source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1170

Last change on this file since 1170 was 1170, checked in by fielding@…, 11 years ago

editorial: introduce more common proxy/gateway terms and
simplify wording of some versioning descriptions.

  • Property svn:eol-style set to native
File size: 247.4 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 request targets 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 identifier (if any)
628   provided for the request target.  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
945   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
946   protocol elements that allow a relative URI without a fragment.
948<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"/>
949  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
950  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
951  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
952  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
953  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
954  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
955  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
956  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
957  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
959  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
962   Each protocol element in HTTP that allows a URI reference will indicate in
963   its ABNF production whether the element allows only a URI in absolute form
964   (absolute-URI), any relative reference (relative-ref), or some other subset
965   of the URI-reference grammar. Unless otherwise indicated, URI references
966   are parsed relative to the request target (the default base URI for both
967   the request and its corresponding response).
970<section title="http URI scheme" anchor="http.uri">
971  <x:anchor-alias value="http-URI"/>
972  <iref item="http URI scheme" primary="true"/>
973  <iref item="URI scheme" subitem="http" primary="true"/>
975   The "http" URI scheme is hereby defined for the purpose of minting
976   identifiers according to their association with the hierarchical
977   namespace governed by a potential HTTP origin server listening for
978   TCP connections on a given port.
979   The HTTP server is identified via the generic syntax's
980   <x:ref>authority</x:ref> component, which includes a host
981   identifier and optional TCP port, and the remainder of the URI is
982   considered to be identifying data corresponding to a resource for
983   which that server might provide an HTTP interface.
985<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
986  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
989   The host identifier within an <x:ref>authority</x:ref> component is
990   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
991   provided as an IP literal or IPv4 address, then the HTTP server is any
992   listener on the indicated TCP port at that IP address. If host is a
993   registered name, then that name is considered an indirect identifier
994   and the recipient might use a name resolution service, such as DNS,
995   to find the address of a listener for that host.
996   The host &MUST-NOT; be empty; if an "http" URI is received with an
997   empty host, then it &MUST; be rejected as invalid.
998   If the port subcomponent is empty or not given, then TCP port 80 is
999   assumed (the default reserved port for WWW services).
1002   Regardless of the form of host identifier, access to that host is not
1003   implied by the mere presence of its name or address. The host might or might
1004   not exist and, even when it does exist, might or might not be running an
1005   HTTP server or listening to the indicated port. The "http" URI scheme
1006   makes use of the delegated nature of Internet names and addresses to
1007   establish a naming authority (whatever entity has the ability to place
1008   an HTTP server at that Internet name or address) and allows that
1009   authority to determine which names are valid and how they might be used.
1012   When an "http" URI is used within a context that calls for access to the
1013   indicated resource, a client &MAY; attempt access by resolving
1014   the host to an IP address, establishing a TCP connection to that address
1015   on the indicated port, and sending an HTTP request message to the server
1016   containing the URI's identifying data as described in <xref target="request"/>.
1017   If the server responds to that request with a non-interim HTTP response
1018   message, as described in <xref target="response"/>, then that response
1019   is considered an authoritative answer to the client's request.
1022   Although HTTP is independent of the transport protocol, the "http"
1023   scheme is specific to TCP-based services because the name delegation
1024   process depends on TCP for establishing authority.
1025   An HTTP service based on some other underlying connection protocol
1026   would presumably be identified using a different URI scheme, just as
1027   the "https" scheme (below) is used for servers that require an SSL/TLS
1028   transport layer on a connection. Other protocols might also be used to
1029   provide access to "http" identified resources &mdash; it is only the
1030   authoritative interface used for mapping the namespace that is
1031   specific to TCP.
1034   The URI generic syntax for authority also includes a deprecated
1035   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1036   for including user authentication information in the URI.  Some
1037   implementations make use of the userinfo component for internal
1038   configuration of authentication information, such as within command
1039   invocation options, configuration files, or bookmark lists, even
1040   though such usage might expose a user identifier or password.
1041   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1042   delimiter) when transmitting an "http" URI in a message.  Recipients
1043   of HTTP messages that contain a URI reference &SHOULD; parse for the
1044   existence of userinfo and treat its presence as an error, likely
1045   indicating that the deprecated subcomponent is being used to obscure
1046   the authority for the sake of phishing attacks.
1050<section title="https URI scheme" anchor="https.uri">
1051   <x:anchor-alias value="https-URI"/>
1052   <iref item="https URI scheme"/>
1053   <iref item="URI scheme" subitem="https"/>
1055   The "https" URI scheme is hereby defined for the purpose of minting
1056   identifiers according to their association with the hierarchical
1057   namespace governed by a potential HTTP origin server listening for
1058   SSL/TLS-secured connections on a given TCP port.
1061   All of the requirements listed above for the "http" scheme are also
1062   requirements for the "https" scheme, except that a default TCP port
1063   of 443 is assumed if the port subcomponent is empty or not given,
1064   and the TCP connection &MUST; be secured for privacy through the
1065   use of strong encryption prior to sending the first HTTP request.
1067<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1068  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1071   Unlike the "http" scheme, responses to "https" identified requests
1072   are never "public" and thus are ineligible for shared caching.
1073   Their default is "private" and might be further constrained via use
1074   of the Cache-Control header field (&header-cache-control;).
1077   Resources made available via the "https" scheme have no shared
1078   identity with the "http" scheme even if their resource identifiers
1079   only differ by the single "s" in the scheme name.  They are
1080   different services governed by different authorities.  However,
1081   some extensions to HTTP that apply to entire host domains, such
1082   as the Cookie protocol, do allow one service to effect communication
1083   with the other services based on host domain matching.
1086   The process for authoritative access to an "https" identified
1087   resource is defined in <xref target="RFC2818"/>.
1091<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1093   Since the "http" and "https" schemes conform to the URI generic syntax,
1094   such URIs are normalized and compared according to the algorithm defined
1095   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1096   described above for each scheme.
1099   If the port is equal to the default port for a scheme, the normal
1100   form is to elide the port subcomponent. Likewise, an empty path
1101   component is equivalent to an absolute path of "/", so the normal
1102   form is to provide a path of "/" instead. The scheme and host
1103   are case-insensitive and normally provided in lowercase; all
1104   other components are compared in a case-sensitive manner.
1105   Characters other than those in the "reserved" set are equivalent
1106   to their percent-encoded octets (see <xref target="RFC3986"
1107   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1110   For example, the following three URIs are equivalent:
1112<figure><artwork type="example">
1118   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1119   If path-abempty is the empty string (i.e., there is no slash "/"
1120   path separator following the authority), then the "http" URI
1121   &MUST; be given as "/" when
1122   used as a request-target (<xref target="request-target"/>). If a proxy
1123   receives a host name which is not a fully qualified domain name, it
1124   &MAY; add its domain to the host name it received. If a proxy receives
1125   a fully qualified domain name, the proxy &MUST-NOT; change the host
1126   name.
1132<section title="HTTP Message" anchor="http.message">
1133<x:anchor-alias value="generic-message"/>
1134<x:anchor-alias value="message.types"/>
1135<x:anchor-alias value="HTTP-message"/>
1136<x:anchor-alias value="start-line"/>
1137<iref item="header section"/>
1138<iref item="headers"/>
1139<iref item="header field"/>
1141   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1142   characters in a format similar to the Internet Message Format
1143   <xref target="RFC5322"/>: zero or more header fields (collectively
1144   referred to as the "headers" or the "header section"), an empty line
1145   indicating the end of the header section, and an optional message-body.
1148   An HTTP message can either be a request from client to server or a
1149   response from server to client.  Syntactically, the two types of message
1150   differ only in the start-line, which is either a Request-Line (for requests)
1151   or a Status-Line (for responses), and in the algorithm for determining
1152   the length of the message-body (<xref target="message.body"/>).
1153   In theory, a client could receive requests and a server could receive
1154   responses, distinguishing them by their different start-line formats,
1155   but in practice servers are implemented to only expect a request
1156   (a response is interpreted as an unknown or invalid request method)
1157   and clients are implemented to only expect a response.
1159<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1160  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1161                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1162                    <x:ref>CRLF</x:ref>
1163                    [ <x:ref>message-body</x:ref> ]
1164  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1167   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1168   header field. The presence of whitespace might be an attempt to trick a
1169   noncompliant implementation of HTTP into ignoring that field or processing
1170   the next line as a new request, either of which might result in security
1171   issues when implementations within the request chain interpret the
1172   same message differently. HTTP/1.1 servers &MUST; reject such a message
1173   with a 400 (Bad Request) response.
1176<section title="Message Parsing Robustness" anchor="message.robustness">
1178   In the interest of robustness, servers &SHOULD; ignore at least one
1179   empty line received where a Request-Line is expected. In other words, if
1180   the server is reading the protocol stream at the beginning of a
1181   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1184   Some old HTTP/1.0 client implementations generate an extra CRLF
1185   after a POST request as a lame workaround for some early server
1186   applications that failed to read message-body content that was
1187   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1188   preface or follow a request with an extra CRLF.  If terminating
1189   the request message-body with a line-ending is desired, then the
1190   client &MUST; include the terminating CRLF octets as part of the
1191   message-body length.
1194   The normal procedure for parsing an HTTP message is to read the
1195   start-line into a structure, read each header field into a hash
1196   table by field name until the empty line, and then use the parsed
1197   data to determine if a message-body is expected.  If a message-body
1198   has been indicated, then it is read as a stream until an amount
1199   of octets equal to the message-body length is read or the connection
1200   is closed.  Care must be taken to parse an HTTP message as a sequence
1201   of octets in an encoding that is a superset of US-ASCII.  Attempting
1202   to parse HTTP as a stream of Unicode characters in a character encoding
1203   like UTF-16 might introduce security flaws due to the differing ways
1204   that such parsers interpret invalid characters.
1207   HTTP allows the set of defined header fields to be extended without
1208   changing the protocol version (see <xref target="header.field.registration"/>).
1209   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1210   proxy is specifically configured to block or otherwise transform such
1211   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1215<section title="Header Fields" anchor="header.fields">
1216  <x:anchor-alias value="header-field"/>
1217  <x:anchor-alias value="field-content"/>
1218  <x:anchor-alias value="field-name"/>
1219  <x:anchor-alias value="field-value"/>
1220  <x:anchor-alias value="OWS"/>
1222   Each HTTP header field consists of a case-insensitive field name
1223   followed by a colon (":"), optional whitespace, and the field value.
1225<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"/>
1226  <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>
1227  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1228  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1229  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1232   No whitespace is allowed between the header field name and colon. For
1233   security reasons, any request message received containing such whitespace
1234   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1235   &MUST; remove any such whitespace from a response message before
1236   forwarding the message downstream.
1239   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1240   preferred. The field value does not include any leading or trailing white
1241   space: OWS occurring before the first non-whitespace character of the
1242   field value or after the last non-whitespace character of the field value
1243   is ignored and &SHOULD; be removed before further processing (as this does
1244   not change the meaning of the header field).
1247   The order in which header fields with differing field names are
1248   received is not significant. However, it is "good practice" to send
1249   header fields that contain control data first, such as Host on
1250   requests and Date on responses, so that implementations can decide
1251   when not to handle a message as early as possible.  A server &MUST;
1252   wait until the entire header section is received before interpreting
1253   a request message, since later header fields might include conditionals,
1254   authentication credentials, or deliberately misleading duplicate
1255   header fields that would impact request processing.
1258   Multiple header fields with the same field name &MUST-NOT; be
1259   sent in a message unless the entire field value for that
1260   header field is defined as a comma-separated list [i.e., #(values)].
1261   Multiple header fields with the same field name can be combined into
1262   one "field-name: field-value" pair, without changing the semantics of the
1263   message, by appending each subsequent field value to the combined
1264   field value in order, separated by a comma. The order in which
1265   header fields with the same field name are received is therefore
1266   significant to the interpretation of the combined field value;
1267   a proxy &MUST-NOT; change the order of these field values when
1268   forwarding a message.
1271  <t>
1272   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1273   practice can occur multiple times, but does not use the list syntax, and
1274   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1275   for details.) Also note that the Set-Cookie2 header field specified in
1276   <xref target="RFC2965"/> does not share this problem.
1277  </t>
1280   Historically, HTTP header field values could be extended over multiple
1281   lines by preceding each extra line with at least one space or horizontal
1282   tab character (line folding). This specification deprecates such line
1283   folding except within the message/http media type
1284   (<xref target=""/>).
1285   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1286   (i.e., that contain any field-content that matches the obs-fold rule) unless
1287   the message is intended for packaging within the message/http media type.
1288   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1289   obs-fold whitespace with a single SP prior to interpreting the field value
1290   or forwarding the message downstream.
1293   Historically, HTTP has allowed field content with text in the ISO-8859-1
1294   <xref target="ISO-8859-1"/> character encoding and supported other
1295   character sets only through use of <xref target="RFC2047"/> encoding.
1296   In practice, most HTTP header field values use only a subset of the
1297   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1298   header fields &SHOULD; limit their field values to US-ASCII characters.
1299   Recipients &SHOULD; treat other (obs-text) octets in field content as
1300   opaque data.
1302<t anchor="rule.comment">
1303  <x:anchor-alias value="comment"/>
1304  <x:anchor-alias value="ctext"/>
1305   Comments can be included in some HTTP header fields by surrounding
1306   the comment text with parentheses. Comments are only allowed in
1307   fields containing "comment" as part of their field value definition.
1309<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1310  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1311  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1312                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1314<t anchor="rule.quoted-cpair">
1315  <x:anchor-alias value="quoted-cpair"/>
1316   The backslash character ("\") can be used as a single-character
1317   quoting mechanism within comment constructs:
1319<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1320  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1323   Producers &SHOULD-NOT; escape characters that do not require escaping
1324   (i.e., other than the backslash character "\" and the parentheses "(" and
1325   ")").
1329<section title="Message Body" anchor="message.body">
1330  <x:anchor-alias value="message-body"/>
1332   The message-body (if any) of an HTTP message is used to carry the
1333   payload body associated with the request or response.
1335<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1336  <x:ref>message-body</x:ref> = *OCTET
1339   The message-body differs from the payload body only when a transfer-coding
1340   has been applied, as indicated by the Transfer-Encoding header field
1341   (<xref target="header.transfer-encoding"/>).  If more than one
1342   Transfer-Encoding header field is present in a message, the multiple
1343   field-values &MUST; be combined into one field-value, according to the
1344   algorithm defined in <xref target="header.fields"/>, before determining
1345   the message-body length.
1348   When one or more transfer-codings are applied to a payload in order to
1349   form the message-body, the Transfer-Encoding header field &MUST; contain
1350   the list of transfer-codings applied. Transfer-Encoding is a property of
1351   the message, not of the payload, and thus &MAY; be added or removed by
1352   any implementation along the request/response chain under the constraints
1353   found in <xref target="transfer.codings"/>.
1356   If a message is received that has multiple Content-Length header fields
1357   (<xref target="header.content-length"/>) with field-values consisting
1358   of the same decimal value, or a single Content-Length header field with
1359   a field value containing a list of identical decimal values (e.g.,
1360   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1361   header fields have been generated or combined by an upstream message
1362   processor, then the recipient &MUST; replace the duplicated fields or
1363   field-values with a single valid Content-Length field containing that
1364   decimal value prior to determining the message-body length.
1367   The rules for when a message-body is allowed in a message differ for
1368   requests and responses.
1371   The presence of a message-body in a request is signaled by the
1372   inclusion of a Content-Length or Transfer-Encoding header field in
1373   the request's header fields, even if the request method does not
1374   define any use for a message-body.  This allows the request
1375   message framing algorithm to be independent of method semantics.
1378   For response messages, whether or not a message-body is included with
1379   a message is dependent on both the request method and the response
1380   status code (<xref target="status.code.and.reason.phrase"/>).
1381   Responses to the HEAD request method never include a message-body
1382   because the associated response header fields (e.g., Transfer-Encoding,
1383   Content-Length, etc.) only indicate what their values would have been
1384   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1385   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1386   All other responses do include a message-body, although the body
1387   &MAY; be of zero length.
1390   The length of the message-body is determined by one of the following
1391   (in order of precedence):
1394  <list style="numbers">
1395    <x:lt><t>
1396     Any response to a HEAD request and any response with a status
1397     code of 100-199, 204, or 304 is always terminated by the first
1398     empty line after the header fields, regardless of the header
1399     fields present in the message, and thus cannot contain a message-body.
1400    </t></x:lt>
1401    <x:lt><t>
1402     If a Transfer-Encoding header field is present
1403     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1404     is the final encoding, the message-body length is determined by reading
1405     and decoding the chunked data until the transfer-coding indicates the
1406     data is complete.
1407    </t>
1408    <t>
1409     If a Transfer-Encoding header field is present in a response and the
1410     "chunked" transfer-coding is not the final encoding, the message-body
1411     length is determined by reading the connection until it is closed by
1412     the server.
1413     If a Transfer-Encoding header field is present in a request and the
1414     "chunked" transfer-coding is not the final encoding, the message-body
1415     length cannot be determined reliably; the server &MUST; respond with
1416     the 400 (Bad Request) status code and then close the connection.
1417    </t>
1418    <t>
1419     If a message is received with both a Transfer-Encoding header field
1420     and a Content-Length header field, the Transfer-Encoding overrides
1421     the Content-Length.
1422     Such a message might indicate an attempt to perform request or response
1423     smuggling (bypass of security-related checks on message routing or content)
1424     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1425     be removed, prior to forwarding the message downstream, or replaced with
1426     the real message-body length after the transfer-coding is decoded.
1427    </t></x:lt>
1428    <x:lt><t>
1429     If a message is received without Transfer-Encoding and with either
1430     multiple Content-Length header fields having differing field-values or
1431     a single Content-Length header field having an invalid value, then the
1432     message framing is invalid and &MUST; be treated as an error to
1433     prevent request or response smuggling.
1434     If this is a request message, the server &MUST; respond with
1435     a 400 (Bad Request) status code and then close the connection.
1436     If this is a response message received by a proxy or gateway, the proxy
1437     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1438     status code as its downstream response, and then close the connection.
1439     If this is a response message received by a user-agent, it &MUST; be
1440     treated as an error by discarding the message and closing the connection.
1441    </t></x:lt>
1442    <x:lt><t>
1443     If a valid Content-Length header field
1444     is present without Transfer-Encoding, its decimal value defines the
1445     message-body length in octets.  If the actual number of octets sent in
1446     the message is less than the indicated Content-Length, the recipient
1447     &MUST; consider the message to be incomplete and treat the connection
1448     as no longer usable.
1449     If the actual number of octets sent in the message is more than the indicated
1450     Content-Length, the recipient &MUST; only process the message-body up to the
1451     field value's number of octets; the remainder of the message &MUST; either
1452     be discarded or treated as the next message in a pipeline.  For the sake of
1453     robustness, a user-agent &MAY; attempt to detect and correct such an error
1454     in message framing if it is parsing the response to the last request on
1455     on a connection and the connection has been closed by the server.
1456    </t></x:lt>
1457    <x:lt><t>
1458     If this is a request message and none of the above are true, then the
1459     message-body length is zero (no message-body is present).
1460    </t></x:lt>
1461    <x:lt><t>
1462     Otherwise, this is a response message without a declared message-body
1463     length, so the message-body length is determined by the number of octets
1464     received prior to the server closing the connection.
1465    </t></x:lt>
1466  </list>
1469   Since there is no way to distinguish a successfully completed,
1470   close-delimited message from a partially-received message interrupted
1471   by network failure, implementations &SHOULD; use encoding or
1472   length-delimited messages whenever possible.  The close-delimiting
1473   feature exists primarily for backwards compatibility with HTTP/1.0.
1476   A server &MAY; reject a request that contains a message-body but
1477   not a Content-Length by responding with 411 (Length Required).
1480   Unless a transfer-coding other than "chunked" has been applied,
1481   a client that sends a request containing a message-body &SHOULD;
1482   use a valid Content-Length header field if the message-body length
1483   is known in advance, rather than the "chunked" encoding, since some
1484   existing services respond to "chunked" with a 411 (Length Required)
1485   status code even though they understand the chunked encoding.  This
1486   is typically because such services are implemented via a gateway that
1487   requires a content-length in advance of being called and the server
1488   is unable or unwilling to buffer the entire request before processing.
1491   A client that sends a request containing a message-body &MUST; include a
1492   valid Content-Length header field if it does not know the server will
1493   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1494   of specific user configuration or by remembering the version of a prior
1495   received response.
1498   Request messages that are prematurely terminated, possibly due to a
1499   cancelled connection or a server-imposed time-out exception, &MUST;
1500   result in closure of the connection; sending an HTTP/1.1 error response
1501   prior to closing the connection is &OPTIONAL;.
1502   Response messages that are prematurely terminated, usually by closure
1503   of the connection prior to receiving the expected number of octets or by
1504   failure to decode a transfer-encoded message-body, &MUST; be recorded
1505   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1506   message-body as if it were complete (i.e., some indication must be given
1507   to the user that an error occurred).  Cache requirements for incomplete
1508   responses are defined in &cache-incomplete;.
1511   A server &MUST; read the entire request message-body or close
1512   the connection after sending its response, since otherwise the
1513   remaining data on a persistent connection would be misinterpreted
1514   as the next request.  Likewise,
1515   a client &MUST; read the entire response message-body if it intends
1516   to reuse the same connection for a subsequent request.  Pipelining
1517   multiple requests on a connection is described in <xref target="pipelining"/>.
1521<section title="General Header Fields" anchor="general.header.fields">
1522  <x:anchor-alias value="general-header"/>
1524   There are a few header fields which have general applicability for
1525   both request and response messages, but which do not apply to the
1526   payload being transferred. These header fields apply only to the
1527   message being transmitted.
1529<texttable align="left">
1530  <ttcol>Header Field Name</ttcol>
1531  <ttcol>Defined in...</ttcol>
1533  <c>Connection</c> <c><xref target="header.connection"/></c>
1534  <c>Date</c> <c><xref target=""/></c>
1535  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1536  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1537  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1538  <c>Via</c> <c><xref target="header.via"/></c>
1543<section title="Request" anchor="request">
1544  <x:anchor-alias value="Request"/>
1546   A request message from a client to a server includes, within the
1547   first line of that message, the method to be applied to the resource,
1548   the identifier of the resource, and the protocol version in use.
1550<!--                 Host                      ; should be moved here eventually -->
1551<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1552  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1553                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1554                  <x:ref>CRLF</x:ref>
1555                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1558<section title="Request-Line" anchor="request-line">
1559  <x:anchor-alias value="Request-Line"/>
1561   The Request-Line begins with a method token, followed by the
1562   request-target and the protocol version, and ending with CRLF. The
1563   elements are separated by SP characters. No CR or LF is allowed
1564   except in the final CRLF sequence.
1566<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1567  <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>
1570<section title="Method" anchor="method">
1571  <x:anchor-alias value="Method"/>
1573   The Method token indicates the request method to be performed on the
1574   target resource. The request method is case-sensitive.
1576<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1577  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1581<section title="request-target" anchor="request-target">
1582  <x:anchor-alias value="request-target"/>
1584   The request-target identifies the target resource upon which to apply the request.
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 "*" ("asterisk form") means that the request does not apply to a
1598   particular resource, but to the server itself. This is only allowed for the
1599   OPTIONS request method. Thus, the only valid example is
1601<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1602OPTIONS * HTTP/1.1
1604<t><iref item="absolute-URI form (of request-target)"/>
1605   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1606   proxy. The proxy is requested to forward the request or service it
1607   from a valid cache, and return the response. Note that the proxy &MAY;
1608   forward the request on to another proxy or directly to the server
1609   specified by the absolute-URI. In order to avoid request loops, a
1610   proxy &MUST; be able to recognize all of its server names, including
1611   any aliases, local variations, and the numeric IP address. An example
1612   Request-Line would be:
1614<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1615GET HTTP/1.1
1618   To allow for transition to absolute-URIs in all requests in future
1619   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1620   form in requests, even though HTTP/1.1 clients will only generate
1621   them in requests to proxies.
1623<t><iref item="authority form (of request-target)"/>
1624   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1626<t><iref item="path-absolute form (of request-target)"/>
1627   The most common form of request-target is that used to identify a
1628   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1629   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1630   the request-target, and the network location of the URI (authority) &MUST;
1631   be transmitted in a Host header field. For example, a client wishing
1632   to retrieve the resource above directly from the origin server would
1633   create a TCP connection to port 80 of the host "" and send
1634   the lines:
1636<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1637GET /pub/WWW/TheProject.html HTTP/1.1
1641   followed by the remainder of the Request. Note that the absolute path
1642   cannot be empty; if none is present in the original URI, it &MUST; be
1643   given as "/" (the server root).
1646   If a proxy receives an OPTIONS request without any path in the
1647   request-target, then the last proxy on the request chain &MUST;
1648   forward the request with "*" as the final request-target.
1651   For example, the request
1652</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1656  would be forwarded by the final proxy as
1657</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1658OPTIONS * HTTP/1.1
1662   after connecting to port 8001 of host "".
1666   The request-target is transmitted in the format specified in
1667   <xref target="http.uri"/>. If the request-target is percent-encoded
1668   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1669   &MUST; decode the request-target in order to
1670   properly interpret the request. Servers &SHOULD; respond to invalid
1671   request-targets with an appropriate status code.
1674   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1675   received request-target when forwarding it to the next inbound server,
1676   except as noted above to replace a null path-absolute with "/" or "*".
1679  <t>
1680    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1681    meaning of the request when the origin server is improperly using
1682    a non-reserved URI character for a reserved purpose.  Implementors
1683    need to be aware that some pre-HTTP/1.1 proxies have been known to
1684    rewrite the request-target.
1685  </t>
1688   HTTP does not place a pre-defined limit on the length of a request-target.
1689   A server &MUST; be prepared to receive URIs of unbounded length and
1690   respond with the 414 (URI Too Long) status code if the received
1691   request-target would be longer than the server wishes to handle
1692   (see &status-414;).
1695   Various ad-hoc limitations on request-target length are found in practice.
1696   It is &RECOMMENDED; that all HTTP senders and recipients support
1697   request-target lengths of 8000 or more octets.
1700  <t>
1701    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1702    are not part of the request-target and thus will not be transmitted
1703    in an HTTP request.
1704  </t>
1709<section title="The Resource Identified by a Request" anchor="">
1711   The exact resource identified by an Internet request is determined by
1712   examining both the request-target and the Host header field.
1715   An origin server that does not allow resources to differ by the
1716   requested host &MAY; ignore the Host header field value when
1717   determining the resource identified by an HTTP/1.1 request. (But see
1718   <xref target=""/>
1719   for other requirements on Host support in HTTP/1.1.)
1722   An origin server that does differentiate resources based on the host
1723   requested (sometimes referred to as virtual hosts or vanity host
1724   names) &MUST; use the following rules for determining the requested
1725   resource on an HTTP/1.1 request:
1726  <list style="numbers">
1727    <t>If request-target is an absolute-URI, the host is part of the
1728     request-target. Any Host header field value in the request &MUST; be
1729     ignored.</t>
1730    <t>If the request-target is not an absolute-URI, and the request includes
1731     a Host header field, the host is determined by the Host header
1732     field value.</t>
1733    <t>If the host as determined by rule 1 or 2 is not a valid host on
1734     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1735  </list>
1738   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1739   attempt to use heuristics (e.g., examination of the URI path for
1740   something unique to a particular host) in order to determine what
1741   exact resource is being requested.
1745<section title="Effective Request URI" anchor="effective.request.uri">
1746  <iref primary="true" item="effective request URI"/>
1747  <iref primary="true" item="target resource"/>
1749   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1750   for the target resource; instead, the URI needs to be inferred from the
1751   request-target, Host header field, and connection context. The result of
1752   this process is called the "effective request URI".  The "target resource"
1753   is the resource identified by the effective request URI.
1756   If the request-target is an absolute-URI, then the effective request URI is
1757   the request-target.
1760   If the request-target uses the path-absolute form or the asterisk form,
1761   and the Host header field is present, then the effective request URI is
1762   constructed by concatenating
1765  <list style="symbols">
1766    <t>
1767      the scheme name: "http" if the request was received over an insecure
1768      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1769      connection,
1770    </t>
1771    <t>
1772      the character sequence "://",
1773    </t>
1774    <t>
1775      the authority component, as specified in the Host header field
1776      (<xref target=""/>), and
1777    </t>
1778    <t>
1779      the request-target obtained from the Request-Line, unless the
1780      request-target is just the asterisk "*".
1781    </t>
1782  </list>
1785   If the request-target uses the path-absolute form or the asterisk form,
1786   and the Host header field is not present, then the effective request URI is
1787   undefined.
1790   Otherwise, when request-target uses the authority form, the effective
1791   request URI is undefined.
1795   Example 1: the effective request URI for the message
1797<artwork type="example" x:indent-with="  ">
1798GET /pub/WWW/TheProject.html HTTP/1.1
1802  (received over an insecure TCP connection) is "http", plus "://", plus the
1803  authority component "", plus the request-target
1804  "/pub/WWW/TheProject.html", thus
1805  "".
1810   Example 2: the effective request URI for the message
1812<artwork type="example" x:indent-with="  ">
1813GET * HTTP/1.1
1817  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1818  authority component "", thus "".
1822   Effective request URIs are compared using the rules described in
1823   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1824   be treated as equivalent to an absolute path of "/".
1831<section title="Response" anchor="response">
1832  <x:anchor-alias value="Response"/>
1834   After receiving and interpreting a request message, a server responds
1835   with an HTTP response message.
1837<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1838  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1839                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1840                  <x:ref>CRLF</x:ref>
1841                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1844<section title="Status-Line" anchor="status-line">
1845  <x:anchor-alias value="Status-Line"/>
1847   The first line of a Response message is the Status-Line, consisting
1848   of the protocol version followed by a numeric status code and its
1849   associated textual phrase, with each element separated by SP
1850   characters. No CR or LF is allowed except in the final CRLF sequence.
1852<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1853  <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>
1856<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1857  <x:anchor-alias value="Reason-Phrase"/>
1858  <x:anchor-alias value="Status-Code"/>
1860   The Status-Code element is a 3-digit integer result code of the
1861   attempt to understand and satisfy the request. These codes are fully
1862   defined in &status-codes;.  The Reason Phrase exists for the sole
1863   purpose of providing a textual description associated with the numeric
1864   status code, out of deference to earlier Internet application protocols
1865   that were more frequently used with interactive text clients.
1866   A client &SHOULD; ignore the content of the Reason Phrase.
1869   The first digit of the Status-Code defines the class of response. The
1870   last two digits do not have any categorization role. There are 5
1871   values for the first digit:
1872  <list style="symbols">
1873    <t>
1874      1xx: Informational - Request received, continuing process
1875    </t>
1876    <t>
1877      2xx: Success - The action was successfully received,
1878        understood, and accepted
1879    </t>
1880    <t>
1881      3xx: Redirection - Further action must be taken in order to
1882        complete the request
1883    </t>
1884    <t>
1885      4xx: Client Error - The request contains bad syntax or cannot
1886        be fulfilled
1887    </t>
1888    <t>
1889      5xx: Server Error - The server failed to fulfill an apparently
1890        valid request
1891    </t>
1892  </list>
1894<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1895  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1896  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1904<section title="Protocol Parameters" anchor="protocol.parameters">
1906<section title="Date/Time Formats: Full Date" anchor="">
1907  <x:anchor-alias value="HTTP-date"/>
1909   HTTP applications have historically allowed three different formats
1910   for date/time stamps. However, the preferred format is a fixed-length subset
1911   of that defined by <xref target="RFC1123"/>:
1913<figure><artwork type="example" x:indent-with="  ">
1914Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1917   The other formats are described here only for compatibility with obsolete
1918   implementations.
1920<figure><artwork type="example" x:indent-with="  ">
1921Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1922Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1925   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1926   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1927   only generate the RFC 1123 format for representing HTTP-date values
1928   in header fields. See <xref target="tolerant.applications"/> for further information.
1931   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1932   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1933   equal to UTC (Coordinated Universal Time). This is indicated in the
1934   first two formats by the inclusion of "GMT" as the three-letter
1935   abbreviation for time zone, and &MUST; be assumed when reading the
1936   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1937   additional whitespace beyond that specifically included as SP in the
1938   grammar.
1940<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1941  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1943<t anchor="">
1944  <x:anchor-alias value="rfc1123-date"/>
1945  <x:anchor-alias value="time-of-day"/>
1946  <x:anchor-alias value="hour"/>
1947  <x:anchor-alias value="minute"/>
1948  <x:anchor-alias value="second"/>
1949  <x:anchor-alias value="day-name"/>
1950  <x:anchor-alias value="day"/>
1951  <x:anchor-alias value="month"/>
1952  <x:anchor-alias value="year"/>
1953  <x:anchor-alias value="GMT"/>
1954  Preferred format:
1956<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"/>
1957  <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>
1958  ; fixed length subset of the format defined in
1959  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1961  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1962               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1963               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1964               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1965               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1966               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1967               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1969  <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>
1970               ; e.g., 02 Jun 1982
1972  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1973  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1974               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1975               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1976               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1977               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1978               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1979               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1980               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1981               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1982               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1983               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1984               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1985  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1987  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1989  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1990                 ; 00:00:00 - 23:59:59
1992  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1993  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1994  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1997  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1998  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1999  same as those defined for the RFC 5322 constructs
2000  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2002<t anchor="">
2003  <x:anchor-alias value="obs-date"/>
2004  <x:anchor-alias value="rfc850-date"/>
2005  <x:anchor-alias value="asctime-date"/>
2006  <x:anchor-alias value="date1"/>
2007  <x:anchor-alias value="date2"/>
2008  <x:anchor-alias value="date3"/>
2009  <x:anchor-alias value="rfc1123-date"/>
2010  <x:anchor-alias value="day-name-l"/>
2011  Obsolete formats:
2013<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2014  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2016<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2017  <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>
2018  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2019                 ; day-month-year (e.g., 02-Jun-82)
2021  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2022         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2023         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2024         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2025         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2026         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2027         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2029<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2030  <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>
2031  <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> ))
2032                 ; month day (e.g., Jun  2)
2035  <t>
2036    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2037    accepting date values that might have been sent by non-HTTP
2038    applications, as is sometimes the case when retrieving or posting
2039    messages via proxies/gateways to SMTP or NNTP.
2040  </t>
2043  <t>
2044    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2045    to their usage within the protocol stream. Clients and servers are
2046    not required to use these formats for user presentation, request
2047    logging, etc.
2048  </t>
2052<section title="Transfer Codings" anchor="transfer.codings">
2053  <x:anchor-alias value="transfer-coding"/>
2054  <x:anchor-alias value="transfer-extension"/>
2056   Transfer-coding values are used to indicate an encoding
2057   transformation that has been, can be, or might need to be applied to a
2058   payload body in order to ensure "safe transport" through the network.
2059   This differs from a content coding in that the transfer-coding is a
2060   property of the message rather than a property of the representation
2061   that is being transferred.
2063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2064  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2065                          / "compress" ; <xref target="compress.coding"/>
2066                          / "deflate" ; <xref target="deflate.coding"/>
2067                          / "gzip" ; <xref target="gzip.coding"/>
2068                          / <x:ref>transfer-extension</x:ref>
2069  <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> )
2071<t anchor="rule.parameter">
2072  <x:anchor-alias value="attribute"/>
2073  <x:anchor-alias value="transfer-parameter"/>
2074  <x:anchor-alias value="value"/>
2075   Parameters are in the form of attribute/value pairs.
2077<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"/>
2078  <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>
2079  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2080  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2083   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2084   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2085   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2088   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2089   MIME, which were designed to enable safe transport of binary data over a
2090   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2091   However, safe transport
2092   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2093   the only unsafe characteristic of message-bodies is the difficulty in
2094   determining the exact message body length (<xref target="message.body"/>),
2095   or the desire to encrypt data over a shared transport.
2098   A server that receives a request message with a transfer-coding it does
2099   not understand &SHOULD; respond with 501 (Not Implemented) and then
2100   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2101   client.
2104<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2105  <iref item="chunked (Coding Format)"/>
2106  <iref item="Coding Format" subitem="chunked"/>
2107  <x:anchor-alias value="chunk"/>
2108  <x:anchor-alias value="Chunked-Body"/>
2109  <x:anchor-alias value="chunk-data"/>
2110  <x:anchor-alias value="chunk-ext"/>
2111  <x:anchor-alias value="chunk-ext-name"/>
2112  <x:anchor-alias value="chunk-ext-val"/>
2113  <x:anchor-alias value="chunk-size"/>
2114  <x:anchor-alias value="last-chunk"/>
2115  <x:anchor-alias value="trailer-part"/>
2116  <x:anchor-alias value="quoted-str-nf"/>
2117  <x:anchor-alias value="qdtext-nf"/>
2119   The chunked encoding modifies the body of a message in order to
2120   transfer it as a series of chunks, each with its own size indicator,
2121   followed by an &OPTIONAL; trailer containing header fields. This
2122   allows dynamically produced content to be transferred along with the
2123   information necessary for the recipient to verify that it has
2124   received the full message.
2126<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"/>
2127  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2128                   <x:ref>last-chunk</x:ref>
2129                   <x:ref>trailer-part</x:ref>
2130                   <x:ref>CRLF</x:ref>
2132  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2133                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2134  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2135  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2137  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2138                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2139  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2140  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2141  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2142  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2144  <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>
2145                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2146  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2147                 ; <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>
2150   The chunk-size field is a string of hex digits indicating the size of
2151   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2152   zero, followed by the trailer, which is terminated by an empty line.
2155   The trailer allows the sender to include additional HTTP header
2156   fields at the end of the message. The Trailer header field can be
2157   used to indicate which header fields are included in a trailer (see
2158   <xref target="header.trailer"/>).
2161   A server using chunked transfer-coding in a response &MUST-NOT; use the
2162   trailer for any header fields unless at least one of the following is
2163   true:
2164  <list style="numbers">
2165    <t>the request included a TE header field that indicates "trailers" is
2166     acceptable in the transfer-coding of the  response, as described in
2167     <xref target="header.te"/>; or,</t>
2169    <t>the trailer fields consist entirely of optional metadata, and the
2170    recipient could use the message (in a manner acceptable to the server where
2171    the field originated) without receiving it. In other words, the server that
2172    generated the header (often but not always the origin server) is willing to
2173    accept the possibility that the trailer fields might be silently discarded
2174    along the path to the client.</t>
2175  </list>
2178   This requirement prevents an interoperability failure when the
2179   message is being received by an HTTP/1.1 (or later) proxy and
2180   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2181   compliance with the protocol would have necessitated a possibly
2182   infinite buffer on the proxy.
2185   A process for decoding the "chunked" transfer-coding
2186   can be represented in pseudo-code as:
2188<figure><artwork type="code">
2189  length := 0
2190  read chunk-size, chunk-ext (if any) and CRLF
2191  while (chunk-size &gt; 0) {
2192     read chunk-data and CRLF
2193     append chunk-data to decoded-body
2194     length := length + chunk-size
2195     read chunk-size and CRLF
2196  }
2197  read header-field
2198  while (header-field not empty) {
2199     append header-field to existing header fields
2200     read header-field
2201  }
2202  Content-Length := length
2203  Remove "chunked" from Transfer-Encoding
2206   All HTTP/1.1 applications &MUST; be able to receive and decode the
2207   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2208   they do not understand.
2211   Since "chunked" is the only transfer-coding required to be understood
2212   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2213   on a persistent connection.  Whenever a transfer-coding is applied to
2214   a payload body in a request, the final transfer-coding applied &MUST;
2215   be "chunked".  If a transfer-coding is applied to a response payload
2216   body, then either the final transfer-coding applied &MUST; be "chunked"
2217   or the message &MUST; be terminated by closing the connection. When the
2218   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2219   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2220   be applied more than once in a message-body.
2224<section title="Compression Codings" anchor="compression.codings">
2226   The codings defined below can be used to compress the payload of a
2227   message.
2230   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2231   is not desirable and is discouraged for future encodings. Their
2232   use here is representative of historical practice, not good
2233   design.
2236   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2237   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2238   equivalent to "gzip" and "compress" respectively.
2241<section title="Compress Coding" anchor="compress.coding">
2242<iref item="compress (Coding Format)"/>
2243<iref item="Coding Format" subitem="compress"/>
2245   The "compress" format is produced by the common UNIX file compression
2246   program "compress". This format is an adaptive Lempel-Ziv-Welch
2247   coding (LZW).
2251<section title="Deflate Coding" anchor="deflate.coding">
2252<iref item="deflate (Coding Format)"/>
2253<iref item="Coding Format" subitem="deflate"/>
2255   The "deflate" format is defined as the "deflate" compression mechanism
2256   (described in <xref target="RFC1951"/>) used inside the "zlib"
2257   data format (<xref target="RFC1950"/>).
2260  <t>
2261    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2262    compressed data without the zlib wrapper.
2263   </t>
2267<section title="Gzip Coding" anchor="gzip.coding">
2268<iref item="gzip (Coding Format)"/>
2269<iref item="Coding Format" subitem="gzip"/>
2271   The "gzip" format is produced by the file compression program
2272   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2273   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2279<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2281   The HTTP Transfer Coding Registry defines the name space for the transfer
2282   coding names.
2285   Registrations &MUST; include the following fields:
2286   <list style="symbols">
2287     <t>Name</t>
2288     <t>Description</t>
2289     <t>Pointer to specification text</t>
2290   </list>
2293   Names of transfer codings &MUST-NOT; overlap with names of content codings
2294   (&content-codings;), unless the encoding transformation is identical (as it
2295   is the case for the compression codings defined in
2296   <xref target="compression.codings"/>).
2299   Values to be added to this name space require a specification
2300   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2301   conform to the purpose of transfer coding defined in this section.
2304   The registry itself is maintained at
2305   <eref target=""/>.
2310<section title="Product Tokens" anchor="product.tokens">
2311  <x:anchor-alias value="product"/>
2312  <x:anchor-alias value="product-version"/>
2314   Product tokens are used to allow communicating applications to
2315   identify themselves by software name and version. Most fields using
2316   product tokens also allow sub-products which form a significant part
2317   of the application to be listed, separated by whitespace. By
2318   convention, the products are listed in order of their significance
2319   for identifying the application.
2321<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2322  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2323  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2326   Examples:
2328<figure><artwork type="example">
2329  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2330  Server: Apache/0.8.4
2333   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2334   used for advertising or other non-essential information. Although any
2335   token character &MAY; appear in a product-version, this token &SHOULD;
2336   only be used for a version identifier (i.e., successive versions of
2337   the same product &SHOULD; only differ in the product-version portion of
2338   the product value).
2342<section title="Quality Values" anchor="quality.values">
2343  <x:anchor-alias value="qvalue"/>
2345   Both transfer codings (TE request header field, <xref target="header.te"/>)
2346   and content negotiation (&content.negotiation;) use short "floating point"
2347   numbers to indicate the relative importance ("weight") of various
2348   negotiable parameters.  A weight is normalized to a real number in
2349   the range 0 through 1, where 0 is the minimum and 1 the maximum
2350   value. If a parameter has a quality value of 0, then content with
2351   this parameter is "not acceptable" for the client. HTTP/1.1
2352   applications &MUST-NOT; generate more than three digits after the
2353   decimal point. User configuration of these values &SHOULD; also be
2354   limited in this fashion.
2356<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2357  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2358                 / ( "1" [ "." 0*3("0") ] )
2361  <t>
2362     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2363     relative degradation in desired quality.
2364  </t>
2370<section title="Connections" anchor="connections">
2372<section title="Persistent Connections" anchor="persistent.connections">
2374<section title="Purpose" anchor="persistent.purpose">
2376   Prior to persistent connections, a separate TCP connection was
2377   established to fetch each URL, increasing the load on HTTP servers
2378   and causing congestion on the Internet. The use of inline images and
2379   other associated data often requires a client to make multiple
2380   requests of the same server in a short amount of time. Analysis of
2381   these performance problems and results from a prototype
2382   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2383   measurements of actual HTTP/1.1 implementations show good
2384   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2385   T/TCP <xref target="Tou1998"/>.
2388   Persistent HTTP connections have a number of advantages:
2389  <list style="symbols">
2390      <t>
2391        By opening and closing fewer TCP connections, CPU time is saved
2392        in routers and hosts (clients, servers, proxies, gateways,
2393        tunnels, or caches), and memory used for TCP protocol control
2394        blocks can be saved in hosts.
2395      </t>
2396      <t>
2397        HTTP requests and responses can be pipelined on a connection.
2398        Pipelining allows a client to make multiple requests without
2399        waiting for each response, allowing a single TCP connection to
2400        be used much more efficiently, with much lower elapsed time.
2401      </t>
2402      <t>
2403        Network congestion is reduced by reducing the number of packets
2404        caused by TCP opens, and by allowing TCP sufficient time to
2405        determine the congestion state of the network.
2406      </t>
2407      <t>
2408        Latency on subsequent requests is reduced since there is no time
2409        spent in TCP's connection opening handshake.
2410      </t>
2411      <t>
2412        HTTP can evolve more gracefully, since errors can be reported
2413        without the penalty of closing the TCP connection. Clients using
2414        future versions of HTTP might optimistically try a new feature,
2415        but if communicating with an older server, retry with old
2416        semantics after an error is reported.
2417      </t>
2418    </list>
2421   HTTP implementations &SHOULD; implement persistent connections.
2425<section title="Overall Operation" anchor="persistent.overall">
2427   A significant difference between HTTP/1.1 and earlier versions of
2428   HTTP is that persistent connections are the default behavior of any
2429   HTTP connection. That is, unless otherwise indicated, the client
2430   &SHOULD; assume that the server will maintain a persistent connection,
2431   even after error responses from the server.
2434   Persistent connections provide a mechanism by which a client and a
2435   server can signal the close of a TCP connection. This signaling takes
2436   place using the Connection header field (<xref target="header.connection"/>). Once a close
2437   has been signaled, the client &MUST-NOT; send any more requests on that
2438   connection.
2441<section title="Negotiation" anchor="persistent.negotiation">
2443   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2444   maintain a persistent connection unless a Connection header field including
2445   the connection-token "close" was sent in the request. If the server
2446   chooses to close the connection immediately after sending the
2447   response, it &SHOULD; send a Connection header field including the
2448   connection-token "close".
2451   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2452   decide to keep it open based on whether the response from a server
2453   contains a Connection header field with the connection-token close. In case
2454   the client does not want to maintain a connection for more than that
2455   request, it &SHOULD; send a Connection header field including the
2456   connection-token close.
2459   If either the client or the server sends the close token in the
2460   Connection header field, that request becomes the last one for the
2461   connection.
2464   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2465   maintained for HTTP versions less than 1.1 unless it is explicitly
2466   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2467   compatibility with HTTP/1.0 clients.
2470   In order to remain persistent, all messages on the connection &MUST;
2471   have a self-defined message length (i.e., one not defined by closure
2472   of the connection), as described in <xref target="message.body"/>.
2476<section title="Pipelining" anchor="pipelining">
2478   A client that supports persistent connections &MAY; "pipeline" its
2479   requests (i.e., send multiple requests without waiting for each
2480   response). A server &MUST; send its responses to those requests in the
2481   same order that the requests were received.
2484   Clients which assume persistent connections and pipeline immediately
2485   after connection establishment &SHOULD; be prepared to retry their
2486   connection if the first pipelined attempt fails. If a client does
2487   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2488   persistent. Clients &MUST; also be prepared to resend their requests if
2489   the server closes the connection before sending all of the
2490   corresponding responses.
2493   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2494   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2495   premature termination of the transport connection could lead to
2496   indeterminate results. A client wishing to send a non-idempotent
2497   request &SHOULD; wait to send that request until it has received the
2498   response status line for the previous request.
2503<section title="Proxy Servers" anchor="persistent.proxy">
2505   It is especially important that proxies correctly implement the
2506   properties of the Connection header field as specified in <xref target="header.connection"/>.
2509   The proxy server &MUST; signal persistent connections separately with
2510   its clients and the origin servers (or other proxy servers) that it
2511   connects to. Each persistent connection applies to only one transport
2512   link.
2515   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2516   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2517   for information and discussion of the problems with the Keep-Alive header field
2518   implemented by many HTTP/1.0 clients).
2521<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2523  <cref anchor="TODO-end-to-end" source="jre">
2524    Restored from <eref target=""/>.
2525    See also <eref target=""/>.
2526  </cref>
2529   For the purpose of defining the behavior of caches and non-caching
2530   proxies, we divide HTTP header fields into two categories:
2531  <list style="symbols">
2532      <t>End-to-end header fields, which are  transmitted to the ultimate
2533        recipient of a request or response. End-to-end header fields in
2534        responses MUST be stored as part of a cache entry and &MUST; be
2535        transmitted in any response formed from a cache entry.</t>
2537      <t>Hop-by-hop header fields, which are meaningful only for a single
2538        transport-level connection, and are not stored by caches or
2539        forwarded by proxies.</t>
2540  </list>
2543   The following HTTP/1.1 header fields are hop-by-hop header fields:
2544  <list style="symbols">
2545      <t>Connection</t>
2546      <t>Keep-Alive</t>
2547      <t>Proxy-Authenticate</t>
2548      <t>Proxy-Authorization</t>
2549      <t>TE</t>
2550      <t>Trailer</t>
2551      <t>Transfer-Encoding</t>
2552      <t>Upgrade</t>
2553  </list>
2556   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2559   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2560   (<xref target="header.connection"/>).
2564<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2566  <cref anchor="TODO-non-mod-headers" source="jre">
2567    Restored from <eref target=""/>.
2568    See also <eref target=""/>.
2569  </cref>
2572   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2573   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2574   modify an end-to-end header field unless the definition of that header field requires
2575   or specifically allows that.
2578   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2579   request or response, and it &MUST-NOT; add any of these fields if not
2580   already present:
2581  <list style="symbols">
2582      <t>Content-Location</t>
2583      <t>Content-MD5</t>
2584      <t>ETag</t>
2585      <t>Last-Modified</t>
2586  </list>
2589   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2590   response:
2591  <list style="symbols">
2592    <t>Expires</t>
2593  </list>
2596   but it &MAY; add any of these fields if not already present. If an
2597   Expires header field is added, it &MUST; be given a field-value identical to
2598   that of the Date header field in that response.
2601   A proxy &MUST-NOT; modify or add any of the following fields in a
2602   message that contains the no-transform cache-control directive, or in
2603   any request:
2604  <list style="symbols">
2605    <t>Content-Encoding</t>
2606    <t>Content-Range</t>
2607    <t>Content-Type</t>
2608  </list>
2611   A transforming proxy &MAY; modify or add these fields to a message
2612   that does not include no-transform, but if it does so, it &MUST; add a
2613   Warning 214 (Transformation applied) if one does not already appear
2614   in the message (see &header-warning;).
2617  <t>
2618    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2619    cause authentication failures if stronger authentication
2620    mechanisms are introduced in later versions of HTTP. Such
2621    authentication mechanisms &MAY; rely on the values of header fields
2622    not listed here.
2623  </t>
2626   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2627   though it &MAY; change the message-body through application or removal
2628   of a transfer-coding (<xref target="transfer.codings"/>).
2634<section title="Practical Considerations" anchor="persistent.practical">
2636   Servers will usually have some time-out value beyond which they will
2637   no longer maintain an inactive connection. Proxy servers might make
2638   this a higher value since it is likely that the client will be making
2639   more connections through the same server. The use of persistent
2640   connections places no requirements on the length (or existence) of
2641   this time-out for either the client or the server.
2644   When a client or server wishes to time-out it &SHOULD; issue a graceful
2645   close on the transport connection. Clients and servers &SHOULD; both
2646   constantly watch for the other side of the transport close, and
2647   respond to it as appropriate. If a client or server does not detect
2648   the other side's close promptly it could cause unnecessary resource
2649   drain on the network.
2652   A client, server, or proxy &MAY; close the transport connection at any
2653   time. For example, a client might have started to send a new request
2654   at the same time that the server has decided to close the "idle"
2655   connection. From the server's point of view, the connection is being
2656   closed while it was idle, but from the client's point of view, a
2657   request is in progress.
2660   This means that clients, servers, and proxies &MUST; be able to recover
2661   from asynchronous close events. Client software &SHOULD; reopen the
2662   transport connection and retransmit the aborted sequence of requests
2663   without user interaction so long as the request sequence is
2664   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2665   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2666   human operator the choice of retrying the request(s). Confirmation by
2667   user-agent software with semantic understanding of the application
2668   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2669   be repeated if the second sequence of requests fails.
2672   Servers &SHOULD; always respond to at least one request per connection,
2673   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2674   middle of transmitting a response, unless a network or client failure
2675   is suspected.
2678   Clients (including proxies) &SHOULD; limit the number of simultaneous
2679   connections that they maintain to a given server (including proxies).
2682   Previous revisions of HTTP gave a specific number of connections as a
2683   ceiling, but this was found to be impractical for many applications. As a
2684   result, this specification does not mandate a particular maximum number of
2685   connections, but instead encourages clients to be conservative when opening
2686   multiple connections.
2689   In particular, while using multiple connections avoids the "head-of-line
2690   blocking" problem (whereby a request that takes significant server-side
2691   processing and/or has a large payload can block subsequent requests on the
2692   same connection), each connection used consumes server resources (sometimes
2693   significantly), and furthermore using multiple connections can cause
2694   undesirable side effects in congested networks.
2697   Note that servers might reject traffic that they deem abusive, including an
2698   excessive number of connections from a client.
2703<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2705<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2707   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2708   flow control mechanisms to resolve temporary overloads, rather than
2709   terminating connections with the expectation that clients will retry.
2710   The latter technique can exacerbate network congestion.
2714<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2716   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2717   the network connection for an error status code while it is transmitting
2718   the request. If the client sees an error status code, it &SHOULD;
2719   immediately cease transmitting the body. If the body is being sent
2720   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2721   empty trailer &MAY; be used to prematurely mark the end of the message.
2722   If the body was preceded by a Content-Length header field, the client &MUST;
2723   close the connection.
2727<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2729   The purpose of the 100 (Continue) status code (see &status-100;) is to
2730   allow a client that is sending a request message with a request body
2731   to determine if the origin server is willing to accept the request
2732   (based on the request header fields) before the client sends the request
2733   body. In some cases, it might either be inappropriate or highly
2734   inefficient for the client to send the body if the server will reject
2735   the message without looking at the body.
2738   Requirements for HTTP/1.1 clients:
2739  <list style="symbols">
2740    <t>
2741        If a client will wait for a 100 (Continue) response before
2742        sending the request body, it &MUST; send an Expect header
2743        field (&header-expect;) with the "100-continue" expectation.
2744    </t>
2745    <t>
2746        A client &MUST-NOT; send an Expect header field (&header-expect;)
2747        with the "100-continue" expectation if it does not intend
2748        to send a request body.
2749    </t>
2750  </list>
2753   Because of the presence of older implementations, the protocol allows
2754   ambiguous situations in which a client might send "Expect: 100-continue"
2755   without receiving either a 417 (Expectation Failed)
2756   or a 100 (Continue) status code. Therefore, when a client sends this
2757   header field to an origin server (possibly via a proxy) from which it
2758   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2759   wait for an indefinite period before sending the request body.
2762   Requirements for HTTP/1.1 origin servers:
2763  <list style="symbols">
2764    <t> Upon receiving a request which includes an Expect header
2765        field with the "100-continue" expectation, an origin server &MUST;
2766        either respond with 100 (Continue) status code and continue to read
2767        from the input stream, or respond with a final status code. The
2768        origin server &MUST-NOT; wait for the request body before sending
2769        the 100 (Continue) response. If it responds with a final status
2770        code, it &MAY; close the transport connection or it &MAY; continue
2771        to read and discard the rest of the request.  It &MUST-NOT;
2772        perform the request method if it returns a final status code.
2773    </t>
2774    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2775        the request message does not include an Expect header
2776        field with the "100-continue" expectation, and &MUST-NOT; send a
2777        100 (Continue) response if such a request comes from an HTTP/1.0
2778        (or earlier) client. There is an exception to this rule: for
2779        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2780        status code in response to an HTTP/1.1 PUT or POST request that does
2781        not include an Expect header field with the "100-continue"
2782        expectation. This exception, the purpose of which is
2783        to minimize any client processing delays associated with an
2784        undeclared wait for 100 (Continue) status code, applies only to
2785        HTTP/1.1 requests, and not to requests with any other HTTP-version
2786        value.
2787    </t>
2788    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2789        already received some or all of the request body for the
2790        corresponding request.
2791    </t>
2792    <t> An origin server that sends a 100 (Continue) response &MUST;
2793    ultimately send a final status code, once the request body is
2794        received and processed, unless it terminates the transport
2795        connection prematurely.
2796    </t>
2797    <t> If an origin server receives a request that does not include an
2798        Expect header field with the "100-continue" expectation,
2799        the request includes a request body, and the server responds
2800        with a final status code before reading the entire request body
2801        from the transport connection, then the server &SHOULD-NOT;  close
2802        the transport connection until it has read the entire request,
2803        or until the client closes the connection. Otherwise, the client
2804        might not reliably receive the response message. However, this
2805        requirement is not be construed as preventing a server from
2806        defending itself against denial-of-service attacks, or from
2807        badly broken client implementations.
2808      </t>
2809    </list>
2812   Requirements for HTTP/1.1 proxies:
2813  <list style="symbols">
2814    <t> If a proxy receives a request that includes an Expect header
2815        field with the "100-continue" expectation, and the proxy
2816        either knows that the next-hop server complies with HTTP/1.1 or
2817        higher, or does not know the HTTP version of the next-hop
2818        server, it &MUST; forward the request, including the Expect header
2819        field.
2820    </t>
2821    <t> If the proxy knows that the version of the next-hop server is
2822        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2823        respond with a 417 (Expectation Failed) status code.
2824    </t>
2825    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2826        numbers received from recently-referenced next-hop servers.
2827    </t>
2828    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2829        request message was received from an HTTP/1.0 (or earlier)
2830        client and did not include an Expect header field with
2831        the "100-continue" expectation. This requirement overrides the
2832        general rule for forwarding of 1xx responses (see &status-1xx;).
2833    </t>
2834  </list>
2838<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2840   If an HTTP/1.1 client sends a request which includes a request body,
2841   but which does not include an Expect header field with the
2842   "100-continue" expectation, and if the client is not directly
2843   connected to an HTTP/1.1 origin server, and if the client sees the
2844   connection close before receiving a status line from the server, the
2845   client &SHOULD; retry the request.  If the client does retry this
2846   request, it &MAY; use the following "binary exponential backoff"
2847   algorithm to be assured of obtaining a reliable response:
2848  <list style="numbers">
2849    <t>
2850      Initiate a new connection to the server
2851    </t>
2852    <t>
2853      Transmit the request-line, header fields, and the CRLF that
2854      indicates the end of header fields.
2855    </t>
2856    <t>
2857      Initialize a variable R to the estimated round-trip time to the
2858         server (e.g., based on the time it took to establish the
2859         connection), or to a constant value of 5 seconds if the round-trip
2860         time is not available.
2861    </t>
2862    <t>
2863       Compute T = R * (2**N), where N is the number of previous
2864         retries of this request.
2865    </t>
2866    <t>
2867       Wait either for an error response from the server, or for T
2868         seconds (whichever comes first)
2869    </t>
2870    <t>
2871       If no error response is received, after T seconds transmit the
2872         body of the request.
2873    </t>
2874    <t>
2875       If client sees that the connection is closed prematurely,
2876         repeat from step 1 until the request is accepted, an error
2877         response is received, or the user becomes impatient and
2878         terminates the retry process.
2879    </t>
2880  </list>
2883   If at any point an error status code is received, the client
2884  <list style="symbols">
2885      <t>&SHOULD-NOT;  continue and</t>
2887      <t>&SHOULD; close the connection if it has not completed sending the
2888        request message.</t>
2889    </list>
2896<section title="Miscellaneous notes that might disappear" anchor="misc">
2897<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2899   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2903<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2905   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2909<section title="Interception of HTTP for access control" anchor="http.intercept">
2911   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2915<section title="Use of HTTP by other protocols" anchor="http.others">
2917   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2918   Extensions of HTTP like WebDAV.</cref>
2922<section title="Use of HTTP by media type specification" anchor="">
2924   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2929<section title="Header Field Definitions" anchor="header.field.definitions">
2931   This section defines the syntax and semantics of HTTP/1.1 header fields
2932   related to message framing and transport protocols.
2935<section title="Connection" anchor="header.connection">
2936  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2937  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2938  <x:anchor-alias value="Connection"/>
2939  <x:anchor-alias value="connection-token"/>
2940  <x:anchor-alias value="Connection-v"/>
2942   The "Connection" header field allows the sender to specify
2943   options that are desired for that particular connection and &MUST-NOT;
2944   be communicated by proxies over further connections.
2947   The Connection header field's value has the following grammar:
2949<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"/>
2950  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2951  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2952  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2955   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2956   message is forwarded and, for each connection-token in this field,
2957   remove any header field(s) from the message with the same name as the
2958   connection-token. Connection options are signaled by the presence of
2959   a connection-token in the Connection header field, not by any
2960   corresponding additional header field(s), since the additional header
2961   field might not be sent if there are no parameters associated with that
2962   connection option.
2965   Message header fields listed in the Connection header field &MUST-NOT; include
2966   end-to-end header fields, such as Cache-Control (&header-cache-control;).
2969   HTTP/1.1 defines the "close" connection option for the sender to
2970   signal that the connection will be closed after completion of the
2971   response. For example,
2973<figure><artwork type="example">
2974  Connection: close
2977   in either the request or the response header fields indicates that
2978   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2979   after the current request/response is complete.
2982   An HTTP/1.1 client that does not support persistent connections &MUST;
2983   include the "close" connection option in every request message.
2986   An HTTP/1.1 server that does not support persistent connections &MUST;
2987   include the "close" connection option in every response message that
2988   does not have a 1xx (Informational) status code.
2991   A system receiving an HTTP/1.0 (or lower-version) message that
2992   includes a Connection header field &MUST;, for each connection-token in this
2993   field, remove and ignore any header field(s) from the message with
2994   the same name as the connection-token. This protects against mistaken
2995   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2999<section title="Content-Length" anchor="header.content-length">
3000  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3001  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3002  <x:anchor-alias value="Content-Length"/>
3003  <x:anchor-alias value="Content-Length-v"/>
3005   The "Content-Length" header field indicates the size of the
3006   message-body, in decimal number of octets, for any message other than
3007   a response to a HEAD request or a response with a status code of 304.
3008   In the case of a response to a HEAD request, Content-Length indicates
3009   the size of the payload body (not including any potential transfer-coding)
3010   that would have been sent had the request been a GET.
3011   In the case of a 304 (Not Modified) response to a GET request,
3012   Content-Length indicates the size of the payload body (not including
3013   any potential transfer-coding) that would have been sent in a 200 (OK)
3014   response.
3016<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
3017  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
3018  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
3021   An example is
3023<figure><artwork type="example">
3024  Content-Length: 3495
3027   Implementations &SHOULD; use this field to indicate the message-body
3028   length when no transfer-coding is being applied and the
3029   payload's body length can be determined prior to being transferred.
3030   <xref target="message.body"/> describes how recipients determine the length
3031   of a message-body.
3034   Any Content-Length greater than or equal to zero is a valid value.
3037   Note that the use of this field in HTTP is significantly different from
3038   the corresponding definition in MIME, where it is an optional field
3039   used within the "message/external-body" content-type.
3043<section title="Date" anchor="">
3044  <iref primary="true" item="Date header field" x:for-anchor=""/>
3045  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3046  <x:anchor-alias value="Date"/>
3047  <x:anchor-alias value="Date-v"/>
3049   The "Date" header field represents the date and time at which
3050   the message was originated, having the same semantics as the Origination
3051   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3052   The field value is an HTTP-date, as described in <xref target=""/>;
3053   it &MUST; be sent in rfc1123-date format.
3055<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3056  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3057  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3060   An example is
3062<figure><artwork type="example">
3063  Date: Tue, 15 Nov 1994 08:12:31 GMT
3066   Origin servers &MUST; include a Date header field in all responses,
3067   except in these cases:
3068  <list style="numbers">
3069      <t>If the response status code is 100 (Continue) or 101 (Switching
3070         Protocols), the response &MAY; include a Date header field, at
3071         the server's option.</t>
3073      <t>If the response status code conveys a server error, e.g., 500
3074         (Internal Server Error) or 503 (Service Unavailable), and it is
3075         inconvenient or impossible to generate a valid Date.</t>
3077      <t>If the server does not have a clock that can provide a
3078         reasonable approximation of the current time, its responses
3079         &MUST-NOT; include a Date header field. In this case, the rules
3080         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3081  </list>
3084   A received message that does not have a Date header field &MUST; be
3085   assigned one by the recipient if the message will be cached by that
3086   recipient or gatewayed via a protocol which requires a Date.
3089   Clients can use the Date header field as well; in order to keep request
3090   messages small, they are advised not to include it when it doesn't convey
3091   any useful information (as it is usually the case for requests that do not
3092   contain a payload).
3095   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3096   time subsequent to the generation of the message. It &SHOULD; represent
3097   the best available approximation of the date and time of message
3098   generation, unless the implementation has no means of generating a
3099   reasonably accurate date and time. In theory, the date ought to
3100   represent the moment just before the payload is generated. In
3101   practice, the date can be generated at any time during the message
3102   origination without affecting its semantic value.
3105<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3107   Some origin server implementations might not have a clock available.
3108   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3109   values to a response, unless these values were associated
3110   with the resource by a system or user with a reliable clock. It &MAY;
3111   assign an Expires value that is known, at or before server
3112   configuration time, to be in the past (this allows "pre-expiration"
3113   of responses without storing separate Expires values for each
3114   resource).
3119<section title="Host" anchor="">
3120  <iref primary="true" item="Host header field" x:for-anchor=""/>
3121  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3122  <x:anchor-alias value="Host"/>
3123  <x:anchor-alias value="Host-v"/>
3125   The "Host" header field specifies the Internet host and port
3126   number of the resource being requested, allowing the origin server or
3127   gateway to differentiate between internally-ambiguous URLs, such as the root
3128   "/" URL of a server for multiple host names on a single IP address.
3131   The Host field value &MUST; represent the naming authority of the origin
3132   server or gateway given by the original URL obtained from the user or
3133   referring resource (generally an http URI, as described in
3134   <xref target="http.uri"/>).
3136<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3137  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3138  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3141   A "host" without any trailing port information implies the default
3142   port for the service requested (e.g., "80" for an HTTP URL). For
3143   example, a request on the origin server for
3144   &lt;; would properly include:
3146<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3147GET /pub/WWW/ HTTP/1.1
3151   A client &MUST; include a Host header field in all HTTP/1.1 request
3152   messages. If the requested URI does not include an Internet host
3153   name for the service being requested, then the Host header field &MUST;
3154   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3155   request message it forwards does contain an appropriate Host header
3156   field that identifies the service being requested by the proxy. All
3157   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3158   status code to any HTTP/1.1 request message which lacks a Host header
3159   field.
3162   See Sections <xref target="" format="counter"/>
3163   and <xref target="" format="counter"/>
3164   for other requirements relating to Host.
3168<section title="TE" anchor="header.te">
3169  <iref primary="true" item="TE header field" x:for-anchor=""/>
3170  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3171  <x:anchor-alias value="TE"/>
3172  <x:anchor-alias value="TE-v"/>
3173  <x:anchor-alias value="t-codings"/>
3174  <x:anchor-alias value="te-params"/>
3175  <x:anchor-alias value="te-ext"/>
3177   The "TE" header field indicates what extension transfer-codings
3178   it is willing to accept in the response, and whether or not it is
3179   willing to accept trailer fields in a chunked transfer-coding.
3182   Its value consists of the keyword "trailers" and/or a comma-separated
3183   list of extension transfer-coding names with optional accept
3184   parameters (as described in <xref target="transfer.codings"/>).
3186<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"/>
3187  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3188  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3189  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3190  <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> )
3191  <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> ]
3194   The presence of the keyword "trailers" indicates that the client is
3195   willing to accept trailer fields in a chunked transfer-coding, as
3196   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3197   transfer-coding values even though it does not itself represent a
3198   transfer-coding.
3201   Examples of its use are:
3203<figure><artwork type="example">
3204  TE: deflate
3205  TE:
3206  TE: trailers, deflate;q=0.5
3209   The TE header field only applies to the immediate connection.
3210   Therefore, the keyword &MUST; be supplied within a Connection header
3211   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3214   A server tests whether a transfer-coding is acceptable, according to
3215   a TE field, using these rules:
3216  <list style="numbers">
3217    <x:lt>
3218      <t>The "chunked" transfer-coding is always acceptable. If the
3219         keyword "trailers" is listed, the client indicates that it is
3220         willing to accept trailer fields in the chunked response on
3221         behalf of itself and any downstream clients. The implication is
3222         that, if given, the client is stating that either all
3223         downstream clients are willing to accept trailer fields in the
3224         forwarded response, or that it will attempt to buffer the
3225         response on behalf of downstream recipients.
3226      </t><t>
3227         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3228         chunked response such that a client can be assured of buffering
3229         the entire response.</t>
3230    </x:lt>
3231    <x:lt>
3232      <t>If the transfer-coding being tested is one of the transfer-codings
3233         listed in the TE field, then it is acceptable unless it
3234         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3235         qvalue of 0 means "not acceptable".)</t>
3236    </x:lt>
3237    <x:lt>
3238      <t>If multiple transfer-codings are acceptable, then the
3239         acceptable transfer-coding with the highest non-zero qvalue is
3240         preferred.  The "chunked" transfer-coding always has a qvalue
3241         of 1.</t>
3242    </x:lt>
3243  </list>
3246   If the TE field-value is empty or if no TE field is present, the only
3247   transfer-coding is "chunked". A message with no transfer-coding is
3248   always acceptable.
3252<section title="Trailer" anchor="header.trailer">
3253  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3254  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3255  <x:anchor-alias value="Trailer"/>
3256  <x:anchor-alias value="Trailer-v"/>
3258   The "Trailer" header field indicates that the given set of
3259   header fields is present in the trailer of a message encoded with
3260   chunked transfer-coding.
3262<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3263  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3264  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3267   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3268   message using chunked transfer-coding with a non-empty trailer. Doing
3269   so allows the recipient to know which header fields to expect in the
3270   trailer.
3273   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3274   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3275   trailer fields in a "chunked" transfer-coding.
3278   Message header fields listed in the Trailer header field &MUST-NOT;
3279   include the following header fields:
3280  <list style="symbols">
3281    <t>Transfer-Encoding</t>
3282    <t>Content-Length</t>
3283    <t>Trailer</t>
3284  </list>
3288<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3289  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3290  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3291  <x:anchor-alias value="Transfer-Encoding"/>
3292  <x:anchor-alias value="Transfer-Encoding-v"/>
3294   The "Transfer-Encoding" header field indicates what transfer-codings
3295   (if any) have been applied to the message body. It differs from
3296   Content-Encoding (&content-codings;) in that transfer-codings are a property
3297   of the message (and therefore are removed by intermediaries), whereas
3298   content-codings are not.
3300<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3301  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3302                        <x:ref>Transfer-Encoding-v</x:ref>
3303  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3306   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3308<figure><artwork type="example">
3309  Transfer-Encoding: chunked
3312   If multiple encodings have been applied to a representation, the transfer-codings
3313   &MUST; be listed in the order in which they were applied.
3314   Additional information about the encoding parameters &MAY; be provided
3315   by other header fields not defined by this specification.
3318   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3319   header field.
3323<section title="Upgrade" anchor="header.upgrade">
3324  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3325  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3326  <x:anchor-alias value="Upgrade"/>
3327  <x:anchor-alias value="Upgrade-v"/>
3329   The "Upgrade" header field allows the client to specify what
3330   additional communication protocols it would like to use, if the server
3331   chooses to switch protocols. Servers can use it to indicate what protocols
3332   they are willing to switch to.
3334<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3335  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3336  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3339   For example,
3341<figure><artwork type="example">
3342  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3345   The Upgrade header field is intended to provide a simple mechanism
3346   for transition from HTTP/1.1 to some other, incompatible protocol. It
3347   does so by allowing the client to advertise its desire to use another
3348   protocol, such as a later version of HTTP with a higher major version
3349   number, even though the current request has been made using HTTP/1.1.
3350   This eases the difficult transition between incompatible protocols by
3351   allowing the client to initiate a request in the more commonly
3352   supported protocol while indicating to the server that it would like
3353   to use a "better" protocol if available (where "better" is determined
3354   by the server, possibly according to the nature of the request method
3355   or target resource).
3358   The Upgrade header field only applies to switching application-layer
3359   protocols upon the existing transport-layer connection. Upgrade
3360   cannot be used to insist on a protocol change; its acceptance and use
3361   by the server is optional. The capabilities and nature of the
3362   application-layer communication after the protocol change is entirely
3363   dependent upon the new protocol chosen, although the first action
3364   after changing the protocol &MUST; be a response to the initial HTTP
3365   request containing the Upgrade header field.
3368   The Upgrade header field only applies to the immediate connection.
3369   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3370   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3371   HTTP/1.1 message.
3374   The Upgrade header field cannot be used to indicate a switch to a
3375   protocol on a different connection. For that purpose, it is more
3376   appropriate to use a 3xx redirection response (&status-3xx;).
3379   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3380   Protocols) responses to indicate which protocol(s) are being switched to,
3381   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3382   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3383   response to indicate that they are willing to upgrade to one of the
3384   specified protocols.
3387   This specification only defines the protocol name "HTTP" for use by
3388   the family of Hypertext Transfer Protocols, as defined by the HTTP
3389   version rules of <xref target="http.version"/> and future updates to this
3390   specification. Additional tokens can be registered with IANA using the
3391   registration procedure defined below. 
3394<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3396   The HTTP Upgrade Token Registry defines the name space for product
3397   tokens used to identify protocols in the Upgrade header field.
3398   Each registered token is associated with contact information and
3399   an optional set of specifications that details how the connection
3400   will be processed after it has been upgraded.
3403   Registrations are allowed on a First Come First Served basis as
3404   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3405   specifications need not be IETF documents or be subject to IESG review.
3406   Registrations are subject to the following rules:
3407  <list style="numbers">
3408    <t>A token, once registered, stays registered forever.</t>
3409    <t>The registration &MUST; name a responsible party for the
3410       registration.</t>
3411    <t>The registration &MUST; name a point of contact.</t>
3412    <t>The registration &MAY; name a set of specifications associated with that
3413       token. Such specifications need not be publicly available.</t>
3414    <t>The responsible party &MAY; change the registration at any time.
3415       The IANA will keep a record of all such changes, and make them
3416       available upon request.</t>
3417    <t>The responsible party for the first registration of a "product"
3418       token &MUST; approve later registrations of a "version" token
3419       together with that "product" token before they can be registered.</t>
3420    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3421       for a token. This will normally only be used in the case when a
3422       responsible party cannot be contacted.</t>
3423  </list>
3430<section title="Via" anchor="header.via">
3431  <iref primary="true" item="Via header field" x:for-anchor=""/>
3432  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3433  <x:anchor-alias value="protocol-name"/>
3434  <x:anchor-alias value="protocol-version"/>
3435  <x:anchor-alias value="pseudonym"/>
3436  <x:anchor-alias value="received-by"/>
3437  <x:anchor-alias value="received-protocol"/>
3438  <x:anchor-alias value="Via"/>
3439  <x:anchor-alias value="Via-v"/>
3441   The "Via" header field &MUST; be used by gateways and proxies to
3442   indicate the intermediate protocols and recipients between the user
3443   agent and the server on requests, and between the origin server and
3444   the client on responses. It is analogous to the "Received" field defined in
3445   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3446   avoiding request loops, and identifying the protocol capabilities of
3447   all senders along the request/response chain.
3449<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"/>
3450  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3451  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3452                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3453  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3454  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3455  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3456  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3457  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3460   The received-protocol indicates the protocol version of the message
3461   received by the server or client along each segment of the
3462   request/response chain. The received-protocol version is appended to
3463   the Via field value when the message is forwarded so that information
3464   about the protocol capabilities of upstream applications remains
3465   visible to all recipients.
3468   The protocol-name is optional if and only if it would be "HTTP". The
3469   received-by field is normally the host and optional port number of a
3470   recipient server or client that subsequently forwarded the message.
3471   However, if the real host is considered to be sensitive information,
3472   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3473   be assumed to be the default port of the received-protocol.
3476   Multiple Via field values represent each proxy or gateway that has
3477   forwarded the message. Each recipient &MUST; append its information
3478   such that the end result is ordered according to the sequence of
3479   forwarding applications.
3482   Comments &MAY; be used in the Via header field to identify the software
3483   of the recipient proxy or gateway, analogous to the User-Agent and
3484   Server header fields. However, all comments in the Via field are
3485   optional and &MAY; be removed by any recipient prior to forwarding the
3486   message.
3489   For example, a request message could be sent from an HTTP/1.0 user
3490   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3491   forward the request to a public proxy at, which completes
3492   the request by forwarding it to the origin server at
3493   The request received by would then have the following
3494   Via header field:
3496<figure><artwork type="example">
3497  Via: 1.0 fred, 1.1 (Apache/1.1)
3500   Proxies and gateways used as a portal through a network firewall
3501   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3502   the firewall region. This information &SHOULD; only be propagated if
3503   explicitly enabled. If not enabled, the received-by host of any host
3504   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3505   for that host.
3508   For organizations that have strong privacy requirements for hiding
3509   internal structures, a proxy &MAY; combine an ordered subsequence of
3510   Via header field entries with identical received-protocol values into
3511   a single such entry. For example,
3513<figure><artwork type="example">
3514  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3517  could be collapsed to
3519<figure><artwork type="example">
3520  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3523   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3524   under the same organizational control and the hosts have already been
3525   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3526   have different received-protocol values.
3532<section title="IANA Considerations" anchor="IANA.considerations">
3534<section title="Header Field Registration" anchor="header.field.registration">
3536   The Message Header Field Registry located at <eref target=""/> shall be updated
3537   with the permanent registrations below (see <xref target="RFC3864"/>):
3539<?BEGININC p1-messaging.iana-headers ?>
3540<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3541<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3542   <ttcol>Header Field Name</ttcol>
3543   <ttcol>Protocol</ttcol>
3544   <ttcol>Status</ttcol>
3545   <ttcol>Reference</ttcol>
3547   <c>Connection</c>
3548   <c>http</c>
3549   <c>standard</c>
3550   <c>
3551      <xref target="header.connection"/>
3552   </c>
3553   <c>Content-Length</c>
3554   <c>http</c>
3555   <c>standard</c>
3556   <c>
3557      <xref target="header.content-length"/>
3558   </c>
3559   <c>Date</c>
3560   <c>http</c>
3561   <c>standard</c>
3562   <c>
3563      <xref target=""/>
3564   </c>
3565   <c>Host</c>
3566   <c>http</c>
3567   <c>standard</c>
3568   <c>
3569      <xref target=""/>
3570   </c>
3571   <c>TE</c>
3572   <c>http</c>
3573   <c>standard</c>
3574   <c>
3575      <xref target="header.te"/>
3576   </c>
3577   <c>Trailer</c>
3578   <c>http</c>
3579   <c>standard</c>
3580   <c>
3581      <xref target="header.trailer"/>
3582   </c>
3583   <c>Transfer-Encoding</c>
3584   <c>http</c>
3585   <c>standard</c>
3586   <c>
3587      <xref target="header.transfer-encoding"/>
3588   </c>
3589   <c>Upgrade</c>
3590   <c>http</c>
3591   <c>standard</c>
3592   <c>
3593      <xref target="header.upgrade"/>
3594   </c>
3595   <c>Via</c>
3596   <c>http</c>
3597   <c>standard</c>
3598   <c>
3599      <xref target="header.via"/>
3600   </c>
3603<?ENDINC p1-messaging.iana-headers ?>
3605   The change controller is: "IETF ( - Internet Engineering Task Force".
3609<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3611   The entries for the "http" and "https" URI Schemes in the registry located at
3612   <eref target=""/>
3613   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3614   and <xref target="https.uri" format="counter"/> of this document
3615   (see <xref target="RFC4395"/>).
3619<section title="Internet Media Type Registrations" anchor="">
3621   This document serves as the specification for the Internet media types
3622   "message/http" and "application/http". The following is to be registered with
3623   IANA (see <xref target="RFC4288"/>).
3625<section title="Internet Media Type message/http" anchor="">
3626<iref item="Media Type" subitem="message/http" primary="true"/>
3627<iref item="message/http Media Type" primary="true"/>
3629   The message/http type can be used to enclose a single HTTP request or
3630   response message, provided that it obeys the MIME restrictions for all
3631   "message" types regarding line length and encodings.
3634  <list style="hanging" x:indent="12em">
3635    <t hangText="Type name:">
3636      message
3637    </t>
3638    <t hangText="Subtype name:">
3639      http
3640    </t>
3641    <t hangText="Required parameters:">
3642      none
3643    </t>
3644    <t hangText="Optional parameters:">
3645      version, msgtype
3646      <list style="hanging">
3647        <t hangText="version:">
3648          The HTTP-Version number of the enclosed message
3649          (e.g., "1.1"). If not present, the version can be
3650          determined from the first line of the body.
3651        </t>
3652        <t hangText="msgtype:">
3653          The message type &mdash; "request" or "response". If not
3654          present, the type can be determined from the first
3655          line of the body.
3656        </t>
3657      </list>
3658    </t>
3659    <t hangText="Encoding considerations:">
3660      only "7bit", "8bit", or "binary" are permitted
3661    </t>
3662    <t hangText="Security considerations:">
3663      none
3664    </t>
3665    <t hangText="Interoperability considerations:">
3666      none
3667    </t>
3668    <t hangText="Published specification:">
3669      This specification (see <xref target=""/>).
3670    </t>
3671    <t hangText="Applications that use this media type:">
3672    </t>
3673    <t hangText="Additional information:">
3674      <list style="hanging">
3675        <t hangText="Magic number(s):">none</t>
3676        <t hangText="File extension(s):">none</t>
3677        <t hangText="Macintosh file type code(s):">none</t>
3678      </list>
3679    </t>
3680    <t hangText="Person and email address to contact for further information:">
3681      See Authors Section.
3682    </t>
3683    <t hangText="Intended usage:">
3684      COMMON
3685    </t>
3686    <t hangText="Restrictions on usage:">
3687      none
3688    </t>
3689    <t hangText="Author/Change controller:">
3690      IESG
3691    </t>
3692  </list>
3695<section title="Internet Media Type application/http" anchor="">
3696<iref item="Media Type" subitem="application/http" primary="true"/>
3697<iref item="application/http Media Type" primary="true"/>
3699   The application/http type can be used to enclose a pipeline of one or more
3700   HTTP request or response messages (not intermixed).
3703  <list style="hanging" x:indent="12em">
3704    <t hangText="Type name:">
3705      application
3706    </t>
3707    <t hangText="Subtype name:">
3708      http
3709    </t>
3710    <t hangText="Required parameters:">
3711      none
3712    </t>
3713    <t hangText="Optional parameters:">
3714      version, msgtype
3715      <list style="hanging">
3716        <t hangText="version:">
3717          The HTTP-Version number of the enclosed messages
3718          (e.g., "1.1"). If not present, the version can be
3719          determined from the first line of the body.
3720        </t>
3721        <t hangText="msgtype:">
3722          The message type &mdash; "request" or "response". If not
3723          present, the type can be determined from the first
3724          line of the body.
3725        </t>
3726      </list>
3727    </t>
3728    <t hangText="Encoding considerations:">
3729      HTTP messages enclosed by this type
3730      are in "binary" format; use of an appropriate
3731      Content-Transfer-Encoding is required when
3732      transmitted via E-mail.
3733    </t>
3734    <t hangText="Security considerations:">
3735      none
3736    </t>
3737    <t hangText="Interoperability considerations:">
3738      none
3739    </t>
3740    <t hangText="Published specification:">
3741      This specification (see <xref target=""/>).
3742    </t>
3743    <t hangText="Applications that use this media type:">
3744    </t>
3745    <t hangText="Additional information:">
3746      <list style="hanging">
3747        <t hangText="Magic number(s):">none</t>
3748        <t hangText="File extension(s):">none</t>
3749        <t hangText="Macintosh file type code(s):">none</t>
3750      </list>
3751    </t>
3752    <t hangText="Person and email address to contact for further information:">
3753      See Authors Section.
3754    </t>
3755    <t hangText="Intended usage:">
3756      COMMON
3757    </t>
3758    <t hangText="Restrictions on usage:">
3759      none
3760    </t>
3761    <t hangText="Author/Change controller:">
3762      IESG
3763    </t>
3764  </list>
3769<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3771   The registration procedure for HTTP Transfer Codings is now defined by
3772   <xref target="transfer.coding.registry"/> of this document.
3775   The HTTP Transfer Codings Registry located at <eref target=""/>
3776   shall be updated with the registrations below:
3778<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3779   <ttcol>Name</ttcol>
3780   <ttcol>Description</ttcol>
3781   <ttcol>Reference</ttcol>
3782   <c>chunked</c>
3783   <c>Transfer in a series of chunks</c>
3784   <c>
3785      <xref target="chunked.encoding"/>
3786   </c>
3787   <c>compress</c>
3788   <c>UNIX "compress" program method</c>
3789   <c>
3790      <xref target="compress.coding"/>
3791   </c>
3792   <c>deflate</c>
3793   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3794   the "zlib" data format (<xref target="RFC1950"/>)
3795   </c>
3796   <c>
3797      <xref target="deflate.coding"/>
3798   </c>
3799   <c>gzip</c>
3800   <c>Same as GNU zip <xref target="RFC1952"/></c>
3801   <c>
3802      <xref target="gzip.coding"/>
3803   </c>
3807<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3809   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3810   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3811   by <xref target="upgrade.token.registry"/> of this document.
3814   The HTTP Status Code Registry located at <eref target=""/>
3815   shall be updated with the registration below:
3817<texttable align="left" suppress-title="true">
3818   <ttcol>Value</ttcol>
3819   <ttcol>Description</ttcol>
3820   <ttcol>Reference</ttcol>
3822   <c>HTTP</c>
3823   <c>Hypertext Transfer Protocol</c>
3824   <c><xref target="http.version"/> of this specification</c>
3825<!-- IANA should add this without our instructions; emailed on June 05, 2009
3826   <c>TLS/1.0</c>
3827   <c>Transport Layer Security</c>
3828   <c><xref target="RFC2817"/></c> -->
3835<section title="Security Considerations" anchor="security.considerations">
3837   This section is meant to inform application developers, information
3838   providers, and users of the security limitations in HTTP/1.1 as
3839   described by this document. The discussion does not include
3840   definitive solutions to the problems revealed, though it does make
3841   some suggestions for reducing security risks.
3844<section title="Personal Information" anchor="personal.information">
3846   HTTP clients are often privy to large amounts of personal information
3847   (e.g., the user's name, location, mail address, passwords, encryption
3848   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3849   leakage of this information.
3850   We very strongly recommend that a convenient interface be provided
3851   for the user to control dissemination of such information, and that
3852   designers and implementors be particularly careful in this area.
3853   History shows that errors in this area often create serious security
3854   and/or privacy problems and generate highly adverse publicity for the
3855   implementor's company.
3859<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3861   A server is in the position to save personal data about a user's
3862   requests which might identify their reading patterns or subjects of
3863   interest. This information is clearly confidential in nature and its
3864   handling can be constrained by law in certain countries. People using
3865   HTTP to provide data are responsible for ensuring that
3866   such material is not distributed without the permission of any
3867   individuals that are identifiable by the published results.
3871<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3873   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3874   the documents returned by HTTP requests to be only those that were
3875   intended by the server administrators. If an HTTP server translates
3876   HTTP URIs directly into file system calls, the server &MUST; take
3877   special care not to serve files that were not intended to be
3878   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3879   other operating systems use ".." as a path component to indicate a
3880   directory level above the current one. On such a system, an HTTP
3881   server &MUST; disallow any such construct in the request-target if it
3882   would otherwise allow access to a resource outside those intended to
3883   be accessible via the HTTP server. Similarly, files intended for
3884   reference only internally to the server (such as access control
3885   files, configuration files, and script code) &MUST; be protected from
3886   inappropriate retrieval, since they might contain sensitive
3887   information. Experience has shown that minor bugs in such HTTP server
3888   implementations have turned into security risks.
3892<section title="DNS Spoofing" anchor="dns.spoofing">
3894   Clients using HTTP rely heavily on the Domain Name Service, and are
3895   thus generally prone to security attacks based on the deliberate
3896   mis-association of IP addresses and DNS names. Clients need to be
3897   cautious in assuming the continuing validity of an IP number/DNS name
3898   association.
3901   In particular, HTTP clients &SHOULD; rely on their name resolver for
3902   confirmation of an IP number/DNS name association, rather than
3903   caching the result of previous host name lookups. Many platforms
3904   already can cache host name lookups locally when appropriate, and
3905   they &SHOULD; be configured to do so. It is proper for these lookups to
3906   be cached, however, only when the TTL (Time To Live) information
3907   reported by the name server makes it likely that the cached
3908   information will remain useful.
3911   If HTTP clients cache the results of host name lookups in order to
3912   achieve a performance improvement, they &MUST; observe the TTL
3913   information reported by DNS.
3916   If HTTP clients do not observe this rule, they could be spoofed when
3917   a previously-accessed server's IP address changes. As network
3918   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3919   possibility of this form of attack will grow. Observing this
3920   requirement thus reduces this potential security vulnerability.
3923   This requirement also improves the load-balancing behavior of clients
3924   for replicated servers using the same DNS name and reduces the
3925   likelihood of a user's experiencing failure in accessing sites which
3926   use that strategy.
3930<section title="Proxies and Caching" anchor="attack.proxies">
3932   By their very nature, HTTP proxies are men-in-the-middle, and
3933   represent an opportunity for man-in-the-middle attacks. Compromise of
3934   the systems on which the proxies run can result in serious security
3935   and privacy problems. Proxies have access to security-related
3936   information, personal information about individual users and
3937   organizations, and proprietary information belonging to users and
3938   content providers. A compromised proxy, or a proxy implemented or
3939   configured without regard to security and privacy considerations,
3940   might be used in the commission of a wide range of potential attacks.
3943   Proxy operators need to protect the systems on which proxies run as
3944   they would protect any system that contains or transports sensitive
3945   information. In particular, log information gathered at proxies often
3946   contains highly sensitive personal information, and/or information
3947   about organizations. Log information needs to be carefully guarded, and
3948   appropriate guidelines for use need to be developed and followed.
3949   (<xref target="abuse.of.server.log.information"/>).
3952   Proxy implementors need to consider the privacy and security
3953   implications of their design and coding decisions, and of the
3954   configuration options they provide to proxy operators (especially the
3955   default configuration).
3958   Users of a proxy need to be aware that proxies are no trustworthier than
3959   the people who run them; HTTP itself cannot solve this problem.
3962   The judicious use of cryptography, when appropriate, might suffice to
3963   protect against a broad range of security and privacy attacks. Such
3964   cryptography is beyond the scope of the HTTP/1.1 specification.
3968<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3970   They exist. They are hard to defend against. Research continues.
3971   Beware.
3976<section title="Acknowledgments" anchor="ack">
3978   HTTP has evolved considerably over the years. It has
3979   benefited from a large and active developer community &mdash; the many
3980   people who have participated on the www-talk mailing list &mdash; and it is
3981   that community which has been most responsible for the success of
3982   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3983   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3984   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3985   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3986   VanHeyningen deserve special recognition for their efforts in
3987   defining early aspects of the protocol.
3990   This document has benefited greatly from the comments of all those
3991   participating in the HTTP-WG. In addition to those already mentioned,
3992   the following individuals have contributed to this specification:
3995   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3996   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3997   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3998   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3999   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4000   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4001   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4002   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4003   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4004   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4005   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4006   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4009   Thanks to the "cave men" of Palo Alto. You know who you are.
4012   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4013   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4014   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4015   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4016   Larry Masinter for their help. And thanks go particularly to Jeff
4017   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4020   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4021   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4022   discovery of many of the problems that this document attempts to
4023   rectify.
4026   This specification makes heavy use of the augmented BNF and generic
4027   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4028   reuses many of the definitions provided by Nathaniel Borenstein and
4029   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4030   specification will help reduce past confusion over the relationship
4031   between HTTP and Internet mail message formats.
4035Acknowledgements TODO list
4037- Jeff Hodges ("effective request URI")
4045<references title="Normative References">
4047<reference anchor="ISO-8859-1">
4048  <front>
4049    <title>
4050     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4051    </title>
4052    <author>
4053      <organization>International Organization for Standardization</organization>
4054    </author>
4055    <date year="1998"/>
4056  </front>
4057  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4060<reference anchor="Part2">
4061  <front>
4062    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4063    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4064      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4065      <address><email></email></address>
4066    </author>
4067    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4068      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4069      <address><email></email></address>
4070    </author>
4071    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4072      <organization abbrev="HP">Hewlett-Packard Company</organization>
4073      <address><email></email></address>
4074    </author>
4075    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4076      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4077      <address><email></email></address>
4078    </author>
4079    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4080      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4081      <address><email></email></address>
4082    </author>
4083    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4084      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4085      <address><email></email></address>
4086    </author>
4087    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4088      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4089      <address><email></email></address>
4090    </author>
4091    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4092      <organization abbrev="W3C">World Wide Web Consortium</organization>
4093      <address><email></email></address>
4094    </author>
4095    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4096      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4097      <address><email></email></address>
4098    </author>
4099    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4100  </front>
4101  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4102  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4105<reference anchor="Part3">
4106  <front>
4107    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4108    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4109      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4110      <address><email></email></address>
4111    </author>
4112    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4113      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4114      <address><email></email></address>
4115    </author>
4116    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4117      <organization abbrev="HP">Hewlett-Packard Company</organization>
4118      <address><email></email></address>
4119    </author>
4120    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4121      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4122      <address><email></email></address>
4123    </author>
4124    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4125      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4126      <address><email></email></address>
4127    </author>
4128    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4129      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4130      <address><email></email></address>
4131    </author>
4132    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4133      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4134      <address><email></email></address>
4135    </author>
4136    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4137      <organization abbrev="W3C">World Wide Web Consortium</organization>
4138      <address><email></email></address>
4139    </author>
4140    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4141      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4142      <address><email></email></address>
4143    </author>
4144    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4145  </front>
4146  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4147  <x:source href="p3-payload.xml" basename="p3-payload"/>
4150<reference anchor="Part6">
4151  <front>
4152    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4153    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4154      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4155      <address><email></email></address>
4156    </author>
4157    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4158      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4159      <address><email></email></address>
4160    </author>
4161    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4162      <organization abbrev="HP">Hewlett-Packard Company</organization>
4163      <address><email></email></address>
4164    </author>
4165    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4166      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4167      <address><email></email></address>
4168    </author>
4169    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4170      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4171      <address><email></email></address>
4172    </author>
4173    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4174      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4175      <address><email></email></address>
4176    </author>
4177    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4178      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4179      <address><email></email></address>
4180    </author>
4181    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4182      <organization abbrev="W3C">World Wide Web Consortium</organization>
4183      <address><email></email></address>
4184    </author>
4185    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4186      <address><email></email></address>
4187    </author>
4188    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4189      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4190      <address><email></email></address>
4191    </author>
4192    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4193  </front>
4194  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4195  <x:source href="p6-cache.xml" basename="p6-cache"/>
4198<reference anchor="RFC5234">
4199  <front>
4200    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4201    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4202      <organization>Brandenburg InternetWorking</organization>
4203      <address>
4204        <email></email>
4205      </address> 
4206    </author>
4207    <author initials="P." surname="Overell" fullname="Paul Overell">
4208      <organization>THUS plc.</organization>
4209      <address>
4210        <email></email>
4211      </address>
4212    </author>
4213    <date month="January" year="2008"/>
4214  </front>
4215  <seriesInfo name="STD" value="68"/>
4216  <seriesInfo name="RFC" value="5234"/>
4219<reference anchor="RFC2119">
4220  <front>
4221    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4222    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4223      <organization>Harvard University</organization>
4224      <address><email></email></address>
4225    </author>
4226    <date month="March" year="1997"/>
4227  </front>
4228  <seriesInfo name="BCP" value="14"/>
4229  <seriesInfo name="RFC" value="2119"/>
4232<reference anchor="RFC3986">
4233 <front>
4234  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4235  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4236    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4237    <address>
4238       <email></email>
4239       <uri></uri>
4240    </address>
4241  </author>
4242  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4243    <organization abbrev="Day Software">Day Software</organization>
4244    <address>
4245      <email></email>
4246      <uri></uri>
4247    </address>
4248  </author>
4249  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4250    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4251    <address>
4252      <email></email>
4253      <uri></uri>
4254    </address>
4255  </author>
4256  <date month='January' year='2005'></date>
4257 </front>
4258 <seriesInfo name="STD" value="66"/>
4259 <seriesInfo name="RFC" value="3986"/>
4262<reference anchor="USASCII">
4263  <front>
4264    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4265    <author>
4266      <organization>American National Standards Institute</organization>
4267    </author>
4268    <date year="1986"/>
4269  </front>
4270  <seriesInfo name="ANSI" value="X3.4"/>
4273<reference anchor="RFC1950">
4274  <front>
4275    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4276    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4277      <organization>Aladdin Enterprises</organization>
4278      <address><email></email></address>
4279    </author>
4280    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4281    <date month="May" year="1996"/>
4282  </front>
4283  <seriesInfo name="RFC" value="1950"/>
4284  <annotation>
4285    RFC 1950 is an Informational RFC, thus it might be less stable than
4286    this specification. On the other hand, this downward reference was
4287    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4288    therefore it is unlikely to cause problems in practice. See also
4289    <xref target="BCP97"/>.
4290  </annotation>
4293<reference anchor="RFC1951">
4294  <front>
4295    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4296    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4297      <organization>Aladdin Enterprises</organization>
4298      <address><email></email></address>
4299    </author>
4300    <date month="May" year="1996"/>
4301  </front>
4302  <seriesInfo name="RFC" value="1951"/>
4303  <annotation>
4304    RFC 1951 is an Informational RFC, thus it might be less stable than
4305    this specification. On the other hand, this downward reference was
4306    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4307    therefore it is unlikely to cause problems in practice. See also
4308    <xref target="BCP97"/>.
4309  </annotation>
4312<reference anchor="RFC1952">
4313  <front>
4314    <title>GZIP file format specification version 4.3</title>
4315    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4316      <organization>Aladdin Enterprises</organization>
4317      <address><email></email></address>
4318    </author>
4319    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4320      <address><email></email></address>
4321    </author>
4322    <author initials="M." surname="Adler" fullname="Mark Adler">
4323      <address><email></email></address>
4324    </author>
4325    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4326      <address><email></email></address>
4327    </author>
4328    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4329      <address><email></email></address>
4330    </author>
4331    <date month="May" year="1996"/>
4332  </front>
4333  <seriesInfo name="RFC" value="1952"/>
4334  <annotation>
4335    RFC 1952 is an Informational RFC, thus it might be less stable than
4336    this specification. On the other hand, this downward reference was
4337    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4338    therefore it is unlikely to cause problems in practice. See also
4339    <xref target="BCP97"/>.
4340  </annotation>
4345<references title="Informative References">
4347<reference anchor="Nie1997" target="">
4348  <front>
4349    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4350    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4351    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4352    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4353    <author initials="H." surname="Lie" fullname="H. Lie"/>
4354    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4355    <date year="1997" month="September"/>
4356  </front>
4357  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4360<reference anchor="Pad1995" target="">
4361  <front>
4362    <title>Improving HTTP Latency</title>
4363    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4364    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4365    <date year="1995" month="December"/>
4366  </front>
4367  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4370<reference anchor="RFC1123">
4371  <front>
4372    <title>Requirements for Internet Hosts - Application and Support</title>
4373    <author initials="R." surname="Braden" fullname="Robert Braden">
4374      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4375      <address><email>Braden@ISI.EDU</email></address>
4376    </author>
4377    <date month="October" year="1989"/>
4378  </front>
4379  <seriesInfo name="STD" value="3"/>
4380  <seriesInfo name="RFC" value="1123"/>
4383<reference anchor="RFC1900">
4384  <front>
4385    <title>Renumbering Needs Work</title>
4386    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4387      <organization>CERN, Computing and Networks Division</organization>
4388      <address><email></email></address>
4389    </author>
4390    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4391      <organization>cisco Systems</organization>
4392      <address><email></email></address>
4393    </author>
4394    <date month="February" year="1996"/>
4395  </front>
4396  <seriesInfo name="RFC" value="1900"/>
4399<reference anchor='RFC1919'>
4400  <front>
4401    <title>Classical versus Transparent IP Proxies</title>
4402    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4403      <address><email></email></address>
4404    </author>
4405    <date year='1996' month='March' />
4406  </front>
4407  <seriesInfo name='RFC' value='1919' />
4410<reference anchor="RFC1945">
4411  <front>
4412    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4413    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4414      <organization>MIT, Laboratory for Computer Science</organization>
4415      <address><email></email></address>
4416    </author>
4417    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4418      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4419      <address><email></email></address>
4420    </author>
4421    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4422      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4423      <address><email></email></address>
4424    </author>
4425    <date month="May" year="1996"/>
4426  </front>
4427  <seriesInfo name="RFC" value="1945"/>
4430<reference anchor="RFC2045">
4431  <front>
4432    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4433    <author initials="N." surname="Freed" fullname="Ned Freed">
4434      <organization>Innosoft International, Inc.</organization>
4435      <address><email></email></address>
4436    </author>
4437    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4438      <organization>First Virtual Holdings</organization>
4439      <address><email></email></address>
4440    </author>
4441    <date month="November" year="1996"/>
4442  </front>
4443  <seriesInfo name="RFC" value="2045"/>
4446<reference anchor="RFC2047">
4447  <front>
4448    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4449    <author initials="K." surname="Moore" fullname="Keith Moore">
4450      <organization>University of Tennessee</organization>
4451      <address><email></email></address>
4452    </author>
4453    <date month="November" year="1996"/>
4454  </front>
4455  <seriesInfo name="RFC" value="2047"/>
4458<reference anchor="RFC2068">
4459  <front>
4460    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4461    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4462      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4463      <address><email></email></address>
4464    </author>
4465    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4466      <organization>MIT Laboratory for Computer Science</organization>
4467      <address><email></email></address>
4468    </author>
4469    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4470      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4471      <address><email></email></address>
4472    </author>
4473    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4474      <organization>MIT Laboratory for Computer Science</organization>
4475      <address><email></email></address>
4476    </author>
4477    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4478      <organization>MIT Laboratory for Computer Science</organization>
4479      <address><email></email></address>
4480    </author>
4481    <date month="January" year="1997"/>
4482  </front>
4483  <seriesInfo name="RFC" value="2068"/>
4486<reference anchor="RFC2145">
4487  <front>
4488    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4489    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4490      <organization>Western Research Laboratory</organization>
4491      <address><email></email></address>
4492    </author>
4493    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4494      <organization>Department of Information and Computer Science</organization>
4495      <address><email></email></address>
4496    </author>
4497    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4498      <organization>MIT Laboratory for Computer Science</organization>
4499      <address><email></email></address>
4500    </author>
4501    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4502      <organization>W3 Consortium</organization>
4503      <address><email></email></address>
4504    </author>
4505    <date month="May" year="1997"/>
4506  </front>
4507  <seriesInfo name="RFC" value="2145"/>
4510<reference anchor="RFC2616">
4511  <front>
4512    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4513    <author initials="R." surname="Fielding" fullname="R. Fielding">
4514      <organization>University of California, Irvine</organization>
4515      <address><email></email></address>
4516    </author>
4517    <author initials="J." surname="Gettys" fullname="J. Gettys">
4518      <organization>W3C</organization>
4519      <address><email></email></address>
4520    </author>
4521    <author initials="J." surname="Mogul" fullname="J. Mogul">
4522      <organization>Compaq Computer Corporation</organization>
4523      <address><email></email></address>
4524    </author>
4525    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4526      <organization>MIT Laboratory for Computer Science</organization>
4527      <address><email></email></address>
4528    </author>
4529    <author initials="L." surname="Masinter" fullname="L. Masinter">
4530      <organization>Xerox Corporation</organization>
4531      <address><email></email></address>
4532    </author>
4533    <author initials="P." surname="Leach" fullname="P. Leach">
4534      <organization>Microsoft Corporation</organization>
4535      <address><email></email></address>
4536    </author>
4537    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4538      <organization>W3C</organization>
4539      <address><email></email></address>
4540    </author>
4541    <date month="June" year="1999"/>
4542  </front>
4543  <seriesInfo name="RFC" value="2616"/>
4546<reference anchor='RFC2817'>
4547  <front>
4548    <title>Upgrading to TLS Within HTTP/1.1</title>
4549    <author initials='R.' surname='Khare' fullname='R. Khare'>
4550      <organization>4K Associates / UC Irvine</organization>
4551      <address><email></email></address>
4552    </author>
4553    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4554      <organization>Agranat Systems, Inc.</organization>
4555      <address><email></email></address>
4556    </author>
4557    <date year='2000' month='May' />
4558  </front>
4559  <seriesInfo name='RFC' value='2817' />
4562<reference anchor='RFC2818'>
4563  <front>
4564    <title>HTTP Over TLS</title>
4565    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4566      <organization>RTFM, Inc.</organization>
4567      <address><email></email></address>
4568    </author>
4569    <date year='2000' month='May' />
4570  </front>
4571  <seriesInfo name='RFC' value='2818' />
4574<reference anchor='RFC2965'>
4575  <front>
4576    <title>HTTP State Management Mechanism</title>
4577    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4578      <organization>Bell Laboratories, Lucent Technologies</organization>
4579      <address><email></email></address>
4580    </author>
4581    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4582      <organization>, Inc.</organization>
4583      <address><email></email></address>
4584    </author>
4585    <date year='2000' month='October' />
4586  </front>
4587  <seriesInfo name='RFC' value='2965' />
4590<reference anchor='RFC3040'>
4591  <front>
4592    <title>Internet Web Replication and Caching Taxonomy</title>
4593    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4594      <organization>Equinix, Inc.</organization>
4595    </author>
4596    <author initials='I.' surname='Melve' fullname='I. Melve'>
4597      <organization>UNINETT</organization>
4598    </author>
4599    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4600      <organization>CacheFlow Inc.</organization>
4601    </author>
4602    <date year='2001' month='January' />
4603  </front>
4604  <seriesInfo name='RFC' value='3040' />
4607<reference anchor='RFC3864'>
4608  <front>
4609    <title>Registration Procedures for Message Header Fields</title>
4610    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4611      <organization>Nine by Nine</organization>
4612      <address><email></email></address>
4613    </author>
4614    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4615      <organization>BEA Systems</organization>
4616      <address><email></email></address>
4617    </author>
4618    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4619      <organization>HP Labs</organization>
4620      <address><email></email></address>
4621    </author>
4622    <date year='2004' month='September' />
4623  </front>
4624  <seriesInfo name='BCP' value='90' />
4625  <seriesInfo name='RFC' value='3864' />
4628<reference anchor="RFC4288">
4629  <front>
4630    <title>Media Type Specifications and Registration Procedures</title>
4631    <author initials="N." surname="Freed" fullname="N. Freed">
4632      <organization>Sun Microsystems</organization>
4633      <address>
4634        <email></email>
4635      </address>
4636    </author>
4637    <author initials="J." surname="Klensin" fullname="J. Klensin">
4638      <address>
4639        <email></email>
4640      </address>
4641    </author>
4642    <date year="2005" month="December"/>
4643  </front>
4644  <seriesInfo name="BCP" value="13"/>
4645  <seriesInfo name="RFC" value="4288"/>
4648<reference anchor='RFC4395'>
4649  <front>
4650    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4651    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4652      <organization>AT&amp;T Laboratories</organization>
4653      <address>
4654        <email></email>
4655      </address>
4656    </author>
4657    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4658      <organization>Qualcomm, Inc.</organization>
4659      <address>
4660        <email></email>
4661      </address>
4662    </author>
4663    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4664      <organization>Adobe Systems</organization>
4665      <address>
4666        <email></email>
4667      </address>
4668    </author>
4669    <date year='2006' month='February' />
4670  </front>
4671  <seriesInfo name='BCP' value='115' />
4672  <seriesInfo name='RFC' value='4395' />
4675<reference anchor='RFC5226'>
4676  <front>
4677    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4678    <author initials='T.' surname='Narten' fullname='T. Narten'>
4679      <organization>IBM</organization>
4680      <address><email></email></address>
4681    </author>
4682    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4683      <organization>Google</organization>
4684      <address><email></email></address>
4685    </author>
4686    <date year='2008' month='May' />
4687  </front>
4688  <seriesInfo name='BCP' value='26' />
4689  <seriesInfo name='RFC' value='5226' />
4692<reference anchor="RFC5322">
4693  <front>
4694    <title>Internet Message Format</title>
4695    <author initials="P." surname="Resnick" fullname="P. Resnick">
4696      <organization>Qualcomm Incorporated</organization>
4697    </author>
4698    <date year="2008" month="October"/>
4699  </front>
4700  <seriesInfo name="RFC" value="5322"/>
4703<reference anchor='draft-ietf-httpstate-cookie'>
4704  <front>
4705    <title>HTTP State Management Mechanism</title>
4706    <author initials="A." surname="Barth" fullname="Adam Barth">
4707      <organization abbrev="U.C. Berkeley">
4708        University of California, Berkeley
4709      </organization>
4710      <address><email></email></address>
4711    </author>
4712    <date year='2011' month='March' />
4713  </front>
4714  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4717<reference anchor='BCP97'>
4718  <front>
4719    <title>Handling Normative References to Standards-Track Documents</title>
4720    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4721      <address>
4722        <email></email>
4723      </address>
4724    </author>
4725    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4726      <organization>MIT</organization>
4727      <address>
4728        <email></email>
4729      </address>
4730    </author>
4731    <date year='2007' month='June' />
4732  </front>
4733  <seriesInfo name='BCP' value='97' />
4734  <seriesInfo name='RFC' value='4897' />
4737<reference anchor="Kri2001" target="">
4738  <front>
4739    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4740    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4741    <date year="2001" month="November"/>
4742  </front>
4743  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4746<reference anchor="Spe" target="">
4747  <front>
4748    <title>Analysis of HTTP Performance Problems</title>
4749    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4750    <date/>
4751  </front>
4754<reference anchor="Tou1998" target="">
4755  <front>
4756  <title>Analysis of HTTP Performance</title>
4757  <author initials="J." surname="Touch" fullname="Joe Touch">
4758    <organization>USC/Information Sciences Institute</organization>
4759    <address><email></email></address>
4760  </author>
4761  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4762    <organization>USC/Information Sciences Institute</organization>
4763    <address><email></email></address>
4764  </author>
4765  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4766    <organization>USC/Information Sciences Institute</organization>
4767    <address><email></email></address>
4768  </author>
4769  <date year="1998" month="Aug"/>
4770  </front>
4771  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4772  <annotation>(original report dated Aug. 1996)</annotation>
4778<section title="Tolerant Applications" anchor="tolerant.applications">
4780   Although this document specifies the requirements for the generation
4781   of HTTP/1.1 messages, not all applications will be correct in their
4782   implementation. We therefore recommend that operational applications
4783   be tolerant of deviations whenever those deviations can be
4784   interpreted unambiguously.
4787   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4788   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4789   &SHOULD; accept any amount of WSP characters between fields, even though
4790   only a single SP is required.
4793   The line terminator for header fields is the sequence CRLF.
4794   However, we recommend that applications, when parsing such headers fields,
4795   recognize a single LF as a line terminator and ignore the leading CR.
4798   The character set of a representation &SHOULD; be labeled as the lowest
4799   common denominator of the character codes used within that representation, with
4800   the exception that not labeling the representation is preferred over labeling
4801   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4804   Additional rules for requirements on parsing and encoding of dates
4805   and other potential problems with date encodings include:
4808  <list style="symbols">
4809     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4810        which appears to be more than 50 years in the future is in fact
4811        in the past (this helps solve the "year 2000" problem).</t>
4813     <t>Although all date formats are specified to be case-sensitive,
4814        recipients &SHOULD; match day, week and timezone names
4815        case-insensitively.</t>
4817     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4818        Expires date as earlier than the proper value, but &MUST-NOT;
4819        internally represent a parsed Expires date as later than the
4820        proper value.</t>
4822     <t>All expiration-related calculations &MUST; be done in GMT. The
4823        local time zone &MUST-NOT; influence the calculation or comparison
4824        of an age or expiration time.</t>
4826     <t>If an HTTP header field incorrectly carries a date value with a time
4827        zone other than GMT, it &MUST; be converted into GMT using the
4828        most conservative possible conversion.</t>
4829  </list>
4833<section title="Compatibility with Previous Versions" anchor="compatibility">
4835   HTTP has been in use by the World-Wide Web global information initiative
4836   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4837   was a simple protocol for hypertext data transfer across the Internet
4838   with only a single request method (GET) and no metadata.
4839   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4840   methods and MIME-like messaging that could include metadata about the data
4841   transferred and modifiers on the request/response semantics. However,
4842   HTTP/1.0 did not sufficiently take into consideration the effects of
4843   hierarchical proxies, caching, the need for persistent connections, or
4844   name-based virtual hosts. The proliferation of incompletely-implemented
4845   applications calling themselves "HTTP/1.0" further necessitated a
4846   protocol version change in order for two communicating applications
4847   to determine each other's true capabilities.
4850   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4851   requirements that enable reliable implementations, adding only
4852   those new features that will either be safely ignored by an HTTP/1.0
4853   recipient or only sent when communicating with a party advertising
4854   compliance with HTTP/1.1.
4857   It is beyond the scope of a protocol specification to mandate
4858   compliance with previous versions. HTTP/1.1 was deliberately
4859   designed, however, to make supporting previous versions easy. It is
4860   worth noting that, at the time of composing this specification, we would
4861   expect general-purpose HTTP/1.1 servers to:
4862  <list style="symbols">
4863     <t>understand any valid request in the format of HTTP/1.0 and
4864        1.1;</t>
4866     <t>respond appropriately with a message in the same major version
4867        used by the client.</t>
4868  </list>
4871   And we would expect HTTP/1.1 clients to:
4872  <list style="symbols">
4873     <t>understand any valid response in the format of HTTP/1.0 or
4874        1.1.</t>
4875  </list>
4878   For most implementations of HTTP/1.0, each connection is established
4879   by the client prior to the request and closed by the server after
4880   sending the response. Some implementations implement the Keep-Alive
4881   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4884<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4886   This section summarizes major differences between versions HTTP/1.0
4887   and HTTP/1.1.
4890<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4892   The requirements that clients and servers support the Host header
4893   field (<xref target=""/>), report an error if it is
4894   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4895   are among the most important changes defined by this
4896   specification.
4899   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4900   addresses and servers; there was no other established mechanism for
4901   distinguishing the intended server of a request than the IP address
4902   to which that request was directed. The changes outlined above will
4903   allow the Internet, once older HTTP clients are no longer common, to
4904   support multiple Web sites from a single IP address, greatly
4905   simplifying large operational Web servers, where allocation of many
4906   IP addresses to a single host has created serious problems. The
4907   Internet will also be able to recover the IP addresses that have been
4908   allocated for the sole purpose of allowing special-purpose domain
4909   names to be used in root-level HTTP URLs. Given the rate of growth of
4910   the Web, and the number of servers already deployed, it is extremely
4911   important that all implementations of HTTP (including updates to
4912   existing HTTP/1.0 applications) correctly implement these
4913   requirements:
4914  <list style="symbols">
4915     <t>Both clients and servers &MUST; support the Host header field.</t>
4917     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4919     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4920        request does not include a Host header field.</t>
4922     <t>Servers &MUST; accept absolute URIs.</t>
4923  </list>
4928<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4930   Some clients and servers might wish to be compatible with some
4931   previous implementations of persistent connections in HTTP/1.0
4932   clients and servers. Persistent connections in HTTP/1.0 are
4933   explicitly negotiated as they are not the default behavior. HTTP/1.0
4934   experimental implementations of persistent connections are faulty,
4935   and the new facilities in HTTP/1.1 are designed to rectify these
4936   problems. The problem was that some existing HTTP/1.0 clients might
4937   send Keep-Alive to a proxy server that doesn't understand
4938   Connection, which would then erroneously forward it to the next
4939   inbound server, which would establish the Keep-Alive connection and
4940   result in a hung HTTP/1.0 proxy waiting for the close on the
4941   response. The result is that HTTP/1.0 clients must be prevented from
4942   using Keep-Alive when talking to proxies.
4945   However, talking to proxies is the most important use of persistent
4946   connections, so that prohibition is clearly unacceptable. Therefore,
4947   we need some other mechanism for indicating a persistent connection
4948   is desired, which is safe to use even when talking to an old proxy
4949   that ignores Connection. Persistent connections are the default for
4950   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4951   declaring non-persistence. See <xref target="header.connection"/>.
4954   The original HTTP/1.0 form of persistent connections (the Connection:
4955   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4959<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4961  Empty list elements in list productions have been deprecated.
4962  (<xref target="notation.abnf"/>)
4965  Rules about implicit linear whitespace between certain grammar productions
4966  have been removed; now it's only allowed when specifically pointed out
4967  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4968  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4969  Non-ASCII content in header fields and reason phrase has been obsoleted and
4970  made opaque (the TEXT rule was removed)
4971  (<xref target="basic.rules"/>)
4974  Clarify that HTTP-Version is case sensitive.
4975  (<xref target="http.version"/>)
4978  Require that invalid whitespace around field-names be rejected.
4979  (<xref target="header.fields"/>)
4982  Require recipients to handle bogus Content-Length header fields as errors.
4983  (<xref target="message.body"/>)
4986  Remove reference to non-existent identity transfer-coding value tokens.
4987  (Sections <xref format="counter" target="message.body"/> and
4988  <xref format="counter" target="transfer.codings"/>)
4991  Update use of abs_path production from RFC 1808 to the path-absolute + query
4992  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4993  request method only.
4994  (<xref target="request-target"/>)
4997  Clarification that the chunk length does not include the count of the octets
4998  in the chunk header and trailer. Furthermore disallowed line folding
4999  in chunk extensions.
5000  (<xref target="chunked.encoding"/>)
5003  Remove hard limit of two connections per server.
5004  (<xref target="persistent.practical"/>)
5007  Clarify exactly when close connection options must be sent.
5008  (<xref target="header.connection"/>)
5011  Define the semantics of the "Upgrade" header field in responses other than
5012  101 (this was incorporated from <xref target="RFC2817"/>).
5013  (<xref target="header.upgrade"/>)
5018<?BEGININC p1-messaging.abnf-appendix ?>
5019<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5021<artwork type="abnf" name="p1-messaging.parsed-abnf">
5022<x:ref>BWS</x:ref> = OWS
5024<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5025<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
5026<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5027 connection-token ] )
5028<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
5029<x:ref>Content-Length-v</x:ref> = 1*DIGIT
5031<x:ref>Date</x:ref> = "Date:" OWS Date-v
5032<x:ref>Date-v</x:ref> = HTTP-date
5034<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5036<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5037<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5038<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5039<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5040 ]
5041<x:ref>Host</x:ref> = "Host:" OWS Host-v
5042<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
5044<x:ref>Method</x:ref> = token
5046<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5048<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5049<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5050<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5051<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5052<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5054<x:ref>Status-Code</x:ref> = 3DIGIT
5055<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5057<x:ref>TE</x:ref> = "TE:" OWS TE-v
5058<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5059<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5060<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5061<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5062<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5063 transfer-coding ] )
5065<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5066<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5067<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5069<x:ref>Via</x:ref> = "Via:" OWS Via-v
5070<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5071 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5072 ] )
5074<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5075<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5076<x:ref>attribute</x:ref> = token
5077<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5079<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5080<x:ref>chunk-data</x:ref> = 1*OCTET
5081<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5082<x:ref>chunk-ext-name</x:ref> = token
5083<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5084<x:ref>chunk-size</x:ref> = 1*HEXDIG
5085<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5086<x:ref>connection-token</x:ref> = token
5087<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5088 / %x2A-5B ; '*'-'['
5089 / %x5D-7E ; ']'-'~'
5090 / obs-text
5092<x:ref>date1</x:ref> = day SP month SP year
5093<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5094<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5095<x:ref>day</x:ref> = 2DIGIT
5096<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5097 / %x54.75.65 ; Tue
5098 / %x57.65.64 ; Wed
5099 / %x54.68.75 ; Thu
5100 / %x46.72.69 ; Fri
5101 / %x53.61.74 ; Sat
5102 / %x53.75.6E ; Sun
5103<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5104 / %x54. ; Tuesday
5105 / %x57.65.64.6E. ; Wednesday
5106 / %x54. ; Thursday
5107 / %x46. ; Friday
5108 / %x53. ; Saturday
5109 / %x53.75.6E.64.61.79 ; Sunday
5111<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5112<x:ref>field-name</x:ref> = token
5113<x:ref>field-value</x:ref> = *( field-content / OWS )
5115<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5116<x:ref>hour</x:ref> = 2DIGIT
5117<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5118<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5120<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5122<x:ref>message-body</x:ref> = *OCTET
5123<x:ref>minute</x:ref> = 2DIGIT
5124<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5125 / %x46.65.62 ; Feb
5126 / %x4D.61.72 ; Mar
5127 / %x41.70.72 ; Apr
5128 / %x4D.61.79 ; May
5129 / %x4A.75.6E ; Jun
5130 / %x4A.75.6C ; Jul
5131 / %x41.75.67 ; Aug
5132 / %x53.65.70 ; Sep
5133 / %x4F.63.74 ; Oct
5134 / %x4E.6F.76 ; Nov
5135 / %x44.65.63 ; Dec
5137<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5138<x:ref>obs-fold</x:ref> = CRLF
5139<x:ref>obs-text</x:ref> = %x80-FF
5141<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5142<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5143<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5144<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5145<x:ref>product</x:ref> = token [ "/" product-version ]
5146<x:ref>product-version</x:ref> = token
5147<x:ref>protocol-name</x:ref> = token
5148<x:ref>protocol-version</x:ref> = token
5149<x:ref>pseudonym</x:ref> = token
5151<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5152 / %x5D-7E ; ']'-'~'
5153 / obs-text
5154<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5155 / %x5D-7E ; ']'-'~'
5156 / obs-text
5157<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5158<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5159<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5160<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5161<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5162<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5164<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5165<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5166<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5167<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5168 / authority
5169<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5170<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5172<x:ref>second</x:ref> = 2DIGIT
5173<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5174 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5175<x:ref>start-line</x:ref> = Request-Line / Status-Line
5177<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5178<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5179 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5180<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5181<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5182<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5183<x:ref>token</x:ref> = 1*tchar
5184<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5185<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5186 transfer-extension
5187<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5188<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5190<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5192<x:ref>value</x:ref> = word
5194<x:ref>word</x:ref> = token / quoted-string
5196<x:ref>year</x:ref> = 4DIGIT
5199<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5200; Chunked-Body defined but not used
5201; Connection defined but not used
5202; Content-Length defined but not used
5203; Date defined but not used
5204; HTTP-message defined but not used
5205; Host defined but not used
5206; Request defined but not used
5207; Response defined but not used
5208; TE defined but not used
5209; Trailer defined but not used
5210; Transfer-Encoding defined but not used
5211; URI-reference defined but not used
5212; Upgrade defined but not used
5213; Via defined but not used
5214; http-URI defined but not used
5215; https-URI defined but not used
5216; partial-URI defined but not used
5217; special defined but not used
5219<?ENDINC p1-messaging.abnf-appendix ?>
5221<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5223<section title="Since RFC 2616">
5225  Extracted relevant partitions from <xref target="RFC2616"/>.
5229<section title="Since draft-ietf-httpbis-p1-messaging-00">
5231  Closed issues:
5232  <list style="symbols">
5233    <t>
5234      <eref target=""/>:
5235      "HTTP Version should be case sensitive"
5236      (<eref target=""/>)
5237    </t>
5238    <t>
5239      <eref target=""/>:
5240      "'unsafe' characters"
5241      (<eref target=""/>)
5242    </t>
5243    <t>
5244      <eref target=""/>:
5245      "Chunk Size Definition"
5246      (<eref target=""/>)
5247    </t>
5248    <t>
5249      <eref target=""/>:
5250      "Message Length"
5251      (<eref target=""/>)
5252    </t>
5253    <t>
5254      <eref target=""/>:
5255      "Media Type Registrations"
5256      (<eref target=""/>)
5257    </t>
5258    <t>
5259      <eref target=""/>:
5260      "URI includes query"
5261      (<eref target=""/>)
5262    </t>
5263    <t>
5264      <eref target=""/>:
5265      "No close on 1xx responses"
5266      (<eref target=""/>)
5267    </t>
5268    <t>
5269      <eref target=""/>:
5270      "Remove 'identity' token references"
5271      (<eref target=""/>)
5272    </t>
5273    <t>
5274      <eref target=""/>:
5275      "Import query BNF"
5276    </t>
5277    <t>
5278      <eref target=""/>:
5279      "qdtext BNF"
5280    </t>
5281    <t>
5282      <eref target=""/>:
5283      "Normative and Informative references"
5284    </t>
5285    <t>
5286      <eref target=""/>:
5287      "RFC2606 Compliance"
5288    </t>
5289    <t>
5290      <eref target=""/>:
5291      "RFC977 reference"
5292    </t>
5293    <t>
5294      <eref target=""/>:
5295      "RFC1700 references"
5296    </t>
5297    <t>
5298      <eref target=""/>:
5299      "inconsistency in date format explanation"
5300    </t>
5301    <t>
5302      <eref target=""/>:
5303      "Date reference typo"
5304    </t>
5305    <t>
5306      <eref target=""/>:
5307      "Informative references"
5308    </t>
5309    <t>
5310      <eref target=""/>:
5311      "ISO-8859-1 Reference"
5312    </t>
5313    <t>
5314      <eref target=""/>:
5315      "Normative up-to-date references"
5316    </t>
5317  </list>
5320  Other changes:
5321  <list style="symbols">
5322    <t>
5323      Update media type registrations to use RFC4288 template.
5324    </t>
5325    <t>
5326      Use names of RFC4234 core rules DQUOTE and WSP,
5327      fix broken ABNF for chunk-data
5328      (work in progress on <eref target=""/>)
5329    </t>
5330  </list>
5334<section title="Since draft-ietf-httpbis-p1-messaging-01">
5336  Closed issues:
5337  <list style="symbols">
5338    <t>
5339      <eref target=""/>:
5340      "Bodies on GET (and other) requests"
5341    </t>
5342    <t>
5343      <eref target=""/>:
5344      "Updating to RFC4288"
5345    </t>
5346    <t>
5347      <eref target=""/>:
5348      "Status Code and Reason Phrase"
5349    </t>
5350    <t>
5351      <eref target=""/>:
5352      "rel_path not used"
5353    </t>
5354  </list>
5357  Ongoing work on ABNF conversion (<eref target=""/>):
5358  <list style="symbols">
5359    <t>
5360      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5361      "trailer-part").
5362    </t>
5363    <t>
5364      Avoid underscore character in rule names ("http_URL" ->
5365      "http-URL", "abs_path" -> "path-absolute").
5366    </t>
5367    <t>
5368      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5369      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5370      have to be updated when switching over to RFC3986.
5371    </t>
5372    <t>
5373      Synchronize core rules with RFC5234.
5374    </t>
5375    <t>
5376      Get rid of prose rules that span multiple lines.
5377    </t>
5378    <t>
5379      Get rid of unused rules LOALPHA and UPALPHA.
5380    </t>
5381    <t>
5382      Move "Product Tokens" section (back) into Part 1, as "token" is used
5383      in the definition of the Upgrade header field.
5384    </t>
5385    <t>
5386      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5387    </t>
5388    <t>
5389      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5390    </t>
5391  </list>
5395<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5397  Closed issues:
5398  <list style="symbols">
5399    <t>
5400      <eref target=""/>:
5401      "HTTP-date vs. rfc1123-date"
5402    </t>
5403    <t>
5404      <eref target=""/>:
5405      "WS in quoted-pair"
5406    </t>
5407  </list>
5410  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5411  <list style="symbols">
5412    <t>
5413      Reference RFC 3984, and update header field registrations for headers defined
5414      in this document.
5415    </t>
5416  </list>
5419  Ongoing work on ABNF conversion (<eref target=""/>):
5420  <list style="symbols">
5421    <t>
5422      Replace string literals when the string really is case-sensitive (HTTP-Version).
5423    </t>
5424  </list>
5428<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5430  Closed issues:
5431  <list style="symbols">
5432    <t>
5433      <eref target=""/>:
5434      "Connection closing"
5435    </t>
5436    <t>
5437      <eref target=""/>:
5438      "Move registrations and registry information to IANA Considerations"
5439    </t>
5440    <t>
5441      <eref target=""/>:
5442      "need new URL for PAD1995 reference"
5443    </t>
5444    <t>
5445      <eref target=""/>:
5446      "IANA Considerations: update HTTP URI scheme registration"
5447    </t>
5448    <t>
5449      <eref target=""/>:
5450      "Cite HTTPS URI scheme definition"
5451    </t>
5452    <t>
5453      <eref target=""/>:
5454      "List-type headers vs Set-Cookie"
5455    </t>
5456  </list>
5459  Ongoing work on ABNF conversion (<eref target=""/>):
5460  <list style="symbols">
5461    <t>
5462      Replace string literals when the string really is case-sensitive (HTTP-Date).
5463    </t>
5464    <t>
5465      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5466    </t>
5467  </list>
5471<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5473  Closed issues:
5474  <list style="symbols">
5475    <t>
5476      <eref target=""/>:
5477      "Out-of-date reference for URIs"
5478    </t>
5479    <t>
5480      <eref target=""/>:
5481      "RFC 2822 is updated by RFC 5322"
5482    </t>
5483  </list>
5486  Ongoing work on ABNF conversion (<eref target=""/>):
5487  <list style="symbols">
5488    <t>
5489      Use "/" instead of "|" for alternatives.
5490    </t>
5491    <t>
5492      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5493    </t>
5494    <t>
5495      Only reference RFC 5234's core rules.
5496    </t>
5497    <t>
5498      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5499      whitespace ("OWS") and required whitespace ("RWS").
5500    </t>
5501    <t>
5502      Rewrite ABNFs to spell out whitespace rules, factor out
5503      header field value format definitions.
5504    </t>
5505  </list>
5509<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5511  Closed issues:
5512  <list style="symbols">
5513    <t>
5514      <eref target=""/>:
5515      "Header LWS"
5516    </t>
5517    <t>
5518      <eref target=""/>:
5519      "Sort 1.3 Terminology"
5520    </t>
5521    <t>
5522      <eref target=""/>:
5523      "RFC2047 encoded words"
5524    </t>
5525    <t>
5526      <eref target=""/>:
5527      "Character Encodings in TEXT"
5528    </t>
5529    <t>
5530      <eref target=""/>:
5531      "Line Folding"
5532    </t>
5533    <t>
5534      <eref target=""/>:
5535      "OPTIONS * and proxies"
5536    </t>
5537    <t>
5538      <eref target=""/>:
5539      "Reason-Phrase BNF"
5540    </t>
5541    <t>
5542      <eref target=""/>:
5543      "Use of TEXT"
5544    </t>
5545    <t>
5546      <eref target=""/>:
5547      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5548    </t>
5549    <t>
5550      <eref target=""/>:
5551      "RFC822 reference left in discussion of date formats"
5552    </t>
5553  </list>
5556  Final work on ABNF conversion (<eref target=""/>):
5557  <list style="symbols">
5558    <t>
5559      Rewrite definition of list rules, deprecate empty list elements.
5560    </t>
5561    <t>
5562      Add appendix containing collected and expanded ABNF.
5563    </t>
5564  </list>
5567  Other changes:
5568  <list style="symbols">
5569    <t>
5570      Rewrite introduction; add mostly new Architecture Section.
5571    </t>
5572    <t>
5573      Move definition of quality values from Part 3 into Part 1;
5574      make TE request header field grammar independent of accept-params (defined in Part 3).
5575    </t>
5576  </list>
5580<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5582  Closed issues:
5583  <list style="symbols">
5584    <t>
5585      <eref target=""/>:
5586      "base for numeric protocol elements"
5587    </t>
5588    <t>
5589      <eref target=""/>:
5590      "comment ABNF"
5591    </t>
5592  </list>
5595  Partly resolved issues:
5596  <list style="symbols">
5597    <t>
5598      <eref target=""/>:
5599      "205 Bodies" (took out language that implied that there might be
5600      methods for which a request body MUST NOT be included)
5601    </t>
5602    <t>
5603      <eref target=""/>:
5604      "editorial improvements around HTTP-date"
5605    </t>
5606  </list>
5610<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5612  Closed issues:
5613  <list style="symbols">
5614    <t>
5615      <eref target=""/>:
5616      "Repeating single-value headers"
5617    </t>
5618    <t>
5619      <eref target=""/>:
5620      "increase connection limit"
5621    </t>
5622    <t>
5623      <eref target=""/>:
5624      "IP addresses in URLs"
5625    </t>
5626    <t>
5627      <eref target=""/>:
5628      "take over HTTP Upgrade Token Registry"
5629    </t>
5630    <t>
5631      <eref target=""/>:
5632      "CR and LF in chunk extension values"
5633    </t>
5634    <t>
5635      <eref target=""/>:
5636      "HTTP/0.9 support"
5637    </t>
5638    <t>
5639      <eref target=""/>:
5640      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5641    </t>
5642    <t>
5643      <eref target=""/>:
5644      "move definitions of gzip/deflate/compress to part 1"
5645    </t>
5646    <t>
5647      <eref target=""/>:
5648      "disallow control characters in quoted-pair"
5649    </t>
5650  </list>
5653  Partly resolved issues:
5654  <list style="symbols">
5655    <t>
5656      <eref target=""/>:
5657      "update IANA requirements wrt Transfer-Coding values" (add the
5658      IANA Considerations subsection)
5659    </t>
5660  </list>
5664<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5666  Closed issues:
5667  <list style="symbols">
5668    <t>
5669      <eref target=""/>:
5670      "header parsing, treatment of leading and trailing OWS"
5671    </t>
5672  </list>
5675  Partly resolved issues:
5676  <list style="symbols">
5677    <t>
5678      <eref target=""/>:
5679      "Placement of 13.5.1 and 13.5.2"
5680    </t>
5681    <t>
5682      <eref target=""/>:
5683      "use of term "word" when talking about header structure"
5684    </t>
5685  </list>
5689<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5691  Closed issues:
5692  <list style="symbols">
5693    <t>
5694      <eref target=""/>:
5695      "Clarification of the term 'deflate'"
5696    </t>
5697    <t>
5698      <eref target=""/>:
5699      "OPTIONS * and proxies"
5700    </t>
5701    <t>
5702      <eref target=""/>:
5703      "MIME-Version not listed in P1, general header fields"
5704    </t>
5705    <t>
5706      <eref target=""/>:
5707      "IANA registry for content/transfer encodings"
5708    </t>
5709    <t>
5710      <eref target=""/>:
5711      "Case-sensitivity of HTTP-date"
5712    </t>
5713    <t>
5714      <eref target=""/>:
5715      "use of term "word" when talking about header structure"
5716    </t>
5717  </list>
5720  Partly resolved issues:
5721  <list style="symbols">
5722    <t>
5723      <eref target=""/>:
5724      "Term for the requested resource's URI"
5725    </t>
5726  </list>
5730<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5732  Closed issues:
5733  <list style="symbols">
5734    <t>
5735      <eref target=""/>:
5736      "Connection Closing"
5737    </t>
5738    <t>
5739      <eref target=""/>:
5740      "Delimiting messages with multipart/byteranges"
5741    </t>
5742    <t>
5743      <eref target=""/>:
5744      "Handling multiple Content-Length headers"
5745    </t>
5746    <t>
5747      <eref target=""/>:
5748      "Clarify entity / representation / variant terminology"
5749    </t>
5750    <t>
5751      <eref target=""/>:
5752      "consider removing the 'changes from 2068' sections"
5753    </t>
5754  </list>
5757  Partly resolved issues:
5758  <list style="symbols">
5759    <t>
5760      <eref target=""/>:
5761      "HTTP(s) URI scheme definitions"
5762    </t>
5763  </list>
5767<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5769  Closed issues:
5770  <list style="symbols">
5771    <t>
5772      <eref target=""/>:
5773      "Trailer requirements"
5774    </t>
5775    <t>
5776      <eref target=""/>:
5777      "Text about clock requirement for caches belongs in p6"
5778    </t>
5779    <t>
5780      <eref target=""/>:
5781      "effective request URI: handling of missing host in HTTP/1.0"
5782    </t>
5783    <t>
5784      <eref target=""/>:
5785      "confusing Date requirements for clients"
5786    </t>
5787  </list>
5790  Partly resolved issues:
5791  <list style="symbols">
5792    <t>
5793      <eref target=""/>:
5794      "Handling multiple Content-Length headers"
5795    </t>
5796  </list>
5800<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5802  Closed issues:
5803  <list style="symbols">
5804    <t>
5805      <eref target=""/>:
5806      "RFC2145 Normative"
5807    </t>
5808    <t>
5809      <eref target=""/>:
5810      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5811    </t>
5812    <t>
5813      <eref target=""/>:
5814      "define 'transparent' proxy"
5815    </t>
5816    <t>
5817      <eref target=""/>:
5818      "Header Classification"
5819    </t>
5820    <t>
5821      <eref target=""/>:
5822      "Is * usable as a request-uri for new methods?"
5823    </t>
5824    <t>
5825      <eref target=""/>:
5826      "Migrate Upgrade details from RFC2817"
5827    </t>
5828    <t>
5829      <eref target=""/>:
5830      "untangle ABNFs for header fields"
5831    </t>
5832    <t>
5833      <eref target=""/>:
5834      "update RFC 2109 reference"
5835    </t>
5836  </list>
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