source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1271

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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 "April">
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 status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
34  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
35  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
36  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc rfcedstyle="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x=''>
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
60    <address>
61      <postal>
62        <street>345 Park Ave</street>
63        <city>San Jose</city>
64        <region>CA</region>
65        <code>95110</code>
66        <country>USA</country>
67      </postal>
68      <email></email>
69      <uri></uri>
70    </address>
71  </author>
73  <author initials="J." surname="Gettys" fullname="Jim Gettys">
74    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
75    <address>
76      <postal>
77        <street>21 Oak Knoll Road</street>
78        <city>Carlisle</city>
79        <region>MA</region>
80        <code>01741</code>
81        <country>USA</country>
82      </postal>
83      <email></email>
84      <uri></uri>
85    </address>
86  </author>
88  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
89    <organization abbrev="HP">Hewlett-Packard Company</organization>
90    <address>
91      <postal>
92        <street>HP Labs, Large Scale Systems Group</street>
93        <street>1501 Page Mill Road, MS 1177</street>
94        <city>Palo Alto</city>
95        <region>CA</region>
96        <code>94304</code>
97        <country>USA</country>
98      </postal>
99      <email></email>
100    </address>
101  </author>
103  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
104    <organization abbrev="Microsoft">Microsoft Corporation</organization>
105    <address>
106      <postal>
107        <street>1 Microsoft Way</street>
108        <city>Redmond</city>
109        <region>WA</region>
110        <code>98052</code>
111        <country>USA</country>
112      </postal>
113      <email></email>
114    </address>
115  </author>
117  <author initials="L." surname="Masinter" fullname="Larry Masinter">
118    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
119    <address>
120      <postal>
121        <street>345 Park Ave</street>
122        <city>San Jose</city>
123        <region>CA</region>
124        <code>95110</code>
125        <country>USA</country>
126      </postal>
127      <email></email>
128      <uri></uri>
129    </address>
130  </author>
132  <author initials="P." surname="Leach" fullname="Paul J. Leach">
133    <organization abbrev="Microsoft">Microsoft Corporation</organization>
134    <address>
135      <postal>
136        <street>1 Microsoft Way</street>
137        <city>Redmond</city>
138        <region>WA</region>
139        <code>98052</code>
140      </postal>
141      <email></email>
142    </address>
143  </author>
145  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
146    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
147    <address>
148      <postal>
149        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
150        <street>The Stata Center, Building 32</street>
151        <street>32 Vassar Street</street>
152        <city>Cambridge</city>
153        <region>MA</region>
154        <code>02139</code>
155        <country>USA</country>
156      </postal>
157      <email></email>
158      <uri></uri>
159    </address>
160  </author>
162  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
163    <organization abbrev="W3C">World Wide Web Consortium</organization>
164    <address>
165      <postal>
166        <street>W3C / ERCIM</street>
167        <street>2004, rte des Lucioles</street>
168        <city>Sophia-Antipolis</city>
169        <region>AM</region>
170        <code>06902</code>
171        <country>France</country>
172      </postal>
173      <email></email>
174      <uri></uri>
175    </address>
176  </author>
178  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
179    <organization abbrev="greenbytes">greenbytes GmbH</organization>
180    <address>
181      <postal>
182        <street>Hafenweg 16</street>
183        <city>Muenster</city><region>NW</region><code>48155</code>
184        <country>Germany</country>
185      </postal>
186      <phone>+49 251 2807760</phone>
187      <facsimile>+49 251 2807761</facsimile>
188      <email></email>
189      <uri></uri>
190    </address>
191  </author>
193  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
194  <workgroup>HTTPbis Working Group</workgroup>
198   The Hypertext Transfer Protocol (HTTP) is an application-level
199   protocol for distributed, collaborative, hypertext information
200   systems. HTTP has been in use by the World Wide Web global information
201   initiative since 1990. This document is Part 1 of the seven-part specification
202   that defines the protocol referred to as "HTTP/1.1" and, taken together,
203   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
204   its associated terminology, defines the "http" and "https" Uniform
205   Resource Identifier (URI) schemes, defines the generic message syntax
206   and parsing requirements for HTTP message frames, and describes
207   general security concerns for implementations.
211<note title="Editorial Note (To be removed by RFC Editor)">
212  <t>
213    Discussion of this draft should take place on the HTTPBIS working group
214    mailing list (, which is archived at
215    <eref target=""/>.
216  </t>
217  <t>
218    The current issues list is at
219    <eref target=""/> and related
220    documents (including fancy diffs) can be found at
221    <eref target=""/>.
222  </t>
223  <t>
224    The changes in this draft are summarized in <xref target="changes.since.14"/>.
225  </t>
229<section title="Introduction" anchor="introduction">
231   The Hypertext Transfer Protocol (HTTP) is an application-level
232   request/response protocol that uses extensible semantics and MIME-like
233   message payloads for flexible interaction with network-based hypertext
234   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
235   standard <xref target="RFC3986"/> to indicate the target resource and
236   relationships between resources.
237   Messages are passed in a format similar to that used by Internet mail
238   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
239   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
240   between HTTP and MIME messages).
243   HTTP is a generic interface protocol for information systems. It is
244   designed to hide the details of how a service is implemented by presenting
245   a uniform interface to clients that is independent of the types of
246   resources provided. Likewise, servers do not need to be aware of each
247   client's purpose: an HTTP request can be considered in isolation rather
248   than being associated with a specific type of client or a predetermined
249   sequence of application steps. The result is a protocol that can be used
250   effectively in many different contexts and for which implementations can
251   evolve independently over time.
254   HTTP is also designed for use as an intermediation protocol for translating
255   communication to and from non-HTTP information systems.
256   HTTP proxies and gateways can provide access to alternative information
257   services by translating their diverse protocols into a hypertext
258   format that can be viewed and manipulated by clients in the same way
259   as HTTP services.
262   One consequence of HTTP flexibility is that the protocol cannot be
263   defined in terms of what occurs behind the interface. Instead, we
264   are limited to defining the syntax of communication, the intent
265   of received communication, and the expected behavior of recipients.
266   If the communication is considered in isolation, then successful
267   actions ought to be reflected in corresponding changes to the
268   observable interface provided by servers. However, since multiple
269   clients might act in parallel and perhaps at cross-purposes, we
270   cannot require that such changes be observable beyond the scope
271   of a single response.
274   This document is Part 1 of the seven-part specification of HTTP,
275   defining the protocol referred to as "HTTP/1.1", obsoleting
276   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
277   Part 1 describes the architectural elements that are used or
278   referred to in HTTP, defines the "http" and "https" URI schemes,
279   describes overall network operation and connection management,
280   and defines HTTP message framing and forwarding requirements.
281   Our goal is to define all of the mechanisms necessary for HTTP message
282   handling that are independent of message semantics, thereby defining the
283   complete set of requirements for message parsers and
284   message-forwarding intermediaries.
287<section title="Requirements" anchor="intro.requirements">
289   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
290   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
291   document are to be interpreted as described in <xref target="RFC2119"/>.
294   An implementation is not compliant if it fails to satisfy one or more
295   of the "MUST" or "REQUIRED" level requirements for the protocols it
296   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
297   level and all the "SHOULD" level requirements for its protocols is said
298   to be "unconditionally compliant"; one that satisfies all the "MUST"
299   level requirements but not all the "SHOULD" level requirements for its
300   protocols is said to be "conditionally compliant".
304<section title="Syntax Notation" anchor="notation">
305<iref primary="true" item="Grammar" subitem="ALPHA"/>
306<iref primary="true" item="Grammar" subitem="CR"/>
307<iref primary="true" item="Grammar" subitem="CRLF"/>
308<iref primary="true" item="Grammar" subitem="CTL"/>
309<iref primary="true" item="Grammar" subitem="DIGIT"/>
310<iref primary="true" item="Grammar" subitem="DQUOTE"/>
311<iref primary="true" item="Grammar" subitem="HEXDIG"/>
312<iref primary="true" item="Grammar" subitem="LF"/>
313<iref primary="true" item="Grammar" subitem="OCTET"/>
314<iref primary="true" item="Grammar" subitem="SP"/>
315<iref primary="true" item="Grammar" subitem="VCHAR"/>
316<iref primary="true" item="Grammar" subitem="WSP"/>
318   This specification uses the Augmented Backus-Naur Form (ABNF) notation
319   of <xref target="RFC5234"/>.
321<t anchor="core.rules">
322  <x:anchor-alias value="ALPHA"/>
323  <x:anchor-alias value="CTL"/>
324  <x:anchor-alias value="CR"/>
325  <x:anchor-alias value="CRLF"/>
326  <x:anchor-alias value="DIGIT"/>
327  <x:anchor-alias value="DQUOTE"/>
328  <x:anchor-alias value="HEXDIG"/>
329  <x:anchor-alias value="LF"/>
330  <x:anchor-alias value="OCTET"/>
331  <x:anchor-alias value="SP"/>
332  <x:anchor-alias value="VCHAR"/>
333  <x:anchor-alias value="WSP"/>
334   The following core rules are included by
335   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
336   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
337   DIGIT (decimal 0-9), DQUOTE (double quote),
338   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
339   OCTET (any 8-bit sequence of data), SP (space),
340   VCHAR (any visible <xref target="USASCII"/> character),
341   and WSP (whitespace).
344   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
345   "obsolete" grammar rules that appear for historical reasons.
348<section title="ABNF Extension: #rule" anchor="notation.abnf">
350  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
351  improve readability.
354  A construct "#" is defined, similar to "*", for defining comma-delimited
355  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
356  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
357  comma (",") and optional whitespace (OWS,
358  <xref target="basic.rules"/>).   
361  Thus,
362</preamble><artwork type="example">
363  1#element =&gt; element *( OWS "," OWS element )
366  and:
367</preamble><artwork type="example">
368  #element =&gt; [ 1#element ]
371  and for n &gt;= 1 and m &gt; 1:
372</preamble><artwork type="example">
373  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
376  For compatibility with legacy list rules, recipients &SHOULD; accept empty
377  list elements. In other words, consumers would follow the list productions:
379<figure><artwork type="example">
380  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
382  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
385  Note that empty elements do not contribute to the count of elements present,
386  though.
389  For example, given these ABNF productions:
391<figure><artwork type="example">
392  example-list      = 1#example-list-elmt
393  example-list-elmt = token ; see <xref target="basic.rules"/>
396  Then these are valid values for example-list (not including the double
397  quotes, which are present for delimitation only):
399<figure><artwork type="example">
400  "foo,bar"
401  " foo ,bar,"
402  "  foo , ,bar,charlie   "
403  "foo ,bar,   charlie "
406  But these values would be invalid, as at least one non-empty element is
407  required:
409<figure><artwork type="example">
410  ""
411  ","
412  ",   ,"
415  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
416  expanded as explained above.
420<section title="Basic Rules" anchor="basic.rules">
421<t anchor="rule.CRLF">
422  <x:anchor-alias value="CRLF"/>
423   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
424   protocol elements other than the message-body
425   (see <xref target="tolerant.applications"/> for tolerant applications).
427<t anchor="rule.LWS">
428   This specification uses three rules to denote the use of linear
429   whitespace: OWS (optional whitespace), RWS (required whitespace), and
430   BWS ("bad" whitespace).
433   The OWS rule is used where zero or more linear whitespace octets might
434   appear. OWS &SHOULD; either not be produced or be produced as a single
435   SP. Multiple OWS octets that occur within field-content &SHOULD;
436   be replaced with a single SP before interpreting the field value or
437   forwarding the message downstream.
440   RWS is used when at least one linear whitespace octet is required to
441   separate field tokens. RWS &SHOULD; be produced as a single SP.
442   Multiple RWS octets that occur within field-content &SHOULD; be
443   replaced with a single SP before interpreting the field value or
444   forwarding the message downstream.
447   BWS is used where the grammar allows optional whitespace for historical
448   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
449   recipients &MUST; accept such bad optional whitespace and remove it before
450   interpreting the field value or forwarding the message downstream.
452<t anchor="rule.whitespace">
453  <x:anchor-alias value="BWS"/>
454  <x:anchor-alias value="OWS"/>
455  <x:anchor-alias value="RWS"/>
456  <x:anchor-alias value="obs-fold"/>
458<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"/>
459  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "optional" whitespace
461  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
462                 ; "required" whitespace
463  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
464                 ; "bad" whitespace
465  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
466                 ; see <xref target="header.fields"/>
468<t anchor="rule.token.separators">
469  <x:anchor-alias value="tchar"/>
470  <x:anchor-alias value="token"/>
471  <x:anchor-alias value="special"/>
472  <x:anchor-alias value="word"/>
473   Many HTTP/1.1 header field values consist of words (token or quoted-string)
474   separated by whitespace or special characters. These special characters
475   &MUST; be in a quoted string to be used within a parameter value (as defined
476   in <xref target="transfer.codings"/>).
478<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"/>
479  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
481  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
483  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
484 -->
485  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
486                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
487                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
488                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
490  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
491                 / ";" / ":" / "\" / DQUOTE / "/" / "["
492                 / "]" / "?" / "=" / "{" / "}"
494<t anchor="rule.quoted-string">
495  <x:anchor-alias value="quoted-string"/>
496  <x:anchor-alias value="qdtext"/>
497  <x:anchor-alias value="obs-text"/>
498   A string of text is parsed as a single word if it is quoted using
499   double-quote marks.
501<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"/>
502  <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>
503  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
504                 ; <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>
505  <x:ref>obs-text</x:ref>       = %x80-FF
507<t anchor="rule.quoted-pair">
508  <x:anchor-alias value="quoted-pair"/>
509   The backslash octet ("\") can be used as a single-octet
510   quoting mechanism within quoted-string constructs:
512<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
513  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
516   Senders &SHOULD-NOT; escape octets that do not require escaping
517   (i.e., other than DQUOTE and the backslash octet).
524<section title="HTTP-related architecture" anchor="architecture">
526   HTTP was created for the World Wide Web architecture
527   and has evolved over time to support the scalability needs of a worldwide
528   hypertext system. Much of that architecture is reflected in the terminology
529   and syntax productions used to define HTTP.
532<section title="Client/Server Messaging" anchor="operation">
533<iref primary="true" item="client"/>
534<iref primary="true" item="server"/>
535<iref primary="true" item="connection"/>
537   HTTP is a stateless request/response protocol that operates by exchanging
538   messages across a reliable transport or session-layer
539   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
540   program that establishes a connection to a server for the purpose of
541   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
542   program that accepts connections in order to service HTTP requests by
543   sending HTTP responses.
545<iref primary="true" item="user agent"/>
546<iref primary="true" item="origin server"/>
547<iref primary="true" item="browser"/>
548<iref primary="true" item="spider"/>
549<iref primary="true" item="sender"/>
550<iref primary="true" item="recipient"/>
552   Note that the terms client and server refer only to the roles that
553   these programs perform for a particular connection.  The same program
554   might act as a client on some connections and a server on others.  We use
555   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
556   such as a WWW browser, editor, or spider (web-traversing robot), and
557   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
558   authoritative responses to a request.  For general requirements, we use
559   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
560   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
561   message.
564   Most HTTP communication consists of a retrieval request (GET) for
565   a representation of some resource identified by a URI.  In the
566   simplest case, this might be accomplished via a single bidirectional
567   connection (===) between the user agent (UA) and the origin server (O).
569<figure><artwork type="drawing">
570         request   &gt;
571    UA ======================================= O
572                                &lt;   response
574<iref primary="true" item="message"/>
575<iref primary="true" item="request"/>
576<iref primary="true" item="response"/>
578   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
579   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
580   protocol version, followed by MIME-like header fields containing
581   request modifiers, client information, and payload metadata, an empty
582   line to indicate the end of the header section, and finally the payload
583   body (if any).
586   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
587   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
588   includes the protocol version, a success or error code, and textual
589   reason phrase, followed by MIME-like header fields containing server
590   information, resource metadata, and payload metadata, an empty line to
591   indicate the end of the header section, and finally the payload body (if any).
594   The following example illustrates a typical message exchange for a
595   GET request on the URI "":
598client request:
599</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
600GET /hello.txt HTTP/1.1
601User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
603Accept: */*
607server response:
608</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
609HTTP/1.1 200 OK
610Date: Mon, 27 Jul 2009 12:28:53 GMT
611Server: Apache
612Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
613ETag: "34aa387-d-1568eb00"
614Accept-Ranges: bytes
615Content-Length: <x:length-of target="exbody"/>
616Vary: Accept-Encoding
617Content-Type: text/plain
619<x:span anchor="exbody">Hello World!
623<section title="Connections and Transport Independence" anchor="transport-independence">
625   HTTP messaging is independent of the underlying transport or
626   session-layer connection protocol(s).  HTTP only presumes a reliable
627   transport with in-order delivery of requests and the corresponding
628   in-order delivery of responses.  The mapping of HTTP request and
629   response structures onto the data units of the underlying transport
630   protocol is outside the scope of this specification.
633   The specific connection protocols to be used for an interaction
634   are determined by client configuration and the target resource's URI.
635   For example, the "http" URI scheme
636   (<xref target="http.uri"/>) indicates a default connection of TCP
637   over IP, with a default TCP port of 80, but the client might be
638   configured to use a proxy via some other connection port or protocol
639   instead of using the defaults.
642   A connection might be used for multiple HTTP request/response exchanges,
643   as defined in <xref target="persistent.connections"/>.
647<section title="Intermediaries" anchor="intermediaries">
648<iref primary="true" item="intermediary"/>
650   HTTP enables the use of intermediaries to satisfy requests through
651   a chain of connections.  There are three common forms of HTTP
652   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
653   a single intermediary might act as an origin server, proxy, gateway,
654   or tunnel, switching behavior based on the nature of each request.
656<figure><artwork type="drawing">
657         &gt;             &gt;             &gt;             &gt;
658    UA =========== A =========== B =========== C =========== O
659               &lt;             &lt;             &lt;             &lt;
662   The figure above shows three intermediaries (A, B, and C) between the
663   user agent and origin server. A request or response message that
664   travels the whole chain will pass through four separate connections.
665   Some HTTP communication options
666   might apply only to the connection with the nearest, non-tunnel
667   neighbor, only to the end-points of the chain, or to all connections
668   along the chain. Although the diagram is linear, each participant might
669   be engaged in multiple, simultaneous communications. For example, B
670   might be receiving requests from many clients other than A, and/or
671   forwarding requests to servers other than C, at the same time that it
672   is handling A's request.
675<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
676<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
677   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
678   to describe various requirements in relation to the directional flow of a
679   message: all messages flow from upstream to downstream.
680   Likewise, we use the terms inbound and outbound to refer to
681   directions in relation to the request path:
682   "<x:dfn>inbound</x:dfn>" means toward the origin server and
683   "<x:dfn>outbound</x:dfn>" means toward the user agent.
685<t><iref primary="true" item="proxy"/>
686   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
687   client, usually via local configuration rules, to receive requests
688   for some type(s) of absolute URI and attempt to satisfy those
689   requests via translation through the HTTP interface.  Some translations
690   are minimal, such as for proxy requests for "http" URIs, whereas
691   other requests might require translation to and from entirely different
692   application-layer protocols. Proxies are often used to group an
693   organization's HTTP requests through a common intermediary for the
694   sake of security, annotation services, or shared caching.
697<iref primary="true" item="transforming proxy"/>
698<iref primary="true" item="non-transforming proxy"/>
699   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
700   or configured to modify request or response messages in a semantically
701   meaningful way (i.e., modifications, beyond those required by normal
702   HTTP processing, that change the message in a way that would be
703   significant to the original sender or potentially significant to
704   downstream recipients).  For example, a transforming proxy might be
705   acting as a shared annotation server (modifying responses to include
706   references to a local annotation database), a malware filter, a
707   format transcoder, or an intranet-to-Internet privacy filter.  Such
708   transformations are presumed to be desired by the client (or client
709   organization) that selected the proxy and are beyond the scope of
710   this specification.  However, when a proxy is not intended to transform
711   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
712   requirements that preserve HTTP message semantics.
714<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
715<iref primary="true" item="accelerator"/>
716   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
717   is a receiving agent that acts
718   as a layer above some other server(s) and translates the received
719   requests to the underlying server's protocol.  Gateways are often
720   used to encapsulate legacy or untrusted information services, to
721   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
722   enable partitioning or load-balancing of HTTP services across
723   multiple machines.
726   A gateway behaves as an origin server on its outbound connection and
727   as a user agent on its inbound connection.
728   All HTTP requirements applicable to an origin server
729   also apply to the outbound communication of a gateway.
730   A gateway communicates with inbound servers using any protocol that
731   it desires, including private extensions to HTTP that are outside
732   the scope of this specification.  However, an HTTP-to-HTTP gateway
733   that wishes to interoperate with third-party HTTP servers &MUST;
734   comply with HTTP user agent requirements on the gateway's inbound
735   connection and &MUST; implement the Connection
736   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
737   header fields for both connections.
739<t><iref primary="true" item="tunnel"/>
740   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
741   without changing the messages. Once active, a tunnel is not
742   considered a party to the HTTP communication, though the tunnel might
743   have been initiated by an HTTP request. A tunnel ceases to exist when
744   both ends of the relayed connection are closed. Tunnels are used to
745   extend a virtual connection through an intermediary, such as when
746   transport-layer security is used to establish private communication
747   through a shared firewall proxy.
749<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
750<iref primary="true" item="captive portal"/>
751   In addition, there may exist network intermediaries that are not
752   considered part of the HTTP communication but nevertheless act as
753   filters or redirecting agents (usually violating HTTP semantics,
754   causing security problems, and otherwise making a mess of things).
755   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
756   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
757   or "<x:dfn>captive portal</x:dfn>",
758   differs from an HTTP proxy because it has not been selected by the client.
759   Instead, the network intermediary redirects outgoing TCP port 80 packets
760   (and occasionally other common port traffic) to an internal HTTP server.
761   Interception proxies are commonly found on public network access points,
762   as a means of enforcing account subscription prior to allowing use of
763   non-local Internet services, and within corporate firewalls to enforce
764   network usage policies.
765   They are indistinguishable from a man-in-the-middle attack.
769<section title="Caches" anchor="caches">
770<iref primary="true" item="cache"/>
772   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
773   subsystem that controls its message storage, retrieval, and deletion.
774   A cache stores cacheable responses in order to reduce the response
775   time and network bandwidth consumption on future, equivalent
776   requests. Any client or server &MAY; employ a cache, though a cache
777   cannot be used by a server while it is acting as a tunnel.
780   The effect of a cache is that the request/response chain is shortened
781   if one of the participants along the chain has a cached response
782   applicable to that request. The following illustrates the resulting
783   chain if B has a cached copy of an earlier response from O (via C)
784   for a request which has not been cached by UA or A.
786<figure><artwork type="drawing">
787            &gt;             &gt;
788       UA =========== A =========== B - - - - - - C - - - - - - O
789                  &lt;             &lt;
791<t><iref primary="true" item="cacheable"/>
792   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
793   the response message for use in answering subsequent requests.
794   Even when a response is cacheable, there might be additional
795   constraints placed by the client or by the origin server on when
796   that cached response can be used for a particular request. HTTP
797   requirements for cache behavior and cacheable responses are
798   defined in &caching-overview;. 
801   There are a wide variety of architectures and configurations
802   of caches and proxies deployed across the World Wide Web and
803   inside large organizations. These systems include national hierarchies
804   of proxy caches to save transoceanic bandwidth, systems that
805   broadcast or multicast cache entries, organizations that distribute
806   subsets of cached data via optical media, and so on.
810<section title="Protocol Versioning" anchor="http.version">
811  <x:anchor-alias value="HTTP-Version"/>
812  <x:anchor-alias value="HTTP-Prot-Name"/>
814   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
815   versions of the protocol. This specification defines version "1.1".
816   The protocol version as a whole indicates the sender's compliance
817   with the set of requirements laid out in that version's corresponding
818   specification of HTTP.
821   The version of an HTTP message is indicated by an HTTP-Version field
822   in the first line of the message. HTTP-Version is case-sensitive.
824<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
825  <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>
826  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
829   The HTTP version number consists of two non-negative decimal integers
830   separated by a "." (period or decimal point).  The first
831   number ("major version") indicates the HTTP messaging syntax, whereas
832   the second number ("minor version") indicates the highest minor
833   version to which the sender is at least conditionally compliant and
834   able to understand for future communication.  The minor version
835   advertises the sender's communication capabilities even when the
836   sender is only using a backwards-compatible subset of the protocol,
837   thereby letting the recipient know that more advanced features can
838   be used in response (by servers) or in future requests (by clients).
841   When comparing HTTP versions, the numbers &MUST; be compared
842   numerically rather than lexically.  For example, HTTP/2.4 is a lower
843   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
844   Leading zeros &MUST; be ignored by recipients and &MUST-NOT; be sent.
847   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
848   <xref target="RFC1945"/> or a recipient whose version is unknown,
849   the HTTP/1.1 message is constructed such that it can be interpreted
850   as a valid HTTP/1.0 message if all of the newer features are ignored.
851   This specification places recipient-version requirements on some
852   new features so that a compliant sender will only use compatible
853   features until it has determined, through configuration or the
854   receipt of a message, that the recipient supports HTTP/1.1.
857   The interpretation of an HTTP header field does not change
858   between minor versions of the same major version, though the default
859   behavior of a recipient in the absence of such a field can change.
860   Unless specified otherwise, header fields defined in HTTP/1.1 are
861   defined for all versions of HTTP/1.x.  In particular, the Host and
862   Connection header fields ought to be implemented by all HTTP/1.x
863   implementations whether or not they advertise compliance with HTTP/1.1.
866   New header fields can be defined such that, when they are
867   understood by a recipient, they might override or enhance the
868   interpretation of previously defined header fields.  When an
869   implementation receives an unrecognized header field, the recipient
870   &MUST; ignore that header field for local processing regardless of
871   the message's HTTP version.  An unrecognized header field received
872   by a proxy &MUST; be forwarded downstream unless the header field's
873   field-name is listed in the message's Connection header-field
874   (see <xref target="header.connection"/>).
875   These requirements allow HTTP's functionality to be enhanced without
876   requiring prior update of all compliant intermediaries.
879   Intermediaries that process HTTP messages (i.e., all intermediaries
880   other than those acting as a tunnel) &MUST; send their own HTTP-Version
881   in forwarded messages.  In other words, they &MUST-NOT; blindly
882   forward the first line of an HTTP message without ensuring that the
883   protocol version matches what the intermediary understands, and
884   is at least conditionally compliant to, for both the receiving and
885   sending of messages.  Forwarding an HTTP message without rewriting
886   the HTTP-Version might result in communication errors when downstream
887   recipients use the message sender's version to determine what features
888   are safe to use for later communication with that sender.
891   An HTTP client &SHOULD; send a request version equal to the highest
892   version for which the client is at least conditionally compliant and
893   whose major version is no higher than the highest version supported
894   by the server, if this is known.  An HTTP client &MUST-NOT; send a
895   version for which it is not at least conditionally compliant.
898   An HTTP client &MAY; send a lower request version if it is known that
899   the server incorrectly implements the HTTP specification, but only
900   after the client has attempted at least one normal request and determined
901   from the response status or header fields (e.g., Server) that the
902   server improperly handles higher request versions.
905   An HTTP server &SHOULD; send a response version equal to the highest
906   version for which the server is at least conditionally compliant and
907   whose major version is less than or equal to the one received in the
908   request.  An HTTP server &MUST-NOT; send a version for which it is not
909   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
910   Version Not Supported) response if it cannot send a response using the
911   major version used in the client's request.
914   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
915   if it is known or suspected that the client incorrectly implements the
916   HTTP specification and is incapable of correctly processing later
917   version responses, such as when a client fails to parse the version
918   number correctly or when an intermediary is known to blindly forward
919   the HTTP-Version even when it doesn't comply with the given minor
920   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
921   performed unless triggered by specific client attributes, such as when
922   one or more of the request header fields (e.g., User-Agent) uniquely
923   match the values sent by a client known to be in error.
926   The intention of HTTP's versioning design is that the major number
927   will only be incremented if an incompatible message syntax is
928   introduced, and that the minor number will only be incremented when
929   changes made to the protocol have the effect of adding to the message
930   semantics or implying additional capabilities of the sender.  However,
931   the minor version was not incremented for the changes introduced between
932   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
933   is specifically avoiding any such changes to the protocol.
937<section title="Uniform Resource Identifiers" anchor="uri">
938<iref primary="true" item="resource"/>
940   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
941   throughout HTTP as the means for identifying resources. URI references
942   are used to target requests, indicate redirects, and define relationships.
943   HTTP does not limit what a resource might be; it merely defines an interface
944   that can be used to interact with a resource via HTTP. More information on
945   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
947  <x:anchor-alias value="URI-reference"/>
948  <x:anchor-alias value="absolute-URI"/>
949  <x:anchor-alias value="relative-part"/>
950  <x:anchor-alias value="authority"/>
951  <x:anchor-alias value="path-abempty"/>
952  <x:anchor-alias value="path-absolute"/>
953  <x:anchor-alias value="port"/>
954  <x:anchor-alias value="query"/>
955  <x:anchor-alias value="uri-host"/>
956  <x:anchor-alias value="partial-URI"/>
958   This specification adopts the definitions of "URI-reference",
959   "absolute-URI", "relative-part", "port", "host",
960   "path-abempty", "path-absolute", "query", and "authority" from the
961   URI generic syntax <xref target="RFC3986"/>.
962   In addition, we define a partial-URI rule for protocol elements
963   that allow a relative URI but not a fragment.
965<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"/>
966  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
967  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
968  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
969  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
970  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
971  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
972  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
973  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
974  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
976  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
979   Each protocol element in HTTP that allows a URI reference will indicate
980   in its ABNF production whether the element allows any form of reference
981   (URI-reference), only a URI in absolute form (absolute-URI), only the
982   path and optional query components, or some combination of the above.
983   Unless otherwise indicated, URI references are parsed relative to the
984   effective request URI, which defines the default base URI for references
985   in both the request and its corresponding response.
988<section title="http URI scheme" anchor="http.uri">
989  <x:anchor-alias value="http-URI"/>
990  <iref item="http URI scheme" primary="true"/>
991  <iref item="URI scheme" subitem="http" primary="true"/>
993   The "http" URI scheme is hereby defined for the purpose of minting
994   identifiers according to their association with the hierarchical
995   namespace governed by a potential HTTP origin server listening for
996   TCP connections on a given port.
998<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
999  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1002   The HTTP origin server is identified by the generic syntax's
1003   <x:ref>authority</x:ref> component, which includes a host identifier
1004   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1005   The remainder of the URI, consisting of both the hierarchical path
1006   component and optional query component, serves as an identifier for
1007   a potential resource within that origin server's name space.
1010   If the host identifier is provided as an IP literal or IPv4 address,
1011   then the origin server is any listener on the indicated TCP port at
1012   that IP address. If host is a registered name, then that name is
1013   considered an indirect identifier and the recipient might use a name
1014   resolution service, such as DNS, to find the address of a listener
1015   for that host.
1016   The host &MUST-NOT; be empty; if an "http" URI is received with an
1017   empty host, then it &MUST; be rejected as invalid.
1018   If the port subcomponent is empty or not given, then TCP port 80 is
1019   assumed (the default reserved port for WWW services).
1022   Regardless of the form of host identifier, access to that host is not
1023   implied by the mere presence of its name or address. The host might or might
1024   not exist and, even when it does exist, might or might not be running an
1025   HTTP server or listening to the indicated port. The "http" URI scheme
1026   makes use of the delegated nature of Internet names and addresses to
1027   establish a naming authority (whatever entity has the ability to place
1028   an HTTP server at that Internet name or address) and allows that
1029   authority to determine which names are valid and how they might be used.
1032   When an "http" URI is used within a context that calls for access to the
1033   indicated resource, a client &MAY; attempt access by resolving
1034   the host to an IP address, establishing a TCP connection to that address
1035   on the indicated port, and sending an HTTP request message to the server
1036   containing the URI's identifying data as described in <xref target="request"/>.
1037   If the server responds to that request with a non-interim HTTP response
1038   message, as described in <xref target="response"/>, then that response
1039   is considered an authoritative answer to the client's request.
1042   Although HTTP is independent of the transport protocol, the "http"
1043   scheme is specific to TCP-based services because the name delegation
1044   process depends on TCP for establishing authority.
1045   An HTTP service based on some other underlying connection protocol
1046   would presumably be identified using a different URI scheme, just as
1047   the "https" scheme (below) is used for servers that require an SSL/TLS
1048   transport layer on a connection. Other protocols might also be used to
1049   provide access to "http" identified resources &mdash; it is only the
1050   authoritative interface used for mapping the namespace that is
1051   specific to TCP.
1054   The URI generic syntax for authority also includes a deprecated
1055   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1056   for including user authentication information in the URI.  Some
1057   implementations make use of the userinfo component for internal
1058   configuration of authentication information, such as within command
1059   invocation options, configuration files, or bookmark lists, even
1060   though such usage might expose a user identifier or password.
1061   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1062   delimiter) when transmitting an "http" URI in a message.  Recipients
1063   of HTTP messages that contain a URI reference &SHOULD; parse for the
1064   existence of userinfo and treat its presence as an error, likely
1065   indicating that the deprecated subcomponent is being used to obscure
1066   the authority for the sake of phishing attacks.
1070<section title="https URI scheme" anchor="https.uri">
1071   <x:anchor-alias value="https-URI"/>
1072   <iref item="https URI scheme"/>
1073   <iref item="URI scheme" subitem="https"/>
1075   The "https" URI scheme is hereby defined for the purpose of minting
1076   identifiers according to their association with the hierarchical
1077   namespace governed by a potential HTTP origin server listening for
1078   SSL/TLS-secured connections on a given TCP port.
1081   All of the requirements listed above for the "http" scheme are also
1082   requirements for the "https" scheme, except that a default TCP port
1083   of 443 is assumed if the port subcomponent is empty or not given,
1084   and the TCP connection &MUST; be secured for privacy through the
1085   use of strong encryption prior to sending the first HTTP request.
1087<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1088  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1091   Unlike the "http" scheme, responses to "https" identified requests
1092   are never "public" and thus &MUST-NOT; be reused for shared caching.
1093   They can, however, be reused in a private cache if the message is
1094   cacheable by default in HTTP or specifically indicated as such by
1095   the Cache-Control header field (&header-cache-control;).
1098   Resources made available via the "https" scheme have no shared
1099   identity with the "http" scheme even if their resource identifiers
1100   indicate the same authority (the same host listening to the same
1101   TCP port).  They are distinct name spaces and are considered to be
1102   distinct origin servers.  However, an extension to HTTP that is
1103   defined to apply to entire host domains, such as the Cookie protocol
1104   <xref target="draft-ietf-httpstate-cookie"/>, can allow information
1105   set by one service to impact communication with other services
1106   within a matching group of host domains.
1109   The process for authoritative access to an "https" identified
1110   resource is defined in <xref target="RFC2818"/>.
1114<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1116   Since the "http" and "https" schemes conform to the URI generic syntax,
1117   such URIs are normalized and compared according to the algorithm defined
1118   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1119   described above for each scheme.
1122   If the port is equal to the default port for a scheme, the normal
1123   form is to elide the port subcomponent. Likewise, an empty path
1124   component is equivalent to an absolute path of "/", so the normal
1125   form is to provide a path of "/" instead. The scheme and host
1126   are case-insensitive and normally provided in lowercase; all
1127   other components are compared in a case-sensitive manner.
1128   Characters other than those in the "reserved" set are equivalent
1129   to their percent-encoded octets (see <xref target="RFC3986"
1130   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1133   For example, the following three URIs are equivalent:
1135<figure><artwork type="example">
1144<section title="Message Format" anchor="http.message">
1145<x:anchor-alias value="generic-message"/>
1146<x:anchor-alias value="message.types"/>
1147<x:anchor-alias value="HTTP-message"/>
1148<x:anchor-alias value="start-line"/>
1149<iref item="header section"/>
1150<iref item="headers"/>
1151<iref item="header field"/>
1153   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1154   octets in a format similar to the Internet Message Format
1155   <xref target="RFC5322"/>: zero or more header fields (collectively
1156   referred to as the "headers" or the "header section"), an empty line
1157   indicating the end of the header section, and an optional message-body.
1160   An HTTP message can either be a request from client to server or a
1161   response from server to client.  Syntactically, the two types of message
1162   differ only in the start-line, which is either a Request-Line (for requests)
1163   or a Status-Line (for responses), and in the algorithm for determining
1164   the length of the message-body (<xref target="message.body"/>).
1165   In theory, a client could receive requests and a server could receive
1166   responses, distinguishing them by their different start-line formats,
1167   but in practice servers are implemented to only expect a request
1168   (a response is interpreted as an unknown or invalid request method)
1169   and clients are implemented to only expect a response.
1171<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1172  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1173                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1174                    <x:ref>CRLF</x:ref>
1175                    [ <x:ref>message-body</x:ref> ]
1176  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1179   Implementations &MUST-NOT; send whitespace between the start-line and
1180   the first header field. The presence of such whitespace in a request
1181   might be an attempt to trick a server into ignoring that field or
1182   processing the line after it as a new request, either of which might
1183   result in a security vulnerability if other implementations within
1184   the request chain interpret the same message differently.
1185   Likewise, the presence of such whitespace in a response might be
1186   ignored by some clients or cause others to cease parsing.
1189<section title="Message Parsing Robustness" anchor="message.robustness">
1191   In the interest of robustness, servers &SHOULD; ignore at least one
1192   empty line received where a Request-Line is expected. In other words, if
1193   the server is reading the protocol stream at the beginning of a
1194   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1197   Some old HTTP/1.0 client implementations send an extra CRLF
1198   after a POST request as a lame workaround for some early server
1199   applications that failed to read message-body content that was
1200   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1201   preface or follow a request with an extra CRLF.  If terminating
1202   the request message-body with a line-ending is desired, then the
1203   client &MUST; include the terminating CRLF octets as part of the
1204   message-body length.
1207   When a server listening only for HTTP request messages, or processing
1208   what appears from the start-line to be an HTTP request message,
1209   receives a sequence of octets that does not match the HTTP-message
1210   grammar aside from the robustness exceptions listed above, the
1211   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1214   The normal procedure for parsing an HTTP message is to read the
1215   start-line into a structure, read each header field into a hash
1216   table by field name until the empty line, and then use the parsed
1217   data to determine if a message-body is expected.  If a message-body
1218   has been indicated, then it is read as a stream until an amount
1219   of octets equal to the message-body length is read or the connection
1220   is closed.  Care must be taken to parse an HTTP message as a sequence
1221   of octets in an encoding that is a superset of US-ASCII.  Attempting
1222   to parse HTTP as a stream of Unicode characters in a character encoding
1223   like UTF-16 might introduce security flaws due to the differing ways
1224   that such parsers interpret invalid characters.
1227   HTTP allows the set of defined header fields to be extended without
1228   changing the protocol version (see <xref target="header.field.registration"/>).
1229   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1230   proxy is specifically configured to block or otherwise transform such
1231   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1235<section title="Header Fields" anchor="header.fields">
1236  <x:anchor-alias value="header-field"/>
1237  <x:anchor-alias value="field-content"/>
1238  <x:anchor-alias value="field-name"/>
1239  <x:anchor-alias value="field-value"/>
1240  <x:anchor-alias value="OWS"/>
1242   Each HTTP header field consists of a case-insensitive field name
1243   followed by a colon (":"), optional whitespace, and the field value.
1245<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"/>
1246  <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>
1247  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1248  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1249  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1252   No whitespace is allowed between the header field name and colon. For
1253   security reasons, any request message received containing such whitespace
1254   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1255   &MUST; remove any such whitespace from a response message before
1256   forwarding the message downstream.
1259   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1260   preferred. The field value does not include any leading or trailing white
1261   space: OWS occurring before the first non-whitespace octet of the
1262   field value or after the last non-whitespace octet of the field value
1263   is ignored and &SHOULD; be removed before further processing (as this does
1264   not change the meaning of the header field).
1267   The order in which header fields with differing field names are
1268   received is not significant. However, it is "good practice" to send
1269   header fields that contain control data first, such as Host on
1270   requests and Date on responses, so that implementations can decide
1271   when not to handle a message as early as possible.  A server &MUST;
1272   wait until the entire header section is received before interpreting
1273   a request message, since later header fields might include conditionals,
1274   authentication credentials, or deliberately misleading duplicate
1275   header fields that would impact request processing.
1278   Multiple header fields with the same field name &MUST-NOT; be
1279   sent in a message unless the entire field value for that
1280   header field is defined as a comma-separated list [i.e., #(values)].
1281   Multiple header fields with the same field name can be combined into
1282   one "field-name: field-value" pair, without changing the semantics of the
1283   message, by appending each subsequent field value to the combined
1284   field value in order, separated by a comma. The order in which
1285   header fields with the same field name are received is therefore
1286   significant to the interpretation of the combined field value;
1287   a proxy &MUST-NOT; change the order of these field values when
1288   forwarding a message.
1291  <t>
1292   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1293   practice can occur multiple times, but does not use the list syntax, and
1294   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1295   for details.) Also note that the Set-Cookie2 header field specified in
1296   <xref target="RFC2965"/> does not share this problem.
1297  </t>
1300   Historically, HTTP header field values could be extended over multiple
1301   lines by preceding each extra line with at least one space or horizontal
1302   tab octet (line folding). This specification deprecates such line
1303   folding except within the message/http media type
1304   (<xref target=""/>).
1305   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1306   (i.e., that contain any field-content that matches the obs-fold rule) unless
1307   the message is intended for packaging within the message/http media type.
1308   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1309   obs-fold whitespace with a single SP prior to interpreting the field value
1310   or forwarding the message downstream.
1313   Historically, HTTP has allowed field content with text in the ISO-8859-1
1314   <xref target="ISO-8859-1"/> character encoding and supported other
1315   character sets only through use of <xref target="RFC2047"/> encoding.
1316   In practice, most HTTP header field values use only a subset of the
1317   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1318   header fields &SHOULD; limit their field values to US-ASCII octets.
1319   Recipients &SHOULD; treat other (obs-text) octets in field content as
1320   opaque data.
1322<t anchor="rule.comment">
1323  <x:anchor-alias value="comment"/>
1324  <x:anchor-alias value="ctext"/>
1325   Comments can be included in some HTTP header fields by surrounding
1326   the comment text with parentheses. Comments are only allowed in
1327   fields containing "comment" as part of their field value definition.
1329<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1330  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1331  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1332                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1334<t anchor="rule.quoted-cpair">
1335  <x:anchor-alias value="quoted-cpair"/>
1336   The backslash octet ("\") can be used as a single-octet
1337   quoting mechanism within comment constructs:
1339<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1340  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1343   Senders &SHOULD-NOT; escape octets that do not require escaping
1344   (i.e., other than the backslash octet "\" and the parentheses "(" and
1345   ")").
1349<section title="Message Body" anchor="message.body">
1350  <x:anchor-alias value="message-body"/>
1352   The message-body (if any) of an HTTP message is used to carry the
1353   payload body associated with the request or response.
1355<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1356  <x:ref>message-body</x:ref> = *OCTET
1359   The message-body differs from the payload body only when a transfer-coding
1360   has been applied, as indicated by the Transfer-Encoding header field
1361   (<xref target="header.transfer-encoding"/>).  If more than one
1362   Transfer-Encoding header field is present in a message, the multiple
1363   field-values &MUST; be combined into one field-value, according to the
1364   algorithm defined in <xref target="header.fields"/>, before determining
1365   the message-body length.
1368   When one or more transfer-codings are applied to a payload in order to
1369   form the message-body, the Transfer-Encoding header field &MUST; contain
1370   the list of transfer-codings applied. Transfer-Encoding is a property of
1371   the message, not of the payload, and thus &MAY; be added or removed by
1372   any implementation along the request/response chain under the constraints
1373   found in <xref target="transfer.codings"/>.
1376   If a message is received that has multiple Content-Length header fields
1377   (<xref target="header.content-length"/>) with field-values consisting
1378   of the same decimal value, or a single Content-Length header field with
1379   a field value containing a list of identical decimal values (e.g.,
1380   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1381   header fields have been generated or combined by an upstream message
1382   processor, then the recipient &MUST; either reject the message as invalid
1383   or replace the duplicated field-values with a single valid Content-Length
1384   field containing that decimal value prior to determining the message-body
1385   length.
1388   The rules for when a message-body is allowed in a message differ for
1389   requests and responses.
1392   The presence of a message-body in a request is signaled by the
1393   inclusion of a Content-Length or Transfer-Encoding header field in
1394   the request's header fields, even if the request method does not
1395   define any use for a message-body.  This allows the request
1396   message framing algorithm to be independent of method semantics.
1399   For response messages, whether or not a message-body is included with
1400   a message is dependent on both the request method and the response
1401   status code (<xref target="status.code.and.reason.phrase"/>).
1402   Responses to the HEAD request method never include a message-body
1403   because the associated response header fields (e.g., Transfer-Encoding,
1404   Content-Length, etc.) only indicate what their values would have been
1405   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1406   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1407   All other responses do include a message-body, although the body
1408   &MAY; be of zero length.
1411   The length of the message-body is determined by one of the following
1412   (in order of precedence):
1415  <list style="numbers">
1416    <x:lt><t>
1417     Any response to a HEAD request and any response with a status
1418     code of 100-199, 204, or 304 is always terminated by the first
1419     empty line after the header fields, regardless of the header
1420     fields present in the message, and thus cannot contain a message-body.
1421    </t></x:lt>
1422    <x:lt><t>
1423     If a Transfer-Encoding header field is present
1424     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1425     is the final encoding, the message-body length is determined by reading
1426     and decoding the chunked data until the transfer-coding indicates the
1427     data is complete.
1428    </t>
1429    <t>
1430     If a Transfer-Encoding header field is present in a response and the
1431     "chunked" transfer-coding is not the final encoding, the message-body
1432     length is determined by reading the connection until it is closed by
1433     the server.
1434     If a Transfer-Encoding header field is present in a request and the
1435     "chunked" transfer-coding is not the final encoding, the message-body
1436     length cannot be determined reliably; the server &MUST; respond with
1437     the 400 (Bad Request) status code and then close the connection.
1438    </t>
1439    <t>
1440     If a message is received with both a Transfer-Encoding header field
1441     and a Content-Length header field, the Transfer-Encoding overrides
1442     the Content-Length.
1443     Such a message might indicate an attempt to perform request or response
1444     smuggling (bypass of security-related checks on message routing or content)
1445     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1446     be removed, prior to forwarding the message downstream, or replaced with
1447     the real message-body length after the transfer-coding is decoded.
1448    </t></x:lt>
1449    <x:lt><t>
1450     If a message is received without Transfer-Encoding and with either
1451     multiple Content-Length header fields having differing field-values or
1452     a single Content-Length header field having an invalid value, then the
1453     message framing is invalid and &MUST; be treated as an error to
1454     prevent request or response smuggling.
1455     If this is a request message, the server &MUST; respond with
1456     a 400 (Bad Request) status code and then close the connection.
1457     If this is a response message received by a proxy, the proxy
1458     &MUST; discard the received response, send a 502 (Bad Gateway)
1459     status code as its downstream response, and then close the connection.
1460     If this is a response message received by a user-agent, it &MUST; be
1461     treated as an error by discarding the message and closing the connection.
1462    </t></x:lt>
1463    <x:lt><t>
1464     If a valid Content-Length header field
1465     is present without Transfer-Encoding, its decimal value defines the
1466     message-body length in octets.  If the actual number of octets sent in
1467     the message is less than the indicated Content-Length, the recipient
1468     &MUST; consider the message to be incomplete and treat the connection
1469     as no longer usable.
1470     If the actual number of octets sent in the message is more than the indicated
1471     Content-Length, the recipient &MUST; only process the message-body up to the
1472     field value's number of octets; the remainder of the message &MUST; either
1473     be discarded or treated as the next message in a pipeline.  For the sake of
1474     robustness, a user-agent &MAY; attempt to detect and correct such an error
1475     in message framing if it is parsing the response to the last request on
1476     on a connection and the connection has been closed by the server.
1477    </t></x:lt>
1478    <x:lt><t>
1479     If this is a request message and none of the above are true, then the
1480     message-body length is zero (no message-body is present).
1481    </t></x:lt>
1482    <x:lt><t>
1483     Otherwise, this is a response message without a declared message-body
1484     length, so the message-body length is determined by the number of octets
1485     received prior to the server closing the connection.
1486    </t></x:lt>
1487  </list>
1490   Since there is no way to distinguish a successfully completed,
1491   close-delimited message from a partially-received message interrupted
1492   by network failure, implementations &SHOULD; use encoding or
1493   length-delimited messages whenever possible.  The close-delimiting
1494   feature exists primarily for backwards compatibility with HTTP/1.0.
1497   A server &MAY; reject a request that contains a message-body but
1498   not a Content-Length by responding with 411 (Length Required).
1501   Unless a transfer-coding other than "chunked" has been applied,
1502   a client that sends a request containing a message-body &SHOULD;
1503   use a valid Content-Length header field if the message-body length
1504   is known in advance, rather than the "chunked" encoding, since some
1505   existing services respond to "chunked" with a 411 (Length Required)
1506   status code even though they understand the chunked encoding.  This
1507   is typically because such services are implemented via a gateway that
1508   requires a content-length in advance of being called and the server
1509   is unable or unwilling to buffer the entire request before processing.
1512   A client that sends a request containing a message-body &MUST; include a
1513   valid Content-Length header field if it does not know the server will
1514   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1515   of specific user configuration or by remembering the version of a prior
1516   received response.
1519   Request messages that are prematurely terminated, possibly due to a
1520   cancelled connection or a server-imposed time-out exception, &MUST;
1521   result in closure of the connection; sending an HTTP/1.1 error response
1522   prior to closing the connection is &OPTIONAL;.
1523   Response messages that are prematurely terminated, usually by closure
1524   of the connection prior to receiving the expected number of octets or by
1525   failure to decode a transfer-encoded message-body, &MUST; be recorded
1526   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1527   message-body as if it were complete (i.e., some indication must be given
1528   to the user that an error occurred).  Cache requirements for incomplete
1529   responses are defined in &cache-incomplete;.
1532   A server &MUST; read the entire request message-body or close
1533   the connection after sending its response, since otherwise the
1534   remaining data on a persistent connection would be misinterpreted
1535   as the next request.  Likewise,
1536   a client &MUST; read the entire response message-body if it intends
1537   to reuse the same connection for a subsequent request.  Pipelining
1538   multiple requests on a connection is described in <xref target="pipelining"/>.
1542<section title="General Header Fields" anchor="general.header.fields">
1543  <x:anchor-alias value="general-header"/>
1545   There are a few header fields which have general applicability for
1546   both request and response messages, but which do not apply to the
1547   payload being transferred. These header fields apply only to the
1548   message being transmitted.
1550<texttable align="left">
1551  <ttcol>Header Field Name</ttcol>
1552  <ttcol>Defined in...</ttcol>
1554  <c>Connection</c> <c><xref target="header.connection"/></c>
1555  <c>Date</c> <c><xref target=""/></c>
1556  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1557  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1558  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1559  <c>Via</c> <c><xref target="header.via"/></c>
1564<section title="Request" anchor="request">
1565  <x:anchor-alias value="Request"/>
1567   A request message from a client to a server begins with a
1568   Request-Line, followed by zero or more header fields, an empty
1569   line signifying the end of the header block, and an optional
1570   message body.
1572<!--                 Host                      ; should be moved here eventually -->
1573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1574  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1575                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1576                  <x:ref>CRLF</x:ref>
1577                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1580<section title="Request-Line" anchor="request-line">
1581  <x:anchor-alias value="Request-Line"/>
1583   The Request-Line begins with a method token, followed by a single
1584   space (SP), the request-target, another single space (SP), the
1585   protocol version, and ending with CRLF.
1587<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1588  <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>
1591<section title="Method" anchor="method">
1592  <x:anchor-alias value="Method"/>
1594   The Method token indicates the request method to be performed on the
1595   target resource. The request method is case-sensitive.
1597<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1598  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1602<section title="request-target" anchor="request-target">
1603  <x:anchor-alias value="request-target"/>
1605   The request-target identifies the target resource upon which to apply
1606   the request.  In most cases, the user agent is provided a URI reference
1607   from which it determines an absolute URI for identifying the target
1608   resource.  When a request to the resource is initiated, all or part
1609   of that URI is used to construct the HTTP request-target.
1611<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1612  <x:ref>request-target</x:ref> = "*"
1613                 / <x:ref>absolute-URI</x:ref>
1614                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1615                 / <x:ref>authority</x:ref>
1618   The four options for request-target are dependent on the nature of the
1619   request.
1621<t><iref item="asterisk form (of request-target)"/>
1622   The asterisk "*" form of request-target, which &MUST-NOT; be used
1623   with any request method other than OPTIONS, means that the request
1624   applies to the server as a whole (the listening process) rather than
1625   to a specific named resource at that server.  For example,
1627<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1628OPTIONS * HTTP/1.1
1630<t><iref item="absolute-URI form (of request-target)"/>
1631   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1632   proxy. The proxy is requested to either forward the request or service it
1633   from a valid cache, and then return the response. Note that the proxy &MAY;
1634   forward the request on to another proxy or directly to the server
1635   specified by the absolute-URI. In order to avoid request loops, a
1636   proxy that forwards requests to other proxies &MUST; be able to
1637   recognize and exclude all of its own server names, including
1638   any aliases, local variations, and the numeric IP address. An example
1639   Request-Line would be:
1641<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1642GET HTTP/1.1
1645   To allow for transition to absolute-URIs in all requests in future
1646   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1647   form in requests, even though HTTP/1.1 clients will only generate
1648   them in requests to proxies.
1651   If a proxy receives a host name that is not a fully qualified domain
1652   name, it &MAY; add its domain to the host name it received. If a proxy
1653   receives a fully qualified domain name, the proxy &MUST-NOT; change
1654   the host name.
1656<t><iref item="authority form (of request-target)"/>
1657   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1659<t><iref item="origin form (of request-target)"/>
1660   The most common form of request-target is that used when making
1661   a request to an origin server ("origin form").
1662   In this case, the absolute path and query components of the URI
1663   &MUST; be transmitted as the request-target, and the authority component
1664   &MUST; be transmitted in a Host header field. For example, a client wishing
1665   to retrieve a representation of the resource, as identified above,
1666   directly from the origin server would open (or reuse) a TCP connection
1667   to port 80 of the host "" and send the lines:
1669<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1670GET /pub/WWW/TheProject.html HTTP/1.1
1674   followed by the remainder of the Request. Note that the origin form
1675   of request-target always starts with an absolute path; if the target
1676   resource's URI path is empty, then an absolute path of "/" &MUST; be
1677   provided in the request-target.
1680   If a proxy receives an OPTIONS request with an absolute-URI form of
1681   request-target in which the URI has an empty path and no query component,
1682   then the last proxy on the request chain &MUST; use a request-target
1683   of "*" when it forwards the request to the indicated origin server.
1686   For example, the request
1687</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1691  would be forwarded by the final proxy as
1692</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1693OPTIONS * HTTP/1.1
1697   after connecting to port 8001 of host "".
1701   The request-target is transmitted in the format specified in
1702   <xref target="http.uri"/>. If the request-target is percent-encoded
1703   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1704   &MUST; decode the request-target in order to
1705   properly interpret the request. Servers &SHOULD; respond to invalid
1706   request-targets with an appropriate status code.
1709   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1710   received request-target when forwarding it to the next inbound server,
1711   except as noted above to replace a null path-absolute with "/" or "*".
1714  <t>
1715    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1716    meaning of the request when the origin server is improperly using
1717    a non-reserved URI character for a reserved purpose.  Implementors
1718    need to be aware that some pre-HTTP/1.1 proxies have been known to
1719    rewrite the request-target.
1720  </t>
1723   HTTP does not place a pre-defined limit on the length of a request-target.
1724   A server &MUST; be prepared to receive URIs of unbounded length and
1725   respond with the 414 (URI Too Long) status code if the received
1726   request-target would be longer than the server wishes to handle
1727   (see &status-414;).
1730   Various ad-hoc limitations on request-target length are found in practice.
1731   It is &RECOMMENDED; that all HTTP senders and recipients support
1732   request-target lengths of 8000 or more octets.
1735  <t>
1736    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1737    are not part of the request-target and thus will not be transmitted
1738    in an HTTP request.
1739  </t>
1744<section title="The Resource Identified by a Request" anchor="">
1746   The exact resource identified by an Internet request is determined by
1747   examining both the request-target and the Host header field.
1750   An origin server that does not allow resources to differ by the
1751   requested host &MAY; ignore the Host header field value when
1752   determining the resource identified by an HTTP/1.1 request. (But see
1753   <xref target=""/>
1754   for other requirements on Host support in HTTP/1.1.)
1757   An origin server that does differentiate resources based on the host
1758   requested (sometimes referred to as virtual hosts or vanity host
1759   names) &MUST; use the following rules for determining the requested
1760   resource on an HTTP/1.1 request:
1761  <list style="numbers">
1762    <t>If request-target is an absolute-URI, the host is part of the
1763     request-target. Any Host header field value in the request &MUST; be
1764     ignored.</t>
1765    <t>If the request-target is not an absolute-URI, and the request includes
1766     a Host header field, the host is determined by the Host header
1767     field value.</t>
1768    <t>If the host as determined by rule 1 or 2 is not a valid host on
1769     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1770  </list>
1773   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1774   attempt to use heuristics (e.g., examination of the URI path for
1775   something unique to a particular host) in order to determine what
1776   exact resource is being requested.
1780<section title="Effective Request URI" anchor="effective.request.uri">
1781  <iref primary="true" item="effective request URI"/>
1782  <iref primary="true" item="target resource"/>
1784   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1785   for the target resource; instead, the URI needs to be inferred from the
1786   request-target, Host header field, and connection context. The result of
1787   this process is called the "effective request URI".  The "target resource"
1788   is the resource identified by the effective request URI.
1791   If the request-target is an absolute-URI, then the effective request URI is
1792   the request-target.
1795   If the request-target uses the path-absolute form or the asterisk form,
1796   and the Host header field is present, then the effective request URI is
1797   constructed by concatenating
1800  <list style="symbols">
1801    <t>
1802      the scheme name: "http" if the request was received over an insecure
1803      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1804      connection,
1805    </t>
1806    <t>
1807      the octet sequence "://",
1808    </t>
1809    <t>
1810      the authority component, as specified in the Host header field
1811      (<xref target=""/>), and
1812    </t>
1813    <t>
1814      the request-target obtained from the Request-Line, unless the
1815      request-target is just the asterisk "*".
1816    </t>
1817  </list>
1820   If the request-target uses the path-absolute form or the asterisk form,
1821   and the Host header field is not present, then the effective request URI is
1822   undefined.
1825   Otherwise, when request-target uses the authority form, the effective
1826   request URI is undefined.
1830   Example 1: the effective request URI for the message
1832<artwork type="example" x:indent-with="  ">
1833GET /pub/WWW/TheProject.html HTTP/1.1
1837  (received over an insecure TCP connection) is "http", plus "://", plus the
1838  authority component "", plus the request-target
1839  "/pub/WWW/TheProject.html", thus
1840  "".
1845   Example 2: the effective request URI for the message
1847<artwork type="example" x:indent-with="  ">
1848GET * HTTP/1.1
1852  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1853  authority component "", thus "".
1857   Effective request URIs are compared using the rules described in
1858   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1859   be treated as equivalent to an absolute path of "/".
1866<section title="Response" anchor="response">
1867  <x:anchor-alias value="Response"/>
1869   After receiving and interpreting a request message, a server responds
1870   with an HTTP response message.
1872<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1873  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1874                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1875                  <x:ref>CRLF</x:ref>
1876                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1879<section title="Status-Line" anchor="status-line">
1880  <x:anchor-alias value="Status-Line"/>
1882   The first line of a Response message is the Status-Line, consisting
1883   of the protocol version, a space (SP), the status code, another space,
1884   a possibly-empty textual phrase describing the status code, and
1885   ending with CRLF.
1887<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1888  <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>
1891<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1892  <x:anchor-alias value="Reason-Phrase"/>
1893  <x:anchor-alias value="Status-Code"/>
1895   The Status-Code element is a 3-digit integer result code of the
1896   attempt to understand and satisfy the request. These codes are fully
1897   defined in &status-codes;.  The Reason Phrase exists for the sole
1898   purpose of providing a textual description associated with the numeric
1899   status code, out of deference to earlier Internet application protocols
1900   that were more frequently used with interactive text clients.
1901   A client &SHOULD; ignore the content of the Reason Phrase.
1904   The first digit of the Status-Code defines the class of response. The
1905   last two digits do not have any categorization role. There are 5
1906   values for the first digit:
1907  <list style="symbols">
1908    <t>
1909      1xx: Informational - Request received, continuing process
1910    </t>
1911    <t>
1912      2xx: Success - The action was successfully received,
1913        understood, and accepted
1914    </t>
1915    <t>
1916      3xx: Redirection - Further action must be taken in order to
1917        complete the request
1918    </t>
1919    <t>
1920      4xx: Client Error - The request contains bad syntax or cannot
1921        be fulfilled
1922    </t>
1923    <t>
1924      5xx: Server Error - The server failed to fulfill an apparently
1925        valid request
1926    </t>
1927  </list>
1929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1930  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1931  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1939<section title="Protocol Parameters" anchor="protocol.parameters">
1941<section title="Date/Time Formats: Full Date" anchor="">
1942  <x:anchor-alias value="HTTP-date"/>
1944   HTTP applications have historically allowed three different formats
1945   for date/time stamps. However, the preferred format is a fixed-length subset
1946   of that defined by <xref target="RFC1123"/>:
1948<figure><artwork type="example" x:indent-with="  ">
1949Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1952   The other formats are described here only for compatibility with obsolete
1953   implementations.
1955<figure><artwork type="example" x:indent-with="  ">
1956Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1957Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1960   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1961   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1962   only generate the RFC 1123 format for representing HTTP-date values
1963   in header fields. See <xref target="tolerant.applications"/> for further information.
1966   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1967   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1968   equal to UTC (Coordinated Universal Time). This is indicated in the
1969   first two formats by the inclusion of "GMT" as the three-letter
1970   abbreviation for time zone, and &MUST; be assumed when reading the
1971   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1972   additional whitespace beyond that specifically included as SP in the
1973   grammar.
1975<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1976  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1978<t anchor="">
1979  <x:anchor-alias value="rfc1123-date"/>
1980  <x:anchor-alias value="time-of-day"/>
1981  <x:anchor-alias value="hour"/>
1982  <x:anchor-alias value="minute"/>
1983  <x:anchor-alias value="second"/>
1984  <x:anchor-alias value="day-name"/>
1985  <x:anchor-alias value="day"/>
1986  <x:anchor-alias value="month"/>
1987  <x:anchor-alias value="year"/>
1988  <x:anchor-alias value="GMT"/>
1989  Preferred format:
1991<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"/>
1992  <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>
1993  ; fixed length subset of the format defined in
1994  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1996  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1997               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1998               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1999               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2000               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2001               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2002               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2004  <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>
2005               ; e.g., 02 Jun 1982
2007  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2008  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2009               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2010               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2011               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2012               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2013               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2014               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2015               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2016               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2017               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2018               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2019               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2020  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2022  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2024  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2025                 ; 00:00:00 - 23:59:59
2027  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2028  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2029  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2032  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2033  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2034  same as those defined for the RFC 5322 constructs
2035  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2037<t anchor="">
2038  <x:anchor-alias value="obs-date"/>
2039  <x:anchor-alias value="rfc850-date"/>
2040  <x:anchor-alias value="asctime-date"/>
2041  <x:anchor-alias value="date1"/>
2042  <x:anchor-alias value="date2"/>
2043  <x:anchor-alias value="date3"/>
2044  <x:anchor-alias value="rfc1123-date"/>
2045  <x:anchor-alias value="day-name-l"/>
2046  Obsolete formats:
2048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2049  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2051<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2052  <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>
2053  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2054                 ; day-month-year (e.g., 02-Jun-82)
2056  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2057         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2058         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2059         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2060         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2061         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2062         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2064<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2065  <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>
2066  <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> ))
2067                 ; month day (e.g., Jun  2)
2070  <t>
2071    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2072    accepting date values that might have been sent by non-HTTP
2073    applications, as is sometimes the case when retrieving or posting
2074    messages via proxies/gateways to SMTP or NNTP.
2075  </t>
2078  <t>
2079    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2080    to their usage within the protocol stream. Clients and servers are
2081    not required to use these formats for user presentation, request
2082    logging, etc.
2083  </t>
2087<section title="Transfer Codings" anchor="transfer.codings">
2088  <x:anchor-alias value="transfer-coding"/>
2089  <x:anchor-alias value="transfer-extension"/>
2091   Transfer-coding values are used to indicate an encoding
2092   transformation that has been, can be, or might need to be applied to a
2093   payload body in order to ensure "safe transport" through the network.
2094   This differs from a content coding in that the transfer-coding is a
2095   property of the message rather than a property of the representation
2096   that is being transferred.
2098<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2099  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2100                          / "compress" ; <xref target="compress.coding"/>
2101                          / "deflate" ; <xref target="deflate.coding"/>
2102                          / "gzip" ; <xref target="gzip.coding"/>
2103                          / <x:ref>transfer-extension</x:ref>
2104  <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> )
2106<t anchor="rule.parameter">
2107  <x:anchor-alias value="attribute"/>
2108  <x:anchor-alias value="transfer-parameter"/>
2109  <x:anchor-alias value="value"/>
2110   Parameters are in the form of attribute/value pairs.
2112<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"/>
2113  <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>
2114  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2115  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2118   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2119   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2120   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2123   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2124   MIME, which were designed to enable safe transport of binary data over a
2125   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2126   However, safe transport
2127   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2128   the only unsafe characteristic of message-bodies is the difficulty in
2129   determining the exact message body length (<xref target="message.body"/>),
2130   or the desire to encrypt data over a shared transport.
2133   A server that receives a request message with a transfer-coding it does
2134   not understand &SHOULD; respond with 501 (Not Implemented) and then
2135   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2136   client.
2139<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2140  <iref item="chunked (Coding Format)"/>
2141  <iref item="Coding Format" subitem="chunked"/>
2142  <x:anchor-alias value="chunk"/>
2143  <x:anchor-alias value="Chunked-Body"/>
2144  <x:anchor-alias value="chunk-data"/>
2145  <x:anchor-alias value="chunk-ext"/>
2146  <x:anchor-alias value="chunk-ext-name"/>
2147  <x:anchor-alias value="chunk-ext-val"/>
2148  <x:anchor-alias value="chunk-size"/>
2149  <x:anchor-alias value="last-chunk"/>
2150  <x:anchor-alias value="trailer-part"/>
2151  <x:anchor-alias value="quoted-str-nf"/>
2152  <x:anchor-alias value="qdtext-nf"/>
2154   The chunked encoding modifies the body of a message in order to
2155   transfer it as a series of chunks, each with its own size indicator,
2156   followed by an &OPTIONAL; trailer containing header fields. This
2157   allows dynamically produced content to be transferred along with the
2158   information necessary for the recipient to verify that it has
2159   received the full message.
2161<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"/>
2162  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2163                   <x:ref>last-chunk</x:ref>
2164                   <x:ref>trailer-part</x:ref>
2165                   <x:ref>CRLF</x:ref>
2167  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2168                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2169  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2170  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2172  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2173                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2174  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2175  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2176  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2177  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2179  <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>
2180                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2181  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2182                 ; <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>
2185   The chunk-size field is a string of hex digits indicating the size of
2186   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2187   zero, followed by the trailer, which is terminated by an empty line.
2190   The trailer allows the sender to include additional HTTP header
2191   fields at the end of the message. The Trailer header field can be
2192   used to indicate which header fields are included in a trailer (see
2193   <xref target="header.trailer"/>).
2196   A server using chunked transfer-coding in a response &MUST-NOT; use the
2197   trailer for any header fields unless at least one of the following is
2198   true:
2199  <list style="numbers">
2200    <t>the request included a TE header field that indicates "trailers" is
2201     acceptable in the transfer-coding of the  response, as described in
2202     <xref target="header.te"/>; or,</t>
2204    <t>the trailer fields consist entirely of optional metadata, and the
2205    recipient could use the message (in a manner acceptable to the server where
2206    the field originated) without receiving it. In other words, the server that
2207    generated the header (often but not always the origin server) is willing to
2208    accept the possibility that the trailer fields might be silently discarded
2209    along the path to the client.</t>
2210  </list>
2213   This requirement prevents an interoperability failure when the
2214   message is being received by an HTTP/1.1 (or later) proxy and
2215   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2216   compliance with the protocol would have necessitated a possibly
2217   infinite buffer on the proxy.
2220   A process for decoding the "chunked" transfer-coding
2221   can be represented in pseudo-code as:
2223<figure><artwork type="code">
2224  length := 0
2225  read chunk-size, chunk-ext (if any) and CRLF
2226  while (chunk-size &gt; 0) {
2227     read chunk-data and CRLF
2228     append chunk-data to decoded-body
2229     length := length + chunk-size
2230     read chunk-size and CRLF
2231  }
2232  read header-field
2233  while (header-field not empty) {
2234     append header-field to existing header fields
2235     read header-field
2236  }
2237  Content-Length := length
2238  Remove "chunked" from Transfer-Encoding
2241   All HTTP/1.1 applications &MUST; be able to receive and decode the
2242   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2243   they do not understand.
2246   Since "chunked" is the only transfer-coding required to be understood
2247   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2248   on a persistent connection.  Whenever a transfer-coding is applied to
2249   a payload body in a request, the final transfer-coding applied &MUST;
2250   be "chunked".  If a transfer-coding is applied to a response payload
2251   body, then either the final transfer-coding applied &MUST; be "chunked"
2252   or the message &MUST; be terminated by closing the connection. When the
2253   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2254   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2255   be applied more than once in a message-body.
2259<section title="Compression Codings" anchor="compression.codings">
2261   The codings defined below can be used to compress the payload of a
2262   message.
2265   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2266   is not desirable and is discouraged for future encodings. Their
2267   use here is representative of historical practice, not good
2268   design.
2271   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2272   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2273   equivalent to "gzip" and "compress" respectively.
2276<section title="Compress Coding" anchor="compress.coding">
2277<iref item="compress (Coding Format)"/>
2278<iref item="Coding Format" subitem="compress"/>
2280   The "compress" format is produced by the common UNIX file compression
2281   program "compress". This format is an adaptive Lempel-Ziv-Welch
2282   coding (LZW).
2286<section title="Deflate Coding" anchor="deflate.coding">
2287<iref item="deflate (Coding Format)"/>
2288<iref item="Coding Format" subitem="deflate"/>
2290   The "deflate" format is defined as the "deflate" compression mechanism
2291   (described in <xref target="RFC1951"/>) used inside the "zlib"
2292   data format (<xref target="RFC1950"/>).
2295  <t>
2296    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2297    compressed data without the zlib wrapper.
2298   </t>
2302<section title="Gzip Coding" anchor="gzip.coding">
2303<iref item="gzip (Coding Format)"/>
2304<iref item="Coding Format" subitem="gzip"/>
2306   The "gzip" format is produced by the file compression program
2307   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2308   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2314<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2316   The HTTP Transfer Coding Registry defines the name space for the transfer
2317   coding names.
2320   Registrations &MUST; include the following fields:
2321   <list style="symbols">
2322     <t>Name</t>
2323     <t>Description</t>
2324     <t>Pointer to specification text</t>
2325   </list>
2328   Names of transfer codings &MUST-NOT; overlap with names of content codings
2329   (&content-codings;), unless the encoding transformation is identical (as it
2330   is the case for the compression codings defined in
2331   <xref target="compression.codings"/>).
2334   Values to be added to this name space require a specification
2335   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2336   conform to the purpose of transfer coding defined in this section.
2339   The registry itself is maintained at
2340   <eref target=""/>.
2345<section title="Product Tokens" anchor="product.tokens">
2346  <x:anchor-alias value="product"/>
2347  <x:anchor-alias value="product-version"/>
2349   Product tokens are used to allow communicating applications to
2350   identify themselves by software name and version. Most fields using
2351   product tokens also allow sub-products which form a significant part
2352   of the application to be listed, separated by whitespace. By
2353   convention, the products are listed in order of their significance
2354   for identifying the application.
2356<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2357  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2358  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2361   Examples:
2363<figure><artwork type="example">
2364  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2365  Server: Apache/0.8.4
2368   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2369   used for advertising or other non-essential information. Although any
2370   token octet &MAY; appear in a product-version, this token &SHOULD;
2371   only be used for a version identifier (i.e., successive versions of
2372   the same product &SHOULD; only differ in the product-version portion of
2373   the product value).
2377<section title="Quality Values" anchor="quality.values">
2378  <x:anchor-alias value="qvalue"/>
2380   Both transfer codings (TE request header field, <xref target="header.te"/>)
2381   and content negotiation (&content.negotiation;) use short "floating point"
2382   numbers to indicate the relative importance ("weight") of various
2383   negotiable parameters.  A weight is normalized to a real number in
2384   the range 0 through 1, where 0 is the minimum and 1 the maximum
2385   value. If a parameter has a quality value of 0, then content with
2386   this parameter is "not acceptable" for the client. HTTP/1.1
2387   applications &MUST-NOT; generate more than three digits after the
2388   decimal point. User configuration of these values &SHOULD; also be
2389   limited in this fashion.
2391<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2392  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2393                 / ( "1" [ "." 0*3("0") ] )
2396  <t>
2397     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2398     relative degradation in desired quality.
2399  </t>
2405<section title="Connections" anchor="connections">
2407<section title="Persistent Connections" anchor="persistent.connections">
2409<section title="Purpose" anchor="persistent.purpose">
2411   Prior to persistent connections, a separate TCP connection was
2412   established for each request, increasing the load on HTTP servers
2413   and causing congestion on the Internet. The use of inline images and
2414   other associated data often requires a client to make multiple
2415   requests of the same server in a short amount of time. Analysis of
2416   these performance problems and results from a prototype
2417   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2418   measurements of actual HTTP/1.1 implementations show good
2419   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2420   T/TCP <xref target="Tou1998"/>.
2423   Persistent HTTP connections have a number of advantages:
2424  <list style="symbols">
2425      <t>
2426        By opening and closing fewer TCP connections, CPU time is saved
2427        in routers and hosts (clients, servers, proxies, gateways,
2428        tunnels, or caches), and memory used for TCP protocol control
2429        blocks can be saved in hosts.
2430      </t>
2431      <t>
2432        HTTP requests and responses can be pipelined on a connection.
2433        Pipelining allows a client to make multiple requests without
2434        waiting for each response, allowing a single TCP connection to
2435        be used much more efficiently, with much lower elapsed time.
2436      </t>
2437      <t>
2438        Network congestion is reduced by reducing the number of packets
2439        caused by TCP opens, and by allowing TCP sufficient time to
2440        determine the congestion state of the network.
2441      </t>
2442      <t>
2443        Latency on subsequent requests is reduced since there is no time
2444        spent in TCP's connection opening handshake.
2445      </t>
2446      <t>
2447        HTTP can evolve more gracefully, since errors can be reported
2448        without the penalty of closing the TCP connection. Clients using
2449        future versions of HTTP might optimistically try a new feature,
2450        but if communicating with an older server, retry with old
2451        semantics after an error is reported.
2452      </t>
2453    </list>
2456   HTTP implementations &SHOULD; implement persistent connections.
2460<section title="Overall Operation" anchor="persistent.overall">
2462   A significant difference between HTTP/1.1 and earlier versions of
2463   HTTP is that persistent connections are the default behavior of any
2464   HTTP connection. That is, unless otherwise indicated, the client
2465   &SHOULD; assume that the server will maintain a persistent connection,
2466   even after error responses from the server.
2469   Persistent connections provide a mechanism by which a client and a
2470   server can signal the close of a TCP connection. This signaling takes
2471   place using the Connection header field (<xref target="header.connection"/>). Once a close
2472   has been signaled, the client &MUST-NOT; send any more requests on that
2473   connection.
2476<section title="Negotiation" anchor="persistent.negotiation">
2478   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2479   maintain a persistent connection unless a Connection header field including
2480   the connection-token "close" was sent in the request. If the server
2481   chooses to close the connection immediately after sending the
2482   response, it &SHOULD; send a Connection header field including the
2483   connection-token "close".
2486   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2487   decide to keep it open based on whether the response from a server
2488   contains a Connection header field with the connection-token close. In case
2489   the client does not want to maintain a connection for more than that
2490   request, it &SHOULD; send a Connection header field including the
2491   connection-token close.
2494   If either the client or the server sends the close token in the
2495   Connection header field, that request becomes the last one for the
2496   connection.
2499   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2500   maintained for HTTP versions less than 1.1 unless it is explicitly
2501   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2502   compatibility with HTTP/1.0 clients.
2505   In order to remain persistent, all messages on the connection &MUST;
2506   have a self-defined message length (i.e., one not defined by closure
2507   of the connection), as described in <xref target="message.body"/>.
2511<section title="Pipelining" anchor="pipelining">
2513   A client that supports persistent connections &MAY; "pipeline" its
2514   requests (i.e., send multiple requests without waiting for each
2515   response). A server &MUST; send its responses to those requests in the
2516   same order that the requests were received.
2519   Clients which assume persistent connections and pipeline immediately
2520   after connection establishment &SHOULD; be prepared to retry their
2521   connection if the first pipelined attempt fails. If a client does
2522   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2523   persistent. Clients &MUST; also be prepared to resend their requests if
2524   the server closes the connection before sending all of the
2525   corresponding responses.
2528   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2529   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2530   premature termination of the transport connection could lead to
2531   indeterminate results. A client wishing to send a non-idempotent
2532   request &SHOULD; wait to send that request until it has received the
2533   response status line for the previous request.
2538<section title="Proxy Servers" anchor="persistent.proxy">
2540   It is especially important that proxies correctly implement the
2541   properties of the Connection header field as specified in <xref target="header.connection"/>.
2544   The proxy server &MUST; signal persistent connections separately with
2545   its clients and the origin servers (or other proxy servers) that it
2546   connects to. Each persistent connection applies to only one transport
2547   link.
2550   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2551   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2552   for information and discussion of the problems with the Keep-Alive header field
2553   implemented by many HTTP/1.0 clients).
2556<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2558  <cref anchor="TODO-end-to-end" source="jre">
2559    Restored from <eref target=""/>.
2560    See also <eref target=""/>.
2561  </cref>
2564   For the purpose of defining the behavior of caches and non-caching
2565   proxies, we divide HTTP header fields into two categories:
2566  <list style="symbols">
2567      <t>End-to-end header fields, which are  transmitted to the ultimate
2568        recipient of a request or response. End-to-end header fields in
2569        responses MUST be stored as part of a cache entry and &MUST; be
2570        transmitted in any response formed from a cache entry.</t>
2572      <t>Hop-by-hop header fields, which are meaningful only for a single
2573        transport-level connection, and are not stored by caches or
2574        forwarded by proxies.</t>
2575  </list>
2578   The following HTTP/1.1 header fields are hop-by-hop header fields:
2579  <list style="symbols">
2580      <t>Connection</t>
2581      <t>Keep-Alive</t>
2582      <t>Proxy-Authenticate</t>
2583      <t>Proxy-Authorization</t>
2584      <t>TE</t>
2585      <t>Trailer</t>
2586      <t>Transfer-Encoding</t>
2587      <t>Upgrade</t>
2588  </list>
2591   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2594   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2595   (<xref target="header.connection"/>).
2599<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2601  <cref anchor="TODO-non-mod-headers" source="jre">
2602    Restored from <eref target=""/>.
2603    See also <eref target=""/>.
2604  </cref>
2607   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2608   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2609   modify an end-to-end header field unless the definition of that header field requires
2610   or specifically allows that.
2613   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2614   request or response, and it &MUST-NOT; add any of these fields if not
2615   already present:
2616  <list style="symbols">
2617    <t>Allow</t>
2618    <t>Content-Location</t>
2619    <t>Content-MD5</t>
2620    <t>ETag</t>
2621    <t>Last-Modified</t>
2622    <t>Server</t>
2623  </list>
2626   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2627   response:
2628  <list style="symbols">
2629    <t>Expires</t>
2630  </list>
2633   but it &MAY; add any of these fields if not already present. If an
2634   Expires header field is added, it &MUST; be given a field-value identical to
2635   that of the Date header field in that response.
2638   A proxy &MUST-NOT; modify or add any of the following fields in a
2639   message that contains the no-transform cache-control directive, or in
2640   any request:
2641  <list style="symbols">
2642    <t>Content-Encoding</t>
2643    <t>Content-Range</t>
2644    <t>Content-Type</t>
2645  </list>
2648   A transforming proxy &MAY; modify or add these fields to a message
2649   that does not include no-transform, but if it does so, it &MUST; add a
2650   Warning 214 (Transformation applied) if one does not already appear
2651   in the message (see &header-warning;).
2654  <t>
2655    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2656    cause authentication failures if stronger authentication
2657    mechanisms are introduced in later versions of HTTP. Such
2658    authentication mechanisms &MAY; rely on the values of header fields
2659    not listed here.
2660  </t>
2663   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2664   though it &MAY; change the message-body through application or removal
2665   of a transfer-coding (<xref target="transfer.codings"/>).
2671<section title="Practical Considerations" anchor="persistent.practical">
2673   Servers will usually have some time-out value beyond which they will
2674   no longer maintain an inactive connection. Proxy servers might make
2675   this a higher value since it is likely that the client will be making
2676   more connections through the same server. The use of persistent
2677   connections places no requirements on the length (or existence) of
2678   this time-out for either the client or the server.
2681   When a client or server wishes to time-out it &SHOULD; issue a graceful
2682   close on the transport connection. Clients and servers &SHOULD; both
2683   constantly watch for the other side of the transport close, and
2684   respond to it as appropriate. If a client or server does not detect
2685   the other side's close promptly it could cause unnecessary resource
2686   drain on the network.
2689   A client, server, or proxy &MAY; close the transport connection at any
2690   time. For example, a client might have started to send a new request
2691   at the same time that the server has decided to close the "idle"
2692   connection. From the server's point of view, the connection is being
2693   closed while it was idle, but from the client's point of view, a
2694   request is in progress.
2697   This means that clients, servers, and proxies &MUST; be able to recover
2698   from asynchronous close events. Client software &SHOULD; reopen the
2699   transport connection and retransmit the aborted sequence of requests
2700   without user interaction so long as the request sequence is
2701   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2702   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2703   human operator the choice of retrying the request(s). Confirmation by
2704   user-agent software with semantic understanding of the application
2705   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2706   be repeated if the second sequence of requests fails.
2709   Servers &SHOULD; always respond to at least one request per connection,
2710   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2711   middle of transmitting a response, unless a network or client failure
2712   is suspected.
2715   Clients (including proxies) &SHOULD; limit the number of simultaneous
2716   connections that they maintain to a given server (including proxies).
2719   Previous revisions of HTTP gave a specific number of connections as a
2720   ceiling, but this was found to be impractical for many applications. As a
2721   result, this specification does not mandate a particular maximum number of
2722   connections, but instead encourages clients to be conservative when opening
2723   multiple connections.
2726   In particular, while using multiple connections avoids the "head-of-line
2727   blocking" problem (whereby a request that takes significant server-side
2728   processing and/or has a large payload can block subsequent requests on the
2729   same connection), each connection used consumes server resources (sometimes
2730   significantly), and furthermore using multiple connections can cause
2731   undesirable side effects in congested networks.
2734   Note that servers might reject traffic that they deem abusive, including an
2735   excessive number of connections from a client.
2740<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2742<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2744   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2745   flow control mechanisms to resolve temporary overloads, rather than
2746   terminating connections with the expectation that clients will retry.
2747   The latter technique can exacerbate network congestion.
2751<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2753   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2754   the network connection for an error status code while it is transmitting
2755   the request. If the client sees an error status code, it &SHOULD;
2756   immediately cease transmitting the body. If the body is being sent
2757   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2758   empty trailer &MAY; be used to prematurely mark the end of the message.
2759   If the body was preceded by a Content-Length header field, the client &MUST;
2760   close the connection.
2764<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2766   The purpose of the 100 (Continue) status code (see &status-100;) is to
2767   allow a client that is sending a request message with a request body
2768   to determine if the origin server is willing to accept the request
2769   (based on the request header fields) before the client sends the request
2770   body. In some cases, it might either be inappropriate or highly
2771   inefficient for the client to send the body if the server will reject
2772   the message without looking at the body.
2775   Requirements for HTTP/1.1 clients:
2776  <list style="symbols">
2777    <t>
2778        If a client will wait for a 100 (Continue) response before
2779        sending the request body, it &MUST; send an Expect header
2780        field (&header-expect;) with the "100-continue" expectation.
2781    </t>
2782    <t>
2783        A client &MUST-NOT; send an Expect header field (&header-expect;)
2784        with the "100-continue" expectation if it does not intend
2785        to send a request body.
2786    </t>
2787  </list>
2790   Because of the presence of older implementations, the protocol allows
2791   ambiguous situations in which a client might send "Expect: 100-continue"
2792   without receiving either a 417 (Expectation Failed)
2793   or a 100 (Continue) status code. Therefore, when a client sends this
2794   header field to an origin server (possibly via a proxy) from which it
2795   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2796   wait for an indefinite period before sending the request body.
2799   Requirements for HTTP/1.1 origin servers:
2800  <list style="symbols">
2801    <t> Upon receiving a request which includes an Expect header
2802        field with the "100-continue" expectation, an origin server &MUST;
2803        either respond with 100 (Continue) status code and continue to read
2804        from the input stream, or respond with a final status code. The
2805        origin server &MUST-NOT; wait for the request body before sending
2806        the 100 (Continue) response. If it responds with a final status
2807        code, it &MAY; close the transport connection or it &MAY; continue
2808        to read and discard the rest of the request.  It &MUST-NOT;
2809        perform the request method if it returns a final status code.
2810    </t>
2811    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2812        the request message does not include an Expect header
2813        field with the "100-continue" expectation, and &MUST-NOT; send a
2814        100 (Continue) response if such a request comes from an HTTP/1.0
2815        (or earlier) client. There is an exception to this rule: for
2816        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2817        status code in response to an HTTP/1.1 PUT or POST request that does
2818        not include an Expect header field with the "100-continue"
2819        expectation. This exception, the purpose of which is
2820        to minimize any client processing delays associated with an
2821        undeclared wait for 100 (Continue) status code, applies only to
2822        HTTP/1.1 requests, and not to requests with any other HTTP-version
2823        value.
2824    </t>
2825    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2826        already received some or all of the request body for the
2827        corresponding request.
2828    </t>
2829    <t> An origin server that sends a 100 (Continue) response &MUST;
2830    ultimately send a final status code, once the request body is
2831        received and processed, unless it terminates the transport
2832        connection prematurely.
2833    </t>
2834    <t> If an origin server receives a request that does not include an
2835        Expect header field with the "100-continue" expectation,
2836        the request includes a request body, and the server responds
2837        with a final status code before reading the entire request body
2838        from the transport connection, then the server &SHOULD-NOT;  close
2839        the transport connection until it has read the entire request,
2840        or until the client closes the connection. Otherwise, the client
2841        might not reliably receive the response message. However, this
2842        requirement is not be construed as preventing a server from
2843        defending itself against denial-of-service attacks, or from
2844        badly broken client implementations.
2845      </t>
2846    </list>
2849   Requirements for HTTP/1.1 proxies:
2850  <list style="symbols">
2851    <t> If a proxy receives a request that includes an Expect header
2852        field with the "100-continue" expectation, and the proxy
2853        either knows that the next-hop server complies with HTTP/1.1 or
2854        higher, or does not know the HTTP version of the next-hop
2855        server, it &MUST; forward the request, including the Expect header
2856        field.
2857    </t>
2858    <t> If the proxy knows that the version of the next-hop server is
2859        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2860        respond with a 417 (Expectation Failed) status code.
2861    </t>
2862    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2863        numbers received from recently-referenced next-hop servers.
2864    </t>
2865    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2866        request message was received from an HTTP/1.0 (or earlier)
2867        client and did not include an Expect header field with
2868        the "100-continue" expectation. This requirement overrides the
2869        general rule for forwarding of 1xx responses (see &status-1xx;).
2870    </t>
2871  </list>
2875<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2877   If an HTTP/1.1 client sends a request which includes a request body,
2878   but which does not include an Expect header field with the
2879   "100-continue" expectation, and if the client is not directly
2880   connected to an HTTP/1.1 origin server, and if the client sees the
2881   connection close before receiving a status line from the server, the
2882   client &SHOULD; retry the request.  If the client does retry this
2883   request, it &MAY; use the following "binary exponential backoff"
2884   algorithm to be assured of obtaining a reliable response:
2885  <list style="numbers">
2886    <t>
2887      Initiate a new connection to the server
2888    </t>
2889    <t>
2890      Transmit the request-line, header fields, and the CRLF that
2891      indicates the end of header fields.
2892    </t>
2893    <t>
2894      Initialize a variable R to the estimated round-trip time to the
2895         server (e.g., based on the time it took to establish the
2896         connection), or to a constant value of 5 seconds if the round-trip
2897         time is not available.
2898    </t>
2899    <t>
2900       Compute T = R * (2**N), where N is the number of previous
2901         retries of this request.
2902    </t>
2903    <t>
2904       Wait either for an error response from the server, or for T
2905         seconds (whichever comes first)
2906    </t>
2907    <t>
2908       If no error response is received, after T seconds transmit the
2909         body of the request.
2910    </t>
2911    <t>
2912       If client sees that the connection is closed prematurely,
2913         repeat from step 1 until the request is accepted, an error
2914         response is received, or the user becomes impatient and
2915         terminates the retry process.
2916    </t>
2917  </list>
2920   If at any point an error status code is received, the client
2921  <list style="symbols">
2922      <t>&SHOULD-NOT;  continue and</t>
2924      <t>&SHOULD; close the connection if it has not completed sending the
2925        request message.</t>
2926    </list>
2933<section title="Miscellaneous notes that might disappear" anchor="misc">
2934<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2936   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2940<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2942   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2946<section title="Interception of HTTP for access control" anchor="http.intercept">
2948   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2952<section title="Use of HTTP by other protocols" anchor="http.others">
2954   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2955   Extensions of HTTP like WebDAV.</cref>
2959<section title="Use of HTTP by media type specification" anchor="">
2961   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2966<section title="Header Field Definitions" anchor="header.field.definitions">
2968   This section defines the syntax and semantics of HTTP header fields
2969   related to message framing and transport protocols.
2972<section title="Connection" anchor="header.connection">
2973  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2974  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2975  <x:anchor-alias value="Connection"/>
2976  <x:anchor-alias value="connection-token"/>
2978   The "Connection" header field allows the sender to specify
2979   options that are desired only for that particular connection.
2980   Such connection options &MUST; be removed or replaced before the
2981   message can be forwarded downstream by a proxy or gateway.
2982   This mechanism also allows the sender to indicate which HTTP
2983   header fields used in the message are only intended for the
2984   immediate recipient ("hop-by-hop"), as opposed to all recipients
2985   on the chain ("end-to-end"), enabling the message to be
2986   self-descriptive and allowing future connection-specific extensions
2987   to be deployed in HTTP without fear that they will be blindly
2988   forwarded by previously deployed intermediaries.
2991   The Connection header field's value has the following grammar:
2993<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2994  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2995  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2998   A proxy or gateway &MUST; parse a received Connection
2999   header field before a message is forwarded and, for each
3000   connection-token in this field, remove any header field(s) from
3001   the message with the same name as the connection-token, and then
3002   remove the Connection header field itself or replace it with the
3003   sender's own connection options for the forwarded message.
3006   A sender &MUST-NOT; include field-names in the Connection header
3007   field-value for fields that are defined as expressing constraints
3008   for all recipients in the request or response chain, such as the
3009   Cache-Control header field (&header-cache-control;).
3012   The connection options do not have to correspond to a header field
3013   present in the message, since a connection-specific header field
3014   might not be needed if there are no parameters associated with that
3015   connection option.  Recipients that trigger certain connection
3016   behavior based on the presence of connection options &MUST; do so
3017   based on the presence of the connection-token rather than only the
3018   presence of the optional header field.  In other words, if the
3019   connection option is received as a header field but not indicated
3020   within the Connection field-value, then the recipient &MUST; ignore
3021   the connection-specific header field because it has likely been
3022   forwarded by an intermediary that is only partially compliant.
3025   When defining new connection options, specifications ought to
3026   carefully consider existing deployed header fields and ensure
3027   that the new connection-token does not share the same name as
3028   an unrelated header field that might already be deployed.
3029   Defining a new connection-token essentially reserves that potential
3030   field-name for carrying additional information related to the
3031   connection option, since it would be unwise for senders to use
3032   that field-name for anything else.
3035   HTTP/1.1 defines the "close" connection option for the sender to
3036   signal that the connection will be closed after completion of the
3037   response. For example,
3039<figure><artwork type="example">
3040  Connection: close
3043   in either the request or the response header fields indicates that
3044   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3045   after the current request/response is complete.
3048   An HTTP/1.1 client that does not support persistent connections &MUST;
3049   include the "close" connection option in every request message.
3052   An HTTP/1.1 server that does not support persistent connections &MUST;
3053   include the "close" connection option in every response message that
3054   does not have a 1xx (Informational) status code.
3058<section title="Content-Length" anchor="header.content-length">
3059  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3060  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3061  <x:anchor-alias value="Content-Length"/>
3063   The "Content-Length" header field indicates the size of the
3064   message-body, in decimal number of octets, for any message other than
3065   a response to a HEAD request or a response with a status code of 304.
3066   In the case of a response to a HEAD request, Content-Length indicates
3067   the size of the payload body (not including any potential transfer-coding)
3068   that would have been sent had the request been a GET.
3069   In the case of a 304 (Not Modified) response to a GET request,
3070   Content-Length indicates the size of the payload body (not including
3071   any potential transfer-coding) that would have been sent in a 200 (OK)
3072   response.
3074<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3075  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3078   An example is
3080<figure><artwork type="example">
3081  Content-Length: 3495
3084   Implementations &SHOULD; use this field to indicate the message-body
3085   length when no transfer-coding is being applied and the
3086   payload's body length can be determined prior to being transferred.
3087   <xref target="message.body"/> describes how recipients determine the length
3088   of a message-body.
3091   Any Content-Length greater than or equal to zero is a valid value.
3094   Note that the use of this field in HTTP is significantly different from
3095   the corresponding definition in MIME, where it is an optional field
3096   used within the "message/external-body" content-type.
3100<section title="Date" anchor="">
3101  <iref primary="true" item="Date header field" x:for-anchor=""/>
3102  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3103  <x:anchor-alias value="Date"/>
3105   The "Date" header field represents the date and time at which
3106   the message was originated, having the same semantics as the Origination
3107   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3108   The field value is an HTTP-date, as described in <xref target=""/>;
3109   it &MUST; be sent in rfc1123-date format.
3111<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3112  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3115   An example is
3117<figure><artwork type="example">
3118  Date: Tue, 15 Nov 1994 08:12:31 GMT
3121   Origin servers &MUST; include a Date header field in all responses,
3122   except in these cases:
3123  <list style="numbers">
3124      <t>If the response status code is 100 (Continue) or 101 (Switching
3125         Protocols), the response &MAY; include a Date header field, at
3126         the server's option.</t>
3128      <t>If the response status code conveys a server error, e.g., 500
3129         (Internal Server Error) or 503 (Service Unavailable), and it is
3130         inconvenient or impossible to generate a valid Date.</t>
3132      <t>If the server does not have a clock that can provide a
3133         reasonable approximation of the current time, its responses
3134         &MUST-NOT; include a Date header field. In this case, the rules
3135         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3136  </list>
3139   A received message that does not have a Date header field &MUST; be
3140   assigned one by the recipient if the message will be cached by that
3141   recipient.
3144   Clients can use the Date header field as well; in order to keep request
3145   messages small, they are advised not to include it when it doesn't convey
3146   any useful information (as it is usually the case for requests that do not
3147   contain a payload).
3150   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3151   time subsequent to the generation of the message. It &SHOULD; represent
3152   the best available approximation of the date and time of message
3153   generation, unless the implementation has no means of generating a
3154   reasonably accurate date and time. In theory, the date ought to
3155   represent the moment just before the payload is generated. In
3156   practice, the date can be generated at any time during the message
3157   origination without affecting its semantic value.
3160<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3162   Some origin server implementations might not have a clock available.
3163   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3164   values to a response, unless these values were associated
3165   with the resource by a system or user with a reliable clock. It &MAY;
3166   assign an Expires value that is known, at or before server
3167   configuration time, to be in the past (this allows "pre-expiration"
3168   of responses without storing separate Expires values for each
3169   resource).
3174<section title="Host" anchor="">
3175  <iref primary="true" item="Host header field" x:for-anchor=""/>
3176  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3177  <x:anchor-alias value="Host"/>
3179   The "Host" header field in a request provides the host and port
3180   information from the target resource's URI, enabling the origin
3181   server to distinguish between resources while servicing requests
3182   for multiple host names on a single IP address.  Since the Host
3183   field-value is critical information for handling a request, it
3184   &SHOULD; be sent as the first header field following the Request-Line.
3186<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3187  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3190   A client &MUST; send a Host header field in all HTTP/1.1 request
3191   messages.  If the target resource's URI includes an authority
3192   component, then the Host field-value &MUST; be identical to that
3193   authority component after excluding any userinfo (<xref target="http.uri"/>).
3194   If the authority component is missing or undefined for the target
3195   resource's URI, then the Host header field &MUST; be sent with an
3196   empty field-value.
3199   For example, a GET request to the origin server for
3200   &lt;; would begin with:
3202<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3203GET /pub/WWW/ HTTP/1.1
3207   The Host header field &MUST; be sent in an HTTP/1.1 request even
3208   if the request-target is in the form of an absolute-URI, since this
3209   allows the Host information to be forwarded through ancient HTTP/1.0
3210   proxies that might not have implemented Host.
3213   When an HTTP/1.1 proxy receives a request with a request-target in
3214   the form of an absolute-URI, the proxy &MUST; ignore the received
3215   Host header field (if any) and instead replace it with the host
3216   information of the request-target.  When a proxy forwards a request,
3217   it &MUST; generate the Host header field based on the received
3218   absolute-URI rather than the received Host.
3221   Since the Host header field acts as an application-level routing
3222   mechanism, it is a frequent target for malware seeking to poison
3223   a shared cache or redirect a request to an unintended server.
3224   An interception proxy is particularly vulnerable if it relies on
3225   the Host header field value for redirecting requests to internal
3226   servers, or for use as a cache key in a shared cache, without
3227   first verifying that the intercepted connection is targeting a
3228   valid IP address for that host.
3231   A server &MUST; respond with a 400 (Bad Request) status code to
3232   any HTTP/1.1 request message that lacks a Host header field and
3233   to any request message that contains more than one Host header field
3234   or a Host header field with an invalid field-value.
3237   See Sections <xref target="" format="counter"/>
3238   and <xref target="" format="counter"/>
3239   for other requirements relating to Host.
3243<section title="TE" anchor="header.te">
3244  <iref primary="true" item="TE header field" x:for-anchor=""/>
3245  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3246  <x:anchor-alias value="TE"/>
3247  <x:anchor-alias value="t-codings"/>
3248  <x:anchor-alias value="te-params"/>
3249  <x:anchor-alias value="te-ext"/>
3251   The "TE" header field indicates what extension transfer-codings
3252   it is willing to accept in the response, and whether or not it is
3253   willing to accept trailer fields in a chunked transfer-coding.
3256   Its value consists of the keyword "trailers" and/or a comma-separated
3257   list of extension transfer-coding names with optional accept
3258   parameters (as described in <xref target="transfer.codings"/>).
3260<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3261  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3262  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3263  <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> )
3264  <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> ]
3267   The presence of the keyword "trailers" indicates that the client is
3268   willing to accept trailer fields in a chunked transfer-coding, as
3269   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3270   transfer-coding values even though it does not itself represent a
3271   transfer-coding.
3274   Examples of its use are:
3276<figure><artwork type="example">
3277  TE: deflate
3278  TE:
3279  TE: trailers, deflate;q=0.5
3282   The TE header field only applies to the immediate connection.
3283   Therefore, the keyword &MUST; be supplied within a Connection header
3284   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3287   A server tests whether a transfer-coding is acceptable, according to
3288   a TE field, using these rules:
3289  <list style="numbers">
3290    <x:lt>
3291      <t>The "chunked" transfer-coding is always acceptable. If the
3292         keyword "trailers" is listed, the client indicates that it is
3293         willing to accept trailer fields in the chunked response on
3294         behalf of itself and any downstream clients. The implication is
3295         that, if given, the client is stating that either all
3296         downstream clients are willing to accept trailer fields in the
3297         forwarded response, or that it will attempt to buffer the
3298         response on behalf of downstream recipients.
3299      </t><t>
3300         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3301         chunked response such that a client can be assured of buffering
3302         the entire response.</t>
3303    </x:lt>
3304    <x:lt>
3305      <t>If the transfer-coding being tested is one of the transfer-codings
3306         listed in the TE field, then it is acceptable unless it
3307         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3308         qvalue of 0 means "not acceptable".)</t>
3309    </x:lt>
3310    <x:lt>
3311      <t>If multiple transfer-codings are acceptable, then the
3312         acceptable transfer-coding with the highest non-zero qvalue is
3313         preferred.  The "chunked" transfer-coding always has a qvalue
3314         of 1.</t>
3315    </x:lt>
3316  </list>
3319   If the TE field-value is empty or if no TE field is present, the only
3320   transfer-coding is "chunked". A message with no transfer-coding is
3321   always acceptable.
3325<section title="Trailer" anchor="header.trailer">
3326  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3327  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3328  <x:anchor-alias value="Trailer"/>
3330   The "Trailer" header field indicates that the given set of
3331   header fields is present in the trailer of a message encoded with
3332   chunked transfer-coding.
3334<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3335  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3338   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3339   message using chunked transfer-coding with a non-empty trailer. Doing
3340   so allows the recipient to know which header fields to expect in the
3341   trailer.
3344   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3345   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3346   trailer fields in a "chunked" transfer-coding.
3349   Message header fields listed in the Trailer header field &MUST-NOT;
3350   include the following header fields:
3351  <list style="symbols">
3352    <t>Transfer-Encoding</t>
3353    <t>Content-Length</t>
3354    <t>Trailer</t>
3355  </list>
3359<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3360  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3361  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3362  <x:anchor-alias value="Transfer-Encoding"/>
3364   The "Transfer-Encoding" header field indicates what transfer-codings
3365   (if any) have been applied to the message body. It differs from
3366   Content-Encoding (&content-codings;) in that transfer-codings are a property
3367   of the message (and therefore are removed by intermediaries), whereas
3368   content-codings are not.
3370<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3371  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3374   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3376<figure><artwork type="example">
3377  Transfer-Encoding: chunked
3380   If multiple encodings have been applied to a representation, the transfer-codings
3381   &MUST; be listed in the order in which they were applied.
3382   Additional information about the encoding parameters &MAY; be provided
3383   by other header fields not defined by this specification.
3386   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3387   header field.
3391<section title="Upgrade" anchor="header.upgrade">
3392  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3393  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3394  <x:anchor-alias value="Upgrade"/>
3396   The "Upgrade" header field allows the client to specify what
3397   additional communication protocols it would like to use, if the server
3398   chooses to switch protocols. Servers can use it to indicate what protocols
3399   they are willing to switch to.
3401<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3402  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3405   For example,
3407<figure><artwork type="example">
3408  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3411   The Upgrade header field is intended to provide a simple mechanism
3412   for transition from HTTP/1.1 to some other, incompatible protocol. It
3413   does so by allowing the client to advertise its desire to use another
3414   protocol, such as a later version of HTTP with a higher major version
3415   number, even though the current request has been made using HTTP/1.1.
3416   This eases the difficult transition between incompatible protocols by
3417   allowing the client to initiate a request in the more commonly
3418   supported protocol while indicating to the server that it would like
3419   to use a "better" protocol if available (where "better" is determined
3420   by the server, possibly according to the nature of the request method
3421   or target resource).
3424   The Upgrade header field only applies to switching application-layer
3425   protocols upon the existing transport-layer connection. Upgrade
3426   cannot be used to insist on a protocol change; its acceptance and use
3427   by the server is optional. The capabilities and nature of the
3428   application-layer communication after the protocol change is entirely
3429   dependent upon the new protocol chosen, although the first action
3430   after changing the protocol &MUST; be a response to the initial HTTP
3431   request containing the Upgrade header field.
3434   The Upgrade header field only applies to the immediate connection.
3435   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3436   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3437   HTTP/1.1 message.
3440   The Upgrade header field cannot be used to indicate a switch to a
3441   protocol on a different connection. For that purpose, it is more
3442   appropriate to use a 3xx redirection response (&status-3xx;).
3445   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3446   Protocols) responses to indicate which protocol(s) are being switched to,
3447   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3448   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3449   response to indicate that they are willing to upgrade to one of the
3450   specified protocols.
3453   This specification only defines the protocol name "HTTP" for use by
3454   the family of Hypertext Transfer Protocols, as defined by the HTTP
3455   version rules of <xref target="http.version"/> and future updates to this
3456   specification. Additional tokens can be registered with IANA using the
3457   registration procedure defined below. 
3460<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3462   The HTTP Upgrade Token Registry defines the name space for product
3463   tokens used to identify protocols in the Upgrade header field.
3464   Each registered token is associated with contact information and
3465   an optional set of specifications that details how the connection
3466   will be processed after it has been upgraded.
3469   Registrations are allowed on a First Come First Served basis as
3470   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3471   specifications need not be IETF documents or be subject to IESG review.
3472   Registrations are subject to the following rules:
3473  <list style="numbers">
3474    <t>A token, once registered, stays registered forever.</t>
3475    <t>The registration &MUST; name a responsible party for the
3476       registration.</t>
3477    <t>The registration &MUST; name a point of contact.</t>
3478    <t>The registration &MAY; name a set of specifications associated with that
3479       token. Such specifications need not be publicly available.</t>
3480    <t>The responsible party &MAY; change the registration at any time.
3481       The IANA will keep a record of all such changes, and make them
3482       available upon request.</t>
3483    <t>The responsible party for the first registration of a "product"
3484       token &MUST; approve later registrations of a "version" token
3485       together with that "product" token before they can be registered.</t>
3486    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3487       for a token. This will normally only be used in the case when a
3488       responsible party cannot be contacted.</t>
3489  </list>
3496<section title="Via" anchor="header.via">
3497  <iref primary="true" item="Via header field" x:for-anchor=""/>
3498  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3499  <x:anchor-alias value="protocol-name"/>
3500  <x:anchor-alias value="protocol-version"/>
3501  <x:anchor-alias value="pseudonym"/>
3502  <x:anchor-alias value="received-by"/>
3503  <x:anchor-alias value="received-protocol"/>
3504  <x:anchor-alias value="Via"/>
3506   The "Via" header field &MUST; be sent by a proxy or gateway to
3507   indicate the intermediate protocols and recipients between the user
3508   agent and the server on requests, and between the origin server and
3509   the client on responses. It is analogous to the "Received" field
3510   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3511   and is intended to be used for tracking message forwards,
3512   avoiding request loops, and identifying the protocol capabilities of
3513   all senders along the request/response chain.
3515<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><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"/>
3516  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3517                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3518  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3519  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3520  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3521  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3522  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3525   The received-protocol indicates the protocol version of the message
3526   received by the server or client along each segment of the
3527   request/response chain. The received-protocol version is appended to
3528   the Via field value when the message is forwarded so that information
3529   about the protocol capabilities of upstream applications remains
3530   visible to all recipients.
3533   The protocol-name is excluded if and only if it would be "HTTP". The
3534   received-by field is normally the host and optional port number of a
3535   recipient server or client that subsequently forwarded the message.
3536   However, if the real host is considered to be sensitive information,
3537   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3538   be assumed to be the default port of the received-protocol.
3541   Multiple Via field values represent each proxy or gateway that has
3542   forwarded the message. Each recipient &MUST; append its information
3543   such that the end result is ordered according to the sequence of
3544   forwarding applications.
3547   Comments &MAY; be used in the Via header field to identify the software
3548   of each recipient, analogous to the User-Agent and Server header fields.
3549   However, all comments in the Via field are optional and &MAY; be removed
3550   by any recipient prior to forwarding the message.
3553   For example, a request message could be sent from an HTTP/1.0 user
3554   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3555   forward the request to a public proxy at, which completes
3556   the request by forwarding it to the origin server at
3557   The request received by would then have the following
3558   Via header field:
3560<figure><artwork type="example">
3561  Via: 1.0 fred, 1.1 (Apache/1.1)
3564   A proxy or gateway used as a portal through a network firewall
3565   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3566   region unless it is explicitly enabled to do so. If not enabled, the
3567   received-by host of any host behind the firewall &SHOULD; be replaced
3568   by an appropriate pseudonym for that host.
3571   For organizations that have strong privacy requirements for hiding
3572   internal structures, a proxy or gateway &MAY; combine an ordered
3573   subsequence of Via header field entries with identical received-protocol
3574   values into a single such entry. For example,
3576<figure><artwork type="example">
3577  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3580  could be collapsed to
3582<figure><artwork type="example">
3583  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3586   Senders &SHOULD-NOT; combine multiple entries unless they are all
3587   under the same organizational control and the hosts have already been
3588   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3589   have different received-protocol values.
3595<section title="IANA Considerations" anchor="IANA.considerations">
3597<section title="Header Field Registration" anchor="header.field.registration">
3599   The Message Header Field Registry located at <eref target=""/> shall be updated
3600   with the permanent registrations below (see <xref target="RFC3864"/>):
3602<?BEGININC p1-messaging.iana-headers ?>
3603<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3604<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3605   <ttcol>Header Field Name</ttcol>
3606   <ttcol>Protocol</ttcol>
3607   <ttcol>Status</ttcol>
3608   <ttcol>Reference</ttcol>
3610   <c>Connection</c>
3611   <c>http</c>
3612   <c>standard</c>
3613   <c>
3614      <xref target="header.connection"/>
3615   </c>
3616   <c>Content-Length</c>
3617   <c>http</c>
3618   <c>standard</c>
3619   <c>
3620      <xref target="header.content-length"/>
3621   </c>
3622   <c>Date</c>
3623   <c>http</c>
3624   <c>standard</c>
3625   <c>
3626      <xref target=""/>
3627   </c>
3628   <c>Host</c>
3629   <c>http</c>
3630   <c>standard</c>
3631   <c>
3632      <xref target=""/>
3633   </c>
3634   <c>TE</c>
3635   <c>http</c>
3636   <c>standard</c>
3637   <c>
3638      <xref target="header.te"/>
3639   </c>
3640   <c>Trailer</c>
3641   <c>http</c>
3642   <c>standard</c>
3643   <c>
3644      <xref target="header.trailer"/>
3645   </c>
3646   <c>Transfer-Encoding</c>
3647   <c>http</c>
3648   <c>standard</c>
3649   <c>
3650      <xref target="header.transfer-encoding"/>
3651   </c>
3652   <c>Upgrade</c>
3653   <c>http</c>
3654   <c>standard</c>
3655   <c>
3656      <xref target="header.upgrade"/>
3657   </c>
3658   <c>Via</c>
3659   <c>http</c>
3660   <c>standard</c>
3661   <c>
3662      <xref target="header.via"/>
3663   </c>
3666<?ENDINC p1-messaging.iana-headers ?>
3668   The change controller is: "IETF ( - Internet Engineering Task Force".
3672<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3674   The entries for the "http" and "https" URI Schemes in the registry located at
3675   <eref target=""/>
3676   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3677   and <xref target="https.uri" format="counter"/> of this document
3678   (see <xref target="RFC4395"/>).
3682<section title="Internet Media Type Registrations" anchor="">
3684   This document serves as the specification for the Internet media types
3685   "message/http" and "application/http". The following is to be registered with
3686   IANA (see <xref target="RFC4288"/>).
3688<section title="Internet Media Type message/http" anchor="">
3689<iref item="Media Type" subitem="message/http" primary="true"/>
3690<iref item="message/http Media Type" primary="true"/>
3692   The message/http type can be used to enclose a single HTTP request or
3693   response message, provided that it obeys the MIME restrictions for all
3694   "message" types regarding line length and encodings.
3697  <list style="hanging" x:indent="12em">
3698    <t hangText="Type name:">
3699      message
3700    </t>
3701    <t hangText="Subtype name:">
3702      http
3703    </t>
3704    <t hangText="Required parameters:">
3705      none
3706    </t>
3707    <t hangText="Optional parameters:">
3708      version, msgtype
3709      <list style="hanging">
3710        <t hangText="version:">
3711          The HTTP-Version number of the enclosed message
3712          (e.g., "1.1"). If not present, the version can be
3713          determined from the first line of the body.
3714        </t>
3715        <t hangText="msgtype:">
3716          The message type &mdash; "request" or "response". If not
3717          present, the type can be determined from the first
3718          line of the body.
3719        </t>
3720      </list>
3721    </t>
3722    <t hangText="Encoding considerations:">
3723      only "7bit", "8bit", or "binary" are permitted
3724    </t>
3725    <t hangText="Security considerations:">
3726      none
3727    </t>
3728    <t hangText="Interoperability considerations:">
3729      none
3730    </t>
3731    <t hangText="Published specification:">
3732      This specification (see <xref target=""/>).
3733    </t>
3734    <t hangText="Applications that use this media type:">
3735    </t>
3736    <t hangText="Additional information:">
3737      <list style="hanging">
3738        <t hangText="Magic number(s):">none</t>
3739        <t hangText="File extension(s):">none</t>
3740        <t hangText="Macintosh file type code(s):">none</t>
3741      </list>
3742    </t>
3743    <t hangText="Person and email address to contact for further information:">
3744      See Authors Section.
3745    </t>
3746    <t hangText="Intended usage:">
3747      COMMON
3748    </t>
3749    <t hangText="Restrictions on usage:">
3750      none
3751    </t>
3752    <t hangText="Author/Change controller:">
3753      IESG
3754    </t>
3755  </list>
3758<section title="Internet Media Type application/http" anchor="">
3759<iref item="Media Type" subitem="application/http" primary="true"/>
3760<iref item="application/http Media Type" primary="true"/>
3762   The application/http type can be used to enclose a pipeline of one or more
3763   HTTP request or response messages (not intermixed).
3766  <list style="hanging" x:indent="12em">
3767    <t hangText="Type name:">
3768      application
3769    </t>
3770    <t hangText="Subtype name:">
3771      http
3772    </t>
3773    <t hangText="Required parameters:">
3774      none
3775    </t>
3776    <t hangText="Optional parameters:">
3777      version, msgtype
3778      <list style="hanging">
3779        <t hangText="version:">
3780          The HTTP-Version number of the enclosed messages
3781          (e.g., "1.1"). If not present, the version can be
3782          determined from the first line of the body.
3783        </t>
3784        <t hangText="msgtype:">
3785          The message type &mdash; "request" or "response". If not
3786          present, the type can be determined from the first
3787          line of the body.
3788        </t>
3789      </list>
3790    </t>
3791    <t hangText="Encoding considerations:">
3792      HTTP messages enclosed by this type
3793      are in "binary" format; use of an appropriate
3794      Content-Transfer-Encoding is required when
3795      transmitted via E-mail.
3796    </t>
3797    <t hangText="Security considerations:">
3798      none
3799    </t>
3800    <t hangText="Interoperability considerations:">
3801      none
3802    </t>
3803    <t hangText="Published specification:">
3804      This specification (see <xref target=""/>).
3805    </t>
3806    <t hangText="Applications that use this media type:">
3807    </t>
3808    <t hangText="Additional information:">
3809      <list style="hanging">
3810        <t hangText="Magic number(s):">none</t>
3811        <t hangText="File extension(s):">none</t>
3812        <t hangText="Macintosh file type code(s):">none</t>
3813      </list>
3814    </t>
3815    <t hangText="Person and email address to contact for further information:">
3816      See Authors Section.
3817    </t>
3818    <t hangText="Intended usage:">
3819      COMMON
3820    </t>
3821    <t hangText="Restrictions on usage:">
3822      none
3823    </t>
3824    <t hangText="Author/Change controller:">
3825      IESG
3826    </t>
3827  </list>
3832<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3834   The registration procedure for HTTP Transfer Codings is now defined by
3835   <xref target="transfer.coding.registry"/> of this document.
3838   The HTTP Transfer Codings Registry located at <eref target=""/>
3839   shall be updated with the registrations below:
3841<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3842   <ttcol>Name</ttcol>
3843   <ttcol>Description</ttcol>
3844   <ttcol>Reference</ttcol>
3845   <c>chunked</c>
3846   <c>Transfer in a series of chunks</c>
3847   <c>
3848      <xref target="chunked.encoding"/>
3849   </c>
3850   <c>compress</c>
3851   <c>UNIX "compress" program method</c>
3852   <c>
3853      <xref target="compress.coding"/>
3854   </c>
3855   <c>deflate</c>
3856   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3857   the "zlib" data format (<xref target="RFC1950"/>)
3858   </c>
3859   <c>
3860      <xref target="deflate.coding"/>
3861   </c>
3862   <c>gzip</c>
3863   <c>Same as GNU zip <xref target="RFC1952"/></c>
3864   <c>
3865      <xref target="gzip.coding"/>
3866   </c>
3870<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3872   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3873   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3874   by <xref target="upgrade.token.registry"/> of this document.
3877   The HTTP Status Code Registry located at <eref target=""/>
3878   shall be updated with the registration below:
3880<texttable align="left" suppress-title="true">
3881   <ttcol>Value</ttcol>
3882   <ttcol>Description</ttcol>
3883   <ttcol>Reference</ttcol>
3885   <c>HTTP</c>
3886   <c>Hypertext Transfer Protocol</c>
3887   <c><xref target="http.version"/> of this specification</c>
3888<!-- IANA should add this without our instructions; emailed on June 05, 2009
3889   <c>TLS/1.0</c>
3890   <c>Transport Layer Security</c>
3891   <c><xref target="RFC2817"/></c> -->
3898<section title="Security Considerations" anchor="security.considerations">
3900   This section is meant to inform application developers, information
3901   providers, and users of the security limitations in HTTP/1.1 as
3902   described by this document. The discussion does not include
3903   definitive solutions to the problems revealed, though it does make
3904   some suggestions for reducing security risks.
3907<section title="Personal Information" anchor="personal.information">
3909   HTTP clients are often privy to large amounts of personal information
3910   (e.g., the user's name, location, mail address, passwords, encryption
3911   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3912   leakage of this information.
3913   We very strongly recommend that a convenient interface be provided
3914   for the user to control dissemination of such information, and that
3915   designers and implementors be particularly careful in this area.
3916   History shows that errors in this area often create serious security
3917   and/or privacy problems and generate highly adverse publicity for the
3918   implementor's company.
3922<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3924   A server is in the position to save personal data about a user's
3925   requests which might identify their reading patterns or subjects of
3926   interest. This information is clearly confidential in nature and its
3927   handling can be constrained by law in certain countries. People using
3928   HTTP to provide data are responsible for ensuring that
3929   such material is not distributed without the permission of any
3930   individuals that are identifiable by the published results.
3934<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3936   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3937   the documents returned by HTTP requests to be only those that were
3938   intended by the server administrators. If an HTTP server translates
3939   HTTP URIs directly into file system calls, the server &MUST; take
3940   special care not to serve files that were not intended to be
3941   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3942   other operating systems use ".." as a path component to indicate a
3943   directory level above the current one. On such a system, an HTTP
3944   server &MUST; disallow any such construct in the request-target if it
3945   would otherwise allow access to a resource outside those intended to
3946   be accessible via the HTTP server. Similarly, files intended for
3947   reference only internally to the server (such as access control
3948   files, configuration files, and script code) &MUST; be protected from
3949   inappropriate retrieval, since they might contain sensitive
3950   information. Experience has shown that minor bugs in such HTTP server
3951   implementations have turned into security risks.
3955<section title="DNS Spoofing" anchor="dns.spoofing">
3957   Clients using HTTP rely heavily on the Domain Name Service, and are
3958   thus generally prone to security attacks based on the deliberate
3959   mis-association of IP addresses and DNS names. Clients need to be
3960   cautious in assuming the continuing validity of an IP number/DNS name
3961   association.
3964   In particular, HTTP clients &SHOULD; rely on their name resolver for
3965   confirmation of an IP number/DNS name association, rather than
3966   caching the result of previous host name lookups. Many platforms
3967   already can cache host name lookups locally when appropriate, and
3968   they &SHOULD; be configured to do so. It is proper for these lookups to
3969   be cached, however, only when the TTL (Time To Live) information
3970   reported by the name server makes it likely that the cached
3971   information will remain useful.
3974   If HTTP clients cache the results of host name lookups in order to
3975   achieve a performance improvement, they &MUST; observe the TTL
3976   information reported by DNS.
3979   If HTTP clients do not observe this rule, they could be spoofed when
3980   a previously-accessed server's IP address changes. As network
3981   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3982   possibility of this form of attack will grow. Observing this
3983   requirement thus reduces this potential security vulnerability.
3986   This requirement also improves the load-balancing behavior of clients
3987   for replicated servers using the same DNS name and reduces the
3988   likelihood of a user's experiencing failure in accessing sites which
3989   use that strategy.
3993<section title="Proxies and Caching" anchor="attack.proxies">
3995   By their very nature, HTTP proxies are men-in-the-middle, and
3996   represent an opportunity for man-in-the-middle attacks. Compromise of
3997   the systems on which the proxies run can result in serious security
3998   and privacy problems. Proxies have access to security-related
3999   information, personal information about individual users and
4000   organizations, and proprietary information belonging to users and
4001   content providers. A compromised proxy, or a proxy implemented or
4002   configured without regard to security and privacy considerations,
4003   might be used in the commission of a wide range of potential attacks.
4006   Proxy operators need to protect the systems on which proxies run as
4007   they would protect any system that contains or transports sensitive
4008   information. In particular, log information gathered at proxies often
4009   contains highly sensitive personal information, and/or information
4010   about organizations. Log information needs to be carefully guarded, and
4011   appropriate guidelines for use need to be developed and followed.
4012   (<xref target="abuse.of.server.log.information"/>).
4015   Proxy implementors need to consider the privacy and security
4016   implications of their design and coding decisions, and of the
4017   configuration options they provide to proxy operators (especially the
4018   default configuration).
4021   Users of a proxy need to be aware that proxies are no trustworthier than
4022   the people who run them; HTTP itself cannot solve this problem.
4025   The judicious use of cryptography, when appropriate, might suffice to
4026   protect against a broad range of security and privacy attacks. Such
4027   cryptography is beyond the scope of the HTTP/1.1 specification.
4031<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4033   They exist. They are hard to defend against. Research continues.
4034   Beware.
4039<section title="Acknowledgments" anchor="ack">
4041   HTTP has evolved considerably over the years. It has
4042   benefited from a large and active developer community &mdash; the many
4043   people who have participated on the www-talk mailing list &mdash; and it is
4044   that community which has been most responsible for the success of
4045   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4046   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4047   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4048   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4049   VanHeyningen deserve special recognition for their efforts in
4050   defining early aspects of the protocol.
4053   This document has benefited greatly from the comments of all those
4054   participating in the HTTP-WG. In addition to those already mentioned,
4055   the following individuals have contributed to this specification:
4058   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4059   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4060   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4061   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4062   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4063   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4064   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4065   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4066   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4067   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4068   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4069   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4072   Thanks to the "cave men" of Palo Alto. You know who you are.
4075   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4076   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4077   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4078   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4079   Larry Masinter for their help. And thanks go particularly to Jeff
4080   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4083   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4084   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4085   discovery of many of the problems that this document attempts to
4086   rectify.
4089   This specification makes heavy use of the augmented BNF and generic
4090   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4091   reuses many of the definitions provided by Nathaniel Borenstein and
4092   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4093   specification will help reduce past confusion over the relationship
4094   between HTTP and Internet mail message formats.
4098Acknowledgements TODO list
4100- Jeff Hodges ("effective request URI")
4108<references title="Normative References">
4110<reference anchor="ISO-8859-1">
4111  <front>
4112    <title>
4113     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4114    </title>
4115    <author>
4116      <organization>International Organization for Standardization</organization>
4117    </author>
4118    <date year="1998"/>
4119  </front>
4120  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4123<reference anchor="Part2">
4124  <front>
4125    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4126    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4127      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4128      <address><email></email></address>
4129    </author>
4130    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4131      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4132      <address><email></email></address>
4133    </author>
4134    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4135      <organization abbrev="HP">Hewlett-Packard Company</organization>
4136      <address><email></email></address>
4137    </author>
4138    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4139      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4140      <address><email></email></address>
4141    </author>
4142    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4143      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4144      <address><email></email></address>
4145    </author>
4146    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4147      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4148      <address><email></email></address>
4149    </author>
4150    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4151      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4152      <address><email></email></address>
4153    </author>
4154    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4155      <organization abbrev="W3C">World Wide Web Consortium</organization>
4156      <address><email></email></address>
4157    </author>
4158    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4159      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4160      <address><email></email></address>
4161    </author>
4162    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4163  </front>
4164  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4165  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4168<reference anchor="Part3">
4169  <front>
4170    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4171    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4172      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4173      <address><email></email></address>
4174    </author>
4175    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4176      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4177      <address><email></email></address>
4178    </author>
4179    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4180      <organization abbrev="HP">Hewlett-Packard Company</organization>
4181      <address><email></email></address>
4182    </author>
4183    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4184      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4185      <address><email></email></address>
4186    </author>
4187    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4188      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4189      <address><email></email></address>
4190    </author>
4191    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4192      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4193      <address><email></email></address>
4194    </author>
4195    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4196      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4197      <address><email></email></address>
4198    </author>
4199    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4200      <organization abbrev="W3C">World Wide Web Consortium</organization>
4201      <address><email></email></address>
4202    </author>
4203    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4204      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4205      <address><email></email></address>
4206    </author>
4207    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4208  </front>
4209  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4210  <x:source href="p3-payload.xml" basename="p3-payload"/>
4213<reference anchor="Part6">
4214  <front>
4215    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4216    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4217      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4218      <address><email></email></address>
4219    </author>
4220    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4221      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4222      <address><email></email></address>
4223    </author>
4224    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4225      <organization abbrev="HP">Hewlett-Packard Company</organization>
4226      <address><email></email></address>
4227    </author>
4228    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4229      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4230      <address><email></email></address>
4231    </author>
4232    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4233      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4234      <address><email></email></address>
4235    </author>
4236    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4237      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4238      <address><email></email></address>
4239    </author>
4240    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4241      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4242      <address><email></email></address>
4243    </author>
4244    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4245      <organization abbrev="W3C">World Wide Web Consortium</organization>
4246      <address><email></email></address>
4247    </author>
4248    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4249      <address><email></email></address>
4250    </author>
4251    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4252      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4253      <address><email></email></address>
4254    </author>
4255    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4256  </front>
4257  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4258  <x:source href="p6-cache.xml" basename="p6-cache"/>
4261<reference anchor="RFC5234">
4262  <front>
4263    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4264    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4265      <organization>Brandenburg InternetWorking</organization>
4266      <address>
4267        <email></email>
4268      </address> 
4269    </author>
4270    <author initials="P." surname="Overell" fullname="Paul Overell">
4271      <organization>THUS plc.</organization>
4272      <address>
4273        <email></email>
4274      </address>
4275    </author>
4276    <date month="January" year="2008"/>
4277  </front>
4278  <seriesInfo name="STD" value="68"/>
4279  <seriesInfo name="RFC" value="5234"/>
4282<reference anchor="RFC2119">
4283  <front>
4284    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4285    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4286      <organization>Harvard University</organization>
4287      <address><email></email></address>
4288    </author>
4289    <date month="March" year="1997"/>
4290  </front>
4291  <seriesInfo name="BCP" value="14"/>
4292  <seriesInfo name="RFC" value="2119"/>
4295<reference anchor="RFC3986">
4296 <front>
4297  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4298  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4299    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4300    <address>
4301       <email></email>
4302       <uri></uri>
4303    </address>
4304  </author>
4305  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4306    <organization abbrev="Day Software">Day Software</organization>
4307    <address>
4308      <email></email>
4309      <uri></uri>
4310    </address>
4311  </author>
4312  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4313    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4314    <address>
4315      <email></email>
4316      <uri></uri>
4317    </address>
4318  </author>
4319  <date month='January' year='2005'></date>
4320 </front>
4321 <seriesInfo name="STD" value="66"/>
4322 <seriesInfo name="RFC" value="3986"/>
4325<reference anchor="USASCII">
4326  <front>
4327    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4328    <author>
4329      <organization>American National Standards Institute</organization>
4330    </author>
4331    <date year="1986"/>
4332  </front>
4333  <seriesInfo name="ANSI" value="X3.4"/>
4336<reference anchor="RFC1950">
4337  <front>
4338    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4339    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4340      <organization>Aladdin Enterprises</organization>
4341      <address><email></email></address>
4342    </author>
4343    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4344    <date month="May" year="1996"/>
4345  </front>
4346  <seriesInfo name="RFC" value="1950"/>
4347  <annotation>
4348    RFC 1950 is an Informational RFC, thus it might be less stable than
4349    this specification. On the other hand, this downward reference was
4350    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4351    therefore it is unlikely to cause problems in practice. See also
4352    <xref target="BCP97"/>.
4353  </annotation>
4356<reference anchor="RFC1951">
4357  <front>
4358    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4359    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4360      <organization>Aladdin Enterprises</organization>
4361      <address><email></email></address>
4362    </author>
4363    <date month="May" year="1996"/>
4364  </front>
4365  <seriesInfo name="RFC" value="1951"/>
4366  <annotation>
4367    RFC 1951 is an Informational RFC, thus it might be less stable than
4368    this specification. On the other hand, this downward reference was
4369    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4370    therefore it is unlikely to cause problems in practice. See also
4371    <xref target="BCP97"/>.
4372  </annotation>
4375<reference anchor="RFC1952">
4376  <front>
4377    <title>GZIP file format specification version 4.3</title>
4378    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4379      <organization>Aladdin Enterprises</organization>
4380      <address><email></email></address>
4381    </author>
4382    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4383      <address><email></email></address>
4384    </author>
4385    <author initials="M." surname="Adler" fullname="Mark Adler">
4386      <address><email></email></address>
4387    </author>
4388    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4389      <address><email></email></address>
4390    </author>
4391    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4392      <address><email></email></address>
4393    </author>
4394    <date month="May" year="1996"/>
4395  </front>
4396  <seriesInfo name="RFC" value="1952"/>
4397  <annotation>
4398    RFC 1952 is an Informational RFC, thus it might be less stable than
4399    this specification. On the other hand, this downward reference was
4400    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4401    therefore it is unlikely to cause problems in practice. See also
4402    <xref target="BCP97"/>.
4403  </annotation>
4408<references title="Informative References">
4410<reference anchor="Nie1997" target="">
4411  <front>
4412    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4413    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4414    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4415    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4416    <author initials="H." surname="Lie" fullname="H. Lie"/>
4417    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4418    <date year="1997" month="September"/>
4419  </front>
4420  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4423<reference anchor="Pad1995" target="">
4424  <front>
4425    <title>Improving HTTP Latency</title>
4426    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4427    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4428    <date year="1995" month="December"/>
4429  </front>
4430  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4433<reference anchor="RFC1123">
4434  <front>
4435    <title>Requirements for Internet Hosts - Application and Support</title>
4436    <author initials="R." surname="Braden" fullname="Robert Braden">
4437      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4438      <address><email>Braden@ISI.EDU</email></address>
4439    </author>
4440    <date month="October" year="1989"/>
4441  </front>
4442  <seriesInfo name="STD" value="3"/>
4443  <seriesInfo name="RFC" value="1123"/>
4446<reference anchor="RFC1900">
4447  <front>
4448    <title>Renumbering Needs Work</title>
4449    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4450      <organization>CERN, Computing and Networks Division</organization>
4451      <address><email></email></address>
4452    </author>
4453    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4454      <organization>cisco Systems</organization>
4455      <address><email></email></address>
4456    </author>
4457    <date month="February" year="1996"/>
4458  </front>
4459  <seriesInfo name="RFC" value="1900"/>
4462<reference anchor='RFC1919'>
4463  <front>
4464    <title>Classical versus Transparent IP Proxies</title>
4465    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4466      <address><email></email></address>
4467    </author>
4468    <date year='1996' month='March' />
4469  </front>
4470  <seriesInfo name='RFC' value='1919' />
4473<reference anchor="RFC1945">
4474  <front>
4475    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4476    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4477      <organization>MIT, Laboratory for Computer Science</organization>
4478      <address><email></email></address>
4479    </author>
4480    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4481      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4482      <address><email></email></address>
4483    </author>
4484    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4485      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4486      <address><email></email></address>
4487    </author>
4488    <date month="May" year="1996"/>
4489  </front>
4490  <seriesInfo name="RFC" value="1945"/>
4493<reference anchor="RFC2045">
4494  <front>
4495    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4496    <author initials="N." surname="Freed" fullname="Ned Freed">
4497      <organization>Innosoft International, Inc.</organization>
4498      <address><email></email></address>
4499    </author>
4500    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4501      <organization>First Virtual Holdings</organization>
4502      <address><email></email></address>
4503    </author>
4504    <date month="November" year="1996"/>
4505  </front>
4506  <seriesInfo name="RFC" value="2045"/>
4509<reference anchor="RFC2047">
4510  <front>
4511    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4512    <author initials="K." surname="Moore" fullname="Keith Moore">
4513      <organization>University of Tennessee</organization>
4514      <address><email></email></address>
4515    </author>
4516    <date month="November" year="1996"/>
4517  </front>
4518  <seriesInfo name="RFC" value="2047"/>
4521<reference anchor="RFC2068">
4522  <front>
4523    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4524    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4525      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4526      <address><email></email></address>
4527    </author>
4528    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4529      <organization>MIT Laboratory for Computer Science</organization>
4530      <address><email></email></address>
4531    </author>
4532    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4533      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4534      <address><email></email></address>
4535    </author>
4536    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4537      <organization>MIT Laboratory for Computer Science</organization>
4538      <address><email></email></address>
4539    </author>
4540    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4541      <organization>MIT Laboratory for Computer Science</organization>
4542      <address><email></email></address>
4543    </author>
4544    <date month="January" year="1997"/>
4545  </front>
4546  <seriesInfo name="RFC" value="2068"/>
4549<reference anchor="RFC2145">
4550  <front>
4551    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4552    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4553      <organization>Western Research Laboratory</organization>
4554      <address><email></email></address>
4555    </author>
4556    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4557      <organization>Department of Information and Computer Science</organization>
4558      <address><email></email></address>
4559    </author>
4560    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4561      <organization>MIT Laboratory for Computer Science</organization>
4562      <address><email></email></address>
4563    </author>
4564    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4565      <organization>W3 Consortium</organization>
4566      <address><email></email></address>
4567    </author>
4568    <date month="May" year="1997"/>
4569  </front>
4570  <seriesInfo name="RFC" value="2145"/>
4573<reference anchor="RFC2616">
4574  <front>
4575    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4576    <author initials="R." surname="Fielding" fullname="R. Fielding">
4577      <organization>University of California, Irvine</organization>
4578      <address><email></email></address>
4579    </author>
4580    <author initials="J." surname="Gettys" fullname="J. Gettys">
4581      <organization>W3C</organization>
4582      <address><email></email></address>
4583    </author>
4584    <author initials="J." surname="Mogul" fullname="J. Mogul">
4585      <organization>Compaq Computer Corporation</organization>
4586      <address><email></email></address>
4587    </author>
4588    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4589      <organization>MIT Laboratory for Computer Science</organization>
4590      <address><email></email></address>
4591    </author>
4592    <author initials="L." surname="Masinter" fullname="L. Masinter">
4593      <organization>Xerox Corporation</organization>
4594      <address><email></email></address>
4595    </author>
4596    <author initials="P." surname="Leach" fullname="P. Leach">
4597      <organization>Microsoft Corporation</organization>
4598      <address><email></email></address>
4599    </author>
4600    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4601      <organization>W3C</organization>
4602      <address><email></email></address>
4603    </author>
4604    <date month="June" year="1999"/>
4605  </front>
4606  <seriesInfo name="RFC" value="2616"/>
4609<reference anchor='RFC2817'>
4610  <front>
4611    <title>Upgrading to TLS Within HTTP/1.1</title>
4612    <author initials='R.' surname='Khare' fullname='R. Khare'>
4613      <organization>4K Associates / UC Irvine</organization>
4614      <address><email></email></address>
4615    </author>
4616    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4617      <organization>Agranat Systems, Inc.</organization>
4618      <address><email></email></address>
4619    </author>
4620    <date year='2000' month='May' />
4621  </front>
4622  <seriesInfo name='RFC' value='2817' />
4625<reference anchor='RFC2818'>
4626  <front>
4627    <title>HTTP Over TLS</title>
4628    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4629      <organization>RTFM, Inc.</organization>
4630      <address><email></email></address>
4631    </author>
4632    <date year='2000' month='May' />
4633  </front>
4634  <seriesInfo name='RFC' value='2818' />
4637<reference anchor='RFC2965'>
4638  <front>
4639    <title>HTTP State Management Mechanism</title>
4640    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4641      <organization>Bell Laboratories, Lucent Technologies</organization>
4642      <address><email></email></address>
4643    </author>
4644    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4645      <organization>, Inc.</organization>
4646      <address><email></email></address>
4647    </author>
4648    <date year='2000' month='October' />
4649  </front>
4650  <seriesInfo name='RFC' value='2965' />
4653<reference anchor='RFC3040'>
4654  <front>
4655    <title>Internet Web Replication and Caching Taxonomy</title>
4656    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4657      <organization>Equinix, Inc.</organization>
4658    </author>
4659    <author initials='I.' surname='Melve' fullname='I. Melve'>
4660      <organization>UNINETT</organization>
4661    </author>
4662    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4663      <organization>CacheFlow Inc.</organization>
4664    </author>
4665    <date year='2001' month='January' />
4666  </front>
4667  <seriesInfo name='RFC' value='3040' />
4670<reference anchor='RFC3864'>
4671  <front>
4672    <title>Registration Procedures for Message Header Fields</title>
4673    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4674      <organization>Nine by Nine</organization>
4675      <address><email></email></address>
4676    </author>
4677    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4678      <organization>BEA Systems</organization>
4679      <address><email></email></address>
4680    </author>
4681    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4682      <organization>HP Labs</organization>
4683      <address><email></email></address>
4684    </author>
4685    <date year='2004' month='September' />
4686  </front>
4687  <seriesInfo name='BCP' value='90' />
4688  <seriesInfo name='RFC' value='3864' />
4691<reference anchor="RFC4288">
4692  <front>
4693    <title>Media Type Specifications and Registration Procedures</title>
4694    <author initials="N." surname="Freed" fullname="N. Freed">
4695      <organization>Sun Microsystems</organization>
4696      <address>
4697        <email></email>
4698      </address>
4699    </author>
4700    <author initials="J." surname="Klensin" fullname="J. Klensin">
4701      <address>
4702        <email></email>
4703      </address>
4704    </author>
4705    <date year="2005" month="December"/>
4706  </front>
4707  <seriesInfo name="BCP" value="13"/>
4708  <seriesInfo name="RFC" value="4288"/>
4711<reference anchor='RFC4395'>
4712  <front>
4713    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4714    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4715      <organization>AT&amp;T Laboratories</organization>
4716      <address>
4717        <email></email>
4718      </address>
4719    </author>
4720    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4721      <organization>Qualcomm, Inc.</organization>
4722      <address>
4723        <email></email>
4724      </address>
4725    </author>
4726    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4727      <organization>Adobe Systems</organization>
4728      <address>
4729        <email></email>
4730      </address>
4731    </author>
4732    <date year='2006' month='February' />
4733  </front>
4734  <seriesInfo name='BCP' value='115' />
4735  <seriesInfo name='RFC' value='4395' />
4738<reference anchor='RFC5226'>
4739  <front>
4740    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4741    <author initials='T.' surname='Narten' fullname='T. Narten'>
4742      <organization>IBM</organization>
4743      <address><email></email></address>
4744    </author>
4745    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4746      <organization>Google</organization>
4747      <address><email></email></address>
4748    </author>
4749    <date year='2008' month='May' />
4750  </front>
4751  <seriesInfo name='BCP' value='26' />
4752  <seriesInfo name='RFC' value='5226' />
4755<reference anchor="RFC5322">
4756  <front>
4757    <title>Internet Message Format</title>
4758    <author initials="P." surname="Resnick" fullname="P. Resnick">
4759      <organization>Qualcomm Incorporated</organization>
4760    </author>
4761    <date year="2008" month="October"/>
4762  </front>
4763  <seriesInfo name="RFC" value="5322"/>
4766<reference anchor='draft-ietf-httpstate-cookie'>
4767  <front>
4768    <title>HTTP State Management Mechanism</title>
4769    <author initials="A." surname="Barth" fullname="Adam Barth">
4770      <organization abbrev="U.C. Berkeley">
4771        University of California, Berkeley
4772      </organization>
4773      <address><email></email></address>
4774    </author>
4775    <date year='2011' month='March' />
4776  </front>
4777  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4780<reference anchor='BCP97'>
4781  <front>
4782    <title>Handling Normative References to Standards-Track Documents</title>
4783    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4784      <address>
4785        <email></email>
4786      </address>
4787    </author>
4788    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4789      <organization>MIT</organization>
4790      <address>
4791        <email></email>
4792      </address>
4793    </author>
4794    <date year='2007' month='June' />
4795  </front>
4796  <seriesInfo name='BCP' value='97' />
4797  <seriesInfo name='RFC' value='4897' />
4800<reference anchor="Kri2001" target="">
4801  <front>
4802    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4803    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4804    <date year="2001" month="November"/>
4805  </front>
4806  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4809<reference anchor="Spe" target="">
4810  <front>
4811    <title>Analysis of HTTP Performance Problems</title>
4812    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4813    <date/>
4814  </front>
4817<reference anchor="Tou1998" target="">
4818  <front>
4819  <title>Analysis of HTTP Performance</title>
4820  <author initials="J." surname="Touch" fullname="Joe Touch">
4821    <organization>USC/Information Sciences Institute</organization>
4822    <address><email></email></address>
4823  </author>
4824  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4825    <organization>USC/Information Sciences Institute</organization>
4826    <address><email></email></address>
4827  </author>
4828  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4829    <organization>USC/Information Sciences Institute</organization>
4830    <address><email></email></address>
4831  </author>
4832  <date year="1998" month="Aug"/>
4833  </front>
4834  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4835  <annotation>(original report dated Aug. 1996)</annotation>
4841<section title="Tolerant Applications" anchor="tolerant.applications">
4843   Although this document specifies the requirements for the generation
4844   of HTTP/1.1 messages, not all applications will be correct in their
4845   implementation. We therefore recommend that operational applications
4846   be tolerant of deviations whenever those deviations can be
4847   interpreted unambiguously.
4850   The line terminator for header fields is the sequence CRLF.
4851   However, we recommend that applications, when parsing such headers fields,
4852   recognize a single LF as a line terminator and ignore the leading CR.
4855   The character encoding of a representation &SHOULD; be labeled as the lowest
4856   common denominator of the character codes used within that representation, with
4857   the exception that not labeling the representation is preferred over labeling
4858   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4861   Additional rules for requirements on parsing and encoding of dates
4862   and other potential problems with date encodings include:
4865  <list style="symbols">
4866     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4867        which appears to be more than 50 years in the future is in fact
4868        in the past (this helps solve the "year 2000" problem).</t>
4870     <t>Although all date formats are specified to be case-sensitive,
4871        recipients &SHOULD; match day, week and timezone names
4872        case-insensitively.</t>
4874     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4875        Expires date as earlier than the proper value, but &MUST-NOT;
4876        internally represent a parsed Expires date as later than the
4877        proper value.</t>
4879     <t>All expiration-related calculations &MUST; be done in GMT. The
4880        local time zone &MUST-NOT; influence the calculation or comparison
4881        of an age or expiration time.</t>
4883     <t>If an HTTP header field incorrectly carries a date value with a time
4884        zone other than GMT, it &MUST; be converted into GMT using the
4885        most conservative possible conversion.</t>
4886  </list>
4890<section title="HTTP Version History" anchor="compatibility">
4892   HTTP has been in use by the World-Wide Web global information initiative
4893   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4894   was a simple protocol for hypertext data transfer across the Internet
4895   with only a single request method (GET) and no metadata.
4896   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4897   methods and MIME-like messaging that could include metadata about the data
4898   transferred and modifiers on the request/response semantics. However,
4899   HTTP/1.0 did not sufficiently take into consideration the effects of
4900   hierarchical proxies, caching, the need for persistent connections, or
4901   name-based virtual hosts. The proliferation of incompletely-implemented
4902   applications calling themselves "HTTP/1.0" further necessitated a
4903   protocol version change in order for two communicating applications
4904   to determine each other's true capabilities.
4907   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4908   requirements that enable reliable implementations, adding only
4909   those new features that will either be safely ignored by an HTTP/1.0
4910   recipient or only sent when communicating with a party advertising
4911   compliance with HTTP/1.1.
4914   It is beyond the scope of a protocol specification to mandate
4915   compliance with previous versions. HTTP/1.1 was deliberately
4916   designed, however, to make supporting previous versions easy.
4917   We would expect a general-purpose HTTP/1.1 server to understand
4918   any valid request in the format of HTTP/1.0 and respond appropriately
4919   with an HTTP/1.1 message that only uses features understood (or
4920   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4921   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4924   Since HTTP/0.9 did not support header fields in a request,
4925   there is no mechanism for it to support name-based virtual
4926   hosts (selection of resource by inspection of the Host header
4927   field).  Any server that implements name-based virtual hosts
4928   ought to disable support for HTTP/0.9.  Most requests that
4929   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4930   requests wherein a buggy client failed to properly encode
4931   linear whitespace found in a URI reference and placed in
4932   the request-target.
4935<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4937   This section summarizes major differences between versions HTTP/1.0
4938   and HTTP/1.1.
4941<section title="Multi-homed Web Servers" anchor="">
4943   The requirements that clients and servers support the Host header
4944   field (<xref target=""/>), report an error if it is
4945   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4946   are among the most important changes defined by HTTP/1.1.
4949   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4950   addresses and servers; there was no other established mechanism for
4951   distinguishing the intended server of a request than the IP address
4952   to which that request was directed. The Host header field was
4953   introduced during the development of HTTP/1.1 and, though it was
4954   quickly implemented by most HTTP/1.0 browsers, additional requirements
4955   were placed on all HTTP/1.1 requests in order to ensure complete
4956   adoption.  At the time of this writing, most HTTP-based services
4957   are dependent upon the Host header field for targeting requests.
4961<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4963   For most implementations of HTTP/1.0, each connection is established
4964   by the client prior to the request and closed by the server after
4965   sending the response. However, some implementations implement the
4966   Keep-Alive version of persistent connections described in
4967   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4970   Some clients and servers might wish to be compatible with some
4971   previous implementations of persistent connections in HTTP/1.0
4972   clients and servers. Persistent connections in HTTP/1.0 are
4973   explicitly negotiated as they are not the default behavior. HTTP/1.0
4974   experimental implementations of persistent connections are faulty,
4975   and the new facilities in HTTP/1.1 are designed to rectify these
4976   problems. The problem was that some existing HTTP/1.0 clients might
4977   send Keep-Alive to a proxy server that doesn't understand
4978   Connection, which would then erroneously forward it to the next
4979   inbound server, which would establish the Keep-Alive connection and
4980   result in a hung HTTP/1.0 proxy waiting for the close on the
4981   response. The result is that HTTP/1.0 clients must be prevented from
4982   using Keep-Alive when talking to proxies.
4985   However, talking to proxies is the most important use of persistent
4986   connections, so that prohibition is clearly unacceptable. Therefore,
4987   we need some other mechanism for indicating a persistent connection
4988   is desired, which is safe to use even when talking to an old proxy
4989   that ignores Connection. Persistent connections are the default for
4990   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4991   declaring non-persistence. See <xref target="header.connection"/>.
4996<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4998  Empty list elements in list productions have been deprecated.
4999  (<xref target="notation.abnf"/>)
5002  Rules about implicit linear whitespace between certain grammar productions
5003  have been removed; now it's only allowed when specifically pointed out
5004  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5005  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5006  Non-ASCII content in header fields and reason phrase has been obsoleted and
5007  made opaque (the TEXT rule was removed)
5008  (<xref target="basic.rules"/>)
5011  Clarify that HTTP-Version is case sensitive.
5012  (<xref target="http.version"/>)
5015  Require that invalid whitespace around field-names be rejected.
5016  (<xref target="header.fields"/>)
5019  Require recipients to handle bogus Content-Length header fields as errors.
5020  (<xref target="message.body"/>)
5023  Remove reference to non-existent identity transfer-coding value tokens.
5024  (Sections <xref format="counter" target="message.body"/> and
5025  <xref format="counter" target="transfer.codings"/>)
5028  Update use of abs_path production from RFC 1808 to the path-absolute + query
5029  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5030  request method only.
5031  (<xref target="request-target"/>)
5034  Clarification that the chunk length does not include the count of the octets
5035  in the chunk header and trailer. Furthermore disallowed line folding
5036  in chunk extensions.
5037  (<xref target="chunked.encoding"/>)
5040  Remove hard limit of two connections per server.
5041  (<xref target="persistent.practical"/>)
5044  Change ABNF productions for header fields to only define the field value.
5045  (<xref target="header.field.definitions"/>)
5048  Clarify exactly when close connection options must be sent.
5049  (<xref target="header.connection"/>)
5052  Define the semantics of the "Upgrade" header field in responses other than
5053  101 (this was incorporated from <xref target="RFC2817"/>).
5054  (<xref target="header.upgrade"/>)
5059<?BEGININC p1-messaging.abnf-appendix ?>
5060<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5062<artwork type="abnf" name="p1-messaging.parsed-abnf">
5063<x:ref>BWS</x:ref> = OWS
5065<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5066<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5067 connection-token ] )
5068<x:ref>Content-Length</x:ref> = 1*DIGIT
5070<x:ref>Date</x:ref> = HTTP-date
5072<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5074<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5075<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5076<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5077<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5078 ]
5079<x:ref>Host</x:ref> = uri-host [ ":" port ]
5081<x:ref>Method</x:ref> = token
5083<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5085<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5086<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5087<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5088<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5089<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5091<x:ref>Status-Code</x:ref> = 3DIGIT
5092<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5094<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5095<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5096<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5097 transfer-coding ] )
5099<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5100<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5102<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5103 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5104 )
5106<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5107<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5108<x:ref>attribute</x:ref> = token
5109<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5111<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5112<x:ref>chunk-data</x:ref> = 1*OCTET
5113<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5114<x:ref>chunk-ext-name</x:ref> = token
5115<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5116<x:ref>chunk-size</x:ref> = 1*HEXDIG
5117<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5118<x:ref>connection-token</x:ref> = token
5119<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5120 / %x2A-5B ; '*'-'['
5121 / %x5D-7E ; ']'-'~'
5122 / obs-text
5124<x:ref>date1</x:ref> = day SP month SP year
5125<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5126<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5127<x:ref>day</x:ref> = 2DIGIT
5128<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5129 / %x54.75.65 ; Tue
5130 / %x57.65.64 ; Wed
5131 / %x54.68.75 ; Thu
5132 / %x46.72.69 ; Fri
5133 / %x53.61.74 ; Sat
5134 / %x53.75.6E ; Sun
5135<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5136 / %x54. ; Tuesday
5137 / %x57.65.64.6E. ; Wednesday
5138 / %x54. ; Thursday
5139 / %x46. ; Friday
5140 / %x53. ; Saturday
5141 / %x53.75.6E.64.61.79 ; Sunday
5143<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5144<x:ref>field-name</x:ref> = token
5145<x:ref>field-value</x:ref> = *( field-content / OWS )
5147<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5148<x:ref>hour</x:ref> = 2DIGIT
5149<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5150<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5152<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5154<x:ref>message-body</x:ref> = *OCTET
5155<x:ref>minute</x:ref> = 2DIGIT
5156<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5157 / %x46.65.62 ; Feb
5158 / %x4D.61.72 ; Mar
5159 / %x41.70.72 ; Apr
5160 / %x4D.61.79 ; May
5161 / %x4A.75.6E ; Jun
5162 / %x4A.75.6C ; Jul
5163 / %x41.75.67 ; Aug
5164 / %x53.65.70 ; Sep
5165 / %x4F.63.74 ; Oct
5166 / %x4E.6F.76 ; Nov
5167 / %x44.65.63 ; Dec
5169<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5170<x:ref>obs-fold</x:ref> = CRLF
5171<x:ref>obs-text</x:ref> = %x80-FF
5173<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5174<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5175<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5176<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5177<x:ref>product</x:ref> = token [ "/" product-version ]
5178<x:ref>product-version</x:ref> = token
5179<x:ref>protocol-name</x:ref> = token
5180<x:ref>protocol-version</x:ref> = token
5181<x:ref>pseudonym</x:ref> = token
5183<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5184 / %x5D-7E ; ']'-'~'
5185 / obs-text
5186<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5187 / %x5D-7E ; ']'-'~'
5188 / obs-text
5189<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5190<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5191<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5192<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5193<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5194<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5196<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5197<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5198<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5199<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5200 / authority
5201<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5202<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5204<x:ref>second</x:ref> = 2DIGIT
5205<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5206 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5207<x:ref>start-line</x:ref> = Request-Line / Status-Line
5209<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5210<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5211 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5212<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5213<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5214<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5215<x:ref>token</x:ref> = 1*tchar
5216<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5217<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5218 transfer-extension
5219<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5220<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5222<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5224<x:ref>value</x:ref> = word
5226<x:ref>word</x:ref> = token / quoted-string
5228<x:ref>year</x:ref> = 4DIGIT
5231<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5232; Chunked-Body defined but not used
5233; Connection defined but not used
5234; Content-Length defined but not used
5235; Date defined but not used
5236; HTTP-message defined but not used
5237; Host defined but not used
5238; Request defined but not used
5239; Response defined but not used
5240; TE defined but not used
5241; Trailer defined but not used
5242; Transfer-Encoding defined but not used
5243; URI-reference defined but not used
5244; Upgrade defined but not used
5245; Via defined but not used
5246; http-URI defined but not used
5247; https-URI defined but not used
5248; partial-URI defined but not used
5249; special defined but not used
5251<?ENDINC p1-messaging.abnf-appendix ?>
5253<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5255<section title="Since RFC 2616">
5257  Extracted relevant partitions from <xref target="RFC2616"/>.
5261<section title="Since draft-ietf-httpbis-p1-messaging-00">
5263  Closed issues:
5264  <list style="symbols">
5265    <t>
5266      <eref target=""/>:
5267      "HTTP Version should be case sensitive"
5268      (<eref target=""/>)
5269    </t>
5270    <t>
5271      <eref target=""/>:
5272      "'unsafe' characters"
5273      (<eref target=""/>)
5274    </t>
5275    <t>
5276      <eref target=""/>:
5277      "Chunk Size Definition"
5278      (<eref target=""/>)
5279    </t>
5280    <t>
5281      <eref target=""/>:
5282      "Message Length"
5283      (<eref target=""/>)
5284    </t>
5285    <t>
5286      <eref target=""/>:
5287      "Media Type Registrations"
5288      (<eref target=""/>)
5289    </t>
5290    <t>
5291      <eref target=""/>:
5292      "URI includes query"
5293      (<eref target=""/>)
5294    </t>
5295    <t>
5296      <eref target=""/>:
5297      "No close on 1xx responses"
5298      (<eref target=""/>)
5299    </t>
5300    <t>
5301      <eref target=""/>:
5302      "Remove 'identity' token references"
5303      (<eref target=""/>)
5304    </t>
5305    <t>
5306      <eref target=""/>:
5307      "Import query BNF"
5308    </t>
5309    <t>
5310      <eref target=""/>:
5311      "qdtext BNF"
5312    </t>
5313    <t>
5314      <eref target=""/>:
5315      "Normative and Informative references"
5316    </t>
5317    <t>
5318      <eref target=""/>:
5319      "RFC2606 Compliance"
5320    </t>
5321    <t>
5322      <eref target=""/>:
5323      "RFC977 reference"
5324    </t>
5325    <t>
5326      <eref target=""/>:
5327      "RFC1700 references"
5328    </t>
5329    <t>
5330      <eref target=""/>:
5331      "inconsistency in date format explanation"
5332    </t>
5333    <t>
5334      <eref target=""/>:
5335      "Date reference typo"
5336    </t>
5337    <t>
5338      <eref target=""/>:
5339      "Informative references"
5340    </t>
5341    <t>
5342      <eref target=""/>:
5343      "ISO-8859-1 Reference"
5344    </t>
5345    <t>
5346      <eref target=""/>:
5347      "Normative up-to-date references"
5348    </t>
5349  </list>
5352  Other changes:
5353  <list style="symbols">
5354    <t>
5355      Update media type registrations to use RFC4288 template.
5356    </t>
5357    <t>
5358      Use names of RFC4234 core rules DQUOTE and WSP,
5359      fix broken ABNF for chunk-data
5360      (work in progress on <eref target=""/>)
5361    </t>
5362  </list>
5366<section title="Since draft-ietf-httpbis-p1-messaging-01">
5368  Closed issues:
5369  <list style="symbols">
5370    <t>
5371      <eref target=""/>:
5372      "Bodies on GET (and other) requests"
5373    </t>
5374    <t>
5375      <eref target=""/>:
5376      "Updating to RFC4288"
5377    </t>
5378    <t>
5379      <eref target=""/>:
5380      "Status Code and Reason Phrase"
5381    </t>
5382    <t>
5383      <eref target=""/>:
5384      "rel_path not used"
5385    </t>
5386  </list>
5389  Ongoing work on ABNF conversion (<eref target=""/>):
5390  <list style="symbols">
5391    <t>
5392      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5393      "trailer-part").
5394    </t>
5395    <t>
5396      Avoid underscore character in rule names ("http_URL" ->
5397      "http-URL", "abs_path" -> "path-absolute").
5398    </t>
5399    <t>
5400      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5401      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5402      have to be updated when switching over to RFC3986.
5403    </t>
5404    <t>
5405      Synchronize core rules with RFC5234.
5406    </t>
5407    <t>
5408      Get rid of prose rules that span multiple lines.
5409    </t>
5410    <t>
5411      Get rid of unused rules LOALPHA and UPALPHA.
5412    </t>
5413    <t>
5414      Move "Product Tokens" section (back) into Part 1, as "token" is used
5415      in the definition of the Upgrade header field.
5416    </t>
5417    <t>
5418      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5419    </t>
5420    <t>
5421      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5422    </t>
5423  </list>
5427<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5429  Closed issues:
5430  <list style="symbols">
5431    <t>
5432      <eref target=""/>:
5433      "HTTP-date vs. rfc1123-date"
5434    </t>
5435    <t>
5436      <eref target=""/>:
5437      "WS in quoted-pair"
5438    </t>
5439  </list>
5442  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5443  <list style="symbols">
5444    <t>
5445      Reference RFC 3984, and update header field registrations for headers defined
5446      in this document.
5447    </t>
5448  </list>
5451  Ongoing work on ABNF conversion (<eref target=""/>):
5452  <list style="symbols">
5453    <t>
5454      Replace string literals when the string really is case-sensitive (HTTP-Version).
5455    </t>
5456  </list>
5460<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5462  Closed issues:
5463  <list style="symbols">
5464    <t>
5465      <eref target=""/>:
5466      "Connection closing"
5467    </t>
5468    <t>
5469      <eref target=""/>:
5470      "Move registrations and registry information to IANA Considerations"
5471    </t>
5472    <t>
5473      <eref target=""/>:
5474      "need new URL for PAD1995 reference"
5475    </t>
5476    <t>
5477      <eref target=""/>:
5478      "IANA Considerations: update HTTP URI scheme registration"
5479    </t>
5480    <t>
5481      <eref target=""/>:
5482      "Cite HTTPS URI scheme definition"
5483    </t>
5484    <t>
5485      <eref target=""/>:
5486      "List-type headers vs Set-Cookie"
5487    </t>
5488  </list>
5491  Ongoing work on ABNF conversion (<eref target=""/>):
5492  <list style="symbols">
5493    <t>
5494      Replace string literals when the string really is case-sensitive (HTTP-Date).
5495    </t>
5496    <t>
5497      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5498    </t>
5499  </list>
5503<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5505  Closed issues:
5506  <list style="symbols">
5507    <t>
5508      <eref target=""/>:
5509      "Out-of-date reference for URIs"
5510    </t>
5511    <t>
5512      <eref target=""/>:
5513      "RFC 2822 is updated by RFC 5322"
5514    </t>
5515  </list>
5518  Ongoing work on ABNF conversion (<eref target=""/>):
5519  <list style="symbols">
5520    <t>
5521      Use "/" instead of "|" for alternatives.
5522    </t>
5523    <t>
5524      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5525    </t>
5526    <t>
5527      Only reference RFC 5234's core rules.
5528    </t>
5529    <t>
5530      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5531      whitespace ("OWS") and required whitespace ("RWS").
5532    </t>
5533    <t>
5534      Rewrite ABNFs to spell out whitespace rules, factor out
5535      header field value format definitions.
5536    </t>
5537  </list>
5541<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5543  Closed issues:
5544  <list style="symbols">
5545    <t>
5546      <eref target=""/>:
5547      "Header LWS"
5548    </t>
5549    <t>
5550      <eref target=""/>:
5551      "Sort 1.3 Terminology"
5552    </t>
5553    <t>
5554      <eref target=""/>:
5555      "RFC2047 encoded words"
5556    </t>
5557    <t>
5558      <eref target=""/>:
5559      "Character Encodings in TEXT"
5560    </t>
5561    <t>
5562      <eref target=""/>:
5563      "Line Folding"
5564    </t>
5565    <t>
5566      <eref target=""/>:
5567      "OPTIONS * and proxies"
5568    </t>
5569    <t>
5570      <eref target=""/>:
5571      "Reason-Phrase BNF"
5572    </t>
5573    <t>
5574      <eref target=""/>:
5575      "Use of TEXT"
5576    </t>
5577    <t>
5578      <eref target=""/>:
5579      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5580    </t>
5581    <t>
5582      <eref target=""/>:
5583      "RFC822 reference left in discussion of date formats"
5584    </t>
5585  </list>
5588  Final work on ABNF conversion (<eref target=""/>):
5589  <list style="symbols">
5590    <t>
5591      Rewrite definition of list rules, deprecate empty list elements.
5592    </t>
5593    <t>
5594      Add appendix containing collected and expanded ABNF.
5595    </t>
5596  </list>
5599  Other changes:
5600  <list style="symbols">
5601    <t>
5602      Rewrite introduction; add mostly new Architecture Section.
5603    </t>
5604    <t>
5605      Move definition of quality values from Part 3 into Part 1;
5606      make TE request header field grammar independent of accept-params (defined in Part 3).
5607    </t>
5608  </list>
5612<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5614  Closed issues:
5615  <list style="symbols">
5616    <t>
5617      <eref target=""/>:
5618      "base for numeric protocol elements"
5619    </t>
5620    <t>
5621      <eref target=""/>:
5622      "comment ABNF"
5623    </t>
5624  </list>
5627  Partly resolved issues:
5628  <list style="symbols">
5629    <t>
5630      <eref target=""/>:
5631      "205 Bodies" (took out language that implied that there might be
5632      methods for which a request body MUST NOT be included)
5633    </t>
5634    <t>
5635      <eref target=""/>:
5636      "editorial improvements around HTTP-date"
5637    </t>
5638  </list>
5642<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5644  Closed issues:
5645  <list style="symbols">
5646    <t>
5647      <eref target=""/>:
5648      "Repeating single-value headers"
5649    </t>
5650    <t>
5651      <eref target=""/>:
5652      "increase connection limit"
5653    </t>
5654    <t>
5655      <eref target=""/>:
5656      "IP addresses in URLs"
5657    </t>
5658    <t>
5659      <eref target=""/>:
5660      "take over HTTP Upgrade Token Registry"
5661    </t>
5662    <t>
5663      <eref target=""/>:
5664      "CR and LF in chunk extension values"
5665    </t>
5666    <t>
5667      <eref target=""/>:
5668      "HTTP/0.9 support"
5669    </t>
5670    <t>
5671      <eref target=""/>:
5672      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5673    </t>
5674    <t>
5675      <eref target=""/>:
5676      "move definitions of gzip/deflate/compress to part 1"
5677    </t>
5678    <t>
5679      <eref target=""/>:
5680      "disallow control characters in quoted-pair"
5681    </t>
5682  </list>
5685  Partly resolved issues:
5686  <list style="symbols">
5687    <t>
5688      <eref target=""/>:
5689      "update IANA requirements wrt Transfer-Coding values" (add the
5690      IANA Considerations subsection)
5691    </t>
5692  </list>
5696<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5698  Closed issues:
5699  <list style="symbols">
5700    <t>
5701      <eref target=""/>:
5702      "header parsing, treatment of leading and trailing OWS"
5703    </t>
5704  </list>
5707  Partly resolved issues:
5708  <list style="symbols">
5709    <t>
5710      <eref target=""/>:
5711      "Placement of 13.5.1 and 13.5.2"
5712    </t>
5713    <t>
5714      <eref target=""/>:
5715      "use of term "word" when talking about header structure"
5716    </t>
5717  </list>
5721<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5723  Closed issues:
5724  <list style="symbols">
5725    <t>
5726      <eref target=""/>:
5727      "Clarification of the term 'deflate'"
5728    </t>
5729    <t>
5730      <eref target=""/>:
5731      "OPTIONS * and proxies"
5732    </t>
5733    <t>
5734      <eref target=""/>:
5735      "MIME-Version not listed in P1, general header fields"
5736    </t>
5737    <t>
5738      <eref target=""/>:
5739      "IANA registry for content/transfer encodings"
5740    </t>
5741    <t>
5742      <eref target=""/>:
5743      "Case-sensitivity of HTTP-date"
5744    </t>
5745    <t>
5746      <eref target=""/>:
5747      "use of term "word" when talking about header structure"
5748    </t>
5749  </list>
5752  Partly resolved issues:
5753  <list style="symbols">
5754    <t>
5755      <eref target=""/>:
5756      "Term for the requested resource's URI"
5757    </t>
5758  </list>
5762<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5764  Closed issues:
5765  <list style="symbols">
5766    <t>
5767      <eref target=""/>:
5768      "Connection Closing"
5769    </t>
5770    <t>
5771      <eref target=""/>:
5772      "Delimiting messages with multipart/byteranges"
5773    </t>
5774    <t>
5775      <eref target=""/>:
5776      "Handling multiple Content-Length headers"
5777    </t>
5778    <t>
5779      <eref target=""/>:
5780      "Clarify entity / representation / variant terminology"
5781    </t>
5782    <t>
5783      <eref target=""/>:
5784      "consider removing the 'changes from 2068' sections"
5785    </t>
5786  </list>
5789  Partly resolved issues:
5790  <list style="symbols">
5791    <t>
5792      <eref target=""/>:
5793      "HTTP(s) URI scheme definitions"
5794    </t>
5795  </list>
5799<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5801  Closed issues:
5802  <list style="symbols">
5803    <t>
5804      <eref target=""/>:
5805      "Trailer requirements"
5806    </t>
5807    <t>
5808      <eref target=""/>:
5809      "Text about clock requirement for caches belongs in p6"
5810    </t>
5811    <t>
5812      <eref target=""/>:
5813      "effective request URI: handling of missing host in HTTP/1.0"
5814    </t>
5815    <t>
5816      <eref target=""/>:
5817      "confusing Date requirements for clients"
5818    </t>
5819  </list>
5822  Partly resolved issues:
5823  <list style="symbols">
5824    <t>
5825      <eref target=""/>:
5826      "Handling multiple Content-Length headers"
5827    </t>
5828  </list>
5832<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5834  Closed issues:
5835  <list style="symbols">
5836    <t>
5837      <eref target=""/>:
5838      "RFC2145 Normative"
5839    </t>
5840    <t>
5841      <eref target=""/>:
5842      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5843    </t>
5844    <t>
5845      <eref target=""/>:
5846      "define 'transparent' proxy"
5847    </t>
5848    <t>
5849      <eref target=""/>:
5850      "Header Classification"
5851    </t>
5852    <t>
5853      <eref target=""/>:
5854      "Is * usable as a request-uri for new methods?"
5855    </t>
5856    <t>
5857      <eref target=""/>:
5858      "Migrate Upgrade details from RFC2817"
5859    </t>
5860    <t>
5861      <eref target=""/>:
5862      "untangle ABNFs for header fields"
5863    </t>
5864    <t>
5865      <eref target=""/>:
5866      "update RFC 2109 reference"
5867    </t>
5868  </list>
5872<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5874  Closed issues:
5875  <list style="symbols">
5876    <t>
5877      <eref target=""/>:
5878      "Allow is not in 13.5.2"
5879    </t>
5880    <t>
5881      <eref target=""/>:
5882      "untangle ABNFs for header fields"
5883    </t>
5884    <t>
5885      <eref target=""/>:
5886      "Content-Length ABNF broken"
5887    </t>
5888  </list>
5892<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5894  None yet.
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