source: draft-ietf-httpbis/latest-roy/p1-messaging.xml @ 361

Last change on this file since 361 was 361, checked in by fielding@…, 11 years ago

expand on when to use HTTP

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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='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>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='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
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='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
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>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
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>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
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>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
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>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
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>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
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>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
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>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
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>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
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>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
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.
211</t>
212</abstract>
213
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 (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.04"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
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).
240</t>
241<t>
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.
251</t>
252<t>
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.
263</t>
264
265<section title="Requirements" anchor="intro.requirements">
266<t>
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"/>.
270</t>
271<t>
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."
279</t>
280</section>
281
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<iref primary="true" item="Grammar" subitem="WSP"/>
296<t anchor="core.rules">
297  <x:anchor-alias value="ALPHA"/>
298  <x:anchor-alias value="CHAR"/>
299  <x:anchor-alias value="CTL"/>
300  <x:anchor-alias value="CR"/>
301  <x:anchor-alias value="CRLF"/>
302  <x:anchor-alias value="DIGIT"/>
303  <x:anchor-alias value="DQUOTE"/>
304  <x:anchor-alias value="HEXDIG"/>
305  <x:anchor-alias value="HTAB"/>
306  <x:anchor-alias value="LF"/>
307  <x:anchor-alias value="OCTET"/>
308  <x:anchor-alias value="SP"/>
309  <x:anchor-alias value="WSP"/>
310   This specification uses the Augmented Backus-Naur Form (ABNF) notation
311   of <xref target="RFC5234"/>.  The following core rules are included by
312   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
313   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
314   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
315   DIGIT (decimal 0-9), DQUOTE (double quote),
316   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
317   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
318   and WSP (white space).
319</t>
320
321<section title="ABNF Extensions" anchor="notation.abnf">
322<t>
323   Two extensions to the ABNF rules of <xref target="RFC5234"/> are used to
324   improve readability.<cref>The current plan is to remove these extensions prior
325   to the last call draft.</cref>
326</t>
327
328<section title="#rule">
329  <t>
330    A construct "#" is defined, similar to "*", for defining lists of
331    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
332    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
333    (",") and &OPTIONAL; linear white space (LWS). This makes the usual
334    form of lists very easy; a rule such as
335    <figure><artwork type="example">
336 ( *<x:ref>LWS</x:ref> element *( *<x:ref>LWS</x:ref> "," *<x:ref>LWS</x:ref> element ))</artwork></figure>
337  </t>
338  <t>
339    can be shown as
340    <figure><artwork type="example">
341 1#element</artwork></figure>
342  </t>
343  <t>
344    Wherever this construct is used, null elements are allowed, but do
345    not contribute to the count of elements present. That is,
346    "(element), , (element) " is permitted, but counts as only two
347    elements. Therefore, where at least one element is required, at
348    least one non-null element &MUST; be present. Default values are 0
349    and infinity so that "#element" allows any number, including zero;
350    "1#element" requires at least one; and "1#2element" allows one or
351    two.
352  </t>
353</section>
354
355<section title="implied *LWS" anchor="implied.LWS">
356  <iref item="implied *LWS" primary="true"/>
357    <t>
358      The grammar described by this specification is word-based. Except
359      where noted otherwise, linear white space (LWS) can be included
360      between any two adjacent words (token or quoted-string), and
361      between adjacent words and separators, without changing the
362      interpretation of a field. At least one delimiter (LWS and/or
363      separators) &MUST; exist between any two tokens (for the definition
364      of "token" below), since they would otherwise be interpreted as a
365      single token.
366    </t>
367</section>
368</section>
369
370<section title="Basic Rules" anchor="basic.rules">
371<t anchor="rule.CRLF">
372   HTTP/1.1 defines the sequence CRLF as the end-of-line marker for all
373   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
374   tolerant applications). The end-of-line marker within an entity-body
375   is defined by its associated media type, as described in &media-types;.
376</t>
377<t anchor="rule.LWS">
378  <x:anchor-alias value="LWS"/>
379   HTTP/1.1 header field values can be folded onto multiple lines if the
380   continuation line begins with a space or horizontal tab. All linear
381   white space, including folding, has the same semantics as SP. A
382   recipient &MAY; replace any linear white space with a single SP before
383   interpreting the field value or forwarding the message downstream.
384</t>
385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
386  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
387</artwork></figure>
388<t anchor="rule.TEXT">
389  <x:anchor-alias value="TEXT"/>
390   The TEXT rule is only used for descriptive field contents and values
391   that are not intended to be interpreted by the message parser. Words
392   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
393   <xref target="ISO-8859-1"/> only when encoded according to the rules of
394   <xref target="RFC2047"/>.
395</t>
396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
397  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
398                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
399</artwork></figure>
400<t>
401   A CRLF is allowed in the definition of TEXT only as part of a header
402   field continuation. It is expected that the folding LWS will be
403   replaced with a single SP before interpretation of the TEXT value.
404</t>
405<t anchor="rule.token.separators">
406  <x:anchor-alias value="tchar"/>
407  <x:anchor-alias value="token"/>
408  <x:anchor-alias value="separators"/>
409   Many HTTP/1.1 header field values consist of words separated by LWS
410   or special characters. These special characters &MUST; be in a quoted
411   string to be used within a parameter value (as defined in
412   <xref target="transfer.codings"/>).
413</t>
414<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"/>
415  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
416                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
417                 / "/" / "[" / "]" / "?" / "="
418                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
419                 
420  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
421                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
422                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
423                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
424                 
425  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
426</artwork></figure>
427<t anchor="rule.comment">
428  <x:anchor-alias value="comment"/>
429  <x:anchor-alias value="ctext"/>
430   Comments can be included in some HTTP header fields by surrounding
431   the comment text with parentheses. Comments are only allowed in
432   fields containing "comment" as part of their field value definition.
433   In all other fields, parentheses are considered part of the field
434   value.
435</t>
436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
437  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
438  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
439</artwork></figure>
440<t anchor="rule.quoted-string">
441  <x:anchor-alias value="quoted-string"/>
442  <x:anchor-alias value="qdtext"/>
443   A string of text is parsed as a single word if it is quoted using
444   double-quote marks.
445</t>
446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
447  <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> )
448  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
449</artwork></figure>
450<t anchor="rule.quoted-pair">
451  <x:anchor-alias value="quoted-pair"/>
452  <x:anchor-alias value="quoted-text"/>
453   The backslash character ("\") &MAY; be used as a single-character
454   quoting mechanism only within quoted-string and comment constructs.
455</t>
456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
457  <x:ref>quoted-text</x:ref>    = %x01-09 /
458                   %x0B-0C /
459                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
460  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
461</artwork></figure>
462</section>
463
464<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
465  <x:anchor-alias value="request-header"/>
466  <x:anchor-alias value="response-header"/>
467  <x:anchor-alias value="accept-params"/>
468  <x:anchor-alias value="entity-body"/>
469  <x:anchor-alias value="entity-header"/>
470  <x:anchor-alias value="Cache-Control"/>
471  <x:anchor-alias value="Pragma"/>
472  <x:anchor-alias value="Warning"/>
473<t>
474  The ABNF rules below are defined in other parts:
475</t>
476<figure><!-- Part2--><artwork type="abnf2616">
477  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
478  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
479</artwork></figure>
480<figure><!-- Part3--><artwork type="abnf2616">
481  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
482  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
483  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
484</artwork></figure>
485<figure><!-- Part6--><artwork type="abnf2616">
486  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
487  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
488  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
489</artwork></figure>
490</section>
491
492</section>
493</section>
494
495<section title="When to use HTTP" anchor="when">
496<t>
497   HTTP is a generic interface protocol for informations systems. It is
498   designed to hide the details of how a service is implemented by presenting
499   a uniform interface to clients that is independent of the types of
500   resources provided. Likewise, servers do not need to be aware of the
501   client's purpose: each HTTP request can be considered independently rather
502   than being associated with a specific type of client or a predetermined
503   sequence of application steps. The result is a protocol that can be used
504   effectively in many different contexts and for which implementations can
505   evolve independently over time.
506</t>
507<t>
508   One consequence of HTTP flexibility is that we cannot define the protocol
509   in terms of how to implement it behind the interface. Instead, we are
510   limited to restricting the syntax of communication, defining the intent
511   of received communication, and the expected behavior of recipients. If
512   the communication is considered in isolation, then successful actions
513   should be reflected in the observable interface provided by servers.
514   However, since many clients are potentially acting in parallel and
515   perhaps at cross-purposes, it would be meaningless to require that such
516   behavior be observable.
517</t>
518<t>
519   This section describes the most common contexts in which a user agent is
520   encouraged or instructed to use HTTP for communication and how such
521   contexts differ in terms of their resulting communication.
522</t>
523
524<section title="Uniform Resource Identifiers" anchor="uri">
525<t>
526   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used in HTTP
527   to indicate the target of a request and to identify additional resources related
528   to that resource, the request, or the response. Each protocol element in HTTP
529   that allows a URI reference will indicate in its ABNF whether the element allows
530   only a URI in absolute form, any relative reference, or some limited subset of
531   the URI-reference grammar. Unless otherwise indicated, relative URI references
532   are to be parsed relative to the URI corresponding to the request target
533   (the base URI).
534</t>
535  <x:anchor-alias value="URI-reference"/>
536  <x:anchor-alias value="absolute-URI"/>
537  <x:anchor-alias value="authority"/>
538  <x:anchor-alias value="fragment"/>
539  <x:anchor-alias value="path-abempty"/>
540  <x:anchor-alias value="path-absolute"/>
541  <x:anchor-alias value="port"/>
542  <x:anchor-alias value="query"/>
543  <x:anchor-alias value="uri-host"/>
544<t>
545   This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port",
546   "host", "path-abempty", "path-absolute", "query", and "authority" from <xref target="RFC3986"/>:
547</t>
548<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"/>
549  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
550  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
551  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
552  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
553  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
554  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
555  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
556  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
557</artwork></figure>
558<t>
559   HTTP does not place an a priori limit on the length of
560   a URI. Servers &MUST; be able to handle the URI of any resource they
561   serve, and &SHOULD; be able to handle URIs of unbounded length if they
562   provide GET-based forms that could generate such URIs. A server
563   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
564   than the server can handle (see &status-414;).
565</t>
566<t>
567  <list>
568    <t>
569      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
570      above 255 bytes, because some older client or proxy
571      implementations might not properly support these lengths.
572    </t>
573  </list>
574</t>
575
576<section title="http URI scheme" anchor="http.uri">
577  <x:anchor-alias value="http-URI"/>
578  <iref item="http URI scheme" primary="true"/>
579  <iref item="URI scheme" subitem="http" primary="true"/>
580<t>
581   The "http" scheme is used to locate network resources via the HTTP
582   protocol. This section defines the syntax and semantics for identifiers
583   using the http or https URI schemes.
584</t>
585<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
586  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
587</artwork></figure>
588<t>
589   If the port is empty or not given, port 80 is assumed. The semantics
590   are that the identified resource is located at the server listening
591   for TCP connections on that port of that host, and the Request-URI
592   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
593   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
594   the path-absolute is not present in the URL, it &MUST; be given as "/" when
595   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
596   receives a host name which is not a fully qualified domain name, it
597   &MAY; add its domain to the host name it received. If a proxy receives
598   a fully qualified domain name, the proxy &MUST-NOT; change the host
599   name.
600</t>
601<t><list><t>
602  <iref item="https URI scheme"/>
603  <iref item="URI scheme" subitem="https"/>
604  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
605</t></list></t>
606</section>
607
608<section title="URI Comparison" anchor="uri.comparison">
609<t>
610   When comparing two URIs to decide if they match or not, a client
611   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
612   URIs, with these exceptions:
613  <list style="symbols">
614    <t>A port that is empty or not given is equivalent to the default
615        port for that URI-reference;</t>
616    <t>Comparisons of host names &MUST; be case-insensitive;</t>
617    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
618    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
619  </list>
620</t>
621<t>
622   Characters other than those in the "reserved" set (see
623   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
624   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
625</t>
626<t>
627   For example, the following three URIs are equivalent:
628</t>
629<figure><artwork type="example">
630   http://example.com:80/~smith/home.html
631   http://EXAMPLE.com/%7Esmith/home.html
632   http://EXAMPLE.com:/%7esmith/home.html
633</artwork></figure>
634</section>
635
636<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
637<t>
638</t>
639</section>
640</section>
641
642<section title="Overall Operation" anchor="intro.overall.operation">
643<t>
644   HTTP is a request/response protocol. A client sends a
645   request to the server in the form of a request method, URI, and
646   protocol version, followed by a MIME-like message containing request
647   modifiers, client information, and possible body content over a
648   connection with a server. The server responds with a status line,
649   including the message's protocol version and a success or error code,
650   followed by a MIME-like message containing server information, entity
651   metainformation, and possible entity-body content.
652</t>
653<t>
654   Most HTTP communication is initiated by a user agent and consists of
655   a request to be applied to a resource on some origin server. In the
656   simplest case, this may be accomplished via a single connection (v)
657   between the user agent (UA) and the origin server (O).
658</t>
659<figure><artwork type="drawing">
660       request chain ------------------------&gt;
661    UA -------------------v------------------- O
662       &lt;----------------------- response chain
663</artwork></figure>
664<t>
665   A more complicated situation occurs when one or more intermediaries
666   are present in the request/response chain. There are three common
667   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
668   forwarding agent, receiving requests for a URI in its absolute form,
669   rewriting all or part of the message, and forwarding the reformatted
670   request toward the server identified by the URI. A gateway is a
671   receiving agent, acting as a layer above some other server(s) and, if
672   necessary, translating the requests to the underlying server's
673   protocol. A tunnel acts as a relay point between two connections
674   without changing the messages; tunnels are used when the
675   communication needs to pass through an intermediary (such as a
676   firewall) even when the intermediary cannot understand the contents
677   of the messages.
678</t>
679<figure><artwork type="drawing">
680       request chain --------------------------------------&gt;
681    UA -----v----- A -----v----- B -----v----- C -----v----- O
682       &lt;------------------------------------- response chain
683</artwork></figure>
684<t>
685   The figure above shows three intermediaries (A, B, and C) between the
686   user agent and origin server. A request or response message that
687   travels the whole chain will pass through four separate connections.
688   This distinction is important because some HTTP communication options
689   may apply only to the connection with the nearest, non-tunnel
690   neighbor, only to the end-points of the chain, or to all connections
691   along the chain. Although the diagram is linear, each participant may
692   be engaged in multiple, simultaneous communications. For example, B
693   may be receiving requests from many clients other than A, and/or
694   forwarding requests to servers other than C, at the same time that it
695   is handling A's request.
696</t>
697<t>
698   Any party to the communication which is not acting as a tunnel may
699   employ an internal cache for handling requests. The effect of a cache
700   is that the request/response chain is shortened if one of the
701   participants along the chain has a cached response applicable to that
702   request. The following illustrates the resulting chain if B has a
703   cached copy of an earlier response from O (via C) for a request which
704   has not been cached by UA or A.
705</t>
706<figure><artwork type="drawing">
707          request chain ----------&gt;
708       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
709          &lt;--------- response chain
710</artwork></figure>
711<t>
712   Not all responses are usefully cacheable, and some requests may
713   contain modifiers which place special requirements on cache behavior.
714   HTTP requirements for cache behavior and cacheable responses are
715   defined in &caching;.
716</t>
717<t>
718   In fact, there are a wide variety of architectures and configurations
719   of caches and proxies currently being experimented with or deployed
720   across the World Wide Web. These systems include national hierarchies
721   of proxy caches to save transoceanic bandwidth, systems that
722   broadcast or multicast cache entries, organizations that distribute
723   subsets of cached data via CD-ROM, and so on. HTTP systems are used
724   in corporate intranets over high-bandwidth links, and for access via
725   PDAs with low-power radio links and intermittent connectivity. The
726   goal of HTTP/1.1 is to support the wide diversity of configurations
727   already deployed while introducing protocol constructs that meet the
728   needs of those who build web applications that require high
729   reliability and, failing that, at least reliable indications of
730   failure.
731</t>
732<t>
733   HTTP communication usually takes place over TCP/IP connections. The
734   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
735   not preclude HTTP from being implemented on top of any other protocol
736   on the Internet, or on other networks. HTTP only presumes a reliable
737   transport; any protocol that provides such guarantees can be used;
738   the mapping of the HTTP/1.1 request and response structures onto the
739   transport data units of the protocol in question is outside the scope
740   of this specification.
741</t>
742<t>
743   In HTTP/1.0, most implementations used a new connection for each
744   request/response exchange. In HTTP/1.1, a connection may be used for
745   one or more request/response exchanges, although connections may be
746   closed for a variety of reasons (see <xref target="persistent.connections"/>).
747</t>
748</section>
749
750<section title="Use of HTTP for proxy communication" anchor="http.proxy">
751<t>
752   Configured to use HTTP to proxy HTTP or other protocols.
753</t>
754</section>
755<section title="Interception of HTTP for access control" anchor="http.intercept">
756<t>
757   Interception of HTTP traffic for initiating access control.
758</t>
759</section>
760<section title="Use of HTTP by other protocols" anchor="http.others">
761<t>
762   Profiles of HTTP defined by other protocol.
763   Extensions of HTTP like WebDAV.
764</t>
765</section>
766<section title="Use of HTTP by media type specification" anchor="http.media">
767<t>
768   Instructions on composing HTTP requests via hypertext formats.
769</t>
770</section>
771</section>
772
773<section title="Protocol Parameters" anchor="protocol.parameters">
774
775<section title="HTTP Version" anchor="http.version">
776  <x:anchor-alias value="HTTP-Version"/>
777  <x:anchor-alias value="HTTP-Prot-Name"/>
778<t>
779   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
780   of the protocol. The protocol versioning policy is intended to allow
781   the sender to indicate the format of a message and its capacity for
782   understanding further HTTP communication, rather than the features
783   obtained via that communication. No change is made to the version
784   number for the addition of message components which do not affect
785   communication behavior or which only add to extensible field values.
786   The &lt;minor&gt; number is incremented when the changes made to the
787   protocol add features which do not change the general message parsing
788   algorithm, but which may add to the message semantics and imply
789   additional capabilities of the sender. The &lt;major&gt; number is
790   incremented when the format of a message within the protocol is
791   changed. See <xref target="RFC2145"/> for a fuller explanation.
792</t>
793<t>
794   The version of an HTTP message is indicated by an HTTP-Version field
795   in the first line of the message. HTTP-Version is case-sensitive.
796</t>
797<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
798  <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>
799  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
800</artwork></figure>
801<t>
802   Note that the major and minor numbers &MUST; be treated as separate
803   integers and that each &MAY; be incremented higher than a single digit.
804   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
805   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
806   &MUST-NOT; be sent.
807</t>
808<t>
809   An application that sends a request or response message that includes
810   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
811   with this specification. Applications that are at least conditionally
812   compliant with this specification &SHOULD; use an HTTP-Version of
813   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
814   not compatible with HTTP/1.0. For more details on when to send
815   specific HTTP-Version values, see <xref target="RFC2145"/>.
816</t>
817<t>
818   The HTTP version of an application is the highest HTTP version for
819   which the application is at least conditionally compliant.
820</t>
821<t>
822   Proxy and gateway applications need to be careful when forwarding
823   messages in protocol versions different from that of the application.
824   Since the protocol version indicates the protocol capability of the
825   sender, a proxy/gateway &MUST-NOT; send a message with a version
826   indicator which is greater than its actual version. If a higher
827   version request is received, the proxy/gateway &MUST; either downgrade
828   the request version, or respond with an error, or switch to tunnel
829   behavior.
830</t>
831<t>
832   Due to interoperability problems with HTTP/1.0 proxies discovered
833   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
834   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
835   they support. The proxy/gateway's response to that request &MUST; be in
836   the same major version as the request.
837</t>
838<t>
839  <list>
840    <t>
841      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
842      of header fields required or forbidden by the versions involved.
843    </t>
844  </list>
845</t>
846</section>
847
848<section title="Date/Time Formats" anchor="date.time.formats">
849<section title="Full Date" anchor="full.date">
850  <x:anchor-alias value="HTTP-date"/>
851  <x:anchor-alias value="obsolete-date"/>
852  <x:anchor-alias value="rfc1123-date"/>
853  <x:anchor-alias value="rfc850-date"/>
854  <x:anchor-alias value="asctime-date"/>
855  <x:anchor-alias value="date1"/>
856  <x:anchor-alias value="date2"/>
857  <x:anchor-alias value="date3"/>
858  <x:anchor-alias value="rfc1123-date"/>
859  <x:anchor-alias value="time"/>
860  <x:anchor-alias value="wkday"/>
861  <x:anchor-alias value="weekday"/>
862  <x:anchor-alias value="month"/>
863<t>
864   HTTP applications have historically allowed three different formats
865   for the representation of date/time stamps:
866</t>
867<figure><artwork type="example">
868   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
869   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
870   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
871</artwork></figure>
872<t>
873   The first format is preferred as an Internet standard and represents
874   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
875   <xref target="RFC822"/>). The other formats are described here only for
876   compatibility with obsolete implementations.
877   HTTP/1.1 clients and servers that parse the date value &MUST; accept
878   all three formats (for compatibility with HTTP/1.0), though they &MUST;
879   only generate the RFC 1123 format for representing HTTP-date values
880   in header fields. See <xref target="tolerant.applications"/> for further information.
881</t>
882<t><list><t>
883      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
884      accepting date values that may have been sent by non-HTTP
885      applications, as is sometimes the case when retrieving or posting
886      messages via proxies/gateways to SMTP or NNTP.
887</t></list></t>
888<t>
889   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
890   (GMT), without exception. For the purposes of HTTP, GMT is exactly
891   equal to UTC (Coordinated Universal Time). This is indicated in the
892   first two formats by the inclusion of "GMT" as the three-letter
893   abbreviation for time zone, and &MUST; be assumed when reading the
894   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
895   additional LWS beyond that specifically included as SP in the
896   grammar.
897</t>
898<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"/>
899  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
900  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
901  <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
902  <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
903  <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>
904  <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>
905                 ; day month year (e.g., 02 Jun 1982)
906  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
907                 ; day-month-year (e.g., 02-Jun-82)
908  <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> ))
909                 ; month day (e.g., Jun  2)
910  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
911                 ; 00:00:00 - 23:59:59
912  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
913               / s-Thu / s-Fri / s-Sat / s-Sun
914  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
915               / l-Thu / l-Fri / l-Sat / l-Sun
916  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
917               / s-May / s-Jun / s-Jul / s-Aug
918               / s-Sep / s-Oct / s-Nov / s-Dec
919               
920  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
921
922  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
923  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
924  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
925  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
926  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
927  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
928  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
929
930  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
931  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
932  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
933  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
934  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
935  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
936  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
937
938  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
939  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
940  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
941  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
942  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
943  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
944  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
945  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
946  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
947  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
948  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
949  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
950</artwork></figure>
951<t>
952      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
953      to their usage within the protocol stream. Clients and servers are
954      not required to use these formats for user presentation, request
955      logging, etc.
956</t>
957</section>
958</section>
959
960<section title="Transfer Codings" anchor="transfer.codings">
961  <x:anchor-alias value="parameter"/>
962  <x:anchor-alias value="transfer-coding"/>
963  <x:anchor-alias value="transfer-extension"/>
964<t>
965   Transfer-coding values are used to indicate an encoding
966   transformation that has been, can be, or may need to be applied to an
967   entity-body in order to ensure "safe transport" through the network.
968   This differs from a content coding in that the transfer-coding is a
969   property of the message, not of the original entity.
970</t>
971<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
972  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
973  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
974</artwork></figure>
975<t anchor="rule.parameter">
976  <x:anchor-alias value="attribute"/>
977  <x:anchor-alias value="parameter"/>
978  <x:anchor-alias value="value"/>
979   Parameters are in  the form of attribute/value pairs.
980</t>
981<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"/>
982  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
983  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
984  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
985</artwork></figure>
986<t>
987   All transfer-coding values are case-insensitive. HTTP/1.1 uses
988   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
989   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
990</t>
991<t>
992   Whenever a transfer-coding is applied to a message-body, the set of
993   transfer-codings &MUST; include "chunked", unless the message indicates it
994   is terminated by closing the connection. When the "chunked" transfer-coding
995   is used, it &MUST; be the last transfer-coding applied to the
996   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
997   than once to a message-body. These rules allow the recipient to
998   determine the transfer-length of the message (<xref target="message.length"/>).
999</t>
1000<t>
1001   Transfer-codings are analogous to the Content-Transfer-Encoding
1002   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1003   binary data over a 7-bit transport service. However, safe transport
1004   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1005   the only unsafe characteristic of message-bodies is the difficulty in
1006   determining the exact body length (<xref target="message.length"/>), or the desire to
1007   encrypt data over a shared transport.
1008</t>
1009<t>
1010   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1011   transfer-coding value tokens. Initially, the registry contains the
1012   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1013   "gzip", "compress", and "deflate" (&content-codings;).
1014</t>
1015<t>
1016   New transfer-coding value tokens &SHOULD; be registered in the same way
1017   as new content-coding value tokens (&content-codings;).
1018</t>
1019<t>
1020   A server which receives an entity-body with a transfer-coding it does
1021   not understand &SHOULD; return 501 (Not Implemented), and close the
1022   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1023   client.
1024</t>
1025
1026<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1027  <x:anchor-alias value="chunk"/>
1028  <x:anchor-alias value="Chunked-Body"/>
1029  <x:anchor-alias value="chunk-data"/>
1030  <x:anchor-alias value="chunk-extension"/>
1031  <x:anchor-alias value="chunk-ext-name"/>
1032  <x:anchor-alias value="chunk-ext-val"/>
1033  <x:anchor-alias value="chunk-size"/>
1034  <x:anchor-alias value="last-chunk"/>
1035  <x:anchor-alias value="trailer-part"/>
1036<t>
1037   The chunked encoding modifies the body of a message in order to
1038   transfer it as a series of chunks, each with its own size indicator,
1039   followed by an &OPTIONAL; trailer containing entity-header fields. This
1040   allows dynamically produced content to be transferred along with the
1041   information necessary for the recipient to verify that it has
1042   received the full message.
1043</t>
1044<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"/>
1045  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1046                   <x:ref>last-chunk</x:ref>
1047                   <x:ref>trailer-part</x:ref>
1048                   <x:ref>CRLF</x:ref>
1049 
1050  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1051                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1052  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1053  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1054 
1055  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1056  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1057  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1058  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1059  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1060</artwork></figure>
1061<t>
1062   The chunk-size field is a string of hex digits indicating the size of
1063   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1064   zero, followed by the trailer, which is terminated by an empty line.
1065</t>
1066<t>
1067   The trailer allows the sender to include additional HTTP header
1068   fields at the end of the message. The Trailer header field can be
1069   used to indicate which header fields are included in a trailer (see
1070   <xref target="header.trailer"/>).
1071</t>
1072<t>
1073   A server using chunked transfer-coding in a response &MUST-NOT; use the
1074   trailer for any header fields unless at least one of the following is
1075   true:
1076  <list style="numbers">
1077    <t>the request included a TE header field that indicates "trailers" is
1078     acceptable in the transfer-coding of the  response, as described in
1079     <xref target="header.te"/>; or,</t>
1080
1081    <t>the server is the origin server for the response, the trailer
1082     fields consist entirely of optional metadata, and the recipient
1083     could use the message (in a manner acceptable to the origin server)
1084     without receiving this metadata.  In other words, the origin server
1085     is willing to accept the possibility that the trailer fields might
1086     be silently discarded along the path to the client.</t>
1087  </list>
1088</t>
1089<t>
1090   This requirement prevents an interoperability failure when the
1091   message is being received by an HTTP/1.1 (or later) proxy and
1092   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1093   compliance with the protocol would have necessitated a possibly
1094   infinite buffer on the proxy.
1095</t>
1096<t>
1097   A process for decoding the "chunked" transfer-coding
1098   can be represented in pseudo-code as:
1099</t>
1100<figure><artwork type="code">
1101    length := 0
1102    read chunk-size, chunk-extension (if any) and CRLF
1103    while (chunk-size &gt; 0) {
1104       read chunk-data and CRLF
1105       append chunk-data to entity-body
1106       length := length + chunk-size
1107       read chunk-size and CRLF
1108    }
1109    read entity-header
1110    while (entity-header not empty) {
1111       append entity-header to existing header fields
1112       read entity-header
1113    }
1114    Content-Length := length
1115    Remove "chunked" from Transfer-Encoding
1116</artwork></figure>
1117<t>
1118   All HTTP/1.1 applications &MUST; be able to receive and decode the
1119   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1120   they do not understand.
1121</t>
1122</section>
1123</section>
1124
1125<section title="Product Tokens" anchor="product.tokens">
1126  <x:anchor-alias value="product"/>
1127  <x:anchor-alias value="product-version"/>
1128<t>
1129   Product tokens are used to allow communicating applications to
1130   identify themselves by software name and version. Most fields using
1131   product tokens also allow sub-products which form a significant part
1132   of the application to be listed, separated by white space. By
1133   convention, the products are listed in order of their significance
1134   for identifying the application.
1135</t>
1136<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1137  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1138  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1139</artwork></figure>
1140<t>
1141   Examples:
1142</t>
1143<figure><artwork type="example">
1144    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1145    Server: Apache/0.8.4
1146</artwork></figure>
1147<t>
1148   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1149   used for advertising or other non-essential information. Although any
1150   token character &MAY; appear in a product-version, this token &SHOULD;
1151   only be used for a version identifier (i.e., successive versions of
1152   the same product &SHOULD; only differ in the product-version portion of
1153   the product value).
1154</t>
1155</section>
1156
1157</section>
1158
1159<section title="HTTP Message" anchor="http.message">
1160
1161<section title="Message Types" anchor="message.types">
1162  <x:anchor-alias value="generic-message"/>
1163  <x:anchor-alias value="HTTP-message"/>
1164  <x:anchor-alias value="start-line"/>
1165<t>
1166   HTTP messages consist of requests from client to server and responses
1167   from server to client.
1168</t>
1169<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1170  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1171</artwork></figure>
1172<t>
1173   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1174   message format of <xref target="RFC5322"/> for transferring entities (the payload
1175   of the message). Both types of message consist of a start-line, zero
1176   or more header fields (also known as "headers"), an empty line (i.e.,
1177   a line with nothing preceding the CRLF) indicating the end of the
1178   header fields, and possibly a message-body.
1179</t>
1180<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1181  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1182                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1183                    <x:ref>CRLF</x:ref>
1184                    [ <x:ref>message-body</x:ref> ]
1185  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1186</artwork></figure>
1187<t>
1188   In the interest of robustness, servers &SHOULD; ignore any empty
1189   line(s) received where a Request-Line is expected. In other words, if
1190   the server is reading the protocol stream at the beginning of a
1191   message and receives a CRLF first, it should ignore the CRLF.
1192</t>
1193<t>
1194   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1195   after a POST request. To restate what is explicitly forbidden by the
1196   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1197   extra CRLF.
1198</t>
1199</section>
1200
1201<section title="Message Headers" anchor="message.headers">
1202  <x:anchor-alias value="field-content"/>
1203  <x:anchor-alias value="field-name"/>
1204  <x:anchor-alias value="field-value"/>
1205  <x:anchor-alias value="message-header"/>
1206<t>
1207   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1208   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1209   entity-header (&entity-header-fields;) fields, follow the same generic format as
1210   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1211   of a name followed by a colon (":") and the field value. Field names
1212   are case-insensitive. The field value &MAY; be preceded by any amount
1213   of LWS, though a single SP is preferred. Header fields can be
1214   extended over multiple lines by preceding each extra line with at
1215   least one SP or HTAB. Applications ought to follow "common form", where
1216   one is known or indicated, when generating HTTP constructs, since
1217   there might exist some implementations that fail to accept anything
1218   beyond the common forms.
1219</t>
1220<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"/>
1221  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1222  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1223  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1224  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1225                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1226                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1227                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1228</artwork></figure>
1229<t>
1230   The field-content does not include any leading or trailing LWS:
1231   linear white space occurring before the first non-whitespace
1232   character of the field-value or after the last non-whitespace
1233   character of the field-value. Such leading or trailing LWS &MAY; be
1234   removed without changing the semantics of the field value. Any LWS
1235   that occurs between field-content &MAY; be replaced with a single SP
1236   before interpreting the field value or forwarding the message
1237   downstream.
1238</t>
1239<t>
1240   The order in which header fields with differing field names are
1241   received is not significant. However, it is "good practice" to send
1242   general-header fields first, followed by request-header or response-header
1243   fields, and ending with the entity-header fields.
1244</t>
1245<t>
1246   Multiple message-header fields with the same field-name &MAY; be
1247   present in a message if and only if the entire field-value for that
1248   header field is defined as a comma-separated list [i.e., #(values)].
1249   It &MUST; be possible to combine the multiple header fields into one
1250   "field-name: field-value" pair, without changing the semantics of the
1251   message, by appending each subsequent field-value to the first, each
1252   separated by a comma. The order in which header fields with the same
1253   field-name are received is therefore significant to the
1254   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1255   change the order of these field values when a message is forwarded.
1256</t>
1257<t>
1258  <list><t>
1259   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1260   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1261   can occur multiple times, but does not use the list syntax, and thus cannot
1262   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1263   for details.) Also note that the Set-Cookie2 header specified in
1264   <xref target="RFC2965"/> does not share this problem.
1265  </t></list>
1266</t>
1267 
1268</section>
1269
1270<section title="Message Body" anchor="message.body">
1271  <x:anchor-alias value="message-body"/>
1272<t>
1273   The message-body (if any) of an HTTP message is used to carry the
1274   entity-body associated with the request or response. The message-body
1275   differs from the entity-body only when a transfer-coding has been
1276   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1277</t>
1278<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1279  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1280               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1281</artwork></figure>
1282<t>
1283   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1284   applied by an application to ensure safe and proper transfer of the
1285   message. Transfer-Encoding is a property of the message, not of the
1286   entity, and thus &MAY; be added or removed by any application along the
1287   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1288   when certain transfer-codings may be used.)
1289</t>
1290<t>
1291   The rules for when a message-body is allowed in a message differ for
1292   requests and responses.
1293</t>
1294<t>
1295   The presence of a message-body in a request is signaled by the
1296   inclusion of a Content-Length or Transfer-Encoding header field in
1297   the request's message-headers. A message-body &MUST-NOT; be included in
1298   a request if the specification of the request method (&method;)
1299   explicitly disallows an entity-body in requests.
1300   When a request message contains both a message-body of non-zero
1301   length and a method that does not define any semantics for that
1302   request message-body, then an origin server &SHOULD; either ignore
1303   the message-body or respond with an appropriate error message
1304   (e.g., 413).  A proxy or gateway, when presented the same request,
1305   &SHOULD; either forward the request inbound with the message-body or
1306   ignore the message-body when determining a response.
1307</t>
1308<t>
1309   For response messages, whether or not a message-body is included with
1310   a message is dependent on both the request method and the response
1311   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1312   &MUST-NOT; include a message-body, even though the presence of entity-header
1313   fields might lead one to believe they do. All 1xx
1314   (informational), 204 (No Content), and 304 (Not Modified) responses
1315   &MUST-NOT; include a message-body. All other responses do include a
1316   message-body, although it &MAY; be of zero length.
1317</t>
1318</section>
1319
1320<section title="Message Length" anchor="message.length">
1321<t>
1322   The transfer-length of a message is the length of the message-body as
1323   it appears in the message; that is, after any transfer-codings have
1324   been applied. When a message-body is included with a message, the
1325   transfer-length of that body is determined by one of the following
1326   (in order of precedence):
1327</t>
1328<t>
1329  <list style="numbers">
1330    <x:lt><t>
1331     Any response message which "&MUST-NOT;" include a message-body (such
1332     as the 1xx, 204, and 304 responses and any response to a HEAD
1333     request) is always terminated by the first empty line after the
1334     header fields, regardless of the entity-header fields present in
1335     the message.
1336    </t></x:lt>
1337    <x:lt><t>
1338     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1339     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1340     is used, the transfer-length is defined by the use of this transfer-coding.
1341     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1342     is not present, the transfer-length is defined by the sender closing the connection.
1343    </t></x:lt>
1344    <x:lt><t>
1345     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1346     decimal value in OCTETs represents both the entity-length and the
1347     transfer-length. The Content-Length header field &MUST-NOT; be sent
1348     if these two lengths are different (i.e., if a Transfer-Encoding
1349     header field is present). If a message is received with both a
1350     Transfer-Encoding header field and a Content-Length header field,
1351     the latter &MUST; be ignored.
1352    </t></x:lt>
1353    <x:lt><t>
1354     If the message uses the media type "multipart/byteranges", and the
1355     transfer-length is not otherwise specified, then this self-delimiting
1356     media type defines the transfer-length. This media type
1357     &MUST-NOT; be used unless the sender knows that the recipient can parse
1358     it; the presence in a request of a Range header with multiple byte-range
1359     specifiers from a 1.1 client implies that the client can parse
1360     multipart/byteranges responses.
1361    <list style="empty"><t>
1362       A range header might be forwarded by a 1.0 proxy that does not
1363       understand multipart/byteranges; in this case the server &MUST;
1364       delimit the message using methods defined in items 1, 3 or 5 of
1365       this section.
1366    </t></list>
1367    </t></x:lt>
1368    <x:lt><t>
1369     By the server closing the connection. (Closing the connection
1370     cannot be used to indicate the end of a request body, since that
1371     would leave no possibility for the server to send back a response.)
1372    </t></x:lt>
1373  </list>
1374</t>
1375<t>
1376   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1377   containing a message-body &MUST; include a valid Content-Length header
1378   field unless the server is known to be HTTP/1.1 compliant. If a
1379   request contains a message-body and a Content-Length is not given,
1380   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1381   determine the length of the message, or with 411 (Length Required) if
1382   it wishes to insist on receiving a valid Content-Length.
1383</t>
1384<t>
1385   All HTTP/1.1 applications that receive entities &MUST; accept the
1386   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1387   to be used for messages when the message length cannot be determined
1388   in advance.
1389</t>
1390<t>
1391   Messages &MUST-NOT; include both a Content-Length header field and a
1392   transfer-coding. If the message does include a
1393   transfer-coding, the Content-Length &MUST; be ignored.
1394</t>
1395<t>
1396   When a Content-Length is given in a message where a message-body is
1397   allowed, its field value &MUST; exactly match the number of OCTETs in
1398   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1399   invalid length is received and detected.
1400</t>
1401</section>
1402
1403<section title="General Header Fields" anchor="general.header.fields">
1404  <x:anchor-alias value="general-header"/>
1405<t>
1406   There are a few header fields which have general applicability for
1407   both request and response messages, but which do not apply to the
1408   entity being transferred. These header fields apply only to the
1409   message being transmitted.
1410</t>
1411<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1412  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1413                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1414                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1415                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1416                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1417                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1418                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1419                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1420                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1421</artwork></figure>
1422<t>
1423   General-header field names can be extended reliably only in
1424   combination with a change in the protocol version. However, new or
1425   experimental header fields may be given the semantics of general
1426   header fields if all parties in the communication recognize them to
1427   be general-header fields. Unrecognized header fields are treated as
1428   entity-header fields.
1429</t>
1430</section>
1431</section>
1432
1433<section title="Request" anchor="request">
1434  <x:anchor-alias value="Request"/>
1435<t>
1436   A request message from a client to a server includes, within the
1437   first line of that message, the method to be applied to the resource,
1438   the identifier of the resource, and the protocol version in use.
1439</t>
1440<!--                 Host                      ; should be moved here eventually -->
1441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1442  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1443                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1444                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1445                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1446                  <x:ref>CRLF</x:ref>
1447                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1448</artwork></figure>
1449
1450<section title="Request-Line" anchor="request-line">
1451  <x:anchor-alias value="Request-Line"/>
1452<t>
1453   The Request-Line begins with a method token, followed by the
1454   Request-URI and the protocol version, and ending with CRLF. The
1455   elements are separated by SP characters. No CR or LF is allowed
1456   except in the final CRLF sequence.
1457</t>
1458<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1459  <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>
1460</artwork></figure>
1461
1462<section title="Method" anchor="method">
1463  <x:anchor-alias value="Method"/>
1464<t>
1465   The Method  token indicates the method to be performed on the
1466   resource identified by the Request-URI. The method is case-sensitive.
1467</t>
1468<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1469  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1470</artwork></figure>
1471</section>
1472
1473<section title="Request-URI" anchor="request-uri">
1474  <x:anchor-alias value="Request-URI"/>
1475<t>
1476   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1477   identifies the resource upon which to apply the request.
1478</t>
1479<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1480  <x:ref>Request-URI</x:ref>    = "*"
1481                 / <x:ref>absolute-URI</x:ref>
1482                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1483                 / <x:ref>authority</x:ref>
1484</artwork></figure>
1485<t>
1486   The four options for Request-URI are dependent on the nature of the
1487   request. The asterisk "*" means that the request does not apply to a
1488   particular resource, but to the server itself, and is only allowed
1489   when the method used does not necessarily apply to a resource. One
1490   example would be
1491</t>
1492<figure><artwork type="example">
1493    OPTIONS * HTTP/1.1
1494</artwork></figure>
1495<t>
1496   The absolute-URI form is &REQUIRED; when the request is being made to a
1497   proxy. The proxy is requested to forward the request or service it
1498   from a valid cache, and return the response. Note that the proxy &MAY;
1499   forward the request on to another proxy or directly to the server
1500   specified by the absolute-URI. In order to avoid request loops, a
1501   proxy &MUST; be able to recognize all of its server names, including
1502   any aliases, local variations, and the numeric IP address. An example
1503   Request-Line would be:
1504</t>
1505<figure><artwork type="example">
1506    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1507</artwork></figure>
1508<t>
1509   To allow for transition to absolute-URIs in all requests in future
1510   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1511   form in requests, even though HTTP/1.1 clients will only generate
1512   them in requests to proxies.
1513</t>
1514<t>
1515   The authority form is only used by the CONNECT method (&CONNECT;).
1516</t>
1517<t>
1518   The most common form of Request-URI is that used to identify a
1519   resource on an origin server or gateway. In this case the absolute
1520   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1521   the Request-URI, and the network location of the URI (authority) &MUST;
1522   be transmitted in a Host header field. For example, a client wishing
1523   to retrieve the resource above directly from the origin server would
1524   create a TCP connection to port 80 of the host "www.example.org" and send
1525   the lines:
1526</t>
1527<figure><artwork type="example">
1528    GET /pub/WWW/TheProject.html HTTP/1.1
1529    Host: www.example.org
1530</artwork></figure>
1531<t>
1532   followed by the remainder of the Request. Note that the absolute path
1533   cannot be empty; if none is present in the original URI, it &MUST; be
1534   given as "/" (the server root).
1535</t>
1536<t>
1537   The Request-URI is transmitted in the format specified in
1538   <xref target="http.uri"/>. If the Request-URI is encoded using the
1539   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1540   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1541   &MUST; decode the Request-URI in order to
1542   properly interpret the request. Servers &SHOULD; respond to invalid
1543   Request-URIs with an appropriate status code.
1544</t>
1545<t>
1546   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1547   received Request-URI when forwarding it to the next inbound server,
1548   except as noted above to replace a null path-absolute with "/".
1549</t>
1550<t>
1551  <list><t>
1552      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1553      meaning of the request when the origin server is improperly using
1554      a non-reserved URI character for a reserved purpose.  Implementors
1555      should be aware that some pre-HTTP/1.1 proxies have been known to
1556      rewrite the Request-URI.
1557  </t></list>
1558</t>
1559</section>
1560</section>
1561
1562<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1563<t>
1564   The exact resource identified by an Internet request is determined by
1565   examining both the Request-URI and the Host header field.
1566</t>
1567<t>
1568   An origin server that does not allow resources to differ by the
1569   requested host &MAY; ignore the Host header field value when
1570   determining the resource identified by an HTTP/1.1 request. (But see
1571   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1572   for other requirements on Host support in HTTP/1.1.)
1573</t>
1574<t>
1575   An origin server that does differentiate resources based on the host
1576   requested (sometimes referred to as virtual hosts or vanity host
1577   names) &MUST; use the following rules for determining the requested
1578   resource on an HTTP/1.1 request:
1579  <list style="numbers">
1580    <t>If Request-URI is an absolute-URI, the host is part of the
1581     Request-URI. Any Host header field value in the request &MUST; be
1582     ignored.</t>
1583    <t>If the Request-URI is not an absolute-URI, and the request includes
1584     a Host header field, the host is determined by the Host header
1585     field value.</t>
1586    <t>If the host as determined by rule 1 or 2 is not a valid host on
1587     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1588  </list>
1589</t>
1590<t>
1591   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1592   attempt to use heuristics (e.g., examination of the URI path for
1593   something unique to a particular host) in order to determine what
1594   exact resource is being requested.
1595</t>
1596</section>
1597
1598</section>
1599
1600
1601<section title="Response" anchor="response">
1602  <x:anchor-alias value="Response"/>
1603<t>
1604   After receiving and interpreting a request message, a server responds
1605   with an HTTP response message.
1606</t>
1607<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1608  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1609                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1610                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1611                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1612                  <x:ref>CRLF</x:ref>
1613                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1614</artwork></figure>
1615
1616<section title="Status-Line" anchor="status-line">
1617  <x:anchor-alias value="Status-Line"/>
1618<t>
1619   The first line of a Response message is the Status-Line, consisting
1620   of the protocol version followed by a numeric status code and its
1621   associated textual phrase, with each element separated by SP
1622   characters. No CR or LF is allowed except in the final CRLF sequence.
1623</t>
1624<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1625  <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>
1626</artwork></figure>
1627
1628<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1629  <x:anchor-alias value="Reason-Phrase"/>
1630  <x:anchor-alias value="Status-Code"/>
1631<t>
1632   The Status-Code element is a 3-digit integer result code of the
1633   attempt to understand and satisfy the request. These codes are fully
1634   defined in &status-codes;.  The Reason Phrase exists for the sole
1635   purpose of providing a textual description associated with the numeric
1636   status code, out of deference to earlier Internet application protocols
1637   that were more frequently used with interactive text clients.
1638   A client &SHOULD; ignore the content of the Reason Phrase.
1639</t>
1640<t>
1641   The first digit of the Status-Code defines the class of response. The
1642   last two digits do not have any categorization role. There are 5
1643   values for the first digit:
1644  <list style="symbols">
1645    <t>
1646      1xx: Informational - Request received, continuing process
1647    </t>
1648    <t>
1649      2xx: Success - The action was successfully received,
1650        understood, and accepted
1651    </t>
1652    <t>
1653      3xx: Redirection - Further action must be taken in order to
1654        complete the request
1655    </t>
1656    <t>
1657      4xx: Client Error - The request contains bad syntax or cannot
1658        be fulfilled
1659    </t>
1660    <t>
1661      5xx: Server Error - The server failed to fulfill an apparently
1662        valid request
1663    </t>
1664  </list>
1665</t>
1666<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"/>
1667  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1668  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1669</artwork></figure>
1670</section>
1671</section>
1672
1673</section>
1674
1675
1676<section title="Connections" anchor="connections">
1677
1678<section title="Persistent Connections" anchor="persistent.connections">
1679
1680<section title="Purpose" anchor="persistent.purpose">
1681<t>
1682   Prior to persistent connections, a separate TCP connection was
1683   established to fetch each URL, increasing the load on HTTP servers
1684   and causing congestion on the Internet. The use of inline images and
1685   other associated data often require a client to make multiple
1686   requests of the same server in a short amount of time. Analysis of
1687   these performance problems and results from a prototype
1688   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1689   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1690   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1691   T/TCP <xref target="Tou1998"/>.
1692</t>
1693<t>
1694   Persistent HTTP connections have a number of advantages:
1695  <list style="symbols">
1696      <t>
1697        By opening and closing fewer TCP connections, CPU time is saved
1698        in routers and hosts (clients, servers, proxies, gateways,
1699        tunnels, or caches), and memory used for TCP protocol control
1700        blocks can be saved in hosts.
1701      </t>
1702      <t>
1703        HTTP requests and responses can be pipelined on a connection.
1704        Pipelining allows a client to make multiple requests without
1705        waiting for each response, allowing a single TCP connection to
1706        be used much more efficiently, with much lower elapsed time.
1707      </t>
1708      <t>
1709        Network congestion is reduced by reducing the number of packets
1710        caused by TCP opens, and by allowing TCP sufficient time to
1711        determine the congestion state of the network.
1712      </t>
1713      <t>
1714        Latency on subsequent requests is reduced since there is no time
1715        spent in TCP's connection opening handshake.
1716      </t>
1717      <t>
1718        HTTP can evolve more gracefully, since errors can be reported
1719        without the penalty of closing the TCP connection. Clients using
1720        future versions of HTTP might optimistically try a new feature,
1721        but if communicating with an older server, retry with old
1722        semantics after an error is reported.
1723      </t>
1724    </list>
1725</t>
1726<t>
1727   HTTP implementations &SHOULD; implement persistent connections.
1728</t>
1729</section>
1730
1731<section title="Overall Operation" anchor="persistent.overall">
1732<t>
1733   A significant difference between HTTP/1.1 and earlier versions of
1734   HTTP is that persistent connections are the default behavior of any
1735   HTTP connection. That is, unless otherwise indicated, the client
1736   &SHOULD; assume that the server will maintain a persistent connection,
1737   even after error responses from the server.
1738</t>
1739<t>
1740   Persistent connections provide a mechanism by which a client and a
1741   server can signal the close of a TCP connection. This signaling takes
1742   place using the Connection header field (<xref target="header.connection"/>). Once a close
1743   has been signaled, the client &MUST-NOT; send any more requests on that
1744   connection.
1745</t>
1746
1747<section title="Negotiation" anchor="persistent.negotiation">
1748<t>
1749   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1750   maintain a persistent connection unless a Connection header including
1751   the connection-token "close" was sent in the request. If the server
1752   chooses to close the connection immediately after sending the
1753   response, it &SHOULD; send a Connection header including the
1754   connection-token close.
1755</t>
1756<t>
1757   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1758   decide to keep it open based on whether the response from a server
1759   contains a Connection header with the connection-token close. In case
1760   the client does not want to maintain a connection for more than that
1761   request, it &SHOULD; send a Connection header including the
1762   connection-token close.
1763</t>
1764<t>
1765   If either the client or the server sends the close token in the
1766   Connection header, that request becomes the last one for the
1767   connection.
1768</t>
1769<t>
1770   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1771   maintained for HTTP versions less than 1.1 unless it is explicitly
1772   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1773   compatibility with HTTP/1.0 clients.
1774</t>
1775<t>
1776   In order to remain persistent, all messages on the connection &MUST;
1777   have a self-defined message length (i.e., one not defined by closure
1778   of the connection), as described in <xref target="message.length"/>.
1779</t>
1780</section>
1781
1782<section title="Pipelining" anchor="pipelining">
1783<t>
1784   A client that supports persistent connections &MAY; "pipeline" its
1785   requests (i.e., send multiple requests without waiting for each
1786   response). A server &MUST; send its responses to those requests in the
1787   same order that the requests were received.
1788</t>
1789<t>
1790   Clients which assume persistent connections and pipeline immediately
1791   after connection establishment &SHOULD; be prepared to retry their
1792   connection if the first pipelined attempt fails. If a client does
1793   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1794   persistent. Clients &MUST; also be prepared to resend their requests if
1795   the server closes the connection before sending all of the
1796   corresponding responses.
1797</t>
1798<t>
1799   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1800   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1801   premature termination of the transport connection could lead to
1802   indeterminate results. A client wishing to send a non-idempotent
1803   request &SHOULD; wait to send that request until it has received the
1804   response status for the previous request.
1805</t>
1806</section>
1807</section>
1808
1809<section title="Proxy Servers" anchor="persistent.proxy">
1810<t>
1811   It is especially important that proxies correctly implement the
1812   properties of the Connection header field as specified in <xref target="header.connection"/>.
1813</t>
1814<t>
1815   The proxy server &MUST; signal persistent connections separately with
1816   its clients and the origin servers (or other proxy servers) that it
1817   connects to. Each persistent connection applies to only one transport
1818   link.
1819</t>
1820<t>
1821   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1822   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1823   discussion of the problems with the Keep-Alive header implemented by
1824   many HTTP/1.0 clients).
1825</t>
1826</section>
1827
1828<section title="Practical Considerations" anchor="persistent.practical">
1829<t>
1830   Servers will usually have some time-out value beyond which they will
1831   no longer maintain an inactive connection. Proxy servers might make
1832   this a higher value since it is likely that the client will be making
1833   more connections through the same server. The use of persistent
1834   connections places no requirements on the length (or existence) of
1835   this time-out for either the client or the server.
1836</t>
1837<t>
1838   When a client or server wishes to time-out it &SHOULD; issue a graceful
1839   close on the transport connection. Clients and servers &SHOULD; both
1840   constantly watch for the other side of the transport close, and
1841   respond to it as appropriate. If a client or server does not detect
1842   the other side's close promptly it could cause unnecessary resource
1843   drain on the network.
1844</t>
1845<t>
1846   A client, server, or proxy &MAY; close the transport connection at any
1847   time. For example, a client might have started to send a new request
1848   at the same time that the server has decided to close the "idle"
1849   connection. From the server's point of view, the connection is being
1850   closed while it was idle, but from the client's point of view, a
1851   request is in progress.
1852</t>
1853<t>
1854   This means that clients, servers, and proxies &MUST; be able to recover
1855   from asynchronous close events. Client software &SHOULD; reopen the
1856   transport connection and retransmit the aborted sequence of requests
1857   without user interaction so long as the request sequence is
1858   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1859   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1860   human operator the choice of retrying the request(s). Confirmation by
1861   user-agent software with semantic understanding of the application
1862   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1863   be repeated if the second sequence of requests fails.
1864</t>
1865<t>
1866   Servers &SHOULD; always respond to at least one request per connection,
1867   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1868   middle of transmitting a response, unless a network or client failure
1869   is suspected.
1870</t>
1871<t>
1872   Clients that use persistent connections &SHOULD; limit the number of
1873   simultaneous connections that they maintain to a given server. A
1874   single-user client &SHOULD-NOT; maintain more than 2 connections with
1875   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1876   another server or proxy, where N is the number of simultaneously
1877   active users. These guidelines are intended to improve HTTP response
1878   times and avoid congestion.
1879</t>
1880</section>
1881</section>
1882
1883<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1884
1885<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1886<t>
1887   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1888   flow control mechanisms to resolve temporary overloads, rather than
1889   terminating connections with the expectation that clients will retry.
1890   The latter technique can exacerbate network congestion.
1891</t>
1892</section>
1893
1894<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1895<t>
1896   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1897   the network connection for an error status while it is transmitting
1898   the request. If the client sees an error status, it &SHOULD;
1899   immediately cease transmitting the body. If the body is being sent
1900   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1901   empty trailer &MAY; be used to prematurely mark the end of the message.
1902   If the body was preceded by a Content-Length header, the client &MUST;
1903   close the connection.
1904</t>
1905</section>
1906
1907<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1908<t>
1909   The purpose of the 100 (Continue) status (see &status-100;) is to
1910   allow a client that is sending a request message with a request body
1911   to determine if the origin server is willing to accept the request
1912   (based on the request headers) before the client sends the request
1913   body. In some cases, it might either be inappropriate or highly
1914   inefficient for the client to send the body if the server will reject
1915   the message without looking at the body.
1916</t>
1917<t>
1918   Requirements for HTTP/1.1 clients:
1919  <list style="symbols">
1920    <t>
1921        If a client will wait for a 100 (Continue) response before
1922        sending the request body, it &MUST; send an Expect request-header
1923        field (&header-expect;) with the "100-continue" expectation.
1924    </t>
1925    <t>
1926        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1927        with the "100-continue" expectation if it does not intend
1928        to send a request body.
1929    </t>
1930  </list>
1931</t>
1932<t>
1933   Because of the presence of older implementations, the protocol allows
1934   ambiguous situations in which a client may send "Expect: 100-continue"
1935   without receiving either a 417 (Expectation Failed) status
1936   or a 100 (Continue) status. Therefore, when a client sends this
1937   header field to an origin server (possibly via a proxy) from which it
1938   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1939   for an indefinite period before sending the request body.
1940</t>
1941<t>
1942   Requirements for HTTP/1.1 origin servers:
1943  <list style="symbols">
1944    <t> Upon receiving a request which includes an Expect request-header
1945        field with the "100-continue" expectation, an origin server &MUST;
1946        either respond with 100 (Continue) status and continue to read
1947        from the input stream, or respond with a final status code. The
1948        origin server &MUST-NOT; wait for the request body before sending
1949        the 100 (Continue) response. If it responds with a final status
1950        code, it &MAY; close the transport connection or it &MAY; continue
1951        to read and discard the rest of the request.  It &MUST-NOT;
1952        perform the requested method if it returns a final status code.
1953    </t>
1954    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1955        the request message does not include an Expect request-header
1956        field with the "100-continue" expectation, and &MUST-NOT; send a
1957        100 (Continue) response if such a request comes from an HTTP/1.0
1958        (or earlier) client. There is an exception to this rule: for
1959        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1960        status in response to an HTTP/1.1 PUT or POST request that does
1961        not include an Expect request-header field with the "100-continue"
1962        expectation. This exception, the purpose of which is
1963        to minimize any client processing delays associated with an
1964        undeclared wait for 100 (Continue) status, applies only to
1965        HTTP/1.1 requests, and not to requests with any other HTTP-version
1966        value.
1967    </t>
1968    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1969        already received some or all of the request body for the
1970        corresponding request.
1971    </t>
1972    <t> An origin server that sends a 100 (Continue) response &MUST;
1973    ultimately send a final status code, once the request body is
1974        received and processed, unless it terminates the transport
1975        connection prematurely.
1976    </t>
1977    <t> If an origin server receives a request that does not include an
1978        Expect request-header field with the "100-continue" expectation,
1979        the request includes a request body, and the server responds
1980        with a final status code before reading the entire request body
1981        from the transport connection, then the server &SHOULD-NOT;  close
1982        the transport connection until it has read the entire request,
1983        or until the client closes the connection. Otherwise, the client
1984        might not reliably receive the response message. However, this
1985        requirement is not be construed as preventing a server from
1986        defending itself against denial-of-service attacks, or from
1987        badly broken client implementations.
1988      </t>
1989    </list>
1990</t>
1991<t>
1992   Requirements for HTTP/1.1 proxies:
1993  <list style="symbols">
1994    <t> If a proxy receives a request that includes an Expect request-header
1995        field with the "100-continue" expectation, and the proxy
1996        either knows that the next-hop server complies with HTTP/1.1 or
1997        higher, or does not know the HTTP version of the next-hop
1998        server, it &MUST; forward the request, including the Expect header
1999        field.
2000    </t>
2001    <t> If the proxy knows that the version of the next-hop server is
2002        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2003        respond with a 417 (Expectation Failed) status.
2004    </t>
2005    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2006        numbers received from recently-referenced next-hop servers.
2007    </t>
2008    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2009        request message was received from an HTTP/1.0 (or earlier)
2010        client and did not include an Expect request-header field with
2011        the "100-continue" expectation. This requirement overrides the
2012        general rule for forwarding of 1xx responses (see &status-1xx;).
2013    </t>
2014  </list>
2015</t>
2016</section>
2017
2018<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2019<t>
2020   If an HTTP/1.1 client sends a request which includes a request body,
2021   but which does not include an Expect request-header field with the
2022   "100-continue" expectation, and if the client is not directly
2023   connected to an HTTP/1.1 origin server, and if the client sees the
2024   connection close before receiving any status from the server, the
2025   client &SHOULD; retry the request.  If the client does retry this
2026   request, it &MAY; use the following "binary exponential backoff"
2027   algorithm to be assured of obtaining a reliable response:
2028  <list style="numbers">
2029    <t>
2030      Initiate a new connection to the server
2031    </t>
2032    <t>
2033      Transmit the request-headers
2034    </t>
2035    <t>
2036      Initialize a variable R to the estimated round-trip time to the
2037         server (e.g., based on the time it took to establish the
2038         connection), or to a constant value of 5 seconds if the round-trip
2039         time is not available.
2040    </t>
2041    <t>
2042       Compute T = R * (2**N), where N is the number of previous
2043         retries of this request.
2044    </t>
2045    <t>
2046       Wait either for an error response from the server, or for T
2047         seconds (whichever comes first)
2048    </t>
2049    <t>
2050       If no error response is received, after T seconds transmit the
2051         body of the request.
2052    </t>
2053    <t>
2054       If client sees that the connection is closed prematurely,
2055         repeat from step 1 until the request is accepted, an error
2056         response is received, or the user becomes impatient and
2057         terminates the retry process.
2058    </t>
2059  </list>
2060</t>
2061<t>
2062   If at any point an error status is received, the client
2063  <list style="symbols">
2064      <t>&SHOULD-NOT;  continue and</t>
2065
2066      <t>&SHOULD; close the connection if it has not completed sending the
2067        request message.</t>
2068    </list>
2069</t>
2070</section>
2071</section>
2072</section>
2073
2074
2075<section title="Header Field Definitions" anchor="header.fields">
2076<t>
2077   This section defines the syntax and semantics of HTTP/1.1 header fields
2078   related to message framing and transport protocols.
2079</t>
2080<t>
2081   For entity-header fields, both sender and recipient refer to either the
2082   client or the server, depending on who sends and who receives the entity.
2083</t>
2084
2085<section title="Connection" anchor="header.connection">
2086  <iref primary="true" item="Connection header" x:for-anchor=""/>
2087  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2088  <x:anchor-alias value="Connection"/>
2089  <x:anchor-alias value="connection-token"/>
2090<t>
2091   The Connection general-header field allows the sender to specify
2092   options that are desired for that particular connection and &MUST-NOT;
2093   be communicated by proxies over further connections.
2094</t>
2095<t>
2096   The Connection header has the following grammar:
2097</t>
2098<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2099  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2100  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2101</artwork></figure>
2102<t>
2103   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2104   message is forwarded and, for each connection-token in this field,
2105   remove any header field(s) from the message with the same name as the
2106   connection-token. Connection options are signaled by the presence of
2107   a connection-token in the Connection header field, not by any
2108   corresponding additional header field(s), since the additional header
2109   field may not be sent if there are no parameters associated with that
2110   connection option.
2111</t>
2112<t>
2113   Message headers listed in the Connection header &MUST-NOT; include
2114   end-to-end headers, such as Cache-Control.
2115</t>
2116<t>
2117   HTTP/1.1 defines the "close" connection option for the sender to
2118   signal that the connection will be closed after completion of the
2119   response. For example,
2120</t>
2121<figure><artwork type="example">
2122    Connection: close
2123</artwork></figure>
2124<t>
2125   in either the request or the response header fields indicates that
2126   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2127   after the current request/response is complete.
2128</t>
2129<t>
2130   An HTTP/1.1 client that does not support persistent connections &MUST;
2131   include the "close" connection option in every request message.
2132</t>
2133<t>
2134   An HTTP/1.1 server that does not support persistent connections &MUST;
2135   include the "close" connection option in every response message that
2136   does not have a 1xx (informational) status code.
2137</t>
2138<t>
2139   A system receiving an HTTP/1.0 (or lower-version) message that
2140   includes a Connection header &MUST;, for each connection-token in this
2141   field, remove and ignore any header field(s) from the message with
2142   the same name as the connection-token. This protects against mistaken
2143   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2144</t>
2145</section>
2146
2147<section title="Content-Length" anchor="header.content-length">
2148  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2149  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2150  <x:anchor-alias value="Content-Length"/>
2151<t>
2152   The Content-Length entity-header field indicates the size of the
2153   entity-body, in decimal number of OCTETs, sent to the recipient or,
2154   in the case of the HEAD method, the size of the entity-body that
2155   would have been sent had the request been a GET.
2156</t>
2157<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2158  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2159</artwork></figure>
2160<t>
2161   An example is
2162</t>
2163<figure><artwork type="example">
2164    Content-Length: 3495
2165</artwork></figure>
2166<t>
2167   Applications &SHOULD; use this field to indicate the transfer-length of
2168   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2169</t>
2170<t>
2171   Any Content-Length greater than or equal to zero is a valid value.
2172   <xref target="message.length"/> describes how to determine the length of a message-body
2173   if a Content-Length is not given.
2174</t>
2175<t>
2176   Note that the meaning of this field is significantly different from
2177   the corresponding definition in MIME, where it is an optional field
2178   used within the "message/external-body" content-type. In HTTP, it
2179   &SHOULD; be sent whenever the message's length can be determined prior
2180   to being transferred, unless this is prohibited by the rules in
2181   <xref target="message.length"/>.
2182</t>
2183</section>
2184
2185<section title="Date" anchor="header.date">
2186  <iref primary="true" item="Date header" x:for-anchor=""/>
2187  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2188  <x:anchor-alias value="Date"/>
2189<t>
2190   The Date general-header field represents the date and time at which
2191   the message was originated, having the same semantics as orig-date in
2192   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2193   HTTP-date, as described in <xref target="full.date"/>;
2194   it &MUST; be sent in rfc1123-date format.
2195</t>
2196<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2197  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2198</artwork></figure>
2199<t>
2200   An example is
2201</t>
2202<figure><artwork type="example">
2203    Date: Tue, 15 Nov 1994 08:12:31 GMT
2204</artwork></figure>
2205<t>
2206   Origin servers &MUST; include a Date header field in all responses,
2207   except in these cases:
2208  <list style="numbers">
2209      <t>If the response status code is 100 (Continue) or 101 (Switching
2210         Protocols), the response &MAY; include a Date header field, at
2211         the server's option.</t>
2212
2213      <t>If the response status code conveys a server error, e.g. 500
2214         (Internal Server Error) or 503 (Service Unavailable), and it is
2215         inconvenient or impossible to generate a valid Date.</t>
2216
2217      <t>If the server does not have a clock that can provide a
2218         reasonable approximation of the current time, its responses
2219         &MUST-NOT; include a Date header field. In this case, the rules
2220         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2221  </list>
2222</t>
2223<t>
2224   A received message that does not have a Date header field &MUST; be
2225   assigned one by the recipient if the message will be cached by that
2226   recipient or gatewayed via a protocol which requires a Date. An HTTP
2227   implementation without a clock &MUST-NOT; cache responses without
2228   revalidating them on every use. An HTTP cache, especially a shared
2229   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2230   clock with a reliable external standard.
2231</t>
2232<t>
2233   Clients &SHOULD; only send a Date header field in messages that include
2234   an entity-body, as in the case of the PUT and POST requests, and even
2235   then it is optional. A client without a clock &MUST-NOT; send a Date
2236   header field in a request.
2237</t>
2238<t>
2239   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2240   time subsequent to the generation of the message. It &SHOULD; represent
2241   the best available approximation of the date and time of message
2242   generation, unless the implementation has no means of generating a
2243   reasonably accurate date and time. In theory, the date ought to
2244   represent the moment just before the entity is generated. In
2245   practice, the date can be generated at any time during the message
2246   origination without affecting its semantic value.
2247</t>
2248
2249<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2250<t>
2251   Some origin server implementations might not have a clock available.
2252   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2253   values to a response, unless these values were associated
2254   with the resource by a system or user with a reliable clock. It &MAY;
2255   assign an Expires value that is known, at or before server
2256   configuration time, to be in the past (this allows "pre-expiration"
2257   of responses without storing separate Expires values for each
2258   resource).
2259</t>
2260</section>
2261</section>
2262
2263<section title="Host" anchor="header.host">
2264  <iref primary="true" item="Host header" x:for-anchor=""/>
2265  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2266  <x:anchor-alias value="Host"/>
2267<t>
2268   The Host request-header field specifies the Internet host and port
2269   number of the resource being requested, as obtained from the original
2270   URI given by the user or referring resource (generally an http URI,
2271   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2272   the naming authority of the origin server or gateway given by the
2273   original URL. This allows the origin server or gateway to
2274   differentiate between internally-ambiguous URLs, such as the root "/"
2275   URL of a server for multiple host names on a single IP address.
2276</t>
2277<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2278  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2279</artwork></figure>
2280<t>
2281   A "host" without any trailing port information implies the default
2282   port for the service requested (e.g., "80" for an HTTP URL). For
2283   example, a request on the origin server for
2284   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2285</t>
2286<figure><artwork type="example">
2287    GET /pub/WWW/ HTTP/1.1
2288    Host: www.example.org
2289</artwork></figure>
2290<t>
2291   A client &MUST; include a Host header field in all HTTP/1.1 request
2292   messages. If the requested URI does not include an Internet host
2293   name for the service being requested, then the Host header field &MUST;
2294   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2295   request message it forwards does contain an appropriate Host header
2296   field that identifies the service being requested by the proxy. All
2297   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2298   status code to any HTTP/1.1 request message which lacks a Host header
2299   field.
2300</t>
2301<t>
2302   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2303   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2304   for other requirements relating to Host.
2305</t>
2306</section>
2307
2308<section title="TE" anchor="header.te">
2309  <iref primary="true" item="TE header" x:for-anchor=""/>
2310  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2311  <x:anchor-alias value="TE"/>
2312  <x:anchor-alias value="t-codings"/>
2313<t>
2314   The TE request-header field indicates what extension transfer-codings
2315   it is willing to accept in the response and whether or not it is
2316   willing to accept trailer fields in a chunked transfer-coding. Its
2317   value may consist of the keyword "trailers" and/or a comma-separated
2318   list of extension transfer-coding names with optional accept
2319   parameters (as described in <xref target="transfer.codings"/>).
2320</t>
2321<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2322  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2323  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2324</artwork></figure>
2325<t>
2326   The presence of the keyword "trailers" indicates that the client is
2327   willing to accept trailer fields in a chunked transfer-coding, as
2328   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2329   transfer-coding values even though it does not itself represent a
2330   transfer-coding.
2331</t>
2332<t>
2333   Examples of its use are:
2334</t>
2335<figure><artwork type="example">
2336    TE: deflate
2337    TE:
2338    TE: trailers, deflate;q=0.5
2339</artwork></figure>
2340<t>
2341   The TE header field only applies to the immediate connection.
2342   Therefore, the keyword &MUST; be supplied within a Connection header
2343   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2344</t>
2345<t>
2346   A server tests whether a transfer-coding is acceptable, according to
2347   a TE field, using these rules:
2348  <list style="numbers">
2349    <x:lt>
2350      <t>The "chunked" transfer-coding is always acceptable. If the
2351         keyword "trailers" is listed, the client indicates that it is
2352         willing to accept trailer fields in the chunked response on
2353         behalf of itself and any downstream clients. The implication is
2354         that, if given, the client is stating that either all
2355         downstream clients are willing to accept trailer fields in the
2356         forwarded response, or that it will attempt to buffer the
2357         response on behalf of downstream recipients.
2358      </t><t>
2359         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2360         chunked response such that a client can be assured of buffering
2361         the entire response.</t>
2362    </x:lt>
2363    <x:lt>
2364      <t>If the transfer-coding being tested is one of the transfer-codings
2365         listed in the TE field, then it is acceptable unless it
2366         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2367         qvalue of 0 means "not acceptable.")</t>
2368    </x:lt>
2369    <x:lt>
2370      <t>If multiple transfer-codings are acceptable, then the
2371         acceptable transfer-coding with the highest non-zero qvalue is
2372         preferred.  The "chunked" transfer-coding always has a qvalue
2373         of 1.</t>
2374    </x:lt>
2375  </list>
2376</t>
2377<t>
2378   If the TE field-value is empty or if no TE field is present, the only
2379   transfer-coding  is "chunked". A message with no transfer-coding is
2380   always acceptable.
2381</t>
2382</section>
2383
2384<section title="Trailer" anchor="header.trailer">
2385  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2386  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2387  <x:anchor-alias value="Trailer"/>
2388<t>
2389   The Trailer general field value indicates that the given set of
2390   header fields is present in the trailer of a message encoded with
2391   chunked transfer-coding.
2392</t>
2393<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2394  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2395</artwork></figure>
2396<t>
2397   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2398   message using chunked transfer-coding with a non-empty trailer. Doing
2399   so allows the recipient to know which header fields to expect in the
2400   trailer.
2401</t>
2402<t>
2403   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2404   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2405   trailer fields in a "chunked" transfer-coding.
2406</t>
2407<t>
2408   Message header fields listed in the Trailer header field &MUST-NOT;
2409   include the following header fields:
2410  <list style="symbols">
2411    <t>Transfer-Encoding</t>
2412    <t>Content-Length</t>
2413    <t>Trailer</t>
2414  </list>
2415</t>
2416</section>
2417
2418<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2419  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2420  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2421  <x:anchor-alias value="Transfer-Encoding"/>
2422<t>
2423   The Transfer-Encoding general-header field indicates what (if any)
2424   type of transformation has been applied to the message body in order
2425   to safely transfer it between the sender and the recipient. This
2426   differs from the content-coding in that the transfer-coding is a
2427   property of the message, not of the entity.
2428</t>
2429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2430  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2431</artwork></figure>
2432<t>
2433   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2434</t>
2435<figure><artwork type="example">
2436  Transfer-Encoding: chunked
2437</artwork></figure>
2438<t>
2439   If multiple encodings have been applied to an entity, the transfer-codings
2440   &MUST; be listed in the order in which they were applied.
2441   Additional information about the encoding parameters &MAY; be provided
2442   by other entity-header fields not defined by this specification.
2443</t>
2444<t>
2445   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2446   header.
2447</t>
2448</section>
2449
2450<section title="Upgrade" anchor="header.upgrade">
2451  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2452  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2453  <x:anchor-alias value="Upgrade"/>
2454<t>
2455   The Upgrade general-header allows the client to specify what
2456   additional communication protocols it supports and would like to use
2457   if the server finds it appropriate to switch protocols. The server
2458   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2459   response to indicate which protocol(s) are being switched.
2460</t>
2461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2462  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2463</artwork></figure>
2464<t>
2465   For example,
2466</t>
2467<figure><artwork type="example">
2468    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2469</artwork></figure>
2470<t>
2471   The Upgrade header field is intended to provide a simple mechanism
2472   for transition from HTTP/1.1 to some other, incompatible protocol. It
2473   does so by allowing the client to advertise its desire to use another
2474   protocol, such as a later version of HTTP with a higher major version
2475   number, even though the current request has been made using HTTP/1.1.
2476   This eases the difficult transition between incompatible protocols by
2477   allowing the client to initiate a request in the more commonly
2478   supported protocol while indicating to the server that it would like
2479   to use a "better" protocol if available (where "better" is determined
2480   by the server, possibly according to the nature of the method and/or
2481   resource being requested).
2482</t>
2483<t>
2484   The Upgrade header field only applies to switching application-layer
2485   protocols upon the existing transport-layer connection. Upgrade
2486   cannot be used to insist on a protocol change; its acceptance and use
2487   by the server is optional. The capabilities and nature of the
2488   application-layer communication after the protocol change is entirely
2489   dependent upon the new protocol chosen, although the first action
2490   after changing the protocol &MUST; be a response to the initial HTTP
2491   request containing the Upgrade header field.
2492</t>
2493<t>
2494   The Upgrade header field only applies to the immediate connection.
2495   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2496   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2497   HTTP/1.1 message.
2498</t>
2499<t>
2500   The Upgrade header field cannot be used to indicate a switch to a
2501   protocol on a different connection. For that purpose, it is more
2502   appropriate to use a 301, 302, 303, or 305 redirection response.
2503</t>
2504<t>
2505   This specification only defines the protocol name "HTTP" for use by
2506   the family of Hypertext Transfer Protocols, as defined by the HTTP
2507   version rules of <xref target="http.version"/> and future updates to this
2508   specification. Any token can be used as a protocol name; however, it
2509   will only be useful if both the client and server associate the name
2510   with the same protocol.
2511</t>
2512</section>
2513
2514<section title="Via" anchor="header.via">
2515  <iref primary="true" item="Via header" x:for-anchor=""/>
2516  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2517  <x:anchor-alias value="protocol-name"/>
2518  <x:anchor-alias value="protocol-version"/>
2519  <x:anchor-alias value="pseudonym"/>
2520  <x:anchor-alias value="received-by"/>
2521  <x:anchor-alias value="received-protocol"/>
2522  <x:anchor-alias value="Via"/>
2523<t>
2524   The Via general-header field &MUST; be used by gateways and proxies to
2525   indicate the intermediate protocols and recipients between the user
2526   agent and the server on requests, and between the origin server and
2527   the client on responses. It is analogous to the "Received" field defined in
2528   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2529   avoiding request loops, and identifying the protocol capabilities of
2530   all senders along the request/response chain.
2531</t>
2532<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"/>
2533  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2534  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2535  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2536  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2537  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2538  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2539</artwork></figure>
2540<t>
2541   The received-protocol indicates the protocol version of the message
2542   received by the server or client along each segment of the
2543   request/response chain. The received-protocol version is appended to
2544   the Via field value when the message is forwarded so that information
2545   about the protocol capabilities of upstream applications remains
2546   visible to all recipients.
2547</t>
2548<t>
2549   The protocol-name is optional if and only if it would be "HTTP". The
2550   received-by field is normally the host and optional port number of a
2551   recipient server or client that subsequently forwarded the message.
2552   However, if the real host is considered to be sensitive information,
2553   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2554   be assumed to be the default port of the received-protocol.
2555</t>
2556<t>
2557   Multiple Via field values represents each proxy or gateway that has
2558   forwarded the message. Each recipient &MUST; append its information
2559   such that the end result is ordered according to the sequence of
2560   forwarding applications.
2561</t>
2562<t>
2563   Comments &MAY; be used in the Via header field to identify the software
2564   of the recipient proxy or gateway, analogous to the User-Agent and
2565   Server header fields. However, all comments in the Via field are
2566   optional and &MAY; be removed by any recipient prior to forwarding the
2567   message.
2568</t>
2569<t>
2570   For example, a request message could be sent from an HTTP/1.0 user
2571   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2572   forward the request to a public proxy at p.example.net, which completes
2573   the request by forwarding it to the origin server at www.example.com.
2574   The request received by www.example.com would then have the following
2575   Via header field:
2576</t>
2577<figure><artwork type="example">
2578    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2579</artwork></figure>
2580<t>
2581   Proxies and gateways used as a portal through a network firewall
2582   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2583   the firewall region. This information &SHOULD; only be propagated if
2584   explicitly enabled. If not enabled, the received-by host of any host
2585   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2586   for that host.
2587</t>
2588<t>
2589   For organizations that have strong privacy requirements for hiding
2590   internal structures, a proxy &MAY; combine an ordered subsequence of
2591   Via header field entries with identical received-protocol values into
2592   a single such entry. For example,
2593</t>
2594<figure><artwork type="example">
2595    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2596</artwork></figure>
2597<t>
2598        could be collapsed to
2599</t>
2600<figure><artwork type="example">
2601    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2602</artwork></figure>
2603<t>
2604   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2605   under the same organizational control and the hosts have already been
2606   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2607   have different received-protocol values.
2608</t>
2609</section>
2610
2611</section>
2612
2613<section title="IANA Considerations" anchor="IANA.considerations">
2614<section title="Message Header Registration" anchor="message.header.registration">
2615<t>
2616   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2617   with the permanent registrations below (see <xref target="RFC3864"/>):
2618</t>
2619<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2620<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2621   <ttcol>Header Field Name</ttcol>
2622   <ttcol>Protocol</ttcol>
2623   <ttcol>Status</ttcol>
2624   <ttcol>Reference</ttcol>
2625
2626   <c>Connection</c>
2627   <c>http</c>
2628   <c>standard</c>
2629   <c>
2630      <xref target="header.connection"/>
2631   </c>
2632   <c>Content-Length</c>
2633   <c>http</c>
2634   <c>standard</c>
2635   <c>
2636      <xref target="header.content-length"/>
2637   </c>
2638   <c>Date</c>
2639   <c>http</c>
2640   <c>standard</c>
2641   <c>
2642      <xref target="header.date"/>
2643   </c>
2644   <c>Host</c>
2645   <c>http</c>
2646   <c>standard</c>
2647   <c>
2648      <xref target="header.host"/>
2649   </c>
2650   <c>TE</c>
2651   <c>http</c>
2652   <c>standard</c>
2653   <c>
2654      <xref target="header.te"/>
2655   </c>
2656   <c>Trailer</c>
2657   <c>http</c>
2658   <c>standard</c>
2659   <c>
2660      <xref target="header.trailer"/>
2661   </c>
2662   <c>Transfer-Encoding</c>
2663   <c>http</c>
2664   <c>standard</c>
2665   <c>
2666      <xref target="header.transfer-encoding"/>
2667   </c>
2668   <c>Upgrade</c>
2669   <c>http</c>
2670   <c>standard</c>
2671   <c>
2672      <xref target="header.upgrade"/>
2673   </c>
2674   <c>Via</c>
2675   <c>http</c>
2676   <c>standard</c>
2677   <c>
2678      <xref target="header.via"/>
2679   </c>
2680</texttable>
2681<!--(END)-->
2682<t>
2683   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2684</t>
2685</section>
2686
2687<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2688<t>
2689   The entry for the "http" URI Scheme in the registry located at
2690   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2691   should be updated to point to <xref target="http.uri"/> of this document
2692   (see <xref target="RFC4395"/>).
2693</t>
2694</section>
2695
2696<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2697<t>
2698   This document serves as the specification for the Internet media types
2699   "message/http" and "application/http". The following is to be registered with
2700   IANA (see <xref target="RFC4288"/>).
2701</t>
2702<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2703<iref item="Media Type" subitem="message/http" primary="true"/>
2704<iref item="message/http Media Type" primary="true"/>
2705<t>
2706   The message/http type can be used to enclose a single HTTP request or
2707   response message, provided that it obeys the MIME restrictions for all
2708   "message" types regarding line length and encodings.
2709</t>
2710<t>
2711  <list style="hanging" x:indent="12em">
2712    <t hangText="Type name:">
2713      message
2714    </t>
2715    <t hangText="Subtype name:">
2716      http
2717    </t>
2718    <t hangText="Required parameters:">
2719      none
2720    </t>
2721    <t hangText="Optional parameters:">
2722      version, msgtype
2723      <list style="hanging">
2724        <t hangText="version:">
2725          The HTTP-Version number of the enclosed message
2726          (e.g., "1.1"). If not present, the version can be
2727          determined from the first line of the body.
2728        </t>
2729        <t hangText="msgtype:">
2730          The message type -- "request" or "response". If not
2731          present, the type can be determined from the first
2732          line of the body.
2733        </t>
2734      </list>
2735    </t>
2736    <t hangText="Encoding considerations:">
2737      only "7bit", "8bit", or "binary" are permitted
2738    </t>
2739    <t hangText="Security considerations:">
2740      none
2741    </t>
2742    <t hangText="Interoperability considerations:">
2743      none
2744    </t>
2745    <t hangText="Published specification:">
2746      This specification (see <xref target="internet.media.type.message.http"/>).
2747    </t>
2748    <t hangText="Applications that use this media type:">
2749    </t>
2750    <t hangText="Additional information:">
2751      <list style="hanging">
2752        <t hangText="Magic number(s):">none</t>
2753        <t hangText="File extension(s):">none</t>
2754        <t hangText="Macintosh file type code(s):">none</t>
2755      </list>
2756    </t>
2757    <t hangText="Person and email address to contact for further information:">
2758      See Authors Section.
2759    </t>
2760                <t hangText="Intended usage:">
2761                  COMMON
2762    </t>
2763                <t hangText="Restrictions on usage:">
2764                  none
2765    </t>
2766    <t hangText="Author/Change controller:">
2767      IESG
2768    </t>
2769  </list>
2770</t>
2771</section>
2772<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2773<iref item="Media Type" subitem="application/http" primary="true"/>
2774<iref item="application/http Media Type" primary="true"/>
2775<t>
2776   The application/http type can be used to enclose a pipeline of one or more
2777   HTTP request or response messages (not intermixed).
2778</t>
2779<t>
2780  <list style="hanging" x:indent="12em">
2781    <t hangText="Type name:">
2782      application
2783    </t>
2784    <t hangText="Subtype name:">
2785      http
2786    </t>
2787    <t hangText="Required parameters:">
2788      none
2789    </t>
2790    <t hangText="Optional parameters:">
2791      version, msgtype
2792      <list style="hanging">
2793        <t hangText="version:">
2794          The HTTP-Version number of the enclosed messages
2795          (e.g., "1.1"). If not present, the version can be
2796          determined from the first line of the body.
2797        </t>
2798        <t hangText="msgtype:">
2799          The message type -- "request" or "response". If not
2800          present, the type can be determined from the first
2801          line of the body.
2802        </t>
2803      </list>
2804    </t>
2805    <t hangText="Encoding considerations:">
2806      HTTP messages enclosed by this type
2807      are in "binary" format; use of an appropriate
2808      Content-Transfer-Encoding is required when
2809      transmitted via E-mail.
2810    </t>
2811    <t hangText="Security considerations:">
2812      none
2813    </t>
2814    <t hangText="Interoperability considerations:">
2815      none
2816    </t>
2817    <t hangText="Published specification:">
2818      This specification (see <xref target="internet.media.type.application.http"/>).
2819    </t>
2820    <t hangText="Applications that use this media type:">
2821    </t>
2822    <t hangText="Additional information:">
2823      <list style="hanging">
2824        <t hangText="Magic number(s):">none</t>
2825        <t hangText="File extension(s):">none</t>
2826        <t hangText="Macintosh file type code(s):">none</t>
2827      </list>
2828    </t>
2829    <t hangText="Person and email address to contact for further information:">
2830      See Authors Section.
2831    </t>
2832                <t hangText="Intended usage:">
2833                  COMMON
2834    </t>
2835                <t hangText="Restrictions on usage:">
2836                  none
2837    </t>
2838    <t hangText="Author/Change controller:">
2839      IESG
2840    </t>
2841  </list>
2842</t>
2843</section>
2844</section>
2845
2846</section>
2847
2848<section title="Security Considerations" anchor="security.considerations">
2849<t>
2850   This section is meant to inform application developers, information
2851   providers, and users of the security limitations in HTTP/1.1 as
2852   described by this document. The discussion does not include
2853   definitive solutions to the problems revealed, though it does make
2854   some suggestions for reducing security risks.
2855</t>
2856
2857<section title="Personal Information" anchor="personal.information">
2858<t>
2859   HTTP clients are often privy to large amounts of personal information
2860   (e.g. the user's name, location, mail address, passwords, encryption
2861   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2862   leakage of this information.
2863   We very strongly recommend that a convenient interface be provided
2864   for the user to control dissemination of such information, and that
2865   designers and implementors be particularly careful in this area.
2866   History shows that errors in this area often create serious security
2867   and/or privacy problems and generate highly adverse publicity for the
2868   implementor's company.
2869</t>
2870</section>
2871
2872<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2873<t>
2874   A server is in the position to save personal data about a user's
2875   requests which might identify their reading patterns or subjects of
2876   interest. This information is clearly confidential in nature and its
2877   handling can be constrained by law in certain countries. People using
2878   HTTP to provide data are responsible for ensuring that
2879   such material is not distributed without the permission of any
2880   individuals that are identifiable by the published results.
2881</t>
2882</section>
2883
2884<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2885<t>
2886   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2887   the documents returned by HTTP requests to be only those that were
2888   intended by the server administrators. If an HTTP server translates
2889   HTTP URIs directly into file system calls, the server &MUST; take
2890   special care not to serve files that were not intended to be
2891   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2892   other operating systems use ".." as a path component to indicate a
2893   directory level above the current one. On such a system, an HTTP
2894   server &MUST; disallow any such construct in the Request-URI if it
2895   would otherwise allow access to a resource outside those intended to
2896   be accessible via the HTTP server. Similarly, files intended for
2897   reference only internally to the server (such as access control
2898   files, configuration files, and script code) &MUST; be protected from
2899   inappropriate retrieval, since they might contain sensitive
2900   information. Experience has shown that minor bugs in such HTTP server
2901   implementations have turned into security risks.
2902</t>
2903</section>
2904
2905<section title="DNS Spoofing" anchor="dns.spoofing">
2906<t>
2907   Clients using HTTP rely heavily on the Domain Name Service, and are
2908   thus generally prone to security attacks based on the deliberate
2909   mis-association of IP addresses and DNS names. Clients need to be
2910   cautious in assuming the continuing validity of an IP number/DNS name
2911   association.
2912</t>
2913<t>
2914   In particular, HTTP clients &SHOULD; rely on their name resolver for
2915   confirmation of an IP number/DNS name association, rather than
2916   caching the result of previous host name lookups. Many platforms
2917   already can cache host name lookups locally when appropriate, and
2918   they &SHOULD; be configured to do so. It is proper for these lookups to
2919   be cached, however, only when the TTL (Time To Live) information
2920   reported by the name server makes it likely that the cached
2921   information will remain useful.
2922</t>
2923<t>
2924   If HTTP clients cache the results of host name lookups in order to
2925   achieve a performance improvement, they &MUST; observe the TTL
2926   information reported by DNS.
2927</t>
2928<t>
2929   If HTTP clients do not observe this rule, they could be spoofed when
2930   a previously-accessed server's IP address changes. As network
2931   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2932   possibility of this form of attack will grow. Observing this
2933   requirement thus reduces this potential security vulnerability.
2934</t>
2935<t>
2936   This requirement also improves the load-balancing behavior of clients
2937   for replicated servers using the same DNS name and reduces the
2938   likelihood of a user's experiencing failure in accessing sites which
2939   use that strategy.
2940</t>
2941</section>
2942
2943<section title="Proxies and Caching" anchor="attack.proxies">
2944<t>
2945   By their very nature, HTTP proxies are men-in-the-middle, and
2946   represent an opportunity for man-in-the-middle attacks. Compromise of
2947   the systems on which the proxies run can result in serious security
2948   and privacy problems. Proxies have access to security-related
2949   information, personal information about individual users and
2950   organizations, and proprietary information belonging to users and
2951   content providers. A compromised proxy, or a proxy implemented or
2952   configured without regard to security and privacy considerations,
2953   might be used in the commission of a wide range of potential attacks.
2954</t>
2955<t>
2956   Proxy operators should protect the systems on which proxies run as
2957   they would protect any system that contains or transports sensitive
2958   information. In particular, log information gathered at proxies often
2959   contains highly sensitive personal information, and/or information
2960   about organizations. Log information should be carefully guarded, and
2961   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2962</t>
2963<t>
2964   Proxy implementors should consider the privacy and security
2965   implications of their design and coding decisions, and of the
2966   configuration options they provide to proxy operators (especially the
2967   default configuration).
2968</t>
2969<t>
2970   Users of a proxy need to be aware that they are no trustworthier than
2971   the people who run the proxy; HTTP itself cannot solve this problem.
2972</t>
2973<t>
2974   The judicious use of cryptography, when appropriate, may suffice to
2975   protect against a broad range of security and privacy attacks. Such
2976   cryptography is beyond the scope of the HTTP/1.1 specification.
2977</t>
2978</section>
2979
2980<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2981<t>
2982   They exist. They are hard to defend against. Research continues.
2983   Beware.
2984</t>
2985</section>
2986</section>
2987
2988<section title="Acknowledgments" anchor="ack">
2989<t>
2990   HTTP has evolved considerably over the years. It has
2991   benefited from a large and active developer community--the many
2992   people who have participated on the www-talk mailing list--and it is
2993   that community which has been most responsible for the success of
2994   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2995   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2996   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2997   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2998   VanHeyningen deserve special recognition for their efforts in
2999   defining early aspects of the protocol.
3000</t>
3001<t>
3002   This document has benefited greatly from the comments of all those
3003   participating in the HTTP-WG. In addition to those already mentioned,
3004   the following individuals have contributed to this specification:
3005</t>
3006<t>
3007   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3008   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3009   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3010   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3011   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3012   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3013   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3014   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3015   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3016   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3017   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3018   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3019   Josh Cohen.
3020</t>
3021<t>
3022   Thanks to the "cave men" of Palo Alto. You know who you are.
3023</t>
3024<t>
3025   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3026   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3027   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3028   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3029   Larry Masinter for their help. And thanks go particularly to Jeff
3030   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3031</t>
3032<t>
3033   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3034   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3035   discovery of many of the problems that this document attempts to
3036   rectify.
3037</t>
3038<t>
3039   This specification makes heavy use of the augmented BNF and generic
3040   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3041   reuses many of the definitions provided by Nathaniel Borenstein and
3042   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3043   specification will help reduce past confusion over the relationship
3044   between HTTP and Internet mail message formats.
3045</t>
3046</section>
3047
3048</middle>
3049<back>
3050
3051<references title="Normative References">
3052
3053<reference anchor="ISO-8859-1">
3054  <front>
3055    <title>
3056     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3057    </title>
3058    <author>
3059      <organization>International Organization for Standardization</organization>
3060    </author>
3061    <date year="1998"/>
3062  </front>
3063  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3064</reference>
3065
3066<reference anchor="Part2">
3067  <front>
3068    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3069    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3070      <organization abbrev="Day Software">Day Software</organization>
3071      <address><email>fielding@gbiv.com</email></address>
3072    </author>
3073    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3074      <organization>One Laptop per Child</organization>
3075      <address><email>jg@laptop.org</email></address>
3076    </author>
3077    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3078      <organization abbrev="HP">Hewlett-Packard Company</organization>
3079      <address><email>JeffMogul@acm.org</email></address>
3080    </author>
3081    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3082      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3083      <address><email>henrikn@microsoft.com</email></address>
3084    </author>
3085    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3086      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3087      <address><email>LMM@acm.org</email></address>
3088    </author>
3089    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3090      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3091      <address><email>paulle@microsoft.com</email></address>
3092    </author>
3093    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3094      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3095      <address><email>timbl@w3.org</email></address>
3096    </author>
3097    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3098      <organization abbrev="W3C">World Wide Web Consortium</organization>
3099      <address><email>ylafon@w3.org</email></address>
3100    </author>
3101    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3102      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3103      <address><email>julian.reschke@greenbytes.de</email></address>
3104    </author>
3105    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3106  </front>
3107  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3108  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3109</reference>
3110
3111<reference anchor="Part3">
3112  <front>
3113    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3114    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3115      <organization abbrev="Day Software">Day Software</organization>
3116      <address><email>fielding@gbiv.com</email></address>
3117    </author>
3118    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3119      <organization>One Laptop per Child</organization>
3120      <address><email>jg@laptop.org</email></address>
3121    </author>
3122    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3123      <organization abbrev="HP">Hewlett-Packard Company</organization>
3124      <address><email>JeffMogul@acm.org</email></address>
3125    </author>
3126    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3127      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3128      <address><email>henrikn@microsoft.com</email></address>
3129    </author>
3130    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3131      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3132      <address><email>LMM@acm.org</email></address>
3133    </author>
3134    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3135      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3136      <address><email>paulle@microsoft.com</email></address>
3137    </author>
3138    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3139      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3140      <address><email>timbl@w3.org</email></address>
3141    </author>
3142    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3143      <organization abbrev="W3C">World Wide Web Consortium</organization>
3144      <address><email>ylafon@w3.org</email></address>
3145    </author>
3146    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3147      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3148      <address><email>julian.reschke@greenbytes.de</email></address>
3149    </author>
3150    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3151  </front>
3152  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3153  <x:source href="p3-payload.xml" basename="p3-payload"/>
3154</reference>
3155
3156<reference anchor="Part5">
3157  <front>
3158    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3159    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3160      <organization abbrev="Day Software">Day Software</organization>
3161      <address><email>fielding@gbiv.com</email></address>
3162    </author>
3163    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3164      <organization>One Laptop per Child</organization>
3165      <address><email>jg@laptop.org</email></address>
3166    </author>
3167    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3168      <organization abbrev="HP">Hewlett-Packard Company</organization>
3169      <address><email>JeffMogul@acm.org</email></address>
3170    </author>
3171    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3172      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3173      <address><email>henrikn@microsoft.com</email></address>
3174    </author>
3175    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3176      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3177      <address><email>LMM@acm.org</email></address>
3178    </author>
3179    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3180      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3181      <address><email>paulle@microsoft.com</email></address>
3182    </author>
3183    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3184      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3185      <address><email>timbl@w3.org</email></address>
3186    </author>
3187    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3188      <organization abbrev="W3C">World Wide Web Consortium</organization>
3189      <address><email>ylafon@w3.org</email></address>
3190    </author>
3191    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3192      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3193      <address><email>julian.reschke@greenbytes.de</email></address>
3194    </author>
3195    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3196  </front>
3197  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3198  <x:source href="p5-range.xml" basename="p5-range"/>
3199</reference>
3200
3201<reference anchor="Part6">
3202  <front>
3203    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3204    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3205      <organization abbrev="Day Software">Day Software</organization>
3206      <address><email>fielding@gbiv.com</email></address>
3207    </author>
3208    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3209      <organization>One Laptop per Child</organization>
3210      <address><email>jg@laptop.org</email></address>
3211    </author>
3212    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3213      <organization abbrev="HP">Hewlett-Packard Company</organization>
3214      <address><email>JeffMogul@acm.org</email></address>
3215    </author>
3216    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3217      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3218      <address><email>henrikn@microsoft.com</email></address>
3219    </author>
3220    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3221      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3222      <address><email>LMM@acm.org</email></address>
3223    </author>
3224    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3225      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3226      <address><email>paulle@microsoft.com</email></address>
3227    </author>
3228    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3229      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3230      <address><email>timbl@w3.org</email></address>
3231    </author>
3232    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3233      <organization abbrev="W3C">World Wide Web Consortium</organization>
3234      <address><email>ylafon@w3.org</email></address>
3235    </author>
3236    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3237      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3238      <address><email>julian.reschke@greenbytes.de</email></address>
3239    </author>
3240    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3241  </front>
3242  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3243  <x:source href="p6-cache.xml" basename="p6-cache"/>
3244</reference>
3245
3246<reference anchor="RFC5234">
3247  <front>
3248    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3249    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3250      <organization>Brandenburg InternetWorking</organization>
3251      <address>
3252      <postal>
3253      <street>675 Spruce Dr.</street>
3254      <city>Sunnyvale</city>
3255      <region>CA</region>
3256      <code>94086</code>
3257      <country>US</country></postal>
3258      <phone>+1.408.246.8253</phone>
3259      <email>dcrocker@bbiw.net</email></address> 
3260    </author>
3261    <author initials="P." surname="Overell" fullname="Paul Overell">
3262      <organization>THUS plc.</organization>
3263      <address>
3264      <postal>
3265      <street>1/2 Berkeley Square</street>
3266      <street>99 Berkely Street</street>
3267      <city>Glasgow</city>
3268      <code>G3 7HR</code>
3269      <country>UK</country></postal>
3270      <email>paul.overell@thus.net</email></address>
3271    </author>
3272    <date month="January" year="2008"/>
3273  </front>
3274  <seriesInfo name="STD" value="68"/>
3275  <seriesInfo name="RFC" value="5234"/>
3276</reference>
3277
3278<reference anchor="RFC2045">
3279  <front>
3280    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3281    <author initials="N." surname="Freed" fullname="Ned Freed">
3282      <organization>Innosoft International, Inc.</organization>
3283      <address><email>ned@innosoft.com</email></address>
3284    </author>
3285    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3286      <organization>First Virtual Holdings</organization>
3287      <address><email>nsb@nsb.fv.com</email></address>
3288    </author>
3289    <date month="November" year="1996"/>
3290  </front>
3291  <seriesInfo name="RFC" value="2045"/>
3292</reference>
3293
3294<reference anchor="RFC2047">
3295  <front>
3296    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3297    <author initials="K." surname="Moore" fullname="Keith Moore">
3298      <organization>University of Tennessee</organization>
3299      <address><email>moore@cs.utk.edu</email></address>
3300    </author>
3301    <date month="November" year="1996"/>
3302  </front>
3303  <seriesInfo name="RFC" value="2047"/>
3304</reference>
3305
3306<reference anchor="RFC2119">
3307  <front>
3308    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3309    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3310      <organization>Harvard University</organization>
3311      <address><email>sob@harvard.edu</email></address>
3312    </author>
3313    <date month="March" year="1997"/>
3314  </front>
3315  <seriesInfo name="BCP" value="14"/>
3316  <seriesInfo name="RFC" value="2119"/>
3317</reference>
3318
3319<reference anchor="RFC3986">
3320 <front>
3321  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3322  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3323    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3324    <address>
3325       <email>timbl@w3.org</email>
3326       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3327    </address>
3328  </author>
3329  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3330    <organization abbrev="Day Software">Day Software</organization>
3331    <address>
3332      <email>fielding@gbiv.com</email>
3333      <uri>http://roy.gbiv.com/</uri>
3334    </address>
3335  </author>
3336  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3337    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3338    <address>
3339      <email>LMM@acm.org</email>
3340      <uri>http://larry.masinter.net/</uri>
3341    </address>
3342  </author>
3343  <date month='January' year='2005'></date>
3344 </front>
3345 <seriesInfo name="RFC" value="3986"/>
3346 <seriesInfo name="STD" value="66"/>
3347</reference>
3348
3349<reference anchor="USASCII">
3350  <front>
3351    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3352    <author>
3353      <organization>American National Standards Institute</organization>
3354    </author>
3355    <date year="1986"/>
3356  </front>
3357  <seriesInfo name="ANSI" value="X3.4"/>
3358</reference>
3359
3360</references>
3361
3362<references title="Informative References">
3363
3364<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3365  <front>
3366    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3367    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3368      <organization/>
3369    </author>
3370    <author initials="J." surname="Gettys" fullname="J. Gettys">
3371      <organization/>
3372    </author>
3373    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3374      <organization/>
3375    </author>
3376    <author initials="H." surname="Lie" fullname="H. Lie">
3377      <organization/>
3378    </author>
3379    <author initials="C." surname="Lilley" fullname="C. Lilley">
3380      <organization/>
3381    </author>
3382    <date year="1997" month="September"/>
3383  </front>
3384  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3385</reference>
3386
3387<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3388  <front>
3389    <title>Improving HTTP Latency</title>
3390    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3391      <organization/>
3392    </author>
3393    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3394      <organization/>
3395    </author>
3396    <date year="1995" month="December"/>
3397  </front>
3398  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3399</reference>
3400
3401<reference anchor="RFC822">
3402  <front>
3403    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3404    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3405      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3406      <address><email>DCrocker@UDel-Relay</email></address>
3407    </author>
3408    <date month="August" day="13" year="1982"/>
3409  </front>
3410  <seriesInfo name="STD" value="11"/>
3411  <seriesInfo name="RFC" value="822"/>
3412</reference>
3413
3414<reference anchor="RFC959">
3415  <front>
3416    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3417    <author initials="J." surname="Postel" fullname="J. Postel">
3418      <organization>Information Sciences Institute (ISI)</organization>
3419    </author>
3420    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3421      <organization/>
3422    </author>
3423    <date month="October" year="1985"/>
3424  </front>
3425  <seriesInfo name="STD" value="9"/>
3426  <seriesInfo name="RFC" value="959"/>
3427</reference>
3428
3429<reference anchor="RFC1123">
3430  <front>
3431    <title>Requirements for Internet Hosts - Application and Support</title>
3432    <author initials="R." surname="Braden" fullname="Robert Braden">
3433      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3434      <address><email>Braden@ISI.EDU</email></address>
3435    </author>
3436    <date month="October" year="1989"/>
3437  </front>
3438  <seriesInfo name="STD" value="3"/>
3439  <seriesInfo name="RFC" value="1123"/>
3440</reference>
3441
3442<reference anchor="RFC1305">
3443  <front>
3444    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3445    <author initials="D." surname="Mills" fullname="David L. Mills">
3446      <organization>University of Delaware, Electrical Engineering Department</organization>
3447      <address><email>mills@udel.edu</email></address>
3448    </author>
3449    <date month="March" year="1992"/>
3450  </front>
3451  <seriesInfo name="RFC" value="1305"/>
3452</reference>
3453
3454<reference anchor="RFC1436">
3455  <front>
3456    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3457    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3458      <organization>University of Minnesota, Computer and Information Services</organization>
3459      <address><email>fxa@boombox.micro.umn.edu</email></address>
3460    </author>
3461    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3462      <organization>University of Minnesota, Computer and Information Services</organization>
3463      <address><email>mpm@boombox.micro.umn.edu</email></address>
3464    </author>
3465    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3466      <organization>University of Minnesota, Computer and Information Services</organization>
3467      <address><email>lindner@boombox.micro.umn.edu</email></address>
3468    </author>
3469    <author initials="D." surname="Johnson" fullname="David Johnson">
3470      <organization>University of Minnesota, Computer and Information Services</organization>
3471      <address><email>dmj@boombox.micro.umn.edu</email></address>
3472    </author>
3473    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3474      <organization>University of Minnesota, Computer and Information Services</organization>
3475      <address><email>daniel@boombox.micro.umn.edu</email></address>
3476    </author>
3477    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3478      <organization>University of Minnesota, Computer and Information Services</organization>
3479      <address><email>alberti@boombox.micro.umn.edu</email></address>
3480    </author>
3481    <date month="March" year="1993"/>
3482  </front>
3483  <seriesInfo name="RFC" value="1436"/>
3484</reference>
3485
3486<reference anchor="RFC1900">
3487  <front>
3488    <title>Renumbering Needs Work</title>
3489    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3490      <organization>CERN, Computing and Networks Division</organization>
3491      <address><email>brian@dxcoms.cern.ch</email></address>
3492    </author>
3493    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3494      <organization>cisco Systems</organization>
3495      <address><email>yakov@cisco.com</email></address>
3496    </author>
3497    <date month="February" year="1996"/>
3498  </front>
3499  <seriesInfo name="RFC" value="1900"/>
3500</reference>
3501
3502<reference anchor="RFC1945">
3503  <front>
3504    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3505    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3506      <organization>MIT, Laboratory for Computer Science</organization>
3507      <address><email>timbl@w3.org</email></address>
3508    </author>
3509    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3510      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3511      <address><email>fielding@ics.uci.edu</email></address>
3512    </author>
3513    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3514      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3515      <address><email>frystyk@w3.org</email></address>
3516    </author>
3517    <date month="May" year="1996"/>
3518  </front>
3519  <seriesInfo name="RFC" value="1945"/>
3520</reference>
3521
3522<reference anchor="RFC2068">
3523  <front>
3524    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3525    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3526      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3527      <address><email>fielding@ics.uci.edu</email></address>
3528    </author>
3529    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3530      <organization>MIT Laboratory for Computer Science</organization>
3531      <address><email>jg@w3.org</email></address>
3532    </author>
3533    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3534      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3535      <address><email>mogul@wrl.dec.com</email></address>
3536    </author>
3537    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3538      <organization>MIT Laboratory for Computer Science</organization>
3539      <address><email>frystyk@w3.org</email></address>
3540    </author>
3541    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3542      <organization>MIT Laboratory for Computer Science</organization>
3543      <address><email>timbl@w3.org</email></address>
3544    </author>
3545    <date month="January" year="1997"/>
3546  </front>
3547  <seriesInfo name="RFC" value="2068"/>
3548</reference>
3549
3550<reference anchor='RFC2109'>
3551  <front>
3552    <title>HTTP State Management Mechanism</title>
3553    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3554      <organization>Bell Laboratories, Lucent Technologies</organization>
3555      <address><email>dmk@bell-labs.com</email></address>
3556    </author>
3557    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3558      <organization>Netscape Communications Corp.</organization>
3559      <address><email>montulli@netscape.com</email></address>
3560    </author>
3561    <date year='1997' month='February' />
3562  </front>
3563  <seriesInfo name='RFC' value='2109' />
3564</reference>
3565
3566<reference anchor="RFC2145">
3567  <front>
3568    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3569    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3570      <organization>Western Research Laboratory</organization>
3571      <address><email>mogul@wrl.dec.com</email></address>
3572    </author>
3573    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3574      <organization>Department of Information and Computer Science</organization>
3575      <address><email>fielding@ics.uci.edu</email></address>
3576    </author>
3577    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3578      <organization>MIT Laboratory for Computer Science</organization>
3579      <address><email>jg@w3.org</email></address>
3580    </author>
3581    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3582      <organization>W3 Consortium</organization>
3583      <address><email>frystyk@w3.org</email></address>
3584    </author>
3585    <date month="May" year="1997"/>
3586  </front>
3587  <seriesInfo name="RFC" value="2145"/>
3588</reference>
3589
3590<reference anchor="RFC2616">
3591  <front>
3592    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3593    <author initials="R." surname="Fielding" fullname="R. Fielding">
3594      <organization>University of California, Irvine</organization>
3595      <address><email>fielding@ics.uci.edu</email></address>
3596    </author>
3597    <author initials="J." surname="Gettys" fullname="J. Gettys">
3598      <organization>W3C</organization>
3599      <address><email>jg@w3.org</email></address>
3600    </author>
3601    <author initials="J." surname="Mogul" fullname="J. Mogul">
3602      <organization>Compaq Computer Corporation</organization>
3603      <address><email>mogul@wrl.dec.com</email></address>
3604    </author>
3605    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3606      <organization>MIT Laboratory for Computer Science</organization>
3607      <address><email>frystyk@w3.org</email></address>
3608    </author>
3609    <author initials="L." surname="Masinter" fullname="L. Masinter">
3610      <organization>Xerox Corporation</organization>
3611      <address><email>masinter@parc.xerox.com</email></address>
3612    </author>
3613    <author initials="P." surname="Leach" fullname="P. Leach">
3614      <organization>Microsoft Corporation</organization>
3615      <address><email>paulle@microsoft.com</email></address>
3616    </author>
3617    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3618      <organization>W3C</organization>
3619      <address><email>timbl@w3.org</email></address>
3620    </author>
3621    <date month="June" year="1999"/>
3622  </front>
3623  <seriesInfo name="RFC" value="2616"/>
3624</reference>
3625
3626<reference anchor='RFC2818'>
3627  <front>
3628    <title>HTTP Over TLS</title>
3629    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3630      <organization>RTFM, Inc.</organization>
3631      <address><email>ekr@rtfm.com</email></address>
3632    </author>
3633    <date year='2000' month='May' />
3634  </front>
3635  <seriesInfo name='RFC' value='2818' />
3636</reference>
3637
3638<reference anchor='RFC2965'>
3639  <front>
3640    <title>HTTP State Management Mechanism</title>
3641    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3642      <organization>Bell Laboratories, Lucent Technologies</organization>
3643      <address><email>dmk@bell-labs.com</email></address>
3644    </author>
3645    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3646      <organization>Epinions.com, Inc.</organization>
3647      <address><email>lou@montulli.org</email></address>
3648    </author>
3649    <date year='2000' month='October' />
3650  </front>
3651  <seriesInfo name='RFC' value='2965' />
3652</reference>
3653
3654<reference anchor='RFC3864'>
3655  <front>
3656    <title>Registration Procedures for Message Header Fields</title>
3657    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3658      <organization>Nine by Nine</organization>
3659      <address><email>GK-IETF@ninebynine.org</email></address>
3660    </author>
3661    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3662      <organization>BEA Systems</organization>
3663      <address><email>mnot@pobox.com</email></address>
3664    </author>
3665    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3666      <organization>HP Labs</organization>
3667      <address><email>JeffMogul@acm.org</email></address>
3668    </author>
3669    <date year='2004' month='September' />
3670  </front>
3671  <seriesInfo name='BCP' value='90' />
3672  <seriesInfo name='RFC' value='3864' />
3673</reference>
3674
3675<reference anchor='RFC3977'>
3676  <front>
3677    <title>Network News Transfer Protocol (NNTP)</title>
3678    <author initials='C.' surname='Feather' fullname='C. Feather'>
3679      <organization>THUS plc</organization>
3680      <address><email>clive@demon.net</email></address>
3681    </author>
3682    <date year='2006' month='October' />
3683  </front>
3684  <seriesInfo name="RFC" value="3977"/>
3685</reference>
3686
3687<reference anchor="RFC4288">
3688  <front>
3689    <title>Media Type Specifications and Registration Procedures</title>
3690    <author initials="N." surname="Freed" fullname="N. Freed">
3691      <organization>Sun Microsystems</organization>
3692      <address>
3693        <email>ned.freed@mrochek.com</email>
3694      </address>
3695    </author>
3696    <author initials="J." surname="Klensin" fullname="J. Klensin">
3697      <organization/>
3698      <address>
3699        <email>klensin+ietf@jck.com</email>
3700      </address>
3701    </author>
3702    <date year="2005" month="December"/>
3703  </front>
3704  <seriesInfo name="BCP" value="13"/>
3705  <seriesInfo name="RFC" value="4288"/>
3706</reference>
3707
3708<reference anchor='RFC4395'>
3709  <front>
3710    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3711    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3712      <organization>AT&amp;T Laboratories</organization>
3713      <address>
3714        <email>tony+urireg@maillennium.att.com</email>
3715      </address>
3716    </author>
3717    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3718      <organization>Qualcomm, Inc.</organization>
3719      <address>
3720        <email>hardie@qualcomm.com</email>
3721      </address>
3722    </author>
3723    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3724      <organization>Adobe Systems</organization>
3725      <address>
3726        <email>LMM@acm.org</email>
3727      </address>
3728    </author>
3729    <date year='2006' month='February' />
3730  </front>
3731  <seriesInfo name='BCP' value='115' />
3732  <seriesInfo name='RFC' value='4395' />
3733</reference>
3734
3735<reference anchor="RFC5322">
3736  <front>
3737    <title>Internet Message Format</title>
3738    <author initials="P." surname="Resnick" fullname="P. Resnick">
3739      <organization>Qualcomm Incorporated</organization>
3740    </author>
3741    <date year="2008" month="October"/>
3742  </front>
3743  <seriesInfo name="RFC" value="5322"/>
3744</reference>
3745
3746<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3747  <front>
3748    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3749    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3750      <organization/>
3751    </author>
3752    <date year="2001" month="November"/>
3753  </front>
3754  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3755</reference>
3756
3757<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3758  <front>
3759  <title>Analysis of HTTP Performance Problems</title>
3760  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3761    <organization/>
3762  </author>
3763  <date/>
3764  </front>
3765</reference>
3766
3767<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3768  <front>
3769  <title>Analysis of HTTP Performance</title>
3770  <author initials="J." surname="Touch" fullname="Joe Touch">
3771    <organization>USC/Information Sciences Institute</organization>
3772    <address><email>touch@isi.edu</email></address>
3773  </author>
3774  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3775    <organization>USC/Information Sciences Institute</organization>
3776    <address><email>johnh@isi.edu</email></address>
3777  </author>
3778  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3779    <organization>USC/Information Sciences Institute</organization>
3780    <address><email>katia@isi.edu</email></address>
3781  </author>
3782  <date year="1998" month="Aug"/>
3783  </front>
3784  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3785  <annotation>(original report dated Aug. 1996)</annotation>
3786</reference>
3787
3788<reference anchor="WAIS">
3789  <front>
3790    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3791    <author initials="F." surname="Davis" fullname="F. Davis">
3792      <organization>Thinking Machines Corporation</organization>
3793    </author>
3794    <author initials="B." surname="Kahle" fullname="B. Kahle">
3795      <organization>Thinking Machines Corporation</organization>
3796    </author>
3797    <author initials="H." surname="Morris" fullname="H. Morris">
3798      <organization>Thinking Machines Corporation</organization>
3799    </author>
3800    <author initials="J." surname="Salem" fullname="J. Salem">
3801      <organization>Thinking Machines Corporation</organization>
3802    </author>
3803    <author initials="T." surname="Shen" fullname="T. Shen">
3804      <organization>Thinking Machines Corporation</organization>
3805    </author>
3806    <author initials="R." surname="Wang" fullname="R. Wang">
3807      <organization>Thinking Machines Corporation</organization>
3808    </author>
3809    <author initials="J." surname="Sui" fullname="J. Sui">
3810      <organization>Thinking Machines Corporation</organization>
3811    </author>
3812    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3813      <organization>Thinking Machines Corporation</organization>
3814    </author>
3815    <date month="April" year="1990"/>
3816  </front>
3817  <seriesInfo name="Thinking Machines Corporation" value=""/>
3818</reference>
3819
3820</references>
3821
3822
3823<section title="Tolerant Applications" anchor="tolerant.applications">
3824<t>
3825   Although this document specifies the requirements for the generation
3826   of HTTP/1.1 messages, not all applications will be correct in their
3827   implementation. We therefore recommend that operational applications
3828   be tolerant of deviations whenever those deviations can be
3829   interpreted unambiguously.
3830</t>
3831<t>
3832   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3833   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3834   accept any amount of SP or HTAB characters between fields, even though
3835   only a single SP is required.
3836</t>
3837<t>
3838   The line terminator for message-header fields is the sequence CRLF.
3839   However, we recommend that applications, when parsing such headers,
3840   recognize a single LF as a line terminator and ignore the leading CR.
3841</t>
3842<t>
3843   The character set of an entity-body &SHOULD; be labeled as the lowest
3844   common denominator of the character codes used within that body, with
3845   the exception that not labeling the entity is preferred over labeling
3846   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3847</t>
3848<t>
3849   Additional rules for requirements on parsing and encoding of dates
3850   and other potential problems with date encodings include:
3851</t>
3852<t>
3853  <list style="symbols">
3854     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3855        which appears to be more than 50 years in the future is in fact
3856        in the past (this helps solve the "year 2000" problem).</t>
3857
3858     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3859        Expires date as earlier than the proper value, but &MUST-NOT;
3860        internally represent a parsed Expires date as later than the
3861        proper value.</t>
3862
3863     <t>All expiration-related calculations &MUST; be done in GMT. The
3864        local time zone &MUST-NOT; influence the calculation or comparison
3865        of an age or expiration time.</t>
3866
3867     <t>If an HTTP header incorrectly carries a date value with a time
3868        zone other than GMT, it &MUST; be converted into GMT using the
3869        most conservative possible conversion.</t>
3870  </list>
3871</t>
3872</section>
3873
3874<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3875<t>
3876   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3877   simplify the process of date comparison. Proxies and gateways from
3878   other protocols &SHOULD; ensure that any Date header field present in a
3879   message conforms to one of the HTTP/1.1 formats and rewrite the date
3880   if necessary.
3881</t>
3882</section>
3883
3884<section title="Compatibility with Previous Versions" anchor="compatibility">
3885<t>
3886   HTTP has been in use by the World-Wide Web global information initiative
3887   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3888   was a simple protocol for hypertext data transfer across the Internet
3889   with only a single method and no metadata.
3890   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3891   methods and MIME-like messaging that could include metadata about the data
3892   transferred and modifiers on the request/response semantics. However,
3893   HTTP/1.0 did not sufficiently take into consideration the effects of
3894   hierarchical proxies, caching, the need for persistent connections, or
3895   name-based virtual hosts. The proliferation of incompletely-implemented
3896   applications calling themselves "HTTP/1.0" further necessitated a
3897   protocol version change in order for two communicating applications
3898   to determine each other's true capabilities.
3899</t>
3900<t>
3901   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3902   requirements that enable reliable implementations, adding only
3903   those new features that will either be safely ignored by an HTTP/1.0
3904   recipient or only sent when communicating with a party advertising
3905   compliance with HTTP/1.1.
3906</t>
3907<t>
3908   It is beyond the scope of a protocol specification to mandate
3909   compliance with previous versions. HTTP/1.1 was deliberately
3910   designed, however, to make supporting previous versions easy. It is
3911   worth noting that, at the time of composing this specification
3912   (1996), we would expect commercial HTTP/1.1 servers to:
3913  <list style="symbols">
3914     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3915        1.1 requests;</t>
3916
3917     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3918        1.1;</t>
3919
3920     <t>respond appropriately with a message in the same major version
3921        used by the client.</t>
3922  </list>
3923</t>
3924<t>
3925   And we would expect HTTP/1.1 clients to:
3926  <list style="symbols">
3927     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3928        responses;</t>
3929
3930     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3931        1.1.</t>
3932  </list>
3933</t>
3934<t>
3935   For most implementations of HTTP/1.0, each connection is established
3936   by the client prior to the request and closed by the server after
3937   sending the response. Some implementations implement the Keep-Alive
3938   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3939</t>
3940
3941<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3942<t>
3943   This section summarizes major differences between versions HTTP/1.0
3944   and HTTP/1.1.
3945</t>
3946
3947<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
3948<t>
3949   The requirements that clients and servers support the Host request-header,
3950   report an error if the Host request-header (<xref target="header.host"/>) is
3951   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3952   are among the most important changes defined by this
3953   specification.
3954</t>
3955<t>
3956   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3957   addresses and servers; there was no other established mechanism for
3958   distinguishing the intended server of a request than the IP address
3959   to which that request was directed. The changes outlined above will
3960   allow the Internet, once older HTTP clients are no longer common, to
3961   support multiple Web sites from a single IP address, greatly
3962   simplifying large operational Web servers, where allocation of many
3963   IP addresses to a single host has created serious problems. The
3964   Internet will also be able to recover the IP addresses that have been
3965   allocated for the sole purpose of allowing special-purpose domain
3966   names to be used in root-level HTTP URLs. Given the rate of growth of
3967   the Web, and the number of servers already deployed, it is extremely
3968   important that all implementations of HTTP (including updates to
3969   existing HTTP/1.0 applications) correctly implement these
3970   requirements:
3971  <list style="symbols">
3972     <t>Both clients and servers &MUST; support the Host request-header.</t>
3973
3974     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3975
3976     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3977        request does not include a Host request-header.</t>
3978
3979     <t>Servers &MUST; accept absolute URIs.</t>
3980  </list>
3981</t>
3982</section>
3983</section>
3984
3985<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3986<t>
3987   Some clients and servers might wish to be compatible with some
3988   previous implementations of persistent connections in HTTP/1.0
3989   clients and servers. Persistent connections in HTTP/1.0 are
3990   explicitly negotiated as they are not the default behavior. HTTP/1.0
3991   experimental implementations of persistent connections are faulty,
3992   and the new facilities in HTTP/1.1 are designed to rectify these
3993   problems. The problem was that some existing 1.0 clients may be
3994   sending Keep-Alive to a proxy server that doesn't understand
3995   Connection, which would then erroneously forward it to the next
3996   inbound server, which would establish the Keep-Alive connection and
3997   result in a hung HTTP/1.0 proxy waiting for the close on the
3998   response. The result is that HTTP/1.0 clients must be prevented from
3999   using Keep-Alive when talking to proxies.
4000</t>
4001<t>
4002   However, talking to proxies is the most important use of persistent
4003   connections, so that prohibition is clearly unacceptable. Therefore,
4004   we need some other mechanism for indicating a persistent connection
4005   is desired, which is safe to use even when talking to an old proxy
4006   that ignores Connection. Persistent connections are the default for
4007   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4008   declaring non-persistence. See <xref target="header.connection"/>.
4009</t>
4010<t>
4011   The original HTTP/1.0 form of persistent connections (the Connection:
4012   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4013</t>
4014</section>
4015
4016<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4017<t>
4018   This specification has been carefully audited to correct and
4019   disambiguate key word usage; RFC 2068 had many problems in respect to
4020   the conventions laid out in <xref target="RFC2119"/>.
4021</t>
4022<t>
4023   Transfer-coding and message lengths all interact in ways that
4024   required fixing exactly when chunked encoding is used (to allow for
4025   transfer encoding that may not be self delimiting); it was important
4026   to straighten out exactly how message lengths are computed. (Sections
4027   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4028   <xref target="header.content-length" format="counter"/>,
4029   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4030</t>
4031<t>
4032   The use and interpretation of HTTP version numbers has been clarified
4033   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4034   version they support to deal with problems discovered in HTTP/1.0
4035   implementations (<xref target="http.version"/>)
4036</t>
4037<t>
4038   Transfer-coding had significant problems, particularly with
4039   interactions with chunked encoding. The solution is that transfer-codings
4040   become as full fledged as content-codings. This involves
4041   adding an IANA registry for transfer-codings (separate from content
4042   codings), a new header field (TE) and enabling trailer headers in the
4043   future. Transfer encoding is a major performance benefit, so it was
4044   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4045   interoperability problem that could have occurred due to interactions
4046   between authentication trailers, chunked encoding and HTTP/1.0
4047   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4048   and <xref target="header.te" format="counter"/>)
4049</t>
4050</section>
4051
4052<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4053<t>
4054  The CHAR rule does not allow the NUL character anymore (this affects
4055  the comment and quoted-string rules).  Furthermore, the quoted-pair
4056  rule does not allow escaping NUL, CR or LF anymore.
4057  (<xref target="basic.rules"/>)
4058</t>
4059<t>
4060  Clarify that HTTP-Version is case sensitive.
4061  (<xref target="http.version"/>)
4062</t>
4063<t>
4064  Remove reference to non-existant identity transfer-coding value tokens.
4065  (Sections <xref format="counter" target="transfer.codings"/> and
4066  <xref format="counter" target="message.length"/>)
4067</t>
4068<t>
4069  Clarification that the chunk length does not include
4070  the count of the octets in the chunk header and trailer.
4071  (<xref target="chunked.transfer.encoding"/>)
4072</t>
4073<t>
4074  Update use of abs_path production from RFC1808 to the path-absolute + query
4075  components of RFC3986.
4076  (<xref target="request-uri"/>)
4077</t>
4078<t>
4079  Clarify exactly when close connection options must be sent.
4080  (<xref target="header.connection"/>)
4081</t>
4082</section>
4083</section>
4084
4085<section title="Terminology" anchor="terminology">
4086<t>
4087   This specification uses a number of terms to refer to the roles
4088   played by participants in, and objects of, the HTTP communication.
4089</t>
4090<t>
4091  <iref item="connection"/>
4092  <x:dfn>connection</x:dfn>
4093  <list>
4094    <t>
4095      A transport layer virtual circuit established between two programs
4096      for the purpose of communication.
4097    </t>
4098  </list>
4099</t>
4100<t>
4101  <iref item="message"/>
4102  <x:dfn>message</x:dfn>
4103  <list>
4104    <t>
4105      The basic unit of HTTP communication, consisting of a structured
4106      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4107      transmitted via the connection.
4108    </t>
4109  </list>
4110</t>
4111<t>
4112  <iref item="request"/>
4113  <x:dfn>request</x:dfn>
4114  <list>
4115    <t>
4116      An HTTP request message, as defined in <xref target="request"/>.
4117    </t>
4118  </list>
4119</t>
4120<t>
4121  <iref item="response"/>
4122  <x:dfn>response</x:dfn>
4123  <list>
4124    <t>
4125      An HTTP response message, as defined in <xref target="response"/>.
4126    </t>
4127  </list>
4128</t>
4129<t>
4130  <iref item="resource"/>
4131  <x:dfn>resource</x:dfn>
4132  <list>
4133    <t>
4134      A network data object or service that can be identified by a URI,
4135      as defined in <xref target="uri"/>. Resources may be available in multiple
4136      representations (e.g. multiple languages, data formats, size, and
4137      resolutions) or vary in other ways.
4138    </t>
4139  </list>
4140</t>
4141<t>
4142  <iref item="entity"/>
4143  <x:dfn>entity</x:dfn>
4144  <list>
4145    <t>
4146      The information transferred as the payload of a request or
4147      response. An entity consists of metainformation in the form of
4148      entity-header fields and content in the form of an entity-body, as
4149      described in &entity;.
4150    </t>
4151  </list>
4152</t>
4153<t>
4154  <iref item="representation"/>
4155  <x:dfn>representation</x:dfn>
4156  <list>
4157    <t>
4158      An entity included with a response that is subject to content
4159      negotiation, as described in &content.negotiation;. There may exist multiple
4160      representations associated with a particular response status.
4161    </t>
4162  </list>
4163</t>
4164<t>
4165  <iref item="content negotiation"/>
4166  <x:dfn>content negotiation</x:dfn>
4167  <list>
4168    <t>
4169      The mechanism for selecting the appropriate representation when
4170      servicing a request, as described in &content.negotiation;. The
4171      representation of entities in any response can be negotiated
4172      (including error responses).
4173    </t>
4174  </list>
4175</t>
4176<t>
4177  <iref item="variant"/>
4178  <x:dfn>variant</x:dfn>
4179  <list>
4180    <t>
4181      A resource may have one, or more than one, representation(s)
4182      associated with it at any given instant. Each of these
4183      representations is termed a `variant'.  Use of the term `variant'
4184      does not necessarily imply that the resource is subject to content
4185      negotiation.
4186    </t>
4187  </list>
4188</t>
4189<t>
4190  <iref item="client"/>
4191  <x:dfn>client</x:dfn>
4192  <list>
4193    <t>
4194      A program that establishes connections for the purpose of sending
4195      requests.
4196    </t>
4197  </list>
4198</t>
4199<t>
4200  <iref item="user agent"/>
4201  <x:dfn>user agent</x:dfn>
4202  <list>
4203    <t>
4204      The client which initiates a request. These are often browsers,
4205      editors, spiders (web-traversing robots), or other end user tools.
4206    </t>
4207  </list>
4208</t>
4209<t>
4210  <iref item="server"/>
4211  <x:dfn>server</x:dfn>
4212  <list>
4213    <t>
4214      An application program that accepts connections in order to
4215      service requests by sending back responses. Any given program may
4216      be capable of being both a client and a server; our use of these
4217      terms refers only to the role being performed by the program for a
4218      particular connection, rather than to the program's capabilities
4219      in general. Likewise, any server may act as an origin server,
4220      proxy, gateway, or tunnel, switching behavior based on the nature
4221      of each request.
4222    </t>
4223  </list>
4224</t>
4225<t>
4226  <iref item="origin server"/>
4227  <x:dfn>origin server</x:dfn>
4228  <list>
4229    <t>
4230      The server on which a given resource resides or is to be created.
4231    </t>
4232  </list>
4233</t>
4234<t>
4235  <iref item="proxy"/>
4236  <x:dfn>proxy</x:dfn>
4237  <list>
4238    <t>
4239      An intermediary program which acts as both a server and a client
4240      for the purpose of making requests on behalf of other clients.
4241      Requests are serviced internally or by passing them on, with
4242      possible translation, to other servers. A proxy &MUST; implement
4243      both the client and server requirements of this specification. A
4244      "transparent proxy" is a proxy that does not modify the request or
4245      response beyond what is required for proxy authentication and
4246      identification. A "non-transparent proxy" is a proxy that modifies
4247      the request or response in order to provide some added service to
4248      the user agent, such as group annotation services, media type
4249      transformation, protocol reduction, or anonymity filtering. Except
4250      where either transparent or non-transparent behavior is explicitly
4251      stated, the HTTP proxy requirements apply to both types of
4252      proxies.
4253    </t>
4254  </list>
4255</t>
4256<t>
4257  <iref item="gateway"/>
4258  <x:dfn>gateway</x:dfn>
4259  <list>
4260    <t>
4261      A server which acts as an intermediary for some other server.
4262      Unlike a proxy, a gateway receives requests as if it were the
4263      origin server for the requested resource; the requesting client
4264      may not be aware that it is communicating with a gateway.
4265    </t>
4266  </list>
4267</t>
4268<t>
4269  <iref item="tunnel"/>
4270  <x:dfn>tunnel</x:dfn>
4271  <list>
4272    <t>
4273      An intermediary program which is acting as a blind relay between
4274      two connections. Once active, a tunnel is not considered a party
4275      to the HTTP communication, though the tunnel may have been
4276      initiated by an HTTP request. The tunnel ceases to exist when both
4277      ends of the relayed connections are closed.
4278    </t>
4279  </list>
4280</t>
4281<t>
4282  <iref item="cache"/>
4283  <x:dfn>cache</x:dfn>
4284  <list>
4285    <t>
4286      A program's local store of response messages and the subsystem
4287      that controls its message storage, retrieval, and deletion. A
4288      cache stores cacheable responses in order to reduce the response
4289      time and network bandwidth consumption on future, equivalent
4290      requests. Any client or server may include a cache, though a cache
4291      cannot be used by a server that is acting as a tunnel.
4292    </t>
4293  </list>
4294</t>
4295<t>
4296  <iref item="cacheable"/>
4297  <x:dfn>cacheable</x:dfn>
4298  <list>
4299    <t>
4300      A response is cacheable if a cache is allowed to store a copy of
4301      the response message for use in answering subsequent requests. The
4302      rules for determining the cacheability of HTTP responses are
4303      defined in &caching;. Even if a resource is cacheable, there may
4304      be additional constraints on whether a cache can use the cached
4305      copy for a particular request.
4306    </t>
4307  </list>
4308</t>
4309<t>
4310  <iref item="upstream"/>
4311  <iref item="downstream"/>
4312  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4313  <list>
4314    <t>
4315      Upstream and downstream describe the flow of a message: all
4316      messages flow from upstream to downstream.
4317    </t>
4318  </list>
4319</t>
4320<t>
4321  <iref item="inbound"/>
4322  <iref item="outbound"/>
4323  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4324  <list>
4325    <t>
4326      Inbound and outbound refer to the request and response paths for
4327      messages: "inbound" means "traveling toward the origin server",
4328      and "outbound" means "traveling toward the user agent"
4329    </t>
4330  </list>
4331</t>
4332</section>
4333
4334<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4335
4336<section title="Since RFC2616">
4337<t>
4338  Extracted relevant partitions from <xref target="RFC2616"/>.
4339</t>
4340</section>
4341
4342<section title="Since draft-ietf-httpbis-p1-messaging-00">
4343<t>
4344  Closed issues:
4345  <list style="symbols">
4346    <t>
4347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4348      "HTTP Version should be case sensitive"
4349      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4350    </t>
4351    <t>
4352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4353      "'unsafe' characters"
4354      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4355    </t>
4356    <t>
4357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4358      "Chunk Size Definition"
4359      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4360    </t>
4361    <t>
4362      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4363      "Message Length"
4364      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4365    </t>
4366    <t>
4367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4368      "Media Type Registrations"
4369      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4370    </t>
4371    <t>
4372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4373      "URI includes query"
4374      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4375    </t>
4376    <t>
4377      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4378      "No close on 1xx responses"
4379      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4380    </t>
4381    <t>
4382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4383      "Remove 'identity' token references"
4384      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4385    </t>
4386    <t>
4387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4388      "Import query BNF"
4389    </t>
4390    <t>
4391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4392      "qdtext BNF"
4393    </t>
4394    <t>
4395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4396      "Normative and Informative references"
4397    </t>
4398    <t>
4399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4400      "RFC2606 Compliance"
4401    </t>
4402    <t>
4403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4404      "RFC977 reference"
4405    </t>
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4408      "RFC1700 references"
4409    </t>
4410    <t>
4411      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4412      "inconsistency in date format explanation"
4413    </t>
4414    <t>
4415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4416      "Date reference typo"
4417    </t>
4418    <t>
4419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4420      "Informative references"
4421    </t>
4422    <t>
4423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4424      "ISO-8859-1 Reference"
4425    </t>
4426    <t>
4427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4428      "Normative up-to-date references"
4429    </t>
4430  </list>
4431</t>
4432<t>
4433  Other changes:
4434  <list style="symbols">
4435    <t>
4436      Update media type registrations to use RFC4288 template.
4437    </t>
4438    <t>
4439      Use names of RFC4234 core rules DQUOTE and HTAB,
4440      fix broken ABNF for chunk-data
4441      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4442    </t>
4443  </list>
4444</t>
4445</section>
4446
4447<section title="Since draft-ietf-httpbis-p1-messaging-01">
4448<t>
4449  Closed issues:
4450  <list style="symbols">
4451    <t>
4452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4453      "Bodies on GET (and other) requests"
4454    </t>
4455    <t>
4456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4457      "Updating to RFC4288"
4458    </t>
4459    <t>
4460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4461      "Status Code and Reason Phrase"
4462    </t>
4463    <t>
4464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4465      "rel_path not used"
4466    </t>
4467  </list>
4468</t>
4469<t>
4470  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4471  <list style="symbols">
4472    <t>
4473      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4474      "trailer-part").
4475    </t>
4476    <t>
4477      Avoid underscore character in rule names ("http_URL" ->
4478      "http-URI", "abs_path" -> "path-absolute").
4479    </t>
4480    <t>
4481      Add rules for terms imported from URI spec ("absolute-URI", "authority",
4482      "path-abempty", "path-absolute", "uri-host", "port", "query").
4483    </t>
4484    <t>
4485      Synchronize core rules with RFC5234 (this includes a change to CHAR
4486      which now excludes NUL).
4487    </t>
4488    <t>
4489      Get rid of prose rules that span multiple lines.
4490    </t>
4491    <t>
4492      Get rid of unused rules LOALPHA and UPALPHA.
4493    </t>
4494    <t>
4495      Move "Product Tokens" section (back) into Part 1, as "token" is used
4496      in the definition of the Upgrade header.
4497    </t>
4498    <t>
4499      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4500    </t>
4501    <t>
4502      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4503    </t>
4504  </list>
4505</t>
4506</section>
4507
4508<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4509<t>
4510  Closed issues:
4511  <list style="symbols">
4512    <t>
4513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4514      "HTTP-date vs. rfc1123-date"
4515    </t>
4516    <t>
4517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4518      "WS in quoted-pair"
4519    </t>
4520  </list>
4521</t>
4522<t>
4523  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4524  <list style="symbols">
4525    <t>
4526      Reference RFC 3984, and update header registrations for headers defined
4527      in this document.
4528    </t>
4529  </list>
4530</t>
4531<t>
4532  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4533  <list style="symbols">
4534    <t>
4535      Replace string literals when the string really is case-sensitive (HTTP-Version).
4536    </t>
4537  </list>
4538</t>
4539</section>
4540
4541<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4542<t>
4543  Closed issues:
4544  <list style="symbols">
4545    <t>
4546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4547      "Connection closing"
4548    </t>
4549    <t>
4550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4551      "Move registrations and registry information to IANA Considerations"
4552    </t>
4553    <t>
4554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4555      "need new URL for PAD1995 reference"
4556    </t>
4557    <t>
4558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4559      "IANA Considerations: update HTTP URI scheme registration"
4560    </t>
4561    <t>
4562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4563      "Cite HTTPS URI scheme definition"
4564    </t>
4565    <t>
4566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4567      "List-type headers vs Set-Cookie"
4568    </t>
4569  </list>
4570</t>
4571<t>
4572  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4573  <list style="symbols">
4574    <t>
4575      Replace string literals when the string really is case-sensitive (HTTP-Date).
4576    </t>
4577    <t>
4578      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4579    </t>
4580  </list>
4581</t>
4582</section>
4583
4584<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4585<t>
4586  Closed issues:
4587  <list style="symbols">
4588    <t>
4589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4590      "RFC 2822 is updated by RFC 5322"
4591    </t>
4592  </list>
4593</t>
4594<t>
4595  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4596  <list style="symbols">
4597    <t>
4598      Use "/" instead of "|" for alternatives.
4599    </t>
4600    <t>
4601      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4602    </t>
4603  </list>
4604</t>
4605</section>
4606
4607</section>
4608
4609</back>
4610</rfc>
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