source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1214

Last change on this file since 1214 was 1214, checked in by fielding@…, 11 years ago

Adjust handling of duplicate content-length to allow recipient
to reject the message. Addresses #95

  • Property svn:eol-style set to native
File size: 249.8 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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 connection. An HTTP
535   "client" is a program that establishes a connection to a server for the
536   purpose of sending one or more HTTP requests.  An HTTP "server" is a
537   program that accepts connections in order to service HTTP requests by
538   sending HTTP responses.
540<iref primary="true" item="user agent"/>
541<iref primary="true" item="origin server"/>
542<iref primary="true" item="browser"/>
543<iref primary="true" item="spider"/>
545   Note that the terms client and server refer only to the roles that
546   these programs perform for a particular connection.  The same program
547   might act as a client on some connections and a server on others.  We use
548   the term "user agent" to refer to the program that initiates a request,
549   such as a WWW browser, editor, or spider (web-traversing robot), and
550   the term "origin server" to refer to the program that can originate
551   authoritative responses to a request.  For general requirements, we use
552   the term "sender" to refer to whichever component sent a given message
553   and the term "recipient" to refer to any component that receives the
554   message.
557   Most HTTP communication consists of a retrieval request (GET) for
558   a representation of some resource identified by a URI.  In the
559   simplest case, this might be accomplished via a single bidirectional
560   connection (===) between the user agent (UA) and the origin server (O).
562<figure><artwork type="drawing">
563         request   &gt;
564    UA ======================================= O
565                                &lt;   response
567<iref primary="true" item="message"/>
568<iref primary="true" item="request"/>
569<iref primary="true" item="response"/>
571   A client sends an HTTP request to the server in the form of a request
572   message (<xref target="request"/>), beginning with a method, URI, and
573   protocol version, followed by MIME-like header fields containing
574   request modifiers, client information, and payload metadata, an empty
575   line to indicate the end of the header section, and finally the payload
576   body (if any).
579   A server responds to the client's request by sending an HTTP response
580   message (<xref target="response"/>), beginning with a status line that
581   includes the protocol version, a success or error code, and textual
582   reason phrase, followed by MIME-like header fields containing server
583   information, resource metadata, and payload metadata, an empty line to
584   indicate the end of the header section, and finally the payload body (if any).
587   The following example illustrates a typical message exchange for a
588   GET request on the URI "":
591client request:
592</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
593GET /hello.txt HTTP/1.1
594User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
596Accept: */*
600server response:
601</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
602HTTP/1.1 200 OK
603Date: Mon, 27 Jul 2009 12:28:53 GMT
604Server: Apache
605Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
606ETag: "34aa387-d-1568eb00"
607Accept-Ranges: bytes
608Content-Length: <x:length-of target="exbody"/>
609Vary: Accept-Encoding
610Content-Type: text/plain
612<x:span anchor="exbody">Hello World!
616<section title="Connections and Transport Independence" anchor="transport-independence">
618   HTTP messaging is independent of the underlying transport or
619   session-layer connection protocol(s).  HTTP only presumes a reliable
620   transport with in-order delivery of requests and the corresponding
621   in-order delivery of responses.  The mapping of HTTP request and
622   response structures onto the data units of the underlying transport
623   protocol is outside the scope of this specification.
626   The specific connection protocols to be used for an interaction
627   are determined by client configuration and the target resource's URI.
628   For example, the "http" URI scheme
629   (<xref target="http.uri"/>) indicates a default connection of TCP
630   over IP, with a default TCP port of 80, but the client might be
631   configured to use a proxy via some other connection port or protocol
632   instead of using the defaults.
635   A connection might be used for multiple HTTP request/response exchanges,
636   as defined in <xref target="persistent.connections"/>.
640<section title="Intermediaries" anchor="intermediaries">
641<iref primary="true" item="intermediary"/>
643   HTTP enables the use of intermediaries to satisfy requests through
644   a chain of connections.  There are three common forms of HTTP
645   intermediary: proxy, gateway, and tunnel.  In some cases,
646   a single intermediary might act as an origin server, proxy, gateway,
647   or tunnel, switching behavior based on the nature of each request.
649<figure><artwork type="drawing">
650         &gt;             &gt;             &gt;             &gt;
651    UA =========== A =========== B =========== C =========== O
652               &lt;             &lt;             &lt;             &lt;
655   The figure above shows three intermediaries (A, B, and C) between the
656   user agent and origin server. A request or response message that
657   travels the whole chain will pass through four separate connections.
658   Some HTTP communication options
659   might apply only to the connection with the nearest, non-tunnel
660   neighbor, only to the end-points of the chain, or to all connections
661   along the chain. Although the diagram is linear, each participant might
662   be engaged in multiple, simultaneous communications. For example, B
663   might be receiving requests from many clients other than A, and/or
664   forwarding requests to servers other than C, at the same time that it
665   is handling A's request.
668<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
669<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
670   We use the terms "upstream" and "downstream" to describe various
671   requirements in relation to the directional flow of a message:
672   all messages flow from upstream to downstream.
673   Likewise, we use the terms "inbound" and "outbound" to refer to
674   directions in relation to the request path: "inbound" means toward
675   the origin server and "outbound" means toward the user agent.
677<t><iref primary="true" item="proxy"/>
678   A "proxy" is a message forwarding agent that is selected by the
679   client, usually via local configuration rules, to receive requests
680   for some type(s) of absolute URI and attempt to satisfy those
681   requests via translation through the HTTP interface.  Some translations
682   are minimal, such as for proxy requests for "http" URIs, whereas
683   other requests might require translation to and from entirely different
684   application-layer protocols. Proxies are often used to group an
685   organization's HTTP requests through a common intermediary for the
686   sake of security, annotation services, or shared caching.
689<iref primary="true" item="transforming proxy"/>
690<iref primary="true" item="non-transforming proxy"/>
691   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
692   or configured to modify request or response messages in a semantically
693   meaningful way (i.e., modifications, beyond those required by normal
694   HTTP processing, that change the message in a way that would be
695   significant to the original sender or potentially significant to
696   downstream recipients).  For example, a transforming proxy might be
697   acting as a shared annotation server (modifying responses to include
698   references to a local annotation database), a malware filter, a
699   format transcoder, or an intranet-to-Internet privacy filter.  Such
700   transformations are presumed to be desired by the client (or client
701   organization) that selected the proxy and are beyond the scope of
702   this specification.  However, when a proxy is not intended to transform
703   a given message, we use the term "non-transforming proxy" to target
704   requirements that preserve HTTP message semantics.
706<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
707<iref primary="true" item="accelerator"/>
708   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
709   as a layer above some other server(s) and translates the received
710   requests to the underlying server's protocol.  Gateways are often
711   used to encapsulate legacy or untrusted information services, to
712   improve server performance through "accelerator" caching, and to
713   enable partitioning or load-balancing of HTTP services across
714   multiple machines.
717   A gateway behaves as an origin server on its outbound connection and
718   as a user agent on its inbound connection.
719   All HTTP requirements applicable to an origin server
720   also apply to the outbound communication of a gateway.
721   A gateway communicates with inbound servers using any protocol that
722   it desires, including private extensions to HTTP that are outside
723   the scope of this specification.  However, an HTTP-to-HTTP gateway
724   that wishes to interoperate with third-party HTTP servers &MUST;
725   comply with HTTP user agent requirements on the gateway's inbound
726   connection and &MUST; implement the Connection
727   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
728   header fields for both connections.
730<t><iref primary="true" item="tunnel"/>
731   A "tunnel" acts as a blind relay between two connections
732   without changing the messages. Once active, a tunnel is not
733   considered a party to the HTTP communication, though the tunnel might
734   have been initiated by an HTTP request. A tunnel ceases to exist when
735   both ends of the relayed connection are closed. Tunnels are used to
736   extend a virtual connection through an intermediary, such as when
737   transport-layer security is used to establish private communication
738   through a shared firewall proxy.
740<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
741<iref primary="true" item="captive portal"/>
742   In addition, there may exist network intermediaries that are not
743   considered part of the HTTP communication but nevertheless act as
744   filters or redirecting agents (usually violating HTTP semantics,
745   causing security problems, and otherwise making a mess of things).
746   Such a network intermediary, often referred to as an "interception proxy"
747   <xref target="RFC3040"/>, "transparent proxy" <xref target="RFC1919"/>,
748   or "captive portal",
749   differs from an HTTP proxy because it has not been selected by the client.
750   Instead, the network intermediary redirects outgoing TCP port 80 packets
751   (and occasionally other common port traffic) to an internal HTTP server.
752   Interception proxies are commonly found on public network access points,
753   as a means of enforcing account subscription prior to allowing use of
754   non-local Internet services, and within corporate firewalls to enforce
755   network usage policies.
756   They are indistinguishable from a man-in-the-middle attack.
760<section title="Caches" anchor="caches">
761<iref primary="true" item="cache"/>
763   A "cache" is a local store of previous response messages and the
764   subsystem that controls its message storage, retrieval, and deletion.
765   A cache stores cacheable responses in order to reduce the response
766   time and network bandwidth consumption on future, equivalent
767   requests. Any client or server &MAY; employ a cache, though a cache
768   cannot be used by a server while it is acting as a tunnel.
771   The effect of a cache is that the request/response chain is shortened
772   if one of the participants along the chain has a cached response
773   applicable to that request. The following illustrates the resulting
774   chain if B has a cached copy of an earlier response from O (via C)
775   for a request which has not been cached by UA or A.
777<figure><artwork type="drawing">
778            &gt;             &gt;
779       UA =========== A =========== B - - - - - - C - - - - - - O
780                  &lt;             &lt;
782<t><iref primary="true" item="cacheable"/>
783   A response is "cacheable" if a cache is allowed to store a copy of
784   the response message for use in answering subsequent requests.
785   Even when a response is cacheable, there might be additional
786   constraints placed by the client or by the origin server on when
787   that cached response can be used for a particular request. HTTP
788   requirements for cache behavior and cacheable responses are
789   defined in &caching-overview;. 
792   There are a wide variety of architectures and configurations
793   of caches and proxies deployed across the World Wide Web and
794   inside large organizations. These systems include national hierarchies
795   of proxy caches to save transoceanic bandwidth, systems that
796   broadcast or multicast cache entries, organizations that distribute
797   subsets of cached data via optical media, and so on.
801<section title="Protocol Versioning" anchor="http.version">
802  <x:anchor-alias value="HTTP-Version"/>
803  <x:anchor-alias value="HTTP-Prot-Name"/>
805   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
806   versions of the protocol. This specification defines version "1.1".
807   The protocol version as a whole indicates the sender's compliance
808   with the set of requirements laid out in that version's corresponding
809   specification of HTTP.
812   The version of an HTTP message is indicated by an HTTP-Version field
813   in the first line of the message. HTTP-Version is case-sensitive.
815<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
816  <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>
817  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
820   The HTTP version number consists of two non-negative decimal integers
821   separated by a "." (period or decimal point).  The first
822   number ("major version") indicates the HTTP messaging syntax, whereas
823   the second number ("minor version") indicates the highest minor
824   version to which the sender is at least conditionally compliant and
825   able to understand for future communication.  The minor version
826   advertises the sender's communication capabilities even when the
827   sender is only using a backwards-compatible subset of the protocol,
828   thereby letting the recipient know that more advanced features can
829   be used in response (by servers) or in future requests (by clients).
832   When comparing HTTP versions, the numbers &MUST; be compared
833   numerically rather than lexically.  For example, HTTP/2.4 is a lower
834   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
835   Leading zeros &MUST; be ignored by recipients and &MUST-NOT; be sent.
838   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
839   <xref target="RFC1945"/> or a recipient whose version is unknown,
840   the HTTP/1.1 message is constructed such that it can be interpreted
841   as a valid HTTP/1.0 message if all of the newer features are ignored.
842   This specification places recipient-version requirements on some
843   new features so that a compliant sender will only use compatible
844   features until it has determined, through configuration or the
845   receipt of a message, that the recipient supports HTTP/1.1.
848   The interpretation of an HTTP header field does not change
849   between minor versions of the same major version, though the default
850   behavior of a recipient in the absence of such a field can change.
851   Unless specified otherwise, header fields defined in HTTP/1.1 are
852   defined for all versions of HTTP/1.x.  In particular, the Host and
853   Connection header fields ought to be implemented by all HTTP/1.x
854   implementations whether or not they advertise compliance with HTTP/1.1.
857   New header fields can be defined such that, when they are
858   understood by a recipient, they might override or enhance the
859   interpretation of previously defined header fields.  When an
860   implementation receives an unrecognized header field, the recipient
861   &MUST; ignore that header field for local processing regardless of
862   the message's HTTP version.  An unrecognized header field received
863   by a proxy &MUST; be forwarded downstream unless the header field's
864   field-name is listed in the message's Connection header-field
865   (see <xref target="header.connection"/>).
866   These requirements allow HTTP's functionality to be enhanced without
867   requiring prior update of all compliant intermediaries.
870   Intermediaries that process HTTP messages (i.e., all intermediaries
871   other than those acting as a tunnel) &MUST; send their own HTTP-Version
872   in forwarded messages.  In other words, they &MUST-NOT; blindly
873   forward the first line of an HTTP message without ensuring that the
874   protocol version matches what the intermediary understands, and
875   is at least conditionally compliant to, for both the receiving and
876   sending of messages.  Forwarding an HTTP message without rewriting
877   the HTTP-Version might result in communication errors when downstream
878   recipients use the message sender's version to determine what features
879   are safe to use for later communication with that sender.
882   An HTTP client &SHOULD; send a request version equal to the highest
883   version for which the client is at least conditionally compliant and
884   whose major version is no higher than the highest version supported
885   by the server, if this is known.  An HTTP client &MUST-NOT; send a
886   version for which it is not at least conditionally compliant.
889   An HTTP client &MAY; send a lower request version if it is known that
890   the server incorrectly implements the HTTP specification, but only
891   after the client has attempted at least one normal request and determined
892   from the response status or header fields (e.g., Server) that the
893   server improperly handles higher request versions.
896   An HTTP server &SHOULD; send a response version equal to the highest
897   version for which the server is at least conditionally compliant and
898   whose major version is less than or equal to the one received in the
899   request.  An HTTP server &MUST-NOT; send a version for which it is not
900   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
901   Version Not Supported) response if it cannot send a response using the
902   major version used in the client's request.
905   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
906   if it is known or suspected that the client incorrectly implements the
907   HTTP specification and is incapable of correctly processing later
908   version responses, such as when a client fails to parse the version
909   number correctly or when an intermediary is known to blindly forward
910   the HTTP-Version even when it doesn't comply with the given minor
911   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
912   performed unless triggered by specific client attributes, such as when
913   one or more of the request header fields (e.g., User-Agent) uniquely
914   match the values sent by a client known to be in error.
917   The intention of HTTP's versioning design is that the major number
918   will only be incremented if an incompatible message syntax is
919   introduced, and that the minor number will only be incremented when
920   changes made to the protocol have the effect of adding to the message
921   semantics or implying additional capabilities of the sender.  However,
922   the minor version was not incremented for the changes introduced between
923   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
924   is specifically avoiding any such changes to the protocol.
928<section title="Uniform Resource Identifiers" anchor="uri">
929<iref primary="true" item="resource"/>
931   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
932   throughout HTTP as the means for identifying resources. URI references
933   are used to target requests, indicate redirects, and define relationships.
934   HTTP does not limit what a resource might be; it merely defines an interface
935   that can be used to interact with a resource via HTTP. More information on
936   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
938  <x:anchor-alias value="URI-reference"/>
939  <x:anchor-alias value="absolute-URI"/>
940  <x:anchor-alias value="relative-part"/>
941  <x:anchor-alias value="authority"/>
942  <x:anchor-alias value="path-abempty"/>
943  <x:anchor-alias value="path-absolute"/>
944  <x:anchor-alias value="port"/>
945  <x:anchor-alias value="query"/>
946  <x:anchor-alias value="uri-host"/>
947  <x:anchor-alias value="partial-URI"/>
949   This specification adopts the definitions of "URI-reference",
950   "absolute-URI", "relative-part", "port", "host",
951   "path-abempty", "path-absolute", "query", and "authority" from the
952   URI generic syntax <xref target="RFC3986"/>.
953   In addition, we define a partial-URI rule for protocol elements
954   that allow a relative URI but not a fragment.
956<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"/>
957  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
958  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
959  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
960  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
961  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
962  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
963  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
964  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
965  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
967  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
970   Each protocol element in HTTP that allows a URI reference will indicate
971   in its ABNF production whether the element allows any form of reference
972   (URI-reference), only a URI in absolute form (absolute-URI), only the
973   path and optional query components, or some combination of the above.
974   Unless otherwise indicated, URI references are parsed relative to the
975   effective request URI, which defines the default base URI for references
976   in both the request and its corresponding response.
979<section title="http URI scheme" anchor="http.uri">
980  <x:anchor-alias value="http-URI"/>
981  <iref item="http URI scheme" primary="true"/>
982  <iref item="URI scheme" subitem="http" primary="true"/>
984   The "http" URI scheme is hereby defined for the purpose of minting
985   identifiers according to their association with the hierarchical
986   namespace governed by a potential HTTP origin server listening for
987   TCP connections on a given port.
989<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
990  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
993   The HTTP origin server is identified by the generic syntax's
994   <x:ref>authority</x:ref> component, which includes a host identifier
995   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
996   The remainder of the URI, consisting of both the hierarchical path
997   component and optional query component, serves as an identifier for
998   a potential resource within that origin server's name space.
1001   If the host identifier is provided as an IP literal or IPv4 address,
1002   then the origin server is any listener on the indicated TCP port at
1003   that IP address. If host is a registered name, then that name is
1004   considered an indirect identifier and the recipient might use a name
1005   resolution service, such as DNS, to find the address of a listener
1006   for that host.
1007   The host &MUST-NOT; be empty; if an "http" URI is received with an
1008   empty host, then it &MUST; be rejected as invalid.
1009   If the port subcomponent is empty or not given, then TCP port 80 is
1010   assumed (the default reserved port for WWW services).
1013   Regardless of the form of host identifier, access to that host is not
1014   implied by the mere presence of its name or address. The host might or might
1015   not exist and, even when it does exist, might or might not be running an
1016   HTTP server or listening to the indicated port. The "http" URI scheme
1017   makes use of the delegated nature of Internet names and addresses to
1018   establish a naming authority (whatever entity has the ability to place
1019   an HTTP server at that Internet name or address) and allows that
1020   authority to determine which names are valid and how they might be used.
1023   When an "http" URI is used within a context that calls for access to the
1024   indicated resource, a client &MAY; attempt access by resolving
1025   the host to an IP address, establishing a TCP connection to that address
1026   on the indicated port, and sending an HTTP request message to the server
1027   containing the URI's identifying data as described in <xref target="request"/>.
1028   If the server responds to that request with a non-interim HTTP response
1029   message, as described in <xref target="response"/>, then that response
1030   is considered an authoritative answer to the client's request.
1033   Although HTTP is independent of the transport protocol, the "http"
1034   scheme is specific to TCP-based services because the name delegation
1035   process depends on TCP for establishing authority.
1036   An HTTP service based on some other underlying connection protocol
1037   would presumably be identified using a different URI scheme, just as
1038   the "https" scheme (below) is used for servers that require an SSL/TLS
1039   transport layer on a connection. Other protocols might also be used to
1040   provide access to "http" identified resources &mdash; it is only the
1041   authoritative interface used for mapping the namespace that is
1042   specific to TCP.
1045   The URI generic syntax for authority also includes a deprecated
1046   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1047   for including user authentication information in the URI.  Some
1048   implementations make use of the userinfo component for internal
1049   configuration of authentication information, such as within command
1050   invocation options, configuration files, or bookmark lists, even
1051   though such usage might expose a user identifier or password.
1052   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1053   delimiter) when transmitting an "http" URI in a message.  Recipients
1054   of HTTP messages that contain a URI reference &SHOULD; parse for the
1055   existence of userinfo and treat its presence as an error, likely
1056   indicating that the deprecated subcomponent is being used to obscure
1057   the authority for the sake of phishing attacks.
1061<section title="https URI scheme" anchor="https.uri">
1062   <x:anchor-alias value="https-URI"/>
1063   <iref item="https URI scheme"/>
1064   <iref item="URI scheme" subitem="https"/>
1066   The "https" URI scheme is hereby defined for the purpose of minting
1067   identifiers according to their association with the hierarchical
1068   namespace governed by a potential HTTP origin server listening for
1069   SSL/TLS-secured connections on a given TCP port.
1072   All of the requirements listed above for the "http" scheme are also
1073   requirements for the "https" scheme, except that a default TCP port
1074   of 443 is assumed if the port subcomponent is empty or not given,
1075   and the TCP connection &MUST; be secured for privacy through the
1076   use of strong encryption prior to sending the first HTTP request.
1078<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1079  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1082   Unlike the "http" scheme, responses to "https" identified requests
1083   are never "public" and thus &MUST-NOT; be reused for shared caching.
1084   They can, however, be reused in a private cache if the message is
1085   cacheable by default in HTTP or specifically indicated as such by
1086   the Cache-Control header field (&header-cache-control;).
1089   Resources made available via the "https" scheme have no shared
1090   identity with the "http" scheme even if their resource identifiers
1091   indicate the same authority (the same host listening to the same
1092   TCP port).  They are distinct name spaces and are considered to be
1093   distinct origin servers.  However, an extension to HTTP that is
1094   defined to apply to entire host domains, such as the Cookie protocol
1095   <xref target="draft-ietf-httpstate-cookie"/>, can allow information
1096   set by one service to impact communication with other services
1097   within a matching group of host domains.
1100   The process for authoritative access to an "https" identified
1101   resource is defined in <xref target="RFC2818"/>.
1105<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1107   Since the "http" and "https" schemes conform to the URI generic syntax,
1108   such URIs are normalized and compared according to the algorithm defined
1109   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1110   described above for each scheme.
1113   If the port is equal to the default port for a scheme, the normal
1114   form is to elide the port subcomponent. Likewise, an empty path
1115   component is equivalent to an absolute path of "/", so the normal
1116   form is to provide a path of "/" instead. The scheme and host
1117   are case-insensitive and normally provided in lowercase; all
1118   other components are compared in a case-sensitive manner.
1119   Characters other than those in the "reserved" set are equivalent
1120   to their percent-encoded octets (see <xref target="RFC3986"
1121   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1124   For example, the following three URIs are equivalent:
1126<figure><artwork type="example">
1135<section title="Message Format" anchor="http.message">
1136<x:anchor-alias value="generic-message"/>
1137<x:anchor-alias value="message.types"/>
1138<x:anchor-alias value="HTTP-message"/>
1139<x:anchor-alias value="start-line"/>
1140<iref item="header section"/>
1141<iref item="headers"/>
1142<iref item="header field"/>
1144   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1145   octets in a format similar to the Internet Message Format
1146   <xref target="RFC5322"/>: zero or more header fields (collectively
1147   referred to as the "headers" or the "header section"), an empty line
1148   indicating the end of the header section, and an optional message-body.
1151   An HTTP message can either be a request from client to server or a
1152   response from server to client.  Syntactically, the two types of message
1153   differ only in the start-line, which is either a Request-Line (for requests)
1154   or a Status-Line (for responses), and in the algorithm for determining
1155   the length of the message-body (<xref target="message.body"/>).
1156   In theory, a client could receive requests and a server could receive
1157   responses, distinguishing them by their different start-line formats,
1158   but in practice servers are implemented to only expect a request
1159   (a response is interpreted as an unknown or invalid request method)
1160   and clients are implemented to only expect a response.
1162<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1163  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1164                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1165                    <x:ref>CRLF</x:ref>
1166                    [ <x:ref>message-body</x:ref> ]
1167  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1170   Implementations &MUST-NOT; send whitespace between the start-line and
1171   the first header field. The presence of such whitespace in a request
1172   might be an attempt to trick a server into ignoring that field or
1173   processing the line after it as a new request, either of which might
1174   result in a security vulnerability if other implementations within
1175   the request chain interpret the same message differently.
1176   Likewise, the presence of such whitespace in a response might be
1177   ignored by some clients or cause others to cease parsing.
1180<section title="Message Parsing Robustness" anchor="message.robustness">
1182   In the interest of robustness, servers &SHOULD; ignore at least one
1183   empty line received where a Request-Line is expected. In other words, if
1184   the server is reading the protocol stream at the beginning of a
1185   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1188   Some old HTTP/1.0 client implementations send an extra CRLF
1189   after a POST request as a lame workaround for some early server
1190   applications that failed to read message-body content that was
1191   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1192   preface or follow a request with an extra CRLF.  If terminating
1193   the request message-body with a line-ending is desired, then the
1194   client &MUST; include the terminating CRLF octets as part of the
1195   message-body length.
1198   When a server listening only for HTTP request messages, or processing
1199   what appears from the start-line to be an HTTP request message,
1200   receives a sequence of octets that does not match the HTTP-message
1201   grammar aside from the robustness exceptions listed above, the
1202   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1205   The normal procedure for parsing an HTTP message is to read the
1206   start-line into a structure, read each header field into a hash
1207   table by field name until the empty line, and then use the parsed
1208   data to determine if a message-body is expected.  If a message-body
1209   has been indicated, then it is read as a stream until an amount
1210   of octets equal to the message-body length is read or the connection
1211   is closed.  Care must be taken to parse an HTTP message as a sequence
1212   of octets in an encoding that is a superset of US-ASCII.  Attempting
1213   to parse HTTP as a stream of Unicode characters in a character encoding
1214   like UTF-16 might introduce security flaws due to the differing ways
1215   that such parsers interpret invalid characters.
1218   HTTP allows the set of defined header fields to be extended without
1219   changing the protocol version (see <xref target="header.field.registration"/>).
1220   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1221   proxy is specifically configured to block or otherwise transform such
1222   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1226<section title="Header Fields" anchor="header.fields">
1227  <x:anchor-alias value="header-field"/>
1228  <x:anchor-alias value="field-content"/>
1229  <x:anchor-alias value="field-name"/>
1230  <x:anchor-alias value="field-value"/>
1231  <x:anchor-alias value="OWS"/>
1233   Each HTTP header field consists of a case-insensitive field name
1234   followed by a colon (":"), optional whitespace, and the field value.
1236<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"/>
1237  <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>
1238  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1239  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1240  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1243   No whitespace is allowed between the header field name and colon. For
1244   security reasons, any request message received containing such whitespace
1245   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1246   &MUST; remove any such whitespace from a response message before
1247   forwarding the message downstream.
1250   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1251   preferred. The field value does not include any leading or trailing white
1252   space: OWS occurring before the first non-whitespace octet of the
1253   field value or after the last non-whitespace octet of the field value
1254   is ignored and &SHOULD; be removed before further processing (as this does
1255   not change the meaning of the header field).
1258   The order in which header fields with differing field names are
1259   received is not significant. However, it is "good practice" to send
1260   header fields that contain control data first, such as Host on
1261   requests and Date on responses, so that implementations can decide
1262   when not to handle a message as early as possible.  A server &MUST;
1263   wait until the entire header section is received before interpreting
1264   a request message, since later header fields might include conditionals,
1265   authentication credentials, or deliberately misleading duplicate
1266   header fields that would impact request processing.
1269   Multiple header fields with the same field name &MUST-NOT; be
1270   sent in a message unless the entire field value for that
1271   header field is defined as a comma-separated list [i.e., #(values)].
1272   Multiple header fields with the same field name can be combined into
1273   one "field-name: field-value" pair, without changing the semantics of the
1274   message, by appending each subsequent field value to the combined
1275   field value in order, separated by a comma. The order in which
1276   header fields with the same field name are received is therefore
1277   significant to the interpretation of the combined field value;
1278   a proxy &MUST-NOT; change the order of these field values when
1279   forwarding a message.
1282  <t>
1283   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1284   practice can occur multiple times, but does not use the list syntax, and
1285   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1286   for details.) Also note that the Set-Cookie2 header field specified in
1287   <xref target="RFC2965"/> does not share this problem.
1288  </t>
1291   Historically, HTTP header field values could be extended over multiple
1292   lines by preceding each extra line with at least one space or horizontal
1293   tab octet (line folding). This specification deprecates such line
1294   folding except within the message/http media type
1295   (<xref target=""/>).
1296   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1297   (i.e., that contain any field-content that matches the obs-fold rule) unless
1298   the message is intended for packaging within the message/http media type.
1299   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1300   obs-fold whitespace with a single SP prior to interpreting the field value
1301   or forwarding the message downstream.
1304   Historically, HTTP has allowed field content with text in the ISO-8859-1
1305   <xref target="ISO-8859-1"/> character encoding and supported other
1306   character sets only through use of <xref target="RFC2047"/> encoding.
1307   In practice, most HTTP header field values use only a subset of the
1308   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1309   header fields &SHOULD; limit their field values to US-ASCII octets.
1310   Recipients &SHOULD; treat other (obs-text) octets in field content as
1311   opaque data.
1313<t anchor="rule.comment">
1314  <x:anchor-alias value="comment"/>
1315  <x:anchor-alias value="ctext"/>
1316   Comments can be included in some HTTP header fields by surrounding
1317   the comment text with parentheses. Comments are only allowed in
1318   fields containing "comment" as part of their field value definition.
1320<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1321  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1322  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1323                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1325<t anchor="rule.quoted-cpair">
1326  <x:anchor-alias value="quoted-cpair"/>
1327   The backslash octet ("\") can be used as a single-octet
1328   quoting mechanism within comment constructs:
1330<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1331  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1334   Senders &SHOULD-NOT; escape octets that do not require escaping
1335   (i.e., other than the backslash octet "\" and the parentheses "(" and
1336   ")").
1340<section title="Message Body" anchor="message.body">
1341  <x:anchor-alias value="message-body"/>
1343   The message-body (if any) of an HTTP message is used to carry the
1344   payload body associated with the request or response.
1346<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1347  <x:ref>message-body</x:ref> = *OCTET
1350   The message-body differs from the payload body only when a transfer-coding
1351   has been applied, as indicated by the Transfer-Encoding header field
1352   (<xref target="header.transfer-encoding"/>).  If more than one
1353   Transfer-Encoding header field is present in a message, the multiple
1354   field-values &MUST; be combined into one field-value, according to the
1355   algorithm defined in <xref target="header.fields"/>, before determining
1356   the message-body length.
1359   When one or more transfer-codings are applied to a payload in order to
1360   form the message-body, the Transfer-Encoding header field &MUST; contain
1361   the list of transfer-codings applied. Transfer-Encoding is a property of
1362   the message, not of the payload, and thus &MAY; be added or removed by
1363   any implementation along the request/response chain under the constraints
1364   found in <xref target="transfer.codings"/>.
1367   If a message is received that has multiple Content-Length header fields
1368   (<xref target="header.content-length"/>) with field-values consisting
1369   of the same decimal value, or a single Content-Length header field with
1370   a field value containing a list of identical decimal values (e.g.,
1371   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1372   header fields have been generated or combined by an upstream message
1373   processor, then the recipient &MUST; either reject the message as invalid
1374   or replace the duplicated field-values with a single valid Content-Length
1375   field containing that decimal value prior to determining the message-body
1376   length.
1379   The rules for when a message-body is allowed in a message differ for
1380   requests and responses.
1383   The presence of a message-body in a request is signaled by the
1384   inclusion of a Content-Length or Transfer-Encoding header field in
1385   the request's header fields, even if the request method does not
1386   define any use for a message-body.  This allows the request
1387   message framing algorithm to be independent of method semantics.
1390   For response messages, whether or not a message-body is included with
1391   a message is dependent on both the request method and the response
1392   status code (<xref target="status.code.and.reason.phrase"/>).
1393   Responses to the HEAD request method never include a message-body
1394   because the associated response header fields (e.g., Transfer-Encoding,
1395   Content-Length, etc.) only indicate what their values would have been
1396   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1397   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1398   All other responses do include a message-body, although the body
1399   &MAY; be of zero length.
1402   The length of the message-body is determined by one of the following
1403   (in order of precedence):
1406  <list style="numbers">
1407    <x:lt><t>
1408     Any response to a HEAD request and any response with a status
1409     code of 100-199, 204, or 304 is always terminated by the first
1410     empty line after the header fields, regardless of the header
1411     fields present in the message, and thus cannot contain a message-body.
1412    </t></x:lt>
1413    <x:lt><t>
1414     If a Transfer-Encoding header field is present
1415     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1416     is the final encoding, the message-body length is determined by reading
1417     and decoding the chunked data until the transfer-coding indicates the
1418     data is complete.
1419    </t>
1420    <t>
1421     If a Transfer-Encoding header field is present in a response and the
1422     "chunked" transfer-coding is not the final encoding, the message-body
1423     length is determined by reading the connection until it is closed by
1424     the server.
1425     If a Transfer-Encoding header field is present in a request and the
1426     "chunked" transfer-coding is not the final encoding, the message-body
1427     length cannot be determined reliably; the server &MUST; respond with
1428     the 400 (Bad Request) status code and then close the connection.
1429    </t>
1430    <t>
1431     If a message is received with both a Transfer-Encoding header field
1432     and a Content-Length header field, the Transfer-Encoding overrides
1433     the Content-Length.
1434     Such a message might indicate an attempt to perform request or response
1435     smuggling (bypass of security-related checks on message routing or content)
1436     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1437     be removed, prior to forwarding the message downstream, or replaced with
1438     the real message-body length after the transfer-coding is decoded.
1439    </t></x:lt>
1440    <x:lt><t>
1441     If a message is received without Transfer-Encoding and with either
1442     multiple Content-Length header fields having differing field-values or
1443     a single Content-Length header field having an invalid value, then the
1444     message framing is invalid and &MUST; be treated as an error to
1445     prevent request or response smuggling.
1446     If this is a request message, the server &MUST; respond with
1447     a 400 (Bad Request) status code and then close the connection.
1448     If this is a response message received by a proxy, the proxy
1449     &MUST; discard the received response, send a 502 (Bad Gateway)
1450     status code as its downstream response, and then close the connection.
1451     If this is a response message received by a user-agent, it &MUST; be
1452     treated as an error by discarding the message and closing the connection.
1453    </t></x:lt>
1454    <x:lt><t>
1455     If a valid Content-Length header field
1456     is present without Transfer-Encoding, its decimal value defines the
1457     message-body length in octets.  If the actual number of octets sent in
1458     the message is less than the indicated Content-Length, the recipient
1459     &MUST; consider the message to be incomplete and treat the connection
1460     as no longer usable.
1461     If the actual number of octets sent in the message is more than the indicated
1462     Content-Length, the recipient &MUST; only process the message-body up to the
1463     field value's number of octets; the remainder of the message &MUST; either
1464     be discarded or treated as the next message in a pipeline.  For the sake of
1465     robustness, a user-agent &MAY; attempt to detect and correct such an error
1466     in message framing if it is parsing the response to the last request on
1467     on a connection and the connection has been closed by the server.
1468    </t></x:lt>
1469    <x:lt><t>
1470     If this is a request message and none of the above are true, then the
1471     message-body length is zero (no message-body is present).
1472    </t></x:lt>
1473    <x:lt><t>
1474     Otherwise, this is a response message without a declared message-body
1475     length, so the message-body length is determined by the number of octets
1476     received prior to the server closing the connection.
1477    </t></x:lt>
1478  </list>
1481   Since there is no way to distinguish a successfully completed,
1482   close-delimited message from a partially-received message interrupted
1483   by network failure, implementations &SHOULD; use encoding or
1484   length-delimited messages whenever possible.  The close-delimiting
1485   feature exists primarily for backwards compatibility with HTTP/1.0.
1488   A server &MAY; reject a request that contains a message-body but
1489   not a Content-Length by responding with 411 (Length Required).
1492   Unless a transfer-coding other than "chunked" has been applied,
1493   a client that sends a request containing a message-body &SHOULD;
1494   use a valid Content-Length header field if the message-body length
1495   is known in advance, rather than the "chunked" encoding, since some
1496   existing services respond to "chunked" with a 411 (Length Required)
1497   status code even though they understand the chunked encoding.  This
1498   is typically because such services are implemented via a gateway that
1499   requires a content-length in advance of being called and the server
1500   is unable or unwilling to buffer the entire request before processing.
1503   A client that sends a request containing a message-body &MUST; include a
1504   valid Content-Length header field if it does not know the server will
1505   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1506   of specific user configuration or by remembering the version of a prior
1507   received response.
1510   Request messages that are prematurely terminated, possibly due to a
1511   cancelled connection or a server-imposed time-out exception, &MUST;
1512   result in closure of the connection; sending an HTTP/1.1 error response
1513   prior to closing the connection is &OPTIONAL;.
1514   Response messages that are prematurely terminated, usually by closure
1515   of the connection prior to receiving the expected number of octets or by
1516   failure to decode a transfer-encoded message-body, &MUST; be recorded
1517   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1518   message-body as if it were complete (i.e., some indication must be given
1519   to the user that an error occurred).  Cache requirements for incomplete
1520   responses are defined in &cache-incomplete;.
1523   A server &MUST; read the entire request message-body or close
1524   the connection after sending its response, since otherwise the
1525   remaining data on a persistent connection would be misinterpreted
1526   as the next request.  Likewise,
1527   a client &MUST; read the entire response message-body if it intends
1528   to reuse the same connection for a subsequent request.  Pipelining
1529   multiple requests on a connection is described in <xref target="pipelining"/>.
1533<section title="General Header Fields" anchor="general.header.fields">
1534  <x:anchor-alias value="general-header"/>
1536   There are a few header fields which have general applicability for
1537   both request and response messages, but which do not apply to the
1538   payload being transferred. These header fields apply only to the
1539   message being transmitted.
1541<texttable align="left">
1542  <ttcol>Header Field Name</ttcol>
1543  <ttcol>Defined in...</ttcol>
1545  <c>Connection</c> <c><xref target="header.connection"/></c>
1546  <c>Date</c> <c><xref target=""/></c>
1547  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1548  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1549  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1550  <c>Via</c> <c><xref target="header.via"/></c>
1555<section title="Request" anchor="request">
1556  <x:anchor-alias value="Request"/>
1558   A request message from a client to a server begins with a
1559   Request-Line, followed by zero or more header fields, an empty
1560   line signifying the end of the header block, and an optional
1561   message body.
1563<!--                 Host                      ; should be moved here eventually -->
1564<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1565  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1566                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1567                  <x:ref>CRLF</x:ref>
1568                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1571<section title="Request-Line" anchor="request-line">
1572  <x:anchor-alias value="Request-Line"/>
1574   The Request-Line begins with a method token, followed by a single
1575   space (SP), the request-target, another single space (SP), the
1576   protocol version, and ending with CRLF.
1578<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1579  <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>
1582<section title="Method" anchor="method">
1583  <x:anchor-alias value="Method"/>
1585   The Method token indicates the request method to be performed on the
1586   target resource. The request method is case-sensitive.
1588<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1589  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1593<section title="request-target" anchor="request-target">
1594  <x:anchor-alias value="request-target"/>
1596   The request-target identifies the target resource upon which to apply
1597   the request.  In most cases, the user agent is provided a URI reference
1598   from which it determines an absolute URI for identifying the target
1599   resource.  When a request to the resource is initiated, all or part
1600   of that URI is used to construct the HTTP request-target.
1602<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1603  <x:ref>request-target</x:ref> = "*"
1604                 / <x:ref>absolute-URI</x:ref>
1605                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1606                 / <x:ref>authority</x:ref>
1609   The four options for request-target are dependent on the nature of the
1610   request.
1612<t><iref item="asterisk form (of request-target)"/>
1613   The asterisk "*" form of request-target, which &MUST-NOT; be used
1614   with any request method other than OPTIONS, means that the request
1615   applies to the server as a whole (the listening process) rather than
1616   to a specific named resource at that server.  For example,
1618<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1619OPTIONS * HTTP/1.1
1621<t><iref item="absolute-URI form (of request-target)"/>
1622   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1623   proxy. The proxy is requested to either forward the request or service it
1624   from a valid cache, and then return the response. Note that the proxy &MAY;
1625   forward the request on to another proxy or directly to the server
1626   specified by the absolute-URI. In order to avoid request loops, a
1627   proxy that forwards requests to other proxies &MUST; be able to
1628   recognize and exclude all of its own server names, including
1629   any aliases, local variations, and the numeric IP address. An example
1630   Request-Line would be:
1632<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1633GET HTTP/1.1
1636   To allow for transition to absolute-URIs in all requests in future
1637   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1638   form in requests, even though HTTP/1.1 clients will only generate
1639   them in requests to proxies.
1642   If a proxy receives a host name that is not a fully qualified domain
1643   name, it &MAY; add its domain to the host name it received. If a proxy
1644   receives a fully qualified domain name, the proxy &MUST-NOT; change
1645   the host name.
1647<t><iref item="authority form (of request-target)"/>
1648   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1650<t><iref item="origin form (of request-target)"/>
1651   The most common form of request-target is that used when making
1652   a request to an origin server ("origin form").
1653   In this case, the absolute path and query components of the URI
1654   &MUST; be transmitted as the request-target, and the authority component
1655   &MUST; be transmitted in a Host header field. For example, a client wishing
1656   to retrieve a representation of the resource, as identified above,
1657   directly from the origin server would open (or reuse) a TCP connection
1658   to port 80 of the host "" and send the lines:
1660<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1661GET /pub/WWW/TheProject.html HTTP/1.1
1665   followed by the remainder of the Request. Note that the origin form
1666   of request-target always starts with an absolute path; if the target
1667   resource's URI path is empty, then an absolute path of "/" &MUST; be
1668   provided in the request-target.
1671   If a proxy receives an OPTIONS request with an absolute-URI form of
1672   request-target in which the URI has an empty path and no query component,
1673   then the last proxy on the request chain &MUST; use a request-target
1674   of "*" when it forwards the request to the indicated origin server.
1677   For example, the request
1678</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1682  would be forwarded by the final proxy as
1683</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1684OPTIONS * HTTP/1.1
1688   after connecting to port 8001 of host "".
1692   The request-target is transmitted in the format specified in
1693   <xref target="http.uri"/>. If the request-target is percent-encoded
1694   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1695   &MUST; decode the request-target in order to
1696   properly interpret the request. Servers &SHOULD; respond to invalid
1697   request-targets with an appropriate status code.
1700   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1701   received request-target when forwarding it to the next inbound server,
1702   except as noted above to replace a null path-absolute with "/" or "*".
1705  <t>
1706    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1707    meaning of the request when the origin server is improperly using
1708    a non-reserved URI character for a reserved purpose.  Implementors
1709    need to be aware that some pre-HTTP/1.1 proxies have been known to
1710    rewrite the request-target.
1711  </t>
1714   HTTP does not place a pre-defined limit on the length of a request-target.
1715   A server &MUST; be prepared to receive URIs of unbounded length and
1716   respond with the 414 (URI Too Long) status code if the received
1717   request-target would be longer than the server wishes to handle
1718   (see &status-414;).
1721   Various ad-hoc limitations on request-target length are found in practice.
1722   It is &RECOMMENDED; that all HTTP senders and recipients support
1723   request-target lengths of 8000 or more octets.
1726  <t>
1727    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1728    are not part of the request-target and thus will not be transmitted
1729    in an HTTP request.
1730  </t>
1735<section title="The Resource Identified by a Request" anchor="">
1737   The exact resource identified by an Internet request is determined by
1738   examining both the request-target and the Host header field.
1741   An origin server that does not allow resources to differ by the
1742   requested host &MAY; ignore the Host header field value when
1743   determining the resource identified by an HTTP/1.1 request. (But see
1744   <xref target=""/>
1745   for other requirements on Host support in HTTP/1.1.)
1748   An origin server that does differentiate resources based on the host
1749   requested (sometimes referred to as virtual hosts or vanity host
1750   names) &MUST; use the following rules for determining the requested
1751   resource on an HTTP/1.1 request:
1752  <list style="numbers">
1753    <t>If request-target is an absolute-URI, the host is part of the
1754     request-target. Any Host header field value in the request &MUST; be
1755     ignored.</t>
1756    <t>If the request-target is not an absolute-URI, and the request includes
1757     a Host header field, the host is determined by the Host header
1758     field value.</t>
1759    <t>If the host as determined by rule 1 or 2 is not a valid host on
1760     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1761  </list>
1764   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1765   attempt to use heuristics (e.g., examination of the URI path for
1766   something unique to a particular host) in order to determine what
1767   exact resource is being requested.
1771<section title="Effective Request URI" anchor="effective.request.uri">
1772  <iref primary="true" item="effective request URI"/>
1773  <iref primary="true" item="target resource"/>
1775   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1776   for the target resource; instead, the URI needs to be inferred from the
1777   request-target, Host header field, and connection context. The result of
1778   this process is called the "effective request URI".  The "target resource"
1779   is the resource identified by the effective request URI.
1782   If the request-target is an absolute-URI, then the effective request URI is
1783   the request-target.
1786   If the request-target uses the path-absolute form or the asterisk form,
1787   and the Host header field is present, then the effective request URI is
1788   constructed by concatenating
1791  <list style="symbols">
1792    <t>
1793      the scheme name: "http" if the request was received over an insecure
1794      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1795      connection,
1796    </t>
1797    <t>
1798      the octet sequence "://",
1799    </t>
1800    <t>
1801      the authority component, as specified in the Host header field
1802      (<xref target=""/>), and
1803    </t>
1804    <t>
1805      the request-target obtained from the Request-Line, unless the
1806      request-target is just the asterisk "*".
1807    </t>
1808  </list>
1811   If the request-target uses the path-absolute form or the asterisk form,
1812   and the Host header field is not present, then the effective request URI is
1813   undefined.
1816   Otherwise, when request-target uses the authority form, the effective
1817   request URI is undefined.
1821   Example 1: the effective request URI for the message
1823<artwork type="example" x:indent-with="  ">
1824GET /pub/WWW/TheProject.html HTTP/1.1
1828  (received over an insecure TCP connection) is "http", plus "://", plus the
1829  authority component "", plus the request-target
1830  "/pub/WWW/TheProject.html", thus
1831  "".
1836   Example 2: the effective request URI for the message
1838<artwork type="example" x:indent-with="  ">
1839GET * HTTP/1.1
1843  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1844  authority component "", thus "".
1848   Effective request URIs are compared using the rules described in
1849   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1850   be treated as equivalent to an absolute path of "/".
1857<section title="Response" anchor="response">
1858  <x:anchor-alias value="Response"/>
1860   After receiving and interpreting a request message, a server responds
1861   with an HTTP response message.
1863<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1864  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1865                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1866                  <x:ref>CRLF</x:ref>
1867                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1870<section title="Status-Line" anchor="status-line">
1871  <x:anchor-alias value="Status-Line"/>
1873   The first line of a Response message is the Status-Line, consisting
1874   of the protocol version, a space (SP), the status code, another space,
1875   a possibly-empty textual phrase describing the status code, and
1876   ending with CRLF.
1878<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1879  <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>
1882<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1883  <x:anchor-alias value="Reason-Phrase"/>
1884  <x:anchor-alias value="Status-Code"/>
1886   The Status-Code element is a 3-digit integer result code of the
1887   attempt to understand and satisfy the request. These codes are fully
1888   defined in &status-codes;.  The Reason Phrase exists for the sole
1889   purpose of providing a textual description associated with the numeric
1890   status code, out of deference to earlier Internet application protocols
1891   that were more frequently used with interactive text clients.
1892   A client &SHOULD; ignore the content of the Reason Phrase.
1895   The first digit of the Status-Code defines the class of response. The
1896   last two digits do not have any categorization role. There are 5
1897   values for the first digit:
1898  <list style="symbols">
1899    <t>
1900      1xx: Informational - Request received, continuing process
1901    </t>
1902    <t>
1903      2xx: Success - The action was successfully received,
1904        understood, and accepted
1905    </t>
1906    <t>
1907      3xx: Redirection - Further action must be taken in order to
1908        complete the request
1909    </t>
1910    <t>
1911      4xx: Client Error - The request contains bad syntax or cannot
1912        be fulfilled
1913    </t>
1914    <t>
1915      5xx: Server Error - The server failed to fulfill an apparently
1916        valid request
1917    </t>
1918  </list>
1920<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1921  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1922  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1930<section title="Protocol Parameters" anchor="protocol.parameters">
1932<section title="Date/Time Formats: Full Date" anchor="">
1933  <x:anchor-alias value="HTTP-date"/>
1935   HTTP applications have historically allowed three different formats
1936   for date/time stamps. However, the preferred format is a fixed-length subset
1937   of that defined by <xref target="RFC1123"/>:
1939<figure><artwork type="example" x:indent-with="  ">
1940Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1943   The other formats are described here only for compatibility with obsolete
1944   implementations.
1946<figure><artwork type="example" x:indent-with="  ">
1947Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1948Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1951   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1952   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1953   only generate the RFC 1123 format for representing HTTP-date values
1954   in header fields. See <xref target="tolerant.applications"/> for further information.
1957   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1958   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1959   equal to UTC (Coordinated Universal Time). This is indicated in the
1960   first two formats by the inclusion of "GMT" as the three-letter
1961   abbreviation for time zone, and &MUST; be assumed when reading the
1962   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1963   additional whitespace beyond that specifically included as SP in the
1964   grammar.
1966<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1967  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1969<t anchor="">
1970  <x:anchor-alias value="rfc1123-date"/>
1971  <x:anchor-alias value="time-of-day"/>
1972  <x:anchor-alias value="hour"/>
1973  <x:anchor-alias value="minute"/>
1974  <x:anchor-alias value="second"/>
1975  <x:anchor-alias value="day-name"/>
1976  <x:anchor-alias value="day"/>
1977  <x:anchor-alias value="month"/>
1978  <x:anchor-alias value="year"/>
1979  <x:anchor-alias value="GMT"/>
1980  Preferred format:
1982<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"/>
1983  <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>
1984  ; fixed length subset of the format defined in
1985  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1987  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1988               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1989               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1990               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1991               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1992               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1993               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1995  <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>
1996               ; e.g., 02 Jun 1982
1998  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1999  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2000               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2001               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2002               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2003               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2004               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2005               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2006               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2007               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2008               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2009               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2010               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2011  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2013  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2015  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2016                 ; 00:00:00 - 23:59:59
2018  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2019  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2020  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2023  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2024  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2025  same as those defined for the RFC 5322 constructs
2026  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2028<t anchor="">
2029  <x:anchor-alias value="obs-date"/>
2030  <x:anchor-alias value="rfc850-date"/>
2031  <x:anchor-alias value="asctime-date"/>
2032  <x:anchor-alias value="date1"/>
2033  <x:anchor-alias value="date2"/>
2034  <x:anchor-alias value="date3"/>
2035  <x:anchor-alias value="rfc1123-date"/>
2036  <x:anchor-alias value="day-name-l"/>
2037  Obsolete formats:
2039<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2040  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2042<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2043  <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>
2044  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2045                 ; day-month-year (e.g., 02-Jun-82)
2047  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2048         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2049         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2050         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2051         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2052         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2053         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2055<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2056  <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>
2057  <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> ))
2058                 ; month day (e.g., Jun  2)
2061  <t>
2062    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2063    accepting date values that might have been sent by non-HTTP
2064    applications, as is sometimes the case when retrieving or posting
2065    messages via proxies/gateways to SMTP or NNTP.
2066  </t>
2069  <t>
2070    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2071    to their usage within the protocol stream. Clients and servers are
2072    not required to use these formats for user presentation, request
2073    logging, etc.
2074  </t>
2078<section title="Transfer Codings" anchor="transfer.codings">
2079  <x:anchor-alias value="transfer-coding"/>
2080  <x:anchor-alias value="transfer-extension"/>
2082   Transfer-coding values are used to indicate an encoding
2083   transformation that has been, can be, or might need to be applied to a
2084   payload body in order to ensure "safe transport" through the network.
2085   This differs from a content coding in that the transfer-coding is a
2086   property of the message rather than a property of the representation
2087   that is being transferred.
2089<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2090  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2091                          / "compress" ; <xref target="compress.coding"/>
2092                          / "deflate" ; <xref target="deflate.coding"/>
2093                          / "gzip" ; <xref target="gzip.coding"/>
2094                          / <x:ref>transfer-extension</x:ref>
2095  <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> )
2097<t anchor="rule.parameter">
2098  <x:anchor-alias value="attribute"/>
2099  <x:anchor-alias value="transfer-parameter"/>
2100  <x:anchor-alias value="value"/>
2101   Parameters are in the form of attribute/value pairs.
2103<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"/>
2104  <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>
2105  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2106  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2109   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2110   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2111   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2114   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2115   MIME, which were designed to enable safe transport of binary data over a
2116   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2117   However, safe transport
2118   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2119   the only unsafe characteristic of message-bodies is the difficulty in
2120   determining the exact message body length (<xref target="message.body"/>),
2121   or the desire to encrypt data over a shared transport.
2124   A server that receives a request message with a transfer-coding it does
2125   not understand &SHOULD; respond with 501 (Not Implemented) and then
2126   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2127   client.
2130<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2131  <iref item="chunked (Coding Format)"/>
2132  <iref item="Coding Format" subitem="chunked"/>
2133  <x:anchor-alias value="chunk"/>
2134  <x:anchor-alias value="Chunked-Body"/>
2135  <x:anchor-alias value="chunk-data"/>
2136  <x:anchor-alias value="chunk-ext"/>
2137  <x:anchor-alias value="chunk-ext-name"/>
2138  <x:anchor-alias value="chunk-ext-val"/>
2139  <x:anchor-alias value="chunk-size"/>
2140  <x:anchor-alias value="last-chunk"/>
2141  <x:anchor-alias value="trailer-part"/>
2142  <x:anchor-alias value="quoted-str-nf"/>
2143  <x:anchor-alias value="qdtext-nf"/>
2145   The chunked encoding modifies the body of a message in order to
2146   transfer it as a series of chunks, each with its own size indicator,
2147   followed by an &OPTIONAL; trailer containing header fields. This
2148   allows dynamically produced content to be transferred along with the
2149   information necessary for the recipient to verify that it has
2150   received the full message.
2152<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"/>
2153  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2154                   <x:ref>last-chunk</x:ref>
2155                   <x:ref>trailer-part</x:ref>
2156                   <x:ref>CRLF</x:ref>
2158  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2159                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2160  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2161  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2163  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2164                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2165  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2166  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2167  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2168  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2170  <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>
2171                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2172  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2173                 ; <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>
2176   The chunk-size field is a string of hex digits indicating the size of
2177   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2178   zero, followed by the trailer, which is terminated by an empty line.
2181   The trailer allows the sender to include additional HTTP header
2182   fields at the end of the message. The Trailer header field can be
2183   used to indicate which header fields are included in a trailer (see
2184   <xref target="header.trailer"/>).
2187   A server using chunked transfer-coding in a response &MUST-NOT; use the
2188   trailer for any header fields unless at least one of the following is
2189   true:
2190  <list style="numbers">
2191    <t>the request included a TE header field that indicates "trailers" is
2192     acceptable in the transfer-coding of the  response, as described in
2193     <xref target="header.te"/>; or,</t>
2195    <t>the trailer fields consist entirely of optional metadata, and the
2196    recipient could use the message (in a manner acceptable to the server where
2197    the field originated) without receiving it. In other words, the server that
2198    generated the header (often but not always the origin server) is willing to
2199    accept the possibility that the trailer fields might be silently discarded
2200    along the path to the client.</t>
2201  </list>
2204   This requirement prevents an interoperability failure when the
2205   message is being received by an HTTP/1.1 (or later) proxy and
2206   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2207   compliance with the protocol would have necessitated a possibly
2208   infinite buffer on the proxy.
2211   A process for decoding the "chunked" transfer-coding
2212   can be represented in pseudo-code as:
2214<figure><artwork type="code">
2215  length := 0
2216  read chunk-size, chunk-ext (if any) and CRLF
2217  while (chunk-size &gt; 0) {
2218     read chunk-data and CRLF
2219     append chunk-data to decoded-body
2220     length := length + chunk-size
2221     read chunk-size and CRLF
2222  }
2223  read header-field
2224  while (header-field not empty) {
2225     append header-field to existing header fields
2226     read header-field
2227  }
2228  Content-Length := length
2229  Remove "chunked" from Transfer-Encoding
2232   All HTTP/1.1 applications &MUST; be able to receive and decode the
2233   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2234   they do not understand.
2237   Since "chunked" is the only transfer-coding required to be understood
2238   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2239   on a persistent connection.  Whenever a transfer-coding is applied to
2240   a payload body in a request, the final transfer-coding applied &MUST;
2241   be "chunked".  If a transfer-coding is applied to a response payload
2242   body, then either the final transfer-coding applied &MUST; be "chunked"
2243   or the message &MUST; be terminated by closing the connection. When the
2244   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2245   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2246   be applied more than once in a message-body.
2250<section title="Compression Codings" anchor="compression.codings">
2252   The codings defined below can be used to compress the payload of a
2253   message.
2256   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2257   is not desirable and is discouraged for future encodings. Their
2258   use here is representative of historical practice, not good
2259   design.
2262   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2263   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2264   equivalent to "gzip" and "compress" respectively.
2267<section title="Compress Coding" anchor="compress.coding">
2268<iref item="compress (Coding Format)"/>
2269<iref item="Coding Format" subitem="compress"/>
2271   The "compress" format is produced by the common UNIX file compression
2272   program "compress". This format is an adaptive Lempel-Ziv-Welch
2273   coding (LZW).
2277<section title="Deflate Coding" anchor="deflate.coding">
2278<iref item="deflate (Coding Format)"/>
2279<iref item="Coding Format" subitem="deflate"/>
2281   The "deflate" format is defined as the "deflate" compression mechanism
2282   (described in <xref target="RFC1951"/>) used inside the "zlib"
2283   data format (<xref target="RFC1950"/>).
2286  <t>
2287    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2288    compressed data without the zlib wrapper.
2289   </t>
2293<section title="Gzip Coding" anchor="gzip.coding">
2294<iref item="gzip (Coding Format)"/>
2295<iref item="Coding Format" subitem="gzip"/>
2297   The "gzip" format is produced by the file compression program
2298   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2299   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2305<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2307   The HTTP Transfer Coding Registry defines the name space for the transfer
2308   coding names.
2311   Registrations &MUST; include the following fields:
2312   <list style="symbols">
2313     <t>Name</t>
2314     <t>Description</t>
2315     <t>Pointer to specification text</t>
2316   </list>
2319   Names of transfer codings &MUST-NOT; overlap with names of content codings
2320   (&content-codings;), unless the encoding transformation is identical (as it
2321   is the case for the compression codings defined in
2322   <xref target="compression.codings"/>).
2325   Values to be added to this name space require a specification
2326   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2327   conform to the purpose of transfer coding defined in this section.
2330   The registry itself is maintained at
2331   <eref target=""/>.
2336<section title="Product Tokens" anchor="product.tokens">
2337  <x:anchor-alias value="product"/>
2338  <x:anchor-alias value="product-version"/>
2340   Product tokens are used to allow communicating applications to
2341   identify themselves by software name and version. Most fields using
2342   product tokens also allow sub-products which form a significant part
2343   of the application to be listed, separated by whitespace. By
2344   convention, the products are listed in order of their significance
2345   for identifying the application.
2347<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2348  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2349  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2352   Examples:
2354<figure><artwork type="example">
2355  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2356  Server: Apache/0.8.4
2359   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2360   used for advertising or other non-essential information. Although any
2361   token octet &MAY; appear in a product-version, this token &SHOULD;
2362   only be used for a version identifier (i.e., successive versions of
2363   the same product &SHOULD; only differ in the product-version portion of
2364   the product value).
2368<section title="Quality Values" anchor="quality.values">
2369  <x:anchor-alias value="qvalue"/>
2371   Both transfer codings (TE request header field, <xref target="header.te"/>)
2372   and content negotiation (&content.negotiation;) use short "floating point"
2373   numbers to indicate the relative importance ("weight") of various
2374   negotiable parameters.  A weight is normalized to a real number in
2375   the range 0 through 1, where 0 is the minimum and 1 the maximum
2376   value. If a parameter has a quality value of 0, then content with
2377   this parameter is "not acceptable" for the client. HTTP/1.1
2378   applications &MUST-NOT; generate more than three digits after the
2379   decimal point. User configuration of these values &SHOULD; also be
2380   limited in this fashion.
2382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2383  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2384                 / ( "1" [ "." 0*3("0") ] )
2387  <t>
2388     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2389     relative degradation in desired quality.
2390  </t>
2396<section title="Connections" anchor="connections">
2398<section title="Persistent Connections" anchor="persistent.connections">
2400<section title="Purpose" anchor="persistent.purpose">
2402   Prior to persistent connections, a separate TCP connection was
2403   established for each request, increasing the load on HTTP servers
2404   and causing congestion on the Internet. The use of inline images and
2405   other associated data often requires a client to make multiple
2406   requests of the same server in a short amount of time. Analysis of
2407   these performance problems and results from a prototype
2408   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2409   measurements of actual HTTP/1.1 implementations show good
2410   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2411   T/TCP <xref target="Tou1998"/>.
2414   Persistent HTTP connections have a number of advantages:
2415  <list style="symbols">
2416      <t>
2417        By opening and closing fewer TCP connections, CPU time is saved
2418        in routers and hosts (clients, servers, proxies, gateways,
2419        tunnels, or caches), and memory used for TCP protocol control
2420        blocks can be saved in hosts.
2421      </t>
2422      <t>
2423        HTTP requests and responses can be pipelined on a connection.
2424        Pipelining allows a client to make multiple requests without
2425        waiting for each response, allowing a single TCP connection to
2426        be used much more efficiently, with much lower elapsed time.
2427      </t>
2428      <t>
2429        Network congestion is reduced by reducing the number of packets
2430        caused by TCP opens, and by allowing TCP sufficient time to
2431        determine the congestion state of the network.
2432      </t>
2433      <t>
2434        Latency on subsequent requests is reduced since there is no time
2435        spent in TCP's connection opening handshake.
2436      </t>
2437      <t>
2438        HTTP can evolve more gracefully, since errors can be reported
2439        without the penalty of closing the TCP connection. Clients using
2440        future versions of HTTP might optimistically try a new feature,
2441        but if communicating with an older server, retry with old
2442        semantics after an error is reported.
2443      </t>
2444    </list>
2447   HTTP implementations &SHOULD; implement persistent connections.
2451<section title="Overall Operation" anchor="persistent.overall">
2453   A significant difference between HTTP/1.1 and earlier versions of
2454   HTTP is that persistent connections are the default behavior of any
2455   HTTP connection. That is, unless otherwise indicated, the client
2456   &SHOULD; assume that the server will maintain a persistent connection,
2457   even after error responses from the server.
2460   Persistent connections provide a mechanism by which a client and a
2461   server can signal the close of a TCP connection. This signaling takes
2462   place using the Connection header field (<xref target="header.connection"/>). Once a close
2463   has been signaled, the client &MUST-NOT; send any more requests on that
2464   connection.
2467<section title="Negotiation" anchor="persistent.negotiation">
2469   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2470   maintain a persistent connection unless a Connection header field including
2471   the connection-token "close" was sent in the request. If the server
2472   chooses to close the connection immediately after sending the
2473   response, it &SHOULD; send a Connection header field including the
2474   connection-token "close".
2477   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2478   decide to keep it open based on whether the response from a server
2479   contains a Connection header field with the connection-token close. In case
2480   the client does not want to maintain a connection for more than that
2481   request, it &SHOULD; send a Connection header field including the
2482   connection-token close.
2485   If either the client or the server sends the close token in the
2486   Connection header field, that request becomes the last one for the
2487   connection.
2490   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2491   maintained for HTTP versions less than 1.1 unless it is explicitly
2492   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2493   compatibility with HTTP/1.0 clients.
2496   In order to remain persistent, all messages on the connection &MUST;
2497   have a self-defined message length (i.e., one not defined by closure
2498   of the connection), as described in <xref target="message.body"/>.
2502<section title="Pipelining" anchor="pipelining">
2504   A client that supports persistent connections &MAY; "pipeline" its
2505   requests (i.e., send multiple requests without waiting for each
2506   response). A server &MUST; send its responses to those requests in the
2507   same order that the requests were received.
2510   Clients which assume persistent connections and pipeline immediately
2511   after connection establishment &SHOULD; be prepared to retry their
2512   connection if the first pipelined attempt fails. If a client does
2513   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2514   persistent. Clients &MUST; also be prepared to resend their requests if
2515   the server closes the connection before sending all of the
2516   corresponding responses.
2519   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2520   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2521   premature termination of the transport connection could lead to
2522   indeterminate results. A client wishing to send a non-idempotent
2523   request &SHOULD; wait to send that request until it has received the
2524   response status line for the previous request.
2529<section title="Proxy Servers" anchor="persistent.proxy">
2531   It is especially important that proxies correctly implement the
2532   properties of the Connection header field as specified in <xref target="header.connection"/>.
2535   The proxy server &MUST; signal persistent connections separately with
2536   its clients and the origin servers (or other proxy servers) that it
2537   connects to. Each persistent connection applies to only one transport
2538   link.
2541   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2542   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2543   for information and discussion of the problems with the Keep-Alive header field
2544   implemented by many HTTP/1.0 clients).
2547<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2549  <cref anchor="TODO-end-to-end" source="jre">
2550    Restored from <eref target=""/>.
2551    See also <eref target=""/>.
2552  </cref>
2555   For the purpose of defining the behavior of caches and non-caching
2556   proxies, we divide HTTP header fields into two categories:
2557  <list style="symbols">
2558      <t>End-to-end header fields, which are  transmitted to the ultimate
2559        recipient of a request or response. End-to-end header fields in
2560        responses MUST be stored as part of a cache entry and &MUST; be
2561        transmitted in any response formed from a cache entry.</t>
2563      <t>Hop-by-hop header fields, which are meaningful only for a single
2564        transport-level connection, and are not stored by caches or
2565        forwarded by proxies.</t>
2566  </list>
2569   The following HTTP/1.1 header fields are hop-by-hop header fields:
2570  <list style="symbols">
2571      <t>Connection</t>
2572      <t>Keep-Alive</t>
2573      <t>Proxy-Authenticate</t>
2574      <t>Proxy-Authorization</t>
2575      <t>TE</t>
2576      <t>Trailer</t>
2577      <t>Transfer-Encoding</t>
2578      <t>Upgrade</t>
2579  </list>
2582   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2585   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2586   (<xref target="header.connection"/>).
2590<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2592  <cref anchor="TODO-non-mod-headers" source="jre">
2593    Restored from <eref target=""/>.
2594    See also <eref target=""/>.
2595  </cref>
2598   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2599   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2600   modify an end-to-end header field unless the definition of that header field requires
2601   or specifically allows that.
2604   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2605   request or response, and it &MUST-NOT; add any of these fields if not
2606   already present:
2607  <list style="symbols">
2608      <t>Content-Location</t>
2609      <t>Content-MD5</t>
2610      <t>ETag</t>
2611      <t>Last-Modified</t>
2612  </list>
2615   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2616   response:
2617  <list style="symbols">
2618    <t>Expires</t>
2619  </list>
2622   but it &MAY; add any of these fields if not already present. If an
2623   Expires header field is added, it &MUST; be given a field-value identical to
2624   that of the Date header field in that response.
2627   A proxy &MUST-NOT; modify or add any of the following fields in a
2628   message that contains the no-transform cache-control directive, or in
2629   any request:
2630  <list style="symbols">
2631    <t>Content-Encoding</t>
2632    <t>Content-Range</t>
2633    <t>Content-Type</t>
2634  </list>
2637   A transforming proxy &MAY; modify or add these fields to a message
2638   that does not include no-transform, but if it does so, it &MUST; add a
2639   Warning 214 (Transformation applied) if one does not already appear
2640   in the message (see &header-warning;).
2643  <t>
2644    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2645    cause authentication failures if stronger authentication
2646    mechanisms are introduced in later versions of HTTP. Such
2647    authentication mechanisms &MAY; rely on the values of header fields
2648    not listed here.
2649  </t>
2652   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2653   though it &MAY; change the message-body through application or removal
2654   of a transfer-coding (<xref target="transfer.codings"/>).
2660<section title="Practical Considerations" anchor="persistent.practical">
2662   Servers will usually have some time-out value beyond which they will
2663   no longer maintain an inactive connection. Proxy servers might make
2664   this a higher value since it is likely that the client will be making
2665   more connections through the same server. The use of persistent
2666   connections places no requirements on the length (or existence) of
2667   this time-out for either the client or the server.
2670   When a client or server wishes to time-out it &SHOULD; issue a graceful
2671   close on the transport connection. Clients and servers &SHOULD; both
2672   constantly watch for the other side of the transport close, and
2673   respond to it as appropriate. If a client or server does not detect
2674   the other side's close promptly it could cause unnecessary resource
2675   drain on the network.
2678   A client, server, or proxy &MAY; close the transport connection at any
2679   time. For example, a client might have started to send a new request
2680   at the same time that the server has decided to close the "idle"
2681   connection. From the server's point of view, the connection is being
2682   closed while it was idle, but from the client's point of view, a
2683   request is in progress.
2686   This means that clients, servers, and proxies &MUST; be able to recover
2687   from asynchronous close events. Client software &SHOULD; reopen the
2688   transport connection and retransmit the aborted sequence of requests
2689   without user interaction so long as the request sequence is
2690   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2691   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2692   human operator the choice of retrying the request(s). Confirmation by
2693   user-agent software with semantic understanding of the application
2694   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2695   be repeated if the second sequence of requests fails.
2698   Servers &SHOULD; always respond to at least one request per connection,
2699   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2700   middle of transmitting a response, unless a network or client failure
2701   is suspected.
2704   Clients (including proxies) &SHOULD; limit the number of simultaneous
2705   connections that they maintain to a given server (including proxies).
2708   Previous revisions of HTTP gave a specific number of connections as a
2709   ceiling, but this was found to be impractical for many applications. As a
2710   result, this specification does not mandate a particular maximum number of
2711   connections, but instead encourages clients to be conservative when opening
2712   multiple connections.
2715   In particular, while using multiple connections avoids the "head-of-line
2716   blocking" problem (whereby a request that takes significant server-side
2717   processing and/or has a large payload can block subsequent requests on the
2718   same connection), each connection used consumes server resources (sometimes
2719   significantly), and furthermore using multiple connections can cause
2720   undesirable side effects in congested networks.
2723   Note that servers might reject traffic that they deem abusive, including an
2724   excessive number of connections from a client.
2729<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2731<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2733   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2734   flow control mechanisms to resolve temporary overloads, rather than
2735   terminating connections with the expectation that clients will retry.
2736   The latter technique can exacerbate network congestion.
2740<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2742   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2743   the network connection for an error status code while it is transmitting
2744   the request. If the client sees an error status code, it &SHOULD;
2745   immediately cease transmitting the body. If the body is being sent
2746   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2747   empty trailer &MAY; be used to prematurely mark the end of the message.
2748   If the body was preceded by a Content-Length header field, the client &MUST;
2749   close the connection.
2753<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2755   The purpose of the 100 (Continue) status code (see &status-100;) is to
2756   allow a client that is sending a request message with a request body
2757   to determine if the origin server is willing to accept the request
2758   (based on the request header fields) before the client sends the request
2759   body. In some cases, it might either be inappropriate or highly
2760   inefficient for the client to send the body if the server will reject
2761   the message without looking at the body.
2764   Requirements for HTTP/1.1 clients:
2765  <list style="symbols">
2766    <t>
2767        If a client will wait for a 100 (Continue) response before
2768        sending the request body, it &MUST; send an Expect header
2769        field (&header-expect;) with the "100-continue" expectation.
2770    </t>
2771    <t>
2772        A client &MUST-NOT; send an Expect header field (&header-expect;)
2773        with the "100-continue" expectation if it does not intend
2774        to send a request body.
2775    </t>
2776  </list>
2779   Because of the presence of older implementations, the protocol allows
2780   ambiguous situations in which a client might send "Expect: 100-continue"
2781   without receiving either a 417 (Expectation Failed)
2782   or a 100 (Continue) status code. Therefore, when a client sends this
2783   header field to an origin server (possibly via a proxy) from which it
2784   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2785   wait for an indefinite period before sending the request body.
2788   Requirements for HTTP/1.1 origin servers:
2789  <list style="symbols">
2790    <t> Upon receiving a request which includes an Expect header
2791        field with the "100-continue" expectation, an origin server &MUST;
2792        either respond with 100 (Continue) status code and continue to read
2793        from the input stream, or respond with a final status code. The
2794        origin server &MUST-NOT; wait for the request body before sending
2795        the 100 (Continue) response. If it responds with a final status
2796        code, it &MAY; close the transport connection or it &MAY; continue
2797        to read and discard the rest of the request.  It &MUST-NOT;
2798        perform the request method if it returns a final status code.
2799    </t>
2800    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2801        the request message does not include an Expect header
2802        field with the "100-continue" expectation, and &MUST-NOT; send a
2803        100 (Continue) response if such a request comes from an HTTP/1.0
2804        (or earlier) client. There is an exception to this rule: for
2805        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2806        status code in response to an HTTP/1.1 PUT or POST request that does
2807        not include an Expect header field with the "100-continue"
2808        expectation. This exception, the purpose of which is
2809        to minimize any client processing delays associated with an
2810        undeclared wait for 100 (Continue) status code, applies only to
2811        HTTP/1.1 requests, and not to requests with any other HTTP-version
2812        value.
2813    </t>
2814    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2815        already received some or all of the request body for the
2816        corresponding request.
2817    </t>
2818    <t> An origin server that sends a 100 (Continue) response &MUST;
2819    ultimately send a final status code, once the request body is
2820        received and processed, unless it terminates the transport
2821        connection prematurely.
2822    </t>
2823    <t> If an origin server receives a request that does not include an
2824        Expect header field with the "100-continue" expectation,
2825        the request includes a request body, and the server responds
2826        with a final status code before reading the entire request body
2827        from the transport connection, then the server &SHOULD-NOT;  close
2828        the transport connection until it has read the entire request,
2829        or until the client closes the connection. Otherwise, the client
2830        might not reliably receive the response message. However, this
2831        requirement is not be construed as preventing a server from
2832        defending itself against denial-of-service attacks, or from
2833        badly broken client implementations.
2834      </t>
2835    </list>
2838   Requirements for HTTP/1.1 proxies:
2839  <list style="symbols">
2840    <t> If a proxy receives a request that includes an Expect header
2841        field with the "100-continue" expectation, and the proxy
2842        either knows that the next-hop server complies with HTTP/1.1 or
2843        higher, or does not know the HTTP version of the next-hop
2844        server, it &MUST; forward the request, including the Expect header
2845        field.
2846    </t>
2847    <t> If the proxy knows that the version of the next-hop server is
2848        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2849        respond with a 417 (Expectation Failed) status code.
2850    </t>
2851    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2852        numbers received from recently-referenced next-hop servers.
2853    </t>
2854    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2855        request message was received from an HTTP/1.0 (or earlier)
2856        client and did not include an Expect header field with
2857        the "100-continue" expectation. This requirement overrides the
2858        general rule for forwarding of 1xx responses (see &status-1xx;).
2859    </t>
2860  </list>
2864<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2866   If an HTTP/1.1 client sends a request which includes a request body,
2867   but which does not include an Expect header field with the
2868   "100-continue" expectation, and if the client is not directly
2869   connected to an HTTP/1.1 origin server, and if the client sees the
2870   connection close before receiving a status line from the server, the
2871   client &SHOULD; retry the request.  If the client does retry this
2872   request, it &MAY; use the following "binary exponential backoff"
2873   algorithm to be assured of obtaining a reliable response:
2874  <list style="numbers">
2875    <t>
2876      Initiate a new connection to the server
2877    </t>
2878    <t>
2879      Transmit the request-line, header fields, and the CRLF that
2880      indicates the end of header fields.
2881    </t>
2882    <t>
2883      Initialize a variable R to the estimated round-trip time to the
2884         server (e.g., based on the time it took to establish the
2885         connection), or to a constant value of 5 seconds if the round-trip
2886         time is not available.
2887    </t>
2888    <t>
2889       Compute T = R * (2**N), where N is the number of previous
2890         retries of this request.
2891    </t>
2892    <t>
2893       Wait either for an error response from the server, or for T
2894         seconds (whichever comes first)
2895    </t>
2896    <t>
2897       If no error response is received, after T seconds transmit the
2898         body of the request.
2899    </t>
2900    <t>
2901       If client sees that the connection is closed prematurely,
2902         repeat from step 1 until the request is accepted, an error
2903         response is received, or the user becomes impatient and
2904         terminates the retry process.
2905    </t>
2906  </list>
2909   If at any point an error status code is received, the client
2910  <list style="symbols">
2911      <t>&SHOULD-NOT;  continue and</t>
2913      <t>&SHOULD; close the connection if it has not completed sending the
2914        request message.</t>
2915    </list>
2922<section title="Miscellaneous notes that might disappear" anchor="misc">
2923<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2925   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2929<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2931   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2935<section title="Interception of HTTP for access control" anchor="http.intercept">
2937   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2941<section title="Use of HTTP by other protocols" anchor="http.others">
2943   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2944   Extensions of HTTP like WebDAV.</cref>
2948<section title="Use of HTTP by media type specification" anchor="">
2950   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2955<section title="Header Field Definitions" anchor="header.field.definitions">
2957   This section defines the syntax and semantics of HTTP header fields
2958   related to message framing and transport protocols.
2961<section title="Connection" anchor="header.connection">
2962  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2963  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2964  <x:anchor-alias value="Connection"/>
2965  <x:anchor-alias value="connection-token"/>
2966  <x:anchor-alias value="Connection-v"/>
2968   The "Connection" header field allows the sender to specify
2969   options that are desired only for that particular connection.
2970   Such connection options &MUST; be removed or replaced before the
2971   message can be forwarded downstream by a proxy or gateway.
2972   This mechanism also allows the sender to indicate which HTTP
2973   header fields used in the message are only intended for the
2974   immediate recipient ("hop-by-hop"), as opposed to all recipients
2975   on the chain ("end-to-end"), enabling the message to be
2976   self-descriptive and allowing future connection-specific extensions
2977   to be deployed in HTTP without fear that they will be blindly
2978   forwarded by previously deployed intermediaries.
2981   The Connection header field's value has the following grammar:
2983<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"/>
2984  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2985  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2986  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2989   A proxy or gateway &MUST; parse a received Connection
2990   header field before a message is forwarded and, for each
2991   connection-token in this field, remove any header field(s) from
2992   the message with the same name as the connection-token, and then
2993   remove the Connection header field itself or replace it with the
2994   sender's own connection options for the forwarded message.
2997   A sender &MUST-NOT; include field-names in the Connection header
2998   field-value for fields that are defined as expressing constraints
2999   for all recipients in the request or response chain, such as the
3000   Cache-Control header field (&header-cache-control;).
3003   The connection options do not have to correspond to a header field
3004   present in the message, since a connection-specific header field
3005   might not be needed if there are no parameters associated with that
3006   connection option.  Recipients that trigger certain connection
3007   behavior based on the presence of connection options &MUST; do so
3008   based on the presence of the connection-token rather than only the
3009   presence of the optional header field.  In other words, if the
3010   connection option is received as a header field but not indicated
3011   within the Connection field-value, then the recipient &MUST; ignore
3012   the connection-specific header field because it has likely been
3013   forwarded by an intermediary that is only partially compliant.
3016   When defining new connection options, specifications ought to
3017   carefully consider existing deployed header fields and ensure
3018   that the new connection-token does not share the same name as
3019   an unrelated header field that might already be deployed.
3020   Defining a new connection-token essentially reserves that potential
3021   field-name for carrying additional information related to the
3022   connection option, since it would be unwise for senders to use
3023   that field-name for anything else.
3026   HTTP/1.1 defines the "close" connection option for the sender to
3027   signal that the connection will be closed after completion of the
3028   response. For example,
3030<figure><artwork type="example">
3031  Connection: close
3034   in either the request or the response header fields indicates that
3035   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3036   after the current request/response is complete.
3039   An HTTP/1.1 client that does not support persistent connections &MUST;
3040   include the "close" connection option in every request message.
3043   An HTTP/1.1 server that does not support persistent connections &MUST;
3044   include the "close" connection option in every response message that
3045   does not have a 1xx (Informational) status code.
3049<section title="Content-Length" anchor="header.content-length">
3050  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3051  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3052  <x:anchor-alias value="Content-Length"/>
3053  <x:anchor-alias value="Content-Length-v"/>
3055   The "Content-Length" header field indicates the size of the
3056   message-body, in decimal number of octets, for any message other than
3057   a response to a HEAD request or a response with a status code of 304.
3058   In the case of a response to a HEAD request, Content-Length indicates
3059   the size of the payload body (not including any potential transfer-coding)
3060   that would have been sent had the request been a GET.
3061   In the case of a 304 (Not Modified) response to a GET request,
3062   Content-Length indicates the size of the payload body (not including
3063   any potential transfer-coding) that would have been sent in a 200 (OK)
3064   response.
3066<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
3067  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
3068  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
3071   An example is
3073<figure><artwork type="example">
3074  Content-Length: 3495
3077   Implementations &SHOULD; use this field to indicate the message-body
3078   length when no transfer-coding is being applied and the
3079   payload's body length can be determined prior to being transferred.
3080   <xref target="message.body"/> describes how recipients determine the length
3081   of a message-body.
3084   Any Content-Length greater than or equal to zero is a valid value.
3087   Note that the use of this field in HTTP is significantly different from
3088   the corresponding definition in MIME, where it is an optional field
3089   used within the "message/external-body" content-type.
3093<section title="Date" anchor="">
3094  <iref primary="true" item="Date header field" x:for-anchor=""/>
3095  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3096  <x:anchor-alias value="Date"/>
3097  <x:anchor-alias value="Date-v"/>
3099   The "Date" header field represents the date and time at which
3100   the message was originated, having the same semantics as the Origination
3101   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3102   The field value is an HTTP-date, as described in <xref target=""/>;
3103   it &MUST; be sent in rfc1123-date format.
3105<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3106  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3107  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3110   An example is
3112<figure><artwork type="example">
3113  Date: Tue, 15 Nov 1994 08:12:31 GMT
3116   Origin servers &MUST; include a Date header field in all responses,
3117   except in these cases:
3118  <list style="numbers">
3119      <t>If the response status code is 100 (Continue) or 101 (Switching
3120         Protocols), the response &MAY; include a Date header field, at
3121         the server's option.</t>
3123      <t>If the response status code conveys a server error, e.g., 500
3124         (Internal Server Error) or 503 (Service Unavailable), and it is
3125         inconvenient or impossible to generate a valid Date.</t>
3127      <t>If the server does not have a clock that can provide a
3128         reasonable approximation of the current time, its responses
3129         &MUST-NOT; include a Date header field. In this case, the rules
3130         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3131  </list>
3134   A received message that does not have a Date header field &MUST; be
3135   assigned one by the recipient if the message will be cached by that
3136   recipient.
3139   Clients can use the Date header field as well; in order to keep request
3140   messages small, they are advised not to include it when it doesn't convey
3141   any useful information (as it is usually the case for requests that do not
3142   contain a payload).
3145   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3146   time subsequent to the generation of the message. It &SHOULD; represent
3147   the best available approximation of the date and time of message
3148   generation, unless the implementation has no means of generating a
3149   reasonably accurate date and time. In theory, the date ought to
3150   represent the moment just before the payload is generated. In
3151   practice, the date can be generated at any time during the message
3152   origination without affecting its semantic value.
3155<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3157   Some origin server implementations might not have a clock available.
3158   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3159   values to a response, unless these values were associated
3160   with the resource by a system or user with a reliable clock. It &MAY;
3161   assign an Expires value that is known, at or before server
3162   configuration time, to be in the past (this allows "pre-expiration"
3163   of responses without storing separate Expires values for each
3164   resource).
3169<section title="Host" anchor="">
3170  <iref primary="true" item="Host header field" x:for-anchor=""/>
3171  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3172  <x:anchor-alias value="Host"/>
3173  <x:anchor-alias value="Host-v"/>
3175   The "Host" header field in a request provides the host and port
3176   information from the target resource's URI, enabling the origin
3177   server to distinguish between resources while servicing requests
3178   for multiple host names on a single IP address.  Since the Host
3179   field-value is critical information for handling a request, it
3180   &SHOULD; be sent as the first header field following the Request-Line.
3182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3183  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3184  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3187   A client &MUST; send a Host header field in all HTTP/1.1 request
3188   messages.  If the target resource's URI includes an authority
3189   component, then the Host field-value &MUST; be identical to that
3190   authority component after excluding any userinfo (<xref target="http.uri"/>).
3191   If the authority component is missing or undefined for the target
3192   resource's URI, then the Host header field &MUST; be sent with an
3193   empty field-value.
3196   For example, a GET request to the origin server for
3197   &lt;; would begin with:
3199<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3200GET /pub/WWW/ HTTP/1.1
3204   The Host header field &MUST; be sent in an HTTP/1.1 request even
3205   if the request-target is in the form of an absolute-URI, since this
3206   allows the Host information to be forwarded through ancient HTTP/1.0
3207   proxies that might not have implemented Host.
3210   When an HTTP/1.1 proxy receives a request with a request-target in
3211   the form of an absolute-URI, the proxy &MUST; ignore the received
3212   Host header field (if any) and instead replace it with the host
3213   information of the request-target.  When a proxy forwards a request,
3214   it &MUST; generate the Host header field based on the received
3215   absolute-URI rather than the received Host.
3218   Since the Host header field acts as an application-level routing
3219   mechanism, it is a frequent target for malware seeking to poison
3220   a shared cache or redirect a request to an unintended server.
3221   An interception proxy is particularly vulnerable if it relies on
3222   the Host header field value for redirecting requests to internal
3223   servers, or for use as a cache key in a shared cache, without
3224   first verifying that the intercepted connection is targeting a
3225   valid IP address for that host.
3228   A server &MUST; respond with a 400 (Bad Request) status code to
3229   any HTTP/1.1 request message that lacks a Host header field and
3230   to any request message that contains more than one Host header field
3231   or a Host header field with an invalid field-value.
3234   See Sections <xref target="" format="counter"/>
3235   and <xref target="" format="counter"/>
3236   for other requirements relating to Host.
3240<section title="TE" anchor="header.te">
3241  <iref primary="true" item="TE header field" x:for-anchor=""/>
3242  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3243  <x:anchor-alias value="TE"/>
3244  <x:anchor-alias value="TE-v"/>
3245  <x:anchor-alias value="t-codings"/>
3246  <x:anchor-alias value="te-params"/>
3247  <x:anchor-alias value="te-ext"/>
3249   The "TE" header field indicates what extension transfer-codings
3250   it is willing to accept in the response, and whether or not it is
3251   willing to accept trailer fields in a chunked transfer-coding.
3254   Its value consists of the keyword "trailers" and/or a comma-separated
3255   list of extension transfer-coding names with optional accept
3256   parameters (as described in <xref target="transfer.codings"/>).
3258<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"/>
3259  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3260  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3261  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3262  <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> )
3263  <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> ]
3266   The presence of the keyword "trailers" indicates that the client is
3267   willing to accept trailer fields in a chunked transfer-coding, as
3268   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3269   transfer-coding values even though it does not itself represent a
3270   transfer-coding.
3273   Examples of its use are:
3275<figure><artwork type="example">
3276  TE: deflate
3277  TE:
3278  TE: trailers, deflate;q=0.5
3281   The TE header field only applies to the immediate connection.
3282   Therefore, the keyword &MUST; be supplied within a Connection header
3283   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3286   A server tests whether a transfer-coding is acceptable, according to
3287   a TE field, using these rules:
3288  <list style="numbers">
3289    <x:lt>
3290      <t>The "chunked" transfer-coding is always acceptable. If the
3291         keyword "trailers" is listed, the client indicates that it is
3292         willing to accept trailer fields in the chunked response on
3293         behalf of itself and any downstream clients. The implication is
3294         that, if given, the client is stating that either all
3295         downstream clients are willing to accept trailer fields in the
3296         forwarded response, or that it will attempt to buffer the
3297         response on behalf of downstream recipients.
3298      </t><t>
3299         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3300         chunked response such that a client can be assured of buffering
3301         the entire response.</t>
3302    </x:lt>
3303    <x:lt>
3304      <t>If the transfer-coding being tested is one of the transfer-codings
3305         listed in the TE field, then it is acceptable unless it
3306         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3307         qvalue of 0 means "not acceptable".)</t>
3308    </x:lt>
3309    <x:lt>
3310      <t>If multiple transfer-codings are acceptable, then the
3311         acceptable transfer-coding with the highest non-zero qvalue is
3312         preferred.  The "chunked" transfer-coding always has a qvalue
3313         of 1.</t>
3314    </x:lt>
3315  </list>
3318   If the TE field-value is empty or if no TE field is present, the only
3319   transfer-coding is "chunked". A message with no transfer-coding is
3320   always acceptable.
3324<section title="Trailer" anchor="header.trailer">
3325  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3326  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3327  <x:anchor-alias value="Trailer"/>
3328  <x:anchor-alias value="Trailer-v"/>
3330   The "Trailer" header field indicates that the given set of
3331   header fields is present in the trailer of a message encoded with
3332   chunked transfer-coding.
3334<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3335  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3336  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3339   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3340   message using chunked transfer-coding with a non-empty trailer. Doing
3341   so allows the recipient to know which header fields to expect in the
3342   trailer.
3345   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3346   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3347   trailer fields in a "chunked" transfer-coding.
3350   Message header fields listed in the Trailer header field &MUST-NOT;
3351   include the following header fields:
3352  <list style="symbols">
3353    <t>Transfer-Encoding</t>
3354    <t>Content-Length</t>
3355    <t>Trailer</t>
3356  </list>
3360<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3361  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3362  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3363  <x:anchor-alias value="Transfer-Encoding"/>
3364  <x:anchor-alias value="Transfer-Encoding-v"/>
3366   The "Transfer-Encoding" header field indicates what transfer-codings
3367   (if any) have been applied to the message body. It differs from
3368   Content-Encoding (&content-codings;) in that transfer-codings are a property
3369   of the message (and therefore are removed by intermediaries), whereas
3370   content-codings are not.
3372<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3373  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3374                        <x:ref>Transfer-Encoding-v</x:ref>
3375  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3378   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3380<figure><artwork type="example">
3381  Transfer-Encoding: chunked
3384   If multiple encodings have been applied to a representation, the transfer-codings
3385   &MUST; be listed in the order in which they were applied.
3386   Additional information about the encoding parameters &MAY; be provided
3387   by other header fields not defined by this specification.
3390   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3391   header field.
3395<section title="Upgrade" anchor="header.upgrade">
3396  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3397  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3398  <x:anchor-alias value="Upgrade"/>
3399  <x:anchor-alias value="Upgrade-v"/>
3401   The "Upgrade" header field allows the client to specify what
3402   additional communication protocols it would like to use, if the server
3403   chooses to switch protocols. Servers can use it to indicate what protocols
3404   they are willing to switch to.
3406<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3407  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3408  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3411   For example,
3413<figure><artwork type="example">
3414  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3417   The Upgrade header field is intended to provide a simple mechanism
3418   for transition from HTTP/1.1 to some other, incompatible protocol. It
3419   does so by allowing the client to advertise its desire to use another
3420   protocol, such as a later version of HTTP with a higher major version
3421   number, even though the current request has been made using HTTP/1.1.
3422   This eases the difficult transition between incompatible protocols by
3423   allowing the client to initiate a request in the more commonly
3424   supported protocol while indicating to the server that it would like
3425   to use a "better" protocol if available (where "better" is determined
3426   by the server, possibly according to the nature of the request method
3427   or target resource).
3430   The Upgrade header field only applies to switching application-layer
3431   protocols upon the existing transport-layer connection. Upgrade
3432   cannot be used to insist on a protocol change; its acceptance and use
3433   by the server is optional. The capabilities and nature of the
3434   application-layer communication after the protocol change is entirely
3435   dependent upon the new protocol chosen, although the first action
3436   after changing the protocol &MUST; be a response to the initial HTTP
3437   request containing the Upgrade header field.
3440   The Upgrade header field only applies to the immediate connection.
3441   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3442   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3443   HTTP/1.1 message.
3446   The Upgrade header field cannot be used to indicate a switch to a
3447   protocol on a different connection. For that purpose, it is more
3448   appropriate to use a 3xx redirection response (&status-3xx;).
3451   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3452   Protocols) responses to indicate which protocol(s) are being switched to,
3453   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3454   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3455   response to indicate that they are willing to upgrade to one of the
3456   specified protocols.
3459   This specification only defines the protocol name "HTTP" for use by
3460   the family of Hypertext Transfer Protocols, as defined by the HTTP
3461   version rules of <xref target="http.version"/> and future updates to this
3462   specification. Additional tokens can be registered with IANA using the
3463   registration procedure defined below. 
3466<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3468   The HTTP Upgrade Token Registry defines the name space for product
3469   tokens used to identify protocols in the Upgrade header field.
3470   Each registered token is associated with contact information and
3471   an optional set of specifications that details how the connection
3472   will be processed after it has been upgraded.
3475   Registrations are allowed on a First Come First Served basis as
3476   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3477   specifications need not be IETF documents or be subject to IESG review.
3478   Registrations are subject to the following rules:
3479  <list style="numbers">
3480    <t>A token, once registered, stays registered forever.</t>
3481    <t>The registration &MUST; name a responsible party for the
3482       registration.</t>
3483    <t>The registration &MUST; name a point of contact.</t>
3484    <t>The registration &MAY; name a set of specifications associated with that
3485       token. Such specifications need not be publicly available.</t>
3486    <t>The responsible party &MAY; change the registration at any time.
3487       The IANA will keep a record of all such changes, and make them
3488       available upon request.</t>
3489    <t>The responsible party for the first registration of a "product"
3490       token &MUST; approve later registrations of a "version" token
3491       together with that "product" token before they can be registered.</t>
3492    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3493       for a token. This will normally only be used in the case when a
3494       responsible party cannot be contacted.</t>
3495  </list>
3502<section title="Via" anchor="header.via">
3503  <iref primary="true" item="Via header field" x:for-anchor=""/>
3504  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3505  <x:anchor-alias value="protocol-name"/>
3506  <x:anchor-alias value="protocol-version"/>
3507  <x:anchor-alias value="pseudonym"/>
3508  <x:anchor-alias value="received-by"/>
3509  <x:anchor-alias value="received-protocol"/>
3510  <x:anchor-alias value="Via"/>
3511  <x:anchor-alias value="Via-v"/>
3513   The "Via" header field &MUST; be sent by a proxy or gateway to
3514   indicate the intermediate protocols and recipients between the user
3515   agent and the server on requests, and between the origin server and
3516   the client on responses. It is analogous to the "Received" field
3517   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3518   and is intended to be used for tracking message forwards,
3519   avoiding request loops, and identifying the protocol capabilities of
3520   all senders along the request/response chain.
3522<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"/>
3523  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3524  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3525                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3526  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3527  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3528  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3529  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3530  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3533   The received-protocol indicates the protocol version of the message
3534   received by the server or client along each segment of the
3535   request/response chain. The received-protocol version is appended to
3536   the Via field value when the message is forwarded so that information
3537   about the protocol capabilities of upstream applications remains
3538   visible to all recipients.
3541   The protocol-name is excluded if and only if it would be "HTTP". The
3542   received-by field is normally the host and optional port number of a
3543   recipient server or client that subsequently forwarded the message.
3544   However, if the real host is considered to be sensitive information,
3545   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3546   be assumed to be the default port of the received-protocol.
3549   Multiple Via field values represent each proxy or gateway that has
3550   forwarded the message. Each recipient &MUST; append its information
3551   such that the end result is ordered according to the sequence of
3552   forwarding applications.
3555   Comments &MAY; be used in the Via header field to identify the software
3556   of each recipient, analogous to the User-Agent and Server header fields.
3557   However, all comments in the Via field are optional and &MAY; be removed
3558   by any recipient prior to forwarding the message.
3561   For example, a request message could be sent from an HTTP/1.0 user
3562   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3563   forward the request to a public proxy at, which completes
3564   the request by forwarding it to the origin server at
3565   The request received by would then have the following
3566   Via header field:
3568<figure><artwork type="example">
3569  Via: 1.0 fred, 1.1 (Apache/1.1)
3572   A proxy or gateway used as a portal through a network firewall
3573   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3574   region unless it is explicitly enabled to do so. If not enabled, the
3575   received-by host of any host behind the firewall &SHOULD; be replaced
3576   by an appropriate pseudonym for that host.
3579   For organizations that have strong privacy requirements for hiding
3580   internal structures, a proxy or gateway &MAY; combine an ordered
3581   subsequence of Via header field entries with identical received-protocol
3582   values into a single such entry. For example,
3584<figure><artwork type="example">
3585  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3588  could be collapsed to
3590<figure><artwork type="example">
3591  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3594   Senders &SHOULD-NOT; combine multiple entries unless they are all
3595   under the same organizational control and the hosts have already been
3596   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3597   have different received-protocol values.
3603<section title="IANA Considerations" anchor="IANA.considerations">
3605<section title="Header Field Registration" anchor="header.field.registration">
3607   The Message Header Field Registry located at <eref target=""/> shall be updated
3608   with the permanent registrations below (see <xref target="RFC3864"/>):
3610<?BEGININC p1-messaging.iana-headers ?>
3611<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3612<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3613   <ttcol>Header Field Name</ttcol>
3614   <ttcol>Protocol</ttcol>
3615   <ttcol>Status</ttcol>
3616   <ttcol>Reference</ttcol>
3618   <c>Connection</c>
3619   <c>http</c>
3620   <c>standard</c>
3621   <c>
3622      <xref target="header.connection"/>
3623   </c>
3624   <c>Content-Length</c>
3625   <c>http</c>
3626   <c>standard</c>
3627   <c>
3628      <xref target="header.content-length"/>
3629   </c>
3630   <c>Date</c>
3631   <c>http</c>
3632   <c>standard</c>
3633   <c>
3634      <xref target=""/>
3635   </c>
3636   <c>Host</c>
3637   <c>http</c>
3638   <c>standard</c>
3639   <c>
3640      <xref target=""/>
3641   </c>
3642   <c>TE</c>
3643   <c>http</c>
3644   <c>standard</c>
3645   <c>
3646      <xref target="header.te"/>
3647   </c>
3648   <c>Trailer</c>
3649   <c>http</c>
3650   <c>standard</c>
3651   <c>
3652      <xref target="header.trailer"/>
3653   </c>
3654   <c>Transfer-Encoding</c>
3655   <c>http</c>
3656   <c>standard</c>
3657   <c>
3658      <xref target="header.transfer-encoding"/>
3659   </c>
3660   <c>Upgrade</c>
3661   <c>http</c>
3662   <c>standard</c>
3663   <c>
3664      <xref target="header.upgrade"/>
3665   </c>
3666   <c>Via</c>
3667   <c>http</c>
3668   <c>standard</c>
3669   <c>
3670      <xref target="header.via"/>
3671   </c>
3674<?ENDINC p1-messaging.iana-headers ?>
3676   The change controller is: "IETF ( - Internet Engineering Task Force".
3680<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3682   The entries for the "http" and "https" URI Schemes in the registry located at
3683   <eref target=""/>
3684   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3685   and <xref target="https.uri" format="counter"/> of this document
3686   (see <xref target="RFC4395"/>).
3690<section title="Internet Media Type Registrations" anchor="">
3692   This document serves as the specification for the Internet media types
3693   "message/http" and "application/http". The following is to be registered with
3694   IANA (see <xref target="RFC4288"/>).
3696<section title="Internet Media Type message/http" anchor="">
3697<iref item="Media Type" subitem="message/http" primary="true"/>
3698<iref item="message/http Media Type" primary="true"/>
3700   The message/http type can be used to enclose a single HTTP request or
3701   response message, provided that it obeys the MIME restrictions for all
3702   "message" types regarding line length and encodings.
3705  <list style="hanging" x:indent="12em">
3706    <t hangText="Type name:">
3707      message
3708    </t>
3709    <t hangText="Subtype name:">
3710      http
3711    </t>
3712    <t hangText="Required parameters:">
3713      none
3714    </t>
3715    <t hangText="Optional parameters:">
3716      version, msgtype
3717      <list style="hanging">
3718        <t hangText="version:">
3719          The HTTP-Version number of the enclosed message
3720          (e.g., "1.1"). If not present, the version can be
3721          determined from the first line of the body.
3722        </t>
3723        <t hangText="msgtype:">
3724          The message type &mdash; "request" or "response". If not
3725          present, the type can be determined from the first
3726          line of the body.
3727        </t>
3728      </list>
3729    </t>
3730    <t hangText="Encoding considerations:">
3731      only "7bit", "8bit", or "binary" are permitted
3732    </t>
3733    <t hangText="Security considerations:">
3734      none
3735    </t>
3736    <t hangText="Interoperability considerations:">
3737      none
3738    </t>
3739    <t hangText="Published specification:">
3740      This specification (see <xref target=""/>).
3741    </t>
3742    <t hangText="Applications that use this media type:">
3743    </t>
3744    <t hangText="Additional information:">
3745      <list style="hanging">
3746        <t hangText="Magic number(s):">none</t>
3747        <t hangText="File extension(s):">none</t>
3748        <t hangText="Macintosh file type code(s):">none</t>
3749      </list>
3750    </t>
3751    <t hangText="Person and email address to contact for further information:">
3752      See Authors Section.
3753    </t>
3754    <t hangText="Intended usage:">
3755      COMMON
3756    </t>
3757    <t hangText="Restrictions on usage:">
3758      none
3759    </t>
3760    <t hangText="Author/Change controller:">
3761      IESG
3762    </t>
3763  </list>
3766<section title="Internet Media Type application/http" anchor="">
3767<iref item="Media Type" subitem="application/http" primary="true"/>
3768<iref item="application/http Media Type" primary="true"/>
3770   The application/http type can be used to enclose a pipeline of one or more
3771   HTTP request or response messages (not intermixed).
3774  <list style="hanging" x:indent="12em">
3775    <t hangText="Type name:">
3776      application
3777    </t>
3778    <t hangText="Subtype name:">
3779      http
3780    </t>
3781    <t hangText="Required parameters:">
3782      none
3783    </t>
3784    <t hangText="Optional parameters:">
3785      version, msgtype
3786      <list style="hanging">
3787        <t hangText="version:">
3788          The HTTP-Version number of the enclosed messages
3789          (e.g., "1.1"). If not present, the version can be
3790          determined from the first line of the body.
3791        </t>
3792        <t hangText="msgtype:">
3793          The message type &mdash; "request" or "response". If not
3794          present, the type can be determined from the first
3795          line of the body.
3796        </t>
3797      </list>
3798    </t>
3799    <t hangText="Encoding considerations:">
3800      HTTP messages enclosed by this type
3801      are in "binary" format; use of an appropriate
3802      Content-Transfer-Encoding is required when
3803      transmitted via E-mail.
3804    </t>
3805    <t hangText="Security considerations:">
3806      none
3807    </t>
3808    <t hangText="Interoperability considerations:">
3809      none
3810    </t>
3811    <t hangText="Published specification:">
3812      This specification (see <xref target=""/>).
3813    </t>
3814    <t hangText="Applications that use this media type:">
3815    </t>
3816    <t hangText="Additional information:">
3817      <list style="hanging">
3818        <t hangText="Magic number(s):">none</t>
3819        <t hangText="File extension(s):">none</t>
3820        <t hangText="Macintosh file type code(s):">none</t>
3821      </list>
3822    </t>
3823    <t hangText="Person and email address to contact for further information:">
3824      See Authors Section.
3825    </t>
3826    <t hangText="Intended usage:">
3827      COMMON
3828    </t>
3829    <t hangText="Restrictions on usage:">
3830      none
3831    </t>
3832    <t hangText="Author/Change controller:">
3833      IESG
3834    </t>
3835  </list>
3840<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3842   The registration procedure for HTTP Transfer Codings is now defined by
3843   <xref target="transfer.coding.registry"/> of this document.
3846   The HTTP Transfer Codings Registry located at <eref target=""/>
3847   shall be updated with the registrations below:
3849<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3850   <ttcol>Name</ttcol>
3851   <ttcol>Description</ttcol>
3852   <ttcol>Reference</ttcol>
3853   <c>chunked</c>
3854   <c>Transfer in a series of chunks</c>
3855   <c>
3856      <xref target="chunked.encoding"/>
3857   </c>
3858   <c>compress</c>
3859   <c>UNIX "compress" program method</c>
3860   <c>
3861      <xref target="compress.coding"/>
3862   </c>
3863   <c>deflate</c>
3864   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3865   the "zlib" data format (<xref target="RFC1950"/>)
3866   </c>
3867   <c>
3868      <xref target="deflate.coding"/>
3869   </c>
3870   <c>gzip</c>
3871   <c>Same as GNU zip <xref target="RFC1952"/></c>
3872   <c>
3873      <xref target="gzip.coding"/>
3874   </c>
3878<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3880   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3881   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3882   by <xref target="upgrade.token.registry"/> of this document.
3885   The HTTP Status Code Registry located at <eref target=""/>
3886   shall be updated with the registration below:
3888<texttable align="left" suppress-title="true">
3889   <ttcol>Value</ttcol>
3890   <ttcol>Description</ttcol>
3891   <ttcol>Reference</ttcol>
3893   <c>HTTP</c>
3894   <c>Hypertext Transfer Protocol</c>
3895   <c><xref target="http.version"/> of this specification</c>
3896<!-- IANA should add this without our instructions; emailed on June 05, 2009
3897   <c>TLS/1.0</c>
3898   <c>Transport Layer Security</c>
3899   <c><xref target="RFC2817"/></c> -->
3906<section title="Security Considerations" anchor="security.considerations">
3908   This section is meant to inform application developers, information
3909   providers, and users of the security limitations in HTTP/1.1 as
3910   described by this document. The discussion does not include
3911   definitive solutions to the problems revealed, though it does make
3912   some suggestions for reducing security risks.
3915<section title="Personal Information" anchor="personal.information">
3917   HTTP clients are often privy to large amounts of personal information
3918   (e.g., the user's name, location, mail address, passwords, encryption
3919   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3920   leakage of this information.
3921   We very strongly recommend that a convenient interface be provided
3922   for the user to control dissemination of such information, and that
3923   designers and implementors be particularly careful in this area.
3924   History shows that errors in this area often create serious security
3925   and/or privacy problems and generate highly adverse publicity for the
3926   implementor's company.
3930<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3932   A server is in the position to save personal data about a user's
3933   requests which might identify their reading patterns or subjects of
3934   interest. This information is clearly confidential in nature and its
3935   handling can be constrained by law in certain countries. People using
3936   HTTP to provide data are responsible for ensuring that
3937   such material is not distributed without the permission of any
3938   individuals that are identifiable by the published results.
3942<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3944   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3945   the documents returned by HTTP requests to be only those that were
3946   intended by the server administrators. If an HTTP server translates
3947   HTTP URIs directly into file system calls, the server &MUST; take
3948   special care not to serve files that were not intended to be
3949   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3950   other operating systems use ".." as a path component to indicate a
3951   directory level above the current one. On such a system, an HTTP
3952   server &MUST; disallow any such construct in the request-target if it
3953   would otherwise allow access to a resource outside those intended to
3954   be accessible via the HTTP server. Similarly, files intended for
3955   reference only internally to the server (such as access control
3956   files, configuration files, and script code) &MUST; be protected from
3957   inappropriate retrieval, since they might contain sensitive
3958   information. Experience has shown that minor bugs in such HTTP server
3959   implementations have turned into security risks.
3963<section title="DNS Spoofing" anchor="dns.spoofing">
3965   Clients using HTTP rely heavily on the Domain Name Service, and are
3966   thus generally prone to security attacks based on the deliberate
3967   mis-association of IP addresses and DNS names. Clients need to be
3968   cautious in assuming the continuing validity of an IP number/DNS name
3969   association.
3972   In particular, HTTP clients &SHOULD; rely on their name resolver for
3973   confirmation of an IP number/DNS name association, rather than
3974   caching the result of previous host name lookups. Many platforms
3975   already can cache host name lookups locally when appropriate, and
3976   they &SHOULD; be configured to do so. It is proper for these lookups to
3977   be cached, however, only when the TTL (Time To Live) information
3978   reported by the name server makes it likely that the cached
3979   information will remain useful.
3982   If HTTP clients cache the results of host name lookups in order to
3983   achieve a performance improvement, they &MUST; observe the TTL
3984   information reported by DNS.
3987   If HTTP clients do not observe this rule, they could be spoofed when
3988   a previously-accessed server's IP address changes. As network
3989   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3990   possibility of this form of attack will grow. Observing this
3991   requirement thus reduces this potential security vulnerability.
3994   This requirement also improves the load-balancing behavior of clients
3995   for replicated servers using the same DNS name and reduces the
3996   likelihood of a user's experiencing failure in accessing sites which
3997   use that strategy.
4001<section title="Proxies and Caching" anchor="attack.proxies">
4003   By their very nature, HTTP proxies are men-in-the-middle, and
4004   represent an opportunity for man-in-the-middle attacks. Compromise of
4005   the systems on which the proxies run can result in serious security
4006   and privacy problems. Proxies have access to security-related
4007   information, personal information about individual users and
4008   organizations, and proprietary information belonging to users and
4009   content providers. A compromised proxy, or a proxy implemented or
4010   configured without regard to security and privacy considerations,
4011   might be used in the commission of a wide range of potential attacks.
4014   Proxy operators need to protect the systems on which proxies run as
4015   they would protect any system that contains or transports sensitive
4016   information. In particular, log information gathered at proxies often
4017   contains highly sensitive personal information, and/or information
4018   about organizations. Log information needs to be carefully guarded, and
4019   appropriate guidelines for use need to be developed and followed.
4020   (<xref target="abuse.of.server.log.information"/>).
4023   Proxy implementors need to consider the privacy and security
4024   implications of their design and coding decisions, and of the
4025   configuration options they provide to proxy operators (especially the
4026   default configuration).
4029   Users of a proxy need to be aware that proxies are no trustworthier than
4030   the people who run them; HTTP itself cannot solve this problem.
4033   The judicious use of cryptography, when appropriate, might suffice to
4034   protect against a broad range of security and privacy attacks. Such
4035   cryptography is beyond the scope of the HTTP/1.1 specification.
4039<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4041   They exist. They are hard to defend against. Research continues.
4042   Beware.
4047<section title="Acknowledgments" anchor="ack">
4049   HTTP has evolved considerably over the years. It has
4050   benefited from a large and active developer community &mdash; the many
4051   people who have participated on the www-talk mailing list &mdash; and it is
4052   that community which has been most responsible for the success of
4053   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4054   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4055   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4056   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4057   VanHeyningen deserve special recognition for their efforts in
4058   defining early aspects of the protocol.
4061   This document has benefited greatly from the comments of all those
4062   participating in the HTTP-WG. In addition to those already mentioned,
4063   the following individuals have contributed to this specification:
4066   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4067   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4068   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4069   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4070   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4071   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4072   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4073   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4074   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4075   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4076   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4077   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4080   Thanks to the "cave men" of Palo Alto. You know who you are.
4083   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4084   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4085   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4086   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4087   Larry Masinter for their help. And thanks go particularly to Jeff
4088   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4091   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4092   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4093   discovery of many of the problems that this document attempts to
4094   rectify.
4097   This specification makes heavy use of the augmented BNF and generic
4098   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4099   reuses many of the definitions provided by Nathaniel Borenstein and
4100   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4101   specification will help reduce past confusion over the relationship
4102   between HTTP and Internet mail message formats.
4106Acknowledgements TODO list
4108- Jeff Hodges ("effective request URI")
4116<references title="Normative References">
4118<reference anchor="ISO-8859-1">
4119  <front>
4120    <title>
4121     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4122    </title>
4123    <author>
4124      <organization>International Organization for Standardization</organization>
4125    </author>
4126    <date year="1998"/>
4127  </front>
4128  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4131<reference anchor="Part2">
4132  <front>
4133    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4134    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4135      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4136      <address><email></email></address>
4137    </author>
4138    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4139      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4140      <address><email></email></address>
4141    </author>
4142    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4143      <organization abbrev="HP">Hewlett-Packard Company</organization>
4144      <address><email></email></address>
4145    </author>
4146    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4147      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4148      <address><email></email></address>
4149    </author>
4150    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4151      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4152      <address><email></email></address>
4153    </author>
4154    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4155      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4156      <address><email></email></address>
4157    </author>
4158    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4159      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4160      <address><email></email></address>
4161    </author>
4162    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4163      <organization abbrev="W3C">World Wide Web Consortium</organization>
4164      <address><email></email></address>
4165    </author>
4166    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4167      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4168      <address><email></email></address>
4169    </author>
4170    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4171  </front>
4172  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4173  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4176<reference anchor="Part3">
4177  <front>
4178    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4179    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4180      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4181      <address><email></email></address>
4182    </author>
4183    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4184      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4185      <address><email></email></address>
4186    </author>
4187    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4188      <organization abbrev="HP">Hewlett-Packard Company</organization>
4189      <address><email></email></address>
4190    </author>
4191    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4192      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4193      <address><email></email></address>
4194    </author>
4195    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4196      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4197      <address><email></email></address>
4198    </author>
4199    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4200      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4201      <address><email></email></address>
4202    </author>
4203    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4204      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4205      <address><email></email></address>
4206    </author>
4207    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4208      <organization abbrev="W3C">World Wide Web Consortium</organization>
4209      <address><email></email></address>
4210    </author>
4211    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4212      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4213      <address><email></email></address>
4214    </author>
4215    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4216  </front>
4217  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4218  <x:source href="p3-payload.xml" basename="p3-payload"/>
4221<reference anchor="Part6">
4222  <front>
4223    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4224    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4225      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4226      <address><email></email></address>
4227    </author>
4228    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4229      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4230      <address><email></email></address>
4231    </author>
4232    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4233      <organization abbrev="HP">Hewlett-Packard Company</organization>
4234      <address><email></email></address>
4235    </author>
4236    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4237      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4238      <address><email></email></address>
4239    </author>
4240    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4241      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4242      <address><email></email></address>
4243    </author>
4244    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4245      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4246      <address><email></email></address>
4247    </author>
4248    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4249      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4250      <address><email></email></address>
4251    </author>
4252    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4253      <organization abbrev="W3C">World Wide Web Consortium</organization>
4254      <address><email></email></address>
4255    </author>
4256    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4257      <address><email></email></address>
4258    </author>
4259    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4260      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4261      <address><email></email></address>
4262    </author>
4263    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4264  </front>
4265  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4266  <x:source href="p6-cache.xml" basename="p6-cache"/>
4269<reference anchor="RFC5234">
4270  <front>
4271    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4272    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4273      <organization>Brandenburg InternetWorking</organization>
4274      <address>
4275        <email></email>
4276      </address> 
4277    </author>
4278    <author initials="P." surname="Overell" fullname="Paul Overell">
4279      <organization>THUS plc.</organization>
4280      <address>
4281        <email></email>
4282      </address>
4283    </author>
4284    <date month="January" year="2008"/>
4285  </front>
4286  <seriesInfo name="STD" value="68"/>
4287  <seriesInfo name="RFC" value="5234"/>
4290<reference anchor="RFC2119">
4291  <front>
4292    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4293    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4294      <organization>Harvard University</organization>
4295      <address><email></email></address>
4296    </author>
4297    <date month="March" year="1997"/>
4298  </front>
4299  <seriesInfo name="BCP" value="14"/>
4300  <seriesInfo name="RFC" value="2119"/>
4303<reference anchor="RFC3986">
4304 <front>
4305  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4306  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4307    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4308    <address>
4309       <email></email>
4310       <uri></uri>
4311    </address>
4312  </author>
4313  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4314    <organization abbrev="Day Software">Day Software</organization>
4315    <address>
4316      <email></email>
4317      <uri></uri>
4318    </address>
4319  </author>
4320  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4321    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4322    <address>
4323      <email></email>
4324      <uri></uri>
4325    </address>
4326  </author>
4327  <date month='January' year='2005'></date>
4328 </front>
4329 <seriesInfo name="STD" value="66"/>
4330 <seriesInfo name="RFC" value="3986"/>
4333<reference anchor="USASCII">
4334  <front>
4335    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4336    <author>
4337      <organization>American National Standards Institute</organization>
4338    </author>
4339    <date year="1986"/>
4340  </front>
4341  <seriesInfo name="ANSI" value="X3.4"/>
4344<reference anchor="RFC1950">
4345  <front>
4346    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4347    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4348      <organization>Aladdin Enterprises</organization>
4349      <address><email></email></address>
4350    </author>
4351    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4352    <date month="May" year="1996"/>
4353  </front>
4354  <seriesInfo name="RFC" value="1950"/>
4355  <annotation>
4356    RFC 1950 is an Informational RFC, thus it might be less stable than
4357    this specification. On the other hand, this downward reference was
4358    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4359    therefore it is unlikely to cause problems in practice. See also
4360    <xref target="BCP97"/>.
4361  </annotation>
4364<reference anchor="RFC1951">
4365  <front>
4366    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4367    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4368      <organization>Aladdin Enterprises</organization>
4369      <address><email></email></address>
4370    </author>
4371    <date month="May" year="1996"/>
4372  </front>
4373  <seriesInfo name="RFC" value="1951"/>
4374  <annotation>
4375    RFC 1951 is an Informational RFC, thus it might be less stable than
4376    this specification. On the other hand, this downward reference was
4377    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4378    therefore it is unlikely to cause problems in practice. See also
4379    <xref target="BCP97"/>.
4380  </annotation>
4383<reference anchor="RFC1952">
4384  <front>
4385    <title>GZIP file format specification version 4.3</title>
4386    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4387      <organization>Aladdin Enterprises</organization>
4388      <address><email></email></address>
4389    </author>
4390    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4391      <address><email></email></address>
4392    </author>
4393    <author initials="M." surname="Adler" fullname="Mark Adler">
4394      <address><email></email></address>
4395    </author>
4396    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4397      <address><email></email></address>
4398    </author>
4399    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4400      <address><email></email></address>
4401    </author>
4402    <date month="May" year="1996"/>
4403  </front>
4404  <seriesInfo name="RFC" value="1952"/>
4405  <annotation>
4406    RFC 1952 is an Informational RFC, thus it might be less stable than
4407    this specification. On the other hand, this downward reference was
4408    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4409    therefore it is unlikely to cause problems in practice. See also
4410    <xref target="BCP97"/>.
4411  </annotation>
4416<references title="Informative References">
4418<reference anchor="Nie1997" target="">
4419  <front>
4420    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4421    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4422    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4423    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4424    <author initials="H." surname="Lie" fullname="H. Lie"/>
4425    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4426    <date year="1997" month="September"/>
4427  </front>
4428  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4431<reference anchor="Pad1995" target="">
4432  <front>
4433    <title>Improving HTTP Latency</title>
4434    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4435    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4436    <date year="1995" month="December"/>
4437  </front>
4438  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4441<reference anchor="RFC1123">
4442  <front>
4443    <title>Requirements for Internet Hosts - Application and Support</title>
4444    <author initials="R." surname="Braden" fullname="Robert Braden">
4445      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4446      <address><email>Braden@ISI.EDU</email></address>
4447    </author>
4448    <date month="October" year="1989"/>
4449  </front>
4450  <seriesInfo name="STD" value="3"/>
4451  <seriesInfo name="RFC" value="1123"/>
4454<reference anchor="RFC1900">
4455  <front>
4456    <title>Renumbering Needs Work</title>
4457    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4458      <organization>CERN, Computing and Networks Division</organization>
4459      <address><email></email></address>
4460    </author>
4461    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4462      <organization>cisco Systems</organization>
4463      <address><email></email></address>
4464    </author>
4465    <date month="February" year="1996"/>
4466  </front>
4467  <seriesInfo name="RFC" value="1900"/>
4470<reference anchor='RFC1919'>
4471  <front>
4472    <title>Classical versus Transparent IP Proxies</title>
4473    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4474      <address><email></email></address>
4475    </author>
4476    <date year='1996' month='March' />
4477  </front>
4478  <seriesInfo name='RFC' value='1919' />
4481<reference anchor="RFC1945">
4482  <front>
4483    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4484    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4485      <organization>MIT, Laboratory for Computer Science</organization>
4486      <address><email></email></address>
4487    </author>
4488    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4489      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4490      <address><email></email></address>
4491    </author>
4492    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4493      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4494      <address><email></email></address>
4495    </author>
4496    <date month="May" year="1996"/>
4497  </front>
4498  <seriesInfo name="RFC" value="1945"/>
4501<reference anchor="RFC2045">
4502  <front>
4503    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4504    <author initials="N." surname="Freed" fullname="Ned Freed">
4505      <organization>Innosoft International, Inc.</organization>
4506      <address><email></email></address>
4507    </author>
4508    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4509      <organization>First Virtual Holdings</organization>
4510      <address><email></email></address>
4511    </author>
4512    <date month="November" year="1996"/>
4513  </front>
4514  <seriesInfo name="RFC" value="2045"/>
4517<reference anchor="RFC2047">
4518  <front>
4519    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4520    <author initials="K." surname="Moore" fullname="Keith Moore">
4521      <organization>University of Tennessee</organization>
4522      <address><email></email></address>
4523    </author>
4524    <date month="November" year="1996"/>
4525  </front>
4526  <seriesInfo name="RFC" value="2047"/>
4529<reference anchor="RFC2068">
4530  <front>
4531    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4532    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4533      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4534      <address><email></email></address>
4535    </author>
4536    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4537      <organization>MIT Laboratory for Computer Science</organization>
4538      <address><email></email></address>
4539    </author>
4540    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4541      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4542      <address><email></email></address>
4543    </author>
4544    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4545      <organization>MIT Laboratory for Computer Science</organization>
4546      <address><email></email></address>
4547    </author>
4548    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4549      <organization>MIT Laboratory for Computer Science</organization>
4550      <address><email></email></address>
4551    </author>
4552    <date month="January" year="1997"/>
4553  </front>
4554  <seriesInfo name="RFC" value="2068"/>
4557<reference anchor="RFC2145">
4558  <front>
4559    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4560    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4561      <organization>Western Research Laboratory</organization>
4562      <address><email></email></address>
4563    </author>
4564    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4565      <organization>Department of Information and Computer Science</organization>
4566      <address><email></email></address>
4567    </author>
4568    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4569      <organization>MIT Laboratory for Computer Science</organization>
4570      <address><email></email></address>
4571    </author>
4572    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4573      <organization>W3 Consortium</organization>
4574      <address><email></email></address>
4575    </author>
4576    <date month="May" year="1997"/>
4577  </front>
4578  <seriesInfo name="RFC" value="2145"/>
4581<reference anchor="RFC2616">
4582  <front>
4583    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4584    <author initials="R." surname="Fielding" fullname="R. Fielding">
4585      <organization>University of California, Irvine</organization>
4586      <address><email></email></address>
4587    </author>
4588    <author initials="J." surname="Gettys" fullname="J. Gettys">
4589      <organization>W3C</organization>
4590      <address><email></email></address>
4591    </author>
4592    <author initials="J." surname="Mogul" fullname="J. Mogul">
4593      <organization>Compaq Computer Corporation</organization>
4594      <address><email></email></address>
4595    </author>
4596    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4597      <organization>MIT Laboratory for Computer Science</organization>
4598      <address><email></email></address>
4599    </author>
4600    <author initials="L." surname="Masinter" fullname="L. Masinter">
4601      <organization>Xerox Corporation</organization>
4602      <address><email></email></address>
4603    </author>
4604    <author initials="P." surname="Leach" fullname="P. Leach">
4605      <organization>Microsoft Corporation</organization>
4606      <address><email></email></address>
4607    </author>
4608    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4609      <organization>W3C</organization>
4610      <address><email></email></address>
4611    </author>
4612    <date month="June" year="1999"/>
4613  </front>
4614  <seriesInfo name="RFC" value="2616"/>
4617<reference anchor='RFC2817'>
4618  <front>
4619    <title>Upgrading to TLS Within HTTP/1.1</title>
4620    <author initials='R.' surname='Khare' fullname='R. Khare'>
4621      <organization>4K Associates / UC Irvine</organization>
4622      <address><email></email></address>
4623    </author>
4624    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4625      <organization>Agranat Systems, Inc.</organization>
4626      <address><email></email></address>
4627    </author>
4628    <date year='2000' month='May' />
4629  </front>
4630  <seriesInfo name='RFC' value='2817' />
4633<reference anchor='RFC2818'>
4634  <front>
4635    <title>HTTP Over TLS</title>
4636    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4637      <organization>RTFM, Inc.</organization>
4638      <address><email></email></address>
4639    </author>
4640    <date year='2000' month='May' />
4641  </front>
4642  <seriesInfo name='RFC' value='2818' />
4645<reference anchor='RFC2965'>
4646  <front>
4647    <title>HTTP State Management Mechanism</title>
4648    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4649      <organization>Bell Laboratories, Lucent Technologies</organization>
4650      <address><email></email></address>
4651    </author>
4652    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4653      <organization>, Inc.</organization>
4654      <address><email></email></address>
4655    </author>
4656    <date year='2000' month='October' />
4657  </front>
4658  <seriesInfo name='RFC' value='2965' />
4661<reference anchor='RFC3040'>
4662  <front>
4663    <title>Internet Web Replication and Caching Taxonomy</title>
4664    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4665      <organization>Equinix, Inc.</organization>
4666    </author>
4667    <author initials='I.' surname='Melve' fullname='I. Melve'>
4668      <organization>UNINETT</organization>
4669    </author>
4670    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4671      <organization>CacheFlow Inc.</organization>
4672    </author>
4673    <date year='2001' month='January' />
4674  </front>
4675  <seriesInfo name='RFC' value='3040' />
4678<reference anchor='RFC3864'>
4679  <front>
4680    <title>Registration Procedures for Message Header Fields</title>
4681    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4682      <organization>Nine by Nine</organization>
4683      <address><email></email></address>
4684    </author>
4685    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4686      <organization>BEA Systems</organization>
4687      <address><email></email></address>
4688    </author>
4689    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4690      <organization>HP Labs</organization>
4691      <address><email></email></address>
4692    </author>
4693    <date year='2004' month='September' />
4694  </front>
4695  <seriesInfo name='BCP' value='90' />
4696  <seriesInfo name='RFC' value='3864' />
4699<reference anchor="RFC4288">
4700  <front>
4701    <title>Media Type Specifications and Registration Procedures</title>
4702    <author initials="N." surname="Freed" fullname="N. Freed">
4703      <organization>Sun Microsystems</organization>
4704      <address>
4705        <email></email>
4706      </address>
4707    </author>
4708    <author initials="J." surname="Klensin" fullname="J. Klensin">
4709      <address>
4710        <email></email>
4711      </address>
4712    </author>
4713    <date year="2005" month="December"/>
4714  </front>
4715  <seriesInfo name="BCP" value="13"/>
4716  <seriesInfo name="RFC" value="4288"/>
4719<reference anchor='RFC4395'>
4720  <front>
4721    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4722    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4723      <organization>AT&amp;T Laboratories</organization>
4724      <address>
4725        <email></email>
4726      </address>
4727    </author>
4728    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4729      <organization>Qualcomm, Inc.</organization>
4730      <address>
4731        <email></email>
4732      </address>
4733    </author>
4734    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4735      <organization>Adobe Systems</organization>
4736      <address>
4737        <email></email>
4738      </address>
4739    </author>
4740    <date year='2006' month='February' />
4741  </front>
4742  <seriesInfo name='BCP' value='115' />
4743  <seriesInfo name='RFC' value='4395' />
4746<reference anchor='RFC5226'>
4747  <front>
4748    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4749    <author initials='T.' surname='Narten' fullname='T. Narten'>
4750      <organization>IBM</organization>
4751      <address><email></email></address>
4752    </author>
4753    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4754      <organization>Google</organization>
4755      <address><email></email></address>
4756    </author>
4757    <date year='2008' month='May' />
4758  </front>
4759  <seriesInfo name='BCP' value='26' />
4760  <seriesInfo name='RFC' value='5226' />
4763<reference anchor="RFC5322">
4764  <front>
4765    <title>Internet Message Format</title>
4766    <author initials="P." surname="Resnick" fullname="P. Resnick">
4767      <organization>Qualcomm Incorporated</organization>
4768    </author>
4769    <date year="2008" month="October"/>
4770  </front>
4771  <seriesInfo name="RFC" value="5322"/>
4774<reference anchor='draft-ietf-httpstate-cookie'>
4775  <front>
4776    <title>HTTP State Management Mechanism</title>
4777    <author initials="A." surname="Barth" fullname="Adam Barth">
4778      <organization abbrev="U.C. Berkeley">
4779        University of California, Berkeley
4780      </organization>
4781      <address><email></email></address>
4782    </author>
4783    <date year='2011' month='March' />
4784  </front>
4785  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4788<reference anchor='BCP97'>
4789  <front>
4790    <title>Handling Normative References to Standards-Track Documents</title>
4791    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4792      <address>
4793        <email></email>
4794      </address>
4795    </author>
4796    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4797      <organization>MIT</organization>
4798      <address>
4799        <email></email>
4800      </address>
4801    </author>
4802    <date year='2007' month='June' />
4803  </front>
4804  <seriesInfo name='BCP' value='97' />
4805  <seriesInfo name='RFC' value='4897' />
4808<reference anchor="Kri2001" target="">
4809  <front>
4810    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4811    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4812    <date year="2001" month="November"/>
4813  </front>
4814  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4817<reference anchor="Spe" target="">
4818  <front>
4819    <title>Analysis of HTTP Performance Problems</title>
4820    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4821    <date/>
4822  </front>
4825<reference anchor="Tou1998" target="">
4826  <front>
4827  <title>Analysis of HTTP Performance</title>
4828  <author initials="J." surname="Touch" fullname="Joe Touch">
4829    <organization>USC/Information Sciences Institute</organization>
4830    <address><email></email></address>
4831  </author>
4832  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4833    <organization>USC/Information Sciences Institute</organization>
4834    <address><email></email></address>
4835  </author>
4836  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4837    <organization>USC/Information Sciences Institute</organization>
4838    <address><email></email></address>
4839  </author>
4840  <date year="1998" month="Aug"/>
4841  </front>
4842  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4843  <annotation>(original report dated Aug. 1996)</annotation>
4849<section title="Tolerant Applications" anchor="tolerant.applications">
4851   Although this document specifies the requirements for the generation
4852   of HTTP/1.1 messages, not all applications will be correct in their
4853   implementation. We therefore recommend that operational applications
4854   be tolerant of deviations whenever those deviations can be
4855   interpreted unambiguously.
4858   The line terminator for header fields is the sequence CRLF.
4859   However, we recommend that applications, when parsing such headers fields,
4860   recognize a single LF as a line terminator and ignore the leading CR.
4863   The character encoding of a representation &SHOULD; be labeled as the lowest
4864   common denominator of the character codes used within that representation, with
4865   the exception that not labeling the representation is preferred over labeling
4866   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4869   Additional rules for requirements on parsing and encoding of dates
4870   and other potential problems with date encodings include:
4873  <list style="symbols">
4874     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4875        which appears to be more than 50 years in the future is in fact
4876        in the past (this helps solve the "year 2000" problem).</t>
4878     <t>Although all date formats are specified to be case-sensitive,
4879        recipients &SHOULD; match day, week and timezone names
4880        case-insensitively.</t>
4882     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4883        Expires date as earlier than the proper value, but &MUST-NOT;
4884        internally represent a parsed Expires date as later than the
4885        proper value.</t>
4887     <t>All expiration-related calculations &MUST; be done in GMT. The
4888        local time zone &MUST-NOT; influence the calculation or comparison
4889        of an age or expiration time.</t>
4891     <t>If an HTTP header field incorrectly carries a date value with a time
4892        zone other than GMT, it &MUST; be converted into GMT using the
4893        most conservative possible conversion.</t>
4894  </list>
4898<section title="HTTP Version History" anchor="compatibility">
4900   HTTP has been in use by the World-Wide Web global information initiative
4901   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4902   was a simple protocol for hypertext data transfer across the Internet
4903   with only a single request method (GET) and no metadata.
4904   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4905   methods and MIME-like messaging that could include metadata about the data
4906   transferred and modifiers on the request/response semantics. However,
4907   HTTP/1.0 did not sufficiently take into consideration the effects of
4908   hierarchical proxies, caching, the need for persistent connections, or
4909   name-based virtual hosts. The proliferation of incompletely-implemented
4910   applications calling themselves "HTTP/1.0" further necessitated a
4911   protocol version change in order for two communicating applications
4912   to determine each other's true capabilities.
4915   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4916   requirements that enable reliable implementations, adding only
4917   those new features that will either be safely ignored by an HTTP/1.0
4918   recipient or only sent when communicating with a party advertising
4919   compliance with HTTP/1.1.
4922   It is beyond the scope of a protocol specification to mandate
4923   compliance with previous versions. HTTP/1.1 was deliberately
4924   designed, however, to make supporting previous versions easy.
4925   We would expect a general-purpose HTTP/1.1 server to understand
4926   any valid request in the format of HTTP/1.0 and respond appropriately
4927   with an HTTP/1.1 message that only uses features understood (or
4928   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4929   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4932   Since HTTP/0.9 did not support header fields in a request,
4933   there is no mechanism for it to support name-based virtual
4934   hosts (selection of resource by inspection of the Host header
4935   field).  Any server that implements name-based virtual hosts
4936   ought to disable support for HTTP/0.9.  Most requests that
4937   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4938   requests wherein a buggy client failed to properly encode
4939   linear whitespace found in a URI reference and placed in
4940   the request-target.
4943<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4945   This section summarizes major differences between versions HTTP/1.0
4946   and HTTP/1.1.
4949<section title="Multi-homed Web Servers" anchor="">
4951   The requirements that clients and servers support the Host header
4952   field (<xref target=""/>), report an error if it is
4953   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4954   are among the most important changes defined by HTTP/1.1.
4957   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4958   addresses and servers; there was no other established mechanism for
4959   distinguishing the intended server of a request than the IP address
4960   to which that request was directed. The Host header field was
4961   introduced during the development of HTTP/1.1 and, though it was
4962   quickly implemented by most HTTP/1.0 browsers, additional requirements
4963   were placed on all HTTP/1.1 requests in order to ensure complete
4964   adoption.  At the time of this writing, most HTTP-based services
4965   are dependent upon the Host header field for targeting requests.
4969<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4971   For most implementations of HTTP/1.0, each connection is established
4972   by the client prior to the request and closed by the server after
4973   sending the response. However, some implementations implement the
4974   Keep-Alive version of persistent connections described in
4975   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4978   Some clients and servers might wish to be compatible with some
4979   previous implementations of persistent connections in HTTP/1.0
4980   clients and servers. Persistent connections in HTTP/1.0 are
4981   explicitly negotiated as they are not the default behavior. HTTP/1.0
4982   experimental implementations of persistent connections are faulty,
4983   and the new facilities in HTTP/1.1 are designed to rectify these
4984   problems. The problem was that some existing HTTP/1.0 clients might
4985   send Keep-Alive to a proxy server that doesn't understand
4986   Connection, which would then erroneously forward it to the next
4987   inbound server, which would establish the Keep-Alive connection and
4988   result in a hung HTTP/1.0 proxy waiting for the close on the
4989   response. The result is that HTTP/1.0 clients must be prevented from
4990   using Keep-Alive when talking to proxies.
4993   However, talking to proxies is the most important use of persistent
4994   connections, so that prohibition is clearly unacceptable. Therefore,
4995   we need some other mechanism for indicating a persistent connection
4996   is desired, which is safe to use even when talking to an old proxy
4997   that ignores Connection. Persistent connections are the default for
4998   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4999   declaring non-persistence. See <xref target="header.connection"/>.
5004<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5006  Empty list elements in list productions have been deprecated.
5007  (<xref target="notation.abnf"/>)
5010  Rules about implicit linear whitespace between certain grammar productions
5011  have been removed; now it's only allowed when specifically pointed out
5012  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5013  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5014  Non-ASCII content in header fields and reason phrase has been obsoleted and
5015  made opaque (the TEXT rule was removed)
5016  (<xref target="basic.rules"/>)
5019  Clarify that HTTP-Version is case sensitive.
5020  (<xref target="http.version"/>)
5023  Require that invalid whitespace around field-names be rejected.
5024  (<xref target="header.fields"/>)
5027  Require recipients to handle bogus Content-Length header fields as errors.
5028  (<xref target="message.body"/>)
5031  Remove reference to non-existent identity transfer-coding value tokens.
5032  (Sections <xref format="counter" target="message.body"/> and
5033  <xref format="counter" target="transfer.codings"/>)
5036  Update use of abs_path production from RFC 1808 to the path-absolute + query
5037  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5038  request method only.
5039  (<xref target="request-target"/>)
5042  Clarification that the chunk length does not include the count of the octets
5043  in the chunk header and trailer. Furthermore disallowed line folding
5044  in chunk extensions.
5045  (<xref target="chunked.encoding"/>)
5048  Remove hard limit of two connections per server.
5049  (<xref target="persistent.practical"/>)
5052  Clarify exactly when close connection options must be sent.
5053  (<xref target="header.connection"/>)
5056  Define the semantics of the "Upgrade" header field in responses other than
5057  101 (this was incorporated from <xref target="RFC2817"/>).
5058  (<xref target="header.upgrade"/>)
5063<?BEGININC p1-messaging.abnf-appendix ?>
5064<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5066<artwork type="abnf" name="p1-messaging.parsed-abnf">
5067<x:ref>BWS</x:ref> = OWS
5069<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5070<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
5071<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5072 connection-token ] )
5073<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
5074<x:ref>Content-Length-v</x:ref> = 1*DIGIT
5076<x:ref>Date</x:ref> = "Date:" OWS Date-v
5077<x:ref>Date-v</x:ref> = HTTP-date
5079<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5081<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5082<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5083<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5084<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5085 ]
5086<x:ref>Host</x:ref> = "Host:" OWS Host-v
5087<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
5089<x:ref>Method</x:ref> = token
5091<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5093<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5094<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5095<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5096<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5097<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5099<x:ref>Status-Code</x:ref> = 3DIGIT
5100<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5102<x:ref>TE</x:ref> = "TE:" OWS TE-v
5103<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5104<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5105<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5106<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5107<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5108 transfer-coding ] )
5110<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5111<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5112<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5114<x:ref>Via</x:ref> = "Via:" OWS Via-v
5115<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5116 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5117 ] )
5119<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5120<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5121<x:ref>attribute</x:ref> = token
5122<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5124<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5125<x:ref>chunk-data</x:ref> = 1*OCTET
5126<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5127<x:ref>chunk-ext-name</x:ref> = token
5128<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5129<x:ref>chunk-size</x:ref> = 1*HEXDIG
5130<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5131<x:ref>connection-token</x:ref> = token
5132<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5133 / %x2A-5B ; '*'-'['
5134 / %x5D-7E ; ']'-'~'
5135 / obs-text
5137<x:ref>date1</x:ref> = day SP month SP year
5138<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5139<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5140<x:ref>day</x:ref> = 2DIGIT
5141<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5142 / %x54.75.65 ; Tue
5143 / %x57.65.64 ; Wed
5144 / %x54.68.75 ; Thu
5145 / %x46.72.69 ; Fri
5146 / %x53.61.74 ; Sat
5147 / %x53.75.6E ; Sun
5148<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5149 / %x54. ; Tuesday
5150 / %x57.65.64.6E. ; Wednesday
5151 / %x54. ; Thursday
5152 / %x46. ; Friday
5153 / %x53. ; Saturday
5154 / %x53.75.6E.64.61.79 ; Sunday
5156<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5157<x:ref>field-name</x:ref> = token
5158<x:ref>field-value</x:ref> = *( field-content / OWS )
5160<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5161<x:ref>hour</x:ref> = 2DIGIT
5162<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5163<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5165<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5167<x:ref>message-body</x:ref> = *OCTET
5168<x:ref>minute</x:ref> = 2DIGIT
5169<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5170 / %x46.65.62 ; Feb
5171 / %x4D.61.72 ; Mar
5172 / %x41.70.72 ; Apr
5173 / %x4D.61.79 ; May
5174 / %x4A.75.6E ; Jun
5175 / %x4A.75.6C ; Jul
5176 / %x41.75.67 ; Aug
5177 / %x53.65.70 ; Sep
5178 / %x4F.63.74 ; Oct
5179 / %x4E.6F.76 ; Nov
5180 / %x44.65.63 ; Dec
5182<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5183<x:ref>obs-fold</x:ref> = CRLF
5184<x:ref>obs-text</x:ref> = %x80-FF
5186<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5187<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5188<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5189<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5190<x:ref>product</x:ref> = token [ "/" product-version ]
5191<x:ref>product-version</x:ref> = token
5192<x:ref>protocol-name</x:ref> = token
5193<x:ref>protocol-version</x:ref> = token
5194<x:ref>pseudonym</x:ref> = token
5196<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5197 / %x5D-7E ; ']'-'~'
5198 / obs-text
5199<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5200 / %x5D-7E ; ']'-'~'
5201 / obs-text
5202<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5203<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5204<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5205<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5206<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5207<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5209<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5210<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5211<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5212<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5213 / authority
5214<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5215<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5217<x:ref>second</x:ref> = 2DIGIT
5218<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5219 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5220<x:ref>start-line</x:ref> = Request-Line / Status-Line
5222<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5223<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5224 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5225<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5226<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5227<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5228<x:ref>token</x:ref> = 1*tchar
5229<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5230<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5231 transfer-extension
5232<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5233<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5235<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5237<x:ref>value</x:ref> = word
5239<x:ref>word</x:ref> = token / quoted-string
5241<x:ref>year</x:ref> = 4DIGIT
5244<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5245; Chunked-Body defined but not used
5246; Connection defined but not used
5247; Content-Length defined but not used
5248; Date defined but not used
5249; HTTP-message defined but not used
5250; Host defined but not used
5251; Request defined but not used
5252; Response defined but not used
5253; TE defined but not used
5254; Trailer defined but not used
5255; Transfer-Encoding defined but not used
5256; URI-reference defined but not used
5257; Upgrade defined but not used
5258; Via defined but not used
5259; http-URI defined but not used
5260; https-URI defined but not used
5261; partial-URI defined but not used
5262; special defined but not used
5264<?ENDINC p1-messaging.abnf-appendix ?>
5266<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5268<section title="Since RFC 2616">
5270  Extracted relevant partitions from <xref target="RFC2616"/>.
5274<section title="Since draft-ietf-httpbis-p1-messaging-00">
5276  Closed issues:
5277  <list style="symbols">
5278    <t>
5279      <eref target=""/>:
5280      "HTTP Version should be case sensitive"
5281      (<eref target=""/>)
5282    </t>
5283    <t>
5284      <eref target=""/>:
5285      "'unsafe' characters"
5286      (<eref target=""/>)
5287    </t>
5288    <t>
5289      <eref target=""/>:
5290      "Chunk Size Definition"
5291      (<eref target=""/>)
5292    </t>
5293    <t>
5294      <eref target=""/>:
5295      "Message Length"
5296      (<eref target=""/>)
5297    </t>
5298    <t>
5299      <eref target=""/>:
5300      "Media Type Registrations"
5301      (<eref target=""/>)
5302    </t>
5303    <t>
5304      <eref target=""/>:
5305      "URI includes query"
5306      (<eref target=""/>)
5307    </t>
5308    <t>
5309      <eref target=""/>:
5310      "No close on 1xx responses"
5311      (<eref target=""/>)
5312    </t>
5313    <t>
5314      <eref target=""/>:
5315      "Remove 'identity' token references"
5316      (<eref target=""/>)
5317    </t>
5318    <t>
5319      <eref target=""/>:
5320      "Import query BNF"
5321    </t>
5322    <t>
5323      <eref target=""/>:
5324      "qdtext BNF"
5325    </t>
5326    <t>
5327      <eref target=""/>:
5328      "Normative and Informative references"
5329    </t>
5330    <t>
5331      <eref target=""/>:
5332      "RFC2606 Compliance"
5333    </t>
5334    <t>
5335      <eref target=""/>:
5336      "RFC977 reference"
5337    </t>
5338    <t>
5339      <eref target=""/>:
5340      "RFC1700 references"
5341    </t>
5342    <t>
5343      <eref target=""/>:
5344      "inconsistency in date format explanation"
5345    </t>
5346    <t>
5347      <eref target=""/>:
5348      "Date reference typo"
5349    </t>
5350    <t>
5351      <eref target=""/>:
5352      "Informative references"
5353    </t>
5354    <t>
5355      <eref target=""/>:
5356      "ISO-8859-1 Reference"
5357    </t>
5358    <t>
5359      <eref target=""/>:
5360      "Normative up-to-date references"
5361    </t>
5362  </list>
5365  Other changes:
5366  <list style="symbols">
5367    <t>
5368      Update media type registrations to use RFC4288 template.
5369    </t>
5370    <t>
5371      Use names of RFC4234 core rules DQUOTE and WSP,
5372      fix broken ABNF for chunk-data
5373      (work in progress on <eref target=""/>)
5374    </t>
5375  </list>
5379<section title="Since draft-ietf-httpbis-p1-messaging-01">
5381  Closed issues:
5382  <list style="symbols">
5383    <t>
5384      <eref target=""/>:
5385      "Bodies on GET (and other) requests"
5386    </t>
5387    <t>
5388      <eref target=""/>:
5389      "Updating to RFC4288"
5390    </t>
5391    <t>
5392      <eref target=""/>:
5393      "Status Code and Reason Phrase"
5394    </t>
5395    <t>
5396      <eref target=""/>:
5397      "rel_path not used"
5398    </t>
5399  </list>
5402  Ongoing work on ABNF conversion (<eref target=""/>):
5403  <list style="symbols">
5404    <t>
5405      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5406      "trailer-part").
5407    </t>
5408    <t>
5409      Avoid underscore character in rule names ("http_URL" ->
5410      "http-URL", "abs_path" -> "path-absolute").
5411    </t>
5412    <t>
5413      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5414      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5415      have to be updated when switching over to RFC3986.
5416    </t>
5417    <t>
5418      Synchronize core rules with RFC5234.
5419    </t>
5420    <t>
5421      Get rid of prose rules that span multiple lines.
5422    </t>
5423    <t>
5424      Get rid of unused rules LOALPHA and UPALPHA.
5425    </t>
5426    <t>
5427      Move "Product Tokens" section (back) into Part 1, as "token" is used
5428      in the definition of the Upgrade header field.
5429    </t>
5430    <t>
5431      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5432    </t>
5433    <t>
5434      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5435    </t>
5436  </list>
5440<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5442  Closed issues:
5443  <list style="symbols">
5444    <t>
5445      <eref target=""/>:
5446      "HTTP-date vs. rfc1123-date"
5447    </t>
5448    <t>
5449      <eref target=""/>:
5450      "WS in quoted-pair"
5451    </t>
5452  </list>
5455  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5456  <list style="symbols">
5457    <t>
5458      Reference RFC 3984, and update header field registrations for headers defined
5459      in this document.
5460    </t>
5461  </list>
5464  Ongoing work on ABNF conversion (<eref target=""/>):
5465  <list style="symbols">
5466    <t>
5467      Replace string literals when the string really is case-sensitive (HTTP-Version).
5468    </t>
5469  </list>
5473<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5475  Closed issues:
5476  <list style="symbols">
5477    <t>
5478      <eref target=""/>:
5479      "Connection closing"
5480    </t>
5481    <t>
5482      <eref target=""/>:
5483      "Move registrations and registry information to IANA Considerations"
5484    </t>
5485    <t>
5486      <eref target=""/>:
5487      "need new URL for PAD1995 reference"
5488    </t>
5489    <t>
5490      <eref target=""/>:
5491      "IANA Considerations: update HTTP URI scheme registration"
5492    </t>
5493    <t>
5494      <eref target=""/>:
5495      "Cite HTTPS URI scheme definition"
5496    </t>
5497    <t>
5498      <eref target=""/>:
5499      "List-type headers vs Set-Cookie"
5500    </t>
5501  </list>
5504  Ongoing work on ABNF conversion (<eref target=""/>):
5505  <list style="symbols">
5506    <t>
5507      Replace string literals when the string really is case-sensitive (HTTP-Date).
5508    </t>
5509    <t>
5510      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5511    </t>
5512  </list>
5516<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5518  Closed issues:
5519  <list style="symbols">
5520    <t>
5521      <eref target=""/>:
5522      "Out-of-date reference for URIs"
5523    </t>
5524    <t>
5525      <eref target=""/>:
5526      "RFC 2822 is updated by RFC 5322"
5527    </t>
5528  </list>
5531  Ongoing work on ABNF conversion (<eref target=""/>):
5532  <list style="symbols">
5533    <t>
5534      Use "/" instead of "|" for alternatives.
5535    </t>
5536    <t>
5537      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5538    </t>
5539    <t>
5540      Only reference RFC 5234's core rules.
5541    </t>
5542    <t>
5543      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5544      whitespace ("OWS") and required whitespace ("RWS").
5545    </t>
5546    <t>
5547      Rewrite ABNFs to spell out whitespace rules, factor out
5548      header field value format definitions.
5549    </t>
5550  </list>
5554<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5556  Closed issues:
5557  <list style="symbols">
5558    <t>
5559      <eref target=""/>:
5560      "Header LWS"
5561    </t>
5562    <t>
5563      <eref target=""/>:
5564      "Sort 1.3 Terminology"
5565    </t>
5566    <t>
5567      <eref target=""/>:
5568      "RFC2047 encoded words"
5569    </t>
5570    <t>
5571      <eref target=""/>:
5572      "Character Encodings in TEXT"
5573    </t>
5574    <t>
5575      <eref target=""/>:
5576      "Line Folding"
5577    </t>
5578    <t>
5579      <eref target=""/>:
5580      "OPTIONS * and proxies"
5581    </t>
5582    <t>
5583      <eref target=""/>:
5584      "Reason-Phrase BNF"
5585    </t>
5586    <t>
5587      <eref target=""/>:
5588      "Use of TEXT"
5589    </t>
5590    <t>
5591      <eref target=""/>:
5592      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5593    </t>
5594    <t>
5595      <eref target=""/>:
5596      "RFC822 reference left in discussion of date formats"
5597    </t>
5598  </list>
5601  Final work on ABNF conversion (<eref target=""/>):
5602  <list style="symbols">
5603    <t>
5604      Rewrite definition of list rules, deprecate empty list elements.
5605    </t>
5606    <t>
5607      Add appendix containing collected and expanded ABNF.
5608    </t>
5609  </list>
5612  Other changes:
5613  <list style="symbols">
5614    <t>
5615      Rewrite introduction; add mostly new Architecture Section.
5616    </t>
5617    <t>
5618      Move definition of quality values from Part 3 into Part 1;
5619      make TE request header field grammar independent of accept-params (defined in Part 3).
5620    </t>
5621  </list>
5625<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5627  Closed issues:
5628  <list style="symbols">
5629    <t>
5630      <eref target=""/>:
5631      "base for numeric protocol elements"
5632    </t>
5633    <t>
5634      <eref target=""/>:
5635      "comment ABNF"
5636    </t>
5637  </list>
5640  Partly resolved issues:
5641  <list style="symbols">
5642    <t>
5643      <eref target=""/>:
5644      "205 Bodies" (took out language that implied that there might be
5645      methods for which a request body MUST NOT be included)
5646    </t>
5647    <t>
5648      <eref target=""/>:
5649      "editorial improvements around HTTP-date"
5650    </t>
5651  </list>
5655<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5657  Closed issues:
5658  <list style="symbols">
5659    <t>
5660      <eref target=""/>:
5661      "Repeating single-value headers"
5662    </t>
5663    <t>
5664      <eref target=""/>:
5665      "increase connection limit"
5666    </t>
5667    <t>
5668      <eref target=""/>:
5669      "IP addresses in URLs"
5670    </t>
5671    <t>
5672      <eref target=""/>:
5673      "take over HTTP Upgrade Token Registry"
5674    </t>
5675    <t>
5676      <eref target=""/>:
5677      "CR and LF in chunk extension values"
5678    </t>
5679    <t>
5680      <eref target=""/>:
5681      "HTTP/0.9 support"
5682    </t>
5683    <t>
5684      <eref target=""/>:
5685      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5686    </t>
5687    <t>
5688      <eref target=""/>:
5689      "move definitions of gzip/deflate/compress to part 1"
5690    </t>
5691    <t>
5692      <eref target=""/>:
5693      "disallow control characters in quoted-pair"
5694    </t>
5695  </list>
5698  Partly resolved issues:
5699  <list style="symbols">
5700    <t>
5701      <eref target=""/>:
5702      "update IANA requirements wrt Transfer-Coding values" (add the
5703      IANA Considerations subsection)
5704    </t>
5705  </list>
5709<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5711  Closed issues:
5712  <list style="symbols">
5713    <t>
5714      <eref target=""/>:
5715      "header parsing, treatment of leading and trailing OWS"
5716    </t>
5717  </list>
5720  Partly resolved issues:
5721  <list style="symbols">
5722    <t>
5723      <eref target=""/>:
5724      "Placement of 13.5.1 and 13.5.2"
5725    </t>
5726    <t>
5727      <eref target=""/>:
5728      "use of term "word" when talking about header structure"
5729    </t>
5730  </list>
5734<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5736  Closed issues:
5737  <list style="symbols">
5738    <t>
5739      <eref target=""/>:
5740      "Clarification of the term 'deflate'"
5741    </t>
5742    <t>
5743      <eref target=""/>:
5744      "OPTIONS * and proxies"
5745    </t>
5746    <t>
5747      <eref target=""/>:
5748      "MIME-Version not listed in P1, general header fields"
5749    </t>
5750    <t>
5751      <eref target=""/>:
5752      "IANA registry for content/transfer encodings"
5753    </t>
5754    <t>
5755      <eref target=""/>:
5756      "Case-sensitivity of HTTP-date"
5757    </t>
5758    <t>
5759      <eref target=""/>:
5760      "use of term "word" when talking about header structure"
5761    </t>
5762  </list>
5765  Partly resolved issues:
5766  <list style="symbols">
5767    <t>
5768      <eref target=""/>:
5769      "Term for the requested resource's URI"
5770    </t>
5771  </list>
5775<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5777  Closed issues:
5778  <list style="symbols">
5779    <t>
5780      <eref target=""/>:
5781      "Connection Closing"
5782    </t>
5783    <t>
5784      <eref target=""/>:
5785      "Delimiting messages with multipart/byteranges"
5786    </t>
5787    <t>
5788      <eref target=""/>:
5789      "Handling multiple Content-Length headers"
5790    </t>
5791    <t>
5792      <eref target=""/>:
5793      "Clarify entity / representation / variant terminology"
5794    </t>
5795    <t>
5796      <eref target=""/>:
5797      "consider removing the 'changes from 2068' sections"
5798    </t>
5799  </list>
5802  Partly resolved issues:
5803  <list style="symbols">
5804    <t>
5805      <eref target=""/>:
5806      "HTTP(s) URI scheme definitions"
5807    </t>
5808  </list>
5812<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5814  Closed issues:
5815  <list style="symbols">
5816    <t>
5817      <eref target=""/>:
5818      "Trailer requirements"
5819    </t>
5820    <t>
5821      <eref target=""/>:
5822      "Text about clock requirement for caches belongs in p6"
5823    </t>
5824    <t>
5825      <eref target=""/>:
5826      "effective request URI: handling of missing host in HTTP/1.0"
5827    </t>
5828    <t>
5829      <eref target=""/>:
5830      "confusing Date requirements for clients"
5831    </t>
5832  </list>
5835  Partly resolved issues:
5836  <list style="symbols">
5837    <t>
5838      <eref target=""/>:
5839      "Handling multiple Content-Length headers"
5840    </t>
5841  </list>
5845<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5847  Closed issues:
5848  <list style="symbols">
5849    <t>
5850      <eref target=""/>:
5851      "RFC2145 Normative"
5852    </t>
5853    <t>
5854      <eref target=""/>:
5855      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5856    </t>
5857    <t>
5858      <eref target=""/>:
5859      "define 'transparent' proxy"
5860    </t>
5861    <t>
5862      <eref target=""/>:
5863      "Header Classification"
5864    </t>
5865    <t>
5866      <eref target=""/>:
5867      "Is * usable as a request-uri for new methods?"
5868    </t>
5869    <t>
5870      <eref target=""/>:
5871      "Migrate Upgrade details from RFC2817"
5872    </t>
5873    <t>
5874      <eref target=""/>:
5875      "untangle ABNFs for header fields"
5876    </t>
5877    <t>
5878      <eref target=""/>:
5879      "update RFC 2109 reference"
5880    </t>
5881  </list>
5885<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5887  None yet.
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