source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1175

Last change on this file since 1175 was 1175, checked in by fielding@…, 11 years ago

On second thought, gateways behave like user agents on the
inbound connection since they decide the inbound target resource.
The distinction is that HTTP-to-HTTP gateways must also implement
Connection and Via. Revises [1173] accordingly.

Improve definition of Connection header field to require that
the Conection field itself be removed (how did we forget that?)
and note the overlap between connection-token and field-name
namespaces. Addresses one half of #256 and #231.

  • Property svn:eol-style set to native
File size: 250.4 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.12"/>.
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 characters might
430   appear. OWS &SHOULD; either not be produced or be produced as a single SP
431   character. Multiple OWS characters 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 character is required to
437   separate field tokens. RWS &SHOULD; be produced as a single SP character.
438   Multiple RWS characters 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 character ("\") can be used as a single-character
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   Producers &SHOULD-NOT; escape characters that do not require escaping
513   (i.e., other than DQUOTE and the backslash character).
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 the "." (period or decimal point) character.  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="HTTP Message" 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   characters 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   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1171   header field. The presence of whitespace might be an attempt to trick a
1172   noncompliant implementation of HTTP into ignoring that field or processing
1173   the next line as a new request, either of which might result in security
1174   issues when implementations within the request chain interpret the
1175   same message differently. HTTP/1.1 servers &MUST; reject such a message
1176   with a 400 (Bad Request) response.
1179<section title="Message Parsing Robustness" anchor="message.robustness">
1181   In the interest of robustness, servers &SHOULD; ignore at least one
1182   empty line received where a Request-Line is expected. In other words, if
1183   the server is reading the protocol stream at the beginning of a
1184   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1187   Some old HTTP/1.0 client implementations generate an extra CRLF
1188   after a POST request as a lame workaround for some early server
1189   applications that failed to read message-body content that was
1190   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1191   preface or follow a request with an extra CRLF.  If terminating
1192   the request message-body with a line-ending is desired, then the
1193   client &MUST; include the terminating CRLF octets as part of the
1194   message-body length.
1197   The normal procedure for parsing an HTTP message is to read the
1198   start-line into a structure, read each header field into a hash
1199   table by field name until the empty line, and then use the parsed
1200   data to determine if a message-body is expected.  If a message-body
1201   has been indicated, then it is read as a stream until an amount
1202   of octets equal to the message-body length is read or the connection
1203   is closed.  Care must be taken to parse an HTTP message as a sequence
1204   of octets in an encoding that is a superset of US-ASCII.  Attempting
1205   to parse HTTP as a stream of Unicode characters in a character encoding
1206   like UTF-16 might introduce security flaws due to the differing ways
1207   that such parsers interpret invalid characters.
1210   HTTP allows the set of defined header fields to be extended without
1211   changing the protocol version (see <xref target="header.field.registration"/>).
1212   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1213   proxy is specifically configured to block or otherwise transform such
1214   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1218<section title="Header Fields" anchor="header.fields">
1219  <x:anchor-alias value="header-field"/>
1220  <x:anchor-alias value="field-content"/>
1221  <x:anchor-alias value="field-name"/>
1222  <x:anchor-alias value="field-value"/>
1223  <x:anchor-alias value="OWS"/>
1225   Each HTTP header field consists of a case-insensitive field name
1226   followed by a colon (":"), optional whitespace, and the field value.
1228<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"/>
1229  <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>
1230  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1231  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1232  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1235   No whitespace is allowed between the header field name and colon. For
1236   security reasons, any request message received containing such whitespace
1237   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1238   &MUST; remove any such whitespace from a response message before
1239   forwarding the message downstream.
1242   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1243   preferred. The field value does not include any leading or trailing white
1244   space: OWS occurring before the first non-whitespace character of the
1245   field value or after the last non-whitespace character of the field value
1246   is ignored and &SHOULD; be removed before further processing (as this does
1247   not change the meaning of the header field).
1250   The order in which header fields with differing field names are
1251   received is not significant. However, it is "good practice" to send
1252   header fields that contain control data first, such as Host on
1253   requests and Date on responses, so that implementations can decide
1254   when not to handle a message as early as possible.  A server &MUST;
1255   wait until the entire header section is received before interpreting
1256   a request message, since later header fields might include conditionals,
1257   authentication credentials, or deliberately misleading duplicate
1258   header fields that would impact request processing.
1261   Multiple header fields with the same field name &MUST-NOT; be
1262   sent in a message unless the entire field value for that
1263   header field is defined as a comma-separated list [i.e., #(values)].
1264   Multiple header fields with the same field name can be combined into
1265   one "field-name: field-value" pair, without changing the semantics of the
1266   message, by appending each subsequent field value to the combined
1267   field value in order, separated by a comma. The order in which
1268   header fields with the same field name are received is therefore
1269   significant to the interpretation of the combined field value;
1270   a proxy &MUST-NOT; change the order of these field values when
1271   forwarding a message.
1274  <t>
1275   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1276   practice can occur multiple times, but does not use the list syntax, and
1277   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1278   for details.) Also note that the Set-Cookie2 header field specified in
1279   <xref target="RFC2965"/> does not share this problem.
1280  </t>
1283   Historically, HTTP header field values could be extended over multiple
1284   lines by preceding each extra line with at least one space or horizontal
1285   tab character (line folding). This specification deprecates such line
1286   folding except within the message/http media type
1287   (<xref target=""/>).
1288   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1289   (i.e., that contain any field-content that matches the obs-fold rule) unless
1290   the message is intended for packaging within the message/http media type.
1291   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1292   obs-fold whitespace with a single SP prior to interpreting the field value
1293   or forwarding the message downstream.
1296   Historically, HTTP has allowed field content with text in the ISO-8859-1
1297   <xref target="ISO-8859-1"/> character encoding and supported other
1298   character sets only through use of <xref target="RFC2047"/> encoding.
1299   In practice, most HTTP header field values use only a subset of the
1300   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1301   header fields &SHOULD; limit their field values to US-ASCII characters.
1302   Recipients &SHOULD; treat other (obs-text) octets in field content as
1303   opaque data.
1305<t anchor="rule.comment">
1306  <x:anchor-alias value="comment"/>
1307  <x:anchor-alias value="ctext"/>
1308   Comments can be included in some HTTP header fields by surrounding
1309   the comment text with parentheses. Comments are only allowed in
1310   fields containing "comment" as part of their field value definition.
1312<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1313  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1314  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1315                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1317<t anchor="rule.quoted-cpair">
1318  <x:anchor-alias value="quoted-cpair"/>
1319   The backslash character ("\") can be used as a single-character
1320   quoting mechanism within comment constructs:
1322<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1323  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1326   Producers &SHOULD-NOT; escape characters that do not require escaping
1327   (i.e., other than the backslash character "\" and the parentheses "(" and
1328   ")").
1332<section title="Message Body" anchor="message.body">
1333  <x:anchor-alias value="message-body"/>
1335   The message-body (if any) of an HTTP message is used to carry the
1336   payload body associated with the request or response.
1338<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1339  <x:ref>message-body</x:ref> = *OCTET
1342   The message-body differs from the payload body only when a transfer-coding
1343   has been applied, as indicated by the Transfer-Encoding header field
1344   (<xref target="header.transfer-encoding"/>).  If more than one
1345   Transfer-Encoding header field is present in a message, the multiple
1346   field-values &MUST; be combined into one field-value, according to the
1347   algorithm defined in <xref target="header.fields"/>, before determining
1348   the message-body length.
1351   When one or more transfer-codings are applied to a payload in order to
1352   form the message-body, the Transfer-Encoding header field &MUST; contain
1353   the list of transfer-codings applied. Transfer-Encoding is a property of
1354   the message, not of the payload, and thus &MAY; be added or removed by
1355   any implementation along the request/response chain under the constraints
1356   found in <xref target="transfer.codings"/>.
1359   If a message is received that has multiple Content-Length header fields
1360   (<xref target="header.content-length"/>) with field-values consisting
1361   of the same decimal value, or a single Content-Length header field with
1362   a field value containing a list of identical decimal values (e.g.,
1363   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1364   header fields have been generated or combined by an upstream message
1365   processor, then the recipient &MUST; replace the duplicated fields or
1366   field-values with a single valid Content-Length field containing that
1367   decimal value prior to determining the message-body length.
1370   The rules for when a message-body is allowed in a message differ for
1371   requests and responses.
1374   The presence of a message-body in a request is signaled by the
1375   inclusion of a Content-Length or Transfer-Encoding header field in
1376   the request's header fields, even if the request method does not
1377   define any use for a message-body.  This allows the request
1378   message framing algorithm to be independent of method semantics.
1381   For response messages, whether or not a message-body is included with
1382   a message is dependent on both the request method and the response
1383   status code (<xref target="status.code.and.reason.phrase"/>).
1384   Responses to the HEAD request method never include a message-body
1385   because the associated response header fields (e.g., Transfer-Encoding,
1386   Content-Length, etc.) only indicate what their values would have been
1387   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1388   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1389   All other responses do include a message-body, although the body
1390   &MAY; be of zero length.
1393   The length of the message-body is determined by one of the following
1394   (in order of precedence):
1397  <list style="numbers">
1398    <x:lt><t>
1399     Any response to a HEAD request and any response with a status
1400     code of 100-199, 204, or 304 is always terminated by the first
1401     empty line after the header fields, regardless of the header
1402     fields present in the message, and thus cannot contain a message-body.
1403    </t></x:lt>
1404    <x:lt><t>
1405     If a Transfer-Encoding header field is present
1406     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1407     is the final encoding, the message-body length is determined by reading
1408     and decoding the chunked data until the transfer-coding indicates the
1409     data is complete.
1410    </t>
1411    <t>
1412     If a Transfer-Encoding header field is present in a response and the
1413     "chunked" transfer-coding is not the final encoding, the message-body
1414     length is determined by reading the connection until it is closed by
1415     the server.
1416     If a Transfer-Encoding header field is present in a request and the
1417     "chunked" transfer-coding is not the final encoding, the message-body
1418     length cannot be determined reliably; the server &MUST; respond with
1419     the 400 (Bad Request) status code and then close the connection.
1420    </t>
1421    <t>
1422     If a message is received with both a Transfer-Encoding header field
1423     and a Content-Length header field, the Transfer-Encoding overrides
1424     the Content-Length.
1425     Such a message might indicate an attempt to perform request or response
1426     smuggling (bypass of security-related checks on message routing or content)
1427     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1428     be removed, prior to forwarding the message downstream, or replaced with
1429     the real message-body length after the transfer-coding is decoded.
1430    </t></x:lt>
1431    <x:lt><t>
1432     If a message is received without Transfer-Encoding and with either
1433     multiple Content-Length header fields having differing field-values or
1434     a single Content-Length header field having an invalid value, then the
1435     message framing is invalid and &MUST; be treated as an error to
1436     prevent request or response smuggling.
1437     If this is a request message, the server &MUST; respond with
1438     a 400 (Bad Request) status code and then close the connection.
1439     If this is a response message received by a proxy, the proxy
1440     &MUST; discard the received response, send a 502 (Bad Gateway)
1441     status code as its downstream response, and then close the connection.
1442     If this is a response message received by a user-agent, it &MUST; be
1443     treated as an error by discarding the message and closing the connection.
1444    </t></x:lt>
1445    <x:lt><t>
1446     If a valid Content-Length header field
1447     is present without Transfer-Encoding, its decimal value defines the
1448     message-body length in octets.  If the actual number of octets sent in
1449     the message is less than the indicated Content-Length, the recipient
1450     &MUST; consider the message to be incomplete and treat the connection
1451     as no longer usable.
1452     If the actual number of octets sent in the message is more than the indicated
1453     Content-Length, the recipient &MUST; only process the message-body up to the
1454     field value's number of octets; the remainder of the message &MUST; either
1455     be discarded or treated as the next message in a pipeline.  For the sake of
1456     robustness, a user-agent &MAY; attempt to detect and correct such an error
1457     in message framing if it is parsing the response to the last request on
1458     on a connection and the connection has been closed by the server.
1459    </t></x:lt>
1460    <x:lt><t>
1461     If this is a request message and none of the above are true, then the
1462     message-body length is zero (no message-body is present).
1463    </t></x:lt>
1464    <x:lt><t>
1465     Otherwise, this is a response message without a declared message-body
1466     length, so the message-body length is determined by the number of octets
1467     received prior to the server closing the connection.
1468    </t></x:lt>
1469  </list>
1472   Since there is no way to distinguish a successfully completed,
1473   close-delimited message from a partially-received message interrupted
1474   by network failure, implementations &SHOULD; use encoding or
1475   length-delimited messages whenever possible.  The close-delimiting
1476   feature exists primarily for backwards compatibility with HTTP/1.0.
1479   A server &MAY; reject a request that contains a message-body but
1480   not a Content-Length by responding with 411 (Length Required).
1483   Unless a transfer-coding other than "chunked" has been applied,
1484   a client that sends a request containing a message-body &SHOULD;
1485   use a valid Content-Length header field if the message-body length
1486   is known in advance, rather than the "chunked" encoding, since some
1487   existing services respond to "chunked" with a 411 (Length Required)
1488   status code even though they understand the chunked encoding.  This
1489   is typically because such services are implemented via a gateway that
1490   requires a content-length in advance of being called and the server
1491   is unable or unwilling to buffer the entire request before processing.
1494   A client that sends a request containing a message-body &MUST; include a
1495   valid Content-Length header field if it does not know the server will
1496   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1497   of specific user configuration or by remembering the version of a prior
1498   received response.
1501   Request messages that are prematurely terminated, possibly due to a
1502   cancelled connection or a server-imposed time-out exception, &MUST;
1503   result in closure of the connection; sending an HTTP/1.1 error response
1504   prior to closing the connection is &OPTIONAL;.
1505   Response messages that are prematurely terminated, usually by closure
1506   of the connection prior to receiving the expected number of octets or by
1507   failure to decode a transfer-encoded message-body, &MUST; be recorded
1508   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1509   message-body as if it were complete (i.e., some indication must be given
1510   to the user that an error occurred).  Cache requirements for incomplete
1511   responses are defined in &cache-incomplete;.
1514   A server &MUST; read the entire request message-body or close
1515   the connection after sending its response, since otherwise the
1516   remaining data on a persistent connection would be misinterpreted
1517   as the next request.  Likewise,
1518   a client &MUST; read the entire response message-body if it intends
1519   to reuse the same connection for a subsequent request.  Pipelining
1520   multiple requests on a connection is described in <xref target="pipelining"/>.
1524<section title="General Header Fields" anchor="general.header.fields">
1525  <x:anchor-alias value="general-header"/>
1527   There are a few header fields which have general applicability for
1528   both request and response messages, but which do not apply to the
1529   payload being transferred. These header fields apply only to the
1530   message being transmitted.
1532<texttable align="left">
1533  <ttcol>Header Field Name</ttcol>
1534  <ttcol>Defined in...</ttcol>
1536  <c>Connection</c> <c><xref target="header.connection"/></c>
1537  <c>Date</c> <c><xref target=""/></c>
1538  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1539  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1540  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1541  <c>Via</c> <c><xref target="header.via"/></c>
1546<section title="Request" anchor="request">
1547  <x:anchor-alias value="Request"/>
1549   A request message from a client to a server includes, within the
1550   first line of that message, the method to be applied to the resource,
1551   the identifier of the resource, and the protocol version in use.
1553<!--                 Host                      ; should be moved here eventually -->
1554<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1555  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1556                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1557                  <x:ref>CRLF</x:ref>
1558                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1561<section title="Request-Line" anchor="request-line">
1562  <x:anchor-alias value="Request-Line"/>
1564   The Request-Line begins with a method token, followed by the
1565   request-target and the protocol version, and ending with CRLF. The
1566   elements are separated by SP characters. No CR or LF is allowed
1567   except in the final CRLF sequence.
1569<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1570  <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>
1573<section title="Method" anchor="method">
1574  <x:anchor-alias value="Method"/>
1576   The Method token indicates the request method to be performed on the
1577   target resource. The request method is case-sensitive.
1579<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1580  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1584<section title="request-target" anchor="request-target">
1585  <x:anchor-alias value="request-target"/>
1587   The request-target identifies the target resource upon which to apply
1588   the request.  In most cases, the user agent is provided a URI reference
1589   from which it determines an absolute URI for identifying the target
1590   resource.  When a request to the resource is initiated, all or part
1591   of that URI is used to construct the HTTP request-target.
1593<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1594  <x:ref>request-target</x:ref> = "*"
1595                 / <x:ref>absolute-URI</x:ref>
1596                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1597                 / <x:ref>authority</x:ref>
1600   The four options for request-target are dependent on the nature of the
1601   request.
1603<t><iref item="asterisk form (of request-target)"/>
1604   The asterisk "*" form of request-target, which &MUST-NOT; be used
1605   with any request method other than OPTIONS, means that the request
1606   applies to the server as a whole (the listening process) rather than
1607   to a specific named resource at that server.  For example,
1609<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1610OPTIONS * HTTP/1.1
1612<t><iref item="absolute-URI form (of request-target)"/>
1613   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1614   proxy. The proxy is requested to either forward the request or service it
1615   from a valid cache, and then return the response. Note that the proxy &MAY;
1616   forward the request on to another proxy or directly to the server
1617   specified by the absolute-URI. In order to avoid request loops, a
1618   proxy that forwards requests to other proxies &MUST; be able to
1619   recognize and exclude all of its own server names, including
1620   any aliases, local variations, and the numeric IP address. An example
1621   Request-Line would be:
1623<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1624GET HTTP/1.1
1627   To allow for transition to absolute-URIs in all requests in future
1628   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1629   form in requests, even though HTTP/1.1 clients will only generate
1630   them in requests to proxies.
1633   If a proxy receives a host name that is not a fully qualified domain
1634   name, it &MAY; add its domain to the host name it received. If a proxy
1635   receives a fully qualified domain name, the proxy &MUST-NOT; change
1636   the host name.
1638<t><iref item="authority form (of request-target)"/>
1639   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1641<t><iref item="origin form (of request-target)"/>
1642   The most common form of request-target is that used when making
1643   a request to an origin server ("origin form").
1644   In this case, the absolute path and query components of the URI
1645   &MUST; be transmitted as the request-target, and the authority component
1646   &MUST; be transmitted in a Host header field. For example, a client wishing
1647   to retrieve a representation of the resource, as identified above,
1648   directly from the origin server would open (or reuse) a TCP connection
1649   to port 80 of the host "" and send the lines:
1651<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1652GET /pub/WWW/TheProject.html HTTP/1.1
1656   followed by the remainder of the Request. Note that the origin form
1657   of request-target always starts with an absolute path; if the target
1658   resource's URI path is empty, then an absolute path of "/" &MUST; be
1659   provided in the request-target.
1662   If a proxy receives an OPTIONS request with an absolute-URI form of
1663   request-target in which the URI has an empty path and no query component,
1664   then the last proxy on the request chain &MUST; use a request-target
1665   of "*" when it forwards the request to the indicated origin server.
1668   For example, the request
1669</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1673  would be forwarded by the final proxy as
1674</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1675OPTIONS * HTTP/1.1
1679   after connecting to port 8001 of host "".
1683   The request-target is transmitted in the format specified in
1684   <xref target="http.uri"/>. If the request-target is percent-encoded
1685   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1686   &MUST; decode the request-target in order to
1687   properly interpret the request. Servers &SHOULD; respond to invalid
1688   request-targets with an appropriate status code.
1691   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1692   received request-target when forwarding it to the next inbound server,
1693   except as noted above to replace a null path-absolute with "/" or "*".
1696  <t>
1697    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1698    meaning of the request when the origin server is improperly using
1699    a non-reserved URI character for a reserved purpose.  Implementors
1700    need to be aware that some pre-HTTP/1.1 proxies have been known to
1701    rewrite the request-target.
1702  </t>
1705   HTTP does not place a pre-defined limit on the length of a request-target.
1706   A server &MUST; be prepared to receive URIs of unbounded length and
1707   respond with the 414 (URI Too Long) status code if the received
1708   request-target would be longer than the server wishes to handle
1709   (see &status-414;).
1712   Various ad-hoc limitations on request-target length are found in practice.
1713   It is &RECOMMENDED; that all HTTP senders and recipients support
1714   request-target lengths of 8000 or more octets.
1717  <t>
1718    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1719    are not part of the request-target and thus will not be transmitted
1720    in an HTTP request.
1721  </t>
1726<section title="The Resource Identified by a Request" anchor="">
1728   The exact resource identified by an Internet request is determined by
1729   examining both the request-target and the Host header field.
1732   An origin server that does not allow resources to differ by the
1733   requested host &MAY; ignore the Host header field value when
1734   determining the resource identified by an HTTP/1.1 request. (But see
1735   <xref target=""/>
1736   for other requirements on Host support in HTTP/1.1.)
1739   An origin server that does differentiate resources based on the host
1740   requested (sometimes referred to as virtual hosts or vanity host
1741   names) &MUST; use the following rules for determining the requested
1742   resource on an HTTP/1.1 request:
1743  <list style="numbers">
1744    <t>If request-target is an absolute-URI, the host is part of the
1745     request-target. Any Host header field value in the request &MUST; be
1746     ignored.</t>
1747    <t>If the request-target is not an absolute-URI, and the request includes
1748     a Host header field, the host is determined by the Host header
1749     field value.</t>
1750    <t>If the host as determined by rule 1 or 2 is not a valid host on
1751     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1752  </list>
1755   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1756   attempt to use heuristics (e.g., examination of the URI path for
1757   something unique to a particular host) in order to determine what
1758   exact resource is being requested.
1762<section title="Effective Request URI" anchor="effective.request.uri">
1763  <iref primary="true" item="effective request URI"/>
1764  <iref primary="true" item="target resource"/>
1766   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1767   for the target resource; instead, the URI needs to be inferred from the
1768   request-target, Host header field, and connection context. The result of
1769   this process is called the "effective request URI".  The "target resource"
1770   is the resource identified by the effective request URI.
1773   If the request-target is an absolute-URI, then the effective request URI is
1774   the request-target.
1777   If the request-target uses the path-absolute form or the asterisk form,
1778   and the Host header field is present, then the effective request URI is
1779   constructed by concatenating
1782  <list style="symbols">
1783    <t>
1784      the scheme name: "http" if the request was received over an insecure
1785      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1786      connection,
1787    </t>
1788    <t>
1789      the character sequence "://",
1790    </t>
1791    <t>
1792      the authority component, as specified in the Host header field
1793      (<xref target=""/>), and
1794    </t>
1795    <t>
1796      the request-target obtained from the Request-Line, unless the
1797      request-target is just the asterisk "*".
1798    </t>
1799  </list>
1802   If the request-target uses the path-absolute form or the asterisk form,
1803   and the Host header field is not present, then the effective request URI is
1804   undefined.
1807   Otherwise, when request-target uses the authority form, the effective
1808   request URI is undefined.
1812   Example 1: the effective request URI for the message
1814<artwork type="example" x:indent-with="  ">
1815GET /pub/WWW/TheProject.html HTTP/1.1
1819  (received over an insecure TCP connection) is "http", plus "://", plus the
1820  authority component "", plus the request-target
1821  "/pub/WWW/TheProject.html", thus
1822  "".
1827   Example 2: the effective request URI for the message
1829<artwork type="example" x:indent-with="  ">
1830GET * HTTP/1.1
1834  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1835  authority component "", thus "".
1839   Effective request URIs are compared using the rules described in
1840   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1841   be treated as equivalent to an absolute path of "/".
1848<section title="Response" anchor="response">
1849  <x:anchor-alias value="Response"/>
1851   After receiving and interpreting a request message, a server responds
1852   with an HTTP response message.
1854<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1855  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1856                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1857                  <x:ref>CRLF</x:ref>
1858                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1861<section title="Status-Line" anchor="status-line">
1862  <x:anchor-alias value="Status-Line"/>
1864   The first line of a Response message is the Status-Line, consisting
1865   of the protocol version followed by a numeric status code and its
1866   associated textual phrase, with each element separated by SP
1867   characters. No CR or LF is allowed except in the final CRLF sequence.
1869<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1870  <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>
1873<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1874  <x:anchor-alias value="Reason-Phrase"/>
1875  <x:anchor-alias value="Status-Code"/>
1877   The Status-Code element is a 3-digit integer result code of the
1878   attempt to understand and satisfy the request. These codes are fully
1879   defined in &status-codes;.  The Reason Phrase exists for the sole
1880   purpose of providing a textual description associated with the numeric
1881   status code, out of deference to earlier Internet application protocols
1882   that were more frequently used with interactive text clients.
1883   A client &SHOULD; ignore the content of the Reason Phrase.
1886   The first digit of the Status-Code defines the class of response. The
1887   last two digits do not have any categorization role. There are 5
1888   values for the first digit:
1889  <list style="symbols">
1890    <t>
1891      1xx: Informational - Request received, continuing process
1892    </t>
1893    <t>
1894      2xx: Success - The action was successfully received,
1895        understood, and accepted
1896    </t>
1897    <t>
1898      3xx: Redirection - Further action must be taken in order to
1899        complete the request
1900    </t>
1901    <t>
1902      4xx: Client Error - The request contains bad syntax or cannot
1903        be fulfilled
1904    </t>
1905    <t>
1906      5xx: Server Error - The server failed to fulfill an apparently
1907        valid request
1908    </t>
1909  </list>
1911<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1912  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1913  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1921<section title="Protocol Parameters" anchor="protocol.parameters">
1923<section title="Date/Time Formats: Full Date" anchor="">
1924  <x:anchor-alias value="HTTP-date"/>
1926   HTTP applications have historically allowed three different formats
1927   for date/time stamps. However, the preferred format is a fixed-length subset
1928   of that defined by <xref target="RFC1123"/>:
1930<figure><artwork type="example" x:indent-with="  ">
1931Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1934   The other formats are described here only for compatibility with obsolete
1935   implementations.
1937<figure><artwork type="example" x:indent-with="  ">
1938Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1939Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1942   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1943   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1944   only generate the RFC 1123 format for representing HTTP-date values
1945   in header fields. See <xref target="tolerant.applications"/> for further information.
1948   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1949   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1950   equal to UTC (Coordinated Universal Time). This is indicated in the
1951   first two formats by the inclusion of "GMT" as the three-letter
1952   abbreviation for time zone, and &MUST; be assumed when reading the
1953   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1954   additional whitespace beyond that specifically included as SP in the
1955   grammar.
1957<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1958  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1960<t anchor="">
1961  <x:anchor-alias value="rfc1123-date"/>
1962  <x:anchor-alias value="time-of-day"/>
1963  <x:anchor-alias value="hour"/>
1964  <x:anchor-alias value="minute"/>
1965  <x:anchor-alias value="second"/>
1966  <x:anchor-alias value="day-name"/>
1967  <x:anchor-alias value="day"/>
1968  <x:anchor-alias value="month"/>
1969  <x:anchor-alias value="year"/>
1970  <x:anchor-alias value="GMT"/>
1971  Preferred format:
1973<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"/>
1974  <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>
1975  ; fixed length subset of the format defined in
1976  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1978  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1979               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1980               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1981               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1982               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1983               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1984               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1986  <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>
1987               ; e.g., 02 Jun 1982
1989  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1990  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1991               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1992               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1993               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1994               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1995               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1996               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1997               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1998               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1999               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2000               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2001               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2002  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2004  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2006  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2007                 ; 00:00:00 - 23:59:59
2009  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2010  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2011  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2014  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2015  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2016  same as those defined for the RFC 5322 constructs
2017  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2019<t anchor="">
2020  <x:anchor-alias value="obs-date"/>
2021  <x:anchor-alias value="rfc850-date"/>
2022  <x:anchor-alias value="asctime-date"/>
2023  <x:anchor-alias value="date1"/>
2024  <x:anchor-alias value="date2"/>
2025  <x:anchor-alias value="date3"/>
2026  <x:anchor-alias value="rfc1123-date"/>
2027  <x:anchor-alias value="day-name-l"/>
2028  Obsolete formats:
2030<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2031  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2033<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2034  <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>
2035  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2036                 ; day-month-year (e.g., 02-Jun-82)
2038  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2039         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2040         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2041         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2042         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2043         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2044         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2046<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2047  <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>
2048  <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> ))
2049                 ; month day (e.g., Jun  2)
2052  <t>
2053    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2054    accepting date values that might have been sent by non-HTTP
2055    applications, as is sometimes the case when retrieving or posting
2056    messages via proxies/gateways to SMTP or NNTP.
2057  </t>
2060  <t>
2061    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2062    to their usage within the protocol stream. Clients and servers are
2063    not required to use these formats for user presentation, request
2064    logging, etc.
2065  </t>
2069<section title="Transfer Codings" anchor="transfer.codings">
2070  <x:anchor-alias value="transfer-coding"/>
2071  <x:anchor-alias value="transfer-extension"/>
2073   Transfer-coding values are used to indicate an encoding
2074   transformation that has been, can be, or might need to be applied to a
2075   payload body in order to ensure "safe transport" through the network.
2076   This differs from a content coding in that the transfer-coding is a
2077   property of the message rather than a property of the representation
2078   that is being transferred.
2080<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2081  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2082                          / "compress" ; <xref target="compress.coding"/>
2083                          / "deflate" ; <xref target="deflate.coding"/>
2084                          / "gzip" ; <xref target="gzip.coding"/>
2085                          / <x:ref>transfer-extension</x:ref>
2086  <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> )
2088<t anchor="rule.parameter">
2089  <x:anchor-alias value="attribute"/>
2090  <x:anchor-alias value="transfer-parameter"/>
2091  <x:anchor-alias value="value"/>
2092   Parameters are in the form of attribute/value pairs.
2094<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"/>
2095  <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>
2096  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2097  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2100   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2101   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2102   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2105   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2106   MIME, which were designed to enable safe transport of binary data over a
2107   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2108   However, safe transport
2109   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2110   the only unsafe characteristic of message-bodies is the difficulty in
2111   determining the exact message body length (<xref target="message.body"/>),
2112   or the desire to encrypt data over a shared transport.
2115   A server that receives a request message with a transfer-coding it does
2116   not understand &SHOULD; respond with 501 (Not Implemented) and then
2117   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2118   client.
2121<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2122  <iref item="chunked (Coding Format)"/>
2123  <iref item="Coding Format" subitem="chunked"/>
2124  <x:anchor-alias value="chunk"/>
2125  <x:anchor-alias value="Chunked-Body"/>
2126  <x:anchor-alias value="chunk-data"/>
2127  <x:anchor-alias value="chunk-ext"/>
2128  <x:anchor-alias value="chunk-ext-name"/>
2129  <x:anchor-alias value="chunk-ext-val"/>
2130  <x:anchor-alias value="chunk-size"/>
2131  <x:anchor-alias value="last-chunk"/>
2132  <x:anchor-alias value="trailer-part"/>
2133  <x:anchor-alias value="quoted-str-nf"/>
2134  <x:anchor-alias value="qdtext-nf"/>
2136   The chunked encoding modifies the body of a message in order to
2137   transfer it as a series of chunks, each with its own size indicator,
2138   followed by an &OPTIONAL; trailer containing header fields. This
2139   allows dynamically produced content to be transferred along with the
2140   information necessary for the recipient to verify that it has
2141   received the full message.
2143<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"/>
2144  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2145                   <x:ref>last-chunk</x:ref>
2146                   <x:ref>trailer-part</x:ref>
2147                   <x:ref>CRLF</x:ref>
2149  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2150                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2151  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2152  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2154  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2155                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2156  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2157  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2158  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2159  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2161  <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>
2162                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2163  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2164                 ; <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>
2167   The chunk-size field is a string of hex digits indicating the size of
2168   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2169   zero, followed by the trailer, which is terminated by an empty line.
2172   The trailer allows the sender to include additional HTTP header
2173   fields at the end of the message. The Trailer header field can be
2174   used to indicate which header fields are included in a trailer (see
2175   <xref target="header.trailer"/>).
2178   A server using chunked transfer-coding in a response &MUST-NOT; use the
2179   trailer for any header fields unless at least one of the following is
2180   true:
2181  <list style="numbers">
2182    <t>the request included a TE header field that indicates "trailers" is
2183     acceptable in the transfer-coding of the  response, as described in
2184     <xref target="header.te"/>; or,</t>
2186    <t>the trailer fields consist entirely of optional metadata, and the
2187    recipient could use the message (in a manner acceptable to the server where
2188    the field originated) without receiving it. In other words, the server that
2189    generated the header (often but not always the origin server) is willing to
2190    accept the possibility that the trailer fields might be silently discarded
2191    along the path to the client.</t>
2192  </list>
2195   This requirement prevents an interoperability failure when the
2196   message is being received by an HTTP/1.1 (or later) proxy and
2197   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2198   compliance with the protocol would have necessitated a possibly
2199   infinite buffer on the proxy.
2202   A process for decoding the "chunked" transfer-coding
2203   can be represented in pseudo-code as:
2205<figure><artwork type="code">
2206  length := 0
2207  read chunk-size, chunk-ext (if any) and CRLF
2208  while (chunk-size &gt; 0) {
2209     read chunk-data and CRLF
2210     append chunk-data to decoded-body
2211     length := length + chunk-size
2212     read chunk-size and CRLF
2213  }
2214  read header-field
2215  while (header-field not empty) {
2216     append header-field to existing header fields
2217     read header-field
2218  }
2219  Content-Length := length
2220  Remove "chunked" from Transfer-Encoding
2223   All HTTP/1.1 applications &MUST; be able to receive and decode the
2224   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2225   they do not understand.
2228   Since "chunked" is the only transfer-coding required to be understood
2229   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2230   on a persistent connection.  Whenever a transfer-coding is applied to
2231   a payload body in a request, the final transfer-coding applied &MUST;
2232   be "chunked".  If a transfer-coding is applied to a response payload
2233   body, then either the final transfer-coding applied &MUST; be "chunked"
2234   or the message &MUST; be terminated by closing the connection. When the
2235   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2236   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2237   be applied more than once in a message-body.
2241<section title="Compression Codings" anchor="compression.codings">
2243   The codings defined below can be used to compress the payload of a
2244   message.
2247   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2248   is not desirable and is discouraged for future encodings. Their
2249   use here is representative of historical practice, not good
2250   design.
2253   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2254   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2255   equivalent to "gzip" and "compress" respectively.
2258<section title="Compress Coding" anchor="compress.coding">
2259<iref item="compress (Coding Format)"/>
2260<iref item="Coding Format" subitem="compress"/>
2262   The "compress" format is produced by the common UNIX file compression
2263   program "compress". This format is an adaptive Lempel-Ziv-Welch
2264   coding (LZW).
2268<section title="Deflate Coding" anchor="deflate.coding">
2269<iref item="deflate (Coding Format)"/>
2270<iref item="Coding Format" subitem="deflate"/>
2272   The "deflate" format is defined as the "deflate" compression mechanism
2273   (described in <xref target="RFC1951"/>) used inside the "zlib"
2274   data format (<xref target="RFC1950"/>).
2277  <t>
2278    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2279    compressed data without the zlib wrapper.
2280   </t>
2284<section title="Gzip Coding" anchor="gzip.coding">
2285<iref item="gzip (Coding Format)"/>
2286<iref item="Coding Format" subitem="gzip"/>
2288   The "gzip" format is produced by the file compression program
2289   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2290   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2296<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2298   The HTTP Transfer Coding Registry defines the name space for the transfer
2299   coding names.
2302   Registrations &MUST; include the following fields:
2303   <list style="symbols">
2304     <t>Name</t>
2305     <t>Description</t>
2306     <t>Pointer to specification text</t>
2307   </list>
2310   Names of transfer codings &MUST-NOT; overlap with names of content codings
2311   (&content-codings;), unless the encoding transformation is identical (as it
2312   is the case for the compression codings defined in
2313   <xref target="compression.codings"/>).
2316   Values to be added to this name space require a specification
2317   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2318   conform to the purpose of transfer coding defined in this section.
2321   The registry itself is maintained at
2322   <eref target=""/>.
2327<section title="Product Tokens" anchor="product.tokens">
2328  <x:anchor-alias value="product"/>
2329  <x:anchor-alias value="product-version"/>
2331   Product tokens are used to allow communicating applications to
2332   identify themselves by software name and version. Most fields using
2333   product tokens also allow sub-products which form a significant part
2334   of the application to be listed, separated by whitespace. By
2335   convention, the products are listed in order of their significance
2336   for identifying the application.
2338<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2339  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2340  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2343   Examples:
2345<figure><artwork type="example">
2346  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2347  Server: Apache/0.8.4
2350   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2351   used for advertising or other non-essential information. Although any
2352   token character &MAY; appear in a product-version, this token &SHOULD;
2353   only be used for a version identifier (i.e., successive versions of
2354   the same product &SHOULD; only differ in the product-version portion of
2355   the product value).
2359<section title="Quality Values" anchor="quality.values">
2360  <x:anchor-alias value="qvalue"/>
2362   Both transfer codings (TE request header field, <xref target="header.te"/>)
2363   and content negotiation (&content.negotiation;) use short "floating point"
2364   numbers to indicate the relative importance ("weight") of various
2365   negotiable parameters.  A weight is normalized to a real number in
2366   the range 0 through 1, where 0 is the minimum and 1 the maximum
2367   value. If a parameter has a quality value of 0, then content with
2368   this parameter is "not acceptable" for the client. HTTP/1.1
2369   applications &MUST-NOT; generate more than three digits after the
2370   decimal point. User configuration of these values &SHOULD; also be
2371   limited in this fashion.
2373<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2374  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2375                 / ( "1" [ "." 0*3("0") ] )
2378  <t>
2379     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2380     relative degradation in desired quality.
2381  </t>
2387<section title="Connections" anchor="connections">
2389<section title="Persistent Connections" anchor="persistent.connections">
2391<section title="Purpose" anchor="persistent.purpose">
2393   Prior to persistent connections, a separate TCP connection was
2394   established for each request, increasing the load on HTTP servers
2395   and causing congestion on the Internet. The use of inline images and
2396   other associated data often requires a client to make multiple
2397   requests of the same server in a short amount of time. Analysis of
2398   these performance problems and results from a prototype
2399   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2400   measurements of actual HTTP/1.1 implementations show good
2401   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2402   T/TCP <xref target="Tou1998"/>.
2405   Persistent HTTP connections have a number of advantages:
2406  <list style="symbols">
2407      <t>
2408        By opening and closing fewer TCP connections, CPU time is saved
2409        in routers and hosts (clients, servers, proxies, gateways,
2410        tunnels, or caches), and memory used for TCP protocol control
2411        blocks can be saved in hosts.
2412      </t>
2413      <t>
2414        HTTP requests and responses can be pipelined on a connection.
2415        Pipelining allows a client to make multiple requests without
2416        waiting for each response, allowing a single TCP connection to
2417        be used much more efficiently, with much lower elapsed time.
2418      </t>
2419      <t>
2420        Network congestion is reduced by reducing the number of packets
2421        caused by TCP opens, and by allowing TCP sufficient time to
2422        determine the congestion state of the network.
2423      </t>
2424      <t>
2425        Latency on subsequent requests is reduced since there is no time
2426        spent in TCP's connection opening handshake.
2427      </t>
2428      <t>
2429        HTTP can evolve more gracefully, since errors can be reported
2430        without the penalty of closing the TCP connection. Clients using
2431        future versions of HTTP might optimistically try a new feature,
2432        but if communicating with an older server, retry with old
2433        semantics after an error is reported.
2434      </t>
2435    </list>
2438   HTTP implementations &SHOULD; implement persistent connections.
2442<section title="Overall Operation" anchor="persistent.overall">
2444   A significant difference between HTTP/1.1 and earlier versions of
2445   HTTP is that persistent connections are the default behavior of any
2446   HTTP connection. That is, unless otherwise indicated, the client
2447   &SHOULD; assume that the server will maintain a persistent connection,
2448   even after error responses from the server.
2451   Persistent connections provide a mechanism by which a client and a
2452   server can signal the close of a TCP connection. This signaling takes
2453   place using the Connection header field (<xref target="header.connection"/>). Once a close
2454   has been signaled, the client &MUST-NOT; send any more requests on that
2455   connection.
2458<section title="Negotiation" anchor="persistent.negotiation">
2460   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2461   maintain a persistent connection unless a Connection header field including
2462   the connection-token "close" was sent in the request. If the server
2463   chooses to close the connection immediately after sending the
2464   response, it &SHOULD; send a Connection header field including the
2465   connection-token "close".
2468   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2469   decide to keep it open based on whether the response from a server
2470   contains a Connection header field with the connection-token close. In case
2471   the client does not want to maintain a connection for more than that
2472   request, it &SHOULD; send a Connection header field including the
2473   connection-token close.
2476   If either the client or the server sends the close token in the
2477   Connection header field, that request becomes the last one for the
2478   connection.
2481   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2482   maintained for HTTP versions less than 1.1 unless it is explicitly
2483   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2484   compatibility with HTTP/1.0 clients.
2487   In order to remain persistent, all messages on the connection &MUST;
2488   have a self-defined message length (i.e., one not defined by closure
2489   of the connection), as described in <xref target="message.body"/>.
2493<section title="Pipelining" anchor="pipelining">
2495   A client that supports persistent connections &MAY; "pipeline" its
2496   requests (i.e., send multiple requests without waiting for each
2497   response). A server &MUST; send its responses to those requests in the
2498   same order that the requests were received.
2501   Clients which assume persistent connections and pipeline immediately
2502   after connection establishment &SHOULD; be prepared to retry their
2503   connection if the first pipelined attempt fails. If a client does
2504   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2505   persistent. Clients &MUST; also be prepared to resend their requests if
2506   the server closes the connection before sending all of the
2507   corresponding responses.
2510   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2511   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2512   premature termination of the transport connection could lead to
2513   indeterminate results. A client wishing to send a non-idempotent
2514   request &SHOULD; wait to send that request until it has received the
2515   response status line for the previous request.
2520<section title="Proxy Servers" anchor="persistent.proxy">
2522   It is especially important that proxies correctly implement the
2523   properties of the Connection header field as specified in <xref target="header.connection"/>.
2526   The proxy server &MUST; signal persistent connections separately with
2527   its clients and the origin servers (or other proxy servers) that it
2528   connects to. Each persistent connection applies to only one transport
2529   link.
2532   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2533   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2534   for information and discussion of the problems with the Keep-Alive header field
2535   implemented by many HTTP/1.0 clients).
2538<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2540  <cref anchor="TODO-end-to-end" source="jre">
2541    Restored from <eref target=""/>.
2542    See also <eref target=""/>.
2543  </cref>
2546   For the purpose of defining the behavior of caches and non-caching
2547   proxies, we divide HTTP header fields into two categories:
2548  <list style="symbols">
2549      <t>End-to-end header fields, which are  transmitted to the ultimate
2550        recipient of a request or response. End-to-end header fields in
2551        responses MUST be stored as part of a cache entry and &MUST; be
2552        transmitted in any response formed from a cache entry.</t>
2554      <t>Hop-by-hop header fields, which are meaningful only for a single
2555        transport-level connection, and are not stored by caches or
2556        forwarded by proxies.</t>
2557  </list>
2560   The following HTTP/1.1 header fields are hop-by-hop header fields:
2561  <list style="symbols">
2562      <t>Connection</t>
2563      <t>Keep-Alive</t>
2564      <t>Proxy-Authenticate</t>
2565      <t>Proxy-Authorization</t>
2566      <t>TE</t>
2567      <t>Trailer</t>
2568      <t>Transfer-Encoding</t>
2569      <t>Upgrade</t>
2570  </list>
2573   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2576   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2577   (<xref target="header.connection"/>).
2581<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2583  <cref anchor="TODO-non-mod-headers" source="jre">
2584    Restored from <eref target=""/>.
2585    See also <eref target=""/>.
2586  </cref>
2589   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2590   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2591   modify an end-to-end header field unless the definition of that header field requires
2592   or specifically allows that.
2595   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2596   request or response, and it &MUST-NOT; add any of these fields if not
2597   already present:
2598  <list style="symbols">
2599      <t>Content-Location</t>
2600      <t>Content-MD5</t>
2601      <t>ETag</t>
2602      <t>Last-Modified</t>
2603  </list>
2606   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2607   response:
2608  <list style="symbols">
2609    <t>Expires</t>
2610  </list>
2613   but it &MAY; add any of these fields if not already present. If an
2614   Expires header field is added, it &MUST; be given a field-value identical to
2615   that of the Date header field in that response.
2618   A proxy &MUST-NOT; modify or add any of the following fields in a
2619   message that contains the no-transform cache-control directive, or in
2620   any request:
2621  <list style="symbols">
2622    <t>Content-Encoding</t>
2623    <t>Content-Range</t>
2624    <t>Content-Type</t>
2625  </list>
2628   A transforming proxy &MAY; modify or add these fields to a message
2629   that does not include no-transform, but if it does so, it &MUST; add a
2630   Warning 214 (Transformation applied) if one does not already appear
2631   in the message (see &header-warning;).
2634  <t>
2635    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2636    cause authentication failures if stronger authentication
2637    mechanisms are introduced in later versions of HTTP. Such
2638    authentication mechanisms &MAY; rely on the values of header fields
2639    not listed here.
2640  </t>
2643   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2644   though it &MAY; change the message-body through application or removal
2645   of a transfer-coding (<xref target="transfer.codings"/>).
2651<section title="Practical Considerations" anchor="persistent.practical">
2653   Servers will usually have some time-out value beyond which they will
2654   no longer maintain an inactive connection. Proxy servers might make
2655   this a higher value since it is likely that the client will be making
2656   more connections through the same server. The use of persistent
2657   connections places no requirements on the length (or existence) of
2658   this time-out for either the client or the server.
2661   When a client or server wishes to time-out it &SHOULD; issue a graceful
2662   close on the transport connection. Clients and servers &SHOULD; both
2663   constantly watch for the other side of the transport close, and
2664   respond to it as appropriate. If a client or server does not detect
2665   the other side's close promptly it could cause unnecessary resource
2666   drain on the network.
2669   A client, server, or proxy &MAY; close the transport connection at any
2670   time. For example, a client might have started to send a new request
2671   at the same time that the server has decided to close the "idle"
2672   connection. From the server's point of view, the connection is being
2673   closed while it was idle, but from the client's point of view, a
2674   request is in progress.
2677   This means that clients, servers, and proxies &MUST; be able to recover
2678   from asynchronous close events. Client software &SHOULD; reopen the
2679   transport connection and retransmit the aborted sequence of requests
2680   without user interaction so long as the request sequence is
2681   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2682   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2683   human operator the choice of retrying the request(s). Confirmation by
2684   user-agent software with semantic understanding of the application
2685   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2686   be repeated if the second sequence of requests fails.
2689   Servers &SHOULD; always respond to at least one request per connection,
2690   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2691   middle of transmitting a response, unless a network or client failure
2692   is suspected.
2695   Clients (including proxies) &SHOULD; limit the number of simultaneous
2696   connections that they maintain to a given server (including proxies).
2699   Previous revisions of HTTP gave a specific number of connections as a
2700   ceiling, but this was found to be impractical for many applications. As a
2701   result, this specification does not mandate a particular maximum number of
2702   connections, but instead encourages clients to be conservative when opening
2703   multiple connections.
2706   In particular, while using multiple connections avoids the "head-of-line
2707   blocking" problem (whereby a request that takes significant server-side
2708   processing and/or has a large payload can block subsequent requests on the
2709   same connection), each connection used consumes server resources (sometimes
2710   significantly), and furthermore using multiple connections can cause
2711   undesirable side effects in congested networks.
2714   Note that servers might reject traffic that they deem abusive, including an
2715   excessive number of connections from a client.
2720<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2722<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2724   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2725   flow control mechanisms to resolve temporary overloads, rather than
2726   terminating connections with the expectation that clients will retry.
2727   The latter technique can exacerbate network congestion.
2731<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2733   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2734   the network connection for an error status code while it is transmitting
2735   the request. If the client sees an error status code, it &SHOULD;
2736   immediately cease transmitting the body. If the body is being sent
2737   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2738   empty trailer &MAY; be used to prematurely mark the end of the message.
2739   If the body was preceded by a Content-Length header field, the client &MUST;
2740   close the connection.
2744<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2746   The purpose of the 100 (Continue) status code (see &status-100;) is to
2747   allow a client that is sending a request message with a request body
2748   to determine if the origin server is willing to accept the request
2749   (based on the request header fields) before the client sends the request
2750   body. In some cases, it might either be inappropriate or highly
2751   inefficient for the client to send the body if the server will reject
2752   the message without looking at the body.
2755   Requirements for HTTP/1.1 clients:
2756  <list style="symbols">
2757    <t>
2758        If a client will wait for a 100 (Continue) response before
2759        sending the request body, it &MUST; send an Expect header
2760        field (&header-expect;) with the "100-continue" expectation.
2761    </t>
2762    <t>
2763        A client &MUST-NOT; send an Expect header field (&header-expect;)
2764        with the "100-continue" expectation if it does not intend
2765        to send a request body.
2766    </t>
2767  </list>
2770   Because of the presence of older implementations, the protocol allows
2771   ambiguous situations in which a client might send "Expect: 100-continue"
2772   without receiving either a 417 (Expectation Failed)
2773   or a 100 (Continue) status code. Therefore, when a client sends this
2774   header field to an origin server (possibly via a proxy) from which it
2775   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2776   wait for an indefinite period before sending the request body.
2779   Requirements for HTTP/1.1 origin servers:
2780  <list style="symbols">
2781    <t> Upon receiving a request which includes an Expect header
2782        field with the "100-continue" expectation, an origin server &MUST;
2783        either respond with 100 (Continue) status code and continue to read
2784        from the input stream, or respond with a final status code. The
2785        origin server &MUST-NOT; wait for the request body before sending
2786        the 100 (Continue) response. If it responds with a final status
2787        code, it &MAY; close the transport connection or it &MAY; continue
2788        to read and discard the rest of the request.  It &MUST-NOT;
2789        perform the request method if it returns a final status code.
2790    </t>
2791    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2792        the request message does not include an Expect header
2793        field with the "100-continue" expectation, and &MUST-NOT; send a
2794        100 (Continue) response if such a request comes from an HTTP/1.0
2795        (or earlier) client. There is an exception to this rule: for
2796        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2797        status code in response to an HTTP/1.1 PUT or POST request that does
2798        not include an Expect header field with the "100-continue"
2799        expectation. This exception, the purpose of which is
2800        to minimize any client processing delays associated with an
2801        undeclared wait for 100 (Continue) status code, applies only to
2802        HTTP/1.1 requests, and not to requests with any other HTTP-version
2803        value.
2804    </t>
2805    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2806        already received some or all of the request body for the
2807        corresponding request.
2808    </t>
2809    <t> An origin server that sends a 100 (Continue) response &MUST;
2810    ultimately send a final status code, once the request body is
2811        received and processed, unless it terminates the transport
2812        connection prematurely.
2813    </t>
2814    <t> If an origin server receives a request that does not include an
2815        Expect header field with the "100-continue" expectation,
2816        the request includes a request body, and the server responds
2817        with a final status code before reading the entire request body
2818        from the transport connection, then the server &SHOULD-NOT;  close
2819        the transport connection until it has read the entire request,
2820        or until the client closes the connection. Otherwise, the client
2821        might not reliably receive the response message. However, this
2822        requirement is not be construed as preventing a server from
2823        defending itself against denial-of-service attacks, or from
2824        badly broken client implementations.
2825      </t>
2826    </list>
2829   Requirements for HTTP/1.1 proxies:
2830  <list style="symbols">
2831    <t> If a proxy receives a request that includes an Expect header
2832        field with the "100-continue" expectation, and the proxy
2833        either knows that the next-hop server complies with HTTP/1.1 or
2834        higher, or does not know the HTTP version of the next-hop
2835        server, it &MUST; forward the request, including the Expect header
2836        field.
2837    </t>
2838    <t> If the proxy knows that the version of the next-hop server is
2839        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2840        respond with a 417 (Expectation Failed) status code.
2841    </t>
2842    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2843        numbers received from recently-referenced next-hop servers.
2844    </t>
2845    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2846        request message was received from an HTTP/1.0 (or earlier)
2847        client and did not include an Expect header field with
2848        the "100-continue" expectation. This requirement overrides the
2849        general rule for forwarding of 1xx responses (see &status-1xx;).
2850    </t>
2851  </list>
2855<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2857   If an HTTP/1.1 client sends a request which includes a request body,
2858   but which does not include an Expect header field with the
2859   "100-continue" expectation, and if the client is not directly
2860   connected to an HTTP/1.1 origin server, and if the client sees the
2861   connection close before receiving a status line from the server, the
2862   client &SHOULD; retry the request.  If the client does retry this
2863   request, it &MAY; use the following "binary exponential backoff"
2864   algorithm to be assured of obtaining a reliable response:
2865  <list style="numbers">
2866    <t>
2867      Initiate a new connection to the server
2868    </t>
2869    <t>
2870      Transmit the request-line, header fields, and the CRLF that
2871      indicates the end of header fields.
2872    </t>
2873    <t>
2874      Initialize a variable R to the estimated round-trip time to the
2875         server (e.g., based on the time it took to establish the
2876         connection), or to a constant value of 5 seconds if the round-trip
2877         time is not available.
2878    </t>
2879    <t>
2880       Compute T = R * (2**N), where N is the number of previous
2881         retries of this request.
2882    </t>
2883    <t>
2884       Wait either for an error response from the server, or for T
2885         seconds (whichever comes first)
2886    </t>
2887    <t>
2888       If no error response is received, after T seconds transmit the
2889         body of the request.
2890    </t>
2891    <t>
2892       If client sees that the connection is closed prematurely,
2893         repeat from step 1 until the request is accepted, an error
2894         response is received, or the user becomes impatient and
2895         terminates the retry process.
2896    </t>
2897  </list>
2900   If at any point an error status code is received, the client
2901  <list style="symbols">
2902      <t>&SHOULD-NOT;  continue and</t>
2904      <t>&SHOULD; close the connection if it has not completed sending the
2905        request message.</t>
2906    </list>
2913<section title="Miscellaneous notes that might disappear" anchor="misc">
2914<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2916   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2920<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2922   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2926<section title="Interception of HTTP for access control" anchor="http.intercept">
2928   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2932<section title="Use of HTTP by other protocols" anchor="http.others">
2934   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2935   Extensions of HTTP like WebDAV.</cref>
2939<section title="Use of HTTP by media type specification" anchor="">
2941   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2946<section title="Header Field Definitions" anchor="header.field.definitions">
2948   This section defines the syntax and semantics of HTTP header fields
2949   related to message framing and transport protocols.
2952<section title="Connection" anchor="header.connection">
2953  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2954  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2955  <x:anchor-alias value="Connection"/>
2956  <x:anchor-alias value="connection-token"/>
2957  <x:anchor-alias value="Connection-v"/>
2959   The "Connection" header field allows the sender to specify
2960   options that are desired only for that particular connection.
2961   Such connection options &MUST; be removed or replaced before the
2962   message can be forwarded downstream by a proxy or gateway.
2963   This mechanism also allows the sender to indicate which HTTP
2964   header fields used in the message are only intended for the
2965   immediate recipient ("hop-by-hop"), as opposed to all recipients
2966   on the chain ("end-to-end"), enabling the message to be
2967   self-descriptive and allowing future connection-specific extensions
2968   to be deployed in HTTP without fear that they will be blindly
2969   forwarded by previously deployed intermediaries.
2972   The Connection header field's value has the following grammar:
2974<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"/>
2975  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2976  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2977  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2980   A proxy or gateway &MUST; parse a received Connection
2981   header field before a message is forwarded and, for each
2982   connection-token in this field, remove any header field(s) from
2983   the message with the same name as the connection-token, and then
2984   remove the Connection header field itself or replace it with the
2985   sender's own connection options for the forwarded message.
2988   A sender &MUST-NOT; include field-names in the Connection header
2989   field-value for fields that are defined as expressing constraints
2990   for all recipients in the request or response chain, such as the
2991   Cache-Control header field (&header-cache-control;).
2994   The connection options do not have to correspond to a header field
2995   present in the message, since a connection-specific header field
2996   might not be needed if there are no parameters associated with that
2997   connection option.  Recipients that trigger certain connection
2998   behavior based on the presence of connection options &MUST; do so
2999   based on the presence of the connection-token rather than only the
3000   presence of the optional header field.  In other words, if the
3001   connection option is received as a header field but not indicated
3002   within the Connection field-value, then the recipient &MUST; ignore
3003   the connection-specific header field because it has likely been
3004   forwarded by an intermediary that is only partially compliant.
3007   When defining new connection options, specifications ought to
3008   carefully consider existing deployed header fields and ensure
3009   that the new connection-token does not share the same name as
3010   an unrelated header field that might already be deployed.
3011   Defining a new connection-token essentially reserves that potential
3012   field-name for carrying additional information related to the
3013   connection option, since it would be unwise for senders to use
3014   that field-name for anything else.
3017   HTTP/1.1 defines the "close" connection option for the sender to
3018   signal that the connection will be closed after completion of the
3019   response. For example,
3021<figure><artwork type="example">
3022  Connection: close
3025   in either the request or the response header fields indicates that
3026   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3027   after the current request/response is complete.
3030   An HTTP/1.1 client that does not support persistent connections &MUST;
3031   include the "close" connection option in every request message.
3034   An HTTP/1.1 server that does not support persistent connections &MUST;
3035   include the "close" connection option in every response message that
3036   does not have a 1xx (Informational) status code.
3040<section title="Content-Length" anchor="header.content-length">
3041  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3042  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3043  <x:anchor-alias value="Content-Length"/>
3044  <x:anchor-alias value="Content-Length-v"/>
3046   The "Content-Length" header field indicates the size of the
3047   message-body, in decimal number of octets, for any message other than
3048   a response to a HEAD request or a response with a status code of 304.
3049   In the case of a response to a HEAD request, Content-Length indicates
3050   the size of the payload body (not including any potential transfer-coding)
3051   that would have been sent had the request been a GET.
3052   In the case of a 304 (Not Modified) response to a GET request,
3053   Content-Length indicates the size of the payload body (not including
3054   any potential transfer-coding) that would have been sent in a 200 (OK)
3055   response.
3057<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
3058  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
3059  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
3062   An example is
3064<figure><artwork type="example">
3065  Content-Length: 3495
3068   Implementations &SHOULD; use this field to indicate the message-body
3069   length when no transfer-coding is being applied and the
3070   payload's body length can be determined prior to being transferred.
3071   <xref target="message.body"/> describes how recipients determine the length
3072   of a message-body.
3075   Any Content-Length greater than or equal to zero is a valid value.
3078   Note that the use of this field in HTTP is significantly different from
3079   the corresponding definition in MIME, where it is an optional field
3080   used within the "message/external-body" content-type.
3084<section title="Date" anchor="">
3085  <iref primary="true" item="Date header field" x:for-anchor=""/>
3086  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3087  <x:anchor-alias value="Date"/>
3088  <x:anchor-alias value="Date-v"/>
3090   The "Date" header field represents the date and time at which
3091   the message was originated, having the same semantics as the Origination
3092   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3093   The field value is an HTTP-date, as described in <xref target=""/>;
3094   it &MUST; be sent in rfc1123-date format.
3096<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3097  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3098  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3101   An example is
3103<figure><artwork type="example">
3104  Date: Tue, 15 Nov 1994 08:12:31 GMT
3107   Origin servers &MUST; include a Date header field in all responses,
3108   except in these cases:
3109  <list style="numbers">
3110      <t>If the response status code is 100 (Continue) or 101 (Switching
3111         Protocols), the response &MAY; include a Date header field, at
3112         the server's option.</t>
3114      <t>If the response status code conveys a server error, e.g., 500
3115         (Internal Server Error) or 503 (Service Unavailable), and it is
3116         inconvenient or impossible to generate a valid Date.</t>
3118      <t>If the server does not have a clock that can provide a
3119         reasonable approximation of the current time, its responses
3120         &MUST-NOT; include a Date header field. In this case, the rules
3121         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3122  </list>
3125   A received message that does not have a Date header field &MUST; be
3126   assigned one by the recipient if the message will be cached by that
3127   recipient.
3130   Clients can use the Date header field as well; in order to keep request
3131   messages small, they are advised not to include it when it doesn't convey
3132   any useful information (as it is usually the case for requests that do not
3133   contain a payload).
3136   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3137   time subsequent to the generation of the message. It &SHOULD; represent
3138   the best available approximation of the date and time of message
3139   generation, unless the implementation has no means of generating a
3140   reasonably accurate date and time. In theory, the date ought to
3141   represent the moment just before the payload is generated. In
3142   practice, the date can be generated at any time during the message
3143   origination without affecting its semantic value.
3146<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3148   Some origin server implementations might not have a clock available.
3149   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3150   values to a response, unless these values were associated
3151   with the resource by a system or user with a reliable clock. It &MAY;
3152   assign an Expires value that is known, at or before server
3153   configuration time, to be in the past (this allows "pre-expiration"
3154   of responses without storing separate Expires values for each
3155   resource).
3160<section title="Host" anchor="">
3161  <iref primary="true" item="Host header field" x:for-anchor=""/>
3162  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3163  <x:anchor-alias value="Host"/>
3164  <x:anchor-alias value="Host-v"/>
3166   The "Host" header field in a request provides the host and port
3167   information from the target resource's URI, enabling the origin
3168   server to distinguish between resources while servicing requests
3169   for multiple host names on a single IP address.  Since the Host
3170   field-value is critical information for handling a request, it
3171   &SHOULD; be sent as the first header field following the Request-Line.
3173<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3174  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3175  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3178   A client &MUST; send a Host header field in all HTTP/1.1 request
3179   messages.  If the target resource's URI includes an authority
3180   component, then the Host field-value &MUST; be identical to that
3181   authority component after excluding any userinfo (<xref target="http.uri"/>).
3182   If the authority component is missing or undefined for the target
3183   resource's URI, then the Host header field &MUST; be sent with an
3184   empty field-value.
3187   For example, a GET request to the origin server for
3188   &lt;; would begin with:
3190<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3191GET /pub/WWW/ HTTP/1.1
3195   The Host header field &MUST; be sent in an HTTP/1.1 request even
3196   if the request-target is in the form of an absolute-URI, since this
3197   allows the Host information to be forwarded through ancient HTTP/1.0
3198   proxies that might not have implemented Host.
3201   When an HTTP/1.1 proxy receives a request with a request-target in
3202   the form of an absolute-URI, the proxy &MUST; ignore the received
3203   Host header field (if any) and instead replace it with the host
3204   information of the request-target.  When a proxy forwards a request,
3205   it &MUST; generate the Host header field based on the received
3206   absolute-URI rather than the received Host.
3209   Since the Host header field acts as an application-level routing
3210   mechanism, it is a frequent target for malware seeking to poison
3211   a shared cache or redirect a request to an unintended server.
3212   An interception proxy is particularly vulnerable if it relies on
3213   the Host header field value for redirecting requests to internal
3214   servers, or for use as a cache key in a shared cache, without
3215   first verifying that the intercepted connection is targeting a
3216   valid IP address for that host.
3219   A server &MUST; respond with a 400 (Bad Request) status code to
3220   any HTTP/1.1 request message that lacks a Host header field and
3221   to any request message that contains more than one Host header field
3222   or a Host header field with an invalid field-value.
3225   See Sections <xref target="" format="counter"/>
3226   and <xref target="" format="counter"/>
3227   for other requirements relating to Host.
3231<section title="TE" anchor="header.te">
3232  <iref primary="true" item="TE header field" x:for-anchor=""/>
3233  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3234  <x:anchor-alias value="TE"/>
3235  <x:anchor-alias value="TE-v"/>
3236  <x:anchor-alias value="t-codings"/>
3237  <x:anchor-alias value="te-params"/>
3238  <x:anchor-alias value="te-ext"/>
3240   The "TE" header field indicates what extension transfer-codings
3241   it is willing to accept in the response, and whether or not it is
3242   willing to accept trailer fields in a chunked transfer-coding.
3245   Its value consists of the keyword "trailers" and/or a comma-separated
3246   list of extension transfer-coding names with optional accept
3247   parameters (as described in <xref target="transfer.codings"/>).
3249<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"/>
3250  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3251  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3252  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3253  <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> )
3254  <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> ]
3257   The presence of the keyword "trailers" indicates that the client is
3258   willing to accept trailer fields in a chunked transfer-coding, as
3259   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3260   transfer-coding values even though it does not itself represent a
3261   transfer-coding.
3264   Examples of its use are:
3266<figure><artwork type="example">
3267  TE: deflate
3268  TE:
3269  TE: trailers, deflate;q=0.5
3272   The TE header field only applies to the immediate connection.
3273   Therefore, the keyword &MUST; be supplied within a Connection header
3274   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3277   A server tests whether a transfer-coding is acceptable, according to
3278   a TE field, using these rules:
3279  <list style="numbers">
3280    <x:lt>
3281      <t>The "chunked" transfer-coding is always acceptable. If the
3282         keyword "trailers" is listed, the client indicates that it is
3283         willing to accept trailer fields in the chunked response on
3284         behalf of itself and any downstream clients. The implication is
3285         that, if given, the client is stating that either all
3286         downstream clients are willing to accept trailer fields in the
3287         forwarded response, or that it will attempt to buffer the
3288         response on behalf of downstream recipients.
3289      </t><t>
3290         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3291         chunked response such that a client can be assured of buffering
3292         the entire response.</t>
3293    </x:lt>
3294    <x:lt>
3295      <t>If the transfer-coding being tested is one of the transfer-codings
3296         listed in the TE field, then it is acceptable unless it
3297         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3298         qvalue of 0 means "not acceptable".)</t>
3299    </x:lt>
3300    <x:lt>
3301      <t>If multiple transfer-codings are acceptable, then the
3302         acceptable transfer-coding with the highest non-zero qvalue is
3303         preferred.  The "chunked" transfer-coding always has a qvalue
3304         of 1.</t>
3305    </x:lt>
3306  </list>
3309   If the TE field-value is empty or if no TE field is present, the only
3310   transfer-coding is "chunked". A message with no transfer-coding is
3311   always acceptable.
3315<section title="Trailer" anchor="header.trailer">
3316  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3317  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3318  <x:anchor-alias value="Trailer"/>
3319  <x:anchor-alias value="Trailer-v"/>
3321   The "Trailer" header field indicates that the given set of
3322   header fields is present in the trailer of a message encoded with
3323   chunked transfer-coding.
3325<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3326  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3327  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3330   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3331   message using chunked transfer-coding with a non-empty trailer. Doing
3332   so allows the recipient to know which header fields to expect in the
3333   trailer.
3336   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3337   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3338   trailer fields in a "chunked" transfer-coding.
3341   Message header fields listed in the Trailer header field &MUST-NOT;
3342   include the following header fields:
3343  <list style="symbols">
3344    <t>Transfer-Encoding</t>
3345    <t>Content-Length</t>
3346    <t>Trailer</t>
3347  </list>
3351<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3352  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3353  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3354  <x:anchor-alias value="Transfer-Encoding"/>
3355  <x:anchor-alias value="Transfer-Encoding-v"/>
3357   The "Transfer-Encoding" header field indicates what transfer-codings
3358   (if any) have been applied to the message body. It differs from
3359   Content-Encoding (&content-codings;) in that transfer-codings are a property
3360   of the message (and therefore are removed by intermediaries), whereas
3361   content-codings are not.
3363<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3364  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3365                        <x:ref>Transfer-Encoding-v</x:ref>
3366  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3369   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3371<figure><artwork type="example">
3372  Transfer-Encoding: chunked
3375   If multiple encodings have been applied to a representation, the transfer-codings
3376   &MUST; be listed in the order in which they were applied.
3377   Additional information about the encoding parameters &MAY; be provided
3378   by other header fields not defined by this specification.
3381   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3382   header field.
3386<section title="Upgrade" anchor="header.upgrade">
3387  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3388  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3389  <x:anchor-alias value="Upgrade"/>
3390  <x:anchor-alias value="Upgrade-v"/>
3392   The "Upgrade" header field allows the client to specify what
3393   additional communication protocols it would like to use, if the server
3394   chooses to switch protocols. Servers can use it to indicate what protocols
3395   they are willing to switch to.
3397<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3398  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3399  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3402   For example,
3404<figure><artwork type="example">
3405  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3408   The Upgrade header field is intended to provide a simple mechanism
3409   for transition from HTTP/1.1 to some other, incompatible protocol. It
3410   does so by allowing the client to advertise its desire to use another
3411   protocol, such as a later version of HTTP with a higher major version
3412   number, even though the current request has been made using HTTP/1.1.
3413   This eases the difficult transition between incompatible protocols by
3414   allowing the client to initiate a request in the more commonly
3415   supported protocol while indicating to the server that it would like
3416   to use a "better" protocol if available (where "better" is determined
3417   by the server, possibly according to the nature of the request method
3418   or target resource).
3421   The Upgrade header field only applies to switching application-layer
3422   protocols upon the existing transport-layer connection. Upgrade
3423   cannot be used to insist on a protocol change; its acceptance and use
3424   by the server is optional. The capabilities and nature of the
3425   application-layer communication after the protocol change is entirely
3426   dependent upon the new protocol chosen, although the first action
3427   after changing the protocol &MUST; be a response to the initial HTTP
3428   request containing the Upgrade header field.
3431   The Upgrade header field only applies to the immediate connection.
3432   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3433   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3434   HTTP/1.1 message.
3437   The Upgrade header field cannot be used to indicate a switch to a
3438   protocol on a different connection. For that purpose, it is more
3439   appropriate to use a 3xx redirection response (&status-3xx;).
3442   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3443   Protocols) responses to indicate which protocol(s) are being switched to,
3444   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3445   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3446   response to indicate that they are willing to upgrade to one of the
3447   specified protocols.
3450   This specification only defines the protocol name "HTTP" for use by
3451   the family of Hypertext Transfer Protocols, as defined by the HTTP
3452   version rules of <xref target="http.version"/> and future updates to this
3453   specification. Additional tokens can be registered with IANA using the
3454   registration procedure defined below. 
3457<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3459   The HTTP Upgrade Token Registry defines the name space for product
3460   tokens used to identify protocols in the Upgrade header field.
3461   Each registered token is associated with contact information and
3462   an optional set of specifications that details how the connection
3463   will be processed after it has been upgraded.
3466   Registrations are allowed on a First Come First Served basis as
3467   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3468   specifications need not be IETF documents or be subject to IESG review.
3469   Registrations are subject to the following rules:
3470  <list style="numbers">
3471    <t>A token, once registered, stays registered forever.</t>
3472    <t>The registration &MUST; name a responsible party for the
3473       registration.</t>
3474    <t>The registration &MUST; name a point of contact.</t>
3475    <t>The registration &MAY; name a set of specifications associated with that
3476       token. Such specifications need not be publicly available.</t>
3477    <t>The responsible party &MAY; change the registration at any time.
3478       The IANA will keep a record of all such changes, and make them
3479       available upon request.</t>
3480    <t>The responsible party for the first registration of a "product"
3481       token &MUST; approve later registrations of a "version" token
3482       together with that "product" token before they can be registered.</t>
3483    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3484       for a token. This will normally only be used in the case when a
3485       responsible party cannot be contacted.</t>
3486  </list>
3493<section title="Via" anchor="header.via">
3494  <iref primary="true" item="Via header field" x:for-anchor=""/>
3495  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3496  <x:anchor-alias value="protocol-name"/>
3497  <x:anchor-alias value="protocol-version"/>
3498  <x:anchor-alias value="pseudonym"/>
3499  <x:anchor-alias value="received-by"/>
3500  <x:anchor-alias value="received-protocol"/>
3501  <x:anchor-alias value="Via"/>
3502  <x:anchor-alias value="Via-v"/>
3504   The "Via" header field &MUST; be sent by a proxy or gateway to
3505   indicate the intermediate protocols and recipients between the user
3506   agent and the server on requests, and between the origin server and
3507   the client on responses. It is analogous to the "Received" field
3508   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3509   and is intended to be used for tracking message forwards,
3510   avoiding request loops, and identifying the protocol capabilities of
3511   all senders along the request/response chain.
3513<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"/>
3514  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3515  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3516                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3517  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3518  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3519  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3520  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3521  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3524   The received-protocol indicates the protocol version of the message
3525   received by the server or client along each segment of the
3526   request/response chain. The received-protocol version is appended to
3527   the Via field value when the message is forwarded so that information
3528   about the protocol capabilities of upstream applications remains
3529   visible to all recipients.
3532   The protocol-name is excluded if and only if it would be "HTTP". The
3533   received-by field is normally the host and optional port number of a
3534   recipient server or client that subsequently forwarded the message.
3535   However, if the real host is considered to be sensitive information,
3536   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3537   be assumed to be the default port of the received-protocol.
3540   Multiple Via field values represent each proxy or gateway that has
3541   forwarded the message. Each recipient &MUST; append its information
3542   such that the end result is ordered according to the sequence of
3543   forwarding applications.
3546   Comments &MAY; be used in the Via header field to identify the software
3547   of each recipient, analogous to the User-Agent and Server header fields.
3548   However, all comments in the Via field are optional and &MAY; be removed
3549   by any recipient prior to forwarding the message.
3552   For example, a request message could be sent from an HTTP/1.0 user
3553   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3554   forward the request to a public proxy at, which completes
3555   the request by forwarding it to the origin server at
3556   The request received by would then have the following
3557   Via header field:
3559<figure><artwork type="example">
3560  Via: 1.0 fred, 1.1 (Apache/1.1)
3563   A proxy or gateway used as a portal through a network firewall
3564   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3565   region unless it is explicitly enabled to do so. If not enabled, the
3566   received-by host of any host behind the firewall &SHOULD; be replaced
3567   by an appropriate pseudonym for that host.
3570   For organizations that have strong privacy requirements for hiding
3571   internal structures, a proxy or gateway &MAY; combine an ordered
3572   subsequence of Via header field entries with identical received-protocol
3573   values into a single such entry. For example,
3575<figure><artwork type="example">
3576  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3579  could be collapsed to
3581<figure><artwork type="example">
3582  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3585   Senders &SHOULD-NOT; combine multiple entries unless they are all
3586   under the same organizational control and the hosts have already been
3587   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3588   have different received-protocol values.
3594<section title="IANA Considerations" anchor="IANA.considerations">
3596<section title="Header Field Registration" anchor="header.field.registration">
3598   The Message Header Field Registry located at <eref target=""/> shall be updated
3599   with the permanent registrations below (see <xref target="RFC3864"/>):
3601<?BEGININC p1-messaging.iana-headers ?>
3602<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3603<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3604   <ttcol>Header Field Name</ttcol>
3605   <ttcol>Protocol</ttcol>
3606   <ttcol>Status</ttcol>
3607   <ttcol>Reference</ttcol>
3609   <c>Connection</c>
3610   <c>http</c>
3611   <c>standard</c>
3612   <c>
3613      <xref target="header.connection"/>
3614   </c>
3615   <c>Content-Length</c>
3616   <c>http</c>
3617   <c>standard</c>
3618   <c>
3619      <xref target="header.content-length"/>
3620   </c>
3621   <c>Date</c>
3622   <c>http</c>
3623   <c>standard</c>
3624   <c>
3625      <xref target=""/>
3626   </c>
3627   <c>Host</c>
3628   <c>http</c>
3629   <c>standard</c>
3630   <c>
3631      <xref target=""/>
3632   </c>
3633   <c>TE</c>
3634   <c>http</c>
3635   <c>standard</c>
3636   <c>
3637      <xref target="header.te"/>
3638   </c>
3639   <c>Trailer</c>
3640   <c>http</c>
3641   <c>standard</c>
3642   <c>
3643      <xref target="header.trailer"/>
3644   </c>
3645   <c>Transfer-Encoding</c>
3646   <c>http</c>
3647   <c>standard</c>
3648   <c>
3649      <xref target="header.transfer-encoding"/>
3650   </c>
3651   <c>Upgrade</c>
3652   <c>http</c>
3653   <c>standard</c>
3654   <c>
3655      <xref target="header.upgrade"/>
3656   </c>
3657   <c>Via</c>
3658   <c>http</c>
3659   <c>standard</c>
3660   <c>
3661      <xref target="header.via"/>
3662   </c>
3665<?ENDINC p1-messaging.iana-headers ?>
3667   The change controller is: "IETF ( - Internet Engineering Task Force".
3671<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3673   The entries for the "http" and "https" URI Schemes in the registry located at
3674   <eref target=""/>
3675   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3676   and <xref target="https.uri" format="counter"/> of this document
3677   (see <xref target="RFC4395"/>).
3681<section title="Internet Media Type Registrations" anchor="">
3683   This document serves as the specification for the Internet media types
3684   "message/http" and "application/http". The following is to be registered with
3685   IANA (see <xref target="RFC4288"/>).
3687<section title="Internet Media Type message/http" anchor="">
3688<iref item="Media Type" subitem="message/http" primary="true"/>
3689<iref item="message/http Media Type" primary="true"/>
3691   The message/http type can be used to enclose a single HTTP request or
3692   response message, provided that it obeys the MIME restrictions for all
3693   "message" types regarding line length and encodings.
3696  <list style="hanging" x:indent="12em">
3697    <t hangText="Type name:">
3698      message
3699    </t>
3700    <t hangText="Subtype name:">
3701      http
3702    </t>
3703    <t hangText="Required parameters:">
3704      none
3705    </t>
3706    <t hangText="Optional parameters:">
3707      version, msgtype
3708      <list style="hanging">
3709        <t hangText="version:">
3710          The HTTP-Version number of the enclosed message
3711          (e.g., "1.1"). If not present, the version can be
3712          determined from the first line of the body.
3713        </t>
3714        <t hangText="msgtype:">
3715          The message type &mdash; "request" or "response". If not
3716          present, the type can be determined from the first
3717          line of the body.
3718        </t>
3719      </list>
3720    </t>
3721    <t hangText="Encoding considerations:">
3722      only "7bit", "8bit", or "binary" are permitted
3723    </t>
3724    <t hangText="Security considerations:">
3725      none
3726    </t>
3727    <t hangText="Interoperability considerations:">
3728      none
3729    </t>
3730    <t hangText="Published specification:">
3731      This specification (see <xref target=""/>).
3732    </t>
3733    <t hangText="Applications that use this media type:">
3734    </t>
3735    <t hangText="Additional information:">
3736      <list style="hanging">
3737        <t hangText="Magic number(s):">none</t>
3738        <t hangText="File extension(s):">none</t>
3739        <t hangText="Macintosh file type code(s):">none</t>
3740      </list>
3741    </t>
3742    <t hangText="Person and email address to contact for further information:">
3743      See Authors Section.
3744    </t>
3745    <t hangText="Intended usage:">
3746      COMMON
3747    </t>
3748    <t hangText="Restrictions on usage:">
3749      none
3750    </t>
3751    <t hangText="Author/Change controller:">
3752      IESG
3753    </t>
3754  </list>
3757<section title="Internet Media Type application/http" anchor="">
3758<iref item="Media Type" subitem="application/http" primary="true"/>
3759<iref item="application/http Media Type" primary="true"/>
3761   The application/http type can be used to enclose a pipeline of one or more
3762   HTTP request or response messages (not intermixed).
3765  <list style="hanging" x:indent="12em">
3766    <t hangText="Type name:">
3767      application
3768    </t>
3769    <t hangText="Subtype name:">
3770      http
3771    </t>
3772    <t hangText="Required parameters:">
3773      none
3774    </t>
3775    <t hangText="Optional parameters:">
3776      version, msgtype
3777      <list style="hanging">
3778        <t hangText="version:">
3779          The HTTP-Version number of the enclosed messages
3780          (e.g., "1.1"). If not present, the version can be
3781          determined from the first line of the body.
3782        </t>
3783        <t hangText="msgtype:">
3784          The message type &mdash; "request" or "response". If not
3785          present, the type can be determined from the first
3786          line of the body.
3787        </t>
3788      </list>
3789    </t>
3790    <t hangText="Encoding considerations:">
3791      HTTP messages enclosed by this type
3792      are in "binary" format; use of an appropriate
3793      Content-Transfer-Encoding is required when
3794      transmitted via E-mail.
3795    </t>
3796    <t hangText="Security considerations:">
3797      none
3798    </t>
3799    <t hangText="Interoperability considerations:">
3800      none
3801    </t>
3802    <t hangText="Published specification:">
3803      This specification (see <xref target=""/>).
3804    </t>
3805    <t hangText="Applications that use this media type:">
3806    </t>
3807    <t hangText="Additional information:">
3808      <list style="hanging">
3809        <t hangText="Magic number(s):">none</t>
3810        <t hangText="File extension(s):">none</t>
3811        <t hangText="Macintosh file type code(s):">none</t>
3812      </list>
3813    </t>
3814    <t hangText="Person and email address to contact for further information:">
3815      See Authors Section.
3816    </t>
3817    <t hangText="Intended usage:">
3818      COMMON
3819    </t>
3820    <t hangText="Restrictions on usage:">
3821      none
3822    </t>
3823    <t hangText="Author/Change controller:">
3824      IESG
3825    </t>
3826  </list>
3831<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3833   The registration procedure for HTTP Transfer Codings is now defined by
3834   <xref target="transfer.coding.registry"/> of this document.
3837   The HTTP Transfer Codings Registry located at <eref target=""/>
3838   shall be updated with the registrations below:
3840<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3841   <ttcol>Name</ttcol>
3842   <ttcol>Description</ttcol>
3843   <ttcol>Reference</ttcol>
3844   <c>chunked</c>
3845   <c>Transfer in a series of chunks</c>
3846   <c>
3847      <xref target="chunked.encoding"/>
3848   </c>
3849   <c>compress</c>
3850   <c>UNIX "compress" program method</c>
3851   <c>
3852      <xref target="compress.coding"/>
3853   </c>
3854   <c>deflate</c>
3855   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3856   the "zlib" data format (<xref target="RFC1950"/>)
3857   </c>
3858   <c>
3859      <xref target="deflate.coding"/>
3860   </c>
3861   <c>gzip</c>
3862   <c>Same as GNU zip <xref target="RFC1952"/></c>
3863   <c>
3864      <xref target="gzip.coding"/>
3865   </c>
3869<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3871   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3872   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3873   by <xref target="upgrade.token.registry"/> of this document.
3876   The HTTP Status Code Registry located at <eref target=""/>
3877   shall be updated with the registration below:
3879<texttable align="left" suppress-title="true">
3880   <ttcol>Value</ttcol>
3881   <ttcol>Description</ttcol>
3882   <ttcol>Reference</ttcol>
3884   <c>HTTP</c>
3885   <c>Hypertext Transfer Protocol</c>
3886   <c><xref target="http.version"/> of this specification</c>
3887<!-- IANA should add this without our instructions; emailed on June 05, 2009
3888   <c>TLS/1.0</c>
3889   <c>Transport Layer Security</c>
3890   <c><xref target="RFC2817"/></c> -->
3897<section title="Security Considerations" anchor="security.considerations">
3899   This section is meant to inform application developers, information
3900   providers, and users of the security limitations in HTTP/1.1 as
3901   described by this document. The discussion does not include
3902   definitive solutions to the problems revealed, though it does make
3903   some suggestions for reducing security risks.
3906<section title="Personal Information" anchor="personal.information">
3908   HTTP clients are often privy to large amounts of personal information
3909   (e.g., the user's name, location, mail address, passwords, encryption
3910   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3911   leakage of this information.
3912   We very strongly recommend that a convenient interface be provided
3913   for the user to control dissemination of such information, and that
3914   designers and implementors be particularly careful in this area.
3915   History shows that errors in this area often create serious security
3916   and/or privacy problems and generate highly adverse publicity for the
3917   implementor's company.
3921<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3923   A server is in the position to save personal data about a user's
3924   requests which might identify their reading patterns or subjects of
3925   interest. This information is clearly confidential in nature and its
3926   handling can be constrained by law in certain countries. People using
3927   HTTP to provide data are responsible for ensuring that
3928   such material is not distributed without the permission of any
3929   individuals that are identifiable by the published results.
3933<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3935   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3936   the documents returned by HTTP requests to be only those that were
3937   intended by the server administrators. If an HTTP server translates
3938   HTTP URIs directly into file system calls, the server &MUST; take
3939   special care not to serve files that were not intended to be
3940   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3941   other operating systems use ".." as a path component to indicate a
3942   directory level above the current one. On such a system, an HTTP
3943   server &MUST; disallow any such construct in the request-target if it
3944   would otherwise allow access to a resource outside those intended to
3945   be accessible via the HTTP server. Similarly, files intended for
3946   reference only internally to the server (such as access control
3947   files, configuration files, and script code) &MUST; be protected from
3948   inappropriate retrieval, since they might contain sensitive
3949   information. Experience has shown that minor bugs in such HTTP server
3950   implementations have turned into security risks.
3954<section title="DNS Spoofing" anchor="dns.spoofing">
3956   Clients using HTTP rely heavily on the Domain Name Service, and are
3957   thus generally prone to security attacks based on the deliberate
3958   mis-association of IP addresses and DNS names. Clients need to be
3959   cautious in assuming the continuing validity of an IP number/DNS name
3960   association.
3963   In particular, HTTP clients &SHOULD; rely on their name resolver for
3964   confirmation of an IP number/DNS name association, rather than
3965   caching the result of previous host name lookups. Many platforms
3966   already can cache host name lookups locally when appropriate, and
3967   they &SHOULD; be configured to do so. It is proper for these lookups to
3968   be cached, however, only when the TTL (Time To Live) information
3969   reported by the name server makes it likely that the cached
3970   information will remain useful.
3973   If HTTP clients cache the results of host name lookups in order to
3974   achieve a performance improvement, they &MUST; observe the TTL
3975   information reported by DNS.
3978   If HTTP clients do not observe this rule, they could be spoofed when
3979   a previously-accessed server's IP address changes. As network
3980   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3981   possibility of this form of attack will grow. Observing this
3982   requirement thus reduces this potential security vulnerability.
3985   This requirement also improves the load-balancing behavior of clients
3986   for replicated servers using the same DNS name and reduces the
3987   likelihood of a user's experiencing failure in accessing sites which
3988   use that strategy.
3992<section title="Proxies and Caching" anchor="attack.proxies">
3994   By their very nature, HTTP proxies are men-in-the-middle, and
3995   represent an opportunity for man-in-the-middle attacks. Compromise of
3996   the systems on which the proxies run can result in serious security
3997   and privacy problems. Proxies have access to security-related
3998   information, personal information about individual users and
3999   organizations, and proprietary information belonging to users and
4000   content providers. A compromised proxy, or a proxy implemented or
4001   configured without regard to security and privacy considerations,
4002   might be used in the commission of a wide range of potential attacks.
4005   Proxy operators need to protect the systems on which proxies run as
4006   they would protect any system that contains or transports sensitive
4007   information. In particular, log information gathered at proxies often
4008   contains highly sensitive personal information, and/or information
4009   about organizations. Log information needs to be carefully guarded, and
4010   appropriate guidelines for use need to be developed and followed.
4011   (<xref target="abuse.of.server.log.information"/>).
4014   Proxy implementors need to consider the privacy and security
4015   implications of their design and coding decisions, and of the
4016   configuration options they provide to proxy operators (especially the
4017   default configuration).
4020   Users of a proxy need to be aware that proxies are no trustworthier than
4021   the people who run them; HTTP itself cannot solve this problem.
4024   The judicious use of cryptography, when appropriate, might suffice to
4025   protect against a broad range of security and privacy attacks. Such
4026   cryptography is beyond the scope of the HTTP/1.1 specification.
4030<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4032   They exist. They are hard to defend against. Research continues.
4033   Beware.
4038<section title="Acknowledgments" anchor="ack">
4040   HTTP has evolved considerably over the years. It has
4041   benefited from a large and active developer community &mdash; the many
4042   people who have participated on the www-talk mailing list &mdash; and it is
4043   that community which has been most responsible for the success of
4044   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4045   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4046   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4047   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4048   VanHeyningen deserve special recognition for their efforts in
4049   defining early aspects of the protocol.
4052   This document has benefited greatly from the comments of all those
4053   participating in the HTTP-WG. In addition to those already mentioned,
4054   the following individuals have contributed to this specification:
4057   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4058   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4059   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4060   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4061   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4062   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4063   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4064   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4065   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4066   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4067   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4068   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4071   Thanks to the "cave men" of Palo Alto. You know who you are.
4074   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4075   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4076   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4077   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4078   Larry Masinter for their help. And thanks go particularly to Jeff
4079   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4082   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4083   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4084   discovery of many of the problems that this document attempts to
4085   rectify.
4088   This specification makes heavy use of the augmented BNF and generic
4089   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4090   reuses many of the definitions provided by Nathaniel Borenstein and
4091   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4092   specification will help reduce past confusion over the relationship
4093   between HTTP and Internet mail message formats.
4097Acknowledgements TODO list
4099- Jeff Hodges ("effective request URI")
4107<references title="Normative References">
4109<reference anchor="ISO-8859-1">
4110  <front>
4111    <title>
4112     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4113    </title>
4114    <author>
4115      <organization>International Organization for Standardization</organization>
4116    </author>
4117    <date year="1998"/>
4118  </front>
4119  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4122<reference anchor="Part2">
4123  <front>
4124    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4125    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4126      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4127      <address><email></email></address>
4128    </author>
4129    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4130      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4131      <address><email></email></address>
4132    </author>
4133    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4134      <organization abbrev="HP">Hewlett-Packard Company</organization>
4135      <address><email></email></address>
4136    </author>
4137    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4138      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4139      <address><email></email></address>
4140    </author>
4141    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4142      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4143      <address><email></email></address>
4144    </author>
4145    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4146      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4147      <address><email></email></address>
4148    </author>
4149    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4150      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4151      <address><email></email></address>
4152    </author>
4153    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4154      <organization abbrev="W3C">World Wide Web Consortium</organization>
4155      <address><email></email></address>
4156    </author>
4157    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4158      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4159      <address><email></email></address>
4160    </author>
4161    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4162  </front>
4163  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4164  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4167<reference anchor="Part3">
4168  <front>
4169    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4170    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4171      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4172      <address><email></email></address>
4173    </author>
4174    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4175      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4176      <address><email></email></address>
4177    </author>
4178    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4179      <organization abbrev="HP">Hewlett-Packard Company</organization>
4180      <address><email></email></address>
4181    </author>
4182    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4183      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4184      <address><email></email></address>
4185    </author>
4186    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4187      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4188      <address><email></email></address>
4189    </author>
4190    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4191      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4192      <address><email></email></address>
4193    </author>
4194    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4195      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4196      <address><email></email></address>
4197    </author>
4198    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4199      <organization abbrev="W3C">World Wide Web Consortium</organization>
4200      <address><email></email></address>
4201    </author>
4202    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4203      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4204      <address><email></email></address>
4205    </author>
4206    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4207  </front>
4208  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4209  <x:source href="p3-payload.xml" basename="p3-payload"/>
4212<reference anchor="Part6">
4213  <front>
4214    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4215    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4216      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4217      <address><email></email></address>
4218    </author>
4219    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4220      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4221      <address><email></email></address>
4222    </author>
4223    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4224      <organization abbrev="HP">Hewlett-Packard Company</organization>
4225      <address><email></email></address>
4226    </author>
4227    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4228      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4229      <address><email></email></address>
4230    </author>
4231    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4232      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4233      <address><email></email></address>
4234    </author>
4235    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4236      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4237      <address><email></email></address>
4238    </author>
4239    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4240      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4241      <address><email></email></address>
4242    </author>
4243    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4244      <organization abbrev="W3C">World Wide Web Consortium</organization>
4245      <address><email></email></address>
4246    </author>
4247    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4248      <address><email></email></address>
4249    </author>
4250    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4251      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4252      <address><email></email></address>
4253    </author>
4254    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4255  </front>
4256  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4257  <x:source href="p6-cache.xml" basename="p6-cache"/>
4260<reference anchor="RFC5234">
4261  <front>
4262    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4263    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4264      <organization>Brandenburg InternetWorking</organization>
4265      <address>
4266        <email></email>
4267      </address> 
4268    </author>
4269    <author initials="P." surname="Overell" fullname="Paul Overell">
4270      <organization>THUS plc.</organization>
4271      <address>
4272        <email></email>
4273      </address>
4274    </author>
4275    <date month="January" year="2008"/>
4276  </front>
4277  <seriesInfo name="STD" value="68"/>
4278  <seriesInfo name="RFC" value="5234"/>
4281<reference anchor="RFC2119">
4282  <front>
4283    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4284    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4285      <organization>Harvard University</organization>
4286      <address><email></email></address>
4287    </author>
4288    <date month="March" year="1997"/>
4289  </front>
4290  <seriesInfo name="BCP" value="14"/>
4291  <seriesInfo name="RFC" value="2119"/>
4294<reference anchor="RFC3986">
4295 <front>
4296  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4297  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4298    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4299    <address>
4300       <email></email>
4301       <uri></uri>
4302    </address>
4303  </author>
4304  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4305    <organization abbrev="Day Software">Day Software</organization>
4306    <address>
4307      <email></email>
4308      <uri></uri>
4309    </address>
4310  </author>
4311  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4312    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4313    <address>
4314      <email></email>
4315      <uri></uri>
4316    </address>
4317  </author>
4318  <date month='January' year='2005'></date>
4319 </front>
4320 <seriesInfo name="STD" value="66"/>
4321 <seriesInfo name="RFC" value="3986"/>
4324<reference anchor="USASCII">
4325  <front>
4326    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4327    <author>
4328      <organization>American National Standards Institute</organization>
4329    </author>
4330    <date year="1986"/>
4331  </front>
4332  <seriesInfo name="ANSI" value="X3.4"/>
4335<reference anchor="RFC1950">
4336  <front>
4337    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4338    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4339      <organization>Aladdin Enterprises</organization>
4340      <address><email></email></address>
4341    </author>
4342    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4343    <date month="May" year="1996"/>
4344  </front>
4345  <seriesInfo name="RFC" value="1950"/>
4346  <annotation>
4347    RFC 1950 is an Informational RFC, thus it might be less stable than
4348    this specification. On the other hand, this downward reference was
4349    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4350    therefore it is unlikely to cause problems in practice. See also
4351    <xref target="BCP97"/>.
4352  </annotation>
4355<reference anchor="RFC1951">
4356  <front>
4357    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4358    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4359      <organization>Aladdin Enterprises</organization>
4360      <address><email></email></address>
4361    </author>
4362    <date month="May" year="1996"/>
4363  </front>
4364  <seriesInfo name="RFC" value="1951"/>
4365  <annotation>
4366    RFC 1951 is an Informational RFC, thus it might be less stable than
4367    this specification. On the other hand, this downward reference was
4368    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4369    therefore it is unlikely to cause problems in practice. See also
4370    <xref target="BCP97"/>.
4371  </annotation>
4374<reference anchor="RFC1952">
4375  <front>
4376    <title>GZIP file format specification version 4.3</title>
4377    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4378      <organization>Aladdin Enterprises</organization>
4379      <address><email></email></address>
4380    </author>
4381    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4382      <address><email></email></address>
4383    </author>
4384    <author initials="M." surname="Adler" fullname="Mark Adler">
4385      <address><email></email></address>
4386    </author>
4387    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4388      <address><email></email></address>
4389    </author>
4390    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4391      <address><email></email></address>
4392    </author>
4393    <date month="May" year="1996"/>
4394  </front>
4395  <seriesInfo name="RFC" value="1952"/>
4396  <annotation>
4397    RFC 1952 is an Informational RFC, thus it might be less stable than
4398    this specification. On the other hand, this downward reference was
4399    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4400    therefore it is unlikely to cause problems in practice. See also
4401    <xref target="BCP97"/>.
4402  </annotation>
4407<references title="Informative References">
4409<reference anchor="Nie1997" target="">
4410  <front>
4411    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4412    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4413    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4414    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4415    <author initials="H." surname="Lie" fullname="H. Lie"/>
4416    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4417    <date year="1997" month="September"/>
4418  </front>
4419  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4422<reference anchor="Pad1995" target="">
4423  <front>
4424    <title>Improving HTTP Latency</title>
4425    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4426    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4427    <date year="1995" month="December"/>
4428  </front>
4429  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4432<reference anchor="RFC1123">
4433  <front>
4434    <title>Requirements for Internet Hosts - Application and Support</title>
4435    <author initials="R." surname="Braden" fullname="Robert Braden">
4436      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4437      <address><email>Braden@ISI.EDU</email></address>
4438    </author>
4439    <date month="October" year="1989"/>
4440  </front>
4441  <seriesInfo name="STD" value="3"/>
4442  <seriesInfo name="RFC" value="1123"/>
4445<reference anchor="RFC1900">
4446  <front>
4447    <title>Renumbering Needs Work</title>
4448    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4449      <organization>CERN, Computing and Networks Division</organization>
4450      <address><email></email></address>
4451    </author>
4452    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4453      <organization>cisco Systems</organization>
4454      <address><email></email></address>
4455    </author>
4456    <date month="February" year="1996"/>
4457  </front>
4458  <seriesInfo name="RFC" value="1900"/>
4461<reference anchor='RFC1919'>
4462  <front>
4463    <title>Classical versus Transparent IP Proxies</title>
4464    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4465      <address><email></email></address>
4466    </author>
4467    <date year='1996' month='March' />
4468  </front>
4469  <seriesInfo name='RFC' value='1919' />
4472<reference anchor="RFC1945">
4473  <front>
4474    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4475    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4476      <organization>MIT, Laboratory for Computer Science</organization>
4477      <address><email></email></address>
4478    </author>
4479    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4480      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4481      <address><email></email></address>
4482    </author>
4483    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4484      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4485      <address><email></email></address>
4486    </author>
4487    <date month="May" year="1996"/>
4488  </front>
4489  <seriesInfo name="RFC" value="1945"/>
4492<reference anchor="RFC2045">
4493  <front>
4494    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4495    <author initials="N." surname="Freed" fullname="Ned Freed">
4496      <organization>Innosoft International, Inc.</organization>
4497      <address><email></email></address>
4498    </author>
4499    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4500      <organization>First Virtual Holdings</organization>
4501      <address><email></email></address>
4502    </author>
4503    <date month="November" year="1996"/>
4504  </front>
4505  <seriesInfo name="RFC" value="2045"/>
4508<reference anchor="RFC2047">
4509  <front>
4510    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4511    <author initials="K." surname="Moore" fullname="Keith Moore">
4512      <organization>University of Tennessee</organization>
4513      <address><email></email></address>
4514    </author>
4515    <date month="November" year="1996"/>
4516  </front>
4517  <seriesInfo name="RFC" value="2047"/>
4520<reference anchor="RFC2068">
4521  <front>
4522    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4523    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4524      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4525      <address><email></email></address>
4526    </author>
4527    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4528      <organization>MIT Laboratory for Computer Science</organization>
4529      <address><email></email></address>
4530    </author>
4531    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4532      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4533      <address><email></email></address>
4534    </author>
4535    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4536      <organization>MIT Laboratory for Computer Science</organization>
4537      <address><email></email></address>
4538    </author>
4539    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4540      <organization>MIT Laboratory for Computer Science</organization>
4541      <address><email></email></address>
4542    </author>
4543    <date month="January" year="1997"/>
4544  </front>
4545  <seriesInfo name="RFC" value="2068"/>
4548<reference anchor="RFC2145">
4549  <front>
4550    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4551    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4552      <organization>Western Research Laboratory</organization>
4553      <address><email></email></address>
4554    </author>
4555    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4556      <organization>Department of Information and Computer Science</organization>
4557      <address><email></email></address>
4558    </author>
4559    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4560      <organization>MIT Laboratory for Computer Science</organization>
4561      <address><email></email></address>
4562    </author>
4563    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4564      <organization>W3 Consortium</organization>
4565      <address><email></email></address>
4566    </author>
4567    <date month="May" year="1997"/>
4568  </front>
4569  <seriesInfo name="RFC" value="2145"/>
4572<reference anchor="RFC2616">
4573  <front>
4574    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4575    <author initials="R." surname="Fielding" fullname="R. Fielding">
4576      <organization>University of California, Irvine</organization>
4577      <address><email></email></address>
4578    </author>
4579    <author initials="J." surname="Gettys" fullname="J. Gettys">
4580      <organization>W3C</organization>
4581      <address><email></email></address>
4582    </author>
4583    <author initials="J." surname="Mogul" fullname="J. Mogul">
4584      <organization>Compaq Computer Corporation</organization>
4585      <address><email></email></address>
4586    </author>
4587    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4588      <organization>MIT Laboratory for Computer Science</organization>
4589      <address><email></email></address>
4590    </author>
4591    <author initials="L." surname="Masinter" fullname="L. Masinter">
4592      <organization>Xerox Corporation</organization>
4593      <address><email></email></address>
4594    </author>
4595    <author initials="P." surname="Leach" fullname="P. Leach">
4596      <organization>Microsoft Corporation</organization>
4597      <address><email></email></address>
4598    </author>
4599    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4600      <organization>W3C</organization>
4601      <address><email></email></address>
4602    </author>
4603    <date month="June" year="1999"/>
4604  </front>
4605  <seriesInfo name="RFC" value="2616"/>
4608<reference anchor='RFC2817'>
4609  <front>
4610    <title>Upgrading to TLS Within HTTP/1.1</title>
4611    <author initials='R.' surname='Khare' fullname='R. Khare'>
4612      <organization>4K Associates / UC Irvine</organization>
4613      <address><email></email></address>
4614    </author>
4615    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4616      <organization>Agranat Systems, Inc.</organization>
4617      <address><email></email></address>
4618    </author>
4619    <date year='2000' month='May' />
4620  </front>
4621  <seriesInfo name='RFC' value='2817' />
4624<reference anchor='RFC2818'>
4625  <front>
4626    <title>HTTP Over TLS</title>
4627    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4628      <organization>RTFM, Inc.</organization>
4629      <address><email></email></address>
4630    </author>
4631    <date year='2000' month='May' />
4632  </front>
4633  <seriesInfo name='RFC' value='2818' />
4636<reference anchor='RFC2965'>
4637  <front>
4638    <title>HTTP State Management Mechanism</title>
4639    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4640      <organization>Bell Laboratories, Lucent Technologies</organization>
4641      <address><email></email></address>
4642    </author>
4643    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4644      <organization>, Inc.</organization>
4645      <address><email></email></address>
4646    </author>
4647    <date year='2000' month='October' />
4648  </front>
4649  <seriesInfo name='RFC' value='2965' />
4652<reference anchor='RFC3040'>
4653  <front>
4654    <title>Internet Web Replication and Caching Taxonomy</title>
4655    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4656      <organization>Equinix, Inc.</organization>
4657    </author>
4658    <author initials='I.' surname='Melve' fullname='I. Melve'>
4659      <organization>UNINETT</organization>
4660    </author>
4661    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4662      <organization>CacheFlow Inc.</organization>
4663    </author>
4664    <date year='2001' month='January' />
4665  </front>
4666  <seriesInfo name='RFC' value='3040' />
4669<reference anchor='RFC3864'>
4670  <front>
4671    <title>Registration Procedures for Message Header Fields</title>
4672    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4673      <organization>Nine by Nine</organization>
4674      <address><email></email></address>
4675    </author>
4676    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4677      <organization>BEA Systems</organization>
4678      <address><email></email></address>
4679    </author>
4680    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4681      <organization>HP Labs</organization>
4682      <address><email></email></address>
4683    </author>
4684    <date year='2004' month='September' />
4685  </front>
4686  <seriesInfo name='BCP' value='90' />
4687  <seriesInfo name='RFC' value='3864' />
4690<reference anchor="RFC4288">
4691  <front>
4692    <title>Media Type Specifications and Registration Procedures</title>
4693    <author initials="N." surname="Freed" fullname="N. Freed">
4694      <organization>Sun Microsystems</organization>
4695      <address>
4696        <email></email>
4697      </address>
4698    </author>
4699    <author initials="J." surname="Klensin" fullname="J. Klensin">
4700      <address>
4701        <email></email>
4702      </address>
4703    </author>
4704    <date year="2005" month="December"/>
4705  </front>
4706  <seriesInfo name="BCP" value="13"/>
4707  <seriesInfo name="RFC" value="4288"/>
4710<reference anchor='RFC4395'>
4711  <front>
4712    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4713    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4714      <organization>AT&amp;T Laboratories</organization>
4715      <address>
4716        <email></email>
4717      </address>
4718    </author>
4719    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4720      <organization>Qualcomm, Inc.</organization>
4721      <address>
4722        <email></email>
4723      </address>
4724    </author>
4725    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4726      <organization>Adobe Systems</organization>
4727      <address>
4728        <email></email>
4729      </address>
4730    </author>
4731    <date year='2006' month='February' />
4732  </front>
4733  <seriesInfo name='BCP' value='115' />
4734  <seriesInfo name='RFC' value='4395' />
4737<reference anchor='RFC5226'>
4738  <front>
4739    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4740    <author initials='T.' surname='Narten' fullname='T. Narten'>
4741      <organization>IBM</organization>
4742      <address><email></email></address>
4743    </author>
4744    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4745      <organization>Google</organization>
4746      <address><email></email></address>
4747    </author>
4748    <date year='2008' month='May' />
4749  </front>
4750  <seriesInfo name='BCP' value='26' />
4751  <seriesInfo name='RFC' value='5226' />
4754<reference anchor="RFC5322">
4755  <front>
4756    <title>Internet Message Format</title>
4757    <author initials="P." surname="Resnick" fullname="P. Resnick">
4758      <organization>Qualcomm Incorporated</organization>
4759    </author>
4760    <date year="2008" month="October"/>
4761  </front>
4762  <seriesInfo name="RFC" value="5322"/>
4765<reference anchor='draft-ietf-httpstate-cookie'>
4766  <front>
4767    <title>HTTP State Management Mechanism</title>
4768    <author initials="A." surname="Barth" fullname="Adam Barth">
4769      <organization abbrev="U.C. Berkeley">
4770        University of California, Berkeley
4771      </organization>
4772      <address><email></email></address>
4773    </author>
4774    <date year='2011' month='March' />
4775  </front>
4776  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4779<reference anchor='BCP97'>
4780  <front>
4781    <title>Handling Normative References to Standards-Track Documents</title>
4782    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4783      <address>
4784        <email></email>
4785      </address>
4786    </author>
4787    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4788      <organization>MIT</organization>
4789      <address>
4790        <email></email>
4791      </address>
4792    </author>
4793    <date year='2007' month='June' />
4794  </front>
4795  <seriesInfo name='BCP' value='97' />
4796  <seriesInfo name='RFC' value='4897' />
4799<reference anchor="Kri2001" target="">
4800  <front>
4801    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4802    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4803    <date year="2001" month="November"/>
4804  </front>
4805  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4808<reference anchor="Spe" target="">
4809  <front>
4810    <title>Analysis of HTTP Performance Problems</title>
4811    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4812    <date/>
4813  </front>
4816<reference anchor="Tou1998" target="">
4817  <front>
4818  <title>Analysis of HTTP Performance</title>
4819  <author initials="J." surname="Touch" fullname="Joe Touch">
4820    <organization>USC/Information Sciences Institute</organization>
4821    <address><email></email></address>
4822  </author>
4823  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4824    <organization>USC/Information Sciences Institute</organization>
4825    <address><email></email></address>
4826  </author>
4827  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4828    <organization>USC/Information Sciences Institute</organization>
4829    <address><email></email></address>
4830  </author>
4831  <date year="1998" month="Aug"/>
4832  </front>
4833  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4834  <annotation>(original report dated Aug. 1996)</annotation>
4840<section title="Tolerant Applications" anchor="tolerant.applications">
4842   Although this document specifies the requirements for the generation
4843   of HTTP/1.1 messages, not all applications will be correct in their
4844   implementation. We therefore recommend that operational applications
4845   be tolerant of deviations whenever those deviations can be
4846   interpreted unambiguously.
4849   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4850   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4851   &SHOULD; accept any amount of WSP characters between fields, even though
4852   only a single SP is required.
4855   The line terminator for header fields is the sequence CRLF.
4856   However, we recommend that applications, when parsing such headers fields,
4857   recognize a single LF as a line terminator and ignore the leading CR.
4860   The character set of a representation &SHOULD; be labeled as the lowest
4861   common denominator of the character codes used within that representation, with
4862   the exception that not labeling the representation is preferred over labeling
4863   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4866   Additional rules for requirements on parsing and encoding of dates
4867   and other potential problems with date encodings include:
4870  <list style="symbols">
4871     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4872        which appears to be more than 50 years in the future is in fact
4873        in the past (this helps solve the "year 2000" problem).</t>
4875     <t>Although all date formats are specified to be case-sensitive,
4876        recipients &SHOULD; match day, week and timezone names
4877        case-insensitively.</t>
4879     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4880        Expires date as earlier than the proper value, but &MUST-NOT;
4881        internally represent a parsed Expires date as later than the
4882        proper value.</t>
4884     <t>All expiration-related calculations &MUST; be done in GMT. The
4885        local time zone &MUST-NOT; influence the calculation or comparison
4886        of an age or expiration time.</t>
4888     <t>If an HTTP header field incorrectly carries a date value with a time
4889        zone other than GMT, it &MUST; be converted into GMT using the
4890        most conservative possible conversion.</t>
4891  </list>
4895<section title="Compatibility with Previous Versions" anchor="compatibility">
4897   HTTP has been in use by the World-Wide Web global information initiative
4898   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4899   was a simple protocol for hypertext data transfer across the Internet
4900   with only a single request method (GET) and no metadata.
4901   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4902   methods and MIME-like messaging that could include metadata about the data
4903   transferred and modifiers on the request/response semantics. However,
4904   HTTP/1.0 did not sufficiently take into consideration the effects of
4905   hierarchical proxies, caching, the need for persistent connections, or
4906   name-based virtual hosts. The proliferation of incompletely-implemented
4907   applications calling themselves "HTTP/1.0" further necessitated a
4908   protocol version change in order for two communicating applications
4909   to determine each other's true capabilities.
4912   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4913   requirements that enable reliable implementations, adding only
4914   those new features that will either be safely ignored by an HTTP/1.0
4915   recipient or only sent when communicating with a party advertising
4916   compliance with HTTP/1.1.
4919   It is beyond the scope of a protocol specification to mandate
4920   compliance with previous versions. HTTP/1.1 was deliberately
4921   designed, however, to make supporting previous versions easy. It is
4922   worth noting that, at the time of composing this specification, we would
4923   expect general-purpose HTTP/1.1 servers to:
4924  <list style="symbols">
4925     <t>understand any valid request in the format of HTTP/1.0 and
4926        1.1;</t>
4928     <t>respond appropriately with a message in the same major version
4929        used by the client.</t>
4930  </list>
4933   And we would expect HTTP/1.1 clients to:
4934  <list style="symbols">
4935     <t>understand any valid response in the format of HTTP/1.0 or
4936        1.1.</t>
4937  </list>
4940   For most implementations of HTTP/1.0, each connection is established
4941   by the client prior to the request and closed by the server after
4942   sending the response. Some implementations implement the Keep-Alive
4943   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4946<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4948   This section summarizes major differences between versions HTTP/1.0
4949   and HTTP/1.1.
4952<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
4954   The requirements that clients and servers support the Host header
4955   field (<xref target=""/>), report an error if it is
4956   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4957   are among the most important changes defined by this
4958   specification.
4961   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4962   addresses and servers; there was no other established mechanism for
4963   distinguishing the intended server of a request than the IP address
4964   to which that request was directed. The changes outlined above will
4965   allow the Internet, once older HTTP clients are no longer common, to
4966   support multiple Web sites from a single IP address, greatly
4967   simplifying large operational Web servers, where allocation of many
4968   IP addresses to a single host has created serious problems. The
4969   Internet will also be able to recover the IP addresses that have been
4970   allocated for the sole purpose of allowing special-purpose domain
4971   names to be used. Given the rate of growth of
4972   the Web, and the number of servers already deployed, it is extremely
4973   important that all implementations of HTTP (including updates to
4974   existing HTTP/1.0 applications) correctly implement these
4975   requirements:
4976  <list style="symbols">
4977     <t>Both clients and servers &MUST; support the Host header field.</t>
4979     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4981     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4982        request does not include a Host header field.</t>
4984     <t>Servers &MUST; accept absolute URIs.</t>
4985  </list>
4990<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4992   Some clients and servers might wish to be compatible with some
4993   previous implementations of persistent connections in HTTP/1.0
4994   clients and servers. Persistent connections in HTTP/1.0 are
4995   explicitly negotiated as they are not the default behavior. HTTP/1.0
4996   experimental implementations of persistent connections are faulty,
4997   and the new facilities in HTTP/1.1 are designed to rectify these
4998   problems. The problem was that some existing HTTP/1.0 clients might
4999   send Keep-Alive to a proxy server that doesn't understand
5000   Connection, which would then erroneously forward it to the next
5001   inbound server, which would establish the Keep-Alive connection and
5002   result in a hung HTTP/1.0 proxy waiting for the close on the
5003   response. The result is that HTTP/1.0 clients must be prevented from
5004   using Keep-Alive when talking to proxies.
5007   However, talking to proxies is the most important use of persistent
5008   connections, so that prohibition is clearly unacceptable. Therefore,
5009   we need some other mechanism for indicating a persistent connection
5010   is desired, which is safe to use even when talking to an old proxy
5011   that ignores Connection. Persistent connections are the default for
5012   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
5013   declaring non-persistence. See <xref target="header.connection"/>.
5016   The original HTTP/1.0 form of persistent connections (the Connection:
5017   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
5021<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5023  Empty list elements in list productions have been deprecated.
5024  (<xref target="notation.abnf"/>)
5027  Rules about implicit linear whitespace between certain grammar productions
5028  have been removed; now it's only allowed when specifically pointed out
5029  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
5030  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5031  Non-ASCII content in header fields and reason phrase has been obsoleted and
5032  made opaque (the TEXT rule was removed)
5033  (<xref target="basic.rules"/>)
5036  Clarify that HTTP-Version is case sensitive.
5037  (<xref target="http.version"/>)
5040  Require that invalid whitespace around field-names be rejected.
5041  (<xref target="header.fields"/>)
5044  Require recipients to handle bogus Content-Length header fields as errors.
5045  (<xref target="message.body"/>)
5048  Remove reference to non-existent identity transfer-coding value tokens.
5049  (Sections <xref format="counter" target="message.body"/> and
5050  <xref format="counter" target="transfer.codings"/>)
5053  Update use of abs_path production from RFC 1808 to the path-absolute + query
5054  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5055  request method only.
5056  (<xref target="request-target"/>)
5059  Clarification that the chunk length does not include the count of the octets
5060  in the chunk header and trailer. Furthermore disallowed line folding
5061  in chunk extensions.
5062  (<xref target="chunked.encoding"/>)
5065  Remove hard limit of two connections per server.
5066  (<xref target="persistent.practical"/>)
5069  Clarify exactly when close connection options must be sent.
5070  (<xref target="header.connection"/>)
5073  Define the semantics of the "Upgrade" header field in responses other than
5074  101 (this was incorporated from <xref target="RFC2817"/>).
5075  (<xref target="header.upgrade"/>)
5080<?BEGININC p1-messaging.abnf-appendix ?>
5081<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5083<artwork type="abnf" name="p1-messaging.parsed-abnf">
5084<x:ref>BWS</x:ref> = OWS
5086<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5087<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
5088<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5089 connection-token ] )
5090<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
5091<x:ref>Content-Length-v</x:ref> = 1*DIGIT
5093<x:ref>Date</x:ref> = "Date:" OWS Date-v
5094<x:ref>Date-v</x:ref> = HTTP-date
5096<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5098<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5099<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5100<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5101<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5102 ]
5103<x:ref>Host</x:ref> = "Host:" OWS Host-v
5104<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
5106<x:ref>Method</x:ref> = token
5108<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5110<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5111<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5112<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5113<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5114<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5116<x:ref>Status-Code</x:ref> = 3DIGIT
5117<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5119<x:ref>TE</x:ref> = "TE:" OWS TE-v
5120<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5121<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5122<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5123<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5124<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5125 transfer-coding ] )
5127<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5128<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5129<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5131<x:ref>Via</x:ref> = "Via:" OWS Via-v
5132<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5133 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5134 ] )
5136<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5137<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5138<x:ref>attribute</x:ref> = token
5139<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5141<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5142<x:ref>chunk-data</x:ref> = 1*OCTET
5143<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5144<x:ref>chunk-ext-name</x:ref> = token
5145<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5146<x:ref>chunk-size</x:ref> = 1*HEXDIG
5147<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5148<x:ref>connection-token</x:ref> = token
5149<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5150 / %x2A-5B ; '*'-'['
5151 / %x5D-7E ; ']'-'~'
5152 / obs-text
5154<x:ref>date1</x:ref> = day SP month SP year
5155<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5156<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5157<x:ref>day</x:ref> = 2DIGIT
5158<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5159 / %x54.75.65 ; Tue
5160 / %x57.65.64 ; Wed
5161 / %x54.68.75 ; Thu
5162 / %x46.72.69 ; Fri
5163 / %x53.61.74 ; Sat
5164 / %x53.75.6E ; Sun
5165<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5166 / %x54. ; Tuesday
5167 / %x57.65.64.6E. ; Wednesday
5168 / %x54. ; Thursday
5169 / %x46. ; Friday
5170 / %x53. ; Saturday
5171 / %x53.75.6E.64.61.79 ; Sunday
5173<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5174<x:ref>field-name</x:ref> = token
5175<x:ref>field-value</x:ref> = *( field-content / OWS )
5177<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5178<x:ref>hour</x:ref> = 2DIGIT
5179<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5180<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5182<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5184<x:ref>message-body</x:ref> = *OCTET
5185<x:ref>minute</x:ref> = 2DIGIT
5186<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5187 / %x46.65.62 ; Feb
5188 / %x4D.61.72 ; Mar
5189 / %x41.70.72 ; Apr
5190 / %x4D.61.79 ; May
5191 / %x4A.75.6E ; Jun
5192 / %x4A.75.6C ; Jul
5193 / %x41.75.67 ; Aug
5194 / %x53.65.70 ; Sep
5195 / %x4F.63.74 ; Oct
5196 / %x4E.6F.76 ; Nov
5197 / %x44.65.63 ; Dec
5199<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5200<x:ref>obs-fold</x:ref> = CRLF
5201<x:ref>obs-text</x:ref> = %x80-FF
5203<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5204<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5205<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5206<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5207<x:ref>product</x:ref> = token [ "/" product-version ]
5208<x:ref>product-version</x:ref> = token
5209<x:ref>protocol-name</x:ref> = token
5210<x:ref>protocol-version</x:ref> = token
5211<x:ref>pseudonym</x:ref> = token
5213<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5214 / %x5D-7E ; ']'-'~'
5215 / obs-text
5216<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5217 / %x5D-7E ; ']'-'~'
5218 / obs-text
5219<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5220<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5221<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5222<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5223<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5224<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5226<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5227<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5228<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5229<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5230 / authority
5231<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5232<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5234<x:ref>second</x:ref> = 2DIGIT
5235<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5236 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5237<x:ref>start-line</x:ref> = Request-Line / Status-Line
5239<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5240<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5241 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5242<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5243<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5244<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5245<x:ref>token</x:ref> = 1*tchar
5246<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5247<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5248 transfer-extension
5249<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5250<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5252<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5254<x:ref>value</x:ref> = word
5256<x:ref>word</x:ref> = token / quoted-string
5258<x:ref>year</x:ref> = 4DIGIT
5261<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5262; Chunked-Body defined but not used
5263; Connection defined but not used
5264; Content-Length defined but not used
5265; Date defined but not used
5266; HTTP-message defined but not used
5267; Host defined but not used
5268; Request defined but not used
5269; Response defined but not used
5270; TE defined but not used
5271; Trailer defined but not used
5272; Transfer-Encoding defined but not used
5273; URI-reference defined but not used
5274; Upgrade defined but not used
5275; Via defined but not used
5276; http-URI defined but not used
5277; https-URI defined but not used
5278; partial-URI defined but not used
5279; special defined but not used
5281<?ENDINC p1-messaging.abnf-appendix ?>
5283<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5285<section title="Since RFC 2616">
5287  Extracted relevant partitions from <xref target="RFC2616"/>.
5291<section title="Since draft-ietf-httpbis-p1-messaging-00">
5293  Closed issues:
5294  <list style="symbols">
5295    <t>
5296      <eref target=""/>:
5297      "HTTP Version should be case sensitive"
5298      (<eref target=""/>)
5299    </t>
5300    <t>
5301      <eref target=""/>:
5302      "'unsafe' characters"
5303      (<eref target=""/>)
5304    </t>
5305    <t>
5306      <eref target=""/>:
5307      "Chunk Size Definition"
5308      (<eref target=""/>)
5309    </t>
5310    <t>
5311      <eref target=""/>:
5312      "Message Length"
5313      (<eref target=""/>)
5314    </t>
5315    <t>
5316      <eref target=""/>:
5317      "Media Type Registrations"
5318      (<eref target=""/>)
5319    </t>
5320    <t>
5321      <eref target=""/>:
5322      "URI includes query"
5323      (<eref target=""/>)
5324    </t>
5325    <t>
5326      <eref target=""/>:
5327      "No close on 1xx responses"
5328      (<eref target=""/>)
5329    </t>
5330    <t>
5331      <eref target=""/>:
5332      "Remove 'identity' token references"
5333      (<eref target=""/>)
5334    </t>
5335    <t>
5336      <eref target=""/>:
5337      "Import query BNF"
5338    </t>
5339    <t>
5340      <eref target=""/>:
5341      "qdtext BNF"
5342    </t>
5343    <t>
5344      <eref target=""/>:
5345      "Normative and Informative references"
5346    </t>
5347    <t>
5348      <eref target=""/>:
5349      "RFC2606 Compliance"
5350    </t>
5351    <t>
5352      <eref target=""/>:
5353      "RFC977 reference"
5354    </t>
5355    <t>
5356      <eref target=""/>:
5357      "RFC1700 references"
5358    </t>
5359    <t>
5360      <eref target=""/>:
5361      "inconsistency in date format explanation"
5362    </t>
5363    <t>
5364      <eref target=""/>:
5365      "Date reference typo"
5366    </t>
5367    <t>
5368      <eref target=""/>:
5369      "Informative references"
5370    </t>
5371    <t>
5372      <eref target=""/>:
5373      "ISO-8859-1 Reference"
5374    </t>
5375    <t>
5376      <eref target=""/>:
5377      "Normative up-to-date references"
5378    </t>
5379  </list>
5382  Other changes:
5383  <list style="symbols">
5384    <t>
5385      Update media type registrations to use RFC4288 template.
5386    </t>
5387    <t>
5388      Use names of RFC4234 core rules DQUOTE and WSP,
5389      fix broken ABNF for chunk-data
5390      (work in progress on <eref target=""/>)
5391    </t>
5392  </list>
5396<section title="Since draft-ietf-httpbis-p1-messaging-01">
5398  Closed issues:
5399  <list style="symbols">
5400    <t>
5401      <eref target=""/>:
5402      "Bodies on GET (and other) requests"
5403    </t>
5404    <t>
5405      <eref target=""/>:
5406      "Updating to RFC4288"
5407    </t>
5408    <t>
5409      <eref target=""/>:
5410      "Status Code and Reason Phrase"
5411    </t>
5412    <t>
5413      <eref target=""/>:
5414      "rel_path not used"
5415    </t>
5416  </list>
5419  Ongoing work on ABNF conversion (<eref target=""/>):
5420  <list style="symbols">
5421    <t>
5422      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5423      "trailer-part").
5424    </t>
5425    <t>
5426      Avoid underscore character in rule names ("http_URL" ->
5427      "http-URL", "abs_path" -> "path-absolute").
5428    </t>
5429    <t>
5430      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5431      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5432      have to be updated when switching over to RFC3986.
5433    </t>
5434    <t>
5435      Synchronize core rules with RFC5234.
5436    </t>
5437    <t>
5438      Get rid of prose rules that span multiple lines.
5439    </t>
5440    <t>
5441      Get rid of unused rules LOALPHA and UPALPHA.
5442    </t>
5443    <t>
5444      Move "Product Tokens" section (back) into Part 1, as "token" is used
5445      in the definition of the Upgrade header field.
5446    </t>
5447    <t>
5448      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5449    </t>
5450    <t>
5451      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5452    </t>
5453  </list>
5457<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5459  Closed issues:
5460  <list style="symbols">
5461    <t>
5462      <eref target=""/>:
5463      "HTTP-date vs. rfc1123-date"
5464    </t>
5465    <t>
5466      <eref target=""/>:
5467      "WS in quoted-pair"
5468    </t>
5469  </list>
5472  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5473  <list style="symbols">
5474    <t>
5475      Reference RFC 3984, and update header field registrations for headers defined
5476      in this document.
5477    </t>
5478  </list>
5481  Ongoing work on ABNF conversion (<eref target=""/>):
5482  <list style="symbols">
5483    <t>
5484      Replace string literals when the string really is case-sensitive (HTTP-Version).
5485    </t>
5486  </list>
5490<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5492  Closed issues:
5493  <list style="symbols">
5494    <t>
5495      <eref target=""/>:
5496      "Connection closing"
5497    </t>
5498    <t>
5499      <eref target=""/>:
5500      "Move registrations and registry information to IANA Considerations"
5501    </t>
5502    <t>
5503      <eref target=""/>:
5504      "need new URL for PAD1995 reference"
5505    </t>
5506    <t>
5507      <eref target=""/>:
5508      "IANA Considerations: update HTTP URI scheme registration"
5509    </t>
5510    <t>
5511      <eref target=""/>:
5512      "Cite HTTPS URI scheme definition"
5513    </t>
5514    <t>
5515      <eref target=""/>:
5516      "List-type headers vs Set-Cookie"
5517    </t>
5518  </list>
5521  Ongoing work on ABNF conversion (<eref target=""/>):
5522  <list style="symbols">
5523    <t>
5524      Replace string literals when the string really is case-sensitive (HTTP-Date).
5525    </t>
5526    <t>
5527      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5528    </t>
5529  </list>
5533<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5535  Closed issues:
5536  <list style="symbols">
5537    <t>
5538      <eref target=""/>:
5539      "Out-of-date reference for URIs"
5540    </t>
5541    <t>
5542      <eref target=""/>:
5543      "RFC 2822 is updated by RFC 5322"
5544    </t>
5545  </list>
5548  Ongoing work on ABNF conversion (<eref target=""/>):
5549  <list style="symbols">
5550    <t>
5551      Use "/" instead of "|" for alternatives.
5552    </t>
5553    <t>
5554      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5555    </t>
5556    <t>
5557      Only reference RFC 5234's core rules.
5558    </t>
5559    <t>
5560      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5561      whitespace ("OWS") and required whitespace ("RWS").
5562    </t>
5563    <t>
5564      Rewrite ABNFs to spell out whitespace rules, factor out
5565      header field value format definitions.
5566    </t>
5567  </list>
5571<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5573  Closed issues:
5574  <list style="symbols">
5575    <t>
5576      <eref target=""/>:
5577      "Header LWS"
5578    </t>
5579    <t>
5580      <eref target=""/>:
5581      "Sort 1.3 Terminology"
5582    </t>
5583    <t>
5584      <eref target=""/>:
5585      "RFC2047 encoded words"
5586    </t>
5587    <t>
5588      <eref target=""/>:
5589      "Character Encodings in TEXT"
5590    </t>
5591    <t>
5592      <eref target=""/>:
5593      "Line Folding"
5594    </t>
5595    <t>
5596      <eref target=""/>:
5597      "OPTIONS * and proxies"
5598    </t>
5599    <t>
5600      <eref target=""/>:
5601      "Reason-Phrase BNF"
5602    </t>
5603    <t>
5604      <eref target=""/>:
5605      "Use of TEXT"
5606    </t>
5607    <t>
5608      <eref target=""/>:
5609      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5610    </t>
5611    <t>
5612      <eref target=""/>:
5613      "RFC822 reference left in discussion of date formats"
5614    </t>
5615  </list>
5618  Final work on ABNF conversion (<eref target=""/>):
5619  <list style="symbols">
5620    <t>
5621      Rewrite definition of list rules, deprecate empty list elements.
5622    </t>
5623    <t>
5624      Add appendix containing collected and expanded ABNF.
5625    </t>
5626  </list>
5629  Other changes:
5630  <list style="symbols">
5631    <t>
5632      Rewrite introduction; add mostly new Architecture Section.
5633    </t>
5634    <t>
5635      Move definition of quality values from Part 3 into Part 1;
5636      make TE request header field grammar independent of accept-params (defined in Part 3).
5637    </t>
5638  </list>
5642<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5644  Closed issues:
5645  <list style="symbols">
5646    <t>
5647      <eref target=""/>:
5648      "base for numeric protocol elements"
5649    </t>
5650    <t>
5651      <eref target=""/>:
5652      "comment ABNF"
5653    </t>
5654  </list>
5657  Partly resolved issues:
5658  <list style="symbols">
5659    <t>
5660      <eref target=""/>:
5661      "205 Bodies" (took out language that implied that there might be
5662      methods for which a request body MUST NOT be included)
5663    </t>
5664    <t>
5665      <eref target=""/>:
5666      "editorial improvements around HTTP-date"
5667    </t>
5668  </list>
5672<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5674  Closed issues:
5675  <list style="symbols">
5676    <t>
5677      <eref target=""/>:
5678      "Repeating single-value headers"
5679    </t>
5680    <t>
5681      <eref target=""/>:
5682      "increase connection limit"
5683    </t>
5684    <t>
5685      <eref target=""/>:
5686      "IP addresses in URLs"
5687    </t>
5688    <t>
5689      <eref target=""/>:
5690      "take over HTTP Upgrade Token Registry"
5691    </t>
5692    <t>
5693      <eref target=""/>:
5694      "CR and LF in chunk extension values"
5695    </t>
5696    <t>
5697      <eref target=""/>:
5698      "HTTP/0.9 support"
5699    </t>
5700    <t>
5701      <eref target=""/>:
5702      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5703    </t>
5704    <t>
5705      <eref target=""/>:
5706      "move definitions of gzip/deflate/compress to part 1"
5707    </t>
5708    <t>
5709      <eref target=""/>:
5710      "disallow control characters in quoted-pair"
5711    </t>
5712  </list>
5715  Partly resolved issues:
5716  <list style="symbols">
5717    <t>
5718      <eref target=""/>:
5719      "update IANA requirements wrt Transfer-Coding values" (add the
5720      IANA Considerations subsection)
5721    </t>
5722  </list>
5726<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5728  Closed issues:
5729  <list style="symbols">
5730    <t>
5731      <eref target=""/>:
5732      "header parsing, treatment of leading and trailing OWS"
5733    </t>
5734  </list>
5737  Partly resolved issues:
5738  <list style="symbols">
5739    <t>
5740      <eref target=""/>:
5741      "Placement of 13.5.1 and 13.5.2"
5742    </t>
5743    <t>
5744      <eref target=""/>:
5745      "use of term "word" when talking about header structure"
5746    </t>
5747  </list>
5751<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5753  Closed issues:
5754  <list style="symbols">
5755    <t>
5756      <eref target=""/>:
5757      "Clarification of the term 'deflate'"
5758    </t>
5759    <t>
5760      <eref target=""/>:
5761      "OPTIONS * and proxies"
5762    </t>
5763    <t>
5764      <eref target=""/>:
5765      "MIME-Version not listed in P1, general header fields"
5766    </t>
5767    <t>
5768      <eref target=""/>:
5769      "IANA registry for content/transfer encodings"
5770    </t>
5771    <t>
5772      <eref target=""/>:
5773      "Case-sensitivity of HTTP-date"
5774    </t>
5775    <t>
5776      <eref target=""/>:
5777      "use of term "word" when talking about header structure"
5778    </t>
5779  </list>
5782  Partly resolved issues:
5783  <list style="symbols">
5784    <t>
5785      <eref target=""/>:
5786      "Term for the requested resource's URI"
5787    </t>
5788  </list>
5792<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5794  Closed issues:
5795  <list style="symbols">
5796    <t>
5797      <eref target=""/>:
5798      "Connection Closing"
5799    </t>
5800    <t>
5801      <eref target=""/>:
5802      "Delimiting messages with multipart/byteranges"
5803    </t>
5804    <t>
5805      <eref target=""/>:
5806      "Handling multiple Content-Length headers"
5807    </t>
5808    <t>
5809      <eref target=""/>:
5810      "Clarify entity / representation / variant terminology"
5811    </t>
5812    <t>
5813      <eref target=""/>:
5814      "consider removing the 'changes from 2068' sections"
5815    </t>
5816  </list>
5819  Partly resolved issues:
5820  <list style="symbols">
5821    <t>
5822      <eref target=""/>:
5823      "HTTP(s) URI scheme definitions"
5824    </t>
5825  </list>
5829<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5831  Closed issues:
5832  <list style="symbols">
5833    <t>
5834      <eref target=""/>:
5835      "Trailer requirements"
5836    </t>
5837    <t>
5838      <eref target=""/>:
5839      "Text about clock requirement for caches belongs in p6"
5840    </t>
5841    <t>
5842      <eref target=""/>:
5843      "effective request URI: handling of missing host in HTTP/1.0"
5844    </t>
5845    <t>
5846      <eref target=""/>:
5847      "confusing Date requirements for clients"
5848    </t>
5849  </list>
5852  Partly resolved issues:
5853  <list style="symbols">
5854    <t>
5855      <eref target=""/>:
5856      "Handling multiple Content-Length headers"
5857    </t>
5858  </list>
5862<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5864  Closed issues:
5865  <list style="symbols">
5866    <t>
5867      <eref target=""/>:
5868      "RFC2145 Normative"
5869    </t>
5870    <t>
5871      <eref target=""/>:
5872      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5873    </t>
5874    <t>
5875      <eref target=""/>:
5876      "define 'transparent' proxy"
5877    </t>
5878    <t>
5879      <eref target=""/>:
5880      "Header Classification"
5881    </t>
5882    <t>
5883      <eref target=""/>:
5884      "Is * usable as a request-uri for new methods?"
5885    </t>
5886    <t>
5887      <eref target=""/>:
5888      "Migrate Upgrade details from RFC2817"
5889    </t>
5890    <t>
5891      <eref target=""/>:
5892      "untangle ABNFs for header fields"
5893    </t>
5894    <t>
5895      <eref target=""/>:
5896      "update RFC 2109 reference"
5897    </t>
5898  </list>
Note: See TracBrowser for help on using the repository browser.