref primary="true" item="browser"/>
543<iref primary="true" item="spider"/>
545   Note that the terms client and server refer only to the roles that
546   these programs perform for a particular connection.  The same program
547   might act as a client on some connections and a server on others.  We use
548   the term "user agent" to refer to the program that initiates a request,
549   such as a WWW browser, editor, or spider (web-traversing robot), and
550   the term "origin server" to refer to the program that can originate
551   authoritative responses to a request.  For general requirements, we use
552   the term "sender" to refer to whichever component sent a given message
553   and the term "recipient" to refer to any component that receives the
554   message.
557   Most HTTP communication consists of a retrieval request (GET) for
558   a representation of some resource identified by a URI.  In the
559   simplest case, this might be accomplished via a single bidirectional
560   connection (===) between the user agent (UA) and the origin server (O).
562<figure><artwork type="drawing">
563         request   &gt;
564    UA ======================================= O
565                                &lt;   response
567<iref primary="true" item="message"/>
568<iref primary="true" item="request"/>
569<iref primary="true" item="response"/>
571   A client sends an HTTP request to the server in the form of a request
572   message (<xref target="request"/>), beginning with a method, URI, and
573   protocol version, followed by MIME-like header fields containing
574   request modifiers, client information, and payload metadata, an empty
575   line to indicate the end of the header section, and finally the payload
576   body (if any).
579   A server responds to the client's request by sending an HTTP response
580   message (<xref target="response"/>), beginning with a status line that
581   includes the protocol version, a success or error code, and textual
582   reason phrase, followed by MIME-like header fields containing server
583   information, resource metadata, and payload metadata, an empty line to
584   indicate the end of the header section, and finally the payload body (if any).
587   The following example illustrates a typical message exchange for a
588   GET request on the URI "":
591client request:
592</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
593GET /hello.txt HTTP/1.1
594User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
596Accept: */*
600server response:
601</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
602HTTP/1.1 200 OK
603Date: Mon, 27 Jul 2009 12:28:53 GMT
604Server: Apache
605Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
606ETag: "34aa387-d-1568eb00"
607Accept-Ranges: bytes
608Content-Length: <x:length-of target="exbody"/>
609Vary: Accept-Encoding
610Content-Type: text/plain
612<x:span anchor="exbody">Hello World!
616<section title="Connections and Transport Independence" anchor="transport-independence">
618   HTTP messaging is independent of the underlying transport or
619   session-layer connection protocol(s).  HTTP only presumes a reliable
620   transport with in-order delivery of requests and the corresponding
621   in-order delivery of responses.  The mapping of HTTP request and
622   response structures onto the data units of the underlying transport
623   protocol is outside the scope of this specification.
626   The specific connection protocols to be used for an interaction
627   are determined by client configuration and the target resource's URI.
628   For example, the "http" URI scheme
629   (<xref target="http.uri"/>) indicates a default connection of TCP
630   over IP, with a default TCP port of 80, but the client might be
631   configured to use a proxy via some other connection port or protocol
632   instead of using the defaults.
635   A connection might be used for multiple HTTP request/response exchanges,
636   as defined in <xref target="persistent.connections"/>.
640<section title="Intermediaries" anchor="intermediaries">
641<iref primary="true" item="intermediary"/>
643   HTTP enables the use of intermediaries to satisfy requests through
644   a chain of connections.  There are three common forms of HTTP
645   intermediary: proxy, gateway, and tunnel.  In some cases,
646   a single intermediary might act as an origin server, proxy, gateway,
647   or tunnel, switching behavior based on the nature of each request.
649<figure><artwork type="drawing">
650         &gt;             &gt;             &gt;             &gt;
651    UA =========== A =========== B =========== C =========== O
652               &lt;             &lt;             &lt;             &lt;
655   The figure above shows three intermediaries (A, B, and C) between the
656   user agent and origin server. A request or response message that
657   travels the whole chain will pass through four separate connections.
658   Some HTTP communication options
659   might apply only to the connection with the nearest, non-tunnel
660   neighbor, only to the end-points of the chain, or to all connections
661   along the chain. Although the diagram is linear, each participant might
662   be engaged in multiple, simultaneous communications. For example, B
663   might be receiving requests from many clients other than A, and/or
664   forwarding requests to servers other than C, at the same time that it
665   is handling A's request.
668<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
669<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
670   We use the terms "upstream" and "downstream" to describe various
671   requirements in relation to the directional flow of a message:
672   all messages flow from upstream to downstream.
673   Likewise, we use the terms "inbound" and "outbound" to refer to
674   directions in relation to the request path: "inbound" means toward
675   the origin server and "outbound" means toward the user agent.
677<t><iref primary="true" item="proxy"/>
678   A "proxy" is a message forwarding agent that is selected by the
679   client, usually via local configuration rules, to receive requests
680   for some type(s) of absolute URI and attempt to satisfy those
681   requests via translation through the HTTP interface.  Some translations
682   are minimal, such as for proxy requests for "http" URIs, whereas
683   other requests might require translation to and from entirely different
684   application-layer protocols. Proxies are often used to group an
685   organization's HTTP requests through a common intermediary for the
686   sake of security, annotation services, or shared caching.
689<iref primary="true" item="transforming proxy"/>
690<iref primary="true" item="non-transforming proxy"/>
691   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
692   or configured to modify request or response messages in a semantically
693   meaningful way (i.e., modifications, beyond those required by normal
694   HTTP processing, that change the message in a way that would be
695   significant to the original sender or potentially significant to
696   downstream recipients).  For example, a transforming proxy might be
697   acting as a shared annotation server (modifying responses to include
698   references to a local annotation database), a malware filter, a
699   format transcoder, or an intranet-to-Internet privacy filter.  Such
700   transformations are presumed to be desired by the client (or client
701   organization) that selected the proxy and are beyond the scope of
702   this specification.  However, when a proxy is not intended to transform
703   a given message, we use the term "non-transforming proxy" to target
704   requirements that preserve HTTP message semantics.
706<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
707<iref primary="true" item="accelerator"/>
708   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
709   as a layer above some other server(s) and translates the received
710   requests to the underlying server's protocol.  Gateways are often
711   used for load balancing, "accelerator" caching, or partitioning
712   HTTP services across multiple machines.
713   Unlike a proxy, a gateway receives requests as if it were the
714   origin server for the target resource; the requesting client
715   will not be aware that it is communicating with a gateway.
716   A gateway communicates with the client as if the gateway is the
717   origin server and thus is subject to all of the requirements on
718   origin servers for that connection.  A gateway communicates
719   with inbound servers using any protocol it desires, including
720   private extensions to HTTP that are outside the scope of this
721   specification.
723<t><iref primary="true" item="tunnel"/>
724   A "tunnel" acts as a blind relay between two connections
725   without changing the messages. Once active, a tunnel is not
726   considered a party to the HTTP communication, though the tunnel might
727   have been initiated by an HTTP request. A tunnel ceases to exist when
728   both ends of the relayed connection are closed. Tunnels are used to
729   extend a virtual connection through an intermediary, such as when
730   transport-layer security is used to establish private communication
731   through a shared firewall proxy.
733<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
734<iref primary="true" item="captive portal"/>
735   In addition, there may exist network intermediaries that are not
736   considered part of the HTTP communication but nevertheless act as
737   filters or redirecting agents (usually violating HTTP semantics,
738   causing security problems, and otherwise making a mess of things).
739   Such a network intermediary, often referred to as an "interception proxy"
740   <xref target="RFC3040"/>, "transparent proxy" <xref target="RFC1919"/>,
741   or "captive portal",
742   differs from an HTTP proxy because it has not been selected by the client.
743   Instead, the network intermediary redirects outgoing TCP port 80 packets
744   (and occasionally other common port traffic) to an internal HTTP server.
745   Interception proxies are commonly found on public network access points,
746   as a means of enforcing account subscription prior to allowing use of
747   non-local Internet services, and within corporate firewalls to enforce
748   network usage policies.
749   They are indistinguishable from a man-in-the-middle attack.
753<section title="Caches" anchor="caches">
754<iref primary="true" item="cache"/>
756   A "cache" is a local store of previous response messages and the
757   subsystem that controls its message storage, retrieval, and deletion.
758   A cache stores cacheable responses in order to reduce the response
759   time and network bandwidth consumption on future, equivalent
760   requests. Any client or server &MAY; employ a cache, though a cache
761   cannot be used by a server while it is acting as a tunnel.
764   The effect of a cache is that the request/response chain is shortened
765   if one of the participants along the chain has a cached response
766   applicable to that request. The following illustrates the resulting
767   chain if B has a cached copy of an earlier response from O (via C)
768   for a request which has not been cached by UA or A.
770<figure><artwork type="drawing">
771            &gt;             &gt;
772       UA =========== A =========== B - - - - - - C - - - - - - O
773                  &lt;             &lt;
775<t><iref primary="true" item="cacheable"/>
776   A response is "cacheable" if a cache is allowed to store a copy of
777   the response message for use in answering subsequent requests.
778   Even when a response is cacheable, there might be additional
779   constraints placed by the client or by the origin server on when
780   that cached response can be used for a particular request. HTTP
781   requirements for cache behavior and cacheable responses are
782   defined in &caching-overview;. 
785   There are a wide variety of architectures and configurations
786   of caches and proxies deployed across the World Wide Web and
787   inside large organizations. These systems include national hierarchies
788   of proxy caches to save transoceanic bandwidth, systems that
789   broadcast or multicast cache entries, organizations that distribute
790   subsets of cached data via optical media, and so on.
794<section title="Protocol Versioning" anchor="http.version">
795  <x:anchor-alias value="HTTP-Version"/>
796  <x:anchor-alias value="HTTP-Prot-Name"/>
798   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
799   versions of the protocol. This specification defines version "1.1".
800   The protocol version as a whole indicates the sender's compliance
801   with the set of requirements laid out in that version's corresponding
802   specification of HTTP.
805   The version of an HTTP message is indicated by an HTTP-Version field
806   in the first line of the message. HTTP-Version is case-sensitive.
808<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
809  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
810  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
813   The HTTP version number consists of two non-negative decimal integers
814   separated by the "." (period or decimal point) character.  The first
815   number ("major version") indicates the HTTP messaging syntax, whereas
816   the second number ("minor version") indicates the highest minor
817   version to which the sender is at least conditionally compliant and
818   able to understand for future communication.  The minor version
819   advertises the sender's communication capabilities even when the
820   sender is only using a backwards-compatible subset of the protocol,
821   thereby letting the recipient know that more advanced features can
822   be used in response (by servers) or in future requests (by clients).
825   When comparing HTTP versions, the numbers &MUST; be compared
826   numerically rather than lexically.  For example, HTTP/2.4 is a lower
827   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
828   Leading zeros &MUST; be ignored by recipients and &MUST-NOT; be sent.
831   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
832   <xref target="RFC1945"/> or a recipient whose version is unknown,
833   the HTTP/1.1 message is constructed such that it can be interpreted
834   as a valid HTTP/1.0 message if all of the newer features are ignored.
835   This specification places recipient-version requirements on some
836   new features so that a compliant sender will only use compatible
837   features until it has determined, through configuration or the
838   receipt of a message, that the recipient supports HTTP/1.1.
841   The interpretation of an HTTP header field does not change
842   between minor versions of the same major version, though the default
843   behavior of a recipient in the absence of such a field can change.
844   Unless specified otherwise, header fields defined in HTTP/1.1 are
845   defined for all versions of HTTP/1.x.  In particular, the Host and
846   Connection header fields ought to be implemented by all HTTP/1.x
847   implementations whether or not they advertise compliance with HTTP/1.1.
850   New header fields can be defined such that, when they are
851   understood by a recipient, they might override or enhance the
852   interpretation of previously defined header fields.  When an
853   implementation receives an unrecognized header field, the recipient
854   &MUST; ignore that header field for local processing regardless of
855   the message's HTTP version.  An unrecognized header field received
856   by a proxy &MUST; be forwarded downstream unless the header field's
857   field-name is listed in the message's Connection header-field
858   (see <xref target="header.connection"/>).
859   These requirements allow HTTP's functionality to be enhanced without
860   requiring prior update of all compliant intermediaries.
863   Intermediaries that process HTTP messages (i.e., all intermediaries
864   other than those acting as a tunnel) &MUST; send their own HTTP-Version
865   in forwarded messages.  In other words, they &MUST-NOT; blindly
866   forward the first line of an HTTP message without ensuring that the
867   protocol version matches what the intermediary understands, and
868   is at least conditionally compliant to, for both the receiving and
869   sending of messages.  Forwarding an HTTP message without rewriting
870   the HTTP-Version might result in communication errors when downstream
871   recipients use the message sender's version to determine what features
872   are safe to use for later communication with that sender.
875   An HTTP client &SHOULD; send a request version equal to the highest
876   version for which the client is at least conditionally compliant and
877   whose major version is no higher than the highest version supported
878   by the server, if this is known.  An HTTP client &MUST-NOT; send a
879   version for which it is not at least conditionally compliant.
882   An HTTP client &MAY; send a lower request version if it is known that
883   the server incorrectly implements the HTTP specification, but only
884   after the client has attempted at least one normal request and determined
885   from the response status or header fields (e.g., Server) that the
886   server improperly handles higher request versions.
889   An HTTP server &SHOULD; send a response version equal to the highest
890   version for which the server is at least conditionally compliant and
891   whose major version is less than or equal to the one received in the
892   request.  An HTTP server &MUST-NOT; send a version for which it is not
893   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
894   Version Not Supported) response if it cannot send a response using the
895   major version used in the client's request.
898   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
899   if it is known or suspected that the client incorrectly implements the
900   HTTP specification and is incapable of correctly processing later
901   version responses, such as when a client fails to parse the version
902   number correctly or when an intermediary is known to blindly forward
903   the HTTP-Version even when it doesn't comply with the given minor
904   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
905   performed unless triggered by specific client attributes, such as when
906   one or more of the request header fields (e.g., User-Agent) uniquely
907   match the values sent by a client known to be in error.
910   The intention of HTTP's versioning design is that the major number
911   will only be incremented if an incompatible message syntax is
912   introduced, and that the minor number will only be incremented when
913   changes made to the protocol have the effect of adding to the message
914   semantics or implying additional capabilities of the sender.  However,
915   the minor version was not incremented for the changes introduced between
916   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
917   is specifically avoiding any such changes to the protocol.
921<section title="Uniform Resource Identifiers" anchor="uri">
922<iref primary="true" item="resource"/>
924   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
925   throughout HTTP as the means for identifying resources. URI references
926   are used to target requests, indicate redirects, and define relationships.
927   HTTP does not limit what a resource might be; it merely defines an interface
928   that can be used to interact with a resource via HTTP. More information on
929   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
931  <x:anchor-alias value="URI-reference"/>
932  <x:anchor-alias value="absolute-URI"/>
933  <x:anchor-alias value="relative-part"/>
934  <x:anchor-alias value="authority"/>
935  <x:anchor-alias value="path-abempty"/>
936  <x:anchor-alias value="path-absolute"/>
937  <x:anchor-alias value="port"/>
938  <x:anchor-alias value="query"/>
939  <x:anchor-alias value="uri-host"/>
940  <x:anchor-alias value="partial-URI"/>
942   This specification adopts the definitions of "URI-reference",
943   "absolute-URI", "relative-part", "port", "host",
944   "path-abempty", "path-absolute", "query", and "authority" from the
945   URI generic syntax <xref target="RFC3986"/>.
946   In addition, we define a partial-URI rule for protocol elements
947   that allow a relative URI but not a fragment.
949<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"/>
950  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
951  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
952  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
953  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
954  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
955  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
956  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
957  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
958  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
960  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
963   Each protocol element in HTTP that allows a URI reference will indicate
964   in its ABNF production whether the element allows any form of reference
965   (URI-reference), only a URI in absolute form (absolute-URI), only the
966   path and optional query components, or some combination of the above.
967   Unless otherwise indicated, URI references are parsed relative to the
968   effective request URI, which defines the default base URI for references
969   in both the request and its corresponding response.
972<section title="http URI scheme" anchor="http.uri">
973  <x:anchor-alias value="http-URI"/>
974  <iref item="http URI scheme" primary="true"/>
975  <iref item="URI scheme" subitem="http" primary="true"/>
977   The "http" URI scheme is hereby defined for the purpose of minting
978   identifiers according to their association with the hierarchical
979   namespace governed by a potential HTTP origin server listening for
980   TCP connections on a given port.
982<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
983  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
986   The HTTP origin server is identified by the generic syntax's
987   <x:ref>authority</x:ref> component, which includes a host identifier
988   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
989   The remainder of the URI, consisting of both the hierarchical path
990   component and optional query component, serves as an identifier for
991   a potential resource within that origin server's name space.
994   If the host identifier is provided as an IP literal or IPv4 address,
995   then the origin server is any listener on the indicated TCP port at
996   that IP address. If host is a registered name, then that name is
997   considered an indirect identifier and the recipient might use a name
998   resolution service, such as DNS, to find the address of a listener
999   for that host.
1000   The host &MUST-NOT; be empty; if an "http" URI is received with an
1001   empty host, then it &MUST; be rejected as invalid.
1002   If the port subcomponent is empty or not given, then TCP port 80 is
1003   assumed (the default reserved port for WWW services).
1006   Regardless of the form of host identifier, access to that host is not
1007   implied by the mere presence of its name or address. The host might or might
1008   not exist and, even when it does exist, might or might not be running an
1009   HTTP server or listening to the indicated port. The "http" URI scheme
1010   makes use of the delegated nature of Internet names and addresses to
1011   establish a naming authority (whatever entity has the ability to place
1012   an HTTP server at that Internet name or address) and allows that
1013   authority to determine which names are valid and how they might be used.
1016   When an "http" URI is used within a context that calls for access to the
1017   indicated resource, a client &MAY; attempt access by resolving
1018   the host to an IP address, establishing a TCP connection to that address
1019   on the indicated port, and sending an HTTP request message to the server
1020   containing the URI's identifying data as described in <xref target="request"/>.
1021   If the server responds to that request with a non-interim HTTP response
1022   message, as described in <xref target="response"/>, then that response
1023   is considered an authoritative answer to the client's request.
1026   Although HTTP is independent of the transport protocol, the "http"
1027   scheme is specific to TCP-based services because the name delegation
1028   process depends on TCP for establishing authority.
1029   An HTTP service based on some other underlying connection protocol
1030   would presumably be identified using a different URI scheme, just as
1031   the "https" scheme (below) is used for servers that require an SSL/TLS
1032   transport layer on a connection. Other protocols might also be used to
1033   provide access to "http" identified resources &mdash; it is only the
1034   authoritative interface used for mapping the namespace that is
1035   specific to TCP.
1038   The URI generic syntax for authority also includes a deprecated
1039   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1040   for including user authentication information in the URI.  Some
1041   implementations make use of the userinfo component for internal
1042   configuration of authentication information, such as within command
1043   invocation options, configuration files, or bookmark lists, even
1044   though such usage might expose a user identifier or password.
1045   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1046   delimiter) when transmitting an "http" URI in a message.  Recipients
1047   of HTTP messages that contain a URI reference &SHOULD; parse for the
1048   existence of userinfo and treat its presence as an error, likely
1049   indicating that the deprecated subcomponent is being used to obscure
1050   the authority for the sake of phishing attacks.
1054<section title="https URI scheme" anchor="https.uri">
1055   <x:anchor-alias value="https-URI"/>
1056   <iref item="https URI scheme"/>
1057   <iref item="URI scheme" subitem="https"/>
1059   The "https" URI scheme is hereby defined for the purpose of minting
1060   identifiers according to their association with the hierarchical
1061   namespace governed by a potential HTTP origin server listening for
1062   SSL/TLS-secured connections on a given TCP port.
1065   All of the requirements listed above for the "http" scheme are also
1066   requirements for the "https" scheme, except that a default TCP port
1067   of 443 is assumed if the port subcomponent is empty or not given,
1068   and the TCP connection &MUST; be secured for privacy through the
1069   use of strong encryption prior to sending the first HTTP request.
1071<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1072  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1075   Unlike the "http" scheme, responses to "https" identified requests
1076   are never "public" and thus &MUST-NOT; be reused for shared caching.
1077   They can, however, be reused in a private cache if the message is
1078   cacheable by default in HTTP or specifically indicated as such by
1079   the Cache-Control header field (&header-cache-control;).
1082   Resources made available via the "https" scheme have no shared
1083   identity with the "http" scheme even if their resource identifiers
1084   indicate the same authority (the same host listening to the same
1085   TCP port).  They are distinct name spaces and are considered to be
1086   distinct origin servers.  However, an extension to HTTP that is
1087   defined to apply to entire host domains, such as the Cookie protocol
1088   <xref target="draft-ietf-httpstate-cookie"/>, can allow information
1089   set by one service to impact communication with other services
1090   within a matching group of host domains.
1093   The process for authoritative access to an "https" identified
1094   resource is defined in <xref target="RFC2818"/>.
1098<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1100   Since the "http" and "https" schemes conform to the URI generic syntax,
1101   such URIs are normalized and compared according to the algorithm defined
1102   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1103   described above for each scheme.
1106   If the port is equal to the default port for a scheme, the normal
1107   form is to elide the port subcomponent. Likewise, an empty path
1108   component is equivalent to an absolute path of "/", so the normal
1109   form is to provide a path of "/" instead. The scheme and host
1110   are case-insensitive and normally provided in lowercase; all
1111   other components are compared in a case-sensitive manner.
1112   Characters other than those in the "reserved" set are equivalent
1113   to their percent-encoded octets (see <xref target="RFC3986"
1114   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1117   For example, the following three URIs are equivalent:
1119<figure><artwork type="example">
1128<section title="HTTP Message" anchor="http.message">
1129<x:anchor-alias value="generic-message"/>
1130<x:anchor-alias value="message.types"/>
1131<x:anchor-alias value="HTTP-message"/>
1132<x:anchor-alias value="start-line"/>
1133<iref item="header section"/>
1134<iref item="headers"/>
1135<iref item="header field"/>
1137   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1138   characters in a format similar to the Internet Message Format
1139   <xref target="RFC5322"/>: zero or more header fields (collectively
1140   referred to as the "headers" or the "header section"), an empty line
1141   indicating the end of the header section, and an optional message-body.
1144   An HTTP message can either be a request from client to server or a
1145   response from server to client.  Syntactically, the two types of message
1146   differ only in the start-line, which is either a Request-Line (for requests)
1147   or a Status-Line (for responses), and in the algorithm for determining
1148   the length of the message-body (<xref target="message.body"/>).
1149   In theory, a client could receive requests and a server could receive
1150   responses, distinguishing them by their different start-line formats,
1151   but in practice servers are implemented to only expect a request
1152   (a response is interpreted as an unknown or invalid request method)
1153   and clients are implemented to only expect a response.
1155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1156  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1157                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1158                    <x:ref>CRLF</x:ref>
1159                    [ <x:ref>message-body</x:ref> ]
1160  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1163   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1164   header field. The presence of whitespace might be an attempt to trick a
1165   noncompliant implementation of HTTP into ignoring that field or processing
1166   the next line as a new request, either of which might result in security
1167   issues when implementations within the request chain interpret the
1168   same message differently. HTTP/1.1 servers &MUST; reject such a message
1169   with a 400 (Bad Request) response.
1172<section title="Message Parsing Robustness" anchor="message.robustness">
1174   In the interest of robustness, servers &SHOULD; ignore at least one
1175   empty line received where a Request-Line is expected. In other words, if
1176   the server is reading the protocol stream at the beginning of a
1177   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1180   Some old HTTP/1.0 client implementations generate an extra CRLF
1181   after a POST request as a lame workaround for some early server
1182   applications that failed to read message-body content that was
1183   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1184   preface or follow a request with an extra CRLF.  If terminating
1185   the request message-body with a line-ending is desired, then the
1186   client &MUST; include the terminating CRLF octets as part of the
1187   message-body length.
1190   The normal procedure for parsing an HTTP message is to read the
1191   start-line into a structure, read each header field into a hash
1192   table by field name until the empty line, and then use the parsed
1193   data to determine if a message-body is expected.  If a message-body
1194   has been indicated, then it is read as a stream until an amount
1195   of octets equal to the message-body length is read or the connection
1196   is closed.  Care must be taken to parse an HTTP message as a sequence
1197   of octets in an encoding that is a superset of US-ASCII.  Attempting
1198   to parse HTTP as a stream of Unicode characters in a character encoding
1199   like UTF-16 might introduce security flaws due to the differing ways
1200   that such parsers interpret invalid characters.
1203   HTTP allows the set of defined header fields to be extended without
1204   changing the protocol version (see <xref target="header.field.registration"/>).
1205   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1206   proxy is specifically configured to block or otherwise transform such
1207   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1211<section title="Header Fields" anchor="header.fields">
1212  <x:anchor-alias value="header-field"/>
1213  <x:anchor-alias value="field-content"/>
1214  <x:anchor-alias value="field-name"/>
1215  <x:anchor-alias value="field-value"/>
1216  <x:anchor-alias value="OWS"/>
1218   Each HTTP header field consists of a case-insensitive field name
1219   followed by a colon (":"), optional whitespace, and the field value.
1221<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"/>
1222  <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>OWS</x:ref>
1223  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1224  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1225  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1228   No whitespace is allowed between the header field name and colon. For
1229   security reasons, any request message received containing such whitespace
1230   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1231   &MUST; remove any such whitespace from a response message before
1232   forwarding the message downstream.
1235   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1236   preferred. The field value does not include any leading or trailing white
1237   space: OWS occurring before the first non-whitespace character of the
1238   field value or after the last non-whitespace character of the field value
1239   is ignored and &SHOULD; be removed before further processing (as this does
1240   not change the meaning of the header field).
1243   The order in which header fields with differing field names are
1244   received is not significant. However, it is "good practice" to send
1245   header fields that contain control data first, such as Host on
1246   requests and Date on responses, so that implementations can decide
1247   when not to handle a message as early as possible.  A server &MUST;
1248   wait until the entire header section is received before interpreting
1249   a request message, since later header fields might include conditionals,
1250   authentication credentials, or deliberately misleading duplicate
1251   header fields that would impact request processing.
1254   Multiple header fields with the same field name &MUST-NOT; be
1255   sent in a message unless the entire field value for that
1256   header field is defined as a comma-separated list [i.e., #(values)].
1257   Multiple header fields with the same field name can be combined into
1258   one "field-name: field-value" pair, without changing the semantics of the
1259   message, by appending each subsequent field value to the combined
1260   field value in order, separated by a comma. The order in which
1261   header fields with the same field name are received is therefore
1262   significant to the interpretation of the combined field value;
1263   a proxy &MUST-NOT; change the order of these field values when
1264   forwarding a message.
1267  <t>
1268   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1269   practice can occur multiple times, but does not use the list syntax, and
1270   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1271   for details.) Also note that the Set-Cookie2 header field specified in
1272   <xref target="RFC2965"/> does not share this problem.
1273  </t>
1276   Historically, HTTP header field values could be extended over multiple
1277   lines by preceding each extra line with at least one space or horizontal
1278   tab character (line folding). This specification deprecates such line
1279   folding except within the message/http media type
1280   (<xref target=""/>).
1281   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1282   (i.e., that contain any field-content that matches the obs-fold rule) unless
1283   the message is intended for packaging within the message/http media type.
1284   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1285   obs-fold whitespace with a single SP prior to interpreting the field value
1286   or forwarding the message downstream.
1289   Historically, HTTP has allowed field content with text in the ISO-8859-1
1290   <xref target="ISO-8859-1"/> character encoding and supported other
1291   character sets only through use of <xref target="RFC2047"/> encoding.
1292   In practice, most HTTP header field values use only a subset of the
1293   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1294   header fields &SHOULD; limit their field values to US-ASCII characters.
1295   Recipients &SHOULD; treat other (obs-text) octets in field content as
1296   opaque data.
1298<t anchor="rule.comment">
1299  <x:anchor-alias value="comment"/>
1300  <x:anchor-alias value="ctext"/>
1301   Comments can be included in some HTTP header fields by surrounding
1302   the comment text with parentheses. Comments are only allowed in
1303   fields containing "comment" as part of their field value definition.
1305<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1306  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1307  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1308                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1310<t anchor="rule.quoted-cpair">
1311  <x:anchor-alias value="quoted-cpair"/>
1312   The backslash character ("\") can be used as a single-character
1313   quoting mechanism within comment constructs:
1315<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1316  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1319   Producers &SHOULD-NOT; escape characters that do not require escaping
1320   (i.e., other than the backslash character "\" and the parentheses "(" and
1321   ")").
1325<section title="Message Body" anchor="message.body">
1326  <x:anchor-alias value="message-body"/>
1328   The message-body (if any) of an HTTP message is used to carry the
1329   payload body associated with the request or response.
1331<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1332  <x:ref>message-body</x:ref> = *OCTET
1335   The message-body differs from the payload body only when a transfer-coding
1336   has been applied, as indicated by the Transfer-Encoding header field
1337   (<xref target="header.transfer-encoding"/>).  If more than one
1338   Transfer-Encoding header field is present in a message, the multiple
1339   field-values &MUST; be combined into one field-value, according to the
1340   algorithm defined in <xref target="header.fields"/>, before determining
1341   the message-body length.
1344   When one or more transfer-codings are applied to a payload in order to
1345   form the message-body, the Transfer-Encoding header field &MUST; contain
1346   the list of transfer-codings applied. Transfer-Encoding is a property of
1347   the message, not of the payload, and thus &MAY; be added or removed by
1348   any implementation along the request/response chain under the constraints
1349   found in <xref target="transfer.codings"/>.
1352   If a message is received that has multiple Content-Length header fields
1353   (<xref target="header.content-length"/>) with field-values consisting
1354   of the same decimal value, or a single Content-Length header field with
1355   a field value containing a list of identical decimal values (e.g.,
1356   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1357   header fields have been generated or combined by an upstream message
1358   processor, then the recipient &MUST; replace the duplicated fields or
1359   field-values with a single valid Content-Length field containing that
1360   decimal value prior to determining the message-body length.
1363   The rules for when a message-body is allowed in a message differ for
1364   requests and responses.
1367   The presence of a message-body in a request is signaled by the
1368   inclusion of a Content-Length or Transfer-Encoding header field in
1369   the request's header fields, even if the request method does not
1370   define any use for a message-body.  This allows the request
1371   message framing algorithm to be independent of method semantics.
1374   For response messages, whether or not a message-body is included with
1375   a message is dependent on both the request method and the response
1376   status code (<xref target="status.code.and.reason.phrase"/>).
1377   Responses to the HEAD request method never include a message-body
1378   because the associated response header fields (e.g., Transfer-Encoding,
1379   Content-Length, etc.) only indicate what their values would have been
1380   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1381   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1382   All other responses do include a message-body, although the body
1383   &MAY; be of zero length.
1386   The length of the message-body is determined by one of the following
1387   (in order of precedence):
1390  <list style="numbers">
1391    <x:lt><t>
1392     Any response to a HEAD request and any response with a status
1393     code of 100-199, 204, or 304 is always terminated by the first
1394     empty line after the header fields, regardless of the header
1395     fields present in the message, and thus cannot contain a message-body.
1396    </t></x:lt>
1397    <x:lt><t>
1398     If a Transfer-Encoding header field is present
1399     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1400     is the final encoding, the message-body length is determined by reading
1401     and decoding the chunked data until the transfer-coding indicates the
1402     data is complete.
1403    </t>
1404    <t>
1405     If a Transfer-Encoding header field is present in a response and the
1406     "chunked" transfer-coding is not the final encoding, the message-body
1407     length is determined by reading the connection until it is closed by
1408     the server.
1409     If a Transfer-Encoding header field is present in a request and the
1410     "chunked" transfer-coding is not the final encoding, the message-body
1411     length cannot be determined reliably; the server &MUST; respond with
1412     the 400 (Bad Request) status code and then close the connection.
1413    </t>
1414    <t>
1415     If a message is received with both a Transfer-Encoding header field
1416     and a Content-Length header field, the Transfer-Encoding overrides
1417     the Content-Length.
1418     Such a message might indicate an attempt to perform request or response
1419     smuggling (bypass of security-related checks on message routing or content)
1420     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1421     be removed, prior to forwarding the message downstream, or replaced with
1422     the real message-body length after the transfer-coding is decoded.
1423    </t></x:lt>
1424    <x:lt><t>
1425     If a message is received without Transfer-Encoding and with either
1426     multiple Content-Length header fields having differing field-values or
1427     a single Content-Length header field having an invalid value, then the
1428     message framing is invalid and &MUST; be treated as an error to
1429     prevent request or response smuggling.
1430     If this is a request message, the server &MUST; respond with
1431     a 400 (Bad Request) status code and then close the connection.
1432     If this is a response message received by a proxy or gateway, the proxy
1433     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1434     status code as its downstream response, and then close the connection.
1435     If this is a response message received by a user-agent, it &MUST; be
1436     treated as an error by discarding the message and closing the connection.
1437    </t></x:lt>
1438    <x:lt><t>
1439     If a valid Content-Length header field
1440     is present without Transfer-Encoding, its decimal value defines the
1441     message-body length in octets.  If the actual number of octets sent in
1442     the message is less than the indicated Content-Length, the recipient
1443     &MUST; consider the message to be incomplete and treat the connection
1444     as no longer usable.
1445     If the actual number of octets sent in the message is more than the indicated
1446     Content-Length, the recipient &MUST; only process the message-body up to the
1447     field value's number of octets; the remainder of the message &MUST; either
1448     be discarded or treated as the next message in a pipeline.  For the sake of
1449     robustness, a user-agent &MAY; attempt to detect and correct such an error
1450     in message framing if it is parsing the response to the last request on
1451     on a connection and the connection has been closed by the server.
1452    </t></x:lt>
1453    <x:lt><t>
1454     If this is a request message and none of the above are true, then the
1455     message-body length is zero (no message-body is present).
1456    </t></x:lt>
1457    <x:lt><t>
1458     Otherwise, this is a response message without a declared message-body
1459     length, so the message-body length is determined by the number of octets
1460     received prior to the server closing the connection.
1461    </t></x:lt>
1462  </list>
1465   Since there is no way to distinguish a successfully completed,
1466   close-delimited message from a partially-received message interrupted
1467   by network failure, implementations &SHOULD; use encoding or
1468   length-delimited messages whenever possible.  The close-delimiting
1469   feature exists primarily for backwards compatibility with HTTP/1.0.
1472   A server &MAY; reject a request that contains a message-body but
1473   not a Content-Length by responding with 411 (Length Required).
1476   Unless a transfer-coding other than "chunked" has been applied,
1477   a client that sends a request containing a message-body &SHOULD;
1478   use a valid Content-Length header field if the message-body length
1479   is known in advance, rather than the "chunked" encoding, since some
1480   existing services respond to "chunked" with a 411 (Length Required)
1481   status code even though they understand the chunked encoding.  This
1482   is typically because such services are implemented via a gateway that
1483   requires a content-length in advance of being called and the server
1484   is unable or unwilling to buffer the entire request before processing.
1487   A client that sends a request containing a message-body &MUST; include a
1488   valid Content-Length header field if it does not know the server will
1489   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1490   of specific user configuration or by remembering the version of a prior
1491   received response.
1494   Request messages that are prematurely terminated, possibly due to a
1495   cancelled connection or a server-imposed time-out exception, &MUST;
1496   result in closure of the connection; sending an HTTP/1.1 error response
1497   prior to closing the connection is &OPTIONAL;.
1498   Response messages that are prematurely terminated, usually by closure
1499   of the connection prior to receiving the expected number of octets or by
1500   failure to decode a transfer-encoded message-body, &MUST; be recorded
1501   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1502   message-body as if it were complete (i.e., some indication must be given
1503   to the user that an error occurred).  Cache requirements for incomplete
1504   responses are defined in &cache-incomplete;.
1507   A server &MUST; read the entire request message-body or close
1508   the connection after sending its response, since otherwise the
1509   remaining data on a persistent connection would be misinterpreted
1510   as the next request.  Likewise,
1511   a client &MUST; read the entire response message-body if it intends
1512   to reuse the same connection for a subsequent request.  Pipelining
1513   multiple requests on a connection is described in <xref target="pipelining"/>.
1517<section title="General Header Fields" anchor="general.header.fields">
1518  <x:anchor-alias value="general-header"/>
1520   There are a few header fields which have general applicability for
1521   both request and response messages, but which do not apply to the
1522   payload being transferred. These header fields apply only to the
1523   message being transmitted.
1525<texttable align="left">
1526  <ttcol>Header Field Name</ttcol>
1527  <ttcol>Defined in...</ttcol>
1529  <c>Connection</c> <c><xref target="header.connection"/></c>
1530  <c>Date</c> <c><xref target=""/></c>
1531  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1532  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1533  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1534  <c>Via</c> <c><xref target="header.via"/></c>
1539<section title="Request" anchor="request">
1540  <x:anchor-alias value="Request"/>
1542   A request message from a client to a server includes, within the
1543   first line of that message, the method to be applied to the resource,
1544   the identifier of the resource, and the protocol version in use.
1546<!--                 Host                      ; should be moved here eventually -->
1547<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1548  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1549                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1550                  <x:ref>CRLF</x:ref>
1551                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1554<section title="Request-Line" anchor="request-line">
1555  <x:anchor-alias value="Request-Line"/>
1557   The Request-Line begins with a method token, followed by the
1558   request-target and the protocol version, and ending with CRLF. The
1559   elements are separated by SP characters. No CR or LF is allowed
1560   except in the final CRLF sequence.
1562<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1563  <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>
1566<section title="Method" anchor="method">
1567  <x:anchor-alias value="Method"/>
1569   The Method token indicates the request method to be performed on the
1570   target resource. The request method is case-sensitive.
1572<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1573  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1577<section title="request-target" anchor="request-target">
1578  <x:anchor-alias value="request-target"/>
1580   The request-target identifies the target resource upon which to apply
1581   the request.  In most cases, the user agent is provided a URI reference
1582   from which it determines an absolute URI for identifying the target
1583   resource.  When a request to the resource is initiated, all or part
1584   of that URI is used to construct the HTTP request-target.
1586<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1587  <x:ref>request-target</x:ref> = "*"
1588                 / <x:ref>absolute-URI</x:ref>
1589                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1590                 / <x:ref>authority</x:ref>
1593   The four options for request-target are dependent on the nature of the
1594   request.
1596<t><iref item="asterisk form (of request-target)"/>
1597   The asterisk "*" form of request-target, which &MUST-NOT; be used
1598   with any request method other than OPTIONS, means that the request
1599   applies to the server as a whole (the listening process) rather than
1600   to a specific named resource at that server.  For example,
1602<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1603OPTIONS * HTTP/1.1
1605<t><iref item="absolute-URI form (of request-target)"/>
1606   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1607   proxy. The proxy is requested to either forward the request or service it
1608   from a valid cache, and then return the response. Note that the proxy &MAY;
1609   forward the request on to another proxy or directly to the server
1610   specified by the absolute-URI. In order to avoid request loops, a
1611   proxy that forwards requests to other proxies &MUST; be able to
1612   recognize and exclude all of its own server names, including
1613   any aliases, local variations, and the numeric IP address. An example
1614   Request-Line would be:
1616<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1617GET HTTP/1.1
1620   To allow for transition to absolute-URIs in all requests in future
1621   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1622   form in requests, even though HTTP/1.1 clients will only generate
1623   them in requests to proxies.
1626   If a proxy receives a host name that is not a fully qualified domain
1627   name, it &MAY; add its domain to the host name it received. If a proxy
1628   receives a fully qualified domain name, the proxy &MUST-NOT; change
1629   the host name.
1631<t><iref item="authority form (of request-target)"/>
1632   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1634<t><iref item="origin form (of request-target)"/>
1635   The most common form of request-target is that used when making
1636   a request to an origin server or gateway ("origin form").
1637   In this case, the absolute path and query components of the URI
1638   &MUST; be transmitted as the request-target, and the authority component
1639   &MUST; be transmitted in a Host header field. For example, a client wishing
1640   to retrieve a representation of the resource, as identified above,
1641   directly from the origin server would open (or reuse) a TCP connection
1642   to port 80 of the host "" and send the lines:
1644<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1645GET /pub/WWW/TheProject.html HTTP/1.1
1649   followed by the remainder of the Request. Note that the origin form
1650   of request-target always starts with an absolute path; if the target
1651   resource's URI path is empty, then an absolute path of "/" &MUST; be
1652   provided in the request-target.
1655   If a proxy receives an OPTIONS request with an absolute-URI form of
1656   request-target in which the URI has an empty path and no query component,
1657   then the last proxy on the request chain &MUST; use a request-target
1658   of "*" when it forwards the request to the indicated origin server.
1661   For example, the request
1662</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1666  would be forwarded by the final proxy as
1667</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1668OPTIONS * HTTP/1.1
1672   after connecting to port 8001 of host "".
1676   The request-target is transmitted in the format specified in
1677   <xref target="http.uri"/>. If the request-target is percent-encoded
1678   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1679   &MUST; decode the request-target in order to
1680   properly interpret the request. Servers &SHOULD; respond to invalid
1681   request-targets with an appropriate status code.
1684   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1685   received request-target when forwarding it to the next inbound server,
1686   except as noted above to replace a null path-absolute with "/" or "*".
1689  <t>
1690    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1691    meaning of the request when the origin server is improperly using
1692    a non-reserved URI character for a reserved purpose.  Implementors
1693    need to be aware that some pre-HTTP/1.1 proxies have been known to
1694    rewrite the request-target.
1695  </t>
1698   HTTP does not place a pre-defined limit on the length of a request-target.
1699   A server &MUST; be prepared to receive URIs of unbounded length and
1700   respond with the 414 (URI Too Long) status code if the received
1701   request-target would be longer than the server wishes to handle
1702   (see &status-414;).
1705   Various ad-hoc limitations on request-target length are found in practice.
1706   It is &RECOMMENDED; that all HTTP senders and recipients support
1707   request-target lengths of 8000 or more octets.
1710  <t>
1711    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1712    are not part of the request-target and thus will not be transmitted
1713    in an HTTP request.
1714  </t>
1719<section title="The Resource Identified by a Request" anchor="">
1721   The exact resource identified by an Internet request is determined by
1722   examining both the request-target and the Host header field.
1725   An origin server that does not allow resources to differ by the
1726   requested host &MAY; ignore the Host header field value when
1727   determining the resource identified by an HTTP/1.1 request. (But see
1728   <xref target=""/>
1729   for other requirements on Host support in HTTP/1.1.)
1732   An origin server that does differentiate resources based on the host
1733   requested (sometimes referred to as virtual hosts or vanity host
1734   names) &MUST; use the following rules for determining the requested
1735   resource on an HTTP/1.1 request:
1736  <list style="numbers">
1737    <t>If request-target is an absolute-URI, the host is part of the
1738     request-target. Any Host header field value in the request &MUST; be
1739     ignored.</t>
1740    <t>If the request-target is not an absolute-URI, and the request includes
1741     a Host header field, the host is determined by the Host header
1742     field value.</t>
1743    <t>If the host as determined by rule 1 or 2 is not a valid host on
1744     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1745  </list>
1748   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1749   attempt to use heuristics (e.g., examination of the URI path for
1750   something unique to a particular host) in order to determine what
1751   exact resource is being requested.
1755<section title="Effective Request URI" anchor="effective.request.uri">
1756  <iref primary="true" item="effective request URI"/>
1757  <iref primary="true" item="target resource"/>
1759   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1760   for the target resource; instead, the URI needs to be inferred from the
1761   request-target, Host header field, and connection context. The result of
1762   this process is called the "effective request URI".  The "target resource"
1763   is the resource identified by the effective request URI.
1766   If the request-target is an absolute-URI, then the effective request URI is
1767   the request-target.
1770   If the request-target uses the path-absolute form or the asterisk form,
1771   and the Host header field is present, then the effective request URI is
1772   constructed by concatenating
1775  <list style="symbols">
1776    <t>
1777      the scheme name: "http" if the request was received over an insecure
1778      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1779      connection,
1780    </t>
1781    <t>
1782      the character sequence "://",
1783    </t>
1784    <t>
1785      the authority component, as specified in the Host header field
1786      (<xref target=""/>), and
1787    </t>
1788    <t>
1789      the request-target obtained from the Request-Line, unless the
1790      request-target is just the asterisk "*".
1791    </t>
1792  </list>
1795   If the request-target uses the path-absolute form or the asterisk form,
1796   and the Host header field is not present, then the effective request URI is
1797   undefined.
1800   Otherwise, when request-target uses the authority form, the effective
1801   request URI is undefined.
1805   Example 1: the effective request URI for the message
1807<artwork type="example" x:indent-with="  ">
1808GET /pub/WWW/TheProject.html HTTP/1.1
1812  (received over an insecure TCP connection) is "http", plus "://", plus the
1813  authority component "", plus the request-target
1814  "/pub/WWW/TheProject.html", thus
1815  "".
1820   Example 2: the effective request URI for the message
1822<artwork type="example" x:indent-with="  ">
1823GET * HTTP/1.1
1827  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1828  authority component "", thus "".
1832   Effective request URIs are compared using the rules described in
1833   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1834   be treated as equivalent to an absolute path of "/".
1841<section title="Response" anchor="response">
1842  <x:anchor-alias value="Response"/>
1844   After receiving and interpreting a request message, a server responds
1845   with an HTTP response message.
1847<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1848  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1849                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1850                  <x:ref>CRLF</x:ref>
1851                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1854<section title="Status-Line" anchor="status-line">
1855  <x:anchor-alias value="Status-Line"/>
1857   The first line of a Response message is the Status-Line, consisting
1858   of the protocol version followed by a numeric status code and its
1859   associated textual phrase, with each element separated by SP
1860   characters. No CR or LF is allowed except in the final CRLF sequence.
1862<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1863  <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>
1866<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1867  <x:anchor-alias value="Reason-Phrase"/>
1868  <x:anchor-alias value="Status-Code"/>
1870   The Status-Code element is a 3-digit integer result code of the
1871   attempt to understand and satisfy the request. These codes are fully
1872   defined in &status-codes;.  The Reason Phrase exists for the sole
1873   purpose of providing a textual description associated with the numeric
1874   status code, out of deference to earlier Internet application protocols
1875   that were more frequently used with interactive text clients.
1876   A client &SHOULD; ignore the content of the Reason Phrase.
1879   The first digit of the Status-Code defines the class of response. The
1880   last two digits do not have any categorization role. There are 5
1881   values for the first digit:
1882  <list style="symbols">
1883    <t>
1884      1xx: Informational - Request received, continuing process
1885    </t>
1886    <t>
1887      2xx: Success - The action was successfully received,
1888        understood, and accepted
1889    </t>
1890    <t>
1891      3xx: Redirection - Further action must be taken in order to
1892        complete the request
1893    </t>
1894    <t>
1895      4xx: Client Error - The request contains bad syntax or cannot
1896        be fulfilled
1897    </t>
1898    <t>
1899      5xx: Server Error - The server failed to fulfill an apparently
1900        valid request
1901    </t>
1902  </list>
1904<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1905  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1906  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1914<section title="Protocol Parameters" anchor="protocol.parameters">
1916<section title="Date/Time Formats: Full Date" anchor="">
1917  <x:anchor-alias value="HTTP-date"/>
1919   HTTP applications have historically allowed three different formats
1920   for date/time stamps. However, the preferred format is a fixed-length subset
1921   of that defined by <xref target="RFC1123"/>:
1923<figure><artwork type="example" x:indent-with="  ">
1924Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1927   The other formats are described here only for compatibility with obsolete
1928   implementations.
1930<figure><artwork type="example" x:indent-with="  ">
1931Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1932Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1935   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1936   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1937   only generate the RFC 1123 format for representing HTTP-date values
1938   in header fields. See <xref target="tolerant.applications"/> for further information.
1941   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1942   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1943   equal to UTC (Coordinated Universal Time). This is indicated in the
1944   first two formats by the inclusion of "GMT" as the three-letter
1945   abbreviation for time zone, and &MUST; be assumed when reading the
1946   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1947   additional whitespace beyond that specifically included as SP in the
1948   grammar.
1950<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1951  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1953<t anchor="">
1954  <x:anchor-alias value="rfc1123-date"/>
1955  <x:anchor-alias value="time-of-day"/>
1956  <x:anchor-alias value="hour"/>
1957  <x:anchor-alias value="minute"/>
1958  <x:anchor-alias value="second"/>
1959  <x:anchor-alias value="day-name"/>
1960  <x:anchor-alias value="day"/>
1961  <x:anchor-alias value="month"/>
1962  <x:anchor-alias value="year"/>
1963  <x:anchor-alias value="GMT"/>
1964  Preferred format:
1966<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
1967  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
1968  ; fixed length subset of the format defined in
1969  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1971  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1972               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1973               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1974               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1975               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1976               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1977               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1979  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
1980               ; e.g., 02 Jun 1982
1982  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1983  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1984               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1985               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1986               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1987               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1988               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1989               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1990               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1991               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1992               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1993               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1994               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1995  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1997  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1999  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2000                 ; 00:00:00 - 23:59:59
2002  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2003  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2004  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2007  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2008  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2009  same as those defined for the RFC 5322 constructs
2010  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2012<t anchor="">
2013  <x:anchor-alias value="obs-date"/>
2014  <x:anchor-alias value="rfc850-date"/>
2015  <x:anchor-alias value="asctime-date"/>
2016  <x:anchor-alias value="date1"/>
2017  <x:anchor-alias value="date2"/>
2018  <x:anchor-alias value="date3"/>
2019  <x:anchor-alias value="rfc1123-date"/>
2020  <x:anchor-alias value="day-name-l"/>
2021  Obsolete formats:
2023<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2024  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2026<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2027  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2028  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2029                 ; day-month-year (e.g., 02-Jun-82)
2031  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2032         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2033         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2034         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2035         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2036         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2037         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2039<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2040  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2041  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
2042                 ; month day (e.g., Jun  2)
2045  <t>
2046    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2047    accepting date values that might have been sent by non-HTTP
2048    applications, as is sometimes the case when retrieving or posting
2049    messages via proxies/gateways to SMTP or NNTP.
2050  </t>
2053  <t>
2054    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2055    to their usage within the protocol stream. Clients and servers are
2056    not required to use these formats for user presentation, request
2057    logging, etc.
2058  </t>
2062<section title="Transfer Codings" anchor="transfer.codings">
2063  <x:anchor-alias value="transfer-coding"/>
2064  <x:anchor-alias value="transfer-extension"/>
2066   Transfer-coding values are used to indicate an encoding
2067   transformation that has been, can be, or might need to be applied to a
2068   payload body in order to ensure "safe transport" through the network.
2069   This differs from a content coding in that the transfer-coding is a
2070   property of the message rather than a property of the representation
2071   that is being transferred.
2073<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2074  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2075                          / "compress" ; <xref target="compress.coding"/>
2076                          / "deflate" ; <xref target="deflate.coding"/>
2077                          / "gzip" ; <xref target="gzip.coding"/>
2078                          / <x:ref>transfer-extension</x:ref>
2079  <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> )
2081<t anchor="rule.parameter">
2082  <x:anchor-alias value="attribute"/>
2083  <x:anchor-alias value="transfer-parameter"/>
2084  <x:anchor-alias value="value"/>
2085   Parameters are in the form of attribute/value pairs.
2087<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"/>
2088  <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>
2089  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2090  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2093   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2094   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2095   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2098   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2099   MIME, which were designed to enable safe transport of binary data over a
2100   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2101   However, safe transport
2102   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2103   the only unsafe characteristic of message-bodies is the difficulty in
2104   determining the exact message body length (<xref target="message.body"/>),
2105   or the desire to encrypt data over a shared transport.
2108   A server that receives a request message with a transfer-coding it does
2109   not understand &SHOULD; respond with 501 (Not Implemented) and then
2110   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2111   client.
2114<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2115  <iref item="chunked (Coding Format)"/>
2116  <iref item="Coding Format" subitem="chunked"/>
2117  <x:anchor-alias value="chunk"/>
2118  <x:anchor-alias value="Chunked-Body"/>
2119  <x:anchor-alias value="chunk-data"/>
2120  <x:anchor-alias value="chunk-ext"/>
2121  <x:anchor-alias value="chunk-ext-name"/>
2122  <x:anchor-alias value="chunk-ext-val"/>
2123  <x:anchor-alias value="chunk-size"/>
2124  <x:anchor-alias value="last-chunk"/>
2125  <x:anchor-alias value="trailer-part"/>
2126  <x:anchor-alias value="quoted-str-nf"/>
2127  <x:anchor-alias value="qdtext-nf"/>
2129   The chunked encoding modifies the body of a message in order to
2130   transfer it as a series of chunks, each with its own size indicator,
2131   followed by an &OPTIONAL; trailer containing header fields. This
2132   allows dynamically produced content to be transferred along with the
2133   information necessary for the recipient to verify that it has
2134   received the full message.
2136<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"/>
2137  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2138                   <x:ref>last-chunk</x:ref>
2139                   <x:ref>trailer-part</x:ref>
2140                   <x:ref>CRLF</x:ref>
2142  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2143                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2144  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2145  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2147  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2148                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2149  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2150  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2151  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2152  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2154  <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>
2155                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2156  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2157                 ; <x:ref>WSP</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
2160   The chunk-size field is a string of hex digits indicating the size of
2161   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2162   zero, followed by the trailer, which is terminated by an empty line.
2165   The trailer allows the sender to include additional HTTP header
2166   fields at the end of the message. The Trailer header field can be
2167   used to indicate which header fields are included in a trailer (see
2168   <xref target="header.trailer"/>).
2171   A server using chunked transfer-coding in a response &MUST-NOT; use the
2172   trailer for any header fields unless at least one of the following is
2173   true:
2174  <list style="numbers">
2175    <t>the request included a TE header field that indicates "trailers" is
2176     acceptable in the transfer-coding of the  response, as described in
2177     <xref target="header.te"/>; or,</t>
2179    <t>the trailer fields consist entirely of optional metadata, and the
2180    recipient could use the message (in a manner acceptable to the server where
2181    the field originated) without receiving it. In other words, the server that
2182    generated the header (often but not always the origin server) is willing to
2183    accept the possibility that the trailer fields might be silently discarded
2184    along the path to the client.</t>
2185  </list>
2188   This requirement prevents an interoperability failure when the
2189   message is being received by an HTTP/1.1 (or later) proxy and
2190   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2191   compliance with the protocol would have necessitated a possibly
2192   infinite buffer on the proxy.
2195   A process for decoding the "chunked" transfer-coding
2196   can be represented in pseudo-code as:
2198<figure><artwork type="code">
2199  length := 0
2200  read chunk-size, chunk-ext (if any) and CRLF
2201  while (chunk-size &gt; 0) {
2202     read chunk-data and CRLF
2203     append chunk-data to decoded-body
2204     length := length + chunk-size
2205     read chunk-size and CRLF
2206  }
2207  read header-field
2208  while (header-field not empty) {
2209     append header-field to existing header fields
2210     read header-field
2211  }
2212  Content-Length := length
2213  Remove "chunked" from Transfer-Encoding
2216   All HTTP/1.1 applications &MUST; be able to receive and decode the
2217   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2218   they do not understand.
2221   Since "chunked" is the only transfer-coding required to be understood
2222   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2223   on a persistent connection.  Whenever a transfer-coding is applied to
2224   a payload body in a request, the final transfer-coding applied &MUST;
2225   be "chunked".  If a transfer-coding is applied to a response payload
2226   body, then either the final transfer-coding applied &MUST; be "chunked"
2227   or the message &MUST; be terminated by closing the connection. When the
2228   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2229   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2230   be applied more than once in a message-body.
2234<section title="Compression Codings" anchor="compression.codings">
2236   The codings defined below can be used to compress the payload of a
2237   message.
2240   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2241   is not desirable and is discouraged for future encodings. Their
2242   use here is representative of historical practice, not good
2243   design.
2246   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2247   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2248   equivalent to "gzip" and "compress" respectively.
2251<section title="Compress Coding" anchor="compress.coding">
2252<iref item="compress (Coding Format)"/>
2253<iref item="Coding Format" subitem="compress"/>
2255   The "compress" format is produced by the common UNIX file compression
2256   program "compress". This format is an adaptive Lempel-Ziv-Welch
2257   coding (LZW).
2261<section title="Deflate Coding" anchor="deflate.coding">
2262<iref item="deflate (Coding Format)"/>
2263<iref item="Coding Format" subitem="deflate"/>
2265   The "deflate" format is defined as the "deflate" compression mechanism
2266   (described in <xref target="RFC1951"/>) used inside the "zlib"
2267   data format (<xref target="RFC1950"/>).
2270  <t>
2271    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2272    compressed data without the zlib wrapper.
2273   </t>
2277<section title="Gzip Coding" anchor="gzip.coding">
2278<iref item="gzip (Coding Format)"/>
2279<iref item="Coding Format" subitem="gzip"/>
2281   The "gzip" format is produced by the file compression program
2282   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2283   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2289<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2291   The HTTP Transfer Coding Registry defines the name space for the transfer
2292   coding names.
2295   Registrations &MUST; include the following fields:
2296   <list style="symbols">
2297     <t>Name</t>
2298     <t>Description</t>
2299     <t>Pointer to specification text</t>
2300   </list>
2303   Names of transfer codings &MUST-NOT; overlap with names of content codings
2304   (&content-codings;), unless the encoding transformation is identical (as it
2305   is the case for the compression codings defined in
2306   <xref target="compression.codings"/>).
2309   Values to be added to this name space require a specification
2310   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2311   conform to the purpose of transfer coding defined in this section.
2314   The registry itself is maintained at
2315   <eref target=""/>.
2320<section title="Product Tokens" anchor="product.tokens">
2321  <x:anchor-alias value="product"/>
2322  <x:anchor-alias value="product-version"/>
2324   Product tokens are used to allow communicating applications to
2325   identify themselves by software name and version. Most fields using
2326   product tokens also allow sub-products which form a significant part
2327   of the application to be listed, separated by whitespace. By
2328   convention, the products are listed in order of their significance
2329   for identifying the application.
2331<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2332  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2333  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2336   Examples:
2338<figure><artwork type="example">
2339  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2340  Server: Apache/0.8.4
2343   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2344   used for advertising or other non-essential information. Although any
2345   token character &MAY; appear in a product-version, this token &SHOULD;
2346   only be used for a version identifier (i.e., successive versions of
2347   the same product &SHOULD; only differ in the product-version portion of
2348   the product value).
2352<section title="Quality Values" anchor="quality.values">
2353  <x:anchor-alias value="qvalue"/>
2355   Both transfer codings (TE request header field, <xref target="header.te"/>)
2356   and content negotiation (&content.negotiation;) use short "floating point"
2357   numbers to indicate the relative importance ("weight") of various
2358   negotiable parameters.  A weight is normalized to a real number in
2359   the range 0 through 1, where 0 is the minimum and 1 the maximum
2360   value. If a parameter has a quality value of 0, then content with
2361   this parameter is "not acceptable" for the client. HTTP/1.1
2362   applications &MUST-NOT; generate more than three digits after the
2363   decimal point. User configuration of these values &SHOULD; also be
2364   limited in this fashion.
2366<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2367  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2368                 / ( "1" [ "." 0*3("0") ] )
2371  <t>
2372     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2373     relative degradation in desired quality.
2374  </t>
2380<section title="Connections" anchor="connections">
2382<section title="Persistent Connections" anchor="persistent.connections">
2384<section title="Purpose" anchor="persistent.purpose">
2386   Prior to persistent connections, a separate TCP connection was
2387   established to fetch each URL, increasing the load on HTTP servers
2388   and causing congestion on the Internet. The use of inline images and
2389   other associated data often requires a client to make multiple
2390   requests of the same server in a short amount of time. Analysis of
2391   these performance problems and results from a prototype
2392   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2393   measurements of actual HTTP/1.1 implementations show good
2394   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2395   T/TCP <xref target="Tou1998"/>.
2398   Persistent HTTP connections have a number of advantages:
2399  <list style="symbols">
2400      <t>
2401        By opening and closing fewer TCP connections, CPU time is saved
2402        in routers and hosts (clients, servers, proxies, gateways,
2403        tunnels, or caches), and memory used for TCP protocol control
2404        blocks can be saved in hosts.
2405      </t>
2406      <t>
2407        HTTP requests and responses can be pipelined on a connection.
2408        Pipelining allows a client to make multiple requests without
2409        waiting for each response, allowing a single TCP connection to
2410        be used much more efficiently, with much lower elapsed time.
2411      </t>
2412      <t>
2413        Network congestion is reduced by reducing the number of packets
2414        caused by TCP opens, and by allowing TCP sufficient time to
2415        determine the congestion state of the network.
2416      </t>
2417      <t>
2418        Latency on subsequent requests is reduced since there is no time
2419        spent in TCP's connection opening handshake.
2420      </t>
2421      <t>
2422        HTTP can evolve more gracefully, since errors can be reported
2423        without the penalty of closing the TCP connection. Clients using
2424        future versions of HTTP might optimistically try a new feature,
2425        but if communicating with an older server, retry with old
2426        semantics after an error is reported.
2427      </t>
2428    </list>
2431   HTTP implementations &SHOULD; implement persistent connections.
2435<section title="Overall Operation" anchor="persistent.overall">
2437   A significant difference between HTTP/1.1 and earlier versions of
2438   HTTP is that persistent connections are the default behavior of any
2439   HTTP connection. That is, unless otherwise indicated, the client
2440   &SHOULD; assume that the server will maintain a persistent connection,
2441   even after error responses from the server.
2444   Persistent connections provide a mechanism by which a client and a
2445   server can signal the close of a TCP connection. This signaling takes
2446   place using the Connection header field (<xref target="header.connection"/>). Once a close
2447   has been signaled, the client &MUST-NOT; send any more requests on that
2448   connection.
2451<section title="Negotiation" anchor="persistent.negotiation">
2453   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2454   maintain a persistent connection unless a Connection header field including
2455   the connection-token "close" was sent in the request. If the server
2456   chooses to close the connection immediately after sending the
2457   response, it &SHOULD; send a Connection header field including the
2458   connection-token "close".
2461   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2462   decide to keep it open based on whether the response from a server
2463   contains a Connection header field with the connection-token close. In case
2464   the client does not want to maintain a connection for more than that
2465   request, it &SHOULD; send a Connection header field including the
2466   connection-token close.
2469   If either the client or the server sends the close token in the
2470   Connection header field, that request becomes the last one for the
2471   connection.
2474   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2475   maintained for HTTP versions less than 1.1 unless it is explicitly
2476   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2477   compatibility with HTTP/1.0 clients.
2480   In order to remain persistent, all messages on the connection &MUST;
2481   have a self-defined message length (i.e., one not defined by closure
2482   of the connection), as described in <xref target="message.body"/>.
2486<section title="Pipelining" anchor="pipelining">
2488   A client that supports persistent connections &MAY; "pipeline" its
2489   requests (i.e., send multiple requests without waiting for each
2490   response). A server &MUST; send its responses to those requests in the
2491   same order that the requests were received.
2494   Clients which assume persistent connections and pipeline immediately
2495   after connection establishment &SHOULD; be prepared to retry their
2496   connection if the first pipelined attempt fails. If a client does
2497   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2498   persistent. Clients &MUST; also be prepared to resend their requests if
2499   the server closes the connection before sending all of the
2500   corresponding responses.
2503   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2504   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2505   premature termination of the transport connection could lead to
2506   indeterminate results. A client wishing to send a non-idempotent
2507   request &SHOULD; wait to send that request until it has received the
2508   response status line for the previous request.
2513<section title="Proxy Servers" anchor="persistent.proxy">
2515   It is especially important that proxies correctly implement the
2516   properties of the Connection header field as specified in <xref target="header.connection"/>.
2519   The proxy server &MUST; signal persistent connections separately with
2520   its clients and the origin servers (or other proxy servers) that it
2521   connects to. Each persistent connection applies to only one transport
2522   link.
2525   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2526   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2527   for information and discussion of the problems with the Keep-Alive header field
2528   implemented by many HTTP/1.0 clients).
2531<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2533  <cref anchor="TODO-end-to-end" source="jre">
2534    Restored from <eref target=""/>.
2535    See also <eref target=""/>.
2536  </cref>
2539   For the purpose of defining the behavior of caches and non-caching
2540   proxies, we divide HTTP header fields into two categories:
2541  <list style="symbols">
2542      <t>End-to-end header fields, which are  transmitted to the ultimate
2543        recipient of a request or response. End-to-end header fields in
2544        responses MUST be stored as part of a cache entry and &MUST; be
2545        transmitted in any response formed from a cache entry.</t>
2547      <t>Hop-by-hop header fields, which are meaningful only for a single
2548        transport-level connection, and are not stored by caches or
2549        forwarded by proxies.</t>
2550  </list>
2553   The following HTTP/1.1 header fields are hop-by-hop header fields:
2554  <list style="symbols">
2555      <t>Connection</t>
2556      <t>Keep-Alive</t>
2557      <t>Proxy-Authenticate</t>
2558      <t>Proxy-Authorization</t>
2559      <t>TE</t>
2560      <t>Trailer</t>
2561      <t>Transfer-Encoding</t>
2562      <t>Upgrade</t>
2563  </list>
2566   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2569   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2570   (<xref target="header.connection"/>).
2574<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2576  <cref anchor="TODO-non-mod-headers" source="jre">
2577    Restored from <eref target=""/>.
2578    See also <eref target=""/>.
2579  </cref>
2582   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2583   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2584   modify an end-to-end header field unless the definition of that header field requires
2585   or specifically allows that.
2588   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2589   request or response, and it &MUST-NOT; add any of these fields if not
2590   already present:
2591  <list style="symbols">
2592      <t>Content-Location</t>
2593      <t>Content-MD5</t>
2594      <t>ETag</t>
2595      <t>Last-Modified</t>
2596  </list>
2599   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2600   response:
2601  <list style="symbols">
2602    <t>Expires</t>
2603  </list>
2606   but it &MAY; add any of these fields if not already present. If an
2607   Expires header field is added, it &MUST; be given a field-value identical to
2608   that of the Date header field in that response.
2611   A proxy &MUST-NOT; modify or add any of the following fields in a
2612   message that contains the no-transform cache-control directive, or in
2613   any request:
2614  <list style="symbols">
2615    <t>Content-Encoding</t>
2616    <t>Content-Range</t>
2617    <t>Content-Type</t>
2618  </list>
2621   A transforming proxy &MAY; modify or add these fields to a message
2622   that does not include no-transform, but if it does so, it &MUST; add a
2623   Warning 214 (Transformation applied) if one does not already appear
2624   in the message (see &header-warning;).
2627  <t>
2628    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2629    cause authentication failures if stronger authentication
2630    mechanisms are introduced in later versions of HTTP. Such
2631    authentication mechanisms &MAY; rely on the values of header fields
2632    not listed here.
2633  </t>
2636   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2637   though it &MAY; change the message-body through application or removal
2638   of a transfer-coding (<xref target="transfer.codings"/>).
2644<section title="Practical Considerations" anchor="persistent.practical">
2646   Servers will usually have some time-out value beyond which they will
2647   no longer maintain an inactive connection. Proxy servers might make
2648   this a higher value since it is likely that the client will be making
2649   more connections through the same server. The use of persistent
2650   connections places no requirements on the length (or existence) of
2651   this time-out for either the client or the server.
2654   When a client or server wishes to time-out it &SHOULD; issue a graceful
2655   close on the transport connection. Clients and servers &SHOULD; both
2656   constantly watch for the other side of the transport close, and
2657   respond to it as appropriate. If a client or server does not detect
2658   the other side's close promptly it could cause unnecessary resource
2659   drain on the network.
2662   A client, server, or proxy &MAY; close the transport connection at any
2663   time. For example, a client might have started to send a new request
2664   at the same time that the server has decided to close the "idle"
2665   connection. From the server's point of view, the connection is being
2666   closed while it was idle, but from the client's point of view, a
2667   request is in progress.
2670   This means that clients, servers, and proxies &MUST; be able to recover
2671   from asynchronous close events. Client software &SHOULD; reopen the
2672   transport connection and retransmit the aborted sequence of requests
2673   without user interaction so long as the request sequence is
2674   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2675   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2676   human operator the choice of retrying the request(s). Confirmation by
2677   user-agent software with semantic understanding of the application
2678   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2679   be repeated if the second sequence of requests fails.
2682   Servers &SHOULD; always respond to at least one request per connection,
2683   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2684   middle of transmitting a response, unless a network or client failure
2685   is suspected.
2688   Clients (including proxies) &SHOULD; limit the number of simultaneous
2689   connections that they maintain to a given server (including proxies).
2692   Previous revisions of HTTP gave a specific number of connections as a
2693   ceiling, but this was found to be impractical for many applications. As a
2694   result, this specification does not mandate a particular maximum number of
2695   connections, but instead encourages clients to be conservative when opening
2696   multiple connections.
2699   In particular, while using multiple connections avoids the "head-of-line
2700   blocking" problem (whereby a request that takes significant server-side
2701   processing and/or has a large payload can block subsequent requests on the
2702   same connection), each connection used consumes server resources (sometimes
2703   significantly), and furthermore using multiple connections can cause
2704   undesirable side effects in congested networks.
2707   Note that servers might reject traffic that they deem abusive, including an
2708   excessive number of connections from a client.
2713<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2715<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2717   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2718   flow control mechanisms to resolve temporary overloads, rather than
2719   terminating connections with the expectation that clients will retry.
2720   The latter technique can exacerbate network congestion.
2724<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2726   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2727   the network connection for an error status code while it is transmitting
2728   the request. If the client sees an error status code, it &SHOULD;
2729   immediately cease transmitting the body. If the body is being sent
2730   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2731   empty trailer &MAY; be used to prematurely mark the end of the message.
2732   If the body was preceded by a Content-Length header field, the client &MUST;
2733   close the connection.
2737<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2739   The purpose of the 100 (Continue) status code (see &status-100;) is to
2740   allow a client that is sending a request message with a request body
2741   to determine if the origin server is willing to accept the request
2742   (based on the request header fields) before the client sends the request
2743   body. In some cases, it might either be inappropriate or highly
2744   inefficient for the client to send the body if the server will reject
2745   the message without looking at the body.
2748   Requirements for HTTP/1.1 clients:
2749  <list style="symbols">
2750    <t>
2751        If a client will wait for a 100 (Continue) response before
2752        sending the request body, it &MUST; send an Expect header
2753        field (&header-expect;) with the "100-continue" expectation.
2754    </t>
2755    <t>
2756        A client &MUST-NOT; send an Expect header field (&header-expect;)
2757        with the "100-continue" expectation if it does not intend
2758        to send a request body.
2759    </t>
2760  </list>
2763   Because of the presence of older implementations, the protocol allows
2764   ambiguous situations in which a client might send "Expect: 100-continue"
2765   without receiving either a 417 (Expectation Failed)
2766   or a 100 (Continue) status code. Therefore, when a client sends this
2767   header field to an origin server (possibly via a proxy) from which it
2768   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2769   wait for an indefinite period before sending the request body.
2772   Requirements for HTTP/1.1 origin servers:
2773  <list style="symbols">
2774    <t> Upon receiving a request which includes an Expect header
2775        field with the "100-continue" expectation, an origin server &MUST;
2776        either respond with 100 (Continue) status code and continue to read
2777        from the input stream, or respond with a final status code. The
2778        origin server &MUST-NOT; wait for the request body before sending
2779        the 100 (Continue) response. If it responds with a final status
2780        code, it &MAY; close the transport connection or it &MAY; continue
2781        to read and discard the rest of the request.  It &MUST-NOT;
2782        perform the request method if it returns a final status code.
2783    </t>
2784    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2785        the request message does not include an Expect header
2786        field with the "100-continue" expectation, and &MUST-NOT; send a
2787        100 (Continue) response if such a request comes from an HTTP/1.0
2788        (or earlier) client. There is an exception to this rule: for
2789        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2790        status code in response to an HTTP/1.1 PUT or POST request that does
2791        not include an Expect header field with the "100-continue"
2792        expectation. This exception, the purpose of which is
2793        to minimize any client processing delays associated with an
2794        undeclared wait for 100 (Continue) status code, applies only to
2795        HTTP/1.1 requests, and not to requests with any other HTTP-version
2796        value.
2797    </t>
2798    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2799        already received some or all of the request body for the
2800        corresponding request.
2801    </t>
2802    <t> An origin server that sends a 100 (Continue) response &MUST;
2803    ultimately send a final status code, once the request body is
2804        received and processed, unless it terminates the transport
2805        connection prematurely.
2806    </t>
2807    <t> If an origin server receives a request that does not include an
2808        Expect header field with the "100-continue" expectation,
2809        the request includes a request body, and the server responds
2810        with a final status code before reading the entire request body
2811        from the transport connection, then the server &SHOULD-NOT;  close
2812        the transport connection until it has read the entire request,
2813        or until the client closes the connection. Otherwise, the client
2814        might not reliably receive the response message. However, this
2815        requirement is not be construed as preventing a server from
2816        defending itself against denial-of-service attacks, or from
2817        badly broken client implementations.
2818      </t>
2819    </list>
2822   Requirements for HTTP/1.1 proxies:
2823  <list style="symbols">
2824    <t> If a proxy receives a request that includes an Expect header
2825        field with the "100-continue" expectation, and the proxy
2826        either knows that the next-hop server complies with HTTP/1.1 or
2827        higher, or does not know the HTTP version of the next-hop
2828        server, it &MUST; forward the request, including the Expect header
2829        field.
2830    </t>
2831    <t> If the proxy knows that the version of the next-hop server is
2832        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2833        respond with a 417 (Expectation Failed) status code.
2834    </t>
2835    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2836        numbers received from recently-referenced next-hop servers.
2837    </t>
2838    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2839        request message was received from an HTTP/1.0 (or earlier)
2840        client and did not include an Expect header field with
2841        the "100-continue" expectation. This requirement overrides the
2842        general rule for forwarding of 1xx responses (see &status-1xx;).
2843    </t>
2844  </list>
2848<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2850   If an HTTP/1.1 client sends a request which includes a request body,
2851   but which does not include an Expect header field with the
2852   "100-continue" expectation, and if the client is not directly
2853   connected to an HTTP/1.1 origin server, and if the client sees the
2854   connection close before receiving a status line from the server, the
2855   client &SHOULD; retry the request.  If the client does retry this
2856   request, it &MAY; use the following "binary exponential backoff"
2857   algorithm to be assured of obtaining a reliable response:
2858  <list style="numbers">
2859    <t>
2860      Initiate a new connection to the server
2861    </t>
2862    <t>
2863      Transmit the request-line, header fields, and the CRLF that
2864      indicates the end of header fields.
2865    </t>
2866    <t>
2867      Initialize a variable R to the estimated round-trip time to the
2868         server (e.g., based on the time it took to establish the
2869         connection), or to a constant value of 5 seconds if the round-trip
2870         time is not available.
2871    </t>
2872    <t>
2873       Compute T = R * (2**N), where N is the number of previous
2874         retries of this request.
2875    </t>
2876    <t>
2877       Wait either for an error response from the server, or for T
2878         seconds (whichever comes first)
2879    </t>
2880    <t>
2881       If no error response is received, after T seconds transmit the
2882         body of the request.
2883    </t>
2884    <t>
2885       If client sees that the connection is closed prematurely,
2886         repeat from step 1 until the request is accepted, an error
2887         response is received, or the user becomes impatient and
2888         terminates the retry process.
2889    </t>
2890  </list>
2893   If at any point an error status code is received, the client
2894  <list style="symbols">
2895      <t>&SHOULD-NOT;  continue and</t>
2897      <t>&SHOULD; close the connection if it has not completed sending the
2898        request message.</t>
2899    </list>
2906<section title="Miscellaneous notes that might disappear" anchor="misc">
2907<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2909   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2913<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2915   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2919<section title="Interception of HTTP for access control" anchor="http.intercept">
2921   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2925<section title="Use of HTTP by other protocols" anchor="http.others">
2927   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2928   Extensions of HTTP like WebDAV.</cref>
2932<section title="Use of HTTP by media type specification" anchor="">
2934   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2939<section title="Header Field Definitions" anchor="header.field.definitions">
2941   This section defines the syntax and semantics of HTTP/1.1 header fields
2942   related to message framing and transport protocols.
2945<section title="Connection" anchor="header.connection">
2946  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2947  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2948  <x:anchor-alias value="Connection"/>
2949  <x:anchor-alias value="connection-token"/>
2950  <x:anchor-alias value="Connection-v"/>
2952   The "Connection" header field allows the sender to specify
2953   options that are desired for that particular connection and &MUST-NOT;
2954   be communicated by proxies over further connections.
2957   The Connection header field's value has the following grammar:
2959<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2960  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2961  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2962  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2965   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2966   message is forwarded and, for each connection-token in this field,
2967   remove any header field(s) from the message with the same name as the
2968   connection-token. Connection options are signaled by the presence of
2969   a connection-token in the Connection header field, not by any
2970   corresponding additional header field(s), since the additional header
2971   field might not be sent if there are no parameters associated with that
2972   connection option.
2975   Message header fields listed in the Connection header field &MUST-NOT; include
2976   end-to-end header fields, such as Cache-Control (&header-cache-control;).
2979   HTTP/1.1 defines the "close" connection option for the sender to
2980   signal that the connection will be closed after completion of the
2981   response. For example,
2983<figure><artwork type="example">
2984  Connection: close
2987   in either the request or the response header fields indicates that
2988   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2989   after the current request/response is complete.
2992   An HTTP/1.1 client that does not support persistent connections &MUST;
2993   include the "close" connection option in every request message.
2996   An HTTP/1.1 server that does not support persistent connections &MUST;
2997   include the "close" connection option in every response message that
2998   does not have a 1xx (Informational) status code.
3001   A system receiving an HTTP/1.0 (or lower-version) message that
3002   includes a Connection header field &MUST;, for each connection-token in this
3003   field, remove and ignore any header field(s) from the message with
3004   the same name as the connection-token. This protects against mistaken
3005   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
3009<section title="Content-Length" anchor="header.content-length">
3010  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3011  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3012  <x:anchor-alias value="Content-Length"/>
3013  <x:anchor-alias value="Content-Length-v"/>
3015   The "Content-Length" header field indicates the size of the
3016   message-body, in decimal number of octets, for any message other than
3017   a response to a HEAD request or a response with a status code of 304.
3018   In the case of a response to a HEAD request, Content-Length indicates
3019   the size of the payload body (not including any potential transfer-coding)
3020   that would have been sent had the request been a GET.
3021   In the case of a 304 (Not Modified) response to a GET request,
3022   Content-Length indicates the size of the payload body (not including
3023   any potential transfer-coding) that would have been sent in a 200 (OK)
3024   response.
3026<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
3027  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
3028  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
3031   An example is
3033<figure><artwork type="example">
3034  Content-Length: 3495
3037   Implementations &SHOULD; use this field to indicate the message-body
3038   length when no transfer-coding is being applied and the
3039   payload's body length can be determined prior to being transferred.
3040   <xref target="message.body"/> describes how recipients determine the length
3041   of a message-body.
3044   Any Content-Length greater than or equal to zero is a valid value.
3047   Note that the use of this field in HTTP is significantly different from
3048   the corresponding definition in MIME, where it is an optional field
3049   used within the "message/external-body" content-type.
3053<section title="Date" anchor="">
3054  <iref primary="true" item="Date header field" x:for-anchor=""/>
3055  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3056  <x:anchor-alias value="Date"/>
3057  <x:anchor-alias value="Date-v"/>
3059   The "Date" header field represents the date and time at which
3060   the message was originated, having the same semantics as the Origination
3061   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3062   The field value is an HTTP-date, as described in <xref target=""/>;
3063   it &MUST; be sent in rfc1123-date format.
3065<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3066  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3067  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3070   An example is
3072<figure><artwork type="example">
3073  Date: Tue, 15 Nov 1994 08:12:31 GMT
3076   Origin servers &MUST; include a Date header field in all responses,
3077   except in these cases:
3078  <list style="numbers">
3079      <t>If the response status code is 100 (Continue) or 101 (Switching
3080         Protocols), the response &MAY; include a Date header field, at
3081         the server's option.</t>
3083      <t>If the response status code conveys a server error, e.g., 500
3084         (Internal Server Error) or 503 (Service Unavailable), and it is
3085         inconvenient or impossible to generate a valid Date.</t>
3087      <t>If the server does not have a clock that can provide a
3088         reasonable approximation of the current time, its responses
3089         &MUST-NOT; include a Date header field. In this case, the rules
3090         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3091  </list>
3094   A received message that does not have a Date header field &MUST; be
3095   assigned one by the recipient if the message will be cached by that
3096   recipient or gatewayed via a protocol which requires a Date.
3099   Clients can use the Date header field as well; in order to keep request
3100   messages small, they are advised not to include it when it doesn't convey
3101   any useful information (as it is usually the case for requests that do not
3102   contain a payload).
3105   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3106   time subsequent to the generation of the message. It &SHOULD; represent
3107   the best available approximation of the date and time of message
3108   generation, unless the implementation has no means of generating a
3109   reasonably accurate date and time. In theory, the date ought to
3110   represent the moment just before the payload is generated. In
3111   practice, the date can be generated at any time during the message
3112   origination without affecting its semantic value.
3115<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3117   Some origin server implementations might not have a clock available.
3118   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3119   values to a response, unless these values were associated
3120   with the resource by a system or user with a reliable clock. It &MAY;
3121   assign an Expires value that is known, at or before server
3122   configuration time, to be in the past (this allows "pre-expiration"
3123   of responses without storing separate Expires values for each
3124   resource).
3129<section title="Host" anchor="">
3130  <iref primary="true" item="Host header field" x:for-anchor=""/>
3131  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3132  <x:anchor-alias value="Host"/>
3133  <x:anchor-alias value="Host-v"/>
3135   The "Host" header field specifies the Internet host and port
3136   number of the resource being requested, allowing the origin server or
3137   gateway to differentiate between internally-ambiguous URLs, such as the root
3138   "/" URL of a server for multiple host names on a single IP address.
3141   The Host field value &MUST; represent the naming authority of the origin
3142   server or gateway given by the original URL obtained from the user or
3143   referring resource (generally an http URI, as described in
3144   <xref target="http.uri"/>).
3146<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3147  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3148  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3151   A "host" without any trailing port information implies the default
3152   port for the service requested (e.g., "80" for an HTTP URL). For
3153   example, a request on the origin server for
3154   &lt;; would properly include:
3156<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3157GET /pub/WWW/ HTTP/1.1
3161   A client &MUST; include a Host header field in all HTTP/1.1 request
3162   messages. If the requested URI does not include an Internet host
3163   name for the service being requested, then the Host header field &MUST;
3164   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3165   request message it forwards does contain an appropriate Host header
3166   field that identifies the service being requested by the proxy. All
3167   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3168   status code to any HTTP/1.1 request message which lacks a Host header
3169   field.
3172   See Sections <xref target="" format="counter"/>
3173   and <xref target="" format="counter"/>
3174   for other requirements relating to Host.
3178<section title="TE" anchor="header.te">
3179  <iref primary="true" item="TE header field" x:for-anchor=""/>
3180  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3181  <x:anchor-alias value="TE"/>
3182  <x:anchor-alias value="TE-v"/>
3183  <x:anchor-alias value="t-codings"/>
3184  <x:anchor-alias value="te-params"/>
3185  <x:anchor-alias value="te-ext"/>
3187   The "TE" header field indicates what extension transfer-codings
3188   it is willing to accept in the response, and whether or not it is
3189   willing to accept trailer fields in a chunked transfer-coding.
3192   Its value consists of the keyword "trailers" and/or a comma-separated
3193   list of extension transfer-coding names with optional accept
3194   parameters (as described in <xref target="transfer.codings"/>).
3196<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3197  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3198  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3199  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3200  <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> )
3201  <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> ]
3204   The presence of the keyword "trailers" indicates that the client is
3205   willing to accept trailer fields in a chunked transfer-coding, as
3206   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3207   transfer-coding values even though it does not itself represent a
3208   transfer-coding.
3211   Examples of its use are:
3213<figure><artwork type="example">
3214  TE: deflate
3215  TE:
3216  TE: trailers, deflate;q=0.5
3219   The TE header field only applies to the immediate connection.
3220   Therefore, the keyword &MUST; be supplied within a Connection header
3221   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3224   A server tests whether a transfer-coding is acceptable, according to
3225   a TE field, using these rules:
3226  <list style="numbers">
3227    <x:lt>
3228      <t>The "chunked" transfer-coding is always acceptable. If the
3229         keyword "trailers" is listed, the client indicates that it is
3230         willing to accept trailer fields in the chunked response on
3231         behalf of itself and any downstream clients. The implication is
3232         that, if given, the client is stating that either all
3233         downstream clients are willing to accept trailer fields in the
3234         forwarded response, or that it will attempt to buffer the
3235         response on behalf of downstream recipients.
3236      </t><t>
3237         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3238         chunked response such that a client can be assured of buffering
3239         the entire response.</t>
3240    </x:lt>
3241    <x:lt>
3242      <t>If the transfer-coding being tested is one of the transfer-codings
3243         listed in the TE field, then it is acceptable unless it
3244         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3245         qvalue of 0 means "not acceptable".)</t>
3246    </x:lt>
3247    <x:lt>
3248      <t>If multiple transfer-codings are acceptable, then the
3249         acceptable transfer-coding with the highest non-zero qvalue is
3250         preferred.  The "chunked" transfer-coding always has a qvalue
3251         of 1.</t>
3252    </x:lt>
3253  </list>
3256   If the TE field-value is empty or if no TE field is present, the only
3257   transfer-coding is "chunked". A message with no transfer-coding is
3258   always acceptable.
3262<section title="Trailer" anchor="header.trailer">
3263  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3264  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3265  <x:anchor-alias value="Trailer"/>
3266  <x:anchor-alias value="Trailer-v"/>
3268   The "Trailer" header field indicates that the given set of
3269   header fields is present in the trailer of a message encoded with
3270   chunked transfer-coding.
3272<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3273  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3274  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3277   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3278   message using chunked transfer-coding with a non-empty trailer. Doing
3279   so allows the recipient to know which header fields to expect in the
3280   trailer.
3283   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3284   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3285   trailer fields in a "chunked" transfer-coding.
3288   Message header fields listed in the Trailer header field &MUST-NOT;
3289   include the following header fields:
3290  <list style="symbols">
3291    <t>Transfer-Encoding</t>
3292    <t>Content-Length</t>
3293    <t>Trailer</t>
3294  </list>
3298<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3299  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3300  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3301  <x:anchor-alias value="Transfer-Encoding"/>
3302  <x:anchor-alias value="Transfer-Encoding-v"/>
3304   The "Transfer-Encoding" header field indicates what transfer-codings
3305   (if any) have been applied to the message body. It differs from
3306   Content-Encoding (&content-codings;) in that transfer-codings are a property
3307   of the message (and therefore are removed by intermediaries), whereas
3308   content-codings are not.
3310<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3311  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3312                        <x:ref>Transfer-Encoding-v</x:ref>
3313  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3316   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3318<figure><artwork type="example">
3319  Transfer-Encoding: chunked
3322   If multiple encodings have been applied to a representation, the transfer-codings
3323   &MUST; be listed in the order in which they were applied.
3324   Additional information about the encoding parameters &MAY; be provided
3325   by other header fields not defined by this specification.
3328   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3329   header field.
3333<section title="Upgrade" anchor="header.upgrade">
3334  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3335  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3336  <x:anchor-alias value="Upgrade"/>
3337  <x:anchor-alias value="Upgrade-v"/>
3339   The "Upgrade" header field allows the client to specify what
3340   additional communication protocols it would like to use, if the server
3341   chooses to switch protocols. Servers can use it to indicate what protocols
3342   they are willing to switch to.
3344<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3345  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3346  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3349   For example,
3351<figure><artwork type="example">
3352  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3355   The Upgrade header field is intended to provide a simple mechanism
3356   for transition from HTTP/1.1 to some other, incompatible protocol. It
3357   does so by allowing the client to advertise its desire to use another
3358   protocol, such as a later version of HTTP with a higher major version
3359   number, even though the current request has been made using HTTP/1.1.
3360   This eases the difficult transition between incompatible protocols by
3361   allowing the client to initiate a request in the more commonly
3362   supported protocol while indicating to the server that it would like
3363   to use a "better" protocol if available (where "better" is determined
3364   by the server, possibly according to the nature of the request method
3365   or target resource).
3368   The Upgrade header field only applies to switching application-layer
3369   protocols upon the existing transport-layer connection. Upgrade
3370   cannot be used to insist on a protocol change; its acceptance and use
3371   by the server is optional. The capabilities and nature of the
3372   application-layer communication after the protocol change is entirely
3373   dependent upon the new protocol chosen, although the first action
3374   after changing the protocol &MUST; be a response to the initial HTTP
3375   request containing the Upgrade header field.
3378   The Upgrade header field only applies to the immediate connection.
3379   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3380   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3381   HTTP/1.1 message.
3384   The Upgrade header field cannot be used to indicate a switch to a
3385   protocol on a different connection. For that purpose, it is more
3386   appropriate to use a 3xx redirection response (&status-3xx;).
3389   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3390   Protocols) responses to indicate which protocol(s) are being switched to,
3391   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3392   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3393   response to indicate that they are willing to upgrade to one of the
3394   specified protocols.
3397   This specification only defines the protocol name "HTTP" for use by
3398   the family of Hypertext Transfer Protocols, as defined by the HTTP
3399   version rules of <xref target="http.version"/> and future updates to this
3400   specification. Additional tokens can be registered with IANA using the
3401   registration procedure defined below. 
3404<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3406   The HTTP Upgrade Token Registry defines the name space for product
3407   tokens used to identify protocols in the Upgrade header field.
3408   Each registered token is associated with contact information and
3409   an optional set of specifications that details how the connection
3410   will be processed after it has been upgraded.
3413   Registrations are allowed on a First Come First Served basis as
3414   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3415   specifications need not be IETF documents or be subject to IESG review.
3416   Registrations are subject to the following rules:
3417  <list style="numbers">
3418    <t>A token, once registered, stays registered forever.</t>
3419    <t>The registration &MUST; name a responsible party for the
3420       registration.</t>
3421    <t>The registration &MUST; name a point of contact.</t>
3422    <t>The registration &MAY; name a set of specifications associated with that
3423       token. Such specifications need not be publicly available.</t>
3424    <t>The responsible party &MAY; change the registration at any time.
3425       The IANA will keep a record of all such changes, and make them
3426       available upon request.</t>
3427    <t>The responsible party for the first registration of a "product"
3428       token &MUST; approve later registrations of a "version" token
3429       together with that "product" token before they can be registered.</t>
3430    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3431       for a token. This will normally only be used in the case when a
3432       responsible party cannot be contacted.</t>
3433  </list>
3440<section title="Via" anchor="header.via">
3441  <iref primary="true" item="Via header field" x:for-anchor=""/>
3442  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3443  <x:anchor-alias value="protocol-name"/>
3444  <x:anchor-alias value="protocol-version"/>
3445  <x:anchor-alias value="pseudonym"/>
3446  <x:anchor-alias value="received-by"/>
3447  <x:anchor-alias value="received-protocol"/>
3448  <x:anchor-alias value="Via"/>
3449  <x:anchor-alias value="Via-v"/>
3451   The "Via" header field &MUST; be used by gateways and proxies to
3452   indicate the intermediate protocols and recipients between the user
3453   agent and the server on requests, and between the origin server and
3454   the client on responses. It is analogous to the "Received" field defined in
3455   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3456   avoiding request loops, and identifying the protocol capabilities of
3457   all senders along the request/response chain.
3459<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><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"/>
3460  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3461  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3462                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3463  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3464  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3465  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3466  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3467  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3470   The received-protocol indicates the protocol version of the message
3471   received by the server or client along each segment of the
3472   request/response chain. The received-protocol version is appended to
3473   the Via field value when the message is forwarded so that information
3474   about the protocol capabilities of upstream applications remains
3475   visible to all recipients.
3478   The protocol-name is optional if and only if it would be "HTTP". The
3479   received-by field is normally the host and optional port number of a
3480   recipient server or client that subsequently forwarded the message.
3481   However, if the real host is considered to be sensitive information,
3482   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3483   be assumed to be the default port of the received-protocol.
3486   Multiple Via field values represent each proxy or gateway that has
3487   forwarded the message. Each recipient &MUST; append its information
3488   such that the end result is ordered according to the sequence of
3489   forwarding applications.
3492   Comments &MAY; be used in the Via header field to identify the software
3493   of the recipient proxy or gateway, analogous to the User-Agent and
3494   Server header fields. However, all comments in the Via field are
3495   optional and &MAY; be removed by any recipient prior to forwarding the
3496   message.
3499   For example, a request message could be sent from an HTTP/1.0 user
3500   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3501   forward the request to a public proxy at, which completes
3502   the request by forwarding it to the origin server at
3503   The request received by would then have the following
3504   Via header field:
3506<figure><artwork type="example">
3507  Via: 1.0 fred, 1.1 (Apache/1.1)
3510   Proxies and gateways used as a portal through a network firewall
3511   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3512   the firewall region. This information &SHOULD; only be propagated if
3513   explicitly enabled. If not enabled, the received-by host of any host
3514   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3515   for that host.
3518   For organizations that have strong privacy requirements for hiding
3519   internal structures, a proxy &MAY; combine an ordered subsequence of
3520   Via header field entries with identical received-protocol values into
3521   a single such entry. For example,
3523<figure><artwork type="example">
3524  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3527  could be collapsed to
3529<figure><artwork type="example">
3530  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3533   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3534   under the same organizational control and the hosts have already been
3535   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3536   have different received-protocol values.
3542<section title="IANA Considerations" anchor="IANA.considerations">
3544<section title="Header Field Registration" anchor="header.field.registration">
3546   The Message Header Field Registry located at <eref target=""/> shall be updated
3547   with the permanent registrations below (see <xref target="RFC3864"/>):
3549<?BEGININC p1-messaging.iana-headers ?>
3550<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3551<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3552   <ttcol>Header Field Name</ttcol>
3553   <ttcol>Protocol</ttcol>
3554   <ttcol>Status</ttcol>
3555   <ttcol>Reference</ttcol>
3557   <c>Connection</c>
3558   <c>http</c>
3559   <c>standard</c>
3560   <c>
3561      <xref target="header.connection"/>
3562   </c>
3563   <c>Content-Length</c>
3564   <c>http</c>
3565   <c>standard</c>
3566   <c>
3567      <xref target="header.content-length"/>
3568   </c>
3569   <c>Date</c>
3570   <c>http</c>
3571   <c>standard</c>
3572   <c>
3573      <xref target=""/>
3574   </c>
3575   <c>Host</c>
3576   <c>http</c>
3577   <c>standard</c>
3578   <c>
3579      <xref target=""/>
3580   </c>
3581   <c>TE</c>
3582   <c>http</c>
3583   <c>standard</c>
3584   <c>
3585      <xref target="header.te"/>
3586   </c>
3587   <c>Trailer</c>
3588   <c>http</c>
3589   <c>standard</c>
3590   <c>
3591      <xref target="header.trailer"/>
3592   </c>
3593   <c>Transfer-Encoding</c>
3594   <c>http</c>
3595   <c>standard</c>
3596   <c>
3597      <xref target="header.transfer-encoding"/>
3598   </c>
3599   <c>Upgrade</c>
3600   <c>http</c>
3601   <c>standard</c>
3602   <c>
3603      <xref target="header.upgrade"/>
3604   </c>
3605   <c>Via</c>
3606   <c>http</c>
3607   <c>standard</c>
3608   <c>
3609      <xref target="header.via"/>
3610   </c>
3613<?ENDINC p1-messaging.iana-headers ?>
3615   The change controller is: "IETF ( - Internet Engineering Task Force".
3619<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3621   The entries for the "http" and "https" URI Schemes in the registry located at
3622   <eref target=""/>
3623   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3624   and <xref target="https.uri" format="counter"/> of this document
3625   (see <xref target="RFC4395"/>).
3629<section title="Internet Media Type Registrations" anchor="">
3631   This document serves as the specification for the Internet media types
3632   "message/http" and "application/http". The following is to be registered with
3633   IANA (see <xref target="RFC4288"/>).
3635<section title="Internet Media Type message/http" anchor="">
3636<iref item="Media Type" subitem="message/http" primary="true"/>
3637<iref item="message/http Media Type" primary="true"/>
3639   The message/http type can be used to enclose a single HTTP request or
3640   response message, provided that it obeys the MIME restrictions for all
3641   "message" types regarding line length and encodings.
3644  <list style="hanging" x:indent="12em">
3645    <t hangText="Type name:">
3646      message
3647    </t>
3648    <t hangText="Subtype name:">
3649      http
3650    </t>
3651    <t hangText="Required parameters:">
3652      none
3653    </t>
3654    <t hangText="Optional parameters:">
3655      version, msgtype
3656      <list style="hanging">
3657        <t hangText="version:">
3658          The HTTP-Version number of the enclosed message
3659          (e.g., "1.1"). If not present, the version can be
3660          determined from the first line of the body.
3661        </t>
3662        <t hangText="msgtype:">
3663          The message type &mdash; "request" or "response". If not
3664          present, the type can be determined from the first
3665          line of the body.
3666        </t>
3667      </list>
3668    </t>
3669    <t hangText="Encoding considerations:">
3670      only "7bit", "8bit", or "binary" are permitted
3671    </t>
3672    <t hangText="Security considerations:">
3673      none
3674    </t>
3675    <t hangText="Interoperability considerations:">
3676      none
3677    </t>
3678    <t hangText="Published specification:">
3679      This specification (see <xref target=""/>).
3680    </t>
3681    <t hangText="Applications that use this media type:">
3682    </t>
3683    <t hangText="Additional information:">
3684      <list style="hanging">
3685        <t hangText="Magic number(s):">none</t>
3686        <t hangText="File extension(s):">none</t>
3687        <t hangText="Macintosh file type code(s):">none</t>
3688      </list>
3689    </t>
3690    <t hangText="Person and email address to contact for further information:">
3691      See Authors Section.
3692    </t>
3693    <t hangText="Intended usage:">
3694      COMMON
3695    </t>
3696    <t hangText="Restrictions on usage:">
3697      none
3698    </t>
3699    <t hangText="Author/Change controller:">
3700      IESG
3701    </t>
3702  </list>
3705<section title="Internet Media Type application/http" anchor="">
3706<iref item="Media Type" subitem="application/http" primary="true"/>
3707<iref item="application/http Media Type" primary="true"/>
3709   The application/http type can be used to enclose a pipeline of one or more
3710   HTTP request or response messages (not intermixed).
3713  <list style="hanging" x:indent="12em">
3714    <t hangText="Type name:">
3715      application
3716    </t>
3717    <t hangText="Subtype name:">
3718      http
3719    </t>
3720    <t hangText="Required parameters:">
3721      none
3722    </t>
3723    <t hangText="Optional parameters:">
3724      version, msgtype
3725      <list style="hanging">
3726        <t hangText="version:">
3727          The HTTP-Version number of the enclosed messages
3728          (e.g., "1.1"). If not present, the version can be
3729          determined from the first line of the body.
3730        </t>
3731        <t hangText="msgtype:">
3732          The message type &mdash; "request" or "response". If not
3733          present, the type can be determined from the first
3734          line of the body.
3735        </t>
3736      </list>
3737    </t>
3738    <t hangText="Encoding considerations:">
3739      HTTP messages enclosed by this type
3740      are in "binary" format; use of an appropriate
3741      Content-Transfer-Encoding is required when
3742      transmitted via E-mail.
3743    </t>
3744    <t hangText="Security considerations:">
3745      none
3746    </t>
3747    <t hangText="Interoperability considerations:">
3748      none
3749    </t>
3750    <t hangText="Published specification:">
3751      This specification (see <xref target=""/>).
3752    </t>
3753    <t hangText="Applications that use this media type:">
3754    </t>
3755    <t hangText="Additional information:">
3756      <list style="hanging">
3757        <t hangText="Magic number(s):">none</t>
3758        <t hangText="File extension(s):">none</t>
3759        <t hangText="Macintosh file type code(s):">none</t>
3760      </list>
3761    </t>
3762    <t hangText="Person and email address to contact for further information:">
3763      See Authors Section.
3764    </t>
3765    <t hangText="Intended usage:">
3766      COMMON
3767    </t>
3768    <t hangText="Restrictions on usage:">
3769      none
3770    </t>
3771    <t hangText="Author/Change controller:">
3772      IESG
3773    </t>
3774  </list>
3779<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3781   The registration procedure for HTTP Transfer Codings is now defined by
3782   <xref target="transfer.coding.registry"/> of this document.
3785   The HTTP Transfer Codings Registry located at <eref target=""/>
3786   shall be updated with the registrations below:
3788<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3789   <ttcol>Name</ttcol>
3790   <ttcol>Description</ttcol>
3791   <ttcol>Reference</ttcol>
3792   <c>chunked</c>
3793   <c>Transfer in a series of chunks</c>
3794   <c>
3795      <xref target="chunked.encoding"/>
3796   </c>
3797   <c>compress</c>
3798   <c>UNIX "compress" program method</c>
3799   <c>
3800      <xref target="compress.coding"/>
3801   </c>
3802   <c>deflate</c>
3803   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3804   the "zlib" data format (<xref target="RFC1950"/>)
3805   </c>
3806   <c>
3807      <xref target="deflate.coding"/>
3808   </c>
3809   <c>gzip</c>
3810   <c>Same as GNU zip <xref target="RFC1952"/></c>
3811   <c>
3812      <xref target="gzip.coding"/>
3813   </c>
3817<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3819   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3820   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3821   by <xref target="upgrade.token.registry"/> of this document.
3824   The HTTP Status Code Registry located at <eref target=""/>
3825   shall be updated with the registration below:
3827<texttable align="left" suppress-title="true">
3828   <ttcol>Value</ttcol>
3829   <ttcol>Description</ttcol>
3830   <ttcol>Reference</ttcol>
3832   <c>HTTP</c>
3833   <c>Hypertext Transfer Protocol</c>
3834   <c><xref target="http.version"/> of this specification</c>
3835<!-- IANA should add this without our instructions; emailed on June 05, 2009
3836   <c>TLS/1.0</c>
3837   <c>Transport Layer Security</c>
3838   <c><xref target="RFC2817"/></c> -->
3845<section title="Security Considerations" anchor="security.considerations">
3847   This section is meant to inform application developers, information
3848   providers, and users of the security limitations in HTTP/1.1 as
3849   described by this document. The discussion does not include
3850   definitive solutions to the problems revealed, though it does make
3851   some suggestions for reducing security risks.
3854<section title="Personal Information" anchor="personal.information">
3856   HTTP clients are often privy to large amounts of personal information
3857   (e.g., the user's name, location, mail address, passwords, encryption
3858   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3859   leakage of this information.
3860   We very strongly recommend that a convenient interface be provided
3861   for the user to control dissemination of such information, and that
3862   designers and implementors be particularly careful in this area.
3863   History shows that errors in this area often create serious security
3864   and/or privacy problems and generate highly adverse publicity for the
3865   implementor's company.
3869<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3871   A server is in the position to save personal data about a user's
3872   requests which might identify their reading patterns or subjects of
3873   interest. This information is clearly confidential in nature and its
3874   handling can be constrained by law in certain countries. People using
3875   HTTP to provide data are responsible for ensuring that
3876   such material is not distributed without the permission of any
3877   individuals that are identifiable by the published results.
3881<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3883   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3884   the documents returned by HTTP requests to be only those that were
3885   intended by the server administrators. If an HTTP server translates
3886   HTTP URIs directly into file system calls, the server &MUST; take
3887   special care not to serve files that were not intended to be
3888   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3889   other operating systems use ".." as a path component to indicate a
3890   directory level above the current one. On such a system, an HTTP
3891   server &MUST; disallow any such construct in the request-target if it
3892   would otherwise allow access to a resource outside those intended to
3893   be accessible via the HTTP server. Similarly, files intended for
3894   reference only internally to the server (such as access control
3895   files, configuration files, and script code) &MUST; be protected from
3896   inappropriate retrieval, since they might contain sensitive
3897   information. Experience has shown that minor bugs in such HTTP server
3898   implementations have turned into security risks.
3902<section title="DNS Spoofing" anchor="dns.spoofing">
3904   Clients using HTTP rely heavily on the Domain Name Service, and are
3905   thus generally prone to security attacks based on the deliberate
3906   mis-association of IP addresses and DNS names. Clients need to be
3907   cautious in assuming the continuing validity of an IP number/DNS name
3908   association.
3911   In particular, HTTP clients &SHOULD; rely on their name resolver for
3912   confirmation of an IP number/DNS name association, rather than
3913   caching the result of previous host name lookups. Many platforms
3914   already can cache host name lookups locally when appropriate, and
3915   they &SHOULD; be configured to do so. It is proper for these lookups to
3916   be cached, however, only when the TTL (Time To Live) information
3917   reported by the name server makes it likely that the cached
3918   information will remain useful.
3921   If HTTP clients cache the results of host name lookups in order to
3922   achieve a performance improvement, they &MUST; observe the TTL
3923   information reported by DNS.
3926   If HTTP clients do not observe this rule, they could be spoofed when
3927   a previously-accessed server's IP address changes. As network
3928   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3929   possibility of this form of attack will grow. Observing this
3930   requirement thus reduces this potential security vulnerability.
3933   This requirement also improves the load-balancing behavior of clients
3934   for replicated servers using the same DNS name and reduces the
3935   likelihood of a user's experiencing failure in accessing sites which
3936   use that strategy.
3940<section title="Proxies and Caching" anchor="attack.proxies">
3942   By their very nature, HTTP proxies are men-in-the-middle, and
3943   represent an opportunity for man-in-the-middle attacks. Compromise of
3944   the systems on which the proxies run can result in serious security
3945   and privacy problems. Proxies have access to security-related
3946   information, personal information about individual users and
3947   organizations, and proprietary information belonging to users and
3948   content providers. A compromised proxy, or a proxy implemented or
3949   configured without regard to security and privacy considerations,
3950   might be used in the commission of a wide range of potential attacks.
3953   Proxy operators need to protect the systems on which proxies run as
3954   they would protect any system that contains or transports sensitive
3955   information. In particular, log information gathered at proxies often
3956   contains highly sensitive personal information, and/or information
3957   about organizations. Log information needs to be carefully guarded, and
3958   appropriate guidelines for use need to be developed and followed.
3959   (<xref target="abuse.of.server.log.information"/>).
3962   Proxy implementors need to consider the privacy and security
3963   implications of their design and coding decisions, and of the
3964   configuration options they provide to proxy operators (especially the
3965   default configuration).
3968   Users of a proxy need to be aware that proxies are no trustworthier than
3969   the people who run them; HTTP itself cannot solve this problem.
3972   The judicious use of cryptography, when appropriate, might suffice to
3973   protect against a broad range of security and privacy attacks. Such
3974   cryptography is beyond the scope of the HTTP/1.1 specification.
3978<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3980   They exist. They are hard to defend against. Research continues.
3981   Beware.
3986<section title="Acknowledgments" anchor="ack">
3988   HTTP has evolved considerably over the years. It has
3989   benefited from a large and active developer community &mdash; the many
3990   people who have participated on the www-talk mailing list &mdash; and it is
3991   that community which has been most responsible for the success of
3992   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3993   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3994   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3995   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3996   VanHeyningen deserve special recognition for their efforts in
3997   defining early aspects of the protocol.
4000   This document has benefited greatly from the comments of all those
4001   participating in the HTTP-WG. In addition to those already mentioned,
4002   the following individuals have contributed to this specification:
4005   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4006   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4007   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4008   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4009   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4010   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4011   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4012   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4013   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4014   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4015   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4016   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4019   Thanks to the "cave men" of Palo Alto. You know who you are.
4022   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4023   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4024   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4025   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4026   Larry Masinter for their help. And thanks go particularly to Jeff
4027   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4030   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4031   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4032   discovery of many of the problems that this document attempts to
4033   rectify.
4036   This specification makes heavy use of the augmented BNF and generic
4037   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4038   reuses many of the definitions provided by Nathaniel Borenstein and
4039   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4040   specification will help reduce past confusion over the relationship
4041   between HTTP and Internet mail message formats.
4045Acknowledgements TODO list
4047- Jeff Hodges ("effective request URI")
4055<references title="Normative References">
4057<reference anchor="ISO-8859-1">
4058  <front>
4059    <title>
4060     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4061    </title>
4062    <author>
4063      <organization>International Organization for Standardization</organization>
4064    </author>
4065    <date year="1998"/>
4066  </front>
4067  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4070<reference anchor="Part2">
4071  <front>
4072    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4073    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4074      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4075      <address><email></email></address>
4076    </author>
4077    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4078      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4079      <address><email></email></address>
4080    </author>
4081    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4082      <organization abbrev="HP">Hewlett-Packard Company</organization>
4083      <address><email></email></address>
4084    </author>
4085    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4086      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4087      <address><email></email></address>
4088    </author>
4089    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4090      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4091      <address><email></email></address>
4092    </author>
4093    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4094      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4095      <address><email></email></address>
4096    </author>
4097    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4098      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4099      <address><email></email></address>
4100    </author>
4101    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4102      <organization abbrev="W3C">World Wide Web Consortium</organization>
4103      <address><email></email></address>
4104    </author>
4105    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4106      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4107      <address><email></email></address>
4108    </author>
4109    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4110  </front>
4111  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4112  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4115<reference anchor="Part3">
4116  <front>
4117    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4118    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4119      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4120      <address><email></email></address>
4121    </author>
4122    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4123      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4124      <address><email></email></address>
4125    </author>
4126    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4127      <organization abbrev="HP">Hewlett-Packard Company</organization>
4128      <address><email></email></address>
4129    </author>
4130    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4131      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4132      <address><email></email></address>
4133    </author>
4134    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4135      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4136      <address><email></email></address>
4137    </author>
4138    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4139      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4140      <address><email></email></address>
4141    </author>
4142    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4143      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4144      <address><email></email></address>
4145    </author>
4146    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4147      <organization abbrev="W3C">World Wide Web Consortium</organization>
4148      <address><email></email></address>
4149    </author>
4150    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4151      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4152      <address><email></email></address>
4153    </author>
4154    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4155  </front>
4156  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4157  <x:source href="p3-payload.xml" basename="p3-payload"/>
4160<reference anchor="Part6">
4161  <front>
4162    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4163    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4164      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4165      <address><email></email></address>
4166    </author>
4167    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4168      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4169      <address><email></email></address>
4170    </author>
4171    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4172      <organization abbrev="HP">Hewlett-Packard Company</organization>
4173      <address><email></email></address>
4174    </author>
4175    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4176      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4177      <address><email></email></address>
4178    </author>
4179    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4180      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4181      <address><email></email></address>
4182    </author>
4183    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4184      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4185      <address><email></email></address>
4186    </author>
4187    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4188      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4189      <address><email></email></address>
4190    </author>
4191    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4192      <organization abbrev="W3C">World Wide Web Consortium</organization>
4193      <address><email></email></address>
4194    </author>
4195    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4196      <address><email></email></address>
4197    </author>
4198    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4199      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4200      <address><email></email></address>
4201    </author>
4202    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4203  </front>
4204  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4205  <x:source href="p6-cache.xml" basename="p6-cache"/>
4208<reference anchor="RFC5234">
4209  <front>
4210    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4211    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4212      <organization>Brandenburg InternetWorking</organization>
4213      <address>
4214        <email></email>
4215      </address> 
4216    </author>
4217    <author initials="P." surname="Overell" fullname="Paul Overell">
4218      <organization>THUS plc.</organization>
4219      <address>
4220        <email></email>
4221      </address>
4222    </author>
4223    <date month="January" year="2008"/>
4224  </front>
4225  <seriesInfo name="STD" value="68"/>
4226  <seriesInfo name="RFC" value="5234"/>
4229<reference anchor="RFC2119">
4230  <front>
4231    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4232    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4233      <organization>Harvard University</organization>
4234      <address><email></email></address>
4235    </author>
4236    <date month="March" year="1997"/>
4237  </front>
4238  <seriesInfo name="BCP" value="14"/>
4239  <seriesInfo name="RFC" value="2119"/>
4242<reference anchor="RFC3986">
4243 <front>
4244  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4245  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4246    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4247    <address>
4248       <email></email>
4249       <uri></uri>
4250    </address>
4251  </author>
4252  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4253    <organization abbrev="Day Software">Day Software</organization>
4254    <address>
4255      <email></email>
4256      <uri></uri>
4257    </address>
4258  </author>
4259  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4260    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4261    <address>
4262      <email></email>
4263      <uri></uri>
4264    </address>
4265  </author>
4266  <date month='January' year='2005'></date>
4267 </front>
4268 <seriesInfo name="STD" value="66"/>
4269 <seriesInfo name="RFC" value="3986"/>
4272<reference anchor="USASCII">
4273  <front>
4274    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4275    <author>
4276      <organization>American National Standards Institute</organization>
4277    </author>
4278    <date year="1986"/>
4279  </front>
4280  <seriesInfo name="ANSI" value="X3.4"/>
4283<reference anchor="RFC1950">
4284  <front>
4285    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4286    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4287      <organization>Aladdin Enterprises</organization>
4288      <address><email></email></address>
4289    </author>
4290    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4291    <date month="May" year="1996"/>
4292  </front>
4293  <seriesInfo name="RFC" value="1950"/>
4294  <annotation>
4295    RFC 1950 is an Informational RFC, thus it might be less stable than
4296    this specification. On the other hand, this downward reference was
4297    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4298    therefore it is unlikely to cause problems in practice. See also
4299    <xref target="BCP97"/>.
4300  </annotation>
4303<reference anchor="RFC1951">
4304  <front>
4305    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4306    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4307      <organization>Aladdin Enterprises</organization>
4308      <address><email></email></address>
4309    </author>
4310    <date month="May" year="1996"/>
4311  </front>
4312  <seriesInfo name="RFC" value="1951"/>
4313  <annotation>
4314    RFC 1951 is an Informational RFC, thus it might be less stable than
4315    this specification. On the other hand, this downward reference was
4316    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4317    therefore it is unlikely to cause problems in practice. See also
4318    <xref target="BCP97"/>.
4319  </annotation>
4322<reference anchor="RFC1952">
4323  <front>
4324    <title>GZIP file format specification version 4.3</title>
4325    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4326      <organization>Aladdin Enterprises</organization>
4327      <address><email></email></address>
4328    </author>
4329    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4330      <address><email></email></address>
4331    </author>
4332    <author initials="M." surname="Adler" fullname="Mark Adler">
4333      <address><email></email></address>
4334    </author>
4335    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4336      <address><email></email></address>
4337    </author>
4338    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4339      <address><email></email></address>
4340    </author>
4341    <date month="May" year="1996"/>
4342  </front>
4343  <seriesInfo name="RFC" value="1952"/>
4344  <annotation>
4345    RFC 1952 is an Informational RFC, thus it might be less stable than
4346    this specification. On the other hand, this downward reference was
4347    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4348    therefore it is unlikely to cause problems in practice. See also
4349    <xref target="BCP97"/>.
4350  </annotation>
4355<references title="Informative References">
4357<reference anchor="Nie1997" target="">
4358  <front>
4359    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4360    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4361    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4362    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4363    <author initials="H." surname="Lie" fullname="H. Lie"/>
4364    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4365    <date year="1997" month="September"/>
4366  </front>
4367  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4370<reference anchor="Pad1995" target="">
4371  <front>
4372    <title>Improving HTTP Latency</title>
4373    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4374    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4375    <date year="1995" month="December"/>
4376  </front>
4377  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4380<reference anchor="RFC1123">
4381  <front>
4382    <title>Requirements for Internet Hosts - Application and Support</title>
4383    <author initials="R." surname="Braden" fullname="Robert Braden">
4384      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4385      <address><email>Braden@ISI.EDU</email></address>
4386    </author>
4387    <date month="October" year="1989"/>
4388  </front>
4389  <seriesInfo name="STD" value="3"/>
4390  <seriesInfo name="RFC" value="1123"/>
4393<reference anchor="RFC1900">
4394  <front>
4395    <title>Renumbering Needs Work</title>
4396    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4397      <organization>CERN, Computing and Networks Division</organization>
4398      <address><email></email></address>
4399    </author>
4400    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4401      <organization>cisco Systems</organization>
4402      <address><email></email></address>
4403    </author>
4404    <date month="February" year="1996"/>
4405  </front>
4406  <seriesInfo name="RFC" value="1900"/>
4409<reference anchor='RFC1919'>
4410  <front>
4411    <title>Classical versus Transparent IP Proxies</title>
4412    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4413      <address><email></email></address>
4414    </author>
4415    <date year='1996' month='March' />
4416  </front>
4417  <seriesInfo name='RFC' value='1919' />
4420<reference anchor="RFC1945">
4421  <front>
4422    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4423    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4424      <organization>MIT, Laboratory for Computer Science</organization>
4425      <address><email></email></address>
4426    </author>
4427    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4428      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4429      <address><email></email></address>
4430    </author>
4431    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4432      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4433      <address><email></email></address>
4434    </author>
4435    <date month="May" year="1996"/>
4436  </front>
4437  <seriesInfo name="RFC" value="1945"/>
4440<reference anchor="RFC2045">
4441  <front>
4442    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4443    <author initials="N." surname="Freed" fullname="Ned Freed">
4444      <organization>Innosoft International, Inc.</organization>
4445      <address><email></email></address>
4446    </author>
4447    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4448      <organization>First Virtual Holdings</organization>
4449      <address><email></email></address>
4450    </author>
4451    <date month="November" year="1996"/>
4452  </front>
4453  <seriesInfo name="RFC" value="2045"/>
4456<reference anchor="RFC2047">
4457  <front>
4458    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4459    <author initials="K." surname="Moore" fullname="Keith Moore">
4460      <organization>University of Tennessee</organization>
4461      <address><email></email></address>
4462    </author>
4463    <date month="November" year="1996"/>
4464  </front>
4465  <seriesInfo name="RFC" value="2047"/>
4468<reference anchor="RFC2068">
4469  <front>
4470    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4471    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4472      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4473      <address><email></email></address>
4474    </author>
4475    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4476      <organization>MIT Laboratory for Computer Science</organization>
4477      <address><email></email></address>
4478    </author>
4479    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4480      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4481      <address><email></email></address>
4482    </author>
4483    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4484      <organization>MIT Laboratory for Computer Science</organization>
4485      <address><email></email></address>
4486    </author>
4487    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4488      <organization>MIT Laboratory for Computer Science</organization>
4489      <address><email></email></address>
4490    </author>
4491    <date month="January" year="1997"/>
4492  </front>
4493  <seriesInfo name="RFC" value="2068"/>
4496<reference anchor="RFC2145">
4497  <front>
4498    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4499    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4500      <organization>Western Research Laboratory</organization>
4501      <address><email></email></address>
4502    </author>
4503    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4504      <organization>Department of Information and Computer Science</organization>
4505      <address><email></email></address>
4506    </author>
4507    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4508      <organization>MIT Laboratory for Computer Science</organization>
4509      <address><email></email></address>
4510    </author>
4511    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4512      <organization>W3 Consortium</organization>
4513      <address><email></email></address>
4514    </author>
4515    <date month="May" year="1997"/>
4516  </front>
4517  <seriesInfo name="RFC" value="2145"/>
4520<reference anchor="RFC2616">
4521  <front>
4522    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4523    <author initials="R." surname="Fielding" fullname="R. Fielding">
4524      <organization>University of California, Irvine</organization>
4525      <address><email></email></address>
4526    </author>
4527    <author initials="J." surname="Gettys" fullname="J. Gettys">
4528      <organization>W3C</organization>
4529      <address><email></email></address>
4530    </author>
4531    <author initials="J." surname="Mogul" fullname="J. Mogul">
4532      <organization>Compaq Computer Corporation</organization>
4533      <address><email></email></address>
4534    </author>
4535    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4536      <organization>MIT Laboratory for Computer Science</organization>
4537      <address><email></email></address>
4538    </author>
4539    <author initials="L." surname="Masinter" fullname="L. Masinter">
4540      <organization>Xerox Corporation</organization>
4541      <address><email></email></address>
4542    </author>
4543    <author initials="P." surname="Leach" fullname="P. Leach">
4544      <organization>Microsoft Corporation</organization>
4545      <address><email></email></address>
4546    </author>
4547    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4548      <organization>W3C</organization>
4549      <address><email></email></address>
4550    </author>
4551    <date month="June" year="1999"/>
4552  </front>
4553  <seriesInfo name="RFC" value="2616"/>
4556<reference anchor='RFC2817'>
4557  <front>
4558    <title>Upgrading to TLS Within HTTP/1.1</title>
4559    <author initials='R.' surname='Khare' fullname='R. Khare'>
4560      <organization>4K Associates / UC Irvine</organization>
4561      <address><email></email></address>
4562    </author>
4563    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4564      <organization>Agranat Systems, Inc.</organization>
4565      <address><email></email></address>
4566    </author>
4567    <date year='2000' month='May' />
4568  </front>
4569  <seriesInfo name='RFC' value='2817' />
4572<reference anchor='RFC2818'>
4573  <front>
4574    <title>HTTP Over TLS</title>
4575    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4576      <organization>RTFM, Inc.</organization>
4577      <address><email></email></address>
4578    </author>
4579    <date year='2000' month='May' />
4580  </front>
4581  <seriesInfo name='RFC' value='2818' />
4584<reference anchor='RFC2965'>
4585  <front>
4586    <title>HTTP State Management Mechanism</title>
4587    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4588      <organization>Bell Laboratories, Lucent Technologies</organization>
4589      <address><email></email></address>
4590    </author>
4591    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4592      <organization>, Inc.</organization>
4593      <address><email></email></address>
4594    </author>
4595    <date year='2000' month='October' />
4596  </front>
4597  <seriesInfo name='RFC' value='2965' />
4600<reference anchor='RFC3040'>
4601  <front>
4602    <title>Internet Web Replication and Caching Taxonomy</title>
4603    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4604      <organization>Equinix, Inc.</organization>
4605    </author>
4606    <author initials='I.' surname='Melve' fullname='I. Melve'>
4607      <organization>UNINETT</organization>
4608    </author>
4609    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4610      <organization>CacheFlow Inc.</organization>
4611    </author>
4612    <date year='2001' month='January' />
4613  </front>
4614  <seriesInfo name='RFC' value='3040' />
4617<reference anchor='RFC3864'>
4618  <front>
4619    <title>Registration Procedures for Message Header Fields</title>
4620    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4621      <organization>Nine by Nine</organization>
4622      <address><email></email></address>
4623    </author>
4624    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4625      <organization>BEA Systems</organization>
4626      <address><email></email></address>
4627    </author>
4628    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4629      <organization>HP Labs</organization>
4630      <address><email></email></address>
4631    </author>
4632    <date year='2004' month='September' />
4633  </front>
4634  <seriesInfo name='BCP' value='90' />
4635  <seriesInfo name='RFC' value='3864' />
4638<reference anchor="RFC4288">
4639  <front>
4640    <title>Media Type Specifications and Registration Procedures</title>
4641    <author initials="N." surname="Freed" fullname="N. Freed">
4642      <organization>Sun Microsystems</organization>
4643      <address>
4644        <email></email>
4645      </address>
4646    </author>
4647    <author initials="J." surname="Klensin" fullname="J. Klensin">
4648      <address>
4649        <email></email>
4650      </address>
4651    </author>
4652    <date year="2005" month="December"/>
4653  </front>
4654  <seriesInfo name="BCP" value="13"/>
4655  <seriesInfo name="RFC" value="4288"/>
4658<reference anchor='RFC4395'>
4659  <front>
4660    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4661    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4662      <organization>AT&amp;T Laboratories</organization>
4663      <address>
4664        <email></email>
4665      </address>
4666    </author>
4667    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4668      <organization>Qualcomm, Inc.</organization>
4669      <address>
4670        <email></email>
4671      </address>
4672    </author>
4673    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4674      <organization>Adobe Systems</organization>
4675      <address>
4676        <email></email>
4677      </address>
4678    </author>
4679    <date year='2006' month='February' />
4680  </front>
4681  <seriesInfo name='BCP' value='115' />
4682  <seriesInfo name='RFC' value='4395' />
4685<reference anchor='RFC5226'>
4686  <front>
4687    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4688    <author initials='T.' surname='Narten' fullname='T. Narten'>
4689      <organization>IBM</organization>
4690      <address><email></email></address>
4691    </author>
4692    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4693      <organization>Google</organization>
4694      <address><email></email></address>
4695    </author>
4696    <date year='2008' month='May' />
4697  </front>
4698  <seriesInfo name='BCP' value='26' />
4699  <seriesInfo name='RFC' value='5226' />
4702<reference anchor="RFC5322">
4703  <front>
4704    <title>Internet Message Format</title>
4705    <author initials="P." surname="Resnick" fullname="P. Resnick">
4706      <organization>Qualcomm Incorporated</organization>
4707    </author>
4708    <date year="2008" month="October"/>
4709  </front>
4710  <seriesInfo name="RFC" value="5322"/>
4713<reference anchor='draft-ietf-httpstate-cookie'>
4714  <front>
4715    <title>HTTP State Management Mechanism</title>
4716    <author initials="A." surname="Barth" fullname="Adam Barth">
4717      <organization abbrev="U.C. Berkeley">
4718        University of California, Berkeley
4719      </organization>
4720      <address><email></email></address>
4721    </author>
4722    <date year='2011' month='March' />
4723  </front>
4724  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4727<reference anchor='BCP97'>
4728  <front>
4729    <title>Handling Normative References to Standards-Track Documents</title>
4730    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4731      <address>
4732        <email></email>
4733      </address>
4734    </author>
4735    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4736      <organization>MIT</organization>
4737      <address>
4738        <email></email>
4739      </address>
4740    </author>
4741    <date year='2007' month='June' />
4742  </front>
4743  <seriesInfo name='BCP' value='97' />
4744  <seriesInfo name='RFC' value='4897' />
4747<reference anchor="Kri2001" target="">
4748  <front>
4749    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4750    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4751    <date year="2001" month="November"/>
4752  </front>
4753  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4756<reference anchor="Spe" target="">
4757  <front>
4758    <title>Analysis of HTTP Performance Problems</title>
4759    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4760    <date/>
4761  </front>
4764<reference anchor="Tou1998" target="">
4765  <front>
4766  <title>Analysis of HTTP Performance</title>
4767  <author initials="J." surname="Touch" fullname="Joe Touch">
4768    <organization>USC/Information Sciences Institute</organization>
4769    <address><email></email></address>
4770  </author>
4771  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4772    <organization>USC/Information Sciences Institute</organization>
4773    <address><email></email></address>
4774  </author>
4775  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4776    <organization>USC/Information Sciences Institute</organization>
4777    <address><email></email></address>
4778  </author>
4779  <date year="1998" month="Aug"/>
4780  </front>
4781  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4782  <annotation>(original report dated Aug. 1996)</annotation>
4788<section title="Tolerant Applications" anchor="tolerant.applications">
4790   Although this document specifies the requirements for the generation
4791   of HTTP/1.1 messages, not all applications will be correct in their
4792   implementation. We therefore recommend that operational applications
4793   be tolerant of deviations whenever those deviations can be
4794   interpreted unambiguously.
4797   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4798   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4799   &SHOULD; accept any amount of WSP characters between fields, even though
4800   only a single SP is required.
4803   The line terminator for header fields is the sequence CRLF.
4804   However, we recommend that applications, when parsing such headers fields,
4805   recognize a single LF as a line terminator and ignore the leading CR.
4808   The character set of a representation &SHOULD; be labeled as the lowest
4809   common denominator of the character codes used within that representation, with
4810   the exception that not labeling the representation is preferred over labeling
4811   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4814   Additional rules for requirements on parsing and encoding of dates
4815   and other potential problems with date encodings include:
4818  <list style="symbols">
4819     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4820        which appears to be more than 50 years in the future is in fact
4821        in the past (this helps solve the "year 2000" problem).</t>
4823     <t>Although all date formats are specified to be case-sensitive,
4824        recipients &SHOULD; match day, week and timezone names
4825        case-insensitively.</t>
4827     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4828        Expires date as earlier than the proper value, but &MUST-NOT;
4829        internally represent a parsed Expires date as later than the
4830        proper value.</t>
4832     <t>All expiration-related calculations &MUST; be done in GMT. The
4833        local time zone &MUST-NOT; influence the calculation or comparison
4834        of an age or expiration time.</t>
4836     <t>If an HTTP header field incorrectly carries a date value with a time
4837        zone other than GMT, it &MUST; be converted into GMT using the
4838        most conservative possible conversion.</t>
4839  </list>
4843<section title="Compatibility with Previous Versions" anchor="compatibility">
4845   HTTP has been in use by the World-Wide Web global information initiative
4846   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4847   was a simple protocol for hypertext data transfer across the Internet
4848   with only a single request method (GET) and no metadata.
4849   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4850   methods and MIME-like messaging that could include metadata about the data
4851   transferred and modifiers on the request/response semantics. However,
4852   HTTP/1.0 did not sufficiently take into consideration the effects of
4853   hierarchical proxies, caching, the need for persistent connections, or
4854   name-based virtual hosts. The proliferation of incompletely-implemented
4855   applications calling themselves "HTTP/1.0" further necessitated a
4856   protocol version change in order for two communicating applications
4857   to determine each other's true capabilities.
4860   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4861   requirements that enable reliable implementations, adding only
4862   those new features that will either be safely ignored by an HTTP/1.0
4863   recipient or only sent when communicating with a party advertising
4864   compliance with HTTP/1.1.
4867   It is beyond the scope of a protocol specification to mandate
4868   compliance with previous versions. HTTP/1.1 was deliberately
4869   designed, however, to make supporting previous versions easy. It is
4870   worth noting that, at the time of composing this specification, we would
4871   expect general-purpose HTTP/1.1 servers to:
4872  <list style="symbols">
4873     <t>understand any valid request in the format of HTTP/1.0 and
4874        1.1;</t>
4876     <t>respond appropriately with a message in the same major version
4877        used by the client.</t>
4878  </list>
4881   And we would expect HTTP/1.1 clients to:
4882  <list style="symbols">
4883     <t>understand any valid response in the format of HTTP/1.0 or
4884        1.1.</t>
4885  </list>
4888   For most implementations of HTTP/1.0, each connection is established
4889   by the client prior to the request and closed by the server after
4890   sending the response. Some implementations implement the Keep-Alive
4891   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4894<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4896   This section summarizes major differences between versions HTTP/1.0
4897   and HTTP/1.1.
4900<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4902   The requirements that clients and servers support the Host header
4903   field (<xref target=""/>), report an error if it is
4904   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4905   are among the most important changes defined by this
4906   specification.
4909   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4910   addresses and servers; there was no other established mechanism for
4911   distinguishing the intended server of a request than the IP address
4912   to which that request was directed. The changes outlined above will
4913   allow the Internet, once older HTTP clients are no longer common, to
4914   support multiple Web sites from a single IP address, greatly
4915   simplifying large operational Web servers, where allocation of many
4916   IP addresses to a single host has created serious problems. The
4917   Internet will also be able to recover the IP addresses that have been
4918   allocated for the sole purpose of allowing special-purpose domain
4919   names to be used in root-level HTTP URLs. Given the rate of growth of
4920   the Web, and the number of servers already deployed, it is extremely
4921   important that all implementations of HTTP (including updates to
4922   existing HTTP/1.0 applications) correctly implement these
4923   requirements:
4924  <list style="symbols">
4925     <t>Both clients and servers &MUST; support the Host header field.</t>
4927     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4929     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4930        request does not include a Host header field.</t>
4932     <t>Servers &MUST; accept absolute URIs.</t>
4933  </list>
4938<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4940   Some clients and servers might wish to be compatible with some
4941   previous implementations of persistent connections in HTTP/1.0
4942   clients and servers. Persistent connections in HTTP/1.0 are
4943   explicitly negotiated as they are not the default behavior. HTTP/1.0
4944   experimental implementations of persistent connections are faulty,
4945   and the new facilities in HTTP/1.1 are designed to rectify these
4946   problems. The problem was that some existing HTTP/1.0 clients might
4947   send Keep-Alive to a proxy server that doesn't understand
4948   Connection, which would then erroneously forward it to the next
4949   inbound server, which would establish the Keep-Alive connection and
4950   result in a hung HTTP/1.0 proxy waiting for the close on the
4951   response. The result is that HTTP/1.0 clients must be prevented from
4952   using Keep-Alive when talking to proxies.
4955   However, talking to proxies is the most important use of persistent
4956   connections, so that prohibition is clearly unacceptable. Therefore,
4957   we need some other mechanism for indicating a persistent connection
4958   is desired, which is safe to use even when talking to an old proxy
4959   that ignores Connection. Persistent connections are the default for
4960   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4961   declaring non-persistence. See <xref target="header.connection"/>.
4964   The original HTTP/1.0 form of persistent connections (the Connection:
4965   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4969<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4971  Empty list elements in list productions have been deprecated.
4972  (<xref target="notation.abnf"/>)
4975  Rules about implicit linear whitespace between certain grammar productions
4976  have been removed; now it's only allowed when specifically pointed out
4977  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4978  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4979  Non-ASCII content in header fields and reason phrase has been obsoleted and
4980  made opaque (the TEXT rule was removed)
4981  (<xref target="basic.rules"/>)
4984  Clarify that HTTP-Version is case sensitive.
4985  (<xref target="http.version"/>)
4988  Require that invalid whitespace around field-names be rejected.
4989  (<xref target="header.fields"/>)
4992  Require recipients to handle bogus Content-Length header fields as errors.
4993  (<xref target="message.body"/>)
4996  Remove reference to non-existent identity transfer-coding value tokens.
4997  (Sections <xref format="counter" target="message.body"/> and
4998  <xref format="counter" target="transfer.codings"/>)
5001  Update use of abs_path production from RFC 1808 to the path-absolute + query
5002  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5003  request method only.
5004  (<xref target="request-target"/>)
5007  Clarification that the chunk length does not include the count of the octets
5008  in the chunk header and trailer. Furthermore disallowed line folding
5009  in chunk extensions.
5010  (<xref target="chunked.encoding"/>)
5013  Remove hard limit of two connections per server.
5014  (<xref target="persistent.practical"/>)
5017  Clarify exactly when close connection options must be sent.
5018  (<xref target="header.connection"/>)
5021  Define the semantics of the "Upgrade" header field in responses other than
5022  101 (this was incorporated from <xref target="RFC2817"/>).
5023  (<xref target="header.upgrade"/>)
5028<?BEGININC p1-messaging.abnf-appendix ?>
5029<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5031<artwork type="abnf" name="p1-messaging.parsed-abnf">
5032<x:ref>BWS</x:ref> = OWS
5034<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5035<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
5036<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5037 connection-token ] )
5038<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
5039<x:ref>Content-Length-v</x:ref> = 1*DIGIT
5041<x:ref>Date</x:ref> = "Date:" OWS Date-v
5042<x:ref>Date-v</x:ref> = HTTP-date
5044<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5046<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5047<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5048<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5049<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5050 ]
5051<x:ref>Host</x:ref> = "Host:" OWS Host-v
5052<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
5054<x:ref>Method</x:ref> = token
5056<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5058<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5059<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5060<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5061<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5062<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5064<x:ref>Status-Code</x:ref> = 3DIGIT
5065<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5067<x:ref>TE</x:ref> = "TE:" OWS TE-v
5068<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5069<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5070<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5071<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5072<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5073 transfer-coding ] )
5075<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5076<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5077<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5079<x:ref>Via</x:ref> = "Via:" OWS Via-v
5080<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5081 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5082 ] )
5084<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5085<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5086<x:ref>attribute</x:ref> = token
5087<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5089<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5090<x:ref>chunk-data</x:ref> = 1*OCTET
5091<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5092<x:ref>chunk-ext-name</x:ref> = token
5093<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5094<x:ref>chunk-size</x:ref> = 1*HEXDIG
5095<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5096<x:ref>connection-token</x:ref> = token
5097<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5098 / %x2A-5B ; '*'-'['
5099 / %x5D-7E ; ']'-'~'
5100 / obs-text
5102<x:ref>date1</x:ref> = day SP month SP year
5103<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5104<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5105<x:ref>day</x:ref> = 2DIGIT
5106<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5107 / %x54.75.65 ; Tue
5108 / %x57.65.64 ; Wed
5109 / %x54.68.75 ; Thu
5110 / %x46.72.69 ; Fri
5111 / %x53.61.74 ; Sat
5112 / %x53.75.6E ; Sun
5113<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5114 / %x54. ; Tuesday
5115 / %x57.65.64.6E. ; Wednesday
5116 / %x54. ; Thursday
5117 / %x46. ; Friday
5118 / %x53. ; Saturday
5119 / %x53.75.6E.64.61.79 ; Sunday
5121<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5122<x:ref>field-name</x:ref> = token
5123<x:ref>field-value</x:ref> = *( field-content / OWS )
5125<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5126<x:ref>hour</x:ref> = 2DIGIT
5127<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5128<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5130<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5132<x:ref>message-body</x:ref> = *OCTET
5133<x:ref>minute</x:ref> = 2DIGIT
5134<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5135 / %x46.65.62 ; Feb
5136 / %x4D.61.72 ; Mar
5137 / %x41.70.72 ; Apr
5138 / %x4D.61.79 ; May
5139 / %x4A.75.6E ; Jun
5140 / %x4A.75.6C ; Jul
5141 / %x41.75.67 ; Aug
5142 / %x53.65.70 ; Sep
5143 / %x4F.63.74 ; Oct
5144 / %x4E.6F.76 ; Nov
5145 / %x44.65.63 ; Dec
5147<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5148<x:ref>obs-fold</x:ref> = CRLF
5149<x:ref>obs-text</x:ref> = %x80-FF
5151<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5152<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5153<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5154<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5155<x:ref>product</x:ref> = token [ "/" product-version ]
5156<x:ref>product-version</x:ref> = token
5157<x:ref>protocol-name</x:ref> = token
5158<x:ref>protocol-version</x:ref> = token
5159<x:ref>pseudonym</x:ref> = token
5161<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5162 / %x5D-7E ; ']'-'~'
5163 / obs-text
5164<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5165 / %x5D-7E ; ']'-'~'
5166 / obs-text
5167<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5168<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5169<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5170<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5171<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5172<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5174<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5175<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5176<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5177<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5178 / authority
5179<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5180<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5182<x:ref>second</x:ref> = 2DIGIT
5183<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5184 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5185<x:ref>start-line</x:ref> = Request-Line / Status-Line
5187<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5188<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5189 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5190<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5191<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5192<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5193<x:ref>token</x:ref> = 1*tchar
5194<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5195<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5196 transfer-extension
5197<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5198<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5200<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5202<x:ref>value</x:ref> = word
5204<x:ref>word</x:ref> = token / quoted-string
5206<x:ref>year</x:ref> = 4DIGIT
5209<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5210; Chunked-Body defined but not used
5211; Connection defined but not used
5212; Content-Length defined but not used
5213; Date defined but not used
5214; HTTP-message defined but not used
5215; Host defined but not used
5216; Request defined but not used
5217; Response defined but not used
5218; TE defined but not used
5219; Trailer defined but not used
5220; Transfer-Encoding defined but not used
5221; URI-reference defined but not used
5222; Upgrade defined but not used
5223; Via defined but not used
5224; http-URI defined but not used
5225; https-URI defined but not used
5226; partial-URI defined but not used
5227; special defined but not used
5229<?ENDINC p1-messaging.abnf-appendix ?>
5231<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5233<section title="Since RFC 2616">
5235  Extracted relevant partitions from <xref target="RFC2616"/>.
5239<section title="Since draft-ietf-httpbis-p1-messaging-00">
5241  Closed issues:
5242  <list style="symbols">
5243    <t>
5244      <eref target=""/>:
5245      "HTTP Version should be case sensitive"
5246      (<eref target=""/>)
5247    </t>
5248    <t>
5249      <eref target=""/>:
5250      "'unsafe' characters"
5251      (<eref target=""/>)
5252    </t>
5253    <t>
5254      <eref target=""/>:
5255      "Chunk Size Definition"
5256      (<eref target=""/>)
5257    </t>
5258    <t>
5259      <eref target=""/>:
5260      "Message Length"
5261      (<eref target=""/>)
5262    </t>
5263    <t>
5264      <eref target=""/>:
5265      "Media Type Registrations"
5266      (<eref target=""/>)
5267    </t>
5268    <t>
5269      <eref target=""/>:
5270      "URI includes query"
5271      (<eref target=""/>)
5272    </t>
5273    <t>
5274      <eref target=""/>:
5275      "No close on 1xx responses"
5276      (<eref target=""/>)
5277    </t>
5278    <t>
5279      <eref target=""/>:
5280      "Remove 'identity' token references"
5281      (<eref target=""/>)
5282    </t>
5283    <t>
5284      <eref target=""/>:
5285      "Import query BNF"
5286    </t>
5287    <t>
5288      <eref target=""/>:
5289      "qdtext BNF"
5290    </t>
5291    <t>
5292      <eref target=""/>:
5293      "Normative and Informative references"
5294    </t>
5295    <t>
5296      <eref target=""/>:
5297      "RFC2606 Compliance"
5298    </t>
5299    <t>
5300      <eref target=""/>:
5301      "RFC977 reference"
5302    </t>
5303    <t>
5304      <eref target=""/>:
5305      "RFC1700 references"
5306    </t>
5307    <t>
5308      <eref target=""/>:
5309      "inconsistency in date format explanation"
5310    </t>
5311    <t>
5312      <eref target=""/>:
5313      "Date reference typo"
5314    </t>
5315    <t>
5316      <eref target=""/>:
5317      "Informative references"
5318    </t>
5319    <t>
5320      <eref target=""/>:
5321      "ISO-8859-1 Reference"
5322    </t>
5323    <t>
5324      <eref target=""/>:
5325      "Normative up-to-date references"
5326    </t>
5327  </list>
5330  Other changes:
5331  <list style="symbols">
5332    <t>
5333      Update media type registrations to use RFC4288 template.
5334    </t>
5335    <t>
5336      Use names of RFC4234 core rules DQUOTE and WSP,
5337      fix broken ABNF for chunk-data
5338      (work in progress on <eref target=""/>)
5339    </t>
5340  </list>
5344<section title="Since draft-ietf-httpbis-p1-messaging-01">
5346  Closed issues:
5347  <list style="symbols">
5348    <t>
5349      <eref target=""/>:
5350      "Bodies on GET (and other) requests"
5351    </t>
5352    <t>
5353      <eref target=""/>:
5354      "Updating to RFC4288"
5355    </t>
5356    <t>
5357      <eref target=""/>:
5358      "Status Code and Reason Phrase"
5359    </t>
5360    <t>
5361      <eref target=""/>:
5362      "rel_path not used"
5363    </t>
5364  </list>
5367  Ongoing work on ABNF conversion (<eref target=""/>):
5368  <list style="symbols">
5369    <t>
5370      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5371      "trailer-part").
5372    </t>
5373    <t>
5374      Avoid underscore character in rule names ("http_URL" ->
5375      "http-URL", "abs_path" -> "path-absolute").
5376    </t>
5377    <t>
5378      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5379      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5380      have to be updated when switching over to RFC3986.
5381    </t>
5382    <t>
5383      Synchronize core rules with RFC5234.
5384    </t>
5385    <t>
5386      Get rid of prose rules that span multiple lines.
5387    </t>
5388    <t>
5389      Get rid of unused rules LOALPHA and UPALPHA.
5390    </t>
5391    <t>
5392      Move "Product Tokens" section (back) into Part 1, as "token" is used
5393      in the definition of the Upgrade header field.
5394    </t>
5395    <t>
5396      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5397    </t>
5398    <t>
5399      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5400    </t>
5401  </list>
5405<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5407  Closed issues:
5408  <list style="symbols">
5409    <t>
5410      <eref target=""/>:
5411      "HTTP-date vs. rfc1123-date"
5412    </t>
5413    <t>
5414      <eref target=""/>:
5415      "WS in quoted-pair"
5416    </t>
5417  </list>
5420  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5421  <list style="symbols">
5422    <t>
5423      Reference RFC 3984, and update header field registrations for headers defined
5424      in this document.
5425    </t>
5426  </list>
5429  Ongoing work on ABNF conversion (<eref target=""/>):
5430  <list style="symbols">
5431    <t>
5432      Replace string literals when the string really is case-sensitive (HTTP-Version).
5433    </t>
5434  </list>
5438<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5440  Closed issues:
5441  <list style="symbols">
5442    <t>
5443      <eref target=""/>:
5444      "Connection closing"
5445    </t>
5446    <t>
5447      <eref target=""/>:
5448      "Move registrations and registry information to IANA Considerations"
5449    </t>
5450    <t>
5451      <eref target=""/>:
5452      "need new URL for PAD1995 reference"
5453    </t>
5454    <t>
5455      <eref target=""/>:
5456      "IANA Considerations: update HTTP URI scheme registration"
5457    </t>
5458    <t>
5459      <eref target=""/>:
5460      "Cite HTTPS URI scheme definition"
5461    </t>
5462    <t>
5463      <eref target=""/>:
5464      "List-type headers vs Set-Cookie"
5465    </t>
5466  </list>
5469  Ongoing work on ABNF conversion (<eref target=""/>):
5470  <list style="symbols">
5471    <t>
5472      Replace string literals when the string really is case-sensitive (HTTP-Date).
5473    </t>
5474    <t>
5475      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5476    </t>
5477  </list>
5481<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5483  Closed issues:
5484  <list style="symbols">
5485    <t>
5486      <eref target=""/>:
5487      "Out-of-date reference for URIs"
5488    </t>
5489    <t>
5490      <eref target=""/>:
5491      "RFC 2822 is updated by RFC 5322"
5492    </t>
5493  </list>
5496  Ongoing work on ABNF conversion (<eref target=""/>):
5497  <list style="symbols">
5498    <t>
5499      Use "/" instead of "|" for alternatives.
5500    </t>
5501    <t>
5502      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5503    </t>
5504    <t>
5505      Only reference RFC 5234's core rules.
5506    </t>
5507    <t>
5508      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5509      whitespace ("OWS") and required whitespace ("RWS").
5510    </t>
5511    <t>
5512      Rewrite ABNFs to spell out whitespace rules, factor out
5513      header field value format definitions.
5514    </t>
5515  </list>
5519<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5521  Closed issues:
5522  <list style="symbols">
5523    <t>
5524      <eref target=""/>:
5525      "Header LWS"
5526    </t>
5527    <t>
5528      <eref target=""/>:
5529      "Sort 1.3 Terminology"
5530    </t>
5531    <t>
5532      <eref target=""/>:
5533      "RFC2047 encoded words"
5534    </t>
5535    <t>
5536      <eref target=""/>:
5537      "Character Encodings in TEXT"
5538    </t>
5539    <t>
5540      <eref target=""/>:
5541      "Line Folding"
5542    </t>
5543    <t>
5544      <eref target=""/>:
5545      "OPTIONS * and proxies"
5546    </t>
5547    <t>
5548      <eref target=""/>:
5549      "Reason-Phrase BNF"
5550    </t>
5551    <t>
5552      <eref target=""/>:
5553      "Use of TEXT"
5554    </t>
5555    <t>
5556      <eref target=""/>:
5557      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5558    </t>
5559    <t>
5560      <eref target=""/>:
5561      "RFC822 reference left in discussion of date formats"
5562    </t>
5563  </list>
5566  Final work on ABNF conversion (<eref target=""/>):
5567  <list style="symbols">
5568    <t>
5569      Rewrite definition of list rules, deprecate empty list elements.
5570    </t>
5571    <t>
5572      Add appendix containing collected and expanded ABNF.
5573    </t>
5574  </list>
5577  Other changes:
5578  <list style="symbols">
5579    <t>
5580      Rewrite introduction; add mostly new Architecture Section.
5581    </t>
5582    <t>
5583      Move definition of quality values from Part 3 into Part 1;
5584      make TE request header field grammar independent of accept-params (defined in Part 3).
5585    </t>
5586  </list>
5590<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5592  Closed issues:
5593  <list style="symbols">
5594    <t>
5595      <eref target=""/>:
5596      "base for numeric protocol elements"
5597    </t>
5598    <t>
5599      <eref target=""/>:
5600      "comment ABNF"
5601    </t>
5602  </list>
5605  Partly resolved issues:
5606  <list style="symbols">
5607    <t>
5608      <eref target=""/>:
5609      "205 Bodies" (took out language that implied that there might be
5610      methods for which a request body MUST NOT be included)
5611    </t>
5612    <t>
5613      <eref target=""/>:
5614      "editorial improvements around HTTP-date"
5615    </t>
5616  </list>
5620<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5622  Closed issues:
5623  <list style="symbols">
5624    <t>
5625      <eref target=""/>:
5626      "Repeating single-value headers"
5627    </t>
5628    <t>
5629      <eref target=""/>:
5630      "increase connection limit"
5631    </t>
5632    <t>
5633      <eref target=""/>:
5634      "IP addresses in URLs"
5635    </t>
5636    <t>
5637      <eref target=""/>:
5638      "take over HTTP Upgrade Token Registry"
5639    </t>
5640    <t>
5641      <eref target=""/>:
5642      "CR and LF in chunk extension values"
5643    </t>
5644    <t>
5645      <eref target=""/>:
5646      "HTTP/0.9 support"
5647    </t>
5648    <t>
5649      <eref target=""/>:
5650      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5651    </t>
5652    <t>
5653      <eref target=""/>:
5654      "move definitions of gzip/deflate/compress to part 1"
5655    </t>
5656    <t>
5657      <eref target=""/>:
5658      "disallow control characters in quoted-pair"
5659    </t>
5660  </list>
5663  Partly resolved issues:
5664  <list style="symbols">
5665    <t>
5666      <eref target=""/>:
5667      "update IANA requirements wrt Transfer-Coding values" (add the
5668      IANA Considerations subsection)
5669    </t>
5670  </list>
5674<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5676  Closed issues:
5677  <list style="symbols">
5678    <t>
5679      <eref target=""/>:
5680      "header parsing, treatment of leading and trailing OWS"
5681    </t>
5682  </list>
5685  Partly resolved issues:
5686  <list style="symbols">
5687    <t>
5688      <eref target=""/>:
5689      "Placement of 13.5.1 and 13.5.2"
5690    </t>
5691    <t>
5692      <eref target=""/>:
5693      "use of term "word" when talking about header structure"
5694    </t>
5695  </list>
5699<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5701  Closed issues:
5702  <list style="symbols">
5703    <t>
5704      <eref target=""/>:
5705      "Clarification of the term 'deflate'"
5706    </t>
5707    <t>
5708      <eref target=""/>:
5709      "OPTIONS * and proxies"
5710    </t>
5711    <t>
5712      <eref target=""/>:
5713      "MIME-Version not listed in P1, general header fields"
5714    </t>
5715    <t>
5716      <eref target=""/>:
5717      "IANA registry for content/transfer encodings"
5718    </t>
5719    <t>
5720      <eref target=""/>:
5721      "Case-sensitivity of HTTP-date"
5722    </t>
5723    <t>
5724      <eref target=""/>:
5725      "use of term "word" when talking about header structure"
5726    </t>
5727  </list>
5730  Partly resolved issues:
5731  <list style="symbols">
5732    <t>
5733      <eref target=""/>:
5734      "Term for the requested resource's URI"
5735    </t>
5736  </list>
5740<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5742  Closed issues:
5743  <list style="symbols">
5744    <t>
5745      <eref target=""/>:
5746      "Connection Closing"
5747    </t>
5748    <t>
5749      <eref target=""/>:
5750      "Delimiting messages with multipart/byteranges"
5751    </t>
5752    <t>
5753      <eref target=""/>:
5754      "Handling multiple Content-Length headers"
5755    </t>
5756    <t>
5757      <eref target=""/>:
5758      "Clarify entity / representation / variant terminology"
5759    </t>
5760    <t>
5761      <eref target=""/>:
5762      "consider removing the 'changes from 2068' sections"
5763    </t>
5764  </list>
5767  Partly resolved issues:
5768  <list style="symbols">
5769    <t>
5770      <eref target=""/>:
5771      "HTTP(s) URI scheme definitions"
5772    </t>
5773  </list>
5777<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5779  Closed issues:
5780  <list style="symbols">
5781    <t>
5782      <eref target=""/>:
5783      "Trailer requirements"
5784    </t>
5785    <t>
5786      <eref target=""/>:
5787      "Text about clock requirement for caches belongs in p6"
5788    </t>
5789    <t>
5790      <eref target=""/>:
5791      "effective request URI: handling of missing host in HTTP/1.0"
5792    </t>
5793    <t>
5794      <eref target=""/>:
5795      "confusing Date requirements for clients"
5796    </t>
5797  </list>
5800  Partly resolved issues:
5801  <list style="symbols">
5802    <t>
5803      <eref target=""/>:
5804      "Handling multiple Content-Length headers"
5805    </t>
5806  </list>
5810<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5812  Closed issues:
5813  <list style="symbols">
5814    <t>
5815      <eref target=""/>:
5816      "RFC2145 Normative"
5817    </t>
5818    <t>
5819      <eref target=""/>:
5820      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5821    </t>
5822    <t>
5823      <eref target=""/>:
5824      "define 'transparent' proxy"
5825    </t>
5826    <t>
5827      <eref target=""/>:
5828      "Header Classification"
5829    </t>
5830    <t>
5831      <eref target=""/>:
5832      "Is * usable as a request-uri for new methods?"
5833    </t>
5834    <t>
5835      <eref target=""/>:
5836      "Migrate Upgrade details from RFC2817"
5837    </t>
5838    <t>
5839      <eref target=""/>:
5840      "untangle ABNFs for header fields"
5841    </t>
5842    <t>
5843      <eref target=""/>:
5844      "update RFC 2109 reference"
5845    </t>
5846  </list>
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