source: draft-ietf-httpbis/latest/p1-messaging.xml @ 972

Last change on this file since 972 was 972, checked in by julian.reschke@…, 10 years ago

lowercase "effective request URI" throughout, use "target resource" instead of "resource identified by the effective request URI" where possible.

  • Property svn:eol-style set to native
File size: 240.3 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 "August">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x=''/>">
18  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#errors.or.incomplete.response.cache.behavior' xmlns:x=''/>">
19  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
20  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
21  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
22  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
23  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
24  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x=''/>">
25  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x=''/>">
26  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
27  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
28  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x=''/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
34  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc rfcedstyle="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x=''>
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Day Software">Day Software</organization>
60    <address>
61      <postal>
62        <street>23 Corporate Plaza DR, Suite 280</street>
63        <city>Newport Beach</city>
64        <region>CA</region>
65        <code>92660</code>
66        <country>USA</country>
67      </postal>
68      <phone>+1-949-706-5300</phone>
69      <facsimile>+1-949-706-5305</facsimile>
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 Systems">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.10"/>.
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.
690<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
691   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
692   as a layer above some other server(s) and translates the received
693   requests to the underlying server's protocol.  Gateways are often
694   used for load balancing or partitioning HTTP services across
695   multiple machines.
696   Unlike a proxy, a gateway receives requests as if it were the
697   origin server for the target resource; the requesting client
698   will not be aware that it is communicating with a gateway.
699   A gateway communicates with the client as if the gateway is the
700   origin server and thus is subject to all of the requirements on
701   origin servers for that connection.  A gateway communicates
702   with inbound servers using any protocol it desires, including
703   private extensions to HTTP that are outside the scope of this
704   specification.
706<t><iref primary="true" item="tunnel"/>
707   A "tunnel" acts as a blind relay between two connections
708   without changing the messages. Once active, a tunnel is not
709   considered a party to the HTTP communication, though the tunnel might
710   have been initiated by an HTTP request. A tunnel ceases to exist when
711   both ends of the relayed connection are closed. Tunnels are used to
712   extend a virtual connection through an intermediary, such as when
713   transport-layer security is used to establish private communication
714   through a shared firewall proxy.
718<section title="Caches" anchor="caches">
719<iref primary="true" item="cache"/>
721   A "cache" is a local store of previous response messages and the
722   subsystem that controls its message storage, retrieval, and deletion.
723   A cache stores cacheable responses in order to reduce the response
724   time and network bandwidth consumption on future, equivalent
725   requests. Any client or server &MAY; employ a cache, though a cache
726   cannot be used by a server while it is acting as a tunnel.
729   The effect of a cache is that the request/response chain is shortened
730   if one of the participants along the chain has a cached response
731   applicable to that request. The following illustrates the resulting
732   chain if B has a cached copy of an earlier response from O (via C)
733   for a request which has not been cached by UA or A.
735<figure><artwork type="drawing">
736            &gt;             &gt;
737       UA =========== A =========== B - - - - - - C - - - - - - O
738                  &lt;             &lt;
740<t><iref primary="true" item="cacheable"/>
741   A response is "cacheable" if a cache is allowed to store a copy of
742   the response message for use in answering subsequent requests.
743   Even when a response is cacheable, there might be additional
744   constraints placed by the client or by the origin server on when
745   that cached response can be used for a particular request. HTTP
746   requirements for cache behavior and cacheable responses are
747   defined in &caching-overview;. 
750   There are a wide variety of architectures and configurations
751   of caches and proxies deployed across the World Wide Web and
752   inside large organizations. These systems include national hierarchies
753   of proxy caches to save transoceanic bandwidth, systems that
754   broadcast or multicast cache entries, organizations that distribute
755   subsets of cached data via optical media, and so on.
759<section title="Transport Independence" anchor="transport-independence">
761  HTTP systems are used in a wide variety of environments, from
762  corporate intranets with high-bandwidth links to long-distance
763  communication over low-power radio links and intermittent connectivity.
766   HTTP communication usually takes place over TCP/IP connections. The
767   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
768   not preclude HTTP from being implemented on top of any other protocol
769   on the Internet, or on other networks. HTTP only presumes a reliable
770   transport; any protocol that provides such guarantees can be used;
771   the mapping of the HTTP/1.1 request and response structures onto the
772   transport data units of the protocol in question is outside the scope
773   of this specification.
776   In HTTP/1.0, most implementations used a new connection for each
777   request/response exchange. In HTTP/1.1, a connection might be used for
778   one or more request/response exchanges, although connections might be
779   closed for a variety of reasons (see <xref target="persistent.connections"/>).
783<section title="HTTP Version" anchor="http.version">
784  <x:anchor-alias value="HTTP-Version"/>
785  <x:anchor-alias value="HTTP-Prot-Name"/>
787   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
788   of the protocol. The protocol versioning policy is intended to allow
789   the sender to indicate the format of a message and its capacity for
790   understanding further HTTP communication, rather than the features
791   obtained via that communication. No change is made to the version
792   number for the addition of message components which do not affect
793   communication behavior or which only add to extensible field values.
794   The &lt;minor&gt; number is incremented when the changes made to the
795   protocol add features which do not change the general message parsing
796   algorithm, but which might add to the message semantics and imply
797   additional capabilities of the sender. The &lt;major&gt; number is
798   incremented when the format of a message within the protocol is
799   changed. See <xref target="RFC2145"/> for a fuller explanation.
802   The version of an HTTP message is indicated by an HTTP-Version field
803   in the first line of the message. HTTP-Version is case-sensitive.
805<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
806  <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>
807  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
810   Note that the major and minor numbers &MUST; be treated as separate
811   integers and that each &MAY; be incremented higher than a single digit.
812   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
813   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
814   &MUST-NOT; be sent.
817   An application that sends a request or response message that includes
818   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
819   with this specification. Applications that are at least conditionally
820   compliant with this specification &SHOULD; use an HTTP-Version of
821   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
822   not compatible with HTTP/1.0. For more details on when to send
823   specific HTTP-Version values, see <xref target="RFC2145"/>.
826   The HTTP version of an application is the highest HTTP version for
827   which the application is at least conditionally compliant.
830   Proxy and gateway applications need to be careful when forwarding
831   messages in protocol versions different from that of the application.
832   Since the protocol version indicates the protocol capability of the
833   sender, a proxy/gateway &MUST-NOT; send a message with a version
834   indicator which is greater than its actual version. If a higher
835   version request is received, the proxy/gateway &MUST; either downgrade
836   the request version, or respond with an error, or switch to tunnel
837   behavior.
840   Due to interoperability problems with HTTP/1.0 proxies discovered
841   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
842   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
843   they support. The proxy/gateway's response to that request &MUST; be in
844   the same major version as the request.
847  <t>
848    <x:h>Note:</x:h> Converting between versions of HTTP might involve modification
849    of header fields required or forbidden by the versions involved.
850  </t>
854<section title="Uniform Resource Identifiers" anchor="uri">
855<iref primary="true" item="resource"/>
857   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
858   throughout HTTP as the means for identifying resources. URI references
859   are used to target requests, indicate redirects, and define relationships.
860   HTTP does not limit what a resource might be; it merely defines an interface
861   that can be used to interact with a resource via HTTP. More information on
862   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
864  <x:anchor-alias value="URI-reference"/>
865  <x:anchor-alias value="absolute-URI"/>
866  <x:anchor-alias value="relative-part"/>
867  <x:anchor-alias value="authority"/>
868  <x:anchor-alias value="path-abempty"/>
869  <x:anchor-alias value="path-absolute"/>
870  <x:anchor-alias value="port"/>
871  <x:anchor-alias value="query"/>
872  <x:anchor-alias value="uri-host"/>
873  <x:anchor-alias value="partial-URI"/>
875   This specification adopts the definitions of "URI-reference",
876   "absolute-URI", "relative-part", "port", "host",
877   "path-abempty", "path-absolute", "query", and "authority" from
878   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
879   protocol elements that allow a relative URI without a fragment.
881<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"/>
882  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
883  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
884  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
885  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
886  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
887  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
888  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
889  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
890  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
892  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
895   Each protocol element in HTTP that allows a URI reference will indicate in
896   its ABNF production whether the element allows only a URI in absolute form
897   (absolute-URI), any relative reference (relative-ref), or some other subset
898   of the URI-reference grammar. Unless otherwise indicated, URI references
899   are parsed relative to the request target (the default base URI for both
900   the request and its corresponding response).
903<section title="http URI scheme" anchor="http.uri">
904  <x:anchor-alias value="http-URI"/>
905  <iref item="http URI scheme" primary="true"/>
906  <iref item="URI scheme" subitem="http" primary="true"/>
908   The "http" URI scheme is hereby defined for the purpose of minting
909   identifiers according to their association with the hierarchical
910   namespace governed by a potential HTTP origin server listening for
911   TCP connections on a given port.
912   The HTTP server is identified via the generic syntax's
913   <x:ref>authority</x:ref> component, which includes a host
914   identifier and optional TCP port, and the remainder of the URI is
915   considered to be identifying data corresponding to a resource for
916   which that server might provide an HTTP interface.
918<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
919  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
922   The host identifier within an <x:ref>authority</x:ref> component is
923   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
924   provided as an IP literal or IPv4 address, then the HTTP server is any
925   listener on the indicated TCP port at that IP address. If host is a
926   registered name, then that name is considered an indirect identifier
927   and the recipient might use a name resolution service, such as DNS,
928   to find the address of a listener for that host.
929   The host &MUST-NOT; be empty; if an "http" URI is received with an
930   empty host, then it &MUST; be rejected as invalid.
931   If the port subcomponent is empty or not given, then TCP port 80 is
932   assumed (the default reserved port for WWW services).
935   Regardless of the form of host identifier, access to that host is not
936   implied by the mere presence of its name or address. The host might or might
937   not exist and, even when it does exist, might or might not be running an
938   HTTP server or listening to the indicated port. The "http" URI scheme
939   makes use of the delegated nature of Internet names and addresses to
940   establish a naming authority (whatever entity has the ability to place
941   an HTTP server at that Internet name or address) and allows that
942   authority to determine which names are valid and how they might be used.
945   When an "http" URI is used within a context that calls for access to the
946   indicated resource, a client &MAY; attempt access by resolving
947   the host to an IP address, establishing a TCP connection to that address
948   on the indicated port, and sending an HTTP request message to the server
949   containing the URI's identifying data as described in <xref target="request"/>.
950   If the server responds to that request with a non-interim HTTP response
951   message, as described in <xref target="response"/>, then that response
952   is considered an authoritative answer to the client's request.
955   Although HTTP is independent of the transport protocol, the "http"
956   scheme is specific to TCP-based services because the name delegation
957   process depends on TCP for establishing authority.
958   An HTTP service based on some other underlying connection protocol
959   would presumably be identified using a different URI scheme, just as
960   the "https" scheme (below) is used for servers that require an SSL/TLS
961   transport layer on a connection. Other protocols might also be used to
962   provide access to "http" identified resources --- it is only the
963   authoritative interface used for mapping the namespace that is
964   specific to TCP.
967   The URI generic syntax for authority also includes a deprecated
968   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
969   for including user authentication information in the URI.  The userinfo
970   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
971   URI.  URI reference recipients &SHOULD; parse for the existence of
972   userinfo and treat its presence as an error, likely indicating that
973   the deprecated subcomponent is being used to obscure the authority
974   for the sake of phishing attacks.
978<section title="https URI scheme" anchor="https.uri">
979   <x:anchor-alias value="https-URI"/>
980   <iref item="https URI scheme"/>
981   <iref item="URI scheme" subitem="https"/>
983   The "https" URI scheme is hereby defined for the purpose of minting
984   identifiers according to their association with the hierarchical
985   namespace governed by a potential HTTP origin server listening for
986   SSL/TLS-secured connections on a given TCP port.
989   All of the requirements listed above for the "http" scheme are also
990   requirements for the "https" scheme, except that a default TCP port
991   of 443 is assumed if the port subcomponent is empty or not given,
992   and the TCP connection &MUST; be secured for privacy through the
993   use of strong encryption prior to sending the first HTTP request.
995<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
996  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
999   Unlike the "http" scheme, responses to "https" identified requests
1000   are never "public" and thus are ineligible for shared caching.
1001   Their default is "private" and might be further constrained via use
1002   of the Cache-Control header field.
1005   Resources made available via the "https" scheme have no shared
1006   identity with the "http" scheme even if their resource identifiers
1007   only differ by the single "s" in the scheme name.  They are
1008   different services governed by different authorities.  However,
1009   some extensions to HTTP that apply to entire host domains, such
1010   as the Cookie protocol, do allow one service to effect communication
1011   with the other services based on host domain matching.
1014   The process for authoritative access to an "https" identified
1015   resource is defined in <xref target="RFC2818"/>.
1019<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1021   Since the "http" and "https" schemes conform to the URI generic syntax,
1022   such URIs are normalized and compared according to the algorithm defined
1023   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1024   described above for each scheme.
1027   If the port is equal to the default port for a scheme, the normal
1028   form is to elide the port subcomponent. Likewise, an empty path
1029   component is equivalent to an absolute path of "/", so the normal
1030   form is to provide a path of "/" instead. The scheme and host
1031   are case-insensitive and normally provided in lowercase; all
1032   other components are compared in a case-sensitive manner.
1033   Characters other than those in the "reserved" set are equivalent
1034   to their percent-encoded octets (see <xref target="RFC3986"
1035   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1038   For example, the following three URIs are equivalent:
1040<figure><artwork type="example">
1046   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1047   If path-abempty is the empty string (i.e., there is no slash "/"
1048   path separator following the authority), then the "http" URI
1049   &MUST; be given as "/" when
1050   used as a request-target (<xref target="request-target"/>). If a proxy
1051   receives a host name which is not a fully qualified domain name, it
1052   &MAY; add its domain to the host name it received. If a proxy receives
1053   a fully qualified domain name, the proxy &MUST-NOT; change the host
1054   name.
1060<section title="HTTP Message" anchor="http.message">
1061<x:anchor-alias value="generic-message"/>
1062<x:anchor-alias value="message.types"/>
1063<x:anchor-alias value="HTTP-message"/>
1064<x:anchor-alias value="start-line"/>
1065<iref item="header section"/>
1066<iref item="headers"/>
1067<iref item="header field"/>
1069   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1070   characters in a format similar to the Internet Message Format
1071   <xref target="RFC5322"/>: zero or more header fields (collectively
1072   referred to as the "headers" or the "header section"), an empty line
1073   indicating the end of the header section, and an optional message-body.
1076   An HTTP message can either be a request from client to server or a
1077   response from server to client.  Syntactically, the two types of message
1078   differ only in the start-line, which is either a Request-Line (for requests)
1079   or a Status-Line (for responses), and in the algorithm for determining
1080   the length of the message-body (<xref target="message.body"/>).
1081   In theory, a client could receive requests and a server could receive
1082   responses, distinguishing them by their different start-line formats,
1083   but in practice servers are implemented to only expect a request
1084   (a response is interpreted as an unknown or invalid request method)
1085   and clients are implemented to only expect a response.
1087<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1088  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1089                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1090                    <x:ref>CRLF</x:ref>
1091                    [ <x:ref>message-body</x:ref> ]
1092  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1095   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1096   header field. The presence of whitespace might be an attempt to trick a
1097   noncompliant implementation of HTTP into ignoring that field or processing
1098   the next line as a new request, either of which might result in security
1099   issues when implementations within the request chain interpret the
1100   same message differently. HTTP/1.1 servers &MUST; reject such a message
1101   with a 400 (Bad Request) response.
1104<section title="Message Parsing Robustness" anchor="message.robustness">
1106   In the interest of robustness, servers &SHOULD; ignore at least one
1107   empty line received where a Request-Line is expected. In other words, if
1108   the server is reading the protocol stream at the beginning of a
1109   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1112   Some old HTTP/1.0 client implementations generate an extra CRLF
1113   after a POST request as a lame workaround for some early server
1114   applications that failed to read message-body content that was
1115   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1116   preface or follow a request with an extra CRLF.  If terminating
1117   the request message-body with a line-ending is desired, then the
1118   client &MUST; include the terminating CRLF octets as part of the
1119   message-body length.
1122   The normal procedure for parsing an HTTP message is to read the
1123   start-line into a structure, read each header field into a hash
1124   table by field name until the empty line, and then use the parsed
1125   data to determine if a message-body is expected.  If a message-body
1126   has been indicated, then it is read as a stream until an amount
1127   of octets equal to the message-body length is read or the connection
1128   is closed.  Care must be taken to parse an HTTP message as a sequence
1129   of octets in an encoding that is a superset of US-ASCII.  Attempting
1130   to parse HTTP as a stream of Unicode characters in a character encoding
1131   like UTF-16 might introduce security flaws due to the differing ways
1132   that such parsers interpret invalid characters.
1135   HTTP allows the set of defined header fields to be extended without
1136   changing the protocol version (see <xref target="header.field.registration"/>).
1137   However, such fields might not be recognized by a downstream recipient
1138   and might be stripped by non-transparent intermediaries.
1139   Unrecognized header fields &MUST; be forwarded by transparent proxies
1140   and &SHOULD; be ignored by a recipient.
1144<section title="Header Fields" anchor="header.fields">
1145  <x:anchor-alias value="header-field"/>
1146  <x:anchor-alias value="field-content"/>
1147  <x:anchor-alias value="field-name"/>
1148  <x:anchor-alias value="field-value"/>
1149  <x:anchor-alias value="OWS"/>
1151   Each HTTP header field consists of a case-insensitive field name
1152   followed by a colon (":"), optional whitespace, and the field value.
1154<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"/>
1155  <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>
1156  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1157  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1158  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1161   No whitespace is allowed between the header field name and colon. For
1162   security reasons, any request message received containing such whitespace
1163   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1164   &MUST; remove any such whitespace from a response message before
1165   forwarding the message downstream.
1168   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1169   preferred. The field value does not include any leading or trailing white
1170   space: OWS occurring before the first non-whitespace character of the
1171   field value or after the last non-whitespace character of the field value
1172   is ignored and &SHOULD; be removed before further processing (as this does
1173   not change the meaning of the header field).
1176   The order in which header fields with differing field names are
1177   received is not significant. However, it is "good practice" to send
1178   header fields that contain control data first, such as Host on
1179   requests and Date on responses, so that implementations can decide
1180   when not to handle a message as early as possible.  A server &MUST;
1181   wait until the entire header section is received before interpreting
1182   a request message, since later header fields might include conditionals,
1183   authentication credentials, or deliberately misleading duplicate
1184   header fields that would impact request processing.
1187   Multiple header fields with the same field name &MUST-NOT; be
1188   sent in a message unless the entire field value for that
1189   header field is defined as a comma-separated list [i.e., #(values)].
1190   Multiple header fields with the same field name can be combined into
1191   one "field-name: field-value" pair, without changing the semantics of the
1192   message, by appending each subsequent field value to the combined
1193   field value in order, separated by a comma. The order in which
1194   header fields with the same field name are received is therefore
1195   significant to the interpretation of the combined field value;
1196   a proxy &MUST-NOT; change the order of these field values when
1197   forwarding a message.
1200  <t>
1201   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1202   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1203   can occur multiple times, but does not use the list syntax, and thus cannot
1204   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1205   for details.) Also note that the Set-Cookie2 header specified in
1206   <xref target="RFC2965"/> does not share this problem.
1207  </t>
1210   Historically, HTTP header field values could be extended over multiple
1211   lines by preceding each extra line with at least one space or horizontal
1212   tab character (line folding). This specification deprecates such line
1213   folding except within the message/http media type
1214   (<xref target=""/>).
1215   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1216   (i.e., that contain any field-content that matches the obs-fold rule) unless
1217   the message is intended for packaging within the message/http media type.
1218   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1219   obs-fold whitespace with a single SP prior to interpreting the field value
1220   or forwarding the message downstream.
1223   Historically, HTTP has allowed field content with text in the ISO-8859-1
1224   <xref target="ISO-8859-1"/> character encoding and supported other
1225   character sets only through use of <xref target="RFC2047"/> encoding.
1226   In practice, most HTTP header field values use only a subset of the
1227   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1228   header fields &SHOULD; limit their field values to US-ASCII characters.
1229   Recipients &SHOULD; treat other (obs-text) octets in field content as
1230   opaque data.
1232<t anchor="rule.comment">
1233  <x:anchor-alias value="comment"/>
1234  <x:anchor-alias value="ctext"/>
1235   Comments can be included in some HTTP header fields by surrounding
1236   the comment text with parentheses. Comments are only allowed in
1237   fields containing "comment" as part of their field value definition.
1239<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1240  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1241  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1242                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1244<t anchor="rule.quoted-cpair">
1245  <x:anchor-alias value="quoted-cpair"/>
1246   The backslash character ("\") can be used as a single-character
1247   quoting mechanism within comment constructs:
1249<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1250  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1253   Producers &SHOULD-NOT; escape characters that do not require escaping
1254   (i.e., other than the backslash character "\" and the parentheses "(" and
1255   ")").
1259<section title="Message Body" anchor="message.body">
1260  <x:anchor-alias value="message-body"/>
1262   The message-body (if any) of an HTTP message is used to carry the
1263   payload body associated with the request or response.
1265<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1266  <x:ref>message-body</x:ref> = *OCTET
1269   The message-body differs from the payload body only when a transfer-coding
1270   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1271   applied to a payload in order to form the message-body, the
1272   Transfer-Encoding header field &MUST; contain the list of
1273   transfer-codings applied. Transfer-Encoding is a property of the message,
1274   not of the payload, and thus &MAY; be added or removed by any implementation
1275   along the request/response chain under the constraints found in
1276   <xref target="transfer.codings"/>.
1279   The rules for when a message-body is allowed in a message differ for
1280   requests and responses.
1283   The presence of a message-body in a request is signaled by the
1284   inclusion of a Content-Length or Transfer-Encoding header field in
1285   the request's header fields, even if the request method does not
1286   define any use for a message-body.  This allows the request
1287   message framing algorithm to be independent of method semantics.
1290   For response messages, whether or not a message-body is included with
1291   a message is dependent on both the request method and the response
1292   status code (<xref target="status.code.and.reason.phrase"/>).
1293   Responses to the HEAD request method never include a message-body
1294   because the associated response header fields (e.g., Transfer-Encoding,
1295   Content-Length, etc.) only indicate what their values would have been
1296   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1297   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1298   All other responses do include a message-body, although the body
1299   &MAY; be of zero length.
1302   The length of the message-body is determined by one of the following
1303   (in order of precedence):
1306  <list style="numbers">
1307    <x:lt><t>
1308     Any response to a HEAD request and any response with a status
1309     code of 100-199, 204, or 304 is always terminated by the first
1310     empty line after the header fields, regardless of the header
1311     fields present in the message, and thus cannot contain a message-body.
1312    </t></x:lt>
1313    <x:lt><t>
1314     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1315     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1316     is the final encoding, the message-body length is determined by reading
1317     and decoding the chunked data until the transfer-coding indicates the
1318     data is complete.
1319    </t>
1320    <t>
1321     If a Transfer-Encoding header field is present in a response and the
1322     "chunked" transfer-coding is not the final encoding, the message-body
1323     length is determined by reading the connection until it is closed by
1324     the server.
1325     If a Transfer-Encoding header field is present in a request and the
1326     "chunked" transfer-coding is not the final encoding, the message-body
1327     length cannot be determined reliably; the server &MUST; respond with
1328     the 400 (Bad Request) status code and then close the connection.
1329    </t>
1330    <t>
1331     If a message is received with both a Transfer-Encoding header field and a
1332     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1333     Such a message might indicate an attempt to perform request or response
1334     smuggling (bypass of security-related checks on message routing or content)
1335     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1336     be removed, prior to forwarding the message downstream, or replaced with
1337     the real message-body length after the transfer-coding is decoded.
1338    </t></x:lt>
1339    <x:lt><t>
1340     If a message is received without Transfer-Encoding and with either
1341     multiple Content-Length header fields or a single Content-Length header
1342     field with an invalid value, then the message framing is invalid and
1343     &MUST; be treated as an error to prevent request or response smuggling.
1344     If this is a request message, the server &MUST; respond with
1345     a 400 (Bad Request) status code and then close the connection.
1346     If this is a response message received by a proxy or gateway, the proxy
1347     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1348     status code as its downstream response, and then close the connection.
1349     If this is a response message received by a user-agent, the message-body
1350     length is determined by reading the connection until it is closed;
1351     an error &SHOULD; be indicated to the user.
1352    </t></x:lt>
1353    <x:lt><t>
1354     If a valid Content-Length header field (<xref target="header.content-length"/>)
1355     is present without Transfer-Encoding, its decimal value defines the
1356     message-body length in octets.  If the actual number of octets sent in
1357     the message is less than the indicated Content-Length, the recipient
1358     &MUST; consider the message to be incomplete and treat the connection
1359     as no longer usable.
1360     If the actual number of octets sent in the message is more than the indicated
1361     Content-Length, the recipient &MUST; only process the message-body up to the
1362     field value's number of octets; the remainder of the message &MUST; either
1363     be discarded or treated as the next message in a pipeline.  For the sake of
1364     robustness, a user-agent &MAY; attempt to detect and correct such an error
1365     in message framing if it is parsing the response to the last request on
1366     on a connection and the connection has been closed by the server.
1367    </t></x:lt>
1368    <x:lt><t>
1369     If this is a request message and none of the above are true, then the
1370     message-body length is zero (no message-body is present).
1371    </t></x:lt>
1372    <x:lt><t>
1373     Otherwise, this is a response message without a declared message-body
1374     length, so the message-body length is determined by the number of octets
1375     received prior to the server closing the connection.
1376    </t></x:lt>
1377  </list>
1380   Since there is no way to distinguish a successfully completed,
1381   close-delimited message from a partially-received message interrupted
1382   by network failure, implementations &SHOULD; use encoding or
1383   length-delimited messages whenever possible.  The close-delimiting
1384   feature exists primarily for backwards compatibility with HTTP/1.0.
1387   A server &MAY; reject a request that contains a message-body but
1388   not a Content-Length by responding with 411 (Length Required).
1391   Unless a transfer-coding other than "chunked" has been applied,
1392   a client that sends a request containing a message-body &SHOULD;
1393   use a valid Content-Length header field if the message-body length
1394   is known in advance, rather than the "chunked" encoding, since some
1395   existing services respond to "chunked" with a 411 (Length Required)
1396   status code even though they understand the chunked encoding.  This
1397   is typically because such services are implemented via a gateway that
1398   requires a content-length in advance of being called and the server
1399   is unable or unwilling to buffer the entire request before processing.
1402   A client that sends a request containing a message-body &MUST; include a
1403   valid Content-Length header field if it does not know the server will
1404   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1405   of specific user configuration or by remembering the version of a prior
1406   received response.
1409   Request messages that are prematurely terminated, possibly due to a
1410   cancelled connection or a server-imposed time-out exception, &MUST;
1411   result in closure of the connection; sending an HTTP/1.1 error response
1412   prior to closing the connection is &OPTIONAL;.
1413   Response messages that are prematurely terminated, usually by closure
1414   of the connection prior to receiving the expected number of octets or by
1415   failure to decode a transfer-encoded message-body, &MUST; be recorded
1416   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1417   message-body as if it were complete (i.e., some indication must be given
1418   to the user that an error occurred).  Cache requirements for incomplete
1419   responses are defined in &cache-incomplete;.
1422   A server &MUST; read the entire request message-body or close
1423   the connection after sending its response, since otherwise the
1424   remaining data on a persistent connection would be misinterpreted
1425   as the next request.  Likewise,
1426   a client &MUST; read the entire response message-body if it intends
1427   to reuse the same connection for a subsequent request.  Pipelining
1428   multiple requests on a connection is described in <xref target="pipelining"/>.
1432<section title="General Header Fields" anchor="general.header.fields">
1433  <x:anchor-alias value="general-header"/>
1435   There are a few header fields which have general applicability for
1436   both request and response messages, but which do not apply to the
1437   payload being transferred. These header fields apply only to the
1438   message being transmitted.
1440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1441  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1442                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1443                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1444                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1445                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1446                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1447                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1448                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1449                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1450                 / <x:ref>MIME-Version</x:ref>             ; &header-mime-version;
1453   General-header field names can be extended reliably only in
1454   combination with a change in the protocol version. However, new or
1455   experimental header fields might be given the semantics of general
1456   header fields if all parties in the communication recognize them to
1457   be general-header fields.
1462<section title="Request" anchor="request">
1463  <x:anchor-alias value="Request"/>
1465   A request message from a client to a server includes, within the
1466   first line of that message, the method to be applied to the resource,
1467   the identifier of the resource, and the protocol version in use.
1469<!--                 Host                      ; should be moved here eventually -->
1470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1471  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1472                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1473                  <x:ref>CRLF</x:ref>
1474                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1477<section title="Request-Line" anchor="request-line">
1478  <x:anchor-alias value="Request-Line"/>
1480   The Request-Line begins with a method token, followed by the
1481   request-target and the protocol version, and ending with CRLF. The
1482   elements are separated by SP characters. No CR or LF is allowed
1483   except in the final CRLF sequence.
1485<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1486  <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>
1489<section title="Method" anchor="method">
1490  <x:anchor-alias value="Method"/>
1492   The Method  token indicates the method to be performed on the
1493   resource identified by the request-target. The method is case-sensitive.
1495<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1496  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1500<section title="request-target" anchor="request-target">
1501  <x:anchor-alias value="request-target"/>
1503   The request-target
1504   identifies the resource upon which to apply the request.
1506<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1507  <x:ref>request-target</x:ref> = "*"
1508                 / <x:ref>absolute-URI</x:ref>
1509                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1510                 / <x:ref>authority</x:ref>
1513   The four options for request-target are dependent on the nature of the
1514   request.
1517   The asterisk "*" means that the request does not apply to a
1518   particular resource, but to the server itself, and is only allowed
1519   when the method used does not necessarily apply to a resource. One
1520   example would be
1522<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1523OPTIONS * HTTP/1.1
1526   The absolute-URI form is &REQUIRED; when the request is being made to a
1527   proxy. The proxy is requested to forward the request or service it
1528   from a valid cache, and return the response. Note that the proxy &MAY;
1529   forward the request on to another proxy or directly to the server
1530   specified by the absolute-URI. In order to avoid request loops, a
1531   proxy &MUST; be able to recognize all of its server names, including
1532   any aliases, local variations, and the numeric IP address. An example
1533   Request-Line would be:
1535<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1536GET HTTP/1.1
1539   To allow for transition to absolute-URIs in all requests in future
1540   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1541   form in requests, even though HTTP/1.1 clients will only generate
1542   them in requests to proxies.
1545   The authority form is only used by the CONNECT method (&CONNECT;).
1548   The most common form of request-target is that used to identify a
1549   resource on an origin server or gateway. In this case the absolute
1550   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1551   the request-target, and the network location of the URI (authority) &MUST;
1552   be transmitted in a Host header field. For example, a client wishing
1553   to retrieve the resource above directly from the origin server would
1554   create a TCP connection to port 80 of the host "" and send
1555   the lines:
1557<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1558GET /pub/WWW/TheProject.html HTTP/1.1
1562   followed by the remainder of the Request. Note that the absolute path
1563   cannot be empty; if none is present in the original URI, it &MUST; be
1564   given as "/" (the server root).
1567   If a proxy receives a request without any path in the request-target and
1568   the method specified is capable of supporting the asterisk form of
1569   request-target, then the last proxy on the request chain &MUST; forward the
1570   request with "*" as the final request-target.
1573   For example, the request
1574</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1578  would be forwarded by the proxy as
1579</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1580OPTIONS * HTTP/1.1
1584   after connecting to port 8001 of host "".
1588   The request-target is transmitted in the format specified in
1589   <xref target="http.uri"/>. If the request-target is percent-encoded
1590   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1591   &MUST; decode the request-target in order to
1592   properly interpret the request. Servers &SHOULD; respond to invalid
1593   request-targets with an appropriate status code.
1596   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1597   received request-target when forwarding it to the next inbound server,
1598   except as noted above to replace a null path-absolute with "/" or "*".
1601  <t>
1602    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1603    meaning of the request when the origin server is improperly using
1604    a non-reserved URI character for a reserved purpose.  Implementors
1605    need to be aware that some pre-HTTP/1.1 proxies have been known to
1606    rewrite the request-target.
1607  </t>
1610   HTTP does not place a pre-defined limit on the length of a request-target.
1611   A server &MUST; be prepared to receive URIs of unbounded length and
1612   respond with the 414 (URI Too Long) status code if the received
1613   request-target would be longer than the server wishes to handle
1614   (see &status-414;).
1617   Various ad-hoc limitations on request-target length are found in practice.
1618   It is &RECOMMENDED; that all HTTP senders and recipients support
1619   request-target lengths of 8000 or more octets.
1622  <t>
1623    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1624    are not part of the request-target and thus will not be transmitted
1625    in an HTTP request.
1626  </t>
1631<section title="The Resource Identified by a Request" anchor="">
1633   The exact resource identified by an Internet request is determined by
1634   examining both the request-target and the Host header field.
1637   An origin server that does not allow resources to differ by the
1638   requested host &MAY; ignore the Host header field value when
1639   determining the resource identified by an HTTP/1.1 request. (But see
1640   <xref target=""/>
1641   for other requirements on Host support in HTTP/1.1.)
1644   An origin server that does differentiate resources based on the host
1645   requested (sometimes referred to as virtual hosts or vanity host
1646   names) &MUST; use the following rules for determining the requested
1647   resource on an HTTP/1.1 request:
1648  <list style="numbers">
1649    <t>If request-target is an absolute-URI, the host is part of the
1650     request-target. Any Host header field value in the request &MUST; be
1651     ignored.</t>
1652    <t>If the request-target is not an absolute-URI, and the request includes
1653     a Host header field, the host is determined by the Host header
1654     field value.</t>
1655    <t>If the host as determined by rule 1 or 2 is not a valid host on
1656     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1657  </list>
1660   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1661   attempt to use heuristics (e.g., examination of the URI path for
1662   something unique to a particular host) in order to determine what
1663   exact resource is being requested.
1667<section title="Effective Request URI" anchor="effective.request.uri">
1668  <iref primary="true" item="effective request URI"/>
1669  <iref primary="true" item="target resource"/>
1671   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1672   for the target resource; instead, the URI needs to be inferred from the
1673   request-target, Host header field, and connection context. The result of
1674   this process is called the "effective request URI".  The "target resource"
1675   is the resource identified by the effective request URI.
1678   If the request-target is an absolute-URI, then the effective request URI is
1679   the request-target.
1682   If the request-target uses the path-absolute (plus optional query) syntax
1683   or if it is just the asterisk "*", then the effective request URI is
1684   constructed by concatenating
1687  <list style="symbols">
1688    <t>
1689      the scheme name: "http" if the request was received over an insecure
1690      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1691      connection,
1692    </t>
1693    <t>
1694      the character sequence "://",
1695    </t>
1696    <t>
1697      the authority component, as specified in the Host header
1698      (<xref target=""/>) and determined by the rules in
1699      <xref target=""/>,
1700      <cref anchor="effrequri-nohost" source="jre">Do we need to include the handling of missing hosts in HTTP/1.0 messages, as
1701      described in <xref target=""/>? -- See <eref target=""/></cref>
1702      and
1703    </t>
1704    <t>
1705      the request-target obtained from the Request-Line, unless the
1706      request-target is just the asterisk "*".
1707    </t>
1708  </list>
1711   Otherwise, when request-target uses the authority form, the effective
1712   Request URI is undefined.
1716   Example 1: the effective request URI for the message
1718<artwork type="example" x:indent-with="  ">
1719GET /pub/WWW/TheProject.html HTTP/1.1
1723  (received over an insecure TCP connection) is "http", plus "://", plus the
1724  authority component "", plus the request-target
1725  "/pub/WWW/TheProject.html", thus
1726  "".
1731   Example 2: the effective request URI for the message
1733<artwork type="example" x:indent-with="  ">
1734GET * HTTP/1.1
1738  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1739  authority component "", thus "".
1743   Effective request URIs are compared using the rules described in
1744   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1745   be treated as equivalent to an absolute path of "/".
1752<section title="Response" anchor="response">
1753  <x:anchor-alias value="Response"/>
1755   After receiving and interpreting a request message, a server responds
1756   with an HTTP response message.
1758<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1759  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1760                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1761                  <x:ref>CRLF</x:ref>
1762                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1765<section title="Status-Line" anchor="status-line">
1766  <x:anchor-alias value="Status-Line"/>
1768   The first line of a Response message is the Status-Line, consisting
1769   of the protocol version followed by a numeric status code and its
1770   associated textual phrase, with each element separated by SP
1771   characters. No CR or LF is allowed except in the final CRLF sequence.
1773<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1774  <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>
1777<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1778  <x:anchor-alias value="Reason-Phrase"/>
1779  <x:anchor-alias value="Status-Code"/>
1781   The Status-Code element is a 3-digit integer result code of the
1782   attempt to understand and satisfy the request. These codes are fully
1783   defined in &status-codes;.  The Reason Phrase exists for the sole
1784   purpose of providing a textual description associated with the numeric
1785   status code, out of deference to earlier Internet application protocols
1786   that were more frequently used with interactive text clients.
1787   A client &SHOULD; ignore the content of the Reason Phrase.
1790   The first digit of the Status-Code defines the class of response. The
1791   last two digits do not have any categorization role. There are 5
1792   values for the first digit:
1793  <list style="symbols">
1794    <t>
1795      1xx: Informational - Request received, continuing process
1796    </t>
1797    <t>
1798      2xx: Success - The action was successfully received,
1799        understood, and accepted
1800    </t>
1801    <t>
1802      3xx: Redirection - Further action must be taken in order to
1803        complete the request
1804    </t>
1805    <t>
1806      4xx: Client Error - The request contains bad syntax or cannot
1807        be fulfilled
1808    </t>
1809    <t>
1810      5xx: Server Error - The server failed to fulfill an apparently
1811        valid request
1812    </t>
1813  </list>
1815<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1816  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1817  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1825<section title="Protocol Parameters" anchor="protocol.parameters">
1827<section title="Date/Time Formats: Full Date" anchor="">
1828  <x:anchor-alias value="HTTP-date"/>
1830   HTTP applications have historically allowed three different formats
1831   for date/time stamps.
1832   However, the preferred format is
1833   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1835<figure><artwork type="example" x:indent-with="  ">
1836Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1839   The other formats are described here only for compatibility with obsolete
1840   implementations.
1842<figure><artwork type="example" x:indent-with="  ">
1843Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1844Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1847   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1848   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1849   only generate the RFC 1123 format for representing HTTP-date values
1850   in header fields. See <xref target="tolerant.applications"/> for further information.
1853   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1854   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1855   equal to UTC (Coordinated Universal Time). This is indicated in the
1856   first two formats by the inclusion of "GMT" as the three-letter
1857   abbreviation for time zone, and &MUST; be assumed when reading the
1858   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1859   additional whitespace beyond that specifically included as SP in the
1860   grammar.
1862<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1863  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1865<t anchor="">
1866  <x:anchor-alias value="rfc1123-date"/>
1867  <x:anchor-alias value="time-of-day"/>
1868  <x:anchor-alias value="hour"/>
1869  <x:anchor-alias value="minute"/>
1870  <x:anchor-alias value="second"/>
1871  <x:anchor-alias value="day-name"/>
1872  <x:anchor-alias value="day"/>
1873  <x:anchor-alias value="month"/>
1874  <x:anchor-alias value="year"/>
1875  <x:anchor-alias value="GMT"/>
1876  Preferred format:
1878<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"/>
1879  <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>
1881  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1882               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1883               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1884               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1885               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1886               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1887               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1889  <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>
1890               ; e.g., 02 Jun 1982
1892  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1893  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1894               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1895               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1896               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1897               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1898               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1899               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1900               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1901               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1902               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1903               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1904               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1905  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1907  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1909  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1910                 ; 00:00:00 - 23:59:59
1912  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1913  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1914  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1917  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1918  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1919  same as those defined for the RFC 5322 constructs
1920  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1922<t anchor="">
1923  <x:anchor-alias value="obs-date"/>
1924  <x:anchor-alias value="rfc850-date"/>
1925  <x:anchor-alias value="asctime-date"/>
1926  <x:anchor-alias value="date1"/>
1927  <x:anchor-alias value="date2"/>
1928  <x:anchor-alias value="date3"/>
1929  <x:anchor-alias value="rfc1123-date"/>
1930  <x:anchor-alias value="day-name-l"/>
1931  Obsolete formats:
1933<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1934  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1936<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1937  <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>
1938  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1939                 ; day-month-year (e.g., 02-Jun-82)
1941  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1942         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1943         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1944         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1945         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1946         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1947         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1949<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1950  <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>
1951  <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> ))
1952                 ; month day (e.g., Jun  2)
1955  <t>
1956    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1957    accepting date values that might have been sent by non-HTTP
1958    applications, as is sometimes the case when retrieving or posting
1959    messages via proxies/gateways to SMTP or NNTP.
1960  </t>
1963  <t>
1964    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1965    to their usage within the protocol stream. Clients and servers are
1966    not required to use these formats for user presentation, request
1967    logging, etc.
1968  </t>
1972<section title="Transfer Codings" anchor="transfer.codings">
1973  <x:anchor-alias value="transfer-coding"/>
1974  <x:anchor-alias value="transfer-extension"/>
1976   Transfer-coding values are used to indicate an encoding
1977   transformation that has been, can be, or might need to be applied to a
1978   payload body in order to ensure "safe transport" through the network.
1979   This differs from a content coding in that the transfer-coding is a
1980   property of the message rather than a property of the representation
1981   that is being transferred.
1983<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1984  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1985                          / "compress" ; <xref target="compress.coding"/>
1986                          / "deflate" ; <xref target="deflate.coding"/>
1987                          / "gzip" ; <xref target="gzip.coding"/>
1988                          / <x:ref>transfer-extension</x:ref>
1989  <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> )
1991<t anchor="rule.parameter">
1992  <x:anchor-alias value="attribute"/>
1993  <x:anchor-alias value="transfer-parameter"/>
1994  <x:anchor-alias value="value"/>
1995   Parameters are in the form of attribute/value pairs.
1997<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"/>
1998  <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>
1999  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2000  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2003   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2004   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2005   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2008   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2009   MIME, which were designed to enable safe transport of binary data over a
2010   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2011   However, safe transport
2012   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2013   the only unsafe characteristic of message-bodies is the difficulty in
2014   determining the exact message body length (<xref target="message.body"/>),
2015   or the desire to encrypt data over a shared transport.
2018   A server that receives a request message with a transfer-coding it does
2019   not understand &SHOULD; respond with 501 (Not Implemented) and then
2020   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2021   client.
2024<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2025  <iref item="chunked (Coding Format)"/>
2026  <iref item="Coding Format" subitem="chunked"/>
2027  <x:anchor-alias value="chunk"/>
2028  <x:anchor-alias value="Chunked-Body"/>
2029  <x:anchor-alias value="chunk-data"/>
2030  <x:anchor-alias value="chunk-ext"/>
2031  <x:anchor-alias value="chunk-ext-name"/>
2032  <x:anchor-alias value="chunk-ext-val"/>
2033  <x:anchor-alias value="chunk-size"/>
2034  <x:anchor-alias value="last-chunk"/>
2035  <x:anchor-alias value="trailer-part"/>
2036  <x:anchor-alias value="quoted-str-nf"/>
2037  <x:anchor-alias value="qdtext-nf"/>
2039   The chunked encoding modifies the body of a message in order to
2040   transfer it as a series of chunks, each with its own size indicator,
2041   followed by an &OPTIONAL; trailer containing header fields. This
2042   allows dynamically produced content to be transferred along with the
2043   information necessary for the recipient to verify that it has
2044   received the full message.
2046<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"/>
2047  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2048                   <x:ref>last-chunk</x:ref>
2049                   <x:ref>trailer-part</x:ref>
2050                   <x:ref>CRLF</x:ref>
2052  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2053                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2054  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2055  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2057  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2058                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2059  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2060  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2061  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2062  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2064  <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>
2065                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2066  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2067                 ; <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>
2070   The chunk-size field is a string of hex digits indicating the size of
2071   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2072   zero, followed by the trailer, which is terminated by an empty line.
2075   The trailer allows the sender to include additional HTTP header
2076   fields at the end of the message. The Trailer header field can be
2077   used to indicate which header fields are included in a trailer (see
2078   <xref target="header.trailer"/>).
2081   A server using chunked transfer-coding in a response &MUST-NOT; use the
2082   trailer for any header fields unless at least one of the following is
2083   true:
2084  <list style="numbers">
2085    <t>the request included a TE header field that indicates "trailers" is
2086     acceptable in the transfer-coding of the  response, as described in
2087     <xref target="header.te"/>; or,</t>
2089    <t>the server is the origin server for the response, the trailer
2090     fields consist entirely of optional metadata, and the recipient
2091     could use the message (in a manner acceptable to the origin server)
2092     without receiving this metadata.  In other words, the origin server
2093     is willing to accept the possibility that the trailer fields might
2094     be silently discarded along the path to the client.</t>
2095  </list>
2098   This requirement prevents an interoperability failure when the
2099   message is being received by an HTTP/1.1 (or later) proxy and
2100   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2101   compliance with the protocol would have necessitated a possibly
2102   infinite buffer on the proxy.
2105   A process for decoding the "chunked" transfer-coding
2106   can be represented in pseudo-code as:
2108<figure><artwork type="code">
2109  length := 0
2110  read chunk-size, chunk-ext (if any) and CRLF
2111  while (chunk-size &gt; 0) {
2112     read chunk-data and CRLF
2113     append chunk-data to decoded-body
2114     length := length + chunk-size
2115     read chunk-size and CRLF
2116  }
2117  read header-field
2118  while (header-field not empty) {
2119     append header-field to existing header fields
2120     read header-field
2121  }
2122  Content-Length := length
2123  Remove "chunked" from Transfer-Encoding
2126   All HTTP/1.1 applications &MUST; be able to receive and decode the
2127   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2128   they do not understand.
2131   Since "chunked" is the only transfer-coding required to be understood
2132   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2133   on a persistent connection.  Whenever a transfer-coding is applied to
2134   a payload body in a request, the final transfer-coding applied &MUST;
2135   be "chunked".  If a transfer-coding is applied to a response payload
2136   body, then either the final transfer-coding applied &MUST; be "chunked"
2137   or the message &MUST; be terminated by closing the connection. When the
2138   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2139   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2140   be applied more than once in a message-body.
2144<section title="Compression Codings" anchor="compression.codings">
2146   The codings defined below can be used to compress the payload of a
2147   message.
2150   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2151   is not desirable and is discouraged for future encodings. Their
2152   use here is representative of historical practice, not good
2153   design.
2156   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2157   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2158   equivalent to "gzip" and "compress" respectively.
2161<section title="Compress Coding" anchor="compress.coding">
2162<iref item="compress (Coding Format)"/>
2163<iref item="Coding Format" subitem="compress"/>
2165   The "compress" format is produced by the common UNIX file compression
2166   program "compress". This format is an adaptive Lempel-Ziv-Welch
2167   coding (LZW).
2171<section title="Deflate Coding" anchor="deflate.coding">
2172<iref item="deflate (Coding Format)"/>
2173<iref item="Coding Format" subitem="deflate"/>
2175   The "deflate" format is defined as the "deflate" compression mechanism
2176   (described in <xref target="RFC1951"/>) used inside the "zlib"
2177   data format (<xref target="RFC1950"/>).
2180  <t>
2181    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2182    compressed data without the zlib wrapper.
2183   </t>
2187<section title="Gzip Coding" anchor="gzip.coding">
2188<iref item="gzip (Coding Format)"/>
2189<iref item="Coding Format" subitem="gzip"/>
2191   The "gzip" format is produced by the file compression program
2192   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2193   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2199<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2201   The HTTP Transfer Coding Registry defines the name space for the transfer
2202   coding names.
2205   Registrations &MUST; include the following fields:
2206   <list style="symbols">
2207     <t>Name</t>
2208     <t>Description</t>
2209     <t>Pointer to specification text</t>
2210   </list>
2213   Names of transfer codings &MUST-NOT; overlap with names of content codings
2214   (&content-codings;), unless the encoding transformation is identical (as it
2215   is the case for the compression codings defined in
2216   <xref target="compression.codings"/>).
2219   Values to be added to this name space require a specification
2220   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2221   conform to the purpose of transfer coding defined in this section.
2224   The registry itself is maintained at
2225   <eref target=""/>.
2230<section title="Product Tokens" anchor="product.tokens">
2231  <x:anchor-alias value="product"/>
2232  <x:anchor-alias value="product-version"/>
2234   Product tokens are used to allow communicating applications to
2235   identify themselves by software name and version. Most fields using
2236   product tokens also allow sub-products which form a significant part
2237   of the application to be listed, separated by whitespace. By
2238   convention, the products are listed in order of their significance
2239   for identifying the application.
2241<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2242  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2243  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2246   Examples:
2248<figure><artwork type="example">
2249  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2250  Server: Apache/0.8.4
2253   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2254   used for advertising or other non-essential information. Although any
2255   token character &MAY; appear in a product-version, this token &SHOULD;
2256   only be used for a version identifier (i.e., successive versions of
2257   the same product &SHOULD; only differ in the product-version portion of
2258   the product value).
2262<section title="Quality Values" anchor="quality.values">
2263  <x:anchor-alias value="qvalue"/>
2265   Both transfer codings (TE request header, <xref target="header.te"/>)
2266   and content negotiation (&content.negotiation;) use short "floating point"
2267   numbers to indicate the relative importance ("weight") of various
2268   negotiable parameters.  A weight is normalized to a real number in
2269   the range 0 through 1, where 0 is the minimum and 1 the maximum
2270   value. If a parameter has a quality value of 0, then content with
2271   this parameter is "not acceptable" for the client. HTTP/1.1
2272   applications &MUST-NOT; generate more than three digits after the
2273   decimal point. User configuration of these values &SHOULD; also be
2274   limited in this fashion.
2276<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2277  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2278                 / ( "1" [ "." 0*3("0") ] )
2281  <t>
2282     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2283     relative degradation in desired quality.
2284  </t>
2290<section title="Connections" anchor="connections">
2292<section title="Persistent Connections" anchor="persistent.connections">
2294<section title="Purpose" anchor="persistent.purpose">
2296   Prior to persistent connections, a separate TCP connection was
2297   established to fetch each URL, increasing the load on HTTP servers
2298   and causing congestion on the Internet. The use of inline images and
2299   other associated data often requires a client to make multiple
2300   requests of the same server in a short amount of time. Analysis of
2301   these performance problems and results from a prototype
2302   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2303   measurements of actual HTTP/1.1 implementations show good
2304   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2305   T/TCP <xref target="Tou1998"/>.
2308   Persistent HTTP connections have a number of advantages:
2309  <list style="symbols">
2310      <t>
2311        By opening and closing fewer TCP connections, CPU time is saved
2312        in routers and hosts (clients, servers, proxies, gateways,
2313        tunnels, or caches), and memory used for TCP protocol control
2314        blocks can be saved in hosts.
2315      </t>
2316      <t>
2317        HTTP requests and responses can be pipelined on a connection.
2318        Pipelining allows a client to make multiple requests without
2319        waiting for each response, allowing a single TCP connection to
2320        be used much more efficiently, with much lower elapsed time.
2321      </t>
2322      <t>
2323        Network congestion is reduced by reducing the number of packets
2324        caused by TCP opens, and by allowing TCP sufficient time to
2325        determine the congestion state of the network.
2326      </t>
2327      <t>
2328        Latency on subsequent requests is reduced since there is no time
2329        spent in TCP's connection opening handshake.
2330      </t>
2331      <t>
2332        HTTP can evolve more gracefully, since errors can be reported
2333        without the penalty of closing the TCP connection. Clients using
2334        future versions of HTTP might optimistically try a new feature,
2335        but if communicating with an older server, retry with old
2336        semantics after an error is reported.
2337      </t>
2338    </list>
2341   HTTP implementations &SHOULD; implement persistent connections.
2345<section title="Overall Operation" anchor="persistent.overall">
2347   A significant difference between HTTP/1.1 and earlier versions of
2348   HTTP is that persistent connections are the default behavior of any
2349   HTTP connection. That is, unless otherwise indicated, the client
2350   &SHOULD; assume that the server will maintain a persistent connection,
2351   even after error responses from the server.
2354   Persistent connections provide a mechanism by which a client and a
2355   server can signal the close of a TCP connection. This signaling takes
2356   place using the Connection header field (<xref target="header.connection"/>). Once a close
2357   has been signaled, the client &MUST-NOT; send any more requests on that
2358   connection.
2361<section title="Negotiation" anchor="persistent.negotiation">
2363   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2364   maintain a persistent connection unless a Connection header including
2365   the connection-token "close" was sent in the request. If the server
2366   chooses to close the connection immediately after sending the
2367   response, it &SHOULD; send a Connection header including the
2368   connection-token "close".
2371   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2372   decide to keep it open based on whether the response from a server
2373   contains a Connection header with the connection-token close. In case
2374   the client does not want to maintain a connection for more than that
2375   request, it &SHOULD; send a Connection header including the
2376   connection-token close.
2379   If either the client or the server sends the close token in the
2380   Connection header, that request becomes the last one for the
2381   connection.
2384   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2385   maintained for HTTP versions less than 1.1 unless it is explicitly
2386   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2387   compatibility with HTTP/1.0 clients.
2390   In order to remain persistent, all messages on the connection &MUST;
2391   have a self-defined message length (i.e., one not defined by closure
2392   of the connection), as described in <xref target="message.body"/>.
2396<section title="Pipelining" anchor="pipelining">
2398   A client that supports persistent connections &MAY; "pipeline" its
2399   requests (i.e., send multiple requests without waiting for each
2400   response). A server &MUST; send its responses to those requests in the
2401   same order that the requests were received.
2404   Clients which assume persistent connections and pipeline immediately
2405   after connection establishment &SHOULD; be prepared to retry their
2406   connection if the first pipelined attempt fails. If a client does
2407   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2408   persistent. Clients &MUST; also be prepared to resend their requests if
2409   the server closes the connection before sending all of the
2410   corresponding responses.
2413   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2414   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2415   premature termination of the transport connection could lead to
2416   indeterminate results. A client wishing to send a non-idempotent
2417   request &SHOULD; wait to send that request until it has received the
2418   response status line for the previous request.
2423<section title="Proxy Servers" anchor="persistent.proxy">
2425   It is especially important that proxies correctly implement the
2426   properties of the Connection header field as specified in <xref target="header.connection"/>.
2429   The proxy server &MUST; signal persistent connections separately with
2430   its clients and the origin servers (or other proxy servers) that it
2431   connects to. Each persistent connection applies to only one transport
2432   link.
2435   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2436   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2437   for information and discussion of the problems with the Keep-Alive header
2438   implemented by many HTTP/1.0 clients).
2441<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2443  <cref anchor="TODO-end-to-end" source="jre">
2444    Restored from <eref target=""/>.
2445    See also <eref target=""/>.
2446  </cref>
2449   For the purpose of defining the behavior of caches and non-caching
2450   proxies, we divide HTTP headers into two categories:
2451  <list style="symbols">
2452      <t>End-to-end headers, which are  transmitted to the ultimate
2453        recipient of a request or response. End-to-end headers in
2454        responses MUST be stored as part of a cache entry and &MUST; be
2455        transmitted in any response formed from a cache entry.</t>
2457      <t>Hop-by-hop headers, which are meaningful only for a single
2458        transport-level connection, and are not stored by caches or
2459        forwarded by proxies.</t>
2460  </list>
2463   The following HTTP/1.1 headers are hop-by-hop headers:
2464  <list style="symbols">
2465      <t>Connection</t>
2466      <t>Keep-Alive</t>
2467      <t>Proxy-Authenticate</t>
2468      <t>Proxy-Authorization</t>
2469      <t>TE</t>
2470      <t>Trailer</t>
2471      <t>Transfer-Encoding</t>
2472      <t>Upgrade</t>
2473  </list>
2476   All other headers defined by HTTP/1.1 are end-to-end headers.
2479   Other hop-by-hop headers &MUST; be listed in a Connection header
2480   (<xref target="header.connection"/>).
2484<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2486  <cref anchor="TODO-non-mod-headers" source="jre">
2487    Restored from <eref target=""/>.
2488    See also <eref target=""/>.
2489  </cref>
2492   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2493   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2494   modify an end-to-end header unless the definition of that header requires
2495   or specifically allows that.
2498   A transparent proxy &MUST-NOT; modify any of the following fields in a
2499   request or response, and it &MUST-NOT; add any of these fields if not
2500   already present:
2501  <list style="symbols">
2502      <t>Content-Location</t>
2503      <t>Content-MD5</t>
2504      <t>ETag</t>
2505      <t>Last-Modified</t>
2506  </list>
2509   A transparent proxy &MUST-NOT; modify any of the following fields in a
2510   response:
2511  <list style="symbols">
2512    <t>Expires</t>
2513  </list>
2516   but it &MAY; add any of these fields if not already present. If an
2517   Expires header is added, it &MUST; be given a field-value identical to
2518   that of the Date header in that response.
2521   A proxy &MUST-NOT; modify or add any of the following fields in a
2522   message that contains the no-transform cache-control directive, or in
2523   any request:
2524  <list style="symbols">
2525    <t>Content-Encoding</t>
2526    <t>Content-Range</t>
2527    <t>Content-Type</t>
2528  </list>
2531   A non-transparent proxy &MAY; modify or add these fields to a message
2532   that does not include no-transform, but if it does so, it &MUST; add a
2533   Warning 214 (Transformation applied) if one does not already appear
2534   in the message (see &header-warning;).
2537  <t>
2538    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2539    cause authentication failures if stronger authentication
2540    mechanisms are introduced in later versions of HTTP. Such
2541    authentication mechanisms &MAY; rely on the values of header fields
2542    not listed here.
2543  </t>
2546   A transparent proxy &MUST; preserve the message payload (&payload;),
2547   though it &MAY; change the message-body through application or removal
2548   of a transfer-coding (<xref target="transfer.codings"/>).
2554<section title="Practical Considerations" anchor="persistent.practical">
2556   Servers will usually have some time-out value beyond which they will
2557   no longer maintain an inactive connection. Proxy servers might make
2558   this a higher value since it is likely that the client will be making
2559   more connections through the same server. The use of persistent
2560   connections places no requirements on the length (or existence) of
2561   this time-out for either the client or the server.
2564   When a client or server wishes to time-out it &SHOULD; issue a graceful
2565   close on the transport connection. Clients and servers &SHOULD; both
2566   constantly watch for the other side of the transport close, and
2567   respond to it as appropriate. If a client or server does not detect
2568   the other side's close promptly it could cause unnecessary resource
2569   drain on the network.
2572   A client, server, or proxy &MAY; close the transport connection at any
2573   time. For example, a client might have started to send a new request
2574   at the same time that the server has decided to close the "idle"
2575   connection. From the server's point of view, the connection is being
2576   closed while it was idle, but from the client's point of view, a
2577   request is in progress.
2580   This means that clients, servers, and proxies &MUST; be able to recover
2581   from asynchronous close events. Client software &SHOULD; reopen the
2582   transport connection and retransmit the aborted sequence of requests
2583   without user interaction so long as the request sequence is
2584   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2585   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2586   human operator the choice of retrying the request(s). Confirmation by
2587   user-agent software with semantic understanding of the application
2588   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2589   be repeated if the second sequence of requests fails.
2592   Servers &SHOULD; always respond to at least one request per connection,
2593   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2594   middle of transmitting a response, unless a network or client failure
2595   is suspected.
2598   Clients (including proxies) &SHOULD; limit the number of simultaneous
2599   connections that they maintain to a given server (including proxies).
2602   Previous revisions of HTTP gave a specific number of connections as a
2603   ceiling, but this was found to be impractical for many applications. As a
2604   result, this specification does not mandate a particular maximum number of
2605   connections, but instead encourages clients to be conservative when opening
2606   multiple connections.
2609   In particular, while using multiple connections avoids the "head-of-line
2610   blocking" problem (whereby a request that takes significant server-side
2611   processing and/or has a large payload can block subsequent requests on the
2612   same connection), each connection used consumes server resources (sometimes
2613   significantly), and furthermore using multiple connections can cause
2614   undesirable side effects in congested networks.
2617   Note that servers might reject traffic that they deem abusive, including an
2618   excessive number of connections from a client.
2623<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2625<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2627   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2628   flow control mechanisms to resolve temporary overloads, rather than
2629   terminating connections with the expectation that clients will retry.
2630   The latter technique can exacerbate network congestion.
2634<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2636   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2637   the network connection for an error status code while it is transmitting
2638   the request. If the client sees an error status code, it &SHOULD;
2639   immediately cease transmitting the body. If the body is being sent
2640   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2641   empty trailer &MAY; be used to prematurely mark the end of the message.
2642   If the body was preceded by a Content-Length header, the client &MUST;
2643   close the connection.
2647<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2649   The purpose of the 100 (Continue) status code (see &status-100;) is to
2650   allow a client that is sending a request message with a request body
2651   to determine if the origin server is willing to accept the request
2652   (based on the request headers) before the client sends the request
2653   body. In some cases, it might either be inappropriate or highly
2654   inefficient for the client to send the body if the server will reject
2655   the message without looking at the body.
2658   Requirements for HTTP/1.1 clients:
2659  <list style="symbols">
2660    <t>
2661        If a client will wait for a 100 (Continue) response before
2662        sending the request body, it &MUST; send an Expect request-header
2663        field (&header-expect;) with the "100-continue" expectation.
2664    </t>
2665    <t>
2666        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2667        with the "100-continue" expectation if it does not intend
2668        to send a request body.
2669    </t>
2670  </list>
2673   Because of the presence of older implementations, the protocol allows
2674   ambiguous situations in which a client might send "Expect: 100-continue"
2675   without receiving either a 417 (Expectation Failed)
2676   or a 100 (Continue) status code. Therefore, when a client sends this
2677   header field to an origin server (possibly via a proxy) from which it
2678   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2679   wait for an indefinite period before sending the request body.
2682   Requirements for HTTP/1.1 origin servers:
2683  <list style="symbols">
2684    <t> Upon receiving a request which includes an Expect request-header
2685        field with the "100-continue" expectation, an origin server &MUST;
2686        either respond with 100 (Continue) status code and continue to read
2687        from the input stream, or respond with a final status code. The
2688        origin server &MUST-NOT; wait for the request body before sending
2689        the 100 (Continue) response. If it responds with a final status
2690        code, it &MAY; close the transport connection or it &MAY; continue
2691        to read and discard the rest of the request.  It &MUST-NOT;
2692        perform the requested method if it returns a final status code.
2693    </t>
2694    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2695        the request message does not include an Expect request-header
2696        field with the "100-continue" expectation, and &MUST-NOT; send a
2697        100 (Continue) response if such a request comes from an HTTP/1.0
2698        (or earlier) client. There is an exception to this rule: for
2699        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2700        status code in response to an HTTP/1.1 PUT or POST request that does
2701        not include an Expect request-header field with the "100-continue"
2702        expectation. This exception, the purpose of which is
2703        to minimize any client processing delays associated with an
2704        undeclared wait for 100 (Continue) status code, applies only to
2705        HTTP/1.1 requests, and not to requests with any other HTTP-version
2706        value.
2707    </t>
2708    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2709        already received some or all of the request body for the
2710        corresponding request.
2711    </t>
2712    <t> An origin server that sends a 100 (Continue) response &MUST;
2713    ultimately send a final status code, once the request body is
2714        received and processed, unless it terminates the transport
2715        connection prematurely.
2716    </t>
2717    <t> If an origin server receives a request that does not include an
2718        Expect request-header field with the "100-continue" expectation,
2719        the request includes a request body, and the server responds
2720        with a final status code before reading the entire request body
2721        from the transport connection, then the server &SHOULD-NOT;  close
2722        the transport connection until it has read the entire request,
2723        or until the client closes the connection. Otherwise, the client
2724        might not reliably receive the response message. However, this
2725        requirement is not be construed as preventing a server from
2726        defending itself against denial-of-service attacks, or from
2727        badly broken client implementations.
2728      </t>
2729    </list>
2732   Requirements for HTTP/1.1 proxies:
2733  <list style="symbols">
2734    <t> If a proxy receives a request that includes an Expect request-header
2735        field with the "100-continue" expectation, and the proxy
2736        either knows that the next-hop server complies with HTTP/1.1 or
2737        higher, or does not know the HTTP version of the next-hop
2738        server, it &MUST; forward the request, including the Expect header
2739        field.
2740    </t>
2741    <t> If the proxy knows that the version of the next-hop server is
2742        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2743        respond with a 417 (Expectation Failed) status code.
2744    </t>
2745    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2746        numbers received from recently-referenced next-hop servers.
2747    </t>
2748    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2749        request message was received from an HTTP/1.0 (or earlier)
2750        client and did not include an Expect request-header field with
2751        the "100-continue" expectation. This requirement overrides the
2752        general rule for forwarding of 1xx responses (see &status-1xx;).
2753    </t>
2754  </list>
2758<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2760   If an HTTP/1.1 client sends a request which includes a request body,
2761   but which does not include an Expect request-header field with the
2762   "100-continue" expectation, and if the client is not directly
2763   connected to an HTTP/1.1 origin server, and if the client sees the
2764   connection close before receiving a status line from the server, the
2765   client &SHOULD; retry the request.  If the client does retry this
2766   request, it &MAY; use the following "binary exponential backoff"
2767   algorithm to be assured of obtaining a reliable response:
2768  <list style="numbers">
2769    <t>
2770      Initiate a new connection to the server
2771    </t>
2772    <t>
2773      Transmit the request-headers
2774    </t>
2775    <t>
2776      Initialize a variable R to the estimated round-trip time to the
2777         server (e.g., based on the time it took to establish the
2778         connection), or to a constant value of 5 seconds if the round-trip
2779         time is not available.
2780    </t>
2781    <t>
2782       Compute T = R * (2**N), where N is the number of previous
2783         retries of this request.
2784    </t>
2785    <t>
2786       Wait either for an error response from the server, or for T
2787         seconds (whichever comes first)
2788    </t>
2789    <t>
2790       If no error response is received, after T seconds transmit the
2791         body of the request.
2792    </t>
2793    <t>
2794       If client sees that the connection is closed prematurely,
2795         repeat from step 1 until the request is accepted, an error
2796         response is received, or the user becomes impatient and
2797         terminates the retry process.
2798    </t>
2799  </list>
2802   If at any point an error status code is received, the client
2803  <list style="symbols">
2804      <t>&SHOULD-NOT;  continue and</t>
2806      <t>&SHOULD; close the connection if it has not completed sending the
2807        request message.</t>
2808    </list>
2815<section title="Miscellaneous notes that might disappear" anchor="misc">
2816<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2818   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2822<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2824   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2828<section title="Interception of HTTP for access control" anchor="http.intercept">
2830   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2834<section title="Use of HTTP by other protocols" anchor="http.others">
2836   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2837   Extensions of HTTP like WebDAV.</cref>
2841<section title="Use of HTTP by media type specification" anchor="">
2843   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2848<section title="Header Field Definitions" anchor="header.field.definitions">
2850   This section defines the syntax and semantics of HTTP/1.1 header fields
2851   related to message framing and transport protocols.
2854<section title="Connection" anchor="header.connection">
2855  <iref primary="true" item="Connection header" x:for-anchor=""/>
2856  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2857  <x:anchor-alias value="Connection"/>
2858  <x:anchor-alias value="connection-token"/>
2859  <x:anchor-alias value="Connection-v"/>
2861   The "Connection" general-header field allows the sender to specify
2862   options that are desired for that particular connection and &MUST-NOT;
2863   be communicated by proxies over further connections.
2866   The Connection header's value has the following grammar:
2868<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"/>
2869  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2870  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2871  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2874   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2875   message is forwarded and, for each connection-token in this field,
2876   remove any header field(s) from the message with the same name as the
2877   connection-token. Connection options are signaled by the presence of
2878   a connection-token in the Connection header field, not by any
2879   corresponding additional header field(s), since the additional header
2880   field might not be sent if there are no parameters associated with that
2881   connection option.
2884   Message headers listed in the Connection header &MUST-NOT; include
2885   end-to-end headers, such as Cache-Control.
2888   HTTP/1.1 defines the "close" connection option for the sender to
2889   signal that the connection will be closed after completion of the
2890   response. For example,
2892<figure><artwork type="example">
2893  Connection: close
2896   in either the request or the response header fields indicates that
2897   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2898   after the current request/response is complete.
2901   An HTTP/1.1 client that does not support persistent connections &MUST;
2902   include the "close" connection option in every request message.
2905   An HTTP/1.1 server that does not support persistent connections &MUST;
2906   include the "close" connection option in every response message that
2907   does not have a 1xx (Informational) status code.
2910   A system receiving an HTTP/1.0 (or lower-version) message that
2911   includes a Connection header &MUST;, for each connection-token in this
2912   field, remove and ignore any header field(s) from the message with
2913   the same name as the connection-token. This protects against mistaken
2914   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2918<section title="Content-Length" anchor="header.content-length">
2919  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2920  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2921  <x:anchor-alias value="Content-Length"/>
2922  <x:anchor-alias value="Content-Length-v"/>
2924   The "Content-Length" header field indicates the size of the
2925   message-body, in decimal number of octets, for any message other than
2926   a response to the HEAD method or a response with a status code of 304.
2927   In the case of responses to the HEAD method, it indicates the size of
2928   the payload body (not including any potential transfer-coding) that
2929   would have been sent had the request been a GET.
2930   In the case of the 304 (Not Modified) response, it indicates the size of
2931   the payload body (not including any potential transfer-coding) that
2932   would have been sent in a 200 (OK) response.
2934<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2935  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2936  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2939   An example is
2941<figure><artwork type="example">
2942  Content-Length: 3495
2945   Implementations &SHOULD; use this field to indicate the message-body
2946   length when no transfer-coding is being applied and the
2947   payload's body length can be determined prior to being transferred.
2948   <xref target="message.body"/> describes how recipients determine the length
2949   of a message-body.
2952   Any Content-Length greater than or equal to zero is a valid value.
2955   Note that the use of this field in HTTP is significantly different from
2956   the corresponding definition in MIME, where it is an optional field
2957   used within the "message/external-body" content-type.
2961<section title="Date" anchor="">
2962  <iref primary="true" item="Date header" x:for-anchor=""/>
2963  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2964  <x:anchor-alias value="Date"/>
2965  <x:anchor-alias value="Date-v"/>
2967   The "Date" general-header field represents the date and time at which
2968   the message was originated, having the same semantics as the Origination
2969   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2970   The field value is an HTTP-date, as described in <xref target=""/>;
2971   it &MUST; be sent in rfc1123-date format.
2973<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2974  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2975  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2978   An example is
2980<figure><artwork type="example">
2981  Date: Tue, 15 Nov 1994 08:12:31 GMT
2984   Origin servers &MUST; include a Date header field in all responses,
2985   except in these cases:
2986  <list style="numbers">
2987      <t>If the response status code is 100 (Continue) or 101 (Switching
2988         Protocols), the response &MAY; include a Date header field, at
2989         the server's option.</t>
2991      <t>If the response status code conveys a server error, e.g., 500
2992         (Internal Server Error) or 503 (Service Unavailable), and it is
2993         inconvenient or impossible to generate a valid Date.</t>
2995      <t>If the server does not have a clock that can provide a
2996         reasonable approximation of the current time, its responses
2997         &MUST-NOT; include a Date header field. In this case, the rules
2998         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2999  </list>
3002   A received message that does not have a Date header field &MUST; be
3003   assigned one by the recipient if the message will be cached by that
3004   recipient or gatewayed via a protocol which requires a Date. An HTTP
3005   implementation without a clock &MUST-NOT; cache responses without
3006   revalidating them on every use. An HTTP cache, especially a shared
3007   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
3008   clock with a reliable external standard.
3011   Clients &SHOULD; only send a Date header field in messages that include
3012   a payload, as is usually the case for PUT and POST requests, and even
3013   then it is optional. A client without a clock &MUST-NOT; send a Date
3014   header field in a request.
3017   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
3018   time subsequent to the generation of the message. It &SHOULD; represent
3019   the best available approximation of the date and time of message
3020   generation, unless the implementation has no means of generating a
3021   reasonably accurate date and time. In theory, the date ought to
3022   represent the moment just before the payload is generated. In
3023   practice, the date can be generated at any time during the message
3024   origination without affecting its semantic value.
3027<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3029   Some origin server implementations might not have a clock available.
3030   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3031   values to a response, unless these values were associated
3032   with the resource by a system or user with a reliable clock. It &MAY;
3033   assign an Expires value that is known, at or before server
3034   configuration time, to be in the past (this allows "pre-expiration"
3035   of responses without storing separate Expires values for each
3036   resource).
3041<section title="Host" anchor="">
3042  <iref primary="true" item="Host header" x:for-anchor=""/>
3043  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3044  <x:anchor-alias value="Host"/>
3045  <x:anchor-alias value="Host-v"/>
3047   The "Host" request-header field specifies the Internet host and port
3048   number of the resource being requested, allowing the origin server or
3049   gateway to differentiate between internally-ambiguous URLs, such as the root
3050   "/" URL of a server for multiple host names on a single IP address.
3053   The Host field value &MUST; represent the naming authority of the origin
3054   server or gateway given by the original URL obtained from the user or
3055   referring resource (generally an http URI, as described in
3056   <xref target="http.uri"/>).
3058<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3059  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3060  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3063   A "host" without any trailing port information implies the default
3064   port for the service requested (e.g., "80" for an HTTP URL). For
3065   example, a request on the origin server for
3066   &lt;; would properly include:
3068<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3069GET /pub/WWW/ HTTP/1.1
3073   A client &MUST; include a Host header field in all HTTP/1.1 request
3074   messages. If the requested URI does not include an Internet host
3075   name for the service being requested, then the Host header field &MUST;
3076   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3077   request message it forwards does contain an appropriate Host header
3078   field that identifies the service being requested by the proxy. All
3079   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3080   status code to any HTTP/1.1 request message which lacks a Host header
3081   field.
3084   See Sections <xref target="" format="counter"/>
3085   and <xref target="" format="counter"/>
3086   for other requirements relating to Host.
3090<section title="TE" anchor="header.te">
3091  <iref primary="true" item="TE header" x:for-anchor=""/>
3092  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3093  <x:anchor-alias value="TE"/>
3094  <x:anchor-alias value="TE-v"/>
3095  <x:anchor-alias value="t-codings"/>
3096  <x:anchor-alias value="te-params"/>
3097  <x:anchor-alias value="te-ext"/>
3099   The "TE" request-header field indicates what extension transfer-codings
3100   it is willing to accept in the response, and whether or not it is
3101   willing to accept trailer fields in a chunked transfer-coding.
3104   Its value might consist of the keyword "trailers" and/or a comma-separated
3105   list of extension transfer-coding names with optional accept
3106   parameters (as described in <xref target="transfer.codings"/>).
3108<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"/>
3109  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3110  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3111  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3112  <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> )
3113  <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> ]
3116   The presence of the keyword "trailers" indicates that the client is
3117   willing to accept trailer fields in a chunked transfer-coding, as
3118   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3119   transfer-coding values even though it does not itself represent a
3120   transfer-coding.
3123   Examples of its use are:
3125<figure><artwork type="example">
3126  TE: deflate
3127  TE:
3128  TE: trailers, deflate;q=0.5
3131   The TE header field only applies to the immediate connection.
3132   Therefore, the keyword &MUST; be supplied within a Connection header
3133   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3136   A server tests whether a transfer-coding is acceptable, according to
3137   a TE field, using these rules:
3138  <list style="numbers">
3139    <x:lt>
3140      <t>The "chunked" transfer-coding is always acceptable. If the
3141         keyword "trailers" is listed, the client indicates that it is
3142         willing to accept trailer fields in the chunked response on
3143         behalf of itself and any downstream clients. The implication is
3144         that, if given, the client is stating that either all
3145         downstream clients are willing to accept trailer fields in the
3146         forwarded response, or that it will attempt to buffer the
3147         response on behalf of downstream recipients.
3148      </t><t>
3149         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3150         chunked response such that a client can be assured of buffering
3151         the entire response.</t>
3152    </x:lt>
3153    <x:lt>
3154      <t>If the transfer-coding being tested is one of the transfer-codings
3155         listed in the TE field, then it is acceptable unless it
3156         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3157         qvalue of 0 means "not acceptable".)</t>
3158    </x:lt>
3159    <x:lt>
3160      <t>If multiple transfer-codings are acceptable, then the
3161         acceptable transfer-coding with the highest non-zero qvalue is
3162         preferred.  The "chunked" transfer-coding always has a qvalue
3163         of 1.</t>
3164    </x:lt>
3165  </list>
3168   If the TE field-value is empty or if no TE field is present, the only
3169   transfer-coding is "chunked". A message with no transfer-coding is
3170   always acceptable.
3174<section title="Trailer" anchor="header.trailer">
3175  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3176  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3177  <x:anchor-alias value="Trailer"/>
3178  <x:anchor-alias value="Trailer-v"/>
3180   The "Trailer" general-header field indicates that the given set of
3181   header fields is present in the trailer of a message encoded with
3182   chunked transfer-coding.
3184<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3185  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3186  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3189   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3190   message using chunked transfer-coding with a non-empty trailer. Doing
3191   so allows the recipient to know which header fields to expect in the
3192   trailer.
3195   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3196   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3197   trailer fields in a "chunked" transfer-coding.
3200   Message header fields listed in the Trailer header field &MUST-NOT;
3201   include the following header fields:
3202  <list style="symbols">
3203    <t>Transfer-Encoding</t>
3204    <t>Content-Length</t>
3205    <t>Trailer</t>
3206  </list>
3210<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3211  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3212  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3213  <x:anchor-alias value="Transfer-Encoding"/>
3214  <x:anchor-alias value="Transfer-Encoding-v"/>
3216   The "Transfer-Encoding" general-header field indicates what transfer-codings
3217   (if any) have been applied to the message body. It differs from
3218   Content-Encoding (&content-codings;) in that transfer-codings are a property
3219   of the message (and therefore are removed by intermediaries), whereas
3220   content-codings are not.
3222<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3223  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3224                        <x:ref>Transfer-Encoding-v</x:ref>
3225  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3228   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3230<figure><artwork type="example">
3231  Transfer-Encoding: chunked
3234   If multiple encodings have been applied to a representation, the transfer-codings
3235   &MUST; be listed in the order in which they were applied.
3236   Additional information about the encoding parameters &MAY; be provided
3237   by other header fields not defined by this specification.
3240   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3241   header.
3245<section title="Upgrade" anchor="header.upgrade">
3246  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3247  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3248  <x:anchor-alias value="Upgrade"/>
3249  <x:anchor-alias value="Upgrade-v"/>
3251   The "Upgrade" general-header field allows the client to specify what
3252   additional communication protocols it would like to use, if the server
3253   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3254   header field within a 101 (Switching Protocols) response to indicate which
3255   protocol(s) are being switched to.
3257<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3258  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3259  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3262   For example,
3264<figure><artwork type="example">
3265  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3268   The Upgrade header field is intended to provide a simple mechanism
3269   for transition from HTTP/1.1 to some other, incompatible protocol. It
3270   does so by allowing the client to advertise its desire to use another
3271   protocol, such as a later version of HTTP with a higher major version
3272   number, even though the current request has been made using HTTP/1.1.
3273   This eases the difficult transition between incompatible protocols by
3274   allowing the client to initiate a request in the more commonly
3275   supported protocol while indicating to the server that it would like
3276   to use a "better" protocol if available (where "better" is determined
3277   by the server, possibly according to the nature of the method and/or
3278   resource being requested).
3281   The Upgrade header field only applies to switching application-layer
3282   protocols upon the existing transport-layer connection. Upgrade
3283   cannot be used to insist on a protocol change; its acceptance and use
3284   by the server is optional. The capabilities and nature of the
3285   application-layer communication after the protocol change is entirely
3286   dependent upon the new protocol chosen, although the first action
3287   after changing the protocol &MUST; be a response to the initial HTTP
3288   request containing the Upgrade header field.
3291   The Upgrade header field only applies to the immediate connection.
3292   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3293   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3294   HTTP/1.1 message.
3297   The Upgrade header field cannot be used to indicate a switch to a
3298   protocol on a different connection. For that purpose, it is more
3299   appropriate to use a 301, 302, 303, or 305 redirection response.
3302   This specification only defines the protocol name "HTTP" for use by
3303   the family of Hypertext Transfer Protocols, as defined by the HTTP
3304   version rules of <xref target="http.version"/> and future updates to this
3305   specification. Additional tokens can be registered with IANA using the
3306   registration procedure defined below. 
3309<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3311   The HTTP Upgrade Token Registry defines the name space for product
3312   tokens used to identify protocols in the Upgrade header field.
3313   Each registered token is associated with contact information and
3314   an optional set of specifications that details how the connection
3315   will be processed after it has been upgraded.
3318   Registrations are allowed on a First Come First Served basis as
3319   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3320   specifications need not be IETF documents or be subject to IESG review.
3321   Registrations are subject to the following rules:
3322  <list style="numbers">
3323    <t>A token, once registered, stays registered forever.</t>
3324    <t>The registration &MUST; name a responsible party for the
3325       registration.</t>
3326    <t>The registration &MUST; name a point of contact.</t>
3327    <t>The registration &MAY; name a set of specifications associated with that
3328       token. Such specifications need not be publicly available.</t>
3329    <t>The responsible party &MAY; change the registration at any time.
3330       The IANA will keep a record of all such changes, and make them
3331       available upon request.</t>
3332    <t>The responsible party for the first registration of a "product"
3333       token &MUST; approve later registrations of a "version" token
3334       together with that "product" token before they can be registered.</t>
3335    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3336       for a token. This will normally only be used in the case when a
3337       responsible party cannot be contacted.</t>
3338  </list>
3345<section title="Via" anchor="header.via">
3346  <iref primary="true" item="Via header" x:for-anchor=""/>
3347  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3348  <x:anchor-alias value="protocol-name"/>
3349  <x:anchor-alias value="protocol-version"/>
3350  <x:anchor-alias value="pseudonym"/>
3351  <x:anchor-alias value="received-by"/>
3352  <x:anchor-alias value="received-protocol"/>
3353  <x:anchor-alias value="Via"/>
3354  <x:anchor-alias value="Via-v"/>
3356   The "Via" general-header field &MUST; be used by gateways and proxies to
3357   indicate the intermediate protocols and recipients between the user
3358   agent and the server on requests, and between the origin server and
3359   the client on responses. It is analogous to the "Received" field defined in
3360   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3361   avoiding request loops, and identifying the protocol capabilities of
3362   all senders along the request/response chain.
3364<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"/>
3365  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3366  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3367                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3368  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3369  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3370  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3371  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3372  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3375   The received-protocol indicates the protocol version of the message
3376   received by the server or client along each segment of the
3377   request/response chain. The received-protocol version is appended to
3378   the Via field value when the message is forwarded so that information
3379   about the protocol capabilities of upstream applications remains
3380   visible to all recipients.
3383   The protocol-name is optional if and only if it would be "HTTP". The
3384   received-by field is normally the host and optional port number of a
3385   recipient server or client that subsequently forwarded the message.
3386   However, if the real host is considered to be sensitive information,
3387   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3388   be assumed to be the default port of the received-protocol.
3391   Multiple Via field values represent each proxy or gateway that has
3392   forwarded the message. Each recipient &MUST; append its information
3393   such that the end result is ordered according to the sequence of
3394   forwarding applications.
3397   Comments &MAY; be used in the Via header field to identify the software
3398   of the recipient proxy or gateway, analogous to the User-Agent and
3399   Server header fields. However, all comments in the Via field are
3400   optional and &MAY; be removed by any recipient prior to forwarding the
3401   message.
3404   For example, a request message could be sent from an HTTP/1.0 user
3405   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3406   forward the request to a public proxy at, which completes
3407   the request by forwarding it to the origin server at
3408   The request received by would then have the following
3409   Via header field:
3411<figure><artwork type="example">
3412  Via: 1.0 fred, 1.1 (Apache/1.1)
3415   Proxies and gateways used as a portal through a network firewall
3416   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3417   the firewall region. This information &SHOULD; only be propagated if
3418   explicitly enabled. If not enabled, the received-by host of any host
3419   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3420   for that host.
3423   For organizations that have strong privacy requirements for hiding
3424   internal structures, a proxy &MAY; combine an ordered subsequence of
3425   Via header field entries with identical received-protocol values into
3426   a single such entry. For example,
3428<figure><artwork type="example">
3429  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3432  could be collapsed to
3434<figure><artwork type="example">
3435  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3438   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3439   under the same organizational control and the hosts have already been
3440   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3441   have different received-protocol values.
3447<section title="IANA Considerations" anchor="IANA.considerations">
3449<section title="Header Field Registration" anchor="header.field.registration">
3451   The Message Header Field Registry located at <eref target=""/> shall be updated
3452   with the permanent registrations below (see <xref target="RFC3864"/>):
3454<?BEGININC p1-messaging.iana-headers ?>
3455<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3456<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3457   <ttcol>Header Field Name</ttcol>
3458   <ttcol>Protocol</ttcol>
3459   <ttcol>Status</ttcol>
3460   <ttcol>Reference</ttcol>
3462   <c>Connection</c>
3463   <c>http</c>
3464   <c>standard</c>
3465   <c>
3466      <xref target="header.connection"/>
3467   </c>
3468   <c>Content-Length</c>
3469   <c>http</c>
3470   <c>standard</c>
3471   <c>
3472      <xref target="header.content-length"/>
3473   </c>
3474   <c>Date</c>
3475   <c>http</c>
3476   <c>standard</c>
3477   <c>
3478      <xref target=""/>
3479   </c>
3480   <c>Host</c>
3481   <c>http</c>
3482   <c>standard</c>
3483   <c>
3484      <xref target=""/>
3485   </c>
3486   <c>TE</c>
3487   <c>http</c>
3488   <c>standard</c>
3489   <c>
3490      <xref target="header.te"/>
3491   </c>
3492   <c>Trailer</c>
3493   <c>http</c>
3494   <c>standard</c>
3495   <c>
3496      <xref target="header.trailer"/>
3497   </c>
3498   <c>Transfer-Encoding</c>
3499   <c>http</c>
3500   <c>standard</c>
3501   <c>
3502      <xref target="header.transfer-encoding"/>
3503   </c>
3504   <c>Upgrade</c>
3505   <c>http</c>
3506   <c>standard</c>
3507   <c>
3508      <xref target="header.upgrade"/>
3509   </c>
3510   <c>Via</c>
3511   <c>http</c>
3512   <c>standard</c>
3513   <c>
3514      <xref target="header.via"/>
3515   </c>
3518<?ENDINC p1-messaging.iana-headers ?>
3520   The change controller is: "IETF ( - Internet Engineering Task Force".
3524<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3526   The entries for the "http" and "https" URI Schemes in the registry located at
3527   <eref target=""/>
3528   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3529   and <xref target="https.uri" format="counter"/> of this document
3530   (see <xref target="RFC4395"/>).
3534<section title="Internet Media Type Registrations" anchor="">
3536   This document serves as the specification for the Internet media types
3537   "message/http" and "application/http". The following is to be registered with
3538   IANA (see <xref target="RFC4288"/>).
3540<section title="Internet Media Type message/http" anchor="">
3541<iref item="Media Type" subitem="message/http" primary="true"/>
3542<iref item="message/http Media Type" primary="true"/>
3544   The message/http type can be used to enclose a single HTTP request or
3545   response message, provided that it obeys the MIME restrictions for all
3546   "message" types regarding line length and encodings.
3549  <list style="hanging" x:indent="12em">
3550    <t hangText="Type name:">
3551      message
3552    </t>
3553    <t hangText="Subtype name:">
3554      http
3555    </t>
3556    <t hangText="Required parameters:">
3557      none
3558    </t>
3559    <t hangText="Optional parameters:">
3560      version, msgtype
3561      <list style="hanging">
3562        <t hangText="version:">
3563          The HTTP-Version number of the enclosed message
3564          (e.g., "1.1"). If not present, the version can be
3565          determined from the first line of the body.
3566        </t>
3567        <t hangText="msgtype:">
3568          The message type -- "request" or "response". If not
3569          present, the type can be determined from the first
3570          line of the body.
3571        </t>
3572      </list>
3573    </t>
3574    <t hangText="Encoding considerations:">
3575      only "7bit", "8bit", or "binary" are permitted
3576    </t>
3577    <t hangText="Security considerations:">
3578      none
3579    </t>
3580    <t hangText="Interoperability considerations:">
3581      none
3582    </t>
3583    <t hangText="Published specification:">
3584      This specification (see <xref target=""/>).
3585    </t>
3586    <t hangText="Applications that use this media type:">
3587    </t>
3588    <t hangText="Additional information:">
3589      <list style="hanging">
3590        <t hangText="Magic number(s):">none</t>
3591        <t hangText="File extension(s):">none</t>
3592        <t hangText="Macintosh file type code(s):">none</t>
3593      </list>
3594    </t>
3595    <t hangText="Person and email address to contact for further information:">
3596      See Authors Section.
3597    </t>
3598    <t hangText="Intended usage:">
3599      COMMON
3600    </t>
3601    <t hangText="Restrictions on usage:">
3602      none
3603    </t>
3604    <t hangText="Author/Change controller:">
3605      IESG
3606    </t>
3607  </list>
3610<section title="Internet Media Type application/http" anchor="">
3611<iref item="Media Type" subitem="application/http" primary="true"/>
3612<iref item="application/http Media Type" primary="true"/>
3614   The application/http type can be used to enclose a pipeline of one or more
3615   HTTP request or response messages (not intermixed).
3618  <list style="hanging" x:indent="12em">
3619    <t hangText="Type name:">
3620      application
3621    </t>
3622    <t hangText="Subtype name:">
3623      http
3624    </t>
3625    <t hangText="Required parameters:">
3626      none
3627    </t>
3628    <t hangText="Optional parameters:">
3629      version, msgtype
3630      <list style="hanging">
3631        <t hangText="version:">
3632          The HTTP-Version number of the enclosed messages
3633          (e.g., "1.1"). If not present, the version can be
3634          determined from the first line of the body.
3635        </t>
3636        <t hangText="msgtype:">
3637          The message type -- "request" or "response". If not
3638          present, the type can be determined from the first
3639          line of the body.
3640        </t>
3641      </list>
3642    </t>
3643    <t hangText="Encoding considerations:">
3644      HTTP messages enclosed by this type
3645      are in "binary" format; use of an appropriate
3646      Content-Transfer-Encoding is required when
3647      transmitted via E-mail.
3648    </t>
3649    <t hangText="Security considerations:">
3650      none
3651    </t>
3652    <t hangText="Interoperability considerations:">
3653      none
3654    </t>
3655    <t hangText="Published specification:">
3656      This specification (see <xref target=""/>).
3657    </t>
3658    <t hangText="Applications that use this media type:">
3659    </t>
3660    <t hangText="Additional information:">
3661      <list style="hanging">
3662        <t hangText="Magic number(s):">none</t>
3663        <t hangText="File extension(s):">none</t>
3664        <t hangText="Macintosh file type code(s):">none</t>
3665      </list>
3666    </t>
3667    <t hangText="Person and email address to contact for further information:">
3668      See Authors Section.
3669    </t>
3670    <t hangText="Intended usage:">
3671      COMMON
3672    </t>
3673    <t hangText="Restrictions on usage:">
3674      none
3675    </t>
3676    <t hangText="Author/Change controller:">
3677      IESG
3678    </t>
3679  </list>
3684<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3686   The registration procedure for HTTP Transfer Codings is now defined by
3687   <xref target="transfer.coding.registry"/> of this document.
3690   The HTTP Transfer Codings Registry located at <eref target=""/>
3691   shall be updated with the registrations below:
3693<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3694   <ttcol>Name</ttcol>
3695   <ttcol>Description</ttcol>
3696   <ttcol>Reference</ttcol>
3697   <c>chunked</c>
3698   <c>Transfer in a series of chunks</c>
3699   <c>
3700      <xref target="chunked.encoding"/>
3701   </c>
3702   <c>compress</c>
3703   <c>UNIX "compress" program method</c>
3704   <c>
3705      <xref target="compress.coding"/>
3706   </c>
3707   <c>deflate</c>
3708   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3709   the "zlib" data format (<xref target="RFC1950"/>)
3710   </c>
3711   <c>
3712      <xref target="deflate.coding"/>
3713   </c>
3714   <c>gzip</c>
3715   <c>Same as GNU zip <xref target="RFC1952"/></c>
3716   <c>
3717      <xref target="gzip.coding"/>
3718   </c>
3722<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3724   The registration procedure for HTTP Upgrade Tokens -- previously defined
3725   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3726   by <xref target="upgrade.token.registry"/> of this document.
3729   The HTTP Status Code Registry located at <eref target=""/>
3730   shall be updated with the registration below:
3732<texttable align="left" suppress-title="true">
3733   <ttcol>Value</ttcol>
3734   <ttcol>Description</ttcol>
3735   <ttcol>Reference</ttcol>
3737   <c>HTTP</c>
3738   <c>Hypertext Transfer Protocol</c>
3739   <c><xref target="http.version"/> of this specification</c>
3740<!-- IANA should add this without our instructions; emailed on June 05, 2009
3741   <c>TLS/1.0</c>
3742   <c>Transport Layer Security</c>
3743   <c><xref target="RFC2817"/></c> -->
3750<section title="Security Considerations" anchor="security.considerations">
3752   This section is meant to inform application developers, information
3753   providers, and users of the security limitations in HTTP/1.1 as
3754   described by this document. The discussion does not include
3755   definitive solutions to the problems revealed, though it does make
3756   some suggestions for reducing security risks.
3759<section title="Personal Information" anchor="personal.information">
3761   HTTP clients are often privy to large amounts of personal information
3762   (e.g., the user's name, location, mail address, passwords, encryption
3763   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3764   leakage of this information.
3765   We very strongly recommend that a convenient interface be provided
3766   for the user to control dissemination of such information, and that
3767   designers and implementors be particularly careful in this area.
3768   History shows that errors in this area often create serious security
3769   and/or privacy problems and generate highly adverse publicity for the
3770   implementor's company.
3774<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3776   A server is in the position to save personal data about a user's
3777   requests which might identify their reading patterns or subjects of
3778   interest. This information is clearly confidential in nature and its
3779   handling can be constrained by law in certain countries. People using
3780   HTTP to provide data are responsible for ensuring that
3781   such material is not distributed without the permission of any
3782   individuals that are identifiable by the published results.
3786<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3788   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3789   the documents returned by HTTP requests to be only those that were
3790   intended by the server administrators. If an HTTP server translates
3791   HTTP URIs directly into file system calls, the server &MUST; take
3792   special care not to serve files that were not intended to be
3793   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3794   other operating systems use ".." as a path component to indicate a
3795   directory level above the current one. On such a system, an HTTP
3796   server &MUST; disallow any such construct in the request-target if it
3797   would otherwise allow access to a resource outside those intended to
3798   be accessible via the HTTP server. Similarly, files intended for
3799   reference only internally to the server (such as access control
3800   files, configuration files, and script code) &MUST; be protected from
3801   inappropriate retrieval, since they might contain sensitive
3802   information. Experience has shown that minor bugs in such HTTP server
3803   implementations have turned into security risks.
3807<section title="DNS Spoofing" anchor="dns.spoofing">
3809   Clients using HTTP rely heavily on the Domain Name Service, and are
3810   thus generally prone to security attacks based on the deliberate
3811   mis-association of IP addresses and DNS names. Clients need to be
3812   cautious in assuming the continuing validity of an IP number/DNS name
3813   association.
3816   In particular, HTTP clients &SHOULD; rely on their name resolver for
3817   confirmation of an IP number/DNS name association, rather than
3818   caching the result of previous host name lookups. Many platforms
3819   already can cache host name lookups locally when appropriate, and
3820   they &SHOULD; be configured to do so. It is proper for these lookups to
3821   be cached, however, only when the TTL (Time To Live) information
3822   reported by the name server makes it likely that the cached
3823   information will remain useful.
3826   If HTTP clients cache the results of host name lookups in order to
3827   achieve a performance improvement, they &MUST; observe the TTL
3828   information reported by DNS.
3831   If HTTP clients do not observe this rule, they could be spoofed when
3832   a previously-accessed server's IP address changes. As network
3833   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3834   possibility of this form of attack will grow. Observing this
3835   requirement thus reduces this potential security vulnerability.
3838   This requirement also improves the load-balancing behavior of clients
3839   for replicated servers using the same DNS name and reduces the
3840   likelihood of a user's experiencing failure in accessing sites which
3841   use that strategy.
3845<section title="Proxies and Caching" anchor="attack.proxies">
3847   By their very nature, HTTP proxies are men-in-the-middle, and
3848   represent an opportunity for man-in-the-middle attacks. Compromise of
3849   the systems on which the proxies run can result in serious security
3850   and privacy problems. Proxies have access to security-related
3851   information, personal information about individual users and
3852   organizations, and proprietary information belonging to users and
3853   content providers. A compromised proxy, or a proxy implemented or
3854   configured without regard to security and privacy considerations,
3855   might be used in the commission of a wide range of potential attacks.
3858   Proxy operators need to protect the systems on which proxies run as
3859   they would protect any system that contains or transports sensitive
3860   information. In particular, log information gathered at proxies often
3861   contains highly sensitive personal information, and/or information
3862   about organizations. Log information needs to be carefully guarded, and
3863   appropriate guidelines for use need to be developed and followed.
3864   (<xref target="abuse.of.server.log.information"/>).
3867   Proxy implementors need to consider the privacy and security
3868   implications of their design and coding decisions, and of the
3869   configuration options they provide to proxy operators (especially the
3870   default configuration).
3873   Users of a proxy need to be aware that proxies are no trustworthier than
3874   the people who run them; HTTP itself cannot solve this problem.
3877   The judicious use of cryptography, when appropriate, might suffice to
3878   protect against a broad range of security and privacy attacks. Such
3879   cryptography is beyond the scope of the HTTP/1.1 specification.
3883<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3885   They exist. They are hard to defend against. Research continues.
3886   Beware.
3891<section title="Acknowledgments" anchor="ack">
3893   HTTP has evolved considerably over the years. It has
3894   benefited from a large and active developer community--the many
3895   people who have participated on the www-talk mailing list--and it is
3896   that community which has been most responsible for the success of
3897   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3898   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3899   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3900   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3901   VanHeyningen deserve special recognition for their efforts in
3902   defining early aspects of the protocol.
3905   This document has benefited greatly from the comments of all those
3906   participating in the HTTP-WG. In addition to those already mentioned,
3907   the following individuals have contributed to this specification:
3910   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3911   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3912   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3913   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3914   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3915   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3916   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3917   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3918   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3919   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3920   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3921   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3924   Thanks to the "cave men" of Palo Alto. You know who you are.
3927   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3928   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3929   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3930   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3931   Larry Masinter for their help. And thanks go particularly to Jeff
3932   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3935   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3936   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3937   discovery of many of the problems that this document attempts to
3938   rectify.
3941   This specification makes heavy use of the augmented BNF and generic
3942   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3943   reuses many of the definitions provided by Nathaniel Borenstein and
3944   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3945   specification will help reduce past confusion over the relationship
3946   between HTTP and Internet mail message formats.
3953<references title="Normative References">
3955<reference anchor="ISO-8859-1">
3956  <front>
3957    <title>
3958     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3959    </title>
3960    <author>
3961      <organization>International Organization for Standardization</organization>
3962    </author>
3963    <date year="1998"/>
3964  </front>
3965  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3968<reference anchor="Part2">
3969  <front>
3970    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3971    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3972      <organization abbrev="Day Software">Day Software</organization>
3973      <address><email></email></address>
3974    </author>
3975    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3976      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3977      <address><email></email></address>
3978    </author>
3979    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3980      <organization abbrev="HP">Hewlett-Packard Company</organization>
3981      <address><email></email></address>
3982    </author>
3983    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3984      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3985      <address><email></email></address>
3986    </author>
3987    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3988      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3989      <address><email></email></address>
3990    </author>
3991    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3992      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3993      <address><email></email></address>
3994    </author>
3995    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3996      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3997      <address><email></email></address>
3998    </author>
3999    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4000      <organization abbrev="W3C">World Wide Web Consortium</organization>
4001      <address><email></email></address>
4002    </author>
4003    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4004      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4005      <address><email></email></address>
4006    </author>
4007    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4008  </front>
4009  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4010  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4013<reference anchor="Part3">
4014  <front>
4015    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4016    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4017      <organization abbrev="Day Software">Day Software</organization>
4018      <address><email></email></address>
4019    </author>
4020    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4021      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4022      <address><email></email></address>
4023    </author>
4024    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4025      <organization abbrev="HP">Hewlett-Packard Company</organization>
4026      <address><email></email></address>
4027    </author>
4028    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4029      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4030      <address><email></email></address>
4031    </author>
4032    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4033      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4034      <address><email></email></address>
4035    </author>
4036    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4037      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4038      <address><email></email></address>
4039    </author>
4040    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4041      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4042      <address><email></email></address>
4043    </author>
4044    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4045      <organization abbrev="W3C">World Wide Web Consortium</organization>
4046      <address><email></email></address>
4047    </author>
4048    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4049      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4050      <address><email></email></address>
4051    </author>
4052    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4053  </front>
4054  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4055  <x:source href="p3-payload.xml" basename="p3-payload"/>
4058<reference anchor="Part6">
4059  <front>
4060    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4061    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4062      <organization abbrev="Day Software">Day Software</organization>
4063      <address><email></email></address>
4064    </author>
4065    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4066      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4067      <address><email></email></address>
4068    </author>
4069    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4070      <organization abbrev="HP">Hewlett-Packard Company</organization>
4071      <address><email></email></address>
4072    </author>
4073    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4074      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4075      <address><email></email></address>
4076    </author>
4077    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4078      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4079      <address><email></email></address>
4080    </author>
4081    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4082      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4083      <address><email></email></address>
4084    </author>
4085    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4086      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4087      <address><email></email></address>
4088    </author>
4089    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4090      <organization abbrev="W3C">World Wide Web Consortium</organization>
4091      <address><email></email></address>
4092    </author>
4093    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4094      <address><email></email></address>
4095    </author>
4096    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4097      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4098      <address><email></email></address>
4099    </author>
4100    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4101  </front>
4102  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4103  <x:source href="p6-cache.xml" basename="p6-cache"/>
4106<reference anchor="RFC5234">
4107  <front>
4108    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4109    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4110      <organization>Brandenburg InternetWorking</organization>
4111      <address>
4112        <email></email>
4113      </address> 
4114    </author>
4115    <author initials="P." surname="Overell" fullname="Paul Overell">
4116      <organization>THUS plc.</organization>
4117      <address>
4118        <email></email>
4119      </address>
4120    </author>
4121    <date month="January" year="2008"/>
4122  </front>
4123  <seriesInfo name="STD" value="68"/>
4124  <seriesInfo name="RFC" value="5234"/>
4127<reference anchor="RFC2119">
4128  <front>
4129    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4130    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4131      <organization>Harvard University</organization>
4132      <address><email></email></address>
4133    </author>
4134    <date month="March" year="1997"/>
4135  </front>
4136  <seriesInfo name="BCP" value="14"/>
4137  <seriesInfo name="RFC" value="2119"/>
4140<reference anchor="RFC3986">
4141 <front>
4142  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4143  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4144    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4145    <address>
4146       <email></email>
4147       <uri></uri>
4148    </address>
4149  </author>
4150  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4151    <organization abbrev="Day Software">Day Software</organization>
4152    <address>
4153      <email></email>
4154      <uri></uri>
4155    </address>
4156  </author>
4157  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4158    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4159    <address>
4160      <email></email>
4161      <uri></uri>
4162    </address>
4163  </author>
4164  <date month='January' year='2005'></date>
4165 </front>
4166 <seriesInfo name="RFC" value="3986"/>
4167 <seriesInfo name="STD" value="66"/>
4170<reference anchor="USASCII">
4171  <front>
4172    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4173    <author>
4174      <organization>American National Standards Institute</organization>
4175    </author>
4176    <date year="1986"/>
4177  </front>
4178  <seriesInfo name="ANSI" value="X3.4"/>
4181<reference anchor="RFC1950">
4182  <front>
4183    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4184    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4185      <organization>Aladdin Enterprises</organization>
4186      <address><email></email></address>
4187    </author>
4188    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4189    <date month="May" year="1996"/>
4190  </front>
4191  <seriesInfo name="RFC" value="1950"/>
4192  <annotation>
4193    RFC 1950 is an Informational RFC, thus it might be less stable than
4194    this specification. On the other hand, this downward reference was
4195    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4196    therefore it is unlikely to cause problems in practice. See also
4197    <xref target="BCP97"/>.
4198  </annotation>
4201<reference anchor="RFC1951">
4202  <front>
4203    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4204    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4205      <organization>Aladdin Enterprises</organization>
4206      <address><email></email></address>
4207    </author>
4208    <date month="May" year="1996"/>
4209  </front>
4210  <seriesInfo name="RFC" value="1951"/>
4211  <annotation>
4212    RFC 1951 is an Informational RFC, thus it might be less stable than
4213    this specification. On the other hand, this downward reference was
4214    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4215    therefore it is unlikely to cause problems in practice. See also
4216    <xref target="BCP97"/>.
4217  </annotation>
4220<reference anchor="RFC1952">
4221  <front>
4222    <title>GZIP file format specification version 4.3</title>
4223    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4224      <organization>Aladdin Enterprises</organization>
4225      <address><email></email></address>
4226    </author>
4227    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4228      <address><email></email></address>
4229    </author>
4230    <author initials="M." surname="Adler" fullname="Mark Adler">
4231      <address><email></email></address>
4232    </author>
4233    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4234      <address><email></email></address>
4235    </author>
4236    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4237      <address><email></email></address>
4238    </author>
4239    <date month="May" year="1996"/>
4240  </front>
4241  <seriesInfo name="RFC" value="1952"/>
4242  <annotation>
4243    RFC 1952 is an Informational RFC, thus it might be less stable than
4244    this specification. On the other hand, this downward reference was
4245    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4246    therefore it is unlikely to cause problems in practice. See also
4247    <xref target="BCP97"/>.
4248  </annotation>
4253<references title="Informative References">
4255<reference anchor="Nie1997" target="">
4256  <front>
4257    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4258    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4259    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4260    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4261    <author initials="H." surname="Lie" fullname="H. Lie"/>
4262    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4263    <date year="1997" month="September"/>
4264  </front>
4265  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4268<reference anchor="Pad1995" target="">
4269  <front>
4270    <title>Improving HTTP Latency</title>
4271    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4272    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4273    <date year="1995" month="December"/>
4274  </front>
4275  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4278<reference anchor="RFC1123">
4279  <front>
4280    <title>Requirements for Internet Hosts - Application and Support</title>
4281    <author initials="R." surname="Braden" fullname="Robert Braden">
4282      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4283      <address><email>Braden@ISI.EDU</email></address>
4284    </author>
4285    <date month="October" year="1989"/>
4286  </front>
4287  <seriesInfo name="STD" value="3"/>
4288  <seriesInfo name="RFC" value="1123"/>
4291<reference anchor="RFC1305">
4292  <front>
4293    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4294    <author initials="D." surname="Mills" fullname="David L. Mills">
4295      <organization>University of Delaware, Electrical Engineering Department</organization>
4296      <address><email></email></address>
4297    </author>
4298    <date month="March" year="1992"/>
4299  </front>
4300  <seriesInfo name="RFC" value="1305"/>
4303<reference anchor="RFC1900">
4304  <front>
4305    <title>Renumbering Needs Work</title>
4306    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4307      <organization>CERN, Computing and Networks Division</organization>
4308      <address><email></email></address>
4309    </author>
4310    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4311      <organization>cisco Systems</organization>
4312      <address><email></email></address>
4313    </author>
4314    <date month="February" year="1996"/>
4315  </front>
4316  <seriesInfo name="RFC" value="1900"/>
4319<reference anchor="RFC1945">
4320  <front>
4321    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4322    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4323      <organization>MIT, Laboratory for Computer Science</organization>
4324      <address><email></email></address>
4325    </author>
4326    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4327      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4328      <address><email></email></address>
4329    </author>
4330    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4331      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4332      <address><email></email></address>
4333    </author>
4334    <date month="May" year="1996"/>
4335  </front>
4336  <seriesInfo name="RFC" value="1945"/>
4339<reference anchor="RFC2045">
4340  <front>
4341    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4342    <author initials="N." surname="Freed" fullname="Ned Freed">
4343      <organization>Innosoft International, Inc.</organization>
4344      <address><email></email></address>
4345    </author>
4346    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4347      <organization>First Virtual Holdings</organization>
4348      <address><email></email></address>
4349    </author>
4350    <date month="November" year="1996"/>
4351  </front>
4352  <seriesInfo name="RFC" value="2045"/>
4355<reference anchor="RFC2047">
4356  <front>
4357    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4358    <author initials="K." surname="Moore" fullname="Keith Moore">
4359      <organization>University of Tennessee</organization>
4360      <address><email></email></address>
4361    </author>
4362    <date month="November" year="1996"/>
4363  </front>
4364  <seriesInfo name="RFC" value="2047"/>
4367<reference anchor="RFC2068">
4368  <front>
4369    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4370    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4371      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4372      <address><email></email></address>
4373    </author>
4374    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4375      <organization>MIT Laboratory for Computer Science</organization>
4376      <address><email></email></address>
4377    </author>
4378    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4379      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4380      <address><email></email></address>
4381    </author>
4382    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4383      <organization>MIT Laboratory for Computer Science</organization>
4384      <address><email></email></address>
4385    </author>
4386    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4387      <organization>MIT Laboratory for Computer Science</organization>
4388      <address><email></email></address>
4389    </author>
4390    <date month="January" year="1997"/>
4391  </front>
4392  <seriesInfo name="RFC" value="2068"/>
4395<reference anchor='RFC2109'>
4396  <front>
4397    <title>HTTP State Management Mechanism</title>
4398    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4399      <organization>Bell Laboratories, Lucent Technologies</organization>
4400      <address><email></email></address>
4401    </author>
4402    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4403      <organization>Netscape Communications Corp.</organization>
4404      <address><email></email></address>
4405    </author>
4406    <date year='1997' month='February' />
4407  </front>
4408  <seriesInfo name='RFC' value='2109' />
4411<reference anchor="RFC2145">
4412  <front>
4413    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4414    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4415      <organization>Western Research Laboratory</organization>
4416      <address><email></email></address>
4417    </author>
4418    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4419      <organization>Department of Information and Computer Science</organization>
4420      <address><email></email></address>
4421    </author>
4422    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4423      <organization>MIT Laboratory for Computer Science</organization>
4424      <address><email></email></address>
4425    </author>
4426    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4427      <organization>W3 Consortium</organization>
4428      <address><email></email></address>
4429    </author>
4430    <date month="May" year="1997"/>
4431  </front>
4432  <seriesInfo name="RFC" value="2145"/>
4435<reference anchor="RFC2616">
4436  <front>
4437    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4438    <author initials="R." surname="Fielding" fullname="R. Fielding">
4439      <organization>University of California, Irvine</organization>
4440      <address><email></email></address>
4441    </author>
4442    <author initials="J." surname="Gettys" fullname="J. Gettys">
4443      <organization>W3C</organization>
4444      <address><email></email></address>
4445    </author>
4446    <author initials="J." surname="Mogul" fullname="J. Mogul">
4447      <organization>Compaq Computer Corporation</organization>
4448      <address><email></email></address>
4449    </author>
4450    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4451      <organization>MIT Laboratory for Computer Science</organization>
4452      <address><email></email></address>
4453    </author>
4454    <author initials="L." surname="Masinter" fullname="L. Masinter">
4455      <organization>Xerox Corporation</organization>
4456      <address><email></email></address>
4457    </author>
4458    <author initials="P." surname="Leach" fullname="P. Leach">
4459      <organization>Microsoft Corporation</organization>
4460      <address><email></email></address>
4461    </author>
4462    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4463      <organization>W3C</organization>
4464      <address><email></email></address>
4465    </author>
4466    <date month="June" year="1999"/>
4467  </front>
4468  <seriesInfo name="RFC" value="2616"/>
4471<reference anchor='RFC2817'>
4472  <front>
4473    <title>Upgrading to TLS Within HTTP/1.1</title>
4474    <author initials='R.' surname='Khare' fullname='R. Khare'>
4475      <organization>4K Associates / UC Irvine</organization>
4476      <address><email></email></address>
4477    </author>
4478    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4479      <organization>Agranat Systems, Inc.</organization>
4480      <address><email></email></address>
4481    </author>
4482    <date year='2000' month='May' />
4483  </front>
4484  <seriesInfo name='RFC' value='2817' />
4487<reference anchor='RFC2818'>
4488  <front>
4489    <title>HTTP Over TLS</title>
4490    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4491      <organization>RTFM, Inc.</organization>
4492      <address><email></email></address>
4493    </author>
4494    <date year='2000' month='May' />
4495  </front>
4496  <seriesInfo name='RFC' value='2818' />
4499<reference anchor='RFC2965'>
4500  <front>
4501    <title>HTTP State Management Mechanism</title>
4502    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4503      <organization>Bell Laboratories, Lucent Technologies</organization>
4504      <address><email></email></address>
4505    </author>
4506    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4507      <organization>, Inc.</organization>
4508      <address><email></email></address>
4509    </author>
4510    <date year='2000' month='October' />
4511  </front>
4512  <seriesInfo name='RFC' value='2965' />
4515<reference anchor='RFC3864'>
4516  <front>
4517    <title>Registration Procedures for Message Header Fields</title>
4518    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4519      <organization>Nine by Nine</organization>
4520      <address><email></email></address>
4521    </author>
4522    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4523      <organization>BEA Systems</organization>
4524      <address><email></email></address>
4525    </author>
4526    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4527      <organization>HP Labs</organization>
4528      <address><email></email></address>
4529    </author>
4530    <date year='2004' month='September' />
4531  </front>
4532  <seriesInfo name='BCP' value='90' />
4533  <seriesInfo name='RFC' value='3864' />
4536<reference anchor="RFC4288">
4537  <front>
4538    <title>Media Type Specifications and Registration Procedures</title>
4539    <author initials="N." surname="Freed" fullname="N. Freed">
4540      <organization>Sun Microsystems</organization>
4541      <address>
4542        <email></email>
4543      </address>
4544    </author>
4545    <author initials="J." surname="Klensin" fullname="J. Klensin">
4546      <address>
4547        <email></email>
4548      </address>
4549    </author>
4550    <date year="2005" month="December"/>
4551  </front>
4552  <seriesInfo name="BCP" value="13"/>
4553  <seriesInfo name="RFC" value="4288"/>
4556<reference anchor='RFC4395'>
4557  <front>
4558    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4559    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4560      <organization>AT&amp;T Laboratories</organization>
4561      <address>
4562        <email></email>
4563      </address>
4564    </author>
4565    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4566      <organization>Qualcomm, Inc.</organization>
4567      <address>
4568        <email></email>
4569      </address>
4570    </author>
4571    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4572      <organization>Adobe Systems</organization>
4573      <address>
4574        <email></email>
4575      </address>
4576    </author>
4577    <date year='2006' month='February' />
4578  </front>
4579  <seriesInfo name='BCP' value='115' />
4580  <seriesInfo name='RFC' value='4395' />
4583<reference anchor='RFC5226'>
4584  <front>
4585    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4586    <author initials='T.' surname='Narten' fullname='T. Narten'>
4587      <organization>IBM</organization>
4588      <address><email></email></address>
4589    </author>
4590    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4591      <organization>Google</organization>
4592      <address><email></email></address>
4593    </author>
4594    <date year='2008' month='May' />
4595  </front>
4596  <seriesInfo name='BCP' value='26' />
4597  <seriesInfo name='RFC' value='5226' />
4600<reference anchor="RFC5322">
4601  <front>
4602    <title>Internet Message Format</title>
4603    <author initials="P." surname="Resnick" fullname="P. Resnick">
4604      <organization>Qualcomm Incorporated</organization>
4605    </author>
4606    <date year="2008" month="October"/>
4607  </front>
4608  <seriesInfo name="RFC" value="5322"/>
4611<reference anchor='BCP97'>
4612  <front>
4613    <title>Handling Normative References to Standards-Track Documents</title>
4614    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4615      <address>
4616        <email></email>
4617      </address>
4618    </author>
4619    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4620      <organization>MIT</organization>
4621      <address>
4622        <email></email>
4623      </address>
4624    </author>
4625    <date year='2007' month='June' />
4626  </front>
4627  <seriesInfo name='BCP' value='97' />
4628  <seriesInfo name='RFC' value='4897' />
4631<reference anchor="Kri2001" target="">
4632  <front>
4633    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4634    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4635    <date year="2001" month="November"/>
4636  </front>
4637  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4640<reference anchor="Spe" target="">
4641  <front>
4642    <title>Analysis of HTTP Performance Problems</title>
4643    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4644    <date/>
4645  </front>
4648<reference anchor="Tou1998" target="">
4649  <front>
4650  <title>Analysis of HTTP Performance</title>
4651  <author initials="J." surname="Touch" fullname="Joe Touch">
4652    <organization>USC/Information Sciences Institute</organization>
4653    <address><email></email></address>
4654  </author>
4655  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4656    <organization>USC/Information Sciences Institute</organization>
4657    <address><email></email></address>
4658  </author>
4659  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4660    <organization>USC/Information Sciences Institute</organization>
4661    <address><email></email></address>
4662  </author>
4663  <date year="1998" month="Aug"/>
4664  </front>
4665  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4666  <annotation>(original report dated Aug. 1996)</annotation>
4672<section title="Tolerant Applications" anchor="tolerant.applications">
4674   Although this document specifies the requirements for the generation
4675   of HTTP/1.1 messages, not all applications will be correct in their
4676   implementation. We therefore recommend that operational applications
4677   be tolerant of deviations whenever those deviations can be
4678   interpreted unambiguously.
4681   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4682   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4683   &SHOULD; accept any amount of WSP characters between fields, even though
4684   only a single SP is required.
4687   The line terminator for header fields is the sequence CRLF.
4688   However, we recommend that applications, when parsing such headers,
4689   recognize a single LF as a line terminator and ignore the leading CR.
4692   The character set of a representation &SHOULD; be labeled as the lowest
4693   common denominator of the character codes used within that representation, with
4694   the exception that not labeling the representation is preferred over labeling
4695   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4698   Additional rules for requirements on parsing and encoding of dates
4699   and other potential problems with date encodings include:
4702  <list style="symbols">
4703     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4704        which appears to be more than 50 years in the future is in fact
4705        in the past (this helps solve the "year 2000" problem).</t>
4707     <t>Although all date formats are specified to be case-sensitive,
4708        recipients &SHOULD; match day, week and timezone names
4709        case-insensitively.</t>
4711     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4712        Expires date as earlier than the proper value, but &MUST-NOT;
4713        internally represent a parsed Expires date as later than the
4714        proper value.</t>
4716     <t>All expiration-related calculations &MUST; be done in GMT. The
4717        local time zone &MUST-NOT; influence the calculation or comparison
4718        of an age or expiration time.</t>
4720     <t>If an HTTP header incorrectly carries a date value with a time
4721        zone other than GMT, it &MUST; be converted into GMT using the
4722        most conservative possible conversion.</t>
4723  </list>
4727<section title="Compatibility with Previous Versions" anchor="compatibility">
4729   HTTP has been in use by the World-Wide Web global information initiative
4730   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4731   was a simple protocol for hypertext data transfer across the Internet
4732   with only a single method and no metadata.
4733   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4734   methods and MIME-like messaging that could include metadata about the data
4735   transferred and modifiers on the request/response semantics. However,
4736   HTTP/1.0 did not sufficiently take into consideration the effects of
4737   hierarchical proxies, caching, the need for persistent connections, or
4738   name-based virtual hosts. The proliferation of incompletely-implemented
4739   applications calling themselves "HTTP/1.0" further necessitated a
4740   protocol version change in order for two communicating applications
4741   to determine each other's true capabilities.
4744   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4745   requirements that enable reliable implementations, adding only
4746   those new features that will either be safely ignored by an HTTP/1.0
4747   recipient or only sent when communicating with a party advertising
4748   compliance with HTTP/1.1.
4751   It is beyond the scope of a protocol specification to mandate
4752   compliance with previous versions. HTTP/1.1 was deliberately
4753   designed, however, to make supporting previous versions easy. It is
4754   worth noting that, at the time of composing this specification, we would
4755   expect general-purpose HTTP/1.1 servers to:
4756  <list style="symbols">
4757     <t>understand any valid request in the format of HTTP/1.0 and
4758        1.1;</t>
4760     <t>respond appropriately with a message in the same major version
4761        used by the client.</t>
4762  </list>
4765   And we would expect HTTP/1.1 clients to:
4766  <list style="symbols">
4767     <t>understand any valid response in the format of HTTP/1.0 or
4768        1.1.</t>
4769  </list>
4772   For most implementations of HTTP/1.0, each connection is established
4773   by the client prior to the request and closed by the server after
4774   sending the response. Some implementations implement the Keep-Alive
4775   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4778<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4780   This section summarizes major differences between versions HTTP/1.0
4781   and HTTP/1.1.
4784<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4786   The requirements that clients and servers support the Host request-header,
4787   report an error if the Host request-header (<xref target=""/>) is
4788   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4789   are among the most important changes defined by this
4790   specification.
4793   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4794   addresses and servers; there was no other established mechanism for
4795   distinguishing the intended server of a request than the IP address
4796   to which that request was directed. The changes outlined above will
4797   allow the Internet, once older HTTP clients are no longer common, to
4798   support multiple Web sites from a single IP address, greatly
4799   simplifying large operational Web servers, where allocation of many
4800   IP addresses to a single host has created serious problems. The
4801   Internet will also be able to recover the IP addresses that have been
4802   allocated for the sole purpose of allowing special-purpose domain
4803   names to be used in root-level HTTP URLs. Given the rate of growth of
4804   the Web, and the number of servers already deployed, it is extremely
4805   important that all implementations of HTTP (including updates to
4806   existing HTTP/1.0 applications) correctly implement these
4807   requirements:
4808  <list style="symbols">
4809     <t>Both clients and servers &MUST; support the Host request-header.</t>
4811     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4813     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4814        request does not include a Host request-header.</t>
4816     <t>Servers &MUST; accept absolute URIs.</t>
4817  </list>
4822<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4824   Some clients and servers might wish to be compatible with some
4825   previous implementations of persistent connections in HTTP/1.0
4826   clients and servers. Persistent connections in HTTP/1.0 are
4827   explicitly negotiated as they are not the default behavior. HTTP/1.0
4828   experimental implementations of persistent connections are faulty,
4829   and the new facilities in HTTP/1.1 are designed to rectify these
4830   problems. The problem was that some existing HTTP/1.0 clients might
4831   send Keep-Alive to a proxy server that doesn't understand
4832   Connection, which would then erroneously forward it to the next
4833   inbound server, which would establish the Keep-Alive connection and
4834   result in a hung HTTP/1.0 proxy waiting for the close on the
4835   response. The result is that HTTP/1.0 clients must be prevented from
4836   using Keep-Alive when talking to proxies.
4839   However, talking to proxies is the most important use of persistent
4840   connections, so that prohibition is clearly unacceptable. Therefore,
4841   we need some other mechanism for indicating a persistent connection
4842   is desired, which is safe to use even when talking to an old proxy
4843   that ignores Connection. Persistent connections are the default for
4844   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4845   declaring non-persistence. See <xref target="header.connection"/>.
4848   The original HTTP/1.0 form of persistent connections (the Connection:
4849   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4853<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4855  Empty list elements in list productions have been deprecated.
4856  (<xref target="notation.abnf"/>)
4859  Rules about implicit linear whitespace between certain grammar productions
4860  have been removed; now it's only allowed when specifically pointed out
4861  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4862  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4863  Non-ASCII content in header fields and reason phrase has been obsoleted and
4864  made opaque (the TEXT rule was removed)
4865  (<xref target="basic.rules"/>)
4868  Clarify that HTTP-Version is case sensitive.
4869  (<xref target="http.version"/>)
4872  Remove reference to non-existent identity transfer-coding value tokens.
4873  (Sections <xref format="counter" target="transfer.codings"/> and
4874  <xref format="counter" target="message.body"/>)
4877  Require that invalid whitespace around field-names be rejected.
4878  (<xref target="header.fields"/>)
4881  Update use of abs_path production from RFC1808 to the path-absolute + query
4882  components of RFC3986.
4883  (<xref target="request-target"/>)
4886  Clarification that the chunk length does not include the count of the octets
4887  in the chunk header and trailer. Furthermore disallowed line folding
4888  in chunk extensions.
4889  (<xref target="chunked.encoding"/>)
4892  Remove hard limit of two connections per server.
4893  (<xref target="persistent.practical"/>)
4896  Clarify exactly when close connection options must be sent.
4897  (<xref target="header.connection"/>)
4902<?BEGININC p1-messaging.abnf-appendix ?>
4903<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4905<artwork type="abnf" name="p1-messaging.parsed-abnf">
4906<x:ref>BWS</x:ref> = OWS
4908<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4909<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4910<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4911<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4912 connection-token ] )
4913<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4914<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4916<x:ref>Date</x:ref> = "Date:" OWS Date-v
4917<x:ref>Date-v</x:ref> = HTTP-date
4919<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4921<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4922<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4923<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4924<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4925 ]
4926<x:ref>Host</x:ref> = "Host:" OWS Host-v
4927<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4929<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4930<x:ref>Method</x:ref> = token
4932<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4934<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4936<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4937<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4938<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
4939<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4940<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
4942<x:ref>Status-Code</x:ref> = 3DIGIT
4943<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4945<x:ref>TE</x:ref> = "TE:" OWS TE-v
4946<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4947<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4948<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4949<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4950<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4951 transfer-coding ] )
4953<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4954<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4955<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4957<x:ref>Via</x:ref> = "Via:" OWS Via-v
4958<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4959 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4960 ] )
4962<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4964<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4965<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4966<x:ref>attribute</x:ref> = token
4967<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4969<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4970<x:ref>chunk-data</x:ref> = 1*OCTET
4971<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4972<x:ref>chunk-ext-name</x:ref> = token
4973<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4974<x:ref>chunk-size</x:ref> = 1*HEXDIG
4975<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4976<x:ref>connection-token</x:ref> = token
4977<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4978 / %x2A-5B ; '*'-'['
4979 / %x5D-7E ; ']'-'~'
4980 / obs-text
4982<x:ref>date1</x:ref> = day SP month SP year
4983<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4984<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4985<x:ref>day</x:ref> = 2DIGIT
4986<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4987 / %x54.75.65 ; Tue
4988 / %x57.65.64 ; Wed
4989 / %x54.68.75 ; Thu
4990 / %x46.72.69 ; Fri
4991 / %x53.61.74 ; Sat
4992 / %x53.75.6E ; Sun
4993<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4994 / %x54. ; Tuesday
4995 / %x57.65.64.6E. ; Wednesday
4996 / %x54. ; Thursday
4997 / %x46. ; Friday
4998 / %x53. ; Saturday
4999 / %x53.75.6E.64.61.79 ; Sunday
5001<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5002<x:ref>field-name</x:ref> = token
5003<x:ref>field-value</x:ref> = *( field-content / OWS )
5005<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5006 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5008<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5009<x:ref>hour</x:ref> = 2DIGIT
5010<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5011<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5013<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5015<x:ref>message-body</x:ref> = *OCTET
5016<x:ref>minute</x:ref> = 2DIGIT
5017<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5018 / %x46.65.62 ; Feb
5019 / %x4D.61.72 ; Mar
5020 / %x41.70.72 ; Apr
5021 / %x4D.61.79 ; May
5022 / %x4A.75.6E ; Jun
5023 / %x4A.75.6C ; Jul
5024 / %x41.75.67 ; Aug
5025 / %x53.65.70 ; Sep
5026 / %x4F.63.74 ; Oct
5027 / %x4E.6F.76 ; Nov
5028 / %x44.65.63 ; Dec
5030<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5031<x:ref>obs-fold</x:ref> = CRLF
5032<x:ref>obs-text</x:ref> = %x80-FF
5034<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5035<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5036<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5037<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5038<x:ref>product</x:ref> = token [ "/" product-version ]
5039<x:ref>product-version</x:ref> = token
5040<x:ref>protocol-name</x:ref> = token
5041<x:ref>protocol-version</x:ref> = token
5042<x:ref>pseudonym</x:ref> = token
5044<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5045 / %x5D-7E ; ']'-'~'
5046 / obs-text
5047<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5048 / %x5D-7E ; ']'-'~'
5049 / obs-text
5050<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5051<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5052<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5053<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5054<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5055<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5057<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5058<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5059<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5060<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5061<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5062 / authority
5063<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5064<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5065<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5067<x:ref>second</x:ref> = 2DIGIT
5068<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5069 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5070<x:ref>start-line</x:ref> = Request-Line / Status-Line
5072<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5073<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5074 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5075<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5076<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5077<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5078<x:ref>token</x:ref> = 1*tchar
5079<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5080<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5081 transfer-extension
5082<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5083<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5085<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5087<x:ref>value</x:ref> = word
5089<x:ref>word</x:ref> = token / quoted-string
5091<x:ref>year</x:ref> = 4DIGIT
5094<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5095; Chunked-Body defined but not used
5096; Content-Length defined but not used
5097; HTTP-message defined but not used
5098; Host defined but not used
5099; Request defined but not used
5100; Response defined but not used
5101; TE defined but not used
5102; URI-reference defined but not used
5103; general-header defined but not used
5104; http-URI defined but not used
5105; https-URI defined but not used
5106; partial-URI defined but not used
5107; request-header defined but not used
5108; response-header defined but not used
5109; special defined but not used
5111<?ENDINC p1-messaging.abnf-appendix ?>
5113<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5115<section title="Since RFC2616">
5117  Extracted relevant partitions from <xref target="RFC2616"/>.
5121<section title="Since draft-ietf-httpbis-p1-messaging-00">
5123  Closed issues:
5124  <list style="symbols">
5125    <t>
5126      <eref target=""/>:
5127      "HTTP Version should be case sensitive"
5128      (<eref target=""/>)
5129    </t>
5130    <t>
5131      <eref target=""/>:
5132      "'unsafe' characters"
5133      (<eref target=""/>)
5134    </t>
5135    <t>
5136      <eref target=""/>:
5137      "Chunk Size Definition"
5138      (<eref target=""/>)
5139    </t>
5140    <t>
5141      <eref target=""/>:
5142      "Message Length"
5143      (<eref target=""/>)
5144    </t>
5145    <t>
5146      <eref target=""/>:
5147      "Media Type Registrations"
5148      (<eref target=""/>)
5149    </t>
5150    <t>
5151      <eref target=""/>:
5152      "URI includes query"
5153      (<eref target=""/>)
5154    </t>
5155    <t>
5156      <eref target=""/>:
5157      "No close on 1xx responses"
5158      (<eref target=""/>)
5159    </t>
5160    <t>
5161      <eref target=""/>:
5162      "Remove 'identity' token references"
5163      (<eref target=""/>)
5164    </t>
5165    <t>
5166      <eref target=""/>:
5167      "Import query BNF"
5168    </t>
5169    <t>
5170      <eref target=""/>:
5171      "qdtext BNF"
5172    </t>
5173    <t>
5174      <eref target=""/>:
5175      "Normative and Informative references"
5176    </t>
5177    <t>
5178      <eref target=""/>:
5179      "RFC2606 Compliance"
5180    </t>
5181    <t>
5182      <eref target=""/>:
5183      "RFC977 reference"
5184    </t>
5185    <t>
5186      <eref target=""/>:
5187      "RFC1700 references"
5188    </t>
5189    <t>
5190      <eref target=""/>:
5191      "inconsistency in date format explanation"
5192    </t>
5193    <t>
5194      <eref target=""/>:
5195      "Date reference typo"
5196    </t>
5197    <t>
5198      <eref target=""/>:
5199      "Informative references"
5200    </t>
5201    <t>
5202      <eref target=""/>:
5203      "ISO-8859-1 Reference"
5204    </t>
5205    <t>
5206      <eref target=""/>:
5207      "Normative up-to-date references"
5208    </t>
5209  </list>
5212  Other changes:
5213  <list style="symbols">
5214    <t>
5215      Update media type registrations to use RFC4288 template.
5216    </t>
5217    <t>
5218      Use names of RFC4234 core rules DQUOTE and WSP,
5219      fix broken ABNF for chunk-data
5220      (work in progress on <eref target=""/>)
5221    </t>
5222  </list>
5226<section title="Since draft-ietf-httpbis-p1-messaging-01">
5228  Closed issues:
5229  <list style="symbols">
5230    <t>
5231      <eref target=""/>:
5232      "Bodies on GET (and other) requests"
5233    </t>
5234    <t>
5235      <eref target=""/>:
5236      "Updating to RFC4288"
5237    </t>
5238    <t>
5239      <eref target=""/>:
5240      "Status Code and Reason Phrase"
5241    </t>
5242    <t>
5243      <eref target=""/>:
5244      "rel_path not used"
5245    </t>
5246  </list>
5249  Ongoing work on ABNF conversion (<eref target=""/>):
5250  <list style="symbols">
5251    <t>
5252      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5253      "trailer-part").
5254    </t>
5255    <t>
5256      Avoid underscore character in rule names ("http_URL" ->
5257      "http-URL", "abs_path" -> "path-absolute").
5258    </t>
5259    <t>
5260      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5261      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5262      have to be updated when switching over to RFC3986.
5263    </t>
5264    <t>
5265      Synchronize core rules with RFC5234.
5266    </t>
5267    <t>
5268      Get rid of prose rules that span multiple lines.
5269    </t>
5270    <t>
5271      Get rid of unused rules LOALPHA and UPALPHA.
5272    </t>
5273    <t>
5274      Move "Product Tokens" section (back) into Part 1, as "token" is used
5275      in the definition of the Upgrade header.
5276    </t>
5277    <t>
5278      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5279    </t>
5280    <t>
5281      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5282    </t>
5283  </list>
5287<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5289  Closed issues:
5290  <list style="symbols">
5291    <t>
5292      <eref target=""/>:
5293      "HTTP-date vs. rfc1123-date"
5294    </t>
5295    <t>
5296      <eref target=""/>:
5297      "WS in quoted-pair"
5298    </t>
5299  </list>
5302  Ongoing work on IANA Message Header Registration (<eref target=""/>):
5303  <list style="symbols">
5304    <t>
5305      Reference RFC 3984, and update header registrations for headers defined
5306      in this document.
5307    </t>
5308  </list>
5311  Ongoing work on ABNF conversion (<eref target=""/>):
5312  <list style="symbols">
5313    <t>
5314      Replace string literals when the string really is case-sensitive (HTTP-Version).
5315    </t>
5316  </list>
5320<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5322  Closed issues:
5323  <list style="symbols">
5324    <t>
5325      <eref target=""/>:
5326      "Connection closing"
5327    </t>
5328    <t>
5329      <eref target=""/>:
5330      "Move registrations and registry information to IANA Considerations"
5331    </t>
5332    <t>
5333      <eref target=""/>:
5334      "need new URL for PAD1995 reference"
5335    </t>
5336    <t>
5337      <eref target=""/>:
5338      "IANA Considerations: update HTTP URI scheme registration"
5339    </t>
5340    <t>
5341      <eref target=""/>:
5342      "Cite HTTPS URI scheme definition"
5343    </t>
5344    <t>
5345      <eref target=""/>:
5346      "List-type headers vs Set-Cookie"
5347    </t>
5348  </list>
5351  Ongoing work on ABNF conversion (<eref target=""/>):
5352  <list style="symbols">
5353    <t>
5354      Replace string literals when the string really is case-sensitive (HTTP-Date).
5355    </t>
5356    <t>
5357      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5358    </t>
5359  </list>
5363<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5365  Closed issues:
5366  <list style="symbols">
5367    <t>
5368      <eref target=""/>:
5369      "Out-of-date reference for URIs"
5370    </t>
5371    <t>
5372      <eref target=""/>:
5373      "RFC 2822 is updated by RFC 5322"
5374    </t>
5375  </list>
5378  Ongoing work on ABNF conversion (<eref target=""/>):
5379  <list style="symbols">
5380    <t>
5381      Use "/" instead of "|" for alternatives.
5382    </t>
5383    <t>
5384      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5385    </t>
5386    <t>
5387      Only reference RFC 5234's core rules.
5388    </t>
5389    <t>
5390      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5391      whitespace ("OWS") and required whitespace ("RWS").
5392    </t>
5393    <t>
5394      Rewrite ABNFs to spell out whitespace rules, factor out
5395      header value format definitions.
5396    </t>
5397  </list>
5401<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5403  Closed issues:
5404  <list style="symbols">
5405    <t>
5406      <eref target=""/>:
5407      "Header LWS"
5408    </t>
5409    <t>
5410      <eref target=""/>:
5411      "Sort 1.3 Terminology"
5412    </t>
5413    <t>
5414      <eref target=""/>:
5415      "RFC2047 encoded words"
5416    </t>
5417    <t>
5418      <eref target=""/>:
5419      "Character Encodings in TEXT"
5420    </t>
5421    <t>
5422      <eref target=""/>:
5423      "Line Folding"
5424    </t>
5425    <t>
5426      <eref target=""/>:
5427      "OPTIONS * and proxies"
5428    </t>
5429    <t>
5430      <eref target=""/>:
5431      "Reason-Phrase BNF"
5432    </t>
5433    <t>
5434      <eref target=""/>:
5435      "Use of TEXT"
5436    </t>
5437    <t>
5438      <eref target=""/>:
5439      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5440    </t>
5441    <t>
5442      <eref target=""/>:
5443      "RFC822 reference left in discussion of date formats"
5444    </t>
5445  </list>
5448  Final work on ABNF conversion (<eref target=""/>):
5449  <list style="symbols">
5450    <t>
5451      Rewrite definition of list rules, deprecate empty list elements.
5452    </t>
5453    <t>
5454      Add appendix containing collected and expanded ABNF.
5455    </t>
5456  </list>
5459  Other changes:
5460  <list style="symbols">
5461    <t>
5462      Rewrite introduction; add mostly new Architecture Section.
5463    </t>
5464    <t>
5465      Move definition of quality values from Part 3 into Part 1;
5466      make TE request header grammar independent of accept-params (defined in Part 3).
5467    </t>
5468  </list>
5472<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5474  Closed issues:
5475  <list style="symbols">
5476    <t>
5477      <eref target=""/>:
5478      "base for numeric protocol elements"
5479    </t>
5480    <t>
5481      <eref target=""/>:
5482      "comment ABNF"
5483    </t>
5484  </list>
5487  Partly resolved issues:
5488  <list style="symbols">
5489    <t>
5490      <eref target=""/>:
5491      "205 Bodies" (took out language that implied that there might be
5492      methods for which a request body MUST NOT be included)
5493    </t>
5494    <t>
5495      <eref target=""/>:
5496      "editorial improvements around HTTP-date"
5497    </t>
5498  </list>
5502<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5504  Closed issues:
5505  <list style="symbols">
5506    <t>
5507      <eref target=""/>:
5508      "Repeating single-value headers"
5509    </t>
5510    <t>
5511      <eref target=""/>:
5512      "increase connection limit"
5513    </t>
5514    <t>
5515      <eref target=""/>:
5516      "IP addresses in URLs"
5517    </t>
5518    <t>
5519      <eref target=""/>:
5520      "take over HTTP Upgrade Token Registry"
5521    </t>
5522    <t>
5523      <eref target=""/>:
5524      "CR and LF in chunk extension values"
5525    </t>
5526    <t>
5527      <eref target=""/>:
5528      "HTTP/0.9 support"
5529    </t>
5530    <t>
5531      <eref target=""/>:
5532      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5533    </t>
5534    <t>
5535      <eref target=""/>:
5536      "move definitions of gzip/deflate/compress to part 1"
5537    </t>
5538    <t>
5539      <eref target=""/>:
5540      "disallow control characters in quoted-pair"
5541    </t>
5542  </list>
5545  Partly resolved issues:
5546  <list style="symbols">
5547    <t>
5548      <eref target=""/>:
5549      "update IANA requirements wrt Transfer-Coding values" (add the
5550      IANA Considerations subsection)
5551    </t>
5552  </list>
5556<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5558  Closed issues:
5559  <list style="symbols">
5560    <t>
5561      <eref target=""/>:
5562      "header parsing, treatment of leading and trailing OWS"
5563    </t>
5564  </list>
5567  Partly resolved issues:
5568  <list style="symbols">
5569    <t>
5570      <eref target=""/>:
5571      "Placement of 13.5.1 and 13.5.2"
5572    </t>
5573    <t>
5574      <eref target=""/>:
5575      "use of term "word" when talking about header structure"
5576    </t>
5577  </list>
5581<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5583  Closed issues:
5584  <list style="symbols">
5585    <t>
5586      <eref target=""/>:
5587      "Clarification of the term 'deflate'"
5588    </t>
5589    <t>
5590      <eref target=""/>:
5591      "OPTIONS * and proxies"
5592    </t>
5593    <t>
5594      <eref target=""/>:
5595      "MIME-Version not listed in P1, general header fields"
5596    </t>
5597    <t>
5598      <eref target=""/>:
5599      "IANA registry for content/transfer encodings"
5600    </t>
5601    <t>
5602      <eref target=""/>:
5603      "Case-sensitivity of HTTP-date"
5604    </t>
5605    <t>
5606      <eref target=""/>:
5607      "use of term "word" when talking about header structure"
5608    </t>
5609  </list>
5612  Partly resolved issues:
5613  <list style="symbols">
5614    <t>
5615      <eref target=""/>:
5616      "Term for the requested resource's URI"
5617    </t>
5618  </list>
5622<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5624  Closed issues:
5625  <list style="symbols">
5626    <t>
5627      <eref target=""/>:
5628      "Connection Closing"
5629    </t>
5630    <t>
5631      <eref target=""/>:
5632      "Delimiting messages with multipart/byteranges"
5633    </t>
5634    <t>
5635      <eref target=""/>:
5636      "Handling multiple Content-Length headers"
5637    </t>
5638    <t>
5639      <eref target=""/>:
5640      "Clarify entity / representation / variant terminology"
5641    </t>
5642    <t>
5643      <eref target=""/>:
5644      "consider removing the 'changes from 2068' sections"
5645    </t>
5646  </list>
5649  Partly resolved issues:
5650  <list style="symbols">
5651    <t>
5652      <eref target=""/>:
5653      "HTTP(s) URI scheme definitions"
5654    </t>
5655  </list>
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