source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1028

Last change on this file since 1028 was 1028, checked in by julian.reschke@…, 11 years ago

add a comment to rfc1123-date ABNF, pointing out the difference to what 1123 says

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File size: 241.2 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 "October">
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.11"/>.
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 field 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 field 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 identifies the resource upon which to apply the request.
1505<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1506  <x:ref>request-target</x:ref> = "*"
1507                 / <x:ref>absolute-URI</x:ref>
1508                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1509                 / <x:ref>authority</x:ref>
1512   The four options for request-target are dependent on the nature of the
1513   request.
1515<t><iref item="asterisk form (of request-target)"/>
1516   The asterisk "*" ("asterisk form") means that the request does not apply to a
1517   particular resource, but to the server itself, and is only allowed
1518   when the method used does not necessarily apply to a resource. One
1519   example would be
1521<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1522OPTIONS * HTTP/1.1
1524<t><iref item="absolute-URI form (of request-target)"/>
1525   The absolute-URI form is &REQUIRED; when the request is being made to a
1526   proxy. The proxy is requested to forward the request or service it
1527   from a valid cache, and return the response. Note that the proxy &MAY;
1528   forward the request on to another proxy or directly to the server
1529   specified by the absolute-URI. In order to avoid request loops, a
1530   proxy &MUST; be able to recognize all of its server names, including
1531   any aliases, local variations, and the numeric IP address. An example
1532   Request-Line would be:
1534<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1535GET HTTP/1.1
1538   To allow for transition to absolute-URIs in all requests in future
1539   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1540   form in requests, even though HTTP/1.1 clients will only generate
1541   them in requests to proxies.
1543<t><iref item="authority form (of request-target)"/>
1544   The authority form is only used by the CONNECT method (&CONNECT;).
1546<t><iref item="path-absolute form (of request-target)"/>
1547   The most common form of request-target is that used to identify a
1548   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1549   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1550   the request-target, and the network location of the URI (authority) &MUST;
1551   be transmitted in a Host header field. For example, a client wishing
1552   to retrieve the resource above directly from the origin server would
1553   create a TCP connection to port 80 of the host "" and send
1554   the lines:
1556<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1557GET /pub/WWW/TheProject.html HTTP/1.1
1561   followed by the remainder of the Request. Note that the absolute path
1562   cannot be empty; if none is present in the original URI, it &MUST; be
1563   given as "/" (the server root).
1566   If a proxy receives a request without any path in the request-target and
1567   the method specified is capable of supporting the asterisk form of
1568   request-target, then the last proxy on the request chain &MUST; forward the
1569   request with "*" as the final request-target.
1572   For example, the request
1573</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1577  would be forwarded by the proxy as
1578</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1579OPTIONS * HTTP/1.1
1583   after connecting to port 8001 of host "".
1587   The request-target is transmitted in the format specified in
1588   <xref target="http.uri"/>. If the request-target is percent-encoded
1589   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1590   &MUST; decode the request-target in order to
1591   properly interpret the request. Servers &SHOULD; respond to invalid
1592   request-targets with an appropriate status code.
1595   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1596   received request-target when forwarding it to the next inbound server,
1597   except as noted above to replace a null path-absolute with "/" or "*".
1600  <t>
1601    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1602    meaning of the request when the origin server is improperly using
1603    a non-reserved URI character for a reserved purpose.  Implementors
1604    need to be aware that some pre-HTTP/1.1 proxies have been known to
1605    rewrite the request-target.
1606  </t>
1609   HTTP does not place a pre-defined limit on the length of a request-target.
1610   A server &MUST; be prepared to receive URIs of unbounded length and
1611   respond with the 414 (URI Too Long) status code if the received
1612   request-target would be longer than the server wishes to handle
1613   (see &status-414;).
1616   Various ad-hoc limitations on request-target length are found in practice.
1617   It is &RECOMMENDED; that all HTTP senders and recipients support
1618   request-target lengths of 8000 or more octets.
1621  <t>
1622    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1623    are not part of the request-target and thus will not be transmitted
1624    in an HTTP request.
1625  </t>
1630<section title="The Resource Identified by a Request" anchor="">
1632   The exact resource identified by an Internet request is determined by
1633   examining both the request-target and the Host header field.
1636   An origin server that does not allow resources to differ by the
1637   requested host &MAY; ignore the Host header field value when
1638   determining the resource identified by an HTTP/1.1 request. (But see
1639   <xref target=""/>
1640   for other requirements on Host support in HTTP/1.1.)
1643   An origin server that does differentiate resources based on the host
1644   requested (sometimes referred to as virtual hosts or vanity host
1645   names) &MUST; use the following rules for determining the requested
1646   resource on an HTTP/1.1 request:
1647  <list style="numbers">
1648    <t>If request-target is an absolute-URI, the host is part of the
1649     request-target. Any Host header field value in the request &MUST; be
1650     ignored.</t>
1651    <t>If the request-target is not an absolute-URI, and the request includes
1652     a Host header field, the host is determined by the Host header
1653     field value.</t>
1654    <t>If the host as determined by rule 1 or 2 is not a valid host on
1655     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1656  </list>
1659   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1660   attempt to use heuristics (e.g., examination of the URI path for
1661   something unique to a particular host) in order to determine what
1662   exact resource is being requested.
1666<section title="Effective Request URI" anchor="effective.request.uri">
1667  <iref primary="true" item="effective request URI"/>
1668  <iref primary="true" item="target resource"/>
1670   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1671   for the target resource; instead, the URI needs to be inferred from the
1672   request-target, Host header field, and connection context. The result of
1673   this process is called the "effective request URI".  The "target resource"
1674   is the resource identified by the effective request URI.
1677   If the request-target is an absolute-URI, then the effective request URI is
1678   the request-target.
1681   If the request-target uses the path-absolute form or the asterisk form,
1682   and the Host header field is present, then the effective request URI is
1683   constructed by concatenating
1686  <list style="symbols">
1687    <t>
1688      the scheme name: "http" if the request was received over an insecure
1689      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1690      connection,
1691    </t>
1692    <t>
1693      the character sequence "://",
1694    </t>
1695    <t>
1696      the authority component, as specified in the Host header field
1697      (<xref target=""/>), and
1698    </t>
1699    <t>
1700      the request-target obtained from the Request-Line, unless the
1701      request-target is just the asterisk "*".
1702    </t>
1703  </list>
1706   If the request-target uses the path-absolute form or the asterisk form,
1707   and the Host header field is not present, then the effective request URI is
1708   undefined.
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. However, the preferred format is a fixed-length subset
1832   of that defined by <xref target="RFC1123"/>:
1834<figure><artwork type="example" x:indent-with="  ">
1835Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1838   The other formats are described here only for compatibility with obsolete
1839   implementations.
1841<figure><artwork type="example" x:indent-with="  ">
1842Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1843Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1846   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1847   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1848   only generate the RFC 1123 format for representing HTTP-date values
1849   in header fields. See <xref target="tolerant.applications"/> for further information.
1852   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1853   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1854   equal to UTC (Coordinated Universal Time). This is indicated in the
1855   first two formats by the inclusion of "GMT" as the three-letter
1856   abbreviation for time zone, and &MUST; be assumed when reading the
1857   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1858   additional whitespace beyond that specifically included as SP in the
1859   grammar.
1861<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1862  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1864<t anchor="">
1865  <x:anchor-alias value="rfc1123-date"/>
1866  <x:anchor-alias value="time-of-day"/>
1867  <x:anchor-alias value="hour"/>
1868  <x:anchor-alias value="minute"/>
1869  <x:anchor-alias value="second"/>
1870  <x:anchor-alias value="day-name"/>
1871  <x:anchor-alias value="day"/>
1872  <x:anchor-alias value="month"/>
1873  <x:anchor-alias value="year"/>
1874  <x:anchor-alias value="GMT"/>
1875  Preferred format:
1877<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"/>
1878  <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>
1879  ; fixed length subset of the format defined in
1880  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1882  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1883               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1884               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1885               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1886               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1887               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1888               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1890  <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>
1891               ; e.g., 02 Jun 1982
1893  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1894  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1895               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1896               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1897               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1898               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1899               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1900               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1901               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1902               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1903               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1904               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1905               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1906  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1908  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1910  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1911                 ; 00:00:00 - 23:59:59
1913  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1914  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1915  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1918  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1919  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1920  same as those defined for the RFC 5322 constructs
1921  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1923<t anchor="">
1924  <x:anchor-alias value="obs-date"/>
1925  <x:anchor-alias value="rfc850-date"/>
1926  <x:anchor-alias value="asctime-date"/>
1927  <x:anchor-alias value="date1"/>
1928  <x:anchor-alias value="date2"/>
1929  <x:anchor-alias value="date3"/>
1930  <x:anchor-alias value="rfc1123-date"/>
1931  <x:anchor-alias value="day-name-l"/>
1932  Obsolete formats:
1934<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1935  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1937<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1938  <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>
1939  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1940                 ; day-month-year (e.g., 02-Jun-82)
1942  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1943         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1944         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1945         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1946         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1947         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1948         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1950<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1951  <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>
1952  <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> ))
1953                 ; month day (e.g., Jun  2)
1956  <t>
1957    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1958    accepting date values that might have been sent by non-HTTP
1959    applications, as is sometimes the case when retrieving or posting
1960    messages via proxies/gateways to SMTP or NNTP.
1961  </t>
1964  <t>
1965    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1966    to their usage within the protocol stream. Clients and servers are
1967    not required to use these formats for user presentation, request
1968    logging, etc.
1969  </t>
1973<section title="Transfer Codings" anchor="transfer.codings">
1974  <x:anchor-alias value="transfer-coding"/>
1975  <x:anchor-alias value="transfer-extension"/>
1977   Transfer-coding values are used to indicate an encoding
1978   transformation that has been, can be, or might need to be applied to a
1979   payload body in order to ensure "safe transport" through the network.
1980   This differs from a content coding in that the transfer-coding is a
1981   property of the message rather than a property of the representation
1982   that is being transferred.
1984<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1985  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1986                          / "compress" ; <xref target="compress.coding"/>
1987                          / "deflate" ; <xref target="deflate.coding"/>
1988                          / "gzip" ; <xref target="gzip.coding"/>
1989                          / <x:ref>transfer-extension</x:ref>
1990  <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> )
1992<t anchor="rule.parameter">
1993  <x:anchor-alias value="attribute"/>
1994  <x:anchor-alias value="transfer-parameter"/>
1995  <x:anchor-alias value="value"/>
1996   Parameters are in the form of attribute/value pairs.
1998<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"/>
1999  <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>
2000  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2001  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2004   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2005   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2006   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2009   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2010   MIME, which were designed to enable safe transport of binary data over a
2011   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2012   However, safe transport
2013   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2014   the only unsafe characteristic of message-bodies is the difficulty in
2015   determining the exact message body length (<xref target="message.body"/>),
2016   or the desire to encrypt data over a shared transport.
2019   A server that receives a request message with a transfer-coding it does
2020   not understand &SHOULD; respond with 501 (Not Implemented) and then
2021   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2022   client.
2025<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2026  <iref item="chunked (Coding Format)"/>
2027  <iref item="Coding Format" subitem="chunked"/>
2028  <x:anchor-alias value="chunk"/>
2029  <x:anchor-alias value="Chunked-Body"/>
2030  <x:anchor-alias value="chunk-data"/>
2031  <x:anchor-alias value="chunk-ext"/>
2032  <x:anchor-alias value="chunk-ext-name"/>
2033  <x:anchor-alias value="chunk-ext-val"/>
2034  <x:anchor-alias value="chunk-size"/>
2035  <x:anchor-alias value="last-chunk"/>
2036  <x:anchor-alias value="trailer-part"/>
2037  <x:anchor-alias value="quoted-str-nf"/>
2038  <x:anchor-alias value="qdtext-nf"/>
2040   The chunked encoding modifies the body of a message in order to
2041   transfer it as a series of chunks, each with its own size indicator,
2042   followed by an &OPTIONAL; trailer containing header fields. This
2043   allows dynamically produced content to be transferred along with the
2044   information necessary for the recipient to verify that it has
2045   received the full message.
2047<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"/>
2048  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2049                   <x:ref>last-chunk</x:ref>
2050                   <x:ref>trailer-part</x:ref>
2051                   <x:ref>CRLF</x:ref>
2053  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2054                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2055  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2056  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2058  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2059                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2060  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2061  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2062  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2063  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2065  <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>
2066                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2067  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2068                 ; <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>
2071   The chunk-size field is a string of hex digits indicating the size of
2072   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2073   zero, followed by the trailer, which is terminated by an empty line.
2076   The trailer allows the sender to include additional HTTP header
2077   fields at the end of the message. The Trailer header field can be
2078   used to indicate which header fields are included in a trailer (see
2079   <xref target="header.trailer"/>).
2082   A server using chunked transfer-coding in a response &MUST-NOT; use the
2083   trailer for any header fields unless at least one of the following is
2084   true:
2085  <list style="numbers">
2086    <t>the request included a TE header field that indicates "trailers" is
2087     acceptable in the transfer-coding of the  response, as described in
2088     <xref target="header.te"/>; or,</t>
2090    <t>the server is the origin server for the response, the trailer
2091     fields consist entirely of optional metadata, and the recipient
2092     could use the message (in a manner acceptable to the origin server)
2093     without receiving this metadata.  In other words, the origin server
2094     is willing to accept the possibility that the trailer fields might
2095     be silently discarded along the path to the client.</t>
2096  </list>
2099   This requirement prevents an interoperability failure when the
2100   message is being received by an HTTP/1.1 (or later) proxy and
2101   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2102   compliance with the protocol would have necessitated a possibly
2103   infinite buffer on the proxy.
2106   A process for decoding the "chunked" transfer-coding
2107   can be represented in pseudo-code as:
2109<figure><artwork type="code">
2110  length := 0
2111  read chunk-size, chunk-ext (if any) and CRLF
2112  while (chunk-size &gt; 0) {
2113     read chunk-data and CRLF
2114     append chunk-data to decoded-body
2115     length := length + chunk-size
2116     read chunk-size and CRLF
2117  }
2118  read header-field
2119  while (header-field not empty) {
2120     append header-field to existing header fields
2121     read header-field
2122  }
2123  Content-Length := length
2124  Remove "chunked" from Transfer-Encoding
2127   All HTTP/1.1 applications &MUST; be able to receive and decode the
2128   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2129   they do not understand.
2132   Since "chunked" is the only transfer-coding required to be understood
2133   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2134   on a persistent connection.  Whenever a transfer-coding is applied to
2135   a payload body in a request, the final transfer-coding applied &MUST;
2136   be "chunked".  If a transfer-coding is applied to a response payload
2137   body, then either the final transfer-coding applied &MUST; be "chunked"
2138   or the message &MUST; be terminated by closing the connection. When the
2139   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2140   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2141   be applied more than once in a message-body.
2145<section title="Compression Codings" anchor="compression.codings">
2147   The codings defined below can be used to compress the payload of a
2148   message.
2151   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2152   is not desirable and is discouraged for future encodings. Their
2153   use here is representative of historical practice, not good
2154   design.
2157   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2158   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2159   equivalent to "gzip" and "compress" respectively.
2162<section title="Compress Coding" anchor="compress.coding">
2163<iref item="compress (Coding Format)"/>
2164<iref item="Coding Format" subitem="compress"/>
2166   The "compress" format is produced by the common UNIX file compression
2167   program "compress". This format is an adaptive Lempel-Ziv-Welch
2168   coding (LZW).
2172<section title="Deflate Coding" anchor="deflate.coding">
2173<iref item="deflate (Coding Format)"/>
2174<iref item="Coding Format" subitem="deflate"/>
2176   The "deflate" format is defined as the "deflate" compression mechanism
2177   (described in <xref target="RFC1951"/>) used inside the "zlib"
2178   data format (<xref target="RFC1950"/>).
2181  <t>
2182    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2183    compressed data without the zlib wrapper.
2184   </t>
2188<section title="Gzip Coding" anchor="gzip.coding">
2189<iref item="gzip (Coding Format)"/>
2190<iref item="Coding Format" subitem="gzip"/>
2192   The "gzip" format is produced by the file compression program
2193   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2194   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2200<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2202   The HTTP Transfer Coding Registry defines the name space for the transfer
2203   coding names.
2206   Registrations &MUST; include the following fields:
2207   <list style="symbols">
2208     <t>Name</t>
2209     <t>Description</t>
2210     <t>Pointer to specification text</t>
2211   </list>
2214   Names of transfer codings &MUST-NOT; overlap with names of content codings
2215   (&content-codings;), unless the encoding transformation is identical (as it
2216   is the case for the compression codings defined in
2217   <xref target="compression.codings"/>).
2220   Values to be added to this name space require a specification
2221   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2222   conform to the purpose of transfer coding defined in this section.
2225   The registry itself is maintained at
2226   <eref target=""/>.
2231<section title="Product Tokens" anchor="product.tokens">
2232  <x:anchor-alias value="product"/>
2233  <x:anchor-alias value="product-version"/>
2235   Product tokens are used to allow communicating applications to
2236   identify themselves by software name and version. Most fields using
2237   product tokens also allow sub-products which form a significant part
2238   of the application to be listed, separated by whitespace. By
2239   convention, the products are listed in order of their significance
2240   for identifying the application.
2242<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2243  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2244  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2247   Examples:
2249<figure><artwork type="example">
2250  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2251  Server: Apache/0.8.4
2254   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2255   used for advertising or other non-essential information. Although any
2256   token character &MAY; appear in a product-version, this token &SHOULD;
2257   only be used for a version identifier (i.e., successive versions of
2258   the same product &SHOULD; only differ in the product-version portion of
2259   the product value).
2263<section title="Quality Values" anchor="quality.values">
2264  <x:anchor-alias value="qvalue"/>
2266   Both transfer codings (TE request header field, <xref target="header.te"/>)
2267   and content negotiation (&content.negotiation;) use short "floating point"
2268   numbers to indicate the relative importance ("weight") of various
2269   negotiable parameters.  A weight is normalized to a real number in
2270   the range 0 through 1, where 0 is the minimum and 1 the maximum
2271   value. If a parameter has a quality value of 0, then content with
2272   this parameter is "not acceptable" for the client. HTTP/1.1
2273   applications &MUST-NOT; generate more than three digits after the
2274   decimal point. User configuration of these values &SHOULD; also be
2275   limited in this fashion.
2277<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2278  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2279                 / ( "1" [ "." 0*3("0") ] )
2282  <t>
2283     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2284     relative degradation in desired quality.
2285  </t>
2291<section title="Connections" anchor="connections">
2293<section title="Persistent Connections" anchor="persistent.connections">
2295<section title="Purpose" anchor="persistent.purpose">
2297   Prior to persistent connections, a separate TCP connection was
2298   established to fetch each URL, increasing the load on HTTP servers
2299   and causing congestion on the Internet. The use of inline images and
2300   other associated data often requires a client to make multiple
2301   requests of the same server in a short amount of time. Analysis of
2302   these performance problems and results from a prototype
2303   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2304   measurements of actual HTTP/1.1 implementations show good
2305   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2306   T/TCP <xref target="Tou1998"/>.
2309   Persistent HTTP connections have a number of advantages:
2310  <list style="symbols">
2311      <t>
2312        By opening and closing fewer TCP connections, CPU time is saved
2313        in routers and hosts (clients, servers, proxies, gateways,
2314        tunnels, or caches), and memory used for TCP protocol control
2315        blocks can be saved in hosts.
2316      </t>
2317      <t>
2318        HTTP requests and responses can be pipelined on a connection.
2319        Pipelining allows a client to make multiple requests without
2320        waiting for each response, allowing a single TCP connection to
2321        be used much more efficiently, with much lower elapsed time.
2322      </t>
2323      <t>
2324        Network congestion is reduced by reducing the number of packets
2325        caused by TCP opens, and by allowing TCP sufficient time to
2326        determine the congestion state of the network.
2327      </t>
2328      <t>
2329        Latency on subsequent requests is reduced since there is no time
2330        spent in TCP's connection opening handshake.
2331      </t>
2332      <t>
2333        HTTP can evolve more gracefully, since errors can be reported
2334        without the penalty of closing the TCP connection. Clients using
2335        future versions of HTTP might optimistically try a new feature,
2336        but if communicating with an older server, retry with old
2337        semantics after an error is reported.
2338      </t>
2339    </list>
2342   HTTP implementations &SHOULD; implement persistent connections.
2346<section title="Overall Operation" anchor="persistent.overall">
2348   A significant difference between HTTP/1.1 and earlier versions of
2349   HTTP is that persistent connections are the default behavior of any
2350   HTTP connection. That is, unless otherwise indicated, the client
2351   &SHOULD; assume that the server will maintain a persistent connection,
2352   even after error responses from the server.
2355   Persistent connections provide a mechanism by which a client and a
2356   server can signal the close of a TCP connection. This signaling takes
2357   place using the Connection header field (<xref target="header.connection"/>). Once a close
2358   has been signaled, the client &MUST-NOT; send any more requests on that
2359   connection.
2362<section title="Negotiation" anchor="persistent.negotiation">
2364   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2365   maintain a persistent connection unless a Connection header field including
2366   the connection-token "close" was sent in the request. If the server
2367   chooses to close the connection immediately after sending the
2368   response, it &SHOULD; send a Connection header field including the
2369   connection-token "close".
2372   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2373   decide to keep it open based on whether the response from a server
2374   contains a Connection header field with the connection-token close. In case
2375   the client does not want to maintain a connection for more than that
2376   request, it &SHOULD; send a Connection header field including the
2377   connection-token close.
2380   If either the client or the server sends the close token in the
2381   Connection header field, that request becomes the last one for the
2382   connection.
2385   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2386   maintained for HTTP versions less than 1.1 unless it is explicitly
2387   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2388   compatibility with HTTP/1.0 clients.
2391   In order to remain persistent, all messages on the connection &MUST;
2392   have a self-defined message length (i.e., one not defined by closure
2393   of the connection), as described in <xref target="message.body"/>.
2397<section title="Pipelining" anchor="pipelining">
2399   A client that supports persistent connections &MAY; "pipeline" its
2400   requests (i.e., send multiple requests without waiting for each
2401   response). A server &MUST; send its responses to those requests in the
2402   same order that the requests were received.
2405   Clients which assume persistent connections and pipeline immediately
2406   after connection establishment &SHOULD; be prepared to retry their
2407   connection if the first pipelined attempt fails. If a client does
2408   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2409   persistent. Clients &MUST; also be prepared to resend their requests if
2410   the server closes the connection before sending all of the
2411   corresponding responses.
2414   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2415   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2416   premature termination of the transport connection could lead to
2417   indeterminate results. A client wishing to send a non-idempotent
2418   request &SHOULD; wait to send that request until it has received the
2419   response status line for the previous request.
2424<section title="Proxy Servers" anchor="persistent.proxy">
2426   It is especially important that proxies correctly implement the
2427   properties of the Connection header field as specified in <xref target="header.connection"/>.
2430   The proxy server &MUST; signal persistent connections separately with
2431   its clients and the origin servers (or other proxy servers) that it
2432   connects to. Each persistent connection applies to only one transport
2433   link.
2436   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2437   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2438   for information and discussion of the problems with the Keep-Alive header field
2439   implemented by many HTTP/1.0 clients).
2442<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2444  <cref anchor="TODO-end-to-end" source="jre">
2445    Restored from <eref target=""/>.
2446    See also <eref target=""/>.
2447  </cref>
2450   For the purpose of defining the behavior of caches and non-caching
2451   proxies, we divide HTTP header fields into two categories:
2452  <list style="symbols">
2453      <t>End-to-end header fields, which are  transmitted to the ultimate
2454        recipient of a request or response. End-to-end header fields in
2455        responses MUST be stored as part of a cache entry and &MUST; be
2456        transmitted in any response formed from a cache entry.</t>
2458      <t>Hop-by-hop header fields, which are meaningful only for a single
2459        transport-level connection, and are not stored by caches or
2460        forwarded by proxies.</t>
2461  </list>
2464   The following HTTP/1.1 header fields are hop-by-hop header fields:
2465  <list style="symbols">
2466      <t>Connection</t>
2467      <t>Keep-Alive</t>
2468      <t>Proxy-Authenticate</t>
2469      <t>Proxy-Authorization</t>
2470      <t>TE</t>
2471      <t>Trailer</t>
2472      <t>Transfer-Encoding</t>
2473      <t>Upgrade</t>
2474  </list>
2477   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2480   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2481   (<xref target="header.connection"/>).
2485<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2487  <cref anchor="TODO-non-mod-headers" source="jre">
2488    Restored from <eref target=""/>.
2489    See also <eref target=""/>.
2490  </cref>
2493   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2494   value of certain end-to-end header fields. A transparent proxy &SHOULD-NOT;
2495   modify an end-to-end header field unless the definition of that header field requires
2496   or specifically allows that.
2499   A transparent proxy &MUST-NOT; modify any of the following fields in a
2500   request or response, and it &MUST-NOT; add any of these fields if not
2501   already present:
2502  <list style="symbols">
2503      <t>Content-Location</t>
2504      <t>Content-MD5</t>
2505      <t>ETag</t>
2506      <t>Last-Modified</t>
2507  </list>
2510   A transparent proxy &MUST-NOT; modify any of the following fields in a
2511   response:
2512  <list style="symbols">
2513    <t>Expires</t>
2514  </list>
2517   but it &MAY; add any of these fields if not already present. If an
2518   Expires header field is added, it &MUST; be given a field-value identical to
2519   that of the Date header field in that response.
2522   A proxy &MUST-NOT; modify or add any of the following fields in a
2523   message that contains the no-transform cache-control directive, or in
2524   any request:
2525  <list style="symbols">
2526    <t>Content-Encoding</t>
2527    <t>Content-Range</t>
2528    <t>Content-Type</t>
2529  </list>
2532   A non-transparent proxy &MAY; modify or add these fields to a message
2533   that does not include no-transform, but if it does so, it &MUST; add a
2534   Warning 214 (Transformation applied) if one does not already appear
2535   in the message (see &header-warning;).
2538  <t>
2539    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2540    cause authentication failures if stronger authentication
2541    mechanisms are introduced in later versions of HTTP. Such
2542    authentication mechanisms &MAY; rely on the values of header fields
2543    not listed here.
2544  </t>
2547   A transparent proxy &MUST; preserve the message payload (&payload;),
2548   though it &MAY; change the message-body through application or removal
2549   of a transfer-coding (<xref target="transfer.codings"/>).
2555<section title="Practical Considerations" anchor="persistent.practical">
2557   Servers will usually have some time-out value beyond which they will
2558   no longer maintain an inactive connection. Proxy servers might make
2559   this a higher value since it is likely that the client will be making
2560   more connections through the same server. The use of persistent
2561   connections places no requirements on the length (or existence) of
2562   this time-out for either the client or the server.
2565   When a client or server wishes to time-out it &SHOULD; issue a graceful
2566   close on the transport connection. Clients and servers &SHOULD; both
2567   constantly watch for the other side of the transport close, and
2568   respond to it as appropriate. If a client or server does not detect
2569   the other side's close promptly it could cause unnecessary resource
2570   drain on the network.
2573   A client, server, or proxy &MAY; close the transport connection at any
2574   time. For example, a client might have started to send a new request
2575   at the same time that the server has decided to close the "idle"
2576   connection. From the server's point of view, the connection is being
2577   closed while it was idle, but from the client's point of view, a
2578   request is in progress.
2581   This means that clients, servers, and proxies &MUST; be able to recover
2582   from asynchronous close events. Client software &SHOULD; reopen the
2583   transport connection and retransmit the aborted sequence of requests
2584   without user interaction so long as the request sequence is
2585   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2586   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2587   human operator the choice of retrying the request(s). Confirmation by
2588   user-agent software with semantic understanding of the application
2589   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2590   be repeated if the second sequence of requests fails.
2593   Servers &SHOULD; always respond to at least one request per connection,
2594   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2595   middle of transmitting a response, unless a network or client failure
2596   is suspected.
2599   Clients (including proxies) &SHOULD; limit the number of simultaneous
2600   connections that they maintain to a given server (including proxies).
2603   Previous revisions of HTTP gave a specific number of connections as a
2604   ceiling, but this was found to be impractical for many applications. As a
2605   result, this specification does not mandate a particular maximum number of
2606   connections, but instead encourages clients to be conservative when opening
2607   multiple connections.
2610   In particular, while using multiple connections avoids the "head-of-line
2611   blocking" problem (whereby a request that takes significant server-side
2612   processing and/or has a large payload can block subsequent requests on the
2613   same connection), each connection used consumes server resources (sometimes
2614   significantly), and furthermore using multiple connections can cause
2615   undesirable side effects in congested networks.
2618   Note that servers might reject traffic that they deem abusive, including an
2619   excessive number of connections from a client.
2624<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2626<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2628   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2629   flow control mechanisms to resolve temporary overloads, rather than
2630   terminating connections with the expectation that clients will retry.
2631   The latter technique can exacerbate network congestion.
2635<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2637   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2638   the network connection for an error status code while it is transmitting
2639   the request. If the client sees an error status code, it &SHOULD;
2640   immediately cease transmitting the body. If the body is being sent
2641   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2642   empty trailer &MAY; be used to prematurely mark the end of the message.
2643   If the body was preceded by a Content-Length header field, the client &MUST;
2644   close the connection.
2648<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2650   The purpose of the 100 (Continue) status code (see &status-100;) is to
2651   allow a client that is sending a request message with a request body
2652   to determine if the origin server is willing to accept the request
2653   (based on the request header fields) before the client sends the request
2654   body. In some cases, it might either be inappropriate or highly
2655   inefficient for the client to send the body if the server will reject
2656   the message without looking at the body.
2659   Requirements for HTTP/1.1 clients:
2660  <list style="symbols">
2661    <t>
2662        If a client will wait for a 100 (Continue) response before
2663        sending the request body, it &MUST; send an Expect request-header
2664        field (&header-expect;) with the "100-continue" expectation.
2665    </t>
2666    <t>
2667        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2668        with the "100-continue" expectation if it does not intend
2669        to send a request body.
2670    </t>
2671  </list>
2674   Because of the presence of older implementations, the protocol allows
2675   ambiguous situations in which a client might send "Expect: 100-continue"
2676   without receiving either a 417 (Expectation Failed)
2677   or a 100 (Continue) status code. Therefore, when a client sends this
2678   header field to an origin server (possibly via a proxy) from which it
2679   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2680   wait for an indefinite period before sending the request body.
2683   Requirements for HTTP/1.1 origin servers:
2684  <list style="symbols">
2685    <t> Upon receiving a request which includes an Expect request-header
2686        field with the "100-continue" expectation, an origin server &MUST;
2687        either respond with 100 (Continue) status code and continue to read
2688        from the input stream, or respond with a final status code. The
2689        origin server &MUST-NOT; wait for the request body before sending
2690        the 100 (Continue) response. If it responds with a final status
2691        code, it &MAY; close the transport connection or it &MAY; continue
2692        to read and discard the rest of the request.  It &MUST-NOT;
2693        perform the requested method if it returns a final status code.
2694    </t>
2695    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2696        the request message does not include an Expect request-header
2697        field with the "100-continue" expectation, and &MUST-NOT; send a
2698        100 (Continue) response if such a request comes from an HTTP/1.0
2699        (or earlier) client. There is an exception to this rule: for
2700        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2701        status code in response to an HTTP/1.1 PUT or POST request that does
2702        not include an Expect request-header field with the "100-continue"
2703        expectation. This exception, the purpose of which is
2704        to minimize any client processing delays associated with an
2705        undeclared wait for 100 (Continue) status code, applies only to
2706        HTTP/1.1 requests, and not to requests with any other HTTP-version
2707        value.
2708    </t>
2709    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2710        already received some or all of the request body for the
2711        corresponding request.
2712    </t>
2713    <t> An origin server that sends a 100 (Continue) response &MUST;
2714    ultimately send a final status code, once the request body is
2715        received and processed, unless it terminates the transport
2716        connection prematurely.
2717    </t>
2718    <t> If an origin server receives a request that does not include an
2719        Expect request-header field with the "100-continue" expectation,
2720        the request includes a request body, and the server responds
2721        with a final status code before reading the entire request body
2722        from the transport connection, then the server &SHOULD-NOT;  close
2723        the transport connection until it has read the entire request,
2724        or until the client closes the connection. Otherwise, the client
2725        might not reliably receive the response message. However, this
2726        requirement is not be construed as preventing a server from
2727        defending itself against denial-of-service attacks, or from
2728        badly broken client implementations.
2729      </t>
2730    </list>
2733   Requirements for HTTP/1.1 proxies:
2734  <list style="symbols">
2735    <t> If a proxy receives a request that includes an Expect request-header
2736        field with the "100-continue" expectation, and the proxy
2737        either knows that the next-hop server complies with HTTP/1.1 or
2738        higher, or does not know the HTTP version of the next-hop
2739        server, it &MUST; forward the request, including the Expect header
2740        field.
2741    </t>
2742    <t> If the proxy knows that the version of the next-hop server is
2743        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2744        respond with a 417 (Expectation Failed) status code.
2745    </t>
2746    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2747        numbers received from recently-referenced next-hop servers.
2748    </t>
2749    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2750        request message was received from an HTTP/1.0 (or earlier)
2751        client and did not include an Expect request-header field with
2752        the "100-continue" expectation. This requirement overrides the
2753        general rule for forwarding of 1xx responses (see &status-1xx;).
2754    </t>
2755  </list>
2759<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2761   If an HTTP/1.1 client sends a request which includes a request body,
2762   but which does not include an Expect request-header field with the
2763   "100-continue" expectation, and if the client is not directly
2764   connected to an HTTP/1.1 origin server, and if the client sees the
2765   connection close before receiving a status line from the server, the
2766   client &SHOULD; retry the request.  If the client does retry this
2767   request, it &MAY; use the following "binary exponential backoff"
2768   algorithm to be assured of obtaining a reliable response:
2769  <list style="numbers">
2770    <t>
2771      Initiate a new connection to the server
2772    </t>
2773    <t>
2774      Transmit the request-header fields
2775    </t>
2776    <t>
2777      Initialize a variable R to the estimated round-trip time to the
2778         server (e.g., based on the time it took to establish the
2779         connection), or to a constant value of 5 seconds if the round-trip
2780         time is not available.
2781    </t>
2782    <t>
2783       Compute T = R * (2**N), where N is the number of previous
2784         retries of this request.
2785    </t>
2786    <t>
2787       Wait either for an error response from the server, or for T
2788         seconds (whichever comes first)
2789    </t>
2790    <t>
2791       If no error response is received, after T seconds transmit the
2792         body of the request.
2793    </t>
2794    <t>
2795       If client sees that the connection is closed prematurely,
2796         repeat from step 1 until the request is accepted, an error
2797         response is received, or the user becomes impatient and
2798         terminates the retry process.
2799    </t>
2800  </list>
2803   If at any point an error status code is received, the client
2804  <list style="symbols">
2805      <t>&SHOULD-NOT;  continue and</t>
2807      <t>&SHOULD; close the connection if it has not completed sending the
2808        request message.</t>
2809    </list>
2816<section title="Miscellaneous notes that might disappear" anchor="misc">
2817<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2819   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2823<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2825   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2829<section title="Interception of HTTP for access control" anchor="http.intercept">
2831   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2835<section title="Use of HTTP by other protocols" anchor="http.others">
2837   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2838   Extensions of HTTP like WebDAV.</cref>
2842<section title="Use of HTTP by media type specification" anchor="">
2844   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2849<section title="Header Field Definitions" anchor="header.field.definitions">
2851   This section defines the syntax and semantics of HTTP/1.1 header fields
2852   related to message framing and transport protocols.
2855<section title="Connection" anchor="header.connection">
2856  <iref primary="true" item="Connection header" x:for-anchor=""/>
2857  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2858  <x:anchor-alias value="Connection"/>
2859  <x:anchor-alias value="connection-token"/>
2860  <x:anchor-alias value="Connection-v"/>
2862   The "Connection" general-header field allows the sender to specify
2863   options that are desired for that particular connection and &MUST-NOT;
2864   be communicated by proxies over further connections.
2867   The Connection header field's value has the following grammar:
2869<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"/>
2870  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2871  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2872  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2875   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2876   message is forwarded and, for each connection-token in this field,
2877   remove any header field(s) from the message with the same name as the
2878   connection-token. Connection options are signaled by the presence of
2879   a connection-token in the Connection header field, not by any
2880   corresponding additional header field(s), since the additional header
2881   field might not be sent if there are no parameters associated with that
2882   connection option.
2885   Message header fields listed in the Connection header field &MUST-NOT; include
2886   end-to-end header fields, such as Cache-Control.
2889   HTTP/1.1 defines the "close" connection option for the sender to
2890   signal that the connection will be closed after completion of the
2891   response. For example,
2893<figure><artwork type="example">
2894  Connection: close
2897   in either the request or the response header fields indicates that
2898   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2899   after the current request/response is complete.
2902   An HTTP/1.1 client that does not support persistent connections &MUST;
2903   include the "close" connection option in every request message.
2906   An HTTP/1.1 server that does not support persistent connections &MUST;
2907   include the "close" connection option in every response message that
2908   does not have a 1xx (Informational) status code.
2911   A system receiving an HTTP/1.0 (or lower-version) message that
2912   includes a Connection header field &MUST;, for each connection-token in this
2913   field, remove and ignore any header field(s) from the message with
2914   the same name as the connection-token. This protects against mistaken
2915   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2919<section title="Content-Length" anchor="header.content-length">
2920  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2921  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2922  <x:anchor-alias value="Content-Length"/>
2923  <x:anchor-alias value="Content-Length-v"/>
2925   The "Content-Length" header field indicates the size of the
2926   message-body, in decimal number of octets, for any message other than
2927   a response to the HEAD method or a response with a status code of 304.
2928   In the case of responses to the HEAD method, it indicates the size of
2929   the payload body (not including any potential transfer-coding) that
2930   would have been sent had the request been a GET.
2931   In the case of the 304 (Not Modified) response, it indicates the size of
2932   the payload body (not including any potential transfer-coding) that
2933   would have been sent in a 200 (OK) response.
2935<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2936  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2937  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2940   An example is
2942<figure><artwork type="example">
2943  Content-Length: 3495
2946   Implementations &SHOULD; use this field to indicate the message-body
2947   length when no transfer-coding is being applied and the
2948   payload's body length can be determined prior to being transferred.
2949   <xref target="message.body"/> describes how recipients determine the length
2950   of a message-body.
2953   Any Content-Length greater than or equal to zero is a valid value.
2956   Note that the use of this field in HTTP is significantly different from
2957   the corresponding definition in MIME, where it is an optional field
2958   used within the "message/external-body" content-type.
2962<section title="Date" anchor="">
2963  <iref primary="true" item="Date header" x:for-anchor=""/>
2964  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2965  <x:anchor-alias value="Date"/>
2966  <x:anchor-alias value="Date-v"/>
2968   The "Date" general-header field represents the date and time at which
2969   the message was originated, having the same semantics as the Origination
2970   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2971   The field value is an HTTP-date, as described in <xref target=""/>;
2972   it &MUST; be sent in rfc1123-date format.
2974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2975  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2976  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2979   An example is
2981<figure><artwork type="example">
2982  Date: Tue, 15 Nov 1994 08:12:31 GMT
2985   Origin servers &MUST; include a Date header field in all responses,
2986   except in these cases:
2987  <list style="numbers">
2988      <t>If the response status code is 100 (Continue) or 101 (Switching
2989         Protocols), the response &MAY; include a Date header field, at
2990         the server's option.</t>
2992      <t>If the response status code conveys a server error, e.g., 500
2993         (Internal Server Error) or 503 (Service Unavailable), and it is
2994         inconvenient or impossible to generate a valid Date.</t>
2996      <t>If the server does not have a clock that can provide a
2997         reasonable approximation of the current time, its responses
2998         &MUST-NOT; include a Date header field. In this case, the rules
2999         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3000  </list>
3003   A received message that does not have a Date header field &MUST; be
3004   assigned one by the recipient if the message will be cached by that
3005   recipient or gatewayed via a protocol which requires a Date. An HTTP
3006   implementation without a clock &MUST-NOT; cache responses without
3007   revalidating them on every use. An HTTP cache, especially a shared
3008   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
3009   clock with a reliable external standard.
3012   Clients &SHOULD; only send a Date header field in messages that include
3013   a payload, as is usually the case for PUT and POST requests, and even
3014   then it is optional. A client without a clock &MUST-NOT; send a Date
3015   header field in a request.
3018   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3019   time subsequent to the generation of the message. It &SHOULD; represent
3020   the best available approximation of the date and time of message
3021   generation, unless the implementation has no means of generating a
3022   reasonably accurate date and time. In theory, the date ought to
3023   represent the moment just before the payload is generated. In
3024   practice, the date can be generated at any time during the message
3025   origination without affecting its semantic value.
3028<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3030   Some origin server implementations might not have a clock available.
3031   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3032   values to a response, unless these values were associated
3033   with the resource by a system or user with a reliable clock. It &MAY;
3034   assign an Expires value that is known, at or before server
3035   configuration time, to be in the past (this allows "pre-expiration"
3036   of responses without storing separate Expires values for each
3037   resource).
3042<section title="Host" anchor="">
3043  <iref primary="true" item="Host header" x:for-anchor=""/>
3044  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3045  <x:anchor-alias value="Host"/>
3046  <x:anchor-alias value="Host-v"/>
3048   The "Host" request-header field specifies the Internet host and port
3049   number of the resource being requested, allowing the origin server or
3050   gateway to differentiate between internally-ambiguous URLs, such as the root
3051   "/" URL of a server for multiple host names on a single IP address.
3054   The Host field value &MUST; represent the naming authority of the origin
3055   server or gateway given by the original URL obtained from the user or
3056   referring resource (generally an http URI, as described in
3057   <xref target="http.uri"/>).
3059<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3060  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3061  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3064   A "host" without any trailing port information implies the default
3065   port for the service requested (e.g., "80" for an HTTP URL). For
3066   example, a request on the origin server for
3067   &lt;; would properly include:
3069<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3070GET /pub/WWW/ HTTP/1.1
3074   A client &MUST; include a Host header field in all HTTP/1.1 request
3075   messages. If the requested URI does not include an Internet host
3076   name for the service being requested, then the Host header field &MUST;
3077   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3078   request message it forwards does contain an appropriate Host header
3079   field that identifies the service being requested by the proxy. All
3080   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3081   status code to any HTTP/1.1 request message which lacks a Host header
3082   field.
3085   See Sections <xref target="" format="counter"/>
3086   and <xref target="" format="counter"/>
3087   for other requirements relating to Host.
3091<section title="TE" anchor="header.te">
3092  <iref primary="true" item="TE header" x:for-anchor=""/>
3093  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3094  <x:anchor-alias value="TE"/>
3095  <x:anchor-alias value="TE-v"/>
3096  <x:anchor-alias value="t-codings"/>
3097  <x:anchor-alias value="te-params"/>
3098  <x:anchor-alias value="te-ext"/>
3100   The "TE" request-header field indicates what extension transfer-codings
3101   it is willing to accept in the response, and whether or not it is
3102   willing to accept trailer fields in a chunked transfer-coding.
3105   Its value consists of the keyword "trailers" and/or a comma-separated
3106   list of extension transfer-coding names with optional accept
3107   parameters (as described in <xref target="transfer.codings"/>).
3109<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"/>
3110  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3111  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3112  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3113  <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> )
3114  <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> ]
3117   The presence of the keyword "trailers" indicates that the client is
3118   willing to accept trailer fields in a chunked transfer-coding, as
3119   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3120   transfer-coding values even though it does not itself represent a
3121   transfer-coding.
3124   Examples of its use are:
3126<figure><artwork type="example">
3127  TE: deflate
3128  TE:
3129  TE: trailers, deflate;q=0.5
3132   The TE header field only applies to the immediate connection.
3133   Therefore, the keyword &MUST; be supplied within a Connection header
3134   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3137   A server tests whether a transfer-coding is acceptable, according to
3138   a TE field, using these rules:
3139  <list style="numbers">
3140    <x:lt>
3141      <t>The "chunked" transfer-coding is always acceptable. If the
3142         keyword "trailers" is listed, the client indicates that it is
3143         willing to accept trailer fields in the chunked response on
3144         behalf of itself and any downstream clients. The implication is
3145         that, if given, the client is stating that either all
3146         downstream clients are willing to accept trailer fields in the
3147         forwarded response, or that it will attempt to buffer the
3148         response on behalf of downstream recipients.
3149      </t><t>
3150         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3151         chunked response such that a client can be assured of buffering
3152         the entire response.</t>
3153    </x:lt>
3154    <x:lt>
3155      <t>If the transfer-coding being tested is one of the transfer-codings
3156         listed in the TE field, then it is acceptable unless it
3157         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3158         qvalue of 0 means "not acceptable".)</t>
3159    </x:lt>
3160    <x:lt>
3161      <t>If multiple transfer-codings are acceptable, then the
3162         acceptable transfer-coding with the highest non-zero qvalue is
3163         preferred.  The "chunked" transfer-coding always has a qvalue
3164         of 1.</t>
3165    </x:lt>
3166  </list>
3169   If the TE field-value is empty or if no TE field is present, the only
3170   transfer-coding is "chunked". A message with no transfer-coding is
3171   always acceptable.
3175<section title="Trailer" anchor="header.trailer">
3176  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3177  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3178  <x:anchor-alias value="Trailer"/>
3179  <x:anchor-alias value="Trailer-v"/>
3181   The "Trailer" general-header field indicates that the given set of
3182   header fields is present in the trailer of a message encoded with
3183   chunked transfer-coding.
3185<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3186  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3187  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3190   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3191   message using chunked transfer-coding with a non-empty trailer. Doing
3192   so allows the recipient to know which header fields to expect in the
3193   trailer.
3196   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3197   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3198   trailer fields in a "chunked" transfer-coding.
3201   Message header fields listed in the Trailer header field &MUST-NOT;
3202   include the following header fields:
3203  <list style="symbols">
3204    <t>Transfer-Encoding</t>
3205    <t>Content-Length</t>
3206    <t>Trailer</t>
3207  </list>
3211<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3212  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3213  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3214  <x:anchor-alias value="Transfer-Encoding"/>
3215  <x:anchor-alias value="Transfer-Encoding-v"/>
3217   The "Transfer-Encoding" general-header field indicates what transfer-codings
3218   (if any) have been applied to the message body. It differs from
3219   Content-Encoding (&content-codings;) in that transfer-codings are a property
3220   of the message (and therefore are removed by intermediaries), whereas
3221   content-codings are not.
3223<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3224  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3225                        <x:ref>Transfer-Encoding-v</x:ref>
3226  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3229   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3231<figure><artwork type="example">
3232  Transfer-Encoding: chunked
3235   If multiple encodings have been applied to a representation, the transfer-codings
3236   &MUST; be listed in the order in which they were applied.
3237   Additional information about the encoding parameters &MAY; be provided
3238   by other header fields not defined by this specification.
3241   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3242   header field.
3246<section title="Upgrade" anchor="header.upgrade">
3247  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3248  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3249  <x:anchor-alias value="Upgrade"/>
3250  <x:anchor-alias value="Upgrade-v"/>
3252   The "Upgrade" general-header field allows the client to specify what
3253   additional communication protocols it would like to use, if the server
3254   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3255   header field within a 101 (Switching Protocols) response to indicate which
3256   protocol(s) are being switched to.
3258<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3259  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3260  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3263   For example,
3265<figure><artwork type="example">
3266  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3269   The Upgrade header field is intended to provide a simple mechanism
3270   for transition from HTTP/1.1 to some other, incompatible protocol. It
3271   does so by allowing the client to advertise its desire to use another
3272   protocol, such as a later version of HTTP with a higher major version
3273   number, even though the current request has been made using HTTP/1.1.
3274   This eases the difficult transition between incompatible protocols by
3275   allowing the client to initiate a request in the more commonly
3276   supported protocol while indicating to the server that it would like
3277   to use a "better" protocol if available (where "better" is determined
3278   by the server, possibly according to the nature of the method and/or
3279   resource being requested).
3282   The Upgrade header field only applies to switching application-layer
3283   protocols upon the existing transport-layer connection. Upgrade
3284   cannot be used to insist on a protocol change; its acceptance and use
3285   by the server is optional. The capabilities and nature of the
3286   application-layer communication after the protocol change is entirely
3287   dependent upon the new protocol chosen, although the first action
3288   after changing the protocol &MUST; be a response to the initial HTTP
3289   request containing the Upgrade header field.
3292   The Upgrade header field only applies to the immediate connection.
3293   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3294   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3295   HTTP/1.1 message.
3298   The Upgrade header field cannot be used to indicate a switch to a
3299   protocol on a different connection. For that purpose, it is more
3300   appropriate to use a 301, 302, 303, or 305 redirection response.
3303   This specification only defines the protocol name "HTTP" for use by
3304   the family of Hypertext Transfer Protocols, as defined by the HTTP
3305   version rules of <xref target="http.version"/> and future updates to this
3306   specification. Additional tokens can be registered with IANA using the
3307   registration procedure defined below. 
3310<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3312   The HTTP Upgrade Token Registry defines the name space for product
3313   tokens used to identify protocols in the Upgrade header field.
3314   Each registered token is associated with contact information and
3315   an optional set of specifications that details how the connection
3316   will be processed after it has been upgraded.
3319   Registrations are allowed on a First Come First Served basis as
3320   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3321   specifications need not be IETF documents or be subject to IESG review.
3322   Registrations are subject to the following rules:
3323  <list style="numbers">
3324    <t>A token, once registered, stays registered forever.</t>
3325    <t>The registration &MUST; name a responsible party for the
3326       registration.</t>
3327    <t>The registration &MUST; name a point of contact.</t>
3328    <t>The registration &MAY; name a set of specifications associated with that
3329       token. Such specifications need not be publicly available.</t>
3330    <t>The responsible party &MAY; change the registration at any time.
3331       The IANA will keep a record of all such changes, and make them
3332       available upon request.</t>
3333    <t>The responsible party for the first registration of a "product"
3334       token &MUST; approve later registrations of a "version" token
3335       together with that "product" token before they can be registered.</t>
3336    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3337       for a token. This will normally only be used in the case when a
3338       responsible party cannot be contacted.</t>
3339  </list>
3346<section title="Via" anchor="header.via">
3347  <iref primary="true" item="Via header" x:for-anchor=""/>
3348  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3349  <x:anchor-alias value="protocol-name"/>
3350  <x:anchor-alias value="protocol-version"/>
3351  <x:anchor-alias value="pseudonym"/>
3352  <x:anchor-alias value="received-by"/>
3353  <x:anchor-alias value="received-protocol"/>
3354  <x:anchor-alias value="Via"/>
3355  <x:anchor-alias value="Via-v"/>
3357   The "Via" general-header field &MUST; be used by gateways and proxies to
3358   indicate the intermediate protocols and recipients between the user
3359   agent and the server on requests, and between the origin server and
3360   the client on responses. It is analogous to the "Received" field defined in
3361   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3362   avoiding request loops, and identifying the protocol capabilities of
3363   all senders along the request/response chain.
3365<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"/>
3366  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3367  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3368                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3369  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3370  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3371  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3372  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3373  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3376   The received-protocol indicates the protocol version of the message
3377   received by the server or client along each segment of the
3378   request/response chain. The received-protocol version is appended to
3379   the Via field value when the message is forwarded so that information
3380   about the protocol capabilities of upstream applications remains
3381   visible to all recipients.
3384   The protocol-name is optional if and only if it would be "HTTP". The
3385   received-by field is normally the host and optional port number of a
3386   recipient server or client that subsequently forwarded the message.
3387   However, if the real host is considered to be sensitive information,
3388   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3389   be assumed to be the default port of the received-protocol.
3392   Multiple Via field values represent each proxy or gateway that has
3393   forwarded the message. Each recipient &MUST; append its information
3394   such that the end result is ordered according to the sequence of
3395   forwarding applications.
3398   Comments &MAY; be used in the Via header field to identify the software
3399   of the recipient proxy or gateway, analogous to the User-Agent and
3400   Server header fields. However, all comments in the Via field are
3401   optional and &MAY; be removed by any recipient prior to forwarding the
3402   message.
3405   For example, a request message could be sent from an HTTP/1.0 user
3406   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3407   forward the request to a public proxy at, which completes
3408   the request by forwarding it to the origin server at
3409   The request received by would then have the following
3410   Via header field:
3412<figure><artwork type="example">
3413  Via: 1.0 fred, 1.1 (Apache/1.1)
3416   Proxies and gateways used as a portal through a network firewall
3417   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3418   the firewall region. This information &SHOULD; only be propagated if
3419   explicitly enabled. If not enabled, the received-by host of any host
3420   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3421   for that host.
3424   For organizations that have strong privacy requirements for hiding
3425   internal structures, a proxy &MAY; combine an ordered subsequence of
3426   Via header field entries with identical received-protocol values into
3427   a single such entry. For example,
3429<figure><artwork type="example">
3430  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3433  could be collapsed to
3435<figure><artwork type="example">
3436  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3439   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3440   under the same organizational control and the hosts have already been
3441   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3442   have different received-protocol values.
3448<section title="IANA Considerations" anchor="IANA.considerations">
3450<section title="Header Field Registration" anchor="header.field.registration">
3452   The Message Header Field Registry located at <eref target=""/> shall be updated
3453   with the permanent registrations below (see <xref target="RFC3864"/>):
3455<?BEGININC p1-messaging.iana-headers ?>
3456<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3457<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3458   <ttcol>Header Field Name</ttcol>
3459   <ttcol>Protocol</ttcol>
3460   <ttcol>Status</ttcol>
3461   <ttcol>Reference</ttcol>
3463   <c>Connection</c>
3464   <c>http</c>
3465   <c>standard</c>
3466   <c>
3467      <xref target="header.connection"/>
3468   </c>
3469   <c>Content-Length</c>
3470   <c>http</c>
3471   <c>standard</c>
3472   <c>
3473      <xref target="header.content-length"/>
3474   </c>
3475   <c>Date</c>
3476   <c>http</c>
3477   <c>standard</c>
3478   <c>
3479      <xref target=""/>
3480   </c>
3481   <c>Host</c>
3482   <c>http</c>
3483   <c>standard</c>
3484   <c>
3485      <xref target=""/>
3486   </c>
3487   <c>TE</c>
3488   <c>http</c>
3489   <c>standard</c>
3490   <c>
3491      <xref target="header.te"/>
3492   </c>
3493   <c>Trailer</c>
3494   <c>http</c>
3495   <c>standard</c>
3496   <c>
3497      <xref target="header.trailer"/>
3498   </c>
3499   <c>Transfer-Encoding</c>
3500   <c>http</c>
3501   <c>standard</c>
3502   <c>
3503      <xref target="header.transfer-encoding"/>
3504   </c>
3505   <c>Upgrade</c>
3506   <c>http</c>
3507   <c>standard</c>
3508   <c>
3509      <xref target="header.upgrade"/>
3510   </c>
3511   <c>Via</c>
3512   <c>http</c>
3513   <c>standard</c>
3514   <c>
3515      <xref target="header.via"/>
3516   </c>
3519<?ENDINC p1-messaging.iana-headers ?>
3521   The change controller is: "IETF ( - Internet Engineering Task Force".
3525<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3527   The entries for the "http" and "https" URI Schemes in the registry located at
3528   <eref target=""/>
3529   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3530   and <xref target="https.uri" format="counter"/> of this document
3531   (see <xref target="RFC4395"/>).
3535<section title="Internet Media Type Registrations" anchor="">
3537   This document serves as the specification for the Internet media types
3538   "message/http" and "application/http". The following is to be registered with
3539   IANA (see <xref target="RFC4288"/>).
3541<section title="Internet Media Type message/http" anchor="">
3542<iref item="Media Type" subitem="message/http" primary="true"/>
3543<iref item="message/http Media Type" primary="true"/>
3545   The message/http type can be used to enclose a single HTTP request or
3546   response message, provided that it obeys the MIME restrictions for all
3547   "message" types regarding line length and encodings.
3550  <list style="hanging" x:indent="12em">
3551    <t hangText="Type name:">
3552      message
3553    </t>
3554    <t hangText="Subtype name:">
3555      http
3556    </t>
3557    <t hangText="Required parameters:">
3558      none
3559    </t>
3560    <t hangText="Optional parameters:">
3561      version, msgtype
3562      <list style="hanging">
3563        <t hangText="version:">
3564          The HTTP-Version number of the enclosed message
3565          (e.g., "1.1"). If not present, the version can be
3566          determined from the first line of the body.
3567        </t>
3568        <t hangText="msgtype:">
3569          The message type -- "request" or "response". If not
3570          present, the type can be determined from the first
3571          line of the body.
3572        </t>
3573      </list>
3574    </t>
3575    <t hangText="Encoding considerations:">
3576      only "7bit", "8bit", or "binary" are permitted
3577    </t>
3578    <t hangText="Security considerations:">
3579      none
3580    </t>
3581    <t hangText="Interoperability considerations:">
3582      none
3583    </t>
3584    <t hangText="Published specification:">
3585      This specification (see <xref target=""/>).
3586    </t>
3587    <t hangText="Applications that use this media type:">
3588    </t>
3589    <t hangText="Additional information:">
3590      <list style="hanging">
3591        <t hangText="Magic number(s):">none</t>
3592        <t hangText="File extension(s):">none</t>
3593        <t hangText="Macintosh file type code(s):">none</t>
3594      </list>
3595    </t>
3596    <t hangText="Person and email address to contact for further information:">
3597      See Authors Section.
3598    </t>
3599    <t hangText="Intended usage:">
3600      COMMON
3601    </t>
3602    <t hangText="Restrictions on usage:">
3603      none
3604    </t>
3605    <t hangText="Author/Change controller:">
3606      IESG
3607    </t>
3608  </list>
3611<section title="Internet Media Type application/http" anchor="">
3612<iref item="Media Type" subitem="application/http" primary="true"/>
3613<iref item="application/http Media Type" primary="true"/>
3615   The application/http type can be used to enclose a pipeline of one or more
3616   HTTP request or response messages (not intermixed).
3619  <list style="hanging" x:indent="12em">
3620    <t hangText="Type name:">
3621      application
3622    </t>
3623    <t hangText="Subtype name:">
3624      http
3625    </t>
3626    <t hangText="Required parameters:">
3627      none
3628    </t>
3629    <t hangText="Optional parameters:">
3630      version, msgtype
3631      <list style="hanging">
3632        <t hangText="version:">
3633          The HTTP-Version number of the enclosed messages
3634          (e.g., "1.1"). If not present, the version can be
3635          determined from the first line of the body.
3636        </t>
3637        <t hangText="msgtype:">
3638          The message type -- "request" or "response". If not
3639          present, the type can be determined from the first
3640          line of the body.
3641        </t>
3642      </list>
3643    </t>
3644    <t hangText="Encoding considerations:">
3645      HTTP messages enclosed by this type
3646      are in "binary" format; use of an appropriate
3647      Content-Transfer-Encoding is required when
3648      transmitted via E-mail.
3649    </t>
3650    <t hangText="Security considerations:">
3651      none
3652    </t>
3653    <t hangText="Interoperability considerations:">
3654      none
3655    </t>
3656    <t hangText="Published specification:">
3657      This specification (see <xref target=""/>).
3658    </t>
3659    <t hangText="Applications that use this media type:">
3660    </t>
3661    <t hangText="Additional information:">
3662      <list style="hanging">
3663        <t hangText="Magic number(s):">none</t>
3664        <t hangText="File extension(s):">none</t>
3665        <t hangText="Macintosh file type code(s):">none</t>
3666      </list>
3667    </t>
3668    <t hangText="Person and email address to contact for further information:">
3669      See Authors Section.
3670    </t>
3671    <t hangText="Intended usage:">
3672      COMMON
3673    </t>
3674    <t hangText="Restrictions on usage:">
3675      none
3676    </t>
3677    <t hangText="Author/Change controller:">
3678      IESG
3679    </t>
3680  </list>
3685<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3687   The registration procedure for HTTP Transfer Codings is now defined by
3688   <xref target="transfer.coding.registry"/> of this document.
3691   The HTTP Transfer Codings Registry located at <eref target=""/>
3692   shall be updated with the registrations below:
3694<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3695   <ttcol>Name</ttcol>
3696   <ttcol>Description</ttcol>
3697   <ttcol>Reference</ttcol>
3698   <c>chunked</c>
3699   <c>Transfer in a series of chunks</c>
3700   <c>
3701      <xref target="chunked.encoding"/>
3702   </c>
3703   <c>compress</c>
3704   <c>UNIX "compress" program method</c>
3705   <c>
3706      <xref target="compress.coding"/>
3707   </c>
3708   <c>deflate</c>
3709   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3710   the "zlib" data format (<xref target="RFC1950"/>)
3711   </c>
3712   <c>
3713      <xref target="deflate.coding"/>
3714   </c>
3715   <c>gzip</c>
3716   <c>Same as GNU zip <xref target="RFC1952"/></c>
3717   <c>
3718      <xref target="gzip.coding"/>
3719   </c>
3723<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3725   The registration procedure for HTTP Upgrade Tokens -- previously defined
3726   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3727   by <xref target="upgrade.token.registry"/> of this document.
3730   The HTTP Status Code Registry located at <eref target=""/>
3731   shall be updated with the registration below:
3733<texttable align="left" suppress-title="true">
3734   <ttcol>Value</ttcol>
3735   <ttcol>Description</ttcol>
3736   <ttcol>Reference</ttcol>
3738   <c>HTTP</c>
3739   <c>Hypertext Transfer Protocol</c>
3740   <c><xref target="http.version"/> of this specification</c>
3741<!-- IANA should add this without our instructions; emailed on June 05, 2009
3742   <c>TLS/1.0</c>
3743   <c>Transport Layer Security</c>
3744   <c><xref target="RFC2817"/></c> -->
3751<section title="Security Considerations" anchor="security.considerations">
3753   This section is meant to inform application developers, information
3754   providers, and users of the security limitations in HTTP/1.1 as
3755   described by this document. The discussion does not include
3756   definitive solutions to the problems revealed, though it does make
3757   some suggestions for reducing security risks.
3760<section title="Personal Information" anchor="personal.information">
3762   HTTP clients are often privy to large amounts of personal information
3763   (e.g., the user's name, location, mail address, passwords, encryption
3764   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3765   leakage of this information.
3766   We very strongly recommend that a convenient interface be provided
3767   for the user to control dissemination of such information, and that
3768   designers and implementors be particularly careful in this area.
3769   History shows that errors in this area often create serious security
3770   and/or privacy problems and generate highly adverse publicity for the
3771   implementor's company.
3775<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3777   A server is in the position to save personal data about a user's
3778   requests which might identify their reading patterns or subjects of
3779   interest. This information is clearly confidential in nature and its
3780   handling can be constrained by law in certain countries. People using
3781   HTTP to provide data are responsible for ensuring that
3782   such material is not distributed without the permission of any
3783   individuals that are identifiable by the published results.
3787<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3789   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3790   the documents returned by HTTP requests to be only those that were
3791   intended by the server administrators. If an HTTP server translates
3792   HTTP URIs directly into file system calls, the server &MUST; take
3793   special care not to serve files that were not intended to be
3794   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3795   other operating systems use ".." as a path component to indicate a
3796   directory level above the current one. On such a system, an HTTP
3797   server &MUST; disallow any such construct in the request-target if it
3798   would otherwise allow access to a resource outside those intended to
3799   be accessible via the HTTP server. Similarly, files intended for
3800   reference only internally to the server (such as access control
3801   files, configuration files, and script code) &MUST; be protected from
3802   inappropriate retrieval, since they might contain sensitive
3803   information. Experience has shown that minor bugs in such HTTP server
3804   implementations have turned into security risks.
3808<section title="DNS Spoofing" anchor="dns.spoofing">
3810   Clients using HTTP rely heavily on the Domain Name Service, and are
3811   thus generally prone to security attacks based on the deliberate
3812   mis-association of IP addresses and DNS names. Clients need to be
3813   cautious in assuming the continuing validity of an IP number/DNS name
3814   association.
3817   In particular, HTTP clients &SHOULD; rely on their name resolver for
3818   confirmation of an IP number/DNS name association, rather than
3819   caching the result of previous host name lookups. Many platforms
3820   already can cache host name lookups locally when appropriate, and
3821   they &SHOULD; be configured to do so. It is proper for these lookups to
3822   be cached, however, only when the TTL (Time To Live) information
3823   reported by the name server makes it likely that the cached
3824   information will remain useful.
3827   If HTTP clients cache the results of host name lookups in order to
3828   achieve a performance improvement, they &MUST; observe the TTL
3829   information reported by DNS.
3832   If HTTP clients do not observe this rule, they could be spoofed when
3833   a previously-accessed server's IP address changes. As network
3834   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3835   possibility of this form of attack will grow. Observing this
3836   requirement thus reduces this potential security vulnerability.
3839   This requirement also improves the load-balancing behavior of clients
3840   for replicated servers using the same DNS name and reduces the
3841   likelihood of a user's experiencing failure in accessing sites which
3842   use that strategy.
3846<section title="Proxies and Caching" anchor="attack.proxies">
3848   By their very nature, HTTP proxies are men-in-the-middle, and
3849   represent an opportunity for man-in-the-middle attacks. Compromise of
3850   the systems on which the proxies run can result in serious security
3851   and privacy problems. Proxies have access to security-related
3852   information, personal information about individual users and
3853   organizations, and proprietary information belonging to users and
3854   content providers. A compromised proxy, or a proxy implemented or
3855   configured without regard to security and privacy considerations,
3856   might be used in the commission of a wide range of potential attacks.
3859   Proxy operators need to protect the systems on which proxies run as
3860   they would protect any system that contains or transports sensitive
3861   information. In particular, log information gathered at proxies often
3862   contains highly sensitive personal information, and/or information
3863   about organizations. Log information needs to be carefully guarded, and
3864   appropriate guidelines for use need to be developed and followed.
3865   (<xref target="abuse.of.server.log.information"/>).
3868   Proxy implementors need to consider the privacy and security
3869   implications of their design and coding decisions, and of the
3870   configuration options they provide to proxy operators (especially the
3871   default configuration).
3874   Users of a proxy need to be aware that proxies are no trustworthier than
3875   the people who run them; HTTP itself cannot solve this problem.
3878   The judicious use of cryptography, when appropriate, might suffice to
3879   protect against a broad range of security and privacy attacks. Such
3880   cryptography is beyond the scope of the HTTP/1.1 specification.
3884<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3886   They exist. They are hard to defend against. Research continues.
3887   Beware.
3892<section title="Acknowledgments" anchor="ack">
3894   HTTP has evolved considerably over the years. It has
3895   benefited from a large and active developer community--the many
3896   people who have participated on the www-talk mailing list--and it is
3897   that community which has been most responsible for the success of
3898   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3899   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3900   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3901   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3902   VanHeyningen deserve special recognition for their efforts in
3903   defining early aspects of the protocol.
3906   This document has benefited greatly from the comments of all those
3907   participating in the HTTP-WG. In addition to those already mentioned,
3908   the following individuals have contributed to this specification:
3911   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3912   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3913   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3914   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3915   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3916   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3917   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3918   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3919   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3920   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3921   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3922   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3925   Thanks to the "cave men" of Palo Alto. You know who you are.
3928   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3929   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3930   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3931   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3932   Larry Masinter for their help. And thanks go particularly to Jeff
3933   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3936   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3937   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3938   discovery of many of the problems that this document attempts to
3939   rectify.
3942   This specification makes heavy use of the augmented BNF and generic
3943   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3944   reuses many of the definitions provided by Nathaniel Borenstein and
3945   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3946   specification will help reduce past confusion over the relationship
3947   between HTTP and Internet mail message formats.
3951Acknowledgements TODO list
3953- Jeff Hodges ("effective request URI")
3961<references title="Normative References">
3963<reference anchor="ISO-8859-1">
3964  <front>
3965    <title>
3966     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3967    </title>
3968    <author>
3969      <organization>International Organization for Standardization</organization>
3970    </author>
3971    <date year="1998"/>
3972  </front>
3973  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3976<reference anchor="Part2">
3977  <front>
3978    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3979    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3980      <organization abbrev="Day Software">Day Software</organization>
3981      <address><email></email></address>
3982    </author>
3983    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3984      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3985      <address><email></email></address>
3986    </author>
3987    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3988      <organization abbrev="HP">Hewlett-Packard Company</organization>
3989      <address><email></email></address>
3990    </author>
3991    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3992      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3993      <address><email></email></address>
3994    </author>
3995    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3996      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3997      <address><email></email></address>
3998    </author>
3999    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4000      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4001      <address><email></email></address>
4002    </author>
4003    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4004      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4005      <address><email></email></address>
4006    </author>
4007    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4008      <organization abbrev="W3C">World Wide Web Consortium</organization>
4009      <address><email></email></address>
4010    </author>
4011    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4012      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4013      <address><email></email></address>
4014    </author>
4015    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4016  </front>
4017  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4018  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4021<reference anchor="Part3">
4022  <front>
4023    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4024    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4025      <organization abbrev="Day Software">Day Software</organization>
4026      <address><email></email></address>
4027    </author>
4028    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4029      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4030      <address><email></email></address>
4031    </author>
4032    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4033      <organization abbrev="HP">Hewlett-Packard Company</organization>
4034      <address><email></email></address>
4035    </author>
4036    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4037      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4038      <address><email></email></address>
4039    </author>
4040    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4041      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4042      <address><email></email></address>
4043    </author>
4044    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4045      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4046      <address><email></email></address>
4047    </author>
4048    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4049      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4050      <address><email></email></address>
4051    </author>
4052    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4053      <organization abbrev="W3C">World Wide Web Consortium</organization>
4054      <address><email></email></address>
4055    </author>
4056    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4057      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4058      <address><email></email></address>
4059    </author>
4060    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4061  </front>
4062  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4063  <x:source href="p3-payload.xml" basename="p3-payload"/>
4066<reference anchor="Part6">
4067  <front>
4068    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4069    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4070      <organization abbrev="Day Software">Day Software</organization>
4071      <address><email></email></address>
4072    </author>
4073    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4074      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4075      <address><email></email></address>
4076    </author>
4077    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4078      <organization abbrev="HP">Hewlett-Packard Company</organization>
4079      <address><email></email></address>
4080    </author>
4081    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4082      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4083      <address><email></email></address>
4084    </author>
4085    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4086      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4087      <address><email></email></address>
4088    </author>
4089    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4090      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4091      <address><email></email></address>
4092    </author>
4093    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4094      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4095      <address><email></email></address>
4096    </author>
4097    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4098      <organization abbrev="W3C">World Wide Web Consortium</organization>
4099      <address><email></email></address>
4100    </author>
4101    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4102      <address><email></email></address>
4103    </author>
4104    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4105      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4106      <address><email></email></address>
4107    </author>
4108    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4109  </front>
4110  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4111  <x:source href="p6-cache.xml" basename="p6-cache"/>
4114<reference anchor="RFC5234">
4115  <front>
4116    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4117    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4118      <organization>Brandenburg InternetWorking</organization>
4119      <address>
4120        <email></email>
4121      </address> 
4122    </author>
4123    <author initials="P." surname="Overell" fullname="Paul Overell">
4124      <organization>THUS plc.</organization>
4125      <address>
4126        <email></email>
4127      </address>
4128    </author>
4129    <date month="January" year="2008"/>
4130  </front>
4131  <seriesInfo name="STD" value="68"/>
4132  <seriesInfo name="RFC" value="5234"/>
4135<reference anchor="RFC2119">
4136  <front>
4137    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4138    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4139      <organization>Harvard University</organization>
4140      <address><email></email></address>
4141    </author>
4142    <date month="March" year="1997"/>
4143  </front>
4144  <seriesInfo name="BCP" value="14"/>
4145  <seriesInfo name="RFC" value="2119"/>
4148<reference anchor="RFC3986">
4149 <front>
4150  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4151  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4152    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4153    <address>
4154       <email></email>
4155       <uri></uri>
4156    </address>
4157  </author>
4158  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4159    <organization abbrev="Day Software">Day Software</organization>
4160    <address>
4161      <email></email>
4162      <uri></uri>
4163    </address>
4164  </author>
4165  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4166    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4167    <address>
4168      <email></email>
4169      <uri></uri>
4170    </address>
4171  </author>
4172  <date month='January' year='2005'></date>
4173 </front>
4174 <seriesInfo name="STD" value="66"/>
4175 <seriesInfo name="RFC" value="3986"/>
4178<reference anchor="USASCII">
4179  <front>
4180    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4181    <author>
4182      <organization>American National Standards Institute</organization>
4183    </author>
4184    <date year="1986"/>
4185  </front>
4186  <seriesInfo name="ANSI" value="X3.4"/>
4189<reference anchor="RFC1950">
4190  <front>
4191    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4192    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4193      <organization>Aladdin Enterprises</organization>
4194      <address><email></email></address>
4195    </author>
4196    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4197    <date month="May" year="1996"/>
4198  </front>
4199  <seriesInfo name="RFC" value="1950"/>
4200  <annotation>
4201    RFC 1950 is an Informational RFC, thus it might be less stable than
4202    this specification. On the other hand, this downward reference was
4203    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4204    therefore it is unlikely to cause problems in practice. See also
4205    <xref target="BCP97"/>.
4206  </annotation>
4209<reference anchor="RFC1951">
4210  <front>
4211    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4212    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4213      <organization>Aladdin Enterprises</organization>
4214      <address><email></email></address>
4215    </author>
4216    <date month="May" year="1996"/>
4217  </front>
4218  <seriesInfo name="RFC" value="1951"/>
4219  <annotation>
4220    RFC 1951 is an Informational RFC, thus it might be less stable than
4221    this specification. On the other hand, this downward reference was
4222    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4223    therefore it is unlikely to cause problems in practice. See also
4224    <xref target="BCP97"/>.
4225  </annotation>
4228<reference anchor="RFC1952">
4229  <front>
4230    <title>GZIP file format specification version 4.3</title>
4231    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4232      <organization>Aladdin Enterprises</organization>
4233      <address><email></email></address>
4234    </author>
4235    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4236      <address><email></email></address>
4237    </author>
4238    <author initials="M." surname="Adler" fullname="Mark Adler">
4239      <address><email></email></address>
4240    </author>
4241    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4242      <address><email></email></address>
4243    </author>
4244    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4245      <address><email></email></address>
4246    </author>
4247    <date month="May" year="1996"/>
4248  </front>
4249  <seriesInfo name="RFC" value="1952"/>
4250  <annotation>
4251    RFC 1952 is an Informational RFC, thus it might be less stable than
4252    this specification. On the other hand, this downward reference was
4253    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4254    therefore it is unlikely to cause problems in practice. See also
4255    <xref target="BCP97"/>.
4256  </annotation>
4261<references title="Informative References">
4263<reference anchor="Nie1997" target="">
4264  <front>
4265    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4266    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4267    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4268    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4269    <author initials="H." surname="Lie" fullname="H. Lie"/>
4270    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4271    <date year="1997" month="September"/>
4272  </front>
4273  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4276<reference anchor="Pad1995" target="">
4277  <front>
4278    <title>Improving HTTP Latency</title>
4279    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4280    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4281    <date year="1995" month="December"/>
4282  </front>
4283  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4286<reference anchor="RFC1123">
4287  <front>
4288    <title>Requirements for Internet Hosts - Application and Support</title>
4289    <author initials="R." surname="Braden" fullname="Robert Braden">
4290      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4291      <address><email>Braden@ISI.EDU</email></address>
4292    </author>
4293    <date month="October" year="1989"/>
4294  </front>
4295  <seriesInfo name="STD" value="3"/>
4296  <seriesInfo name="RFC" value="1123"/>
4299<reference anchor="RFC1305">
4300  <front>
4301    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4302    <author initials="D." surname="Mills" fullname="David L. Mills">
4303      <organization>University of Delaware, Electrical Engineering Department</organization>
4304      <address><email></email></address>
4305    </author>
4306    <date month="March" year="1992"/>
4307  </front>
4308  <seriesInfo name="RFC" value="1305"/>
4311<reference anchor="RFC1900">
4312  <front>
4313    <title>Renumbering Needs Work</title>
4314    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4315      <organization>CERN, Computing and Networks Division</organization>
4316      <address><email></email></address>
4317    </author>
4318    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4319      <organization>cisco Systems</organization>
4320      <address><email></email></address>
4321    </author>
4322    <date month="February" year="1996"/>
4323  </front>
4324  <seriesInfo name="RFC" value="1900"/>
4327<reference anchor="RFC1945">
4328  <front>
4329    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4330    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4331      <organization>MIT, Laboratory for Computer Science</organization>
4332      <address><email></email></address>
4333    </author>
4334    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4335      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4336      <address><email></email></address>
4337    </author>
4338    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4339      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4340      <address><email></email></address>
4341    </author>
4342    <date month="May" year="1996"/>
4343  </front>
4344  <seriesInfo name="RFC" value="1945"/>
4347<reference anchor="RFC2045">
4348  <front>
4349    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4350    <author initials="N." surname="Freed" fullname="Ned Freed">
4351      <organization>Innosoft International, Inc.</organization>
4352      <address><email></email></address>
4353    </author>
4354    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4355      <organization>First Virtual Holdings</organization>
4356      <address><email></email></address>
4357    </author>
4358    <date month="November" year="1996"/>
4359  </front>
4360  <seriesInfo name="RFC" value="2045"/>
4363<reference anchor="RFC2047">
4364  <front>
4365    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4366    <author initials="K." surname="Moore" fullname="Keith Moore">
4367      <organization>University of Tennessee</organization>
4368      <address><email></email></address>
4369    </author>
4370    <date month="November" year="1996"/>
4371  </front>
4372  <seriesInfo name="RFC" value="2047"/>
4375<reference anchor="RFC2068">
4376  <front>
4377    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4378    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4379      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4380      <address><email></email></address>
4381    </author>
4382    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4383      <organization>MIT Laboratory for Computer Science</organization>
4384      <address><email></email></address>
4385    </author>
4386    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4387      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4388      <address><email></email></address>
4389    </author>
4390    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4391      <organization>MIT Laboratory for Computer Science</organization>
4392      <address><email></email></address>
4393    </author>
4394    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4395      <organization>MIT Laboratory for Computer Science</organization>
4396      <address><email></email></address>
4397    </author>
4398    <date month="January" year="1997"/>
4399  </front>
4400  <seriesInfo name="RFC" value="2068"/>
4403<reference anchor='RFC2109'>
4404  <front>
4405    <title>HTTP State Management Mechanism</title>
4406    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4407      <organization>Bell Laboratories, Lucent Technologies</organization>
4408      <address><email></email></address>
4409    </author>
4410    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4411      <organization>Netscape Communications Corp.</organization>
4412      <address><email></email></address>
4413    </author>
4414    <date year='1997' month='February' />
4415  </front>
4416  <seriesInfo name='RFC' value='2109' />
4419<reference anchor="RFC2145">
4420  <front>
4421    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4422    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4423      <organization>Western Research Laboratory</organization>
4424      <address><email></email></address>
4425    </author>
4426    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4427      <organization>Department of Information and Computer Science</organization>
4428      <address><email></email></address>
4429    </author>
4430    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4431      <organization>MIT Laboratory for Computer Science</organization>
4432      <address><email></email></address>
4433    </author>
4434    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4435      <organization>W3 Consortium</organization>
4436      <address><email></email></address>
4437    </author>
4438    <date month="May" year="1997"/>
4439  </front>
4440  <seriesInfo name="RFC" value="2145"/>
4443<reference anchor="RFC2616">
4444  <front>
4445    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4446    <author initials="R." surname="Fielding" fullname="R. Fielding">
4447      <organization>University of California, Irvine</organization>
4448      <address><email></email></address>
4449    </author>
4450    <author initials="J." surname="Gettys" fullname="J. Gettys">
4451      <organization>W3C</organization>
4452      <address><email></email></address>
4453    </author>
4454    <author initials="J." surname="Mogul" fullname="J. Mogul">
4455      <organization>Compaq Computer Corporation</organization>
4456      <address><email></email></address>
4457    </author>
4458    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4459      <organization>MIT Laboratory for Computer Science</organization>
4460      <address><email></email></address>
4461    </author>
4462    <author initials="L." surname="Masinter" fullname="L. Masinter">
4463      <organization>Xerox Corporation</organization>
4464      <address><email></email></address>
4465    </author>
4466    <author initials="P." surname="Leach" fullname="P. Leach">
4467      <organization>Microsoft Corporation</organization>
4468      <address><email></email></address>
4469    </author>
4470    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4471      <organization>W3C</organization>
4472      <address><email></email></address>
4473    </author>
4474    <date month="June" year="1999"/>
4475  </front>
4476  <seriesInfo name="RFC" value="2616"/>
4479<reference anchor='RFC2817'>
4480  <front>
4481    <title>Upgrading to TLS Within HTTP/1.1</title>
4482    <author initials='R.' surname='Khare' fullname='R. Khare'>
4483      <organization>4K Associates / UC Irvine</organization>
4484      <address><email></email></address>
4485    </author>
4486    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4487      <organization>Agranat Systems, Inc.</organization>
4488      <address><email></email></address>
4489    </author>
4490    <date year='2000' month='May' />
4491  </front>
4492  <seriesInfo name='RFC' value='2817' />
4495<reference anchor='RFC2818'>
4496  <front>
4497    <title>HTTP Over TLS</title>
4498    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4499      <organization>RTFM, Inc.</organization>
4500      <address><email></email></address>
4501    </author>
4502    <date year='2000' month='May' />
4503  </front>
4504  <seriesInfo name='RFC' value='2818' />
4507<reference anchor='RFC2965'>
4508  <front>
4509    <title>HTTP State Management Mechanism</title>
4510    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4511      <organization>Bell Laboratories, Lucent Technologies</organization>
4512      <address><email></email></address>
4513    </author>
4514    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4515      <organization>, Inc.</organization>
4516      <address><email></email></address>
4517    </author>
4518    <date year='2000' month='October' />
4519  </front>
4520  <seriesInfo name='RFC' value='2965' />
4523<reference anchor='RFC3864'>
4524  <front>
4525    <title>Registration Procedures for Message Header Fields</title>
4526    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4527      <organization>Nine by Nine</organization>
4528      <address><email></email></address>
4529    </author>
4530    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4531      <organization>BEA Systems</organization>
4532      <address><email></email></address>
4533    </author>
4534    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4535      <organization>HP Labs</organization>
4536      <address><email></email></address>
4537    </author>
4538    <date year='2004' month='September' />
4539  </front>
4540  <seriesInfo name='BCP' value='90' />
4541  <seriesInfo name='RFC' value='3864' />
4544<reference anchor="RFC4288">
4545  <front>
4546    <title>Media Type Specifications and Registration Procedures</title>
4547    <author initials="N." surname="Freed" fullname="N. Freed">
4548      <organization>Sun Microsystems</organization>
4549      <address>
4550        <email></email>
4551      </address>
4552    </author>
4553    <author initials="J." surname="Klensin" fullname="J. Klensin">
4554      <address>
4555        <email></email>
4556      </address>
4557    </author>
4558    <date year="2005" month="December"/>
4559  </front>
4560  <seriesInfo name="BCP" value="13"/>
4561  <seriesInfo name="RFC" value="4288"/>
4564<reference anchor='RFC4395'>
4565  <front>
4566    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4567    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4568      <organization>AT&amp;T Laboratories</organization>
4569      <address>
4570        <email></email>
4571      </address>
4572    </author>
4573    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4574      <organization>Qualcomm, Inc.</organization>
4575      <address>
4576        <email></email>
4577      </address>
4578    </author>
4579    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4580      <organization>Adobe Systems</organization>
4581      <address>
4582        <email></email>
4583      </address>
4584    </author>
4585    <date year='2006' month='February' />
4586  </front>
4587  <seriesInfo name='BCP' value='115' />
4588  <seriesInfo name='RFC' value='4395' />
4591<reference anchor='RFC5226'>
4592  <front>
4593    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4594    <author initials='T.' surname='Narten' fullname='T. Narten'>
4595      <organization>IBM</organization>
4596      <address><email></email></address>
4597    </author>
4598    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4599      <organization>Google</organization>
4600      <address><email></email></address>
4601    </author>
4602    <date year='2008' month='May' />
4603  </front>
4604  <seriesInfo name='BCP' value='26' />
4605  <seriesInfo name='RFC' value='5226' />
4608<reference anchor="RFC5322">
4609  <front>
4610    <title>Internet Message Format</title>
4611    <author initials="P." surname="Resnick" fullname="P. Resnick">
4612      <organization>Qualcomm Incorporated</organization>
4613    </author>
4614    <date year="2008" month="October"/>
4615  </front>
4616  <seriesInfo name="RFC" value="5322"/>
4619<reference anchor='BCP97'>
4620  <front>
4621    <title>Handling Normative References to Standards-Track Documents</title>
4622    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4623      <address>
4624        <email></email>
4625      </address>
4626    </author>
4627    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4628      <organization>MIT</organization>
4629      <address>
4630        <email></email>
4631      </address>
4632    </author>
4633    <date year='2007' month='June' />
4634  </front>
4635  <seriesInfo name='BCP' value='97' />
4636  <seriesInfo name='RFC' value='4897' />
4639<reference anchor="Kri2001" target="">
4640  <front>
4641    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4642    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4643    <date year="2001" month="November"/>
4644  </front>
4645  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4648<reference anchor="Spe" target="">
4649  <front>
4650    <title>Analysis of HTTP Performance Problems</title>
4651    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4652    <date/>
4653  </front>
4656<reference anchor="Tou1998" target="">
4657  <front>
4658  <title>Analysis of HTTP Performance</title>
4659  <author initials="J." surname="Touch" fullname="Joe Touch">
4660    <organization>USC/Information Sciences Institute</organization>
4661    <address><email></email></address>
4662  </author>
4663  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4664    <organization>USC/Information Sciences Institute</organization>
4665    <address><email></email></address>
4666  </author>
4667  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4668    <organization>USC/Information Sciences Institute</organization>
4669    <address><email></email></address>
4670  </author>
4671  <date year="1998" month="Aug"/>
4672  </front>
4673  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4674  <annotation>(original report dated Aug. 1996)</annotation>
4680<section title="Tolerant Applications" anchor="tolerant.applications">
4682   Although this document specifies the requirements for the generation
4683   of HTTP/1.1 messages, not all applications will be correct in their
4684   implementation. We therefore recommend that operational applications
4685   be tolerant of deviations whenever those deviations can be
4686   interpreted unambiguously.
4689   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4690   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4691   &SHOULD; accept any amount of WSP characters between fields, even though
4692   only a single SP is required.
4695   The line terminator for header fields is the sequence CRLF.
4696   However, we recommend that applications, when parsing such headers fields,
4697   recognize a single LF as a line terminator and ignore the leading CR.
4700   The character set of a representation &SHOULD; be labeled as the lowest
4701   common denominator of the character codes used within that representation, with
4702   the exception that not labeling the representation is preferred over labeling
4703   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4706   Additional rules for requirements on parsing and encoding of dates
4707   and other potential problems with date encodings include:
4710  <list style="symbols">
4711     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4712        which appears to be more than 50 years in the future is in fact
4713        in the past (this helps solve the "year 2000" problem).</t>
4715     <t>Although all date formats are specified to be case-sensitive,
4716        recipients &SHOULD; match day, week and timezone names
4717        case-insensitively.</t>
4719     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4720        Expires date as earlier than the proper value, but &MUST-NOT;
4721        internally represent a parsed Expires date as later than the
4722        proper value.</t>
4724     <t>All expiration-related calculations &MUST; be done in GMT. The
4725        local time zone &MUST-NOT; influence the calculation or comparison
4726        of an age or expiration time.</t>
4728     <t>If an HTTP header field incorrectly carries a date value with a time
4729        zone other than GMT, it &MUST; be converted into GMT using the
4730        most conservative possible conversion.</t>
4731  </list>
4735<section title="Compatibility with Previous Versions" anchor="compatibility">
4737   HTTP has been in use by the World-Wide Web global information initiative
4738   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4739   was a simple protocol for hypertext data transfer across the Internet
4740   with only a single method and no metadata.
4741   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4742   methods and MIME-like messaging that could include metadata about the data
4743   transferred and modifiers on the request/response semantics. However,
4744   HTTP/1.0 did not sufficiently take into consideration the effects of
4745   hierarchical proxies, caching, the need for persistent connections, or
4746   name-based virtual hosts. The proliferation of incompletely-implemented
4747   applications calling themselves "HTTP/1.0" further necessitated a
4748   protocol version change in order for two communicating applications
4749   to determine each other's true capabilities.
4752   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4753   requirements that enable reliable implementations, adding only
4754   those new features that will either be safely ignored by an HTTP/1.0
4755   recipient or only sent when communicating with a party advertising
4756   compliance with HTTP/1.1.
4759   It is beyond the scope of a protocol specification to mandate
4760   compliance with previous versions. HTTP/1.1 was deliberately
4761   designed, however, to make supporting previous versions easy. It is
4762   worth noting that, at the time of composing this specification, we would
4763   expect general-purpose HTTP/1.1 servers to:
4764  <list style="symbols">
4765     <t>understand any valid request in the format of HTTP/1.0 and
4766        1.1;</t>
4768     <t>respond appropriately with a message in the same major version
4769        used by the client.</t>
4770  </list>
4773   And we would expect HTTP/1.1 clients to:
4774  <list style="symbols">
4775     <t>understand any valid response in the format of HTTP/1.0 or
4776        1.1.</t>
4777  </list>
4780   For most implementations of HTTP/1.0, each connection is established
4781   by the client prior to the request and closed by the server after
4782   sending the response. Some implementations implement the Keep-Alive
4783   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4786<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4788   This section summarizes major differences between versions HTTP/1.0
4789   and HTTP/1.1.
4792<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4794   The requirements that clients and servers support the Host request-header
4795   field (<xref target=""/>), report an error if it is
4796   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4797   are among the most important changes defined by this
4798   specification.
4801   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4802   addresses and servers; there was no other established mechanism for
4803   distinguishing the intended server of a request than the IP address
4804   to which that request was directed. The changes outlined above will
4805   allow the Internet, once older HTTP clients are no longer common, to
4806   support multiple Web sites from a single IP address, greatly
4807   simplifying large operational Web servers, where allocation of many
4808   IP addresses to a single host has created serious problems. The
4809   Internet will also be able to recover the IP addresses that have been
4810   allocated for the sole purpose of allowing special-purpose domain
4811   names to be used in root-level HTTP URLs. Given the rate of growth of
4812   the Web, and the number of servers already deployed, it is extremely
4813   important that all implementations of HTTP (including updates to
4814   existing HTTP/1.0 applications) correctly implement these
4815   requirements:
4816  <list style="symbols">
4817     <t>Both clients and servers &MUST; support the Host request-header field.</t>
4819     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4821     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4822        request does not include a Host request-header field.</t>
4824     <t>Servers &MUST; accept absolute URIs.</t>
4825  </list>
4830<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4832   Some clients and servers might wish to be compatible with some
4833   previous implementations of persistent connections in HTTP/1.0
4834   clients and servers. Persistent connections in HTTP/1.0 are
4835   explicitly negotiated as they are not the default behavior. HTTP/1.0
4836   experimental implementations of persistent connections are faulty,
4837   and the new facilities in HTTP/1.1 are designed to rectify these
4838   problems. The problem was that some existing HTTP/1.0 clients might
4839   send Keep-Alive to a proxy server that doesn't understand
4840   Connection, which would then erroneously forward it to the next
4841   inbound server, which would establish the Keep-Alive connection and
4842   result in a hung HTTP/1.0 proxy waiting for the close on the
4843   response. The result is that HTTP/1.0 clients must be prevented from
4844   using Keep-Alive when talking to proxies.
4847   However, talking to proxies is the most important use of persistent
4848   connections, so that prohibition is clearly unacceptable. Therefore,
4849   we need some other mechanism for indicating a persistent connection
4850   is desired, which is safe to use even when talking to an old proxy
4851   that ignores Connection. Persistent connections are the default for
4852   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4853   declaring non-persistence. See <xref target="header.connection"/>.
4856   The original HTTP/1.0 form of persistent connections (the Connection:
4857   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4861<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4863  Empty list elements in list productions have been deprecated.
4864  (<xref target="notation.abnf"/>)
4867  Rules about implicit linear whitespace between certain grammar productions
4868  have been removed; now it's only allowed when specifically pointed out
4869  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4870  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4871  Non-ASCII content in header fields and reason phrase has been obsoleted and
4872  made opaque (the TEXT rule was removed)
4873  (<xref target="basic.rules"/>)
4876  Clarify that HTTP-Version is case sensitive.
4877  (<xref target="http.version"/>)
4880  Require that invalid whitespace around field-names be rejected.
4881  (<xref target="header.fields"/>)
4884  Require recipients to handle bogus Content-Length header fields as errors.
4885  (<xref target="message.body"/>)
4888  Remove reference to non-existent identity transfer-coding value tokens.
4889  (Sections <xref format="counter" target="message.body"/> and
4890  <xref format="counter" target="transfer.codings"/>)
4893  Update use of abs_path production from RFC 1808 to the path-absolute + query
4894  components of RFC 3986.
4895  (<xref target="request-target"/>)
4898  Clarification that the chunk length does not include the count of the octets
4899  in the chunk header and trailer. Furthermore disallowed line folding
4900  in chunk extensions.
4901  (<xref target="chunked.encoding"/>)
4904  Remove hard limit of two connections per server.
4905  (<xref target="persistent.practical"/>)
4908  Clarify exactly when close connection options must be sent.
4909  (<xref target="header.connection"/>)
4914<?BEGININC p1-messaging.abnf-appendix ?>
4915<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4917<artwork type="abnf" name="p1-messaging.parsed-abnf">
4918<x:ref>BWS</x:ref> = OWS
4920<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4921<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4922<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4923<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4924 connection-token ] )
4925<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4926<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4928<x:ref>Date</x:ref> = "Date:" OWS Date-v
4929<x:ref>Date-v</x:ref> = HTTP-date
4931<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4933<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4934<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4935<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4936<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4937 ]
4938<x:ref>Host</x:ref> = "Host:" OWS Host-v
4939<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4941<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4942<x:ref>Method</x:ref> = token
4944<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4946<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4948<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4949<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4950<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
4951<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4952<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
4954<x:ref>Status-Code</x:ref> = 3DIGIT
4955<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4957<x:ref>TE</x:ref> = "TE:" OWS TE-v
4958<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4959<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4960<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4961<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4962<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4963 transfer-coding ] )
4965<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4966<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4967<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4969<x:ref>Via</x:ref> = "Via:" OWS Via-v
4970<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4971 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4972 ] )
4974<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4976<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4977<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4978<x:ref>attribute</x:ref> = token
4979<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4981<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4982<x:ref>chunk-data</x:ref> = 1*OCTET
4983<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4984<x:ref>chunk-ext-name</x:ref> = token
4985<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4986<x:ref>chunk-size</x:ref> = 1*HEXDIG
4987<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4988<x:ref>connection-token</x:ref> = token
4989<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4990 / %x2A-5B ; '*'-'['
4991 / %x5D-7E ; ']'-'~'
4992 / obs-text
4994<x:ref>date1</x:ref> = day SP month SP year
4995<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4996<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4997<x:ref>day</x:ref> = 2DIGIT
4998<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4999 / %x54.75.65 ; Tue
5000 / %x57.65.64 ; Wed
5001 / %x54.68.75 ; Thu
5002 / %x46.72.69 ; Fri
5003 / %x53.61.74 ; Sat
5004 / %x53.75.6E ; Sun
5005<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5006 / %x54. ; Tuesday
5007 / %x57.65.64.6E. ; Wednesday
5008 / %x54. ; Thursday
5009 / %x46. ; Friday
5010 / %x53. ; Saturday
5011 / %x53.75.6E.64.61.79 ; Sunday
5013<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5014<x:ref>field-name</x:ref> = token
5015<x:ref>field-value</x:ref> = *( field-content / OWS )
5017<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5018 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5020<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5021<x:ref>hour</x:ref> = 2DIGIT
5022<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5023<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5025<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5027<x:ref>message-body</x:ref> = *OCTET
5028<x:ref>minute</x:ref> = 2DIGIT
5029<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5030 / %x46.65.62 ; Feb
5031 / %x4D.61.72 ; Mar
5032 / %x41.70.72 ; Apr
5033 / %x4D.61.79 ; May
5034 / %x4A.75.6E ; Jun
5035 / %x4A.75.6C ; Jul
5036 / %x41.75.67 ; Aug
5037 / %x53.65.70 ; Sep
5038 / %x4F.63.74 ; Oct
5039 / %x4E.6F.76 ; Nov
5040 / %x44.65.63 ; Dec
5042<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5043<x:ref>obs-fold</x:ref> = CRLF
5044<x:ref>obs-text</x:ref> = %x80-FF
5046<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5047<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5048<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5049<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5050<x:ref>product</x:ref> = token [ "/" product-version ]
5051<x:ref>product-version</x:ref> = token
5052<x:ref>protocol-name</x:ref> = token
5053<x:ref>protocol-version</x:ref> = token
5054<x:ref>pseudonym</x:ref> = token
5056<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5057 / %x5D-7E ; ']'-'~'
5058 / obs-text
5059<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5060 / %x5D-7E ; ']'-'~'
5061 / obs-text
5062<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5063<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5064<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5065<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5066<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5067<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5069<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5070<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5071<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5072<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5073<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5074 / authority
5075<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5076<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5077<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5079<x:ref>second</x:ref> = 2DIGIT
5080<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5081 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5082<x:ref>start-line</x:ref> = Request-Line / Status-Line
5084<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5085<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5086 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5087<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5088<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5089<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5090<x:ref>token</x:ref> = 1*tchar
5091<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5092<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5093 transfer-extension
5094<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5095<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5097<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5099<x:ref>value</x:ref> = word
5101<x:ref>word</x:ref> = token / quoted-string
5103<x:ref>year</x:ref> = 4DIGIT
5106<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5107; Chunked-Body defined but not used
5108; Content-Length defined but not used
5109; HTTP-message defined but not used
5110; Host defined but not used
5111; Request defined but not used
5112; Response defined but not used
5113; TE defined but not used
5114; URI-reference defined but not used
5115; general-header defined but not used
5116; http-URI defined but not used
5117; https-URI defined but not used
5118; partial-URI defined but not used
5119; request-header defined but not used
5120; response-header defined but not used
5121; special defined but not used
5123<?ENDINC p1-messaging.abnf-appendix ?>
5125<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5127<section title="Since RFC 2616">
5129  Extracted relevant partitions from <xref target="RFC2616"/>.
5133<section title="Since draft-ietf-httpbis-p1-messaging-00">
5135  Closed issues:
5136  <list style="symbols">
5137    <t>
5138      <eref target=""/>:
5139      "HTTP Version should be case sensitive"
5140      (<eref target=""/>)
5141    </t>
5142    <t>
5143      <eref target=""/>:
5144      "'unsafe' characters"
5145      (<eref target=""/>)
5146    </t>
5147    <t>
5148      <eref target=""/>:
5149      "Chunk Size Definition"
5150      (<eref target=""/>)
5151    </t>
5152    <t>
5153      <eref target=""/>:
5154      "Message Length"
5155      (<eref target=""/>)
5156    </t>
5157    <t>
5158      <eref target=""/>:
5159      "Media Type Registrations"
5160      (<eref target=""/>)
5161    </t>
5162    <t>
5163      <eref target=""/>:
5164      "URI includes query"
5165      (<eref target=""/>)
5166    </t>
5167    <t>
5168      <eref target=""/>:
5169      "No close on 1xx responses"
5170      (<eref target=""/>)
5171    </t>
5172    <t>
5173      <eref target=""/>:
5174      "Remove 'identity' token references"
5175      (<eref target=""/>)
5176    </t>
5177    <t>
5178      <eref target=""/>:
5179      "Import query BNF"
5180    </t>
5181    <t>
5182      <eref target=""/>:
5183      "qdtext BNF"
5184    </t>
5185    <t>
5186      <eref target=""/>:
5187      "Normative and Informative references"
5188    </t>
5189    <t>
5190      <eref target=""/>:
5191      "RFC2606 Compliance"
5192    </t>
5193    <t>
5194      <eref target=""/>:
5195      "RFC977 reference"
5196    </t>
5197    <t>
5198      <eref target=""/>:
5199      "RFC1700 references"
5200    </t>
5201    <t>
5202      <eref target=""/>:
5203      "inconsistency in date format explanation"
5204    </t>
5205    <t>
5206      <eref target=""/>:
5207      "Date reference typo"
5208    </t>
5209    <t>
5210      <eref target=""/>:
5211      "Informative references"
5212    </t>
5213    <t>
5214      <eref target=""/>:
5215      "ISO-8859-1 Reference"
5216    </t>
5217    <t>
5218      <eref target=""/>:
5219      "Normative up-to-date references"
5220    </t>
5221  </list>
5224  Other changes:
5225  <list style="symbols">
5226    <t>
5227      Update media type registrations to use RFC4288 template.
5228    </t>
5229    <t>
5230      Use names of RFC4234 core rules DQUOTE and WSP,
5231      fix broken ABNF for chunk-data
5232      (work in progress on <eref target=""/>)
5233    </t>
5234  </list>
5238<section title="Since draft-ietf-httpbis-p1-messaging-01">
5240  Closed issues:
5241  <list style="symbols">
5242    <t>
5243      <eref target=""/>:
5244      "Bodies on GET (and other) requests"
5245    </t>
5246    <t>
5247      <eref target=""/>:
5248      "Updating to RFC4288"
5249    </t>
5250    <t>
5251      <eref target=""/>:
5252      "Status Code and Reason Phrase"
5253    </t>
5254    <t>
5255      <eref target=""/>:
5256      "rel_path not used"
5257    </t>
5258  </list>
5261  Ongoing work on ABNF conversion (<eref target=""/>):
5262  <list style="symbols">
5263    <t>
5264      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5265      "trailer-part").
5266    </t>
5267    <t>
5268      Avoid underscore character in rule names ("http_URL" ->
5269      "http-URL", "abs_path" -> "path-absolute").
5270    </t>
5271    <t>
5272      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5273      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5274      have to be updated when switching over to RFC3986.
5275    </t>
5276    <t>
5277      Synchronize core rules with RFC5234.
5278    </t>
5279    <t>
5280      Get rid of prose rules that span multiple lines.
5281    </t>
5282    <t>
5283      Get rid of unused rules LOALPHA and UPALPHA.
5284    </t>
5285    <t>
5286      Move "Product Tokens" section (back) into Part 1, as "token" is used
5287      in the definition of the Upgrade header field.
5288    </t>
5289    <t>
5290      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5291    </t>
5292    <t>
5293      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5294    </t>
5295  </list>
5299<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5301  Closed issues:
5302  <list style="symbols">
5303    <t>
5304      <eref target=""/>:
5305      "HTTP-date vs. rfc1123-date"
5306    </t>
5307    <t>
5308      <eref target=""/>:
5309      "WS in quoted-pair"
5310    </t>
5311  </list>
5314  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5315  <list style="symbols">
5316    <t>
5317      Reference RFC 3984, and update header field registrations for headers defined
5318      in this document.
5319    </t>
5320  </list>
5323  Ongoing work on ABNF conversion (<eref target=""/>):
5324  <list style="symbols">
5325    <t>
5326      Replace string literals when the string really is case-sensitive (HTTP-Version).
5327    </t>
5328  </list>
5332<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5334  Closed issues:
5335  <list style="symbols">
5336    <t>
5337      <eref target=""/>:
5338      "Connection closing"
5339    </t>
5340    <t>
5341      <eref target=""/>:
5342      "Move registrations and registry information to IANA Considerations"
5343    </t>
5344    <t>
5345      <eref target=""/>:
5346      "need new URL for PAD1995 reference"
5347    </t>
5348    <t>
5349      <eref target=""/>:
5350      "IANA Considerations: update HTTP URI scheme registration"
5351    </t>
5352    <t>
5353      <eref target=""/>:
5354      "Cite HTTPS URI scheme definition"
5355    </t>
5356    <t>
5357      <eref target=""/>:
5358      "List-type headers vs Set-Cookie"
5359    </t>
5360  </list>
5363  Ongoing work on ABNF conversion (<eref target=""/>):
5364  <list style="symbols">
5365    <t>
5366      Replace string literals when the string really is case-sensitive (HTTP-Date).
5367    </t>
5368    <t>
5369      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5370    </t>
5371  </list>
5375<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5377  Closed issues:
5378  <list style="symbols">
5379    <t>
5380      <eref target=""/>:
5381      "Out-of-date reference for URIs"
5382    </t>
5383    <t>
5384      <eref target=""/>:
5385      "RFC 2822 is updated by RFC 5322"
5386    </t>
5387  </list>
5390  Ongoing work on ABNF conversion (<eref target=""/>):
5391  <list style="symbols">
5392    <t>
5393      Use "/" instead of "|" for alternatives.
5394    </t>
5395    <t>
5396      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5397    </t>
5398    <t>
5399      Only reference RFC 5234's core rules.
5400    </t>
5401    <t>
5402      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5403      whitespace ("OWS") and required whitespace ("RWS").
5404    </t>
5405    <t>
5406      Rewrite ABNFs to spell out whitespace rules, factor out
5407      header field value format definitions.
5408    </t>
5409  </list>
5413<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5415  Closed issues:
5416  <list style="symbols">
5417    <t>
5418      <eref target=""/>:
5419      "Header LWS"
5420    </t>
5421    <t>
5422      <eref target=""/>:
5423      "Sort 1.3 Terminology"
5424    </t>
5425    <t>
5426      <eref target=""/>:
5427      "RFC2047 encoded words"
5428    </t>
5429    <t>
5430      <eref target=""/>:
5431      "Character Encodings in TEXT"
5432    </t>
5433    <t>
5434      <eref target=""/>:
5435      "Line Folding"
5436    </t>
5437    <t>
5438      <eref target=""/>:
5439      "OPTIONS * and proxies"
5440    </t>
5441    <t>
5442      <eref target=""/>:
5443      "Reason-Phrase BNF"
5444    </t>
5445    <t>
5446      <eref target=""/>:
5447      "Use of TEXT"
5448    </t>
5449    <t>
5450      <eref target=""/>:
5451      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5452    </t>
5453    <t>
5454      <eref target=""/>:
5455      "RFC822 reference left in discussion of date formats"
5456    </t>
5457  </list>
5460  Final work on ABNF conversion (<eref target=""/>):
5461  <list style="symbols">
5462    <t>
5463      Rewrite definition of list rules, deprecate empty list elements.
5464    </t>
5465    <t>
5466      Add appendix containing collected and expanded ABNF.
5467    </t>
5468  </list>
5471  Other changes:
5472  <list style="symbols">
5473    <t>
5474      Rewrite introduction; add mostly new Architecture Section.
5475    </t>
5476    <t>
5477      Move definition of quality values from Part 3 into Part 1;
5478      make TE request header field grammar independent of accept-params (defined in Part 3).
5479    </t>
5480  </list>
5484<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5486  Closed issues:
5487  <list style="symbols">
5488    <t>
5489      <eref target=""/>:
5490      "base for numeric protocol elements"
5491    </t>
5492    <t>
5493      <eref target=""/>:
5494      "comment ABNF"
5495    </t>
5496  </list>
5499  Partly resolved issues:
5500  <list style="symbols">
5501    <t>
5502      <eref target=""/>:
5503      "205 Bodies" (took out language that implied that there might be
5504      methods for which a request body MUST NOT be included)
5505    </t>
5506    <t>
5507      <eref target=""/>:
5508      "editorial improvements around HTTP-date"
5509    </t>
5510  </list>
5514<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5516  Closed issues:
5517  <list style="symbols">
5518    <t>
5519      <eref target=""/>:
5520      "Repeating single-value headers"
5521    </t>
5522    <t>
5523      <eref target=""/>:
5524      "increase connection limit"
5525    </t>
5526    <t>
5527      <eref target=""/>:
5528      "IP addresses in URLs"
5529    </t>
5530    <t>
5531      <eref target=""/>:
5532      "take over HTTP Upgrade Token Registry"
5533    </t>
5534    <t>
5535      <eref target=""/>:
5536      "CR and LF in chunk extension values"
5537    </t>
5538    <t>
5539      <eref target=""/>:
5540      "HTTP/0.9 support"
5541    </t>
5542    <t>
5543      <eref target=""/>:
5544      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5545    </t>
5546    <t>
5547      <eref target=""/>:
5548      "move definitions of gzip/deflate/compress to part 1"
5549    </t>
5550    <t>
5551      <eref target=""/>:
5552      "disallow control characters in quoted-pair"
5553    </t>
5554  </list>
5557  Partly resolved issues:
5558  <list style="symbols">
5559    <t>
5560      <eref target=""/>:
5561      "update IANA requirements wrt Transfer-Coding values" (add the
5562      IANA Considerations subsection)
5563    </t>
5564  </list>
5568<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5570  Closed issues:
5571  <list style="symbols">
5572    <t>
5573      <eref target=""/>:
5574      "header parsing, treatment of leading and trailing OWS"
5575    </t>
5576  </list>
5579  Partly resolved issues:
5580  <list style="symbols">
5581    <t>
5582      <eref target=""/>:
5583      "Placement of 13.5.1 and 13.5.2"
5584    </t>
5585    <t>
5586      <eref target=""/>:
5587      "use of term "word" when talking about header structure"
5588    </t>
5589  </list>
5593<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5595  Closed issues:
5596  <list style="symbols">
5597    <t>
5598      <eref target=""/>:
5599      "Clarification of the term 'deflate'"
5600    </t>
5601    <t>
5602      <eref target=""/>:
5603      "OPTIONS * and proxies"
5604    </t>
5605    <t>
5606      <eref target=""/>:
5607      "MIME-Version not listed in P1, general header fields"
5608    </t>
5609    <t>
5610      <eref target=""/>:
5611      "IANA registry for content/transfer encodings"
5612    </t>
5613    <t>
5614      <eref target=""/>:
5615      "Case-sensitivity of HTTP-date"
5616    </t>
5617    <t>
5618      <eref target=""/>:
5619      "use of term "word" when talking about header structure"
5620    </t>
5621  </list>
5624  Partly resolved issues:
5625  <list style="symbols">
5626    <t>
5627      <eref target=""/>:
5628      "Term for the requested resource's URI"
5629    </t>
5630  </list>
5634<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5636  Closed issues:
5637  <list style="symbols">
5638    <t>
5639      <eref target=""/>:
5640      "Connection Closing"
5641    </t>
5642    <t>
5643      <eref target=""/>:
5644      "Delimiting messages with multipart/byteranges"
5645    </t>
5646    <t>
5647      <eref target=""/>:
5648      "Handling multiple Content-Length headers"
5649    </t>
5650    <t>
5651      <eref target=""/>:
5652      "Clarify entity / representation / variant terminology"
5653    </t>
5654    <t>
5655      <eref target=""/>:
5656      "consider removing the 'changes from 2068' sections"
5657    </t>
5658  </list>
5661  Partly resolved issues:
5662  <list style="symbols">
5663    <t>
5664      <eref target=""/>:
5665      "HTTP(s) URI scheme definitions"
5666    </t>
5667  </list>
5671<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5673  Closed issues:
5674  <list style="symbols">
5675    <t>
5676      <eref target=""/>:
5677      "effective request URI: handling of missing host in HTTP/1.0"
5678    </t>
5679  </list>
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