source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1324

Last change on this file since 1324 was 1324, checked in by julian.reschke@…, 12 years ago

mention NTLM as something that violates the stalessness requirement (see #288)

  • Property svn:eol-style set to native
File size: 253.6 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.14"/>.
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   Senders &SHOULD-NOT; escape octets that do not require escaping
519   (i.e., other than DQUOTE and the backslash octet).
526<section title="HTTP-related architecture" anchor="architecture">
528   HTTP was created for the World Wide Web architecture
529   and has evolved over time to support the scalability needs of a worldwide
530   hypertext system. Much of that architecture is reflected in the terminology
531   and syntax productions used to define HTTP.
534<section title="Client/Server Messaging" anchor="operation">
535<iref primary="true" item="client"/>
536<iref primary="true" item="server"/>
537<iref primary="true" item="connection"/>
539   HTTP is a stateless request/response protocol that operates by exchanging
540   messages across a reliable transport or session-layer
541   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
542   program that establishes a connection to a server for the purpose of
543   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
544   program that accepts connections in order to service HTTP requests by
545   sending HTTP responses.
547<iref primary="true" item="user agent"/>
548<iref primary="true" item="origin server"/>
549<iref primary="true" item="browser"/>
550<iref primary="true" item="spider"/>
551<iref primary="true" item="sender"/>
552<iref primary="true" item="recipient"/>
554   Note that the terms client and server refer only to the roles that
555   these programs perform for a particular connection.  The same program
556   might act as a client on some connections and a server on others.  We use
557   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
558   such as a WWW browser, editor, or spider (web-traversing robot), and
559   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
560   authoritative responses to a request.  For general requirements, we use
561   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
562   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
563   message.
566   Most HTTP communication consists of a retrieval request (GET) for
567   a representation of some resource identified by a URI.  In the
568   simplest case, this might be accomplished via a single bidirectional
569   connection (===) between the user agent (UA) and the origin server (O).
571<figure><artwork type="drawing">
572         request   &gt;
573    UA ======================================= O
574                                &lt;   response
576<iref primary="true" item="message"/>
577<iref primary="true" item="request"/>
578<iref primary="true" item="response"/>
580   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
581   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
582   protocol version, followed by MIME-like header fields containing
583   request modifiers, client information, and payload metadata, an empty
584   line to indicate the end of the header section, and finally the payload
585   body (if any).
588   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
589   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
590   includes the protocol version, a success or error code, and textual
591   reason phrase, followed by MIME-like header fields containing server
592   information, resource metadata, and payload metadata, an empty line to
593   indicate the end of the header section, and finally the payload body (if any).
596   The following example illustrates a typical message exchange for a
597   GET request on the URI "":
600client request:
601</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
602GET /hello.txt HTTP/1.1
603User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
605Accept: */*
609server response:
610</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
611HTTP/1.1 200 OK
612Date: Mon, 27 Jul 2009 12:28:53 GMT
613Server: Apache
614Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
615ETag: "34aa387-d-1568eb00"
616Accept-Ranges: bytes
617Content-Length: <x:length-of target="exbody"/>
618Vary: Accept-Encoding
619Content-Type: text/plain
621<x:span anchor="exbody">Hello World!
625<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
627   Fundamentally, HTTP is a message-based protocol. Although message bodies can
628   be chunked (<xref target="chunked.encoding"/>) and implementations often
629   make parts of a message available progressively, this is not required, and
630   some widely-used implementations only make a message available when it is
631   complete. Furthermore, while most proxies will progressively stream messages,
632   some amount of buffering will take place, and some proxies might buffer
633   messages to perform transformations, check content or provide other services.
636   Therefore, extensions to and uses of HTTP cannot rely on the availability of
637   a partial message, or assume that messages will not be buffered. There are
638   strategies that can be used to test for buffering in a given connection, but
639   it should be understood that behaviors can differ across connections, and
640   between requests and responses.
643   Recipients &MUST; consider every message in a connection in isolation;
644   because HTTP is a stateless protocol, it cannot be assumed that two requests
645   on the same connection are from the same client or share any other common
646   attributes. In particular, intermediaries might mix requests from different
647   clients into a single server connection. Note that some existing HTTP
648   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
649   potentially causing interoperability and security problems.
653<section title="Connections and Transport Independence" anchor="transport-independence">
655   HTTP messaging is independent of the underlying transport or
656   session-layer connection protocol(s).  HTTP only presumes a reliable
657   transport with in-order delivery of requests and the corresponding
658   in-order delivery of responses.  The mapping of HTTP request and
659   response structures onto the data units of the underlying transport
660   protocol is outside the scope of this specification.
663   The specific connection protocols to be used for an interaction
664   are determined by client configuration and the target resource's URI.
665   For example, the "http" URI scheme
666   (<xref target="http.uri"/>) indicates a default connection of TCP
667   over IP, with a default TCP port of 80, but the client might be
668   configured to use a proxy via some other connection port or protocol
669   instead of using the defaults.
672   A connection might be used for multiple HTTP request/response exchanges,
673   as defined in <xref target="persistent.connections"/>.
677<section title="Intermediaries" anchor="intermediaries">
678<iref primary="true" item="intermediary"/>
680   HTTP enables the use of intermediaries to satisfy requests through
681   a chain of connections.  There are three common forms of HTTP
682   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
683   a single intermediary might act as an origin server, proxy, gateway,
684   or tunnel, switching behavior based on the nature of each request.
686<figure><artwork type="drawing">
687         &gt;             &gt;             &gt;             &gt;
688    <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>
689               &lt;             &lt;             &lt;             &lt;
692   The figure above shows three intermediaries (A, B, and C) between the
693   user agent and origin server. A request or response message that
694   travels the whole chain will pass through four separate connections.
695   Some HTTP communication options
696   might apply only to the connection with the nearest, non-tunnel
697   neighbor, only to the end-points of the chain, or to all connections
698   along the chain. Although the diagram is linear, each participant might
699   be engaged in multiple, simultaneous communications. For example, B
700   might be receiving requests from many clients other than A, and/or
701   forwarding requests to servers other than C, at the same time that it
702   is handling A's request.
705<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
706<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
707   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
708   to describe various requirements in relation to the directional flow of a
709   message: all messages flow from upstream to downstream.
710   Likewise, we use the terms inbound and outbound to refer to
711   directions in relation to the request path:
712   "<x:dfn>inbound</x:dfn>" means toward the origin server and
713   "<x:dfn>outbound</x:dfn>" means toward the user agent.
715<t><iref primary="true" item="proxy"/>
716   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
717   client, usually via local configuration rules, to receive requests
718   for some type(s) of absolute URI and attempt to satisfy those
719   requests via translation through the HTTP interface.  Some translations
720   are minimal, such as for proxy requests for "http" URIs, whereas
721   other requests might require translation to and from entirely different
722   application-layer protocols. Proxies are often used to group an
723   organization's HTTP requests through a common intermediary for the
724   sake of security, annotation services, or shared caching.
727<iref primary="true" item="transforming proxy"/>
728<iref primary="true" item="non-transforming proxy"/>
729   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
730   or configured to modify request or response messages in a semantically
731   meaningful way (i.e., modifications, beyond those required by normal
732   HTTP processing, that change the message in a way that would be
733   significant to the original sender or potentially significant to
734   downstream recipients).  For example, a transforming proxy might be
735   acting as a shared annotation server (modifying responses to include
736   references to a local annotation database), a malware filter, a
737   format transcoder, or an intranet-to-Internet privacy filter.  Such
738   transformations are presumed to be desired by the client (or client
739   organization) that selected the proxy and are beyond the scope of
740   this specification.  However, when a proxy is not intended to transform
741   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
742   requirements that preserve HTTP message semantics. See &status-203; and
743   &header-warning; for status and warning codes related to transformations.
745<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
746<iref primary="true" item="accelerator"/>
747   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
748   is a receiving agent that acts
749   as a layer above some other server(s) and translates the received
750   requests to the underlying server's protocol.  Gateways are often
751   used to encapsulate legacy or untrusted information services, to
752   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
753   enable partitioning or load-balancing of HTTP services across
754   multiple machines.
757   A gateway behaves as an origin server on its outbound connection and
758   as a user agent on its inbound connection.
759   All HTTP requirements applicable to an origin server
760   also apply to the outbound communication of a gateway.
761   A gateway communicates with inbound servers using any protocol that
762   it desires, including private extensions to HTTP that are outside
763   the scope of this specification.  However, an HTTP-to-HTTP gateway
764   that wishes to interoperate with third-party HTTP servers &MUST;
765   comply with HTTP user agent requirements on the gateway's inbound
766   connection and &MUST; implement the Connection
767   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
768   header fields for both connections.
770<t><iref primary="true" item="tunnel"/>
771   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
772   without changing the messages. Once active, a tunnel is not
773   considered a party to the HTTP communication, though the tunnel might
774   have been initiated by an HTTP request. A tunnel ceases to exist when
775   both ends of the relayed connection are closed. Tunnels are used to
776   extend a virtual connection through an intermediary, such as when
777   transport-layer security is used to establish private communication
778   through a shared firewall proxy.
780<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
781<iref primary="true" item="captive portal"/>
782   In addition, there may exist network intermediaries that are not
783   considered part of the HTTP communication but nevertheless act as
784   filters or redirecting agents (usually violating HTTP semantics,
785   causing security problems, and otherwise making a mess of things).
786   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
787   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
788   or "<x:dfn>captive portal</x:dfn>",
789   differs from an HTTP proxy because it has not been selected by the client.
790   Instead, the network intermediary redirects outgoing TCP port 80 packets
791   (and occasionally other common port traffic) to an internal HTTP server.
792   Interception proxies are commonly found on public network access points,
793   as a means of enforcing account subscription prior to allowing use of
794   non-local Internet services, and within corporate firewalls to enforce
795   network usage policies.
796   They are indistinguishable from a man-in-the-middle attack.
800<section title="Caches" anchor="caches">
801<iref primary="true" item="cache"/>
803   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
804   subsystem that controls its message storage, retrieval, and deletion.
805   A cache stores cacheable responses in order to reduce the response
806   time and network bandwidth consumption on future, equivalent
807   requests. Any client or server &MAY; employ a cache, though a cache
808   cannot be used by a server while it is acting as a tunnel.
811   The effect of a cache is that the request/response chain is shortened
812   if one of the participants along the chain has a cached response
813   applicable to that request. The following illustrates the resulting
814   chain if B has a cached copy of an earlier response from O (via C)
815   for a request which has not been cached by UA or A.
817<figure><artwork type="drawing">
818            &gt;             &gt;
819       UA =========== A =========== B - - - - - - C - - - - - - O
820                  &lt;             &lt;
822<t><iref primary="true" item="cacheable"/>
823   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
824   the response message for use in answering subsequent requests.
825   Even when a response is cacheable, there might be additional
826   constraints placed by the client or by the origin server on when
827   that cached response can be used for a particular request. HTTP
828   requirements for cache behavior and cacheable responses are
829   defined in &caching-overview;. 
832   There are a wide variety of architectures and configurations
833   of caches and proxies deployed across the World Wide Web and
834   inside large organizations. These systems include national hierarchies
835   of proxy caches to save transoceanic bandwidth, systems that
836   broadcast or multicast cache entries, organizations that distribute
837   subsets of cached data via optical media, and so on.
841<section title="Protocol Versioning" anchor="http.version">
842  <x:anchor-alias value="HTTP-Version"/>
843  <x:anchor-alias value="HTTP-Prot-Name"/>
845   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
846   versions of the protocol. This specification defines version "1.1".
847   The protocol version as a whole indicates the sender's compliance
848   with the set of requirements laid out in that version's corresponding
849   specification of HTTP.
852   The version of an HTTP message is indicated by an HTTP-Version field
853   in the first line of the message. HTTP-Version is case-sensitive.
855<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
856  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
857  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
860   The HTTP version number consists of two decimal digits separated by a "."
861   (period or decimal point).  The first digit ("major version") indicates the
862   HTTP messaging syntax, whereas the second digit ("minor version") indicates
863   the highest minor version to which the sender is at least conditionally
864   compliant and able to understand for future communication.  The minor
865   version advertises the sender's communication capabilities even when the
866   sender is only using a backwards-compatible subset of the protocol,
867   thereby letting the recipient know that more advanced features can
868   be used in response (by servers) or in future requests (by clients).
871   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
872   <xref target="RFC1945"/> or a recipient whose version is unknown,
873   the HTTP/1.1 message is constructed such that it can be interpreted
874   as a valid HTTP/1.0 message if all of the newer features are ignored.
875   This specification places recipient-version requirements on some
876   new features so that a compliant sender will only use compatible
877   features until it has determined, through configuration or the
878   receipt of a message, that the recipient supports HTTP/1.1.
881   The interpretation of an HTTP header field does not change
882   between minor versions of the same major version, though the default
883   behavior of a recipient in the absence of such a field can change.
884   Unless specified otherwise, header fields defined in HTTP/1.1 are
885   defined for all versions of HTTP/1.x.  In particular, the Host and
886   Connection header fields ought to be implemented by all HTTP/1.x
887   implementations whether or not they advertise compliance with HTTP/1.1.
890   New header fields can be defined such that, when they are
891   understood by a recipient, they might override or enhance the
892   interpretation of previously defined header fields.  When an
893   implementation receives an unrecognized header field, the recipient
894   &MUST; ignore that header field for local processing regardless of
895   the message's HTTP version.  An unrecognized header field received
896   by a proxy &MUST; be forwarded downstream unless the header field's
897   field-name is listed in the message's Connection header-field
898   (see <xref target="header.connection"/>).
899   These requirements allow HTTP's functionality to be enhanced without
900   requiring prior update of all compliant intermediaries.
903   Intermediaries that process HTTP messages (i.e., all intermediaries
904   other than those acting as a tunnel) &MUST; send their own HTTP-Version
905   in forwarded messages.  In other words, they &MUST-NOT; blindly
906   forward the first line of an HTTP message without ensuring that the
907   protocol version matches what the intermediary understands, and
908   is at least conditionally compliant to, for both the receiving and
909   sending of messages.  Forwarding an HTTP message without rewriting
910   the HTTP-Version might result in communication errors when downstream
911   recipients use the message sender's version to determine what features
912   are safe to use for later communication with that sender.
915   An HTTP client &SHOULD; send a request version equal to the highest
916   version for which the client is at least conditionally compliant and
917   whose major version is no higher than the highest version supported
918   by the server, if this is known.  An HTTP client &MUST-NOT; send a
919   version for which it is not at least conditionally compliant.
922   An HTTP client &MAY; send a lower request version if it is known that
923   the server incorrectly implements the HTTP specification, but only
924   after the client has attempted at least one normal request and determined
925   from the response status or header fields (e.g., Server) that the
926   server improperly handles higher request versions.
929   An HTTP server &SHOULD; send a response version equal to the highest
930   version for which the server is at least conditionally compliant and
931   whose major version is less than or equal to the one received in the
932   request.  An HTTP server &MUST-NOT; send a version for which it is not
933   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
934   Version Not Supported) response if it cannot send a response using the
935   major version used in the client's request.
938   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
939   if it is known or suspected that the client incorrectly implements the
940   HTTP specification and is incapable of correctly processing later
941   version responses, such as when a client fails to parse the version
942   number correctly or when an intermediary is known to blindly forward
943   the HTTP-Version even when it doesn't comply with the given minor
944   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
945   performed unless triggered by specific client attributes, such as when
946   one or more of the request header fields (e.g., User-Agent) uniquely
947   match the values sent by a client known to be in error.
950   The intention of HTTP's versioning design is that the major number
951   will only be incremented if an incompatible message syntax is
952   introduced, and that the minor number will only be incremented when
953   changes made to the protocol have the effect of adding to the message
954   semantics or implying additional capabilities of the sender.  However,
955   the minor version was not incremented for the changes introduced between
956   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
957   is specifically avoiding any such changes to the protocol.
961<section title="Uniform Resource Identifiers" anchor="uri">
962<iref primary="true" item="resource"/>
964   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
965   throughout HTTP as the means for identifying resources. URI references
966   are used to target requests, indicate redirects, and define relationships.
967   HTTP does not limit what a resource might be; it merely defines an interface
968   that can be used to interact with a resource via HTTP. More information on
969   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
971  <x:anchor-alias value="URI-reference"/>
972  <x:anchor-alias value="absolute-URI"/>
973  <x:anchor-alias value="relative-part"/>
974  <x:anchor-alias value="authority"/>
975  <x:anchor-alias value="path-abempty"/>
976  <x:anchor-alias value="path-absolute"/>
977  <x:anchor-alias value="port"/>
978  <x:anchor-alias value="query"/>
979  <x:anchor-alias value="uri-host"/>
980  <x:anchor-alias value="partial-URI"/>
982   This specification adopts the definitions of "URI-reference",
983   "absolute-URI", "relative-part", "port", "host",
984   "path-abempty", "path-absolute", "query", and "authority" from the
985   URI generic syntax <xref target="RFC3986"/>.
986   In addition, we define a partial-URI rule for protocol elements
987   that allow a relative URI but not a fragment.
989<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"/>
990  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
991  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
992  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
993  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
994  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
995  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
996  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
997  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
998  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
1000  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
1003   Each protocol element in HTTP that allows a URI reference will indicate
1004   in its ABNF production whether the element allows any form of reference
1005   (URI-reference), only a URI in absolute form (absolute-URI), only the
1006   path and optional query components, or some combination of the above.
1007   Unless otherwise indicated, URI references are parsed relative to the
1008   effective request URI, which defines the default base URI for references
1009   in both the request and its corresponding response.
1012<section title="http URI scheme" anchor="http.uri">
1013  <x:anchor-alias value="http-URI"/>
1014  <iref item="http URI scheme" primary="true"/>
1015  <iref item="URI scheme" subitem="http" primary="true"/>
1017   The "http" URI scheme is hereby defined for the purpose of minting
1018   identifiers according to their association with the hierarchical
1019   namespace governed by a potential HTTP origin server listening for
1020   TCP connections on a given port.
1022<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1023  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1026   The HTTP origin server is identified by the generic syntax's
1027   <x:ref>authority</x:ref> component, which includes a host identifier
1028   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1029   The remainder of the URI, consisting of both the hierarchical path
1030   component and optional query component, serves as an identifier for
1031   a potential resource within that origin server's name space.
1034   If the host identifier is provided as an IP literal or IPv4 address,
1035   then the origin server is any listener on the indicated TCP port at
1036   that IP address. If host is a registered name, then that name is
1037   considered an indirect identifier and the recipient might use a name
1038   resolution service, such as DNS, to find the address of a listener
1039   for that host.
1040   The host &MUST-NOT; be empty; if an "http" URI is received with an
1041   empty host, then it &MUST; be rejected as invalid.
1042   If the port subcomponent is empty or not given, then TCP port 80 is
1043   assumed (the default reserved port for WWW services).
1046   Regardless of the form of host identifier, access to that host is not
1047   implied by the mere presence of its name or address. The host might or might
1048   not exist and, even when it does exist, might or might not be running an
1049   HTTP server or listening to the indicated port. The "http" URI scheme
1050   makes use of the delegated nature of Internet names and addresses to
1051   establish a naming authority (whatever entity has the ability to place
1052   an HTTP server at that Internet name or address) and allows that
1053   authority to determine which names are valid and how they might be used.
1056   When an "http" URI is used within a context that calls for access to the
1057   indicated resource, a client &MAY; attempt access by resolving
1058   the host to an IP address, establishing a TCP connection to that address
1059   on the indicated port, and sending an HTTP request message to the server
1060   containing the URI's identifying data as described in <xref target="request"/>.
1061   If the server responds to that request with a non-interim HTTP response
1062   message, as described in <xref target="response"/>, then that response
1063   is considered an authoritative answer to the client's request.
1066   Although HTTP is independent of the transport protocol, the "http"
1067   scheme is specific to TCP-based services because the name delegation
1068   process depends on TCP for establishing authority.
1069   An HTTP service based on some other underlying connection protocol
1070   would presumably be identified using a different URI scheme, just as
1071   the "https" scheme (below) is used for servers that require an SSL/TLS
1072   transport layer on a connection. Other protocols might also be used to
1073   provide access to "http" identified resources &mdash; it is only the
1074   authoritative interface used for mapping the namespace that is
1075   specific to TCP.
1078   The URI generic syntax for authority also includes a deprecated
1079   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1080   for including user authentication information in the URI.  Some
1081   implementations make use of the userinfo component for internal
1082   configuration of authentication information, such as within command
1083   invocation options, configuration files, or bookmark lists, even
1084   though such usage might expose a user identifier or password.
1085   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1086   delimiter) when transmitting an "http" URI in a message.  Recipients
1087   of HTTP messages that contain a URI reference &SHOULD; parse for the
1088   existence of userinfo and treat its presence as an error, likely
1089   indicating that the deprecated subcomponent is being used to obscure
1090   the authority for the sake of phishing attacks.
1094<section title="https URI scheme" anchor="https.uri">
1095   <x:anchor-alias value="https-URI"/>
1096   <iref item="https URI scheme"/>
1097   <iref item="URI scheme" subitem="https"/>
1099   The "https" URI scheme is hereby defined for the purpose of minting
1100   identifiers according to their association with the hierarchical
1101   namespace governed by a potential HTTP origin server listening for
1102   SSL/TLS-secured connections on a given TCP port.
1105   All of the requirements listed above for the "http" scheme are also
1106   requirements for the "https" scheme, except that a default TCP port
1107   of 443 is assumed if the port subcomponent is empty or not given,
1108   and the TCP connection &MUST; be secured for privacy through the
1109   use of strong encryption prior to sending the first HTTP request.
1111<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1112  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1115   Unlike the "http" scheme, responses to "https" identified requests
1116   are never "public" and thus &MUST-NOT; be reused for shared caching.
1117   They can, however, be reused in a private cache if the message is
1118   cacheable by default in HTTP or specifically indicated as such by
1119   the Cache-Control header field (&header-cache-control;).
1122   Resources made available via the "https" scheme have no shared
1123   identity with the "http" scheme even if their resource identifiers
1124   indicate the same authority (the same host listening to the same
1125   TCP port).  They are distinct name spaces and are considered to be
1126   distinct origin servers.  However, an extension to HTTP that is
1127   defined to apply to entire host domains, such as the Cookie protocol
1128   <xref target="RFC6265"/>, can allow information
1129   set by one service to impact communication with other services
1130   within a matching group of host domains.
1133   The process for authoritative access to an "https" identified
1134   resource is defined in <xref target="RFC2818"/>.
1138<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1140   Since the "http" and "https" schemes conform to the URI generic syntax,
1141   such URIs are normalized and compared according to the algorithm defined
1142   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1143   described above for each scheme.
1146   If the port is equal to the default port for a scheme, the normal
1147   form is to elide the port subcomponent. Likewise, an empty path
1148   component is equivalent to an absolute path of "/", so the normal
1149   form is to provide a path of "/" instead. The scheme and host
1150   are case-insensitive and normally provided in lowercase; all
1151   other components are compared in a case-sensitive manner.
1152   Characters other than those in the "reserved" set are equivalent
1153   to their percent-encoded octets (see <xref target="RFC3986"
1154   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1157   For example, the following three URIs are equivalent:
1159<figure><artwork type="example">
1168<section title="Message Format" anchor="http.message">
1169<x:anchor-alias value="generic-message"/>
1170<x:anchor-alias value="message.types"/>
1171<x:anchor-alias value="HTTP-message"/>
1172<x:anchor-alias value="start-line"/>
1173<iref item="header section"/>
1174<iref item="headers"/>
1175<iref item="header field"/>
1177   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1178   octets in a format similar to the Internet Message Format
1179   <xref target="RFC5322"/>: zero or more header fields (collectively
1180   referred to as the "headers" or the "header section"), an empty line
1181   indicating the end of the header section, and an optional message-body.
1184   An HTTP message can either be a request from client to server or a
1185   response from server to client.  Syntactically, the two types of message
1186   differ only in the start-line, which is either a Request-Line (for requests)
1187   or a Status-Line (for responses), and in the algorithm for determining
1188   the length of the message-body (<xref target="message.body"/>).
1189   In theory, a client could receive requests and a server could receive
1190   responses, distinguishing them by their different start-line formats,
1191   but in practice servers are implemented to only expect a request
1192   (a response is interpreted as an unknown or invalid request method)
1193   and clients are implemented to only expect a response.
1195<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1196  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1197                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1198                    <x:ref>CRLF</x:ref>
1199                    [ <x:ref>message-body</x:ref> ]
1200  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1203   Implementations &MUST-NOT; send whitespace between the start-line and
1204   the first header field. The presence of such whitespace in a request
1205   might be an attempt to trick a server into ignoring that field or
1206   processing the line after it as a new request, either of which might
1207   result in a security vulnerability if other implementations within
1208   the request chain interpret the same message differently.
1209   Likewise, the presence of such whitespace in a response might be
1210   ignored by some clients or cause others to cease parsing.
1213<section title="Message Parsing Robustness" anchor="message.robustness">
1215   In the interest of robustness, servers &SHOULD; ignore at least one
1216   empty line received where a Request-Line is expected. In other words, if
1217   the server is reading the protocol stream at the beginning of a
1218   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1221   Some old HTTP/1.0 client implementations send an extra CRLF
1222   after a POST request as a lame workaround for some early server
1223   applications that failed to read message-body content that was
1224   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1225   preface or follow a request with an extra CRLF.  If terminating
1226   the request message-body with a line-ending is desired, then the
1227   client &MUST; include the terminating CRLF octets as part of the
1228   message-body length.
1231   When a server listening only for HTTP request messages, or processing
1232   what appears from the start-line to be an HTTP request message,
1233   receives a sequence of octets that does not match the HTTP-message
1234   grammar aside from the robustness exceptions listed above, the
1235   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1238   The normal procedure for parsing an HTTP message is to read the
1239   start-line into a structure, read each header field into a hash
1240   table by field name until the empty line, and then use the parsed
1241   data to determine if a message-body is expected.  If a message-body
1242   has been indicated, then it is read as a stream until an amount
1243   of octets equal to the message-body length is read or the connection
1244   is closed.  Care must be taken to parse an HTTP message as a sequence
1245   of octets in an encoding that is a superset of US-ASCII.  Attempting
1246   to parse HTTP as a stream of Unicode characters in a character encoding
1247   like UTF-16 might introduce security flaws due to the differing ways
1248   that such parsers interpret invalid characters.
1251   HTTP allows the set of defined header fields to be extended without
1252   changing the protocol version (see <xref target="header.field.registration"/>).
1253   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1254   proxy is specifically configured to block or otherwise transform such
1255   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1259<section title="Header Fields" anchor="header.fields">
1260  <x:anchor-alias value="header-field"/>
1261  <x:anchor-alias value="field-content"/>
1262  <x:anchor-alias value="field-name"/>
1263  <x:anchor-alias value="field-value"/>
1264  <x:anchor-alias value="OWS"/>
1266   Each HTTP header field consists of a case-insensitive field name
1267   followed by a colon (":"), optional whitespace, and the field value.
1269<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"/>
1270  <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>
1271  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1272  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1273  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1276   No whitespace is allowed between the header field name and colon. For
1277   security reasons, any request message received containing such whitespace
1278   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1279   &MUST; remove any such whitespace from a response message before
1280   forwarding the message downstream.
1283   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1284   preferred. The field value does not include any leading or trailing white
1285   space: OWS occurring before the first non-whitespace octet of the
1286   field value or after the last non-whitespace octet of the field value
1287   is ignored and &SHOULD; be removed before further processing (as this does
1288   not change the meaning of the header field).
1291   The order in which header fields with differing field names are
1292   received is not significant. However, it is "good practice" to send
1293   header fields that contain control data first, such as Host on
1294   requests and Date on responses, so that implementations can decide
1295   when not to handle a message as early as possible.  A server &MUST;
1296   wait until the entire header section is received before interpreting
1297   a request message, since later header fields might include conditionals,
1298   authentication credentials, or deliberately misleading duplicate
1299   header fields that would impact request processing.
1302   Multiple header fields with the same field name &MUST-NOT; be
1303   sent in a message unless the entire field value for that
1304   header field is defined as a comma-separated list [i.e., #(values)].
1305   Multiple header fields with the same field name can be combined into
1306   one "field-name: field-value" pair, without changing the semantics of the
1307   message, by appending each subsequent field value to the combined
1308   field value in order, separated by a comma. The order in which
1309   header fields with the same field name are received is therefore
1310   significant to the interpretation of the combined field value;
1311   a proxy &MUST-NOT; change the order of these field values when
1312   forwarding a message.
1315  <t>
1316   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1317   practice can occur multiple times, but does not use the list syntax, and
1318   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1319   for details.) Also note that the Set-Cookie2 header field specified in
1320   <xref target="RFC2965"/> does not share this problem.
1321  </t>
1324   Historically, HTTP header field values could be extended over multiple
1325   lines by preceding each extra line with at least one space or horizontal
1326   tab octet (line folding). This specification deprecates such line
1327   folding except within the message/http media type
1328   (<xref target=""/>).
1329   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1330   (i.e., that contain any field-content that matches the obs-fold rule) unless
1331   the message is intended for packaging within the message/http media type.
1332   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1333   obs-fold whitespace with a single SP prior to interpreting the field value
1334   or forwarding the message downstream.
1337   Historically, HTTP has allowed field content with text in the ISO-8859-1
1338   <xref target="ISO-8859-1"/> character encoding and supported other
1339   character sets only through use of <xref target="RFC2047"/> encoding.
1340   In practice, most HTTP header field values use only a subset of the
1341   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1342   header fields &SHOULD; limit their field values to US-ASCII octets.
1343   Recipients &SHOULD; treat other (obs-text) octets in field content as
1344   opaque data.
1346<t anchor="rule.comment">
1347  <x:anchor-alias value="comment"/>
1348  <x:anchor-alias value="ctext"/>
1349   Comments can be included in some HTTP header fields by surrounding
1350   the comment text with parentheses. Comments are only allowed in
1351   fields containing "comment" as part of their field value definition.
1353<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1354  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1355  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1356                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1358<t anchor="rule.quoted-cpair">
1359  <x:anchor-alias value="quoted-cpair"/>
1360   The backslash octet ("\") can be used as a single-octet
1361   quoting mechanism within comment constructs:
1363<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1364  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1367   Senders &SHOULD-NOT; escape octets that do not require escaping
1368   (i.e., other than the backslash octet "\" and the parentheses "(" and
1369   ")").
1372   HTTP does not place a pre-defined limit on the length of header fields,
1373   either in isolation or as a set. A server &MUST; be prepared to receive
1374   request header fields of unbounded length and respond with a 4xx status
1375   code if the received header field(s) would be longer than the server wishes
1376   to handle.
1379   A client that receives response headers that are longer than it wishes to
1380   handle can only treat it as a server error.
1383   Various ad-hoc limitations on header length are found in practice. It is
1384   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1385   combined header fields have 4000 or more octets.
1389<section title="Message Body" anchor="message.body">
1390  <x:anchor-alias value="message-body"/>
1392   The message-body (if any) of an HTTP message is used to carry the
1393   payload body associated with the request or response.
1395<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1396  <x:ref>message-body</x:ref> = *OCTET
1399   The message-body differs from the payload body only when a transfer-coding
1400   has been applied, as indicated by the Transfer-Encoding header field
1401   (<xref target="header.transfer-encoding"/>).  If more than one
1402   Transfer-Encoding header field is present in a message, the multiple
1403   field-values &MUST; be combined into one field-value, according to the
1404   algorithm defined in <xref target="header.fields"/>, before determining
1405   the message-body length.
1408   When one or more transfer-codings are applied to a payload in order to
1409   form the message-body, the Transfer-Encoding header field &MUST; contain
1410   the list of transfer-codings applied. Transfer-Encoding is a property of
1411   the message, not of the payload, and thus &MAY; be added or removed by
1412   any implementation along the request/response chain under the constraints
1413   found in <xref target="transfer.codings"/>.
1416   If a message is received that has multiple Content-Length header fields
1417   (<xref target="header.content-length"/>) with field-values consisting
1418   of the same decimal value, or a single Content-Length header field with
1419   a field value containing a list of identical decimal values (e.g.,
1420   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1421   header fields have been generated or combined by an upstream message
1422   processor, then the recipient &MUST; either reject the message as invalid
1423   or replace the duplicated field-values with a single valid Content-Length
1424   field containing that decimal value prior to determining the message-body
1425   length.
1428   The rules for when a message-body is allowed in a message differ for
1429   requests and responses.
1432   The presence of a message-body in a request is signaled by the
1433   inclusion of a Content-Length or Transfer-Encoding header field in
1434   the request's header fields, even if the request method does not
1435   define any use for a message-body.  This allows the request
1436   message framing algorithm to be independent of method semantics.
1439   For response messages, whether or not a message-body is included with
1440   a message is dependent on both the request method and the response
1441   status code (<xref target="status.code.and.reason.phrase"/>).
1442   Responses to the HEAD request method never include a message-body
1443   because the associated response header fields (e.g., Transfer-Encoding,
1444   Content-Length, etc.) only indicate what their values would have been
1445   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1446   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1447   All other responses do include a message-body, although the body
1448   &MAY; be of zero length.
1451   The length of the message-body is determined by one of the following
1452   (in order of precedence):
1455  <list style="numbers">
1456    <x:lt><t>
1457     Any response to a HEAD request and any response with a status
1458     code of 100-199, 204, or 304 is always terminated by the first
1459     empty line after the header fields, regardless of the header
1460     fields present in the message, and thus cannot contain a message-body.
1461    </t></x:lt>
1462    <x:lt><t>
1463     If a Transfer-Encoding header field is present
1464     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1465     is the final encoding, the message-body length is determined by reading
1466     and decoding the chunked data until the transfer-coding indicates the
1467     data is complete.
1468    </t>
1469    <t>
1470     If a Transfer-Encoding header field is present in a response and the
1471     "chunked" transfer-coding is not the final encoding, the message-body
1472     length is determined by reading the connection until it is closed by
1473     the server.
1474     If a Transfer-Encoding header field is present in a request and the
1475     "chunked" transfer-coding is not the final encoding, the message-body
1476     length cannot be determined reliably; the server &MUST; respond with
1477     the 400 (Bad Request) status code and then close the connection.
1478    </t>
1479    <t>
1480     If a message is received with both a Transfer-Encoding header field
1481     and a Content-Length header field, the Transfer-Encoding overrides
1482     the Content-Length.
1483     Such a message might indicate an attempt to perform request or response
1484     smuggling (bypass of security-related checks on message routing or content)
1485     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1486     be removed, prior to forwarding the message downstream, or replaced with
1487     the real message-body length after the transfer-coding is decoded.
1488    </t></x:lt>
1489    <x:lt><t>
1490     If a message is received without Transfer-Encoding and with either
1491     multiple Content-Length header fields having differing field-values or
1492     a single Content-Length header field having an invalid value, then the
1493     message framing is invalid and &MUST; be treated as an error to
1494     prevent request or response smuggling.
1495     If this is a request message, the server &MUST; respond with
1496     a 400 (Bad Request) status code and then close the connection.
1497     If this is a response message received by a proxy, the proxy
1498     &MUST; discard the received response, send a 502 (Bad Gateway)
1499     status code as its downstream response, and then close the connection.
1500     If this is a response message received by a user-agent, it &MUST; be
1501     treated as an error by discarding the message and closing the connection.
1502    </t></x:lt>
1503    <x:lt><t>
1504     If a valid Content-Length header field
1505     is present without Transfer-Encoding, its decimal value defines the
1506     message-body length in octets.  If the actual number of octets sent in
1507     the message is less than the indicated Content-Length, the recipient
1508     &MUST; consider the message to be incomplete and treat the connection
1509     as no longer usable.
1510     If the actual number of octets sent in the message is more than the indicated
1511     Content-Length, the recipient &MUST; only process the message-body up to the
1512     field value's number of octets; the remainder of the message &MUST; either
1513     be discarded or treated as the next message in a pipeline.  For the sake of
1514     robustness, a user-agent &MAY; attempt to detect and correct such an error
1515     in message framing if it is parsing the response to the last request on
1516     on a connection and the connection has been closed by the server.
1517    </t></x:lt>
1518    <x:lt><t>
1519     If this is a request message and none of the above are true, then the
1520     message-body length is zero (no message-body is present).
1521    </t></x:lt>
1522    <x:lt><t>
1523     Otherwise, this is a response message without a declared message-body
1524     length, so the message-body length is determined by the number of octets
1525     received prior to the server closing the connection.
1526    </t></x:lt>
1527  </list>
1530   Since there is no way to distinguish a successfully completed,
1531   close-delimited message from a partially-received message interrupted
1532   by network failure, implementations &SHOULD; use encoding or
1533   length-delimited messages whenever possible.  The close-delimiting
1534   feature exists primarily for backwards compatibility with HTTP/1.0.
1537   A server &MAY; reject a request that contains a message-body but
1538   not a Content-Length by responding with 411 (Length Required).
1541   Unless a transfer-coding other than "chunked" has been applied,
1542   a client that sends a request containing a message-body &SHOULD;
1543   use a valid Content-Length header field if the message-body length
1544   is known in advance, rather than the "chunked" encoding, since some
1545   existing services respond to "chunked" with a 411 (Length Required)
1546   status code even though they understand the chunked encoding.  This
1547   is typically because such services are implemented via a gateway that
1548   requires a content-length in advance of being called and the server
1549   is unable or unwilling to buffer the entire request before processing.
1552   A client that sends a request containing a message-body &MUST; include a
1553   valid Content-Length header field if it does not know the server will
1554   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1555   of specific user configuration or by remembering the version of a prior
1556   received response.
1559   Request messages that are prematurely terminated, possibly due to a
1560   cancelled connection or a server-imposed time-out exception, &MUST;
1561   result in closure of the connection; sending an HTTP/1.1 error response
1562   prior to closing the connection is &OPTIONAL;.
1563   Response messages that are prematurely terminated, usually by closure
1564   of the connection prior to receiving the expected number of octets or by
1565   failure to decode a transfer-encoded message-body, &MUST; be recorded
1566   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1567   message-body as if it were complete (i.e., some indication must be given
1568   to the user that an error occurred).  Cache requirements for incomplete
1569   responses are defined in &cache-incomplete;.
1572   A server &MUST; read the entire request message-body or close
1573   the connection after sending its response, since otherwise the
1574   remaining data on a persistent connection would be misinterpreted
1575   as the next request.  Likewise,
1576   a client &MUST; read the entire response message-body if it intends
1577   to reuse the same connection for a subsequent request.  Pipelining
1578   multiple requests on a connection is described in <xref target="pipelining"/>.
1582<section title="General Header Fields" anchor="general.header.fields">
1583  <x:anchor-alias value="general-header"/>
1585   There are a few header fields which have general applicability for
1586   both request and response messages, but which do not apply to the
1587   payload being transferred. These header fields apply only to the
1588   message being transmitted.
1590<texttable align="left">
1591  <ttcol>Header Field Name</ttcol>
1592  <ttcol>Defined in...</ttcol>
1594  <c>Connection</c> <c><xref target="header.connection"/></c>
1595  <c>Date</c> <c><xref target=""/></c>
1596  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1597  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1598  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1599  <c>Via</c> <c><xref target="header.via"/></c>
1604<section title="Request" anchor="request">
1605  <x:anchor-alias value="Request"/>
1607   A request message from a client to a server begins with a
1608   Request-Line, followed by zero or more header fields, an empty
1609   line signifying the end of the header block, and an optional
1610   message body.
1612<!--                 Host                      ; should be moved here eventually -->
1613<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1614  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1615                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1616                  <x:ref>CRLF</x:ref>
1617                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1620<section title="Request-Line" anchor="request-line">
1621  <x:anchor-alias value="Request-Line"/>
1623   The Request-Line begins with a method token, followed by a single
1624   space (SP), the request-target, another single space (SP), the
1625   protocol version, and ending with CRLF.
1627<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1628  <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>
1631<section title="Method" anchor="method">
1632  <x:anchor-alias value="Method"/>
1634   The Method token indicates the request method to be performed on the
1635   target resource. The request method is case-sensitive.
1637<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1638  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1642<section title="request-target" anchor="request-target">
1643  <x:anchor-alias value="request-target"/>
1645   The request-target identifies the target resource upon which to apply
1646   the request.  In most cases, the user agent is provided a URI reference
1647   from which it determines an absolute URI for identifying the target
1648   resource.  When a request to the resource is initiated, all or part
1649   of that URI is used to construct the HTTP request-target.
1651<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1652  <x:ref>request-target</x:ref> = "*"
1653                 / <x:ref>absolute-URI</x:ref>
1654                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1655                 / <x:ref>authority</x:ref>
1658   The four options for request-target are dependent on the nature of the
1659   request.
1661<t><iref item="asterisk form (of request-target)"/>
1662   The asterisk "*" form of request-target, which &MUST-NOT; be used
1663   with any request method other than OPTIONS, means that the request
1664   applies to the server as a whole (the listening process) rather than
1665   to a specific named resource at that server.  For example,
1667<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1668OPTIONS * HTTP/1.1
1670<t><iref item="absolute-URI form (of request-target)"/>
1671   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1672   proxy. The proxy is requested to either forward the request or service it
1673   from a valid cache, and then return the response. Note that the proxy &MAY;
1674   forward the request on to another proxy or directly to the server
1675   specified by the absolute-URI. In order to avoid request loops, a
1676   proxy that forwards requests to other proxies &MUST; be able to
1677   recognize and exclude all of its own server names, including
1678   any aliases, local variations, and the numeric IP address. An example
1679   Request-Line would be:
1681<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1682GET HTTP/1.1
1685   To allow for transition to absolute-URIs in all requests in future
1686   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1687   form in requests, even though HTTP/1.1 clients will only generate
1688   them in requests to proxies.
1691   If a proxy receives a host name that is not a fully qualified domain
1692   name, it &MAY; add its domain to the host name it received. If a proxy
1693   receives a fully qualified domain name, the proxy &MUST-NOT; change
1694   the host name.
1696<t><iref item="authority form (of request-target)"/>
1697   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1699<t><iref item="origin form (of request-target)"/>
1700   The most common form of request-target is that used when making
1701   a request to an origin server ("origin form").
1702   In this case, the absolute path and query components of the URI
1703   &MUST; be transmitted as the request-target, and the authority component
1704   &MUST; be transmitted in a Host header field. For example, a client wishing
1705   to retrieve a representation of the resource, as identified above,
1706   directly from the origin server would open (or reuse) a TCP connection
1707   to port 80 of the host "" and send the lines:
1709<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1710GET /pub/WWW/TheProject.html HTTP/1.1
1714   followed by the remainder of the Request. Note that the origin form
1715   of request-target always starts with an absolute path; if the target
1716   resource's URI path is empty, then an absolute path of "/" &MUST; be
1717   provided in the request-target.
1720   If a proxy receives an OPTIONS request with an absolute-URI form of
1721   request-target in which the URI has an empty path and no query component,
1722   then the last proxy on the request chain &MUST; use a request-target
1723   of "*" when it forwards the request to the indicated origin server.
1726   For example, the request
1727</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1731  would be forwarded by the final proxy as
1732</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1733OPTIONS * HTTP/1.1
1737   after connecting to port 8001 of host "".
1741   The request-target is transmitted in the format specified in
1742   <xref target="http.uri"/>. If the request-target is percent-encoded
1743   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1744   &MUST; decode the request-target in order to
1745   properly interpret the request. Servers &SHOULD; respond to invalid
1746   request-targets with an appropriate status code.
1749   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1750   received request-target when forwarding it to the next inbound server,
1751   except as noted above to replace a null path-absolute with "/" or "*".
1754  <t>
1755    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1756    meaning of the request when the origin server is improperly using
1757    a non-reserved URI character for a reserved purpose.  Implementors
1758    need to be aware that some pre-HTTP/1.1 proxies have been known to
1759    rewrite the request-target.
1760  </t>
1763   HTTP does not place a pre-defined limit on the length of a request-target.
1764   A server &MUST; be prepared to receive URIs of unbounded length and
1765   respond with the 414 (URI Too Long) status code if the received
1766   request-target would be longer than the server wishes to handle
1767   (see &status-414;).
1770   Various ad-hoc limitations on request-target length are found in practice.
1771   It is &RECOMMENDED; that all HTTP senders and recipients support
1772   request-target lengths of 8000 or more octets.
1775  <t>
1776    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1777    are not part of the request-target and thus will not be transmitted
1778    in an HTTP request.
1779  </t>
1784<section title="The Resource Identified by a Request" anchor="">
1786   The exact resource identified by an Internet request is determined by
1787   examining both the request-target and the Host header field.
1790   An origin server that does not allow resources to differ by the
1791   requested host &MAY; ignore the Host header field value when
1792   determining the resource identified by an HTTP/1.1 request. (But see
1793   <xref target=""/>
1794   for other requirements on Host support in HTTP/1.1.)
1797   An origin server that does differentiate resources based on the host
1798   requested (sometimes referred to as virtual hosts or vanity host
1799   names) &MUST; use the following rules for determining the requested
1800   resource on an HTTP/1.1 request:
1801  <list style="numbers">
1802    <t>If request-target is an absolute-URI, the host is part of the
1803     request-target. Any Host header field value in the request &MUST; be
1804     ignored.</t>
1805    <t>If the request-target is not an absolute-URI, and the request includes
1806     a Host header field, the host is determined by the Host header
1807     field value.</t>
1808    <t>If the host as determined by rule 1 or 2 is not a valid host on
1809     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1810  </list>
1813   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1814   attempt to use heuristics (e.g., examination of the URI path for
1815   something unique to a particular host) in order to determine what
1816   exact resource is being requested.
1820<section title="Effective Request URI" anchor="effective.request.uri">
1821  <iref primary="true" item="effective request URI"/>
1822  <iref primary="true" item="target resource"/>
1824   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1825   for the target resource; instead, the URI needs to be inferred from the
1826   request-target, Host header field, and connection context. The result of
1827   this process is called the "effective request URI".  The "target resource"
1828   is the resource identified by the effective request URI.
1831   If the request-target is an absolute-URI, then the effective request URI is
1832   the request-target.
1835   If the request-target uses the path-absolute form or the asterisk form,
1836   and the Host header field is present, then the effective request URI is
1837   constructed by concatenating
1840  <list style="symbols">
1841    <t>
1842      the scheme name: "http" if the request was received over an insecure
1843      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1844      connection,
1845    </t>
1846    <t>
1847      the octet sequence "://",
1848    </t>
1849    <t>
1850      the authority component, as specified in the Host header field
1851      (<xref target=""/>), and
1852    </t>
1853    <t>
1854      the request-target obtained from the Request-Line, unless the
1855      request-target is just the asterisk "*".
1856    </t>
1857  </list>
1860   If the request-target uses the path-absolute form or the asterisk form,
1861   and the Host header field is not present, then the effective request URI is
1862   undefined.
1865   Otherwise, when request-target uses the authority form, the effective
1866   request URI is undefined.
1870   Example 1: the effective request URI for the message
1872<artwork type="example" x:indent-with="  ">
1873GET /pub/WWW/TheProject.html HTTP/1.1
1877  (received over an insecure TCP connection) is "http", plus "://", plus the
1878  authority component "", plus the request-target
1879  "/pub/WWW/TheProject.html", thus
1880  "".
1885   Example 2: the effective request URI for the message
1887<artwork type="example" x:indent-with="  ">
1888GET * HTTP/1.1
1892  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1893  authority component "", thus "".
1897   Effective request URIs are compared using the rules described in
1898   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1899   be treated as equivalent to an absolute path of "/".
1906<section title="Response" anchor="response">
1907  <x:anchor-alias value="Response"/>
1909   After receiving and interpreting a request message, a server responds
1910   with an HTTP response message.
1912<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1913  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1914                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1915                  <x:ref>CRLF</x:ref>
1916                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1919<section title="Status-Line" anchor="status-line">
1920  <x:anchor-alias value="Status-Line"/>
1922   The first line of a Response message is the Status-Line, consisting
1923   of the protocol version, a space (SP), the status code, another space,
1924   a possibly-empty textual phrase describing the status code, and
1925   ending with CRLF.
1927<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1928  <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>
1931<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1932  <x:anchor-alias value="Reason-Phrase"/>
1933  <x:anchor-alias value="Status-Code"/>
1935   The Status-Code element is a 3-digit integer result code of the
1936   attempt to understand and satisfy the request. These codes are fully
1937   defined in &status-codes;.  The Reason Phrase exists for the sole
1938   purpose of providing a textual description associated with the numeric
1939   status code, out of deference to earlier Internet application protocols
1940   that were more frequently used with interactive text clients.
1941   A client &SHOULD; ignore the content of the Reason Phrase.
1944   The first digit of the Status-Code defines the class of response. The
1945   last two digits do not have any categorization role. There are 5
1946   values for the first digit:
1947  <list style="symbols">
1948    <t>
1949      1xx: Informational - Request received, continuing process
1950    </t>
1951    <t>
1952      2xx: Success - The action was successfully received,
1953        understood, and accepted
1954    </t>
1955    <t>
1956      3xx: Redirection - Further action must be taken in order to
1957        complete the request
1958    </t>
1959    <t>
1960      4xx: Client Error - The request contains bad syntax or cannot
1961        be fulfilled
1962    </t>
1963    <t>
1964      5xx: Server Error - The server failed to fulfill an apparently
1965        valid request
1966    </t>
1967  </list>
1969<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1970  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1971  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1979<section title="Protocol Parameters" anchor="protocol.parameters">
1981<section title="Date/Time Formats: Full Date" anchor="">
1982  <x:anchor-alias value="HTTP-date"/>
1984   HTTP applications have historically allowed three different formats
1985   for date/time stamps. However, the preferred format is a fixed-length subset
1986   of that defined by <xref target="RFC1123"/>:
1988<figure><artwork type="example" x:indent-with="  ">
1989Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1992   The other formats are described here only for compatibility with obsolete
1993   implementations.
1995<figure><artwork type="example" x:indent-with="  ">
1996Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1997Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2000   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2001   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2002   only generate the RFC 1123 format for representing HTTP-date values
2003   in header fields. See <xref target="tolerant.applications"/> for further information.
2006   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2007   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2008   equal to UTC (Coordinated Universal Time). This is indicated in the
2009   first two formats by the inclusion of "GMT" as the three-letter
2010   abbreviation for time zone, and &MUST; be assumed when reading the
2011   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2012   additional whitespace beyond that specifically included as SP in the
2013   grammar.
2015<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2016  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2018<t anchor="">
2019  <x:anchor-alias value="rfc1123-date"/>
2020  <x:anchor-alias value="time-of-day"/>
2021  <x:anchor-alias value="hour"/>
2022  <x:anchor-alias value="minute"/>
2023  <x:anchor-alias value="second"/>
2024  <x:anchor-alias value="day-name"/>
2025  <x:anchor-alias value="day"/>
2026  <x:anchor-alias value="month"/>
2027  <x:anchor-alias value="year"/>
2028  <x:anchor-alias value="GMT"/>
2029  Preferred format:
2031<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"/>
2032  <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>
2033  ; fixed length subset of the format defined in
2034  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2036  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2037               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2038               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2039               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2040               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2041               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2042               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2044  <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>
2045               ; e.g., 02 Jun 1982
2047  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2048  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2049               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2050               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2051               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2052               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2053               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2054               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2055               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2056               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2057               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2058               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2059               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2060  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2062  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2064  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2065                 ; 00:00:00 - 23:59:59
2067  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2068  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2069  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2072  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2073  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2074  same as those defined for the RFC 5322 constructs
2075  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2077<t anchor="">
2078  <x:anchor-alias value="obs-date"/>
2079  <x:anchor-alias value="rfc850-date"/>
2080  <x:anchor-alias value="asctime-date"/>
2081  <x:anchor-alias value="date1"/>
2082  <x:anchor-alias value="date2"/>
2083  <x:anchor-alias value="date3"/>
2084  <x:anchor-alias value="rfc1123-date"/>
2085  <x:anchor-alias value="day-name-l"/>
2086  Obsolete formats:
2088<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2089  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2091<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2092  <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>
2093  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2094                 ; day-month-year (e.g., 02-Jun-82)
2096  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2097         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2098         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2099         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2100         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2101         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2102         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2104<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2105  <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>
2106  <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> ))
2107                 ; month day (e.g., Jun  2)
2110  <t>
2111    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2112    accepting date values that might have been sent by non-HTTP
2113    applications, as is sometimes the case when retrieving or posting
2114    messages via proxies/gateways to SMTP or NNTP.
2115  </t>
2118  <t>
2119    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2120    to their usage within the protocol stream. Clients and servers are
2121    not required to use these formats for user presentation, request
2122    logging, etc.
2123  </t>
2127<section title="Transfer Codings" anchor="transfer.codings">
2128  <x:anchor-alias value="transfer-coding"/>
2129  <x:anchor-alias value="transfer-extension"/>
2131   Transfer-coding values are used to indicate an encoding
2132   transformation that has been, can be, or might need to be applied to a
2133   payload body in order to ensure "safe transport" through the network.
2134   This differs from a content coding in that the transfer-coding is a
2135   property of the message rather than a property of the representation
2136   that is being transferred.
2138<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2139  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2140                          / "compress" ; <xref target="compress.coding"/>
2141                          / "deflate" ; <xref target="deflate.coding"/>
2142                          / "gzip" ; <xref target="gzip.coding"/>
2143                          / <x:ref>transfer-extension</x:ref>
2144  <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> )
2146<t anchor="rule.parameter">
2147  <x:anchor-alias value="attribute"/>
2148  <x:anchor-alias value="transfer-parameter"/>
2149  <x:anchor-alias value="value"/>
2150   Parameters are in the form of attribute/value pairs.
2152<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"/>
2153  <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>
2154  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2155  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2158   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2159   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2160   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2163   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2164   MIME, which were designed to enable safe transport of binary data over a
2165   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2166   However, safe transport
2167   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2168   the only unsafe characteristic of message-bodies is the difficulty in
2169   determining the exact message body length (<xref target="message.body"/>),
2170   or the desire to encrypt data over a shared transport.
2173   A server that receives a request message with a transfer-coding it does
2174   not understand &SHOULD; respond with 501 (Not Implemented) and then
2175   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2176   client.
2179<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2180  <iref item="chunked (Coding Format)"/>
2181  <iref item="Coding Format" subitem="chunked"/>
2182  <x:anchor-alias value="chunk"/>
2183  <x:anchor-alias value="Chunked-Body"/>
2184  <x:anchor-alias value="chunk-data"/>
2185  <x:anchor-alias value="chunk-ext"/>
2186  <x:anchor-alias value="chunk-ext-name"/>
2187  <x:anchor-alias value="chunk-ext-val"/>
2188  <x:anchor-alias value="chunk-size"/>
2189  <x:anchor-alias value="last-chunk"/>
2190  <x:anchor-alias value="trailer-part"/>
2191  <x:anchor-alias value="quoted-str-nf"/>
2192  <x:anchor-alias value="qdtext-nf"/>
2194   The chunked encoding modifies the body of a message in order to
2195   transfer it as a series of chunks, each with its own size indicator,
2196   followed by an &OPTIONAL; trailer containing header fields. This
2197   allows dynamically produced content to be transferred along with the
2198   information necessary for the recipient to verify that it has
2199   received the full message.
2201<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"/>
2202  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2203                   <x:ref>last-chunk</x:ref>
2204                   <x:ref>trailer-part</x:ref>
2205                   <x:ref>CRLF</x:ref>
2207  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2208                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2209  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2210  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2212  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2213                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2214  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2215  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2216  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2217  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2219  <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>
2220                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2221  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2222                 ; <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>
2225   The chunk-size field is a string of hex digits indicating the size of
2226   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2227   zero, followed by the trailer, which is terminated by an empty line.
2230   The trailer allows the sender to include additional HTTP header
2231   fields at the end of the message. The Trailer header field can be
2232   used to indicate which header fields are included in a trailer (see
2233   <xref target="header.trailer"/>).
2236   A server using chunked transfer-coding in a response &MUST-NOT; use the
2237   trailer for any header fields unless at least one of the following is
2238   true:
2239  <list style="numbers">
2240    <t>the request included a TE header field that indicates "trailers" is
2241     acceptable in the transfer-coding of the  response, as described in
2242     <xref target="header.te"/>; or,</t>
2244    <t>the trailer fields consist entirely of optional metadata, and the
2245    recipient could use the message (in a manner acceptable to the server where
2246    the field originated) without receiving it. In other words, the server that
2247    generated the header (often but not always the origin server) is willing to
2248    accept the possibility that the trailer fields might be silently discarded
2249    along the path to the client.</t>
2250  </list>
2253   This requirement prevents an interoperability failure when the
2254   message is being received by an HTTP/1.1 (or later) proxy and
2255   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2256   compliance with the protocol would have necessitated a possibly
2257   infinite buffer on the proxy.
2260   A process for decoding the "chunked" transfer-coding
2261   can be represented in pseudo-code as:
2263<figure><artwork type="code">
2264  length := 0
2265  read chunk-size, chunk-ext (if any) and CRLF
2266  while (chunk-size &gt; 0) {
2267     read chunk-data and CRLF
2268     append chunk-data to decoded-body
2269     length := length + chunk-size
2270     read chunk-size and CRLF
2271  }
2272  read header-field
2273  while (header-field not empty) {
2274     append header-field to existing header fields
2275     read header-field
2276  }
2277  Content-Length := length
2278  Remove "chunked" from Transfer-Encoding
2281   All HTTP/1.1 applications &MUST; be able to receive and decode the
2282   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2283   they do not understand.
2286   Since "chunked" is the only transfer-coding required to be understood
2287   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2288   on a persistent connection.  Whenever a transfer-coding is applied to
2289   a payload body in a request, the final transfer-coding applied &MUST;
2290   be "chunked".  If a transfer-coding is applied to a response payload
2291   body, then either the final transfer-coding applied &MUST; be "chunked"
2292   or the message &MUST; be terminated by closing the connection. When the
2293   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2294   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2295   be applied more than once in a message-body.
2299<section title="Compression Codings" anchor="compression.codings">
2301   The codings defined below can be used to compress the payload of a
2302   message.
2305   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2306   is not desirable and is discouraged for future encodings. Their
2307   use here is representative of historical practice, not good
2308   design.
2311   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2312   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2313   equivalent to "gzip" and "compress" respectively.
2316<section title="Compress Coding" anchor="compress.coding">
2317<iref item="compress (Coding Format)"/>
2318<iref item="Coding Format" subitem="compress"/>
2320   The "compress" format is produced by the common UNIX file compression
2321   program "compress". This format is an adaptive Lempel-Ziv-Welch
2322   coding (LZW).
2326<section title="Deflate Coding" anchor="deflate.coding">
2327<iref item="deflate (Coding Format)"/>
2328<iref item="Coding Format" subitem="deflate"/>
2330   The "deflate" format is defined as the "deflate" compression mechanism
2331   (described in <xref target="RFC1951"/>) used inside the "zlib"
2332   data format (<xref target="RFC1950"/>).
2335  <t>
2336    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2337    compressed data without the zlib wrapper.
2338   </t>
2342<section title="Gzip Coding" anchor="gzip.coding">
2343<iref item="gzip (Coding Format)"/>
2344<iref item="Coding Format" subitem="gzip"/>
2346   The "gzip" format is produced by the file compression program
2347   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2348   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2354<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2356   The HTTP Transfer Coding Registry defines the name space for the transfer
2357   coding names.
2360   Registrations &MUST; include the following fields:
2361   <list style="symbols">
2362     <t>Name</t>
2363     <t>Description</t>
2364     <t>Pointer to specification text</t>
2365   </list>
2368   Names of transfer codings &MUST-NOT; overlap with names of content codings
2369   (&content-codings;), unless the encoding transformation is identical (as it
2370   is the case for the compression codings defined in
2371   <xref target="compression.codings"/>).
2374   Values to be added to this name space require a specification
2375   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2376   conform to the purpose of transfer coding defined in this section.
2379   The registry itself is maintained at
2380   <eref target=""/>.
2385<section title="Product Tokens" anchor="product.tokens">
2386  <x:anchor-alias value="product"/>
2387  <x:anchor-alias value="product-version"/>
2389   Product tokens are used to allow communicating applications to
2390   identify themselves by software name and version. Most fields using
2391   product tokens also allow sub-products which form a significant part
2392   of the application to be listed, separated by whitespace. By
2393   convention, the products are listed in order of their significance
2394   for identifying the application.
2396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2397  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2398  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2401   Examples:
2403<figure><artwork type="example">
2404  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2405  Server: Apache/0.8.4
2408   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2409   used for advertising or other non-essential information. Although any
2410   token octet &MAY; appear in a product-version, this token &SHOULD;
2411   only be used for a version identifier (i.e., successive versions of
2412   the same product &SHOULD; only differ in the product-version portion of
2413   the product value).
2417<section title="Quality Values" anchor="quality.values">
2418  <x:anchor-alias value="qvalue"/>
2420   Both transfer codings (TE request header field, <xref target="header.te"/>)
2421   and content negotiation (&content.negotiation;) use short "floating point"
2422   numbers to indicate the relative importance ("weight") of various
2423   negotiable parameters.  A weight is normalized to a real number in
2424   the range 0 through 1, where 0 is the minimum and 1 the maximum
2425   value. If a parameter has a quality value of 0, then content with
2426   this parameter is "not acceptable" for the client. HTTP/1.1
2427   applications &MUST-NOT; generate more than three digits after the
2428   decimal point. User configuration of these values &SHOULD; also be
2429   limited in this fashion.
2431<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2432  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2433                 / ( "1" [ "." 0*3("0") ] )
2436  <t>
2437     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2438     relative degradation in desired quality.
2439  </t>
2445<section title="Connections" anchor="connections">
2447<section title="Persistent Connections" anchor="persistent.connections">
2449<section title="Purpose" anchor="persistent.purpose">
2451   Prior to persistent connections, a separate TCP connection was
2452   established for each request, increasing the load on HTTP servers
2453   and causing congestion on the Internet. The use of inline images and
2454   other associated data often requires a client to make multiple
2455   requests of the same server in a short amount of time. Analysis of
2456   these performance problems and results from a prototype
2457   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2458   measurements of actual HTTP/1.1 implementations show good
2459   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2460   T/TCP <xref target="Tou1998"/>.
2463   Persistent HTTP connections have a number of advantages:
2464  <list style="symbols">
2465      <t>
2466        By opening and closing fewer TCP connections, CPU time is saved
2467        in routers and hosts (clients, servers, proxies, gateways,
2468        tunnels, or caches), and memory used for TCP protocol control
2469        blocks can be saved in hosts.
2470      </t>
2471      <t>
2472        HTTP requests and responses can be pipelined on a connection.
2473        Pipelining allows a client to make multiple requests without
2474        waiting for each response, allowing a single TCP connection to
2475        be used much more efficiently, with much lower elapsed time.
2476      </t>
2477      <t>
2478        Network congestion is reduced by reducing the number of packets
2479        caused by TCP opens, and by allowing TCP sufficient time to
2480        determine the congestion state of the network.
2481      </t>
2482      <t>
2483        Latency on subsequent requests is reduced since there is no time
2484        spent in TCP's connection opening handshake.
2485      </t>
2486      <t>
2487        HTTP can evolve more gracefully, since errors can be reported
2488        without the penalty of closing the TCP connection. Clients using
2489        future versions of HTTP might optimistically try a new feature,
2490        but if communicating with an older server, retry with old
2491        semantics after an error is reported.
2492      </t>
2493    </list>
2496   HTTP implementations &SHOULD; implement persistent connections.
2500<section title="Overall Operation" anchor="persistent.overall">
2502   A significant difference between HTTP/1.1 and earlier versions of
2503   HTTP is that persistent connections are the default behavior of any
2504   HTTP connection. That is, unless otherwise indicated, the client
2505   &SHOULD; assume that the server will maintain a persistent connection,
2506   even after error responses from the server.
2509   Persistent connections provide a mechanism by which a client and a
2510   server can signal the close of a TCP connection. This signaling takes
2511   place using the Connection header field (<xref target="header.connection"/>). Once a close
2512   has been signaled, the client &MUST-NOT; send any more requests on that
2513   connection.
2516<section title="Negotiation" anchor="persistent.negotiation">
2518   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2519   maintain a persistent connection unless a Connection header field including
2520   the connection-token "close" was sent in the request. If the server
2521   chooses to close the connection immediately after sending the
2522   response, it &SHOULD; send a Connection header field including the
2523   connection-token "close".
2526   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2527   decide to keep it open based on whether the response from a server
2528   contains a Connection header field with the connection-token close. In case
2529   the client does not want to maintain a connection for more than that
2530   request, it &SHOULD; send a Connection header field including the
2531   connection-token close.
2534   If either the client or the server sends the close token in the
2535   Connection header field, that request becomes the last one for the
2536   connection.
2539   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2540   maintained for HTTP versions less than 1.1 unless it is explicitly
2541   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2542   compatibility with HTTP/1.0 clients.
2545   In order to remain persistent, all messages on the connection &MUST;
2546   have a self-defined message length (i.e., one not defined by closure
2547   of the connection), as described in <xref target="message.body"/>.
2551<section title="Pipelining" anchor="pipelining">
2553   A client that supports persistent connections &MAY; "pipeline" its
2554   requests (i.e., send multiple requests without waiting for each
2555   response). A server &MUST; send its responses to those requests in the
2556   same order that the requests were received.
2559   Clients which assume persistent connections and pipeline immediately
2560   after connection establishment &SHOULD; be prepared to retry their
2561   connection if the first pipelined attempt fails. If a client does
2562   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2563   persistent. Clients &MUST; also be prepared to resend their requests if
2564   the server closes the connection before sending all of the
2565   corresponding responses.
2568   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2569   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2570   premature termination of the transport connection could lead to
2571   indeterminate results. A client wishing to send a non-idempotent
2572   request &SHOULD; wait to send that request until it has received the
2573   response status line for the previous request.
2578<section title="Proxy Servers" anchor="persistent.proxy">
2580   It is especially important that proxies correctly implement the
2581   properties of the Connection header field as specified in <xref target="header.connection"/>.
2584   The proxy server &MUST; signal persistent connections separately with
2585   its clients and the origin servers (or other proxy servers) that it
2586   connects to. Each persistent connection applies to only one transport
2587   link.
2590   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2591   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2592   for information and discussion of the problems with the Keep-Alive header field
2593   implemented by many HTTP/1.0 clients).
2596<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2598  <cref anchor="TODO-end-to-end" source="jre">
2599    Restored from <eref target=""/>.
2600    See also <eref target=""/>.
2601  </cref>
2604   For the purpose of defining the behavior of caches and non-caching
2605   proxies, we divide HTTP header fields into two categories:
2606  <list style="symbols">
2607      <t>End-to-end header fields, which are  transmitted to the ultimate
2608        recipient of a request or response. End-to-end header fields in
2609        responses MUST be stored as part of a cache entry and &MUST; be
2610        transmitted in any response formed from a cache entry.</t>
2612      <t>Hop-by-hop header fields, which are meaningful only for a single
2613        transport-level connection, and are not stored by caches or
2614        forwarded by proxies.</t>
2615  </list>
2618   The following HTTP/1.1 header fields are hop-by-hop header fields:
2619  <list style="symbols">
2620      <t>Connection</t>
2621      <t>Keep-Alive</t>
2622      <t>Proxy-Authenticate</t>
2623      <t>Proxy-Authorization</t>
2624      <t>TE</t>
2625      <t>Trailer</t>
2626      <t>Transfer-Encoding</t>
2627      <t>Upgrade</t>
2628  </list>
2631   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2634   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2635   (<xref target="header.connection"/>).
2639<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2641  <cref anchor="TODO-non-mod-headers" source="jre">
2642    Restored from <eref target=""/>.
2643    See also <eref target=""/>.
2644  </cref>
2647   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2648   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2649   modify an end-to-end header field unless the definition of that header field requires
2650   or specifically allows that.
2653   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2654   request or response, and it &MUST-NOT; add any of these fields if not
2655   already present:
2656  <list style="symbols">
2657    <t>Allow</t>
2658    <t>Content-Location</t>
2659    <t>Content-MD5</t>
2660    <t>ETag</t>
2661    <t>Last-Modified</t>
2662    <t>Server</t>
2663  </list>
2666   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2667   response:
2668  <list style="symbols">
2669    <t>Expires</t>
2670  </list>
2673   but it &MAY; add any of these fields if not already present. If an
2674   Expires header field is added, it &MUST; be given a field-value identical to
2675   that of the Date header field in that response.
2678   A proxy &MUST-NOT; modify or add any of the following fields in a
2679   message that contains the no-transform cache-control directive, or in
2680   any request:
2681  <list style="symbols">
2682    <t>Content-Encoding</t>
2683    <t>Content-Range</t>
2684    <t>Content-Type</t>
2685  </list>
2688   A transforming proxy &MAY; modify or add these fields to a message
2689   that does not include no-transform, but if it does so, it &MUST; add a
2690   Warning 214 (Transformation applied) if one does not already appear
2691   in the message (see &header-warning;).
2694  <t>
2695    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2696    cause authentication failures if stronger authentication
2697    mechanisms are introduced in later versions of HTTP. Such
2698    authentication mechanisms &MAY; rely on the values of header fields
2699    not listed here.
2700  </t>
2703   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2704   though it &MAY; change the message-body through application or removal
2705   of a transfer-coding (<xref target="transfer.codings"/>).
2711<section title="Practical Considerations" anchor="persistent.practical">
2713   Servers will usually have some time-out value beyond which they will
2714   no longer maintain an inactive connection. Proxy servers might make
2715   this a higher value since it is likely that the client will be making
2716   more connections through the same server. The use of persistent
2717   connections places no requirements on the length (or existence) of
2718   this time-out for either the client or the server.
2721   When a client or server wishes to time-out it &SHOULD; issue a graceful
2722   close on the transport connection. Clients and servers &SHOULD; both
2723   constantly watch for the other side of the transport close, and
2724   respond to it as appropriate. If a client or server does not detect
2725   the other side's close promptly it could cause unnecessary resource
2726   drain on the network.
2729   A client, server, or proxy &MAY; close the transport connection at any
2730   time. For example, a client might have started to send a new request
2731   at the same time that the server has decided to close the "idle"
2732   connection. From the server's point of view, the connection is being
2733   closed while it was idle, but from the client's point of view, a
2734   request is in progress.
2737   This means that clients, servers, and proxies &MUST; be able to recover
2738   from asynchronous close events. Client software &SHOULD; reopen the
2739   transport connection and retransmit the aborted sequence of requests
2740   without user interaction so long as the request sequence is
2741   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2742   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2743   human operator the choice of retrying the request(s). Confirmation by
2744   user-agent software with semantic understanding of the application
2745   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2746   be repeated if the second sequence of requests fails.
2749   Servers &SHOULD; always respond to at least one request per connection,
2750   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2751   middle of transmitting a response, unless a network or client failure
2752   is suspected.
2755   Clients (including proxies) &SHOULD; limit the number of simultaneous
2756   connections that they maintain to a given server (including proxies).
2759   Previous revisions of HTTP gave a specific number of connections as a
2760   ceiling, but this was found to be impractical for many applications. As a
2761   result, this specification does not mandate a particular maximum number of
2762   connections, but instead encourages clients to be conservative when opening
2763   multiple connections.
2766   In particular, while using multiple connections avoids the "head-of-line
2767   blocking" problem (whereby a request that takes significant server-side
2768   processing and/or has a large payload can block subsequent requests on the
2769   same connection), each connection used consumes server resources (sometimes
2770   significantly), and furthermore using multiple connections can cause
2771   undesirable side effects in congested networks.
2774   Note that servers might reject traffic that they deem abusive, including an
2775   excessive number of connections from a client.
2780<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2782<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2784   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2785   flow control mechanisms to resolve temporary overloads, rather than
2786   terminating connections with the expectation that clients will retry.
2787   The latter technique can exacerbate network congestion.
2791<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2793   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2794   the network connection for an error status code while it is transmitting
2795   the request. If the client sees an error status code, it &SHOULD;
2796   immediately cease transmitting the body. If the body is being sent
2797   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2798   empty trailer &MAY; be used to prematurely mark the end of the message.
2799   If the body was preceded by a Content-Length header field, the client &MUST;
2800   close the connection.
2804<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2806   The purpose of the 100 (Continue) status code (see &status-100;) is to
2807   allow a client that is sending a request message with a request body
2808   to determine if the origin server is willing to accept the request
2809   (based on the request header fields) before the client sends the request
2810   body. In some cases, it might either be inappropriate or highly
2811   inefficient for the client to send the body if the server will reject
2812   the message without looking at the body.
2815   Requirements for HTTP/1.1 clients:
2816  <list style="symbols">
2817    <t>
2818        If a client will wait for a 100 (Continue) response before
2819        sending the request body, it &MUST; send an Expect header
2820        field (&header-expect;) with the "100-continue" expectation.
2821    </t>
2822    <t>
2823        A client &MUST-NOT; send an Expect header field (&header-expect;)
2824        with the "100-continue" expectation if it does not intend
2825        to send a request body.
2826    </t>
2827  </list>
2830   Because of the presence of older implementations, the protocol allows
2831   ambiguous situations in which a client might send "Expect: 100-continue"
2832   without receiving either a 417 (Expectation Failed)
2833   or a 100 (Continue) status code. Therefore, when a client sends this
2834   header field to an origin server (possibly via a proxy) from which it
2835   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2836   wait for an indefinite period before sending the request body.
2839   Requirements for HTTP/1.1 origin servers:
2840  <list style="symbols">
2841    <t> Upon receiving a request which includes an Expect header
2842        field with the "100-continue" expectation, an origin server &MUST;
2843        either respond with 100 (Continue) status code and continue to read
2844        from the input stream, or respond with a final status code. The
2845        origin server &MUST-NOT; wait for the request body before sending
2846        the 100 (Continue) response. If it responds with a final status
2847        code, it &MAY; close the transport connection or it &MAY; continue
2848        to read and discard the rest of the request.  It &MUST-NOT;
2849        perform the request method if it returns a final status code.
2850    </t>
2851    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2852        the request message does not include an Expect header
2853        field with the "100-continue" expectation, and &MUST-NOT; send a
2854        100 (Continue) response if such a request comes from an HTTP/1.0
2855        (or earlier) client. There is an exception to this rule: for
2856        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2857        status code in response to an HTTP/1.1 PUT or POST request that does
2858        not include an Expect header field with the "100-continue"
2859        expectation. This exception, the purpose of which is
2860        to minimize any client processing delays associated with an
2861        undeclared wait for 100 (Continue) status code, applies only to
2862        HTTP/1.1 requests, and not to requests with any other HTTP-version
2863        value.
2864    </t>
2865    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2866        already received some or all of the request body for the
2867        corresponding request.
2868    </t>
2869    <t> An origin server that sends a 100 (Continue) response &MUST;
2870    ultimately send a final status code, once the request body is
2871        received and processed, unless it terminates the transport
2872        connection prematurely.
2873    </t>
2874    <t> If an origin server receives a request that does not include an
2875        Expect header field with the "100-continue" expectation,
2876        the request includes a request body, and the server responds
2877        with a final status code before reading the entire request body
2878        from the transport connection, then the server &SHOULD-NOT;  close
2879        the transport connection until it has read the entire request,
2880        or until the client closes the connection. Otherwise, the client
2881        might not reliably receive the response message. However, this
2882        requirement is not be construed as preventing a server from
2883        defending itself against denial-of-service attacks, or from
2884        badly broken client implementations.
2885      </t>
2886    </list>
2889   Requirements for HTTP/1.1 proxies:
2890  <list style="symbols">
2891    <t> If a proxy receives a request that includes an Expect header
2892        field with the "100-continue" expectation, and the proxy
2893        either knows that the next-hop server complies with HTTP/1.1 or
2894        higher, or does not know the HTTP version of the next-hop
2895        server, it &MUST; forward the request, including the Expect header
2896        field.
2897    </t>
2898    <t> If the proxy knows that the version of the next-hop server is
2899        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2900        respond with a 417 (Expectation Failed) status code.
2901    </t>
2902    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2903        numbers received from recently-referenced next-hop servers.
2904    </t>
2905    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2906        request message was received from an HTTP/1.0 (or earlier)
2907        client and did not include an Expect header field with
2908        the "100-continue" expectation. This requirement overrides the
2909        general rule for forwarding of 1xx responses (see &status-1xx;).
2910    </t>
2911  </list>
2915<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2917   If an HTTP/1.1 client sends a request which includes a request body,
2918   but which does not include an Expect header field with the
2919   "100-continue" expectation, and if the client is not directly
2920   connected to an HTTP/1.1 origin server, and if the client sees the
2921   connection close before receiving a status line from the server, the
2922   client &SHOULD; retry the request.  If the client does retry this
2923   request, it &MAY; use the following "binary exponential backoff"
2924   algorithm to be assured of obtaining a reliable response:
2925  <list style="numbers">
2926    <t>
2927      Initiate a new connection to the server
2928    </t>
2929    <t>
2930      Transmit the request-line, header fields, and the CRLF that
2931      indicates the end of header fields.
2932    </t>
2933    <t>
2934      Initialize a variable R to the estimated round-trip time to the
2935         server (e.g., based on the time it took to establish the
2936         connection), or to a constant value of 5 seconds if the round-trip
2937         time is not available.
2938    </t>
2939    <t>
2940       Compute T = R * (2**N), where N is the number of previous
2941         retries of this request.
2942    </t>
2943    <t>
2944       Wait either for an error response from the server, or for T
2945         seconds (whichever comes first)
2946    </t>
2947    <t>
2948       If no error response is received, after T seconds transmit the
2949         body of the request.
2950    </t>
2951    <t>
2952       If client sees that the connection is closed prematurely,
2953         repeat from step 1 until the request is accepted, an error
2954         response is received, or the user becomes impatient and
2955         terminates the retry process.
2956    </t>
2957  </list>
2960   If at any point an error status code is received, the client
2961  <list style="symbols">
2962      <t>&SHOULD-NOT;  continue and</t>
2964      <t>&SHOULD; close the connection if it has not completed sending the
2965        request message.</t>
2966    </list>
2973<section title="Miscellaneous notes that might disappear" anchor="misc">
2974<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2976   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2980<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2982   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2986<section title="Interception of HTTP for access control" anchor="http.intercept">
2988   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2992<section title="Use of HTTP by other protocols" anchor="http.others">
2994   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2995   Extensions of HTTP like WebDAV.</cref>
2999<section title="Use of HTTP by media type specification" anchor="">
3001   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3006<section title="Header Field Definitions" anchor="header.field.definitions">
3008   This section defines the syntax and semantics of HTTP header fields
3009   related to message framing and transport protocols.
3012<section title="Connection" anchor="header.connection">
3013  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3014  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3015  <x:anchor-alias value="Connection"/>
3016  <x:anchor-alias value="connection-token"/>
3018   The "Connection" header field allows the sender to specify
3019   options that are desired only for that particular connection.
3020   Such connection options &MUST; be removed or replaced before the
3021   message can be forwarded downstream by a proxy or gateway.
3022   This mechanism also allows the sender to indicate which HTTP
3023   header fields used in the message are only intended for the
3024   immediate recipient ("hop-by-hop"), as opposed to all recipients
3025   on the chain ("end-to-end"), enabling the message to be
3026   self-descriptive and allowing future connection-specific extensions
3027   to be deployed in HTTP without fear that they will be blindly
3028   forwarded by previously deployed intermediaries.
3031   The Connection header field's value has the following grammar:
3033<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3034  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3035  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3038   A proxy or gateway &MUST; parse a received Connection
3039   header field before a message is forwarded and, for each
3040   connection-token in this field, remove any header field(s) from
3041   the message with the same name as the connection-token, and then
3042   remove the Connection header field itself or replace it with the
3043   sender's own connection options for the forwarded message.
3046   A sender &MUST-NOT; include field-names in the Connection header
3047   field-value for fields that are defined as expressing constraints
3048   for all recipients in the request or response chain, such as the
3049   Cache-Control header field (&header-cache-control;).
3052   The connection options do not have to correspond to a header field
3053   present in the message, since a connection-specific header field
3054   might not be needed if there are no parameters associated with that
3055   connection option.  Recipients that trigger certain connection
3056   behavior based on the presence of connection options &MUST; do so
3057   based on the presence of the connection-token rather than only the
3058   presence of the optional header field.  In other words, if the
3059   connection option is received as a header field but not indicated
3060   within the Connection field-value, then the recipient &MUST; ignore
3061   the connection-specific header field because it has likely been
3062   forwarded by an intermediary that is only partially compliant.
3065   When defining new connection options, specifications ought to
3066   carefully consider existing deployed header fields and ensure
3067   that the new connection-token does not share the same name as
3068   an unrelated header field that might already be deployed.
3069   Defining a new connection-token essentially reserves that potential
3070   field-name for carrying additional information related to the
3071   connection option, since it would be unwise for senders to use
3072   that field-name for anything else.
3075   HTTP/1.1 defines the "close" connection option for the sender to
3076   signal that the connection will be closed after completion of the
3077   response. For example,
3079<figure><artwork type="example">
3080  Connection: close
3083   in either the request or the response header fields indicates that
3084   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3085   after the current request/response is complete.
3088   An HTTP/1.1 client that does not support persistent connections &MUST;
3089   include the "close" connection option in every request message.
3092   An HTTP/1.1 server that does not support persistent connections &MUST;
3093   include the "close" connection option in every response message that
3094   does not have a 1xx (Informational) status code.
3098<section title="Content-Length" anchor="header.content-length">
3099  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3100  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3101  <x:anchor-alias value="Content-Length"/>
3103   The "Content-Length" header field indicates the size of the
3104   message-body, in decimal number of octets, for any message other than
3105   a response to a HEAD request or a response with a status code of 304.
3106   In the case of a response to a HEAD request, Content-Length indicates
3107   the size of the payload body (not including any potential transfer-coding)
3108   that would have been sent had the request been a GET.
3109   In the case of a 304 (Not Modified) response to a GET request,
3110   Content-Length indicates the size of the payload body (not including
3111   any potential transfer-coding) that would have been sent in a 200 (OK)
3112   response.
3114<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3115  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3118   An example is
3120<figure><artwork type="example">
3121  Content-Length: 3495
3124   Implementations &SHOULD; use this field to indicate the message-body
3125   length when no transfer-coding is being applied and the
3126   payload's body length can be determined prior to being transferred.
3127   <xref target="message.body"/> describes how recipients determine the length
3128   of a message-body.
3131   Any Content-Length greater than or equal to zero is a valid value.
3134   Note that the use of this field in HTTP is significantly different from
3135   the corresponding definition in MIME, where it is an optional field
3136   used within the "message/external-body" content-type.
3140<section title="Date" anchor="">
3141  <iref primary="true" item="Date header field" x:for-anchor=""/>
3142  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3143  <x:anchor-alias value="Date"/>
3145   The "Date" header field represents the date and time at which
3146   the message was originated, having the same semantics as the Origination
3147   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3148   The field value is an HTTP-date, as described in <xref target=""/>;
3149   it &MUST; be sent in rfc1123-date format.
3151<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3152  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3155   An example is
3157<figure><artwork type="example">
3158  Date: Tue, 15 Nov 1994 08:12:31 GMT
3161   Origin servers &MUST; include a Date header field in all responses,
3162   except in these cases:
3163  <list style="numbers">
3164      <t>If the response status code is 100 (Continue) or 101 (Switching
3165         Protocols), the response &MAY; include a Date header field, at
3166         the server's option.</t>
3168      <t>If the response status code conveys a server error, e.g., 500
3169         (Internal Server Error) or 503 (Service Unavailable), and it is
3170         inconvenient or impossible to generate a valid Date.</t>
3172      <t>If the server does not have a clock that can provide a
3173         reasonable approximation of the current time, its responses
3174         &MUST-NOT; include a Date header field. In this case, the rules
3175         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3176  </list>
3179   A received message that does not have a Date header field &MUST; be
3180   assigned one by the recipient if the message will be cached by that
3181   recipient.
3184   Clients can use the Date header field as well; in order to keep request
3185   messages small, they are advised not to include it when it doesn't convey
3186   any useful information (as it is usually the case for requests that do not
3187   contain a payload).
3190   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3191   time subsequent to the generation of the message. It &SHOULD; represent
3192   the best available approximation of the date and time of message
3193   generation, unless the implementation has no means of generating a
3194   reasonably accurate date and time. In theory, the date ought to
3195   represent the moment just before the payload is generated. In
3196   practice, the date can be generated at any time during the message
3197   origination without affecting its semantic value.
3200<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3202   Some origin server implementations might not have a clock available.
3203   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3204   values to a response, unless these values were associated
3205   with the resource by a system or user with a reliable clock. It &MAY;
3206   assign an Expires value that is known, at or before server
3207   configuration time, to be in the past (this allows "pre-expiration"
3208   of responses without storing separate Expires values for each
3209   resource).
3214<section title="Host" anchor="">
3215  <iref primary="true" item="Host header field" x:for-anchor=""/>
3216  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3217  <x:anchor-alias value="Host"/>
3219   The "Host" header field in a request provides the host and port
3220   information from the target resource's URI, enabling the origin
3221   server to distinguish between resources while servicing requests
3222   for multiple host names on a single IP address.  Since the Host
3223   field-value is critical information for handling a request, it
3224   &SHOULD; be sent as the first header field following the Request-Line.
3226<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3227  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3230   A client &MUST; send a Host header field in all HTTP/1.1 request
3231   messages.  If the target resource's URI includes an authority
3232   component, then the Host field-value &MUST; be identical to that
3233   authority component after excluding any userinfo (<xref target="http.uri"/>).
3234   If the authority component is missing or undefined for the target
3235   resource's URI, then the Host header field &MUST; be sent with an
3236   empty field-value.
3239   For example, a GET request to the origin server for
3240   &lt;; would begin with:
3242<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3243GET /pub/WWW/ HTTP/1.1
3247   The Host header field &MUST; be sent in an HTTP/1.1 request even
3248   if the request-target is in the form of an absolute-URI, since this
3249   allows the Host information to be forwarded through ancient HTTP/1.0
3250   proxies that might not have implemented Host.
3253   When an HTTP/1.1 proxy receives a request with a request-target in
3254   the form of an absolute-URI, the proxy &MUST; ignore the received
3255   Host header field (if any) and instead replace it with the host
3256   information of the request-target.  When a proxy forwards a request,
3257   it &MUST; generate the Host header field based on the received
3258   absolute-URI rather than the received Host.
3261   Since the Host header field acts as an application-level routing
3262   mechanism, it is a frequent target for malware seeking to poison
3263   a shared cache or redirect a request to an unintended server.
3264   An interception proxy is particularly vulnerable if it relies on
3265   the Host header field value for redirecting requests to internal
3266   servers, or for use as a cache key in a shared cache, without
3267   first verifying that the intercepted connection is targeting a
3268   valid IP address for that host.
3271   A server &MUST; respond with a 400 (Bad Request) status code to
3272   any HTTP/1.1 request message that lacks a Host header field and
3273   to any request message that contains more than one Host header field
3274   or a Host header field with an invalid field-value.
3277   See Sections <xref target="" format="counter"/>
3278   and <xref target="" format="counter"/>
3279   for other requirements relating to Host.
3283<section title="TE" anchor="header.te">
3284  <iref primary="true" item="TE header field" x:for-anchor=""/>
3285  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3286  <x:anchor-alias value="TE"/>
3287  <x:anchor-alias value="t-codings"/>
3288  <x:anchor-alias value="te-params"/>
3289  <x:anchor-alias value="te-ext"/>
3291   The "TE" header field indicates what extension transfer-codings
3292   it is willing to accept in the response, and whether or not it is
3293   willing to accept trailer fields in a chunked transfer-coding.
3296   Its value consists of the keyword "trailers" and/or a comma-separated
3297   list of extension transfer-coding names with optional accept
3298   parameters (as described in <xref target="transfer.codings"/>).
3300<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"/>
3301  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3302  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3303  <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> )
3304  <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> ]
3307   The presence of the keyword "trailers" indicates that the client is
3308   willing to accept trailer fields in a chunked transfer-coding, as
3309   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3310   transfer-coding values even though it does not itself represent a
3311   transfer-coding.
3314   Examples of its use are:
3316<figure><artwork type="example">
3317  TE: deflate
3318  TE:
3319  TE: trailers, deflate;q=0.5
3322   The TE header field only applies to the immediate connection.
3323   Therefore, the keyword &MUST; be supplied within a Connection header
3324   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3327   A server tests whether a transfer-coding is acceptable, according to
3328   a TE field, using these rules:
3329  <list style="numbers">
3330    <x:lt>
3331      <t>The "chunked" transfer-coding is always acceptable. If the
3332         keyword "trailers" is listed, the client indicates that it is
3333         willing to accept trailer fields in the chunked response on
3334         behalf of itself and any downstream clients. The implication is
3335         that, if given, the client is stating that either all
3336         downstream clients are willing to accept trailer fields in the
3337         forwarded response, or that it will attempt to buffer the
3338         response on behalf of downstream recipients.
3339      </t><t>
3340         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3341         chunked response such that a client can be assured of buffering
3342         the entire response.</t>
3343    </x:lt>
3344    <x:lt>
3345      <t>If the transfer-coding being tested is one of the transfer-codings
3346         listed in the TE field, then it is acceptable unless it
3347         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3348         qvalue of 0 means "not acceptable".)</t>
3349    </x:lt>
3350    <x:lt>
3351      <t>If multiple transfer-codings are acceptable, then the
3352         acceptable transfer-coding with the highest non-zero qvalue is
3353         preferred.  The "chunked" transfer-coding always has a qvalue
3354         of 1.</t>
3355    </x:lt>
3356  </list>
3359   If the TE field-value is empty or if no TE field is present, the only
3360   transfer-coding is "chunked". A message with no transfer-coding is
3361   always acceptable.
3365<section title="Trailer" anchor="header.trailer">
3366  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3367  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3368  <x:anchor-alias value="Trailer"/>
3370   The "Trailer" header field indicates that the given set of
3371   header fields is present in the trailer of a message encoded with
3372   chunked transfer-coding.
3374<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3375  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3378   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3379   message using chunked transfer-coding with a non-empty trailer. Doing
3380   so allows the recipient to know which header fields to expect in the
3381   trailer.
3384   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3385   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3386   trailer fields in a "chunked" transfer-coding.
3389   Message header fields listed in the Trailer header field &MUST-NOT;
3390   include the following header fields:
3391  <list style="symbols">
3392    <t>Transfer-Encoding</t>
3393    <t>Content-Length</t>
3394    <t>Trailer</t>
3395  </list>
3399<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3400  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3401  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3402  <x:anchor-alias value="Transfer-Encoding"/>
3404   The "Transfer-Encoding" header field indicates what transfer-codings
3405   (if any) have been applied to the message body. It differs from
3406   Content-Encoding (&content-codings;) in that transfer-codings are a property
3407   of the message (and therefore are removed by intermediaries), whereas
3408   content-codings are not.
3410<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3411  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3414   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3416<figure><artwork type="example">
3417  Transfer-Encoding: chunked
3420   If multiple encodings have been applied to a representation, the transfer-codings
3421   &MUST; be listed in the order in which they were applied.
3422   Additional information about the encoding parameters &MAY; be provided
3423   by other header fields not defined by this specification.
3426   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3427   header field.
3431<section title="Upgrade" anchor="header.upgrade">
3432  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3433  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3434  <x:anchor-alias value="Upgrade"/>
3436   The "Upgrade" header field allows the client to specify what
3437   additional communication protocols it would like to use, if the server
3438   chooses to switch protocols. Servers can use it to indicate what protocols
3439   they are willing to switch to.
3441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3442  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3445   For example,
3447<figure><artwork type="example">
3448  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3451   The Upgrade header field is intended to provide a simple mechanism
3452   for transition from HTTP/1.1 to some other, incompatible protocol. It
3453   does so by allowing the client to advertise its desire to use another
3454   protocol, such as a later version of HTTP with a higher major version
3455   number, even though the current request has been made using HTTP/1.1.
3456   This eases the difficult transition between incompatible protocols by
3457   allowing the client to initiate a request in the more commonly
3458   supported protocol while indicating to the server that it would like
3459   to use a "better" protocol if available (where "better" is determined
3460   by the server, possibly according to the nature of the request method
3461   or target resource).
3464   The Upgrade header field only applies to switching application-layer
3465   protocols upon the existing transport-layer connection. Upgrade
3466   cannot be used to insist on a protocol change; its acceptance and use
3467   by the server is optional. The capabilities and nature of the
3468   application-layer communication after the protocol change is entirely
3469   dependent upon the new protocol chosen, although the first action
3470   after changing the protocol &MUST; be a response to the initial HTTP
3471   request containing the Upgrade header field.
3474   The Upgrade header field only applies to the immediate connection.
3475   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3476   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3477   HTTP/1.1 message.
3480   The Upgrade header field cannot be used to indicate a switch to a
3481   protocol on a different connection. For that purpose, it is more
3482   appropriate to use a 3xx redirection response (&status-3xx;).
3485   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3486   Protocols) responses to indicate which protocol(s) are being switched to,
3487   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3488   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3489   response to indicate that they are willing to upgrade to one of the
3490   specified protocols.
3493   This specification only defines the protocol name "HTTP" for use by
3494   the family of Hypertext Transfer Protocols, as defined by the HTTP
3495   version rules of <xref target="http.version"/> and future updates to this
3496   specification. Additional tokens can be registered with IANA using the
3497   registration procedure defined below. 
3500<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3502   The HTTP Upgrade Token Registry defines the name space for product
3503   tokens used to identify protocols in the Upgrade header field.
3504   Each registered token is associated with contact information and
3505   an optional set of specifications that details how the connection
3506   will be processed after it has been upgraded.
3509   Registrations are allowed on a First Come First Served basis as
3510   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3511   specifications need not be IETF documents or be subject to IESG review.
3512   Registrations are subject to the following rules:
3513  <list style="numbers">
3514    <t>A token, once registered, stays registered forever.</t>
3515    <t>The registration &MUST; name a responsible party for the
3516       registration.</t>
3517    <t>The registration &MUST; name a point of contact.</t>
3518    <t>The registration &MAY; name a set of specifications associated with that
3519       token. Such specifications need not be publicly available.</t>
3520    <t>The responsible party &MAY; change the registration at any time.
3521       The IANA will keep a record of all such changes, and make them
3522       available upon request.</t>
3523    <t>The responsible party for the first registration of a "product"
3524       token &MUST; approve later registrations of a "version" token
3525       together with that "product" token before they can be registered.</t>
3526    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3527       for a token. This will normally only be used in the case when a
3528       responsible party cannot be contacted.</t>
3529  </list>
3536<section title="Via" anchor="header.via">
3537  <iref primary="true" item="Via header field" x:for-anchor=""/>
3538  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3539  <x:anchor-alias value="protocol-name"/>
3540  <x:anchor-alias value="protocol-version"/>
3541  <x:anchor-alias value="pseudonym"/>
3542  <x:anchor-alias value="received-by"/>
3543  <x:anchor-alias value="received-protocol"/>
3544  <x:anchor-alias value="Via"/>
3546   The "Via" header field &MUST; be sent by a proxy or gateway to
3547   indicate the intermediate protocols and recipients between the user
3548   agent and the server on requests, and between the origin server and
3549   the client on responses. It is analogous to the "Received" field
3550   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3551   and is intended to be used for tracking message forwards,
3552   avoiding request loops, and identifying the protocol capabilities of
3553   all senders along the request/response chain.
3555<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"/>
3556  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3557                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3558  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3559  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3560  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3561  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3562  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3565   The received-protocol indicates the protocol version of the message
3566   received by the server or client along each segment of the
3567   request/response chain. The received-protocol version is appended to
3568   the Via field value when the message is forwarded so that information
3569   about the protocol capabilities of upstream applications remains
3570   visible to all recipients.
3573   The protocol-name is excluded if and only if it would be "HTTP". The
3574   received-by field is normally the host and optional port number of a
3575   recipient server or client that subsequently forwarded the message.
3576   However, if the real host is considered to be sensitive information,
3577   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3578   be assumed to be the default port of the received-protocol.
3581   Multiple Via field values represent each proxy or gateway that has
3582   forwarded the message. Each recipient &MUST; append its information
3583   such that the end result is ordered according to the sequence of
3584   forwarding applications.
3587   Comments &MAY; be used in the Via header field to identify the software
3588   of each recipient, analogous to the User-Agent and Server header fields.
3589   However, all comments in the Via field are optional and &MAY; be removed
3590   by any recipient prior to forwarding the message.
3593   For example, a request message could be sent from an HTTP/1.0 user
3594   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3595   forward the request to a public proxy at, which completes
3596   the request by forwarding it to the origin server at
3597   The request received by would then have the following
3598   Via header field:
3600<figure><artwork type="example">
3601  Via: 1.0 fred, 1.1 (Apache/1.1)
3604   A proxy or gateway used as a portal through a network firewall
3605   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3606   region unless it is explicitly enabled to do so. If not enabled, the
3607   received-by host of any host behind the firewall &SHOULD; be replaced
3608   by an appropriate pseudonym for that host.
3611   For organizations that have strong privacy requirements for hiding
3612   internal structures, a proxy or gateway &MAY; combine an ordered
3613   subsequence of Via header field entries with identical received-protocol
3614   values into a single such entry. For example,
3616<figure><artwork type="example">
3617  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3620  could be collapsed to
3622<figure><artwork type="example">
3623  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3626   Senders &SHOULD-NOT; combine multiple entries unless they are all
3627   under the same organizational control and the hosts have already been
3628   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3629   have different received-protocol values.
3635<section title="IANA Considerations" anchor="IANA.considerations">
3637<section title="Header Field Registration" anchor="header.field.registration">
3639   The Message Header Field Registry located at <eref target=""/> shall be updated
3640   with the permanent registrations below (see <xref target="RFC3864"/>):
3642<?BEGININC p1-messaging.iana-headers ?>
3643<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3644<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3645   <ttcol>Header Field Name</ttcol>
3646   <ttcol>Protocol</ttcol>
3647   <ttcol>Status</ttcol>
3648   <ttcol>Reference</ttcol>
3650   <c>Connection</c>
3651   <c>http</c>
3652   <c>standard</c>
3653   <c>
3654      <xref target="header.connection"/>
3655   </c>
3656   <c>Content-Length</c>
3657   <c>http</c>
3658   <c>standard</c>
3659   <c>
3660      <xref target="header.content-length"/>
3661   </c>
3662   <c>Date</c>
3663   <c>http</c>
3664   <c>standard</c>
3665   <c>
3666      <xref target=""/>
3667   </c>
3668   <c>Host</c>
3669   <c>http</c>
3670   <c>standard</c>
3671   <c>
3672      <xref target=""/>
3673   </c>
3674   <c>TE</c>
3675   <c>http</c>
3676   <c>standard</c>
3677   <c>
3678      <xref target="header.te"/>
3679   </c>
3680   <c>Trailer</c>
3681   <c>http</c>
3682   <c>standard</c>
3683   <c>
3684      <xref target="header.trailer"/>
3685   </c>
3686   <c>Transfer-Encoding</c>
3687   <c>http</c>
3688   <c>standard</c>
3689   <c>
3690      <xref target="header.transfer-encoding"/>
3691   </c>
3692   <c>Upgrade</c>
3693   <c>http</c>
3694   <c>standard</c>
3695   <c>
3696      <xref target="header.upgrade"/>
3697   </c>
3698   <c>Via</c>
3699   <c>http</c>
3700   <c>standard</c>
3701   <c>
3702      <xref target="header.via"/>
3703   </c>
3706<?ENDINC p1-messaging.iana-headers ?>
3708   The change controller is: "IETF ( - Internet Engineering Task Force".
3712<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3714   The entries for the "http" and "https" URI Schemes in the registry located at
3715   <eref target=""/>
3716   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3717   and <xref target="https.uri" format="counter"/> of this document
3718   (see <xref target="RFC4395"/>).
3722<section title="Internet Media Type Registrations" anchor="">
3724   This document serves as the specification for the Internet media types
3725   "message/http" and "application/http". The following is to be registered with
3726   IANA (see <xref target="RFC4288"/>).
3728<section title="Internet Media Type message/http" anchor="">
3729<iref item="Media Type" subitem="message/http" primary="true"/>
3730<iref item="message/http Media Type" primary="true"/>
3732   The message/http type can be used to enclose a single HTTP request or
3733   response message, provided that it obeys the MIME restrictions for all
3734   "message" types regarding line length and encodings.
3737  <list style="hanging" x:indent="12em">
3738    <t hangText="Type name:">
3739      message
3740    </t>
3741    <t hangText="Subtype name:">
3742      http
3743    </t>
3744    <t hangText="Required parameters:">
3745      none
3746    </t>
3747    <t hangText="Optional parameters:">
3748      version, msgtype
3749      <list style="hanging">
3750        <t hangText="version:">
3751          The HTTP-Version number of the enclosed message
3752          (e.g., "1.1"). If not present, the version can be
3753          determined from the first line of the body.
3754        </t>
3755        <t hangText="msgtype:">
3756          The message type &mdash; "request" or "response". If not
3757          present, the type can be determined from the first
3758          line of the body.
3759        </t>
3760      </list>
3761    </t>
3762    <t hangText="Encoding considerations:">
3763      only "7bit", "8bit", or "binary" are permitted
3764    </t>
3765    <t hangText="Security considerations:">
3766      none
3767    </t>
3768    <t hangText="Interoperability considerations:">
3769      none
3770    </t>
3771    <t hangText="Published specification:">
3772      This specification (see <xref target=""/>).
3773    </t>
3774    <t hangText="Applications that use this media type:">
3775    </t>
3776    <t hangText="Additional information:">
3777      <list style="hanging">
3778        <t hangText="Magic number(s):">none</t>
3779        <t hangText="File extension(s):">none</t>
3780        <t hangText="Macintosh file type code(s):">none</t>
3781      </list>
3782    </t>
3783    <t hangText="Person and email address to contact for further information:">
3784      See Authors Section.
3785    </t>
3786    <t hangText="Intended usage:">
3787      COMMON
3788    </t>
3789    <t hangText="Restrictions on usage:">
3790      none
3791    </t>
3792    <t hangText="Author/Change controller:">
3793      IESG
3794    </t>
3795  </list>
3798<section title="Internet Media Type application/http" anchor="">
3799<iref item="Media Type" subitem="application/http" primary="true"/>
3800<iref item="application/http Media Type" primary="true"/>
3802   The application/http type can be used to enclose a pipeline of one or more
3803   HTTP request or response messages (not intermixed).
3806  <list style="hanging" x:indent="12em">
3807    <t hangText="Type name:">
3808      application
3809    </t>
3810    <t hangText="Subtype name:">
3811      http
3812    </t>
3813    <t hangText="Required parameters:">
3814      none
3815    </t>
3816    <t hangText="Optional parameters:">
3817      version, msgtype
3818      <list style="hanging">
3819        <t hangText="version:">
3820          The HTTP-Version number of the enclosed messages
3821          (e.g., "1.1"). If not present, the version can be
3822          determined from the first line of the body.
3823        </t>
3824        <t hangText="msgtype:">
3825          The message type &mdash; "request" or "response". If not
3826          present, the type can be determined from the first
3827          line of the body.
3828        </t>
3829      </list>
3830    </t>
3831    <t hangText="Encoding considerations:">
3832      HTTP messages enclosed by this type
3833      are in "binary" format; use of an appropriate
3834      Content-Transfer-Encoding is required when
3835      transmitted via E-mail.
3836    </t>
3837    <t hangText="Security considerations:">
3838      none
3839    </t>
3840    <t hangText="Interoperability considerations:">
3841      none
3842    </t>
3843    <t hangText="Published specification:">
3844      This specification (see <xref target=""/>).
3845    </t>
3846    <t hangText="Applications that use this media type:">
3847    </t>
3848    <t hangText="Additional information:">
3849      <list style="hanging">
3850        <t hangText="Magic number(s):">none</t>
3851        <t hangText="File extension(s):">none</t>
3852        <t hangText="Macintosh file type code(s):">none</t>
3853      </list>
3854    </t>
3855    <t hangText="Person and email address to contact for further information:">
3856      See Authors Section.
3857    </t>
3858    <t hangText="Intended usage:">
3859      COMMON
3860    </t>
3861    <t hangText="Restrictions on usage:">
3862      none
3863    </t>
3864    <t hangText="Author/Change controller:">
3865      IESG
3866    </t>
3867  </list>
3872<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3874   The registration procedure for HTTP Transfer Codings is now defined by
3875   <xref target="transfer.coding.registry"/> of this document.
3878   The HTTP Transfer Codings Registry located at <eref target=""/>
3879   shall be updated with the registrations below:
3881<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3882   <ttcol>Name</ttcol>
3883   <ttcol>Description</ttcol>
3884   <ttcol>Reference</ttcol>
3885   <c>chunked</c>
3886   <c>Transfer in a series of chunks</c>
3887   <c>
3888      <xref target="chunked.encoding"/>
3889   </c>
3890   <c>compress</c>
3891   <c>UNIX "compress" program method</c>
3892   <c>
3893      <xref target="compress.coding"/>
3894   </c>
3895   <c>deflate</c>
3896   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3897   the "zlib" data format (<xref target="RFC1950"/>)
3898   </c>
3899   <c>
3900      <xref target="deflate.coding"/>
3901   </c>
3902   <c>gzip</c>
3903   <c>Same as GNU zip <xref target="RFC1952"/></c>
3904   <c>
3905      <xref target="gzip.coding"/>
3906   </c>
3910<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3912   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3913   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3914   by <xref target="upgrade.token.registry"/> of this document.
3917   The HTTP Status Code Registry located at <eref target=""/>
3918   shall be updated with the registration below:
3920<texttable align="left" suppress-title="true">
3921   <ttcol>Value</ttcol>
3922   <ttcol>Description</ttcol>
3923   <ttcol>Reference</ttcol>
3925   <c>HTTP</c>
3926   <c>Hypertext Transfer Protocol</c>
3927   <c><xref target="http.version"/> of this specification</c>
3928<!-- IANA should add this without our instructions; emailed on June 05, 2009
3929   <c>TLS/1.0</c>
3930   <c>Transport Layer Security</c>
3931   <c><xref target="RFC2817"/></c> -->
3938<section title="Security Considerations" anchor="security.considerations">
3940   This section is meant to inform application developers, information
3941   providers, and users of the security limitations in HTTP/1.1 as
3942   described by this document. The discussion does not include
3943   definitive solutions to the problems revealed, though it does make
3944   some suggestions for reducing security risks.
3947<section title="Personal Information" anchor="personal.information">
3949   HTTP clients are often privy to large amounts of personal information
3950   (e.g., the user's name, location, mail address, passwords, encryption
3951   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3952   leakage of this information.
3953   We very strongly recommend that a convenient interface be provided
3954   for the user to control dissemination of such information, and that
3955   designers and implementors be particularly careful in this area.
3956   History shows that errors in this area often create serious security
3957   and/or privacy problems and generate highly adverse publicity for the
3958   implementor's company.
3962<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3964   A server is in the position to save personal data about a user's
3965   requests which might identify their reading patterns or subjects of
3966   interest. This information is clearly confidential in nature and its
3967   handling can be constrained by law in certain countries. People using
3968   HTTP to provide data are responsible for ensuring that
3969   such material is not distributed without the permission of any
3970   individuals that are identifiable by the published results.
3974<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3976   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3977   the documents returned by HTTP requests to be only those that were
3978   intended by the server administrators. If an HTTP server translates
3979   HTTP URIs directly into file system calls, the server &MUST; take
3980   special care not to serve files that were not intended to be
3981   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3982   other operating systems use ".." as a path component to indicate a
3983   directory level above the current one. On such a system, an HTTP
3984   server &MUST; disallow any such construct in the request-target if it
3985   would otherwise allow access to a resource outside those intended to
3986   be accessible via the HTTP server. Similarly, files intended for
3987   reference only internally to the server (such as access control
3988   files, configuration files, and script code) &MUST; be protected from
3989   inappropriate retrieval, since they might contain sensitive
3990   information. Experience has shown that minor bugs in such HTTP server
3991   implementations have turned into security risks.
3995<section title="DNS Spoofing" anchor="dns.spoofing">
3997   Clients using HTTP rely heavily on the Domain Name Service, and are
3998   thus generally prone to security attacks based on the deliberate
3999   mis-association of IP addresses and DNS names. Clients need to be
4000   cautious in assuming the continuing validity of an IP number/DNS name
4001   association.
4004   In particular, HTTP clients &SHOULD; rely on their name resolver for
4005   confirmation of an IP number/DNS name association, rather than
4006   caching the result of previous host name lookups. Many platforms
4007   already can cache host name lookups locally when appropriate, and
4008   they &SHOULD; be configured to do so. It is proper for these lookups to
4009   be cached, however, only when the TTL (Time To Live) information
4010   reported by the name server makes it likely that the cached
4011   information will remain useful.
4014   If HTTP clients cache the results of host name lookups in order to
4015   achieve a performance improvement, they &MUST; observe the TTL
4016   information reported by DNS.
4019   If HTTP clients do not observe this rule, they could be spoofed when
4020   a previously-accessed server's IP address changes. As network
4021   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
4022   possibility of this form of attack will grow. Observing this
4023   requirement thus reduces this potential security vulnerability.
4026   This requirement also improves the load-balancing behavior of clients
4027   for replicated servers using the same DNS name and reduces the
4028   likelihood of a user's experiencing failure in accessing sites which
4029   use that strategy.
4033<section title="Proxies and Caching" anchor="attack.proxies">
4035   By their very nature, HTTP proxies are men-in-the-middle, and
4036   represent an opportunity for man-in-the-middle attacks. Compromise of
4037   the systems on which the proxies run can result in serious security
4038   and privacy problems. Proxies have access to security-related
4039   information, personal information about individual users and
4040   organizations, and proprietary information belonging to users and
4041   content providers. A compromised proxy, or a proxy implemented or
4042   configured without regard to security and privacy considerations,
4043   might be used in the commission of a wide range of potential attacks.
4046   Proxy operators need to protect the systems on which proxies run as
4047   they would protect any system that contains or transports sensitive
4048   information. In particular, log information gathered at proxies often
4049   contains highly sensitive personal information, and/or information
4050   about organizations. Log information needs to be carefully guarded, and
4051   appropriate guidelines for use need to be developed and followed.
4052   (<xref target="abuse.of.server.log.information"/>).
4055   Proxy implementors need to consider the privacy and security
4056   implications of their design and coding decisions, and of the
4057   configuration options they provide to proxy operators (especially the
4058   default configuration).
4061   Users of a proxy need to be aware that proxies are no trustworthier than
4062   the people who run them; HTTP itself cannot solve this problem.
4065   The judicious use of cryptography, when appropriate, might suffice to
4066   protect against a broad range of security and privacy attacks. Such
4067   cryptography is beyond the scope of the HTTP/1.1 specification.
4071<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4073   Because HTTP uses mostly textual, character-delimited fields, attackers can
4074   overflow buffers in implementations, and/or perform a Denial of Service
4075   against implementations that accept fields with unlimited lengths.
4078   To promote interoperability, this specification makes specific
4079   recommendations for size limits on request-targets (<xref target="request-target"/>)
4080   and blocks of header fields (<xref target="header.fields"/>). These are
4081   minimum recommendations, chosen to be supportable even by implementations
4082   with limited resources; it is expected that most implementations will choose
4083   substantially higher limits.
4086   This specification also provides a way for servers to reject messages that
4087   have request-targets that are too long (&status-414;) or request entities
4088   that are too large (&status-4xx;).
4091   Other fields (including but not limited to request methods, response status
4092   phrases, header field-names, and body chunks) &SHOULD; be limited by
4093   implementations carefully, so as to not impede interoperability.
4097<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4099   They exist. They are hard to defend against. Research continues.
4100   Beware.
4105<section title="Acknowledgments" anchor="ack">
4107   HTTP has evolved considerably over the years. It has
4108   benefited from a large and active developer community &mdash; the many
4109   people who have participated on the www-talk mailing list &mdash; and it is
4110   that community which has been most responsible for the success of
4111   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4112   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4113   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4114   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4115   VanHeyningen deserve special recognition for their efforts in
4116   defining early aspects of the protocol.
4119   This document has benefited greatly from the comments of all those
4120   participating in the HTTP-WG. In addition to those already mentioned,
4121   the following individuals have contributed to this specification:
4124   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4125   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4126   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4127   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4128   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4129   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4130   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4131   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4132   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4133   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4134   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4135   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4138   Thanks to the "cave men" of Palo Alto. You know who you are.
4141   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4142   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4143   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4144   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4145   Larry Masinter for their help. And thanks go particularly to Jeff
4146   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4149   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4150   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4151   discovery of many of the problems that this document attempts to
4152   rectify.
4155   This specification makes heavy use of the augmented BNF and generic
4156   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4157   reuses many of the definitions provided by Nathaniel Borenstein and
4158   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4159   specification will help reduce past confusion over the relationship
4160   between HTTP and Internet mail message formats.
4164Acknowledgements TODO list
4166- Jeff Hodges ("effective request URI")
4174<references title="Normative References">
4176<reference anchor="ISO-8859-1">
4177  <front>
4178    <title>
4179     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4180    </title>
4181    <author>
4182      <organization>International Organization for Standardization</organization>
4183    </author>
4184    <date year="1998"/>
4185  </front>
4186  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4189<reference anchor="Part2">
4190  <front>
4191    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4192    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4193      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4194      <address><email></email></address>
4195    </author>
4196    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4197      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4198      <address><email></email></address>
4199    </author>
4200    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4201      <organization abbrev="HP">Hewlett-Packard Company</organization>
4202      <address><email></email></address>
4203    </author>
4204    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4205      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4206      <address><email></email></address>
4207    </author>
4208    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4209      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4210      <address><email></email></address>
4211    </author>
4212    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4213      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4214      <address><email></email></address>
4215    </author>
4216    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4217      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4218      <address><email></email></address>
4219    </author>
4220    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4221      <organization abbrev="W3C">World Wide Web Consortium</organization>
4222      <address><email></email></address>
4223    </author>
4224    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4225      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4226      <address><email></email></address>
4227    </author>
4228    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4229  </front>
4230  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4231  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4234<reference anchor="Part3">
4235  <front>
4236    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4237    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4238      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4239      <address><email></email></address>
4240    </author>
4241    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4242      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4243      <address><email></email></address>
4244    </author>
4245    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4246      <organization abbrev="HP">Hewlett-Packard Company</organization>
4247      <address><email></email></address>
4248    </author>
4249    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4250      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4251      <address><email></email></address>
4252    </author>
4253    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4254      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4255      <address><email></email></address>
4256    </author>
4257    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4258      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4259      <address><email></email></address>
4260    </author>
4261    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4262      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4263      <address><email></email></address>
4264    </author>
4265    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4266      <organization abbrev="W3C">World Wide Web Consortium</organization>
4267      <address><email></email></address>
4268    </author>
4269    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4270      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4271      <address><email></email></address>
4272    </author>
4273    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4274  </front>
4275  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4276  <x:source href="p3-payload.xml" basename="p3-payload"/>
4279<reference anchor="Part6">
4280  <front>
4281    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4282    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4283      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4284      <address><email></email></address>
4285    </author>
4286    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4287      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4288      <address><email></email></address>
4289    </author>
4290    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4291      <organization abbrev="HP">Hewlett-Packard Company</organization>
4292      <address><email></email></address>
4293    </author>
4294    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4295      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4296      <address><email></email></address>
4297    </author>
4298    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4299      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4300      <address><email></email></address>
4301    </author>
4302    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4303      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4304      <address><email></email></address>
4305    </author>
4306    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4307      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4308      <address><email></email></address>
4309    </author>
4310    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4311      <organization abbrev="W3C">World Wide Web Consortium</organization>
4312      <address><email></email></address>
4313    </author>
4314    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4315      <address><email></email></address>
4316    </author>
4317    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4318      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4319      <address><email></email></address>
4320    </author>
4321    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4322  </front>
4323  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4324  <x:source href="p6-cache.xml" basename="p6-cache"/>
4327<reference anchor="RFC5234">
4328  <front>
4329    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4330    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4331      <organization>Brandenburg InternetWorking</organization>
4332      <address>
4333        <email></email>
4334      </address> 
4335    </author>
4336    <author initials="P." surname="Overell" fullname="Paul Overell">
4337      <organization>THUS plc.</organization>
4338      <address>
4339        <email></email>
4340      </address>
4341    </author>
4342    <date month="January" year="2008"/>
4343  </front>
4344  <seriesInfo name="STD" value="68"/>
4345  <seriesInfo name="RFC" value="5234"/>
4348<reference anchor="RFC2119">
4349  <front>
4350    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4351    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4352      <organization>Harvard University</organization>
4353      <address><email></email></address>
4354    </author>
4355    <date month="March" year="1997"/>
4356  </front>
4357  <seriesInfo name="BCP" value="14"/>
4358  <seriesInfo name="RFC" value="2119"/>
4361<reference anchor="RFC3986">
4362 <front>
4363  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4364  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4365    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4366    <address>
4367       <email></email>
4368       <uri></uri>
4369    </address>
4370  </author>
4371  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4372    <organization abbrev="Day Software">Day Software</organization>
4373    <address>
4374      <email></email>
4375      <uri></uri>
4376    </address>
4377  </author>
4378  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4379    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4380    <address>
4381      <email></email>
4382      <uri></uri>
4383    </address>
4384  </author>
4385  <date month='January' year='2005'></date>
4386 </front>
4387 <seriesInfo name="STD" value="66"/>
4388 <seriesInfo name="RFC" value="3986"/>
4391<reference anchor="USASCII">
4392  <front>
4393    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4394    <author>
4395      <organization>American National Standards Institute</organization>
4396    </author>
4397    <date year="1986"/>
4398  </front>
4399  <seriesInfo name="ANSI" value="X3.4"/>
4402<reference anchor="RFC1950">
4403  <front>
4404    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4405    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4406      <organization>Aladdin Enterprises</organization>
4407      <address><email></email></address>
4408    </author>
4409    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4410    <date month="May" year="1996"/>
4411  </front>
4412  <seriesInfo name="RFC" value="1950"/>
4413  <annotation>
4414    RFC 1950 is an Informational RFC, thus it might be less stable than
4415    this specification. On the other hand, this downward reference was
4416    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4417    therefore it is unlikely to cause problems in practice. See also
4418    <xref target="BCP97"/>.
4419  </annotation>
4422<reference anchor="RFC1951">
4423  <front>
4424    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4425    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4426      <organization>Aladdin Enterprises</organization>
4427      <address><email></email></address>
4428    </author>
4429    <date month="May" year="1996"/>
4430  </front>
4431  <seriesInfo name="RFC" value="1951"/>
4432  <annotation>
4433    RFC 1951 is an Informational RFC, thus it might be less stable than
4434    this specification. On the other hand, this downward reference was
4435    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4436    therefore it is unlikely to cause problems in practice. See also
4437    <xref target="BCP97"/>.
4438  </annotation>
4441<reference anchor="RFC1952">
4442  <front>
4443    <title>GZIP file format specification version 4.3</title>
4444    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4445      <organization>Aladdin Enterprises</organization>
4446      <address><email></email></address>
4447    </author>
4448    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4449      <address><email></email></address>
4450    </author>
4451    <author initials="M." surname="Adler" fullname="Mark Adler">
4452      <address><email></email></address>
4453    </author>
4454    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4455      <address><email></email></address>
4456    </author>
4457    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4458      <address><email></email></address>
4459    </author>
4460    <date month="May" year="1996"/>
4461  </front>
4462  <seriesInfo name="RFC" value="1952"/>
4463  <annotation>
4464    RFC 1952 is an Informational RFC, thus it might be less stable than
4465    this specification. On the other hand, this downward reference was
4466    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4467    therefore it is unlikely to cause problems in practice. See also
4468    <xref target="BCP97"/>.
4469  </annotation>
4474<references title="Informative References">
4476<reference anchor="Nie1997" target="">
4477  <front>
4478    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4479    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4480    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4481    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4482    <author initials="H." surname="Lie" fullname="H. Lie"/>
4483    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4484    <date year="1997" month="September"/>
4485  </front>
4486  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4489<reference anchor="Pad1995" target="">
4490  <front>
4491    <title>Improving HTTP Latency</title>
4492    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4493    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4494    <date year="1995" month="December"/>
4495  </front>
4496  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4499<reference anchor="RFC1123">
4500  <front>
4501    <title>Requirements for Internet Hosts - Application and Support</title>
4502    <author initials="R." surname="Braden" fullname="Robert Braden">
4503      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4504      <address><email>Braden@ISI.EDU</email></address>
4505    </author>
4506    <date month="October" year="1989"/>
4507  </front>
4508  <seriesInfo name="STD" value="3"/>
4509  <seriesInfo name="RFC" value="1123"/>
4512<reference anchor="RFC1900">
4513  <front>
4514    <title>Renumbering Needs Work</title>
4515    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4516      <organization>CERN, Computing and Networks Division</organization>
4517      <address><email></email></address>
4518    </author>
4519    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4520      <organization>cisco Systems</organization>
4521      <address><email></email></address>
4522    </author>
4523    <date month="February" year="1996"/>
4524  </front>
4525  <seriesInfo name="RFC" value="1900"/>
4528<reference anchor='RFC1919'>
4529  <front>
4530    <title>Classical versus Transparent IP Proxies</title>
4531    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4532      <address><email></email></address>
4533    </author>
4534    <date year='1996' month='March' />
4535  </front>
4536  <seriesInfo name='RFC' value='1919' />
4539<reference anchor="RFC1945">
4540  <front>
4541    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4542    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4543      <organization>MIT, Laboratory for Computer Science</organization>
4544      <address><email></email></address>
4545    </author>
4546    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4547      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4548      <address><email></email></address>
4549    </author>
4550    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4551      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4552      <address><email></email></address>
4553    </author>
4554    <date month="May" year="1996"/>
4555  </front>
4556  <seriesInfo name="RFC" value="1945"/>
4559<reference anchor="RFC2045">
4560  <front>
4561    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4562    <author initials="N." surname="Freed" fullname="Ned Freed">
4563      <organization>Innosoft International, Inc.</organization>
4564      <address><email></email></address>
4565    </author>
4566    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4567      <organization>First Virtual Holdings</organization>
4568      <address><email></email></address>
4569    </author>
4570    <date month="November" year="1996"/>
4571  </front>
4572  <seriesInfo name="RFC" value="2045"/>
4575<reference anchor="RFC2047">
4576  <front>
4577    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4578    <author initials="K." surname="Moore" fullname="Keith Moore">
4579      <organization>University of Tennessee</organization>
4580      <address><email></email></address>
4581    </author>
4582    <date month="November" year="1996"/>
4583  </front>
4584  <seriesInfo name="RFC" value="2047"/>
4587<reference anchor="RFC2068">
4588  <front>
4589    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4590    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4591      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4592      <address><email></email></address>
4593    </author>
4594    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4595      <organization>MIT Laboratory for Computer Science</organization>
4596      <address><email></email></address>
4597    </author>
4598    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4599      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4600      <address><email></email></address>
4601    </author>
4602    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4603      <organization>MIT Laboratory for Computer Science</organization>
4604      <address><email></email></address>
4605    </author>
4606    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4607      <organization>MIT Laboratory for Computer Science</organization>
4608      <address><email></email></address>
4609    </author>
4610    <date month="January" year="1997"/>
4611  </front>
4612  <seriesInfo name="RFC" value="2068"/>
4615<reference anchor="RFC2145">
4616  <front>
4617    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4618    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4619      <organization>Western Research Laboratory</organization>
4620      <address><email></email></address>
4621    </author>
4622    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4623      <organization>Department of Information and Computer Science</organization>
4624      <address><email></email></address>
4625    </author>
4626    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4627      <organization>MIT Laboratory for Computer Science</organization>
4628      <address><email></email></address>
4629    </author>
4630    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4631      <organization>W3 Consortium</organization>
4632      <address><email></email></address>
4633    </author>
4634    <date month="May" year="1997"/>
4635  </front>
4636  <seriesInfo name="RFC" value="2145"/>
4639<reference anchor="RFC2616">
4640  <front>
4641    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4642    <author initials="R." surname="Fielding" fullname="R. Fielding">
4643      <organization>University of California, Irvine</organization>
4644      <address><email></email></address>
4645    </author>
4646    <author initials="J." surname="Gettys" fullname="J. Gettys">
4647      <organization>W3C</organization>
4648      <address><email></email></address>
4649    </author>
4650    <author initials="J." surname="Mogul" fullname="J. Mogul">
4651      <organization>Compaq Computer Corporation</organization>
4652      <address><email></email></address>
4653    </author>
4654    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4655      <organization>MIT Laboratory for Computer Science</organization>
4656      <address><email></email></address>
4657    </author>
4658    <author initials="L." surname="Masinter" fullname="L. Masinter">
4659      <organization>Xerox Corporation</organization>
4660      <address><email></email></address>
4661    </author>
4662    <author initials="P." surname="Leach" fullname="P. Leach">
4663      <organization>Microsoft Corporation</organization>
4664      <address><email></email></address>
4665    </author>
4666    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4667      <organization>W3C</organization>
4668      <address><email></email></address>
4669    </author>
4670    <date month="June" year="1999"/>
4671  </front>
4672  <seriesInfo name="RFC" value="2616"/>
4675<reference anchor='RFC2817'>
4676  <front>
4677    <title>Upgrading to TLS Within HTTP/1.1</title>
4678    <author initials='R.' surname='Khare' fullname='R. Khare'>
4679      <organization>4K Associates / UC Irvine</organization>
4680      <address><email></email></address>
4681    </author>
4682    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4683      <organization>Agranat Systems, Inc.</organization>
4684      <address><email></email></address>
4685    </author>
4686    <date year='2000' month='May' />
4687  </front>
4688  <seriesInfo name='RFC' value='2817' />
4691<reference anchor='RFC2818'>
4692  <front>
4693    <title>HTTP Over TLS</title>
4694    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4695      <organization>RTFM, Inc.</organization>
4696      <address><email></email></address>
4697    </author>
4698    <date year='2000' month='May' />
4699  </front>
4700  <seriesInfo name='RFC' value='2818' />
4703<reference anchor='RFC2965'>
4704  <front>
4705    <title>HTTP State Management Mechanism</title>
4706    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4707      <organization>Bell Laboratories, Lucent Technologies</organization>
4708      <address><email></email></address>
4709    </author>
4710    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4711      <organization>, Inc.</organization>
4712      <address><email></email></address>
4713    </author>
4714    <date year='2000' month='October' />
4715  </front>
4716  <seriesInfo name='RFC' value='2965' />
4719<reference anchor='RFC3040'>
4720  <front>
4721    <title>Internet Web Replication and Caching Taxonomy</title>
4722    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4723      <organization>Equinix, Inc.</organization>
4724    </author>
4725    <author initials='I.' surname='Melve' fullname='I. Melve'>
4726      <organization>UNINETT</organization>
4727    </author>
4728    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4729      <organization>CacheFlow Inc.</organization>
4730    </author>
4731    <date year='2001' month='January' />
4732  </front>
4733  <seriesInfo name='RFC' value='3040' />
4736<reference anchor='RFC3864'>
4737  <front>
4738    <title>Registration Procedures for Message Header Fields</title>
4739    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4740      <organization>Nine by Nine</organization>
4741      <address><email></email></address>
4742    </author>
4743    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4744      <organization>BEA Systems</organization>
4745      <address><email></email></address>
4746    </author>
4747    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4748      <organization>HP Labs</organization>
4749      <address><email></email></address>
4750    </author>
4751    <date year='2004' month='September' />
4752  </front>
4753  <seriesInfo name='BCP' value='90' />
4754  <seriesInfo name='RFC' value='3864' />
4757<reference anchor="RFC4288">
4758  <front>
4759    <title>Media Type Specifications and Registration Procedures</title>
4760    <author initials="N." surname="Freed" fullname="N. Freed">
4761      <organization>Sun Microsystems</organization>
4762      <address>
4763        <email></email>
4764      </address>
4765    </author>
4766    <author initials="J." surname="Klensin" fullname="J. Klensin">
4767      <address>
4768        <email></email>
4769      </address>
4770    </author>
4771    <date year="2005" month="December"/>
4772  </front>
4773  <seriesInfo name="BCP" value="13"/>
4774  <seriesInfo name="RFC" value="4288"/>
4777<reference anchor='RFC4395'>
4778  <front>
4779    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4780    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4781      <organization>AT&amp;T Laboratories</organization>
4782      <address>
4783        <email></email>
4784      </address>
4785    </author>
4786    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4787      <organization>Qualcomm, Inc.</organization>
4788      <address>
4789        <email></email>
4790      </address>
4791    </author>
4792    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4793      <organization>Adobe Systems</organization>
4794      <address>
4795        <email></email>
4796      </address>
4797    </author>
4798    <date year='2006' month='February' />
4799  </front>
4800  <seriesInfo name='BCP' value='115' />
4801  <seriesInfo name='RFC' value='4395' />
4804<reference anchor='RFC4559'>
4805  <front>
4806    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4807    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4808    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4809    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4810    <date year='2006' month='June' />
4811  </front>
4812  <seriesInfo name='RFC' value='4559' />
4815<reference anchor='RFC5226'>
4816  <front>
4817    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4818    <author initials='T.' surname='Narten' fullname='T. Narten'>
4819      <organization>IBM</organization>
4820      <address><email></email></address>
4821    </author>
4822    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4823      <organization>Google</organization>
4824      <address><email></email></address>
4825    </author>
4826    <date year='2008' month='May' />
4827  </front>
4828  <seriesInfo name='BCP' value='26' />
4829  <seriesInfo name='RFC' value='5226' />
4832<reference anchor="RFC5322">
4833  <front>
4834    <title>Internet Message Format</title>
4835    <author initials="P." surname="Resnick" fullname="P. Resnick">
4836      <organization>Qualcomm Incorporated</organization>
4837    </author>
4838    <date year="2008" month="October"/>
4839  </front>
4840  <seriesInfo name="RFC" value="5322"/>
4843<reference anchor="RFC6265">
4844  <front>
4845    <title>HTTP State Management Mechanism</title>
4846    <author initials="A." surname="Barth" fullname="Adam Barth">
4847      <organization abbrev="U.C. Berkeley">
4848        University of California, Berkeley
4849      </organization>
4850      <address><email></email></address>
4851    </author>
4852    <date year="2011" month="April" />
4853  </front>
4854  <seriesInfo name="RFC" value="6265"/>
4857<reference anchor='BCP97'>
4858  <front>
4859    <title>Handling Normative References to Standards-Track Documents</title>
4860    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4861      <address>
4862        <email></email>
4863      </address>
4864    </author>
4865    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4866      <organization>MIT</organization>
4867      <address>
4868        <email></email>
4869      </address>
4870    </author>
4871    <date year='2007' month='June' />
4872  </front>
4873  <seriesInfo name='BCP' value='97' />
4874  <seriesInfo name='RFC' value='4897' />
4877<reference anchor="Kri2001" target="">
4878  <front>
4879    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4880    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4881    <date year="2001" month="November"/>
4882  </front>
4883  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4886<reference anchor="Spe" target="">
4887  <front>
4888    <title>Analysis of HTTP Performance Problems</title>
4889    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4890    <date/>
4891  </front>
4894<reference anchor="Tou1998" target="">
4895  <front>
4896  <title>Analysis of HTTP Performance</title>
4897  <author initials="J." surname="Touch" fullname="Joe Touch">
4898    <organization>USC/Information Sciences Institute</organization>
4899    <address><email></email></address>
4900  </author>
4901  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4902    <organization>USC/Information Sciences Institute</organization>
4903    <address><email></email></address>
4904  </author>
4905  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4906    <organization>USC/Information Sciences Institute</organization>
4907    <address><email></email></address>
4908  </author>
4909  <date year="1998" month="Aug"/>
4910  </front>
4911  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4912  <annotation>(original report dated Aug. 1996)</annotation>
4918<section title="Tolerant Applications" anchor="tolerant.applications">
4920   Although this document specifies the requirements for the generation
4921   of HTTP/1.1 messages, not all applications will be correct in their
4922   implementation. We therefore recommend that operational applications
4923   be tolerant of deviations whenever those deviations can be
4924   interpreted unambiguously.
4927   The line terminator for header fields is the sequence CRLF.
4928   However, we recommend that applications, when parsing such headers fields,
4929   recognize a single LF as a line terminator and ignore the leading CR.
4932   The character encoding of a representation &SHOULD; be labeled as the lowest
4933   common denominator of the character codes used within that representation, with
4934   the exception that not labeling the representation is preferred over labeling
4935   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4938   Additional rules for requirements on parsing and encoding of dates
4939   and other potential problems with date encodings include:
4942  <list style="symbols">
4943     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4944        which appears to be more than 50 years in the future is in fact
4945        in the past (this helps solve the "year 2000" problem).</t>
4947     <t>Although all date formats are specified to be case-sensitive,
4948        recipients &SHOULD; match day, week and timezone names
4949        case-insensitively.</t>
4951     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4952        Expires date as earlier than the proper value, but &MUST-NOT;
4953        internally represent a parsed Expires date as later than the
4954        proper value.</t>
4956     <t>All expiration-related calculations &MUST; be done in GMT. The
4957        local time zone &MUST-NOT; influence the calculation or comparison
4958        of an age or expiration time.</t>
4960     <t>If an HTTP header field incorrectly carries a date value with a time
4961        zone other than GMT, it &MUST; be converted into GMT using the
4962        most conservative possible conversion.</t>
4963  </list>
4967<section title="HTTP Version History" anchor="compatibility">
4969   HTTP has been in use by the World-Wide Web global information initiative
4970   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4971   was a simple protocol for hypertext data transfer across the Internet
4972   with only a single request method (GET) and no metadata.
4973   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4974   methods and MIME-like messaging that could include metadata about the data
4975   transferred and modifiers on the request/response semantics. However,
4976   HTTP/1.0 did not sufficiently take into consideration the effects of
4977   hierarchical proxies, caching, the need for persistent connections, or
4978   name-based virtual hosts. The proliferation of incompletely-implemented
4979   applications calling themselves "HTTP/1.0" further necessitated a
4980   protocol version change in order for two communicating applications
4981   to determine each other's true capabilities.
4984   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4985   requirements that enable reliable implementations, adding only
4986   those new features that will either be safely ignored by an HTTP/1.0
4987   recipient or only sent when communicating with a party advertising
4988   compliance with HTTP/1.1.
4991   It is beyond the scope of a protocol specification to mandate
4992   compliance with previous versions. HTTP/1.1 was deliberately
4993   designed, however, to make supporting previous versions easy.
4994   We would expect a general-purpose HTTP/1.1 server to understand
4995   any valid request in the format of HTTP/1.0 and respond appropriately
4996   with an HTTP/1.1 message that only uses features understood (or
4997   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4998   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
5001   Since HTTP/0.9 did not support header fields in a request,
5002   there is no mechanism for it to support name-based virtual
5003   hosts (selection of resource by inspection of the Host header
5004   field).  Any server that implements name-based virtual hosts
5005   ought to disable support for HTTP/0.9.  Most requests that
5006   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
5007   requests wherein a buggy client failed to properly encode
5008   linear whitespace found in a URI reference and placed in
5009   the request-target.
5012<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
5014   This section summarizes major differences between versions HTTP/1.0
5015   and HTTP/1.1.
5018<section title="Multi-homed Web Servers" anchor="">
5020   The requirements that clients and servers support the Host header
5021   field (<xref target=""/>), report an error if it is
5022   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
5023   are among the most important changes defined by HTTP/1.1.
5026   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
5027   addresses and servers; there was no other established mechanism for
5028   distinguishing the intended server of a request than the IP address
5029   to which that request was directed. The Host header field was
5030   introduced during the development of HTTP/1.1 and, though it was
5031   quickly implemented by most HTTP/1.0 browsers, additional requirements
5032   were placed on all HTTP/1.1 requests in order to ensure complete
5033   adoption.  At the time of this writing, most HTTP-based services
5034   are dependent upon the Host header field for targeting requests.
5038<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
5040   For most implementations of HTTP/1.0, each connection is established
5041   by the client prior to the request and closed by the server after
5042   sending the response. However, some implementations implement the
5043   Keep-Alive version of persistent connections described in
5044   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
5047   Some clients and servers might wish to be compatible with some
5048   previous implementations of persistent connections in HTTP/1.0
5049   clients and servers. Persistent connections in HTTP/1.0 are
5050   explicitly negotiated as they are not the default behavior. HTTP/1.0
5051   experimental implementations of persistent connections are faulty,
5052   and the new facilities in HTTP/1.1 are designed to rectify these
5053   problems. The problem was that some existing HTTP/1.0 clients might
5054   send Keep-Alive to a proxy server that doesn't understand
5055   Connection, which would then erroneously forward it to the next
5056   inbound server, which would establish the Keep-Alive connection and
5057   result in a hung HTTP/1.0 proxy waiting for the close on the
5058   response. The result is that HTTP/1.0 clients must be prevented from
5059   using Keep-Alive when talking to proxies.
5062   However, talking to proxies is the most important use of persistent
5063   connections, so that prohibition is clearly unacceptable. Therefore,
5064   we need some other mechanism for indicating a persistent connection
5065   is desired, which is safe to use even when talking to an old proxy
5066   that ignores Connection. Persistent connections are the default for
5067   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
5068   declaring non-persistence. See <xref target="header.connection"/>.
5073<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5075  Empty list elements in list productions have been deprecated.
5076  (<xref target="notation.abnf"/>)
5079  Rules about implicit linear whitespace between certain grammar productions
5080  have been removed; now it's only allowed when specifically pointed out
5081  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5082  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5083  Non-ASCII content in header fields and reason phrase has been obsoleted and
5084  made opaque (the TEXT rule was removed)
5085  (<xref target="basic.rules"/>)
5088  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5089  sensitive. Restrict the version numbers to be single digits due to the fact
5090  that implementations are known to handle multi-digit version numbers
5091  incorrectly.
5092  (<xref target="http.version"/>)
5095  Require that invalid whitespace around field-names be rejected.
5096  (<xref target="header.fields"/>)
5099  Require recipients to handle bogus Content-Length header fields as errors.
5100  (<xref target="message.body"/>)
5103  Remove reference to non-existent identity transfer-coding value tokens.
5104  (Sections <xref format="counter" target="message.body"/> and
5105  <xref format="counter" target="transfer.codings"/>)
5108  Update use of abs_path production from RFC 1808 to the path-absolute + query
5109  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5110  request method only.
5111  (<xref target="request-target"/>)
5114  Clarification that the chunk length does not include the count of the octets
5115  in the chunk header and trailer. Furthermore disallowed line folding
5116  in chunk extensions.
5117  (<xref target="chunked.encoding"/>)
5120  Remove hard limit of two connections per server.
5121  (<xref target="persistent.practical"/>)
5124  Change ABNF productions for header fields to only define the field value.
5125  (<xref target="header.field.definitions"/>)
5128  Clarify exactly when close connection options must be sent.
5129  (<xref target="header.connection"/>)
5132  Define the semantics of the "Upgrade" header field in responses other than
5133  101 (this was incorporated from <xref target="RFC2817"/>).
5134  (<xref target="header.upgrade"/>)
5139<?BEGININC p1-messaging.abnf-appendix ?>
5140<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5142<artwork type="abnf" name="p1-messaging.parsed-abnf">
5143<x:ref>BWS</x:ref> = OWS
5145<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5146<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5147 connection-token ] )
5148<x:ref>Content-Length</x:ref> = 1*DIGIT
5150<x:ref>Date</x:ref> = HTTP-date
5152<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5154<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5155<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5156<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5157<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5158 ]
5159<x:ref>Host</x:ref> = uri-host [ ":" port ]
5161<x:ref>Method</x:ref> = token
5163<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5165<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5166<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5167<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5168<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5169<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5171<x:ref>Status-Code</x:ref> = 3DIGIT
5172<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5174<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5175<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5176<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5177 transfer-coding ] )
5179<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5180<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5182<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5183 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5184 )
5186<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5187<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5188<x:ref>attribute</x:ref> = token
5189<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5191<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5192<x:ref>chunk-data</x:ref> = 1*OCTET
5193<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5194<x:ref>chunk-ext-name</x:ref> = token
5195<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5196<x:ref>chunk-size</x:ref> = 1*HEXDIG
5197<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5198<x:ref>connection-token</x:ref> = token
5199<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5200 / %x2A-5B ; '*'-'['
5201 / %x5D-7E ; ']'-'~'
5202 / obs-text
5204<x:ref>date1</x:ref> = day SP month SP year
5205<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5206<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5207<x:ref>day</x:ref> = 2DIGIT
5208<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5209 / %x54.75.65 ; Tue
5210 / %x57.65.64 ; Wed
5211 / %x54.68.75 ; Thu
5212 / %x46.72.69 ; Fri
5213 / %x53.61.74 ; Sat
5214 / %x53.75.6E ; Sun
5215<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5216 / %x54. ; Tuesday
5217 / %x57.65.64.6E. ; Wednesday
5218 / %x54. ; Thursday
5219 / %x46. ; Friday
5220 / %x53. ; Saturday
5221 / %x53.75.6E.64.61.79 ; Sunday
5223<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5224<x:ref>field-name</x:ref> = token
5225<x:ref>field-value</x:ref> = *( field-content / OWS )
5227<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5228<x:ref>hour</x:ref> = 2DIGIT
5229<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5230<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5232<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5234<x:ref>message-body</x:ref> = *OCTET
5235<x:ref>minute</x:ref> = 2DIGIT
5236<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5237 / %x46.65.62 ; Feb
5238 / %x4D.61.72 ; Mar
5239 / %x41.70.72 ; Apr
5240 / %x4D.61.79 ; May
5241 / %x4A.75.6E ; Jun
5242 / %x4A.75.6C ; Jul
5243 / %x41.75.67 ; Aug
5244 / %x53.65.70 ; Sep
5245 / %x4F.63.74 ; Oct
5246 / %x4E.6F.76 ; Nov
5247 / %x44.65.63 ; Dec
5249<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5250<x:ref>obs-fold</x:ref> = CRLF
5251<x:ref>obs-text</x:ref> = %x80-FF
5253<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5254<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5255<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5256<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5257<x:ref>product</x:ref> = token [ "/" product-version ]
5258<x:ref>product-version</x:ref> = token
5259<x:ref>protocol-name</x:ref> = token
5260<x:ref>protocol-version</x:ref> = token
5261<x:ref>pseudonym</x:ref> = token
5263<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5264 / %x5D-7E ; ']'-'~'
5265 / obs-text
5266<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5267 / %x5D-7E ; ']'-'~'
5268 / obs-text
5269<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5270<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5271<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5272<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5273<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5274<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5276<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5277<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5278<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5279<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5280 / authority
5281<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5282<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5284<x:ref>second</x:ref> = 2DIGIT
5285<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5286 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5287<x:ref>start-line</x:ref> = Request-Line / Status-Line
5289<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5290<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5291 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5292<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5293<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5294<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5295<x:ref>token</x:ref> = 1*tchar
5296<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5297<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5298 transfer-extension
5299<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5300<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5302<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5304<x:ref>value</x:ref> = word
5306<x:ref>word</x:ref> = token / quoted-string
5308<x:ref>year</x:ref> = 4DIGIT
5311<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5312; Chunked-Body defined but not used
5313; Connection defined but not used
5314; Content-Length defined but not used
5315; Date defined but not used
5316; HTTP-message defined but not used
5317; Host defined but not used
5318; Request defined but not used
5319; Response defined but not used
5320; TE defined but not used
5321; Trailer defined but not used
5322; Transfer-Encoding defined but not used
5323; URI-reference defined but not used
5324; Upgrade defined but not used
5325; Via defined but not used
5326; http-URI defined but not used
5327; https-URI defined but not used
5328; partial-URI defined but not used
5329; special defined but not used
5331<?ENDINC p1-messaging.abnf-appendix ?>
5333<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5335<section title="Since RFC 2616">
5337  Extracted relevant partitions from <xref target="RFC2616"/>.
5341<section title="Since draft-ietf-httpbis-p1-messaging-00">
5343  Closed issues:
5344  <list style="symbols">
5345    <t>
5346      <eref target=""/>:
5347      "HTTP Version should be case sensitive"
5348      (<eref target=""/>)
5349    </t>
5350    <t>
5351      <eref target=""/>:
5352      "'unsafe' characters"
5353      (<eref target=""/>)
5354    </t>
5355    <t>
5356      <eref target=""/>:
5357      "Chunk Size Definition"
5358      (<eref target=""/>)
5359    </t>
5360    <t>
5361      <eref target=""/>:
5362      "Message Length"
5363      (<eref target=""/>)
5364    </t>
5365    <t>
5366      <eref target=""/>:
5367      "Media Type Registrations"
5368      (<eref target=""/>)
5369    </t>
5370    <t>
5371      <eref target=""/>:
5372      "URI includes query"
5373      (<eref target=""/>)
5374    </t>
5375    <t>
5376      <eref target=""/>:
5377      "No close on 1xx responses"
5378      (<eref target=""/>)
5379    </t>
5380    <t>
5381      <eref target=""/>:
5382      "Remove 'identity' token references"
5383      (<eref target=""/>)
5384    </t>
5385    <t>
5386      <eref target=""/>:
5387      "Import query BNF"
5388    </t>
5389    <t>
5390      <eref target=""/>:
5391      "qdtext BNF"
5392    </t>
5393    <t>
5394      <eref target=""/>:
5395      "Normative and Informative references"
5396    </t>
5397    <t>
5398      <eref target=""/>:
5399      "RFC2606 Compliance"
5400    </t>
5401    <t>
5402      <eref target=""/>:
5403      "RFC977 reference"
5404    </t>
5405    <t>
5406      <eref target=""/>:
5407      "RFC1700 references"
5408    </t>
5409    <t>
5410      <eref target=""/>:
5411      "inconsistency in date format explanation"
5412    </t>
5413    <t>
5414      <eref target=""/>:
5415      "Date reference typo"
5416    </t>
5417    <t>
5418      <eref target=""/>:
5419      "Informative references"
5420    </t>
5421    <t>
5422      <eref target=""/>:
5423      "ISO-8859-1 Reference"
5424    </t>
5425    <t>
5426      <eref target=""/>:
5427      "Normative up-to-date references"
5428    </t>
5429  </list>
5432  Other changes:
5433  <list style="symbols">
5434    <t>
5435      Update media type registrations to use RFC4288 template.
5436    </t>
5437    <t>
5438      Use names of RFC4234 core rules DQUOTE and WSP,
5439      fix broken ABNF for chunk-data
5440      (work in progress on <eref target=""/>)
5441    </t>
5442  </list>
5446<section title="Since draft-ietf-httpbis-p1-messaging-01">
5448  Closed issues:
5449  <list style="symbols">
5450    <t>
5451      <eref target=""/>:
5452      "Bodies on GET (and other) requests"
5453    </t>
5454    <t>
5455      <eref target=""/>:
5456      "Updating to RFC4288"
5457    </t>
5458    <t>
5459      <eref target=""/>:
5460      "Status Code and Reason Phrase"
5461    </t>
5462    <t>
5463      <eref target=""/>:
5464      "rel_path not used"
5465    </t>
5466  </list>
5469  Ongoing work on ABNF conversion (<eref target=""/>):
5470  <list style="symbols">
5471    <t>
5472      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5473      "trailer-part").
5474    </t>
5475    <t>
5476      Avoid underscore character in rule names ("http_URL" ->
5477      "http-URL", "abs_path" -> "path-absolute").
5478    </t>
5479    <t>
5480      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5481      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5482      have to be updated when switching over to RFC3986.
5483    </t>
5484    <t>
5485      Synchronize core rules with RFC5234.
5486    </t>
5487    <t>
5488      Get rid of prose rules that span multiple lines.
5489    </t>
5490    <t>
5491      Get rid of unused rules LOALPHA and UPALPHA.
5492    </t>
5493    <t>
5494      Move "Product Tokens" section (back) into Part 1, as "token" is used
5495      in the definition of the Upgrade header field.
5496    </t>
5497    <t>
5498      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5499    </t>
5500    <t>
5501      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5502    </t>
5503  </list>
5507<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5509  Closed issues:
5510  <list style="symbols">
5511    <t>
5512      <eref target=""/>:
5513      "HTTP-date vs. rfc1123-date"
5514    </t>
5515    <t>
5516      <eref target=""/>:
5517      "WS in quoted-pair"
5518    </t>
5519  </list>
5522  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5523  <list style="symbols">
5524    <t>
5525      Reference RFC 3984, and update header field registrations for headers defined
5526      in this document.
5527    </t>
5528  </list>
5531  Ongoing work on ABNF conversion (<eref target=""/>):
5532  <list style="symbols">
5533    <t>
5534      Replace string literals when the string really is case-sensitive (HTTP-Version).
5535    </t>
5536  </list>
5540<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5542  Closed issues:
5543  <list style="symbols">
5544    <t>
5545      <eref target=""/>:
5546      "Connection closing"
5547    </t>
5548    <t>
5549      <eref target=""/>:
5550      "Move registrations and registry information to IANA Considerations"
5551    </t>
5552    <t>
5553      <eref target=""/>:
5554      "need new URL for PAD1995 reference"
5555    </t>
5556    <t>
5557      <eref target=""/>:
5558      "IANA Considerations: update HTTP URI scheme registration"
5559    </t>
5560    <t>
5561      <eref target=""/>:
5562      "Cite HTTPS URI scheme definition"
5563    </t>
5564    <t>
5565      <eref target=""/>:
5566      "List-type headers vs Set-Cookie"
5567    </t>
5568  </list>
5571  Ongoing work on ABNF conversion (<eref target=""/>):
5572  <list style="symbols">
5573    <t>
5574      Replace string literals when the string really is case-sensitive (HTTP-Date).
5575    </t>
5576    <t>
5577      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5578    </t>
5579  </list>
5583<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5585  Closed issues:
5586  <list style="symbols">
5587    <t>
5588      <eref target=""/>:
5589      "Out-of-date reference for URIs"
5590    </t>
5591    <t>
5592      <eref target=""/>:
5593      "RFC 2822 is updated by RFC 5322"
5594    </t>
5595  </list>
5598  Ongoing work on ABNF conversion (<eref target=""/>):
5599  <list style="symbols">
5600    <t>
5601      Use "/" instead of "|" for alternatives.
5602    </t>
5603    <t>
5604      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5605    </t>
5606    <t>
5607      Only reference RFC 5234's core rules.
5608    </t>
5609    <t>
5610      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5611      whitespace ("OWS") and required whitespace ("RWS").
5612    </t>
5613    <t>
5614      Rewrite ABNFs to spell out whitespace rules, factor out
5615      header field value format definitions.
5616    </t>
5617  </list>
5621<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5623  Closed issues:
5624  <list style="symbols">
5625    <t>
5626      <eref target=""/>:
5627      "Header LWS"
5628    </t>
5629    <t>
5630      <eref target=""/>:
5631      "Sort 1.3 Terminology"
5632    </t>
5633    <t>
5634      <eref target=""/>:
5635      "RFC2047 encoded words"
5636    </t>
5637    <t>
5638      <eref target=""/>:
5639      "Character Encodings in TEXT"
5640    </t>
5641    <t>
5642      <eref target=""/>:
5643      "Line Folding"
5644    </t>
5645    <t>
5646      <eref target=""/>:
5647      "OPTIONS * and proxies"
5648    </t>
5649    <t>
5650      <eref target=""/>:
5651      "Reason-Phrase BNF"
5652    </t>
5653    <t>
5654      <eref target=""/>:
5655      "Use of TEXT"
5656    </t>
5657    <t>
5658      <eref target=""/>:
5659      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5660    </t>
5661    <t>
5662      <eref target=""/>:
5663      "RFC822 reference left in discussion of date formats"
5664    </t>
5665  </list>
5668  Final work on ABNF conversion (<eref target=""/>):
5669  <list style="symbols">
5670    <t>
5671      Rewrite definition of list rules, deprecate empty list elements.
5672    </t>
5673    <t>
5674      Add appendix containing collected and expanded ABNF.
5675    </t>
5676  </list>
5679  Other changes:
5680  <list style="symbols">
5681    <t>
5682      Rewrite introduction; add mostly new Architecture Section.
5683    </t>
5684    <t>
5685      Move definition of quality values from Part 3 into Part 1;
5686      make TE request header field grammar independent of accept-params (defined in Part 3).
5687    </t>
5688  </list>
5692<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5694  Closed issues:
5695  <list style="symbols">
5696    <t>
5697      <eref target=""/>:
5698      "base for numeric protocol elements"
5699    </t>
5700    <t>
5701      <eref target=""/>:
5702      "comment ABNF"
5703    </t>
5704  </list>
5707  Partly resolved issues:
5708  <list style="symbols">
5709    <t>
5710      <eref target=""/>:
5711      "205 Bodies" (took out language that implied that there might be
5712      methods for which a request body MUST NOT be included)
5713    </t>
5714    <t>
5715      <eref target=""/>:
5716      "editorial improvements around HTTP-date"
5717    </t>
5718  </list>
5722<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5724  Closed issues:
5725  <list style="symbols">
5726    <t>
5727      <eref target=""/>:
5728      "Repeating single-value headers"
5729    </t>
5730    <t>
5731      <eref target=""/>:
5732      "increase connection limit"
5733    </t>
5734    <t>
5735      <eref target=""/>:
5736      "IP addresses in URLs"
5737    </t>
5738    <t>
5739      <eref target=""/>:
5740      "take over HTTP Upgrade Token Registry"
5741    </t>
5742    <t>
5743      <eref target=""/>:
5744      "CR and LF in chunk extension values"
5745    </t>
5746    <t>
5747      <eref target=""/>:
5748      "HTTP/0.9 support"
5749    </t>
5750    <t>
5751      <eref target=""/>:
5752      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5753    </t>
5754    <t>
5755      <eref target=""/>:
5756      "move definitions of gzip/deflate/compress to part 1"
5757    </t>
5758    <t>
5759      <eref target=""/>:
5760      "disallow control characters in quoted-pair"
5761    </t>
5762  </list>
5765  Partly resolved issues:
5766  <list style="symbols">
5767    <t>
5768      <eref target=""/>:
5769      "update IANA requirements wrt Transfer-Coding values" (add the
5770      IANA Considerations subsection)
5771    </t>
5772  </list>
5776<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5778  Closed issues:
5779  <list style="symbols">
5780    <t>
5781      <eref target=""/>:
5782      "header parsing, treatment of leading and trailing OWS"
5783    </t>
5784  </list>
5787  Partly resolved issues:
5788  <list style="symbols">
5789    <t>
5790      <eref target=""/>:
5791      "Placement of 13.5.1 and 13.5.2"
5792    </t>
5793    <t>
5794      <eref target=""/>:
5795      "use of term "word" when talking about header structure"
5796    </t>
5797  </list>
5801<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5803  Closed issues:
5804  <list style="symbols">
5805    <t>
5806      <eref target=""/>:
5807      "Clarification of the term 'deflate'"
5808    </t>
5809    <t>
5810      <eref target=""/>:
5811      "OPTIONS * and proxies"
5812    </t>
5813    <t>
5814      <eref target=""/>:
5815      "MIME-Version not listed in P1, general header fields"
5816    </t>
5817    <t>
5818      <eref target=""/>:
5819      "IANA registry for content/transfer encodings"
5820    </t>
5821    <t>
5822      <eref target=""/>:
5823      "Case-sensitivity of HTTP-date"
5824    </t>
5825    <t>
5826      <eref target=""/>:
5827      "use of term "word" when talking about header structure"
5828    </t>
5829  </list>
5832  Partly resolved issues:
5833  <list style="symbols">
5834    <t>
5835      <eref target=""/>:
5836      "Term for the requested resource's URI"
5837    </t>
5838  </list>
5842<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5844  Closed issues:
5845  <list style="symbols">
5846    <t>
5847      <eref target=""/>:
5848      "Connection Closing"
5849    </t>
5850    <t>
5851      <eref target=""/>:
5852      "Delimiting messages with multipart/byteranges"
5853    </t>
5854    <t>
5855      <eref target=""/>:
5856      "Handling multiple Content-Length headers"
5857    </t>
5858    <t>
5859      <eref target=""/>:
5860      "Clarify entity / representation / variant terminology"
5861    </t>
5862    <t>
5863      <eref target=""/>:
5864      "consider removing the 'changes from 2068' sections"
5865    </t>
5866  </list>
5869  Partly resolved issues:
5870  <list style="symbols">
5871    <t>
5872      <eref target=""/>:
5873      "HTTP(s) URI scheme definitions"
5874    </t>
5875  </list>
5879<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5881  Closed issues:
5882  <list style="symbols">
5883    <t>
5884      <eref target=""/>:
5885      "Trailer requirements"
5886    </t>
5887    <t>
5888      <eref target=""/>:
5889      "Text about clock requirement for caches belongs in p6"
5890    </t>
5891    <t>
5892      <eref target=""/>:
5893      "effective request URI: handling of missing host in HTTP/1.0"
5894    </t>
5895    <t>
5896      <eref target=""/>:
5897      "confusing Date requirements for clients"
5898    </t>
5899  </list>
5902  Partly resolved issues:
5903  <list style="symbols">
5904    <t>
5905      <eref target=""/>:
5906      "Handling multiple Content-Length headers"
5907    </t>
5908  </list>
5912<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5914  Closed issues:
5915  <list style="symbols">
5916    <t>
5917      <eref target=""/>:
5918      "RFC2145 Normative"
5919    </t>
5920    <t>
5921      <eref target=""/>:
5922      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5923    </t>
5924    <t>
5925      <eref target=""/>:
5926      "define 'transparent' proxy"
5927    </t>
5928    <t>
5929      <eref target=""/>:
5930      "Header Classification"
5931    </t>
5932    <t>
5933      <eref target=""/>:
5934      "Is * usable as a request-uri for new methods?"
5935    </t>
5936    <t>
5937      <eref target=""/>:
5938      "Migrate Upgrade details from RFC2817"
5939    </t>
5940    <t>
5941      <eref target=""/>:
5942      "untangle ABNFs for header fields"
5943    </t>
5944    <t>
5945      <eref target=""/>:
5946      "update RFC 2109 reference"
5947    </t>
5948  </list>
5952<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5954  Closed issues:
5955  <list style="symbols">
5956    <t>
5957      <eref target=""/>:
5958      "Allow is not in 13.5.2"
5959    </t>
5960    <t>
5961      <eref target=""/>:
5962      "untangle ABNFs for header fields"
5963    </t>
5964    <t>
5965      <eref target=""/>:
5966      "Content-Length ABNF broken"
5967    </t>
5968  </list>
5972<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5974  Closed issues:
5975  <list style="symbols">
5976    <t>
5977      <eref target=""/>:
5978      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5979    </t>
5980    <t>
5981      <eref target=""/>:
5982      "Recommend minimum sizes for protocol elements"
5983    </t>
5984    <t>
5985      <eref target=""/>:
5986      "Set expectations around buffering"
5987    </t>
5988    <t>
5989      <eref target=""/>:
5990      "Considering messages in isolation"
5991    </t>
5992  </list>
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