source: draft-ietf-httpbis/latest-roy/p1-messaging.xml @ 346

Last change on this file since 346 was 346, checked in by julian.reschke@…, 14 years ago

Move Terminology Section to the back.

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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.04"/>.
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">
283<iref primary="true" item="Grammar" subitem="ALPHA"/>
284<iref primary="true" item="Grammar" subitem="CHAR"/>
285<iref primary="true" item="Grammar" subitem="CR"/>
286<iref primary="true" item="Grammar" subitem="CRLF"/>
287<iref primary="true" item="Grammar" subitem="CTL"/>
288<iref primary="true" item="Grammar" subitem="DIGIT"/>
289<iref primary="true" item="Grammar" subitem="DQUOTE"/>
290<iref primary="true" item="Grammar" subitem="HEXDIG"/>
291<iref primary="true" item="Grammar" subitem="HTAB"/>
292<iref primary="true" item="Grammar" subitem="LF"/>
293<iref primary="true" item="Grammar" subitem="OCTET"/>
294<iref primary="true" item="Grammar" subitem="SP"/>
295<t anchor="core.rules">
296  <x:anchor-alias value="ALPHA"/>
297  <x:anchor-alias value="CHAR"/>
298  <x:anchor-alias value="CTL"/>
299  <x:anchor-alias value="CR"/>
300  <x:anchor-alias value="CRLF"/>
301  <x:anchor-alias value="DIGIT"/>
302  <x:anchor-alias value="DQUOTE"/>
303  <x:anchor-alias value="HEXDIG"/>
304  <x:anchor-alias value="HTAB"/>
305  <x:anchor-alias value="LF"/>
306  <x:anchor-alias value="OCTET"/>
307  <x:anchor-alias value="SP"/>
308   This specification uses the Augmented Backus-Naur Form (ABNF) notation
309   of <xref target="RFC5234"/>.  The following core rules are included by
310   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
311   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
312   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
313   DIGIT (decimal 0-9), DQUOTE (double quote),
314   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
315   LF (line feed), OCTET (any 8-bit sequence of data), and SP (space).
318<section title="ABNF Extensions" anchor="notation.abnf">
320   Two extensions to the ABNF rules of <xref target="RFC5234"/> are used to
321   improve readability. [The current plan is to remove these extensions prior
322   to the last call draft.]
325<section title="#rule">
326  <t>
327    A construct "#" is defined, similar to "*", for defining lists of
328    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
329    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
330    (",") and &OPTIONAL; linear white space (LWS). This makes the usual
331    form of lists very easy; a rule such as
332    <figure><artwork type="example">
333 ( *<x:ref>LWS</x:ref> element *( *<x:ref>LWS</x:ref> "," *<x:ref>LWS</x:ref> element ))</artwork></figure>
334  </t>
335  <t>
336    can be shown as
337    <figure><artwork type="example">
338 1#element</artwork></figure>
339  </t>
340  <t>
341    Wherever this construct is used, null elements are allowed, but do
342    not contribute to the count of elements present. That is,
343    "(element), , (element) " is permitted, but counts as only two
344    elements. Therefore, where at least one element is required, at
345    least one non-null element &MUST; be present. Default values are 0
346    and infinity so that "#element" allows any number, including zero;
347    "1#element" requires at least one; and "1#2element" allows one or
348    two.
349  </t>
352<section title="implied *LWS" anchor="implied.LWS">
353  <iref item="implied *LWS" primary="true"/>
354    <t>
355      The grammar described by this specification is word-based. Except
356      where noted otherwise, linear white space (LWS) can be included
357      between any two adjacent words (token or quoted-string), and
358      between adjacent words and separators, without changing the
359      interpretation of a field. At least one delimiter (LWS and/or
360      separators) &MUST; exist between any two tokens (for the definition
361      of "token" below), since they would otherwise be interpreted as a
362      single token.
363    </t>
367<section title="Basic Rules" anchor="basic.rules">
368<t anchor="rule.CRLF">
369   HTTP/1.1 defines the sequence CRLF as the end-of-line marker for all
370   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
371   tolerant applications). The end-of-line marker within an entity-body
372   is defined by its associated media type, as described in &media-types;.
374<t anchor="rule.LWS">
375  <x:anchor-alias value="LWS"/>
376   HTTP/1.1 header field values can be folded onto multiple lines if the
377   continuation line begins with a space or horizontal tab. All linear
378   white space, including folding, has the same semantics as SP. A
379   recipient &MAY; replace any linear white space with a single SP before
380   interpreting the field value or forwarding the message downstream.
382<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
383  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
385<t anchor="rule.TEXT">
386  <x:anchor-alias value="TEXT"/>
387   The TEXT rule is only used for descriptive field contents and values
388   that are not intended to be interpreted by the message parser. Words
389   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
390   <xref target="ISO-8859-1"/> only when encoded according to the rules of
391   <xref target="RFC2047"/>.
393<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
394  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
395                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
398   A CRLF is allowed in the definition of TEXT only as part of a header
399   field continuation. It is expected that the folding LWS will be
400   replaced with a single SP before interpretation of the TEXT value.
402<t anchor="rule.token.separators">
403  <x:anchor-alias value="tchar"/>
404  <x:anchor-alias value="token"/>
405  <x:anchor-alias value="separators"/>
406   Many HTTP/1.1 header field values consist of words separated by LWS
407   or special characters. These special characters &MUST; be in a quoted
408   string to be used within a parameter value (as defined in
409   <xref target="transfer.codings"/>).
411<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"/>
412  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
413                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
414                 / "/" / "[" / "]" / "?" / "="
415                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
417  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
418                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
419                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
420                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
422  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
424<t anchor="rule.comment">
425  <x:anchor-alias value="comment"/>
426  <x:anchor-alias value="ctext"/>
427   Comments can be included in some HTTP header fields by surrounding
428   the comment text with parentheses. Comments are only allowed in
429   fields containing "comment" as part of their field value definition.
430   In all other fields, parentheses are considered part of the field
431   value.
433<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
434  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
435  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
437<t anchor="rule.quoted-string">
438  <x:anchor-alias value="quoted-string"/>
439  <x:anchor-alias value="qdtext"/>
440   A string of text is parsed as a single word if it is quoted using
441   double-quote marks.
443<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
444  <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> )
445  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
447<t anchor="rule.quoted-pair">
448  <x:anchor-alias value="quoted-pair"/>
449  <x:anchor-alias value="quoted-text"/>
450   The backslash character ("\") &MAY; be used as a single-character
451   quoting mechanism only within quoted-string and comment constructs.
453<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
454  <x:ref>quoted-text</x:ref>    = %x01-09 /
455                   %x0B-0C /
456                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
457  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
461<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
462  <x:anchor-alias value="request-header"/>
463  <x:anchor-alias value="response-header"/>
464  <x:anchor-alias value="accept-params"/>
465  <x:anchor-alias value="entity-body"/>
466  <x:anchor-alias value="entity-header"/>
467  <x:anchor-alias value="Cache-Control"/>
468  <x:anchor-alias value="Pragma"/>
469  <x:anchor-alias value="Warning"/>
471  The ABNF rules below are defined in other parts:
473<figure><!-- Part2--><artwork type="abnf2616">
474  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
475  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
477<figure><!-- Part3--><artwork type="abnf2616">
478  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
479  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
480  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
482<figure><!-- Part6--><artwork type="abnf2616">
483  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
484  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
485  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
492<section title="When to use HTTP" anchor="when">
494<section title="Uniform Resource Identifiers" anchor="uri">
496   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used in HTTP
497   to indicate the target of a request and to identify additional resources related
498   to that resource, the request, or the response. Each protocol element in HTTP
499   that allows a URI reference will indicate in its ABNF whether the element allows
500   only a URI in absolute form, any relative reference, or some limited subset of
501   the URI-reference grammar. Unless otherwise indicated, relative URI references
502   are to be parsed relative to the URI corresponding to the request target
503   (the base URI).
505  <x:anchor-alias value="URI-reference"/>
506  <x:anchor-alias value="absolute-URI"/>
507  <x:anchor-alias value="authority"/>
508  <x:anchor-alias value="fragment"/>
509  <x:anchor-alias value="path-abempty"/>
510  <x:anchor-alias value="path-absolute"/>
511  <x:anchor-alias value="port"/>
512  <x:anchor-alias value="query"/>
513  <x:anchor-alias value="uri-host"/>
515   This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port",
516   "host", "path-abempty", "path-absolute", "query", and "authority" from <xref target="RFC3986"/>:
518<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"/>
519  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
520  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
521  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
522  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
523  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
524  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
525  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
526  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
529   HTTP does not place an a priori limit on the length of
530   a URI. Servers &MUST; be able to handle the URI of any resource they
531   serve, and &SHOULD; be able to handle URIs of unbounded length if they
532   provide GET-based forms that could generate such URIs. A server
533   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
534   than the server can handle (see &status-414;).
537  <list>
538    <t>
539      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
540      above 255 bytes, because some older client or proxy
541      implementations might not properly support these lengths.
542    </t>
543  </list>
546<section title="http URI scheme" anchor="http.uri">
547  <x:anchor-alias value="http-URI"/>
548  <iref item="http URI scheme" primary="true"/>
549  <iref item="URI scheme" subitem="http" primary="true"/>
551   The "http" scheme is used to locate network resources via the HTTP
552   protocol. This section defines the syntax and semantics for identifiers
553   using the http or https URI schemes.
555<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
556  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
559   If the port is empty or not given, port 80 is assumed. The semantics
560   are that the identified resource is located at the server listening
561   for TCP connections on that port of that host, and the Request-URI
562   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
563   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
564   the path-absolute is not present in the URL, it &MUST; be given as "/" when
565   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
566   receives a host name which is not a fully qualified domain name, it
567   &MAY; add its domain to the host name it received. If a proxy receives
568   a fully qualified domain name, the proxy &MUST-NOT; change the host
569   name.
572  <iref item="https URI scheme"/>
573  <iref item="URI scheme" subitem="https"/>
574  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
578<section title="URI Comparison" anchor="uri.comparison">
580   When comparing two URIs to decide if they match or not, a client
581   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
582   URIs, with these exceptions:
583  <list style="symbols">
584    <t>A port that is empty or not given is equivalent to the default
585        port for that URI-reference;</t>
586    <t>Comparisons of host names &MUST; be case-insensitive;</t>
587    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
588    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
589  </list>
592   Characters other than those in the "reserved" set (see
593   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
594   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
597   For example, the following three URIs are equivalent:
599<figure><artwork type="example">
607<section title="Overall Operation" anchor="intro.overall.operation">
609   HTTP is a request/response protocol. A client sends a
610   request to the server in the form of a request method, URI, and
611   protocol version, followed by a MIME-like message containing request
612   modifiers, client information, and possible body content over a
613   connection with a server. The server responds with a status line,
614   including the message's protocol version and a success or error code,
615   followed by a MIME-like message containing server information, entity
616   metainformation, and possible entity-body content.
619   Most HTTP communication is initiated by a user agent and consists of
620   a request to be applied to a resource on some origin server. In the
621   simplest case, this may be accomplished via a single connection (v)
622   between the user agent (UA) and the origin server (O).
624<figure><artwork type="drawing">
625       request chain ------------------------&gt;
626    UA -------------------v------------------- O
627       &lt;----------------------- response chain
630   A more complicated situation occurs when one or more intermediaries
631   are present in the request/response chain. There are three common
632   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
633   forwarding agent, receiving requests for a URI in its absolute form,
634   rewriting all or part of the message, and forwarding the reformatted
635   request toward the server identified by the URI. A gateway is a
636   receiving agent, acting as a layer above some other server(s) and, if
637   necessary, translating the requests to the underlying server's
638   protocol. A tunnel acts as a relay point between two connections
639   without changing the messages; tunnels are used when the
640   communication needs to pass through an intermediary (such as a
641   firewall) even when the intermediary cannot understand the contents
642   of the messages.
644<figure><artwork type="drawing">
645       request chain --------------------------------------&gt;
646    UA -----v----- A -----v----- B -----v----- C -----v----- O
647       &lt;------------------------------------- response chain
650   The figure above shows three intermediaries (A, B, and C) between the
651   user agent and origin server. A request or response message that
652   travels the whole chain will pass through four separate connections.
653   This distinction is important because some HTTP communication options
654   may apply only to the connection with the nearest, non-tunnel
655   neighbor, only to the end-points of the chain, or to all connections
656   along the chain. Although the diagram is linear, each participant may
657   be engaged in multiple, simultaneous communications. For example, B
658   may be receiving requests from many clients other than A, and/or
659   forwarding requests to servers other than C, at the same time that it
660   is handling A's request.
663   Any party to the communication which is not acting as a tunnel may
664   employ an internal cache for handling requests. The effect of a cache
665   is that the request/response chain is shortened if one of the
666   participants along the chain has a cached response applicable to that
667   request. The following illustrates the resulting chain if B has a
668   cached copy of an earlier response from O (via C) for a request which
669   has not been cached by UA or A.
671<figure><artwork type="drawing">
672          request chain ----------&gt;
673       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
674          &lt;--------- response chain
677   Not all responses are usefully cacheable, and some requests may
678   contain modifiers which place special requirements on cache behavior.
679   HTTP requirements for cache behavior and cacheable responses are
680   defined in &caching;.
683   In fact, there are a wide variety of architectures and configurations
684   of caches and proxies currently being experimented with or deployed
685   across the World Wide Web. These systems include national hierarchies
686   of proxy caches to save transoceanic bandwidth, systems that
687   broadcast or multicast cache entries, organizations that distribute
688   subsets of cached data via CD-ROM, and so on. HTTP systems are used
689   in corporate intranets over high-bandwidth links, and for access via
690   PDAs with low-power radio links and intermittent connectivity. The
691   goal of HTTP/1.1 is to support the wide diversity of configurations
692   already deployed while introducing protocol constructs that meet the
693   needs of those who build web applications that require high
694   reliability and, failing that, at least reliable indications of
695   failure.
698   HTTP communication usually takes place over TCP/IP connections. The
699   default port is TCP 80 (<eref target=""/>), but other ports can be used. This does
700   not preclude HTTP from being implemented on top of any other protocol
701   on the Internet, or on other networks. HTTP only presumes a reliable
702   transport; any protocol that provides such guarantees can be used;
703   the mapping of the HTTP/1.1 request and response structures onto the
704   transport data units of the protocol in question is outside the scope
705   of this specification.
708   In HTTP/1.0, most implementations used a new connection for each
709   request/response exchange. In HTTP/1.1, a connection may be used for
710   one or more request/response exchanges, although connections may be
711   closed for a variety of reasons (see <xref target="persistent.connections"/>).
716<section title="Protocol Parameters" anchor="protocol.parameters">
718<section title="HTTP Version" anchor="http.version">
719  <x:anchor-alias value="HTTP-Version"/>
720  <x:anchor-alias value="HTTP-Prot-Name"/>
722   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
723   of the protocol. The protocol versioning policy is intended to allow
724   the sender to indicate the format of a message and its capacity for
725   understanding further HTTP communication, rather than the features
726   obtained via that communication. No change is made to the version
727   number for the addition of message components which do not affect
728   communication behavior or which only add to extensible field values.
729   The &lt;minor&gt; number is incremented when the changes made to the
730   protocol add features which do not change the general message parsing
731   algorithm, but which may add to the message semantics and imply
732   additional capabilities of the sender. The &lt;major&gt; number is
733   incremented when the format of a message within the protocol is
734   changed. See <xref target="RFC2145"/> for a fuller explanation.
737   The version of an HTTP message is indicated by an HTTP-Version field
738   in the first line of the message. HTTP-Version is case-sensitive.
740<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
741  <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>
742  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
745   Note that the major and minor numbers &MUST; be treated as separate
746   integers and that each &MAY; be incremented higher than a single digit.
747   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
748   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
749   &MUST-NOT; be sent.
752   An application that sends a request or response message that includes
753   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
754   with this specification. Applications that are at least conditionally
755   compliant with this specification &SHOULD; use an HTTP-Version of
756   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
757   not compatible with HTTP/1.0. For more details on when to send
758   specific HTTP-Version values, see <xref target="RFC2145"/>.
761   The HTTP version of an application is the highest HTTP version for
762   which the application is at least conditionally compliant.
765   Proxy and gateway applications need to be careful when forwarding
766   messages in protocol versions different from that of the application.
767   Since the protocol version indicates the protocol capability of the
768   sender, a proxy/gateway &MUST-NOT; send a message with a version
769   indicator which is greater than its actual version. If a higher
770   version request is received, the proxy/gateway &MUST; either downgrade
771   the request version, or respond with an error, or switch to tunnel
772   behavior.
775   Due to interoperability problems with HTTP/1.0 proxies discovered
776   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
777   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
778   they support. The proxy/gateway's response to that request &MUST; be in
779   the same major version as the request.
782  <list>
783    <t>
784      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
785      of header fields required or forbidden by the versions involved.
786    </t>
787  </list>
791<section title="Date/Time Formats" anchor="date.time.formats">
792<section title="Full Date" anchor="">
793  <x:anchor-alias value="HTTP-date"/>
794  <x:anchor-alias value="obsolete-date"/>
795  <x:anchor-alias value="rfc1123-date"/>
796  <x:anchor-alias value="rfc850-date"/>
797  <x:anchor-alias value="asctime-date"/>
798  <x:anchor-alias value="date1"/>
799  <x:anchor-alias value="date2"/>
800  <x:anchor-alias value="date3"/>
801  <x:anchor-alias value="rfc1123-date"/>
802  <x:anchor-alias value="time"/>
803  <x:anchor-alias value="wkday"/>
804  <x:anchor-alias value="weekday"/>
805  <x:anchor-alias value="month"/>
807   HTTP applications have historically allowed three different formats
808   for the representation of date/time stamps:
810<figure><artwork type="example">
811   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
812   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
813   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
816   The first format is preferred as an Internet standard and represents
817   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
818   <xref target="RFC822"/>). The other formats are described here only for
819   compatibility with obsolete implementations.
820   HTTP/1.1 clients and servers that parse the date value &MUST; accept
821   all three formats (for compatibility with HTTP/1.0), though they &MUST;
822   only generate the RFC 1123 format for representing HTTP-date values
823   in header fields. See <xref target="tolerant.applications"/> for further information.
826      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
827      accepting date values that may have been sent by non-HTTP
828      applications, as is sometimes the case when retrieving or posting
829      messages via proxies/gateways to SMTP or NNTP.
832   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
833   (GMT), without exception. For the purposes of HTTP, GMT is exactly
834   equal to UTC (Coordinated Universal Time). This is indicated in the
835   first two formats by the inclusion of "GMT" as the three-letter
836   abbreviation for time zone, and &MUST; be assumed when reading the
837   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
838   additional LWS beyond that specifically included as SP in the
839   grammar.
841<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"/>
842  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
843  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
844  <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
845  <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
846  <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>
847  <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>
848                 ; day month year (e.g., 02 Jun 1982)
849  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
850                 ; day-month-year (e.g., 02-Jun-82)
851  <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> ))
852                 ; month day (e.g., Jun  2)
853  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
854                 ; 00:00:00 - 23:59:59
855  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
856               / s-Thu / s-Fri / s-Sat / s-Sun
857  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
858               / l-Thu / l-Fri / l-Sat / l-Sun
859  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
860               / s-May / s-Jun / s-Jul / s-Aug
861               / s-Sep / s-Oct / s-Nov / s-Dec
863  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
865  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
866  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
867  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
868  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
869  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
870  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
871  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
873  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
874  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
875  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
876  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
877  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
878  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
879  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
881  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
882  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
883  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
884  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
885  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
886  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
887  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
888  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
889  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
890  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
891  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
892  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
895      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
896      to their usage within the protocol stream. Clients and servers are
897      not required to use these formats for user presentation, request
898      logging, etc.
903<section title="Transfer Codings" anchor="transfer.codings">
904  <x:anchor-alias value="parameter"/>
905  <x:anchor-alias value="transfer-coding"/>
906  <x:anchor-alias value="transfer-extension"/>
908   Transfer-coding values are used to indicate an encoding
909   transformation that has been, can be, or may need to be applied to an
910   entity-body in order to ensure "safe transport" through the network.
911   This differs from a content coding in that the transfer-coding is a
912   property of the message, not of the original entity.
914<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
915  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
916  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
918<t anchor="rule.parameter">
919  <x:anchor-alias value="attribute"/>
920  <x:anchor-alias value="parameter"/>
921  <x:anchor-alias value="value"/>
922   Parameters are in  the form of attribute/value pairs.
924<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"/>
925  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
926  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
927  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
930   All transfer-coding values are case-insensitive. HTTP/1.1 uses
931   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
932   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
935   Whenever a transfer-coding is applied to a message-body, the set of
936   transfer-codings &MUST; include "chunked", unless the message indicates it
937   is terminated by closing the connection. When the "chunked" transfer-coding
938   is used, it &MUST; be the last transfer-coding applied to the
939   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
940   than once to a message-body. These rules allow the recipient to
941   determine the transfer-length of the message (<xref target="message.length"/>).
944   Transfer-codings are analogous to the Content-Transfer-Encoding
945   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
946   binary data over a 7-bit transport service. However, safe transport
947   has a different focus for an 8bit-clean transfer protocol. In HTTP,
948   the only unsafe characteristic of message-bodies is the difficulty in
949   determining the exact body length (<xref target="message.length"/>), or the desire to
950   encrypt data over a shared transport.
953   The Internet Assigned Numbers Authority (IANA) acts as a registry for
954   transfer-coding value tokens. Initially, the registry contains the
955   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
956   "gzip", "compress", and "deflate" (&content-codings;).
959   New transfer-coding value tokens &SHOULD; be registered in the same way
960   as new content-coding value tokens (&content-codings;).
963   A server which receives an entity-body with a transfer-coding it does
964   not understand &SHOULD; return 501 (Not Implemented), and close the
965   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
966   client.
969<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
970  <x:anchor-alias value="chunk"/>
971  <x:anchor-alias value="Chunked-Body"/>
972  <x:anchor-alias value="chunk-data"/>
973  <x:anchor-alias value="chunk-extension"/>
974  <x:anchor-alias value="chunk-ext-name"/>
975  <x:anchor-alias value="chunk-ext-val"/>
976  <x:anchor-alias value="chunk-size"/>
977  <x:anchor-alias value="last-chunk"/>
978  <x:anchor-alias value="trailer-part"/>
980   The chunked encoding modifies the body of a message in order to
981   transfer it as a series of chunks, each with its own size indicator,
982   followed by an &OPTIONAL; trailer containing entity-header fields. This
983   allows dynamically produced content to be transferred along with the
984   information necessary for the recipient to verify that it has
985   received the full message.
987<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"/>
988  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
989                   <x:ref>last-chunk</x:ref>
990                   <x:ref>trailer-part</x:ref>
991                   <x:ref>CRLF</x:ref>
993  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
994                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
995  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
996  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
998  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
999  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1000  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1001  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1002  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1005   The chunk-size field is a string of hex digits indicating the size of
1006   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1007   zero, followed by the trailer, which is terminated by an empty line.
1010   The trailer allows the sender to include additional HTTP header
1011   fields at the end of the message. The Trailer header field can be
1012   used to indicate which header fields are included in a trailer (see
1013   <xref target="header.trailer"/>).
1016   A server using chunked transfer-coding in a response &MUST-NOT; use the
1017   trailer for any header fields unless at least one of the following is
1018   true:
1019  <list style="numbers">
1020    <t>the request included a TE header field that indicates "trailers" is
1021     acceptable in the transfer-coding of the  response, as described in
1022     <xref target="header.te"/>; or,</t>
1024    <t>the server is the origin server for the response, the trailer
1025     fields consist entirely of optional metadata, and the recipient
1026     could use the message (in a manner acceptable to the origin server)
1027     without receiving this metadata.  In other words, the origin server
1028     is willing to accept the possibility that the trailer fields might
1029     be silently discarded along the path to the client.</t>
1030  </list>
1033   This requirement prevents an interoperability failure when the
1034   message is being received by an HTTP/1.1 (or later) proxy and
1035   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1036   compliance with the protocol would have necessitated a possibly
1037   infinite buffer on the proxy.
1040   A process for decoding the "chunked" transfer-coding
1041   can be represented in pseudo-code as:
1043<figure><artwork type="code">
1044    length := 0
1045    read chunk-size, chunk-extension (if any) and CRLF
1046    while (chunk-size &gt; 0) {
1047       read chunk-data and CRLF
1048       append chunk-data to entity-body
1049       length := length + chunk-size
1050       read chunk-size and CRLF
1051    }
1052    read entity-header
1053    while (entity-header not empty) {
1054       append entity-header to existing header fields
1055       read entity-header
1056    }
1057    Content-Length := length
1058    Remove "chunked" from Transfer-Encoding
1061   All HTTP/1.1 applications &MUST; be able to receive and decode the
1062   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1063   they do not understand.
1068<section title="Product Tokens" anchor="product.tokens">
1069  <x:anchor-alias value="product"/>
1070  <x:anchor-alias value="product-version"/>
1072   Product tokens are used to allow communicating applications to
1073   identify themselves by software name and version. Most fields using
1074   product tokens also allow sub-products which form a significant part
1075   of the application to be listed, separated by white space. By
1076   convention, the products are listed in order of their significance
1077   for identifying the application.
1079<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1080  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1081  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1084   Examples:
1086<figure><artwork type="example">
1087    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1088    Server: Apache/0.8.4
1091   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1092   used for advertising or other non-essential information. Although any
1093   token character &MAY; appear in a product-version, this token &SHOULD;
1094   only be used for a version identifier (i.e., successive versions of
1095   the same product &SHOULD; only differ in the product-version portion of
1096   the product value).
1102<section title="HTTP Message" anchor="http.message">
1104<section title="Message Types" anchor="message.types">
1105  <x:anchor-alias value="generic-message"/>
1106  <x:anchor-alias value="HTTP-message"/>
1107  <x:anchor-alias value="start-line"/>
1109   HTTP messages consist of requests from client to server and responses
1110   from server to client.
1112<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1113  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1116   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1117   message format of <xref target="RFC5322"/> for transferring entities (the payload
1118   of the message). Both types of message consist of a start-line, zero
1119   or more header fields (also known as "headers"), an empty line (i.e.,
1120   a line with nothing preceding the CRLF) indicating the end of the
1121   header fields, and possibly a message-body.
1123<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1124  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1125                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1126                    <x:ref>CRLF</x:ref>
1127                    [ <x:ref>message-body</x:ref> ]
1128  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1131   In the interest of robustness, servers &SHOULD; ignore any empty
1132   line(s) received where a Request-Line is expected. In other words, if
1133   the server is reading the protocol stream at the beginning of a
1134   message and receives a CRLF first, it should ignore the CRLF.
1137   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1138   after a POST request. To restate what is explicitly forbidden by the
1139   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1140   extra CRLF.
1144<section title="Message Headers" anchor="message.headers">
1145  <x:anchor-alias value="field-content"/>
1146  <x:anchor-alias value="field-name"/>
1147  <x:anchor-alias value="field-value"/>
1148  <x:anchor-alias value="message-header"/>
1150   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1151   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1152   entity-header (&entity-header-fields;) fields, follow the same generic format as
1153   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1154   of a name followed by a colon (":") and the field value. Field names
1155   are case-insensitive. The field value &MAY; be preceded by any amount
1156   of LWS, though a single SP is preferred. Header fields can be
1157   extended over multiple lines by preceding each extra line with at
1158   least one SP or HTAB. Applications ought to follow "common form", where
1159   one is known or indicated, when generating HTTP constructs, since
1160   there might exist some implementations that fail to accept anything
1161   beyond the common forms.
1163<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"/>
1164  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1165  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1166  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1167  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1168                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1169                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1170                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1173   The field-content does not include any leading or trailing LWS:
1174   linear white space occurring before the first non-whitespace
1175   character of the field-value or after the last non-whitespace
1176   character of the field-value. Such leading or trailing LWS &MAY; be
1177   removed without changing the semantics of the field value. Any LWS
1178   that occurs between field-content &MAY; be replaced with a single SP
1179   before interpreting the field value or forwarding the message
1180   downstream.
1183   The order in which header fields with differing field names are
1184   received is not significant. However, it is "good practice" to send
1185   general-header fields first, followed by request-header or response-header
1186   fields, and ending with the entity-header fields.
1189   Multiple message-header fields with the same field-name &MAY; be
1190   present in a message if and only if the entire field-value for that
1191   header field is defined as a comma-separated list [i.e., #(values)].
1192   It &MUST; be possible to combine the multiple header fields into one
1193   "field-name: field-value" pair, without changing the semantics of the
1194   message, by appending each subsequent field-value to the first, each
1195   separated by a comma. The order in which header fields with the same
1196   field-name are received is therefore significant to the
1197   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1198   change the order of these field values when a message is forwarded.
1201  <list><t>
1202   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1203   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1204   can occur multiple times, but does not use the list syntax, and thus cannot
1205   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1206   for details.) Also note that the Set-Cookie2 header specified in
1207   <xref target="RFC2965"/> does not share this problem.
1208  </t></list>
1213<section title="Message Body" anchor="message.body">
1214  <x:anchor-alias value="message-body"/>
1216   The message-body (if any) of an HTTP message is used to carry the
1217   entity-body associated with the request or response. The message-body
1218   differs from the entity-body only when a transfer-coding has been
1219   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1221<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1222  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1223               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1226   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1227   applied by an application to ensure safe and proper transfer of the
1228   message. Transfer-Encoding is a property of the message, not of the
1229   entity, and thus &MAY; be added or removed by any application along the
1230   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1231   when certain transfer-codings may be used.)
1234   The rules for when a message-body is allowed in a message differ for
1235   requests and responses.
1238   The presence of a message-body in a request is signaled by the
1239   inclusion of a Content-Length or Transfer-Encoding header field in
1240   the request's message-headers. A message-body &MUST-NOT; be included in
1241   a request if the specification of the request method (&method;)
1242   explicitly disallows an entity-body in requests.
1243   When a request message contains both a message-body of non-zero
1244   length and a method that does not define any semantics for that
1245   request message-body, then an origin server &SHOULD; either ignore
1246   the message-body or respond with an appropriate error message
1247   (e.g., 413).  A proxy or gateway, when presented the same request,
1248   &SHOULD; either forward the request inbound with the message-body or
1249   ignore the message-body when determining a response.
1252   For response messages, whether or not a message-body is included with
1253   a message is dependent on both the request method and the response
1254   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1255   &MUST-NOT; include a message-body, even though the presence of entity-header
1256   fields might lead one to believe they do. All 1xx
1257   (informational), 204 (No Content), and 304 (Not Modified) responses
1258   &MUST-NOT; include a message-body. All other responses do include a
1259   message-body, although it &MAY; be of zero length.
1263<section title="Message Length" anchor="message.length">
1265   The transfer-length of a message is the length of the message-body as
1266   it appears in the message; that is, after any transfer-codings have
1267   been applied. When a message-body is included with a message, the
1268   transfer-length of that body is determined by one of the following
1269   (in order of precedence):
1272  <list style="numbers">
1273    <x:lt><t>
1274     Any response message which "&MUST-NOT;" include a message-body (such
1275     as the 1xx, 204, and 304 responses and any response to a HEAD
1276     request) is always terminated by the first empty line after the
1277     header fields, regardless of the entity-header fields present in
1278     the message.
1279    </t></x:lt>
1280    <x:lt><t>
1281     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1282     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1283     is used, the transfer-length is defined by the use of this transfer-coding.
1284     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1285     is not present, the transfer-length is defined by the sender closing the connection.
1286    </t></x:lt>
1287    <x:lt><t>
1288     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1289     decimal value in OCTETs represents both the entity-length and the
1290     transfer-length. The Content-Length header field &MUST-NOT; be sent
1291     if these two lengths are different (i.e., if a Transfer-Encoding
1292     header field is present). If a message is received with both a
1293     Transfer-Encoding header field and a Content-Length header field,
1294     the latter &MUST; be ignored.
1295    </t></x:lt>
1296    <x:lt><t>
1297     If the message uses the media type "multipart/byteranges", and the
1298     transfer-length is not otherwise specified, then this self-delimiting
1299     media type defines the transfer-length. This media type
1300     &MUST-NOT; be used unless the sender knows that the recipient can parse
1301     it; the presence in a request of a Range header with multiple byte-range
1302     specifiers from a 1.1 client implies that the client can parse
1303     multipart/byteranges responses.
1304    <list style="empty"><t>
1305       A range header might be forwarded by a 1.0 proxy that does not
1306       understand multipart/byteranges; in this case the server &MUST;
1307       delimit the message using methods defined in items 1, 3 or 5 of
1308       this section.
1309    </t></list>
1310    </t></x:lt>
1311    <x:lt><t>
1312     By the server closing the connection. (Closing the connection
1313     cannot be used to indicate the end of a request body, since that
1314     would leave no possibility for the server to send back a response.)
1315    </t></x:lt>
1316  </list>
1319   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1320   containing a message-body &MUST; include a valid Content-Length header
1321   field unless the server is known to be HTTP/1.1 compliant. If a
1322   request contains a message-body and a Content-Length is not given,
1323   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1324   determine the length of the message, or with 411 (Length Required) if
1325   it wishes to insist on receiving a valid Content-Length.
1328   All HTTP/1.1 applications that receive entities &MUST; accept the
1329   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1330   to be used for messages when the message length cannot be determined
1331   in advance.
1334   Messages &MUST-NOT; include both a Content-Length header field and a
1335   transfer-coding. If the message does include a
1336   transfer-coding, the Content-Length &MUST; be ignored.
1339   When a Content-Length is given in a message where a message-body is
1340   allowed, its field value &MUST; exactly match the number of OCTETs in
1341   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1342   invalid length is received and detected.
1346<section title="General Header Fields" anchor="general.header.fields">
1347  <x:anchor-alias value="general-header"/>
1349   There are a few header fields which have general applicability for
1350   both request and response messages, but which do not apply to the
1351   entity being transferred. These header fields apply only to the
1352   message being transmitted.
1354<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1355  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1356                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1357                 / <x:ref>Date</x:ref>                     ; <xref target=""/>
1358                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1359                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1360                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1361                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1362                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1363                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1366   General-header field names can be extended reliably only in
1367   combination with a change in the protocol version. However, new or
1368   experimental header fields may be given the semantics of general
1369   header fields if all parties in the communication recognize them to
1370   be general-header fields. Unrecognized header fields are treated as
1371   entity-header fields.
1376<section title="Request" anchor="request">
1377  <x:anchor-alias value="Request"/>
1379   A request message from a client to a server includes, within the
1380   first line of that message, the method to be applied to the resource,
1381   the identifier of the resource, and the protocol version in use.
1383<!--                 Host                      ; should be moved here eventually -->
1384<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1385  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1386                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1387                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1388                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1389                  <x:ref>CRLF</x:ref>
1390                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1393<section title="Request-Line" anchor="request-line">
1394  <x:anchor-alias value="Request-Line"/>
1396   The Request-Line begins with a method token, followed by the
1397   Request-URI and the protocol version, and ending with CRLF. The
1398   elements are separated by SP characters. No CR or LF is allowed
1399   except in the final CRLF sequence.
1401<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1402  <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>
1405<section title="Method" anchor="method">
1406  <x:anchor-alias value="Method"/>
1408   The Method  token indicates the method to be performed on the
1409   resource identified by the Request-URI. The method is case-sensitive.
1411<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1412  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1416<section title="Request-URI" anchor="request-uri">
1417  <x:anchor-alias value="Request-URI"/>
1419   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1420   identifies the resource upon which to apply the request.
1422<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1423  <x:ref>Request-URI</x:ref>    = "*"
1424                 / <x:ref>absolute-URI</x:ref>
1425                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1426                 / <x:ref>authority</x:ref>
1429   The four options for Request-URI are dependent on the nature of the
1430   request. The asterisk "*" means that the request does not apply to a
1431   particular resource, but to the server itself, and is only allowed
1432   when the method used does not necessarily apply to a resource. One
1433   example would be
1435<figure><artwork type="example">
1436    OPTIONS * HTTP/1.1
1439   The absolute-URI form is &REQUIRED; when the request is being made to a
1440   proxy. The proxy is requested to forward the request or service it
1441   from a valid cache, and return the response. Note that the proxy &MAY;
1442   forward the request on to another proxy or directly to the server
1443   specified by the absolute-URI. In order to avoid request loops, a
1444   proxy &MUST; be able to recognize all of its server names, including
1445   any aliases, local variations, and the numeric IP address. An example
1446   Request-Line would be:
1448<figure><artwork type="example">
1449    GET HTTP/1.1
1452   To allow for transition to absolute-URIs in all requests in future
1453   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1454   form in requests, even though HTTP/1.1 clients will only generate
1455   them in requests to proxies.
1458   The authority form is only used by the CONNECT method (&CONNECT;).
1461   The most common form of Request-URI is that used to identify a
1462   resource on an origin server or gateway. In this case the absolute
1463   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1464   the Request-URI, and the network location of the URI (authority) &MUST;
1465   be transmitted in a Host header field. For example, a client wishing
1466   to retrieve the resource above directly from the origin server would
1467   create a TCP connection to port 80 of the host "" and send
1468   the lines:
1470<figure><artwork type="example">
1471    GET /pub/WWW/TheProject.html HTTP/1.1
1472    Host:
1475   followed by the remainder of the Request. Note that the absolute path
1476   cannot be empty; if none is present in the original URI, it &MUST; be
1477   given as "/" (the server root).
1480   The Request-URI is transmitted in the format specified in
1481   <xref target="http.uri"/>. If the Request-URI is encoded using the
1482   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1483   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1484   &MUST; decode the Request-URI in order to
1485   properly interpret the request. Servers &SHOULD; respond to invalid
1486   Request-URIs with an appropriate status code.
1489   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1490   received Request-URI when forwarding it to the next inbound server,
1491   except as noted above to replace a null path-absolute with "/".
1494  <list><t>
1495      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1496      meaning of the request when the origin server is improperly using
1497      a non-reserved URI character for a reserved purpose.  Implementors
1498      should be aware that some pre-HTTP/1.1 proxies have been known to
1499      rewrite the Request-URI.
1500  </t></list>
1505<section title="The Resource Identified by a Request" anchor="">
1507   The exact resource identified by an Internet request is determined by
1508   examining both the Request-URI and the Host header field.
1511   An origin server that does not allow resources to differ by the
1512   requested host &MAY; ignore the Host header field value when
1513   determining the resource identified by an HTTP/1.1 request. (But see
1514   <xref target=""/>
1515   for other requirements on Host support in HTTP/1.1.)
1518   An origin server that does differentiate resources based on the host
1519   requested (sometimes referred to as virtual hosts or vanity host
1520   names) &MUST; use the following rules for determining the requested
1521   resource on an HTTP/1.1 request:
1522  <list style="numbers">
1523    <t>If Request-URI is an absolute-URI, the host is part of the
1524     Request-URI. Any Host header field value in the request &MUST; be
1525     ignored.</t>
1526    <t>If the Request-URI is not an absolute-URI, and the request includes
1527     a Host header field, the host is determined by the Host header
1528     field value.</t>
1529    <t>If the host as determined by rule 1 or 2 is not a valid host on
1530     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1531  </list>
1534   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1535   attempt to use heuristics (e.g., examination of the URI path for
1536   something unique to a particular host) in order to determine what
1537   exact resource is being requested.
1544<section title="Response" anchor="response">
1545  <x:anchor-alias value="Response"/>
1547   After receiving and interpreting a request message, a server responds
1548   with an HTTP response message.
1550<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1551  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1552                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1553                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1554                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1555                  <x:ref>CRLF</x:ref>
1556                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1559<section title="Status-Line" anchor="status-line">
1560  <x:anchor-alias value="Status-Line"/>
1562   The first line of a Response message is the Status-Line, consisting
1563   of the protocol version followed by a numeric status code and its
1564   associated textual phrase, with each element separated by SP
1565   characters. No CR or LF is allowed except in the final CRLF sequence.
1567<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1568  <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>
1571<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1572  <x:anchor-alias value="Reason-Phrase"/>
1573  <x:anchor-alias value="Status-Code"/>
1575   The Status-Code element is a 3-digit integer result code of the
1576   attempt to understand and satisfy the request. These codes are fully
1577   defined in &status-codes;.  The Reason Phrase exists for the sole
1578   purpose of providing a textual description associated with the numeric
1579   status code, out of deference to earlier Internet application protocols
1580   that were more frequently used with interactive text clients.
1581   A client &SHOULD; ignore the content of the Reason Phrase.
1584   The first digit of the Status-Code defines the class of response. The
1585   last two digits do not have any categorization role. There are 5
1586   values for the first digit:
1587  <list style="symbols">
1588    <t>
1589      1xx: Informational - Request received, continuing process
1590    </t>
1591    <t>
1592      2xx: Success - The action was successfully received,
1593        understood, and accepted
1594    </t>
1595    <t>
1596      3xx: Redirection - Further action must be taken in order to
1597        complete the request
1598    </t>
1599    <t>
1600      4xx: Client Error - The request contains bad syntax or cannot
1601        be fulfilled
1602    </t>
1603    <t>
1604      5xx: Server Error - The server failed to fulfill an apparently
1605        valid request
1606    </t>
1607  </list>
1609<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"/>
1610  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1611  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1619<section title="Connections" anchor="connections">
1621<section title="Persistent Connections" anchor="persistent.connections">
1623<section title="Purpose" anchor="persistent.purpose">
1625   Prior to persistent connections, a separate TCP connection was
1626   established to fetch each URL, increasing the load on HTTP servers
1627   and causing congestion on the Internet. The use of inline images and
1628   other associated data often require a client to make multiple
1629   requests of the same server in a short amount of time. Analysis of
1630   these performance problems and results from a prototype
1631   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1632   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1633   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1634   T/TCP <xref target="Tou1998"/>.
1637   Persistent HTTP connections have a number of advantages:
1638  <list style="symbols">
1639      <t>
1640        By opening and closing fewer TCP connections, CPU time is saved
1641        in routers and hosts (clients, servers, proxies, gateways,
1642        tunnels, or caches), and memory used for TCP protocol control
1643        blocks can be saved in hosts.
1644      </t>
1645      <t>
1646        HTTP requests and responses can be pipelined on a connection.
1647        Pipelining allows a client to make multiple requests without
1648        waiting for each response, allowing a single TCP connection to
1649        be used much more efficiently, with much lower elapsed time.
1650      </t>
1651      <t>
1652        Network congestion is reduced by reducing the number of packets
1653        caused by TCP opens, and by allowing TCP sufficient time to
1654        determine the congestion state of the network.
1655      </t>
1656      <t>
1657        Latency on subsequent requests is reduced since there is no time
1658        spent in TCP's connection opening handshake.
1659      </t>
1660      <t>
1661        HTTP can evolve more gracefully, since errors can be reported
1662        without the penalty of closing the TCP connection. Clients using
1663        future versions of HTTP might optimistically try a new feature,
1664        but if communicating with an older server, retry with old
1665        semantics after an error is reported.
1666      </t>
1667    </list>
1670   HTTP implementations &SHOULD; implement persistent connections.
1674<section title="Overall Operation" anchor="persistent.overall">
1676   A significant difference between HTTP/1.1 and earlier versions of
1677   HTTP is that persistent connections are the default behavior of any
1678   HTTP connection. That is, unless otherwise indicated, the client
1679   &SHOULD; assume that the server will maintain a persistent connection,
1680   even after error responses from the server.
1683   Persistent connections provide a mechanism by which a client and a
1684   server can signal the close of a TCP connection. This signaling takes
1685   place using the Connection header field (<xref target="header.connection"/>). Once a close
1686   has been signaled, the client &MUST-NOT; send any more requests on that
1687   connection.
1690<section title="Negotiation" anchor="persistent.negotiation">
1692   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1693   maintain a persistent connection unless a Connection header including
1694   the connection-token "close" was sent in the request. If the server
1695   chooses to close the connection immediately after sending the
1696   response, it &SHOULD; send a Connection header including the
1697   connection-token close.
1700   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1701   decide to keep it open based on whether the response from a server
1702   contains a Connection header with the connection-token close. In case
1703   the client does not want to maintain a connection for more than that
1704   request, it &SHOULD; send a Connection header including the
1705   connection-token close.
1708   If either the client or the server sends the close token in the
1709   Connection header, that request becomes the last one for the
1710   connection.
1713   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1714   maintained for HTTP versions less than 1.1 unless it is explicitly
1715   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1716   compatibility with HTTP/1.0 clients.
1719   In order to remain persistent, all messages on the connection &MUST;
1720   have a self-defined message length (i.e., one not defined by closure
1721   of the connection), as described in <xref target="message.length"/>.
1725<section title="Pipelining" anchor="pipelining">
1727   A client that supports persistent connections &MAY; "pipeline" its
1728   requests (i.e., send multiple requests without waiting for each
1729   response). A server &MUST; send its responses to those requests in the
1730   same order that the requests were received.
1733   Clients which assume persistent connections and pipeline immediately
1734   after connection establishment &SHOULD; be prepared to retry their
1735   connection if the first pipelined attempt fails. If a client does
1736   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1737   persistent. Clients &MUST; also be prepared to resend their requests if
1738   the server closes the connection before sending all of the
1739   corresponding responses.
1742   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1743   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1744   premature termination of the transport connection could lead to
1745   indeterminate results. A client wishing to send a non-idempotent
1746   request &SHOULD; wait to send that request until it has received the
1747   response status for the previous request.
1752<section title="Proxy Servers" anchor="persistent.proxy">
1754   It is especially important that proxies correctly implement the
1755   properties of the Connection header field as specified in <xref target="header.connection"/>.
1758   The proxy server &MUST; signal persistent connections separately with
1759   its clients and the origin servers (or other proxy servers) that it
1760   connects to. Each persistent connection applies to only one transport
1761   link.
1764   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1765   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1766   discussion of the problems with the Keep-Alive header implemented by
1767   many HTTP/1.0 clients).
1771<section title="Practical Considerations" anchor="persistent.practical">
1773   Servers will usually have some time-out value beyond which they will
1774   no longer maintain an inactive connection. Proxy servers might make
1775   this a higher value since it is likely that the client will be making
1776   more connections through the same server. The use of persistent
1777   connections places no requirements on the length (or existence) of
1778   this time-out for either the client or the server.
1781   When a client or server wishes to time-out it &SHOULD; issue a graceful
1782   close on the transport connection. Clients and servers &SHOULD; both
1783   constantly watch for the other side of the transport close, and
1784   respond to it as appropriate. If a client or server does not detect
1785   the other side's close promptly it could cause unnecessary resource
1786   drain on the network.
1789   A client, server, or proxy &MAY; close the transport connection at any
1790   time. For example, a client might have started to send a new request
1791   at the same time that the server has decided to close the "idle"
1792   connection. From the server's point of view, the connection is being
1793   closed while it was idle, but from the client's point of view, a
1794   request is in progress.
1797   This means that clients, servers, and proxies &MUST; be able to recover
1798   from asynchronous close events. Client software &SHOULD; reopen the
1799   transport connection and retransmit the aborted sequence of requests
1800   without user interaction so long as the request sequence is
1801   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1802   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1803   human operator the choice of retrying the request(s). Confirmation by
1804   user-agent software with semantic understanding of the application
1805   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1806   be repeated if the second sequence of requests fails.
1809   Servers &SHOULD; always respond to at least one request per connection,
1810   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1811   middle of transmitting a response, unless a network or client failure
1812   is suspected.
1815   Clients that use persistent connections &SHOULD; limit the number of
1816   simultaneous connections that they maintain to a given server. A
1817   single-user client &SHOULD-NOT; maintain more than 2 connections with
1818   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1819   another server or proxy, where N is the number of simultaneously
1820   active users. These guidelines are intended to improve HTTP response
1821   times and avoid congestion.
1826<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1828<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1830   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1831   flow control mechanisms to resolve temporary overloads, rather than
1832   terminating connections with the expectation that clients will retry.
1833   The latter technique can exacerbate network congestion.
1837<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1839   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1840   the network connection for an error status while it is transmitting
1841   the request. If the client sees an error status, it &SHOULD;
1842   immediately cease transmitting the body. If the body is being sent
1843   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1844   empty trailer &MAY; be used to prematurely mark the end of the message.
1845   If the body was preceded by a Content-Length header, the client &MUST;
1846   close the connection.
1850<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1852   The purpose of the 100 (Continue) status (see &status-100;) is to
1853   allow a client that is sending a request message with a request body
1854   to determine if the origin server is willing to accept the request
1855   (based on the request headers) before the client sends the request
1856   body. In some cases, it might either be inappropriate or highly
1857   inefficient for the client to send the body if the server will reject
1858   the message without looking at the body.
1861   Requirements for HTTP/1.1 clients:
1862  <list style="symbols">
1863    <t>
1864        If a client will wait for a 100 (Continue) response before
1865        sending the request body, it &MUST; send an Expect request-header
1866        field (&header-expect;) with the "100-continue" expectation.
1867    </t>
1868    <t>
1869        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1870        with the "100-continue" expectation if it does not intend
1871        to send a request body.
1872    </t>
1873  </list>
1876   Because of the presence of older implementations, the protocol allows
1877   ambiguous situations in which a client may send "Expect: 100-continue"
1878   without receiving either a 417 (Expectation Failed) status
1879   or a 100 (Continue) status. Therefore, when a client sends this
1880   header field to an origin server (possibly via a proxy) from which it
1881   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1882   for an indefinite period before sending the request body.
1885   Requirements for HTTP/1.1 origin servers:
1886  <list style="symbols">
1887    <t> Upon receiving a request which includes an Expect request-header
1888        field with the "100-continue" expectation, an origin server &MUST;
1889        either respond with 100 (Continue) status and continue to read
1890        from the input stream, or respond with a final status code. The
1891        origin server &MUST-NOT; wait for the request body before sending
1892        the 100 (Continue) response. If it responds with a final status
1893        code, it &MAY; close the transport connection or it &MAY; continue
1894        to read and discard the rest of the request.  It &MUST-NOT;
1895        perform the requested method if it returns a final status code.
1896    </t>
1897    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1898        the request message does not include an Expect request-header
1899        field with the "100-continue" expectation, and &MUST-NOT; send a
1900        100 (Continue) response if such a request comes from an HTTP/1.0
1901        (or earlier) client. There is an exception to this rule: for
1902        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1903        status in response to an HTTP/1.1 PUT or POST request that does
1904        not include an Expect request-header field with the "100-continue"
1905        expectation. This exception, the purpose of which is
1906        to minimize any client processing delays associated with an
1907        undeclared wait for 100 (Continue) status, applies only to
1908        HTTP/1.1 requests, and not to requests with any other HTTP-version
1909        value.
1910    </t>
1911    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1912        already received some or all of the request body for the
1913        corresponding request.
1914    </t>
1915    <t> An origin server that sends a 100 (Continue) response &MUST;
1916    ultimately send a final status code, once the request body is
1917        received and processed, unless it terminates the transport
1918        connection prematurely.
1919    </t>
1920    <t> If an origin server receives a request that does not include an
1921        Expect request-header field with the "100-continue" expectation,
1922        the request includes a request body, and the server responds
1923        with a final status code before reading the entire request body
1924        from the transport connection, then the server &SHOULD-NOT;  close
1925        the transport connection until it has read the entire request,
1926        or until the client closes the connection. Otherwise, the client
1927        might not reliably receive the response message. However, this
1928        requirement is not be construed as preventing a server from
1929        defending itself against denial-of-service attacks, or from
1930        badly broken client implementations.
1931      </t>
1932    </list>
1935   Requirements for HTTP/1.1 proxies:
1936  <list style="symbols">
1937    <t> If a proxy receives a request that includes an Expect request-header
1938        field with the "100-continue" expectation, and the proxy
1939        either knows that the next-hop server complies with HTTP/1.1 or
1940        higher, or does not know the HTTP version of the next-hop
1941        server, it &MUST; forward the request, including the Expect header
1942        field.
1943    </t>
1944    <t> If the proxy knows that the version of the next-hop server is
1945        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1946        respond with a 417 (Expectation Failed) status.
1947    </t>
1948    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1949        numbers received from recently-referenced next-hop servers.
1950    </t>
1951    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1952        request message was received from an HTTP/1.0 (or earlier)
1953        client and did not include an Expect request-header field with
1954        the "100-continue" expectation. This requirement overrides the
1955        general rule for forwarding of 1xx responses (see &status-1xx;).
1956    </t>
1957  </list>
1961<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1963   If an HTTP/1.1 client sends a request which includes a request body,
1964   but which does not include an Expect request-header field with the
1965   "100-continue" expectation, and if the client is not directly
1966   connected to an HTTP/1.1 origin server, and if the client sees the
1967   connection close before receiving any status from the server, the
1968   client &SHOULD; retry the request.  If the client does retry this
1969   request, it &MAY; use the following "binary exponential backoff"
1970   algorithm to be assured of obtaining a reliable response:
1971  <list style="numbers">
1972    <t>
1973      Initiate a new connection to the server
1974    </t>
1975    <t>
1976      Transmit the request-headers
1977    </t>
1978    <t>
1979      Initialize a variable R to the estimated round-trip time to the
1980         server (e.g., based on the time it took to establish the
1981         connection), or to a constant value of 5 seconds if the round-trip
1982         time is not available.
1983    </t>
1984    <t>
1985       Compute T = R * (2**N), where N is the number of previous
1986         retries of this request.
1987    </t>
1988    <t>
1989       Wait either for an error response from the server, or for T
1990         seconds (whichever comes first)
1991    </t>
1992    <t>
1993       If no error response is received, after T seconds transmit the
1994         body of the request.
1995    </t>
1996    <t>
1997       If client sees that the connection is closed prematurely,
1998         repeat from step 1 until the request is accepted, an error
1999         response is received, or the user becomes impatient and
2000         terminates the retry process.
2001    </t>
2002  </list>
2005   If at any point an error status is received, the client
2006  <list style="symbols">
2007      <t>&SHOULD-NOT;  continue and</t>
2009      <t>&SHOULD; close the connection if it has not completed sending the
2010        request message.</t>
2011    </list>
2018<section title="Header Field Definitions" anchor="header.fields">
2020   This section defines the syntax and semantics of HTTP/1.1 header fields
2021   related to message framing and transport protocols.
2024   For entity-header fields, both sender and recipient refer to either the
2025   client or the server, depending on who sends and who receives the entity.
2028<section title="Connection" anchor="header.connection">
2029  <iref primary="true" item="Connection header" x:for-anchor=""/>
2030  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2031  <x:anchor-alias value="Connection"/>
2032  <x:anchor-alias value="connection-token"/>
2034   The Connection general-header field allows the sender to specify
2035   options that are desired for that particular connection and &MUST-NOT;
2036   be communicated by proxies over further connections.
2039   The Connection header has the following grammar:
2041<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2042  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2043  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2046   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2047   message is forwarded and, for each connection-token in this field,
2048   remove any header field(s) from the message with the same name as the
2049   connection-token. Connection options are signaled by the presence of
2050   a connection-token in the Connection header field, not by any
2051   corresponding additional header field(s), since the additional header
2052   field may not be sent if there are no parameters associated with that
2053   connection option.
2056   Message headers listed in the Connection header &MUST-NOT; include
2057   end-to-end headers, such as Cache-Control.
2060   HTTP/1.1 defines the "close" connection option for the sender to
2061   signal that the connection will be closed after completion of the
2062   response. For example,
2064<figure><artwork type="example">
2065    Connection: close
2068   in either the request or the response header fields indicates that
2069   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2070   after the current request/response is complete.
2073   An HTTP/1.1 client that does not support persistent connections &MUST;
2074   include the "close" connection option in every request message.
2077   An HTTP/1.1 server that does not support persistent connections &MUST;
2078   include the "close" connection option in every response message that
2079   does not have a 1xx (informational) status code.
2082   A system receiving an HTTP/1.0 (or lower-version) message that
2083   includes a Connection header &MUST;, for each connection-token in this
2084   field, remove and ignore any header field(s) from the message with
2085   the same name as the connection-token. This protects against mistaken
2086   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2090<section title="Content-Length" anchor="header.content-length">
2091  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2092  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2093  <x:anchor-alias value="Content-Length"/>
2095   The Content-Length entity-header field indicates the size of the
2096   entity-body, in decimal number of OCTETs, sent to the recipient or,
2097   in the case of the HEAD method, the size of the entity-body that
2098   would have been sent had the request been a GET.
2100<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2101  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2104   An example is
2106<figure><artwork type="example">
2107    Content-Length: 3495
2110   Applications &SHOULD; use this field to indicate the transfer-length of
2111   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2114   Any Content-Length greater than or equal to zero is a valid value.
2115   <xref target="message.length"/> describes how to determine the length of a message-body
2116   if a Content-Length is not given.
2119   Note that the meaning of this field is significantly different from
2120   the corresponding definition in MIME, where it is an optional field
2121   used within the "message/external-body" content-type. In HTTP, it
2122   &SHOULD; be sent whenever the message's length can be determined prior
2123   to being transferred, unless this is prohibited by the rules in
2124   <xref target="message.length"/>.
2128<section title="Date" anchor="">
2129  <iref primary="true" item="Date header" x:for-anchor=""/>
2130  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2131  <x:anchor-alias value="Date"/>
2133   The Date general-header field represents the date and time at which
2134   the message was originated, having the same semantics as orig-date in
2135   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2136   HTTP-date, as described in <xref target=""/>;
2137   it &MUST; be sent in rfc1123-date format.
2139<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2140  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2143   An example is
2145<figure><artwork type="example">
2146    Date: Tue, 15 Nov 1994 08:12:31 GMT
2149   Origin servers &MUST; include a Date header field in all responses,
2150   except in these cases:
2151  <list style="numbers">
2152      <t>If the response status code is 100 (Continue) or 101 (Switching
2153         Protocols), the response &MAY; include a Date header field, at
2154         the server's option.</t>
2156      <t>If the response status code conveys a server error, e.g. 500
2157         (Internal Server Error) or 503 (Service Unavailable), and it is
2158         inconvenient or impossible to generate a valid Date.</t>
2160      <t>If the server does not have a clock that can provide a
2161         reasonable approximation of the current time, its responses
2162         &MUST-NOT; include a Date header field. In this case, the rules
2163         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2164  </list>
2167   A received message that does not have a Date header field &MUST; be
2168   assigned one by the recipient if the message will be cached by that
2169   recipient or gatewayed via a protocol which requires a Date. An HTTP
2170   implementation without a clock &MUST-NOT; cache responses without
2171   revalidating them on every use. An HTTP cache, especially a shared
2172   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2173   clock with a reliable external standard.
2176   Clients &SHOULD; only send a Date header field in messages that include
2177   an entity-body, as in the case of the PUT and POST requests, and even
2178   then it is optional. A client without a clock &MUST-NOT; send a Date
2179   header field in a request.
2182   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2183   time subsequent to the generation of the message. It &SHOULD; represent
2184   the best available approximation of the date and time of message
2185   generation, unless the implementation has no means of generating a
2186   reasonably accurate date and time. In theory, the date ought to
2187   represent the moment just before the entity is generated. In
2188   practice, the date can be generated at any time during the message
2189   origination without affecting its semantic value.
2192<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2194   Some origin server implementations might not have a clock available.
2195   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2196   values to a response, unless these values were associated
2197   with the resource by a system or user with a reliable clock. It &MAY;
2198   assign an Expires value that is known, at or before server
2199   configuration time, to be in the past (this allows "pre-expiration"
2200   of responses without storing separate Expires values for each
2201   resource).
2206<section title="Host" anchor="">
2207  <iref primary="true" item="Host header" x:for-anchor=""/>
2208  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2209  <x:anchor-alias value="Host"/>
2211   The Host request-header field specifies the Internet host and port
2212   number of the resource being requested, as obtained from the original
2213   URI given by the user or referring resource (generally an http URI,
2214   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2215   the naming authority of the origin server or gateway given by the
2216   original URL. This allows the origin server or gateway to
2217   differentiate between internally-ambiguous URLs, such as the root "/"
2218   URL of a server for multiple host names on a single IP address.
2220<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2221  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2224   A "host" without any trailing port information implies the default
2225   port for the service requested (e.g., "80" for an HTTP URL). For
2226   example, a request on the origin server for
2227   &lt;; would properly include:
2229<figure><artwork type="example">
2230    GET /pub/WWW/ HTTP/1.1
2231    Host:
2234   A client &MUST; include a Host header field in all HTTP/1.1 request
2235   messages. If the requested URI does not include an Internet host
2236   name for the service being requested, then the Host header field &MUST;
2237   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2238   request message it forwards does contain an appropriate Host header
2239   field that identifies the service being requested by the proxy. All
2240   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2241   status code to any HTTP/1.1 request message which lacks a Host header
2242   field.
2245   See Sections <xref target="" format="counter"/>
2246   and <xref target="" format="counter"/>
2247   for other requirements relating to Host.
2251<section title="TE" anchor="header.te">
2252  <iref primary="true" item="TE header" x:for-anchor=""/>
2253  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2254  <x:anchor-alias value="TE"/>
2255  <x:anchor-alias value="t-codings"/>
2257   The TE request-header field indicates what extension transfer-codings
2258   it is willing to accept in the response and whether or not it is
2259   willing to accept trailer fields in a chunked transfer-coding. Its
2260   value may consist of the keyword "trailers" and/or a comma-separated
2261   list of extension transfer-coding names with optional accept
2262   parameters (as described in <xref target="transfer.codings"/>).
2264<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2265  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2266  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2269   The presence of the keyword "trailers" indicates that the client is
2270   willing to accept trailer fields in a chunked transfer-coding, as
2271   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2272   transfer-coding values even though it does not itself represent a
2273   transfer-coding.
2276   Examples of its use are:
2278<figure><artwork type="example">
2279    TE: deflate
2280    TE:
2281    TE: trailers, deflate;q=0.5
2284   The TE header field only applies to the immediate connection.
2285   Therefore, the keyword &MUST; be supplied within a Connection header
2286   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2289   A server tests whether a transfer-coding is acceptable, according to
2290   a TE field, using these rules:
2291  <list style="numbers">
2292    <x:lt>
2293      <t>The "chunked" transfer-coding is always acceptable. If the
2294         keyword "trailers" is listed, the client indicates that it is
2295         willing to accept trailer fields in the chunked response on
2296         behalf of itself and any downstream clients. The implication is
2297         that, if given, the client is stating that either all
2298         downstream clients are willing to accept trailer fields in the
2299         forwarded response, or that it will attempt to buffer the
2300         response on behalf of downstream recipients.
2301      </t><t>
2302         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2303         chunked response such that a client can be assured of buffering
2304         the entire response.</t>
2305    </x:lt>
2306    <x:lt>
2307      <t>If the transfer-coding being tested is one of the transfer-codings
2308         listed in the TE field, then it is acceptable unless it
2309         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2310         qvalue of 0 means "not acceptable.")</t>
2311    </x:lt>
2312    <x:lt>
2313      <t>If multiple transfer-codings are acceptable, then the
2314         acceptable transfer-coding with the highest non-zero qvalue is
2315         preferred.  The "chunked" transfer-coding always has a qvalue
2316         of 1.</t>
2317    </x:lt>
2318  </list>
2321   If the TE field-value is empty or if no TE field is present, the only
2322   transfer-coding  is "chunked". A message with no transfer-coding is
2323   always acceptable.
2327<section title="Trailer" anchor="header.trailer">
2328  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2329  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2330  <x:anchor-alias value="Trailer"/>
2332   The Trailer general field value indicates that the given set of
2333   header fields is present in the trailer of a message encoded with
2334   chunked transfer-coding.
2336<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2337  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2340   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2341   message using chunked transfer-coding with a non-empty trailer. Doing
2342   so allows the recipient to know which header fields to expect in the
2343   trailer.
2346   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2347   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2348   trailer fields in a "chunked" transfer-coding.
2351   Message header fields listed in the Trailer header field &MUST-NOT;
2352   include the following header fields:
2353  <list style="symbols">
2354    <t>Transfer-Encoding</t>
2355    <t>Content-Length</t>
2356    <t>Trailer</t>
2357  </list>
2361<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2362  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2363  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2364  <x:anchor-alias value="Transfer-Encoding"/>
2366   The Transfer-Encoding general-header field indicates what (if any)
2367   type of transformation has been applied to the message body in order
2368   to safely transfer it between the sender and the recipient. This
2369   differs from the content-coding in that the transfer-coding is a
2370   property of the message, not of the entity.
2372<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2373  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2376   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2378<figure><artwork type="example">
2379  Transfer-Encoding: chunked
2382   If multiple encodings have been applied to an entity, the transfer-codings
2383   &MUST; be listed in the order in which they were applied.
2384   Additional information about the encoding parameters &MAY; be provided
2385   by other entity-header fields not defined by this specification.
2388   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2389   header.
2393<section title="Upgrade" anchor="header.upgrade">
2394  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2395  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2396  <x:anchor-alias value="Upgrade"/>
2398   The Upgrade general-header allows the client to specify what
2399   additional communication protocols it supports and would like to use
2400   if the server finds it appropriate to switch protocols. The server
2401   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2402   response to indicate which protocol(s) are being switched.
2404<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2405  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2408   For example,
2410<figure><artwork type="example">
2411    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2414   The Upgrade header field is intended to provide a simple mechanism
2415   for transition from HTTP/1.1 to some other, incompatible protocol. It
2416   does so by allowing the client to advertise its desire to use another
2417   protocol, such as a later version of HTTP with a higher major version
2418   number, even though the current request has been made using HTTP/1.1.
2419   This eases the difficult transition between incompatible protocols by
2420   allowing the client to initiate a request in the more commonly
2421   supported protocol while indicating to the server that it would like
2422   to use a "better" protocol if available (where "better" is determined
2423   by the server, possibly according to the nature of the method and/or
2424   resource being requested).
2427   The Upgrade header field only applies to switching application-layer
2428   protocols upon the existing transport-layer connection. Upgrade
2429   cannot be used to insist on a protocol change; its acceptance and use
2430   by the server is optional. The capabilities and nature of the
2431   application-layer communication after the protocol change is entirely
2432   dependent upon the new protocol chosen, although the first action
2433   after changing the protocol &MUST; be a response to the initial HTTP
2434   request containing the Upgrade header field.
2437   The Upgrade header field only applies to the immediate connection.
2438   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2439   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2440   HTTP/1.1 message.
2443   The Upgrade header field cannot be used to indicate a switch to a
2444   protocol on a different connection. For that purpose, it is more
2445   appropriate to use a 301, 302, 303, or 305 redirection response.
2448   This specification only defines the protocol name "HTTP" for use by
2449   the family of Hypertext Transfer Protocols, as defined by the HTTP
2450   version rules of <xref target="http.version"/> and future updates to this
2451   specification. Any token can be used as a protocol name; however, it
2452   will only be useful if both the client and server associate the name
2453   with the same protocol.
2457<section title="Via" anchor="header.via">
2458  <iref primary="true" item="Via header" x:for-anchor=""/>
2459  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2460  <x:anchor-alias value="protocol-name"/>
2461  <x:anchor-alias value="protocol-version"/>
2462  <x:anchor-alias value="pseudonym"/>
2463  <x:anchor-alias value="received-by"/>
2464  <x:anchor-alias value="received-protocol"/>
2465  <x:anchor-alias value="Via"/>
2467   The Via general-header field &MUST; be used by gateways and proxies to
2468   indicate the intermediate protocols and recipients between the user
2469   agent and the server on requests, and between the origin server and
2470   the client on responses. It is analogous to the "Received" field defined in
2471   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2472   avoiding request loops, and identifying the protocol capabilities of
2473   all senders along the request/response chain.
2475<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"/>
2476  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2477  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2478  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2479  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2480  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2481  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2484   The received-protocol indicates the protocol version of the message
2485   received by the server or client along each segment of the
2486   request/response chain. The received-protocol version is appended to
2487   the Via field value when the message is forwarded so that information
2488   about the protocol capabilities of upstream applications remains
2489   visible to all recipients.
2492   The protocol-name is optional if and only if it would be "HTTP". The
2493   received-by field is normally the host and optional port number of a
2494   recipient server or client that subsequently forwarded the message.
2495   However, if the real host is considered to be sensitive information,
2496   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2497   be assumed to be the default port of the received-protocol.
2500   Multiple Via field values represents each proxy or gateway that has
2501   forwarded the message. Each recipient &MUST; append its information
2502   such that the end result is ordered according to the sequence of
2503   forwarding applications.
2506   Comments &MAY; be used in the Via header field to identify the software
2507   of the recipient proxy or gateway, analogous to the User-Agent and
2508   Server header fields. However, all comments in the Via field are
2509   optional and &MAY; be removed by any recipient prior to forwarding the
2510   message.
2513   For example, a request message could be sent from an HTTP/1.0 user
2514   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2515   forward the request to a public proxy at, which completes
2516   the request by forwarding it to the origin server at
2517   The request received by would then have the following
2518   Via header field:
2520<figure><artwork type="example">
2521    Via: 1.0 fred, 1.1 (Apache/1.1)
2524   Proxies and gateways used as a portal through a network firewall
2525   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2526   the firewall region. This information &SHOULD; only be propagated if
2527   explicitly enabled. If not enabled, the received-by host of any host
2528   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2529   for that host.
2532   For organizations that have strong privacy requirements for hiding
2533   internal structures, a proxy &MAY; combine an ordered subsequence of
2534   Via header field entries with identical received-protocol values into
2535   a single such entry. For example,
2537<figure><artwork type="example">
2538    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2541        could be collapsed to
2543<figure><artwork type="example">
2544    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2547   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2548   under the same organizational control and the hosts have already been
2549   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2550   have different received-protocol values.
2556<section title="IANA Considerations" anchor="IANA.considerations">
2557<section title="Message Header Registration" anchor="message.header.registration">
2559   The Message Header Registry located at <eref target=""/> should be updated
2560   with the permanent registrations below (see <xref target="RFC3864"/>):
2562<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2563<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2564   <ttcol>Header Field Name</ttcol>
2565   <ttcol>Protocol</ttcol>
2566   <ttcol>Status</ttcol>
2567   <ttcol>Reference</ttcol>
2569   <c>Connection</c>
2570   <c>http</c>
2571   <c>standard</c>
2572   <c>
2573      <xref target="header.connection"/>
2574   </c>
2575   <c>Content-Length</c>
2576   <c>http</c>
2577   <c>standard</c>
2578   <c>
2579      <xref target="header.content-length"/>
2580   </c>
2581   <c>Date</c>
2582   <c>http</c>
2583   <c>standard</c>
2584   <c>
2585      <xref target=""/>
2586   </c>
2587   <c>Host</c>
2588   <c>http</c>
2589   <c>standard</c>
2590   <c>
2591      <xref target=""/>
2592   </c>
2593   <c>TE</c>
2594   <c>http</c>
2595   <c>standard</c>
2596   <c>
2597      <xref target="header.te"/>
2598   </c>
2599   <c>Trailer</c>
2600   <c>http</c>
2601   <c>standard</c>
2602   <c>
2603      <xref target="header.trailer"/>
2604   </c>
2605   <c>Transfer-Encoding</c>
2606   <c>http</c>
2607   <c>standard</c>
2608   <c>
2609      <xref target="header.transfer-encoding"/>
2610   </c>
2611   <c>Upgrade</c>
2612   <c>http</c>
2613   <c>standard</c>
2614   <c>
2615      <xref target="header.upgrade"/>
2616   </c>
2617   <c>Via</c>
2618   <c>http</c>
2619   <c>standard</c>
2620   <c>
2621      <xref target="header.via"/>
2622   </c>
2626   The change controller is: "IETF ( - Internet Engineering Task Force".
2630<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2632   The entry for the "http" URI Scheme in the registry located at
2633   <eref target=""/>
2634   should be updated to point to <xref target="http.uri"/> of this document
2635   (see <xref target="RFC4395"/>).
2639<section title="Internet Media Type Registrations" anchor="">
2641   This document serves as the specification for the Internet media types
2642   "message/http" and "application/http". The following is to be registered with
2643   IANA (see <xref target="RFC4288"/>).
2645<section title="Internet Media Type message/http" anchor="">
2646<iref item="Media Type" subitem="message/http" primary="true"/>
2647<iref item="message/http Media Type" primary="true"/>
2649   The message/http type can be used to enclose a single HTTP request or
2650   response message, provided that it obeys the MIME restrictions for all
2651   "message" types regarding line length and encodings.
2654  <list style="hanging" x:indent="12em">
2655    <t hangText="Type name:">
2656      message
2657    </t>
2658    <t hangText="Subtype name:">
2659      http
2660    </t>
2661    <t hangText="Required parameters:">
2662      none
2663    </t>
2664    <t hangText="Optional parameters:">
2665      version, msgtype
2666      <list style="hanging">
2667        <t hangText="version:">
2668          The HTTP-Version number of the enclosed message
2669          (e.g., "1.1"). If not present, the version can be
2670          determined from the first line of the body.
2671        </t>
2672        <t hangText="msgtype:">
2673          The message type -- "request" or "response". If not
2674          present, the type can be determined from the first
2675          line of the body.
2676        </t>
2677      </list>
2678    </t>
2679    <t hangText="Encoding considerations:">
2680      only "7bit", "8bit", or "binary" are permitted
2681    </t>
2682    <t hangText="Security considerations:">
2683      none
2684    </t>
2685    <t hangText="Interoperability considerations:">
2686      none
2687    </t>
2688    <t hangText="Published specification:">
2689      This specification (see <xref target=""/>).
2690    </t>
2691    <t hangText="Applications that use this media type:">
2692    </t>
2693    <t hangText="Additional information:">
2694      <list style="hanging">
2695        <t hangText="Magic number(s):">none</t>
2696        <t hangText="File extension(s):">none</t>
2697        <t hangText="Macintosh file type code(s):">none</t>
2698      </list>
2699    </t>
2700    <t hangText="Person and email address to contact for further information:">
2701      See Authors Section.
2702    </t>
2703                <t hangText="Intended usage:">
2704                  COMMON
2705    </t>
2706                <t hangText="Restrictions on usage:">
2707                  none
2708    </t>
2709    <t hangText="Author/Change controller:">
2710      IESG
2711    </t>
2712  </list>
2715<section title="Internet Media Type application/http" anchor="">
2716<iref item="Media Type" subitem="application/http" primary="true"/>
2717<iref item="application/http Media Type" primary="true"/>
2719   The application/http type can be used to enclose a pipeline of one or more
2720   HTTP request or response messages (not intermixed).
2723  <list style="hanging" x:indent="12em">
2724    <t hangText="Type name:">
2725      application
2726    </t>
2727    <t hangText="Subtype name:">
2728      http
2729    </t>
2730    <t hangText="Required parameters:">
2731      none
2732    </t>
2733    <t hangText="Optional parameters:">
2734      version, msgtype
2735      <list style="hanging">
2736        <t hangText="version:">
2737          The HTTP-Version number of the enclosed messages
2738          (e.g., "1.1"). If not present, the version can be
2739          determined from the first line of the body.
2740        </t>
2741        <t hangText="msgtype:">
2742          The message type -- "request" or "response". If not
2743          present, the type can be determined from the first
2744          line of the body.
2745        </t>
2746      </list>
2747    </t>
2748    <t hangText="Encoding considerations:">
2749      HTTP messages enclosed by this type
2750      are in "binary" format; use of an appropriate
2751      Content-Transfer-Encoding is required when
2752      transmitted via E-mail.
2753    </t>
2754    <t hangText="Security considerations:">
2755      none
2756    </t>
2757    <t hangText="Interoperability considerations:">
2758      none
2759    </t>
2760    <t hangText="Published specification:">
2761      This specification (see <xref target=""/>).
2762    </t>
2763    <t hangText="Applications that use this media type:">
2764    </t>
2765    <t hangText="Additional information:">
2766      <list style="hanging">
2767        <t hangText="Magic number(s):">none</t>
2768        <t hangText="File extension(s):">none</t>
2769        <t hangText="Macintosh file type code(s):">none</t>
2770      </list>
2771    </t>
2772    <t hangText="Person and email address to contact for further information:">
2773      See Authors Section.
2774    </t>
2775                <t hangText="Intended usage:">
2776                  COMMON
2777    </t>
2778                <t hangText="Restrictions on usage:">
2779                  none
2780    </t>
2781    <t hangText="Author/Change controller:">
2782      IESG
2783    </t>
2784  </list>
2791<section title="Security Considerations" anchor="security.considerations">
2793   This section is meant to inform application developers, information
2794   providers, and users of the security limitations in HTTP/1.1 as
2795   described by this document. The discussion does not include
2796   definitive solutions to the problems revealed, though it does make
2797   some suggestions for reducing security risks.
2800<section title="Personal Information" anchor="personal.information">
2802   HTTP clients are often privy to large amounts of personal information
2803   (e.g. the user's name, location, mail address, passwords, encryption
2804   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2805   leakage of this information.
2806   We very strongly recommend that a convenient interface be provided
2807   for the user to control dissemination of such information, and that
2808   designers and implementors be particularly careful in this area.
2809   History shows that errors in this area often create serious security
2810   and/or privacy problems and generate highly adverse publicity for the
2811   implementor's company.
2815<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2817   A server is in the position to save personal data about a user's
2818   requests which might identify their reading patterns or subjects of
2819   interest. This information is clearly confidential in nature and its
2820   handling can be constrained by law in certain countries. People using
2821   HTTP to provide data are responsible for ensuring that
2822   such material is not distributed without the permission of any
2823   individuals that are identifiable by the published results.
2827<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2829   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2830   the documents returned by HTTP requests to be only those that were
2831   intended by the server administrators. If an HTTP server translates
2832   HTTP URIs directly into file system calls, the server &MUST; take
2833   special care not to serve files that were not intended to be
2834   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2835   other operating systems use ".." as a path component to indicate a
2836   directory level above the current one. On such a system, an HTTP
2837   server &MUST; disallow any such construct in the Request-URI if it
2838   would otherwise allow access to a resource outside those intended to
2839   be accessible via the HTTP server. Similarly, files intended for
2840   reference only internally to the server (such as access control
2841   files, configuration files, and script code) &MUST; be protected from
2842   inappropriate retrieval, since they might contain sensitive
2843   information. Experience has shown that minor bugs in such HTTP server
2844   implementations have turned into security risks.
2848<section title="DNS Spoofing" anchor="dns.spoofing">
2850   Clients using HTTP rely heavily on the Domain Name Service, and are
2851   thus generally prone to security attacks based on the deliberate
2852   mis-association of IP addresses and DNS names. Clients need to be
2853   cautious in assuming the continuing validity of an IP number/DNS name
2854   association.
2857   In particular, HTTP clients &SHOULD; rely on their name resolver for
2858   confirmation of an IP number/DNS name association, rather than
2859   caching the result of previous host name lookups. Many platforms
2860   already can cache host name lookups locally when appropriate, and
2861   they &SHOULD; be configured to do so. It is proper for these lookups to
2862   be cached, however, only when the TTL (Time To Live) information
2863   reported by the name server makes it likely that the cached
2864   information will remain useful.
2867   If HTTP clients cache the results of host name lookups in order to
2868   achieve a performance improvement, they &MUST; observe the TTL
2869   information reported by DNS.
2872   If HTTP clients do not observe this rule, they could be spoofed when
2873   a previously-accessed server's IP address changes. As network
2874   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2875   possibility of this form of attack will grow. Observing this
2876   requirement thus reduces this potential security vulnerability.
2879   This requirement also improves the load-balancing behavior of clients
2880   for replicated servers using the same DNS name and reduces the
2881   likelihood of a user's experiencing failure in accessing sites which
2882   use that strategy.
2886<section title="Proxies and Caching" anchor="attack.proxies">
2888   By their very nature, HTTP proxies are men-in-the-middle, and
2889   represent an opportunity for man-in-the-middle attacks. Compromise of
2890   the systems on which the proxies run can result in serious security
2891   and privacy problems. Proxies have access to security-related
2892   information, personal information about individual users and
2893   organizations, and proprietary information belonging to users and
2894   content providers. A compromised proxy, or a proxy implemented or
2895   configured without regard to security and privacy considerations,
2896   might be used in the commission of a wide range of potential attacks.
2899   Proxy operators should protect the systems on which proxies run as
2900   they would protect any system that contains or transports sensitive
2901   information. In particular, log information gathered at proxies often
2902   contains highly sensitive personal information, and/or information
2903   about organizations. Log information should be carefully guarded, and
2904   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2907   Proxy implementors should consider the privacy and security
2908   implications of their design and coding decisions, and of the
2909   configuration options they provide to proxy operators (especially the
2910   default configuration).
2913   Users of a proxy need to be aware that they are no trustworthier than
2914   the people who run the proxy; HTTP itself cannot solve this problem.
2917   The judicious use of cryptography, when appropriate, may suffice to
2918   protect against a broad range of security and privacy attacks. Such
2919   cryptography is beyond the scope of the HTTP/1.1 specification.
2923<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2925   They exist. They are hard to defend against. Research continues.
2926   Beware.
2931<section title="Acknowledgments" anchor="ack">
2933   HTTP has evolved considerably over the years. It has
2934   benefited from a large and active developer community--the many
2935   people who have participated on the www-talk mailing list--and it is
2936   that community which has been most responsible for the success of
2937   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2938   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2939   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2940   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2941   VanHeyningen deserve special recognition for their efforts in
2942   defining early aspects of the protocol.
2945   This document has benefited greatly from the comments of all those
2946   participating in the HTTP-WG. In addition to those already mentioned,
2947   the following individuals have contributed to this specification:
2950   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2951   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2952   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2953   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2954   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2955   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2956   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2957   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2958   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2959   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2960   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2961   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2962   Josh Cohen.
2965   Thanks to the "cave men" of Palo Alto. You know who you are.
2968   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2969   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2970   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2971   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2972   Larry Masinter for their help. And thanks go particularly to Jeff
2973   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2976   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2977   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2978   discovery of many of the problems that this document attempts to
2979   rectify.
2982   This specification makes heavy use of the augmented BNF and generic
2983   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2984   reuses many of the definitions provided by Nathaniel Borenstein and
2985   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2986   specification will help reduce past confusion over the relationship
2987   between HTTP and Internet mail message formats.
2994<references title="Normative References">
2996<reference anchor="ISO-8859-1">
2997  <front>
2998    <title>
2999     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3000    </title>
3001    <author>
3002      <organization>International Organization for Standardization</organization>
3003    </author>
3004    <date year="1998"/>
3005  </front>
3006  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3009<reference anchor="Part2">
3010  <front>
3011    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3012    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3013      <organization abbrev="Day Software">Day Software</organization>
3014      <address><email></email></address>
3015    </author>
3016    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3017      <organization>One Laptop per Child</organization>
3018      <address><email></email></address>
3019    </author>
3020    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3021      <organization abbrev="HP">Hewlett-Packard Company</organization>
3022      <address><email></email></address>
3023    </author>
3024    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3025      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3026      <address><email></email></address>
3027    </author>
3028    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3029      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3030      <address><email></email></address>
3031    </author>
3032    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3033      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3034      <address><email></email></address>
3035    </author>
3036    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3037      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3038      <address><email></email></address>
3039    </author>
3040    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3041      <organization abbrev="W3C">World Wide Web Consortium</organization>
3042      <address><email></email></address>
3043    </author>
3044    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3045      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3046      <address><email></email></address>
3047    </author>
3048    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3049  </front>
3050  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3051  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3054<reference anchor="Part3">
3055  <front>
3056    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3057    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3058      <organization abbrev="Day Software">Day Software</organization>
3059      <address><email></email></address>
3060    </author>
3061    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3062      <organization>One Laptop per Child</organization>
3063      <address><email></email></address>
3064    </author>
3065    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3066      <organization abbrev="HP">Hewlett-Packard Company</organization>
3067      <address><email></email></address>
3068    </author>
3069    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3070      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3071      <address><email></email></address>
3072    </author>
3073    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3074      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3075      <address><email></email></address>
3076    </author>
3077    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3078      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3079      <address><email></email></address>
3080    </author>
3081    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3082      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3083      <address><email></email></address>
3084    </author>
3085    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3086      <organization abbrev="W3C">World Wide Web Consortium</organization>
3087      <address><email></email></address>
3088    </author>
3089    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3090      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3091      <address><email></email></address>
3092    </author>
3093    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3094  </front>
3095  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3096  <x:source href="p3-payload.xml" basename="p3-payload"/>
3099<reference anchor="Part5">
3100  <front>
3101    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3102    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3103      <organization abbrev="Day Software">Day Software</organization>
3104      <address><email></email></address>
3105    </author>
3106    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3107      <organization>One Laptop per Child</organization>
3108      <address><email></email></address>
3109    </author>
3110    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3111      <organization abbrev="HP">Hewlett-Packard Company</organization>
3112      <address><email></email></address>
3113    </author>
3114    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3115      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3116      <address><email></email></address>
3117    </author>
3118    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3119      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3120      <address><email></email></address>
3121    </author>
3122    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3123      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3124      <address><email></email></address>
3125    </author>
3126    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3127      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3128      <address><email></email></address>
3129    </author>
3130    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3131      <organization abbrev="W3C">World Wide Web Consortium</organization>
3132      <address><email></email></address>
3133    </author>
3134    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3135      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3136      <address><email></email></address>
3137    </author>
3138    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3139  </front>
3140  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3141  <x:source href="p5-range.xml" basename="p5-range"/>
3144<reference anchor="Part6">
3145  <front>
3146    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3147    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3148      <organization abbrev="Day Software">Day Software</organization>
3149      <address><email></email></address>
3150    </author>
3151    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3152      <organization>One Laptop per Child</organization>
3153      <address><email></email></address>
3154    </author>
3155    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3156      <organization abbrev="HP">Hewlett-Packard Company</organization>
3157      <address><email></email></address>
3158    </author>
3159    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3160      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3161      <address><email></email></address>
3162    </author>
3163    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3164      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3165      <address><email></email></address>
3166    </author>
3167    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3168      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3169      <address><email></email></address>
3170    </author>
3171    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3172      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3173      <address><email></email></address>
3174    </author>
3175    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3176      <organization abbrev="W3C">World Wide Web Consortium</organization>
3177      <address><email></email></address>
3178    </author>
3179    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3180      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3181      <address><email></email></address>
3182    </author>
3183    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3184  </front>
3185  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3186  <x:source href="p6-cache.xml" basename="p6-cache"/>
3189<reference anchor="RFC5234">
3190  <front>
3191    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3192    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3193      <organization>Brandenburg InternetWorking</organization>
3194      <address>
3195      <postal>
3196      <street>675 Spruce Dr.</street>
3197      <city>Sunnyvale</city>
3198      <region>CA</region>
3199      <code>94086</code>
3200      <country>US</country></postal>
3201      <phone>+1.408.246.8253</phone>
3202      <email></email></address> 
3203    </author>
3204    <author initials="P." surname="Overell" fullname="Paul Overell">
3205      <organization>THUS plc.</organization>
3206      <address>
3207      <postal>
3208      <street>1/2 Berkeley Square</street>
3209      <street>99 Berkely Street</street>
3210      <city>Glasgow</city>
3211      <code>G3 7HR</code>
3212      <country>UK</country></postal>
3213      <email></email></address>
3214    </author>
3215    <date month="January" year="2008"/>
3216  </front>
3217  <seriesInfo name="STD" value="68"/>
3218  <seriesInfo name="RFC" value="5234"/>
3221<reference anchor="RFC2045">
3222  <front>
3223    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3224    <author initials="N." surname="Freed" fullname="Ned Freed">
3225      <organization>Innosoft International, Inc.</organization>
3226      <address><email></email></address>
3227    </author>
3228    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3229      <organization>First Virtual Holdings</organization>
3230      <address><email></email></address>
3231    </author>
3232    <date month="November" year="1996"/>
3233  </front>
3234  <seriesInfo name="RFC" value="2045"/>
3237<reference anchor="RFC2047">
3238  <front>
3239    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3240    <author initials="K." surname="Moore" fullname="Keith Moore">
3241      <organization>University of Tennessee</organization>
3242      <address><email></email></address>
3243    </author>
3244    <date month="November" year="1996"/>
3245  </front>
3246  <seriesInfo name="RFC" value="2047"/>
3249<reference anchor="RFC2119">
3250  <front>
3251    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3252    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3253      <organization>Harvard University</organization>
3254      <address><email></email></address>
3255    </author>
3256    <date month="March" year="1997"/>
3257  </front>
3258  <seriesInfo name="BCP" value="14"/>
3259  <seriesInfo name="RFC" value="2119"/>
3262<reference anchor="RFC3986">
3263 <front>
3264  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3265  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3266    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3267    <address>
3268       <email></email>
3269       <uri></uri>
3270    </address>
3271  </author>
3272  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3273    <organization abbrev="Day Software">Day Software</organization>
3274    <address>
3275      <email></email>
3276      <uri></uri>
3277    </address>
3278  </author>
3279  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3280    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3281    <address>
3282      <email></email>
3283      <uri></uri>
3284    </address>
3285  </author>
3286  <date month='January' year='2005'></date>
3287 </front>
3288 <seriesInfo name="RFC" value="3986"/>
3289 <seriesInfo name="STD" value="66"/>
3292<reference anchor="USASCII">
3293  <front>
3294    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3295    <author>
3296      <organization>American National Standards Institute</organization>
3297    </author>
3298    <date year="1986"/>
3299  </front>
3300  <seriesInfo name="ANSI" value="X3.4"/>
3305<references title="Informative References">
3307<reference anchor="Nie1997" target="">
3308  <front>
3309    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3310    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3311      <organization/>
3312    </author>
3313    <author initials="J." surname="Gettys" fullname="J. Gettys">
3314      <organization/>
3315    </author>
3316    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3317      <organization/>
3318    </author>
3319    <author initials="H." surname="Lie" fullname="H. Lie">
3320      <organization/>
3321    </author>
3322    <author initials="C." surname="Lilley" fullname="C. Lilley">
3323      <organization/>
3324    </author>
3325    <date year="1997" month="September"/>
3326  </front>
3327  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3330<reference anchor="Pad1995" target="">
3331  <front>
3332    <title>Improving HTTP Latency</title>
3333    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3334      <organization/>
3335    </author>
3336    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3337      <organization/>
3338    </author>
3339    <date year="1995" month="December"/>
3340  </front>
3341  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3344<reference anchor="RFC822">
3345  <front>
3346    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3347    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3348      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3349      <address><email>DCrocker@UDel-Relay</email></address>
3350    </author>
3351    <date month="August" day="13" year="1982"/>
3352  </front>
3353  <seriesInfo name="STD" value="11"/>
3354  <seriesInfo name="RFC" value="822"/>
3357<reference anchor="RFC959">
3358  <front>
3359    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3360    <author initials="J." surname="Postel" fullname="J. Postel">
3361      <organization>Information Sciences Institute (ISI)</organization>
3362    </author>
3363    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3364      <organization/>
3365    </author>
3366    <date month="October" year="1985"/>
3367  </front>
3368  <seriesInfo name="STD" value="9"/>
3369  <seriesInfo name="RFC" value="959"/>
3372<reference anchor="RFC1123">
3373  <front>
3374    <title>Requirements for Internet Hosts - Application and Support</title>
3375    <author initials="R." surname="Braden" fullname="Robert Braden">
3376      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3377      <address><email>Braden@ISI.EDU</email></address>
3378    </author>
3379    <date month="October" year="1989"/>
3380  </front>
3381  <seriesInfo name="STD" value="3"/>
3382  <seriesInfo name="RFC" value="1123"/>
3385<reference anchor="RFC1305">
3386  <front>
3387    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3388    <author initials="D." surname="Mills" fullname="David L. Mills">
3389      <organization>University of Delaware, Electrical Engineering Department</organization>
3390      <address><email></email></address>
3391    </author>
3392    <date month="March" year="1992"/>
3393  </front>
3394  <seriesInfo name="RFC" value="1305"/>
3397<reference anchor="RFC1436">
3398  <front>
3399    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3400    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3401      <organization>University of Minnesota, Computer and Information Services</organization>
3402      <address><email></email></address>
3403    </author>
3404    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3405      <organization>University of Minnesota, Computer and Information Services</organization>
3406      <address><email></email></address>
3407    </author>
3408    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3409      <organization>University of Minnesota, Computer and Information Services</organization>
3410      <address><email></email></address>
3411    </author>
3412    <author initials="D." surname="Johnson" fullname="David Johnson">
3413      <organization>University of Minnesota, Computer and Information Services</organization>
3414      <address><email></email></address>
3415    </author>
3416    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3417      <organization>University of Minnesota, Computer and Information Services</organization>
3418      <address><email></email></address>
3419    </author>
3420    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3421      <organization>University of Minnesota, Computer and Information Services</organization>
3422      <address><email></email></address>
3423    </author>
3424    <date month="March" year="1993"/>
3425  </front>
3426  <seriesInfo name="RFC" value="1436"/>
3429<reference anchor="RFC1900">
3430  <front>
3431    <title>Renumbering Needs Work</title>
3432    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3433      <organization>CERN, Computing and Networks Division</organization>
3434      <address><email></email></address>
3435    </author>
3436    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3437      <organization>cisco Systems</organization>
3438      <address><email></email></address>
3439    </author>
3440    <date month="February" year="1996"/>
3441  </front>
3442  <seriesInfo name="RFC" value="1900"/>
3445<reference anchor="RFC1945">
3446  <front>
3447    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3448    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3449      <organization>MIT, Laboratory for Computer Science</organization>
3450      <address><email></email></address>
3451    </author>
3452    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3453      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3454      <address><email></email></address>
3455    </author>
3456    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3457      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3458      <address><email></email></address>
3459    </author>
3460    <date month="May" year="1996"/>
3461  </front>
3462  <seriesInfo name="RFC" value="1945"/>
3465<reference anchor="RFC2068">
3466  <front>
3467    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3468    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3469      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3470      <address><email></email></address>
3471    </author>
3472    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3473      <organization>MIT Laboratory for Computer Science</organization>
3474      <address><email></email></address>
3475    </author>
3476    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3477      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3478      <address><email></email></address>
3479    </author>
3480    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3481      <organization>MIT Laboratory for Computer Science</organization>
3482      <address><email></email></address>
3483    </author>
3484    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3485      <organization>MIT Laboratory for Computer Science</organization>
3486      <address><email></email></address>
3487    </author>
3488    <date month="January" year="1997"/>
3489  </front>
3490  <seriesInfo name="RFC" value="2068"/>
3493<reference anchor='RFC2109'>
3494  <front>
3495    <title>HTTP State Management Mechanism</title>
3496    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3497      <organization>Bell Laboratories, Lucent Technologies</organization>
3498      <address><email></email></address>
3499    </author>
3500    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3501      <organization>Netscape Communications Corp.</organization>
3502      <address><email></email></address>
3503    </author>
3504    <date year='1997' month='February' />
3505  </front>
3506  <seriesInfo name='RFC' value='2109' />
3509<reference anchor="RFC2145">
3510  <front>
3511    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3512    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3513      <organization>Western Research Laboratory</organization>
3514      <address><email></email></address>
3515    </author>
3516    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3517      <organization>Department of Information and Computer Science</organization>
3518      <address><email></email></address>
3519    </author>
3520    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3521      <organization>MIT Laboratory for Computer Science</organization>
3522      <address><email></email></address>
3523    </author>
3524    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3525      <organization>W3 Consortium</organization>
3526      <address><email></email></address>
3527    </author>
3528    <date month="May" year="1997"/>
3529  </front>
3530  <seriesInfo name="RFC" value="2145"/>
3533<reference anchor="RFC2616">
3534  <front>
3535    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3536    <author initials="R." surname="Fielding" fullname="R. Fielding">
3537      <organization>University of California, Irvine</organization>
3538      <address><email></email></address>
3539    </author>
3540    <author initials="J." surname="Gettys" fullname="J. Gettys">
3541      <organization>W3C</organization>
3542      <address><email></email></address>
3543    </author>
3544    <author initials="J." surname="Mogul" fullname="J. Mogul">
3545      <organization>Compaq Computer Corporation</organization>
3546      <address><email></email></address>
3547    </author>
3548    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3549      <organization>MIT Laboratory for Computer Science</organization>
3550      <address><email></email></address>
3551    </author>
3552    <author initials="L." surname="Masinter" fullname="L. Masinter">
3553      <organization>Xerox Corporation</organization>
3554      <address><email></email></address>
3555    </author>
3556    <author initials="P." surname="Leach" fullname="P. Leach">
3557      <organization>Microsoft Corporation</organization>
3558      <address><email></email></address>
3559    </author>
3560    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3561      <organization>W3C</organization>
3562      <address><email></email></address>
3563    </author>
3564    <date month="June" year="1999"/>
3565  </front>
3566  <seriesInfo name="RFC" value="2616"/>
3569<reference anchor='RFC2818'>
3570  <front>
3571    <title>HTTP Over TLS</title>
3572    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3573      <organization>RTFM, Inc.</organization>
3574      <address><email></email></address>
3575    </author>
3576    <date year='2000' month='May' />
3577  </front>
3578  <seriesInfo name='RFC' value='2818' />
3581<reference anchor='RFC2965'>
3582  <front>
3583    <title>HTTP State Management Mechanism</title>
3584    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3585      <organization>Bell Laboratories, Lucent Technologies</organization>
3586      <address><email></email></address>
3587    </author>
3588    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3589      <organization>, Inc.</organization>
3590      <address><email></email></address>
3591    </author>
3592    <date year='2000' month='October' />
3593  </front>
3594  <seriesInfo name='RFC' value='2965' />
3597<reference anchor='RFC3864'>
3598  <front>
3599    <title>Registration Procedures for Message Header Fields</title>
3600    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3601      <organization>Nine by Nine</organization>
3602      <address><email></email></address>
3603    </author>
3604    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3605      <organization>BEA Systems</organization>
3606      <address><email></email></address>
3607    </author>
3608    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3609      <organization>HP Labs</organization>
3610      <address><email></email></address>
3611    </author>
3612    <date year='2004' month='September' />
3613  </front>
3614  <seriesInfo name='BCP' value='90' />
3615  <seriesInfo name='RFC' value='3864' />
3618<reference anchor='RFC3977'>
3619  <front>
3620    <title>Network News Transfer Protocol (NNTP)</title>
3621    <author initials='C.' surname='Feather' fullname='C. Feather'>
3622      <organization>THUS plc</organization>
3623      <address><email></email></address>
3624    </author>
3625    <date year='2006' month='October' />
3626  </front>
3627  <seriesInfo name="RFC" value="3977"/>
3630<reference anchor="RFC4288">
3631  <front>
3632    <title>Media Type Specifications and Registration Procedures</title>
3633    <author initials="N." surname="Freed" fullname="N. Freed">
3634      <organization>Sun Microsystems</organization>
3635      <address>
3636        <email></email>
3637      </address>
3638    </author>
3639    <author initials="J." surname="Klensin" fullname="J. Klensin">
3640      <organization/>
3641      <address>
3642        <email></email>
3643      </address>
3644    </author>
3645    <date year="2005" month="December"/>
3646  </front>
3647  <seriesInfo name="BCP" value="13"/>
3648  <seriesInfo name="RFC" value="4288"/>
3651<reference anchor='RFC4395'>
3652  <front>
3653    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3654    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3655      <organization>AT&amp;T Laboratories</organization>
3656      <address>
3657        <email></email>
3658      </address>
3659    </author>
3660    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3661      <organization>Qualcomm, Inc.</organization>
3662      <address>
3663        <email></email>
3664      </address>
3665    </author>
3666    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3667      <organization>Adobe Systems</organization>
3668      <address>
3669        <email></email>
3670      </address>
3671    </author>
3672    <date year='2006' month='February' />
3673  </front>
3674  <seriesInfo name='BCP' value='115' />
3675  <seriesInfo name='RFC' value='4395' />
3678<reference anchor="RFC5322">
3679  <front>
3680    <title>Internet Message Format</title>
3681    <author initials="P." surname="Resnick" fullname="P. Resnick">
3682      <organization>Qualcomm Incorporated</organization>
3683    </author>
3684    <date year="2008" month="October"/>
3685  </front>
3686  <seriesInfo name="RFC" value="5322"/>
3689<reference anchor="Kri2001" target="">
3690  <front>
3691    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3692    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3693      <organization/>
3694    </author>
3695    <date year="2001" month="November"/>
3696  </front>
3697  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3700<reference anchor="Spe" target="">
3701  <front>
3702  <title>Analysis of HTTP Performance Problems</title>
3703  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3704    <organization/>
3705  </author>
3706  <date/>
3707  </front>
3710<reference anchor="Tou1998" target="">
3711  <front>
3712  <title>Analysis of HTTP Performance</title>
3713  <author initials="J." surname="Touch" fullname="Joe Touch">
3714    <organization>USC/Information Sciences Institute</organization>
3715    <address><email></email></address>
3716  </author>
3717  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3718    <organization>USC/Information Sciences Institute</organization>
3719    <address><email></email></address>
3720  </author>
3721  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3722    <organization>USC/Information Sciences Institute</organization>
3723    <address><email></email></address>
3724  </author>
3725  <date year="1998" month="Aug"/>
3726  </front>
3727  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3728  <annotation>(original report dated Aug. 1996)</annotation>
3731<reference anchor="WAIS">
3732  <front>
3733    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3734    <author initials="F." surname="Davis" fullname="F. Davis">
3735      <organization>Thinking Machines Corporation</organization>
3736    </author>
3737    <author initials="B." surname="Kahle" fullname="B. Kahle">
3738      <organization>Thinking Machines Corporation</organization>
3739    </author>
3740    <author initials="H." surname="Morris" fullname="H. Morris">
3741      <organization>Thinking Machines Corporation</organization>
3742    </author>
3743    <author initials="J." surname="Salem" fullname="J. Salem">
3744      <organization>Thinking Machines Corporation</organization>
3745    </author>
3746    <author initials="T." surname="Shen" fullname="T. Shen">
3747      <organization>Thinking Machines Corporation</organization>
3748    </author>
3749    <author initials="R." surname="Wang" fullname="R. Wang">
3750      <organization>Thinking Machines Corporation</organization>
3751    </author>
3752    <author initials="J." surname="Sui" fullname="J. Sui">
3753      <organization>Thinking Machines Corporation</organization>
3754    </author>
3755    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3756      <organization>Thinking Machines Corporation</organization>
3757    </author>
3758    <date month="April" year="1990"/>
3759  </front>
3760  <seriesInfo name="Thinking Machines Corporation" value=""/>
3766<section title="Tolerant Applications" anchor="tolerant.applications">
3768   Although this document specifies the requirements for the generation
3769   of HTTP/1.1 messages, not all applications will be correct in their
3770   implementation. We therefore recommend that operational applications
3771   be tolerant of deviations whenever those deviations can be
3772   interpreted unambiguously.
3775   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3776   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3777   accept any amount of SP or HTAB characters between fields, even though
3778   only a single SP is required.
3781   The line terminator for message-header fields is the sequence CRLF.
3782   However, we recommend that applications, when parsing such headers,
3783   recognize a single LF as a line terminator and ignore the leading CR.
3786   The character set of an entity-body &SHOULD; be labeled as the lowest
3787   common denominator of the character codes used within that body, with
3788   the exception that not labeling the entity is preferred over labeling
3789   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3792   Additional rules for requirements on parsing and encoding of dates
3793   and other potential problems with date encodings include:
3796  <list style="symbols">
3797     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3798        which appears to be more than 50 years in the future is in fact
3799        in the past (this helps solve the "year 2000" problem).</t>
3801     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3802        Expires date as earlier than the proper value, but &MUST-NOT;
3803        internally represent a parsed Expires date as later than the
3804        proper value.</t>
3806     <t>All expiration-related calculations &MUST; be done in GMT. The
3807        local time zone &MUST-NOT; influence the calculation or comparison
3808        of an age or expiration time.</t>
3810     <t>If an HTTP header incorrectly carries a date value with a time
3811        zone other than GMT, it &MUST; be converted into GMT using the
3812        most conservative possible conversion.</t>
3813  </list>
3817<section title="Conversion of Date Formats" anchor="">
3819   HTTP/1.1 uses a restricted set of date formats (<xref target=""/>) to
3820   simplify the process of date comparison. Proxies and gateways from
3821   other protocols &SHOULD; ensure that any Date header field present in a
3822   message conforms to one of the HTTP/1.1 formats and rewrite the date
3823   if necessary.
3827<section title="Compatibility with Previous Versions" anchor="compatibility">
3829   HTTP has been in use by the World-Wide Web global information initiative
3830   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3831   was a simple protocol for hypertext data transfer across the Internet
3832   with only a single method and no metadata.
3833   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3834   methods and MIME-like messaging that could include metadata about the data
3835   transferred and modifiers on the request/response semantics. However,
3836   HTTP/1.0 did not sufficiently take into consideration the effects of
3837   hierarchical proxies, caching, the need for persistent connections, or
3838   name-based virtual hosts. The proliferation of incompletely-implemented
3839   applications calling themselves "HTTP/1.0" further necessitated a
3840   protocol version change in order for two communicating applications
3841   to determine each other's true capabilities.
3844   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3845   requirements that enable reliable implementations, adding only
3846   those new features that will either be safely ignored by an HTTP/1.0
3847   recipient or only sent when communicating with a party advertising
3848   compliance with HTTP/1.1.
3851   It is beyond the scope of a protocol specification to mandate
3852   compliance with previous versions. HTTP/1.1 was deliberately
3853   designed, however, to make supporting previous versions easy. It is
3854   worth noting that, at the time of composing this specification
3855   (1996), we would expect commercial HTTP/1.1 servers to:
3856  <list style="symbols">
3857     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3858        1.1 requests;</t>
3860     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3861        1.1;</t>
3863     <t>respond appropriately with a message in the same major version
3864        used by the client.</t>
3865  </list>
3868   And we would expect HTTP/1.1 clients to:
3869  <list style="symbols">
3870     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3871        responses;</t>
3873     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3874        1.1.</t>
3875  </list>
3878   For most implementations of HTTP/1.0, each connection is established
3879   by the client prior to the request and closed by the server after
3880   sending the response. Some implementations implement the Keep-Alive
3881   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3884<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3886   This section summarizes major differences between versions HTTP/1.0
3887   and HTTP/1.1.
3890<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="">
3892   The requirements that clients and servers support the Host request-header,
3893   report an error if the Host request-header (<xref target=""/>) is
3894   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3895   are among the most important changes defined by this
3896   specification.
3899   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3900   addresses and servers; there was no other established mechanism for
3901   distinguishing the intended server of a request than the IP address
3902   to which that request was directed. The changes outlined above will
3903   allow the Internet, once older HTTP clients are no longer common, to
3904   support multiple Web sites from a single IP address, greatly
3905   simplifying large operational Web servers, where allocation of many
3906   IP addresses to a single host has created serious problems. The
3907   Internet will also be able to recover the IP addresses that have been
3908   allocated for the sole purpose of allowing special-purpose domain
3909   names to be used in root-level HTTP URLs. Given the rate of growth of
3910   the Web, and the number of servers already deployed, it is extremely
3911   important that all implementations of HTTP (including updates to
3912   existing HTTP/1.0 applications) correctly implement these
3913   requirements:
3914  <list style="symbols">
3915     <t>Both clients and servers &MUST; support the Host request-header.</t>
3917     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3919     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3920        request does not include a Host request-header.</t>
3922     <t>Servers &MUST; accept absolute URIs.</t>
3923  </list>
3928<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3930   Some clients and servers might wish to be compatible with some
3931   previous implementations of persistent connections in HTTP/1.0
3932   clients and servers. Persistent connections in HTTP/1.0 are
3933   explicitly negotiated as they are not the default behavior. HTTP/1.0
3934   experimental implementations of persistent connections are faulty,
3935   and the new facilities in HTTP/1.1 are designed to rectify these
3936   problems. The problem was that some existing 1.0 clients may be
3937   sending Keep-Alive to a proxy server that doesn't understand
3938   Connection, which would then erroneously forward it to the next
3939   inbound server, which would establish the Keep-Alive connection and
3940   result in a hung HTTP/1.0 proxy waiting for the close on the
3941   response. The result is that HTTP/1.0 clients must be prevented from
3942   using Keep-Alive when talking to proxies.
3945   However, talking to proxies is the most important use of persistent
3946   connections, so that prohibition is clearly unacceptable. Therefore,
3947   we need some other mechanism for indicating a persistent connection
3948   is desired, which is safe to use even when talking to an old proxy
3949   that ignores Connection. Persistent connections are the default for
3950   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3951   declaring non-persistence. See <xref target="header.connection"/>.
3954   The original HTTP/1.0 form of persistent connections (the Connection:
3955   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3959<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3961   This specification has been carefully audited to correct and
3962   disambiguate key word usage; RFC 2068 had many problems in respect to
3963   the conventions laid out in <xref target="RFC2119"/>.
3966   Transfer-coding and message lengths all interact in ways that
3967   required fixing exactly when chunked encoding is used (to allow for
3968   transfer encoding that may not be self delimiting); it was important
3969   to straighten out exactly how message lengths are computed. (Sections
3970   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
3971   <xref target="header.content-length" format="counter"/>,
3972   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
3975   The use and interpretation of HTTP version numbers has been clarified
3976   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
3977   version they support to deal with problems discovered in HTTP/1.0
3978   implementations (<xref target="http.version"/>)
3981   Transfer-coding had significant problems, particularly with
3982   interactions with chunked encoding. The solution is that transfer-codings
3983   become as full fledged as content-codings. This involves
3984   adding an IANA registry for transfer-codings (separate from content
3985   codings), a new header field (TE) and enabling trailer headers in the
3986   future. Transfer encoding is a major performance benefit, so it was
3987   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
3988   interoperability problem that could have occurred due to interactions
3989   between authentication trailers, chunked encoding and HTTP/1.0
3990   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
3991   and <xref target="header.te" format="counter"/>)
3995<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3997  The CHAR rule does not allow the NUL character anymore (this affects
3998  the comment and quoted-string rules).  Furthermore, the quoted-pair
3999  rule does not allow escaping NUL, CR or LF anymore.
4000  (<xref target="basic.rules"/>)
4003  Clarify that HTTP-Version is case sensitive.
4004  (<xref target="http.version"/>)
4007  Remove reference to non-existant identity transfer-coding value tokens.
4008  (Sections <xref format="counter" target="transfer.codings"/> and
4009  <xref format="counter" target="message.length"/>)
4012  Clarification that the chunk length does not include
4013  the count of the octets in the chunk header and trailer.
4014  (<xref target="chunked.transfer.encoding"/>)
4017  Update use of abs_path production from RFC1808 to the path-absolute + query
4018  components of RFC3986.
4019  (<xref target="request-uri"/>)
4022  Clarify exactly when close connection options must be sent.
4023  (<xref target="header.connection"/>)
4028<section title="Terminology" anchor="terminology">
4030   This specification uses a number of terms to refer to the roles
4031   played by participants in, and objects of, the HTTP communication.
4034  <iref item="connection"/>
4035  <x:dfn>connection</x:dfn>
4036  <list>
4037    <t>
4038      A transport layer virtual circuit established between two programs
4039      for the purpose of communication.
4040    </t>
4041  </list>
4044  <iref item="message"/>
4045  <x:dfn>message</x:dfn>
4046  <list>
4047    <t>
4048      The basic unit of HTTP communication, consisting of a structured
4049      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4050      transmitted via the connection.
4051    </t>
4052  </list>
4055  <iref item="request"/>
4056  <x:dfn>request</x:dfn>
4057  <list>
4058    <t>
4059      An HTTP request message, as defined in <xref target="request"/>.
4060    </t>
4061  </list>
4064  <iref item="response"/>
4065  <x:dfn>response</x:dfn>
4066  <list>
4067    <t>
4068      An HTTP response message, as defined in <xref target="response"/>.
4069    </t>
4070  </list>
4073  <iref item="resource"/>
4074  <x:dfn>resource</x:dfn>
4075  <list>
4076    <t>
4077      A network data object or service that can be identified by a URI,
4078      as defined in <xref target="uri"/>. Resources may be available in multiple
4079      representations (e.g. multiple languages, data formats, size, and
4080      resolutions) or vary in other ways.
4081    </t>
4082  </list>
4085  <iref item="entity"/>
4086  <x:dfn>entity</x:dfn>
4087  <list>
4088    <t>
4089      The information transferred as the payload of a request or
4090      response. An entity consists of metainformation in the form of
4091      entity-header fields and content in the form of an entity-body, as
4092      described in &entity;.
4093    </t>
4094  </list>
4097  <iref item="representation"/>
4098  <x:dfn>representation</x:dfn>
4099  <list>
4100    <t>
4101      An entity included with a response that is subject to content
4102      negotiation, as described in &content.negotiation;. There may exist multiple
4103      representations associated with a particular response status.
4104    </t>
4105  </list>
4108  <iref item="content negotiation"/>
4109  <x:dfn>content negotiation</x:dfn>
4110  <list>
4111    <t>
4112      The mechanism for selecting the appropriate representation when
4113      servicing a request, as described in &content.negotiation;. The
4114      representation of entities in any response can be negotiated
4115      (including error responses).
4116    </t>
4117  </list>
4120  <iref item="variant"/>
4121  <x:dfn>variant</x:dfn>
4122  <list>
4123    <t>
4124      A resource may have one, or more than one, representation(s)
4125      associated with it at any given instant. Each of these
4126      representations is termed a `variant'.  Use of the term `variant'
4127      does not necessarily imply that the resource is subject to content
4128      negotiation.
4129    </t>
4130  </list>
4133  <iref item="client"/>
4134  <x:dfn>client</x:dfn>
4135  <list>
4136    <t>
4137      A program that establishes connections for the purpose of sending
4138      requests.
4139    </t>
4140  </list>
4143  <iref item="user agent"/>
4144  <x:dfn>user agent</x:dfn>
4145  <list>
4146    <t>
4147      The client which initiates a request. These are often browsers,
4148      editors, spiders (web-traversing robots), or other end user tools.
4149    </t>
4150  </list>
4153  <iref item="server"/>
4154  <x:dfn>server</x:dfn>
4155  <list>
4156    <t>
4157      An application program that accepts connections in order to
4158      service requests by sending back responses. Any given program may
4159      be capable of being both a client and a server; our use of these
4160      terms refers only to the role being performed by the program for a
4161      particular connection, rather than to the program's capabilities
4162      in general. Likewise, any server may act as an origin server,
4163      proxy, gateway, or tunnel, switching behavior based on the nature
4164      of each request.
4165    </t>
4166  </list>
4169  <iref item="origin server"/>
4170  <x:dfn>origin server</x:dfn>
4171  <list>
4172    <t>
4173      The server on which a given resource resides or is to be created.
4174    </t>
4175  </list>
4178  <iref item="proxy"/>
4179  <x:dfn>proxy</x:dfn>
4180  <list>
4181    <t>
4182      An intermediary program which acts as both a server and a client
4183      for the purpose of making requests on behalf of other clients.
4184      Requests are serviced internally or by passing them on, with
4185      possible translation, to other servers. A proxy &MUST; implement
4186      both the client and server requirements of this specification. A
4187      "transparent proxy" is a proxy that does not modify the request or
4188      response beyond what is required for proxy authentication and
4189      identification. A "non-transparent proxy" is a proxy that modifies
4190      the request or response in order to provide some added service to
4191      the user agent, such as group annotation services, media type
4192      transformation, protocol reduction, or anonymity filtering. Except
4193      where either transparent or non-transparent behavior is explicitly
4194      stated, the HTTP proxy requirements apply to both types of
4195      proxies.
4196    </t>
4197  </list>
4200  <iref item="gateway"/>
4201  <x:dfn>gateway</x:dfn>
4202  <list>
4203    <t>
4204      A server which acts as an intermediary for some other server.
4205      Unlike a proxy, a gateway receives requests as if it were the
4206      origin server for the requested resource; the requesting client
4207      may not be aware that it is communicating with a gateway.
4208    </t>
4209  </list>
4212  <iref item="tunnel"/>
4213  <x:dfn>tunnel</x:dfn>
4214  <list>
4215    <t>
4216      An intermediary program which is acting as a blind relay between
4217      two connections. Once active, a tunnel is not considered a party
4218      to the HTTP communication, though the tunnel may have been
4219      initiated by an HTTP request. The tunnel ceases to exist when both
4220      ends of the relayed connections are closed.
4221    </t>
4222  </list>
4225  <iref item="cache"/>
4226  <x:dfn>cache</x:dfn>
4227  <list>
4228    <t>
4229      A program's local store of response messages and the subsystem
4230      that controls its message storage, retrieval, and deletion. A
4231      cache stores cacheable responses in order to reduce the response
4232      time and network bandwidth consumption on future, equivalent
4233      requests. Any client or server may include a cache, though a cache
4234      cannot be used by a server that is acting as a tunnel.
4235    </t>
4236  </list>
4239  <iref item="cacheable"/>
4240  <x:dfn>cacheable</x:dfn>
4241  <list>
4242    <t>
4243      A response is cacheable if a cache is allowed to store a copy of
4244      the response message for use in answering subsequent requests. The
4245      rules for determining the cacheability of HTTP responses are
4246      defined in &caching;. Even if a resource is cacheable, there may
4247      be additional constraints on whether a cache can use the cached
4248      copy for a particular request.
4249    </t>
4250  </list>
4253  <iref item="upstream"/>
4254  <iref item="downstream"/>
4255  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4256  <list>
4257    <t>
4258      Upstream and downstream describe the flow of a message: all
4259      messages flow from upstream to downstream.
4260    </t>
4261  </list>
4264  <iref item="inbound"/>
4265  <iref item="outbound"/>
4266  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4267  <list>
4268    <t>
4269      Inbound and outbound refer to the request and response paths for
4270      messages: "inbound" means "traveling toward the origin server",
4271      and "outbound" means "traveling toward the user agent"
4272    </t>
4273  </list>
4277<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4279<section title="Since RFC2616">
4281  Extracted relevant partitions from <xref target="RFC2616"/>.
4285<section title="Since draft-ietf-httpbis-p1-messaging-00">
4287  Closed issues:
4288  <list style="symbols">
4289    <t>
4290      <eref target=""/>:
4291      "HTTP Version should be case sensitive"
4292      (<eref target=""/>)
4293    </t>
4294    <t>
4295      <eref target=""/>:
4296      "'unsafe' characters"
4297      (<eref target=""/>)
4298    </t>
4299    <t>
4300      <eref target=""/>:
4301      "Chunk Size Definition"
4302      (<eref target=""/>)
4303    </t>
4304    <t>
4305      <eref target=""/>:
4306      "Message Length"
4307      (<eref target=""/>)
4308    </t>
4309    <t>
4310      <eref target=""/>:
4311      "Media Type Registrations"
4312      (<eref target=""/>)
4313    </t>
4314    <t>
4315      <eref target=""/>:
4316      "URI includes query"
4317      (<eref target=""/>)
4318    </t>
4319    <t>
4320      <eref target=""/>:
4321      "No close on 1xx responses"
4322      (<eref target=""/>)
4323    </t>
4324    <t>
4325      <eref target=""/>:
4326      "Remove 'identity' token references"
4327      (<eref target=""/>)
4328    </t>
4329    <t>
4330      <eref target=""/>:
4331      "Import query BNF"
4332    </t>
4333    <t>
4334      <eref target=""/>:
4335      "qdtext BNF"
4336    </t>
4337    <t>
4338      <eref target=""/>:
4339      "Normative and Informative references"
4340    </t>
4341    <t>
4342      <eref target=""/>:
4343      "RFC2606 Compliance"
4344    </t>
4345    <t>
4346      <eref target=""/>:
4347      "RFC977 reference"
4348    </t>
4349    <t>
4350      <eref target=""/>:
4351      "RFC1700 references"
4352    </t>
4353    <t>
4354      <eref target=""/>:
4355      "inconsistency in date format explanation"
4356    </t>
4357    <t>
4358      <eref target=""/>:
4359      "Date reference typo"
4360    </t>
4361    <t>
4362      <eref target=""/>:
4363      "Informative references"
4364    </t>
4365    <t>
4366      <eref target=""/>:
4367      "ISO-8859-1 Reference"
4368    </t>
4369    <t>
4370      <eref target=""/>:
4371      "Normative up-to-date references"
4372    </t>
4373  </list>
4376  Other changes:
4377  <list style="symbols">
4378    <t>
4379      Update media type registrations to use RFC4288 template.
4380    </t>
4381    <t>
4382      Use names of RFC4234 core rules DQUOTE and HTAB,
4383      fix broken ABNF for chunk-data
4384      (work in progress on <eref target=""/>)
4385    </t>
4386  </list>
4390<section title="Since draft-ietf-httpbis-p1-messaging-01">
4392  Closed issues:
4393  <list style="symbols">
4394    <t>
4395      <eref target=""/>:
4396      "Bodies on GET (and other) requests"
4397    </t>
4398    <t>
4399      <eref target=""/>:
4400      "Updating to RFC4288"
4401    </t>
4402    <t>
4403      <eref target=""/>:
4404      "Status Code and Reason Phrase"
4405    </t>
4406    <t>
4407      <eref target=""/>:
4408      "rel_path not used"
4409    </t>
4410  </list>
4413  Ongoing work on ABNF conversion (<eref target=""/>):
4414  <list style="symbols">
4415    <t>
4416      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4417      "trailer-part").
4418    </t>
4419    <t>
4420      Avoid underscore character in rule names ("http_URL" ->
4421      "http-URI", "abs_path" -> "path-absolute").
4422    </t>
4423    <t>
4424      Add rules for terms imported from URI spec ("absolute-URI", "authority",
4425      "path-abempty", "path-absolute", "uri-host", "port", "query").
4426    </t>
4427    <t>
4428      Synchronize core rules with RFC5234 (this includes a change to CHAR
4429      which now excludes NUL).
4430    </t>
4431    <t>
4432      Get rid of prose rules that span multiple lines.
4433    </t>
4434    <t>
4435      Get rid of unused rules LOALPHA and UPALPHA.
4436    </t>
4437    <t>
4438      Move "Product Tokens" section (back) into Part 1, as "token" is used
4439      in the definition of the Upgrade header.
4440    </t>
4441    <t>
4442      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4443    </t>
4444    <t>
4445      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4446    </t>
4447  </list>
4451<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4453  Closed issues:
4454  <list style="symbols">
4455    <t>
4456      <eref target=""/>:
4457      "HTTP-date vs. rfc1123-date"
4458    </t>
4459    <t>
4460      <eref target=""/>:
4461      "WS in quoted-pair"
4462    </t>
4463  </list>
4466  Ongoing work on IANA Message Header Registration (<eref target=""/>):
4467  <list style="symbols">
4468    <t>
4469      Reference RFC 3984, and update header registrations for headers defined
4470      in this document.
4471    </t>
4472  </list>
4475  Ongoing work on ABNF conversion (<eref target=""/>):
4476  <list style="symbols">
4477    <t>
4478      Replace string literals when the string really is case-sensitive (HTTP-Version).
4479    </t>
4480  </list>
4484<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4486  Closed issues:
4487  <list style="symbols">
4488    <t>
4489      <eref target=""/>:
4490      "Connection closing"
4491    </t>
4492    <t>
4493      <eref target=""/>:
4494      "Move registrations and registry information to IANA Considerations"
4495    </t>
4496    <t>
4497      <eref target=""/>:
4498      "need new URL for PAD1995 reference"
4499    </t>
4500    <t>
4501      <eref target=""/>:
4502      "IANA Considerations: update HTTP URI scheme registration"
4503    </t>
4504    <t>
4505      <eref target=""/>:
4506      "Cite HTTPS URI scheme definition"
4507    </t>
4508    <t>
4509      <eref target=""/>:
4510      "List-type headers vs Set-Cookie"
4511    </t>
4512  </list>
4515  Ongoing work on ABNF conversion (<eref target=""/>):
4516  <list style="symbols">
4517    <t>
4518      Replace string literals when the string really is case-sensitive (HTTP-Date).
4519    </t>
4520    <t>
4521      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4522    </t>
4523  </list>
4527<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4529  Closed issues:
4530  <list style="symbols">
4531    <t>
4532      <eref target=""/>:
4533      "RFC 2822 is updated by RFC 5322"
4534    </t>
4535  </list>
4538  Ongoing work on ABNF conversion (<eref target=""/>):
4539  <list style="symbols">
4540    <t>
4541      Use "/" instead of "|" for alternatives.
4542    </t>
4543    <t>
4544      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4545    </t>
4546  </list>
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