source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1390

Last change on this file since 1390 was 1390, checked in by fielding@…, 11 years ago

Be intolerant. Move cache date requirements hiding in appendix to p6.

  • Property svn:eol-style set to native
File size: 250.2 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 "August">
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='#response.cacheability' 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 protocol for
201   distributed, collaborative, hypertext information systems. HTTP has been in
202   use by the World Wide Web global information initiative since 1990. This
203   document is Part 1 of the seven-part specification that defines the protocol
204   referred to as "HTTP/1.1" and, taken together, obsoletes
205   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
206   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
207   2068</xref>.
210   Part 1 provides an overview of HTTP and its associated terminology, defines
211   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
212   the generic message syntax and parsing requirements for HTTP message frames,
213   and describes general security concerns for implementations.
216   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
217   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
218   (on using CONNECT for TLS upgrades) and moves them to historic status.
222<note title="Editorial Note (To be removed by RFC Editor)">
223  <t>
224    Discussion of this draft should take place on the HTTPBIS working group
225    mailing list (, which is archived at
226    <eref target=""/>.
227  </t>
228  <t>
229    The current issues list is at
230    <eref target=""/> and related
231    documents (including fancy diffs) can be found at
232    <eref target=""/>.
233  </t>
234  <t>
235    The changes in this draft are summarized in <xref target="changes.since.15"/>.
236  </t>
240<section title="Introduction" anchor="introduction">
242   The Hypertext Transfer Protocol (HTTP) is an application-level
243   request/response protocol that uses extensible semantics and MIME-like
244   message payloads for flexible interaction with network-based hypertext
245   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
246   standard <xref target="RFC3986"/> to indicate the target resource and
247   relationships between resources.
248   Messages are passed in a format similar to that used by Internet mail
249   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
250   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
251   between HTTP and MIME messages).
254   HTTP is a generic interface protocol for information systems. It is
255   designed to hide the details of how a service is implemented by presenting
256   a uniform interface to clients that is independent of the types of
257   resources provided. Likewise, servers do not need to be aware of each
258   client's purpose: an HTTP request can be considered in isolation rather
259   than being associated with a specific type of client or a predetermined
260   sequence of application steps. The result is a protocol that can be used
261   effectively in many different contexts and for which implementations can
262   evolve independently over time.
265   HTTP is also designed for use as an intermediation protocol for translating
266   communication to and from non-HTTP information systems.
267   HTTP proxies and gateways can provide access to alternative information
268   services by translating their diverse protocols into a hypertext
269   format that can be viewed and manipulated by clients in the same way
270   as HTTP services.
273   One consequence of HTTP flexibility is that the protocol cannot be
274   defined in terms of what occurs behind the interface. Instead, we
275   are limited to defining the syntax of communication, the intent
276   of received communication, and the expected behavior of recipients.
277   If the communication is considered in isolation, then successful
278   actions ought to be reflected in corresponding changes to the
279   observable interface provided by servers. However, since multiple
280   clients might act in parallel and perhaps at cross-purposes, we
281   cannot require that such changes be observable beyond the scope
282   of a single response.
285   This document is Part 1 of the seven-part specification of HTTP,
286   defining the protocol referred to as "HTTP/1.1", obsoleting
287   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
288   Part 1 describes the architectural elements that are used or
289   referred to in HTTP, defines the "http" and "https" URI schemes,
290   describes overall network operation and connection management,
291   and defines HTTP message framing and forwarding requirements.
292   Our goal is to define all of the mechanisms necessary for HTTP message
293   handling that are independent of message semantics, thereby defining the
294   complete set of requirements for message parsers and
295   message-forwarding intermediaries.
298<section title="Requirements" anchor="intro.requirements">
300   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
301   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
302   document are to be interpreted as described in <xref target="RFC2119"/>.
305   An implementation is not compliant if it fails to satisfy one or more
306   of the "MUST" or "REQUIRED" level requirements for the protocols it
307   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
308   level and all the "SHOULD" level requirements for its protocols is said
309   to be "unconditionally compliant"; one that satisfies all the "MUST"
310   level requirements but not all the "SHOULD" level requirements for its
311   protocols is said to be "conditionally compliant".
315<section title="Syntax Notation" anchor="notation">
316<iref primary="true" item="Grammar" subitem="ALPHA"/>
317<iref primary="true" item="Grammar" subitem="CR"/>
318<iref primary="true" item="Grammar" subitem="CRLF"/>
319<iref primary="true" item="Grammar" subitem="CTL"/>
320<iref primary="true" item="Grammar" subitem="DIGIT"/>
321<iref primary="true" item="Grammar" subitem="DQUOTE"/>
322<iref primary="true" item="Grammar" subitem="HEXDIG"/>
323<iref primary="true" item="Grammar" subitem="LF"/>
324<iref primary="true" item="Grammar" subitem="OCTET"/>
325<iref primary="true" item="Grammar" subitem="SP"/>
326<iref primary="true" item="Grammar" subitem="VCHAR"/>
327<iref primary="true" item="Grammar" subitem="WSP"/>
329   This specification uses the Augmented Backus-Naur Form (ABNF) notation
330   of <xref target="RFC5234"/>.
332<t anchor="core.rules">
333  <x:anchor-alias value="ALPHA"/>
334  <x:anchor-alias value="CTL"/>
335  <x:anchor-alias value="CR"/>
336  <x:anchor-alias value="CRLF"/>
337  <x:anchor-alias value="DIGIT"/>
338  <x:anchor-alias value="DQUOTE"/>
339  <x:anchor-alias value="HEXDIG"/>
340  <x:anchor-alias value="LF"/>
341  <x:anchor-alias value="OCTET"/>
342  <x:anchor-alias value="SP"/>
343  <x:anchor-alias value="VCHAR"/>
344  <x:anchor-alias value="WSP"/>
345   The following core rules are included by
346   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
347   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
348   DIGIT (decimal 0-9), DQUOTE (double quote),
349   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
350   OCTET (any 8-bit sequence of data), SP (space),
351   VCHAR (any visible <xref target="USASCII"/> character),
352   and WSP (whitespace).
355   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
356   "obsolete" grammar rules that appear for historical reasons.
359<section title="ABNF Extension: #rule" anchor="notation.abnf">
361  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
362  improve readability.
365  A construct "#" is defined, similar to "*", for defining comma-delimited
366  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
367  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
368  comma (",") and optional whitespace (OWS,
369  <xref target="basic.rules"/>).   
372  Thus,
373</preamble><artwork type="example">
374  1#element =&gt; element *( OWS "," OWS element )
377  and:
378</preamble><artwork type="example">
379  #element =&gt; [ 1#element ]
382  and for n &gt;= 1 and m &gt; 1:
383</preamble><artwork type="example">
384  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
387  For compatibility with legacy list rules, recipients &SHOULD; accept empty
388  list elements. In other words, consumers would follow the list productions:
390<figure><artwork type="example">
391  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
393  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
396  Note that empty elements do not contribute to the count of elements present,
397  though.
400  For example, given these ABNF productions:
402<figure><artwork type="example">
403  example-list      = 1#example-list-elmt
404  example-list-elmt = token ; see <xref target="basic.rules"/>
407  Then these are valid values for example-list (not including the double
408  quotes, which are present for delimitation only):
410<figure><artwork type="example">
411  "foo,bar"
412  " foo ,bar,"
413  "  foo , ,bar,charlie   "
414  "foo ,bar,   charlie "
417  But these values would be invalid, as at least one non-empty element is
418  required:
420<figure><artwork type="example">
421  ""
422  ","
423  ",   ,"
426  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
427  expanded as explained above.
431<section title="Basic Rules" anchor="basic.rules">
432<t anchor="rule.LWS">
433   This specification uses three rules to denote the use of linear
434   whitespace: OWS (optional whitespace), RWS (required whitespace), and
435   BWS ("bad" whitespace).
437<t anchor="rule.OWS">
438   The OWS rule is used where zero or more linear whitespace octets might
439   appear. OWS &SHOULD; either not be produced or be produced as a single
440   SP. Multiple OWS octets that occur within field-content &SHOULD;
441   be replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
444<t anchor="rule.RWS">
445   RWS is used when at least one linear whitespace octet is required to
446   separate field tokens. RWS &SHOULD; be produced as a single SP.
447   Multiple RWS octets that occur within field-content &SHOULD; be
448   replaced with a single SP before interpreting the field value or
449   forwarding the message downstream.
451<t anchor="rule.BWS">
452   BWS is used where the grammar allows optional whitespace for historical
453   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
454   recipients &MUST; accept such bad optional whitespace and remove it before
455   interpreting the field value or forwarding the message downstream.
457<t anchor="rule.whitespace">
458  <x:anchor-alias value="BWS"/>
459  <x:anchor-alias value="OWS"/>
460  <x:anchor-alias value="RWS"/>
461  <x:anchor-alias value="obs-fold"/>
463<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"/>
464  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
465                 ; "optional" whitespace
466  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
467                 ; "required" whitespace
468  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
469                 ; "bad" whitespace
470  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
471                 ; see <xref target="header.fields"/>
473<t anchor="rule.token.separators">
474  <x:anchor-alias value="tchar"/>
475  <x:anchor-alias value="token"/>
476  <x:anchor-alias value="special"/>
477  <x:anchor-alias value="word"/>
478   Many HTTP/1.1 header field values consist of words (token or quoted-string)
479   separated by whitespace or special characters. These special characters
480   &MUST; be in a quoted string to be used within a parameter value (as defined
481   in <xref target="transfer.codings"/>).
483<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"/>
484  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
486  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
488  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
489 -->
490  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
491                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
492                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
493                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
495  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
496                 / ";" / ":" / "\" / DQUOTE / "/" / "["
497                 / "]" / "?" / "=" / "{" / "}"
499<t anchor="rule.quoted-string">
500  <x:anchor-alias value="quoted-string"/>
501  <x:anchor-alias value="qdtext"/>
502  <x:anchor-alias value="obs-text"/>
503   A string of text is parsed as a single word if it is quoted using
504   double-quote marks.
506<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"/>
507  <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>
508  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
509                 ; <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>
510  <x:ref>obs-text</x:ref>       = %x80-FF
512<t anchor="rule.quoted-pair">
513  <x:anchor-alias value="quoted-pair"/>
514   The backslash octet ("\") can be used as a single-octet
515   quoting mechanism within quoted-string constructs:
517<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
518  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
521   Recipients that process the value of the quoted-string &MUST; handle a
522   quoted-pair as if it were replaced by the octet following the backslash.
525   Senders &SHOULD-NOT; escape octets that do not require escaping
526   (i.e., other than DQUOTE and the backslash octet).
533<section title="HTTP-related architecture" anchor="architecture">
535   HTTP was created for the World Wide Web architecture
536   and has evolved over time to support the scalability needs of a worldwide
537   hypertext system. Much of that architecture is reflected in the terminology
538   and syntax productions used to define HTTP.
541<section title="Client/Server Messaging" anchor="operation">
542<iref primary="true" item="client"/>
543<iref primary="true" item="server"/>
544<iref primary="true" item="connection"/>
546   HTTP is a stateless request/response protocol that operates by exchanging
547   messages across a reliable transport or session-layer
548   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
549   program that establishes a connection to a server for the purpose of
550   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
551   program that accepts connections in order to service HTTP requests by
552   sending HTTP responses.
554<iref primary="true" item="user agent"/>
555<iref primary="true" item="origin server"/>
556<iref primary="true" item="browser"/>
557<iref primary="true" item="spider"/>
558<iref primary="true" item="sender"/>
559<iref primary="true" item="recipient"/>
561   Note that the terms client and server refer only to the roles that
562   these programs perform for a particular connection.  The same program
563   might act as a client on some connections and a server on others.  We use
564   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
565   such as a WWW browser, editor, or spider (web-traversing robot), and
566   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
567   authoritative responses to a request.  For general requirements, we use
568   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
569   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
570   message.
573   Most HTTP communication consists of a retrieval request (GET) for
574   a representation of some resource identified by a URI.  In the
575   simplest case, this might be accomplished via a single bidirectional
576   connection (===) between the user agent (UA) and the origin server (O).
578<figure><artwork type="drawing">
579         request   &gt;
580    UA ======================================= O
581                                &lt;   response
583<iref primary="true" item="message"/>
584<iref primary="true" item="request"/>
585<iref primary="true" item="response"/>
587   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
588   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
589   protocol version, followed by MIME-like header fields containing
590   request modifiers, client information, and payload metadata, an empty
591   line to indicate the end of the header section, and finally the payload
592   body (if any).
595   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
596   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
597   includes the protocol version, a success or error code, and textual
598   reason phrase, followed by MIME-like header fields containing server
599   information, resource metadata, and payload metadata, an empty line to
600   indicate the end of the header section, and finally the payload body (if any).
603   The following example illustrates a typical message exchange for a
604   GET request on the URI "":
607client request:
608</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
609GET /hello.txt HTTP/1.1
610User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
612Accept: */*
616server response:
617</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
618HTTP/1.1 200 OK
619Date: Mon, 27 Jul 2009 12:28:53 GMT
620Server: Apache
621Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
622ETag: "34aa387-d-1568eb00"
623Accept-Ranges: bytes
624Content-Length: <x:length-of target="exbody"/>
625Vary: Accept-Encoding
626Content-Type: text/plain
628<x:span anchor="exbody">Hello World!
632<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
634   Fundamentally, HTTP is a message-based protocol. Although message bodies can
635   be chunked (<xref target="chunked.encoding"/>) and implementations often
636   make parts of a message available progressively, this is not required, and
637   some widely-used implementations only make a message available when it is
638   complete. Furthermore, while most proxies will progressively stream messages,
639   some amount of buffering will take place, and some proxies might buffer
640   messages to perform transformations, check content or provide other services.
643   Therefore, extensions to and uses of HTTP cannot rely on the availability of
644   a partial message, or assume that messages will not be buffered. There are
645   strategies that can be used to test for buffering in a given connection, but
646   it should be understood that behaviors can differ across connections, and
647   between requests and responses.
650   Recipients &MUST; consider every message in a connection in isolation;
651   because HTTP is a stateless protocol, it cannot be assumed that two requests
652   on the same connection are from the same client or share any other common
653   attributes. In particular, intermediaries might mix requests from different
654   clients into a single server connection. Note that some existing HTTP
655   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
656   potentially causing interoperability and security problems.
660<section title="Connections and Transport Independence" anchor="transport-independence">
662   HTTP messaging is independent of the underlying transport or
663   session-layer connection protocol(s).  HTTP only presumes a reliable
664   transport with in-order delivery of requests and the corresponding
665   in-order delivery of responses.  The mapping of HTTP request and
666   response structures onto the data units of the underlying transport
667   protocol is outside the scope of this specification.
670   The specific connection protocols to be used for an interaction
671   are determined by client configuration and the target resource's URI.
672   For example, the "http" URI scheme
673   (<xref target="http.uri"/>) indicates a default connection of TCP
674   over IP, with a default TCP port of 80, but the client might be
675   configured to use a proxy via some other connection port or protocol
676   instead of using the defaults.
679   A connection might be used for multiple HTTP request/response exchanges,
680   as defined in <xref target="persistent.connections"/>.
684<section title="Intermediaries" anchor="intermediaries">
685<iref primary="true" item="intermediary"/>
687   HTTP enables the use of intermediaries to satisfy requests through
688   a chain of connections.  There are three common forms of HTTP
689   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
690   a single intermediary might act as an origin server, proxy, gateway,
691   or tunnel, switching behavior based on the nature of each request.
693<figure><artwork type="drawing">
694         &gt;             &gt;             &gt;             &gt;
695    <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>
696               &lt;             &lt;             &lt;             &lt;
699   The figure above shows three intermediaries (A, B, and C) between the
700   user agent and origin server. A request or response message that
701   travels the whole chain will pass through four separate connections.
702   Some HTTP communication options
703   might apply only to the connection with the nearest, non-tunnel
704   neighbor, only to the end-points of the chain, or to all connections
705   along the chain. Although the diagram is linear, each participant might
706   be engaged in multiple, simultaneous communications. For example, B
707   might be receiving requests from many clients other than A, and/or
708   forwarding requests to servers other than C, at the same time that it
709   is handling A's request.
712<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
713<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
714   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
715   to describe various requirements in relation to the directional flow of a
716   message: all messages flow from upstream to downstream.
717   Likewise, we use the terms inbound and outbound to refer to
718   directions in relation to the request path:
719   "<x:dfn>inbound</x:dfn>" means toward the origin server and
720   "<x:dfn>outbound</x:dfn>" means toward the user agent.
722<t><iref primary="true" item="proxy"/>
723   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
724   client, usually via local configuration rules, to receive requests
725   for some type(s) of absolute URI and attempt to satisfy those
726   requests via translation through the HTTP interface.  Some translations
727   are minimal, such as for proxy requests for "http" URIs, whereas
728   other requests might require translation to and from entirely different
729   application-layer protocols. Proxies are often used to group an
730   organization's HTTP requests through a common intermediary for the
731   sake of security, annotation services, or shared caching.
734<iref primary="true" item="transforming proxy"/>
735<iref primary="true" item="non-transforming proxy"/>
736   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
737   or configured to modify request or response messages in a semantically
738   meaningful way (i.e., modifications, beyond those required by normal
739   HTTP processing, that change the message in a way that would be
740   significant to the original sender or potentially significant to
741   downstream recipients).  For example, a transforming proxy might be
742   acting as a shared annotation server (modifying responses to include
743   references to a local annotation database), a malware filter, a
744   format transcoder, or an intranet-to-Internet privacy filter.  Such
745   transformations are presumed to be desired by the client (or client
746   organization) that selected the proxy and are beyond the scope of
747   this specification.  However, when a proxy is not intended to transform
748   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
749   requirements that preserve HTTP message semantics. See &status-203; and
750   &header-warning; for status and warning codes related to transformations.
752<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
753<iref primary="true" item="accelerator"/>
754   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
755   is a receiving agent that acts
756   as a layer above some other server(s) and translates the received
757   requests to the underlying server's protocol.  Gateways are often
758   used to encapsulate legacy or untrusted information services, to
759   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
760   enable partitioning or load-balancing of HTTP services across
761   multiple machines.
764   A gateway behaves as an origin server on its outbound connection and
765   as a user agent on its inbound connection.
766   All HTTP requirements applicable to an origin server
767   also apply to the outbound communication of a gateway.
768   A gateway communicates with inbound servers using any protocol that
769   it desires, including private extensions to HTTP that are outside
770   the scope of this specification.  However, an HTTP-to-HTTP gateway
771   that wishes to interoperate with third-party HTTP servers &MUST;
772   comply with HTTP user agent requirements on the gateway's inbound
773   connection and &MUST; implement the Connection
774   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
775   header fields for both connections.
777<t><iref primary="true" item="tunnel"/>
778   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
779   without changing the messages. Once active, a tunnel is not
780   considered a party to the HTTP communication, though the tunnel might
781   have been initiated by an HTTP request. A tunnel ceases to exist when
782   both ends of the relayed connection are closed. Tunnels are used to
783   extend a virtual connection through an intermediary, such as when
784   transport-layer security is used to establish private communication
785   through a shared firewall proxy.
787<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
788<iref primary="true" item="captive portal"/>
789   In addition, there may exist network intermediaries that are not
790   considered part of the HTTP communication but nevertheless act as
791   filters or redirecting agents (usually violating HTTP semantics,
792   causing security problems, and otherwise making a mess of things).
793   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
794   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
795   or "<x:dfn>captive portal</x:dfn>",
796   differs from an HTTP proxy because it has not been selected by the client.
797   Instead, the network intermediary redirects outgoing TCP port 80 packets
798   (and occasionally other common port traffic) to an internal HTTP server.
799   Interception proxies are commonly found on public network access points,
800   as a means of enforcing account subscription prior to allowing use of
801   non-local Internet services, and within corporate firewalls to enforce
802   network usage policies.
803   They are indistinguishable from a man-in-the-middle attack.
807<section title="Caches" anchor="caches">
808<iref primary="true" item="cache"/>
810   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
811   subsystem that controls its message storage, retrieval, and deletion.
812   A cache stores cacheable responses in order to reduce the response
813   time and network bandwidth consumption on future, equivalent
814   requests. Any client or server &MAY; employ a cache, though a cache
815   cannot be used by a server while it is acting as a tunnel.
818   The effect of a cache is that the request/response chain is shortened
819   if one of the participants along the chain has a cached response
820   applicable to that request. The following illustrates the resulting
821   chain if B has a cached copy of an earlier response from O (via C)
822   for a request which has not been cached by UA or A.
824<figure><artwork type="drawing">
825            &gt;             &gt;
826       UA =========== A =========== B - - - - - - C - - - - - - O
827                  &lt;             &lt;
829<t><iref primary="true" item="cacheable"/>
830   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
831   the response message for use in answering subsequent requests.
832   Even when a response is cacheable, there might be additional
833   constraints placed by the client or by the origin server on when
834   that cached response can be used for a particular request. HTTP
835   requirements for cache behavior and cacheable responses are
836   defined in &caching-overview;. 
839   There are a wide variety of architectures and configurations
840   of caches and proxies deployed across the World Wide Web and
841   inside large organizations. These systems include national hierarchies
842   of proxy caches to save transoceanic bandwidth, systems that
843   broadcast or multicast cache entries, organizations that distribute
844   subsets of cached data via optical media, and so on.
848<section title="Protocol Versioning" anchor="http.version">
849  <x:anchor-alias value="HTTP-Version"/>
850  <x:anchor-alias value="HTTP-Prot-Name"/>
852   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
853   versions of the protocol. This specification defines version "1.1".
854   The protocol version as a whole indicates the sender's compliance
855   with the set of requirements laid out in that version's corresponding
856   specification of HTTP.
859   The version of an HTTP message is indicated by an HTTP-Version field
860   in the first line of the message. HTTP-Version is case-sensitive.
862<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
863  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
864  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
867   The HTTP version number consists of two decimal digits separated by a "."
868   (period or decimal point).  The first digit ("major version") indicates the
869   HTTP messaging syntax, whereas the second digit ("minor version") indicates
870   the highest minor version to which the sender is at least conditionally
871   compliant and able to understand for future communication.  The minor
872   version advertises the sender's communication capabilities even when the
873   sender is only using a backwards-compatible subset of the protocol,
874   thereby letting the recipient know that more advanced features can
875   be used in response (by servers) or in future requests (by clients).
878   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
879   <xref target="RFC1945"/> or a recipient whose version is unknown,
880   the HTTP/1.1 message is constructed such that it can be interpreted
881   as a valid HTTP/1.0 message if all of the newer features are ignored.
882   This specification places recipient-version requirements on some
883   new features so that a compliant sender will only use compatible
884   features until it has determined, through configuration or the
885   receipt of a message, that the recipient supports HTTP/1.1.
888   The interpretation of an HTTP header field does not change
889   between minor versions of the same major version, though the default
890   behavior of a recipient in the absence of such a field can change.
891   Unless specified otherwise, header fields defined in HTTP/1.1 are
892   defined for all versions of HTTP/1.x.  In particular, the Host and
893   Connection header fields ought to be implemented by all HTTP/1.x
894   implementations whether or not they advertise compliance with HTTP/1.1.
897   New header fields can be defined such that, when they are
898   understood by a recipient, they might override or enhance the
899   interpretation of previously defined header fields.  When an
900   implementation receives an unrecognized header field, the recipient
901   &MUST; ignore that header field for local processing regardless of
902   the message's HTTP version.  An unrecognized header field received
903   by a proxy &MUST; be forwarded downstream unless the header field's
904   field-name is listed in the message's Connection header-field
905   (see <xref target="header.connection"/>).
906   These requirements allow HTTP's functionality to be enhanced without
907   requiring prior update of all compliant intermediaries.
910   Intermediaries that process HTTP messages (i.e., all intermediaries
911   other than those acting as a tunnel) &MUST; send their own HTTP-Version
912   in forwarded messages.  In other words, they &MUST-NOT; blindly
913   forward the first line of an HTTP message without ensuring that the
914   protocol version matches what the intermediary understands, and
915   is at least conditionally compliant to, for both the receiving and
916   sending of messages.  Forwarding an HTTP message without rewriting
917   the HTTP-Version might result in communication errors when downstream
918   recipients use the message sender's version to determine what features
919   are safe to use for later communication with that sender.
922   An HTTP client &SHOULD; send a request version equal to the highest
923   version for which the client is at least conditionally compliant and
924   whose major version is no higher than the highest version supported
925   by the server, if this is known.  An HTTP client &MUST-NOT; send a
926   version for which it is not at least conditionally compliant.
929   An HTTP client &MAY; send a lower request version if it is known that
930   the server incorrectly implements the HTTP specification, but only
931   after the client has attempted at least one normal request and determined
932   from the response status or header fields (e.g., Server) that the
933   server improperly handles higher request versions.
936   An HTTP server &SHOULD; send a response version equal to the highest
937   version for which the server is at least conditionally compliant and
938   whose major version is less than or equal to the one received in the
939   request.  An HTTP server &MUST-NOT; send a version for which it is not
940   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
941   Version Not Supported) response if it cannot send a response using the
942   major version used in the client's request.
945   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
946   if it is known or suspected that the client incorrectly implements the
947   HTTP specification and is incapable of correctly processing later
948   version responses, such as when a client fails to parse the version
949   number correctly or when an intermediary is known to blindly forward
950   the HTTP-Version even when it doesn't comply with the given minor
951   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
952   performed unless triggered by specific client attributes, such as when
953   one or more of the request header fields (e.g., User-Agent) uniquely
954   match the values sent by a client known to be in error.
957   The intention of HTTP's versioning design is that the major number
958   will only be incremented if an incompatible message syntax is
959   introduced, and that the minor number will only be incremented when
960   changes made to the protocol have the effect of adding to the message
961   semantics or implying additional capabilities of the sender.  However,
962   the minor version was not incremented for the changes introduced between
963   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
964   is specifically avoiding any such changes to the protocol.
968<section title="Uniform Resource Identifiers" anchor="uri">
969<iref primary="true" item="resource"/>
971   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
972   throughout HTTP as the means for identifying resources. URI references
973   are used to target requests, indicate redirects, and define relationships.
974   HTTP does not limit what a resource might be; it merely defines an interface
975   that can be used to interact with a resource via HTTP. More information on
976   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
978  <x:anchor-alias value="URI-reference"/>
979  <x:anchor-alias value="absolute-URI"/>
980  <x:anchor-alias value="relative-part"/>
981  <x:anchor-alias value="authority"/>
982  <x:anchor-alias value="path-abempty"/>
983  <x:anchor-alias value="path-absolute"/>
984  <x:anchor-alias value="port"/>
985  <x:anchor-alias value="query"/>
986  <x:anchor-alias value="uri-host"/>
987  <x:anchor-alias value="partial-URI"/>
989   This specification adopts the definitions of "URI-reference",
990   "absolute-URI", "relative-part", "port", "host",
991   "path-abempty", "path-absolute", "query", and "authority" from the
992   URI generic syntax <xref target="RFC3986"/>.
993   In addition, we define a partial-URI rule for protocol elements
994   that allow a relative URI but not a fragment.
996<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"/>
997  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
998  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
999  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
1000  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
1001  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
1002  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
1003  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
1004  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
1005  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
1007  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
1010   Each protocol element in HTTP that allows a URI reference will indicate
1011   in its ABNF production whether the element allows any form of reference
1012   (URI-reference), only a URI in absolute form (absolute-URI), only the
1013   path and optional query components, or some combination of the above.
1014   Unless otherwise indicated, URI references are parsed relative to the
1015   effective request URI, which defines the default base URI for references
1016   in both the request and its corresponding response.
1019<section title="http URI scheme" anchor="http.uri">
1020  <x:anchor-alias value="http-URI"/>
1021  <iref item="http URI scheme" primary="true"/>
1022  <iref item="URI scheme" subitem="http" primary="true"/>
1024   The "http" URI scheme is hereby defined for the purpose of minting
1025   identifiers according to their association with the hierarchical
1026   namespace governed by a potential HTTP origin server listening for
1027   TCP connections on a given port.
1029<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1030  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1033   The HTTP origin server is identified by the generic syntax's
1034   <x:ref>authority</x:ref> component, which includes a host identifier
1035   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1036   The remainder of the URI, consisting of both the hierarchical path
1037   component and optional query component, serves as an identifier for
1038   a potential resource within that origin server's name space.
1041   If the host identifier is provided as an IP literal or IPv4 address,
1042   then the origin server is any listener on the indicated TCP port at
1043   that IP address. If host is a registered name, then that name is
1044   considered an indirect identifier and the recipient might use a name
1045   resolution service, such as DNS, to find the address of a listener
1046   for that host.
1047   The host &MUST-NOT; be empty; if an "http" URI is received with an
1048   empty host, then it &MUST; be rejected as invalid.
1049   If the port subcomponent is empty or not given, then TCP port 80 is
1050   assumed (the default reserved port for WWW services).
1053   Regardless of the form of host identifier, access to that host is not
1054   implied by the mere presence of its name or address. The host might or might
1055   not exist and, even when it does exist, might or might not be running an
1056   HTTP server or listening to the indicated port. The "http" URI scheme
1057   makes use of the delegated nature of Internet names and addresses to
1058   establish a naming authority (whatever entity has the ability to place
1059   an HTTP server at that Internet name or address) and allows that
1060   authority to determine which names are valid and how they might be used.
1063   When an "http" URI is used within a context that calls for access to the
1064   indicated resource, a client &MAY; attempt access by resolving
1065   the host to an IP address, establishing a TCP connection to that address
1066   on the indicated port, and sending an HTTP request message to the server
1067   containing the URI's identifying data as described in <xref target="request"/>.
1068   If the server responds to that request with a non-interim HTTP response
1069   message, as described in <xref target="response"/>, then that response
1070   is considered an authoritative answer to the client's request.
1073   Although HTTP is independent of the transport protocol, the "http"
1074   scheme is specific to TCP-based services because the name delegation
1075   process depends on TCP for establishing authority.
1076   An HTTP service based on some other underlying connection protocol
1077   would presumably be identified using a different URI scheme, just as
1078   the "https" scheme (below) is used for servers that require an SSL/TLS
1079   transport layer on a connection. Other protocols might also be used to
1080   provide access to "http" identified resources &mdash; it is only the
1081   authoritative interface used for mapping the namespace that is
1082   specific to TCP.
1085   The URI generic syntax for authority also includes a deprecated
1086   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1087   for including user authentication information in the URI.  Some
1088   implementations make use of the userinfo component for internal
1089   configuration of authentication information, such as within command
1090   invocation options, configuration files, or bookmark lists, even
1091   though such usage might expose a user identifier or password.
1092   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1093   delimiter) when transmitting an "http" URI in a message.  Recipients
1094   of HTTP messages that contain a URI reference &SHOULD; parse for the
1095   existence of userinfo and treat its presence as an error, likely
1096   indicating that the deprecated subcomponent is being used to obscure
1097   the authority for the sake of phishing attacks.
1101<section title="https URI scheme" anchor="https.uri">
1102   <x:anchor-alias value="https-URI"/>
1103   <iref item="https URI scheme"/>
1104   <iref item="URI scheme" subitem="https"/>
1106   The "https" URI scheme is hereby defined for the purpose of minting
1107   identifiers according to their association with the hierarchical
1108   namespace governed by a potential HTTP origin server listening for
1109   SSL/TLS-secured connections on a given TCP port.
1112   All of the requirements listed above for the "http" scheme are also
1113   requirements for the "https" scheme, except that a default TCP port
1114   of 443 is assumed if the port subcomponent is empty or not given,
1115   and the TCP connection &MUST; be secured for privacy through the
1116   use of strong encryption prior to sending the first HTTP request.
1118<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1119  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1122   Unlike the "http" scheme, responses to "https" identified requests
1123   are never "public" and thus &MUST-NOT; be reused for shared caching.
1124   They can, however, be reused in a private cache if the message is
1125   cacheable by default in HTTP or specifically indicated as such by
1126   the Cache-Control header field (&header-cache-control;).
1129   Resources made available via the "https" scheme have no shared
1130   identity with the "http" scheme even if their resource identifiers
1131   indicate the same authority (the same host listening to the same
1132   TCP port).  They are distinct name spaces and are considered to be
1133   distinct origin servers.  However, an extension to HTTP that is
1134   defined to apply to entire host domains, such as the Cookie protocol
1135   <xref target="RFC6265"/>, can allow information
1136   set by one service to impact communication with other services
1137   within a matching group of host domains.
1140   The process for authoritative access to an "https" identified
1141   resource is defined in <xref target="RFC2818"/>.
1145<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1147   Since the "http" and "https" schemes conform to the URI generic syntax,
1148   such URIs are normalized and compared according to the algorithm defined
1149   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1150   described above for each scheme.
1153   If the port is equal to the default port for a scheme, the normal
1154   form is to elide the port subcomponent. Likewise, an empty path
1155   component is equivalent to an absolute path of "/", so the normal
1156   form is to provide a path of "/" instead. The scheme and host
1157   are case-insensitive and normally provided in lowercase; all
1158   other components are compared in a case-sensitive manner.
1159   Characters other than those in the "reserved" set are equivalent
1160   to their percent-encoded octets (see <xref target="RFC3986"
1161   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1164   For example, the following three URIs are equivalent:
1166<figure><artwork type="example">
1175<section title="Message Format" anchor="http.message">
1176<x:anchor-alias value="generic-message"/>
1177<x:anchor-alias value="message.types"/>
1178<x:anchor-alias value="HTTP-message"/>
1179<x:anchor-alias value="start-line"/>
1180<iref item="header section"/>
1181<iref item="headers"/>
1182<iref item="header field"/>
1184   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1185   octets in a format similar to the Internet Message Format
1186   <xref target="RFC5322"/>: zero or more header fields (collectively
1187   referred to as the "headers" or the "header section"), an empty line
1188   indicating the end of the header section, and an optional message-body.
1191   An HTTP message can either be a request from client to server or a
1192   response from server to client.  Syntactically, the two types of message
1193   differ only in the start-line, which is either a Request-Line (for requests)
1194   or a Status-Line (for responses), and in the algorithm for determining
1195   the length of the message-body (<xref target="message.body"/>).
1196   In theory, a client could receive requests and a server could receive
1197   responses, distinguishing them by their different start-line formats,
1198   but in practice servers are implemented to only expect a request
1199   (a response is interpreted as an unknown or invalid request method)
1200   and clients are implemented to only expect a response.
1202<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1203  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1204                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1205                    <x:ref>CRLF</x:ref>
1206                    [ <x:ref>message-body</x:ref> ]
1207  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1210   Implementations &MUST-NOT; send whitespace between the start-line and
1211   the first header field. The presence of such whitespace in a request
1212   might be an attempt to trick a server into ignoring that field or
1213   processing the line after it as a new request, either of which might
1214   result in a security vulnerability if other implementations within
1215   the request chain interpret the same message differently.
1216   Likewise, the presence of such whitespace in a response might be
1217   ignored by some clients or cause others to cease parsing.
1220<section title="Message Parsing Robustness" anchor="message.robustness">
1222   In the interest of robustness, servers &SHOULD; ignore at least one
1223   empty line received where a Request-Line is expected. In other words, if
1224   the server is reading the protocol stream at the beginning of a
1225   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1226   Likewise, although the line terminator for the start-line and header
1227   fields is the sequence CRLF, we recommend that recipients recognize a
1228   single LF as a line terminator and ignore any CR.
1231   Some old HTTP/1.0 client implementations send an extra CRLF
1232   after a POST request as a lame workaround for some early server
1233   applications that failed to read message-body content that was
1234   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1235   preface or follow a request with an extra CRLF.  If terminating
1236   the request message-body with a line-ending is desired, then the
1237   client &MUST; include the terminating CRLF octets as part of the
1238   message-body length.
1241   When a server listening only for HTTP request messages, or processing
1242   what appears from the start-line to be an HTTP request message,
1243   receives a sequence of octets that does not match the HTTP-message
1244   grammar aside from the robustness exceptions listed above, the
1245   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1248   The normal procedure for parsing an HTTP message is to read the
1249   start-line into a structure, read each header field into a hash
1250   table by field name until the empty line, and then use the parsed
1251   data to determine if a message-body is expected.  If a message-body
1252   has been indicated, then it is read as a stream until an amount
1253   of octets equal to the message-body length is read or the connection
1254   is closed.  Care must be taken to parse an HTTP message as a sequence
1255   of octets in an encoding that is a superset of US-ASCII.  Attempting
1256   to parse HTTP as a stream of Unicode characters in a character encoding
1257   like UTF-16 might introduce security flaws due to the differing ways
1258   that such parsers interpret invalid characters.
1261   HTTP allows the set of defined header fields to be extended without
1262   changing the protocol version (see <xref target="header.field.registration"/>).
1263   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1264   proxy is specifically configured to block or otherwise transform such
1265   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1269<section title="Header Fields" anchor="header.fields">
1270  <x:anchor-alias value="header-field"/>
1271  <x:anchor-alias value="field-content"/>
1272  <x:anchor-alias value="field-name"/>
1273  <x:anchor-alias value="field-value"/>
1274  <x:anchor-alias value="OWS"/>
1276   Each HTTP header field consists of a case-insensitive field name
1277   followed by a colon (":"), optional whitespace, and the field value.
1279<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"/>
1280  <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>
1281  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1282  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1283  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1286   No whitespace is allowed between the header field name and colon. For
1287   security reasons, any request message received containing such whitespace
1288   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1289   &MUST; remove any such whitespace from a response message before
1290   forwarding the message downstream.
1293   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1294   preferred. The field value does not include any leading or trailing white
1295   space: OWS occurring before the first non-whitespace octet of the
1296   field value or after the last non-whitespace octet of the field value
1297   is ignored and &SHOULD; be removed before further processing (as this does
1298   not change the meaning of the header field).
1301   The order in which header fields with differing field names are
1302   received is not significant. However, it is "good practice" to send
1303   header fields that contain control data first, such as Host on
1304   requests and Date on responses, so that implementations can decide
1305   when not to handle a message as early as possible.  A server &MUST;
1306   wait until the entire header section is received before interpreting
1307   a request message, since later header fields might include conditionals,
1308   authentication credentials, or deliberately misleading duplicate
1309   header fields that would impact request processing.
1312   Multiple header fields with the same field name &MUST-NOT; be
1313   sent in a message unless the entire field value for that
1314   header field is defined as a comma-separated list [i.e., #(values)].
1315   Multiple header fields with the same field name can be combined into
1316   one "field-name: field-value" pair, without changing the semantics of the
1317   message, by appending each subsequent field value to the combined
1318   field value in order, separated by a comma. The order in which
1319   header fields with the same field name are received is therefore
1320   significant to the interpretation of the combined field value;
1321   a proxy &MUST-NOT; change the order of these field values when
1322   forwarding a message.
1325  <t>
1326   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1327   practice can occur multiple times, but does not use the list syntax, and
1328   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1329   for details.) Also note that the Set-Cookie2 header field specified in
1330   <xref target="RFC2965"/> does not share this problem.
1331  </t>
1334   Historically, HTTP header field values could be extended over multiple
1335   lines by preceding each extra line with at least one space or horizontal
1336   tab octet (line folding). This specification deprecates such line
1337   folding except within the message/http media type
1338   (<xref target=""/>).
1339   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1340   (i.e., that contain any field-content that matches the obs-fold rule) unless
1341   the message is intended for packaging within the message/http media type.
1342   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1343   obs-fold whitespace with a single SP prior to interpreting the field value
1344   or forwarding the message downstream.
1347   Historically, HTTP has allowed field content with text in the ISO-8859-1
1348   <xref target="ISO-8859-1"/> character encoding and supported other
1349   character sets only through use of <xref target="RFC2047"/> encoding.
1350   In practice, most HTTP header field values use only a subset of the
1351   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1352   header fields &SHOULD; limit their field values to US-ASCII octets.
1353   Recipients &SHOULD; treat other (obs-text) octets in field content as
1354   opaque data.
1356<t anchor="rule.comment">
1357  <x:anchor-alias value="comment"/>
1358  <x:anchor-alias value="ctext"/>
1359   Comments can be included in some HTTP header fields by surrounding
1360   the comment text with parentheses. Comments are only allowed in
1361   fields containing "comment" as part of their field value definition.
1363<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1364  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1365  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1366                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1368<t anchor="rule.quoted-cpair">
1369  <x:anchor-alias value="quoted-cpair"/>
1370   The backslash octet ("\") can be used as a single-octet
1371   quoting mechanism within comment constructs:
1373<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1374  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1377   Senders &SHOULD-NOT; escape octets that do not require escaping
1378   (i.e., other than the backslash octet "\" and the parentheses "(" and
1379   ")").
1382   HTTP does not place a pre-defined limit on the length of header fields,
1383   either in isolation or as a set. A server &MUST; be prepared to receive
1384   request header fields of unbounded length and respond with a 4xx status
1385   code if the received header field(s) would be longer than the server wishes
1386   to handle.
1389   A client that receives response headers that are longer than it wishes to
1390   handle can only treat it as a server error.
1393   Various ad-hoc limitations on header length are found in practice. It is
1394   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1395   combined header fields have 4000 or more octets.
1399<section title="Message Body" anchor="message.body">
1400  <x:anchor-alias value="message-body"/>
1402   The message-body (if any) of an HTTP message is used to carry the
1403   payload body associated with the request or response.
1405<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1406  <x:ref>message-body</x:ref> = *OCTET
1409   The message-body differs from the payload body only when a transfer-coding
1410   has been applied, as indicated by the Transfer-Encoding header field
1411   (<xref target="header.transfer-encoding"/>).  If more than one
1412   Transfer-Encoding header field is present in a message, the multiple
1413   field-values &MUST; be combined into one field-value, according to the
1414   algorithm defined in <xref target="header.fields"/>, before determining
1415   the message-body length.
1418   When one or more transfer-codings are applied to a payload in order to
1419   form the message-body, the Transfer-Encoding header field &MUST; contain
1420   the list of transfer-codings applied. Transfer-Encoding is a property of
1421   the message, not of the payload, and thus &MAY; be added or removed by
1422   any implementation along the request/response chain under the constraints
1423   found in <xref target="transfer.codings"/>.
1426   If a message is received that has multiple Content-Length header fields
1427   (<xref target="header.content-length"/>) with field-values consisting
1428   of the same decimal value, or a single Content-Length header field with
1429   a field value containing a list of identical decimal values (e.g.,
1430   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1431   header fields have been generated or combined by an upstream message
1432   processor, then the recipient &MUST; either reject the message as invalid
1433   or replace the duplicated field-values with a single valid Content-Length
1434   field containing that decimal value prior to determining the message-body
1435   length.
1438   The rules for when a message-body is allowed in a message differ for
1439   requests and responses.
1442   The presence of a message-body in a request is signaled by the
1443   inclusion of a Content-Length or Transfer-Encoding header field in
1444   the request's header fields, even if the request method does not
1445   define any use for a message-body.  This allows the request
1446   message framing algorithm to be independent of method semantics.
1449   For response messages, whether or not a message-body is included with
1450   a message is dependent on both the request method and the response
1451   status code (<xref target="status.code.and.reason.phrase"/>).
1452   Responses to the HEAD request method never include a message-body
1453   because the associated response header fields (e.g., Transfer-Encoding,
1454   Content-Length, etc.) only indicate what their values would have been
1455   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1456   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1457   All other responses do include a message-body, although the body
1458   &MAY; be of zero length.
1461   The length of the message-body is determined by one of the following
1462   (in order of precedence):
1465  <list style="numbers">
1466    <x:lt><t>
1467     Any response to a HEAD request and any response with a status
1468     code of 100-199, 204, or 304 is always terminated by the first
1469     empty line after the header fields, regardless of the header
1470     fields present in the message, and thus cannot contain a message-body.
1471    </t></x:lt>
1472    <x:lt><t>
1473     If a Transfer-Encoding header field is present
1474     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1475     is the final encoding, the message-body length is determined by reading
1476     and decoding the chunked data until the transfer-coding indicates the
1477     data is complete.
1478    </t>
1479    <t>
1480     If a Transfer-Encoding header field is present in a response and the
1481     "chunked" transfer-coding is not the final encoding, the message-body
1482     length is determined by reading the connection until it is closed by
1483     the server.
1484     If a Transfer-Encoding header field is present in a request and the
1485     "chunked" transfer-coding is not the final encoding, the message-body
1486     length cannot be determined reliably; the server &MUST; respond with
1487     the 400 (Bad Request) status code and then close the connection.
1488    </t>
1489    <t>
1490     If a message is received with both a Transfer-Encoding header field
1491     and a Content-Length header field, the Transfer-Encoding overrides
1492     the Content-Length.
1493     Such a message might indicate an attempt to perform request or response
1494     smuggling (bypass of security-related checks on message routing or content)
1495     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1496     be removed, prior to forwarding the message downstream, or replaced with
1497     the real message-body length after the transfer-coding is decoded.
1498    </t></x:lt>
1499    <x:lt><t>
1500     If a message is received without Transfer-Encoding and with either
1501     multiple Content-Length header fields having differing field-values or
1502     a single Content-Length header field having an invalid value, then the
1503     message framing is invalid and &MUST; be treated as an error to
1504     prevent request or response smuggling.
1505     If this is a request message, the server &MUST; respond with
1506     a 400 (Bad Request) status code and then close the connection.
1507     If this is a response message received by a proxy, the proxy
1508     &MUST; discard the received response, send a 502 (Bad Gateway)
1509     status code as its downstream response, and then close the connection.
1510     If this is a response message received by a user-agent, it &MUST; be
1511     treated as an error by discarding the message and closing the connection.
1512    </t></x:lt>
1513    <x:lt><t>
1514     If a valid Content-Length header field
1515     is present without Transfer-Encoding, its decimal value defines the
1516     message-body length in octets.  If the actual number of octets sent in
1517     the message is less than the indicated Content-Length, the recipient
1518     &MUST; consider the message to be incomplete and treat the connection
1519     as no longer usable.
1520     If the actual number of octets sent in the message is more than the indicated
1521     Content-Length, the recipient &MUST; only process the message-body up to the
1522     field value's number of octets; the remainder of the message &MUST; either
1523     be discarded or treated as the next message in a pipeline.  For the sake of
1524     robustness, a user-agent &MAY; attempt to detect and correct such an error
1525     in message framing if it is parsing the response to the last request on
1526     a connection and the connection has been closed by the server.
1527    </t></x:lt>
1528    <x:lt><t>
1529     If this is a request message and none of the above are true, then the
1530     message-body length is zero (no message-body is present).
1531    </t></x:lt>
1532    <x:lt><t>
1533     Otherwise, this is a response message without a declared message-body
1534     length, so the message-body length is determined by the number of octets
1535     received prior to the server closing the connection.
1536    </t></x:lt>
1537  </list>
1540   Since there is no way to distinguish a successfully completed,
1541   close-delimited message from a partially-received message interrupted
1542   by network failure, implementations &SHOULD; use encoding or
1543   length-delimited messages whenever possible.  The close-delimiting
1544   feature exists primarily for backwards compatibility with HTTP/1.0.
1547   A server &MAY; reject a request that contains a message-body but
1548   not a Content-Length by responding with 411 (Length Required).
1551   Unless a transfer-coding other than "chunked" has been applied,
1552   a client that sends a request containing a message-body &SHOULD;
1553   use a valid Content-Length header field if the message-body length
1554   is known in advance, rather than the "chunked" encoding, since some
1555   existing services respond to "chunked" with a 411 (Length Required)
1556   status code even though they understand the chunked encoding.  This
1557   is typically because such services are implemented via a gateway that
1558   requires a content-length in advance of being called and the server
1559   is unable or unwilling to buffer the entire request before processing.
1562   A client that sends a request containing a message-body &MUST; include a
1563   valid Content-Length header field if it does not know the server will
1564   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1565   of specific user configuration or by remembering the version of a prior
1566   received response.
1570<section anchor="incomplete.messages" title="Incomplete Messages">
1572   Request messages that are prematurely terminated, possibly due to a
1573   cancelled connection or a server-imposed time-out exception, &MUST;
1574   result in closure of the connection; sending an HTTP/1.1 error response
1575   prior to closing the connection is &OPTIONAL;.
1578   Response messages that are prematurely terminated, usually by closure
1579   of the connection prior to receiving the expected number of octets or by
1580   failure to decode a transfer-encoded message-body, &MUST; be recorded
1581   as incomplete.  A response that terminates in the middle of the header
1582   block (before the empty line is received) cannot be assumed to convey the
1583   full semantics of the response and &MUST; be treated as an error.
1586   A message-body that uses the chunked transfer encoding is
1587   incomplete if the zero-sized chunk that terminates the encoding has not
1588   been received.  A message that uses a valid Content-Length is incomplete
1589   if the size of the message-body received (in octets) is less than the
1590   value given by Content-Length.  A response that has neither chunked
1591   transfer encoding nor Content-Length is terminated by closure of the
1592   connection, and thus is considered complete regardless of the number of
1593   message-body octets received, provided that the header block was received
1594   intact.
1597   A user agent &MUST-NOT; render an incomplete response message-body as if
1598   it were complete (i.e., some indication must be given to the user that an
1599   error occurred).  Cache requirements for incomplete responses are defined
1600   in &cache-incomplete;.
1603   A server &MUST; read the entire request message-body or close
1604   the connection after sending its response, since otherwise the
1605   remaining data on a persistent connection would be misinterpreted
1606   as the next request.  Likewise,
1607   a client &MUST; read the entire response message-body if it intends
1608   to reuse the same connection for a subsequent request.  Pipelining
1609   multiple requests on a connection is described in <xref target="pipelining"/>.
1613<section title="General Header Fields" anchor="general.header.fields">
1614  <x:anchor-alias value="general-header"/>
1616   There are a few header fields which have general applicability for
1617   both request and response messages, but which do not apply to the
1618   payload being transferred. These header fields apply only to the
1619   message being transmitted.
1621<texttable align="left">
1622  <ttcol>Header Field Name</ttcol>
1623  <ttcol>Defined in...</ttcol>
1625  <c>Connection</c> <c><xref target="header.connection"/></c>
1626  <c>Date</c> <c><xref target=""/></c>
1627  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1628  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1629  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1630  <c>Via</c> <c><xref target="header.via"/></c>
1635<section title="Request" anchor="request">
1636  <x:anchor-alias value="Request"/>
1638   A request message from a client to a server begins with a
1639   Request-Line, followed by zero or more header fields, an empty
1640   line signifying the end of the header block, and an optional
1641   message body.
1643<!--                 Host                      ; should be moved here eventually -->
1644<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1645  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1646                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1647                  <x:ref>CRLF</x:ref>
1648                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1651<section title="Request-Line" anchor="request-line">
1652  <x:anchor-alias value="Request-Line"/>
1654   The Request-Line begins with a method token, followed by a single
1655   space (SP), the request-target, another single space (SP), the
1656   protocol version, and ending with CRLF.
1658<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1659  <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>
1662<section title="Method" anchor="method">
1663  <x:anchor-alias value="Method"/>
1665   The Method token indicates the request method to be performed on the
1666   target resource. The request method is case-sensitive.
1668<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1669  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1673<section title="request-target" anchor="request-target">
1674  <x:anchor-alias value="request-target"/>
1676   The request-target identifies the target resource upon which to apply
1677   the request.  In most cases, the user agent is provided a URI reference
1678   from which it determines an absolute URI for identifying the target
1679   resource.  When a request to the resource is initiated, all or part
1680   of that URI is used to construct the HTTP request-target.
1682<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1683  <x:ref>request-target</x:ref> = "*"
1684                 / <x:ref>absolute-URI</x:ref>
1685                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1686                 / <x:ref>authority</x:ref>
1689   The four options for request-target are dependent on the nature of the
1690   request.
1692<t><iref item="asterisk form (of request-target)"/>
1693   The asterisk "*" form of request-target, which &MUST-NOT; be used
1694   with any request method other than OPTIONS, means that the request
1695   applies to the server as a whole (the listening process) rather than
1696   to a specific named resource at that server.  For example,
1698<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1699OPTIONS * HTTP/1.1
1701<t><iref item="absolute-URI form (of request-target)"/>
1702   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1703   proxy. The proxy is requested to either forward the request or service it
1704   from a valid cache, and then return the response. Note that the proxy &MAY;
1705   forward the request on to another proxy or directly to the server
1706   specified by the absolute-URI. In order to avoid request loops, a
1707   proxy that forwards requests to other proxies &MUST; be able to
1708   recognize and exclude all of its own server names, including
1709   any aliases, local variations, and the numeric IP address. An example
1710   Request-Line would be:
1712<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1713GET HTTP/1.1
1716   To allow for transition to absolute-URIs in all requests in future
1717   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1718   form in requests, even though HTTP/1.1 clients will only generate
1719   them in requests to proxies.
1722   If a proxy receives a host name that is not a fully qualified domain
1723   name, it &MAY; add its domain to the host name it received. If a proxy
1724   receives a fully qualified domain name, the proxy &MUST-NOT; change
1725   the host name.
1727<t><iref item="authority form (of request-target)"/>
1728   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1730<t><iref item="origin form (of request-target)"/>
1731   The most common form of request-target is that used when making
1732   a request to an origin server ("origin form").
1733   In this case, the absolute path and query components of the URI
1734   &MUST; be transmitted as the request-target, and the authority component
1735   &MUST; be transmitted in a Host header field. For example, a client wishing
1736   to retrieve a representation of the resource, as identified above,
1737   directly from the origin server would open (or reuse) a TCP connection
1738   to port 80 of the host "" and send the lines:
1740<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1741GET /pub/WWW/TheProject.html HTTP/1.1
1745   followed by the remainder of the Request. Note that the origin form
1746   of request-target always starts with an absolute path; if the target
1747   resource's URI path is empty, then an absolute path of "/" &MUST; be
1748   provided in the request-target.
1751   If a proxy receives an OPTIONS request with an absolute-URI form of
1752   request-target in which the URI has an empty path and no query component,
1753   then the last proxy on the request chain &MUST; use a request-target
1754   of "*" when it forwards the request to the indicated origin server.
1757   For example, the request
1758</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1762  would be forwarded by the final proxy as
1763</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1764OPTIONS * HTTP/1.1
1768   after connecting to port 8001 of host "".
1772   The request-target is transmitted in the format specified in
1773   <xref target="http.uri"/>. If the request-target is percent-encoded
1774   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1775   &MUST; decode the request-target in order to
1776   properly interpret the request. Servers &SHOULD; respond to invalid
1777   request-targets with an appropriate status code.
1780   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1781   received request-target when forwarding it to the next inbound server,
1782   except as noted above to replace a null path-absolute with "/" or "*".
1785  <t>
1786    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1787    meaning of the request when the origin server is improperly using
1788    a non-reserved URI character for a reserved purpose.  Implementors
1789    need to be aware that some pre-HTTP/1.1 proxies have been known to
1790    rewrite the request-target.
1791  </t>
1794   HTTP does not place a pre-defined limit on the length of a request-target.
1795   A server &MUST; be prepared to receive URIs of unbounded length and
1796   respond with the 414 (URI Too Long) status code if the received
1797   request-target would be longer than the server wishes to handle
1798   (see &status-414;).
1801   Various ad-hoc limitations on request-target length are found in practice.
1802   It is &RECOMMENDED; that all HTTP senders and recipients support
1803   request-target lengths of 8000 or more octets.
1806  <t>
1807    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1808    are not part of the request-target and thus will not be transmitted
1809    in an HTTP request.
1810  </t>
1815<section title="The Resource Identified by a Request" anchor="">
1817   The exact resource identified by an Internet request is determined by
1818   examining both the request-target and the Host header field.
1821   An origin server that does not allow resources to differ by the
1822   requested host &MAY; ignore the Host header field value when
1823   determining the resource identified by an HTTP/1.1 request. (But see
1824   <xref target=""/>
1825   for other requirements on Host support in HTTP/1.1.)
1828   An origin server that does differentiate resources based on the host
1829   requested (sometimes referred to as virtual hosts or vanity host
1830   names) &MUST; use the following rules for determining the requested
1831   resource on an HTTP/1.1 request:
1832  <list style="numbers">
1833    <t>If request-target is an absolute-URI, the host is part of the
1834     request-target. Any Host header field value in the request &MUST; be
1835     ignored.</t>
1836    <t>If the request-target is not an absolute-URI, and the request includes
1837     a Host header field, the host is determined by the Host header
1838     field value.</t>
1839    <t>If the host as determined by rule 1 or 2 is not a valid host on
1840     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1841  </list>
1844   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1845   attempt to use heuristics (e.g., examination of the URI path for
1846   something unique to a particular host) in order to determine what
1847   exact resource is being requested.
1851<section title="Effective Request URI" anchor="effective.request.uri">
1852  <iref primary="true" item="effective request URI"/>
1853  <iref primary="true" item="target resource"/>
1855   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1856   for the target resource; instead, the URI needs to be inferred from the
1857   request-target, Host header field, and connection context. The result of
1858   this process is called the "effective request URI".  The "target resource"
1859   is the resource identified by the effective request URI.
1862   If the request-target is an absolute-URI, then the effective request URI is
1863   the request-target.
1866   If the request-target uses the path-absolute form or the asterisk form,
1867   and the Host header field is present, then the effective request URI is
1868   constructed by concatenating
1871  <list style="symbols">
1872    <t>
1873      the scheme name: "http" if the request was received over an insecure
1874      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1875      connection,
1876    </t>
1877    <t>
1878      the octet sequence "://",
1879    </t>
1880    <t>
1881      the authority component, as specified in the Host header field
1882      (<xref target=""/>), and
1883    </t>
1884    <t>
1885      the request-target obtained from the Request-Line, unless the
1886      request-target is just the asterisk "*".
1887    </t>
1888  </list>
1891   If the request-target uses the path-absolute form or the asterisk form,
1892   and the Host header field is not present, then the effective request URI is
1893   undefined.
1896   Otherwise, when request-target uses the authority form, the effective
1897   request URI is undefined.
1901   Example 1: the effective request URI for the message
1903<artwork type="example" x:indent-with="  ">
1904GET /pub/WWW/TheProject.html HTTP/1.1
1908  (received over an insecure TCP connection) is "http", plus "://", plus the
1909  authority component "", plus the request-target
1910  "/pub/WWW/TheProject.html", thus
1911  "".
1916   Example 2: the effective request URI for the message
1918<artwork type="example" x:indent-with="  ">
1919OPTIONS * HTTP/1.1
1923  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1924  authority component "", thus "".
1928   Effective request URIs are compared using the rules described in
1929   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1930   be treated as equivalent to an absolute path of "/".
1937<section title="Response" anchor="response">
1938  <x:anchor-alias value="Response"/>
1940   After receiving and interpreting a request message, a server responds
1941   with an HTTP response message.
1943<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1944  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1945                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1946                  <x:ref>CRLF</x:ref>
1947                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1950<section title="Status-Line" anchor="status-line">
1951  <x:anchor-alias value="Status-Line"/>
1953   The first line of a Response message is the Status-Line, consisting
1954   of the protocol version, a space (SP), the status code, another space,
1955   a possibly-empty textual phrase describing the status code, and
1956   ending with CRLF.
1958<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1959  <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>
1962<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1963  <x:anchor-alias value="Reason-Phrase"/>
1964  <x:anchor-alias value="Status-Code"/>
1966   The Status-Code element is a 3-digit integer result code of the
1967   attempt to understand and satisfy the request. These codes are fully
1968   defined in &status-codes;.  The Reason Phrase exists for the sole
1969   purpose of providing a textual description associated with the numeric
1970   status code, out of deference to earlier Internet application protocols
1971   that were more frequently used with interactive text clients.
1972   A client &SHOULD; ignore the content of the Reason Phrase.
1975   The first digit of the Status-Code defines the class of response. The
1976   last two digits do not have any categorization role. There are 5
1977   values for the first digit:
1978  <list style="symbols">
1979    <t>
1980      1xx: Informational - Request received, continuing process
1981    </t>
1982    <t>
1983      2xx: Success - The action was successfully received,
1984        understood, and accepted
1985    </t>
1986    <t>
1987      3xx: Redirection - Further action must be taken in order to
1988        complete the request
1989    </t>
1990    <t>
1991      4xx: Client Error - The request contains bad syntax or cannot
1992        be fulfilled
1993    </t>
1994    <t>
1995      5xx: Server Error - The server failed to fulfill an apparently
1996        valid request
1997    </t>
1998  </list>
2000<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
2001  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
2002  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
2010<section title="Protocol Parameters" anchor="protocol.parameters">
2012<section title="Date/Time Formats: Full Date" anchor="">
2013  <x:anchor-alias value="HTTP-date"/>
2015   HTTP applications have historically allowed three different formats
2016   for date/time stamps. However, the preferred format is a fixed-length subset
2017   of that defined by <xref target="RFC1123"/>:
2019<figure><artwork type="example" x:indent-with="  ">
2020Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2023   The other formats are described here only for compatibility with obsolete
2024   implementations.
2026<figure><artwork type="example" x:indent-with="  ">
2027Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2028Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2031   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2032   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2033   only generate the RFC 1123 format for representing HTTP-date values
2034   in header fields.
2037   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2038   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2039   equal to UTC (Coordinated Universal Time). This is indicated in the
2040   first two formats by the inclusion of "GMT" as the three-letter
2041   abbreviation for time zone, and &MUST; be assumed when reading the
2042   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2043   additional whitespace beyond that specifically included as SP in the
2044   grammar.
2046<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2047  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2049<t anchor="">
2050  <x:anchor-alias value="rfc1123-date"/>
2051  <x:anchor-alias value="time-of-day"/>
2052  <x:anchor-alias value="hour"/>
2053  <x:anchor-alias value="minute"/>
2054  <x:anchor-alias value="second"/>
2055  <x:anchor-alias value="day-name"/>
2056  <x:anchor-alias value="day"/>
2057  <x:anchor-alias value="month"/>
2058  <x:anchor-alias value="year"/>
2059  <x:anchor-alias value="GMT"/>
2060  Preferred format:
2062<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"/>
2063  <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>
2064  ; fixed length subset of the format defined in
2065  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2067  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2068               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2069               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2070               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2071               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2072               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2073               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2075  <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>
2076               ; e.g., 02 Jun 1982
2078  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2079  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2080               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2081               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2082               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2083               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2084               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2085               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2086               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2087               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2088               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2089               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2090               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2091  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2093  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2095  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2096                 ; 00:00:00 - 23:59:59
2098  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2099  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2100  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2103  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2104  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2105  same as those defined for the RFC 5322 constructs
2106  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2108<t anchor="">
2109  <x:anchor-alias value="obs-date"/>
2110  <x:anchor-alias value="rfc850-date"/>
2111  <x:anchor-alias value="asctime-date"/>
2112  <x:anchor-alias value="date1"/>
2113  <x:anchor-alias value="date2"/>
2114  <x:anchor-alias value="date3"/>
2115  <x:anchor-alias value="rfc1123-date"/>
2116  <x:anchor-alias value="day-name-l"/>
2117  Obsolete formats:
2119<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2120  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2122<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2123  <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>
2124  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2125                 ; day-month-year (e.g., 02-Jun-82)
2127  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2128         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2129         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2130         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2131         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2132         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2133         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2135<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2136  <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>
2137  <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> ))
2138                 ; month day (e.g., Jun  2)
2141  <t>
2142    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2143    accepting date values that might have been sent by non-HTTP
2144    applications, as is sometimes the case when retrieving or posting
2145    messages via proxies/gateways to SMTP or NNTP.
2146  </t>
2149  <t>
2150    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2151    to their usage within the protocol stream. Clients and servers are
2152    not required to use these formats for user presentation, request
2153    logging, etc.
2154  </t>
2158<section title="Transfer Codings" anchor="transfer.codings">
2159  <x:anchor-alias value="transfer-coding"/>
2160  <x:anchor-alias value="transfer-extension"/>
2162   Transfer-coding values are used to indicate an encoding
2163   transformation that has been, can be, or might need to be applied to a
2164   payload body in order to ensure "safe transport" through the network.
2165   This differs from a content coding in that the transfer-coding is a
2166   property of the message rather than a property of the representation
2167   that is being transferred.
2169<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2170  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2171                          / "compress" ; <xref target="compress.coding"/>
2172                          / "deflate" ; <xref target="deflate.coding"/>
2173                          / "gzip" ; <xref target="gzip.coding"/>
2174                          / <x:ref>transfer-extension</x:ref>
2175  <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> )
2177<t anchor="rule.parameter">
2178  <x:anchor-alias value="attribute"/>
2179  <x:anchor-alias value="transfer-parameter"/>
2180  <x:anchor-alias value="value"/>
2181   Parameters are in the form of attribute/value pairs.
2183<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"/>
2184  <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>
2185  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2186  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2189   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2190   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2191   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2194   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2195   MIME, which were designed to enable safe transport of binary data over a
2196   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2197   However, safe transport
2198   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2199   the only unsafe characteristic of message-bodies is the difficulty in
2200   determining the exact message body length (<xref target="message.body"/>),
2201   or the desire to encrypt data over a shared transport.
2204   A server that receives a request message with a transfer-coding it does
2205   not understand &SHOULD; respond with 501 (Not Implemented) and then
2206   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2207   client.
2210<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2211  <iref item="chunked (Coding Format)"/>
2212  <iref item="Coding Format" subitem="chunked"/>
2213  <x:anchor-alias value="chunk"/>
2214  <x:anchor-alias value="Chunked-Body"/>
2215  <x:anchor-alias value="chunk-data"/>
2216  <x:anchor-alias value="chunk-ext"/>
2217  <x:anchor-alias value="chunk-ext-name"/>
2218  <x:anchor-alias value="chunk-ext-val"/>
2219  <x:anchor-alias value="chunk-size"/>
2220  <x:anchor-alias value="last-chunk"/>
2221  <x:anchor-alias value="trailer-part"/>
2222  <x:anchor-alias value="quoted-str-nf"/>
2223  <x:anchor-alias value="qdtext-nf"/>
2225   The chunked encoding modifies the body of a message in order to
2226   transfer it as a series of chunks, each with its own size indicator,
2227   followed by an &OPTIONAL; trailer containing header fields. This
2228   allows dynamically produced content to be transferred along with the
2229   information necessary for the recipient to verify that it has
2230   received the full message.
2232<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"/>
2233  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2234                   <x:ref>last-chunk</x:ref>
2235                   <x:ref>trailer-part</x:ref>
2236                   <x:ref>CRLF</x:ref>
2238  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2239                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2240  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2241  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2243  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2244                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2245  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2246  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2247  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2248  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2250  <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>
2251                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2252  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2253                 ; <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>
2256   The chunk-size field is a string of hex digits indicating the size of
2257   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2258   zero, followed by the trailer, which is terminated by an empty line.
2261   The trailer allows the sender to include additional HTTP header
2262   fields at the end of the message. The Trailer header field can be
2263   used to indicate which header fields are included in a trailer (see
2264   <xref target="header.trailer"/>).
2267   A server using chunked transfer-coding in a response &MUST-NOT; use the
2268   trailer for any header fields unless at least one of the following is
2269   true:
2270  <list style="numbers">
2271    <t>the request included a TE header field that indicates "trailers" is
2272     acceptable in the transfer-coding of the  response, as described in
2273     <xref target="header.te"/>; or,</t>
2275    <t>the trailer fields consist entirely of optional metadata, and the
2276    recipient could use the message (in a manner acceptable to the server where
2277    the field originated) without receiving it. In other words, the server that
2278    generated the header (often but not always the origin server) is willing to
2279    accept the possibility that the trailer fields might be silently discarded
2280    along the path to the client.</t>
2281  </list>
2284   This requirement prevents an interoperability failure when the
2285   message is being received by an HTTP/1.1 (or later) proxy and
2286   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2287   compliance with the protocol would have necessitated a possibly
2288   infinite buffer on the proxy.
2291   A process for decoding the "chunked" transfer-coding
2292   can be represented in pseudo-code as:
2294<figure><artwork type="code">
2295  length := 0
2296  read chunk-size, chunk-ext (if any) and CRLF
2297  while (chunk-size &gt; 0) {
2298     read chunk-data and CRLF
2299     append chunk-data to decoded-body
2300     length := length + chunk-size
2301     read chunk-size and CRLF
2302  }
2303  read header-field
2304  while (header-field not empty) {
2305     append header-field to existing header fields
2306     read header-field
2307  }
2308  Content-Length := length
2309  Remove "chunked" from Transfer-Encoding
2312   All HTTP/1.1 applications &MUST; be able to receive and decode the
2313   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2314   they do not understand.
2317   Since "chunked" is the only transfer-coding required to be understood
2318   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2319   on a persistent connection.  Whenever a transfer-coding is applied to
2320   a payload body in a request, the final transfer-coding applied &MUST;
2321   be "chunked".  If a transfer-coding is applied to a response payload
2322   body, then either the final transfer-coding applied &MUST; be "chunked"
2323   or the message &MUST; be terminated by closing the connection. When the
2324   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2325   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2326   be applied more than once in a message-body.
2330<section title="Compression Codings" anchor="compression.codings">
2332   The codings defined below can be used to compress the payload of a
2333   message.
2336   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2337   is not desirable and is discouraged for future encodings. Their
2338   use here is representative of historical practice, not good
2339   design.
2342   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2343   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2344   equivalent to "gzip" and "compress" respectively.
2347<section title="Compress Coding" anchor="compress.coding">
2348<iref item="compress (Coding Format)"/>
2349<iref item="Coding Format" subitem="compress"/>
2351   The "compress" format is produced by the common UNIX file compression
2352   program "compress". This format is an adaptive Lempel-Ziv-Welch
2353   coding (LZW).
2357<section title="Deflate Coding" anchor="deflate.coding">
2358<iref item="deflate (Coding Format)"/>
2359<iref item="Coding Format" subitem="deflate"/>
2361   The "deflate" format is defined as the "deflate" compression mechanism
2362   (described in <xref target="RFC1951"/>) used inside the "zlib"
2363   data format (<xref target="RFC1950"/>).
2366  <t>
2367    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2368    compressed data without the zlib wrapper.
2369   </t>
2373<section title="Gzip Coding" anchor="gzip.coding">
2374<iref item="gzip (Coding Format)"/>
2375<iref item="Coding Format" subitem="gzip"/>
2377   The "gzip" format is produced by the file compression program
2378   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2379   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2385<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2387   The HTTP Transfer Coding Registry defines the name space for the transfer
2388   coding names.
2391   Registrations &MUST; include the following fields:
2392   <list style="symbols">
2393     <t>Name</t>
2394     <t>Description</t>
2395     <t>Pointer to specification text</t>
2396   </list>
2399   Names of transfer codings &MUST-NOT; overlap with names of content codings
2400   (&content-codings;), unless the encoding transformation is identical (as it
2401   is the case for the compression codings defined in
2402   <xref target="compression.codings"/>).
2405   Values to be added to this name space require a specification
2406   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2407   conform to the purpose of transfer coding defined in this section.
2410   The registry itself is maintained at
2411   <eref target=""/>.
2416<section title="Product Tokens" anchor="product.tokens">
2417  <x:anchor-alias value="product"/>
2418  <x:anchor-alias value="product-version"/>
2420   Product tokens are used to allow communicating applications to
2421   identify themselves by software name and version. Most fields using
2422   product tokens also allow sub-products which form a significant part
2423   of the application to be listed, separated by whitespace. By
2424   convention, the products are listed in order of their significance
2425   for identifying the application.
2427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2428  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2429  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2432   Examples:
2434<figure><artwork type="example">
2435  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2436  Server: Apache/0.8.4
2439   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2440   used for advertising or other non-essential information. Although any
2441   token octet &MAY; appear in a product-version, this token &SHOULD;
2442   only be used for a version identifier (i.e., successive versions of
2443   the same product &SHOULD; only differ in the product-version portion of
2444   the product value).
2448<section title="Quality Values" anchor="quality.values">
2449  <x:anchor-alias value="qvalue"/>
2451   Both transfer codings (TE request header field, <xref target="header.te"/>)
2452   and content negotiation (&content.negotiation;) use short "floating point"
2453   numbers to indicate the relative importance ("weight") of various
2454   negotiable parameters.  A weight is normalized to a real number in
2455   the range 0 through 1, where 0 is the minimum and 1 the maximum
2456   value. If a parameter has a quality value of 0, then content with
2457   this parameter is "not acceptable" for the client. HTTP/1.1
2458   applications &MUST-NOT; generate more than three digits after the
2459   decimal point. User configuration of these values &SHOULD; also be
2460   limited in this fashion.
2462<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2463  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2464                 / ( "1" [ "." 0*3("0") ] )
2467  <t>
2468     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2469     relative degradation in desired quality.
2470  </t>
2476<section title="Connections" anchor="connections">
2478<section title="Persistent Connections" anchor="persistent.connections">
2480<section title="Purpose" anchor="persistent.purpose">
2482   Prior to persistent connections, a separate TCP connection was
2483   established for each request, increasing the load on HTTP servers
2484   and causing congestion on the Internet. The use of inline images and
2485   other associated data often requires a client to make multiple
2486   requests of the same server in a short amount of time. Analysis of
2487   these performance problems and results from a prototype
2488   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2489   measurements of actual HTTP/1.1 implementations show good
2490   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2491   T/TCP <xref target="Tou1998"/>.
2494   Persistent HTTP connections have a number of advantages:
2495  <list style="symbols">
2496      <t>
2497        By opening and closing fewer TCP connections, CPU time is saved
2498        in routers and hosts (clients, servers, proxies, gateways,
2499        tunnels, or caches), and memory used for TCP protocol control
2500        blocks can be saved in hosts.
2501      </t>
2502      <t>
2503        HTTP requests and responses can be pipelined on a connection.
2504        Pipelining allows a client to make multiple requests without
2505        waiting for each response, allowing a single TCP connection to
2506        be used much more efficiently, with much lower elapsed time.
2507      </t>
2508      <t>
2509        Network congestion is reduced by reducing the number of packets
2510        caused by TCP opens, and by allowing TCP sufficient time to
2511        determine the congestion state of the network.
2512      </t>
2513      <t>
2514        Latency on subsequent requests is reduced since there is no time
2515        spent in TCP's connection opening handshake.
2516      </t>
2517      <t>
2518        HTTP can evolve more gracefully, since errors can be reported
2519        without the penalty of closing the TCP connection. Clients using
2520        future versions of HTTP might optimistically try a new feature,
2521        but if communicating with an older server, retry with old
2522        semantics after an error is reported.
2523      </t>
2524    </list>
2527   HTTP implementations &SHOULD; implement persistent connections.
2531<section title="Overall Operation" anchor="persistent.overall">
2533   A significant difference between HTTP/1.1 and earlier versions of
2534   HTTP is that persistent connections are the default behavior of any
2535   HTTP connection. That is, unless otherwise indicated, the client
2536   &SHOULD; assume that the server will maintain a persistent connection,
2537   even after error responses from the server.
2540   Persistent connections provide a mechanism by which a client and a
2541   server can signal the close of a TCP connection. This signaling takes
2542   place using the Connection header field (<xref target="header.connection"/>). Once a close
2543   has been signaled, the client &MUST-NOT; send any more requests on that
2544   connection.
2547<section title="Negotiation" anchor="persistent.negotiation">
2549   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2550   maintain a persistent connection unless a Connection header field including
2551   the connection-token "close" was sent in the request. If the server
2552   chooses to close the connection immediately after sending the
2553   response, it &SHOULD; send a Connection header field including the
2554   connection-token "close".
2557   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2558   decide to keep it open based on whether the response from a server
2559   contains a Connection header field with the connection-token close. In case
2560   the client does not want to maintain a connection for more than that
2561   request, it &SHOULD; send a Connection header field including the
2562   connection-token close.
2565   If either the client or the server sends the close token in the
2566   Connection header field, that request becomes the last one for the
2567   connection.
2570   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2571   maintained for HTTP versions less than 1.1 unless it is explicitly
2572   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2573   compatibility with HTTP/1.0 clients.
2576   In order to remain persistent, all messages on the connection &MUST;
2577   have a self-defined message length (i.e., one not defined by closure
2578   of the connection), as described in <xref target="message.body"/>.
2582<section title="Pipelining" anchor="pipelining">
2584   A client that supports persistent connections &MAY; "pipeline" its
2585   requests (i.e., send multiple requests without waiting for each
2586   response). A server &MUST; send its responses to those requests in the
2587   same order that the requests were received.
2590   Clients which assume persistent connections and pipeline immediately
2591   after connection establishment &SHOULD; be prepared to retry their
2592   connection if the first pipelined attempt fails. If a client does
2593   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2594   persistent. Clients &MUST; also be prepared to resend their requests if
2595   the server closes the connection before sending all of the
2596   corresponding responses.
2599   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2600   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2601   premature termination of the transport connection could lead to
2602   indeterminate results. A client wishing to send a non-idempotent
2603   request &SHOULD; wait to send that request until it has received the
2604   response status line for the previous request.
2609<section title="Proxy Servers" anchor="persistent.proxy">
2611   It is especially important that proxies correctly implement the
2612   properties of the Connection header field as specified in <xref target="header.connection"/>.
2615   The proxy server &MUST; signal persistent connections separately with
2616   its clients and the origin servers (or other proxy servers) that it
2617   connects to. Each persistent connection applies to only one transport
2618   link.
2621   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2622   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2623   for information and discussion of the problems with the Keep-Alive header field
2624   implemented by many HTTP/1.0 clients).
2627<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2629  <cref anchor="TODO-end-to-end" source="jre">
2630    Restored from <eref target=""/>.
2631    See also <eref target=""/>.
2632  </cref>
2635   For the purpose of defining the behavior of caches and non-caching
2636   proxies, we divide HTTP header fields into two categories:
2637  <list style="symbols">
2638      <t>End-to-end header fields, which are  transmitted to the ultimate
2639        recipient of a request or response. End-to-end header fields in
2640        responses MUST be stored as part of a cache entry and &MUST; be
2641        transmitted in any response formed from a cache entry.</t>
2643      <t>Hop-by-hop header fields, which are meaningful only for a single
2644        transport-level connection, and are not stored by caches or
2645        forwarded by proxies.</t>
2646  </list>
2649   The following HTTP/1.1 header fields are hop-by-hop header fields:
2650  <list style="symbols">
2651      <t>Connection</t>
2652      <t>Keep-Alive</t>
2653      <t>Proxy-Authenticate</t>
2654      <t>Proxy-Authorization</t>
2655      <t>TE</t>
2656      <t>Trailer</t>
2657      <t>Transfer-Encoding</t>
2658      <t>Upgrade</t>
2659  </list>
2662   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2665   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2666   (<xref target="header.connection"/>).
2670<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2672  <cref anchor="TODO-non-mod-headers" source="jre">
2673    Restored from <eref target=""/>.
2674    See also <eref target=""/>.
2675  </cref>
2678   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2679   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2680   modify an end-to-end header field unless the definition of that header field requires
2681   or specifically allows that.
2684   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2685   request or response, and it &MUST-NOT; add any of these fields if not
2686   already present:
2687  <list style="symbols">
2688    <t>Allow</t>
2689    <t>Content-Location</t>
2690    <t>Content-MD5</t>
2691    <t>ETag</t>
2692    <t>Last-Modified</t>
2693    <t>Server</t>
2694  </list>
2697   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2698   response:
2699  <list style="symbols">
2700    <t>Expires</t>
2701  </list>
2704   but it &MAY; add any of these fields if not already present. If an
2705   Expires header field is added, it &MUST; be given a field-value identical to
2706   that of the Date header field in that response.
2709   A proxy &MUST-NOT; modify or add any of the following fields in a
2710   message that contains the no-transform cache-control directive, or in
2711   any request:
2712  <list style="symbols">
2713    <t>Content-Encoding</t>
2714    <t>Content-Range</t>
2715    <t>Content-Type</t>
2716  </list>
2719   A transforming proxy &MAY; modify or add these fields to a message
2720   that does not include no-transform, but if it does so, it &MUST; add a
2721   Warning 214 (Transformation applied) if one does not already appear
2722   in the message (see &header-warning;).
2725  <t>
2726    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2727    cause authentication failures if stronger authentication
2728    mechanisms are introduced in later versions of HTTP. Such
2729    authentication mechanisms &MAY; rely on the values of header fields
2730    not listed here.
2731  </t>
2734   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2735   though it &MAY; change the message-body through application or removal
2736   of a transfer-coding (<xref target="transfer.codings"/>).
2742<section title="Practical Considerations" anchor="persistent.practical">
2744   Servers will usually have some time-out value beyond which they will
2745   no longer maintain an inactive connection. Proxy servers might make
2746   this a higher value since it is likely that the client will be making
2747   more connections through the same server. The use of persistent
2748   connections places no requirements on the length (or existence) of
2749   this time-out for either the client or the server.
2752   When a client or server wishes to time-out it &SHOULD; issue a graceful
2753   close on the transport connection. Clients and servers &SHOULD; both
2754   constantly watch for the other side of the transport close, and
2755   respond to it as appropriate. If a client or server does not detect
2756   the other side's close promptly it could cause unnecessary resource
2757   drain on the network.
2760   A client, server, or proxy &MAY; close the transport connection at any
2761   time. For example, a client might have started to send a new request
2762   at the same time that the server has decided to close the "idle"
2763   connection. From the server's point of view, the connection is being
2764   closed while it was idle, but from the client's point of view, a
2765   request is in progress.
2768   This means that clients, servers, and proxies &MUST; be able to recover
2769   from asynchronous close events. Client software &SHOULD; reopen the
2770   transport connection and retransmit the aborted sequence of requests
2771   without user interaction so long as the request sequence is
2772   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2773   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2774   human operator the choice of retrying the request(s). Confirmation by
2775   user-agent software with semantic understanding of the application
2776   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2777   be repeated if the second sequence of requests fails.
2780   Servers &SHOULD; always respond to at least one request per connection,
2781   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2782   middle of transmitting a response, unless a network or client failure
2783   is suspected.
2786   Clients (including proxies) &SHOULD; limit the number of simultaneous
2787   connections that they maintain to a given server (including proxies).
2790   Previous revisions of HTTP gave a specific number of connections as a
2791   ceiling, but this was found to be impractical for many applications. As a
2792   result, this specification does not mandate a particular maximum number of
2793   connections, but instead encourages clients to be conservative when opening
2794   multiple connections.
2797   In particular, while using multiple connections avoids the "head-of-line
2798   blocking" problem (whereby a request that takes significant server-side
2799   processing and/or has a large payload can block subsequent requests on the
2800   same connection), each connection used consumes server resources (sometimes
2801   significantly), and furthermore using multiple connections can cause
2802   undesirable side effects in congested networks.
2805   Note that servers might reject traffic that they deem abusive, including an
2806   excessive number of connections from a client.
2811<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2813<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2815   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2816   flow control mechanisms to resolve temporary overloads, rather than
2817   terminating connections with the expectation that clients will retry.
2818   The latter technique can exacerbate network congestion.
2822<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2824   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2825   the network connection for an error status code while it is transmitting
2826   the request. If the client sees an error status code, it &SHOULD;
2827   immediately cease transmitting the body. If the body is being sent
2828   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2829   empty trailer &MAY; be used to prematurely mark the end of the message.
2830   If the body was preceded by a Content-Length header field, the client &MUST;
2831   close the connection.
2835<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2837   The purpose of the 100 (Continue) status code (see &status-100;) is to
2838   allow a client that is sending a request message with a request body
2839   to determine if the origin server is willing to accept the request
2840   (based on the request header fields) before the client sends the request
2841   body. In some cases, it might either be inappropriate or highly
2842   inefficient for the client to send the body if the server will reject
2843   the message without looking at the body.
2846   Requirements for HTTP/1.1 clients:
2847  <list style="symbols">
2848    <t>
2849        If a client will wait for a 100 (Continue) response before
2850        sending the request body, it &MUST; send an Expect header
2851        field (&header-expect;) with the "100-continue" expectation.
2852    </t>
2853    <t>
2854        A client &MUST-NOT; send an Expect header field (&header-expect;)
2855        with the "100-continue" expectation if it does not intend
2856        to send a request body.
2857    </t>
2858  </list>
2861   Because of the presence of older implementations, the protocol allows
2862   ambiguous situations in which a client might send "Expect: 100-continue"
2863   without receiving either a 417 (Expectation Failed)
2864   or a 100 (Continue) status code. Therefore, when a client sends this
2865   header field to an origin server (possibly via a proxy) from which it
2866   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2867   wait for an indefinite period before sending the request body.
2870   Requirements for HTTP/1.1 origin servers:
2871  <list style="symbols">
2872    <t> Upon receiving a request which includes an Expect header
2873        field with the "100-continue" expectation, an origin server &MUST;
2874        either respond with 100 (Continue) status code and continue to read
2875        from the input stream, or respond with a final status code. The
2876        origin server &MUST-NOT; wait for the request body before sending
2877        the 100 (Continue) response. If it responds with a final status
2878        code, it &MAY; close the transport connection or it &MAY; continue
2879        to read and discard the rest of the request.  It &MUST-NOT;
2880        perform the request method if it returns a final status code.
2881    </t>
2882    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2883        the request message does not include an Expect header
2884        field with the "100-continue" expectation, and &MUST-NOT; send a
2885        100 (Continue) response if such a request comes from an HTTP/1.0
2886        (or earlier) client. There is an exception to this rule: for
2887        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2888        status code in response to an HTTP/1.1 PUT or POST request that does
2889        not include an Expect header field with the "100-continue"
2890        expectation. This exception, the purpose of which is
2891        to minimize any client processing delays associated with an
2892        undeclared wait for 100 (Continue) status code, applies only to
2893        HTTP/1.1 requests, and not to requests with any other HTTP-version
2894        value.
2895    </t>
2896    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2897        already received some or all of the request body for the
2898        corresponding request.
2899    </t>
2900    <t> An origin server that sends a 100 (Continue) response &MUST;
2901    ultimately send a final status code, once the request body is
2902        received and processed, unless it terminates the transport
2903        connection prematurely.
2904    </t>
2905    <t> If an origin server receives a request that does not include an
2906        Expect header field with the "100-continue" expectation,
2907        the request includes a request body, and the server responds
2908        with a final status code before reading the entire request body
2909        from the transport connection, then the server &SHOULD-NOT;  close
2910        the transport connection until it has read the entire request,
2911        or until the client closes the connection. Otherwise, the client
2912        might not reliably receive the response message. However, this
2913        requirement is not be construed as preventing a server from
2914        defending itself against denial-of-service attacks, or from
2915        badly broken client implementations.
2916      </t>
2917    </list>
2920   Requirements for HTTP/1.1 proxies:
2921  <list style="symbols">
2922    <t> If a proxy receives a request that includes an Expect header
2923        field with the "100-continue" expectation, and the proxy
2924        either knows that the next-hop server complies with HTTP/1.1 or
2925        higher, or does not know the HTTP version of the next-hop
2926        server, it &MUST; forward the request, including the Expect header
2927        field.
2928    </t>
2929    <t> If the proxy knows that the version of the next-hop server is
2930        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2931        respond with a 417 (Expectation Failed) status code.
2932    </t>
2933    <t> Proxies &SHOULD; maintain a record of the HTTP version
2934        numbers received from recently-referenced next-hop servers.
2935    </t>
2936    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2937        request message was received from an HTTP/1.0 (or earlier)
2938        client and did not include an Expect header field with
2939        the "100-continue" expectation. This requirement overrides the
2940        general rule for forwarding of 1xx responses (see &status-1xx;).
2941    </t>
2942  </list>
2946<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2948   If an HTTP/1.1 client sends a request which includes a request body,
2949   but which does not include an Expect header field with the
2950   "100-continue" expectation, and if the client is not directly
2951   connected to an HTTP/1.1 origin server, and if the client sees the
2952   connection close before receiving a status line from the server, the
2953   client &SHOULD; retry the request.  If the client does retry this
2954   request, it &MAY; use the following "binary exponential backoff"
2955   algorithm to be assured of obtaining a reliable response:
2956  <list style="numbers">
2957    <t>
2958      Initiate a new connection to the server
2959    </t>
2960    <t>
2961      Transmit the request-line, header fields, and the CRLF that
2962      indicates the end of header fields.
2963    </t>
2964    <t>
2965      Initialize a variable R to the estimated round-trip time to the
2966         server (e.g., based on the time it took to establish the
2967         connection), or to a constant value of 5 seconds if the round-trip
2968         time is not available.
2969    </t>
2970    <t>
2971       Compute T = R * (2**N), where N is the number of previous
2972         retries of this request.
2973    </t>
2974    <t>
2975       Wait either for an error response from the server, or for T
2976         seconds (whichever comes first)
2977    </t>
2978    <t>
2979       If no error response is received, after T seconds transmit the
2980         body of the request.
2981    </t>
2982    <t>
2983       If client sees that the connection is closed prematurely,
2984         repeat from step 1 until the request is accepted, an error
2985         response is received, or the user becomes impatient and
2986         terminates the retry process.
2987    </t>
2988  </list>
2991   If at any point an error status code is received, the client
2992  <list style="symbols">
2993      <t>&SHOULD-NOT;  continue and</t>
2995      <t>&SHOULD; close the connection if it has not completed sending the
2996        request message.</t>
2997    </list>
3004<section title="Miscellaneous notes that might disappear" anchor="misc">
3005<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
3007   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
3011<section title="Use of HTTP for proxy communication" anchor="http.proxy">
3013   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
3017<section title="Interception of HTTP for access control" anchor="http.intercept">
3019   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
3023<section title="Use of HTTP by other protocols" anchor="http.others">
3025   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3026   Extensions of HTTP like WebDAV.</cref>
3030<section title="Use of HTTP by media type specification" anchor="">
3032   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3037<section title="Header Field Definitions" anchor="header.field.definitions">
3039   This section defines the syntax and semantics of HTTP header fields
3040   related to message framing and transport protocols.
3043<section title="Connection" anchor="header.connection">
3044  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3045  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3046  <x:anchor-alias value="Connection"/>
3047  <x:anchor-alias value="connection-token"/>
3049   The "Connection" header field allows the sender to specify
3050   options that are desired only for that particular connection.
3051   Such connection options &MUST; be removed or replaced before the
3052   message can be forwarded downstream by a proxy or gateway.
3053   This mechanism also allows the sender to indicate which HTTP
3054   header fields used in the message are only intended for the
3055   immediate recipient ("hop-by-hop"), as opposed to all recipients
3056   on the chain ("end-to-end"), enabling the message to be
3057   self-descriptive and allowing future connection-specific extensions
3058   to be deployed in HTTP without fear that they will be blindly
3059   forwarded by previously deployed intermediaries.
3062   The Connection header field's value has the following grammar:
3064<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3065  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3066  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3069   A proxy or gateway &MUST; parse a received Connection
3070   header field before a message is forwarded and, for each
3071   connection-token in this field, remove any header field(s) from
3072   the message with the same name as the connection-token, and then
3073   remove the Connection header field itself or replace it with the
3074   sender's own connection options for the forwarded message.
3077   A sender &MUST-NOT; include field-names in the Connection header
3078   field-value for fields that are defined as expressing constraints
3079   for all recipients in the request or response chain, such as the
3080   Cache-Control header field (&header-cache-control;).
3083   The connection options do not have to correspond to a header field
3084   present in the message, since a connection-specific header field
3085   might not be needed if there are no parameters associated with that
3086   connection option.  Recipients that trigger certain connection
3087   behavior based on the presence of connection options &MUST; do so
3088   based on the presence of the connection-token rather than only the
3089   presence of the optional header field.  In other words, if the
3090   connection option is received as a header field but not indicated
3091   within the Connection field-value, then the recipient &MUST; ignore
3092   the connection-specific header field because it has likely been
3093   forwarded by an intermediary that is only partially compliant.
3096   When defining new connection options, specifications ought to
3097   carefully consider existing deployed header fields and ensure
3098   that the new connection-token does not share the same name as
3099   an unrelated header field that might already be deployed.
3100   Defining a new connection-token essentially reserves that potential
3101   field-name for carrying additional information related to the
3102   connection option, since it would be unwise for senders to use
3103   that field-name for anything else.
3106   HTTP/1.1 defines the "close" connection option for the sender to
3107   signal that the connection will be closed after completion of the
3108   response. For example,
3110<figure><artwork type="example">
3111  Connection: close
3114   in either the request or the response header fields indicates that
3115   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3116   after the current request/response is complete.
3119   An HTTP/1.1 client that does not support persistent connections &MUST;
3120   include the "close" connection option in every request message.
3123   An HTTP/1.1 server that does not support persistent connections &MUST;
3124   include the "close" connection option in every response message that
3125   does not have a 1xx (Informational) status code.
3129<section title="Content-Length" anchor="header.content-length">
3130  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3131  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3132  <x:anchor-alias value="Content-Length"/>
3134   The "Content-Length" header field indicates the size of the
3135   message-body, in decimal number of octets, for any message other than
3136   a response to a HEAD request or a response with a status code of 304.
3137   In the case of a response to a HEAD request, Content-Length indicates
3138   the size of the payload body (not including any potential transfer-coding)
3139   that would have been sent had the request been a GET.
3140   In the case of a 304 (Not Modified) response to a GET request,
3141   Content-Length indicates the size of the payload body (not including
3142   any potential transfer-coding) that would have been sent in a 200 (OK)
3143   response.
3145<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3146  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3149   An example is
3151<figure><artwork type="example">
3152  Content-Length: 3495
3155   Implementations &SHOULD; use this field to indicate the message-body
3156   length when no transfer-coding is being applied and the
3157   payload's body length can be determined prior to being transferred.
3158   <xref target="message.body"/> describes how recipients determine the length
3159   of a message-body.
3162   Any Content-Length greater than or equal to zero is a valid value.
3165   Note that the use of this field in HTTP is significantly different from
3166   the corresponding definition in MIME, where it is an optional field
3167   used within the "message/external-body" content-type.
3171<section title="Date" anchor="">
3172  <iref primary="true" item="Date header field" x:for-anchor=""/>
3173  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3174  <x:anchor-alias value="Date"/>
3176   The "Date" header field represents the date and time at which
3177   the message was originated, having the same semantics as the Origination
3178   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3179   The field value is an HTTP-date, as described in <xref target=""/>;
3180   it &MUST; be sent in rfc1123-date format.
3182<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3183  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3186   An example is
3188<figure><artwork type="example">
3189  Date: Tue, 15 Nov 1994 08:12:31 GMT
3192   Origin servers &MUST; include a Date header field in all responses,
3193   except in these cases:
3194  <list style="numbers">
3195      <t>If the response status code is 100 (Continue) or 101 (Switching
3196         Protocols), the response &MAY; include a Date header field, at
3197         the server's option.</t>
3199      <t>If the response status code conveys a server error, e.g., 500
3200         (Internal Server Error) or 503 (Service Unavailable), and it is
3201         inconvenient or impossible to generate a valid Date.</t>
3203      <t>If the server does not have a clock that can provide a
3204         reasonable approximation of the current time, its responses
3205         &MUST-NOT; include a Date header field. In this case, the rules
3206         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3207  </list>
3210   A received message that does not have a Date header field &MUST; be
3211   assigned one by the recipient if the message will be cached by that
3212   recipient.
3215   Clients can use the Date header field as well; in order to keep request
3216   messages small, they are advised not to include it when it doesn't convey
3217   any useful information (as it is usually the case for requests that do not
3218   contain a payload).
3221   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3222   time subsequent to the generation of the message. It &SHOULD; represent
3223   the best available approximation of the date and time of message
3224   generation, unless the implementation has no means of generating a
3225   reasonably accurate date and time. In theory, the date ought to
3226   represent the moment just before the payload is generated. In
3227   practice, the date can be generated at any time during the message
3228   origination without affecting its semantic value.
3231<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3233   Some origin server implementations might not have a clock available.
3234   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3235   values to a response, unless these values were associated
3236   with the resource by a system or user with a reliable clock. It &MAY;
3237   assign an Expires value that is known, at or before server
3238   configuration time, to be in the past (this allows "pre-expiration"
3239   of responses without storing separate Expires values for each
3240   resource).
3245<section title="Host" anchor="">
3246  <iref primary="true" item="Host header field" x:for-anchor=""/>
3247  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3248  <x:anchor-alias value="Host"/>
3250   The "Host" header field in a request provides the host and port
3251   information from the target resource's URI, enabling the origin
3252   server to distinguish between resources while servicing requests
3253   for multiple host names on a single IP address.  Since the Host
3254   field-value is critical information for handling a request, it
3255   &SHOULD; be sent as the first header field following the Request-Line.
3257<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3258  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3261   A client &MUST; send a Host header field in all HTTP/1.1 request
3262   messages.  If the target resource's URI includes an authority
3263   component, then the Host field-value &MUST; be identical to that
3264   authority component after excluding any userinfo (<xref target="http.uri"/>).
3265   If the authority component is missing or undefined for the target
3266   resource's URI, then the Host header field &MUST; be sent with an
3267   empty field-value.
3270   For example, a GET request to the origin server for
3271   &lt;; would begin with:
3273<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3274GET /pub/WWW/ HTTP/1.1
3278   The Host header field &MUST; be sent in an HTTP/1.1 request even
3279   if the request-target is in the form of an absolute-URI, since this
3280   allows the Host information to be forwarded through ancient HTTP/1.0
3281   proxies that might not have implemented Host.
3284   When an HTTP/1.1 proxy receives a request with a request-target in
3285   the form of an absolute-URI, the proxy &MUST; ignore the received
3286   Host header field (if any) and instead replace it with the host
3287   information of the request-target.  When a proxy forwards a request,
3288   it &MUST; generate the Host header field based on the received
3289   absolute-URI rather than the received Host.
3292   Since the Host header field acts as an application-level routing
3293   mechanism, it is a frequent target for malware seeking to poison
3294   a shared cache or redirect a request to an unintended server.
3295   An interception proxy is particularly vulnerable if it relies on
3296   the Host header field value for redirecting requests to internal
3297   servers, or for use as a cache key in a shared cache, without
3298   first verifying that the intercepted connection is targeting a
3299   valid IP address for that host.
3302   A server &MUST; respond with a 400 (Bad Request) status code to
3303   any HTTP/1.1 request message that lacks a Host header field and
3304   to any request message that contains more than one Host header field
3305   or a Host header field with an invalid field-value.
3308   See Sections <xref target="" format="counter"/>
3309   and <xref target="" format="counter"/>
3310   for other requirements relating to Host.
3314<section title="TE" anchor="header.te">
3315  <iref primary="true" item="TE header field" x:for-anchor=""/>
3316  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3317  <x:anchor-alias value="TE"/>
3318  <x:anchor-alias value="t-codings"/>
3319  <x:anchor-alias value="te-params"/>
3320  <x:anchor-alias value="te-ext"/>
3322   The "TE" header field indicates what extension transfer-codings
3323   it is willing to accept in the response, and whether or not it is
3324   willing to accept trailer fields in a chunked transfer-coding.
3327   Its value consists of the keyword "trailers" and/or a comma-separated
3328   list of extension transfer-coding names with optional accept
3329   parameters (as described in <xref target="transfer.codings"/>).
3331<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"/>
3332  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3333  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3334  <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> )
3335  <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> ]
3338   The presence of the keyword "trailers" indicates that the client is
3339   willing to accept trailer fields in a chunked transfer-coding, as
3340   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3341   transfer-coding values even though it does not itself represent a
3342   transfer-coding.
3345   Examples of its use are:
3347<figure><artwork type="example">
3348  TE: deflate
3349  TE:
3350  TE: trailers, deflate;q=0.5
3353   The TE header field only applies to the immediate connection.
3354   Therefore, the keyword &MUST; be supplied within a Connection header
3355   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3358   A server tests whether a transfer-coding is acceptable, according to
3359   a TE field, using these rules:
3360  <list style="numbers">
3361    <x:lt>
3362      <t>The "chunked" transfer-coding is always acceptable. If the
3363         keyword "trailers" is listed, the client indicates that it is
3364         willing to accept trailer fields in the chunked response on
3365         behalf of itself and any downstream clients. The implication is
3366         that, if given, the client is stating that either all
3367         downstream clients are willing to accept trailer fields in the
3368         forwarded response, or that it will attempt to buffer the
3369         response on behalf of downstream recipients.
3370      </t><t>
3371         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3372         chunked response such that a client can be assured of buffering
3373         the entire response.</t>
3374    </x:lt>
3375    <x:lt>
3376      <t>If the transfer-coding being tested is one of the transfer-codings
3377         listed in the TE field, then it is acceptable unless it
3378         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3379         qvalue of 0 means "not acceptable".)</t>
3380    </x:lt>
3381    <x:lt>
3382      <t>If multiple transfer-codings are acceptable, then the
3383         acceptable transfer-coding with the highest non-zero qvalue is
3384         preferred.  The "chunked" transfer-coding always has a qvalue
3385         of 1.</t>
3386    </x:lt>
3387  </list>
3390   If the TE field-value is empty or if no TE field is present, the only
3391   transfer-coding is "chunked". A message with no transfer-coding is
3392   always acceptable.
3396<section title="Trailer" anchor="header.trailer">
3397  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3398  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3399  <x:anchor-alias value="Trailer"/>
3401   The "Trailer" header field indicates that the given set of
3402   header fields is present in the trailer of a message encoded with
3403   chunked transfer-coding.
3405<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3406  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3409   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3410   message using chunked transfer-coding with a non-empty trailer. Doing
3411   so allows the recipient to know which header fields to expect in the
3412   trailer.
3415   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3416   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3417   trailer fields in a "chunked" transfer-coding.
3420   Message header fields listed in the Trailer header field &MUST-NOT;
3421   include the following header fields:
3422  <list style="symbols">
3423    <t>Transfer-Encoding</t>
3424    <t>Content-Length</t>
3425    <t>Trailer</t>
3426  </list>
3430<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3431  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3432  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3433  <x:anchor-alias value="Transfer-Encoding"/>
3435   The "Transfer-Encoding" header field indicates what transfer-codings
3436   (if any) have been applied to the message body. It differs from
3437   Content-Encoding (&content-codings;) in that transfer-codings are a property
3438   of the message (and therefore are removed by intermediaries), whereas
3439   content-codings are not.
3441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3442  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3445   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3447<figure><artwork type="example">
3448  Transfer-Encoding: chunked
3451   If multiple encodings have been applied to a representation, the transfer-codings
3452   &MUST; be listed in the order in which they were applied.
3453   Additional information about the encoding parameters &MAY; be provided
3454   by other header fields not defined by this specification.
3457   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3458   header field.
3462<section title="Upgrade" anchor="header.upgrade">
3463  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3464  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3465  <x:anchor-alias value="Upgrade"/>
3467   The "Upgrade" header field allows the client to specify what
3468   additional communication protocols it would like to use, if the server
3469   chooses to switch protocols. Servers can use it to indicate what protocols
3470   they are willing to switch to.
3472<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3473  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3476   For example,
3478<figure><artwork type="example">
3479  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3482   The Upgrade header field is intended to provide a simple mechanism
3483   for transition from HTTP/1.1 to some other, incompatible protocol. It
3484   does so by allowing the client to advertise its desire to use another
3485   protocol, such as a later version of HTTP with a higher major version
3486   number, even though the current request has been made using HTTP/1.1.
3487   This eases the difficult transition between incompatible protocols by
3488   allowing the client to initiate a request in the more commonly
3489   supported protocol while indicating to the server that it would like
3490   to use a "better" protocol if available (where "better" is determined
3491   by the server, possibly according to the nature of the request method
3492   or target resource).
3495   The Upgrade header field only applies to switching application-layer
3496   protocols upon the existing transport-layer connection. Upgrade
3497   cannot be used to insist on a protocol change; its acceptance and use
3498   by the server is optional. The capabilities and nature of the
3499   application-layer communication after the protocol change is entirely
3500   dependent upon the new protocol chosen, although the first action
3501   after changing the protocol &MUST; be a response to the initial HTTP
3502   request containing the Upgrade header field.
3505   The Upgrade header field only applies to the immediate connection.
3506   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3507   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3508   HTTP/1.1 message.
3511   The Upgrade header field cannot be used to indicate a switch to a
3512   protocol on a different connection. For that purpose, it is more
3513   appropriate to use a 3xx redirection response (&status-3xx;).
3516   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3517   Protocols) responses to indicate which protocol(s) are being switched to,
3518   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3519   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3520   response to indicate that they are willing to upgrade to one of the
3521   specified protocols.
3524   This specification only defines the protocol name "HTTP" for use by
3525   the family of Hypertext Transfer Protocols, as defined by the HTTP
3526   version rules of <xref target="http.version"/> and future updates to this
3527   specification. Additional tokens can be registered with IANA using the
3528   registration procedure defined below. 
3531<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3533   The HTTP Upgrade Token Registry defines the name space for product
3534   tokens used to identify protocols in the Upgrade header field.
3535   Each registered token is associated with contact information and
3536   an optional set of specifications that details how the connection
3537   will be processed after it has been upgraded.
3540   Registrations are allowed on a First Come First Served basis as
3541   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3542   specifications need not be IETF documents or be subject to IESG review.
3543   Registrations are subject to the following rules:
3544  <list style="numbers">
3545    <t>A token, once registered, stays registered forever.</t>
3546    <t>The registration &MUST; name a responsible party for the
3547       registration.</t>
3548    <t>The registration &MUST; name a point of contact.</t>
3549    <t>The registration &MAY; name a set of specifications associated with that
3550       token. Such specifications need not be publicly available.</t>
3551    <t>The responsible party &MAY; change the registration at any time.
3552       The IANA will keep a record of all such changes, and make them
3553       available upon request.</t>
3554    <t>The responsible party for the first registration of a "product"
3555       token &MUST; approve later registrations of a "version" token
3556       together with that "product" token before they can be registered.</t>
3557    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3558       for a token. This will normally only be used in the case when a
3559       responsible party cannot be contacted.</t>
3560  </list>
3567<section title="Via" anchor="header.via">
3568  <iref primary="true" item="Via header field" x:for-anchor=""/>
3569  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3570  <x:anchor-alias value="protocol-name"/>
3571  <x:anchor-alias value="protocol-version"/>
3572  <x:anchor-alias value="pseudonym"/>
3573  <x:anchor-alias value="received-by"/>
3574  <x:anchor-alias value="received-protocol"/>
3575  <x:anchor-alias value="Via"/>
3577   The "Via" header field &MUST; be sent by a proxy or gateway to
3578   indicate the intermediate protocols and recipients between the user
3579   agent and the server on requests, and between the origin server and
3580   the client on responses. It is analogous to the "Received" field
3581   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3582   and is intended to be used for tracking message forwards,
3583   avoiding request loops, and identifying the protocol capabilities of
3584   all senders along the request/response chain.
3586<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"/>
3587  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3588                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3589  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3590  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3591  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3592  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3593  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3596   The received-protocol indicates the protocol version of the message
3597   received by the server or client along each segment of the
3598   request/response chain. The received-protocol version is appended to
3599   the Via field value when the message is forwarded so that information
3600   about the protocol capabilities of upstream applications remains
3601   visible to all recipients.
3604   The protocol-name is excluded if and only if it would be "HTTP". The
3605   received-by field is normally the host and optional port number of a
3606   recipient server or client that subsequently forwarded the message.
3607   However, if the real host is considered to be sensitive information,
3608   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3609   be assumed to be the default port of the received-protocol.
3612   Multiple Via field values represent each proxy or gateway that has
3613   forwarded the message. Each recipient &MUST; append its information
3614   such that the end result is ordered according to the sequence of
3615   forwarding applications.
3618   Comments &MAY; be used in the Via header field to identify the software
3619   of each recipient, analogous to the User-Agent and Server header fields.
3620   However, all comments in the Via field are optional and &MAY; be removed
3621   by any recipient prior to forwarding the message.
3624   For example, a request message could be sent from an HTTP/1.0 user
3625   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3626   forward the request to a public proxy at, which completes
3627   the request by forwarding it to the origin server at
3628   The request received by would then have the following
3629   Via header field:
3631<figure><artwork type="example">
3632  Via: 1.0 fred, 1.1 (Apache/1.1)
3635   A proxy or gateway used as a portal through a network firewall
3636   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3637   region unless it is explicitly enabled to do so. If not enabled, the
3638   received-by host of any host behind the firewall &SHOULD; be replaced
3639   by an appropriate pseudonym for that host.
3642   For organizations that have strong privacy requirements for hiding
3643   internal structures, a proxy or gateway &MAY; combine an ordered
3644   subsequence of Via header field entries with identical received-protocol
3645   values into a single such entry. For example,
3647<figure><artwork type="example">
3648  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3651  could be collapsed to
3653<figure><artwork type="example">
3654  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3657   Senders &SHOULD-NOT; combine multiple entries unless they are all
3658   under the same organizational control and the hosts have already been
3659   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3660   have different received-protocol values.
3666<section title="IANA Considerations" anchor="IANA.considerations">
3668<section title="Header Field Registration" anchor="header.field.registration">
3670   The Message Header Field Registry located at <eref target=""/> shall be updated
3671   with the permanent registrations below (see <xref target="RFC3864"/>):
3673<?BEGININC p1-messaging.iana-headers ?>
3674<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3675<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3676   <ttcol>Header Field Name</ttcol>
3677   <ttcol>Protocol</ttcol>
3678   <ttcol>Status</ttcol>
3679   <ttcol>Reference</ttcol>
3681   <c>Connection</c>
3682   <c>http</c>
3683   <c>standard</c>
3684   <c>
3685      <xref target="header.connection"/>
3686   </c>
3687   <c>Content-Length</c>
3688   <c>http</c>
3689   <c>standard</c>
3690   <c>
3691      <xref target="header.content-length"/>
3692   </c>
3693   <c>Date</c>
3694   <c>http</c>
3695   <c>standard</c>
3696   <c>
3697      <xref target=""/>
3698   </c>
3699   <c>Host</c>
3700   <c>http</c>
3701   <c>standard</c>
3702   <c>
3703      <xref target=""/>
3704   </c>
3705   <c>TE</c>
3706   <c>http</c>
3707   <c>standard</c>
3708   <c>
3709      <xref target="header.te"/>
3710   </c>
3711   <c>Trailer</c>
3712   <c>http</c>
3713   <c>standard</c>
3714   <c>
3715      <xref target="header.trailer"/>
3716   </c>
3717   <c>Transfer-Encoding</c>
3718   <c>http</c>
3719   <c>standard</c>
3720   <c>
3721      <xref target="header.transfer-encoding"/>
3722   </c>
3723   <c>Upgrade</c>
3724   <c>http</c>
3725   <c>standard</c>
3726   <c>
3727      <xref target="header.upgrade"/>
3728   </c>
3729   <c>Via</c>
3730   <c>http</c>
3731   <c>standard</c>
3732   <c>
3733      <xref target="header.via"/>
3734   </c>
3737<?ENDINC p1-messaging.iana-headers ?>
3739   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3740   HTTP header field would be in conflict with the use of the "close" connection
3741   option for the "Connection" header field (<xref target="header.connection"/>).
3743<texttable align="left" suppress-title="true">
3744   <ttcol>Header Field Name</ttcol>
3745   <ttcol>Protocol</ttcol>
3746   <ttcol>Status</ttcol>
3747   <ttcol>Reference</ttcol>
3749   <c>Close</c>
3750   <c>http</c>
3751   <c>reserved</c>
3752   <c>
3753      <xref target="header.field.registration"/>
3754   </c>
3757   The change controller is: "IETF ( - Internet Engineering Task Force".
3761<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3763   The entries for the "http" and "https" URI Schemes in the registry located at
3764   <eref target=""/>
3765   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3766   and <xref target="https.uri" format="counter"/> of this document
3767   (see <xref target="RFC4395"/>).
3771<section title="Internet Media Type Registrations" anchor="">
3773   This document serves as the specification for the Internet media types
3774   "message/http" and "application/http". The following is to be registered with
3775   IANA (see <xref target="RFC4288"/>).
3777<section title="Internet Media Type message/http" anchor="">
3778<iref item="Media Type" subitem="message/http" primary="true"/>
3779<iref item="message/http Media Type" primary="true"/>
3781   The message/http type can be used to enclose a single HTTP request or
3782   response message, provided that it obeys the MIME restrictions for all
3783   "message" types regarding line length and encodings.
3786  <list style="hanging" x:indent="12em">
3787    <t hangText="Type name:">
3788      message
3789    </t>
3790    <t hangText="Subtype name:">
3791      http
3792    </t>
3793    <t hangText="Required parameters:">
3794      none
3795    </t>
3796    <t hangText="Optional parameters:">
3797      version, msgtype
3798      <list style="hanging">
3799        <t hangText="version:">
3800          The HTTP-Version number of the enclosed message
3801          (e.g., "1.1"). If not present, the version can be
3802          determined from the first line of the body.
3803        </t>
3804        <t hangText="msgtype:">
3805          The message type &mdash; "request" or "response". If not
3806          present, the type can be determined from the first
3807          line of the body.
3808        </t>
3809      </list>
3810    </t>
3811    <t hangText="Encoding considerations:">
3812      only "7bit", "8bit", or "binary" are permitted
3813    </t>
3814    <t hangText="Security considerations:">
3815      none
3816    </t>
3817    <t hangText="Interoperability considerations:">
3818      none
3819    </t>
3820    <t hangText="Published specification:">
3821      This specification (see <xref target=""/>).
3822    </t>
3823    <t hangText="Applications that use this media type:">
3824    </t>
3825    <t hangText="Additional information:">
3826      <list style="hanging">
3827        <t hangText="Magic number(s):">none</t>
3828        <t hangText="File extension(s):">none</t>
3829        <t hangText="Macintosh file type code(s):">none</t>
3830      </list>
3831    </t>
3832    <t hangText="Person and email address to contact for further information:">
3833      See Authors Section.
3834    </t>
3835    <t hangText="Intended usage:">
3836      COMMON
3837    </t>
3838    <t hangText="Restrictions on usage:">
3839      none
3840    </t>
3841    <t hangText="Author/Change controller:">
3842      IESG
3843    </t>
3844  </list>
3847<section title="Internet Media Type application/http" anchor="">
3848<iref item="Media Type" subitem="application/http" primary="true"/>
3849<iref item="application/http Media Type" primary="true"/>
3851   The application/http type can be used to enclose a pipeline of one or more
3852   HTTP request or response messages (not intermixed).
3855  <list style="hanging" x:indent="12em">
3856    <t hangText="Type name:">
3857      application
3858    </t>
3859    <t hangText="Subtype name:">
3860      http
3861    </t>
3862    <t hangText="Required parameters:">
3863      none
3864    </t>
3865    <t hangText="Optional parameters:">
3866      version, msgtype
3867      <list style="hanging">
3868        <t hangText="version:">
3869          The HTTP-Version number of the enclosed messages
3870          (e.g., "1.1"). If not present, the version can be
3871          determined from the first line of the body.
3872        </t>
3873        <t hangText="msgtype:">
3874          The message type &mdash; "request" or "response". If not
3875          present, the type can be determined from the first
3876          line of the body.
3877        </t>
3878      </list>
3879    </t>
3880    <t hangText="Encoding considerations:">
3881      HTTP messages enclosed by this type
3882      are in "binary" format; use of an appropriate
3883      Content-Transfer-Encoding is required when
3884      transmitted via E-mail.
3885    </t>
3886    <t hangText="Security considerations:">
3887      none
3888    </t>
3889    <t hangText="Interoperability considerations:">
3890      none
3891    </t>
3892    <t hangText="Published specification:">
3893      This specification (see <xref target=""/>).
3894    </t>
3895    <t hangText="Applications that use this media type:">
3896    </t>
3897    <t hangText="Additional information:">
3898      <list style="hanging">
3899        <t hangText="Magic number(s):">none</t>
3900        <t hangText="File extension(s):">none</t>
3901        <t hangText="Macintosh file type code(s):">none</t>
3902      </list>
3903    </t>
3904    <t hangText="Person and email address to contact for further information:">
3905      See Authors Section.
3906    </t>
3907    <t hangText="Intended usage:">
3908      COMMON
3909    </t>
3910    <t hangText="Restrictions on usage:">
3911      none
3912    </t>
3913    <t hangText="Author/Change controller:">
3914      IESG
3915    </t>
3916  </list>
3921<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3923   The registration procedure for HTTP Transfer Codings is now defined by
3924   <xref target="transfer.coding.registry"/> of this document.
3927   The HTTP Transfer Codings Registry located at <eref target=""/>
3928   shall be updated with the registrations below:
3930<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3931   <ttcol>Name</ttcol>
3932   <ttcol>Description</ttcol>
3933   <ttcol>Reference</ttcol>
3934   <c>chunked</c>
3935   <c>Transfer in a series of chunks</c>
3936   <c>
3937      <xref target="chunked.encoding"/>
3938   </c>
3939   <c>compress</c>
3940   <c>UNIX "compress" program method</c>
3941   <c>
3942      <xref target="compress.coding"/>
3943   </c>
3944   <c>deflate</c>
3945   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3946   the "zlib" data format (<xref target="RFC1950"/>)
3947   </c>
3948   <c>
3949      <xref target="deflate.coding"/>
3950   </c>
3951   <c>gzip</c>
3952   <c>Same as GNU zip <xref target="RFC1952"/></c>
3953   <c>
3954      <xref target="gzip.coding"/>
3955   </c>
3959<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3961   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3962   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3963   by <xref target="upgrade.token.registry"/> of this document.
3966   The HTTP Status Code Registry located at <eref target=""/>
3967   shall be updated with the registration below:
3969<texttable align="left" suppress-title="true">
3970   <ttcol>Value</ttcol>
3971   <ttcol>Description</ttcol>
3972   <ttcol>Reference</ttcol>
3974   <c>HTTP</c>
3975   <c>Hypertext Transfer Protocol</c>
3976   <c><xref target="http.version"/> of this specification</c>
3983<section title="Security Considerations" anchor="security.considerations">
3985   This section is meant to inform application developers, information
3986   providers, and users of the security limitations in HTTP/1.1 as
3987   described by this document. The discussion does not include
3988   definitive solutions to the problems revealed, though it does make
3989   some suggestions for reducing security risks.
3992<section title="Personal Information" anchor="personal.information">
3994   HTTP clients are often privy to large amounts of personal information
3995   (e.g., the user's name, location, mail address, passwords, encryption
3996   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3997   leakage of this information.
3998   We very strongly recommend that a convenient interface be provided
3999   for the user to control dissemination of such information, and that
4000   designers and implementors be particularly careful in this area.
4001   History shows that errors in this area often create serious security
4002   and/or privacy problems and generate highly adverse publicity for the
4003   implementor's company.
4007<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
4009   A server is in the position to save personal data about a user's
4010   requests which might identify their reading patterns or subjects of
4011   interest. This information is clearly confidential in nature and its
4012   handling can be constrained by law in certain countries. People using
4013   HTTP to provide data are responsible for ensuring that
4014   such material is not distributed without the permission of any
4015   individuals that are identifiable by the published results.
4019<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
4021   Implementations of HTTP origin servers &SHOULD; be careful to restrict
4022   the documents returned by HTTP requests to be only those that were
4023   intended by the server administrators. If an HTTP server translates
4024   HTTP URIs directly into file system calls, the server &MUST; take
4025   special care not to serve files that were not intended to be
4026   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
4027   other operating systems use ".." as a path component to indicate a
4028   directory level above the current one. On such a system, an HTTP
4029   server &MUST; disallow any such construct in the request-target if it
4030   would otherwise allow access to a resource outside those intended to
4031   be accessible via the HTTP server. Similarly, files intended for
4032   reference only internally to the server (such as access control
4033   files, configuration files, and script code) &MUST; be protected from
4034   inappropriate retrieval, since they might contain sensitive
4035   information. Experience has shown that minor bugs in such HTTP server
4036   implementations have turned into security risks.
4040<section title="DNS-related Attacks" anchor="dns.related.attacks">
4042   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
4043   generally prone to security attacks based on the deliberate misassociation
4044   of IP addresses and DNS names not protected by DNSSec. Clients need to be
4045   cautious in assuming the validity of an IP number/DNS name association unless
4046   the response is protected by DNSSec (<xref target="RFC4033"/>).
4050<section title="Proxies and Caching" anchor="attack.proxies">
4052   By their very nature, HTTP proxies are men-in-the-middle, and
4053   represent an opportunity for man-in-the-middle attacks. Compromise of
4054   the systems on which the proxies run can result in serious security
4055   and privacy problems. Proxies have access to security-related
4056   information, personal information about individual users and
4057   organizations, and proprietary information belonging to users and
4058   content providers. A compromised proxy, or a proxy implemented or
4059   configured without regard to security and privacy considerations,
4060   might be used in the commission of a wide range of potential attacks.
4063   Proxy operators need to protect the systems on which proxies run as
4064   they would protect any system that contains or transports sensitive
4065   information. In particular, log information gathered at proxies often
4066   contains highly sensitive personal information, and/or information
4067   about organizations. Log information needs to be carefully guarded, and
4068   appropriate guidelines for use need to be developed and followed.
4069   (<xref target="abuse.of.server.log.information"/>).
4072   Proxy implementors need to consider the privacy and security
4073   implications of their design and coding decisions, and of the
4074   configuration options they provide to proxy operators (especially the
4075   default configuration).
4078   Users of a proxy need to be aware that proxies are no trustworthier than
4079   the people who run them; HTTP itself cannot solve this problem.
4082   The judicious use of cryptography, when appropriate, might suffice to
4083   protect against a broad range of security and privacy attacks. Such
4084   cryptography is beyond the scope of the HTTP/1.1 specification.
4088<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4090   Because HTTP uses mostly textual, character-delimited fields, attackers can
4091   overflow buffers in implementations, and/or perform a Denial of Service
4092   against implementations that accept fields with unlimited lengths.
4095   To promote interoperability, this specification makes specific
4096   recommendations for size limits on request-targets (<xref target="request-target"/>)
4097   and blocks of header fields (<xref target="header.fields"/>). These are
4098   minimum recommendations, chosen to be supportable even by implementations
4099   with limited resources; it is expected that most implementations will choose
4100   substantially higher limits.
4103   This specification also provides a way for servers to reject messages that
4104   have request-targets that are too long (&status-414;) or request entities
4105   that are too large (&status-4xx;).
4108   Other fields (including but not limited to request methods, response status
4109   phrases, header field-names, and body chunks) &SHOULD; be limited by
4110   implementations carefully, so as to not impede interoperability.
4114<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4116   They exist. They are hard to defend against. Research continues.
4117   Beware.
4122<section title="Acknowledgments" anchor="acks">
4124   This document revision builds on the work that went into
4125   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
4126   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
4127   acknowledgements.
4130  <cref anchor="todoacks">Insert HTTPbis-specific acknowledgements here.</cref>
4134Acknowledgements TODO list
4136- Jeff Hodges ("effective request URI")
4144<references title="Normative References">
4146<reference anchor="ISO-8859-1">
4147  <front>
4148    <title>
4149     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4150    </title>
4151    <author>
4152      <organization>International Organization for Standardization</organization>
4153    </author>
4154    <date year="1998"/>
4155  </front>
4156  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4159<reference anchor="Part2">
4160  <front>
4161    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4162    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4163      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4164      <address><email></email></address>
4165    </author>
4166    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4167      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4168      <address><email></email></address>
4169    </author>
4170    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4171      <organization abbrev="HP">Hewlett-Packard Company</organization>
4172      <address><email></email></address>
4173    </author>
4174    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4175      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4176      <address><email></email></address>
4177    </author>
4178    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4179      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4180      <address><email></email></address>
4181    </author>
4182    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4183      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4184      <address><email></email></address>
4185    </author>
4186    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4187      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4188      <address><email></email></address>
4189    </author>
4190    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4191      <organization abbrev="W3C">World Wide Web Consortium</organization>
4192      <address><email></email></address>
4193    </author>
4194    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4195      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4196      <address><email></email></address>
4197    </author>
4198    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4199  </front>
4200  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4201  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4204<reference anchor="Part3">
4205  <front>
4206    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4207    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4208      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4209      <address><email></email></address>
4210    </author>
4211    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4212      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4213      <address><email></email></address>
4214    </author>
4215    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4216      <organization abbrev="HP">Hewlett-Packard Company</organization>
4217      <address><email></email></address>
4218    </author>
4219    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4220      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4221      <address><email></email></address>
4222    </author>
4223    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4224      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4225      <address><email></email></address>
4226    </author>
4227    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4228      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4229      <address><email></email></address>
4230    </author>
4231    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4232      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4233      <address><email></email></address>
4234    </author>
4235    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4236      <organization abbrev="W3C">World Wide Web Consortium</organization>
4237      <address><email></email></address>
4238    </author>
4239    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4240      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4241      <address><email></email></address>
4242    </author>
4243    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4244  </front>
4245  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4246  <x:source href="p3-payload.xml" basename="p3-payload"/>
4249<reference anchor="Part6">
4250  <front>
4251    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4252    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4253      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4254      <address><email></email></address>
4255    </author>
4256    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4257      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4258      <address><email></email></address>
4259    </author>
4260    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4261      <organization abbrev="HP">Hewlett-Packard Company</organization>
4262      <address><email></email></address>
4263    </author>
4264    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4265      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4266      <address><email></email></address>
4267    </author>
4268    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4269      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4270      <address><email></email></address>
4271    </author>
4272    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4273      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4274      <address><email></email></address>
4275    </author>
4276    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4277      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4278      <address><email></email></address>
4279    </author>
4280    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4281      <organization abbrev="W3C">World Wide Web Consortium</organization>
4282      <address><email></email></address>
4283    </author>
4284    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4285      <address><email></email></address>
4286    </author>
4287    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4288      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4289      <address><email></email></address>
4290    </author>
4291    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4292  </front>
4293  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4294  <x:source href="p6-cache.xml" basename="p6-cache"/>
4297<reference anchor="RFC5234">
4298  <front>
4299    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4300    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4301      <organization>Brandenburg InternetWorking</organization>
4302      <address>
4303        <email></email>
4304      </address> 
4305    </author>
4306    <author initials="P." surname="Overell" fullname="Paul Overell">
4307      <organization>THUS plc.</organization>
4308      <address>
4309        <email></email>
4310      </address>
4311    </author>
4312    <date month="January" year="2008"/>
4313  </front>
4314  <seriesInfo name="STD" value="68"/>
4315  <seriesInfo name="RFC" value="5234"/>
4318<reference anchor="RFC2119">
4319  <front>
4320    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4321    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4322      <organization>Harvard University</organization>
4323      <address><email></email></address>
4324    </author>
4325    <date month="March" year="1997"/>
4326  </front>
4327  <seriesInfo name="BCP" value="14"/>
4328  <seriesInfo name="RFC" value="2119"/>
4331<reference anchor="RFC3986">
4332 <front>
4333  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4334  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4335    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4336    <address>
4337       <email></email>
4338       <uri></uri>
4339    </address>
4340  </author>
4341  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4342    <organization abbrev="Day Software">Day Software</organization>
4343    <address>
4344      <email></email>
4345      <uri></uri>
4346    </address>
4347  </author>
4348  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4349    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4350    <address>
4351      <email></email>
4352      <uri></uri>
4353    </address>
4354  </author>
4355  <date month='January' year='2005'></date>
4356 </front>
4357 <seriesInfo name="STD" value="66"/>
4358 <seriesInfo name="RFC" value="3986"/>
4361<reference anchor="USASCII">
4362  <front>
4363    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4364    <author>
4365      <organization>American National Standards Institute</organization>
4366    </author>
4367    <date year="1986"/>
4368  </front>
4369  <seriesInfo name="ANSI" value="X3.4"/>
4372<reference anchor="RFC1950">
4373  <front>
4374    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4375    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4376      <organization>Aladdin Enterprises</organization>
4377      <address><email></email></address>
4378    </author>
4379    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4380    <date month="May" year="1996"/>
4381  </front>
4382  <seriesInfo name="RFC" value="1950"/>
4383  <annotation>
4384    RFC 1950 is an Informational RFC, thus it might be less stable than
4385    this specification. On the other hand, this downward reference was
4386    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4387    therefore it is unlikely to cause problems in practice. See also
4388    <xref target="BCP97"/>.
4389  </annotation>
4392<reference anchor="RFC1951">
4393  <front>
4394    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4395    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4396      <organization>Aladdin Enterprises</organization>
4397      <address><email></email></address>
4398    </author>
4399    <date month="May" year="1996"/>
4400  </front>
4401  <seriesInfo name="RFC" value="1951"/>
4402  <annotation>
4403    RFC 1951 is an Informational RFC, thus it might be less stable than
4404    this specification. On the other hand, this downward reference was
4405    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4406    therefore it is unlikely to cause problems in practice. See also
4407    <xref target="BCP97"/>.
4408  </annotation>
4411<reference anchor="RFC1952">
4412  <front>
4413    <title>GZIP file format specification version 4.3</title>
4414    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4415      <organization>Aladdin Enterprises</organization>
4416      <address><email></email></address>
4417    </author>
4418    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4419      <address><email></email></address>
4420    </author>
4421    <author initials="M." surname="Adler" fullname="Mark Adler">
4422      <address><email></email></address>
4423    </author>
4424    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4425      <address><email></email></address>
4426    </author>
4427    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4428      <address><email></email></address>
4429    </author>
4430    <date month="May" year="1996"/>
4431  </front>
4432  <seriesInfo name="RFC" value="1952"/>
4433  <annotation>
4434    RFC 1952 is an Informational RFC, thus it might be less stable than
4435    this specification. On the other hand, this downward reference was
4436    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4437    therefore it is unlikely to cause problems in practice. See also
4438    <xref target="BCP97"/>.
4439  </annotation>
4444<references title="Informative References">
4446<reference anchor="Nie1997" target="">
4447  <front>
4448    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4449    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4450    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4451    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4452    <author initials="H." surname="Lie" fullname="H. Lie"/>
4453    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4454    <date year="1997" month="September"/>
4455  </front>
4456  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4459<reference anchor="Pad1995" target="">
4460  <front>
4461    <title>Improving HTTP Latency</title>
4462    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4463    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4464    <date year="1995" month="December"/>
4465  </front>
4466  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4469<reference anchor="RFC1123">
4470  <front>
4471    <title>Requirements for Internet Hosts - Application and Support</title>
4472    <author initials="R." surname="Braden" fullname="Robert Braden">
4473      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4474      <address><email>Braden@ISI.EDU</email></address>
4475    </author>
4476    <date month="October" year="1989"/>
4477  </front>
4478  <seriesInfo name="STD" value="3"/>
4479  <seriesInfo name="RFC" value="1123"/>
4482<reference anchor='RFC1919'>
4483  <front>
4484    <title>Classical versus Transparent IP Proxies</title>
4485    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4486      <address><email></email></address>
4487    </author>
4488    <date year='1996' month='March' />
4489  </front>
4490  <seriesInfo name='RFC' value='1919' />
4493<reference anchor="RFC1945">
4494  <front>
4495    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4496    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4497      <organization>MIT, Laboratory for Computer Science</organization>
4498      <address><email></email></address>
4499    </author>
4500    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4501      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4502      <address><email></email></address>
4503    </author>
4504    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4505      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4506      <address><email></email></address>
4507    </author>
4508    <date month="May" year="1996"/>
4509  </front>
4510  <seriesInfo name="RFC" value="1945"/>
4513<reference anchor="RFC2045">
4514  <front>
4515    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4516    <author initials="N." surname="Freed" fullname="Ned Freed">
4517      <organization>Innosoft International, Inc.</organization>
4518      <address><email></email></address>
4519    </author>
4520    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4521      <organization>First Virtual Holdings</organization>
4522      <address><email></email></address>
4523    </author>
4524    <date month="November" year="1996"/>
4525  </front>
4526  <seriesInfo name="RFC" value="2045"/>
4529<reference anchor="RFC2047">
4530  <front>
4531    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4532    <author initials="K." surname="Moore" fullname="Keith Moore">
4533      <organization>University of Tennessee</organization>
4534      <address><email></email></address>
4535    </author>
4536    <date month="November" year="1996"/>
4537  </front>
4538  <seriesInfo name="RFC" value="2047"/>
4541<reference anchor="RFC2068">
4542  <front>
4543    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4544    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4545      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4546      <address><email></email></address>
4547    </author>
4548    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4549      <organization>MIT Laboratory for Computer Science</organization>
4550      <address><email></email></address>
4551    </author>
4552    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4553      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4554      <address><email></email></address>
4555    </author>
4556    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4557      <organization>MIT Laboratory for Computer Science</organization>
4558      <address><email></email></address>
4559    </author>
4560    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4561      <organization>MIT Laboratory for Computer Science</organization>
4562      <address><email></email></address>
4563    </author>
4564    <date month="January" year="1997"/>
4565  </front>
4566  <seriesInfo name="RFC" value="2068"/>
4569<reference anchor="RFC2145">
4570  <front>
4571    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4572    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4573      <organization>Western Research Laboratory</organization>
4574      <address><email></email></address>
4575    </author>
4576    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4577      <organization>Department of Information and Computer Science</organization>
4578      <address><email></email></address>
4579    </author>
4580    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4581      <organization>MIT Laboratory for Computer Science</organization>
4582      <address><email></email></address>
4583    </author>
4584    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4585      <organization>W3 Consortium</organization>
4586      <address><email></email></address>
4587    </author>
4588    <date month="May" year="1997"/>
4589  </front>
4590  <seriesInfo name="RFC" value="2145"/>
4593<reference anchor="RFC2616">
4594  <front>
4595    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4596    <author initials="R." surname="Fielding" fullname="R. Fielding">
4597      <organization>University of California, Irvine</organization>
4598      <address><email></email></address>
4599    </author>
4600    <author initials="J." surname="Gettys" fullname="J. Gettys">
4601      <organization>W3C</organization>
4602      <address><email></email></address>
4603    </author>
4604    <author initials="J." surname="Mogul" fullname="J. Mogul">
4605      <organization>Compaq Computer Corporation</organization>
4606      <address><email></email></address>
4607    </author>
4608    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4609      <organization>MIT Laboratory for Computer Science</organization>
4610      <address><email></email></address>
4611    </author>
4612    <author initials="L." surname="Masinter" fullname="L. Masinter">
4613      <organization>Xerox Corporation</organization>
4614      <address><email></email></address>
4615    </author>
4616    <author initials="P." surname="Leach" fullname="P. Leach">
4617      <organization>Microsoft Corporation</organization>
4618      <address><email></email></address>
4619    </author>
4620    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4621      <organization>W3C</organization>
4622      <address><email></email></address>
4623    </author>
4624    <date month="June" year="1999"/>
4625  </front>
4626  <seriesInfo name="RFC" value="2616"/>
4629<reference anchor='RFC2817'>
4630  <front>
4631    <title>Upgrading to TLS Within HTTP/1.1</title>
4632    <author initials='R.' surname='Khare' fullname='R. Khare'>
4633      <organization>4K Associates / UC Irvine</organization>
4634      <address><email></email></address>
4635    </author>
4636    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4637      <organization>Agranat Systems, Inc.</organization>
4638      <address><email></email></address>
4639    </author>
4640    <date year='2000' month='May' />
4641  </front>
4642  <seriesInfo name='RFC' value='2817' />
4645<reference anchor='RFC2818'>
4646  <front>
4647    <title>HTTP Over TLS</title>
4648    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4649      <organization>RTFM, Inc.</organization>
4650      <address><email></email></address>
4651    </author>
4652    <date year='2000' month='May' />
4653  </front>
4654  <seriesInfo name='RFC' value='2818' />
4657<reference anchor='RFC2965'>
4658  <front>
4659    <title>HTTP State Management Mechanism</title>
4660    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4661      <organization>Bell Laboratories, Lucent Technologies</organization>
4662      <address><email></email></address>
4663    </author>
4664    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4665      <organization>, Inc.</organization>
4666      <address><email></email></address>
4667    </author>
4668    <date year='2000' month='October' />
4669  </front>
4670  <seriesInfo name='RFC' value='2965' />
4673<reference anchor='RFC3040'>
4674  <front>
4675    <title>Internet Web Replication and Caching Taxonomy</title>
4676    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4677      <organization>Equinix, Inc.</organization>
4678    </author>
4679    <author initials='I.' surname='Melve' fullname='I. Melve'>
4680      <organization>UNINETT</organization>
4681    </author>
4682    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4683      <organization>CacheFlow Inc.</organization>
4684    </author>
4685    <date year='2001' month='January' />
4686  </front>
4687  <seriesInfo name='RFC' value='3040' />
4690<reference anchor='RFC3864'>
4691  <front>
4692    <title>Registration Procedures for Message Header Fields</title>
4693    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4694      <organization>Nine by Nine</organization>
4695      <address><email></email></address>
4696    </author>
4697    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4698      <organization>BEA Systems</organization>
4699      <address><email></email></address>
4700    </author>
4701    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4702      <organization>HP Labs</organization>
4703      <address><email></email></address>
4704    </author>
4705    <date year='2004' month='September' />
4706  </front>
4707  <seriesInfo name='BCP' value='90' />
4708  <seriesInfo name='RFC' value='3864' />
4711<reference anchor='RFC4033'>
4712  <front>
4713    <title>DNS Security Introduction and Requirements</title>
4714    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4715    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4716    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4717    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4718    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4719    <date year='2005' month='March' />
4720  </front>
4721  <seriesInfo name='RFC' value='4033' />
4724<reference anchor="RFC4288">
4725  <front>
4726    <title>Media Type Specifications and Registration Procedures</title>
4727    <author initials="N." surname="Freed" fullname="N. Freed">
4728      <organization>Sun Microsystems</organization>
4729      <address>
4730        <email></email>
4731      </address>
4732    </author>
4733    <author initials="J." surname="Klensin" fullname="J. Klensin">
4734      <address>
4735        <email></email>
4736      </address>
4737    </author>
4738    <date year="2005" month="December"/>
4739  </front>
4740  <seriesInfo name="BCP" value="13"/>
4741  <seriesInfo name="RFC" value="4288"/>
4744<reference anchor='RFC4395'>
4745  <front>
4746    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4747    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4748      <organization>AT&amp;T Laboratories</organization>
4749      <address>
4750        <email></email>
4751      </address>
4752    </author>
4753    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4754      <organization>Qualcomm, Inc.</organization>
4755      <address>
4756        <email></email>
4757      </address>
4758    </author>
4759    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4760      <organization>Adobe Systems</organization>
4761      <address>
4762        <email></email>
4763      </address>
4764    </author>
4765    <date year='2006' month='February' />
4766  </front>
4767  <seriesInfo name='BCP' value='115' />
4768  <seriesInfo name='RFC' value='4395' />
4771<reference anchor='RFC4559'>
4772  <front>
4773    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4774    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4775    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4776    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4777    <date year='2006' month='June' />
4778  </front>
4779  <seriesInfo name='RFC' value='4559' />
4782<reference anchor='RFC5226'>
4783  <front>
4784    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4785    <author initials='T.' surname='Narten' fullname='T. Narten'>
4786      <organization>IBM</organization>
4787      <address><email></email></address>
4788    </author>
4789    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4790      <organization>Google</organization>
4791      <address><email></email></address>
4792    </author>
4793    <date year='2008' month='May' />
4794  </front>
4795  <seriesInfo name='BCP' value='26' />
4796  <seriesInfo name='RFC' value='5226' />
4799<reference anchor="RFC5322">
4800  <front>
4801    <title>Internet Message Format</title>
4802    <author initials="P." surname="Resnick" fullname="P. Resnick">
4803      <organization>Qualcomm Incorporated</organization>
4804    </author>
4805    <date year="2008" month="October"/>
4806  </front>
4807  <seriesInfo name="RFC" value="5322"/>
4810<reference anchor="RFC6265">
4811  <front>
4812    <title>HTTP State Management Mechanism</title>
4813    <author initials="A." surname="Barth" fullname="Adam Barth">
4814      <organization abbrev="U.C. Berkeley">
4815        University of California, Berkeley
4816      </organization>
4817      <address><email></email></address>
4818    </author>
4819    <date year="2011" month="April" />
4820  </front>
4821  <seriesInfo name="RFC" value="6265"/>
4824<reference anchor='BCP97'>
4825  <front>
4826    <title>Handling Normative References to Standards-Track Documents</title>
4827    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4828      <address>
4829        <email></email>
4830      </address>
4831    </author>
4832    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4833      <organization>MIT</organization>
4834      <address>
4835        <email></email>
4836      </address>
4837    </author>
4838    <date year='2007' month='June' />
4839  </front>
4840  <seriesInfo name='BCP' value='97' />
4841  <seriesInfo name='RFC' value='4897' />
4844<reference anchor="Kri2001" target="">
4845  <front>
4846    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4847    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4848    <date year="2001" month="November"/>
4849  </front>
4850  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4853<reference anchor="Spe" target="">
4854  <front>
4855    <title>Analysis of HTTP Performance Problems</title>
4856    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4857    <date/>
4858  </front>
4861<reference anchor="Tou1998" target="">
4862  <front>
4863  <title>Analysis of HTTP Performance</title>
4864  <author initials="J." surname="Touch" fullname="Joe Touch">
4865    <organization>USC/Information Sciences Institute</organization>
4866    <address><email></email></address>
4867  </author>
4868  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4869    <organization>USC/Information Sciences Institute</organization>
4870    <address><email></email></address>
4871  </author>
4872  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4873    <organization>USC/Information Sciences Institute</organization>
4874    <address><email></email></address>
4875  </author>
4876  <date year="1998" month="Aug"/>
4877  </front>
4878  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4879  <annotation>(original report dated Aug. 1996)</annotation>
4885<section title="HTTP Version History" anchor="compatibility">
4887   HTTP has been in use by the World-Wide Web global information initiative
4888   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4889   was a simple protocol for hypertext data transfer across the Internet
4890   with only a single request method (GET) and no metadata.
4891   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4892   methods and MIME-like messaging that could include metadata about the data
4893   transferred and modifiers on the request/response semantics. However,
4894   HTTP/1.0 did not sufficiently take into consideration the effects of
4895   hierarchical proxies, caching, the need for persistent connections, or
4896   name-based virtual hosts. The proliferation of incompletely-implemented
4897   applications calling themselves "HTTP/1.0" further necessitated a
4898   protocol version change in order for two communicating applications
4899   to determine each other's true capabilities.
4902   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4903   requirements that enable reliable implementations, adding only
4904   those new features that will either be safely ignored by an HTTP/1.0
4905   recipient or only sent when communicating with a party advertising
4906   compliance with HTTP/1.1.
4909   It is beyond the scope of a protocol specification to mandate
4910   compliance with previous versions. HTTP/1.1 was deliberately
4911   designed, however, to make supporting previous versions easy.
4912   We would expect a general-purpose HTTP/1.1 server to understand
4913   any valid request in the format of HTTP/1.0 and respond appropriately
4914   with an HTTP/1.1 message that only uses features understood (or
4915   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4916   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4919   Since HTTP/0.9 did not support header fields in a request,
4920   there is no mechanism for it to support name-based virtual
4921   hosts (selection of resource by inspection of the Host header
4922   field).  Any server that implements name-based virtual hosts
4923   ought to disable support for HTTP/0.9.  Most requests that
4924   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4925   requests wherein a buggy client failed to properly encode
4926   linear whitespace found in a URI reference and placed in
4927   the request-target.
4930<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4932   This section summarizes major differences between versions HTTP/1.0
4933   and HTTP/1.1.
4936<section title="Multi-homed Web Servers" anchor="">
4938   The requirements that clients and servers support the Host header
4939   field (<xref target=""/>), report an error if it is
4940   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4941   are among the most important changes defined by HTTP/1.1.
4944   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4945   addresses and servers; there was no other established mechanism for
4946   distinguishing the intended server of a request than the IP address
4947   to which that request was directed. The Host header field was
4948   introduced during the development of HTTP/1.1 and, though it was
4949   quickly implemented by most HTTP/1.0 browsers, additional requirements
4950   were placed on all HTTP/1.1 requests in order to ensure complete
4951   adoption.  At the time of this writing, most HTTP-based services
4952   are dependent upon the Host header field for targeting requests.
4956<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4958   For most implementations of HTTP/1.0, each connection is established
4959   by the client prior to the request and closed by the server after
4960   sending the response. However, some implementations implement the
4961   Keep-Alive version of persistent connections described in
4962   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4965   Some clients and servers might wish to be compatible with some
4966   previous implementations of persistent connections in HTTP/1.0
4967   clients and servers. Persistent connections in HTTP/1.0 are
4968   explicitly negotiated as they are not the default behavior. HTTP/1.0
4969   experimental implementations of persistent connections are faulty,
4970   and the new facilities in HTTP/1.1 are designed to rectify these
4971   problems. The problem was that some existing HTTP/1.0 clients might
4972   send Keep-Alive to a proxy server that doesn't understand
4973   Connection, which would then erroneously forward it to the next
4974   inbound server, which would establish the Keep-Alive connection and
4975   result in a hung HTTP/1.0 proxy waiting for the close on the
4976   response. The result is that HTTP/1.0 clients must be prevented from
4977   using Keep-Alive when talking to proxies.
4980   However, talking to proxies is the most important use of persistent
4981   connections, so that prohibition is clearly unacceptable. Therefore,
4982   we need some other mechanism for indicating a persistent connection
4983   is desired, which is safe to use even when talking to an old proxy
4984   that ignores Connection. Persistent connections are the default for
4985   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4986   declaring non-persistence. See <xref target="header.connection"/>.
4991<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4993  Empty list elements in list productions have been deprecated.
4994  (<xref target="notation.abnf"/>)
4997  Rules about implicit linear whitespace between certain grammar productions
4998  have been removed; now it's only allowed when specifically pointed out
4999  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5000  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5001  Non-ASCII content in header fields and reason phrase has been obsoleted and
5002  made opaque (the TEXT rule was removed)
5003  (<xref target="basic.rules"/>)
5006  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5007  sensitive. Restrict the version numbers to be single digits due to the fact
5008  that implementations are known to handle multi-digit version numbers
5009  incorrectly.
5010  (<xref target="http.version"/>)
5013  Require that invalid whitespace around field-names be rejected.
5014  (<xref target="header.fields"/>)
5017  Require recipients to handle bogus Content-Length header fields as errors.
5018  (<xref target="message.body"/>)
5021  Remove reference to non-existent identity transfer-coding value tokens.
5022  (Sections <xref format="counter" target="message.body"/> and
5023  <xref format="counter" target="transfer.codings"/>)
5026  Update use of abs_path production from RFC 1808 to the path-absolute + query
5027  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5028  request method only.
5029  (<xref target="request-target"/>)
5032  Clarification that the chunk length does not include the count of the octets
5033  in the chunk header and trailer. Furthermore disallowed line folding
5034  in chunk extensions.
5035  (<xref target="chunked.encoding"/>)
5038  Remove hard limit of two connections per server.
5039  (<xref target="persistent.practical"/>)
5042  Change ABNF productions for header fields to only define the field value.
5043  (<xref target="header.field.definitions"/>)
5046  Clarify exactly when close connection options must be sent.
5047  (<xref target="header.connection"/>)
5050  Define the semantics of the "Upgrade" header field in responses other than
5051  101 (this was incorporated from <xref target="RFC2817"/>).
5052  (<xref target="header.upgrade"/>)
5057<?BEGININC p1-messaging.abnf-appendix ?>
5058<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5060<artwork type="abnf" name="p1-messaging.parsed-abnf">
5061<x:ref>BWS</x:ref> = OWS
5063<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5064<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5065 connection-token ] )
5066<x:ref>Content-Length</x:ref> = 1*DIGIT
5068<x:ref>Date</x:ref> = HTTP-date
5070<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5072<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5073<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5074<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5075<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5076 ]
5077<x:ref>Host</x:ref> = uri-host [ ":" port ]
5079<x:ref>Method</x:ref> = token
5081<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5083<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5084<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5085<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5086<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5087<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5089<x:ref>Status-Code</x:ref> = 3DIGIT
5090<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5092<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5093<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5094<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5095 transfer-coding ] )
5097<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5098<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5100<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5101 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5102 )
5104<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5105<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5106<x:ref>attribute</x:ref> = token
5107<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5109<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5110<x:ref>chunk-data</x:ref> = 1*OCTET
5111<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5112<x:ref>chunk-ext-name</x:ref> = token
5113<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5114<x:ref>chunk-size</x:ref> = 1*HEXDIG
5115<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5116<x:ref>connection-token</x:ref> = token
5117<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5118 / %x2A-5B ; '*'-'['
5119 / %x5D-7E ; ']'-'~'
5120 / obs-text
5122<x:ref>date1</x:ref> = day SP month SP year
5123<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5124<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5125<x:ref>day</x:ref> = 2DIGIT
5126<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5127 / %x54.75.65 ; Tue
5128 / %x57.65.64 ; Wed
5129 / %x54.68.75 ; Thu
5130 / %x46.72.69 ; Fri
5131 / %x53.61.74 ; Sat
5132 / %x53.75.6E ; Sun
5133<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5134 / %x54. ; Tuesday
5135 / %x57.65.64.6E. ; Wednesday
5136 / %x54. ; Thursday
5137 / %x46. ; Friday
5138 / %x53. ; Saturday
5139 / %x53.75.6E.64.61.79 ; Sunday
5141<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5142<x:ref>field-name</x:ref> = token
5143<x:ref>field-value</x:ref> = *( field-content / OWS )
5145<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5146<x:ref>hour</x:ref> = 2DIGIT
5147<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5148<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5150<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5152<x:ref>message-body</x:ref> = *OCTET
5153<x:ref>minute</x:ref> = 2DIGIT
5154<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5155 / %x46.65.62 ; Feb
5156 / %x4D.61.72 ; Mar
5157 / %x41.70.72 ; Apr
5158 / %x4D.61.79 ; May
5159 / %x4A.75.6E ; Jun
5160 / %x4A.75.6C ; Jul
5161 / %x41.75.67 ; Aug
5162 / %x53.65.70 ; Sep
5163 / %x4F.63.74 ; Oct
5164 / %x4E.6F.76 ; Nov
5165 / %x44.65.63 ; Dec
5167<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5168<x:ref>obs-fold</x:ref> = CRLF
5169<x:ref>obs-text</x:ref> = %x80-FF
5171<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5172<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5173<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5174<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5175<x:ref>product</x:ref> = token [ "/" product-version ]
5176<x:ref>product-version</x:ref> = token
5177<x:ref>protocol-name</x:ref> = token
5178<x:ref>protocol-version</x:ref> = token
5179<x:ref>pseudonym</x:ref> = token
5181<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5182 / %x5D-7E ; ']'-'~'
5183 / obs-text
5184<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5185 / %x5D-7E ; ']'-'~'
5186 / obs-text
5187<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5188<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5189<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5190<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5191<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5192<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5194<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5195<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5196<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5197<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5198 / authority
5199<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5200<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5202<x:ref>second</x:ref> = 2DIGIT
5203<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5204 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5205<x:ref>start-line</x:ref> = Request-Line / Status-Line
5207<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5208<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5209 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5210<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5211<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5212<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5213<x:ref>token</x:ref> = 1*tchar
5214<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5215<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5216 transfer-extension
5217<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5218<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5220<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5222<x:ref>value</x:ref> = word
5224<x:ref>word</x:ref> = token / quoted-string
5226<x:ref>year</x:ref> = 4DIGIT
5229<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5230; Chunked-Body defined but not used
5231; Connection defined but not used
5232; Content-Length defined but not used
5233; Date defined but not used
5234; HTTP-message defined but not used
5235; Host defined but not used
5236; Request defined but not used
5237; Response defined but not used
5238; TE defined but not used
5239; Trailer defined but not used
5240; Transfer-Encoding defined but not used
5241; URI-reference defined but not used
5242; Upgrade defined but not used
5243; Via defined but not used
5244; http-URI defined but not used
5245; https-URI defined but not used
5246; partial-URI defined but not used
5247; special defined but not used
5249<?ENDINC p1-messaging.abnf-appendix ?>
5251<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5253<section title="Since RFC 2616">
5255  Extracted relevant partitions from <xref target="RFC2616"/>.
5259<section title="Since draft-ietf-httpbis-p1-messaging-00">
5261  Closed issues:
5262  <list style="symbols">
5263    <t>
5264      <eref target=""/>:
5265      "HTTP Version should be case sensitive"
5266      (<eref target=""/>)
5267    </t>
5268    <t>
5269      <eref target=""/>:
5270      "'unsafe' characters"
5271      (<eref target=""/>)
5272    </t>
5273    <t>
5274      <eref target=""/>:
5275      "Chunk Size Definition"
5276      (<eref target=""/>)
5277    </t>
5278    <t>
5279      <eref target=""/>:
5280      "Message Length"
5281      (<eref target=""/>)
5282    </t>
5283    <t>
5284      <eref target=""/>:
5285      "Media Type Registrations"
5286      (<eref target=""/>)
5287    </t>
5288    <t>
5289      <eref target=""/>:
5290      "URI includes query"
5291      (<eref target=""/>)
5292    </t>
5293    <t>
5294      <eref target=""/>:
5295      "No close on 1xx responses"
5296      (<eref target=""/>)
5297    </t>
5298    <t>
5299      <eref target=""/>:
5300      "Remove 'identity' token references"
5301      (<eref target=""/>)
5302    </t>
5303    <t>
5304      <eref target=""/>:
5305      "Import query BNF"
5306    </t>
5307    <t>
5308      <eref target=""/>:
5309      "qdtext BNF"
5310    </t>
5311    <t>
5312      <eref target=""/>:
5313      "Normative and Informative references"
5314    </t>
5315    <t>
5316      <eref target=""/>:
5317      "RFC2606 Compliance"
5318    </t>
5319    <t>
5320      <eref target=""/>:
5321      "RFC977 reference"
5322    </t>
5323    <t>
5324      <eref target=""/>:
5325      "RFC1700 references"
5326    </t>
5327    <t>
5328      <eref target=""/>:
5329      "inconsistency in date format explanation"
5330    </t>
5331    <t>
5332      <eref target=""/>:
5333      "Date reference typo"
5334    </t>
5335    <t>
5336      <eref target=""/>:
5337      "Informative references"
5338    </t>
5339    <t>
5340      <eref target=""/>:
5341      "ISO-8859-1 Reference"
5342    </t>
5343    <t>
5344      <eref target=""/>:
5345      "Normative up-to-date references"
5346    </t>
5347  </list>
5350  Other changes:
5351  <list style="symbols">
5352    <t>
5353      Update media type registrations to use RFC4288 template.
5354    </t>
5355    <t>
5356      Use names of RFC4234 core rules DQUOTE and WSP,
5357      fix broken ABNF for chunk-data
5358      (work in progress on <eref target=""/>)
5359    </t>
5360  </list>
5364<section title="Since draft-ietf-httpbis-p1-messaging-01">
5366  Closed issues:
5367  <list style="symbols">
5368    <t>
5369      <eref target=""/>:
5370      "Bodies on GET (and other) requests"
5371    </t>
5372    <t>
5373      <eref target=""/>:
5374      "Updating to RFC4288"
5375    </t>
5376    <t>
5377      <eref target=""/>:
5378      "Status Code and Reason Phrase"
5379    </t>
5380    <t>
5381      <eref target=""/>:
5382      "rel_path not used"
5383    </t>
5384  </list>
5387  Ongoing work on ABNF conversion (<eref target=""/>):
5388  <list style="symbols">
5389    <t>
5390      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5391      "trailer-part").
5392    </t>
5393    <t>
5394      Avoid underscore character in rule names ("http_URL" ->
5395      "http-URL", "abs_path" -> "path-absolute").
5396    </t>
5397    <t>
5398      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5399      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5400      have to be updated when switching over to RFC3986.
5401    </t>
5402    <t>
5403      Synchronize core rules with RFC5234.
5404    </t>
5405    <t>
5406      Get rid of prose rules that span multiple lines.
5407    </t>
5408    <t>
5409      Get rid of unused rules LOALPHA and UPALPHA.
5410    </t>
5411    <t>
5412      Move "Product Tokens" section (back) into Part 1, as "token" is used
5413      in the definition of the Upgrade header field.
5414    </t>
5415    <t>
5416      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5417    </t>
5418    <t>
5419      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5420    </t>
5421  </list>
5425<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5427  Closed issues:
5428  <list style="symbols">
5429    <t>
5430      <eref target=""/>:
5431      "HTTP-date vs. rfc1123-date"
5432    </t>
5433    <t>
5434      <eref target=""/>:
5435      "WS in quoted-pair"
5436    </t>
5437  </list>
5440  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5441  <list style="symbols">
5442    <t>
5443      Reference RFC 3984, and update header field registrations for headers defined
5444      in this document.
5445    </t>
5446  </list>
5449  Ongoing work on ABNF conversion (<eref target=""/>):
5450  <list style="symbols">
5451    <t>
5452      Replace string literals when the string really is case-sensitive (HTTP-Version).
5453    </t>
5454  </list>
5458<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5460  Closed issues:
5461  <list style="symbols">
5462    <t>
5463      <eref target=""/>:
5464      "Connection closing"
5465    </t>
5466    <t>
5467      <eref target=""/>:
5468      "Move registrations and registry information to IANA Considerations"
5469    </t>
5470    <t>
5471      <eref target=""/>:
5472      "need new URL for PAD1995 reference"
5473    </t>
5474    <t>
5475      <eref target=""/>:
5476      "IANA Considerations: update HTTP URI scheme registration"
5477    </t>
5478    <t>
5479      <eref target=""/>:
5480      "Cite HTTPS URI scheme definition"
5481    </t>
5482    <t>
5483      <eref target=""/>:
5484      "List-type headers vs Set-Cookie"
5485    </t>
5486  </list>
5489  Ongoing work on ABNF conversion (<eref target=""/>):
5490  <list style="symbols">
5491    <t>
5492      Replace string literals when the string really is case-sensitive (HTTP-Date).
5493    </t>
5494    <t>
5495      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5496    </t>
5497  </list>
5501<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5503  Closed issues:
5504  <list style="symbols">
5505    <t>
5506      <eref target=""/>:
5507      "Out-of-date reference for URIs"
5508    </t>
5509    <t>
5510      <eref target=""/>:
5511      "RFC 2822 is updated by RFC 5322"
5512    </t>
5513  </list>
5516  Ongoing work on ABNF conversion (<eref target=""/>):
5517  <list style="symbols">
5518    <t>
5519      Use "/" instead of "|" for alternatives.
5520    </t>
5521    <t>
5522      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5523    </t>
5524    <t>
5525      Only reference RFC 5234's core rules.
5526    </t>
5527    <t>
5528      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5529      whitespace ("OWS") and required whitespace ("RWS").
5530    </t>
5531    <t>
5532      Rewrite ABNFs to spell out whitespace rules, factor out
5533      header field value format definitions.
5534    </t>
5535  </list>
5539<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5541  Closed issues:
5542  <list style="symbols">
5543    <t>
5544      <eref target=""/>:
5545      "Header LWS"
5546    </t>
5547    <t>
5548      <eref target=""/>:
5549      "Sort 1.3 Terminology"
5550    </t>
5551    <t>
5552      <eref target=""/>:
5553      "RFC2047 encoded words"
5554    </t>
5555    <t>
5556      <eref target=""/>:
5557      "Character Encodings in TEXT"
5558    </t>
5559    <t>
5560      <eref target=""/>:
5561      "Line Folding"
5562    </t>
5563    <t>
5564      <eref target=""/>:
5565      "OPTIONS * and proxies"
5566    </t>
5567    <t>
5568      <eref target=""/>:
5569      "Reason-Phrase BNF"
5570    </t>
5571    <t>
5572      <eref target=""/>:
5573      "Use of TEXT"
5574    </t>
5575    <t>
5576      <eref target=""/>:
5577      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5578    </t>
5579    <t>
5580      <eref target=""/>:
5581      "RFC822 reference left in discussion of date formats"
5582    </t>
5583  </list>
5586  Final work on ABNF conversion (<eref target=""/>):
5587  <list style="symbols">
5588    <t>
5589      Rewrite definition of list rules, deprecate empty list elements.
5590    </t>
5591    <t>
5592      Add appendix containing collected and expanded ABNF.
5593    </t>
5594  </list>
5597  Other changes:
5598  <list style="symbols">
5599    <t>
5600      Rewrite introduction; add mostly new Architecture Section.
5601    </t>
5602    <t>
5603      Move definition of quality values from Part 3 into Part 1;
5604      make TE request header field grammar independent of accept-params (defined in Part 3).
5605    </t>
5606  </list>
5610<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5612  Closed issues:
5613  <list style="symbols">
5614    <t>
5615      <eref target=""/>:
5616      "base for numeric protocol elements"
5617    </t>
5618    <t>
5619      <eref target=""/>:
5620      "comment ABNF"
5621    </t>
5622  </list>
5625  Partly resolved issues:
5626  <list style="symbols">
5627    <t>
5628      <eref target=""/>:
5629      "205 Bodies" (took out language that implied that there might be
5630      methods for which a request body MUST NOT be included)
5631    </t>
5632    <t>
5633      <eref target=""/>:
5634      "editorial improvements around HTTP-date"
5635    </t>
5636  </list>
5640<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5642  Closed issues:
5643  <list style="symbols">
5644    <t>
5645      <eref target=""/>:
5646      "Repeating single-value headers"
5647    </t>
5648    <t>
5649      <eref target=""/>:
5650      "increase connection limit"
5651    </t>
5652    <t>
5653      <eref target=""/>:
5654      "IP addresses in URLs"
5655    </t>
5656    <t>
5657      <eref target=""/>:
5658      "take over HTTP Upgrade Token Registry"
5659    </t>
5660    <t>
5661      <eref target=""/>:
5662      "CR and LF in chunk extension values"
5663    </t>
5664    <t>
5665      <eref target=""/>:
5666      "HTTP/0.9 support"
5667    </t>
5668    <t>
5669      <eref target=""/>:
5670      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5671    </t>
5672    <t>
5673      <eref target=""/>:
5674      "move definitions of gzip/deflate/compress to part 1"
5675    </t>
5676    <t>
5677      <eref target=""/>:
5678      "disallow control characters in quoted-pair"
5679    </t>
5680  </list>
5683  Partly resolved issues:
5684  <list style="symbols">
5685    <t>
5686      <eref target=""/>:
5687      "update IANA requirements wrt Transfer-Coding values" (add the
5688      IANA Considerations subsection)
5689    </t>
5690  </list>
5694<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5696  Closed issues:
5697  <list style="symbols">
5698    <t>
5699      <eref target=""/>:
5700      "header parsing, treatment of leading and trailing OWS"
5701    </t>
5702  </list>
5705  Partly resolved issues:
5706  <list style="symbols">
5707    <t>
5708      <eref target=""/>:
5709      "Placement of 13.5.1 and 13.5.2"
5710    </t>
5711    <t>
5712      <eref target=""/>:
5713      "use of term "word" when talking about header structure"
5714    </t>
5715  </list>
5719<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5721  Closed issues:
5722  <list style="symbols">
5723    <t>
5724      <eref target=""/>:
5725      "Clarification of the term 'deflate'"
5726    </t>
5727    <t>
5728      <eref target=""/>:
5729      "OPTIONS * and proxies"
5730    </t>
5731    <t>
5732      <eref target=""/>:
5733      "MIME-Version not listed in P1, general header fields"
5734    </t>
5735    <t>
5736      <eref target=""/>:
5737      "IANA registry for content/transfer encodings"
5738    </t>
5739    <t>
5740      <eref target=""/>:
5741      "Case-sensitivity of HTTP-date"
5742    </t>
5743    <t>
5744      <eref target=""/>:
5745      "use of term "word" when talking about header structure"
5746    </t>
5747  </list>
5750  Partly resolved issues:
5751  <list style="symbols">
5752    <t>
5753      <eref target=""/>:
5754      "Term for the requested resource's URI"
5755    </t>
5756  </list>
5760<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5762  Closed issues:
5763  <list style="symbols">
5764    <t>
5765      <eref target=""/>:
5766      "Connection Closing"
5767    </t>
5768    <t>
5769      <eref target=""/>:
5770      "Delimiting messages with multipart/byteranges"
5771    </t>
5772    <t>
5773      <eref target=""/>:
5774      "Handling multiple Content-Length headers"
5775    </t>
5776    <t>
5777      <eref target=""/>:
5778      "Clarify entity / representation / variant terminology"
5779    </t>
5780    <t>
5781      <eref target=""/>:
5782      "consider removing the 'changes from 2068' sections"
5783    </t>
5784  </list>
5787  Partly resolved issues:
5788  <list style="symbols">
5789    <t>
5790      <eref target=""/>:
5791      "HTTP(s) URI scheme definitions"
5792    </t>
5793  </list>
5797<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5799  Closed issues:
5800  <list style="symbols">
5801    <t>
5802      <eref target=""/>:
5803      "Trailer requirements"
5804    </t>
5805    <t>
5806      <eref target=""/>:
5807      "Text about clock requirement for caches belongs in p6"
5808    </t>
5809    <t>
5810      <eref target=""/>:
5811      "effective request URI: handling of missing host in HTTP/1.0"
5812    </t>
5813    <t>
5814      <eref target=""/>:
5815      "confusing Date requirements for clients"
5816    </t>
5817  </list>
5820  Partly resolved issues:
5821  <list style="symbols">
5822    <t>
5823      <eref target=""/>:
5824      "Handling multiple Content-Length headers"
5825    </t>
5826  </list>
5830<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5832  Closed issues:
5833  <list style="symbols">
5834    <t>
5835      <eref target=""/>:
5836      "RFC2145 Normative"
5837    </t>
5838    <t>
5839      <eref target=""/>:
5840      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5841    </t>
5842    <t>
5843      <eref target=""/>:
5844      "define 'transparent' proxy"
5845    </t>
5846    <t>
5847      <eref target=""/>:
5848      "Header Classification"
5849    </t>
5850    <t>
5851      <eref target=""/>:
5852      "Is * usable as a request-uri for new methods?"
5853    </t>
5854    <t>
5855      <eref target=""/>:
5856      "Migrate Upgrade details from RFC2817"
5857    </t>
5858    <t>
5859      <eref target=""/>:
5860      "untangle ABNFs for header fields"
5861    </t>
5862    <t>
5863      <eref target=""/>:
5864      "update RFC 2109 reference"
5865    </t>
5866  </list>
5870<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5872  Closed issues:
5873  <list style="symbols">
5874    <t>
5875      <eref target=""/>:
5876      "Allow is not in 13.5.2"
5877    </t>
5878    <t>
5879      <eref target=""/>:
5880      "Handling multiple Content-Length headers"
5881    </t>
5882    <t>
5883      <eref target=""/>:
5884      "untangle ABNFs for header fields"
5885    </t>
5886    <t>
5887      <eref target=""/>:
5888      "Content-Length ABNF broken"
5889    </t>
5890  </list>
5894<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5896  Closed issues:
5897  <list style="symbols">
5898    <t>
5899      <eref target=""/>:
5900      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5901    </t>
5902    <t>
5903      <eref target=""/>:
5904      "Recommend minimum sizes for protocol elements"
5905    </t>
5906    <t>
5907      <eref target=""/>:
5908      "Set expectations around buffering"
5909    </t>
5910    <t>
5911      <eref target=""/>:
5912      "Considering messages in isolation"
5913    </t>
5914  </list>
5918<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5920  Closed issues:
5921  <list style="symbols">
5922    <t>
5923      <eref target=""/>:
5924      "DNS Spoofing / DNS Binding advice"
5925    </t>
5926    <t>
5927      <eref target=""/>:
5928      "move RFCs 2145, 2616, 2817 to Historic status"
5929    </t>
5930    <t>
5931      <eref target=""/>:
5932      "\-escaping in quoted strings"
5933    </t>
5934    <t>
5935      <eref target=""/>:
5936      "'Close' should be reserved in the HTTP header field registry"
5937    </t>
5938  </list>
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