source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1392

Last change on this file since 1392 was 1392, checked in by fielding@…, 11 years ago

Change multiple whitespace trimming recommendation to reflect
the common practice of using SP to erase line folding without
copying the buffer.

  • Property svn:eol-style set to native
File size: 250.4 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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; either
441   be replaced with a single SP or transformed to all SP octets (each WSP
442   octet other than SP replaced with SP) before interpreting the field value
443   or forwarding the message downstream.
445<t anchor="rule.RWS">
446   RWS is used when at least one linear whitespace octet is required to
447   separate field tokens. RWS &SHOULD; be produced as a single SP.
448   Multiple RWS octets octets that occur within field-content &SHOULD; either
449   be replaced with a single SP or transformed to all SP octets (each WSP
450   octet other than SP replaced with SP) before interpreting the field value
451   or forwarding the message downstream.
453<t anchor="rule.BWS">
454   BWS is used where the grammar allows optional whitespace for historical
455   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
456   recipients &MUST; accept such bad optional whitespace and remove it before
457   interpreting the field value or forwarding the message downstream.
459<t anchor="rule.whitespace">
460  <x:anchor-alias value="BWS"/>
461  <x:anchor-alias value="OWS"/>
462  <x:anchor-alias value="RWS"/>
463  <x:anchor-alias value="obs-fold"/>
465<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"/>
466  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
467                 ; "optional" whitespace
468  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
469                 ; "required" whitespace
470  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
471                 ; "bad" whitespace
472  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
473                 ; see <xref target="header.fields"/>
475<t anchor="rule.token.separators">
476  <x:anchor-alias value="tchar"/>
477  <x:anchor-alias value="token"/>
478  <x:anchor-alias value="special"/>
479  <x:anchor-alias value="word"/>
480   Many HTTP/1.1 header field values consist of words (token or quoted-string)
481   separated by whitespace or special characters. These special characters
482   &MUST; be in a quoted string to be used within a parameter value (as defined
483   in <xref target="transfer.codings"/>).
485<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"/>
486  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
488  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
490  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
491 -->
492  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
493                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
494                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
495                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
497  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
498                 / ";" / ":" / "\" / DQUOTE / "/" / "["
499                 / "]" / "?" / "=" / "{" / "}"
501<t anchor="rule.quoted-string">
502  <x:anchor-alias value="quoted-string"/>
503  <x:anchor-alias value="qdtext"/>
504  <x:anchor-alias value="obs-text"/>
505   A string of text is parsed as a single word if it is quoted using
506   double-quote marks.
508<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"/>
509  <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>
510  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
511                 ; <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>
512  <x:ref>obs-text</x:ref>       = %x80-FF
514<t anchor="rule.quoted-pair">
515  <x:anchor-alias value="quoted-pair"/>
516   The backslash octet ("\") can be used as a single-octet
517   quoting mechanism within quoted-string constructs:
519<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
520  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
523   Recipients that process the value of the quoted-string &MUST; handle a
524   quoted-pair as if it were replaced by the octet following the backslash.
527   Senders &SHOULD-NOT; escape octets that do not require escaping
528   (i.e., other than DQUOTE and the backslash octet).
535<section title="HTTP-related architecture" anchor="architecture">
537   HTTP was created for the World Wide Web architecture
538   and has evolved over time to support the scalability needs of a worldwide
539   hypertext system. Much of that architecture is reflected in the terminology
540   and syntax productions used to define HTTP.
543<section title="Client/Server Messaging" anchor="operation">
544<iref primary="true" item="client"/>
545<iref primary="true" item="server"/>
546<iref primary="true" item="connection"/>
548   HTTP is a stateless request/response protocol that operates by exchanging
549   messages across a reliable transport or session-layer
550   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
551   program that establishes a connection to a server for the purpose of
552   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
553   program that accepts connections in order to service HTTP requests by
554   sending HTTP responses.
556<iref primary="true" item="user agent"/>
557<iref primary="true" item="origin server"/>
558<iref primary="true" item="browser"/>
559<iref primary="true" item="spider"/>
560<iref primary="true" item="sender"/>
561<iref primary="true" item="recipient"/>
563   Note that the terms client and server refer only to the roles that
564   these programs perform for a particular connection.  The same program
565   might act as a client on some connections and a server on others.  We use
566   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
567   such as a WWW browser, editor, or spider (web-traversing robot), and
568   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
569   authoritative responses to a request.  For general requirements, we use
570   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
571   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
572   message.
575   Most HTTP communication consists of a retrieval request (GET) for
576   a representation of some resource identified by a URI.  In the
577   simplest case, this might be accomplished via a single bidirectional
578   connection (===) between the user agent (UA) and the origin server (O).
580<figure><artwork type="drawing">
581         request   &gt;
582    UA ======================================= O
583                                &lt;   response
585<iref primary="true" item="message"/>
586<iref primary="true" item="request"/>
587<iref primary="true" item="response"/>
589   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
590   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
591   protocol version, followed by MIME-like header fields containing
592   request modifiers, client information, and payload metadata, an empty
593   line to indicate the end of the header section, and finally the payload
594   body (if any).
597   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
598   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
599   includes the protocol version, a success or error code, and textual
600   reason phrase, followed by MIME-like header fields containing server
601   information, resource metadata, and payload metadata, an empty line to
602   indicate the end of the header section, and finally the payload body (if any).
605   The following example illustrates a typical message exchange for a
606   GET request on the URI "":
609client request:
610</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
611GET /hello.txt HTTP/1.1
612User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
614Accept: */*
618server response:
619</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
620HTTP/1.1 200 OK
621Date: Mon, 27 Jul 2009 12:28:53 GMT
622Server: Apache
623Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
624ETag: "34aa387-d-1568eb00"
625Accept-Ranges: bytes
626Content-Length: <x:length-of target="exbody"/>
627Vary: Accept-Encoding
628Content-Type: text/plain
630<x:span anchor="exbody">Hello World!
634<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
636   Fundamentally, HTTP is a message-based protocol. Although message bodies can
637   be chunked (<xref target="chunked.encoding"/>) and implementations often
638   make parts of a message available progressively, this is not required, and
639   some widely-used implementations only make a message available when it is
640   complete. Furthermore, while most proxies will progressively stream messages,
641   some amount of buffering will take place, and some proxies might buffer
642   messages to perform transformations, check content or provide other services.
645   Therefore, extensions to and uses of HTTP cannot rely on the availability of
646   a partial message, or assume that messages will not be buffered. There are
647   strategies that can be used to test for buffering in a given connection, but
648   it should be understood that behaviors can differ across connections, and
649   between requests and responses.
652   Recipients &MUST; consider every message in a connection in isolation;
653   because HTTP is a stateless protocol, it cannot be assumed that two requests
654   on the same connection are from the same client or share any other common
655   attributes. In particular, intermediaries might mix requests from different
656   clients into a single server connection. Note that some existing HTTP
657   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
658   potentially causing interoperability and security problems.
662<section title="Connections and Transport Independence" anchor="transport-independence">
664   HTTP messaging is independent of the underlying transport or
665   session-layer connection protocol(s).  HTTP only presumes a reliable
666   transport with in-order delivery of requests and the corresponding
667   in-order delivery of responses.  The mapping of HTTP request and
668   response structures onto the data units of the underlying transport
669   protocol is outside the scope of this specification.
672   The specific connection protocols to be used for an interaction
673   are determined by client configuration and the target resource's URI.
674   For example, the "http" URI scheme
675   (<xref target="http.uri"/>) indicates a default connection of TCP
676   over IP, with a default TCP port of 80, but the client might be
677   configured to use a proxy via some other connection port or protocol
678   instead of using the defaults.
681   A connection might be used for multiple HTTP request/response exchanges,
682   as defined in <xref target="persistent.connections"/>.
686<section title="Intermediaries" anchor="intermediaries">
687<iref primary="true" item="intermediary"/>
689   HTTP enables the use of intermediaries to satisfy requests through
690   a chain of connections.  There are three common forms of HTTP
691   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
692   a single intermediary might act as an origin server, proxy, gateway,
693   or tunnel, switching behavior based on the nature of each request.
695<figure><artwork type="drawing">
696         &gt;             &gt;             &gt;             &gt;
697    <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>
698               &lt;             &lt;             &lt;             &lt;
701   The figure above shows three intermediaries (A, B, and C) between the
702   user agent and origin server. A request or response message that
703   travels the whole chain will pass through four separate connections.
704   Some HTTP communication options
705   might apply only to the connection with the nearest, non-tunnel
706   neighbor, only to the end-points of the chain, or to all connections
707   along the chain. Although the diagram is linear, each participant might
708   be engaged in multiple, simultaneous communications. For example, B
709   might be receiving requests from many clients other than A, and/or
710   forwarding requests to servers other than C, at the same time that it
711   is handling A's request.
714<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
715<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
716   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
717   to describe various requirements in relation to the directional flow of a
718   message: all messages flow from upstream to downstream.
719   Likewise, we use the terms inbound and outbound to refer to
720   directions in relation to the request path:
721   "<x:dfn>inbound</x:dfn>" means toward the origin server and
722   "<x:dfn>outbound</x:dfn>" means toward the user agent.
724<t><iref primary="true" item="proxy"/>
725   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
726   client, usually via local configuration rules, to receive requests
727   for some type(s) of absolute URI and attempt to satisfy those
728   requests via translation through the HTTP interface.  Some translations
729   are minimal, such as for proxy requests for "http" URIs, whereas
730   other requests might require translation to and from entirely different
731   application-layer protocols. Proxies are often used to group an
732   organization's HTTP requests through a common intermediary for the
733   sake of security, annotation services, or shared caching.
736<iref primary="true" item="transforming proxy"/>
737<iref primary="true" item="non-transforming proxy"/>
738   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
739   or configured to modify request or response messages in a semantically
740   meaningful way (i.e., modifications, beyond those required by normal
741   HTTP processing, that change the message in a way that would be
742   significant to the original sender or potentially significant to
743   downstream recipients).  For example, a transforming proxy might be
744   acting as a shared annotation server (modifying responses to include
745   references to a local annotation database), a malware filter, a
746   format transcoder, or an intranet-to-Internet privacy filter.  Such
747   transformations are presumed to be desired by the client (or client
748   organization) that selected the proxy and are beyond the scope of
749   this specification.  However, when a proxy is not intended to transform
750   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
751   requirements that preserve HTTP message semantics. See &status-203; and
752   &header-warning; for status and warning codes related to transformations.
754<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
755<iref primary="true" item="accelerator"/>
756   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
757   is a receiving agent that acts
758   as a layer above some other server(s) and translates the received
759   requests to the underlying server's protocol.  Gateways are often
760   used to encapsulate legacy or untrusted information services, to
761   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
762   enable partitioning or load-balancing of HTTP services across
763   multiple machines.
766   A gateway behaves as an origin server on its outbound connection and
767   as a user agent on its inbound connection.
768   All HTTP requirements applicable to an origin server
769   also apply to the outbound communication of a gateway.
770   A gateway communicates with inbound servers using any protocol that
771   it desires, including private extensions to HTTP that are outside
772   the scope of this specification.  However, an HTTP-to-HTTP gateway
773   that wishes to interoperate with third-party HTTP servers &MUST;
774   comply with HTTP user agent requirements on the gateway's inbound
775   connection and &MUST; implement the Connection
776   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
777   header fields for both connections.
779<t><iref primary="true" item="tunnel"/>
780   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
781   without changing the messages. Once active, a tunnel is not
782   considered a party to the HTTP communication, though the tunnel might
783   have been initiated by an HTTP request. A tunnel ceases to exist when
784   both ends of the relayed connection are closed. Tunnels are used to
785   extend a virtual connection through an intermediary, such as when
786   transport-layer security is used to establish private communication
787   through a shared firewall proxy.
789<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
790<iref primary="true" item="captive portal"/>
791   In addition, there may exist network intermediaries that are not
792   considered part of the HTTP communication but nevertheless act as
793   filters or redirecting agents (usually violating HTTP semantics,
794   causing security problems, and otherwise making a mess of things).
795   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
796   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
797   or "<x:dfn>captive portal</x:dfn>",
798   differs from an HTTP proxy because it has not been selected by the client.
799   Instead, the network intermediary redirects outgoing TCP port 80 packets
800   (and occasionally other common port traffic) to an internal HTTP server.
801   Interception proxies are commonly found on public network access points,
802   as a means of enforcing account subscription prior to allowing use of
803   non-local Internet services, and within corporate firewalls to enforce
804   network usage policies.
805   They are indistinguishable from a man-in-the-middle attack.
809<section title="Caches" anchor="caches">
810<iref primary="true" item="cache"/>
812   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
813   subsystem that controls its message storage, retrieval, and deletion.
814   A cache stores cacheable responses in order to reduce the response
815   time and network bandwidth consumption on future, equivalent
816   requests. Any client or server &MAY; employ a cache, though a cache
817   cannot be used by a server while it is acting as a tunnel.
820   The effect of a cache is that the request/response chain is shortened
821   if one of the participants along the chain has a cached response
822   applicable to that request. The following illustrates the resulting
823   chain if B has a cached copy of an earlier response from O (via C)
824   for a request which has not been cached by UA or A.
826<figure><artwork type="drawing">
827            &gt;             &gt;
828       UA =========== A =========== B - - - - - - C - - - - - - O
829                  &lt;             &lt;
831<t><iref primary="true" item="cacheable"/>
832   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
833   the response message for use in answering subsequent requests.
834   Even when a response is cacheable, there might be additional
835   constraints placed by the client or by the origin server on when
836   that cached response can be used for a particular request. HTTP
837   requirements for cache behavior and cacheable responses are
838   defined in &caching-overview;. 
841   There are a wide variety of architectures and configurations
842   of caches and proxies deployed across the World Wide Web and
843   inside large organizations. These systems include national hierarchies
844   of proxy caches to save transoceanic bandwidth, systems that
845   broadcast or multicast cache entries, organizations that distribute
846   subsets of cached data via optical media, and so on.
850<section title="Protocol Versioning" anchor="http.version">
851  <x:anchor-alias value="HTTP-Version"/>
852  <x:anchor-alias value="HTTP-Prot-Name"/>
854   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
855   versions of the protocol. This specification defines version "1.1".
856   The protocol version as a whole indicates the sender's compliance
857   with the set of requirements laid out in that version's corresponding
858   specification of HTTP.
861   The version of an HTTP message is indicated by an HTTP-Version field
862   in the first line of the message. HTTP-Version is case-sensitive.
864<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
865  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
866  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
869   The HTTP version number consists of two decimal digits separated by a "."
870   (period or decimal point).  The first digit ("major version") indicates the
871   HTTP messaging syntax, whereas the second digit ("minor version") indicates
872   the highest minor version to which the sender is at least conditionally
873   compliant and able to understand for future communication.  The minor
874   version advertises the sender's communication capabilities even when the
875   sender is only using a backwards-compatible subset of the protocol,
876   thereby letting the recipient know that more advanced features can
877   be used in response (by servers) or in future requests (by clients).
880   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
881   <xref target="RFC1945"/> or a recipient whose version is unknown,
882   the HTTP/1.1 message is constructed such that it can be interpreted
883   as a valid HTTP/1.0 message if all of the newer features are ignored.
884   This specification places recipient-version requirements on some
885   new features so that a compliant sender will only use compatible
886   features until it has determined, through configuration or the
887   receipt of a message, that the recipient supports HTTP/1.1.
890   The interpretation of an HTTP header field does not change
891   between minor versions of the same major version, though the default
892   behavior of a recipient in the absence of such a field can change.
893   Unless specified otherwise, header fields defined in HTTP/1.1 are
894   defined for all versions of HTTP/1.x.  In particular, the Host and
895   Connection header fields ought to be implemented by all HTTP/1.x
896   implementations whether or not they advertise compliance with HTTP/1.1.
899   New header fields can be defined such that, when they are
900   understood by a recipient, they might override or enhance the
901   interpretation of previously defined header fields.  When an
902   implementation receives an unrecognized header field, the recipient
903   &MUST; ignore that header field for local processing regardless of
904   the message's HTTP version.  An unrecognized header field received
905   by a proxy &MUST; be forwarded downstream unless the header field's
906   field-name is listed in the message's Connection header-field
907   (see <xref target="header.connection"/>).
908   These requirements allow HTTP's functionality to be enhanced without
909   requiring prior update of all compliant intermediaries.
912   Intermediaries that process HTTP messages (i.e., all intermediaries
913   other than those acting as a tunnel) &MUST; send their own HTTP-Version
914   in forwarded messages.  In other words, they &MUST-NOT; blindly
915   forward the first line of an HTTP message without ensuring that the
916   protocol version matches what the intermediary understands, and
917   is at least conditionally compliant to, for both the receiving and
918   sending of messages.  Forwarding an HTTP message without rewriting
919   the HTTP-Version might result in communication errors when downstream
920   recipients use the message sender's version to determine what features
921   are safe to use for later communication with that sender.
924   An HTTP client &SHOULD; send a request version equal to the highest
925   version for which the client is at least conditionally compliant and
926   whose major version is no higher than the highest version supported
927   by the server, if this is known.  An HTTP client &MUST-NOT; send a
928   version for which it is not at least conditionally compliant.
931   An HTTP client &MAY; send a lower request version if it is known that
932   the server incorrectly implements the HTTP specification, but only
933   after the client has attempted at least one normal request and determined
934   from the response status or header fields (e.g., Server) that the
935   server improperly handles higher request versions.
938   An HTTP server &SHOULD; send a response version equal to the highest
939   version for which the server is at least conditionally compliant and
940   whose major version is less than or equal to the one received in the
941   request.  An HTTP server &MUST-NOT; send a version for which it is not
942   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
943   Version Not Supported) response if it cannot send a response using the
944   major version used in the client's request.
947   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
948   if it is known or suspected that the client incorrectly implements the
949   HTTP specification and is incapable of correctly processing later
950   version responses, such as when a client fails to parse the version
951   number correctly or when an intermediary is known to blindly forward
952   the HTTP-Version even when it doesn't comply with the given minor
953   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
954   performed unless triggered by specific client attributes, such as when
955   one or more of the request header fields (e.g., User-Agent) uniquely
956   match the values sent by a client known to be in error.
959   The intention of HTTP's versioning design is that the major number
960   will only be incremented if an incompatible message syntax is
961   introduced, and that the minor number will only be incremented when
962   changes made to the protocol have the effect of adding to the message
963   semantics or implying additional capabilities of the sender.  However,
964   the minor version was not incremented for the changes introduced between
965   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
966   is specifically avoiding any such changes to the protocol.
970<section title="Uniform Resource Identifiers" anchor="uri">
971<iref primary="true" item="resource"/>
973   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
974   throughout HTTP as the means for identifying resources. URI references
975   are used to target requests, indicate redirects, and define relationships.
976   HTTP does not limit what a resource might be; it merely defines an interface
977   that can be used to interact with a resource via HTTP. More information on
978   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
980  <x:anchor-alias value="URI-reference"/>
981  <x:anchor-alias value="absolute-URI"/>
982  <x:anchor-alias value="relative-part"/>
983  <x:anchor-alias value="authority"/>
984  <x:anchor-alias value="path-abempty"/>
985  <x:anchor-alias value="path-absolute"/>
986  <x:anchor-alias value="port"/>
987  <x:anchor-alias value="query"/>
988  <x:anchor-alias value="uri-host"/>
989  <x:anchor-alias value="partial-URI"/>
991   This specification adopts the definitions of "URI-reference",
992   "absolute-URI", "relative-part", "port", "host",
993   "path-abempty", "path-absolute", "query", and "authority" from the
994   URI generic syntax <xref target="RFC3986"/>.
995   In addition, we define a partial-URI rule for protocol elements
996   that allow a relative URI but not a fragment.
998<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"/>
999  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
1000  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
1001  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
1002  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
1003  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
1004  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
1005  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
1006  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
1007  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
1009  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
1012   Each protocol element in HTTP that allows a URI reference will indicate
1013   in its ABNF production whether the element allows any form of reference
1014   (URI-reference), only a URI in absolute form (absolute-URI), only the
1015   path and optional query components, or some combination of the above.
1016   Unless otherwise indicated, URI references are parsed relative to the
1017   effective request URI, which defines the default base URI for references
1018   in both the request and its corresponding response.
1021<section title="http URI scheme" anchor="http.uri">
1022  <x:anchor-alias value="http-URI"/>
1023  <iref item="http URI scheme" primary="true"/>
1024  <iref item="URI scheme" subitem="http" primary="true"/>
1026   The "http" URI scheme is hereby defined for the purpose of minting
1027   identifiers according to their association with the hierarchical
1028   namespace governed by a potential HTTP origin server listening for
1029   TCP connections on a given port.
1031<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1032  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1035   The HTTP origin server is identified by the generic syntax's
1036   <x:ref>authority</x:ref> component, which includes a host identifier
1037   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1038   The remainder of the URI, consisting of both the hierarchical path
1039   component and optional query component, serves as an identifier for
1040   a potential resource within that origin server's name space.
1043   If the host identifier is provided as an IP literal or IPv4 address,
1044   then the origin server is any listener on the indicated TCP port at
1045   that IP address. If host is a registered name, then that name is
1046   considered an indirect identifier and the recipient might use a name
1047   resolution service, such as DNS, to find the address of a listener
1048   for that host.
1049   The host &MUST-NOT; be empty; if an "http" URI is received with an
1050   empty host, then it &MUST; be rejected as invalid.
1051   If the port subcomponent is empty or not given, then TCP port 80 is
1052   assumed (the default reserved port for WWW services).
1055   Regardless of the form of host identifier, access to that host is not
1056   implied by the mere presence of its name or address. The host might or might
1057   not exist and, even when it does exist, might or might not be running an
1058   HTTP server or listening to the indicated port. The "http" URI scheme
1059   makes use of the delegated nature of Internet names and addresses to
1060   establish a naming authority (whatever entity has the ability to place
1061   an HTTP server at that Internet name or address) and allows that
1062   authority to determine which names are valid and how they might be used.
1065   When an "http" URI is used within a context that calls for access to the
1066   indicated resource, a client &MAY; attempt access by resolving
1067   the host to an IP address, establishing a TCP connection to that address
1068   on the indicated port, and sending an HTTP request message to the server
1069   containing the URI's identifying data as described in <xref target="request"/>.
1070   If the server responds to that request with a non-interim HTTP response
1071   message, as described in <xref target="response"/>, then that response
1072   is considered an authoritative answer to the client's request.
1075   Although HTTP is independent of the transport protocol, the "http"
1076   scheme is specific to TCP-based services because the name delegation
1077   process depends on TCP for establishing authority.
1078   An HTTP service based on some other underlying connection protocol
1079   would presumably be identified using a different URI scheme, just as
1080   the "https" scheme (below) is used for servers that require an SSL/TLS
1081   transport layer on a connection. Other protocols might also be used to
1082   provide access to "http" identified resources &mdash; it is only the
1083   authoritative interface used for mapping the namespace that is
1084   specific to TCP.
1087   The URI generic syntax for authority also includes a deprecated
1088   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1089   for including user authentication information in the URI.  Some
1090   implementations make use of the userinfo component for internal
1091   configuration of authentication information, such as within command
1092   invocation options, configuration files, or bookmark lists, even
1093   though such usage might expose a user identifier or password.
1094   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1095   delimiter) when transmitting an "http" URI in a message.  Recipients
1096   of HTTP messages that contain a URI reference &SHOULD; parse for the
1097   existence of userinfo and treat its presence as an error, likely
1098   indicating that the deprecated subcomponent is being used to obscure
1099   the authority for the sake of phishing attacks.
1103<section title="https URI scheme" anchor="https.uri">
1104   <x:anchor-alias value="https-URI"/>
1105   <iref item="https URI scheme"/>
1106   <iref item="URI scheme" subitem="https"/>
1108   The "https" URI scheme is hereby defined for the purpose of minting
1109   identifiers according to their association with the hierarchical
1110   namespace governed by a potential HTTP origin server listening for
1111   SSL/TLS-secured connections on a given TCP port.
1114   All of the requirements listed above for the "http" scheme are also
1115   requirements for the "https" scheme, except that a default TCP port
1116   of 443 is assumed if the port subcomponent is empty or not given,
1117   and the TCP connection &MUST; be secured for privacy through the
1118   use of strong encryption prior to sending the first HTTP request.
1120<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1121  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1124   Unlike the "http" scheme, responses to "https" identified requests
1125   are never "public" and thus &MUST-NOT; be reused for shared caching.
1126   They can, however, be reused in a private cache if the message is
1127   cacheable by default in HTTP or specifically indicated as such by
1128   the Cache-Control header field (&header-cache-control;).
1131   Resources made available via the "https" scheme have no shared
1132   identity with the "http" scheme even if their resource identifiers
1133   indicate the same authority (the same host listening to the same
1134   TCP port).  They are distinct name spaces and are considered to be
1135   distinct origin servers.  However, an extension to HTTP that is
1136   defined to apply to entire host domains, such as the Cookie protocol
1137   <xref target="RFC6265"/>, can allow information
1138   set by one service to impact communication with other services
1139   within a matching group of host domains.
1142   The process for authoritative access to an "https" identified
1143   resource is defined in <xref target="RFC2818"/>.
1147<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1149   Since the "http" and "https" schemes conform to the URI generic syntax,
1150   such URIs are normalized and compared according to the algorithm defined
1151   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1152   described above for each scheme.
1155   If the port is equal to the default port for a scheme, the normal
1156   form is to elide the port subcomponent. Likewise, an empty path
1157   component is equivalent to an absolute path of "/", so the normal
1158   form is to provide a path of "/" instead. The scheme and host
1159   are case-insensitive and normally provided in lowercase; all
1160   other components are compared in a case-sensitive manner.
1161   Characters other than those in the "reserved" set are equivalent
1162   to their percent-encoded octets (see <xref target="RFC3986"
1163   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1166   For example, the following three URIs are equivalent:
1168<figure><artwork type="example">
1177<section title="Message Format" anchor="http.message">
1178<x:anchor-alias value="generic-message"/>
1179<x:anchor-alias value="message.types"/>
1180<x:anchor-alias value="HTTP-message"/>
1181<x:anchor-alias value="start-line"/>
1182<iref item="header section"/>
1183<iref item="headers"/>
1184<iref item="header field"/>
1186   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1187   octets in a format similar to the Internet Message Format
1188   <xref target="RFC5322"/>: zero or more header fields (collectively
1189   referred to as the "headers" or the "header section"), an empty line
1190   indicating the end of the header section, and an optional message-body.
1193   An HTTP message can either be a request from client to server or a
1194   response from server to client.  Syntactically, the two types of message
1195   differ only in the start-line, which is either a Request-Line (for requests)
1196   or a Status-Line (for responses), and in the algorithm for determining
1197   the length of the message-body (<xref target="message.body"/>).
1198   In theory, a client could receive requests and a server could receive
1199   responses, distinguishing them by their different start-line formats,
1200   but in practice servers are implemented to only expect a request
1201   (a response is interpreted as an unknown or invalid request method)
1202   and clients are implemented to only expect a response.
1204<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1205  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1206                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1207                    <x:ref>CRLF</x:ref>
1208                    [ <x:ref>message-body</x:ref> ]
1209  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1212   Implementations &MUST-NOT; send whitespace between the start-line and
1213   the first header field. The presence of such whitespace in a request
1214   might be an attempt to trick a server into ignoring that field or
1215   processing the line after it as a new request, either of which might
1216   result in a security vulnerability if other implementations within
1217   the request chain interpret the same message differently.
1218   Likewise, the presence of such whitespace in a response might be
1219   ignored by some clients or cause others to cease parsing.
1222<section title="Message Parsing Robustness" anchor="message.robustness">
1224   In the interest of robustness, servers &SHOULD; ignore at least one
1225   empty line received where a Request-Line is expected. In other words, if
1226   the server is reading the protocol stream at the beginning of a
1227   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1228   Likewise, although the line terminator for the start-line and header
1229   fields is the sequence CRLF, we recommend that recipients recognize a
1230   single LF as a line terminator and ignore any CR.
1233   Some old HTTP/1.0 client implementations send an extra CRLF
1234   after a POST request as a lame workaround for some early server
1235   applications that failed to read message-body content that was
1236   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1237   preface or follow a request with an extra CRLF.  If terminating
1238   the request message-body with a line-ending is desired, then the
1239   client &MUST; include the terminating CRLF octets as part of the
1240   message-body length.
1243   When a server listening only for HTTP request messages, or processing
1244   what appears from the start-line to be an HTTP request message,
1245   receives a sequence of octets that does not match the HTTP-message
1246   grammar aside from the robustness exceptions listed above, the
1247   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1250   The normal procedure for parsing an HTTP message is to read the
1251   start-line into a structure, read each header field into a hash
1252   table by field name until the empty line, and then use the parsed
1253   data to determine if a message-body is expected.  If a message-body
1254   has been indicated, then it is read as a stream until an amount
1255   of octets equal to the message-body length is read or the connection
1256   is closed.  Care must be taken to parse an HTTP message as a sequence
1257   of octets in an encoding that is a superset of US-ASCII.  Attempting
1258   to parse HTTP as a stream of Unicode characters in a character encoding
1259   like UTF-16 might introduce security flaws due to the differing ways
1260   that such parsers interpret invalid characters.
1263   HTTP allows the set of defined header fields to be extended without
1264   changing the protocol version (see <xref target="header.field.registration"/>).
1265   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1266   proxy is specifically configured to block or otherwise transform such
1267   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1271<section title="Header Fields" anchor="header.fields">
1272  <x:anchor-alias value="header-field"/>
1273  <x:anchor-alias value="field-content"/>
1274  <x:anchor-alias value="field-name"/>
1275  <x:anchor-alias value="field-value"/>
1276  <x:anchor-alias value="OWS"/>
1278   Each HTTP header field consists of a case-insensitive field name
1279   followed by a colon (":"), optional whitespace, and the field value.
1281<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"/>
1282  <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>
1283  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1284  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1285  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1288   No whitespace is allowed between the header field name and colon. For
1289   security reasons, any request message received containing such whitespace
1290   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1291   &MUST; remove any such whitespace from a response message before
1292   forwarding the message downstream.
1295   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1296   preferred. The field value does not include any leading or trailing white
1297   space: OWS occurring before the first non-whitespace octet of the
1298   field value or after the last non-whitespace octet of the field value
1299   is ignored and &SHOULD; be removed before further processing (as this does
1300   not change the meaning of the header field).
1303   The order in which header fields with differing field names are
1304   received is not significant. However, it is "good practice" to send
1305   header fields that contain control data first, such as Host on
1306   requests and Date on responses, so that implementations can decide
1307   when not to handle a message as early as possible.  A server &MUST;
1308   wait until the entire header section is received before interpreting
1309   a request message, since later header fields might include conditionals,
1310   authentication credentials, or deliberately misleading duplicate
1311   header fields that would impact request processing.
1314   Multiple header fields with the same field name &MUST-NOT; be
1315   sent in a message unless the entire field value for that
1316   header field is defined as a comma-separated list [i.e., #(values)].
1317   Multiple header fields with the same field name can be combined into
1318   one "field-name: field-value" pair, without changing the semantics of the
1319   message, by appending each subsequent field value to the combined
1320   field value in order, separated by a comma. The order in which
1321   header fields with the same field name are received is therefore
1322   significant to the interpretation of the combined field value;
1323   a proxy &MUST-NOT; change the order of these field values when
1324   forwarding a message.
1327  <t>
1328   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1329   practice can occur multiple times, but does not use the list syntax, and
1330   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1331   for details.) Also note that the Set-Cookie2 header field specified in
1332   <xref target="RFC2965"/> does not share this problem.
1333  </t>
1336   Historically, HTTP header field values could be extended over multiple
1337   lines by preceding each extra line with at least one space or horizontal
1338   tab octet (line folding). This specification deprecates such line
1339   folding except within the message/http media type
1340   (<xref target=""/>).
1341   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1342   (i.e., that contain any field-content that matches the obs-fold rule) unless
1343   the message is intended for packaging within the message/http media type.
1344   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1345   obs-fold whitespace with a single SP prior to interpreting the field value
1346   or forwarding the message downstream.
1349   Historically, HTTP has allowed field content with text in the ISO-8859-1
1350   <xref target="ISO-8859-1"/> character encoding and supported other
1351   character sets only through use of <xref target="RFC2047"/> encoding.
1352   In practice, most HTTP header field values use only a subset of the
1353   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1354   header fields &SHOULD; limit their field values to US-ASCII octets.
1355   Recipients &SHOULD; treat other (obs-text) octets in field content as
1356   opaque data.
1358<t anchor="rule.comment">
1359  <x:anchor-alias value="comment"/>
1360  <x:anchor-alias value="ctext"/>
1361   Comments can be included in some HTTP header fields by surrounding
1362   the comment text with parentheses. Comments are only allowed in
1363   fields containing "comment" as part of their field value definition.
1365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1366  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1367  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1368                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1370<t anchor="rule.quoted-cpair">
1371  <x:anchor-alias value="quoted-cpair"/>
1372   The backslash octet ("\") can be used as a single-octet
1373   quoting mechanism within comment constructs:
1375<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1376  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1379   Senders &SHOULD-NOT; escape octets that do not require escaping
1380   (i.e., other than the backslash octet "\" and the parentheses "(" and
1381   ")").
1384   HTTP does not place a pre-defined limit on the length of header fields,
1385   either in isolation or as a set. A server &MUST; be prepared to receive
1386   request header fields of unbounded length and respond with a 4xx status
1387   code if the received header field(s) would be longer than the server wishes
1388   to handle.
1391   A client that receives response headers that are longer than it wishes to
1392   handle can only treat it as a server error.
1395   Various ad-hoc limitations on header length are found in practice. It is
1396   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1397   combined header fields have 4000 or more octets.
1401<section title="Message Body" anchor="message.body">
1402  <x:anchor-alias value="message-body"/>
1404   The message-body (if any) of an HTTP message is used to carry the
1405   payload body associated with the request or response.
1407<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1408  <x:ref>message-body</x:ref> = *OCTET
1411   The message-body differs from the payload body only when a transfer-coding
1412   has been applied, as indicated by the Transfer-Encoding header field
1413   (<xref target="header.transfer-encoding"/>).  If more than one
1414   Transfer-Encoding header field is present in a message, the multiple
1415   field-values &MUST; be combined into one field-value, according to the
1416   algorithm defined in <xref target="header.fields"/>, before determining
1417   the message-body length.
1420   When one or more transfer-codings are applied to a payload in order to
1421   form the message-body, the Transfer-Encoding header field &MUST; contain
1422   the list of transfer-codings applied. Transfer-Encoding is a property of
1423   the message, not of the payload, and thus &MAY; be added or removed by
1424   any implementation along the request/response chain under the constraints
1425   found in <xref target="transfer.codings"/>.
1428   If a message is received that has multiple Content-Length header fields
1429   (<xref target="header.content-length"/>) with field-values consisting
1430   of the same decimal value, or a single Content-Length header field with
1431   a field value containing a list of identical decimal values (e.g.,
1432   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1433   header fields have been generated or combined by an upstream message
1434   processor, then the recipient &MUST; either reject the message as invalid
1435   or replace the duplicated field-values with a single valid Content-Length
1436   field containing that decimal value prior to determining the message-body
1437   length.
1440   The rules for when a message-body is allowed in a message differ for
1441   requests and responses.
1444   The presence of a message-body in a request is signaled by the
1445   inclusion of a Content-Length or Transfer-Encoding header field in
1446   the request's header fields, even if the request method does not
1447   define any use for a message-body.  This allows the request
1448   message framing algorithm to be independent of method semantics.
1451   For response messages, whether or not a message-body is included with
1452   a message is dependent on both the request method and the response
1453   status code (<xref target="status.code.and.reason.phrase"/>).
1454   Responses to the HEAD request method never include a message-body
1455   because the associated response header fields (e.g., Transfer-Encoding,
1456   Content-Length, etc.) only indicate what their values would have been
1457   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1458   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1459   All other responses do include a message-body, although the body
1460   &MAY; be of zero length.
1463   The length of the message-body is determined by one of the following
1464   (in order of precedence):
1467  <list style="numbers">
1468    <x:lt><t>
1469     Any response to a HEAD request and any response with a status
1470     code of 100-199, 204, or 304 is always terminated by the first
1471     empty line after the header fields, regardless of the header
1472     fields present in the message, and thus cannot contain a message-body.
1473    </t></x:lt>
1474    <x:lt><t>
1475     If a Transfer-Encoding header field is present
1476     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1477     is the final encoding, the message-body length is determined by reading
1478     and decoding the chunked data until the transfer-coding indicates the
1479     data is complete.
1480    </t>
1481    <t>
1482     If a Transfer-Encoding header field is present in a response and the
1483     "chunked" transfer-coding is not the final encoding, the message-body
1484     length is determined by reading the connection until it is closed by
1485     the server.
1486     If a Transfer-Encoding header field is present in a request and the
1487     "chunked" transfer-coding is not the final encoding, the message-body
1488     length cannot be determined reliably; the server &MUST; respond with
1489     the 400 (Bad Request) status code and then close the connection.
1490    </t>
1491    <t>
1492     If a message is received with both a Transfer-Encoding header field
1493     and a Content-Length header field, the Transfer-Encoding overrides
1494     the Content-Length.
1495     Such a message might indicate an attempt to perform request or response
1496     smuggling (bypass of security-related checks on message routing or content)
1497     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1498     be removed, prior to forwarding the message downstream, or replaced with
1499     the real message-body length after the transfer-coding is decoded.
1500    </t></x:lt>
1501    <x:lt><t>
1502     If a message is received without Transfer-Encoding and with either
1503     multiple Content-Length header fields having differing field-values or
1504     a single Content-Length header field having an invalid value, then the
1505     message framing is invalid and &MUST; be treated as an error to
1506     prevent request or response smuggling.
1507     If this is a request message, the server &MUST; respond with
1508     a 400 (Bad Request) status code and then close the connection.
1509     If this is a response message received by a proxy, the proxy
1510     &MUST; discard the received response, send a 502 (Bad Gateway)
1511     status code as its downstream response, and then close the connection.
1512     If this is a response message received by a user-agent, it &MUST; be
1513     treated as an error by discarding the message and closing the connection.
1514    </t></x:lt>
1515    <x:lt><t>
1516     If a valid Content-Length header field
1517     is present without Transfer-Encoding, its decimal value defines the
1518     message-body length in octets.  If the actual number of octets sent in
1519     the message is less than the indicated Content-Length, the recipient
1520     &MUST; consider the message to be incomplete and treat the connection
1521     as no longer usable.
1522     If the actual number of octets sent in the message is more than the indicated
1523     Content-Length, the recipient &MUST; only process the message-body up to the
1524     field value's number of octets; the remainder of the message &MUST; either
1525     be discarded or treated as the next message in a pipeline.  For the sake of
1526     robustness, a user-agent &MAY; attempt to detect and correct such an error
1527     in message framing if it is parsing the response to the last request on
1528     a connection and the connection has been closed by the server.
1529    </t></x:lt>
1530    <x:lt><t>
1531     If this is a request message and none of the above are true, then the
1532     message-body length is zero (no message-body is present).
1533    </t></x:lt>
1534    <x:lt><t>
1535     Otherwise, this is a response message without a declared message-body
1536     length, so the message-body length is determined by the number of octets
1537     received prior to the server closing the connection.
1538    </t></x:lt>
1539  </list>
1542   Since there is no way to distinguish a successfully completed,
1543   close-delimited message from a partially-received message interrupted
1544   by network failure, implementations &SHOULD; use encoding or
1545   length-delimited messages whenever possible.  The close-delimiting
1546   feature exists primarily for backwards compatibility with HTTP/1.0.
1549   A server &MAY; reject a request that contains a message-body but
1550   not a Content-Length by responding with 411 (Length Required).
1553   Unless a transfer-coding other than "chunked" has been applied,
1554   a client that sends a request containing a message-body &SHOULD;
1555   use a valid Content-Length header field if the message-body length
1556   is known in advance, rather than the "chunked" encoding, since some
1557   existing services respond to "chunked" with a 411 (Length Required)
1558   status code even though they understand the chunked encoding.  This
1559   is typically because such services are implemented via a gateway that
1560   requires a content-length in advance of being called and the server
1561   is unable or unwilling to buffer the entire request before processing.
1564   A client that sends a request containing a message-body &MUST; include a
1565   valid Content-Length header field if it does not know the server will
1566   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1567   of specific user configuration or by remembering the version of a prior
1568   received response.
1572<section anchor="incomplete.messages" title="Incomplete Messages">
1574   Request messages that are prematurely terminated, possibly due to a
1575   cancelled connection or a server-imposed time-out exception, &MUST;
1576   result in closure of the connection; sending an HTTP/1.1 error response
1577   prior to closing the connection is &OPTIONAL;.
1580   Response messages that are prematurely terminated, usually by closure
1581   of the connection prior to receiving the expected number of octets or by
1582   failure to decode a transfer-encoded message-body, &MUST; be recorded
1583   as incomplete.  A response that terminates in the middle of the header
1584   block (before the empty line is received) cannot be assumed to convey the
1585   full semantics of the response and &MUST; be treated as an error.
1588   A message-body that uses the chunked transfer encoding is
1589   incomplete if the zero-sized chunk that terminates the encoding has not
1590   been received.  A message that uses a valid Content-Length is incomplete
1591   if the size of the message-body received (in octets) is less than the
1592   value given by Content-Length.  A response that has neither chunked
1593   transfer encoding nor Content-Length is terminated by closure of the
1594   connection, and thus is considered complete regardless of the number of
1595   message-body octets received, provided that the header block was received
1596   intact.
1599   A user agent &MUST-NOT; render an incomplete response message-body as if
1600   it were complete (i.e., some indication must be given to the user that an
1601   error occurred).  Cache requirements for incomplete responses are defined
1602   in &cache-incomplete;.
1605   A server &MUST; read the entire request message-body or close
1606   the connection after sending its response, since otherwise the
1607   remaining data on a persistent connection would be misinterpreted
1608   as the next request.  Likewise,
1609   a client &MUST; read the entire response message-body if it intends
1610   to reuse the same connection for a subsequent request.  Pipelining
1611   multiple requests on a connection is described in <xref target="pipelining"/>.
1615<section title="General Header Fields" anchor="general.header.fields">
1616  <x:anchor-alias value="general-header"/>
1618   There are a few header fields which have general applicability for
1619   both request and response messages, but which do not apply to the
1620   payload being transferred. These header fields apply only to the
1621   message being transmitted.
1623<texttable align="left">
1624  <ttcol>Header Field Name</ttcol>
1625  <ttcol>Defined in...</ttcol>
1627  <c>Connection</c> <c><xref target="header.connection"/></c>
1628  <c>Date</c> <c><xref target=""/></c>
1629  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1630  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1631  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1632  <c>Via</c> <c><xref target="header.via"/></c>
1637<section title="Request" anchor="request">
1638  <x:anchor-alias value="Request"/>
1640   A request message from a client to a server begins with a
1641   Request-Line, followed by zero or more header fields, an empty
1642   line signifying the end of the header block, and an optional
1643   message body.
1645<!--                 Host                      ; should be moved here eventually -->
1646<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1647  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1648                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1649                  <x:ref>CRLF</x:ref>
1650                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1653<section title="Request-Line" anchor="request-line">
1654  <x:anchor-alias value="Request-Line"/>
1656   The Request-Line begins with a method token, followed by a single
1657   space (SP), the request-target, another single space (SP), the
1658   protocol version, and ending with CRLF.
1660<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1661  <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>
1664<section title="Method" anchor="method">
1665  <x:anchor-alias value="Method"/>
1667   The Method token indicates the request method to be performed on the
1668   target resource. The request method is case-sensitive.
1670<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1671  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1675<section title="request-target" anchor="request-target">
1676  <x:anchor-alias value="request-target"/>
1678   The request-target identifies the target resource upon which to apply
1679   the request.  In most cases, the user agent is provided a URI reference
1680   from which it determines an absolute URI for identifying the target
1681   resource.  When a request to the resource is initiated, all or part
1682   of that URI is used to construct the HTTP request-target.
1684<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1685  <x:ref>request-target</x:ref> = "*"
1686                 / <x:ref>absolute-URI</x:ref>
1687                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1688                 / <x:ref>authority</x:ref>
1691   The four options for request-target are dependent on the nature of the
1692   request.
1694<t><iref item="asterisk form (of request-target)"/>
1695   The asterisk "*" form of request-target, which &MUST-NOT; be used
1696   with any request method other than OPTIONS, means that the request
1697   applies to the server as a whole (the listening process) rather than
1698   to a specific named resource at that server.  For example,
1700<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1701OPTIONS * HTTP/1.1
1703<t><iref item="absolute-URI form (of request-target)"/>
1704   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1705   proxy. The proxy is requested to either forward the request or service it
1706   from a valid cache, and then return the response. Note that the proxy &MAY;
1707   forward the request on to another proxy or directly to the server
1708   specified by the absolute-URI. In order to avoid request loops, a
1709   proxy that forwards requests to other proxies &MUST; be able to
1710   recognize and exclude all of its own server names, including
1711   any aliases, local variations, and the numeric IP address. An example
1712   Request-Line would be:
1714<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1715GET HTTP/1.1
1718   To allow for transition to absolute-URIs in all requests in future
1719   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1720   form in requests, even though HTTP/1.1 clients will only generate
1721   them in requests to proxies.
1724   If a proxy receives a host name that is not a fully qualified domain
1725   name, it &MAY; add its domain to the host name it received. If a proxy
1726   receives a fully qualified domain name, the proxy &MUST-NOT; change
1727   the host name.
1729<t><iref item="authority form (of request-target)"/>
1730   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1732<t><iref item="origin form (of request-target)"/>
1733   The most common form of request-target is that used when making
1734   a request to an origin server ("origin form").
1735   In this case, the absolute path and query components of the URI
1736   &MUST; be transmitted as the request-target, and the authority component
1737   &MUST; be transmitted in a Host header field. For example, a client wishing
1738   to retrieve a representation of the resource, as identified above,
1739   directly from the origin server would open (or reuse) a TCP connection
1740   to port 80 of the host "" and send the lines:
1742<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1743GET /pub/WWW/TheProject.html HTTP/1.1
1747   followed by the remainder of the Request. Note that the origin form
1748   of request-target always starts with an absolute path; if the target
1749   resource's URI path is empty, then an absolute path of "/" &MUST; be
1750   provided in the request-target.
1753   If a proxy receives an OPTIONS request with an absolute-URI form of
1754   request-target in which the URI has an empty path and no query component,
1755   then the last proxy on the request chain &MUST; use a request-target
1756   of "*" when it forwards the request to the indicated origin server.
1759   For example, the request
1760</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1764  would be forwarded by the final proxy as
1765</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1766OPTIONS * HTTP/1.1
1770   after connecting to port 8001 of host "".
1774   The request-target is transmitted in the format specified in
1775   <xref target="http.uri"/>. If the request-target is percent-encoded
1776   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1777   &MUST; decode the request-target in order to
1778   properly interpret the request. Servers &SHOULD; respond to invalid
1779   request-targets with an appropriate status code.
1782   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1783   received request-target when forwarding it to the next inbound server,
1784   except as noted above to replace a null path-absolute with "/" or "*".
1787  <t>
1788    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1789    meaning of the request when the origin server is improperly using
1790    a non-reserved URI character for a reserved purpose.  Implementors
1791    need to be aware that some pre-HTTP/1.1 proxies have been known to
1792    rewrite the request-target.
1793  </t>
1796   HTTP does not place a pre-defined limit on the length of a request-target.
1797   A server &MUST; be prepared to receive URIs of unbounded length and
1798   respond with the 414 (URI Too Long) status code if the received
1799   request-target would be longer than the server wishes to handle
1800   (see &status-414;).
1803   Various ad-hoc limitations on request-target length are found in practice.
1804   It is &RECOMMENDED; that all HTTP senders and recipients support
1805   request-target lengths of 8000 or more octets.
1808  <t>
1809    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1810    are not part of the request-target and thus will not be transmitted
1811    in an HTTP request.
1812  </t>
1817<section title="The Resource Identified by a Request" anchor="">
1819   The exact resource identified by an Internet request is determined by
1820   examining both the request-target and the Host header field.
1823   An origin server that does not allow resources to differ by the
1824   requested host &MAY; ignore the Host header field value when
1825   determining the resource identified by an HTTP/1.1 request. (But see
1826   <xref target=""/>
1827   for other requirements on Host support in HTTP/1.1.)
1830   An origin server that does differentiate resources based on the host
1831   requested (sometimes referred to as virtual hosts or vanity host
1832   names) &MUST; use the following rules for determining the requested
1833   resource on an HTTP/1.1 request:
1834  <list style="numbers">
1835    <t>If request-target is an absolute-URI, the host is part of the
1836     request-target. Any Host header field value in the request &MUST; be
1837     ignored.</t>
1838    <t>If the request-target is not an absolute-URI, and the request includes
1839     a Host header field, the host is determined by the Host header
1840     field value.</t>
1841    <t>If the host as determined by rule 1 or 2 is not a valid host on
1842     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1843  </list>
1846   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1847   attempt to use heuristics (e.g., examination of the URI path for
1848   something unique to a particular host) in order to determine what
1849   exact resource is being requested.
1853<section title="Effective Request URI" anchor="effective.request.uri">
1854  <iref primary="true" item="effective request URI"/>
1855  <iref primary="true" item="target resource"/>
1857   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1858   for the target resource; instead, the URI needs to be inferred from the
1859   request-target, Host header field, and connection context. The result of
1860   this process is called the "effective request URI".  The "target resource"
1861   is the resource identified by the effective request URI.
1864   If the request-target is an absolute-URI, then the effective request URI is
1865   the request-target.
1868   If the request-target uses the path-absolute form or the asterisk form,
1869   and the Host header field is present, then the effective request URI is
1870   constructed by concatenating
1873  <list style="symbols">
1874    <t>
1875      the scheme name: "http" if the request was received over an insecure
1876      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1877      connection,
1878    </t>
1879    <t>
1880      the octet sequence "://",
1881    </t>
1882    <t>
1883      the authority component, as specified in the Host header field
1884      (<xref target=""/>), and
1885    </t>
1886    <t>
1887      the request-target obtained from the Request-Line, unless the
1888      request-target is just the asterisk "*".
1889    </t>
1890  </list>
1893   If the request-target uses the path-absolute form or the asterisk form,
1894   and the Host header field is not present, then the effective request URI is
1895   undefined.
1898   Otherwise, when request-target uses the authority form, the effective
1899   request URI is undefined.
1903   Example 1: the effective request URI for the message
1905<artwork type="example" x:indent-with="  ">
1906GET /pub/WWW/TheProject.html HTTP/1.1
1910  (received over an insecure TCP connection) is "http", plus "://", plus the
1911  authority component "", plus the request-target
1912  "/pub/WWW/TheProject.html", thus
1913  "".
1918   Example 2: the effective request URI for the message
1920<artwork type="example" x:indent-with="  ">
1921OPTIONS * HTTP/1.1
1925  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1926  authority component "", thus "".
1930   Effective request URIs are compared using the rules described in
1931   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1932   be treated as equivalent to an absolute path of "/".
1939<section title="Response" anchor="response">
1940  <x:anchor-alias value="Response"/>
1942   After receiving and interpreting a request message, a server responds
1943   with an HTTP response message.
1945<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1946  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1947                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1948                  <x:ref>CRLF</x:ref>
1949                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1952<section title="Status-Line" anchor="status-line">
1953  <x:anchor-alias value="Status-Line"/>
1955   The first line of a Response message is the Status-Line, consisting
1956   of the protocol version, a space (SP), the status code, another space,
1957   a possibly-empty textual phrase describing the status code, and
1958   ending with CRLF.
1960<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1961  <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>
1964<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1965  <x:anchor-alias value="Reason-Phrase"/>
1966  <x:anchor-alias value="Status-Code"/>
1968   The Status-Code element is a 3-digit integer result code of the
1969   attempt to understand and satisfy the request. These codes are fully
1970   defined in &status-codes;.  The Reason Phrase exists for the sole
1971   purpose of providing a textual description associated with the numeric
1972   status code, out of deference to earlier Internet application protocols
1973   that were more frequently used with interactive text clients.
1974   A client &SHOULD; ignore the content of the Reason Phrase.
1977   The first digit of the Status-Code defines the class of response. The
1978   last two digits do not have any categorization role. There are 5
1979   values for the first digit:
1980  <list style="symbols">
1981    <t>
1982      1xx: Informational - Request received, continuing process
1983    </t>
1984    <t>
1985      2xx: Success - The action was successfully received,
1986        understood, and accepted
1987    </t>
1988    <t>
1989      3xx: Redirection - Further action must be taken in order to
1990        complete the request
1991    </t>
1992    <t>
1993      4xx: Client Error - The request contains bad syntax or cannot
1994        be fulfilled
1995    </t>
1996    <t>
1997      5xx: Server Error - The server failed to fulfill an apparently
1998        valid request
1999    </t>
2000  </list>
2002<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
2003  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
2004  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
2012<section title="Protocol Parameters" anchor="protocol.parameters">
2014<section title="Date/Time Formats: Full Date" anchor="">
2015  <x:anchor-alias value="HTTP-date"/>
2017   HTTP applications have historically allowed three different formats
2018   for date/time stamps. However, the preferred format is a fixed-length subset
2019   of that defined by <xref target="RFC1123"/>:
2021<figure><artwork type="example" x:indent-with="  ">
2022Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2025   The other formats are described here only for compatibility with obsolete
2026   implementations.
2028<figure><artwork type="example" x:indent-with="  ">
2029Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2030Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2033   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2034   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2035   only generate the RFC 1123 format for representing HTTP-date values
2036   in header fields.
2039   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2040   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2041   equal to UTC (Coordinated Universal Time). This is indicated in the
2042   first two formats by the inclusion of "GMT" as the three-letter
2043   abbreviation for time zone, and &MUST; be assumed when reading the
2044   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2045   additional whitespace beyond that specifically included as SP in the
2046   grammar.
2048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2049  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2051<t anchor="">
2052  <x:anchor-alias value="rfc1123-date"/>
2053  <x:anchor-alias value="time-of-day"/>
2054  <x:anchor-alias value="hour"/>
2055  <x:anchor-alias value="minute"/>
2056  <x:anchor-alias value="second"/>
2057  <x:anchor-alias value="day-name"/>
2058  <x:anchor-alias value="day"/>
2059  <x:anchor-alias value="month"/>
2060  <x:anchor-alias value="year"/>
2061  <x:anchor-alias value="GMT"/>
2062  Preferred format:
2064<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"/>
2065  <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>
2066  ; fixed length subset of the format defined in
2067  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2069  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2070               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2071               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2072               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2073               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2074               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2075               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2077  <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>
2078               ; e.g., 02 Jun 1982
2080  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2081  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2082               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2083               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2084               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2085               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2086               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2087               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2088               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2089               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2090               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2091               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2092               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2093  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2095  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2097  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2098                 ; 00:00:00 - 23:59:59
2100  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2101  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2102  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2105  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2106  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2107  same as those defined for the RFC 5322 constructs
2108  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2110<t anchor="">
2111  <x:anchor-alias value="obs-date"/>
2112  <x:anchor-alias value="rfc850-date"/>
2113  <x:anchor-alias value="asctime-date"/>
2114  <x:anchor-alias value="date1"/>
2115  <x:anchor-alias value="date2"/>
2116  <x:anchor-alias value="date3"/>
2117  <x:anchor-alias value="rfc1123-date"/>
2118  <x:anchor-alias value="day-name-l"/>
2119  Obsolete formats:
2121<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2122  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2124<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2125  <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>
2126  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2127                 ; day-month-year (e.g., 02-Jun-82)
2129  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2130         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2131         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2132         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2133         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2134         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2135         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2137<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2138  <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>
2139  <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> ))
2140                 ; month day (e.g., Jun  2)
2143  <t>
2144    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2145    accepting date values that might have been sent by non-HTTP
2146    applications, as is sometimes the case when retrieving or posting
2147    messages via proxies/gateways to SMTP or NNTP.
2148  </t>
2151  <t>
2152    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2153    to their usage within the protocol stream. Clients and servers are
2154    not required to use these formats for user presentation, request
2155    logging, etc.
2156  </t>
2160<section title="Transfer Codings" anchor="transfer.codings">
2161  <x:anchor-alias value="transfer-coding"/>
2162  <x:anchor-alias value="transfer-extension"/>
2164   Transfer-coding values are used to indicate an encoding
2165   transformation that has been, can be, or might need to be applied to a
2166   payload body in order to ensure "safe transport" through the network.
2167   This differs from a content coding in that the transfer-coding is a
2168   property of the message rather than a property of the representation
2169   that is being transferred.
2171<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2172  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2173                          / "compress" ; <xref target="compress.coding"/>
2174                          / "deflate" ; <xref target="deflate.coding"/>
2175                          / "gzip" ; <xref target="gzip.coding"/>
2176                          / <x:ref>transfer-extension</x:ref>
2177  <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> )
2179<t anchor="rule.parameter">
2180  <x:anchor-alias value="attribute"/>
2181  <x:anchor-alias value="transfer-parameter"/>
2182  <x:anchor-alias value="value"/>
2183   Parameters are in the form of attribute/value pairs.
2185<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"/>
2186  <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>
2187  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2188  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2191   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2192   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2193   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2196   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2197   MIME, which were designed to enable safe transport of binary data over a
2198   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2199   However, safe transport
2200   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2201   the only unsafe characteristic of message-bodies is the difficulty in
2202   determining the exact message body length (<xref target="message.body"/>),
2203   or the desire to encrypt data over a shared transport.
2206   A server that receives a request message with a transfer-coding it does
2207   not understand &SHOULD; respond with 501 (Not Implemented) and then
2208   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2209   client.
2212<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2213  <iref item="chunked (Coding Format)"/>
2214  <iref item="Coding Format" subitem="chunked"/>
2215  <x:anchor-alias value="chunk"/>
2216  <x:anchor-alias value="Chunked-Body"/>
2217  <x:anchor-alias value="chunk-data"/>
2218  <x:anchor-alias value="chunk-ext"/>
2219  <x:anchor-alias value="chunk-ext-name"/>
2220  <x:anchor-alias value="chunk-ext-val"/>
2221  <x:anchor-alias value="chunk-size"/>
2222  <x:anchor-alias value="last-chunk"/>
2223  <x:anchor-alias value="trailer-part"/>
2224  <x:anchor-alias value="quoted-str-nf"/>
2225  <x:anchor-alias value="qdtext-nf"/>
2227   The chunked encoding modifies the body of a message in order to
2228   transfer it as a series of chunks, each with its own size indicator,
2229   followed by an &OPTIONAL; trailer containing header fields. This
2230   allows dynamically produced content to be transferred along with the
2231   information necessary for the recipient to verify that it has
2232   received the full message.
2234<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"/>
2235  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2236                   <x:ref>last-chunk</x:ref>
2237                   <x:ref>trailer-part</x:ref>
2238                   <x:ref>CRLF</x:ref>
2240  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2241                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2242  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2243  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2245  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2246                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2247  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2248  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2249  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2250  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2252  <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>
2253                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2254  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2255                 ; <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>
2258   The chunk-size field is a string of hex digits indicating the size of
2259   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2260   zero, followed by the trailer, which is terminated by an empty line.
2263   The trailer allows the sender to include additional HTTP header
2264   fields at the end of the message. The Trailer header field can be
2265   used to indicate which header fields are included in a trailer (see
2266   <xref target="header.trailer"/>).
2269   A server using chunked transfer-coding in a response &MUST-NOT; use the
2270   trailer for any header fields unless at least one of the following is
2271   true:
2272  <list style="numbers">
2273    <t>the request included a TE header field that indicates "trailers" is
2274     acceptable in the transfer-coding of the  response, as described in
2275     <xref target="header.te"/>; or,</t>
2277    <t>the trailer fields consist entirely of optional metadata, and the
2278    recipient could use the message (in a manner acceptable to the server where
2279    the field originated) without receiving it. In other words, the server that
2280    generated the header (often but not always the origin server) is willing to
2281    accept the possibility that the trailer fields might be silently discarded
2282    along the path to the client.</t>
2283  </list>
2286   This requirement prevents an interoperability failure when the
2287   message is being received by an HTTP/1.1 (or later) proxy and
2288   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2289   compliance with the protocol would have necessitated a possibly
2290   infinite buffer on the proxy.
2293   A process for decoding the "chunked" transfer-coding
2294   can be represented in pseudo-code as:
2296<figure><artwork type="code">
2297  length := 0
2298  read chunk-size, chunk-ext (if any) and CRLF
2299  while (chunk-size &gt; 0) {
2300     read chunk-data and CRLF
2301     append chunk-data to decoded-body
2302     length := length + chunk-size
2303     read chunk-size and CRLF
2304  }
2305  read header-field
2306  while (header-field not empty) {
2307     append header-field to existing header fields
2308     read header-field
2309  }
2310  Content-Length := length
2311  Remove "chunked" from Transfer-Encoding
2314   All HTTP/1.1 applications &MUST; be able to receive and decode the
2315   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2316   they do not understand.
2319   Since "chunked" is the only transfer-coding required to be understood
2320   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2321   on a persistent connection.  Whenever a transfer-coding is applied to
2322   a payload body in a request, the final transfer-coding applied &MUST;
2323   be "chunked".  If a transfer-coding is applied to a response payload
2324   body, then either the final transfer-coding applied &MUST; be "chunked"
2325   or the message &MUST; be terminated by closing the connection. When the
2326   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2327   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2328   be applied more than once in a message-body.
2332<section title="Compression Codings" anchor="compression.codings">
2334   The codings defined below can be used to compress the payload of a
2335   message.
2338   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2339   is not desirable and is discouraged for future encodings. Their
2340   use here is representative of historical practice, not good
2341   design.
2344   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2345   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2346   equivalent to "gzip" and "compress" respectively.
2349<section title="Compress Coding" anchor="compress.coding">
2350<iref item="compress (Coding Format)"/>
2351<iref item="Coding Format" subitem="compress"/>
2353   The "compress" format is produced by the common UNIX file compression
2354   program "compress". This format is an adaptive Lempel-Ziv-Welch
2355   coding (LZW).
2359<section title="Deflate Coding" anchor="deflate.coding">
2360<iref item="deflate (Coding Format)"/>
2361<iref item="Coding Format" subitem="deflate"/>
2363   The "deflate" format is defined as the "deflate" compression mechanism
2364   (described in <xref target="RFC1951"/>) used inside the "zlib"
2365   data format (<xref target="RFC1950"/>).
2368  <t>
2369    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2370    compressed data without the zlib wrapper.
2371   </t>
2375<section title="Gzip Coding" anchor="gzip.coding">
2376<iref item="gzip (Coding Format)"/>
2377<iref item="Coding Format" subitem="gzip"/>
2379   The "gzip" format is produced by the file compression program
2380   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2381   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2387<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2389   The HTTP Transfer Coding Registry defines the name space for the transfer
2390   coding names.
2393   Registrations &MUST; include the following fields:
2394   <list style="symbols">
2395     <t>Name</t>
2396     <t>Description</t>
2397     <t>Pointer to specification text</t>
2398   </list>
2401   Names of transfer codings &MUST-NOT; overlap with names of content codings
2402   (&content-codings;), unless the encoding transformation is identical (as it
2403   is the case for the compression codings defined in
2404   <xref target="compression.codings"/>).
2407   Values to be added to this name space require a specification
2408   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2409   conform to the purpose of transfer coding defined in this section.
2412   The registry itself is maintained at
2413   <eref target=""/>.
2418<section title="Product Tokens" anchor="product.tokens">
2419  <x:anchor-alias value="product"/>
2420  <x:anchor-alias value="product-version"/>
2422   Product tokens are used to allow communicating applications to
2423   identify themselves by software name and version. Most fields using
2424   product tokens also allow sub-products which form a significant part
2425   of the application to be listed, separated by whitespace. By
2426   convention, the products are listed in order of their significance
2427   for identifying the application.
2429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2430  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2431  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2434   Examples:
2436<figure><artwork type="example">
2437  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2438  Server: Apache/0.8.4
2441   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2442   used for advertising or other non-essential information. Although any
2443   token octet &MAY; appear in a product-version, this token &SHOULD;
2444   only be used for a version identifier (i.e., successive versions of
2445   the same product &SHOULD; only differ in the product-version portion of
2446   the product value).
2450<section title="Quality Values" anchor="quality.values">
2451  <x:anchor-alias value="qvalue"/>
2453   Both transfer codings (TE request header field, <xref target="header.te"/>)
2454   and content negotiation (&content.negotiation;) use short "floating point"
2455   numbers to indicate the relative importance ("weight") of various
2456   negotiable parameters.  A weight is normalized to a real number in
2457   the range 0 through 1, where 0 is the minimum and 1 the maximum
2458   value. If a parameter has a quality value of 0, then content with
2459   this parameter is "not acceptable" for the client. HTTP/1.1
2460   applications &MUST-NOT; generate more than three digits after the
2461   decimal point. User configuration of these values &SHOULD; also be
2462   limited in this fashion.
2464<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2465  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2466                 / ( "1" [ "." 0*3("0") ] )
2469  <t>
2470     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2471     relative degradation in desired quality.
2472  </t>
2478<section title="Connections" anchor="connections">
2480<section title="Persistent Connections" anchor="persistent.connections">
2482<section title="Purpose" anchor="persistent.purpose">
2484   Prior to persistent connections, a separate TCP connection was
2485   established for each request, increasing the load on HTTP servers
2486   and causing congestion on the Internet. The use of inline images and
2487   other associated data often requires a client to make multiple
2488   requests of the same server in a short amount of time. Analysis of
2489   these performance problems and results from a prototype
2490   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2491   measurements of actual HTTP/1.1 implementations show good
2492   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2493   T/TCP <xref target="Tou1998"/>.
2496   Persistent HTTP connections have a number of advantages:
2497  <list style="symbols">
2498      <t>
2499        By opening and closing fewer TCP connections, CPU time is saved
2500        in routers and hosts (clients, servers, proxies, gateways,
2501        tunnels, or caches), and memory used for TCP protocol control
2502        blocks can be saved in hosts.
2503      </t>
2504      <t>
2505        HTTP requests and responses can be pipelined on a connection.
2506        Pipelining allows a client to make multiple requests without
2507        waiting for each response, allowing a single TCP connection to
2508        be used much more efficiently, with much lower elapsed time.
2509      </t>
2510      <t>
2511        Network congestion is reduced by reducing the number of packets
2512        caused by TCP opens, and by allowing TCP sufficient time to
2513        determine the congestion state of the network.
2514      </t>
2515      <t>
2516        Latency on subsequent requests is reduced since there is no time
2517        spent in TCP's connection opening handshake.
2518      </t>
2519      <t>
2520        HTTP can evolve more gracefully, since errors can be reported
2521        without the penalty of closing the TCP connection. Clients using
2522        future versions of HTTP might optimistically try a new feature,
2523        but if communicating with an older server, retry with old
2524        semantics after an error is reported.
2525      </t>
2526    </list>
2529   HTTP implementations &SHOULD; implement persistent connections.
2533<section title="Overall Operation" anchor="persistent.overall">
2535   A significant difference between HTTP/1.1 and earlier versions of
2536   HTTP is that persistent connections are the default behavior of any
2537   HTTP connection. That is, unless otherwise indicated, the client
2538   &SHOULD; assume that the server will maintain a persistent connection,
2539   even after error responses from the server.
2542   Persistent connections provide a mechanism by which a client and a
2543   server can signal the close of a TCP connection. This signaling takes
2544   place using the Connection header field (<xref target="header.connection"/>). Once a close
2545   has been signaled, the client &MUST-NOT; send any more requests on that
2546   connection.
2549<section title="Negotiation" anchor="persistent.negotiation">
2551   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2552   maintain a persistent connection unless a Connection header field including
2553   the connection-token "close" was sent in the request. If the server
2554   chooses to close the connection immediately after sending the
2555   response, it &SHOULD; send a Connection header field including the
2556   connection-token "close".
2559   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2560   decide to keep it open based on whether the response from a server
2561   contains a Connection header field with the connection-token close. In case
2562   the client does not want to maintain a connection for more than that
2563   request, it &SHOULD; send a Connection header field including the
2564   connection-token close.
2567   If either the client or the server sends the close token in the
2568   Connection header field, that request becomes the last one for the
2569   connection.
2572   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2573   maintained for HTTP versions less than 1.1 unless it is explicitly
2574   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2575   compatibility with HTTP/1.0 clients.
2578   In order to remain persistent, all messages on the connection &MUST;
2579   have a self-defined message length (i.e., one not defined by closure
2580   of the connection), as described in <xref target="message.body"/>.
2584<section title="Pipelining" anchor="pipelining">
2586   A client that supports persistent connections &MAY; "pipeline" its
2587   requests (i.e., send multiple requests without waiting for each
2588   response). A server &MUST; send its responses to those requests in the
2589   same order that the requests were received.
2592   Clients which assume persistent connections and pipeline immediately
2593   after connection establishment &SHOULD; be prepared to retry their
2594   connection if the first pipelined attempt fails. If a client does
2595   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2596   persistent. Clients &MUST; also be prepared to resend their requests if
2597   the server closes the connection before sending all of the
2598   corresponding responses.
2601   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2602   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2603   premature termination of the transport connection could lead to
2604   indeterminate results. A client wishing to send a non-idempotent
2605   request &SHOULD; wait to send that request until it has received the
2606   response status line for the previous request.
2611<section title="Proxy Servers" anchor="persistent.proxy">
2613   It is especially important that proxies correctly implement the
2614   properties of the Connection header field as specified in <xref target="header.connection"/>.
2617   The proxy server &MUST; signal persistent connections separately with
2618   its clients and the origin servers (or other proxy servers) that it
2619   connects to. Each persistent connection applies to only one transport
2620   link.
2623   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2624   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2625   for information and discussion of the problems with the Keep-Alive header field
2626   implemented by many HTTP/1.0 clients).
2629<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2631  <cref anchor="TODO-end-to-end" source="jre">
2632    Restored from <eref target=""/>.
2633    See also <eref target=""/>.
2634  </cref>
2637   For the purpose of defining the behavior of caches and non-caching
2638   proxies, we divide HTTP header fields into two categories:
2639  <list style="symbols">
2640      <t>End-to-end header fields, which are  transmitted to the ultimate
2641        recipient of a request or response. End-to-end header fields in
2642        responses MUST be stored as part of a cache entry and &MUST; be
2643        transmitted in any response formed from a cache entry.</t>
2645      <t>Hop-by-hop header fields, which are meaningful only for a single
2646        transport-level connection, and are not stored by caches or
2647        forwarded by proxies.</t>
2648  </list>
2651   The following HTTP/1.1 header fields are hop-by-hop header fields:
2652  <list style="symbols">
2653      <t>Connection</t>
2654      <t>Keep-Alive</t>
2655      <t>Proxy-Authenticate</t>
2656      <t>Proxy-Authorization</t>
2657      <t>TE</t>
2658      <t>Trailer</t>
2659      <t>Transfer-Encoding</t>
2660      <t>Upgrade</t>
2661  </list>
2664   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2667   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2668   (<xref target="header.connection"/>).
2672<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2674  <cref anchor="TODO-non-mod-headers" source="jre">
2675    Restored from <eref target=""/>.
2676    See also <eref target=""/>.
2677  </cref>
2680   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2681   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2682   modify an end-to-end header field unless the definition of that header field requires
2683   or specifically allows that.
2686   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2687   request or response, and it &MUST-NOT; add any of these fields if not
2688   already present:
2689  <list style="symbols">
2690    <t>Allow</t>
2691    <t>Content-Location</t>
2692    <t>Content-MD5</t>
2693    <t>ETag</t>
2694    <t>Last-Modified</t>
2695    <t>Server</t>
2696  </list>
2699   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2700   response:
2701  <list style="symbols">
2702    <t>Expires</t>
2703  </list>
2706   but it &MAY; add any of these fields if not already present. If an
2707   Expires header field is added, it &MUST; be given a field-value identical to
2708   that of the Date header field in that response.
2711   A proxy &MUST-NOT; modify or add any of the following fields in a
2712   message that contains the no-transform cache-control directive, or in
2713   any request:
2714  <list style="symbols">
2715    <t>Content-Encoding</t>
2716    <t>Content-Range</t>
2717    <t>Content-Type</t>
2718  </list>
2721   A transforming proxy &MAY; modify or add these fields to a message
2722   that does not include no-transform, but if it does so, it &MUST; add a
2723   Warning 214 (Transformation applied) if one does not already appear
2724   in the message (see &header-warning;).
2727  <t>
2728    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2729    cause authentication failures if stronger authentication
2730    mechanisms are introduced in later versions of HTTP. Such
2731    authentication mechanisms &MAY; rely on the values of header fields
2732    not listed here.
2733  </t>
2736   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2737   though it &MAY; change the message-body through application or removal
2738   of a transfer-coding (<xref target="transfer.codings"/>).
2744<section title="Practical Considerations" anchor="persistent.practical">
2746   Servers will usually have some time-out value beyond which they will
2747   no longer maintain an inactive connection. Proxy servers might make
2748   this a higher value since it is likely that the client will be making
2749   more connections through the same server. The use of persistent
2750   connections places no requirements on the length (or existence) of
2751   this time-out for either the client or the server.
2754   When a client or server wishes to time-out it &SHOULD; issue a graceful
2755   close on the transport connection. Clients and servers &SHOULD; both
2756   constantly watch for the other side of the transport close, and
2757   respond to it as appropriate. If a client or server does not detect
2758   the other side's close promptly it could cause unnecessary resource
2759   drain on the network.
2762   A client, server, or proxy &MAY; close the transport connection at any
2763   time. For example, a client might have started to send a new request
2764   at the same time that the server has decided to close the "idle"
2765   connection. From the server's point of view, the connection is being
2766   closed while it was idle, but from the client's point of view, a
2767   request is in progress.
2770   This means that clients, servers, and proxies &MUST; be able to recover
2771   from asynchronous close events. Client software &SHOULD; reopen the
2772   transport connection and retransmit the aborted sequence of requests
2773   without user interaction so long as the request sequence is
2774   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2775   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2776   human operator the choice of retrying the request(s). Confirmation by
2777   user-agent software with semantic understanding of the application
2778   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2779   be repeated if the second sequence of requests fails.
2782   Servers &SHOULD; always respond to at least one request per connection,
2783   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2784   middle of transmitting a response, unless a network or client failure
2785   is suspected.
2788   Clients (including proxies) &SHOULD; limit the number of simultaneous
2789   connections that they maintain to a given server (including proxies).
2792   Previous revisions of HTTP gave a specific number of connections as a
2793   ceiling, but this was found to be impractical for many applications. As a
2794   result, this specification does not mandate a particular maximum number of
2795   connections, but instead encourages clients to be conservative when opening
2796   multiple connections.
2799   In particular, while using multiple connections avoids the "head-of-line
2800   blocking" problem (whereby a request that takes significant server-side
2801   processing and/or has a large payload can block subsequent requests on the
2802   same connection), each connection used consumes server resources (sometimes
2803   significantly), and furthermore using multiple connections can cause
2804   undesirable side effects in congested networks.
2807   Note that servers might reject traffic that they deem abusive, including an
2808   excessive number of connections from a client.
2813<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2815<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2817   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2818   flow control mechanisms to resolve temporary overloads, rather than
2819   terminating connections with the expectation that clients will retry.
2820   The latter technique can exacerbate network congestion.
2824<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2826   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2827   the network connection for an error status code while it is transmitting
2828   the request. If the client sees an error status code, it &SHOULD;
2829   immediately cease transmitting the body. If the body is being sent
2830   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2831   empty trailer &MAY; be used to prematurely mark the end of the message.
2832   If the body was preceded by a Content-Length header field, the client &MUST;
2833   close the connection.
2837<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2839   The purpose of the 100 (Continue) status code (see &status-100;) is to
2840   allow a client that is sending a request message with a request body
2841   to determine if the origin server is willing to accept the request
2842   (based on the request header fields) before the client sends the request
2843   body. In some cases, it might either be inappropriate or highly
2844   inefficient for the client to send the body if the server will reject
2845   the message without looking at the body.
2848   Requirements for HTTP/1.1 clients:
2849  <list style="symbols">
2850    <t>
2851        If a client will wait for a 100 (Continue) response before
2852        sending the request body, it &MUST; send an Expect header
2853        field (&header-expect;) with the "100-continue" expectation.
2854    </t>
2855    <t>
2856        A client &MUST-NOT; send an Expect header field (&header-expect;)
2857        with the "100-continue" expectation if it does not intend
2858        to send a request body.
2859    </t>
2860  </list>
2863   Because of the presence of older implementations, the protocol allows
2864   ambiguous situations in which a client might send "Expect: 100-continue"
2865   without receiving either a 417 (Expectation Failed)
2866   or a 100 (Continue) status code. Therefore, when a client sends this
2867   header field to an origin server (possibly via a proxy) from which it
2868   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2869   wait for an indefinite period before sending the request body.
2872   Requirements for HTTP/1.1 origin servers:
2873  <list style="symbols">
2874    <t> Upon receiving a request which includes an Expect header
2875        field with the "100-continue" expectation, an origin server &MUST;
2876        either respond with 100 (Continue) status code and continue to read
2877        from the input stream, or respond with a final status code. The
2878        origin server &MUST-NOT; wait for the request body before sending
2879        the 100 (Continue) response. If it responds with a final status
2880        code, it &MAY; close the transport connection or it &MAY; continue
2881        to read and discard the rest of the request.  It &MUST-NOT;
2882        perform the request method if it returns a final status code.
2883    </t>
2884    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2885        the request message does not include an Expect header
2886        field with the "100-continue" expectation, and &MUST-NOT; send a
2887        100 (Continue) response if such a request comes from an HTTP/1.0
2888        (or earlier) client. There is an exception to this rule: for
2889        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2890        status code in response to an HTTP/1.1 PUT or POST request that does
2891        not include an Expect header field with the "100-continue"
2892        expectation. This exception, the purpose of which is
2893        to minimize any client processing delays associated with an
2894        undeclared wait for 100 (Continue) status code, applies only to
2895        HTTP/1.1 requests, and not to requests with any other HTTP-version
2896        value.
2897    </t>
2898    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2899        already received some or all of the request body for the
2900        corresponding request.
2901    </t>
2902    <t> An origin server that sends a 100 (Continue) response &MUST;
2903    ultimately send a final status code, once the request body is
2904        received and processed, unless it terminates the transport
2905        connection prematurely.
2906    </t>
2907    <t> If an origin server receives a request that does not include an
2908        Expect header field with the "100-continue" expectation,
2909        the request includes a request body, and the server responds
2910        with a final status code before reading the entire request body
2911        from the transport connection, then the server &SHOULD-NOT;  close
2912        the transport connection until it has read the entire request,
2913        or until the client closes the connection. Otherwise, the client
2914        might not reliably receive the response message. However, this
2915        requirement is not be construed as preventing a server from
2916        defending itself against denial-of-service attacks, or from
2917        badly broken client implementations.
2918      </t>
2919    </list>
2922   Requirements for HTTP/1.1 proxies:
2923  <list style="symbols">
2924    <t> If a proxy receives a request that includes an Expect header
2925        field with the "100-continue" expectation, and the proxy
2926        either knows that the next-hop server complies with HTTP/1.1 or
2927        higher, or does not know the HTTP version of the next-hop
2928        server, it &MUST; forward the request, including the Expect header
2929        field.
2930    </t>
2931    <t> If the proxy knows that the version of the next-hop server is
2932        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2933        respond with a 417 (Expectation Failed) status code.
2934    </t>
2935    <t> Proxies &SHOULD; maintain a record of the HTTP version
2936        numbers received from recently-referenced next-hop servers.
2937    </t>
2938    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2939        request message was received from an HTTP/1.0 (or earlier)
2940        client and did not include an Expect header field with
2941        the "100-continue" expectation. This requirement overrides the
2942        general rule for forwarding of 1xx responses (see &status-1xx;).
2943    </t>
2944  </list>
2948<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2950   If an HTTP/1.1 client sends a request which includes a request body,
2951   but which does not include an Expect header field with the
2952   "100-continue" expectation, and if the client is not directly
2953   connected to an HTTP/1.1 origin server, and if the client sees the
2954   connection close before receiving a status line from the server, the
2955   client &SHOULD; retry the request.  If the client does retry this
2956   request, it &MAY; use the following "binary exponential backoff"
2957   algorithm to be assured of obtaining a reliable response:
2958  <list style="numbers">
2959    <t>
2960      Initiate a new connection to the server
2961    </t>
2962    <t>
2963      Transmit the request-line, header fields, and the CRLF that
2964      indicates the end of header fields.
2965    </t>
2966    <t>
2967      Initialize a variable R to the estimated round-trip time to the
2968         server (e.g., based on the time it took to establish the
2969         connection), or to a constant value of 5 seconds if the round-trip
2970         time is not available.
2971    </t>
2972    <t>
2973       Compute T = R * (2**N), where N is the number of previous
2974         retries of this request.
2975    </t>
2976    <t>
2977       Wait either for an error response from the server, or for T
2978         seconds (whichever comes first)
2979    </t>
2980    <t>
2981       If no error response is received, after T seconds transmit the
2982         body of the request.
2983    </t>
2984    <t>
2985       If client sees that the connection is closed prematurely,
2986         repeat from step 1 until the request is accepted, an error
2987         response is received, or the user becomes impatient and
2988         terminates the retry process.
2989    </t>
2990  </list>
2993   If at any point an error status code is received, the client
2994  <list style="symbols">
2995      <t>&SHOULD-NOT;  continue and</t>
2997      <t>&SHOULD; close the connection if it has not completed sending the
2998        request message.</t>
2999    </list>
3006<section title="Miscellaneous notes that might disappear" anchor="misc">
3007<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
3009   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
3013<section title="Use of HTTP for proxy communication" anchor="http.proxy">
3015   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
3019<section title="Interception of HTTP for access control" anchor="http.intercept">
3021   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
3025<section title="Use of HTTP by other protocols" anchor="http.others">
3027   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3028   Extensions of HTTP like WebDAV.</cref>
3032<section title="Use of HTTP by media type specification" anchor="">
3034   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3039<section title="Header Field Definitions" anchor="header.field.definitions">
3041   This section defines the syntax and semantics of HTTP header fields
3042   related to message framing and transport protocols.
3045<section title="Connection" anchor="header.connection">
3046  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3047  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3048  <x:anchor-alias value="Connection"/>
3049  <x:anchor-alias value="connection-token"/>
3051   The "Connection" header field allows the sender to specify
3052   options that are desired only for that particular connection.
3053   Such connection options &MUST; be removed or replaced before the
3054   message can be forwarded downstream by a proxy or gateway.
3055   This mechanism also allows the sender to indicate which HTTP
3056   header fields used in the message are only intended for the
3057   immediate recipient ("hop-by-hop"), as opposed to all recipients
3058   on the chain ("end-to-end"), enabling the message to be
3059   self-descriptive and allowing future connection-specific extensions
3060   to be deployed in HTTP without fear that they will be blindly
3061   forwarded by previously deployed intermediaries.
3064   The Connection header field's value has the following grammar:
3066<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3067  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3068  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3071   A proxy or gateway &MUST; parse a received Connection
3072   header field before a message is forwarded and, for each
3073   connection-token in this field, remove any header field(s) from
3074   the message with the same name as the connection-token, and then
3075   remove the Connection header field itself or replace it with the
3076   sender's own connection options for the forwarded message.
3079   A sender &MUST-NOT; include field-names in the Connection header
3080   field-value for fields that are defined as expressing constraints
3081   for all recipients in the request or response chain, such as the
3082   Cache-Control header field (&header-cache-control;).
3085   The connection options do not have to correspond to a header field
3086   present in the message, since a connection-specific header field
3087   might not be needed if there are no parameters associated with that
3088   connection option.  Recipients that trigger certain connection
3089   behavior based on the presence of connection options &MUST; do so
3090   based on the presence of the connection-token rather than only the
3091   presence of the optional header field.  In other words, if the
3092   connection option is received as a header field but not indicated
3093   within the Connection field-value, then the recipient &MUST; ignore
3094   the connection-specific header field because it has likely been
3095   forwarded by an intermediary that is only partially compliant.
3098   When defining new connection options, specifications ought to
3099   carefully consider existing deployed header fields and ensure
3100   that the new connection-token does not share the same name as
3101   an unrelated header field that might already be deployed.
3102   Defining a new connection-token essentially reserves that potential
3103   field-name for carrying additional information related to the
3104   connection option, since it would be unwise for senders to use
3105   that field-name for anything else.
3108   HTTP/1.1 defines the "close" connection option for the sender to
3109   signal that the connection will be closed after completion of the
3110   response. For example,
3112<figure><artwork type="example">
3113  Connection: close
3116   in either the request or the response header fields indicates that
3117   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3118   after the current request/response is complete.
3121   An HTTP/1.1 client that does not support persistent connections &MUST;
3122   include the "close" connection option in every request message.
3125   An HTTP/1.1 server that does not support persistent connections &MUST;
3126   include the "close" connection option in every response message that
3127   does not have a 1xx (Informational) status code.
3131<section title="Content-Length" anchor="header.content-length">
3132  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3133  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3134  <x:anchor-alias value="Content-Length"/>
3136   The "Content-Length" header field indicates the size of the
3137   message-body, in decimal number of octets, for any message other than
3138   a response to a HEAD request or a response with a status code of 304.
3139   In the case of a response to a HEAD request, Content-Length indicates
3140   the size of the payload body (not including any potential transfer-coding)
3141   that would have been sent had the request been a GET.
3142   In the case of a 304 (Not Modified) response to a GET request,
3143   Content-Length indicates the size of the payload body (not including
3144   any potential transfer-coding) that would have been sent in a 200 (OK)
3145   response.
3147<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3148  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3151   An example is
3153<figure><artwork type="example">
3154  Content-Length: 3495
3157   Implementations &SHOULD; use this field to indicate the message-body
3158   length when no transfer-coding is being applied and the
3159   payload's body length can be determined prior to being transferred.
3160   <xref target="message.body"/> describes how recipients determine the length
3161   of a message-body.
3164   Any Content-Length greater than or equal to zero is a valid value.
3167   Note that the use of this field in HTTP is significantly different from
3168   the corresponding definition in MIME, where it is an optional field
3169   used within the "message/external-body" content-type.
3173<section title="Date" anchor="">
3174  <iref primary="true" item="Date header field" x:for-anchor=""/>
3175  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3176  <x:anchor-alias value="Date"/>
3178   The "Date" header field represents the date and time at which
3179   the message was originated, having the same semantics as the Origination
3180   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3181   The field value is an HTTP-date, as described in <xref target=""/>;
3182   it &MUST; be sent in rfc1123-date format.
3184<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3185  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3188   An example is
3190<figure><artwork type="example">
3191  Date: Tue, 15 Nov 1994 08:12:31 GMT
3194   Origin servers &MUST; include a Date header field in all responses,
3195   except in these cases:
3196  <list style="numbers">
3197      <t>If the response status code is 100 (Continue) or 101 (Switching
3198         Protocols), the response &MAY; include a Date header field, at
3199         the server's option.</t>
3201      <t>If the response status code conveys a server error, e.g., 500
3202         (Internal Server Error) or 503 (Service Unavailable), and it is
3203         inconvenient or impossible to generate a valid Date.</t>
3205      <t>If the server does not have a clock that can provide a
3206         reasonable approximation of the current time, its responses
3207         &MUST-NOT; include a Date header field. In this case, the rules
3208         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3209  </list>
3212   A received message that does not have a Date header field &MUST; be
3213   assigned one by the recipient if the message will be cached by that
3214   recipient.
3217   Clients can use the Date header field as well; in order to keep request
3218   messages small, they are advised not to include it when it doesn't convey
3219   any useful information (as it is usually the case for requests that do not
3220   contain a payload).
3223   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3224   time subsequent to the generation of the message. It &SHOULD; represent
3225   the best available approximation of the date and time of message
3226   generation, unless the implementation has no means of generating a
3227   reasonably accurate date and time. In theory, the date ought to
3228   represent the moment just before the payload is generated. In
3229   practice, the date can be generated at any time during the message
3230   origination without affecting its semantic value.
3233<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3235   Some origin server implementations might not have a clock available.
3236   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3237   values to a response, unless these values were associated
3238   with the resource by a system or user with a reliable clock. It &MAY;
3239   assign an Expires value that is known, at or before server
3240   configuration time, to be in the past (this allows "pre-expiration"
3241   of responses without storing separate Expires values for each
3242   resource).
3247<section title="Host" anchor="">
3248  <iref primary="true" item="Host header field" x:for-anchor=""/>
3249  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3250  <x:anchor-alias value="Host"/>
3252   The "Host" header field in a request provides the host and port
3253   information from the target resource's URI, enabling the origin
3254   server to distinguish between resources while servicing requests
3255   for multiple host names on a single IP address.  Since the Host
3256   field-value is critical information for handling a request, it
3257   &SHOULD; be sent as the first header field following the Request-Line.
3259<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3260  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3263   A client &MUST; send a Host header field in all HTTP/1.1 request
3264   messages.  If the target resource's URI includes an authority
3265   component, then the Host field-value &MUST; be identical to that
3266   authority component after excluding any userinfo (<xref target="http.uri"/>).
3267   If the authority component is missing or undefined for the target
3268   resource's URI, then the Host header field &MUST; be sent with an
3269   empty field-value.
3272   For example, a GET request to the origin server for
3273   &lt;; would begin with:
3275<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3276GET /pub/WWW/ HTTP/1.1
3280   The Host header field &MUST; be sent in an HTTP/1.1 request even
3281   if the request-target is in the form of an absolute-URI, since this
3282   allows the Host information to be forwarded through ancient HTTP/1.0
3283   proxies that might not have implemented Host.
3286   When an HTTP/1.1 proxy receives a request with a request-target in
3287   the form of an absolute-URI, the proxy &MUST; ignore the received
3288   Host header field (if any) and instead replace it with the host
3289   information of the request-target.  When a proxy forwards a request,
3290   it &MUST; generate the Host header field based on the received
3291   absolute-URI rather than the received Host.
3294   Since the Host header field acts as an application-level routing
3295   mechanism, it is a frequent target for malware seeking to poison
3296   a shared cache or redirect a request to an unintended server.
3297   An interception proxy is particularly vulnerable if it relies on
3298   the Host header field value for redirecting requests to internal
3299   servers, or for use as a cache key in a shared cache, without
3300   first verifying that the intercepted connection is targeting a
3301   valid IP address for that host.
3304   A server &MUST; respond with a 400 (Bad Request) status code to
3305   any HTTP/1.1 request message that lacks a Host header field and
3306   to any request message that contains more than one Host header field
3307   or a Host header field with an invalid field-value.
3310   See Sections <xref target="" format="counter"/>
3311   and <xref target="" format="counter"/>
3312   for other requirements relating to Host.
3316<section title="TE" anchor="header.te">
3317  <iref primary="true" item="TE header field" x:for-anchor=""/>
3318  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3319  <x:anchor-alias value="TE"/>
3320  <x:anchor-alias value="t-codings"/>
3321  <x:anchor-alias value="te-params"/>
3322  <x:anchor-alias value="te-ext"/>
3324   The "TE" header field indicates what extension transfer-codings
3325   it is willing to accept in the response, and whether or not it is
3326   willing to accept trailer fields in a chunked transfer-coding.
3329   Its value consists of the keyword "trailers" and/or a comma-separated
3330   list of extension transfer-coding names with optional accept
3331   parameters (as described in <xref target="transfer.codings"/>).
3333<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"/>
3334  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3335  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3336  <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> )
3337  <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> ]
3340   The presence of the keyword "trailers" indicates that the client is
3341   willing to accept trailer fields in a chunked transfer-coding, as
3342   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3343   transfer-coding values even though it does not itself represent a
3344   transfer-coding.
3347   Examples of its use are:
3349<figure><artwork type="example">
3350  TE: deflate
3351  TE:
3352  TE: trailers, deflate;q=0.5
3355   The TE header field only applies to the immediate connection.
3356   Therefore, the keyword &MUST; be supplied within a Connection header
3357   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3360   A server tests whether a transfer-coding is acceptable, according to
3361   a TE field, using these rules:
3362  <list style="numbers">
3363    <x:lt>
3364      <t>The "chunked" transfer-coding is always acceptable. If the
3365         keyword "trailers" is listed, the client indicates that it is
3366         willing to accept trailer fields in the chunked response on
3367         behalf of itself and any downstream clients. The implication is
3368         that, if given, the client is stating that either all
3369         downstream clients are willing to accept trailer fields in the
3370         forwarded response, or that it will attempt to buffer the
3371         response on behalf of downstream recipients.
3372      </t><t>
3373         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3374         chunked response such that a client can be assured of buffering
3375         the entire response.</t>
3376    </x:lt>
3377    <x:lt>
3378      <t>If the transfer-coding being tested is one of the transfer-codings
3379         listed in the TE field, then it is acceptable unless it
3380         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3381         qvalue of 0 means "not acceptable".)</t>
3382    </x:lt>
3383    <x:lt>
3384      <t>If multiple transfer-codings are acceptable, then the
3385         acceptable transfer-coding with the highest non-zero qvalue is
3386         preferred.  The "chunked" transfer-coding always has a qvalue
3387         of 1.</t>
3388    </x:lt>
3389  </list>
3392   If the TE field-value is empty or if no TE field is present, the only
3393   transfer-coding is "chunked". A message with no transfer-coding is
3394   always acceptable.
3398<section title="Trailer" anchor="header.trailer">
3399  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3400  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3401  <x:anchor-alias value="Trailer"/>
3403   The "Trailer" header field indicates that the given set of
3404   header fields is present in the trailer of a message encoded with
3405   chunked transfer-coding.
3407<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3408  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3411   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3412   message using chunked transfer-coding with a non-empty trailer. Doing
3413   so allows the recipient to know which header fields to expect in the
3414   trailer.
3417   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3418   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3419   trailer fields in a "chunked" transfer-coding.
3422   Message header fields listed in the Trailer header field &MUST-NOT;
3423   include the following header fields:
3424  <list style="symbols">
3425    <t>Transfer-Encoding</t>
3426    <t>Content-Length</t>
3427    <t>Trailer</t>
3428  </list>
3432<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3433  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3434  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3435  <x:anchor-alias value="Transfer-Encoding"/>
3437   The "Transfer-Encoding" header field indicates what transfer-codings
3438   (if any) have been applied to the message body. It differs from
3439   Content-Encoding (&content-codings;) in that transfer-codings are a property
3440   of the message (and therefore are removed by intermediaries), whereas
3441   content-codings are not.
3443<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3444  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3447   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3449<figure><artwork type="example">
3450  Transfer-Encoding: chunked
3453   If multiple encodings have been applied to a representation, the transfer-codings
3454   &MUST; be listed in the order in which they were applied.
3455   Additional information about the encoding parameters &MAY; be provided
3456   by other header fields not defined by this specification.
3459   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3460   header field.
3464<section title="Upgrade" anchor="header.upgrade">
3465  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3466  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3467  <x:anchor-alias value="Upgrade"/>
3469   The "Upgrade" header field allows the client to specify what
3470   additional communication protocols it would like to use, if the server
3471   chooses to switch protocols. Servers can use it to indicate what protocols
3472   they are willing to switch to.
3474<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3475  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3478   For example,
3480<figure><artwork type="example">
3481  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3484   The Upgrade header field is intended to provide a simple mechanism
3485   for transition from HTTP/1.1 to some other, incompatible protocol. It
3486   does so by allowing the client to advertise its desire to use another
3487   protocol, such as a later version of HTTP with a higher major version
3488   number, even though the current request has been made using HTTP/1.1.
3489   This eases the difficult transition between incompatible protocols by
3490   allowing the client to initiate a request in the more commonly
3491   supported protocol while indicating to the server that it would like
3492   to use a "better" protocol if available (where "better" is determined
3493   by the server, possibly according to the nature of the request method
3494   or target resource).
3497   The Upgrade header field only applies to switching application-layer
3498   protocols upon the existing transport-layer connection. Upgrade
3499   cannot be used to insist on a protocol change; its acceptance and use
3500   by the server is optional. The capabilities and nature of the
3501   application-layer communication after the protocol change is entirely
3502   dependent upon the new protocol chosen, although the first action
3503   after changing the protocol &MUST; be a response to the initial HTTP
3504   request containing the Upgrade header field.
3507   The Upgrade header field only applies to the immediate connection.
3508   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3509   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3510   HTTP/1.1 message.
3513   The Upgrade header field cannot be used to indicate a switch to a
3514   protocol on a different connection. For that purpose, it is more
3515   appropriate to use a 3xx redirection response (&status-3xx;).
3518   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3519   Protocols) responses to indicate which protocol(s) are being switched to,
3520   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3521   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3522   response to indicate that they are willing to upgrade to one of the
3523   specified protocols.
3526   This specification only defines the protocol name "HTTP" for use by
3527   the family of Hypertext Transfer Protocols, as defined by the HTTP
3528   version rules of <xref target="http.version"/> and future updates to this
3529   specification. Additional tokens can be registered with IANA using the
3530   registration procedure defined below. 
3533<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3535   The HTTP Upgrade Token Registry defines the name space for product
3536   tokens used to identify protocols in the Upgrade header field.
3537   Each registered token is associated with contact information and
3538   an optional set of specifications that details how the connection
3539   will be processed after it has been upgraded.
3542   Registrations are allowed on a First Come First Served basis as
3543   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3544   specifications need not be IETF documents or be subject to IESG review.
3545   Registrations are subject to the following rules:
3546  <list style="numbers">
3547    <t>A token, once registered, stays registered forever.</t>
3548    <t>The registration &MUST; name a responsible party for the
3549       registration.</t>
3550    <t>The registration &MUST; name a point of contact.</t>
3551    <t>The registration &MAY; name a set of specifications associated with that
3552       token. Such specifications need not be publicly available.</t>
3553    <t>The responsible party &MAY; change the registration at any time.
3554       The IANA will keep a record of all such changes, and make them
3555       available upon request.</t>
3556    <t>The responsible party for the first registration of a "product"
3557       token &MUST; approve later registrations of a "version" token
3558       together with that "product" token before they can be registered.</t>
3559    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3560       for a token. This will normally only be used in the case when a
3561       responsible party cannot be contacted.</t>
3562  </list>
3569<section title="Via" anchor="header.via">
3570  <iref primary="true" item="Via header field" x:for-anchor=""/>
3571  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3572  <x:anchor-alias value="protocol-name"/>
3573  <x:anchor-alias value="protocol-version"/>
3574  <x:anchor-alias value="pseudonym"/>
3575  <x:anchor-alias value="received-by"/>
3576  <x:anchor-alias value="received-protocol"/>
3577  <x:anchor-alias value="Via"/>
3579   The "Via" header field &MUST; be sent by a proxy or gateway to
3580   indicate the intermediate protocols and recipients between the user
3581   agent and the server on requests, and between the origin server and
3582   the client on responses. It is analogous to the "Received" field
3583   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3584   and is intended to be used for tracking message forwards,
3585   avoiding request loops, and identifying the protocol capabilities of
3586   all senders along the request/response chain.
3588<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"/>
3589  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3590                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3591  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3592  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3593  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3594  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3595  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3598   The received-protocol indicates the protocol version of the message
3599   received by the server or client along each segment of the
3600   request/response chain. The received-protocol version is appended to
3601   the Via field value when the message is forwarded so that information
3602   about the protocol capabilities of upstream applications remains
3603   visible to all recipients.
3606   The protocol-name is excluded if and only if it would be "HTTP". The
3607   received-by field is normally the host and optional port number of a
3608   recipient server or client that subsequently forwarded the message.
3609   However, if the real host is considered to be sensitive information,
3610   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3611   be assumed to be the default port of the received-protocol.
3614   Multiple Via field values represent each proxy or gateway that has
3615   forwarded the message. Each recipient &MUST; append its information
3616   such that the end result is ordered according to the sequence of
3617   forwarding applications.
3620   Comments &MAY; be used in the Via header field to identify the software
3621   of each recipient, analogous to the User-Agent and Server header fields.
3622   However, all comments in the Via field are optional and &MAY; be removed
3623   by any recipient prior to forwarding the message.
3626   For example, a request message could be sent from an HTTP/1.0 user
3627   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3628   forward the request to a public proxy at, which completes
3629   the request by forwarding it to the origin server at
3630   The request received by would then have the following
3631   Via header field:
3633<figure><artwork type="example">
3634  Via: 1.0 fred, 1.1 (Apache/1.1)
3637   A proxy or gateway used as a portal through a network firewall
3638   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3639   region unless it is explicitly enabled to do so. If not enabled, the
3640   received-by host of any host behind the firewall &SHOULD; be replaced
3641   by an appropriate pseudonym for that host.
3644   For organizations that have strong privacy requirements for hiding
3645   internal structures, a proxy or gateway &MAY; combine an ordered
3646   subsequence of Via header field entries with identical received-protocol
3647   values into a single such entry. For example,
3649<figure><artwork type="example">
3650  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3653  could be collapsed to
3655<figure><artwork type="example">
3656  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3659   Senders &SHOULD-NOT; combine multiple entries unless they are all
3660   under the same organizational control and the hosts have already been
3661   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3662   have different received-protocol values.
3668<section title="IANA Considerations" anchor="IANA.considerations">
3670<section title="Header Field Registration" anchor="header.field.registration">
3672   The Message Header Field Registry located at <eref target=""/> shall be updated
3673   with the permanent registrations below (see <xref target="RFC3864"/>):
3675<?BEGININC p1-messaging.iana-headers ?>
3676<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3677<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3678   <ttcol>Header Field Name</ttcol>
3679   <ttcol>Protocol</ttcol>
3680   <ttcol>Status</ttcol>
3681   <ttcol>Reference</ttcol>
3683   <c>Connection</c>
3684   <c>http</c>
3685   <c>standard</c>
3686   <c>
3687      <xref target="header.connection"/>
3688   </c>
3689   <c>Content-Length</c>
3690   <c>http</c>
3691   <c>standard</c>
3692   <c>
3693      <xref target="header.content-length"/>
3694   </c>
3695   <c>Date</c>
3696   <c>http</c>
3697   <c>standard</c>
3698   <c>
3699      <xref target=""/>
3700   </c>
3701   <c>Host</c>
3702   <c>http</c>
3703   <c>standard</c>
3704   <c>
3705      <xref target=""/>
3706   </c>
3707   <c>TE</c>
3708   <c>http</c>
3709   <c>standard</c>
3710   <c>
3711      <xref target="header.te"/>
3712   </c>
3713   <c>Trailer</c>
3714   <c>http</c>
3715   <c>standard</c>
3716   <c>
3717      <xref target="header.trailer"/>
3718   </c>
3719   <c>Transfer-Encoding</c>
3720   <c>http</c>
3721   <c>standard</c>
3722   <c>
3723      <xref target="header.transfer-encoding"/>
3724   </c>
3725   <c>Upgrade</c>
3726   <c>http</c>
3727   <c>standard</c>
3728   <c>
3729      <xref target="header.upgrade"/>
3730   </c>
3731   <c>Via</c>
3732   <c>http</c>
3733   <c>standard</c>
3734   <c>
3735      <xref target="header.via"/>
3736   </c>
3739<?ENDINC p1-messaging.iana-headers ?>
3741   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3742   HTTP header field would be in conflict with the use of the "close" connection
3743   option for the "Connection" header field (<xref target="header.connection"/>).
3745<texttable align="left" suppress-title="true">
3746   <ttcol>Header Field Name</ttcol>
3747   <ttcol>Protocol</ttcol>
3748   <ttcol>Status</ttcol>
3749   <ttcol>Reference</ttcol>
3751   <c>Close</c>
3752   <c>http</c>
3753   <c>reserved</c>
3754   <c>
3755      <xref target="header.field.registration"/>
3756   </c>
3759   The change controller is: "IETF ( - Internet Engineering Task Force".
3763<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3765   The entries for the "http" and "https" URI Schemes in the registry located at
3766   <eref target=""/>
3767   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3768   and <xref target="https.uri" format="counter"/> of this document
3769   (see <xref target="RFC4395"/>).
3773<section title="Internet Media Type Registrations" anchor="">
3775   This document serves as the specification for the Internet media types
3776   "message/http" and "application/http". The following is to be registered with
3777   IANA (see <xref target="RFC4288"/>).
3779<section title="Internet Media Type message/http" anchor="">
3780<iref item="Media Type" subitem="message/http" primary="true"/>
3781<iref item="message/http Media Type" primary="true"/>
3783   The message/http type can be used to enclose a single HTTP request or
3784   response message, provided that it obeys the MIME restrictions for all
3785   "message" types regarding line length and encodings.
3788  <list style="hanging" x:indent="12em">
3789    <t hangText="Type name:">
3790      message
3791    </t>
3792    <t hangText="Subtype name:">
3793      http
3794    </t>
3795    <t hangText="Required parameters:">
3796      none
3797    </t>
3798    <t hangText="Optional parameters:">
3799      version, msgtype
3800      <list style="hanging">
3801        <t hangText="version:">
3802          The HTTP-Version number of the enclosed message
3803          (e.g., "1.1"). If not present, the version can be
3804          determined from the first line of the body.
3805        </t>
3806        <t hangText="msgtype:">
3807          The message type &mdash; "request" or "response". If not
3808          present, the type can be determined from the first
3809          line of the body.
3810        </t>
3811      </list>
3812    </t>
3813    <t hangText="Encoding considerations:">
3814      only "7bit", "8bit", or "binary" are permitted
3815    </t>
3816    <t hangText="Security considerations:">
3817      none
3818    </t>
3819    <t hangText="Interoperability considerations:">
3820      none
3821    </t>
3822    <t hangText="Published specification:">
3823      This specification (see <xref target=""/>).
3824    </t>
3825    <t hangText="Applications that use this media type:">
3826    </t>
3827    <t hangText="Additional information:">
3828      <list style="hanging">
3829        <t hangText="Magic number(s):">none</t>
3830        <t hangText="File extension(s):">none</t>
3831        <t hangText="Macintosh file type code(s):">none</t>
3832      </list>
3833    </t>
3834    <t hangText="Person and email address to contact for further information:">
3835      See Authors Section.
3836    </t>
3837    <t hangText="Intended usage:">
3838      COMMON
3839    </t>
3840    <t hangText="Restrictions on usage:">
3841      none
3842    </t>
3843    <t hangText="Author/Change controller:">
3844      IESG
3845    </t>
3846  </list>
3849<section title="Internet Media Type application/http" anchor="">
3850<iref item="Media Type" subitem="application/http" primary="true"/>
3851<iref item="application/http Media Type" primary="true"/>
3853   The application/http type can be used to enclose a pipeline of one or more
3854   HTTP request or response messages (not intermixed).
3857  <list style="hanging" x:indent="12em">
3858    <t hangText="Type name:">
3859      application
3860    </t>
3861    <t hangText="Subtype name:">
3862      http
3863    </t>
3864    <t hangText="Required parameters:">
3865      none
3866    </t>
3867    <t hangText="Optional parameters:">
3868      version, msgtype
3869      <list style="hanging">
3870        <t hangText="version:">
3871          The HTTP-Version number of the enclosed messages
3872          (e.g., "1.1"). If not present, the version can be
3873          determined from the first line of the body.
3874        </t>
3875        <t hangText="msgtype:">
3876          The message type &mdash; "request" or "response". If not
3877          present, the type can be determined from the first
3878          line of the body.
3879        </t>
3880      </list>
3881    </t>
3882    <t hangText="Encoding considerations:">
3883      HTTP messages enclosed by this type
3884      are in "binary" format; use of an appropriate
3885      Content-Transfer-Encoding is required when
3886      transmitted via E-mail.
3887    </t>
3888    <t hangText="Security considerations:">
3889      none
3890    </t>
3891    <t hangText="Interoperability considerations:">
3892      none
3893    </t>
3894    <t hangText="Published specification:">
3895      This specification (see <xref target=""/>).
3896    </t>
3897    <t hangText="Applications that use this media type:">
3898    </t>
3899    <t hangText="Additional information:">
3900      <list style="hanging">
3901        <t hangText="Magic number(s):">none</t>
3902        <t hangText="File extension(s):">none</t>
3903        <t hangText="Macintosh file type code(s):">none</t>
3904      </list>
3905    </t>
3906    <t hangText="Person and email address to contact for further information:">
3907      See Authors Section.
3908    </t>
3909    <t hangText="Intended usage:">
3910      COMMON
3911    </t>
3912    <t hangText="Restrictions on usage:">
3913      none
3914    </t>
3915    <t hangText="Author/Change controller:">
3916      IESG
3917    </t>
3918  </list>
3923<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3925   The registration procedure for HTTP Transfer Codings is now defined by
3926   <xref target="transfer.coding.registry"/> of this document.
3929   The HTTP Transfer Codings Registry located at <eref target=""/>
3930   shall be updated with the registrations below:
3932<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3933   <ttcol>Name</ttcol>
3934   <ttcol>Description</ttcol>
3935   <ttcol>Reference</ttcol>
3936   <c>chunked</c>
3937   <c>Transfer in a series of chunks</c>
3938   <c>
3939      <xref target="chunked.encoding"/>
3940   </c>
3941   <c>compress</c>
3942   <c>UNIX "compress" program method</c>
3943   <c>
3944      <xref target="compress.coding"/>
3945   </c>
3946   <c>deflate</c>
3947   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3948   the "zlib" data format (<xref target="RFC1950"/>)
3949   </c>
3950   <c>
3951      <xref target="deflate.coding"/>
3952   </c>
3953   <c>gzip</c>
3954   <c>Same as GNU zip <xref target="RFC1952"/></c>
3955   <c>
3956      <xref target="gzip.coding"/>
3957   </c>
3961<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3963   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3964   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3965   by <xref target="upgrade.token.registry"/> of this document.
3968   The HTTP Status Code Registry located at <eref target=""/>
3969   shall be updated with the registration below:
3971<texttable align="left" suppress-title="true">
3972   <ttcol>Value</ttcol>
3973   <ttcol>Description</ttcol>
3974   <ttcol>Reference</ttcol>
3976   <c>HTTP</c>
3977   <c>Hypertext Transfer Protocol</c>
3978   <c><xref target="http.version"/> of this specification</c>
3985<section title="Security Considerations" anchor="security.considerations">
3987   This section is meant to inform application developers, information
3988   providers, and users of the security limitations in HTTP/1.1 as
3989   described by this document. The discussion does not include
3990   definitive solutions to the problems revealed, though it does make
3991   some suggestions for reducing security risks.
3994<section title="Personal Information" anchor="personal.information">
3996   HTTP clients are often privy to large amounts of personal information
3997   (e.g., the user's name, location, mail address, passwords, encryption
3998   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3999   leakage of this information.
4000   We very strongly recommend that a convenient interface be provided
4001   for the user to control dissemination of such information, and that
4002   designers and implementors be particularly careful in this area.
4003   History shows that errors in this area often create serious security
4004   and/or privacy problems and generate highly adverse publicity for the
4005   implementor's company.
4009<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
4011   A server is in the position to save personal data about a user's
4012   requests which might identify their reading patterns or subjects of
4013   interest. This information is clearly confidential in nature and its
4014   handling can be constrained by law in certain countries. People using
4015   HTTP to provide data are responsible for ensuring that
4016   such material is not distributed without the permission of any
4017   individuals that are identifiable by the published results.
4021<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
4023   Implementations of HTTP origin servers &SHOULD; be careful to restrict
4024   the documents returned by HTTP requests to be only those that were
4025   intended by the server administrators. If an HTTP server translates
4026   HTTP URIs directly into file system calls, the server &MUST; take
4027   special care not to serve files that were not intended to be
4028   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
4029   other operating systems use ".." as a path component to indicate a
4030   directory level above the current one. On such a system, an HTTP
4031   server &MUST; disallow any such construct in the request-target if it
4032   would otherwise allow access to a resource outside those intended to
4033   be accessible via the HTTP server. Similarly, files intended for
4034   reference only internally to the server (such as access control
4035   files, configuration files, and script code) &MUST; be protected from
4036   inappropriate retrieval, since they might contain sensitive
4037   information. Experience has shown that minor bugs in such HTTP server
4038   implementations have turned into security risks.
4042<section title="DNS-related Attacks" anchor="dns.related.attacks">
4044   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
4045   generally prone to security attacks based on the deliberate misassociation
4046   of IP addresses and DNS names not protected by DNSSec. Clients need to be
4047   cautious in assuming the validity of an IP number/DNS name association unless
4048   the response is protected by DNSSec (<xref target="RFC4033"/>).
4052<section title="Proxies and Caching" anchor="attack.proxies">
4054   By their very nature, HTTP proxies are men-in-the-middle, and
4055   represent an opportunity for man-in-the-middle attacks. Compromise of
4056   the systems on which the proxies run can result in serious security
4057   and privacy problems. Proxies have access to security-related
4058   information, personal information about individual users and
4059   organizations, and proprietary information belonging to users and
4060   content providers. A compromised proxy, or a proxy implemented or
4061   configured without regard to security and privacy considerations,
4062   might be used in the commission of a wide range of potential attacks.
4065   Proxy operators need to protect the systems on which proxies run as
4066   they would protect any system that contains or transports sensitive
4067   information. In particular, log information gathered at proxies often
4068   contains highly sensitive personal information, and/or information
4069   about organizations. Log information needs to be carefully guarded, and
4070   appropriate guidelines for use need to be developed and followed.
4071   (<xref target="abuse.of.server.log.information"/>).
4074   Proxy implementors need to consider the privacy and security
4075   implications of their design and coding decisions, and of the
4076   configuration options they provide to proxy operators (especially the
4077   default configuration).
4080   Users of a proxy need to be aware that proxies are no trustworthier than
4081   the people who run them; HTTP itself cannot solve this problem.
4084   The judicious use of cryptography, when appropriate, might suffice to
4085   protect against a broad range of security and privacy attacks. Such
4086   cryptography is beyond the scope of the HTTP/1.1 specification.
4090<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4092   Because HTTP uses mostly textual, character-delimited fields, attackers can
4093   overflow buffers in implementations, and/or perform a Denial of Service
4094   against implementations that accept fields with unlimited lengths.
4097   To promote interoperability, this specification makes specific
4098   recommendations for size limits on request-targets (<xref target="request-target"/>)
4099   and blocks of header fields (<xref target="header.fields"/>). These are
4100   minimum recommendations, chosen to be supportable even by implementations
4101   with limited resources; it is expected that most implementations will choose
4102   substantially higher limits.
4105   This specification also provides a way for servers to reject messages that
4106   have request-targets that are too long (&status-414;) or request entities
4107   that are too large (&status-4xx;).
4110   Other fields (including but not limited to request methods, response status
4111   phrases, header field-names, and body chunks) &SHOULD; be limited by
4112   implementations carefully, so as to not impede interoperability.
4116<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4118   They exist. They are hard to defend against. Research continues.
4119   Beware.
4124<section title="Acknowledgments" anchor="acks">
4126   This document revision builds on the work that went into
4127   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
4128   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
4129   acknowledgements.
4132  <cref anchor="todoacks">Insert HTTPbis-specific acknowledgements here.</cref>
4136Acknowledgements TODO list
4138- Jeff Hodges ("effective request URI")
4146<references title="Normative References">
4148<reference anchor="ISO-8859-1">
4149  <front>
4150    <title>
4151     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4152    </title>
4153    <author>
4154      <organization>International Organization for Standardization</organization>
4155    </author>
4156    <date year="1998"/>
4157  </front>
4158  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4161<reference anchor="Part2">
4162  <front>
4163    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4164    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4165      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4166      <address><email></email></address>
4167    </author>
4168    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4169      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4170      <address><email></email></address>
4171    </author>
4172    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4173      <organization abbrev="HP">Hewlett-Packard Company</organization>
4174      <address><email></email></address>
4175    </author>
4176    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4177      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4178      <address><email></email></address>
4179    </author>
4180    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4181      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4182      <address><email></email></address>
4183    </author>
4184    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4185      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4186      <address><email></email></address>
4187    </author>
4188    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4189      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4190      <address><email></email></address>
4191    </author>
4192    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4193      <organization abbrev="W3C">World Wide Web Consortium</organization>
4194      <address><email></email></address>
4195    </author>
4196    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4197      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4198      <address><email></email></address>
4199    </author>
4200    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4201  </front>
4202  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4203  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4206<reference anchor="Part3">
4207  <front>
4208    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4209    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4210      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4211      <address><email></email></address>
4212    </author>
4213    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4214      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4215      <address><email></email></address>
4216    </author>
4217    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4218      <organization abbrev="HP">Hewlett-Packard Company</organization>
4219      <address><email></email></address>
4220    </author>
4221    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4222      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4223      <address><email></email></address>
4224    </author>
4225    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4226      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4227      <address><email></email></address>
4228    </author>
4229    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4230      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4231      <address><email></email></address>
4232    </author>
4233    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4234      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4235      <address><email></email></address>
4236    </author>
4237    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4238      <organization abbrev="W3C">World Wide Web Consortium</organization>
4239      <address><email></email></address>
4240    </author>
4241    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4242      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4243      <address><email></email></address>
4244    </author>
4245    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4246  </front>
4247  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4248  <x:source href="p3-payload.xml" basename="p3-payload"/>
4251<reference anchor="Part6">
4252  <front>
4253    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4254    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4255      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4256      <address><email></email></address>
4257    </author>
4258    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4259      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4260      <address><email></email></address>
4261    </author>
4262    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4263      <organization abbrev="HP">Hewlett-Packard Company</organization>
4264      <address><email></email></address>
4265    </author>
4266    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4267      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4268      <address><email></email></address>
4269    </author>
4270    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4271      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4272      <address><email></email></address>
4273    </author>
4274    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4275      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4276      <address><email></email></address>
4277    </author>
4278    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4279      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4280      <address><email></email></address>
4281    </author>
4282    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4283      <organization abbrev="W3C">World Wide Web Consortium</organization>
4284      <address><email></email></address>
4285    </author>
4286    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4287      <address><email></email></address>
4288    </author>
4289    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4290      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4291      <address><email></email></address>
4292    </author>
4293    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4294  </front>
4295  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4296  <x:source href="p6-cache.xml" basename="p6-cache"/>
4299<reference anchor="RFC5234">
4300  <front>
4301    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4302    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4303      <organization>Brandenburg InternetWorking</organization>
4304      <address>
4305        <email></email>
4306      </address> 
4307    </author>
4308    <author initials="P." surname="Overell" fullname="Paul Overell">
4309      <organization>THUS plc.</organization>
4310      <address>
4311        <email></email>
4312      </address>
4313    </author>
4314    <date month="January" year="2008"/>
4315  </front>
4316  <seriesInfo name="STD" value="68"/>
4317  <seriesInfo name="RFC" value="5234"/>
4320<reference anchor="RFC2119">
4321  <front>
4322    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4323    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4324      <organization>Harvard University</organization>
4325      <address><email></email></address>
4326    </author>
4327    <date month="March" year="1997"/>
4328  </front>
4329  <seriesInfo name="BCP" value="14"/>
4330  <seriesInfo name="RFC" value="2119"/>
4333<reference anchor="RFC3986">
4334 <front>
4335  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4336  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4337    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4338    <address>
4339       <email></email>
4340       <uri></uri>
4341    </address>
4342  </author>
4343  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4344    <organization abbrev="Day Software">Day Software</organization>
4345    <address>
4346      <email></email>
4347      <uri></uri>
4348    </address>
4349  </author>
4350  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4351    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4352    <address>
4353      <email></email>
4354      <uri></uri>
4355    </address>
4356  </author>
4357  <date month='January' year='2005'></date>
4358 </front>
4359 <seriesInfo name="STD" value="66"/>
4360 <seriesInfo name="RFC" value="3986"/>
4363<reference anchor="USASCII">
4364  <front>
4365    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4366    <author>
4367      <organization>American National Standards Institute</organization>
4368    </author>
4369    <date year="1986"/>
4370  </front>
4371  <seriesInfo name="ANSI" value="X3.4"/>
4374<reference anchor="RFC1950">
4375  <front>
4376    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4377    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4378      <organization>Aladdin Enterprises</organization>
4379      <address><email></email></address>
4380    </author>
4381    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4382    <date month="May" year="1996"/>
4383  </front>
4384  <seriesInfo name="RFC" value="1950"/>
4385  <annotation>
4386    RFC 1950 is an Informational RFC, thus it might be less stable than
4387    this specification. On the other hand, this downward reference was
4388    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4389    therefore it is unlikely to cause problems in practice. See also
4390    <xref target="BCP97"/>.
4391  </annotation>
4394<reference anchor="RFC1951">
4395  <front>
4396    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4397    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4398      <organization>Aladdin Enterprises</organization>
4399      <address><email></email></address>
4400    </author>
4401    <date month="May" year="1996"/>
4402  </front>
4403  <seriesInfo name="RFC" value="1951"/>
4404  <annotation>
4405    RFC 1951 is an Informational RFC, thus it might be less stable than
4406    this specification. On the other hand, this downward reference was
4407    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4408    therefore it is unlikely to cause problems in practice. See also
4409    <xref target="BCP97"/>.
4410  </annotation>
4413<reference anchor="RFC1952">
4414  <front>
4415    <title>GZIP file format specification version 4.3</title>
4416    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4417      <organization>Aladdin Enterprises</organization>
4418      <address><email></email></address>
4419    </author>
4420    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4421      <address><email></email></address>
4422    </author>
4423    <author initials="M." surname="Adler" fullname="Mark Adler">
4424      <address><email></email></address>
4425    </author>
4426    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4427      <address><email></email></address>
4428    </author>
4429    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4430      <address><email></email></address>
4431    </author>
4432    <date month="May" year="1996"/>
4433  </front>
4434  <seriesInfo name="RFC" value="1952"/>
4435  <annotation>
4436    RFC 1952 is an Informational RFC, thus it might be less stable than
4437    this specification. On the other hand, this downward reference was
4438    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4439    therefore it is unlikely to cause problems in practice. See also
4440    <xref target="BCP97"/>.
4441  </annotation>
4446<references title="Informative References">
4448<reference anchor="Nie1997" target="">
4449  <front>
4450    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4451    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4452    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4453    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4454    <author initials="H." surname="Lie" fullname="H. Lie"/>
4455    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4456    <date year="1997" month="September"/>
4457  </front>
4458  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4461<reference anchor="Pad1995" target="">
4462  <front>
4463    <title>Improving HTTP Latency</title>
4464    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4465    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4466    <date year="1995" month="December"/>
4467  </front>
4468  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4471<reference anchor="RFC1123">
4472  <front>
4473    <title>Requirements for Internet Hosts - Application and Support</title>
4474    <author initials="R." surname="Braden" fullname="Robert Braden">
4475      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4476      <address><email>Braden@ISI.EDU</email></address>
4477    </author>
4478    <date month="October" year="1989"/>
4479  </front>
4480  <seriesInfo name="STD" value="3"/>
4481  <seriesInfo name="RFC" value="1123"/>
4484<reference anchor='RFC1919'>
4485  <front>
4486    <title>Classical versus Transparent IP Proxies</title>
4487    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4488      <address><email></email></address>
4489    </author>
4490    <date year='1996' month='March' />
4491  </front>
4492  <seriesInfo name='RFC' value='1919' />
4495<reference anchor="RFC1945">
4496  <front>
4497    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4498    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4499      <organization>MIT, Laboratory for Computer Science</organization>
4500      <address><email></email></address>
4501    </author>
4502    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4503      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4504      <address><email></email></address>
4505    </author>
4506    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4507      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4508      <address><email></email></address>
4509    </author>
4510    <date month="May" year="1996"/>
4511  </front>
4512  <seriesInfo name="RFC" value="1945"/>
4515<reference anchor="RFC2045">
4516  <front>
4517    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4518    <author initials="N." surname="Freed" fullname="Ned Freed">
4519      <organization>Innosoft International, Inc.</organization>
4520      <address><email></email></address>
4521    </author>
4522    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4523      <organization>First Virtual Holdings</organization>
4524      <address><email></email></address>
4525    </author>
4526    <date month="November" year="1996"/>
4527  </front>
4528  <seriesInfo name="RFC" value="2045"/>
4531<reference anchor="RFC2047">
4532  <front>
4533    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4534    <author initials="K." surname="Moore" fullname="Keith Moore">
4535      <organization>University of Tennessee</organization>
4536      <address><email></email></address>
4537    </author>
4538    <date month="November" year="1996"/>
4539  </front>
4540  <seriesInfo name="RFC" value="2047"/>
4543<reference anchor="RFC2068">
4544  <front>
4545    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4546    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4547      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4548      <address><email></email></address>
4549    </author>
4550    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4551      <organization>MIT Laboratory for Computer Science</organization>
4552      <address><email></email></address>
4553    </author>
4554    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4555      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4556      <address><email></email></address>
4557    </author>
4558    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4559      <organization>MIT Laboratory for Computer Science</organization>
4560      <address><email></email></address>
4561    </author>
4562    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4563      <organization>MIT Laboratory for Computer Science</organization>
4564      <address><email></email></address>
4565    </author>
4566    <date month="January" year="1997"/>
4567  </front>
4568  <seriesInfo name="RFC" value="2068"/>
4571<reference anchor="RFC2145">
4572  <front>
4573    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4574    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4575      <organization>Western Research Laboratory</organization>
4576      <address><email></email></address>
4577    </author>
4578    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4579      <organization>Department of Information and Computer Science</organization>
4580      <address><email></email></address>
4581    </author>
4582    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4583      <organization>MIT Laboratory for Computer Science</organization>
4584      <address><email></email></address>
4585    </author>
4586    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4587      <organization>W3 Consortium</organization>
4588      <address><email></email></address>
4589    </author>
4590    <date month="May" year="1997"/>
4591  </front>
4592  <seriesInfo name="RFC" value="2145"/>
4595<reference anchor="RFC2616">
4596  <front>
4597    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4598    <author initials="R." surname="Fielding" fullname="R. Fielding">
4599      <organization>University of California, Irvine</organization>
4600      <address><email></email></address>
4601    </author>
4602    <author initials="J." surname="Gettys" fullname="J. Gettys">
4603      <organization>W3C</organization>
4604      <address><email></email></address>
4605    </author>
4606    <author initials="J." surname="Mogul" fullname="J. Mogul">
4607      <organization>Compaq Computer Corporation</organization>
4608      <address><email></email></address>
4609    </author>
4610    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4611      <organization>MIT Laboratory for Computer Science</organization>
4612      <address><email></email></address>
4613    </author>
4614    <author initials="L." surname="Masinter" fullname="L. Masinter">
4615      <organization>Xerox Corporation</organization>
4616      <address><email></email></address>
4617    </author>
4618    <author initials="P." surname="Leach" fullname="P. Leach">
4619      <organization>Microsoft Corporation</organization>
4620      <address><email></email></address>
4621    </author>
4622    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4623      <organization>W3C</organization>
4624      <address><email></email></address>
4625    </author>
4626    <date month="June" year="1999"/>
4627  </front>
4628  <seriesInfo name="RFC" value="2616"/>
4631<reference anchor='RFC2817'>
4632  <front>
4633    <title>Upgrading to TLS Within HTTP/1.1</title>
4634    <author initials='R.' surname='Khare' fullname='R. Khare'>
4635      <organization>4K Associates / UC Irvine</organization>
4636      <address><email></email></address>
4637    </author>
4638    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4639      <organization>Agranat Systems, Inc.</organization>
4640      <address><email></email></address>
4641    </author>
4642    <date year='2000' month='May' />
4643  </front>
4644  <seriesInfo name='RFC' value='2817' />
4647<reference anchor='RFC2818'>
4648  <front>
4649    <title>HTTP Over TLS</title>
4650    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4651      <organization>RTFM, Inc.</organization>
4652      <address><email></email></address>
4653    </author>
4654    <date year='2000' month='May' />
4655  </front>
4656  <seriesInfo name='RFC' value='2818' />
4659<reference anchor='RFC2965'>
4660  <front>
4661    <title>HTTP State Management Mechanism</title>
4662    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4663      <organization>Bell Laboratories, Lucent Technologies</organization>
4664      <address><email></email></address>
4665    </author>
4666    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4667      <organization>, Inc.</organization>
4668      <address><email></email></address>
4669    </author>
4670    <date year='2000' month='October' />
4671  </front>
4672  <seriesInfo name='RFC' value='2965' />
4675<reference anchor='RFC3040'>
4676  <front>
4677    <title>Internet Web Replication and Caching Taxonomy</title>
4678    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4679      <organization>Equinix, Inc.</organization>
4680    </author>
4681    <author initials='I.' surname='Melve' fullname='I. Melve'>
4682      <organization>UNINETT</organization>
4683    </author>
4684    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4685      <organization>CacheFlow Inc.</organization>
4686    </author>
4687    <date year='2001' month='January' />
4688  </front>
4689  <seriesInfo name='RFC' value='3040' />
4692<reference anchor='RFC3864'>
4693  <front>
4694    <title>Registration Procedures for Message Header Fields</title>
4695    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4696      <organization>Nine by Nine</organization>
4697      <address><email></email></address>
4698    </author>
4699    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4700      <organization>BEA Systems</organization>
4701      <address><email></email></address>
4702    </author>
4703    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4704      <organization>HP Labs</organization>
4705      <address><email></email></address>
4706    </author>
4707    <date year='2004' month='September' />
4708  </front>
4709  <seriesInfo name='BCP' value='90' />
4710  <seriesInfo name='RFC' value='3864' />
4713<reference anchor='RFC4033'>
4714  <front>
4715    <title>DNS Security Introduction and Requirements</title>
4716    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4717    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4718    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4719    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4720    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4721    <date year='2005' month='March' />
4722  </front>
4723  <seriesInfo name='RFC' value='4033' />
4726<reference anchor="RFC4288">
4727  <front>
4728    <title>Media Type Specifications and Registration Procedures</title>
4729    <author initials="N." surname="Freed" fullname="N. Freed">
4730      <organization>Sun Microsystems</organization>
4731      <address>
4732        <email></email>
4733      </address>
4734    </author>
4735    <author initials="J." surname="Klensin" fullname="J. Klensin">
4736      <address>
4737        <email></email>
4738      </address>
4739    </author>
4740    <date year="2005" month="December"/>
4741  </front>
4742  <seriesInfo name="BCP" value="13"/>
4743  <seriesInfo name="RFC" value="4288"/>
4746<reference anchor='RFC4395'>
4747  <front>
4748    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4749    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4750      <organization>AT&amp;T Laboratories</organization>
4751      <address>
4752        <email></email>
4753      </address>
4754    </author>
4755    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4756      <organization>Qualcomm, Inc.</organization>
4757      <address>
4758        <email></email>
4759      </address>
4760    </author>
4761    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4762      <organization>Adobe Systems</organization>
4763      <address>
4764        <email></email>
4765      </address>
4766    </author>
4767    <date year='2006' month='February' />
4768  </front>
4769  <seriesInfo name='BCP' value='115' />
4770  <seriesInfo name='RFC' value='4395' />
4773<reference anchor='RFC4559'>
4774  <front>
4775    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4776    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4777    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4778    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4779    <date year='2006' month='June' />
4780  </front>
4781  <seriesInfo name='RFC' value='4559' />
4784<reference anchor='RFC5226'>
4785  <front>
4786    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4787    <author initials='T.' surname='Narten' fullname='T. Narten'>
4788      <organization>IBM</organization>
4789      <address><email></email></address>
4790    </author>
4791    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4792      <organization>Google</organization>
4793      <address><email></email></address>
4794    </author>
4795    <date year='2008' month='May' />
4796  </front>
4797  <seriesInfo name='BCP' value='26' />
4798  <seriesInfo name='RFC' value='5226' />
4801<reference anchor="RFC5322">
4802  <front>
4803    <title>Internet Message Format</title>
4804    <author initials="P." surname="Resnick" fullname="P. Resnick">
4805      <organization>Qualcomm Incorporated</organization>
4806    </author>
4807    <date year="2008" month="October"/>
4808  </front>
4809  <seriesInfo name="RFC" value="5322"/>
4812<reference anchor="RFC6265">
4813  <front>
4814    <title>HTTP State Management Mechanism</title>
4815    <author initials="A." surname="Barth" fullname="Adam Barth">
4816      <organization abbrev="U.C. Berkeley">
4817        University of California, Berkeley
4818      </organization>
4819      <address><email></email></address>
4820    </author>
4821    <date year="2011" month="April" />
4822  </front>
4823  <seriesInfo name="RFC" value="6265"/>
4826<reference anchor='BCP97'>
4827  <front>
4828    <title>Handling Normative References to Standards-Track Documents</title>
4829    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4830      <address>
4831        <email></email>
4832      </address>
4833    </author>
4834    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4835      <organization>MIT</organization>
4836      <address>
4837        <email></email>
4838      </address>
4839    </author>
4840    <date year='2007' month='June' />
4841  </front>
4842  <seriesInfo name='BCP' value='97' />
4843  <seriesInfo name='RFC' value='4897' />
4846<reference anchor="Kri2001" target="">
4847  <front>
4848    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4849    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4850    <date year="2001" month="November"/>
4851  </front>
4852  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4855<reference anchor="Spe" target="">
4856  <front>
4857    <title>Analysis of HTTP Performance Problems</title>
4858    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4859    <date/>
4860  </front>
4863<reference anchor="Tou1998" target="">
4864  <front>
4865  <title>Analysis of HTTP Performance</title>
4866  <author initials="J." surname="Touch" fullname="Joe Touch">
4867    <organization>USC/Information Sciences Institute</organization>
4868    <address><email></email></address>
4869  </author>
4870  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4871    <organization>USC/Information Sciences Institute</organization>
4872    <address><email></email></address>
4873  </author>
4874  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4875    <organization>USC/Information Sciences Institute</organization>
4876    <address><email></email></address>
4877  </author>
4878  <date year="1998" month="Aug"/>
4879  </front>
4880  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4881  <annotation>(original report dated Aug. 1996)</annotation>
4887<section title="HTTP Version History" anchor="compatibility">
4889   HTTP has been in use by the World-Wide Web global information initiative
4890   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4891   was a simple protocol for hypertext data transfer across the Internet
4892   with only a single request method (GET) and no metadata.
4893   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4894   methods and MIME-like messaging that could include metadata about the data
4895   transferred and modifiers on the request/response semantics. However,
4896   HTTP/1.0 did not sufficiently take into consideration the effects of
4897   hierarchical proxies, caching, the need for persistent connections, or
4898   name-based virtual hosts. The proliferation of incompletely-implemented
4899   applications calling themselves "HTTP/1.0" further necessitated a
4900   protocol version change in order for two communicating applications
4901   to determine each other's true capabilities.
4904   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4905   requirements that enable reliable implementations, adding only
4906   those new features that will either be safely ignored by an HTTP/1.0
4907   recipient or only sent when communicating with a party advertising
4908   compliance with HTTP/1.1.
4911   It is beyond the scope of a protocol specification to mandate
4912   compliance with previous versions. HTTP/1.1 was deliberately
4913   designed, however, to make supporting previous versions easy.
4914   We would expect a general-purpose HTTP/1.1 server to understand
4915   any valid request in the format of HTTP/1.0 and respond appropriately
4916   with an HTTP/1.1 message that only uses features understood (or
4917   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4918   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4921   Since HTTP/0.9 did not support header fields in a request,
4922   there is no mechanism for it to support name-based virtual
4923   hosts (selection of resource by inspection of the Host header
4924   field).  Any server that implements name-based virtual hosts
4925   ought to disable support for HTTP/0.9.  Most requests that
4926   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4927   requests wherein a buggy client failed to properly encode
4928   linear whitespace found in a URI reference and placed in
4929   the request-target.
4932<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4934   This section summarizes major differences between versions HTTP/1.0
4935   and HTTP/1.1.
4938<section title="Multi-homed Web Servers" anchor="">
4940   The requirements that clients and servers support the Host header
4941   field (<xref target=""/>), report an error if it is
4942   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4943   are among the most important changes defined by HTTP/1.1.
4946   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4947   addresses and servers; there was no other established mechanism for
4948   distinguishing the intended server of a request than the IP address
4949   to which that request was directed. The Host header field was
4950   introduced during the development of HTTP/1.1 and, though it was
4951   quickly implemented by most HTTP/1.0 browsers, additional requirements
4952   were placed on all HTTP/1.1 requests in order to ensure complete
4953   adoption.  At the time of this writing, most HTTP-based services
4954   are dependent upon the Host header field for targeting requests.
4958<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4960   For most implementations of HTTP/1.0, each connection is established
4961   by the client prior to the request and closed by the server after
4962   sending the response. However, some implementations implement the
4963   Keep-Alive version of persistent connections described in
4964   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4967   Some clients and servers might wish to be compatible with some
4968   previous implementations of persistent connections in HTTP/1.0
4969   clients and servers. Persistent connections in HTTP/1.0 are
4970   explicitly negotiated as they are not the default behavior. HTTP/1.0
4971   experimental implementations of persistent connections are faulty,
4972   and the new facilities in HTTP/1.1 are designed to rectify these
4973   problems. The problem was that some existing HTTP/1.0 clients might
4974   send Keep-Alive to a proxy server that doesn't understand
4975   Connection, which would then erroneously forward it to the next
4976   inbound server, which would establish the Keep-Alive connection and
4977   result in a hung HTTP/1.0 proxy waiting for the close on the
4978   response. The result is that HTTP/1.0 clients must be prevented from
4979   using Keep-Alive when talking to proxies.
4982   However, talking to proxies is the most important use of persistent
4983   connections, so that prohibition is clearly unacceptable. Therefore,
4984   we need some other mechanism for indicating a persistent connection
4985   is desired, which is safe to use even when talking to an old proxy
4986   that ignores Connection. Persistent connections are the default for
4987   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4988   declaring non-persistence. See <xref target="header.connection"/>.
4993<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4995  Empty list elements in list productions have been deprecated.
4996  (<xref target="notation.abnf"/>)
4999  Rules about implicit linear whitespace between certain grammar productions
5000  have been removed; now it's only allowed when specifically pointed out
5001  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5002  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5003  Non-ASCII content in header fields and reason phrase has been obsoleted and
5004  made opaque (the TEXT rule was removed)
5005  (<xref target="basic.rules"/>)
5008  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5009  sensitive. Restrict the version numbers to be single digits due to the fact
5010  that implementations are known to handle multi-digit version numbers
5011  incorrectly.
5012  (<xref target="http.version"/>)
5015  Require that invalid whitespace around field-names be rejected.
5016  (<xref target="header.fields"/>)
5019  Require recipients to handle bogus Content-Length header fields as errors.
5020  (<xref target="message.body"/>)
5023  Remove reference to non-existent identity transfer-coding value tokens.
5024  (Sections <xref format="counter" target="message.body"/> and
5025  <xref format="counter" target="transfer.codings"/>)
5028  Update use of abs_path production from RFC 1808 to the path-absolute + query
5029  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5030  request method only.
5031  (<xref target="request-target"/>)
5034  Clarification that the chunk length does not include the count of the octets
5035  in the chunk header and trailer. Furthermore disallowed line folding
5036  in chunk extensions.
5037  (<xref target="chunked.encoding"/>)
5040  Remove hard limit of two connections per server.
5041  (<xref target="persistent.practical"/>)
5044  Change ABNF productions for header fields to only define the field value.
5045  (<xref target="header.field.definitions"/>)
5048  Clarify exactly when close connection options must be sent.
5049  (<xref target="header.connection"/>)
5052  Define the semantics of the "Upgrade" header field in responses other than
5053  101 (this was incorporated from <xref target="RFC2817"/>).
5054  (<xref target="header.upgrade"/>)
5059<?BEGININC p1-messaging.abnf-appendix ?>
5060<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5062<artwork type="abnf" name="p1-messaging.parsed-abnf">
5063<x:ref>BWS</x:ref> = OWS
5065<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5066<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5067 connection-token ] )
5068<x:ref>Content-Length</x:ref> = 1*DIGIT
5070<x:ref>Date</x:ref> = HTTP-date
5072<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5074<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5075<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5076<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5077<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5078 ]
5079<x:ref>Host</x:ref> = uri-host [ ":" port ]
5081<x:ref>Method</x:ref> = token
5083<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5085<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5086<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5087<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5088<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5089<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5091<x:ref>Status-Code</x:ref> = 3DIGIT
5092<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5094<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5095<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5096<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5097 transfer-coding ] )
5099<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5100<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5102<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5103 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5104 )
5106<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5107<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5108<x:ref>attribute</x:ref> = token
5109<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5111<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5112<x:ref>chunk-data</x:ref> = 1*OCTET
5113<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5114<x:ref>chunk-ext-name</x:ref> = token
5115<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5116<x:ref>chunk-size</x:ref> = 1*HEXDIG
5117<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5118<x:ref>connection-token</x:ref> = token
5119<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5120 / %x2A-5B ; '*'-'['
5121 / %x5D-7E ; ']'-'~'
5122 / obs-text
5124<x:ref>date1</x:ref> = day SP month SP year
5125<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5126<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5127<x:ref>day</x:ref> = 2DIGIT
5128<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5129 / %x54.75.65 ; Tue
5130 / %x57.65.64 ; Wed
5131 / %x54.68.75 ; Thu
5132 / %x46.72.69 ; Fri
5133 / %x53.61.74 ; Sat
5134 / %x53.75.6E ; Sun
5135<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5136 / %x54. ; Tuesday
5137 / %x57.65.64.6E. ; Wednesday
5138 / %x54. ; Thursday
5139 / %x46. ; Friday
5140 / %x53. ; Saturday
5141 / %x53.75.6E.64.61.79 ; Sunday
5143<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5144<x:ref>field-name</x:ref> = token
5145<x:ref>field-value</x:ref> = *( field-content / OWS )
5147<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5148<x:ref>hour</x:ref> = 2DIGIT
5149<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5150<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5152<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5154<x:ref>message-body</x:ref> = *OCTET
5155<x:ref>minute</x:ref> = 2DIGIT
5156<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5157 / %x46.65.62 ; Feb
5158 / %x4D.61.72 ; Mar
5159 / %x41.70.72 ; Apr
5160 / %x4D.61.79 ; May
5161 / %x4A.75.6E ; Jun
5162 / %x4A.75.6C ; Jul
5163 / %x41.75.67 ; Aug
5164 / %x53.65.70 ; Sep
5165 / %x4F.63.74 ; Oct
5166 / %x4E.6F.76 ; Nov
5167 / %x44.65.63 ; Dec
5169<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5170<x:ref>obs-fold</x:ref> = CRLF
5171<x:ref>obs-text</x:ref> = %x80-FF
5173<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5174<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5175<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5176<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5177<x:ref>product</x:ref> = token [ "/" product-version ]
5178<x:ref>product-version</x:ref> = token
5179<x:ref>protocol-name</x:ref> = token
5180<x:ref>protocol-version</x:ref> = token
5181<x:ref>pseudonym</x:ref> = token
5183<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5184 / %x5D-7E ; ']'-'~'
5185 / obs-text
5186<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5187 / %x5D-7E ; ']'-'~'
5188 / obs-text
5189<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5190<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5191<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5192<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5193<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5194<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5196<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5197<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5198<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5199<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5200 / authority
5201<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5202<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5204<x:ref>second</x:ref> = 2DIGIT
5205<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5206 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5207<x:ref>start-line</x:ref> = Request-Line / Status-Line
5209<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5210<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5211 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5212<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5213<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5214<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5215<x:ref>token</x:ref> = 1*tchar
5216<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5217<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5218 transfer-extension
5219<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5220<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5222<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5224<x:ref>value</x:ref> = word
5226<x:ref>word</x:ref> = token / quoted-string
5228<x:ref>year</x:ref> = 4DIGIT
5231<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5232; Chunked-Body defined but not used
5233; Connection defined but not used
5234; Content-Length defined but not used
5235; Date defined but not used
5236; HTTP-message defined but not used
5237; Host defined but not used
5238; Request defined but not used
5239; Response defined but not used
5240; TE defined but not used
5241; Trailer defined but not used
5242; Transfer-Encoding defined but not used
5243; URI-reference defined but not used
5244; Upgrade defined but not used
5245; Via defined but not used
5246; http-URI defined but not used
5247; https-URI defined but not used
5248; partial-URI defined but not used
5249; special defined but not used
5251<?ENDINC p1-messaging.abnf-appendix ?>
5253<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5255<section title="Since RFC 2616">
5257  Extracted relevant partitions from <xref target="RFC2616"/>.
5261<section title="Since draft-ietf-httpbis-p1-messaging-00">
5263  Closed issues:
5264  <list style="symbols">
5265    <t>
5266      <eref target=""/>:
5267      "HTTP Version should be case sensitive"
5268      (<eref target=""/>)
5269    </t>
5270    <t>
5271      <eref target=""/>:
5272      "'unsafe' characters"
5273      (<eref target=""/>)
5274    </t>
5275    <t>
5276      <eref target=""/>:
5277      "Chunk Size Definition"
5278      (<eref target=""/>)
5279    </t>
5280    <t>
5281      <eref target=""/>:
5282      "Message Length"
5283      (<eref target=""/>)
5284    </t>
5285    <t>
5286      <eref target=""/>:
5287      "Media Type Registrations"
5288      (<eref target=""/>)
5289    </t>
5290    <t>
5291      <eref target=""/>:
5292      "URI includes query"
5293      (<eref target=""/>)
5294    </t>
5295    <t>
5296      <eref target=""/>:
5297      "No close on 1xx responses"
5298      (<eref target=""/>)
5299    </t>
5300    <t>
5301      <eref target=""/>:
5302      "Remove 'identity' token references"
5303      (<eref target=""/>)
5304    </t>
5305    <t>
5306      <eref target=""/>:
5307      "Import query BNF"
5308    </t>
5309    <t>
5310      <eref target=""/>:
5311      "qdtext BNF"
5312    </t>
5313    <t>
5314      <eref target=""/>:
5315      "Normative and Informative references"
5316    </t>
5317    <t>
5318      <eref target=""/>:
5319      "RFC2606 Compliance"
5320    </t>
5321    <t>
5322      <eref target=""/>:
5323      "RFC977 reference"
5324    </t>
5325    <t>
5326      <eref target=""/>:
5327      "RFC1700 references"
5328    </t>
5329    <t>
5330      <eref target=""/>:
5331      "inconsistency in date format explanation"
5332    </t>
5333    <t>
5334      <eref target=""/>:
5335      "Date reference typo"
5336    </t>
5337    <t>
5338      <eref target=""/>:
5339      "Informative references"
5340    </t>
5341    <t>
5342      <eref target=""/>:
5343      "ISO-8859-1 Reference"
5344    </t>
5345    <t>
5346      <eref target=""/>:
5347      "Normative up-to-date references"
5348    </t>
5349  </list>
5352  Other changes:
5353  <list style="symbols">
5354    <t>
5355      Update media type registrations to use RFC4288 template.
5356    </t>
5357    <t>
5358      Use names of RFC4234 core rules DQUOTE and WSP,
5359      fix broken ABNF for chunk-data
5360      (work in progress on <eref target=""/>)
5361    </t>
5362  </list>
5366<section title="Since draft-ietf-httpbis-p1-messaging-01">
5368  Closed issues:
5369  <list style="symbols">
5370    <t>
5371      <eref target=""/>:
5372      "Bodies on GET (and other) requests"
5373    </t>
5374    <t>
5375      <eref target=""/>:
5376      "Updating to RFC4288"
5377    </t>
5378    <t>
5379      <eref target=""/>:
5380      "Status Code and Reason Phrase"
5381    </t>
5382    <t>
5383      <eref target=""/>:
5384      "rel_path not used"
5385    </t>
5386  </list>
5389  Ongoing work on ABNF conversion (<eref target=""/>):
5390  <list style="symbols">
5391    <t>
5392      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5393      "trailer-part").
5394    </t>
5395    <t>
5396      Avoid underscore character in rule names ("http_URL" ->
5397      "http-URL", "abs_path" -> "path-absolute").
5398    </t>
5399    <t>
5400      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5401      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5402      have to be updated when switching over to RFC3986.
5403    </t>
5404    <t>
5405      Synchronize core rules with RFC5234.
5406    </t>
5407    <t>
5408      Get rid of prose rules that span multiple lines.
5409    </t>
5410    <t>
5411      Get rid of unused rules LOALPHA and UPALPHA.
5412    </t>
5413    <t>
5414      Move "Product Tokens" section (back) into Part 1, as "token" is used
5415      in the definition of the Upgrade header field.
5416    </t>
5417    <t>
5418      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5419    </t>
5420    <t>
5421      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5422    </t>
5423  </list>
5427<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5429  Closed issues:
5430  <list style="symbols">
5431    <t>
5432      <eref target=""/>:
5433      "HTTP-date vs. rfc1123-date"
5434    </t>
5435    <t>
5436      <eref target=""/>:
5437      "WS in quoted-pair"
5438    </t>
5439  </list>
5442  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5443  <list style="symbols">
5444    <t>
5445      Reference RFC 3984, and update header field registrations for headers defined
5446      in this document.
5447    </t>
5448  </list>
5451  Ongoing work on ABNF conversion (<eref target=""/>):
5452  <list style="symbols">
5453    <t>
5454      Replace string literals when the string really is case-sensitive (HTTP-Version).
5455    </t>
5456  </list>
5460<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5462  Closed issues:
5463  <list style="symbols">
5464    <t>
5465      <eref target=""/>:
5466      "Connection closing"
5467    </t>
5468    <t>
5469      <eref target=""/>:
5470      "Move registrations and registry information to IANA Considerations"
5471    </t>
5472    <t>
5473      <eref target=""/>:
5474      "need new URL for PAD1995 reference"
5475    </t>
5476    <t>
5477      <eref target=""/>:
5478      "IANA Considerations: update HTTP URI scheme registration"
5479    </t>
5480    <t>
5481      <eref target=""/>:
5482      "Cite HTTPS URI scheme definition"
5483    </t>
5484    <t>
5485      <eref target=""/>:
5486      "List-type headers vs Set-Cookie"
5487    </t>
5488  </list>
5491  Ongoing work on ABNF conversion (<eref target=""/>):
5492  <list style="symbols">
5493    <t>
5494      Replace string literals when the string really is case-sensitive (HTTP-Date).
5495    </t>
5496    <t>
5497      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5498    </t>
5499  </list>
5503<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5505  Closed issues:
5506  <list style="symbols">
5507    <t>
5508      <eref target=""/>:
5509      "Out-of-date reference for URIs"
5510    </t>
5511    <t>
5512      <eref target=""/>:
5513      "RFC 2822 is updated by RFC 5322"
5514    </t>
5515  </list>
5518  Ongoing work on ABNF conversion (<eref target=""/>):
5519  <list style="symbols">
5520    <t>
5521      Use "/" instead of "|" for alternatives.
5522    </t>
5523    <t>
5524      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5525    </t>
5526    <t>
5527      Only reference RFC 5234's core rules.
5528    </t>
5529    <t>
5530      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5531      whitespace ("OWS") and required whitespace ("RWS").
5532    </t>
5533    <t>
5534      Rewrite ABNFs to spell out whitespace rules, factor out
5535      header field value format definitions.
5536    </t>
5537  </list>
5541<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5543  Closed issues:
5544  <list style="symbols">
5545    <t>
5546      <eref target=""/>:
5547      "Header LWS"
5548    </t>
5549    <t>
5550      <eref target=""/>:
5551      "Sort 1.3 Terminology"
5552    </t>
5553    <t>
5554      <eref target=""/>:
5555      "RFC2047 encoded words"
5556    </t>
5557    <t>
5558      <eref target=""/>:
5559      "Character Encodings in TEXT"
5560    </t>
5561    <t>
5562      <eref target=""/>:
5563      "Line Folding"
5564    </t>
5565    <t>
5566      <eref target=""/>:
5567      "OPTIONS * and proxies"
5568    </t>
5569    <t>
5570      <eref target=""/>:
5571      "Reason-Phrase BNF"
5572    </t>
5573    <t>
5574      <eref target=""/>:
5575      "Use of TEXT"
5576    </t>
5577    <t>
5578      <eref target=""/>:
5579      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5580    </t>
5581    <t>
5582      <eref target=""/>:
5583      "RFC822 reference left in discussion of date formats"
5584    </t>
5585  </list>
5588  Final work on ABNF conversion (<eref target=""/>):
5589  <list style="symbols">
5590    <t>
5591      Rewrite definition of list rules, deprecate empty list elements.
5592    </t>
5593    <t>
5594      Add appendix containing collected and expanded ABNF.
5595    </t>
5596  </list>
5599  Other changes:
5600  <list style="symbols">
5601    <t>
5602      Rewrite introduction; add mostly new Architecture Section.
5603    </t>
5604    <t>
5605      Move definition of quality values from Part 3 into Part 1;
5606      make TE request header field grammar independent of accept-params (defined in Part 3).
5607    </t>
5608  </list>
5612<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5614  Closed issues:
5615  <list style="symbols">
5616    <t>
5617      <eref target=""/>:
5618      "base for numeric protocol elements"
5619    </t>
5620    <t>
5621      <eref target=""/>:
5622      "comment ABNF"
5623    </t>
5624  </list>
5627  Partly resolved issues:
5628  <list style="symbols">
5629    <t>
5630      <eref target=""/>:
5631      "205 Bodies" (took out language that implied that there might be
5632      methods for which a request body MUST NOT be included)
5633    </t>
5634    <t>
5635      <eref target=""/>:
5636      "editorial improvements around HTTP-date"
5637    </t>
5638  </list>
5642<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5644  Closed issues:
5645  <list style="symbols">
5646    <t>
5647      <eref target=""/>:
5648      "Repeating single-value headers"
5649    </t>
5650    <t>
5651      <eref target=""/>:
5652      "increase connection limit"
5653    </t>
5654    <t>
5655      <eref target=""/>:
5656      "IP addresses in URLs"
5657    </t>
5658    <t>
5659      <eref target=""/>:
5660      "take over HTTP Upgrade Token Registry"
5661    </t>
5662    <t>
5663      <eref target=""/>:
5664      "CR and LF in chunk extension values"
5665    </t>
5666    <t>
5667      <eref target=""/>:
5668      "HTTP/0.9 support"
5669    </t>
5670    <t>
5671      <eref target=""/>:
5672      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5673    </t>
5674    <t>
5675      <eref target=""/>:
5676      "move definitions of gzip/deflate/compress to part 1"
5677    </t>
5678    <t>
5679      <eref target=""/>:
5680      "disallow control characters in quoted-pair"
5681    </t>
5682  </list>
5685  Partly resolved issues:
5686  <list style="symbols">
5687    <t>
5688      <eref target=""/>:
5689      "update IANA requirements wrt Transfer-Coding values" (add the
5690      IANA Considerations subsection)
5691    </t>
5692  </list>
5696<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5698  Closed issues:
5699  <list style="symbols">
5700    <t>
5701      <eref target=""/>:
5702      "header parsing, treatment of leading and trailing OWS"
5703    </t>
5704  </list>
5707  Partly resolved issues:
5708  <list style="symbols">
5709    <t>
5710      <eref target=""/>:
5711      "Placement of 13.5.1 and 13.5.2"
5712    </t>
5713    <t>
5714      <eref target=""/>:
5715      "use of term "word" when talking about header structure"
5716    </t>
5717  </list>
5721<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5723  Closed issues:
5724  <list style="symbols">
5725    <t>
5726      <eref target=""/>:
5727      "Clarification of the term 'deflate'"
5728    </t>
5729    <t>
5730      <eref target=""/>:
5731      "OPTIONS * and proxies"
5732    </t>
5733    <t>
5734      <eref target=""/>:
5735      "MIME-Version not listed in P1, general header fields"
5736    </t>
5737    <t>
5738      <eref target=""/>:
5739      "IANA registry for content/transfer encodings"
5740    </t>
5741    <t>
5742      <eref target=""/>:
5743      "Case-sensitivity of HTTP-date"
5744    </t>
5745    <t>
5746      <eref target=""/>:
5747      "use of term "word" when talking about header structure"
5748    </t>
5749  </list>
5752  Partly resolved issues:
5753  <list style="symbols">
5754    <t>
5755      <eref target=""/>:
5756      "Term for the requested resource's URI"
5757    </t>
5758  </list>
5762<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5764  Closed issues:
5765  <list style="symbols">
5766    <t>
5767      <eref target=""/>:
5768      "Connection Closing"
5769    </t>
5770    <t>
5771      <eref target=""/>:
5772      "Delimiting messages with multipart/byteranges"
5773    </t>
5774    <t>
5775      <eref target=""/>:
5776      "Handling multiple Content-Length headers"
5777    </t>
5778    <t>
5779      <eref target=""/>:
5780      "Clarify entity / representation / variant terminology"
5781    </t>
5782    <t>
5783      <eref target=""/>:
5784      "consider removing the 'changes from 2068' sections"
5785    </t>
5786  </list>
5789  Partly resolved issues:
5790  <list style="symbols">
5791    <t>
5792      <eref target=""/>:
5793      "HTTP(s) URI scheme definitions"
5794    </t>
5795  </list>
5799<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5801  Closed issues:
5802  <list style="symbols">
5803    <t>
5804      <eref target=""/>:
5805      "Trailer requirements"
5806    </t>
5807    <t>
5808      <eref target=""/>:
5809      "Text about clock requirement for caches belongs in p6"
5810    </t>
5811    <t>
5812      <eref target=""/>:
5813      "effective request URI: handling of missing host in HTTP/1.0"
5814    </t>
5815    <t>
5816      <eref target=""/>:
5817      "confusing Date requirements for clients"
5818    </t>
5819  </list>
5822  Partly resolved issues:
5823  <list style="symbols">
5824    <t>
5825      <eref target=""/>:
5826      "Handling multiple Content-Length headers"
5827    </t>
5828  </list>
5832<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5834  Closed issues:
5835  <list style="symbols">
5836    <t>
5837      <eref target=""/>:
5838      "RFC2145 Normative"
5839    </t>
5840    <t>
5841      <eref target=""/>:
5842      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5843    </t>
5844    <t>
5845      <eref target=""/>:
5846      "define 'transparent' proxy"
5847    </t>
5848    <t>
5849      <eref target=""/>:
5850      "Header Classification"
5851    </t>
5852    <t>
5853      <eref target=""/>:
5854      "Is * usable as a request-uri for new methods?"
5855    </t>
5856    <t>
5857      <eref target=""/>:
5858      "Migrate Upgrade details from RFC2817"
5859    </t>
5860    <t>
5861      <eref target=""/>:
5862      "untangle ABNFs for header fields"
5863    </t>
5864    <t>
5865      <eref target=""/>:
5866      "update RFC 2109 reference"
5867    </t>
5868  </list>
5872<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5874  Closed issues:
5875  <list style="symbols">
5876    <t>
5877      <eref target=""/>:
5878      "Allow is not in 13.5.2"
5879    </t>
5880    <t>
5881      <eref target=""/>:
5882      "Handling multiple Content-Length headers"
5883    </t>
5884    <t>
5885      <eref target=""/>:
5886      "untangle ABNFs for header fields"
5887    </t>
5888    <t>
5889      <eref target=""/>:
5890      "Content-Length ABNF broken"
5891    </t>
5892  </list>
5896<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5898  Closed issues:
5899  <list style="symbols">
5900    <t>
5901      <eref target=""/>:
5902      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5903    </t>
5904    <t>
5905      <eref target=""/>:
5906      "Recommend minimum sizes for protocol elements"
5907    </t>
5908    <t>
5909      <eref target=""/>:
5910      "Set expectations around buffering"
5911    </t>
5912    <t>
5913      <eref target=""/>:
5914      "Considering messages in isolation"
5915    </t>
5916  </list>
5920<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5922  Closed issues:
5923  <list style="symbols">
5924    <t>
5925      <eref target=""/>:
5926      "DNS Spoofing / DNS Binding advice"
5927    </t>
5928    <t>
5929      <eref target=""/>:
5930      "move RFCs 2145, 2616, 2817 to Historic status"
5931    </t>
5932    <t>
5933      <eref target=""/>:
5934      "\-escaping in quoted strings"
5935    </t>
5936    <t>
5937      <eref target=""/>:
5938      "'Close' should be reserved in the HTTP header field registry"
5939    </t>
5940  </list>
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