source: draft-ietf-httpbis/latest/p1-messaging.xml @ 601

Last change on this file since 601 was 601, checked in by julian.reschke@…, 14 years ago

List Mark Nottingham as author/editor of Part6.

  • Property svn:eol-style set to native
File size: 211.3 KB
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns=''>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns=''>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns=''>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns=''>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns=''>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns=''>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns=''>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns=''>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns=''>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns=''>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2009">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x=''/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x=''/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x=''/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x=''/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x=''/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x=''/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x=''/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x=''/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x=''/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' 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-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
34  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc-ext allow-markup-in-artwork="yes" ?>
49<?rfc-ext include-references-in-index="yes" ?>
50<rfc obsoletes="2616" category="std" x:maturity-level="draft"
51     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
52     xmlns:x=''>
55  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
57  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
58    <organization abbrev="Day Software">Day Software</organization>
59    <address>
60      <postal>
61        <street>23 Corporate Plaza DR, Suite 280</street>
62        <city>Newport Beach</city>
63        <region>CA</region>
64        <code>92660</code>
65        <country>USA</country>
66      </postal>
67      <phone>+1-949-706-5300</phone>
68      <facsimile>+1-949-706-5305</facsimile>
69      <email></email>
70      <uri></uri>
71    </address>
72  </author>
74  <author initials="J." surname="Gettys" fullname="Jim Gettys">
75    <organization>One Laptop per Child</organization>
76    <address>
77      <postal>
78        <street>21 Oak Knoll Road</street>
79        <city>Carlisle</city>
80        <region>MA</region>
81        <code>01741</code>
82        <country>USA</country>
83      </postal>
84      <email></email>
85      <uri></uri>
86    </address>
87  </author>
89  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
90    <organization abbrev="HP">Hewlett-Packard Company</organization>
91    <address>
92      <postal>
93        <street>HP Labs, Large Scale Systems Group</street>
94        <street>1501 Page Mill Road, MS 1177</street>
95        <city>Palo Alto</city>
96        <region>CA</region>
97        <code>94304</code>
98        <country>USA</country>
99      </postal>
100      <email></email>
101    </address>
102  </author>
104  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
105    <organization abbrev="Microsoft">Microsoft Corporation</organization>
106    <address>
107      <postal>
108        <street>1 Microsoft Way</street>
109        <city>Redmond</city>
110        <region>WA</region>
111        <code>98052</code>
112        <country>USA</country>
113      </postal>
114      <email></email>
115    </address>
116  </author>
118  <author initials="L." surname="Masinter" fullname="Larry Masinter">
119    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
120    <address>
121      <postal>
122        <street>345 Park Ave</street>
123        <city>San Jose</city>
124        <region>CA</region>
125        <code>95110</code>
126        <country>USA</country>
127      </postal>
128      <email></email>
129      <uri></uri>
130    </address>
131  </author>
133  <author initials="P." surname="Leach" fullname="Paul J. Leach">
134    <organization abbrev="Microsoft">Microsoft Corporation</organization>
135    <address>
136      <postal>
137        <street>1 Microsoft Way</street>
138        <city>Redmond</city>
139        <region>WA</region>
140        <code>98052</code>
141      </postal>
142      <email></email>
143    </address>
144  </author>
146  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
147    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
148    <address>
149      <postal>
150        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
151        <street>The Stata Center, Building 32</street>
152        <street>32 Vassar Street</street>
153        <city>Cambridge</city>
154        <region>MA</region>
155        <code>02139</code>
156        <country>USA</country>
157      </postal>
158      <email></email>
159      <uri></uri>
160    </address>
161  </author>
163  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
164    <organization abbrev="W3C">World Wide Web Consortium</organization>
165    <address>
166      <postal>
167        <street>W3C / ERCIM</street>
168        <street>2004, rte des Lucioles</street>
169        <city>Sophia-Antipolis</city>
170        <region>AM</region>
171        <code>06902</code>
172        <country>France</country>
173      </postal>
174      <email></email>
175      <uri></uri>
176    </address>
177  </author>
179  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
180    <organization abbrev="greenbytes">greenbytes GmbH</organization>
181    <address>
182      <postal>
183        <street>Hafenweg 16</street>
184        <city>Muenster</city><region>NW</region><code>48155</code>
185        <country>Germany</country>
186      </postal>
187      <phone>+49 251 2807760</phone>   
188      <facsimile>+49 251 2807761</facsimile>   
189      <email></email>       
190      <uri></uri>     
191    </address>
192  </author>
194  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
195  <workgroup>HTTPbis Working Group</workgroup>
199   The Hypertext Transfer Protocol (HTTP) is an application-level
200   protocol for distributed, collaborative, hypertext information
201   systems. HTTP has been in use by the World Wide Web global information
202   initiative since 1990. This document is Part 1 of the seven-part specification
203   that defines the protocol referred to as "HTTP/1.1" and, taken together,
204   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
205   its associated terminology, defines the "http" and "https" Uniform
206   Resource Identifier (URI) schemes, defines the generic message syntax
207   and parsing requirements for HTTP message frames, and describes
208   general security concerns for implementations.
212<note title="Editorial Note (To be removed by RFC Editor)">
213  <t>
214    Discussion of this draft should take place on the HTTPBIS working group
215    mailing list ( The current issues list is
216    at <eref target=""/>
217    and related documents (including fancy diffs) can be found at
218    <eref target=""/>.
219  </t>
220  <t>
221    The changes in this draft are summarized in <xref target="changes.since.06"/>.
222  </t>
226<section title="Introduction" anchor="introduction">
228   The Hypertext Transfer Protocol (HTTP) is an application-level
229   request/response protocol that uses extensible semantics and MIME-like
230   message payloads for flexible interaction with network-based hypertext
231   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
232   standard <xref target="RFC3986"/> to indicate request targets and
233   relationships between resources.
234   Messages are passed in a format similar to that used by Internet mail
235   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
236   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
237   between HTTP and MIME messages).
240   HTTP is a generic interface protocol for information systems. It is
241   designed to hide the details of how a service is implemented by presenting
242   a uniform interface to clients that is independent of the types of
243   resources provided. Likewise, servers do not need to be aware of each
244   client's purpose: an HTTP request can be considered in isolation rather
245   than being associated with a specific type of client or a predetermined
246   sequence of application steps. The result is a protocol that can be used
247   effectively in many different contexts and for which implementations can
248   evolve independently over time.
251   HTTP is also designed for use as a generic protocol for translating
252   communication to and from other Internet information systems.
253   HTTP proxies and gateways provide access to alternative information
254   services by translating their diverse protocols into a hypertext
255   format that can be viewed and manipulated by clients in the same way
256   as HTTP services.
259   One consequence of HTTP flexibility is that the protocol cannot be
260   defined in terms of what occurs behind the interface. Instead, we
261   are limited to defining the syntax of communication, the intent
262   of received communication, and the expected behavior of recipients.
263   If the communication is considered in isolation, then successful
264   actions should be reflected in corresponding changes to the
265   observable interface provided by servers. However, since multiple
266   clients may act in parallel and perhaps at cross-purposes, we
267   cannot require that such changes be observable beyond the scope
268   of a single response.
271   This document is Part 1 of the seven-part specification of HTTP,
272   defining the protocol referred to as "HTTP/1.1" and obsoleting
273   <xref target="RFC2616"/>.
274   Part 1 describes the architectural elements that are used or
275   referred to in HTTP and defines the URI schemes specific to
276   HTTP-based resources, overall network operation, connection
277   management, and HTTP message framing and forwarding requirements.
278   Our goal is to define all of the mechanisms necessary for HTTP message
279   handling that are independent of message semantics, thereby defining the
280   complete set of requirements for message parsers and
281   message-forwarding intermediaries.
284<section title="Requirements" anchor="intro.requirements">
286   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
287   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
288   document are to be interpreted as described in <xref target="RFC2119"/>.
291   An implementation is not compliant if it fails to satisfy one or more
292   of the &MUST; or &REQUIRED; level requirements for the protocols it
293   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
294   level and all the &SHOULD; level requirements for its protocols is said
295   to be "unconditionally compliant"; one that satisfies all the &MUST;
296   level requirements but not all the &SHOULD; level requirements for its
297   protocols is said to be "conditionally compliant."
301<section title="Syntax Notation" anchor="notation">
302<iref primary="true" item="Grammar" subitem="ALPHA"/>
303<iref primary="true" item="Grammar" subitem="CR"/>
304<iref primary="true" item="Grammar" subitem="CRLF"/>
305<iref primary="true" item="Grammar" subitem="CTL"/>
306<iref primary="true" item="Grammar" subitem="DIGIT"/>
307<iref primary="true" item="Grammar" subitem="DQUOTE"/>
308<iref primary="true" item="Grammar" subitem="HEXDIG"/>
309<iref primary="true" item="Grammar" subitem="LF"/>
310<iref primary="true" item="Grammar" subitem="OCTET"/>
311<iref primary="true" item="Grammar" subitem="SP"/>
312<iref primary="true" item="Grammar" subitem="VCHAR"/>
313<iref primary="true" item="Grammar" subitem="WSP"/>
315   This specification uses the Augmented Backus-Naur Form (ABNF) notation
316   of <xref target="RFC5234"/>.
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CTL"/>
321  <x:anchor-alias value="CR"/>
322  <x:anchor-alias value="CRLF"/>
323  <x:anchor-alias value="DIGIT"/>
324  <x:anchor-alias value="DQUOTE"/>
325  <x:anchor-alias value="HEXDIG"/>
326  <x:anchor-alias value="LF"/>
327  <x:anchor-alias value="OCTET"/>
328  <x:anchor-alias value="SP"/>
329  <x:anchor-alias value="VCHAR"/>
330  <x:anchor-alias value="WSP"/>
331   The following core rules are included by
332   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334   DIGIT (decimal 0-9), DQUOTE (double quote),
335   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336   OCTET (any 8-bit sequence of data), SP (space),
337   VCHAR (any visible <xref target="USASCII"/> character),
338   and WSP (whitespace).
341<section title="ABNF Extension: #rule" anchor="notation.abnf">
342  <t>
343    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
344    improve readability.
345  </t>
346  <t>
347    A construct "#" is defined, similar to "*", for defining lists of
348    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
349    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
350    (",") and optional whitespace (OWS).   
351  </t>
352  <figure><preamble>
353    Thus,
354</preamble><artwork type="example">
355  1#element =&gt; element *( OWS "," OWS element )
357  <figure><preamble>
358    and:
359</preamble><artwork type="example">
360  #element =&gt; [ 1#element ]
362  <figure><preamble>
363    and for n &gt;= 1 and m &gt; 1:
364</preamble><artwork type="example">
365  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
367  <t>
368    For compatibility with legacy list rules, recipients &SHOULD; accept empty
369    list elements. In other words, consumers would follow the list productions:
370  </t>
371<figure><artwork type="example">
372  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
374  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
377  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
378  expanded as explained above.
382<section title="Basic Rules" anchor="basic.rules">
383<t anchor="rule.CRLF">
384  <x:anchor-alias value="CRLF"/>
385   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
386   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
387   tolerant applications). The end-of-line marker within an entity-body
388   is defined by its associated media type, as described in &media-types;.
390<t anchor="rule.LWS">
391   This specification uses three rules to denote the use of linear
392   whitespace: OWS (optional whitespace), RWS (required whitespace), and
393   BWS ("bad" whitespace).
396   The OWS rule is used where zero or more linear whitespace characters may
397   appear. OWS &SHOULD; either not be produced or be produced as a single SP
398   character. Multiple OWS characters that occur within field-content &SHOULD;
399   be replaced with a single SP before interpreting the field value or
400   forwarding the message downstream.
403   RWS is used when at least one linear whitespace character is required to
404   separate field tokens. RWS &SHOULD; be produced as a single SP character.
405   Multiple RWS characters that occur within field-content &SHOULD; be
406   replaced with a single SP before interpreting the field value or
407   forwarding the message downstream.
410   BWS is used where the grammar allows optional whitespace for historical
411   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
412   recipients &MUST; accept such bad optional whitespace and remove it before
413   interpreting the field value or forwarding the message downstream.
415<t anchor="rule.whitespace">
416  <x:anchor-alias value="BWS"/>
417  <x:anchor-alias value="OWS"/>
418  <x:anchor-alias value="RWS"/>
419  <x:anchor-alias value="obs-fold"/>
421<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"/>
422  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
423                 ; "optional" whitespace
424  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
425                 ; "required" whitespace
426  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
427                 ; "bad" whitespace
428  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
429                 ; see <xref target="message.headers"/>
431<t anchor="rule.token.separators">
432  <x:anchor-alias value="tchar"/>
433  <x:anchor-alias value="token"/>
434   Many HTTP/1.1 header field values consist of words separated by whitespace
435   or special characters. These special characters &MUST; be in a quoted
436   string to be used within a parameter value (as defined in
437   <xref target="transfer.codings"/>).
439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
440  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
441                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
442                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
444  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
446<t anchor="rule.quoted-string">
447  <x:anchor-alias value="quoted-string"/>
448  <x:anchor-alias value="qdtext"/>
449  <x:anchor-alias value="obs-text"/>
450   A string of text is parsed as a single word if it is quoted using
451   double-quote marks.
453<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"/>
454  <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>
455  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
456                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref>
457  <x:ref>obs-text</x:ref>       = %x80-FF
459<t anchor="rule.quoted-pair">
460  <x:anchor-alias value="quoted-pair"/>
461  <x:anchor-alias value="quoted-text"/>
462   The backslash character ("\") &MAY; be used as a single-character
463   quoting mechanism only within quoted-string and comment constructs.
465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
466  <x:ref>quoted-text</x:ref>    = %x01-09 /
467                   %x0B-0C /
468                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
469  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
473<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
474  <x:anchor-alias value="request-header"/>
475  <x:anchor-alias value="response-header"/>
476  <x:anchor-alias value="entity-body"/>
477  <x:anchor-alias value="entity-header"/>
478  <x:anchor-alias value="Cache-Control"/>
479  <x:anchor-alias value="Pragma"/>
480  <x:anchor-alias value="Warning"/>
482  The ABNF rules below are defined in other parts:
484<figure><!-- Part2--><artwork type="abnf2616">
485  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
486  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
488<figure><!-- Part3--><artwork type="abnf2616">
489  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
490  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
492<figure><!-- Part6--><artwork type="abnf2616">
493  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
494  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
495  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
502<section title="HTTP architecture" anchor="architecture">
504   HTTP was created with a specific architecture in mind, the World Wide Web,
505   and has evolved over time to support the scalability needs of a worldwide
506   hypertext system. Much of that architecture is reflected in the terminology
507   and syntax productions used to define HTTP.
510<section title="Uniform Resource Identifiers" anchor="uri">
512   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
513   throughout HTTP as the means for identifying resources. URI references
514   are used to target requests, redirect responses, and define relationships.
515   HTTP does not limit what a resource may be; it merely defines an interface
516   that can be used to interact with a resource via HTTP. More information on
517   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
519  <x:anchor-alias value="URI"/>
520  <x:anchor-alias value="URI-reference"/>
521  <x:anchor-alias value="absolute-URI"/>
522  <x:anchor-alias value="relative-part"/>
523  <x:anchor-alias value="authority"/>
524  <x:anchor-alias value="fragment"/>
525  <x:anchor-alias value="path-abempty"/>
526  <x:anchor-alias value="path-absolute"/>
527  <x:anchor-alias value="port"/>
528  <x:anchor-alias value="query"/>
529  <x:anchor-alias value="uri-host"/>
530  <x:anchor-alias value="partial-URI"/>
532   This specification adopts the definitions of "URI-reference",
533   "absolute-URI", "relative-part", "fragment", "port", "host",
534   "path-abempty", "path-absolute", "query", and "authority" from
535   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
536   protocol elements that allow a relative URI without a fragment.
538<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"/>
539  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
540  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
541  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
542  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
543  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
544  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
545  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
546  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
547  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
548  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
549  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
551  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
554   Each protocol element in HTTP that allows a URI reference will indicate in
555   its ABNF production whether the element allows only a URI in absolute form
556   (absolute-URI), any relative reference (relative-ref), or some other subset
557   of the URI-reference grammar. Unless otherwise indicated, URI references
558   are parsed relative to the request target (the default base URI for both
559   the request and its corresponding response).
562<section title="http URI scheme" anchor="http.uri">
563  <x:anchor-alias value="http-URI"/>
564  <iref item="http URI scheme" primary="true"/>
565  <iref item="URI scheme" subitem="http" primary="true"/>
567   The "http" scheme is used to locate network resources via the HTTP
568   protocol.
570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
571  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
574   If the port is empty or not given, port 80 is assumed. The semantics
575   are that the identified resource is located at the server listening
576   for TCP connections on that port of that host, and the request-target
577   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
578   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
579   the path-absolute is not present in the URL, it &MUST; be given as "/" when
580   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
581   receives a host name which is not a fully qualified domain name, it
582   &MAY; add its domain to the host name it received. If a proxy receives
583   a fully qualified domain name, the proxy &MUST-NOT; change the host
584   name.
588<section title="https URI scheme" anchor="https.uri">
589   <iref item="https URI scheme"/>
590   <iref item="URI scheme" subitem="https"/>
592   <cref>TBD: Define and explain purpose of https scheme.</cref>
595  <t>
596    <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
597  </t>
601<section title="URI Comparison" anchor="uri.comparison">
603   When comparing two URIs to decide if they match or not, a client
604   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
605   URIs, with these exceptions:
606  <list style="symbols">
607    <t>A port that is empty or not given is equivalent to the default
608        port for that URI-reference;</t>
609    <t>Comparisons of host names &MUST; be case-insensitive;</t>
610    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
611    <t>An empty path-absolute is equivalent to a path-absolute of "/".</t>
612    <t>Characters other than those in the "reserved" set are equivalent to their
613       percent-encoded octets (see <xref target="RFC3986" x:fmt="," x:sec="2.1"/>).
614    </t>
615  </list>
618   For example, the following three URIs are equivalent:
620<figure><artwork type="example">
627<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
633<section title="Overall Operation" anchor="intro.overall.operation">
635   HTTP is a request/response protocol. A client sends a
636   request to the server in the form of a request method, URI, and
637   protocol version, followed by a MIME-like message containing request
638   modifiers, client information, and possible body content over a
639   connection with a server. The server responds with a status line,
640   including the message's protocol version and a success or error code,
641   followed by a MIME-like message containing server information, entity
642   metainformation, and possible entity-body content.
645   Most HTTP communication is initiated by a user agent and consists of
646   a request to be applied to a resource on some origin server. In the
647   simplest case, this may be accomplished via a single connection (v)
648   between the user agent (UA) and the origin server (O).
650<figure><artwork type="drawing">
651       request chain ------------------------&gt;
652    UA -------------------v------------------- O
653       &lt;----------------------- response chain
656   A more complicated situation occurs when one or more intermediaries
657   are present in the request/response chain. There are three common
658   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
659   forwarding agent, receiving requests for a URI in its absolute form,
660   rewriting all or part of the message, and forwarding the reformatted
661   request toward the server identified by the URI. A gateway is a
662   receiving agent, acting as a layer above some other server(s) and, if
663   necessary, translating the requests to the underlying server's
664   protocol. A tunnel acts as a relay point between two connections
665   without changing the messages; tunnels are used when the
666   communication needs to pass through an intermediary (such as a
667   firewall) even when the intermediary cannot understand the contents
668   of the messages.
670<figure><artwork type="drawing">
671       request chain --------------------------------------&gt;
672    UA -----v----- A -----v----- B -----v----- C -----v----- O
673       &lt;------------------------------------- response chain
676   The figure above shows three intermediaries (A, B, and C) between the
677   user agent and origin server. A request or response message that
678   travels the whole chain will pass through four separate connections.
679   This distinction is important because some HTTP communication options
680   may apply only to the connection with the nearest, non-tunnel
681   neighbor, only to the end-points of the chain, or to all connections
682   along the chain. Although the diagram is linear, each participant may
683   be engaged in multiple, simultaneous communications. For example, B
684   may be receiving requests from many clients other than A, and/or
685   forwarding requests to servers other than C, at the same time that it
686   is handling A's request.
689   Any party to the communication which is not acting as a tunnel may
690   employ an internal cache for handling requests. The effect of a cache
691   is that the request/response chain is shortened if one of the
692   participants along the chain has a cached response applicable to that
693   request. The following illustrates the resulting chain if B has a
694   cached copy of an earlier response from O (via C) for a request which
695   has not been cached by UA or A.
697<figure><artwork type="drawing">
698          request chain ----------&gt;
699       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
700          &lt;--------- response chain
703   Not all responses are usefully cacheable, and some requests may
704   contain modifiers which place special requirements on cache behavior.
705   HTTP requirements for cache behavior and cacheable responses are
706   defined in &caching;.
709   In fact, there are a wide variety of architectures and configurations
710   of caches and proxies currently being experimented with or deployed
711   across the World Wide Web. These systems include national hierarchies
712   of proxy caches to save transoceanic bandwidth, systems that
713   broadcast or multicast cache entries, organizations that distribute
714   subsets of cached data via CD-ROM, and so on. HTTP systems are used
715   in corporate intranets over high-bandwidth links, and for access via
716   PDAs with low-power radio links and intermittent connectivity. The
717   goal of HTTP/1.1 is to support the wide diversity of configurations
718   already deployed while introducing protocol constructs that meet the
719   needs of those who build web applications that require high
720   reliability and, failing that, at least reliable indications of
721   failure.
724   HTTP communication usually takes place over TCP/IP connections. The
725   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
726   not preclude HTTP from being implemented on top of any other protocol
727   on the Internet, or on other networks. HTTP only presumes a reliable
728   transport; any protocol that provides such guarantees can be used;
729   the mapping of the HTTP/1.1 request and response structures onto the
730   transport data units of the protocol in question is outside the scope
731   of this specification.
734   In HTTP/1.0, most implementations used a new connection for each
735   request/response exchange. In HTTP/1.1, a connection may be used for
736   one or more request/response exchanges, although connections may be
737   closed for a variety of reasons (see <xref target="persistent.connections"/>).
741<section title="Use of HTTP for proxy communication" anchor="http.proxy">
743   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
746<section title="Interception of HTTP for access control" anchor="http.intercept">
748   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
751<section title="Use of HTTP by other protocols" anchor="http.others">
753   <cref>TBD: Profiles of HTTP defined by other protocol.
754   Extensions of HTTP like WebDAV.</cref>
757<section title="Use of HTTP by media type specification" anchor="">
759   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
764<section title="Protocol Parameters" anchor="protocol.parameters">
766<section title="HTTP Version" anchor="http.version">
767  <x:anchor-alias value="HTTP-Version"/>
768  <x:anchor-alias value="HTTP-Prot-Name"/>
770   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
771   of the protocol. The protocol versioning policy is intended to allow
772   the sender to indicate the format of a message and its capacity for
773   understanding further HTTP communication, rather than the features
774   obtained via that communication. No change is made to the version
775   number for the addition of message components which do not affect
776   communication behavior or which only add to extensible field values.
777   The &lt;minor&gt; number is incremented when the changes made to the
778   protocol add features which do not change the general message parsing
779   algorithm, but which may add to the message semantics and imply
780   additional capabilities of the sender. The &lt;major&gt; number is
781   incremented when the format of a message within the protocol is
782   changed. See <xref target="RFC2145"/> for a fuller explanation.
785   The version of an HTTP message is indicated by an HTTP-Version field
786   in the first line of the message. HTTP-Version is case-sensitive.
788<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
789  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
790  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
793   Note that the major and minor numbers &MUST; be treated as separate
794   integers and that each &MAY; be incremented higher than a single digit.
795   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
796   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
797   &MUST-NOT; be sent.
800   An application that sends a request or response message that includes
801   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
802   with this specification. Applications that are at least conditionally
803   compliant with this specification &SHOULD; use an HTTP-Version of
804   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
805   not compatible with HTTP/1.0. For more details on when to send
806   specific HTTP-Version values, see <xref target="RFC2145"/>.
809   The HTTP version of an application is the highest HTTP version for
810   which the application is at least conditionally compliant.
813   Proxy and gateway applications need to be careful when forwarding
814   messages in protocol versions different from that of the application.
815   Since the protocol version indicates the protocol capability of the
816   sender, a proxy/gateway &MUST-NOT; send a message with a version
817   indicator which is greater than its actual version. If a higher
818   version request is received, the proxy/gateway &MUST; either downgrade
819   the request version, or respond with an error, or switch to tunnel
820   behavior.
823   Due to interoperability problems with HTTP/1.0 proxies discovered
824   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
825   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
826   they support. The proxy/gateway's response to that request &MUST; be in
827   the same major version as the request.
830  <t>
831    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
832    of header fields required or forbidden by the versions involved.
833  </t>
837<section title="Date/Time Formats: Full Date" anchor="">
838  <x:anchor-alias value="HTTP-date"/>
840   HTTP applications have historically allowed three different formats
841   for the representation of date/time stamps:
843<figure><artwork type="example">
844  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
845  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
846  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
849   The first format is preferred as an Internet standard and represents
850   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
851   other formats are described here only for
852   compatibility with obsolete implementations.
853   HTTP/1.1 clients and servers that parse the date value &MUST; accept
854   all three formats (for compatibility with HTTP/1.0), though they &MUST;
855   only generate the RFC 1123 format for representing HTTP-date values
856   in header fields. See <xref target="tolerant.applications"/> for further information.
859   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
860   (GMT), without exception. For the purposes of HTTP, GMT is exactly
861   equal to UTC (Coordinated Universal Time). This is indicated in the
862   first two formats by the inclusion of "GMT" as the three-letter
863   abbreviation for time zone, and &MUST; be assumed when reading the
864   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
865   additional whitespace beyond that specifically included as SP in the
866   grammar.
868<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
869  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
871<t anchor="">
872  <x:anchor-alias value="rfc1123-date"/>
873  <x:anchor-alias value="time-of-day"/>
874  <x:anchor-alias value="hour"/>
875  <x:anchor-alias value="minute"/>
876  <x:anchor-alias value="second"/>
877  <x:anchor-alias value="day-name"/>
878  <x:anchor-alias value="day"/>
879  <x:anchor-alias value="month"/>
880  <x:anchor-alias value="year"/>
881  <x:anchor-alias value="GMT"/>
882  Preferred format:
884<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"/>
885  <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>
887  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
888               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
889               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
890               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
891               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
892               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
893               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
895  <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>
896               ; e.g., 02 Jun 1982
898  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
899  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
900               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
901               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
902               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
903               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
904               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
905               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
906               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
907               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
908               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
909               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
910               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
911  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
913  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
915  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
916                 ; 00:00:00 - 23:59:59
918  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
919  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
920  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
923  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
924  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
925  same as those defined for the RFC 5322 constructs
926  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
928<t anchor="">
929  <x:anchor-alias value="obs-date"/>
930  <x:anchor-alias value="rfc850-date"/>
931  <x:anchor-alias value="asctime-date"/>
932  <x:anchor-alias value="date1"/>
933  <x:anchor-alias value="date2"/>
934  <x:anchor-alias value="date3"/>
935  <x:anchor-alias value="rfc1123-date"/>
936  <x:anchor-alias value="day-name-l"/>
937  Obsolete formats:
939<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
940  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
942<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
943  <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>
944  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
945                 ; day-month-year (e.g., 02-Jun-82)
947  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
948         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
949         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
950         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
951         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
952         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
953         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
955<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
956  <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>
957  <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> ))
958                 ; month day (e.g., Jun  2)
961  <t>
962    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
963    accepting date values that may have been sent by non-HTTP
964    applications, as is sometimes the case when retrieving or posting
965    messages via proxies/gateways to SMTP or NNTP.
966  </t>
969  <t>
970    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
971    to their usage within the protocol stream. Clients and servers are
972    not required to use these formats for user presentation, request
973    logging, etc.
974  </t>
978<section title="Transfer Codings" anchor="transfer.codings">
979  <x:anchor-alias value="transfer-coding"/>
980  <x:anchor-alias value="transfer-extension"/>
982   Transfer-coding values are used to indicate an encoding
983   transformation that has been, can be, or may need to be applied to an
984   entity-body in order to ensure "safe transport" through the network.
985   This differs from a content coding in that the transfer-coding is a
986   property of the message, not of the original entity.
988<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
989  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
990  <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> )
992<t anchor="rule.parameter">
993  <x:anchor-alias value="attribute"/>
994  <x:anchor-alias value="transfer-parameter"/>
995  <x:anchor-alias value="value"/>
996   Parameters are in  the form of attribute/value pairs.
998<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"/>
999  <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>
1000  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1001  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1004   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1005   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1006   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1009   Whenever a transfer-coding is applied to a message-body, the set of
1010   transfer-codings &MUST; include "chunked", unless the message indicates it
1011   is terminated by closing the connection. When the "chunked" transfer-coding
1012   is used, it &MUST; be the last transfer-coding applied to the
1013   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1014   than once to a message-body. These rules allow the recipient to
1015   determine the transfer-length of the message (<xref target="message.length"/>).
1018   Transfer-codings are analogous to the Content-Transfer-Encoding
1019   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1020   binary data over a 7-bit transport service. However, safe transport
1021   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1022   the only unsafe characteristic of message-bodies is the difficulty in
1023   determining the exact body length (<xref target="message.length"/>), or the desire to
1024   encrypt data over a shared transport.
1027   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1028   transfer-coding value tokens. Initially, the registry contains the
1029   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1030   "gzip", "compress", and "deflate" (&content-codings;).
1033   New transfer-coding value tokens &SHOULD; be registered in the same way
1034   as new content-coding value tokens (&content-codings;).
1037   A server which receives an entity-body with a transfer-coding it does
1038   not understand &SHOULD; return 501 (Not Implemented), and close the
1039   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1040   client.
1043<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1044  <x:anchor-alias value="chunk"/>
1045  <x:anchor-alias value="Chunked-Body"/>
1046  <x:anchor-alias value="chunk-data"/>
1047  <x:anchor-alias value="chunk-ext"/>
1048  <x:anchor-alias value="chunk-ext-name"/>
1049  <x:anchor-alias value="chunk-ext-val"/>
1050  <x:anchor-alias value="chunk-size"/>
1051  <x:anchor-alias value="last-chunk"/>
1052  <x:anchor-alias value="trailer-part"/>
1054   The chunked encoding modifies the body of a message in order to
1055   transfer it as a series of chunks, each with its own size indicator,
1056   followed by an &OPTIONAL; trailer containing entity-header fields. This
1057   allows dynamically produced content to be transferred along with the
1058   information necessary for the recipient to verify that it has
1059   received the full message.
1061<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"/>
1062  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1063                   <x:ref>last-chunk</x:ref>
1064                   <x:ref>trailer-part</x:ref>
1065                   <x:ref>CRLF</x:ref>
1067  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1068                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1069  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1070  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1072  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1073                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1074  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1075  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1076  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1077  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1080   The chunk-size field is a string of hex digits indicating the size of
1081   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1082   zero, followed by the trailer, which is terminated by an empty line.
1085   The trailer allows the sender to include additional HTTP header
1086   fields at the end of the message. The Trailer header field can be
1087   used to indicate which header fields are included in a trailer (see
1088   <xref target="header.trailer"/>).
1091   A server using chunked transfer-coding in a response &MUST-NOT; use the
1092   trailer for any header fields unless at least one of the following is
1093   true:
1094  <list style="numbers">
1095    <t>the request included a TE header field that indicates "trailers" is
1096     acceptable in the transfer-coding of the  response, as described in
1097     <xref target="header.te"/>; or,</t>
1099    <t>the server is the origin server for the response, the trailer
1100     fields consist entirely of optional metadata, and the recipient
1101     could use the message (in a manner acceptable to the origin server)
1102     without receiving this metadata.  In other words, the origin server
1103     is willing to accept the possibility that the trailer fields might
1104     be silently discarded along the path to the client.</t>
1105  </list>
1108   This requirement prevents an interoperability failure when the
1109   message is being received by an HTTP/1.1 (or later) proxy and
1110   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1111   compliance with the protocol would have necessitated a possibly
1112   infinite buffer on the proxy.
1115   A process for decoding the "chunked" transfer-coding
1116   can be represented in pseudo-code as:
1118<figure><artwork type="code">
1119  length := 0
1120  read chunk-size, chunk-ext (if any) and CRLF
1121  while (chunk-size &gt; 0) {
1122     read chunk-data and CRLF
1123     append chunk-data to entity-body
1124     length := length + chunk-size
1125     read chunk-size and CRLF
1126  }
1127  read entity-header
1128  while (entity-header not empty) {
1129     append entity-header to existing header fields
1130     read entity-header
1131  }
1132  Content-Length := length
1133  Remove "chunked" from Transfer-Encoding
1136   All HTTP/1.1 applications &MUST; be able to receive and decode the
1137   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1138   they do not understand.
1143<section title="Product Tokens" anchor="product.tokens">
1144  <x:anchor-alias value="product"/>
1145  <x:anchor-alias value="product-version"/>
1147   Product tokens are used to allow communicating applications to
1148   identify themselves by software name and version. Most fields using
1149   product tokens also allow sub-products which form a significant part
1150   of the application to be listed, separated by whitespace. By
1151   convention, the products are listed in order of their significance
1152   for identifying the application.
1154<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1155  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1156  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1159   Examples:
1161<figure><artwork type="example">
1162  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1163  Server: Apache/0.8.4
1166   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1167   used for advertising or other non-essential information. Although any
1168   token character &MAY; appear in a product-version, this token &SHOULD;
1169   only be used for a version identifier (i.e., successive versions of
1170   the same product &SHOULD; only differ in the product-version portion of
1171   the product value).
1175<section title="Quality Values" anchor="quality.values">
1176  <x:anchor-alias value="qvalue"/>
1178   Both transfer codings (TE request header, <xref target="header.te"/>)
1179   and content negotiation (&content.negotiation;) use short "floating point"
1180   numbers to indicate the relative importance ("weight") of various
1181   negotiable parameters.  A weight is normalized to a real number in
1182   the range 0 through 1, where 0 is the minimum and 1 the maximum
1183   value. If a parameter has a quality value of 0, then content with
1184   this parameter is `not acceptable' for the client. HTTP/1.1
1185   applications &MUST-NOT; generate more than three digits after the
1186   decimal point. User configuration of these values &SHOULD; also be
1187   limited in this fashion.
1189<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1190  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1191                 / ( "1" [ "." 0*3("0") ] )
1194  <t>
1195     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1196     relative degradation in desired quality.
1197  </t>
1203<section title="HTTP Message" anchor="http.message">
1205<section title="Message Types" anchor="message.types">
1206  <x:anchor-alias value="generic-message"/>
1207  <x:anchor-alias value="HTTP-message"/>
1208  <x:anchor-alias value="start-line"/>
1210   HTTP messages consist of requests from client to server and responses
1211   from server to client.
1213<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1214  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1217   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1218   message format of <xref target="RFC5322"/> for transferring entities (the payload
1219   of the message). Both types of message consist of a start-line, zero
1220   or more header fields (also known as "headers"), an empty line (i.e.,
1221   a line with nothing preceding the CRLF) indicating the end of the
1222   header fields, and possibly a message-body.
1224<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1225  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1226                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1227                    <x:ref>CRLF</x:ref>
1228                    [ <x:ref>message-body</x:ref> ]
1229  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1232   In the interest of robustness, servers &SHOULD; ignore any empty
1233   line(s) received where a Request-Line is expected. In other words, if
1234   the server is reading the protocol stream at the beginning of a
1235   message and receives a CRLF first, it should ignore the CRLF.
1238   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1239   after a POST request. To restate what is explicitly forbidden by the
1240   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1241   extra CRLF.
1244   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1245   header field. The presence of whitespace might be an attempt to trick a
1246   noncompliant implementation of HTTP into ignoring that field or processing
1247   the next line as a new request, either of which may result in security
1248   issues when implementations within the request chain interpret the
1249   same message differently. HTTP/1.1 servers &MUST; reject such a message
1250   with a 400 (Bad Request) response.
1254<section title="Message Headers" anchor="message.headers">
1255  <x:anchor-alias value="field-content"/>
1256  <x:anchor-alias value="field-name"/>
1257  <x:anchor-alias value="field-value"/>
1258  <x:anchor-alias value="message-header"/>
1260   HTTP header fields follow the same general format as Internet messages in
1261   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1262   of a name followed by a colon (":"), optional whitespace, and the field
1263   value. Field names are case-insensitive.
1265<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-header"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1266  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1267  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1268  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1269  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1272   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1273   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1274   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1275   header field-values use only a subset of the US-ASCII charset
1276   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1277   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1278   (obs-text) octets in field-content as opaque data.
1281   No whitespace is allowed between the header field-name and colon. For
1282   security reasons, any request message received containing such whitespace
1283   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1284   whitespace in a response message &MUST; be removed.
1287   The field value &MAY; be preceded by optional whitespace; a single SP is
1288   preferred. The field-value does not include any leading or trailing white
1289   space: OWS occurring before the first non-whitespace character of the
1290   field-value or after the last non-whitespace character of the field-value
1291   is ignored and &MAY; be removed without changing the meaning of the header
1292   field.
1295   Historically, HTTP header field values could be extended over multiple
1296   lines by preceding each extra line with at least one space or horizontal
1297   tab character (line folding). This specification deprecates such line
1298   folding except within the message/http media type
1299   (<xref target=""/>).
1300   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1301   (i.e., that contain any field-content that matches the obs-fold rule) unless
1302   the message is intended for packaging within the message/http media type.
1303   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1304   obs-fold whitespace with a single SP prior to interpreting the field value
1305   or forwarding the message downstream.
1307<t anchor="rule.comment">
1308  <x:anchor-alias value="comment"/>
1309  <x:anchor-alias value="ctext"/>
1310   Comments can be included in some HTTP header fields by surrounding
1311   the comment text with parentheses. Comments are only allowed in
1312   fields containing "comment" as part of their field value definition.
1313   In all other fields, parentheses are considered part of the field
1314   value.
1316<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1317  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1318  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1319                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1322   The order in which header fields with differing field names are
1323   received is not significant. However, it is "good practice" to send
1324   general-header fields first, followed by request-header or response-header
1325   fields, and ending with the entity-header fields.
1328   Multiple message-header fields with the same field-name &MAY; be
1329   present in a message if and only if the entire field-value for that
1330   header field is defined as a comma-separated list [i.e., #(values)].
1331   It &MUST; be possible to combine the multiple header fields into one
1332   "field-name: field-value" pair, without changing the semantics of the
1333   message, by appending each subsequent field-value to the first, each
1334   separated by a comma. The order in which header fields with the same
1335   field-name are received is therefore significant to the
1336   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1337   change the order of these field values when a message is forwarded.
1340  <t>
1341   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1342   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1343   can occur multiple times, but does not use the list syntax, and thus cannot
1344   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1345   for details.) Also note that the Set-Cookie2 header specified in
1346   <xref target="RFC2965"/> does not share this problem.
1347  </t>
1352<section title="Message Body" anchor="message.body">
1353  <x:anchor-alias value="message-body"/>
1355   The message-body (if any) of an HTTP message is used to carry the
1356   entity-body associated with the request or response. The message-body
1357   differs from the entity-body only when a transfer-coding has been
1358   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1360<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1361  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1362               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1365   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1366   applied by an application to ensure safe and proper transfer of the
1367   message. Transfer-Encoding is a property of the message, not of the
1368   entity, and thus &MAY; be added or removed by any application along the
1369   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1370   when certain transfer-codings may be used.)
1373   The rules for when a message-body is allowed in a message differ for
1374   requests and responses.
1377   The presence of a message-body in a request is signaled by the
1378   inclusion of a Content-Length or Transfer-Encoding header field in
1379   the request's message-headers.
1380   When a request message contains both a message-body of non-zero
1381   length and a method that does not define any semantics for that
1382   request message-body, then an origin server &SHOULD; either ignore
1383   the message-body or respond with an appropriate error message
1384   (e.g., 413).  A proxy or gateway, when presented the same request,
1385   &SHOULD; either forward the request inbound with the message-body or
1386   ignore the message-body when determining a response.
1389   For response messages, whether or not a message-body is included with
1390   a message is dependent on both the request method and the response
1391   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1392   &MUST-NOT; include a message-body, even though the presence of entity-header
1393   fields might lead one to believe they do. All 1xx
1394   (informational), 204 (No Content), and 304 (Not Modified) responses
1395   &MUST-NOT; include a message-body. All other responses do include a
1396   message-body, although it &MAY; be of zero length.
1400<section title="Message Length" anchor="message.length">
1402   The transfer-length of a message is the length of the message-body as
1403   it appears in the message; that is, after any transfer-codings have
1404   been applied. When a message-body is included with a message, the
1405   transfer-length of that body is determined by one of the following
1406   (in order of precedence):
1409  <list style="numbers">
1410    <x:lt><t>
1411     Any response message which "&MUST-NOT;" include a message-body (such
1412     as the 1xx, 204, and 304 responses and any response to a HEAD
1413     request) is always terminated by the first empty line after the
1414     header fields, regardless of the entity-header fields present in
1415     the message.
1416    </t></x:lt>
1417    <x:lt><t>
1418     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1419     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1420     is used, the transfer-length is defined by the use of this transfer-coding.
1421     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1422     is not present, the transfer-length is defined by the sender closing the connection.
1423    </t></x:lt>
1424    <x:lt><t>
1425     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1426     value in OCTETs represents both the entity-length and the
1427     transfer-length. The Content-Length header field &MUST-NOT; be sent
1428     if these two lengths are different (i.e., if a Transfer-Encoding
1429     header field is present). If a message is received with both a
1430     Transfer-Encoding header field and a Content-Length header field,
1431     the latter &MUST; be ignored.
1432    </t></x:lt>
1433    <x:lt><t>
1434     If the message uses the media type "multipart/byteranges", and the
1435     transfer-length is not otherwise specified, then this self-delimiting
1436     media type defines the transfer-length. This media type
1437     &MUST-NOT; be used unless the sender knows that the recipient can parse
1438     it; the presence in a request of a Range header with multiple byte-range
1439     specifiers from a 1.1 client implies that the client can parse
1440     multipart/byteranges responses.
1441    <list style="empty"><t>
1442       A range header might be forwarded by a 1.0 proxy that does not
1443       understand multipart/byteranges; in this case the server &MUST;
1444       delimit the message using methods defined in items 1, 3 or 5 of
1445       this section.
1446    </t></list>
1447    </t></x:lt>
1448    <x:lt><t>
1449     By the server closing the connection. (Closing the connection
1450     cannot be used to indicate the end of a request body, since that
1451     would leave no possibility for the server to send back a response.)
1452    </t></x:lt>
1453  </list>
1456   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1457   containing a message-body &MUST; include a valid Content-Length header
1458   field unless the server is known to be HTTP/1.1 compliant. If a
1459   request contains a message-body and a Content-Length is not given,
1460   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1461   determine the length of the message, or with 411 (Length Required) if
1462   it wishes to insist on receiving a valid Content-Length.
1465   All HTTP/1.1 applications that receive entities &MUST; accept the
1466   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1467   to be used for messages when the message length cannot be determined
1468   in advance.
1471   Messages &MUST-NOT; include both a Content-Length header field and a
1472   transfer-coding. If the message does include a
1473   transfer-coding, the Content-Length &MUST; be ignored.
1476   When a Content-Length is given in a message where a message-body is
1477   allowed, its field value &MUST; exactly match the number of OCTETs in
1478   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1479   invalid length is received and detected.
1483<section title="General Header Fields" anchor="general.header.fields">
1484  <x:anchor-alias value="general-header"/>
1486   There are a few header fields which have general applicability for
1487   both request and response messages, but which do not apply to the
1488   entity being transferred. These header fields apply only to the
1489   message being transmitted.
1491<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1492  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1493                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1494                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1495                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1496                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1497                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1498                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1499                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1500                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1503   General-header field names can be extended reliably only in
1504   combination with a change in the protocol version. However, new or
1505   experimental header fields may be given the semantics of general
1506   header fields if all parties in the communication recognize them to
1507   be general-header fields. Unrecognized header fields are treated as
1508   entity-header fields.
1513<section title="Request" anchor="request">
1514  <x:anchor-alias value="Request"/>
1516   A request message from a client to a server includes, within the
1517   first line of that message, the method to be applied to the resource,
1518   the identifier of the resource, and the protocol version in use.
1520<!--                 Host                      ; should be moved here eventually -->
1521<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1522  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1523                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1524                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1525                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1526                  <x:ref>CRLF</x:ref>
1527                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1530<section title="Request-Line" anchor="request-line">
1531  <x:anchor-alias value="Request-Line"/>
1533   The Request-Line begins with a method token, followed by the
1534   request-target and the protocol version, and ending with CRLF. The
1535   elements are separated by SP characters. No CR or LF is allowed
1536   except in the final CRLF sequence.
1538<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1539  <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>
1542<section title="Method" anchor="method">
1543  <x:anchor-alias value="Method"/>
1545   The Method  token indicates the method to be performed on the
1546   resource identified by the request-target. The method is case-sensitive.
1548<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1549  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1553<section title="request-target" anchor="request-target">
1554  <x:anchor-alias value="request-target"/>
1556   The request-target
1557   identifies the resource upon which to apply the request.
1559<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1560  <x:ref>request-target</x:ref> = "*"
1561                 / <x:ref>absolute-URI</x:ref>
1562                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1563                 / <x:ref>authority</x:ref>
1566   The four options for request-target are dependent on the nature of the
1567   request. The asterisk "*" means that the request does not apply to a
1568   particular resource, but to the server itself, and is only allowed
1569   when the method used does not necessarily apply to a resource. One
1570   example would be
1572<figure><artwork type="example">
1573  OPTIONS * HTTP/1.1
1576   The absolute-URI form is &REQUIRED; when the request is being made to a
1577   proxy. The proxy is requested to forward the request or service it
1578   from a valid cache, and return the response. Note that the proxy &MAY;
1579   forward the request on to another proxy or directly to the server
1580   specified by the absolute-URI. In order to avoid request loops, a
1581   proxy &MUST; be able to recognize all of its server names, including
1582   any aliases, local variations, and the numeric IP address. An example
1583   Request-Line would be:
1585<figure><artwork type="example">
1586  GET HTTP/1.1
1589   To allow for transition to absolute-URIs in all requests in future
1590   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1591   form in requests, even though HTTP/1.1 clients will only generate
1592   them in requests to proxies.
1595   The authority form is only used by the CONNECT method (&CONNECT;).
1598   The most common form of request-target is that used to identify a
1599   resource on an origin server or gateway. In this case the absolute
1600   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1601   the request-target, and the network location of the URI (authority) &MUST;
1602   be transmitted in a Host header field. For example, a client wishing
1603   to retrieve the resource above directly from the origin server would
1604   create a TCP connection to port 80 of the host "" and send
1605   the lines:
1607<figure><artwork type="example">
1608  GET /pub/WWW/TheProject.html HTTP/1.1
1609  Host:
1612   followed by the remainder of the Request. Note that the absolute path
1613   cannot be empty; if none is present in the original URI, it &MUST; be
1614   given as "/" (the server root).
1617   If a proxy receives a request without any path in the request-target and
1618   the method specified is capable of supporting the asterisk form of
1619   request-target, then the last proxy on the request chain &MUST; forward the
1620   request with "*" as the final request-target.
1623   For example, the request
1624</preamble><artwork type="example">
1625  OPTIONS HTTP/1.1
1628  would be forwarded by the proxy as
1629</preamble><artwork type="example">
1630  OPTIONS * HTTP/1.1
1631  Host:
1634   after connecting to port 8001 of host "".
1638   The request-target is transmitted in the format specified in
1639   <xref target="http.uri"/>. If the request-target is percent-encoded
1640   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1641   &MUST; decode the request-target in order to
1642   properly interpret the request. Servers &SHOULD; respond to invalid
1643   request-targets with an appropriate status code.
1646   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1647   received request-target when forwarding it to the next inbound server,
1648   except as noted above to replace a null path-absolute with "/".
1651  <t>
1652    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1653    meaning of the request when the origin server is improperly using
1654    a non-reserved URI character for a reserved purpose.  Implementors
1655    should be aware that some pre-HTTP/1.1 proxies have been known to
1656    rewrite the request-target.
1657  </t>
1660   HTTP does not place a pre-defined limit on the length of a request-target.
1661   A server &MUST; be prepared to receive URIs of unbounded length and
1662   respond with the 414 (URI Too Long) status if the received
1663   request-target would be longer than the server wishes to handle
1664   (see &status-414;).
1667   Various ad-hoc limitations on request-target length are found in practice.
1668   It is &RECOMMENDED; that all HTTP senders and recipients support
1669   request-target lengths of 8000 or more OCTETs.
1674<section title="The Resource Identified by a Request" anchor="">
1676   The exact resource identified by an Internet request is determined by
1677   examining both the request-target and the Host header field.
1680   An origin server that does not allow resources to differ by the
1681   requested host &MAY; ignore the Host header field value when
1682   determining the resource identified by an HTTP/1.1 request. (But see
1683   <xref target=""/>
1684   for other requirements on Host support in HTTP/1.1.)
1687   An origin server that does differentiate resources based on the host
1688   requested (sometimes referred to as virtual hosts or vanity host
1689   names) &MUST; use the following rules for determining the requested
1690   resource on an HTTP/1.1 request:
1691  <list style="numbers">
1692    <t>If request-target is an absolute-URI, the host is part of the
1693     request-target. Any Host header field value in the request &MUST; be
1694     ignored.</t>
1695    <t>If the request-target is not an absolute-URI, and the request includes
1696     a Host header field, the host is determined by the Host header
1697     field value.</t>
1698    <t>If the host as determined by rule 1 or 2 is not a valid host on
1699     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1700  </list>
1703   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1704   attempt to use heuristics (e.g., examination of the URI path for
1705   something unique to a particular host) in order to determine what
1706   exact resource is being requested.
1713<section title="Response" anchor="response">
1714  <x:anchor-alias value="Response"/>
1716   After receiving and interpreting a request message, a server responds
1717   with an HTTP response message.
1719<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1720  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1721                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1722                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1723                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1724                  <x:ref>CRLF</x:ref>
1725                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1728<section title="Status-Line" anchor="status-line">
1729  <x:anchor-alias value="Status-Line"/>
1731   The first line of a Response message is the Status-Line, consisting
1732   of the protocol version followed by a numeric status code and its
1733   associated textual phrase, with each element separated by SP
1734   characters. No CR or LF is allowed except in the final CRLF sequence.
1736<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1737  <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>
1740<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1741  <x:anchor-alias value="Reason-Phrase"/>
1742  <x:anchor-alias value="Status-Code"/>
1744   The Status-Code element is a 3-digit integer result code of the
1745   attempt to understand and satisfy the request. These codes are fully
1746   defined in &status-codes;.  The Reason Phrase exists for the sole
1747   purpose of providing a textual description associated with the numeric
1748   status code, out of deference to earlier Internet application protocols
1749   that were more frequently used with interactive text clients.
1750   A client &SHOULD; ignore the content of the Reason Phrase.
1753   The first digit of the Status-Code defines the class of response. The
1754   last two digits do not have any categorization role. There are 5
1755   values for the first digit:
1756  <list style="symbols">
1757    <t>
1758      1xx: Informational - Request received, continuing process
1759    </t>
1760    <t>
1761      2xx: Success - The action was successfully received,
1762        understood, and accepted
1763    </t>
1764    <t>
1765      3xx: Redirection - Further action must be taken in order to
1766        complete the request
1767    </t>
1768    <t>
1769      4xx: Client Error - The request contains bad syntax or cannot
1770        be fulfilled
1771    </t>
1772    <t>
1773      5xx: Server Error - The server failed to fulfill an apparently
1774        valid request
1775    </t>
1776  </list>
1778<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1779  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1780  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1788<section title="Connections" anchor="connections">
1790<section title="Persistent Connections" anchor="persistent.connections">
1792<section title="Purpose" anchor="persistent.purpose">
1794   Prior to persistent connections, a separate TCP connection was
1795   established to fetch each URL, increasing the load on HTTP servers
1796   and causing congestion on the Internet. The use of inline images and
1797   other associated data often require a client to make multiple
1798   requests of the same server in a short amount of time. Analysis of
1799   these performance problems and results from a prototype
1800   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1801   measurements of actual HTTP/1.1 implementations show good
1802   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1803   T/TCP <xref target="Tou1998"/>.
1806   Persistent HTTP connections have a number of advantages:
1807  <list style="symbols">
1808      <t>
1809        By opening and closing fewer TCP connections, CPU time is saved
1810        in routers and hosts (clients, servers, proxies, gateways,
1811        tunnels, or caches), and memory used for TCP protocol control
1812        blocks can be saved in hosts.
1813      </t>
1814      <t>
1815        HTTP requests and responses can be pipelined on a connection.
1816        Pipelining allows a client to make multiple requests without
1817        waiting for each response, allowing a single TCP connection to
1818        be used much more efficiently, with much lower elapsed time.
1819      </t>
1820      <t>
1821        Network congestion is reduced by reducing the number of packets
1822        caused by TCP opens, and by allowing TCP sufficient time to
1823        determine the congestion state of the network.
1824      </t>
1825      <t>
1826        Latency on subsequent requests is reduced since there is no time
1827        spent in TCP's connection opening handshake.
1828      </t>
1829      <t>
1830        HTTP can evolve more gracefully, since errors can be reported
1831        without the penalty of closing the TCP connection. Clients using
1832        future versions of HTTP might optimistically try a new feature,
1833        but if communicating with an older server, retry with old
1834        semantics after an error is reported.
1835      </t>
1836    </list>
1839   HTTP implementations &SHOULD; implement persistent connections.
1843<section title="Overall Operation" anchor="persistent.overall">
1845   A significant difference between HTTP/1.1 and earlier versions of
1846   HTTP is that persistent connections are the default behavior of any
1847   HTTP connection. That is, unless otherwise indicated, the client
1848   &SHOULD; assume that the server will maintain a persistent connection,
1849   even after error responses from the server.
1852   Persistent connections provide a mechanism by which a client and a
1853   server can signal the close of a TCP connection. This signaling takes
1854   place using the Connection header field (<xref target="header.connection"/>). Once a close
1855   has been signaled, the client &MUST-NOT; send any more requests on that
1856   connection.
1859<section title="Negotiation" anchor="persistent.negotiation">
1861   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1862   maintain a persistent connection unless a Connection header including
1863   the connection-token "close" was sent in the request. If the server
1864   chooses to close the connection immediately after sending the
1865   response, it &SHOULD; send a Connection header including the
1866   connection-token close.
1869   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1870   decide to keep it open based on whether the response from a server
1871   contains a Connection header with the connection-token close. In case
1872   the client does not want to maintain a connection for more than that
1873   request, it &SHOULD; send a Connection header including the
1874   connection-token close.
1877   If either the client or the server sends the close token in the
1878   Connection header, that request becomes the last one for the
1879   connection.
1882   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1883   maintained for HTTP versions less than 1.1 unless it is explicitly
1884   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1885   compatibility with HTTP/1.0 clients.
1888   In order to remain persistent, all messages on the connection &MUST;
1889   have a self-defined message length (i.e., one not defined by closure
1890   of the connection), as described in <xref target="message.length"/>.
1894<section title="Pipelining" anchor="pipelining">
1896   A client that supports persistent connections &MAY; "pipeline" its
1897   requests (i.e., send multiple requests without waiting for each
1898   response). A server &MUST; send its responses to those requests in the
1899   same order that the requests were received.
1902   Clients which assume persistent connections and pipeline immediately
1903   after connection establishment &SHOULD; be prepared to retry their
1904   connection if the first pipelined attempt fails. If a client does
1905   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1906   persistent. Clients &MUST; also be prepared to resend their requests if
1907   the server closes the connection before sending all of the
1908   corresponding responses.
1911   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1912   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1913   premature termination of the transport connection could lead to
1914   indeterminate results. A client wishing to send a non-idempotent
1915   request &SHOULD; wait to send that request until it has received the
1916   response status for the previous request.
1921<section title="Proxy Servers" anchor="persistent.proxy">
1923   It is especially important that proxies correctly implement the
1924   properties of the Connection header field as specified in <xref target="header.connection"/>.
1927   The proxy server &MUST; signal persistent connections separately with
1928   its clients and the origin servers (or other proxy servers) that it
1929   connects to. Each persistent connection applies to only one transport
1930   link.
1933   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1934   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
1935   for information and discussion of the problems with the Keep-Alive header
1936   implemented by many HTTP/1.0 clients).
1940<section title="Practical Considerations" anchor="persistent.practical">
1942   Servers will usually have some time-out value beyond which they will
1943   no longer maintain an inactive connection. Proxy servers might make
1944   this a higher value since it is likely that the client will be making
1945   more connections through the same server. The use of persistent
1946   connections places no requirements on the length (or existence) of
1947   this time-out for either the client or the server.
1950   When a client or server wishes to time-out it &SHOULD; issue a graceful
1951   close on the transport connection. Clients and servers &SHOULD; both
1952   constantly watch for the other side of the transport close, and
1953   respond to it as appropriate. If a client or server does not detect
1954   the other side's close promptly it could cause unnecessary resource
1955   drain on the network.
1958   A client, server, or proxy &MAY; close the transport connection at any
1959   time. For example, a client might have started to send a new request
1960   at the same time that the server has decided to close the "idle"
1961   connection. From the server's point of view, the connection is being
1962   closed while it was idle, but from the client's point of view, a
1963   request is in progress.
1966   This means that clients, servers, and proxies &MUST; be able to recover
1967   from asynchronous close events. Client software &SHOULD; reopen the
1968   transport connection and retransmit the aborted sequence of requests
1969   without user interaction so long as the request sequence is
1970   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1971   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1972   human operator the choice of retrying the request(s). Confirmation by
1973   user-agent software with semantic understanding of the application
1974   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1975   be repeated if the second sequence of requests fails.
1978   Servers &SHOULD; always respond to at least one request per connection,
1979   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1980   middle of transmitting a response, unless a network or client failure
1981   is suspected.
1984   Clients that use persistent connections &SHOULD; limit the number of
1985   simultaneous connections that they maintain to a given server. A
1986   single-user client &SHOULD-NOT; maintain more than 2 connections with
1987   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1988   another server or proxy, where N is the number of simultaneously
1989   active users. These guidelines are intended to improve HTTP response
1990   times and avoid congestion.
1995<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1997<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1999   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2000   flow control mechanisms to resolve temporary overloads, rather than
2001   terminating connections with the expectation that clients will retry.
2002   The latter technique can exacerbate network congestion.
2006<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2008   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2009   the network connection for an error status while it is transmitting
2010   the request. If the client sees an error status, it &SHOULD;
2011   immediately cease transmitting the body. If the body is being sent
2012   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2013   empty trailer &MAY; be used to prematurely mark the end of the message.
2014   If the body was preceded by a Content-Length header, the client &MUST;
2015   close the connection.
2019<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2021   The purpose of the 100 (Continue) status (see &status-100;) is to
2022   allow a client that is sending a request message with a request body
2023   to determine if the origin server is willing to accept the request
2024   (based on the request headers) before the client sends the request
2025   body. In some cases, it might either be inappropriate or highly
2026   inefficient for the client to send the body if the server will reject
2027   the message without looking at the body.
2030   Requirements for HTTP/1.1 clients:
2031  <list style="symbols">
2032    <t>
2033        If a client will wait for a 100 (Continue) response before
2034        sending the request body, it &MUST; send an Expect request-header
2035        field (&header-expect;) with the "100-continue" expectation.
2036    </t>
2037    <t>
2038        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2039        with the "100-continue" expectation if it does not intend
2040        to send a request body.
2041    </t>
2042  </list>
2045   Because of the presence of older implementations, the protocol allows
2046   ambiguous situations in which a client may send "Expect: 100-continue"
2047   without receiving either a 417 (Expectation Failed) status
2048   or a 100 (Continue) status. Therefore, when a client sends this
2049   header field to an origin server (possibly via a proxy) from which it
2050   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2051   for an indefinite period before sending the request body.
2054   Requirements for HTTP/1.1 origin servers:
2055  <list style="symbols">
2056    <t> Upon receiving a request which includes an Expect request-header
2057        field with the "100-continue" expectation, an origin server &MUST;
2058        either respond with 100 (Continue) status and continue to read
2059        from the input stream, or respond with a final status code. The
2060        origin server &MUST-NOT; wait for the request body before sending
2061        the 100 (Continue) response. If it responds with a final status
2062        code, it &MAY; close the transport connection or it &MAY; continue
2063        to read and discard the rest of the request.  It &MUST-NOT;
2064        perform the requested method if it returns a final status code.
2065    </t>
2066    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2067        the request message does not include an Expect request-header
2068        field with the "100-continue" expectation, and &MUST-NOT; send a
2069        100 (Continue) response if such a request comes from an HTTP/1.0
2070        (or earlier) client. There is an exception to this rule: for
2071        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2072        status in response to an HTTP/1.1 PUT or POST request that does
2073        not include an Expect request-header field with the "100-continue"
2074        expectation. This exception, the purpose of which is
2075        to minimize any client processing delays associated with an
2076        undeclared wait for 100 (Continue) status, applies only to
2077        HTTP/1.1 requests, and not to requests with any other HTTP-version
2078        value.
2079    </t>
2080    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2081        already received some or all of the request body for the
2082        corresponding request.
2083    </t>
2084    <t> An origin server that sends a 100 (Continue) response &MUST;
2085    ultimately send a final status code, once the request body is
2086        received and processed, unless it terminates the transport
2087        connection prematurely.
2088    </t>
2089    <t> If an origin server receives a request that does not include an
2090        Expect request-header field with the "100-continue" expectation,
2091        the request includes a request body, and the server responds
2092        with a final status code before reading the entire request body
2093        from the transport connection, then the server &SHOULD-NOT;  close
2094        the transport connection until it has read the entire request,
2095        or until the client closes the connection. Otherwise, the client
2096        might not reliably receive the response message. However, this
2097        requirement is not be construed as preventing a server from
2098        defending itself against denial-of-service attacks, or from
2099        badly broken client implementations.
2100      </t>
2101    </list>
2104   Requirements for HTTP/1.1 proxies:
2105  <list style="symbols">
2106    <t> If a proxy receives a request that includes an Expect request-header
2107        field with the "100-continue" expectation, and the proxy
2108        either knows that the next-hop server complies with HTTP/1.1 or
2109        higher, or does not know the HTTP version of the next-hop
2110        server, it &MUST; forward the request, including the Expect header
2111        field.
2112    </t>
2113    <t> If the proxy knows that the version of the next-hop server is
2114        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2115        respond with a 417 (Expectation Failed) status.
2116    </t>
2117    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2118        numbers received from recently-referenced next-hop servers.
2119    </t>
2120    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2121        request message was received from an HTTP/1.0 (or earlier)
2122        client and did not include an Expect request-header field with
2123        the "100-continue" expectation. This requirement overrides the
2124        general rule for forwarding of 1xx responses (see &status-1xx;).
2125    </t>
2126  </list>
2130<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2132   If an HTTP/1.1 client sends a request which includes a request body,
2133   but which does not include an Expect request-header field with the
2134   "100-continue" expectation, and if the client is not directly
2135   connected to an HTTP/1.1 origin server, and if the client sees the
2136   connection close before receiving any status from the server, the
2137   client &SHOULD; retry the request.  If the client does retry this
2138   request, it &MAY; use the following "binary exponential backoff"
2139   algorithm to be assured of obtaining a reliable response:
2140  <list style="numbers">
2141    <t>
2142      Initiate a new connection to the server
2143    </t>
2144    <t>
2145      Transmit the request-headers
2146    </t>
2147    <t>
2148      Initialize a variable R to the estimated round-trip time to the
2149         server (e.g., based on the time it took to establish the
2150         connection), or to a constant value of 5 seconds if the round-trip
2151         time is not available.
2152    </t>
2153    <t>
2154       Compute T = R * (2**N), where N is the number of previous
2155         retries of this request.
2156    </t>
2157    <t>
2158       Wait either for an error response from the server, or for T
2159         seconds (whichever comes first)
2160    </t>
2161    <t>
2162       If no error response is received, after T seconds transmit the
2163         body of the request.
2164    </t>
2165    <t>
2166       If client sees that the connection is closed prematurely,
2167         repeat from step 1 until the request is accepted, an error
2168         response is received, or the user becomes impatient and
2169         terminates the retry process.
2170    </t>
2171  </list>
2174   If at any point an error status is received, the client
2175  <list style="symbols">
2176      <t>&SHOULD-NOT;  continue and</t>
2178      <t>&SHOULD; close the connection if it has not completed sending the
2179        request message.</t>
2180    </list>
2187<section title="Header Field Definitions" anchor="header.fields">
2189   This section defines the syntax and semantics of HTTP/1.1 header fields
2190   related to message framing and transport protocols.
2193   For entity-header fields, both sender and recipient refer to either the
2194   client or the server, depending on who sends and who receives the entity.
2197<section title="Connection" anchor="header.connection">
2198  <iref primary="true" item="Connection header" x:for-anchor=""/>
2199  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2200  <x:anchor-alias value="Connection"/>
2201  <x:anchor-alias value="connection-token"/>
2202  <x:anchor-alias value="Connection-v"/>
2204   The general-header field "Connection" allows the sender to specify
2205   options that are desired for that particular connection and &MUST-NOT;
2206   be communicated by proxies over further connections.
2209   The Connection header's value has the following grammar:
2211<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2212  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2213  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2214  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2217   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2218   message is forwarded and, for each connection-token in this field,
2219   remove any header field(s) from the message with the same name as the
2220   connection-token. Connection options are signaled by the presence of
2221   a connection-token in the Connection header field, not by any
2222   corresponding additional header field(s), since the additional header
2223   field may not be sent if there are no parameters associated with that
2224   connection option.
2227   Message headers listed in the Connection header &MUST-NOT; include
2228   end-to-end headers, such as Cache-Control.
2231   HTTP/1.1 defines the "close" connection option for the sender to
2232   signal that the connection will be closed after completion of the
2233   response. For example,
2235<figure><artwork type="example">
2236  Connection: close
2239   in either the request or the response header fields indicates that
2240   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2241   after the current request/response is complete.
2244   An HTTP/1.1 client that does not support persistent connections &MUST;
2245   include the "close" connection option in every request message.
2248   An HTTP/1.1 server that does not support persistent connections &MUST;
2249   include the "close" connection option in every response message that
2250   does not have a 1xx (informational) status code.
2253   A system receiving an HTTP/1.0 (or lower-version) message that
2254   includes a Connection header &MUST;, for each connection-token in this
2255   field, remove and ignore any header field(s) from the message with
2256   the same name as the connection-token. This protects against mistaken
2257   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2261<section title="Content-Length" anchor="header.content-length">
2262  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2263  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2264  <x:anchor-alias value="Content-Length"/>
2265  <x:anchor-alias value="Content-Length-v"/>
2267   The entity-header field "Content-Length" indicates the size of the
2268   entity-body, in number of OCTETs, sent to the recipient or,
2269   in the case of the HEAD method, the size of the entity-body that
2270   would have been sent had the request been a GET.
2272<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2273  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2274  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2277   An example is
2279<figure><artwork type="example">
2280  Content-Length: 3495
2283   Applications &SHOULD; use this field to indicate the transfer-length of
2284   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2287   Any Content-Length greater than or equal to zero is a valid value.
2288   <xref target="message.length"/> describes how to determine the length of a message-body
2289   if a Content-Length is not given.
2292   Note that the meaning of this field is significantly different from
2293   the corresponding definition in MIME, where it is an optional field
2294   used within the "message/external-body" content-type. In HTTP, it
2295   &SHOULD; be sent whenever the message's length can be determined prior
2296   to being transferred, unless this is prohibited by the rules in
2297   <xref target="message.length"/>.
2301<section title="Date" anchor="">
2302  <iref primary="true" item="Date header" x:for-anchor=""/>
2303  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2304  <x:anchor-alias value="Date"/>
2305  <x:anchor-alias value="Date-v"/>
2307   The general-header field "Date" represents the date and time at which
2308   the message was originated, having the same semantics as orig-date in
2309   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2310   HTTP-date, as described in <xref target=""/>;
2311   it &MUST; be sent in rfc1123-date format.
2313<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2314  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2315  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2318   An example is
2320<figure><artwork type="example">
2321  Date: Tue, 15 Nov 1994 08:12:31 GMT
2324   Origin servers &MUST; include a Date header field in all responses,
2325   except in these cases:
2326  <list style="numbers">
2327      <t>If the response status code is 100 (Continue) or 101 (Switching
2328         Protocols), the response &MAY; include a Date header field, at
2329         the server's option.</t>
2331      <t>If the response status code conveys a server error, e.g. 500
2332         (Internal Server Error) or 503 (Service Unavailable), and it is
2333         inconvenient or impossible to generate a valid Date.</t>
2335      <t>If the server does not have a clock that can provide a
2336         reasonable approximation of the current time, its responses
2337         &MUST-NOT; include a Date header field. In this case, the rules
2338         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2339  </list>
2342   A received message that does not have a Date header field &MUST; be
2343   assigned one by the recipient if the message will be cached by that
2344   recipient or gatewayed via a protocol which requires a Date. An HTTP
2345   implementation without a clock &MUST-NOT; cache responses without
2346   revalidating them on every use. An HTTP cache, especially a shared
2347   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2348   clock with a reliable external standard.
2351   Clients &SHOULD; only send a Date header field in messages that include
2352   an entity-body, as in the case of the PUT and POST requests, and even
2353   then it is optional. A client without a clock &MUST-NOT; send a Date
2354   header field in a request.
2357   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2358   time subsequent to the generation of the message. It &SHOULD; represent
2359   the best available approximation of the date and time of message
2360   generation, unless the implementation has no means of generating a
2361   reasonably accurate date and time. In theory, the date ought to
2362   represent the moment just before the entity is generated. In
2363   practice, the date can be generated at any time during the message
2364   origination without affecting its semantic value.
2367<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2369   Some origin server implementations might not have a clock available.
2370   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2371   values to a response, unless these values were associated
2372   with the resource by a system or user with a reliable clock. It &MAY;
2373   assign an Expires value that is known, at or before server
2374   configuration time, to be in the past (this allows "pre-expiration"
2375   of responses without storing separate Expires values for each
2376   resource).
2381<section title="Host" anchor="">
2382  <iref primary="true" item="Host header" x:for-anchor=""/>
2383  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2384  <x:anchor-alias value="Host"/>
2385  <x:anchor-alias value="Host-v"/>
2387   The request-header field "Host" specifies the Internet host and port
2388   number of the resource being requested, as obtained from the original
2389   URI given by the user or referring resource (generally an http URI,
2390   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2391   the naming authority of the origin server or gateway given by the
2392   original URL. This allows the origin server or gateway to
2393   differentiate between internally-ambiguous URLs, such as the root "/"
2394   URL of a server for multiple host names on a single IP address.
2396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2397  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2398  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2401   A "host" without any trailing port information implies the default
2402   port for the service requested (e.g., "80" for an HTTP URL). For
2403   example, a request on the origin server for
2404   &lt;; would properly include:
2406<figure><artwork type="example">
2407  GET /pub/WWW/ HTTP/1.1
2408  Host:
2411   A client &MUST; include a Host header field in all HTTP/1.1 request
2412   messages. If the requested URI does not include an Internet host
2413   name for the service being requested, then the Host header field &MUST;
2414   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2415   request message it forwards does contain an appropriate Host header
2416   field that identifies the service being requested by the proxy. All
2417   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2418   status code to any HTTP/1.1 request message which lacks a Host header
2419   field.
2422   See Sections <xref target="" format="counter"/>
2423   and <xref target="" format="counter"/>
2424   for other requirements relating to Host.
2428<section title="TE" anchor="header.te">
2429  <iref primary="true" item="TE header" x:for-anchor=""/>
2430  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2431  <x:anchor-alias value="TE"/>
2432  <x:anchor-alias value="TE-v"/>
2433  <x:anchor-alias value="t-codings"/>
2434  <x:anchor-alias value="te-params"/>
2435  <x:anchor-alias value="te-ext"/>
2437   The request-header field "TE" indicates what extension transfer-codings
2438   it is willing to accept in the response and whether or not it is
2439   willing to accept trailer fields in a chunked transfer-coding. Its
2440   value may consist of the keyword "trailers" and/or a comma-separated
2441   list of extension transfer-coding names with optional accept
2442   parameters (as described in <xref target="transfer.codings"/>).
2444<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2445  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2446  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2447  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2448  <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> )
2449  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2452   The presence of the keyword "trailers" indicates that the client is
2453   willing to accept trailer fields in a chunked transfer-coding, as
2454   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2455   transfer-coding values even though it does not itself represent a
2456   transfer-coding.
2459   Examples of its use are:
2461<figure><artwork type="example">
2462  TE: deflate
2463  TE:
2464  TE: trailers, deflate;q=0.5
2467   The TE header field only applies to the immediate connection.
2468   Therefore, the keyword &MUST; be supplied within a Connection header
2469   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2472   A server tests whether a transfer-coding is acceptable, according to
2473   a TE field, using these rules:
2474  <list style="numbers">
2475    <x:lt>
2476      <t>The "chunked" transfer-coding is always acceptable. If the
2477         keyword "trailers" is listed, the client indicates that it is
2478         willing to accept trailer fields in the chunked response on
2479         behalf of itself and any downstream clients. The implication is
2480         that, if given, the client is stating that either all
2481         downstream clients are willing to accept trailer fields in the
2482         forwarded response, or that it will attempt to buffer the
2483         response on behalf of downstream recipients.
2484      </t><t>
2485         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2486         chunked response such that a client can be assured of buffering
2487         the entire response.</t>
2488    </x:lt>
2489    <x:lt>
2490      <t>If the transfer-coding being tested is one of the transfer-codings
2491         listed in the TE field, then it is acceptable unless it
2492         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2493         qvalue of 0 means "not acceptable.")</t>
2494    </x:lt>
2495    <x:lt>
2496      <t>If multiple transfer-codings are acceptable, then the
2497         acceptable transfer-coding with the highest non-zero qvalue is
2498         preferred.  The "chunked" transfer-coding always has a qvalue
2499         of 1.</t>
2500    </x:lt>
2501  </list>
2504   If the TE field-value is empty or if no TE field is present, the only
2505   transfer-coding is "chunked". A message with no transfer-coding is
2506   always acceptable.
2510<section title="Trailer" anchor="header.trailer">
2511  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2512  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2513  <x:anchor-alias value="Trailer"/>
2514  <x:anchor-alias value="Trailer-v"/>
2516   The general field "Trailer" indicates that the given set of
2517   header fields is present in the trailer of a message encoded with
2518   chunked transfer-coding.
2520<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2521  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2522  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2525   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2526   message using chunked transfer-coding with a non-empty trailer. Doing
2527   so allows the recipient to know which header fields to expect in the
2528   trailer.
2531   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2532   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2533   trailer fields in a "chunked" transfer-coding.
2536   Message header fields listed in the Trailer header field &MUST-NOT;
2537   include the following header fields:
2538  <list style="symbols">
2539    <t>Transfer-Encoding</t>
2540    <t>Content-Length</t>
2541    <t>Trailer</t>
2542  </list>
2546<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2547  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2548  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2549  <x:anchor-alias value="Transfer-Encoding"/>
2550  <x:anchor-alias value="Transfer-Encoding-v"/>
2552   The general-header "Transfer-Encoding" field indicates what (if any)
2553   type of transformation has been applied to the message body in order
2554   to safely transfer it between the sender and the recipient. This
2555   differs from the content-coding in that the transfer-coding is a
2556   property of the message, not of the entity.
2558<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2559  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2560                        <x:ref>Transfer-Encoding-v</x:ref>
2561  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2564   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2566<figure><artwork type="example">
2567  Transfer-Encoding: chunked
2570   If multiple encodings have been applied to an entity, the transfer-codings
2571   &MUST; be listed in the order in which they were applied.
2572   Additional information about the encoding parameters &MAY; be provided
2573   by other entity-header fields not defined by this specification.
2576   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2577   header.
2581<section title="Upgrade" anchor="header.upgrade">
2582  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2583  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2584  <x:anchor-alias value="Upgrade"/>
2585  <x:anchor-alias value="Upgrade-v"/>
2587   The general-header "Upgrade" allows the client to specify what
2588   additional communication protocols it supports and would like to use
2589   if the server finds it appropriate to switch protocols. The server
2590   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2591   response to indicate which protocol(s) are being switched.
2593<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2594  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2595  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2598   For example,
2600<figure><artwork type="example">
2601  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2604   The Upgrade header field is intended to provide a simple mechanism
2605   for transition from HTTP/1.1 to some other, incompatible protocol. It
2606   does so by allowing the client to advertise its desire to use another
2607   protocol, such as a later version of HTTP with a higher major version
2608   number, even though the current request has been made using HTTP/1.1.
2609   This eases the difficult transition between incompatible protocols by
2610   allowing the client to initiate a request in the more commonly
2611   supported protocol while indicating to the server that it would like
2612   to use a "better" protocol if available (where "better" is determined
2613   by the server, possibly according to the nature of the method and/or
2614   resource being requested).
2617   The Upgrade header field only applies to switching application-layer
2618   protocols upon the existing transport-layer connection. Upgrade
2619   cannot be used to insist on a protocol change; its acceptance and use
2620   by the server is optional. The capabilities and nature of the
2621   application-layer communication after the protocol change is entirely
2622   dependent upon the new protocol chosen, although the first action
2623   after changing the protocol &MUST; be a response to the initial HTTP
2624   request containing the Upgrade header field.
2627   The Upgrade header field only applies to the immediate connection.
2628   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2629   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2630   HTTP/1.1 message.
2633   The Upgrade header field cannot be used to indicate a switch to a
2634   protocol on a different connection. For that purpose, it is more
2635   appropriate to use a 301, 302, 303, or 305 redirection response.
2638   This specification only defines the protocol name "HTTP" for use by
2639   the family of Hypertext Transfer Protocols, as defined by the HTTP
2640   version rules of <xref target="http.version"/> and future updates to this
2641   specification. Any token can be used as a protocol name; however, it
2642   will only be useful if both the client and server associate the name
2643   with the same protocol.
2647<section title="Via" anchor="header.via">
2648  <iref primary="true" item="Via header" x:for-anchor=""/>
2649  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2650  <x:anchor-alias value="protocol-name"/>
2651  <x:anchor-alias value="protocol-version"/>
2652  <x:anchor-alias value="pseudonym"/>
2653  <x:anchor-alias value="received-by"/>
2654  <x:anchor-alias value="received-protocol"/>
2655  <x:anchor-alias value="Via"/>
2656  <x:anchor-alias value="Via-v"/>
2658   The general-header field "Via" &MUST; be used by gateways and proxies to
2659   indicate the intermediate protocols and recipients between the user
2660   agent and the server on requests, and between the origin server and
2661   the client on responses. It is analogous to the "Received" field defined in
2662   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2663   avoiding request loops, and identifying the protocol capabilities of
2664   all senders along the request/response chain.
2666<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><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"/>
2667  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2668  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2669                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2670  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2671  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2672  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2673  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2674  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2677   The received-protocol indicates the protocol version of the message
2678   received by the server or client along each segment of the
2679   request/response chain. The received-protocol version is appended to
2680   the Via field value when the message is forwarded so that information
2681   about the protocol capabilities of upstream applications remains
2682   visible to all recipients.
2685   The protocol-name is optional if and only if it would be "HTTP". The
2686   received-by field is normally the host and optional port number of a
2687   recipient server or client that subsequently forwarded the message.
2688   However, if the real host is considered to be sensitive information,
2689   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2690   be assumed to be the default port of the received-protocol.
2693   Multiple Via field values represents each proxy or gateway that has
2694   forwarded the message. Each recipient &MUST; append its information
2695   such that the end result is ordered according to the sequence of
2696   forwarding applications.
2699   Comments &MAY; be used in the Via header field to identify the software
2700   of the recipient proxy or gateway, analogous to the User-Agent and
2701   Server header fields. However, all comments in the Via field are
2702   optional and &MAY; be removed by any recipient prior to forwarding the
2703   message.
2706   For example, a request message could be sent from an HTTP/1.0 user
2707   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2708   forward the request to a public proxy at, which completes
2709   the request by forwarding it to the origin server at
2710   The request received by would then have the following
2711   Via header field:
2713<figure><artwork type="example">
2714  Via: 1.0 fred, 1.1 (Apache/1.1)
2717   Proxies and gateways used as a portal through a network firewall
2718   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2719   the firewall region. This information &SHOULD; only be propagated if
2720   explicitly enabled. If not enabled, the received-by host of any host
2721   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2722   for that host.
2725   For organizations that have strong privacy requirements for hiding
2726   internal structures, a proxy &MAY; combine an ordered subsequence of
2727   Via header field entries with identical received-protocol values into
2728   a single such entry. For example,
2730<figure><artwork type="example">
2731  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2734        could be collapsed to
2736<figure><artwork type="example">
2737  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2740   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2741   under the same organizational control and the hosts have already been
2742   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2743   have different received-protocol values.
2749<section title="IANA Considerations" anchor="IANA.considerations">
2750<section title="Message Header Registration" anchor="message.header.registration">
2752   The Message Header Registry located at <eref target=""/> should be updated
2753   with the permanent registrations below (see <xref target="RFC3864"/>):
2755<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2756<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2757   <ttcol>Header Field Name</ttcol>
2758   <ttcol>Protocol</ttcol>
2759   <ttcol>Status</ttcol>
2760   <ttcol>Reference</ttcol>
2762   <c>Connection</c>
2763   <c>http</c>
2764   <c>standard</c>
2765   <c>
2766      <xref target="header.connection"/>
2767   </c>
2768   <c>Content-Length</c>
2769   <c>http</c>
2770   <c>standard</c>
2771   <c>
2772      <xref target="header.content-length"/>
2773   </c>
2774   <c>Date</c>
2775   <c>http</c>
2776   <c>standard</c>
2777   <c>
2778      <xref target=""/>
2779   </c>
2780   <c>Host</c>
2781   <c>http</c>
2782   <c>standard</c>
2783   <c>
2784      <xref target=""/>
2785   </c>
2786   <c>TE</c>
2787   <c>http</c>
2788   <c>standard</c>
2789   <c>
2790      <xref target="header.te"/>
2791   </c>
2792   <c>Trailer</c>
2793   <c>http</c>
2794   <c>standard</c>
2795   <c>
2796      <xref target="header.trailer"/>
2797   </c>
2798   <c>Transfer-Encoding</c>
2799   <c>http</c>
2800   <c>standard</c>
2801   <c>
2802      <xref target="header.transfer-encoding"/>
2803   </c>
2804   <c>Upgrade</c>
2805   <c>http</c>
2806   <c>standard</c>
2807   <c>
2808      <xref target="header.upgrade"/>
2809   </c>
2810   <c>Via</c>
2811   <c>http</c>
2812   <c>standard</c>
2813   <c>
2814      <xref target="header.via"/>
2815   </c>
2819   The change controller is: "IETF ( - Internet Engineering Task Force".
2823<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2825   The entry for the "http" URI Scheme in the registry located at
2826   <eref target=""/>
2827   should be updated to point to <xref target="http.uri"/> of this document
2828   (see <xref target="RFC4395"/>).
2832<section title="Internet Media Type Registrations" anchor="">
2834   This document serves as the specification for the Internet media types
2835   "message/http" and "application/http". The following is to be registered with
2836   IANA (see <xref target="RFC4288"/>).
2838<section title="Internet Media Type message/http" anchor="">
2839<iref item="Media Type" subitem="message/http" primary="true"/>
2840<iref item="message/http Media Type" primary="true"/>
2842   The message/http type can be used to enclose a single HTTP request or
2843   response message, provided that it obeys the MIME restrictions for all
2844   "message" types regarding line length and encodings.
2847  <list style="hanging" x:indent="12em">
2848    <t hangText="Type name:">
2849      message
2850    </t>
2851    <t hangText="Subtype name:">
2852      http
2853    </t>
2854    <t hangText="Required parameters:">
2855      none
2856    </t>
2857    <t hangText="Optional parameters:">
2858      version, msgtype
2859      <list style="hanging">
2860        <t hangText="version:">
2861          The HTTP-Version number of the enclosed message
2862          (e.g., "1.1"). If not present, the version can be
2863          determined from the first line of the body.
2864        </t>
2865        <t hangText="msgtype:">
2866          The message type -- "request" or "response". If not
2867          present, the type can be determined from the first
2868          line of the body.
2869        </t>
2870      </list>
2871    </t>
2872    <t hangText="Encoding considerations:">
2873      only "7bit", "8bit", or "binary" are permitted
2874    </t>
2875    <t hangText="Security considerations:">
2876      none
2877    </t>
2878    <t hangText="Interoperability considerations:">
2879      none
2880    </t>
2881    <t hangText="Published specification:">
2882      This specification (see <xref target=""/>).
2883    </t>
2884    <t hangText="Applications that use this media type:">
2885    </t>
2886    <t hangText="Additional information:">
2887      <list style="hanging">
2888        <t hangText="Magic number(s):">none</t>
2889        <t hangText="File extension(s):">none</t>
2890        <t hangText="Macintosh file type code(s):">none</t>
2891      </list>
2892    </t>
2893    <t hangText="Person and email address to contact for further information:">
2894      See Authors Section.
2895    </t>
2896                <t hangText="Intended usage:">
2897                  COMMON
2898    </t>
2899                <t hangText="Restrictions on usage:">
2900                  none
2901    </t>
2902    <t hangText="Author/Change controller:">
2903      IESG
2904    </t>
2905  </list>
2908<section title="Internet Media Type application/http" anchor="">
2909<iref item="Media Type" subitem="application/http" primary="true"/>
2910<iref item="application/http Media Type" primary="true"/>
2912   The application/http type can be used to enclose a pipeline of one or more
2913   HTTP request or response messages (not intermixed).
2916  <list style="hanging" x:indent="12em">
2917    <t hangText="Type name:">
2918      application
2919    </t>
2920    <t hangText="Subtype name:">
2921      http
2922    </t>
2923    <t hangText="Required parameters:">
2924      none
2925    </t>
2926    <t hangText="Optional parameters:">
2927      version, msgtype
2928      <list style="hanging">
2929        <t hangText="version:">
2930          The HTTP-Version number of the enclosed messages
2931          (e.g., "1.1"). If not present, the version can be
2932          determined from the first line of the body.
2933        </t>
2934        <t hangText="msgtype:">
2935          The message type -- "request" or "response". If not
2936          present, the type can be determined from the first
2937          line of the body.
2938        </t>
2939      </list>
2940    </t>
2941    <t hangText="Encoding considerations:">
2942      HTTP messages enclosed by this type
2943      are in "binary" format; use of an appropriate
2944      Content-Transfer-Encoding is required when
2945      transmitted via E-mail.
2946    </t>
2947    <t hangText="Security considerations:">
2948      none
2949    </t>
2950    <t hangText="Interoperability considerations:">
2951      none
2952    </t>
2953    <t hangText="Published specification:">
2954      This specification (see <xref target=""/>).
2955    </t>
2956    <t hangText="Applications that use this media type:">
2957    </t>
2958    <t hangText="Additional information:">
2959      <list style="hanging">
2960        <t hangText="Magic number(s):">none</t>
2961        <t hangText="File extension(s):">none</t>
2962        <t hangText="Macintosh file type code(s):">none</t>
2963      </list>
2964    </t>
2965    <t hangText="Person and email address to contact for further information:">
2966      See Authors Section.
2967    </t>
2968                <t hangText="Intended usage:">
2969                  COMMON
2970    </t>
2971                <t hangText="Restrictions on usage:">
2972                  none
2973    </t>
2974    <t hangText="Author/Change controller:">
2975      IESG
2976    </t>
2977  </list>
2984<section title="Security Considerations" anchor="security.considerations">
2986   This section is meant to inform application developers, information
2987   providers, and users of the security limitations in HTTP/1.1 as
2988   described by this document. The discussion does not include
2989   definitive solutions to the problems revealed, though it does make
2990   some suggestions for reducing security risks.
2993<section title="Personal Information" anchor="personal.information">
2995   HTTP clients are often privy to large amounts of personal information
2996   (e.g. the user's name, location, mail address, passwords, encryption
2997   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2998   leakage of this information.
2999   We very strongly recommend that a convenient interface be provided
3000   for the user to control dissemination of such information, and that
3001   designers and implementors be particularly careful in this area.
3002   History shows that errors in this area often create serious security
3003   and/or privacy problems and generate highly adverse publicity for the
3004   implementor's company.
3008<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3010   A server is in the position to save personal data about a user's
3011   requests which might identify their reading patterns or subjects of
3012   interest. This information is clearly confidential in nature and its
3013   handling can be constrained by law in certain countries. People using
3014   HTTP to provide data are responsible for ensuring that
3015   such material is not distributed without the permission of any
3016   individuals that are identifiable by the published results.
3020<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3022   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3023   the documents returned by HTTP requests to be only those that were
3024   intended by the server administrators. If an HTTP server translates
3025   HTTP URIs directly into file system calls, the server &MUST; take
3026   special care not to serve files that were not intended to be
3027   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3028   other operating systems use ".." as a path component to indicate a
3029   directory level above the current one. On such a system, an HTTP
3030   server &MUST; disallow any such construct in the request-target if it
3031   would otherwise allow access to a resource outside those intended to
3032   be accessible via the HTTP server. Similarly, files intended for
3033   reference only internally to the server (such as access control
3034   files, configuration files, and script code) &MUST; be protected from
3035   inappropriate retrieval, since they might contain sensitive
3036   information. Experience has shown that minor bugs in such HTTP server
3037   implementations have turned into security risks.
3041<section title="DNS Spoofing" anchor="dns.spoofing">
3043   Clients using HTTP rely heavily on the Domain Name Service, and are
3044   thus generally prone to security attacks based on the deliberate
3045   mis-association of IP addresses and DNS names. Clients need to be
3046   cautious in assuming the continuing validity of an IP number/DNS name
3047   association.
3050   In particular, HTTP clients &SHOULD; rely on their name resolver for
3051   confirmation of an IP number/DNS name association, rather than
3052   caching the result of previous host name lookups. Many platforms
3053   already can cache host name lookups locally when appropriate, and
3054   they &SHOULD; be configured to do so. It is proper for these lookups to
3055   be cached, however, only when the TTL (Time To Live) information
3056   reported by the name server makes it likely that the cached
3057   information will remain useful.
3060   If HTTP clients cache the results of host name lookups in order to
3061   achieve a performance improvement, they &MUST; observe the TTL
3062   information reported by DNS.
3065   If HTTP clients do not observe this rule, they could be spoofed when
3066   a previously-accessed server's IP address changes. As network
3067   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3068   possibility of this form of attack will grow. Observing this
3069   requirement thus reduces this potential security vulnerability.
3072   This requirement also improves the load-balancing behavior of clients
3073   for replicated servers using the same DNS name and reduces the
3074   likelihood of a user's experiencing failure in accessing sites which
3075   use that strategy.
3079<section title="Proxies and Caching" anchor="attack.proxies">
3081   By their very nature, HTTP proxies are men-in-the-middle, and
3082   represent an opportunity for man-in-the-middle attacks. Compromise of
3083   the systems on which the proxies run can result in serious security
3084   and privacy problems. Proxies have access to security-related
3085   information, personal information about individual users and
3086   organizations, and proprietary information belonging to users and
3087   content providers. A compromised proxy, or a proxy implemented or
3088   configured without regard to security and privacy considerations,
3089   might be used in the commission of a wide range of potential attacks.
3092   Proxy operators should protect the systems on which proxies run as
3093   they would protect any system that contains or transports sensitive
3094   information. In particular, log information gathered at proxies often
3095   contains highly sensitive personal information, and/or information
3096   about organizations. Log information should be carefully guarded, and
3097   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3100   Proxy implementors should consider the privacy and security
3101   implications of their design and coding decisions, and of the
3102   configuration options they provide to proxy operators (especially the
3103   default configuration).
3106   Users of a proxy need to be aware that they are no trustworthier than
3107   the people who run the proxy; HTTP itself cannot solve this problem.
3110   The judicious use of cryptography, when appropriate, may suffice to
3111   protect against a broad range of security and privacy attacks. Such
3112   cryptography is beyond the scope of the HTTP/1.1 specification.
3116<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3118   They exist. They are hard to defend against. Research continues.
3119   Beware.
3124<section title="Acknowledgments" anchor="ack">
3126   HTTP has evolved considerably over the years. It has
3127   benefited from a large and active developer community--the many
3128   people who have participated on the www-talk mailing list--and it is
3129   that community which has been most responsible for the success of
3130   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3131   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3132   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3133   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3134   VanHeyningen deserve special recognition for their efforts in
3135   defining early aspects of the protocol.
3138   This document has benefited greatly from the comments of all those
3139   participating in the HTTP-WG. In addition to those already mentioned,
3140   the following individuals have contributed to this specification:
3143   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3144   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3145   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3146   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3147   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3148   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3149   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3150   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3151   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3152   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3153   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3154   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3155   Josh Cohen.
3158   Thanks to the "cave men" of Palo Alto. You know who you are.
3161   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3162   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3163   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3164   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3165   Larry Masinter for their help. And thanks go particularly to Jeff
3166   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3169   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3170   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3171   discovery of many of the problems that this document attempts to
3172   rectify.
3175   This specification makes heavy use of the augmented BNF and generic
3176   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3177   reuses many of the definitions provided by Nathaniel Borenstein and
3178   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3179   specification will help reduce past confusion over the relationship
3180   between HTTP and Internet mail message formats.
3187<references title="Normative References">
3189<reference anchor="ISO-8859-1">
3190  <front>
3191    <title>
3192     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3193    </title>
3194    <author>
3195      <organization>International Organization for Standardization</organization>
3196    </author>
3197    <date year="1998"/>
3198  </front>
3199  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3202<reference anchor="Part2">
3203  <front>
3204    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3205    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3206      <organization abbrev="Day Software">Day Software</organization>
3207      <address><email></email></address>
3208    </author>
3209    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3210      <organization>One Laptop per Child</organization>
3211      <address><email></email></address>
3212    </author>
3213    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3214      <organization abbrev="HP">Hewlett-Packard Company</organization>
3215      <address><email></email></address>
3216    </author>
3217    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3218      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3219      <address><email></email></address>
3220    </author>
3221    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3222      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3223      <address><email></email></address>
3224    </author>
3225    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3226      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3227      <address><email></email></address>
3228    </author>
3229    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3230      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3231      <address><email></email></address>
3232    </author>
3233    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3234      <organization abbrev="W3C">World Wide Web Consortium</organization>
3235      <address><email></email></address>
3236    </author>
3237    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3238      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3239      <address><email></email></address>
3240    </author>
3241    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3242  </front>
3243  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3244  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3247<reference anchor="Part3">
3248  <front>
3249    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3250    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3251      <organization abbrev="Day Software">Day Software</organization>
3252      <address><email></email></address>
3253    </author>
3254    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3255      <organization>One Laptop per Child</organization>
3256      <address><email></email></address>
3257    </author>
3258    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3259      <organization abbrev="HP">Hewlett-Packard Company</organization>
3260      <address><email></email></address>
3261    </author>
3262    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3263      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3264      <address><email></email></address>
3265    </author>
3266    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3267      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3268      <address><email></email></address>
3269    </author>
3270    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3271      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3272      <address><email></email></address>
3273    </author>
3274    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3275      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3276      <address><email></email></address>
3277    </author>
3278    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3279      <organization abbrev="W3C">World Wide Web Consortium</organization>
3280      <address><email></email></address>
3281    </author>
3282    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3283      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3284      <address><email></email></address>
3285    </author>
3286    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3287  </front>
3288  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3289  <x:source href="p3-payload.xml" basename="p3-payload"/>
3292<reference anchor="Part5">
3293  <front>
3294    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3295    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3296      <organization abbrev="Day Software">Day Software</organization>
3297      <address><email></email></address>
3298    </author>
3299    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3300      <organization>One Laptop per Child</organization>
3301      <address><email></email></address>
3302    </author>
3303    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3304      <organization abbrev="HP">Hewlett-Packard Company</organization>
3305      <address><email></email></address>
3306    </author>
3307    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3308      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3309      <address><email></email></address>
3310    </author>
3311    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3312      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3313      <address><email></email></address>
3314    </author>
3315    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3316      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3317      <address><email></email></address>
3318    </author>
3319    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3320      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3321      <address><email></email></address>
3322    </author>
3323    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3324      <organization abbrev="W3C">World Wide Web Consortium</organization>
3325      <address><email></email></address>
3326    </author>
3327    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3328      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3329      <address><email></email></address>
3330    </author>
3331    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3332  </front>
3333  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3334  <x:source href="p5-range.xml" basename="p5-range"/>
3337<reference anchor="Part6">
3338  <front>
3339    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3340    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3341      <organization abbrev="Day Software">Day Software</organization>
3342      <address><email></email></address>
3343    </author>
3344    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3345      <organization>One Laptop per Child</organization>
3346      <address><email></email></address>
3347    </author>
3348    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3349      <organization abbrev="HP">Hewlett-Packard Company</organization>
3350      <address><email></email></address>
3351    </author>
3352    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3353      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3354      <address><email></email></address>
3355    </author>
3356    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3357      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3358      <address><email></email></address>
3359    </author>
3360    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3361      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3362      <address><email></email></address>
3363    </author>
3364    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3365      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3366      <address><email></email></address>
3367    </author>
3368    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3369      <organization abbrev="W3C">World Wide Web Consortium</organization>
3370      <address><email></email></address>
3371    </author>
3372    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3373      <organization />
3374      <address><email></email></address>
3375    </author>
3376    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3377      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3378      <address><email></email></address>
3379    </author>
3380    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3381  </front>
3382  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3383  <x:source href="p6-cache.xml" basename="p6-cache"/>
3386<reference anchor="RFC5234">
3387  <front>
3388    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3389    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3390      <organization>Brandenburg InternetWorking</organization>
3391      <address>
3392      <postal>
3393      <street>675 Spruce Dr.</street>
3394      <city>Sunnyvale</city>
3395      <region>CA</region>
3396      <code>94086</code>
3397      <country>US</country></postal>
3398      <phone>+1.408.246.8253</phone>
3399      <email></email></address> 
3400    </author>
3401    <author initials="P." surname="Overell" fullname="Paul Overell">
3402      <organization>THUS plc.</organization>
3403      <address>
3404      <postal>
3405      <street>1/2 Berkeley Square</street>
3406      <street>99 Berkely Street</street>
3407      <city>Glasgow</city>
3408      <code>G3 7HR</code>
3409      <country>UK</country></postal>
3410      <email></email></address>
3411    </author>
3412    <date month="January" year="2008"/>
3413  </front>
3414  <seriesInfo name="STD" value="68"/>
3415  <seriesInfo name="RFC" value="5234"/>
3418<reference anchor="RFC2119">
3419  <front>
3420    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3421    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3422      <organization>Harvard University</organization>
3423      <address><email></email></address>
3424    </author>
3425    <date month="March" year="1997"/>
3426  </front>
3427  <seriesInfo name="BCP" value="14"/>
3428  <seriesInfo name="RFC" value="2119"/>
3431<reference anchor="RFC3986">
3432 <front>
3433  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3434  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3435    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3436    <address>
3437       <email></email>
3438       <uri></uri>
3439    </address>
3440  </author>
3441  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3442    <organization abbrev="Day Software">Day Software</organization>
3443    <address>
3444      <email></email>
3445      <uri></uri>
3446    </address>
3447  </author>
3448  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3449    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3450    <address>
3451      <email></email>
3452      <uri></uri>
3453    </address>
3454  </author>
3455  <date month='January' year='2005'></date>
3456 </front>
3457 <seriesInfo name="RFC" value="3986"/>
3458 <seriesInfo name="STD" value="66"/>
3461<reference anchor="USASCII">
3462  <front>
3463    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3464    <author>
3465      <organization>American National Standards Institute</organization>
3466    </author>
3467    <date year="1986"/>
3468  </front>
3469  <seriesInfo name="ANSI" value="X3.4"/>
3474<references title="Informative References">
3476<reference anchor="Nie1997" target="">
3477  <front>
3478    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3479    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3480      <organization/>
3481    </author>
3482    <author initials="J." surname="Gettys" fullname="J. Gettys">
3483      <organization/>
3484    </author>
3485    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3486      <organization/>
3487    </author>
3488    <author initials="H." surname="Lie" fullname="H. Lie">
3489      <organization/>
3490    </author>
3491    <author initials="C." surname="Lilley" fullname="C. Lilley">
3492      <organization/>
3493    </author>
3494    <date year="1997" month="September"/>
3495  </front>
3496  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3499<reference anchor="Pad1995" target="">
3500  <front>
3501    <title>Improving HTTP Latency</title>
3502    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3503      <organization/>
3504    </author>
3505    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3506      <organization/>
3507    </author>
3508    <date year="1995" month="December"/>
3509  </front>
3510  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3513<reference anchor="RFC1123">
3514  <front>
3515    <title>Requirements for Internet Hosts - Application and Support</title>
3516    <author initials="R." surname="Braden" fullname="Robert Braden">
3517      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3518      <address><email>Braden@ISI.EDU</email></address>
3519    </author>
3520    <date month="October" year="1989"/>
3521  </front>
3522  <seriesInfo name="STD" value="3"/>
3523  <seriesInfo name="RFC" value="1123"/>
3526<reference anchor="RFC1305">
3527  <front>
3528    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3529    <author initials="D." surname="Mills" fullname="David L. Mills">
3530      <organization>University of Delaware, Electrical Engineering Department</organization>
3531      <address><email></email></address>
3532    </author>
3533    <date month="March" year="1992"/>
3534  </front>
3535  <seriesInfo name="RFC" value="1305"/>
3538<reference anchor="RFC1900">
3539  <front>
3540    <title>Renumbering Needs Work</title>
3541    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3542      <organization>CERN, Computing and Networks Division</organization>
3543      <address><email></email></address>
3544    </author>
3545    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3546      <organization>cisco Systems</organization>
3547      <address><email></email></address>
3548    </author>
3549    <date month="February" year="1996"/>
3550  </front>
3551  <seriesInfo name="RFC" value="1900"/>
3554<reference anchor="RFC1945">
3555  <front>
3556    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3557    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3558      <organization>MIT, Laboratory for Computer Science</organization>
3559      <address><email></email></address>
3560    </author>
3561    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3562      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3563      <address><email></email></address>
3564    </author>
3565    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3566      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3567      <address><email></email></address>
3568    </author>
3569    <date month="May" year="1996"/>
3570  </front>
3571  <seriesInfo name="RFC" value="1945"/>
3574<reference anchor="RFC2045">
3575  <front>
3576    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3577    <author initials="N." surname="Freed" fullname="Ned Freed">
3578      <organization>Innosoft International, Inc.</organization>
3579      <address><email></email></address>
3580    </author>
3581    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3582      <organization>First Virtual Holdings</organization>
3583      <address><email></email></address>
3584    </author>
3585    <date month="November" year="1996"/>
3586  </front>
3587  <seriesInfo name="RFC" value="2045"/>
3590<reference anchor="RFC2047">
3591  <front>
3592    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3593    <author initials="K." surname="Moore" fullname="Keith Moore">
3594      <organization>University of Tennessee</organization>
3595      <address><email></email></address>
3596    </author>
3597    <date month="November" year="1996"/>
3598  </front>
3599  <seriesInfo name="RFC" value="2047"/>
3602<reference anchor="RFC2068">
3603  <front>
3604    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3605    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3606      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3607      <address><email></email></address>
3608    </author>
3609    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3610      <organization>MIT Laboratory for Computer Science</organization>
3611      <address><email></email></address>
3612    </author>
3613    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3614      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3615      <address><email></email></address>
3616    </author>
3617    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3618      <organization>MIT Laboratory for Computer Science</organization>
3619      <address><email></email></address>
3620    </author>
3621    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3622      <organization>MIT Laboratory for Computer Science</organization>
3623      <address><email></email></address>
3624    </author>
3625    <date month="January" year="1997"/>
3626  </front>
3627  <seriesInfo name="RFC" value="2068"/>
3630<reference anchor='RFC2109'>
3631  <front>
3632    <title>HTTP State Management Mechanism</title>
3633    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3634      <organization>Bell Laboratories, Lucent Technologies</organization>
3635      <address><email></email></address>
3636    </author>
3637    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3638      <organization>Netscape Communications Corp.</organization>
3639      <address><email></email></address>
3640    </author>
3641    <date year='1997' month='February' />
3642  </front>
3643  <seriesInfo name='RFC' value='2109' />
3646<reference anchor="RFC2145">
3647  <front>
3648    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3649    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3650      <organization>Western Research Laboratory</organization>
3651      <address><email></email></address>
3652    </author>
3653    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3654      <organization>Department of Information and Computer Science</organization>
3655      <address><email></email></address>
3656    </author>
3657    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3658      <organization>MIT Laboratory for Computer Science</organization>
3659      <address><email></email></address>
3660    </author>
3661    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3662      <organization>W3 Consortium</organization>
3663      <address><email></email></address>
3664    </author>
3665    <date month="May" year="1997"/>
3666  </front>
3667  <seriesInfo name="RFC" value="2145"/>
3670<reference anchor="RFC2616">
3671  <front>
3672    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3673    <author initials="R." surname="Fielding" fullname="R. Fielding">
3674      <organization>University of California, Irvine</organization>
3675      <address><email></email></address>
3676    </author>
3677    <author initials="J." surname="Gettys" fullname="J. Gettys">
3678      <organization>W3C</organization>
3679      <address><email></email></address>
3680    </author>
3681    <author initials="J." surname="Mogul" fullname="J. Mogul">
3682      <organization>Compaq Computer Corporation</organization>
3683      <address><email></email></address>
3684    </author>
3685    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3686      <organization>MIT Laboratory for Computer Science</organization>
3687      <address><email></email></address>
3688    </author>
3689    <author initials="L." surname="Masinter" fullname="L. Masinter">
3690      <organization>Xerox Corporation</organization>
3691      <address><email></email></address>
3692    </author>
3693    <author initials="P." surname="Leach" fullname="P. Leach">
3694      <organization>Microsoft Corporation</organization>
3695      <address><email></email></address>
3696    </author>
3697    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3698      <organization>W3C</organization>
3699      <address><email></email></address>
3700    </author>
3701    <date month="June" year="1999"/>
3702  </front>
3703  <seriesInfo name="RFC" value="2616"/>
3706<reference anchor='RFC2818'>
3707  <front>
3708    <title>HTTP Over TLS</title>
3709    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3710      <organization>RTFM, Inc.</organization>
3711      <address><email></email></address>
3712    </author>
3713    <date year='2000' month='May' />
3714  </front>
3715  <seriesInfo name='RFC' value='2818' />
3718<reference anchor='RFC2965'>
3719  <front>
3720    <title>HTTP State Management Mechanism</title>
3721    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3722      <organization>Bell Laboratories, Lucent Technologies</organization>
3723      <address><email></email></address>
3724    </author>
3725    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3726      <organization>, Inc.</organization>
3727      <address><email></email></address>
3728    </author>
3729    <date year='2000' month='October' />
3730  </front>
3731  <seriesInfo name='RFC' value='2965' />
3734<reference anchor='RFC3864'>
3735  <front>
3736    <title>Registration Procedures for Message Header Fields</title>
3737    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3738      <organization>Nine by Nine</organization>
3739      <address><email></email></address>
3740    </author>
3741    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3742      <organization>BEA Systems</organization>
3743      <address><email></email></address>
3744    </author>
3745    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3746      <organization>HP Labs</organization>
3747      <address><email></email></address>
3748    </author>
3749    <date year='2004' month='September' />
3750  </front>
3751  <seriesInfo name='BCP' value='90' />
3752  <seriesInfo name='RFC' value='3864' />
3755<reference anchor="RFC4288">
3756  <front>
3757    <title>Media Type Specifications and Registration Procedures</title>
3758    <author initials="N." surname="Freed" fullname="N. Freed">
3759      <organization>Sun Microsystems</organization>
3760      <address>
3761        <email></email>
3762      </address>
3763    </author>
3764    <author initials="J." surname="Klensin" fullname="J. Klensin">
3765      <organization/>
3766      <address>
3767        <email></email>
3768      </address>
3769    </author>
3770    <date year="2005" month="December"/>
3771  </front>
3772  <seriesInfo name="BCP" value="13"/>
3773  <seriesInfo name="RFC" value="4288"/>
3776<reference anchor='RFC4395'>
3777  <front>
3778    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3779    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3780      <organization>AT&amp;T Laboratories</organization>
3781      <address>
3782        <email></email>
3783      </address>
3784    </author>
3785    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3786      <organization>Qualcomm, Inc.</organization>
3787      <address>
3788        <email></email>
3789      </address>
3790    </author>
3791    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3792      <organization>Adobe Systems</organization>
3793      <address>
3794        <email></email>
3795      </address>
3796    </author>
3797    <date year='2006' month='February' />
3798  </front>
3799  <seriesInfo name='BCP' value='115' />
3800  <seriesInfo name='RFC' value='4395' />
3803<reference anchor="RFC5322">
3804  <front>
3805    <title>Internet Message Format</title>
3806    <author initials="P." surname="Resnick" fullname="P. Resnick">
3807      <organization>Qualcomm Incorporated</organization>
3808    </author>
3809    <date year="2008" month="October"/>
3810  </front>
3811  <seriesInfo name="RFC" value="5322"/>
3814<reference anchor="Kri2001" target="">
3815  <front>
3816    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3817    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3818      <organization/>
3819    </author>
3820    <date year="2001" month="November"/>
3821  </front>
3822  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3825<reference anchor="Spe" target="">
3826  <front>
3827  <title>Analysis of HTTP Performance Problems</title>
3828  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3829    <organization/>
3830  </author>
3831  <date/>
3832  </front>
3835<reference anchor="Tou1998" target="">
3836  <front>
3837  <title>Analysis of HTTP Performance</title>
3838  <author initials="J." surname="Touch" fullname="Joe Touch">
3839    <organization>USC/Information Sciences Institute</organization>
3840    <address><email></email></address>
3841  </author>
3842  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3843    <organization>USC/Information Sciences Institute</organization>
3844    <address><email></email></address>
3845  </author>
3846  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3847    <organization>USC/Information Sciences Institute</organization>
3848    <address><email></email></address>
3849  </author>
3850  <date year="1998" month="Aug"/>
3851  </front>
3852  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3853  <annotation>(original report dated Aug. 1996)</annotation>
3859<section title="Tolerant Applications" anchor="tolerant.applications">
3861   Although this document specifies the requirements for the generation
3862   of HTTP/1.1 messages, not all applications will be correct in their
3863   implementation. We therefore recommend that operational applications
3864   be tolerant of deviations whenever those deviations can be
3865   interpreted unambiguously.
3868   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3869   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3870   accept any amount of WSP characters between fields, even though
3871   only a single SP is required.
3874   The line terminator for message-header fields is the sequence CRLF.
3875   However, we recommend that applications, when parsing such headers,
3876   recognize a single LF as a line terminator and ignore the leading CR.
3879   The character set of an entity-body &SHOULD; be labeled as the lowest
3880   common denominator of the character codes used within that body, with
3881   the exception that not labeling the entity is preferred over labeling
3882   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3885   Additional rules for requirements on parsing and encoding of dates
3886   and other potential problems with date encodings include:
3889  <list style="symbols">
3890     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3891        which appears to be more than 50 years in the future is in fact
3892        in the past (this helps solve the "year 2000" problem).</t>
3894     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3895        Expires date as earlier than the proper value, but &MUST-NOT;
3896        internally represent a parsed Expires date as later than the
3897        proper value.</t>
3899     <t>All expiration-related calculations &MUST; be done in GMT. The
3900        local time zone &MUST-NOT; influence the calculation or comparison
3901        of an age or expiration time.</t>
3903     <t>If an HTTP header incorrectly carries a date value with a time
3904        zone other than GMT, it &MUST; be converted into GMT using the
3905        most conservative possible conversion.</t>
3906  </list>
3910<section title="Compatibility with Previous Versions" anchor="compatibility">
3912   HTTP has been in use by the World-Wide Web global information initiative
3913   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3914   was a simple protocol for hypertext data transfer across the Internet
3915   with only a single method and no metadata.
3916   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3917   methods and MIME-like messaging that could include metadata about the data
3918   transferred and modifiers on the request/response semantics. However,
3919   HTTP/1.0 did not sufficiently take into consideration the effects of
3920   hierarchical proxies, caching, the need for persistent connections, or
3921   name-based virtual hosts. The proliferation of incompletely-implemented
3922   applications calling themselves "HTTP/1.0" further necessitated a
3923   protocol version change in order for two communicating applications
3924   to determine each other's true capabilities.
3927   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3928   requirements that enable reliable implementations, adding only
3929   those new features that will either be safely ignored by an HTTP/1.0
3930   recipient or only sent when communicating with a party advertising
3931   compliance with HTTP/1.1.
3934   It is beyond the scope of a protocol specification to mandate
3935   compliance with previous versions. HTTP/1.1 was deliberately
3936   designed, however, to make supporting previous versions easy. It is
3937   worth noting that, at the time of composing this specification
3938   (1996), we would expect commercial HTTP/1.1 servers to:
3939  <list style="symbols">
3940     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3941        1.1 requests;</t>
3943     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3944        1.1;</t>
3946     <t>respond appropriately with a message in the same major version
3947        used by the client.</t>
3948  </list>
3951   And we would expect HTTP/1.1 clients to:
3952  <list style="symbols">
3953     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3954        responses;</t>
3956     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3957        1.1.</t>
3958  </list>
3961   For most implementations of HTTP/1.0, each connection is established
3962   by the client prior to the request and closed by the server after
3963   sending the response. Some implementations implement the Keep-Alive
3964   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3967<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3969   This section summarizes major differences between versions HTTP/1.0
3970   and HTTP/1.1.
3973<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
3975   The requirements that clients and servers support the Host request-header,
3976   report an error if the Host request-header (<xref target=""/>) is
3977   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3978   are among the most important changes defined by this
3979   specification.
3982   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3983   addresses and servers; there was no other established mechanism for
3984   distinguishing the intended server of a request than the IP address
3985   to which that request was directed. The changes outlined above will
3986   allow the Internet, once older HTTP clients are no longer common, to
3987   support multiple Web sites from a single IP address, greatly
3988   simplifying large operational Web servers, where allocation of many
3989   IP addresses to a single host has created serious problems. The
3990   Internet will also be able to recover the IP addresses that have been
3991   allocated for the sole purpose of allowing special-purpose domain
3992   names to be used in root-level HTTP URLs. Given the rate of growth of
3993   the Web, and the number of servers already deployed, it is extremely
3994   important that all implementations of HTTP (including updates to
3995   existing HTTP/1.0 applications) correctly implement these
3996   requirements:
3997  <list style="symbols">
3998     <t>Both clients and servers &MUST; support the Host request-header.</t>
4000     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4002     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4003        request does not include a Host request-header.</t>
4005     <t>Servers &MUST; accept absolute URIs.</t>
4006  </list>
4011<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4013   Some clients and servers might wish to be compatible with some
4014   previous implementations of persistent connections in HTTP/1.0
4015   clients and servers. Persistent connections in HTTP/1.0 are
4016   explicitly negotiated as they are not the default behavior. HTTP/1.0
4017   experimental implementations of persistent connections are faulty,
4018   and the new facilities in HTTP/1.1 are designed to rectify these
4019   problems. The problem was that some existing 1.0 clients may be
4020   sending Keep-Alive to a proxy server that doesn't understand
4021   Connection, which would then erroneously forward it to the next
4022   inbound server, which would establish the Keep-Alive connection and
4023   result in a hung HTTP/1.0 proxy waiting for the close on the
4024   response. The result is that HTTP/1.0 clients must be prevented from
4025   using Keep-Alive when talking to proxies.
4028   However, talking to proxies is the most important use of persistent
4029   connections, so that prohibition is clearly unacceptable. Therefore,
4030   we need some other mechanism for indicating a persistent connection
4031   is desired, which is safe to use even when talking to an old proxy
4032   that ignores Connection. Persistent connections are the default for
4033   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4034   declaring non-persistence. See <xref target="header.connection"/>.
4037   The original HTTP/1.0 form of persistent connections (the Connection:
4038   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4042<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4044   This specification has been carefully audited to correct and
4045   disambiguate key word usage; RFC 2068 had many problems in respect to
4046   the conventions laid out in <xref target="RFC2119"/>.
4049   Transfer-coding and message lengths all interact in ways that
4050   required fixing exactly when chunked encoding is used (to allow for
4051   transfer encoding that may not be self delimiting); it was important
4052   to straighten out exactly how message lengths are computed. (Sections
4053   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4054   <xref target="header.content-length" format="counter"/>,
4055   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4058   The use and interpretation of HTTP version numbers has been clarified
4059   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4060   version they support to deal with problems discovered in HTTP/1.0
4061   implementations (<xref target="http.version"/>)
4064   Quality Values of zero should indicate that "I don't want something"
4065   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4068   Transfer-coding had significant problems, particularly with
4069   interactions with chunked encoding. The solution is that transfer-codings
4070   become as full fledged as content-codings. This involves
4071   adding an IANA registry for transfer-codings (separate from content
4072   codings), a new header field (TE) and enabling trailer headers in the
4073   future. Transfer encoding is a major performance benefit, so it was
4074   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4075   interoperability problem that could have occurred due to interactions
4076   between authentication trailers, chunked encoding and HTTP/1.0
4077   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4078   and <xref target="header.te" format="counter"/>)
4082<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4084  Empty list elements in list productions have been deprecated.
4085  (<xref target="notation.abnf"/>)
4088  Rules about implicit linear whitespace between certain grammar productions
4089  have been removed; now it's only allowed when specifically pointed out
4090  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4091  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4092  Non-ASCII content in header fields and reason phrase has been obsoleted and
4093  made opaque (the TEXT rule was removed)
4094  (<xref target="basic.rules"/>)
4097  Clarify that HTTP-Version is case sensitive.
4098  (<xref target="http.version"/>)
4101  Remove reference to non-existant identity transfer-coding value tokens.
4102  (Sections <xref format="counter" target="transfer.codings"/> and
4103  <xref format="counter" target="message.length"/>)
4106  Clarification that the chunk length does not include
4107  the count of the octets in the chunk header and trailer.
4108  (<xref target="chunked.transfer.encoding"/>)
4111  Require that invalid whitespace around field-names be rejected.
4112  (<xref target="message.headers"/>)
4115  Update use of abs_path production from RFC1808 to the path-absolute + query
4116  components of RFC3986.
4117  (<xref target="request-target"/>)
4120  Clarify exactly when close connection options must be sent.
4121  (<xref target="header.connection"/>)
4126<section title="Terminology" anchor="terminology">
4128   This specification uses a number of terms to refer to the roles
4129   played by participants in, and objects of, the HTTP communication.
4132  <iref item="cache"/>
4133  <x:dfn>cache</x:dfn>
4134  <list>
4135    <t>
4136      A program's local store of response messages and the subsystem
4137      that controls its message storage, retrieval, and deletion. A
4138      cache stores cacheable responses in order to reduce the response
4139      time and network bandwidth consumption on future, equivalent
4140      requests. Any client or server may include a cache, though a cache
4141      cannot be used by a server that is acting as a tunnel.
4142    </t>
4143  </list>
4146  <iref item="cacheable"/>
4147  <x:dfn>cacheable</x:dfn>
4148  <list>
4149    <t>
4150      A response is cacheable if a cache is allowed to store a copy of
4151      the response message for use in answering subsequent requests. The
4152      rules for determining the cacheability of HTTP responses are
4153      defined in &caching;. Even if a resource is cacheable, there may
4154      be additional constraints on whether a cache can use the cached
4155      copy for a particular request.
4156    </t>
4157  </list>
4160  <iref item="client"/>
4161  <x:dfn>client</x:dfn>
4162  <list>
4163    <t>
4164      A program that establishes connections for the purpose of sending
4165      requests.
4166    </t>
4167  </list>
4170  <iref item="connection"/>
4171  <x:dfn>connection</x:dfn>
4172  <list>
4173    <t>
4174      A transport layer virtual circuit established between two programs
4175      for the purpose of communication.
4176    </t>
4177  </list>
4180  <iref item="content negotiation"/>
4181  <x:dfn>content negotiation</x:dfn>
4182  <list>
4183    <t>
4184      The mechanism for selecting the appropriate representation when
4185      servicing a request, as described in &content.negotiation;. The
4186      representation of entities in any response can be negotiated
4187      (including error responses).
4188    </t>
4189  </list>
4192  <iref item="entity"/>
4193  <x:dfn>entity</x:dfn>
4194  <list>
4195    <t>
4196      The information transferred as the payload of a request or
4197      response. An entity consists of metainformation in the form of
4198      entity-header fields and content in the form of an entity-body, as
4199      described in &entity;.
4200    </t>
4201  </list>
4204  <iref item="gateway"/>
4205  <x:dfn>gateway</x:dfn>
4206  <list>
4207    <t>
4208      A server which acts as an intermediary for some other server.
4209      Unlike a proxy, a gateway receives requests as if it were the
4210      origin server for the requested resource; the requesting client
4211      may not be aware that it is communicating with a gateway.
4212    </t>
4213  </list>
4216  <iref item="inbound"/>
4217  <iref item="outbound"/>
4218  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4219  <list>
4220    <t>
4221      Inbound and outbound refer to the request and response paths for
4222      messages: "inbound" means "traveling toward the origin server",
4223      and "outbound" means "traveling toward the user agent"
4224    </t>
4225  </list>
4228  <iref item="message"/>
4229  <x:dfn>message</x:dfn>
4230  <list>
4231    <t>
4232      The basic unit of HTTP communication, consisting of a structured
4233      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4234      transmitted via the connection.
4235    </t>
4236  </list>
4239  <iref item="origin server"/>
4240  <x:dfn>origin server</x:dfn>
4241  <list>
4242    <t>
4243      The server on which a given resource resides or is to be created.
4244    </t>
4245  </list>
4248  <iref item="proxy"/>
4249  <x:dfn>proxy</x:dfn>
4250  <list>
4251    <t>
4252      An intermediary program which acts as both a server and a client
4253      for the purpose of making requests on behalf of other clients.
4254      Requests are serviced internally or by passing them on, with
4255      possible translation, to other servers. A proxy &MUST; implement
4256      both the client and server requirements of this specification. A
4257      "transparent proxy" is a proxy that does not modify the request or
4258      response beyond what is required for proxy authentication and
4259      identification. A "non-transparent proxy" is a proxy that modifies
4260      the request or response in order to provide some added service to
4261      the user agent, such as group annotation services, media type
4262      transformation, protocol reduction, or anonymity filtering. Except
4263      where either transparent or non-transparent behavior is explicitly
4264      stated, the HTTP proxy requirements apply to both types of
4265      proxies.
4266    </t>
4267  </list>
4270  <iref item="request"/>
4271  <x:dfn>request</x:dfn>
4272  <list>
4273    <t>
4274      An HTTP request message, as defined in <xref target="request"/>.
4275    </t>
4276  </list>
4279  <iref item="resource"/>
4280  <x:dfn>resource</x:dfn>
4281  <list>
4282    <t>
4283      A network data object or service that can be identified by a URI,
4284      as defined in <xref target="uri"/>. Resources may be available in multiple
4285      representations (e.g. multiple languages, data formats, size, and
4286      resolutions) or vary in other ways.
4287    </t>
4288  </list>
4291  <iref item="response"/>
4292  <x:dfn>response</x:dfn>
4293  <list>
4294    <t>
4295      An HTTP response message, as defined in <xref target="response"/>.
4296    </t>
4297  </list>
4300  <iref item="representation"/>
4301  <x:dfn>representation</x:dfn>
4302  <list>
4303    <t>
4304      An entity included with a response that is subject to content
4305      negotiation, as described in &content.negotiation;. There may exist multiple
4306      representations associated with a particular response status.
4307    </t>
4308  </list>
4311  <iref item="server"/>
4312  <x:dfn>server</x:dfn>
4313  <list>
4314    <t>
4315      An application program that accepts connections in order to
4316      service requests by sending back responses. Any given program may
4317      be capable of being both a client and a server; our use of these
4318      terms refers only to the role being performed by the program for a
4319      particular connection, rather than to the program's capabilities
4320      in general. Likewise, any server may act as an origin server,
4321      proxy, gateway, or tunnel, switching behavior based on the nature
4322      of each request.
4323    </t>
4324  </list>
4327  <iref item="tunnel"/>
4328  <x:dfn>tunnel</x:dfn>
4329  <list>
4330    <t>
4331      An intermediary program which is acting as a blind relay between
4332      two connections. Once active, a tunnel is not considered a party
4333      to the HTTP communication, though the tunnel may have been
4334      initiated by an HTTP request. The tunnel ceases to exist when both
4335      ends of the relayed connections are closed.
4336    </t>
4337  </list>
4340  <iref item="upstream"/>
4341  <iref item="downstream"/>
4342  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4343  <list>
4344    <t>
4345      Upstream and downstream describe the flow of a message: all
4346      messages flow from upstream to downstream.
4347    </t>
4348  </list>
4351  <iref item="user agent"/>
4352  <x:dfn>user agent</x:dfn>
4353  <list>
4354    <t>
4355      The client which initiates a request. These are often browsers,
4356      editors, spiders (web-traversing robots), or other end user tools.
4357    </t>
4358  </list>
4361  <iref item="variant"/>
4362  <x:dfn>variant</x:dfn>
4363  <list>
4364    <t>
4365      A resource may have one, or more than one, representation(s)
4366      associated with it at any given instant. Each of these
4367      representations is termed a `variant'.  Use of the term `variant'
4368      does not necessarily imply that the resource is subject to content
4369      negotiation.
4370    </t>
4371  </list>
4375<section xmlns:x="" title="Collected ABNF" anchor="collected.abnf">
4377<artwork type="abnf" name="p1-messaging.parsed-abnf">
4378<x:ref>BWS</x:ref> = OWS
4380<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4381<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4382<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4383<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4384 connection-token ] )
4385<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4386<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4388<x:ref>Date</x:ref> = "Date:" OWS Date-v
4389<x:ref>Date-v</x:ref> = HTTP-date
4391<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4393<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4394<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4395<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4396<x:ref>HTTP-message</x:ref> = Request / Response
4397<x:ref>Host</x:ref> = "Host:" OWS Host-v
4398<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4400<x:ref>Method</x:ref> = token
4402<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4404<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4406<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4407<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4408<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4409 entity-header ) CRLF ) CRLF [ message-body ]
4410<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4411<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4412 entity-header ) CRLF ) CRLF [ message-body ]
4414<x:ref>Status-Code</x:ref> = 3DIGIT
4415<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4417<x:ref>TE</x:ref> = "TE:" OWS TE-v
4418<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4419<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4420<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4421<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4422<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4423 transfer-coding ] )
4425<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4426<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4427<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4428<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4430<x:ref>Via</x:ref> = "Via:" OWS Via-v
4431<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4432 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4433 ] )
4435<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4437<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4438<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4439<x:ref>attribute</x:ref> = token
4440<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4442<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4443<x:ref>chunk-data</x:ref> = 1*OCTET
4444<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4445<x:ref>chunk-ext-name</x:ref> = token
4446<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4447<x:ref>chunk-size</x:ref> = 1*HEXDIG
4448<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4449<x:ref>connection-token</x:ref> = token
4450<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4451 / %x2A-5B ; '*'-'['
4452 / %x5D-7E ; ']'-'~'
4453 / obs-text
4455<x:ref>date1</x:ref> = day SP month SP year
4456<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4457<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4458<x:ref>day</x:ref> = 2DIGIT
4459<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4460 / %x54.75.65 ; Tue
4461 / %x57.65.64 ; Wed
4462 / %x54.68.75 ; Thu
4463 / %x46.72.69 ; Fri
4464 / %x53.61.74 ; Sat
4465 / %x53.75.6E ; Sun
4466<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4467 / %x54. ; Tuesday
4468 / %x57.65.64.6E. ; Wednesday
4469 / %x54. ; Thursday
4470 / %x46. ; Friday
4471 / %x53. ; Saturday
4472 / %x53.75.6E.64.61.79 ; Sunday
4474<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4475<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4477<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4478<x:ref>field-name</x:ref> = token
4479<x:ref>field-value</x:ref> = *( field-content / OWS )
4480<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4482<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4483 / Transfer-Encoding / Upgrade / Via / Warning
4484<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4485 message-body ]
4487<x:ref>hour</x:ref> = 2DIGIT
4488<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4490<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4492<x:ref>message-body</x:ref> = entity-body /
4493 &lt;entity-body encoded as per Transfer-Encoding&gt;
4494<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4495<x:ref>minute</x:ref> = 2DIGIT
4496<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4497 / %x46.65.62 ; Feb
4498 / %x4D.61.72 ; Mar
4499 / %x41.70.72 ; Apr
4500 / %x4D.61.79 ; May
4501 / %x4A.75.6E ; Jun
4502 / %x4A.75.6C ; Jul
4503 / %x41.75.67 ; Aug
4504 / %x53.65.70 ; Sep
4505 / %x4F.63.74 ; Oct
4506 / %x4E.6F.76 ; Nov
4507 / %x44.65.63 ; Dec
4509<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4510<x:ref>obs-fold</x:ref> = CRLF
4511<x:ref>obs-text</x:ref> = %x80-FF
4513<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4514<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4515<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4516<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4517<x:ref>product</x:ref> = token [ "/" product-version ]
4518<x:ref>product-version</x:ref> = token
4519<x:ref>protocol-name</x:ref> = token
4520<x:ref>protocol-version</x:ref> = token
4521<x:ref>pseudonym</x:ref> = token
4523<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4524 / %x5D-7E ; ']'-'~'
4525 / obs-text
4526<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4527<x:ref>quoted-pair</x:ref> = "\" quoted-text
4528<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4529<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4530<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4532<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4533<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4534<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4535<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4536<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4537 / authority
4538<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4539<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4540<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4542<x:ref>second</x:ref> = 2DIGIT
4543<x:ref>start-line</x:ref> = Request-Line / Status-Line
4545<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4546<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4547 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4548<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4549<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4550<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4551<x:ref>token</x:ref> = 1*tchar
4552<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4553<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4554<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4555<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4557<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4559<x:ref>value</x:ref> = token / quoted-string
4561<x:ref>year</x:ref> = 4DIGIT
4564<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4565; Chunked-Body defined but not used
4566; Content-Length defined but not used
4567; HTTP-message defined but not used
4568; Host defined but not used
4569; TE defined but not used
4570; URI defined but not used
4571; URI-reference defined but not used
4572; fragment defined but not used
4573; generic-message defined but not used
4574; http-URI defined but not used
4575; partial-URI defined but not used
4578<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4580<section title="Since RFC2616">
4582  Extracted relevant partitions from <xref target="RFC2616"/>.
4586<section title="Since draft-ietf-httpbis-p1-messaging-00">
4588  Closed issues:
4589  <list style="symbols">
4590    <t>
4591      <eref target=""/>:
4592      "HTTP Version should be case sensitive"
4593      (<eref target=""/>)
4594    </t>
4595    <t>
4596      <eref target=""/>:
4597      "'unsafe' characters"
4598      (<eref target=""/>)
4599    </t>
4600    <t>
4601      <eref target=""/>:
4602      "Chunk Size Definition"
4603      (<eref target=""/>)
4604    </t>
4605    <t>
4606      <eref target=""/>:
4607      "Message Length"
4608      (<eref target=""/>)
4609    </t>
4610    <t>
4611      <eref target=""/>:
4612      "Media Type Registrations"
4613      (<eref target=""/>)
4614    </t>
4615    <t>
4616      <eref target=""/>:
4617      "URI includes query"
4618      (<eref target=""/>)
4619    </t>
4620    <t>
4621      <eref target=""/>:
4622      "No close on 1xx responses"
4623      (<eref target=""/>)
4624    </t>
4625    <t>
4626      <eref target=""/>:
4627      "Remove 'identity' token references"
4628      (<eref target=""/>)
4629    </t>
4630    <t>
4631      <eref target=""/>:
4632      "Import query BNF"
4633    </t>
4634    <t>
4635      <eref target=""/>:
4636      "qdtext BNF"
4637    </t>
4638    <t>
4639      <eref target=""/>:
4640      "Normative and Informative references"
4641    </t>
4642    <t>
4643      <eref target=""/>:
4644      "RFC2606 Compliance"
4645    </t>
4646    <t>
4647      <eref target=""/>:
4648      "RFC977 reference"
4649    </t>
4650    <t>
4651      <eref target=""/>:
4652      "RFC1700 references"
4653    </t>
4654    <t>
4655      <eref target=""/>:
4656      "inconsistency in date format explanation"
4657    </t>
4658    <t>
4659      <eref target=""/>:
4660      "Date reference typo"
4661    </t>
4662    <t>
4663      <eref target=""/>:
4664      "Informative references"
4665    </t>
4666    <t>
4667      <eref target=""/>:
4668      "ISO-8859-1 Reference"
4669    </t>
4670    <t>
4671      <eref target=""/>:
4672      "Normative up-to-date references"
4673    </t>
4674  </list>
4677  Other changes:
4678  <list style="symbols">
4679    <t>
4680      Update media type registrations to use RFC4288 template.
4681    </t>
4682    <t>
4683      Use names of RFC4234 core rules DQUOTE and WSP,
4684      fix broken ABNF for chunk-data
4685      (work in progress on <eref target=""/>)
4686    </t>
4687  </list>
4691<section title="Since draft-ietf-httpbis-p1-messaging-01">
4693  Closed issues:
4694  <list style="symbols">
4695    <t>
4696      <eref target=""/>:
4697      "Bodies on GET (and other) requests"
4698    </t>
4699    <t>
4700      <eref target=""/>:
4701      "Updating to RFC4288"
4702    </t>
4703    <t>
4704      <eref target=""/>:
4705      "Status Code and Reason Phrase"
4706    </t>
4707    <t>
4708      <eref target=""/>:
4709      "rel_path not used"
4710    </t>
4711  </list>
4714  Ongoing work on ABNF conversion (<eref target=""/>):
4715  <list style="symbols">
4716    <t>
4717      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4718      "trailer-part").
4719    </t>
4720    <t>
4721      Avoid underscore character in rule names ("http_URL" ->
4722      "http-URL", "abs_path" -> "path-absolute").
4723    </t>
4724    <t>
4725      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4726      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4727      have to be updated when switching over to RFC3986.
4728    </t>
4729    <t>
4730      Synchronize core rules with RFC5234.
4731    </t>
4732    <t>
4733      Get rid of prose rules that span multiple lines.
4734    </t>
4735    <t>
4736      Get rid of unused rules LOALPHA and UPALPHA.
4737    </t>
4738    <t>
4739      Move "Product Tokens" section (back) into Part 1, as "token" is used
4740      in the definition of the Upgrade header.
4741    </t>
4742    <t>
4743      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4744    </t>
4745    <t>
4746      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4747    </t>
4748  </list>
4752<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4754  Closed issues:
4755  <list style="symbols">
4756    <t>
4757      <eref target=""/>:
4758      "HTTP-date vs. rfc1123-date"
4759    </t>
4760    <t>
4761      <eref target=""/>:
4762      "WS in quoted-pair"
4763    </t>
4764  </list>
4767  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4768  <list style="symbols">
4769    <t>
4770      Reference RFC 3984, and update header registrations for headers defined
4771      in this document.
4772    </t>
4773  </list>
4776  Ongoing work on ABNF conversion (<eref target=""/>):
4777  <list style="symbols">
4778    <t>
4779      Replace string literals when the string really is case-sensitive (HTTP-Version).
4780    </t>
4781  </list>
4785<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4787  Closed issues:
4788  <list style="symbols">
4789    <t>
4790      <eref target=""/>:
4791      "Connection closing"
4792    </t>
4793    <t>
4794      <eref target=""/>:
4795      "Move registrations and registry information to IANA Considerations"
4796    </t>
4797    <t>
4798      <eref target=""/>:
4799      "need new URL for PAD1995 reference"
4800    </t>
4801    <t>
4802      <eref target=""/>:
4803      "IANA Considerations: update HTTP URI scheme registration"
4804    </t>
4805    <t>
4806      <eref target=""/>:
4807      "Cite HTTPS URI scheme definition"
4808    </t>
4809    <t>
4810      <eref target=""/>:
4811      "List-type headers vs Set-Cookie"
4812    </t>
4813  </list>
4816  Ongoing work on ABNF conversion (<eref target=""/>):
4817  <list style="symbols">
4818    <t>
4819      Replace string literals when the string really is case-sensitive (HTTP-Date).
4820    </t>
4821    <t>
4822      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4823    </t>
4824  </list>
4828<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4830  Closed issues:
4831  <list style="symbols">
4832    <t>
4833      <eref target=""/>:
4834      "Out-of-date reference for URIs"
4835    </t>
4836    <t>
4837      <eref target=""/>:
4838      "RFC 2822 is updated by RFC 5322"
4839    </t>
4840  </list>
4843  Ongoing work on ABNF conversion (<eref target=""/>):
4844  <list style="symbols">
4845    <t>
4846      Use "/" instead of "|" for alternatives.
4847    </t>
4848    <t>
4849      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4850    </t>
4851    <t>
4852      Only reference RFC 5234's core rules.
4853    </t>
4854    <t>
4855      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4856      whitespace ("OWS") and required whitespace ("RWS").
4857    </t>
4858    <t>
4859      Rewrite ABNFs to spell out whitespace rules, factor out
4860      header value format definitions.
4861    </t>
4862  </list>
4866<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4868  Closed issues:
4869  <list style="symbols">
4870    <t>
4871      <eref target=""/>:
4872      "Header LWS"
4873    </t>
4874    <t>
4875      <eref target=""/>:
4876      "Sort 1.3 Terminology"
4877    </t>
4878    <t>
4879      <eref target=""/>:
4880      "RFC2047 encoded words"
4881    </t>
4882    <t>
4883      <eref target=""/>:
4884      "Character Encodings in TEXT"
4885    </t>
4886    <t>
4887      <eref target=""/>:
4888      "Line Folding"
4889    </t>
4890    <t>
4891      <eref target=""/>:
4892      "OPTIONS * and proxies"
4893    </t>
4894    <t>
4895      <eref target=""/>:
4896      "Reason-Phrase BNF"
4897    </t>
4898    <t>
4899      <eref target=""/>:
4900      "Use of TEXT"
4901    </t>
4902    <t>
4903      <eref target=""/>:
4904      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4905    </t>
4906    <t>
4907      <eref target=""/>:
4908      "RFC822 reference left in discussion of date formats"
4909    </t>
4910  </list>
4913  Final work on ABNF conversion (<eref target=""/>):
4914  <list style="symbols">
4915    <t>
4916      Rewrite definition of list rules, deprecate empty list elements.
4917    </t>
4918    <t>
4919      Add appendix containing collected and expanded ABNF.
4920    </t>
4921  </list>
4924  Other changes:
4925  <list style="symbols">
4926    <t>
4927      Rewrite introduction; add mostly new Architecture Section.
4928    </t>
4929    <t>
4930      Move definition of quality values from Part 3 into Part 1;
4931      make TE request header grammar independent of accept-params (defined in Part 3).
4932    </t>
4933  </list>
4937<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4939  Closed issues:
4940  <list style="symbols">
4941    <t>
4942      <eref target=""/>:
4943      "base for numeric protocol elements"
4944    </t>
4945    <t>
4946      <eref target=""/>:
4947      "comment ABNF"
4948    </t>
4949  </list>
4952  Partly resolved issues:
4953  <list style="symbols">
4954    <t>
4955      <eref target=""/>:
4956      "205 Bodies" (took out language that implied that there may be
4957      methods for which a request body MUST NOT be included)
4958    </t>
4959    <t>
4960      <eref target=""/>:
4961      "editorial improvements around HTTP-date"
4962    </t>
4963  </list>
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