source: draft-ietf-httpbis/16/p1-messaging.xml @ 1500

Last change on this file since 1500 was 1500, checked in by julian.reschke@…, 11 years ago

fix mime types

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 251.6 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
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;" day="24"/>
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, <xref target="basic.rules"/>).   
371  Thus,
372</preamble><artwork type="example">
373  1#element =&gt; element *( OWS "," OWS element )
376  and:
377</preamble><artwork type="example">
378  #element =&gt; [ 1#element ]
381  and for n &gt;= 1 and m &gt; 1:
382</preamble><artwork type="example">
383  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
386  For compatibility with legacy list rules, recipients &SHOULD; accept empty
387  list elements. In other words, consumers would follow the list productions:
389<figure><artwork type="example">
390  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
392  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
395  Note that empty elements do not contribute to the count of elements present,
396  though.
399  For example, given these ABNF productions:
401<figure><artwork type="example">
402  example-list      = 1#example-list-elmt
403  example-list-elmt = token ; see <xref target="field.rules"/>
406  Then these are valid values for example-list (not including the double
407  quotes, which are present for delimitation only):
409<figure><artwork type="example">
410  "foo,bar"
411  " foo ,bar,"
412  "  foo , ,bar,charlie   "
413  "foo ,bar,   charlie "
416  But these values would be invalid, as at least one non-empty element is
417  required:
419<figure><artwork type="example">
420  ""
421  ","
422  ",   ,"
425  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
426  expanded as explained above.
430<section title="Basic Rules" anchor="basic.rules">
431<t anchor="rule.LWS">
432   This specification uses three rules to denote the use of linear
433   whitespace: OWS (optional whitespace), RWS (required whitespace), and
434   BWS ("bad" whitespace).
436<t anchor="rule.OWS">
437   The OWS rule is used where zero or more linear whitespace octets might
438   appear. OWS &SHOULD; either not be produced or be produced as a single
439   SP. Multiple OWS octets that occur within field-content &SHOULD; either
440   be replaced with a single SP or transformed to all SP octets (each WSP
441   octet other than SP replaced with SP) before interpreting the field value
442   or forwarding the message downstream.
444<t anchor="rule.RWS">
445   RWS is used when at least one linear whitespace octet is required to
446   separate field tokens. RWS &SHOULD; be produced as a single SP.
447   Multiple RWS octets octets that occur within field-content &SHOULD; either
448   be replaced with a single SP or transformed to all SP octets (each WSP
449   octet other than SP replaced with SP) before interpreting the field value
450   or forwarding the message downstream.
452<t anchor="rule.BWS">
453   BWS is used where the grammar allows optional whitespace for historical
454   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
455   recipients &MUST; accept such bad optional whitespace and remove it before
456   interpreting the field value or forwarding the message downstream.
458<t anchor="rule.whitespace">
459  <x:anchor-alias value="BWS"/>
460  <x:anchor-alias value="OWS"/>
461  <x:anchor-alias value="RWS"/>
462  <x:anchor-alias value="obs-fold"/>
464<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"/>
465  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
466                 ; "optional" whitespace
467  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
468                 ; "required" whitespace
469  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
470                 ; "bad" whitespace
471  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
472                 ; see <xref target="header.fields"/>
478<section title="HTTP-related architecture" anchor="architecture">
480   HTTP was created for the World Wide Web architecture
481   and has evolved over time to support the scalability needs of a worldwide
482   hypertext system. Much of that architecture is reflected in the terminology
483   and syntax productions used to define HTTP.
486<section title="Client/Server Messaging" anchor="operation">
487<iref primary="true" item="client"/>
488<iref primary="true" item="server"/>
489<iref primary="true" item="connection"/>
491   HTTP is a stateless request/response protocol that operates by exchanging
492   messages across a reliable transport or session-layer
493   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
494   program that establishes a connection to a server for the purpose of
495   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
496   program that accepts connections in order to service HTTP requests by
497   sending HTTP responses.
499<iref primary="true" item="user agent"/>
500<iref primary="true" item="origin server"/>
501<iref primary="true" item="browser"/>
502<iref primary="true" item="spider"/>
503<iref primary="true" item="sender"/>
504<iref primary="true" item="recipient"/>
506   Note that the terms client and server refer only to the roles that
507   these programs perform for a particular connection.  The same program
508   might act as a client on some connections and a server on others.  We use
509   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
510   such as a WWW browser, editor, or spider (web-traversing robot), and
511   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
512   authoritative responses to a request.  For general requirements, we use
513   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
514   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
515   message.
518   Most HTTP communication consists of a retrieval request (GET) for
519   a representation of some resource identified by a URI.  In the
520   simplest case, this might be accomplished via a single bidirectional
521   connection (===) between the user agent (UA) and the origin server (O).
523<figure><artwork type="drawing">
524         request   &gt;
525    UA ======================================= O
526                                &lt;   response
528<iref primary="true" item="message"/>
529<iref primary="true" item="request"/>
530<iref primary="true" item="response"/>
532   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
533   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
534   protocol version, followed by MIME-like header fields containing
535   request modifiers, client information, and payload metadata, an empty
536   line to indicate the end of the header section, and finally the payload
537   body (if any).
540   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
541   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
542   includes the protocol version, a success or error code, and textual
543   reason phrase, followed by MIME-like header fields containing server
544   information, resource metadata, and payload metadata, an empty line to
545   indicate the end of the header section, and finally the payload body (if any).
548   The following example illustrates a typical message exchange for a
549   GET request on the URI "":
552client request:
553</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
554GET /hello.txt HTTP/1.1
555User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
557Accept: */*
561server response:
562</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
563HTTP/1.1 200 OK
564Date: Mon, 27 Jul 2009 12:28:53 GMT
565Server: Apache
566Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
567ETag: "34aa387-d-1568eb00"
568Accept-Ranges: bytes
569Content-Length: <x:length-of target="exbody"/>
570Vary: Accept-Encoding
571Content-Type: text/plain
573<x:span anchor="exbody">Hello World!
577<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
579   Fundamentally, HTTP is a message-based protocol. Although message bodies can
580   be chunked (<xref target="chunked.encoding"/>) and implementations often
581   make parts of a message available progressively, this is not required, and
582   some widely-used implementations only make a message available when it is
583   complete. Furthermore, while most proxies will progressively stream messages,
584   some amount of buffering will take place, and some proxies might buffer
585   messages to perform transformations, check content or provide other services.
588   Therefore, extensions to and uses of HTTP cannot rely on the availability of
589   a partial message, or assume that messages will not be buffered. There are
590   strategies that can be used to test for buffering in a given connection, but
591   it should be understood that behaviors can differ across connections, and
592   between requests and responses.
595   Recipients &MUST; consider every message in a connection in isolation;
596   because HTTP is a stateless protocol, it cannot be assumed that two requests
597   on the same connection are from the same client or share any other common
598   attributes. In particular, intermediaries might mix requests from different
599   clients into a single server connection. Note that some existing HTTP
600   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
601   potentially causing interoperability and security problems.
605<section title="Connections and Transport Independence" anchor="transport-independence">
607   HTTP messaging is independent of the underlying transport or
608   session-layer connection protocol(s).  HTTP only presumes a reliable
609   transport with in-order delivery of requests and the corresponding
610   in-order delivery of responses.  The mapping of HTTP request and
611   response structures onto the data units of the underlying transport
612   protocol is outside the scope of this specification.
615   The specific connection protocols to be used for an interaction
616   are determined by client configuration and the target resource's URI.
617   For example, the "http" URI scheme
618   (<xref target="http.uri"/>) indicates a default connection of TCP
619   over IP, with a default TCP port of 80, but the client might be
620   configured to use a proxy via some other connection port or protocol
621   instead of using the defaults.
624   A connection might be used for multiple HTTP request/response exchanges,
625   as defined in <xref target="persistent.connections"/>.
629<section title="Intermediaries" anchor="intermediaries">
630<iref primary="true" item="intermediary"/>
632   HTTP enables the use of intermediaries to satisfy requests through
633   a chain of connections.  There are three common forms of HTTP
634   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
635   a single intermediary might act as an origin server, proxy, gateway,
636   or tunnel, switching behavior based on the nature of each request.
638<figure><artwork type="drawing">
639         &gt;             &gt;             &gt;             &gt;
640    <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>
641               &lt;             &lt;             &lt;             &lt;
644   The figure above shows three intermediaries (A, B, and C) between the
645   user agent and origin server. A request or response message that
646   travels the whole chain will pass through four separate connections.
647   Some HTTP communication options
648   might apply only to the connection with the nearest, non-tunnel
649   neighbor, only to the end-points of the chain, or to all connections
650   along the chain. Although the diagram is linear, each participant might
651   be engaged in multiple, simultaneous communications. For example, B
652   might be receiving requests from many clients other than A, and/or
653   forwarding requests to servers other than C, at the same time that it
654   is handling A's request.
657<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
658<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
659   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
660   to describe various requirements in relation to the directional flow of a
661   message: all messages flow from upstream to downstream.
662   Likewise, we use the terms inbound and outbound to refer to
663   directions in relation to the request path:
664   "<x:dfn>inbound</x:dfn>" means toward the origin server and
665   "<x:dfn>outbound</x:dfn>" means toward the user agent.
667<t><iref primary="true" item="proxy"/>
668   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
669   client, usually via local configuration rules, to receive requests
670   for some type(s) of absolute URI and attempt to satisfy those
671   requests via translation through the HTTP interface.  Some translations
672   are minimal, such as for proxy requests for "http" URIs, whereas
673   other requests might require translation to and from entirely different
674   application-layer protocols. Proxies are often used to group an
675   organization's HTTP requests through a common intermediary for the
676   sake of security, annotation services, or shared caching.
679<iref primary="true" item="transforming proxy"/>
680<iref primary="true" item="non-transforming proxy"/>
681   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
682   or configured to modify request or response messages in a semantically
683   meaningful way (i.e., modifications, beyond those required by normal
684   HTTP processing, that change the message in a way that would be
685   significant to the original sender or potentially significant to
686   downstream recipients).  For example, a transforming proxy might be
687   acting as a shared annotation server (modifying responses to include
688   references to a local annotation database), a malware filter, a
689   format transcoder, or an intranet-to-Internet privacy filter.  Such
690   transformations are presumed to be desired by the client (or client
691   organization) that selected the proxy and are beyond the scope of
692   this specification.  However, when a proxy is not intended to transform
693   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
694   requirements that preserve HTTP message semantics. See &status-203; and
695   &header-warning; for status and warning codes related to transformations.
697<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
698<iref primary="true" item="accelerator"/>
699   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
700   is a receiving agent that acts
701   as a layer above some other server(s) and translates the received
702   requests to the underlying server's protocol.  Gateways are often
703   used to encapsulate legacy or untrusted information services, to
704   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
705   enable partitioning or load-balancing of HTTP services across
706   multiple machines.
709   A gateway behaves as an origin server on its outbound connection and
710   as a user agent on its inbound connection.
711   All HTTP requirements applicable to an origin server
712   also apply to the outbound communication of a gateway.
713   A gateway communicates with inbound servers using any protocol that
714   it desires, including private extensions to HTTP that are outside
715   the scope of this specification.  However, an HTTP-to-HTTP gateway
716   that wishes to interoperate with third-party HTTP servers &MUST;
717   comply with HTTP user agent requirements on the gateway's inbound
718   connection and &MUST; implement the Connection
719   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
720   header fields for both connections.
722<t><iref primary="true" item="tunnel"/>
723   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
724   without changing the messages. Once active, a tunnel is not
725   considered a party to the HTTP communication, though the tunnel might
726   have been initiated by an HTTP request. A tunnel ceases to exist when
727   both ends of the relayed connection are closed. Tunnels are used to
728   extend a virtual connection through an intermediary, such as when
729   transport-layer security is used to establish private communication
730   through a shared firewall proxy.
732<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
733<iref primary="true" item="captive portal"/>
734   In addition, there may exist network intermediaries that are not
735   considered part of the HTTP communication but nevertheless act as
736   filters or redirecting agents (usually violating HTTP semantics,
737   causing security problems, and otherwise making a mess of things).
738   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
739   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
740   or "<x:dfn>captive portal</x:dfn>",
741   differs from an HTTP proxy because it has not been selected by the client.
742   Instead, the network intermediary redirects outgoing TCP port 80 packets
743   (and occasionally other common port traffic) to an internal HTTP server.
744   Interception proxies are commonly found on public network access points,
745   as a means of enforcing account subscription prior to allowing use of
746   non-local Internet services, and within corporate firewalls to enforce
747   network usage policies.
748   They are indistinguishable from a man-in-the-middle attack.
752<section title="Caches" anchor="caches">
753<iref primary="true" item="cache"/>
755   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
756   subsystem that controls its message storage, retrieval, and deletion.
757   A cache stores cacheable responses in order to reduce the response
758   time and network bandwidth consumption on future, equivalent
759   requests. Any client or server &MAY; employ a cache, though a cache
760   cannot be used by a server while it is acting as a tunnel.
763   The effect of a cache is that the request/response chain is shortened
764   if one of the participants along the chain has a cached response
765   applicable to that request. The following illustrates the resulting
766   chain if B has a cached copy of an earlier response from O (via C)
767   for a request which has not been cached by UA or A.
769<figure><artwork type="drawing">
770            &gt;             &gt;
771       UA =========== A =========== B - - - - - - C - - - - - - O
772                  &lt;             &lt;
774<t><iref primary="true" item="cacheable"/>
775   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
776   the response message for use in answering subsequent requests.
777   Even when a response is cacheable, there might be additional
778   constraints placed by the client or by the origin server on when
779   that cached response can be used for a particular request. HTTP
780   requirements for cache behavior and cacheable responses are
781   defined in &caching-overview;. 
784   There are a wide variety of architectures and configurations
785   of caches and proxies deployed across the World Wide Web and
786   inside large organizations. These systems include national hierarchies
787   of proxy caches to save transoceanic bandwidth, systems that
788   broadcast or multicast cache entries, organizations that distribute
789   subsets of cached data via optical media, and so on.
793<section title="Protocol Versioning" anchor="http.version">
794  <x:anchor-alias value="HTTP-Version"/>
795  <x:anchor-alias value="HTTP-Prot-Name"/>
797   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
798   versions of the protocol. This specification defines version "1.1".
799   The protocol version as a whole indicates the sender's compliance
800   with the set of requirements laid out in that version's corresponding
801   specification of HTTP.
804   The version of an HTTP message is indicated by an HTTP-Version field
805   in the first line of the message. HTTP-Version is case-sensitive.
807<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
808  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
809  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
812   The HTTP version number consists of two decimal digits separated by a "."
813   (period or decimal point).  The first digit ("major version") indicates the
814   HTTP messaging syntax, whereas the second digit ("minor version") indicates
815   the highest minor version to which the sender is at least conditionally
816   compliant and able to understand for future communication.  The minor
817   version advertises the sender's communication capabilities even when the
818   sender is only using a backwards-compatible subset of the protocol,
819   thereby letting the recipient know that more advanced features can
820   be used in response (by servers) or in future requests (by clients).
823   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
824   <xref target="RFC1945"/> or a recipient whose version is unknown,
825   the HTTP/1.1 message is constructed such that it can be interpreted
826   as a valid HTTP/1.0 message if all of the newer features are ignored.
827   This specification places recipient-version requirements on some
828   new features so that a compliant sender will only use compatible
829   features until it has determined, through configuration or the
830   receipt of a message, that the recipient supports HTTP/1.1.
833   The interpretation of an HTTP header field does not change
834   between minor versions of the same major version, though the default
835   behavior of a recipient in the absence of such a field can change.
836   Unless specified otherwise, header fields defined in HTTP/1.1 are
837   defined for all versions of HTTP/1.x.  In particular, the Host and
838   Connection header fields ought to be implemented by all HTTP/1.x
839   implementations whether or not they advertise compliance with HTTP/1.1.
842   New header fields can be defined such that, when they are
843   understood by a recipient, they might override or enhance the
844   interpretation of previously defined header fields.  When an
845   implementation receives an unrecognized header field, the recipient
846   &MUST; ignore that header field for local processing regardless of
847   the message's HTTP version.  An unrecognized header field received
848   by a proxy &MUST; be forwarded downstream unless the header field's
849   field-name is listed in the message's Connection header-field
850   (see <xref target="header.connection"/>).
851   These requirements allow HTTP's functionality to be enhanced without
852   requiring prior update of all compliant intermediaries.
855   Intermediaries that process HTTP messages (i.e., all intermediaries
856   other than those acting as a tunnel) &MUST; send their own HTTP-Version
857   in forwarded messages.  In other words, they &MUST-NOT; blindly
858   forward the first line of an HTTP message without ensuring that the
859   protocol version matches what the intermediary understands, and
860   is at least conditionally compliant to, for both the receiving and
861   sending of messages.  Forwarding an HTTP message without rewriting
862   the HTTP-Version might result in communication errors when downstream
863   recipients use the message sender's version to determine what features
864   are safe to use for later communication with that sender.
867   An HTTP client &SHOULD; send a request version equal to the highest
868   version for which the client is at least conditionally compliant and
869   whose major version is no higher than the highest version supported
870   by the server, if this is known.  An HTTP client &MUST-NOT; send a
871   version for which it is not at least conditionally compliant.
874   An HTTP client &MAY; send a lower request version if it is known that
875   the server incorrectly implements the HTTP specification, but only
876   after the client has attempted at least one normal request and determined
877   from the response status or header fields (e.g., Server) that the
878   server improperly handles higher request versions.
881   An HTTP server &SHOULD; send a response version equal to the highest
882   version for which the server is at least conditionally compliant and
883   whose major version is less than or equal to the one received in the
884   request.  An HTTP server &MUST-NOT; send a version for which it is not
885   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
886   Version Not Supported) response if it cannot send a response using the
887   major version used in the client's request.
890   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
891   if it is known or suspected that the client incorrectly implements the
892   HTTP specification and is incapable of correctly processing later
893   version responses, such as when a client fails to parse the version
894   number correctly or when an intermediary is known to blindly forward
895   the HTTP-Version even when it doesn't comply with the given minor
896   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
897   performed unless triggered by specific client attributes, such as when
898   one or more of the request header fields (e.g., User-Agent) uniquely
899   match the values sent by a client known to be in error.
902   The intention of HTTP's versioning design is that the major number
903   will only be incremented if an incompatible message syntax is
904   introduced, and that the minor number will only be incremented when
905   changes made to the protocol have the effect of adding to the message
906   semantics or implying additional capabilities of the sender.  However,
907   the minor version was not incremented for the changes introduced between
908   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
909   is specifically avoiding any such changes to the protocol.
913<section title="Uniform Resource Identifiers" anchor="uri">
914<iref primary="true" item="resource"/>
916   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
917   throughout HTTP as the means for identifying resources. URI references
918   are used to target requests, indicate redirects, and define relationships.
919   HTTP does not limit what a resource might be; it merely defines an interface
920   that can be used to interact with a resource via HTTP. More information on
921   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
923  <x:anchor-alias value="URI-reference"/>
924  <x:anchor-alias value="absolute-URI"/>
925  <x:anchor-alias value="relative-part"/>
926  <x:anchor-alias value="authority"/>
927  <x:anchor-alias value="path-abempty"/>
928  <x:anchor-alias value="path-absolute"/>
929  <x:anchor-alias value="port"/>
930  <x:anchor-alias value="query"/>
931  <x:anchor-alias value="uri-host"/>
932  <x:anchor-alias value="partial-URI"/>
934   This specification adopts the definitions of "URI-reference",
935   "absolute-URI", "relative-part", "port", "host",
936   "path-abempty", "path-absolute", "query", and "authority" from the
937   URI generic syntax <xref target="RFC3986"/>.
938   In addition, we define a partial-URI rule for protocol elements
939   that allow a relative URI but not a fragment.
941<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"/>
942  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
943  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
944  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
945  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
946  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
947  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
948  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
949  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
950  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
952  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
955   Each protocol element in HTTP that allows a URI reference will indicate
956   in its ABNF production whether the element allows any form of reference
957   (URI-reference), only a URI in absolute form (absolute-URI), only the
958   path and optional query components, or some combination of the above.
959   Unless otherwise indicated, URI references are parsed relative to the
960   effective request URI, which defines the default base URI for references
961   in both the request and its corresponding response.
964<section title="http URI scheme" anchor="http.uri">
965  <x:anchor-alias value="http-URI"/>
966  <iref item="http URI scheme" primary="true"/>
967  <iref item="URI scheme" subitem="http" primary="true"/>
969   The "http" URI scheme is hereby defined for the purpose of minting
970   identifiers according to their association with the hierarchical
971   namespace governed by a potential HTTP origin server listening for
972   TCP connections on a given port.
974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
975  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
978   The HTTP origin server is identified by the generic syntax's
979   <x:ref>authority</x:ref> component, which includes a host identifier
980   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
981   The remainder of the URI, consisting of both the hierarchical path
982   component and optional query component, serves as an identifier for
983   a potential resource within that origin server's name space.
986   If the host identifier is provided as an IP literal or IPv4 address,
987   then the origin server is any listener on the indicated TCP port at
988   that IP address. If host is a registered name, then that name is
989   considered an indirect identifier and the recipient might use a name
990   resolution service, such as DNS, to find the address of a listener
991   for that host.
992   The host &MUST-NOT; be empty; if an "http" URI is received with an
993   empty host, then it &MUST; be rejected as invalid.
994   If the port subcomponent is empty or not given, then TCP port 80 is
995   assumed (the default reserved port for WWW services).
998   Regardless of the form of host identifier, access to that host is not
999   implied by the mere presence of its name or address. The host might or might
1000   not exist and, even when it does exist, might or might not be running an
1001   HTTP server or listening to the indicated port. The "http" URI scheme
1002   makes use of the delegated nature of Internet names and addresses to
1003   establish a naming authority (whatever entity has the ability to place
1004   an HTTP server at that Internet name or address) and allows that
1005   authority to determine which names are valid and how they might be used.
1008   When an "http" URI is used within a context that calls for access to the
1009   indicated resource, a client &MAY; attempt access by resolving
1010   the host to an IP address, establishing a TCP connection to that address
1011   on the indicated port, and sending an HTTP request message to the server
1012   containing the URI's identifying data as described in <xref target="request"/>.
1013   If the server responds to that request with a non-interim HTTP response
1014   message, as described in <xref target="response"/>, then that response
1015   is considered an authoritative answer to the client's request.
1018   Although HTTP is independent of the transport protocol, the "http"
1019   scheme is specific to TCP-based services because the name delegation
1020   process depends on TCP for establishing authority.
1021   An HTTP service based on some other underlying connection protocol
1022   would presumably be identified using a different URI scheme, just as
1023   the "https" scheme (below) is used for servers that require an SSL/TLS
1024   transport layer on a connection. Other protocols might also be used to
1025   provide access to "http" identified resources &mdash; it is only the
1026   authoritative interface used for mapping the namespace that is
1027   specific to TCP.
1030   The URI generic syntax for authority also includes a deprecated
1031   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1032   for including user authentication information in the URI.  Some
1033   implementations make use of the userinfo component for internal
1034   configuration of authentication information, such as within command
1035   invocation options, configuration files, or bookmark lists, even
1036   though such usage might expose a user identifier or password.
1037   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1038   delimiter) when transmitting an "http" URI in a message.  Recipients
1039   of HTTP messages that contain a URI reference &SHOULD; parse for the
1040   existence of userinfo and treat its presence as an error, likely
1041   indicating that the deprecated subcomponent is being used to obscure
1042   the authority for the sake of phishing attacks.
1046<section title="https URI scheme" anchor="https.uri">
1047   <x:anchor-alias value="https-URI"/>
1048   <iref item="https URI scheme"/>
1049   <iref item="URI scheme" subitem="https"/>
1051   The "https" URI scheme is hereby defined for the purpose of minting
1052   identifiers according to their association with the hierarchical
1053   namespace governed by a potential HTTP origin server listening for
1054   SSL/TLS-secured connections on a given TCP port.
1057   All of the requirements listed above for the "http" scheme are also
1058   requirements for the "https" scheme, except that a default TCP port
1059   of 443 is assumed if the port subcomponent is empty or not given,
1060   and the TCP connection &MUST; be secured for privacy through the
1061   use of strong encryption prior to sending the first HTTP request.
1063<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1064  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1067   Unlike the "http" scheme, responses to "https" identified requests
1068   are never "public" and thus &MUST-NOT; be reused for shared caching.
1069   They can, however, be reused in a private cache if the message is
1070   cacheable by default in HTTP or specifically indicated as such by
1071   the Cache-Control header field (&header-cache-control;).
1074   Resources made available via the "https" scheme have no shared
1075   identity with the "http" scheme even if their resource identifiers
1076   indicate the same authority (the same host listening to the same
1077   TCP port).  They are distinct name spaces and are considered to be
1078   distinct origin servers.  However, an extension to HTTP that is
1079   defined to apply to entire host domains, such as the Cookie protocol
1080   <xref target="RFC6265"/>, can allow information
1081   set by one service to impact communication with other services
1082   within a matching group of host domains.
1085   The process for authoritative access to an "https" identified
1086   resource is defined in <xref target="RFC2818"/>.
1090<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1092   Since the "http" and "https" schemes conform to the URI generic syntax,
1093   such URIs are normalized and compared according to the algorithm defined
1094   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1095   described above for each scheme.
1098   If the port is equal to the default port for a scheme, the normal
1099   form is to elide the port subcomponent. Likewise, an empty path
1100   component is equivalent to an absolute path of "/", so the normal
1101   form is to provide a path of "/" instead. The scheme and host
1102   are case-insensitive and normally provided in lowercase; all
1103   other components are compared in a case-sensitive manner.
1104   Characters other than those in the "reserved" set are equivalent
1105   to their percent-encoded octets (see <xref target="RFC3986"
1106   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1109   For example, the following three URIs are equivalent:
1111<figure><artwork type="example">
1120<section title="Message Format" anchor="http.message">
1121<x:anchor-alias value="generic-message"/>
1122<x:anchor-alias value="message.types"/>
1123<x:anchor-alias value="HTTP-message"/>
1124<x:anchor-alias value="start-line"/>
1125<iref item="header section"/>
1126<iref item="headers"/>
1127<iref item="header field"/>
1129   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1130   octets in a format similar to the Internet Message Format
1131   <xref target="RFC5322"/>: zero or more header fields (collectively
1132   referred to as the "headers" or the "header section"), an empty line
1133   indicating the end of the header section, and an optional message-body.
1136   An HTTP message can either be a request from client to server or a
1137   response from server to client.  Syntactically, the two types of message
1138   differ only in the start-line, which is either a Request-Line (for requests)
1139   or a Status-Line (for responses), and in the algorithm for determining
1140   the length of the message-body (<xref target="message.body"/>).
1141   In theory, a client could receive requests and a server could receive
1142   responses, distinguishing them by their different start-line formats,
1143   but in practice servers are implemented to only expect a request
1144   (a response is interpreted as an unknown or invalid request method)
1145   and clients are implemented to only expect a response.
1147<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1148  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1149                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1150                    <x:ref>CRLF</x:ref>
1151                    [ <x:ref>message-body</x:ref> ]
1152  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1155   Implementations &MUST-NOT; send whitespace between the start-line and
1156   the first header field. The presence of such whitespace in a request
1157   might be an attempt to trick a server into ignoring that field or
1158   processing the line after it as a new request, either of which might
1159   result in a security vulnerability if other implementations within
1160   the request chain interpret the same message differently.
1161   Likewise, the presence of such whitespace in a response might be
1162   ignored by some clients or cause others to cease parsing.
1165<section title="Message Parsing and Robustness" anchor="message.robustness">
1167   The normal procedure for parsing an HTTP message is to read the
1168   start-line into a structure, read each header field into a hash
1169   table by field name until the empty line, and then use the parsed
1170   data to determine if a message-body is expected.  If a message-body
1171   has been indicated, then it is read as a stream until an amount
1172   of octets equal to the message-body length is read or the connection
1173   is closed.
1176   Care must be taken to parse an HTTP message as a sequence
1177   of octets in an encoding that is a superset of US-ASCII.  Attempting
1178   to parse HTTP as a stream of Unicode characters in a character encoding
1179   like UTF-16 might introduce security flaws due to the differing ways
1180   that such parsers interpret invalid characters.
1183   Older HTTP/1.0 client implementations might send an extra CRLF
1184   after a POST request as a lame workaround for some early server
1185   applications that failed to read message-body content that was
1186   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1187   preface or follow a request with an extra CRLF.  If terminating
1188   the request message-body with a line-ending is desired, then the
1189   client &MUST; include the terminating CRLF octets as part of the
1190   message-body length.
1193   In the interest of robustness, servers &SHOULD; ignore at least one
1194   empty line received where a Request-Line is expected. In other words, if
1195   the server is reading the protocol stream at the beginning of a
1196   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1197   Likewise, although the line terminator for the start-line and header
1198   fields is the sequence CRLF, we recommend that recipients recognize a
1199   single LF as a line terminator and ignore any CR.
1202   When a server listening only for HTTP request messages, or processing
1203   what appears from the start-line to be an HTTP request message,
1204   receives a sequence of octets that does not match the HTTP-message
1205   grammar aside from the robustness exceptions listed above, the
1206   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1210<section title="Header Fields" anchor="header.fields">
1211  <x:anchor-alias value="header-field"/>
1212  <x:anchor-alias value="field-content"/>
1213  <x:anchor-alias value="field-name"/>
1214  <x:anchor-alias value="field-value"/>
1215  <x:anchor-alias value="OWS"/>
1217   Each HTTP header field consists of a case-insensitive field name
1218   followed by a colon (":"), optional whitespace, and the field value.
1220<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"/>
1221  <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>
1222  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1223  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1224  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1227   The field-name token labels the corresponding field-value as having the
1228   semantics defined by that header field.  For example, the Date header field
1229   is defined in <xref target=""/> as containing the origination
1230   timestamp for the message in which it appears.
1233   HTTP header fields are fully extensible: there is no limit on the
1234   introduction of new field names, each presumably defining new semantics,
1235   or on the number of header fields used in a given message.  Existing
1236   fields are defined in each part of this specification and in many other
1237   specifications outside the standards process.
1238   New header fields can be introduced without changing the protocol version
1239   if their defined semantics allow them to be safely ignored by recipients
1240   that do not recognize them.
1243   New HTTP header fields &SHOULD; be registered with IANA according
1244   to the procedures in <xref target="header.field.registration"/>.
1245   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1246   field-name is listed in the Connection header field
1247   (<xref target="header.connection"/>) or the proxy is specifically
1248   configured to block or otherwise transform such fields.
1249   Unrecognized header fields &SHOULD; be ignored by other recipients.
1252   The order in which header fields with differing field names are
1253   received is not significant. However, it is "good practice" to send
1254   header fields that contain control data first, such as Host on
1255   requests and Date on responses, so that implementations can decide
1256   when not to handle a message as early as possible.  A server &MUST;
1257   wait until the entire header section is received before interpreting
1258   a request message, since later header fields might include conditionals,
1259   authentication credentials, or deliberately misleading duplicate
1260   header fields that would impact request processing.
1263   Multiple header fields with the same field name &MUST-NOT; be
1264   sent in a message unless the entire field value for that
1265   header field is defined as a comma-separated list [i.e., #(values)].
1266   Multiple header fields with the same field name can be combined into
1267   one "field-name: field-value" pair, without changing the semantics of the
1268   message, by appending each subsequent field value to the combined
1269   field value in order, separated by a comma. The order in which
1270   header fields with the same field name are received is therefore
1271   significant to the interpretation of the combined field value;
1272   a proxy &MUST-NOT; change the order of these field values when
1273   forwarding a message.
1276  <t>
1277   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1278   practice can occur multiple times, but does not use the list syntax, and
1279   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1280   for details.) Also note that the Set-Cookie2 header field specified in
1281   <xref target="RFC2965"/> does not share this problem.
1282  </t>
1285<section title="Field Parsing" anchor="field.parsing">
1287   No whitespace is allowed between the header field-name and colon.
1288   In the past, differences in the handling of such whitespace have led to
1289   security vulnerabilities in request routing and response handling.
1290   Any received request message that contains whitespace between a header
1291   field-name and colon &MUST; be rejected with a response code of 400
1292   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1293   message before forwarding the message downstream.
1296   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1297   preferred. The field value does not include any leading or trailing white
1298   space: OWS occurring before the first non-whitespace octet of the
1299   field value or after the last non-whitespace octet of the field value
1300   is ignored and &SHOULD; be removed before further processing (as this does
1301   not change the meaning of the header field).
1304   Historically, HTTP header field values could be extended over multiple
1305   lines by preceding each extra line with at least one space or horizontal
1306   tab octet (line folding). This specification deprecates such line
1307   folding except within the message/http media type
1308   (<xref target=""/>).
1309   HTTP senders &MUST-NOT; produce messages that include line folding
1310   (i.e., that contain any field-content that matches the obs-fold rule) unless
1311   the message is intended for packaging within the message/http media type.
1312   HTTP recipients &SHOULD; accept line folding and replace any embedded
1313   obs-fold whitespace with either a single SP or a matching number of SP
1314   octets (to avoid buffer copying) prior to interpreting the field value or
1315   forwarding the message downstream.
1318   Historically, HTTP has allowed field content with text in the ISO-8859-1
1319   <xref target="ISO-8859-1"/> character encoding and supported other
1320   character sets only through use of <xref target="RFC2047"/> encoding.
1321   In practice, most HTTP header field values use only a subset of the
1322   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1323   header fields &SHOULD; limit their field values to US-ASCII octets.
1324   Recipients &SHOULD; treat other (obs-text) octets in field content as
1325   opaque data.
1329<section title="Field Length" anchor="field.length">
1331   HTTP does not place a pre-defined limit on the length of header fields,
1332   either in isolation or as a set. A server &MUST; be prepared to receive
1333   request header fields of unbounded length and respond with a 4xx status
1334   code if the received header field(s) would be longer than the server wishes
1335   to handle.
1338   A client that receives response headers that are longer than it wishes to
1339   handle can only treat it as a server error.
1342   Various ad-hoc limitations on header length are found in practice. It is
1343   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1344   combined header fields have 4000 or more octets.
1348<section title="Common Field ABNF Rules" anchor="field.rules">
1349<t anchor="rule.token.separators">
1350  <x:anchor-alias value="tchar"/>
1351  <x:anchor-alias value="token"/>
1352  <x:anchor-alias value="special"/>
1353  <x:anchor-alias value="word"/>
1354   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1355   separated by whitespace or special characters. These special characters
1356   &MUST; be in a quoted string to be used within a parameter value (as defined
1357   in <xref target="transfer.codings"/>).
1359<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"/>
1360  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1362  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1364  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1365 -->
1366  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1367                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1368                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1369                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1371  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1372                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1373                 / "]" / "?" / "=" / "{" / "}"
1375<t anchor="rule.quoted-string">
1376  <x:anchor-alias value="quoted-string"/>
1377  <x:anchor-alias value="qdtext"/>
1378  <x:anchor-alias value="obs-text"/>
1379   A string of text is parsed as a single word if it is quoted using
1380   double-quote marks.
1382<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"/>
1383  <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>
1384  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1385  <x:ref>obs-text</x:ref>       = %x80-FF
1387<t anchor="rule.quoted-pair">
1388  <x:anchor-alias value="quoted-pair"/>
1389   The backslash octet ("\") can be used as a single-octet
1390   quoting mechanism within quoted-string constructs:
1392<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1393  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1396   Recipients that process the value of the quoted-string &MUST; handle a
1397   quoted-pair as if it were replaced by the octet following the backslash.
1400   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1401   escaping (i.e., other than DQUOTE and the backslash octet).
1403<t anchor="rule.comment">
1404  <x:anchor-alias value="comment"/>
1405  <x:anchor-alias value="ctext"/>
1406   Comments can be included in some HTTP header fields by surrounding
1407   the comment text with parentheses. Comments are only allowed in
1408   fields containing "comment" as part of their field value definition.
1410<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1411  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1412  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1414<t anchor="rule.quoted-cpair">
1415  <x:anchor-alias value="quoted-cpair"/>
1416   The backslash octet ("\") can be used as a single-octet
1417   quoting mechanism within comment constructs:
1419<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1420  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1423   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1424   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1429<section title="Message Body" anchor="message.body">
1430  <x:anchor-alias value="message-body"/>
1432   The message-body (if any) of an HTTP message is used to carry the
1433   payload body associated with the request or response.
1435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1436  <x:ref>message-body</x:ref> = *OCTET
1439   The message-body differs from the payload body only when a transfer-coding
1440   has been applied, as indicated by the Transfer-Encoding header field
1441   (<xref target="header.transfer-encoding"/>).  If more than one
1442   Transfer-Encoding header field is present in a message, the multiple
1443   field-values &MUST; be combined into one field-value, according to the
1444   algorithm defined in <xref target="header.fields"/>, before determining
1445   the message-body length.
1448   When one or more transfer-codings are applied to a payload in order to
1449   form the message-body, the Transfer-Encoding header field &MUST; contain
1450   the list of transfer-codings applied. Transfer-Encoding is a property of
1451   the message, not of the payload, and thus &MAY; be added or removed by
1452   any implementation along the request/response chain under the constraints
1453   found in <xref target="transfer.codings"/>.
1456   If a message is received that has multiple Content-Length header fields
1457   (<xref target="header.content-length"/>) with field-values consisting
1458   of the same decimal value, or a single Content-Length header field with
1459   a field value containing a list of identical decimal values (e.g.,
1460   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1461   header fields have been generated or combined by an upstream message
1462   processor, then the recipient &MUST; either reject the message as invalid
1463   or replace the duplicated field-values with a single valid Content-Length
1464   field containing that decimal value prior to determining the message-body
1465   length.
1468   The rules for when a message-body is allowed in a message differ for
1469   requests and responses.
1472   The presence of a message-body in a request is signaled by the
1473   inclusion of a Content-Length or Transfer-Encoding header field in
1474   the request's header fields, even if the request method does not
1475   define any use for a message-body.  This allows the request
1476   message framing algorithm to be independent of method semantics.
1479   For response messages, whether or not a message-body is included with
1480   a message is dependent on both the request method and the response
1481   status code (<xref target="status.code.and.reason.phrase"/>).
1482   Responses to the HEAD request method never include a message-body
1483   because the associated response header fields (e.g., Transfer-Encoding,
1484   Content-Length, etc.) only indicate what their values would have been
1485   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1486   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1487   All other responses do include a message-body, although the body
1488   &MAY; be of zero length.
1491   The length of the message-body is determined by one of the following
1492   (in order of precedence):
1495  <list style="numbers">
1496    <x:lt><t>
1497     Any response to a HEAD request and any response with a status
1498     code of 100-199, 204, or 304 is always terminated by the first
1499     empty line after the header fields, regardless of the header
1500     fields present in the message, and thus cannot contain a message-body.
1501    </t></x:lt>
1502    <x:lt><t>
1503     If a Transfer-Encoding header field is present
1504     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1505     is the final encoding, the message-body length is determined by reading
1506     and decoding the chunked data until the transfer-coding indicates the
1507     data is complete.
1508    </t>
1509    <t>
1510     If a Transfer-Encoding header field is present in a response and the
1511     "chunked" transfer-coding is not the final encoding, the message-body
1512     length is determined by reading the connection until it is closed by
1513     the server.
1514     If a Transfer-Encoding header field is present in a request and the
1515     "chunked" transfer-coding is not the final encoding, the message-body
1516     length cannot be determined reliably; the server &MUST; respond with
1517     the 400 (Bad Request) status code and then close the connection.
1518    </t>
1519    <t>
1520     If a message is received with both a Transfer-Encoding header field
1521     and a Content-Length header field, the Transfer-Encoding overrides
1522     the Content-Length.
1523     Such a message might indicate an attempt to perform request or response
1524     smuggling (bypass of security-related checks on message routing or content)
1525     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1526     be removed, prior to forwarding the message downstream, or replaced with
1527     the real message-body length after the transfer-coding is decoded.
1528    </t></x:lt>
1529    <x:lt><t>
1530     If a message is received without Transfer-Encoding and with either
1531     multiple Content-Length header fields having differing field-values or
1532     a single Content-Length header field having an invalid value, then the
1533     message framing is invalid and &MUST; be treated as an error to
1534     prevent request or response smuggling.
1535     If this is a request message, the server &MUST; respond with
1536     a 400 (Bad Request) status code and then close the connection.
1537     If this is a response message received by a proxy, the proxy
1538     &MUST; discard the received response, send a 502 (Bad Gateway)
1539     status code as its downstream response, and then close the connection.
1540     If this is a response message received by a user-agent, it &MUST; be
1541     treated as an error by discarding the message and closing the connection.
1542    </t></x:lt>
1543    <x:lt><t>
1544     If a valid Content-Length header field
1545     is present without Transfer-Encoding, its decimal value defines the
1546     message-body length in octets.  If the actual number of octets sent in
1547     the message is less than the indicated Content-Length, the recipient
1548     &MUST; consider the message to be incomplete and treat the connection
1549     as no longer usable.
1550     If the actual number of octets sent in the message is more than the indicated
1551     Content-Length, the recipient &MUST; only process the message-body up to the
1552     field value's number of octets; the remainder of the message &MUST; either
1553     be discarded or treated as the next message in a pipeline.  For the sake of
1554     robustness, a user-agent &MAY; attempt to detect and correct such an error
1555     in message framing if it is parsing the response to the last request on
1556     a connection and the connection has been closed by the server.
1557    </t></x:lt>
1558    <x:lt><t>
1559     If this is a request message and none of the above are true, then the
1560     message-body length is zero (no message-body is present).
1561    </t></x:lt>
1562    <x:lt><t>
1563     Otherwise, this is a response message without a declared message-body
1564     length, so the message-body length is determined by the number of octets
1565     received prior to the server closing the connection.
1566    </t></x:lt>
1567  </list>
1570   Since there is no way to distinguish a successfully completed,
1571   close-delimited message from a partially-received message interrupted
1572   by network failure, implementations &SHOULD; use encoding or
1573   length-delimited messages whenever possible.  The close-delimiting
1574   feature exists primarily for backwards compatibility with HTTP/1.0.
1577   A server &MAY; reject a request that contains a message-body but
1578   not a Content-Length by responding with 411 (Length Required).
1581   Unless a transfer-coding other than "chunked" has been applied,
1582   a client that sends a request containing a message-body &SHOULD;
1583   use a valid Content-Length header field if the message-body length
1584   is known in advance, rather than the "chunked" encoding, since some
1585   existing services respond to "chunked" with a 411 (Length Required)
1586   status code even though they understand the chunked encoding.  This
1587   is typically because such services are implemented via a gateway that
1588   requires a content-length in advance of being called and the server
1589   is unable or unwilling to buffer the entire request before processing.
1592   A client that sends a request containing a message-body &MUST; include a
1593   valid Content-Length header field if it does not know the server will
1594   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1595   of specific user configuration or by remembering the version of a prior
1596   received response.
1600<section anchor="incomplete.messages" title="Incomplete Messages">
1602   Request messages that are prematurely terminated, possibly due to a
1603   cancelled connection or a server-imposed time-out exception, &MUST;
1604   result in closure of the connection; sending an HTTP/1.1 error response
1605   prior to closing the connection is &OPTIONAL;.
1608   Response messages that are prematurely terminated, usually by closure
1609   of the connection prior to receiving the expected number of octets or by
1610   failure to decode a transfer-encoded message-body, &MUST; be recorded
1611   as incomplete.  A response that terminates in the middle of the header
1612   block (before the empty line is received) cannot be assumed to convey the
1613   full semantics of the response and &MUST; be treated as an error.
1616   A message-body that uses the chunked transfer encoding is
1617   incomplete if the zero-sized chunk that terminates the encoding has not
1618   been received.  A message that uses a valid Content-Length is incomplete
1619   if the size of the message-body received (in octets) is less than the
1620   value given by Content-Length.  A response that has neither chunked
1621   transfer encoding nor Content-Length is terminated by closure of the
1622   connection, and thus is considered complete regardless of the number of
1623   message-body octets received, provided that the header block was received
1624   intact.
1627   A user agent &MUST-NOT; render an incomplete response message-body as if
1628   it were complete (i.e., some indication must be given to the user that an
1629   error occurred).  Cache requirements for incomplete responses are defined
1630   in &cache-incomplete;.
1633   A server &MUST; read the entire request message-body or close
1634   the connection after sending its response, since otherwise the
1635   remaining data on a persistent connection would be misinterpreted
1636   as the next request.  Likewise,
1637   a client &MUST; read the entire response message-body if it intends
1638   to reuse the same connection for a subsequent request.  Pipelining
1639   multiple requests on a connection is described in <xref target="pipelining"/>.
1643<section title="General Header Fields" anchor="general.header.fields">
1644  <x:anchor-alias value="general-header"/>
1646   There are a few header fields which have general applicability for
1647   both request and response messages, but which do not apply to the
1648   payload being transferred. These header fields apply only to the
1649   message being transmitted.
1651<texttable align="left">
1652  <ttcol>Header Field Name</ttcol>
1653  <ttcol>Defined in...</ttcol>
1655  <c>Connection</c> <c><xref target="header.connection"/></c>
1656  <c>Date</c> <c><xref target=""/></c>
1657  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1658  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1659  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1660  <c>Via</c> <c><xref target="header.via"/></c>
1665<section title="Request" anchor="request">
1666  <x:anchor-alias value="Request"/>
1668   A request message from a client to a server begins with a
1669   Request-Line, followed by zero or more header fields, an empty
1670   line signifying the end of the header block, and an optional
1671   message body.
1673<!--                 Host                      ; should be moved here eventually -->
1674<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1675  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1676                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1677                  <x:ref>CRLF</x:ref>
1678                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1681<section title="Request-Line" anchor="request-line">
1682  <x:anchor-alias value="Request-Line"/>
1684   The Request-Line begins with a method token, followed by a single
1685   space (SP), the request-target, another single space (SP), the
1686   protocol version, and ending with CRLF.
1688<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1689  <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>
1692<section title="Method" anchor="method">
1693  <x:anchor-alias value="Method"/>
1695   The Method token indicates the request method to be performed on the
1696   target resource. The request method is case-sensitive.
1698<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1699  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1703<section title="request-target" anchor="request-target">
1704  <x:anchor-alias value="request-target"/>
1706   The request-target identifies the target resource upon which to apply
1707   the request.  In most cases, the user agent is provided a URI reference
1708   from which it determines an absolute URI for identifying the target
1709   resource.  When a request to the resource is initiated, all or part
1710   of that URI is used to construct the HTTP request-target.
1712<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1713  <x:ref>request-target</x:ref> = "*"
1714                 / <x:ref>absolute-URI</x:ref>
1715                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1716                 / <x:ref>authority</x:ref>
1719   The four options for request-target are dependent on the nature of the
1720   request.
1722<t><iref item="asterisk form (of request-target)"/>
1723   The asterisk "*" form of request-target, which &MUST-NOT; be used
1724   with any request method other than OPTIONS, means that the request
1725   applies to the server as a whole (the listening process) rather than
1726   to a specific named resource at that server.  For example,
1728<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1729OPTIONS * HTTP/1.1
1731<t><iref item="absolute-URI form (of request-target)"/>
1732   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1733   proxy. The proxy is requested to either forward the request or service it
1734   from a valid cache, and then return the response. Note that the proxy &MAY;
1735   forward the request on to another proxy or directly to the server
1736   specified by the absolute-URI. In order to avoid request loops, a
1737   proxy that forwards requests to other proxies &MUST; be able to
1738   recognize and exclude all of its own server names, including
1739   any aliases, local variations, and the numeric IP address. An example
1740   Request-Line would be:
1742<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1743GET HTTP/1.1
1746   To allow for transition to absolute-URIs in all requests in future
1747   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1748   form in requests, even though HTTP/1.1 clients will only generate
1749   them in requests to proxies.
1752   If a proxy receives a host name that is not a fully qualified domain
1753   name, it &MAY; add its domain to the host name it received. If a proxy
1754   receives a fully qualified domain name, the proxy &MUST-NOT; change
1755   the host name.
1757<t><iref item="authority form (of request-target)"/>
1758   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1760<t><iref item="origin form (of request-target)"/>
1761   The most common form of request-target is that used when making
1762   a request to an origin server ("origin form").
1763   In this case, the absolute path and query components of the URI
1764   &MUST; be transmitted as the request-target, and the authority component
1765   &MUST; be transmitted in a Host header field. For example, a client wishing
1766   to retrieve a representation of the resource, as identified above,
1767   directly from the origin server would open (or reuse) a TCP connection
1768   to port 80 of the host "" and send the lines:
1770<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1771GET /pub/WWW/TheProject.html HTTP/1.1
1775   followed by the remainder of the Request. Note that the origin form
1776   of request-target always starts with an absolute path; if the target
1777   resource's URI path is empty, then an absolute path of "/" &MUST; be
1778   provided in the request-target.
1781   If a proxy receives an OPTIONS request with an absolute-URI form of
1782   request-target in which the URI has an empty path and no query component,
1783   then the last proxy on the request chain &MUST; use a request-target
1784   of "*" when it forwards the request to the indicated origin server.
1787   For example, the request
1788</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1792  would be forwarded by the final proxy as
1793</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1794OPTIONS * HTTP/1.1
1798   after connecting to port 8001 of host "".
1802   The request-target is transmitted in the format specified in
1803   <xref target="http.uri"/>. If the request-target is percent-encoded
1804   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1805   &MUST; decode the request-target in order to
1806   properly interpret the request. Servers &SHOULD; respond to invalid
1807   request-targets with an appropriate status code.
1810   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1811   received request-target when forwarding it to the next inbound server,
1812   except as noted above to replace a null path-absolute with "/" or "*".
1815  <t>
1816    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1817    meaning of the request when the origin server is improperly using
1818    a non-reserved URI character for a reserved purpose.  Implementors
1819    need to be aware that some pre-HTTP/1.1 proxies have been known to
1820    rewrite the request-target.
1821  </t>
1824   HTTP does not place a pre-defined limit on the length of a request-target.
1825   A server &MUST; be prepared to receive URIs of unbounded length and
1826   respond with the 414 (URI Too Long) status code if the received
1827   request-target would be longer than the server wishes to handle
1828   (see &status-414;).
1831   Various ad-hoc limitations on request-target length are found in practice.
1832   It is &RECOMMENDED; that all HTTP senders and recipients support
1833   request-target lengths of 8000 or more octets.
1836  <t>
1837    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1838    are not part of the request-target and thus will not be transmitted
1839    in an HTTP request.
1840  </t>
1845<section title="The Resource Identified by a Request" anchor="">
1847   The exact resource identified by an Internet request is determined by
1848   examining both the request-target and the Host header field.
1851   An origin server that does not allow resources to differ by the
1852   requested host &MAY; ignore the Host header field value when
1853   determining the resource identified by an HTTP/1.1 request. (But see
1854   <xref target=""/>
1855   for other requirements on Host support in HTTP/1.1.)
1858   An origin server that does differentiate resources based on the host
1859   requested (sometimes referred to as virtual hosts or vanity host
1860   names) &MUST; use the following rules for determining the requested
1861   resource on an HTTP/1.1 request:
1862  <list style="numbers">
1863    <t>If request-target is an absolute-URI, the host is part of the
1864     request-target. Any Host header field value in the request &MUST; be
1865     ignored.</t>
1866    <t>If the request-target is not an absolute-URI, and the request includes
1867     a Host header field, the host is determined by the Host header
1868     field value.</t>
1869    <t>If the host as determined by rule 1 or 2 is not a valid host on
1870     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1871  </list>
1874   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1875   attempt to use heuristics (e.g., examination of the URI path for
1876   something unique to a particular host) in order to determine what
1877   exact resource is being requested.
1881<section title="Effective Request URI" anchor="effective.request.uri">
1882  <iref primary="true" item="effective request URI"/>
1883  <iref primary="true" item="target resource"/>
1885   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1886   for the target resource; instead, the URI needs to be inferred from the
1887   request-target, Host header field, and connection context. The result of
1888   this process is called the "effective request URI".  The "target resource"
1889   is the resource identified by the effective request URI.
1892   If the request-target is an absolute-URI, then the effective request URI is
1893   the request-target.
1896   If the request-target uses the path-absolute form or the asterisk form,
1897   and the Host header field is present, then the effective request URI is
1898   constructed by concatenating
1901  <list style="symbols">
1902    <t>
1903      the scheme name: "http" if the request was received over an insecure
1904      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1905      connection,
1906    </t>
1907    <t>
1908      the octet sequence "://",
1909    </t>
1910    <t>
1911      the authority component, as specified in the Host header field
1912      (<xref target=""/>), and
1913    </t>
1914    <t>
1915      the request-target obtained from the Request-Line, unless the
1916      request-target is just the asterisk "*".
1917    </t>
1918  </list>
1921   If the request-target uses the path-absolute form or the asterisk form,
1922   and the Host header field is not present, then the effective request URI is
1923   undefined.
1926   Otherwise, when request-target uses the authority form, the effective
1927   request URI is undefined.
1931   Example 1: the effective request URI for the message
1933<artwork type="example" x:indent-with="  ">
1934GET /pub/WWW/TheProject.html HTTP/1.1
1938  (received over an insecure TCP connection) is "http", plus "://", plus the
1939  authority component "", plus the request-target
1940  "/pub/WWW/TheProject.html", thus
1941  "".
1946   Example 2: the effective request URI for the message
1948<artwork type="example" x:indent-with="  ">
1949OPTIONS * HTTP/1.1
1953  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1954  authority component "", thus "".
1958   Effective request URIs are compared using the rules described in
1959   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1960   be treated as equivalent to an absolute path of "/".
1967<section title="Response" anchor="response">
1968  <x:anchor-alias value="Response"/>
1970   After receiving and interpreting a request message, a server responds
1971   with an HTTP response message.
1973<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1974  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1975                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1976                  <x:ref>CRLF</x:ref>
1977                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1980<section title="Status-Line" anchor="status-line">
1981  <x:anchor-alias value="Status-Line"/>
1983   The first line of a Response message is the Status-Line, consisting
1984   of the protocol version, a space (SP), the status code, another space,
1985   a possibly-empty textual phrase describing the status code, and
1986   ending with CRLF.
1988<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1989  <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>
1992<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1993  <x:anchor-alias value="Reason-Phrase"/>
1994  <x:anchor-alias value="Status-Code"/>
1996   The Status-Code element is a 3-digit integer result code of the
1997   attempt to understand and satisfy the request. These codes are fully
1998   defined in &status-codes;.  The Reason Phrase exists for the sole
1999   purpose of providing a textual description associated with the numeric
2000   status code, out of deference to earlier Internet application protocols
2001   that were more frequently used with interactive text clients.
2002   A client &SHOULD; ignore the content of the Reason Phrase.
2005   The first digit of the Status-Code defines the class of response. The
2006   last two digits do not have any categorization role. There are 5
2007   values for the first digit:
2008  <list style="symbols">
2009    <t>
2010      1xx: Informational - Request received, continuing process
2011    </t>
2012    <t>
2013      2xx: Success - The action was successfully received,
2014        understood, and accepted
2015    </t>
2016    <t>
2017      3xx: Redirection - Further action must be taken in order to
2018        complete the request
2019    </t>
2020    <t>
2021      4xx: Client Error - The request contains bad syntax or cannot
2022        be fulfilled
2023    </t>
2024    <t>
2025      5xx: Server Error - The server failed to fulfill an apparently
2026        valid request
2027    </t>
2028  </list>
2030<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
2031  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
2032  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
2040<section title="Protocol Parameters" anchor="protocol.parameters">
2042<section title="Date/Time Formats: Full Date" anchor="">
2043  <x:anchor-alias value="HTTP-date"/>
2045   HTTP applications have historically allowed three different formats
2046   for date/time stamps. However, the preferred format is a fixed-length subset
2047   of that defined by <xref target="RFC1123"/>:
2049<figure><artwork type="example" x:indent-with="  ">
2050Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2053   The other formats are described here only for compatibility with obsolete
2054   implementations.
2056<figure><artwork type="example" x:indent-with="  ">
2057Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2058Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2061   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2062   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2063   only generate the RFC 1123 format for representing HTTP-date values
2064   in header fields.
2067   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2068   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2069   equal to UTC (Coordinated Universal Time). This is indicated in the
2070   first two formats by the inclusion of "GMT" as the three-letter
2071   abbreviation for time zone, and &MUST; be assumed when reading the
2072   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2073   additional whitespace beyond that specifically included as SP in the
2074   grammar.
2076<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2077  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2079<t anchor="">
2080  <x:anchor-alias value="rfc1123-date"/>
2081  <x:anchor-alias value="time-of-day"/>
2082  <x:anchor-alias value="hour"/>
2083  <x:anchor-alias value="minute"/>
2084  <x:anchor-alias value="second"/>
2085  <x:anchor-alias value="day-name"/>
2086  <x:anchor-alias value="day"/>
2087  <x:anchor-alias value="month"/>
2088  <x:anchor-alias value="year"/>
2089  <x:anchor-alias value="GMT"/>
2090  Preferred format:
2092<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"/>
2093  <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>
2094  ; fixed length subset of the format defined in
2095  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2097  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2098               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2099               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2100               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2101               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2102               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2103               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2105  <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>
2106               ; e.g., 02 Jun 1982
2108  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2109  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2110               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2111               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2112               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2113               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2114               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2115               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2116               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2117               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2118               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2119               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2120               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2121  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2123  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2125  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2126                 ; 00:00:00 - 23:59:59
2128  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2129  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2130  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2133  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2134  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2135  same as those defined for the RFC 5322 constructs
2136  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2138<t anchor="">
2139  <x:anchor-alias value="obs-date"/>
2140  <x:anchor-alias value="rfc850-date"/>
2141  <x:anchor-alias value="asctime-date"/>
2142  <x:anchor-alias value="date1"/>
2143  <x:anchor-alias value="date2"/>
2144  <x:anchor-alias value="date3"/>
2145  <x:anchor-alias value="rfc1123-date"/>
2146  <x:anchor-alias value="day-name-l"/>
2147  Obsolete formats:
2149<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2150  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
2152<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2153  <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>
2154  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2155                 ; day-month-year (e.g., 02-Jun-82)
2157  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2158         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2159         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2160         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2161         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2162         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2163         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2165<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2166  <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>
2167  <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> ))
2168                 ; month day (e.g., Jun  2)
2171  <t>
2172    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2173    accepting date values that might have been sent by non-HTTP
2174    applications, as is sometimes the case when retrieving or posting
2175    messages via proxies/gateways to SMTP or NNTP.
2176  </t>
2179  <t>
2180    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2181    to their usage within the protocol stream. Clients and servers are
2182    not required to use these formats for user presentation, request
2183    logging, etc.
2184  </t>
2188<section title="Transfer Codings" anchor="transfer.codings">
2189  <x:anchor-alias value="transfer-coding"/>
2190  <x:anchor-alias value="transfer-extension"/>
2192   Transfer-coding values are used to indicate an encoding
2193   transformation that has been, can be, or might need to be applied to a
2194   payload body in order to ensure "safe transport" through the network.
2195   This differs from a content coding in that the transfer-coding is a
2196   property of the message rather than a property of the representation
2197   that is being transferred.
2199<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2200  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2201                          / "compress" ; <xref target="compress.coding"/>
2202                          / "deflate" ; <xref target="deflate.coding"/>
2203                          / "gzip" ; <xref target="gzip.coding"/>
2204                          / <x:ref>transfer-extension</x:ref>
2205  <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> )
2207<t anchor="rule.parameter">
2208  <x:anchor-alias value="attribute"/>
2209  <x:anchor-alias value="transfer-parameter"/>
2210  <x:anchor-alias value="value"/>
2211   Parameters are in the form of attribute/value pairs.
2213<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"/>
2214  <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>
2215  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2216  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2219   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2220   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2221   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2224   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2225   MIME, which were designed to enable safe transport of binary data over a
2226   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2227   However, safe transport
2228   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2229   the only unsafe characteristic of message-bodies is the difficulty in
2230   determining the exact message body length (<xref target="message.body"/>),
2231   or the desire to encrypt data over a shared transport.
2234   A server that receives a request message with a transfer-coding it does
2235   not understand &SHOULD; respond with 501 (Not Implemented) and then
2236   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2237   client.
2240<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2241  <iref item="chunked (Coding Format)"/>
2242  <iref item="Coding Format" subitem="chunked"/>
2243  <x:anchor-alias value="chunk"/>
2244  <x:anchor-alias value="Chunked-Body"/>
2245  <x:anchor-alias value="chunk-data"/>
2246  <x:anchor-alias value="chunk-ext"/>
2247  <x:anchor-alias value="chunk-ext-name"/>
2248  <x:anchor-alias value="chunk-ext-val"/>
2249  <x:anchor-alias value="chunk-size"/>
2250  <x:anchor-alias value="last-chunk"/>
2251  <x:anchor-alias value="trailer-part"/>
2252  <x:anchor-alias value="quoted-str-nf"/>
2253  <x:anchor-alias value="qdtext-nf"/>
2255   The chunked encoding modifies the body of a message in order to
2256   transfer it as a series of chunks, each with its own size indicator,
2257   followed by an &OPTIONAL; trailer containing header fields. This
2258   allows dynamically produced content to be transferred along with the
2259   information necessary for the recipient to verify that it has
2260   received the full message.
2262<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"/>
2263  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2264                   <x:ref>last-chunk</x:ref>
2265                   <x:ref>trailer-part</x:ref>
2266                   <x:ref>CRLF</x:ref>
2268  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2269                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2270  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2271  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2273  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2274                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2275  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2276  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2277  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2278  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2280  <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>
2281                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2282  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2283                 ; <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>
2286   The chunk-size field is a string of hex digits indicating the size of
2287   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2288   zero, followed by the trailer, which is terminated by an empty line.
2291   The trailer allows the sender to include additional HTTP header
2292   fields at the end of the message. The Trailer header field can be
2293   used to indicate which header fields are included in a trailer (see
2294   <xref target="header.trailer"/>).
2297   A server using chunked transfer-coding in a response &MUST-NOT; use the
2298   trailer for any header fields unless at least one of the following is
2299   true:
2300  <list style="numbers">
2301    <t>the request included a TE header field that indicates "trailers" is
2302     acceptable in the transfer-coding of the  response, as described in
2303     <xref target="header.te"/>; or,</t>
2305    <t>the trailer fields consist entirely of optional metadata, and the
2306    recipient could use the message (in a manner acceptable to the server where
2307    the field originated) without receiving it. In other words, the server that
2308    generated the header (often but not always the origin server) is willing to
2309    accept the possibility that the trailer fields might be silently discarded
2310    along the path to the client.</t>
2311  </list>
2314   This requirement prevents an interoperability failure when the
2315   message is being received by an HTTP/1.1 (or later) proxy and
2316   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2317   compliance with the protocol would have necessitated a possibly
2318   infinite buffer on the proxy.
2321   A process for decoding the "chunked" transfer-coding
2322   can be represented in pseudo-code as:
2324<figure><artwork type="code">
2325  length := 0
2326  read chunk-size, chunk-ext (if any) and CRLF
2327  while (chunk-size &gt; 0) {
2328     read chunk-data and CRLF
2329     append chunk-data to decoded-body
2330     length := length + chunk-size
2331     read chunk-size and CRLF
2332  }
2333  read header-field
2334  while (header-field not empty) {
2335     append header-field to existing header fields
2336     read header-field
2337  }
2338  Content-Length := length
2339  Remove "chunked" from Transfer-Encoding
2342   All HTTP/1.1 applications &MUST; be able to receive and decode the
2343   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2344   they do not understand.
2347   Since "chunked" is the only transfer-coding required to be understood
2348   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2349   on a persistent connection.  Whenever a transfer-coding is applied to
2350   a payload body in a request, the final transfer-coding applied &MUST;
2351   be "chunked".  If a transfer-coding is applied to a response payload
2352   body, then either the final transfer-coding applied &MUST; be "chunked"
2353   or the message &MUST; be terminated by closing the connection. When the
2354   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2355   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2356   be applied more than once in a message-body.
2360<section title="Compression Codings" anchor="compression.codings">
2362   The codings defined below can be used to compress the payload of a
2363   message.
2366   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2367   is not desirable and is discouraged for future encodings. Their
2368   use here is representative of historical practice, not good
2369   design.
2372   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2373   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2374   equivalent to "gzip" and "compress" respectively.
2377<section title="Compress Coding" anchor="compress.coding">
2378<iref item="compress (Coding Format)"/>
2379<iref item="Coding Format" subitem="compress"/>
2381   The "compress" format is produced by the common UNIX file compression
2382   program "compress". This format is an adaptive Lempel-Ziv-Welch
2383   coding (LZW).
2387<section title="Deflate Coding" anchor="deflate.coding">
2388<iref item="deflate (Coding Format)"/>
2389<iref item="Coding Format" subitem="deflate"/>
2391   The "deflate" format is defined as the "deflate" compression mechanism
2392   (described in <xref target="RFC1951"/>) used inside the "zlib"
2393   data format (<xref target="RFC1950"/>).
2396  <t>
2397    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2398    compressed data without the zlib wrapper.
2399   </t>
2403<section title="Gzip Coding" anchor="gzip.coding">
2404<iref item="gzip (Coding Format)"/>
2405<iref item="Coding Format" subitem="gzip"/>
2407   The "gzip" format is produced by the file compression program
2408   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2409   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2415<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2417   The HTTP Transfer Coding Registry defines the name space for the transfer
2418   coding names.
2421   Registrations &MUST; include the following fields:
2422   <list style="symbols">
2423     <t>Name</t>
2424     <t>Description</t>
2425     <t>Pointer to specification text</t>
2426   </list>
2429   Names of transfer codings &MUST-NOT; overlap with names of content codings
2430   (&content-codings;), unless the encoding transformation is identical (as it
2431   is the case for the compression codings defined in
2432   <xref target="compression.codings"/>).
2435   Values to be added to this name space require a specification
2436   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2437   conform to the purpose of transfer coding defined in this section.
2440   The registry itself is maintained at
2441   <eref target=""/>.
2446<section title="Product Tokens" anchor="product.tokens">
2447  <x:anchor-alias value="product"/>
2448  <x:anchor-alias value="product-version"/>
2450   Product tokens are used to allow communicating applications to
2451   identify themselves by software name and version. Most fields using
2452   product tokens also allow sub-products which form a significant part
2453   of the application to be listed, separated by whitespace. By
2454   convention, the products are listed in order of their significance
2455   for identifying the application.
2457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2458  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2459  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2462   Examples:
2464<figure><artwork type="example">
2465  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2466  Server: Apache/0.8.4
2469   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2470   used for advertising or other non-essential information. Although any
2471   token octet &MAY; appear in a product-version, this token &SHOULD;
2472   only be used for a version identifier (i.e., successive versions of
2473   the same product &SHOULD; only differ in the product-version portion of
2474   the product value).
2478<section title="Quality Values" anchor="quality.values">
2479  <x:anchor-alias value="qvalue"/>
2481   Both transfer codings (TE request header field, <xref target="header.te"/>)
2482   and content negotiation (&content.negotiation;) use short "floating point"
2483   numbers to indicate the relative importance ("weight") of various
2484   negotiable parameters.  A weight is normalized to a real number in
2485   the range 0 through 1, where 0 is the minimum and 1 the maximum
2486   value. If a parameter has a quality value of 0, then content with
2487   this parameter is "not acceptable" for the client. HTTP/1.1
2488   applications &MUST-NOT; generate more than three digits after the
2489   decimal point. User configuration of these values &SHOULD; also be
2490   limited in this fashion.
2492<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2493  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2494                 / ( "1" [ "." 0*3("0") ] )
2497  <t>
2498     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2499     relative degradation in desired quality.
2500  </t>
2506<section title="Connections" anchor="connections">
2508<section title="Persistent Connections" anchor="persistent.connections">
2510<section title="Purpose" anchor="persistent.purpose">
2512   Prior to persistent connections, a separate TCP connection was
2513   established for each request, increasing the load on HTTP servers
2514   and causing congestion on the Internet. The use of inline images and
2515   other associated data often requires a client to make multiple
2516   requests of the same server in a short amount of time. Analysis of
2517   these performance problems and results from a prototype
2518   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2519   measurements of actual HTTP/1.1 implementations show good
2520   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2521   T/TCP <xref target="Tou1998"/>.
2524   Persistent HTTP connections have a number of advantages:
2525  <list style="symbols">
2526      <t>
2527        By opening and closing fewer TCP connections, CPU time is saved
2528        in routers and hosts (clients, servers, proxies, gateways,
2529        tunnels, or caches), and memory used for TCP protocol control
2530        blocks can be saved in hosts.
2531      </t>
2532      <t>
2533        HTTP requests and responses can be pipelined on a connection.
2534        Pipelining allows a client to make multiple requests without
2535        waiting for each response, allowing a single TCP connection to
2536        be used much more efficiently, with much lower elapsed time.
2537      </t>
2538      <t>
2539        Network congestion is reduced by reducing the number of packets
2540        caused by TCP opens, and by allowing TCP sufficient time to
2541        determine the congestion state of the network.
2542      </t>
2543      <t>
2544        Latency on subsequent requests is reduced since there is no time
2545        spent in TCP's connection opening handshake.
2546      </t>
2547      <t>
2548        HTTP can evolve more gracefully, since errors can be reported
2549        without the penalty of closing the TCP connection. Clients using
2550        future versions of HTTP might optimistically try a new feature,
2551        but if communicating with an older server, retry with old
2552        semantics after an error is reported.
2553      </t>
2554    </list>
2557   HTTP implementations &SHOULD; implement persistent connections.
2561<section title="Overall Operation" anchor="persistent.overall">
2563   A significant difference between HTTP/1.1 and earlier versions of
2564   HTTP is that persistent connections are the default behavior of any
2565   HTTP connection. That is, unless otherwise indicated, the client
2566   &SHOULD; assume that the server will maintain a persistent connection,
2567   even after error responses from the server.
2570   Persistent connections provide a mechanism by which a client and a
2571   server can signal the close of a TCP connection. This signaling takes
2572   place using the Connection header field (<xref target="header.connection"/>). Once a close
2573   has been signaled, the client &MUST-NOT; send any more requests on that
2574   connection.
2577<section title="Negotiation" anchor="persistent.negotiation">
2579   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2580   maintain a persistent connection unless a Connection header field including
2581   the connection-token "close" was sent in the request. If the server
2582   chooses to close the connection immediately after sending the
2583   response, it &SHOULD; send a Connection header field including the
2584   connection-token "close".
2587   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2588   decide to keep it open based on whether the response from a server
2589   contains a Connection header field with the connection-token close. In case
2590   the client does not want to maintain a connection for more than that
2591   request, it &SHOULD; send a Connection header field including the
2592   connection-token close.
2595   If either the client or the server sends the close token in the
2596   Connection header field, that request becomes the last one for the
2597   connection.
2600   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2601   maintained for HTTP versions less than 1.1 unless it is explicitly
2602   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2603   compatibility with HTTP/1.0 clients.
2606   In order to remain persistent, all messages on the connection &MUST;
2607   have a self-defined message length (i.e., one not defined by closure
2608   of the connection), as described in <xref target="message.body"/>.
2612<section title="Pipelining" anchor="pipelining">
2614   A client that supports persistent connections &MAY; "pipeline" its
2615   requests (i.e., send multiple requests without waiting for each
2616   response). A server &MUST; send its responses to those requests in the
2617   same order that the requests were received.
2620   Clients which assume persistent connections and pipeline immediately
2621   after connection establishment &SHOULD; be prepared to retry their
2622   connection if the first pipelined attempt fails. If a client does
2623   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2624   persistent. Clients &MUST; also be prepared to resend their requests if
2625   the server closes the connection before sending all of the
2626   corresponding responses.
2629   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2630   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2631   premature termination of the transport connection could lead to
2632   indeterminate results. A client wishing to send a non-idempotent
2633   request &SHOULD; wait to send that request until it has received the
2634   response status line for the previous request.
2639<section title="Proxy Servers" anchor="persistent.proxy">
2641   It is especially important that proxies correctly implement the
2642   properties of the Connection header field as specified in <xref target="header.connection"/>.
2645   The proxy server &MUST; signal persistent connections separately with
2646   its clients and the origin servers (or other proxy servers) that it
2647   connects to. Each persistent connection applies to only one transport
2648   link.
2651   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2652   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2653   for information and discussion of the problems with the Keep-Alive header field
2654   implemented by many HTTP/1.0 clients).
2657<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2659  <cref anchor="TODO-end-to-end" source="jre">
2660    Restored from <eref target=""/>.
2661    See also <eref target=""/>.
2662  </cref>
2665   For the purpose of defining the behavior of caches and non-caching
2666   proxies, we divide HTTP header fields into two categories:
2667  <list style="symbols">
2668      <t>End-to-end header fields, which are  transmitted to the ultimate
2669        recipient of a request or response. End-to-end header fields in
2670        responses MUST be stored as part of a cache entry and &MUST; be
2671        transmitted in any response formed from a cache entry.</t>
2673      <t>Hop-by-hop header fields, which are meaningful only for a single
2674        transport-level connection, and are not stored by caches or
2675        forwarded by proxies.</t>
2676  </list>
2679   The following HTTP/1.1 header fields are hop-by-hop header fields:
2680  <list style="symbols">
2681      <t>Connection</t>
2682      <t>Keep-Alive</t>
2683      <t>Proxy-Authenticate</t>
2684      <t>Proxy-Authorization</t>
2685      <t>TE</t>
2686      <t>Trailer</t>
2687      <t>Transfer-Encoding</t>
2688      <t>Upgrade</t>
2689  </list>
2692   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2695   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2696   (<xref target="header.connection"/>).
2700<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2702  <cref anchor="TODO-non-mod-headers" source="jre">
2703    Restored from <eref target=""/>.
2704    See also <eref target=""/>.
2705  </cref>
2708   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2709   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2710   modify an end-to-end header field unless the definition of that header field requires
2711   or specifically allows that.
2714   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2715   request or response, and it &MUST-NOT; add any of these fields if not
2716   already present:
2717  <list style="symbols">
2718    <t>Allow</t>
2719    <t>Content-Location</t>
2720    <t>Content-MD5</t>
2721    <t>ETag</t>
2722    <t>Last-Modified</t>
2723    <t>Server</t>
2724  </list>
2727   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2728   response:
2729  <list style="symbols">
2730    <t>Expires</t>
2731  </list>
2734   but it &MAY; add any of these fields if not already present. If an
2735   Expires header field is added, it &MUST; be given a field-value identical to
2736   that of the Date header field in that response.
2739   A proxy &MUST-NOT; modify or add any of the following fields in a
2740   message that contains the no-transform cache-control directive, or in
2741   any request:
2742  <list style="symbols">
2743    <t>Content-Encoding</t>
2744    <t>Content-Range</t>
2745    <t>Content-Type</t>
2746  </list>
2749   A transforming proxy &MAY; modify or add these fields to a message
2750   that does not include no-transform, but if it does so, it &MUST; add a
2751   Warning 214 (Transformation applied) if one does not already appear
2752   in the message (see &header-warning;).
2755  <t>
2756    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2757    cause authentication failures if stronger authentication
2758    mechanisms are introduced in later versions of HTTP. Such
2759    authentication mechanisms &MAY; rely on the values of header fields
2760    not listed here.
2761  </t>
2764   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2765   though it &MAY; change the message-body through application or removal
2766   of a transfer-coding (<xref target="transfer.codings"/>).
2772<section title="Practical Considerations" anchor="persistent.practical">
2774   Servers will usually have some time-out value beyond which they will
2775   no longer maintain an inactive connection. Proxy servers might make
2776   this a higher value since it is likely that the client will be making
2777   more connections through the same server. The use of persistent
2778   connections places no requirements on the length (or existence) of
2779   this time-out for either the client or the server.
2782   When a client or server wishes to time-out it &SHOULD; issue a graceful
2783   close on the transport connection. Clients and servers &SHOULD; both
2784   constantly watch for the other side of the transport close, and
2785   respond to it as appropriate. If a client or server does not detect
2786   the other side's close promptly it could cause unnecessary resource
2787   drain on the network.
2790   A client, server, or proxy &MAY; close the transport connection at any
2791   time. For example, a client might have started to send a new request
2792   at the same time that the server has decided to close the "idle"
2793   connection. From the server's point of view, the connection is being
2794   closed while it was idle, but from the client's point of view, a
2795   request is in progress.
2798   This means that clients, servers, and proxies &MUST; be able to recover
2799   from asynchronous close events. Client software &SHOULD; reopen the
2800   transport connection and retransmit the aborted sequence of requests
2801   without user interaction so long as the request sequence is
2802   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2803   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2804   human operator the choice of retrying the request(s). Confirmation by
2805   user-agent software with semantic understanding of the application
2806   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
2807   be repeated if the second sequence of requests fails.
2810   Servers &SHOULD; always respond to at least one request per connection,
2811   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2812   middle of transmitting a response, unless a network or client failure
2813   is suspected.
2816   Clients (including proxies) &SHOULD; limit the number of simultaneous
2817   connections that they maintain to a given server (including proxies).
2820   Previous revisions of HTTP gave a specific number of connections as a
2821   ceiling, but this was found to be impractical for many applications. As a
2822   result, this specification does not mandate a particular maximum number of
2823   connections, but instead encourages clients to be conservative when opening
2824   multiple connections.
2827   In particular, while using multiple connections avoids the "head-of-line
2828   blocking" problem (whereby a request that takes significant server-side
2829   processing and/or has a large payload can block subsequent requests on the
2830   same connection), each connection used consumes server resources (sometimes
2831   significantly), and furthermore using multiple connections can cause
2832   undesirable side effects in congested networks.
2835   Note that servers might reject traffic that they deem abusive, including an
2836   excessive number of connections from a client.
2841<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2843<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2845   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2846   flow control mechanisms to resolve temporary overloads, rather than
2847   terminating connections with the expectation that clients will retry.
2848   The latter technique can exacerbate network congestion.
2852<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2854   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2855   the network connection for an error status code while it is transmitting
2856   the request. If the client sees an error status code, it &SHOULD;
2857   immediately cease transmitting the body. If the body is being sent
2858   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2859   empty trailer &MAY; be used to prematurely mark the end of the message.
2860   If the body was preceded by a Content-Length header field, the client &MUST;
2861   close the connection.
2865<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2867   The purpose of the 100 (Continue) status code (see &status-100;) is to
2868   allow a client that is sending a request message with a request body
2869   to determine if the origin server is willing to accept the request
2870   (based on the request header fields) before the client sends the request
2871   body. In some cases, it might either be inappropriate or highly
2872   inefficient for the client to send the body if the server will reject
2873   the message without looking at the body.
2876   Requirements for HTTP/1.1 clients:
2877  <list style="symbols">
2878    <t>
2879        If a client will wait for a 100 (Continue) response before
2880        sending the request body, it &MUST; send an Expect header
2881        field (&header-expect;) with the "100-continue" expectation.
2882    </t>
2883    <t>
2884        A client &MUST-NOT; send an Expect header field (&header-expect;)
2885        with the "100-continue" expectation if it does not intend
2886        to send a request body.
2887    </t>
2888  </list>
2891   Because of the presence of older implementations, the protocol allows
2892   ambiguous situations in which a client might send "Expect: 100-continue"
2893   without receiving either a 417 (Expectation Failed)
2894   or a 100 (Continue) status code. Therefore, when a client sends this
2895   header field to an origin server (possibly via a proxy) from which it
2896   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2897   wait for an indefinite period before sending the request body.
2900   Requirements for HTTP/1.1 origin servers:
2901  <list style="symbols">
2902    <t> Upon receiving a request which includes an Expect header
2903        field with the "100-continue" expectation, an origin server &MUST;
2904        either respond with 100 (Continue) status code and continue to read
2905        from the input stream, or respond with a final status code. The
2906        origin server &MUST-NOT; wait for the request body before sending
2907        the 100 (Continue) response. If it responds with a final status
2908        code, it &MAY; close the transport connection or it &MAY; continue
2909        to read and discard the rest of the request.  It &MUST-NOT;
2910        perform the request method if it returns a final status code.
2911    </t>
2912    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2913        the request message does not include an Expect header
2914        field with the "100-continue" expectation, and &MUST-NOT; send a
2915        100 (Continue) response if such a request comes from an HTTP/1.0
2916        (or earlier) client. There is an exception to this rule: for
2917        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2918        status code in response to an HTTP/1.1 PUT or POST request that does
2919        not include an Expect header field with the "100-continue"
2920        expectation. This exception, the purpose of which is
2921        to minimize any client processing delays associated with an
2922        undeclared wait for 100 (Continue) status code, applies only to
2923        HTTP/1.1 requests, and not to requests with any other HTTP-version
2924        value.
2925    </t>
2926    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2927        already received some or all of the request body for the
2928        corresponding request.
2929    </t>
2930    <t> An origin server that sends a 100 (Continue) response &MUST;
2931    ultimately send a final status code, once the request body is
2932        received and processed, unless it terminates the transport
2933        connection prematurely.
2934    </t>
2935    <t> If an origin server receives a request that does not include an
2936        Expect header field with the "100-continue" expectation,
2937        the request includes a request body, and the server responds
2938        with a final status code before reading the entire request body
2939        from the transport connection, then the server &SHOULD-NOT;  close
2940        the transport connection until it has read the entire request,
2941        or until the client closes the connection. Otherwise, the client
2942        might not reliably receive the response message. However, this
2943        requirement is not be construed as preventing a server from
2944        defending itself against denial-of-service attacks, or from
2945        badly broken client implementations.
2946      </t>
2947    </list>
2950   Requirements for HTTP/1.1 proxies:
2951  <list style="symbols">
2952    <t> If a proxy receives a request that includes an Expect header
2953        field with the "100-continue" expectation, and the proxy
2954        either knows that the next-hop server complies with HTTP/1.1 or
2955        higher, or does not know the HTTP version of the next-hop
2956        server, it &MUST; forward the request, including the Expect header
2957        field.
2958    </t>
2959    <t> If the proxy knows that the version of the next-hop server is
2960        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2961        respond with a 417 (Expectation Failed) status code.
2962    </t>
2963    <t> Proxies &SHOULD; maintain a record of the HTTP version
2964        numbers received from recently-referenced next-hop servers.
2965    </t>
2966    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2967        request message was received from an HTTP/1.0 (or earlier)
2968        client and did not include an Expect header field with
2969        the "100-continue" expectation. This requirement overrides the
2970        general rule for forwarding of 1xx responses (see &status-1xx;).
2971    </t>
2972  </list>
2976<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2978   If an HTTP/1.1 client sends a request which includes a request body,
2979   but which does not include an Expect header field with the
2980   "100-continue" expectation, and if the client is not directly
2981   connected to an HTTP/1.1 origin server, and if the client sees the
2982   connection close before receiving a status line from the server, the
2983   client &SHOULD; retry the request.  If the client does retry this
2984   request, it &MAY; use the following "binary exponential backoff"
2985   algorithm to be assured of obtaining a reliable response:
2986  <list style="numbers">
2987    <t>
2988      Initiate a new connection to the server
2989    </t>
2990    <t>
2991      Transmit the request-line, header fields, and the CRLF that
2992      indicates the end of header fields.
2993    </t>
2994    <t>
2995      Initialize a variable R to the estimated round-trip time to the
2996         server (e.g., based on the time it took to establish the
2997         connection), or to a constant value of 5 seconds if the round-trip
2998         time is not available.
2999    </t>
3000    <t>
3001       Compute T = R * (2**N), where N is the number of previous
3002         retries of this request.
3003    </t>
3004    <t>
3005       Wait either for an error response from the server, or for T
3006         seconds (whichever comes first)
3007    </t>
3008    <t>
3009       If no error response is received, after T seconds transmit the
3010         body of the request.
3011    </t>
3012    <t>
3013       If client sees that the connection is closed prematurely,
3014         repeat from step 1 until the request is accepted, an error
3015         response is received, or the user becomes impatient and
3016         terminates the retry process.
3017    </t>
3018  </list>
3021   If at any point an error status code is received, the client
3022  <list style="symbols">
3023      <t>&SHOULD-NOT;  continue and</t>
3025      <t>&SHOULD; close the connection if it has not completed sending the
3026        request message.</t>
3027    </list>
3034<section title="Miscellaneous notes that might disappear" anchor="misc">
3035<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
3037   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
3041<section title="Use of HTTP for proxy communication" anchor="http.proxy">
3043   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
3047<section title="Interception of HTTP for access control" anchor="http.intercept">
3049   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
3053<section title="Use of HTTP by other protocols" anchor="http.others">
3055   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3056   Extensions of HTTP like WebDAV.</cref>
3060<section title="Use of HTTP by media type specification" anchor="">
3062   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3067<section title="Header Field Definitions" anchor="header.field.definitions">
3069   This section defines the syntax and semantics of HTTP header fields
3070   related to message framing and transport protocols.
3073<section title="Connection" anchor="header.connection">
3074  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3075  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3076  <x:anchor-alias value="Connection"/>
3077  <x:anchor-alias value="connection-token"/>
3079   The "Connection" header field allows the sender to specify
3080   options that are desired only for that particular connection.
3081   Such connection options &MUST; be removed or replaced before the
3082   message can be forwarded downstream by a proxy or gateway.
3083   This mechanism also allows the sender to indicate which HTTP
3084   header fields used in the message are only intended for the
3085   immediate recipient ("hop-by-hop"), as opposed to all recipients
3086   on the chain ("end-to-end"), enabling the message to be
3087   self-descriptive and allowing future connection-specific extensions
3088   to be deployed in HTTP without fear that they will be blindly
3089   forwarded by previously deployed intermediaries.
3092   The Connection header field's value has the following grammar:
3094<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3095  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3096  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3099   A proxy or gateway &MUST; parse a received Connection
3100   header field before a message is forwarded and, for each
3101   connection-token in this field, remove any header field(s) from
3102   the message with the same name as the connection-token, and then
3103   remove the Connection header field itself or replace it with the
3104   sender's own connection options for the forwarded message.
3107   A sender &MUST-NOT; include field-names in the Connection header
3108   field-value for fields that are defined as expressing constraints
3109   for all recipients in the request or response chain, such as the
3110   Cache-Control header field (&header-cache-control;).
3113   The connection options do not have to correspond to a header field
3114   present in the message, since a connection-specific header field
3115   might not be needed if there are no parameters associated with that
3116   connection option.  Recipients that trigger certain connection
3117   behavior based on the presence of connection options &MUST; do so
3118   based on the presence of the connection-token rather than only the
3119   presence of the optional header field.  In other words, if the
3120   connection option is received as a header field but not indicated
3121   within the Connection field-value, then the recipient &MUST; ignore
3122   the connection-specific header field because it has likely been
3123   forwarded by an intermediary that is only partially compliant.
3126   When defining new connection options, specifications ought to
3127   carefully consider existing deployed header fields and ensure
3128   that the new connection-token does not share the same name as
3129   an unrelated header field that might already be deployed.
3130   Defining a new connection-token essentially reserves that potential
3131   field-name for carrying additional information related to the
3132   connection option, since it would be unwise for senders to use
3133   that field-name for anything else.
3136   HTTP/1.1 defines the "close" connection option for the sender to
3137   signal that the connection will be closed after completion of the
3138   response. For example,
3140<figure><artwork type="example">
3141  Connection: close
3144   in either the request or the response header fields indicates that
3145   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3146   after the current request/response is complete.
3149   An HTTP/1.1 client that does not support persistent connections &MUST;
3150   include the "close" connection option in every request message.
3153   An HTTP/1.1 server that does not support persistent connections &MUST;
3154   include the "close" connection option in every response message that
3155   does not have a 1xx (Informational) status code.
3159<section title="Content-Length" anchor="header.content-length">
3160  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3161  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3162  <x:anchor-alias value="Content-Length"/>
3164   The "Content-Length" header field indicates the size of the
3165   message-body, in decimal number of octets, for any message other than
3166   a response to a HEAD request or a response with a status code of 304.
3167   In the case of a response to a HEAD request, Content-Length indicates
3168   the size of the payload body (not including any potential transfer-coding)
3169   that would have been sent had the request been a GET.
3170   In the case of a 304 (Not Modified) response to a GET request,
3171   Content-Length indicates the size of the payload body (not including
3172   any potential transfer-coding) that would have been sent in a 200 (OK)
3173   response.
3175<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3176  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3179   An example is
3181<figure><artwork type="example">
3182  Content-Length: 3495
3185   Implementations &SHOULD; use this field to indicate the message-body
3186   length when no transfer-coding is being applied and the
3187   payload's body length can be determined prior to being transferred.
3188   <xref target="message.body"/> describes how recipients determine the length
3189   of a message-body.
3192   Any Content-Length greater than or equal to zero is a valid value.
3195   Note that the use of this field in HTTP is significantly different from
3196   the corresponding definition in MIME, where it is an optional field
3197   used within the "message/external-body" content-type.
3201<section title="Date" anchor="">
3202  <iref primary="true" item="Date header field" x:for-anchor=""/>
3203  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3204  <x:anchor-alias value="Date"/>
3206   The "Date" header field represents the date and time at which
3207   the message was originated, having the same semantics as the Origination
3208   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3209   The field value is an HTTP-date, as described in <xref target=""/>;
3210   it &MUST; be sent in rfc1123-date format.
3212<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3213  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3216   An example is
3218<figure><artwork type="example">
3219  Date: Tue, 15 Nov 1994 08:12:31 GMT
3222   Origin servers &MUST; include a Date header field in all responses,
3223   except in these cases:
3224  <list style="numbers">
3225      <t>If the response status code is 100 (Continue) or 101 (Switching
3226         Protocols), the response &MAY; include a Date header field, at
3227         the server's option.</t>
3229      <t>If the response status code conveys a server error, e.g., 500
3230         (Internal Server Error) or 503 (Service Unavailable), and it is
3231         inconvenient or impossible to generate a valid Date.</t>
3233      <t>If the server does not have a clock that can provide a
3234         reasonable approximation of the current time, its responses
3235         &MUST-NOT; include a Date header field. In this case, the rules
3236         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3237  </list>
3240   A received message that does not have a Date header field &MUST; be
3241   assigned one by the recipient if the message will be cached by that
3242   recipient.
3245   Clients can use the Date header field as well; in order to keep request
3246   messages small, they are advised not to include it when it doesn't convey
3247   any useful information (as it is usually the case for requests that do not
3248   contain a payload).
3251   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3252   time subsequent to the generation of the message. It &SHOULD; represent
3253   the best available approximation of the date and time of message
3254   generation, unless the implementation has no means of generating a
3255   reasonably accurate date and time. In theory, the date ought to
3256   represent the moment just before the payload is generated. In
3257   practice, the date can be generated at any time during the message
3258   origination without affecting its semantic value.
3261<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3263   Some origin server implementations might not have a clock available.
3264   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3265   values to a response, unless these values were associated
3266   with the resource by a system or user with a reliable clock. It &MAY;
3267   assign an Expires value that is known, at or before server
3268   configuration time, to be in the past (this allows "pre-expiration"
3269   of responses without storing separate Expires values for each
3270   resource).
3275<section title="Host" anchor="">
3276  <iref primary="true" item="Host header field" x:for-anchor=""/>
3277  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3278  <x:anchor-alias value="Host"/>
3280   The "Host" header field in a request provides the host and port
3281   information from the target resource's URI, enabling the origin
3282   server to distinguish between resources while servicing requests
3283   for multiple host names on a single IP address.  Since the Host
3284   field-value is critical information for handling a request, it
3285   &SHOULD; be sent as the first header field following the Request-Line.
3287<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3288  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3291   A client &MUST; send a Host header field in all HTTP/1.1 request
3292   messages.  If the target resource's URI includes an authority
3293   component, then the Host field-value &MUST; be identical to that
3294   authority component after excluding any userinfo (<xref target="http.uri"/>).
3295   If the authority component is missing or undefined for the target
3296   resource's URI, then the Host header field &MUST; be sent with an
3297   empty field-value.
3300   For example, a GET request to the origin server for
3301   &lt;; would begin with:
3303<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3304GET /pub/WWW/ HTTP/1.1
3308   The Host header field &MUST; be sent in an HTTP/1.1 request even
3309   if the request-target is in the form of an absolute-URI, since this
3310   allows the Host information to be forwarded through ancient HTTP/1.0
3311   proxies that might not have implemented Host.
3314   When an HTTP/1.1 proxy receives a request with a request-target in
3315   the form of an absolute-URI, the proxy &MUST; ignore the received
3316   Host header field (if any) and instead replace it with the host
3317   information of the request-target.  When a proxy forwards a request,
3318   it &MUST; generate the Host header field based on the received
3319   absolute-URI rather than the received Host.
3322   Since the Host header field acts as an application-level routing
3323   mechanism, it is a frequent target for malware seeking to poison
3324   a shared cache or redirect a request to an unintended server.
3325   An interception proxy is particularly vulnerable if it relies on
3326   the Host header field value for redirecting requests to internal
3327   servers, or for use as a cache key in a shared cache, without
3328   first verifying that the intercepted connection is targeting a
3329   valid IP address for that host.
3332   A server &MUST; respond with a 400 (Bad Request) status code to
3333   any HTTP/1.1 request message that lacks a Host header field and
3334   to any request message that contains more than one Host header field
3335   or a Host header field with an invalid field-value.
3338   See Sections <xref target="" format="counter"/>
3339   and <xref target="" format="counter"/>
3340   for other requirements relating to Host.
3344<section title="TE" anchor="header.te">
3345  <iref primary="true" item="TE header field" x:for-anchor=""/>
3346  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3347  <x:anchor-alias value="TE"/>
3348  <x:anchor-alias value="t-codings"/>
3349  <x:anchor-alias value="te-params"/>
3350  <x:anchor-alias value="te-ext"/>
3352   The "TE" header field indicates what extension transfer-codings
3353   it is willing to accept in the response, and whether or not it is
3354   willing to accept trailer fields in a chunked transfer-coding.
3357   Its value consists of the keyword "trailers" and/or a comma-separated
3358   list of extension transfer-coding names with optional accept
3359   parameters (as described in <xref target="transfer.codings"/>).
3361<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"/>
3362  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3363  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3364  <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> )
3365  <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> ]
3368   The presence of the keyword "trailers" indicates that the client is
3369   willing to accept trailer fields in a chunked transfer-coding, as
3370   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3371   transfer-coding values even though it does not itself represent a
3372   transfer-coding.
3375   Examples of its use are:
3377<figure><artwork type="example">
3378  TE: deflate
3379  TE:
3380  TE: trailers, deflate;q=0.5
3383   The TE header field only applies to the immediate connection.
3384   Therefore, the keyword &MUST; be supplied within a Connection header
3385   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3388   A server tests whether a transfer-coding is acceptable, according to
3389   a TE field, using these rules:
3390  <list style="numbers">
3391    <x:lt>
3392      <t>The "chunked" transfer-coding is always acceptable. If the
3393         keyword "trailers" is listed, the client indicates that it is
3394         willing to accept trailer fields in the chunked response on
3395         behalf of itself and any downstream clients. The implication is
3396         that, if given, the client is stating that either all
3397         downstream clients are willing to accept trailer fields in the
3398         forwarded response, or that it will attempt to buffer the
3399         response on behalf of downstream recipients.
3400      </t><t>
3401         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3402         chunked response such that a client can be assured of buffering
3403         the entire response.</t>
3404    </x:lt>
3405    <x:lt>
3406      <t>If the transfer-coding being tested is one of the transfer-codings
3407         listed in the TE field, then it is acceptable unless it
3408         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3409         qvalue of 0 means "not acceptable".)</t>
3410    </x:lt>
3411    <x:lt>
3412      <t>If multiple transfer-codings are acceptable, then the
3413         acceptable transfer-coding with the highest non-zero qvalue is
3414         preferred.  The "chunked" transfer-coding always has a qvalue
3415         of 1.</t>
3416    </x:lt>
3417  </list>
3420   If the TE field-value is empty or if no TE field is present, the only
3421   transfer-coding is "chunked". A message with no transfer-coding is
3422   always acceptable.
3426<section title="Trailer" anchor="header.trailer">
3427  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3428  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3429  <x:anchor-alias value="Trailer"/>
3431   The "Trailer" header field indicates that the given set of
3432   header fields is present in the trailer of a message encoded with
3433   chunked transfer-coding.
3435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3436  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3439   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3440   message using chunked transfer-coding with a non-empty trailer. Doing
3441   so allows the recipient to know which header fields to expect in the
3442   trailer.
3445   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3446   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3447   trailer fields in a "chunked" transfer-coding.
3450   Message header fields listed in the Trailer header field &MUST-NOT;
3451   include the following header fields:
3452  <list style="symbols">
3453    <t>Transfer-Encoding</t>
3454    <t>Content-Length</t>
3455    <t>Trailer</t>
3456  </list>
3460<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3461  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3462  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3463  <x:anchor-alias value="Transfer-Encoding"/>
3465   The "Transfer-Encoding" header field indicates what transfer-codings
3466   (if any) have been applied to the message body. It differs from
3467   Content-Encoding (&content-codings;) in that transfer-codings are a property
3468   of the message (and therefore are removed by intermediaries), whereas
3469   content-codings are not.
3471<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3472  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3475   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3477<figure><artwork type="example">
3478  Transfer-Encoding: chunked
3481   If multiple encodings have been applied to a representation, the transfer-codings
3482   &MUST; be listed in the order in which they were applied.
3483   Additional information about the encoding parameters &MAY; be provided
3484   by other header fields not defined by this specification.
3487   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3488   header field.
3492<section title="Upgrade" anchor="header.upgrade">
3493  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3494  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3495  <x:anchor-alias value="Upgrade"/>
3497   The "Upgrade" header field allows the client to specify what
3498   additional communication protocols it would like to use, if the server
3499   chooses to switch protocols. Servers can use it to indicate what protocols
3500   they are willing to switch to.
3502<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3503  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3506   For example,
3508<figure><artwork type="example">
3509  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3512   The Upgrade header field is intended to provide a simple mechanism
3513   for transition from HTTP/1.1 to some other, incompatible protocol. It
3514   does so by allowing the client to advertise its desire to use another
3515   protocol, such as a later version of HTTP with a higher major version
3516   number, even though the current request has been made using HTTP/1.1.
3517   This eases the difficult transition between incompatible protocols by
3518   allowing the client to initiate a request in the more commonly
3519   supported protocol while indicating to the server that it would like
3520   to use a "better" protocol if available (where "better" is determined
3521   by the server, possibly according to the nature of the request method
3522   or target resource).
3525   The Upgrade header field only applies to switching application-layer
3526   protocols upon the existing transport-layer connection. Upgrade
3527   cannot be used to insist on a protocol change; its acceptance and use
3528   by the server is optional. The capabilities and nature of the
3529   application-layer communication after the protocol change is entirely
3530   dependent upon the new protocol chosen, although the first action
3531   after changing the protocol &MUST; be a response to the initial HTTP
3532   request containing the Upgrade header field.
3535   The Upgrade header field only applies to the immediate connection.
3536   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3537   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3538   HTTP/1.1 message.
3541   The Upgrade header field cannot be used to indicate a switch to a
3542   protocol on a different connection. For that purpose, it is more
3543   appropriate to use a 3xx redirection response (&status-3xx;).
3546   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3547   Protocols) responses to indicate which protocol(s) are being switched to,
3548   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3549   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3550   response to indicate that they are willing to upgrade to one of the
3551   specified protocols.
3554   This specification only defines the protocol name "HTTP" for use by
3555   the family of Hypertext Transfer Protocols, as defined by the HTTP
3556   version rules of <xref target="http.version"/> and future updates to this
3557   specification. Additional tokens can be registered with IANA using the
3558   registration procedure defined below. 
3561<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3563   The HTTP Upgrade Token Registry defines the name space for product
3564   tokens used to identify protocols in the Upgrade header field.
3565   Each registered token is associated with contact information and
3566   an optional set of specifications that details how the connection
3567   will be processed after it has been upgraded.
3570   Registrations are allowed on a First Come First Served basis as
3571   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3572   specifications need not be IETF documents or be subject to IESG review.
3573   Registrations are subject to the following rules:
3574  <list style="numbers">
3575    <t>A token, once registered, stays registered forever.</t>
3576    <t>The registration &MUST; name a responsible party for the
3577       registration.</t>
3578    <t>The registration &MUST; name a point of contact.</t>
3579    <t>The registration &MAY; name a set of specifications associated with that
3580       token. Such specifications need not be publicly available.</t>
3581    <t>The responsible party &MAY; change the registration at any time.
3582       The IANA will keep a record of all such changes, and make them
3583       available upon request.</t>
3584    <t>The responsible party for the first registration of a "product"
3585       token &MUST; approve later registrations of a "version" token
3586       together with that "product" token before they can be registered.</t>
3587    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3588       for a token. This will normally only be used in the case when a
3589       responsible party cannot be contacted.</t>
3590  </list>
3597<section title="Via" anchor="header.via">
3598  <iref primary="true" item="Via header field" x:for-anchor=""/>
3599  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3600  <x:anchor-alias value="protocol-name"/>
3601  <x:anchor-alias value="protocol-version"/>
3602  <x:anchor-alias value="pseudonym"/>
3603  <x:anchor-alias value="received-by"/>
3604  <x:anchor-alias value="received-protocol"/>
3605  <x:anchor-alias value="Via"/>
3607   The "Via" header field &MUST; be sent by a proxy or gateway to
3608   indicate the intermediate protocols and recipients between the user
3609   agent and the server on requests, and between the origin server and
3610   the client on responses. It is analogous to the "Received" field
3611   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3612   and is intended to be used for tracking message forwards,
3613   avoiding request loops, and identifying the protocol capabilities of
3614   all senders along the request/response chain.
3616<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"/>
3617  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3618                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3619  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3620  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3621  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3622  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3623  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3626   The received-protocol indicates the protocol version of the message
3627   received by the server or client along each segment of the
3628   request/response chain. The received-protocol version is appended to
3629   the Via field value when the message is forwarded so that information
3630   about the protocol capabilities of upstream applications remains
3631   visible to all recipients.
3634   The protocol-name is excluded if and only if it would be "HTTP". The
3635   received-by field is normally the host and optional port number of a
3636   recipient server or client that subsequently forwarded the message.
3637   However, if the real host is considered to be sensitive information,
3638   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3639   be assumed to be the default port of the received-protocol.
3642   Multiple Via field values represent each proxy or gateway that has
3643   forwarded the message. Each recipient &MUST; append its information
3644   such that the end result is ordered according to the sequence of
3645   forwarding applications.
3648   Comments &MAY; be used in the Via header field to identify the software
3649   of each recipient, analogous to the User-Agent and Server header fields.
3650   However, all comments in the Via field are optional and &MAY; be removed
3651   by any recipient prior to forwarding the message.
3654   For example, a request message could be sent from an HTTP/1.0 user
3655   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3656   forward the request to a public proxy at, which completes
3657   the request by forwarding it to the origin server at
3658   The request received by would then have the following
3659   Via header field:
3661<figure><artwork type="example">
3662  Via: 1.0 fred, 1.1 (Apache/1.1)
3665   A proxy or gateway used as a portal through a network firewall
3666   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3667   region unless it is explicitly enabled to do so. If not enabled, the
3668   received-by host of any host behind the firewall &SHOULD; be replaced
3669   by an appropriate pseudonym for that host.
3672   For organizations that have strong privacy requirements for hiding
3673   internal structures, a proxy or gateway &MAY; combine an ordered
3674   subsequence of Via header field entries with identical received-protocol
3675   values into a single such entry. For example,
3677<figure><artwork type="example">
3678  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3681  could be collapsed to
3683<figure><artwork type="example">
3684  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3687   Senders &SHOULD-NOT; combine multiple entries unless they are all
3688   under the same organizational control and the hosts have already been
3689   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3690   have different received-protocol values.
3696<section title="IANA Considerations" anchor="IANA.considerations">
3698<section title="Header Field Registration" anchor="header.field.registration">
3700   The Message Header Field Registry located at <eref target=""/> shall be updated
3701   with the permanent registrations below (see <xref target="RFC3864"/>):
3703<?BEGININC p1-messaging.iana-headers ?>
3704<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3705<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3706   <ttcol>Header Field Name</ttcol>
3707   <ttcol>Protocol</ttcol>
3708   <ttcol>Status</ttcol>
3709   <ttcol>Reference</ttcol>
3711   <c>Connection</c>
3712   <c>http</c>
3713   <c>standard</c>
3714   <c>
3715      <xref target="header.connection"/>
3716   </c>
3717   <c>Content-Length</c>
3718   <c>http</c>
3719   <c>standard</c>
3720   <c>
3721      <xref target="header.content-length"/>
3722   </c>
3723   <c>Date</c>
3724   <c>http</c>
3725   <c>standard</c>
3726   <c>
3727      <xref target=""/>
3728   </c>
3729   <c>Host</c>
3730   <c>http</c>
3731   <c>standard</c>
3732   <c>
3733      <xref target=""/>
3734   </c>
3735   <c>TE</c>
3736   <c>http</c>
3737   <c>standard</c>
3738   <c>
3739      <xref target="header.te"/>
3740   </c>
3741   <c>Trailer</c>
3742   <c>http</c>
3743   <c>standard</c>
3744   <c>
3745      <xref target="header.trailer"/>
3746   </c>
3747   <c>Transfer-Encoding</c>
3748   <c>http</c>
3749   <c>standard</c>
3750   <c>
3751      <xref target="header.transfer-encoding"/>
3752   </c>
3753   <c>Upgrade</c>
3754   <c>http</c>
3755   <c>standard</c>
3756   <c>
3757      <xref target="header.upgrade"/>
3758   </c>
3759   <c>Via</c>
3760   <c>http</c>
3761   <c>standard</c>
3762   <c>
3763      <xref target="header.via"/>
3764   </c>
3767<?ENDINC p1-messaging.iana-headers ?>
3769   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3770   HTTP header field would be in conflict with the use of the "close" connection
3771   option for the "Connection" header field (<xref target="header.connection"/>).
3773<texttable align="left" suppress-title="true">
3774   <ttcol>Header Field Name</ttcol>
3775   <ttcol>Protocol</ttcol>
3776   <ttcol>Status</ttcol>
3777   <ttcol>Reference</ttcol>
3779   <c>Close</c>
3780   <c>http</c>
3781   <c>reserved</c>
3782   <c>
3783      <xref target="header.field.registration"/>
3784   </c>
3787   The change controller is: "IETF ( - Internet Engineering Task Force".
3791<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3793   The entries for the "http" and "https" URI Schemes in the registry located at
3794   <eref target=""/>
3795   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3796   and <xref target="https.uri" format="counter"/> of this document
3797   (see <xref target="RFC4395"/>).
3801<section title="Internet Media Type Registrations" anchor="">
3803   This document serves as the specification for the Internet media types
3804   "message/http" and "application/http". The following is to be registered with
3805   IANA (see <xref target="RFC4288"/>).
3807<section title="Internet Media Type message/http" anchor="">
3808<iref item="Media Type" subitem="message/http" primary="true"/>
3809<iref item="message/http Media Type" primary="true"/>
3811   The message/http type can be used to enclose a single HTTP request or
3812   response message, provided that it obeys the MIME restrictions for all
3813   "message" types regarding line length and encodings.
3816  <list style="hanging" x:indent="12em">
3817    <t hangText="Type name:">
3818      message
3819    </t>
3820    <t hangText="Subtype name:">
3821      http
3822    </t>
3823    <t hangText="Required parameters:">
3824      none
3825    </t>
3826    <t hangText="Optional parameters:">
3827      version, msgtype
3828      <list style="hanging">
3829        <t hangText="version:">
3830          The HTTP-Version number of the enclosed message
3831          (e.g., "1.1"). If not present, the version can be
3832          determined from the first line of the body.
3833        </t>
3834        <t hangText="msgtype:">
3835          The message type &mdash; "request" or "response". If not
3836          present, the type can be determined from the first
3837          line of the body.
3838        </t>
3839      </list>
3840    </t>
3841    <t hangText="Encoding considerations:">
3842      only "7bit", "8bit", or "binary" are permitted
3843    </t>
3844    <t hangText="Security considerations:">
3845      none
3846    </t>
3847    <t hangText="Interoperability considerations:">
3848      none
3849    </t>
3850    <t hangText="Published specification:">
3851      This specification (see <xref target=""/>).
3852    </t>
3853    <t hangText="Applications that use this media type:">
3854    </t>
3855    <t hangText="Additional information:">
3856      <list style="hanging">
3857        <t hangText="Magic number(s):">none</t>
3858        <t hangText="File extension(s):">none</t>
3859        <t hangText="Macintosh file type code(s):">none</t>
3860      </list>
3861    </t>
3862    <t hangText="Person and email address to contact for further information:">
3863      See Authors Section.
3864    </t>
3865    <t hangText="Intended usage:">
3866      COMMON
3867    </t>
3868    <t hangText="Restrictions on usage:">
3869      none
3870    </t>
3871    <t hangText="Author/Change controller:">
3872      IESG
3873    </t>
3874  </list>
3877<section title="Internet Media Type application/http" anchor="">
3878<iref item="Media Type" subitem="application/http" primary="true"/>
3879<iref item="application/http Media Type" primary="true"/>
3881   The application/http type can be used to enclose a pipeline of one or more
3882   HTTP request or response messages (not intermixed).
3885  <list style="hanging" x:indent="12em">
3886    <t hangText="Type name:">
3887      application
3888    </t>
3889    <t hangText="Subtype name:">
3890      http
3891    </t>
3892    <t hangText="Required parameters:">
3893      none
3894    </t>
3895    <t hangText="Optional parameters:">
3896      version, msgtype
3897      <list style="hanging">
3898        <t hangText="version:">
3899          The HTTP-Version number of the enclosed messages
3900          (e.g., "1.1"). If not present, the version can be
3901          determined from the first line of the body.
3902        </t>
3903        <t hangText="msgtype:">
3904          The message type &mdash; "request" or "response". If not
3905          present, the type can be determined from the first
3906          line of the body.
3907        </t>
3908      </list>
3909    </t>
3910    <t hangText="Encoding considerations:">
3911      HTTP messages enclosed by this type
3912      are in "binary" format; use of an appropriate
3913      Content-Transfer-Encoding is required when
3914      transmitted via E-mail.
3915    </t>
3916    <t hangText="Security considerations:">
3917      none
3918    </t>
3919    <t hangText="Interoperability considerations:">
3920      none
3921    </t>
3922    <t hangText="Published specification:">
3923      This specification (see <xref target=""/>).
3924    </t>
3925    <t hangText="Applications that use this media type:">
3926    </t>
3927    <t hangText="Additional information:">
3928      <list style="hanging">
3929        <t hangText="Magic number(s):">none</t>
3930        <t hangText="File extension(s):">none</t>
3931        <t hangText="Macintosh file type code(s):">none</t>
3932      </list>
3933    </t>
3934    <t hangText="Person and email address to contact for further information:">
3935      See Authors Section.
3936    </t>
3937    <t hangText="Intended usage:">
3938      COMMON
3939    </t>
3940    <t hangText="Restrictions on usage:">
3941      none
3942    </t>
3943    <t hangText="Author/Change controller:">
3944      IESG
3945    </t>
3946  </list>
3951<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3953   The registration procedure for HTTP Transfer Codings is now defined by
3954   <xref target="transfer.coding.registry"/> of this document.
3957   The HTTP Transfer Codings Registry located at <eref target=""/>
3958   shall be updated with the registrations below:
3960<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3961   <ttcol>Name</ttcol>
3962   <ttcol>Description</ttcol>
3963   <ttcol>Reference</ttcol>
3964   <c>chunked</c>
3965   <c>Transfer in a series of chunks</c>
3966   <c>
3967      <xref target="chunked.encoding"/>
3968   </c>
3969   <c>compress</c>
3970   <c>UNIX "compress" program method</c>
3971   <c>
3972      <xref target="compress.coding"/>
3973   </c>
3974   <c>deflate</c>
3975   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3976   the "zlib" data format (<xref target="RFC1950"/>)
3977   </c>
3978   <c>
3979      <xref target="deflate.coding"/>
3980   </c>
3981   <c>gzip</c>
3982   <c>Same as GNU zip <xref target="RFC1952"/></c>
3983   <c>
3984      <xref target="gzip.coding"/>
3985   </c>
3989<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3991   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3992   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3993   by <xref target="upgrade.token.registry"/> of this document.
3996   The HTTP Status Code Registry located at <eref target=""/>
3997   shall be updated with the registration below:
3999<texttable align="left" suppress-title="true">
4000   <ttcol>Value</ttcol>
4001   <ttcol>Description</ttcol>
4002   <ttcol>Reference</ttcol>
4004   <c>HTTP</c>
4005   <c>Hypertext Transfer Protocol</c>
4006   <c><xref target="http.version"/> of this specification</c>
4013<section title="Security Considerations" anchor="security.considerations">
4015   This section is meant to inform application developers, information
4016   providers, and users of the security limitations in HTTP/1.1 as
4017   described by this document. The discussion does not include
4018   definitive solutions to the problems revealed, though it does make
4019   some suggestions for reducing security risks.
4022<section title="Personal Information" anchor="personal.information">
4024   HTTP clients are often privy to large amounts of personal information
4025   (e.g., the user's name, location, mail address, passwords, encryption
4026   keys, etc.), and &SHOULD; be very careful to prevent unintentional
4027   leakage of this information.
4028   We very strongly recommend that a convenient interface be provided
4029   for the user to control dissemination of such information, and that
4030   designers and implementors be particularly careful in this area.
4031   History shows that errors in this area often create serious security
4032   and/or privacy problems and generate highly adverse publicity for the
4033   implementor's company.
4037<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
4039   A server is in the position to save personal data about a user's
4040   requests which might identify their reading patterns or subjects of
4041   interest. This information is clearly confidential in nature and its
4042   handling can be constrained by law in certain countries. People using
4043   HTTP to provide data are responsible for ensuring that
4044   such material is not distributed without the permission of any
4045   individuals that are identifiable by the published results.
4049<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
4051   Implementations of HTTP origin servers &SHOULD; be careful to restrict
4052   the documents returned by HTTP requests to be only those that were
4053   intended by the server administrators. If an HTTP server translates
4054   HTTP URIs directly into file system calls, the server &MUST; take
4055   special care not to serve files that were not intended to be
4056   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
4057   other operating systems use ".." as a path component to indicate a
4058   directory level above the current one. On such a system, an HTTP
4059   server &MUST; disallow any such construct in the request-target if it
4060   would otherwise allow access to a resource outside those intended to
4061   be accessible via the HTTP server. Similarly, files intended for
4062   reference only internally to the server (such as access control
4063   files, configuration files, and script code) &MUST; be protected from
4064   inappropriate retrieval, since they might contain sensitive
4065   information. Experience has shown that minor bugs in such HTTP server
4066   implementations have turned into security risks.
4070<section title="DNS-related Attacks" anchor="dns.related.attacks">
4072   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
4073   generally prone to security attacks based on the deliberate misassociation
4074   of IP addresses and DNS names not protected by DNSSec. Clients need to be
4075   cautious in assuming the validity of an IP number/DNS name association unless
4076   the response is protected by DNSSec (<xref target="RFC4033"/>).
4080<section title="Proxies and Caching" anchor="attack.proxies">
4082   By their very nature, HTTP proxies are men-in-the-middle, and
4083   represent an opportunity for man-in-the-middle attacks. Compromise of
4084   the systems on which the proxies run can result in serious security
4085   and privacy problems. Proxies have access to security-related
4086   information, personal information about individual users and
4087   organizations, and proprietary information belonging to users and
4088   content providers. A compromised proxy, or a proxy implemented or
4089   configured without regard to security and privacy considerations,
4090   might be used in the commission of a wide range of potential attacks.
4093   Proxy operators need to protect the systems on which proxies run as
4094   they would protect any system that contains or transports sensitive
4095   information. In particular, log information gathered at proxies often
4096   contains highly sensitive personal information, and/or information
4097   about organizations. Log information needs to be carefully guarded, and
4098   appropriate guidelines for use need to be developed and followed.
4099   (<xref target="abuse.of.server.log.information"/>).
4102   Proxy implementors need to consider the privacy and security
4103   implications of their design and coding decisions, and of the
4104   configuration options they provide to proxy operators (especially the
4105   default configuration).
4108   Users of a proxy need to be aware that proxies are no trustworthier than
4109   the people who run them; HTTP itself cannot solve this problem.
4112   The judicious use of cryptography, when appropriate, might suffice to
4113   protect against a broad range of security and privacy attacks. Such
4114   cryptography is beyond the scope of the HTTP/1.1 specification.
4118<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4120   Because HTTP uses mostly textual, character-delimited fields, attackers can
4121   overflow buffers in implementations, and/or perform a Denial of Service
4122   against implementations that accept fields with unlimited lengths.
4125   To promote interoperability, this specification makes specific
4126   recommendations for size limits on request-targets (<xref target="request-target"/>)
4127   and blocks of header fields (<xref target="header.fields"/>). These are
4128   minimum recommendations, chosen to be supportable even by implementations
4129   with limited resources; it is expected that most implementations will choose
4130   substantially higher limits.
4133   This specification also provides a way for servers to reject messages that
4134   have request-targets that are too long (&status-414;) or request entities
4135   that are too large (&status-4xx;).
4138   Other fields (including but not limited to request methods, response status
4139   phrases, header field-names, and body chunks) &SHOULD; be limited by
4140   implementations carefully, so as to not impede interoperability.
4144<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4146   They exist. They are hard to defend against. Research continues.
4147   Beware.
4152<section title="Acknowledgments" anchor="acks">
4154   This document revision builds on the work that went into
4155   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
4156   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
4157   acknowledgements.
4160  <cref anchor="todoacks">Insert HTTPbis-specific acknowledgements here.</cref>
4164Acknowledgements TODO list
4166- Jeff Hodges ("effective request URI")
4174<references title="Normative References">
4176<reference anchor="ISO-8859-1">
4177  <front>
4178    <title>
4179     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4180    </title>
4181    <author>
4182      <organization>International Organization for Standardization</organization>
4183    </author>
4184    <date year="1998"/>
4185  </front>
4186  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4189<reference anchor="Part2">
4190  <front>
4191    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4192    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4193      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4194      <address><email></email></address>
4195    </author>
4196    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4197      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4198      <address><email></email></address>
4199    </author>
4200    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4201      <organization abbrev="HP">Hewlett-Packard Company</organization>
4202      <address><email></email></address>
4203    </author>
4204    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4205      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4206      <address><email></email></address>
4207    </author>
4208    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4209      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4210      <address><email></email></address>
4211    </author>
4212    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4213      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4214      <address><email></email></address>
4215    </author>
4216    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4217      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4218      <address><email></email></address>
4219    </author>
4220    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4221      <organization abbrev="W3C">World Wide Web Consortium</organization>
4222      <address><email></email></address>
4223    </author>
4224    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4225      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4226      <address><email></email></address>
4227    </author>
4228    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4229  </front>
4230  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4231  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4234<reference anchor="Part3">
4235  <front>
4236    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4237    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4238      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4239      <address><email></email></address>
4240    </author>
4241    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4242      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4243      <address><email></email></address>
4244    </author>
4245    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4246      <organization abbrev="HP">Hewlett-Packard Company</organization>
4247      <address><email></email></address>
4248    </author>
4249    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4250      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4251      <address><email></email></address>
4252    </author>
4253    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4254      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4255      <address><email></email></address>
4256    </author>
4257    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4258      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4259      <address><email></email></address>
4260    </author>
4261    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4262      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4263      <address><email></email></address>
4264    </author>
4265    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4266      <organization abbrev="W3C">World Wide Web Consortium</organization>
4267      <address><email></email></address>
4268    </author>
4269    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4270      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4271      <address><email></email></address>
4272    </author>
4273    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4274  </front>
4275  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4276  <x:source href="p3-payload.xml" basename="p3-payload"/>
4279<reference anchor="Part6">
4280  <front>
4281    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4282    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4283      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4284      <address><email></email></address>
4285    </author>
4286    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4287      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4288      <address><email></email></address>
4289    </author>
4290    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4291      <organization abbrev="HP">Hewlett-Packard Company</organization>
4292      <address><email></email></address>
4293    </author>
4294    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4295      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4296      <address><email></email></address>
4297    </author>
4298    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4299      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4300      <address><email></email></address>
4301    </author>
4302    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4303      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4304      <address><email></email></address>
4305    </author>
4306    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4307      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4308      <address><email></email></address>
4309    </author>
4310    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4311      <organization abbrev="W3C">World Wide Web Consortium</organization>
4312      <address><email></email></address>
4313    </author>
4314    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4315      <address><email></email></address>
4316    </author>
4317    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4318      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4319      <address><email></email></address>
4320    </author>
4321    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4322  </front>
4323  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4324  <x:source href="p6-cache.xml" basename="p6-cache"/>
4327<reference anchor="RFC5234">
4328  <front>
4329    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4330    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4331      <organization>Brandenburg InternetWorking</organization>
4332      <address>
4333        <email></email>
4334      </address> 
4335    </author>
4336    <author initials="P." surname="Overell" fullname="Paul Overell">
4337      <organization>THUS plc.</organization>
4338      <address>
4339        <email></email>
4340      </address>
4341    </author>
4342    <date month="January" year="2008"/>
4343  </front>
4344  <seriesInfo name="STD" value="68"/>
4345  <seriesInfo name="RFC" value="5234"/>
4348<reference anchor="RFC2119">
4349  <front>
4350    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4351    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4352      <organization>Harvard University</organization>
4353      <address><email></email></address>
4354    </author>
4355    <date month="March" year="1997"/>
4356  </front>
4357  <seriesInfo name="BCP" value="14"/>
4358  <seriesInfo name="RFC" value="2119"/>
4361<reference anchor="RFC3986">
4362 <front>
4363  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4364  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4365    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4366    <address>
4367       <email></email>
4368       <uri></uri>
4369    </address>
4370  </author>
4371  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4372    <organization abbrev="Day Software">Day Software</organization>
4373    <address>
4374      <email></email>
4375      <uri></uri>
4376    </address>
4377  </author>
4378  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4379    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4380    <address>
4381      <email></email>
4382      <uri></uri>
4383    </address>
4384  </author>
4385  <date month='January' year='2005'></date>
4386 </front>
4387 <seriesInfo name="STD" value="66"/>
4388 <seriesInfo name="RFC" value="3986"/>
4391<reference anchor="USASCII">
4392  <front>
4393    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4394    <author>
4395      <organization>American National Standards Institute</organization>
4396    </author>
4397    <date year="1986"/>
4398  </front>
4399  <seriesInfo name="ANSI" value="X3.4"/>
4402<reference anchor="RFC1950">
4403  <front>
4404    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4405    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4406      <organization>Aladdin Enterprises</organization>
4407      <address><email></email></address>
4408    </author>
4409    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4410    <date month="May" year="1996"/>
4411  </front>
4412  <seriesInfo name="RFC" value="1950"/>
4413  <annotation>
4414    RFC 1950 is an Informational RFC, thus it might be less stable than
4415    this specification. On the other hand, this downward reference was
4416    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4417    therefore it is unlikely to cause problems in practice. See also
4418    <xref target="BCP97"/>.
4419  </annotation>
4422<reference anchor="RFC1951">
4423  <front>
4424    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4425    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4426      <organization>Aladdin Enterprises</organization>
4427      <address><email></email></address>
4428    </author>
4429    <date month="May" year="1996"/>
4430  </front>
4431  <seriesInfo name="RFC" value="1951"/>
4432  <annotation>
4433    RFC 1951 is an Informational RFC, thus it might be less stable than
4434    this specification. On the other hand, this downward reference was
4435    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4436    therefore it is unlikely to cause problems in practice. See also
4437    <xref target="BCP97"/>.
4438  </annotation>
4441<reference anchor="RFC1952">
4442  <front>
4443    <title>GZIP file format specification version 4.3</title>
4444    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4445      <organization>Aladdin Enterprises</organization>
4446      <address><email></email></address>
4447    </author>
4448    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4449      <address><email></email></address>
4450    </author>
4451    <author initials="M." surname="Adler" fullname="Mark Adler">
4452      <address><email></email></address>
4453    </author>
4454    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4455      <address><email></email></address>
4456    </author>
4457    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4458      <address><email></email></address>
4459    </author>
4460    <date month="May" year="1996"/>
4461  </front>
4462  <seriesInfo name="RFC" value="1952"/>
4463  <annotation>
4464    RFC 1952 is an Informational RFC, thus it might be less stable than
4465    this specification. On the other hand, this downward reference was
4466    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4467    therefore it is unlikely to cause problems in practice. See also
4468    <xref target="BCP97"/>.
4469  </annotation>
4474<references title="Informative References">
4476<reference anchor="Nie1997" target="">
4477  <front>
4478    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4479    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4480    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4481    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4482    <author initials="H." surname="Lie" fullname="H. Lie"/>
4483    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4484    <date year="1997" month="September"/>
4485  </front>
4486  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4489<reference anchor="Pad1995" target="">
4490  <front>
4491    <title>Improving HTTP Latency</title>
4492    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4493    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4494    <date year="1995" month="December"/>
4495  </front>
4496  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4499<reference anchor="RFC1123">
4500  <front>
4501    <title>Requirements for Internet Hosts - Application and Support</title>
4502    <author initials="R." surname="Braden" fullname="Robert Braden">
4503      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4504      <address><email>Braden@ISI.EDU</email></address>
4505    </author>
4506    <date month="October" year="1989"/>
4507  </front>
4508  <seriesInfo name="STD" value="3"/>
4509  <seriesInfo name="RFC" value="1123"/>
4512<reference anchor='RFC1919'>
4513  <front>
4514    <title>Classical versus Transparent IP Proxies</title>
4515    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4516      <address><email></email></address>
4517    </author>
4518    <date year='1996' month='March' />
4519  </front>
4520  <seriesInfo name='RFC' value='1919' />
4523<reference anchor="RFC1945">
4524  <front>
4525    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4526    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4527      <organization>MIT, Laboratory for Computer Science</organization>
4528      <address><email></email></address>
4529    </author>
4530    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4531      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4532      <address><email></email></address>
4533    </author>
4534    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4535      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4536      <address><email></email></address>
4537    </author>
4538    <date month="May" year="1996"/>
4539  </front>
4540  <seriesInfo name="RFC" value="1945"/>
4543<reference anchor="RFC2045">
4544  <front>
4545    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4546    <author initials="N." surname="Freed" fullname="Ned Freed">
4547      <organization>Innosoft International, Inc.</organization>
4548      <address><email></email></address>
4549    </author>
4550    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4551      <organization>First Virtual Holdings</organization>
4552      <address><email></email></address>
4553    </author>
4554    <date month="November" year="1996"/>
4555  </front>
4556  <seriesInfo name="RFC" value="2045"/>
4559<reference anchor="RFC2047">
4560  <front>
4561    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4562    <author initials="K." surname="Moore" fullname="Keith Moore">
4563      <organization>University of Tennessee</organization>
4564      <address><email></email></address>
4565    </author>
4566    <date month="November" year="1996"/>
4567  </front>
4568  <seriesInfo name="RFC" value="2047"/>
4571<reference anchor="RFC2068">
4572  <front>
4573    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4574    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4575      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4576      <address><email></email></address>
4577    </author>
4578    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4579      <organization>MIT Laboratory for Computer Science</organization>
4580      <address><email></email></address>
4581    </author>
4582    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4583      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4584      <address><email></email></address>
4585    </author>
4586    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4587      <organization>MIT Laboratory for Computer Science</organization>
4588      <address><email></email></address>
4589    </author>
4590    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4591      <organization>MIT Laboratory for Computer Science</organization>
4592      <address><email></email></address>
4593    </author>
4594    <date month="January" year="1997"/>
4595  </front>
4596  <seriesInfo name="RFC" value="2068"/>
4599<reference anchor="RFC2145">
4600  <front>
4601    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4602    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4603      <organization>Western Research Laboratory</organization>
4604      <address><email></email></address>
4605    </author>
4606    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4607      <organization>Department of Information and Computer Science</organization>
4608      <address><email></email></address>
4609    </author>
4610    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4611      <organization>MIT Laboratory for Computer Science</organization>
4612      <address><email></email></address>
4613    </author>
4614    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4615      <organization>W3 Consortium</organization>
4616      <address><email></email></address>
4617    </author>
4618    <date month="May" year="1997"/>
4619  </front>
4620  <seriesInfo name="RFC" value="2145"/>
4623<reference anchor="RFC2616">
4624  <front>
4625    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4626    <author initials="R." surname="Fielding" fullname="R. Fielding">
4627      <organization>University of California, Irvine</organization>
4628      <address><email></email></address>
4629    </author>
4630    <author initials="J." surname="Gettys" fullname="J. Gettys">
4631      <organization>W3C</organization>
4632      <address><email></email></address>
4633    </author>
4634    <author initials="J." surname="Mogul" fullname="J. Mogul">
4635      <organization>Compaq Computer Corporation</organization>
4636      <address><email></email></address>
4637    </author>
4638    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4639      <organization>MIT Laboratory for Computer Science</organization>
4640      <address><email></email></address>
4641    </author>
4642    <author initials="L." surname="Masinter" fullname="L. Masinter">
4643      <organization>Xerox Corporation</organization>
4644      <address><email></email></address>
4645    </author>
4646    <author initials="P." surname="Leach" fullname="P. Leach">
4647      <organization>Microsoft Corporation</organization>
4648      <address><email></email></address>
4649    </author>
4650    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4651      <organization>W3C</organization>
4652      <address><email></email></address>
4653    </author>
4654    <date month="June" year="1999"/>
4655  </front>
4656  <seriesInfo name="RFC" value="2616"/>
4659<reference anchor='RFC2817'>
4660  <front>
4661    <title>Upgrading to TLS Within HTTP/1.1</title>
4662    <author initials='R.' surname='Khare' fullname='R. Khare'>
4663      <organization>4K Associates / UC Irvine</organization>
4664      <address><email></email></address>
4665    </author>
4666    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4667      <organization>Agranat Systems, Inc.</organization>
4668      <address><email></email></address>
4669    </author>
4670    <date year='2000' month='May' />
4671  </front>
4672  <seriesInfo name='RFC' value='2817' />
4675<reference anchor='RFC2818'>
4676  <front>
4677    <title>HTTP Over TLS</title>
4678    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4679      <organization>RTFM, Inc.</organization>
4680      <address><email></email></address>
4681    </author>
4682    <date year='2000' month='May' />
4683  </front>
4684  <seriesInfo name='RFC' value='2818' />
4687<reference anchor='RFC2965'>
4688  <front>
4689    <title>HTTP State Management Mechanism</title>
4690    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4691      <organization>Bell Laboratories, Lucent Technologies</organization>
4692      <address><email></email></address>
4693    </author>
4694    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4695      <organization>, Inc.</organization>
4696      <address><email></email></address>
4697    </author>
4698    <date year='2000' month='October' />
4699  </front>
4700  <seriesInfo name='RFC' value='2965' />
4703<reference anchor='RFC3040'>
4704  <front>
4705    <title>Internet Web Replication and Caching Taxonomy</title>
4706    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4707      <organization>Equinix, Inc.</organization>
4708    </author>
4709    <author initials='I.' surname='Melve' fullname='I. Melve'>
4710      <organization>UNINETT</organization>
4711    </author>
4712    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4713      <organization>CacheFlow Inc.</organization>
4714    </author>
4715    <date year='2001' month='January' />
4716  </front>
4717  <seriesInfo name='RFC' value='3040' />
4720<reference anchor='RFC3864'>
4721  <front>
4722    <title>Registration Procedures for Message Header Fields</title>
4723    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4724      <organization>Nine by Nine</organization>
4725      <address><email></email></address>
4726    </author>
4727    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4728      <organization>BEA Systems</organization>
4729      <address><email></email></address>
4730    </author>
4731    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4732      <organization>HP Labs</organization>
4733      <address><email></email></address>
4734    </author>
4735    <date year='2004' month='September' />
4736  </front>
4737  <seriesInfo name='BCP' value='90' />
4738  <seriesInfo name='RFC' value='3864' />
4741<reference anchor='RFC4033'>
4742  <front>
4743    <title>DNS Security Introduction and Requirements</title>
4744    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4745    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4746    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4747    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4748    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4749    <date year='2005' month='March' />
4750  </front>
4751  <seriesInfo name='RFC' value='4033' />
4754<reference anchor="RFC4288">
4755  <front>
4756    <title>Media Type Specifications and Registration Procedures</title>
4757    <author initials="N." surname="Freed" fullname="N. Freed">
4758      <organization>Sun Microsystems</organization>
4759      <address>
4760        <email></email>
4761      </address>
4762    </author>
4763    <author initials="J." surname="Klensin" fullname="J. Klensin">
4764      <address>
4765        <email></email>
4766      </address>
4767    </author>
4768    <date year="2005" month="December"/>
4769  </front>
4770  <seriesInfo name="BCP" value="13"/>
4771  <seriesInfo name="RFC" value="4288"/>
4774<reference anchor='RFC4395'>
4775  <front>
4776    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4777    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4778      <organization>AT&amp;T Laboratories</organization>
4779      <address>
4780        <email></email>
4781      </address>
4782    </author>
4783    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4784      <organization>Qualcomm, Inc.</organization>
4785      <address>
4786        <email></email>
4787      </address>
4788    </author>
4789    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4790      <organization>Adobe Systems</organization>
4791      <address>
4792        <email></email>
4793      </address>
4794    </author>
4795    <date year='2006' month='February' />
4796  </front>
4797  <seriesInfo name='BCP' value='115' />
4798  <seriesInfo name='RFC' value='4395' />
4801<reference anchor='RFC4559'>
4802  <front>
4803    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4804    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4805    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4806    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4807    <date year='2006' month='June' />
4808  </front>
4809  <seriesInfo name='RFC' value='4559' />
4812<reference anchor='RFC5226'>
4813  <front>
4814    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4815    <author initials='T.' surname='Narten' fullname='T. Narten'>
4816      <organization>IBM</organization>
4817      <address><email></email></address>
4818    </author>
4819    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4820      <organization>Google</organization>
4821      <address><email></email></address>
4822    </author>
4823    <date year='2008' month='May' />
4824  </front>
4825  <seriesInfo name='BCP' value='26' />
4826  <seriesInfo name='RFC' value='5226' />
4829<reference anchor="RFC5322">
4830  <front>
4831    <title>Internet Message Format</title>
4832    <author initials="P." surname="Resnick" fullname="P. Resnick">
4833      <organization>Qualcomm Incorporated</organization>
4834    </author>
4835    <date year="2008" month="October"/>
4836  </front>
4837  <seriesInfo name="RFC" value="5322"/>
4840<reference anchor="RFC6265">
4841  <front>
4842    <title>HTTP State Management Mechanism</title>
4843    <author initials="A." surname="Barth" fullname="Adam Barth">
4844      <organization abbrev="U.C. Berkeley">
4845        University of California, Berkeley
4846      </organization>
4847      <address><email></email></address>
4848    </author>
4849    <date year="2011" month="April" />
4850  </front>
4851  <seriesInfo name="RFC" value="6265"/>
4854<reference anchor='BCP97'>
4855  <front>
4856    <title>Handling Normative References to Standards-Track Documents</title>
4857    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4858      <address>
4859        <email></email>
4860      </address>
4861    </author>
4862    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4863      <organization>MIT</organization>
4864      <address>
4865        <email></email>
4866      </address>
4867    </author>
4868    <date year='2007' month='June' />
4869  </front>
4870  <seriesInfo name='BCP' value='97' />
4871  <seriesInfo name='RFC' value='4897' />
4874<reference anchor="Kri2001" target="">
4875  <front>
4876    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4877    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4878    <date year="2001" month="November"/>
4879  </front>
4880  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4883<reference anchor="Spe" target="">
4884  <front>
4885    <title>Analysis of HTTP Performance Problems</title>
4886    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4887    <date/>
4888  </front>
4891<reference anchor="Tou1998" target="">
4892  <front>
4893  <title>Analysis of HTTP Performance</title>
4894  <author initials="J." surname="Touch" fullname="Joe Touch">
4895    <organization>USC/Information Sciences Institute</organization>
4896    <address><email></email></address>
4897  </author>
4898  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4899    <organization>USC/Information Sciences Institute</organization>
4900    <address><email></email></address>
4901  </author>
4902  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4903    <organization>USC/Information Sciences Institute</organization>
4904    <address><email></email></address>
4905  </author>
4906  <date year="1998" month="Aug"/>
4907  </front>
4908  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4909  <annotation>(original report dated Aug. 1996)</annotation>
4915<section title="HTTP Version History" anchor="compatibility">
4917   HTTP has been in use by the World-Wide Web global information initiative
4918   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4919   was a simple protocol for hypertext data transfer across the Internet
4920   with only a single request method (GET) and no metadata.
4921   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4922   methods and MIME-like messaging that could include metadata about the data
4923   transferred and modifiers on the request/response semantics. However,
4924   HTTP/1.0 did not sufficiently take into consideration the effects of
4925   hierarchical proxies, caching, the need for persistent connections, or
4926   name-based virtual hosts. The proliferation of incompletely-implemented
4927   applications calling themselves "HTTP/1.0" further necessitated a
4928   protocol version change in order for two communicating applications
4929   to determine each other's true capabilities.
4932   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4933   requirements that enable reliable implementations, adding only
4934   those new features that will either be safely ignored by an HTTP/1.0
4935   recipient or only sent when communicating with a party advertising
4936   compliance with HTTP/1.1.
4939   It is beyond the scope of a protocol specification to mandate
4940   compliance with previous versions. HTTP/1.1 was deliberately
4941   designed, however, to make supporting previous versions easy.
4942   We would expect a general-purpose HTTP/1.1 server to understand
4943   any valid request in the format of HTTP/1.0 and respond appropriately
4944   with an HTTP/1.1 message that only uses features understood (or
4945   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4946   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4949   Since HTTP/0.9 did not support header fields in a request,
4950   there is no mechanism for it to support name-based virtual
4951   hosts (selection of resource by inspection of the Host header
4952   field).  Any server that implements name-based virtual hosts
4953   ought to disable support for HTTP/0.9.  Most requests that
4954   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4955   requests wherein a buggy client failed to properly encode
4956   linear whitespace found in a URI reference and placed in
4957   the request-target.
4960<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4962   This section summarizes major differences between versions HTTP/1.0
4963   and HTTP/1.1.
4966<section title="Multi-homed Web Servers" anchor="">
4968   The requirements that clients and servers support the Host header
4969   field (<xref target=""/>), report an error if it is
4970   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4971   are among the most important changes defined by HTTP/1.1.
4974   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4975   addresses and servers; there was no other established mechanism for
4976   distinguishing the intended server of a request than the IP address
4977   to which that request was directed. The Host header field was
4978   introduced during the development of HTTP/1.1 and, though it was
4979   quickly implemented by most HTTP/1.0 browsers, additional requirements
4980   were placed on all HTTP/1.1 requests in order to ensure complete
4981   adoption.  At the time of this writing, most HTTP-based services
4982   are dependent upon the Host header field for targeting requests.
4986<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4988   For most implementations of HTTP/1.0, each connection is established
4989   by the client prior to the request and closed by the server after
4990   sending the response. However, some implementations implement the
4991   Keep-Alive version of persistent connections described in
4992   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4995   Some clients and servers might wish to be compatible with some
4996   previous implementations of persistent connections in HTTP/1.0
4997   clients and servers. Persistent connections in HTTP/1.0 are
4998   explicitly negotiated as they are not the default behavior. HTTP/1.0
4999   experimental implementations of persistent connections are faulty,
5000   and the new facilities in HTTP/1.1 are designed to rectify these
5001   problems. The problem was that some existing HTTP/1.0 clients might
5002   send Keep-Alive to a proxy server that doesn't understand
5003   Connection, which would then erroneously forward it to the next
5004   inbound server, which would establish the Keep-Alive connection and
5005   result in a hung HTTP/1.0 proxy waiting for the close on the
5006   response. The result is that HTTP/1.0 clients must be prevented from
5007   using Keep-Alive when talking to proxies.
5010   However, talking to proxies is the most important use of persistent
5011   connections, so that prohibition is clearly unacceptable. Therefore,
5012   we need some other mechanism for indicating a persistent connection
5013   is desired, which is safe to use even when talking to an old proxy
5014   that ignores Connection. Persistent connections are the default for
5015   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
5016   declaring non-persistence. See <xref target="header.connection"/>.
5021<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
5023  Empty list elements in list productions have been deprecated.
5024  (<xref target="notation.abnf"/>)
5027  Rules about implicit linear whitespace between certain grammar productions
5028  have been removed; now it's only allowed when specifically pointed out
5029  in the ABNF.
5030  (<xref target="basic.rules"/>)
5033  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5034  sensitive. Restrict the version numbers to be single digits due to the fact
5035  that implementations are known to handle multi-digit version numbers
5036  incorrectly.
5037  (<xref target="http.version"/>)
5040  Require that invalid whitespace around field-names be rejected.
5041  (<xref target="header.fields"/>)
5044  The NUL octet is no longer allowed in comment and quoted-string
5045  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5046  Non-ASCII content in header fields and reason phrase has been obsoleted and
5047  made opaque (the TEXT rule was removed).
5048  (<xref target="field.rules"/>)
5051  Require recipients to handle bogus Content-Length header fields as errors.
5052  (<xref target="message.body"/>)
5055  Remove reference to non-existent identity transfer-coding value tokens.
5056  (Sections <xref format="counter" target="message.body"/> and
5057  <xref format="counter" target="transfer.codings"/>)
5060  Update use of abs_path production from RFC 1808 to the path-absolute + query
5061  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5062  request method only.
5063  (<xref target="request-target"/>)
5066  Clarification that the chunk length does not include the count of the octets
5067  in the chunk header and trailer. Furthermore disallowed line folding
5068  in chunk extensions.
5069  (<xref target="chunked.encoding"/>)
5072  Remove hard limit of two connections per server.
5073  (<xref target="persistent.practical"/>)
5076  Change ABNF productions for header fields to only define the field value.
5077  (<xref target="header.field.definitions"/>)
5080  Clarify exactly when close connection options must be sent.
5081  (<xref target="header.connection"/>)
5084  Define the semantics of the "Upgrade" header field in responses other than
5085  101 (this was incorporated from <xref target="RFC2817"/>).
5086  (<xref target="header.upgrade"/>)
5091<?BEGININC p1-messaging.abnf-appendix ?>
5092<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
5094<artwork type="abnf" name="p1-messaging.parsed-abnf">
5095<x:ref>BWS</x:ref> = OWS
5097<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5098<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5099 connection-token ] )
5100<x:ref>Content-Length</x:ref> = 1*DIGIT
5102<x:ref>Date</x:ref> = HTTP-date
5104<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5106<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5107<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5108<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5109<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5110 ]
5111<x:ref>Host</x:ref> = uri-host [ ":" port ]
5113<x:ref>Method</x:ref> = token
5115<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5117<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5118<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5119<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5120<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5121<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5123<x:ref>Status-Code</x:ref> = 3DIGIT
5124<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5126<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5127<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5128<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5129 transfer-coding ] )
5131<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5132<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5134<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5135 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5136 )
5138<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5139<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5140<x:ref>attribute</x:ref> = token
5141<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5143<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5144<x:ref>chunk-data</x:ref> = 1*OCTET
5145<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5146<x:ref>chunk-ext-name</x:ref> = token
5147<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5148<x:ref>chunk-size</x:ref> = 1*HEXDIG
5149<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5150<x:ref>connection-token</x:ref> = token
5151<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5152 / %x2A-5B ; '*'-'['
5153 / %x5D-7E ; ']'-'~'
5154 / obs-text
5156<x:ref>date1</x:ref> = day SP month SP year
5157<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5158<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5159<x:ref>day</x:ref> = 2DIGIT
5160<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5161 / %x54.75.65 ; Tue
5162 / %x57.65.64 ; Wed
5163 / %x54.68.75 ; Thu
5164 / %x46.72.69 ; Fri
5165 / %x53.61.74 ; Sat
5166 / %x53.75.6E ; Sun
5167<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5168 / %x54. ; Tuesday
5169 / %x57.65.64.6E. ; Wednesday
5170 / %x54. ; Thursday
5171 / %x46. ; Friday
5172 / %x53. ; Saturday
5173 / %x53.75.6E.64.61.79 ; Sunday
5175<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5176<x:ref>field-name</x:ref> = token
5177<x:ref>field-value</x:ref> = *( field-content / OWS )
5179<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5180<x:ref>hour</x:ref> = 2DIGIT
5181<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5182<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5184<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5186<x:ref>message-body</x:ref> = *OCTET
5187<x:ref>minute</x:ref> = 2DIGIT
5188<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5189 / %x46.65.62 ; Feb
5190 / %x4D.61.72 ; Mar
5191 / %x41.70.72 ; Apr
5192 / %x4D.61.79 ; May
5193 / %x4A.75.6E ; Jun
5194 / %x4A.75.6C ; Jul
5195 / %x41.75.67 ; Aug
5196 / %x53.65.70 ; Sep
5197 / %x4F.63.74 ; Oct
5198 / %x4E.6F.76 ; Nov
5199 / %x44.65.63 ; Dec
5201<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5202<x:ref>obs-fold</x:ref> = CRLF
5203<x:ref>obs-text</x:ref> = %x80-FF
5205<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5206<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5207<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5208<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5209<x:ref>product</x:ref> = token [ "/" product-version ]
5210<x:ref>product-version</x:ref> = token
5211<x:ref>protocol-name</x:ref> = token
5212<x:ref>protocol-version</x:ref> = token
5213<x:ref>pseudonym</x:ref> = token
5215<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5216 / %x5D-7E ; ']'-'~'
5217 / obs-text
5218<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5219 / %x5D-7E ; ']'-'~'
5220 / obs-text
5221<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5222<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5223<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5224<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5225<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5226<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5228<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5229<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5230<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5231<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5232 / authority
5233<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5234<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5236<x:ref>second</x:ref> = 2DIGIT
5237<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5238 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5239<x:ref>start-line</x:ref> = Request-Line / Status-Line
5241<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5242<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5243 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5244<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5245<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5246<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5247<x:ref>token</x:ref> = 1*tchar
5248<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5249<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5250 transfer-extension
5251<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5252<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5254<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5256<x:ref>value</x:ref> = word
5258<x:ref>word</x:ref> = token / quoted-string
5260<x:ref>year</x:ref> = 4DIGIT
5263<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5264; Chunked-Body defined but not used
5265; Connection defined but not used
5266; Content-Length defined but not used
5267; Date defined but not used
5268; HTTP-message defined but not used
5269; Host defined but not used
5270; Request defined but not used
5271; Response defined but not used
5272; TE defined but not used
5273; Trailer defined but not used
5274; Transfer-Encoding defined but not used
5275; URI-reference defined but not used
5276; Upgrade defined but not used
5277; Via defined but not used
5278; http-URI defined but not used
5279; https-URI defined but not used
5280; partial-URI defined but not used
5281; special defined but not used
5283<?ENDINC p1-messaging.abnf-appendix ?>
5285<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5287<section title="Since RFC 2616">
5289  Extracted relevant partitions from <xref target="RFC2616"/>.
5293<section title="Since draft-ietf-httpbis-p1-messaging-00">
5295  Closed issues:
5296  <list style="symbols">
5297    <t>
5298      <eref target=""/>:
5299      "HTTP Version should be case sensitive"
5300      (<eref target=""/>)
5301    </t>
5302    <t>
5303      <eref target=""/>:
5304      "'unsafe' characters"
5305      (<eref target=""/>)
5306    </t>
5307    <t>
5308      <eref target=""/>:
5309      "Chunk Size Definition"
5310      (<eref target=""/>)
5311    </t>
5312    <t>
5313      <eref target=""/>:
5314      "Message Length"
5315      (<eref target=""/>)
5316    </t>
5317    <t>
5318      <eref target=""/>:
5319      "Media Type Registrations"
5320      (<eref target=""/>)
5321    </t>
5322    <t>
5323      <eref target=""/>:
5324      "URI includes query"
5325      (<eref target=""/>)
5326    </t>
5327    <t>
5328      <eref target=""/>:
5329      "No close on 1xx responses"
5330      (<eref target=""/>)
5331    </t>
5332    <t>
5333      <eref target=""/>:
5334      "Remove 'identity' token references"
5335      (<eref target=""/>)
5336    </t>
5337    <t>
5338      <eref target=""/>:
5339      "Import query BNF"
5340    </t>
5341    <t>
5342      <eref target=""/>:
5343      "qdtext BNF"
5344    </t>
5345    <t>
5346      <eref target=""/>:
5347      "Normative and Informative references"
5348    </t>
5349    <t>
5350      <eref target=""/>:
5351      "RFC2606 Compliance"
5352    </t>
5353    <t>
5354      <eref target=""/>:
5355      "RFC977 reference"
5356    </t>
5357    <t>
5358      <eref target=""/>:
5359      "RFC1700 references"
5360    </t>
5361    <t>
5362      <eref target=""/>:
5363      "inconsistency in date format explanation"
5364    </t>
5365    <t>
5366      <eref target=""/>:
5367      "Date reference typo"
5368    </t>
5369    <t>
5370      <eref target=""/>:
5371      "Informative references"
5372    </t>
5373    <t>
5374      <eref target=""/>:
5375      "ISO-8859-1 Reference"
5376    </t>
5377    <t>
5378      <eref target=""/>:
5379      "Normative up-to-date references"
5380    </t>
5381  </list>
5384  Other changes:
5385  <list style="symbols">
5386    <t>
5387      Update media type registrations to use RFC4288 template.
5388    </t>
5389    <t>
5390      Use names of RFC4234 core rules DQUOTE and WSP,
5391      fix broken ABNF for chunk-data
5392      (work in progress on <eref target=""/>)
5393    </t>
5394  </list>
5398<section title="Since draft-ietf-httpbis-p1-messaging-01">
5400  Closed issues:
5401  <list style="symbols">
5402    <t>
5403      <eref target=""/>:
5404      "Bodies on GET (and other) requests"
5405    </t>
5406    <t>
5407      <eref target=""/>:
5408      "Updating to RFC4288"
5409    </t>
5410    <t>
5411      <eref target=""/>:
5412      "Status Code and Reason Phrase"
5413    </t>
5414    <t>
5415      <eref target=""/>:
5416      "rel_path not used"
5417    </t>
5418  </list>
5421  Ongoing work on ABNF conversion (<eref target=""/>):
5422  <list style="symbols">
5423    <t>
5424      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5425      "trailer-part").
5426    </t>
5427    <t>
5428      Avoid underscore character in rule names ("http_URL" ->
5429      "http-URL", "abs_path" -> "path-absolute").
5430    </t>
5431    <t>
5432      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5433      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5434      have to be updated when switching over to RFC3986.
5435    </t>
5436    <t>
5437      Synchronize core rules with RFC5234.
5438    </t>
5439    <t>
5440      Get rid of prose rules that span multiple lines.
5441    </t>
5442    <t>
5443      Get rid of unused rules LOALPHA and UPALPHA.
5444    </t>
5445    <t>
5446      Move "Product Tokens" section (back) into Part 1, as "token" is used
5447      in the definition of the Upgrade header field.
5448    </t>
5449    <t>
5450      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5451    </t>
5452    <t>
5453      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5454    </t>
5455  </list>
5459<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5461  Closed issues:
5462  <list style="symbols">
5463    <t>
5464      <eref target=""/>:
5465      "HTTP-date vs. rfc1123-date"
5466    </t>
5467    <t>
5468      <eref target=""/>:
5469      "WS in quoted-pair"
5470    </t>
5471  </list>
5474  Ongoing work on IANA Message Header Field Registration (<eref target=""/>):
5475  <list style="symbols">
5476    <t>
5477      Reference RFC 3984, and update header field registrations for headers defined
5478      in this document.
5479    </t>
5480  </list>
5483  Ongoing work on ABNF conversion (<eref target=""/>):
5484  <list style="symbols">
5485    <t>
5486      Replace string literals when the string really is case-sensitive (HTTP-Version).
5487    </t>
5488  </list>
5492<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5494  Closed issues:
5495  <list style="symbols">
5496    <t>
5497      <eref target=""/>:
5498      "Connection closing"
5499    </t>
5500    <t>
5501      <eref target=""/>:
5502      "Move registrations and registry information to IANA Considerations"
5503    </t>
5504    <t>
5505      <eref target=""/>:
5506      "need new URL for PAD1995 reference"
5507    </t>
5508    <t>
5509      <eref target=""/>:
5510      "IANA Considerations: update HTTP URI scheme registration"
5511    </t>
5512    <t>
5513      <eref target=""/>:
5514      "Cite HTTPS URI scheme definition"
5515    </t>
5516    <t>
5517      <eref target=""/>:
5518      "List-type headers vs Set-Cookie"
5519    </t>
5520  </list>
5523  Ongoing work on ABNF conversion (<eref target=""/>):
5524  <list style="symbols">
5525    <t>
5526      Replace string literals when the string really is case-sensitive (HTTP-Date).
5527    </t>
5528    <t>
5529      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5530    </t>
5531  </list>
5535<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5537  Closed issues:
5538  <list style="symbols">
5539    <t>
5540      <eref target=""/>:
5541      "Out-of-date reference for URIs"
5542    </t>
5543    <t>
5544      <eref target=""/>:
5545      "RFC 2822 is updated by RFC 5322"
5546    </t>
5547  </list>
5550  Ongoing work on ABNF conversion (<eref target=""/>):
5551  <list style="symbols">
5552    <t>
5553      Use "/" instead of "|" for alternatives.
5554    </t>
5555    <t>
5556      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5557    </t>
5558    <t>
5559      Only reference RFC 5234's core rules.
5560    </t>
5561    <t>
5562      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5563      whitespace ("OWS") and required whitespace ("RWS").
5564    </t>
5565    <t>
5566      Rewrite ABNFs to spell out whitespace rules, factor out
5567      header field value format definitions.
5568    </t>
5569  </list>
5573<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5575  Closed issues:
5576  <list style="symbols">
5577    <t>
5578      <eref target=""/>:
5579      "Header LWS"
5580    </t>
5581    <t>
5582      <eref target=""/>:
5583      "Sort 1.3 Terminology"
5584    </t>
5585    <t>
5586      <eref target=""/>:
5587      "RFC2047 encoded words"
5588    </t>
5589    <t>
5590      <eref target=""/>:
5591      "Character Encodings in TEXT"
5592    </t>
5593    <t>
5594      <eref target=""/>:
5595      "Line Folding"
5596    </t>
5597    <t>
5598      <eref target=""/>:
5599      "OPTIONS * and proxies"
5600    </t>
5601    <t>
5602      <eref target=""/>:
5603      "Reason-Phrase BNF"
5604    </t>
5605    <t>
5606      <eref target=""/>:
5607      "Use of TEXT"
5608    </t>
5609    <t>
5610      <eref target=""/>:
5611      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5612    </t>
5613    <t>
5614      <eref target=""/>:
5615      "RFC822 reference left in discussion of date formats"
5616    </t>
5617  </list>
5620  Final work on ABNF conversion (<eref target=""/>):
5621  <list style="symbols">
5622    <t>
5623      Rewrite definition of list rules, deprecate empty list elements.
5624    </t>
5625    <t>
5626      Add appendix containing collected and expanded ABNF.
5627    </t>
5628  </list>
5631  Other changes:
5632  <list style="symbols">
5633    <t>
5634      Rewrite introduction; add mostly new Architecture Section.
5635    </t>
5636    <t>
5637      Move definition of quality values from Part 3 into Part 1;
5638      make TE request header field grammar independent of accept-params (defined in Part 3).
5639    </t>
5640  </list>
5644<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5646  Closed issues:
5647  <list style="symbols">
5648    <t>
5649      <eref target=""/>:
5650      "base for numeric protocol elements"
5651    </t>
5652    <t>
5653      <eref target=""/>:
5654      "comment ABNF"
5655    </t>
5656  </list>
5659  Partly resolved issues:
5660  <list style="symbols">
5661    <t>
5662      <eref target=""/>:
5663      "205 Bodies" (took out language that implied that there might be
5664      methods for which a request body MUST NOT be included)
5665    </t>
5666    <t>
5667      <eref target=""/>:
5668      "editorial improvements around HTTP-date"
5669    </t>
5670  </list>
5674<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5676  Closed issues:
5677  <list style="symbols">
5678    <t>
5679      <eref target=""/>:
5680      "Repeating single-value headers"
5681    </t>
5682    <t>
5683      <eref target=""/>:
5684      "increase connection limit"
5685    </t>
5686    <t>
5687      <eref target=""/>:
5688      "IP addresses in URLs"
5689    </t>
5690    <t>
5691      <eref target=""/>:
5692      "take over HTTP Upgrade Token Registry"
5693    </t>
5694    <t>
5695      <eref target=""/>:
5696      "CR and LF in chunk extension values"
5697    </t>
5698    <t>
5699      <eref target=""/>:
5700      "HTTP/0.9 support"
5701    </t>
5702    <t>
5703      <eref target=""/>:
5704      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5705    </t>
5706    <t>
5707      <eref target=""/>:
5708      "move definitions of gzip/deflate/compress to part 1"
5709    </t>
5710    <t>
5711      <eref target=""/>:
5712      "disallow control characters in quoted-pair"
5713    </t>
5714  </list>
5717  Partly resolved issues:
5718  <list style="symbols">
5719    <t>
5720      <eref target=""/>:
5721      "update IANA requirements wrt Transfer-Coding values" (add the
5722      IANA Considerations subsection)
5723    </t>
5724  </list>
5728<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5730  Closed issues:
5731  <list style="symbols">
5732    <t>
5733      <eref target=""/>:
5734      "header parsing, treatment of leading and trailing OWS"
5735    </t>
5736  </list>
5739  Partly resolved issues:
5740  <list style="symbols">
5741    <t>
5742      <eref target=""/>:
5743      "Placement of 13.5.1 and 13.5.2"
5744    </t>
5745    <t>
5746      <eref target=""/>:
5747      "use of term "word" when talking about header structure"
5748    </t>
5749  </list>
5753<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5755  Closed issues:
5756  <list style="symbols">
5757    <t>
5758      <eref target=""/>:
5759      "Clarification of the term 'deflate'"
5760    </t>
5761    <t>
5762      <eref target=""/>:
5763      "OPTIONS * and proxies"
5764    </t>
5765    <t>
5766      <eref target=""/>:
5767      "MIME-Version not listed in P1, general header fields"
5768    </t>
5769    <t>
5770      <eref target=""/>:
5771      "IANA registry for content/transfer encodings"
5772    </t>
5773    <t>
5774      <eref target=""/>:
5775      "Case-sensitivity of HTTP-date"
5776    </t>
5777    <t>
5778      <eref target=""/>:
5779      "use of term "word" when talking about header structure"
5780    </t>
5781  </list>
5784  Partly resolved issues:
5785  <list style="symbols">
5786    <t>
5787      <eref target=""/>:
5788      "Term for the requested resource's URI"
5789    </t>
5790  </list>
5794<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5796  Closed issues:
5797  <list style="symbols">
5798    <t>
5799      <eref target=""/>:
5800      "Connection Closing"
5801    </t>
5802    <t>
5803      <eref target=""/>:
5804      "Delimiting messages with multipart/byteranges"
5805    </t>
5806    <t>
5807      <eref target=""/>:
5808      "Handling multiple Content-Length headers"
5809    </t>
5810    <t>
5811      <eref target=""/>:
5812      "Clarify entity / representation / variant terminology"
5813    </t>
5814    <t>
5815      <eref target=""/>:
5816      "consider removing the 'changes from 2068' sections"
5817    </t>
5818  </list>
5821  Partly resolved issues:
5822  <list style="symbols">
5823    <t>
5824      <eref target=""/>:
5825      "HTTP(s) URI scheme definitions"
5826    </t>
5827  </list>
5831<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5833  Closed issues:
5834  <list style="symbols">
5835    <t>
5836      <eref target=""/>:
5837      "Trailer requirements"
5838    </t>
5839    <t>
5840      <eref target=""/>:
5841      "Text about clock requirement for caches belongs in p6"
5842    </t>
5843    <t>
5844      <eref target=""/>:
5845      "effective request URI: handling of missing host in HTTP/1.0"
5846    </t>
5847    <t>
5848      <eref target=""/>:
5849      "confusing Date requirements for clients"
5850    </t>
5851  </list>
5854  Partly resolved issues:
5855  <list style="symbols">
5856    <t>
5857      <eref target=""/>:
5858      "Handling multiple Content-Length headers"
5859    </t>
5860  </list>
5864<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5866  Closed issues:
5867  <list style="symbols">
5868    <t>
5869      <eref target=""/>:
5870      "RFC2145 Normative"
5871    </t>
5872    <t>
5873      <eref target=""/>:
5874      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5875    </t>
5876    <t>
5877      <eref target=""/>:
5878      "define 'transparent' proxy"
5879    </t>
5880    <t>
5881      <eref target=""/>:
5882      "Header Classification"
5883    </t>
5884    <t>
5885      <eref target=""/>:
5886      "Is * usable as a request-uri for new methods?"
5887    </t>
5888    <t>
5889      <eref target=""/>:
5890      "Migrate Upgrade details from RFC2817"
5891    </t>
5892    <t>
5893      <eref target=""/>:
5894      "untangle ABNFs for header fields"
5895    </t>
5896    <t>
5897      <eref target=""/>:
5898      "update RFC 2109 reference"
5899    </t>
5900  </list>
5904<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5906  Closed issues:
5907  <list style="symbols">
5908    <t>
5909      <eref target=""/>:
5910      "Allow is not in 13.5.2"
5911    </t>
5912    <t>
5913      <eref target=""/>:
5914      "Handling multiple Content-Length headers"
5915    </t>
5916    <t>
5917      <eref target=""/>:
5918      "untangle ABNFs for header fields"
5919    </t>
5920    <t>
5921      <eref target=""/>:
5922      "Content-Length ABNF broken"
5923    </t>
5924  </list>
5928<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5930  Closed issues:
5931  <list style="symbols">
5932    <t>
5933      <eref target=""/>:
5934      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5935    </t>
5936    <t>
5937      <eref target=""/>:
5938      "Recommend minimum sizes for protocol elements"
5939    </t>
5940    <t>
5941      <eref target=""/>:
5942      "Set expectations around buffering"
5943    </t>
5944    <t>
5945      <eref target=""/>:
5946      "Considering messages in isolation"
5947    </t>
5948  </list>
5952<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5954  Closed issues:
5955  <list style="symbols">
5956    <t>
5957      <eref target=""/>:
5958      "DNS Spoofing / DNS Binding advice"
5959    </t>
5960    <t>
5961      <eref target=""/>:
5962      "move RFCs 2145, 2616, 2817 to Historic status"
5963    </t>
5964    <t>
5965      <eref target=""/>:
5966      "\-escaping in quoted strings"
5967    </t>
5968    <t>
5969      <eref target=""/>:
5970      "'Close' should be reserved in the HTTP header field registry"
5971    </t>
5972  </list>
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