source: draft-ietf-httpbis/latest/p1-messaging.xml @ 991

Last change on this file since 991 was 991, checked in by julian.reschke@…, 12 years ago

introduce the terms "path-absolute form" and "asterisk form" (of request-target) (related to #221)

  • Property svn:eol-style set to native
File size: 240.6 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 "September">
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 as implemented in
1202   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1203   can occur multiple times, but does not use the list syntax, and thus cannot
1204   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1205   for details.) Also note that the Set-Cookie2 header specified in
1206   <xref target="RFC2965"/> does not share this problem.
1207  </t>
1210   Historically, HTTP header field values could be extended over multiple
1211   lines by preceding each extra line with at least one space or horizontal
1212   tab character (line folding). This specification deprecates such line
1213   folding except within the message/http media type
1214   (<xref target=""/>).
1215   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1216   (i.e., that contain any field-content that matches the obs-fold rule) unless
1217   the message is intended for packaging within the message/http media type.
1218   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1219   obs-fold whitespace with a single SP prior to interpreting the field value
1220   or forwarding the message downstream.
1223   Historically, HTTP has allowed field content with text in the ISO-8859-1
1224   <xref target="ISO-8859-1"/> character encoding and supported other
1225   character sets only through use of <xref target="RFC2047"/> encoding.
1226   In practice, most HTTP header field values use only a subset of the
1227   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1228   header fields &SHOULD; limit their field values to US-ASCII characters.
1229   Recipients &SHOULD; treat other (obs-text) octets in field content as
1230   opaque data.
1232<t anchor="rule.comment">
1233  <x:anchor-alias value="comment"/>
1234  <x:anchor-alias value="ctext"/>
1235   Comments can be included in some HTTP header fields by surrounding
1236   the comment text with parentheses. Comments are only allowed in
1237   fields containing "comment" as part of their field value definition.
1239<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1240  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1241  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1242                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1244<t anchor="rule.quoted-cpair">
1245  <x:anchor-alias value="quoted-cpair"/>
1246   The backslash character ("\") can be used as a single-character
1247   quoting mechanism within comment constructs:
1249<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1250  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1253   Producers &SHOULD-NOT; escape characters that do not require escaping
1254   (i.e., other than the backslash character "\" and the parentheses "(" and
1255   ")").
1259<section title="Message Body" anchor="message.body">
1260  <x:anchor-alias value="message-body"/>
1262   The message-body (if any) of an HTTP message is used to carry the
1263   payload body associated with the request or response.
1265<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1266  <x:ref>message-body</x:ref> = *OCTET
1269   The message-body differs from the payload body only when a transfer-coding
1270   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1271   applied to a payload in order to form the message-body, the
1272   Transfer-Encoding header field &MUST; contain the list of
1273   transfer-codings applied. Transfer-Encoding is a property of the message,
1274   not of the payload, and thus &MAY; be added or removed by any implementation
1275   along the request/response chain under the constraints found in
1276   <xref target="transfer.codings"/>.
1279   The rules for when a message-body is allowed in a message differ for
1280   requests and responses.
1283   The presence of a message-body in a request is signaled by the
1284   inclusion of a Content-Length or Transfer-Encoding header field in
1285   the request's header fields, even if the request method does not
1286   define any use for a message-body.  This allows the request
1287   message framing algorithm to be independent of method semantics.
1290   For response messages, whether or not a message-body is included with
1291   a message is dependent on both the request method and the response
1292   status code (<xref target="status.code.and.reason.phrase"/>).
1293   Responses to the HEAD request method never include a message-body
1294   because the associated response header fields (e.g., Transfer-Encoding,
1295   Content-Length, etc.) only indicate what their values would have been
1296   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1297   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1298   All other responses do include a message-body, although the body
1299   &MAY; be of zero length.
1302   The length of the message-body is determined by one of the following
1303   (in order of precedence):
1306  <list style="numbers">
1307    <x:lt><t>
1308     Any response to a HEAD request and any response with a status
1309     code of 100-199, 204, or 304 is always terminated by the first
1310     empty line after the header fields, regardless of the header
1311     fields present in the message, and thus cannot contain a message-body.
1312    </t></x:lt>
1313    <x:lt><t>
1314     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1315     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1316     is the final encoding, the message-body length is determined by reading
1317     and decoding the chunked data until the transfer-coding indicates the
1318     data is complete.
1319    </t>
1320    <t>
1321     If a Transfer-Encoding header field is present in a response and the
1322     "chunked" transfer-coding is not the final encoding, the message-body
1323     length is determined by reading the connection until it is closed by
1324     the server.
1325     If a Transfer-Encoding header field is present in a request and the
1326     "chunked" transfer-coding is not the final encoding, the message-body
1327     length cannot be determined reliably; the server &MUST; respond with
1328     the 400 (Bad Request) status code and then close the connection.
1329    </t>
1330    <t>
1331     If a message is received with both a Transfer-Encoding header field and a
1332     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1333     Such a message might indicate an attempt to perform request or response
1334     smuggling (bypass of security-related checks on message routing or content)
1335     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1336     be removed, prior to forwarding the message downstream, or replaced with
1337     the real message-body length after the transfer-coding is decoded.
1338    </t></x:lt>
1339    <x:lt><t>
1340     If a message is received without Transfer-Encoding and with either
1341     multiple Content-Length header fields or a single Content-Length header
1342     field with an invalid value, then the message framing is invalid and
1343     &MUST; be treated as an error to prevent request or response smuggling.
1344     If this is a request message, the server &MUST; respond with
1345     a 400 (Bad Request) status code and then close the connection.
1346     If this is a response message received by a proxy or gateway, the proxy
1347     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1348     status code as its downstream response, and then close the connection.
1349     If this is a response message received by a user-agent, the message-body
1350     length is determined by reading the connection until it is closed;
1351     an error &SHOULD; be indicated to the user.
1352    </t></x:lt>
1353    <x:lt><t>
1354     If a valid Content-Length header field (<xref target="header.content-length"/>)
1355     is present without Transfer-Encoding, its decimal value defines the
1356     message-body length in octets.  If the actual number of octets sent in
1357     the message is less than the indicated Content-Length, the recipient
1358     &MUST; consider the message to be incomplete and treat the connection
1359     as no longer usable.
1360     If the actual number of octets sent in the message is more than the indicated
1361     Content-Length, the recipient &MUST; only process the message-body up to the
1362     field value's number of octets; the remainder of the message &MUST; either
1363     be discarded or treated as the next message in a pipeline.  For the sake of
1364     robustness, a user-agent &MAY; attempt to detect and correct such an error
1365     in message framing if it is parsing the response to the last request on
1366     on a connection and the connection has been closed by the server.
1367    </t></x:lt>
1368    <x:lt><t>
1369     If this is a request message and none of the above are true, then the
1370     message-body length is zero (no message-body is present).
1371    </t></x:lt>
1372    <x:lt><t>
1373     Otherwise, this is a response message without a declared message-body
1374     length, so the message-body length is determined by the number of octets
1375     received prior to the server closing the connection.
1376    </t></x:lt>
1377  </list>
1380   Since there is no way to distinguish a successfully completed,
1381   close-delimited message from a partially-received message interrupted
1382   by network failure, implementations &SHOULD; use encoding or
1383   length-delimited messages whenever possible.  The close-delimiting
1384   feature exists primarily for backwards compatibility with HTTP/1.0.
1387   A server &MAY; reject a request that contains a message-body but
1388   not a Content-Length by responding with 411 (Length Required).
1391   Unless a transfer-coding other than "chunked" has been applied,
1392   a client that sends a request containing a message-body &SHOULD;
1393   use a valid Content-Length header field if the message-body length
1394   is known in advance, rather than the "chunked" encoding, since some
1395   existing services respond to "chunked" with a 411 (Length Required)
1396   status code even though they understand the chunked encoding.  This
1397   is typically because such services are implemented via a gateway that
1398   requires a content-length in advance of being called and the server
1399   is unable or unwilling to buffer the entire request before processing.
1402   A client that sends a request containing a message-body &MUST; include a
1403   valid Content-Length header field if it does not know the server will
1404   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1405   of specific user configuration or by remembering the version of a prior
1406   received response.
1409   Request messages that are prematurely terminated, possibly due to a
1410   cancelled connection or a server-imposed time-out exception, &MUST;
1411   result in closure of the connection; sending an HTTP/1.1 error response
1412   prior to closing the connection is &OPTIONAL;.
1413   Response messages that are prematurely terminated, usually by closure
1414   of the connection prior to receiving the expected number of octets or by
1415   failure to decode a transfer-encoded message-body, &MUST; be recorded
1416   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1417   message-body as if it were complete (i.e., some indication must be given
1418   to the user that an error occurred).  Cache requirements for incomplete
1419   responses are defined in &cache-incomplete;.
1422   A server &MUST; read the entire request message-body or close
1423   the connection after sending its response, since otherwise the
1424   remaining data on a persistent connection would be misinterpreted
1425   as the next request.  Likewise,
1426   a client &MUST; read the entire response message-body if it intends
1427   to reuse the same connection for a subsequent request.  Pipelining
1428   multiple requests on a connection is described in <xref target="pipelining"/>.
1432<section title="General Header Fields" anchor="general.header.fields">
1433  <x:anchor-alias value="general-header"/>
1435   There are a few header fields which have general applicability for
1436   both request and response messages, but which do not apply to the
1437   payload being transferred. These header fields apply only to the
1438   message being transmitted.
1440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1441  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1442                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1443                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1444                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1445                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1446                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1447                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1448                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1449                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1450                 / <x:ref>MIME-Version</x:ref>             ; &header-mime-version;
1453   General-header field names can be extended reliably only in
1454   combination with a change in the protocol version. However, new or
1455   experimental header fields might be given the semantics of general
1456   header fields if all parties in the communication recognize them to
1457   be general-header fields.
1462<section title="Request" anchor="request">
1463  <x:anchor-alias value="Request"/>
1465   A request message from a client to a server includes, within the
1466   first line of that message, the method to be applied to the resource,
1467   the identifier of the resource, and the protocol version in use.
1469<!--                 Host                      ; should be moved here eventually -->
1470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1471  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1472                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1473                  <x:ref>CRLF</x:ref>
1474                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1477<section title="Request-Line" anchor="request-line">
1478  <x:anchor-alias value="Request-Line"/>
1480   The Request-Line begins with a method token, followed by the
1481   request-target and the protocol version, and ending with CRLF. The
1482   elements are separated by SP characters. No CR or LF is allowed
1483   except in the final CRLF sequence.
1485<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1486  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1489<section title="Method" anchor="method">
1490  <x:anchor-alias value="Method"/>
1492   The Method  token indicates the method to be performed on the
1493   resource identified by the request-target. The method is case-sensitive.
1495<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1496  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1500<section title="request-target" anchor="request-target">
1501  <x:anchor-alias value="request-target"/>
1503   The request-target 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   then the effective request URI is constructed by concatenating
1685  <list style="symbols">
1686    <t>
1687      the scheme name: "http" if the request was received over an insecure
1688      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1689      connection,
1690    </t>
1691    <t>
1692      the character sequence "://",
1693    </t>
1694    <t>
1695      the authority component, as specified in the Host header field
1696      (<xref target=""/>) and determined by the rules in
1697      <xref target=""/>,
1698      <cref anchor="effrequri-nohost" source="jre">Do we need to include the handling of missing hosts in HTTP/1.0 messages, as
1699      described in <xref target=""/>? -- See <eref target=""/></cref>
1700      and
1701    </t>
1702    <t>
1703      the request-target obtained from the Request-Line, unless the
1704      request-target is just the asterisk "*".
1705    </t>
1706  </list>
1709   Otherwise, when request-target uses the authority form, the effective
1710   request URI is undefined.
1714   Example 1: the effective request URI for the message
1716<artwork type="example" x:indent-with="  ">
1717GET /pub/WWW/TheProject.html HTTP/1.1
1721  (received over an insecure TCP connection) is "http", plus "://", plus the
1722  authority component "", plus the request-target
1723  "/pub/WWW/TheProject.html", thus
1724  "".
1729   Example 2: the effective request URI for the message
1731<artwork type="example" x:indent-with="  ">
1732GET * HTTP/1.1
1736  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1737  authority component "", thus "".
1741   Effective request URIs are compared using the rules described in
1742   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1743   be treated as equivalent to an absolute path of "/".
1750<section title="Response" anchor="response">
1751  <x:anchor-alias value="Response"/>
1753   After receiving and interpreting a request message, a server responds
1754   with an HTTP response message.
1756<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1757  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1758                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1759                  <x:ref>CRLF</x:ref>
1760                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1763<section title="Status-Line" anchor="status-line">
1764  <x:anchor-alias value="Status-Line"/>
1766   The first line of a Response message is the Status-Line, consisting
1767   of the protocol version followed by a numeric status code and its
1768   associated textual phrase, with each element separated by SP
1769   characters. No CR or LF is allowed except in the final CRLF sequence.
1771<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1772  <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>
1775<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1776  <x:anchor-alias value="Reason-Phrase"/>
1777  <x:anchor-alias value="Status-Code"/>
1779   The Status-Code element is a 3-digit integer result code of the
1780   attempt to understand and satisfy the request. These codes are fully
1781   defined in &status-codes;.  The Reason Phrase exists for the sole
1782   purpose of providing a textual description associated with the numeric
1783   status code, out of deference to earlier Internet application protocols
1784   that were more frequently used with interactive text clients.
1785   A client &SHOULD; ignore the content of the Reason Phrase.
1788   The first digit of the Status-Code defines the class of response. The
1789   last two digits do not have any categorization role. There are 5
1790   values for the first digit:
1791  <list style="symbols">
1792    <t>
1793      1xx: Informational - Request received, continuing process
1794    </t>
1795    <t>
1796      2xx: Success - The action was successfully received,
1797        understood, and accepted
1798    </t>
1799    <t>
1800      3xx: Redirection - Further action must be taken in order to
1801        complete the request
1802    </t>
1803    <t>
1804      4xx: Client Error - The request contains bad syntax or cannot
1805        be fulfilled
1806    </t>
1807    <t>
1808      5xx: Server Error - The server failed to fulfill an apparently
1809        valid request
1810    </t>
1811  </list>
1813<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"/>
1814  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1815  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1823<section title="Protocol Parameters" anchor="protocol.parameters">
1825<section title="Date/Time Formats: Full Date" anchor="">
1826  <x:anchor-alias value="HTTP-date"/>
1828   HTTP applications have historically allowed three different formats
1829   for date/time stamps.
1830   However, the preferred format is
1831   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1833<figure><artwork type="example" x:indent-with="  ">
1834Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1837   The other formats are described here only for compatibility with obsolete
1838   implementations.
1840<figure><artwork type="example" x:indent-with="  ">
1841Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1842Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1845   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1846   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1847   only generate the RFC 1123 format for representing HTTP-date values
1848   in header fields. See <xref target="tolerant.applications"/> for further information.
1851   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1852   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1853   equal to UTC (Coordinated Universal Time). This is indicated in the
1854   first two formats by the inclusion of "GMT" as the three-letter
1855   abbreviation for time zone, and &MUST; be assumed when reading the
1856   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1857   additional whitespace beyond that specifically included as SP in the
1858   grammar.
1860<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1861  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1863<t anchor="">
1864  <x:anchor-alias value="rfc1123-date"/>
1865  <x:anchor-alias value="time-of-day"/>
1866  <x:anchor-alias value="hour"/>
1867  <x:anchor-alias value="minute"/>
1868  <x:anchor-alias value="second"/>
1869  <x:anchor-alias value="day-name"/>
1870  <x:anchor-alias value="day"/>
1871  <x:anchor-alias value="month"/>
1872  <x:anchor-alias value="year"/>
1873  <x:anchor-alias value="GMT"/>
1874  Preferred format:
1876<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"/>
1877  <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  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1880               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1881               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1882               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1883               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1884               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1885               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1887  <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>
1888               ; e.g., 02 Jun 1982
1890  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1891  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1892               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1893               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1894               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1895               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1896               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1897               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1898               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1899               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1900               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1901               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1902               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1903  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1905  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1907  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1908                 ; 00:00:00 - 23:59:59
1910  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1911  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1912  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1915  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1916  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1917  same as those defined for the RFC 5322 constructs
1918  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1920<t anchor="">
1921  <x:anchor-alias value="obs-date"/>
1922  <x:anchor-alias value="rfc850-date"/>
1923  <x:anchor-alias value="asctime-date"/>
1924  <x:anchor-alias value="date1"/>
1925  <x:anchor-alias value="date2"/>
1926  <x:anchor-alias value="date3"/>
1927  <x:anchor-alias value="rfc1123-date"/>
1928  <x:anchor-alias value="day-name-l"/>
1929  Obsolete formats:
1931<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1932  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1934<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1935  <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>
1936  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1937                 ; day-month-year (e.g., 02-Jun-82)
1939  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1940         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1941         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1942         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1943         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1944         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1945         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1947<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1948  <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>
1949  <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> ))
1950                 ; month day (e.g., Jun  2)
1953  <t>
1954    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1955    accepting date values that might have been sent by non-HTTP
1956    applications, as is sometimes the case when retrieving or posting
1957    messages via proxies/gateways to SMTP or NNTP.
1958  </t>
1961  <t>
1962    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1963    to their usage within the protocol stream. Clients and servers are
1964    not required to use these formats for user presentation, request
1965    logging, etc.
1966  </t>
1970<section title="Transfer Codings" anchor="transfer.codings">
1971  <x:anchor-alias value="transfer-coding"/>
1972  <x:anchor-alias value="transfer-extension"/>
1974   Transfer-coding values are used to indicate an encoding
1975   transformation that has been, can be, or might need to be applied to a
1976   payload body in order to ensure "safe transport" through the network.
1977   This differs from a content coding in that the transfer-coding is a
1978   property of the message rather than a property of the representation
1979   that is being transferred.
1981<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1982  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1983                          / "compress" ; <xref target="compress.coding"/>
1984                          / "deflate" ; <xref target="deflate.coding"/>
1985                          / "gzip" ; <xref target="gzip.coding"/>
1986                          / <x:ref>transfer-extension</x:ref>
1987  <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> )
1989<t anchor="rule.parameter">
1990  <x:anchor-alias value="attribute"/>
1991  <x:anchor-alias value="transfer-parameter"/>
1992  <x:anchor-alias value="value"/>
1993   Parameters are in the form of attribute/value pairs.
1995<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"/>
1996  <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>
1997  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1998  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2001   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2002   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2003   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2006   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2007   MIME, which were designed to enable safe transport of binary data over a
2008   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2009   However, safe transport
2010   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2011   the only unsafe characteristic of message-bodies is the difficulty in
2012   determining the exact message body length (<xref target="message.body"/>),
2013   or the desire to encrypt data over a shared transport.
2016   A server that receives a request message with a transfer-coding it does
2017   not understand &SHOULD; respond with 501 (Not Implemented) and then
2018   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2019   client.
2022<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2023  <iref item="chunked (Coding Format)"/>
2024  <iref item="Coding Format" subitem="chunked"/>
2025  <x:anchor-alias value="chunk"/>
2026  <x:anchor-alias value="Chunked-Body"/>
2027  <x:anchor-alias value="chunk-data"/>
2028  <x:anchor-alias value="chunk-ext"/>
2029  <x:anchor-alias value="chunk-ext-name"/>
2030  <x:anchor-alias value="chunk-ext-val"/>
2031  <x:anchor-alias value="chunk-size"/>
2032  <x:anchor-alias value="last-chunk"/>
2033  <x:anchor-alias value="trailer-part"/>
2034  <x:anchor-alias value="quoted-str-nf"/>
2035  <x:anchor-alias value="qdtext-nf"/>
2037   The chunked encoding modifies the body of a message in order to
2038   transfer it as a series of chunks, each with its own size indicator,
2039   followed by an &OPTIONAL; trailer containing header fields. This
2040   allows dynamically produced content to be transferred along with the
2041   information necessary for the recipient to verify that it has
2042   received the full message.
2044<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"/>
2045  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2046                   <x:ref>last-chunk</x:ref>
2047                   <x:ref>trailer-part</x:ref>
2048                   <x:ref>CRLF</x:ref>
2050  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2051                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2052  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2053  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2055  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2056                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2057  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2058  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2059  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2060  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2062  <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>
2063                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2064  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2065                 ; <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>
2068   The chunk-size field is a string of hex digits indicating the size of
2069   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2070   zero, followed by the trailer, which is terminated by an empty line.
2073   The trailer allows the sender to include additional HTTP header
2074   fields at the end of the message. The Trailer header field can be
2075   used to indicate which header fields are included in a trailer (see
2076   <xref target="header.trailer"/>).
2079   A server using chunked transfer-coding in a response &MUST-NOT; use the
2080   trailer for any header fields unless at least one of the following is
2081   true:
2082  <list style="numbers">
2083    <t>the request included a TE header field that indicates "trailers" is
2084     acceptable in the transfer-coding of the  response, as described in
2085     <xref target="header.te"/>; or,</t>
2087    <t>the server is the origin server for the response, the trailer
2088     fields consist entirely of optional metadata, and the recipient
2089     could use the message (in a manner acceptable to the origin server)
2090     without receiving this metadata.  In other words, the origin server
2091     is willing to accept the possibility that the trailer fields might
2092     be silently discarded along the path to the client.</t>
2093  </list>
2096   This requirement prevents an interoperability failure when the
2097   message is being received by an HTTP/1.1 (or later) proxy and
2098   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2099   compliance with the protocol would have necessitated a possibly
2100   infinite buffer on the proxy.
2103   A process for decoding the "chunked" transfer-coding
2104   can be represented in pseudo-code as:
2106<figure><artwork type="code">
2107  length := 0
2108  read chunk-size, chunk-ext (if any) and CRLF
2109  while (chunk-size &gt; 0) {
2110     read chunk-data and CRLF
2111     append chunk-data to decoded-body
2112     length := length + chunk-size
2113     read chunk-size and CRLF
2114  }
2115  read header-field
2116  while (header-field not empty) {
2117     append header-field to existing header fields
2118     read header-field
2119  }
2120  Content-Length := length
2121  Remove "chunked" from Transfer-Encoding
2124   All HTTP/1.1 applications &MUST; be able to receive and decode the
2125   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2126   they do not understand.
2129   Since "chunked" is the only transfer-coding required to be understood
2130   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2131   on a persistent connection.  Whenever a transfer-coding is applied to
2132   a payload body in a request, the final transfer-coding applied &MUST;
2133   be "chunked".  If a transfer-coding is applied to a response payload
2134   body, then either the final transfer-coding applied &MUST; be "chunked"
2135   or the message &MUST; be terminated by closing the connection. When the
2136   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2137   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2138   be applied more than once in a message-body.
2142<section title="Compression Codings" anchor="compression.codings">
2144   The codings defined below can be used to compress the payload of a
2145   message.
2148   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2149   is not desirable and is discouraged for future encodings. Their
2150   use here is representative of historical practice, not good
2151   design.
2154   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2155   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2156   equivalent to "gzip" and "compress" respectively.
2159<section title="Compress Coding" anchor="compress.coding">
2160<iref item="compress (Coding Format)"/>
2161<iref item="Coding Format" subitem="compress"/>
2163   The "compress" format is produced by the common UNIX file compression
2164   program "compress". This format is an adaptive Lempel-Ziv-Welch
2165   coding (LZW).
2169<section title="Deflate Coding" anchor="deflate.coding">
2170<iref item="deflate (Coding Format)"/>
2171<iref item="Coding Format" subitem="deflate"/>
2173   The "deflate" format is defined as the "deflate" compression mechanism
2174   (described in <xref target="RFC1951"/>) used inside the "zlib"
2175   data format (<xref target="RFC1950"/>).
2178  <t>
2179    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2180    compressed data without the zlib wrapper.
2181   </t>
2185<section title="Gzip Coding" anchor="gzip.coding">
2186<iref item="gzip (Coding Format)"/>
2187<iref item="Coding Format" subitem="gzip"/>
2189   The "gzip" format is produced by the file compression program
2190   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2191   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2197<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2199   The HTTP Transfer Coding Registry defines the name space for the transfer
2200   coding names.
2203   Registrations &MUST; include the following fields:
2204   <list style="symbols">
2205     <t>Name</t>
2206     <t>Description</t>
2207     <t>Pointer to specification text</t>
2208   </list>
2211   Names of transfer codings &MUST-NOT; overlap with names of content codings
2212   (&content-codings;), unless the encoding transformation is identical (as it
2213   is the case for the compression codings defined in
2214   <xref target="compression.codings"/>).
2217   Values to be added to this name space require a specification
2218   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2219   conform to the purpose of transfer coding defined in this section.
2222   The registry itself is maintained at
2223   <eref target=""/>.
2228<section title="Product Tokens" anchor="product.tokens">
2229  <x:anchor-alias value="product"/>
2230  <x:anchor-alias value="product-version"/>
2232   Product tokens are used to allow communicating applications to
2233   identify themselves by software name and version. Most fields using
2234   product tokens also allow sub-products which form a significant part
2235   of the application to be listed, separated by whitespace. By
2236   convention, the products are listed in order of their significance
2237   for identifying the application.
2239<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2240  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2241  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2244   Examples:
2246<figure><artwork type="example">
2247  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2248  Server: Apache/0.8.4
2251   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2252   used for advertising or other non-essential information. Although any
2253   token character &MAY; appear in a product-version, this token &SHOULD;
2254   only be used for a version identifier (i.e., successive versions of
2255   the same product &SHOULD; only differ in the product-version portion of
2256   the product value).
2260<section title="Quality Values" anchor="quality.values">
2261  <x:anchor-alias value="qvalue"/>
2263   Both transfer codings (TE request header, <xref target="header.te"/>)
2264   and content negotiation (&content.negotiation;) use short "floating point"
2265   numbers to indicate the relative importance ("weight") of various
2266   negotiable parameters.  A weight is normalized to a real number in
2267   the range 0 through 1, where 0 is the minimum and 1 the maximum
2268   value. If a parameter has a quality value of 0, then content with
2269   this parameter is "not acceptable" for the client. HTTP/1.1
2270   applications &MUST-NOT; generate more than three digits after the
2271   decimal point. User configuration of these values &SHOULD; also be
2272   limited in this fashion.
2274<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2275  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2276                 / ( "1" [ "." 0*3("0") ] )
2279  <t>
2280     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2281     relative degradation in desired quality.
2282  </t>
2288<section title="Connections" anchor="connections">
2290<section title="Persistent Connections" anchor="persistent.connections">
2292<section title="Purpose" anchor="persistent.purpose">
2294   Prior to persistent connections, a separate TCP connection was
2295   established to fetch each URL, increasing the load on HTTP servers
2296   and causing congestion on the Internet. The use of inline images and
2297   other associated data often requires a client to make multiple
2298   requests of the same server in a short amount of time. Analysis of
2299   these performance problems and results from a prototype
2300   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2301   measurements of actual HTTP/1.1 implementations show good
2302   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2303   T/TCP <xref target="Tou1998"/>.
2306   Persistent HTTP connections have a number of advantages:
2307  <list style="symbols">
2308      <t>
2309        By opening and closing fewer TCP connections, CPU time is saved
2310        in routers and hosts (clients, servers, proxies, gateways,
2311        tunnels, or caches), and memory used for TCP protocol control
2312        blocks can be saved in hosts.
2313      </t>
2314      <t>
2315        HTTP requests and responses can be pipelined on a connection.
2316        Pipelining allows a client to make multiple requests without
2317        waiting for each response, allowing a single TCP connection to
2318        be used much more efficiently, with much lower elapsed time.
2319      </t>
2320      <t>
2321        Network congestion is reduced by reducing the number of packets
2322        caused by TCP opens, and by allowing TCP sufficient time to
2323        determine the congestion state of the network.
2324      </t>
2325      <t>
2326        Latency on subsequent requests is reduced since there is no time
2327        spent in TCP's connection opening handshake.
2328      </t>
2329      <t>
2330        HTTP can evolve more gracefully, since errors can be reported
2331        without the penalty of closing the TCP connection. Clients using
2332        future versions of HTTP might optimistically try a new feature,
2333        but if communicating with an older server, retry with old
2334        semantics after an error is reported.
2335      </t>
2336    </list>
2339   HTTP implementations &SHOULD; implement persistent connections.
2343<section title="Overall Operation" anchor="persistent.overall">
2345   A significant difference between HTTP/1.1 and earlier versions of
2346   HTTP is that persistent connections are the default behavior of any
2347   HTTP connection. That is, unless otherwise indicated, the client
2348   &SHOULD; assume that the server will maintain a persistent connection,
2349   even after error responses from the server.
2352   Persistent connections provide a mechanism by which a client and a
2353   server can signal the close of a TCP connection. This signaling takes
2354   place using the Connection header field (<xref target="header.connection"/>). Once a close
2355   has been signaled, the client &MUST-NOT; send any more requests on that
2356   connection.
2359<section title="Negotiation" anchor="persistent.negotiation">
2361   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2362   maintain a persistent connection unless a Connection header including
2363   the connection-token "close" was sent in the request. If the server
2364   chooses to close the connection immediately after sending the
2365   response, it &SHOULD; send a Connection header including the
2366   connection-token "close".
2369   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2370   decide to keep it open based on whether the response from a server
2371   contains a Connection header with the connection-token close. In case
2372   the client does not want to maintain a connection for more than that
2373   request, it &SHOULD; send a Connection header including the
2374   connection-token close.
2377   If either the client or the server sends the close token in the
2378   Connection header, that request becomes the last one for the
2379   connection.
2382   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2383   maintained for HTTP versions less than 1.1 unless it is explicitly
2384   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2385   compatibility with HTTP/1.0 clients.
2388   In order to remain persistent, all messages on the connection &MUST;
2389   have a self-defined message length (i.e., one not defined by closure
2390   of the connection), as described in <xref target="message.body"/>.
2394<section title="Pipelining" anchor="pipelining">
2396   A client that supports persistent connections &MAY; "pipeline" its
2397   requests (i.e., send multiple requests without waiting for each
2398   response). A server &MUST; send its responses to those requests in the
2399   same order that the requests were received.
2402   Clients which assume persistent connections and pipeline immediately
2403   after connection establishment &SHOULD; be prepared to retry their
2404   connection if the first pipelined attempt fails. If a client does
2405   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2406   persistent. Clients &MUST; also be prepared to resend their requests if
2407   the server closes the connection before sending all of the
2408   corresponding responses.
2411   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2412   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2413   premature termination of the transport connection could lead to
2414   indeterminate results. A client wishing to send a non-idempotent
2415   request &SHOULD; wait to send that request until it has received the
2416   response status line for the previous request.
2421<section title="Proxy Servers" anchor="persistent.proxy">
2423   It is especially important that proxies correctly implement the
2424   properties of the Connection header field as specified in <xref target="header.connection"/>.
2427   The proxy server &MUST; signal persistent connections separately with
2428   its clients and the origin servers (or other proxy servers) that it
2429   connects to. Each persistent connection applies to only one transport
2430   link.
2433   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2434   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2435   for information and discussion of the problems with the Keep-Alive header
2436   implemented by many HTTP/1.0 clients).
2439<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2441  <cref anchor="TODO-end-to-end" source="jre">
2442    Restored from <eref target=""/>.
2443    See also <eref target=""/>.
2444  </cref>
2447   For the purpose of defining the behavior of caches and non-caching
2448   proxies, we divide HTTP headers into two categories:
2449  <list style="symbols">
2450      <t>End-to-end headers, which are  transmitted to the ultimate
2451        recipient of a request or response. End-to-end headers in
2452        responses MUST be stored as part of a cache entry and &MUST; be
2453        transmitted in any response formed from a cache entry.</t>
2455      <t>Hop-by-hop headers, which are meaningful only for a single
2456        transport-level connection, and are not stored by caches or
2457        forwarded by proxies.</t>
2458  </list>
2461   The following HTTP/1.1 headers are hop-by-hop headers:
2462  <list style="symbols">
2463      <t>Connection</t>
2464      <t>Keep-Alive</t>
2465      <t>Proxy-Authenticate</t>
2466      <t>Proxy-Authorization</t>
2467      <t>TE</t>
2468      <t>Trailer</t>
2469      <t>Transfer-Encoding</t>
2470      <t>Upgrade</t>
2471  </list>
2474   All other headers defined by HTTP/1.1 are end-to-end headers.
2477   Other hop-by-hop headers &MUST; be listed in a Connection header
2478   (<xref target="header.connection"/>).
2482<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2484  <cref anchor="TODO-non-mod-headers" source="jre">
2485    Restored from <eref target=""/>.
2486    See also <eref target=""/>.
2487  </cref>
2490   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2491   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2492   modify an end-to-end header unless the definition of that header requires
2493   or specifically allows that.
2496   A transparent proxy &MUST-NOT; modify any of the following fields in a
2497   request or response, and it &MUST-NOT; add any of these fields if not
2498   already present:
2499  <list style="symbols">
2500      <t>Content-Location</t>
2501      <t>Content-MD5</t>
2502      <t>ETag</t>
2503      <t>Last-Modified</t>
2504  </list>
2507   A transparent proxy &MUST-NOT; modify any of the following fields in a
2508   response:
2509  <list style="symbols">
2510    <t>Expires</t>
2511  </list>
2514   but it &MAY; add any of these fields if not already present. If an
2515   Expires header is added, it &MUST; be given a field-value identical to
2516   that of the Date header in that response.
2519   A proxy &MUST-NOT; modify or add any of the following fields in a
2520   message that contains the no-transform cache-control directive, or in
2521   any request:
2522  <list style="symbols">
2523    <t>Content-Encoding</t>
2524    <t>Content-Range</t>
2525    <t>Content-Type</t>
2526  </list>
2529   A non-transparent proxy &MAY; modify or add these fields to a message
2530   that does not include no-transform, but if it does so, it &MUST; add a
2531   Warning 214 (Transformation applied) if one does not already appear
2532   in the message (see &header-warning;).
2535  <t>
2536    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2537    cause authentication failures if stronger authentication
2538    mechanisms are introduced in later versions of HTTP. Such
2539    authentication mechanisms &MAY; rely on the values of header fields
2540    not listed here.
2541  </t>
2544   A transparent proxy &MUST; preserve the message payload (&payload;),
2545   though it &MAY; change the message-body through application or removal
2546   of a transfer-coding (<xref target="transfer.codings"/>).
2552<section title="Practical Considerations" anchor="persistent.practical">
2554   Servers will usually have some time-out value beyond which they will
2555   no longer maintain an inactive connection. Proxy servers might make
2556   this a higher value since it is likely that the client will be making
2557   more connections through the same server. The use of persistent
2558   connections places no requirements on the length (or existence) of
2559   this time-out for either the client or the server.
2562   When a client or server wishes to time-out it &SHOULD; issue a graceful
2563   close on the transport connection. Clients and servers &SHOULD; both
2564   constantly watch for the other side of the transport close, and
2565   respond to it as appropriate. If a client or server does not detect
2566   the other side's close promptly it could cause unnecessary resource
2567   drain on the network.
2570   A client, server, or proxy &MAY; close the transport connection at any
2571   time. For example, a client might have started to send a new request
2572   at the same time that the server has decided to close the "idle"
2573   connection. From the server's point of view, the connection is being
2574   closed while it was idle, but from the client's point of view, a
2575   request is in progress.
2578   This means that clients, servers, and proxies &MUST; be able to recover
2579   from asynchronous close events. Client software &SHOULD; reopen the
2580   transport connection and retransmit the aborted sequence of requests
2581   without user interaction so long as the request sequence is
2582   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2583   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2584   human operator the choice of retrying the request(s). Confirmation by
2585   user-agent software with semantic understanding of the application
2586   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2587   be repeated if the second sequence of requests fails.
2590   Servers &SHOULD; always respond to at least one request per connection,
2591   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2592   middle of transmitting a response, unless a network or client failure
2593   is suspected.
2596   Clients (including proxies) &SHOULD; limit the number of simultaneous
2597   connections that they maintain to a given server (including proxies).
2600   Previous revisions of HTTP gave a specific number of connections as a
2601   ceiling, but this was found to be impractical for many applications. As a
2602   result, this specification does not mandate a particular maximum number of
2603   connections, but instead encourages clients to be conservative when opening
2604   multiple connections.
2607   In particular, while using multiple connections avoids the "head-of-line
2608   blocking" problem (whereby a request that takes significant server-side
2609   processing and/or has a large payload can block subsequent requests on the
2610   same connection), each connection used consumes server resources (sometimes
2611   significantly), and furthermore using multiple connections can cause
2612   undesirable side effects in congested networks.
2615   Note that servers might reject traffic that they deem abusive, including an
2616   excessive number of connections from a client.
2621<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2623<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2625   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2626   flow control mechanisms to resolve temporary overloads, rather than
2627   terminating connections with the expectation that clients will retry.
2628   The latter technique can exacerbate network congestion.
2632<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2634   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2635   the network connection for an error status code while it is transmitting
2636   the request. If the client sees an error status code, it &SHOULD;
2637   immediately cease transmitting the body. If the body is being sent
2638   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2639   empty trailer &MAY; be used to prematurely mark the end of the message.
2640   If the body was preceded by a Content-Length header, the client &MUST;
2641   close the connection.
2645<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2647   The purpose of the 100 (Continue) status code (see &status-100;) is to
2648   allow a client that is sending a request message with a request body
2649   to determine if the origin server is willing to accept the request
2650   (based on the request headers) before the client sends the request
2651   body. In some cases, it might either be inappropriate or highly
2652   inefficient for the client to send the body if the server will reject
2653   the message without looking at the body.
2656   Requirements for HTTP/1.1 clients:
2657  <list style="symbols">
2658    <t>
2659        If a client will wait for a 100 (Continue) response before
2660        sending the request body, it &MUST; send an Expect request-header
2661        field (&header-expect;) with the "100-continue" expectation.
2662    </t>
2663    <t>
2664        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2665        with the "100-continue" expectation if it does not intend
2666        to send a request body.
2667    </t>
2668  </list>
2671   Because of the presence of older implementations, the protocol allows
2672   ambiguous situations in which a client might send "Expect: 100-continue"
2673   without receiving either a 417 (Expectation Failed)
2674   or a 100 (Continue) status code. Therefore, when a client sends this
2675   header field to an origin server (possibly via a proxy) from which it
2676   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2677   wait for an indefinite period before sending the request body.
2680   Requirements for HTTP/1.1 origin servers:
2681  <list style="symbols">
2682    <t> Upon receiving a request which includes an Expect request-header
2683        field with the "100-continue" expectation, an origin server &MUST;
2684        either respond with 100 (Continue) status code and continue to read
2685        from the input stream, or respond with a final status code. The
2686        origin server &MUST-NOT; wait for the request body before sending
2687        the 100 (Continue) response. If it responds with a final status
2688        code, it &MAY; close the transport connection or it &MAY; continue
2689        to read and discard the rest of the request.  It &MUST-NOT;
2690        perform the requested method if it returns a final status code.
2691    </t>
2692    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2693        the request message does not include an Expect request-header
2694        field with the "100-continue" expectation, and &MUST-NOT; send a
2695        100 (Continue) response if such a request comes from an HTTP/1.0
2696        (or earlier) client. There is an exception to this rule: for
2697        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2698        status code in response to an HTTP/1.1 PUT or POST request that does
2699        not include an Expect request-header field with the "100-continue"
2700        expectation. This exception, the purpose of which is
2701        to minimize any client processing delays associated with an
2702        undeclared wait for 100 (Continue) status code, applies only to
2703        HTTP/1.1 requests, and not to requests with any other HTTP-version
2704        value.
2705    </t>
2706    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2707        already received some or all of the request body for the
2708        corresponding request.
2709    </t>
2710    <t> An origin server that sends a 100 (Continue) response &MUST;
2711    ultimately send a final status code, once the request body is
2712        received and processed, unless it terminates the transport
2713        connection prematurely.
2714    </t>
2715    <t> If an origin server receives a request that does not include an
2716        Expect request-header field with the "100-continue" expectation,
2717        the request includes a request body, and the server responds
2718        with a final status code before reading the entire request body
2719        from the transport connection, then the server &SHOULD-NOT;  close
2720        the transport connection until it has read the entire request,
2721        or until the client closes the connection. Otherwise, the client
2722        might not reliably receive the response message. However, this
2723        requirement is not be construed as preventing a server from
2724        defending itself against denial-of-service attacks, or from
2725        badly broken client implementations.
2726      </t>
2727    </list>
2730   Requirements for HTTP/1.1 proxies:
2731  <list style="symbols">
2732    <t> If a proxy receives a request that includes an Expect request-header
2733        field with the "100-continue" expectation, and the proxy
2734        either knows that the next-hop server complies with HTTP/1.1 or
2735        higher, or does not know the HTTP version of the next-hop
2736        server, it &MUST; forward the request, including the Expect header
2737        field.
2738    </t>
2739    <t> If the proxy knows that the version of the next-hop server is
2740        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2741        respond with a 417 (Expectation Failed) status code.
2742    </t>
2743    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2744        numbers received from recently-referenced next-hop servers.
2745    </t>
2746    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2747        request message was received from an HTTP/1.0 (or earlier)
2748        client and did not include an Expect request-header field with
2749        the "100-continue" expectation. This requirement overrides the
2750        general rule for forwarding of 1xx responses (see &status-1xx;).
2751    </t>
2752  </list>
2756<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2758   If an HTTP/1.1 client sends a request which includes a request body,
2759   but which does not include an Expect request-header field with the
2760   "100-continue" expectation, and if the client is not directly
2761   connected to an HTTP/1.1 origin server, and if the client sees the
2762   connection close before receiving a status line from the server, the
2763   client &SHOULD; retry the request.  If the client does retry this
2764   request, it &MAY; use the following "binary exponential backoff"
2765   algorithm to be assured of obtaining a reliable response:
2766  <list style="numbers">
2767    <t>
2768      Initiate a new connection to the server
2769    </t>
2770    <t>
2771      Transmit the request-headers
2772    </t>
2773    <t>
2774      Initialize a variable R to the estimated round-trip time to the
2775         server (e.g., based on the time it took to establish the
2776         connection), or to a constant value of 5 seconds if the round-trip
2777         time is not available.
2778    </t>
2779    <t>
2780       Compute T = R * (2**N), where N is the number of previous
2781         retries of this request.
2782    </t>
2783    <t>
2784       Wait either for an error response from the server, or for T
2785         seconds (whichever comes first)
2786    </t>
2787    <t>
2788       If no error response is received, after T seconds transmit the
2789         body of the request.
2790    </t>
2791    <t>
2792       If client sees that the connection is closed prematurely,
2793         repeat from step 1 until the request is accepted, an error
2794         response is received, or the user becomes impatient and
2795         terminates the retry process.
2796    </t>
2797  </list>
2800   If at any point an error status code is received, the client
2801  <list style="symbols">
2802      <t>&SHOULD-NOT;  continue and</t>
2804      <t>&SHOULD; close the connection if it has not completed sending the
2805        request message.</t>
2806    </list>
2813<section title="Miscellaneous notes that might disappear" anchor="misc">
2814<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2816   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2820<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2822   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2826<section title="Interception of HTTP for access control" anchor="http.intercept">
2828   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2832<section title="Use of HTTP by other protocols" anchor="http.others">
2834   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2835   Extensions of HTTP like WebDAV.</cref>
2839<section title="Use of HTTP by media type specification" anchor="">
2841   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2846<section title="Header Field Definitions" anchor="header.field.definitions">
2848   This section defines the syntax and semantics of HTTP/1.1 header fields
2849   related to message framing and transport protocols.
2852<section title="Connection" anchor="header.connection">
2853  <iref primary="true" item="Connection header" x:for-anchor=""/>
2854  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2855  <x:anchor-alias value="Connection"/>
2856  <x:anchor-alias value="connection-token"/>
2857  <x:anchor-alias value="Connection-v"/>
2859   The "Connection" general-header field allows the sender to specify
2860   options that are desired for that particular connection and &MUST-NOT;
2861   be communicated by proxies over further connections.
2864   The Connection header's value has the following grammar:
2866<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"/>
2867  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2868  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2869  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2872   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2873   message is forwarded and, for each connection-token in this field,
2874   remove any header field(s) from the message with the same name as the
2875   connection-token. Connection options are signaled by the presence of
2876   a connection-token in the Connection header field, not by any
2877   corresponding additional header field(s), since the additional header
2878   field might not be sent if there are no parameters associated with that
2879   connection option.
2882   Message headers listed in the Connection header &MUST-NOT; include
2883   end-to-end headers, such as Cache-Control.
2886   HTTP/1.1 defines the "close" connection option for the sender to
2887   signal that the connection will be closed after completion of the
2888   response. For example,
2890<figure><artwork type="example">
2891  Connection: close
2894   in either the request or the response header fields indicates that
2895   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2896   after the current request/response is complete.
2899   An HTTP/1.1 client that does not support persistent connections &MUST;
2900   include the "close" connection option in every request message.
2903   An HTTP/1.1 server that does not support persistent connections &MUST;
2904   include the "close" connection option in every response message that
2905   does not have a 1xx (Informational) status code.
2908   A system receiving an HTTP/1.0 (or lower-version) message that
2909   includes a Connection header &MUST;, for each connection-token in this
2910   field, remove and ignore any header field(s) from the message with
2911   the same name as the connection-token. This protects against mistaken
2912   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2916<section title="Content-Length" anchor="header.content-length">
2917  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2918  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2919  <x:anchor-alias value="Content-Length"/>
2920  <x:anchor-alias value="Content-Length-v"/>
2922   The "Content-Length" header field indicates the size of the
2923   message-body, in decimal number of octets, for any message other than
2924   a response to the HEAD method or a response with a status code of 304.
2925   In the case of responses to the HEAD method, it indicates the size of
2926   the payload body (not including any potential transfer-coding) that
2927   would have been sent had the request been a GET.
2928   In the case of the 304 (Not Modified) response, it indicates the size of
2929   the payload body (not including any potential transfer-coding) that
2930   would have been sent in a 200 (OK) response.
2932<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2933  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2934  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2937   An example is
2939<figure><artwork type="example">
2940  Content-Length: 3495
2943   Implementations &SHOULD; use this field to indicate the message-body
2944   length when no transfer-coding is being applied and the
2945   payload's body length can be determined prior to being transferred.
2946   <xref target="message.body"/> describes how recipients determine the length
2947   of a message-body.
2950   Any Content-Length greater than or equal to zero is a valid value.
2953   Note that the use of this field in HTTP is significantly different from
2954   the corresponding definition in MIME, where it is an optional field
2955   used within the "message/external-body" content-type.
2959<section title="Date" anchor="">
2960  <iref primary="true" item="Date header" x:for-anchor=""/>
2961  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2962  <x:anchor-alias value="Date"/>
2963  <x:anchor-alias value="Date-v"/>
2965   The "Date" general-header field represents the date and time at which
2966   the message was originated, having the same semantics as the Origination
2967   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2968   The field value is an HTTP-date, as described in <xref target=""/>;
2969   it &MUST; be sent in rfc1123-date format.
2971<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2972  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2973  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2976   An example is
2978<figure><artwork type="example">
2979  Date: Tue, 15 Nov 1994 08:12:31 GMT
2982   Origin servers &MUST; include a Date header field in all responses,
2983   except in these cases:
2984  <list style="numbers">
2985      <t>If the response status code is 100 (Continue) or 101 (Switching
2986         Protocols), the response &MAY; include a Date header field, at
2987         the server's option.</t>
2989      <t>If the response status code conveys a server error, e.g., 500
2990         (Internal Server Error) or 503 (Service Unavailable), and it is
2991         inconvenient or impossible to generate a valid Date.</t>
2993      <t>If the server does not have a clock that can provide a
2994         reasonable approximation of the current time, its responses
2995         &MUST-NOT; include a Date header field. In this case, the rules
2996         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2997  </list>
3000   A received message that does not have a Date header field &MUST; be
3001   assigned one by the recipient if the message will be cached by that
3002   recipient or gatewayed via a protocol which requires a Date. An HTTP
3003   implementation without a clock &MUST-NOT; cache responses without
3004   revalidating them on every use. An HTTP cache, especially a shared
3005   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
3006   clock with a reliable external standard.
3009   Clients &SHOULD; only send a Date header field in messages that include
3010   a payload, as is usually the case for PUT and POST requests, and even
3011   then it is optional. A client without a clock &MUST-NOT; send a Date
3012   header field in a request.
3015   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
3016   time subsequent to the generation of the message. It &SHOULD; represent
3017   the best available approximation of the date and time of message
3018   generation, unless the implementation has no means of generating a
3019   reasonably accurate date and time. In theory, the date ought to
3020   represent the moment just before the payload is generated. In
3021   practice, the date can be generated at any time during the message
3022   origination without affecting its semantic value.
3025<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3027   Some origin server implementations might not have a clock available.
3028   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3029   values to a response, unless these values were associated
3030   with the resource by a system or user with a reliable clock. It &MAY;
3031   assign an Expires value that is known, at or before server
3032   configuration time, to be in the past (this allows "pre-expiration"
3033   of responses without storing separate Expires values for each
3034   resource).
3039<section title="Host" anchor="">
3040  <iref primary="true" item="Host header" x:for-anchor=""/>
3041  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3042  <x:anchor-alias value="Host"/>
3043  <x:anchor-alias value="Host-v"/>
3045   The "Host" request-header field specifies the Internet host and port
3046   number of the resource being requested, allowing the origin server or
3047   gateway to differentiate between internally-ambiguous URLs, such as the root
3048   "/" URL of a server for multiple host names on a single IP address.
3051   The Host field value &MUST; represent the naming authority of the origin
3052   server or gateway given by the original URL obtained from the user or
3053   referring resource (generally an http URI, as described in
3054   <xref target="http.uri"/>).
3056<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3057  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3058  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3061   A "host" without any trailing port information implies the default
3062   port for the service requested (e.g., "80" for an HTTP URL). For
3063   example, a request on the origin server for
3064   &lt;; would properly include:
3066<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3067GET /pub/WWW/ HTTP/1.1
3071   A client &MUST; include a Host header field in all HTTP/1.1 request
3072   messages. If the requested URI does not include an Internet host
3073   name for the service being requested, then the Host header field &MUST;
3074   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3075   request message it forwards does contain an appropriate Host header
3076   field that identifies the service being requested by the proxy. All
3077   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3078   status code to any HTTP/1.1 request message which lacks a Host header
3079   field.
3082   See Sections <xref target="" format="counter"/>
3083   and <xref target="" format="counter"/>
3084   for other requirements relating to Host.
3088<section title="TE" anchor="header.te">
3089  <iref primary="true" item="TE header" x:for-anchor=""/>
3090  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3091  <x:anchor-alias value="TE"/>
3092  <x:anchor-alias value="TE-v"/>
3093  <x:anchor-alias value="t-codings"/>
3094  <x:anchor-alias value="te-params"/>
3095  <x:anchor-alias value="te-ext"/>
3097   The "TE" request-header field indicates what extension transfer-codings
3098   it is willing to accept in the response, and whether or not it is
3099   willing to accept trailer fields in a chunked transfer-coding.
3102   Its value consists of the keyword "trailers" and/or a comma-separated
3103   list of extension transfer-coding names with optional accept
3104   parameters (as described in <xref target="transfer.codings"/>).
3106<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"/>
3107  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3108  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3109  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3110  <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> )
3111  <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> ]
3114   The presence of the keyword "trailers" indicates that the client is
3115   willing to accept trailer fields in a chunked transfer-coding, as
3116   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3117   transfer-coding values even though it does not itself represent a
3118   transfer-coding.
3121   Examples of its use are:
3123<figure><artwork type="example">
3124  TE: deflate
3125  TE:
3126  TE: trailers, deflate;q=0.5
3129   The TE header field only applies to the immediate connection.
3130   Therefore, the keyword &MUST; be supplied within a Connection header
3131   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3134   A server tests whether a transfer-coding is acceptable, according to
3135   a TE field, using these rules:
3136  <list style="numbers">
3137    <x:lt>
3138      <t>The "chunked" transfer-coding is always acceptable. If the
3139         keyword "trailers" is listed, the client indicates that it is
3140         willing to accept trailer fields in the chunked response on
3141         behalf of itself and any downstream clients. The implication is
3142         that, if given, the client is stating that either all
3143         downstream clients are willing to accept trailer fields in the
3144         forwarded response, or that it will attempt to buffer the
3145         response on behalf of downstream recipients.
3146      </t><t>
3147         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3148         chunked response such that a client can be assured of buffering
3149         the entire response.</t>
3150    </x:lt>
3151    <x:lt>
3152      <t>If the transfer-coding being tested is one of the transfer-codings
3153         listed in the TE field, then it is acceptable unless it
3154         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3155         qvalue of 0 means "not acceptable".)</t>
3156    </x:lt>
3157    <x:lt>
3158      <t>If multiple transfer-codings are acceptable, then the
3159         acceptable transfer-coding with the highest non-zero qvalue is
3160         preferred.  The "chunked" transfer-coding always has a qvalue
3161         of 1.</t>
3162    </x:lt>
3163  </list>
3166   If the TE field-value is empty or if no TE field is present, the only
3167   transfer-coding is "chunked". A message with no transfer-coding is
3168   always acceptable.
3172<section title="Trailer" anchor="header.trailer">
3173  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3174  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3175  <x:anchor-alias value="Trailer"/>
3176  <x:anchor-alias value="Trailer-v"/>
3178   The "Trailer" general-header field indicates that the given set of
3179   header fields is present in the trailer of a message encoded with
3180   chunked transfer-coding.
3182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3183  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3184  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3187   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3188   message using chunked transfer-coding with a non-empty trailer. Doing
3189   so allows the recipient to know which header fields to expect in the
3190   trailer.
3193   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3194   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3195   trailer fields in a "chunked" transfer-coding.
3198   Message header fields listed in the Trailer header field &MUST-NOT;
3199   include the following header fields:
3200  <list style="symbols">
3201    <t>Transfer-Encoding</t>
3202    <t>Content-Length</t>
3203    <t>Trailer</t>
3204  </list>
3208<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3209  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3210  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3211  <x:anchor-alias value="Transfer-Encoding"/>
3212  <x:anchor-alias value="Transfer-Encoding-v"/>
3214   The "Transfer-Encoding" general-header field indicates what transfer-codings
3215   (if any) have been applied to the message body. It differs from
3216   Content-Encoding (&content-codings;) in that transfer-codings are a property
3217   of the message (and therefore are removed by intermediaries), whereas
3218   content-codings are not.
3220<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3221  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3222                        <x:ref>Transfer-Encoding-v</x:ref>
3223  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3226   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3228<figure><artwork type="example">
3229  Transfer-Encoding: chunked
3232   If multiple encodings have been applied to a representation, the transfer-codings
3233   &MUST; be listed in the order in which they were applied.
3234   Additional information about the encoding parameters &MAY; be provided
3235   by other header fields not defined by this specification.
3238   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3239   header.
3243<section title="Upgrade" anchor="header.upgrade">
3244  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3245  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3246  <x:anchor-alias value="Upgrade"/>
3247  <x:anchor-alias value="Upgrade-v"/>
3249   The "Upgrade" general-header field allows the client to specify what
3250   additional communication protocols it would like to use, if the server
3251   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3252   header field within a 101 (Switching Protocols) response to indicate which
3253   protocol(s) are being switched to.
3255<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3256  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3257  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3260   For example,
3262<figure><artwork type="example">
3263  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3266   The Upgrade header field is intended to provide a simple mechanism
3267   for transition from HTTP/1.1 to some other, incompatible protocol. It
3268   does so by allowing the client to advertise its desire to use another
3269   protocol, such as a later version of HTTP with a higher major version
3270   number, even though the current request has been made using HTTP/1.1.
3271   This eases the difficult transition between incompatible protocols by
3272   allowing the client to initiate a request in the more commonly
3273   supported protocol while indicating to the server that it would like
3274   to use a "better" protocol if available (where "better" is determined
3275   by the server, possibly according to the nature of the method and/or
3276   resource being requested).
3279   The Upgrade header field only applies to switching application-layer
3280   protocols upon the existing transport-layer connection. Upgrade
3281   cannot be used to insist on a protocol change; its acceptance and use
3282   by the server is optional. The capabilities and nature of the
3283   application-layer communication after the protocol change is entirely
3284   dependent upon the new protocol chosen, although the first action
3285   after changing the protocol &MUST; be a response to the initial HTTP
3286   request containing the Upgrade header field.
3289   The Upgrade header field only applies to the immediate connection.
3290   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3291   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3292   HTTP/1.1 message.
3295   The Upgrade header field cannot be used to indicate a switch to a
3296   protocol on a different connection. For that purpose, it is more
3297   appropriate to use a 301, 302, 303, or 305 redirection response.
3300   This specification only defines the protocol name "HTTP" for use by
3301   the family of Hypertext Transfer Protocols, as defined by the HTTP
3302   version rules of <xref target="http.version"/> and future updates to this
3303   specification. Additional tokens can be registered with IANA using the
3304   registration procedure defined below. 
3307<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3309   The HTTP Upgrade Token Registry defines the name space for product
3310   tokens used to identify protocols in the Upgrade header field.
3311   Each registered token is associated with contact information and
3312   an optional set of specifications that details how the connection
3313   will be processed after it has been upgraded.
3316   Registrations are allowed on a First Come First Served basis as
3317   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3318   specifications need not be IETF documents or be subject to IESG review.
3319   Registrations are subject to the following rules:
3320  <list style="numbers">
3321    <t>A token, once registered, stays registered forever.</t>
3322    <t>The registration &MUST; name a responsible party for the
3323       registration.</t>
3324    <t>The registration &MUST; name a point of contact.</t>
3325    <t>The registration &MAY; name a set of specifications associated with that
3326       token. Such specifications need not be publicly available.</t>
3327    <t>The responsible party &MAY; change the registration at any time.
3328       The IANA will keep a record of all such changes, and make them
3329       available upon request.</t>
3330    <t>The responsible party for the first registration of a "product"
3331       token &MUST; approve later registrations of a "version" token
3332       together with that "product" token before they can be registered.</t>
3333    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3334       for a token. This will normally only be used in the case when a
3335       responsible party cannot be contacted.</t>
3336  </list>
3343<section title="Via" anchor="header.via">
3344  <iref primary="true" item="Via header" x:for-anchor=""/>
3345  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3346  <x:anchor-alias value="protocol-name"/>
3347  <x:anchor-alias value="protocol-version"/>
3348  <x:anchor-alias value="pseudonym"/>
3349  <x:anchor-alias value="received-by"/>
3350  <x:anchor-alias value="received-protocol"/>
3351  <x:anchor-alias value="Via"/>
3352  <x:anchor-alias value="Via-v"/>
3354   The "Via" general-header field &MUST; be used by gateways and proxies to
3355   indicate the intermediate protocols and recipients between the user
3356   agent and the server on requests, and between the origin server and
3357   the client on responses. It is analogous to the "Received" field defined in
3358   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3359   avoiding request loops, and identifying the protocol capabilities of
3360   all senders along the request/response chain.
3362<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"/>
3363  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3364  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3365                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3366  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3367  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3368  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3369  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3370  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3373   The received-protocol indicates the protocol version of the message
3374   received by the server or client along each segment of the
3375   request/response chain. The received-protocol version is appended to
3376   the Via field value when the message is forwarded so that information
3377   about the protocol capabilities of upstream applications remains
3378   visible to all recipients.
3381   The protocol-name is optional if and only if it would be "HTTP". The
3382   received-by field is normally the host and optional port number of a
3383   recipient server or client that subsequently forwarded the message.
3384   However, if the real host is considered to be sensitive information,
3385   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3386   be assumed to be the default port of the received-protocol.
3389   Multiple Via field values represent each proxy or gateway that has
3390   forwarded the message. Each recipient &MUST; append its information
3391   such that the end result is ordered according to the sequence of
3392   forwarding applications.
3395   Comments &MAY; be used in the Via header field to identify the software
3396   of the recipient proxy or gateway, analogous to the User-Agent and
3397   Server header fields. However, all comments in the Via field are
3398   optional and &MAY; be removed by any recipient prior to forwarding the
3399   message.
3402   For example, a request message could be sent from an HTTP/1.0 user
3403   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3404   forward the request to a public proxy at, which completes
3405   the request by forwarding it to the origin server at
3406   The request received by would then have the following
3407   Via header field:
3409<figure><artwork type="example">
3410  Via: 1.0 fred, 1.1 (Apache/1.1)
3413   Proxies and gateways used as a portal through a network firewall
3414   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3415   the firewall region. This information &SHOULD; only be propagated if
3416   explicitly enabled. If not enabled, the received-by host of any host
3417   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3418   for that host.
3421   For organizations that have strong privacy requirements for hiding
3422   internal structures, a proxy &MAY; combine an ordered subsequence of
3423   Via header field entries with identical received-protocol values into
3424   a single such entry. For example,
3426<figure><artwork type="example">
3427  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3430  could be collapsed to
3432<figure><artwork type="example">
3433  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3436   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3437   under the same organizational control and the hosts have already been
3438   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3439   have different received-protocol values.
3445<section title="IANA Considerations" anchor="IANA.considerations">
3447<section title="Header Field Registration" anchor="header.field.registration">
3449   The Message Header Field Registry located at <eref target=""/> shall be updated
3450   with the permanent registrations below (see <xref target="RFC3864"/>):
3452<?BEGININC p1-messaging.iana-headers ?>
3453<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3454<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3455   <ttcol>Header Field Name</ttcol>
3456   <ttcol>Protocol</ttcol>
3457   <ttcol>Status</ttcol>
3458   <ttcol>Reference</ttcol>
3460   <c>Connection</c>
3461   <c>http</c>
3462   <c>standard</c>
3463   <c>
3464      <xref target="header.connection"/>
3465   </c>
3466   <c>Content-Length</c>
3467   <c>http</c>
3468   <c>standard</c>
3469   <c>
3470      <xref target="header.content-length"/>
3471   </c>
3472   <c>Date</c>
3473   <c>http</c>
3474   <c>standard</c>
3475   <c>
3476      <xref target=""/>
3477   </c>
3478   <c>Host</c>
3479   <c>http</c>
3480   <c>standard</c>
3481   <c>
3482      <xref target=""/>
3483   </c>
3484   <c>TE</c>
3485   <c>http</c>
3486   <c>standard</c>
3487   <c>
3488      <xref target="header.te"/>
3489   </c>
3490   <c>Trailer</c>
3491   <c>http</c>
3492   <c>standard</c>
3493   <c>
3494      <xref target="header.trailer"/>
3495   </c>
3496   <c>Transfer-Encoding</c>
3497   <c>http</c>
3498   <c>standard</c>
3499   <c>
3500      <xref target="header.transfer-encoding"/>
3501   </c>
3502   <c>Upgrade</c>
3503   <c>http</c>
3504   <c>standard</c>
3505   <c>
3506      <xref target="header.upgrade"/>
3507   </c>
3508   <c>Via</c>
3509   <c>http</c>
3510   <c>standard</c>
3511   <c>
3512      <xref target="header.via"/>
3513   </c>
3516<?ENDINC p1-messaging.iana-headers ?>
3518   The change controller is: "IETF ( - Internet Engineering Task Force".
3522<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3524   The entries for the "http" and "https" URI Schemes in the registry located at
3525   <eref target=""/>
3526   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3527   and <xref target="https.uri" format="counter"/> of this document
3528   (see <xref target="RFC4395"/>).
3532<section title="Internet Media Type Registrations" anchor="">
3534   This document serves as the specification for the Internet media types
3535   "message/http" and "application/http". The following is to be registered with
3536   IANA (see <xref target="RFC4288"/>).
3538<section title="Internet Media Type message/http" anchor="">
3539<iref item="Media Type" subitem="message/http" primary="true"/>
3540<iref item="message/http Media Type" primary="true"/>
3542   The message/http type can be used to enclose a single HTTP request or
3543   response message, provided that it obeys the MIME restrictions for all
3544   "message" types regarding line length and encodings.
3547  <list style="hanging" x:indent="12em">
3548    <t hangText="Type name:">
3549      message
3550    </t>
3551    <t hangText="Subtype name:">
3552      http
3553    </t>
3554    <t hangText="Required parameters:">
3555      none
3556    </t>
3557    <t hangText="Optional parameters:">
3558      version, msgtype
3559      <list style="hanging">
3560        <t hangText="version:">
3561          The HTTP-Version number of the enclosed message
3562          (e.g., "1.1"). If not present, the version can be
3563          determined from the first line of the body.
3564        </t>
3565        <t hangText="msgtype:">
3566          The message type -- "request" or "response". If not
3567          present, the type can be determined from the first
3568          line of the body.
3569        </t>
3570      </list>
3571    </t>
3572    <t hangText="Encoding considerations:">
3573      only "7bit", "8bit", or "binary" are permitted
3574    </t>
3575    <t hangText="Security considerations:">
3576      none
3577    </t>
3578    <t hangText="Interoperability considerations:">
3579      none
3580    </t>
3581    <t hangText="Published specification:">
3582      This specification (see <xref target=""/>).
3583    </t>
3584    <t hangText="Applications that use this media type:">
3585    </t>
3586    <t hangText="Additional information:">
3587      <list style="hanging">
3588        <t hangText="Magic number(s):">none</t>
3589        <t hangText="File extension(s):">none</t>
3590        <t hangText="Macintosh file type code(s):">none</t>
3591      </list>
3592    </t>
3593    <t hangText="Person and email address to contact for further information:">
3594      See Authors Section.
3595    </t>
3596    <t hangText="Intended usage:">
3597      COMMON
3598    </t>
3599    <t hangText="Restrictions on usage:">
3600      none
3601    </t>
3602    <t hangText="Author/Change controller:">
3603      IESG
3604    </t>
3605  </list>
3608<section title="Internet Media Type application/http" anchor="">
3609<iref item="Media Type" subitem="application/http" primary="true"/>
3610<iref item="application/http Media Type" primary="true"/>
3612   The application/http type can be used to enclose a pipeline of one or more
3613   HTTP request or response messages (not intermixed).
3616  <list style="hanging" x:indent="12em">
3617    <t hangText="Type name:">
3618      application
3619    </t>
3620    <t hangText="Subtype name:">
3621      http
3622    </t>
3623    <t hangText="Required parameters:">
3624      none
3625    </t>
3626    <t hangText="Optional parameters:">
3627      version, msgtype
3628      <list style="hanging">
3629        <t hangText="version:">
3630          The HTTP-Version number of the enclosed messages
3631          (e.g., "1.1"). If not present, the version can be
3632          determined from the first line of the body.
3633        </t>
3634        <t hangText="msgtype:">
3635          The message type -- "request" or "response". If not
3636          present, the type can be determined from the first
3637          line of the body.
3638        </t>
3639      </list>
3640    </t>
3641    <t hangText="Encoding considerations:">
3642      HTTP messages enclosed by this type
3643      are in "binary" format; use of an appropriate
3644      Content-Transfer-Encoding is required when
3645      transmitted via E-mail.
3646    </t>
3647    <t hangText="Security considerations:">
3648      none
3649    </t>
3650    <t hangText="Interoperability considerations:">
3651      none
3652    </t>
3653    <t hangText="Published specification:">
3654      This specification (see <xref target=""/>).
3655    </t>
3656    <t hangText="Applications that use this media type:">
3657    </t>
3658    <t hangText="Additional information:">
3659      <list style="hanging">
3660        <t hangText="Magic number(s):">none</t>
3661        <t hangText="File extension(s):">none</t>
3662        <t hangText="Macintosh file type code(s):">none</t>
3663      </list>
3664    </t>
3665    <t hangText="Person and email address to contact for further information:">
3666      See Authors Section.
3667    </t>
3668    <t hangText="Intended usage:">
3669      COMMON
3670    </t>
3671    <t hangText="Restrictions on usage:">
3672      none
3673    </t>
3674    <t hangText="Author/Change controller:">
3675      IESG
3676    </t>
3677  </list>
3682<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3684   The registration procedure for HTTP Transfer Codings is now defined by
3685   <xref target="transfer.coding.registry"/> of this document.
3688   The HTTP Transfer Codings Registry located at <eref target=""/>
3689   shall be updated with the registrations below:
3691<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3692   <ttcol>Name</ttcol>
3693   <ttcol>Description</ttcol>
3694   <ttcol>Reference</ttcol>
3695   <c>chunked</c>
3696   <c>Transfer in a series of chunks</c>
3697   <c>
3698      <xref target="chunked.encoding"/>
3699   </c>
3700   <c>compress</c>
3701   <c>UNIX "compress" program method</c>
3702   <c>
3703      <xref target="compress.coding"/>
3704   </c>
3705   <c>deflate</c>
3706   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3707   the "zlib" data format (<xref target="RFC1950"/>)
3708   </c>
3709   <c>
3710      <xref target="deflate.coding"/>
3711   </c>
3712   <c>gzip</c>
3713   <c>Same as GNU zip <xref target="RFC1952"/></c>
3714   <c>
3715      <xref target="gzip.coding"/>
3716   </c>
3720<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3722   The registration procedure for HTTP Upgrade Tokens -- previously defined
3723   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3724   by <xref target="upgrade.token.registry"/> of this document.
3727   The HTTP Status Code Registry located at <eref target=""/>
3728   shall be updated with the registration below:
3730<texttable align="left" suppress-title="true">
3731   <ttcol>Value</ttcol>
3732   <ttcol>Description</ttcol>
3733   <ttcol>Reference</ttcol>
3735   <c>HTTP</c>
3736   <c>Hypertext Transfer Protocol</c>
3737   <c><xref target="http.version"/> of this specification</c>
3738<!-- IANA should add this without our instructions; emailed on June 05, 2009
3739   <c>TLS/1.0</c>
3740   <c>Transport Layer Security</c>
3741   <c><xref target="RFC2817"/></c> -->
3748<section title="Security Considerations" anchor="security.considerations">
3750   This section is meant to inform application developers, information
3751   providers, and users of the security limitations in HTTP/1.1 as
3752   described by this document. The discussion does not include
3753   definitive solutions to the problems revealed, though it does make
3754   some suggestions for reducing security risks.
3757<section title="Personal Information" anchor="personal.information">
3759   HTTP clients are often privy to large amounts of personal information
3760   (e.g., the user's name, location, mail address, passwords, encryption
3761   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3762   leakage of this information.
3763   We very strongly recommend that a convenient interface be provided
3764   for the user to control dissemination of such information, and that
3765   designers and implementors be particularly careful in this area.
3766   History shows that errors in this area often create serious security
3767   and/or privacy problems and generate highly adverse publicity for the
3768   implementor's company.
3772<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3774   A server is in the position to save personal data about a user's
3775   requests which might identify their reading patterns or subjects of
3776   interest. This information is clearly confidential in nature and its
3777   handling can be constrained by law in certain countries. People using
3778   HTTP to provide data are responsible for ensuring that
3779   such material is not distributed without the permission of any
3780   individuals that are identifiable by the published results.
3784<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3786   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3787   the documents returned by HTTP requests to be only those that were
3788   intended by the server administrators. If an HTTP server translates
3789   HTTP URIs directly into file system calls, the server &MUST; take
3790   special care not to serve files that were not intended to be
3791   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3792   other operating systems use ".." as a path component to indicate a
3793   directory level above the current one. On such a system, an HTTP
3794   server &MUST; disallow any such construct in the request-target if it
3795   would otherwise allow access to a resource outside those intended to
3796   be accessible via the HTTP server. Similarly, files intended for
3797   reference only internally to the server (such as access control
3798   files, configuration files, and script code) &MUST; be protected from
3799   inappropriate retrieval, since they might contain sensitive
3800   information. Experience has shown that minor bugs in such HTTP server
3801   implementations have turned into security risks.
3805<section title="DNS Spoofing" anchor="dns.spoofing">
3807   Clients using HTTP rely heavily on the Domain Name Service, and are
3808   thus generally prone to security attacks based on the deliberate
3809   mis-association of IP addresses and DNS names. Clients need to be
3810   cautious in assuming the continuing validity of an IP number/DNS name
3811   association.
3814   In particular, HTTP clients &SHOULD; rely on their name resolver for
3815   confirmation of an IP number/DNS name association, rather than
3816   caching the result of previous host name lookups. Many platforms
3817   already can cache host name lookups locally when appropriate, and
3818   they &SHOULD; be configured to do so. It is proper for these lookups to
3819   be cached, however, only when the TTL (Time To Live) information
3820   reported by the name server makes it likely that the cached
3821   information will remain useful.
3824   If HTTP clients cache the results of host name lookups in order to
3825   achieve a performance improvement, they &MUST; observe the TTL
3826   information reported by DNS.
3829   If HTTP clients do not observe this rule, they could be spoofed when
3830   a previously-accessed server's IP address changes. As network
3831   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3832   possibility of this form of attack will grow. Observing this
3833   requirement thus reduces this potential security vulnerability.
3836   This requirement also improves the load-balancing behavior of clients
3837   for replicated servers using the same DNS name and reduces the
3838   likelihood of a user's experiencing failure in accessing sites which
3839   use that strategy.
3843<section title="Proxies and Caching" anchor="attack.proxies">
3845   By their very nature, HTTP proxies are men-in-the-middle, and
3846   represent an opportunity for man-in-the-middle attacks. Compromise of
3847   the systems on which the proxies run can result in serious security
3848   and privacy problems. Proxies have access to security-related
3849   information, personal information about individual users and
3850   organizations, and proprietary information belonging to users and
3851   content providers. A compromised proxy, or a proxy implemented or
3852   configured without regard to security and privacy considerations,
3853   might be used in the commission of a wide range of potential attacks.
3856   Proxy operators need to protect the systems on which proxies run as
3857   they would protect any system that contains or transports sensitive
3858   information. In particular, log information gathered at proxies often
3859   contains highly sensitive personal information, and/or information
3860   about organizations. Log information needs to be carefully guarded, and
3861   appropriate guidelines for use need to be developed and followed.
3862   (<xref target="abuse.of.server.log.information"/>).
3865   Proxy implementors need to consider the privacy and security
3866   implications of their design and coding decisions, and of the
3867   configuration options they provide to proxy operators (especially the
3868   default configuration).
3871   Users of a proxy need to be aware that proxies are no trustworthier than
3872   the people who run them; HTTP itself cannot solve this problem.
3875   The judicious use of cryptography, when appropriate, might suffice to
3876   protect against a broad range of security and privacy attacks. Such
3877   cryptography is beyond the scope of the HTTP/1.1 specification.
3881<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3883   They exist. They are hard to defend against. Research continues.
3884   Beware.
3889<section title="Acknowledgments" anchor="ack">
3891   HTTP has evolved considerably over the years. It has
3892   benefited from a large and active developer community--the many
3893   people who have participated on the www-talk mailing list--and it is
3894   that community which has been most responsible for the success of
3895   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3896   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3897   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3898   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3899   VanHeyningen deserve special recognition for their efforts in
3900   defining early aspects of the protocol.
3903   This document has benefited greatly from the comments of all those
3904   participating in the HTTP-WG. In addition to those already mentioned,
3905   the following individuals have contributed to this specification:
3908   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3909   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3910   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3911   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3912   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3913   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3914   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3915   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3916   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3917   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3918   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3919   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3922   Thanks to the "cave men" of Palo Alto. You know who you are.
3925   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3926   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3927   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3928   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3929   Larry Masinter for their help. And thanks go particularly to Jeff
3930   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3933   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3934   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3935   discovery of many of the problems that this document attempts to
3936   rectify.
3939   This specification makes heavy use of the augmented BNF and generic
3940   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3941   reuses many of the definitions provided by Nathaniel Borenstein and
3942   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3943   specification will help reduce past confusion over the relationship
3944   between HTTP and Internet mail message formats.
3951<references title="Normative References">
3953<reference anchor="ISO-8859-1">
3954  <front>
3955    <title>
3956     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3957    </title>
3958    <author>
3959      <organization>International Organization for Standardization</organization>
3960    </author>
3961    <date year="1998"/>
3962  </front>
3963  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3966<reference anchor="Part2">
3967  <front>
3968    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3969    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3970      <organization abbrev="Day Software">Day Software</organization>
3971      <address><email></email></address>
3972    </author>
3973    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3974      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3975      <address><email></email></address>
3976    </author>
3977    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3978      <organization abbrev="HP">Hewlett-Packard Company</organization>
3979      <address><email></email></address>
3980    </author>
3981    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3982      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3983      <address><email></email></address>
3984    </author>
3985    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3986      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3987      <address><email></email></address>
3988    </author>
3989    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3990      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3991      <address><email></email></address>
3992    </author>
3993    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3994      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3995      <address><email></email></address>
3996    </author>
3997    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3998      <organization abbrev="W3C">World Wide Web Consortium</organization>
3999      <address><email></email></address>
4000    </author>
4001    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4002      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4003      <address><email></email></address>
4004    </author>
4005    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4006  </front>
4007  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4008  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4011<reference anchor="Part3">
4012  <front>
4013    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4014    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4015      <organization abbrev="Day Software">Day Software</organization>
4016      <address><email></email></address>
4017    </author>
4018    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4019      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4020      <address><email></email></address>
4021    </author>
4022    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4023      <organization abbrev="HP">Hewlett-Packard Company</organization>
4024      <address><email></email></address>
4025    </author>
4026    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4027      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4028      <address><email></email></address>
4029    </author>
4030    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4031      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4032      <address><email></email></address>
4033    </author>
4034    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4035      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4036      <address><email></email></address>
4037    </author>
4038    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4039      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4040      <address><email></email></address>
4041    </author>
4042    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4043      <organization abbrev="W3C">World Wide Web Consortium</organization>
4044      <address><email></email></address>
4045    </author>
4046    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4047      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4048      <address><email></email></address>
4049    </author>
4050    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4051  </front>
4052  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4053  <x:source href="p3-payload.xml" basename="p3-payload"/>
4056<reference anchor="Part6">
4057  <front>
4058    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4059    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4060      <organization abbrev="Day Software">Day Software</organization>
4061      <address><email></email></address>
4062    </author>
4063    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4064      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4065      <address><email></email></address>
4066    </author>
4067    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4068      <organization abbrev="HP">Hewlett-Packard Company</organization>
4069      <address><email></email></address>
4070    </author>
4071    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4072      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4073      <address><email></email></address>
4074    </author>
4075    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4076      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4077      <address><email></email></address>
4078    </author>
4079    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4080      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4081      <address><email></email></address>
4082    </author>
4083    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4084      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4085      <address><email></email></address>
4086    </author>
4087    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4088      <organization abbrev="W3C">World Wide Web Consortium</organization>
4089      <address><email></email></address>
4090    </author>
4091    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4092      <address><email></email></address>
4093    </author>
4094    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4095      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4096      <address><email></email></address>
4097    </author>
4098    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4099  </front>
4100  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4101  <x:source href="p6-cache.xml" basename="p6-cache"/>
4104<reference anchor="RFC5234">
4105  <front>
4106    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4107    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4108      <organization>Brandenburg InternetWorking</organization>
4109      <address>
4110        <email></email>
4111      </address> 
4112    </author>
4113    <author initials="P." surname="Overell" fullname="Paul Overell">
4114      <organization>THUS plc.</organization>
4115      <address>
4116        <email></email>
4117      </address>
4118    </author>
4119    <date month="January" year="2008"/>
4120  </front>
4121  <seriesInfo name="STD" value="68"/>
4122  <seriesInfo name="RFC" value="5234"/>
4125<reference anchor="RFC2119">
4126  <front>
4127    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4128    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4129      <organization>Harvard University</organization>
4130      <address><email></email></address>
4131    </author>
4132    <date month="March" year="1997"/>
4133  </front>
4134  <seriesInfo name="BCP" value="14"/>
4135  <seriesInfo name="RFC" value="2119"/>
4138<reference anchor="RFC3986">
4139 <front>
4140  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4141  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4142    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4143    <address>
4144       <email></email>
4145       <uri></uri>
4146    </address>
4147  </author>
4148  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4149    <organization abbrev="Day Software">Day Software</organization>
4150    <address>
4151      <email></email>
4152      <uri></uri>
4153    </address>
4154  </author>
4155  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4156    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4157    <address>
4158      <email></email>
4159      <uri></uri>
4160    </address>
4161  </author>
4162  <date month='January' year='2005'></date>
4163 </front>
4164 <seriesInfo name="RFC" value="3986"/>
4165 <seriesInfo name="STD" value="66"/>
4168<reference anchor="USASCII">
4169  <front>
4170    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4171    <author>
4172      <organization>American National Standards Institute</organization>
4173    </author>
4174    <date year="1986"/>
4175  </front>
4176  <seriesInfo name="ANSI" value="X3.4"/>
4179<reference anchor="RFC1950">
4180  <front>
4181    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4182    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4183      <organization>Aladdin Enterprises</organization>
4184      <address><email></email></address>
4185    </author>
4186    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4187    <date month="May" year="1996"/>
4188  </front>
4189  <seriesInfo name="RFC" value="1950"/>
4190  <annotation>
4191    RFC 1950 is an Informational RFC, thus it might be less stable than
4192    this specification. On the other hand, this downward reference was
4193    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4194    therefore it is unlikely to cause problems in practice. See also
4195    <xref target="BCP97"/>.
4196  </annotation>
4199<reference anchor="RFC1951">
4200  <front>
4201    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4202    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4203      <organization>Aladdin Enterprises</organization>
4204      <address><email></email></address>
4205    </author>
4206    <date month="May" year="1996"/>
4207  </front>
4208  <seriesInfo name="RFC" value="1951"/>
4209  <annotation>
4210    RFC 1951 is an Informational RFC, thus it might be less stable than
4211    this specification. On the other hand, this downward reference was
4212    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4213    therefore it is unlikely to cause problems in practice. See also
4214    <xref target="BCP97"/>.
4215  </annotation>
4218<reference anchor="RFC1952">
4219  <front>
4220    <title>GZIP file format specification version 4.3</title>
4221    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4222      <organization>Aladdin Enterprises</organization>
4223      <address><email></email></address>
4224    </author>
4225    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4226      <address><email></email></address>
4227    </author>
4228    <author initials="M." surname="Adler" fullname="Mark Adler">
4229      <address><email></email></address>
4230    </author>
4231    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4232      <address><email></email></address>
4233    </author>
4234    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4235      <address><email></email></address>
4236    </author>
4237    <date month="May" year="1996"/>
4238  </front>
4239  <seriesInfo name="RFC" value="1952"/>
4240  <annotation>
4241    RFC 1952 is an Informational RFC, thus it might be less stable than
4242    this specification. On the other hand, this downward reference was
4243    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4244    therefore it is unlikely to cause problems in practice. See also
4245    <xref target="BCP97"/>.
4246  </annotation>
4251<references title="Informative References">
4253<reference anchor="Nie1997" target="">
4254  <front>
4255    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4256    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4257    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4258    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4259    <author initials="H." surname="Lie" fullname="H. Lie"/>
4260    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4261    <date year="1997" month="September"/>
4262  </front>
4263  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4266<reference anchor="Pad1995" target="">
4267  <front>
4268    <title>Improving HTTP Latency</title>
4269    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4270    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4271    <date year="1995" month="December"/>
4272  </front>
4273  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4276<reference anchor="RFC1123">
4277  <front>
4278    <title>Requirements for Internet Hosts - Application and Support</title>
4279    <author initials="R." surname="Braden" fullname="Robert Braden">
4280      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4281      <address><email>Braden@ISI.EDU</email></address>
4282    </author>
4283    <date month="October" year="1989"/>
4284  </front>
4285  <seriesInfo name="STD" value="3"/>
4286  <seriesInfo name="RFC" value="1123"/>
4289<reference anchor="RFC1305">
4290  <front>
4291    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4292    <author initials="D." surname="Mills" fullname="David L. Mills">
4293      <organization>University of Delaware, Electrical Engineering Department</organization>
4294      <address><email></email></address>
4295    </author>
4296    <date month="March" year="1992"/>
4297  </front>
4298  <seriesInfo name="RFC" value="1305"/>
4301<reference anchor="RFC1900">
4302  <front>
4303    <title>Renumbering Needs Work</title>
4304    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4305      <organization>CERN, Computing and Networks Division</organization>
4306      <address><email></email></address>
4307    </author>
4308    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4309      <organization>cisco Systems</organization>
4310      <address><email></email></address>
4311    </author>
4312    <date month="February" year="1996"/>
4313  </front>
4314  <seriesInfo name="RFC" value="1900"/>
4317<reference anchor="RFC1945">
4318  <front>
4319    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4320    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4321      <organization>MIT, Laboratory for Computer Science</organization>
4322      <address><email></email></address>
4323    </author>
4324    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4325      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4326      <address><email></email></address>
4327    </author>
4328    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4329      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4330      <address><email></email></address>
4331    </author>
4332    <date month="May" year="1996"/>
4333  </front>
4334  <seriesInfo name="RFC" value="1945"/>
4337<reference anchor="RFC2045">
4338  <front>
4339    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4340    <author initials="N." surname="Freed" fullname="Ned Freed">
4341      <organization>Innosoft International, Inc.</organization>
4342      <address><email></email></address>
4343    </author>
4344    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4345      <organization>First Virtual Holdings</organization>
4346      <address><email></email></address>
4347    </author>
4348    <date month="November" year="1996"/>
4349  </front>
4350  <seriesInfo name="RFC" value="2045"/>
4353<reference anchor="RFC2047">
4354  <front>
4355    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4356    <author initials="K." surname="Moore" fullname="Keith Moore">
4357      <organization>University of Tennessee</organization>
4358      <address><email></email></address>
4359    </author>
4360    <date month="November" year="1996"/>
4361  </front>
4362  <seriesInfo name="RFC" value="2047"/>
4365<reference anchor="RFC2068">
4366  <front>
4367    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4368    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4369      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4370      <address><email></email></address>
4371    </author>
4372    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4373      <organization>MIT Laboratory for Computer Science</organization>
4374      <address><email></email></address>
4375    </author>
4376    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4377      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4378      <address><email></email></address>
4379    </author>
4380    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4381      <organization>MIT Laboratory for Computer Science</organization>
4382      <address><email></email></address>
4383    </author>
4384    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4385      <organization>MIT Laboratory for Computer Science</organization>
4386      <address><email></email></address>
4387    </author>
4388    <date month="January" year="1997"/>
4389  </front>
4390  <seriesInfo name="RFC" value="2068"/>
4393<reference anchor='RFC2109'>
4394  <front>
4395    <title>HTTP State Management Mechanism</title>
4396    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4397      <organization>Bell Laboratories, Lucent Technologies</organization>
4398      <address><email></email></address>
4399    </author>
4400    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4401      <organization>Netscape Communications Corp.</organization>
4402      <address><email></email></address>
4403    </author>
4404    <date year='1997' month='February' />
4405  </front>
4406  <seriesInfo name='RFC' value='2109' />
4409<reference anchor="RFC2145">
4410  <front>
4411    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4412    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4413      <organization>Western Research Laboratory</organization>
4414      <address><email></email></address>
4415    </author>
4416    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4417      <organization>Department of Information and Computer Science</organization>
4418      <address><email></email></address>
4419    </author>
4420    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4421      <organization>MIT Laboratory for Computer Science</organization>
4422      <address><email></email></address>
4423    </author>
4424    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4425      <organization>W3 Consortium</organization>
4426      <address><email></email></address>
4427    </author>
4428    <date month="May" year="1997"/>
4429  </front>
4430  <seriesInfo name="RFC" value="2145"/>
4433<reference anchor="RFC2616">
4434  <front>
4435    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4436    <author initials="R." surname="Fielding" fullname="R. Fielding">
4437      <organization>University of California, Irvine</organization>
4438      <address><email></email></address>
4439    </author>
4440    <author initials="J." surname="Gettys" fullname="J. Gettys">
4441      <organization>W3C</organization>
4442      <address><email></email></address>
4443    </author>
4444    <author initials="J." surname="Mogul" fullname="J. Mogul">
4445      <organization>Compaq Computer Corporation</organization>
4446      <address><email></email></address>
4447    </author>
4448    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4449      <organization>MIT Laboratory for Computer Science</organization>
4450      <address><email></email></address>
4451    </author>
4452    <author initials="L." surname="Masinter" fullname="L. Masinter">
4453      <organization>Xerox Corporation</organization>
4454      <address><email></email></address>
4455    </author>
4456    <author initials="P." surname="Leach" fullname="P. Leach">
4457      <organization>Microsoft Corporation</organization>
4458      <address><email></email></address>
4459    </author>
4460    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4461      <organization>W3C</organization>
4462      <address><email></email></address>
4463    </author>
4464    <date month="June" year="1999"/>
4465  </front>
4466  <seriesInfo name="RFC" value="2616"/>
4469<reference anchor='RFC2817'>
4470  <front>
4471    <title>Upgrading to TLS Within HTTP/1.1</title>
4472    <author initials='R.' surname='Khare' fullname='R. Khare'>
4473      <organization>4K Associates / UC Irvine</organization>
4474      <address><email></email></address>
4475    </author>
4476    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4477      <organization>Agranat Systems, Inc.</organization>
4478      <address><email></email></address>
4479    </author>
4480    <date year='2000' month='May' />
4481  </front>
4482  <seriesInfo name='RFC' value='2817' />
4485<reference anchor='RFC2818'>
4486  <front>
4487    <title>HTTP Over TLS</title>
4488    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4489      <organization>RTFM, Inc.</organization>
4490      <address><email></email></address>
4491    </author>
4492    <date year='2000' month='May' />
4493  </front>
4494  <seriesInfo name='RFC' value='2818' />
4497<reference anchor='RFC2965'>
4498  <front>
4499    <title>HTTP State Management Mechanism</title>
4500    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4501      <organization>Bell Laboratories, Lucent Technologies</organization>
4502      <address><email></email></address>
4503    </author>
4504    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4505      <organization>, Inc.</organization>
4506      <address><email></email></address>
4507    </author>
4508    <date year='2000' month='October' />
4509  </front>
4510  <seriesInfo name='RFC' value='2965' />
4513<reference anchor='RFC3864'>
4514  <front>
4515    <title>Registration Procedures for Message Header Fields</title>
4516    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4517      <organization>Nine by Nine</organization>
4518      <address><email></email></address>
4519    </author>
4520    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4521      <organization>BEA Systems</organization>
4522      <address><email></email></address>
4523    </author>
4524    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4525      <organization>HP Labs</organization>
4526      <address><email></email></address>
4527    </author>
4528    <date year='2004' month='September' />
4529  </front>
4530  <seriesInfo name='BCP' value='90' />
4531  <seriesInfo name='RFC' value='3864' />
4534<reference anchor="RFC4288">
4535  <front>
4536    <title>Media Type Specifications and Registration Procedures</title>
4537    <author initials="N." surname="Freed" fullname="N. Freed">
4538      <organization>Sun Microsystems</organization>
4539      <address>
4540        <email></email>
4541      </address>
4542    </author>
4543    <author initials="J." surname="Klensin" fullname="J. Klensin">
4544      <address>
4545        <email></email>
4546      </address>
4547    </author>
4548    <date year="2005" month="December"/>
4549  </front>
4550  <seriesInfo name="BCP" value="13"/>
4551  <seriesInfo name="RFC" value="4288"/>
4554<reference anchor='RFC4395'>
4555  <front>
4556    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4557    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4558      <organization>AT&amp;T Laboratories</organization>
4559      <address>
4560        <email></email>
4561      </address>
4562    </author>
4563    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4564      <organization>Qualcomm, Inc.</organization>
4565      <address>
4566        <email></email>
4567      </address>
4568    </author>
4569    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4570      <organization>Adobe Systems</organization>
4571      <address>
4572        <email></email>
4573      </address>
4574    </author>
4575    <date year='2006' month='February' />
4576  </front>
4577  <seriesInfo name='BCP' value='115' />
4578  <seriesInfo name='RFC' value='4395' />
4581<reference anchor='RFC5226'>
4582  <front>
4583    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4584    <author initials='T.' surname='Narten' fullname='T. Narten'>
4585      <organization>IBM</organization>
4586      <address><email></email></address>
4587    </author>
4588    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4589      <organization>Google</organization>
4590      <address><email></email></address>
4591    </author>
4592    <date year='2008' month='May' />
4593  </front>
4594  <seriesInfo name='BCP' value='26' />
4595  <seriesInfo name='RFC' value='5226' />
4598<reference anchor="RFC5322">
4599  <front>
4600    <title>Internet Message Format</title>
4601    <author initials="P." surname="Resnick" fullname="P. Resnick">
4602      <organization>Qualcomm Incorporated</organization>
4603    </author>
4604    <date year="2008" month="October"/>
4605  </front>
4606  <seriesInfo name="RFC" value="5322"/>
4609<reference anchor='BCP97'>
4610  <front>
4611    <title>Handling Normative References to Standards-Track Documents</title>
4612    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4613      <address>
4614        <email></email>
4615      </address>
4616    </author>
4617    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4618      <organization>MIT</organization>
4619      <address>
4620        <email></email>
4621      </address>
4622    </author>
4623    <date year='2007' month='June' />
4624  </front>
4625  <seriesInfo name='BCP' value='97' />
4626  <seriesInfo name='RFC' value='4897' />
4629<reference anchor="Kri2001" target="">
4630  <front>
4631    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4632    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4633    <date year="2001" month="November"/>
4634  </front>
4635  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4638<reference anchor="Spe" target="">
4639  <front>
4640    <title>Analysis of HTTP Performance Problems</title>
4641    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4642    <date/>
4643  </front>
4646<reference anchor="Tou1998" target="">
4647  <front>
4648  <title>Analysis of HTTP Performance</title>
4649  <author initials="J." surname="Touch" fullname="Joe Touch">
4650    <organization>USC/Information Sciences Institute</organization>
4651    <address><email></email></address>
4652  </author>
4653  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4654    <organization>USC/Information Sciences Institute</organization>
4655    <address><email></email></address>
4656  </author>
4657  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4658    <organization>USC/Information Sciences Institute</organization>
4659    <address><email></email></address>
4660  </author>
4661  <date year="1998" month="Aug"/>
4662  </front>
4663  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4664  <annotation>(original report dated Aug. 1996)</annotation>
4670<section title="Tolerant Applications" anchor="tolerant.applications">
4672   Although this document specifies the requirements for the generation
4673   of HTTP/1.1 messages, not all applications will be correct in their
4674   implementation. We therefore recommend that operational applications
4675   be tolerant of deviations whenever those deviations can be
4676   interpreted unambiguously.
4679   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4680   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4681   &SHOULD; accept any amount of WSP characters between fields, even though
4682   only a single SP is required.
4685   The line terminator for header fields is the sequence CRLF.
4686   However, we recommend that applications, when parsing such headers,
4687   recognize a single LF as a line terminator and ignore the leading CR.
4690   The character set of a representation &SHOULD; be labeled as the lowest
4691   common denominator of the character codes used within that representation, with
4692   the exception that not labeling the representation is preferred over labeling
4693   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4696   Additional rules for requirements on parsing and encoding of dates
4697   and other potential problems with date encodings include:
4700  <list style="symbols">
4701     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4702        which appears to be more than 50 years in the future is in fact
4703        in the past (this helps solve the "year 2000" problem).</t>
4705     <t>Although all date formats are specified to be case-sensitive,
4706        recipients &SHOULD; match day, week and timezone names
4707        case-insensitively.</t>
4709     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4710        Expires date as earlier than the proper value, but &MUST-NOT;
4711        internally represent a parsed Expires date as later than the
4712        proper value.</t>
4714     <t>All expiration-related calculations &MUST; be done in GMT. The
4715        local time zone &MUST-NOT; influence the calculation or comparison
4716        of an age or expiration time.</t>
4718     <t>If an HTTP header incorrectly carries a date value with a time
4719        zone other than GMT, it &MUST; be converted into GMT using the
4720        most conservative possible conversion.</t>
4721  </list>
4725<section title="Compatibility with Previous Versions" anchor="compatibility">
4727   HTTP has been in use by the World-Wide Web global information initiative
4728   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4729   was a simple protocol for hypertext data transfer across the Internet
4730   with only a single method and no metadata.
4731   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4732   methods and MIME-like messaging that could include metadata about the data
4733   transferred and modifiers on the request/response semantics. However,
4734   HTTP/1.0 did not sufficiently take into consideration the effects of
4735   hierarchical proxies, caching, the need for persistent connections, or
4736   name-based virtual hosts. The proliferation of incompletely-implemented
4737   applications calling themselves "HTTP/1.0" further necessitated a
4738   protocol version change in order for two communicating applications
4739   to determine each other's true capabilities.
4742   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4743   requirements that enable reliable implementations, adding only
4744   those new features that will either be safely ignored by an HTTP/1.0
4745   recipient or only sent when communicating with a party advertising
4746   compliance with HTTP/1.1.
4749   It is beyond the scope of a protocol specification to mandate
4750   compliance with previous versions. HTTP/1.1 was deliberately
4751   designed, however, to make supporting previous versions easy. It is
4752   worth noting that, at the time of composing this specification, we would
4753   expect general-purpose HTTP/1.1 servers to:
4754  <list style="symbols">
4755     <t>understand any valid request in the format of HTTP/1.0 and
4756        1.1;</t>
4758     <t>respond appropriately with a message in the same major version
4759        used by the client.</t>
4760  </list>
4763   And we would expect HTTP/1.1 clients to:
4764  <list style="symbols">
4765     <t>understand any valid response in the format of HTTP/1.0 or
4766        1.1.</t>
4767  </list>
4770   For most implementations of HTTP/1.0, each connection is established
4771   by the client prior to the request and closed by the server after
4772   sending the response. Some implementations implement the Keep-Alive
4773   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4776<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4778   This section summarizes major differences between versions HTTP/1.0
4779   and HTTP/1.1.
4782<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4784   The requirements that clients and servers support the Host request-header,
4785   report an error if the Host request-header (<xref target=""/>) is
4786   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4787   are among the most important changes defined by this
4788   specification.
4791   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4792   addresses and servers; there was no other established mechanism for
4793   distinguishing the intended server of a request than the IP address
4794   to which that request was directed. The changes outlined above will
4795   allow the Internet, once older HTTP clients are no longer common, to
4796   support multiple Web sites from a single IP address, greatly
4797   simplifying large operational Web servers, where allocation of many
4798   IP addresses to a single host has created serious problems. The
4799   Internet will also be able to recover the IP addresses that have been
4800   allocated for the sole purpose of allowing special-purpose domain
4801   names to be used in root-level HTTP URLs. Given the rate of growth of
4802   the Web, and the number of servers already deployed, it is extremely
4803   important that all implementations of HTTP (including updates to
4804   existing HTTP/1.0 applications) correctly implement these
4805   requirements:
4806  <list style="symbols">
4807     <t>Both clients and servers &MUST; support the Host request-header.</t>
4809     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4811     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4812        request does not include a Host request-header.</t>
4814     <t>Servers &MUST; accept absolute URIs.</t>
4815  </list>
4820<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4822   Some clients and servers might wish to be compatible with some
4823   previous implementations of persistent connections in HTTP/1.0
4824   clients and servers. Persistent connections in HTTP/1.0 are
4825   explicitly negotiated as they are not the default behavior. HTTP/1.0
4826   experimental implementations of persistent connections are faulty,
4827   and the new facilities in HTTP/1.1 are designed to rectify these
4828   problems. The problem was that some existing HTTP/1.0 clients might
4829   send Keep-Alive to a proxy server that doesn't understand
4830   Connection, which would then erroneously forward it to the next
4831   inbound server, which would establish the Keep-Alive connection and
4832   result in a hung HTTP/1.0 proxy waiting for the close on the
4833   response. The result is that HTTP/1.0 clients must be prevented from
4834   using Keep-Alive when talking to proxies.
4837   However, talking to proxies is the most important use of persistent
4838   connections, so that prohibition is clearly unacceptable. Therefore,
4839   we need some other mechanism for indicating a persistent connection
4840   is desired, which is safe to use even when talking to an old proxy
4841   that ignores Connection. Persistent connections are the default for
4842   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4843   declaring non-persistence. See <xref target="header.connection"/>.
4846   The original HTTP/1.0 form of persistent connections (the Connection:
4847   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4851<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4853  Empty list elements in list productions have been deprecated.
4854  (<xref target="notation.abnf"/>)
4857  Rules about implicit linear whitespace between certain grammar productions
4858  have been removed; now it's only allowed when specifically pointed out
4859  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4860  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4861  Non-ASCII content in header fields and reason phrase has been obsoleted and
4862  made opaque (the TEXT rule was removed)
4863  (<xref target="basic.rules"/>)
4866  Clarify that HTTP-Version is case sensitive.
4867  (<xref target="http.version"/>)
4870  Remove reference to non-existent identity transfer-coding value tokens.
4871  (Sections <xref format="counter" target="transfer.codings"/> and
4872  <xref format="counter" target="message.body"/>)
4875  Require that invalid whitespace around field-names be rejected.
4876  (<xref target="header.fields"/>)
4879  Update use of abs_path production from RFC1808 to the path-absolute + query
4880  components of RFC3986.
4881  (<xref target="request-target"/>)
4884  Clarification that the chunk length does not include the count of the octets
4885  in the chunk header and trailer. Furthermore disallowed line folding
4886  in chunk extensions.
4887  (<xref target="chunked.encoding"/>)
4890  Remove hard limit of two connections per server.
4891  (<xref target="persistent.practical"/>)
4894  Clarify exactly when close connection options must be sent.
4895  (<xref target="header.connection"/>)
4900<?BEGININC p1-messaging.abnf-appendix ?>
4901<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4903<artwork type="abnf" name="p1-messaging.parsed-abnf">
4904<x:ref>BWS</x:ref> = OWS
4906<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4907<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4908<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4909<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4910 connection-token ] )
4911<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4912<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4914<x:ref>Date</x:ref> = "Date:" OWS Date-v
4915<x:ref>Date-v</x:ref> = HTTP-date
4917<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4919<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4920<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4921<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4922<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4923 ]
4924<x:ref>Host</x:ref> = "Host:" OWS Host-v
4925<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4927<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4928<x:ref>Method</x:ref> = token
4930<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4932<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4934<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4935<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4936<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
4937<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4938<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
4940<x:ref>Status-Code</x:ref> = 3DIGIT
4941<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4943<x:ref>TE</x:ref> = "TE:" OWS TE-v
4944<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4945<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4946<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4947<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4948<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4949 transfer-coding ] )
4951<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4952<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4953<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4955<x:ref>Via</x:ref> = "Via:" OWS Via-v
4956<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4957 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4958 ] )
4960<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4962<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4963<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4964<x:ref>attribute</x:ref> = token
4965<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4967<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4968<x:ref>chunk-data</x:ref> = 1*OCTET
4969<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4970<x:ref>chunk-ext-name</x:ref> = token
4971<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4972<x:ref>chunk-size</x:ref> = 1*HEXDIG
4973<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4974<x:ref>connection-token</x:ref> = token
4975<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4976 / %x2A-5B ; '*'-'['
4977 / %x5D-7E ; ']'-'~'
4978 / obs-text
4980<x:ref>date1</x:ref> = day SP month SP year
4981<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4982<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4983<x:ref>day</x:ref> = 2DIGIT
4984<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4985 / %x54.75.65 ; Tue
4986 / %x57.65.64 ; Wed
4987 / %x54.68.75 ; Thu
4988 / %x46.72.69 ; Fri
4989 / %x53.61.74 ; Sat
4990 / %x53.75.6E ; Sun
4991<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4992 / %x54. ; Tuesday
4993 / %x57.65.64.6E. ; Wednesday
4994 / %x54. ; Thursday
4995 / %x46. ; Friday
4996 / %x53. ; Saturday
4997 / %x53.75.6E.64.61.79 ; Sunday
4999<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5000<x:ref>field-name</x:ref> = token
5001<x:ref>field-value</x:ref> = *( field-content / OWS )
5003<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5004 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5006<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5007<x:ref>hour</x:ref> = 2DIGIT
5008<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5009<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5011<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5013<x:ref>message-body</x:ref> = *OCTET
5014<x:ref>minute</x:ref> = 2DIGIT
5015<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5016 / %x46.65.62 ; Feb
5017 / %x4D.61.72 ; Mar
5018 / %x41.70.72 ; Apr
5019 / %x4D.61.79 ; May
5020 / %x4A.75.6E ; Jun
5021 / %x4A.75.6C ; Jul
5022 / %x41.75.67 ; Aug
5023 / %x53.65.70 ; Sep
5024 / %x4F.63.74 ; Oct
5025 / %x4E.6F.76 ; Nov
5026 / %x44.65.63 ; Dec
5028<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5029<x:ref>obs-fold</x:ref> = CRLF
5030<x:ref>obs-text</x:ref> = %x80-FF
5032<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5033<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5034<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5035<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5036<x:ref>product</x:ref> = token [ "/" product-version ]
5037<x:ref>product-version</x:ref> = token
5038<x:ref>protocol-name</x:ref> = token
5039<x:ref>protocol-version</x:ref> = token
5040<x:ref>pseudonym</x:ref> = token
5042<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5043 / %x5D-7E ; ']'-'~'
5044 / obs-text
5045<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5046 / %x5D-7E ; ']'-'~'
5047 / obs-text
5048<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5049<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5050<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5051<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5052<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5053<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5055<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5056<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5057<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5058<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5059<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5060 / authority
5061<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5062<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5063<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5065<x:ref>second</x:ref> = 2DIGIT
5066<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5067 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5068<x:ref>start-line</x:ref> = Request-Line / Status-Line
5070<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5071<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5072 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5073<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5074<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5075<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5076<x:ref>token</x:ref> = 1*tchar
5077<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5078<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5079 transfer-extension
5080<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5081<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5083<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5085<x:ref>value</x:ref> = word
5087<x:ref>word</x:ref> = token / quoted-string
5089<x:ref>year</x:ref> = 4DIGIT
5092<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5093; Chunked-Body defined but not used
5094; Content-Length defined but not used
5095; HTTP-message defined but not used
5096; Host defined but not used
5097; Request defined but not used
5098; Response defined but not used
5099; TE defined but not used
5100; URI-reference defined but not used
5101; general-header defined but not used
5102; http-URI defined but not used
5103; https-URI defined but not used
5104; partial-URI defined but not used
5105; request-header defined but not used
5106; response-header defined but not used
5107; special defined but not used
5109<?ENDINC p1-messaging.abnf-appendix ?>
5111<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5113<section title="Since RFC2616">
5115  Extracted relevant partitions from <xref target="RFC2616"/>.
5119<section title="Since draft-ietf-httpbis-p1-messaging-00">
5121  Closed issues:
5122  <list style="symbols">
5123    <t>
5124      <eref target=""/>:
5125      "HTTP Version should be case sensitive"
5126      (<eref target=""/>)
5127    </t>
5128    <t>
5129      <eref target=""/>:
5130      "'unsafe' characters"
5131      (<eref target=""/>)
5132    </t>
5133    <t>
5134      <eref target=""/>:
5135      "Chunk Size Definition"
5136      (<eref target=""/>)
5137    </t>
5138    <t>
5139      <eref target=""/>:
5140      "Message Length"
5141      (<eref target=""/>)
5142    </t>
5143    <t>
5144      <eref target=""/>:
5145      "Media Type Registrations"
5146      (<eref target=""/>)
5147    </t>
5148    <t>
5149      <eref target=""/>:
5150      "URI includes query"
5151      (<eref target=""/>)
5152    </t>
5153    <t>
5154      <eref target=""/>:
5155      "No close on 1xx responses"
5156      (<eref target=""/>)
5157    </t>
5158    <t>
5159      <eref target=""/>:
5160      "Remove 'identity' token references"
5161      (<eref target=""/>)
5162    </t>
5163    <t>
5164      <eref target=""/>:
5165      "Import query BNF"
5166    </t>
5167    <t>
5168      <eref target=""/>:
5169      "qdtext BNF"
5170    </t>
5171    <t>
5172      <eref target=""/>:
5173      "Normative and Informative references"
5174    </t>
5175    <t>
5176      <eref target=""/>:
5177      "RFC2606 Compliance"
5178    </t>
5179    <t>
5180      <eref target=""/>:
5181      "RFC977 reference"
5182    </t>
5183    <t>
5184      <eref target=""/>:
5185      "RFC1700 references"
5186    </t>
5187    <t>
5188      <eref target=""/>:
5189      "inconsistency in date format explanation"
5190    </t>
5191    <t>
5192      <eref target=""/>:
5193      "Date reference typo"
5194    </t>
5195    <t>
5196      <eref target=""/>:
5197      "Informative references"
5198    </t>
5199    <t>
5200      <eref target=""/>:
5201      "ISO-8859-1 Reference"
5202    </t>
5203    <t>
5204      <eref target=""/>:
5205      "Normative up-to-date references"
5206    </t>
5207  </list>
5210  Other changes:
5211  <list style="symbols">
5212    <t>
5213      Update media type registrations to use RFC4288 template.
5214    </t>
5215    <t>
5216      Use names of RFC4234 core rules DQUOTE and WSP,
5217      fix broken ABNF for chunk-data
5218      (work in progress on <eref target=""/>)
5219    </t>
5220  </list>
5224<section title="Since draft-ietf-httpbis-p1-messaging-01">
5226  Closed issues:
5227  <list style="symbols">
5228    <t>
5229      <eref target=""/>:
5230      "Bodies on GET (and other) requests"
5231    </t>
5232    <t>
5233      <eref target=""/>:
5234      "Updating to RFC4288"
5235    </t>
5236    <t>
5237      <eref target=""/>:
5238      "Status Code and Reason Phrase"
5239    </t>
5240    <t>
5241      <eref target=""/>:
5242      "rel_path not used"
5243    </t>
5244  </list>
5247  Ongoing work on ABNF conversion (<eref target=""/>):
5248  <list style="symbols">
5249    <t>
5250      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5251      "trailer-part").
5252    </t>
5253    <t>
5254      Avoid underscore character in rule names ("http_URL" ->
5255      "http-URL", "abs_path" -> "path-absolute").
5256    </t>
5257    <t>
5258      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5259      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5260      have to be updated when switching over to RFC3986.
5261    </t>
5262    <t>
5263      Synchronize core rules with RFC5234.
5264    </t>
5265    <t>
5266      Get rid of prose rules that span multiple lines.
5267    </t>
5268    <t>
5269      Get rid of unused rules LOALPHA and UPALPHA.
5270    </t>
5271    <t>
5272      Move "Product Tokens" section (back) into Part 1, as "token" is used
5273      in the definition of the Upgrade header.
5274    </t>
5275    <t>
5276      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5277    </t>
5278    <t>
5279      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5280    </t>
5281  </list>
5285<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5287  Closed issues:
5288  <list style="symbols">
5289    <t>
5290      <eref target=""/>:
5291      "HTTP-date vs. rfc1123-date"
5292    </t>
5293    <t>
5294      <eref target=""/>:
5295      "WS in quoted-pair"
5296    </t>
5297  </list>
5300  Ongoing work on IANA Message Header Registration (<eref target=""/>):
5301  <list style="symbols">
5302    <t>
5303      Reference RFC 3984, and update header registrations for headers defined
5304      in this document.
5305    </t>
5306  </list>
5309  Ongoing work on ABNF conversion (<eref target=""/>):
5310  <list style="symbols">
5311    <t>
5312      Replace string literals when the string really is case-sensitive (HTTP-Version).
5313    </t>
5314  </list>
5318<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5320  Closed issues:
5321  <list style="symbols">
5322    <t>
5323      <eref target=""/>:
5324      "Connection closing"
5325    </t>
5326    <t>
5327      <eref target=""/>:
5328      "Move registrations and registry information to IANA Considerations"
5329    </t>
5330    <t>
5331      <eref target=""/>:
5332      "need new URL for PAD1995 reference"
5333    </t>
5334    <t>
5335      <eref target=""/>:
5336      "IANA Considerations: update HTTP URI scheme registration"
5337    </t>
5338    <t>
5339      <eref target=""/>:
5340      "Cite HTTPS URI scheme definition"
5341    </t>
5342    <t>
5343      <eref target=""/>:
5344      "List-type headers vs Set-Cookie"
5345    </t>
5346  </list>
5349  Ongoing work on ABNF conversion (<eref target=""/>):
5350  <list style="symbols">
5351    <t>
5352      Replace string literals when the string really is case-sensitive (HTTP-Date).
5353    </t>
5354    <t>
5355      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5356    </t>
5357  </list>
5361<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5363  Closed issues:
5364  <list style="symbols">
5365    <t>
5366      <eref target=""/>:
5367      "Out-of-date reference for URIs"
5368    </t>
5369    <t>
5370      <eref target=""/>:
5371      "RFC 2822 is updated by RFC 5322"
5372    </t>
5373  </list>
5376  Ongoing work on ABNF conversion (<eref target=""/>):
5377  <list style="symbols">
5378    <t>
5379      Use "/" instead of "|" for alternatives.
5380    </t>
5381    <t>
5382      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5383    </t>
5384    <t>
5385      Only reference RFC 5234's core rules.
5386    </t>
5387    <t>
5388      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5389      whitespace ("OWS") and required whitespace ("RWS").
5390    </t>
5391    <t>
5392      Rewrite ABNFs to spell out whitespace rules, factor out
5393      header value format definitions.
5394    </t>
5395  </list>
5399<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5401  Closed issues:
5402  <list style="symbols">
5403    <t>
5404      <eref target=""/>:
5405      "Header LWS"
5406    </t>
5407    <t>
5408      <eref target=""/>:
5409      "Sort 1.3 Terminology"
5410    </t>
5411    <t>
5412      <eref target=""/>:
5413      "RFC2047 encoded words"
5414    </t>
5415    <t>
5416      <eref target=""/>:
5417      "Character Encodings in TEXT"
5418    </t>
5419    <t>
5420      <eref target=""/>:
5421      "Line Folding"
5422    </t>
5423    <t>
5424      <eref target=""/>:
5425      "OPTIONS * and proxies"
5426    </t>
5427    <t>
5428      <eref target=""/>:
5429      "Reason-Phrase BNF"
5430    </t>
5431    <t>
5432      <eref target=""/>:
5433      "Use of TEXT"
5434    </t>
5435    <t>
5436      <eref target=""/>:
5437      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5438    </t>
5439    <t>
5440      <eref target=""/>:
5441      "RFC822 reference left in discussion of date formats"
5442    </t>
5443  </list>
5446  Final work on ABNF conversion (<eref target=""/>):
5447  <list style="symbols">
5448    <t>
5449      Rewrite definition of list rules, deprecate empty list elements.
5450    </t>
5451    <t>
5452      Add appendix containing collected and expanded ABNF.
5453    </t>
5454  </list>
5457  Other changes:
5458  <list style="symbols">
5459    <t>
5460      Rewrite introduction; add mostly new Architecture Section.
5461    </t>
5462    <t>
5463      Move definition of quality values from Part 3 into Part 1;
5464      make TE request header grammar independent of accept-params (defined in Part 3).
5465    </t>
5466  </list>
5470<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5472  Closed issues:
5473  <list style="symbols">
5474    <t>
5475      <eref target=""/>:
5476      "base for numeric protocol elements"
5477    </t>
5478    <t>
5479      <eref target=""/>:
5480      "comment ABNF"
5481    </t>
5482  </list>
5485  Partly resolved issues:
5486  <list style="symbols">
5487    <t>
5488      <eref target=""/>:
5489      "205 Bodies" (took out language that implied that there might be
5490      methods for which a request body MUST NOT be included)
5491    </t>
5492    <t>
5493      <eref target=""/>:
5494      "editorial improvements around HTTP-date"
5495    </t>
5496  </list>
5500<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5502  Closed issues:
5503  <list style="symbols">
5504    <t>
5505      <eref target=""/>:
5506      "Repeating single-value headers"
5507    </t>
5508    <t>
5509      <eref target=""/>:
5510      "increase connection limit"
5511    </t>
5512    <t>
5513      <eref target=""/>:
5514      "IP addresses in URLs"
5515    </t>
5516    <t>
5517      <eref target=""/>:
5518      "take over HTTP Upgrade Token Registry"
5519    </t>
5520    <t>
5521      <eref target=""/>:
5522      "CR and LF in chunk extension values"
5523    </t>
5524    <t>
5525      <eref target=""/>:
5526      "HTTP/0.9 support"
5527    </t>
5528    <t>
5529      <eref target=""/>:
5530      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5531    </t>
5532    <t>
5533      <eref target=""/>:
5534      "move definitions of gzip/deflate/compress to part 1"
5535    </t>
5536    <t>
5537      <eref target=""/>:
5538      "disallow control characters in quoted-pair"
5539    </t>
5540  </list>
5543  Partly resolved issues:
5544  <list style="symbols">
5545    <t>
5546      <eref target=""/>:
5547      "update IANA requirements wrt Transfer-Coding values" (add the
5548      IANA Considerations subsection)
5549    </t>
5550  </list>
5554<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5556  Closed issues:
5557  <list style="symbols">
5558    <t>
5559      <eref target=""/>:
5560      "header parsing, treatment of leading and trailing OWS"
5561    </t>
5562  </list>
5565  Partly resolved issues:
5566  <list style="symbols">
5567    <t>
5568      <eref target=""/>:
5569      "Placement of 13.5.1 and 13.5.2"
5570    </t>
5571    <t>
5572      <eref target=""/>:
5573      "use of term "word" when talking about header structure"
5574    </t>
5575  </list>
5579<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5581  Closed issues:
5582  <list style="symbols">
5583    <t>
5584      <eref target=""/>:
5585      "Clarification of the term 'deflate'"
5586    </t>
5587    <t>
5588      <eref target=""/>:
5589      "OPTIONS * and proxies"
5590    </t>
5591    <t>
5592      <eref target=""/>:
5593      "MIME-Version not listed in P1, general header fields"
5594    </t>
5595    <t>
5596      <eref target=""/>:
5597      "IANA registry for content/transfer encodings"
5598    </t>
5599    <t>
5600      <eref target=""/>:
5601      "Case-sensitivity of HTTP-date"
5602    </t>
5603    <t>
5604      <eref target=""/>:
5605      "use of term "word" when talking about header structure"
5606    </t>
5607  </list>
5610  Partly resolved issues:
5611  <list style="symbols">
5612    <t>
5613      <eref target=""/>:
5614      "Term for the requested resource's URI"
5615    </t>
5616  </list>
5620<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5622  Closed issues:
5623  <list style="symbols">
5624    <t>
5625      <eref target=""/>:
5626      "Connection Closing"
5627    </t>
5628    <t>
5629      <eref target=""/>:
5630      "Delimiting messages with multipart/byteranges"
5631    </t>
5632    <t>
5633      <eref target=""/>:
5634      "Handling multiple Content-Length headers"
5635    </t>
5636    <t>
5637      <eref target=""/>:
5638      "Clarify entity / representation / variant terminology"
5639    </t>
5640    <t>
5641      <eref target=""/>:
5642      "consider removing the 'changes from 2068' sections"
5643    </t>
5644  </list>
5647  Partly resolved issues:
5648  <list style="symbols">
5649    <t>
5650      <eref target=""/>:
5651      "HTTP(s) URI scheme definitions"
5652    </t>
5653  </list>
5657<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5659  None yet.
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