source: draft-ietf-httpbis/latest/p1-messaging.xml @ 390

Last change on this file since 390 was 390, checked in by julian.reschke@…, 11 years ago

reorganize Notation section

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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.05"/>.
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 Extension: #rule" anchor="notation.abnf">
322  <t>
323    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
324    improve readability.
325  </t>
326  <t>
327    A construct "#" is defined, similar to "*", for defining lists of
328    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
329    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
330    (",") and &OPTIONAL; linear white space (OWS). This makes the usual
331    form of lists very easy; a rule such as
332    <figure><artwork type="example">
333 ( *<x:ref>OWS</x:ref> element *( *<x:ref>OWS</x:ref> "," *<x:ref>OWS</x:ref> element ))</artwork></figure>
334  </t>
335  <t>
336    can be shown as
337    <figure><artwork type="example">
338 1#element</artwork></figure>
339  </t>
340  <t>
341    Wherever this construct is used, null elements are allowed, but do
342    not contribute to the count of elements present. That is,
343    "(element), , (element) " is permitted, but counts as only two
344    elements. Therefore, where at least one element is required, at
345    least one non-null element &MUST; be present. Default values are 0
346    and infinity so that "#element" allows any number, including zero;
347    "1#element" requires at least one; and "1#2element" allows one or
348    two.
349  </t>
350  <t>
351    <cref anchor="abnf.list">
352      At a later point of time, we may want to add an appendix containing
353      the whole ABNF, with the list rules expanded to strict RFC 5234
354      notation.
355    </cref>
356  </t>
357</section>
358
359<section title="Basic Rules" anchor="basic.rules">
360<t anchor="rule.CRLF">
361  <x:anchor-alias value="CRLF"/>
362   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
363   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
364   tolerant applications). The end-of-line marker within an entity-body
365   is defined by its associated media type, as described in &media-types;.
366</t>
367<t anchor="rule.LWS">
368   All linear white space (LWS) in header field-values has the same semantics as SP. A
369   recipient &MAY; replace any such linear white space with a single SP before
370   interpreting the field value or forwarding the message downstream.
371</t>
372<t>
373   Historically, HTTP/1.1 header field values allow linear white space folding across
374   multiple lines. However, this specification deprecates its use; senders &MUST-NOT; 
375   produce messages that include LWS folding (i.e., use the obs-fold rule), except
376   within the message/http media type (<xref target="internet.media.type.message.http"/>).
377   Receivers &SHOULD; still parse folded linear white space.
378</t>
379<t>
380   This specification uses three rules to denote the use of linear white space;
381   BWS ("Bad" White Space), OWS (Optional White Space), and RWS (Required White Space).
382</t>
383<t>
384   "Bad" white space is allowed by the BNF, but senders &SHOULD-NOT; produce it in messages.
385   Receivers &MUST; accept it in incoming messages.
386</t>
387<t>
388   Required white space is used when at least one linear white space character
389   is required to separate field tokens. In all such cases, a single SP character
390   &SHOULD; be used.
391</t>
392<t anchor="rule.whitespace">
393  <x:anchor-alias value="BWS"/>
394  <x:anchor-alias value="OWS"/>
395  <x:anchor-alias value="RWS"/>
396  <x:anchor-alias value="obs-fold"/>
397</t>
398<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
399  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
400                 ; "optional" white space
401  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
402                 ; "required" white space
403  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
404                 ; "bad" white space
405  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
406</artwork></figure>
407<t anchor="rule.TEXT">
408  <x:anchor-alias value="TEXT"/>
409   The TEXT rule is only used for descriptive field contents and values
410   that are not intended to be interpreted by the message parser. Words
411   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
412   <xref target="ISO-8859-1"/> only when encoded according to the rules of
413   <xref target="RFC2047"/>.
414</t>
415<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
416  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>OWS</x:ref>
417                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>OWS</x:ref>
418</artwork></figure>
419<t>
420   A CRLF is allowed in the definition of TEXT only as part of a header
421   field continuation. It is expected that the folding LWS will be
422   replaced with a single SP before interpretation of the TEXT value.
423</t>
424<t anchor="rule.token.separators">
425  <x:anchor-alias value="tchar"/>
426  <x:anchor-alias value="token"/>
427   Many HTTP/1.1 header field values consist of words separated by LWS
428   or special characters. These special characters &MUST; be in a quoted
429   string to be used within a parameter value (as defined in
430   <xref target="transfer.codings"/>).
431</t>
432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
433  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
434                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
435                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
436                 
437  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
438</artwork></figure>
439<t anchor="rule.comment">
440  <x:anchor-alias value="comment"/>
441  <x:anchor-alias value="ctext"/>
442   Comments can be included in some HTTP header fields by surrounding
443   the comment text with parentheses. Comments are only allowed in
444   fields containing "comment" as part of their field value definition.
445   In all other fields, parentheses are considered part of the field
446   value.
447</t>
448<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
449  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
450  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
451</artwork></figure>
452<t anchor="rule.quoted-string">
453  <x:anchor-alias value="quoted-string"/>
454  <x:anchor-alias value="qdtext"/>
455   A string of text is parsed as a single word if it is quoted using
456   double-quote marks.
457</t>
458<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
459  <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>
460  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
461</artwork></figure>
462<t anchor="rule.quoted-pair">
463  <x:anchor-alias value="quoted-pair"/>
464  <x:anchor-alias value="quoted-text"/>
465   The backslash character ("\") &MAY; be used as a single-character
466   quoting mechanism only within quoted-string and comment constructs.
467</t>
468<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
469  <x:ref>quoted-text</x:ref>    = %x01-09 /
470                   %x0B-0C /
471                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
472  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
473</artwork></figure>
474</section>
475
476<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
477  <x:anchor-alias value="request-header"/>
478  <x:anchor-alias value="response-header"/>
479  <x:anchor-alias value="accept-params"/>
480  <x:anchor-alias value="entity-body"/>
481  <x:anchor-alias value="entity-header"/>
482  <x:anchor-alias value="Cache-Control"/>
483  <x:anchor-alias value="Pragma"/>
484  <x:anchor-alias value="Warning"/>
485<t>
486  The ABNF rules below are defined in other parts:
487</t>
488<figure><!-- Part2--><artwork type="abnf2616">
489  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
490  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
491</artwork></figure>
492<figure><!-- Part3--><artwork type="abnf2616">
493  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
494  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
495  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
496</artwork></figure>
497<figure><!-- Part6--><artwork type="abnf2616">
498  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
499  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
500  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
501</artwork></figure>
502</section>
503
504</section>
505
506<section title="Overall Operation" anchor="intro.overall.operation">
507<t>
508   HTTP is a request/response protocol. A client sends a
509   request to the server in the form of a request method, URI, and
510   protocol version, followed by a MIME-like message containing request
511   modifiers, client information, and possible body content over a
512   connection with a server. The server responds with a status line,
513   including the message's protocol version and a success or error code,
514   followed by a MIME-like message containing server information, entity
515   metainformation, and possible entity-body content. The relationship
516   between HTTP and MIME is described in &diff2045entity;.
517</t>
518<t>
519   Most HTTP communication is initiated by a user agent and consists of
520   a request to be applied to a resource on some origin server. In the
521   simplest case, this may be accomplished via a single connection (v)
522   between the user agent (UA) and the origin server (O).
523</t>
524<figure><artwork type="drawing">
525       request chain ------------------------&gt;
526    UA -------------------v------------------- O
527       &lt;----------------------- response chain
528</artwork></figure>
529<t>
530   A more complicated situation occurs when one or more intermediaries
531   are present in the request/response chain. There are three common
532   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
533   forwarding agent, receiving requests for a URI in its absolute form,
534   rewriting all or part of the message, and forwarding the reformatted
535   request toward the server identified by the URI. A gateway is a
536   receiving agent, acting as a layer above some other server(s) and, if
537   necessary, translating the requests to the underlying server's
538   protocol. A tunnel acts as a relay point between two connections
539   without changing the messages; tunnels are used when the
540   communication needs to pass through an intermediary (such as a
541   firewall) even when the intermediary cannot understand the contents
542   of the messages.
543</t>
544<figure><artwork type="drawing">
545       request chain --------------------------------------&gt;
546    UA -----v----- A -----v----- B -----v----- C -----v----- O
547       &lt;------------------------------------- response chain
548</artwork></figure>
549<t>
550   The figure above shows three intermediaries (A, B, and C) between the
551   user agent and origin server. A request or response message that
552   travels the whole chain will pass through four separate connections.
553   This distinction is important because some HTTP communication options
554   may apply only to the connection with the nearest, non-tunnel
555   neighbor, only to the end-points of the chain, or to all connections
556   along the chain. Although the diagram is linear, each participant may
557   be engaged in multiple, simultaneous communications. For example, B
558   may be receiving requests from many clients other than A, and/or
559   forwarding requests to servers other than C, at the same time that it
560   is handling A's request.
561</t>
562<t>
563   Any party to the communication which is not acting as a tunnel may
564   employ an internal cache for handling requests. The effect of a cache
565   is that the request/response chain is shortened if one of the
566   participants along the chain has a cached response applicable to that
567   request. The following illustrates the resulting chain if B has a
568   cached copy of an earlier response from O (via C) for a request which
569   has not been cached by UA or A.
570</t>
571<figure><artwork type="drawing">
572          request chain ----------&gt;
573       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
574          &lt;--------- response chain
575</artwork></figure>
576<t>
577   Not all responses are usefully cacheable, and some requests may
578   contain modifiers which place special requirements on cache behavior.
579   HTTP requirements for cache behavior and cacheable responses are
580   defined in &caching;.
581</t>
582<t>
583   In fact, there are a wide variety of architectures and configurations
584   of caches and proxies currently being experimented with or deployed
585   across the World Wide Web. These systems include national hierarchies
586   of proxy caches to save transoceanic bandwidth, systems that
587   broadcast or multicast cache entries, organizations that distribute
588   subsets of cached data via CD-ROM, and so on. HTTP systems are used
589   in corporate intranets over high-bandwidth links, and for access via
590   PDAs with low-power radio links and intermittent connectivity. The
591   goal of HTTP/1.1 is to support the wide diversity of configurations
592   already deployed while introducing protocol constructs that meet the
593   needs of those who build web applications that require high
594   reliability and, failing that, at least reliable indications of
595   failure.
596</t>
597<t>
598   HTTP communication usually takes place over TCP/IP connections. The
599   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
600   not preclude HTTP from being implemented on top of any other protocol
601   on the Internet, or on other networks. HTTP only presumes a reliable
602   transport; any protocol that provides such guarantees can be used;
603   the mapping of the HTTP/1.1 request and response structures onto the
604   transport data units of the protocol in question is outside the scope
605   of this specification.
606</t>
607<t>
608   In HTTP/1.0, most implementations used a new connection for each
609   request/response exchange. In HTTP/1.1, a connection may be used for
610   one or more request/response exchanges, although connections may be
611   closed for a variety of reasons (see <xref target="persistent.connections"/>).
612</t>
613</section>
614</section>
615
616
617<section title="Protocol Parameters" anchor="protocol.parameters">
618
619<section title="HTTP Version" anchor="http.version">
620  <x:anchor-alias value="HTTP-Version"/>
621  <x:anchor-alias value="HTTP-Prot-Name"/>
622<t>
623   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
624   of the protocol. The protocol versioning policy is intended to allow
625   the sender to indicate the format of a message and its capacity for
626   understanding further HTTP communication, rather than the features
627   obtained via that communication. No change is made to the version
628   number for the addition of message components which do not affect
629   communication behavior or which only add to extensible field values.
630   The &lt;minor&gt; number is incremented when the changes made to the
631   protocol add features which do not change the general message parsing
632   algorithm, but which may add to the message semantics and imply
633   additional capabilities of the sender. The &lt;major&gt; number is
634   incremented when the format of a message within the protocol is
635   changed. See <xref target="RFC2145"/> for a fuller explanation.
636</t>
637<t>
638   The version of an HTTP message is indicated by an HTTP-Version field
639   in the first line of the message. HTTP-Version is case-sensitive.
640</t>
641<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
642  <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>
643  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
644</artwork></figure>
645<t>
646   Note that the major and minor numbers &MUST; be treated as separate
647   integers and that each &MAY; be incremented higher than a single digit.
648   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
649   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
650   &MUST-NOT; be sent.
651</t>
652<t>
653   An application that sends a request or response message that includes
654   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
655   with this specification. Applications that are at least conditionally
656   compliant with this specification &SHOULD; use an HTTP-Version of
657   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
658   not compatible with HTTP/1.0. For more details on when to send
659   specific HTTP-Version values, see <xref target="RFC2145"/>.
660</t>
661<t>
662   The HTTP version of an application is the highest HTTP version for
663   which the application is at least conditionally compliant.
664</t>
665<t>
666   Proxy and gateway applications need to be careful when forwarding
667   messages in protocol versions different from that of the application.
668   Since the protocol version indicates the protocol capability of the
669   sender, a proxy/gateway &MUST-NOT; send a message with a version
670   indicator which is greater than its actual version. If a higher
671   version request is received, the proxy/gateway &MUST; either downgrade
672   the request version, or respond with an error, or switch to tunnel
673   behavior.
674</t>
675<t>
676   Due to interoperability problems with HTTP/1.0 proxies discovered
677   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
678   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
679   they support. The proxy/gateway's response to that request &MUST; be in
680   the same major version as the request.
681</t>
682<t>
683  <list>
684    <t>
685      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
686      of header fields required or forbidden by the versions involved.
687    </t>
688  </list>
689</t>
690</section>
691
692<section title="Uniform Resource Identifiers" anchor="uri">
693<t>
694   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used in HTTP
695   to indicate the target of a request and to identify additional resources related
696   to that resource, the request, or the response. Each protocol element in HTTP
697   that allows a URI reference will indicate in its ABNF whether the element allows
698   only a URI in absolute form, any relative reference, or some limited subset of
699   the URI-reference grammar. Unless otherwise indicated, relative URI references
700   are to be parsed relative to the URI corresponding to the request target
701   (the base URI).
702</t>
703  <x:anchor-alias value="URI-reference"/>
704  <x:anchor-alias value="absolute-URI"/>
705  <x:anchor-alias value="authority"/>
706  <x:anchor-alias value="fragment"/>
707  <x:anchor-alias value="path-abempty"/>
708  <x:anchor-alias value="path-absolute"/>
709  <x:anchor-alias value="port"/>
710  <x:anchor-alias value="query"/>
711  <x:anchor-alias value="relativeURI"/>
712  <x:anchor-alias value="relative-part"/>
713  <x:anchor-alias value="uri-host"/>
714<t>
715   This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port",
716   "host", "path-abempty", "path-absolute", "query", and "authority" from <xref target="RFC3986"/>:
717</t>
718<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"/><iref primary="true" item="Grammar" subitem="relativeURI"/><iref primary="true" item="Grammar" subitem="relative-part"/>
719  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
720  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
721  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
722  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
723  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
724  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
725  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
726  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
727
728  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>>
729  <x:ref>relativeURI</x:ref>   = <x:ref>relative-part</x:ref> [ "?" <x:ref>query</x:ref> ]
730</artwork></figure>
731<t>
732   HTTP does not place an a priori limit on the length of
733   a URI. Servers &MUST; be able to handle the URI of any resource they
734   serve, and &SHOULD; be able to handle URIs of unbounded length if they
735   provide GET-based forms that could generate such URIs. A server
736   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
737   than the server can handle (see &status-414;).
738</t>
739<t>
740  <list>
741    <t>
742      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
743      above 255 bytes, because some older client or proxy
744      implementations might not properly support these lengths.
745    </t>
746  </list>
747</t>
748
749<section title="http URI scheme" anchor="http.uri">
750  <x:anchor-alias value="http-URI"/>
751  <iref item="http URI scheme" primary="true"/>
752  <iref item="URI scheme" subitem="http" primary="true"/>
753<t>
754   The "http" scheme is used to locate network resources via the HTTP
755   protocol. This section defines the syntax and semantics for identifiers
756   using the http or https URI schemes.
757</t>
758<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
759  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
760</artwork></figure>
761<t>
762   If the port is empty or not given, port 80 is assumed. The semantics
763   are that the identified resource is located at the server listening
764   for TCP connections on that port of that host, and the Request-URI
765   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
766   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
767   the path-absolute is not present in the URL, it &MUST; be given as "/" when
768   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
769   receives a host name which is not a fully qualified domain name, it
770   &MAY; add its domain to the host name it received. If a proxy receives
771   a fully qualified domain name, the proxy &MUST-NOT; change the host
772   name.
773</t>
774<t><list><t>
775  <iref item="https URI scheme"/>
776  <iref item="URI scheme" subitem="https"/>
777  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
778</t></list></t>
779</section>
780
781<section title="URI Comparison" anchor="uri.comparison">
782<t>
783   When comparing two URIs to decide if they match or not, a client
784   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
785   URIs, with these exceptions:
786  <list style="symbols">
787    <t>A port that is empty or not given is equivalent to the default
788        port for that URI-reference;</t>
789    <t>Comparisons of host names &MUST; be case-insensitive;</t>
790    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
791    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
792  </list>
793</t>
794<t>
795   Characters other than those in the "reserved" set (see
796   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
797   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
798</t>
799<t>
800   For example, the following three URIs are equivalent:
801</t>
802<figure><artwork type="example">
803   http://example.com:80/~smith/home.html
804   http://EXAMPLE.com/%7Esmith/home.html
805   http://EXAMPLE.com:/%7esmith/home.html
806</artwork></figure>
807</section>
808</section>
809
810<section title="Date/Time Formats" anchor="date.time.formats">
811<section title="Full Date" anchor="full.date">
812  <x:anchor-alias value="HTTP-date"/>
813  <x:anchor-alias value="obsolete-date"/>
814  <x:anchor-alias value="rfc1123-date"/>
815  <x:anchor-alias value="rfc850-date"/>
816  <x:anchor-alias value="asctime-date"/>
817  <x:anchor-alias value="date1"/>
818  <x:anchor-alias value="date2"/>
819  <x:anchor-alias value="date3"/>
820  <x:anchor-alias value="rfc1123-date"/>
821  <x:anchor-alias value="time"/>
822  <x:anchor-alias value="wkday"/>
823  <x:anchor-alias value="weekday"/>
824  <x:anchor-alias value="month"/>
825<t>
826   HTTP applications have historically allowed three different formats
827   for the representation of date/time stamps:
828</t>
829<figure><artwork type="example">
830   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
831   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
832   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
833</artwork></figure>
834<t>
835   The first format is preferred as an Internet standard and represents
836   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
837   other formats are described here only for
838   compatibility with obsolete implementations.
839   HTTP/1.1 clients and servers that parse the date value &MUST; accept
840   all three formats (for compatibility with HTTP/1.0), though they &MUST;
841   only generate the RFC 1123 format for representing HTTP-date values
842   in header fields. See <xref target="tolerant.applications"/> for further information.
843</t>
844<t><list><t>
845      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
846      accepting date values that may have been sent by non-HTTP
847      applications, as is sometimes the case when retrieving or posting
848      messages via proxies/gateways to SMTP or NNTP.
849</t></list></t>
850<t>
851   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
852   (GMT), without exception. For the purposes of HTTP, GMT is exactly
853   equal to UTC (Coordinated Universal Time). This is indicated in the
854   first two formats by the inclusion of "GMT" as the three-letter
855   abbreviation for time zone, and &MUST; be assumed when reading the
856   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
857   additional LWS beyond that specifically included as SP in the
858   grammar.
859</t>
860<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"/>
861  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
862  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
863  <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
864  <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
865  <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>
866  <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>
867                 ; day month year (e.g., 02 Jun 1982)
868  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
869                 ; day-month-year (e.g., 02-Jun-82)
870  <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> ))
871                 ; month day (e.g., Jun  2)
872  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
873                 ; 00:00:00 - 23:59:59
874  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
875               / s-Thu / s-Fri / s-Sat / s-Sun
876  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
877               / l-Thu / l-Fri / l-Sat / l-Sun
878  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
879               / s-May / s-Jun / s-Jul / s-Aug
880               / s-Sep / s-Oct / s-Nov / s-Dec
881               
882  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
883
884  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
885  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
886  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
887  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
888  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
889  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
890  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
891
892  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
893  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
894  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
895  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
896  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
897  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
898  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
899
900  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
901  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
902  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
903  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
904  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
905  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
906  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
907  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
908  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
909  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
910  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
911  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
912</artwork></figure>
913<t>
914      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
915      to their usage within the protocol stream. Clients and servers are
916      not required to use these formats for user presentation, request
917      logging, etc.
918</t>
919</section>
920</section>
921
922<section title="Transfer Codings" anchor="transfer.codings">
923  <x:anchor-alias value="parameter"/>
924  <x:anchor-alias value="transfer-coding"/>
925  <x:anchor-alias value="transfer-extension"/>
926<t>
927   Transfer-coding values are used to indicate an encoding
928   transformation that has been, can be, or may need to be applied to an
929   entity-body in order to ensure "safe transport" through the network.
930   This differs from a content coding in that the transfer-coding is a
931   property of the message, not of the original entity.
932</t>
933<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
934  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
935  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
936</artwork></figure>
937<t anchor="rule.parameter">
938  <x:anchor-alias value="attribute"/>
939  <x:anchor-alias value="parameter"/>
940  <x:anchor-alias value="value"/>
941   Parameters are in  the form of attribute/value pairs.
942</t>
943<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"/>
944  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
945  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
946  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
947</artwork></figure>
948<t>
949   All transfer-coding values are case-insensitive. HTTP/1.1 uses
950   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
951   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
952</t>
953<t>
954   Whenever a transfer-coding is applied to a message-body, the set of
955   transfer-codings &MUST; include "chunked", unless the message indicates it
956   is terminated by closing the connection. When the "chunked" transfer-coding
957   is used, it &MUST; be the last transfer-coding applied to the
958   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
959   than once to a message-body. These rules allow the recipient to
960   determine the transfer-length of the message (<xref target="message.length"/>).
961</t>
962<t>
963   Transfer-codings are analogous to the Content-Transfer-Encoding
964   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
965   binary data over a 7-bit transport service. However, safe transport
966   has a different focus for an 8bit-clean transfer protocol. In HTTP,
967   the only unsafe characteristic of message-bodies is the difficulty in
968   determining the exact body length (<xref target="message.length"/>), or the desire to
969   encrypt data over a shared transport.
970</t>
971<t>
972   The Internet Assigned Numbers Authority (IANA) acts as a registry for
973   transfer-coding value tokens. Initially, the registry contains the
974   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
975   "gzip", "compress", and "deflate" (&content-codings;).
976</t>
977<t>
978   New transfer-coding value tokens &SHOULD; be registered in the same way
979   as new content-coding value tokens (&content-codings;).
980</t>
981<t>
982   A server which receives an entity-body with a transfer-coding it does
983   not understand &SHOULD; return 501 (Not Implemented), and close the
984   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
985   client.
986</t>
987
988<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
989  <x:anchor-alias value="chunk"/>
990  <x:anchor-alias value="Chunked-Body"/>
991  <x:anchor-alias value="chunk-data"/>
992  <x:anchor-alias value="chunk-ext"/>
993  <x:anchor-alias value="chunk-ext-name"/>
994  <x:anchor-alias value="chunk-ext-val"/>
995  <x:anchor-alias value="chunk-size"/>
996  <x:anchor-alias value="last-chunk"/>
997  <x:anchor-alias value="trailer-part"/>
998<t>
999   The chunked encoding modifies the body of a message in order to
1000   transfer it as a series of chunks, each with its own size indicator,
1001   followed by an &OPTIONAL; trailer containing entity-header fields. This
1002   allows dynamically produced content to be transferred along with the
1003   information necessary for the recipient to verify that it has
1004   received the full message.
1005</t>
1006<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/>
1007  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1008                   <x:ref>last-chunk</x:ref>
1009                   <x:ref>trailer-part</x:ref>
1010                   <x:ref>CRLF</x:ref>
1011 
1012  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1013                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1014  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1015  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1016 
1017  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1018                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1019  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1020  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1021  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1022  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1023</artwork></figure>
1024<t>
1025   The chunk-size field is a string of hex digits indicating the size of
1026   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1027   zero, followed by the trailer, which is terminated by an empty line.
1028</t>
1029<t>
1030   The trailer allows the sender to include additional HTTP header
1031   fields at the end of the message. The Trailer header field can be
1032   used to indicate which header fields are included in a trailer (see
1033   <xref target="header.trailer"/>).
1034</t>
1035<t>
1036   A server using chunked transfer-coding in a response &MUST-NOT; use the
1037   trailer for any header fields unless at least one of the following is
1038   true:
1039  <list style="numbers">
1040    <t>the request included a TE header field that indicates "trailers" is
1041     acceptable in the transfer-coding of the  response, as described in
1042     <xref target="header.te"/>; or,</t>
1043
1044    <t>the server is the origin server for the response, the trailer
1045     fields consist entirely of optional metadata, and the recipient
1046     could use the message (in a manner acceptable to the origin server)
1047     without receiving this metadata.  In other words, the origin server
1048     is willing to accept the possibility that the trailer fields might
1049     be silently discarded along the path to the client.</t>
1050  </list>
1051</t>
1052<t>
1053   This requirement prevents an interoperability failure when the
1054   message is being received by an HTTP/1.1 (or later) proxy and
1055   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1056   compliance with the protocol would have necessitated a possibly
1057   infinite buffer on the proxy.
1058</t>
1059<t>
1060   A process for decoding the "chunked" transfer-coding
1061   can be represented in pseudo-code as:
1062</t>
1063<figure><artwork type="code">
1064  length := 0
1065  read chunk-size, chunk-ext (if any) and CRLF
1066  while (chunk-size &gt; 0) {
1067     read chunk-data and CRLF
1068     append chunk-data to entity-body
1069     length := length + chunk-size
1070     read chunk-size and CRLF
1071  }
1072  read entity-header
1073  while (entity-header not empty) {
1074     append entity-header to existing header fields
1075     read entity-header
1076  }
1077  Content-Length := length
1078  Remove "chunked" from Transfer-Encoding
1079</artwork></figure>
1080<t>
1081   All HTTP/1.1 applications &MUST; be able to receive and decode the
1082   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1083   they do not understand.
1084</t>
1085</section>
1086</section>
1087
1088<section title="Product Tokens" anchor="product.tokens">
1089  <x:anchor-alias value="product"/>
1090  <x:anchor-alias value="product-version"/>
1091<t>
1092   Product tokens are used to allow communicating applications to
1093   identify themselves by software name and version. Most fields using
1094   product tokens also allow sub-products which form a significant part
1095   of the application to be listed, separated by white space. By
1096   convention, the products are listed in order of their significance
1097   for identifying the application.
1098</t>
1099<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1100  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1101  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1102</artwork></figure>
1103<t>
1104   Examples:
1105</t>
1106<figure><artwork type="example">
1107    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1108    Server: Apache/0.8.4
1109</artwork></figure>
1110<t>
1111   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1112   used for advertising or other non-essential information. Although any
1113   token character &MAY; appear in a product-version, this token &SHOULD;
1114   only be used for a version identifier (i.e., successive versions of
1115   the same product &SHOULD; only differ in the product-version portion of
1116   the product value).
1117</t>
1118</section>
1119
1120</section>
1121
1122<section title="HTTP Message" anchor="http.message">
1123
1124<section title="Message Types" anchor="message.types">
1125  <x:anchor-alias value="generic-message"/>
1126  <x:anchor-alias value="HTTP-message"/>
1127  <x:anchor-alias value="start-line"/>
1128<t>
1129   HTTP messages consist of requests from client to server and responses
1130   from server to client.
1131</t>
1132<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1133  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1134</artwork></figure>
1135<t>
1136   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1137   message format of <xref target="RFC5322"/> for transferring entities (the payload
1138   of the message). Both types of message consist of a start-line, zero
1139   or more header fields (also known as "headers"), an empty line (i.e.,
1140   a line with nothing preceding the CRLF) indicating the end of the
1141   header fields, and possibly a message-body.
1142</t>
1143<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1144  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1145                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1146                    <x:ref>CRLF</x:ref>
1147                    [ <x:ref>message-body</x:ref> ]
1148  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1149</artwork></figure>
1150<t>
1151   In the interest of robustness, servers &SHOULD; ignore any empty
1152   line(s) received where a Request-Line is expected. In other words, if
1153   the server is reading the protocol stream at the beginning of a
1154   message and receives a CRLF first, it should ignore the CRLF.
1155</t>
1156<t>
1157   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1158   after a POST request. To restate what is explicitly forbidden by the
1159   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1160   extra CRLF.
1161</t>
1162</section>
1163
1164<section title="Message Headers" anchor="message.headers">
1165  <x:anchor-alias value="field-content"/>
1166  <x:anchor-alias value="field-name"/>
1167  <x:anchor-alias value="field-value"/>
1168  <x:anchor-alias value="message-header"/>
1169<t>
1170   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1171   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1172   entity-header (&entity-header-fields;) fields, follow the same generic format as
1173   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1174   of a name followed by a colon (":") and the field value. Field names
1175   are case-insensitive. The field value &MAY; be preceded by any amount
1176   of LWS, though a single SP is preferred. Header fields can be
1177   extended over multiple lines by preceding each extra line with at
1178   least one SP or HTAB. Applications ought to follow "common form", where
1179   one is known or indicated, when generating HTTP constructs, since
1180   there might exist some implementations that fail to accept anything
1181   beyond the common forms.
1182</t>
1183<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"/>
1184  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1185  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1186  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1187  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1188</artwork></figure>
1189<t>
1190  <cref>whitespace between field-name and colon is an error and MUST NOT be accepted</cref>
1191</t>
1192<t>
1193   The field-content does not include any leading or trailing LWS:
1194   linear white space occurring before the first non-whitespace
1195   character of the field-value or after the last non-whitespace
1196   character of the field-value. Such leading or trailing LWS &MAY; be
1197   removed without changing the semantics of the field value. Any LWS
1198   that occurs between field-content &MAY; be replaced with a single SP
1199   before interpreting the field value or forwarding the message
1200   downstream.
1201</t>
1202<t>
1203   The order in which header fields with differing field names are
1204   received is not significant. However, it is "good practice" to send
1205   general-header fields first, followed by request-header or response-header
1206   fields, and ending with the entity-header fields.
1207</t>
1208<t>
1209   Multiple message-header fields with the same field-name &MAY; be
1210   present in a message if and only if the entire field-value for that
1211   header field is defined as a comma-separated list [i.e., #(values)].
1212   It &MUST; be possible to combine the multiple header fields into one
1213   "field-name: field-value" pair, without changing the semantics of the
1214   message, by appending each subsequent field-value to the first, each
1215   separated by a comma. The order in which header fields with the same
1216   field-name are received is therefore significant to the
1217   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1218   change the order of these field values when a message is forwarded.
1219</t>
1220<t>
1221  <list><t>
1222   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1223   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1224   can occur multiple times, but does not use the list syntax, and thus cannot
1225   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1226   for details.) Also note that the Set-Cookie2 header specified in
1227   <xref target="RFC2965"/> does not share this problem.
1228  </t></list>
1229</t>
1230 
1231</section>
1232
1233<section title="Message Body" anchor="message.body">
1234  <x:anchor-alias value="message-body"/>
1235<t>
1236   The message-body (if any) of an HTTP message is used to carry the
1237   entity-body associated with the request or response. The message-body
1238   differs from the entity-body only when a transfer-coding has been
1239   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1240</t>
1241<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1242  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1243               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1244</artwork></figure>
1245<t>
1246   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1247   applied by an application to ensure safe and proper transfer of the
1248   message. Transfer-Encoding is a property of the message, not of the
1249   entity, and thus &MAY; be added or removed by any application along the
1250   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1251   when certain transfer-codings may be used.)
1252</t>
1253<t>
1254   The rules for when a message-body is allowed in a message differ for
1255   requests and responses.
1256</t>
1257<t>
1258   The presence of a message-body in a request is signaled by the
1259   inclusion of a Content-Length or Transfer-Encoding header field in
1260   the request's message-headers. A message-body &MUST-NOT; be included in
1261   a request if the specification of the request method (&method;)
1262   explicitly disallows an entity-body in requests.
1263   When a request message contains both a message-body of non-zero
1264   length and a method that does not define any semantics for that
1265   request message-body, then an origin server &SHOULD; either ignore
1266   the message-body or respond with an appropriate error message
1267   (e.g., 413).  A proxy or gateway, when presented the same request,
1268   &SHOULD; either forward the request inbound with the message-body or
1269   ignore the message-body when determining a response.
1270</t>
1271<t>
1272   For response messages, whether or not a message-body is included with
1273   a message is dependent on both the request method and the response
1274   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1275   &MUST-NOT; include a message-body, even though the presence of entity-header
1276   fields might lead one to believe they do. All 1xx
1277   (informational), 204 (No Content), and 304 (Not Modified) responses
1278   &MUST-NOT; include a message-body. All other responses do include a
1279   message-body, although it &MAY; be of zero length.
1280</t>
1281</section>
1282
1283<section title="Message Length" anchor="message.length">
1284<t>
1285   The transfer-length of a message is the length of the message-body as
1286   it appears in the message; that is, after any transfer-codings have
1287   been applied. When a message-body is included with a message, the
1288   transfer-length of that body is determined by one of the following
1289   (in order of precedence):
1290</t>
1291<t>
1292  <list style="numbers">
1293    <x:lt><t>
1294     Any response message which "&MUST-NOT;" include a message-body (such
1295     as the 1xx, 204, and 304 responses and any response to a HEAD
1296     request) is always terminated by the first empty line after the
1297     header fields, regardless of the entity-header fields present in
1298     the message.
1299    </t></x:lt>
1300    <x:lt><t>
1301     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1302     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1303     is used, the transfer-length is defined by the use of this transfer-coding.
1304     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1305     is not present, the transfer-length is defined by the sender closing the connection.
1306    </t></x:lt>
1307    <x:lt><t>
1308     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1309     decimal value in OCTETs represents both the entity-length and the
1310     transfer-length. The Content-Length header field &MUST-NOT; be sent
1311     if these two lengths are different (i.e., if a Transfer-Encoding
1312     header field is present). If a message is received with both a
1313     Transfer-Encoding header field and a Content-Length header field,
1314     the latter &MUST; be ignored.
1315    </t></x:lt>
1316    <x:lt><t>
1317     If the message uses the media type "multipart/byteranges", and the
1318     transfer-length is not otherwise specified, then this self-delimiting
1319     media type defines the transfer-length. This media type
1320     &MUST-NOT; be used unless the sender knows that the recipient can parse
1321     it; the presence in a request of a Range header with multiple byte-range
1322     specifiers from a 1.1 client implies that the client can parse
1323     multipart/byteranges responses.
1324    <list style="empty"><t>
1325       A range header might be forwarded by a 1.0 proxy that does not
1326       understand multipart/byteranges; in this case the server &MUST;
1327       delimit the message using methods defined in items 1, 3 or 5 of
1328       this section.
1329    </t></list>
1330    </t></x:lt>
1331    <x:lt><t>
1332     By the server closing the connection. (Closing the connection
1333     cannot be used to indicate the end of a request body, since that
1334     would leave no possibility for the server to send back a response.)
1335    </t></x:lt>
1336  </list>
1337</t>
1338<t>
1339   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1340   containing a message-body &MUST; include a valid Content-Length header
1341   field unless the server is known to be HTTP/1.1 compliant. If a
1342   request contains a message-body and a Content-Length is not given,
1343   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1344   determine the length of the message, or with 411 (Length Required) if
1345   it wishes to insist on receiving a valid Content-Length.
1346</t>
1347<t>
1348   All HTTP/1.1 applications that receive entities &MUST; accept the
1349   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1350   to be used for messages when the message length cannot be determined
1351   in advance.
1352</t>
1353<t>
1354   Messages &MUST-NOT; include both a Content-Length header field and a
1355   transfer-coding. If the message does include a
1356   transfer-coding, the Content-Length &MUST; be ignored.
1357</t>
1358<t>
1359   When a Content-Length is given in a message where a message-body is
1360   allowed, its field value &MUST; exactly match the number of OCTETs in
1361   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1362   invalid length is received and detected.
1363</t>
1364</section>
1365
1366<section title="General Header Fields" anchor="general.header.fields">
1367  <x:anchor-alias value="general-header"/>
1368<t>
1369   There are a few header fields which have general applicability for
1370   both request and response messages, but which do not apply to the
1371   entity being transferred. These header fields apply only to the
1372   message being transmitted.
1373</t>
1374<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1375  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1376                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1377                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1378                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1379                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1380                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1381                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1382                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1383                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1384</artwork></figure>
1385<t>
1386   General-header field names can be extended reliably only in
1387   combination with a change in the protocol version. However, new or
1388   experimental header fields may be given the semantics of general
1389   header fields if all parties in the communication recognize them to
1390   be general-header fields. Unrecognized header fields are treated as
1391   entity-header fields.
1392</t>
1393</section>
1394</section>
1395
1396<section title="Request" anchor="request">
1397  <x:anchor-alias value="Request"/>
1398<t>
1399   A request message from a client to a server includes, within the
1400   first line of that message, the method to be applied to the resource,
1401   the identifier of the resource, and the protocol version in use.
1402</t>
1403<!--                 Host                      ; should be moved here eventually -->
1404<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1405  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1406                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1407                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1408                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1409                  <x:ref>CRLF</x:ref>
1410                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1411</artwork></figure>
1412
1413<section title="Request-Line" anchor="request-line">
1414  <x:anchor-alias value="Request-Line"/>
1415<t>
1416   The Request-Line begins with a method token, followed by the
1417   Request-URI and the protocol version, and ending with CRLF. The
1418   elements are separated by SP characters. No CR or LF is allowed
1419   except in the final CRLF sequence.
1420</t>
1421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1422  <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>
1423</artwork></figure>
1424
1425<section title="Method" anchor="method">
1426  <x:anchor-alias value="Method"/>
1427<t>
1428   The Method  token indicates the method to be performed on the
1429   resource identified by the Request-URI. The method is case-sensitive.
1430</t>
1431<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1432  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1433</artwork></figure>
1434</section>
1435
1436<section title="Request-URI" anchor="request-uri">
1437  <x:anchor-alias value="Request-URI"/>
1438<t>
1439   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1440   identifies the resource upon which to apply the request.
1441</t>
1442<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1443  <x:ref>Request-URI</x:ref>    = "*"
1444                 / <x:ref>absolute-URI</x:ref>
1445                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1446                 / <x:ref>authority</x:ref>
1447</artwork></figure>
1448<t>
1449   The four options for Request-URI are dependent on the nature of the
1450   request. The asterisk "*" means that the request does not apply to a
1451   particular resource, but to the server itself, and is only allowed
1452   when the method used does not necessarily apply to a resource. One
1453   example would be
1454</t>
1455<figure><artwork type="example">
1456    OPTIONS * HTTP/1.1
1457</artwork></figure>
1458<t>
1459   The absolute-URI form is &REQUIRED; when the request is being made to a
1460   proxy. The proxy is requested to forward the request or service it
1461   from a valid cache, and return the response. Note that the proxy &MAY;
1462   forward the request on to another proxy or directly to the server
1463   specified by the absolute-URI. In order to avoid request loops, a
1464   proxy &MUST; be able to recognize all of its server names, including
1465   any aliases, local variations, and the numeric IP address. An example
1466   Request-Line would be:
1467</t>
1468<figure><artwork type="example">
1469    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1470</artwork></figure>
1471<t>
1472   To allow for transition to absolute-URIs in all requests in future
1473   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1474   form in requests, even though HTTP/1.1 clients will only generate
1475   them in requests to proxies.
1476</t>
1477<t>
1478   The authority form is only used by the CONNECT method (&CONNECT;).
1479</t>
1480<t>
1481   The most common form of Request-URI is that used to identify a
1482   resource on an origin server or gateway. In this case the absolute
1483   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1484   the Request-URI, and the network location of the URI (authority) &MUST;
1485   be transmitted in a Host header field. For example, a client wishing
1486   to retrieve the resource above directly from the origin server would
1487   create a TCP connection to port 80 of the host "www.example.org" and send
1488   the lines:
1489</t>
1490<figure><artwork type="example">
1491    GET /pub/WWW/TheProject.html HTTP/1.1
1492    Host: www.example.org
1493</artwork></figure>
1494<t>
1495   followed by the remainder of the Request. Note that the absolute path
1496   cannot be empty; if none is present in the original URI, it &MUST; be
1497   given as "/" (the server root).
1498</t>
1499<t>
1500   The Request-URI is transmitted in the format specified in
1501   <xref target="http.uri"/>. If the Request-URI is encoded using the
1502   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1503   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1504   &MUST; decode the Request-URI in order to
1505   properly interpret the request. Servers &SHOULD; respond to invalid
1506   Request-URIs with an appropriate status code.
1507</t>
1508<t>
1509   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1510   received Request-URI when forwarding it to the next inbound server,
1511   except as noted above to replace a null path-absolute with "/".
1512</t>
1513<t>
1514  <list><t>
1515      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1516      meaning of the request when the origin server is improperly using
1517      a non-reserved URI character for a reserved purpose.  Implementors
1518      should be aware that some pre-HTTP/1.1 proxies have been known to
1519      rewrite the Request-URI.
1520  </t></list>
1521</t>
1522</section>
1523</section>
1524
1525<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1526<t>
1527   The exact resource identified by an Internet request is determined by
1528   examining both the Request-URI and the Host header field.
1529</t>
1530<t>
1531   An origin server that does not allow resources to differ by the
1532   requested host &MAY; ignore the Host header field value when
1533   determining the resource identified by an HTTP/1.1 request. (But see
1534   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1535   for other requirements on Host support in HTTP/1.1.)
1536</t>
1537<t>
1538   An origin server that does differentiate resources based on the host
1539   requested (sometimes referred to as virtual hosts or vanity host
1540   names) &MUST; use the following rules for determining the requested
1541   resource on an HTTP/1.1 request:
1542  <list style="numbers">
1543    <t>If Request-URI is an absolute-URI, the host is part of the
1544     Request-URI. Any Host header field value in the request &MUST; be
1545     ignored.</t>
1546    <t>If the Request-URI is not an absolute-URI, and the request includes
1547     a Host header field, the host is determined by the Host header
1548     field value.</t>
1549    <t>If the host as determined by rule 1 or 2 is not a valid host on
1550     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1551  </list>
1552</t>
1553<t>
1554   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1555   attempt to use heuristics (e.g., examination of the URI path for
1556   something unique to a particular host) in order to determine what
1557   exact resource is being requested.
1558</t>
1559</section>
1560
1561</section>
1562
1563
1564<section title="Response" anchor="response">
1565  <x:anchor-alias value="Response"/>
1566<t>
1567   After receiving and interpreting a request message, a server responds
1568   with an HTTP response message.
1569</t>
1570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1571  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1572                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1573                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1574                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1575                  <x:ref>CRLF</x:ref>
1576                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1577</artwork></figure>
1578
1579<section title="Status-Line" anchor="status-line">
1580  <x:anchor-alias value="Status-Line"/>
1581<t>
1582   The first line of a Response message is the Status-Line, consisting
1583   of the protocol version followed by a numeric status code and its
1584   associated textual phrase, with each element separated by SP
1585   characters. No CR or LF is allowed except in the final CRLF sequence.
1586</t>
1587<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1588  <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>
1589</artwork></figure>
1590
1591<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1592  <x:anchor-alias value="Reason-Phrase"/>
1593  <x:anchor-alias value="Status-Code"/>
1594<t>
1595   The Status-Code element is a 3-digit integer result code of the
1596   attempt to understand and satisfy the request. These codes are fully
1597   defined in &status-codes;.  The Reason Phrase exists for the sole
1598   purpose of providing a textual description associated with the numeric
1599   status code, out of deference to earlier Internet application protocols
1600   that were more frequently used with interactive text clients.
1601   A client &SHOULD; ignore the content of the Reason Phrase.
1602</t>
1603<t>
1604   The first digit of the Status-Code defines the class of response. The
1605   last two digits do not have any categorization role. There are 5
1606   values for the first digit:
1607  <list style="symbols">
1608    <t>
1609      1xx: Informational - Request received, continuing process
1610    </t>
1611    <t>
1612      2xx: Success - The action was successfully received,
1613        understood, and accepted
1614    </t>
1615    <t>
1616      3xx: Redirection - Further action must be taken in order to
1617        complete the request
1618    </t>
1619    <t>
1620      4xx: Client Error - The request contains bad syntax or cannot
1621        be fulfilled
1622    </t>
1623    <t>
1624      5xx: Server Error - The server failed to fulfill an apparently
1625        valid request
1626    </t>
1627  </list>
1628</t>
1629<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"/>
1630  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1631  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1632</artwork></figure>
1633</section>
1634</section>
1635
1636</section>
1637
1638
1639<section title="Connections" anchor="connections">
1640
1641<section title="Persistent Connections" anchor="persistent.connections">
1642
1643<section title="Purpose" anchor="persistent.purpose">
1644<t>
1645   Prior to persistent connections, a separate TCP connection was
1646   established to fetch each URL, increasing the load on HTTP servers
1647   and causing congestion on the Internet. The use of inline images and
1648   other associated data often require a client to make multiple
1649   requests of the same server in a short amount of time. Analysis of
1650   these performance problems and results from a prototype
1651   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1652   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1653   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1654   T/TCP <xref target="Tou1998"/>.
1655</t>
1656<t>
1657   Persistent HTTP connections have a number of advantages:
1658  <list style="symbols">
1659      <t>
1660        By opening and closing fewer TCP connections, CPU time is saved
1661        in routers and hosts (clients, servers, proxies, gateways,
1662        tunnels, or caches), and memory used for TCP protocol control
1663        blocks can be saved in hosts.
1664      </t>
1665      <t>
1666        HTTP requests and responses can be pipelined on a connection.
1667        Pipelining allows a client to make multiple requests without
1668        waiting for each response, allowing a single TCP connection to
1669        be used much more efficiently, with much lower elapsed time.
1670      </t>
1671      <t>
1672        Network congestion is reduced by reducing the number of packets
1673        caused by TCP opens, and by allowing TCP sufficient time to
1674        determine the congestion state of the network.
1675      </t>
1676      <t>
1677        Latency on subsequent requests is reduced since there is no time
1678        spent in TCP's connection opening handshake.
1679      </t>
1680      <t>
1681        HTTP can evolve more gracefully, since errors can be reported
1682        without the penalty of closing the TCP connection. Clients using
1683        future versions of HTTP might optimistically try a new feature,
1684        but if communicating with an older server, retry with old
1685        semantics after an error is reported.
1686      </t>
1687    </list>
1688</t>
1689<t>
1690   HTTP implementations &SHOULD; implement persistent connections.
1691</t>
1692</section>
1693
1694<section title="Overall Operation" anchor="persistent.overall">
1695<t>
1696   A significant difference between HTTP/1.1 and earlier versions of
1697   HTTP is that persistent connections are the default behavior of any
1698   HTTP connection. That is, unless otherwise indicated, the client
1699   &SHOULD; assume that the server will maintain a persistent connection,
1700   even after error responses from the server.
1701</t>
1702<t>
1703   Persistent connections provide a mechanism by which a client and a
1704   server can signal the close of a TCP connection. This signaling takes
1705   place using the Connection header field (<xref target="header.connection"/>). Once a close
1706   has been signaled, the client &MUST-NOT; send any more requests on that
1707   connection.
1708</t>
1709
1710<section title="Negotiation" anchor="persistent.negotiation">
1711<t>
1712   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1713   maintain a persistent connection unless a Connection header including
1714   the connection-token "close" was sent in the request. If the server
1715   chooses to close the connection immediately after sending the
1716   response, it &SHOULD; send a Connection header including the
1717   connection-token close.
1718</t>
1719<t>
1720   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1721   decide to keep it open based on whether the response from a server
1722   contains a Connection header with the connection-token close. In case
1723   the client does not want to maintain a connection for more than that
1724   request, it &SHOULD; send a Connection header including the
1725   connection-token close.
1726</t>
1727<t>
1728   If either the client or the server sends the close token in the
1729   Connection header, that request becomes the last one for the
1730   connection.
1731</t>
1732<t>
1733   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1734   maintained for HTTP versions less than 1.1 unless it is explicitly
1735   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1736   compatibility with HTTP/1.0 clients.
1737</t>
1738<t>
1739   In order to remain persistent, all messages on the connection &MUST;
1740   have a self-defined message length (i.e., one not defined by closure
1741   of the connection), as described in <xref target="message.length"/>.
1742</t>
1743</section>
1744
1745<section title="Pipelining" anchor="pipelining">
1746<t>
1747   A client that supports persistent connections &MAY; "pipeline" its
1748   requests (i.e., send multiple requests without waiting for each
1749   response). A server &MUST; send its responses to those requests in the
1750   same order that the requests were received.
1751</t>
1752<t>
1753   Clients which assume persistent connections and pipeline immediately
1754   after connection establishment &SHOULD; be prepared to retry their
1755   connection if the first pipelined attempt fails. If a client does
1756   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1757   persistent. Clients &MUST; also be prepared to resend their requests if
1758   the server closes the connection before sending all of the
1759   corresponding responses.
1760</t>
1761<t>
1762   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1763   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1764   premature termination of the transport connection could lead to
1765   indeterminate results. A client wishing to send a non-idempotent
1766   request &SHOULD; wait to send that request until it has received the
1767   response status for the previous request.
1768</t>
1769</section>
1770</section>
1771
1772<section title="Proxy Servers" anchor="persistent.proxy">
1773<t>
1774   It is especially important that proxies correctly implement the
1775   properties of the Connection header field as specified in <xref target="header.connection"/>.
1776</t>
1777<t>
1778   The proxy server &MUST; signal persistent connections separately with
1779   its clients and the origin servers (or other proxy servers) that it
1780   connects to. Each persistent connection applies to only one transport
1781   link.
1782</t>
1783<t>
1784   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1785   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1786   discussion of the problems with the Keep-Alive header implemented by
1787   many HTTP/1.0 clients).
1788</t>
1789</section>
1790
1791<section title="Practical Considerations" anchor="persistent.practical">
1792<t>
1793   Servers will usually have some time-out value beyond which they will
1794   no longer maintain an inactive connection. Proxy servers might make
1795   this a higher value since it is likely that the client will be making
1796   more connections through the same server. The use of persistent
1797   connections places no requirements on the length (or existence) of
1798   this time-out for either the client or the server.
1799</t>
1800<t>
1801   When a client or server wishes to time-out it &SHOULD; issue a graceful
1802   close on the transport connection. Clients and servers &SHOULD; both
1803   constantly watch for the other side of the transport close, and
1804   respond to it as appropriate. If a client or server does not detect
1805   the other side's close promptly it could cause unnecessary resource
1806   drain on the network.
1807</t>
1808<t>
1809   A client, server, or proxy &MAY; close the transport connection at any
1810   time. For example, a client might have started to send a new request
1811   at the same time that the server has decided to close the "idle"
1812   connection. From the server's point of view, the connection is being
1813   closed while it was idle, but from the client's point of view, a
1814   request is in progress.
1815</t>
1816<t>
1817   This means that clients, servers, and proxies &MUST; be able to recover
1818   from asynchronous close events. Client software &SHOULD; reopen the
1819   transport connection and retransmit the aborted sequence of requests
1820   without user interaction so long as the request sequence is
1821   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1822   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1823   human operator the choice of retrying the request(s). Confirmation by
1824   user-agent software with semantic understanding of the application
1825   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1826   be repeated if the second sequence of requests fails.
1827</t>
1828<t>
1829   Servers &SHOULD; always respond to at least one request per connection,
1830   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1831   middle of transmitting a response, unless a network or client failure
1832   is suspected.
1833</t>
1834<t>
1835   Clients that use persistent connections &SHOULD; limit the number of
1836   simultaneous connections that they maintain to a given server. A
1837   single-user client &SHOULD-NOT; maintain more than 2 connections with
1838   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1839   another server or proxy, where N is the number of simultaneously
1840   active users. These guidelines are intended to improve HTTP response
1841   times and avoid congestion.
1842</t>
1843</section>
1844</section>
1845
1846<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1847
1848<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1849<t>
1850   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1851   flow control mechanisms to resolve temporary overloads, rather than
1852   terminating connections with the expectation that clients will retry.
1853   The latter technique can exacerbate network congestion.
1854</t>
1855</section>
1856
1857<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1858<t>
1859   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1860   the network connection for an error status while it is transmitting
1861   the request. If the client sees an error status, it &SHOULD;
1862   immediately cease transmitting the body. If the body is being sent
1863   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1864   empty trailer &MAY; be used to prematurely mark the end of the message.
1865   If the body was preceded by a Content-Length header, the client &MUST;
1866   close the connection.
1867</t>
1868</section>
1869
1870<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1871<t>
1872   The purpose of the 100 (Continue) status (see &status-100;) is to
1873   allow a client that is sending a request message with a request body
1874   to determine if the origin server is willing to accept the request
1875   (based on the request headers) before the client sends the request
1876   body. In some cases, it might either be inappropriate or highly
1877   inefficient for the client to send the body if the server will reject
1878   the message without looking at the body.
1879</t>
1880<t>
1881   Requirements for HTTP/1.1 clients:
1882  <list style="symbols">
1883    <t>
1884        If a client will wait for a 100 (Continue) response before
1885        sending the request body, it &MUST; send an Expect request-header
1886        field (&header-expect;) with the "100-continue" expectation.
1887    </t>
1888    <t>
1889        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1890        with the "100-continue" expectation if it does not intend
1891        to send a request body.
1892    </t>
1893  </list>
1894</t>
1895<t>
1896   Because of the presence of older implementations, the protocol allows
1897   ambiguous situations in which a client may send "Expect: 100-continue"
1898   without receiving either a 417 (Expectation Failed) status
1899   or a 100 (Continue) status. Therefore, when a client sends this
1900   header field to an origin server (possibly via a proxy) from which it
1901   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1902   for an indefinite period before sending the request body.
1903</t>
1904<t>
1905   Requirements for HTTP/1.1 origin servers:
1906  <list style="symbols">
1907    <t> Upon receiving a request which includes an Expect request-header
1908        field with the "100-continue" expectation, an origin server &MUST;
1909        either respond with 100 (Continue) status and continue to read
1910        from the input stream, or respond with a final status code. The
1911        origin server &MUST-NOT; wait for the request body before sending
1912        the 100 (Continue) response. If it responds with a final status
1913        code, it &MAY; close the transport connection or it &MAY; continue
1914        to read and discard the rest of the request.  It &MUST-NOT;
1915        perform the requested method if it returns a final status code.
1916    </t>
1917    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1918        the request message does not include an Expect request-header
1919        field with the "100-continue" expectation, and &MUST-NOT; send a
1920        100 (Continue) response if such a request comes from an HTTP/1.0
1921        (or earlier) client. There is an exception to this rule: for
1922        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1923        status in response to an HTTP/1.1 PUT or POST request that does
1924        not include an Expect request-header field with the "100-continue"
1925        expectation. This exception, the purpose of which is
1926        to minimize any client processing delays associated with an
1927        undeclared wait for 100 (Continue) status, applies only to
1928        HTTP/1.1 requests, and not to requests with any other HTTP-version
1929        value.
1930    </t>
1931    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1932        already received some or all of the request body for the
1933        corresponding request.
1934    </t>
1935    <t> An origin server that sends a 100 (Continue) response &MUST;
1936    ultimately send a final status code, once the request body is
1937        received and processed, unless it terminates the transport
1938        connection prematurely.
1939    </t>
1940    <t> If an origin server receives a request that does not include an
1941        Expect request-header field with the "100-continue" expectation,
1942        the request includes a request body, and the server responds
1943        with a final status code before reading the entire request body
1944        from the transport connection, then the server &SHOULD-NOT;  close
1945        the transport connection until it has read the entire request,
1946        or until the client closes the connection. Otherwise, the client
1947        might not reliably receive the response message. However, this
1948        requirement is not be construed as preventing a server from
1949        defending itself against denial-of-service attacks, or from
1950        badly broken client implementations.
1951      </t>
1952    </list>
1953</t>
1954<t>
1955   Requirements for HTTP/1.1 proxies:
1956  <list style="symbols">
1957    <t> If a proxy receives a request that includes an Expect request-header
1958        field with the "100-continue" expectation, and the proxy
1959        either knows that the next-hop server complies with HTTP/1.1 or
1960        higher, or does not know the HTTP version of the next-hop
1961        server, it &MUST; forward the request, including the Expect header
1962        field.
1963    </t>
1964    <t> If the proxy knows that the version of the next-hop server is
1965        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1966        respond with a 417 (Expectation Failed) status.
1967    </t>
1968    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1969        numbers received from recently-referenced next-hop servers.
1970    </t>
1971    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1972        request message was received from an HTTP/1.0 (or earlier)
1973        client and did not include an Expect request-header field with
1974        the "100-continue" expectation. This requirement overrides the
1975        general rule for forwarding of 1xx responses (see &status-1xx;).
1976    </t>
1977  </list>
1978</t>
1979</section>
1980
1981<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1982<t>
1983   If an HTTP/1.1 client sends a request which includes a request body,
1984   but which does not include an Expect request-header field with the
1985   "100-continue" expectation, and if the client is not directly
1986   connected to an HTTP/1.1 origin server, and if the client sees the
1987   connection close before receiving any status from the server, the
1988   client &SHOULD; retry the request.  If the client does retry this
1989   request, it &MAY; use the following "binary exponential backoff"
1990   algorithm to be assured of obtaining a reliable response:
1991  <list style="numbers">
1992    <t>
1993      Initiate a new connection to the server
1994    </t>
1995    <t>
1996      Transmit the request-headers
1997    </t>
1998    <t>
1999      Initialize a variable R to the estimated round-trip time to the
2000         server (e.g., based on the time it took to establish the
2001         connection), or to a constant value of 5 seconds if the round-trip
2002         time is not available.
2003    </t>
2004    <t>
2005       Compute T = R * (2**N), where N is the number of previous
2006         retries of this request.
2007    </t>
2008    <t>
2009       Wait either for an error response from the server, or for T
2010         seconds (whichever comes first)
2011    </t>
2012    <t>
2013       If no error response is received, after T seconds transmit the
2014         body of the request.
2015    </t>
2016    <t>
2017       If client sees that the connection is closed prematurely,
2018         repeat from step 1 until the request is accepted, an error
2019         response is received, or the user becomes impatient and
2020         terminates the retry process.
2021    </t>
2022  </list>
2023</t>
2024<t>
2025   If at any point an error status is received, the client
2026  <list style="symbols">
2027      <t>&SHOULD-NOT;  continue and</t>
2028
2029      <t>&SHOULD; close the connection if it has not completed sending the
2030        request message.</t>
2031    </list>
2032</t>
2033</section>
2034</section>
2035</section>
2036
2037
2038<section title="Header Field Definitions" anchor="header.fields">
2039<t>
2040   This section defines the syntax and semantics of HTTP/1.1 header fields
2041   related to message framing and transport protocols.
2042</t>
2043<t>
2044   For entity-header fields, both sender and recipient refer to either the
2045   client or the server, depending on who sends and who receives the entity.
2046</t>
2047
2048<section title="Connection" anchor="header.connection">
2049  <iref primary="true" item="Connection header" x:for-anchor=""/>
2050  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2051  <x:anchor-alias value="Connection"/>
2052  <x:anchor-alias value="connection-token"/>
2053  <x:anchor-alias value="Connection-v"/>
2054<t>
2055   The general-header field "Connection" allows the sender to specify
2056   options that are desired for that particular connection and &MUST-NOT;
2057   be communicated by proxies over further connections.
2058</t>
2059<t>
2060   The Connection header's value has the following grammar:
2061</t>
2062<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2063  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2064  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2065  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2066</artwork></figure>
2067<t>
2068   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2069   message is forwarded and, for each connection-token in this field,
2070   remove any header field(s) from the message with the same name as the
2071   connection-token. Connection options are signaled by the presence of
2072   a connection-token in the Connection header field, not by any
2073   corresponding additional header field(s), since the additional header
2074   field may not be sent if there are no parameters associated with that
2075   connection option.
2076</t>
2077<t>
2078   Message headers listed in the Connection header &MUST-NOT; include
2079   end-to-end headers, such as Cache-Control.
2080</t>
2081<t>
2082   HTTP/1.1 defines the "close" connection option for the sender to
2083   signal that the connection will be closed after completion of the
2084   response. For example,
2085</t>
2086<figure><artwork type="example">
2087  Connection: close
2088</artwork></figure>
2089<t>
2090   in either the request or the response header fields indicates that
2091   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2092   after the current request/response is complete.
2093</t>
2094<t>
2095   An HTTP/1.1 client that does not support persistent connections &MUST;
2096   include the "close" connection option in every request message.
2097</t>
2098<t>
2099   An HTTP/1.1 server that does not support persistent connections &MUST;
2100   include the "close" connection option in every response message that
2101   does not have a 1xx (informational) status code.
2102</t>
2103<t>
2104   A system receiving an HTTP/1.0 (or lower-version) message that
2105   includes a Connection header &MUST;, for each connection-token in this
2106   field, remove and ignore any header field(s) from the message with
2107   the same name as the connection-token. This protects against mistaken
2108   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2109</t>
2110</section>
2111
2112<section title="Content-Length" anchor="header.content-length">
2113  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2114  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2115  <x:anchor-alias value="Content-Length"/>
2116  <x:anchor-alias value="Content-Length-v"/>
2117<t>
2118   The entity-header field "Content-Length" indicates the size of the
2119   entity-body, in decimal number of OCTETs, sent to the recipient or,
2120   in the case of the HEAD method, the size of the entity-body that
2121   would have been sent had the request been a GET.
2122</t>
2123<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2124  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2125  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2126</artwork></figure>
2127<t>
2128   An example is
2129</t>
2130<figure><artwork type="example">
2131  Content-Length: 3495
2132</artwork></figure>
2133<t>
2134   Applications &SHOULD; use this field to indicate the transfer-length of
2135   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2136</t>
2137<t>
2138   Any Content-Length greater than or equal to zero is a valid value.
2139   <xref target="message.length"/> describes how to determine the length of a message-body
2140   if a Content-Length is not given.
2141</t>
2142<t>
2143   Note that the meaning of this field is significantly different from
2144   the corresponding definition in MIME, where it is an optional field
2145   used within the "message/external-body" content-type. In HTTP, it
2146   &SHOULD; be sent whenever the message's length can be determined prior
2147   to being transferred, unless this is prohibited by the rules in
2148   <xref target="message.length"/>.
2149</t>
2150</section>
2151
2152<section title="Date" anchor="header.date">
2153  <iref primary="true" item="Date header" x:for-anchor=""/>
2154  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2155  <x:anchor-alias value="Date"/>
2156  <x:anchor-alias value="Date-v"/>
2157<t>
2158   The general-header field "Date" represents the date and time at which
2159   the message was originated, having the same semantics as orig-date in
2160   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2161   HTTP-date, as described in <xref target="full.date"/>;
2162   it &MUST; be sent in rfc1123-date format.
2163</t>
2164<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2165  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2166  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2167</artwork></figure>
2168<t>
2169   An example is
2170</t>
2171<figure><artwork type="example">
2172  Date: Tue, 15 Nov 1994 08:12:31 GMT
2173</artwork></figure>
2174<t>
2175   Origin servers &MUST; include a Date header field in all responses,
2176   except in these cases:
2177  <list style="numbers">
2178      <t>If the response status code is 100 (Continue) or 101 (Switching
2179         Protocols), the response &MAY; include a Date header field, at
2180         the server's option.</t>
2181
2182      <t>If the response status code conveys a server error, e.g. 500
2183         (Internal Server Error) or 503 (Service Unavailable), and it is
2184         inconvenient or impossible to generate a valid Date.</t>
2185
2186      <t>If the server does not have a clock that can provide a
2187         reasonable approximation of the current time, its responses
2188         &MUST-NOT; include a Date header field. In this case, the rules
2189         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2190  </list>
2191</t>
2192<t>
2193   A received message that does not have a Date header field &MUST; be
2194   assigned one by the recipient if the message will be cached by that
2195   recipient or gatewayed via a protocol which requires a Date. An HTTP
2196   implementation without a clock &MUST-NOT; cache responses without
2197   revalidating them on every use. An HTTP cache, especially a shared
2198   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2199   clock with a reliable external standard.
2200</t>
2201<t>
2202   Clients &SHOULD; only send a Date header field in messages that include
2203   an entity-body, as in the case of the PUT and POST requests, and even
2204   then it is optional. A client without a clock &MUST-NOT; send a Date
2205   header field in a request.
2206</t>
2207<t>
2208   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2209   time subsequent to the generation of the message. It &SHOULD; represent
2210   the best available approximation of the date and time of message
2211   generation, unless the implementation has no means of generating a
2212   reasonably accurate date and time. In theory, the date ought to
2213   represent the moment just before the entity is generated. In
2214   practice, the date can be generated at any time during the message
2215   origination without affecting its semantic value.
2216</t>
2217
2218<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2219<t>
2220   Some origin server implementations might not have a clock available.
2221   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2222   values to a response, unless these values were associated
2223   with the resource by a system or user with a reliable clock. It &MAY;
2224   assign an Expires value that is known, at or before server
2225   configuration time, to be in the past (this allows "pre-expiration"
2226   of responses without storing separate Expires values for each
2227   resource).
2228</t>
2229</section>
2230</section>
2231
2232<section title="Host" anchor="header.host">
2233  <iref primary="true" item="Host header" x:for-anchor=""/>
2234  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2235  <x:anchor-alias value="Host"/>
2236  <x:anchor-alias value="Host-v"/>
2237<t>
2238   The request-header field "Host" specifies the Internet host and port
2239   number of the resource being requested, as obtained from the original
2240   URI given by the user or referring resource (generally an HTTP URL,
2241   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2242   the naming authority of the origin server or gateway given by the
2243   original URL. This allows the origin server or gateway to
2244   differentiate between internally-ambiguous URLs, such as the root "/"
2245   URL of a server for multiple host names on a single IP address.
2246</t>
2247<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2248  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2249  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2250</artwork></figure>
2251<t>
2252   A "host" without any trailing port information implies the default
2253   port for the service requested (e.g., "80" for an HTTP URL). For
2254   example, a request on the origin server for
2255   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2256</t>
2257<figure><artwork type="example">
2258  GET /pub/WWW/ HTTP/1.1
2259  Host: www.example.org
2260</artwork></figure>
2261<t>
2262   A client &MUST; include a Host header field in all HTTP/1.1 request
2263   messages. If the requested URI does not include an Internet host
2264   name for the service being requested, then the Host header field &MUST;
2265   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2266   request message it forwards does contain an appropriate Host header
2267   field that identifies the service being requested by the proxy. All
2268   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2269   status code to any HTTP/1.1 request message which lacks a Host header
2270   field.
2271</t>
2272<t>
2273   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2274   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2275   for other requirements relating to Host.
2276</t>
2277</section>
2278
2279<section title="TE" anchor="header.te">
2280  <iref primary="true" item="TE header" x:for-anchor=""/>
2281  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2282  <x:anchor-alias value="TE"/>
2283  <x:anchor-alias value="TE-v"/>
2284  <x:anchor-alias value="t-codings"/>
2285<t>
2286   The request-header field "TE" indicates what extension transfer-codings
2287   it is willing to accept in the response and whether or not it is
2288   willing to accept trailer fields in a chunked transfer-coding. Its
2289   value may consist of the keyword "trailers" and/or a comma-separated
2290   list of extension transfer-coding names with optional accept
2291   parameters (as described in <xref target="transfer.codings"/>).
2292</t>
2293<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2294  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2295  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2296  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2297</artwork></figure>
2298<t>
2299   The presence of the keyword "trailers" indicates that the client is
2300   willing to accept trailer fields in a chunked transfer-coding, as
2301   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2302   transfer-coding values even though it does not itself represent a
2303   transfer-coding.
2304</t>
2305<t>
2306   Examples of its use are:
2307</t>
2308<figure><artwork type="example">
2309  TE: deflate
2310  TE:
2311  TE: trailers, deflate;q=0.5
2312</artwork></figure>
2313<t>
2314   The TE header field only applies to the immediate connection.
2315   Therefore, the keyword &MUST; be supplied within a Connection header
2316   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2317</t>
2318<t>
2319   A server tests whether a transfer-coding is acceptable, according to
2320   a TE field, using these rules:
2321  <list style="numbers">
2322    <x:lt>
2323      <t>The "chunked" transfer-coding is always acceptable. If the
2324         keyword "trailers" is listed, the client indicates that it is
2325         willing to accept trailer fields in the chunked response on
2326         behalf of itself and any downstream clients. The implication is
2327         that, if given, the client is stating that either all
2328         downstream clients are willing to accept trailer fields in the
2329         forwarded response, or that it will attempt to buffer the
2330         response on behalf of downstream recipients.
2331      </t><t>
2332         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2333         chunked response such that a client can be assured of buffering
2334         the entire response.</t>
2335    </x:lt>
2336    <x:lt>
2337      <t>If the transfer-coding being tested is one of the transfer-codings
2338         listed in the TE field, then it is acceptable unless it
2339         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2340         qvalue of 0 means "not acceptable.")</t>
2341    </x:lt>
2342    <x:lt>
2343      <t>If multiple transfer-codings are acceptable, then the
2344         acceptable transfer-coding with the highest non-zero qvalue is
2345         preferred.  The "chunked" transfer-coding always has a qvalue
2346         of 1.</t>
2347    </x:lt>
2348  </list>
2349</t>
2350<t>
2351   If the TE field-value is empty or if no TE field is present, the only
2352   transfer-coding  is "chunked". A message with no transfer-coding is
2353   always acceptable.
2354</t>
2355</section>
2356
2357<section title="Trailer" anchor="header.trailer">
2358  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2359  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2360  <x:anchor-alias value="Trailer"/>
2361  <x:anchor-alias value="Trailer-v"/>
2362<t>
2363   The general field "Trailer" indicates that the given set of
2364   header fields is present in the trailer of a message encoded with
2365   chunked transfer-coding.
2366</t>
2367<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2368  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2369  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2370</artwork></figure>
2371<t>
2372   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2373   message using chunked transfer-coding with a non-empty trailer. Doing
2374   so allows the recipient to know which header fields to expect in the
2375   trailer.
2376</t>
2377<t>
2378   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2379   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2380   trailer fields in a "chunked" transfer-coding.
2381</t>
2382<t>
2383   Message header fields listed in the Trailer header field &MUST-NOT;
2384   include the following header fields:
2385  <list style="symbols">
2386    <t>Transfer-Encoding</t>
2387    <t>Content-Length</t>
2388    <t>Trailer</t>
2389  </list>
2390</t>
2391</section>
2392
2393<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2394  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2395  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2396  <x:anchor-alias value="Transfer-Encoding"/>
2397  <x:anchor-alias value="Transfer-Encoding-v"/>
2398<t>
2399   The general-header "Transfer-Encoding" field indicates what (if any)
2400   type of transformation has been applied to the message body in order
2401   to safely transfer it between the sender and the recipient. This
2402   differs from the content-coding in that the transfer-coding is a
2403   property of the message, not of the entity.
2404</t>
2405<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2406  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2407                        <x:ref>Transfer-Encoding-v</x:ref>
2408  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2409</artwork></figure>
2410<t>
2411   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2412</t>
2413<figure><artwork type="example">
2414  Transfer-Encoding: chunked
2415</artwork></figure>
2416<t>
2417   If multiple encodings have been applied to an entity, the transfer-codings
2418   &MUST; be listed in the order in which they were applied.
2419   Additional information about the encoding parameters &MAY; be provided
2420   by other entity-header fields not defined by this specification.
2421</t>
2422<t>
2423   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2424   header.
2425</t>
2426</section>
2427
2428<section title="Upgrade" anchor="header.upgrade">
2429  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2430  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2431  <x:anchor-alias value="Upgrade"/>
2432  <x:anchor-alias value="Upgrade-v"/>
2433<t>
2434   The general-header "Upgrade" allows the client to specify what
2435   additional communication protocols it supports and would like to use
2436   if the server finds it appropriate to switch protocols. The server
2437   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2438   response to indicate which protocol(s) are being switched.
2439</t>
2440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2441  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2442  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2443</artwork></figure>
2444<t>
2445   For example,
2446</t>
2447<figure><artwork type="example">
2448  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2449</artwork></figure>
2450<t>
2451   The Upgrade header field is intended to provide a simple mechanism
2452   for transition from HTTP/1.1 to some other, incompatible protocol. It
2453   does so by allowing the client to advertise its desire to use another
2454   protocol, such as a later version of HTTP with a higher major version
2455   number, even though the current request has been made using HTTP/1.1.
2456   This eases the difficult transition between incompatible protocols by
2457   allowing the client to initiate a request in the more commonly
2458   supported protocol while indicating to the server that it would like
2459   to use a "better" protocol if available (where "better" is determined
2460   by the server, possibly according to the nature of the method and/or
2461   resource being requested).
2462</t>
2463<t>
2464   The Upgrade header field only applies to switching application-layer
2465   protocols upon the existing transport-layer connection. Upgrade
2466   cannot be used to insist on a protocol change; its acceptance and use
2467   by the server is optional. The capabilities and nature of the
2468   application-layer communication after the protocol change is entirely
2469   dependent upon the new protocol chosen, although the first action
2470   after changing the protocol &MUST; be a response to the initial HTTP
2471   request containing the Upgrade header field.
2472</t>
2473<t>
2474   The Upgrade header field only applies to the immediate connection.
2475   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2476   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2477   HTTP/1.1 message.
2478</t>
2479<t>
2480   The Upgrade header field cannot be used to indicate a switch to a
2481   protocol on a different connection. For that purpose, it is more
2482   appropriate to use a 301, 302, 303, or 305 redirection response.
2483</t>
2484<t>
2485   This specification only defines the protocol name "HTTP" for use by
2486   the family of Hypertext Transfer Protocols, as defined by the HTTP
2487   version rules of <xref target="http.version"/> and future updates to this
2488   specification. Any token can be used as a protocol name; however, it
2489   will only be useful if both the client and server associate the name
2490   with the same protocol.
2491</t>
2492</section>
2493
2494<section title="Via" anchor="header.via">
2495  <iref primary="true" item="Via header" x:for-anchor=""/>
2496  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2497  <x:anchor-alias value="protocol-name"/>
2498  <x:anchor-alias value="protocol-version"/>
2499  <x:anchor-alias value="pseudonym"/>
2500  <x:anchor-alias value="received-by"/>
2501  <x:anchor-alias value="received-protocol"/>
2502  <x:anchor-alias value="Via"/>
2503  <x:anchor-alias value="Via-v"/>
2504<t>
2505   The general-header field "Via" &MUST; be used by gateways and proxies to
2506   indicate the intermediate protocols and recipients between the user
2507   agent and the server on requests, and between the origin server and
2508   the client on responses. It is analogous to the "Received" field defined in
2509   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2510   avoiding request loops, and identifying the protocol capabilities of
2511   all senders along the request/response chain.
2512</t>
2513<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2514  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2515  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2516                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2517  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2518  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2519  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2520  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2521  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2522</artwork></figure>
2523<t>
2524   The received-protocol indicates the protocol version of the message
2525   received by the server or client along each segment of the
2526   request/response chain. The received-protocol version is appended to
2527   the Via field value when the message is forwarded so that information
2528   about the protocol capabilities of upstream applications remains
2529   visible to all recipients.
2530</t>
2531<t>
2532   The protocol-name is optional if and only if it would be "HTTP". The
2533   received-by field is normally the host and optional port number of a
2534   recipient server or client that subsequently forwarded the message.
2535   However, if the real host is considered to be sensitive information,
2536   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2537   be assumed to be the default port of the received-protocol.
2538</t>
2539<t>
2540   Multiple Via field values represents each proxy or gateway that has
2541   forwarded the message. Each recipient &MUST; append its information
2542   such that the end result is ordered according to the sequence of
2543   forwarding applications.
2544</t>
2545<t>
2546   Comments &MAY; be used in the Via header field to identify the software
2547   of the recipient proxy or gateway, analogous to the User-Agent and
2548   Server header fields. However, all comments in the Via field are
2549   optional and &MAY; be removed by any recipient prior to forwarding the
2550   message.
2551</t>
2552<t>
2553   For example, a request message could be sent from an HTTP/1.0 user
2554   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2555   forward the request to a public proxy at p.example.net, which completes
2556   the request by forwarding it to the origin server at www.example.com.
2557   The request received by www.example.com would then have the following
2558   Via header field:
2559</t>
2560<figure><artwork type="example">
2561  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2562</artwork></figure>
2563<t>
2564   Proxies and gateways used as a portal through a network firewall
2565   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2566   the firewall region. This information &SHOULD; only be propagated if
2567   explicitly enabled. If not enabled, the received-by host of any host
2568   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2569   for that host.
2570</t>
2571<t>
2572   For organizations that have strong privacy requirements for hiding
2573   internal structures, a proxy &MAY; combine an ordered subsequence of
2574   Via header field entries with identical received-protocol values into
2575   a single such entry. For example,
2576</t>
2577<figure><artwork type="example">
2578  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2579</artwork></figure>
2580<t>
2581        could be collapsed to
2582</t>
2583<figure><artwork type="example">
2584  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2585</artwork></figure>
2586<t>
2587   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2588   under the same organizational control and the hosts have already been
2589   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2590   have different received-protocol values.
2591</t>
2592</section>
2593
2594</section>
2595
2596<section title="IANA Considerations" anchor="IANA.considerations">
2597<section title="Message Header Registration" anchor="message.header.registration">
2598<t>
2599   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2600   with the permanent registrations below (see <xref target="RFC3864"/>):
2601</t>
2602<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2603<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2604   <ttcol>Header Field Name</ttcol>
2605   <ttcol>Protocol</ttcol>
2606   <ttcol>Status</ttcol>
2607   <ttcol>Reference</ttcol>
2608
2609   <c>Connection</c>
2610   <c>http</c>
2611   <c>standard</c>
2612   <c>
2613      <xref target="header.connection"/>
2614   </c>
2615   <c>Content-Length</c>
2616   <c>http</c>
2617   <c>standard</c>
2618   <c>
2619      <xref target="header.content-length"/>
2620   </c>
2621   <c>Date</c>
2622   <c>http</c>
2623   <c>standard</c>
2624   <c>
2625      <xref target="header.date"/>
2626   </c>
2627   <c>Host</c>
2628   <c>http</c>
2629   <c>standard</c>
2630   <c>
2631      <xref target="header.host"/>
2632   </c>
2633   <c>TE</c>
2634   <c>http</c>
2635   <c>standard</c>
2636   <c>
2637      <xref target="header.te"/>
2638   </c>
2639   <c>Trailer</c>
2640   <c>http</c>
2641   <c>standard</c>
2642   <c>
2643      <xref target="header.trailer"/>
2644   </c>
2645   <c>Transfer-Encoding</c>
2646   <c>http</c>
2647   <c>standard</c>
2648   <c>
2649      <xref target="header.transfer-encoding"/>
2650   </c>
2651   <c>Upgrade</c>
2652   <c>http</c>
2653   <c>standard</c>
2654   <c>
2655      <xref target="header.upgrade"/>
2656   </c>
2657   <c>Via</c>
2658   <c>http</c>
2659   <c>standard</c>
2660   <c>
2661      <xref target="header.via"/>
2662   </c>
2663</texttable>
2664<!--(END)-->
2665<t>
2666   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2667</t>
2668</section>
2669
2670<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2671<t>
2672   The entry for the "http" URI Scheme in the registry located at
2673   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2674   should be updated to point to <xref target="http.uri"/> of this document
2675   (see <xref target="RFC4395"/>).
2676</t>
2677</section>
2678
2679<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2680<t>
2681   This document serves as the specification for the Internet media types
2682   "message/http" and "application/http". The following is to be registered with
2683   IANA (see <xref target="RFC4288"/>).
2684</t>
2685<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2686<iref item="Media Type" subitem="message/http" primary="true"/>
2687<iref item="message/http Media Type" primary="true"/>
2688<t>
2689   The message/http type can be used to enclose a single HTTP request or
2690   response message, provided that it obeys the MIME restrictions for all
2691   "message" types regarding line length and encodings.
2692</t>
2693<t>
2694  <list style="hanging" x:indent="12em">
2695    <t hangText="Type name:">
2696      message
2697    </t>
2698    <t hangText="Subtype name:">
2699      http
2700    </t>
2701    <t hangText="Required parameters:">
2702      none
2703    </t>
2704    <t hangText="Optional parameters:">
2705      version, msgtype
2706      <list style="hanging">
2707        <t hangText="version:">
2708          The HTTP-Version number of the enclosed message
2709          (e.g., "1.1"). If not present, the version can be
2710          determined from the first line of the body.
2711        </t>
2712        <t hangText="msgtype:">
2713          The message type -- "request" or "response". If not
2714          present, the type can be determined from the first
2715          line of the body.
2716        </t>
2717      </list>
2718    </t>
2719    <t hangText="Encoding considerations:">
2720      only "7bit", "8bit", or "binary" are permitted
2721    </t>
2722    <t hangText="Security considerations:">
2723      none
2724    </t>
2725    <t hangText="Interoperability considerations:">
2726      none
2727    </t>
2728    <t hangText="Published specification:">
2729      This specification (see <xref target="internet.media.type.message.http"/>).
2730    </t>
2731    <t hangText="Applications that use this media type:">
2732    </t>
2733    <t hangText="Additional information:">
2734      <list style="hanging">
2735        <t hangText="Magic number(s):">none</t>
2736        <t hangText="File extension(s):">none</t>
2737        <t hangText="Macintosh file type code(s):">none</t>
2738      </list>
2739    </t>
2740    <t hangText="Person and email address to contact for further information:">
2741      See Authors Section.
2742    </t>
2743                <t hangText="Intended usage:">
2744                  COMMON
2745    </t>
2746                <t hangText="Restrictions on usage:">
2747                  none
2748    </t>
2749    <t hangText="Author/Change controller:">
2750      IESG
2751    </t>
2752  </list>
2753</t>
2754</section>
2755<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2756<iref item="Media Type" subitem="application/http" primary="true"/>
2757<iref item="application/http Media Type" primary="true"/>
2758<t>
2759   The application/http type can be used to enclose a pipeline of one or more
2760   HTTP request or response messages (not intermixed).
2761</t>
2762<t>
2763  <list style="hanging" x:indent="12em">
2764    <t hangText="Type name:">
2765      application
2766    </t>
2767    <t hangText="Subtype name:">
2768      http
2769    </t>
2770    <t hangText="Required parameters:">
2771      none
2772    </t>
2773    <t hangText="Optional parameters:">
2774      version, msgtype
2775      <list style="hanging">
2776        <t hangText="version:">
2777          The HTTP-Version number of the enclosed messages
2778          (e.g., "1.1"). If not present, the version can be
2779          determined from the first line of the body.
2780        </t>
2781        <t hangText="msgtype:">
2782          The message type -- "request" or "response". If not
2783          present, the type can be determined from the first
2784          line of the body.
2785        </t>
2786      </list>
2787    </t>
2788    <t hangText="Encoding considerations:">
2789      HTTP messages enclosed by this type
2790      are in "binary" format; use of an appropriate
2791      Content-Transfer-Encoding is required when
2792      transmitted via E-mail.
2793    </t>
2794    <t hangText="Security considerations:">
2795      none
2796    </t>
2797    <t hangText="Interoperability considerations:">
2798      none
2799    </t>
2800    <t hangText="Published specification:">
2801      This specification (see <xref target="internet.media.type.application.http"/>).
2802    </t>
2803    <t hangText="Applications that use this media type:">
2804    </t>
2805    <t hangText="Additional information:">
2806      <list style="hanging">
2807        <t hangText="Magic number(s):">none</t>
2808        <t hangText="File extension(s):">none</t>
2809        <t hangText="Macintosh file type code(s):">none</t>
2810      </list>
2811    </t>
2812    <t hangText="Person and email address to contact for further information:">
2813      See Authors Section.
2814    </t>
2815                <t hangText="Intended usage:">
2816                  COMMON
2817    </t>
2818                <t hangText="Restrictions on usage:">
2819                  none
2820    </t>
2821    <t hangText="Author/Change controller:">
2822      IESG
2823    </t>
2824  </list>
2825</t>
2826</section>
2827</section>
2828
2829</section>
2830
2831<section title="Security Considerations" anchor="security.considerations">
2832<t>
2833   This section is meant to inform application developers, information
2834   providers, and users of the security limitations in HTTP/1.1 as
2835   described by this document. The discussion does not include
2836   definitive solutions to the problems revealed, though it does make
2837   some suggestions for reducing security risks.
2838</t>
2839
2840<section title="Personal Information" anchor="personal.information">
2841<t>
2842   HTTP clients are often privy to large amounts of personal information
2843   (e.g. the user's name, location, mail address, passwords, encryption
2844   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2845   leakage of this information.
2846   We very strongly recommend that a convenient interface be provided
2847   for the user to control dissemination of such information, and that
2848   designers and implementors be particularly careful in this area.
2849   History shows that errors in this area often create serious security
2850   and/or privacy problems and generate highly adverse publicity for the
2851   implementor's company.
2852</t>
2853</section>
2854
2855<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2856<t>
2857   A server is in the position to save personal data about a user's
2858   requests which might identify their reading patterns or subjects of
2859   interest. This information is clearly confidential in nature and its
2860   handling can be constrained by law in certain countries. People using
2861   HTTP to provide data are responsible for ensuring that
2862   such material is not distributed without the permission of any
2863   individuals that are identifiable by the published results.
2864</t>
2865</section>
2866
2867<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2868<t>
2869   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2870   the documents returned by HTTP requests to be only those that were
2871   intended by the server administrators. If an HTTP server translates
2872   HTTP URIs directly into file system calls, the server &MUST; take
2873   special care not to serve files that were not intended to be
2874   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2875   other operating systems use ".." as a path component to indicate a
2876   directory level above the current one. On such a system, an HTTP
2877   server &MUST; disallow any such construct in the Request-URI if it
2878   would otherwise allow access to a resource outside those intended to
2879   be accessible via the HTTP server. Similarly, files intended for
2880   reference only internally to the server (such as access control
2881   files, configuration files, and script code) &MUST; be protected from
2882   inappropriate retrieval, since they might contain sensitive
2883   information. Experience has shown that minor bugs in such HTTP server
2884   implementations have turned into security risks.
2885</t>
2886</section>
2887
2888<section title="DNS Spoofing" anchor="dns.spoofing">
2889<t>
2890   Clients using HTTP rely heavily on the Domain Name Service, and are
2891   thus generally prone to security attacks based on the deliberate
2892   mis-association of IP addresses and DNS names. Clients need to be
2893   cautious in assuming the continuing validity of an IP number/DNS name
2894   association.
2895</t>
2896<t>
2897   In particular, HTTP clients &SHOULD; rely on their name resolver for
2898   confirmation of an IP number/DNS name association, rather than
2899   caching the result of previous host name lookups. Many platforms
2900   already can cache host name lookups locally when appropriate, and
2901   they &SHOULD; be configured to do so. It is proper for these lookups to
2902   be cached, however, only when the TTL (Time To Live) information
2903   reported by the name server makes it likely that the cached
2904   information will remain useful.
2905</t>
2906<t>
2907   If HTTP clients cache the results of host name lookups in order to
2908   achieve a performance improvement, they &MUST; observe the TTL
2909   information reported by DNS.
2910</t>
2911<t>
2912   If HTTP clients do not observe this rule, they could be spoofed when
2913   a previously-accessed server's IP address changes. As network
2914   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2915   possibility of this form of attack will grow. Observing this
2916   requirement thus reduces this potential security vulnerability.
2917</t>
2918<t>
2919   This requirement also improves the load-balancing behavior of clients
2920   for replicated servers using the same DNS name and reduces the
2921   likelihood of a user's experiencing failure in accessing sites which
2922   use that strategy.
2923</t>
2924</section>
2925
2926<section title="Proxies and Caching" anchor="attack.proxies">
2927<t>
2928   By their very nature, HTTP proxies are men-in-the-middle, and
2929   represent an opportunity for man-in-the-middle attacks. Compromise of
2930   the systems on which the proxies run can result in serious security
2931   and privacy problems. Proxies have access to security-related
2932   information, personal information about individual users and
2933   organizations, and proprietary information belonging to users and
2934   content providers. A compromised proxy, or a proxy implemented or
2935   configured without regard to security and privacy considerations,
2936   might be used in the commission of a wide range of potential attacks.
2937</t>
2938<t>
2939   Proxy operators should protect the systems on which proxies run as
2940   they would protect any system that contains or transports sensitive
2941   information. In particular, log information gathered at proxies often
2942   contains highly sensitive personal information, and/or information
2943   about organizations. Log information should be carefully guarded, and
2944   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2945</t>
2946<t>
2947   Proxy implementors should consider the privacy and security
2948   implications of their design and coding decisions, and of the
2949   configuration options they provide to proxy operators (especially the
2950   default configuration).
2951</t>
2952<t>
2953   Users of a proxy need to be aware that they are no trustworthier than
2954   the people who run the proxy; HTTP itself cannot solve this problem.
2955</t>
2956<t>
2957   The judicious use of cryptography, when appropriate, may suffice to
2958   protect against a broad range of security and privacy attacks. Such
2959   cryptography is beyond the scope of the HTTP/1.1 specification.
2960</t>
2961</section>
2962
2963<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2964<t>
2965   They exist. They are hard to defend against. Research continues.
2966   Beware.
2967</t>
2968</section>
2969</section>
2970
2971<section title="Acknowledgments" anchor="ack">
2972<t>
2973   HTTP has evolved considerably over the years. It has
2974   benefited from a large and active developer community--the many
2975   people who have participated on the www-talk mailing list--and it is
2976   that community which has been most responsible for the success of
2977   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2978   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2979   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2980   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2981   VanHeyningen deserve special recognition for their efforts in
2982   defining early aspects of the protocol.
2983</t>
2984<t>
2985   This document has benefited greatly from the comments of all those
2986   participating in the HTTP-WG. In addition to those already mentioned,
2987   the following individuals have contributed to this specification:
2988</t>
2989<t>
2990   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2991   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2992   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2993   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2994   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2995   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2996   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2997   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2998   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2999   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3000   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3001   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3002   Josh Cohen.
3003</t>
3004<t>
3005   Thanks to the "cave men" of Palo Alto. You know who you are.
3006</t>
3007<t>
3008   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3009   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3010   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3011   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3012   Larry Masinter for their help. And thanks go particularly to Jeff
3013   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3014</t>
3015<t>
3016   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3017   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3018   discovery of many of the problems that this document attempts to
3019   rectify.
3020</t>
3021<t>
3022   This specification makes heavy use of the augmented BNF and generic
3023   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3024   reuses many of the definitions provided by Nathaniel Borenstein and
3025   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3026   specification will help reduce past confusion over the relationship
3027   between HTTP and Internet mail message formats.
3028</t>
3029</section>
3030
3031</middle>
3032<back>
3033
3034<references title="Normative References">
3035
3036<reference anchor="ISO-8859-1">
3037  <front>
3038    <title>
3039     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3040    </title>
3041    <author>
3042      <organization>International Organization for Standardization</organization>
3043    </author>
3044    <date year="1998"/>
3045  </front>
3046  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3047</reference>
3048
3049<reference anchor="Part2">
3050  <front>
3051    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3052    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3053      <organization abbrev="Day Software">Day Software</organization>
3054      <address><email>fielding@gbiv.com</email></address>
3055    </author>
3056    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3057      <organization>One Laptop per Child</organization>
3058      <address><email>jg@laptop.org</email></address>
3059    </author>
3060    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3061      <organization abbrev="HP">Hewlett-Packard Company</organization>
3062      <address><email>JeffMogul@acm.org</email></address>
3063    </author>
3064    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3065      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3066      <address><email>henrikn@microsoft.com</email></address>
3067    </author>
3068    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3069      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3070      <address><email>LMM@acm.org</email></address>
3071    </author>
3072    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3073      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3074      <address><email>paulle@microsoft.com</email></address>
3075    </author>
3076    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3077      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3078      <address><email>timbl@w3.org</email></address>
3079    </author>
3080    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3081      <organization abbrev="W3C">World Wide Web Consortium</organization>
3082      <address><email>ylafon@w3.org</email></address>
3083    </author>
3084    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3085      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3086      <address><email>julian.reschke@greenbytes.de</email></address>
3087    </author>
3088    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3089  </front>
3090  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3091  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3092</reference>
3093
3094<reference anchor="Part3">
3095  <front>
3096    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3097    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3098      <organization abbrev="Day Software">Day Software</organization>
3099      <address><email>fielding@gbiv.com</email></address>
3100    </author>
3101    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3102      <organization>One Laptop per Child</organization>
3103      <address><email>jg@laptop.org</email></address>
3104    </author>
3105    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3106      <organization abbrev="HP">Hewlett-Packard Company</organization>
3107      <address><email>JeffMogul@acm.org</email></address>
3108    </author>
3109    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3110      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3111      <address><email>henrikn@microsoft.com</email></address>
3112    </author>
3113    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3114      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3115      <address><email>LMM@acm.org</email></address>
3116    </author>
3117    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3118      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3119      <address><email>paulle@microsoft.com</email></address>
3120    </author>
3121    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3122      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3123      <address><email>timbl@w3.org</email></address>
3124    </author>
3125    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3126      <organization abbrev="W3C">World Wide Web Consortium</organization>
3127      <address><email>ylafon@w3.org</email></address>
3128    </author>
3129    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3130      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3131      <address><email>julian.reschke@greenbytes.de</email></address>
3132    </author>
3133    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3134  </front>
3135  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3136  <x:source href="p3-payload.xml" basename="p3-payload"/>
3137</reference>
3138
3139<reference anchor="Part5">
3140  <front>
3141    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3142    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3143      <organization abbrev="Day Software">Day Software</organization>
3144      <address><email>fielding@gbiv.com</email></address>
3145    </author>
3146    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3147      <organization>One Laptop per Child</organization>
3148      <address><email>jg@laptop.org</email></address>
3149    </author>
3150    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3151      <organization abbrev="HP">Hewlett-Packard Company</organization>
3152      <address><email>JeffMogul@acm.org</email></address>
3153    </author>
3154    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3155      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3156      <address><email>henrikn@microsoft.com</email></address>
3157    </author>
3158    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3159      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3160      <address><email>LMM@acm.org</email></address>
3161    </author>
3162    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3163      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3164      <address><email>paulle@microsoft.com</email></address>
3165    </author>
3166    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3167      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3168      <address><email>timbl@w3.org</email></address>
3169    </author>
3170    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3171      <organization abbrev="W3C">World Wide Web Consortium</organization>
3172      <address><email>ylafon@w3.org</email></address>
3173    </author>
3174    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3175      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3176      <address><email>julian.reschke@greenbytes.de</email></address>
3177    </author>
3178    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3179  </front>
3180  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3181  <x:source href="p5-range.xml" basename="p5-range"/>
3182</reference>
3183
3184<reference anchor="Part6">
3185  <front>
3186    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3187    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3188      <organization abbrev="Day Software">Day Software</organization>
3189      <address><email>fielding@gbiv.com</email></address>
3190    </author>
3191    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3192      <organization>One Laptop per Child</organization>
3193      <address><email>jg@laptop.org</email></address>
3194    </author>
3195    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3196      <organization abbrev="HP">Hewlett-Packard Company</organization>
3197      <address><email>JeffMogul@acm.org</email></address>
3198    </author>
3199    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3200      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3201      <address><email>henrikn@microsoft.com</email></address>
3202    </author>
3203    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3204      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3205      <address><email>LMM@acm.org</email></address>
3206    </author>
3207    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3208      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3209      <address><email>paulle@microsoft.com</email></address>
3210    </author>
3211    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3212      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3213      <address><email>timbl@w3.org</email></address>
3214    </author>
3215    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3216      <organization abbrev="W3C">World Wide Web Consortium</organization>
3217      <address><email>ylafon@w3.org</email></address>
3218    </author>
3219    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3220      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3221      <address><email>julian.reschke@greenbytes.de</email></address>
3222    </author>
3223    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3224  </front>
3225  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3226  <x:source href="p6-cache.xml" basename="p6-cache"/>
3227</reference>
3228
3229<reference anchor="RFC5234">
3230  <front>
3231    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3232    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3233      <organization>Brandenburg InternetWorking</organization>
3234      <address>
3235      <postal>
3236      <street>675 Spruce Dr.</street>
3237      <city>Sunnyvale</city>
3238      <region>CA</region>
3239      <code>94086</code>
3240      <country>US</country></postal>
3241      <phone>+1.408.246.8253</phone>
3242      <email>dcrocker@bbiw.net</email></address> 
3243    </author>
3244    <author initials="P." surname="Overell" fullname="Paul Overell">
3245      <organization>THUS plc.</organization>
3246      <address>
3247      <postal>
3248      <street>1/2 Berkeley Square</street>
3249      <street>99 Berkely Street</street>
3250      <city>Glasgow</city>
3251      <code>G3 7HR</code>
3252      <country>UK</country></postal>
3253      <email>paul.overell@thus.net</email></address>
3254    </author>
3255    <date month="January" year="2008"/>
3256  </front>
3257  <seriesInfo name="STD" value="68"/>
3258  <seriesInfo name="RFC" value="5234"/>
3259</reference>
3260
3261<reference anchor="RFC2045">
3262  <front>
3263    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3264    <author initials="N." surname="Freed" fullname="Ned Freed">
3265      <organization>Innosoft International, Inc.</organization>
3266      <address><email>ned@innosoft.com</email></address>
3267    </author>
3268    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3269      <organization>First Virtual Holdings</organization>
3270      <address><email>nsb@nsb.fv.com</email></address>
3271    </author>
3272    <date month="November" year="1996"/>
3273  </front>
3274  <seriesInfo name="RFC" value="2045"/>
3275</reference>
3276
3277<reference anchor="RFC2047">
3278  <front>
3279    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3280    <author initials="K." surname="Moore" fullname="Keith Moore">
3281      <organization>University of Tennessee</organization>
3282      <address><email>moore@cs.utk.edu</email></address>
3283    </author>
3284    <date month="November" year="1996"/>
3285  </front>
3286  <seriesInfo name="RFC" value="2047"/>
3287</reference>
3288
3289<reference anchor="RFC2119">
3290  <front>
3291    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3292    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3293      <organization>Harvard University</organization>
3294      <address><email>sob@harvard.edu</email></address>
3295    </author>
3296    <date month="March" year="1997"/>
3297  </front>
3298  <seriesInfo name="BCP" value="14"/>
3299  <seriesInfo name="RFC" value="2119"/>
3300</reference>
3301
3302<reference anchor="RFC3986">
3303 <front>
3304  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3305  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3306    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3307    <address>
3308       <email>timbl@w3.org</email>
3309       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3310    </address>
3311  </author>
3312  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3313    <organization abbrev="Day Software">Day Software</organization>
3314    <address>
3315      <email>fielding@gbiv.com</email>
3316      <uri>http://roy.gbiv.com/</uri>
3317    </address>
3318  </author>
3319  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3320    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3321    <address>
3322      <email>LMM@acm.org</email>
3323      <uri>http://larry.masinter.net/</uri>
3324    </address>
3325  </author>
3326  <date month='January' year='2005'></date>
3327 </front>
3328 <seriesInfo name="RFC" value="3986"/>
3329 <seriesInfo name="STD" value="66"/>
3330</reference>
3331
3332<reference anchor="USASCII">
3333  <front>
3334    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3335    <author>
3336      <organization>American National Standards Institute</organization>
3337    </author>
3338    <date year="1986"/>
3339  </front>
3340  <seriesInfo name="ANSI" value="X3.4"/>
3341</reference>
3342
3343</references>
3344
3345<references title="Informative References">
3346
3347<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3348  <front>
3349    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3350    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3351      <organization/>
3352    </author>
3353    <author initials="J." surname="Gettys" fullname="J. Gettys">
3354      <organization/>
3355    </author>
3356    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3357      <organization/>
3358    </author>
3359    <author initials="H." surname="Lie" fullname="H. Lie">
3360      <organization/>
3361    </author>
3362    <author initials="C." surname="Lilley" fullname="C. Lilley">
3363      <organization/>
3364    </author>
3365    <date year="1997" month="September"/>
3366  </front>
3367  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3368</reference>
3369
3370<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3371  <front>
3372    <title>Improving HTTP Latency</title>
3373    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3374      <organization/>
3375    </author>
3376    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3377      <organization/>
3378    </author>
3379    <date year="1995" month="December"/>
3380  </front>
3381  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3382</reference>
3383
3384<reference anchor="RFC959">
3385  <front>
3386    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3387    <author initials="J." surname="Postel" fullname="J. Postel">
3388      <organization>Information Sciences Institute (ISI)</organization>
3389    </author>
3390    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3391      <organization/>
3392    </author>
3393    <date month="October" year="1985"/>
3394  </front>
3395  <seriesInfo name="STD" value="9"/>
3396  <seriesInfo name="RFC" value="959"/>
3397</reference>
3398
3399<reference anchor="RFC1123">
3400  <front>
3401    <title>Requirements for Internet Hosts - Application and Support</title>
3402    <author initials="R." surname="Braden" fullname="Robert Braden">
3403      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3404      <address><email>Braden@ISI.EDU</email></address>
3405    </author>
3406    <date month="October" year="1989"/>
3407  </front>
3408  <seriesInfo name="STD" value="3"/>
3409  <seriesInfo name="RFC" value="1123"/>
3410</reference>
3411
3412<reference anchor="RFC1305">
3413  <front>
3414    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3415    <author initials="D." surname="Mills" fullname="David L. Mills">
3416      <organization>University of Delaware, Electrical Engineering Department</organization>
3417      <address><email>mills@udel.edu</email></address>
3418    </author>
3419    <date month="March" year="1992"/>
3420  </front>
3421  <seriesInfo name="RFC" value="1305"/>
3422</reference>
3423
3424<reference anchor="RFC1436">
3425  <front>
3426    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3427    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3428      <organization>University of Minnesota, Computer and Information Services</organization>
3429      <address><email>fxa@boombox.micro.umn.edu</email></address>
3430    </author>
3431    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3432      <organization>University of Minnesota, Computer and Information Services</organization>
3433      <address><email>mpm@boombox.micro.umn.edu</email></address>
3434    </author>
3435    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3436      <organization>University of Minnesota, Computer and Information Services</organization>
3437      <address><email>lindner@boombox.micro.umn.edu</email></address>
3438    </author>
3439    <author initials="D." surname="Johnson" fullname="David Johnson">
3440      <organization>University of Minnesota, Computer and Information Services</organization>
3441      <address><email>dmj@boombox.micro.umn.edu</email></address>
3442    </author>
3443    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3444      <organization>University of Minnesota, Computer and Information Services</organization>
3445      <address><email>daniel@boombox.micro.umn.edu</email></address>
3446    </author>
3447    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3448      <organization>University of Minnesota, Computer and Information Services</organization>
3449      <address><email>alberti@boombox.micro.umn.edu</email></address>
3450    </author>
3451    <date month="March" year="1993"/>
3452  </front>
3453  <seriesInfo name="RFC" value="1436"/>
3454</reference>
3455
3456<reference anchor="RFC1900">
3457  <front>
3458    <title>Renumbering Needs Work</title>
3459    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3460      <organization>CERN, Computing and Networks Division</organization>
3461      <address><email>brian@dxcoms.cern.ch</email></address>
3462    </author>
3463    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3464      <organization>cisco Systems</organization>
3465      <address><email>yakov@cisco.com</email></address>
3466    </author>
3467    <date month="February" year="1996"/>
3468  </front>
3469  <seriesInfo name="RFC" value="1900"/>
3470</reference>
3471
3472<reference anchor="RFC1945">
3473  <front>
3474    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3475    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3476      <organization>MIT, Laboratory for Computer Science</organization>
3477      <address><email>timbl@w3.org</email></address>
3478    </author>
3479    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3480      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3481      <address><email>fielding@ics.uci.edu</email></address>
3482    </author>
3483    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3484      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3485      <address><email>frystyk@w3.org</email></address>
3486    </author>
3487    <date month="May" year="1996"/>
3488  </front>
3489  <seriesInfo name="RFC" value="1945"/>
3490</reference>
3491
3492<reference anchor="RFC2068">
3493  <front>
3494    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3495    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3496      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3497      <address><email>fielding@ics.uci.edu</email></address>
3498    </author>
3499    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3500      <organization>MIT Laboratory for Computer Science</organization>
3501      <address><email>jg@w3.org</email></address>
3502    </author>
3503    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3504      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3505      <address><email>mogul@wrl.dec.com</email></address>
3506    </author>
3507    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3508      <organization>MIT Laboratory for Computer Science</organization>
3509      <address><email>frystyk@w3.org</email></address>
3510    </author>
3511    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3512      <organization>MIT Laboratory for Computer Science</organization>
3513      <address><email>timbl@w3.org</email></address>
3514    </author>
3515    <date month="January" year="1997"/>
3516  </front>
3517  <seriesInfo name="RFC" value="2068"/>
3518</reference>
3519
3520<reference anchor='RFC2109'>
3521  <front>
3522    <title>HTTP State Management Mechanism</title>
3523    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3524      <organization>Bell Laboratories, Lucent Technologies</organization>
3525      <address><email>dmk@bell-labs.com</email></address>
3526    </author>
3527    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3528      <organization>Netscape Communications Corp.</organization>
3529      <address><email>montulli@netscape.com</email></address>
3530    </author>
3531    <date year='1997' month='February' />
3532  </front>
3533  <seriesInfo name='RFC' value='2109' />
3534</reference>
3535
3536<reference anchor="RFC2145">
3537  <front>
3538    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3539    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3540      <organization>Western Research Laboratory</organization>
3541      <address><email>mogul@wrl.dec.com</email></address>
3542    </author>
3543    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3544      <organization>Department of Information and Computer Science</organization>
3545      <address><email>fielding@ics.uci.edu</email></address>
3546    </author>
3547    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3548      <organization>MIT Laboratory for Computer Science</organization>
3549      <address><email>jg@w3.org</email></address>
3550    </author>
3551    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3552      <organization>W3 Consortium</organization>
3553      <address><email>frystyk@w3.org</email></address>
3554    </author>
3555    <date month="May" year="1997"/>
3556  </front>
3557  <seriesInfo name="RFC" value="2145"/>
3558</reference>
3559
3560<reference anchor="RFC2616">
3561  <front>
3562    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3563    <author initials="R." surname="Fielding" fullname="R. Fielding">
3564      <organization>University of California, Irvine</organization>
3565      <address><email>fielding@ics.uci.edu</email></address>
3566    </author>
3567    <author initials="J." surname="Gettys" fullname="J. Gettys">
3568      <organization>W3C</organization>
3569      <address><email>jg@w3.org</email></address>
3570    </author>
3571    <author initials="J." surname="Mogul" fullname="J. Mogul">
3572      <organization>Compaq Computer Corporation</organization>
3573      <address><email>mogul@wrl.dec.com</email></address>
3574    </author>
3575    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3576      <organization>MIT Laboratory for Computer Science</organization>
3577      <address><email>frystyk@w3.org</email></address>
3578    </author>
3579    <author initials="L." surname="Masinter" fullname="L. Masinter">
3580      <organization>Xerox Corporation</organization>
3581      <address><email>masinter@parc.xerox.com</email></address>
3582    </author>
3583    <author initials="P." surname="Leach" fullname="P. Leach">
3584      <organization>Microsoft Corporation</organization>
3585      <address><email>paulle@microsoft.com</email></address>
3586    </author>
3587    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3588      <organization>W3C</organization>
3589      <address><email>timbl@w3.org</email></address>
3590    </author>
3591    <date month="June" year="1999"/>
3592  </front>
3593  <seriesInfo name="RFC" value="2616"/>
3594</reference>
3595
3596<reference anchor='RFC2818'>
3597  <front>
3598    <title>HTTP Over TLS</title>
3599    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3600      <organization>RTFM, Inc.</organization>
3601      <address><email>ekr@rtfm.com</email></address>
3602    </author>
3603    <date year='2000' month='May' />
3604  </front>
3605  <seriesInfo name='RFC' value='2818' />
3606</reference>
3607
3608<reference anchor='RFC2965'>
3609  <front>
3610    <title>HTTP State Management Mechanism</title>
3611    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3612      <organization>Bell Laboratories, Lucent Technologies</organization>
3613      <address><email>dmk@bell-labs.com</email></address>
3614    </author>
3615    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3616      <organization>Epinions.com, Inc.</organization>
3617      <address><email>lou@montulli.org</email></address>
3618    </author>
3619    <date year='2000' month='October' />
3620  </front>
3621  <seriesInfo name='RFC' value='2965' />
3622</reference>
3623
3624<reference anchor='RFC3864'>
3625  <front>
3626    <title>Registration Procedures for Message Header Fields</title>
3627    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3628      <organization>Nine by Nine</organization>
3629      <address><email>GK-IETF@ninebynine.org</email></address>
3630    </author>
3631    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3632      <organization>BEA Systems</organization>
3633      <address><email>mnot@pobox.com</email></address>
3634    </author>
3635    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3636      <organization>HP Labs</organization>
3637      <address><email>JeffMogul@acm.org</email></address>
3638    </author>
3639    <date year='2004' month='September' />
3640  </front>
3641  <seriesInfo name='BCP' value='90' />
3642  <seriesInfo name='RFC' value='3864' />
3643</reference>
3644
3645<reference anchor='RFC3977'>
3646  <front>
3647    <title>Network News Transfer Protocol (NNTP)</title>
3648    <author initials='C.' surname='Feather' fullname='C. Feather'>
3649      <organization>THUS plc</organization>
3650      <address><email>clive@demon.net</email></address>
3651    </author>
3652    <date year='2006' month='October' />
3653  </front>
3654  <seriesInfo name="RFC" value="3977"/>
3655</reference>
3656
3657<reference anchor="RFC4288">
3658  <front>
3659    <title>Media Type Specifications and Registration Procedures</title>
3660    <author initials="N." surname="Freed" fullname="N. Freed">
3661      <organization>Sun Microsystems</organization>
3662      <address>
3663        <email>ned.freed@mrochek.com</email>
3664      </address>
3665    </author>
3666    <author initials="J." surname="Klensin" fullname="J. Klensin">
3667      <organization/>
3668      <address>
3669        <email>klensin+ietf@jck.com</email>
3670      </address>
3671    </author>
3672    <date year="2005" month="December"/>
3673  </front>
3674  <seriesInfo name="BCP" value="13"/>
3675  <seriesInfo name="RFC" value="4288"/>
3676</reference>
3677
3678<reference anchor='RFC4395'>
3679  <front>
3680    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3681    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3682      <organization>AT&amp;T Laboratories</organization>
3683      <address>
3684        <email>tony+urireg@maillennium.att.com</email>
3685      </address>
3686    </author>
3687    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3688      <organization>Qualcomm, Inc.</organization>
3689      <address>
3690        <email>hardie@qualcomm.com</email>
3691      </address>
3692    </author>
3693    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3694      <organization>Adobe Systems</organization>
3695      <address>
3696        <email>LMM@acm.org</email>
3697      </address>
3698    </author>
3699    <date year='2006' month='February' />
3700  </front>
3701  <seriesInfo name='BCP' value='115' />
3702  <seriesInfo name='RFC' value='4395' />
3703</reference>
3704
3705<reference anchor="RFC5322">
3706  <front>
3707    <title>Internet Message Format</title>
3708    <author initials="P." surname="Resnick" fullname="P. Resnick">
3709      <organization>Qualcomm Incorporated</organization>
3710    </author>
3711    <date year="2008" month="October"/>
3712  </front> 
3713  <seriesInfo name="RFC" value="5322"/>
3714</reference>
3715
3716<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3717  <front>
3718    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3719    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3720      <organization/>
3721    </author>
3722    <date year="2001" month="November"/>
3723  </front>
3724  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3725</reference>
3726
3727<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3728  <front>
3729  <title>Analysis of HTTP Performance Problems</title>
3730  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3731    <organization/>
3732  </author>
3733  <date/>
3734  </front>
3735</reference>
3736
3737<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3738  <front>
3739  <title>Analysis of HTTP Performance</title>
3740  <author initials="J." surname="Touch" fullname="Joe Touch">
3741    <organization>USC/Information Sciences Institute</organization>
3742    <address><email>touch@isi.edu</email></address>
3743  </author>
3744  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3745    <organization>USC/Information Sciences Institute</organization>
3746    <address><email>johnh@isi.edu</email></address>
3747  </author>
3748  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3749    <organization>USC/Information Sciences Institute</organization>
3750    <address><email>katia@isi.edu</email></address>
3751  </author>
3752  <date year="1998" month="Aug"/>
3753  </front>
3754  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3755  <annotation>(original report dated Aug. 1996)</annotation>
3756</reference>
3757
3758<reference anchor="WAIS">
3759  <front>
3760    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3761    <author initials="F." surname="Davis" fullname="F. Davis">
3762      <organization>Thinking Machines Corporation</organization>
3763    </author>
3764    <author initials="B." surname="Kahle" fullname="B. Kahle">
3765      <organization>Thinking Machines Corporation</organization>
3766    </author>
3767    <author initials="H." surname="Morris" fullname="H. Morris">
3768      <organization>Thinking Machines Corporation</organization>
3769    </author>
3770    <author initials="J." surname="Salem" fullname="J. Salem">
3771      <organization>Thinking Machines Corporation</organization>
3772    </author>
3773    <author initials="T." surname="Shen" fullname="T. Shen">
3774      <organization>Thinking Machines Corporation</organization>
3775    </author>
3776    <author initials="R." surname="Wang" fullname="R. Wang">
3777      <organization>Thinking Machines Corporation</organization>
3778    </author>
3779    <author initials="J." surname="Sui" fullname="J. Sui">
3780      <organization>Thinking Machines Corporation</organization>
3781    </author>
3782    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3783      <organization>Thinking Machines Corporation</organization>
3784    </author>
3785    <date month="April" year="1990"/>
3786  </front>
3787  <seriesInfo name="Thinking Machines Corporation" value=""/>
3788</reference>
3789
3790</references>
3791
3792
3793<section title="Tolerant Applications" anchor="tolerant.applications">
3794<t>
3795   Although this document specifies the requirements for the generation
3796   of HTTP/1.1 messages, not all applications will be correct in their
3797   implementation. We therefore recommend that operational applications
3798   be tolerant of deviations whenever those deviations can be
3799   interpreted unambiguously.
3800</t>
3801<t>
3802   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3803   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3804   accept any amount of SP or HTAB characters between fields, even though
3805   only a single SP is required.
3806</t>
3807<t>
3808   The line terminator for message-header fields is the sequence CRLF.
3809   However, we recommend that applications, when parsing such headers,
3810   recognize a single LF as a line terminator and ignore the leading CR.
3811</t>
3812<t>
3813   The character set of an entity-body &SHOULD; be labeled as the lowest
3814   common denominator of the character codes used within that body, with
3815   the exception that not labeling the entity is preferred over labeling
3816   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3817</t>
3818<t>
3819   Additional rules for requirements on parsing and encoding of dates
3820   and other potential problems with date encodings include:
3821</t>
3822<t>
3823  <list style="symbols">
3824     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3825        which appears to be more than 50 years in the future is in fact
3826        in the past (this helps solve the "year 2000" problem).</t>
3827
3828     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3829        Expires date as earlier than the proper value, but &MUST-NOT;
3830        internally represent a parsed Expires date as later than the
3831        proper value.</t>
3832
3833     <t>All expiration-related calculations &MUST; be done in GMT. The
3834        local time zone &MUST-NOT; influence the calculation or comparison
3835        of an age or expiration time.</t>
3836
3837     <t>If an HTTP header incorrectly carries a date value with a time
3838        zone other than GMT, it &MUST; be converted into GMT using the
3839        most conservative possible conversion.</t>
3840  </list>
3841</t>
3842</section>
3843
3844<section title="Compatibility with Previous Versions" anchor="compatibility">
3845<t>
3846   HTTP has been in use by the World-Wide Web global information initiative
3847   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3848   was a simple protocol for hypertext data transfer across the Internet
3849   with only a single method and no metadata.
3850   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3851   methods and MIME-like messaging that could include metadata about the data
3852   transferred and modifiers on the request/response semantics. However,
3853   HTTP/1.0 did not sufficiently take into consideration the effects of
3854   hierarchical proxies, caching, the need for persistent connections, or
3855   name-based virtual hosts. The proliferation of incompletely-implemented
3856   applications calling themselves "HTTP/1.0" further necessitated a
3857   protocol version change in order for two communicating applications
3858   to determine each other's true capabilities.
3859</t>
3860<t>
3861   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3862   requirements that enable reliable implementations, adding only
3863   those new features that will either be safely ignored by an HTTP/1.0
3864   recipient or only sent when communicating with a party advertising
3865   compliance with HTTP/1.1.
3866</t>
3867<t>
3868   It is beyond the scope of a protocol specification to mandate
3869   compliance with previous versions. HTTP/1.1 was deliberately
3870   designed, however, to make supporting previous versions easy. It is
3871   worth noting that, at the time of composing this specification
3872   (1996), we would expect commercial HTTP/1.1 servers to:
3873  <list style="symbols">
3874     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3875        1.1 requests;</t>
3876
3877     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3878        1.1;</t>
3879
3880     <t>respond appropriately with a message in the same major version
3881        used by the client.</t>
3882  </list>
3883</t>
3884<t>
3885   And we would expect HTTP/1.1 clients to:
3886  <list style="symbols">
3887     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3888        responses;</t>
3889
3890     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3891        1.1.</t>
3892  </list>
3893</t>
3894<t>
3895   For most implementations of HTTP/1.0, each connection is established
3896   by the client prior to the request and closed by the server after
3897   sending the response. Some implementations implement the Keep-Alive
3898   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3899</t>
3900
3901<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3902<t>
3903   This section summarizes major differences between versions HTTP/1.0
3904   and HTTP/1.1.
3905</t>
3906
3907<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">
3908<t>
3909   The requirements that clients and servers support the Host request-header,
3910   report an error if the Host request-header (<xref target="header.host"/>) is
3911   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3912   are among the most important changes defined by this
3913   specification.
3914</t>
3915<t>
3916   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3917   addresses and servers; there was no other established mechanism for
3918   distinguishing the intended server of a request than the IP address
3919   to which that request was directed. The changes outlined above will
3920   allow the Internet, once older HTTP clients are no longer common, to
3921   support multiple Web sites from a single IP address, greatly
3922   simplifying large operational Web servers, where allocation of many
3923   IP addresses to a single host has created serious problems. The
3924   Internet will also be able to recover the IP addresses that have been
3925   allocated for the sole purpose of allowing special-purpose domain
3926   names to be used in root-level HTTP URLs. Given the rate of growth of
3927   the Web, and the number of servers already deployed, it is extremely
3928   important that all implementations of HTTP (including updates to
3929   existing HTTP/1.0 applications) correctly implement these
3930   requirements:
3931  <list style="symbols">
3932     <t>Both clients and servers &MUST; support the Host request-header.</t>
3933
3934     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3935
3936     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3937        request does not include a Host request-header.</t>
3938
3939     <t>Servers &MUST; accept absolute URIs.</t>
3940  </list>
3941</t>
3942</section>
3943</section>
3944
3945<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3946<t>
3947   Some clients and servers might wish to be compatible with some
3948   previous implementations of persistent connections in HTTP/1.0
3949   clients and servers. Persistent connections in HTTP/1.0 are
3950   explicitly negotiated as they are not the default behavior. HTTP/1.0
3951   experimental implementations of persistent connections are faulty,
3952   and the new facilities in HTTP/1.1 are designed to rectify these
3953   problems. The problem was that some existing 1.0 clients may be
3954   sending Keep-Alive to a proxy server that doesn't understand
3955   Connection, which would then erroneously forward it to the next
3956   inbound server, which would establish the Keep-Alive connection and
3957   result in a hung HTTP/1.0 proxy waiting for the close on the
3958   response. The result is that HTTP/1.0 clients must be prevented from
3959   using Keep-Alive when talking to proxies.
3960</t>
3961<t>
3962   However, talking to proxies is the most important use of persistent
3963   connections, so that prohibition is clearly unacceptable. Therefore,
3964   we need some other mechanism for indicating a persistent connection
3965   is desired, which is safe to use even when talking to an old proxy
3966   that ignores Connection. Persistent connections are the default for
3967   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3968   declaring non-persistence. See <xref target="header.connection"/>.
3969</t>
3970<t>
3971   The original HTTP/1.0 form of persistent connections (the Connection:
3972   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3973</t>
3974</section>
3975
3976<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3977<t>
3978   This specification has been carefully audited to correct and
3979   disambiguate key word usage; RFC 2068 had many problems in respect to
3980   the conventions laid out in <xref target="RFC2119"/>.
3981</t>
3982<t>
3983   Transfer-coding and message lengths all interact in ways that
3984   required fixing exactly when chunked encoding is used (to allow for
3985   transfer encoding that may not be self delimiting); it was important
3986   to straighten out exactly how message lengths are computed. (Sections
3987   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
3988   <xref target="header.content-length" format="counter"/>,
3989   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
3990</t>
3991<t>
3992   The use and interpretation of HTTP version numbers has been clarified
3993   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
3994   version they support to deal with problems discovered in HTTP/1.0
3995   implementations (<xref target="http.version"/>)
3996</t>
3997<t>
3998   Transfer-coding had significant problems, particularly with
3999   interactions with chunked encoding. The solution is that transfer-codings
4000   become as full fledged as content-codings. This involves
4001   adding an IANA registry for transfer-codings (separate from content
4002   codings), a new header field (TE) and enabling trailer headers in the
4003   future. Transfer encoding is a major performance benefit, so it was
4004   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4005   interoperability problem that could have occurred due to interactions
4006   between authentication trailers, chunked encoding and HTTP/1.0
4007   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4008   and <xref target="header.te" format="counter"/>)
4009</t>
4010</section>
4011
4012<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4013<t>
4014  Rules about implicit linear white space between certain grammar productions
4015  have been removed; now it's only allowed when specifically pointed out
4016  in the ABNF.
4017  The CHAR rule does not allow the NUL character anymore (this affects
4018  the comment and quoted-string rules).  Furthermore, the quoted-pair
4019  rule does not allow escaping NUL, CR or LF anymore.
4020  (<xref target="basic.rules"/>)
4021</t>
4022<t>
4023  Clarify that HTTP-Version is case sensitive.
4024  (<xref target="http.version"/>)
4025</t>
4026<t>
4027  Remove reference to non-existant identity transfer-coding value tokens.
4028  (Sections <xref format="counter" target="transfer.codings"/> and
4029  <xref format="counter" target="message.length"/>)
4030</t>
4031<t>
4032  Clarification that the chunk length does not include
4033  the count of the octets in the chunk header and trailer.
4034  (<xref target="chunked.transfer.encoding"/>)
4035</t>
4036<t>
4037  Update use of abs_path production from RFC1808 to the path-absolute + query
4038  components of RFC3986.
4039  (<xref target="request-uri"/>)
4040</t>
4041<t>
4042  Clarify exactly when close connection options must be sent.
4043  (<xref target="header.connection"/>)
4044</t>
4045</section>
4046</section>
4047
4048<section title="Terminology" anchor="terminology">
4049<t>
4050   This specification uses a number of terms to refer to the roles
4051   played by participants in, and objects of, the HTTP communication.
4052</t>
4053<t>
4054  <iref item="connection"/>
4055  <x:dfn>connection</x:dfn>
4056  <list>
4057    <t>
4058      A transport layer virtual circuit established between two programs
4059      for the purpose of communication.
4060    </t>
4061  </list>
4062</t>
4063<t>
4064  <iref item="message"/>
4065  <x:dfn>message</x:dfn>
4066  <list>
4067    <t>
4068      The basic unit of HTTP communication, consisting of a structured
4069      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4070      transmitted via the connection.
4071    </t>
4072  </list>
4073</t>
4074<t>
4075  <iref item="request"/>
4076  <x:dfn>request</x:dfn>
4077  <list>
4078    <t>
4079      An HTTP request message, as defined in <xref target="request"/>.
4080    </t>
4081  </list>
4082</t>
4083<t>
4084  <iref item="response"/>
4085  <x:dfn>response</x:dfn>
4086  <list>
4087    <t>
4088      An HTTP response message, as defined in <xref target="response"/>.
4089    </t>
4090  </list>
4091</t>
4092<t>
4093  <iref item="resource"/>
4094  <x:dfn>resource</x:dfn>
4095  <list>
4096    <t>
4097      A network data object or service that can be identified by a URI,
4098      as defined in <xref target="uri"/>. Resources may be available in multiple
4099      representations (e.g. multiple languages, data formats, size, and
4100      resolutions) or vary in other ways.
4101    </t>
4102  </list>
4103</t>
4104<t>
4105  <iref item="entity"/>
4106  <x:dfn>entity</x:dfn>
4107  <list>
4108    <t>
4109      The information transferred as the payload of a request or
4110      response. An entity consists of metainformation in the form of
4111      entity-header fields and content in the form of an entity-body, as
4112      described in &entity;.
4113    </t>
4114  </list>
4115</t>
4116<t>
4117  <iref item="representation"/>
4118  <x:dfn>representation</x:dfn>
4119  <list>
4120    <t>
4121      An entity included with a response that is subject to content
4122      negotiation, as described in &content.negotiation;. There may exist multiple
4123      representations associated with a particular response status.
4124    </t>
4125  </list>
4126</t>
4127<t>
4128  <iref item="content negotiation"/>
4129  <x:dfn>content negotiation</x:dfn>
4130  <list>
4131    <t>
4132      The mechanism for selecting the appropriate representation when
4133      servicing a request, as described in &content.negotiation;. The
4134      representation of entities in any response can be negotiated
4135      (including error responses).
4136    </t>
4137  </list>
4138</t>
4139<t>
4140  <iref item="variant"/>
4141  <x:dfn>variant</x:dfn>
4142  <list>
4143    <t>
4144      A resource may have one, or more than one, representation(s)
4145      associated with it at any given instant. Each of these
4146      representations is termed a `variant'.  Use of the term `variant'
4147      does not necessarily imply that the resource is subject to content
4148      negotiation.
4149    </t>
4150  </list>
4151</t>
4152<t>
4153  <iref item="client"/>
4154  <x:dfn>client</x:dfn>
4155  <list>
4156    <t>
4157      A program that establishes connections for the purpose of sending
4158      requests.
4159    </t>
4160  </list>
4161</t>
4162<t>
4163  <iref item="user agent"/>
4164  <x:dfn>user agent</x:dfn>
4165  <list>
4166    <t>
4167      The client which initiates a request. These are often browsers,
4168      editors, spiders (web-traversing robots), or other end user tools.
4169    </t>
4170  </list>
4171</t>
4172<t>
4173  <iref item="server"/>
4174  <x:dfn>server</x:dfn>
4175  <list>
4176    <t>
4177      An application program that accepts connections in order to
4178      service requests by sending back responses. Any given program may
4179      be capable of being both a client and a server; our use of these
4180      terms refers only to the role being performed by the program for a
4181      particular connection, rather than to the program's capabilities
4182      in general. Likewise, any server may act as an origin server,
4183      proxy, gateway, or tunnel, switching behavior based on the nature
4184      of each request.
4185    </t>
4186  </list>
4187</t>
4188<t>
4189  <iref item="origin server"/>
4190  <x:dfn>origin server</x:dfn>
4191  <list>
4192    <t>
4193      The server on which a given resource resides or is to be created.
4194    </t>
4195  </list>
4196</t>
4197<t>
4198  <iref item="proxy"/>
4199  <x:dfn>proxy</x:dfn>
4200  <list>
4201    <t>
4202      An intermediary program which acts as both a server and a client
4203      for the purpose of making requests on behalf of other clients.
4204      Requests are serviced internally or by passing them on, with
4205      possible translation, to other servers. A proxy &MUST; implement
4206      both the client and server requirements of this specification. A
4207      "transparent proxy" is a proxy that does not modify the request or
4208      response beyond what is required for proxy authentication and
4209      identification. A "non-transparent proxy" is a proxy that modifies
4210      the request or response in order to provide some added service to
4211      the user agent, such as group annotation services, media type
4212      transformation, protocol reduction, or anonymity filtering. Except
4213      where either transparent or non-transparent behavior is explicitly
4214      stated, the HTTP proxy requirements apply to both types of
4215      proxies.
4216    </t>
4217  </list>
4218</t>
4219<t>
4220  <iref item="gateway"/>
4221  <x:dfn>gateway</x:dfn>
4222  <list>
4223    <t>
4224      A server which acts as an intermediary for some other server.
4225      Unlike a proxy, a gateway receives requests as if it were the
4226      origin server for the requested resource; the requesting client
4227      may not be aware that it is communicating with a gateway.
4228    </t>
4229  </list>
4230</t>
4231<t>
4232  <iref item="tunnel"/>
4233  <x:dfn>tunnel</x:dfn>
4234  <list>
4235    <t>
4236      An intermediary program which is acting as a blind relay between
4237      two connections. Once active, a tunnel is not considered a party
4238      to the HTTP communication, though the tunnel may have been
4239      initiated by an HTTP request. The tunnel ceases to exist when both
4240      ends of the relayed connections are closed.
4241    </t>
4242  </list>
4243</t>
4244<t>
4245  <iref item="cache"/>
4246  <x:dfn>cache</x:dfn>
4247  <list>
4248    <t>
4249      A program's local store of response messages and the subsystem
4250      that controls its message storage, retrieval, and deletion. A
4251      cache stores cacheable responses in order to reduce the response
4252      time and network bandwidth consumption on future, equivalent
4253      requests. Any client or server may include a cache, though a cache
4254      cannot be used by a server that is acting as a tunnel.
4255    </t>
4256  </list>
4257</t>
4258<t>
4259  <iref item="cacheable"/>
4260  <x:dfn>cacheable</x:dfn>
4261  <list>
4262    <t>
4263      A response is cacheable if a cache is allowed to store a copy of
4264      the response message for use in answering subsequent requests. The
4265      rules for determining the cacheability of HTTP responses are
4266      defined in &caching;. Even if a resource is cacheable, there may
4267      be additional constraints on whether a cache can use the cached
4268      copy for a particular request.
4269    </t>
4270  </list>
4271</t>
4272<t>
4273  <iref item="upstream"/>
4274  <iref item="downstream"/>
4275  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4276  <list>
4277    <t>
4278      Upstream and downstream describe the flow of a message: all
4279      messages flow from upstream to downstream.
4280    </t>
4281  </list>
4282</t>
4283<t>
4284  <iref item="inbound"/>
4285  <iref item="outbound"/>
4286  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4287  <list>
4288    <t>
4289      Inbound and outbound refer to the request and response paths for
4290      messages: "inbound" means "traveling toward the origin server",
4291      and "outbound" means "traveling toward the user agent"
4292    </t>
4293  </list>
4294</t>
4295</section>
4296
4297<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4298
4299<section title="Since RFC2616">
4300<t>
4301  Extracted relevant partitions from <xref target="RFC2616"/>.
4302</t>
4303</section>
4304
4305<section title="Since draft-ietf-httpbis-p1-messaging-00">
4306<t>
4307  Closed issues:
4308  <list style="symbols"> 
4309    <t>
4310      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4311      "HTTP Version should be case sensitive"
4312      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4313    </t>
4314    <t>
4315      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4316      "'unsafe' characters"
4317      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4318    </t>
4319    <t>
4320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4321      "Chunk Size Definition"
4322      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4323    </t>
4324    <t>
4325      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4326      "Message Length"
4327      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4328    </t>
4329    <t>
4330      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4331      "Media Type Registrations"
4332      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4333    </t>
4334    <t>
4335      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4336      "URI includes query"
4337      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4338    </t>
4339    <t>
4340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4341      "No close on 1xx responses"
4342      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4343    </t>
4344    <t>
4345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4346      "Remove 'identity' token references"
4347      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4348    </t>
4349    <t>
4350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4351      "Import query BNF"
4352    </t>
4353    <t>
4354      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4355      "qdtext BNF"
4356    </t>
4357    <t>
4358      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4359      "Normative and Informative references"
4360    </t>
4361    <t>
4362      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4363      "RFC2606 Compliance"
4364    </t>
4365    <t>
4366      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4367      "RFC977 reference"
4368    </t>
4369    <t>
4370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4371      "RFC1700 references"
4372    </t>
4373    <t>
4374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4375      "inconsistency in date format explanation"
4376    </t>
4377    <t>
4378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4379      "Date reference typo"
4380    </t>
4381    <t>
4382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4383      "Informative references"
4384    </t>
4385    <t>
4386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4387      "ISO-8859-1 Reference"
4388    </t>
4389    <t>
4390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4391      "Normative up-to-date references"
4392    </t>
4393  </list>
4394</t>
4395<t>
4396  Other changes:
4397  <list style="symbols"> 
4398    <t>
4399      Update media type registrations to use RFC4288 template.
4400    </t>
4401    <t>
4402      Use names of RFC4234 core rules DQUOTE and HTAB,
4403      fix broken ABNF for chunk-data
4404      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4405    </t>
4406  </list>
4407</t>
4408</section>
4409
4410<section title="Since draft-ietf-httpbis-p1-messaging-01">
4411<t>
4412  Closed issues:
4413  <list style="symbols"> 
4414    <t>
4415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4416      "Bodies on GET (and other) requests"
4417    </t>
4418    <t>
4419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4420      "Updating to RFC4288"
4421    </t>
4422    <t>
4423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4424      "Status Code and Reason Phrase"
4425    </t>
4426    <t>
4427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4428      "rel_path not used"
4429    </t>
4430  </list>
4431</t>
4432<t>
4433  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4434  <list style="symbols"> 
4435    <t>
4436      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4437      "trailer-part").
4438    </t>
4439    <t>
4440      Avoid underscore character in rule names ("http_URL" ->
4441      "http-URL", "abs_path" -> "path-absolute").
4442    </t>
4443    <t>
4444      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4445      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4446      have to be updated when switching over to RFC3986.
4447    </t>
4448    <t>
4449      Synchronize core rules with RFC5234 (this includes a change to CHAR
4450      which now excludes NUL).
4451    </t>
4452    <t>
4453      Get rid of prose rules that span multiple lines.
4454    </t>
4455    <t>
4456      Get rid of unused rules LOALPHA and UPALPHA.
4457    </t>
4458    <t>
4459      Move "Product Tokens" section (back) into Part 1, as "token" is used
4460      in the definition of the Upgrade header.
4461    </t>
4462    <t>
4463      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4464    </t>
4465    <t>
4466      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4467    </t>
4468  </list>
4469</t>
4470</section>
4471
4472<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4473<t>
4474  Closed issues:
4475  <list style="symbols"> 
4476    <t>
4477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4478      "HTTP-date vs. rfc1123-date"
4479    </t>
4480    <t>
4481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4482      "WS in quoted-pair"
4483    </t>
4484  </list>
4485</t>
4486<t>
4487  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4488  <list style="symbols"> 
4489    <t>
4490      Reference RFC 3984, and update header registrations for headers defined
4491      in this document.
4492    </t>
4493  </list>
4494</t>
4495<t>
4496  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4497  <list style="symbols"> 
4498    <t>
4499      Replace string literals when the string really is case-sensitive (HTTP-Version).
4500    </t>
4501  </list>
4502</t>
4503</section>
4504
4505<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4506<t>
4507  Closed issues:
4508  <list style="symbols"> 
4509    <t>
4510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4511      "Connection closing"
4512    </t>
4513    <t>
4514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4515      "Move registrations and registry information to IANA Considerations"
4516    </t>
4517    <t>
4518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4519      "need new URL for PAD1995 reference"
4520    </t>
4521    <t>
4522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4523      "IANA Considerations: update HTTP URI scheme registration"
4524    </t>
4525    <t>
4526      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4527      "Cite HTTPS URI scheme definition"
4528    </t>
4529    <t>
4530      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4531      "List-type headers vs Set-Cookie"
4532    </t>
4533  </list>
4534</t>
4535<t>
4536  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4537  <list style="symbols"> 
4538    <t>
4539      Replace string literals when the string really is case-sensitive (HTTP-Date).
4540    </t>
4541    <t>
4542      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4543    </t>
4544  </list>
4545</t>
4546</section>
4547
4548<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4549<t>
4550  Closed issues:
4551  <list style="symbols"> 
4552    <t>
4553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4554      "Out-of-date reference for URIs"
4555    </t>
4556    <t>
4557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4558      "RFC 2822 is updated by RFC 5322"
4559    </t>
4560  </list>
4561</t>
4562<t>
4563  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4564  <list style="symbols"> 
4565    <t>
4566      Use "/" instead of "|" for alternatives.
4567    </t>
4568    <t>
4569      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4570    </t>
4571    <t>
4572      Only reference RFC 5234's core rules.
4573    </t>
4574    <t>
4575      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4576      whitespace ("OWS") and required whitespace ("RWS").
4577    </t>
4578    <t>
4579      Rewrite ABNFs to spell out whitespace rules, factor out
4580      header value format definitions.
4581    </t>
4582  </list>
4583</t>
4584</section>
4585
4586<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4587<t>
4588  Closed issues:
4589  <list style="symbols"> 
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4592      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4593    </t>
4594    <t>
4595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4596      "RFC822 reference left in discussion of date formats"
4597    </t>
4598  </list>
4599</t>
4600</section>
4601
4602</section>
4603
4604</back>
4605</rfc>
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