source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1361

Last change on this file since 1361 was 1361, checked in by julian.reschke@…, 11 years ago

define \-escaping in quoted strings for characters other than \ and DQUOTE (see #270)

  • Property svn:eol-style set to native
File size: 254.7 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 "July">
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-203             "<xref target='Part2' x:rel='#status.203' xmlns:x=''/>">
37  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x=''/>">
38  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x=''/>">
39  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
41<?rfc toc="yes" ?>
42<?rfc symrefs="yes" ?>
43<?rfc sortrefs="yes" ?>
44<?rfc compact="yes"?>
45<?rfc subcompact="no" ?>
46<?rfc linkmailto="no" ?>
47<?rfc editing="no" ?>
48<?rfc comments="yes"?>
49<?rfc inline="yes"?>
50<?rfc rfcedstyle="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
54     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x=''>
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
62    <address>
63      <postal>
64        <street>345 Park Ave</street>
65        <city>San Jose</city>
66        <region>CA</region>
67        <code>95110</code>
68        <country>USA</country>
69      </postal>
70      <email></email>
71      <uri></uri>
72    </address>
73  </author>
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email></email>
86      <uri></uri>
87    </address>
88  </author>
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email></email>
102    </address>
103  </author>
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email></email>
116    </address>
117  </author>
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email></email>
130      <uri></uri>
131    </address>
132  </author>
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email></email>
144    </address>
145  </author>
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email></email>
160      <uri></uri>
161    </address>
162  </author>
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email></email>
176      <uri></uri>
177    </address>
178  </author>
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email></email>
191      <uri></uri>
192    </address>
193  </author>
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list (, which is archived at
217    <eref target=""/>.
218  </t>
219  <t>
220    The current issues list is at
221    <eref target=""/> and related
222    documents (including fancy diffs) can be found at
223    <eref target=""/>.
224  </t>
225  <t>
226    The changes in this draft are summarized in <xref target="changes.since.15"/>.
227  </t>
231<section title="Introduction" anchor="introduction">
233   The Hypertext Transfer Protocol (HTTP) is an application-level
234   request/response protocol that uses extensible semantics and MIME-like
235   message payloads for flexible interaction with network-based hypertext
236   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
237   standard <xref target="RFC3986"/> to indicate the target resource and
238   relationships between resources.
239   Messages are passed in a format similar to that used by Internet mail
240   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
241   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
242   between HTTP and MIME messages).
245   HTTP is a generic interface protocol for information systems. It is
246   designed to hide the details of how a service is implemented by presenting
247   a uniform interface to clients that is independent of the types of
248   resources provided. Likewise, servers do not need to be aware of each
249   client's purpose: an HTTP request can be considered in isolation rather
250   than being associated with a specific type of client or a predetermined
251   sequence of application steps. The result is a protocol that can be used
252   effectively in many different contexts and for which implementations can
253   evolve independently over time.
256   HTTP is also designed for use as an intermediation protocol for translating
257   communication to and from non-HTTP information systems.
258   HTTP proxies and gateways can provide access to alternative information
259   services by translating their diverse protocols into a hypertext
260   format that can be viewed and manipulated by clients in the same way
261   as HTTP services.
264   One consequence of HTTP flexibility is that the protocol cannot be
265   defined in terms of what occurs behind the interface. Instead, we
266   are limited to defining the syntax of communication, the intent
267   of received communication, and the expected behavior of recipients.
268   If the communication is considered in isolation, then successful
269   actions ought to be reflected in corresponding changes to the
270   observable interface provided by servers. However, since multiple
271   clients might act in parallel and perhaps at cross-purposes, we
272   cannot require that such changes be observable beyond the scope
273   of a single response.
276   This document is Part 1 of the seven-part specification of HTTP,
277   defining the protocol referred to as "HTTP/1.1", obsoleting
278   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
279   Part 1 describes the architectural elements that are used or
280   referred to in HTTP, defines the "http" and "https" URI schemes,
281   describes overall network operation and connection management,
282   and defines HTTP message framing and forwarding requirements.
283   Our goal is to define all of the mechanisms necessary for HTTP message
284   handling that are independent of message semantics, thereby defining the
285   complete set of requirements for message parsers and
286   message-forwarding intermediaries.
289<section title="Requirements" anchor="intro.requirements">
291   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
292   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
293   document are to be interpreted as described in <xref target="RFC2119"/>.
296   An implementation is not compliant if it fails to satisfy one or more
297   of the "MUST" or "REQUIRED" level requirements for the protocols it
298   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
299   level and all the "SHOULD" level requirements for its protocols is said
300   to be "unconditionally compliant"; one that satisfies all the "MUST"
301   level requirements but not all the "SHOULD" level requirements for its
302   protocols is said to be "conditionally compliant".
306<section title="Syntax Notation" anchor="notation">
307<iref primary="true" item="Grammar" subitem="ALPHA"/>
308<iref primary="true" item="Grammar" subitem="CR"/>
309<iref primary="true" item="Grammar" subitem="CRLF"/>
310<iref primary="true" item="Grammar" subitem="CTL"/>
311<iref primary="true" item="Grammar" subitem="DIGIT"/>
312<iref primary="true" item="Grammar" subitem="DQUOTE"/>
313<iref primary="true" item="Grammar" subitem="HEXDIG"/>
314<iref primary="true" item="Grammar" subitem="LF"/>
315<iref primary="true" item="Grammar" subitem="OCTET"/>
316<iref primary="true" item="Grammar" subitem="SP"/>
317<iref primary="true" item="Grammar" subitem="VCHAR"/>
318<iref primary="true" item="Grammar" subitem="WSP"/>
320   This specification uses the Augmented Backus-Naur Form (ABNF) notation
321   of <xref target="RFC5234"/>.
323<t anchor="core.rules">
324  <x:anchor-alias value="ALPHA"/>
325  <x:anchor-alias value="CTL"/>
326  <x:anchor-alias value="CR"/>
327  <x:anchor-alias value="CRLF"/>
328  <x:anchor-alias value="DIGIT"/>
329  <x:anchor-alias value="DQUOTE"/>
330  <x:anchor-alias value="HEXDIG"/>
331  <x:anchor-alias value="LF"/>
332  <x:anchor-alias value="OCTET"/>
333  <x:anchor-alias value="SP"/>
334  <x:anchor-alias value="VCHAR"/>
335  <x:anchor-alias value="WSP"/>
336   The following core rules are included by
337   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
338   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
339   DIGIT (decimal 0-9), DQUOTE (double quote),
340   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
341   OCTET (any 8-bit sequence of data), SP (space),
342   VCHAR (any visible <xref target="USASCII"/> character),
343   and WSP (whitespace).
346   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
347   "obsolete" grammar rules that appear for historical reasons.
350<section title="ABNF Extension: #rule" anchor="notation.abnf">
352  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
353  improve readability.
356  A construct "#" is defined, similar to "*", for defining comma-delimited
357  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
358  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
359  comma (",") and optional whitespace (OWS,
360  <xref target="basic.rules"/>).   
363  Thus,
364</preamble><artwork type="example">
365  1#element =&gt; element *( OWS "," OWS element )
368  and:
369</preamble><artwork type="example">
370  #element =&gt; [ 1#element ]
373  and for n &gt;= 1 and m &gt; 1:
374</preamble><artwork type="example">
375  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
378  For compatibility with legacy list rules, recipients &SHOULD; accept empty
379  list elements. In other words, consumers would follow the list productions:
381<figure><artwork type="example">
382  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
384  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
387  Note that empty elements do not contribute to the count of elements present,
388  though.
391  For example, given these ABNF productions:
393<figure><artwork type="example">
394  example-list      = 1#example-list-elmt
395  example-list-elmt = token ; see <xref target="basic.rules"/>
398  Then these are valid values for example-list (not including the double
399  quotes, which are present for delimitation only):
401<figure><artwork type="example">
402  "foo,bar"
403  " foo ,bar,"
404  "  foo , ,bar,charlie   "
405  "foo ,bar,   charlie "
408  But these values would be invalid, as at least one non-empty element is
409  required:
411<figure><artwork type="example">
412  ""
413  ","
414  ",   ,"
417  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
418  expanded as explained above.
422<section title="Basic Rules" anchor="basic.rules">
423<t anchor="rule.CRLF">
424  <x:anchor-alias value="CRLF"/>
425   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
426   protocol elements other than the message-body
427   (see <xref target="tolerant.applications"/> for tolerant applications).
429<t anchor="rule.LWS">
430   This specification uses three rules to denote the use of linear
431   whitespace: OWS (optional whitespace), RWS (required whitespace), and
432   BWS ("bad" whitespace).
435   The OWS rule is used where zero or more linear whitespace octets might
436   appear. OWS &SHOULD; either not be produced or be produced as a single
437   SP. Multiple OWS octets that occur within field-content &SHOULD;
438   be replaced with a single SP before interpreting the field value or
439   forwarding the message downstream.
442   RWS is used when at least one linear whitespace octet is required to
443   separate field tokens. RWS &SHOULD; be produced as a single SP.
444   Multiple RWS octets that occur within field-content &SHOULD; be
445   replaced with a single SP before interpreting the field value or
446   forwarding the message downstream.
449   BWS is used where the grammar allows optional whitespace for historical
450   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
451   recipients &MUST; accept such bad optional whitespace and remove it before
452   interpreting the field value or forwarding the message downstream.
454<t anchor="rule.whitespace">
455  <x:anchor-alias value="BWS"/>
456  <x:anchor-alias value="OWS"/>
457  <x:anchor-alias value="RWS"/>
458  <x:anchor-alias value="obs-fold"/>
460<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"/>
461  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
462                 ; "optional" whitespace
463  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
464                 ; "required" whitespace
465  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
466                 ; "bad" whitespace
467  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
468                 ; see <xref target="header.fields"/>
470<t anchor="rule.token.separators">
471  <x:anchor-alias value="tchar"/>
472  <x:anchor-alias value="token"/>
473  <x:anchor-alias value="special"/>
474  <x:anchor-alias value="word"/>
475   Many HTTP/1.1 header field values consist of words (token or quoted-string)
476   separated by whitespace or special characters. These special characters
477   &MUST; be in a quoted string to be used within a parameter value (as defined
478   in <xref target="transfer.codings"/>).
480<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"/>
481  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
483  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
485  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
486 -->
487  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
488                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
489                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
490                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
492  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
493                 / ";" / ":" / "\" / DQUOTE / "/" / "["
494                 / "]" / "?" / "=" / "{" / "}"
496<t anchor="rule.quoted-string">
497  <x:anchor-alias value="quoted-string"/>
498  <x:anchor-alias value="qdtext"/>
499  <x:anchor-alias value="obs-text"/>
500   A string of text is parsed as a single word if it is quoted using
501   double-quote marks.
503<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"/>
504  <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>
505  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
506                 ; <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>
507  <x:ref>obs-text</x:ref>       = %x80-FF
509<t anchor="rule.quoted-pair">
510  <x:anchor-alias value="quoted-pair"/>
511   The backslash octet ("\") can be used as a single-octet
512   quoting mechanism within quoted-string constructs:
514<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
515  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
518   Recipients that process the value of the quoted-string &MUST; handle a
519   quoted-pair as if it were replaced by the octet following the backslash.
522   Senders &SHOULD-NOT; escape octets that do not require escaping
523   (i.e., other than DQUOTE and the backslash octet).
530<section title="HTTP-related architecture" anchor="architecture">
532   HTTP was created for the World Wide Web architecture
533   and has evolved over time to support the scalability needs of a worldwide
534   hypertext system. Much of that architecture is reflected in the terminology
535   and syntax productions used to define HTTP.
538<section title="Client/Server Messaging" anchor="operation">
539<iref primary="true" item="client"/>
540<iref primary="true" item="server"/>
541<iref primary="true" item="connection"/>
543   HTTP is a stateless request/response protocol that operates by exchanging
544   messages across a reliable transport or session-layer
545   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
546   program that establishes a connection to a server for the purpose of
547   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
548   program that accepts connections in order to service HTTP requests by
549   sending HTTP responses.
551<iref primary="true" item="user agent"/>
552<iref primary="true" item="origin server"/>
553<iref primary="true" item="browser"/>
554<iref primary="true" item="spider"/>
555<iref primary="true" item="sender"/>
556<iref primary="true" item="recipient"/>
558   Note that the terms client and server refer only to the roles that
559   these programs perform for a particular connection.  The same program
560   might act as a client on some connections and a server on others.  We use
561   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
562   such as a WWW browser, editor, or spider (web-traversing robot), and
563   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
564   authoritative responses to a request.  For general requirements, we use
565   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
566   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
567   message.
570   Most HTTP communication consists of a retrieval request (GET) for
571   a representation of some resource identified by a URI.  In the
572   simplest case, this might be accomplished via a single bidirectional
573   connection (===) between the user agent (UA) and the origin server (O).
575<figure><artwork type="drawing">
576         request   &gt;
577    UA ======================================= O
578                                &lt;   response
580<iref primary="true" item="message"/>
581<iref primary="true" item="request"/>
582<iref primary="true" item="response"/>
584   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
585   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
586   protocol version, followed by MIME-like header fields containing
587   request modifiers, client information, and payload metadata, an empty
588   line to indicate the end of the header section, and finally the payload
589   body (if any).
592   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
593   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
594   includes the protocol version, a success or error code, and textual
595   reason phrase, followed by MIME-like header fields containing server
596   information, resource metadata, and payload metadata, an empty line to
597   indicate the end of the header section, and finally the payload body (if any).
600   The following example illustrates a typical message exchange for a
601   GET request on the URI "":
604client request:
605</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
606GET /hello.txt HTTP/1.1
607User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
609Accept: */*
613server response:
614</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
615HTTP/1.1 200 OK
616Date: Mon, 27 Jul 2009 12:28:53 GMT
617Server: Apache
618Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
619ETag: "34aa387-d-1568eb00"
620Accept-Ranges: bytes
621Content-Length: <x:length-of target="exbody"/>
622Vary: Accept-Encoding
623Content-Type: text/plain
625<x:span anchor="exbody">Hello World!
629<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
631   Fundamentally, HTTP is a message-based protocol. Although message bodies can
632   be chunked (<xref target="chunked.encoding"/>) and implementations often
633   make parts of a message available progressively, this is not required, and
634   some widely-used implementations only make a message available when it is
635   complete. Furthermore, while most proxies will progressively stream messages,
636   some amount of buffering will take place, and some proxies might buffer
637   messages to perform transformations, check content or provide other services.
640   Therefore, extensions to and uses of HTTP cannot rely on the availability of
641   a partial message, or assume that messages will not be buffered. There are
642   strategies that can be used to test for buffering in a given connection, but
643   it should be understood that behaviors can differ across connections, and
644   between requests and responses.
647   Recipients &MUST; consider every message in a connection in isolation;
648   because HTTP is a stateless protocol, it cannot be assumed that two requests
649   on the same connection are from the same client or share any other common
650   attributes. In particular, intermediaries might mix requests from different
651   clients into a single server connection. Note that some existing HTTP
652   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
653   potentially causing interoperability and security problems.
657<section title="Connections and Transport Independence" anchor="transport-independence">
659   HTTP messaging is independent of the underlying transport or
660   session-layer connection protocol(s).  HTTP only presumes a reliable
661   transport with in-order delivery of requests and the corresponding
662   in-order delivery of responses.  The mapping of HTTP request and
663   response structures onto the data units of the underlying transport
664   protocol is outside the scope of this specification.
667   The specific connection protocols to be used for an interaction
668   are determined by client configuration and the target resource's URI.
669   For example, the "http" URI scheme
670   (<xref target="http.uri"/>) indicates a default connection of TCP
671   over IP, with a default TCP port of 80, but the client might be
672   configured to use a proxy via some other connection port or protocol
673   instead of using the defaults.
676   A connection might be used for multiple HTTP request/response exchanges,
677   as defined in <xref target="persistent.connections"/>.
681<section title="Intermediaries" anchor="intermediaries">
682<iref primary="true" item="intermediary"/>
684   HTTP enables the use of intermediaries to satisfy requests through
685   a chain of connections.  There are three common forms of HTTP
686   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
687   a single intermediary might act as an origin server, proxy, gateway,
688   or tunnel, switching behavior based on the nature of each request.
690<figure><artwork type="drawing">
691         &gt;             &gt;             &gt;             &gt;
692    <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> =========== <x:highlight>C</x:highlight> =========== <x:highlight>O</x:highlight>
693               &lt;             &lt;             &lt;             &lt;
696   The figure above shows three intermediaries (A, B, and C) between the
697   user agent and origin server. A request or response message that
698   travels the whole chain will pass through four separate connections.
699   Some HTTP communication options
700   might apply only to the connection with the nearest, non-tunnel
701   neighbor, only to the end-points of the chain, or to all connections
702   along the chain. Although the diagram is linear, each participant might
703   be engaged in multiple, simultaneous communications. For example, B
704   might be receiving requests from many clients other than A, and/or
705   forwarding requests to servers other than C, at the same time that it
706   is handling A's request.
709<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
710<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
711   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
712   to describe various requirements in relation to the directional flow of a
713   message: all messages flow from upstream to downstream.
714   Likewise, we use the terms inbound and outbound to refer to
715   directions in relation to the request path:
716   "<x:dfn>inbound</x:dfn>" means toward the origin server and
717   "<x:dfn>outbound</x:dfn>" means toward the user agent.
719<t><iref primary="true" item="proxy"/>
720   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
721   client, usually via local configuration rules, to receive requests
722   for some type(s) of absolute URI and attempt to satisfy those
723   requests via translation through the HTTP interface.  Some translations
724   are minimal, such as for proxy requests for "http" URIs, whereas
725   other requests might require translation to and from entirely different
726   application-layer protocols. Proxies are often used to group an
727   organization's HTTP requests through a common intermediary for the
728   sake of security, annotation services, or shared caching.
731<iref primary="true" item="transforming proxy"/>
732<iref primary="true" item="non-transforming proxy"/>
733   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
734   or configured to modify request or response messages in a semantically
735   meaningful way (i.e., modifications, beyond those required by normal
736   HTTP processing, that change the message in a way that would be
737   significant to the original sender or potentially significant to
738   downstream recipients).  For example, a transforming proxy might be
739   acting as a shared annotation server (modifying responses to include
740   references to a local annotation database), a malware filter, a
741   format transcoder, or an intranet-to-Internet privacy filter.  Such
742   transformations are presumed to be desired by the client (or client
743   organization) that selected the proxy and are beyond the scope of
744   this specification.  However, when a proxy is not intended to transform
745   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
746   requirements that preserve HTTP message semantics. See &status-203; and
747   &header-warning; for status and warning codes related to transformations.
749<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
750<iref primary="true" item="accelerator"/>
751   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
752   is a receiving agent that acts
753   as a layer above some other server(s) and translates the received
754   requests to the underlying server's protocol.  Gateways are often
755   used to encapsulate legacy or untrusted information services, to
756   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
757   enable partitioning or load-balancing of HTTP services across
758   multiple machines.
761   A gateway behaves as an origin server on its outbound connection and
762   as a user agent on its inbound connection.
763   All HTTP requirements applicable to an origin server
764   also apply to the outbound communication of a gateway.
765   A gateway communicates with inbound servers using any protocol that
766   it desires, including private extensions to HTTP that are outside
767   the scope of this specification.  However, an HTTP-to-HTTP gateway
768   that wishes to interoperate with third-party HTTP servers &MUST;
769   comply with HTTP user agent requirements on the gateway's inbound
770   connection and &MUST; implement the Connection
771   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
772   header fields for both connections.
774<t><iref primary="true" item="tunnel"/>
775   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
776   without changing the messages. Once active, a tunnel is not
777   considered a party to the HTTP communication, though the tunnel might
778   have been initiated by an HTTP request. A tunnel ceases to exist when
779   both ends of the relayed connection are closed. Tunnels are used to
780   extend a virtual connection through an intermediary, such as when
781   transport-layer security is used to establish private communication
782   through a shared firewall proxy.
784<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
785<iref primary="true" item="captive portal"/>
786   In addition, there may exist network intermediaries that are not
787   considered part of the HTTP communication but nevertheless act as
788   filters or redirecting agents (usually violating HTTP semantics,
789   causing security problems, and otherwise making a mess of things).
790   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
791   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
792   or "<x:dfn>captive portal</x:dfn>",
793   differs from an HTTP proxy because it has not been selected by the client.
794   Instead, the network intermediary redirects outgoing TCP port 80 packets
795   (and occasionally other common port traffic) to an internal HTTP server.
796   Interception proxies are commonly found on public network access points,
797   as a means of enforcing account subscription prior to allowing use of
798   non-local Internet services, and within corporate firewalls to enforce
799   network usage policies.
800   They are indistinguishable from a man-in-the-middle attack.
804<section title="Caches" anchor="caches">
805<iref primary="true" item="cache"/>
807   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
808   subsystem that controls its message storage, retrieval, and deletion.
809   A cache stores cacheable responses in order to reduce the response
810   time and network bandwidth consumption on future, equivalent
811   requests. Any client or server &MAY; employ a cache, though a cache
812   cannot be used by a server while it is acting as a tunnel.
815   The effect of a cache is that the request/response chain is shortened
816   if one of the participants along the chain has a cached response
817   applicable to that request. The following illustrates the resulting
818   chain if B has a cached copy of an earlier response from O (via C)
819   for a request which has not been cached by UA or A.
821<figure><artwork type="drawing">
822            &gt;             &gt;
823       UA =========== A =========== B - - - - - - C - - - - - - O
824                  &lt;             &lt;
826<t><iref primary="true" item="cacheable"/>
827   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
828   the response message for use in answering subsequent requests.
829   Even when a response is cacheable, there might be additional
830   constraints placed by the client or by the origin server on when
831   that cached response can be used for a particular request. HTTP
832   requirements for cache behavior and cacheable responses are
833   defined in &caching-overview;. 
836   There are a wide variety of architectures and configurations
837   of caches and proxies deployed across the World Wide Web and
838   inside large organizations. These systems include national hierarchies
839   of proxy caches to save transoceanic bandwidth, systems that
840   broadcast or multicast cache entries, organizations that distribute
841   subsets of cached data via optical media, and so on.
845<section title="Protocol Versioning" anchor="http.version">
846  <x:anchor-alias value="HTTP-Version"/>
847  <x:anchor-alias value="HTTP-Prot-Name"/>
849   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
850   versions of the protocol. This specification defines version "1.1".
851   The protocol version as a whole indicates the sender's compliance
852   with the set of requirements laid out in that version's corresponding
853   specification of HTTP.
856   The version of an HTTP message is indicated by an HTTP-Version field
857   in the first line of the message. HTTP-Version is case-sensitive.
859<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
860  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
861  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
864   The HTTP version number consists of two decimal digits separated by a "."
865   (period or decimal point).  The first digit ("major version") indicates the
866   HTTP messaging syntax, whereas the second digit ("minor version") indicates
867   the highest minor version to which the sender is at least conditionally
868   compliant and able to understand for future communication.  The minor
869   version advertises the sender's communication capabilities even when the
870   sender is only using a backwards-compatible subset of the protocol,
871   thereby letting the recipient know that more advanced features can
872   be used in response (by servers) or in future requests (by clients).
875   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
876   <xref target="RFC1945"/> or a recipient whose version is unknown,
877   the HTTP/1.1 message is constructed such that it can be interpreted
878   as a valid HTTP/1.0 message if all of the newer features are ignored.
879   This specification places recipient-version requirements on some
880   new features so that a compliant sender will only use compatible
881   features until it has determined, through configuration or the
882   receipt of a message, that the recipient supports HTTP/1.1.
885   The interpretation of an HTTP header field does not change
886   between minor versions of the same major version, though the default
887   behavior of a recipient in the absence of such a field can change.
888   Unless specified otherwise, header fields defined in HTTP/1.1 are
889   defined for all versions of HTTP/1.x.  In particular, the Host and
890   Connection header fields ought to be implemented by all HTTP/1.x
891   implementations whether or not they advertise compliance with HTTP/1.1.
894   New header fields can be defined such that, when they are
895   understood by a recipient, they might override or enhance the
896   interpretation of previously defined header fields.  When an
897   implementation receives an unrecognized header field, the recipient
898   &MUST; ignore that header field for local processing regardless of
899   the message's HTTP version.  An unrecognized header field received
900   by a proxy &MUST; be forwarded downstream unless the header field's
901   field-name is listed in the message's Connection header-field
902   (see <xref target="header.connection"/>).
903   These requirements allow HTTP's functionality to be enhanced without
904   requiring prior update of all compliant intermediaries.
907   Intermediaries that process HTTP messages (i.e., all intermediaries
908   other than those acting as a tunnel) &MUST; send their own HTTP-Version
909   in forwarded messages.  In other words, they &MUST-NOT; blindly
910   forward the first line of an HTTP message without ensuring that the
911   protocol version matches what the intermediary understands, and
912   is at least conditionally compliant to, for both the receiving and
913   sending of messages.  Forwarding an HTTP message without rewriting
914   the HTTP-Version might result in communication errors when downstream
915   recipients use the message sender's version to determine what features
916   are safe to use for later communication with that sender.
919   An HTTP client &SHOULD; send a request version equal to the highest
920   version for which the client is at least conditionally compliant and
921   whose major version is no higher than the highest version supported
922   by the server, if this is known.  An HTTP client &MUST-NOT; send a
923   version for which it is not at least conditionally compliant.
926   An HTTP client &MAY; send a lower request version if it is known that
927   the server incorrectly implements the HTTP specification, but only
928   after the client has attempted at least one normal request and determined
929   from the response status or header fields (e.g., Server) that the
930   server improperly handles higher request versions.
933   An HTTP server &SHOULD; send a response version equal to the highest
934   version for which the server is at least conditionally compliant and
935   whose major version is less than or equal to the one received in the
936   request.  An HTTP server &MUST-NOT; send a version for which it is not
937   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
938   Version Not Supported) response if it cannot send a response using the
939   major version used in the client's request.
942   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
943   if it is known or suspected that the client incorrectly implements the
944   HTTP specification and is incapable of correctly processing later
945   version responses, such as when a client fails to parse the version
946   number correctly or when an intermediary is known to blindly forward
947   the HTTP-Version even when it doesn't comply with the given minor
948   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
949   performed unless triggered by specific client attributes, such as when
950   one or more of the request header fields (e.g., User-Agent) uniquely
951   match the values sent by a client known to be in error.
954   The intention of HTTP's versioning design is that the major number
955   will only be incremented if an incompatible message syntax is
956   introduced, and that the minor number will only be incremented when
957   changes made to the protocol have the effect of adding to the message
958   semantics or implying additional capabilities of the sender.  However,
959   the minor version was not incremented for the changes introduced between
960   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
961   is specifically avoiding any such changes to the protocol.
965<section title="Uniform Resource Identifiers" anchor="uri">
966<iref primary="true" item="resource"/>
968   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
969   throughout HTTP as the means for identifying resources. URI references
970   are used to target requests, indicate redirects, and define relationships.
971   HTTP does not limit what a resource might be; it merely defines an interface
972   that can be used to interact with a resource via HTTP. More information on
973   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
975  <x:anchor-alias value="URI-reference"/>
976  <x:anchor-alias value="absolute-URI"/>
977  <x:anchor-alias value="relative-part"/>
978  <x:anchor-alias value="authority"/>
979  <x:anchor-alias value="path-abempty"/>
980  <x:anchor-alias value="path-absolute"/>
981  <x:anchor-alias value="port"/>
982  <x:anchor-alias value="query"/>
983  <x:anchor-alias value="uri-host"/>
984  <x:anchor-alias value="partial-URI"/>
986   This specification adopts the definitions of "URI-reference",
987   "absolute-URI", "relative-part", "port", "host",
988   "path-abempty", "path-absolute", "query", and "authority" from the
989   URI generic syntax <xref target="RFC3986"/>.
990   In addition, we define a partial-URI rule for protocol elements
991   that allow a relative URI but not a fragment.
993<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"/>
994  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
995  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
996  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
997  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
998  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
999  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
1000  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
1001  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
1002  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
1004  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
1007   Each protocol element in HTTP that allows a URI reference will indicate
1008   in its ABNF production whether the element allows any form of reference
1009   (URI-reference), only a URI in absolute form (absolute-URI), only the
1010   path and optional query components, or some combination of the above.
1011   Unless otherwise indicated, URI references are parsed relative to the
1012   effective request URI, which defines the default base URI for references
1013   in both the request and its corresponding response.
1016<section title="http URI scheme" anchor="http.uri">
1017  <x:anchor-alias value="http-URI"/>
1018  <iref item="http URI scheme" primary="true"/>
1019  <iref item="URI scheme" subitem="http" primary="true"/>
1021   The "http" URI scheme is hereby defined for the purpose of minting
1022   identifiers according to their association with the hierarchical
1023   namespace governed by a potential HTTP origin server listening for
1024   TCP connections on a given port.
1026<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1027  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1030   The HTTP origin server is identified by the generic syntax's
1031   <x:ref>authority</x:ref> component, which includes a host identifier
1032   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1033   The remainder of the URI, consisting of both the hierarchical path
1034   component and optional query component, serves as an identifier for
1035   a potential resource within that origin server's name space.
1038   If the host identifier is provided as an IP literal or IPv4 address,
1039   then the origin server is any listener on the indicated TCP port at
1040   that IP address. If host is a registered name, then that name is
1041   considered an indirect identifier and the recipient might use a name
1042   resolution service, such as DNS, to find the address of a listener
1043   for that host.
1044   The host &MUST-NOT; be empty; if an "http" URI is received with an
1045   empty host, then it &MUST; be rejected as invalid.
1046   If the port subcomponent is empty or not given, then TCP port 80 is
1047   assumed (the default reserved port for WWW services).
1050   Regardless of the form of host identifier, access to that host is not
1051   implied by the mere presence of its name or address. The host might or might
1052   not exist and, even when it does exist, might or might not be running an
1053   HTTP server or listening to the indicated port. The "http" URI scheme
1054   makes use of the delegated nature of Internet names and addresses to
1055   establish a naming authority (whatever entity has the ability to place
1056   an HTTP server at that Internet name or address) and allows that
1057   authority to determine which names are valid and how they might be used.
1060   When an "http" URI is used within a context that calls for access to the
1061   indicated resource, a client &MAY; attempt access by resolving
1062   the host to an IP address, establishing a TCP connection to that address
1063   on the indicated port, and sending an HTTP request message to the server
1064   containing the URI's identifying data as described in <xref target="request"/>.
1065   If the server responds to that request with a non-interim HTTP response
1066   message, as described in <xref target="response"/>, then that response
1067   is considered an authoritative answer to the client's request.
1070   Although HTTP is independent of the transport protocol, the "http"
1071   scheme is specific to TCP-based services because the name delegation
1072   process depends on TCP for establishing authority.
1073   An HTTP service based on some other underlying connection protocol
1074   would presumably be identified using a different URI scheme, just as
1075   the "https" scheme (below) is used for servers that require an SSL/TLS
1076   transport layer on a connection. Other protocols might also be used to
1077   provide access to "http" identified resources &mdash; it is only the
1078   authoritative interface used for mapping the namespace that is
1079   specific to TCP.
1082   The URI generic syntax for authority also includes a deprecated
1083   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1084   for including user authentication information in the URI.  Some
1085   implementations make use of the userinfo component for internal
1086   configuration of authentication information, such as within command
1087   invocation options, configuration files, or bookmark lists, even
1088   though such usage might expose a user identifier or password.
1089   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1090   delimiter) when transmitting an "http" URI in a message.  Recipients
1091   of HTTP messages that contain a URI reference &SHOULD; parse for the
1092   existence of userinfo and treat its presence as an error, likely
1093   indicating that the deprecated subcomponent is being used to obscure
1094   the authority for the sake of phishing attacks.
1098<section title="https URI scheme" anchor="https.uri">
1099   <x:anchor-alias value="https-URI"/>
1100   <iref item="https URI scheme"/>
1101   <iref item="URI scheme" subitem="https"/>
1103   The "https" URI scheme is hereby defined for the purpose of minting
1104   identifiers according to their association with the hierarchical
1105   namespace governed by a potential HTTP origin server listening for
1106   SSL/TLS-secured connections on a given TCP port.
1109   All of the requirements listed above for the "http" scheme are also
1110   requirements for the "https" scheme, except that a default TCP port
1111   of 443 is assumed if the port subcomponent is empty or not given,
1112   and the TCP connection &MUST; be secured for privacy through the
1113   use of strong encryption prior to sending the first HTTP request.
1115<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1116  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1119   Unlike the "http" scheme, responses to "https" identified requests
1120   are never "public" and thus &MUST-NOT; be reused for shared caching.
1121   They can, however, be reused in a private cache if the message is
1122   cacheable by default in HTTP or specifically indicated as such by
1123   the Cache-Control header field (&header-cache-control;).
1126   Resources made available via the "https" scheme have no shared
1127   identity with the "http" scheme even if their resource identifiers
1128   indicate the same authority (the same host listening to the same
1129   TCP port).  They are distinct name spaces and are considered to be
1130   distinct origin servers.  However, an extension to HTTP that is
1131   defined to apply to entire host domains, such as the Cookie protocol
1132   <xref target="RFC6265"/>, can allow information
1133   set by one service to impact communication with other services
1134   within a matching group of host domains.
1137   The process for authoritative access to an "https" identified
1138   resource is defined in <xref target="RFC2818"/>.
1142<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1144   Since the "http" and "https" schemes conform to the URI generic syntax,
1145   such URIs are normalized and compared according to the algorithm defined
1146   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1147   described above for each scheme.
1150   If the port is equal to the default port for a scheme, the normal
1151   form is to elide the port subcomponent. Likewise, an empty path
1152   component is equivalent to an absolute path of "/", so the normal
1153   form is to provide a path of "/" instead. The scheme and host
1154   are case-insensitive and normally provided in lowercase; all
1155   other components are compared in a case-sensitive manner.
1156   Characters other than those in the "reserved" set are equivalent
1157   to their percent-encoded octets (see <xref target="RFC3986"
1158   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1161   For example, the following three URIs are equivalent:
1163<figure><artwork type="example">
1172<section title="Message Format" anchor="http.message">
1173<x:anchor-alias value="generic-message"/>
1174<x:anchor-alias value="message.types"/>
1175<x:anchor-alias value="HTTP-message"/>
1176<x:anchor-alias value="start-line"/>
1177<iref item="header section"/>
1178<iref item="headers"/>
1179<iref item="header field"/>
1181   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1182   octets in a format similar to the Internet Message Format
1183   <xref target="RFC5322"/>: zero or more header fields (collectively
1184   referred to as the "headers" or the "header section"), an empty line
1185   indicating the end of the header section, and an optional message-body.
1188   An HTTP message can either be a request from client to server or a
1189   response from server to client.  Syntactically, the two types of message
1190   differ only in the start-line, which is either a Request-Line (for requests)
1191   or a Status-Line (for responses), and in the algorithm for determining
1192   the length of the message-body (<xref target="message.body"/>).
1193   In theory, a client could receive requests and a server could receive
1194   responses, distinguishing them by their different start-line formats,
1195   but in practice servers are implemented to only expect a request
1196   (a response is interpreted as an unknown or invalid request method)
1197   and clients are implemented to only expect a response.
1199<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1200  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1201                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1202                    <x:ref>CRLF</x:ref>
1203                    [ <x:ref>message-body</x:ref> ]
1204  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1207   Implementations &MUST-NOT; send whitespace between the start-line and
1208   the first header field. The presence of such whitespace in a request
1209   might be an attempt to trick a server into ignoring that field or
1210   processing the line after it as a new request, either of which might
1211   result in a security vulnerability if other implementations within
1212   the request chain interpret the same message differently.
1213   Likewise, the presence of such whitespace in a response might be
1214   ignored by some clients or cause others to cease parsing.
1217<section title="Message Parsing Robustness" anchor="message.robustness">
1219   In the interest of robustness, servers &SHOULD; ignore at least one
1220   empty line received where a Request-Line is expected. In other words, if
1221   the server is reading the protocol stream at the beginning of a
1222   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1225   Some old HTTP/1.0 client implementations send an extra CRLF
1226   after a POST request as a lame workaround for some early server
1227   applications that failed to read message-body content that was
1228   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1229   preface or follow a request with an extra CRLF.  If terminating
1230   the request message-body with a line-ending is desired, then the
1231   client &MUST; include the terminating CRLF octets as part of the
1232   message-body length.
1235   When a server listening only for HTTP request messages, or processing
1236   what appears from the start-line to be an HTTP request message,
1237   receives a sequence of octets that does not match the HTTP-message
1238   grammar aside from the robustness exceptions listed above, the
1239   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1242   The normal procedure for parsing an HTTP message is to read the
1243   start-line into a structure, read each header field into a hash
1244   table by field name until the empty line, and then use the parsed
1245   data to determine if a message-body is expected.  If a message-body
1246   has been indicated, then it is read as a stream until an amount
1247   of octets equal to the message-body length is read or the connection
1248   is closed.  Care must be taken to parse an HTTP message as a sequence
1249   of octets in an encoding that is a superset of US-ASCII.  Attempting
1250   to parse HTTP as a stream of Unicode characters in a character encoding
1251   like UTF-16 might introduce security flaws due to the differing ways
1252   that such parsers interpret invalid characters.
1255   HTTP allows the set of defined header fields to be extended without
1256   changing the protocol version (see <xref target="header.field.registration"/>).
1257   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1258   proxy is specifically configured to block or otherwise transform such
1259   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1263<section title="Header Fields" anchor="header.fields">
1264  <x:anchor-alias value="header-field"/>
1265  <x:anchor-alias value="field-content"/>
1266  <x:anchor-alias value="field-name"/>
1267  <x:anchor-alias value="field-value"/>
1268  <x:anchor-alias value="OWS"/>
1270   Each HTTP header field consists of a case-insensitive field name
1271   followed by a colon (":"), optional whitespace, and the field value.
1273<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"/>
1274  <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>
1275  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1276  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1277  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1280   No whitespace is allowed between the header field name and colon. For
1281   security reasons, any request message received containing such whitespace
1282   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1283   &MUST; remove any such whitespace from a response message before
1284   forwarding the message downstream.
1287   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1288   preferred. The field value does not include any leading or trailing white
1289   space: OWS occurring before the first non-whitespace octet of the
1290   field value or after the last non-whitespace octet of the field value
1291   is ignored and &SHOULD; be removed before further processing (as this does
1292   not change the meaning of the header field).
1295   The order in which header fields with differing field names are
1296   received is not significant. However, it is "good practice" to send
1297   header fields that contain control data first, such as Host on
1298   requests and Date on responses, so that implementations can decide
1299   when not to handle a message as early as possible.  A server &MUST;
1300   wait until the entire header section is received before interpreting
1301   a request message, since later header fields might include conditionals,
1302   authentication credentials, or deliberately misleading duplicate
1303   header fields that would impact request processing.
1306   Multiple header fields with the same field name &MUST-NOT; be
1307   sent in a message unless the entire field value for that
1308   header field is defined as a comma-separated list [i.e., #(values)].
1309   Multiple header fields with the same field name can be combined into
1310   one "field-name: field-value" pair, without changing the semantics of the
1311   message, by appending each subsequent field value to the combined
1312   field value in order, separated by a comma. The order in which
1313   header fields with the same field name are received is therefore
1314   significant to the interpretation of the combined field value;
1315   a proxy &MUST-NOT; change the order of these field values when
1316   forwarding a message.
1319  <t>
1320   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1321   practice can occur multiple times, but does not use the list syntax, and
1322   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1323   for details.) Also note that the Set-Cookie2 header field specified in
1324   <xref target="RFC2965"/> does not share this problem.
1325  </t>
1328   Historically, HTTP header field values could be extended over multiple
1329   lines by preceding each extra line with at least one space or horizontal
1330   tab octet (line folding). This specification deprecates such line
1331   folding except within the message/http media type
1332   (<xref target=""/>).
1333   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1334   (i.e., that contain any field-content that matches the obs-fold rule) unless
1335   the message is intended for packaging within the message/http media type.
1336   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1337   obs-fold whitespace with a single SP prior to interpreting the field value
1338   or forwarding the message downstream.
1341   Historically, HTTP has allowed field content with text in the ISO-8859-1
1342   <xref target="ISO-8859-1"/> character encoding and supported other
1343   character sets only through use of <xref target="RFC2047"/> encoding.
1344   In practice, most HTTP header field values use only a subset of the
1345   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1346   header fields &SHOULD; limit their field values to US-ASCII octets.
1347   Recipients &SHOULD; treat other (obs-text) octets in field content as
1348   opaque data.
1350<t anchor="rule.comment">
1351  <x:anchor-alias value="comment"/>
1352  <x:anchor-alias value="ctext"/>
1353   Comments can be included in some HTTP header fields by surrounding
1354   the comment text with parentheses. Comments are only allowed in
1355   fields containing "comment" as part of their field value definition.
1357<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1358  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1359  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1360                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1362<t anchor="rule.quoted-cpair">
1363  <x:anchor-alias value="quoted-cpair"/>
1364   The backslash octet ("\") can be used as a single-octet
1365   quoting mechanism within comment constructs:
1367<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1368  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1371   Senders &SHOULD-NOT; escape octets that do not require escaping
1372   (i.e., other than the backslash octet "\" and the parentheses "(" and
1373   ")").
1376   HTTP does not place a pre-defined limit on the length of header fields,
1377   either in isolation or as a set. A server &MUST; be prepared to receive
1378   request header fields of unbounded length and respond with a 4xx status
1379   code if the received header field(s) would be longer than the server wishes
1380   to handle.
1383   A client that receives response headers that are longer than it wishes to
1384   handle can only treat it as a server error.
1387   Various ad-hoc limitations on header length are found in practice. It is
1388   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1389   combined header fields have 4000 or more octets.
1393<section title="Message Body" anchor="message.body">
1394  <x:anchor-alias value="message-body"/>
1396   The message-body (if any) of an HTTP message is used to carry the
1397   payload body associated with the request or response.
1399<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1400  <x:ref>message-body</x:ref> = *OCTET
1403   The message-body differs from the payload body only when a transfer-coding
1404   has been applied, as indicated by the Transfer-Encoding header field
1405   (<xref target="header.transfer-encoding"/>).  If more than one
1406   Transfer-Encoding header field is present in a message, the multiple
1407   field-values &MUST; be combined into one field-value, according to the
1408   algorithm defined in <xref target="header.fields"/>, before determining
1409   the message-body length.
1412   When one or more transfer-codings are applied to a payload in order to
1413   form the message-body, the Transfer-Encoding header field &MUST; contain
1414   the list of transfer-codings applied. Transfer-Encoding is a property of
1415   the message, not of the payload, and thus &MAY; be added or removed by
1416   any implementation along the request/response chain under the constraints
1417   found in <xref target="transfer.codings"/>.
1420   If a message is received that has multiple Content-Length header fields
1421   (<xref target="header.content-length"/>) with field-values consisting
1422   of the same decimal value, or a single Content-Length header field with
1423   a field value containing a list of identical decimal values (e.g.,
1424   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1425   header fields have been generated or combined by an upstream message
1426   processor, then the recipient &MUST; either reject the message as invalid
1427   or replace the duplicated field-values with a single valid Content-Length
1428   field containing that decimal value prior to determining the message-body
1429   length.
1432   The rules for when a message-body is allowed in a message differ for
1433   requests and responses.
1436   The presence of a message-body in a request is signaled by the
1437   inclusion of a Content-Length or Transfer-Encoding header field in
1438   the request's header fields, even if the request method does not
1439   define any use for a message-body.  This allows the request
1440   message framing algorithm to be independent of method semantics.
1443   For response messages, whether or not a message-body is included with
1444   a message is dependent on both the request method and the response
1445   status code (<xref target="status.code.and.reason.phrase"/>).
1446   Responses to the HEAD request method never include a message-body
1447   because the associated response header fields (e.g., Transfer-Encoding,
1448   Content-Length, etc.) only indicate what their values would have been
1449   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1450   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1451   All other responses do include a message-body, although the body
1452   &MAY; be of zero length.
1455   The length of the message-body is determined by one of the following
1456   (in order of precedence):
1459  <list style="numbers">
1460    <x:lt><t>
1461     Any response to a HEAD request and any response with a status
1462     code of 100-199, 204, or 304 is always terminated by the first
1463     empty line after the header fields, regardless of the header
1464     fields present in the message, and thus cannot contain a message-body.
1465    </t></x:lt>
1466    <x:lt><t>
1467     If a Transfer-Encoding header field is present
1468     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1469     is the final encoding, the message-body length is determined by reading
1470     and decoding the chunked data until the transfer-coding indicates the
1471     data is complete.
1472    </t>
1473    <t>
1474     If a Transfer-Encoding header field is present in a response and the
1475     "chunked" transfer-coding is not the final encoding, the message-body
1476     length is determined by reading the connection until it is closed by
1477     the server.
1478     If a Transfer-Encoding header field is present in a request and the
1479     "chunked" transfer-coding is not the final encoding, the message-body
1480     length cannot be determined reliably; the server &MUST; respond with
1481     the 400 (Bad Request) status code and then close the connection.
1482    </t>
1483    <t>
1484     If a message is received with both a Transfer-Encoding header field
1485     and a Content-Length header field, the Transfer-Encoding overrides
1486     the Content-Length.
1487     Such a message might indicate an attempt to perform request or response
1488     smuggling (bypass of security-related checks on message routing or content)
1489     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1490     be removed, prior to forwarding the message downstream, or replaced with
1491     the real message-body length after the transfer-coding is decoded.
1492    </t></x:lt>
1493    <x:lt><t>
1494     If a message is received without Transfer-Encoding and with either
1495     multiple Content-Length header fields having differing field-values or
1496     a single Content-Length header field having an invalid value, then the
1497     message framing is invalid and &MUST; be treated as an error to
1498     prevent request or response smuggling.
1499     If this is a request message, the server &MUST; respond with
1500     a 400 (Bad Request) status code and then close the connection.
1501     If this is a response message received by a proxy, the proxy
1502     &MUST; discard the received response, send a 502 (Bad Gateway)
1503     status code as its downstream response, and then close the connection.
1504     If this is a response message received by a user-agent, it &MUST; be
1505     treated as an error by discarding the message and closing the connection.
1506    </t></x:lt>
1507    <x:lt><t>
1508     If a valid Content-Length header field
1509     is present without Transfer-Encoding, its decimal value defines the
1510     message-body length in octets.  If the actual number of octets sent in
1511     the message is less than the indicated Content-Length, the recipient
1512     &MUST; consider the message to be incomplete and treat the connection
1513     as no longer usable.
1514     If the actual number of octets sent in the message is more than the indicated
1515     Content-Length, the recipient &MUST; only process the message-body up to the
1516     field value's number of octets; the remainder of the message &MUST; either
1517     be discarded or treated as the next message in a pipeline.  For the sake of
1518     robustness, a user-agent &MAY; attempt to detect and correct such an error
1519     in message framing if it is parsing the response to the last request on
1520     on a connection and the connection has been closed by the server.
1521    </t></x:lt>
1522    <x:lt><t>
1523     If this is a request message and none of the above are true, then the
1524     message-body length is zero (no message-body is present).
1525    </t></x:lt>
1526    <x:lt><t>
1527     Otherwise, this is a response message without a declared message-body
1528     length, so the message-body length is determined by the number of octets
1529     received prior to the server closing the connection.
1530    </t></x:lt>
1531  </list>
1534   Since there is no way to distinguish a successfully completed,
1535   close-delimited message from a partially-received message interrupted
1536   by network failure, implementations &SHOULD; use encoding or
1537   length-delimited messages whenever possible.  The close-delimiting
1538   feature exists primarily for backwards compatibility with HTTP/1.0.
1541   A server &MAY; reject a request that contains a message-body but
1542   not a Content-Length by responding with 411 (Length Required).
1545   Unless a transfer-coding other than "chunked" has been applied,
1546   a client that sends a request containing a message-body &SHOULD;
1547   use a valid Content-Length header field if the message-body length
1548   is known in advance, rather than the "chunked" encoding, since some
1549   existing services respond to "chunked" with a 411 (Length Required)
1550   status code even though they understand the chunked encoding.  This
1551   is typically because such services are implemented via a gateway that
1552   requires a content-length in advance of being called and the server
1553   is unable or unwilling to buffer the entire request before processing.
1556   A client that sends a request containing a message-body &MUST; include a
1557   valid Content-Length header field if it does not know the server will
1558   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1559   of specific user configuration or by remembering the version of a prior
1560   received response.
1563   Request messages that are prematurely terminated, possibly due to a
1564   cancelled connection or a server-imposed time-out exception, &MUST;
1565   result in closure of the connection; sending an HTTP/1.1 error response
1566   prior to closing the connection is &OPTIONAL;.
1567   Response messages that are prematurely terminated, usually by closure
1568   of the connection prior to receiving the expected number of octets or by
1569   failure to decode a transfer-encoded message-body, &MUST; be recorded
1570   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1571   message-body as if it were complete (i.e., some indication must be given
1572   to the user that an error occurred).  Cache requirements for incomplete
1573   responses are defined in &cache-incomplete;.
1576   A server &MUST; read the entire request message-body or close
1577   the connection after sending its response, since otherwise the
1578   remaining data on a persistent connection would be misinterpreted
1579   as the next request.  Likewise,
1580   a client &MUST; read the entire response message-body if it intends
1581   to reuse the same connection for a subsequent request.  Pipelining
1582   multiple requests on a connection is described in <xref target="pipelining"/>.
1586<section title="General Header Fields" anchor="general.header.fields">
1587  <x:anchor-alias value="general-header"/>
1589   There are a few header fields which have general applicability for
1590   both request and response messages, but which do not apply to the
1591   payload being transferred. These header fields apply only to the
1592   message being transmitted.
1594<texttable align="left">
1595  <ttcol>Header Field Name</ttcol>
1596  <ttcol>Defined in...</ttcol>
1598  <c>Connection</c> <c><xref target="header.connection"/></c>
1599  <c>Date</c> <c><xref target=""/></c>
1600  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1601  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1602  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1603  <c>Via</c> <c><xref target="header.via"/></c>
1608<section title="Request" anchor="request">
1609  <x:anchor-alias value="Request"/>
1611   A request message from a client to a server begins with a
1612   Request-Line, followed by zero or more header fields, an empty
1613   line signifying the end of the header block, and an optional
1614   message body.
1616<!--                 Host                      ; should be moved here eventually -->
1617<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1618  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1619                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1620                  <x:ref>CRLF</x:ref>
1621                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1624<section title="Request-Line" anchor="request-line">
1625  <x:anchor-alias value="Request-Line"/>
1627   The Request-Line begins with a method token, followed by a single
1628   space (SP), the request-target, another single space (SP), the
1629   protocol version, and ending with CRLF.
1631<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1632  <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>
1635<section title="Method" anchor="method">
1636  <x:anchor-alias value="Method"/>
1638   The Method token indicates the request method to be performed on the
1639   target resource. The request method is case-sensitive.
1641<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1642  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1646<section title="request-target" anchor="request-target">
1647  <x:anchor-alias value="request-target"/>
1649   The request-target identifies the target resource upon which to apply
1650   the request.  In most cases, the user agent is provided a URI reference
1651   from which it determines an absolute URI for identifying the target
1652   resource.  When a request to the resource is initiated, all or part
1653   of that URI is used to construct the HTTP request-target.
1655<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1656  <x:ref>request-target</x:ref> = "*"
1657                 / <x:ref>absolute-URI</x:ref>
1658                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1659                 / <x:ref>authority</x:ref>
1662   The four options for request-target are dependent on the nature of the
1663   request.
1665<t><iref item="asterisk form (of request-target)"/>
1666   The asterisk "*" form of request-target, which &MUST-NOT; be used
1667   with any request method other than OPTIONS, means that the request
1668   applies to the server as a whole (the listening process) rather than
1669   to a specific named resource at that server.  For example,
1671<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1672OPTIONS * HTTP/1.1
1674<t><iref item="absolute-URI form (of request-target)"/>
1675   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1676   proxy. The proxy is requested to either forward the request or service it
1677   from a valid cache, and then return the response. Note that the proxy &MAY;
1678   forward the request on to another proxy or directly to the server
1679   specified by the absolute-URI. In order to avoid request loops, a
1680   proxy that forwards requests to other proxies &MUST; be able to
1681   recognize and exclude all of its own server names, including
1682   any aliases, local variations, and the numeric IP address. An example
1683   Request-Line would be:
1685<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1686GET HTTP/1.1
1689   To allow for transition to absolute-URIs in all requests in future
1690   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1691   form in requests, even though HTTP/1.1 clients will only generate
1692   them in requests to proxies.
1695   If a proxy receives a host name that is not a fully qualified domain
1696   name, it &MAY; add its domain to the host name it received. If a proxy
1697   receives a fully qualified domain name, the proxy &MUST-NOT; change
1698   the host name.
1700<t><iref item="authority form (of request-target)"/>
1701   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1703<t><iref item="origin form (of request-target)"/>
1704   The most common form of request-target is that used when making
1705   a request to an origin server ("origin form").
1706   In this case, the absolute path and query components of the URI
1707   &MUST; be transmitted as the request-target, and the authority component
1708   &MUST; be transmitted in a Host header field. For example, a client wishing
1709   to retrieve a representation of the resource, as identified above,
1710   directly from the origin server would open (or reuse) a TCP connection
1711   to port 80 of the host "" and send the lines:
1713<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1714GET /pub/WWW/TheProject.html HTTP/1.1
1718   followed by the remainder of the Request. Note that the origin form
1719   of request-target always starts with an absolute path; if the target
1720   resource's URI path is empty, then an absolute path of "/" &MUST; be
1721   provided in the request-target.
1724   If a proxy receives an OPTIONS request with an absolute-URI form of
1725   request-target in which the URI has an empty path and no query component,
1726   then the last proxy on the request chain &MUST; use a request-target
1727   of "*" when it forwards the request to the indicated origin server.
1730   For example, the request
1731</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1735  would be forwarded by the final proxy as
1736</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1737OPTIONS * HTTP/1.1
1741   after connecting to port 8001 of host "".
1745   The request-target is transmitted in the format specified in
1746   <xref target="http.uri"/>. If the request-target is percent-encoded
1747   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1748   &MUST; decode the request-target in order to
1749   properly interpret the request. Servers &SHOULD; respond to invalid
1750   request-targets with an appropriate status code.
1753   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1754   received request-target when forwarding it to the next inbound server,
1755   except as noted above to replace a null path-absolute with "/" or "*".
1758  <t>
1759    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1760    meaning of the request when the origin server is improperly using
1761    a non-reserved URI character for a reserved purpose.  Implementors
1762    need to be aware that some pre-HTTP/1.1 proxies have been known to
1763    rewrite the request-target.
1764  </t>
1767   HTTP does not place a pre-defined limit on the length of a request-target.
1768   A server &MUST; be prepared to receive URIs of unbounded length and
1769   respond with the 414 (URI Too Long) status code if the received
1770   request-target would be longer than the server wishes to handle
1771   (see &status-414;).
1774   Various ad-hoc limitations on request-target length are found in practice.
1775   It is &RECOMMENDED; that all HTTP senders and recipients support
1776   request-target lengths of 8000 or more octets.
1779  <t>
1780    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1781    are not part of the request-target and thus will not be transmitted
1782    in an HTTP request.
1783  </t>
1788<section title="The Resource Identified by a Request" anchor="">
1790   The exact resource identified by an Internet request is determined by
1791   examining both the request-target and the Host header field.
1794   An origin server that does not allow resources to differ by the
1795   requested host &MAY; ignore the Host header field value when
1796   determining the resource identified by an HTTP/1.1 request. (But see
1797   <xref target=""/>
1798   for other requirements on Host support in HTTP/1.1.)
1801   An origin server that does differentiate resources based on the host
1802   requested (sometimes referred to as virtual hosts or vanity host
1803   names) &MUST; use the following rules for determining the requested
1804   resource on an HTTP/1.1 request:
1805  <list style="numbers">
1806    <t>If request-target is an absolute-URI, the host is part of the
1807     request-target. Any Host header field value in the request &MUST; be
1808     ignored.</t>
1809    <t>If the request-target is not an absolute-URI, and the request includes
1810     a Host header field, the host is determined by the Host header
1811     field value.</t>
1812    <t>If the host as determined by rule 1 or 2 is not a valid host on
1813     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1814  </list>
1817   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1818   attempt to use heuristics (e.g., examination of the URI path for
1819   something unique to a particular host) in order to determine what
1820   exact resource is being requested.
1824<section title="Effective Request URI" anchor="effective.request.uri">
1825  <iref primary="true" item="effective request URI"/>
1826  <iref primary="true" item="target resource"/>
1828   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1829   for the target resource; instead, the URI needs to be inferred from the
1830   request-target, Host header field, and connection context. The result of
1831   this process is called the "effective request URI".  The "target resource"
1832   is the resource identified by the effective request URI.
1835   If the request-target is an absolute-URI, then the effective request URI is
1836   the request-target.
1839   If the request-target uses the path-absolute form or the asterisk form,
1840   and the Host header field is present, then the effective request URI is
1841   constructed by concatenating
1844  <list style="symbols">
1845    <t>
1846      the scheme name: "http" if the request was received over an insecure
1847      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1848      connection,
1849    </t>
1850    <t>
1851      the octet sequence "://",
1852    </t>
1853    <t>
1854      the authority component, as specified in the Host header field
1855      (<xref target=""/>), and
1856    </t>
1857    <t>
1858      the request-target obtained from the Request-Line, unless the
1859      request-target is just the asterisk "*".
1860    </t>
1861  </list>
1864   If the request-target uses the path-absolute form or the asterisk form,
1865   and the Host header field is not present, then the effective request URI is
1866   undefined.
1869   Otherwise, when request-target uses the authority form, the effective
1870   request URI is undefined.
1874   Example 1: the effective request URI for the message
1876<artwork type="example" x:indent-with="  ">
1877GET /pub/WWW/TheProject.html HTTP/1.1
1881  (received over an insecure TCP connection) is "http", plus "://", plus the
1882  authority component "", plus the request-target
1883  "/pub/WWW/TheProject.html", thus
1884  "".
1889   Example 2: the effective request URI for the message
1891<artwork type="example" x:indent-with="  ">
1892OPTIONS * HTTP/1.1
1896  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1897  authority component "", thus "".
1901   Effective request URIs are compared using the rules described in
1902   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1903   be treated as equivalent to an absolute path of "/".
1910<section title="Response" anchor="response">
1911  <x:anchor-alias value="Response"/>
1913   After receiving and interpreting a request message, a server responds
1914   with an HTTP response message.
1916<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1917  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1918                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1919                  <x:ref>CRLF</x:ref>
1920                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1923<section title="Status-Line" anchor="status-line">
1924  <x:anchor-alias value="Status-Line"/>
1926   The first line of a Response message is the Status-Line, consisting
1927   of the protocol version, a space (SP), the status code, another space,
1928   a possibly-empty textual phrase describing the status code, and
1929   ending with CRLF.
1931<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1932  <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>
1935<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1936  <x:anchor-alias value="Reason-Phrase"/>
1937  <x:anchor-alias value="Status-Code"/>
1939   The Status-Code element is a 3-digit integer result code of the
1940   attempt to understand and satisfy the request. These codes are fully
1941   defined in &status-codes;.  The Reason Phrase exists for the sole
1942   purpose of providing a textual description associated with the numeric
1943   status code, out of deference to earlier Internet application protocols
1944   that were more frequently used with interactive text clients.
1945   A client &SHOULD; ignore the content of the Reason Phrase.
1948   The first digit of the Status-Code defines the class of response. The
1949   last two digits do not have any categorization role. There are 5
1950   values for the first digit:
1951  <list style="symbols">
1952    <t>
1953      1xx: Informational - Request received, continuing process
1954    </t>
1955    <t>
1956      2xx: Success - The action was successfully received,
1957        understood, and accepted
1958    </t>
1959    <t>
1960      3xx: Redirection - Further action must be taken in order to
1961        complete the request
1962    </t>
1963    <t>
1964      4xx: Client Error - The request contains bad syntax or cannot
1965        be fulfilled
1966    </t>
1967    <t>
1968      5xx: Server Error - The server failed to fulfill an apparently
1969        valid request
1970    </t>
1971  </list>
1973<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1974  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1975  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1983<section title="Protocol Parameters" anchor="protocol.parameters">
1985<section title="Date/Time Formats: Full Date" anchor="">
1986  <x:anchor-alias value="HTTP-date"/>
1988   HTTP applications have historically allowed three different formats
1989   for date/time stamps. However, the preferred format is a fixed-length subset
1990   of that defined by <xref target="RFC1123"/>:
1992<figure><artwork type="example" x:indent-with="  ">
1993Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1996   The other formats are described here only for compatibility with obsolete
1997   implementations.
1999<figure><artwork type="example" x:indent-with="  ">
2000Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2001Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2004   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2005   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2006   only generate the RFC 1123 format for representing HTTP-date values
2007   in header fields. See <xref target="tolerant.applications"/> for further information.
2010   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2011   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2012   equal to UTC (Coordinated Universal Time). This is indicated in the
2013   first two formats by the inclusion of "GMT" as the three-letter
2014   abbreviation for time zone, and &MUST; be assumed when reading the
2015   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2016   additional whitespace beyond that specifically included as SP in the
2017   grammar.
2019<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2020  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2022<t anchor="">
2023  <x:anchor-alias value="rfc1123-date"/>
2024  <x:anchor-alias value="time-of-day"/>
2025  <x:anchor-alias value="hour"/>
2026  <x:anchor-alias value="minute"/>
2027  <x:anchor-alias value="second"/>
2028  <x:anchor-alias value="day-name"/>
2029  <x:anchor-alias value="day"/>
2030  <x:anchor-alias value="month"/>
2031  <x:anchor-alias value="year"/>
2032  <x:anchor-alias value="GMT"/>
2033  Preferred format:
2035<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"/>
2036  <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>
2037  ; fixed length subset of the format defined in
2038  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2040  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2041               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2042               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2043               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2044               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2045               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2046               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2048  <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>
2049               ; e.g., 02 Jun 1982
2051  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2052  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2053               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2054               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2055               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2056               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2057               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2058               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2059               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2060               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2061               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2062               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2063               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2064  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2066  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2068  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2069                 ; 00:00:00 - 23:59:59
2071  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2072  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2073  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2076  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2077  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2078  same as those defined for the RFC 5322 constructs
2079  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2081<t anchor="">
2082  <x:anchor-alias value="obs-date"/>
2083  <x:anchor-alias value="rfc850-date"/>
2084  <x:anchor-alias value="asctime-date"/>
2085  <x:anchor-alias value="date1"/>
2086  <x:anchor-alias value="date2"/>
2087  <x:anchor-alias value="date3"/>
2088  <x:anchor-alias value="rfc1123-date"/>
2089  <x:anchor-alias value="day-name-l"/>
2090  Obsolete formats:
2092<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2093  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2095<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2096  <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>
2097  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2098                 ; day-month-year (e.g., 02-Jun-82)
2100  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2101         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2102         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2103         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2104         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2105         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2106         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2108<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2109  <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>
2110  <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> ))
2111                 ; month day (e.g., Jun  2)
2114  <t>
2115    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2116    accepting date values that might have been sent by non-HTTP
2117    applications, as is sometimes the case when retrieving or posting
2118    messages via proxies/gateways to SMTP or NNTP.
2119  </t>
2122  <t>
2123    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2124    to their usage within the protocol stream. Clients and servers are
2125    not required to use these formats for user presentation, request
2126    logging, etc.
2127  </t>
2131<section title="Transfer Codings" anchor="transfer.codings">
2132  <x:anchor-alias value="transfer-coding"/>
2133  <x:anchor-alias value="transfer-extension"/>
2135   Transfer-coding values are used to indicate an encoding
2136   transformation that has been, can be, or might need to be applied to a
2137   payload body in order to ensure "safe transport" through the network.
2138   This differs from a content coding in that the transfer-coding is a
2139   property of the message rather than a property of the representation
2140   that is being transferred.
2142<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2143  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2144                          / "compress" ; <xref target="compress.coding"/>
2145                          / "deflate" ; <xref target="deflate.coding"/>
2146                          / "gzip" ; <xref target="gzip.coding"/>
2147                          / <x:ref>transfer-extension</x:ref>
2148  <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> )
2150<t anchor="rule.parameter">
2151  <x:anchor-alias value="attribute"/>
2152  <x:anchor-alias value="transfer-parameter"/>
2153  <x:anchor-alias value="value"/>
2154   Parameters are in the form of attribute/value pairs.
2156<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"/>
2157  <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>
2158  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2159  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2162   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2163   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2164   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2167   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2168   MIME, which were designed to enable safe transport of binary data over a
2169   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2170   However, safe transport
2171   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2172   the only unsafe characteristic of message-bodies is the difficulty in
2173   determining the exact message body length (<xref target="message.body"/>),
2174   or the desire to encrypt data over a shared transport.
2177   A server that receives a request message with a transfer-coding it does
2178   not understand &SHOULD; respond with 501 (Not Implemented) and then
2179   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2180   client.
2183<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2184  <iref item="chunked (Coding Format)"/>
2185  <iref item="Coding Format" subitem="chunked"/>
2186  <x:anchor-alias value="chunk"/>
2187  <x:anchor-alias value="Chunked-Body"/>
2188  <x:anchor-alias value="chunk-data"/>
2189  <x:anchor-alias value="chunk-ext"/>
2190  <x:anchor-alias value="chunk-ext-name"/>
2191  <x:anchor-alias value="chunk-ext-val"/>
2192  <x:anchor-alias value="chunk-size"/>
2193  <x:anchor-alias value="last-chunk"/>
2194  <x:anchor-alias value="trailer-part"/>
2195  <x:anchor-alias value="quoted-str-nf"/>
2196  <x:anchor-alias value="qdtext-nf"/>
2198   The chunked encoding modifies the body of a message in order to
2199   transfer it as a series of chunks, each with its own size indicator,
2200   followed by an &OPTIONAL; trailer containing header fields. This
2201   allows dynamically produced content to be transferred along with the
2202   information necessary for the recipient to verify that it has
2203   received the full message.
2205<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"/>
2206  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2207                   <x:ref>last-chunk</x:ref>
2208                   <x:ref>trailer-part</x:ref>
2209                   <x:ref>CRLF</x:ref>
2211  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2212                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2213  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2214  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2216  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2217                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2218  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2219  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2220  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2221  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2223  <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>
2224                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2225  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2226                 ; <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>
2229   The chunk-size field is a string of hex digits indicating the size of
2230   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2231   zero, followed by the trailer, which is terminated by an empty line.
2234   The trailer allows the sender to include additional HTTP header
2235   fields at the end of the message. The Trailer header field can be
2236   used to indicate which header fields are included in a trailer (see
2237   <xref target="header.trailer"/>).
2240   A server using chunked transfer-coding in a response &MUST-NOT; use the
2241   trailer for any header fields unless at least one of the following is
2242   true:
2243  <list style="numbers">
2244    <t>the request included a TE header field that indicates "trailers" is
2245     acceptable in the transfer-coding of the  response, as described in
2246     <xref target="header.te"/>; or,</t>
2248    <t>the trailer fields consist entirely of optional metadata, and the
2249    recipient could use the message (in a manner acceptable to the server where
2250    the field originated) without receiving it. In other words, the server that
2251    generated the header (often but not always the origin server) is willing to
2252    accept the possibility that the trailer fields might be silently discarded
2253    along the path to the client.</t>
2254  </list>
2257   This requirement prevents an interoperability failure when the
2258   message is being received by an HTTP/1.1 (or later) proxy and
2259   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2260   compliance with the protocol would have necessitated a possibly
2261   infinite buffer on the proxy.
2264   A process for decoding the "chunked" transfer-coding
2265   can be represented in pseudo-code as:
2267<figure><artwork type="code">
2268  length := 0
2269  read chunk-size, chunk-ext (if any) and CRLF
2270  while (chunk-size &gt; 0) {
2271     read chunk-data and CRLF
2272     append chunk-data to decoded-body
2273     length := length + chunk-size
2274     read chunk-size and CRLF
2275  }
2276  read header-field
2277  while (header-field not empty) {
2278     append header-field to existing header fields
2279     read header-field
2280  }
2281  Content-Length := length
2282  Remove "chunked" from Transfer-Encoding
2285   All HTTP/1.1 applications &MUST; be able to receive and decode the
2286   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2287   they do not understand.
2290   Since "chunked" is the only transfer-coding required to be understood
2291   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2292   on a persistent connection.  Whenever a transfer-coding is applied to
2293   a payload body in a request, the final transfer-coding applied &MUST;
2294   be "chunked".  If a transfer-coding is applied to a response payload
2295   body, then either the final transfer-coding applied &MUST; be "chunked"
2296   or the message &MUST; be terminated by closing the connection. When the
2297   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2298   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2299   be applied more than once in a message-body.
2303<section title="Compression Codings" anchor="compression.codings">
2305   The codings defined below can be used to compress the payload of a
2306   message.
2309   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2310   is not desirable and is discouraged for future encodings. Their
2311   use here is representative of historical practice, not good
2312   design.
2315   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2316   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2317   equivalent to "gzip" and "compress" respectively.
2320<section title="Compress Coding" anchor="compress.coding">
2321<iref item="compress (Coding Format)"/>
2322<iref item="Coding Format" subitem="compress"/>
2324   The "compress" format is produced by the common UNIX file compression
2325   program "compress". This format is an adaptive Lempel-Ziv-Welch
2326   coding (LZW).
2330<section title="Deflate Coding" anchor="deflate.coding">
2331<iref item="deflate (Coding Format)"/>
2332<iref item="Coding Format" subitem="deflate"/>
2334   The "deflate" format is defined as the "deflate" compression mechanism
2335   (described in <xref target="RFC1951"/>) used inside the "zlib"
2336   data format (<xref target="RFC1950"/>).
2339  <t>
2340    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2341    compressed data without the zlib wrapper.
2342   </t>
2346<section title="Gzip Coding" anchor="gzip.coding">
2347<iref item="gzip (Coding Format)"/>
2348<iref item="Coding Format" subitem="gzip"/>
2350   The "gzip" format is produced by the file compression program
2351   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2352   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2358<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2360   The HTTP Transfer Coding Registry defines the name space for the transfer
2361   coding names.
2364   Registrations &MUST; include the following fields:
2365   <list style="symbols">
2366     <t>Name</t>
2367     <t>Description</t>
2368     <t>Pointer to specification text</t>
2369   </list>
2372   Names of transfer codings &MUST-NOT; overlap with names of content codings
2373   (&content-codings;), unless the encoding transformation is identical (as it
2374   is the case for the compression codings defined in
2375   <xref target="compression.codings"/>).
2378   Values to be added to this name space require a specification
2379   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2380   conform to the purpose of transfer coding defined in this section.
2383   The registry itself is maintained at
2384   <eref target=""/>.
2389<section title="Product Tokens" anchor="product.tokens">
2390  <x:anchor-alias value="product"/>
2391  <x:anchor-alias value="product-version"/>
2393   Product tokens are used to allow communicating applications to
2394   identify themselves by software name and version. Most fields using
2395   product tokens also allow sub-products which form a significant part
2396   of the application to be listed, separated by whitespace. By
2397   convention, the products are listed in order of their significance
2398   for identifying the application.
2400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2401  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2402  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2405   Examples:
2407<figure><artwork type="example">
2408  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2409  Server: Apache/0.8.4
2412   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2413   used for advertising or other non-essential information. Although any
2414   token octet &MAY; appear in a product-version, this token &SHOULD;
2415   only be used for a version identifier (i.e., successive versions of
2416   the same product &SHOULD; only differ in the product-version portion of
2417   the product value).
2421<section title="Quality Values" anchor="quality.values">
2422  <x:anchor-alias value="qvalue"/>
2424   Both transfer codings (TE request header field, <xref target="header.te"/>)
2425   and content negotiation (&content.negotiation;) use short "floating point"
2426   numbers to indicate the relative importance ("weight") of various
2427   negotiable parameters.  A weight is normalized to a real number in
2428   the range 0 through 1, where 0 is the minimum and 1 the maximum
2429   value. If a parameter has a quality value of 0, then content with
2430   this parameter is "not acceptable" for the client. HTTP/1.1
2431   applications &MUST-NOT; generate more than three digits after the
2432   decimal point. User configuration of these values &SHOULD; also be
2433   limited in this fashion.
2435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2436  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2437                 / ( "1" [ "." 0*3("0") ] )
2440  <t>
2441     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2442     relative degradation in desired quality.
2443  </t>
2449<section title="Connections" anchor="connections">
2451<section title="Persistent Connections" anchor="persistent.connections">
2453<section title="Purpose" anchor="persistent.purpose">
2455   Prior to persistent connections, a separate TCP connection was
2456   established for each request, increasing the load on HTTP servers
2457   and causing congestion on the Internet. The use of inline images and
2458   other associated data often requires a client to make multiple
2459   requests of the same server in a short amount of time. Analysis of
2460   these performance problems and results from a prototype
2461   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2462   measurements of actual HTTP/1.1 implementations show good
2463   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2464   T/TCP <xref target="Tou1998"/>.
2467   Persistent HTTP connections have a number of advantages:
2468  <list style="symbols">
2469      <t>
2470        By opening and closing fewer TCP connections, CPU time is saved
2471        in routers and hosts (clients, servers, proxies, gateways,
2472        tunnels, or caches), and memory used for TCP protocol control
2473        blocks can be saved in hosts.
2474      </t>
2475      <t>
2476        HTTP requests and responses can be pipelined on a connection.
2477        Pipelining allows a client to make multiple requests without
2478        waiting for each response, allowing a single TCP connection to
2479        be used much more efficiently, with much lower elapsed time.
2480      </t>
2481      <t>
2482        Network congestion is reduced by reducing the number of packets
2483        caused by TCP opens, and by allowing TCP sufficient time to
2484        determine the congestion state of the network.
2485      </t>
2486      <t>
2487        Latency on subsequent requests is reduced since there is no time
2488        spent in TCP's connection opening handshake.
2489      </t>
2490      <t>
2491        HTTP can evolve more gracefully, since errors can be reported
2492        without the penalty of closing the TCP connection. Clients using
2493        future versions of HTTP might optimistically try a new feature,
2494        but if communicating with an older server, retry with old
2495        semantics after an error is reported.
2496      </t>
2497    </list>
2500   HTTP implementations &SHOULD; implement persistent connections.
2504<section title="Overall Operation" anchor="persistent.overall">
2506   A significant difference between HTTP/1.1 and earlier versions of
2507   HTTP is that persistent connections are the default behavior of any
2508   HTTP connection. That is, unless otherwise indicated, the client
2509   &SHOULD; assume that the server will maintain a persistent connection,
2510   even after error responses from the server.
2513   Persistent connections provide a mechanism by which a client and a
2514   server can signal the close of a TCP connection. This signaling takes
2515   place using the Connection header field (<xref target="header.connection"/>). Once a close
2516   has been signaled, the client &MUST-NOT; send any more requests on that
2517   connection.
2520<section title="Negotiation" anchor="persistent.negotiation">
2522   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2523   maintain a persistent connection unless a Connection header field including
2524   the connection-token "close" was sent in the request. If the server
2525   chooses to close the connection immediately after sending the
2526   response, it &SHOULD; send a Connection header field including the
2527   connection-token "close".
2530   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2531   decide to keep it open based on whether the response from a server
2532   contains a Connection header field with the connection-token close. In case
2533   the client does not want to maintain a connection for more than that
2534   request, it &SHOULD; send a Connection header field including the
2535   connection-token close.
2538   If either the client or the server sends the close token in the
2539   Connection header field, that request becomes the last one for the
2540   connection.
2543   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2544   maintained for HTTP versions less than 1.1 unless it is explicitly
2545   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2546   compatibility with HTTP/1.0 clients.
2549   In order to remain persistent, all messages on the connection &MUST;
2550   have a self-defined message length (i.e., one not defined by closure
2551   of the connection), as described in <xref target="message.body"/>.
2555<section title="Pipelining" anchor="pipelining">
2557   A client that supports persistent connections &MAY; "pipeline" its
2558   requests (i.e., send multiple requests without waiting for each
2559   response). A server &MUST; send its responses to those requests in the
2560   same order that the requests were received.
2563   Clients which assume persistent connections and pipeline immediately
2564   after connection establishment &SHOULD; be prepared to retry their
2565   connection if the first pipelined attempt fails. If a client does
2566   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2567   persistent. Clients &MUST; also be prepared to resend their requests if
2568   the server closes the connection before sending all of the
2569   corresponding responses.
2572   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2573   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2574   premature termination of the transport connection could lead to
2575   indeterminate results. A client wishing to send a non-idempotent
2576   request &SHOULD; wait to send that request until it has received the
2577   response status line for the previous request.
2582<section title="Proxy Servers" anchor="persistent.proxy">
2584   It is especially important that proxies correctly implement the
2585   properties of the Connection header field as specified in <xref target="header.connection"/>.
2588   The proxy server &MUST; signal persistent connections separately with
2589   its clients and the origin servers (or other proxy servers) that it
2590   connects to. Each persistent connection applies to only one transport
2591   link.
2594   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2595   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2596   for information and discussion of the problems with the Keep-Alive header field
2597   implemented by many HTTP/1.0 clients).
2600<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2602  <cref anchor="TODO-end-to-end" source="jre">
2603    Restored from <eref target=""/>.
2604    See also <eref target=""/>.
2605  </cref>
2608   For the purpose of defining the behavior of caches and non-caching
2609   proxies, we divide HTTP header fields into two categories:
2610  <list style="symbols">
2611      <t>End-to-end header fields, which are  transmitted to the ultimate
2612        recipient of a request or response. End-to-end header fields in
2613        responses MUST be stored as part of a cache entry and &MUST; be
2614        transmitted in any response formed from a cache entry.</t>
2616      <t>Hop-by-hop header fields, which are meaningful only for a single
2617        transport-level connection, and are not stored by caches or
2618        forwarded by proxies.</t>
2619  </list>
2622   The following HTTP/1.1 header fields are hop-by-hop header fields:
2623  <list style="symbols">
2624      <t>Connection</t>
2625      <t>Keep-Alive</t>
2626      <t>Proxy-Authenticate</t>
2627      <t>Proxy-Authorization</t>
2628      <t>TE</t>
2629      <t>Trailer</t>
2630      <t>Transfer-Encoding</t>
2631      <t>Upgrade</t>
2632  </list>
2635   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2638   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2639   (<xref target="header.connection"/>).
2643<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2645  <cref anchor="TODO-non-mod-headers" source="jre">
2646    Restored from <eref target=""/>.
2647    See also <eref target=""/>.
2648  </cref>
2651   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2652   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2653   modify an end-to-end header field unless the definition of that header field requires
2654   or specifically allows that.
2657   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2658   request or response, and it &MUST-NOT; add any of these fields if not
2659   already present:
2660  <list style="symbols">
2661    <t>Allow</t>
2662    <t>Content-Location</t>
2663    <t>Content-MD5</t>
2664    <t>ETag</t>
2665    <t>Last-Modified</t>
2666    <t>Server</t>
2667  </list>
2670   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2671   response:
2672  <list style="symbols">
2673    <t>Expires</t>
2674  </list>
2677   but it &MAY; add any of these fields if not already present. If an
2678   Expires header field is added, it &MUST; be given a field-value identical to
2679   that of the Date header field in that response.
2682   A proxy &MUST-NOT; modify or add any of the following fields in a
2683   message that contains the no-transform cache-control directive, or in
2684   any request:
2685  <list style="symbols">
2686    <t>Content-Encoding</t>
2687    <t>Content-Range</t>
2688    <t>Content-Type</t>
2689  </list>
2692   A transforming proxy &MAY; modify or add these fields to a message
2693   that does not include no-transform, but if it does so, it &MUST; add a
2694   Warning 214 (Transformation applied) if one does not already appear
2695   in the message (see &header-warning;).
2698  <t>
2699    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2700    cause authentication failures if stronger authentication
2701    mechanisms are introduced in later versions of HTTP. Such
2702    authentication mechanisms &MAY; rely on the values of header fields
2703    not listed here.
2704  </t>
2707   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2708   though it &MAY; change the message-body through application or removal
2709   of a transfer-coding (<xref target="transfer.codings"/>).
2715<section title="Practical Considerations" anchor="persistent.practical">
2717   Servers will usually have some time-out value beyond which they will
2718   no longer maintain an inactive connection. Proxy servers might make
2719   this a higher value since it is likely that the client will be making
2720   more connections through the same server. The use of persistent
2721   connections places no requirements on the length (or existence) of
2722   this time-out for either the client or the server.
2725   When a client or server wishes to time-out it &SHOULD; issue a graceful
2726   close on the transport connection. Clients and servers &SHOULD; both
2727   constantly watch for the other side of the transport close, and
2728   respond to it as appropriate. If a client or server does not detect
2729   the other side's close promptly it could cause unnecessary resource
2730   drain on the network.
2733   A client, server, or proxy &MAY; close the transport connection at any
2734   time. For example, a client might have started to send a new request
2735   at the same time that the server has decided to close the "idle"
2736   connection. From the server's point of view, the connection is being
2737   closed while it was idle, but from the client's point of view, a
2738   request is in progress.
2741   This means that clients, servers, and proxies &MUST; be able to recover
2742   from asynchronous close events. Client software &SHOULD; reopen the
2743   transport connection and retransmit the aborted sequence of requests
2744   without user interaction so long as the request sequence is
2745   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2746   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2747   human operator the choice of retrying the request(s). Confirmation by
2748   user-agent software with semantic understanding of the application
2749   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2750   be repeated if the second sequence of requests fails.
2753   Servers &SHOULD; always respond to at least one request per connection,
2754   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2755   middle of transmitting a response, unless a network or client failure
2756   is suspected.
2759   Clients (including proxies) &SHOULD; limit the number of simultaneous
2760   connections that they maintain to a given server (including proxies).
2763   Previous revisions of HTTP gave a specific number of connections as a
2764   ceiling, but this was found to be impractical for many applications. As a
2765   result, this specification does not mandate a particular maximum number of
2766   connections, but instead encourages clients to be conservative when opening
2767   multiple connections.
2770   In particular, while using multiple connections avoids the "head-of-line
2771   blocking" problem (whereby a request that takes significant server-side
2772   processing and/or has a large payload can block subsequent requests on the
2773   same connection), each connection used consumes server resources (sometimes
2774   significantly), and furthermore using multiple connections can cause
2775   undesirable side effects in congested networks.
2778   Note that servers might reject traffic that they deem abusive, including an
2779   excessive number of connections from a client.
2784<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2786<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2788   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2789   flow control mechanisms to resolve temporary overloads, rather than
2790   terminating connections with the expectation that clients will retry.
2791   The latter technique can exacerbate network congestion.
2795<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2797   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2798   the network connection for an error status code while it is transmitting
2799   the request. If the client sees an error status code, it &SHOULD;
2800   immediately cease transmitting the body. If the body is being sent
2801   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2802   empty trailer &MAY; be used to prematurely mark the end of the message.
2803   If the body was preceded by a Content-Length header field, the client &MUST;
2804   close the connection.
2808<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2810   The purpose of the 100 (Continue) status code (see &status-100;) is to
2811   allow a client that is sending a request message with a request body
2812   to determine if the origin server is willing to accept the request
2813   (based on the request header fields) before the client sends the request
2814   body. In some cases, it might either be inappropriate or highly
2815   inefficient for the client to send the body if the server will reject
2816   the message without looking at the body.
2819   Requirements for HTTP/1.1 clients:
2820  <list style="symbols">
2821    <t>
2822        If a client will wait for a 100 (Continue) response before
2823        sending the request body, it &MUST; send an Expect header
2824        field (&header-expect;) with the "100-continue" expectation.
2825    </t>
2826    <t>
2827        A client &MUST-NOT; send an Expect header field (&header-expect;)
2828        with the "100-continue" expectation if it does not intend
2829        to send a request body.
2830    </t>
2831  </list>
2834   Because of the presence of older implementations, the protocol allows
2835   ambiguous situations in which a client might send "Expect: 100-continue"
2836   without receiving either a 417 (Expectation Failed)
2837   or a 100 (Continue) status code. Therefore, when a client sends this
2838   header field to an origin server (possibly via a proxy) from which it
2839   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2840   wait for an indefinite period before sending the request body.
2843   Requirements for HTTP/1.1 origin servers:
2844  <list style="symbols">
2845    <t> Upon receiving a request which includes an Expect header
2846        field with the "100-continue" expectation, an origin server &MUST;
2847        either respond with 100 (Continue) status code and continue to read
2848        from the input stream, or respond with a final status code. The
2849        origin server &MUST-NOT; wait for the request body before sending
2850        the 100 (Continue) response. If it responds with a final status
2851        code, it &MAY; close the transport connection or it &MAY; continue
2852        to read and discard the rest of the request.  It &MUST-NOT;
2853        perform the request method if it returns a final status code.
2854    </t>
2855    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2856        the request message does not include an Expect header
2857        field with the "100-continue" expectation, and &MUST-NOT; send a
2858        100 (Continue) response if such a request comes from an HTTP/1.0
2859        (or earlier) client. There is an exception to this rule: for
2860        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2861        status code in response to an HTTP/1.1 PUT or POST request that does
2862        not include an Expect header field with the "100-continue"
2863        expectation. This exception, the purpose of which is
2864        to minimize any client processing delays associated with an
2865        undeclared wait for 100 (Continue) status code, applies only to
2866        HTTP/1.1 requests, and not to requests with any other HTTP-version
2867        value.
2868    </t>
2869    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2870        already received some or all of the request body for the
2871        corresponding request.
2872    </t>
2873    <t> An origin server that sends a 100 (Continue) response &MUST;
2874    ultimately send a final status code, once the request body is
2875        received and processed, unless it terminates the transport
2876        connection prematurely.
2877    </t>
2878    <t> If an origin server receives a request that does not include an
2879        Expect header field with the "100-continue" expectation,
2880        the request includes a request body, and the server responds
2881        with a final status code before reading the entire request body
2882        from the transport connection, then the server &SHOULD-NOT;  close
2883        the transport connection until it has read the entire request,
2884        or until the client closes the connection. Otherwise, the client
2885        might not reliably receive the response message. However, this
2886        requirement is not be construed as preventing a server from
2887        defending itself against denial-of-service attacks, or from
2888        badly broken client implementations.
2889      </t>
2890    </list>
2893   Requirements for HTTP/1.1 proxies:
2894  <list style="symbols">
2895    <t> If a proxy receives a request that includes an Expect header
2896        field with the "100-continue" expectation, and the proxy
2897        either knows that the next-hop server complies with HTTP/1.1 or
2898        higher, or does not know the HTTP version of the next-hop
2899        server, it &MUST; forward the request, including the Expect header
2900        field.
2901    </t>
2902    <t> If the proxy knows that the version of the next-hop server is
2903        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2904        respond with a 417 (Expectation Failed) status code.
2905    </t>
2906    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2907        numbers received from recently-referenced next-hop servers.
2908    </t>
2909    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2910        request message was received from an HTTP/1.0 (or earlier)
2911        client and did not include an Expect header field with
2912        the "100-continue" expectation. This requirement overrides the
2913        general rule for forwarding of 1xx responses (see &status-1xx;).
2914    </t>
2915  </list>
2919<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2921   If an HTTP/1.1 client sends a request which includes a request body,
2922   but which does not include an Expect header field with the
2923   "100-continue" expectation, and if the client is not directly
2924   connected to an HTTP/1.1 origin server, and if the client sees the
2925   connection close before receiving a status line from the server, the
2926   client &SHOULD; retry the request.  If the client does retry this
2927   request, it &MAY; use the following "binary exponential backoff"
2928   algorithm to be assured of obtaining a reliable response:
2929  <list style="numbers">
2930    <t>
2931      Initiate a new connection to the server
2932    </t>
2933    <t>
2934      Transmit the request-line, header fields, and the CRLF that
2935      indicates the end of header fields.
2936    </t>
2937    <t>
2938      Initialize a variable R to the estimated round-trip time to the
2939         server (e.g., based on the time it took to establish the
2940         connection), or to a constant value of 5 seconds if the round-trip
2941         time is not available.
2942    </t>
2943    <t>
2944       Compute T = R * (2**N), where N is the number of previous
2945         retries of this request.
2946    </t>
2947    <t>
2948       Wait either for an error response from the server, or for T
2949         seconds (whichever comes first)
2950    </t>
2951    <t>
2952       If no error response is received, after T seconds transmit the
2953         body of the request.
2954    </t>
2955    <t>
2956       If client sees that the connection is closed prematurely,
2957         repeat from step 1 until the request is accepted, an error
2958         response is received, or the user becomes impatient and
2959         terminates the retry process.
2960    </t>
2961  </list>
2964   If at any point an error status code is received, the client
2965  <list style="symbols">
2966      <t>&SHOULD-NOT;  continue and</t>
2968      <t>&SHOULD; close the connection if it has not completed sending the
2969        request message.</t>
2970    </list>
2977<section title="Miscellaneous notes that might disappear" anchor="misc">
2978<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2980   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2984<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2986   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2990<section title="Interception of HTTP for access control" anchor="http.intercept">
2992   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2996<section title="Use of HTTP by other protocols" anchor="http.others">
2998   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2999   Extensions of HTTP like WebDAV.</cref>
3003<section title="Use of HTTP by media type specification" anchor="">
3005   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3010<section title="Header Field Definitions" anchor="header.field.definitions">
3012   This section defines the syntax and semantics of HTTP header fields
3013   related to message framing and transport protocols.
3016<section title="Connection" anchor="header.connection">
3017  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3018  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3019  <x:anchor-alias value="Connection"/>
3020  <x:anchor-alias value="connection-token"/>
3022   The "Connection" header field allows the sender to specify
3023   options that are desired only for that particular connection.
3024   Such connection options &MUST; be removed or replaced before the
3025   message can be forwarded downstream by a proxy or gateway.
3026   This mechanism also allows the sender to indicate which HTTP
3027   header fields used in the message are only intended for the
3028   immediate recipient ("hop-by-hop"), as opposed to all recipients
3029   on the chain ("end-to-end"), enabling the message to be
3030   self-descriptive and allowing future connection-specific extensions
3031   to be deployed in HTTP without fear that they will be blindly
3032   forwarded by previously deployed intermediaries.
3035   The Connection header field's value has the following grammar:
3037<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3038  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3039  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3042   A proxy or gateway &MUST; parse a received Connection
3043   header field before a message is forwarded and, for each
3044   connection-token in this field, remove any header field(s) from
3045   the message with the same name as the connection-token, and then
3046   remove the Connection header field itself or replace it with the
3047   sender's own connection options for the forwarded message.
3050   A sender &MUST-NOT; include field-names in the Connection header
3051   field-value for fields that are defined as expressing constraints
3052   for all recipients in the request or response chain, such as the
3053   Cache-Control header field (&header-cache-control;).
3056   The connection options do not have to correspond to a header field
3057   present in the message, since a connection-specific header field
3058   might not be needed if there are no parameters associated with that
3059   connection option.  Recipients that trigger certain connection
3060   behavior based on the presence of connection options &MUST; do so
3061   based on the presence of the connection-token rather than only the
3062   presence of the optional header field.  In other words, if the
3063   connection option is received as a header field but not indicated
3064   within the Connection field-value, then the recipient &MUST; ignore
3065   the connection-specific header field because it has likely been
3066   forwarded by an intermediary that is only partially compliant.
3069   When defining new connection options, specifications ought to
3070   carefully consider existing deployed header fields and ensure
3071   that the new connection-token does not share the same name as
3072   an unrelated header field that might already be deployed.
3073   Defining a new connection-token essentially reserves that potential
3074   field-name for carrying additional information related to the
3075   connection option, since it would be unwise for senders to use
3076   that field-name for anything else.
3079   HTTP/1.1 defines the "close" connection option for the sender to
3080   signal that the connection will be closed after completion of the
3081   response. For example,
3083<figure><artwork type="example">
3084  Connection: close
3087   in either the request or the response header fields indicates that
3088   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3089   after the current request/response is complete.
3092   An HTTP/1.1 client that does not support persistent connections &MUST;
3093   include the "close" connection option in every request message.
3096   An HTTP/1.1 server that does not support persistent connections &MUST;
3097   include the "close" connection option in every response message that
3098   does not have a 1xx (Informational) status code.
3102<section title="Content-Length" anchor="header.content-length">
3103  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3104  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3105  <x:anchor-alias value="Content-Length"/>
3107   The "Content-Length" header field indicates the size of the
3108   message-body, in decimal number of octets, for any message other than
3109   a response to a HEAD request or a response with a status code of 304.
3110   In the case of a response to a HEAD request, Content-Length indicates
3111   the size of the payload body (not including any potential transfer-coding)
3112   that would have been sent had the request been a GET.
3113   In the case of a 304 (Not Modified) response to a GET request,
3114   Content-Length indicates the size of the payload body (not including
3115   any potential transfer-coding) that would have been sent in a 200 (OK)
3116   response.
3118<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3119  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3122   An example is
3124<figure><artwork type="example">
3125  Content-Length: 3495
3128   Implementations &SHOULD; use this field to indicate the message-body
3129   length when no transfer-coding is being applied and the
3130   payload's body length can be determined prior to being transferred.
3131   <xref target="message.body"/> describes how recipients determine the length
3132   of a message-body.
3135   Any Content-Length greater than or equal to zero is a valid value.
3138   Note that the use of this field in HTTP is significantly different from
3139   the corresponding definition in MIME, where it is an optional field
3140   used within the "message/external-body" content-type.
3144<section title="Date" anchor="">
3145  <iref primary="true" item="Date header field" x:for-anchor=""/>
3146  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3147  <x:anchor-alias value="Date"/>
3149   The "Date" header field represents the date and time at which
3150   the message was originated, having the same semantics as the Origination
3151   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3152   The field value is an HTTP-date, as described in <xref target=""/>;
3153   it &MUST; be sent in rfc1123-date format.
3155<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3156  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3159   An example is
3161<figure><artwork type="example">
3162  Date: Tue, 15 Nov 1994 08:12:31 GMT
3165   Origin servers &MUST; include a Date header field in all responses,
3166   except in these cases:
3167  <list style="numbers">
3168      <t>If the response status code is 100 (Continue) or 101 (Switching
3169         Protocols), the response &MAY; include a Date header field, at
3170         the server's option.</t>
3172      <t>If the response status code conveys a server error, e.g., 500
3173         (Internal Server Error) or 503 (Service Unavailable), and it is
3174         inconvenient or impossible to generate a valid Date.</t>
3176      <t>If the server does not have a clock that can provide a
3177         reasonable approximation of the current time, its responses
3178         &MUST-NOT; include a Date header field. In this case, the rules
3179         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3180  </list>
3183   A received message that does not have a Date header field &MUST; be
3184   assigned one by the recipient if the message will be cached by that
3185   recipient.
3188   Clients can use the Date header field as well; in order to keep request
3189   messages small, they are advised not to include it when it doesn't convey
3190   any useful information (as it is usually the case for requests that do not
3191   contain a payload).
3194   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3195   time subsequent to the generation of the message. It &SHOULD; represent
3196   the best available approximation of the date and time of message
3197   generation, unless the implementation has no means of generating a
3198   reasonably accurate date and time. In theory, the date ought to
3199   represent the moment just before the payload is generated. In
3200   practice, the date can be generated at any time during the message
3201   origination without affecting its semantic value.
3204<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3206   Some origin server implementations might not have a clock available.
3207   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3208   values to a response, unless these values were associated
3209   with the resource by a system or user with a reliable clock. It &MAY;
3210   assign an Expires value that is known, at or before server
3211   configuration time, to be in the past (this allows "pre-expiration"
3212   of responses without storing separate Expires values for each
3213   resource).
3218<section title="Host" anchor="">
3219  <iref primary="true" item="Host header field" x:for-anchor=""/>
3220  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3221  <x:anchor-alias value="Host"/>
3223   The "Host" header field in a request provides the host and port
3224   information from the target resource's URI, enabling the origin
3225   server to distinguish between resources while servicing requests
3226   for multiple host names on a single IP address.  Since the Host
3227   field-value is critical information for handling a request, it
3228   &SHOULD; be sent as the first header field following the Request-Line.
3230<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3231  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3234   A client &MUST; send a Host header field in all HTTP/1.1 request
3235   messages.  If the target resource's URI includes an authority
3236   component, then the Host field-value &MUST; be identical to that
3237   authority component after excluding any userinfo (<xref target="http.uri"/>).
3238   If the authority component is missing or undefined for the target
3239   resource's URI, then the Host header field &MUST; be sent with an
3240   empty field-value.
3243   For example, a GET request to the origin server for
3244   &lt;; would begin with:
3246<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3247GET /pub/WWW/ HTTP/1.1
3251   The Host header field &MUST; be sent in an HTTP/1.1 request even
3252   if the request-target is in the form of an absolute-URI, since this
3253   allows the Host information to be forwarded through ancient HTTP/1.0
3254   proxies that might not have implemented Host.
3257   When an HTTP/1.1 proxy receives a request with a request-target in
3258   the form of an absolute-URI, the proxy &MUST; ignore the received
3259   Host header field (if any) and instead replace it with the host
3260   information of the request-target.  When a proxy forwards a request,
3261   it &MUST; generate the Host header field based on the received
3262   absolute-URI rather than the received Host.
3265   Since the Host header field acts as an application-level routing
3266   mechanism, it is a frequent target for malware seeking to poison
3267   a shared cache or redirect a request to an unintended server.
3268   An interception proxy is particularly vulnerable if it relies on
3269   the Host header field value for redirecting requests to internal
3270   servers, or for use as a cache key in a shared cache, without
3271   first verifying that the intercepted connection is targeting a
3272   valid IP address for that host.
3275   A server &MUST; respond with a 400 (Bad Request) status code to
3276   any HTTP/1.1 request message that lacks a Host header field and
3277   to any request message that contains more than one Host header field
3278   or a Host header field with an invalid field-value.
3281   See Sections <xref target="" format="counter"/>
3282   and <xref target="" format="counter"/>
3283   for other requirements relating to Host.
3287<section title="TE" anchor="header.te">
3288  <iref primary="true" item="TE header field" x:for-anchor=""/>
3289  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3290  <x:anchor-alias value="TE"/>
3291  <x:anchor-alias value="t-codings"/>
3292  <x:anchor-alias value="te-params"/>
3293  <x:anchor-alias value="te-ext"/>
3295   The "TE" header field indicates what extension transfer-codings
3296   it is willing to accept in the response, and whether or not it is
3297   willing to accept trailer fields in a chunked transfer-coding.
3300   Its value consists of the keyword "trailers" and/or a comma-separated
3301   list of extension transfer-coding names with optional accept
3302   parameters (as described in <xref target="transfer.codings"/>).
3304<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3305  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3306  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3307  <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> )
3308  <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> ]
3311   The presence of the keyword "trailers" indicates that the client is
3312   willing to accept trailer fields in a chunked transfer-coding, as
3313   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3314   transfer-coding values even though it does not itself represent a
3315   transfer-coding.
3318   Examples of its use are:
3320<figure><artwork type="example">
3321  TE: deflate
3322  TE:
3323  TE: trailers, deflate;q=0.5
3326   The TE header field only applies to the immediate connection.
3327   Therefore, the keyword &MUST; be supplied within a Connection header
3328   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3331   A server tests whether a transfer-coding is acceptable, according to
3332   a TE field, using these rules:
3333  <list style="numbers">
3334    <x:lt>
3335      <t>The "chunked" transfer-coding is always acceptable. If the
3336         keyword "trailers" is listed, the client indicates that it is
3337         willing to accept trailer fields in the chunked response on
3338         behalf of itself and any downstream clients. The implication is
3339         that, if given, the client is stating that either all
3340         downstream clients are willing to accept trailer fields in the
3341         forwarded response, or that it will attempt to buffer the
3342         response on behalf of downstream recipients.
3343      </t><t>
3344         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3345         chunked response such that a client can be assured of buffering
3346         the entire response.</t>
3347    </x:lt>
3348    <x:lt>
3349      <t>If the transfer-coding being tested is one of the transfer-codings
3350         listed in the TE field, then it is acceptable unless it
3351         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3352         qvalue of 0 means "not acceptable".)</t>
3353    </x:lt>
3354    <x:lt>
3355      <t>If multiple transfer-codings are acceptable, then the
3356         acceptable transfer-coding with the highest non-zero qvalue is
3357         preferred.  The "chunked" transfer-coding always has a qvalue
3358         of 1.</t>
3359    </x:lt>
3360  </list>
3363   If the TE field-value is empty or if no TE field is present, the only
3364   transfer-coding is "chunked". A message with no transfer-coding is
3365   always acceptable.
3369<section title="Trailer" anchor="header.trailer">
3370  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3371  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3372  <x:anchor-alias value="Trailer"/>
3374   The "Trailer" header field indicates that the given set of
3375   header fields is present in the trailer of a message encoded with
3376   chunked transfer-coding.
3378<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3379  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3382   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3383   message using chunked transfer-coding with a non-empty trailer. Doing
3384   so allows the recipient to know which header fields to expect in the
3385   trailer.
3388   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3389   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3390   trailer fields in a "chunked" transfer-coding.
3393   Message header fields listed in the Trailer header field &MUST-NOT;
3394   include the following header fields:
3395  <list style="symbols">
3396    <t>Transfer-Encoding</t>
3397    <t>Content-Length</t>
3398    <t>Trailer</t>
3399  </list>
3403<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3404  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3405  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3406  <x:anchor-alias value="Transfer-Encoding"/>
3408   The "Transfer-Encoding" header field indicates what transfer-codings
3409   (if any) have been applied to the message body. It differs from
3410   Content-Encoding (&content-codings;) in that transfer-codings are a property
3411   of the message (and therefore are removed by intermediaries), whereas
3412   content-codings are not.
3414<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3415  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3418   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3420<figure><artwork type="example">
3421  Transfer-Encoding: chunked
3424   If multiple encodings have been applied to a representation, the transfer-codings
3425   &MUST; be listed in the order in which they were applied.
3426   Additional information about the encoding parameters &MAY; be provided
3427   by other header fields not defined by this specification.
3430   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3431   header field.
3435<section title="Upgrade" anchor="header.upgrade">
3436  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3437  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3438  <x:anchor-alias value="Upgrade"/>
3440   The "Upgrade" header field allows the client to specify what
3441   additional communication protocols it would like to use, if the server
3442   chooses to switch protocols. Servers can use it to indicate what protocols
3443   they are willing to switch to.
3445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3446  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3449   For example,
3451<figure><artwork type="example">
3452  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3455   The Upgrade header field is intended to provide a simple mechanism
3456   for transition from HTTP/1.1 to some other, incompatible protocol. It
3457   does so by allowing the client to advertise its desire to use another
3458   protocol, such as a later version of HTTP with a higher major version
3459   number, even though the current request has been made using HTTP/1.1.
3460   This eases the difficult transition between incompatible protocols by
3461   allowing the client to initiate a request in the more commonly
3462   supported protocol while indicating to the server that it would like
3463   to use a "better" protocol if available (where "better" is determined
3464   by the server, possibly according to the nature of the request method
3465   or target resource).
3468   The Upgrade header field only applies to switching application-layer
3469   protocols upon the existing transport-layer connection. Upgrade
3470   cannot be used to insist on a protocol change; its acceptance and use
3471   by the server is optional. The capabilities and nature of the
3472   application-layer communication after the protocol change is entirely
3473   dependent upon the new protocol chosen, although the first action
3474   after changing the protocol &MUST; be a response to the initial HTTP
3475   request containing the Upgrade header field.
3478   The Upgrade header field only applies to the immediate connection.
3479   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3480   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3481   HTTP/1.1 message.
3484   The Upgrade header field cannot be used to indicate a switch to a
3485   protocol on a different connection. For that purpose, it is more
3486   appropriate to use a 3xx redirection response (&status-3xx;).
3489   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3490   Protocols) responses to indicate which protocol(s) are being switched to,
3491   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3492   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3493   response to indicate that they are willing to upgrade to one of the
3494   specified protocols.
3497   This specification only defines the protocol name "HTTP" for use by
3498   the family of Hypertext Transfer Protocols, as defined by the HTTP
3499   version rules of <xref target="http.version"/> and future updates to this
3500   specification. Additional tokens can be registered with IANA using the
3501   registration procedure defined below. 
3504<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3506   The HTTP Upgrade Token Registry defines the name space for product
3507   tokens used to identify protocols in the Upgrade header field.
3508   Each registered token is associated with contact information and
3509   an optional set of specifications that details how the connection
3510   will be processed after it has been upgraded.
3513   Registrations are allowed on a First Come First Served basis as
3514   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3515   specifications need not be IETF documents or be subject to IESG review.
3516   Registrations are subject to the following rules:
3517  <list style="numbers">
3518    <t>A token, once registered, stays registered forever.</t>
3519    <t>The registration &MUST; name a responsible party for the
3520       registration.</t>
3521    <t>The registration &MUST; name a point of contact.</t>
3522    <t>The registration &MAY; name a set of specifications associated with that
3523       token. Such specifications need not be publicly available.</t>
3524    <t>The responsible party &MAY; change the registration at any time.
3525       The IANA will keep a record of all such changes, and make them
3526       available upon request.</t>
3527    <t>The responsible party for the first registration of a "product"
3528       token &MUST; approve later registrations of a "version" token
3529       together with that "product" token before they can be registered.</t>
3530    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3531       for a token. This will normally only be used in the case when a
3532       responsible party cannot be contacted.</t>
3533  </list>
3540<section title="Via" anchor="header.via">
3541  <iref primary="true" item="Via header field" x:for-anchor=""/>
3542  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3543  <x:anchor-alias value="protocol-name"/>
3544  <x:anchor-alias value="protocol-version"/>
3545  <x:anchor-alias value="pseudonym"/>
3546  <x:anchor-alias value="received-by"/>
3547  <x:anchor-alias value="received-protocol"/>
3548  <x:anchor-alias value="Via"/>
3550   The "Via" header field &MUST; be sent by a proxy or gateway to
3551   indicate the intermediate protocols and recipients between the user
3552   agent and the server on requests, and between the origin server and
3553   the client on responses. It is analogous to the "Received" field
3554   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3555   and is intended to be used for tracking message forwards,
3556   avoiding request loops, and identifying the protocol capabilities of
3557   all senders along the request/response chain.
3559<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
3560  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3561                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3562  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3563  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3564  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3565  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3566  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3569   The received-protocol indicates the protocol version of the message
3570   received by the server or client along each segment of the
3571   request/response chain. The received-protocol version is appended to
3572   the Via field value when the message is forwarded so that information
3573   about the protocol capabilities of upstream applications remains
3574   visible to all recipients.
3577   The protocol-name is excluded if and only if it would be "HTTP". The
3578   received-by field is normally the host and optional port number of a
3579   recipient server or client that subsequently forwarded the message.
3580   However, if the real host is considered to be sensitive information,
3581   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3582   be assumed to be the default port of the received-protocol.
3585   Multiple Via field values represent each proxy or gateway that has
3586   forwarded the message. Each recipient &MUST; append its information
3587   such that the end result is ordered according to the sequence of
3588   forwarding applications.
3591   Comments &MAY; be used in the Via header field to identify the software
3592   of each recipient, analogous to the User-Agent and Server header fields.
3593   However, all comments in the Via field are optional and &MAY; be removed
3594   by any recipient prior to forwarding the message.
3597   For example, a request message could be sent from an HTTP/1.0 user
3598   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3599   forward the request to a public proxy at, which completes
3600   the request by forwarding it to the origin server at
3601   The request received by would then have the following
3602   Via header field:
3604<figure><artwork type="example">
3605  Via: 1.0 fred, 1.1 (Apache/1.1)
3608   A proxy or gateway used as a portal through a network firewall
3609   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3610   region unless it is explicitly enabled to do so. If not enabled, the
3611   received-by host of any host behind the firewall &SHOULD; be replaced
3612   by an appropriate pseudonym for that host.
3615   For organizations that have strong privacy requirements for hiding
3616   internal structures, a proxy or gateway &MAY; combine an ordered
3617   subsequence of Via header field entries with identical received-protocol
3618   values into a single such entry. For example,
3620<figure><artwork type="example">
3621  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3624  could be collapsed to
3626<figure><artwork type="example">
3627  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3630   Senders &SHOULD-NOT; combine multiple entries unless they are all
3631   under the same organizational control and the hosts have already been
3632   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3633   have different received-protocol values.
3639<section title="IANA Considerations" anchor="IANA.considerations">
3641<section title="Header Field Registration" anchor="header.field.registration">
3643   The Message Header Field Registry located at <eref target=""/> shall be updated
3644   with the permanent registrations below (see <xref target="RFC3864"/>):
3646<?BEGININC p1-messaging.iana-headers ?>
3647<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3648<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3649   <ttcol>Header Field Name</ttcol>
3650   <ttcol>Protocol</ttcol>
3651   <ttcol>Status</ttcol>
3652   <ttcol>Reference</ttcol>
3654   <c>Connection</c>
3655   <c>http</c>
3656   <c>standard</c>
3657   <c>
3658      <xref target="header.connection"/>
3659   </c>
3660   <c>Content-Length</c>
3661   <c>http</c>
3662   <c>standard</c>
3663   <c>
3664      <xref target="header.content-length"/>
3665   </c>
3666   <c>Date</c>
3667   <c>http</c>
3668   <c>standard</c>
3669   <c>
3670      <xref target=""/>
3671   </c>
3672   <c>Host</c>
3673   <c>http</c>
3674   <c>standard</c>
3675   <c>
3676      <xref target=""/>
3677   </c>
3678   <c>TE</c>
3679   <c>http</c>
3680   <c>standard</c>
3681   <c>
3682      <xref target="header.te"/>
3683   </c>
3684   <c>Trailer</c>
3685   <c>http</c>
3686   <c>standard</c>
3687   <c>
3688      <xref target="header.trailer"/>
3689   </c>
3690   <c>Transfer-Encoding</c>
3691   <c>http</c>
3692   <c>standard</c>
3693   <c>
3694      <xref target="header.transfer-encoding"/>
3695   </c>
3696   <c>Upgrade</c>
3697   <c>http</c>
3698   <c>standard</c>
3699   <c>
3700      <xref target="header.upgrade"/>
3701   </c>
3702   <c>Via</c>
3703   <c>http</c>
3704   <c>standard</c>
3705   <c>
3706      <xref target="header.via"/>
3707   </c>
3710<?ENDINC p1-messaging.iana-headers ?>
3712   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3713   HTTP header field would be in conflict with the use of the "close" connection
3714   option for the "Connection" header field (<xref target="header.connection"/>).
3716<texttable align="left" suppress-title="true">
3717   <ttcol>Header Field Name</ttcol>
3718   <ttcol>Protocol</ttcol>
3719   <ttcol>Status</ttcol>
3720   <ttcol>Reference</ttcol>
3722   <c>Close</c>
3723   <c>http</c>
3724   <c>reserved</c>
3725   <c>
3726      <xref target="header.field.registration"/>
3727   </c>
3730   The change controller is: "IETF ( - Internet Engineering Task Force".
3734<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3736   The entries for the "http" and "https" URI Schemes in the registry located at
3737   <eref target=""/>
3738   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3739   and <xref target="https.uri" format="counter"/> of this document
3740   (see <xref target="RFC4395"/>).
3744<section title="Internet Media Type Registrations" anchor="">
3746   This document serves as the specification for the Internet media types
3747   "message/http" and "application/http". The following is to be registered with
3748   IANA (see <xref target="RFC4288"/>).
3750<section title="Internet Media Type message/http" anchor="">
3751<iref item="Media Type" subitem="message/http" primary="true"/>
3752<iref item="message/http Media Type" primary="true"/>
3754   The message/http type can be used to enclose a single HTTP request or
3755   response message, provided that it obeys the MIME restrictions for all
3756   "message" types regarding line length and encodings.
3759  <list style="hanging" x:indent="12em">
3760    <t hangText="Type name:">
3761      message
3762    </t>
3763    <t hangText="Subtype name:">
3764      http
3765    </t>
3766    <t hangText="Required parameters:">
3767      none
3768    </t>
3769    <t hangText="Optional parameters:">
3770      version, msgtype
3771      <list style="hanging">
3772        <t hangText="version:">
3773          The HTTP-Version number of the enclosed message
3774          (e.g., "1.1"). If not present, the version can be
3775          determined from the first line of the body.
3776        </t>
3777        <t hangText="msgtype:">
3778          The message type &mdash; "request" or "response". If not
3779          present, the type can be determined from the first
3780          line of the body.
3781        </t>
3782      </list>
3783    </t>
3784    <t hangText="Encoding considerations:">
3785      only "7bit", "8bit", or "binary" are permitted
3786    </t>
3787    <t hangText="Security considerations:">
3788      none
3789    </t>
3790    <t hangText="Interoperability considerations:">
3791      none
3792    </t>
3793    <t hangText="Published specification:">
3794      This specification (see <xref target=""/>).
3795    </t>
3796    <t hangText="Applications that use this media type:">
3797    </t>
3798    <t hangText="Additional information:">
3799      <list style="hanging">
3800        <t hangText="Magic number(s):">none</t>
3801        <t hangText="File extension(s):">none</t>
3802        <t hangText="Macintosh file type code(s):">none</t>
3803      </list>
3804    </t>
3805    <t hangText="Person and email address to contact for further information:">
3806      See Authors Section.
3807    </t>
3808    <t hangText="Intended usage:">
3809      COMMON
3810    </t>
3811    <t hangText="Restrictions on usage:">
3812      none
3813    </t>
3814    <t hangText="Author/Change controller:">
3815      IESG
3816    </t>
3817  </list>
3820<section title="Internet Media Type application/http" anchor="">
3821<iref item="Media Type" subitem="application/http" primary="true"/>
3822<iref item="application/http Media Type" primary="true"/>
3824   The application/http type can be used to enclose a pipeline of one or more
3825   HTTP request or response messages (not intermixed).
3828  <list style="hanging" x:indent="12em">
3829    <t hangText="Type name:">
3830      application
3831    </t>
3832    <t hangText="Subtype name:">
3833      http
3834    </t>
3835    <t hangText="Required parameters:">
3836      none
3837    </t>
3838    <t hangText="Optional parameters:">
3839      version, msgtype
3840      <list style="hanging">
3841        <t hangText="version:">
3842          The HTTP-Version number of the enclosed messages
3843          (e.g., "1.1"). If not present, the version can be
3844          determined from the first line of the body.
3845        </t>
3846        <t hangText="msgtype:">
3847          The message type &mdash; "request" or "response". If not
3848          present, the type can be determined from the first
3849          line of the body.
3850        </t>
3851      </list>
3852    </t>
3853    <t hangText="Encoding considerations:">
3854      HTTP messages enclosed by this type
3855      are in "binary" format; use of an appropriate
3856      Content-Transfer-Encoding is required when
3857      transmitted via E-mail.
3858    </t>
3859    <t hangText="Security considerations:">
3860      none
3861    </t>
3862    <t hangText="Interoperability considerations:">
3863      none
3864    </t>
3865    <t hangText="Published specification:">
3866      This specification (see <xref target=""/>).
3867    </t>
3868    <t hangText="Applications that use this media type:">
3869    </t>
3870    <t hangText="Additional information:">
3871      <list style="hanging">
3872        <t hangText="Magic number(s):">none</t>
3873        <t hangText="File extension(s):">none</t>
3874        <t hangText="Macintosh file type code(s):">none</t>
3875      </list>
3876    </t>
3877    <t hangText="Person and email address to contact for further information:">
3878      See Authors Section.
3879    </t>
3880    <t hangText="Intended usage:">
3881      COMMON
3882    </t>
3883    <t hangText="Restrictions on usage:">
3884      none
3885    </t>
3886    <t hangText="Author/Change controller:">
3887      IESG
3888    </t>
3889  </list>
3894<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3896   The registration procedure for HTTP Transfer Codings is now defined by
3897   <xref target="transfer.coding.registry"/> of this document.
3900   The HTTP Transfer Codings Registry located at <eref target=""/>
3901   shall be updated with the registrations below:
3903<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3904   <ttcol>Name</ttcol>
3905   <ttcol>Description</ttcol>
3906   <ttcol>Reference</ttcol>
3907   <c>chunked</c>
3908   <c>Transfer in a series of chunks</c>
3909   <c>
3910      <xref target="chunked.encoding"/>
3911   </c>
3912   <c>compress</c>
3913   <c>UNIX "compress" program method</c>
3914   <c>
3915      <xref target="compress.coding"/>
3916   </c>
3917   <c>deflate</c>
3918   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3919   the "zlib" data format (<xref target="RFC1950"/>)
3920   </c>
3921   <c>
3922      <xref target="deflate.coding"/>
3923   </c>
3924   <c>gzip</c>
3925   <c>Same as GNU zip <xref target="RFC1952"/></c>
3926   <c>
3927      <xref target="gzip.coding"/>
3928   </c>
3932<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3934   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3935   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3936   by <xref target="upgrade.token.registry"/> of this document.
3939   The HTTP Status Code Registry located at <eref target=""/>
3940   shall be updated with the registration below:
3942<texttable align="left" suppress-title="true">
3943   <ttcol>Value</ttcol>
3944   <ttcol>Description</ttcol>
3945   <ttcol>Reference</ttcol>
3947   <c>HTTP</c>
3948   <c>Hypertext Transfer Protocol</c>
3949   <c><xref target="http.version"/> of this specification</c>
3956<section title="Security Considerations" anchor="security.considerations">
3958   This section is meant to inform application developers, information
3959   providers, and users of the security limitations in HTTP/1.1 as
3960   described by this document. The discussion does not include
3961   definitive solutions to the problems revealed, though it does make
3962   some suggestions for reducing security risks.
3965<section title="Personal Information" anchor="personal.information">
3967   HTTP clients are often privy to large amounts of personal information
3968   (e.g., the user's name, location, mail address, passwords, encryption
3969   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3970   leakage of this information.
3971   We very strongly recommend that a convenient interface be provided
3972   for the user to control dissemination of such information, and that
3973   designers and implementors be particularly careful in this area.
3974   History shows that errors in this area often create serious security
3975   and/or privacy problems and generate highly adverse publicity for the
3976   implementor's company.
3980<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3982   A server is in the position to save personal data about a user's
3983   requests which might identify their reading patterns or subjects of
3984   interest. This information is clearly confidential in nature and its
3985   handling can be constrained by law in certain countries. People using
3986   HTTP to provide data are responsible for ensuring that
3987   such material is not distributed without the permission of any
3988   individuals that are identifiable by the published results.
3992<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3994   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3995   the documents returned by HTTP requests to be only those that were
3996   intended by the server administrators. If an HTTP server translates
3997   HTTP URIs directly into file system calls, the server &MUST; take
3998   special care not to serve files that were not intended to be
3999   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
4000   other operating systems use ".." as a path component to indicate a
4001   directory level above the current one. On such a system, an HTTP
4002   server &MUST; disallow any such construct in the request-target if it
4003   would otherwise allow access to a resource outside those intended to
4004   be accessible via the HTTP server. Similarly, files intended for
4005   reference only internally to the server (such as access control
4006   files, configuration files, and script code) &MUST; be protected from
4007   inappropriate retrieval, since they might contain sensitive
4008   information. Experience has shown that minor bugs in such HTTP server
4009   implementations have turned into security risks.
4013<section title="DNS Spoofing" anchor="dns.spoofing">
4015   Clients using HTTP rely heavily on the Domain Name Service, and are
4016   thus generally prone to security attacks based on the deliberate
4017   mis-association of IP addresses and DNS names. Clients need to be
4018   cautious in assuming the continuing validity of an IP number/DNS name
4019   association.
4022   In particular, HTTP clients &SHOULD; rely on their name resolver for
4023   confirmation of an IP number/DNS name association, rather than
4024   caching the result of previous host name lookups. Many platforms
4025   already can cache host name lookups locally when appropriate, and
4026   they &SHOULD; be configured to do so. It is proper for these lookups to
4027   be cached, however, only when the TTL (Time To Live) information
4028   reported by the name server makes it likely that the cached
4029   information will remain useful.
4032   If HTTP clients cache the results of host name lookups in order to
4033   achieve a performance improvement, they &MUST; observe the TTL
4034   information reported by DNS.
4037   If HTTP clients do not observe this rule, they could be spoofed when
4038   a previously-accessed server's IP address changes. As network
4039   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
4040   possibility of this form of attack will grow. Observing this
4041   requirement thus reduces this potential security vulnerability.
4044   This requirement also improves the load-balancing behavior of clients
4045   for replicated servers using the same DNS name and reduces the
4046   likelihood of a user's experiencing failure in accessing sites which
4047   use that strategy.
4051<section title="Proxies and Caching" anchor="attack.proxies">
4053   By their very nature, HTTP proxies are men-in-the-middle, and
4054   represent an opportunity for man-in-the-middle attacks. Compromise of
4055   the systems on which the proxies run can result in serious security
4056   and privacy problems. Proxies have access to security-related
4057   information, personal information about individual users and
4058   organizations, and proprietary information belonging to users and
4059   content providers. A compromised proxy, or a proxy implemented or
4060   configured without regard to security and privacy considerations,
4061   might be used in the commission of a wide range of potential attacks.
4064   Proxy operators need to protect the systems on which proxies run as
4065   they would protect any system that contains or transports sensitive
4066   information. In particular, log information gathered at proxies often
4067   contains highly sensitive personal information, and/or information
4068   about organizations. Log information needs to be carefully guarded, and
4069   appropriate guidelines for use need to be developed and followed.
4070   (<xref target="abuse.of.server.log.information"/>).
4073   Proxy implementors need to consider the privacy and security
4074   implications of their design and coding decisions, and of the
4075   configuration options they provide to proxy operators (especially the
4076   default configuration).
4079   Users of a proxy need to be aware that proxies are no trustworthier than
4080   the people who run them; HTTP itself cannot solve this problem.
4083   The judicious use of cryptography, when appropriate, might suffice to
4084   protect against a broad range of security and privacy attacks. Such
4085   cryptography is beyond the scope of the HTTP/1.1 specification.
4089<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4091   Because HTTP uses mostly textual, character-delimited fields, attackers can
4092   overflow buffers in implementations, and/or perform a Denial of Service
4093   against implementations that accept fields with unlimited lengths.
4096   To promote interoperability, this specification makes specific
4097   recommendations for size limits on request-targets (<xref target="request-target"/>)
4098   and blocks of header fields (<xref target="header.fields"/>). These are
4099   minimum recommendations, chosen to be supportable even by implementations
4100   with limited resources; it is expected that most implementations will choose
4101   substantially higher limits.
4104   This specification also provides a way for servers to reject messages that
4105   have request-targets that are too long (&status-414;) or request entities
4106   that are too large (&status-4xx;).
4109   Other fields (including but not limited to request methods, response status
4110   phrases, header field-names, and body chunks) &SHOULD; be limited by
4111   implementations carefully, so as to not impede interoperability.
4115<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4117   They exist. They are hard to defend against. Research continues.
4118   Beware.
4123<section title="Acknowledgments" anchor="ack">
4125   HTTP has evolved considerably over the years. It has
4126   benefited from a large and active developer community &mdash; the many
4127   people who have participated on the www-talk mailing list &mdash; and it is
4128   that community which has been most responsible for the success of
4129   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4130   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4131   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4132   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4133   VanHeyningen deserve special recognition for their efforts in
4134   defining early aspects of the protocol.
4137   This document has benefited greatly from the comments of all those
4138   participating in the HTTP-WG. In addition to those already mentioned,
4139   the following individuals have contributed to this specification:
4142   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4143   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4144   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4145   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4146   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4147   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4148   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4149   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4150   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4151   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4152   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4153   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4156   Thanks to the "cave men" of Palo Alto. You know who you are.
4159   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4160   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4161   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4162   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4163   Larry Masinter for their help. And thanks go particularly to Jeff
4164   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4167   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4168   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4169   discovery of many of the problems that this document attempts to
4170   rectify.
4173   This specification makes heavy use of the augmented BNF and generic
4174   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4175   reuses many of the definitions provided by Nathaniel Borenstein and
4176   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4177   specification will help reduce past confusion over the relationship
4178   between HTTP and Internet mail message formats.
4182Acknowledgements TODO list
4184- Jeff Hodges ("effective request URI")
4192<references title="Normative References">
4194<reference anchor="ISO-8859-1">
4195  <front>
4196    <title>
4197     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4198    </title>
4199    <author>
4200      <organization>International Organization for Standardization</organization>
4201    </author>
4202    <date year="1998"/>
4203  </front>
4204  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4207<reference anchor="Part2">
4208  <front>
4209    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4210    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4211      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4212      <address><email></email></address>
4213    </author>
4214    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4215      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4216      <address><email></email></address>
4217    </author>
4218    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4219      <organization abbrev="HP">Hewlett-Packard Company</organization>
4220      <address><email></email></address>
4221    </author>
4222    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4223      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4224      <address><email></email></address>
4225    </author>
4226    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4227      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4228      <address><email></email></address>
4229    </author>
4230    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4231      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4232      <address><email></email></address>
4233    </author>
4234    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4235      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4236      <address><email></email></address>
4237    </author>
4238    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4239      <organization abbrev="W3C">World Wide Web Consortium</organization>
4240      <address><email></email></address>
4241    </author>
4242    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4243      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4244      <address><email></email></address>
4245    </author>
4246    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4247  </front>
4248  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4249  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4252<reference anchor="Part3">
4253  <front>
4254    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4255    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4256      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4257      <address><email></email></address>
4258    </author>
4259    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4260      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4261      <address><email></email></address>
4262    </author>
4263    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4264      <organization abbrev="HP">Hewlett-Packard Company</organization>
4265      <address><email></email></address>
4266    </author>
4267    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4268      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4269      <address><email></email></address>
4270    </author>
4271    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4272      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4273      <address><email></email></address>
4274    </author>
4275    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4276      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4277      <address><email></email></address>
4278    </author>
4279    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4280      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4281      <address><email></email></address>
4282    </author>
4283    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4284      <organization abbrev="W3C">World Wide Web Consortium</organization>
4285      <address><email></email></address>
4286    </author>
4287    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4288      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4289      <address><email></email></address>
4290    </author>
4291    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4292  </front>
4293  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4294  <x:source href="p3-payload.xml" basename="p3-payload"/>
4297<reference anchor="Part6">
4298  <front>
4299    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4300    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4301      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4302      <address><email></email></address>
4303    </author>
4304    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4305      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4306      <address><email></email></address>
4307    </author>
4308    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4309      <organization abbrev="HP">Hewlett-Packard Company</organization>
4310      <address><email></email></address>
4311    </author>
4312    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4313      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4314      <address><email></email></address>
4315    </author>
4316    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4317      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4318      <address><email></email></address>
4319    </author>
4320    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4321      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4322      <address><email></email></address>
4323    </author>
4324    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4325      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4326      <address><email></email></address>
4327    </author>
4328    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4329      <organization abbrev="W3C">World Wide Web Consortium</organization>
4330      <address><email></email></address>
4331    </author>
4332    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4333      <address><email></email></address>
4334    </author>
4335    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4336      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4337      <address><email></email></address>
4338    </author>
4339    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4340  </front>
4341  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4342  <x:source href="p6-cache.xml" basename="p6-cache"/>
4345<reference anchor="RFC5234">
4346  <front>
4347    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4348    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4349      <organization>Brandenburg InternetWorking</organization>
4350      <address>
4351        <email></email>
4352      </address> 
4353    </author>
4354    <author initials="P." surname="Overell" fullname="Paul Overell">
4355      <organization>THUS plc.</organization>
4356      <address>
4357        <email></email>
4358      </address>
4359    </author>
4360    <date month="January" year="2008"/>
4361  </front>
4362  <seriesInfo name="STD" value="68"/>
4363  <seriesInfo name="RFC" value="5234"/>
4366<reference anchor="RFC2119">
4367  <front>
4368    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4369    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4370      <organization>Harvard University</organization>
4371      <address><email></email></address>
4372    </author>
4373    <date month="March" year="1997"/>
4374  </front>
4375  <seriesInfo name="BCP" value="14"/>
4376  <seriesInfo name="RFC" value="2119"/>
4379<reference anchor="RFC3986">
4380 <front>
4381  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4382  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4383    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4384    <address>
4385       <email></email>
4386       <uri></uri>
4387    </address>
4388  </author>
4389  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4390    <organization abbrev="Day Software">Day Software</organization>
4391    <address>
4392      <email></email>
4393      <uri></uri>
4394    </address>
4395  </author>
4396  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4397    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4398    <address>
4399      <email></email>
4400      <uri></uri>
4401    </address>
4402  </author>
4403  <date month='January' year='2005'></date>
4404 </front>
4405 <seriesInfo name="STD" value="66"/>
4406 <seriesInfo name="RFC" value="3986"/>
4409<reference anchor="USASCII">
4410  <front>
4411    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4412    <author>
4413      <organization>American National Standards Institute</organization>
4414    </author>
4415    <date year="1986"/>
4416  </front>
4417  <seriesInfo name="ANSI" value="X3.4"/>
4420<reference anchor="RFC1950">
4421  <front>
4422    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4423    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4424      <organization>Aladdin Enterprises</organization>
4425      <address><email></email></address>
4426    </author>
4427    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4428    <date month="May" year="1996"/>
4429  </front>
4430  <seriesInfo name="RFC" value="1950"/>
4431  <annotation>
4432    RFC 1950 is an Informational RFC, thus it might be less stable than
4433    this specification. On the other hand, this downward reference was
4434    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4435    therefore it is unlikely to cause problems in practice. See also
4436    <xref target="BCP97"/>.
4437  </annotation>
4440<reference anchor="RFC1951">
4441  <front>
4442    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4443    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4444      <organization>Aladdin Enterprises</organization>
4445      <address><email></email></address>
4446    </author>
4447    <date month="May" year="1996"/>
4448  </front>
4449  <seriesInfo name="RFC" value="1951"/>
4450  <annotation>
4451    RFC 1951 is an Informational RFC, thus it might be less stable than
4452    this specification. On the other hand, this downward reference was
4453    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4454    therefore it is unlikely to cause problems in practice. See also
4455    <xref target="BCP97"/>.
4456  </annotation>
4459<reference anchor="RFC1952">
4460  <front>
4461    <title>GZIP file format specification version 4.3</title>
4462    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4463      <organization>Aladdin Enterprises</organization>
4464      <address><email></email></address>
4465    </author>
4466    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4467      <address><email></email></address>
4468    </author>
4469    <author initials="M." surname="Adler" fullname="Mark Adler">
4470      <address><email></email></address>
4471    </author>
4472    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4473      <address><email></email></address>
4474    </author>
4475    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4476      <address><email></email></address>
4477    </author>
4478    <date month="May" year="1996"/>
4479  </front>
4480  <seriesInfo name="RFC" value="1952"/>
4481  <annotation>
4482    RFC 1952 is an Informational RFC, thus it might be less stable than
4483    this specification. On the other hand, this downward reference was
4484    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4485    therefore it is unlikely to cause problems in practice. See also
4486    <xref target="BCP97"/>.
4487  </annotation>
4492<references title="Informative References">
4494<reference anchor="Nie1997" target="">
4495  <front>
4496    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4497    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4498    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4499    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4500    <author initials="H." surname="Lie" fullname="H. Lie"/>
4501    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4502    <date year="1997" month="September"/>
4503  </front>
4504  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4507<reference anchor="Pad1995" target="">
4508  <front>
4509    <title>Improving HTTP Latency</title>
4510    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4511    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4512    <date year="1995" month="December"/>
4513  </front>
4514  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4517<reference anchor="RFC1123">
4518  <front>
4519    <title>Requirements for Internet Hosts - Application and Support</title>
4520    <author initials="R." surname="Braden" fullname="Robert Braden">
4521      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4522      <address><email>Braden@ISI.EDU</email></address>
4523    </author>
4524    <date month="October" year="1989"/>
4525  </front>
4526  <seriesInfo name="STD" value="3"/>
4527  <seriesInfo name="RFC" value="1123"/>
4530<reference anchor="RFC1900">
4531  <front>
4532    <title>Renumbering Needs Work</title>
4533    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4534      <organization>CERN, Computing and Networks Division</organization>
4535      <address><email></email></address>
4536    </author>
4537    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4538      <organization>cisco Systems</organization>
4539      <address><email></email></address>
4540    </author>
4541    <date month="February" year="1996"/>
4542  </front>
4543  <seriesInfo name="RFC" value="1900"/>
4546<reference anchor='RFC1919'>
4547  <front>
4548    <title>Classical versus Transparent IP Proxies</title>
4549    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4550      <address><email></email></address>
4551    </author>
4552    <date year='1996' month='March' />
4553  </front>
4554  <seriesInfo name='RFC' value='1919' />
4557<reference anchor="RFC1945">
4558  <front>
4559    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4560    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4561      <organization>MIT, Laboratory for Computer Science</organization>
4562      <address><email></email></address>
4563    </author>
4564    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4565      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4566      <address><email></email></address>
4567    </author>
4568    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4569      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4570      <address><email></email></address>
4571    </author>
4572    <date month="May" year="1996"/>
4573  </front>
4574  <seriesInfo name="RFC" value="1945"/>
4577<reference anchor="RFC2045">
4578  <front>
4579    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4580    <author initials="N." surname="Freed" fullname="Ned Freed">
4581      <organization>Innosoft International, Inc.</organization>
4582      <address><email></email></address>
4583    </author>
4584    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4585      <organization>First Virtual Holdings</organization>
4586      <address><email></email></address>
4587    </author>
4588    <date month="November" year="1996"/>
4589  </front>
4590  <seriesInfo name="RFC" value="2045"/>
4593<reference anchor="RFC2047">
4594  <front>
4595    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4596    <author initials="K." surname="Moore" fullname="Keith Moore">
4597      <organization>University of Tennessee</organization>
4598      <address><email></email></address>
4599    </author>
4600    <date month="November" year="1996"/>
4601  </front>
4602  <seriesInfo name="RFC" value="2047"/>
4605<reference anchor="RFC2068">
4606  <front>
4607    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4608    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4609      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4610      <address><email></email></address>
4611    </author>
4612    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4613      <organization>MIT Laboratory for Computer Science</organization>
4614      <address><email></email></address>
4615    </author>
4616    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4617      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4618      <address><email></email></address>
4619    </author>
4620    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4621      <organization>MIT Laboratory for Computer Science</organization>
4622      <address><email></email></address>
4623    </author>
4624    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4625      <organization>MIT Laboratory for Computer Science</organization>
4626      <address><email></email></address>
4627    </author>
4628    <date month="January" year="1997"/>
4629  </front>
4630  <seriesInfo name="RFC" value="2068"/>
4633<reference anchor="RFC2145">
4634  <front>
4635    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4636    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4637      <organization>Western Research Laboratory</organization>
4638      <address><email></email></address>
4639    </author>
4640    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4641      <organization>Department of Information and Computer Science</organization>
4642      <address><email></email></address>
4643    </author>
4644    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4645      <organization>MIT Laboratory for Computer Science</organization>
4646      <address><email></email></address>
4647    </author>
4648    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4649      <organization>W3 Consortium</organization>
4650      <address><email></email></address>
4651    </author>
4652    <date month="May" year="1997"/>
4653  </front>
4654  <seriesInfo name="RFC" value="2145"/>
4657<reference anchor="RFC2616">
4658  <front>
4659    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4660    <author initials="R." surname="Fielding" fullname="R. Fielding">
4661      <organization>University of California, Irvine</organization>
4662      <address><email></email></address>
4663    </author>
4664    <author initials="J." surname="Gettys" fullname="J. Gettys">
4665      <organization>W3C</organization>
4666      <address><email></email></address>
4667    </author>
4668    <author initials="J." surname="Mogul" fullname="J. Mogul">
4669      <organization>Compaq Computer Corporation</organization>
4670      <address><email></email></address>
4671    </author>
4672    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4673      <organization>MIT Laboratory for Computer Science</organization>
4674      <address><email></email></address>
4675    </author>
4676    <author initials="L." surname="Masinter" fullname="L. Masinter">
4677      <organization>Xerox Corporation</organization>
4678      <address><email></email></address>
4679    </author>
4680    <author initials="P." surname="Leach" fullname="P. Leach">
4681      <organization>Microsoft Corporation</organization>
4682      <address><email></email></address>
4683    </author>
4684    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4685      <organization>W3C</organization>
4686      <address><email></email></address>
4687    </author>
4688    <date month="June" year="1999"/>
4689  </front>
4690  <seriesInfo name="RFC" value="2616"/>
4693<reference anchor='RFC2817'>
4694  <front>
4695    <title>Upgrading to TLS Within HTTP/1.1</title>
4696    <author initials='R.' surname='Khare' fullname='R. Khare'>
4697      <organization>4K Associates / UC Irvine</organization>
4698      <address><email></email></address>
4699    </author>
4700    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4701      <organization>Agranat Systems, Inc.</organization>
4702      <address><email></email></address>
4703    </author>
4704    <date year='2000' month='May' />
4705  </front>
4706  <seriesInfo name='RFC' value='2817' />
4709<reference anchor='RFC2818'>
4710  <front>
4711    <title>HTTP Over TLS</title>
4712    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4713      <organization>RTFM, Inc.</organization>
4714      <address><email></email></address>
4715    </author>
4716    <date year='2000' month='May' />
4717  </front>
4718  <seriesInfo name='RFC' value='2818' />
4721<reference anchor='RFC2965'>
4722  <front>
4723    <title>HTTP State Management Mechanism</title>
4724    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4725      <organization>Bell Laboratories, Lucent Technologies</organization>
4726      <address><email></email></address>
4727    </author>
4728    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4729      <organization>, Inc.</organization>
4730      <address><email></email></address>
4731    </author>
4732    <date year='2000' month='October' />
4733  </front>
4734  <seriesInfo name='RFC' value='2965' />
4737<reference anchor='RFC3040'>
4738  <front>
4739    <title>Internet Web Replication and Caching Taxonomy</title>
4740    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4741      <organization>Equinix, Inc.</organization>
4742    </author>
4743    <author initials='I.' surname='Melve' fullname='I. Melve'>
4744      <organization>UNINETT</organization>
4745    </author>
4746    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4747      <organization>CacheFlow Inc.</organization>
4748    </author>
4749    <date year='2001' month='January' />
4750  </front>
4751  <seriesInfo name='RFC' value='3040' />
4754<reference anchor='RFC3864'>
4755  <front>
4756    <title>Registration Procedures for Message Header Fields</title>
4757    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4758      <organization>Nine by Nine</organization>
4759      <address><email></email></address>
4760    </author>
4761    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4762      <organization>BEA Systems</organization>
4763      <address><email></email></address>
4764    </author>
4765    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4766      <organization>HP Labs</organization>
4767      <address><email></email></address>
4768    </author>
4769    <date year='2004' month='September' />
4770  </front>
4771  <seriesInfo name='BCP' value='90' />
4772  <seriesInfo name='RFC' value='3864' />
4775<reference anchor="RFC4288">
4776  <front>
4777    <title>Media Type Specifications and Registration Procedures</title>
4778    <author initials="N." surname="Freed" fullname="N. Freed">
4779      <organization>Sun Microsystems</organization>
4780      <address>
4781        <email></email>
4782      </address>
4783    </author>
4784    <author initials="J." surname="Klensin" fullname="J. Klensin">
4785      <address>
4786        <email></email>
4787      </address>
4788    </author>
4789    <date year="2005" month="December"/>
4790  </front>
4791  <seriesInfo name="BCP" value="13"/>
4792  <seriesInfo name="RFC" value="4288"/>
4795<reference anchor='RFC4395'>
4796  <front>
4797    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4798    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4799      <organization>AT&amp;T Laboratories</organization>
4800      <address>
4801        <email></email>
4802      </address>
4803    </author>
4804    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4805      <organization>Qualcomm, Inc.</organization>
4806      <address>
4807        <email></email>
4808      </address>
4809    </author>
4810    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4811      <organization>Adobe Systems</organization>
4812      <address>
4813        <email></email>
4814      </address>
4815    </author>
4816    <date year='2006' month='February' />
4817  </front>
4818  <seriesInfo name='BCP' value='115' />
4819  <seriesInfo name='RFC' value='4395' />
4822<reference anchor='RFC4559'>
4823  <front>
4824    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4825    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4826    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4827    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4828    <date year='2006' month='June' />
4829  </front>
4830  <seriesInfo name='RFC' value='4559' />
4833<reference anchor='RFC5226'>
4834  <front>
4835    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4836    <author initials='T.' surname='Narten' fullname='T. Narten'>
4837      <organization>IBM</organization>
4838      <address><email></email></address>
4839    </author>
4840    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4841      <organization>Google</organization>
4842      <address><email></email></address>
4843    </author>
4844    <date year='2008' month='May' />
4845  </front>
4846  <seriesInfo name='BCP' value='26' />
4847  <seriesInfo name='RFC' value='5226' />
4850<reference anchor="RFC5322">
4851  <front>
4852    <title>Internet Message Format</title>
4853    <author initials="P." surname="Resnick" fullname="P. Resnick">
4854      <organization>Qualcomm Incorporated</organization>
4855    </author>
4856    <date year="2008" month="October"/>
4857  </front>
4858  <seriesInfo name="RFC" value="5322"/>
4861<reference anchor="RFC6265">
4862  <front>
4863    <title>HTTP State Management Mechanism</title>
4864    <author initials="A." surname="Barth" fullname="Adam Barth">
4865      <organization abbrev="U.C. Berkeley">
4866        University of California, Berkeley
4867      </organization>
4868      <address><email></email></address>
4869    </author>
4870    <date year="2011" month="April" />
4871  </front>
4872  <seriesInfo name="RFC" value="6265"/>
4875<reference anchor='BCP97'>
4876  <front>
4877    <title>Handling Normative References to Standards-Track Documents</title>
4878    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4879      <address>
4880        <email></email>
4881      </address>
4882    </author>
4883    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4884      <organization>MIT</organization>
4885      <address>
4886        <email></email>
4887      </address>
4888    </author>
4889    <date year='2007' month='June' />
4890  </front>
4891  <seriesInfo name='BCP' value='97' />
4892  <seriesInfo name='RFC' value='4897' />
4895<reference anchor="Kri2001" target="">
4896  <front>
4897    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4898    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4899    <date year="2001" month="November"/>
4900  </front>
4901  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4904<reference anchor="Spe" target="">
4905  <front>
4906    <title>Analysis of HTTP Performance Problems</title>
4907    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4908    <date/>
4909  </front>
4912<reference anchor="Tou1998" target="">
4913  <front>
4914  <title>Analysis of HTTP Performance</title>
4915  <author initials="J." surname="Touch" fullname="Joe Touch">
4916    <organization>USC/Information Sciences Institute</organization>
4917    <address><email></email></address>
4918  </author>
4919  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4920    <organization>USC/Information Sciences Institute</organization>
4921    <address><email></email></address>
4922  </author>
4923  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4924    <organization>USC/Information Sciences Institute</organization>
4925    <address><email></email></address>
4926  </author>
4927  <date year="1998" month="Aug"/>
4928  </front>
4929  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4930  <annotation>(original report dated Aug. 1996)</annotation>
4936<section title="Tolerant Applications" anchor="tolerant.applications">
4938   Although this document specifies the requirements for the generation
4939   of HTTP/1.1 messages, not all applications will be correct in their
4940   implementation. We therefore recommend that operational applications
4941   be tolerant of deviations whenever those deviations can be
4942   interpreted unambiguously.
4945   The line terminator for header fields is the sequence CRLF.
4946   However, we recommend that applications, when parsing such headers fields,
4947   recognize a single LF as a line terminator and ignore the leading CR.
4950   The character encoding of a representation &SHOULD; be labeled as the lowest
4951   common denominator of the character codes used within that representation, with
4952   the exception that not labeling the representation is preferred over labeling
4953   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4956   Additional rules for requirements on parsing and encoding of dates
4957   and other potential problems with date encodings include:
4960  <list style="symbols">
4961     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4962        which appears to be more than 50 years in the future is in fact
4963        in the past (this helps solve the "year 2000" problem).</t>
4965     <t>Although all date formats are specified to be case-sensitive,
4966        recipients &SHOULD; match day, week and timezone names
4967        case-insensitively.</t>
4969     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4970        Expires date as earlier than the proper value, but &MUST-NOT;
4971        internally represent a parsed Expires date as later than the
4972        proper value.</t>
4974     <t>All expiration-related calculations &MUST; be done in GMT. The
4975        local time zone &MUST-NOT; influence the calculation or comparison
4976        of an age or expiration time.</t>
4978     <t>If an HTTP header field incorrectly carries a date value with a time
4979        zone other than GMT, it &MUST; be converted into GMT using the
4980        most conservative possible conversion.</t>
4981  </list>
4985<section title="HTTP Version History" anchor="compatibility">
4987   HTTP has been in use by the World-Wide Web global information initiative
4988   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4989   was a simple protocol for hypertext data transfer across the Internet
4990   with only a single request method (GET) and no metadata.
4991   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4992   methods and MIME-like messaging that could include metadata about the data
4993   transferred and modifiers on the request/response semantics. However,
4994   HTTP/1.0 did not sufficiently take into consideration the effects of
4995   hierarchical proxies, caching, the need for persistent connections, or
4996   name-based virtual hosts. The proliferation of incompletely-implemented
4997   applications calling themselves "HTTP/1.0" further necessitated a
4998   protocol version change in order for two communicating applications
4999   to determine each other's true capabilities.
5002   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
5003   requirements that enable reliable implementations, adding only
5004   those new features that will either be safely ignored by an HTTP/1.0
5005   recipient or only sent when communicating with a party advertising
5006   compliance with HTTP/1.1.
5009   It is beyond the scope of a protocol specification to mandate
5010   compliance with previous versions. HTTP/1.1 was deliberately
5011   designed, however, to make supporting previous versions easy.
5012   We would expect a general-purpose HTTP/1.1 server to understand
5013   any valid request in the format of HTTP/1.0 and respond appropriately
5014   with an HTTP/1.1 message that only uses features understood (or
5015   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
5016   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
5019   Since HTTP/0.9 did not support header fields in a request,
5020   there is no mechanism for it to support name-based virtual
5021   hosts (selection of resource by inspection of the Host header
5022   field).  Any server that implements name-based virtual hosts
5023   ought to disable support for HTTP/0.9.  Most requests that
5024   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
5025   requests wherein a buggy client failed to properly encode
5026   linear whitespace found in a URI reference and placed in
5027   the request-target.
5030<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
5032   This section summarizes major differences between versions HTTP/1.0
5033   and HTTP/1.1.
5036<section title="Multi-homed Web Servers" anchor="">
5038   The requirements that clients and servers support the Host header
5039   field (<xref target=""/>), report an error if it is
5040   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
5041   are among the most important changes defined by HTTP/1.1.
5044   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
5045   addresses and servers; there was no other established mechanism for
5046   distinguishing the intended server of a request than the IP address
5047   to which that request was directed. The Host header field was
5048   introduced during the development of HTTP/1.1 and, though it was
5049   quickly implemented by most HTTP/1.0 browsers, additional requirements
5050   were placed on all HTTP/1.1 requests in order to ensure complete
5051   adoption.  At the time of this writing, most HTTP-based services
5052   are dependent upon the Host header field for targeting requests.
5056<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
5058   For most implementations of HTTP/1.0, each connection is established
5059   by the client prior to the request and closed by the server after
5060   sending the response. However, some implementations implement the
5061   Keep-Alive version of persistent connections described in
5062   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
5065   Some clients and servers might wish to be compatible with some
5066   previous implementations of persistent connections in HTTP/1.0
5067   clients and servers. Persistent connections in HTTP/1.0 are
5068   explicitly negotiated as they are not the default behavior. HTTP/1.0
5069   experimental implementations of persistent connections are faulty,
5070   and the new facilities in HTTP/1.1 are designed to rectify these
5071   problems. The problem was that some existing HTTP/1.0 clients might
5072   send Keep-Alive to a proxy server that doesn't understand
5073   Connection, which would then erroneously forward it to the next
5074   inbound server, which would establish the Keep-Alive connection and
5075   result in a hung HTTP/1.0 proxy waiting for the close on the
5076   response. The result is that HTTP/1.0 clients must be prevented from
5077   using Keep-Alive when talking to proxies.
5080   However, talking to proxies is the most important use of persistent
5081   connections, so that prohibition is clearly unacceptable. Therefore,
5082   we need some other mechanism for indicating a persistent connection
5083   is desired, which is safe to use even when talking to an old proxy
5084   that ignores Connection. Persistent connections are the default for
5085   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
5086   declaring non-persistence. See <xref target="header.connection"/>.
5091<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5093  Empty list elements in list productions have been deprecated.
5094  (<xref target="notation.abnf"/>)
5097  Rules about implicit linear whitespace between certain grammar productions
5098  have been removed; now it's only allowed when specifically pointed out
5099  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5100  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5101  Non-ASCII content in header fields and reason phrase has been obsoleted and
5102  made opaque (the TEXT rule was removed)
5103  (<xref target="basic.rules"/>)
5106  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5107  sensitive. Restrict the version numbers to be single digits due to the fact
5108  that implementations are known to handle multi-digit version numbers
5109  incorrectly.
5110  (<xref target="http.version"/>)
5113  Require that invalid whitespace around field-names be rejected.
5114  (<xref target="header.fields"/>)
5117  Require recipients to handle bogus Content-Length header fields as errors.
5118  (<xref target="message.body"/>)
5121  Remove reference to non-existent identity transfer-coding value tokens.
5122  (Sections <xref format="counter" target="message.body"/> and
5123  <xref format="counter" target="transfer.codings"/>)
5126  Update use of abs_path production from RFC 1808 to the path-absolute + query
5127  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5128  request method only.
5129  (<xref target="request-target"/>)
5132  Clarification that the chunk length does not include the count of the octets
5133  in the chunk header and trailer. Furthermore disallowed line folding
5134  in chunk extensions.
5135  (<xref target="chunked.encoding"/>)
5138  Remove hard limit of two connections per server.
5139  (<xref target="persistent.practical"/>)
5142  Change ABNF productions for header fields to only define the field value.
5143  (<xref target="header.field.definitions"/>)
5146  Clarify exactly when close connection options must be sent.
5147  (<xref target="header.connection"/>)
5150  Define the semantics of the "Upgrade" header field in responses other than
5151  101 (this was incorporated from <xref target="RFC2817"/>).
5152  (<xref target="header.upgrade"/>)
5157<?BEGININC p1-messaging.abnf-appendix ?>
5158<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5160<artwork type="abnf" name="p1-messaging.parsed-abnf">
5161<x:ref>BWS</x:ref> = OWS
5163<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5164<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5165 connection-token ] )
5166<x:ref>Content-Length</x:ref> = 1*DIGIT
5168<x:ref>Date</x:ref> = HTTP-date
5170<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5172<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5173<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5174<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5175<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5176 ]
5177<x:ref>Host</x:ref> = uri-host [ ":" port ]
5179<x:ref>Method</x:ref> = token
5181<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5183<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5184<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5185<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5186<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5187<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5189<x:ref>Status-Code</x:ref> = 3DIGIT
5190<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5192<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5193<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5194<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5195 transfer-coding ] )
5197<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5198<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5200<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5201 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5202 )
5204<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5205<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5206<x:ref>attribute</x:ref> = token
5207<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5209<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5210<x:ref>chunk-data</x:ref> = 1*OCTET
5211<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5212<x:ref>chunk-ext-name</x:ref> = token
5213<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5214<x:ref>chunk-size</x:ref> = 1*HEXDIG
5215<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5216<x:ref>connection-token</x:ref> = token
5217<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5218 / %x2A-5B ; '*'-'['
5219 / %x5D-7E ; ']'-'~'
5220 / obs-text
5222<x:ref>date1</x:ref> = day SP month SP year
5223<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5224<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5225<x:ref>day</x:ref> = 2DIGIT
5226<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5227 / %x54.75.65 ; Tue
5228 / %x57.65.64 ; Wed
5229 / %x54.68.75 ; Thu
5230 / %x46.72.69 ; Fri
5231 / %x53.61.74 ; Sat
5232 / %x53.75.6E ; Sun
5233<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5234 / %x54. ; Tuesday
5235 / %x57.65.64.6E. ; Wednesday
5236 / %x54. ; Thursday
5237 / %x46. ; Friday
5238 / %x53. ; Saturday
5239 / %x53.75.6E.64.61.79 ; Sunday
5241<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5242<x:ref>field-name</x:ref> = token
5243<x:ref>field-value</x:ref> = *( field-content / OWS )
5245<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5246<x:ref>hour</x:ref> = 2DIGIT
5247<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5248<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5250<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5252<x:ref>message-body</x:ref> = *OCTET
5253<x:ref>minute</x:ref> = 2DIGIT
5254<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5255 / %x46.65.62 ; Feb
5256 / %x4D.61.72 ; Mar
5257 / %x41.70.72 ; Apr
5258 / %x4D.61.79 ; May
5259 / %x4A.75.6E ; Jun
5260 / %x4A.75.6C ; Jul
5261 / %x41.75.67 ; Aug
5262 / %x53.65.70 ; Sep
5263 / %x4F.63.74 ; Oct
5264 / %x4E.6F.76 ; Nov
5265 / %x44.65.63 ; Dec
5267<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5268<x:ref>obs-fold</x:ref> = CRLF
5269<x:ref>obs-text</x:ref> = %x80-FF
5271<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5272<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5273<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5274<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5275<x:ref>product</x:ref> = token [ "/" product-version ]
5276<x:ref>product-version</x:ref> = token
5277<x:ref>protocol-name</x:ref> = token
5278<x:ref>protocol-version</x:ref> = token
5279<x:ref>pseudonym</x:ref> = token
5281<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5282 / %x5D-7E ; ']'-'~'
5283 / obs-text
5284<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5285 / %x5D-7E ; ']'-'~'
5286 / obs-text
5287<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5288<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5289<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5290<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5291<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5292<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5294<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5295<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5296<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5297<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5298 / authority
5299<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5300<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5302<x:ref>second</x:ref> = 2DIGIT
5303<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5304 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5305<x:ref>start-line</x:ref> = Request-Line / Status-Line
5307<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5308<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5309 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5310<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5311<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5312<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5313<x:ref>token</x:ref> = 1*tchar
5314<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5315<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5316 transfer-extension
5317<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5318<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5320<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5322<x:ref>value</x:ref> = word
5324<x:ref>word</x:ref> = token / quoted-string
5326<x:ref>year</x:ref> = 4DIGIT
5329<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5330; Chunked-Body defined but not used
5331; Connection defined but not used
5332; Content-Length defined but not used
5333; Date defined but not used
5334; HTTP-message defined but not used
5335; Host defined but not used
5336; Request defined but not used
5337; Response defined but not used
5338; TE defined but not used
5339; Trailer defined but not used
5340; Transfer-Encoding defined but not used
5341; URI-reference defined but not used
5342; Upgrade defined but not used
5343; Via defined but not used
5344; http-URI defined but not used
5345; https-URI defined but not used
5346; partial-URI defined but not used
5347; special defined but not used
5349<?ENDINC p1-messaging.abnf-appendix ?>
5351<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5353<section title="Since RFC 2616">
5355  Extracted relevant partitions from <xref target="RFC2616"/>.
5359<section title="Since draft-ietf-httpbis-p1-messaging-00">
5361  Closed issues:
5362  <list style="symbols">
5363    <t>
5364      <eref target=""/>:
5365      "HTTP Version should be case sensitive"
5366      (<eref target=""/>)
5367    </t>
5368    <t>
5369      <eref target=""/>:
5370      "'unsafe' characters"
5371      (<eref target=""/>)
5372    </t>
5373    <t>
5374      <eref target=""/>:
5375      "Chunk Size Definition"
5376      (<eref target=""/>)
5377    </t>
5378    <t>
5379      <eref target=""/>:
5380      "Message Length"
5381      (<eref target=""/>)
5382    </t>
5383    <t>
5384      <eref target=""/>:
5385      "Media Type Registrations"
5386      (<eref target=""/>)
5387    </t>
5388    <t>
5389      <eref target=""/>:
5390      "URI includes query"
5391      (<eref target=""/>)
5392    </t>
5393    <t>
5394      <eref target=""/>:
5395      "No close on 1xx responses"
5396      (<eref target=""/>)
5397    </t>
5398    <t>
5399      <eref target=""/>:
5400      "Remove 'identity' token references"
5401      (<eref target=""/>)
5402    </t>
5403    <t>
5404      <eref target=""/>:
5405      "Import query BNF"
5406    </t>
5407    <t>
5408      <eref target=""/>:
5409      "qdtext BNF"
5410    </t>
5411    <t>
5412      <eref target=""/>:
5413      "Normative and Informative references"
5414    </t>
5415    <t>
5416      <eref target=""/>:
5417      "RFC2606 Compliance"
5418    </t>
5419    <t>
5420      <eref target=""/>:
5421      "RFC977 reference"
5422    </t>
5423    <t>
5424      <eref target=""/>:
5425      "RFC1700 references"
5426    </t>
5427    <t>
5428      <eref target=""/>:
5429      "inconsistency in date format explanation"
5430    </t>
5431    <t>
5432      <eref target=""/>:
5433      "Date reference typo"
5434    </t>
5435    <t>
5436      <eref target=""/>:
5437      "Informative references"
5438    </t>
5439    <t>
5440      <eref target=""/>:
5441      "ISO-8859-1 Reference"
5442    </t>
5443    <t>
5444      <eref target=""/>:
5445      "Normative up-to-date references"
5446    </t>
5447  </list>
5450  Other changes:
5451  <list style="symbols">
5452    <t>
5453      Update media type registrations to use RFC4288 template.
5454    </t>
5455    <t>
5456      Use names of RFC4234 core rules DQUOTE and WSP,
5457      fix broken ABNF for chunk-data
5458      (work in progress on <eref target=""/>)
5459    </t>
5460  </list>
5464<section title="Since draft-ietf-httpbis-p1-messaging-01">
5466  Closed issues:
5467  <list style="symbols">
5468    <t>
5469      <eref target=""/>:
5470      "Bodies on GET (and other) requests"
5471    </t>
5472    <t>
5473      <eref target=""/>:
5474      "Updating to RFC4288"
5475    </t>
5476    <t>
5477      <eref target=""/>:
5478      "Status Code and Reason Phrase"
5479    </t>
5480    <t>
5481      <eref target=""/>:
5482      "rel_path not used"
5483    </t>
5484  </list>
5487  Ongoing work on ABNF conversion (<eref target=""/>):
5488  <list style="symbols">
5489    <t>
5490      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5491      "trailer-part").
5492    </t>
5493    <t>
5494      Avoid underscore character in rule names ("http_URL" ->
5495      "http-URL", "abs_path" -> "path-absolute").
5496    </t>
5497    <t>
5498      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5499      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5500      have to be updated when switching over to RFC3986.
5501    </t>
5502    <t>
5503      Synchronize core rules with RFC5234.
5504    </t>
5505    <t>
5506      Get rid of prose rules that span multiple lines.
5507    </t>
5508    <t>
5509      Get rid of unused rules LOALPHA and UPALPHA.
5510    </t>
5511    <t>
5512      Move "Product Tokens" section (back) into Part 1, as "token" is used
5513      in the definition of the Upgrade header field.
5514    </t>
5515    <t>
5516      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5517    </t>
5518    <t>
5519      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5520    </t>
5521  </list>
5525<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5527  Closed issues:
5528  <list style="symbols">
5529    <t>
5530      <eref target=""/>:
5531      "HTTP-date vs. rfc1123-date"
5532    </t>
5533    <t>
5534      <eref target=""/>:
5535      "WS in quoted-pair"
5536    </t>
5537  </list>
5540  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5541  <list style="symbols">
5542    <t>
5543      Reference RFC 3984, and update header field registrations for headers defined
5544      in this document.
5545    </t>
5546  </list>
5549  Ongoing work on ABNF conversion (<eref target=""/>):
5550  <list style="symbols">
5551    <t>
5552      Replace string literals when the string really is case-sensitive (HTTP-Version).
5553    </t>
5554  </list>
5558<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5560  Closed issues:
5561  <list style="symbols">
5562    <t>
5563      <eref target=""/>:
5564      "Connection closing"
5565    </t>
5566    <t>
5567      <eref target=""/>:
5568      "Move registrations and registry information to IANA Considerations"
5569    </t>
5570    <t>
5571      <eref target=""/>:
5572      "need new URL for PAD1995 reference"
5573    </t>
5574    <t>
5575      <eref target=""/>:
5576      "IANA Considerations: update HTTP URI scheme registration"
5577    </t>
5578    <t>
5579      <eref target=""/>:
5580      "Cite HTTPS URI scheme definition"
5581    </t>
5582    <t>
5583      <eref target=""/>:
5584      "List-type headers vs Set-Cookie"
5585    </t>
5586  </list>
5589  Ongoing work on ABNF conversion (<eref target=""/>):
5590  <list style="symbols">
5591    <t>
5592      Replace string literals when the string really is case-sensitive (HTTP-Date).
5593    </t>
5594    <t>
5595      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5596    </t>
5597  </list>
5601<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5603  Closed issues:
5604  <list style="symbols">
5605    <t>
5606      <eref target=""/>:
5607      "Out-of-date reference for URIs"
5608    </t>
5609    <t>
5610      <eref target=""/>:
5611      "RFC 2822 is updated by RFC 5322"
5612    </t>
5613  </list>
5616  Ongoing work on ABNF conversion (<eref target=""/>):
5617  <list style="symbols">
5618    <t>
5619      Use "/" instead of "|" for alternatives.
5620    </t>
5621    <t>
5622      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5623    </t>
5624    <t>
5625      Only reference RFC 5234's core rules.
5626    </t>
5627    <t>
5628      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5629      whitespace ("OWS") and required whitespace ("RWS").
5630    </t>
5631    <t>
5632      Rewrite ABNFs to spell out whitespace rules, factor out
5633      header field value format definitions.
5634    </t>
5635  </list>
5639<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5641  Closed issues:
5642  <list style="symbols">
5643    <t>
5644      <eref target=""/>:
5645      "Header LWS"
5646    </t>
5647    <t>
5648      <eref target=""/>:
5649      "Sort 1.3 Terminology"
5650    </t>
5651    <t>
5652      <eref target=""/>:
5653      "RFC2047 encoded words"
5654    </t>
5655    <t>
5656      <eref target=""/>:
5657      "Character Encodings in TEXT"
5658    </t>
5659    <t>
5660      <eref target=""/>:
5661      "Line Folding"
5662    </t>
5663    <t>
5664      <eref target=""/>:
5665      "OPTIONS * and proxies"
5666    </t>
5667    <t>
5668      <eref target=""/>:
5669      "Reason-Phrase BNF"
5670    </t>
5671    <t>
5672      <eref target=""/>:
5673      "Use of TEXT"
5674    </t>
5675    <t>
5676      <eref target=""/>:
5677      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5678    </t>
5679    <t>
5680      <eref target=""/>:
5681      "RFC822 reference left in discussion of date formats"
5682    </t>
5683  </list>
5686  Final work on ABNF conversion (<eref target=""/>):
5687  <list style="symbols">
5688    <t>
5689      Rewrite definition of list rules, deprecate empty list elements.
5690    </t>
5691    <t>
5692      Add appendix containing collected and expanded ABNF.
5693    </t>
5694  </list>
5697  Other changes:
5698  <list style="symbols">
5699    <t>
5700      Rewrite introduction; add mostly new Architecture Section.
5701    </t>
5702    <t>
5703      Move definition of quality values from Part 3 into Part 1;
5704      make TE request header field grammar independent of accept-params (defined in Part 3).
5705    </t>
5706  </list>
5710<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5712  Closed issues:
5713  <list style="symbols">
5714    <t>
5715      <eref target=""/>:
5716      "base for numeric protocol elements"
5717    </t>
5718    <t>
5719      <eref target=""/>:
5720      "comment ABNF"
5721    </t>
5722  </list>
5725  Partly resolved issues:
5726  <list style="symbols">
5727    <t>
5728      <eref target=""/>:
5729      "205 Bodies" (took out language that implied that there might be
5730      methods for which a request body MUST NOT be included)
5731    </t>
5732    <t>
5733      <eref target=""/>:
5734      "editorial improvements around HTTP-date"
5735    </t>
5736  </list>
5740<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5742  Closed issues:
5743  <list style="symbols">
5744    <t>
5745      <eref target=""/>:
5746      "Repeating single-value headers"
5747    </t>
5748    <t>
5749      <eref target=""/>:
5750      "increase connection limit"
5751    </t>
5752    <t>
5753      <eref target=""/>:
5754      "IP addresses in URLs"
5755    </t>
5756    <t>
5757      <eref target=""/>:
5758      "take over HTTP Upgrade Token Registry"
5759    </t>
5760    <t>
5761      <eref target=""/>:
5762      "CR and LF in chunk extension values"
5763    </t>
5764    <t>
5765      <eref target=""/>:
5766      "HTTP/0.9 support"
5767    </t>
5768    <t>
5769      <eref target=""/>:
5770      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5771    </t>
5772    <t>
5773      <eref target=""/>:
5774      "move definitions of gzip/deflate/compress to part 1"
5775    </t>
5776    <t>
5777      <eref target=""/>:
5778      "disallow control characters in quoted-pair"
5779    </t>
5780  </list>
5783  Partly resolved issues:
5784  <list style="symbols">
5785    <t>
5786      <eref target=""/>:
5787      "update IANA requirements wrt Transfer-Coding values" (add the
5788      IANA Considerations subsection)
5789    </t>
5790  </list>
5794<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5796  Closed issues:
5797  <list style="symbols">
5798    <t>
5799      <eref target=""/>:
5800      "header parsing, treatment of leading and trailing OWS"
5801    </t>
5802  </list>
5805  Partly resolved issues:
5806  <list style="symbols">
5807    <t>
5808      <eref target=""/>:
5809      "Placement of 13.5.1 and 13.5.2"
5810    </t>
5811    <t>
5812      <eref target=""/>:
5813      "use of term "word" when talking about header structure"
5814    </t>
5815  </list>
5819<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5821  Closed issues:
5822  <list style="symbols">
5823    <t>
5824      <eref target=""/>:
5825      "Clarification of the term 'deflate'"
5826    </t>
5827    <t>
5828      <eref target=""/>:
5829      "OPTIONS * and proxies"
5830    </t>
5831    <t>
5832      <eref target=""/>:
5833      "MIME-Version not listed in P1, general header fields"
5834    </t>
5835    <t>
5836      <eref target=""/>:
5837      "IANA registry for content/transfer encodings"
5838    </t>
5839    <t>
5840      <eref target=""/>:
5841      "Case-sensitivity of HTTP-date"
5842    </t>
5843    <t>
5844      <eref target=""/>:
5845      "use of term "word" when talking about header structure"
5846    </t>
5847  </list>
5850  Partly resolved issues:
5851  <list style="symbols">
5852    <t>
5853      <eref target=""/>:
5854      "Term for the requested resource's URI"
5855    </t>
5856  </list>
5860<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5862  Closed issues:
5863  <list style="symbols">
5864    <t>
5865      <eref target=""/>:
5866      "Connection Closing"
5867    </t>
5868    <t>
5869      <eref target=""/>:
5870      "Delimiting messages with multipart/byteranges"
5871    </t>
5872    <t>
5873      <eref target=""/>:
5874      "Handling multiple Content-Length headers"
5875    </t>
5876    <t>
5877      <eref target=""/>:
5878      "Clarify entity / representation / variant terminology"
5879    </t>
5880    <t>
5881      <eref target=""/>:
5882      "consider removing the 'changes from 2068' sections"
5883    </t>
5884  </list>
5887  Partly resolved issues:
5888  <list style="symbols">
5889    <t>
5890      <eref target=""/>:
5891      "HTTP(s) URI scheme definitions"
5892    </t>
5893  </list>
5897<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5899  Closed issues:
5900  <list style="symbols">
5901    <t>
5902      <eref target=""/>:
5903      "Trailer requirements"
5904    </t>
5905    <t>
5906      <eref target=""/>:
5907      "Text about clock requirement for caches belongs in p6"
5908    </t>
5909    <t>
5910      <eref target=""/>:
5911      "effective request URI: handling of missing host in HTTP/1.0"
5912    </t>
5913    <t>
5914      <eref target=""/>:
5915      "confusing Date requirements for clients"
5916    </t>
5917  </list>
5920  Partly resolved issues:
5921  <list style="symbols">
5922    <t>
5923      <eref target=""/>:
5924      "Handling multiple Content-Length headers"
5925    </t>
5926  </list>
5930<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5932  Closed issues:
5933  <list style="symbols">
5934    <t>
5935      <eref target=""/>:
5936      "RFC2145 Normative"
5937    </t>
5938    <t>
5939      <eref target=""/>:
5940      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5941    </t>
5942    <t>
5943      <eref target=""/>:
5944      "define 'transparent' proxy"
5945    </t>
5946    <t>
5947      <eref target=""/>:
5948      "Header Classification"
5949    </t>
5950    <t>
5951      <eref target=""/>:
5952      "Is * usable as a request-uri for new methods?"
5953    </t>
5954    <t>
5955      <eref target=""/>:
5956      "Migrate Upgrade details from RFC2817"
5957    </t>
5958    <t>
5959      <eref target=""/>:
5960      "untangle ABNFs for header fields"
5961    </t>
5962    <t>
5963      <eref target=""/>:
5964      "update RFC 2109 reference"
5965    </t>
5966  </list>
5970<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5972  Closed issues:
5973  <list style="symbols">
5974    <t>
5975      <eref target=""/>:
5976      "Allow is not in 13.5.2"
5977    </t>
5978    <t>
5979      <eref target=""/>:
5980      "Handling multiple Content-Length headers"
5981    </t>
5982    <t>
5983      <eref target=""/>:
5984      "untangle ABNFs for header fields"
5985    </t>
5986    <t>
5987      <eref target=""/>:
5988      "Content-Length ABNF broken"
5989    </t>
5990  </list>
5994<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5996  Closed issues:
5997  <list style="symbols">
5998    <t>
5999      <eref target=""/>:
6000      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
6001    </t>
6002    <t>
6003      <eref target=""/>:
6004      "Recommend minimum sizes for protocol elements"
6005    </t>
6006    <t>
6007      <eref target=""/>:
6008      "Set expectations around buffering"
6009    </t>
6010    <t>
6011      <eref target=""/>:
6012      "Considering messages in isolation"
6013    </t>
6014  </list>
6018<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
6020  Closed issues:
6021  <list style="symbols">
6022    <t>
6023      <eref target=""/>:
6024      "\-escaping in quoted strings"
6025    </t>
6026    <t>
6027      <eref target=""/>:
6028      "'Close' should be reserved in the HTTP header field registry"
6029    </t>
6030  </list>
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