source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1138

Last change on this file since 1138 was 1138, checked in by julian.reschke@…, 11 years ago

remove header field ABNF dependencies; replace with Overview tables (see #276)

  • Property svn:eol-style set to native
File size: 245.0 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 "February">
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 request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
38  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
39  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
41<?rfc toc="yes" ?>
42<?rfc symrefs="yes" ?>
43<?rfc sortrefs="yes" ?>
44<?rfc compact="yes"?>
45<?rfc subcompact="no" ?>
46<?rfc linkmailto="no" ?>
47<?rfc editing="no" ?>
48<?rfc comments="yes"?>
49<?rfc inline="yes"?>
50<?rfc rfcedstyle="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
54     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x=''>
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
62    <address>
63      <postal>
64        <street>345 Park Ave</street>
65        <city>San Jose</city>
66        <region>CA</region>
67        <code>95110</code>
68        <country>USA</country>
69      </postal>
70      <email></email>
71      <uri></uri>
72    </address>
73  </author>
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email></email>
86      <uri></uri>
87    </address>
88  </author>
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email></email>
102    </address>
103  </author>
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email></email>
116    </address>
117  </author>
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email></email>
130      <uri></uri>
131    </address>
132  </author>
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email></email>
144    </address>
145  </author>
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email></email>
160      <uri></uri>
161    </address>
162  </author>
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email></email>
176      <uri></uri>
177    </address>
178  </author>
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email></email>
191      <uri></uri>
192    </address>
193  </author>
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list ( The current issues list is
217    at <eref target=""/>
218    and related documents (including fancy diffs) can be found at
219    <eref target=""/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.12"/>.
223  </t>
227<section title="Introduction" anchor="introduction">
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
238   between HTTP and MIME messages).
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
252   HTTP is also designed for use as an intermediation protocol for translating
253   communication to and from non-HTTP information systems.
254   HTTP proxies and gateways can provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions ought to be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients might act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1" and obsoleting
274   <xref target="RFC2616"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP, defines the "http" and "https" URI schemes,
277   describes overall network operation and connection management,
278   and defines HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
285<section title="Requirements" anchor="intro.requirements">
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
292   An implementation is not compliant if it fails to satisfy one or more
293   of the "MUST" or "REQUIRED" level requirements for the protocols it
294   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
295   level and all the "SHOULD" level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the "MUST"
297   level requirements but not all the "SHOULD" level requirements for its
298   protocols is said to be "conditionally compliant".
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
342   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
343   "obsolete" grammar rules that appear for historical reasons.
346<section title="ABNF Extension: #rule" anchor="notation.abnf">
348  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
349  improve readability.
352  A construct "#" is defined, similar to "*", for defining comma-delimited
353  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
354  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
355  comma (",") and optional whitespace (OWS,
356  <xref target="basic.rules"/>).   
359  Thus,
360</preamble><artwork type="example">
361  1#element =&gt; element *( OWS "," OWS element )
364  and:
365</preamble><artwork type="example">
366  #element =&gt; [ 1#element ]
369  and for n &gt;= 1 and m &gt; 1:
370</preamble><artwork type="example">
371  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
374  For compatibility with legacy list rules, recipients &SHOULD; accept empty
375  list elements. In other words, consumers would follow the list productions:
377<figure><artwork type="example">
378  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
380  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
383  Note that empty elements do not contribute to the count of elements present,
384  though.
387  For example, given these ABNF productions:
389<figure><artwork type="example">
390  example-list      = 1#example-list-elmt
391  example-list-elmt = token ; see <xref target="basic.rules"/>
394  Then these are valid values for example-list (not including the double
395  quotes, which are present for delimitation only):
397<figure><artwork type="example">
398  "foo,bar"
399  " foo ,bar,"
400  "  foo , ,bar,charlie   "
401  "foo ,bar,   charlie "
404  But these values would be invalid, as at least one non-empty element is
405  required:
407<figure><artwork type="example">
408  ""
409  ","
410  ",   ,"
413  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
414  expanded as explained above.
418<section title="Basic Rules" anchor="basic.rules">
419<t anchor="rule.CRLF">
420  <x:anchor-alias value="CRLF"/>
421   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
422   protocol elements other than the message-body
423   (see <xref target="tolerant.applications"/> for tolerant applications).
425<t anchor="rule.LWS">
426   This specification uses three rules to denote the use of linear
427   whitespace: OWS (optional whitespace), RWS (required whitespace), and
428   BWS ("bad" whitespace).
431   The OWS rule is used where zero or more linear whitespace characters might
432   appear. OWS &SHOULD; either not be produced or be produced as a single SP
433   character. Multiple OWS characters that occur within field-content &SHOULD;
434   be replaced with a single SP before interpreting the field value or
435   forwarding the message downstream.
438   RWS is used when at least one linear whitespace character is required to
439   separate field tokens. RWS &SHOULD; be produced as a single SP character.
440   Multiple RWS characters that occur within field-content &SHOULD; be
441   replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
445   BWS is used where the grammar allows optional whitespace for historical
446   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
447   recipients &MUST; accept such bad optional whitespace and remove it before
448   interpreting the field value or forwarding the message downstream.
450<t anchor="rule.whitespace">
451  <x:anchor-alias value="BWS"/>
452  <x:anchor-alias value="OWS"/>
453  <x:anchor-alias value="RWS"/>
454  <x:anchor-alias value="obs-fold"/>
456<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"/>
457  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "optional" whitespace
459  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "required" whitespace
461  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
462                 ; "bad" whitespace
463  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
464                 ; see <xref target="header.fields"/>
466<t anchor="rule.token.separators">
467  <x:anchor-alias value="tchar"/>
468  <x:anchor-alias value="token"/>
469  <x:anchor-alias value="special"/>
470  <x:anchor-alias value="word"/>
471   Many HTTP/1.1 header field values consist of words (token or quoted-string)
472   separated by whitespace or special characters. These special characters
473   &MUST; be in a quoted string to be used within a parameter value (as defined
474   in <xref target="transfer.codings"/>).
476<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"/>
477  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
479  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
481  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
482 -->
483  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
484                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
485                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
486                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
488  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
489                 / ";" / ":" / "\" / DQUOTE / "/" / "["
490                 / "]" / "?" / "=" / "{" / "}"
492<t anchor="rule.quoted-string">
493  <x:anchor-alias value="quoted-string"/>
494  <x:anchor-alias value="qdtext"/>
495  <x:anchor-alias value="obs-text"/>
496   A string of text is parsed as a single word if it is quoted using
497   double-quote marks.
499<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"/>
500  <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>
501  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
502                 ; <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>
503  <x:ref>obs-text</x:ref>       = %x80-FF
505<t anchor="rule.quoted-pair">
506  <x:anchor-alias value="quoted-pair"/>
507   The backslash character ("\") can be used as a single-character
508   quoting mechanism within quoted-string constructs:
510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
511  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
514   Producers &SHOULD-NOT; escape characters that do not require escaping
515   (i.e., other than DQUOTE and the backslash character).
519<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
520  <x:anchor-alias value="request-header"/>
521  <x:anchor-alias value="response-header"/>
522  <x:anchor-alias value="Cache-Control"/>
523  <x:anchor-alias value="Pragma"/>
524  <x:anchor-alias value="Warning"/>
525  <x:anchor-alias value="MIME-Version"/>
527  The ABNF rules below are defined in other parts:
529<figure><!-- Part2--><artwork type="abnf2616">
530  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
531  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
533<figure><!-- Part3--><artwork type="abnf2616">
534  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&gt;
536<figure><!-- Part6--><artwork type="abnf2616">
537  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
538  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
539  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
546<section title="HTTP-related architecture" anchor="architecture">
548   HTTP was created for the World Wide Web architecture
549   and has evolved over time to support the scalability needs of a worldwide
550   hypertext system. Much of that architecture is reflected in the terminology
551   and syntax productions used to define HTTP.
554<section title="Client/Server Messaging" anchor="operation">
555<iref primary="true" item="client"/>
556<iref primary="true" item="server"/>
557<iref primary="true" item="connection"/>
559   HTTP is a stateless request/response protocol that operates by exchanging
560   messages across a reliable transport or session-layer connection. An HTTP
561   "client" is a program that establishes a connection to a server for the
562   purpose of sending one or more HTTP requests.  An HTTP "server" is a
563   program that accepts connections in order to service HTTP requests by
564   sending HTTP responses.
566<iref primary="true" item="user agent"/>
567<iref primary="true" item="origin server"/>
568<iref primary="true" item="browser"/>
569<iref primary="true" item="spider"/>
571   Note that the terms client and server refer only to the roles that
572   these programs perform for a particular connection.  The same program
573   might act as a client on some connections and a server on others.  We use
574   the term "user agent" to refer to the program that initiates a request,
575   such as a WWW browser, editor, or spider (web-traversing robot), and
576   the term "origin server" to refer to the program that can originate
577   authoritative responses to a request.  For general requirements, we use
578   the term "sender" to refer to whichever component sent a given message
579   and the term "recipient" to refer to any component that receives the
580   message.
583   Most HTTP communication consists of a retrieval request (GET) for
584   a representation of some resource identified by a URI.  In the
585   simplest case, this might be accomplished via a single bidirectional
586   connection (===) between the user agent (UA) and the origin server (O).
588<figure><artwork type="drawing">
589         request   &gt;
590    UA ======================================= O
591                                &lt;   response
593<iref primary="true" item="message"/>
594<iref primary="true" item="request"/>
595<iref primary="true" item="response"/>
597   A client sends an HTTP request to the server in the form of a request
598   message (<xref target="request"/>), beginning with a method, URI, and
599   protocol version, followed by MIME-like header fields containing
600   request modifiers, client information, and payload metadata, an empty
601   line to indicate the end of the header section, and finally the payload
602   body (if any).
605   A server responds to the client's request by sending an HTTP response
606   message (<xref target="response"/>), beginning with a status line that
607   includes the protocol version, a success or error code, and textual
608   reason phrase, followed by MIME-like header fields containing server
609   information, resource metadata, and payload metadata, an empty line to
610   indicate the end of the header section, and finally the payload body (if any).
613   The following example illustrates a typical message exchange for a
614   GET request on the URI "":
617client request:
618</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
619GET /hello.txt HTTP/1.1
620User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
622Accept: */*
626server response:
627</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
628HTTP/1.1 200 OK
629Date: Mon, 27 Jul 2009 12:28:53 GMT
630Server: Apache
631Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
632ETag: "34aa387-d-1568eb00"
633Accept-Ranges: bytes
634Content-Length: <x:length-of target="exbody"/>
635Vary: Accept-Encoding
636Content-Type: text/plain
638<x:span anchor="exbody">Hello World!
642<section title="Intermediaries" anchor="intermediaries">
643<iref primary="true" item="intermediary"/>
645   A more complicated situation occurs when one or more intermediaries
646   are present in the request/response chain. There are three common
647   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
648   a single intermediary might act as an origin server, proxy, gateway,
649   or tunnel, switching behavior based on the nature of each request.
651<figure><artwork type="drawing">
652         &gt;             &gt;             &gt;             &gt;
653    UA =========== A =========== B =========== C =========== O
654               &lt;             &lt;             &lt;             &lt;
657   The figure above shows three intermediaries (A, B, and C) between the
658   user agent and origin server. A request or response message that
659   travels the whole chain will pass through four separate connections.
660   Some HTTP communication options
661   might apply only to the connection with the nearest, non-tunnel
662   neighbor, only to the end-points of the chain, or to all connections
663   along the chain. Although the diagram is linear, each participant might
664   be engaged in multiple, simultaneous communications. For example, B
665   might be receiving requests from many clients other than A, and/or
666   forwarding requests to servers other than C, at the same time that it
667   is handling A's request.
670<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
671<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
672   We use the terms "upstream" and "downstream" to describe various
673   requirements in relation to the directional flow of a message:
674   all messages flow from upstream to downstream.
675   Likewise, we use the terms "inbound" and "outbound" to refer to
676   directions in relation to the request path: "inbound" means toward
677   the origin server and "outbound" means toward the user agent.
679<t><iref primary="true" item="proxy"/>
680   A "proxy" is a message forwarding agent that is selected by the
681   client, usually via local configuration rules, to receive requests
682   for some type(s) of absolute URI and attempt to satisfy those
683   requests via translation through the HTTP interface.  Some translations
684   are minimal, such as for proxy requests for "http" URIs, whereas
685   other requests might require translation to and from entirely different
686   application-layer protocols. Proxies are often used to group an
687   organization's HTTP requests through a common intermediary for the
688   sake of security, annotation services, or shared caching.
691<iref primary="true" item="transforming proxy"/>
692<iref primary="true" item="non-transforming proxy"/>
693   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
694   or configured to modify request or response messages in a semantically
695   meaningful way (i.e., modifications, beyond those required by normal
696   HTTP processing, that change the message in a way that would be
697   significant to the original sender or potentially significant to
698   downstream recipients).  For example, a transforming proxy might be
699   acting as a shared annotation server (modifying responses to include
700   references to a local annotation database), a malware filter, a
701   format transcoder, or an intranet-to-Internet privacy filter.  Such
702   transformations are presumed to be desired by the client (or client
703   organization) that selected the proxy and are beyond the scope of
704   this specification.  However, when a proxy is not intended to transform
705   a given message, we use the term "non-transforming proxy" to target
706   requirements that preserve HTTP message semantics.
708<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
709   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
710   as a layer above some other server(s) and translates the received
711   requests to the underlying server's protocol.  Gateways are often
712   used for load balancing or partitioning HTTP services across
713   multiple machines.
714   Unlike a proxy, a gateway receives requests as if it were the
715   origin server for the target resource; the requesting client
716   will not be aware that it is communicating with a gateway.
717   A gateway communicates with the client as if the gateway is the
718   origin server and thus is subject to all of the requirements on
719   origin servers for that connection.  A gateway communicates
720   with inbound servers using any protocol it desires, including
721   private extensions to HTTP that are outside the scope of this
722   specification.
724<t><iref primary="true" item="tunnel"/>
725   A "tunnel" acts as a blind relay between two connections
726   without changing the messages. Once active, a tunnel is not
727   considered a party to the HTTP communication, though the tunnel might
728   have been initiated by an HTTP request. A tunnel ceases to exist when
729   both ends of the relayed connection are closed. Tunnels are used to
730   extend a virtual connection through an intermediary, such as when
731   transport-layer security is used to establish private communication
732   through a shared firewall proxy.
734<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
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, referred to as an "interception proxy"
740   <xref target="RFC3040"/> or "transparent proxy" <xref target="RFC1919"/>,
741   differs from an HTTP proxy because it has not been selected by the client.
742   Instead, the network intermediary redirects outgoing TCP port 80 packets
743   (and occasionally other common port traffic) to an internal HTTP server.
744   Interception proxies are commonly found on public network access points
745   as a means of enforcing account subscription prior to allowing use of
746   non-local Internet services.  They are indistinguishable from a
747   man-in-the-middle attack.
751<section title="Caches" anchor="caches">
752<iref primary="true" item="cache"/>
754   A "cache" is a local store of previous response messages and the
755   subsystem that controls its message storage, retrieval, and deletion.
756   A cache stores cacheable responses in order to reduce the response
757   time and network bandwidth consumption on future, equivalent
758   requests. Any client or server &MAY; employ a cache, though a cache
759   cannot be used by a server while it is acting as a tunnel.
762   The effect of a cache is that the request/response chain is shortened
763   if one of the participants along the chain has a cached response
764   applicable to that request. The following illustrates the resulting
765   chain if B has a cached copy of an earlier response from O (via C)
766   for a request which has not been cached by UA or A.
768<figure><artwork type="drawing">
769            &gt;             &gt;
770       UA =========== A =========== B - - - - - - C - - - - - - O
771                  &lt;             &lt;
773<t><iref primary="true" item="cacheable"/>
774   A response is "cacheable" if a cache is allowed to store a copy of
775   the response message for use in answering subsequent requests.
776   Even when a response is cacheable, there might be additional
777   constraints placed by the client or by the origin server on when
778   that cached response can be used for a particular request. HTTP
779   requirements for cache behavior and cacheable responses are
780   defined in &caching-overview;. 
783   There are a wide variety of architectures and configurations
784   of caches and proxies deployed across the World Wide Web and
785   inside large organizations. These systems include national hierarchies
786   of proxy caches to save transoceanic bandwidth, systems that
787   broadcast or multicast cache entries, organizations that distribute
788   subsets of cached data via optical media, and so on.
792<section title="Transport Independence" anchor="transport-independence">
794  HTTP systems are used in a wide variety of environments, from
795  corporate intranets with high-bandwidth links to long-distance
796  communication over low-power radio links and intermittent connectivity.
799   HTTP communication usually takes place over TCP/IP connections. The
800   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
801   not preclude HTTP from being implemented on top of any other protocol
802   on the Internet, or on other networks. HTTP only presumes a reliable
803   transport; any protocol that provides such guarantees can be used;
804   the mapping of the HTTP/1.1 request and response structures onto the
805   transport data units of the protocol in question is outside the scope
806   of this specification.
809   In HTTP/1.0, most implementations used a new connection for each
810   request/response exchange. In HTTP/1.1, a connection might be used for
811   one or more request/response exchanges, although connections might be
812   closed for a variety of reasons (see <xref target="persistent.connections"/>).
816<section title="HTTP Version" anchor="http.version">
817  <x:anchor-alias value="HTTP-Version"/>
818  <x:anchor-alias value="HTTP-Prot-Name"/>
820   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
821   of the protocol. The protocol versioning policy is intended to allow
822   the sender to indicate the format of a message and its capacity for
823   understanding further HTTP communication, rather than the features
824   obtained via that communication. No change is made to the version
825   number for the addition of message components which do not affect
826   communication behavior or which only add to extensible field values.
827   The &lt;minor&gt; number is incremented when the changes made to the
828   protocol add features which do not change the general message parsing
829   algorithm, but which might add to the message semantics and imply
830   additional capabilities of the sender. The &lt;major&gt; number is
831   incremented when the format of a message within the protocol is
832   changed. See <xref target="RFC2145"/> for a fuller explanation.
835   The version of an HTTP message is indicated by an HTTP-Version field
836   in the first line of the message. HTTP-Version is case-sensitive.
838<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
839  <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>
840  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
843   Note that the major and minor numbers &MUST; be treated as separate
844   integers and that each &MAY; be incremented higher than a single digit.
845   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
846   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
847   &MUST-NOT; be sent.
850   An application that sends a request or response message that includes
851   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
852   with this specification. Applications that are at least conditionally
853   compliant with this specification &SHOULD; use an HTTP-Version of
854   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
855   not compatible with HTTP/1.0. For more details on when to send
856   specific HTTP-Version values, see <xref target="RFC2145"/>.
859   The HTTP version of an application is the highest HTTP version for
860   which the application is at least conditionally compliant.
863   Proxy and gateway applications need to be careful when forwarding
864   messages in protocol versions different from that of the application.
865   Since the protocol version indicates the protocol capability of the
866   sender, a proxy/gateway &MUST-NOT; send a message with a version
867   indicator which is greater than its actual version. If a higher
868   version request is received, the proxy/gateway &MUST; either downgrade
869   the request version, or respond with an error, or switch to tunnel
870   behavior.
873   Due to interoperability problems with HTTP/1.0 proxies discovered
874   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
875   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
876   they support. The proxy/gateway's response to that request &MUST; be in
877   the same major version as the request.
880  <t>
881    <x:h>Note:</x:h> Converting between versions of HTTP might involve modification
882    of header fields required or forbidden by the versions involved.
883  </t>
887<section title="Uniform Resource Identifiers" anchor="uri">
888<iref primary="true" item="resource"/>
890   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
891   throughout HTTP as the means for identifying resources. URI references
892   are used to target requests, indicate redirects, and define relationships.
893   HTTP does not limit what a resource might be; it merely defines an interface
894   that can be used to interact with a resource via HTTP. More information on
895   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
897  <x:anchor-alias value="URI-reference"/>
898  <x:anchor-alias value="absolute-URI"/>
899  <x:anchor-alias value="relative-part"/>
900  <x:anchor-alias value="authority"/>
901  <x:anchor-alias value="path-abempty"/>
902  <x:anchor-alias value="path-absolute"/>
903  <x:anchor-alias value="port"/>
904  <x:anchor-alias value="query"/>
905  <x:anchor-alias value="uri-host"/>
906  <x:anchor-alias value="partial-URI"/>
908   This specification adopts the definitions of "URI-reference",
909   "absolute-URI", "relative-part", "port", "host",
910   "path-abempty", "path-absolute", "query", and "authority" from
911   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
912   protocol elements that allow a relative URI without a fragment.
914<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"/>
915  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
916  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
917  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
918  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
919  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
920  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
921  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
922  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
923  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
925  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
928   Each protocol element in HTTP that allows a URI reference will indicate in
929   its ABNF production whether the element allows only a URI in absolute form
930   (absolute-URI), any relative reference (relative-ref), or some other subset
931   of the URI-reference grammar. Unless otherwise indicated, URI references
932   are parsed relative to the request target (the default base URI for both
933   the request and its corresponding response).
936<section title="http URI scheme" anchor="http.uri">
937  <x:anchor-alias value="http-URI"/>
938  <iref item="http URI scheme" primary="true"/>
939  <iref item="URI scheme" subitem="http" primary="true"/>
941   The "http" URI scheme is hereby defined for the purpose of minting
942   identifiers according to their association with the hierarchical
943   namespace governed by a potential HTTP origin server listening for
944   TCP connections on a given port.
945   The HTTP server is identified via the generic syntax's
946   <x:ref>authority</x:ref> component, which includes a host
947   identifier and optional TCP port, and the remainder of the URI is
948   considered to be identifying data corresponding to a resource for
949   which that server might provide an HTTP interface.
951<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
952  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
955   The host identifier within an <x:ref>authority</x:ref> component is
956   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
957   provided as an IP literal or IPv4 address, then the HTTP server is any
958   listener on the indicated TCP port at that IP address. If host is a
959   registered name, then that name is considered an indirect identifier
960   and the recipient might use a name resolution service, such as DNS,
961   to find the address of a listener for that host.
962   The host &MUST-NOT; be empty; if an "http" URI is received with an
963   empty host, then it &MUST; be rejected as invalid.
964   If the port subcomponent is empty or not given, then TCP port 80 is
965   assumed (the default reserved port for WWW services).
968   Regardless of the form of host identifier, access to that host is not
969   implied by the mere presence of its name or address. The host might or might
970   not exist and, even when it does exist, might or might not be running an
971   HTTP server or listening to the indicated port. The "http" URI scheme
972   makes use of the delegated nature of Internet names and addresses to
973   establish a naming authority (whatever entity has the ability to place
974   an HTTP server at that Internet name or address) and allows that
975   authority to determine which names are valid and how they might be used.
978   When an "http" URI is used within a context that calls for access to the
979   indicated resource, a client &MAY; attempt access by resolving
980   the host to an IP address, establishing a TCP connection to that address
981   on the indicated port, and sending an HTTP request message to the server
982   containing the URI's identifying data as described in <xref target="request"/>.
983   If the server responds to that request with a non-interim HTTP response
984   message, as described in <xref target="response"/>, then that response
985   is considered an authoritative answer to the client's request.
988   Although HTTP is independent of the transport protocol, the "http"
989   scheme is specific to TCP-based services because the name delegation
990   process depends on TCP for establishing authority.
991   An HTTP service based on some other underlying connection protocol
992   would presumably be identified using a different URI scheme, just as
993   the "https" scheme (below) is used for servers that require an SSL/TLS
994   transport layer on a connection. Other protocols might also be used to
995   provide access to "http" identified resources &mdash; it is only the
996   authoritative interface used for mapping the namespace that is
997   specific to TCP.
1000   The URI generic syntax for authority also includes a deprecated
1001   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1002   for including user authentication information in the URI.  The userinfo
1003   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
1004   URI.  URI reference recipients &SHOULD; parse for the existence of
1005   userinfo and treat its presence as an error, likely indicating that
1006   the deprecated subcomponent is being used to obscure the authority
1007   for the sake of phishing attacks.
1011<section title="https URI scheme" anchor="https.uri">
1012   <x:anchor-alias value="https-URI"/>
1013   <iref item="https URI scheme"/>
1014   <iref item="URI scheme" subitem="https"/>
1016   The "https" URI scheme is hereby defined for the purpose of minting
1017   identifiers according to their association with the hierarchical
1018   namespace governed by a potential HTTP origin server listening for
1019   SSL/TLS-secured connections on a given TCP port.
1022   All of the requirements listed above for the "http" scheme are also
1023   requirements for the "https" scheme, except that a default TCP port
1024   of 443 is assumed if the port subcomponent is empty or not given,
1025   and the TCP connection &MUST; be secured for privacy through the
1026   use of strong encryption prior to sending the first HTTP request.
1028<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1029  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1032   Unlike the "http" scheme, responses to "https" identified requests
1033   are never "public" and thus are ineligible for shared caching.
1034   Their default is "private" and might be further constrained via use
1035   of the Cache-Control header field.
1038   Resources made available via the "https" scheme have no shared
1039   identity with the "http" scheme even if their resource identifiers
1040   only differ by the single "s" in the scheme name.  They are
1041   different services governed by different authorities.  However,
1042   some extensions to HTTP that apply to entire host domains, such
1043   as the Cookie protocol, do allow one service to effect communication
1044   with the other services based on host domain matching.
1047   The process for authoritative access to an "https" identified
1048   resource is defined in <xref target="RFC2818"/>.
1052<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1054   Since the "http" and "https" schemes conform to the URI generic syntax,
1055   such URIs are normalized and compared according to the algorithm defined
1056   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1057   described above for each scheme.
1060   If the port is equal to the default port for a scheme, the normal
1061   form is to elide the port subcomponent. Likewise, an empty path
1062   component is equivalent to an absolute path of "/", so the normal
1063   form is to provide a path of "/" instead. The scheme and host
1064   are case-insensitive and normally provided in lowercase; all
1065   other components are compared in a case-sensitive manner.
1066   Characters other than those in the "reserved" set are equivalent
1067   to their percent-encoded octets (see <xref target="RFC3986"
1068   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1071   For example, the following three URIs are equivalent:
1073<figure><artwork type="example">
1079   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1080   If path-abempty is the empty string (i.e., there is no slash "/"
1081   path separator following the authority), then the "http" URI
1082   &MUST; be given as "/" when
1083   used as a request-target (<xref target="request-target"/>). If a proxy
1084   receives a host name which is not a fully qualified domain name, it
1085   &MAY; add its domain to the host name it received. If a proxy receives
1086   a fully qualified domain name, the proxy &MUST-NOT; change the host
1087   name.
1093<section title="HTTP Message" anchor="http.message">
1094<x:anchor-alias value="generic-message"/>
1095<x:anchor-alias value="message.types"/>
1096<x:anchor-alias value="HTTP-message"/>
1097<x:anchor-alias value="start-line"/>
1098<iref item="header section"/>
1099<iref item="headers"/>
1100<iref item="header field"/>
1102   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1103   characters in a format similar to the Internet Message Format
1104   <xref target="RFC5322"/>: zero or more header fields (collectively
1105   referred to as the "headers" or the "header section"), an empty line
1106   indicating the end of the header section, and an optional message-body.
1109   An HTTP message can either be a request from client to server or a
1110   response from server to client.  Syntactically, the two types of message
1111   differ only in the start-line, which is either a Request-Line (for requests)
1112   or a Status-Line (for responses), and in the algorithm for determining
1113   the length of the message-body (<xref target="message.body"/>).
1114   In theory, a client could receive requests and a server could receive
1115   responses, distinguishing them by their different start-line formats,
1116   but in practice servers are implemented to only expect a request
1117   (a response is interpreted as an unknown or invalid request method)
1118   and clients are implemented to only expect a response.
1120<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1121  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1122                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1123                    <x:ref>CRLF</x:ref>
1124                    [ <x:ref>message-body</x:ref> ]
1125  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1128   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1129   header field. The presence of whitespace might be an attempt to trick a
1130   noncompliant implementation of HTTP into ignoring that field or processing
1131   the next line as a new request, either of which might result in security
1132   issues when implementations within the request chain interpret the
1133   same message differently. HTTP/1.1 servers &MUST; reject such a message
1134   with a 400 (Bad Request) response.
1137<section title="Message Parsing Robustness" anchor="message.robustness">
1139   In the interest of robustness, servers &SHOULD; ignore at least one
1140   empty line received where a Request-Line is expected. In other words, if
1141   the server is reading the protocol stream at the beginning of a
1142   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1145   Some old HTTP/1.0 client implementations generate an extra CRLF
1146   after a POST request as a lame workaround for some early server
1147   applications that failed to read message-body content that was
1148   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1149   preface or follow a request with an extra CRLF.  If terminating
1150   the request message-body with a line-ending is desired, then the
1151   client &MUST; include the terminating CRLF octets as part of the
1152   message-body length.
1155   The normal procedure for parsing an HTTP message is to read the
1156   start-line into a structure, read each header field into a hash
1157   table by field name until the empty line, and then use the parsed
1158   data to determine if a message-body is expected.  If a message-body
1159   has been indicated, then it is read as a stream until an amount
1160   of octets equal to the message-body length is read or the connection
1161   is closed.  Care must be taken to parse an HTTP message as a sequence
1162   of octets in an encoding that is a superset of US-ASCII.  Attempting
1163   to parse HTTP as a stream of Unicode characters in a character encoding
1164   like UTF-16 might introduce security flaws due to the differing ways
1165   that such parsers interpret invalid characters.
1168   HTTP allows the set of defined header fields to be extended without
1169   changing the protocol version (see <xref target="header.field.registration"/>).
1170   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1171   proxy is specifically configured to block or otherwise transform such
1172   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1176<section title="Header Fields" anchor="header.fields">
1177  <x:anchor-alias value="header-field"/>
1178  <x:anchor-alias value="field-content"/>
1179  <x:anchor-alias value="field-name"/>
1180  <x:anchor-alias value="field-value"/>
1181  <x:anchor-alias value="OWS"/>
1183   Each HTTP header field consists of a case-insensitive field name
1184   followed by a colon (":"), optional whitespace, and the field value.
1186<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"/>
1187  <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>
1188  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1189  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1190  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1193   No whitespace is allowed between the header field name and colon. For
1194   security reasons, any request message received containing such whitespace
1195   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1196   &MUST; remove any such whitespace from a response message before
1197   forwarding the message downstream.
1200   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1201   preferred. The field value does not include any leading or trailing white
1202   space: OWS occurring before the first non-whitespace character of the
1203   field value or after the last non-whitespace character of the field value
1204   is ignored and &SHOULD; be removed before further processing (as this does
1205   not change the meaning of the header field).
1208   The order in which header fields with differing field names are
1209   received is not significant. However, it is "good practice" to send
1210   header fields that contain control data first, such as Host on
1211   requests and Date on responses, so that implementations can decide
1212   when not to handle a message as early as possible.  A server &MUST;
1213   wait until the entire header section is received before interpreting
1214   a request message, since later header fields might include conditionals,
1215   authentication credentials, or deliberately misleading duplicate
1216   header fields that would impact request processing.
1219   Multiple header fields with the same field name &MUST-NOT; be
1220   sent in a message unless the entire field value for that
1221   header field is defined as a comma-separated list [i.e., #(values)].
1222   Multiple header fields with the same field name can be combined into
1223   one "field-name: field-value" pair, without changing the semantics of the
1224   message, by appending each subsequent field value to the combined
1225   field value in order, separated by a comma. The order in which
1226   header fields with the same field name are received is therefore
1227   significant to the interpretation of the combined field value;
1228   a proxy &MUST-NOT; change the order of these field values when
1229   forwarding a message.
1232  <t>
1233   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1234   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1235   can occur multiple times, but does not use the list syntax, and thus cannot
1236   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1237   for details.) Also note that the Set-Cookie2 header field specified in
1238   <xref target="RFC2965"/> does not share this problem.
1239  </t>
1242   Historically, HTTP header field values could be extended over multiple
1243   lines by preceding each extra line with at least one space or horizontal
1244   tab character (line folding). This specification deprecates such line
1245   folding except within the message/http media type
1246   (<xref target=""/>).
1247   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1248   (i.e., that contain any field-content that matches the obs-fold rule) unless
1249   the message is intended for packaging within the message/http media type.
1250   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1251   obs-fold whitespace with a single SP prior to interpreting the field value
1252   or forwarding the message downstream.
1255   Historically, HTTP has allowed field content with text in the ISO-8859-1
1256   <xref target="ISO-8859-1"/> character encoding and supported other
1257   character sets only through use of <xref target="RFC2047"/> encoding.
1258   In practice, most HTTP header field values use only a subset of the
1259   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1260   header fields &SHOULD; limit their field values to US-ASCII characters.
1261   Recipients &SHOULD; treat other (obs-text) octets in field content as
1262   opaque data.
1264<t anchor="rule.comment">
1265  <x:anchor-alias value="comment"/>
1266  <x:anchor-alias value="ctext"/>
1267   Comments can be included in some HTTP header fields by surrounding
1268   the comment text with parentheses. Comments are only allowed in
1269   fields containing "comment" as part of their field value definition.
1271<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1272  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1273  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1274                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1276<t anchor="rule.quoted-cpair">
1277  <x:anchor-alias value="quoted-cpair"/>
1278   The backslash character ("\") can be used as a single-character
1279   quoting mechanism within comment constructs:
1281<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1282  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1285   Producers &SHOULD-NOT; escape characters that do not require escaping
1286   (i.e., other than the backslash character "\" and the parentheses "(" and
1287   ")").
1291<section title="Message Body" anchor="message.body">
1292  <x:anchor-alias value="message-body"/>
1294   The message-body (if any) of an HTTP message is used to carry the
1295   payload body associated with the request or response.
1297<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1298  <x:ref>message-body</x:ref> = *OCTET
1301   The message-body differs from the payload body only when a transfer-coding
1302   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1303   applied to a payload in order to form the message-body, the
1304   Transfer-Encoding header field &MUST; contain the list of
1305   transfer-codings applied. Transfer-Encoding is a property of the message,
1306   not of the payload, and thus &MAY; be added or removed by any implementation
1307   along the request/response chain under the constraints found in
1308   <xref target="transfer.codings"/>.
1311   The rules for when a message-body is allowed in a message differ for
1312   requests and responses.
1315   The presence of a message-body in a request is signaled by the
1316   inclusion of a Content-Length or Transfer-Encoding header field in
1317   the request's header fields, even if the request method does not
1318   define any use for a message-body.  This allows the request
1319   message framing algorithm to be independent of method semantics.
1322   For response messages, whether or not a message-body is included with
1323   a message is dependent on both the request method and the response
1324   status code (<xref target="status.code.and.reason.phrase"/>).
1325   Responses to the HEAD request method never include a message-body
1326   because the associated response header fields (e.g., Transfer-Encoding,
1327   Content-Length, etc.) only indicate what their values would have been
1328   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1329   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1330   All other responses do include a message-body, although the body
1331   &MAY; be of zero length.
1334   The length of the message-body is determined by one of the following
1335   (in order of precedence):
1338  <list style="numbers">
1339    <x:lt><t>
1340     Any response to a HEAD request and any response with a status
1341     code of 100-199, 204, or 304 is always terminated by the first
1342     empty line after the header fields, regardless of the header
1343     fields present in the message, and thus cannot contain a message-body.
1344    </t></x:lt>
1345    <x:lt><t>
1346     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1347     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1348     is the final encoding, the message-body length is determined by reading
1349     and decoding the chunked data until the transfer-coding indicates the
1350     data is complete.
1351    </t>
1352    <t>
1353     If a Transfer-Encoding header field is present in a response and the
1354     "chunked" transfer-coding is not the final encoding, the message-body
1355     length is determined by reading the connection until it is closed by
1356     the server.
1357     If a Transfer-Encoding header field is present in a request and the
1358     "chunked" transfer-coding is not the final encoding, the message-body
1359     length cannot be determined reliably; the server &MUST; respond with
1360     the 400 (Bad Request) status code and then close the connection.
1361    </t>
1362    <t>
1363     If a message is received with both a Transfer-Encoding header field and a
1364     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1365     Such a message might indicate an attempt to perform request or response
1366     smuggling (bypass of security-related checks on message routing or content)
1367     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1368     be removed, prior to forwarding the message downstream, or replaced with
1369     the real message-body length after the transfer-coding is decoded.
1370    </t></x:lt>
1371    <x:lt><t>
1372     If a message is received without Transfer-Encoding and with either
1373     multiple Content-Length header fields or a single Content-Length header
1374     field with an invalid value, then the message framing is invalid and
1375     &MUST; be treated as an error to prevent request or response smuggling.
1376     If this is a request message, the server &MUST; respond with
1377     a 400 (Bad Request) status code and then close the connection.
1378     If this is a response message received by a proxy or gateway, the proxy
1379     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1380     status code as its downstream response, and then close the connection.
1381     If this is a response message received by a user-agent, it &SHOULD; be
1382     treated as an error by discarding the message and closing the connection.
1383    </t></x:lt>
1384    <x:lt><t>
1385     If a valid Content-Length header field (<xref target="header.content-length"/>)
1386     is present without Transfer-Encoding, its decimal value defines the
1387     message-body length in octets.  If the actual number of octets sent in
1388     the message is less than the indicated Content-Length, the recipient
1389     &MUST; consider the message to be incomplete and treat the connection
1390     as no longer usable.
1391     If the actual number of octets sent in the message is more than the indicated
1392     Content-Length, the recipient &MUST; only process the message-body up to the
1393     field value's number of octets; the remainder of the message &MUST; either
1394     be discarded or treated as the next message in a pipeline.  For the sake of
1395     robustness, a user-agent &MAY; attempt to detect and correct such an error
1396     in message framing if it is parsing the response to the last request on
1397     on a connection and the connection has been closed by the server.
1398    </t></x:lt>
1399    <x:lt><t>
1400     If this is a request message and none of the above are true, then the
1401     message-body length is zero (no message-body is present).
1402    </t></x:lt>
1403    <x:lt><t>
1404     Otherwise, this is a response message without a declared message-body
1405     length, so the message-body length is determined by the number of octets
1406     received prior to the server closing the connection.
1407    </t></x:lt>
1408  </list>
1411   Since there is no way to distinguish a successfully completed,
1412   close-delimited message from a partially-received message interrupted
1413   by network failure, implementations &SHOULD; use encoding or
1414   length-delimited messages whenever possible.  The close-delimiting
1415   feature exists primarily for backwards compatibility with HTTP/1.0.
1418   A server &MAY; reject a request that contains a message-body but
1419   not a Content-Length by responding with 411 (Length Required).
1422   Unless a transfer-coding other than "chunked" has been applied,
1423   a client that sends a request containing a message-body &SHOULD;
1424   use a valid Content-Length header field if the message-body length
1425   is known in advance, rather than the "chunked" encoding, since some
1426   existing services respond to "chunked" with a 411 (Length Required)
1427   status code even though they understand the chunked encoding.  This
1428   is typically because such services are implemented via a gateway that
1429   requires a content-length in advance of being called and the server
1430   is unable or unwilling to buffer the entire request before processing.
1433   A client that sends a request containing a message-body &MUST; include a
1434   valid Content-Length header field if it does not know the server will
1435   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1436   of specific user configuration or by remembering the version of a prior
1437   received response.
1440   Request messages that are prematurely terminated, possibly due to a
1441   cancelled connection or a server-imposed time-out exception, &MUST;
1442   result in closure of the connection; sending an HTTP/1.1 error response
1443   prior to closing the connection is &OPTIONAL;.
1444   Response messages that are prematurely terminated, usually by closure
1445   of the connection prior to receiving the expected number of octets or by
1446   failure to decode a transfer-encoded message-body, &MUST; be recorded
1447   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1448   message-body as if it were complete (i.e., some indication must be given
1449   to the user that an error occurred).  Cache requirements for incomplete
1450   responses are defined in &cache-incomplete;.
1453   A server &MUST; read the entire request message-body or close
1454   the connection after sending its response, since otherwise the
1455   remaining data on a persistent connection would be misinterpreted
1456   as the next request.  Likewise,
1457   a client &MUST; read the entire response message-body if it intends
1458   to reuse the same connection for a subsequent request.  Pipelining
1459   multiple requests on a connection is described in <xref target="pipelining"/>.
1463<section title="General Header Fields" anchor="general.header.fields">
1464  <x:anchor-alias value="general-header"/>
1466   There are a few header fields which have general applicability for
1467   both request and response messages, but which do not apply to the
1468   payload being transferred. These header fields apply only to the
1469   message being transmitted.
1471<texttable align="left">
1472  <ttcol>Header Field Name</ttcol>
1473  <ttcol>Defined in...</ttcol>
1475  <c>Connection</c> <c><xref target="header.connection"/></c>
1476  <c>Date</c> <c><xref target=""/></c>
1477  <c>Pragma</c> <c>&header-pragma;</c>
1478  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1479  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1480  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1481  <c>Via</c> <c><xref target="header.via"/></c>
1482  <c>Warning</c> <c>&header-warning;</c>
1483  <c>MIME-Version</c> <c>&header-mime-version;</c>
1486   General-header field names can be extended reliably only in
1487   combination with a change in the protocol version. However, new or
1488   experimental header fields might be given the semantics of general
1489   header fields if all parties in the communication recognize them to
1490   be general-header fields.
1495<section title="Request" anchor="request">
1496  <x:anchor-alias value="Request"/>
1498   A request message from a client to a server includes, within the
1499   first line of that message, the method to be applied to the resource,
1500   the identifier of the resource, and the protocol version in use.
1502<!--                 Host                      ; should be moved here eventually -->
1503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1504  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1505                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1506                  <x:ref>CRLF</x:ref>
1507                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1510<section title="Request-Line" anchor="request-line">
1511  <x:anchor-alias value="Request-Line"/>
1513   The Request-Line begins with a method token, followed by the
1514   request-target and the protocol version, and ending with CRLF. The
1515   elements are separated by SP characters. No CR or LF is allowed
1516   except in the final CRLF sequence.
1518<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1519  <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>
1522<section title="Method" anchor="method">
1523  <x:anchor-alias value="Method"/>
1525   The Method  token indicates the method to be performed on the
1526   resource identified by the request-target. The method is case-sensitive.
1528<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1529  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1533<section title="request-target" anchor="request-target">
1534  <x:anchor-alias value="request-target"/>
1536   The request-target identifies the resource upon which to apply the request.
1538<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1539  <x:ref>request-target</x:ref> = "*"
1540                 / <x:ref>absolute-URI</x:ref>
1541                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1542                 / <x:ref>authority</x:ref>
1545   The four options for request-target are dependent on the nature of the
1546   request.
1548<t><iref item="asterisk form (of request-target)"/>
1549   The asterisk "*" ("asterisk form") means that the request does not apply to a
1550   particular resource, but to the server itself. This is only allowed for the
1551   OPTIONS method. Thus, the only valid example is
1553<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1554OPTIONS * HTTP/1.1
1556<t><iref item="absolute-URI form (of request-target)"/>
1557   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1558   proxy. The proxy is requested to forward the request or service it
1559   from a valid cache, and return the response. Note that the proxy &MAY;
1560   forward the request on to another proxy or directly to the server
1561   specified by the absolute-URI. In order to avoid request loops, a
1562   proxy &MUST; be able to recognize all of its server names, including
1563   any aliases, local variations, and the numeric IP address. An example
1564   Request-Line would be:
1566<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1567GET HTTP/1.1
1570   To allow for transition to absolute-URIs in all requests in future
1571   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1572   form in requests, even though HTTP/1.1 clients will only generate
1573   them in requests to proxies.
1575<t><iref item="authority form (of request-target)"/>
1576   The "authority form" is only used by the CONNECT method (&CONNECT;).
1578<t><iref item="path-absolute form (of request-target)"/>
1579   The most common form of request-target is that used to identify a
1580   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1581   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1582   the request-target, and the network location of the URI (authority) &MUST;
1583   be transmitted in a Host header field. For example, a client wishing
1584   to retrieve the resource above directly from the origin server would
1585   create a TCP connection to port 80 of the host "" and send
1586   the lines:
1588<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1589GET /pub/WWW/TheProject.html HTTP/1.1
1593   followed by the remainder of the Request. Note that the absolute path
1594   cannot be empty; if none is present in the original URI, it &MUST; be
1595   given as "/" (the server root).
1598   If a proxy receives a request without any path in the request-target and
1599   the method specified is capable of supporting the asterisk form of
1600   request-target, then the last proxy on the request chain &MUST; forward the
1601   request with "*" as the final request-target.
1604   For example, the request
1605</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1609  would be forwarded by the proxy as
1610</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1611OPTIONS * HTTP/1.1
1615   after connecting to port 8001 of host "".
1619   The request-target is transmitted in the format specified in
1620   <xref target="http.uri"/>. If the request-target is percent-encoded
1621   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1622   &MUST; decode the request-target in order to
1623   properly interpret the request. Servers &SHOULD; respond to invalid
1624   request-targets with an appropriate status code.
1627   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1628   received request-target when forwarding it to the next inbound server,
1629   except as noted above to replace a null path-absolute with "/" or "*".
1632  <t>
1633    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1634    meaning of the request when the origin server is improperly using
1635    a non-reserved URI character for a reserved purpose.  Implementors
1636    need to be aware that some pre-HTTP/1.1 proxies have been known to
1637    rewrite the request-target.
1638  </t>
1641   HTTP does not place a pre-defined limit on the length of a request-target.
1642   A server &MUST; be prepared to receive URIs of unbounded length and
1643   respond with the 414 (URI Too Long) status code if the received
1644   request-target would be longer than the server wishes to handle
1645   (see &status-414;).
1648   Various ad-hoc limitations on request-target length are found in practice.
1649   It is &RECOMMENDED; that all HTTP senders and recipients support
1650   request-target lengths of 8000 or more octets.
1653  <t>
1654    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1655    are not part of the request-target and thus will not be transmitted
1656    in an HTTP request.
1657  </t>
1662<section title="The Resource Identified by a Request" anchor="">
1664   The exact resource identified by an Internet request is determined by
1665   examining both the request-target and the Host header field.
1668   An origin server that does not allow resources to differ by the
1669   requested host &MAY; ignore the Host header field value when
1670   determining the resource identified by an HTTP/1.1 request. (But see
1671   <xref target=""/>
1672   for other requirements on Host support in HTTP/1.1.)
1675   An origin server that does differentiate resources based on the host
1676   requested (sometimes referred to as virtual hosts or vanity host
1677   names) &MUST; use the following rules for determining the requested
1678   resource on an HTTP/1.1 request:
1679  <list style="numbers">
1680    <t>If request-target is an absolute-URI, the host is part of the
1681     request-target. Any Host header field value in the request &MUST; be
1682     ignored.</t>
1683    <t>If the request-target is not an absolute-URI, and the request includes
1684     a Host header field, the host is determined by the Host header
1685     field value.</t>
1686    <t>If the host as determined by rule 1 or 2 is not a valid host on
1687     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1688  </list>
1691   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1692   attempt to use heuristics (e.g., examination of the URI path for
1693   something unique to a particular host) in order to determine what
1694   exact resource is being requested.
1698<section title="Effective Request URI" anchor="effective.request.uri">
1699  <iref primary="true" item="effective request URI"/>
1700  <iref primary="true" item="target resource"/>
1702   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1703   for the target resource; instead, the URI needs to be inferred from the
1704   request-target, Host header field, and connection context. The result of
1705   this process is called the "effective request URI".  The "target resource"
1706   is the resource identified by the effective request URI.
1709   If the request-target is an absolute-URI, then the effective request URI is
1710   the request-target.
1713   If the request-target uses the path-absolute form or the asterisk form,
1714   and the Host header field is present, then the effective request URI is
1715   constructed by concatenating
1718  <list style="symbols">
1719    <t>
1720      the scheme name: "http" if the request was received over an insecure
1721      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1722      connection,
1723    </t>
1724    <t>
1725      the character sequence "://",
1726    </t>
1727    <t>
1728      the authority component, as specified in the Host header field
1729      (<xref target=""/>), and
1730    </t>
1731    <t>
1732      the request-target obtained from the Request-Line, unless the
1733      request-target is just the asterisk "*".
1734    </t>
1735  </list>
1738   If the request-target uses the path-absolute form or the asterisk form,
1739   and the Host header field is not present, then the effective request URI is
1740   undefined.
1743   Otherwise, when request-target uses the authority form, the effective
1744   request URI is undefined.
1748   Example 1: the effective request URI for the message
1750<artwork type="example" x:indent-with="  ">
1751GET /pub/WWW/TheProject.html HTTP/1.1
1755  (received over an insecure TCP connection) is "http", plus "://", plus the
1756  authority component "", plus the request-target
1757  "/pub/WWW/TheProject.html", thus
1758  "".
1763   Example 2: the effective request URI for the message
1765<artwork type="example" x:indent-with="  ">
1766GET * HTTP/1.1
1770  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1771  authority component "", thus "".
1775   Effective request URIs are compared using the rules described in
1776   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1777   be treated as equivalent to an absolute path of "/".
1784<section title="Response" anchor="response">
1785  <x:anchor-alias value="Response"/>
1787   After receiving and interpreting a request message, a server responds
1788   with an HTTP response message.
1790<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1791  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1792                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1793                  <x:ref>CRLF</x:ref>
1794                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1797<section title="Status-Line" anchor="status-line">
1798  <x:anchor-alias value="Status-Line"/>
1800   The first line of a Response message is the Status-Line, consisting
1801   of the protocol version followed by a numeric status code and its
1802   associated textual phrase, with each element separated by SP
1803   characters. No CR or LF is allowed except in the final CRLF sequence.
1805<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1806  <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>
1809<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1810  <x:anchor-alias value="Reason-Phrase"/>
1811  <x:anchor-alias value="Status-Code"/>
1813   The Status-Code element is a 3-digit integer result code of the
1814   attempt to understand and satisfy the request. These codes are fully
1815   defined in &status-codes;.  The Reason Phrase exists for the sole
1816   purpose of providing a textual description associated with the numeric
1817   status code, out of deference to earlier Internet application protocols
1818   that were more frequently used with interactive text clients.
1819   A client &SHOULD; ignore the content of the Reason Phrase.
1822   The first digit of the Status-Code defines the class of response. The
1823   last two digits do not have any categorization role. There are 5
1824   values for the first digit:
1825  <list style="symbols">
1826    <t>
1827      1xx: Informational - Request received, continuing process
1828    </t>
1829    <t>
1830      2xx: Success - The action was successfully received,
1831        understood, and accepted
1832    </t>
1833    <t>
1834      3xx: Redirection - Further action must be taken in order to
1835        complete the request
1836    </t>
1837    <t>
1838      4xx: Client Error - The request contains bad syntax or cannot
1839        be fulfilled
1840    </t>
1841    <t>
1842      5xx: Server Error - The server failed to fulfill an apparently
1843        valid request
1844    </t>
1845  </list>
1847<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1848  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1849  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1857<section title="Protocol Parameters" anchor="protocol.parameters">
1859<section title="Date/Time Formats: Full Date" anchor="">
1860  <x:anchor-alias value="HTTP-date"/>
1862   HTTP applications have historically allowed three different formats
1863   for date/time stamps. However, the preferred format is a fixed-length subset
1864   of that defined by <xref target="RFC1123"/>:
1866<figure><artwork type="example" x:indent-with="  ">
1867Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1870   The other formats are described here only for compatibility with obsolete
1871   implementations.
1873<figure><artwork type="example" x:indent-with="  ">
1874Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1875Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1878   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1879   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1880   only generate the RFC 1123 format for representing HTTP-date values
1881   in header fields. See <xref target="tolerant.applications"/> for further information.
1884   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1885   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1886   equal to UTC (Coordinated Universal Time). This is indicated in the
1887   first two formats by the inclusion of "GMT" as the three-letter
1888   abbreviation for time zone, and &MUST; be assumed when reading the
1889   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1890   additional whitespace beyond that specifically included as SP in the
1891   grammar.
1893<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1894  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1896<t anchor="">
1897  <x:anchor-alias value="rfc1123-date"/>
1898  <x:anchor-alias value="time-of-day"/>
1899  <x:anchor-alias value="hour"/>
1900  <x:anchor-alias value="minute"/>
1901  <x:anchor-alias value="second"/>
1902  <x:anchor-alias value="day-name"/>
1903  <x:anchor-alias value="day"/>
1904  <x:anchor-alias value="month"/>
1905  <x:anchor-alias value="year"/>
1906  <x:anchor-alias value="GMT"/>
1907  Preferred format:
1909<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"/>
1910  <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>
1911  ; fixed length subset of the format defined in
1912  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1914  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1915               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1916               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1917               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1918               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1919               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1920               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1922  <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>
1923               ; e.g., 02 Jun 1982
1925  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1926  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1927               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1928               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1929               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1930               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1931               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1932               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1933               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1934               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1935               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1936               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1937               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1938  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1940  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1942  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1943                 ; 00:00:00 - 23:59:59
1945  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1946  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1947  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1950  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1951  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1952  same as those defined for the RFC 5322 constructs
1953  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1955<t anchor="">
1956  <x:anchor-alias value="obs-date"/>
1957  <x:anchor-alias value="rfc850-date"/>
1958  <x:anchor-alias value="asctime-date"/>
1959  <x:anchor-alias value="date1"/>
1960  <x:anchor-alias value="date2"/>
1961  <x:anchor-alias value="date3"/>
1962  <x:anchor-alias value="rfc1123-date"/>
1963  <x:anchor-alias value="day-name-l"/>
1964  Obsolete formats:
1966<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1967  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1969<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1970  <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>
1971  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1972                 ; day-month-year (e.g., 02-Jun-82)
1974  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1975         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1976         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1977         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1978         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1979         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1980         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1982<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1983  <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>
1984  <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> ))
1985                 ; month day (e.g., Jun  2)
1988  <t>
1989    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1990    accepting date values that might have been sent by non-HTTP
1991    applications, as is sometimes the case when retrieving or posting
1992    messages via proxies/gateways to SMTP or NNTP.
1993  </t>
1996  <t>
1997    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1998    to their usage within the protocol stream. Clients and servers are
1999    not required to use these formats for user presentation, request
2000    logging, etc.
2001  </t>
2005<section title="Transfer Codings" anchor="transfer.codings">
2006  <x:anchor-alias value="transfer-coding"/>
2007  <x:anchor-alias value="transfer-extension"/>
2009   Transfer-coding values are used to indicate an encoding
2010   transformation that has been, can be, or might need to be applied to a
2011   payload body in order to ensure "safe transport" through the network.
2012   This differs from a content coding in that the transfer-coding is a
2013   property of the message rather than a property of the representation
2014   that is being transferred.
2016<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2017  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2018                          / "compress" ; <xref target="compress.coding"/>
2019                          / "deflate" ; <xref target="deflate.coding"/>
2020                          / "gzip" ; <xref target="gzip.coding"/>
2021                          / <x:ref>transfer-extension</x:ref>
2022  <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> )
2024<t anchor="rule.parameter">
2025  <x:anchor-alias value="attribute"/>
2026  <x:anchor-alias value="transfer-parameter"/>
2027  <x:anchor-alias value="value"/>
2028   Parameters are in the form of attribute/value pairs.
2030<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"/>
2031  <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>
2032  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2033  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2036   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2037   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2038   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2041   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2042   MIME, which were designed to enable safe transport of binary data over a
2043   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2044   However, safe transport
2045   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2046   the only unsafe characteristic of message-bodies is the difficulty in
2047   determining the exact message body length (<xref target="message.body"/>),
2048   or the desire to encrypt data over a shared transport.
2051   A server that receives a request message with a transfer-coding it does
2052   not understand &SHOULD; respond with 501 (Not Implemented) and then
2053   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2054   client.
2057<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2058  <iref item="chunked (Coding Format)"/>
2059  <iref item="Coding Format" subitem="chunked"/>
2060  <x:anchor-alias value="chunk"/>
2061  <x:anchor-alias value="Chunked-Body"/>
2062  <x:anchor-alias value="chunk-data"/>
2063  <x:anchor-alias value="chunk-ext"/>
2064  <x:anchor-alias value="chunk-ext-name"/>
2065  <x:anchor-alias value="chunk-ext-val"/>
2066  <x:anchor-alias value="chunk-size"/>
2067  <x:anchor-alias value="last-chunk"/>
2068  <x:anchor-alias value="trailer-part"/>
2069  <x:anchor-alias value="quoted-str-nf"/>
2070  <x:anchor-alias value="qdtext-nf"/>
2072   The chunked encoding modifies the body of a message in order to
2073   transfer it as a series of chunks, each with its own size indicator,
2074   followed by an &OPTIONAL; trailer containing header fields. This
2075   allows dynamically produced content to be transferred along with the
2076   information necessary for the recipient to verify that it has
2077   received the full message.
2079<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"/>
2080  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2081                   <x:ref>last-chunk</x:ref>
2082                   <x:ref>trailer-part</x:ref>
2083                   <x:ref>CRLF</x:ref>
2085  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2086                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2087  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2088  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2090  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2091                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2092  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2093  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2094  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2095  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2097  <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>
2098                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2099  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2100                 ; <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>
2103   The chunk-size field is a string of hex digits indicating the size of
2104   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2105   zero, followed by the trailer, which is terminated by an empty line.
2108   The trailer allows the sender to include additional HTTP header
2109   fields at the end of the message. The Trailer header field can be
2110   used to indicate which header fields are included in a trailer (see
2111   <xref target="header.trailer"/>).
2114   A server using chunked transfer-coding in a response &MUST-NOT; use the
2115   trailer for any header fields unless at least one of the following is
2116   true:
2117  <list style="numbers">
2118    <t>the request included a TE header field that indicates "trailers" is
2119     acceptable in the transfer-coding of the  response, as described in
2120     <xref target="header.te"/>; or,</t>
2122    <t>the trailer fields consist entirely of optional metadata, and the
2123    recipient could use the message (in a manner acceptable to the server where
2124    the field originated) without receiving it. In other words, the server that
2125    generated the header (often but not always the origin server) is willing to
2126    accept the possibility that the trailer fields might be silently discarded
2127    along the path to the client.</t>
2128  </list>
2131   This requirement prevents an interoperability failure when the
2132   message is being received by an HTTP/1.1 (or later) proxy and
2133   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2134   compliance with the protocol would have necessitated a possibly
2135   infinite buffer on the proxy.
2138   A process for decoding the "chunked" transfer-coding
2139   can be represented in pseudo-code as:
2141<figure><artwork type="code">
2142  length := 0
2143  read chunk-size, chunk-ext (if any) and CRLF
2144  while (chunk-size &gt; 0) {
2145     read chunk-data and CRLF
2146     append chunk-data to decoded-body
2147     length := length + chunk-size
2148     read chunk-size and CRLF
2149  }
2150  read header-field
2151  while (header-field not empty) {
2152     append header-field to existing header fields
2153     read header-field
2154  }
2155  Content-Length := length
2156  Remove "chunked" from Transfer-Encoding
2159   All HTTP/1.1 applications &MUST; be able to receive and decode the
2160   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2161   they do not understand.
2164   Since "chunked" is the only transfer-coding required to be understood
2165   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2166   on a persistent connection.  Whenever a transfer-coding is applied to
2167   a payload body in a request, the final transfer-coding applied &MUST;
2168   be "chunked".  If a transfer-coding is applied to a response payload
2169   body, then either the final transfer-coding applied &MUST; be "chunked"
2170   or the message &MUST; be terminated by closing the connection. When the
2171   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2172   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2173   be applied more than once in a message-body.
2177<section title="Compression Codings" anchor="compression.codings">
2179   The codings defined below can be used to compress the payload of a
2180   message.
2183   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2184   is not desirable and is discouraged for future encodings. Their
2185   use here is representative of historical practice, not good
2186   design.
2189   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2190   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2191   equivalent to "gzip" and "compress" respectively.
2194<section title="Compress Coding" anchor="compress.coding">
2195<iref item="compress (Coding Format)"/>
2196<iref item="Coding Format" subitem="compress"/>
2198   The "compress" format is produced by the common UNIX file compression
2199   program "compress". This format is an adaptive Lempel-Ziv-Welch
2200   coding (LZW).
2204<section title="Deflate Coding" anchor="deflate.coding">
2205<iref item="deflate (Coding Format)"/>
2206<iref item="Coding Format" subitem="deflate"/>
2208   The "deflate" format is defined as the "deflate" compression mechanism
2209   (described in <xref target="RFC1951"/>) used inside the "zlib"
2210   data format (<xref target="RFC1950"/>).
2213  <t>
2214    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2215    compressed data without the zlib wrapper.
2216   </t>
2220<section title="Gzip Coding" anchor="gzip.coding">
2221<iref item="gzip (Coding Format)"/>
2222<iref item="Coding Format" subitem="gzip"/>
2224   The "gzip" format is produced by the file compression program
2225   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2226   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2232<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2234   The HTTP Transfer Coding Registry defines the name space for the transfer
2235   coding names.
2238   Registrations &MUST; include the following fields:
2239   <list style="symbols">
2240     <t>Name</t>
2241     <t>Description</t>
2242     <t>Pointer to specification text</t>
2243   </list>
2246   Names of transfer codings &MUST-NOT; overlap with names of content codings
2247   (&content-codings;), unless the encoding transformation is identical (as it
2248   is the case for the compression codings defined in
2249   <xref target="compression.codings"/>).
2252   Values to be added to this name space require a specification
2253   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2254   conform to the purpose of transfer coding defined in this section.
2257   The registry itself is maintained at
2258   <eref target=""/>.
2263<section title="Product Tokens" anchor="product.tokens">
2264  <x:anchor-alias value="product"/>
2265  <x:anchor-alias value="product-version"/>
2267   Product tokens are used to allow communicating applications to
2268   identify themselves by software name and version. Most fields using
2269   product tokens also allow sub-products which form a significant part
2270   of the application to be listed, separated by whitespace. By
2271   convention, the products are listed in order of their significance
2272   for identifying the application.
2274<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2275  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2276  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2279   Examples:
2281<figure><artwork type="example">
2282  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2283  Server: Apache/0.8.4
2286   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2287   used for advertising or other non-essential information. Although any
2288   token character &MAY; appear in a product-version, this token &SHOULD;
2289   only be used for a version identifier (i.e., successive versions of
2290   the same product &SHOULD; only differ in the product-version portion of
2291   the product value).
2295<section title="Quality Values" anchor="quality.values">
2296  <x:anchor-alias value="qvalue"/>
2298   Both transfer codings (TE request header field, <xref target="header.te"/>)
2299   and content negotiation (&content.negotiation;) use short "floating point"
2300   numbers to indicate the relative importance ("weight") of various
2301   negotiable parameters.  A weight is normalized to a real number in
2302   the range 0 through 1, where 0 is the minimum and 1 the maximum
2303   value. If a parameter has a quality value of 0, then content with
2304   this parameter is "not acceptable" for the client. HTTP/1.1
2305   applications &MUST-NOT; generate more than three digits after the
2306   decimal point. User configuration of these values &SHOULD; also be
2307   limited in this fashion.
2309<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2310  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2311                 / ( "1" [ "." 0*3("0") ] )
2314  <t>
2315     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2316     relative degradation in desired quality.
2317  </t>
2323<section title="Connections" anchor="connections">
2325<section title="Persistent Connections" anchor="persistent.connections">
2327<section title="Purpose" anchor="persistent.purpose">
2329   Prior to persistent connections, a separate TCP connection was
2330   established to fetch each URL, increasing the load on HTTP servers
2331   and causing congestion on the Internet. The use of inline images and
2332   other associated data often requires a client to make multiple
2333   requests of the same server in a short amount of time. Analysis of
2334   these performance problems and results from a prototype
2335   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2336   measurements of actual HTTP/1.1 implementations show good
2337   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2338   T/TCP <xref target="Tou1998"/>.
2341   Persistent HTTP connections have a number of advantages:
2342  <list style="symbols">
2343      <t>
2344        By opening and closing fewer TCP connections, CPU time is saved
2345        in routers and hosts (clients, servers, proxies, gateways,
2346        tunnels, or caches), and memory used for TCP protocol control
2347        blocks can be saved in hosts.
2348      </t>
2349      <t>
2350        HTTP requests and responses can be pipelined on a connection.
2351        Pipelining allows a client to make multiple requests without
2352        waiting for each response, allowing a single TCP connection to
2353        be used much more efficiently, with much lower elapsed time.
2354      </t>
2355      <t>
2356        Network congestion is reduced by reducing the number of packets
2357        caused by TCP opens, and by allowing TCP sufficient time to
2358        determine the congestion state of the network.
2359      </t>
2360      <t>
2361        Latency on subsequent requests is reduced since there is no time
2362        spent in TCP's connection opening handshake.
2363      </t>
2364      <t>
2365        HTTP can evolve more gracefully, since errors can be reported
2366        without the penalty of closing the TCP connection. Clients using
2367        future versions of HTTP might optimistically try a new feature,
2368        but if communicating with an older server, retry with old
2369        semantics after an error is reported.
2370      </t>
2371    </list>
2374   HTTP implementations &SHOULD; implement persistent connections.
2378<section title="Overall Operation" anchor="persistent.overall">
2380   A significant difference between HTTP/1.1 and earlier versions of
2381   HTTP is that persistent connections are the default behavior of any
2382   HTTP connection. That is, unless otherwise indicated, the client
2383   &SHOULD; assume that the server will maintain a persistent connection,
2384   even after error responses from the server.
2387   Persistent connections provide a mechanism by which a client and a
2388   server can signal the close of a TCP connection. This signaling takes
2389   place using the Connection header field (<xref target="header.connection"/>). Once a close
2390   has been signaled, the client &MUST-NOT; send any more requests on that
2391   connection.
2394<section title="Negotiation" anchor="persistent.negotiation">
2396   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2397   maintain a persistent connection unless a Connection header field including
2398   the connection-token "close" was sent in the request. If the server
2399   chooses to close the connection immediately after sending the
2400   response, it &SHOULD; send a Connection header field including the
2401   connection-token "close".
2404   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2405   decide to keep it open based on whether the response from a server
2406   contains a Connection header field with the connection-token close. In case
2407   the client does not want to maintain a connection for more than that
2408   request, it &SHOULD; send a Connection header field including the
2409   connection-token close.
2412   If either the client or the server sends the close token in the
2413   Connection header field, that request becomes the last one for the
2414   connection.
2417   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2418   maintained for HTTP versions less than 1.1 unless it is explicitly
2419   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2420   compatibility with HTTP/1.0 clients.
2423   In order to remain persistent, all messages on the connection &MUST;
2424   have a self-defined message length (i.e., one not defined by closure
2425   of the connection), as described in <xref target="message.body"/>.
2429<section title="Pipelining" anchor="pipelining">
2431   A client that supports persistent connections &MAY; "pipeline" its
2432   requests (i.e., send multiple requests without waiting for each
2433   response). A server &MUST; send its responses to those requests in the
2434   same order that the requests were received.
2437   Clients which assume persistent connections and pipeline immediately
2438   after connection establishment &SHOULD; be prepared to retry their
2439   connection if the first pipelined attempt fails. If a client does
2440   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2441   persistent. Clients &MUST; also be prepared to resend their requests if
2442   the server closes the connection before sending all of the
2443   corresponding responses.
2446   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2447   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2448   premature termination of the transport connection could lead to
2449   indeterminate results. A client wishing to send a non-idempotent
2450   request &SHOULD; wait to send that request until it has received the
2451   response status line for the previous request.
2456<section title="Proxy Servers" anchor="persistent.proxy">
2458   It is especially important that proxies correctly implement the
2459   properties of the Connection header field as specified in <xref target="header.connection"/>.
2462   The proxy server &MUST; signal persistent connections separately with
2463   its clients and the origin servers (or other proxy servers) that it
2464   connects to. Each persistent connection applies to only one transport
2465   link.
2468   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2469   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2470   for information and discussion of the problems with the Keep-Alive header field
2471   implemented by many HTTP/1.0 clients).
2474<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2476  <cref anchor="TODO-end-to-end" source="jre">
2477    Restored from <eref target=""/>.
2478    See also <eref target=""/>.
2479  </cref>
2482   For the purpose of defining the behavior of caches and non-caching
2483   proxies, we divide HTTP header fields into two categories:
2484  <list style="symbols">
2485      <t>End-to-end header fields, which are  transmitted to the ultimate
2486        recipient of a request or response. End-to-end header fields in
2487        responses MUST be stored as part of a cache entry and &MUST; be
2488        transmitted in any response formed from a cache entry.</t>
2490      <t>Hop-by-hop header fields, which are meaningful only for a single
2491        transport-level connection, and are not stored by caches or
2492        forwarded by proxies.</t>
2493  </list>
2496   The following HTTP/1.1 header fields are hop-by-hop header fields:
2497  <list style="symbols">
2498      <t>Connection</t>
2499      <t>Keep-Alive</t>
2500      <t>Proxy-Authenticate</t>
2501      <t>Proxy-Authorization</t>
2502      <t>TE</t>
2503      <t>Trailer</t>
2504      <t>Transfer-Encoding</t>
2505      <t>Upgrade</t>
2506  </list>
2509   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2512   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2513   (<xref target="header.connection"/>).
2517<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2519  <cref anchor="TODO-non-mod-headers" source="jre">
2520    Restored from <eref target=""/>.
2521    See also <eref target=""/>.
2522  </cref>
2525   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2526   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2527   modify an end-to-end header field unless the definition of that header field requires
2528   or specifically allows that.
2531   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2532   request or response, and it &MUST-NOT; add any of these fields if not
2533   already present:
2534  <list style="symbols">
2535      <t>Content-Location</t>
2536      <t>Content-MD5</t>
2537      <t>ETag</t>
2538      <t>Last-Modified</t>
2539  </list>
2542   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2543   response:
2544  <list style="symbols">
2545    <t>Expires</t>
2546  </list>
2549   but it &MAY; add any of these fields if not already present. If an
2550   Expires header field is added, it &MUST; be given a field-value identical to
2551   that of the Date header field in that response.
2554   A proxy &MUST-NOT; modify or add any of the following fields in a
2555   message that contains the no-transform cache-control directive, or in
2556   any request:
2557  <list style="symbols">
2558    <t>Content-Encoding</t>
2559    <t>Content-Range</t>
2560    <t>Content-Type</t>
2561  </list>
2564   A transforming proxy &MAY; modify or add these fields to a message
2565   that does not include no-transform, but if it does so, it &MUST; add a
2566   Warning 214 (Transformation applied) if one does not already appear
2567   in the message (see &header-warning;).
2570  <t>
2571    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2572    cause authentication failures if stronger authentication
2573    mechanisms are introduced in later versions of HTTP. Such
2574    authentication mechanisms &MAY; rely on the values of header fields
2575    not listed here.
2576  </t>
2579   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2580   though it &MAY; change the message-body through application or removal
2581   of a transfer-coding (<xref target="transfer.codings"/>).
2587<section title="Practical Considerations" anchor="persistent.practical">
2589   Servers will usually have some time-out value beyond which they will
2590   no longer maintain an inactive connection. Proxy servers might make
2591   this a higher value since it is likely that the client will be making
2592   more connections through the same server. The use of persistent
2593   connections places no requirements on the length (or existence) of
2594   this time-out for either the client or the server.
2597   When a client or server wishes to time-out it &SHOULD; issue a graceful
2598   close on the transport connection. Clients and servers &SHOULD; both
2599   constantly watch for the other side of the transport close, and
2600   respond to it as appropriate. If a client or server does not detect
2601   the other side's close promptly it could cause unnecessary resource
2602   drain on the network.
2605   A client, server, or proxy &MAY; close the transport connection at any
2606   time. For example, a client might have started to send a new request
2607   at the same time that the server has decided to close the "idle"
2608   connection. From the server's point of view, the connection is being
2609   closed while it was idle, but from the client's point of view, a
2610   request is in progress.
2613   This means that clients, servers, and proxies &MUST; be able to recover
2614   from asynchronous close events. Client software &SHOULD; reopen the
2615   transport connection and retransmit the aborted sequence of requests
2616   without user interaction so long as the request sequence is
2617   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2618   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2619   human operator the choice of retrying the request(s). Confirmation by
2620   user-agent software with semantic understanding of the application
2621   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2622   be repeated if the second sequence of requests fails.
2625   Servers &SHOULD; always respond to at least one request per connection,
2626   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2627   middle of transmitting a response, unless a network or client failure
2628   is suspected.
2631   Clients (including proxies) &SHOULD; limit the number of simultaneous
2632   connections that they maintain to a given server (including proxies).
2635   Previous revisions of HTTP gave a specific number of connections as a
2636   ceiling, but this was found to be impractical for many applications. As a
2637   result, this specification does not mandate a particular maximum number of
2638   connections, but instead encourages clients to be conservative when opening
2639   multiple connections.
2642   In particular, while using multiple connections avoids the "head-of-line
2643   blocking" problem (whereby a request that takes significant server-side
2644   processing and/or has a large payload can block subsequent requests on the
2645   same connection), each connection used consumes server resources (sometimes
2646   significantly), and furthermore using multiple connections can cause
2647   undesirable side effects in congested networks.
2650   Note that servers might reject traffic that they deem abusive, including an
2651   excessive number of connections from a client.
2656<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2658<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2660   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2661   flow control mechanisms to resolve temporary overloads, rather than
2662   terminating connections with the expectation that clients will retry.
2663   The latter technique can exacerbate network congestion.
2667<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2669   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2670   the network connection for an error status code while it is transmitting
2671   the request. If the client sees an error status code, it &SHOULD;
2672   immediately cease transmitting the body. If the body is being sent
2673   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2674   empty trailer &MAY; be used to prematurely mark the end of the message.
2675   If the body was preceded by a Content-Length header field, the client &MUST;
2676   close the connection.
2680<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2682   The purpose of the 100 (Continue) status code (see &status-100;) is to
2683   allow a client that is sending a request message with a request body
2684   to determine if the origin server is willing to accept the request
2685   (based on the request header fields) before the client sends the request
2686   body. In some cases, it might either be inappropriate or highly
2687   inefficient for the client to send the body if the server will reject
2688   the message without looking at the body.
2691   Requirements for HTTP/1.1 clients:
2692  <list style="symbols">
2693    <t>
2694        If a client will wait for a 100 (Continue) response before
2695        sending the request body, it &MUST; send an Expect request-header
2696        field (&header-expect;) with the "100-continue" expectation.
2697    </t>
2698    <t>
2699        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2700        with the "100-continue" expectation if it does not intend
2701        to send a request body.
2702    </t>
2703  </list>
2706   Because of the presence of older implementations, the protocol allows
2707   ambiguous situations in which a client might send "Expect: 100-continue"
2708   without receiving either a 417 (Expectation Failed)
2709   or a 100 (Continue) status code. Therefore, when a client sends this
2710   header field to an origin server (possibly via a proxy) from which it
2711   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2712   wait for an indefinite period before sending the request body.
2715   Requirements for HTTP/1.1 origin servers:
2716  <list style="symbols">
2717    <t> Upon receiving a request which includes an Expect request-header
2718        field with the "100-continue" expectation, an origin server &MUST;
2719        either respond with 100 (Continue) status code and continue to read
2720        from the input stream, or respond with a final status code. The
2721        origin server &MUST-NOT; wait for the request body before sending
2722        the 100 (Continue) response. If it responds with a final status
2723        code, it &MAY; close the transport connection or it &MAY; continue
2724        to read and discard the rest of the request.  It &MUST-NOT;
2725        perform the requested method if it returns a final status code.
2726    </t>
2727    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2728        the request message does not include an Expect request-header
2729        field with the "100-continue" expectation, and &MUST-NOT; send a
2730        100 (Continue) response if such a request comes from an HTTP/1.0
2731        (or earlier) client. There is an exception to this rule: for
2732        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2733        status code in response to an HTTP/1.1 PUT or POST request that does
2734        not include an Expect request-header field with the "100-continue"
2735        expectation. This exception, the purpose of which is
2736        to minimize any client processing delays associated with an
2737        undeclared wait for 100 (Continue) status code, applies only to
2738        HTTP/1.1 requests, and not to requests with any other HTTP-version
2739        value.
2740    </t>
2741    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2742        already received some or all of the request body for the
2743        corresponding request.
2744    </t>
2745    <t> An origin server that sends a 100 (Continue) response &MUST;
2746    ultimately send a final status code, once the request body is
2747        received and processed, unless it terminates the transport
2748        connection prematurely.
2749    </t>
2750    <t> If an origin server receives a request that does not include an
2751        Expect request-header field with the "100-continue" expectation,
2752        the request includes a request body, and the server responds
2753        with a final status code before reading the entire request body
2754        from the transport connection, then the server &SHOULD-NOT;  close
2755        the transport connection until it has read the entire request,
2756        or until the client closes the connection. Otherwise, the client
2757        might not reliably receive the response message. However, this
2758        requirement is not be construed as preventing a server from
2759        defending itself against denial-of-service attacks, or from
2760        badly broken client implementations.
2761      </t>
2762    </list>
2765   Requirements for HTTP/1.1 proxies:
2766  <list style="symbols">
2767    <t> If a proxy receives a request that includes an Expect request-header
2768        field with the "100-continue" expectation, and the proxy
2769        either knows that the next-hop server complies with HTTP/1.1 or
2770        higher, or does not know the HTTP version of the next-hop
2771        server, it &MUST; forward the request, including the Expect header
2772        field.
2773    </t>
2774    <t> If the proxy knows that the version of the next-hop server is
2775        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2776        respond with a 417 (Expectation Failed) status code.
2777    </t>
2778    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2779        numbers received from recently-referenced next-hop servers.
2780    </t>
2781    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2782        request message was received from an HTTP/1.0 (or earlier)
2783        client and did not include an Expect request-header field with
2784        the "100-continue" expectation. This requirement overrides the
2785        general rule for forwarding of 1xx responses (see &status-1xx;).
2786    </t>
2787  </list>
2791<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2793   If an HTTP/1.1 client sends a request which includes a request body,
2794   but which does not include an Expect request-header field with the
2795   "100-continue" expectation, and if the client is not directly
2796   connected to an HTTP/1.1 origin server, and if the client sees the
2797   connection close before receiving a status line from the server, the
2798   client &SHOULD; retry the request.  If the client does retry this
2799   request, it &MAY; use the following "binary exponential backoff"
2800   algorithm to be assured of obtaining a reliable response:
2801  <list style="numbers">
2802    <t>
2803      Initiate a new connection to the server
2804    </t>
2805    <t>
2806      Transmit the request-header fields
2807    </t>
2808    <t>
2809      Initialize a variable R to the estimated round-trip time to the
2810         server (e.g., based on the time it took to establish the
2811         connection), or to a constant value of 5 seconds if the round-trip
2812         time is not available.
2813    </t>
2814    <t>
2815       Compute T = R * (2**N), where N is the number of previous
2816         retries of this request.
2817    </t>
2818    <t>
2819       Wait either for an error response from the server, or for T
2820         seconds (whichever comes first)
2821    </t>
2822    <t>
2823       If no error response is received, after T seconds transmit the
2824         body of the request.
2825    </t>
2826    <t>
2827       If client sees that the connection is closed prematurely,
2828         repeat from step 1 until the request is accepted, an error
2829         response is received, or the user becomes impatient and
2830         terminates the retry process.
2831    </t>
2832  </list>
2835   If at any point an error status code is received, the client
2836  <list style="symbols">
2837      <t>&SHOULD-NOT;  continue and</t>
2839      <t>&SHOULD; close the connection if it has not completed sending the
2840        request message.</t>
2841    </list>
2848<section title="Miscellaneous notes that might disappear" anchor="misc">
2849<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2851   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2855<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2857   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2861<section title="Interception of HTTP for access control" anchor="http.intercept">
2863   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2867<section title="Use of HTTP by other protocols" anchor="http.others">
2869   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2870   Extensions of HTTP like WebDAV.</cref>
2874<section title="Use of HTTP by media type specification" anchor="">
2876   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2881<section title="Header Field Definitions" anchor="header.field.definitions">
2883   This section defines the syntax and semantics of HTTP/1.1 header fields
2884   related to message framing and transport protocols.
2887<section title="Connection" anchor="header.connection">
2888  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2889  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2890  <x:anchor-alias value="Connection"/>
2891  <x:anchor-alias value="connection-token"/>
2892  <x:anchor-alias value="Connection-v"/>
2894   The "Connection" general-header field allows the sender to specify
2895   options that are desired for that particular connection and &MUST-NOT;
2896   be communicated by proxies over further connections.
2899   The Connection header field's value has the following grammar:
2901<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"/>
2902  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2903  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2904  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2907   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2908   message is forwarded and, for each connection-token in this field,
2909   remove any header field(s) from the message with the same name as the
2910   connection-token. Connection options are signaled by the presence of
2911   a connection-token in the Connection header field, not by any
2912   corresponding additional header field(s), since the additional header
2913   field might not be sent if there are no parameters associated with that
2914   connection option.
2917   Message header fields listed in the Connection header field &MUST-NOT; include
2918   end-to-end header fields, such as Cache-Control.
2921   HTTP/1.1 defines the "close" connection option for the sender to
2922   signal that the connection will be closed after completion of the
2923   response. For example,
2925<figure><artwork type="example">
2926  Connection: close
2929   in either the request or the response header fields indicates that
2930   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2931   after the current request/response is complete.
2934   An HTTP/1.1 client that does not support persistent connections &MUST;
2935   include the "close" connection option in every request message.
2938   An HTTP/1.1 server that does not support persistent connections &MUST;
2939   include the "close" connection option in every response message that
2940   does not have a 1xx (Informational) status code.
2943   A system receiving an HTTP/1.0 (or lower-version) message that
2944   includes a Connection header field &MUST;, for each connection-token in this
2945   field, remove and ignore any header field(s) from the message with
2946   the same name as the connection-token. This protects against mistaken
2947   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2951<section title="Content-Length" anchor="header.content-length">
2952  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
2953  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
2954  <x:anchor-alias value="Content-Length"/>
2955  <x:anchor-alias value="Content-Length-v"/>
2957   The "Content-Length" header field indicates the size of the
2958   message-body, in decimal number of octets, for any message other than
2959   a response to the HEAD method or a response with a status code of 304.
2960   In the case of responses to the HEAD method, it indicates the size of
2961   the payload body (not including any potential transfer-coding) that
2962   would have been sent had the request been a GET.
2963   In the case of the 304 (Not Modified) response, it indicates the size of
2964   the payload body (not including any potential transfer-coding) that
2965   would have been sent in a 200 (OK) response.
2967<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2968  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2969  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2972   An example is
2974<figure><artwork type="example">
2975  Content-Length: 3495
2978   Implementations &SHOULD; use this field to indicate the message-body
2979   length when no transfer-coding is being applied and the
2980   payload's body length can be determined prior to being transferred.
2981   <xref target="message.body"/> describes how recipients determine the length
2982   of a message-body.
2985   Any Content-Length greater than or equal to zero is a valid value.
2988   Note that the use of this field in HTTP is significantly different from
2989   the corresponding definition in MIME, where it is an optional field
2990   used within the "message/external-body" content-type.
2994<section title="Date" anchor="">
2995  <iref primary="true" item="Date header field" x:for-anchor=""/>
2996  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2997  <x:anchor-alias value="Date"/>
2998  <x:anchor-alias value="Date-v"/>
3000   The "Date" general-header field represents the date and time at which
3001   the message was originated, having the same semantics as the Origination
3002   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3003   The field value is an HTTP-date, as described in <xref target=""/>;
3004   it &MUST; be sent in rfc1123-date format.
3006<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3007  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3008  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3011   An example is
3013<figure><artwork type="example">
3014  Date: Tue, 15 Nov 1994 08:12:31 GMT
3017   Origin servers &MUST; include a Date header field in all responses,
3018   except in these cases:
3019  <list style="numbers">
3020      <t>If the response status code is 100 (Continue) or 101 (Switching
3021         Protocols), the response &MAY; include a Date header field, at
3022         the server's option.</t>
3024      <t>If the response status code conveys a server error, e.g., 500
3025         (Internal Server Error) or 503 (Service Unavailable), and it is
3026         inconvenient or impossible to generate a valid Date.</t>
3028      <t>If the server does not have a clock that can provide a
3029         reasonable approximation of the current time, its responses
3030         &MUST-NOT; include a Date header field. In this case, the rules
3031         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3032  </list>
3035   A received message that does not have a Date header field &MUST; be
3036   assigned one by the recipient if the message will be cached by that
3037   recipient or gatewayed via a protocol which requires a Date.
3040   Clients can use the Date header field as well; in order to keep request
3041   messages small, they are advised not to include it when it doesn't convey
3042   any useful information (as it is usually the case for requests that do not
3043   contain a payload).
3046   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3047   time subsequent to the generation of the message. It &SHOULD; represent
3048   the best available approximation of the date and time of message
3049   generation, unless the implementation has no means of generating a
3050   reasonably accurate date and time. In theory, the date ought to
3051   represent the moment just before the payload is generated. In
3052   practice, the date can be generated at any time during the message
3053   origination without affecting its semantic value.
3056<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3058   Some origin server implementations might not have a clock available.
3059   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3060   values to a response, unless these values were associated
3061   with the resource by a system or user with a reliable clock. It &MAY;
3062   assign an Expires value that is known, at or before server
3063   configuration time, to be in the past (this allows "pre-expiration"
3064   of responses without storing separate Expires values for each
3065   resource).
3070<section title="Host" anchor="">
3071  <iref primary="true" item="Host header field" x:for-anchor=""/>
3072  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3073  <x:anchor-alias value="Host"/>
3074  <x:anchor-alias value="Host-v"/>
3076   The "Host" request-header field specifies the Internet host and port
3077   number of the resource being requested, allowing the origin server or
3078   gateway to differentiate between internally-ambiguous URLs, such as the root
3079   "/" URL of a server for multiple host names on a single IP address.
3082   The Host field value &MUST; represent the naming authority of the origin
3083   server or gateway given by the original URL obtained from the user or
3084   referring resource (generally an http URI, as described in
3085   <xref target="http.uri"/>).
3087<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3088  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3089  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3092   A "host" without any trailing port information implies the default
3093   port for the service requested (e.g., "80" for an HTTP URL). For
3094   example, a request on the origin server for
3095   &lt;; would properly include:
3097<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3098GET /pub/WWW/ HTTP/1.1
3102   A client &MUST; include a Host header field in all HTTP/1.1 request
3103   messages. If the requested URI does not include an Internet host
3104   name for the service being requested, then the Host header field &MUST;
3105   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3106   request message it forwards does contain an appropriate Host header
3107   field that identifies the service being requested by the proxy. All
3108   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3109   status code to any HTTP/1.1 request message which lacks a Host header
3110   field.
3113   See Sections <xref target="" format="counter"/>
3114   and <xref target="" format="counter"/>
3115   for other requirements relating to Host.
3119<section title="TE" anchor="header.te">
3120  <iref primary="true" item="TE header field" x:for-anchor=""/>
3121  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3122  <x:anchor-alias value="TE"/>
3123  <x:anchor-alias value="TE-v"/>
3124  <x:anchor-alias value="t-codings"/>
3125  <x:anchor-alias value="te-params"/>
3126  <x:anchor-alias value="te-ext"/>
3128   The "TE" request-header field indicates what extension transfer-codings
3129   it is willing to accept in the response, and whether or not it is
3130   willing to accept trailer fields in a chunked transfer-coding.
3133   Its value consists of the keyword "trailers" and/or a comma-separated
3134   list of extension transfer-coding names with optional accept
3135   parameters (as described in <xref target="transfer.codings"/>).
3137<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"/>
3138  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3139  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3140  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3141  <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> )
3142  <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> ]
3145   The presence of the keyword "trailers" indicates that the client is
3146   willing to accept trailer fields in a chunked transfer-coding, as
3147   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3148   transfer-coding values even though it does not itself represent a
3149   transfer-coding.
3152   Examples of its use are:
3154<figure><artwork type="example">
3155  TE: deflate
3156  TE:
3157  TE: trailers, deflate;q=0.5
3160   The TE header field only applies to the immediate connection.
3161   Therefore, the keyword &MUST; be supplied within a Connection header
3162   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3165   A server tests whether a transfer-coding is acceptable, according to
3166   a TE field, using these rules:
3167  <list style="numbers">
3168    <x:lt>
3169      <t>The "chunked" transfer-coding is always acceptable. If the
3170         keyword "trailers" is listed, the client indicates that it is
3171         willing to accept trailer fields in the chunked response on
3172         behalf of itself and any downstream clients. The implication is
3173         that, if given, the client is stating that either all
3174         downstream clients are willing to accept trailer fields in the
3175         forwarded response, or that it will attempt to buffer the
3176         response on behalf of downstream recipients.
3177      </t><t>
3178         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3179         chunked response such that a client can be assured of buffering
3180         the entire response.</t>
3181    </x:lt>
3182    <x:lt>
3183      <t>If the transfer-coding being tested is one of the transfer-codings
3184         listed in the TE field, then it is acceptable unless it
3185         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3186         qvalue of 0 means "not acceptable".)</t>
3187    </x:lt>
3188    <x:lt>
3189      <t>If multiple transfer-codings are acceptable, then the
3190         acceptable transfer-coding with the highest non-zero qvalue is
3191         preferred.  The "chunked" transfer-coding always has a qvalue
3192         of 1.</t>
3193    </x:lt>
3194  </list>
3197   If the TE field-value is empty or if no TE field is present, the only
3198   transfer-coding is "chunked". A message with no transfer-coding is
3199   always acceptable.
3203<section title="Trailer" anchor="header.trailer">
3204  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3205  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3206  <x:anchor-alias value="Trailer"/>
3207  <x:anchor-alias value="Trailer-v"/>
3209   The "Trailer" general-header field indicates that the given set of
3210   header fields is present in the trailer of a message encoded with
3211   chunked transfer-coding.
3213<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3214  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3215  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3218   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3219   message using chunked transfer-coding with a non-empty trailer. Doing
3220   so allows the recipient to know which header fields to expect in the
3221   trailer.
3224   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3225   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3226   trailer fields in a "chunked" transfer-coding.
3229   Message header fields listed in the Trailer header field &MUST-NOT;
3230   include the following header fields:
3231  <list style="symbols">
3232    <t>Transfer-Encoding</t>
3233    <t>Content-Length</t>
3234    <t>Trailer</t>
3235  </list>
3239<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3240  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3241  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3242  <x:anchor-alias value="Transfer-Encoding"/>
3243  <x:anchor-alias value="Transfer-Encoding-v"/>
3245   The "Transfer-Encoding" general-header field indicates what transfer-codings
3246   (if any) have been applied to the message body. It differs from
3247   Content-Encoding (&content-codings;) in that transfer-codings are a property
3248   of the message (and therefore are removed by intermediaries), whereas
3249   content-codings are not.
3251<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3252  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3253                        <x:ref>Transfer-Encoding-v</x:ref>
3254  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3257   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3259<figure><artwork type="example">
3260  Transfer-Encoding: chunked
3263   If multiple encodings have been applied to a representation, the transfer-codings
3264   &MUST; be listed in the order in which they were applied.
3265   Additional information about the encoding parameters &MAY; be provided
3266   by other header fields not defined by this specification.
3269   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3270   header field.
3274<section title="Upgrade" anchor="header.upgrade">
3275  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3276  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3277  <x:anchor-alias value="Upgrade"/>
3278  <x:anchor-alias value="Upgrade-v"/>
3280   The "Upgrade" general-header field allows the client to specify what
3281   additional communication protocols it would like to use, if the server
3282   chooses to switch protocols. Servers can use it to indicate what protocols
3283   they are willing to switch to.
3285<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3286  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3287  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3290   For example,
3292<figure><artwork type="example">
3293  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3296   The Upgrade header field is intended to provide a simple mechanism
3297   for transition from HTTP/1.1 to some other, incompatible protocol. It
3298   does so by allowing the client to advertise its desire to use another
3299   protocol, such as a later version of HTTP with a higher major version
3300   number, even though the current request has been made using HTTP/1.1.
3301   This eases the difficult transition between incompatible protocols by
3302   allowing the client to initiate a request in the more commonly
3303   supported protocol while indicating to the server that it would like
3304   to use a "better" protocol if available (where "better" is determined
3305   by the server, possibly according to the nature of the method and/or
3306   resource being requested).
3309   The Upgrade header field only applies to switching application-layer
3310   protocols upon the existing transport-layer connection. Upgrade
3311   cannot be used to insist on a protocol change; its acceptance and use
3312   by the server is optional. The capabilities and nature of the
3313   application-layer communication after the protocol change is entirely
3314   dependent upon the new protocol chosen, although the first action
3315   after changing the protocol &MUST; be a response to the initial HTTP
3316   request containing the Upgrade header field.
3319   The Upgrade header field only applies to the immediate connection.
3320   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3321   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3322   HTTP/1.1 message.
3325   The Upgrade header field cannot be used to indicate a switch to a
3326   protocol on a different connection. For that purpose, it is more
3327   appropriate to use a 3xx redirection response (&status-3xx;).
3330   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3331   Protocols) responses to indicate which protocol(s) are being switched to,
3332   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3333   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3334   response to indicate that they are willing to upgrade to one of the
3335   specified protocols.
3338   This specification only defines the protocol name "HTTP" for use by
3339   the family of Hypertext Transfer Protocols, as defined by the HTTP
3340   version rules of <xref target="http.version"/> and future updates to this
3341   specification. Additional tokens can be registered with IANA using the
3342   registration procedure defined below. 
3345<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3347   The HTTP Upgrade Token Registry defines the name space for product
3348   tokens used to identify protocols in the Upgrade header field.
3349   Each registered token is associated with contact information and
3350   an optional set of specifications that details how the connection
3351   will be processed after it has been upgraded.
3354   Registrations are allowed on a First Come First Served basis as
3355   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3356   specifications need not be IETF documents or be subject to IESG review.
3357   Registrations are subject to the following rules:
3358  <list style="numbers">
3359    <t>A token, once registered, stays registered forever.</t>
3360    <t>The registration &MUST; name a responsible party for the
3361       registration.</t>
3362    <t>The registration &MUST; name a point of contact.</t>
3363    <t>The registration &MAY; name a set of specifications associated with that
3364       token. Such specifications need not be publicly available.</t>
3365    <t>The responsible party &MAY; change the registration at any time.
3366       The IANA will keep a record of all such changes, and make them
3367       available upon request.</t>
3368    <t>The responsible party for the first registration of a "product"
3369       token &MUST; approve later registrations of a "version" token
3370       together with that "product" token before they can be registered.</t>
3371    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3372       for a token. This will normally only be used in the case when a
3373       responsible party cannot be contacted.</t>
3374  </list>
3381<section title="Via" anchor="header.via">
3382  <iref primary="true" item="Via header field" x:for-anchor=""/>
3383  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3384  <x:anchor-alias value="protocol-name"/>
3385  <x:anchor-alias value="protocol-version"/>
3386  <x:anchor-alias value="pseudonym"/>
3387  <x:anchor-alias value="received-by"/>
3388  <x:anchor-alias value="received-protocol"/>
3389  <x:anchor-alias value="Via"/>
3390  <x:anchor-alias value="Via-v"/>
3392   The "Via" general-header field &MUST; be used by gateways and proxies to
3393   indicate the intermediate protocols and recipients between the user
3394   agent and the server on requests, and between the origin server and
3395   the client on responses. It is analogous to the "Received" field defined in
3396   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3397   avoiding request loops, and identifying the protocol capabilities of
3398   all senders along the request/response chain.
3400<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"/>
3401  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3402  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3403                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3404  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3405  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3406  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3407  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3408  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3411   The received-protocol indicates the protocol version of the message
3412   received by the server or client along each segment of the
3413   request/response chain. The received-protocol version is appended to
3414   the Via field value when the message is forwarded so that information
3415   about the protocol capabilities of upstream applications remains
3416   visible to all recipients.
3419   The protocol-name is optional if and only if it would be "HTTP". The
3420   received-by field is normally the host and optional port number of a
3421   recipient server or client that subsequently forwarded the message.
3422   However, if the real host is considered to be sensitive information,
3423   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3424   be assumed to be the default port of the received-protocol.
3427   Multiple Via field values represent each proxy or gateway that has
3428   forwarded the message. Each recipient &MUST; append its information
3429   such that the end result is ordered according to the sequence of
3430   forwarding applications.
3433   Comments &MAY; be used in the Via header field to identify the software
3434   of the recipient proxy or gateway, analogous to the User-Agent and
3435   Server header fields. However, all comments in the Via field are
3436   optional and &MAY; be removed by any recipient prior to forwarding the
3437   message.
3440   For example, a request message could be sent from an HTTP/1.0 user
3441   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3442   forward the request to a public proxy at, which completes
3443   the request by forwarding it to the origin server at
3444   The request received by would then have the following
3445   Via header field:
3447<figure><artwork type="example">
3448  Via: 1.0 fred, 1.1 (Apache/1.1)
3451   Proxies and gateways used as a portal through a network firewall
3452   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3453   the firewall region. This information &SHOULD; only be propagated if
3454   explicitly enabled. If not enabled, the received-by host of any host
3455   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3456   for that host.
3459   For organizations that have strong privacy requirements for hiding
3460   internal structures, a proxy &MAY; combine an ordered subsequence of
3461   Via header field entries with identical received-protocol values into
3462   a single such entry. For example,
3464<figure><artwork type="example">
3465  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3468  could be collapsed to
3470<figure><artwork type="example">
3471  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3474   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3475   under the same organizational control and the hosts have already been
3476   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3477   have different received-protocol values.
3483<section title="IANA Considerations" anchor="IANA.considerations">
3485<section title="Header Field Registration" anchor="header.field.registration">
3487   The Message Header Field Registry located at <eref target=""/> shall be updated
3488   with the permanent registrations below (see <xref target="RFC3864"/>):
3490<?BEGININC p1-messaging.iana-headers ?>
3491<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3492<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3493   <ttcol>Header Field Name</ttcol>
3494   <ttcol>Protocol</ttcol>
3495   <ttcol>Status</ttcol>
3496   <ttcol>Reference</ttcol>
3498   <c>Connection</c>
3499   <c>http</c>
3500   <c>standard</c>
3501   <c>
3502      <xref target="header.connection"/>
3503   </c>
3504   <c>Content-Length</c>
3505   <c>http</c>
3506   <c>standard</c>
3507   <c>
3508      <xref target="header.content-length"/>
3509   </c>
3510   <c>Date</c>
3511   <c>http</c>
3512   <c>standard</c>
3513   <c>
3514      <xref target=""/>
3515   </c>
3516   <c>Host</c>
3517   <c>http</c>
3518   <c>standard</c>
3519   <c>
3520      <xref target=""/>
3521   </c>
3522   <c>TE</c>
3523   <c>http</c>
3524   <c>standard</c>
3525   <c>
3526      <xref target="header.te"/>
3527   </c>
3528   <c>Trailer</c>
3529   <c>http</c>
3530   <c>standard</c>
3531   <c>
3532      <xref target="header.trailer"/>
3533   </c>
3534   <c>Transfer-Encoding</c>
3535   <c>http</c>
3536   <c>standard</c>
3537   <c>
3538      <xref target="header.transfer-encoding"/>
3539   </c>
3540   <c>Upgrade</c>
3541   <c>http</c>
3542   <c>standard</c>
3543   <c>
3544      <xref target="header.upgrade"/>
3545   </c>
3546   <c>Via</c>
3547   <c>http</c>
3548   <c>standard</c>
3549   <c>
3550      <xref target="header.via"/>
3551   </c>
3554<?ENDINC p1-messaging.iana-headers ?>
3556   The change controller is: "IETF ( - Internet Engineering Task Force".
3560<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3562   The entries for the "http" and "https" URI Schemes in the registry located at
3563   <eref target=""/>
3564   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3565   and <xref target="https.uri" format="counter"/> of this document
3566   (see <xref target="RFC4395"/>).
3570<section title="Internet Media Type Registrations" anchor="">
3572   This document serves as the specification for the Internet media types
3573   "message/http" and "application/http". The following is to be registered with
3574   IANA (see <xref target="RFC4288"/>).
3576<section title="Internet Media Type message/http" anchor="">
3577<iref item="Media Type" subitem="message/http" primary="true"/>
3578<iref item="message/http Media Type" primary="true"/>
3580   The message/http type can be used to enclose a single HTTP request or
3581   response message, provided that it obeys the MIME restrictions for all
3582   "message" types regarding line length and encodings.
3585  <list style="hanging" x:indent="12em">
3586    <t hangText="Type name:">
3587      message
3588    </t>
3589    <t hangText="Subtype name:">
3590      http
3591    </t>
3592    <t hangText="Required parameters:">
3593      none
3594    </t>
3595    <t hangText="Optional parameters:">
3596      version, msgtype
3597      <list style="hanging">
3598        <t hangText="version:">
3599          The HTTP-Version number of the enclosed message
3600          (e.g., "1.1"). If not present, the version can be
3601          determined from the first line of the body.
3602        </t>
3603        <t hangText="msgtype:">
3604          The message type &mdash; "request" or "response". If not
3605          present, the type can be determined from the first
3606          line of the body.
3607        </t>
3608      </list>
3609    </t>
3610    <t hangText="Encoding considerations:">
3611      only "7bit", "8bit", or "binary" are permitted
3612    </t>
3613    <t hangText="Security considerations:">
3614      none
3615    </t>
3616    <t hangText="Interoperability considerations:">
3617      none
3618    </t>
3619    <t hangText="Published specification:">
3620      This specification (see <xref target=""/>).
3621    </t>
3622    <t hangText="Applications that use this media type:">
3623    </t>
3624    <t hangText="Additional information:">
3625      <list style="hanging">
3626        <t hangText="Magic number(s):">none</t>
3627        <t hangText="File extension(s):">none</t>
3628        <t hangText="Macintosh file type code(s):">none</t>
3629      </list>
3630    </t>
3631    <t hangText="Person and email address to contact for further information:">
3632      See Authors Section.
3633    </t>
3634    <t hangText="Intended usage:">
3635      COMMON
3636    </t>
3637    <t hangText="Restrictions on usage:">
3638      none
3639    </t>
3640    <t hangText="Author/Change controller:">
3641      IESG
3642    </t>
3643  </list>
3646<section title="Internet Media Type application/http" anchor="">
3647<iref item="Media Type" subitem="application/http" primary="true"/>
3648<iref item="application/http Media Type" primary="true"/>
3650   The application/http type can be used to enclose a pipeline of one or more
3651   HTTP request or response messages (not intermixed).
3654  <list style="hanging" x:indent="12em">
3655    <t hangText="Type name:">
3656      application
3657    </t>
3658    <t hangText="Subtype name:">
3659      http
3660    </t>
3661    <t hangText="Required parameters:">
3662      none
3663    </t>
3664    <t hangText="Optional parameters:">
3665      version, msgtype
3666      <list style="hanging">
3667        <t hangText="version:">
3668          The HTTP-Version number of the enclosed messages
3669          (e.g., "1.1"). If not present, the version can be
3670          determined from the first line of the body.
3671        </t>
3672        <t hangText="msgtype:">
3673          The message type &mdash; "request" or "response". If not
3674          present, the type can be determined from the first
3675          line of the body.
3676        </t>
3677      </list>
3678    </t>
3679    <t hangText="Encoding considerations:">
3680      HTTP messages enclosed by this type
3681      are in "binary" format; use of an appropriate
3682      Content-Transfer-Encoding is required when
3683      transmitted via E-mail.
3684    </t>
3685    <t hangText="Security considerations:">
3686      none
3687    </t>
3688    <t hangText="Interoperability considerations:">
3689      none
3690    </t>
3691    <t hangText="Published specification:">
3692      This specification (see <xref target=""/>).
3693    </t>
3694    <t hangText="Applications that use this media type:">
3695    </t>
3696    <t hangText="Additional information:">
3697      <list style="hanging">
3698        <t hangText="Magic number(s):">none</t>
3699        <t hangText="File extension(s):">none</t>
3700        <t hangText="Macintosh file type code(s):">none</t>
3701      </list>
3702    </t>
3703    <t hangText="Person and email address to contact for further information:">
3704      See Authors Section.
3705    </t>
3706    <t hangText="Intended usage:">
3707      COMMON
3708    </t>
3709    <t hangText="Restrictions on usage:">
3710      none
3711    </t>
3712    <t hangText="Author/Change controller:">
3713      IESG
3714    </t>
3715  </list>
3720<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3722   The registration procedure for HTTP Transfer Codings is now defined by
3723   <xref target="transfer.coding.registry"/> of this document.
3726   The HTTP Transfer Codings Registry located at <eref target=""/>
3727   shall be updated with the registrations below:
3729<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3730   <ttcol>Name</ttcol>
3731   <ttcol>Description</ttcol>
3732   <ttcol>Reference</ttcol>
3733   <c>chunked</c>
3734   <c>Transfer in a series of chunks</c>
3735   <c>
3736      <xref target="chunked.encoding"/>
3737   </c>
3738   <c>compress</c>
3739   <c>UNIX "compress" program method</c>
3740   <c>
3741      <xref target="compress.coding"/>
3742   </c>
3743   <c>deflate</c>
3744   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3745   the "zlib" data format (<xref target="RFC1950"/>)
3746   </c>
3747   <c>
3748      <xref target="deflate.coding"/>
3749   </c>
3750   <c>gzip</c>
3751   <c>Same as GNU zip <xref target="RFC1952"/></c>
3752   <c>
3753      <xref target="gzip.coding"/>
3754   </c>
3758<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3760   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3761   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3762   by <xref target="upgrade.token.registry"/> of this document.
3765   The HTTP Status Code Registry located at <eref target=""/>
3766   shall be updated with the registration below:
3768<texttable align="left" suppress-title="true">
3769   <ttcol>Value</ttcol>
3770   <ttcol>Description</ttcol>
3771   <ttcol>Reference</ttcol>
3773   <c>HTTP</c>
3774   <c>Hypertext Transfer Protocol</c>
3775   <c><xref target="http.version"/> of this specification</c>
3776<!-- IANA should add this without our instructions; emailed on June 05, 2009
3777   <c>TLS/1.0</c>
3778   <c>Transport Layer Security</c>
3779   <c><xref target="RFC2817"/></c> -->
3786<section title="Security Considerations" anchor="security.considerations">
3788   This section is meant to inform application developers, information
3789   providers, and users of the security limitations in HTTP/1.1 as
3790   described by this document. The discussion does not include
3791   definitive solutions to the problems revealed, though it does make
3792   some suggestions for reducing security risks.
3795<section title="Personal Information" anchor="personal.information">
3797   HTTP clients are often privy to large amounts of personal information
3798   (e.g., the user's name, location, mail address, passwords, encryption
3799   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3800   leakage of this information.
3801   We very strongly recommend that a convenient interface be provided
3802   for the user to control dissemination of such information, and that
3803   designers and implementors be particularly careful in this area.
3804   History shows that errors in this area often create serious security
3805   and/or privacy problems and generate highly adverse publicity for the
3806   implementor's company.
3810<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3812   A server is in the position to save personal data about a user's
3813   requests which might identify their reading patterns or subjects of
3814   interest. This information is clearly confidential in nature and its
3815   handling can be constrained by law in certain countries. People using
3816   HTTP to provide data are responsible for ensuring that
3817   such material is not distributed without the permission of any
3818   individuals that are identifiable by the published results.
3822<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3824   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3825   the documents returned by HTTP requests to be only those that were
3826   intended by the server administrators. If an HTTP server translates
3827   HTTP URIs directly into file system calls, the server &MUST; take
3828   special care not to serve files that were not intended to be
3829   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3830   other operating systems use ".." as a path component to indicate a
3831   directory level above the current one. On such a system, an HTTP
3832   server &MUST; disallow any such construct in the request-target if it
3833   would otherwise allow access to a resource outside those intended to
3834   be accessible via the HTTP server. Similarly, files intended for
3835   reference only internally to the server (such as access control
3836   files, configuration files, and script code) &MUST; be protected from
3837   inappropriate retrieval, since they might contain sensitive
3838   information. Experience has shown that minor bugs in such HTTP server
3839   implementations have turned into security risks.
3843<section title="DNS Spoofing" anchor="dns.spoofing">
3845   Clients using HTTP rely heavily on the Domain Name Service, and are
3846   thus generally prone to security attacks based on the deliberate
3847   mis-association of IP addresses and DNS names. Clients need to be
3848   cautious in assuming the continuing validity of an IP number/DNS name
3849   association.
3852   In particular, HTTP clients &SHOULD; rely on their name resolver for
3853   confirmation of an IP number/DNS name association, rather than
3854   caching the result of previous host name lookups. Many platforms
3855   already can cache host name lookups locally when appropriate, and
3856   they &SHOULD; be configured to do so. It is proper for these lookups to
3857   be cached, however, only when the TTL (Time To Live) information
3858   reported by the name server makes it likely that the cached
3859   information will remain useful.
3862   If HTTP clients cache the results of host name lookups in order to
3863   achieve a performance improvement, they &MUST; observe the TTL
3864   information reported by DNS.
3867   If HTTP clients do not observe this rule, they could be spoofed when
3868   a previously-accessed server's IP address changes. As network
3869   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3870   possibility of this form of attack will grow. Observing this
3871   requirement thus reduces this potential security vulnerability.
3874   This requirement also improves the load-balancing behavior of clients
3875   for replicated servers using the same DNS name and reduces the
3876   likelihood of a user's experiencing failure in accessing sites which
3877   use that strategy.
3881<section title="Proxies and Caching" anchor="attack.proxies">
3883   By their very nature, HTTP proxies are men-in-the-middle, and
3884   represent an opportunity for man-in-the-middle attacks. Compromise of
3885   the systems on which the proxies run can result in serious security
3886   and privacy problems. Proxies have access to security-related
3887   information, personal information about individual users and
3888   organizations, and proprietary information belonging to users and
3889   content providers. A compromised proxy, or a proxy implemented or
3890   configured without regard to security and privacy considerations,
3891   might be used in the commission of a wide range of potential attacks.
3894   Proxy operators need to protect the systems on which proxies run as
3895   they would protect any system that contains or transports sensitive
3896   information. In particular, log information gathered at proxies often
3897   contains highly sensitive personal information, and/or information
3898   about organizations. Log information needs to be carefully guarded, and
3899   appropriate guidelines for use need to be developed and followed.
3900   (<xref target="abuse.of.server.log.information"/>).
3903   Proxy implementors need to consider the privacy and security
3904   implications of their design and coding decisions, and of the
3905   configuration options they provide to proxy operators (especially the
3906   default configuration).
3909   Users of a proxy need to be aware that proxies are no trustworthier than
3910   the people who run them; HTTP itself cannot solve this problem.
3913   The judicious use of cryptography, when appropriate, might suffice to
3914   protect against a broad range of security and privacy attacks. Such
3915   cryptography is beyond the scope of the HTTP/1.1 specification.
3919<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3921   They exist. They are hard to defend against. Research continues.
3922   Beware.
3927<section title="Acknowledgments" anchor="ack">
3929   HTTP has evolved considerably over the years. It has
3930   benefited from a large and active developer community &mdash; the many
3931   people who have participated on the www-talk mailing list &mdash; and it is
3932   that community which has been most responsible for the success of
3933   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3934   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3935   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3936   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3937   VanHeyningen deserve special recognition for their efforts in
3938   defining early aspects of the protocol.
3941   This document has benefited greatly from the comments of all those
3942   participating in the HTTP-WG. In addition to those already mentioned,
3943   the following individuals have contributed to this specification:
3946   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3947   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3948   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3949   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3950   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3951   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3952   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3953   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3954   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3955   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3956   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3957   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3960   Thanks to the "cave men" of Palo Alto. You know who you are.
3963   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3964   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3965   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3966   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3967   Larry Masinter for their help. And thanks go particularly to Jeff
3968   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3971   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3972   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3973   discovery of many of the problems that this document attempts to
3974   rectify.
3977   This specification makes heavy use of the augmented BNF and generic
3978   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3979   reuses many of the definitions provided by Nathaniel Borenstein and
3980   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3981   specification will help reduce past confusion over the relationship
3982   between HTTP and Internet mail message formats.
3986Acknowledgements TODO list
3988- Jeff Hodges ("effective request URI")
3996<references title="Normative References">
3998<reference anchor="ISO-8859-1">
3999  <front>
4000    <title>
4001     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4002    </title>
4003    <author>
4004      <organization>International Organization for Standardization</organization>
4005    </author>
4006    <date year="1998"/>
4007  </front>
4008  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4011<reference anchor="Part2">
4012  <front>
4013    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4014    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4015      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4016      <address><email></email></address>
4017    </author>
4018    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4019      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4020      <address><email></email></address>
4021    </author>
4022    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4023      <organization abbrev="HP">Hewlett-Packard Company</organization>
4024      <address><email></email></address>
4025    </author>
4026    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4027      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4028      <address><email></email></address>
4029    </author>
4030    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4031      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4032      <address><email></email></address>
4033    </author>
4034    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4035      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4036      <address><email></email></address>
4037    </author>
4038    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4039      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4040      <address><email></email></address>
4041    </author>
4042    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4043      <organization abbrev="W3C">World Wide Web Consortium</organization>
4044      <address><email></email></address>
4045    </author>
4046    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4047      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4048      <address><email></email></address>
4049    </author>
4050    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4051  </front>
4052  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4053  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4056<reference anchor="Part3">
4057  <front>
4058    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4059    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4060      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4061      <address><email></email></address>
4062    </author>
4063    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4064      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4065      <address><email></email></address>
4066    </author>
4067    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4068      <organization abbrev="HP">Hewlett-Packard Company</organization>
4069      <address><email></email></address>
4070    </author>
4071    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4072      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4073      <address><email></email></address>
4074    </author>
4075    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4076      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4077      <address><email></email></address>
4078    </author>
4079    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4080      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4081      <address><email></email></address>
4082    </author>
4083    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4084      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4085      <address><email></email></address>
4086    </author>
4087    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4088      <organization abbrev="W3C">World Wide Web Consortium</organization>
4089      <address><email></email></address>
4090    </author>
4091    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4092      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4093      <address><email></email></address>
4094    </author>
4095    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4096  </front>
4097  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4098  <x:source href="p3-payload.xml" basename="p3-payload"/>
4101<reference anchor="Part6">
4102  <front>
4103    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4104    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4105      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4106      <address><email></email></address>
4107    </author>
4108    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4109      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4110      <address><email></email></address>
4111    </author>
4112    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4113      <organization abbrev="HP">Hewlett-Packard Company</organization>
4114      <address><email></email></address>
4115    </author>
4116    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4117      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4118      <address><email></email></address>
4119    </author>
4120    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4121      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4122      <address><email></email></address>
4123    </author>
4124    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4125      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4126      <address><email></email></address>
4127    </author>
4128    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4129      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4130      <address><email></email></address>
4131    </author>
4132    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4133      <organization abbrev="W3C">World Wide Web Consortium</organization>
4134      <address><email></email></address>
4135    </author>
4136    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4137      <address><email></email></address>
4138    </author>
4139    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4140      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4141      <address><email></email></address>
4142    </author>
4143    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4144  </front>
4145  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4146  <x:source href="p6-cache.xml" basename="p6-cache"/>
4149<reference anchor="RFC5234">
4150  <front>
4151    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4152    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4153      <organization>Brandenburg InternetWorking</organization>
4154      <address>
4155        <email></email>
4156      </address> 
4157    </author>
4158    <author initials="P." surname="Overell" fullname="Paul Overell">
4159      <organization>THUS plc.</organization>
4160      <address>
4161        <email></email>
4162      </address>
4163    </author>
4164    <date month="January" year="2008"/>
4165  </front>
4166  <seriesInfo name="STD" value="68"/>
4167  <seriesInfo name="RFC" value="5234"/>
4170<reference anchor="RFC2119">
4171  <front>
4172    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4173    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4174      <organization>Harvard University</organization>
4175      <address><email></email></address>
4176    </author>
4177    <date month="March" year="1997"/>
4178  </front>
4179  <seriesInfo name="BCP" value="14"/>
4180  <seriesInfo name="RFC" value="2119"/>
4183<reference anchor="RFC3986">
4184 <front>
4185  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4186  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4187    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4188    <address>
4189       <email></email>
4190       <uri></uri>
4191    </address>
4192  </author>
4193  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4194    <organization abbrev="Day Software">Day Software</organization>
4195    <address>
4196      <email></email>
4197      <uri></uri>
4198    </address>
4199  </author>
4200  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4201    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4202    <address>
4203      <email></email>
4204      <uri></uri>
4205    </address>
4206  </author>
4207  <date month='January' year='2005'></date>
4208 </front>
4209 <seriesInfo name="STD" value="66"/>
4210 <seriesInfo name="RFC" value="3986"/>
4213<reference anchor="USASCII">
4214  <front>
4215    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4216    <author>
4217      <organization>American National Standards Institute</organization>
4218    </author>
4219    <date year="1986"/>
4220  </front>
4221  <seriesInfo name="ANSI" value="X3.4"/>
4224<reference anchor="RFC1950">
4225  <front>
4226    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4227    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4228      <organization>Aladdin Enterprises</organization>
4229      <address><email></email></address>
4230    </author>
4231    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4232    <date month="May" year="1996"/>
4233  </front>
4234  <seriesInfo name="RFC" value="1950"/>
4235  <annotation>
4236    RFC 1950 is an Informational RFC, thus it might be less stable than
4237    this specification. On the other hand, this downward reference was
4238    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4239    therefore it is unlikely to cause problems in practice. See also
4240    <xref target="BCP97"/>.
4241  </annotation>
4244<reference anchor="RFC1951">
4245  <front>
4246    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4247    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4248      <organization>Aladdin Enterprises</organization>
4249      <address><email></email></address>
4250    </author>
4251    <date month="May" year="1996"/>
4252  </front>
4253  <seriesInfo name="RFC" value="1951"/>
4254  <annotation>
4255    RFC 1951 is an Informational RFC, thus it might be less stable than
4256    this specification. On the other hand, this downward reference was
4257    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4258    therefore it is unlikely to cause problems in practice. See also
4259    <xref target="BCP97"/>.
4260  </annotation>
4263<reference anchor="RFC1952">
4264  <front>
4265    <title>GZIP file format specification version 4.3</title>
4266    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4267      <organization>Aladdin Enterprises</organization>
4268      <address><email></email></address>
4269    </author>
4270    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4271      <address><email></email></address>
4272    </author>
4273    <author initials="M." surname="Adler" fullname="Mark Adler">
4274      <address><email></email></address>
4275    </author>
4276    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4277      <address><email></email></address>
4278    </author>
4279    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4280      <address><email></email></address>
4281    </author>
4282    <date month="May" year="1996"/>
4283  </front>
4284  <seriesInfo name="RFC" value="1952"/>
4285  <annotation>
4286    RFC 1952 is an Informational RFC, thus it might be less stable than
4287    this specification. On the other hand, this downward reference was
4288    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4289    therefore it is unlikely to cause problems in practice. See also
4290    <xref target="BCP97"/>.
4291  </annotation>
4296<references title="Informative References">
4298<reference anchor="Nie1997" target="">
4299  <front>
4300    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4301    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4302    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4303    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4304    <author initials="H." surname="Lie" fullname="H. Lie"/>
4305    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4306    <date year="1997" month="September"/>
4307  </front>
4308  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4311<reference anchor="Pad1995" target="">
4312  <front>
4313    <title>Improving HTTP Latency</title>
4314    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4315    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4316    <date year="1995" month="December"/>
4317  </front>
4318  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4321<reference anchor="RFC1123">
4322  <front>
4323    <title>Requirements for Internet Hosts - Application and Support</title>
4324    <author initials="R." surname="Braden" fullname="Robert Braden">
4325      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4326      <address><email>Braden@ISI.EDU</email></address>
4327    </author>
4328    <date month="October" year="1989"/>
4329  </front>
4330  <seriesInfo name="STD" value="3"/>
4331  <seriesInfo name="RFC" value="1123"/>
4334<reference anchor="RFC1900">
4335  <front>
4336    <title>Renumbering Needs Work</title>
4337    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4338      <organization>CERN, Computing and Networks Division</organization>
4339      <address><email></email></address>
4340    </author>
4341    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4342      <organization>cisco Systems</organization>
4343      <address><email></email></address>
4344    </author>
4345    <date month="February" year="1996"/>
4346  </front>
4347  <seriesInfo name="RFC" value="1900"/>
4350<reference anchor='RFC1919'>
4351  <front>
4352    <title>Classical versus Transparent IP Proxies</title>
4353    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4354      <address><email></email></address>
4355    </author>
4356    <date year='1996' month='March' />
4357  </front>
4358  <seriesInfo name='RFC' value='1919' />
4361<reference anchor="RFC1945">
4362  <front>
4363    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4364    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4365      <organization>MIT, Laboratory for Computer Science</organization>
4366      <address><email></email></address>
4367    </author>
4368    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4369      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4370      <address><email></email></address>
4371    </author>
4372    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4373      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4374      <address><email></email></address>
4375    </author>
4376    <date month="May" year="1996"/>
4377  </front>
4378  <seriesInfo name="RFC" value="1945"/>
4381<reference anchor="RFC2045">
4382  <front>
4383    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4384    <author initials="N." surname="Freed" fullname="Ned Freed">
4385      <organization>Innosoft International, Inc.</organization>
4386      <address><email></email></address>
4387    </author>
4388    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4389      <organization>First Virtual Holdings</organization>
4390      <address><email></email></address>
4391    </author>
4392    <date month="November" year="1996"/>
4393  </front>
4394  <seriesInfo name="RFC" value="2045"/>
4397<reference anchor="RFC2047">
4398  <front>
4399    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4400    <author initials="K." surname="Moore" fullname="Keith Moore">
4401      <organization>University of Tennessee</organization>
4402      <address><email></email></address>
4403    </author>
4404    <date month="November" year="1996"/>
4405  </front>
4406  <seriesInfo name="RFC" value="2047"/>
4409<reference anchor="RFC2068">
4410  <front>
4411    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4412    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4413      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4414      <address><email></email></address>
4415    </author>
4416    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4417      <organization>MIT Laboratory for Computer Science</organization>
4418      <address><email></email></address>
4419    </author>
4420    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4421      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4422      <address><email></email></address>
4423    </author>
4424    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4425      <organization>MIT Laboratory for Computer Science</organization>
4426      <address><email></email></address>
4427    </author>
4428    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4429      <organization>MIT Laboratory for Computer Science</organization>
4430      <address><email></email></address>
4431    </author>
4432    <date month="January" year="1997"/>
4433  </front>
4434  <seriesInfo name="RFC" value="2068"/>
4437<reference anchor='RFC2109'>
4438  <front>
4439    <title>HTTP State Management Mechanism</title>
4440    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4441      <organization>Bell Laboratories, Lucent Technologies</organization>
4442      <address><email></email></address>
4443    </author>
4444    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4445      <organization>Netscape Communications Corp.</organization>
4446      <address><email></email></address>
4447    </author>
4448    <date year='1997' month='February' />
4449  </front>
4450  <seriesInfo name='RFC' value='2109' />
4453<reference anchor="RFC2145">
4454  <front>
4455    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4456    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4457      <organization>Western Research Laboratory</organization>
4458      <address><email></email></address>
4459    </author>
4460    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4461      <organization>Department of Information and Computer Science</organization>
4462      <address><email></email></address>
4463    </author>
4464    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4465      <organization>MIT Laboratory for Computer Science</organization>
4466      <address><email></email></address>
4467    </author>
4468    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4469      <organization>W3 Consortium</organization>
4470      <address><email></email></address>
4471    </author>
4472    <date month="May" year="1997"/>
4473  </front>
4474  <seriesInfo name="RFC" value="2145"/>
4477<reference anchor="RFC2616">
4478  <front>
4479    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4480    <author initials="R." surname="Fielding" fullname="R. Fielding">
4481      <organization>University of California, Irvine</organization>
4482      <address><email></email></address>
4483    </author>
4484    <author initials="J." surname="Gettys" fullname="J. Gettys">
4485      <organization>W3C</organization>
4486      <address><email></email></address>
4487    </author>
4488    <author initials="J." surname="Mogul" fullname="J. Mogul">
4489      <organization>Compaq Computer Corporation</organization>
4490      <address><email></email></address>
4491    </author>
4492    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4493      <organization>MIT Laboratory for Computer Science</organization>
4494      <address><email></email></address>
4495    </author>
4496    <author initials="L." surname="Masinter" fullname="L. Masinter">
4497      <organization>Xerox Corporation</organization>
4498      <address><email></email></address>
4499    </author>
4500    <author initials="P." surname="Leach" fullname="P. Leach">
4501      <organization>Microsoft Corporation</organization>
4502      <address><email></email></address>
4503    </author>
4504    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4505      <organization>W3C</organization>
4506      <address><email></email></address>
4507    </author>
4508    <date month="June" year="1999"/>
4509  </front>
4510  <seriesInfo name="RFC" value="2616"/>
4513<reference anchor='RFC2817'>
4514  <front>
4515    <title>Upgrading to TLS Within HTTP/1.1</title>
4516    <author initials='R.' surname='Khare' fullname='R. Khare'>
4517      <organization>4K Associates / UC Irvine</organization>
4518      <address><email></email></address>
4519    </author>
4520    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4521      <organization>Agranat Systems, Inc.</organization>
4522      <address><email></email></address>
4523    </author>
4524    <date year='2000' month='May' />
4525  </front>
4526  <seriesInfo name='RFC' value='2817' />
4529<reference anchor='RFC2818'>
4530  <front>
4531    <title>HTTP Over TLS</title>
4532    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4533      <organization>RTFM, Inc.</organization>
4534      <address><email></email></address>
4535    </author>
4536    <date year='2000' month='May' />
4537  </front>
4538  <seriesInfo name='RFC' value='2818' />
4541<reference anchor='RFC2965'>
4542  <front>
4543    <title>HTTP State Management Mechanism</title>
4544    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4545      <organization>Bell Laboratories, Lucent Technologies</organization>
4546      <address><email></email></address>
4547    </author>
4548    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4549      <organization>, Inc.</organization>
4550      <address><email></email></address>
4551    </author>
4552    <date year='2000' month='October' />
4553  </front>
4554  <seriesInfo name='RFC' value='2965' />
4557<reference anchor='RFC3040'>
4558  <front>
4559    <title>Internet Web Replication and Caching Taxonomy</title>
4560    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4561      <organization>Equinix, Inc.</organization>
4562    </author>
4563    <author initials='I.' surname='Melve' fullname='I. Melve'>
4564      <organization>UNINETT</organization>
4565    </author>
4566    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4567      <organization>CacheFlow Inc.</organization>
4568    </author>
4569    <date year='2001' month='January' />
4570  </front>
4571  <seriesInfo name='RFC' value='3040' />
4574<reference anchor='RFC3864'>
4575  <front>
4576    <title>Registration Procedures for Message Header Fields</title>
4577    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4578      <organization>Nine by Nine</organization>
4579      <address><email></email></address>
4580    </author>
4581    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4582      <organization>BEA Systems</organization>
4583      <address><email></email></address>
4584    </author>
4585    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4586      <organization>HP Labs</organization>
4587      <address><email></email></address>
4588    </author>
4589    <date year='2004' month='September' />
4590  </front>
4591  <seriesInfo name='BCP' value='90' />
4592  <seriesInfo name='RFC' value='3864' />
4595<reference anchor="RFC4288">
4596  <front>
4597    <title>Media Type Specifications and Registration Procedures</title>
4598    <author initials="N." surname="Freed" fullname="N. Freed">
4599      <organization>Sun Microsystems</organization>
4600      <address>
4601        <email></email>
4602      </address>
4603    </author>
4604    <author initials="J." surname="Klensin" fullname="J. Klensin">
4605      <address>
4606        <email></email>
4607      </address>
4608    </author>
4609    <date year="2005" month="December"/>
4610  </front>
4611  <seriesInfo name="BCP" value="13"/>
4612  <seriesInfo name="RFC" value="4288"/>
4615<reference anchor='RFC4395'>
4616  <front>
4617    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4618    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4619      <organization>AT&amp;T Laboratories</organization>
4620      <address>
4621        <email></email>
4622      </address>
4623    </author>
4624    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4625      <organization>Qualcomm, Inc.</organization>
4626      <address>
4627        <email></email>
4628      </address>
4629    </author>
4630    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4631      <organization>Adobe Systems</organization>
4632      <address>
4633        <email></email>
4634      </address>
4635    </author>
4636    <date year='2006' month='February' />
4637  </front>
4638  <seriesInfo name='BCP' value='115' />
4639  <seriesInfo name='RFC' value='4395' />
4642<reference anchor='RFC5226'>
4643  <front>
4644    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4645    <author initials='T.' surname='Narten' fullname='T. Narten'>
4646      <organization>IBM</organization>
4647      <address><email></email></address>
4648    </author>
4649    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4650      <organization>Google</organization>
4651      <address><email></email></address>
4652    </author>
4653    <date year='2008' month='May' />
4654  </front>
4655  <seriesInfo name='BCP' value='26' />
4656  <seriesInfo name='RFC' value='5226' />
4659<reference anchor="RFC5322">
4660  <front>
4661    <title>Internet Message Format</title>
4662    <author initials="P." surname="Resnick" fullname="P. Resnick">
4663      <organization>Qualcomm Incorporated</organization>
4664    </author>
4665    <date year="2008" month="October"/>
4666  </front>
4667  <seriesInfo name="RFC" value="5322"/>
4670<reference anchor='BCP97'>
4671  <front>
4672    <title>Handling Normative References to Standards-Track Documents</title>
4673    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4674      <address>
4675        <email></email>
4676      </address>
4677    </author>
4678    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4679      <organization>MIT</organization>
4680      <address>
4681        <email></email>
4682      </address>
4683    </author>
4684    <date year='2007' month='June' />
4685  </front>
4686  <seriesInfo name='BCP' value='97' />
4687  <seriesInfo name='RFC' value='4897' />
4690<reference anchor="Kri2001" target="">
4691  <front>
4692    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4693    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4694    <date year="2001" month="November"/>
4695  </front>
4696  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4699<reference anchor="Spe" target="">
4700  <front>
4701    <title>Analysis of HTTP Performance Problems</title>
4702    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4703    <date/>
4704  </front>
4707<reference anchor="Tou1998" target="">
4708  <front>
4709  <title>Analysis of HTTP Performance</title>
4710  <author initials="J." surname="Touch" fullname="Joe Touch">
4711    <organization>USC/Information Sciences Institute</organization>
4712    <address><email></email></address>
4713  </author>
4714  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4715    <organization>USC/Information Sciences Institute</organization>
4716    <address><email></email></address>
4717  </author>
4718  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4719    <organization>USC/Information Sciences Institute</organization>
4720    <address><email></email></address>
4721  </author>
4722  <date year="1998" month="Aug"/>
4723  </front>
4724  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4725  <annotation>(original report dated Aug. 1996)</annotation>
4731<section title="Tolerant Applications" anchor="tolerant.applications">
4733   Although this document specifies the requirements for the generation
4734   of HTTP/1.1 messages, not all applications will be correct in their
4735   implementation. We therefore recommend that operational applications
4736   be tolerant of deviations whenever those deviations can be
4737   interpreted unambiguously.
4740   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4741   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4742   &SHOULD; accept any amount of WSP characters between fields, even though
4743   only a single SP is required.
4746   The line terminator for header fields is the sequence CRLF.
4747   However, we recommend that applications, when parsing such headers fields,
4748   recognize a single LF as a line terminator and ignore the leading CR.
4751   The character set of a representation &SHOULD; be labeled as the lowest
4752   common denominator of the character codes used within that representation, with
4753   the exception that not labeling the representation is preferred over labeling
4754   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4757   Additional rules for requirements on parsing and encoding of dates
4758   and other potential problems with date encodings include:
4761  <list style="symbols">
4762     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4763        which appears to be more than 50 years in the future is in fact
4764        in the past (this helps solve the "year 2000" problem).</t>
4766     <t>Although all date formats are specified to be case-sensitive,
4767        recipients &SHOULD; match day, week and timezone names
4768        case-insensitively.</t>
4770     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4771        Expires date as earlier than the proper value, but &MUST-NOT;
4772        internally represent a parsed Expires date as later than the
4773        proper value.</t>
4775     <t>All expiration-related calculations &MUST; be done in GMT. The
4776        local time zone &MUST-NOT; influence the calculation or comparison
4777        of an age or expiration time.</t>
4779     <t>If an HTTP header field incorrectly carries a date value with a time
4780        zone other than GMT, it &MUST; be converted into GMT using the
4781        most conservative possible conversion.</t>
4782  </list>
4786<section title="Compatibility with Previous Versions" anchor="compatibility">
4788   HTTP has been in use by the World-Wide Web global information initiative
4789   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4790   was a simple protocol for hypertext data transfer across the Internet
4791   with only a single method and no metadata.
4792   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4793   methods and MIME-like messaging that could include metadata about the data
4794   transferred and modifiers on the request/response semantics. However,
4795   HTTP/1.0 did not sufficiently take into consideration the effects of
4796   hierarchical proxies, caching, the need for persistent connections, or
4797   name-based virtual hosts. The proliferation of incompletely-implemented
4798   applications calling themselves "HTTP/1.0" further necessitated a
4799   protocol version change in order for two communicating applications
4800   to determine each other's true capabilities.
4803   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4804   requirements that enable reliable implementations, adding only
4805   those new features that will either be safely ignored by an HTTP/1.0
4806   recipient or only sent when communicating with a party advertising
4807   compliance with HTTP/1.1.
4810   It is beyond the scope of a protocol specification to mandate
4811   compliance with previous versions. HTTP/1.1 was deliberately
4812   designed, however, to make supporting previous versions easy. It is
4813   worth noting that, at the time of composing this specification, we would
4814   expect general-purpose HTTP/1.1 servers to:
4815  <list style="symbols">
4816     <t>understand any valid request in the format of HTTP/1.0 and
4817        1.1;</t>
4819     <t>respond appropriately with a message in the same major version
4820        used by the client.</t>
4821  </list>
4824   And we would expect HTTP/1.1 clients to:
4825  <list style="symbols">
4826     <t>understand any valid response in the format of HTTP/1.0 or
4827        1.1.</t>
4828  </list>
4831   For most implementations of HTTP/1.0, each connection is established
4832   by the client prior to the request and closed by the server after
4833   sending the response. Some implementations implement the Keep-Alive
4834   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4837<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4839   This section summarizes major differences between versions HTTP/1.0
4840   and HTTP/1.1.
4843<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4845   The requirements that clients and servers support the Host request-header
4846   field (<xref target=""/>), report an error if it is
4847   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4848   are among the most important changes defined by this
4849   specification.
4852   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4853   addresses and servers; there was no other established mechanism for
4854   distinguishing the intended server of a request than the IP address
4855   to which that request was directed. The changes outlined above will
4856   allow the Internet, once older HTTP clients are no longer common, to
4857   support multiple Web sites from a single IP address, greatly
4858   simplifying large operational Web servers, where allocation of many
4859   IP addresses to a single host has created serious problems. The
4860   Internet will also be able to recover the IP addresses that have been
4861   allocated for the sole purpose of allowing special-purpose domain
4862   names to be used in root-level HTTP URLs. Given the rate of growth of
4863   the Web, and the number of servers already deployed, it is extremely
4864   important that all implementations of HTTP (including updates to
4865   existing HTTP/1.0 applications) correctly implement these
4866   requirements:
4867  <list style="symbols">
4868     <t>Both clients and servers &MUST; support the Host request-header field.</t>
4870     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4872     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4873        request does not include a Host request-header field.</t>
4875     <t>Servers &MUST; accept absolute URIs.</t>
4876  </list>
4881<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4883   Some clients and servers might wish to be compatible with some
4884   previous implementations of persistent connections in HTTP/1.0
4885   clients and servers. Persistent connections in HTTP/1.0 are
4886   explicitly negotiated as they are not the default behavior. HTTP/1.0
4887   experimental implementations of persistent connections are faulty,
4888   and the new facilities in HTTP/1.1 are designed to rectify these
4889   problems. The problem was that some existing HTTP/1.0 clients might
4890   send Keep-Alive to a proxy server that doesn't understand
4891   Connection, which would then erroneously forward it to the next
4892   inbound server, which would establish the Keep-Alive connection and
4893   result in a hung HTTP/1.0 proxy waiting for the close on the
4894   response. The result is that HTTP/1.0 clients must be prevented from
4895   using Keep-Alive when talking to proxies.
4898   However, talking to proxies is the most important use of persistent
4899   connections, so that prohibition is clearly unacceptable. Therefore,
4900   we need some other mechanism for indicating a persistent connection
4901   is desired, which is safe to use even when talking to an old proxy
4902   that ignores Connection. Persistent connections are the default for
4903   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4904   declaring non-persistence. See <xref target="header.connection"/>.
4907   The original HTTP/1.0 form of persistent connections (the Connection:
4908   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4912<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4914  Empty list elements in list productions have been deprecated.
4915  (<xref target="notation.abnf"/>)
4918  Rules about implicit linear whitespace between certain grammar productions
4919  have been removed; now it's only allowed when specifically pointed out
4920  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4921  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4922  Non-ASCII content in header fields and reason phrase has been obsoleted and
4923  made opaque (the TEXT rule was removed)
4924  (<xref target="basic.rules"/>)
4927  Clarify that HTTP-Version is case sensitive.
4928  (<xref target="http.version"/>)
4931  Require that invalid whitespace around field-names be rejected.
4932  (<xref target="header.fields"/>)
4935  Require recipients to handle bogus Content-Length header fields as errors.
4936  (<xref target="message.body"/>)
4939  Remove reference to non-existent identity transfer-coding value tokens.
4940  (Sections <xref format="counter" target="message.body"/> and
4941  <xref format="counter" target="transfer.codings"/>)
4944  Update use of abs_path production from RFC 1808 to the path-absolute + query
4945  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4946  method only.
4947  (<xref target="request-target"/>)
4950  Clarification that the chunk length does not include the count of the octets
4951  in the chunk header and trailer. Furthermore disallowed line folding
4952  in chunk extensions.
4953  (<xref target="chunked.encoding"/>)
4956  Remove hard limit of two connections per server.
4957  (<xref target="persistent.practical"/>)
4960  Clarify exactly when close connection options must be sent.
4961  (<xref target="header.connection"/>)
4964  Define the semantics of the "Upgrade" header field in responses other than
4965  101 (this was incorporated from <xref target="RFC2817"/>).
4966  (<xref target="header.upgrade"/>)
4971<?BEGININC p1-messaging.abnf-appendix ?>
4972<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4974<artwork type="abnf" name="p1-messaging.parsed-abnf">
4975<x:ref>BWS</x:ref> = OWS
4977<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4978<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4979<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4980<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4981 connection-token ] )
4982<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4983<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4985<x:ref>Date</x:ref> = "Date:" OWS Date-v
4986<x:ref>Date-v</x:ref> = HTTP-date
4988<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4990<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4991<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4992<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4993<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4994 ]
4995<x:ref>Host</x:ref> = "Host:" OWS Host-v
4996<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4998<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4999<x:ref>Method</x:ref> = token
5001<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5003<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
5005<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5006<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5007<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5008<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5009<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5011<x:ref>Status-Code</x:ref> = 3DIGIT
5012<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5014<x:ref>TE</x:ref> = "TE:" OWS TE-v
5015<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5016<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5017<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5018<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5019<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5020 transfer-coding ] )
5022<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5023<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5024<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5026<x:ref>Via</x:ref> = "Via:" OWS Via-v
5027<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5028 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5029 ] )
5031<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
5033<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5034<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5035<x:ref>attribute</x:ref> = token
5036<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5038<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5039<x:ref>chunk-data</x:ref> = 1*OCTET
5040<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5041<x:ref>chunk-ext-name</x:ref> = token
5042<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5043<x:ref>chunk-size</x:ref> = 1*HEXDIG
5044<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5045<x:ref>connection-token</x:ref> = token
5046<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5047 / %x2A-5B ; '*'-'['
5048 / %x5D-7E ; ']'-'~'
5049 / obs-text
5051<x:ref>date1</x:ref> = day SP month SP year
5052<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5053<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5054<x:ref>day</x:ref> = 2DIGIT
5055<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5056 / %x54.75.65 ; Tue
5057 / %x57.65.64 ; Wed
5058 / %x54.68.75 ; Thu
5059 / %x46.72.69 ; Fri
5060 / %x53.61.74 ; Sat
5061 / %x53.75.6E ; Sun
5062<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5063 / %x54. ; Tuesday
5064 / %x57.65.64.6E. ; Wednesday
5065 / %x54. ; Thursday
5066 / %x46. ; Friday
5067 / %x53. ; Saturday
5068 / %x53.75.6E.64.61.79 ; Sunday
5070<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5071<x:ref>field-name</x:ref> = token
5072<x:ref>field-value</x:ref> = *( field-content / OWS )
5074<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5075<x:ref>hour</x:ref> = 2DIGIT
5076<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5077<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5079<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5081<x:ref>message-body</x:ref> = *OCTET
5082<x:ref>minute</x:ref> = 2DIGIT
5083<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5084 / %x46.65.62 ; Feb
5085 / %x4D.61.72 ; Mar
5086 / %x41.70.72 ; Apr
5087 / %x4D.61.79 ; May
5088 / %x4A.75.6E ; Jun
5089 / %x4A.75.6C ; Jul
5090 / %x41.75.67 ; Aug
5091 / %x53.65.70 ; Sep
5092 / %x4F.63.74 ; Oct
5093 / %x4E.6F.76 ; Nov
5094 / %x44.65.63 ; Dec
5096<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5097<x:ref>obs-fold</x:ref> = CRLF
5098<x:ref>obs-text</x:ref> = %x80-FF
5100<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5101<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5102<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5103<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5104<x:ref>product</x:ref> = token [ "/" product-version ]
5105<x:ref>product-version</x:ref> = token
5106<x:ref>protocol-name</x:ref> = token
5107<x:ref>protocol-version</x:ref> = token
5108<x:ref>pseudonym</x:ref> = token
5110<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5111 / %x5D-7E ; ']'-'~'
5112 / obs-text
5113<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5114 / %x5D-7E ; ']'-'~'
5115 / obs-text
5116<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5117<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5118<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5119<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5120<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5121<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5123<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5124<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5125<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5126<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5127<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5128 / authority
5129<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5130<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5131<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5133<x:ref>second</x:ref> = 2DIGIT
5134<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5135 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5136<x:ref>start-line</x:ref> = Request-Line / Status-Line
5138<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5139<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5140 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5141<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5142<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5143<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5144<x:ref>token</x:ref> = 1*tchar
5145<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5146<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5147 transfer-extension
5148<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5149<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5151<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5153<x:ref>value</x:ref> = word
5155<x:ref>word</x:ref> = token / quoted-string
5157<x:ref>year</x:ref> = 4DIGIT
5160<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5161; Cache-Control defined but not used
5162; Chunked-Body defined but not used
5163; Connection defined but not used
5164; Content-Length defined but not used
5165; Date defined but not used
5166; HTTP-message defined but not used
5167; Host defined but not used
5168; MIME-Version defined but not used
5169; Pragma defined but not used
5170; Request defined but not used
5171; Response defined but not used
5172; TE defined but not used
5173; Trailer defined but not used
5174; Transfer-Encoding defined but not used
5175; URI-reference defined but not used
5176; Upgrade defined but not used
5177; Via defined but not used
5178; Warning defined but not used
5179; http-URI defined but not used
5180; https-URI defined but not used
5181; partial-URI defined but not used
5182; request-header defined but not used
5183; response-header defined but not used
5184; special defined but not used
5186<?ENDINC p1-messaging.abnf-appendix ?>
5188<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5190<section title="Since RFC 2616">
5192  Extracted relevant partitions from <xref target="RFC2616"/>.
5196<section title="Since draft-ietf-httpbis-p1-messaging-00">
5198  Closed issues:
5199  <list style="symbols">
5200    <t>
5201      <eref target=""/>:
5202      "HTTP Version should be case sensitive"
5203      (<eref target=""/>)
5204    </t>
5205    <t>
5206      <eref target=""/>:
5207      "'unsafe' characters"
5208      (<eref target=""/>)
5209    </t>
5210    <t>
5211      <eref target=""/>:
5212      "Chunk Size Definition"
5213      (<eref target=""/>)
5214    </t>
5215    <t>
5216      <eref target=""/>:
5217      "Message Length"
5218      (<eref target=""/>)
5219    </t>
5220    <t>
5221      <eref target=""/>:
5222      "Media Type Registrations"
5223      (<eref target=""/>)
5224    </t>
5225    <t>
5226      <eref target=""/>:
5227      "URI includes query"
5228      (<eref target=""/>)
5229    </t>
5230    <t>
5231      <eref target=""/>:
5232      "No close on 1xx responses"
5233      (<eref target=""/>)
5234    </t>
5235    <t>
5236      <eref target=""/>:
5237      "Remove 'identity' token references"
5238      (<eref target=""/>)
5239    </t>
5240    <t>
5241      <eref target=""/>:
5242      "Import query BNF"
5243    </t>
5244    <t>
5245      <eref target=""/>:
5246      "qdtext BNF"
5247    </t>
5248    <t>
5249      <eref target=""/>:
5250      "Normative and Informative references"
5251    </t>
5252    <t>
5253      <eref target=""/>:
5254      "RFC2606 Compliance"
5255    </t>
5256    <t>
5257      <eref target=""/>:
5258      "RFC977 reference"
5259    </t>
5260    <t>
5261      <eref target=""/>:
5262      "RFC1700 references"
5263    </t>
5264    <t>
5265      <eref target=""/>:
5266      "inconsistency in date format explanation"
5267    </t>
5268    <t>
5269      <eref target=""/>:
5270      "Date reference typo"
5271    </t>
5272    <t>
5273      <eref target=""/>:
5274      "Informative references"
5275    </t>
5276    <t>
5277      <eref target=""/>:
5278      "ISO-8859-1 Reference"
5279    </t>
5280    <t>
5281      <eref target=""/>:
5282      "Normative up-to-date references"
5283    </t>
5284  </list>
5287  Other changes:
5288  <list style="symbols">
5289    <t>
5290      Update media type registrations to use RFC4288 template.
5291    </t>
5292    <t>
5293      Use names of RFC4234 core rules DQUOTE and WSP,
5294      fix broken ABNF for chunk-data
5295      (work in progress on <eref target=""/>)
5296    </t>
5297  </list>
5301<section title="Since draft-ietf-httpbis-p1-messaging-01">
5303  Closed issues:
5304  <list style="symbols">
5305    <t>
5306      <eref target=""/>:
5307      "Bodies on GET (and other) requests"
5308    </t>
5309    <t>
5310      <eref target=""/>:
5311      "Updating to RFC4288"
5312    </t>
5313    <t>
5314      <eref target=""/>:
5315      "Status Code and Reason Phrase"
5316    </t>
5317    <t>
5318      <eref target=""/>:
5319      "rel_path not used"
5320    </t>
5321  </list>
5324  Ongoing work on ABNF conversion (<eref target=""/>):
5325  <list style="symbols">
5326    <t>
5327      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5328      "trailer-part").
5329    </t>
5330    <t>
5331      Avoid underscore character in rule names ("http_URL" ->
5332      "http-URL", "abs_path" -> "path-absolute").
5333    </t>
5334    <t>
5335      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5336      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5337      have to be updated when switching over to RFC3986.
5338    </t>
5339    <t>
5340      Synchronize core rules with RFC5234.
5341    </t>
5342    <t>
5343      Get rid of prose rules that span multiple lines.
5344    </t>
5345    <t>
5346      Get rid of unused rules LOALPHA and UPALPHA.
5347    </t>
5348    <t>
5349      Move "Product Tokens" section (back) into Part 1, as "token" is used
5350      in the definition of the Upgrade header field.
5351    </t>
5352    <t>
5353      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5354    </t>
5355    <t>
5356      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5357    </t>
5358  </list>
5362<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5364  Closed issues:
5365  <list style="symbols">
5366    <t>
5367      <eref target=""/>:
5368      "HTTP-date vs. rfc1123-date"
5369    </t>
5370    <t>
5371      <eref target=""/>:
5372      "WS in quoted-pair"
5373    </t>
5374  </list>
5377  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5378  <list style="symbols">
5379    <t>
5380      Reference RFC 3984, and update header field registrations for headers defined
5381      in this document.
5382    </t>
5383  </list>
5386  Ongoing work on ABNF conversion (<eref target=""/>):
5387  <list style="symbols">
5388    <t>
5389      Replace string literals when the string really is case-sensitive (HTTP-Version).
5390    </t>
5391  </list>
5395<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5397  Closed issues:
5398  <list style="symbols">
5399    <t>
5400      <eref target=""/>:
5401      "Connection closing"
5402    </t>
5403    <t>
5404      <eref target=""/>:
5405      "Move registrations and registry information to IANA Considerations"
5406    </t>
5407    <t>
5408      <eref target=""/>:
5409      "need new URL for PAD1995 reference"
5410    </t>
5411    <t>
5412      <eref target=""/>:
5413      "IANA Considerations: update HTTP URI scheme registration"
5414    </t>
5415    <t>
5416      <eref target=""/>:
5417      "Cite HTTPS URI scheme definition"
5418    </t>
5419    <t>
5420      <eref target=""/>:
5421      "List-type headers vs Set-Cookie"
5422    </t>
5423  </list>
5426  Ongoing work on ABNF conversion (<eref target=""/>):
5427  <list style="symbols">
5428    <t>
5429      Replace string literals when the string really is case-sensitive (HTTP-Date).
5430    </t>
5431    <t>
5432      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5433    </t>
5434  </list>
5438<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5440  Closed issues:
5441  <list style="symbols">
5442    <t>
5443      <eref target=""/>:
5444      "Out-of-date reference for URIs"
5445    </t>
5446    <t>
5447      <eref target=""/>:
5448      "RFC 2822 is updated by RFC 5322"
5449    </t>
5450  </list>
5453  Ongoing work on ABNF conversion (<eref target=""/>):
5454  <list style="symbols">
5455    <t>
5456      Use "/" instead of "|" for alternatives.
5457    </t>
5458    <t>
5459      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5460    </t>
5461    <t>
5462      Only reference RFC 5234's core rules.
5463    </t>
5464    <t>
5465      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5466      whitespace ("OWS") and required whitespace ("RWS").
5467    </t>
5468    <t>
5469      Rewrite ABNFs to spell out whitespace rules, factor out
5470      header field value format definitions.
5471    </t>
5472  </list>
5476<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5478  Closed issues:
5479  <list style="symbols">
5480    <t>
5481      <eref target=""/>:
5482      "Header LWS"
5483    </t>
5484    <t>
5485      <eref target=""/>:
5486      "Sort 1.3 Terminology"
5487    </t>
5488    <t>
5489      <eref target=""/>:
5490      "RFC2047 encoded words"
5491    </t>
5492    <t>
5493      <eref target=""/>:
5494      "Character Encodings in TEXT"
5495    </t>
5496    <t>
5497      <eref target=""/>:
5498      "Line Folding"
5499    </t>
5500    <t>
5501      <eref target=""/>:
5502      "OPTIONS * and proxies"
5503    </t>
5504    <t>
5505      <eref target=""/>:
5506      "Reason-Phrase BNF"
5507    </t>
5508    <t>
5509      <eref target=""/>:
5510      "Use of TEXT"
5511    </t>
5512    <t>
5513      <eref target=""/>:
5514      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5515    </t>
5516    <t>
5517      <eref target=""/>:
5518      "RFC822 reference left in discussion of date formats"
5519    </t>
5520  </list>
5523  Final work on ABNF conversion (<eref target=""/>):
5524  <list style="symbols">
5525    <t>
5526      Rewrite definition of list rules, deprecate empty list elements.
5527    </t>
5528    <t>
5529      Add appendix containing collected and expanded ABNF.
5530    </t>
5531  </list>
5534  Other changes:
5535  <list style="symbols">
5536    <t>
5537      Rewrite introduction; add mostly new Architecture Section.
5538    </t>
5539    <t>
5540      Move definition of quality values from Part 3 into Part 1;
5541      make TE request header field grammar independent of accept-params (defined in Part 3).
5542    </t>
5543  </list>
5547<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5549  Closed issues:
5550  <list style="symbols">
5551    <t>
5552      <eref target=""/>:
5553      "base for numeric protocol elements"
5554    </t>
5555    <t>
5556      <eref target=""/>:
5557      "comment ABNF"
5558    </t>
5559  </list>
5562  Partly resolved issues:
5563  <list style="symbols">
5564    <t>
5565      <eref target=""/>:
5566      "205 Bodies" (took out language that implied that there might be
5567      methods for which a request body MUST NOT be included)
5568    </t>
5569    <t>
5570      <eref target=""/>:
5571      "editorial improvements around HTTP-date"
5572    </t>
5573  </list>
5577<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5579  Closed issues:
5580  <list style="symbols">
5581    <t>
5582      <eref target=""/>:
5583      "Repeating single-value headers"
5584    </t>
5585    <t>
5586      <eref target=""/>:
5587      "increase connection limit"
5588    </t>
5589    <t>
5590      <eref target=""/>:
5591      "IP addresses in URLs"
5592    </t>
5593    <t>
5594      <eref target=""/>:
5595      "take over HTTP Upgrade Token Registry"
5596    </t>
5597    <t>
5598      <eref target=""/>:
5599      "CR and LF in chunk extension values"
5600    </t>
5601    <t>
5602      <eref target=""/>:
5603      "HTTP/0.9 support"
5604    </t>
5605    <t>
5606      <eref target=""/>:
5607      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5608    </t>
5609    <t>
5610      <eref target=""/>:
5611      "move definitions of gzip/deflate/compress to part 1"
5612    </t>
5613    <t>
5614      <eref target=""/>:
5615      "disallow control characters in quoted-pair"
5616    </t>
5617  </list>
5620  Partly resolved issues:
5621  <list style="symbols">
5622    <t>
5623      <eref target=""/>:
5624      "update IANA requirements wrt Transfer-Coding values" (add the
5625      IANA Considerations subsection)
5626    </t>
5627  </list>
5631<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5633  Closed issues:
5634  <list style="symbols">
5635    <t>
5636      <eref target=""/>:
5637      "header parsing, treatment of leading and trailing OWS"
5638    </t>
5639  </list>
5642  Partly resolved issues:
5643  <list style="symbols">
5644    <t>
5645      <eref target=""/>:
5646      "Placement of 13.5.1 and 13.5.2"
5647    </t>
5648    <t>
5649      <eref target=""/>:
5650      "use of term "word" when talking about header structure"
5651    </t>
5652  </list>
5656<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5658  Closed issues:
5659  <list style="symbols">
5660    <t>
5661      <eref target=""/>:
5662      "Clarification of the term 'deflate'"
5663    </t>
5664    <t>
5665      <eref target=""/>:
5666      "OPTIONS * and proxies"
5667    </t>
5668    <t>
5669      <eref target=""/>:
5670      "MIME-Version not listed in P1, general header fields"
5671    </t>
5672    <t>
5673      <eref target=""/>:
5674      "IANA registry for content/transfer encodings"
5675    </t>
5676    <t>
5677      <eref target=""/>:
5678      "Case-sensitivity of HTTP-date"
5679    </t>
5680    <t>
5681      <eref target=""/>:
5682      "use of term "word" when talking about header structure"
5683    </t>
5684  </list>
5687  Partly resolved issues:
5688  <list style="symbols">
5689    <t>
5690      <eref target=""/>:
5691      "Term for the requested resource's URI"
5692    </t>
5693  </list>
5697<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5699  Closed issues:
5700  <list style="symbols">
5701    <t>
5702      <eref target=""/>:
5703      "Connection Closing"
5704    </t>
5705    <t>
5706      <eref target=""/>:
5707      "Delimiting messages with multipart/byteranges"
5708    </t>
5709    <t>
5710      <eref target=""/>:
5711      "Handling multiple Content-Length headers"
5712    </t>
5713    <t>
5714      <eref target=""/>:
5715      "Clarify entity / representation / variant terminology"
5716    </t>
5717    <t>
5718      <eref target=""/>:
5719      "consider removing the 'changes from 2068' sections"
5720    </t>
5721  </list>
5724  Partly resolved issues:
5725  <list style="symbols">
5726    <t>
5727      <eref target=""/>:
5728      "HTTP(s) URI scheme definitions"
5729    </t>
5730  </list>
5734<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5736  Closed issues:
5737  <list style="symbols">
5738    <t>
5739      <eref target=""/>:
5740      "Trailer requirements"
5741    </t>
5742    <t>
5743      <eref target=""/>:
5744      "Text about clock requirement for caches belongs in p6"
5745    </t>
5746    <t>
5747      <eref target=""/>:
5748      "effective request URI: handling of missing host in HTTP/1.0"
5749    </t>
5750    <t>
5751      <eref target=""/>:
5752      "confusing Date requirements for clients"
5753    </t>
5754  </list>
5757  Partly resolved issues:
5758  <list style="symbols">
5759    <t>
5760      <eref target=""/>:
5761      "Handling multiple Content-Length headers"
5762    </t>
5763  </list>
5767<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5769  Closed issues:
5770  <list style="symbols">
5771    <t>
5772      <eref target=""/>:
5773      "define 'transparent' proxy"
5774    </t>
5775    <t>
5776      <eref target=""/>:
5777      "Is * usable as a request-uri for new methods?"
5778    </t>
5779    <t>
5780      <eref target=""/>:
5781      "Migrate Upgrade details from RFC2817"
5782    </t>
5783    <t>
5784      <eref target=""/>:
5785      "untangle ABNFs for header fields"
5786    </t>
5787  </list>
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