source: draft-ietf-httpbis/latest-roy/p1-messaging.xml @ 350

Last change on this file since 350 was 350, checked in by julian.reschke@…, 11 years ago

resync with trunk wrt core rules (related to #36)

  • Property svn:eol-style set to native
File size: 195.4 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.04"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypermedia
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate resource targets for
235   interaction and to identify other resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
239   between HTTP and MIME messages).
240</t>
241<t>
242   HTTP is also designed for use as a generic protocol for translating
243   communication to and from other Internet information systems, such as
244   USENET news services via NNTP <xref target="RFC3977"/>,
245   file services via FTP <xref target="RFC959"/>,
246   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
247   HTTP proxies and gateways provide access to alternative information
248   services by translating their diverse protocols into a hypermedia
249   format that can be viewed and manipulated by clients in the same way
250   as HTTP services.
251</t>
252<t>
253   This document is Part 1 of the seven-part specification of HTTP,
254   defining the protocol referred to as "HTTP/1.1" and obsoleting
255   <xref target="RFC2616"/>.
256   Part 1 defines how clients determine when to use HTTP, the URI schemes
257   specific to HTTP-based resources, overall network operation with
258   transport protocol connection management, and HTTP message framing.
259   Our goal is to define all of the mechanisms necessary for HTTP message
260   handling that are independent of message semantics, thereby defining the
261   complete set of requirements for an HTTP message relay or generic
262   message parser.
263</t>
264
265<section title="Requirements" anchor="intro.requirements">
266<t>
267   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
268   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
269   document are to be interpreted as described in <xref target="RFC2119"/>.
270</t>
271<t>
272   An implementation is not compliant if it fails to satisfy one or more
273   of the &MUST; or &REQUIRED; level requirements for the protocols it
274   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
275   level and all the &SHOULD; level requirements for its protocols is said
276   to be "unconditionally compliant"; one that satisfies all the &MUST;
277   level requirements but not all the &SHOULD; level requirements for its
278   protocols is said to be "conditionally compliant."
279</t>
280</section>
281
282<section title="Syntax Notation" anchor="notation">
283<iref primary="true" item="Grammar" subitem="ALPHA"/>
284<iref primary="true" item="Grammar" subitem="CHAR"/>
285<iref primary="true" item="Grammar" subitem="CR"/>
286<iref primary="true" item="Grammar" subitem="CRLF"/>
287<iref primary="true" item="Grammar" subitem="CTL"/>
288<iref primary="true" item="Grammar" subitem="DIGIT"/>
289<iref primary="true" item="Grammar" subitem="DQUOTE"/>
290<iref primary="true" item="Grammar" subitem="HEXDIG"/>
291<iref primary="true" item="Grammar" subitem="HTAB"/>
292<iref primary="true" item="Grammar" subitem="LF"/>
293<iref primary="true" item="Grammar" subitem="OCTET"/>
294<iref primary="true" item="Grammar" subitem="SP"/>
295<iref primary="true" item="Grammar" subitem="WSP"/>
296<t anchor="core.rules">
297  <x:anchor-alias value="ALPHA"/>
298  <x:anchor-alias value="CHAR"/>
299  <x:anchor-alias value="CTL"/>
300  <x:anchor-alias value="CR"/>
301  <x:anchor-alias value="CRLF"/>
302  <x:anchor-alias value="DIGIT"/>
303  <x:anchor-alias value="DQUOTE"/>
304  <x:anchor-alias value="HEXDIG"/>
305  <x:anchor-alias value="HTAB"/>
306  <x:anchor-alias value="LF"/>
307  <x:anchor-alias value="OCTET"/>
308  <x:anchor-alias value="SP"/>
309  <x:anchor-alias value="WSP"/>
310   This specification uses the Augmented Backus-Naur Form (ABNF) notation
311   of <xref target="RFC5234"/>.  The following core rules are included by
312   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
313   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
314   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
315   DIGIT (decimal 0-9), DQUOTE (double quote),
316   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
317   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
318   and WSP (white space).
319</t>
320
321<section title="ABNF Extensions" anchor="notation.abnf">
322<t>
323   Two extensions to the ABNF rules of <xref target="RFC5234"/> are used to
324   improve readability.<cref>The current plan is to remove these extensions prior
325   to the last call draft.</cref>
326</t>
327
328<section title="#rule">
329  <t>
330    A construct "#" is defined, similar to "*", for defining lists of
331    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
332    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
333    (",") and &OPTIONAL; linear white space (LWS). This makes the usual
334    form of lists very easy; a rule such as
335    <figure><artwork type="example">
336 ( *<x:ref>LWS</x:ref> element *( *<x:ref>LWS</x:ref> "," *<x:ref>LWS</x:ref> element ))</artwork></figure>
337  </t>
338  <t>
339    can be shown as
340    <figure><artwork type="example">
341 1#element</artwork></figure>
342  </t>
343  <t>
344    Wherever this construct is used, null elements are allowed, but do
345    not contribute to the count of elements present. That is,
346    "(element), , (element) " is permitted, but counts as only two
347    elements. Therefore, where at least one element is required, at
348    least one non-null element &MUST; be present. Default values are 0
349    and infinity so that "#element" allows any number, including zero;
350    "1#element" requires at least one; and "1#2element" allows one or
351    two.
352  </t>
353</section>
354
355<section title="implied *LWS" anchor="implied.LWS">
356  <iref item="implied *LWS" primary="true"/>
357    <t>
358      The grammar described by this specification is word-based. Except
359      where noted otherwise, linear white space (LWS) can be included
360      between any two adjacent words (token or quoted-string), and
361      between adjacent words and separators, without changing the
362      interpretation of a field. At least one delimiter (LWS and/or
363      separators) &MUST; exist between any two tokens (for the definition
364      of "token" below), since they would otherwise be interpreted as a
365      single token.
366    </t>
367</section>
368</section>
369
370<section title="Basic Rules" anchor="basic.rules">
371<t anchor="rule.CRLF">
372   HTTP/1.1 defines the sequence CRLF as the end-of-line marker for all
373   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
374   tolerant applications). The end-of-line marker within an entity-body
375   is defined by its associated media type, as described in &media-types;.
376</t>
377<t anchor="rule.LWS">
378  <x:anchor-alias value="LWS"/>
379   HTTP/1.1 header field values can be folded onto multiple lines if the
380   continuation line begins with a space or horizontal tab. All linear
381   white space, including folding, has the same semantics as SP. A
382   recipient &MAY; replace any linear white space with a single SP before
383   interpreting the field value or forwarding the message downstream.
384</t>
385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="LWS"/>
386  <x:ref>LWS</x:ref>            = [<x:ref>CRLF</x:ref>] 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
387</artwork></figure>
388<t anchor="rule.TEXT">
389  <x:anchor-alias value="TEXT"/>
390   The TEXT rule is only used for descriptive field contents and values
391   that are not intended to be interpreted by the message parser. Words
392   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
393   <xref target="ISO-8859-1"/> only when encoded according to the rules of
394   <xref target="RFC2047"/>.
395</t>
396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
397  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>LWS</x:ref>
398                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>LWS</x:ref>
399</artwork></figure>
400<t>
401   A CRLF is allowed in the definition of TEXT only as part of a header
402   field continuation. It is expected that the folding LWS will be
403   replaced with a single SP before interpretation of the TEXT value.
404</t>
405<t anchor="rule.token.separators">
406  <x:anchor-alias value="tchar"/>
407  <x:anchor-alias value="token"/>
408  <x:anchor-alias value="separators"/>
409   Many HTTP/1.1 header field values consist of words separated by LWS
410   or special characters. These special characters &MUST; be in a quoted
411   string to be used within a parameter value (as defined in
412   <xref target="transfer.codings"/>).
413</t>
414<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="separators"/>
415  <x:ref>separators</x:ref>     = "(" / ")" / "&lt;" / "&gt;" / "@"
416                 / "," / ";" / ":" / "\" / <x:ref>DQUOTE</x:ref>
417                 / "/" / "[" / "]" / "?" / "="
418                 / "{" / "}" / <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref>
419                 
420  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
421                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
422                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
423                 ; any <x:ref>CHAR</x:ref> except <x:ref>CTL</x:ref>s or <x:ref>separators</x:ref>
424                 
425  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
426</artwork></figure>
427<t anchor="rule.comment">
428  <x:anchor-alias value="comment"/>
429  <x:anchor-alias value="ctext"/>
430   Comments can be included in some HTTP header fields by surrounding
431   the comment text with parentheses. Comments are only allowed in
432   fields containing "comment" as part of their field value definition.
433   In all other fields, parentheses are considered part of the field
434   value.
435</t>
436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
437  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
438  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
439</artwork></figure>
440<t anchor="rule.quoted-string">
441  <x:anchor-alias value="quoted-string"/>
442  <x:anchor-alias value="qdtext"/>
443   A string of text is parsed as a single word if it is quoted using
444   double-quote marks.
445</t>
446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
447  <x:ref>quoted-string</x:ref>  = ( <x:ref>DQUOTE</x:ref> *(<x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref> )
448  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
449</artwork></figure>
450<t anchor="rule.quoted-pair">
451  <x:anchor-alias value="quoted-pair"/>
452  <x:anchor-alias value="quoted-text"/>
453   The backslash character ("\") &MAY; be used as a single-character
454   quoting mechanism only within quoted-string and comment constructs.
455</t>
456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
457  <x:ref>quoted-text</x:ref>    = %x01-09 /
458                   %x0B-0C /
459                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
460  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
461</artwork></figure>
462</section>
463
464<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
465  <x:anchor-alias value="request-header"/>
466  <x:anchor-alias value="response-header"/>
467  <x:anchor-alias value="accept-params"/>
468  <x:anchor-alias value="entity-body"/>
469  <x:anchor-alias value="entity-header"/>
470  <x:anchor-alias value="Cache-Control"/>
471  <x:anchor-alias value="Pragma"/>
472  <x:anchor-alias value="Warning"/>
473<t>
474  The ABNF rules below are defined in other parts:
475</t>
476<figure><!-- Part2--><artwork type="abnf2616">
477  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
478  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
479</artwork></figure>
480<figure><!-- Part3--><artwork type="abnf2616">
481  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
482  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
483  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
484</artwork></figure>
485<figure><!-- Part6--><artwork type="abnf2616">
486  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
487  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
488  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
489</artwork></figure>
490</section>
491
492</section>
493</section>
494
495<section title="When to use HTTP" anchor="when">
496
497<section title="Uniform Resource Identifiers" anchor="uri">
498<t>
499   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used in HTTP
500   to indicate the target of a request and to identify additional resources related
501   to that resource, the request, or the response. Each protocol element in HTTP
502   that allows a URI reference will indicate in its ABNF whether the element allows
503   only a URI in absolute form, any relative reference, or some limited subset of
504   the URI-reference grammar. Unless otherwise indicated, relative URI references
505   are to be parsed relative to the URI corresponding to the request target
506   (the base URI).
507</t>
508  <x:anchor-alias value="URI-reference"/>
509  <x:anchor-alias value="absolute-URI"/>
510  <x:anchor-alias value="authority"/>
511  <x:anchor-alias value="fragment"/>
512  <x:anchor-alias value="path-abempty"/>
513  <x:anchor-alias value="path-absolute"/>
514  <x:anchor-alias value="port"/>
515  <x:anchor-alias value="query"/>
516  <x:anchor-alias value="uri-host"/>
517<t>
518   This specification adopts the definitions of "URI-reference", "absolute-URI", "fragment", "port",
519   "host", "path-abempty", "path-absolute", "query", and "authority" from <xref target="RFC3986"/>:
520</t>
521<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"/>
522  <x:ref>absolute-URI</x:ref>   = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
523  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
524  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
525  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
526  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
527  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
528  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
529  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
530</artwork></figure>
531<t>
532   HTTP does not place an a priori limit on the length of
533   a URI. Servers &MUST; be able to handle the URI of any resource they
534   serve, and &SHOULD; be able to handle URIs of unbounded length if they
535   provide GET-based forms that could generate such URIs. A server
536   &SHOULD; return 414 (Request-URI Too Long) status if a URI is longer
537   than the server can handle (see &status-414;).
538</t>
539<t>
540  <list>
541    <t>
542      <x:h>Note:</x:h> Servers ought to be cautious about depending on URI lengths
543      above 255 bytes, because some older client or proxy
544      implementations might not properly support these lengths.
545    </t>
546  </list>
547</t>
548
549<section title="http URI scheme" anchor="http.uri">
550  <x:anchor-alias value="http-URI"/>
551  <iref item="http URI scheme" primary="true"/>
552  <iref item="URI scheme" subitem="http" primary="true"/>
553<t>
554   The "http" scheme is used to locate network resources via the HTTP
555   protocol. This section defines the syntax and semantics for identifiers
556   using the http or https URI schemes.
557</t>
558<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
559  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
560</artwork></figure>
561<t>
562   If the port is empty or not given, port 80 is assumed. The semantics
563   are that the identified resource is located at the server listening
564   for TCP connections on that port of that host, and the Request-URI
565   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
566   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
567   the path-absolute is not present in the URL, it &MUST; be given as "/" when
568   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
569   receives a host name which is not a fully qualified domain name, it
570   &MAY; add its domain to the host name it received. If a proxy receives
571   a fully qualified domain name, the proxy &MUST-NOT; change the host
572   name.
573</t>
574<t><list><t>
575  <iref item="https URI scheme"/>
576  <iref item="URI scheme" subitem="https"/>
577  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
578</t></list></t>
579</section>
580
581<section title="URI Comparison" anchor="uri.comparison">
582<t>
583   When comparing two URIs to decide if they match or not, a client
584   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
585   URIs, with these exceptions:
586  <list style="symbols">
587    <t>A port that is empty or not given is equivalent to the default
588        port for that URI-reference;</t>
589    <t>Comparisons of host names &MUST; be case-insensitive;</t>
590    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
591    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
592  </list>
593</t>
594<t>
595   Characters other than those in the "reserved" set (see
596   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
597   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
598</t>
599<t>
600   For example, the following three URIs are equivalent:
601</t>
602<figure><artwork type="example">
603   http://example.com:80/~smith/home.html
604   http://EXAMPLE.com/%7Esmith/home.html
605   http://EXAMPLE.com:/%7esmith/home.html
606</artwork></figure>
607</section>
608</section>
609
610<section title="Overall Operation" anchor="intro.overall.operation">
611<t>
612   HTTP is a request/response protocol. A client sends a
613   request to the server in the form of a request method, URI, and
614   protocol version, followed by a MIME-like message containing request
615   modifiers, client information, and possible body content over a
616   connection with a server. The server responds with a status line,
617   including the message's protocol version and a success or error code,
618   followed by a MIME-like message containing server information, entity
619   metainformation, and possible entity-body content.
620</t>
621<t>
622   Most HTTP communication is initiated by a user agent and consists of
623   a request to be applied to a resource on some origin server. In the
624   simplest case, this may be accomplished via a single connection (v)
625   between the user agent (UA) and the origin server (O).
626</t>
627<figure><artwork type="drawing">
628       request chain ------------------------&gt;
629    UA -------------------v------------------- O
630       &lt;----------------------- response chain
631</artwork></figure>
632<t>
633   A more complicated situation occurs when one or more intermediaries
634   are present in the request/response chain. There are three common
635   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
636   forwarding agent, receiving requests for a URI in its absolute form,
637   rewriting all or part of the message, and forwarding the reformatted
638   request toward the server identified by the URI. A gateway is a
639   receiving agent, acting as a layer above some other server(s) and, if
640   necessary, translating the requests to the underlying server's
641   protocol. A tunnel acts as a relay point between two connections
642   without changing the messages; tunnels are used when the
643   communication needs to pass through an intermediary (such as a
644   firewall) even when the intermediary cannot understand the contents
645   of the messages.
646</t>
647<figure><artwork type="drawing">
648       request chain --------------------------------------&gt;
649    UA -----v----- A -----v----- B -----v----- C -----v----- O
650       &lt;------------------------------------- response chain
651</artwork></figure>
652<t>
653   The figure above shows three intermediaries (A, B, and C) between the
654   user agent and origin server. A request or response message that
655   travels the whole chain will pass through four separate connections.
656   This distinction is important because some HTTP communication options
657   may apply only to the connection with the nearest, non-tunnel
658   neighbor, only to the end-points of the chain, or to all connections
659   along the chain. Although the diagram is linear, each participant may
660   be engaged in multiple, simultaneous communications. For example, B
661   may be receiving requests from many clients other than A, and/or
662   forwarding requests to servers other than C, at the same time that it
663   is handling A's request.
664</t>
665<t>
666   Any party to the communication which is not acting as a tunnel may
667   employ an internal cache for handling requests. The effect of a cache
668   is that the request/response chain is shortened if one of the
669   participants along the chain has a cached response applicable to that
670   request. The following illustrates the resulting chain if B has a
671   cached copy of an earlier response from O (via C) for a request which
672   has not been cached by UA or A.
673</t>
674<figure><artwork type="drawing">
675          request chain ----------&gt;
676       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
677          &lt;--------- response chain
678</artwork></figure>
679<t>
680   Not all responses are usefully cacheable, and some requests may
681   contain modifiers which place special requirements on cache behavior.
682   HTTP requirements for cache behavior and cacheable responses are
683   defined in &caching;.
684</t>
685<t>
686   In fact, there are a wide variety of architectures and configurations
687   of caches and proxies currently being experimented with or deployed
688   across the World Wide Web. These systems include national hierarchies
689   of proxy caches to save transoceanic bandwidth, systems that
690   broadcast or multicast cache entries, organizations that distribute
691   subsets of cached data via CD-ROM, and so on. HTTP systems are used
692   in corporate intranets over high-bandwidth links, and for access via
693   PDAs with low-power radio links and intermittent connectivity. The
694   goal of HTTP/1.1 is to support the wide diversity of configurations
695   already deployed while introducing protocol constructs that meet the
696   needs of those who build web applications that require high
697   reliability and, failing that, at least reliable indications of
698   failure.
699</t>
700<t>
701   HTTP communication usually takes place over TCP/IP connections. The
702   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
703   not preclude HTTP from being implemented on top of any other protocol
704   on the Internet, or on other networks. HTTP only presumes a reliable
705   transport; any protocol that provides such guarantees can be used;
706   the mapping of the HTTP/1.1 request and response structures onto the
707   transport data units of the protocol in question is outside the scope
708   of this specification.
709</t>
710<t>
711   In HTTP/1.0, most implementations used a new connection for each
712   request/response exchange. In HTTP/1.1, a connection may be used for
713   one or more request/response exchanges, although connections may be
714   closed for a variety of reasons (see <xref target="persistent.connections"/>).
715</t>
716</section>
717</section>
718
719<section title="Protocol Parameters" anchor="protocol.parameters">
720
721<section title="HTTP Version" anchor="http.version">
722  <x:anchor-alias value="HTTP-Version"/>
723  <x:anchor-alias value="HTTP-Prot-Name"/>
724<t>
725   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
726   of the protocol. The protocol versioning policy is intended to allow
727   the sender to indicate the format of a message and its capacity for
728   understanding further HTTP communication, rather than the features
729   obtained via that communication. No change is made to the version
730   number for the addition of message components which do not affect
731   communication behavior or which only add to extensible field values.
732   The &lt;minor&gt; number is incremented when the changes made to the
733   protocol add features which do not change the general message parsing
734   algorithm, but which may add to the message semantics and imply
735   additional capabilities of the sender. The &lt;major&gt; number is
736   incremented when the format of a message within the protocol is
737   changed. See <xref target="RFC2145"/> for a fuller explanation.
738</t>
739<t>
740   The version of an HTTP message is indicated by an HTTP-Version field
741   in the first line of the message. HTTP-Version is case-sensitive.
742</t>
743<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
744  <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>
745  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
746</artwork></figure>
747<t>
748   Note that the major and minor numbers &MUST; be treated as separate
749   integers and that each &MAY; be incremented higher than a single digit.
750   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
751   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
752   &MUST-NOT; be sent.
753</t>
754<t>
755   An application that sends a request or response message that includes
756   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
757   with this specification. Applications that are at least conditionally
758   compliant with this specification &SHOULD; use an HTTP-Version of
759   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
760   not compatible with HTTP/1.0. For more details on when to send
761   specific HTTP-Version values, see <xref target="RFC2145"/>.
762</t>
763<t>
764   The HTTP version of an application is the highest HTTP version for
765   which the application is at least conditionally compliant.
766</t>
767<t>
768   Proxy and gateway applications need to be careful when forwarding
769   messages in protocol versions different from that of the application.
770   Since the protocol version indicates the protocol capability of the
771   sender, a proxy/gateway &MUST-NOT; send a message with a version
772   indicator which is greater than its actual version. If a higher
773   version request is received, the proxy/gateway &MUST; either downgrade
774   the request version, or respond with an error, or switch to tunnel
775   behavior.
776</t>
777<t>
778   Due to interoperability problems with HTTP/1.0 proxies discovered
779   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
780   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
781   they support. The proxy/gateway's response to that request &MUST; be in
782   the same major version as the request.
783</t>
784<t>
785  <list>
786    <t>
787      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
788      of header fields required or forbidden by the versions involved.
789    </t>
790  </list>
791</t>
792</section>
793
794<section title="Date/Time Formats" anchor="date.time.formats">
795<section title="Full Date" anchor="full.date">
796  <x:anchor-alias value="HTTP-date"/>
797  <x:anchor-alias value="obsolete-date"/>
798  <x:anchor-alias value="rfc1123-date"/>
799  <x:anchor-alias value="rfc850-date"/>
800  <x:anchor-alias value="asctime-date"/>
801  <x:anchor-alias value="date1"/>
802  <x:anchor-alias value="date2"/>
803  <x:anchor-alias value="date3"/>
804  <x:anchor-alias value="rfc1123-date"/>
805  <x:anchor-alias value="time"/>
806  <x:anchor-alias value="wkday"/>
807  <x:anchor-alias value="weekday"/>
808  <x:anchor-alias value="month"/>
809<t>
810   HTTP applications have historically allowed three different formats
811   for the representation of date/time stamps:
812</t>
813<figure><artwork type="example">
814   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
815   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
816   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
817</artwork></figure>
818<t>
819   The first format is preferred as an Internet standard and represents
820   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
821   <xref target="RFC822"/>). The other formats are described here only for
822   compatibility with obsolete implementations.
823   HTTP/1.1 clients and servers that parse the date value &MUST; accept
824   all three formats (for compatibility with HTTP/1.0), though they &MUST;
825   only generate the RFC 1123 format for representing HTTP-date values
826   in header fields. See <xref target="tolerant.applications"/> for further information.
827</t>
828<t><list><t>
829      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
830      accepting date values that may have been sent by non-HTTP
831      applications, as is sometimes the case when retrieving or posting
832      messages via proxies/gateways to SMTP or NNTP.
833</t></list></t>
834<t>
835   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
836   (GMT), without exception. For the purposes of HTTP, GMT is exactly
837   equal to UTC (Coordinated Universal Time). This is indicated in the
838   first two formats by the inclusion of "GMT" as the three-letter
839   abbreviation for time zone, and &MUST; be assumed when reading the
840   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
841   additional LWS beyond that specifically included as SP in the
842   grammar.
843</t>
844<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"/>
845  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
846  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
847  <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
848  <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
849  <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>
850  <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>
851                 ; day month year (e.g., 02 Jun 1982)
852  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
853                 ; day-month-year (e.g., 02-Jun-82)
854  <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> ))
855                 ; month day (e.g., Jun  2)
856  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
857                 ; 00:00:00 - 23:59:59
858  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
859               / s-Thu / s-Fri / s-Sat / s-Sun
860  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
861               / l-Thu / l-Fri / l-Sat / l-Sun
862  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
863               / s-May / s-Jun / s-Jul / s-Aug
864               / s-Sep / s-Oct / s-Nov / s-Dec
865               
866  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
867
868  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
869  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
870  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
871  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
872  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
873  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
874  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
875
876  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
877  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
878  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
879  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
880  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
881  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
882  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
883
884  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
885  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
886  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
887  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
888  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
889  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
890  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
891  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
892  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
893  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
894  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
895  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
896</artwork></figure>
897<t>
898      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
899      to their usage within the protocol stream. Clients and servers are
900      not required to use these formats for user presentation, request
901      logging, etc.
902</t>
903</section>
904</section>
905
906<section title="Transfer Codings" anchor="transfer.codings">
907  <x:anchor-alias value="parameter"/>
908  <x:anchor-alias value="transfer-coding"/>
909  <x:anchor-alias value="transfer-extension"/>
910<t>
911   Transfer-coding values are used to indicate an encoding
912   transformation that has been, can be, or may need to be applied to an
913   entity-body in order to ensure "safe transport" through the network.
914   This differs from a content coding in that the transfer-coding is a
915   property of the message, not of the original entity.
916</t>
917<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
918  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
919  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( ";" <x:ref>parameter</x:ref> )
920</artwork></figure>
921<t anchor="rule.parameter">
922  <x:anchor-alias value="attribute"/>
923  <x:anchor-alias value="parameter"/>
924  <x:anchor-alias value="value"/>
925   Parameters are in  the form of attribute/value pairs.
926</t>
927<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"/>
928  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> "=" <x:ref>value</x:ref>
929  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
930  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
931</artwork></figure>
932<t>
933   All transfer-coding values are case-insensitive. HTTP/1.1 uses
934   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
935   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
936</t>
937<t>
938   Whenever a transfer-coding is applied to a message-body, the set of
939   transfer-codings &MUST; include "chunked", unless the message indicates it
940   is terminated by closing the connection. When the "chunked" transfer-coding
941   is used, it &MUST; be the last transfer-coding applied to the
942   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
943   than once to a message-body. These rules allow the recipient to
944   determine the transfer-length of the message (<xref target="message.length"/>).
945</t>
946<t>
947   Transfer-codings are analogous to the Content-Transfer-Encoding
948   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
949   binary data over a 7-bit transport service. However, safe transport
950   has a different focus for an 8bit-clean transfer protocol. In HTTP,
951   the only unsafe characteristic of message-bodies is the difficulty in
952   determining the exact body length (<xref target="message.length"/>), or the desire to
953   encrypt data over a shared transport.
954</t>
955<t>
956   The Internet Assigned Numbers Authority (IANA) acts as a registry for
957   transfer-coding value tokens. Initially, the registry contains the
958   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
959   "gzip", "compress", and "deflate" (&content-codings;).
960</t>
961<t>
962   New transfer-coding value tokens &SHOULD; be registered in the same way
963   as new content-coding value tokens (&content-codings;).
964</t>
965<t>
966   A server which receives an entity-body with a transfer-coding it does
967   not understand &SHOULD; return 501 (Not Implemented), and close the
968   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
969   client.
970</t>
971
972<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
973  <x:anchor-alias value="chunk"/>
974  <x:anchor-alias value="Chunked-Body"/>
975  <x:anchor-alias value="chunk-data"/>
976  <x:anchor-alias value="chunk-extension"/>
977  <x:anchor-alias value="chunk-ext-name"/>
978  <x:anchor-alias value="chunk-ext-val"/>
979  <x:anchor-alias value="chunk-size"/>
980  <x:anchor-alias value="last-chunk"/>
981  <x:anchor-alias value="trailer-part"/>
982<t>
983   The chunked encoding modifies the body of a message in order to
984   transfer it as a series of chunks, each with its own size indicator,
985   followed by an &OPTIONAL; trailer containing entity-header fields. This
986   allows dynamically produced content to be transferred along with the
987   information necessary for the recipient to verify that it has
988   received the full message.
989</t>
990<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-extension"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/>
991  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
992                   <x:ref>last-chunk</x:ref>
993                   <x:ref>trailer-part</x:ref>
994                   <x:ref>CRLF</x:ref>
995 
996  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
997                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
998  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
999  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-extension</x:ref> ] <x:ref>CRLF</x:ref>
1000 
1001  <x:ref>chunk-extension</x:ref>= *( ";" <x:ref>chunk-ext-name</x:ref> [ "=" <x:ref>chunk-ext-val</x:ref> ] )
1002  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1003  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1004  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1005  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1006</artwork></figure>
1007<t>
1008   The chunk-size field is a string of hex digits indicating the size of
1009   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1010   zero, followed by the trailer, which is terminated by an empty line.
1011</t>
1012<t>
1013   The trailer allows the sender to include additional HTTP header
1014   fields at the end of the message. The Trailer header field can be
1015   used to indicate which header fields are included in a trailer (see
1016   <xref target="header.trailer"/>).
1017</t>
1018<t>
1019   A server using chunked transfer-coding in a response &MUST-NOT; use the
1020   trailer for any header fields unless at least one of the following is
1021   true:
1022  <list style="numbers">
1023    <t>the request included a TE header field that indicates "trailers" is
1024     acceptable in the transfer-coding of the  response, as described in
1025     <xref target="header.te"/>; or,</t>
1026
1027    <t>the server is the origin server for the response, the trailer
1028     fields consist entirely of optional metadata, and the recipient
1029     could use the message (in a manner acceptable to the origin server)
1030     without receiving this metadata.  In other words, the origin server
1031     is willing to accept the possibility that the trailer fields might
1032     be silently discarded along the path to the client.</t>
1033  </list>
1034</t>
1035<t>
1036   This requirement prevents an interoperability failure when the
1037   message is being received by an HTTP/1.1 (or later) proxy and
1038   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1039   compliance with the protocol would have necessitated a possibly
1040   infinite buffer on the proxy.
1041</t>
1042<t>
1043   A process for decoding the "chunked" transfer-coding
1044   can be represented in pseudo-code as:
1045</t>
1046<figure><artwork type="code">
1047    length := 0
1048    read chunk-size, chunk-extension (if any) and CRLF
1049    while (chunk-size &gt; 0) {
1050       read chunk-data and CRLF
1051       append chunk-data to entity-body
1052       length := length + chunk-size
1053       read chunk-size and CRLF
1054    }
1055    read entity-header
1056    while (entity-header not empty) {
1057       append entity-header to existing header fields
1058       read entity-header
1059    }
1060    Content-Length := length
1061    Remove "chunked" from Transfer-Encoding
1062</artwork></figure>
1063<t>
1064   All HTTP/1.1 applications &MUST; be able to receive and decode the
1065   "chunked" transfer-coding, and &MUST; ignore chunk-extension extensions
1066   they do not understand.
1067</t>
1068</section>
1069</section>
1070
1071<section title="Product Tokens" anchor="product.tokens">
1072  <x:anchor-alias value="product"/>
1073  <x:anchor-alias value="product-version"/>
1074<t>
1075   Product tokens are used to allow communicating applications to
1076   identify themselves by software name and version. Most fields using
1077   product tokens also allow sub-products which form a significant part
1078   of the application to be listed, separated by white space. By
1079   convention, the products are listed in order of their significance
1080   for identifying the application.
1081</t>
1082<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1083  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1084  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1085</artwork></figure>
1086<t>
1087   Examples:
1088</t>
1089<figure><artwork type="example">
1090    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1091    Server: Apache/0.8.4
1092</artwork></figure>
1093<t>
1094   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1095   used for advertising or other non-essential information. Although any
1096   token character &MAY; appear in a product-version, this token &SHOULD;
1097   only be used for a version identifier (i.e., successive versions of
1098   the same product &SHOULD; only differ in the product-version portion of
1099   the product value).
1100</t>
1101</section>
1102
1103</section>
1104
1105<section title="HTTP Message" anchor="http.message">
1106
1107<section title="Message Types" anchor="message.types">
1108  <x:anchor-alias value="generic-message"/>
1109  <x:anchor-alias value="HTTP-message"/>
1110  <x:anchor-alias value="start-line"/>
1111<t>
1112   HTTP messages consist of requests from client to server and responses
1113   from server to client.
1114</t>
1115<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1116  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1117</artwork></figure>
1118<t>
1119   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1120   message format of <xref target="RFC5322"/> for transferring entities (the payload
1121   of the message). Both types of message consist of a start-line, zero
1122   or more header fields (also known as "headers"), an empty line (i.e.,
1123   a line with nothing preceding the CRLF) indicating the end of the
1124   header fields, and possibly a message-body.
1125</t>
1126<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1127  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1128                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1129                    <x:ref>CRLF</x:ref>
1130                    [ <x:ref>message-body</x:ref> ]
1131  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1132</artwork></figure>
1133<t>
1134   In the interest of robustness, servers &SHOULD; ignore any empty
1135   line(s) received where a Request-Line is expected. In other words, if
1136   the server is reading the protocol stream at the beginning of a
1137   message and receives a CRLF first, it should ignore the CRLF.
1138</t>
1139<t>
1140   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1141   after a POST request. To restate what is explicitly forbidden by the
1142   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1143   extra CRLF.
1144</t>
1145</section>
1146
1147<section title="Message Headers" anchor="message.headers">
1148  <x:anchor-alias value="field-content"/>
1149  <x:anchor-alias value="field-name"/>
1150  <x:anchor-alias value="field-value"/>
1151  <x:anchor-alias value="message-header"/>
1152<t>
1153   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1154   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1155   entity-header (&entity-header-fields;) fields, follow the same generic format as
1156   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1157   of a name followed by a colon (":") and the field value. Field names
1158   are case-insensitive. The field value &MAY; be preceded by any amount
1159   of LWS, though a single SP is preferred. Header fields can be
1160   extended over multiple lines by preceding each extra line with at
1161   least one SP or HTAB. Applications ought to follow "common form", where
1162   one is known or indicated, when generating HTTP constructs, since
1163   there might exist some implementations that fail to accept anything
1164   beyond the common forms.
1165</t>
1166<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"/>
1167  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1168  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1169  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>LWS</x:ref> )
1170  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1171                   ; the <x:ref>OCTET</x:ref>s making up the field-value
1172                   ; and consisting of either *<x:ref>TEXT</x:ref> or combinations
1173                   ; of <x:ref>token</x:ref>, <x:ref>separators</x:ref>, and <x:ref>quoted-string</x:ref>
1174</artwork></figure>
1175<t>
1176   The field-content does not include any leading or trailing LWS:
1177   linear white space occurring before the first non-whitespace
1178   character of the field-value or after the last non-whitespace
1179   character of the field-value. Such leading or trailing LWS &MAY; be
1180   removed without changing the semantics of the field value. Any LWS
1181   that occurs between field-content &MAY; be replaced with a single SP
1182   before interpreting the field value or forwarding the message
1183   downstream.
1184</t>
1185<t>
1186   The order in which header fields with differing field names are
1187   received is not significant. However, it is "good practice" to send
1188   general-header fields first, followed by request-header or response-header
1189   fields, and ending with the entity-header fields.
1190</t>
1191<t>
1192   Multiple message-header fields with the same field-name &MAY; be
1193   present in a message if and only if the entire field-value for that
1194   header field is defined as a comma-separated list [i.e., #(values)].
1195   It &MUST; be possible to combine the multiple header fields into one
1196   "field-name: field-value" pair, without changing the semantics of the
1197   message, by appending each subsequent field-value to the first, each
1198   separated by a comma. The order in which header fields with the same
1199   field-name are received is therefore significant to the
1200   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1201   change the order of these field values when a message is forwarded.
1202</t>
1203<t>
1204  <list><t>
1205   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1206   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1207   can occur multiple times, but does not use the list syntax, and thus cannot
1208   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1209   for details.) Also note that the Set-Cookie2 header specified in
1210   <xref target="RFC2965"/> does not share this problem.
1211  </t></list>
1212</t>
1213 
1214</section>
1215
1216<section title="Message Body" anchor="message.body">
1217  <x:anchor-alias value="message-body"/>
1218<t>
1219   The message-body (if any) of an HTTP message is used to carry the
1220   entity-body associated with the request or response. The message-body
1221   differs from the entity-body only when a transfer-coding has been
1222   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1223</t>
1224<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1225  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1226               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1227</artwork></figure>
1228<t>
1229   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1230   applied by an application to ensure safe and proper transfer of the
1231   message. Transfer-Encoding is a property of the message, not of the
1232   entity, and thus &MAY; be added or removed by any application along the
1233   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1234   when certain transfer-codings may be used.)
1235</t>
1236<t>
1237   The rules for when a message-body is allowed in a message differ for
1238   requests and responses.
1239</t>
1240<t>
1241   The presence of a message-body in a request is signaled by the
1242   inclusion of a Content-Length or Transfer-Encoding header field in
1243   the request's message-headers. A message-body &MUST-NOT; be included in
1244   a request if the specification of the request method (&method;)
1245   explicitly disallows an entity-body in requests.
1246   When a request message contains both a message-body of non-zero
1247   length and a method that does not define any semantics for that
1248   request message-body, then an origin server &SHOULD; either ignore
1249   the message-body or respond with an appropriate error message
1250   (e.g., 413).  A proxy or gateway, when presented the same request,
1251   &SHOULD; either forward the request inbound with the message-body or
1252   ignore the message-body when determining a response.
1253</t>
1254<t>
1255   For response messages, whether or not a message-body is included with
1256   a message is dependent on both the request method and the response
1257   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1258   &MUST-NOT; include a message-body, even though the presence of entity-header
1259   fields might lead one to believe they do. All 1xx
1260   (informational), 204 (No Content), and 304 (Not Modified) responses
1261   &MUST-NOT; include a message-body. All other responses do include a
1262   message-body, although it &MAY; be of zero length.
1263</t>
1264</section>
1265
1266<section title="Message Length" anchor="message.length">
1267<t>
1268   The transfer-length of a message is the length of the message-body as
1269   it appears in the message; that is, after any transfer-codings have
1270   been applied. When a message-body is included with a message, the
1271   transfer-length of that body is determined by one of the following
1272   (in order of precedence):
1273</t>
1274<t>
1275  <list style="numbers">
1276    <x:lt><t>
1277     Any response message which "&MUST-NOT;" include a message-body (such
1278     as the 1xx, 204, and 304 responses and any response to a HEAD
1279     request) is always terminated by the first empty line after the
1280     header fields, regardless of the entity-header fields present in
1281     the message.
1282    </t></x:lt>
1283    <x:lt><t>
1284     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1285     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1286     is used, the transfer-length is defined by the use of this transfer-coding.
1287     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1288     is not present, the transfer-length is defined by the sender closing the connection.
1289    </t></x:lt>
1290    <x:lt><t>
1291     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1292     decimal value in OCTETs represents both the entity-length and the
1293     transfer-length. The Content-Length header field &MUST-NOT; be sent
1294     if these two lengths are different (i.e., if a Transfer-Encoding
1295     header field is present). If a message is received with both a
1296     Transfer-Encoding header field and a Content-Length header field,
1297     the latter &MUST; be ignored.
1298    </t></x:lt>
1299    <x:lt><t>
1300     If the message uses the media type "multipart/byteranges", and the
1301     transfer-length is not otherwise specified, then this self-delimiting
1302     media type defines the transfer-length. This media type
1303     &MUST-NOT; be used unless the sender knows that the recipient can parse
1304     it; the presence in a request of a Range header with multiple byte-range
1305     specifiers from a 1.1 client implies that the client can parse
1306     multipart/byteranges responses.
1307    <list style="empty"><t>
1308       A range header might be forwarded by a 1.0 proxy that does not
1309       understand multipart/byteranges; in this case the server &MUST;
1310       delimit the message using methods defined in items 1, 3 or 5 of
1311       this section.
1312    </t></list>
1313    </t></x:lt>
1314    <x:lt><t>
1315     By the server closing the connection. (Closing the connection
1316     cannot be used to indicate the end of a request body, since that
1317     would leave no possibility for the server to send back a response.)
1318    </t></x:lt>
1319  </list>
1320</t>
1321<t>
1322   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1323   containing a message-body &MUST; include a valid Content-Length header
1324   field unless the server is known to be HTTP/1.1 compliant. If a
1325   request contains a message-body and a Content-Length is not given,
1326   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1327   determine the length of the message, or with 411 (Length Required) if
1328   it wishes to insist on receiving a valid Content-Length.
1329</t>
1330<t>
1331   All HTTP/1.1 applications that receive entities &MUST; accept the
1332   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1333   to be used for messages when the message length cannot be determined
1334   in advance.
1335</t>
1336<t>
1337   Messages &MUST-NOT; include both a Content-Length header field and a
1338   transfer-coding. If the message does include a
1339   transfer-coding, the Content-Length &MUST; be ignored.
1340</t>
1341<t>
1342   When a Content-Length is given in a message where a message-body is
1343   allowed, its field value &MUST; exactly match the number of OCTETs in
1344   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1345   invalid length is received and detected.
1346</t>
1347</section>
1348
1349<section title="General Header Fields" anchor="general.header.fields">
1350  <x:anchor-alias value="general-header"/>
1351<t>
1352   There are a few header fields which have general applicability for
1353   both request and response messages, but which do not apply to the
1354   entity being transferred. These header fields apply only to the
1355   message being transmitted.
1356</t>
1357<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1358  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1359                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1360                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1361                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1362                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1363                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1364                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1365                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1366                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1367</artwork></figure>
1368<t>
1369   General-header field names can be extended reliably only in
1370   combination with a change in the protocol version. However, new or
1371   experimental header fields may be given the semantics of general
1372   header fields if all parties in the communication recognize them to
1373   be general-header fields. Unrecognized header fields are treated as
1374   entity-header fields.
1375</t>
1376</section>
1377</section>
1378
1379<section title="Request" anchor="request">
1380  <x:anchor-alias value="Request"/>
1381<t>
1382   A request message from a client to a server includes, within the
1383   first line of that message, the method to be applied to the resource,
1384   the identifier of the resource, and the protocol version in use.
1385</t>
1386<!--                 Host                      ; should be moved here eventually -->
1387<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1388  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1389                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1390                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1391                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1392                  <x:ref>CRLF</x:ref>
1393                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1394</artwork></figure>
1395
1396<section title="Request-Line" anchor="request-line">
1397  <x:anchor-alias value="Request-Line"/>
1398<t>
1399   The Request-Line begins with a method token, followed by the
1400   Request-URI and the protocol version, and ending with CRLF. The
1401   elements are separated by SP characters. No CR or LF is allowed
1402   except in the final CRLF sequence.
1403</t>
1404<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1405  <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>
1406</artwork></figure>
1407
1408<section title="Method" anchor="method">
1409  <x:anchor-alias value="Method"/>
1410<t>
1411   The Method  token indicates the method to be performed on the
1412   resource identified by the Request-URI. The method is case-sensitive.
1413</t>
1414<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1415  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1416</artwork></figure>
1417</section>
1418
1419<section title="Request-URI" anchor="request-uri">
1420  <x:anchor-alias value="Request-URI"/>
1421<t>
1422   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1423   identifies the resource upon which to apply the request.
1424</t>
1425<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-URI"/>
1426  <x:ref>Request-URI</x:ref>    = "*"
1427                 / <x:ref>absolute-URI</x:ref>
1428                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1429                 / <x:ref>authority</x:ref>
1430</artwork></figure>
1431<t>
1432   The four options for Request-URI are dependent on the nature of the
1433   request. The asterisk "*" means that the request does not apply to a
1434   particular resource, but to the server itself, and is only allowed
1435   when the method used does not necessarily apply to a resource. One
1436   example would be
1437</t>
1438<figure><artwork type="example">
1439    OPTIONS * HTTP/1.1
1440</artwork></figure>
1441<t>
1442   The absolute-URI form is &REQUIRED; when the request is being made to a
1443   proxy. The proxy is requested to forward the request or service it
1444   from a valid cache, and return the response. Note that the proxy &MAY;
1445   forward the request on to another proxy or directly to the server
1446   specified by the absolute-URI. In order to avoid request loops, a
1447   proxy &MUST; be able to recognize all of its server names, including
1448   any aliases, local variations, and the numeric IP address. An example
1449   Request-Line would be:
1450</t>
1451<figure><artwork type="example">
1452    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1453</artwork></figure>
1454<t>
1455   To allow for transition to absolute-URIs in all requests in future
1456   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1457   form in requests, even though HTTP/1.1 clients will only generate
1458   them in requests to proxies.
1459</t>
1460<t>
1461   The authority form is only used by the CONNECT method (&CONNECT;).
1462</t>
1463<t>
1464   The most common form of Request-URI is that used to identify a
1465   resource on an origin server or gateway. In this case the absolute
1466   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1467   the Request-URI, and the network location of the URI (authority) &MUST;
1468   be transmitted in a Host header field. For example, a client wishing
1469   to retrieve the resource above directly from the origin server would
1470   create a TCP connection to port 80 of the host "www.example.org" and send
1471   the lines:
1472</t>
1473<figure><artwork type="example">
1474    GET /pub/WWW/TheProject.html HTTP/1.1
1475    Host: www.example.org
1476</artwork></figure>
1477<t>
1478   followed by the remainder of the Request. Note that the absolute path
1479   cannot be empty; if none is present in the original URI, it &MUST; be
1480   given as "/" (the server root).
1481</t>
1482<t>
1483   The Request-URI is transmitted in the format specified in
1484   <xref target="http.uri"/>. If the Request-URI is encoded using the
1485   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1486   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1487   &MUST; decode the Request-URI in order to
1488   properly interpret the request. Servers &SHOULD; respond to invalid
1489   Request-URIs with an appropriate status code.
1490</t>
1491<t>
1492   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1493   received Request-URI when forwarding it to the next inbound server,
1494   except as noted above to replace a null path-absolute with "/".
1495</t>
1496<t>
1497  <list><t>
1498      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1499      meaning of the request when the origin server is improperly using
1500      a non-reserved URI character for a reserved purpose.  Implementors
1501      should be aware that some pre-HTTP/1.1 proxies have been known to
1502      rewrite the Request-URI.
1503  </t></list>
1504</t>
1505</section>
1506</section>
1507
1508<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1509<t>
1510   The exact resource identified by an Internet request is determined by
1511   examining both the Request-URI and the Host header field.
1512</t>
1513<t>
1514   An origin server that does not allow resources to differ by the
1515   requested host &MAY; ignore the Host header field value when
1516   determining the resource identified by an HTTP/1.1 request. (But see
1517   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1518   for other requirements on Host support in HTTP/1.1.)
1519</t>
1520<t>
1521   An origin server that does differentiate resources based on the host
1522   requested (sometimes referred to as virtual hosts or vanity host
1523   names) &MUST; use the following rules for determining the requested
1524   resource on an HTTP/1.1 request:
1525  <list style="numbers">
1526    <t>If Request-URI is an absolute-URI, the host is part of the
1527     Request-URI. Any Host header field value in the request &MUST; be
1528     ignored.</t>
1529    <t>If the Request-URI is not an absolute-URI, and the request includes
1530     a Host header field, the host is determined by the Host header
1531     field value.</t>
1532    <t>If the host as determined by rule 1 or 2 is not a valid host on
1533     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1534  </list>
1535</t>
1536<t>
1537   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1538   attempt to use heuristics (e.g., examination of the URI path for
1539   something unique to a particular host) in order to determine what
1540   exact resource is being requested.
1541</t>
1542</section>
1543
1544</section>
1545
1546
1547<section title="Response" anchor="response">
1548  <x:anchor-alias value="Response"/>
1549<t>
1550   After receiving and interpreting a request message, a server responds
1551   with an HTTP response message.
1552</t>
1553<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1554  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1555                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1556                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1557                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1558                  <x:ref>CRLF</x:ref>
1559                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1560</artwork></figure>
1561
1562<section title="Status-Line" anchor="status-line">
1563  <x:anchor-alias value="Status-Line"/>
1564<t>
1565   The first line of a Response message is the Status-Line, consisting
1566   of the protocol version followed by a numeric status code and its
1567   associated textual phrase, with each element separated by SP
1568   characters. No CR or LF is allowed except in the final CRLF sequence.
1569</t>
1570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1571  <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>
1572</artwork></figure>
1573
1574<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1575  <x:anchor-alias value="Reason-Phrase"/>
1576  <x:anchor-alias value="Status-Code"/>
1577<t>
1578   The Status-Code element is a 3-digit integer result code of the
1579   attempt to understand and satisfy the request. These codes are fully
1580   defined in &status-codes;.  The Reason Phrase exists for the sole
1581   purpose of providing a textual description associated with the numeric
1582   status code, out of deference to earlier Internet application protocols
1583   that were more frequently used with interactive text clients.
1584   A client &SHOULD; ignore the content of the Reason Phrase.
1585</t>
1586<t>
1587   The first digit of the Status-Code defines the class of response. The
1588   last two digits do not have any categorization role. There are 5
1589   values for the first digit:
1590  <list style="symbols">
1591    <t>
1592      1xx: Informational - Request received, continuing process
1593    </t>
1594    <t>
1595      2xx: Success - The action was successfully received,
1596        understood, and accepted
1597    </t>
1598    <t>
1599      3xx: Redirection - Further action must be taken in order to
1600        complete the request
1601    </t>
1602    <t>
1603      4xx: Client Error - The request contains bad syntax or cannot
1604        be fulfilled
1605    </t>
1606    <t>
1607      5xx: Server Error - The server failed to fulfill an apparently
1608        valid request
1609    </t>
1610  </list>
1611</t>
1612<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"/>
1613  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1614  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1615</artwork></figure>
1616</section>
1617</section>
1618
1619</section>
1620
1621
1622<section title="Connections" anchor="connections">
1623
1624<section title="Persistent Connections" anchor="persistent.connections">
1625
1626<section title="Purpose" anchor="persistent.purpose">
1627<t>
1628   Prior to persistent connections, a separate TCP connection was
1629   established to fetch each URL, increasing the load on HTTP servers
1630   and causing congestion on the Internet. The use of inline images and
1631   other associated data often require a client to make multiple
1632   requests of the same server in a short amount of time. Analysis of
1633   these performance problems and results from a prototype
1634   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1635   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1636   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1637   T/TCP <xref target="Tou1998"/>.
1638</t>
1639<t>
1640   Persistent HTTP connections have a number of advantages:
1641  <list style="symbols">
1642      <t>
1643        By opening and closing fewer TCP connections, CPU time is saved
1644        in routers and hosts (clients, servers, proxies, gateways,
1645        tunnels, or caches), and memory used for TCP protocol control
1646        blocks can be saved in hosts.
1647      </t>
1648      <t>
1649        HTTP requests and responses can be pipelined on a connection.
1650        Pipelining allows a client to make multiple requests without
1651        waiting for each response, allowing a single TCP connection to
1652        be used much more efficiently, with much lower elapsed time.
1653      </t>
1654      <t>
1655        Network congestion is reduced by reducing the number of packets
1656        caused by TCP opens, and by allowing TCP sufficient time to
1657        determine the congestion state of the network.
1658      </t>
1659      <t>
1660        Latency on subsequent requests is reduced since there is no time
1661        spent in TCP's connection opening handshake.
1662      </t>
1663      <t>
1664        HTTP can evolve more gracefully, since errors can be reported
1665        without the penalty of closing the TCP connection. Clients using
1666        future versions of HTTP might optimistically try a new feature,
1667        but if communicating with an older server, retry with old
1668        semantics after an error is reported.
1669      </t>
1670    </list>
1671</t>
1672<t>
1673   HTTP implementations &SHOULD; implement persistent connections.
1674</t>
1675</section>
1676
1677<section title="Overall Operation" anchor="persistent.overall">
1678<t>
1679   A significant difference between HTTP/1.1 and earlier versions of
1680   HTTP is that persistent connections are the default behavior of any
1681   HTTP connection. That is, unless otherwise indicated, the client
1682   &SHOULD; assume that the server will maintain a persistent connection,
1683   even after error responses from the server.
1684</t>
1685<t>
1686   Persistent connections provide a mechanism by which a client and a
1687   server can signal the close of a TCP connection. This signaling takes
1688   place using the Connection header field (<xref target="header.connection"/>). Once a close
1689   has been signaled, the client &MUST-NOT; send any more requests on that
1690   connection.
1691</t>
1692
1693<section title="Negotiation" anchor="persistent.negotiation">
1694<t>
1695   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1696   maintain a persistent connection unless a Connection header including
1697   the connection-token "close" was sent in the request. If the server
1698   chooses to close the connection immediately after sending the
1699   response, it &SHOULD; send a Connection header including the
1700   connection-token close.
1701</t>
1702<t>
1703   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1704   decide to keep it open based on whether the response from a server
1705   contains a Connection header with the connection-token close. In case
1706   the client does not want to maintain a connection for more than that
1707   request, it &SHOULD; send a Connection header including the
1708   connection-token close.
1709</t>
1710<t>
1711   If either the client or the server sends the close token in the
1712   Connection header, that request becomes the last one for the
1713   connection.
1714</t>
1715<t>
1716   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1717   maintained for HTTP versions less than 1.1 unless it is explicitly
1718   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1719   compatibility with HTTP/1.0 clients.
1720</t>
1721<t>
1722   In order to remain persistent, all messages on the connection &MUST;
1723   have a self-defined message length (i.e., one not defined by closure
1724   of the connection), as described in <xref target="message.length"/>.
1725</t>
1726</section>
1727
1728<section title="Pipelining" anchor="pipelining">
1729<t>
1730   A client that supports persistent connections &MAY; "pipeline" its
1731   requests (i.e., send multiple requests without waiting for each
1732   response). A server &MUST; send its responses to those requests in the
1733   same order that the requests were received.
1734</t>
1735<t>
1736   Clients which assume persistent connections and pipeline immediately
1737   after connection establishment &SHOULD; be prepared to retry their
1738   connection if the first pipelined attempt fails. If a client does
1739   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1740   persistent. Clients &MUST; also be prepared to resend their requests if
1741   the server closes the connection before sending all of the
1742   corresponding responses.
1743</t>
1744<t>
1745   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1746   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1747   premature termination of the transport connection could lead to
1748   indeterminate results. A client wishing to send a non-idempotent
1749   request &SHOULD; wait to send that request until it has received the
1750   response status for the previous request.
1751</t>
1752</section>
1753</section>
1754
1755<section title="Proxy Servers" anchor="persistent.proxy">
1756<t>
1757   It is especially important that proxies correctly implement the
1758   properties of the Connection header field as specified in <xref target="header.connection"/>.
1759</t>
1760<t>
1761   The proxy server &MUST; signal persistent connections separately with
1762   its clients and the origin servers (or other proxy servers) that it
1763   connects to. Each persistent connection applies to only one transport
1764   link.
1765</t>
1766<t>
1767   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1768   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1769   discussion of the problems with the Keep-Alive header implemented by
1770   many HTTP/1.0 clients).
1771</t>
1772</section>
1773
1774<section title="Practical Considerations" anchor="persistent.practical">
1775<t>
1776   Servers will usually have some time-out value beyond which they will
1777   no longer maintain an inactive connection. Proxy servers might make
1778   this a higher value since it is likely that the client will be making
1779   more connections through the same server. The use of persistent
1780   connections places no requirements on the length (or existence) of
1781   this time-out for either the client or the server.
1782</t>
1783<t>
1784   When a client or server wishes to time-out it &SHOULD; issue a graceful
1785   close on the transport connection. Clients and servers &SHOULD; both
1786   constantly watch for the other side of the transport close, and
1787   respond to it as appropriate. If a client or server does not detect
1788   the other side's close promptly it could cause unnecessary resource
1789   drain on the network.
1790</t>
1791<t>
1792   A client, server, or proxy &MAY; close the transport connection at any
1793   time. For example, a client might have started to send a new request
1794   at the same time that the server has decided to close the "idle"
1795   connection. From the server's point of view, the connection is being
1796   closed while it was idle, but from the client's point of view, a
1797   request is in progress.
1798</t>
1799<t>
1800   This means that clients, servers, and proxies &MUST; be able to recover
1801   from asynchronous close events. Client software &SHOULD; reopen the
1802   transport connection and retransmit the aborted sequence of requests
1803   without user interaction so long as the request sequence is
1804   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1805   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1806   human operator the choice of retrying the request(s). Confirmation by
1807   user-agent software with semantic understanding of the application
1808   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1809   be repeated if the second sequence of requests fails.
1810</t>
1811<t>
1812   Servers &SHOULD; always respond to at least one request per connection,
1813   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1814   middle of transmitting a response, unless a network or client failure
1815   is suspected.
1816</t>
1817<t>
1818   Clients that use persistent connections &SHOULD; limit the number of
1819   simultaneous connections that they maintain to a given server. A
1820   single-user client &SHOULD-NOT; maintain more than 2 connections with
1821   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1822   another server or proxy, where N is the number of simultaneously
1823   active users. These guidelines are intended to improve HTTP response
1824   times and avoid congestion.
1825</t>
1826</section>
1827</section>
1828
1829<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1830
1831<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1832<t>
1833   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1834   flow control mechanisms to resolve temporary overloads, rather than
1835   terminating connections with the expectation that clients will retry.
1836   The latter technique can exacerbate network congestion.
1837</t>
1838</section>
1839
1840<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1841<t>
1842   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1843   the network connection for an error status while it is transmitting
1844   the request. If the client sees an error status, it &SHOULD;
1845   immediately cease transmitting the body. If the body is being sent
1846   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1847   empty trailer &MAY; be used to prematurely mark the end of the message.
1848   If the body was preceded by a Content-Length header, the client &MUST;
1849   close the connection.
1850</t>
1851</section>
1852
1853<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1854<t>
1855   The purpose of the 100 (Continue) status (see &status-100;) is to
1856   allow a client that is sending a request message with a request body
1857   to determine if the origin server is willing to accept the request
1858   (based on the request headers) before the client sends the request
1859   body. In some cases, it might either be inappropriate or highly
1860   inefficient for the client to send the body if the server will reject
1861   the message without looking at the body.
1862</t>
1863<t>
1864   Requirements for HTTP/1.1 clients:
1865  <list style="symbols">
1866    <t>
1867        If a client will wait for a 100 (Continue) response before
1868        sending the request body, it &MUST; send an Expect request-header
1869        field (&header-expect;) with the "100-continue" expectation.
1870    </t>
1871    <t>
1872        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1873        with the "100-continue" expectation if it does not intend
1874        to send a request body.
1875    </t>
1876  </list>
1877</t>
1878<t>
1879   Because of the presence of older implementations, the protocol allows
1880   ambiguous situations in which a client may send "Expect: 100-continue"
1881   without receiving either a 417 (Expectation Failed) status
1882   or a 100 (Continue) status. Therefore, when a client sends this
1883   header field to an origin server (possibly via a proxy) from which it
1884   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1885   for an indefinite period before sending the request body.
1886</t>
1887<t>
1888   Requirements for HTTP/1.1 origin servers:
1889  <list style="symbols">
1890    <t> Upon receiving a request which includes an Expect request-header
1891        field with the "100-continue" expectation, an origin server &MUST;
1892        either respond with 100 (Continue) status and continue to read
1893        from the input stream, or respond with a final status code. The
1894        origin server &MUST-NOT; wait for the request body before sending
1895        the 100 (Continue) response. If it responds with a final status
1896        code, it &MAY; close the transport connection or it &MAY; continue
1897        to read and discard the rest of the request.  It &MUST-NOT;
1898        perform the requested method if it returns a final status code.
1899    </t>
1900    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1901        the request message does not include an Expect request-header
1902        field with the "100-continue" expectation, and &MUST-NOT; send a
1903        100 (Continue) response if such a request comes from an HTTP/1.0
1904        (or earlier) client. There is an exception to this rule: for
1905        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1906        status in response to an HTTP/1.1 PUT or POST request that does
1907        not include an Expect request-header field with the "100-continue"
1908        expectation. This exception, the purpose of which is
1909        to minimize any client processing delays associated with an
1910        undeclared wait for 100 (Continue) status, applies only to
1911        HTTP/1.1 requests, and not to requests with any other HTTP-version
1912        value.
1913    </t>
1914    <t> An origin server &MAY; omit a 100 (Continue) response if it has
1915        already received some or all of the request body for the
1916        corresponding request.
1917    </t>
1918    <t> An origin server that sends a 100 (Continue) response &MUST;
1919    ultimately send a final status code, once the request body is
1920        received and processed, unless it terminates the transport
1921        connection prematurely.
1922    </t>
1923    <t> If an origin server receives a request that does not include an
1924        Expect request-header field with the "100-continue" expectation,
1925        the request includes a request body, and the server responds
1926        with a final status code before reading the entire request body
1927        from the transport connection, then the server &SHOULD-NOT;  close
1928        the transport connection until it has read the entire request,
1929        or until the client closes the connection. Otherwise, the client
1930        might not reliably receive the response message. However, this
1931        requirement is not be construed as preventing a server from
1932        defending itself against denial-of-service attacks, or from
1933        badly broken client implementations.
1934      </t>
1935    </list>
1936</t>
1937<t>
1938   Requirements for HTTP/1.1 proxies:
1939  <list style="symbols">
1940    <t> If a proxy receives a request that includes an Expect request-header
1941        field with the "100-continue" expectation, and the proxy
1942        either knows that the next-hop server complies with HTTP/1.1 or
1943        higher, or does not know the HTTP version of the next-hop
1944        server, it &MUST; forward the request, including the Expect header
1945        field.
1946    </t>
1947    <t> If the proxy knows that the version of the next-hop server is
1948        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
1949        respond with a 417 (Expectation Failed) status.
1950    </t>
1951    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
1952        numbers received from recently-referenced next-hop servers.
1953    </t>
1954    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
1955        request message was received from an HTTP/1.0 (or earlier)
1956        client and did not include an Expect request-header field with
1957        the "100-continue" expectation. This requirement overrides the
1958        general rule for forwarding of 1xx responses (see &status-1xx;).
1959    </t>
1960  </list>
1961</t>
1962</section>
1963
1964<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
1965<t>
1966   If an HTTP/1.1 client sends a request which includes a request body,
1967   but which does not include an Expect request-header field with the
1968   "100-continue" expectation, and if the client is not directly
1969   connected to an HTTP/1.1 origin server, and if the client sees the
1970   connection close before receiving any status from the server, the
1971   client &SHOULD; retry the request.  If the client does retry this
1972   request, it &MAY; use the following "binary exponential backoff"
1973   algorithm to be assured of obtaining a reliable response:
1974  <list style="numbers">
1975    <t>
1976      Initiate a new connection to the server
1977    </t>
1978    <t>
1979      Transmit the request-headers
1980    </t>
1981    <t>
1982      Initialize a variable R to the estimated round-trip time to the
1983         server (e.g., based on the time it took to establish the
1984         connection), or to a constant value of 5 seconds if the round-trip
1985         time is not available.
1986    </t>
1987    <t>
1988       Compute T = R * (2**N), where N is the number of previous
1989         retries of this request.
1990    </t>
1991    <t>
1992       Wait either for an error response from the server, or for T
1993         seconds (whichever comes first)
1994    </t>
1995    <t>
1996       If no error response is received, after T seconds transmit the
1997         body of the request.
1998    </t>
1999    <t>
2000       If client sees that the connection is closed prematurely,
2001         repeat from step 1 until the request is accepted, an error
2002         response is received, or the user becomes impatient and
2003         terminates the retry process.
2004    </t>
2005  </list>
2006</t>
2007<t>
2008   If at any point an error status is received, the client
2009  <list style="symbols">
2010      <t>&SHOULD-NOT;  continue and</t>
2011
2012      <t>&SHOULD; close the connection if it has not completed sending the
2013        request message.</t>
2014    </list>
2015</t>
2016</section>
2017</section>
2018</section>
2019
2020
2021<section title="Header Field Definitions" anchor="header.fields">
2022<t>
2023   This section defines the syntax and semantics of HTTP/1.1 header fields
2024   related to message framing and transport protocols.
2025</t>
2026<t>
2027   For entity-header fields, both sender and recipient refer to either the
2028   client or the server, depending on who sends and who receives the entity.
2029</t>
2030
2031<section title="Connection" anchor="header.connection">
2032  <iref primary="true" item="Connection header" x:for-anchor=""/>
2033  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2034  <x:anchor-alias value="Connection"/>
2035  <x:anchor-alias value="connection-token"/>
2036<t>
2037   The Connection general-header field allows the sender to specify
2038   options that are desired for that particular connection and &MUST-NOT;
2039   be communicated by proxies over further connections.
2040</t>
2041<t>
2042   The Connection header has the following grammar:
2043</t>
2044<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2045  <x:ref>Connection</x:ref> = "Connection" ":" 1#(<x:ref>connection-token</x:ref>)
2046  <x:ref>connection-token</x:ref>  = <x:ref>token</x:ref>
2047</artwork></figure>
2048<t>
2049   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2050   message is forwarded and, for each connection-token in this field,
2051   remove any header field(s) from the message with the same name as the
2052   connection-token. Connection options are signaled by the presence of
2053   a connection-token in the Connection header field, not by any
2054   corresponding additional header field(s), since the additional header
2055   field may not be sent if there are no parameters associated with that
2056   connection option.
2057</t>
2058<t>
2059   Message headers listed in the Connection header &MUST-NOT; include
2060   end-to-end headers, such as Cache-Control.
2061</t>
2062<t>
2063   HTTP/1.1 defines the "close" connection option for the sender to
2064   signal that the connection will be closed after completion of the
2065   response. For example,
2066</t>
2067<figure><artwork type="example">
2068    Connection: close
2069</artwork></figure>
2070<t>
2071   in either the request or the response header fields indicates that
2072   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2073   after the current request/response is complete.
2074</t>
2075<t>
2076   An HTTP/1.1 client that does not support persistent connections &MUST;
2077   include the "close" connection option in every request message.
2078</t>
2079<t>
2080   An HTTP/1.1 server that does not support persistent connections &MUST;
2081   include the "close" connection option in every response message that
2082   does not have a 1xx (informational) status code.
2083</t>
2084<t>
2085   A system receiving an HTTP/1.0 (or lower-version) message that
2086   includes a Connection header &MUST;, for each connection-token in this
2087   field, remove and ignore any header field(s) from the message with
2088   the same name as the connection-token. This protects against mistaken
2089   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2090</t>
2091</section>
2092
2093<section title="Content-Length" anchor="header.content-length">
2094  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2095  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2096  <x:anchor-alias value="Content-Length"/>
2097<t>
2098   The Content-Length entity-header field indicates the size of the
2099   entity-body, in decimal number of OCTETs, sent to the recipient or,
2100   in the case of the HEAD method, the size of the entity-body that
2101   would have been sent had the request been a GET.
2102</t>
2103<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2104  <x:ref>Content-Length</x:ref>    = "Content-Length" ":" 1*<x:ref>DIGIT</x:ref>
2105</artwork></figure>
2106<t>
2107   An example is
2108</t>
2109<figure><artwork type="example">
2110    Content-Length: 3495
2111</artwork></figure>
2112<t>
2113   Applications &SHOULD; use this field to indicate the transfer-length of
2114   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2115</t>
2116<t>
2117   Any Content-Length greater than or equal to zero is a valid value.
2118   <xref target="message.length"/> describes how to determine the length of a message-body
2119   if a Content-Length is not given.
2120</t>
2121<t>
2122   Note that the meaning of this field is significantly different from
2123   the corresponding definition in MIME, where it is an optional field
2124   used within the "message/external-body" content-type. In HTTP, it
2125   &SHOULD; be sent whenever the message's length can be determined prior
2126   to being transferred, unless this is prohibited by the rules in
2127   <xref target="message.length"/>.
2128</t>
2129</section>
2130
2131<section title="Date" anchor="header.date">
2132  <iref primary="true" item="Date header" x:for-anchor=""/>
2133  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2134  <x:anchor-alias value="Date"/>
2135<t>
2136   The Date general-header field represents the date and time at which
2137   the message was originated, having the same semantics as orig-date in
2138   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2139   HTTP-date, as described in <xref target="full.date"/>;
2140   it &MUST; be sent in rfc1123-date format.
2141</t>
2142<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2143  <x:ref>Date</x:ref>  = "Date" ":" <x:ref>HTTP-date</x:ref>
2144</artwork></figure>
2145<t>
2146   An example is
2147</t>
2148<figure><artwork type="example">
2149    Date: Tue, 15 Nov 1994 08:12:31 GMT
2150</artwork></figure>
2151<t>
2152   Origin servers &MUST; include a Date header field in all responses,
2153   except in these cases:
2154  <list style="numbers">
2155      <t>If the response status code is 100 (Continue) or 101 (Switching
2156         Protocols), the response &MAY; include a Date header field, at
2157         the server's option.</t>
2158
2159      <t>If the response status code conveys a server error, e.g. 500
2160         (Internal Server Error) or 503 (Service Unavailable), and it is
2161         inconvenient or impossible to generate a valid Date.</t>
2162
2163      <t>If the server does not have a clock that can provide a
2164         reasonable approximation of the current time, its responses
2165         &MUST-NOT; include a Date header field. In this case, the rules
2166         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2167  </list>
2168</t>
2169<t>
2170   A received message that does not have a Date header field &MUST; be
2171   assigned one by the recipient if the message will be cached by that
2172   recipient or gatewayed via a protocol which requires a Date. An HTTP
2173   implementation without a clock &MUST-NOT; cache responses without
2174   revalidating them on every use. An HTTP cache, especially a shared
2175   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2176   clock with a reliable external standard.
2177</t>
2178<t>
2179   Clients &SHOULD; only send a Date header field in messages that include
2180   an entity-body, as in the case of the PUT and POST requests, and even
2181   then it is optional. A client without a clock &MUST-NOT; send a Date
2182   header field in a request.
2183</t>
2184<t>
2185   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2186   time subsequent to the generation of the message. It &SHOULD; represent
2187   the best available approximation of the date and time of message
2188   generation, unless the implementation has no means of generating a
2189   reasonably accurate date and time. In theory, the date ought to
2190   represent the moment just before the entity is generated. In
2191   practice, the date can be generated at any time during the message
2192   origination without affecting its semantic value.
2193</t>
2194
2195<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2196<t>
2197   Some origin server implementations might not have a clock available.
2198   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2199   values to a response, unless these values were associated
2200   with the resource by a system or user with a reliable clock. It &MAY;
2201   assign an Expires value that is known, at or before server
2202   configuration time, to be in the past (this allows "pre-expiration"
2203   of responses without storing separate Expires values for each
2204   resource).
2205</t>
2206</section>
2207</section>
2208
2209<section title="Host" anchor="header.host">
2210  <iref primary="true" item="Host header" x:for-anchor=""/>
2211  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2212  <x:anchor-alias value="Host"/>
2213<t>
2214   The Host request-header field specifies the Internet host and port
2215   number of the resource being requested, as obtained from the original
2216   URI given by the user or referring resource (generally an http URI,
2217   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2218   the naming authority of the origin server or gateway given by the
2219   original URL. This allows the origin server or gateway to
2220   differentiate between internally-ambiguous URLs, such as the root "/"
2221   URL of a server for multiple host names on a single IP address.
2222</t>
2223<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
2224  <x:ref>Host</x:ref> = "Host" ":" <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2225</artwork></figure>
2226<t>
2227   A "host" without any trailing port information implies the default
2228   port for the service requested (e.g., "80" for an HTTP URL). For
2229   example, a request on the origin server for
2230   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2231</t>
2232<figure><artwork type="example">
2233    GET /pub/WWW/ HTTP/1.1
2234    Host: www.example.org
2235</artwork></figure>
2236<t>
2237   A client &MUST; include a Host header field in all HTTP/1.1 request
2238   messages. If the requested URI does not include an Internet host
2239   name for the service being requested, then the Host header field &MUST;
2240   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2241   request message it forwards does contain an appropriate Host header
2242   field that identifies the service being requested by the proxy. All
2243   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2244   status code to any HTTP/1.1 request message which lacks a Host header
2245   field.
2246</t>
2247<t>
2248   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2249   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2250   for other requirements relating to Host.
2251</t>
2252</section>
2253
2254<section title="TE" anchor="header.te">
2255  <iref primary="true" item="TE header" x:for-anchor=""/>
2256  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2257  <x:anchor-alias value="TE"/>
2258  <x:anchor-alias value="t-codings"/>
2259<t>
2260   The TE request-header field indicates what extension transfer-codings
2261   it is willing to accept in the response and whether or not it is
2262   willing to accept trailer fields in a chunked transfer-coding. Its
2263   value may consist of the keyword "trailers" and/or a comma-separated
2264   list of extension transfer-coding names with optional accept
2265   parameters (as described in <xref target="transfer.codings"/>).
2266</t>
2267<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/>
2268  <x:ref>TE</x:ref>        = "TE" ":" #( <x:ref>t-codings</x:ref> )
2269  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2270</artwork></figure>
2271<t>
2272   The presence of the keyword "trailers" indicates that the client is
2273   willing to accept trailer fields in a chunked transfer-coding, as
2274   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2275   transfer-coding values even though it does not itself represent a
2276   transfer-coding.
2277</t>
2278<t>
2279   Examples of its use are:
2280</t>
2281<figure><artwork type="example">
2282    TE: deflate
2283    TE:
2284    TE: trailers, deflate;q=0.5
2285</artwork></figure>
2286<t>
2287   The TE header field only applies to the immediate connection.
2288   Therefore, the keyword &MUST; be supplied within a Connection header
2289   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2290</t>
2291<t>
2292   A server tests whether a transfer-coding is acceptable, according to
2293   a TE field, using these rules:
2294  <list style="numbers">
2295    <x:lt>
2296      <t>The "chunked" transfer-coding is always acceptable. If the
2297         keyword "trailers" is listed, the client indicates that it is
2298         willing to accept trailer fields in the chunked response on
2299         behalf of itself and any downstream clients. The implication is
2300         that, if given, the client is stating that either all
2301         downstream clients are willing to accept trailer fields in the
2302         forwarded response, or that it will attempt to buffer the
2303         response on behalf of downstream recipients.
2304      </t><t>
2305         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2306         chunked response such that a client can be assured of buffering
2307         the entire response.</t>
2308    </x:lt>
2309    <x:lt>
2310      <t>If the transfer-coding being tested is one of the transfer-codings
2311         listed in the TE field, then it is acceptable unless it
2312         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2313         qvalue of 0 means "not acceptable.")</t>
2314    </x:lt>
2315    <x:lt>
2316      <t>If multiple transfer-codings are acceptable, then the
2317         acceptable transfer-coding with the highest non-zero qvalue is
2318         preferred.  The "chunked" transfer-coding always has a qvalue
2319         of 1.</t>
2320    </x:lt>
2321  </list>
2322</t>
2323<t>
2324   If the TE field-value is empty or if no TE field is present, the only
2325   transfer-coding  is "chunked". A message with no transfer-coding is
2326   always acceptable.
2327</t>
2328</section>
2329
2330<section title="Trailer" anchor="header.trailer">
2331  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2332  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2333  <x:anchor-alias value="Trailer"/>
2334<t>
2335   The Trailer general field value indicates that the given set of
2336   header fields is present in the trailer of a message encoded with
2337   chunked transfer-coding.
2338</t>
2339<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2340  <x:ref>Trailer</x:ref>  = "Trailer" ":" 1#<x:ref>field-name</x:ref>
2341</artwork></figure>
2342<t>
2343   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2344   message using chunked transfer-coding with a non-empty trailer. Doing
2345   so allows the recipient to know which header fields to expect in the
2346   trailer.
2347</t>
2348<t>
2349   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2350   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2351   trailer fields in a "chunked" transfer-coding.
2352</t>
2353<t>
2354   Message header fields listed in the Trailer header field &MUST-NOT;
2355   include the following header fields:
2356  <list style="symbols">
2357    <t>Transfer-Encoding</t>
2358    <t>Content-Length</t>
2359    <t>Trailer</t>
2360  </list>
2361</t>
2362</section>
2363
2364<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2365  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2366  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2367  <x:anchor-alias value="Transfer-Encoding"/>
2368<t>
2369   The Transfer-Encoding general-header field indicates what (if any)
2370   type of transformation has been applied to the message body in order
2371   to safely transfer it between the sender and the recipient. This
2372   differs from the content-coding in that the transfer-coding is a
2373   property of the message, not of the entity.
2374</t>
2375<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
2376  <x:ref>Transfer-Encoding</x:ref>       = "Transfer-Encoding" ":" 1#<x:ref>transfer-coding</x:ref>
2377</artwork></figure>
2378<t>
2379   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2380</t>
2381<figure><artwork type="example">
2382  Transfer-Encoding: chunked
2383</artwork></figure>
2384<t>
2385   If multiple encodings have been applied to an entity, the transfer-codings
2386   &MUST; be listed in the order in which they were applied.
2387   Additional information about the encoding parameters &MAY; be provided
2388   by other entity-header fields not defined by this specification.
2389</t>
2390<t>
2391   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2392   header.
2393</t>
2394</section>
2395
2396<section title="Upgrade" anchor="header.upgrade">
2397  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2398  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2399  <x:anchor-alias value="Upgrade"/>
2400<t>
2401   The Upgrade general-header allows the client to specify what
2402   additional communication protocols it supports and would like to use
2403   if the server finds it appropriate to switch protocols. The server
2404   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2405   response to indicate which protocol(s) are being switched.
2406</t>
2407<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
2408  <x:ref>Upgrade</x:ref>        = "Upgrade" ":" 1#<x:ref>product</x:ref>
2409</artwork></figure>
2410<t>
2411   For example,
2412</t>
2413<figure><artwork type="example">
2414    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2415</artwork></figure>
2416<t>
2417   The Upgrade header field is intended to provide a simple mechanism
2418   for transition from HTTP/1.1 to some other, incompatible protocol. It
2419   does so by allowing the client to advertise its desire to use another
2420   protocol, such as a later version of HTTP with a higher major version
2421   number, even though the current request has been made using HTTP/1.1.
2422   This eases the difficult transition between incompatible protocols by
2423   allowing the client to initiate a request in the more commonly
2424   supported protocol while indicating to the server that it would like
2425   to use a "better" protocol if available (where "better" is determined
2426   by the server, possibly according to the nature of the method and/or
2427   resource being requested).
2428</t>
2429<t>
2430   The Upgrade header field only applies to switching application-layer
2431   protocols upon the existing transport-layer connection. Upgrade
2432   cannot be used to insist on a protocol change; its acceptance and use
2433   by the server is optional. The capabilities and nature of the
2434   application-layer communication after the protocol change is entirely
2435   dependent upon the new protocol chosen, although the first action
2436   after changing the protocol &MUST; be a response to the initial HTTP
2437   request containing the Upgrade header field.
2438</t>
2439<t>
2440   The Upgrade header field only applies to the immediate connection.
2441   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2442   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2443   HTTP/1.1 message.
2444</t>
2445<t>
2446   The Upgrade header field cannot be used to indicate a switch to a
2447   protocol on a different connection. For that purpose, it is more
2448   appropriate to use a 301, 302, 303, or 305 redirection response.
2449</t>
2450<t>
2451   This specification only defines the protocol name "HTTP" for use by
2452   the family of Hypertext Transfer Protocols, as defined by the HTTP
2453   version rules of <xref target="http.version"/> and future updates to this
2454   specification. Any token can be used as a protocol name; however, it
2455   will only be useful if both the client and server associate the name
2456   with the same protocol.
2457</t>
2458</section>
2459
2460<section title="Via" anchor="header.via">
2461  <iref primary="true" item="Via header" x:for-anchor=""/>
2462  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2463  <x:anchor-alias value="protocol-name"/>
2464  <x:anchor-alias value="protocol-version"/>
2465  <x:anchor-alias value="pseudonym"/>
2466  <x:anchor-alias value="received-by"/>
2467  <x:anchor-alias value="received-protocol"/>
2468  <x:anchor-alias value="Via"/>
2469<t>
2470   The Via general-header field &MUST; be used by gateways and proxies to
2471   indicate the intermediate protocols and recipients between the user
2472   agent and the server on requests, and between the origin server and
2473   the client on responses. It is analogous to the "Received" field defined in
2474   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2475   avoiding request loops, and identifying the protocol capabilities of
2476   all senders along the request/response chain.
2477</t>
2478<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2479  <x:ref>Via</x:ref> =  "Via" ":" 1#( <x:ref>received-protocol</x:ref> <x:ref>received-by</x:ref> [ <x:ref>comment</x:ref> ] )
2480  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2481  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2482  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2483  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2484  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2485</artwork></figure>
2486<t>
2487   The received-protocol indicates the protocol version of the message
2488   received by the server or client along each segment of the
2489   request/response chain. The received-protocol version is appended to
2490   the Via field value when the message is forwarded so that information
2491   about the protocol capabilities of upstream applications remains
2492   visible to all recipients.
2493</t>
2494<t>
2495   The protocol-name is optional if and only if it would be "HTTP". The
2496   received-by field is normally the host and optional port number of a
2497   recipient server or client that subsequently forwarded the message.
2498   However, if the real host is considered to be sensitive information,
2499   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2500   be assumed to be the default port of the received-protocol.
2501</t>
2502<t>
2503   Multiple Via field values represents each proxy or gateway that has
2504   forwarded the message. Each recipient &MUST; append its information
2505   such that the end result is ordered according to the sequence of
2506   forwarding applications.
2507</t>
2508<t>
2509   Comments &MAY; be used in the Via header field to identify the software
2510   of the recipient proxy or gateway, analogous to the User-Agent and
2511   Server header fields. However, all comments in the Via field are
2512   optional and &MAY; be removed by any recipient prior to forwarding the
2513   message.
2514</t>
2515<t>
2516   For example, a request message could be sent from an HTTP/1.0 user
2517   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2518   forward the request to a public proxy at p.example.net, which completes
2519   the request by forwarding it to the origin server at www.example.com.
2520   The request received by www.example.com would then have the following
2521   Via header field:
2522</t>
2523<figure><artwork type="example">
2524    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2525</artwork></figure>
2526<t>
2527   Proxies and gateways used as a portal through a network firewall
2528   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2529   the firewall region. This information &SHOULD; only be propagated if
2530   explicitly enabled. If not enabled, the received-by host of any host
2531   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2532   for that host.
2533</t>
2534<t>
2535   For organizations that have strong privacy requirements for hiding
2536   internal structures, a proxy &MAY; combine an ordered subsequence of
2537   Via header field entries with identical received-protocol values into
2538   a single such entry. For example,
2539</t>
2540<figure><artwork type="example">
2541    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2542</artwork></figure>
2543<t>
2544        could be collapsed to
2545</t>
2546<figure><artwork type="example">
2547    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2548</artwork></figure>
2549<t>
2550   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2551   under the same organizational control and the hosts have already been
2552   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2553   have different received-protocol values.
2554</t>
2555</section>
2556
2557</section>
2558
2559<section title="IANA Considerations" anchor="IANA.considerations">
2560<section title="Message Header Registration" anchor="message.header.registration">
2561<t>
2562   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2563   with the permanent registrations below (see <xref target="RFC3864"/>):
2564</t>
2565<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2566<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2567   <ttcol>Header Field Name</ttcol>
2568   <ttcol>Protocol</ttcol>
2569   <ttcol>Status</ttcol>
2570   <ttcol>Reference</ttcol>
2571
2572   <c>Connection</c>
2573   <c>http</c>
2574   <c>standard</c>
2575   <c>
2576      <xref target="header.connection"/>
2577   </c>
2578   <c>Content-Length</c>
2579   <c>http</c>
2580   <c>standard</c>
2581   <c>
2582      <xref target="header.content-length"/>
2583   </c>
2584   <c>Date</c>
2585   <c>http</c>
2586   <c>standard</c>
2587   <c>
2588      <xref target="header.date"/>
2589   </c>
2590   <c>Host</c>
2591   <c>http</c>
2592   <c>standard</c>
2593   <c>
2594      <xref target="header.host"/>
2595   </c>
2596   <c>TE</c>
2597   <c>http</c>
2598   <c>standard</c>
2599   <c>
2600      <xref target="header.te"/>
2601   </c>
2602   <c>Trailer</c>
2603   <c>http</c>
2604   <c>standard</c>
2605   <c>
2606      <xref target="header.trailer"/>
2607   </c>
2608   <c>Transfer-Encoding</c>
2609   <c>http</c>
2610   <c>standard</c>
2611   <c>
2612      <xref target="header.transfer-encoding"/>
2613   </c>
2614   <c>Upgrade</c>
2615   <c>http</c>
2616   <c>standard</c>
2617   <c>
2618      <xref target="header.upgrade"/>
2619   </c>
2620   <c>Via</c>
2621   <c>http</c>
2622   <c>standard</c>
2623   <c>
2624      <xref target="header.via"/>
2625   </c>
2626</texttable>
2627<!--(END)-->
2628<t>
2629   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2630</t>
2631</section>
2632
2633<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2634<t>
2635   The entry for the "http" URI Scheme in the registry located at
2636   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2637   should be updated to point to <xref target="http.uri"/> of this document
2638   (see <xref target="RFC4395"/>).
2639</t>
2640</section>
2641
2642<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2643<t>
2644   This document serves as the specification for the Internet media types
2645   "message/http" and "application/http". The following is to be registered with
2646   IANA (see <xref target="RFC4288"/>).
2647</t>
2648<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2649<iref item="Media Type" subitem="message/http" primary="true"/>
2650<iref item="message/http Media Type" primary="true"/>
2651<t>
2652   The message/http type can be used to enclose a single HTTP request or
2653   response message, provided that it obeys the MIME restrictions for all
2654   "message" types regarding line length and encodings.
2655</t>
2656<t>
2657  <list style="hanging" x:indent="12em">
2658    <t hangText="Type name:">
2659      message
2660    </t>
2661    <t hangText="Subtype name:">
2662      http
2663    </t>
2664    <t hangText="Required parameters:">
2665      none
2666    </t>
2667    <t hangText="Optional parameters:">
2668      version, msgtype
2669      <list style="hanging">
2670        <t hangText="version:">
2671          The HTTP-Version number of the enclosed message
2672          (e.g., "1.1"). If not present, the version can be
2673          determined from the first line of the body.
2674        </t>
2675        <t hangText="msgtype:">
2676          The message type -- "request" or "response". If not
2677          present, the type can be determined from the first
2678          line of the body.
2679        </t>
2680      </list>
2681    </t>
2682    <t hangText="Encoding considerations:">
2683      only "7bit", "8bit", or "binary" are permitted
2684    </t>
2685    <t hangText="Security considerations:">
2686      none
2687    </t>
2688    <t hangText="Interoperability considerations:">
2689      none
2690    </t>
2691    <t hangText="Published specification:">
2692      This specification (see <xref target="internet.media.type.message.http"/>).
2693    </t>
2694    <t hangText="Applications that use this media type:">
2695    </t>
2696    <t hangText="Additional information:">
2697      <list style="hanging">
2698        <t hangText="Magic number(s):">none</t>
2699        <t hangText="File extension(s):">none</t>
2700        <t hangText="Macintosh file type code(s):">none</t>
2701      </list>
2702    </t>
2703    <t hangText="Person and email address to contact for further information:">
2704      See Authors Section.
2705    </t>
2706                <t hangText="Intended usage:">
2707                  COMMON
2708    </t>
2709                <t hangText="Restrictions on usage:">
2710                  none
2711    </t>
2712    <t hangText="Author/Change controller:">
2713      IESG
2714    </t>
2715  </list>
2716</t>
2717</section>
2718<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2719<iref item="Media Type" subitem="application/http" primary="true"/>
2720<iref item="application/http Media Type" primary="true"/>
2721<t>
2722   The application/http type can be used to enclose a pipeline of one or more
2723   HTTP request or response messages (not intermixed).
2724</t>
2725<t>
2726  <list style="hanging" x:indent="12em">
2727    <t hangText="Type name:">
2728      application
2729    </t>
2730    <t hangText="Subtype name:">
2731      http
2732    </t>
2733    <t hangText="Required parameters:">
2734      none
2735    </t>
2736    <t hangText="Optional parameters:">
2737      version, msgtype
2738      <list style="hanging">
2739        <t hangText="version:">
2740          The HTTP-Version number of the enclosed messages
2741          (e.g., "1.1"). If not present, the version can be
2742          determined from the first line of the body.
2743        </t>
2744        <t hangText="msgtype:">
2745          The message type -- "request" or "response". If not
2746          present, the type can be determined from the first
2747          line of the body.
2748        </t>
2749      </list>
2750    </t>
2751    <t hangText="Encoding considerations:">
2752      HTTP messages enclosed by this type
2753      are in "binary" format; use of an appropriate
2754      Content-Transfer-Encoding is required when
2755      transmitted via E-mail.
2756    </t>
2757    <t hangText="Security considerations:">
2758      none
2759    </t>
2760    <t hangText="Interoperability considerations:">
2761      none
2762    </t>
2763    <t hangText="Published specification:">
2764      This specification (see <xref target="internet.media.type.application.http"/>).
2765    </t>
2766    <t hangText="Applications that use this media type:">
2767    </t>
2768    <t hangText="Additional information:">
2769      <list style="hanging">
2770        <t hangText="Magic number(s):">none</t>
2771        <t hangText="File extension(s):">none</t>
2772        <t hangText="Macintosh file type code(s):">none</t>
2773      </list>
2774    </t>
2775    <t hangText="Person and email address to contact for further information:">
2776      See Authors Section.
2777    </t>
2778                <t hangText="Intended usage:">
2779                  COMMON
2780    </t>
2781                <t hangText="Restrictions on usage:">
2782                  none
2783    </t>
2784    <t hangText="Author/Change controller:">
2785      IESG
2786    </t>
2787  </list>
2788</t>
2789</section>
2790</section>
2791
2792</section>
2793
2794<section title="Security Considerations" anchor="security.considerations">
2795<t>
2796   This section is meant to inform application developers, information
2797   providers, and users of the security limitations in HTTP/1.1 as
2798   described by this document. The discussion does not include
2799   definitive solutions to the problems revealed, though it does make
2800   some suggestions for reducing security risks.
2801</t>
2802
2803<section title="Personal Information" anchor="personal.information">
2804<t>
2805   HTTP clients are often privy to large amounts of personal information
2806   (e.g. the user's name, location, mail address, passwords, encryption
2807   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2808   leakage of this information.
2809   We very strongly recommend that a convenient interface be provided
2810   for the user to control dissemination of such information, and that
2811   designers and implementors be particularly careful in this area.
2812   History shows that errors in this area often create serious security
2813   and/or privacy problems and generate highly adverse publicity for the
2814   implementor's company.
2815</t>
2816</section>
2817
2818<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2819<t>
2820   A server is in the position to save personal data about a user's
2821   requests which might identify their reading patterns or subjects of
2822   interest. This information is clearly confidential in nature and its
2823   handling can be constrained by law in certain countries. People using
2824   HTTP to provide data are responsible for ensuring that
2825   such material is not distributed without the permission of any
2826   individuals that are identifiable by the published results.
2827</t>
2828</section>
2829
2830<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2831<t>
2832   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2833   the documents returned by HTTP requests to be only those that were
2834   intended by the server administrators. If an HTTP server translates
2835   HTTP URIs directly into file system calls, the server &MUST; take
2836   special care not to serve files that were not intended to be
2837   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2838   other operating systems use ".." as a path component to indicate a
2839   directory level above the current one. On such a system, an HTTP
2840   server &MUST; disallow any such construct in the Request-URI if it
2841   would otherwise allow access to a resource outside those intended to
2842   be accessible via the HTTP server. Similarly, files intended for
2843   reference only internally to the server (such as access control
2844   files, configuration files, and script code) &MUST; be protected from
2845   inappropriate retrieval, since they might contain sensitive
2846   information. Experience has shown that minor bugs in such HTTP server
2847   implementations have turned into security risks.
2848</t>
2849</section>
2850
2851<section title="DNS Spoofing" anchor="dns.spoofing">
2852<t>
2853   Clients using HTTP rely heavily on the Domain Name Service, and are
2854   thus generally prone to security attacks based on the deliberate
2855   mis-association of IP addresses and DNS names. Clients need to be
2856   cautious in assuming the continuing validity of an IP number/DNS name
2857   association.
2858</t>
2859<t>
2860   In particular, HTTP clients &SHOULD; rely on their name resolver for
2861   confirmation of an IP number/DNS name association, rather than
2862   caching the result of previous host name lookups. Many platforms
2863   already can cache host name lookups locally when appropriate, and
2864   they &SHOULD; be configured to do so. It is proper for these lookups to
2865   be cached, however, only when the TTL (Time To Live) information
2866   reported by the name server makes it likely that the cached
2867   information will remain useful.
2868</t>
2869<t>
2870   If HTTP clients cache the results of host name lookups in order to
2871   achieve a performance improvement, they &MUST; observe the TTL
2872   information reported by DNS.
2873</t>
2874<t>
2875   If HTTP clients do not observe this rule, they could be spoofed when
2876   a previously-accessed server's IP address changes. As network
2877   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2878   possibility of this form of attack will grow. Observing this
2879   requirement thus reduces this potential security vulnerability.
2880</t>
2881<t>
2882   This requirement also improves the load-balancing behavior of clients
2883   for replicated servers using the same DNS name and reduces the
2884   likelihood of a user's experiencing failure in accessing sites which
2885   use that strategy.
2886</t>
2887</section>
2888
2889<section title="Proxies and Caching" anchor="attack.proxies">
2890<t>
2891   By their very nature, HTTP proxies are men-in-the-middle, and
2892   represent an opportunity for man-in-the-middle attacks. Compromise of
2893   the systems on which the proxies run can result in serious security
2894   and privacy problems. Proxies have access to security-related
2895   information, personal information about individual users and
2896   organizations, and proprietary information belonging to users and
2897   content providers. A compromised proxy, or a proxy implemented or
2898   configured without regard to security and privacy considerations,
2899   might be used in the commission of a wide range of potential attacks.
2900</t>
2901<t>
2902   Proxy operators should protect the systems on which proxies run as
2903   they would protect any system that contains or transports sensitive
2904   information. In particular, log information gathered at proxies often
2905   contains highly sensitive personal information, and/or information
2906   about organizations. Log information should be carefully guarded, and
2907   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
2908</t>
2909<t>
2910   Proxy implementors should consider the privacy and security
2911   implications of their design and coding decisions, and of the
2912   configuration options they provide to proxy operators (especially the
2913   default configuration).
2914</t>
2915<t>
2916   Users of a proxy need to be aware that they are no trustworthier than
2917   the people who run the proxy; HTTP itself cannot solve this problem.
2918</t>
2919<t>
2920   The judicious use of cryptography, when appropriate, may suffice to
2921   protect against a broad range of security and privacy attacks. Such
2922   cryptography is beyond the scope of the HTTP/1.1 specification.
2923</t>
2924</section>
2925
2926<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
2927<t>
2928   They exist. They are hard to defend against. Research continues.
2929   Beware.
2930</t>
2931</section>
2932</section>
2933
2934<section title="Acknowledgments" anchor="ack">
2935<t>
2936   HTTP has evolved considerably over the years. It has
2937   benefited from a large and active developer community--the many
2938   people who have participated on the www-talk mailing list--and it is
2939   that community which has been most responsible for the success of
2940   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
2941   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
2942   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
2943   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
2944   VanHeyningen deserve special recognition for their efforts in
2945   defining early aspects of the protocol.
2946</t>
2947<t>
2948   This document has benefited greatly from the comments of all those
2949   participating in the HTTP-WG. In addition to those already mentioned,
2950   the following individuals have contributed to this specification:
2951</t>
2952<t>
2953   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
2954   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
2955   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
2956   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
2957   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
2958   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
2959   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
2960   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
2961   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
2962   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
2963   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
2964   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
2965   Josh Cohen.
2966</t>
2967<t>
2968   Thanks to the "cave men" of Palo Alto. You know who you are.
2969</t>
2970<t>
2971   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
2972   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
2973   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
2974   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
2975   Larry Masinter for their help. And thanks go particularly to Jeff
2976   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
2977</t>
2978<t>
2979   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
2980   Frystyk implemented RFC 2068 early, and we wish to thank them for the
2981   discovery of many of the problems that this document attempts to
2982   rectify.
2983</t>
2984<t>
2985   This specification makes heavy use of the augmented BNF and generic
2986   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
2987   reuses many of the definitions provided by Nathaniel Borenstein and
2988   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
2989   specification will help reduce past confusion over the relationship
2990   between HTTP and Internet mail message formats.
2991</t>
2992</section>
2993
2994</middle>
2995<back>
2996
2997<references title="Normative References">
2998
2999<reference anchor="ISO-8859-1">
3000  <front>
3001    <title>
3002     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3003    </title>
3004    <author>
3005      <organization>International Organization for Standardization</organization>
3006    </author>
3007    <date year="1998"/>
3008  </front>
3009  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3010</reference>
3011
3012<reference anchor="Part2">
3013  <front>
3014    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3015    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3016      <organization abbrev="Day Software">Day Software</organization>
3017      <address><email>fielding@gbiv.com</email></address>
3018    </author>
3019    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3020      <organization>One Laptop per Child</organization>
3021      <address><email>jg@laptop.org</email></address>
3022    </author>
3023    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3024      <organization abbrev="HP">Hewlett-Packard Company</organization>
3025      <address><email>JeffMogul@acm.org</email></address>
3026    </author>
3027    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3028      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3029      <address><email>henrikn@microsoft.com</email></address>
3030    </author>
3031    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3032      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3033      <address><email>LMM@acm.org</email></address>
3034    </author>
3035    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3036      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3037      <address><email>paulle@microsoft.com</email></address>
3038    </author>
3039    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3040      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3041      <address><email>timbl@w3.org</email></address>
3042    </author>
3043    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3044      <organization abbrev="W3C">World Wide Web Consortium</organization>
3045      <address><email>ylafon@w3.org</email></address>
3046    </author>
3047    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3048      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3049      <address><email>julian.reschke@greenbytes.de</email></address>
3050    </author>
3051    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3052  </front>
3053  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3054  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3055</reference>
3056
3057<reference anchor="Part3">
3058  <front>
3059    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3060    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3061      <organization abbrev="Day Software">Day Software</organization>
3062      <address><email>fielding@gbiv.com</email></address>
3063    </author>
3064    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3065      <organization>One Laptop per Child</organization>
3066      <address><email>jg@laptop.org</email></address>
3067    </author>
3068    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3069      <organization abbrev="HP">Hewlett-Packard Company</organization>
3070      <address><email>JeffMogul@acm.org</email></address>
3071    </author>
3072    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3073      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3074      <address><email>henrikn@microsoft.com</email></address>
3075    </author>
3076    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3077      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3078      <address><email>LMM@acm.org</email></address>
3079    </author>
3080    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3081      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3082      <address><email>paulle@microsoft.com</email></address>
3083    </author>
3084    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3085      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3086      <address><email>timbl@w3.org</email></address>
3087    </author>
3088    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3089      <organization abbrev="W3C">World Wide Web Consortium</organization>
3090      <address><email>ylafon@w3.org</email></address>
3091    </author>
3092    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3093      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3094      <address><email>julian.reschke@greenbytes.de</email></address>
3095    </author>
3096    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3097  </front>
3098  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3099  <x:source href="p3-payload.xml" basename="p3-payload"/>
3100</reference>
3101
3102<reference anchor="Part5">
3103  <front>
3104    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3105    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3106      <organization abbrev="Day Software">Day Software</organization>
3107      <address><email>fielding@gbiv.com</email></address>
3108    </author>
3109    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3110      <organization>One Laptop per Child</organization>
3111      <address><email>jg@laptop.org</email></address>
3112    </author>
3113    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3114      <organization abbrev="HP">Hewlett-Packard Company</organization>
3115      <address><email>JeffMogul@acm.org</email></address>
3116    </author>
3117    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3118      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3119      <address><email>henrikn@microsoft.com</email></address>
3120    </author>
3121    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3122      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3123      <address><email>LMM@acm.org</email></address>
3124    </author>
3125    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3126      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3127      <address><email>paulle@microsoft.com</email></address>
3128    </author>
3129    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3130      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3131      <address><email>timbl@w3.org</email></address>
3132    </author>
3133    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3134      <organization abbrev="W3C">World Wide Web Consortium</organization>
3135      <address><email>ylafon@w3.org</email></address>
3136    </author>
3137    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3138      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3139      <address><email>julian.reschke@greenbytes.de</email></address>
3140    </author>
3141    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3142  </front>
3143  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3144  <x:source href="p5-range.xml" basename="p5-range"/>
3145</reference>
3146
3147<reference anchor="Part6">
3148  <front>
3149    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3150    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3151      <organization abbrev="Day Software">Day Software</organization>
3152      <address><email>fielding@gbiv.com</email></address>
3153    </author>
3154    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3155      <organization>One Laptop per Child</organization>
3156      <address><email>jg@laptop.org</email></address>
3157    </author>
3158    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3159      <organization abbrev="HP">Hewlett-Packard Company</organization>
3160      <address><email>JeffMogul@acm.org</email></address>
3161    </author>
3162    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3163      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3164      <address><email>henrikn@microsoft.com</email></address>
3165    </author>
3166    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3167      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3168      <address><email>LMM@acm.org</email></address>
3169    </author>
3170    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3171      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3172      <address><email>paulle@microsoft.com</email></address>
3173    </author>
3174    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3175      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3176      <address><email>timbl@w3.org</email></address>
3177    </author>
3178    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3179      <organization abbrev="W3C">World Wide Web Consortium</organization>
3180      <address><email>ylafon@w3.org</email></address>
3181    </author>
3182    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3183      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3184      <address><email>julian.reschke@greenbytes.de</email></address>
3185    </author>
3186    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3187  </front>
3188  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3189  <x:source href="p6-cache.xml" basename="p6-cache"/>
3190</reference>
3191
3192<reference anchor="RFC5234">
3193  <front>
3194    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3195    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3196      <organization>Brandenburg InternetWorking</organization>
3197      <address>
3198      <postal>
3199      <street>675 Spruce Dr.</street>
3200      <city>Sunnyvale</city>
3201      <region>CA</region>
3202      <code>94086</code>
3203      <country>US</country></postal>
3204      <phone>+1.408.246.8253</phone>
3205      <email>dcrocker@bbiw.net</email></address> 
3206    </author>
3207    <author initials="P." surname="Overell" fullname="Paul Overell">
3208      <organization>THUS plc.</organization>
3209      <address>
3210      <postal>
3211      <street>1/2 Berkeley Square</street>
3212      <street>99 Berkely Street</street>
3213      <city>Glasgow</city>
3214      <code>G3 7HR</code>
3215      <country>UK</country></postal>
3216      <email>paul.overell@thus.net</email></address>
3217    </author>
3218    <date month="January" year="2008"/>
3219  </front>
3220  <seriesInfo name="STD" value="68"/>
3221  <seriesInfo name="RFC" value="5234"/>
3222</reference>
3223
3224<reference anchor="RFC2045">
3225  <front>
3226    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3227    <author initials="N." surname="Freed" fullname="Ned Freed">
3228      <organization>Innosoft International, Inc.</organization>
3229      <address><email>ned@innosoft.com</email></address>
3230    </author>
3231    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3232      <organization>First Virtual Holdings</organization>
3233      <address><email>nsb@nsb.fv.com</email></address>
3234    </author>
3235    <date month="November" year="1996"/>
3236  </front>
3237  <seriesInfo name="RFC" value="2045"/>
3238</reference>
3239
3240<reference anchor="RFC2047">
3241  <front>
3242    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3243    <author initials="K." surname="Moore" fullname="Keith Moore">
3244      <organization>University of Tennessee</organization>
3245      <address><email>moore@cs.utk.edu</email></address>
3246    </author>
3247    <date month="November" year="1996"/>
3248  </front>
3249  <seriesInfo name="RFC" value="2047"/>
3250</reference>
3251
3252<reference anchor="RFC2119">
3253  <front>
3254    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3255    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3256      <organization>Harvard University</organization>
3257      <address><email>sob@harvard.edu</email></address>
3258    </author>
3259    <date month="March" year="1997"/>
3260  </front>
3261  <seriesInfo name="BCP" value="14"/>
3262  <seriesInfo name="RFC" value="2119"/>
3263</reference>
3264
3265<reference anchor="RFC3986">
3266 <front>
3267  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3268  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3269    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3270    <address>
3271       <email>timbl@w3.org</email>
3272       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3273    </address>
3274  </author>
3275  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3276    <organization abbrev="Day Software">Day Software</organization>
3277    <address>
3278      <email>fielding@gbiv.com</email>
3279      <uri>http://roy.gbiv.com/</uri>
3280    </address>
3281  </author>
3282  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3283    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3284    <address>
3285      <email>LMM@acm.org</email>
3286      <uri>http://larry.masinter.net/</uri>
3287    </address>
3288  </author>
3289  <date month='January' year='2005'></date>
3290 </front>
3291 <seriesInfo name="RFC" value="3986"/>
3292 <seriesInfo name="STD" value="66"/>
3293</reference>
3294
3295<reference anchor="USASCII">
3296  <front>
3297    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3298    <author>
3299      <organization>American National Standards Institute</organization>
3300    </author>
3301    <date year="1986"/>
3302  </front>
3303  <seriesInfo name="ANSI" value="X3.4"/>
3304</reference>
3305
3306</references>
3307
3308<references title="Informative References">
3309
3310<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3311  <front>
3312    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3313    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3314      <organization/>
3315    </author>
3316    <author initials="J." surname="Gettys" fullname="J. Gettys">
3317      <organization/>
3318    </author>
3319    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3320      <organization/>
3321    </author>
3322    <author initials="H." surname="Lie" fullname="H. Lie">
3323      <organization/>
3324    </author>
3325    <author initials="C." surname="Lilley" fullname="C. Lilley">
3326      <organization/>
3327    </author>
3328    <date year="1997" month="September"/>
3329  </front>
3330  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3331</reference>
3332
3333<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3334  <front>
3335    <title>Improving HTTP Latency</title>
3336    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3337      <organization/>
3338    </author>
3339    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3340      <organization/>
3341    </author>
3342    <date year="1995" month="December"/>
3343  </front>
3344  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3345</reference>
3346
3347<reference anchor="RFC822">
3348  <front>
3349    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3350    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3351      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3352      <address><email>DCrocker@UDel-Relay</email></address>
3353    </author>
3354    <date month="August" day="13" year="1982"/>
3355  </front>
3356  <seriesInfo name="STD" value="11"/>
3357  <seriesInfo name="RFC" value="822"/>
3358</reference>
3359
3360<reference anchor="RFC959">
3361  <front>
3362    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3363    <author initials="J." surname="Postel" fullname="J. Postel">
3364      <organization>Information Sciences Institute (ISI)</organization>
3365    </author>
3366    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3367      <organization/>
3368    </author>
3369    <date month="October" year="1985"/>
3370  </front>
3371  <seriesInfo name="STD" value="9"/>
3372  <seriesInfo name="RFC" value="959"/>
3373</reference>
3374
3375<reference anchor="RFC1123">
3376  <front>
3377    <title>Requirements for Internet Hosts - Application and Support</title>
3378    <author initials="R." surname="Braden" fullname="Robert Braden">
3379      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3380      <address><email>Braden@ISI.EDU</email></address>
3381    </author>
3382    <date month="October" year="1989"/>
3383  </front>
3384  <seriesInfo name="STD" value="3"/>
3385  <seriesInfo name="RFC" value="1123"/>
3386</reference>
3387
3388<reference anchor="RFC1305">
3389  <front>
3390    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3391    <author initials="D." surname="Mills" fullname="David L. Mills">
3392      <organization>University of Delaware, Electrical Engineering Department</organization>
3393      <address><email>mills@udel.edu</email></address>
3394    </author>
3395    <date month="March" year="1992"/>
3396  </front>
3397  <seriesInfo name="RFC" value="1305"/>
3398</reference>
3399
3400<reference anchor="RFC1436">
3401  <front>
3402    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3403    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3404      <organization>University of Minnesota, Computer and Information Services</organization>
3405      <address><email>fxa@boombox.micro.umn.edu</email></address>
3406    </author>
3407    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3408      <organization>University of Minnesota, Computer and Information Services</organization>
3409      <address><email>mpm@boombox.micro.umn.edu</email></address>
3410    </author>
3411    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3412      <organization>University of Minnesota, Computer and Information Services</organization>
3413      <address><email>lindner@boombox.micro.umn.edu</email></address>
3414    </author>
3415    <author initials="D." surname="Johnson" fullname="David Johnson">
3416      <organization>University of Minnesota, Computer and Information Services</organization>
3417      <address><email>dmj@boombox.micro.umn.edu</email></address>
3418    </author>
3419    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3420      <organization>University of Minnesota, Computer and Information Services</organization>
3421      <address><email>daniel@boombox.micro.umn.edu</email></address>
3422    </author>
3423    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3424      <organization>University of Minnesota, Computer and Information Services</organization>
3425      <address><email>alberti@boombox.micro.umn.edu</email></address>
3426    </author>
3427    <date month="March" year="1993"/>
3428  </front>
3429  <seriesInfo name="RFC" value="1436"/>
3430</reference>
3431
3432<reference anchor="RFC1900">
3433  <front>
3434    <title>Renumbering Needs Work</title>
3435    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3436      <organization>CERN, Computing and Networks Division</organization>
3437      <address><email>brian@dxcoms.cern.ch</email></address>
3438    </author>
3439    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3440      <organization>cisco Systems</organization>
3441      <address><email>yakov@cisco.com</email></address>
3442    </author>
3443    <date month="February" year="1996"/>
3444  </front>
3445  <seriesInfo name="RFC" value="1900"/>
3446</reference>
3447
3448<reference anchor="RFC1945">
3449  <front>
3450    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3451    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3452      <organization>MIT, Laboratory for Computer Science</organization>
3453      <address><email>timbl@w3.org</email></address>
3454    </author>
3455    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3456      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3457      <address><email>fielding@ics.uci.edu</email></address>
3458    </author>
3459    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3460      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3461      <address><email>frystyk@w3.org</email></address>
3462    </author>
3463    <date month="May" year="1996"/>
3464  </front>
3465  <seriesInfo name="RFC" value="1945"/>
3466</reference>
3467
3468<reference anchor="RFC2068">
3469  <front>
3470    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3471    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3472      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3473      <address><email>fielding@ics.uci.edu</email></address>
3474    </author>
3475    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3476      <organization>MIT Laboratory for Computer Science</organization>
3477      <address><email>jg@w3.org</email></address>
3478    </author>
3479    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3480      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3481      <address><email>mogul@wrl.dec.com</email></address>
3482    </author>
3483    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3484      <organization>MIT Laboratory for Computer Science</organization>
3485      <address><email>frystyk@w3.org</email></address>
3486    </author>
3487    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3488      <organization>MIT Laboratory for Computer Science</organization>
3489      <address><email>timbl@w3.org</email></address>
3490    </author>
3491    <date month="January" year="1997"/>
3492  </front>
3493  <seriesInfo name="RFC" value="2068"/>
3494</reference>
3495
3496<reference anchor='RFC2109'>
3497  <front>
3498    <title>HTTP State Management Mechanism</title>
3499    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3500      <organization>Bell Laboratories, Lucent Technologies</organization>
3501      <address><email>dmk@bell-labs.com</email></address>
3502    </author>
3503    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3504      <organization>Netscape Communications Corp.</organization>
3505      <address><email>montulli@netscape.com</email></address>
3506    </author>
3507    <date year='1997' month='February' />
3508  </front>
3509  <seriesInfo name='RFC' value='2109' />
3510</reference>
3511
3512<reference anchor="RFC2145">
3513  <front>
3514    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3515    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3516      <organization>Western Research Laboratory</organization>
3517      <address><email>mogul@wrl.dec.com</email></address>
3518    </author>
3519    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3520      <organization>Department of Information and Computer Science</organization>
3521      <address><email>fielding@ics.uci.edu</email></address>
3522    </author>
3523    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3524      <organization>MIT Laboratory for Computer Science</organization>
3525      <address><email>jg@w3.org</email></address>
3526    </author>
3527    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3528      <organization>W3 Consortium</organization>
3529      <address><email>frystyk@w3.org</email></address>
3530    </author>
3531    <date month="May" year="1997"/>
3532  </front>
3533  <seriesInfo name="RFC" value="2145"/>
3534</reference>
3535
3536<reference anchor="RFC2616">
3537  <front>
3538    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3539    <author initials="R." surname="Fielding" fullname="R. Fielding">
3540      <organization>University of California, Irvine</organization>
3541      <address><email>fielding@ics.uci.edu</email></address>
3542    </author>
3543    <author initials="J." surname="Gettys" fullname="J. Gettys">
3544      <organization>W3C</organization>
3545      <address><email>jg@w3.org</email></address>
3546    </author>
3547    <author initials="J." surname="Mogul" fullname="J. Mogul">
3548      <organization>Compaq Computer Corporation</organization>
3549      <address><email>mogul@wrl.dec.com</email></address>
3550    </author>
3551    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3552      <organization>MIT Laboratory for Computer Science</organization>
3553      <address><email>frystyk@w3.org</email></address>
3554    </author>
3555    <author initials="L." surname="Masinter" fullname="L. Masinter">
3556      <organization>Xerox Corporation</organization>
3557      <address><email>masinter@parc.xerox.com</email></address>
3558    </author>
3559    <author initials="P." surname="Leach" fullname="P. Leach">
3560      <organization>Microsoft Corporation</organization>
3561      <address><email>paulle@microsoft.com</email></address>
3562    </author>
3563    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3564      <organization>W3C</organization>
3565      <address><email>timbl@w3.org</email></address>
3566    </author>
3567    <date month="June" year="1999"/>
3568  </front>
3569  <seriesInfo name="RFC" value="2616"/>
3570</reference>
3571
3572<reference anchor='RFC2818'>
3573  <front>
3574    <title>HTTP Over TLS</title>
3575    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3576      <organization>RTFM, Inc.</organization>
3577      <address><email>ekr@rtfm.com</email></address>
3578    </author>
3579    <date year='2000' month='May' />
3580  </front>
3581  <seriesInfo name='RFC' value='2818' />
3582</reference>
3583
3584<reference anchor='RFC2965'>
3585  <front>
3586    <title>HTTP State Management Mechanism</title>
3587    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3588      <organization>Bell Laboratories, Lucent Technologies</organization>
3589      <address><email>dmk@bell-labs.com</email></address>
3590    </author>
3591    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3592      <organization>Epinions.com, Inc.</organization>
3593      <address><email>lou@montulli.org</email></address>
3594    </author>
3595    <date year='2000' month='October' />
3596  </front>
3597  <seriesInfo name='RFC' value='2965' />
3598</reference>
3599
3600<reference anchor='RFC3864'>
3601  <front>
3602    <title>Registration Procedures for Message Header Fields</title>
3603    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3604      <organization>Nine by Nine</organization>
3605      <address><email>GK-IETF@ninebynine.org</email></address>
3606    </author>
3607    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3608      <organization>BEA Systems</organization>
3609      <address><email>mnot@pobox.com</email></address>
3610    </author>
3611    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3612      <organization>HP Labs</organization>
3613      <address><email>JeffMogul@acm.org</email></address>
3614    </author>
3615    <date year='2004' month='September' />
3616  </front>
3617  <seriesInfo name='BCP' value='90' />
3618  <seriesInfo name='RFC' value='3864' />
3619</reference>
3620
3621<reference anchor='RFC3977'>
3622  <front>
3623    <title>Network News Transfer Protocol (NNTP)</title>
3624    <author initials='C.' surname='Feather' fullname='C. Feather'>
3625      <organization>THUS plc</organization>
3626      <address><email>clive@demon.net</email></address>
3627    </author>
3628    <date year='2006' month='October' />
3629  </front>
3630  <seriesInfo name="RFC" value="3977"/>
3631</reference>
3632
3633<reference anchor="RFC4288">
3634  <front>
3635    <title>Media Type Specifications and Registration Procedures</title>
3636    <author initials="N." surname="Freed" fullname="N. Freed">
3637      <organization>Sun Microsystems</organization>
3638      <address>
3639        <email>ned.freed@mrochek.com</email>
3640      </address>
3641    </author>
3642    <author initials="J." surname="Klensin" fullname="J. Klensin">
3643      <organization/>
3644      <address>
3645        <email>klensin+ietf@jck.com</email>
3646      </address>
3647    </author>
3648    <date year="2005" month="December"/>
3649  </front>
3650  <seriesInfo name="BCP" value="13"/>
3651  <seriesInfo name="RFC" value="4288"/>
3652</reference>
3653
3654<reference anchor='RFC4395'>
3655  <front>
3656    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3657    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3658      <organization>AT&amp;T Laboratories</organization>
3659      <address>
3660        <email>tony+urireg@maillennium.att.com</email>
3661      </address>
3662    </author>
3663    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3664      <organization>Qualcomm, Inc.</organization>
3665      <address>
3666        <email>hardie@qualcomm.com</email>
3667      </address>
3668    </author>
3669    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3670      <organization>Adobe Systems</organization>
3671      <address>
3672        <email>LMM@acm.org</email>
3673      </address>
3674    </author>
3675    <date year='2006' month='February' />
3676  </front>
3677  <seriesInfo name='BCP' value='115' />
3678  <seriesInfo name='RFC' value='4395' />
3679</reference>
3680
3681<reference anchor="RFC5322">
3682  <front>
3683    <title>Internet Message Format</title>
3684    <author initials="P." surname="Resnick" fullname="P. Resnick">
3685      <organization>Qualcomm Incorporated</organization>
3686    </author>
3687    <date year="2008" month="October"/>
3688  </front>
3689  <seriesInfo name="RFC" value="5322"/>
3690</reference>
3691
3692<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3693  <front>
3694    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3695    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3696      <organization/>
3697    </author>
3698    <date year="2001" month="November"/>
3699  </front>
3700  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3701</reference>
3702
3703<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3704  <front>
3705  <title>Analysis of HTTP Performance Problems</title>
3706  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3707    <organization/>
3708  </author>
3709  <date/>
3710  </front>
3711</reference>
3712
3713<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3714  <front>
3715  <title>Analysis of HTTP Performance</title>
3716  <author initials="J." surname="Touch" fullname="Joe Touch">
3717    <organization>USC/Information Sciences Institute</organization>
3718    <address><email>touch@isi.edu</email></address>
3719  </author>
3720  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3721    <organization>USC/Information Sciences Institute</organization>
3722    <address><email>johnh@isi.edu</email></address>
3723  </author>
3724  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3725    <organization>USC/Information Sciences Institute</organization>
3726    <address><email>katia@isi.edu</email></address>
3727  </author>
3728  <date year="1998" month="Aug"/>
3729  </front>
3730  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3731  <annotation>(original report dated Aug. 1996)</annotation>
3732</reference>
3733
3734<reference anchor="WAIS">
3735  <front>
3736    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3737    <author initials="F." surname="Davis" fullname="F. Davis">
3738      <organization>Thinking Machines Corporation</organization>
3739    </author>
3740    <author initials="B." surname="Kahle" fullname="B. Kahle">
3741      <organization>Thinking Machines Corporation</organization>
3742    </author>
3743    <author initials="H." surname="Morris" fullname="H. Morris">
3744      <organization>Thinking Machines Corporation</organization>
3745    </author>
3746    <author initials="J." surname="Salem" fullname="J. Salem">
3747      <organization>Thinking Machines Corporation</organization>
3748    </author>
3749    <author initials="T." surname="Shen" fullname="T. Shen">
3750      <organization>Thinking Machines Corporation</organization>
3751    </author>
3752    <author initials="R." surname="Wang" fullname="R. Wang">
3753      <organization>Thinking Machines Corporation</organization>
3754    </author>
3755    <author initials="J." surname="Sui" fullname="J. Sui">
3756      <organization>Thinking Machines Corporation</organization>
3757    </author>
3758    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3759      <organization>Thinking Machines Corporation</organization>
3760    </author>
3761    <date month="April" year="1990"/>
3762  </front>
3763  <seriesInfo name="Thinking Machines Corporation" value=""/>
3764</reference>
3765
3766</references>
3767
3768
3769<section title="Tolerant Applications" anchor="tolerant.applications">
3770<t>
3771   Although this document specifies the requirements for the generation
3772   of HTTP/1.1 messages, not all applications will be correct in their
3773   implementation. We therefore recommend that operational applications
3774   be tolerant of deviations whenever those deviations can be
3775   interpreted unambiguously.
3776</t>
3777<t>
3778   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3779   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3780   accept any amount of SP or HTAB characters between fields, even though
3781   only a single SP is required.
3782</t>
3783<t>
3784   The line terminator for message-header fields is the sequence CRLF.
3785   However, we recommend that applications, when parsing such headers,
3786   recognize a single LF as a line terminator and ignore the leading CR.
3787</t>
3788<t>
3789   The character set of an entity-body &SHOULD; be labeled as the lowest
3790   common denominator of the character codes used within that body, with
3791   the exception that not labeling the entity is preferred over labeling
3792   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3793</t>
3794<t>
3795   Additional rules for requirements on parsing and encoding of dates
3796   and other potential problems with date encodings include:
3797</t>
3798<t>
3799  <list style="symbols">
3800     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3801        which appears to be more than 50 years in the future is in fact
3802        in the past (this helps solve the "year 2000" problem).</t>
3803
3804     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3805        Expires date as earlier than the proper value, but &MUST-NOT;
3806        internally represent a parsed Expires date as later than the
3807        proper value.</t>
3808
3809     <t>All expiration-related calculations &MUST; be done in GMT. The
3810        local time zone &MUST-NOT; influence the calculation or comparison
3811        of an age or expiration time.</t>
3812
3813     <t>If an HTTP header incorrectly carries a date value with a time
3814        zone other than GMT, it &MUST; be converted into GMT using the
3815        most conservative possible conversion.</t>
3816  </list>
3817</t>
3818</section>
3819
3820<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
3821<t>
3822   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
3823   simplify the process of date comparison. Proxies and gateways from
3824   other protocols &SHOULD; ensure that any Date header field present in a
3825   message conforms to one of the HTTP/1.1 formats and rewrite the date
3826   if necessary.
3827</t>
3828</section>
3829
3830<section title="Compatibility with Previous Versions" anchor="compatibility">
3831<t>
3832   HTTP has been in use by the World-Wide Web global information initiative
3833   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3834   was a simple protocol for hypertext data transfer across the Internet
3835   with only a single method and no metadata.
3836   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3837   methods and MIME-like messaging that could include metadata about the data
3838   transferred and modifiers on the request/response semantics. However,
3839   HTTP/1.0 did not sufficiently take into consideration the effects of
3840   hierarchical proxies, caching, the need for persistent connections, or
3841   name-based virtual hosts. The proliferation of incompletely-implemented
3842   applications calling themselves "HTTP/1.0" further necessitated a
3843   protocol version change in order for two communicating applications
3844   to determine each other's true capabilities.
3845</t>
3846<t>
3847   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3848   requirements that enable reliable implementations, adding only
3849   those new features that will either be safely ignored by an HTTP/1.0
3850   recipient or only sent when communicating with a party advertising
3851   compliance with HTTP/1.1.
3852</t>
3853<t>
3854   It is beyond the scope of a protocol specification to mandate
3855   compliance with previous versions. HTTP/1.1 was deliberately
3856   designed, however, to make supporting previous versions easy. It is
3857   worth noting that, at the time of composing this specification
3858   (1996), we would expect commercial HTTP/1.1 servers to:
3859  <list style="symbols">
3860     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3861        1.1 requests;</t>
3862
3863     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3864        1.1;</t>
3865
3866     <t>respond appropriately with a message in the same major version
3867        used by the client.</t>
3868  </list>
3869</t>
3870<t>
3871   And we would expect HTTP/1.1 clients to:
3872  <list style="symbols">
3873     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3874        responses;</t>
3875
3876     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3877        1.1.</t>
3878  </list>
3879</t>
3880<t>
3881   For most implementations of HTTP/1.0, each connection is established
3882   by the client prior to the request and closed by the server after
3883   sending the response. Some implementations implement the Keep-Alive
3884   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3885</t>
3886
3887<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3888<t>
3889   This section summarizes major differences between versions HTTP/1.0
3890   and HTTP/1.1.
3891</t>
3892
3893<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">
3894<t>
3895   The requirements that clients and servers support the Host request-header,
3896   report an error if the Host request-header (<xref target="header.host"/>) is
3897   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
3898   are among the most important changes defined by this
3899   specification.
3900</t>
3901<t>
3902   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3903   addresses and servers; there was no other established mechanism for
3904   distinguishing the intended server of a request than the IP address
3905   to which that request was directed. The changes outlined above will
3906   allow the Internet, once older HTTP clients are no longer common, to
3907   support multiple Web sites from a single IP address, greatly
3908   simplifying large operational Web servers, where allocation of many
3909   IP addresses to a single host has created serious problems. The
3910   Internet will also be able to recover the IP addresses that have been
3911   allocated for the sole purpose of allowing special-purpose domain
3912   names to be used in root-level HTTP URLs. Given the rate of growth of
3913   the Web, and the number of servers already deployed, it is extremely
3914   important that all implementations of HTTP (including updates to
3915   existing HTTP/1.0 applications) correctly implement these
3916   requirements:
3917  <list style="symbols">
3918     <t>Both clients and servers &MUST; support the Host request-header.</t>
3919
3920     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3921
3922     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3923        request does not include a Host request-header.</t>
3924
3925     <t>Servers &MUST; accept absolute URIs.</t>
3926  </list>
3927</t>
3928</section>
3929</section>
3930
3931<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3932<t>
3933   Some clients and servers might wish to be compatible with some
3934   previous implementations of persistent connections in HTTP/1.0
3935   clients and servers. Persistent connections in HTTP/1.0 are
3936   explicitly negotiated as they are not the default behavior. HTTP/1.0
3937   experimental implementations of persistent connections are faulty,
3938   and the new facilities in HTTP/1.1 are designed to rectify these
3939   problems. The problem was that some existing 1.0 clients may be
3940   sending Keep-Alive to a proxy server that doesn't understand
3941   Connection, which would then erroneously forward it to the next
3942   inbound server, which would establish the Keep-Alive connection and
3943   result in a hung HTTP/1.0 proxy waiting for the close on the
3944   response. The result is that HTTP/1.0 clients must be prevented from
3945   using Keep-Alive when talking to proxies.
3946</t>
3947<t>
3948   However, talking to proxies is the most important use of persistent
3949   connections, so that prohibition is clearly unacceptable. Therefore,
3950   we need some other mechanism for indicating a persistent connection
3951   is desired, which is safe to use even when talking to an old proxy
3952   that ignores Connection. Persistent connections are the default for
3953   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3954   declaring non-persistence. See <xref target="header.connection"/>.
3955</t>
3956<t>
3957   The original HTTP/1.0 form of persistent connections (the Connection:
3958   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3959</t>
3960</section>
3961
3962<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3963<t>
3964   This specification has been carefully audited to correct and
3965   disambiguate key word usage; RFC 2068 had many problems in respect to
3966   the conventions laid out in <xref target="RFC2119"/>.
3967</t>
3968<t>
3969   Transfer-coding and message lengths all interact in ways that
3970   required fixing exactly when chunked encoding is used (to allow for
3971   transfer encoding that may not be self delimiting); it was important
3972   to straighten out exactly how message lengths are computed. (Sections
3973   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
3974   <xref target="header.content-length" format="counter"/>,
3975   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
3976</t>
3977<t>
3978   The use and interpretation of HTTP version numbers has been clarified
3979   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
3980   version they support to deal with problems discovered in HTTP/1.0
3981   implementations (<xref target="http.version"/>)
3982</t>
3983<t>
3984   Transfer-coding had significant problems, particularly with
3985   interactions with chunked encoding. The solution is that transfer-codings
3986   become as full fledged as content-codings. This involves
3987   adding an IANA registry for transfer-codings (separate from content
3988   codings), a new header field (TE) and enabling trailer headers in the
3989   future. Transfer encoding is a major performance benefit, so it was
3990   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
3991   interoperability problem that could have occurred due to interactions
3992   between authentication trailers, chunked encoding and HTTP/1.0
3993   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
3994   and <xref target="header.te" format="counter"/>)
3995</t>
3996</section>
3997
3998<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3999<t>
4000  The CHAR rule does not allow the NUL character anymore (this affects
4001  the comment and quoted-string rules).  Furthermore, the quoted-pair
4002  rule does not allow escaping NUL, CR or LF anymore.
4003  (<xref target="basic.rules"/>)
4004</t>
4005<t>
4006  Clarify that HTTP-Version is case sensitive.
4007  (<xref target="http.version"/>)
4008</t>
4009<t>
4010  Remove reference to non-existant identity transfer-coding value tokens.
4011  (Sections <xref format="counter" target="transfer.codings"/> and
4012  <xref format="counter" target="message.length"/>)
4013</t>
4014<t>
4015  Clarification that the chunk length does not include
4016  the count of the octets in the chunk header and trailer.
4017  (<xref target="chunked.transfer.encoding"/>)
4018</t>
4019<t>
4020  Update use of abs_path production from RFC1808 to the path-absolute + query
4021  components of RFC3986.
4022  (<xref target="request-uri"/>)
4023</t>
4024<t>
4025  Clarify exactly when close connection options must be sent.
4026  (<xref target="header.connection"/>)
4027</t>
4028</section>
4029</section>
4030
4031<section title="Terminology" anchor="terminology">
4032<t>
4033   This specification uses a number of terms to refer to the roles
4034   played by participants in, and objects of, the HTTP communication.
4035</t>
4036<t>
4037  <iref item="connection"/>
4038  <x:dfn>connection</x:dfn>
4039  <list>
4040    <t>
4041      A transport layer virtual circuit established between two programs
4042      for the purpose of communication.
4043    </t>
4044  </list>
4045</t>
4046<t>
4047  <iref item="message"/>
4048  <x:dfn>message</x:dfn>
4049  <list>
4050    <t>
4051      The basic unit of HTTP communication, consisting of a structured
4052      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4053      transmitted via the connection.
4054    </t>
4055  </list>
4056</t>
4057<t>
4058  <iref item="request"/>
4059  <x:dfn>request</x:dfn>
4060  <list>
4061    <t>
4062      An HTTP request message, as defined in <xref target="request"/>.
4063    </t>
4064  </list>
4065</t>
4066<t>
4067  <iref item="response"/>
4068  <x:dfn>response</x:dfn>
4069  <list>
4070    <t>
4071      An HTTP response message, as defined in <xref target="response"/>.
4072    </t>
4073  </list>
4074</t>
4075<t>
4076  <iref item="resource"/>
4077  <x:dfn>resource</x:dfn>
4078  <list>
4079    <t>
4080      A network data object or service that can be identified by a URI,
4081      as defined in <xref target="uri"/>. Resources may be available in multiple
4082      representations (e.g. multiple languages, data formats, size, and
4083      resolutions) or vary in other ways.
4084    </t>
4085  </list>
4086</t>
4087<t>
4088  <iref item="entity"/>
4089  <x:dfn>entity</x:dfn>
4090  <list>
4091    <t>
4092      The information transferred as the payload of a request or
4093      response. An entity consists of metainformation in the form of
4094      entity-header fields and content in the form of an entity-body, as
4095      described in &entity;.
4096    </t>
4097  </list>
4098</t>
4099<t>
4100  <iref item="representation"/>
4101  <x:dfn>representation</x:dfn>
4102  <list>
4103    <t>
4104      An entity included with a response that is subject to content
4105      negotiation, as described in &content.negotiation;. There may exist multiple
4106      representations associated with a particular response status.
4107    </t>
4108  </list>
4109</t>
4110<t>
4111  <iref item="content negotiation"/>
4112  <x:dfn>content negotiation</x:dfn>
4113  <list>
4114    <t>
4115      The mechanism for selecting the appropriate representation when
4116      servicing a request, as described in &content.negotiation;. The
4117      representation of entities in any response can be negotiated
4118      (including error responses).
4119    </t>
4120  </list>
4121</t>
4122<t>
4123  <iref item="variant"/>
4124  <x:dfn>variant</x:dfn>
4125  <list>
4126    <t>
4127      A resource may have one, or more than one, representation(s)
4128      associated with it at any given instant. Each of these
4129      representations is termed a `variant'.  Use of the term `variant'
4130      does not necessarily imply that the resource is subject to content
4131      negotiation.
4132    </t>
4133  </list>
4134</t>
4135<t>
4136  <iref item="client"/>
4137  <x:dfn>client</x:dfn>
4138  <list>
4139    <t>
4140      A program that establishes connections for the purpose of sending
4141      requests.
4142    </t>
4143  </list>
4144</t>
4145<t>
4146  <iref item="user agent"/>
4147  <x:dfn>user agent</x:dfn>
4148  <list>
4149    <t>
4150      The client which initiates a request. These are often browsers,
4151      editors, spiders (web-traversing robots), or other end user tools.
4152    </t>
4153  </list>
4154</t>
4155<t>
4156  <iref item="server"/>
4157  <x:dfn>server</x:dfn>
4158  <list>
4159    <t>
4160      An application program that accepts connections in order to
4161      service requests by sending back responses. Any given program may
4162      be capable of being both a client and a server; our use of these
4163      terms refers only to the role being performed by the program for a
4164      particular connection, rather than to the program's capabilities
4165      in general. Likewise, any server may act as an origin server,
4166      proxy, gateway, or tunnel, switching behavior based on the nature
4167      of each request.
4168    </t>
4169  </list>
4170</t>
4171<t>
4172  <iref item="origin server"/>
4173  <x:dfn>origin server</x:dfn>
4174  <list>
4175    <t>
4176      The server on which a given resource resides or is to be created.
4177    </t>
4178  </list>
4179</t>
4180<t>
4181  <iref item="proxy"/>
4182  <x:dfn>proxy</x:dfn>
4183  <list>
4184    <t>
4185      An intermediary program which acts as both a server and a client
4186      for the purpose of making requests on behalf of other clients.
4187      Requests are serviced internally or by passing them on, with
4188      possible translation, to other servers. A proxy &MUST; implement
4189      both the client and server requirements of this specification. A
4190      "transparent proxy" is a proxy that does not modify the request or
4191      response beyond what is required for proxy authentication and
4192      identification. A "non-transparent proxy" is a proxy that modifies
4193      the request or response in order to provide some added service to
4194      the user agent, such as group annotation services, media type
4195      transformation, protocol reduction, or anonymity filtering. Except
4196      where either transparent or non-transparent behavior is explicitly
4197      stated, the HTTP proxy requirements apply to both types of
4198      proxies.
4199    </t>
4200  </list>
4201</t>
4202<t>
4203  <iref item="gateway"/>
4204  <x:dfn>gateway</x:dfn>
4205  <list>
4206    <t>
4207      A server which acts as an intermediary for some other server.
4208      Unlike a proxy, a gateway receives requests as if it were the
4209      origin server for the requested resource; the requesting client
4210      may not be aware that it is communicating with a gateway.
4211    </t>
4212  </list>
4213</t>
4214<t>
4215  <iref item="tunnel"/>
4216  <x:dfn>tunnel</x:dfn>
4217  <list>
4218    <t>
4219      An intermediary program which is acting as a blind relay between
4220      two connections. Once active, a tunnel is not considered a party
4221      to the HTTP communication, though the tunnel may have been
4222      initiated by an HTTP request. The tunnel ceases to exist when both
4223      ends of the relayed connections are closed.
4224    </t>
4225  </list>
4226</t>
4227<t>
4228  <iref item="cache"/>
4229  <x:dfn>cache</x:dfn>
4230  <list>
4231    <t>
4232      A program's local store of response messages and the subsystem
4233      that controls its message storage, retrieval, and deletion. A
4234      cache stores cacheable responses in order to reduce the response
4235      time and network bandwidth consumption on future, equivalent
4236      requests. Any client or server may include a cache, though a cache
4237      cannot be used by a server that is acting as a tunnel.
4238    </t>
4239  </list>
4240</t>
4241<t>
4242  <iref item="cacheable"/>
4243  <x:dfn>cacheable</x:dfn>
4244  <list>
4245    <t>
4246      A response is cacheable if a cache is allowed to store a copy of
4247      the response message for use in answering subsequent requests. The
4248      rules for determining the cacheability of HTTP responses are
4249      defined in &caching;. Even if a resource is cacheable, there may
4250      be additional constraints on whether a cache can use the cached
4251      copy for a particular request.
4252    </t>
4253  </list>
4254</t>
4255<t>
4256  <iref item="upstream"/>
4257  <iref item="downstream"/>
4258  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4259  <list>
4260    <t>
4261      Upstream and downstream describe the flow of a message: all
4262      messages flow from upstream to downstream.
4263    </t>
4264  </list>
4265</t>
4266<t>
4267  <iref item="inbound"/>
4268  <iref item="outbound"/>
4269  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4270  <list>
4271    <t>
4272      Inbound and outbound refer to the request and response paths for
4273      messages: "inbound" means "traveling toward the origin server",
4274      and "outbound" means "traveling toward the user agent"
4275    </t>
4276  </list>
4277</t>
4278</section>
4279
4280<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4281
4282<section title="Since RFC2616">
4283<t>
4284  Extracted relevant partitions from <xref target="RFC2616"/>.
4285</t>
4286</section>
4287
4288<section title="Since draft-ietf-httpbis-p1-messaging-00">
4289<t>
4290  Closed issues:
4291  <list style="symbols">
4292    <t>
4293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4294      "HTTP Version should be case sensitive"
4295      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4296    </t>
4297    <t>
4298      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4299      "'unsafe' characters"
4300      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4301    </t>
4302    <t>
4303      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4304      "Chunk Size Definition"
4305      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4306    </t>
4307    <t>
4308      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4309      "Message Length"
4310      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4311    </t>
4312    <t>
4313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4314      "Media Type Registrations"
4315      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4316    </t>
4317    <t>
4318      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4319      "URI includes query"
4320      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4321    </t>
4322    <t>
4323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4324      "No close on 1xx responses"
4325      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4326    </t>
4327    <t>
4328      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4329      "Remove 'identity' token references"
4330      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4331    </t>
4332    <t>
4333      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4334      "Import query BNF"
4335    </t>
4336    <t>
4337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4338      "qdtext BNF"
4339    </t>
4340    <t>
4341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4342      "Normative and Informative references"
4343    </t>
4344    <t>
4345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4346      "RFC2606 Compliance"
4347    </t>
4348    <t>
4349      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4350      "RFC977 reference"
4351    </t>
4352    <t>
4353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4354      "RFC1700 references"
4355    </t>
4356    <t>
4357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4358      "inconsistency in date format explanation"
4359    </t>
4360    <t>
4361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4362      "Date reference typo"
4363    </t>
4364    <t>
4365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4366      "Informative references"
4367    </t>
4368    <t>
4369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4370      "ISO-8859-1 Reference"
4371    </t>
4372    <t>
4373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4374      "Normative up-to-date references"
4375    </t>
4376  </list>
4377</t>
4378<t>
4379  Other changes:
4380  <list style="symbols">
4381    <t>
4382      Update media type registrations to use RFC4288 template.
4383    </t>
4384    <t>
4385      Use names of RFC4234 core rules DQUOTE and HTAB,
4386      fix broken ABNF for chunk-data
4387      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4388    </t>
4389  </list>
4390</t>
4391</section>
4392
4393<section title="Since draft-ietf-httpbis-p1-messaging-01">
4394<t>
4395  Closed issues:
4396  <list style="symbols">
4397    <t>
4398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4399      "Bodies on GET (and other) requests"
4400    </t>
4401    <t>
4402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4403      "Updating to RFC4288"
4404    </t>
4405    <t>
4406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4407      "Status Code and Reason Phrase"
4408    </t>
4409    <t>
4410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4411      "rel_path not used"
4412    </t>
4413  </list>
4414</t>
4415<t>
4416  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4417  <list style="symbols">
4418    <t>
4419      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4420      "trailer-part").
4421    </t>
4422    <t>
4423      Avoid underscore character in rule names ("http_URL" ->
4424      "http-URI", "abs_path" -> "path-absolute").
4425    </t>
4426    <t>
4427      Add rules for terms imported from URI spec ("absolute-URI", "authority",
4428      "path-abempty", "path-absolute", "uri-host", "port", "query").
4429    </t>
4430    <t>
4431      Synchronize core rules with RFC5234 (this includes a change to CHAR
4432      which now excludes NUL).
4433    </t>
4434    <t>
4435      Get rid of prose rules that span multiple lines.
4436    </t>
4437    <t>
4438      Get rid of unused rules LOALPHA and UPALPHA.
4439    </t>
4440    <t>
4441      Move "Product Tokens" section (back) into Part 1, as "token" is used
4442      in the definition of the Upgrade header.
4443    </t>
4444    <t>
4445      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4446    </t>
4447    <t>
4448      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4449    </t>
4450  </list>
4451</t>
4452</section>
4453
4454<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4455<t>
4456  Closed issues:
4457  <list style="symbols">
4458    <t>
4459      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4460      "HTTP-date vs. rfc1123-date"
4461    </t>
4462    <t>
4463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4464      "WS in quoted-pair"
4465    </t>
4466  </list>
4467</t>
4468<t>
4469  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4470  <list style="symbols">
4471    <t>
4472      Reference RFC 3984, and update header registrations for headers defined
4473      in this document.
4474    </t>
4475  </list>
4476</t>
4477<t>
4478  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4479  <list style="symbols">
4480    <t>
4481      Replace string literals when the string really is case-sensitive (HTTP-Version).
4482    </t>
4483  </list>
4484</t>
4485</section>
4486
4487<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4488<t>
4489  Closed issues:
4490  <list style="symbols">
4491    <t>
4492      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4493      "Connection closing"
4494    </t>
4495    <t>
4496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4497      "Move registrations and registry information to IANA Considerations"
4498    </t>
4499    <t>
4500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4501      "need new URL for PAD1995 reference"
4502    </t>
4503    <t>
4504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4505      "IANA Considerations: update HTTP URI scheme registration"
4506    </t>
4507    <t>
4508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4509      "Cite HTTPS URI scheme definition"
4510    </t>
4511    <t>
4512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4513      "List-type headers vs Set-Cookie"
4514    </t>
4515  </list>
4516</t>
4517<t>
4518  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4519  <list style="symbols">
4520    <t>
4521      Replace string literals when the string really is case-sensitive (HTTP-Date).
4522    </t>
4523    <t>
4524      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4525    </t>
4526  </list>
4527</t>
4528</section>
4529
4530<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4531<t>
4532  Closed issues:
4533  <list style="symbols">
4534    <t>
4535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4536      "RFC 2822 is updated by RFC 5322"
4537    </t>
4538  </list>
4539</t>
4540<t>
4541  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4542  <list style="symbols">
4543    <t>
4544      Use "/" instead of "|" for alternatives.
4545    </t>
4546    <t>
4547      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4548    </t>
4549  </list>
4550</t>
4551</section>
4552
4553</section>
4554
4555</back>
4556</rfc>
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