source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1107

Last change on this file since 1107 was 1107, checked in by fielding@…, 11 years ago

Change the undefined use of "transparent proxy" to a definition
of transforming and non-transforming proxies. Add new definitions
for "intercepts" and the other kind of "transparent proxy".
Should we add informational references to RFC1919 and RFC3040 ?

Addresses #210

  • Property svn:eol-style set to native
File size: 243.8 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "February">
16  <!ENTITY ID-YEAR "2011">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x=''/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#errors.or.incomplete.response.cache.behavior' xmlns:x=''/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x=''/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x=''/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
29  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x=''/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
33  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
38  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
39  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
41<?rfc toc="yes" ?>
42<?rfc symrefs="yes" ?>
43<?rfc sortrefs="yes" ?>
44<?rfc compact="yes"?>
45<?rfc subcompact="no" ?>
46<?rfc linkmailto="no" ?>
47<?rfc editing="no" ?>
48<?rfc comments="yes"?>
49<?rfc inline="yes"?>
50<?rfc rfcedstyle="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
54     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x=''>
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
62    <address>
63      <postal>
64        <street>345 Park Ave</street>
65        <city>San Jose</city>
66        <region>CA</region>
67        <code>95110</code>
68        <country>USA</country>
69      </postal>
70      <email></email>
71      <uri></uri>
72    </address>
73  </author>
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email></email>
86      <uri></uri>
87    </address>
88  </author>
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email></email>
102    </address>
103  </author>
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email></email>
116    </address>
117  </author>
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email></email>
130      <uri></uri>
131    </address>
132  </author>
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email></email>
144    </address>
145  </author>
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email></email>
160      <uri></uri>
161    </address>
162  </author>
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email></email>
176      <uri></uri>
177    </address>
178  </author>
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email></email>
191      <uri></uri>
192    </address>
193  </author>
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list ( The current issues list is
217    at <eref target=""/>
218    and related documents (including fancy diffs) can be found at
219    <eref target=""/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.12"/>.
223  </t>
227<section title="Introduction" anchor="introduction">
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
238   between HTTP and MIME messages).
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
252   HTTP is also designed for use as an intermediation protocol for translating
253   communication to and from non-HTTP information systems.
254   HTTP proxies and gateways can provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions ought to be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients might act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1" and obsoleting
274   <xref target="RFC2616"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP, defines the "http" and "https" URI schemes,
277   describes overall network operation and connection management,
278   and defines HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
285<section title="Requirements" anchor="intro.requirements">
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
292   An implementation is not compliant if it fails to satisfy one or more
293   of the "MUST" or "REQUIRED" level requirements for the protocols it
294   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
295   level and all the "SHOULD" level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the "MUST"
297   level requirements but not all the "SHOULD" level requirements for its
298   protocols is said to be "conditionally compliant".
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
342   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
343   "obsolete" grammar rules that appear for historical reasons.
346<section title="ABNF Extension: #rule" anchor="notation.abnf">
348  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
349  improve readability.
352  A construct "#" is defined, similar to "*", for defining comma-delimited
353  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
354  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
355  comma (",") and optional whitespace (OWS,
356  <xref target="basic.rules"/>).   
359  Thus,
360</preamble><artwork type="example">
361  1#element =&gt; element *( OWS "," OWS element )
364  and:
365</preamble><artwork type="example">
366  #element =&gt; [ 1#element ]
369  and for n &gt;= 1 and m &gt; 1:
370</preamble><artwork type="example">
371  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
374  For compatibility with legacy list rules, recipients &SHOULD; accept empty
375  list elements. In other words, consumers would follow the list productions:
377<figure><artwork type="example">
378  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
380  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
383  Note that empty elements do not contribute to the count of elements present,
384  though.
387  For example, given these ABNF productions:
389<figure><artwork type="example">
390  example-list      = 1#example-list-elmt
391  example-list-elmt = token ; see <xref target="basic.rules"/>
394  Then these are valid values for example-list (not including the double
395  quotes, which are present for delimitation only):
397<figure><artwork type="example">
398  "foo,bar"
399  " foo ,bar,"
400  "  foo , ,bar,charlie   "
401  "foo ,bar,   charlie "
404  But these values would be invalid, as at least one non-empty element is
405  required:
407<figure><artwork type="example">
408  ""
409  ","
410  ",   ,"
413  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
414  expanded as explained above.
418<section title="Basic Rules" anchor="basic.rules">
419<t anchor="rule.CRLF">
420  <x:anchor-alias value="CRLF"/>
421   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
422   protocol elements other than the message-body
423   (see <xref target="tolerant.applications"/> for tolerant applications).
425<t anchor="rule.LWS">
426   This specification uses three rules to denote the use of linear
427   whitespace: OWS (optional whitespace), RWS (required whitespace), and
428   BWS ("bad" whitespace).
431   The OWS rule is used where zero or more linear whitespace characters might
432   appear. OWS &SHOULD; either not be produced or be produced as a single SP
433   character. Multiple OWS characters that occur within field-content &SHOULD;
434   be replaced with a single SP before interpreting the field value or
435   forwarding the message downstream.
438   RWS is used when at least one linear whitespace character is required to
439   separate field tokens. RWS &SHOULD; be produced as a single SP character.
440   Multiple RWS characters that occur within field-content &SHOULD; be
441   replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
445   BWS is used where the grammar allows optional whitespace for historical
446   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
447   recipients &MUST; accept such bad optional whitespace and remove it before
448   interpreting the field value or forwarding the message downstream.
450<t anchor="rule.whitespace">
451  <x:anchor-alias value="BWS"/>
452  <x:anchor-alias value="OWS"/>
453  <x:anchor-alias value="RWS"/>
454  <x:anchor-alias value="obs-fold"/>
456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
457  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "optional" whitespace
459  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "required" whitespace
461  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
462                 ; "bad" whitespace
463  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
464                 ; see <xref target="header.fields"/>
466<t anchor="rule.token.separators">
467  <x:anchor-alias value="tchar"/>
468  <x:anchor-alias value="token"/>
469  <x:anchor-alias value="special"/>
470  <x:anchor-alias value="word"/>
471   Many HTTP/1.1 header field values consist of words (token or quoted-string)
472   separated by whitespace or special characters. These special characters
473   &MUST; be in a quoted string to be used within a parameter value (as defined
474   in <xref target="transfer.codings"/>).
476<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
477  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
479  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
481  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
482 -->
483  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
484                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
485                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
486                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
488  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
489                 / ";" / ":" / "\" / DQUOTE / "/" / "["
490                 / "]" / "?" / "=" / "{" / "}"
492<t anchor="rule.quoted-string">
493  <x:anchor-alias value="quoted-string"/>
494  <x:anchor-alias value="qdtext"/>
495  <x:anchor-alias value="obs-text"/>
496   A string of text is parsed as a single word if it is quoted using
497   double-quote marks.
499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
500  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
501  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
502                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
503  <x:ref>obs-text</x:ref>       = %x80-FF
505<t anchor="rule.quoted-pair">
506  <x:anchor-alias value="quoted-pair"/>
507   The backslash character ("\") can be used as a single-character
508   quoting mechanism within quoted-string constructs:
510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
511  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
514   Producers &SHOULD-NOT; escape characters that do not require escaping
515   (i.e., other than DQUOTE and the backslash character).
519<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
520  <x:anchor-alias value="request-header"/>
521  <x:anchor-alias value="response-header"/>
522  <x:anchor-alias value="Cache-Control"/>
523  <x:anchor-alias value="Pragma"/>
524  <x:anchor-alias value="Warning"/>
525  <x:anchor-alias value="MIME-Version"/>
527  The ABNF rules below are defined in other parts:
529<figure><!-- Part2--><artwork type="abnf2616">
530  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
531  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
533<figure><!-- Part3--><artwork type="abnf2616">
534  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&gt;
536<figure><!-- Part6--><artwork type="abnf2616">
537  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
538  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
539  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
546<section title="HTTP-related architecture" anchor="architecture">
548   HTTP was created for the World Wide Web architecture
549   and has evolved over time to support the scalability needs of a worldwide
550   hypertext system. Much of that architecture is reflected in the terminology
551   and syntax productions used to define HTTP.
554<section title="Client/Server Messaging" anchor="operation">
555<iref primary="true" item="client"/>
556<iref primary="true" item="server"/>
557<iref primary="true" item="connection"/>
559   HTTP is a stateless request/response protocol that operates by exchanging
560   messages across a reliable transport or session-layer connection. An HTTP
561   "client" is a program that establishes a connection to a server for the
562   purpose of sending one or more HTTP requests.  An HTTP "server" is a
563   program that accepts connections in order to service HTTP requests by
564   sending HTTP responses.
566<iref primary="true" item="user agent"/>
567<iref primary="true" item="origin server"/>
568<iref primary="true" item="browser"/>
569<iref primary="true" item="spider"/>
571   Note that the terms client and server refer only to the roles that
572   these programs perform for a particular connection.  The same program
573   might act as a client on some connections and a server on others.  We use
574   the term "user agent" to refer to the program that initiates a request,
575   such as a WWW browser, editor, or spider (web-traversing robot), and
576   the term "origin server" to refer to the program that can originate
577   authoritative responses to a request.  For general requirements, we use
578   the term "sender" to refer to whichever component sent a given message
579   and the term "recipient" to refer to any component that receives the
580   message.
583   Most HTTP communication consists of a retrieval request (GET) for
584   a representation of some resource identified by a URI.  In the
585   simplest case, this might be accomplished via a single bidirectional
586   connection (===) between the user agent (UA) and the origin server (O).
588<figure><artwork type="drawing">
589         request   &gt;
590    UA ======================================= O
591                                &lt;   response
593<iref primary="true" item="message"/>
594<iref primary="true" item="request"/>
595<iref primary="true" item="response"/>
597   A client sends an HTTP request to the server in the form of a request
598   message (<xref target="request"/>), beginning with a method, URI, and
599   protocol version, followed by MIME-like header fields containing
600   request modifiers, client information, and payload metadata, an empty
601   line to indicate the end of the header section, and finally the payload
602   body (if any).
605   A server responds to the client's request by sending an HTTP response
606   message (<xref target="response"/>), beginning with a status line that
607   includes the protocol version, a success or error code, and textual
608   reason phrase, followed by MIME-like header fields containing server
609   information, resource metadata, and payload metadata, an empty line to
610   indicate the end of the header section, and finally the payload body (if any).
613   The following example illustrates a typical message exchange for a
614   GET request on the URI "":
617client request:
618</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
619GET /hello.txt HTTP/1.1
620User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
622Accept: */*
626server response:
627</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
628HTTP/1.1 200 OK
629Date: Mon, 27 Jul 2009 12:28:53 GMT
630Server: Apache
631Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
632ETag: "34aa387-d-1568eb00"
633Accept-Ranges: bytes
634Content-Length: <x:length-of target="exbody"/>
635Vary: Accept-Encoding
636Content-Type: text/plain
638<x:span anchor="exbody">Hello World!
642<section title="Intermediaries" anchor="intermediaries">
643<iref primary="true" item="intermediary"/>
645   A more complicated situation occurs when one or more intermediaries
646   are present in the request/response chain. There are three common
647   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
648   a single intermediary might act as an origin server, proxy, gateway,
649   or tunnel, switching behavior based on the nature of each request.
651<figure><artwork type="drawing">
652         &gt;             &gt;             &gt;             &gt;
653    UA =========== A =========== B =========== C =========== O
654               &lt;             &lt;             &lt;             &lt;
657   The figure above shows three intermediaries (A, B, and C) between the
658   user agent and origin server. A request or response message that
659   travels the whole chain will pass through four separate connections.
660   Some HTTP communication options
661   might apply only to the connection with the nearest, non-tunnel
662   neighbor, only to the end-points of the chain, or to all connections
663   along the chain. Although the diagram is linear, each participant might
664   be engaged in multiple, simultaneous communications. For example, B
665   might be receiving requests from many clients other than A, and/or
666   forwarding requests to servers other than C, at the same time that it
667   is handling A's request.
670<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
671<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
672   We use the terms "upstream" and "downstream" to describe various
673   requirements in relation to the directional flow of a message:
674   all messages flow from upstream to downstream.
675   Likewise, we use the terms "inbound" and "outbound" to refer to
676   directions in relation to the request path: "inbound" means toward
677   the origin server and "outbound" means toward the user agent.
679<t><iref primary="true" item="proxy"/>
680   A "proxy" is a message forwarding agent that is selected by the
681   client, usually via local configuration rules, to receive requests
682   for some type(s) of absolute URI and attempt to satisfy those
683   requests via translation through the HTTP interface.  Some translations
684   are minimal, such as for proxy requests for "http" URIs, whereas
685   other requests might require translation to and from entirely different
686   application-layer protocols. Proxies are often used to group an
687   organization's HTTP requests through a common intermediary for the
688   sake of security, annotation services, or shared caching.
691<iref primary="true" item="transforming proxy"/>
692<iref primary="true" item="non-transforming proxy"/>
693   An HTTP-to-HTTP proxy is called a "transforming proxy" if it designed
694   or configured to modify request or response messages in a semantically
695   meaningful way (i.e., modifications, beyond those required by normal
696   HTTP processing, that change the message in a way that would be
697   significant to the original sender or potentially significant to
698   downstream recipients).  For example, a transforming proxy might be
699   acting as a shared annotation server (modifying responses to include
700   references to a local annotation database), a malware filter, a
701   format transcoder, or an intranet-to-Internet privacy filter.  Such
702   transformations are presumed to be desired by the client (or client
703   organization) that selected the proxy and are beyond the scope of
704   this specification.  However, when a proxy is not intended to transform
705   a given message, we use the term "non-transforming proxy" to target
706   requirements that preserve HTTP message semantics.
708<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
709   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
710   as a layer above some other server(s) and translates the received
711   requests to the underlying server's protocol.  Gateways are often
712   used for load balancing or partitioning HTTP services across
713   multiple machines.
714   Unlike a proxy, a gateway receives requests as if it were the
715   origin server for the target resource; the requesting client
716   will not be aware that it is communicating with a gateway.
717   A gateway communicates with the client as if the gateway is the
718   origin server and thus is subject to all of the requirements on
719   origin servers for that connection.  A gateway communicates
720   with inbound servers using any protocol it desires, including
721   private extensions to HTTP that are outside the scope of this
722   specification.
724<t><iref primary="true" item="tunnel"/>
725   A "tunnel" acts as a blind relay between two connections
726   without changing the messages. Once active, a tunnel is not
727   considered a party to the HTTP communication, though the tunnel might
728   have been initiated by an HTTP request. A tunnel ceases to exist when
729   both ends of the relayed connection are closed. Tunnels are used to
730   extend a virtual connection through an intermediary, such as when
731   transport-layer security is used to establish private communication
732   through a shared firewall proxy.
734<t><iref primary="true" item="intercept"/><iref primary="true" item="transparent proxy"/>
735   In addition, there may exist network intermediaries that are not
736   considered part of the HTTP communication but nevertheless act as
737   filters or redirecting agents (usually violating HTTP semantics,
738   causing security problems, and otherwise making a mess of things).
739   These network intermediaries are often referred to as "intercepts"
740   or "transparent proxies", and are commonly found on public network
741   access points as a means of enforcing account subscription prior to
742   allowing use of non-local Internet services.
746<section title="Caches" anchor="caches">
747<iref primary="true" item="cache"/>
749   A "cache" is a local store of previous response messages and the
750   subsystem that controls its message storage, retrieval, and deletion.
751   A cache stores cacheable responses in order to reduce the response
752   time and network bandwidth consumption on future, equivalent
753   requests. Any client or server &MAY; employ a cache, though a cache
754   cannot be used by a server while it is acting as a tunnel.
757   The effect of a cache is that the request/response chain is shortened
758   if one of the participants along the chain has a cached response
759   applicable to that request. The following illustrates the resulting
760   chain if B has a cached copy of an earlier response from O (via C)
761   for a request which has not been cached by UA or A.
763<figure><artwork type="drawing">
764            &gt;             &gt;
765       UA =========== A =========== B - - - - - - C - - - - - - O
766                  &lt;             &lt;
768<t><iref primary="true" item="cacheable"/>
769   A response is "cacheable" if a cache is allowed to store a copy of
770   the response message for use in answering subsequent requests.
771   Even when a response is cacheable, there might be additional
772   constraints placed by the client or by the origin server on when
773   that cached response can be used for a particular request. HTTP
774   requirements for cache behavior and cacheable responses are
775   defined in &caching-overview;. 
778   There are a wide variety of architectures and configurations
779   of caches and proxies deployed across the World Wide Web and
780   inside large organizations. These systems include national hierarchies
781   of proxy caches to save transoceanic bandwidth, systems that
782   broadcast or multicast cache entries, organizations that distribute
783   subsets of cached data via optical media, and so on.
787<section title="Transport Independence" anchor="transport-independence">
789  HTTP systems are used in a wide variety of environments, from
790  corporate intranets with high-bandwidth links to long-distance
791  communication over low-power radio links and intermittent connectivity.
794   HTTP communication usually takes place over TCP/IP connections. The
795   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
796   not preclude HTTP from being implemented on top of any other protocol
797   on the Internet, or on other networks. HTTP only presumes a reliable
798   transport; any protocol that provides such guarantees can be used;
799   the mapping of the HTTP/1.1 request and response structures onto the
800   transport data units of the protocol in question is outside the scope
801   of this specification.
804   In HTTP/1.0, most implementations used a new connection for each
805   request/response exchange. In HTTP/1.1, a connection might be used for
806   one or more request/response exchanges, although connections might be
807   closed for a variety of reasons (see <xref target="persistent.connections"/>).
811<section title="HTTP Version" anchor="http.version">
812  <x:anchor-alias value="HTTP-Version"/>
813  <x:anchor-alias value="HTTP-Prot-Name"/>
815   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
816   of the protocol. The protocol versioning policy is intended to allow
817   the sender to indicate the format of a message and its capacity for
818   understanding further HTTP communication, rather than the features
819   obtained via that communication. No change is made to the version
820   number for the addition of message components which do not affect
821   communication behavior or which only add to extensible field values.
822   The &lt;minor&gt; number is incremented when the changes made to the
823   protocol add features which do not change the general message parsing
824   algorithm, but which might add to the message semantics and imply
825   additional capabilities of the sender. The &lt;major&gt; number is
826   incremented when the format of a message within the protocol is
827   changed. See <xref target="RFC2145"/> for a fuller explanation.
830   The version of an HTTP message is indicated by an HTTP-Version field
831   in the first line of the message. HTTP-Version is case-sensitive.
833<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
834  <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>
835  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
838   Note that the major and minor numbers &MUST; be treated as separate
839   integers and that each &MAY; be incremented higher than a single digit.
840   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
841   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
842   &MUST-NOT; be sent.
845   An application that sends a request or response message that includes
846   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
847   with this specification. Applications that are at least conditionally
848   compliant with this specification &SHOULD; use an HTTP-Version of
849   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
850   not compatible with HTTP/1.0. For more details on when to send
851   specific HTTP-Version values, see <xref target="RFC2145"/>.
854   The HTTP version of an application is the highest HTTP version for
855   which the application is at least conditionally compliant.
858   Proxy and gateway applications need to be careful when forwarding
859   messages in protocol versions different from that of the application.
860   Since the protocol version indicates the protocol capability of the
861   sender, a proxy/gateway &MUST-NOT; send a message with a version
862   indicator which is greater than its actual version. If a higher
863   version request is received, the proxy/gateway &MUST; either downgrade
864   the request version, or respond with an error, or switch to tunnel
865   behavior.
868   Due to interoperability problems with HTTP/1.0 proxies discovered
869   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
870   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
871   they support. The proxy/gateway's response to that request &MUST; be in
872   the same major version as the request.
875  <t>
876    <x:h>Note:</x:h> Converting between versions of HTTP might involve modification
877    of header fields required or forbidden by the versions involved.
878  </t>
882<section title="Uniform Resource Identifiers" anchor="uri">
883<iref primary="true" item="resource"/>
885   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
886   throughout HTTP as the means for identifying resources. URI references
887   are used to target requests, indicate redirects, and define relationships.
888   HTTP does not limit what a resource might be; it merely defines an interface
889   that can be used to interact with a resource via HTTP. More information on
890   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
892  <x:anchor-alias value="URI-reference"/>
893  <x:anchor-alias value="absolute-URI"/>
894  <x:anchor-alias value="relative-part"/>
895  <x:anchor-alias value="authority"/>
896  <x:anchor-alias value="path-abempty"/>
897  <x:anchor-alias value="path-absolute"/>
898  <x:anchor-alias value="port"/>
899  <x:anchor-alias value="query"/>
900  <x:anchor-alias value="uri-host"/>
901  <x:anchor-alias value="partial-URI"/>
903   This specification adopts the definitions of "URI-reference",
904   "absolute-URI", "relative-part", "port", "host",
905   "path-abempty", "path-absolute", "query", and "authority" from
906   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
907   protocol elements that allow a relative URI without a fragment.
909<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"/>
910  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
911  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
912  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
913  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
914  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
915  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
916  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
917  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
918  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
920  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
923   Each protocol element in HTTP that allows a URI reference will indicate in
924   its ABNF production whether the element allows only a URI in absolute form
925   (absolute-URI), any relative reference (relative-ref), or some other subset
926   of the URI-reference grammar. Unless otherwise indicated, URI references
927   are parsed relative to the request target (the default base URI for both
928   the request and its corresponding response).
931<section title="http URI scheme" anchor="http.uri">
932  <x:anchor-alias value="http-URI"/>
933  <iref item="http URI scheme" primary="true"/>
934  <iref item="URI scheme" subitem="http" primary="true"/>
936   The "http" URI scheme is hereby defined for the purpose of minting
937   identifiers according to their association with the hierarchical
938   namespace governed by a potential HTTP origin server listening for
939   TCP connections on a given port.
940   The HTTP server is identified via the generic syntax's
941   <x:ref>authority</x:ref> component, which includes a host
942   identifier and optional TCP port, and the remainder of the URI is
943   considered to be identifying data corresponding to a resource for
944   which that server might provide an HTTP interface.
946<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
947  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
950   The host identifier within an <x:ref>authority</x:ref> component is
951   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
952   provided as an IP literal or IPv4 address, then the HTTP server is any
953   listener on the indicated TCP port at that IP address. If host is a
954   registered name, then that name is considered an indirect identifier
955   and the recipient might use a name resolution service, such as DNS,
956   to find the address of a listener for that host.
957   The host &MUST-NOT; be empty; if an "http" URI is received with an
958   empty host, then it &MUST; be rejected as invalid.
959   If the port subcomponent is empty or not given, then TCP port 80 is
960   assumed (the default reserved port for WWW services).
963   Regardless of the form of host identifier, access to that host is not
964   implied by the mere presence of its name or address. The host might or might
965   not exist and, even when it does exist, might or might not be running an
966   HTTP server or listening to the indicated port. The "http" URI scheme
967   makes use of the delegated nature of Internet names and addresses to
968   establish a naming authority (whatever entity has the ability to place
969   an HTTP server at that Internet name or address) and allows that
970   authority to determine which names are valid and how they might be used.
973   When an "http" URI is used within a context that calls for access to the
974   indicated resource, a client &MAY; attempt access by resolving
975   the host to an IP address, establishing a TCP connection to that address
976   on the indicated port, and sending an HTTP request message to the server
977   containing the URI's identifying data as described in <xref target="request"/>.
978   If the server responds to that request with a non-interim HTTP response
979   message, as described in <xref target="response"/>, then that response
980   is considered an authoritative answer to the client's request.
983   Although HTTP is independent of the transport protocol, the "http"
984   scheme is specific to TCP-based services because the name delegation
985   process depends on TCP for establishing authority.
986   An HTTP service based on some other underlying connection protocol
987   would presumably be identified using a different URI scheme, just as
988   the "https" scheme (below) is used for servers that require an SSL/TLS
989   transport layer on a connection. Other protocols might also be used to
990   provide access to "http" identified resources &mdash; it is only the
991   authoritative interface used for mapping the namespace that is
992   specific to TCP.
995   The URI generic syntax for authority also includes a deprecated
996   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
997   for including user authentication information in the URI.  The userinfo
998   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
999   URI.  URI reference recipients &SHOULD; parse for the existence of
1000   userinfo and treat its presence as an error, likely indicating that
1001   the deprecated subcomponent is being used to obscure the authority
1002   for the sake of phishing attacks.
1006<section title="https URI scheme" anchor="https.uri">
1007   <x:anchor-alias value="https-URI"/>
1008   <iref item="https URI scheme"/>
1009   <iref item="URI scheme" subitem="https"/>
1011   The "https" URI scheme is hereby defined for the purpose of minting
1012   identifiers according to their association with the hierarchical
1013   namespace governed by a potential HTTP origin server listening for
1014   SSL/TLS-secured connections on a given TCP port.
1017   All of the requirements listed above for the "http" scheme are also
1018   requirements for the "https" scheme, except that a default TCP port
1019   of 443 is assumed if the port subcomponent is empty or not given,
1020   and the TCP connection &MUST; be secured for privacy through the
1021   use of strong encryption prior to sending the first HTTP request.
1023<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1024  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1027   Unlike the "http" scheme, responses to "https" identified requests
1028   are never "public" and thus are ineligible for shared caching.
1029   Their default is "private" and might be further constrained via use
1030   of the Cache-Control header field.
1033   Resources made available via the "https" scheme have no shared
1034   identity with the "http" scheme even if their resource identifiers
1035   only differ by the single "s" in the scheme name.  They are
1036   different services governed by different authorities.  However,
1037   some extensions to HTTP that apply to entire host domains, such
1038   as the Cookie protocol, do allow one service to effect communication
1039   with the other services based on host domain matching.
1042   The process for authoritative access to an "https" identified
1043   resource is defined in <xref target="RFC2818"/>.
1047<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1049   Since the "http" and "https" schemes conform to the URI generic syntax,
1050   such URIs are normalized and compared according to the algorithm defined
1051   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1052   described above for each scheme.
1055   If the port is equal to the default port for a scheme, the normal
1056   form is to elide the port subcomponent. Likewise, an empty path
1057   component is equivalent to an absolute path of "/", so the normal
1058   form is to provide a path of "/" instead. The scheme and host
1059   are case-insensitive and normally provided in lowercase; all
1060   other components are compared in a case-sensitive manner.
1061   Characters other than those in the "reserved" set are equivalent
1062   to their percent-encoded octets (see <xref target="RFC3986"
1063   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1066   For example, the following three URIs are equivalent:
1068<figure><artwork type="example">
1074   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1075   If path-abempty is the empty string (i.e., there is no slash "/"
1076   path separator following the authority), then the "http" URI
1077   &MUST; be given as "/" when
1078   used as a request-target (<xref target="request-target"/>). If a proxy
1079   receives a host name which is not a fully qualified domain name, it
1080   &MAY; add its domain to the host name it received. If a proxy receives
1081   a fully qualified domain name, the proxy &MUST-NOT; change the host
1082   name.
1088<section title="HTTP Message" anchor="http.message">
1089<x:anchor-alias value="generic-message"/>
1090<x:anchor-alias value="message.types"/>
1091<x:anchor-alias value="HTTP-message"/>
1092<x:anchor-alias value="start-line"/>
1093<iref item="header section"/>
1094<iref item="headers"/>
1095<iref item="header field"/>
1097   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1098   characters in a format similar to the Internet Message Format
1099   <xref target="RFC5322"/>: zero or more header fields (collectively
1100   referred to as the "headers" or the "header section"), an empty line
1101   indicating the end of the header section, and an optional message-body.
1104   An HTTP message can either be a request from client to server or a
1105   response from server to client.  Syntactically, the two types of message
1106   differ only in the start-line, which is either a Request-Line (for requests)
1107   or a Status-Line (for responses), and in the algorithm for determining
1108   the length of the message-body (<xref target="message.body"/>).
1109   In theory, a client could receive requests and a server could receive
1110   responses, distinguishing them by their different start-line formats,
1111   but in practice servers are implemented to only expect a request
1112   (a response is interpreted as an unknown or invalid request method)
1113   and clients are implemented to only expect a response.
1115<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1116  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1117                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1118                    <x:ref>CRLF</x:ref>
1119                    [ <x:ref>message-body</x:ref> ]
1120  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1123   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1124   header field. The presence of whitespace might be an attempt to trick a
1125   noncompliant implementation of HTTP into ignoring that field or processing
1126   the next line as a new request, either of which might result in security
1127   issues when implementations within the request chain interpret the
1128   same message differently. HTTP/1.1 servers &MUST; reject such a message
1129   with a 400 (Bad Request) response.
1132<section title="Message Parsing Robustness" anchor="message.robustness">
1134   In the interest of robustness, servers &SHOULD; ignore at least one
1135   empty line received where a Request-Line is expected. In other words, if
1136   the server is reading the protocol stream at the beginning of a
1137   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1140   Some old HTTP/1.0 client implementations generate an extra CRLF
1141   after a POST request as a lame workaround for some early server
1142   applications that failed to read message-body content that was
1143   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1144   preface or follow a request with an extra CRLF.  If terminating
1145   the request message-body with a line-ending is desired, then the
1146   client &MUST; include the terminating CRLF octets as part of the
1147   message-body length.
1150   The normal procedure for parsing an HTTP message is to read the
1151   start-line into a structure, read each header field into a hash
1152   table by field name until the empty line, and then use the parsed
1153   data to determine if a message-body is expected.  If a message-body
1154   has been indicated, then it is read as a stream until an amount
1155   of octets equal to the message-body length is read or the connection
1156   is closed.  Care must be taken to parse an HTTP message as a sequence
1157   of octets in an encoding that is a superset of US-ASCII.  Attempting
1158   to parse HTTP as a stream of Unicode characters in a character encoding
1159   like UTF-16 might introduce security flaws due to the differing ways
1160   that such parsers interpret invalid characters.
1163   HTTP allows the set of defined header fields to be extended without
1164   changing the protocol version (see <xref target="header.field.registration"/>).
1165   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1166   proxy is specifically configured to block or otherwise transform such
1167   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1171<section title="Header Fields" anchor="header.fields">
1172  <x:anchor-alias value="header-field"/>
1173  <x:anchor-alias value="field-content"/>
1174  <x:anchor-alias value="field-name"/>
1175  <x:anchor-alias value="field-value"/>
1176  <x:anchor-alias value="OWS"/>
1178   Each HTTP header field consists of a case-insensitive field name
1179   followed by a colon (":"), optional whitespace, and the field value.
1181<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"/>
1182  <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>
1183  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1184  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1185  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1188   No whitespace is allowed between the header field name and colon. For
1189   security reasons, any request message received containing such whitespace
1190   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1191   &MUST; remove any such whitespace from a response message before
1192   forwarding the message downstream.
1195   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1196   preferred. The field value does not include any leading or trailing white
1197   space: OWS occurring before the first non-whitespace character of the
1198   field value or after the last non-whitespace character of the field value
1199   is ignored and &SHOULD; be removed before further processing (as this does
1200   not change the meaning of the header field).
1203   The order in which header fields with differing field names are
1204   received is not significant. However, it is "good practice" to send
1205   header fields that contain control data first, such as Host on
1206   requests and Date on responses, so that implementations can decide
1207   when not to handle a message as early as possible.  A server &MUST;
1208   wait until the entire header section is received before interpreting
1209   a request message, since later header fields might include conditionals,
1210   authentication credentials, or deliberately misleading duplicate
1211   header fields that would impact request processing.
1214   Multiple header fields with the same field name &MUST-NOT; be
1215   sent in a message unless the entire field value for that
1216   header field is defined as a comma-separated list [i.e., #(values)].
1217   Multiple header fields with the same field name can be combined into
1218   one "field-name: field-value" pair, without changing the semantics of the
1219   message, by appending each subsequent field value to the combined
1220   field value in order, separated by a comma. The order in which
1221   header fields with the same field name are received is therefore
1222   significant to the interpretation of the combined field value;
1223   a proxy &MUST-NOT; change the order of these field values when
1224   forwarding a message.
1227  <t>
1228   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1229   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1230   can occur multiple times, but does not use the list syntax, and thus cannot
1231   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1232   for details.) Also note that the Set-Cookie2 header field specified in
1233   <xref target="RFC2965"/> does not share this problem.
1234  </t>
1237   Historically, HTTP header field values could be extended over multiple
1238   lines by preceding each extra line with at least one space or horizontal
1239   tab character (line folding). This specification deprecates such line
1240   folding except within the message/http media type
1241   (<xref target=""/>).
1242   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1243   (i.e., that contain any field-content that matches the obs-fold rule) unless
1244   the message is intended for packaging within the message/http media type.
1245   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1246   obs-fold whitespace with a single SP prior to interpreting the field value
1247   or forwarding the message downstream.
1250   Historically, HTTP has allowed field content with text in the ISO-8859-1
1251   <xref target="ISO-8859-1"/> character encoding and supported other
1252   character sets only through use of <xref target="RFC2047"/> encoding.
1253   In practice, most HTTP header field values use only a subset of the
1254   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1255   header fields &SHOULD; limit their field values to US-ASCII characters.
1256   Recipients &SHOULD; treat other (obs-text) octets in field content as
1257   opaque data.
1259<t anchor="rule.comment">
1260  <x:anchor-alias value="comment"/>
1261  <x:anchor-alias value="ctext"/>
1262   Comments can be included in some HTTP header fields by surrounding
1263   the comment text with parentheses. Comments are only allowed in
1264   fields containing "comment" as part of their field value definition.
1266<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1267  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1268  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1269                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1271<t anchor="rule.quoted-cpair">
1272  <x:anchor-alias value="quoted-cpair"/>
1273   The backslash character ("\") can be used as a single-character
1274   quoting mechanism within comment constructs:
1276<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1277  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1280   Producers &SHOULD-NOT; escape characters that do not require escaping
1281   (i.e., other than the backslash character "\" and the parentheses "(" and
1282   ")").
1286<section title="Message Body" anchor="message.body">
1287  <x:anchor-alias value="message-body"/>
1289   The message-body (if any) of an HTTP message is used to carry the
1290   payload body associated with the request or response.
1292<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1293  <x:ref>message-body</x:ref> = *OCTET
1296   The message-body differs from the payload body only when a transfer-coding
1297   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1298   applied to a payload in order to form the message-body, the
1299   Transfer-Encoding header field &MUST; contain the list of
1300   transfer-codings applied. Transfer-Encoding is a property of the message,
1301   not of the payload, and thus &MAY; be added or removed by any implementation
1302   along the request/response chain under the constraints found in
1303   <xref target="transfer.codings"/>.
1306   The rules for when a message-body is allowed in a message differ for
1307   requests and responses.
1310   The presence of a message-body in a request is signaled by the
1311   inclusion of a Content-Length or Transfer-Encoding header field in
1312   the request's header fields, even if the request method does not
1313   define any use for a message-body.  This allows the request
1314   message framing algorithm to be independent of method semantics.
1317   For response messages, whether or not a message-body is included with
1318   a message is dependent on both the request method and the response
1319   status code (<xref target="status.code.and.reason.phrase"/>).
1320   Responses to the HEAD request method never include a message-body
1321   because the associated response header fields (e.g., Transfer-Encoding,
1322   Content-Length, etc.) only indicate what their values would have been
1323   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1324   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1325   All other responses do include a message-body, although the body
1326   &MAY; be of zero length.
1329   The length of the message-body is determined by one of the following
1330   (in order of precedence):
1333  <list style="numbers">
1334    <x:lt><t>
1335     Any response to a HEAD request and any response with a status
1336     code of 100-199, 204, or 304 is always terminated by the first
1337     empty line after the header fields, regardless of the header
1338     fields present in the message, and thus cannot contain a message-body.
1339    </t></x:lt>
1340    <x:lt><t>
1341     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1342     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1343     is the final encoding, the message-body length is determined by reading
1344     and decoding the chunked data until the transfer-coding indicates the
1345     data is complete.
1346    </t>
1347    <t>
1348     If a Transfer-Encoding header field is present in a response and the
1349     "chunked" transfer-coding is not the final encoding, the message-body
1350     length is determined by reading the connection until it is closed by
1351     the server.
1352     If a Transfer-Encoding header field is present in a request and the
1353     "chunked" transfer-coding is not the final encoding, the message-body
1354     length cannot be determined reliably; the server &MUST; respond with
1355     the 400 (Bad Request) status code and then close the connection.
1356    </t>
1357    <t>
1358     If a message is received with both a Transfer-Encoding header field and a
1359     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1360     Such a message might indicate an attempt to perform request or response
1361     smuggling (bypass of security-related checks on message routing or content)
1362     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1363     be removed, prior to forwarding the message downstream, or replaced with
1364     the real message-body length after the transfer-coding is decoded.
1365    </t></x:lt>
1366    <x:lt><t>
1367     If a message is received without Transfer-Encoding and with either
1368     multiple Content-Length header fields or a single Content-Length header
1369     field with an invalid value, then the message framing is invalid and
1370     &MUST; be treated as an error to prevent request or response smuggling.
1371     If this is a request message, the server &MUST; respond with
1372     a 400 (Bad Request) status code and then close the connection.
1373     If this is a response message received by a proxy or gateway, the proxy
1374     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1375     status code as its downstream response, and then close the connection.
1376     If this is a response message received by a user-agent, it &SHOULD; be
1377     treated as an error by discarding the message and closing the connection.
1378    </t></x:lt>
1379    <x:lt><t>
1380     If a valid Content-Length header field (<xref target="header.content-length"/>)
1381     is present without Transfer-Encoding, its decimal value defines the
1382     message-body length in octets.  If the actual number of octets sent in
1383     the message is less than the indicated Content-Length, the recipient
1384     &MUST; consider the message to be incomplete and treat the connection
1385     as no longer usable.
1386     If the actual number of octets sent in the message is more than the indicated
1387     Content-Length, the recipient &MUST; only process the message-body up to the
1388     field value's number of octets; the remainder of the message &MUST; either
1389     be discarded or treated as the next message in a pipeline.  For the sake of
1390     robustness, a user-agent &MAY; attempt to detect and correct such an error
1391     in message framing if it is parsing the response to the last request on
1392     on a connection and the connection has been closed by the server.
1393    </t></x:lt>
1394    <x:lt><t>
1395     If this is a request message and none of the above are true, then the
1396     message-body length is zero (no message-body is present).
1397    </t></x:lt>
1398    <x:lt><t>
1399     Otherwise, this is a response message without a declared message-body
1400     length, so the message-body length is determined by the number of octets
1401     received prior to the server closing the connection.
1402    </t></x:lt>
1403  </list>
1406   Since there is no way to distinguish a successfully completed,
1407   close-delimited message from a partially-received message interrupted
1408   by network failure, implementations &SHOULD; use encoding or
1409   length-delimited messages whenever possible.  The close-delimiting
1410   feature exists primarily for backwards compatibility with HTTP/1.0.
1413   A server &MAY; reject a request that contains a message-body but
1414   not a Content-Length by responding with 411 (Length Required).
1417   Unless a transfer-coding other than "chunked" has been applied,
1418   a client that sends a request containing a message-body &SHOULD;
1419   use a valid Content-Length header field if the message-body length
1420   is known in advance, rather than the "chunked" encoding, since some
1421   existing services respond to "chunked" with a 411 (Length Required)
1422   status code even though they understand the chunked encoding.  This
1423   is typically because such services are implemented via a gateway that
1424   requires a content-length in advance of being called and the server
1425   is unable or unwilling to buffer the entire request before processing.
1428   A client that sends a request containing a message-body &MUST; include a
1429   valid Content-Length header field if it does not know the server will
1430   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1431   of specific user configuration or by remembering the version of a prior
1432   received response.
1435   Request messages that are prematurely terminated, possibly due to a
1436   cancelled connection or a server-imposed time-out exception, &MUST;
1437   result in closure of the connection; sending an HTTP/1.1 error response
1438   prior to closing the connection is &OPTIONAL;.
1439   Response messages that are prematurely terminated, usually by closure
1440   of the connection prior to receiving the expected number of octets or by
1441   failure to decode a transfer-encoded message-body, &MUST; be recorded
1442   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1443   message-body as if it were complete (i.e., some indication must be given
1444   to the user that an error occurred).  Cache requirements for incomplete
1445   responses are defined in &cache-incomplete;.
1448   A server &MUST; read the entire request message-body or close
1449   the connection after sending its response, since otherwise the
1450   remaining data on a persistent connection would be misinterpreted
1451   as the next request.  Likewise,
1452   a client &MUST; read the entire response message-body if it intends
1453   to reuse the same connection for a subsequent request.  Pipelining
1454   multiple requests on a connection is described in <xref target="pipelining"/>.
1458<section title="General Header Fields" anchor="general.header.fields">
1459  <x:anchor-alias value="general-header"/>
1461   There are a few header fields which have general applicability for
1462   both request and response messages, but which do not apply to the
1463   payload being transferred. These header fields apply only to the
1464   message being transmitted.
1466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1467  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1468                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1469                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1470                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1471                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1472                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1473                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1474                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1475                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1476                 / <x:ref>MIME-Version</x:ref>             ; &header-mime-version;
1479   General-header field names can be extended reliably only in
1480   combination with a change in the protocol version. However, new or
1481   experimental header fields might be given the semantics of general
1482   header fields if all parties in the communication recognize them to
1483   be general-header fields.
1488<section title="Request" anchor="request">
1489  <x:anchor-alias value="Request"/>
1491   A request message from a client to a server includes, within the
1492   first line of that message, the method to be applied to the resource,
1493   the identifier of the resource, and the protocol version in use.
1495<!--                 Host                      ; should be moved here eventually -->
1496<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1497  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1498                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1499                  <x:ref>CRLF</x:ref>
1500                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1503<section title="Request-Line" anchor="request-line">
1504  <x:anchor-alias value="Request-Line"/>
1506   The Request-Line begins with a method token, followed by the
1507   request-target and the protocol version, and ending with CRLF. The
1508   elements are separated by SP characters. No CR or LF is allowed
1509   except in the final CRLF sequence.
1511<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1512  <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>
1515<section title="Method" anchor="method">
1516  <x:anchor-alias value="Method"/>
1518   The Method  token indicates the method to be performed on the
1519   resource identified by the request-target. The method is case-sensitive.
1521<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1522  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1526<section title="request-target" anchor="request-target">
1527  <x:anchor-alias value="request-target"/>
1529   The request-target identifies the resource upon which to apply the request.
1531<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1532  <x:ref>request-target</x:ref> = "*"
1533                 / <x:ref>absolute-URI</x:ref>
1534                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1535                 / <x:ref>authority</x:ref>
1538   The four options for request-target are dependent on the nature of the
1539   request.
1541<t><iref item="asterisk form (of request-target)"/>
1542   The asterisk "*" ("asterisk form") means that the request does not apply to a
1543   particular resource, but to the server itself. This is only allowed for the
1544   OPTIONS method. Thus, the only valid example is
1546<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1547OPTIONS * HTTP/1.1
1549<t><iref item="absolute-URI form (of request-target)"/>
1550   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1551   proxy. The proxy is requested to forward the request or service it
1552   from a valid cache, and return the response. Note that the proxy &MAY;
1553   forward the request on to another proxy or directly to the server
1554   specified by the absolute-URI. In order to avoid request loops, a
1555   proxy &MUST; be able to recognize all of its server names, including
1556   any aliases, local variations, and the numeric IP address. An example
1557   Request-Line would be:
1559<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1560GET HTTP/1.1
1563   To allow for transition to absolute-URIs in all requests in future
1564   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1565   form in requests, even though HTTP/1.1 clients will only generate
1566   them in requests to proxies.
1568<t><iref item="authority form (of request-target)"/>
1569   The "authority form" is only used by the CONNECT method (&CONNECT;).
1571<t><iref item="path-absolute form (of request-target)"/>
1572   The most common form of request-target is that used to identify a
1573   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1574   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1575   the request-target, and the network location of the URI (authority) &MUST;
1576   be transmitted in a Host header field. For example, a client wishing
1577   to retrieve the resource above directly from the origin server would
1578   create a TCP connection to port 80 of the host "" and send
1579   the lines:
1581<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1582GET /pub/WWW/TheProject.html HTTP/1.1
1586   followed by the remainder of the Request. Note that the absolute path
1587   cannot be empty; if none is present in the original URI, it &MUST; be
1588   given as "/" (the server root).
1591   If a proxy receives a request without any path in the request-target and
1592   the method specified is capable of supporting the asterisk form of
1593   request-target, then the last proxy on the request chain &MUST; forward the
1594   request with "*" as the final request-target.
1597   For example, the request
1598</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1602  would be forwarded by the proxy as
1603</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1604OPTIONS * HTTP/1.1
1608   after connecting to port 8001 of host "".
1612   The request-target is transmitted in the format specified in
1613   <xref target="http.uri"/>. If the request-target is percent-encoded
1614   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1615   &MUST; decode the request-target in order to
1616   properly interpret the request. Servers &SHOULD; respond to invalid
1617   request-targets with an appropriate status code.
1620   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1621   received request-target when forwarding it to the next inbound server,
1622   except as noted above to replace a null path-absolute with "/" or "*".
1625  <t>
1626    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1627    meaning of the request when the origin server is improperly using
1628    a non-reserved URI character for a reserved purpose.  Implementors
1629    need to be aware that some pre-HTTP/1.1 proxies have been known to
1630    rewrite the request-target.
1631  </t>
1634   HTTP does not place a pre-defined limit on the length of a request-target.
1635   A server &MUST; be prepared to receive URIs of unbounded length and
1636   respond with the 414 (URI Too Long) status code if the received
1637   request-target would be longer than the server wishes to handle
1638   (see &status-414;).
1641   Various ad-hoc limitations on request-target length are found in practice.
1642   It is &RECOMMENDED; that all HTTP senders and recipients support
1643   request-target lengths of 8000 or more octets.
1646  <t>
1647    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1648    are not part of the request-target and thus will not be transmitted
1649    in an HTTP request.
1650  </t>
1655<section title="The Resource Identified by a Request" anchor="">
1657   The exact resource identified by an Internet request is determined by
1658   examining both the request-target and the Host header field.
1661   An origin server that does not allow resources to differ by the
1662   requested host &MAY; ignore the Host header field value when
1663   determining the resource identified by an HTTP/1.1 request. (But see
1664   <xref target=""/>
1665   for other requirements on Host support in HTTP/1.1.)
1668   An origin server that does differentiate resources based on the host
1669   requested (sometimes referred to as virtual hosts or vanity host
1670   names) &MUST; use the following rules for determining the requested
1671   resource on an HTTP/1.1 request:
1672  <list style="numbers">
1673    <t>If request-target is an absolute-URI, the host is part of the
1674     request-target. Any Host header field value in the request &MUST; be
1675     ignored.</t>
1676    <t>If the request-target is not an absolute-URI, and the request includes
1677     a Host header field, the host is determined by the Host header
1678     field value.</t>
1679    <t>If the host as determined by rule 1 or 2 is not a valid host on
1680     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1681  </list>
1684   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1685   attempt to use heuristics (e.g., examination of the URI path for
1686   something unique to a particular host) in order to determine what
1687   exact resource is being requested.
1691<section title="Effective Request URI" anchor="effective.request.uri">
1692  <iref primary="true" item="effective request URI"/>
1693  <iref primary="true" item="target resource"/>
1695   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1696   for the target resource; instead, the URI needs to be inferred from the
1697   request-target, Host header field, and connection context. The result of
1698   this process is called the "effective request URI".  The "target resource"
1699   is the resource identified by the effective request URI.
1702   If the request-target is an absolute-URI, then the effective request URI is
1703   the request-target.
1706   If the request-target uses the path-absolute form or the asterisk form,
1707   and the Host header field is present, then the effective request URI is
1708   constructed by concatenating
1711  <list style="symbols">
1712    <t>
1713      the scheme name: "http" if the request was received over an insecure
1714      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1715      connection,
1716    </t>
1717    <t>
1718      the character sequence "://",
1719    </t>
1720    <t>
1721      the authority component, as specified in the Host header field
1722      (<xref target=""/>), and
1723    </t>
1724    <t>
1725      the request-target obtained from the Request-Line, unless the
1726      request-target is just the asterisk "*".
1727    </t>
1728  </list>
1731   If the request-target uses the path-absolute form or the asterisk form,
1732   and the Host header field is not present, then the effective request URI is
1733   undefined.
1736   Otherwise, when request-target uses the authority form, the effective
1737   request URI is undefined.
1741   Example 1: the effective request URI for the message
1743<artwork type="example" x:indent-with="  ">
1744GET /pub/WWW/TheProject.html HTTP/1.1
1748  (received over an insecure TCP connection) is "http", plus "://", plus the
1749  authority component "", plus the request-target
1750  "/pub/WWW/TheProject.html", thus
1751  "".
1756   Example 2: the effective request URI for the message
1758<artwork type="example" x:indent-with="  ">
1759GET * HTTP/1.1
1763  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1764  authority component "", thus "".
1768   Effective request URIs are compared using the rules described in
1769   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1770   be treated as equivalent to an absolute path of "/".
1777<section title="Response" anchor="response">
1778  <x:anchor-alias value="Response"/>
1780   After receiving and interpreting a request message, a server responds
1781   with an HTTP response message.
1783<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1784  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1785                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1786                  <x:ref>CRLF</x:ref>
1787                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1790<section title="Status-Line" anchor="status-line">
1791  <x:anchor-alias value="Status-Line"/>
1793   The first line of a Response message is the Status-Line, consisting
1794   of the protocol version followed by a numeric status code and its
1795   associated textual phrase, with each element separated by SP
1796   characters. No CR or LF is allowed except in the final CRLF sequence.
1798<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1799  <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>
1802<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1803  <x:anchor-alias value="Reason-Phrase"/>
1804  <x:anchor-alias value="Status-Code"/>
1806   The Status-Code element is a 3-digit integer result code of the
1807   attempt to understand and satisfy the request. These codes are fully
1808   defined in &status-codes;.  The Reason Phrase exists for the sole
1809   purpose of providing a textual description associated with the numeric
1810   status code, out of deference to earlier Internet application protocols
1811   that were more frequently used with interactive text clients.
1812   A client &SHOULD; ignore the content of the Reason Phrase.
1815   The first digit of the Status-Code defines the class of response. The
1816   last two digits do not have any categorization role. There are 5
1817   values for the first digit:
1818  <list style="symbols">
1819    <t>
1820      1xx: Informational - Request received, continuing process
1821    </t>
1822    <t>
1823      2xx: Success - The action was successfully received,
1824        understood, and accepted
1825    </t>
1826    <t>
1827      3xx: Redirection - Further action must be taken in order to
1828        complete the request
1829    </t>
1830    <t>
1831      4xx: Client Error - The request contains bad syntax or cannot
1832        be fulfilled
1833    </t>
1834    <t>
1835      5xx: Server Error - The server failed to fulfill an apparently
1836        valid request
1837    </t>
1838  </list>
1840<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"/>
1841  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1842  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1850<section title="Protocol Parameters" anchor="protocol.parameters">
1852<section title="Date/Time Formats: Full Date" anchor="">
1853  <x:anchor-alias value="HTTP-date"/>
1855   HTTP applications have historically allowed three different formats
1856   for date/time stamps. However, the preferred format is a fixed-length subset
1857   of that defined by <xref target="RFC1123"/>:
1859<figure><artwork type="example" x:indent-with="  ">
1860Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1863   The other formats are described here only for compatibility with obsolete
1864   implementations.
1866<figure><artwork type="example" x:indent-with="  ">
1867Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1868Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1871   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1872   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1873   only generate the RFC 1123 format for representing HTTP-date values
1874   in header fields. See <xref target="tolerant.applications"/> for further information.
1877   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1878   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1879   equal to UTC (Coordinated Universal Time). This is indicated in the
1880   first two formats by the inclusion of "GMT" as the three-letter
1881   abbreviation for time zone, and &MUST; be assumed when reading the
1882   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1883   additional whitespace beyond that specifically included as SP in the
1884   grammar.
1886<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1887  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1889<t anchor="">
1890  <x:anchor-alias value="rfc1123-date"/>
1891  <x:anchor-alias value="time-of-day"/>
1892  <x:anchor-alias value="hour"/>
1893  <x:anchor-alias value="minute"/>
1894  <x:anchor-alias value="second"/>
1895  <x:anchor-alias value="day-name"/>
1896  <x:anchor-alias value="day"/>
1897  <x:anchor-alias value="month"/>
1898  <x:anchor-alias value="year"/>
1899  <x:anchor-alias value="GMT"/>
1900  Preferred format:
1902<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"/>
1903  <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>
1904  ; fixed length subset of the format defined in
1905  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1907  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1908               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1909               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1910               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1911               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1912               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1913               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1915  <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>
1916               ; e.g., 02 Jun 1982
1918  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1919  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1920               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1921               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1922               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1923               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1924               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1925               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1926               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1927               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1928               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1929               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1930               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1931  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1933  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1935  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1936                 ; 00:00:00 - 23:59:59
1938  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1939  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1940  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1943  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1944  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1945  same as those defined for the RFC 5322 constructs
1946  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1948<t anchor="">
1949  <x:anchor-alias value="obs-date"/>
1950  <x:anchor-alias value="rfc850-date"/>
1951  <x:anchor-alias value="asctime-date"/>
1952  <x:anchor-alias value="date1"/>
1953  <x:anchor-alias value="date2"/>
1954  <x:anchor-alias value="date3"/>
1955  <x:anchor-alias value="rfc1123-date"/>
1956  <x:anchor-alias value="day-name-l"/>
1957  Obsolete formats:
1959<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1960  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
1962<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1963  <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>
1964  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1965                 ; day-month-year (e.g., 02-Jun-82)
1967  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1968         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1969         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1970         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1971         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1972         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1973         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1975<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1976  <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>
1977  <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> ))
1978                 ; month day (e.g., Jun  2)
1981  <t>
1982    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1983    accepting date values that might have been sent by non-HTTP
1984    applications, as is sometimes the case when retrieving or posting
1985    messages via proxies/gateways to SMTP or NNTP.
1986  </t>
1989  <t>
1990    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1991    to their usage within the protocol stream. Clients and servers are
1992    not required to use these formats for user presentation, request
1993    logging, etc.
1994  </t>
1998<section title="Transfer Codings" anchor="transfer.codings">
1999  <x:anchor-alias value="transfer-coding"/>
2000  <x:anchor-alias value="transfer-extension"/>
2002   Transfer-coding values are used to indicate an encoding
2003   transformation that has been, can be, or might need to be applied to a
2004   payload body in order to ensure "safe transport" through the network.
2005   This differs from a content coding in that the transfer-coding is a
2006   property of the message rather than a property of the representation
2007   that is being transferred.
2009<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2010  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2011                          / "compress" ; <xref target="compress.coding"/>
2012                          / "deflate" ; <xref target="deflate.coding"/>
2013                          / "gzip" ; <xref target="gzip.coding"/>
2014                          / <x:ref>transfer-extension</x:ref>
2015  <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> )
2017<t anchor="rule.parameter">
2018  <x:anchor-alias value="attribute"/>
2019  <x:anchor-alias value="transfer-parameter"/>
2020  <x:anchor-alias value="value"/>
2021   Parameters are in the form of attribute/value pairs.
2023<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"/>
2024  <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>
2025  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2026  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2029   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2030   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2031   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2034   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2035   MIME, which were designed to enable safe transport of binary data over a
2036   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2037   However, safe transport
2038   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2039   the only unsafe characteristic of message-bodies is the difficulty in
2040   determining the exact message body length (<xref target="message.body"/>),
2041   or the desire to encrypt data over a shared transport.
2044   A server that receives a request message with a transfer-coding it does
2045   not understand &SHOULD; respond with 501 (Not Implemented) and then
2046   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2047   client.
2050<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2051  <iref item="chunked (Coding Format)"/>
2052  <iref item="Coding Format" subitem="chunked"/>
2053  <x:anchor-alias value="chunk"/>
2054  <x:anchor-alias value="Chunked-Body"/>
2055  <x:anchor-alias value="chunk-data"/>
2056  <x:anchor-alias value="chunk-ext"/>
2057  <x:anchor-alias value="chunk-ext-name"/>
2058  <x:anchor-alias value="chunk-ext-val"/>
2059  <x:anchor-alias value="chunk-size"/>
2060  <x:anchor-alias value="last-chunk"/>
2061  <x:anchor-alias value="trailer-part"/>
2062  <x:anchor-alias value="quoted-str-nf"/>
2063  <x:anchor-alias value="qdtext-nf"/>
2065   The chunked encoding modifies the body of a message in order to
2066   transfer it as a series of chunks, each with its own size indicator,
2067   followed by an &OPTIONAL; trailer containing header fields. This
2068   allows dynamically produced content to be transferred along with the
2069   information necessary for the recipient to verify that it has
2070   received the full message.
2072<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"/>
2073  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2074                   <x:ref>last-chunk</x:ref>
2075                   <x:ref>trailer-part</x:ref>
2076                   <x:ref>CRLF</x:ref>
2078  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2079                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2080  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2081  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2083  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2084                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2085  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2086  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2087  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2088  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2090  <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>
2091                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2092  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2093                 ; <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>
2096   The chunk-size field is a string of hex digits indicating the size of
2097   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2098   zero, followed by the trailer, which is terminated by an empty line.
2101   The trailer allows the sender to include additional HTTP header
2102   fields at the end of the message. The Trailer header field can be
2103   used to indicate which header fields are included in a trailer (see
2104   <xref target="header.trailer"/>).
2107   A server using chunked transfer-coding in a response &MUST-NOT; use the
2108   trailer for any header fields unless at least one of the following is
2109   true:
2110  <list style="numbers">
2111    <t>the request included a TE header field that indicates "trailers" is
2112     acceptable in the transfer-coding of the  response, as described in
2113     <xref target="header.te"/>; or,</t>
2115    <t>the trailer fields consist entirely of optional metadata, and the
2116    recipient could use the message (in a manner acceptable to the server where
2117    the field originated) without receiving it. In other words, the server that
2118    generated the header (often but not always the origin server) is willing to
2119    accept the possibility that the trailer fields might be silently discarded
2120    along the path to the client.</t>
2121  </list>
2124   This requirement prevents an interoperability failure when the
2125   message is being received by an HTTP/1.1 (or later) proxy and
2126   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2127   compliance with the protocol would have necessitated a possibly
2128   infinite buffer on the proxy.
2131   A process for decoding the "chunked" transfer-coding
2132   can be represented in pseudo-code as:
2134<figure><artwork type="code">
2135  length := 0
2136  read chunk-size, chunk-ext (if any) and CRLF
2137  while (chunk-size &gt; 0) {
2138     read chunk-data and CRLF
2139     append chunk-data to decoded-body
2140     length := length + chunk-size
2141     read chunk-size and CRLF
2142  }
2143  read header-field
2144  while (header-field not empty) {
2145     append header-field to existing header fields
2146     read header-field
2147  }
2148  Content-Length := length
2149  Remove "chunked" from Transfer-Encoding
2152   All HTTP/1.1 applications &MUST; be able to receive and decode the
2153   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2154   they do not understand.
2157   Since "chunked" is the only transfer-coding required to be understood
2158   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2159   on a persistent connection.  Whenever a transfer-coding is applied to
2160   a payload body in a request, the final transfer-coding applied &MUST;
2161   be "chunked".  If a transfer-coding is applied to a response payload
2162   body, then either the final transfer-coding applied &MUST; be "chunked"
2163   or the message &MUST; be terminated by closing the connection. When the
2164   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2165   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2166   be applied more than once in a message-body.
2170<section title="Compression Codings" anchor="compression.codings">
2172   The codings defined below can be used to compress the payload of a
2173   message.
2176   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2177   is not desirable and is discouraged for future encodings. Their
2178   use here is representative of historical practice, not good
2179   design.
2182   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2183   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2184   equivalent to "gzip" and "compress" respectively.
2187<section title="Compress Coding" anchor="compress.coding">
2188<iref item="compress (Coding Format)"/>
2189<iref item="Coding Format" subitem="compress"/>
2191   The "compress" format is produced by the common UNIX file compression
2192   program "compress". This format is an adaptive Lempel-Ziv-Welch
2193   coding (LZW).
2197<section title="Deflate Coding" anchor="deflate.coding">
2198<iref item="deflate (Coding Format)"/>
2199<iref item="Coding Format" subitem="deflate"/>
2201   The "deflate" format is defined as the "deflate" compression mechanism
2202   (described in <xref target="RFC1951"/>) used inside the "zlib"
2203   data format (<xref target="RFC1950"/>).
2206  <t>
2207    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2208    compressed data without the zlib wrapper.
2209   </t>
2213<section title="Gzip Coding" anchor="gzip.coding">
2214<iref item="gzip (Coding Format)"/>
2215<iref item="Coding Format" subitem="gzip"/>
2217   The "gzip" format is produced by the file compression program
2218   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2219   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2225<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2227   The HTTP Transfer Coding Registry defines the name space for the transfer
2228   coding names.
2231   Registrations &MUST; include the following fields:
2232   <list style="symbols">
2233     <t>Name</t>
2234     <t>Description</t>
2235     <t>Pointer to specification text</t>
2236   </list>
2239   Names of transfer codings &MUST-NOT; overlap with names of content codings
2240   (&content-codings;), unless the encoding transformation is identical (as it
2241   is the case for the compression codings defined in
2242   <xref target="compression.codings"/>).
2245   Values to be added to this name space require a specification
2246   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2247   conform to the purpose of transfer coding defined in this section.
2250   The registry itself is maintained at
2251   <eref target=""/>.
2256<section title="Product Tokens" anchor="product.tokens">
2257  <x:anchor-alias value="product"/>
2258  <x:anchor-alias value="product-version"/>
2260   Product tokens are used to allow communicating applications to
2261   identify themselves by software name and version. Most fields using
2262   product tokens also allow sub-products which form a significant part
2263   of the application to be listed, separated by whitespace. By
2264   convention, the products are listed in order of their significance
2265   for identifying the application.
2267<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2268  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2269  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2272   Examples:
2274<figure><artwork type="example">
2275  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2276  Server: Apache/0.8.4
2279   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2280   used for advertising or other non-essential information. Although any
2281   token character &MAY; appear in a product-version, this token &SHOULD;
2282   only be used for a version identifier (i.e., successive versions of
2283   the same product &SHOULD; only differ in the product-version portion of
2284   the product value).
2288<section title="Quality Values" anchor="quality.values">
2289  <x:anchor-alias value="qvalue"/>
2291   Both transfer codings (TE request header field, <xref target="header.te"/>)
2292   and content negotiation (&content.negotiation;) use short "floating point"
2293   numbers to indicate the relative importance ("weight") of various
2294   negotiable parameters.  A weight is normalized to a real number in
2295   the range 0 through 1, where 0 is the minimum and 1 the maximum
2296   value. If a parameter has a quality value of 0, then content with
2297   this parameter is "not acceptable" for the client. HTTP/1.1
2298   applications &MUST-NOT; generate more than three digits after the
2299   decimal point. User configuration of these values &SHOULD; also be
2300   limited in this fashion.
2302<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2303  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2304                 / ( "1" [ "." 0*3("0") ] )
2307  <t>
2308     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2309     relative degradation in desired quality.
2310  </t>
2316<section title="Connections" anchor="connections">
2318<section title="Persistent Connections" anchor="persistent.connections">
2320<section title="Purpose" anchor="persistent.purpose">
2322   Prior to persistent connections, a separate TCP connection was
2323   established to fetch each URL, increasing the load on HTTP servers
2324   and causing congestion on the Internet. The use of inline images and
2325   other associated data often requires a client to make multiple
2326   requests of the same server in a short amount of time. Analysis of
2327   these performance problems and results from a prototype
2328   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2329   measurements of actual HTTP/1.1 implementations show good
2330   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2331   T/TCP <xref target="Tou1998"/>.
2334   Persistent HTTP connections have a number of advantages:
2335  <list style="symbols">
2336      <t>
2337        By opening and closing fewer TCP connections, CPU time is saved
2338        in routers and hosts (clients, servers, proxies, gateways,
2339        tunnels, or caches), and memory used for TCP protocol control
2340        blocks can be saved in hosts.
2341      </t>
2342      <t>
2343        HTTP requests and responses can be pipelined on a connection.
2344        Pipelining allows a client to make multiple requests without
2345        waiting for each response, allowing a single TCP connection to
2346        be used much more efficiently, with much lower elapsed time.
2347      </t>
2348      <t>
2349        Network congestion is reduced by reducing the number of packets
2350        caused by TCP opens, and by allowing TCP sufficient time to
2351        determine the congestion state of the network.
2352      </t>
2353      <t>
2354        Latency on subsequent requests is reduced since there is no time
2355        spent in TCP's connection opening handshake.
2356      </t>
2357      <t>
2358        HTTP can evolve more gracefully, since errors can be reported
2359        without the penalty of closing the TCP connection. Clients using
2360        future versions of HTTP might optimistically try a new feature,
2361        but if communicating with an older server, retry with old
2362        semantics after an error is reported.
2363      </t>
2364    </list>
2367   HTTP implementations &SHOULD; implement persistent connections.
2371<section title="Overall Operation" anchor="persistent.overall">
2373   A significant difference between HTTP/1.1 and earlier versions of
2374   HTTP is that persistent connections are the default behavior of any
2375   HTTP connection. That is, unless otherwise indicated, the client
2376   &SHOULD; assume that the server will maintain a persistent connection,
2377   even after error responses from the server.
2380   Persistent connections provide a mechanism by which a client and a
2381   server can signal the close of a TCP connection. This signaling takes
2382   place using the Connection header field (<xref target="header.connection"/>). Once a close
2383   has been signaled, the client &MUST-NOT; send any more requests on that
2384   connection.
2387<section title="Negotiation" anchor="persistent.negotiation">
2389   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2390   maintain a persistent connection unless a Connection header field including
2391   the connection-token "close" was sent in the request. If the server
2392   chooses to close the connection immediately after sending the
2393   response, it &SHOULD; send a Connection header field including the
2394   connection-token "close".
2397   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2398   decide to keep it open based on whether the response from a server
2399   contains a Connection header field with the connection-token close. In case
2400   the client does not want to maintain a connection for more than that
2401   request, it &SHOULD; send a Connection header field including the
2402   connection-token close.
2405   If either the client or the server sends the close token in the
2406   Connection header field, that request becomes the last one for the
2407   connection.
2410   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2411   maintained for HTTP versions less than 1.1 unless it is explicitly
2412   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2413   compatibility with HTTP/1.0 clients.
2416   In order to remain persistent, all messages on the connection &MUST;
2417   have a self-defined message length (i.e., one not defined by closure
2418   of the connection), as described in <xref target="message.body"/>.
2422<section title="Pipelining" anchor="pipelining">
2424   A client that supports persistent connections &MAY; "pipeline" its
2425   requests (i.e., send multiple requests without waiting for each
2426   response). A server &MUST; send its responses to those requests in the
2427   same order that the requests were received.
2430   Clients which assume persistent connections and pipeline immediately
2431   after connection establishment &SHOULD; be prepared to retry their
2432   connection if the first pipelined attempt fails. If a client does
2433   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2434   persistent. Clients &MUST; also be prepared to resend their requests if
2435   the server closes the connection before sending all of the
2436   corresponding responses.
2439   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2440   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2441   premature termination of the transport connection could lead to
2442   indeterminate results. A client wishing to send a non-idempotent
2443   request &SHOULD; wait to send that request until it has received the
2444   response status line for the previous request.
2449<section title="Proxy Servers" anchor="persistent.proxy">
2451   It is especially important that proxies correctly implement the
2452   properties of the Connection header field as specified in <xref target="header.connection"/>.
2455   The proxy server &MUST; signal persistent connections separately with
2456   its clients and the origin servers (or other proxy servers) that it
2457   connects to. Each persistent connection applies to only one transport
2458   link.
2461   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2462   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2463   for information and discussion of the problems with the Keep-Alive header field
2464   implemented by many HTTP/1.0 clients).
2467<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2469  <cref anchor="TODO-end-to-end" source="jre">
2470    Restored from <eref target=""/>.
2471    See also <eref target=""/>.
2472  </cref>
2475   For the purpose of defining the behavior of caches and non-caching
2476   proxies, we divide HTTP header fields into two categories:
2477  <list style="symbols">
2478      <t>End-to-end header fields, which are  transmitted to the ultimate
2479        recipient of a request or response. End-to-end header fields in
2480        responses MUST be stored as part of a cache entry and &MUST; be
2481        transmitted in any response formed from a cache entry.</t>
2483      <t>Hop-by-hop header fields, which are meaningful only for a single
2484        transport-level connection, and are not stored by caches or
2485        forwarded by proxies.</t>
2486  </list>
2489   The following HTTP/1.1 header fields are hop-by-hop header fields:
2490  <list style="symbols">
2491      <t>Connection</t>
2492      <t>Keep-Alive</t>
2493      <t>Proxy-Authenticate</t>
2494      <t>Proxy-Authorization</t>
2495      <t>TE</t>
2496      <t>Trailer</t>
2497      <t>Transfer-Encoding</t>
2498      <t>Upgrade</t>
2499  </list>
2502   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2505   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2506   (<xref target="header.connection"/>).
2510<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2512  <cref anchor="TODO-non-mod-headers" source="jre">
2513    Restored from <eref target=""/>.
2514    See also <eref target=""/>.
2515  </cref>
2518   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2519   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2520   modify an end-to-end header field unless the definition of that header field requires
2521   or specifically allows that.
2524   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2525   request or response, and it &MUST-NOT; add any of these fields if not
2526   already present:
2527  <list style="symbols">
2528      <t>Content-Location</t>
2529      <t>Content-MD5</t>
2530      <t>ETag</t>
2531      <t>Last-Modified</t>
2532  </list>
2535   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2536   response:
2537  <list style="symbols">
2538    <t>Expires</t>
2539  </list>
2542   but it &MAY; add any of these fields if not already present. If an
2543   Expires header field is added, it &MUST; be given a field-value identical to
2544   that of the Date header field in that response.
2547   A proxy &MUST-NOT; modify or add any of the following fields in a
2548   message that contains the no-transform cache-control directive, or in
2549   any request:
2550  <list style="symbols">
2551    <t>Content-Encoding</t>
2552    <t>Content-Range</t>
2553    <t>Content-Type</t>
2554  </list>
2557   A transforming proxy &MAY; modify or add these fields to a message
2558   that does not include no-transform, but if it does so, it &MUST; add a
2559   Warning 214 (Transformation applied) if one does not already appear
2560   in the message (see &header-warning;).
2563  <t>
2564    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2565    cause authentication failures if stronger authentication
2566    mechanisms are introduced in later versions of HTTP. Such
2567    authentication mechanisms &MAY; rely on the values of header fields
2568    not listed here.
2569  </t>
2572   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2573   though it &MAY; change the message-body through application or removal
2574   of a transfer-coding (<xref target="transfer.codings"/>).
2580<section title="Practical Considerations" anchor="persistent.practical">
2582   Servers will usually have some time-out value beyond which they will
2583   no longer maintain an inactive connection. Proxy servers might make
2584   this a higher value since it is likely that the client will be making
2585   more connections through the same server. The use of persistent
2586   connections places no requirements on the length (or existence) of
2587   this time-out for either the client or the server.
2590   When a client or server wishes to time-out it &SHOULD; issue a graceful
2591   close on the transport connection. Clients and servers &SHOULD; both
2592   constantly watch for the other side of the transport close, and
2593   respond to it as appropriate. If a client or server does not detect
2594   the other side's close promptly it could cause unnecessary resource
2595   drain on the network.
2598   A client, server, or proxy &MAY; close the transport connection at any
2599   time. For example, a client might have started to send a new request
2600   at the same time that the server has decided to close the "idle"
2601   connection. From the server's point of view, the connection is being
2602   closed while it was idle, but from the client's point of view, a
2603   request is in progress.
2606   This means that clients, servers, and proxies &MUST; be able to recover
2607   from asynchronous close events. Client software &SHOULD; reopen the
2608   transport connection and retransmit the aborted sequence of requests
2609   without user interaction so long as the request sequence is
2610   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2611   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2612   human operator the choice of retrying the request(s). Confirmation by
2613   user-agent software with semantic understanding of the application
2614   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2615   be repeated if the second sequence of requests fails.
2618   Servers &SHOULD; always respond to at least one request per connection,
2619   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2620   middle of transmitting a response, unless a network or client failure
2621   is suspected.
2624   Clients (including proxies) &SHOULD; limit the number of simultaneous
2625   connections that they maintain to a given server (including proxies).
2628   Previous revisions of HTTP gave a specific number of connections as a
2629   ceiling, but this was found to be impractical for many applications. As a
2630   result, this specification does not mandate a particular maximum number of
2631   connections, but instead encourages clients to be conservative when opening
2632   multiple connections.
2635   In particular, while using multiple connections avoids the "head-of-line
2636   blocking" problem (whereby a request that takes significant server-side
2637   processing and/or has a large payload can block subsequent requests on the
2638   same connection), each connection used consumes server resources (sometimes
2639   significantly), and furthermore using multiple connections can cause
2640   undesirable side effects in congested networks.
2643   Note that servers might reject traffic that they deem abusive, including an
2644   excessive number of connections from a client.
2649<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2651<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2653   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2654   flow control mechanisms to resolve temporary overloads, rather than
2655   terminating connections with the expectation that clients will retry.
2656   The latter technique can exacerbate network congestion.
2660<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2662   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2663   the network connection for an error status code while it is transmitting
2664   the request. If the client sees an error status code, it &SHOULD;
2665   immediately cease transmitting the body. If the body is being sent
2666   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2667   empty trailer &MAY; be used to prematurely mark the end of the message.
2668   If the body was preceded by a Content-Length header field, the client &MUST;
2669   close the connection.
2673<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2675   The purpose of the 100 (Continue) status code (see &status-100;) is to
2676   allow a client that is sending a request message with a request body
2677   to determine if the origin server is willing to accept the request
2678   (based on the request header fields) before the client sends the request
2679   body. In some cases, it might either be inappropriate or highly
2680   inefficient for the client to send the body if the server will reject
2681   the message without looking at the body.
2684   Requirements for HTTP/1.1 clients:
2685  <list style="symbols">
2686    <t>
2687        If a client will wait for a 100 (Continue) response before
2688        sending the request body, it &MUST; send an Expect request-header
2689        field (&header-expect;) with the "100-continue" expectation.
2690    </t>
2691    <t>
2692        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2693        with the "100-continue" expectation if it does not intend
2694        to send a request body.
2695    </t>
2696  </list>
2699   Because of the presence of older implementations, the protocol allows
2700   ambiguous situations in which a client might send "Expect: 100-continue"
2701   without receiving either a 417 (Expectation Failed)
2702   or a 100 (Continue) status code. Therefore, when a client sends this
2703   header field to an origin server (possibly via a proxy) from which it
2704   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2705   wait for an indefinite period before sending the request body.
2708   Requirements for HTTP/1.1 origin servers:
2709  <list style="symbols">
2710    <t> Upon receiving a request which includes an Expect request-header
2711        field with the "100-continue" expectation, an origin server &MUST;
2712        either respond with 100 (Continue) status code and continue to read
2713        from the input stream, or respond with a final status code. The
2714        origin server &MUST-NOT; wait for the request body before sending
2715        the 100 (Continue) response. If it responds with a final status
2716        code, it &MAY; close the transport connection or it &MAY; continue
2717        to read and discard the rest of the request.  It &MUST-NOT;
2718        perform the requested method if it returns a final status code.
2719    </t>
2720    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2721        the request message does not include an Expect request-header
2722        field with the "100-continue" expectation, and &MUST-NOT; send a
2723        100 (Continue) response if such a request comes from an HTTP/1.0
2724        (or earlier) client. There is an exception to this rule: for
2725        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2726        status code in response to an HTTP/1.1 PUT or POST request that does
2727        not include an Expect request-header field with the "100-continue"
2728        expectation. This exception, the purpose of which is
2729        to minimize any client processing delays associated with an
2730        undeclared wait for 100 (Continue) status code, applies only to
2731        HTTP/1.1 requests, and not to requests with any other HTTP-version
2732        value.
2733    </t>
2734    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2735        already received some or all of the request body for the
2736        corresponding request.
2737    </t>
2738    <t> An origin server that sends a 100 (Continue) response &MUST;
2739    ultimately send a final status code, once the request body is
2740        received and processed, unless it terminates the transport
2741        connection prematurely.
2742    </t>
2743    <t> If an origin server receives a request that does not include an
2744        Expect request-header field with the "100-continue" expectation,
2745        the request includes a request body, and the server responds
2746        with a final status code before reading the entire request body
2747        from the transport connection, then the server &SHOULD-NOT;  close
2748        the transport connection until it has read the entire request,
2749        or until the client closes the connection. Otherwise, the client
2750        might not reliably receive the response message. However, this
2751        requirement is not be construed as preventing a server from
2752        defending itself against denial-of-service attacks, or from
2753        badly broken client implementations.
2754      </t>
2755    </list>
2758   Requirements for HTTP/1.1 proxies:
2759  <list style="symbols">
2760    <t> If a proxy receives a request that includes an Expect request-header
2761        field with the "100-continue" expectation, and the proxy
2762        either knows that the next-hop server complies with HTTP/1.1 or
2763        higher, or does not know the HTTP version of the next-hop
2764        server, it &MUST; forward the request, including the Expect header
2765        field.
2766    </t>
2767    <t> If the proxy knows that the version of the next-hop server is
2768        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2769        respond with a 417 (Expectation Failed) status code.
2770    </t>
2771    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2772        numbers received from recently-referenced next-hop servers.
2773    </t>
2774    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2775        request message was received from an HTTP/1.0 (or earlier)
2776        client and did not include an Expect request-header field with
2777        the "100-continue" expectation. This requirement overrides the
2778        general rule for forwarding of 1xx responses (see &status-1xx;).
2779    </t>
2780  </list>
2784<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2786   If an HTTP/1.1 client sends a request which includes a request body,
2787   but which does not include an Expect request-header field with the
2788   "100-continue" expectation, and if the client is not directly
2789   connected to an HTTP/1.1 origin server, and if the client sees the
2790   connection close before receiving a status line from the server, the
2791   client &SHOULD; retry the request.  If the client does retry this
2792   request, it &MAY; use the following "binary exponential backoff"
2793   algorithm to be assured of obtaining a reliable response:
2794  <list style="numbers">
2795    <t>
2796      Initiate a new connection to the server
2797    </t>
2798    <t>
2799      Transmit the request-header fields
2800    </t>
2801    <t>
2802      Initialize a variable R to the estimated round-trip time to the
2803         server (e.g., based on the time it took to establish the
2804         connection), or to a constant value of 5 seconds if the round-trip
2805         time is not available.
2806    </t>
2807    <t>
2808       Compute T = R * (2**N), where N is the number of previous
2809         retries of this request.
2810    </t>
2811    <t>
2812       Wait either for an error response from the server, or for T
2813         seconds (whichever comes first)
2814    </t>
2815    <t>
2816       If no error response is received, after T seconds transmit the
2817         body of the request.
2818    </t>
2819    <t>
2820       If client sees that the connection is closed prematurely,
2821         repeat from step 1 until the request is accepted, an error
2822         response is received, or the user becomes impatient and
2823         terminates the retry process.
2824    </t>
2825  </list>
2828   If at any point an error status code is received, the client
2829  <list style="symbols">
2830      <t>&SHOULD-NOT;  continue and</t>
2832      <t>&SHOULD; close the connection if it has not completed sending the
2833        request message.</t>
2834    </list>
2841<section title="Miscellaneous notes that might disappear" anchor="misc">
2842<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2844   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2848<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2850   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2854<section title="Interception of HTTP for access control" anchor="http.intercept">
2856   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2860<section title="Use of HTTP by other protocols" anchor="http.others">
2862   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2863   Extensions of HTTP like WebDAV.</cref>
2867<section title="Use of HTTP by media type specification" anchor="">
2869   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2874<section title="Header Field Definitions" anchor="header.field.definitions">
2876   This section defines the syntax and semantics of HTTP/1.1 header fields
2877   related to message framing and transport protocols.
2880<section title="Connection" anchor="header.connection">
2881  <iref primary="true" item="Connection header" x:for-anchor=""/>
2882  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2883  <x:anchor-alias value="Connection"/>
2884  <x:anchor-alias value="connection-token"/>
2885  <x:anchor-alias value="Connection-v"/>
2887   The "Connection" general-header field allows the sender to specify
2888   options that are desired for that particular connection and &MUST-NOT;
2889   be communicated by proxies over further connections.
2892   The Connection header field's value has the following grammar:
2894<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"/>
2895  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2896  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2897  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2900   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2901   message is forwarded and, for each connection-token in this field,
2902   remove any header field(s) from the message with the same name as the
2903   connection-token. Connection options are signaled by the presence of
2904   a connection-token in the Connection header field, not by any
2905   corresponding additional header field(s), since the additional header
2906   field might not be sent if there are no parameters associated with that
2907   connection option.
2910   Message header fields listed in the Connection header field &MUST-NOT; include
2911   end-to-end header fields, such as Cache-Control.
2914   HTTP/1.1 defines the "close" connection option for the sender to
2915   signal that the connection will be closed after completion of the
2916   response. For example,
2918<figure><artwork type="example">
2919  Connection: close
2922   in either the request or the response header fields indicates that
2923   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2924   after the current request/response is complete.
2927   An HTTP/1.1 client that does not support persistent connections &MUST;
2928   include the "close" connection option in every request message.
2931   An HTTP/1.1 server that does not support persistent connections &MUST;
2932   include the "close" connection option in every response message that
2933   does not have a 1xx (Informational) status code.
2936   A system receiving an HTTP/1.0 (or lower-version) message that
2937   includes a Connection header field &MUST;, for each connection-token in this
2938   field, remove and ignore any header field(s) from the message with
2939   the same name as the connection-token. This protects against mistaken
2940   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2944<section title="Content-Length" anchor="header.content-length">
2945  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2946  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2947  <x:anchor-alias value="Content-Length"/>
2948  <x:anchor-alias value="Content-Length-v"/>
2950   The "Content-Length" header field indicates the size of the
2951   message-body, in decimal number of octets, for any message other than
2952   a response to the HEAD method or a response with a status code of 304.
2953   In the case of responses to the HEAD method, it indicates the size of
2954   the payload body (not including any potential transfer-coding) that
2955   would have been sent had the request been a GET.
2956   In the case of the 304 (Not Modified) response, it indicates the size of
2957   the payload body (not including any potential transfer-coding) that
2958   would have been sent in a 200 (OK) response.
2960<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2961  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2962  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2965   An example is
2967<figure><artwork type="example">
2968  Content-Length: 3495
2971   Implementations &SHOULD; use this field to indicate the message-body
2972   length when no transfer-coding is being applied and the
2973   payload's body length can be determined prior to being transferred.
2974   <xref target="message.body"/> describes how recipients determine the length
2975   of a message-body.
2978   Any Content-Length greater than or equal to zero is a valid value.
2981   Note that the use of this field in HTTP is significantly different from
2982   the corresponding definition in MIME, where it is an optional field
2983   used within the "message/external-body" content-type.
2987<section title="Date" anchor="">
2988  <iref primary="true" item="Date header" x:for-anchor=""/>
2989  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2990  <x:anchor-alias value="Date"/>
2991  <x:anchor-alias value="Date-v"/>
2993   The "Date" general-header field represents the date and time at which
2994   the message was originated, having the same semantics as the Origination
2995   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2996   The field value is an HTTP-date, as described in <xref target=""/>;
2997   it &MUST; be sent in rfc1123-date format.
2999<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3000  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3001  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3004   An example is
3006<figure><artwork type="example">
3007  Date: Tue, 15 Nov 1994 08:12:31 GMT
3010   Origin servers &MUST; include a Date header field in all responses,
3011   except in these cases:
3012  <list style="numbers">
3013      <t>If the response status code is 100 (Continue) or 101 (Switching
3014         Protocols), the response &MAY; include a Date header field, at
3015         the server's option.</t>
3017      <t>If the response status code conveys a server error, e.g., 500
3018         (Internal Server Error) or 503 (Service Unavailable), and it is
3019         inconvenient or impossible to generate a valid Date.</t>
3021      <t>If the server does not have a clock that can provide a
3022         reasonable approximation of the current time, its responses
3023         &MUST-NOT; include a Date header field. In this case, the rules
3024         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3025  </list>
3028   A received message that does not have a Date header field &MUST; be
3029   assigned one by the recipient if the message will be cached by that
3030   recipient or gatewayed via a protocol which requires a Date.
3033   Clients can use the Date header field as well; in order to keep request
3034   messages small, they are advised not to include it when it doesn't convey
3035   any useful information (as it is usually the case for requests that do not
3036   contain a payload).
3039   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3040   time subsequent to the generation of the message. It &SHOULD; represent
3041   the best available approximation of the date and time of message
3042   generation, unless the implementation has no means of generating a
3043   reasonably accurate date and time. In theory, the date ought to
3044   represent the moment just before the payload is generated. In
3045   practice, the date can be generated at any time during the message
3046   origination without affecting its semantic value.
3049<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3051   Some origin server implementations might not have a clock available.
3052   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3053   values to a response, unless these values were associated
3054   with the resource by a system or user with a reliable clock. It &MAY;
3055   assign an Expires value that is known, at or before server
3056   configuration time, to be in the past (this allows "pre-expiration"
3057   of responses without storing separate Expires values for each
3058   resource).
3063<section title="Host" anchor="">
3064  <iref primary="true" item="Host header" x:for-anchor=""/>
3065  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3066  <x:anchor-alias value="Host"/>
3067  <x:anchor-alias value="Host-v"/>
3069   The "Host" request-header field specifies the Internet host and port
3070   number of the resource being requested, allowing the origin server or
3071   gateway to differentiate between internally-ambiguous URLs, such as the root
3072   "/" URL of a server for multiple host names on a single IP address.
3075   The Host field value &MUST; represent the naming authority of the origin
3076   server or gateway given by the original URL obtained from the user or
3077   referring resource (generally an http URI, as described in
3078   <xref target="http.uri"/>).
3080<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3081  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3082  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3085   A "host" without any trailing port information implies the default
3086   port for the service requested (e.g., "80" for an HTTP URL). For
3087   example, a request on the origin server for
3088   &lt;; would properly include:
3090<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3091GET /pub/WWW/ HTTP/1.1
3095   A client &MUST; include a Host header field in all HTTP/1.1 request
3096   messages. If the requested URI does not include an Internet host
3097   name for the service being requested, then the Host header field &MUST;
3098   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3099   request message it forwards does contain an appropriate Host header
3100   field that identifies the service being requested by the proxy. All
3101   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3102   status code to any HTTP/1.1 request message which lacks a Host header
3103   field.
3106   See Sections <xref target="" format="counter"/>
3107   and <xref target="" format="counter"/>
3108   for other requirements relating to Host.
3112<section title="TE" anchor="header.te">
3113  <iref primary="true" item="TE header" x:for-anchor=""/>
3114  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3115  <x:anchor-alias value="TE"/>
3116  <x:anchor-alias value="TE-v"/>
3117  <x:anchor-alias value="t-codings"/>
3118  <x:anchor-alias value="te-params"/>
3119  <x:anchor-alias value="te-ext"/>
3121   The "TE" request-header field indicates what extension transfer-codings
3122   it is willing to accept in the response, and whether or not it is
3123   willing to accept trailer fields in a chunked transfer-coding.
3126   Its value consists of the keyword "trailers" and/or a comma-separated
3127   list of extension transfer-coding names with optional accept
3128   parameters (as described in <xref target="transfer.codings"/>).
3130<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"/>
3131  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3132  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3133  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3134  <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> )
3135  <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> ]
3138   The presence of the keyword "trailers" indicates that the client is
3139   willing to accept trailer fields in a chunked transfer-coding, as
3140   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3141   transfer-coding values even though it does not itself represent a
3142   transfer-coding.
3145   Examples of its use are:
3147<figure><artwork type="example">
3148  TE: deflate
3149  TE:
3150  TE: trailers, deflate;q=0.5
3153   The TE header field only applies to the immediate connection.
3154   Therefore, the keyword &MUST; be supplied within a Connection header
3155   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3158   A server tests whether a transfer-coding is acceptable, according to
3159   a TE field, using these rules:
3160  <list style="numbers">
3161    <x:lt>
3162      <t>The "chunked" transfer-coding is always acceptable. If the
3163         keyword "trailers" is listed, the client indicates that it is
3164         willing to accept trailer fields in the chunked response on
3165         behalf of itself and any downstream clients. The implication is
3166         that, if given, the client is stating that either all
3167         downstream clients are willing to accept trailer fields in the
3168         forwarded response, or that it will attempt to buffer the
3169         response on behalf of downstream recipients.
3170      </t><t>
3171         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3172         chunked response such that a client can be assured of buffering
3173         the entire response.</t>
3174    </x:lt>
3175    <x:lt>
3176      <t>If the transfer-coding being tested is one of the transfer-codings
3177         listed in the TE field, then it is acceptable unless it
3178         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3179         qvalue of 0 means "not acceptable".)</t>
3180    </x:lt>
3181    <x:lt>
3182      <t>If multiple transfer-codings are acceptable, then the
3183         acceptable transfer-coding with the highest non-zero qvalue is
3184         preferred.  The "chunked" transfer-coding always has a qvalue
3185         of 1.</t>
3186    </x:lt>
3187  </list>
3190   If the TE field-value is empty or if no TE field is present, the only
3191   transfer-coding is "chunked". A message with no transfer-coding is
3192   always acceptable.
3196<section title="Trailer" anchor="header.trailer">
3197  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3198  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3199  <x:anchor-alias value="Trailer"/>
3200  <x:anchor-alias value="Trailer-v"/>
3202   The "Trailer" general-header field indicates that the given set of
3203   header fields is present in the trailer of a message encoded with
3204   chunked transfer-coding.
3206<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3207  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3208  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3211   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3212   message using chunked transfer-coding with a non-empty trailer. Doing
3213   so allows the recipient to know which header fields to expect in the
3214   trailer.
3217   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3218   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3219   trailer fields in a "chunked" transfer-coding.
3222   Message header fields listed in the Trailer header field &MUST-NOT;
3223   include the following header fields:
3224  <list style="symbols">
3225    <t>Transfer-Encoding</t>
3226    <t>Content-Length</t>
3227    <t>Trailer</t>
3228  </list>
3232<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3233  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3234  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3235  <x:anchor-alias value="Transfer-Encoding"/>
3236  <x:anchor-alias value="Transfer-Encoding-v"/>
3238   The "Transfer-Encoding" general-header field indicates what transfer-codings
3239   (if any) have been applied to the message body. It differs from
3240   Content-Encoding (&content-codings;) in that transfer-codings are a property
3241   of the message (and therefore are removed by intermediaries), whereas
3242   content-codings are not.
3244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3245  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3246                        <x:ref>Transfer-Encoding-v</x:ref>
3247  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3250   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3252<figure><artwork type="example">
3253  Transfer-Encoding: chunked
3256   If multiple encodings have been applied to a representation, the transfer-codings
3257   &MUST; be listed in the order in which they were applied.
3258   Additional information about the encoding parameters &MAY; be provided
3259   by other header fields not defined by this specification.
3262   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3263   header field.
3267<section title="Upgrade" anchor="header.upgrade">
3268  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3269  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3270  <x:anchor-alias value="Upgrade"/>
3271  <x:anchor-alias value="Upgrade-v"/>
3273   The "Upgrade" general-header field allows the client to specify what
3274   additional communication protocols it would like to use, if the server
3275   chooses to switch protocols. Servers can use it to indicate what protocols
3276   they are willing to switch to.
3278<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3279  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3280  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3283   For example,
3285<figure><artwork type="example">
3286  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3289   The Upgrade header field is intended to provide a simple mechanism
3290   for transition from HTTP/1.1 to some other, incompatible protocol. It
3291   does so by allowing the client to advertise its desire to use another
3292   protocol, such as a later version of HTTP with a higher major version
3293   number, even though the current request has been made using HTTP/1.1.
3294   This eases the difficult transition between incompatible protocols by
3295   allowing the client to initiate a request in the more commonly
3296   supported protocol while indicating to the server that it would like
3297   to use a "better" protocol if available (where "better" is determined
3298   by the server, possibly according to the nature of the method and/or
3299   resource being requested).
3302   The Upgrade header field only applies to switching application-layer
3303   protocols upon the existing transport-layer connection. Upgrade
3304   cannot be used to insist on a protocol change; its acceptance and use
3305   by the server is optional. The capabilities and nature of the
3306   application-layer communication after the protocol change is entirely
3307   dependent upon the new protocol chosen, although the first action
3308   after changing the protocol &MUST; be a response to the initial HTTP
3309   request containing the Upgrade header field.
3312   The Upgrade header field only applies to the immediate connection.
3313   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3314   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3315   HTTP/1.1 message.
3318   The Upgrade header field cannot be used to indicate a switch to a
3319   protocol on a different connection. For that purpose, it is more
3320   appropriate to use a 3xx redirection response (&status-3xx;).
3323   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3324   Protocols) responses to indicate which protocol(s) are being switched to,
3325   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3326   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3327   response to indicate that they are willing to upgrade to one of the
3328   specified protocols.
3331   This specification only defines the protocol name "HTTP" for use by
3332   the family of Hypertext Transfer Protocols, as defined by the HTTP
3333   version rules of <xref target="http.version"/> and future updates to this
3334   specification. Additional tokens can be registered with IANA using the
3335   registration procedure defined below. 
3338<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3340   The HTTP Upgrade Token Registry defines the name space for product
3341   tokens used to identify protocols in the Upgrade header field.
3342   Each registered token is associated with contact information and
3343   an optional set of specifications that details how the connection
3344   will be processed after it has been upgraded.
3347   Registrations are allowed on a First Come First Served basis as
3348   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3349   specifications need not be IETF documents or be subject to IESG review.
3350   Registrations are subject to the following rules:
3351  <list style="numbers">
3352    <t>A token, once registered, stays registered forever.</t>
3353    <t>The registration &MUST; name a responsible party for the
3354       registration.</t>
3355    <t>The registration &MUST; name a point of contact.</t>
3356    <t>The registration &MAY; name a set of specifications associated with that
3357       token. Such specifications need not be publicly available.</t>
3358    <t>The responsible party &MAY; change the registration at any time.
3359       The IANA will keep a record of all such changes, and make them
3360       available upon request.</t>
3361    <t>The responsible party for the first registration of a "product"
3362       token &MUST; approve later registrations of a "version" token
3363       together with that "product" token before they can be registered.</t>
3364    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3365       for a token. This will normally only be used in the case when a
3366       responsible party cannot be contacted.</t>
3367  </list>
3374<section title="Via" anchor="header.via">
3375  <iref primary="true" item="Via header" x:for-anchor=""/>
3376  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3377  <x:anchor-alias value="protocol-name"/>
3378  <x:anchor-alias value="protocol-version"/>
3379  <x:anchor-alias value="pseudonym"/>
3380  <x:anchor-alias value="received-by"/>
3381  <x:anchor-alias value="received-protocol"/>
3382  <x:anchor-alias value="Via"/>
3383  <x:anchor-alias value="Via-v"/>
3385   The "Via" general-header field &MUST; be used by gateways and proxies to
3386   indicate the intermediate protocols and recipients between the user
3387   agent and the server on requests, and between the origin server and
3388   the client on responses. It is analogous to the "Received" field defined in
3389   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3390   avoiding request loops, and identifying the protocol capabilities of
3391   all senders along the request/response chain.
3393<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"/>
3394  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3395  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3396                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3397  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3398  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3399  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3400  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3401  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3404   The received-protocol indicates the protocol version of the message
3405   received by the server or client along each segment of the
3406   request/response chain. The received-protocol version is appended to
3407   the Via field value when the message is forwarded so that information
3408   about the protocol capabilities of upstream applications remains
3409   visible to all recipients.
3412   The protocol-name is optional if and only if it would be "HTTP". The
3413   received-by field is normally the host and optional port number of a
3414   recipient server or client that subsequently forwarded the message.
3415   However, if the real host is considered to be sensitive information,
3416   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3417   be assumed to be the default port of the received-protocol.
3420   Multiple Via field values represent each proxy or gateway that has
3421   forwarded the message. Each recipient &MUST; append its information
3422   such that the end result is ordered according to the sequence of
3423   forwarding applications.
3426   Comments &MAY; be used in the Via header field to identify the software
3427   of the recipient proxy or gateway, analogous to the User-Agent and
3428   Server header fields. However, all comments in the Via field are
3429   optional and &MAY; be removed by any recipient prior to forwarding the
3430   message.
3433   For example, a request message could be sent from an HTTP/1.0 user
3434   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3435   forward the request to a public proxy at, which completes
3436   the request by forwarding it to the origin server at
3437   The request received by would then have the following
3438   Via header field:
3440<figure><artwork type="example">
3441  Via: 1.0 fred, 1.1 (Apache/1.1)
3444   Proxies and gateways used as a portal through a network firewall
3445   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3446   the firewall region. This information &SHOULD; only be propagated if
3447   explicitly enabled. If not enabled, the received-by host of any host
3448   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3449   for that host.
3452   For organizations that have strong privacy requirements for hiding
3453   internal structures, a proxy &MAY; combine an ordered subsequence of
3454   Via header field entries with identical received-protocol values into
3455   a single such entry. For example,
3457<figure><artwork type="example">
3458  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3461  could be collapsed to
3463<figure><artwork type="example">
3464  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3467   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3468   under the same organizational control and the hosts have already been
3469   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3470   have different received-protocol values.
3476<section title="IANA Considerations" anchor="IANA.considerations">
3478<section title="Header Field Registration" anchor="header.field.registration">
3480   The Message Header Field Registry located at <eref target=""/> shall be updated
3481   with the permanent registrations below (see <xref target="RFC3864"/>):
3483<?BEGININC p1-messaging.iana-headers ?>
3484<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3485<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3486   <ttcol>Header Field Name</ttcol>
3487   <ttcol>Protocol</ttcol>
3488   <ttcol>Status</ttcol>
3489   <ttcol>Reference</ttcol>
3491   <c>Connection</c>
3492   <c>http</c>
3493   <c>standard</c>
3494   <c>
3495      <xref target="header.connection"/>
3496   </c>
3497   <c>Content-Length</c>
3498   <c>http</c>
3499   <c>standard</c>
3500   <c>
3501      <xref target="header.content-length"/>
3502   </c>
3503   <c>Date</c>
3504   <c>http</c>
3505   <c>standard</c>
3506   <c>
3507      <xref target=""/>
3508   </c>
3509   <c>Host</c>
3510   <c>http</c>
3511   <c>standard</c>
3512   <c>
3513      <xref target=""/>
3514   </c>
3515   <c>TE</c>
3516   <c>http</c>
3517   <c>standard</c>
3518   <c>
3519      <xref target="header.te"/>
3520   </c>
3521   <c>Trailer</c>
3522   <c>http</c>
3523   <c>standard</c>
3524   <c>
3525      <xref target="header.trailer"/>
3526   </c>
3527   <c>Transfer-Encoding</c>
3528   <c>http</c>
3529   <c>standard</c>
3530   <c>
3531      <xref target="header.transfer-encoding"/>
3532   </c>
3533   <c>Upgrade</c>
3534   <c>http</c>
3535   <c>standard</c>
3536   <c>
3537      <xref target="header.upgrade"/>
3538   </c>
3539   <c>Via</c>
3540   <c>http</c>
3541   <c>standard</c>
3542   <c>
3543      <xref target="header.via"/>
3544   </c>
3547<?ENDINC p1-messaging.iana-headers ?>
3549   The change controller is: "IETF ( - Internet Engineering Task Force".
3553<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3555   The entries for the "http" and "https" URI Schemes in the registry located at
3556   <eref target=""/>
3557   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3558   and <xref target="https.uri" format="counter"/> of this document
3559   (see <xref target="RFC4395"/>).
3563<section title="Internet Media Type Registrations" anchor="">
3565   This document serves as the specification for the Internet media types
3566   "message/http" and "application/http". The following is to be registered with
3567   IANA (see <xref target="RFC4288"/>).
3569<section title="Internet Media Type message/http" anchor="">
3570<iref item="Media Type" subitem="message/http" primary="true"/>
3571<iref item="message/http Media Type" primary="true"/>
3573   The message/http type can be used to enclose a single HTTP request or
3574   response message, provided that it obeys the MIME restrictions for all
3575   "message" types regarding line length and encodings.
3578  <list style="hanging" x:indent="12em">
3579    <t hangText="Type name:">
3580      message
3581    </t>
3582    <t hangText="Subtype name:">
3583      http
3584    </t>
3585    <t hangText="Required parameters:">
3586      none
3587    </t>
3588    <t hangText="Optional parameters:">
3589      version, msgtype
3590      <list style="hanging">
3591        <t hangText="version:">
3592          The HTTP-Version number of the enclosed message
3593          (e.g., "1.1"). If not present, the version can be
3594          determined from the first line of the body.
3595        </t>
3596        <t hangText="msgtype:">
3597          The message type &mdash; "request" or "response". If not
3598          present, the type can be determined from the first
3599          line of the body.
3600        </t>
3601      </list>
3602    </t>
3603    <t hangText="Encoding considerations:">
3604      only "7bit", "8bit", or "binary" are permitted
3605    </t>
3606    <t hangText="Security considerations:">
3607      none
3608    </t>
3609    <t hangText="Interoperability considerations:">
3610      none
3611    </t>
3612    <t hangText="Published specification:">
3613      This specification (see <xref target=""/>).
3614    </t>
3615    <t hangText="Applications that use this media type:">
3616    </t>
3617    <t hangText="Additional information:">
3618      <list style="hanging">
3619        <t hangText="Magic number(s):">none</t>
3620        <t hangText="File extension(s):">none</t>
3621        <t hangText="Macintosh file type code(s):">none</t>
3622      </list>
3623    </t>
3624    <t hangText="Person and email address to contact for further information:">
3625      See Authors Section.
3626    </t>
3627    <t hangText="Intended usage:">
3628      COMMON
3629    </t>
3630    <t hangText="Restrictions on usage:">
3631      none
3632    </t>
3633    <t hangText="Author/Change controller:">
3634      IESG
3635    </t>
3636  </list>
3639<section title="Internet Media Type application/http" anchor="">
3640<iref item="Media Type" subitem="application/http" primary="true"/>
3641<iref item="application/http Media Type" primary="true"/>
3643   The application/http type can be used to enclose a pipeline of one or more
3644   HTTP request or response messages (not intermixed).
3647  <list style="hanging" x:indent="12em">
3648    <t hangText="Type name:">
3649      application
3650    </t>
3651    <t hangText="Subtype name:">
3652      http
3653    </t>
3654    <t hangText="Required parameters:">
3655      none
3656    </t>
3657    <t hangText="Optional parameters:">
3658      version, msgtype
3659      <list style="hanging">
3660        <t hangText="version:">
3661          The HTTP-Version number of the enclosed messages
3662          (e.g., "1.1"). If not present, the version can be
3663          determined from the first line of the body.
3664        </t>
3665        <t hangText="msgtype:">
3666          The message type &mdash; "request" or "response". If not
3667          present, the type can be determined from the first
3668          line of the body.
3669        </t>
3670      </list>
3671    </t>
3672    <t hangText="Encoding considerations:">
3673      HTTP messages enclosed by this type
3674      are in "binary" format; use of an appropriate
3675      Content-Transfer-Encoding is required when
3676      transmitted via E-mail.
3677    </t>
3678    <t hangText="Security considerations:">
3679      none
3680    </t>
3681    <t hangText="Interoperability considerations:">
3682      none
3683    </t>
3684    <t hangText="Published specification:">
3685      This specification (see <xref target=""/>).
3686    </t>
3687    <t hangText="Applications that use this media type:">
3688    </t>
3689    <t hangText="Additional information:">
3690      <list style="hanging">
3691        <t hangText="Magic number(s):">none</t>
3692        <t hangText="File extension(s):">none</t>
3693        <t hangText="Macintosh file type code(s):">none</t>
3694      </list>
3695    </t>
3696    <t hangText="Person and email address to contact for further information:">
3697      See Authors Section.
3698    </t>
3699    <t hangText="Intended usage:">
3700      COMMON
3701    </t>
3702    <t hangText="Restrictions on usage:">
3703      none
3704    </t>
3705    <t hangText="Author/Change controller:">
3706      IESG
3707    </t>
3708  </list>
3713<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3715   The registration procedure for HTTP Transfer Codings is now defined by
3716   <xref target="transfer.coding.registry"/> of this document.
3719   The HTTP Transfer Codings Registry located at <eref target=""/>
3720   shall be updated with the registrations below:
3722<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3723   <ttcol>Name</ttcol>
3724   <ttcol>Description</ttcol>
3725   <ttcol>Reference</ttcol>
3726   <c>chunked</c>
3727   <c>Transfer in a series of chunks</c>
3728   <c>
3729      <xref target="chunked.encoding"/>
3730   </c>
3731   <c>compress</c>
3732   <c>UNIX "compress" program method</c>
3733   <c>
3734      <xref target="compress.coding"/>
3735   </c>
3736   <c>deflate</c>
3737   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3738   the "zlib" data format (<xref target="RFC1950"/>)
3739   </c>
3740   <c>
3741      <xref target="deflate.coding"/>
3742   </c>
3743   <c>gzip</c>
3744   <c>Same as GNU zip <xref target="RFC1952"/></c>
3745   <c>
3746      <xref target="gzip.coding"/>
3747   </c>
3751<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3753   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3754   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3755   by <xref target="upgrade.token.registry"/> of this document.
3758   The HTTP Status Code Registry located at <eref target=""/>
3759   shall be updated with the registration below:
3761<texttable align="left" suppress-title="true">
3762   <ttcol>Value</ttcol>
3763   <ttcol>Description</ttcol>
3764   <ttcol>Reference</ttcol>
3766   <c>HTTP</c>
3767   <c>Hypertext Transfer Protocol</c>
3768   <c><xref target="http.version"/> of this specification</c>
3769<!-- IANA should add this without our instructions; emailed on June 05, 2009
3770   <c>TLS/1.0</c>
3771   <c>Transport Layer Security</c>
3772   <c><xref target="RFC2817"/></c> -->
3779<section title="Security Considerations" anchor="security.considerations">
3781   This section is meant to inform application developers, information
3782   providers, and users of the security limitations in HTTP/1.1 as
3783   described by this document. The discussion does not include
3784   definitive solutions to the problems revealed, though it does make
3785   some suggestions for reducing security risks.
3788<section title="Personal Information" anchor="personal.information">
3790   HTTP clients are often privy to large amounts of personal information
3791   (e.g., the user's name, location, mail address, passwords, encryption
3792   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3793   leakage of this information.
3794   We very strongly recommend that a convenient interface be provided
3795   for the user to control dissemination of such information, and that
3796   designers and implementors be particularly careful in this area.
3797   History shows that errors in this area often create serious security
3798   and/or privacy problems and generate highly adverse publicity for the
3799   implementor's company.
3803<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3805   A server is in the position to save personal data about a user's
3806   requests which might identify their reading patterns or subjects of
3807   interest. This information is clearly confidential in nature and its
3808   handling can be constrained by law in certain countries. People using
3809   HTTP to provide data are responsible for ensuring that
3810   such material is not distributed without the permission of any
3811   individuals that are identifiable by the published results.
3815<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3817   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3818   the documents returned by HTTP requests to be only those that were
3819   intended by the server administrators. If an HTTP server translates
3820   HTTP URIs directly into file system calls, the server &MUST; take
3821   special care not to serve files that were not intended to be
3822   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3823   other operating systems use ".." as a path component to indicate a
3824   directory level above the current one. On such a system, an HTTP
3825   server &MUST; disallow any such construct in the request-target if it
3826   would otherwise allow access to a resource outside those intended to
3827   be accessible via the HTTP server. Similarly, files intended for
3828   reference only internally to the server (such as access control
3829   files, configuration files, and script code) &MUST; be protected from
3830   inappropriate retrieval, since they might contain sensitive
3831   information. Experience has shown that minor bugs in such HTTP server
3832   implementations have turned into security risks.
3836<section title="DNS Spoofing" anchor="dns.spoofing">
3838   Clients using HTTP rely heavily on the Domain Name Service, and are
3839   thus generally prone to security attacks based on the deliberate
3840   mis-association of IP addresses and DNS names. Clients need to be
3841   cautious in assuming the continuing validity of an IP number/DNS name
3842   association.
3845   In particular, HTTP clients &SHOULD; rely on their name resolver for
3846   confirmation of an IP number/DNS name association, rather than
3847   caching the result of previous host name lookups. Many platforms
3848   already can cache host name lookups locally when appropriate, and
3849   they &SHOULD; be configured to do so. It is proper for these lookups to
3850   be cached, however, only when the TTL (Time To Live) information
3851   reported by the name server makes it likely that the cached
3852   information will remain useful.
3855   If HTTP clients cache the results of host name lookups in order to
3856   achieve a performance improvement, they &MUST; observe the TTL
3857   information reported by DNS.
3860   If HTTP clients do not observe this rule, they could be spoofed when
3861   a previously-accessed server's IP address changes. As network
3862   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3863   possibility of this form of attack will grow. Observing this
3864   requirement thus reduces this potential security vulnerability.
3867   This requirement also improves the load-balancing behavior of clients
3868   for replicated servers using the same DNS name and reduces the
3869   likelihood of a user's experiencing failure in accessing sites which
3870   use that strategy.
3874<section title="Proxies and Caching" anchor="attack.proxies">
3876   By their very nature, HTTP proxies are men-in-the-middle, and
3877   represent an opportunity for man-in-the-middle attacks. Compromise of
3878   the systems on which the proxies run can result in serious security
3879   and privacy problems. Proxies have access to security-related
3880   information, personal information about individual users and
3881   organizations, and proprietary information belonging to users and
3882   content providers. A compromised proxy, or a proxy implemented or
3883   configured without regard to security and privacy considerations,
3884   might be used in the commission of a wide range of potential attacks.
3887   Proxy operators need to protect the systems on which proxies run as
3888   they would protect any system that contains or transports sensitive
3889   information. In particular, log information gathered at proxies often
3890   contains highly sensitive personal information, and/or information
3891   about organizations. Log information needs to be carefully guarded, and
3892   appropriate guidelines for use need to be developed and followed.
3893   (<xref target="abuse.of.server.log.information"/>).
3896   Proxy implementors need to consider the privacy and security
3897   implications of their design and coding decisions, and of the
3898   configuration options they provide to proxy operators (especially the
3899   default configuration).
3902   Users of a proxy need to be aware that proxies are no trustworthier than
3903   the people who run them; HTTP itself cannot solve this problem.
3906   The judicious use of cryptography, when appropriate, might suffice to
3907   protect against a broad range of security and privacy attacks. Such
3908   cryptography is beyond the scope of the HTTP/1.1 specification.
3912<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3914   They exist. They are hard to defend against. Research continues.
3915   Beware.
3920<section title="Acknowledgments" anchor="ack">
3922   HTTP has evolved considerably over the years. It has
3923   benefited from a large and active developer community &mdash; the many
3924   people who have participated on the www-talk mailing list &mdash; and it is
3925   that community which has been most responsible for the success of
3926   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3927   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3928   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3929   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3930   VanHeyningen deserve special recognition for their efforts in
3931   defining early aspects of the protocol.
3934   This document has benefited greatly from the comments of all those
3935   participating in the HTTP-WG. In addition to those already mentioned,
3936   the following individuals have contributed to this specification:
3939   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3940   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3941   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3942   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3943   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3944   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3945   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3946   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3947   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3948   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3949   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3950   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3953   Thanks to the "cave men" of Palo Alto. You know who you are.
3956   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3957   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3958   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3959   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3960   Larry Masinter for their help. And thanks go particularly to Jeff
3961   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3964   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3965   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3966   discovery of many of the problems that this document attempts to
3967   rectify.
3970   This specification makes heavy use of the augmented BNF and generic
3971   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3972   reuses many of the definitions provided by Nathaniel Borenstein and
3973   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3974   specification will help reduce past confusion over the relationship
3975   between HTTP and Internet mail message formats.
3979Acknowledgements TODO list
3981- Jeff Hodges ("effective request URI")
3989<references title="Normative References">
3991<reference anchor="ISO-8859-1">
3992  <front>
3993    <title>
3994     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3995    </title>
3996    <author>
3997      <organization>International Organization for Standardization</organization>
3998    </author>
3999    <date year="1998"/>
4000  </front>
4001  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4004<reference anchor="Part2">
4005  <front>
4006    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4007    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4008      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4009      <address><email></email></address>
4010    </author>
4011    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4012      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4013      <address><email></email></address>
4014    </author>
4015    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4016      <organization abbrev="HP">Hewlett-Packard Company</organization>
4017      <address><email></email></address>
4018    </author>
4019    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4020      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4021      <address><email></email></address>
4022    </author>
4023    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4024      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4025      <address><email></email></address>
4026    </author>
4027    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4028      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4029      <address><email></email></address>
4030    </author>
4031    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4032      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4033      <address><email></email></address>
4034    </author>
4035    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4036      <organization abbrev="W3C">World Wide Web Consortium</organization>
4037      <address><email></email></address>
4038    </author>
4039    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4040      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4041      <address><email></email></address>
4042    </author>
4043    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4044  </front>
4045  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4046  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4049<reference anchor="Part3">
4050  <front>
4051    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4052    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4053      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4054      <address><email></email></address>
4055    </author>
4056    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4057      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4058      <address><email></email></address>
4059    </author>
4060    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4061      <organization abbrev="HP">Hewlett-Packard Company</organization>
4062      <address><email></email></address>
4063    </author>
4064    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4065      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4066      <address><email></email></address>
4067    </author>
4068    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4069      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4070      <address><email></email></address>
4071    </author>
4072    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4073      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4074      <address><email></email></address>
4075    </author>
4076    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4077      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4078      <address><email></email></address>
4079    </author>
4080    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4081      <organization abbrev="W3C">World Wide Web Consortium</organization>
4082      <address><email></email></address>
4083    </author>
4084    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4085      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4086      <address><email></email></address>
4087    </author>
4088    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4089  </front>
4090  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4091  <x:source href="p3-payload.xml" basename="p3-payload"/>
4094<reference anchor="Part6">
4095  <front>
4096    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4097    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4098      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4099      <address><email></email></address>
4100    </author>
4101    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4102      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4103      <address><email></email></address>
4104    </author>
4105    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4106      <organization abbrev="HP">Hewlett-Packard Company</organization>
4107      <address><email></email></address>
4108    </author>
4109    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4110      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4111      <address><email></email></address>
4112    </author>
4113    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4114      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4115      <address><email></email></address>
4116    </author>
4117    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4118      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4119      <address><email></email></address>
4120    </author>
4121    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4122      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4123      <address><email></email></address>
4124    </author>
4125    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4126      <organization abbrev="W3C">World Wide Web Consortium</organization>
4127      <address><email></email></address>
4128    </author>
4129    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4130      <address><email></email></address>
4131    </author>
4132    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4133      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4134      <address><email></email></address>
4135    </author>
4136    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4137  </front>
4138  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4139  <x:source href="p6-cache.xml" basename="p6-cache"/>
4142<reference anchor="RFC5234">
4143  <front>
4144    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4145    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4146      <organization>Brandenburg InternetWorking</organization>
4147      <address>
4148        <email></email>
4149      </address> 
4150    </author>
4151    <author initials="P." surname="Overell" fullname="Paul Overell">
4152      <organization>THUS plc.</organization>
4153      <address>
4154        <email></email>
4155      </address>
4156    </author>
4157    <date month="January" year="2008"/>
4158  </front>
4159  <seriesInfo name="STD" value="68"/>
4160  <seriesInfo name="RFC" value="5234"/>
4163<reference anchor="RFC2119">
4164  <front>
4165    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4166    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4167      <organization>Harvard University</organization>
4168      <address><email></email></address>
4169    </author>
4170    <date month="March" year="1997"/>
4171  </front>
4172  <seriesInfo name="BCP" value="14"/>
4173  <seriesInfo name="RFC" value="2119"/>
4176<reference anchor="RFC3986">
4177 <front>
4178  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4179  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4180    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4181    <address>
4182       <email></email>
4183       <uri></uri>
4184    </address>
4185  </author>
4186  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4187    <organization abbrev="Day Software">Day Software</organization>
4188    <address>
4189      <email></email>
4190      <uri></uri>
4191    </address>
4192  </author>
4193  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4194    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4195    <address>
4196      <email></email>
4197      <uri></uri>
4198    </address>
4199  </author>
4200  <date month='January' year='2005'></date>
4201 </front>
4202 <seriesInfo name="STD" value="66"/>
4203 <seriesInfo name="RFC" value="3986"/>
4206<reference anchor="USASCII">
4207  <front>
4208    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4209    <author>
4210      <organization>American National Standards Institute</organization>
4211    </author>
4212    <date year="1986"/>
4213  </front>
4214  <seriesInfo name="ANSI" value="X3.4"/>
4217<reference anchor="RFC1950">
4218  <front>
4219    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4220    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4221      <organization>Aladdin Enterprises</organization>
4222      <address><email></email></address>
4223    </author>
4224    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4225    <date month="May" year="1996"/>
4226  </front>
4227  <seriesInfo name="RFC" value="1950"/>
4228  <annotation>
4229    RFC 1950 is an Informational RFC, thus it might be less stable than
4230    this specification. On the other hand, this downward reference was
4231    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4232    therefore it is unlikely to cause problems in practice. See also
4233    <xref target="BCP97"/>.
4234  </annotation>
4237<reference anchor="RFC1951">
4238  <front>
4239    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4240    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4241      <organization>Aladdin Enterprises</organization>
4242      <address><email></email></address>
4243    </author>
4244    <date month="May" year="1996"/>
4245  </front>
4246  <seriesInfo name="RFC" value="1951"/>
4247  <annotation>
4248    RFC 1951 is an Informational RFC, thus it might be less stable than
4249    this specification. On the other hand, this downward reference was
4250    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4251    therefore it is unlikely to cause problems in practice. See also
4252    <xref target="BCP97"/>.
4253  </annotation>
4256<reference anchor="RFC1952">
4257  <front>
4258    <title>GZIP file format specification version 4.3</title>
4259    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4260      <organization>Aladdin Enterprises</organization>
4261      <address><email></email></address>
4262    </author>
4263    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4264      <address><email></email></address>
4265    </author>
4266    <author initials="M." surname="Adler" fullname="Mark Adler">
4267      <address><email></email></address>
4268    </author>
4269    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4270      <address><email></email></address>
4271    </author>
4272    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4273      <address><email></email></address>
4274    </author>
4275    <date month="May" year="1996"/>
4276  </front>
4277  <seriesInfo name="RFC" value="1952"/>
4278  <annotation>
4279    RFC 1952 is an Informational RFC, thus it might be less stable than
4280    this specification. On the other hand, this downward reference was
4281    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4282    therefore it is unlikely to cause problems in practice. See also
4283    <xref target="BCP97"/>.
4284  </annotation>
4289<references title="Informative References">
4291<reference anchor="Nie1997" target="">
4292  <front>
4293    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4294    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4295    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4296    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4297    <author initials="H." surname="Lie" fullname="H. Lie"/>
4298    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4299    <date year="1997" month="September"/>
4300  </front>
4301  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4304<reference anchor="Pad1995" target="">
4305  <front>
4306    <title>Improving HTTP Latency</title>
4307    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4308    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4309    <date year="1995" month="December"/>
4310  </front>
4311  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4314<reference anchor="RFC1123">
4315  <front>
4316    <title>Requirements for Internet Hosts - Application and Support</title>
4317    <author initials="R." surname="Braden" fullname="Robert Braden">
4318      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4319      <address><email>Braden@ISI.EDU</email></address>
4320    </author>
4321    <date month="October" year="1989"/>
4322  </front>
4323  <seriesInfo name="STD" value="3"/>
4324  <seriesInfo name="RFC" value="1123"/>
4327<reference anchor="RFC1900">
4328  <front>
4329    <title>Renumbering Needs Work</title>
4330    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4331      <organization>CERN, Computing and Networks Division</organization>
4332      <address><email></email></address>
4333    </author>
4334    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4335      <organization>cisco Systems</organization>
4336      <address><email></email></address>
4337    </author>
4338    <date month="February" year="1996"/>
4339  </front>
4340  <seriesInfo name="RFC" value="1900"/>
4343<reference anchor="RFC1945">
4344  <front>
4345    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4346    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4347      <organization>MIT, Laboratory for Computer Science</organization>
4348      <address><email></email></address>
4349    </author>
4350    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4351      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4352      <address><email></email></address>
4353    </author>
4354    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4355      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4356      <address><email></email></address>
4357    </author>
4358    <date month="May" year="1996"/>
4359  </front>
4360  <seriesInfo name="RFC" value="1945"/>
4363<reference anchor="RFC2045">
4364  <front>
4365    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4366    <author initials="N." surname="Freed" fullname="Ned Freed">
4367      <organization>Innosoft International, Inc.</organization>
4368      <address><email></email></address>
4369    </author>
4370    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4371      <organization>First Virtual Holdings</organization>
4372      <address><email></email></address>
4373    </author>
4374    <date month="November" year="1996"/>
4375  </front>
4376  <seriesInfo name="RFC" value="2045"/>
4379<reference anchor="RFC2047">
4380  <front>
4381    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4382    <author initials="K." surname="Moore" fullname="Keith Moore">
4383      <organization>University of Tennessee</organization>
4384      <address><email></email></address>
4385    </author>
4386    <date month="November" year="1996"/>
4387  </front>
4388  <seriesInfo name="RFC" value="2047"/>
4391<reference anchor="RFC2068">
4392  <front>
4393    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4394    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4395      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4396      <address><email></email></address>
4397    </author>
4398    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4399      <organization>MIT Laboratory for Computer Science</organization>
4400      <address><email></email></address>
4401    </author>
4402    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4403      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4404      <address><email></email></address>
4405    </author>
4406    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4407      <organization>MIT Laboratory for Computer Science</organization>
4408      <address><email></email></address>
4409    </author>
4410    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4411      <organization>MIT Laboratory for Computer Science</organization>
4412      <address><email></email></address>
4413    </author>
4414    <date month="January" year="1997"/>
4415  </front>
4416  <seriesInfo name="RFC" value="2068"/>
4419<reference anchor='RFC2109'>
4420  <front>
4421    <title>HTTP State Management Mechanism</title>
4422    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4423      <organization>Bell Laboratories, Lucent Technologies</organization>
4424      <address><email></email></address>
4425    </author>
4426    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4427      <organization>Netscape Communications Corp.</organization>
4428      <address><email></email></address>
4429    </author>
4430    <date year='1997' month='February' />
4431  </front>
4432  <seriesInfo name='RFC' value='2109' />
4435<reference anchor="RFC2145">
4436  <front>
4437    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4438    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4439      <organization>Western Research Laboratory</organization>
4440      <address><email></email></address>
4441    </author>
4442    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4443      <organization>Department of Information and Computer Science</organization>
4444      <address><email></email></address>
4445    </author>
4446    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4447      <organization>MIT Laboratory for Computer Science</organization>
4448      <address><email></email></address>
4449    </author>
4450    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4451      <organization>W3 Consortium</organization>
4452      <address><email></email></address>
4453    </author>
4454    <date month="May" year="1997"/>
4455  </front>
4456  <seriesInfo name="RFC" value="2145"/>
4459<reference anchor="RFC2616">
4460  <front>
4461    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4462    <author initials="R." surname="Fielding" fullname="R. Fielding">
4463      <organization>University of California, Irvine</organization>
4464      <address><email></email></address>
4465    </author>
4466    <author initials="J." surname="Gettys" fullname="J. Gettys">
4467      <organization>W3C</organization>
4468      <address><email></email></address>
4469    </author>
4470    <author initials="J." surname="Mogul" fullname="J. Mogul">
4471      <organization>Compaq Computer Corporation</organization>
4472      <address><email></email></address>
4473    </author>
4474    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4475      <organization>MIT Laboratory for Computer Science</organization>
4476      <address><email></email></address>
4477    </author>
4478    <author initials="L." surname="Masinter" fullname="L. Masinter">
4479      <organization>Xerox Corporation</organization>
4480      <address><email></email></address>
4481    </author>
4482    <author initials="P." surname="Leach" fullname="P. Leach">
4483      <organization>Microsoft Corporation</organization>
4484      <address><email></email></address>
4485    </author>
4486    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4487      <organization>W3C</organization>
4488      <address><email></email></address>
4489    </author>
4490    <date month="June" year="1999"/>
4491  </front>
4492  <seriesInfo name="RFC" value="2616"/>
4495<reference anchor='RFC2817'>
4496  <front>
4497    <title>Upgrading to TLS Within HTTP/1.1</title>
4498    <author initials='R.' surname='Khare' fullname='R. Khare'>
4499      <organization>4K Associates / UC Irvine</organization>
4500      <address><email></email></address>
4501    </author>
4502    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4503      <organization>Agranat Systems, Inc.</organization>
4504      <address><email></email></address>
4505    </author>
4506    <date year='2000' month='May' />
4507  </front>
4508  <seriesInfo name='RFC' value='2817' />
4511<reference anchor='RFC2818'>
4512  <front>
4513    <title>HTTP Over TLS</title>
4514    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4515      <organization>RTFM, Inc.</organization>
4516      <address><email></email></address>
4517    </author>
4518    <date year='2000' month='May' />
4519  </front>
4520  <seriesInfo name='RFC' value='2818' />
4523<reference anchor='RFC2965'>
4524  <front>
4525    <title>HTTP State Management Mechanism</title>
4526    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4527      <organization>Bell Laboratories, Lucent Technologies</organization>
4528      <address><email></email></address>
4529    </author>
4530    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4531      <organization>, Inc.</organization>
4532      <address><email></email></address>
4533    </author>
4534    <date year='2000' month='October' />
4535  </front>
4536  <seriesInfo name='RFC' value='2965' />
4539<reference anchor='RFC3864'>
4540  <front>
4541    <title>Registration Procedures for Message Header Fields</title>
4542    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4543      <organization>Nine by Nine</organization>
4544      <address><email></email></address>
4545    </author>
4546    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4547      <organization>BEA Systems</organization>
4548      <address><email></email></address>
4549    </author>
4550    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4551      <organization>HP Labs</organization>
4552      <address><email></email></address>
4553    </author>
4554    <date year='2004' month='September' />
4555  </front>
4556  <seriesInfo name='BCP' value='90' />
4557  <seriesInfo name='RFC' value='3864' />
4560<reference anchor="RFC4288">
4561  <front>
4562    <title>Media Type Specifications and Registration Procedures</title>
4563    <author initials="N." surname="Freed" fullname="N. Freed">
4564      <organization>Sun Microsystems</organization>
4565      <address>
4566        <email></email>
4567      </address>
4568    </author>
4569    <author initials="J." surname="Klensin" fullname="J. Klensin">
4570      <address>
4571        <email></email>
4572      </address>
4573    </author>
4574    <date year="2005" month="December"/>
4575  </front>
4576  <seriesInfo name="BCP" value="13"/>
4577  <seriesInfo name="RFC" value="4288"/>
4580<reference anchor='RFC4395'>
4581  <front>
4582    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4583    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4584      <organization>AT&amp;T Laboratories</organization>
4585      <address>
4586        <email></email>
4587      </address>
4588    </author>
4589    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4590      <organization>Qualcomm, Inc.</organization>
4591      <address>
4592        <email></email>
4593      </address>
4594    </author>
4595    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4596      <organization>Adobe Systems</organization>
4597      <address>
4598        <email></email>
4599      </address>
4600    </author>
4601    <date year='2006' month='February' />
4602  </front>
4603  <seriesInfo name='BCP' value='115' />
4604  <seriesInfo name='RFC' value='4395' />
4607<reference anchor='RFC5226'>
4608  <front>
4609    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4610    <author initials='T.' surname='Narten' fullname='T. Narten'>
4611      <organization>IBM</organization>
4612      <address><email></email></address>
4613    </author>
4614    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4615      <organization>Google</organization>
4616      <address><email></email></address>
4617    </author>
4618    <date year='2008' month='May' />
4619  </front>
4620  <seriesInfo name='BCP' value='26' />
4621  <seriesInfo name='RFC' value='5226' />
4624<reference anchor="RFC5322">
4625  <front>
4626    <title>Internet Message Format</title>
4627    <author initials="P." surname="Resnick" fullname="P. Resnick">
4628      <organization>Qualcomm Incorporated</organization>
4629    </author>
4630    <date year="2008" month="October"/>
4631  </front>
4632  <seriesInfo name="RFC" value="5322"/>
4635<reference anchor='BCP97'>
4636  <front>
4637    <title>Handling Normative References to Standards-Track Documents</title>
4638    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4639      <address>
4640        <email></email>
4641      </address>
4642    </author>
4643    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4644      <organization>MIT</organization>
4645      <address>
4646        <email></email>
4647      </address>
4648    </author>
4649    <date year='2007' month='June' />
4650  </front>
4651  <seriesInfo name='BCP' value='97' />
4652  <seriesInfo name='RFC' value='4897' />
4655<reference anchor="Kri2001" target="">
4656  <front>
4657    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4658    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4659    <date year="2001" month="November"/>
4660  </front>
4661  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4664<reference anchor="Spe" target="">
4665  <front>
4666    <title>Analysis of HTTP Performance Problems</title>
4667    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4668    <date/>
4669  </front>
4672<reference anchor="Tou1998" target="">
4673  <front>
4674  <title>Analysis of HTTP Performance</title>
4675  <author initials="J." surname="Touch" fullname="Joe Touch">
4676    <organization>USC/Information Sciences Institute</organization>
4677    <address><email></email></address>
4678  </author>
4679  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4680    <organization>USC/Information Sciences Institute</organization>
4681    <address><email></email></address>
4682  </author>
4683  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4684    <organization>USC/Information Sciences Institute</organization>
4685    <address><email></email></address>
4686  </author>
4687  <date year="1998" month="Aug"/>
4688  </front>
4689  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4690  <annotation>(original report dated Aug. 1996)</annotation>
4696<section title="Tolerant Applications" anchor="tolerant.applications">
4698   Although this document specifies the requirements for the generation
4699   of HTTP/1.1 messages, not all applications will be correct in their
4700   implementation. We therefore recommend that operational applications
4701   be tolerant of deviations whenever those deviations can be
4702   interpreted unambiguously.
4705   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4706   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4707   &SHOULD; accept any amount of WSP characters between fields, even though
4708   only a single SP is required.
4711   The line terminator for header fields is the sequence CRLF.
4712   However, we recommend that applications, when parsing such headers fields,
4713   recognize a single LF as a line terminator and ignore the leading CR.
4716   The character set of a representation &SHOULD; be labeled as the lowest
4717   common denominator of the character codes used within that representation, with
4718   the exception that not labeling the representation is preferred over labeling
4719   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4722   Additional rules for requirements on parsing and encoding of dates
4723   and other potential problems with date encodings include:
4726  <list style="symbols">
4727     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4728        which appears to be more than 50 years in the future is in fact
4729        in the past (this helps solve the "year 2000" problem).</t>
4731     <t>Although all date formats are specified to be case-sensitive,
4732        recipients &SHOULD; match day, week and timezone names
4733        case-insensitively.</t>
4735     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4736        Expires date as earlier than the proper value, but &MUST-NOT;
4737        internally represent a parsed Expires date as later than the
4738        proper value.</t>
4740     <t>All expiration-related calculations &MUST; be done in GMT. The
4741        local time zone &MUST-NOT; influence the calculation or comparison
4742        of an age or expiration time.</t>
4744     <t>If an HTTP header field incorrectly carries a date value with a time
4745        zone other than GMT, it &MUST; be converted into GMT using the
4746        most conservative possible conversion.</t>
4747  </list>
4751<section title="Compatibility with Previous Versions" anchor="compatibility">
4753   HTTP has been in use by the World-Wide Web global information initiative
4754   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4755   was a simple protocol for hypertext data transfer across the Internet
4756   with only a single method and no metadata.
4757   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4758   methods and MIME-like messaging that could include metadata about the data
4759   transferred and modifiers on the request/response semantics. However,
4760   HTTP/1.0 did not sufficiently take into consideration the effects of
4761   hierarchical proxies, caching, the need for persistent connections, or
4762   name-based virtual hosts. The proliferation of incompletely-implemented
4763   applications calling themselves "HTTP/1.0" further necessitated a
4764   protocol version change in order for two communicating applications
4765   to determine each other's true capabilities.
4768   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4769   requirements that enable reliable implementations, adding only
4770   those new features that will either be safely ignored by an HTTP/1.0
4771   recipient or only sent when communicating with a party advertising
4772   compliance with HTTP/1.1.
4775   It is beyond the scope of a protocol specification to mandate
4776   compliance with previous versions. HTTP/1.1 was deliberately
4777   designed, however, to make supporting previous versions easy. It is
4778   worth noting that, at the time of composing this specification, we would
4779   expect general-purpose HTTP/1.1 servers to:
4780  <list style="symbols">
4781     <t>understand any valid request in the format of HTTP/1.0 and
4782        1.1;</t>
4784     <t>respond appropriately with a message in the same major version
4785        used by the client.</t>
4786  </list>
4789   And we would expect HTTP/1.1 clients to:
4790  <list style="symbols">
4791     <t>understand any valid response in the format of HTTP/1.0 or
4792        1.1.</t>
4793  </list>
4796   For most implementations of HTTP/1.0, each connection is established
4797   by the client prior to the request and closed by the server after
4798   sending the response. Some implementations implement the Keep-Alive
4799   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4802<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4804   This section summarizes major differences between versions HTTP/1.0
4805   and HTTP/1.1.
4808<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4810   The requirements that clients and servers support the Host request-header
4811   field (<xref target=""/>), report an error if it is
4812   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4813   are among the most important changes defined by this
4814   specification.
4817   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4818   addresses and servers; there was no other established mechanism for
4819   distinguishing the intended server of a request than the IP address
4820   to which that request was directed. The changes outlined above will
4821   allow the Internet, once older HTTP clients are no longer common, to
4822   support multiple Web sites from a single IP address, greatly
4823   simplifying large operational Web servers, where allocation of many
4824   IP addresses to a single host has created serious problems. The
4825   Internet will also be able to recover the IP addresses that have been
4826   allocated for the sole purpose of allowing special-purpose domain
4827   names to be used in root-level HTTP URLs. Given the rate of growth of
4828   the Web, and the number of servers already deployed, it is extremely
4829   important that all implementations of HTTP (including updates to
4830   existing HTTP/1.0 applications) correctly implement these
4831   requirements:
4832  <list style="symbols">
4833     <t>Both clients and servers &MUST; support the Host request-header field.</t>
4835     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4837     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4838        request does not include a Host request-header field.</t>
4840     <t>Servers &MUST; accept absolute URIs.</t>
4841  </list>
4846<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4848   Some clients and servers might wish to be compatible with some
4849   previous implementations of persistent connections in HTTP/1.0
4850   clients and servers. Persistent connections in HTTP/1.0 are
4851   explicitly negotiated as they are not the default behavior. HTTP/1.0
4852   experimental implementations of persistent connections are faulty,
4853   and the new facilities in HTTP/1.1 are designed to rectify these
4854   problems. The problem was that some existing HTTP/1.0 clients might
4855   send Keep-Alive to a proxy server that doesn't understand
4856   Connection, which would then erroneously forward it to the next
4857   inbound server, which would establish the Keep-Alive connection and
4858   result in a hung HTTP/1.0 proxy waiting for the close on the
4859   response. The result is that HTTP/1.0 clients must be prevented from
4860   using Keep-Alive when talking to proxies.
4863   However, talking to proxies is the most important use of persistent
4864   connections, so that prohibition is clearly unacceptable. Therefore,
4865   we need some other mechanism for indicating a persistent connection
4866   is desired, which is safe to use even when talking to an old proxy
4867   that ignores Connection. Persistent connections are the default for
4868   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4869   declaring non-persistence. See <xref target="header.connection"/>.
4872   The original HTTP/1.0 form of persistent connections (the Connection:
4873   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4877<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4879  Empty list elements in list productions have been deprecated.
4880  (<xref target="notation.abnf"/>)
4883  Rules about implicit linear whitespace between certain grammar productions
4884  have been removed; now it's only allowed when specifically pointed out
4885  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4886  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4887  Non-ASCII content in header fields and reason phrase has been obsoleted and
4888  made opaque (the TEXT rule was removed)
4889  (<xref target="basic.rules"/>)
4892  Clarify that HTTP-Version is case sensitive.
4893  (<xref target="http.version"/>)
4896  Require that invalid whitespace around field-names be rejected.
4897  (<xref target="header.fields"/>)
4900  Require recipients to handle bogus Content-Length header fields as errors.
4901  (<xref target="message.body"/>)
4904  Remove reference to non-existent identity transfer-coding value tokens.
4905  (Sections <xref format="counter" target="message.body"/> and
4906  <xref format="counter" target="transfer.codings"/>)
4909  Update use of abs_path production from RFC 1808 to the path-absolute + query
4910  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4911  method only.
4912  (<xref target="request-target"/>)
4915  Clarification that the chunk length does not include the count of the octets
4916  in the chunk header and trailer. Furthermore disallowed line folding
4917  in chunk extensions.
4918  (<xref target="chunked.encoding"/>)
4921  Remove hard limit of two connections per server.
4922  (<xref target="persistent.practical"/>)
4925  Clarify exactly when close connection options must be sent.
4926  (<xref target="header.connection"/>)
4929  Define the semantics of the "Upgrade" header field in responses other than
4930  101 (this was incorporated from <xref target="RFC2817"/>).
4931  (<xref target="header.upgrade"/>)
4936<?BEGININC p1-messaging.abnf-appendix ?>
4937<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4939<artwork type="abnf" name="p1-messaging.parsed-abnf">
4940<x:ref>BWS</x:ref> = OWS
4942<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4943<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4944<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4945<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4946 connection-token ] )
4947<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4948<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4950<x:ref>Date</x:ref> = "Date:" OWS Date-v
4951<x:ref>Date-v</x:ref> = HTTP-date
4953<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4955<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4956<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4957<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4958<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4959 ]
4960<x:ref>Host</x:ref> = "Host:" OWS Host-v
4961<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4963<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4964<x:ref>Method</x:ref> = token
4966<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4968<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4970<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4971<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4972<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
4973<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4974<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
4976<x:ref>Status-Code</x:ref> = 3DIGIT
4977<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4979<x:ref>TE</x:ref> = "TE:" OWS TE-v
4980<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4981<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4982<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4983<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4984<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4985 transfer-coding ] )
4987<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4988<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4989<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4991<x:ref>Via</x:ref> = "Via:" OWS Via-v
4992<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4993 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4994 ] )
4996<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4998<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4999<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5000<x:ref>attribute</x:ref> = token
5001<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5003<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5004<x:ref>chunk-data</x:ref> = 1*OCTET
5005<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5006<x:ref>chunk-ext-name</x:ref> = token
5007<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5008<x:ref>chunk-size</x:ref> = 1*HEXDIG
5009<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5010<x:ref>connection-token</x:ref> = token
5011<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5012 / %x2A-5B ; '*'-'['
5013 / %x5D-7E ; ']'-'~'
5014 / obs-text
5016<x:ref>date1</x:ref> = day SP month SP year
5017<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5018<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5019<x:ref>day</x:ref> = 2DIGIT
5020<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5021 / %x54.75.65 ; Tue
5022 / %x57.65.64 ; Wed
5023 / %x54.68.75 ; Thu
5024 / %x46.72.69 ; Fri
5025 / %x53.61.74 ; Sat
5026 / %x53.75.6E ; Sun
5027<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5028 / %x54. ; Tuesday
5029 / %x57.65.64.6E. ; Wednesday
5030 / %x54. ; Thursday
5031 / %x46. ; Friday
5032 / %x53. ; Saturday
5033 / %x53.75.6E.64.61.79 ; Sunday
5035<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5036<x:ref>field-name</x:ref> = token
5037<x:ref>field-value</x:ref> = *( field-content / OWS )
5039<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5040 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5042<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5043<x:ref>hour</x:ref> = 2DIGIT
5044<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5045<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5047<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5049<x:ref>message-body</x:ref> = *OCTET
5050<x:ref>minute</x:ref> = 2DIGIT
5051<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5052 / %x46.65.62 ; Feb
5053 / %x4D.61.72 ; Mar
5054 / %x41.70.72 ; Apr
5055 / %x4D.61.79 ; May
5056 / %x4A.75.6E ; Jun
5057 / %x4A.75.6C ; Jul
5058 / %x41.75.67 ; Aug
5059 / %x53.65.70 ; Sep
5060 / %x4F.63.74 ; Oct
5061 / %x4E.6F.76 ; Nov
5062 / %x44.65.63 ; Dec
5064<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5065<x:ref>obs-fold</x:ref> = CRLF
5066<x:ref>obs-text</x:ref> = %x80-FF
5068<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5069<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5070<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5071<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5072<x:ref>product</x:ref> = token [ "/" product-version ]
5073<x:ref>product-version</x:ref> = token
5074<x:ref>protocol-name</x:ref> = token
5075<x:ref>protocol-version</x:ref> = token
5076<x:ref>pseudonym</x:ref> = token
5078<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5079 / %x5D-7E ; ']'-'~'
5080 / obs-text
5081<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5082 / %x5D-7E ; ']'-'~'
5083 / obs-text
5084<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5085<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5086<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5087<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5088<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5089<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5091<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5092<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5093<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5094<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5095<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5096 / authority
5097<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5098<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5099<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5101<x:ref>second</x:ref> = 2DIGIT
5102<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5103 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5104<x:ref>start-line</x:ref> = Request-Line / Status-Line
5106<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5107<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5108 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5109<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5110<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5111<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5112<x:ref>token</x:ref> = 1*tchar
5113<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5114<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5115 transfer-extension
5116<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5117<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5119<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5121<x:ref>value</x:ref> = word
5123<x:ref>word</x:ref> = token / quoted-string
5125<x:ref>year</x:ref> = 4DIGIT
5128<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5129; Chunked-Body defined but not used
5130; Content-Length defined but not used
5131; HTTP-message defined but not used
5132; Host defined but not used
5133; Request defined but not used
5134; Response defined but not used
5135; TE defined but not used
5136; URI-reference defined but not used
5137; general-header defined but not used
5138; http-URI defined but not used
5139; https-URI defined but not used
5140; partial-URI defined but not used
5141; request-header defined but not used
5142; response-header defined but not used
5143; special defined but not used
5145<?ENDINC p1-messaging.abnf-appendix ?>
5147<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5149<section title="Since RFC 2616">
5151  Extracted relevant partitions from <xref target="RFC2616"/>.
5155<section title="Since draft-ietf-httpbis-p1-messaging-00">
5157  Closed issues:
5158  <list style="symbols">
5159    <t>
5160      <eref target=""/>:
5161      "HTTP Version should be case sensitive"
5162      (<eref target=""/>)
5163    </t>
5164    <t>
5165      <eref target=""/>:
5166      "'unsafe' characters"
5167      (<eref target=""/>)
5168    </t>
5169    <t>
5170      <eref target=""/>:
5171      "Chunk Size Definition"
5172      (<eref target=""/>)
5173    </t>
5174    <t>
5175      <eref target=""/>:
5176      "Message Length"
5177      (<eref target=""/>)
5178    </t>
5179    <t>
5180      <eref target=""/>:
5181      "Media Type Registrations"
5182      (<eref target=""/>)
5183    </t>
5184    <t>
5185      <eref target=""/>:
5186      "URI includes query"
5187      (<eref target=""/>)
5188    </t>
5189    <t>
5190      <eref target=""/>:
5191      "No close on 1xx responses"
5192      (<eref target=""/>)
5193    </t>
5194    <t>
5195      <eref target=""/>:
5196      "Remove 'identity' token references"
5197      (<eref target=""/>)
5198    </t>
5199    <t>
5200      <eref target=""/>:
5201      "Import query BNF"
5202    </t>
5203    <t>
5204      <eref target=""/>:
5205      "qdtext BNF"
5206    </t>
5207    <t>
5208      <eref target=""/>:
5209      "Normative and Informative references"
5210    </t>
5211    <t>
5212      <eref target=""/>:
5213      "RFC2606 Compliance"
5214    </t>
5215    <t>
5216      <eref target=""/>:
5217      "RFC977 reference"
5218    </t>
5219    <t>
5220      <eref target=""/>:
5221      "RFC1700 references"
5222    </t>
5223    <t>
5224      <eref target=""/>:
5225      "inconsistency in date format explanation"
5226    </t>
5227    <t>
5228      <eref target=""/>:
5229      "Date reference typo"
5230    </t>
5231    <t>
5232      <eref target=""/>:
5233      "Informative references"
5234    </t>
5235    <t>
5236      <eref target=""/>:
5237      "ISO-8859-1 Reference"
5238    </t>
5239    <t>
5240      <eref target=""/>:
5241      "Normative up-to-date references"
5242    </t>
5243  </list>
5246  Other changes:
5247  <list style="symbols">
5248    <t>
5249      Update media type registrations to use RFC4288 template.
5250    </t>
5251    <t>
5252      Use names of RFC4234 core rules DQUOTE and WSP,
5253      fix broken ABNF for chunk-data
5254      (work in progress on <eref target=""/>)
5255    </t>
5256  </list>
5260<section title="Since draft-ietf-httpbis-p1-messaging-01">
5262  Closed issues:
5263  <list style="symbols">
5264    <t>
5265      <eref target=""/>:
5266      "Bodies on GET (and other) requests"
5267    </t>
5268    <t>
5269      <eref target=""/>:
5270      "Updating to RFC4288"
5271    </t>
5272    <t>
5273      <eref target=""/>:
5274      "Status Code and Reason Phrase"
5275    </t>
5276    <t>
5277      <eref target=""/>:
5278      "rel_path not used"
5279    </t>
5280  </list>
5283  Ongoing work on ABNF conversion (<eref target=""/>):
5284  <list style="symbols">
5285    <t>
5286      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5287      "trailer-part").
5288    </t>
5289    <t>
5290      Avoid underscore character in rule names ("http_URL" ->
5291      "http-URL", "abs_path" -> "path-absolute").
5292    </t>
5293    <t>
5294      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5295      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5296      have to be updated when switching over to RFC3986.
5297    </t>
5298    <t>
5299      Synchronize core rules with RFC5234.
5300    </t>
5301    <t>
5302      Get rid of prose rules that span multiple lines.
5303    </t>
5304    <t>
5305      Get rid of unused rules LOALPHA and UPALPHA.
5306    </t>
5307    <t>
5308      Move "Product Tokens" section (back) into Part 1, as "token" is used
5309      in the definition of the Upgrade header field.
5310    </t>
5311    <t>
5312      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5313    </t>
5314    <t>
5315      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5316    </t>
5317  </list>
5321<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5323  Closed issues:
5324  <list style="symbols">
5325    <t>
5326      <eref target=""/>:
5327      "HTTP-date vs. rfc1123-date"
5328    </t>
5329    <t>
5330      <eref target=""/>:
5331      "WS in quoted-pair"
5332    </t>
5333  </list>
5336  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5337  <list style="symbols">
5338    <t>
5339      Reference RFC 3984, and update header field registrations for headers defined
5340      in this document.
5341    </t>
5342  </list>
5345  Ongoing work on ABNF conversion (<eref target=""/>):
5346  <list style="symbols">
5347    <t>
5348      Replace string literals when the string really is case-sensitive (HTTP-Version).
5349    </t>
5350  </list>
5354<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5356  Closed issues:
5357  <list style="symbols">
5358    <t>
5359      <eref target=""/>:
5360      "Connection closing"
5361    </t>
5362    <t>
5363      <eref target=""/>:
5364      "Move registrations and registry information to IANA Considerations"
5365    </t>
5366    <t>
5367      <eref target=""/>:
5368      "need new URL for PAD1995 reference"
5369    </t>
5370    <t>
5371      <eref target=""/>:
5372      "IANA Considerations: update HTTP URI scheme registration"
5373    </t>
5374    <t>
5375      <eref target=""/>:
5376      "Cite HTTPS URI scheme definition"
5377    </t>
5378    <t>
5379      <eref target=""/>:
5380      "List-type headers vs Set-Cookie"
5381    </t>
5382  </list>
5385  Ongoing work on ABNF conversion (<eref target=""/>):
5386  <list style="symbols">
5387    <t>
5388      Replace string literals when the string really is case-sensitive (HTTP-Date).
5389    </t>
5390    <t>
5391      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5392    </t>
5393  </list>
5397<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5399  Closed issues:
5400  <list style="symbols">
5401    <t>
5402      <eref target=""/>:
5403      "Out-of-date reference for URIs"
5404    </t>
5405    <t>
5406      <eref target=""/>:
5407      "RFC 2822 is updated by RFC 5322"
5408    </t>
5409  </list>
5412  Ongoing work on ABNF conversion (<eref target=""/>):
5413  <list style="symbols">
5414    <t>
5415      Use "/" instead of "|" for alternatives.
5416    </t>
5417    <t>
5418      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5419    </t>
5420    <t>
5421      Only reference RFC 5234's core rules.
5422    </t>
5423    <t>
5424      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5425      whitespace ("OWS") and required whitespace ("RWS").
5426    </t>
5427    <t>
5428      Rewrite ABNFs to spell out whitespace rules, factor out
5429      header field value format definitions.
5430    </t>
5431  </list>
5435<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5437  Closed issues:
5438  <list style="symbols">
5439    <t>
5440      <eref target=""/>:
5441      "Header LWS"
5442    </t>
5443    <t>
5444      <eref target=""/>:
5445      "Sort 1.3 Terminology"
5446    </t>
5447    <t>
5448      <eref target=""/>:
5449      "RFC2047 encoded words"
5450    </t>
5451    <t>
5452      <eref target=""/>:
5453      "Character Encodings in TEXT"
5454    </t>
5455    <t>
5456      <eref target=""/>:
5457      "Line Folding"
5458    </t>
5459    <t>
5460      <eref target=""/>:
5461      "OPTIONS * and proxies"
5462    </t>
5463    <t>
5464      <eref target=""/>:
5465      "Reason-Phrase BNF"
5466    </t>
5467    <t>
5468      <eref target=""/>:
5469      "Use of TEXT"
5470    </t>
5471    <t>
5472      <eref target=""/>:
5473      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5474    </t>
5475    <t>
5476      <eref target=""/>:
5477      "RFC822 reference left in discussion of date formats"
5478    </t>
5479  </list>
5482  Final work on ABNF conversion (<eref target=""/>):
5483  <list style="symbols">
5484    <t>
5485      Rewrite definition of list rules, deprecate empty list elements.
5486    </t>
5487    <t>
5488      Add appendix containing collected and expanded ABNF.
5489    </t>
5490  </list>
5493  Other changes:
5494  <list style="symbols">
5495    <t>
5496      Rewrite introduction; add mostly new Architecture Section.
5497    </t>
5498    <t>
5499      Move definition of quality values from Part 3 into Part 1;
5500      make TE request header field grammar independent of accept-params (defined in Part 3).
5501    </t>
5502  </list>
5506<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5508  Closed issues:
5509  <list style="symbols">
5510    <t>
5511      <eref target=""/>:
5512      "base for numeric protocol elements"
5513    </t>
5514    <t>
5515      <eref target=""/>:
5516      "comment ABNF"
5517    </t>
5518  </list>
5521  Partly resolved issues:
5522  <list style="symbols">
5523    <t>
5524      <eref target=""/>:
5525      "205 Bodies" (took out language that implied that there might be
5526      methods for which a request body MUST NOT be included)
5527    </t>
5528    <t>
5529      <eref target=""/>:
5530      "editorial improvements around HTTP-date"
5531    </t>
5532  </list>
5536<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5538  Closed issues:
5539  <list style="symbols">
5540    <t>
5541      <eref target=""/>:
5542      "Repeating single-value headers"
5543    </t>
5544    <t>
5545      <eref target=""/>:
5546      "increase connection limit"
5547    </t>
5548    <t>
5549      <eref target=""/>:
5550      "IP addresses in URLs"
5551    </t>
5552    <t>
5553      <eref target=""/>:
5554      "take over HTTP Upgrade Token Registry"
5555    </t>
5556    <t>
5557      <eref target=""/>:
5558      "CR and LF in chunk extension values"
5559    </t>
5560    <t>
5561      <eref target=""/>:
5562      "HTTP/0.9 support"
5563    </t>
5564    <t>
5565      <eref target=""/>:
5566      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5567    </t>
5568    <t>
5569      <eref target=""/>:
5570      "move definitions of gzip/deflate/compress to part 1"
5571    </t>
5572    <t>
5573      <eref target=""/>:
5574      "disallow control characters in quoted-pair"
5575    </t>
5576  </list>
5579  Partly resolved issues:
5580  <list style="symbols">
5581    <t>
5582      <eref target=""/>:
5583      "update IANA requirements wrt Transfer-Coding values" (add the
5584      IANA Considerations subsection)
5585    </t>
5586  </list>
5590<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5592  Closed issues:
5593  <list style="symbols">
5594    <t>
5595      <eref target=""/>:
5596      "header parsing, treatment of leading and trailing OWS"
5597    </t>
5598  </list>
5601  Partly resolved issues:
5602  <list style="symbols">
5603    <t>
5604      <eref target=""/>:
5605      "Placement of 13.5.1 and 13.5.2"
5606    </t>
5607    <t>
5608      <eref target=""/>:
5609      "use of term "word" when talking about header structure"
5610    </t>
5611  </list>
5615<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5617  Closed issues:
5618  <list style="symbols">
5619    <t>
5620      <eref target=""/>:
5621      "Clarification of the term 'deflate'"
5622    </t>
5623    <t>
5624      <eref target=""/>:
5625      "OPTIONS * and proxies"
5626    </t>
5627    <t>
5628      <eref target=""/>:
5629      "MIME-Version not listed in P1, general header fields"
5630    </t>
5631    <t>
5632      <eref target=""/>:
5633      "IANA registry for content/transfer encodings"
5634    </t>
5635    <t>
5636      <eref target=""/>:
5637      "Case-sensitivity of HTTP-date"
5638    </t>
5639    <t>
5640      <eref target=""/>:
5641      "use of term "word" when talking about header structure"
5642    </t>
5643  </list>
5646  Partly resolved issues:
5647  <list style="symbols">
5648    <t>
5649      <eref target=""/>:
5650      "Term for the requested resource's URI"
5651    </t>
5652  </list>
5656<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5658  Closed issues:
5659  <list style="symbols">
5660    <t>
5661      <eref target=""/>:
5662      "Connection Closing"
5663    </t>
5664    <t>
5665      <eref target=""/>:
5666      "Delimiting messages with multipart/byteranges"
5667    </t>
5668    <t>
5669      <eref target=""/>:
5670      "Handling multiple Content-Length headers"
5671    </t>
5672    <t>
5673      <eref target=""/>:
5674      "Clarify entity / representation / variant terminology"
5675    </t>
5676    <t>
5677      <eref target=""/>:
5678      "consider removing the 'changes from 2068' sections"
5679    </t>
5680  </list>
5683  Partly resolved issues:
5684  <list style="symbols">
5685    <t>
5686      <eref target=""/>:
5687      "HTTP(s) URI scheme definitions"
5688    </t>
5689  </list>
5693<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5695  Closed issues:
5696  <list style="symbols">
5697    <t>
5698      <eref target=""/>:
5699      "Trailer requirements"
5700    </t>
5701    <t>
5702      <eref target=""/>:
5703      "Text about clock requirement for caches belongs in p6"
5704    </t>
5705    <t>
5706      <eref target=""/>:
5707      "effective request URI: handling of missing host in HTTP/1.0"
5708    </t>
5709    <t>
5710      <eref target=""/>:
5711      "confusing Date requirements for clients"
5712    </t>
5713  </list>
5716  Partly resolved issues:
5717  <list style="symbols">
5718    <t>
5719      <eref target=""/>:
5720      "Handling multiple Content-Length headers"
5721    </t>
5722  </list>
5726<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5728  Closed issues:
5729  <list style="symbols">
5730    <t>
5731      <eref target=""/>:
5732      "Is * usable as a request-uri for new methods?"
5733    </t>
5734    <t>
5735      <eref target=""/>:
5736      "Migrate Upgrade details from RFC2817"
5737    </t>
5738  </list>
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