source: draft-ietf-httpbis/latest-roy/p1-messaging.xml @ 341

Last change on this file since 341 was 341, checked in by fielding@…, 14 years ago

Rewrite intro. Update URIs to RFC3986

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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 "November">
16  <!ENTITY ID-YEAR "2008">
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-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x=''/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x=''/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x=''/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x=''/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x=''/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x=''/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x=''/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x=''/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x=''/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x=''/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='' xmlns:x=''/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x=''/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x=''/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x=''/>">
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x=''>
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email></email>
73      <uri></uri>
74    </address>
75  </author>
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email></email>
88      <uri></uri>
89    </address>
90  </author>
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email></email>
104    </address>
105  </author>
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email></email>
118    </address>
119  </author>
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email></email>
132      <uri></uri>
133    </address>
134  </author>
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email></email>
146    </address>
147  </author>
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email></email>
162      <uri></uri>
163    </address>
164  </author>
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email></email>
178      <uri></uri>
179    </address>
180  </author>
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email></email>       
193      <uri></uri>     
194    </address>
195  </author>
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list ( The current issues list is
218    at <eref target=""/>
219    and related documents (including fancy diffs) can be found at
220    <eref target=""/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.02"/>.
224  </t>
228<section title="Introduction" anchor="introduction">
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypermedia
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate resource targets for
235   interaction and to identify other resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
239   between HTTP and MIME messages).
242   HTTP is also designed for use as a generic protocol for translating
243   communication to and from other Internet information systems, such as
244   USENET news services via NNTP <xref target="RFC3977"/>,
245   file services via FTP <xref target="RFC959"/>,
246   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
247   HTTP proxies and gateways provide access to alternative information
248   services by translating their diverse protocols into a hypermedia
249   format that can be viewed and manipulated by clients in the same way
250   as HTTP services.
253   This document is Part 1 of the seven-part specification of HTTP,
254   defining the protocol referred to as "HTTP/1.1" and obsoleting
255   <xref target="RFC2616"/>.
256   Part 1 defines how clients determine when to use HTTP, the URI schemes
257   specific to HTTP-based resources, overall network operation with
258   transport protocol connection management, and HTTP message framing.
259   Our goal is to define all of the mechanisms necessary for HTTP message
260   handling that are independent of message semantics, thereby defining the
261   complete set of requirements for an HTTP message relay or generic
262   message parser.
265<section title="Requirements" anchor="intro.requirements">
267   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
268   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
269   document are to be interpreted as described in <xref target="RFC2119"/>.
272   An implementation is not compliant if it fails to satisfy one or more
273   of the &MUST; or &REQUIRED; level requirements for the protocols it
274   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
275   level and all the &SHOULD; level requirements for its protocols is said
276   to be "unconditionally compliant"; one that satisfies all the &MUST;
277   level requirements but not all the &SHOULD; level requirements for its
278   protocols is said to be "conditionally compliant."
282<section title="Syntax Notation" anchor="notation">
284   This specification uses the Augmented Backus-Naur Form (ABNF) notation
285   of <xref target="RFC5234"/>, including its core ABNF syntax rules:
286   ALPHA (letters), CR (carriage return), DIGIT (decimal digits),
287   DQUOTE (double quote), HEXDIG (hexadecimal digits), LF (line feed),
288   and SP (space).
290<t anchor="core.rules">
291  <x:anchor-alias value="OCTET"/>
292  <x:anchor-alias value="CHAR"/>
293  <x:anchor-alias value="ALPHA"/>
294  <x:anchor-alias value="DIGIT"/>
295  <x:anchor-alias value="CTL"/>
296  <x:anchor-alias value="CR"/>
297  <x:anchor-alias value="LF"/>
298  <x:anchor-alias value="SP"/>
299  <x:anchor-alias value="HTAB"/>
300  <x:anchor-alias value="DQUOTE"/>
301   The following rules are used throughout this specification to
302   describe basic parsing constructs. The US-ASCII coded character set
303   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
305<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OCTET"/><iref primary="true" item="Grammar" subitem="CHAR"/><iref primary="true" item="Grammar" subitem="ALPHA"/><iref primary="true" item="Grammar" subitem="DIGIT"/><iref primary="true" item="Grammar" subitem="CTL"/><iref primary="true" item="Grammar" subitem="CR"/><iref primary="true" item="Grammar" subitem="LF"/><iref primary="true" item="Grammar" subitem="SP"/><iref primary="true" item="Grammar" subitem="HTAB"/><iref primary="true" item="Grammar" subitem="DQUOTE"/>
306  <x:ref>OCTET</x:ref>          = %x00-FF
307                   ; any 8-bit sequence of data
308  <x:ref>CHAR</x:ref>           = %x01-7F
309                   ; any US-ASCII character, excluding NUL
310  <x:ref>ALPHA</x:ref>          = %x41-5A / %x61-7A
311                   ; A-Z / a-z
312  <x:ref>DIGIT</x:ref>          = %x30-39
313                   ; any US-ASCII digit "0".."9"
314  <x:ref>CTL</x:ref>            = %x00-1F / %x7F
315                   ; (octets 0 - 31) and DEL (127)
316  <x:ref>CR</x:ref>             = %x0D
317                   ; US-ASCII CR, carriage return (13)
318  <x:ref>LF</x:ref>             = %x0A
319                   ; US-ASCII LF, linefeed (10)
320  <x:ref>SP</x:ref>             = %x20
321                   ; US-ASCII SP, space (32)
322  <x:ref>HTAB</x:ref>           = %x09
323                   ; US-ASCII HT, horizontal-tab (9)
324  <x:ref>DQUOTE</x:ref>         = %x22
325                   ; US-ASCII double-quote mark (34)
328<section title="Augmented BNF" anchor="notation.abnf">
330   All of the mechanisms specified in this document are described in
331   both prose and an augmented Backus-Naur Form (ABNF) based on that
332   defined in <xref target="RFC5234"/>. Implementors will need to be
333   familiar with the notation in order to understand this specification. The
334   extensions to ABNF used in this specification are described below.
337<section title="#rule">
338  <t>
339    A construct "#" is defined, similar to "*", for defining lists of
340    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
341    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
342    (",") and &OPTIONAL; linear white space (LWS). This makes the usual
343    form of lists very easy; a rule such as
344    <figure><artwork type="example">
345 ( *<x:ref>LWS</x:ref> element *( *<x:ref>LWS</x:ref> "," *<x:ref>LWS</x:ref> element ))</artwork></figure>
346  </t>
347  <t>
348    can be shown as
349    <figure><artwork type="example">
350 1#element</artwork></figure>
351  </t>
352  <t>
353    Wherever this construct is used, null elements are allowed, but do
354    not contribute to the count of elements present. That is,
355    "(element), , (element) " is permitted, but counts as only two
356    elements. Therefore, where at least one element is required, at
357    least one non-null element &MUST; be present. Default values are 0
358    and infinity so that "#element" allows any number, including zero;
359    "1#element" requires at least one; and "1#2element" allows one or
360    two.
361  </t>
364<section title="implied *LWS" anchor="implied.LWS">
365  <iref item="implied *LWS" primary="true"/>
366    <t>
367      The grammar described by this specification is word-based. Except
368      where noted otherwise, linear white space (LWS) can be included
369      between any two adjacent words (token or quoted-string), and
370      between adjacent words and separators, without changing the
371      interpretation of a field. At least one delimiter (LWS and/or
372      separators) &MUST; exist between any two tokens (for the definition
373      of "token" below), since they would otherwise be interpreted as a
374      single token.
375    </t>
379<section title="Basic Rules" anchor="basic.rules">
380<t anchor="rule.CRLF">
381  <x:anchor-alias value="CRLF"/>
382   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
383   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
384   tolerant applications). The end-of-line marker within an entity-body
385   is defined by its associated media type, as described in &media-types;.
387<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="CRLF"/>
388  <x:ref>CRLF</x:ref>           = <x:ref>CR</x:ref> LF
390<t anchor="rule.LWS">
391  <x:anchor-alias value="LWS"/>
392   HTTP/1.1 header field values can be folded onto multiple lines if the
393   continuation line begins with a space or horizontal tab. All linear
394   white space, including folding, has the same semantics as SP. A
395   recipient &MAY; replace any linear white space with a single SP before
396   interpreting the field value or forwarding the message downstream.
398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
399  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
401<t anchor="rule.TEXT">
402  <x:anchor-alias value="TEXT"/>
403   The TEXT rule is only used for descriptive field contents and values
404   that are not intended to be interpreted by the message parser. Words
405   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
406   <xref target="ISO-8859-1"/> only when encoded according to the rules of
407   <xref target="RFC2047"/>.
409<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
410  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
411                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
414   A CRLF is allowed in the definition of TEXT only as part of a header
415   field continuation. It is expected that the folding LWS will be
416   replaced with a single SP before interpretation of the TEXT value.
418<t anchor="rule.HEXDIG">
419  <x:anchor-alias value="HEXDIG"/>
420   Hexadecimal numeric characters are used in several protocol elements.
422<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HEXDIG"/>
423  <x:ref>HEXDIG</x:ref>         = "A" / "B" / "C" / "D" / "E" / "F"
424                 / "a" / "b" / "c" / "d" / "e" / "f" / <x:ref>DIGIT</x:ref>
426<t anchor="rule.token.separators">
427  <x:anchor-alias value="tchar"/>
428  <x:anchor-alias value="token"/>
429  <x:anchor-alias value="separators"/>
430   Many HTTP/1.1 header field values consist of words separated by LWS
431   or special characters. These special characters &MUST; be in a quoted
432   string to be used within a parameter value (as defined in
433   <xref target="transfer.codings"/>).
435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="separators"/>
436  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
437                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
438                 / "/" / "[" / "]" / "?" / "="
439                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
441  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
442                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
443                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
444                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
446  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
448<t anchor="rule.comment">
449  <x:anchor-alias value="comment"/>
450  <x:anchor-alias value="ctext"/>
451   Comments can be included in some HTTP header fields by surrounding
452   the comment text with parentheses. Comments are only allowed in
453   fields containing "comment" as part of their field value definition.
454   In all other fields, parentheses are considered part of the field
455   value.
457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
458  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
459  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
461<t anchor="rule.quoted-string">
462  <x:anchor-alias value="quoted-string"/>
463  <x:anchor-alias value="qdtext"/>
464   A string of text is parsed as a single word if it is quoted using
465   double-quote marks.
467<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
468  <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> )
469  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
471<t anchor="rule.quoted-pair">
472  <x:anchor-alias value="quoted-pair"/>
473  <x:anchor-alias value="quoted-text"/>
474   The backslash character ("\") &MAY; be used as a single-character
475   quoting mechanism only within quoted-string and comment constructs.
477<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
478  <x:ref>quoted-text</x:ref>    = %x01-09 /
479                   %x0B-0C /
480                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
481  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
485<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
486  <x:anchor-alias value="request-header"/>
487  <x:anchor-alias value="response-header"/>
488  <x:anchor-alias value="accept-params"/>
489  <x:anchor-alias value="entity-body"/>
490  <x:anchor-alias value="entity-header"/>
491  <x:anchor-alias value="Cache-Control"/>
492  <x:anchor-alias value="Pragma"/>
493  <x:anchor-alias value="Warning"/>
495  The ABNF rules below are defined in other parts:
497<figure><!-- Part2--><artwork type="abnf2616">
498  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
499  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
501<figure><!-- Part3--><artwork type="abnf2616">
502  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
503  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
504  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
506<figure><!-- Part6--><artwork type="abnf2616">
507  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
508  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
509  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
516<section title="When to use HTTP" anchor="when">
518<section title="Uniform Resource Identifiers" anchor="uri">
520   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used in HTTP
521   to indicate the target of a request and to identify additional resources related
522   to that resource, the request, or the response. Each protocol element in HTTP
523   that allows a URI reference will indicate in its ABNF whether the element allows
524   only a URI in absolute form, any relative reference, or some limited subset of
525   the URI-reference grammar. Unless otherwise indicated, relative URI references
526   are to be parsed relative to the URI corresponding to the request target
527   (the base URI).
529  <x:anchor-alias value="URI-reference"/>
530  <x:anchor-alias value="absolute-URI"/>
531  <x:anchor-alias value="authority"/>
532  <x:anchor-alias value="fragment"/>
533  <x:anchor-alias value="path-abempty"/>
534  <x:anchor-alias value="path-absolute"/>
535  <x:anchor-alias value="port"/>
536  <x:anchor-alias value="query"/>
537  <x:anchor-alias value="uri-host"/>
539   This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port",
540   "host", "path-abempty", "path-absolute", "query", and "authority" from <xref target="RFC3986"/>:
542<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"/>
543  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
544  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
545  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
546  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
547  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
548  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
549  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
550  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
553   HTTP does not place an a priori limit on the length of
554   a URI. Servers &MUST; be able to handle the URI of any resource they
555   serve, and &SHOULD; be able to handle URIs of unbounded length if they
556   provide GET-based forms that could generate such URIs. A server
557   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
558   than the server can handle (see &status-414;).
561  <list>
562    <t>
563      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
564      above 255 bytes, because some older client or proxy
565      implementations might not properly support these lengths.
566    </t>
567  </list>
570<section title="http URI scheme" anchor="http.uri">
571  <x:anchor-alias value="http-URI"/>
572  <iref item="http URI scheme" primary="true"/>
573  <iref item="URI scheme" subitem="http" primary="true"/>
575   The "http" scheme is used to locate network resources via the HTTP
576   protocol. This section defines the syntax and semantics for identifiers
577   using the http or https URI schemes.
579<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
580  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
583   If the port is empty or not given, port 80 is assumed. The semantics
584   are that the identified resource is located at the server listening
585   for TCP connections on that port of that host, and the Request-URI
586   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
587   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
588   the path-absolute is not present in the URL, it &MUST; be given as "/" when
589   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
590   receives a host name which is not a fully qualified domain name, it
591   &MAY; add its domain to the host name it received. If a proxy receives
592   a fully qualified domain name, the proxy &MUST-NOT; change the host
593   name.
596  <iref item="https URI scheme"/>
597  <iref item="URI scheme" subitem="https"/>
598  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
602<section title="URI Comparison" anchor="uri.comparison">
604   When comparing two URIs to decide if they match or not, a client
605   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
606   URIs, with these exceptions:
607  <list style="symbols">
608    <t>A port that is empty or not given is equivalent to the default
609        port for that URI-reference;</t>
610    <t>Comparisons of host names &MUST; be case-insensitive;</t>
611    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
612    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
613  </list>
616   Characters other than those in the "reserved" set (see
617   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
618   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
621   For example, the following three URIs are equivalent:
623<figure><artwork type="example">
631<section title="Overall Operation" anchor="intro.overall.operation">
633   HTTP is a request/response protocol. A client sends a
634   request to the server in the form of a request method, URI, and
635   protocol version, followed by a MIME-like message containing request
636   modifiers, client information, and possible body content over a
637   connection with a server. The server responds with a status line,
638   including the message's protocol version and a success or error code,
639   followed by a MIME-like message containing server information, entity
640   metainformation, and possible entity-body content.
643   Most HTTP communication is initiated by a user agent and consists of
644   a request to be applied to a resource on some origin server. In the
645   simplest case, this may be accomplished via a single connection (v)
646   between the user agent (UA) and the origin server (O).
648<figure><artwork type="drawing">
649       request chain ------------------------&gt;
650    UA -------------------v------------------- O
651       &lt;----------------------- response chain
654   A more complicated situation occurs when one or more intermediaries
655   are present in the request/response chain. There are three common
656   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
657   forwarding agent, receiving requests for a URI in its absolute form,
658   rewriting all or part of the message, and forwarding the reformatted
659   request toward the server identified by the URI. A gateway is a
660   receiving agent, acting as a layer above some other server(s) and, if
661   necessary, translating the requests to the underlying server's
662   protocol. A tunnel acts as a relay point between two connections
663   without changing the messages; tunnels are used when the
664   communication needs to pass through an intermediary (such as a
665   firewall) even when the intermediary cannot understand the contents
666   of the messages.
668<figure><artwork type="drawing">
669       request chain --------------------------------------&gt;
670    UA -----v----- A -----v----- B -----v----- C -----v----- O
671       &lt;------------------------------------- response chain
674   The figure above shows three intermediaries (A, B, and C) between the
675   user agent and origin server. A request or response message that
676   travels the whole chain will pass through four separate connections.
677   This distinction is important because some HTTP communication options
678   may apply only to the connection with the nearest, non-tunnel
679   neighbor, only to the end-points of the chain, or to all connections
680   along the chain. Although the diagram is linear, each participant may
681   be engaged in multiple, simultaneous communications. For example, B
682   may be receiving requests from many clients other than A, and/or
683   forwarding requests to servers other than C, at the same time that it
684   is handling A's request.
687   Any party to the communication which is not acting as a tunnel may
688   employ an internal cache for handling requests. The effect of a cache
689   is that the request/response chain is shortened if one of the
690   participants along the chain has a cached response applicable to that
691   request. The following illustrates the resulting chain if B has a
692   cached copy of an earlier response from O (via C) for a request which
693   has not been cached by UA or A.
695<figure><artwork type="drawing">
696          request chain ----------&gt;
697       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
698          &lt;--------- response chain
701   Not all responses are usefully cacheable, and some requests may
702   contain modifiers which place special requirements on cache behavior.
703   HTTP requirements for cache behavior and cacheable responses are
704   defined in &caching;.
707   In fact, there are a wide variety of architectures and configurations
708   of caches and proxies currently being experimented with or deployed
709   across the World Wide Web. These systems include national hierarchies
710   of proxy caches to save transoceanic bandwidth, systems that
711   broadcast or multicast cache entries, organizations that distribute
712   subsets of cached data via CD-ROM, and so on. HTTP systems are used
713   in corporate intranets over high-bandwidth links, and for access via
714   PDAs with low-power radio links and intermittent connectivity. The
715   goal of HTTP/1.1 is to support the wide diversity of configurations
716   already deployed while introducing protocol constructs that meet the
717   needs of those who build web applications that require high
718   reliability and, failing that, at least reliable indications of
719   failure.
722   HTTP communication usually takes place over TCP/IP connections. The
723   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
724   not preclude HTTP from being implemented on top of any other protocol
725   on the Internet, or on other networks. HTTP only presumes a reliable
726   transport; any protocol that provides such guarantees can be used;
727   the mapping of the HTTP/1.1 request and response structures onto the
728   transport data units of the protocol in question is outside the scope
729   of this specification.
732   In HTTP/1.0, most implementations used a new connection for each
733   request/response exchange. In HTTP/1.1, a connection may be used for
734   one or more request/response exchanges, although connections may be
735   closed for a variety of reasons (see <xref target="persistent.connections"/>).
740<section title="Protocol Parameters" anchor="protocol.parameters">
742<section title="HTTP Version" anchor="http.version">
743  <x:anchor-alias value="HTTP-Version"/>
744  <x:anchor-alias value="HTTP-Prot-Name"/>
746   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
747   of the protocol. The protocol versioning policy is intended to allow
748   the sender to indicate the format of a message and its capacity for
749   understanding further HTTP communication, rather than the features
750   obtained via that communication. No change is made to the version
751   number for the addition of message components which do not affect
752   communication behavior or which only add to extensible field values.
753   The &lt;minor&gt; number is incremented when the changes made to the
754   protocol add features which do not change the general message parsing
755   algorithm, but which may add to the message semantics and imply
756   additional capabilities of the sender. The &lt;major&gt; number is
757   incremented when the format of a message within the protocol is
758   changed. See <xref target="RFC2145"/> for a fuller explanation.
761   The version of an HTTP message is indicated by an HTTP-Version field
762   in the first line of the message. HTTP-Version is case-sensitive.
764<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
765  <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>
766  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
769   Note that the major and minor numbers &MUST; be treated as separate
770   integers and that each &MAY; be incremented higher than a single digit.
771   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
772   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
773   &MUST-NOT; be sent.
776   An application that sends a request or response message that includes
777   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
778   with this specification. Applications that are at least conditionally
779   compliant with this specification &SHOULD; use an HTTP-Version of
780   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
781   not compatible with HTTP/1.0. For more details on when to send
782   specific HTTP-Version values, see <xref target="RFC2145"/>.
785   The HTTP version of an application is the highest HTTP version for
786   which the application is at least conditionally compliant.
789   Proxy and gateway applications need to be careful when forwarding
790   messages in protocol versions different from that of the application.
791   Since the protocol version indicates the protocol capability of the
792   sender, a proxy/gateway &MUST-NOT; send a message with a version
793   indicator which is greater than its actual version. If a higher
794   version request is received, the proxy/gateway &MUST; either downgrade
795   the request version, or respond with an error, or switch to tunnel
796   behavior.
799   Due to interoperability problems with HTTP/1.0 proxies discovered
800   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
801   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
802   they support. The proxy/gateway's response to that request &MUST; be in
803   the same major version as the request.
806  <list>
807    <t>
808      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
809      of header fields required or forbidden by the versions involved.
810    </t>
811  </list>
815<section title="Date/Time Formats" anchor="date.time.formats">
816<section title="Full Date" anchor="">
817  <x:anchor-alias value="HTTP-date"/>
818  <x:anchor-alias value="obsolete-date"/>
819  <x:anchor-alias value="rfc1123-date"/>
820  <x:anchor-alias value="rfc850-date"/>
821  <x:anchor-alias value="asctime-date"/>
822  <x:anchor-alias value="date1"/>
823  <x:anchor-alias value="date2"/>
824  <x:anchor-alias value="date3"/>
825  <x:anchor-alias value="rfc1123-date"/>
826  <x:anchor-alias value="time"/>
827  <x:anchor-alias value="wkday"/>
828  <x:anchor-alias value="weekday"/>
829  <x:anchor-alias value="month"/>
831   HTTP applications have historically allowed three different formats
832   for the representation of date/time stamps:
834<figure><artwork type="example">
835   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
836   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
837   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
840   The first format is preferred as an Internet standard and represents
841   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
842   <xref target="RFC822"/>). The other formats are described here only for
843   compatibility with obsolete implementations.
844   HTTP/1.1 clients and servers that parse the date value &MUST; accept
845   all three formats (for compatibility with HTTP/1.0), though they &MUST;
846   only generate the RFC 1123 format for representing HTTP-date values
847   in header fields. See <xref target="tolerant.applications"/> for further information.
850      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
851      accepting date values that may have been sent by non-HTTP
852      applications, as is sometimes the case when retrieving or posting
853      messages via proxies/gateways to SMTP or NNTP.
856   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
857   (GMT), without exception. For the purposes of HTTP, GMT is exactly
858   equal to UTC (Coordinated Universal Time). This is indicated in the
859   first two formats by the inclusion of "GMT" as the three-letter
860   abbreviation for time zone, and &MUST; be assumed when reading the
861   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
862   additional LWS beyond that specifically included as SP in the
863   grammar.
865<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="obsolete-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/>
866  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
867  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
868  <x:ref>rfc1123-date</x:ref> = <x:ref>wkday</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
869  <x:ref>rfc850-date</x:ref>  = <x:ref>weekday</x:ref> "," <x:ref>SP</x:ref> date2 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
870  <x:ref>asctime-date</x:ref> = <x:ref>wkday</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
871  <x:ref>date1</x:ref>        = 2<x:ref>DIGIT</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
872                 ; day month year (e.g., 02 Jun 1982)
873  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
874                 ; day-month-year (e.g., 02-Jun-82)
875  <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> ))
876                 ; month day (e.g., Jun  2)
877  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
878                 ; 00:00:00 - 23:59:59
879  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
880               / s-Thu / s-Fri / s-Sat / s-Sun
881  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
882               / l-Thu / l-Fri / l-Sat / l-Sun
883  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
884               / s-May / s-Jun / s-Jul / s-Aug
885               / s-Sep / s-Oct / s-Nov / s-Dec
887  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
889  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
890  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
891  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
892  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
893  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
894  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
895  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
897  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
898  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
899  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
900  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
901  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
902  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
903  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
905  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
906  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
907  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
908  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
909  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
910  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
911  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
912  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
913  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
914  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
915  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
916  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
919      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
920      to their usage within the protocol stream. Clients and servers are
921      not required to use these formats for user presentation, request
922      logging, etc.
927<section title="Transfer Codings" anchor="transfer.codings">
928  <x:anchor-alias value="parameter"/>
929  <x:anchor-alias value="transfer-coding"/>
930  <x:anchor-alias value="transfer-extension"/>
932   Transfer-coding values are used to indicate an encoding
933   transformation that has been, can be, or may need to be applied to an
934   entity-body in order to ensure "safe transport" through the network.
935   This differs from a content coding in that the transfer-coding is a
936   property of the message, not of the original entity.
938<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
939  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
940  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
942<t anchor="rule.parameter">
943  <x:anchor-alias value="attribute"/>
944  <x:anchor-alias value="parameter"/>
945  <x:anchor-alias value="value"/>
946   Parameters are in  the form of attribute/value pairs.
948<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
949  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
950  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
951  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
954   All transfer-coding values are case-insensitive. HTTP/1.1 uses
955   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
956   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
959   Whenever a transfer-coding is applied to a message-body, the set of
960   transfer-codings &MUST; include "chunked", unless the message indicates it
961   is terminated by closing the connection. When the "chunked" transfer-coding
962   is used, it &MUST; be the last transfer-coding applied to the
963   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
964   than once to a message-body. These rules allow the recipient to
965   determine the transfer-length of the message (<xref target="message.length"/>).
968   Transfer-codings are analogous to the Content-Transfer-Encoding
969   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
970   binary data over a 7-bit transport service. However, safe transport
971   has a different focus for an 8bit-clean transfer protocol. In HTTP,
972   the only unsafe characteristic of message-bodies is the difficulty in
973   determining the exact body length (<xref target="message.length"/>), or the desire to
974   encrypt data over a shared transport.
977   The Internet Assigned Numbers Authority (IANA) acts as a registry for
978   transfer-coding value tokens. Initially, the registry contains the
979   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
980   "gzip", "compress", and "deflate" (&content-codings;).
983   New transfer-coding value tokens &SHOULD; be registered in the same way
984   as new content-coding value tokens (&content-codings;).
987   A server which receives an entity-body with a transfer-coding it does
988   not understand &SHOULD; return 501 (Not Implemented), and close the
989   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
990   client.
993<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
994  <x:anchor-alias value="chunk"/>
995  <x:anchor-alias value="Chunked-Body"/>
996  <x:anchor-alias value="chunk-data"/>
997  <x:anchor-alias value="chunk-extension"/>
998  <x:anchor-alias value="chunk-ext-name"/>
999  <x:anchor-alias value="chunk-ext-val"/>
1000  <x:anchor-alias value="chunk-size"/>
1001  <x:anchor-alias value="last-chunk"/>
1002  <x:anchor-alias value="trailer-part"/>
1004   The chunked encoding modifies the body of a message in order to
1005   transfer it as a series of chunks, each with its own size indicator,
1006   followed by an &OPTIONAL; trailer containing entity-header fields. This
1007   allows dynamically produced content to be transferred along with the
1008   information necessary for the recipient to verify that it has
1009   received the full message.
1011<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-extension"/><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"/>
1012  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1013                   <x:ref>last-chunk</x:ref>
1014                   <x:ref>trailer-part</x:ref>
1015                   <x:ref>CRLF</x:ref>
1017  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1018                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1019  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1020  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1022  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1023  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1024  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1025  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1026  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1029   The chunk-size field is a string of hex digits indicating the size of
1030   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1031   zero, followed by the trailer, which is terminated by an empty line.
1034   The trailer allows the sender to include additional HTTP header
1035   fields at the end of the message. The Trailer header field can be
1036   used to indicate which header fields are included in a trailer (see
1037   <xref target="header.trailer"/>).
1040   A server using chunked transfer-coding in a response &MUST-NOT; use the
1041   trailer for any header fields unless at least one of the following is
1042   true:
1043  <list style="numbers">
1044    <t>the request included a TE header field that indicates "trailers" is
1045     acceptable in the transfer-coding of the  response, as described in
1046     <xref target="header.te"/>; or,</t>
1048    <t>the server is the origin server for the response, the trailer
1049     fields consist entirely of optional metadata, and the recipient
1050     could use the message (in a manner acceptable to the origin server)
1051     without receiving this metadata.  In other words, the origin server
1052     is willing to accept the possibility that the trailer fields might
1053     be silently discarded along the path to the client.</t>
1054  </list>
1057   This requirement prevents an interoperability failure when the
1058   message is being received by an HTTP/1.1 (or later) proxy and
1059   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1060   compliance with the protocol would have necessitated a possibly
1061   infinite buffer on the proxy.
1064   A process for decoding the "chunked" transfer-coding
1065   can be represented in pseudo-code as:
1067<figure><artwork type="code">
1068    length := 0
1069    read chunk-size, chunk-extension (if any) and CRLF
1070    while (chunk-size &gt; 0) {
1071       read chunk-data and CRLF
1072       append chunk-data to entity-body
1073       length := length + chunk-size
1074       read chunk-size and CRLF
1075    }
1076    read entity-header
1077    while (entity-header not empty) {
1078       append entity-header to existing header fields
1079       read entity-header
1080    }
1081    Content-Length := length
1082    Remove "chunked" from Transfer-Encoding
1085   All HTTP/1.1 applications &MUST; be able to receive and decode the
1086   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1087   they do not understand.
1092<section title="Product Tokens" anchor="product.tokens">
1093  <x:anchor-alias value="product"/>
1094  <x:anchor-alias value="product-version"/>
1096   Product tokens are used to allow communicating applications to
1097   identify themselves by software name and version. Most fields using
1098   product tokens also allow sub-products which form a significant part
1099   of the application to be listed, separated by white space. By
1100   convention, the products are listed in order of their significance
1101   for identifying the application.
1103<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1104  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1105  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1108   Examples:
1110<figure><artwork type="example">
1111    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1112    Server: Apache/0.8.4
1115   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1116   used for advertising or other non-essential information. Although any
1117   token character &MAY; appear in a product-version, this token &SHOULD;
1118   only be used for a version identifier (i.e., successive versions of
1119   the same product &SHOULD; only differ in the product-version portion of
1120   the product value).
1126<section title="HTTP Message" anchor="http.message">
1128<section title="Message Types" anchor="message.types">
1129  <x:anchor-alias value="generic-message"/>
1130  <x:anchor-alias value="HTTP-message"/>
1131  <x:anchor-alias value="start-line"/>
1133   HTTP messages consist of requests from client to server and responses
1134   from server to client.
1136<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1137  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1140   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1141   message format of <xref target="RFC5322"/> for transferring entities (the payload
1142   of the message). Both types of message consist of a start-line, zero
1143   or more header fields (also known as "headers"), an empty line (i.e.,
1144   a line with nothing preceding the CRLF) indicating the end of the
1145   header fields, and possibly a message-body.
1147<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1148  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1149                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1150                    <x:ref>CRLF</x:ref>
1151                    [ <x:ref>message-body</x:ref> ]
1152  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1155   In the interest of robustness, servers &SHOULD; ignore any empty
1156   line(s) received where a Request-Line is expected. In other words, if
1157   the server is reading the protocol stream at the beginning of a
1158   message and receives a CRLF first, it should ignore the CRLF.
1161   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1162   after a POST request. To restate what is explicitly forbidden by the
1163   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1164   extra CRLF.
1168<section title="Message Headers" anchor="message.headers">
1169  <x:anchor-alias value="field-content"/>
1170  <x:anchor-alias value="field-name"/>
1171  <x:anchor-alias value="field-value"/>
1172  <x:anchor-alias value="message-header"/>
1174   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1175   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1176   entity-header (&entity-header-fields;) fields, follow the same generic format as
1177   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1178   of a name followed by a colon (":") and the field value. Field names
1179   are case-insensitive. The field value &MAY; be preceded by any amount
1180   of LWS, though a single SP is preferred. Header fields can be
1181   extended over multiple lines by preceding each extra line with at
1182   least one SP or HTAB. Applications ought to follow "common form", where
1183   one is known or indicated, when generating HTTP constructs, since
1184   there might exist some implementations that fail to accept anything
1185   beyond the common forms.
1187<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"/>
1188  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1189  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1190  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1191  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1192                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1193                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1194                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1197   The field-content does not include any leading or trailing LWS:
1198   linear white space occurring before the first non-whitespace
1199   character of the field-value or after the last non-whitespace
1200   character of the field-value. Such leading or trailing LWS &MAY; be
1201   removed without changing the semantics of the field value. Any LWS
1202   that occurs between field-content &MAY; be replaced with a single SP
1203   before interpreting the field value or forwarding the message
1204   downstream.
1207   The order in which header fields with differing field names are
1208   received is not significant. However, it is "good practice" to send
1209   general-header fields first, followed by request-header or response-header
1210   fields, and ending with the entity-header fields.
1213   Multiple message-header fields with the same field-name &MAY; be
1214   present in a message if and only if the entire field-value for that
1215   header field is defined as a comma-separated list [i.e., #(values)].
1216   It &MUST; be possible to combine the multiple header fields into one
1217   "field-name: field-value" pair, without changing the semantics of the
1218   message, by appending each subsequent field-value to the first, each
1219   separated by a comma. The order in which header fields with the same
1220   field-name are received is therefore significant to the
1221   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1222   change the order of these field values when a message is forwarded.
1225  <list><t>
1226   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1227   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1228   can occur multiple times, but does not use the list syntax, and thus cannot
1229   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1230   for details.) Also note that the Set-Cookie2 header specified in
1231   <xref target="RFC2965"/> does not share this problem.
1232  </t></list>
1237<section title="Message Body" anchor="message.body">
1238  <x:anchor-alias value="message-body"/>
1240   The message-body (if any) of an HTTP message is used to carry the
1241   entity-body associated with the request or response. The message-body
1242   differs from the entity-body only when a transfer-coding has been
1243   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1245<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1246  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1247               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1250   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1251   applied by an application to ensure safe and proper transfer of the
1252   message. Transfer-Encoding is a property of the message, not of the
1253   entity, and thus &MAY; be added or removed by any application along the
1254   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1255   when certain transfer-codings may be used.)
1258   The rules for when a message-body is allowed in a message differ for
1259   requests and responses.
1262   The presence of a message-body in a request is signaled by the
1263   inclusion of a Content-Length or Transfer-Encoding header field in
1264   the request's message-headers. A message-body &MUST-NOT; be included in
1265   a request if the specification of the request method (&method;)
1266   explicitly disallows an entity-body in requests.
1267   When a request message contains both a message-body of non-zero
1268   length and a method that does not define any semantics for that
1269   request message-body, then an origin server &SHOULD; either ignore
1270   the message-body or respond with an appropriate error message
1271   (e.g., 413).  A proxy or gateway, when presented the same request,
1272   &SHOULD; either forward the request inbound with the message-body or
1273   ignore the message-body when determining a response.
1276   For response messages, whether or not a message-body is included with
1277   a message is dependent on both the request method and the response
1278   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1279   &MUST-NOT; include a message-body, even though the presence of entity-header
1280   fields might lead one to believe they do. All 1xx
1281   (informational), 204 (No Content), and 304 (Not Modified) responses
1282   &MUST-NOT; include a message-body. All other responses do include a
1283   message-body, although it &MAY; be of zero length.
1287<section title="Message Length" anchor="message.length">
1289   The transfer-length of a message is the length of the message-body as
1290   it appears in the message; that is, after any transfer-codings have
1291   been applied. When a message-body is included with a message, the
1292   transfer-length of that body is determined by one of the following
1293   (in order of precedence):
1296  <list style="numbers">
1297    <x:lt><t>
1298     Any response message which "&MUST-NOT;" include a message-body (such
1299     as the 1xx, 204, and 304 responses and any response to a HEAD
1300     request) is always terminated by the first empty line after the
1301     header fields, regardless of the entity-header fields present in
1302     the message.
1303    </t></x:lt>
1304    <x:lt><t>
1305     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1306     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1307     is used, the transfer-length is defined by the use of this transfer-coding.
1308     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1309     is not present, the transfer-length is defined by the sender closing the connection.
1310    </t></x:lt>
1311    <x:lt><t>
1312     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1313     decimal value in OCTETs represents both the entity-length and the
1314     transfer-length. The Content-Length header field &MUST-NOT; be sent
1315     if these two lengths are different (i.e., if a Transfer-Encoding
1316     header field is present). If a message is received with both a
1317     Transfer-Encoding header field and a Content-Length header field,
1318     the latter &MUST; be ignored.
1319    </t></x:lt>
1320    <x:lt><t>
1321     If the message uses the media type "multipart/byteranges", and the
1322     transfer-length is not otherwise specified, then this self-delimiting
1323     media type defines the transfer-length. This media type
1324     &MUST-NOT; be used unless the sender knows that the recipient can parse
1325     it; the presence in a request of a Range header with multiple byte-range
1326     specifiers from a 1.1 client implies that the client can parse
1327     multipart/byteranges responses.
1328    <list style="empty"><t>
1329       A range header might be forwarded by a 1.0 proxy that does not
1330       understand multipart/byteranges; in this case the server &MUST;
1331       delimit the message using methods defined in items 1, 3 or 5 of
1332       this section.
1333    </t></list>
1334    </t></x:lt>
1335    <x:lt><t>
1336     By the server closing the connection. (Closing the connection
1337     cannot be used to indicate the end of a request body, since that
1338     would leave no possibility for the server to send back a response.)
1339    </t></x:lt>
1340  </list>
1343   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1344   containing a message-body &MUST; include a valid Content-Length header
1345   field unless the server is known to be HTTP/1.1 compliant. If a
1346   request contains a message-body and a Content-Length is not given,
1347   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1348   determine the length of the message, or with 411 (Length Required) if
1349   it wishes to insist on receiving a valid Content-Length.
1352   All HTTP/1.1 applications that receive entities &MUST; accept the
1353   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1354   to be used for messages when the message length cannot be determined
1355   in advance.
1358   Messages &MUST-NOT; include both a Content-Length header field and a
1359   transfer-coding. If the message does include a
1360   transfer-coding, the Content-Length &MUST; be ignored.
1363   When a Content-Length is given in a message where a message-body is
1364   allowed, its field value &MUST; exactly match the number of OCTETs in
1365   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1366   invalid length is received and detected.
1370<section title="General Header Fields" anchor="general.header.fields">
1371  <x:anchor-alias value="general-header"/>
1373   There are a few header fields which have general applicability for
1374   both request and response messages, but which do not apply to the
1375   entity being transferred. These header fields apply only to the
1376   message being transmitted.
1378<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1379  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1380                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1381                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1382                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1383                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1384                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1385                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1386                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1387                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1390   General-header field names can be extended reliably only in
1391   combination with a change in the protocol version. However, new or
1392   experimental header fields may be given the semantics of general
1393   header fields if all parties in the communication recognize them to
1394   be general-header fields. Unrecognized header fields are treated as
1395   entity-header fields.
1400<section title="Request" anchor="request">
1401  <x:anchor-alias value="Request"/>
1403   A request message from a client to a server includes, within the
1404   first line of that message, the method to be applied to the resource,
1405   the identifier of the resource, and the protocol version in use.
1407<!--                 Host                      ; should be moved here eventually -->
1408<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1409  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1410                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1411                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1412                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1413                  <x:ref>CRLF</x:ref>
1414                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1417<section title="Request-Line" anchor="request-line">
1418  <x:anchor-alias value="Request-Line"/>
1420   The Request-Line begins with a method token, followed by the
1421   Request-URI and the protocol version, and ending with CRLF. The
1422   elements are separated by SP characters. No CR or LF is allowed
1423   except in the final CRLF sequence.
1425<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1426  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>Request-URI</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1429<section title="Method" anchor="method">
1430  <x:anchor-alias value="Method"/>
1432   The Method  token indicates the method to be performed on the
1433   resource identified by the Request-URI. The method is case-sensitive.
1435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1436  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1440<section title="Request-URI" anchor="request-uri">
1441  <x:anchor-alias value="Request-URI"/>
1443   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1444   identifies the resource upon which to apply the request.
1446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1447  <x:ref>Request-URI</x:ref>    = "*"
1448                 / <x:ref>absolute-URI</x:ref>
1449                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1450                 / <x:ref>authority</x:ref>
1453   The four options for Request-URI are dependent on the nature of the
1454   request. The asterisk "*" means that the request does not apply to a
1455   particular resource, but to the server itself, and is only allowed
1456   when the method used does not necessarily apply to a resource. One
1457   example would be
1459<figure><artwork type="example">
1460    OPTIONS * HTTP/1.1
1463   The absolute-URI form is &REQUIRED; when the request is being made to a
1464   proxy. The proxy is requested to forward the request or service it
1465   from a valid cache, and return the response. Note that the proxy &MAY;
1466   forward the request on to another proxy or directly to the server
1467   specified by the absolute-URI. In order to avoid request loops, a
1468   proxy &MUST; be able to recognize all of its server names, including
1469   any aliases, local variations, and the numeric IP address. An example
1470   Request-Line would be:
1472<figure><artwork type="example">
1473    GET HTTP/1.1
1476   To allow for transition to absolute-URIs in all requests in future
1477   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1478   form in requests, even though HTTP/1.1 clients will only generate
1479   them in requests to proxies.
1482   The authority form is only used by the CONNECT method (&CONNECT;).
1485   The most common form of Request-URI is that used to identify a
1486   resource on an origin server or gateway. In this case the absolute
1487   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1488   the Request-URI, and the network location of the URI (authority) &MUST;
1489   be transmitted in a Host header field. For example, a client wishing
1490   to retrieve the resource above directly from the origin server would
1491   create a TCP connection to port 80 of the host "" and send
1492   the lines:
1494<figure><artwork type="example">
1495    GET /pub/WWW/TheProject.html HTTP/1.1
1496    Host:
1499   followed by the remainder of the Request. Note that the absolute path
1500   cannot be empty; if none is present in the original URI, it &MUST; be
1501   given as "/" (the server root).
1504   The Request-URI is transmitted in the format specified in
1505   <xref target="http.uri"/>. If the Request-URI is encoded using the
1506   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1507   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1508   &MUST; decode the Request-URI in order to
1509   properly interpret the request. Servers &SHOULD; respond to invalid
1510   Request-URIs with an appropriate status code.
1513   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1514   received Request-URI when forwarding it to the next inbound server,
1515   except as noted above to replace a null path-absolute with "/".
1518  <list><t>
1519      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1520      meaning of the request when the origin server is improperly using
1521      a non-reserved URI character for a reserved purpose.  Implementors
1522      should be aware that some pre-HTTP/1.1 proxies have been known to
1523      rewrite the Request-URI.
1524  </t></list>
1529<section title="The Resource Identified by a Request" anchor="">
1531   The exact resource identified by an Internet request is determined by
1532   examining both the Request-URI and the Host header field.
1535   An origin server that does not allow resources to differ by the
1536   requested host &MAY; ignore the Host header field value when
1537   determining the resource identified by an HTTP/1.1 request. (But see
1538   <xref target=""/>
1539   for other requirements on Host support in HTTP/1.1.)
1542   An origin server that does differentiate resources based on the host
1543   requested (sometimes referred to as virtual hosts or vanity host
1544   names) &MUST; use the following rules for determining the requested
1545   resource on an HTTP/1.1 request:
1546  <list style="numbers">
1547    <t>If Request-URI is an absolute-URI, the host is part of the
1548     Request-URI. Any Host header field value in the request &MUST; be
1549     ignored.</t>
1550    <t>If the Request-URI is not an absolute-URI, and the request includes
1551     a Host header field, the host is determined by the Host header
1552     field value.</t>
1553    <t>If the host as determined by rule 1 or 2 is not a valid host on
1554     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1555  </list>
1558   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1559   attempt to use heuristics (e.g., examination of the URI path for
1560   something unique to a particular host) in order to determine what
1561   exact resource is being requested.
1568<section title="Response" anchor="response">
1569  <x:anchor-alias value="Response"/>
1571   After receiving and interpreting a request message, a server responds
1572   with an HTTP response message.
1574<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1575  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1576                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1577                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1578                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1579                  <x:ref>CRLF</x:ref>
1580                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1583<section title="Status-Line" anchor="status-line">
1584  <x:anchor-alias value="Status-Line"/>
1586   The first line of a Response message is the Status-Line, consisting
1587   of the protocol version followed by a numeric status code and its
1588   associated textual phrase, with each element separated by SP
1589   characters. No CR or LF is allowed except in the final CRLF sequence.
1591<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1592  <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>
1595<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1596  <x:anchor-alias value="Reason-Phrase"/>
1597  <x:anchor-alias value="Status-Code"/>
1599   The Status-Code element is a 3-digit integer result code of the
1600   attempt to understand and satisfy the request. These codes are fully
1601   defined in &status-codes;.  The Reason Phrase exists for the sole
1602   purpose of providing a textual description associated with the numeric
1603   status code, out of deference to earlier Internet application protocols
1604   that were more frequently used with interactive text clients.
1605   A client &SHOULD; ignore the content of the Reason Phrase.
1608   The first digit of the Status-Code defines the class of response. The
1609   last two digits do not have any categorization role. There are 5
1610   values for the first digit:
1611  <list style="symbols">
1612    <t>
1613      1xx: Informational - Request received, continuing process
1614    </t>
1615    <t>
1616      2xx: Success - The action was successfully received,
1617        understood, and accepted
1618    </t>
1619    <t>
1620      3xx: Redirection - Further action must be taken in order to
1621        complete the request
1622    </t>
1623    <t>
1624      4xx: Client Error - The request contains bad syntax or cannot
1625        be fulfilled
1626    </t>
1627    <t>
1628      5xx: Server Error - The server failed to fulfill an apparently
1629        valid request
1630    </t>
1631  </list>
1633<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"/>
1634  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1635  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1643<section title="Connections" anchor="connections">
1645<section title="Persistent Connections" anchor="persistent.connections">
1647<section title="Purpose" anchor="persistent.purpose">
1649   Prior to persistent connections, a separate TCP connection was
1650   established to fetch each URL, increasing the load on HTTP servers
1651   and causing congestion on the Internet. The use of inline images and
1652   other associated data often require a client to make multiple
1653   requests of the same server in a short amount of time. Analysis of
1654   these performance problems and results from a prototype
1655   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1656   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1657   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1658   T/TCP <xref target="Tou1998"/>.
1661   Persistent HTTP connections have a number of advantages:
1662  <list style="symbols">
1663      <t>
1664        By opening and closing fewer TCP connections, CPU time is saved
1665        in routers and hosts (clients, servers, proxies, gateways,
1666        tunnels, or caches), and memory used for TCP protocol control
1667        blocks can be saved in hosts.
1668      </t>
1669      <t>
1670        HTTP requests and responses can be pipelined on a connection.
1671        Pipelining allows a client to make multiple requests without
1672        waiting for each response, allowing a single TCP connection to
1673        be used much more efficiently, with much lower elapsed time.
1674      </t>
1675      <t>
1676        Network congestion is reduced by reducing the number of packets
1677        caused by TCP opens, and by allowing TCP sufficient time to
1678        determine the congestion state of the network.
1679      </t>
1680      <t>
1681        Latency on subsequent requests is reduced since there is no time
1682        spent in TCP's connection opening handshake.
1683      </t>
1684      <t>
1685        HTTP can evolve more gracefully, since errors can be reported
1686        without the penalty of closing the TCP connection. Clients using
1687        future versions of HTTP might optimistically try a new feature,
1688        but if communicating with an older server, retry with old
1689        semantics after an error is reported.
1690      </t>
1691    </list>
1694   HTTP implementations &SHOULD; implement persistent connections.
1698<section title="Overall Operation" anchor="persistent.overall">
1700   A significant difference between HTTP/1.1 and earlier versions of
1701   HTTP is that persistent connections are the default behavior of any
1702   HTTP connection. That is, unless otherwise indicated, the client
1703   &SHOULD; assume that the server will maintain a persistent connection,
1704   even after error responses from the server.
1707   Persistent connections provide a mechanism by which a client and a
1708   server can signal the close of a TCP connection. This signaling takes
1709   place using the Connection header field (<xref target="header.connection"/>). Once a close
1710   has been signaled, the client &MUST-NOT; send any more requests on that
1711   connection.
1714<section title="Negotiation" anchor="persistent.negotiation">
1716   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1717   maintain a persistent connection unless a Connection header including
1718   the connection-token "close" was sent in the request. If the server
1719   chooses to close the connection immediately after sending the
1720   response, it &SHOULD; send a Connection header including the
1721   connection-token close.
1724   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1725   decide to keep it open based on whether the response from a server
1726   contains a Connection header with the connection-token close. In case
1727   the client does not want to maintain a connection for more than that
1728   request, it &SHOULD; send a Connection header including the
1729   connection-token close.
1732   If either the client or the server sends the close token in the
1733   Connection header, that request becomes the last one for the
1734   connection.
1737   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1738   maintained for HTTP versions less than 1.1 unless it is explicitly
1739   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1740   compatibility with HTTP/1.0 clients.
1743   In order to remain persistent, all messages on the connection &MUST;
1744   have a self-defined message length (i.e., one not defined by closure
1745   of the connection), as described in <xref target="message.length"/>.
1749<section title="Pipelining" anchor="pipelining">
1751   A client that supports persistent connections &MAY; "pipeline" its
1752   requests (i.e., send multiple requests without waiting for each
1753   response). A server &MUST; send its responses to those requests in the
1754   same order that the requests were received.
1757   Clients which assume persistent connections and pipeline immediately
1758   after connection establishment &SHOULD; be prepared to retry their
1759   connection if the first pipelined attempt fails. If a client does
1760   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1761   persistent. Clients &MUST; also be prepared to resend their requests if
1762   the server closes the connection before sending all of the
1763   corresponding responses.
1766   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1767   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1768   premature termination of the transport connection could lead to
1769   indeterminate results. A client wishing to send a non-idempotent
1770   request &SHOULD; wait to send that request until it has received the
1771   response status for the previous request.
1776<section title="Proxy Servers" anchor="persistent.proxy">
1778   It is especially important that proxies correctly implement the
1779   properties of the Connection header field as specified in <xref target="header.connection"/>.
1782   The proxy server &MUST; signal persistent connections separately with
1783   its clients and the origin servers (or other proxy servers) that it
1784   connects to. Each persistent connection applies to only one transport
1785   link.
1788   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1789   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1790   discussion of the problems with the Keep-Alive header implemented by
1791   many HTTP/1.0 clients).
1795<section title="Practical Considerations" anchor="persistent.practical">
1797   Servers will usually have some time-out value beyond which they will
1798   no longer maintain an inactive connection. Proxy servers might make
1799   this a higher value since it is likely that the client will be making
1800   more connections through the same server. The use of persistent
1801   connections places no requirements on the length (or existence) of
1802   this time-out for either the client or the server.
1805   When a client or server wishes to time-out it &SHOULD; issue a graceful
1806   close on the transport connection. Clients and servers &SHOULD; both
1807   constantly watch for the other side of the transport close, and
1808   respond to it as appropriate. If a client or server does not detect
1809   the other side's close promptly it could cause unnecessary resource
1810   drain on the network.
1813   A client, server, or proxy &MAY; close the transport connection at any
1814   time. For example, a client might have started to send a new request
1815   at the same time that the server has decided to close the "idle"
1816   connection. From the server's point of view, the connection is being
1817   closed while it was idle, but from the client's point of view, a
1818   request is in progress.
1821   This means that clients, servers, and proxies &MUST; be able to recover
1822   from asynchronous close events. Client software &SHOULD; reopen the
1823   transport connection and retransmit the aborted sequence of requests
1824   without user interaction so long as the request sequence is
1825   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1826   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1827   human operator the choice of retrying the request(s). Confirmation by
1828   user-agent software with semantic understanding of the application
1829   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1830   be repeated if the second sequence of requests fails.
1833   Servers &SHOULD; always respond to at least one request per connection,
1834   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1835   middle of transmitting a response, unless a network or client failure
1836   is suspected.
1839   Clients that use persistent connections &SHOULD; limit the number of
1840   simultaneous connections that they maintain to a given server. A
1841   single-user client &SHOULD-NOT; maintain more than 2 connections with
1842   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1843   another server or proxy, where N is the number of simultaneously
1844   active users. These guidelines are intended to improve HTTP response
1845   times and avoid congestion.
1850<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1852<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1854   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1855   flow control mechanisms to resolve temporary overloads, rather than
1856   terminating connections with the expectation that clients will retry.
1857   The latter technique can exacerbate network congestion.
1861<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1863   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1864   the network connection for an error status while it is transmitting
1865   the request. If the client sees an error status, it &SHOULD;
1866   immediately cease transmitting the body. If the body is being sent
1867   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1868   empty trailer &MAY; be used to prematurely mark the end of the message.
1869   If the body was preceded by a Content-Length header, the client &MUST;
1870   close the connection.
1874<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1876   The purpose of the 100 (Continue) status (see &status-100;) is to
1877   allow a client that is sending a request message with a request body
1878   to determine if the origin server is willing to accept the request
1879   (based on the request headers) before the client sends the request
1880   body. In some cases, it might either be inappropriate or highly
1881   inefficient for the client to send the body if the server will reject
1882   the message without looking at the body.
1885   Requirements for HTTP/1.1 clients:
1886  <list style="symbols">
1887    <t>
1888        If a client will wait for a 100 (Continue) response before
1889        sending the request body, it &MUST; send an Expect request-header
1890        field (&header-expect;) with the "100-continue" expectation.
1891    </t>
1892    <t>
1893        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1894        with the "100-continue" expectation if it does not intend
1895        to send a request body.
1896    </t>
1897  </list>
1900   Because of the presence of older implementations, the protocol allows
1901   ambiguous situations in which a client may send "Expect: 100-continue"
1902   without receiving either a 417 (Expectation Failed) status
1903   or a 100 (Continue) status. Therefore, when a client sends this
1904   header field to an origin server (possibly via a proxy) from which it
1905   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1906   for an indefinite period before sending the request body.
1909   Requirements for HTTP/1.1 origin servers:
1910  <list style="symbols">
1911    <t> Upon receiving a request which includes an Expect request-header
1912        field with the "100-continue" expectation, an origin server &MUST;
1913        either respond with 100 (Continue) status and continue to read
1914        from the input stream, or respond with a final status code. The
1915        origin server &MUST-NOT; wait for the request body before sending
1916        the 100 (Continue) response. If it responds with a final status
1917        code, it &MAY; close the transport connection or it &MAY; continue
1918        to read and discard the rest of the request.  It &MUST-NOT;
1919        perform the requested method if it returns a final status code.
1920    </t>
1921    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1922        the request message does not include an Expect request-header
1923        field with the "100-continue" expectation, and &MUST-NOT; send a
1924        100 (Continue) response if such a request comes from an HTTP/1.0
1925        (or earlier) client. There is an exception to this rule: for
1926        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1927        status in response to an HTTP/1.1 PUT or POST request that does
1928        not include an Expect request-header field with the "100-continue"
1929        expectation. This exception, the purpose of which is
1930        to minimize any client processing delays associated with an
1931        undeclared wait for 100 (Continue) status, applies only to
1932        HTTP/1.1 requests, and not to requests with any other HTTP-version
1933        value.
1934    </t>
1935    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1936        already received some or all of the request body for the
1937        corresponding request.
1938    </t>
1939    <t> An origin server that sends a 100 (Continue) response &MUST;
1940    ultimately send a final status code, once the request body is
1941        received and processed, unless it terminates the transport
1942        connection prematurely.
1943    </t>
1944    <t> If an origin server receives a request that does not include an
1945        Expect request-header field with the "100-continue" expectation,
1946        the request includes a request body, and the server responds
1947        with a final status code before reading the entire request body
1948        from the transport connection, then the server &SHOULD-NOT;  close
1949        the transport connection until it has read the entire request,
1950        or until the client closes the connection. Otherwise, the client
1951        might not reliably receive the response message. However, this
1952        requirement is not be construed as preventing a server from
1953        defending itself against denial-of-service attacks, or from
1954        badly broken client implementations.
1955      </t>
1956    </list>
1959   Requirements for HTTP/1.1 proxies:
1960  <list style="symbols">
1961    <t> If a proxy receives a request that includes an Expect request-header
1962        field with the "100-continue" expectation, and the proxy
1963        either knows that the next-hop server complies with HTTP/1.1 or
1964        higher, or does not know the HTTP version of the next-hop
1965        server, it &MUST; forward the request, including the Expect header
1966        field.
1967    </t>
1968    <t> If the proxy knows that the version of the next-hop server is
1969        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1970        respond with a 417 (Expectation Failed) status.
1971    </t>
1972    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1973        numbers received from recently-referenced next-hop servers.
1974    </t>
1975    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1976        request message was received from an HTTP/1.0 (or earlier)
1977        client and did not include an Expect request-header field with
1978        the "100-continue" expectation. This requirement overrides the
1979        general rule for forwarding of 1xx responses (see &status-1xx;).
1980    </t>
1981  </list>
1985<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1987   If an HTTP/1.1 client sends a request which includes a request body,
1988   but which does not include an Expect request-header field with the
1989   "100-continue" expectation, and if the client is not directly
1990   connected to an HTTP/1.1 origin server, and if the client sees the
1991   connection close before receiving any status from the server, the
1992   client &SHOULD; retry the request.  If the client does retry this
1993   request, it &MAY; use the following "binary exponential backoff"
1994   algorithm to be assured of obtaining a reliable response:
1995  <list style="numbers">
1996    <t>
1997      Initiate a new connection to the server
1998    </t>
1999    <t>
2000      Transmit the request-headers
2001    </t>
2002    <t>
2003      Initialize a variable R to the estimated round-trip time to the
2004         server (e.g., based on the time it took to establish the
2005         connection), or to a constant value of 5 seconds if the round-trip
2006         time is not available.
2007    </t>
2008    <t>
2009       Compute T = R * (2**N), where N is the number of previous
2010         retries of this request.
2011    </t>
2012    <t>
2013       Wait either for an error response from the server, or for T
2014         seconds (whichever comes first)
2015    </t>
2016    <t>
2017       If no error response is received, after T seconds transmit the
2018         body of the request.
2019    </t>
2020    <t>
2021       If client sees that the connection is closed prematurely,
2022         repeat from step 1 until the request is accepted, an error
2023         response is received, or the user becomes impatient and
2024         terminates the retry process.
2025    </t>
2026  </list>
2029   If at any point an error status is received, the client
2030  <list style="symbols">
2031      <t>&SHOULD-NOT;  continue and</t>
2033      <t>&SHOULD; close the connection if it has not completed sending the
2034        request message.</t>
2035    </list>
2042<section title="Header Field Definitions" anchor="header.fields">
2044   This section defines the syntax and semantics of HTTP/1.1 header fields
2045   related to message framing and transport protocols.
2048   For entity-header fields, both sender and recipient refer to either the
2049   client or the server, depending on who sends and who receives the entity.
2052<section title="Connection" anchor="header.connection">
2053  <iref primary="true" item="Connection header" x:for-anchor=""/>
2054  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2055  <x:anchor-alias value="Connection"/>
2056  <x:anchor-alias value="connection-token"/>
2058   The Connection general-header field allows the sender to specify
2059   options that are desired for that particular connection and &MUST-NOT;
2060   be communicated by proxies over further connections.
2063   The Connection header has the following grammar:
2065<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2066  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2067  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2070   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2071   message is forwarded and, for each connection-token in this field,
2072   remove any header field(s) from the message with the same name as the
2073   connection-token. Connection options are signaled by the presence of
2074   a connection-token in the Connection header field, not by any
2075   corresponding additional header field(s), since the additional header
2076   field may not be sent if there are no parameters associated with that
2077   connection option.
2080   Message headers listed in the Connection header &MUST-NOT; include
2081   end-to-end headers, such as Cache-Control.
2084   HTTP/1.1 defines the "close" connection option for the sender to
2085   signal that the connection will be closed after completion of the
2086   response. For example,
2088<figure><artwork type="example">
2089    Connection: close
2092   in either the request or the response header fields indicates that
2093   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2094   after the current request/response is complete.
2097   An HTTP/1.1 client that does not support persistent connections &MUST;
2098   include the "close" connection option in every request message.
2101   An HTTP/1.1 server that does not support persistent connections &MUST;
2102   include the "close" connection option in every response message that
2103   does not have a 1xx (informational) status code.
2106   A system receiving an HTTP/1.0 (or lower-version) message that
2107   includes a Connection header &MUST;, for each connection-token in this
2108   field, remove and ignore any header field(s) from the message with
2109   the same name as the connection-token. This protects against mistaken
2110   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2114<section title="Content-Length" anchor="header.content-length">
2115  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2116  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2117  <x:anchor-alias value="Content-Length"/>
2119   The Content-Length entity-header field indicates the size of the
2120   entity-body, in decimal number of OCTETs, sent to the recipient or,
2121   in the case of the HEAD method, the size of the entity-body that
2122   would have been sent had the request been a GET.
2124<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2125  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2128   An example is
2130<figure><artwork type="example">
2131    Content-Length: 3495
2134   Applications &SHOULD; use this field to indicate the transfer-length of
2135   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2138   Any Content-Length greater than or equal to zero is a valid value.
2139   <xref target="message.length"/> describes how to determine the length of a message-body
2140   if a Content-Length is not given.
2143   Note that the meaning of this field is significantly different from
2144   the corresponding definition in MIME, where it is an optional field
2145   used within the "message/external-body" content-type. In HTTP, it
2146   &SHOULD; be sent whenever the message's length can be determined prior
2147   to being transferred, unless this is prohibited by the rules in
2148   <xref target="message.length"/>.
2152<section title="Date" anchor="">
2153  <iref primary="true" item="Date header" x:for-anchor=""/>
2154  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2155  <x:anchor-alias value="Date"/>
2157   The Date general-header field represents the date and time at which
2158   the message was originated, having the same semantics as orig-date in
2159   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2160   HTTP-date, as described in <xref target=""/>;
2161   it &MUST; be sent in rfc1123-date format.
2163<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2164  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2167   An example is
2169<figure><artwork type="example">
2170    Date: Tue, 15 Nov 1994 08:12:31 GMT
2173   Origin servers &MUST; include a Date header field in all responses,
2174   except in these cases:
2175  <list style="numbers">
2176      <t>If the response status code is 100 (Continue) or 101 (Switching
2177         Protocols), the response &MAY; include a Date header field, at
2178         the server's option.</t>
2180      <t>If the response status code conveys a server error, e.g. 500
2181         (Internal Server Error) or 503 (Service Unavailable), and it is
2182         inconvenient or impossible to generate a valid Date.</t>
2184      <t>If the server does not have a clock that can provide a
2185         reasonable approximation of the current time, its responses
2186         &MUST-NOT; include a Date header field. In this case, the rules
2187         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2188  </list>
2191   A received message that does not have a Date header field &MUST; be
2192   assigned one by the recipient if the message will be cached by that
2193   recipient or gatewayed via a protocol which requires a Date. An HTTP
2194   implementation without a clock &MUST-NOT; cache responses without
2195   revalidating them on every use. An HTTP cache, especially a shared
2196   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2197   clock with a reliable external standard.
2200   Clients &SHOULD; only send a Date header field in messages that include
2201   an entity-body, as in the case of the PUT and POST requests, and even
2202   then it is optional. A client without a clock &MUST-NOT; send a Date
2203   header field in a request.
2206   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2207   time subsequent to the generation of the message. It &SHOULD; represent
2208   the best available approximation of the date and time of message
2209   generation, unless the implementation has no means of generating a
2210   reasonably accurate date and time. In theory, the date ought to
2211   represent the moment just before the entity is generated. In
2212   practice, the date can be generated at any time during the message
2213   origination without affecting its semantic value.
2216<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2218   Some origin server implementations might not have a clock available.
2219   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2220   values to a response, unless these values were associated
2221   with the resource by a system or user with a reliable clock. It &MAY;
2222   assign an Expires value that is known, at or before server
2223   configuration time, to be in the past (this allows "pre-expiration"
2224   of responses without storing separate Expires values for each
2225   resource).
2230<section title="Host" anchor="">
2231  <iref primary="true" item="Host header" x:for-anchor=""/>
2232  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2233  <x:anchor-alias value="Host"/>
2235   The Host request-header field specifies the Internet host and port
2236   number of the resource being requested, as obtained from the original
2237   URI given by the user or referring resource (generally an http URI,
2238   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2239   the naming authority of the origin server or gateway given by the
2240   original URL. This allows the origin server or gateway to
2241   differentiate between internally-ambiguous URLs, such as the root "/"
2242   URL of a server for multiple host names on a single IP address.
2244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2245  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2248   A "host" without any trailing port information implies the default
2249   port for the service requested (e.g., "80" for an HTTP URL). For
2250   example, a request on the origin server for
2251   &lt;; would properly include:
2253<figure><artwork type="example">
2254    GET /pub/WWW/ HTTP/1.1
2255    Host:
2258   A client &MUST; include a Host header field in all HTTP/1.1 request
2259   messages. If the requested URI does not include an Internet host
2260   name for the service being requested, then the Host header field &MUST;
2261   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2262   request message it forwards does contain an appropriate Host header
2263   field that identifies the service being requested by the proxy. All
2264   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2265   status code to any HTTP/1.1 request message which lacks a Host header
2266   field.
2269   See Sections <xref target="" format="counter"/>
2270   and <xref target="" format="counter"/>
2271   for other requirements relating to Host.
2275<section title="TE" anchor="header.te">
2276  <iref primary="true" item="TE header" x:for-anchor=""/>
2277  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2278  <x:anchor-alias value="TE"/>
2279  <x:anchor-alias value="t-codings"/>
2281   The TE request-header field indicates what extension transfer-codings
2282   it is willing to accept in the response and whether or not it is
2283   willing to accept trailer fields in a chunked transfer-coding. Its
2284   value may consist of the keyword "trailers" and/or a comma-separated
2285   list of extension transfer-coding names with optional accept
2286   parameters (as described in <xref target="transfer.codings"/>).
2288<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2289  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2290  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2293   The presence of the keyword "trailers" indicates that the client is
2294   willing to accept trailer fields in a chunked transfer-coding, as
2295   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2296   transfer-coding values even though it does not itself represent a
2297   transfer-coding.
2300   Examples of its use are:
2302<figure><artwork type="example">
2303    TE: deflate
2304    TE:
2305    TE: trailers, deflate;q=0.5
2308   The TE header field only applies to the immediate connection.
2309   Therefore, the keyword &MUST; be supplied within a Connection header
2310   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2313   A server tests whether a transfer-coding is acceptable, according to
2314   a TE field, using these rules:
2315  <list style="numbers">
2316    <x:lt>
2317      <t>The "chunked" transfer-coding is always acceptable. If the
2318         keyword "trailers" is listed, the client indicates that it is
2319         willing to accept trailer fields in the chunked response on
2320         behalf of itself and any downstream clients. The implication is
2321         that, if given, the client is stating that either all
2322         downstream clients are willing to accept trailer fields in the
2323         forwarded response, or that it will attempt to buffer the
2324         response on behalf of downstream recipients.
2325      </t><t>
2326         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2327         chunked response such that a client can be assured of buffering
2328         the entire response.</t>
2329    </x:lt>
2330    <x:lt>
2331      <t>If the transfer-coding being tested is one of the transfer-codings
2332         listed in the TE field, then it is acceptable unless it
2333         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2334         qvalue of 0 means "not acceptable.")</t>
2335    </x:lt>
2336    <x:lt>
2337      <t>If multiple transfer-codings are acceptable, then the
2338         acceptable transfer-coding with the highest non-zero qvalue is
2339         preferred.  The "chunked" transfer-coding always has a qvalue
2340         of 1.</t>
2341    </x:lt>
2342  </list>
2345   If the TE field-value is empty or if no TE field is present, the only
2346   transfer-coding  is "chunked". A message with no transfer-coding is
2347   always acceptable.
2351<section title="Trailer" anchor="header.trailer">
2352  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2353  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2354  <x:anchor-alias value="Trailer"/>
2356   The Trailer general field value indicates that the given set of
2357   header fields is present in the trailer of a message encoded with
2358   chunked transfer-coding.
2360<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2361  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2364   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2365   message using chunked transfer-coding with a non-empty trailer. Doing
2366   so allows the recipient to know which header fields to expect in the
2367   trailer.
2370   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2371   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2372   trailer fields in a "chunked" transfer-coding.
2375   Message header fields listed in the Trailer header field &MUST-NOT;
2376   include the following header fields:
2377  <list style="symbols">
2378    <t>Transfer-Encoding</t>
2379    <t>Content-Length</t>
2380    <t>Trailer</t>
2381  </list>
2385<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2386  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2387  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2388  <x:anchor-alias value="Transfer-Encoding"/>
2390   The Transfer-Encoding general-header field indicates what (if any)
2391   type of transformation has been applied to the message body in order
2392   to safely transfer it between the sender and the recipient. This
2393   differs from the content-coding in that the transfer-coding is a
2394   property of the message, not of the entity.
2396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2397  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2400   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2402<figure><artwork type="example">
2403  Transfer-Encoding: chunked
2406   If multiple encodings have been applied to an entity, the transfer-codings
2407   &MUST; be listed in the order in which they were applied.
2408   Additional information about the encoding parameters &MAY; be provided
2409   by other entity-header fields not defined by this specification.
2412   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2413   header.
2417<section title="Upgrade" anchor="header.upgrade">
2418  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2419  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2420  <x:anchor-alias value="Upgrade"/>
2422   The Upgrade general-header allows the client to specify what
2423   additional communication protocols it supports and would like to use
2424   if the server finds it appropriate to switch protocols. The server
2425   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2426   response to indicate which protocol(s) are being switched.
2428<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2429  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2432   For example,
2434<figure><artwork type="example">
2435    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2438   The Upgrade header field is intended to provide a simple mechanism
2439   for transition from HTTP/1.1 to some other, incompatible protocol. It
2440   does so by allowing the client to advertise its desire to use another
2441   protocol, such as a later version of HTTP with a higher major version
2442   number, even though the current request has been made using HTTP/1.1.
2443   This eases the difficult transition between incompatible protocols by
2444   allowing the client to initiate a request in the more commonly
2445   supported protocol while indicating to the server that it would like
2446   to use a "better" protocol if available (where "better" is determined
2447   by the server, possibly according to the nature of the method and/or
2448   resource being requested).
2451   The Upgrade header field only applies to switching application-layer
2452   protocols upon the existing transport-layer connection. Upgrade
2453   cannot be used to insist on a protocol change; its acceptance and use
2454   by the server is optional. The capabilities and nature of the
2455   application-layer communication after the protocol change is entirely
2456   dependent upon the new protocol chosen, although the first action
2457   after changing the protocol &MUST; be a response to the initial HTTP
2458   request containing the Upgrade header field.
2461   The Upgrade header field only applies to the immediate connection.
2462   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2463   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2464   HTTP/1.1 message.
2467   The Upgrade header field cannot be used to indicate a switch to a
2468   protocol on a different connection. For that purpose, it is more
2469   appropriate to use a 301, 302, 303, or 305 redirection response.
2472   This specification only defines the protocol name "HTTP" for use by
2473   the family of Hypertext Transfer Protocols, as defined by the HTTP
2474   version rules of <xref target="http.version"/> and future updates to this
2475   specification. Any token can be used as a protocol name; however, it
2476   will only be useful if both the client and server associate the name
2477   with the same protocol.
2481<section title="Via" anchor="header.via">
2482  <iref primary="true" item="Via header" x:for-anchor=""/>
2483  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2484  <x:anchor-alias value="protocol-name"/>
2485  <x:anchor-alias value="protocol-version"/>
2486  <x:anchor-alias value="pseudonym"/>
2487  <x:anchor-alias value="received-by"/>
2488  <x:anchor-alias value="received-protocol"/>
2489  <x:anchor-alias value="Via"/>
2491   The Via general-header field &MUST; be used by gateways and proxies to
2492   indicate the intermediate protocols and recipients between the user
2493   agent and the server on requests, and between the origin server and
2494   the client on responses. It is analogous to the "Received" field defined in
2495   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2496   avoiding request loops, and identifying the protocol capabilities of
2497   all senders along the request/response chain.
2499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2500  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2501  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2502  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2503  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2504  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2505  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2508   The received-protocol indicates the protocol version of the message
2509   received by the server or client along each segment of the
2510   request/response chain. The received-protocol version is appended to
2511   the Via field value when the message is forwarded so that information
2512   about the protocol capabilities of upstream applications remains
2513   visible to all recipients.
2516   The protocol-name is optional if and only if it would be "HTTP". The
2517   received-by field is normally the host and optional port number of a
2518   recipient server or client that subsequently forwarded the message.
2519   However, if the real host is considered to be sensitive information,
2520   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2521   be assumed to be the default port of the received-protocol.
2524   Multiple Via field values represents each proxy or gateway that has
2525   forwarded the message. Each recipient &MUST; append its information
2526   such that the end result is ordered according to the sequence of
2527   forwarding applications.
2530   Comments &MAY; be used in the Via header field to identify the software
2531   of the recipient proxy or gateway, analogous to the User-Agent and
2532   Server header fields. However, all comments in the Via field are
2533   optional and &MAY; be removed by any recipient prior to forwarding the
2534   message.
2537   For example, a request message could be sent from an HTTP/1.0 user
2538   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2539   forward the request to a public proxy at, which completes
2540   the request by forwarding it to the origin server at
2541   The request received by would then have the following
2542   Via header field:
2544<figure><artwork type="example">
2545    Via: 1.0 fred, 1.1 (Apache/1.1)
2548   Proxies and gateways used as a portal through a network firewall
2549   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2550   the firewall region. This information &SHOULD; only be propagated if
2551   explicitly enabled. If not enabled, the received-by host of any host
2552   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2553   for that host.
2556   For organizations that have strong privacy requirements for hiding
2557   internal structures, a proxy &MAY; combine an ordered subsequence of
2558   Via header field entries with identical received-protocol values into
2559   a single such entry. For example,
2561<figure><artwork type="example">
2562    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2565        could be collapsed to
2567<figure><artwork type="example">
2568    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2571   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2572   under the same organizational control and the hosts have already been
2573   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2574   have different received-protocol values.
2580<section title="IANA Considerations" anchor="IANA.considerations">
2581<section title="Message Header Registration" anchor="message.header.registration">
2583   The Message Header Registry located at <eref target=""/> should be updated
2584   with the permanent registrations below (see <xref target="RFC3864"/>):
2586<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2587<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2588   <ttcol>Header Field Name</ttcol>
2589   <ttcol>Protocol</ttcol>
2590   <ttcol>Status</ttcol>
2591   <ttcol>Reference</ttcol>
2593   <c>Connection</c>
2594   <c>http</c>
2595   <c>standard</c>
2596   <c>
2597      <xref target="header.connection"/>
2598   </c>
2599   <c>Content-Length</c>
2600   <c>http</c>
2601   <c>standard</c>
2602   <c>
2603      <xref target="header.content-length"/>
2604   </c>
2605   <c>Date</c>
2606   <c>http</c>
2607   <c>standard</c>
2608   <c>
2609      <xref target=""/>
2610   </c>
2611   <c>Host</c>
2612   <c>http</c>
2613   <c>standard</c>
2614   <c>
2615      <xref target=""/>
2616   </c>
2617   <c>TE</c>
2618   <c>http</c>
2619   <c>standard</c>
2620   <c>
2621      <xref target="header.te"/>
2622   </c>
2623   <c>Trailer</c>
2624   <c>http</c>
2625   <c>standard</c>
2626   <c>
2627      <xref target="header.trailer"/>
2628   </c>
2629   <c>Transfer-Encoding</c>
2630   <c>http</c>
2631   <c>standard</c>
2632   <c>
2633      <xref target="header.transfer-encoding"/>
2634   </c>
2635   <c>Upgrade</c>
2636   <c>http</c>
2637   <c>standard</c>
2638   <c>
2639      <xref target="header.upgrade"/>
2640   </c>
2641   <c>Via</c>
2642   <c>http</c>
2643   <c>standard</c>
2644   <c>
2645      <xref target="header.via"/>
2646   </c>
2650   The change controller is: "IETF ( - Internet Engineering Task Force".
2654<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2656   The entry for the "http" URI Scheme in the registry located at
2657   <eref target=""/>
2658   should be updated to point to <xref target="http.uri"/> of this document
2659   (see <xref target="RFC4395"/>).
2663<section title="Internet Media Type Registrations" anchor="">
2665   This document serves as the specification for the Internet media types
2666   "message/http" and "application/http". The following is to be registered with
2667   IANA (see <xref target="RFC4288"/>).
2669<section title="Internet Media Type message/http" anchor="">
2670<iref item="Media Type" subitem="message/http" primary="true"/>
2671<iref item="message/http Media Type" primary="true"/>
2673   The message/http type can be used to enclose a single HTTP request or
2674   response message, provided that it obeys the MIME restrictions for all
2675   "message" types regarding line length and encodings.
2678  <list style="hanging" x:indent="12em">
2679    <t hangText="Type name:">
2680      message
2681    </t>
2682    <t hangText="Subtype name:">
2683      http
2684    </t>
2685    <t hangText="Required parameters:">
2686      none
2687    </t>
2688    <t hangText="Optional parameters:">
2689      version, msgtype
2690      <list style="hanging">
2691        <t hangText="version:">
2692          The HTTP-Version number of the enclosed message
2693          (e.g., "1.1"). If not present, the version can be
2694          determined from the first line of the body.
2695        </t>
2696        <t hangText="msgtype:">
2697          The message type -- "request" or "response". If not
2698          present, the type can be determined from the first
2699          line of the body.
2700        </t>
2701      </list>
2702    </t>
2703    <t hangText="Encoding considerations:">
2704      only "7bit", "8bit", or "binary" are permitted
2705    </t>
2706    <t hangText="Security considerations:">
2707      none
2708    </t>
2709    <t hangText="Interoperability considerations:">
2710      none
2711    </t>
2712    <t hangText="Published specification:">
2713      This specification (see <xref target=""/>).
2714    </t>
2715    <t hangText="Applications that use this media type:">
2716    </t>
2717    <t hangText="Additional information:">
2718      <list style="hanging">
2719        <t hangText="Magic number(s):">none</t>
2720        <t hangText="File extension(s):">none</t>
2721        <t hangText="Macintosh file type code(s):">none</t>
2722      </list>
2723    </t>
2724    <t hangText="Person and email address to contact for further information:">
2725      See Authors Section.
2726    </t>
2727                <t hangText="Intended usage:">
2728                  COMMON
2729    </t>
2730                <t hangText="Restrictions on usage:">
2731                  none
2732    </t>
2733    <t hangText="Author/Change controller:">
2734      IESG
2735    </t>
2736  </list>
2739<section title="Internet Media Type application/http" anchor="">
2740<iref item="Media Type" subitem="application/http" primary="true"/>
2741<iref item="application/http Media Type" primary="true"/>
2743   The application/http type can be used to enclose a pipeline of one or more
2744   HTTP request or response messages (not intermixed).
2747  <list style="hanging" x:indent="12em">
2748    <t hangText="Type name:">
2749      application
2750    </t>
2751    <t hangText="Subtype name:">
2752      http
2753    </t>
2754    <t hangText="Required parameters:">
2755      none
2756    </t>
2757    <t hangText="Optional parameters:">
2758      version, msgtype
2759      <list style="hanging">
2760        <t hangText="version:">
2761          The HTTP-Version number of the enclosed messages
2762          (e.g., "1.1"). If not present, the version can be
2763          determined from the first line of the body.
2764        </t>
2765        <t hangText="msgtype:">
2766          The message type -- "request" or "response". If not
2767          present, the type can be determined from the first
2768          line of the body.
2769        </t>
2770      </list>
2771    </t>
2772    <t hangText="Encoding considerations:">
2773      HTTP messages enclosed by this type
2774      are in "binary" format; use of an appropriate
2775      Content-Transfer-Encoding is required when
2776      transmitted via E-mail.
2777    </t>
2778    <t hangText="Security considerations:">
2779      none
2780    </t>
2781    <t hangText="Interoperability considerations:">
2782      none
2783    </t>
2784    <t hangText="Published specification:">
2785      This specification (see <xref target=""/>).
2786    </t>
2787    <t hangText="Applications that use this media type:">
2788    </t>
2789    <t hangText="Additional information:">
2790      <list style="hanging">
2791        <t hangText="Magic number(s):">none</t>
2792        <t hangText="File extension(s):">none</t>
2793        <t hangText="Macintosh file type code(s):">none</t>
2794      </list>
2795    </t>
2796    <t hangText="Person and email address to contact for further information:">
2797      See Authors Section.
2798    </t>
2799                <t hangText="Intended usage:">
2800                  COMMON
2801    </t>
2802                <t hangText="Restrictions on usage:">
2803                  none
2804    </t>
2805    <t hangText="Author/Change controller:">
2806      IESG
2807    </t>
2808  </list>
2815<section title="Security Considerations" anchor="security.considerations">
2817   This section is meant to inform application developers, information
2818   providers, and users of the security limitations in HTTP/1.1 as
2819   described by this document. The discussion does not include
2820   definitive solutions to the problems revealed, though it does make
2821   some suggestions for reducing security risks.
2824<section title="Personal Information" anchor="personal.information">
2826   HTTP clients are often privy to large amounts of personal information
2827   (e.g. the user's name, location, mail address, passwords, encryption
2828   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2829   leakage of this information.
2830   We very strongly recommend that a convenient interface be provided
2831   for the user to control dissemination of such information, and that
2832   designers and implementors be particularly careful in this area.
2833   History shows that errors in this area often create serious security
2834   and/or privacy problems and generate highly adverse publicity for the
2835   implementor's company.
2839<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2841   A server is in the position to save personal data about a user's
2842   requests which might identify their reading patterns or subjects of
2843   interest. This information is clearly confidential in nature and its
2844   handling can be constrained by law in certain countries. People using
2845   HTTP to provide data are responsible for ensuring that
2846   such material is not distributed without the permission of any
2847   individuals that are identifiable by the published results.
2851<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2853   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2854   the documents returned by HTTP requests to be only those that were
2855   intended by the server administrators. If an HTTP server translates
2856   HTTP URIs directly into file system calls, the server &MUST; take
2857   special care not to serve files that were not intended to be
2858   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2859   other operating systems use ".." as a path component to indicate a
2860   directory level above the current one. On such a system, an HTTP
2861   server &MUST; disallow any such construct in the Request-URI if it
2862   would otherwise allow access to a resource outside those intended to
2863   be accessible via the HTTP server. Similarly, files intended for
2864   reference only internally to the server (such as access control
2865   files, configuration files, and script code) &MUST; be protected from
2866   inappropriate retrieval, since they might contain sensitive
2867   information. Experience has shown that minor bugs in such HTTP server
2868   implementations have turned into security risks.
2872<section title="DNS Spoofing" anchor="dns.spoofing">
2874   Clients using HTTP rely heavily on the Domain Name Service, and are
2875   thus generally prone to security attacks based on the deliberate
2876   mis-association of IP addresses and DNS names. Clients need to be
2877   cautious in assuming the continuing validity of an IP number/DNS name
2878   association.
2881   In particular, HTTP clients &SHOULD; rely on their name resolver for
2882   confirmation of an IP number/DNS name association, rather than
2883   caching the result of previous host name lookups. Many platforms
2884   already can cache host name lookups locally when appropriate, and
2885   they &SHOULD; be configured to do so. It is proper for these lookups to
2886   be cached, however, only when the TTL (Time To Live) information
2887   reported by the name server makes it likely that the cached
2888   information will remain useful.
2891   If HTTP clients cache the results of host name lookups in order to
2892   achieve a performance improvement, they &MUST; observe the TTL
2893   information reported by DNS.
2896   If HTTP clients do not observe this rule, they could be spoofed when
2897   a previously-accessed server's IP address changes. As network
2898   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2899   possibility of this form of attack will grow. Observing this
2900   requirement thus reduces this potential security vulnerability.
2903   This requirement also improves the load-balancing behavior of clients
2904   for replicated servers using the same DNS name and reduces the
2905   likelihood of a user's experiencing failure in accessing sites which
2906   use that strategy.
2910<section title="Proxies and Caching" anchor="attack.proxies">
2912   By their very nature, HTTP proxies are men-in-the-middle, and
2913   represent an opportunity for man-in-the-middle attacks. Compromise of
2914   the systems on which the proxies run can result in serious security
2915   and privacy problems. Proxies have access to security-related
2916   information, personal information about individual users and
2917   organizations, and proprietary information belonging to users and
2918   content providers. A compromised proxy, or a proxy implemented or
2919   configured without regard to security and privacy considerations,
2920   might be used in the commission of a wide range of potential attacks.
2923   Proxy operators should protect the systems on which proxies run as
2924   they would protect any system that contains or transports sensitive
2925   information. In particular, log information gathered at proxies often
2926   contains highly sensitive personal information, and/or information
2927   about organizations. Log information should be carefully guarded, and
2928   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2931   Proxy implementors should consider the privacy and security
2932   implications of their design and coding decisions, and of the
2933   configuration options they provide to proxy operators (especially the
2934   default configuration).
2937   Users of a proxy need to be aware that they are no trustworthier than
2938   the people who run the proxy; HTTP itself cannot solve this problem.
2941   The judicious use of cryptography, when appropriate, may suffice to
2942   protect against a broad range of security and privacy attacks. Such
2943   cryptography is beyond the scope of the HTTP/1.1 specification.
2947<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2949   They exist. They are hard to defend against. Research continues.
2950   Beware.
2955<section title="Acknowledgments" anchor="ack">
2957   HTTP has evolved considerably over the years. It has
2958   benefited from a large and active developer community--the many
2959   people who have participated on the www-talk mailing list--and it is
2960   that community which has been most responsible for the success of
2961   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2962   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2963   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2964   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2965   VanHeyningen deserve special recognition for their efforts in
2966   defining early aspects of the protocol.
2969   This document has benefited greatly from the comments of all those
2970   participating in the HTTP-WG. In addition to those already mentioned,
2971   the following individuals have contributed to this specification:
2974   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2975   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2976   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2977   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2978   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2979   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2980   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2981   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2982   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2983   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2984   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2985   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2986   Josh Cohen.
2989   Thanks to the "cave men" of Palo Alto. You know who you are.
2992   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2993   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2994   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2995   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2996   Larry Masinter for their help. And thanks go particularly to Jeff
2997   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3000   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3001   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3002   discovery of many of the problems that this document attempts to
3003   rectify.
3006   This specification makes heavy use of the augmented BNF and generic
3007   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3008   reuses many of the definitions provided by Nathaniel Borenstein and
3009   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3010   specification will help reduce past confusion over the relationship
3011   between HTTP and Internet mail message formats.
3018<references title="Normative References">
3020<reference anchor="ISO-8859-1">
3021  <front>
3022    <title>
3023     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3024    </title>
3025    <author>
3026      <organization>International Organization for Standardization</organization>
3027    </author>
3028    <date year="1998"/>
3029  </front>
3030  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3033<reference anchor="Part2">
3034  <front>
3035    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3036    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3037      <organization abbrev="Day Software">Day Software</organization>
3038      <address><email></email></address>
3039    </author>
3040    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3041      <organization>One Laptop per Child</organization>
3042      <address><email></email></address>
3043    </author>
3044    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3045      <organization abbrev="HP">Hewlett-Packard Company</organization>
3046      <address><email></email></address>
3047    </author>
3048    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3049      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3050      <address><email></email></address>
3051    </author>
3052    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3053      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3054      <address><email></email></address>
3055    </author>
3056    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3057      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3058      <address><email></email></address>
3059    </author>
3060    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3061      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3062      <address><email></email></address>
3063    </author>
3064    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3065      <organization abbrev="W3C">World Wide Web Consortium</organization>
3066      <address><email></email></address>
3067    </author>
3068    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3069      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3070      <address><email></email></address>
3071    </author>
3072    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3073  </front>
3074  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3075  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3078<reference anchor="Part3">
3079  <front>
3080    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3081    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3082      <organization abbrev="Day Software">Day Software</organization>
3083      <address><email></email></address>
3084    </author>
3085    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3086      <organization>One Laptop per Child</organization>
3087      <address><email></email></address>
3088    </author>
3089    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3090      <organization abbrev="HP">Hewlett-Packard Company</organization>
3091      <address><email></email></address>
3092    </author>
3093    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3094      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3095      <address><email></email></address>
3096    </author>
3097    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3098      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3099      <address><email></email></address>
3100    </author>
3101    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3102      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3103      <address><email></email></address>
3104    </author>
3105    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3106      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3107      <address><email></email></address>
3108    </author>
3109    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3110      <organization abbrev="W3C">World Wide Web Consortium</organization>
3111      <address><email></email></address>
3112    </author>
3113    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3114      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3115      <address><email></email></address>
3116    </author>
3117    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3118  </front>
3119  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3120  <x:source href="p3-payload.xml" basename="p3-payload"/>
3123<reference anchor="Part5">
3124  <front>
3125    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3126    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3127      <organization abbrev="Day Software">Day Software</organization>
3128      <address><email></email></address>
3129    </author>
3130    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3131      <organization>One Laptop per Child</organization>
3132      <address><email></email></address>
3133    </author>
3134    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3135      <organization abbrev="HP">Hewlett-Packard Company</organization>
3136      <address><email></email></address>
3137    </author>
3138    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3139      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3140      <address><email></email></address>
3141    </author>
3142    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3143      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3144      <address><email></email></address>
3145    </author>
3146    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3147      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3148      <address><email></email></address>
3149    </author>
3150    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3151      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3152      <address><email></email></address>
3153    </author>
3154    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3155      <organization abbrev="W3C">World Wide Web Consortium</organization>
3156      <address><email></email></address>
3157    </author>
3158    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3159      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3160      <address><email></email></address>
3161    </author>
3162    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3163  </front>
3164  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3165  <x:source href="p5-range.xml" basename="p5-range"/>
3168<reference anchor="Part6">
3169  <front>
3170    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3171    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3172      <organization abbrev="Day Software">Day Software</organization>
3173      <address><email></email></address>
3174    </author>
3175    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3176      <organization>One Laptop per Child</organization>
3177      <address><email></email></address>
3178    </author>
3179    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3180      <organization abbrev="HP">Hewlett-Packard Company</organization>
3181      <address><email></email></address>
3182    </author>
3183    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3184      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3185      <address><email></email></address>
3186    </author>
3187    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3188      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3189      <address><email></email></address>
3190    </author>
3191    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3192      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3193      <address><email></email></address>
3194    </author>
3195    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3196      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3197      <address><email></email></address>
3198    </author>
3199    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3200      <organization abbrev="W3C">World Wide Web Consortium</organization>
3201      <address><email></email></address>
3202    </author>
3203    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3204      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3205      <address><email></email></address>
3206    </author>
3207    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3208  </front>
3209  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3210  <x:source href="p6-cache.xml" basename="p6-cache"/>
3213<reference anchor="RFC5234">
3214  <front>
3215    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3216    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3217      <organization>Brandenburg InternetWorking</organization>
3218      <address>
3219      <postal>
3220      <street>675 Spruce Dr.</street>
3221      <city>Sunnyvale</city>
3222      <region>CA</region>
3223      <code>94086</code>
3224      <country>US</country></postal>
3225      <phone>+1.408.246.8253</phone>
3226      <email></email></address> 
3227    </author>
3228    <author initials="P." surname="Overell" fullname="Paul Overell">
3229      <organization>THUS plc.</organization>
3230      <address>
3231      <postal>
3232      <street>1/2 Berkeley Square</street>
3233      <street>99 Berkely Street</street>
3234      <city>Glasgow</city>
3235      <code>G3 7HR</code>
3236      <country>UK</country></postal>
3237      <email></email></address>
3238    </author>
3239    <date month="January" year="2008"/>
3240  </front>
3241  <seriesInfo name="STD" value="68"/>
3242  <seriesInfo name="RFC" value="5234"/>
3245<reference anchor="RFC2045">
3246  <front>
3247    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3248    <author initials="N." surname="Freed" fullname="Ned Freed">
3249      <organization>Innosoft International, Inc.</organization>
3250      <address><email></email></address>
3251    </author>
3252    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3253      <organization>First Virtual Holdings</organization>
3254      <address><email></email></address>
3255    </author>
3256    <date month="November" year="1996"/>
3257  </front>
3258  <seriesInfo name="RFC" value="2045"/>
3261<reference anchor="RFC2047">
3262  <front>
3263    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3264    <author initials="K." surname="Moore" fullname="Keith Moore">
3265      <organization>University of Tennessee</organization>
3266      <address><email></email></address>
3267    </author>
3268    <date month="November" year="1996"/>
3269  </front>
3270  <seriesInfo name="RFC" value="2047"/>
3273<reference anchor="RFC2119">
3274  <front>
3275    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3276    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3277      <organization>Harvard University</organization>
3278      <address><email></email></address>
3279    </author>
3280    <date month="March" year="1997"/>
3281  </front>
3282  <seriesInfo name="BCP" value="14"/>
3283  <seriesInfo name="RFC" value="2119"/>
3286<reference anchor="RFC3986">
3287 <front>
3288  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3289  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3290    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3291    <address>
3292       <email></email>
3293       <uri></uri>
3294    </address>
3295  </author>
3296  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3297    <organization abbrev="Day Software">Day Software</organization>
3298    <address>
3299      <email></email>
3300      <uri></uri>
3301    </address>
3302  </author>
3303  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3304    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3305    <address>
3306      <email></email>
3307      <uri></uri>
3308    </address>
3309  </author>
3310  <date month='January' year='2005'></date>
3311 </front>
3312 <seriesInfo name="RFC" value="3986"/>
3313 <seriesInfo name="STD" value="66"/>
3316<reference anchor="USASCII">
3317  <front>
3318    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3319    <author>
3320      <organization>American National Standards Institute</organization>
3321    </author>
3322    <date year="1986"/>
3323  </front>
3324  <seriesInfo name="ANSI" value="X3.4"/>
3329<references title="Informative References">
3331<reference anchor="Nie1997" target="">
3332  <front>
3333    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3334    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3335      <organization/>
3336    </author>
3337    <author initials="J." surname="Gettys" fullname="J. Gettys">
3338      <organization/>
3339    </author>
3340    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3341      <organization/>
3342    </author>
3343    <author initials="H." surname="Lie" fullname="H. Lie">
3344      <organization/>
3345    </author>
3346    <author initials="C." surname="Lilley" fullname="C. Lilley">
3347      <organization/>
3348    </author>
3349    <date year="1997" month="September"/>
3350  </front>
3351  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3354<reference anchor="Pad1995" target="">
3355  <front>
3356    <title>Improving HTTP Latency</title>
3357    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3358      <organization/>
3359    </author>
3360    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3361      <organization/>
3362    </author>
3363    <date year="1995" month="December"/>
3364  </front>
3365  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3368<reference anchor="RFC822">
3369  <front>
3370    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3371    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3372      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3373      <address><email>DCrocker@UDel-Relay</email></address>
3374    </author>
3375    <date month="August" day="13" year="1982"/>
3376  </front>
3377  <seriesInfo name="STD" value="11"/>
3378  <seriesInfo name="RFC" value="822"/>
3381<reference anchor="RFC959">
3382  <front>
3383    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3384    <author initials="J." surname="Postel" fullname="J. Postel">
3385      <organization>Information Sciences Institute (ISI)</organization>
3386    </author>
3387    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3388      <organization/>
3389    </author>
3390    <date month="October" year="1985"/>
3391  </front>
3392  <seriesInfo name="STD" value="9"/>
3393  <seriesInfo name="RFC" value="959"/>
3396<reference anchor="RFC1123">
3397  <front>
3398    <title>Requirements for Internet Hosts - Application and Support</title>
3399    <author initials="R." surname="Braden" fullname="Robert Braden">
3400      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3401      <address><email>Braden@ISI.EDU</email></address>
3402    </author>
3403    <date month="October" year="1989"/>
3404  </front>
3405  <seriesInfo name="STD" value="3"/>
3406  <seriesInfo name="RFC" value="1123"/>
3409<reference anchor="RFC1305">
3410  <front>
3411    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3412    <author initials="D." surname="Mills" fullname="David L. Mills">
3413      <organization>University of Delaware, Electrical Engineering Department</organization>
3414      <address><email></email></address>
3415    </author>
3416    <date month="March" year="1992"/>
3417  </front>
3418  <seriesInfo name="RFC" value="1305"/>
3421<reference anchor="RFC1436">
3422  <front>
3423    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3424    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3425      <organization>University of Minnesota, Computer and Information Services</organization>
3426      <address><email></email></address>
3427    </author>
3428    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3429      <organization>University of Minnesota, Computer and Information Services</organization>
3430      <address><email></email></address>
3431    </author>
3432    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3433      <organization>University of Minnesota, Computer and Information Services</organization>
3434      <address><email></email></address>
3435    </author>
3436    <author initials="D." surname="Johnson" fullname="David Johnson">
3437      <organization>University of Minnesota, Computer and Information Services</organization>
3438      <address><email></email></address>
3439    </author>
3440    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3441      <organization>University of Minnesota, Computer and Information Services</organization>
3442      <address><email></email></address>
3443    </author>
3444    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3445      <organization>University of Minnesota, Computer and Information Services</organization>
3446      <address><email></email></address>
3447    </author>
3448    <date month="March" year="1993"/>
3449  </front>
3450  <seriesInfo name="RFC" value="1436"/>
3453<reference anchor="RFC1900">
3454  <front>
3455    <title>Renumbering Needs Work</title>
3456    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3457      <organization>CERN, Computing and Networks Division</organization>
3458      <address><email></email></address>
3459    </author>
3460    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3461      <organization>cisco Systems</organization>
3462      <address><email></email></address>
3463    </author>
3464    <date month="February" year="1996"/>
3465  </front>
3466  <seriesInfo name="RFC" value="1900"/>
3469<reference anchor="RFC1945">
3470  <front>
3471    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3472    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3473      <organization>MIT, Laboratory for Computer Science</organization>
3474      <address><email></email></address>
3475    </author>
3476    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3477      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3478      <address><email></email></address>
3479    </author>
3480    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3481      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3482      <address><email></email></address>
3483    </author>
3484    <date month="May" year="1996"/>
3485  </front>
3486  <seriesInfo name="RFC" value="1945"/>
3489<reference anchor="RFC2068">
3490  <front>
3491    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3492    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3493      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3494      <address><email></email></address>
3495    </author>
3496    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3497      <organization>MIT Laboratory for Computer Science</organization>
3498      <address><email></email></address>
3499    </author>
3500    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3501      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3502      <address><email></email></address>
3503    </author>
3504    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3505      <organization>MIT Laboratory for Computer Science</organization>
3506      <address><email></email></address>
3507    </author>
3508    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3509      <organization>MIT Laboratory for Computer Science</organization>
3510      <address><email></email></address>
3511    </author>
3512    <date month="January" year="1997"/>
3513  </front>
3514  <seriesInfo name="RFC" value="2068"/>
3517<reference anchor='RFC2109'>
3518  <front>
3519    <title>HTTP State Management Mechanism</title>
3520    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3521      <organization>Bell Laboratories, Lucent Technologies</organization>
3522      <address><email></email></address>
3523    </author>
3524    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3525      <organization>Netscape Communications Corp.</organization>
3526      <address><email></email></address>
3527    </author>
3528    <date year='1997' month='February' />
3529  </front>
3530  <seriesInfo name='RFC' value='2109' />
3533<reference anchor="RFC2145">
3534  <front>
3535    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3536    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3537      <organization>Western Research Laboratory</organization>
3538      <address><email></email></address>
3539    </author>
3540    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3541      <organization>Department of Information and Computer Science</organization>
3542      <address><email></email></address>
3543    </author>
3544    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3545      <organization>MIT Laboratory for Computer Science</organization>
3546      <address><email></email></address>
3547    </author>
3548    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3549      <organization>W3 Consortium</organization>
3550      <address><email></email></address>
3551    </author>
3552    <date month="May" year="1997"/>
3553  </front>
3554  <seriesInfo name="RFC" value="2145"/>
3557<reference anchor="RFC2616">
3558  <front>
3559    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3560    <author initials="R." surname="Fielding" fullname="R. Fielding">
3561      <organization>University of California, Irvine</organization>
3562      <address><email></email></address>
3563    </author>
3564    <author initials="J." surname="Gettys" fullname="J. Gettys">
3565      <organization>W3C</organization>
3566      <address><email></email></address>
3567    </author>
3568    <author initials="J." surname="Mogul" fullname="J. Mogul">
3569      <organization>Compaq Computer Corporation</organization>
3570      <address><email></email></address>
3571    </author>
3572    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3573      <organization>MIT Laboratory for Computer Science</organization>
3574      <address><email></email></address>
3575    </author>
3576    <author initials="L." surname="Masinter" fullname="L. Masinter">
3577      <organization>Xerox Corporation</organization>
3578      <address><email></email></address>
3579    </author>
3580    <author initials="P." surname="Leach" fullname="P. Leach">
3581      <organization>Microsoft Corporation</organization>
3582      <address><email></email></address>
3583    </author>
3584    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3585      <organization>W3C</organization>
3586      <address><email></email></address>
3587    </author>
3588    <date month="June" year="1999"/>
3589  </front>
3590  <seriesInfo name="RFC" value="2616"/>
3593<reference anchor='RFC2818'>
3594  <front>
3595    <title>HTTP Over TLS</title>
3596    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3597      <organization>RTFM, Inc.</organization>
3598      <address><email></email></address>
3599    </author>
3600    <date year='2000' month='May' />
3601  </front>
3602  <seriesInfo name='RFC' value='2818' />
3605<reference anchor='RFC2965'>
3606  <front>
3607    <title>HTTP State Management Mechanism</title>
3608    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3609      <organization>Bell Laboratories, Lucent Technologies</organization>
3610      <address><email></email></address>
3611    </author>
3612    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3613      <organization>, Inc.</organization>
3614      <address><email></email></address>
3615    </author>
3616    <date year='2000' month='October' />
3617  </front>
3618  <seriesInfo name='RFC' value='2965' />
3621<reference anchor='RFC3864'>
3622  <front>
3623    <title>Registration Procedures for Message Header Fields</title>
3624    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3625      <organization>Nine by Nine</organization>
3626      <address><email></email></address>
3627    </author>
3628    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3629      <organization>BEA Systems</organization>
3630      <address><email></email></address>
3631    </author>
3632    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3633      <organization>HP Labs</organization>
3634      <address><email></email></address>
3635    </author>
3636    <date year='2004' month='September' />
3637  </front>
3638  <seriesInfo name='BCP' value='90' />
3639  <seriesInfo name='RFC' value='3864' />
3642<reference anchor='RFC3977'>
3643  <front>
3644    <title>Network News Transfer Protocol (NNTP)</title>
3645    <author initials='C.' surname='Feather' fullname='C. Feather'>
3646      <organization>THUS plc</organization>
3647      <address><email></email></address>
3648    </author>
3649    <date year='2006' month='October' />
3650  </front>
3651  <seriesInfo name="RFC" value="3977"/>
3654<reference anchor="RFC4288">
3655  <front>
3656    <title>Media Type Specifications and Registration Procedures</title>
3657    <author initials="N." surname="Freed" fullname="N. Freed">
3658      <organization>Sun Microsystems</organization>
3659      <address>
3660        <email></email>
3661      </address>
3662    </author>
3663    <author initials="J." surname="Klensin" fullname="J. Klensin">
3664      <organization/>
3665      <address>
3666        <email></email>
3667      </address>
3668    </author>
3669    <date year="2005" month="December"/>
3670  </front>
3671  <seriesInfo name="BCP" value="13"/>
3672  <seriesInfo name="RFC" value="4288"/>
3675<reference anchor='RFC4395'>
3676  <front>
3677    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3678    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3679      <organization>AT&amp;T Laboratories</organization>
3680      <address>
3681        <email></email>
3682      </address>
3683    </author>
3684    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3685      <organization>Qualcomm, Inc.</organization>
3686      <address>
3687        <email></email>
3688      </address>
3689    </author>
3690    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3691      <organization>Adobe Systems</organization>
3692      <address>
3693        <email></email>
3694      </address>
3695    </author>
3696    <date year='2006' month='February' />
3697  </front>
3698  <seriesInfo name='BCP' value='115' />
3699  <seriesInfo name='RFC' value='4395' />
3702<reference anchor="RFC5322">
3703  <front>
3704    <title>Internet Message Format</title>
3705    <author initials="P." surname="Resnick" fullname="P. Resnick">
3706      <organization>Qualcomm Incorporated</organization>
3707    </author>
3708    <date year="2008" month="October"/>
3709  </front>
3710  <seriesInfo name="RFC" value="5322"/>
3713<reference anchor="Kri2001" target="">
3714  <front>
3715    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3716    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3717      <organization/>
3718    </author>
3719    <date year="2001" month="November"/>
3720  </front>
3721  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3724<reference anchor="Spe" target="">
3725  <front>
3726  <title>Analysis of HTTP Performance Problems</title>
3727  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3728    <organization/>
3729  </author>
3730  <date/>
3731  </front>
3734<reference anchor="Tou1998" target="">
3735  <front>
3736  <title>Analysis of HTTP Performance</title>
3737  <author initials="J." surname="Touch" fullname="Joe Touch">
3738    <organization>USC/Information Sciences Institute</organization>
3739    <address><email></email></address>
3740  </author>
3741  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3742    <organization>USC/Information Sciences Institute</organization>
3743    <address><email></email></address>
3744  </author>
3745  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3746    <organization>USC/Information Sciences Institute</organization>
3747    <address><email></email></address>
3748  </author>
3749  <date year="1998" month="Aug"/>
3750  </front>
3751  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3752  <annotation>(original report dated Aug. 1996)</annotation>
3755<reference anchor="WAIS">
3756  <front>
3757    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3758    <author initials="F." surname="Davis" fullname="F. Davis">
3759      <organization>Thinking Machines Corporation</organization>
3760    </author>
3761    <author initials="B." surname="Kahle" fullname="B. Kahle">
3762      <organization>Thinking Machines Corporation</organization>
3763    </author>
3764    <author initials="H." surname="Morris" fullname="H. Morris">
3765      <organization>Thinking Machines Corporation</organization>
3766    </author>
3767    <author initials="J." surname="Salem" fullname="J. Salem">
3768      <organization>Thinking Machines Corporation</organization>
3769    </author>
3770    <author initials="T." surname="Shen" fullname="T. Shen">
3771      <organization>Thinking Machines Corporation</organization>
3772    </author>
3773    <author initials="R." surname="Wang" fullname="R. Wang">
3774      <organization>Thinking Machines Corporation</organization>
3775    </author>
3776    <author initials="J." surname="Sui" fullname="J. Sui">
3777      <organization>Thinking Machines Corporation</organization>
3778    </author>
3779    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3780      <organization>Thinking Machines Corporation</organization>
3781    </author>
3782    <date month="April" year="1990"/>
3783  </front>
3784  <seriesInfo name="Thinking Machines Corporation" value=""/>
3790<section title="Tolerant Applications" anchor="tolerant.applications">
3792   Although this document specifies the requirements for the generation
3793   of HTTP/1.1 messages, not all applications will be correct in their
3794   implementation. We therefore recommend that operational applications
3795   be tolerant of deviations whenever those deviations can be
3796   interpreted unambiguously.
3799   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3800   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3801   accept any amount of SP or HTAB characters between fields, even though
3802   only a single SP is required.
3805   The line terminator for message-header fields is the sequence CRLF.
3806   However, we recommend that applications, when parsing such headers,
3807   recognize a single LF as a line terminator and ignore the leading CR.
3810   The character set of an entity-body &SHOULD; be labeled as the lowest
3811   common denominator of the character codes used within that body, with
3812   the exception that not labeling the entity is preferred over labeling
3813   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3816   Additional rules for requirements on parsing and encoding of dates
3817   and other potential problems with date encodings include:
3820  <list style="symbols">
3821     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3822        which appears to be more than 50 years in the future is in fact
3823        in the past (this helps solve the "year 2000" problem).</t>
3825     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3826        Expires date as earlier than the proper value, but &MUST-NOT;
3827        internally represent a parsed Expires date as later than the
3828        proper value.</t>
3830     <t>All expiration-related calculations &MUST; be done in GMT. The
3831        local time zone &MUST-NOT; influence the calculation or comparison
3832        of an age or expiration time.</t>
3834     <t>If an HTTP header incorrectly carries a date value with a time
3835        zone other than GMT, it &MUST; be converted into GMT using the
3836        most conservative possible conversion.</t>
3837  </list>
3841<section title="Conversion of Date Formats" anchor="">
3843   HTTP/1.1 uses a restricted set of date formats (<xref target=""/>) to
3844   simplify the process of date comparison. Proxies and gateways from
3845   other protocols &SHOULD; ensure that any Date header field present in a
3846   message conforms to one of the HTTP/1.1 formats and rewrite the date
3847   if necessary.
3851<section title="Compatibility with Previous Versions" anchor="compatibility">
3853   HTTP has been in use by the World-Wide Web global information initiative
3854   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3855   was a simple protocol for hypertext data transfer across the Internet
3856   with only a single method and no metadata.
3857   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3858   methods and MIME-like messaging that could include metadata about the data
3859   transferred and modifiers on the request/response semantics. However,
3860   HTTP/1.0 did not sufficiently take into consideration the effects of
3861   hierarchical proxies, caching, the need for persistent connections, or
3862   name-based virtual hosts. The proliferation of incompletely-implemented
3863   applications calling themselves "HTTP/1.0" further necessitated a
3864   protocol version change in order for two communicating applications
3865   to determine each other's true capabilities.
3868   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3869   requirements that enable reliable implementations, adding only
3870   those new features that will either be safely ignored by an HTTP/1.0
3871   recipient or only sent when communicating with a party advertising
3872   compliance with HTTP/1.1.
3875   It is beyond the scope of a protocol specification to mandate
3876   compliance with previous versions. HTTP/1.1 was deliberately
3877   designed, however, to make supporting previous versions easy. It is
3878   worth noting that, at the time of composing this specification
3879   (1996), we would expect commercial HTTP/1.1 servers to:
3880  <list style="symbols">
3881     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3882        1.1 requests;</t>
3884     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3885        1.1;</t>
3887     <t>respond appropriately with a message in the same major version
3888        used by the client.</t>
3889  </list>
3892   And we would expect HTTP/1.1 clients to:
3893  <list style="symbols">
3894     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3895        responses;</t>
3897     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3898        1.1.</t>
3899  </list>
3902   For most implementations of HTTP/1.0, each connection is established
3903   by the client prior to the request and closed by the server after
3904   sending the response. Some implementations implement the Keep-Alive
3905   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3908<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3910   This section summarizes major differences between versions HTTP/1.0
3911   and HTTP/1.1.
3914<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
3916   The requirements that clients and servers support the Host request-header,
3917   report an error if the Host request-header (<xref target=""/>) is
3918   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3919   are among the most important changes defined by this
3920   specification.
3923   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3924   addresses and servers; there was no other established mechanism for
3925   distinguishing the intended server of a request than the IP address
3926   to which that request was directed. The changes outlined above will
3927   allow the Internet, once older HTTP clients are no longer common, to
3928   support multiple Web sites from a single IP address, greatly
3929   simplifying large operational Web servers, where allocation of many
3930   IP addresses to a single host has created serious problems. The
3931   Internet will also be able to recover the IP addresses that have been
3932   allocated for the sole purpose of allowing special-purpose domain
3933   names to be used in root-level HTTP URLs. Given the rate of growth of
3934   the Web, and the number of servers already deployed, it is extremely
3935   important that all implementations of HTTP (including updates to
3936   existing HTTP/1.0 applications) correctly implement these
3937   requirements:
3938  <list style="symbols">
3939     <t>Both clients and servers &MUST; support the Host request-header.</t>
3941     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3943     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3944        request does not include a Host request-header.</t>
3946     <t>Servers &MUST; accept absolute URIs.</t>
3947  </list>
3952<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3954   Some clients and servers might wish to be compatible with some
3955   previous implementations of persistent connections in HTTP/1.0
3956   clients and servers. Persistent connections in HTTP/1.0 are
3957   explicitly negotiated as they are not the default behavior. HTTP/1.0
3958   experimental implementations of persistent connections are faulty,
3959   and the new facilities in HTTP/1.1 are designed to rectify these
3960   problems. The problem was that some existing 1.0 clients may be
3961   sending Keep-Alive to a proxy server that doesn't understand
3962   Connection, which would then erroneously forward it to the next
3963   inbound server, which would establish the Keep-Alive connection and
3964   result in a hung HTTP/1.0 proxy waiting for the close on the
3965   response. The result is that HTTP/1.0 clients must be prevented from
3966   using Keep-Alive when talking to proxies.
3969   However, talking to proxies is the most important use of persistent
3970   connections, so that prohibition is clearly unacceptable. Therefore,
3971   we need some other mechanism for indicating a persistent connection
3972   is desired, which is safe to use even when talking to an old proxy
3973   that ignores Connection. Persistent connections are the default for
3974   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3975   declaring non-persistence. See <xref target="header.connection"/>.
3978   The original HTTP/1.0 form of persistent connections (the Connection:
3979   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3983<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3985   This specification has been carefully audited to correct and
3986   disambiguate key word usage; RFC 2068 had many problems in respect to
3987   the conventions laid out in <xref target="RFC2119"/>.
3990   Transfer-coding and message lengths all interact in ways that
3991   required fixing exactly when chunked encoding is used (to allow for
3992   transfer encoding that may not be self delimiting); it was important
3993   to straighten out exactly how message lengths are computed. (Sections
3994   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
3995   <xref target="header.content-length" format="counter"/>,
3996   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
3999   The use and interpretation of HTTP version numbers has been clarified
4000   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4001   version they support to deal with problems discovered in HTTP/1.0
4002   implementations (<xref target="http.version"/>)
4005   Transfer-coding had significant problems, particularly with
4006   interactions with chunked encoding. The solution is that transfer-codings
4007   become as full fledged as content-codings. This involves
4008   adding an IANA registry for transfer-codings (separate from content
4009   codings), a new header field (TE) and enabling trailer headers in the
4010   future. Transfer encoding is a major performance benefit, so it was
4011   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4012   interoperability problem that could have occurred due to interactions
4013   between authentication trailers, chunked encoding and HTTP/1.0
4014   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4015   and <xref target="header.te" format="counter"/>)
4019<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4021  The CHAR rule does not allow the NUL character anymore (this affects
4022  the comment and quoted-string rules).  Furthermore, the quoted-pair
4023  rule does not allow escaping NUL, CR or LF anymore.
4024  (<xref target="basic.rules"/>)
4027  Clarify that HTTP-Version is case sensitive.
4028  (<xref target="http.version"/>)
4031  Remove reference to non-existant identity transfer-coding value tokens.
4032  (Sections <xref format="counter" target="transfer.codings"/> and
4033  <xref format="counter" target="message.length"/>)
4036  Clarification that the chunk length does not include
4037  the count of the octets in the chunk header and trailer.
4038  (<xref target="chunked.transfer.encoding"/>)
4041  Update use of abs_path production from RFC1808 to the path-absolute + query
4042  components of RFC3986.
4043  (<xref target="request-uri"/>)
4046  Clarify exactly when close connection options must be sent.
4047  (<xref target="header.connection"/>)
4052<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4054<section title="Since RFC2616">
4056  Extracted relevant partitions from <xref target="RFC2616"/>.
4060<section title="Since draft-ietf-httpbis-p1-messaging-00">
4062  Closed issues:
4063  <list style="symbols">
4064    <t>
4065      <eref target=""/>:
4066      "HTTP Version should be case sensitive"
4067      (<eref target=""/>)
4068    </t>
4069    <t>
4070      <eref target=""/>:
4071      "'unsafe' characters"
4072      (<eref target=""/>)
4073    </t>
4074    <t>
4075      <eref target=""/>:
4076      "Chunk Size Definition"
4077      (<eref target=""/>)
4078    </t>
4079    <t>
4080      <eref target=""/>:
4081      "Message Length"
4082      (<eref target=""/>)
4083    </t>
4084    <t>
4085      <eref target=""/>:
4086      "Media Type Registrations"
4087      (<eref target=""/>)
4088    </t>
4089    <t>
4090      <eref target=""/>:
4091      "URI includes query"
4092      (<eref target=""/>)
4093    </t>
4094    <t>
4095      <eref target=""/>:
4096      "No close on 1xx responses"
4097      (<eref target=""/>)
4098    </t>
4099    <t>
4100      <eref target=""/>:
4101      "Remove 'identity' token references"
4102      (<eref target=""/>)
4103    </t>
4104    <t>
4105      <eref target=""/>:
4106      "Import query BNF"
4107    </t>
4108    <t>
4109      <eref target=""/>:
4110      "qdtext BNF"
4111    </t>
4112    <t>
4113      <eref target=""/>:
4114      "Normative and Informative references"
4115    </t>
4116    <t>
4117      <eref target=""/>:
4118      "RFC2606 Compliance"
4119    </t>
4120    <t>
4121      <eref target=""/>:
4122      "RFC977 reference"
4123    </t>
4124    <t>
4125      <eref target=""/>:
4126      "RFC1700 references"
4127    </t>
4128    <t>
4129      <eref target=""/>:
4130      "inconsistency in date format explanation"
4131    </t>
4132    <t>
4133      <eref target=""/>:
4134      "Date reference typo"
4135    </t>
4136    <t>
4137      <eref target=""/>:
4138      "Informative references"
4139    </t>
4140    <t>
4141      <eref target=""/>:
4142      "ISO-8859-1 Reference"
4143    </t>
4144    <t>
4145      <eref target=""/>:
4146      "Normative up-to-date references"
4147    </t>
4148  </list>
4151  Other changes:
4152  <list style="symbols">
4153    <t>
4154      Update media type registrations to use RFC4288 template.
4155    </t>
4156    <t>
4157      Use names of RFC4234 core rules DQUOTE and HTAB,
4158      fix broken ABNF for chunk-data
4159      (work in progress on <eref target=""/>)
4160    </t>
4161  </list>
4165<section title="Since draft-ietf-httpbis-p1-messaging-01">
4167  Closed issues:
4168  <list style="symbols">
4169    <t>
4170      <eref target=""/>:
4171      "Bodies on GET (and other) requests"
4172    </t>
4173    <t>
4174      <eref target=""/>:
4175      "Updating to RFC4288"
4176    </t>
4177    <t>
4178      <eref target=""/>:
4179      "Status Code and Reason Phrase"
4180    </t>
4181    <t>
4182      <eref target=""/>:
4183      "rel_path not used"
4184    </t>
4185  </list>
4188  Ongoing work on ABNF conversion (<eref target=""/>):
4189  <list style="symbols">
4190    <t>
4191      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4192      "trailer-part").
4193    </t>
4194    <t>
4195      Avoid underscore character in rule names ("http_URL" ->
4196      "http-URI", "abs_path" -> "path-absolute").
4197    </t>
4198    <t>
4199      Add rules for terms imported from URI spec ("absolute-URI", "authority",
4200      "path-abempty", "path-absolute", "uri-host", "port", "query").
4201    </t>
4202    <t>
4203      Synchronize core rules with RFC5234 (this includes a change to CHAR
4204      which now excludes NUL).
4205    </t>
4206    <t>
4207      Get rid of prose rules that span multiple lines.
4208    </t>
4209    <t>
4210      Get rid of unused rules LOALPHA and UPALPHA.
4211    </t>
4212    <t>
4213      Move "Product Tokens" section (back) into Part 1, as "token" is used
4214      in the definition of the Upgrade header.
4215    </t>
4216    <t>
4217      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4218    </t>
4219    <t>
4220      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4221    </t>
4222  </list>
4226<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4228  Closed issues:
4229  <list style="symbols">
4230    <t>
4231      <eref target=""/>:
4232      "HTTP-date vs. rfc1123-date"
4233    </t>
4234    <t>
4235      <eref target=""/>:
4236      "WS in quoted-pair"
4237    </t>
4238  </list>
4241  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4242  <list style="symbols">
4243    <t>
4244      Reference RFC 3984, and update header registrations for headers defined
4245      in this document.
4246    </t>
4247  </list>
4250  Ongoing work on ABNF conversion (<eref target=""/>):
4251  <list style="symbols">
4252    <t>
4253      Replace string literals when the string really is case-sensitive (HTTP-Version).
4254    </t>
4255  </list>
4259<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4261  Closed issues:
4262  <list style="symbols">
4263    <t>
4264      <eref target=""/>:
4265      "Connection closing"
4266    </t>
4267    <t>
4268      <eref target=""/>:
4269      "Move registrations and registry information to IANA Considerations"
4270    </t>
4271    <t>
4272      <eref target=""/>:
4273      "need new URL for PAD1995 reference"
4274    </t>
4275    <t>
4276      <eref target=""/>:
4277      "IANA Considerations: update HTTP URI scheme registration"
4278    </t>
4279    <t>
4280      <eref target=""/>:
4281      "Cite HTTPS URI scheme definition"
4282    </t>
4283    <t>
4284      <eref target=""/>:
4285      "List-type headers vs Set-Cookie"
4286    </t>
4287  </list>
4290  Ongoing work on ABNF conversion (<eref target=""/>):
4291  <list style="symbols">
4292    <t>
4293      Replace string literals when the string really is case-sensitive (HTTP-Date).
4294    </t>
4295    <t>
4296      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4297    </t>
4298  </list>
4302<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4304  Closed issues:
4305  <list style="symbols">
4306    <t>
4307      <eref target=""/>:
4308      "RFC 2822 is updated by RFC 5322"
4309    </t>
4310  </list>
4313  Ongoing work on ABNF conversion (<eref target=""/>):
4314  <list style="symbols">
4315    <t>
4316      Use "/" instead of "|" for alternatives.
4317    </t>
4318    <t>
4319      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4320    </t>
4321  </list>
4327<section title="Terminology" anchor="intro.terminology">
4329   This specification uses a number of terms to refer to the roles
4330   played by participants in, and objects of, the HTTP communication.
4333  <iref item="connection"/>
4334  <x:dfn>connection</x:dfn>
4335  <list>
4336    <t>
4337      A transport layer virtual circuit established between two programs
4338      for the purpose of communication.
4339    </t>
4340  </list>
4343  <iref item="message"/>
4344  <x:dfn>message</x:dfn>
4345  <list>
4346    <t>
4347      The basic unit of HTTP communication, consisting of a structured
4348      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4349      transmitted via the connection.
4350    </t>
4351  </list>
4354  <iref item="request"/>
4355  <x:dfn>request</x:dfn>
4356  <list>
4357    <t>
4358      An HTTP request message, as defined in <xref target="request"/>.
4359    </t>
4360  </list>
4363  <iref item="response"/>
4364  <x:dfn>response</x:dfn>
4365  <list>
4366    <t>
4367      An HTTP response message, as defined in <xref target="response"/>.
4368    </t>
4369  </list>
4372  <iref item="resource"/>
4373  <x:dfn>resource</x:dfn>
4374  <list>
4375    <t>
4376      A network data object or service that can be identified by a URI,
4377      as defined in <xref target="uri"/>. Resources may be available in multiple
4378      representations (e.g. multiple languages, data formats, size, and
4379      resolutions) or vary in other ways.
4380    </t>
4381  </list>
4384  <iref item="entity"/>
4385  <x:dfn>entity</x:dfn>
4386  <list>
4387    <t>
4388      The information transferred as the payload of a request or
4389      response. An entity consists of metainformation in the form of
4390      entity-header fields and content in the form of an entity-body, as
4391      described in &entity;.
4392    </t>
4393  </list>
4396  <iref item="representation"/>
4397  <x:dfn>representation</x:dfn>
4398  <list>
4399    <t>
4400      An entity included with a response that is subject to content
4401      negotiation, as described in &content.negotiation;. There may exist multiple
4402      representations associated with a particular response status.
4403    </t>
4404  </list>
4407  <iref item="content negotiation"/>
4408  <x:dfn>content negotiation</x:dfn>
4409  <list>
4410    <t>
4411      The mechanism for selecting the appropriate representation when
4412      servicing a request, as described in &content.negotiation;. The
4413      representation of entities in any response can be negotiated
4414      (including error responses).
4415    </t>
4416  </list>
4419  <iref item="variant"/>
4420  <x:dfn>variant</x:dfn>
4421  <list>
4422    <t>
4423      A resource may have one, or more than one, representation(s)
4424      associated with it at any given instant. Each of these
4425      representations is termed a `variant'.  Use of the term `variant'
4426      does not necessarily imply that the resource is subject to content
4427      negotiation.
4428    </t>
4429  </list>
4432  <iref item="client"/>
4433  <x:dfn>client</x:dfn>
4434  <list>
4435    <t>
4436      A program that establishes connections for the purpose of sending
4437      requests.
4438    </t>
4439  </list>
4442  <iref item="user agent"/>
4443  <x:dfn>user agent</x:dfn>
4444  <list>
4445    <t>
4446      The client which initiates a request. These are often browsers,
4447      editors, spiders (web-traversing robots), or other end user tools.
4448    </t>
4449  </list>
4452  <iref item="server"/>
4453  <x:dfn>server</x:dfn>
4454  <list>
4455    <t>
4456      An application program that accepts connections in order to
4457      service requests by sending back responses. Any given program may
4458      be capable of being both a client and a server; our use of these
4459      terms refers only to the role being performed by the program for a
4460      particular connection, rather than to the program's capabilities
4461      in general. Likewise, any server may act as an origin server,
4462      proxy, gateway, or tunnel, switching behavior based on the nature
4463      of each request.
4464    </t>
4465  </list>
4468  <iref item="origin server"/>
4469  <x:dfn>origin server</x:dfn>
4470  <list>
4471    <t>
4472      The server on which a given resource resides or is to be created.
4473    </t>
4474  </list>
4477  <iref item="proxy"/>
4478  <x:dfn>proxy</x:dfn>
4479  <list>
4480    <t>
4481      An intermediary program which acts as both a server and a client
4482      for the purpose of making requests on behalf of other clients.
4483      Requests are serviced internally or by passing them on, with
4484      possible translation, to other servers. A proxy &MUST; implement
4485      both the client and server requirements of this specification. A
4486      "transparent proxy" is a proxy that does not modify the request or
4487      response beyond what is required for proxy authentication and
4488      identification. A "non-transparent proxy" is a proxy that modifies
4489      the request or response in order to provide some added service to
4490      the user agent, such as group annotation services, media type
4491      transformation, protocol reduction, or anonymity filtering. Except
4492      where either transparent or non-transparent behavior is explicitly
4493      stated, the HTTP proxy requirements apply to both types of
4494      proxies.
4495    </t>
4496  </list>
4499  <iref item="gateway"/>
4500  <x:dfn>gateway</x:dfn>
4501  <list>
4502    <t>
4503      A server which acts as an intermediary for some other server.
4504      Unlike a proxy, a gateway receives requests as if it were the
4505      origin server for the requested resource; the requesting client
4506      may not be aware that it is communicating with a gateway.
4507    </t>
4508  </list>
4511  <iref item="tunnel"/>
4512  <x:dfn>tunnel</x:dfn>
4513  <list>
4514    <t>
4515      An intermediary program which is acting as a blind relay between
4516      two connections. Once active, a tunnel is not considered a party
4517      to the HTTP communication, though the tunnel may have been
4518      initiated by an HTTP request. The tunnel ceases to exist when both
4519      ends of the relayed connections are closed.
4520    </t>
4521  </list>
4524  <iref item="cache"/>
4525  <x:dfn>cache</x:dfn>
4526  <list>
4527    <t>
4528      A program's local store of response messages and the subsystem
4529      that controls its message storage, retrieval, and deletion. A
4530      cache stores cacheable responses in order to reduce the response
4531      time and network bandwidth consumption on future, equivalent
4532      requests. Any client or server may include a cache, though a cache
4533      cannot be used by a server that is acting as a tunnel.
4534    </t>
4535  </list>
4538  <iref item="cacheable"/>
4539  <x:dfn>cacheable</x:dfn>
4540  <list>
4541    <t>
4542      A response is cacheable if a cache is allowed to store a copy of
4543      the response message for use in answering subsequent requests. The
4544      rules for determining the cacheability of HTTP responses are
4545      defined in &caching;. Even if a resource is cacheable, there may
4546      be additional constraints on whether a cache can use the cached
4547      copy for a particular request.
4548    </t>
4549  </list>
4552  <iref item="upstream"/>
4553  <iref item="downstream"/>
4554  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4555  <list>
4556    <t>
4557      Upstream and downstream describe the flow of a message: all
4558      messages flow from upstream to downstream.
4559    </t>
4560  </list>
4563  <iref item="inbound"/>
4564  <iref item="outbound"/>
4565  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4566  <list>
4567    <t>
4568      Inbound and outbound refer to the request and response paths for
4569      messages: "inbound" means "traveling toward the origin server",
4570      and "outbound" means "traveling toward the user agent"
4571    </t>
4572  </list>
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