source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1229

Last change on this file since 1229 was 1229, checked in by julian.reschke@…, 10 years ago

fix bug in Content-Length ABNF (see #286)

  • Property svn:eol-style set to native
File size: 250.5 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
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 ( The current issues list is
215    at <eref target=""/>
216    and related documents (including fancy diffs) can be found at
217    <eref target=""/>.
218  </t>
219  <t>
220    The changes in this draft are summarized in <xref target="changes.since.13"/>.
221  </t>
225<section title="Introduction" anchor="introduction">
227   The Hypertext Transfer Protocol (HTTP) is an application-level
228   request/response protocol that uses extensible semantics and MIME-like
229   message payloads for flexible interaction with network-based hypertext
230   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
231   standard <xref target="RFC3986"/> to indicate the target resource and
232   relationships between resources.
233   Messages are passed in a format similar to that used by Internet mail
234   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
235   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
236   between HTTP and MIME messages).
239   HTTP is a generic interface protocol for information systems. It is
240   designed to hide the details of how a service is implemented by presenting
241   a uniform interface to clients that is independent of the types of
242   resources provided. Likewise, servers do not need to be aware of each
243   client's purpose: an HTTP request can be considered in isolation rather
244   than being associated with a specific type of client or a predetermined
245   sequence of application steps. The result is a protocol that can be used
246   effectively in many different contexts and for which implementations can
247   evolve independently over time.
250   HTTP is also designed for use as an intermediation protocol for translating
251   communication to and from non-HTTP information systems.
252   HTTP proxies and gateways can provide access to alternative information
253   services by translating their diverse protocols into a hypertext
254   format that can be viewed and manipulated by clients in the same way
255   as HTTP services.
258   One consequence of HTTP flexibility is that the protocol cannot be
259   defined in terms of what occurs behind the interface. Instead, we
260   are limited to defining the syntax of communication, the intent
261   of received communication, and the expected behavior of recipients.
262   If the communication is considered in isolation, then successful
263   actions ought to be reflected in corresponding changes to the
264   observable interface provided by servers. However, since multiple
265   clients might act in parallel and perhaps at cross-purposes, we
266   cannot require that such changes be observable beyond the scope
267   of a single response.
270   This document is Part 1 of the seven-part specification of HTTP,
271   defining the protocol referred to as "HTTP/1.1", obsoleting
272   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
273   Part 1 describes the architectural elements that are used or
274   referred to in HTTP, defines the "http" and "https" URI schemes,
275   describes overall network operation and connection management,
276   and defines HTTP message framing and forwarding requirements.
277   Our goal is to define all of the mechanisms necessary for HTTP message
278   handling that are independent of message semantics, thereby defining the
279   complete set of requirements for message parsers and
280   message-forwarding intermediaries.
283<section title="Requirements" anchor="intro.requirements">
285   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
286   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
287   document are to be interpreted as described in <xref target="RFC2119"/>.
290   An implementation is not compliant if it fails to satisfy one or more
291   of the "MUST" or "REQUIRED" level requirements for the protocols it
292   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
293   level and all the "SHOULD" level requirements for its protocols is said
294   to be "unconditionally compliant"; one that satisfies all the "MUST"
295   level requirements but not all the "SHOULD" level requirements for its
296   protocols is said to be "conditionally compliant".
300<section title="Syntax Notation" anchor="notation">
301<iref primary="true" item="Grammar" subitem="ALPHA"/>
302<iref primary="true" item="Grammar" subitem="CR"/>
303<iref primary="true" item="Grammar" subitem="CRLF"/>
304<iref primary="true" item="Grammar" subitem="CTL"/>
305<iref primary="true" item="Grammar" subitem="DIGIT"/>
306<iref primary="true" item="Grammar" subitem="DQUOTE"/>
307<iref primary="true" item="Grammar" subitem="HEXDIG"/>
308<iref primary="true" item="Grammar" subitem="LF"/>
309<iref primary="true" item="Grammar" subitem="OCTET"/>
310<iref primary="true" item="Grammar" subitem="SP"/>
311<iref primary="true" item="Grammar" subitem="VCHAR"/>
312<iref primary="true" item="Grammar" subitem="WSP"/>
314   This specification uses the Augmented Backus-Naur Form (ABNF) notation
315   of <xref target="RFC5234"/>.
317<t anchor="core.rules">
318  <x:anchor-alias value="ALPHA"/>
319  <x:anchor-alias value="CTL"/>
320  <x:anchor-alias value="CR"/>
321  <x:anchor-alias value="CRLF"/>
322  <x:anchor-alias value="DIGIT"/>
323  <x:anchor-alias value="DQUOTE"/>
324  <x:anchor-alias value="HEXDIG"/>
325  <x:anchor-alias value="LF"/>
326  <x:anchor-alias value="OCTET"/>
327  <x:anchor-alias value="SP"/>
328  <x:anchor-alias value="VCHAR"/>
329  <x:anchor-alias value="WSP"/>
330   The following core rules are included by
331   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
332   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
333   DIGIT (decimal 0-9), DQUOTE (double quote),
334   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
335   OCTET (any 8-bit sequence of data), SP (space),
336   VCHAR (any visible <xref target="USASCII"/> character),
337   and WSP (whitespace).
340   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
341   "obsolete" grammar rules that appear for historical reasons.
344<section title="ABNF Extension: #rule" anchor="notation.abnf">
346  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
347  improve readability.
350  A construct "#" is defined, similar to "*", for defining comma-delimited
351  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
352  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
353  comma (",") and optional whitespace (OWS,
354  <xref target="basic.rules"/>).   
357  Thus,
358</preamble><artwork type="example">
359  1#element =&gt; element *( OWS "," OWS element )
362  and:
363</preamble><artwork type="example">
364  #element =&gt; [ 1#element ]
367  and for n &gt;= 1 and m &gt; 1:
368</preamble><artwork type="example">
369  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
372  For compatibility with legacy list rules, recipients &SHOULD; accept empty
373  list elements. In other words, consumers would follow the list productions:
375<figure><artwork type="example">
376  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
378  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
381  Note that empty elements do not contribute to the count of elements present,
382  though.
385  For example, given these ABNF productions:
387<figure><artwork type="example">
388  example-list      = 1#example-list-elmt
389  example-list-elmt = token ; see <xref target="basic.rules"/>
392  Then these are valid values for example-list (not including the double
393  quotes, which are present for delimitation only):
395<figure><artwork type="example">
396  "foo,bar"
397  " foo ,bar,"
398  "  foo , ,bar,charlie   "
399  "foo ,bar,   charlie "
402  But these values would be invalid, as at least one non-empty element is
403  required:
405<figure><artwork type="example">
406  ""
407  ","
408  ",   ,"
411  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
412  expanded as explained above.
416<section title="Basic Rules" anchor="basic.rules">
417<t anchor="rule.CRLF">
418  <x:anchor-alias value="CRLF"/>
419   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
420   protocol elements other than the message-body
421   (see <xref target="tolerant.applications"/> for tolerant applications).
423<t anchor="rule.LWS">
424   This specification uses three rules to denote the use of linear
425   whitespace: OWS (optional whitespace), RWS (required whitespace), and
426   BWS ("bad" whitespace).
429   The OWS rule is used where zero or more linear whitespace octets might
430   appear. OWS &SHOULD; either not be produced or be produced as a single
431   SP. Multiple OWS octets that occur within field-content &SHOULD;
432   be replaced with a single SP before interpreting the field value or
433   forwarding the message downstream.
436   RWS is used when at least one linear whitespace octet is required to
437   separate field tokens. RWS &SHOULD; be produced as a single SP.
438   Multiple RWS octets that occur within field-content &SHOULD; be
439   replaced with a single SP before interpreting the field value or
440   forwarding the message downstream.
443   BWS is used where the grammar allows optional whitespace for historical
444   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
445   recipients &MUST; accept such bad optional whitespace and remove it before
446   interpreting the field value or forwarding the message downstream.
448<t anchor="rule.whitespace">
449  <x:anchor-alias value="BWS"/>
450  <x:anchor-alias value="OWS"/>
451  <x:anchor-alias value="RWS"/>
452  <x:anchor-alias value="obs-fold"/>
454<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"/>
455  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
456                 ; "optional" whitespace
457  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "required" whitespace
459  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
460                 ; "bad" whitespace
461  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
462                 ; see <xref target="header.fields"/>
464<t anchor="rule.token.separators">
465  <x:anchor-alias value="tchar"/>
466  <x:anchor-alias value="token"/>
467  <x:anchor-alias value="special"/>
468  <x:anchor-alias value="word"/>
469   Many HTTP/1.1 header field values consist of words (token or quoted-string)
470   separated by whitespace or special characters. These special characters
471   &MUST; be in a quoted string to be used within a parameter value (as defined
472   in <xref target="transfer.codings"/>).
474<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"/>
475  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
477  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
479  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
480 -->
481  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
482                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
483                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
484                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
486  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
487                 / ";" / ":" / "\" / DQUOTE / "/" / "["
488                 / "]" / "?" / "=" / "{" / "}"
490<t anchor="rule.quoted-string">
491  <x:anchor-alias value="quoted-string"/>
492  <x:anchor-alias value="qdtext"/>
493  <x:anchor-alias value="obs-text"/>
494   A string of text is parsed as a single word if it is quoted using
495   double-quote marks.
497<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"/>
498  <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>
499  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
500                 ; <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>
501  <x:ref>obs-text</x:ref>       = %x80-FF
503<t anchor="rule.quoted-pair">
504  <x:anchor-alias value="quoted-pair"/>
505   The backslash octet ("\") can be used as a single-octet
506   quoting mechanism within quoted-string constructs:
508<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
509  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
512   Senders &SHOULD-NOT; escape octets that do not require escaping
513   (i.e., other than DQUOTE and the backslash octet).
520<section title="HTTP-related architecture" anchor="architecture">
522   HTTP was created for the World Wide Web architecture
523   and has evolved over time to support the scalability needs of a worldwide
524   hypertext system. Much of that architecture is reflected in the terminology
525   and syntax productions used to define HTTP.
528<section title="Client/Server Messaging" anchor="operation">
529<iref primary="true" item="client"/>
530<iref primary="true" item="server"/>
531<iref primary="true" item="connection"/>
533   HTTP is a stateless request/response protocol that operates by exchanging
534   messages across a reliable transport or session-layer
535   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
536   program that establishes a connection to a server for the purpose of
537   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
538   program that accepts connections in order to service HTTP requests by
539   sending HTTP responses.
541<iref primary="true" item="user agent"/>
542<iref primary="true" item="origin server"/>
543<iref primary="true" item="browser"/>
544<iref primary="true" item="spider"/>
545<iref primary="true" item="sender"/>
546<iref primary="true" item="recipient"/>
548   Note that the terms client and server refer only to the roles that
549   these programs perform for a particular connection.  The same program
550   might act as a client on some connections and a server on others.  We use
551   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
552   such as a WWW browser, editor, or spider (web-traversing robot), and
553   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
554   authoritative responses to a request.  For general requirements, we use
555   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
556   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
557   message.
560   Most HTTP communication consists of a retrieval request (GET) for
561   a representation of some resource identified by a URI.  In the
562   simplest case, this might be accomplished via a single bidirectional
563   connection (===) between the user agent (UA) and the origin server (O).
565<figure><artwork type="drawing">
566         request   &gt;
567    UA ======================================= O
568                                &lt;   response
570<iref primary="true" item="message"/>
571<iref primary="true" item="request"/>
572<iref primary="true" item="response"/>
574   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
575   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
576   protocol version, followed by MIME-like header fields containing
577   request modifiers, client information, and payload metadata, an empty
578   line to indicate the end of the header section, and finally the payload
579   body (if any).
582   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
583   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
584   includes the protocol version, a success or error code, and textual
585   reason phrase, followed by MIME-like header fields containing server
586   information, resource metadata, and payload metadata, an empty line to
587   indicate the end of the header section, and finally the payload body (if any).
590   The following example illustrates a typical message exchange for a
591   GET request on the URI "":
594client request:
595</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
596GET /hello.txt HTTP/1.1
597User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
599Accept: */*
603server response:
604</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
605HTTP/1.1 200 OK
606Date: Mon, 27 Jul 2009 12:28:53 GMT
607Server: Apache
608Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
609ETag: "34aa387-d-1568eb00"
610Accept-Ranges: bytes
611Content-Length: <x:length-of target="exbody"/>
612Vary: Accept-Encoding
613Content-Type: text/plain
615<x:span anchor="exbody">Hello World!
619<section title="Connections and Transport Independence" anchor="transport-independence">
621   HTTP messaging is independent of the underlying transport or
622   session-layer connection protocol(s).  HTTP only presumes a reliable
623   transport with in-order delivery of requests and the corresponding
624   in-order delivery of responses.  The mapping of HTTP request and
625   response structures onto the data units of the underlying transport
626   protocol is outside the scope of this specification.
629   The specific connection protocols to be used for an interaction
630   are determined by client configuration and the target resource's URI.
631   For example, the "http" URI scheme
632   (<xref target="http.uri"/>) indicates a default connection of TCP
633   over IP, with a default TCP port of 80, but the client might be
634   configured to use a proxy via some other connection port or protocol
635   instead of using the defaults.
638   A connection might be used for multiple HTTP request/response exchanges,
639   as defined in <xref target="persistent.connections"/>.
643<section title="Intermediaries" anchor="intermediaries">
644<iref primary="true" item="intermediary"/>
646   HTTP enables the use of intermediaries to satisfy requests through
647   a chain of connections.  There are three common forms of HTTP
648   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
649   a single intermediary might act as an origin server, proxy, gateway,
650   or tunnel, switching behavior based on the nature of each request.
652<figure><artwork type="drawing">
653         &gt;             &gt;             &gt;             &gt;
654    UA =========== A =========== B =========== C =========== O
655               &lt;             &lt;             &lt;             &lt;
658   The figure above shows three intermediaries (A, B, and C) between the
659   user agent and origin server. A request or response message that
660   travels the whole chain will pass through four separate connections.
661   Some HTTP communication options
662   might apply only to the connection with the nearest, non-tunnel
663   neighbor, only to the end-points of the chain, or to all connections
664   along the chain. Although the diagram is linear, each participant might
665   be engaged in multiple, simultaneous communications. For example, B
666   might be receiving requests from many clients other than A, and/or
667   forwarding requests to servers other than C, at the same time that it
668   is handling A's request.
671<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
672<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
673   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
674   to describe various requirements in relation to the directional flow of a
675   message: all messages flow from upstream to downstream.
676   Likewise, we use the terms inbound and outbound to refer to
677   directions in relation to the request path:
678   "<x:dfn>inbound</x:dfn>" means toward the origin server and
679   "<x:dfn>outbound</x:dfn>" means toward the user agent.
681<t><iref primary="true" item="proxy"/>
682   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
683   client, usually via local configuration rules, to receive requests
684   for some type(s) of absolute URI and attempt to satisfy those
685   requests via translation through the HTTP interface.  Some translations
686   are minimal, such as for proxy requests for "http" URIs, whereas
687   other requests might require translation to and from entirely different
688   application-layer protocols. Proxies are often used to group an
689   organization's HTTP requests through a common intermediary for the
690   sake of security, annotation services, or shared caching.
693<iref primary="true" item="transforming proxy"/>
694<iref primary="true" item="non-transforming proxy"/>
695   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
696   or configured to modify request or response messages in a semantically
697   meaningful way (i.e., modifications, beyond those required by normal
698   HTTP processing, that change the message in a way that would be
699   significant to the original sender or potentially significant to
700   downstream recipients).  For example, a transforming proxy might be
701   acting as a shared annotation server (modifying responses to include
702   references to a local annotation database), a malware filter, a
703   format transcoder, or an intranet-to-Internet privacy filter.  Such
704   transformations are presumed to be desired by the client (or client
705   organization) that selected the proxy and are beyond the scope of
706   this specification.  However, when a proxy is not intended to transform
707   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
708   requirements that preserve HTTP message semantics.
710<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
711<iref primary="true" item="accelerator"/>
712   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
713   is a receiving agent that acts
714   as a layer above some other server(s) and translates the received
715   requests to the underlying server's protocol.  Gateways are often
716   used to encapsulate legacy or untrusted information services, to
717   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
718   enable partitioning or load-balancing of HTTP services across
719   multiple machines.
722   A gateway behaves as an origin server on its outbound connection and
723   as a user agent on its inbound connection.
724   All HTTP requirements applicable to an origin server
725   also apply to the outbound communication of a gateway.
726   A gateway communicates with inbound servers using any protocol that
727   it desires, including private extensions to HTTP that are outside
728   the scope of this specification.  However, an HTTP-to-HTTP gateway
729   that wishes to interoperate with third-party HTTP servers &MUST;
730   comply with HTTP user agent requirements on the gateway's inbound
731   connection and &MUST; implement the Connection
732   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
733   header fields for both connections.
735<t><iref primary="true" item="tunnel"/>
736   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
737   without changing the messages. Once active, a tunnel is not
738   considered a party to the HTTP communication, though the tunnel might
739   have been initiated by an HTTP request. A tunnel ceases to exist when
740   both ends of the relayed connection are closed. Tunnels are used to
741   extend a virtual connection through an intermediary, such as when
742   transport-layer security is used to establish private communication
743   through a shared firewall proxy.
745<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
746<iref primary="true" item="captive portal"/>
747   In addition, there may exist network intermediaries that are not
748   considered part of the HTTP communication but nevertheless act as
749   filters or redirecting agents (usually violating HTTP semantics,
750   causing security problems, and otherwise making a mess of things).
751   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
752   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
753   or "<x:dfn>captive portal</x:dfn>",
754   differs from an HTTP proxy because it has not been selected by the client.
755   Instead, the network intermediary redirects outgoing TCP port 80 packets
756   (and occasionally other common port traffic) to an internal HTTP server.
757   Interception proxies are commonly found on public network access points,
758   as a means of enforcing account subscription prior to allowing use of
759   non-local Internet services, and within corporate firewalls to enforce
760   network usage policies.
761   They are indistinguishable from a man-in-the-middle attack.
765<section title="Caches" anchor="caches">
766<iref primary="true" item="cache"/>
768   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
769   subsystem that controls its message storage, retrieval, and deletion.
770   A cache stores cacheable responses in order to reduce the response
771   time and network bandwidth consumption on future, equivalent
772   requests. Any client or server &MAY; employ a cache, though a cache
773   cannot be used by a server while it is acting as a tunnel.
776   The effect of a cache is that the request/response chain is shortened
777   if one of the participants along the chain has a cached response
778   applicable to that request. The following illustrates the resulting
779   chain if B has a cached copy of an earlier response from O (via C)
780   for a request which has not been cached by UA or A.
782<figure><artwork type="drawing">
783            &gt;             &gt;
784       UA =========== A =========== B - - - - - - C - - - - - - O
785                  &lt;             &lt;
787<t><iref primary="true" item="cacheable"/>
788   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
789   the response message for use in answering subsequent requests.
790   Even when a response is cacheable, there might be additional
791   constraints placed by the client or by the origin server on when
792   that cached response can be used for a particular request. HTTP
793   requirements for cache behavior and cacheable responses are
794   defined in &caching-overview;. 
797   There are a wide variety of architectures and configurations
798   of caches and proxies deployed across the World Wide Web and
799   inside large organizations. These systems include national hierarchies
800   of proxy caches to save transoceanic bandwidth, systems that
801   broadcast or multicast cache entries, organizations that distribute
802   subsets of cached data via optical media, and so on.
806<section title="Protocol Versioning" anchor="http.version">
807  <x:anchor-alias value="HTTP-Version"/>
808  <x:anchor-alias value="HTTP-Prot-Name"/>
810   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
811   versions of the protocol. This specification defines version "1.1".
812   The protocol version as a whole indicates the sender's compliance
813   with the set of requirements laid out in that version's corresponding
814   specification of HTTP.
817   The version of an HTTP message is indicated by an HTTP-Version field
818   in the first line of the message. HTTP-Version is case-sensitive.
820<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
821  <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>
822  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
825   The HTTP version number consists of two non-negative decimal integers
826   separated by a "." (period or decimal point).  The first
827   number ("major version") indicates the HTTP messaging syntax, whereas
828   the second number ("minor version") indicates the highest minor
829   version to which the sender is at least conditionally compliant and
830   able to understand for future communication.  The minor version
831   advertises the sender's communication capabilities even when the
832   sender is only using a backwards-compatible subset of the protocol,
833   thereby letting the recipient know that more advanced features can
834   be used in response (by servers) or in future requests (by clients).
837   When comparing HTTP versions, the numbers &MUST; be compared
838   numerically rather than lexically.  For example, HTTP/2.4 is a lower
839   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
840   Leading zeros &MUST; be ignored by recipients and &MUST-NOT; be sent.
843   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
844   <xref target="RFC1945"/> or a recipient whose version is unknown,
845   the HTTP/1.1 message is constructed such that it can be interpreted
846   as a valid HTTP/1.0 message if all of the newer features are ignored.
847   This specification places recipient-version requirements on some
848   new features so that a compliant sender will only use compatible
849   features until it has determined, through configuration or the
850   receipt of a message, that the recipient supports HTTP/1.1.
853   The interpretation of an HTTP header field does not change
854   between minor versions of the same major version, though the default
855   behavior of a recipient in the absence of such a field can change.
856   Unless specified otherwise, header fields defined in HTTP/1.1 are
857   defined for all versions of HTTP/1.x.  In particular, the Host and
858   Connection header fields ought to be implemented by all HTTP/1.x
859   implementations whether or not they advertise compliance with HTTP/1.1.
862   New header fields can be defined such that, when they are
863   understood by a recipient, they might override or enhance the
864   interpretation of previously defined header fields.  When an
865   implementation receives an unrecognized header field, the recipient
866   &MUST; ignore that header field for local processing regardless of
867   the message's HTTP version.  An unrecognized header field received
868   by a proxy &MUST; be forwarded downstream unless the header field's
869   field-name is listed in the message's Connection header-field
870   (see <xref target="header.connection"/>).
871   These requirements allow HTTP's functionality to be enhanced without
872   requiring prior update of all compliant intermediaries.
875   Intermediaries that process HTTP messages (i.e., all intermediaries
876   other than those acting as a tunnel) &MUST; send their own HTTP-Version
877   in forwarded messages.  In other words, they &MUST-NOT; blindly
878   forward the first line of an HTTP message without ensuring that the
879   protocol version matches what the intermediary understands, and
880   is at least conditionally compliant to, for both the receiving and
881   sending of messages.  Forwarding an HTTP message without rewriting
882   the HTTP-Version might result in communication errors when downstream
883   recipients use the message sender's version to determine what features
884   are safe to use for later communication with that sender.
887   An HTTP client &SHOULD; send a request version equal to the highest
888   version for which the client is at least conditionally compliant and
889   whose major version is no higher than the highest version supported
890   by the server, if this is known.  An HTTP client &MUST-NOT; send a
891   version for which it is not at least conditionally compliant.
894   An HTTP client &MAY; send a lower request version if it is known that
895   the server incorrectly implements the HTTP specification, but only
896   after the client has attempted at least one normal request and determined
897   from the response status or header fields (e.g., Server) that the
898   server improperly handles higher request versions.
901   An HTTP server &SHOULD; send a response version equal to the highest
902   version for which the server is at least conditionally compliant and
903   whose major version is less than or equal to the one received in the
904   request.  An HTTP server &MUST-NOT; send a version for which it is not
905   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
906   Version Not Supported) response if it cannot send a response using the
907   major version used in the client's request.
910   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
911   if it is known or suspected that the client incorrectly implements the
912   HTTP specification and is incapable of correctly processing later
913   version responses, such as when a client fails to parse the version
914   number correctly or when an intermediary is known to blindly forward
915   the HTTP-Version even when it doesn't comply with the given minor
916   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
917   performed unless triggered by specific client attributes, such as when
918   one or more of the request header fields (e.g., User-Agent) uniquely
919   match the values sent by a client known to be in error.
922   The intention of HTTP's versioning design is that the major number
923   will only be incremented if an incompatible message syntax is
924   introduced, and that the minor number will only be incremented when
925   changes made to the protocol have the effect of adding to the message
926   semantics or implying additional capabilities of the sender.  However,
927   the minor version was not incremented for the changes introduced between
928   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
929   is specifically avoiding any such changes to the protocol.
933<section title="Uniform Resource Identifiers" anchor="uri">
934<iref primary="true" item="resource"/>
936   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
937   throughout HTTP as the means for identifying resources. URI references
938   are used to target requests, indicate redirects, and define relationships.
939   HTTP does not limit what a resource might be; it merely defines an interface
940   that can be used to interact with a resource via HTTP. More information on
941   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
943  <x:anchor-alias value="URI-reference"/>
944  <x:anchor-alias value="absolute-URI"/>
945  <x:anchor-alias value="relative-part"/>
946  <x:anchor-alias value="authority"/>
947  <x:anchor-alias value="path-abempty"/>
948  <x:anchor-alias value="path-absolute"/>
949  <x:anchor-alias value="port"/>
950  <x:anchor-alias value="query"/>
951  <x:anchor-alias value="uri-host"/>
952  <x:anchor-alias value="partial-URI"/>
954   This specification adopts the definitions of "URI-reference",
955   "absolute-URI", "relative-part", "port", "host",
956   "path-abempty", "path-absolute", "query", and "authority" from the
957   URI generic syntax <xref target="RFC3986"/>.
958   In addition, we define a partial-URI rule for protocol elements
959   that allow a relative URI but not a fragment.
961<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"/>
962  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
963  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
964  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
965  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
966  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
967  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
968  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
969  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
970  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
972  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
975   Each protocol element in HTTP that allows a URI reference will indicate
976   in its ABNF production whether the element allows any form of reference
977   (URI-reference), only a URI in absolute form (absolute-URI), only the
978   path and optional query components, or some combination of the above.
979   Unless otherwise indicated, URI references are parsed relative to the
980   effective request URI, which defines the default base URI for references
981   in both the request and its corresponding response.
984<section title="http URI scheme" anchor="http.uri">
985  <x:anchor-alias value="http-URI"/>
986  <iref item="http URI scheme" primary="true"/>
987  <iref item="URI scheme" subitem="http" primary="true"/>
989   The "http" URI scheme is hereby defined for the purpose of minting
990   identifiers according to their association with the hierarchical
991   namespace governed by a potential HTTP origin server listening for
992   TCP connections on a given port.
994<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
995  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
998   The HTTP origin server is identified by the generic syntax's
999   <x:ref>authority</x:ref> component, which includes a host identifier
1000   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1001   The remainder of the URI, consisting of both the hierarchical path
1002   component and optional query component, serves as an identifier for
1003   a potential resource within that origin server's name space.
1006   If the host identifier is provided as an IP literal or IPv4 address,
1007   then the origin server is any listener on the indicated TCP port at
1008   that IP address. If host is a registered name, then that name is
1009   considered an indirect identifier and the recipient might use a name
1010   resolution service, such as DNS, to find the address of a listener
1011   for that host.
1012   The host &MUST-NOT; be empty; if an "http" URI is received with an
1013   empty host, then it &MUST; be rejected as invalid.
1014   If the port subcomponent is empty or not given, then TCP port 80 is
1015   assumed (the default reserved port for WWW services).
1018   Regardless of the form of host identifier, access to that host is not
1019   implied by the mere presence of its name or address. The host might or might
1020   not exist and, even when it does exist, might or might not be running an
1021   HTTP server or listening to the indicated port. The "http" URI scheme
1022   makes use of the delegated nature of Internet names and addresses to
1023   establish a naming authority (whatever entity has the ability to place
1024   an HTTP server at that Internet name or address) and allows that
1025   authority to determine which names are valid and how they might be used.
1028   When an "http" URI is used within a context that calls for access to the
1029   indicated resource, a client &MAY; attempt access by resolving
1030   the host to an IP address, establishing a TCP connection to that address
1031   on the indicated port, and sending an HTTP request message to the server
1032   containing the URI's identifying data as described in <xref target="request"/>.
1033   If the server responds to that request with a non-interim HTTP response
1034   message, as described in <xref target="response"/>, then that response
1035   is considered an authoritative answer to the client's request.
1038   Although HTTP is independent of the transport protocol, the "http"
1039   scheme is specific to TCP-based services because the name delegation
1040   process depends on TCP for establishing authority.
1041   An HTTP service based on some other underlying connection protocol
1042   would presumably be identified using a different URI scheme, just as
1043   the "https" scheme (below) is used for servers that require an SSL/TLS
1044   transport layer on a connection. Other protocols might also be used to
1045   provide access to "http" identified resources &mdash; it is only the
1046   authoritative interface used for mapping the namespace that is
1047   specific to TCP.
1050   The URI generic syntax for authority also includes a deprecated
1051   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1052   for including user authentication information in the URI.  Some
1053   implementations make use of the userinfo component for internal
1054   configuration of authentication information, such as within command
1055   invocation options, configuration files, or bookmark lists, even
1056   though such usage might expose a user identifier or password.
1057   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1058   delimiter) when transmitting an "http" URI in a message.  Recipients
1059   of HTTP messages that contain a URI reference &SHOULD; parse for the
1060   existence of userinfo and treat its presence as an error, likely
1061   indicating that the deprecated subcomponent is being used to obscure
1062   the authority for the sake of phishing attacks.
1066<section title="https URI scheme" anchor="https.uri">
1067   <x:anchor-alias value="https-URI"/>
1068   <iref item="https URI scheme"/>
1069   <iref item="URI scheme" subitem="https"/>
1071   The "https" URI scheme is hereby defined for the purpose of minting
1072   identifiers according to their association with the hierarchical
1073   namespace governed by a potential HTTP origin server listening for
1074   SSL/TLS-secured connections on a given TCP port.
1077   All of the requirements listed above for the "http" scheme are also
1078   requirements for the "https" scheme, except that a default TCP port
1079   of 443 is assumed if the port subcomponent is empty or not given,
1080   and the TCP connection &MUST; be secured for privacy through the
1081   use of strong encryption prior to sending the first HTTP request.
1083<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1084  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1087   Unlike the "http" scheme, responses to "https" identified requests
1088   are never "public" and thus &MUST-NOT; be reused for shared caching.
1089   They can, however, be reused in a private cache if the message is
1090   cacheable by default in HTTP or specifically indicated as such by
1091   the Cache-Control header field (&header-cache-control;).
1094   Resources made available via the "https" scheme have no shared
1095   identity with the "http" scheme even if their resource identifiers
1096   indicate the same authority (the same host listening to the same
1097   TCP port).  They are distinct name spaces and are considered to be
1098   distinct origin servers.  However, an extension to HTTP that is
1099   defined to apply to entire host domains, such as the Cookie protocol
1100   <xref target="draft-ietf-httpstate-cookie"/>, can allow information
1101   set by one service to impact communication with other services
1102   within a matching group of host domains.
1105   The process for authoritative access to an "https" identified
1106   resource is defined in <xref target="RFC2818"/>.
1110<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1112   Since the "http" and "https" schemes conform to the URI generic syntax,
1113   such URIs are normalized and compared according to the algorithm defined
1114   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1115   described above for each scheme.
1118   If the port is equal to the default port for a scheme, the normal
1119   form is to elide the port subcomponent. Likewise, an empty path
1120   component is equivalent to an absolute path of "/", so the normal
1121   form is to provide a path of "/" instead. The scheme and host
1122   are case-insensitive and normally provided in lowercase; all
1123   other components are compared in a case-sensitive manner.
1124   Characters other than those in the "reserved" set are equivalent
1125   to their percent-encoded octets (see <xref target="RFC3986"
1126   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1129   For example, the following three URIs are equivalent:
1131<figure><artwork type="example">
1140<section title="Message Format" anchor="http.message">
1141<x:anchor-alias value="generic-message"/>
1142<x:anchor-alias value="message.types"/>
1143<x:anchor-alias value="HTTP-message"/>
1144<x:anchor-alias value="start-line"/>
1145<iref item="header section"/>
1146<iref item="headers"/>
1147<iref item="header field"/>
1149   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1150   octets in a format similar to the Internet Message Format
1151   <xref target="RFC5322"/>: zero or more header fields (collectively
1152   referred to as the "headers" or the "header section"), an empty line
1153   indicating the end of the header section, and an optional message-body.
1156   An HTTP message can either be a request from client to server or a
1157   response from server to client.  Syntactically, the two types of message
1158   differ only in the start-line, which is either a Request-Line (for requests)
1159   or a Status-Line (for responses), and in the algorithm for determining
1160   the length of the message-body (<xref target="message.body"/>).
1161   In theory, a client could receive requests and a server could receive
1162   responses, distinguishing them by their different start-line formats,
1163   but in practice servers are implemented to only expect a request
1164   (a response is interpreted as an unknown or invalid request method)
1165   and clients are implemented to only expect a response.
1167<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1168  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1169                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1170                    <x:ref>CRLF</x:ref>
1171                    [ <x:ref>message-body</x:ref> ]
1172  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1175   Implementations &MUST-NOT; send whitespace between the start-line and
1176   the first header field. The presence of such whitespace in a request
1177   might be an attempt to trick a server into ignoring that field or
1178   processing the line after it as a new request, either of which might
1179   result in a security vulnerability if other implementations within
1180   the request chain interpret the same message differently.
1181   Likewise, the presence of such whitespace in a response might be
1182   ignored by some clients or cause others to cease parsing.
1185<section title="Message Parsing Robustness" anchor="message.robustness">
1187   In the interest of robustness, servers &SHOULD; ignore at least one
1188   empty line received where a Request-Line is expected. In other words, if
1189   the server is reading the protocol stream at the beginning of a
1190   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1193   Some old HTTP/1.0 client implementations send an extra CRLF
1194   after a POST request as a lame workaround for some early server
1195   applications that failed to read message-body content that was
1196   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1197   preface or follow a request with an extra CRLF.  If terminating
1198   the request message-body with a line-ending is desired, then the
1199   client &MUST; include the terminating CRLF octets as part of the
1200   message-body length.
1203   When a server listening only for HTTP request messages, or processing
1204   what appears from the start-line to be an HTTP request message,
1205   receives a sequence of octets that does not match the HTTP-message
1206   grammar aside from the robustness exceptions listed above, the
1207   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1210   The normal procedure for parsing an HTTP message is to read the
1211   start-line into a structure, read each header field into a hash
1212   table by field name until the empty line, and then use the parsed
1213   data to determine if a message-body is expected.  If a message-body
1214   has been indicated, then it is read as a stream until an amount
1215   of octets equal to the message-body length is read or the connection
1216   is closed.  Care must be taken to parse an HTTP message as a sequence
1217   of octets in an encoding that is a superset of US-ASCII.  Attempting
1218   to parse HTTP as a stream of Unicode characters in a character encoding
1219   like UTF-16 might introduce security flaws due to the differing ways
1220   that such parsers interpret invalid characters.
1223   HTTP allows the set of defined header fields to be extended without
1224   changing the protocol version (see <xref target="header.field.registration"/>).
1225   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1226   proxy is specifically configured to block or otherwise transform such
1227   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1231<section title="Header Fields" anchor="header.fields">
1232  <x:anchor-alias value="header-field"/>
1233  <x:anchor-alias value="field-content"/>
1234  <x:anchor-alias value="field-name"/>
1235  <x:anchor-alias value="field-value"/>
1236  <x:anchor-alias value="OWS"/>
1238   Each HTTP header field consists of a case-insensitive field name
1239   followed by a colon (":"), optional whitespace, and the field value.
1241<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"/>
1242  <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>
1243  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1244  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1245  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1248   No whitespace is allowed between the header field name and colon. For
1249   security reasons, any request message received containing such whitespace
1250   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1251   &MUST; remove any such whitespace from a response message before
1252   forwarding the message downstream.
1255   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1256   preferred. The field value does not include any leading or trailing white
1257   space: OWS occurring before the first non-whitespace octet of the
1258   field value or after the last non-whitespace octet of the field value
1259   is ignored and &SHOULD; be removed before further processing (as this does
1260   not change the meaning of the header field).
1263   The order in which header fields with differing field names are
1264   received is not significant. However, it is "good practice" to send
1265   header fields that contain control data first, such as Host on
1266   requests and Date on responses, so that implementations can decide
1267   when not to handle a message as early as possible.  A server &MUST;
1268   wait until the entire header section is received before interpreting
1269   a request message, since later header fields might include conditionals,
1270   authentication credentials, or deliberately misleading duplicate
1271   header fields that would impact request processing.
1274   Multiple header fields with the same field name &MUST-NOT; be
1275   sent in a message unless the entire field value for that
1276   header field is defined as a comma-separated list [i.e., #(values)].
1277   Multiple header fields with the same field name can be combined into
1278   one "field-name: field-value" pair, without changing the semantics of the
1279   message, by appending each subsequent field value to the combined
1280   field value in order, separated by a comma. The order in which
1281   header fields with the same field name are received is therefore
1282   significant to the interpretation of the combined field value;
1283   a proxy &MUST-NOT; change the order of these field values when
1284   forwarding a message.
1287  <t>
1288   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1289   practice can occur multiple times, but does not use the list syntax, and
1290   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1291   for details.) Also note that the Set-Cookie2 header field specified in
1292   <xref target="RFC2965"/> does not share this problem.
1293  </t>
1296   Historically, HTTP header field values could be extended over multiple
1297   lines by preceding each extra line with at least one space or horizontal
1298   tab octet (line folding). This specification deprecates such line
1299   folding except within the message/http media type
1300   (<xref target=""/>).
1301   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1302   (i.e., that contain any field-content that matches the obs-fold rule) unless
1303   the message is intended for packaging within the message/http media type.
1304   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1305   obs-fold whitespace with a single SP prior to interpreting the field value
1306   or forwarding the message downstream.
1309   Historically, HTTP has allowed field content with text in the ISO-8859-1
1310   <xref target="ISO-8859-1"/> character encoding and supported other
1311   character sets only through use of <xref target="RFC2047"/> encoding.
1312   In practice, most HTTP header field values use only a subset of the
1313   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1314   header fields &SHOULD; limit their field values to US-ASCII octets.
1315   Recipients &SHOULD; treat other (obs-text) octets in field content as
1316   opaque data.
1318<t anchor="rule.comment">
1319  <x:anchor-alias value="comment"/>
1320  <x:anchor-alias value="ctext"/>
1321   Comments can be included in some HTTP header fields by surrounding
1322   the comment text with parentheses. Comments are only allowed in
1323   fields containing "comment" as part of their field value definition.
1325<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1326  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1327  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1328                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1330<t anchor="rule.quoted-cpair">
1331  <x:anchor-alias value="quoted-cpair"/>
1332   The backslash octet ("\") can be used as a single-octet
1333   quoting mechanism within comment constructs:
1335<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1336  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1339   Senders &SHOULD-NOT; escape octets that do not require escaping
1340   (i.e., other than the backslash octet "\" and the parentheses "(" and
1341   ")").
1345<section title="Message Body" anchor="message.body">
1346  <x:anchor-alias value="message-body"/>
1348   The message-body (if any) of an HTTP message is used to carry the
1349   payload body associated with the request or response.
1351<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1352  <x:ref>message-body</x:ref> = *OCTET
1355   The message-body differs from the payload body only when a transfer-coding
1356   has been applied, as indicated by the Transfer-Encoding header field
1357   (<xref target="header.transfer-encoding"/>).  If more than one
1358   Transfer-Encoding header field is present in a message, the multiple
1359   field-values &MUST; be combined into one field-value, according to the
1360   algorithm defined in <xref target="header.fields"/>, before determining
1361   the message-body length.
1364   When one or more transfer-codings are applied to a payload in order to
1365   form the message-body, the Transfer-Encoding header field &MUST; contain
1366   the list of transfer-codings applied. Transfer-Encoding is a property of
1367   the message, not of the payload, and thus &MAY; be added or removed by
1368   any implementation along the request/response chain under the constraints
1369   found in <xref target="transfer.codings"/>.
1372   If a message is received that has multiple Content-Length header fields
1373   (<xref target="header.content-length"/>) with field-values consisting
1374   of the same decimal value, or a single Content-Length header field with
1375   a field value containing a list of identical decimal values (e.g.,
1376   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1377   header fields have been generated or combined by an upstream message
1378   processor, then the recipient &MUST; either reject the message as invalid
1379   or replace the duplicated field-values with a single valid Content-Length
1380   field containing that decimal value prior to determining the message-body
1381   length.
1384   The rules for when a message-body is allowed in a message differ for
1385   requests and responses.
1388   The presence of a message-body in a request is signaled by the
1389   inclusion of a Content-Length or Transfer-Encoding header field in
1390   the request's header fields, even if the request method does not
1391   define any use for a message-body.  This allows the request
1392   message framing algorithm to be independent of method semantics.
1395   For response messages, whether or not a message-body is included with
1396   a message is dependent on both the request method and the response
1397   status code (<xref target="status.code.and.reason.phrase"/>).
1398   Responses to the HEAD request method never include a message-body
1399   because the associated response header fields (e.g., Transfer-Encoding,
1400   Content-Length, etc.) only indicate what their values would have been
1401   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1402   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1403   All other responses do include a message-body, although the body
1404   &MAY; be of zero length.
1407   The length of the message-body is determined by one of the following
1408   (in order of precedence):
1411  <list style="numbers">
1412    <x:lt><t>
1413     Any response to a HEAD request and any response with a status
1414     code of 100-199, 204, or 304 is always terminated by the first
1415     empty line after the header fields, regardless of the header
1416     fields present in the message, and thus cannot contain a message-body.
1417    </t></x:lt>
1418    <x:lt><t>
1419     If a Transfer-Encoding header field is present
1420     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1421     is the final encoding, the message-body length is determined by reading
1422     and decoding the chunked data until the transfer-coding indicates the
1423     data is complete.
1424    </t>
1425    <t>
1426     If a Transfer-Encoding header field is present in a response and the
1427     "chunked" transfer-coding is not the final encoding, the message-body
1428     length is determined by reading the connection until it is closed by
1429     the server.
1430     If a Transfer-Encoding header field is present in a request and the
1431     "chunked" transfer-coding is not the final encoding, the message-body
1432     length cannot be determined reliably; the server &MUST; respond with
1433     the 400 (Bad Request) status code and then close the connection.
1434    </t>
1435    <t>
1436     If a message is received with both a Transfer-Encoding header field
1437     and a Content-Length header field, the Transfer-Encoding overrides
1438     the Content-Length.
1439     Such a message might indicate an attempt to perform request or response
1440     smuggling (bypass of security-related checks on message routing or content)
1441     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1442     be removed, prior to forwarding the message downstream, or replaced with
1443     the real message-body length after the transfer-coding is decoded.
1444    </t></x:lt>
1445    <x:lt><t>
1446     If a message is received without Transfer-Encoding and with either
1447     multiple Content-Length header fields having differing field-values or
1448     a single Content-Length header field having an invalid value, then the
1449     message framing is invalid and &MUST; be treated as an error to
1450     prevent request or response smuggling.
1451     If this is a request message, the server &MUST; respond with
1452     a 400 (Bad Request) status code and then close the connection.
1453     If this is a response message received by a proxy, the proxy
1454     &MUST; discard the received response, send a 502 (Bad Gateway)
1455     status code as its downstream response, and then close the connection.
1456     If this is a response message received by a user-agent, it &MUST; be
1457     treated as an error by discarding the message and closing the connection.
1458    </t></x:lt>
1459    <x:lt><t>
1460     If a valid Content-Length header field
1461     is present without Transfer-Encoding, its decimal value defines the
1462     message-body length in octets.  If the actual number of octets sent in
1463     the message is less than the indicated Content-Length, the recipient
1464     &MUST; consider the message to be incomplete and treat the connection
1465     as no longer usable.
1466     If the actual number of octets sent in the message is more than the indicated
1467     Content-Length, the recipient &MUST; only process the message-body up to the
1468     field value's number of octets; the remainder of the message &MUST; either
1469     be discarded or treated as the next message in a pipeline.  For the sake of
1470     robustness, a user-agent &MAY; attempt to detect and correct such an error
1471     in message framing if it is parsing the response to the last request on
1472     on a connection and the connection has been closed by the server.
1473    </t></x:lt>
1474    <x:lt><t>
1475     If this is a request message and none of the above are true, then the
1476     message-body length is zero (no message-body is present).
1477    </t></x:lt>
1478    <x:lt><t>
1479     Otherwise, this is a response message without a declared message-body
1480     length, so the message-body length is determined by the number of octets
1481     received prior to the server closing the connection.
1482    </t></x:lt>
1483  </list>
1486   Since there is no way to distinguish a successfully completed,
1487   close-delimited message from a partially-received message interrupted
1488   by network failure, implementations &SHOULD; use encoding or
1489   length-delimited messages whenever possible.  The close-delimiting
1490   feature exists primarily for backwards compatibility with HTTP/1.0.
1493   A server &MAY; reject a request that contains a message-body but
1494   not a Content-Length by responding with 411 (Length Required).
1497   Unless a transfer-coding other than "chunked" has been applied,
1498   a client that sends a request containing a message-body &SHOULD;
1499   use a valid Content-Length header field if the message-body length
1500   is known in advance, rather than the "chunked" encoding, since some
1501   existing services respond to "chunked" with a 411 (Length Required)
1502   status code even though they understand the chunked encoding.  This
1503   is typically because such services are implemented via a gateway that
1504   requires a content-length in advance of being called and the server
1505   is unable or unwilling to buffer the entire request before processing.
1508   A client that sends a request containing a message-body &MUST; include a
1509   valid Content-Length header field if it does not know the server will
1510   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1511   of specific user configuration or by remembering the version of a prior
1512   received response.
1515   Request messages that are prematurely terminated, possibly due to a
1516   cancelled connection or a server-imposed time-out exception, &MUST;
1517   result in closure of the connection; sending an HTTP/1.1 error response
1518   prior to closing the connection is &OPTIONAL;.
1519   Response messages that are prematurely terminated, usually by closure
1520   of the connection prior to receiving the expected number of octets or by
1521   failure to decode a transfer-encoded message-body, &MUST; be recorded
1522   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1523   message-body as if it were complete (i.e., some indication must be given
1524   to the user that an error occurred).  Cache requirements for incomplete
1525   responses are defined in &cache-incomplete;.
1528   A server &MUST; read the entire request message-body or close
1529   the connection after sending its response, since otherwise the
1530   remaining data on a persistent connection would be misinterpreted
1531   as the next request.  Likewise,
1532   a client &MUST; read the entire response message-body if it intends
1533   to reuse the same connection for a subsequent request.  Pipelining
1534   multiple requests on a connection is described in <xref target="pipelining"/>.
1538<section title="General Header Fields" anchor="general.header.fields">
1539  <x:anchor-alias value="general-header"/>
1541   There are a few header fields which have general applicability for
1542   both request and response messages, but which do not apply to the
1543   payload being transferred. These header fields apply only to the
1544   message being transmitted.
1546<texttable align="left">
1547  <ttcol>Header Field Name</ttcol>
1548  <ttcol>Defined in...</ttcol>
1550  <c>Connection</c> <c><xref target="header.connection"/></c>
1551  <c>Date</c> <c><xref target=""/></c>
1552  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1553  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1554  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1555  <c>Via</c> <c><xref target="header.via"/></c>
1560<section title="Request" anchor="request">
1561  <x:anchor-alias value="Request"/>
1563   A request message from a client to a server begins with a
1564   Request-Line, followed by zero or more header fields, an empty
1565   line signifying the end of the header block, and an optional
1566   message body.
1568<!--                 Host                      ; should be moved here eventually -->
1569<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1570  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1571                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1572                  <x:ref>CRLF</x:ref>
1573                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1576<section title="Request-Line" anchor="request-line">
1577  <x:anchor-alias value="Request-Line"/>
1579   The Request-Line begins with a method token, followed by a single
1580   space (SP), the request-target, another single space (SP), the
1581   protocol version, and ending with CRLF.
1583<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1584  <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>
1587<section title="Method" anchor="method">
1588  <x:anchor-alias value="Method"/>
1590   The Method token indicates the request method to be performed on the
1591   target resource. The request method is case-sensitive.
1593<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1594  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1598<section title="request-target" anchor="request-target">
1599  <x:anchor-alias value="request-target"/>
1601   The request-target identifies the target resource upon which to apply
1602   the request.  In most cases, the user agent is provided a URI reference
1603   from which it determines an absolute URI for identifying the target
1604   resource.  When a request to the resource is initiated, all or part
1605   of that URI is used to construct the HTTP request-target.
1607<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1608  <x:ref>request-target</x:ref> = "*"
1609                 / <x:ref>absolute-URI</x:ref>
1610                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1611                 / <x:ref>authority</x:ref>
1614   The four options for request-target are dependent on the nature of the
1615   request.
1617<t><iref item="asterisk form (of request-target)"/>
1618   The asterisk "*" form of request-target, which &MUST-NOT; be used
1619   with any request method other than OPTIONS, means that the request
1620   applies to the server as a whole (the listening process) rather than
1621   to a specific named resource at that server.  For example,
1623<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1624OPTIONS * HTTP/1.1
1626<t><iref item="absolute-URI form (of request-target)"/>
1627   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1628   proxy. The proxy is requested to either forward the request or service it
1629   from a valid cache, and then return the response. Note that the proxy &MAY;
1630   forward the request on to another proxy or directly to the server
1631   specified by the absolute-URI. In order to avoid request loops, a
1632   proxy that forwards requests to other proxies &MUST; be able to
1633   recognize and exclude all of its own server names, including
1634   any aliases, local variations, and the numeric IP address. An example
1635   Request-Line would be:
1637<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1638GET HTTP/1.1
1641   To allow for transition to absolute-URIs in all requests in future
1642   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1643   form in requests, even though HTTP/1.1 clients will only generate
1644   them in requests to proxies.
1647   If a proxy receives a host name that is not a fully qualified domain
1648   name, it &MAY; add its domain to the host name it received. If a proxy
1649   receives a fully qualified domain name, the proxy &MUST-NOT; change
1650   the host name.
1652<t><iref item="authority form (of request-target)"/>
1653   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1655<t><iref item="origin form (of request-target)"/>
1656   The most common form of request-target is that used when making
1657   a request to an origin server ("origin form").
1658   In this case, the absolute path and query components of the URI
1659   &MUST; be transmitted as the request-target, and the authority component
1660   &MUST; be transmitted in a Host header field. For example, a client wishing
1661   to retrieve a representation of the resource, as identified above,
1662   directly from the origin server would open (or reuse) a TCP connection
1663   to port 80 of the host "" and send the lines:
1665<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1666GET /pub/WWW/TheProject.html HTTP/1.1
1670   followed by the remainder of the Request. Note that the origin form
1671   of request-target always starts with an absolute path; if the target
1672   resource's URI path is empty, then an absolute path of "/" &MUST; be
1673   provided in the request-target.
1676   If a proxy receives an OPTIONS request with an absolute-URI form of
1677   request-target in which the URI has an empty path and no query component,
1678   then the last proxy on the request chain &MUST; use a request-target
1679   of "*" when it forwards the request to the indicated origin server.
1682   For example, the request
1683</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1687  would be forwarded by the final proxy as
1688</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1689OPTIONS * HTTP/1.1
1693   after connecting to port 8001 of host "".
1697   The request-target is transmitted in the format specified in
1698   <xref target="http.uri"/>. If the request-target is percent-encoded
1699   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1700   &MUST; decode the request-target in order to
1701   properly interpret the request. Servers &SHOULD; respond to invalid
1702   request-targets with an appropriate status code.
1705   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1706   received request-target when forwarding it to the next inbound server,
1707   except as noted above to replace a null path-absolute with "/" or "*".
1710  <t>
1711    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1712    meaning of the request when the origin server is improperly using
1713    a non-reserved URI character for a reserved purpose.  Implementors
1714    need to be aware that some pre-HTTP/1.1 proxies have been known to
1715    rewrite the request-target.
1716  </t>
1719   HTTP does not place a pre-defined limit on the length of a request-target.
1720   A server &MUST; be prepared to receive URIs of unbounded length and
1721   respond with the 414 (URI Too Long) status code if the received
1722   request-target would be longer than the server wishes to handle
1723   (see &status-414;).
1726   Various ad-hoc limitations on request-target length are found in practice.
1727   It is &RECOMMENDED; that all HTTP senders and recipients support
1728   request-target lengths of 8000 or more octets.
1731  <t>
1732    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1733    are not part of the request-target and thus will not be transmitted
1734    in an HTTP request.
1735  </t>
1740<section title="The Resource Identified by a Request" anchor="">
1742   The exact resource identified by an Internet request is determined by
1743   examining both the request-target and the Host header field.
1746   An origin server that does not allow resources to differ by the
1747   requested host &MAY; ignore the Host header field value when
1748   determining the resource identified by an HTTP/1.1 request. (But see
1749   <xref target=""/>
1750   for other requirements on Host support in HTTP/1.1.)
1753   An origin server that does differentiate resources based on the host
1754   requested (sometimes referred to as virtual hosts or vanity host
1755   names) &MUST; use the following rules for determining the requested
1756   resource on an HTTP/1.1 request:
1757  <list style="numbers">
1758    <t>If request-target is an absolute-URI, the host is part of the
1759     request-target. Any Host header field value in the request &MUST; be
1760     ignored.</t>
1761    <t>If the request-target is not an absolute-URI, and the request includes
1762     a Host header field, the host is determined by the Host header
1763     field value.</t>
1764    <t>If the host as determined by rule 1 or 2 is not a valid host on
1765     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1766  </list>
1769   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1770   attempt to use heuristics (e.g., examination of the URI path for
1771   something unique to a particular host) in order to determine what
1772   exact resource is being requested.
1776<section title="Effective Request URI" anchor="effective.request.uri">
1777  <iref primary="true" item="effective request URI"/>
1778  <iref primary="true" item="target resource"/>
1780   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1781   for the target resource; instead, the URI needs to be inferred from the
1782   request-target, Host header field, and connection context. The result of
1783   this process is called the "effective request URI".  The "target resource"
1784   is the resource identified by the effective request URI.
1787   If the request-target is an absolute-URI, then the effective request URI is
1788   the request-target.
1791   If the request-target uses the path-absolute form or the asterisk form,
1792   and the Host header field is present, then the effective request URI is
1793   constructed by concatenating
1796  <list style="symbols">
1797    <t>
1798      the scheme name: "http" if the request was received over an insecure
1799      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1800      connection,
1801    </t>
1802    <t>
1803      the octet sequence "://",
1804    </t>
1805    <t>
1806      the authority component, as specified in the Host header field
1807      (<xref target=""/>), and
1808    </t>
1809    <t>
1810      the request-target obtained from the Request-Line, unless the
1811      request-target is just the asterisk "*".
1812    </t>
1813  </list>
1816   If the request-target uses the path-absolute form or the asterisk form,
1817   and the Host header field is not present, then the effective request URI is
1818   undefined.
1821   Otherwise, when request-target uses the authority form, the effective
1822   request URI is undefined.
1826   Example 1: the effective request URI for the message
1828<artwork type="example" x:indent-with="  ">
1829GET /pub/WWW/TheProject.html HTTP/1.1
1833  (received over an insecure TCP connection) is "http", plus "://", plus the
1834  authority component "", plus the request-target
1835  "/pub/WWW/TheProject.html", thus
1836  "".
1841   Example 2: the effective request URI for the message
1843<artwork type="example" x:indent-with="  ">
1844GET * HTTP/1.1
1848  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1849  authority component "", thus "".
1853   Effective request URIs are compared using the rules described in
1854   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1855   be treated as equivalent to an absolute path of "/".
1862<section title="Response" anchor="response">
1863  <x:anchor-alias value="Response"/>
1865   After receiving and interpreting a request message, a server responds
1866   with an HTTP response message.
1868<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1869  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1870                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1871                  <x:ref>CRLF</x:ref>
1872                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1875<section title="Status-Line" anchor="status-line">
1876  <x:anchor-alias value="Status-Line"/>
1878   The first line of a Response message is the Status-Line, consisting
1879   of the protocol version, a space (SP), the status code, another space,
1880   a possibly-empty textual phrase describing the status code, and
1881   ending with CRLF.
1883<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1884  <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>
1887<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1888  <x:anchor-alias value="Reason-Phrase"/>
1889  <x:anchor-alias value="Status-Code"/>
1891   The Status-Code element is a 3-digit integer result code of the
1892   attempt to understand and satisfy the request. These codes are fully
1893   defined in &status-codes;.  The Reason Phrase exists for the sole
1894   purpose of providing a textual description associated with the numeric
1895   status code, out of deference to earlier Internet application protocols
1896   that were more frequently used with interactive text clients.
1897   A client &SHOULD; ignore the content of the Reason Phrase.
1900   The first digit of the Status-Code defines the class of response. The
1901   last two digits do not have any categorization role. There are 5
1902   values for the first digit:
1903  <list style="symbols">
1904    <t>
1905      1xx: Informational - Request received, continuing process
1906    </t>
1907    <t>
1908      2xx: Success - The action was successfully received,
1909        understood, and accepted
1910    </t>
1911    <t>
1912      3xx: Redirection - Further action must be taken in order to
1913        complete the request
1914    </t>
1915    <t>
1916      4xx: Client Error - The request contains bad syntax or cannot
1917        be fulfilled
1918    </t>
1919    <t>
1920      5xx: Server Error - The server failed to fulfill an apparently
1921        valid request
1922    </t>
1923  </list>
1925<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1926  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1927  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1935<section title="Protocol Parameters" anchor="protocol.parameters">
1937<section title="Date/Time Formats: Full Date" anchor="">
1938  <x:anchor-alias value="HTTP-date"/>
1940   HTTP applications have historically allowed three different formats
1941   for date/time stamps. However, the preferred format is a fixed-length subset
1942   of that defined by <xref target="RFC1123"/>:
1944<figure><artwork type="example" x:indent-with="  ">
1945Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1948   The other formats are described here only for compatibility with obsolete
1949   implementations.
1951<figure><artwork type="example" x:indent-with="  ">
1952Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1953Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1956   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1957   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1958   only generate the RFC 1123 format for representing HTTP-date values
1959   in header fields. See <xref target="tolerant.applications"/> for further information.
1962   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1963   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1964   equal to UTC (Coordinated Universal Time). This is indicated in the
1965   first two formats by the inclusion of "GMT" as the three-letter
1966   abbreviation for time zone, and &MUST; be assumed when reading the
1967   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1968   additional whitespace beyond that specifically included as SP in the
1969   grammar.
1971<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1972  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1974<t anchor="">
1975  <x:anchor-alias value="rfc1123-date"/>
1976  <x:anchor-alias value="time-of-day"/>
1977  <x:anchor-alias value="hour"/>
1978  <x:anchor-alias value="minute"/>
1979  <x:anchor-alias value="second"/>
1980  <x:anchor-alias value="day-name"/>
1981  <x:anchor-alias value="day"/>
1982  <x:anchor-alias value="month"/>
1983  <x:anchor-alias value="year"/>
1984  <x:anchor-alias value="GMT"/>
1985  Preferred format:
1987<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"/>
1988  <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>
1989  ; fixed length subset of the format defined in
1990  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1992  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1993               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1994               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1995               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1996               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1997               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1998               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2000  <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>
2001               ; e.g., 02 Jun 1982
2003  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2004  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2005               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2006               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2007               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2008               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2009               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2010               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2011               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2012               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2013               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2014               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2015               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2016  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2018  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2020  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2021                 ; 00:00:00 - 23:59:59
2023  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2024  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2025  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2028  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2029  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2030  same as those defined for the RFC 5322 constructs
2031  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2033<t anchor="">
2034  <x:anchor-alias value="obs-date"/>
2035  <x:anchor-alias value="rfc850-date"/>
2036  <x:anchor-alias value="asctime-date"/>
2037  <x:anchor-alias value="date1"/>
2038  <x:anchor-alias value="date2"/>
2039  <x:anchor-alias value="date3"/>
2040  <x:anchor-alias value="rfc1123-date"/>
2041  <x:anchor-alias value="day-name-l"/>
2042  Obsolete formats:
2044<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2045  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2047<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2048  <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>
2049  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2050                 ; day-month-year (e.g., 02-Jun-82)
2052  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2053         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2054         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2055         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2056         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2057         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2058         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2060<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2061  <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>
2062  <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> ))
2063                 ; month day (e.g., Jun  2)
2066  <t>
2067    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2068    accepting date values that might have been sent by non-HTTP
2069    applications, as is sometimes the case when retrieving or posting
2070    messages via proxies/gateways to SMTP or NNTP.
2071  </t>
2074  <t>
2075    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2076    to their usage within the protocol stream. Clients and servers are
2077    not required to use these formats for user presentation, request
2078    logging, etc.
2079  </t>
2083<section title="Transfer Codings" anchor="transfer.codings">
2084  <x:anchor-alias value="transfer-coding"/>
2085  <x:anchor-alias value="transfer-extension"/>
2087   Transfer-coding values are used to indicate an encoding
2088   transformation that has been, can be, or might need to be applied to a
2089   payload body in order to ensure "safe transport" through the network.
2090   This differs from a content coding in that the transfer-coding is a
2091   property of the message rather than a property of the representation
2092   that is being transferred.
2094<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2095  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2096                          / "compress" ; <xref target="compress.coding"/>
2097                          / "deflate" ; <xref target="deflate.coding"/>
2098                          / "gzip" ; <xref target="gzip.coding"/>
2099                          / <x:ref>transfer-extension</x:ref>
2100  <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> )
2102<t anchor="rule.parameter">
2103  <x:anchor-alias value="attribute"/>
2104  <x:anchor-alias value="transfer-parameter"/>
2105  <x:anchor-alias value="value"/>
2106   Parameters are in the form of attribute/value pairs.
2108<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"/>
2109  <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>
2110  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2111  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2114   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2115   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2116   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2119   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2120   MIME, which were designed to enable safe transport of binary data over a
2121   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2122   However, safe transport
2123   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2124   the only unsafe characteristic of message-bodies is the difficulty in
2125   determining the exact message body length (<xref target="message.body"/>),
2126   or the desire to encrypt data over a shared transport.
2129   A server that receives a request message with a transfer-coding it does
2130   not understand &SHOULD; respond with 501 (Not Implemented) and then
2131   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2132   client.
2135<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2136  <iref item="chunked (Coding Format)"/>
2137  <iref item="Coding Format" subitem="chunked"/>
2138  <x:anchor-alias value="chunk"/>
2139  <x:anchor-alias value="Chunked-Body"/>
2140  <x:anchor-alias value="chunk-data"/>
2141  <x:anchor-alias value="chunk-ext"/>
2142  <x:anchor-alias value="chunk-ext-name"/>
2143  <x:anchor-alias value="chunk-ext-val"/>
2144  <x:anchor-alias value="chunk-size"/>
2145  <x:anchor-alias value="last-chunk"/>
2146  <x:anchor-alias value="trailer-part"/>
2147  <x:anchor-alias value="quoted-str-nf"/>
2148  <x:anchor-alias value="qdtext-nf"/>
2150   The chunked encoding modifies the body of a message in order to
2151   transfer it as a series of chunks, each with its own size indicator,
2152   followed by an &OPTIONAL; trailer containing header fields. This
2153   allows dynamically produced content to be transferred along with the
2154   information necessary for the recipient to verify that it has
2155   received the full message.
2157<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"/>
2158  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2159                   <x:ref>last-chunk</x:ref>
2160                   <x:ref>trailer-part</x:ref>
2161                   <x:ref>CRLF</x:ref>
2163  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2164                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2165  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2166  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2168  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2169                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2170  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2171  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2172  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2173  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2175  <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>
2176                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2177  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2178                 ; <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>
2181   The chunk-size field is a string of hex digits indicating the size of
2182   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2183   zero, followed by the trailer, which is terminated by an empty line.
2186   The trailer allows the sender to include additional HTTP header
2187   fields at the end of the message. The Trailer header field can be
2188   used to indicate which header fields are included in a trailer (see
2189   <xref target="header.trailer"/>).
2192   A server using chunked transfer-coding in a response &MUST-NOT; use the
2193   trailer for any header fields unless at least one of the following is
2194   true:
2195  <list style="numbers">
2196    <t>the request included a TE header field that indicates "trailers" is
2197     acceptable in the transfer-coding of the  response, as described in
2198     <xref target="header.te"/>; or,</t>
2200    <t>the trailer fields consist entirely of optional metadata, and the
2201    recipient could use the message (in a manner acceptable to the server where
2202    the field originated) without receiving it. In other words, the server that
2203    generated the header (often but not always the origin server) is willing to
2204    accept the possibility that the trailer fields might be silently discarded
2205    along the path to the client.</t>
2206  </list>
2209   This requirement prevents an interoperability failure when the
2210   message is being received by an HTTP/1.1 (or later) proxy and
2211   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2212   compliance with the protocol would have necessitated a possibly
2213   infinite buffer on the proxy.
2216   A process for decoding the "chunked" transfer-coding
2217   can be represented in pseudo-code as:
2219<figure><artwork type="code">
2220  length := 0
2221  read chunk-size, chunk-ext (if any) and CRLF
2222  while (chunk-size &gt; 0) {
2223     read chunk-data and CRLF
2224     append chunk-data to decoded-body
2225     length := length + chunk-size
2226     read chunk-size and CRLF
2227  }
2228  read header-field
2229  while (header-field not empty) {
2230     append header-field to existing header fields
2231     read header-field
2232  }
2233  Content-Length := length
2234  Remove "chunked" from Transfer-Encoding
2237   All HTTP/1.1 applications &MUST; be able to receive and decode the
2238   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2239   they do not understand.
2242   Since "chunked" is the only transfer-coding required to be understood
2243   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2244   on a persistent connection.  Whenever a transfer-coding is applied to
2245   a payload body in a request, the final transfer-coding applied &MUST;
2246   be "chunked".  If a transfer-coding is applied to a response payload
2247   body, then either the final transfer-coding applied &MUST; be "chunked"
2248   or the message &MUST; be terminated by closing the connection. When the
2249   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2250   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2251   be applied more than once in a message-body.
2255<section title="Compression Codings" anchor="compression.codings">
2257   The codings defined below can be used to compress the payload of a
2258   message.
2261   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2262   is not desirable and is discouraged for future encodings. Their
2263   use here is representative of historical practice, not good
2264   design.
2267   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2268   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2269   equivalent to "gzip" and "compress" respectively.
2272<section title="Compress Coding" anchor="compress.coding">
2273<iref item="compress (Coding Format)"/>
2274<iref item="Coding Format" subitem="compress"/>
2276   The "compress" format is produced by the common UNIX file compression
2277   program "compress". This format is an adaptive Lempel-Ziv-Welch
2278   coding (LZW).
2282<section title="Deflate Coding" anchor="deflate.coding">
2283<iref item="deflate (Coding Format)"/>
2284<iref item="Coding Format" subitem="deflate"/>
2286   The "deflate" format is defined as the "deflate" compression mechanism
2287   (described in <xref target="RFC1951"/>) used inside the "zlib"
2288   data format (<xref target="RFC1950"/>).
2291  <t>
2292    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2293    compressed data without the zlib wrapper.
2294   </t>
2298<section title="Gzip Coding" anchor="gzip.coding">
2299<iref item="gzip (Coding Format)"/>
2300<iref item="Coding Format" subitem="gzip"/>
2302   The "gzip" format is produced by the file compression program
2303   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2304   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2310<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2312   The HTTP Transfer Coding Registry defines the name space for the transfer
2313   coding names.
2316   Registrations &MUST; include the following fields:
2317   <list style="symbols">
2318     <t>Name</t>
2319     <t>Description</t>
2320     <t>Pointer to specification text</t>
2321   </list>
2324   Names of transfer codings &MUST-NOT; overlap with names of content codings
2325   (&content-codings;), unless the encoding transformation is identical (as it
2326   is the case for the compression codings defined in
2327   <xref target="compression.codings"/>).
2330   Values to be added to this name space require a specification
2331   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2332   conform to the purpose of transfer coding defined in this section.
2335   The registry itself is maintained at
2336   <eref target=""/>.
2341<section title="Product Tokens" anchor="product.tokens">
2342  <x:anchor-alias value="product"/>
2343  <x:anchor-alias value="product-version"/>
2345   Product tokens are used to allow communicating applications to
2346   identify themselves by software name and version. Most fields using
2347   product tokens also allow sub-products which form a significant part
2348   of the application to be listed, separated by whitespace. By
2349   convention, the products are listed in order of their significance
2350   for identifying the application.
2352<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2353  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2354  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2357   Examples:
2359<figure><artwork type="example">
2360  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2361  Server: Apache/0.8.4
2364   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2365   used for advertising or other non-essential information. Although any
2366   token octet &MAY; appear in a product-version, this token &SHOULD;
2367   only be used for a version identifier (i.e., successive versions of
2368   the same product &SHOULD; only differ in the product-version portion of
2369   the product value).
2373<section title="Quality Values" anchor="quality.values">
2374  <x:anchor-alias value="qvalue"/>
2376   Both transfer codings (TE request header field, <xref target="header.te"/>)
2377   and content negotiation (&content.negotiation;) use short "floating point"
2378   numbers to indicate the relative importance ("weight") of various
2379   negotiable parameters.  A weight is normalized to a real number in
2380   the range 0 through 1, where 0 is the minimum and 1 the maximum
2381   value. If a parameter has a quality value of 0, then content with
2382   this parameter is "not acceptable" for the client. HTTP/1.1
2383   applications &MUST-NOT; generate more than three digits after the
2384   decimal point. User configuration of these values &SHOULD; also be
2385   limited in this fashion.
2387<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2388  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2389                 / ( "1" [ "." 0*3("0") ] )
2392  <t>
2393     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2394     relative degradation in desired quality.
2395  </t>
2401<section title="Connections" anchor="connections">
2403<section title="Persistent Connections" anchor="persistent.connections">
2405<section title="Purpose" anchor="persistent.purpose">
2407   Prior to persistent connections, a separate TCP connection was
2408   established for each request, increasing the load on HTTP servers
2409   and causing congestion on the Internet. The use of inline images and
2410   other associated data often requires a client to make multiple
2411   requests of the same server in a short amount of time. Analysis of
2412   these performance problems and results from a prototype
2413   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2414   measurements of actual HTTP/1.1 implementations show good
2415   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2416   T/TCP <xref target="Tou1998"/>.
2419   Persistent HTTP connections have a number of advantages:
2420  <list style="symbols">
2421      <t>
2422        By opening and closing fewer TCP connections, CPU time is saved
2423        in routers and hosts (clients, servers, proxies, gateways,
2424        tunnels, or caches), and memory used for TCP protocol control
2425        blocks can be saved in hosts.
2426      </t>
2427      <t>
2428        HTTP requests and responses can be pipelined on a connection.
2429        Pipelining allows a client to make multiple requests without
2430        waiting for each response, allowing a single TCP connection to
2431        be used much more efficiently, with much lower elapsed time.
2432      </t>
2433      <t>
2434        Network congestion is reduced by reducing the number of packets
2435        caused by TCP opens, and by allowing TCP sufficient time to
2436        determine the congestion state of the network.
2437      </t>
2438      <t>
2439        Latency on subsequent requests is reduced since there is no time
2440        spent in TCP's connection opening handshake.
2441      </t>
2442      <t>
2443        HTTP can evolve more gracefully, since errors can be reported
2444        without the penalty of closing the TCP connection. Clients using
2445        future versions of HTTP might optimistically try a new feature,
2446        but if communicating with an older server, retry with old
2447        semantics after an error is reported.
2448      </t>
2449    </list>
2452   HTTP implementations &SHOULD; implement persistent connections.
2456<section title="Overall Operation" anchor="persistent.overall">
2458   A significant difference between HTTP/1.1 and earlier versions of
2459   HTTP is that persistent connections are the default behavior of any
2460   HTTP connection. That is, unless otherwise indicated, the client
2461   &SHOULD; assume that the server will maintain a persistent connection,
2462   even after error responses from the server.
2465   Persistent connections provide a mechanism by which a client and a
2466   server can signal the close of a TCP connection. This signaling takes
2467   place using the Connection header field (<xref target="header.connection"/>). Once a close
2468   has been signaled, the client &MUST-NOT; send any more requests on that
2469   connection.
2472<section title="Negotiation" anchor="persistent.negotiation">
2474   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2475   maintain a persistent connection unless a Connection header field including
2476   the connection-token "close" was sent in the request. If the server
2477   chooses to close the connection immediately after sending the
2478   response, it &SHOULD; send a Connection header field including the
2479   connection-token "close".
2482   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2483   decide to keep it open based on whether the response from a server
2484   contains a Connection header field with the connection-token close. In case
2485   the client does not want to maintain a connection for more than that
2486   request, it &SHOULD; send a Connection header field including the
2487   connection-token close.
2490   If either the client or the server sends the close token in the
2491   Connection header field, that request becomes the last one for the
2492   connection.
2495   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2496   maintained for HTTP versions less than 1.1 unless it is explicitly
2497   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2498   compatibility with HTTP/1.0 clients.
2501   In order to remain persistent, all messages on the connection &MUST;
2502   have a self-defined message length (i.e., one not defined by closure
2503   of the connection), as described in <xref target="message.body"/>.
2507<section title="Pipelining" anchor="pipelining">
2509   A client that supports persistent connections &MAY; "pipeline" its
2510   requests (i.e., send multiple requests without waiting for each
2511   response). A server &MUST; send its responses to those requests in the
2512   same order that the requests were received.
2515   Clients which assume persistent connections and pipeline immediately
2516   after connection establishment &SHOULD; be prepared to retry their
2517   connection if the first pipelined attempt fails. If a client does
2518   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2519   persistent. Clients &MUST; also be prepared to resend their requests if
2520   the server closes the connection before sending all of the
2521   corresponding responses.
2524   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2525   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2526   premature termination of the transport connection could lead to
2527   indeterminate results. A client wishing to send a non-idempotent
2528   request &SHOULD; wait to send that request until it has received the
2529   response status line for the previous request.
2534<section title="Proxy Servers" anchor="persistent.proxy">
2536   It is especially important that proxies correctly implement the
2537   properties of the Connection header field as specified in <xref target="header.connection"/>.
2540   The proxy server &MUST; signal persistent connections separately with
2541   its clients and the origin servers (or other proxy servers) that it
2542   connects to. Each persistent connection applies to only one transport
2543   link.
2546   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2547   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2548   for information and discussion of the problems with the Keep-Alive header field
2549   implemented by many HTTP/1.0 clients).
2552<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2554  <cref anchor="TODO-end-to-end" source="jre">
2555    Restored from <eref target=""/>.
2556    See also <eref target=""/>.
2557  </cref>
2560   For the purpose of defining the behavior of caches and non-caching
2561   proxies, we divide HTTP header fields into two categories:
2562  <list style="symbols">
2563      <t>End-to-end header fields, which are  transmitted to the ultimate
2564        recipient of a request or response. End-to-end header fields in
2565        responses MUST be stored as part of a cache entry and &MUST; be
2566        transmitted in any response formed from a cache entry.</t>
2568      <t>Hop-by-hop header fields, which are meaningful only for a single
2569        transport-level connection, and are not stored by caches or
2570        forwarded by proxies.</t>
2571  </list>
2574   The following HTTP/1.1 header fields are hop-by-hop header fields:
2575  <list style="symbols">
2576      <t>Connection</t>
2577      <t>Keep-Alive</t>
2578      <t>Proxy-Authenticate</t>
2579      <t>Proxy-Authorization</t>
2580      <t>TE</t>
2581      <t>Trailer</t>
2582      <t>Transfer-Encoding</t>
2583      <t>Upgrade</t>
2584  </list>
2587   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2590   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2591   (<xref target="header.connection"/>).
2595<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2597  <cref anchor="TODO-non-mod-headers" source="jre">
2598    Restored from <eref target=""/>.
2599    See also <eref target=""/>.
2600  </cref>
2603   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2604   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2605   modify an end-to-end header field unless the definition of that header field requires
2606   or specifically allows that.
2609   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2610   request or response, and it &MUST-NOT; add any of these fields if not
2611   already present:
2612  <list style="symbols">
2613      <t>Content-Location</t>
2614      <t>Content-MD5</t>
2615      <t>ETag</t>
2616      <t>Last-Modified</t>
2617  </list>
2620   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2621   response:
2622  <list style="symbols">
2623    <t>Expires</t>
2624  </list>
2627   but it &MAY; add any of these fields if not already present. If an
2628   Expires header field is added, it &MUST; be given a field-value identical to
2629   that of the Date header field in that response.
2632   A proxy &MUST-NOT; modify or add any of the following fields in a
2633   message that contains the no-transform cache-control directive, or in
2634   any request:
2635  <list style="symbols">
2636    <t>Content-Encoding</t>
2637    <t>Content-Range</t>
2638    <t>Content-Type</t>
2639  </list>
2642   A transforming proxy &MAY; modify or add these fields to a message
2643   that does not include no-transform, but if it does so, it &MUST; add a
2644   Warning 214 (Transformation applied) if one does not already appear
2645   in the message (see &header-warning;).
2648  <t>
2649    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2650    cause authentication failures if stronger authentication
2651    mechanisms are introduced in later versions of HTTP. Such
2652    authentication mechanisms &MAY; rely on the values of header fields
2653    not listed here.
2654  </t>
2657   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2658   though it &MAY; change the message-body through application or removal
2659   of a transfer-coding (<xref target="transfer.codings"/>).
2665<section title="Practical Considerations" anchor="persistent.practical">
2667   Servers will usually have some time-out value beyond which they will
2668   no longer maintain an inactive connection. Proxy servers might make
2669   this a higher value since it is likely that the client will be making
2670   more connections through the same server. The use of persistent
2671   connections places no requirements on the length (or existence) of
2672   this time-out for either the client or the server.
2675   When a client or server wishes to time-out it &SHOULD; issue a graceful
2676   close on the transport connection. Clients and servers &SHOULD; both
2677   constantly watch for the other side of the transport close, and
2678   respond to it as appropriate. If a client or server does not detect
2679   the other side's close promptly it could cause unnecessary resource
2680   drain on the network.
2683   A client, server, or proxy &MAY; close the transport connection at any
2684   time. For example, a client might have started to send a new request
2685   at the same time that the server has decided to close the "idle"
2686   connection. From the server's point of view, the connection is being
2687   closed while it was idle, but from the client's point of view, a
2688   request is in progress.
2691   This means that clients, servers, and proxies &MUST; be able to recover
2692   from asynchronous close events. Client software &SHOULD; reopen the
2693   transport connection and retransmit the aborted sequence of requests
2694   without user interaction so long as the request sequence is
2695   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2696   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2697   human operator the choice of retrying the request(s). Confirmation by
2698   user-agent software with semantic understanding of the application
2699   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2700   be repeated if the second sequence of requests fails.
2703   Servers &SHOULD; always respond to at least one request per connection,
2704   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2705   middle of transmitting a response, unless a network or client failure
2706   is suspected.
2709   Clients (including proxies) &SHOULD; limit the number of simultaneous
2710   connections that they maintain to a given server (including proxies).
2713   Previous revisions of HTTP gave a specific number of connections as a
2714   ceiling, but this was found to be impractical for many applications. As a
2715   result, this specification does not mandate a particular maximum number of
2716   connections, but instead encourages clients to be conservative when opening
2717   multiple connections.
2720   In particular, while using multiple connections avoids the "head-of-line
2721   blocking" problem (whereby a request that takes significant server-side
2722   processing and/or has a large payload can block subsequent requests on the
2723   same connection), each connection used consumes server resources (sometimes
2724   significantly), and furthermore using multiple connections can cause
2725   undesirable side effects in congested networks.
2728   Note that servers might reject traffic that they deem abusive, including an
2729   excessive number of connections from a client.
2734<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2736<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2738   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2739   flow control mechanisms to resolve temporary overloads, rather than
2740   terminating connections with the expectation that clients will retry.
2741   The latter technique can exacerbate network congestion.
2745<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2747   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2748   the network connection for an error status code while it is transmitting
2749   the request. If the client sees an error status code, it &SHOULD;
2750   immediately cease transmitting the body. If the body is being sent
2751   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2752   empty trailer &MAY; be used to prematurely mark the end of the message.
2753   If the body was preceded by a Content-Length header field, the client &MUST;
2754   close the connection.
2758<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2760   The purpose of the 100 (Continue) status code (see &status-100;) is to
2761   allow a client that is sending a request message with a request body
2762   to determine if the origin server is willing to accept the request
2763   (based on the request header fields) before the client sends the request
2764   body. In some cases, it might either be inappropriate or highly
2765   inefficient for the client to send the body if the server will reject
2766   the message without looking at the body.
2769   Requirements for HTTP/1.1 clients:
2770  <list style="symbols">
2771    <t>
2772        If a client will wait for a 100 (Continue) response before
2773        sending the request body, it &MUST; send an Expect header
2774        field (&header-expect;) with the "100-continue" expectation.
2775    </t>
2776    <t>
2777        A client &MUST-NOT; send an Expect header field (&header-expect;)
2778        with the "100-continue" expectation if it does not intend
2779        to send a request body.
2780    </t>
2781  </list>
2784   Because of the presence of older implementations, the protocol allows
2785   ambiguous situations in which a client might send "Expect: 100-continue"
2786   without receiving either a 417 (Expectation Failed)
2787   or a 100 (Continue) status code. Therefore, when a client sends this
2788   header field to an origin server (possibly via a proxy) from which it
2789   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2790   wait for an indefinite period before sending the request body.
2793   Requirements for HTTP/1.1 origin servers:
2794  <list style="symbols">
2795    <t> Upon receiving a request which includes an Expect header
2796        field with the "100-continue" expectation, an origin server &MUST;
2797        either respond with 100 (Continue) status code and continue to read
2798        from the input stream, or respond with a final status code. The
2799        origin server &MUST-NOT; wait for the request body before sending
2800        the 100 (Continue) response. If it responds with a final status
2801        code, it &MAY; close the transport connection or it &MAY; continue
2802        to read and discard the rest of the request.  It &MUST-NOT;
2803        perform the request method if it returns a final status code.
2804    </t>
2805    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2806        the request message does not include an Expect header
2807        field with the "100-continue" expectation, and &MUST-NOT; send a
2808        100 (Continue) response if such a request comes from an HTTP/1.0
2809        (or earlier) client. There is an exception to this rule: for
2810        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2811        status code in response to an HTTP/1.1 PUT or POST request that does
2812        not include an Expect header field with the "100-continue"
2813        expectation. This exception, the purpose of which is
2814        to minimize any client processing delays associated with an
2815        undeclared wait for 100 (Continue) status code, applies only to
2816        HTTP/1.1 requests, and not to requests with any other HTTP-version
2817        value.
2818    </t>
2819    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2820        already received some or all of the request body for the
2821        corresponding request.
2822    </t>
2823    <t> An origin server that sends a 100 (Continue) response &MUST;
2824    ultimately send a final status code, once the request body is
2825        received and processed, unless it terminates the transport
2826        connection prematurely.
2827    </t>
2828    <t> If an origin server receives a request that does not include an
2829        Expect header field with the "100-continue" expectation,
2830        the request includes a request body, and the server responds
2831        with a final status code before reading the entire request body
2832        from the transport connection, then the server &SHOULD-NOT;  close
2833        the transport connection until it has read the entire request,
2834        or until the client closes the connection. Otherwise, the client
2835        might not reliably receive the response message. However, this
2836        requirement is not be construed as preventing a server from
2837        defending itself against denial-of-service attacks, or from
2838        badly broken client implementations.
2839      </t>
2840    </list>
2843   Requirements for HTTP/1.1 proxies:
2844  <list style="symbols">
2845    <t> If a proxy receives a request that includes an Expect header
2846        field with the "100-continue" expectation, and the proxy
2847        either knows that the next-hop server complies with HTTP/1.1 or
2848        higher, or does not know the HTTP version of the next-hop
2849        server, it &MUST; forward the request, including the Expect header
2850        field.
2851    </t>
2852    <t> If the proxy knows that the version of the next-hop server is
2853        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2854        respond with a 417 (Expectation Failed) status code.
2855    </t>
2856    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2857        numbers received from recently-referenced next-hop servers.
2858    </t>
2859    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2860        request message was received from an HTTP/1.0 (or earlier)
2861        client and did not include an Expect header field with
2862        the "100-continue" expectation. This requirement overrides the
2863        general rule for forwarding of 1xx responses (see &status-1xx;).
2864    </t>
2865  </list>
2869<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2871   If an HTTP/1.1 client sends a request which includes a request body,
2872   but which does not include an Expect header field with the
2873   "100-continue" expectation, and if the client is not directly
2874   connected to an HTTP/1.1 origin server, and if the client sees the
2875   connection close before receiving a status line from the server, the
2876   client &SHOULD; retry the request.  If the client does retry this
2877   request, it &MAY; use the following "binary exponential backoff"
2878   algorithm to be assured of obtaining a reliable response:
2879  <list style="numbers">
2880    <t>
2881      Initiate a new connection to the server
2882    </t>
2883    <t>
2884      Transmit the request-line, header fields, and the CRLF that
2885      indicates the end of header fields.
2886    </t>
2887    <t>
2888      Initialize a variable R to the estimated round-trip time to the
2889         server (e.g., based on the time it took to establish the
2890         connection), or to a constant value of 5 seconds if the round-trip
2891         time is not available.
2892    </t>
2893    <t>
2894       Compute T = R * (2**N), where N is the number of previous
2895         retries of this request.
2896    </t>
2897    <t>
2898       Wait either for an error response from the server, or for T
2899         seconds (whichever comes first)
2900    </t>
2901    <t>
2902       If no error response is received, after T seconds transmit the
2903         body of the request.
2904    </t>
2905    <t>
2906       If client sees that the connection is closed prematurely,
2907         repeat from step 1 until the request is accepted, an error
2908         response is received, or the user becomes impatient and
2909         terminates the retry process.
2910    </t>
2911  </list>
2914   If at any point an error status code is received, the client
2915  <list style="symbols">
2916      <t>&SHOULD-NOT;  continue and</t>
2918      <t>&SHOULD; close the connection if it has not completed sending the
2919        request message.</t>
2920    </list>
2927<section title="Miscellaneous notes that might disappear" anchor="misc">
2928<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2930   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2934<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2936   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2940<section title="Interception of HTTP for access control" anchor="http.intercept">
2942   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2946<section title="Use of HTTP by other protocols" anchor="http.others">
2948   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2949   Extensions of HTTP like WebDAV.</cref>
2953<section title="Use of HTTP by media type specification" anchor="">
2955   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2960<section title="Header Field Definitions" anchor="header.field.definitions">
2962   This section defines the syntax and semantics of HTTP header fields
2963   related to message framing and transport protocols.
2966<section title="Connection" anchor="header.connection">
2967  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2968  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2969  <x:anchor-alias value="Connection"/>
2970  <x:anchor-alias value="connection-token"/>
2971  <x:anchor-alias value="Connection-v"/>
2973   The "Connection" header field allows the sender to specify
2974   options that are desired only for that particular connection.
2975   Such connection options &MUST; be removed or replaced before the
2976   message can be forwarded downstream by a proxy or gateway.
2977   This mechanism also allows the sender to indicate which HTTP
2978   header fields used in the message are only intended for the
2979   immediate recipient ("hop-by-hop"), as opposed to all recipients
2980   on the chain ("end-to-end"), enabling the message to be
2981   self-descriptive and allowing future connection-specific extensions
2982   to be deployed in HTTP without fear that they will be blindly
2983   forwarded by previously deployed intermediaries.
2986   The Connection header field's value has the following grammar:
2988<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2989  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2990  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2991  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2994   A proxy or gateway &MUST; parse a received Connection
2995   header field before a message is forwarded and, for each
2996   connection-token in this field, remove any header field(s) from
2997   the message with the same name as the connection-token, and then
2998   remove the Connection header field itself or replace it with the
2999   sender's own connection options for the forwarded message.
3002   A sender &MUST-NOT; include field-names in the Connection header
3003   field-value for fields that are defined as expressing constraints
3004   for all recipients in the request or response chain, such as the
3005   Cache-Control header field (&header-cache-control;).
3008   The connection options do not have to correspond to a header field
3009   present in the message, since a connection-specific header field
3010   might not be needed if there are no parameters associated with that
3011   connection option.  Recipients that trigger certain connection
3012   behavior based on the presence of connection options &MUST; do so
3013   based on the presence of the connection-token rather than only the
3014   presence of the optional header field.  In other words, if the
3015   connection option is received as a header field but not indicated
3016   within the Connection field-value, then the recipient &MUST; ignore
3017   the connection-specific header field because it has likely been
3018   forwarded by an intermediary that is only partially compliant.
3021   When defining new connection options, specifications ought to
3022   carefully consider existing deployed header fields and ensure
3023   that the new connection-token does not share the same name as
3024   an unrelated header field that might already be deployed.
3025   Defining a new connection-token essentially reserves that potential
3026   field-name for carrying additional information related to the
3027   connection option, since it would be unwise for senders to use
3028   that field-name for anything else.
3031   HTTP/1.1 defines the "close" connection option for the sender to
3032   signal that the connection will be closed after completion of the
3033   response. For example,
3035<figure><artwork type="example">
3036  Connection: close
3039   in either the request or the response header fields indicates that
3040   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3041   after the current request/response is complete.
3044   An HTTP/1.1 client that does not support persistent connections &MUST;
3045   include the "close" connection option in every request message.
3048   An HTTP/1.1 server that does not support persistent connections &MUST;
3049   include the "close" connection option in every response message that
3050   does not have a 1xx (Informational) status code.
3054<section title="Content-Length" anchor="header.content-length">
3055  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3056  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3057  <x:anchor-alias value="Content-Length"/>
3058  <x:anchor-alias value="Content-Length-v"/>
3060   The "Content-Length" header field indicates the size of the
3061   message-body, in decimal number of octets, for any message other than
3062   a response to a HEAD request or a response with a status code of 304.
3063   In the case of a response to a HEAD request, Content-Length indicates
3064   the size of the payload body (not including any potential transfer-coding)
3065   that would have been sent had the request been a GET.
3066   In the case of a 304 (Not Modified) response to a GET request,
3067   Content-Length indicates the size of the payload body (not including
3068   any potential transfer-coding) that would have been sent in a 200 (OK)
3069   response.
3071<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
3072  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> <x:ref>Content-Length-v</x:ref>
3073  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
3076   An example is
3078<figure><artwork type="example">
3079  Content-Length: 3495
3082   Implementations &SHOULD; use this field to indicate the message-body
3083   length when no transfer-coding is being applied and the
3084   payload's body length can be determined prior to being transferred.
3085   <xref target="message.body"/> describes how recipients determine the length
3086   of a message-body.
3089   Any Content-Length greater than or equal to zero is a valid value.
3092   Note that the use of this field in HTTP is significantly different from
3093   the corresponding definition in MIME, where it is an optional field
3094   used within the "message/external-body" content-type.
3098<section title="Date" anchor="">
3099  <iref primary="true" item="Date header field" x:for-anchor=""/>
3100  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3101  <x:anchor-alias value="Date"/>
3102  <x:anchor-alias value="Date-v"/>
3104   The "Date" header field represents the date and time at which
3105   the message was originated, having the same semantics as the Origination
3106   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3107   The field value is an HTTP-date, as described in <xref target=""/>;
3108   it &MUST; be sent in rfc1123-date format.
3110<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3111  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3112  <x:ref>Date-v</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"/>
3178  <x:anchor-alias value="Host-v"/>
3180   The "Host" header field in a request provides the host and port
3181   information from the target resource's URI, enabling the origin
3182   server to distinguish between resources while servicing requests
3183   for multiple host names on a single IP address.  Since the Host
3184   field-value is critical information for handling a request, it
3185   &SHOULD; be sent as the first header field following the Request-Line.
3187<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3188  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3189  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3192   A client &MUST; send a Host header field in all HTTP/1.1 request
3193   messages.  If the target resource's URI includes an authority
3194   component, then the Host field-value &MUST; be identical to that
3195   authority component after excluding any userinfo (<xref target="http.uri"/>).
3196   If the authority component is missing or undefined for the target
3197   resource's URI, then the Host header field &MUST; be sent with an
3198   empty field-value.
3201   For example, a GET request to the origin server for
3202   &lt;; would begin with:
3204<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3205GET /pub/WWW/ HTTP/1.1
3209   The Host header field &MUST; be sent in an HTTP/1.1 request even
3210   if the request-target is in the form of an absolute-URI, since this
3211   allows the Host information to be forwarded through ancient HTTP/1.0
3212   proxies that might not have implemented Host.
3215   When an HTTP/1.1 proxy receives a request with a request-target in
3216   the form of an absolute-URI, the proxy &MUST; ignore the received
3217   Host header field (if any) and instead replace it with the host
3218   information of the request-target.  When a proxy forwards a request,
3219   it &MUST; generate the Host header field based on the received
3220   absolute-URI rather than the received Host.
3223   Since the Host header field acts as an application-level routing
3224   mechanism, it is a frequent target for malware seeking to poison
3225   a shared cache or redirect a request to an unintended server.
3226   An interception proxy is particularly vulnerable if it relies on
3227   the Host header field value for redirecting requests to internal
3228   servers, or for use as a cache key in a shared cache, without
3229   first verifying that the intercepted connection is targeting a
3230   valid IP address for that host.
3233   A server &MUST; respond with a 400 (Bad Request) status code to
3234   any HTTP/1.1 request message that lacks a Host header field and
3235   to any request message that contains more than one Host header field
3236   or a Host header field with an invalid field-value.
3239   See Sections <xref target="" format="counter"/>
3240   and <xref target="" format="counter"/>
3241   for other requirements relating to Host.
3245<section title="TE" anchor="header.te">
3246  <iref primary="true" item="TE header field" x:for-anchor=""/>
3247  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3248  <x:anchor-alias value="TE"/>
3249  <x:anchor-alias value="TE-v"/>
3250  <x:anchor-alias value="t-codings"/>
3251  <x:anchor-alias value="te-params"/>
3252  <x:anchor-alias value="te-ext"/>
3254   The "TE" header field indicates what extension transfer-codings
3255   it is willing to accept in the response, and whether or not it is
3256   willing to accept trailer fields in a chunked transfer-coding.
3259   Its value consists of the keyword "trailers" and/or a comma-separated
3260   list of extension transfer-coding names with optional accept
3261   parameters (as described in <xref target="transfer.codings"/>).
3263<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3264  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3265  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3266  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3267  <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> )
3268  <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> ]
3271   The presence of the keyword "trailers" indicates that the client is
3272   willing to accept trailer fields in a chunked transfer-coding, as
3273   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3274   transfer-coding values even though it does not itself represent a
3275   transfer-coding.
3278   Examples of its use are:
3280<figure><artwork type="example">
3281  TE: deflate
3282  TE:
3283  TE: trailers, deflate;q=0.5
3286   The TE header field only applies to the immediate connection.
3287   Therefore, the keyword &MUST; be supplied within a Connection header
3288   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3291   A server tests whether a transfer-coding is acceptable, according to
3292   a TE field, using these rules:
3293  <list style="numbers">
3294    <x:lt>
3295      <t>The "chunked" transfer-coding is always acceptable. If the
3296         keyword "trailers" is listed, the client indicates that it is
3297         willing to accept trailer fields in the chunked response on
3298         behalf of itself and any downstream clients. The implication is
3299         that, if given, the client is stating that either all
3300         downstream clients are willing to accept trailer fields in the
3301         forwarded response, or that it will attempt to buffer the
3302         response on behalf of downstream recipients.
3303      </t><t>
3304         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3305         chunked response such that a client can be assured of buffering
3306         the entire response.</t>
3307    </x:lt>
3308    <x:lt>
3309      <t>If the transfer-coding being tested is one of the transfer-codings
3310         listed in the TE field, then it is acceptable unless it
3311         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3312         qvalue of 0 means "not acceptable".)</t>
3313    </x:lt>
3314    <x:lt>
3315      <t>If multiple transfer-codings are acceptable, then the
3316         acceptable transfer-coding with the highest non-zero qvalue is
3317         preferred.  The "chunked" transfer-coding always has a qvalue
3318         of 1.</t>
3319    </x:lt>
3320  </list>
3323   If the TE field-value is empty or if no TE field is present, the only
3324   transfer-coding is "chunked". A message with no transfer-coding is
3325   always acceptable.
3329<section title="Trailer" anchor="header.trailer">
3330  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3331  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3332  <x:anchor-alias value="Trailer"/>
3333  <x:anchor-alias value="Trailer-v"/>
3335   The "Trailer" header field indicates that the given set of
3336   header fields is present in the trailer of a message encoded with
3337   chunked transfer-coding.
3339<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3340  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3341  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3344   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3345   message using chunked transfer-coding with a non-empty trailer. Doing
3346   so allows the recipient to know which header fields to expect in the
3347   trailer.
3350   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3351   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3352   trailer fields in a "chunked" transfer-coding.
3355   Message header fields listed in the Trailer header field &MUST-NOT;
3356   include the following header fields:
3357  <list style="symbols">
3358    <t>Transfer-Encoding</t>
3359    <t>Content-Length</t>
3360    <t>Trailer</t>
3361  </list>
3365<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3366  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3367  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3368  <x:anchor-alias value="Transfer-Encoding"/>
3369  <x:anchor-alias value="Transfer-Encoding-v"/>
3371   The "Transfer-Encoding" header field indicates what transfer-codings
3372   (if any) have been applied to the message body. It differs from
3373   Content-Encoding (&content-codings;) in that transfer-codings are a property
3374   of the message (and therefore are removed by intermediaries), whereas
3375   content-codings are not.
3377<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3378  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3379                        <x:ref>Transfer-Encoding-v</x:ref>
3380  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3383   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3385<figure><artwork type="example">
3386  Transfer-Encoding: chunked
3389   If multiple encodings have been applied to a representation, the transfer-codings
3390   &MUST; be listed in the order in which they were applied.
3391   Additional information about the encoding parameters &MAY; be provided
3392   by other header fields not defined by this specification.
3395   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3396   header field.
3400<section title="Upgrade" anchor="header.upgrade">
3401  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3402  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3403  <x:anchor-alias value="Upgrade"/>
3404  <x:anchor-alias value="Upgrade-v"/>
3406   The "Upgrade" header field allows the client to specify what
3407   additional communication protocols it would like to use, if the server
3408   chooses to switch protocols. Servers can use it to indicate what protocols
3409   they are willing to switch to.
3411<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3412  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3413  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3416   For example,
3418<figure><artwork type="example">
3419  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3422   The Upgrade header field is intended to provide a simple mechanism
3423   for transition from HTTP/1.1 to some other, incompatible protocol. It
3424   does so by allowing the client to advertise its desire to use another
3425   protocol, such as a later version of HTTP with a higher major version
3426   number, even though the current request has been made using HTTP/1.1.
3427   This eases the difficult transition between incompatible protocols by
3428   allowing the client to initiate a request in the more commonly
3429   supported protocol while indicating to the server that it would like
3430   to use a "better" protocol if available (where "better" is determined
3431   by the server, possibly according to the nature of the request method
3432   or target resource).
3435   The Upgrade header field only applies to switching application-layer
3436   protocols upon the existing transport-layer connection. Upgrade
3437   cannot be used to insist on a protocol change; its acceptance and use
3438   by the server is optional. The capabilities and nature of the
3439   application-layer communication after the protocol change is entirely
3440   dependent upon the new protocol chosen, although the first action
3441   after changing the protocol &MUST; be a response to the initial HTTP
3442   request containing the Upgrade header field.
3445   The Upgrade header field only applies to the immediate connection.
3446   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3447   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3448   HTTP/1.1 message.
3451   The Upgrade header field cannot be used to indicate a switch to a
3452   protocol on a different connection. For that purpose, it is more
3453   appropriate to use a 3xx redirection response (&status-3xx;).
3456   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3457   Protocols) responses to indicate which protocol(s) are being switched to,
3458   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3459   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3460   response to indicate that they are willing to upgrade to one of the
3461   specified protocols.
3464   This specification only defines the protocol name "HTTP" for use by
3465   the family of Hypertext Transfer Protocols, as defined by the HTTP
3466   version rules of <xref target="http.version"/> and future updates to this
3467   specification. Additional tokens can be registered with IANA using the
3468   registration procedure defined below. 
3471<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3473   The HTTP Upgrade Token Registry defines the name space for product
3474   tokens used to identify protocols in the Upgrade header field.
3475   Each registered token is associated with contact information and
3476   an optional set of specifications that details how the connection
3477   will be processed after it has been upgraded.
3480   Registrations are allowed on a First Come First Served basis as
3481   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3482   specifications need not be IETF documents or be subject to IESG review.
3483   Registrations are subject to the following rules:
3484  <list style="numbers">
3485    <t>A token, once registered, stays registered forever.</t>
3486    <t>The registration &MUST; name a responsible party for the
3487       registration.</t>
3488    <t>The registration &MUST; name a point of contact.</t>
3489    <t>The registration &MAY; name a set of specifications associated with that
3490       token. Such specifications need not be publicly available.</t>
3491    <t>The responsible party &MAY; change the registration at any time.
3492       The IANA will keep a record of all such changes, and make them
3493       available upon request.</t>
3494    <t>The responsible party for the first registration of a "product"
3495       token &MUST; approve later registrations of a "version" token
3496       together with that "product" token before they can be registered.</t>
3497    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3498       for a token. This will normally only be used in the case when a
3499       responsible party cannot be contacted.</t>
3500  </list>
3507<section title="Via" anchor="header.via">
3508  <iref primary="true" item="Via header field" x:for-anchor=""/>
3509  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3510  <x:anchor-alias value="protocol-name"/>
3511  <x:anchor-alias value="protocol-version"/>
3512  <x:anchor-alias value="pseudonym"/>
3513  <x:anchor-alias value="received-by"/>
3514  <x:anchor-alias value="received-protocol"/>
3515  <x:anchor-alias value="Via"/>
3516  <x:anchor-alias value="Via-v"/>
3518   The "Via" header field &MUST; be sent by a proxy or gateway to
3519   indicate the intermediate protocols and recipients between the user
3520   agent and the server on requests, and between the origin server and
3521   the client on responses. It is analogous to the "Received" field
3522   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3523   and is intended to be used for tracking message forwards,
3524   avoiding request loops, and identifying the protocol capabilities of
3525   all senders along the request/response chain.
3527<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
3528  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3529  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3530                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3531  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3532  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3533  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3534  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3535  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3538   The received-protocol indicates the protocol version of the message
3539   received by the server or client along each segment of the
3540   request/response chain. The received-protocol version is appended to
3541   the Via field value when the message is forwarded so that information
3542   about the protocol capabilities of upstream applications remains
3543   visible to all recipients.
3546   The protocol-name is excluded if and only if it would be "HTTP". The
3547   received-by field is normally the host and optional port number of a
3548   recipient server or client that subsequently forwarded the message.
3549   However, if the real host is considered to be sensitive information,
3550   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3551   be assumed to be the default port of the received-protocol.
3554   Multiple Via field values represent each proxy or gateway that has
3555   forwarded the message. Each recipient &MUST; append its information
3556   such that the end result is ordered according to the sequence of
3557   forwarding applications.
3560   Comments &MAY; be used in the Via header field to identify the software
3561   of each recipient, analogous to the User-Agent and Server header fields.
3562   However, all comments in the Via field are optional and &MAY; be removed
3563   by any recipient prior to forwarding the message.
3566   For example, a request message could be sent from an HTTP/1.0 user
3567   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3568   forward the request to a public proxy at, which completes
3569   the request by forwarding it to the origin server at
3570   The request received by would then have the following
3571   Via header field:
3573<figure><artwork type="example">
3574  Via: 1.0 fred, 1.1 (Apache/1.1)
3577   A proxy or gateway used as a portal through a network firewall
3578   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3579   region unless it is explicitly enabled to do so. If not enabled, the
3580   received-by host of any host behind the firewall &SHOULD; be replaced
3581   by an appropriate pseudonym for that host.
3584   For organizations that have strong privacy requirements for hiding
3585   internal structures, a proxy or gateway &MAY; combine an ordered
3586   subsequence of Via header field entries with identical received-protocol
3587   values into a single such entry. For example,
3589<figure><artwork type="example">
3590  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3593  could be collapsed to
3595<figure><artwork type="example">
3596  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3599   Senders &SHOULD-NOT; combine multiple entries unless they are all
3600   under the same organizational control and the hosts have already been
3601   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3602   have different received-protocol values.
3608<section title="IANA Considerations" anchor="IANA.considerations">
3610<section title="Header Field Registration" anchor="header.field.registration">
3612   The Message Header Field Registry located at <eref target=""/> shall be updated
3613   with the permanent registrations below (see <xref target="RFC3864"/>):
3615<?BEGININC p1-messaging.iana-headers ?>
3616<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3617<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3618   <ttcol>Header Field Name</ttcol>
3619   <ttcol>Protocol</ttcol>
3620   <ttcol>Status</ttcol>
3621   <ttcol>Reference</ttcol>
3623   <c>Connection</c>
3624   <c>http</c>
3625   <c>standard</c>
3626   <c>
3627      <xref target="header.connection"/>
3628   </c>
3629   <c>Content-Length</c>
3630   <c>http</c>
3631   <c>standard</c>
3632   <c>
3633      <xref target="header.content-length"/>
3634   </c>
3635   <c>Date</c>
3636   <c>http</c>
3637   <c>standard</c>
3638   <c>
3639      <xref target=""/>
3640   </c>
3641   <c>Host</c>
3642   <c>http</c>
3643   <c>standard</c>
3644   <c>
3645      <xref target=""/>
3646   </c>
3647   <c>TE</c>
3648   <c>http</c>
3649   <c>standard</c>
3650   <c>
3651      <xref target="header.te"/>
3652   </c>
3653   <c>Trailer</c>
3654   <c>http</c>
3655   <c>standard</c>
3656   <c>
3657      <xref target="header.trailer"/>
3658   </c>
3659   <c>Transfer-Encoding</c>
3660   <c>http</c>
3661   <c>standard</c>
3662   <c>
3663      <xref target="header.transfer-encoding"/>
3664   </c>
3665   <c>Upgrade</c>
3666   <c>http</c>
3667   <c>standard</c>
3668   <c>
3669      <xref target="header.upgrade"/>
3670   </c>
3671   <c>Via</c>
3672   <c>http</c>
3673   <c>standard</c>
3674   <c>
3675      <xref target="header.via"/>
3676   </c>
3679<?ENDINC p1-messaging.iana-headers ?>
3681   The change controller is: "IETF ( - Internet Engineering Task Force".
3685<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3687   The entries for the "http" and "https" URI Schemes in the registry located at
3688   <eref target=""/>
3689   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3690   and <xref target="https.uri" format="counter"/> of this document
3691   (see <xref target="RFC4395"/>).
3695<section title="Internet Media Type Registrations" anchor="">
3697   This document serves as the specification for the Internet media types
3698   "message/http" and "application/http". The following is to be registered with
3699   IANA (see <xref target="RFC4288"/>).
3701<section title="Internet Media Type message/http" anchor="">
3702<iref item="Media Type" subitem="message/http" primary="true"/>
3703<iref item="message/http Media Type" primary="true"/>
3705   The message/http type can be used to enclose a single HTTP request or
3706   response message, provided that it obeys the MIME restrictions for all
3707   "message" types regarding line length and encodings.
3710  <list style="hanging" x:indent="12em">
3711    <t hangText="Type name:">
3712      message
3713    </t>
3714    <t hangText="Subtype name:">
3715      http
3716    </t>
3717    <t hangText="Required parameters:">
3718      none
3719    </t>
3720    <t hangText="Optional parameters:">
3721      version, msgtype
3722      <list style="hanging">
3723        <t hangText="version:">
3724          The HTTP-Version number of the enclosed message
3725          (e.g., "1.1"). If not present, the version can be
3726          determined from the first line of the body.
3727        </t>
3728        <t hangText="msgtype:">
3729          The message type &mdash; "request" or "response". If not
3730          present, the type can be determined from the first
3731          line of the body.
3732        </t>
3733      </list>
3734    </t>
3735    <t hangText="Encoding considerations:">
3736      only "7bit", "8bit", or "binary" are permitted
3737    </t>
3738    <t hangText="Security considerations:">
3739      none
3740    </t>
3741    <t hangText="Interoperability considerations:">
3742      none
3743    </t>
3744    <t hangText="Published specification:">
3745      This specification (see <xref target=""/>).
3746    </t>
3747    <t hangText="Applications that use this media type:">
3748    </t>
3749    <t hangText="Additional information:">
3750      <list style="hanging">
3751        <t hangText="Magic number(s):">none</t>
3752        <t hangText="File extension(s):">none</t>
3753        <t hangText="Macintosh file type code(s):">none</t>
3754      </list>
3755    </t>
3756    <t hangText="Person and email address to contact for further information:">
3757      See Authors Section.
3758    </t>
3759    <t hangText="Intended usage:">
3760      COMMON
3761    </t>
3762    <t hangText="Restrictions on usage:">
3763      none
3764    </t>
3765    <t hangText="Author/Change controller:">
3766      IESG
3767    </t>
3768  </list>
3771<section title="Internet Media Type application/http" anchor="">
3772<iref item="Media Type" subitem="application/http" primary="true"/>
3773<iref item="application/http Media Type" primary="true"/>
3775   The application/http type can be used to enclose a pipeline of one or more
3776   HTTP request or response messages (not intermixed).
3779  <list style="hanging" x:indent="12em">
3780    <t hangText="Type name:">
3781      application
3782    </t>
3783    <t hangText="Subtype name:">
3784      http
3785    </t>
3786    <t hangText="Required parameters:">
3787      none
3788    </t>
3789    <t hangText="Optional parameters:">
3790      version, msgtype
3791      <list style="hanging">
3792        <t hangText="version:">
3793          The HTTP-Version number of the enclosed messages
3794          (e.g., "1.1"). If not present, the version can be
3795          determined from the first line of the body.
3796        </t>
3797        <t hangText="msgtype:">
3798          The message type &mdash; "request" or "response". If not
3799          present, the type can be determined from the first
3800          line of the body.
3801        </t>
3802      </list>
3803    </t>
3804    <t hangText="Encoding considerations:">
3805      HTTP messages enclosed by this type
3806      are in "binary" format; use of an appropriate
3807      Content-Transfer-Encoding is required when
3808      transmitted via E-mail.
3809    </t>
3810    <t hangText="Security considerations:">
3811      none
3812    </t>
3813    <t hangText="Interoperability considerations:">
3814      none
3815    </t>
3816    <t hangText="Published specification:">
3817      This specification (see <xref target=""/>).
3818    </t>
3819    <t hangText="Applications that use this media type:">
3820    </t>
3821    <t hangText="Additional information:">
3822      <list style="hanging">
3823        <t hangText="Magic number(s):">none</t>
3824        <t hangText="File extension(s):">none</t>
3825        <t hangText="Macintosh file type code(s):">none</t>
3826      </list>
3827    </t>
3828    <t hangText="Person and email address to contact for further information:">
3829      See Authors Section.
3830    </t>
3831    <t hangText="Intended usage:">
3832      COMMON
3833    </t>
3834    <t hangText="Restrictions on usage:">
3835      none
3836    </t>
3837    <t hangText="Author/Change controller:">
3838      IESG
3839    </t>
3840  </list>
3845<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3847   The registration procedure for HTTP Transfer Codings is now defined by
3848   <xref target="transfer.coding.registry"/> of this document.
3851   The HTTP Transfer Codings Registry located at <eref target=""/>
3852   shall be updated with the registrations below:
3854<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3855   <ttcol>Name</ttcol>
3856   <ttcol>Description</ttcol>
3857   <ttcol>Reference</ttcol>
3858   <c>chunked</c>
3859   <c>Transfer in a series of chunks</c>
3860   <c>
3861      <xref target="chunked.encoding"/>
3862   </c>
3863   <c>compress</c>
3864   <c>UNIX "compress" program method</c>
3865   <c>
3866      <xref target="compress.coding"/>
3867   </c>
3868   <c>deflate</c>
3869   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3870   the "zlib" data format (<xref target="RFC1950"/>)
3871   </c>
3872   <c>
3873      <xref target="deflate.coding"/>
3874   </c>
3875   <c>gzip</c>
3876   <c>Same as GNU zip <xref target="RFC1952"/></c>
3877   <c>
3878      <xref target="gzip.coding"/>
3879   </c>
3883<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3885   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3886   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3887   by <xref target="upgrade.token.registry"/> of this document.
3890   The HTTP Status Code Registry located at <eref target=""/>
3891   shall be updated with the registration below:
3893<texttable align="left" suppress-title="true">
3894   <ttcol>Value</ttcol>
3895   <ttcol>Description</ttcol>
3896   <ttcol>Reference</ttcol>
3898   <c>HTTP</c>
3899   <c>Hypertext Transfer Protocol</c>
3900   <c><xref target="http.version"/> of this specification</c>
3901<!-- IANA should add this without our instructions; emailed on June 05, 2009
3902   <c>TLS/1.0</c>
3903   <c>Transport Layer Security</c>
3904   <c><xref target="RFC2817"/></c> -->
3911<section title="Security Considerations" anchor="security.considerations">
3913   This section is meant to inform application developers, information
3914   providers, and users of the security limitations in HTTP/1.1 as
3915   described by this document. The discussion does not include
3916   definitive solutions to the problems revealed, though it does make
3917   some suggestions for reducing security risks.
3920<section title="Personal Information" anchor="personal.information">
3922   HTTP clients are often privy to large amounts of personal information
3923   (e.g., the user's name, location, mail address, passwords, encryption
3924   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3925   leakage of this information.
3926   We very strongly recommend that a convenient interface be provided
3927   for the user to control dissemination of such information, and that
3928   designers and implementors be particularly careful in this area.
3929   History shows that errors in this area often create serious security
3930   and/or privacy problems and generate highly adverse publicity for the
3931   implementor's company.
3935<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3937   A server is in the position to save personal data about a user's
3938   requests which might identify their reading patterns or subjects of
3939   interest. This information is clearly confidential in nature and its
3940   handling can be constrained by law in certain countries. People using
3941   HTTP to provide data are responsible for ensuring that
3942   such material is not distributed without the permission of any
3943   individuals that are identifiable by the published results.
3947<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3949   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3950   the documents returned by HTTP requests to be only those that were
3951   intended by the server administrators. If an HTTP server translates
3952   HTTP URIs directly into file system calls, the server &MUST; take
3953   special care not to serve files that were not intended to be
3954   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3955   other operating systems use ".." as a path component to indicate a
3956   directory level above the current one. On such a system, an HTTP
3957   server &MUST; disallow any such construct in the request-target if it
3958   would otherwise allow access to a resource outside those intended to
3959   be accessible via the HTTP server. Similarly, files intended for
3960   reference only internally to the server (such as access control
3961   files, configuration files, and script code) &MUST; be protected from
3962   inappropriate retrieval, since they might contain sensitive
3963   information. Experience has shown that minor bugs in such HTTP server
3964   implementations have turned into security risks.
3968<section title="DNS Spoofing" anchor="dns.spoofing">
3970   Clients using HTTP rely heavily on the Domain Name Service, and are
3971   thus generally prone to security attacks based on the deliberate
3972   mis-association of IP addresses and DNS names. Clients need to be
3973   cautious in assuming the continuing validity of an IP number/DNS name
3974   association.
3977   In particular, HTTP clients &SHOULD; rely on their name resolver for
3978   confirmation of an IP number/DNS name association, rather than
3979   caching the result of previous host name lookups. Many platforms
3980   already can cache host name lookups locally when appropriate, and
3981   they &SHOULD; be configured to do so. It is proper for these lookups to
3982   be cached, however, only when the TTL (Time To Live) information
3983   reported by the name server makes it likely that the cached
3984   information will remain useful.
3987   If HTTP clients cache the results of host name lookups in order to
3988   achieve a performance improvement, they &MUST; observe the TTL
3989   information reported by DNS.
3992   If HTTP clients do not observe this rule, they could be spoofed when
3993   a previously-accessed server's IP address changes. As network
3994   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3995   possibility of this form of attack will grow. Observing this
3996   requirement thus reduces this potential security vulnerability.
3999   This requirement also improves the load-balancing behavior of clients
4000   for replicated servers using the same DNS name and reduces the
4001   likelihood of a user's experiencing failure in accessing sites which
4002   use that strategy.
4006<section title="Proxies and Caching" anchor="attack.proxies">
4008   By their very nature, HTTP proxies are men-in-the-middle, and
4009   represent an opportunity for man-in-the-middle attacks. Compromise of
4010   the systems on which the proxies run can result in serious security
4011   and privacy problems. Proxies have access to security-related
4012   information, personal information about individual users and
4013   organizations, and proprietary information belonging to users and
4014   content providers. A compromised proxy, or a proxy implemented or
4015   configured without regard to security and privacy considerations,
4016   might be used in the commission of a wide range of potential attacks.
4019   Proxy operators need to protect the systems on which proxies run as
4020   they would protect any system that contains or transports sensitive
4021   information. In particular, log information gathered at proxies often
4022   contains highly sensitive personal information, and/or information
4023   about organizations. Log information needs to be carefully guarded, and
4024   appropriate guidelines for use need to be developed and followed.
4025   (<xref target="abuse.of.server.log.information"/>).
4028   Proxy implementors need to consider the privacy and security
4029   implications of their design and coding decisions, and of the
4030   configuration options they provide to proxy operators (especially the
4031   default configuration).
4034   Users of a proxy need to be aware that proxies are no trustworthier than
4035   the people who run them; HTTP itself cannot solve this problem.
4038   The judicious use of cryptography, when appropriate, might suffice to
4039   protect against a broad range of security and privacy attacks. Such
4040   cryptography is beyond the scope of the HTTP/1.1 specification.
4044<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4046   They exist. They are hard to defend against. Research continues.
4047   Beware.
4052<section title="Acknowledgments" anchor="ack">
4054   HTTP has evolved considerably over the years. It has
4055   benefited from a large and active developer community &mdash; the many
4056   people who have participated on the www-talk mailing list &mdash; and it is
4057   that community which has been most responsible for the success of
4058   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4059   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4060   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4061   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4062   VanHeyningen deserve special recognition for their efforts in
4063   defining early aspects of the protocol.
4066   This document has benefited greatly from the comments of all those
4067   participating in the HTTP-WG. In addition to those already mentioned,
4068   the following individuals have contributed to this specification:
4071   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4072   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4073   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4074   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4075   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4076   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4077   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4078   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4079   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4080   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4081   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4082   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4085   Thanks to the "cave men" of Palo Alto. You know who you are.
4088   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4089   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4090   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4091   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4092   Larry Masinter for their help. And thanks go particularly to Jeff
4093   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4096   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4097   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4098   discovery of many of the problems that this document attempts to
4099   rectify.
4102   This specification makes heavy use of the augmented BNF and generic
4103   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4104   reuses many of the definitions provided by Nathaniel Borenstein and
4105   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4106   specification will help reduce past confusion over the relationship
4107   between HTTP and Internet mail message formats.
4111Acknowledgements TODO list
4113- Jeff Hodges ("effective request URI")
4121<references title="Normative References">
4123<reference anchor="ISO-8859-1">
4124  <front>
4125    <title>
4126     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4127    </title>
4128    <author>
4129      <organization>International Organization for Standardization</organization>
4130    </author>
4131    <date year="1998"/>
4132  </front>
4133  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4136<reference anchor="Part2">
4137  <front>
4138    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4139    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4140      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4141      <address><email></email></address>
4142    </author>
4143    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4144      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4145      <address><email></email></address>
4146    </author>
4147    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4148      <organization abbrev="HP">Hewlett-Packard Company</organization>
4149      <address><email></email></address>
4150    </author>
4151    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4152      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4153      <address><email></email></address>
4154    </author>
4155    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4156      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4157      <address><email></email></address>
4158    </author>
4159    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4160      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4161      <address><email></email></address>
4162    </author>
4163    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4164      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4165      <address><email></email></address>
4166    </author>
4167    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4168      <organization abbrev="W3C">World Wide Web Consortium</organization>
4169      <address><email></email></address>
4170    </author>
4171    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4172      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4173      <address><email></email></address>
4174    </author>
4175    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4176  </front>
4177  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4178  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4181<reference anchor="Part3">
4182  <front>
4183    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4184    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4185      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4186      <address><email></email></address>
4187    </author>
4188    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4189      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4190      <address><email></email></address>
4191    </author>
4192    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4193      <organization abbrev="HP">Hewlett-Packard Company</organization>
4194      <address><email></email></address>
4195    </author>
4196    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4197      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4198      <address><email></email></address>
4199    </author>
4200    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4201      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4202      <address><email></email></address>
4203    </author>
4204    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4205      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4206      <address><email></email></address>
4207    </author>
4208    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4209      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4210      <address><email></email></address>
4211    </author>
4212    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4213      <organization abbrev="W3C">World Wide Web Consortium</organization>
4214      <address><email></email></address>
4215    </author>
4216    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4217      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4218      <address><email></email></address>
4219    </author>
4220    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4221  </front>
4222  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4223  <x:source href="p3-payload.xml" basename="p3-payload"/>
4226<reference anchor="Part6">
4227  <front>
4228    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4229    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4230      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4231      <address><email></email></address>
4232    </author>
4233    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4234      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4235      <address><email></email></address>
4236    </author>
4237    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4238      <organization abbrev="HP">Hewlett-Packard Company</organization>
4239      <address><email></email></address>
4240    </author>
4241    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4242      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4243      <address><email></email></address>
4244    </author>
4245    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4246      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4247      <address><email></email></address>
4248    </author>
4249    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4250      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4251      <address><email></email></address>
4252    </author>
4253    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4254      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4255      <address><email></email></address>
4256    </author>
4257    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4258      <organization abbrev="W3C">World Wide Web Consortium</organization>
4259      <address><email></email></address>
4260    </author>
4261    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4262      <address><email></email></address>
4263    </author>
4264    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4265      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4266      <address><email></email></address>
4267    </author>
4268    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4269  </front>
4270  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4271  <x:source href="p6-cache.xml" basename="p6-cache"/>
4274<reference anchor="RFC5234">
4275  <front>
4276    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4277    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4278      <organization>Brandenburg InternetWorking</organization>
4279      <address>
4280        <email></email>
4281      </address> 
4282    </author>
4283    <author initials="P." surname="Overell" fullname="Paul Overell">
4284      <organization>THUS plc.</organization>
4285      <address>
4286        <email></email>
4287      </address>
4288    </author>
4289    <date month="January" year="2008"/>
4290  </front>
4291  <seriesInfo name="STD" value="68"/>
4292  <seriesInfo name="RFC" value="5234"/>
4295<reference anchor="RFC2119">
4296  <front>
4297    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4298    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4299      <organization>Harvard University</organization>
4300      <address><email></email></address>
4301    </author>
4302    <date month="March" year="1997"/>
4303  </front>
4304  <seriesInfo name="BCP" value="14"/>
4305  <seriesInfo name="RFC" value="2119"/>
4308<reference anchor="RFC3986">
4309 <front>
4310  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4311  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4312    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4313    <address>
4314       <email></email>
4315       <uri></uri>
4316    </address>
4317  </author>
4318  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4319    <organization abbrev="Day Software">Day Software</organization>
4320    <address>
4321      <email></email>
4322      <uri></uri>
4323    </address>
4324  </author>
4325  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4326    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4327    <address>
4328      <email></email>
4329      <uri></uri>
4330    </address>
4331  </author>
4332  <date month='January' year='2005'></date>
4333 </front>
4334 <seriesInfo name="STD" value="66"/>
4335 <seriesInfo name="RFC" value="3986"/>
4338<reference anchor="USASCII">
4339  <front>
4340    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4341    <author>
4342      <organization>American National Standards Institute</organization>
4343    </author>
4344    <date year="1986"/>
4345  </front>
4346  <seriesInfo name="ANSI" value="X3.4"/>
4349<reference anchor="RFC1950">
4350  <front>
4351    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4352    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4353      <organization>Aladdin Enterprises</organization>
4354      <address><email></email></address>
4355    </author>
4356    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4357    <date month="May" year="1996"/>
4358  </front>
4359  <seriesInfo name="RFC" value="1950"/>
4360  <annotation>
4361    RFC 1950 is an Informational RFC, thus it might be less stable than
4362    this specification. On the other hand, this downward reference was
4363    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4364    therefore it is unlikely to cause problems in practice. See also
4365    <xref target="BCP97"/>.
4366  </annotation>
4369<reference anchor="RFC1951">
4370  <front>
4371    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4372    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4373      <organization>Aladdin Enterprises</organization>
4374      <address><email></email></address>
4375    </author>
4376    <date month="May" year="1996"/>
4377  </front>
4378  <seriesInfo name="RFC" value="1951"/>
4379  <annotation>
4380    RFC 1951 is an Informational RFC, thus it might be less stable than
4381    this specification. On the other hand, this downward reference was
4382    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4383    therefore it is unlikely to cause problems in practice. See also
4384    <xref target="BCP97"/>.
4385  </annotation>
4388<reference anchor="RFC1952">
4389  <front>
4390    <title>GZIP file format specification version 4.3</title>
4391    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4392      <organization>Aladdin Enterprises</organization>
4393      <address><email></email></address>
4394    </author>
4395    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4396      <address><email></email></address>
4397    </author>
4398    <author initials="M." surname="Adler" fullname="Mark Adler">
4399      <address><email></email></address>
4400    </author>
4401    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4402      <address><email></email></address>
4403    </author>
4404    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4405      <address><email></email></address>
4406    </author>
4407    <date month="May" year="1996"/>
4408  </front>
4409  <seriesInfo name="RFC" value="1952"/>
4410  <annotation>
4411    RFC 1952 is an Informational RFC, thus it might be less stable than
4412    this specification. On the other hand, this downward reference was
4413    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4414    therefore it is unlikely to cause problems in practice. See also
4415    <xref target="BCP97"/>.
4416  </annotation>
4421<references title="Informative References">
4423<reference anchor="Nie1997" target="">
4424  <front>
4425    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4426    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4427    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4428    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4429    <author initials="H." surname="Lie" fullname="H. Lie"/>
4430    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4431    <date year="1997" month="September"/>
4432  </front>
4433  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4436<reference anchor="Pad1995" target="">
4437  <front>
4438    <title>Improving HTTP Latency</title>
4439    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4440    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4441    <date year="1995" month="December"/>
4442  </front>
4443  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4446<reference anchor="RFC1123">
4447  <front>
4448    <title>Requirements for Internet Hosts - Application and Support</title>
4449    <author initials="R." surname="Braden" fullname="Robert Braden">
4450      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4451      <address><email>Braden@ISI.EDU</email></address>
4452    </author>
4453    <date month="October" year="1989"/>
4454  </front>
4455  <seriesInfo name="STD" value="3"/>
4456  <seriesInfo name="RFC" value="1123"/>
4459<reference anchor="RFC1900">
4460  <front>
4461    <title>Renumbering Needs Work</title>
4462    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4463      <organization>CERN, Computing and Networks Division</organization>
4464      <address><email></email></address>
4465    </author>
4466    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4467      <organization>cisco Systems</organization>
4468      <address><email></email></address>
4469    </author>
4470    <date month="February" year="1996"/>
4471  </front>
4472  <seriesInfo name="RFC" value="1900"/>
4475<reference anchor='RFC1919'>
4476  <front>
4477    <title>Classical versus Transparent IP Proxies</title>
4478    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4479      <address><email></email></address>
4480    </author>
4481    <date year='1996' month='March' />
4482  </front>
4483  <seriesInfo name='RFC' value='1919' />
4486<reference anchor="RFC1945">
4487  <front>
4488    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4489    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4490      <organization>MIT, Laboratory for Computer Science</organization>
4491      <address><email></email></address>
4492    </author>
4493    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4494      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4495      <address><email></email></address>
4496    </author>
4497    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4498      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4499      <address><email></email></address>
4500    </author>
4501    <date month="May" year="1996"/>
4502  </front>
4503  <seriesInfo name="RFC" value="1945"/>
4506<reference anchor="RFC2045">
4507  <front>
4508    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4509    <author initials="N." surname="Freed" fullname="Ned Freed">
4510      <organization>Innosoft International, Inc.</organization>
4511      <address><email></email></address>
4512    </author>
4513    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4514      <organization>First Virtual Holdings</organization>
4515      <address><email></email></address>
4516    </author>
4517    <date month="November" year="1996"/>
4518  </front>
4519  <seriesInfo name="RFC" value="2045"/>
4522<reference anchor="RFC2047">
4523  <front>
4524    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4525    <author initials="K." surname="Moore" fullname="Keith Moore">
4526      <organization>University of Tennessee</organization>
4527      <address><email></email></address>
4528    </author>
4529    <date month="November" year="1996"/>
4530  </front>
4531  <seriesInfo name="RFC" value="2047"/>
4534<reference anchor="RFC2068">
4535  <front>
4536    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4537    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4538      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4539      <address><email></email></address>
4540    </author>
4541    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4542      <organization>MIT Laboratory for Computer Science</organization>
4543      <address><email></email></address>
4544    </author>
4545    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4546      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4547      <address><email></email></address>
4548    </author>
4549    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4550      <organization>MIT Laboratory for Computer Science</organization>
4551      <address><email></email></address>
4552    </author>
4553    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4554      <organization>MIT Laboratory for Computer Science</organization>
4555      <address><email></email></address>
4556    </author>
4557    <date month="January" year="1997"/>
4558  </front>
4559  <seriesInfo name="RFC" value="2068"/>
4562<reference anchor="RFC2145">
4563  <front>
4564    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4565    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4566      <organization>Western Research Laboratory</organization>
4567      <address><email></email></address>
4568    </author>
4569    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4570      <organization>Department of Information and Computer Science</organization>
4571      <address><email></email></address>
4572    </author>
4573    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4574      <organization>MIT Laboratory for Computer Science</organization>
4575      <address><email></email></address>
4576    </author>
4577    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4578      <organization>W3 Consortium</organization>
4579      <address><email></email></address>
4580    </author>
4581    <date month="May" year="1997"/>
4582  </front>
4583  <seriesInfo name="RFC" value="2145"/>
4586<reference anchor="RFC2616">
4587  <front>
4588    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4589    <author initials="R." surname="Fielding" fullname="R. Fielding">
4590      <organization>University of California, Irvine</organization>
4591      <address><email></email></address>
4592    </author>
4593    <author initials="J." surname="Gettys" fullname="J. Gettys">
4594      <organization>W3C</organization>
4595      <address><email></email></address>
4596    </author>
4597    <author initials="J." surname="Mogul" fullname="J. Mogul">
4598      <organization>Compaq Computer Corporation</organization>
4599      <address><email></email></address>
4600    </author>
4601    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4602      <organization>MIT Laboratory for Computer Science</organization>
4603      <address><email></email></address>
4604    </author>
4605    <author initials="L." surname="Masinter" fullname="L. Masinter">
4606      <organization>Xerox Corporation</organization>
4607      <address><email></email></address>
4608    </author>
4609    <author initials="P." surname="Leach" fullname="P. Leach">
4610      <organization>Microsoft Corporation</organization>
4611      <address><email></email></address>
4612    </author>
4613    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4614      <organization>W3C</organization>
4615      <address><email></email></address>
4616    </author>
4617    <date month="June" year="1999"/>
4618  </front>
4619  <seriesInfo name="RFC" value="2616"/>
4622<reference anchor='RFC2817'>
4623  <front>
4624    <title>Upgrading to TLS Within HTTP/1.1</title>
4625    <author initials='R.' surname='Khare' fullname='R. Khare'>
4626      <organization>4K Associates / UC Irvine</organization>
4627      <address><email></email></address>
4628    </author>
4629    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4630      <organization>Agranat Systems, Inc.</organization>
4631      <address><email></email></address>
4632    </author>
4633    <date year='2000' month='May' />
4634  </front>
4635  <seriesInfo name='RFC' value='2817' />
4638<reference anchor='RFC2818'>
4639  <front>
4640    <title>HTTP Over TLS</title>
4641    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4642      <organization>RTFM, Inc.</organization>
4643      <address><email></email></address>
4644    </author>
4645    <date year='2000' month='May' />
4646  </front>
4647  <seriesInfo name='RFC' value='2818' />
4650<reference anchor='RFC2965'>
4651  <front>
4652    <title>HTTP State Management Mechanism</title>
4653    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4654      <organization>Bell Laboratories, Lucent Technologies</organization>
4655      <address><email></email></address>
4656    </author>
4657    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4658      <organization>, Inc.</organization>
4659      <address><email></email></address>
4660    </author>
4661    <date year='2000' month='October' />
4662  </front>
4663  <seriesInfo name='RFC' value='2965' />
4666<reference anchor='RFC3040'>
4667  <front>
4668    <title>Internet Web Replication and Caching Taxonomy</title>
4669    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4670      <organization>Equinix, Inc.</organization>
4671    </author>
4672    <author initials='I.' surname='Melve' fullname='I. Melve'>
4673      <organization>UNINETT</organization>
4674    </author>
4675    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4676      <organization>CacheFlow Inc.</organization>
4677    </author>
4678    <date year='2001' month='January' />
4679  </front>
4680  <seriesInfo name='RFC' value='3040' />
4683<reference anchor='RFC3864'>
4684  <front>
4685    <title>Registration Procedures for Message Header Fields</title>
4686    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4687      <organization>Nine by Nine</organization>
4688      <address><email></email></address>
4689    </author>
4690    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4691      <organization>BEA Systems</organization>
4692      <address><email></email></address>
4693    </author>
4694    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4695      <organization>HP Labs</organization>
4696      <address><email></email></address>
4697    </author>
4698    <date year='2004' month='September' />
4699  </front>
4700  <seriesInfo name='BCP' value='90' />
4701  <seriesInfo name='RFC' value='3864' />
4704<reference anchor="RFC4288">
4705  <front>
4706    <title>Media Type Specifications and Registration Procedures</title>
4707    <author initials="N." surname="Freed" fullname="N. Freed">
4708      <organization>Sun Microsystems</organization>
4709      <address>
4710        <email></email>
4711      </address>
4712    </author>
4713    <author initials="J." surname="Klensin" fullname="J. Klensin">
4714      <address>
4715        <email></email>
4716      </address>
4717    </author>
4718    <date year="2005" month="December"/>
4719  </front>
4720  <seriesInfo name="BCP" value="13"/>
4721  <seriesInfo name="RFC" value="4288"/>
4724<reference anchor='RFC4395'>
4725  <front>
4726    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4727    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4728      <organization>AT&amp;T Laboratories</organization>
4729      <address>
4730        <email></email>
4731      </address>
4732    </author>
4733    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4734      <organization>Qualcomm, Inc.</organization>
4735      <address>
4736        <email></email>
4737      </address>
4738    </author>
4739    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4740      <organization>Adobe Systems</organization>
4741      <address>
4742        <email></email>
4743      </address>
4744    </author>
4745    <date year='2006' month='February' />
4746  </front>
4747  <seriesInfo name='BCP' value='115' />
4748  <seriesInfo name='RFC' value='4395' />
4751<reference anchor='RFC5226'>
4752  <front>
4753    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4754    <author initials='T.' surname='Narten' fullname='T. Narten'>
4755      <organization>IBM</organization>
4756      <address><email></email></address>
4757    </author>
4758    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4759      <organization>Google</organization>
4760      <address><email></email></address>
4761    </author>
4762    <date year='2008' month='May' />
4763  </front>
4764  <seriesInfo name='BCP' value='26' />
4765  <seriesInfo name='RFC' value='5226' />
4768<reference anchor="RFC5322">
4769  <front>
4770    <title>Internet Message Format</title>
4771    <author initials="P." surname="Resnick" fullname="P. Resnick">
4772      <organization>Qualcomm Incorporated</organization>
4773    </author>
4774    <date year="2008" month="October"/>
4775  </front>
4776  <seriesInfo name="RFC" value="5322"/>
4779<reference anchor='draft-ietf-httpstate-cookie'>
4780  <front>
4781    <title>HTTP State Management Mechanism</title>
4782    <author initials="A." surname="Barth" fullname="Adam Barth">
4783      <organization abbrev="U.C. Berkeley">
4784        University of California, Berkeley
4785      </organization>
4786      <address><email></email></address>
4787    </author>
4788    <date year='2011' month='March' />
4789  </front>
4790  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4793<reference anchor='BCP97'>
4794  <front>
4795    <title>Handling Normative References to Standards-Track Documents</title>
4796    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4797      <address>
4798        <email></email>
4799      </address>
4800    </author>
4801    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4802      <organization>MIT</organization>
4803      <address>
4804        <email></email>
4805      </address>
4806    </author>
4807    <date year='2007' month='June' />
4808  </front>
4809  <seriesInfo name='BCP' value='97' />
4810  <seriesInfo name='RFC' value='4897' />
4813<reference anchor="Kri2001" target="">
4814  <front>
4815    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4816    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4817    <date year="2001" month="November"/>
4818  </front>
4819  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4822<reference anchor="Spe" target="">
4823  <front>
4824    <title>Analysis of HTTP Performance Problems</title>
4825    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4826    <date/>
4827  </front>
4830<reference anchor="Tou1998" target="">
4831  <front>
4832  <title>Analysis of HTTP Performance</title>
4833  <author initials="J." surname="Touch" fullname="Joe Touch">
4834    <organization>USC/Information Sciences Institute</organization>
4835    <address><email></email></address>
4836  </author>
4837  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4838    <organization>USC/Information Sciences Institute</organization>
4839    <address><email></email></address>
4840  </author>
4841  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4842    <organization>USC/Information Sciences Institute</organization>
4843    <address><email></email></address>
4844  </author>
4845  <date year="1998" month="Aug"/>
4846  </front>
4847  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4848  <annotation>(original report dated Aug. 1996)</annotation>
4854<section title="Tolerant Applications" anchor="tolerant.applications">
4856   Although this document specifies the requirements for the generation
4857   of HTTP/1.1 messages, not all applications will be correct in their
4858   implementation. We therefore recommend that operational applications
4859   be tolerant of deviations whenever those deviations can be
4860   interpreted unambiguously.
4863   The line terminator for header fields is the sequence CRLF.
4864   However, we recommend that applications, when parsing such headers fields,
4865   recognize a single LF as a line terminator and ignore the leading CR.
4868   The character encoding of a representation &SHOULD; be labeled as the lowest
4869   common denominator of the character codes used within that representation, with
4870   the exception that not labeling the representation is preferred over labeling
4871   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4874   Additional rules for requirements on parsing and encoding of dates
4875   and other potential problems with date encodings include:
4878  <list style="symbols">
4879     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4880        which appears to be more than 50 years in the future is in fact
4881        in the past (this helps solve the "year 2000" problem).</t>
4883     <t>Although all date formats are specified to be case-sensitive,
4884        recipients &SHOULD; match day, week and timezone names
4885        case-insensitively.</t>
4887     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4888        Expires date as earlier than the proper value, but &MUST-NOT;
4889        internally represent a parsed Expires date as later than the
4890        proper value.</t>
4892     <t>All expiration-related calculations &MUST; be done in GMT. The
4893        local time zone &MUST-NOT; influence the calculation or comparison
4894        of an age or expiration time.</t>
4896     <t>If an HTTP header field incorrectly carries a date value with a time
4897        zone other than GMT, it &MUST; be converted into GMT using the
4898        most conservative possible conversion.</t>
4899  </list>
4903<section title="HTTP Version History" anchor="compatibility">
4905   HTTP has been in use by the World-Wide Web global information initiative
4906   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4907   was a simple protocol for hypertext data transfer across the Internet
4908   with only a single request method (GET) and no metadata.
4909   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4910   methods and MIME-like messaging that could include metadata about the data
4911   transferred and modifiers on the request/response semantics. However,
4912   HTTP/1.0 did not sufficiently take into consideration the effects of
4913   hierarchical proxies, caching, the need for persistent connections, or
4914   name-based virtual hosts. The proliferation of incompletely-implemented
4915   applications calling themselves "HTTP/1.0" further necessitated a
4916   protocol version change in order for two communicating applications
4917   to determine each other's true capabilities.
4920   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4921   requirements that enable reliable implementations, adding only
4922   those new features that will either be safely ignored by an HTTP/1.0
4923   recipient or only sent when communicating with a party advertising
4924   compliance with HTTP/1.1.
4927   It is beyond the scope of a protocol specification to mandate
4928   compliance with previous versions. HTTP/1.1 was deliberately
4929   designed, however, to make supporting previous versions easy.
4930   We would expect a general-purpose HTTP/1.1 server to understand
4931   any valid request in the format of HTTP/1.0 and respond appropriately
4932   with an HTTP/1.1 message that only uses features understood (or
4933   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4934   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4937   Since HTTP/0.9 did not support header fields in a request,
4938   there is no mechanism for it to support name-based virtual
4939   hosts (selection of resource by inspection of the Host header
4940   field).  Any server that implements name-based virtual hosts
4941   ought to disable support for HTTP/0.9.  Most requests that
4942   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4943   requests wherein a buggy client failed to properly encode
4944   linear whitespace found in a URI reference and placed in
4945   the request-target.
4948<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4950   This section summarizes major differences between versions HTTP/1.0
4951   and HTTP/1.1.
4954<section title="Multi-homed Web Servers" anchor="">
4956   The requirements that clients and servers support the Host header
4957   field (<xref target=""/>), report an error if it is
4958   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4959   are among the most important changes defined by HTTP/1.1.
4962   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4963   addresses and servers; there was no other established mechanism for
4964   distinguishing the intended server of a request than the IP address
4965   to which that request was directed. The Host header field was
4966   introduced during the development of HTTP/1.1 and, though it was
4967   quickly implemented by most HTTP/1.0 browsers, additional requirements
4968   were placed on all HTTP/1.1 requests in order to ensure complete
4969   adoption.  At the time of this writing, most HTTP-based services
4970   are dependent upon the Host header field for targeting requests.
4974<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4976   For most implementations of HTTP/1.0, each connection is established
4977   by the client prior to the request and closed by the server after
4978   sending the response. However, some implementations implement the
4979   Keep-Alive version of persistent connections described in
4980   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4983   Some clients and servers might wish to be compatible with some
4984   previous implementations of persistent connections in HTTP/1.0
4985   clients and servers. Persistent connections in HTTP/1.0 are
4986   explicitly negotiated as they are not the default behavior. HTTP/1.0
4987   experimental implementations of persistent connections are faulty,
4988   and the new facilities in HTTP/1.1 are designed to rectify these
4989   problems. The problem was that some existing HTTP/1.0 clients might
4990   send Keep-Alive to a proxy server that doesn't understand
4991   Connection, which would then erroneously forward it to the next
4992   inbound server, which would establish the Keep-Alive connection and
4993   result in a hung HTTP/1.0 proxy waiting for the close on the
4994   response. The result is that HTTP/1.0 clients must be prevented from
4995   using Keep-Alive when talking to proxies.
4998   However, talking to proxies is the most important use of persistent
4999   connections, so that prohibition is clearly unacceptable. Therefore,
5000   we need some other mechanism for indicating a persistent connection
5001   is desired, which is safe to use even when talking to an old proxy
5002   that ignores Connection. Persistent connections are the default for
5003   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
5004   declaring non-persistence. See <xref target="header.connection"/>.
5009<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5011  Empty list elements in list productions have been deprecated.
5012  (<xref target="notation.abnf"/>)
5015  Rules about implicit linear whitespace between certain grammar productions
5016  have been removed; now it's only allowed when specifically pointed out
5017  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5018  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5019  Non-ASCII content in header fields and reason phrase has been obsoleted and
5020  made opaque (the TEXT rule was removed)
5021  (<xref target="basic.rules"/>)
5024  Clarify that HTTP-Version is case sensitive.
5025  (<xref target="http.version"/>)
5028  Require that invalid whitespace around field-names be rejected.
5029  (<xref target="header.fields"/>)
5032  Require recipients to handle bogus Content-Length header fields as errors.
5033  (<xref target="message.body"/>)
5036  Remove reference to non-existent identity transfer-coding value tokens.
5037  (Sections <xref format="counter" target="message.body"/> and
5038  <xref format="counter" target="transfer.codings"/>)
5041  Update use of abs_path production from RFC 1808 to the path-absolute + query
5042  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5043  request method only.
5044  (<xref target="request-target"/>)
5047  Clarification that the chunk length does not include the count of the octets
5048  in the chunk header and trailer. Furthermore disallowed line folding
5049  in chunk extensions.
5050  (<xref target="chunked.encoding"/>)
5053  Remove hard limit of two connections per server.
5054  (<xref target="persistent.practical"/>)
5057  Clarify exactly when close connection options must be sent.
5058  (<xref target="header.connection"/>)
5061  Define the semantics of the "Upgrade" header field in responses other than
5062  101 (this was incorporated from <xref target="RFC2817"/>).
5063  (<xref target="header.upgrade"/>)
5068<?BEGININC p1-messaging.abnf-appendix ?>
5069<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5071<artwork type="abnf" name="p1-messaging.parsed-abnf">
5072<x:ref>BWS</x:ref> = OWS
5074<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5075<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
5076<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5077 connection-token ] )
5078<x:ref>Content-Length</x:ref> = "Content-Length:" OWS Content-Length-v
5079<x:ref>Content-Length-v</x:ref> = 1*DIGIT
5081<x:ref>Date</x:ref> = "Date:" OWS Date-v
5082<x:ref>Date-v</x:ref> = HTTP-date
5084<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5086<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5087<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5088<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5089<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5090 ]
5091<x:ref>Host</x:ref> = "Host:" OWS Host-v
5092<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
5094<x:ref>Method</x:ref> = token
5096<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5098<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5099<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5100<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5101<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5102<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5104<x:ref>Status-Code</x:ref> = 3DIGIT
5105<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5107<x:ref>TE</x:ref> = "TE:" OWS TE-v
5108<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5109<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5110<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5111<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5112<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5113 transfer-coding ] )
5115<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5116<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5117<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5119<x:ref>Via</x:ref> = "Via:" OWS Via-v
5120<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5121 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5122 ] )
5124<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5125<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5126<x:ref>attribute</x:ref> = token
5127<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5129<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5130<x:ref>chunk-data</x:ref> = 1*OCTET
5131<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5132<x:ref>chunk-ext-name</x:ref> = token
5133<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5134<x:ref>chunk-size</x:ref> = 1*HEXDIG
5135<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5136<x:ref>connection-token</x:ref> = token
5137<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5138 / %x2A-5B ; '*'-'['
5139 / %x5D-7E ; ']'-'~'
5140 / obs-text
5142<x:ref>date1</x:ref> = day SP month SP year
5143<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5144<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5145<x:ref>day</x:ref> = 2DIGIT
5146<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5147 / %x54.75.65 ; Tue
5148 / %x57.65.64 ; Wed
5149 / %x54.68.75 ; Thu
5150 / %x46.72.69 ; Fri
5151 / %x53.61.74 ; Sat
5152 / %x53.75.6E ; Sun
5153<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5154 / %x54. ; Tuesday
5155 / %x57.65.64.6E. ; Wednesday
5156 / %x54. ; Thursday
5157 / %x46. ; Friday
5158 / %x53. ; Saturday
5159 / %x53.75.6E.64.61.79 ; Sunday
5161<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5162<x:ref>field-name</x:ref> = token
5163<x:ref>field-value</x:ref> = *( field-content / OWS )
5165<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5166<x:ref>hour</x:ref> = 2DIGIT
5167<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5168<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5170<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5172<x:ref>message-body</x:ref> = *OCTET
5173<x:ref>minute</x:ref> = 2DIGIT
5174<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5175 / %x46.65.62 ; Feb
5176 / %x4D.61.72 ; Mar
5177 / %x41.70.72 ; Apr
5178 / %x4D.61.79 ; May
5179 / %x4A.75.6E ; Jun
5180 / %x4A.75.6C ; Jul
5181 / %x41.75.67 ; Aug
5182 / %x53.65.70 ; Sep
5183 / %x4F.63.74 ; Oct
5184 / %x4E.6F.76 ; Nov
5185 / %x44.65.63 ; Dec
5187<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5188<x:ref>obs-fold</x:ref> = CRLF
5189<x:ref>obs-text</x:ref> = %x80-FF
5191<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5192<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5193<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5194<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5195<x:ref>product</x:ref> = token [ "/" product-version ]
5196<x:ref>product-version</x:ref> = token
5197<x:ref>protocol-name</x:ref> = token
5198<x:ref>protocol-version</x:ref> = token
5199<x:ref>pseudonym</x:ref> = token
5201<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5202 / %x5D-7E ; ']'-'~'
5203 / obs-text
5204<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5205 / %x5D-7E ; ']'-'~'
5206 / obs-text
5207<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5208<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5209<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5210<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5211<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5212<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5214<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5215<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5216<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5217<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5218 / authority
5219<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5220<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5222<x:ref>second</x:ref> = 2DIGIT
5223<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5224 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5225<x:ref>start-line</x:ref> = Request-Line / Status-Line
5227<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5228<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5229 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5230<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5231<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5232<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5233<x:ref>token</x:ref> = 1*tchar
5234<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5235<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5236 transfer-extension
5237<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5238<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5240<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5242<x:ref>value</x:ref> = word
5244<x:ref>word</x:ref> = token / quoted-string
5246<x:ref>year</x:ref> = 4DIGIT
5249<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5250; Chunked-Body defined but not used
5251; Connection defined but not used
5252; Content-Length defined but not used
5253; Date defined but not used
5254; HTTP-message defined but not used
5255; Host defined but not used
5256; Request defined but not used
5257; Response defined but not used
5258; TE defined but not used
5259; Trailer defined but not used
5260; Transfer-Encoding defined but not used
5261; URI-reference defined but not used
5262; Upgrade defined but not used
5263; Via defined but not used
5264; http-URI defined but not used
5265; https-URI defined but not used
5266; partial-URI defined but not used
5267; special defined but not used
5269<?ENDINC p1-messaging.abnf-appendix ?>
5271<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5273<section title="Since RFC 2616">
5275  Extracted relevant partitions from <xref target="RFC2616"/>.
5279<section title="Since draft-ietf-httpbis-p1-messaging-00">
5281  Closed issues:
5282  <list style="symbols">
5283    <t>
5284      <eref target=""/>:
5285      "HTTP Version should be case sensitive"
5286      (<eref target=""/>)
5287    </t>
5288    <t>
5289      <eref target=""/>:
5290      "'unsafe' characters"
5291      (<eref target=""/>)
5292    </t>
5293    <t>
5294      <eref target=""/>:
5295      "Chunk Size Definition"
5296      (<eref target=""/>)
5297    </t>
5298    <t>
5299      <eref target=""/>:
5300      "Message Length"
5301      (<eref target=""/>)
5302    </t>
5303    <t>
5304      <eref target=""/>:
5305      "Media Type Registrations"
5306      (<eref target=""/>)
5307    </t>
5308    <t>
5309      <eref target=""/>:
5310      "URI includes query"
5311      (<eref target=""/>)
5312    </t>
5313    <t>
5314      <eref target=""/>:
5315      "No close on 1xx responses"
5316      (<eref target=""/>)
5317    </t>
5318    <t>
5319      <eref target=""/>:
5320      "Remove 'identity' token references"
5321      (<eref target=""/>)
5322    </t>
5323    <t>
5324      <eref target=""/>:
5325      "Import query BNF"
5326    </t>
5327    <t>
5328      <eref target=""/>:
5329      "qdtext BNF"
5330    </t>
5331    <t>
5332      <eref target=""/>:
5333      "Normative and Informative references"
5334    </t>
5335    <t>
5336      <eref target=""/>:
5337      "RFC2606 Compliance"
5338    </t>
5339    <t>
5340      <eref target=""/>:
5341      "RFC977 reference"
5342    </t>
5343    <t>
5344      <eref target=""/>:
5345      "RFC1700 references"
5346    </t>
5347    <t>
5348      <eref target=""/>:
5349      "inconsistency in date format explanation"
5350    </t>
5351    <t>
5352      <eref target=""/>:
5353      "Date reference typo"
5354    </t>
5355    <t>
5356      <eref target=""/>:
5357      "Informative references"
5358    </t>
5359    <t>
5360      <eref target=""/>:
5361      "ISO-8859-1 Reference"
5362    </t>
5363    <t>
5364      <eref target=""/>:
5365      "Normative up-to-date references"
5366    </t>
5367  </list>
5370  Other changes:
5371  <list style="symbols">
5372    <t>
5373      Update media type registrations to use RFC4288 template.
5374    </t>
5375    <t>
5376      Use names of RFC4234 core rules DQUOTE and WSP,
5377      fix broken ABNF for chunk-data
5378      (work in progress on <eref target=""/>)
5379    </t>
5380  </list>
5384<section title="Since draft-ietf-httpbis-p1-messaging-01">
5386  Closed issues:
5387  <list style="symbols">
5388    <t>
5389      <eref target=""/>:
5390      "Bodies on GET (and other) requests"
5391    </t>
5392    <t>
5393      <eref target=""/>:
5394      "Updating to RFC4288"
5395    </t>
5396    <t>
5397      <eref target=""/>:
5398      "Status Code and Reason Phrase"
5399    </t>
5400    <t>
5401      <eref target=""/>:
5402      "rel_path not used"
5403    </t>
5404  </list>
5407  Ongoing work on ABNF conversion (<eref target=""/>):
5408  <list style="symbols">
5409    <t>
5410      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5411      "trailer-part").
5412    </t>
5413    <t>
5414      Avoid underscore character in rule names ("http_URL" ->
5415      "http-URL", "abs_path" -> "path-absolute").
5416    </t>
5417    <t>
5418      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5419      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5420      have to be updated when switching over to RFC3986.
5421    </t>
5422    <t>
5423      Synchronize core rules with RFC5234.
5424    </t>
5425    <t>
5426      Get rid of prose rules that span multiple lines.
5427    </t>
5428    <t>
5429      Get rid of unused rules LOALPHA and UPALPHA.
5430    </t>
5431    <t>
5432      Move "Product Tokens" section (back) into Part 1, as "token" is used
5433      in the definition of the Upgrade header field.
5434    </t>
5435    <t>
5436      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5437    </t>
5438    <t>
5439      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5440    </t>
5441  </list>
5445<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5447  Closed issues:
5448  <list style="symbols">
5449    <t>
5450      <eref target=""/>:
5451      "HTTP-date vs. rfc1123-date"
5452    </t>
5453    <t>
5454      <eref target=""/>:
5455      "WS in quoted-pair"
5456    </t>
5457  </list>
5460  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5461  <list style="symbols">
5462    <t>
5463      Reference RFC 3984, and update header field registrations for headers defined
5464      in this document.
5465    </t>
5466  </list>
5469  Ongoing work on ABNF conversion (<eref target=""/>):
5470  <list style="symbols">
5471    <t>
5472      Replace string literals when the string really is case-sensitive (HTTP-Version).
5473    </t>
5474  </list>
5478<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5480  Closed issues:
5481  <list style="symbols">
5482    <t>
5483      <eref target=""/>:
5484      "Connection closing"
5485    </t>
5486    <t>
5487      <eref target=""/>:
5488      "Move registrations and registry information to IANA Considerations"
5489    </t>
5490    <t>
5491      <eref target=""/>:
5492      "need new URL for PAD1995 reference"
5493    </t>
5494    <t>
5495      <eref target=""/>:
5496      "IANA Considerations: update HTTP URI scheme registration"
5497    </t>
5498    <t>
5499      <eref target=""/>:
5500      "Cite HTTPS URI scheme definition"
5501    </t>
5502    <t>
5503      <eref target=""/>:
5504      "List-type headers vs Set-Cookie"
5505    </t>
5506  </list>
5509  Ongoing work on ABNF conversion (<eref target=""/>):
5510  <list style="symbols">
5511    <t>
5512      Replace string literals when the string really is case-sensitive (HTTP-Date).
5513    </t>
5514    <t>
5515      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5516    </t>
5517  </list>
5521<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5523  Closed issues:
5524  <list style="symbols">
5525    <t>
5526      <eref target=""/>:
5527      "Out-of-date reference for URIs"
5528    </t>
5529    <t>
5530      <eref target=""/>:
5531      "RFC 2822 is updated by RFC 5322"
5532    </t>
5533  </list>
5536  Ongoing work on ABNF conversion (<eref target=""/>):
5537  <list style="symbols">
5538    <t>
5539      Use "/" instead of "|" for alternatives.
5540    </t>
5541    <t>
5542      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5543    </t>
5544    <t>
5545      Only reference RFC 5234's core rules.
5546    </t>
5547    <t>
5548      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5549      whitespace ("OWS") and required whitespace ("RWS").
5550    </t>
5551    <t>
5552      Rewrite ABNFs to spell out whitespace rules, factor out
5553      header field value format definitions.
5554    </t>
5555  </list>
5559<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5561  Closed issues:
5562  <list style="symbols">
5563    <t>
5564      <eref target=""/>:
5565      "Header LWS"
5566    </t>
5567    <t>
5568      <eref target=""/>:
5569      "Sort 1.3 Terminology"
5570    </t>
5571    <t>
5572      <eref target=""/>:
5573      "RFC2047 encoded words"
5574    </t>
5575    <t>
5576      <eref target=""/>:
5577      "Character Encodings in TEXT"
5578    </t>
5579    <t>
5580      <eref target=""/>:
5581      "Line Folding"
5582    </t>
5583    <t>
5584      <eref target=""/>:
5585      "OPTIONS * and proxies"
5586    </t>
5587    <t>
5588      <eref target=""/>:
5589      "Reason-Phrase BNF"
5590    </t>
5591    <t>
5592      <eref target=""/>:
5593      "Use of TEXT"
5594    </t>
5595    <t>
5596      <eref target=""/>:
5597      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5598    </t>
5599    <t>
5600      <eref target=""/>:
5601      "RFC822 reference left in discussion of date formats"
5602    </t>
5603  </list>
5606  Final work on ABNF conversion (<eref target=""/>):
5607  <list style="symbols">
5608    <t>
5609      Rewrite definition of list rules, deprecate empty list elements.
5610    </t>
5611    <t>
5612      Add appendix containing collected and expanded ABNF.
5613    </t>
5614  </list>
5617  Other changes:
5618  <list style="symbols">
5619    <t>
5620      Rewrite introduction; add mostly new Architecture Section.
5621    </t>
5622    <t>
5623      Move definition of quality values from Part 3 into Part 1;
5624      make TE request header field grammar independent of accept-params (defined in Part 3).
5625    </t>
5626  </list>
5630<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5632  Closed issues:
5633  <list style="symbols">
5634    <t>
5635      <eref target=""/>:
5636      "base for numeric protocol elements"
5637    </t>
5638    <t>
5639      <eref target=""/>:
5640      "comment ABNF"
5641    </t>
5642  </list>
5645  Partly resolved issues:
5646  <list style="symbols">
5647    <t>
5648      <eref target=""/>:
5649      "205 Bodies" (took out language that implied that there might be
5650      methods for which a request body MUST NOT be included)
5651    </t>
5652    <t>
5653      <eref target=""/>:
5654      "editorial improvements around HTTP-date"
5655    </t>
5656  </list>
5660<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5662  Closed issues:
5663  <list style="symbols">
5664    <t>
5665      <eref target=""/>:
5666      "Repeating single-value headers"
5667    </t>
5668    <t>
5669      <eref target=""/>:
5670      "increase connection limit"
5671    </t>
5672    <t>
5673      <eref target=""/>:
5674      "IP addresses in URLs"
5675    </t>
5676    <t>
5677      <eref target=""/>:
5678      "take over HTTP Upgrade Token Registry"
5679    </t>
5680    <t>
5681      <eref target=""/>:
5682      "CR and LF in chunk extension values"
5683    </t>
5684    <t>
5685      <eref target=""/>:
5686      "HTTP/0.9 support"
5687    </t>
5688    <t>
5689      <eref target=""/>:
5690      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5691    </t>
5692    <t>
5693      <eref target=""/>:
5694      "move definitions of gzip/deflate/compress to part 1"
5695    </t>
5696    <t>
5697      <eref target=""/>:
5698      "disallow control characters in quoted-pair"
5699    </t>
5700  </list>
5703  Partly resolved issues:
5704  <list style="symbols">
5705    <t>
5706      <eref target=""/>:
5707      "update IANA requirements wrt Transfer-Coding values" (add the
5708      IANA Considerations subsection)
5709    </t>
5710  </list>
5714<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5716  Closed issues:
5717  <list style="symbols">
5718    <t>
5719      <eref target=""/>:
5720      "header parsing, treatment of leading and trailing OWS"
5721    </t>
5722  </list>
5725  Partly resolved issues:
5726  <list style="symbols">
5727    <t>
5728      <eref target=""/>:
5729      "Placement of 13.5.1 and 13.5.2"
5730    </t>
5731    <t>
5732      <eref target=""/>:
5733      "use of term "word" when talking about header structure"
5734    </t>
5735  </list>
5739<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5741  Closed issues:
5742  <list style="symbols">
5743    <t>
5744      <eref target=""/>:
5745      "Clarification of the term 'deflate'"
5746    </t>
5747    <t>
5748      <eref target=""/>:
5749      "OPTIONS * and proxies"
5750    </t>
5751    <t>
5752      <eref target=""/>:
5753      "MIME-Version not listed in P1, general header fields"
5754    </t>
5755    <t>
5756      <eref target=""/>:
5757      "IANA registry for content/transfer encodings"
5758    </t>
5759    <t>
5760      <eref target=""/>:
5761      "Case-sensitivity of HTTP-date"
5762    </t>
5763    <t>
5764      <eref target=""/>:
5765      "use of term "word" when talking about header structure"
5766    </t>
5767  </list>
5770  Partly resolved issues:
5771  <list style="symbols">
5772    <t>
5773      <eref target=""/>:
5774      "Term for the requested resource's URI"
5775    </t>
5776  </list>
5780<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5782  Closed issues:
5783  <list style="symbols">
5784    <t>
5785      <eref target=""/>:
5786      "Connection Closing"
5787    </t>
5788    <t>
5789      <eref target=""/>:
5790      "Delimiting messages with multipart/byteranges"
5791    </t>
5792    <t>
5793      <eref target=""/>:
5794      "Handling multiple Content-Length headers"
5795    </t>
5796    <t>
5797      <eref target=""/>:
5798      "Clarify entity / representation / variant terminology"
5799    </t>
5800    <t>
5801      <eref target=""/>:
5802      "consider removing the 'changes from 2068' sections"
5803    </t>
5804  </list>
5807  Partly resolved issues:
5808  <list style="symbols">
5809    <t>
5810      <eref target=""/>:
5811      "HTTP(s) URI scheme definitions"
5812    </t>
5813  </list>
5817<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5819  Closed issues:
5820  <list style="symbols">
5821    <t>
5822      <eref target=""/>:
5823      "Trailer requirements"
5824    </t>
5825    <t>
5826      <eref target=""/>:
5827      "Text about clock requirement for caches belongs in p6"
5828    </t>
5829    <t>
5830      <eref target=""/>:
5831      "effective request URI: handling of missing host in HTTP/1.0"
5832    </t>
5833    <t>
5834      <eref target=""/>:
5835      "confusing Date requirements for clients"
5836    </t>
5837  </list>
5840  Partly resolved issues:
5841  <list style="symbols">
5842    <t>
5843      <eref target=""/>:
5844      "Handling multiple Content-Length headers"
5845    </t>
5846  </list>
5850<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5852  Closed issues:
5853  <list style="symbols">
5854    <t>
5855      <eref target=""/>:
5856      "RFC2145 Normative"
5857    </t>
5858    <t>
5859      <eref target=""/>:
5860      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5861    </t>
5862    <t>
5863      <eref target=""/>:
5864      "define 'transparent' proxy"
5865    </t>
5866    <t>
5867      <eref target=""/>:
5868      "Header Classification"
5869    </t>
5870    <t>
5871      <eref target=""/>:
5872      "Is * usable as a request-uri for new methods?"
5873    </t>
5874    <t>
5875      <eref target=""/>:
5876      "Migrate Upgrade details from RFC2817"
5877    </t>
5878    <t>
5879      <eref target=""/>:
5880      "untangle ABNFs for header fields"
5881    </t>
5882    <t>
5883      <eref target=""/>:
5884      "update RFC 2109 reference"
5885    </t>
5886  </list>
5890<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5892  Closed issues:
5893  <list style="symbols">
5894    <t>
5895      <eref target=""/>:
5896      "Content-Length ABNF broken"
5897    </t>
5898  </list>
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