source: draft-ietf-httpbis/latest/p1-messaging.xml @ 621

Last change on this file since 621 was 621, checked in by fielding@…, 11 years ago

Define http and https URI schemes: addresses #58, #128, #159
Resolves #157: removed reference to RFC1900 use of IP addresses in URI.

  • Property svn:eol-style set to native
File size: 215.2 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2009">
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-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38]>
39<?rfc toc="yes" ?>
40<?rfc symrefs="yes" ?>
41<?rfc sortrefs="yes" ?>
42<?rfc compact="yes"?>
43<?rfc subcompact="no" ?>
44<?rfc linkmailto="no" ?>
45<?rfc editing="no" ?>
46<?rfc comments="yes"?>
47<?rfc inline="yes"?>
48<?rfc-ext allow-markup-in-artwork="yes" ?>
49<?rfc-ext include-references-in-index="yes" ?>
50<rfc obsoletes="2616" category="std" x:maturity-level="draft"
51     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
52     xmlns:x='http://purl.org/net/xml2rfc/ext'>
53<front>
54
55  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
56
57  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
58    <organization abbrev="Day Software">Day Software</organization>
59    <address>
60      <postal>
61        <street>23 Corporate Plaza DR, Suite 280</street>
62        <city>Newport Beach</city>
63        <region>CA</region>
64        <code>92660</code>
65        <country>USA</country>
66      </postal>
67      <phone>+1-949-706-5300</phone>
68      <facsimile>+1-949-706-5305</facsimile>
69      <email>fielding@gbiv.com</email>
70      <uri>http://roy.gbiv.com/</uri>
71    </address>
72  </author>
73
74  <author initials="J." surname="Gettys" fullname="Jim Gettys">
75    <organization>One Laptop per Child</organization>
76    <address>
77      <postal>
78        <street>21 Oak Knoll Road</street>
79        <city>Carlisle</city>
80        <region>MA</region>
81        <code>01741</code>
82        <country>USA</country>
83      </postal>
84      <email>jg@laptop.org</email>
85      <uri>http://www.laptop.org/</uri>
86    </address>
87  </author>
88 
89  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
90    <organization abbrev="HP">Hewlett-Packard Company</organization>
91    <address>
92      <postal>
93        <street>HP Labs, Large Scale Systems Group</street>
94        <street>1501 Page Mill Road, MS 1177</street>
95        <city>Palo Alto</city>
96        <region>CA</region>
97        <code>94304</code>
98        <country>USA</country>
99      </postal>
100      <email>JeffMogul@acm.org</email>
101    </address>
102  </author>
103
104  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
105    <organization abbrev="Microsoft">Microsoft Corporation</organization>
106    <address>
107      <postal>
108        <street>1 Microsoft Way</street>
109        <city>Redmond</city>
110        <region>WA</region>
111        <code>98052</code>
112        <country>USA</country>
113      </postal>
114      <email>henrikn@microsoft.com</email>
115    </address>
116  </author>
117
118  <author initials="L." surname="Masinter" fullname="Larry Masinter">
119    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
120    <address>
121      <postal>
122        <street>345 Park Ave</street>
123        <city>San Jose</city>
124        <region>CA</region>
125        <code>95110</code>
126        <country>USA</country>
127      </postal>
128      <email>LMM@acm.org</email>
129      <uri>http://larry.masinter.net/</uri>
130    </address>
131  </author>
132 
133  <author initials="P." surname="Leach" fullname="Paul J. Leach">
134    <organization abbrev="Microsoft">Microsoft Corporation</organization>
135    <address>
136      <postal>
137        <street>1 Microsoft Way</street>
138        <city>Redmond</city>
139        <region>WA</region>
140        <code>98052</code>
141      </postal>
142      <email>paulle@microsoft.com</email>
143    </address>
144  </author>
145   
146  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
147    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
148    <address>
149      <postal>
150        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
151        <street>The Stata Center, Building 32</street>
152        <street>32 Vassar Street</street>
153        <city>Cambridge</city>
154        <region>MA</region>
155        <code>02139</code>
156        <country>USA</country>
157      </postal>
158      <email>timbl@w3.org</email>
159      <uri>http://www.w3.org/People/Berners-Lee/</uri>
160    </address>
161  </author>
162
163  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
164    <organization abbrev="W3C">World Wide Web Consortium</organization>
165    <address>
166      <postal>
167        <street>W3C / ERCIM</street>
168        <street>2004, rte des Lucioles</street>
169        <city>Sophia-Antipolis</city>
170        <region>AM</region>
171        <code>06902</code>
172        <country>France</country>
173      </postal>
174      <email>ylafon@w3.org</email>
175      <uri>http://www.raubacapeu.net/people/yves/</uri>
176    </address>
177  </author>
178
179  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
180    <organization abbrev="greenbytes">greenbytes GmbH</organization>
181    <address>
182      <postal>
183        <street>Hafenweg 16</street>
184        <city>Muenster</city><region>NW</region><code>48155</code>
185        <country>Germany</country>
186      </postal>
187      <phone>+49 251 2807760</phone>
188      <facsimile>+49 251 2807761</facsimile>
189      <email>julian.reschke@greenbytes.de</email>
190      <uri>http://greenbytes.de/tech/webdav/</uri>
191    </address>
192  </author>
193
194  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
195  <workgroup>HTTPbis Working Group</workgroup>
196
197<abstract>
198<t>
199   The Hypertext Transfer Protocol (HTTP) is an application-level
200   protocol for distributed, collaborative, hypertext information
201   systems. HTTP has been in use by the World Wide Web global information
202   initiative since 1990. This document is Part 1 of the seven-part specification
203   that defines the protocol referred to as "HTTP/1.1" and, taken together,
204   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
205   its associated terminology, defines the "http" and "https" Uniform
206   Resource Identifier (URI) schemes, defines the generic message syntax
207   and parsing requirements for HTTP message frames, and describes
208   general security concerns for implementations.
209</t>
210</abstract>
211
212<note title="Editorial Note (To be removed by RFC Editor)">
213  <t>
214    Discussion of this draft should take place on the HTTPBIS working group
215    mailing list (ietf-http-wg@w3.org). The current issues list is
216    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
217    and related documents (including fancy diffs) can be found at
218    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
219  </t>
220  <t>
221    The changes in this draft are summarized in <xref target="changes.since.07"/>.
222  </t>
223</note>
224</front>
225<middle>
226<section title="Introduction" anchor="introduction">
227<t>
228   The Hypertext Transfer Protocol (HTTP) is an application-level
229   request/response protocol that uses extensible semantics and MIME-like
230   message payloads for flexible interaction with network-based hypertext
231   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
232   standard <xref target="RFC3986"/> to indicate request targets and
233   relationships between resources.
234   Messages are passed in a format similar to that used by Internet mail
235   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
236   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
237   between HTTP and MIME messages).
238</t>
239<t>
240   HTTP is a generic interface protocol for information systems. It is
241   designed to hide the details of how a service is implemented by presenting
242   a uniform interface to clients that is independent of the types of
243   resources provided. Likewise, servers do not need to be aware of each
244   client's purpose: an HTTP request can be considered in isolation rather
245   than being associated with a specific type of client or a predetermined
246   sequence of application steps. The result is a protocol that can be used
247   effectively in many different contexts and for which implementations can
248   evolve independently over time.
249</t>
250<t>
251   HTTP is also designed for use as a generic protocol for translating
252   communication to and from other Internet information systems.
253   HTTP proxies and gateways provide access to alternative information
254   services by translating their diverse protocols into a hypertext
255   format that can be viewed and manipulated by clients in the same way
256   as HTTP services.
257</t>
258<t>
259   One consequence of HTTP flexibility is that the protocol cannot be
260   defined in terms of what occurs behind the interface. Instead, we
261   are limited to defining the syntax of communication, the intent
262   of received communication, and the expected behavior of recipients.
263   If the communication is considered in isolation, then successful
264   actions should be reflected in corresponding changes to the
265   observable interface provided by servers. However, since multiple
266   clients may act in parallel and perhaps at cross-purposes, we
267   cannot require that such changes be observable beyond the scope
268   of a single response.
269</t>
270<t>
271   This document is Part 1 of the seven-part specification of HTTP,
272   defining the protocol referred to as "HTTP/1.1" and obsoleting
273   <xref target="RFC2616"/>.
274   Part 1 describes the architectural elements that are used or
275   referred to in HTTP, defines the "http" and "https" URI schemes,
276   describes overall network operation and connection management,
277   and defines HTTP message framing and forwarding requirements.
278   Our goal is to define all of the mechanisms necessary for HTTP message
279   handling that are independent of message semantics, thereby defining the
280   complete set of requirements for message parsers and
281   message-forwarding intermediaries.
282</t>
283
284<section title="Requirements" anchor="intro.requirements">
285<t>
286   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
287   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
288   document are to be interpreted as described in <xref target="RFC2119"/>.
289</t>
290<t>
291   An implementation is not compliant if it fails to satisfy one or more
292   of the &MUST; or &REQUIRED; level requirements for the protocols it
293   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
294   level and all the &SHOULD; level requirements for its protocols is said
295   to be "unconditionally compliant"; one that satisfies all the &MUST;
296   level requirements but not all the &SHOULD; level requirements for its
297   protocols is said to be "conditionally compliant."
298</t>
299</section>
300
301<section title="Syntax Notation" anchor="notation">
302<iref primary="true" item="Grammar" subitem="ALPHA"/>
303<iref primary="true" item="Grammar" subitem="CR"/>
304<iref primary="true" item="Grammar" subitem="CRLF"/>
305<iref primary="true" item="Grammar" subitem="CTL"/>
306<iref primary="true" item="Grammar" subitem="DIGIT"/>
307<iref primary="true" item="Grammar" subitem="DQUOTE"/>
308<iref primary="true" item="Grammar" subitem="HEXDIG"/>
309<iref primary="true" item="Grammar" subitem="LF"/>
310<iref primary="true" item="Grammar" subitem="OCTET"/>
311<iref primary="true" item="Grammar" subitem="SP"/>
312<iref primary="true" item="Grammar" subitem="VCHAR"/>
313<iref primary="true" item="Grammar" subitem="WSP"/>
314<t>
315   This specification uses the Augmented Backus-Naur Form (ABNF) notation
316   of <xref target="RFC5234"/>.
317</t>
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CTL"/>
321  <x:anchor-alias value="CR"/>
322  <x:anchor-alias value="CRLF"/>
323  <x:anchor-alias value="DIGIT"/>
324  <x:anchor-alias value="DQUOTE"/>
325  <x:anchor-alias value="HEXDIG"/>
326  <x:anchor-alias value="LF"/>
327  <x:anchor-alias value="OCTET"/>
328  <x:anchor-alias value="SP"/>
329  <x:anchor-alias value="VCHAR"/>
330  <x:anchor-alias value="WSP"/>
331   The following core rules are included by
332   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334   DIGIT (decimal 0-9), DQUOTE (double quote),
335   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336   OCTET (any 8-bit sequence of data), SP (space),
337   VCHAR (any visible <xref target="USASCII"/> character),
338   and WSP (whitespace).
339</t>
340
341<section title="ABNF Extension: #rule" anchor="notation.abnf">
342  <t>
343    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
344    improve readability.
345  </t>
346  <t>
347    A construct "#" is defined, similar to "*", for defining lists of
348    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
349    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
350    (",") and optional whitespace (OWS).   
351  </t>
352  <figure><preamble>
353    Thus,
354</preamble><artwork type="example">
355  1#element =&gt; element *( OWS "," OWS element )
356</artwork></figure>
357  <figure><preamble>
358    and:
359</preamble><artwork type="example">
360  #element =&gt; [ 1#element ]
361</artwork></figure>
362  <figure><preamble>
363    and for n &gt;= 1 and m &gt; 1:
364</preamble><artwork type="example">
365  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
366</artwork></figure>
367  <t>
368    For compatibility with legacy list rules, recipients &SHOULD; accept empty
369    list elements. In other words, consumers would follow the list productions:
370  </t>
371<figure><artwork type="example">
372  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
373 
374  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
375</artwork></figure> 
376<t>
377  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
378  expanded as explained above.
379</t>
380</section>
381
382<section title="Basic Rules" anchor="basic.rules">
383<t anchor="rule.CRLF">
384  <x:anchor-alias value="CRLF"/>
385   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
386   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
387   tolerant applications). The end-of-line marker within an entity-body
388   is defined by its associated media type, as described in &media-types;.
389</t>
390<t anchor="rule.LWS">
391   This specification uses three rules to denote the use of linear
392   whitespace: OWS (optional whitespace), RWS (required whitespace), and
393   BWS ("bad" whitespace).
394</t>
395<t>
396   The OWS rule is used where zero or more linear whitespace characters may
397   appear. OWS &SHOULD; either not be produced or be produced as a single SP
398   character. Multiple OWS characters that occur within field-content &SHOULD;
399   be replaced with a single SP before interpreting the field value or
400   forwarding the message downstream.
401</t>
402<t>
403   RWS is used when at least one linear whitespace character is required to
404   separate field tokens. RWS &SHOULD; be produced as a single SP character.
405   Multiple RWS characters that occur within field-content &SHOULD; be
406   replaced with a single SP before interpreting the field value or
407   forwarding the message downstream.
408</t>
409<t>
410   BWS is used where the grammar allows optional whitespace for historical
411   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
412   recipients &MUST; accept such bad optional whitespace and remove it before
413   interpreting the field value or forwarding the message downstream.
414</t>
415<t anchor="rule.whitespace">
416  <x:anchor-alias value="BWS"/>
417  <x:anchor-alias value="OWS"/>
418  <x:anchor-alias value="RWS"/>
419  <x:anchor-alias value="obs-fold"/>
420</t>
421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
422  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
423                 ; "optional" whitespace
424  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
425                 ; "required" whitespace
426  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
427                 ; "bad" whitespace
428  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
429                 ; see <xref target="message.headers"/>
430</artwork></figure>
431<t anchor="rule.token.separators">
432  <x:anchor-alias value="tchar"/>
433  <x:anchor-alias value="token"/>
434   Many HTTP/1.1 header field values consist of words separated by whitespace
435   or special characters. These special characters &MUST; be in a quoted
436   string to be used within a parameter value (as defined in
437   <xref target="transfer.codings"/>).
438</t>
439<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
440  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
441                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
442                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
443                 
444  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
445</artwork></figure>
446<t anchor="rule.quoted-string">
447  <x:anchor-alias value="quoted-string"/>
448  <x:anchor-alias value="qdtext"/>
449  <x:anchor-alias value="obs-text"/>
450   A string of text is parsed as a single word if it is quoted using
451   double-quote marks.
452</t>
453<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
454  <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>
455  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
456                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
457  <x:ref>obs-text</x:ref>       = %x80-FF
458</artwork></figure>
459<t anchor="rule.quoted-pair">
460  <x:anchor-alias value="quoted-pair"/>
461  <x:anchor-alias value="quoted-text"/>
462   The backslash character ("\") &MAY; be used as a single-character
463   quoting mechanism only within quoted-string and comment constructs.
464</t>
465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
466  <x:ref>quoted-text</x:ref>    = %x01-09 /
467                   %x0B-0C /
468                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
469  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
470</artwork></figure>
471</section>
472
473<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
474  <x:anchor-alias value="request-header"/>
475  <x:anchor-alias value="response-header"/>
476  <x:anchor-alias value="entity-body"/>
477  <x:anchor-alias value="entity-header"/>
478  <x:anchor-alias value="Cache-Control"/>
479  <x:anchor-alias value="Pragma"/>
480  <x:anchor-alias value="Warning"/>
481<t>
482  The ABNF rules below are defined in other parts:
483</t>
484<figure><!-- Part2--><artwork type="abnf2616">
485  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
486  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
487</artwork></figure>
488<figure><!-- Part3--><artwork type="abnf2616">
489  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
490  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
491</artwork></figure>
492<figure><!-- Part6--><artwork type="abnf2616">
493  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
494  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
495  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
496</artwork></figure>
497</section>
498
499</section>
500</section>
501
502<section title="HTTP architecture" anchor="architecture">
503<t>
504   HTTP was created for the World Wide Web architecture
505   and has evolved over time to support the scalability needs of a worldwide
506   hypertext system. Much of that architecture is reflected in the terminology
507   and syntax productions used to define HTTP.
508</t>
509
510<section title="Uniform Resource Identifiers" anchor="uri">
511<iref primary="true" item="resource"/>
512<t>
513   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
514   throughout HTTP as the means for identifying resources. URI references
515   are used to target requests, indicate redirects, and define relationships.
516   HTTP does not limit what a resource may be; it merely defines an interface
517   that can be used to interact with a resource via HTTP. More information on
518   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
519</t>
520  <x:anchor-alias value="URI"/>
521  <x:anchor-alias value="URI-reference"/>
522  <x:anchor-alias value="absolute-URI"/>
523  <x:anchor-alias value="relative-part"/>
524  <x:anchor-alias value="authority"/>
525  <x:anchor-alias value="fragment"/>
526  <x:anchor-alias value="path-abempty"/>
527  <x:anchor-alias value="path-absolute"/>
528  <x:anchor-alias value="port"/>
529  <x:anchor-alias value="query"/>
530  <x:anchor-alias value="uri-host"/>
531  <x:anchor-alias value="partial-URI"/>
532<t>
533   This specification adopts the definitions of "URI-reference",
534   "absolute-URI", "relative-part", "fragment", "port", "host",
535   "path-abempty", "path-absolute", "query", and "authority" from
536   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
537   protocol elements that allow a relative URI without a fragment.
538</t>
539<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"/>
540  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
541  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
542  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
543  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
544  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
545  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
546  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
547  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
548  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
549  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
550  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
551 
552  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
553</artwork></figure>
554<t>
555   Each protocol element in HTTP that allows a URI reference will indicate in
556   its ABNF production whether the element allows only a URI in absolute form
557   (absolute-URI), any relative reference (relative-ref), or some other subset
558   of the URI-reference grammar. Unless otherwise indicated, URI references
559   are parsed relative to the request target (the default base URI for both
560   the request and its corresponding response).
561</t>
562
563<section title="http URI scheme" anchor="http.uri">
564  <x:anchor-alias value="http-URI"/>
565  <iref item="http URI scheme" primary="true"/>
566  <iref item="URI scheme" subitem="http" primary="true"/>
567<t>
568   The "http" URI scheme is hereby defined for the purpose of minting
569   identifiers according to their association with the hierarchical
570   namespace governed by a potential HTTP origin server listening for
571   TCP connections on a given port.
572   The HTTP server is identified via the generic syntax's
573   <x:ref>authority</x:ref> component, which includes a host
574   identifier and optional TCP port, and the remainder of the URI is
575   considered to be identifying data corresponding to a resource for
576   which that server might provide an HTTP interface.
577</t>
578<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
579  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
580</artwork></figure>
581<t>
582   The host identifier within an <x:ref>authority</x:ref> component is
583   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
584   provided as an IP literal or IPv4 address, then the HTTP server is any
585   listener on the indicated TCP port at that IP address. If host is a
586   registered name, then that name is considered an indirect identifier
587   and the recipient might use a name resolution service, such as DNS,
588   to find the address of a listener for that host.
589   The host &MUST-NOT; be empty; if an "http" URI is received with an
590   empty host, then it &MUST; be rejected as invalid.
591   If the port subcomponent is empty or not given, then TCP port 80 is
592   assumed (the default reserved port for WWW services).
593</t>
594<t>
595   Regardless of the form of host identifier, access to that host is not
596   implied by the mere presence of its name or address. The host may or may
597   not exist and, even when it does exist, may or may not be running an
598   HTTP server or listening to the indicated port. The "http" URI scheme
599   makes use of the delegated nature of Internet names and addresses to
600   establish a naming authority (whatever entity has the ability to place
601   an HTTP server at that Internet name or address) and allows that
602   authority to determine which names are valid and how they might be used.
603</t>
604<t>
605   When an "http" URI is used within a context that calls for access to the
606   indicated resource, a client &MAY; attempt access by resolving
607   the host to an IP address, establishing a TCP connection to that address
608   on the indicated port, and sending an HTTP request message to the server
609   containing the URI's identifying data as described in <xref target="request"/>.
610   If the server responds to that request with a non-interim HTTP response
611   message, as described in <xref target="response"/>, then that response
612   is considered an authoritative answer to the client's request.
613</t>
614<t>
615   Although HTTP is independent of the transport protocol, the "http"
616   scheme is specific to TCP-based services because the name delegation
617   process depends on TCP for establishing authority.
618   An HTTP service based on some other underlying connection protocol
619   would presumably be identified using a different URI scheme, just as
620   the "https" scheme (below) is used for servers that require an SSL/TLS
621   transport layer on a connection. Other protocols may also be used to
622   provide access to "http" identified resources --- it is only the
623   authoritative interface used for mapping the namespace that is
624   specific to TCP.
625</t>
626</section>
627
628<section title="https URI scheme" anchor="https.uri">
629   <iref item="https URI scheme"/>
630   <iref item="URI scheme" subitem="https"/>
631<t>
632   The "https" URI scheme is hereby defined for the purpose of minting
633   identifiers according to their association with the hierarchical
634   namespace governed by a potential HTTP origin server listening for
635   SSL/TLS-secured connections on a given TCP port.
636   The host and port are determined in the same way
637   as for the "http" scheme, except that a default TCP port of 443
638   is assumed if the port subcomponent is empty or not given.
639</t>
640<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
641  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
642</artwork></figure>
643<t>
644   The primary difference between the "http" and "https" schemes is
645   that interaction with the latter is required to be secured for
646   privacy through the use of strong encryption. The URI cannot be
647   sent in a request until the connection is secure. Likewise, the
648   default for caching is that each response that would be considered
649   "public" under the "http" scheme is instead treated as "private"
650   and thus not eligible for shared caching.
651</t>
652<t>
653   The process for authoritative access to an "https" identified
654   resource is defined in <xref target="RFC2818"/>.
655</t>
656</section>
657
658<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
659<t>
660   Since the "http" and "https" schemes conform to the URI generic syntax,
661   such URIs are normalized and compared according to the algorithm defined
662   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
663   described above for each scheme.
664</t>
665<t>
666   If the port is equal to the default port for a scheme, the normal
667   form is to elide the port subcomponent. Likewise, an empty path
668   component is equivalent to an absolute path of "/", so the normal
669   form is to provide a path of "/" instead. The scheme and host
670   are case-insensitive and normally provided in lowercase; all
671   other components are compared in a case-sensitive manner.
672   Characters other than those in the "reserved" set are equivalent
673   to their percent-encoded octets (see <xref target="RFC3986"
674   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
675</t>
676<t>
677   For example, the following three URIs are equivalent:
678</t>
679<figure><artwork type="example">
680   http://example.com:80/~smith/home.html
681   http://EXAMPLE.com/%7Esmith/home.html
682   http://EXAMPLE.com:/%7esmith/home.html
683</artwork></figure>
684<t>
685   <cref>[[This paragraph does not belong here. --Roy]]</cref>
686   If path-abempty is the empty string (i.e., there is no slash "/"
687   path separator following the authority), then the "http" URI
688   &MUST; be given as "/" when
689   used as a request-target (<xref target="request-target"/>). If a proxy
690   receives a host name which is not a fully qualified domain name, it
691   &MAY; add its domain to the host name it received. If a proxy receives
692   a fully qualified domain name, the proxy &MUST-NOT; change the host
693   name.
694</t>
695</section>
696
697<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
698<t>
699   <cref>TBS: describe why aliases like webcal are harmful.</cref>
700</t>
701</section>
702</section>
703
704<section title="Overall Operation" anchor="intro.overall.operation">
705<t>
706   HTTP is a request/response protocol. A client sends a
707   request to the server in the form of a request method, URI, and
708   protocol version, followed by a MIME-like message containing request
709   modifiers, client information, and possible body content over a
710   connection with a server. The server responds with a status line,
711   including the message's protocol version and a success or error code,
712   followed by a MIME-like message containing server information, entity
713   metadata, and possible entity-body content.
714</t>
715<t>
716   Most HTTP communication is initiated by a user agent and consists of
717   a request to be applied to a resource via the HTTP interface provided
718   by some origin server. In the
719   simplest case, this may be accomplished via a single connection (v)
720   between the user agent (UA) and the origin server (O).
721</t>
722<figure><artwork type="drawing">
723       request chain ------------------------&gt;
724    UA -------------------v------------------- O
725       &lt;----------------------- response chain
726</artwork></figure>
727<t>
728   A more complicated situation occurs when one or more intermediaries
729   are present in the request/response chain. There are three common
730   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
731   forwarding agent, receiving requests for a URI in its absolute form,
732   rewriting all or part of the message, and forwarding the reformatted
733   request toward the server identified by the URI. A gateway is a
734   receiving agent, acting as a layer above some other server(s) and, if
735   necessary, translating the requests to the underlying server's
736   protocol. A tunnel acts as a relay point between two connections
737   without changing the messages; tunnels are used when the
738   communication needs to pass through an intermediary (such as a
739   firewall) even when the intermediary cannot understand the contents
740   of the messages.
741</t>
742<figure><artwork type="drawing">
743       request chain --------------------------------------&gt;
744    UA -----v----- A -----v----- B -----v----- C -----v----- O
745       &lt;------------------------------------- response chain
746</artwork></figure>
747<t>
748   The figure above shows three intermediaries (A, B, and C) between the
749   user agent and origin server. A request or response message that
750   travels the whole chain will pass through four separate connections.
751   This distinction is important because some HTTP communication options
752   may apply only to the connection with the nearest, non-tunnel
753   neighbor, only to the end-points of the chain, or to all connections
754   along the chain. Although the diagram is linear, each participant may
755   be engaged in multiple, simultaneous communications. For example, B
756   may be receiving requests from many clients other than A, and/or
757   forwarding requests to servers other than C, at the same time that it
758   is handling A's request.
759</t>
760<t>
761   Any party to the communication which is not acting as a tunnel may
762   employ an internal cache for handling requests. The effect of a cache
763   is that the request/response chain is shortened if one of the
764   participants along the chain has a cached response applicable to that
765   request. The following illustrates the resulting chain if B has a
766   cached copy of an earlier response from O (via C) for a request which
767   has not been cached by UA or A.
768</t>
769<figure><artwork type="drawing">
770          request chain ----------&gt;
771       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
772          &lt;--------- response chain
773</artwork></figure>
774<t>
775   Not all responses are usefully cacheable, and some requests may
776   contain modifiers which place special requirements on cache behavior.
777   HTTP requirements for cache behavior and cacheable responses are
778   defined in &caching;.
779</t>
780<t>
781   In fact, there are a wide variety of architectures and configurations
782   of caches and proxies currently being experimented with or deployed
783   across the World Wide Web. These systems include national hierarchies
784   of proxy caches to save transoceanic bandwidth, systems that
785   broadcast or multicast cache entries, organizations that distribute
786   subsets of cached data via CD-ROM, and so on. HTTP systems are used
787   in corporate intranets over high-bandwidth links, and for access via
788   PDAs with low-power radio links and intermittent connectivity. The
789   goal of HTTP/1.1 is to support the wide diversity of configurations
790   already deployed while introducing protocol constructs that meet the
791   needs of those who build web applications that require high
792   reliability and, failing that, at least reliable indications of
793   failure.
794</t>
795<t>
796   HTTP communication usually takes place over TCP/IP connections. The
797   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
798   not preclude HTTP from being implemented on top of any other protocol
799   on the Internet, or on other networks. HTTP only presumes a reliable
800   transport; any protocol that provides such guarantees can be used;
801   the mapping of the HTTP/1.1 request and response structures onto the
802   transport data units of the protocol in question is outside the scope
803   of this specification.
804</t>
805<t>
806   In HTTP/1.0, most implementations used a new connection for each
807   request/response exchange. In HTTP/1.1, a connection may be used for
808   one or more request/response exchanges, although connections may be
809   closed for a variety of reasons (see <xref target="persistent.connections"/>).
810</t>
811</section>
812
813<section title="Use of HTTP for proxy communication" anchor="http.proxy">
814<t>
815   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
816</t>
817</section>
818<section title="Interception of HTTP for access control" anchor="http.intercept">
819<t>
820   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
821</t>
822</section>
823<section title="Use of HTTP by other protocols" anchor="http.others">
824<t>
825   <cref>TBD: Profiles of HTTP defined by other protocol.
826   Extensions of HTTP like WebDAV.</cref>
827</t>
828</section>
829<section title="Use of HTTP by media type specification" anchor="http.media">
830<t>
831   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
832</t>
833</section>
834</section>
835
836<section title="Protocol Parameters" anchor="protocol.parameters">
837
838<section title="HTTP Version" anchor="http.version">
839  <x:anchor-alias value="HTTP-Version"/>
840  <x:anchor-alias value="HTTP-Prot-Name"/>
841<t>
842   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
843   of the protocol. The protocol versioning policy is intended to allow
844   the sender to indicate the format of a message and its capacity for
845   understanding further HTTP communication, rather than the features
846   obtained via that communication. No change is made to the version
847   number for the addition of message components which do not affect
848   communication behavior or which only add to extensible field values.
849   The &lt;minor&gt; number is incremented when the changes made to the
850   protocol add features which do not change the general message parsing
851   algorithm, but which may add to the message semantics and imply
852   additional capabilities of the sender. The &lt;major&gt; number is
853   incremented when the format of a message within the protocol is
854   changed. See <xref target="RFC2145"/> for a fuller explanation.
855</t>
856<t>
857   The version of an HTTP message is indicated by an HTTP-Version field
858   in the first line of the message. HTTP-Version is case-sensitive.
859</t>
860<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
861  <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>
862  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
863</artwork></figure>
864<t>
865   Note that the major and minor numbers &MUST; be treated as separate
866   integers and that each &MAY; be incremented higher than a single digit.
867   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
868   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
869   &MUST-NOT; be sent.
870</t>
871<t>
872   An application that sends a request or response message that includes
873   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
874   with this specification. Applications that are at least conditionally
875   compliant with this specification &SHOULD; use an HTTP-Version of
876   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
877   not compatible with HTTP/1.0. For more details on when to send
878   specific HTTP-Version values, see <xref target="RFC2145"/>.
879</t>
880<t>
881   The HTTP version of an application is the highest HTTP version for
882   which the application is at least conditionally compliant.
883</t>
884<t>
885   Proxy and gateway applications need to be careful when forwarding
886   messages in protocol versions different from that of the application.
887   Since the protocol version indicates the protocol capability of the
888   sender, a proxy/gateway &MUST-NOT; send a message with a version
889   indicator which is greater than its actual version. If a higher
890   version request is received, the proxy/gateway &MUST; either downgrade
891   the request version, or respond with an error, or switch to tunnel
892   behavior.
893</t>
894<t>
895   Due to interoperability problems with HTTP/1.0 proxies discovered
896   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
897   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
898   they support. The proxy/gateway's response to that request &MUST; be in
899   the same major version as the request.
900</t>
901<x:note>
902  <t>
903    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
904    of header fields required or forbidden by the versions involved.
905  </t>
906</x:note>
907</section>
908
909<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
910  <x:anchor-alias value="HTTP-date"/>
911<t>
912   HTTP applications have historically allowed three different formats
913   for the representation of date/time stamps:
914</t>
915<figure><artwork type="example">
916  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
917  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
918  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
919</artwork></figure>
920<t>
921   The first format is preferred as an Internet standard and represents
922   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
923   other formats are described here only for
924   compatibility with obsolete implementations.
925   HTTP/1.1 clients and servers that parse the date value &MUST; accept
926   all three formats (for compatibility with HTTP/1.0), though they &MUST;
927   only generate the RFC 1123 format for representing HTTP-date values
928   in header fields. See <xref target="tolerant.applications"/> for further information.
929</t>
930<t>
931   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
932   (GMT), without exception. For the purposes of HTTP, GMT is exactly
933   equal to UTC (Coordinated Universal Time). This is indicated in the
934   first two formats by the inclusion of "GMT" as the three-letter
935   abbreviation for time zone, and &MUST; be assumed when reading the
936   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
937   additional whitespace beyond that specifically included as SP in the
938   grammar.
939</t>
940<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
941  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
942</artwork></figure>
943<t anchor="preferred.date.format">
944  <x:anchor-alias value="rfc1123-date"/>
945  <x:anchor-alias value="time-of-day"/>
946  <x:anchor-alias value="hour"/>
947  <x:anchor-alias value="minute"/>
948  <x:anchor-alias value="second"/>
949  <x:anchor-alias value="day-name"/>
950  <x:anchor-alias value="day"/>
951  <x:anchor-alias value="month"/>
952  <x:anchor-alias value="year"/>
953  <x:anchor-alias value="GMT"/>
954  Preferred format:
955</t>
956<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
957  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
958
959  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
960               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
961               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
962               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
963               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
964               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
965               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
966               
967  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
968               ; e.g., 02 Jun 1982
969
970  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
971  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
972               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
973               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
974               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
975               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
976               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
977               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
978               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
979               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
980               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
981               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
982               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
983  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
984
985  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
986
987  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
988                 ; 00:00:00 - 23:59:59
989                 
990  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
991  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
992  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
993</artwork></figure>
994<t>
995  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
996  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
997  same as those defined for the RFC 5322 constructs
998  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
999</t>
1000<t anchor="obsolete.date.formats">
1001  <x:anchor-alias value="obs-date"/>
1002  <x:anchor-alias value="rfc850-date"/>
1003  <x:anchor-alias value="asctime-date"/>
1004  <x:anchor-alias value="date1"/>
1005  <x:anchor-alias value="date2"/>
1006  <x:anchor-alias value="date3"/>
1007  <x:anchor-alias value="rfc1123-date"/>
1008  <x:anchor-alias value="day-name-l"/>
1009  Obsolete formats:
1010</t>
1011<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1012  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1013</artwork></figure>
1014<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1015  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
1016  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1017                 ; day-month-year (e.g., 02-Jun-82)
1018
1019  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1020         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1021         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1022         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1023         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1024         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1025         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1026</artwork></figure>
1027<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1028  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
1029  <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> ))
1030                 ; month day (e.g., Jun  2)
1031</artwork></figure>
1032<x:note>
1033  <t>
1034    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1035    accepting date values that may have been sent by non-HTTP
1036    applications, as is sometimes the case when retrieving or posting
1037    messages via proxies/gateways to SMTP or NNTP.
1038  </t>
1039</x:note>
1040<x:note>
1041  <t>
1042    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1043    to their usage within the protocol stream. Clients and servers are
1044    not required to use these formats for user presentation, request
1045    logging, etc.
1046  </t>
1047</x:note>
1048</section>
1049
1050<section title="Transfer Codings" anchor="transfer.codings">
1051  <x:anchor-alias value="transfer-coding"/>
1052  <x:anchor-alias value="transfer-extension"/>
1053<t>
1054   Transfer-coding values are used to indicate an encoding
1055   transformation that has been, can be, or may need to be applied to an
1056   entity-body in order to ensure "safe transport" through the network.
1057   This differs from a content coding in that the transfer-coding is a
1058   property of the message, not of the original entity.
1059</t>
1060<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1061  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
1062  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
1063</artwork></figure>
1064<t anchor="rule.parameter">
1065  <x:anchor-alias value="attribute"/>
1066  <x:anchor-alias value="transfer-parameter"/>
1067  <x:anchor-alias value="value"/>
1068   Parameters are in  the form of attribute/value pairs.
1069</t>
1070<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1071  <x:ref>transfer-parameter</x:ref>      = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1072  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1073  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1074</artwork></figure>
1075<t>
1076   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1077   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1078   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1079</t>
1080<t>
1081   Whenever a transfer-coding is applied to a message-body, the set of
1082   transfer-codings &MUST; include "chunked", unless the message indicates it
1083   is terminated by closing the connection. When the "chunked" transfer-coding
1084   is used, it &MUST; be the last transfer-coding applied to the
1085   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1086   than once to a message-body. These rules allow the recipient to
1087   determine the transfer-length of the message (<xref target="message.length"/>).
1088</t>
1089<t>
1090   Transfer-codings are analogous to the Content-Transfer-Encoding
1091   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1092   binary data over a 7-bit transport service. However, safe transport
1093   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1094   the only unsafe characteristic of message-bodies is the difficulty in
1095   determining the exact body length (<xref target="message.length"/>), or the desire to
1096   encrypt data over a shared transport.
1097</t>
1098<t>
1099   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1100   transfer-coding value tokens. Initially, the registry contains the
1101   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1102   "gzip", "compress", and "deflate" (&content-codings;).
1103</t>
1104<t>
1105   New transfer-coding value tokens &SHOULD; be registered in the same way
1106   as new content-coding value tokens (&content-codings;).
1107</t>
1108<t>
1109   A server which receives an entity-body with a transfer-coding it does
1110   not understand &SHOULD; return 501 (Not Implemented), and close the
1111   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1112   client.
1113</t>
1114
1115<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1116  <x:anchor-alias value="chunk"/>
1117  <x:anchor-alias value="Chunked-Body"/>
1118  <x:anchor-alias value="chunk-data"/>
1119  <x:anchor-alias value="chunk-ext"/>
1120  <x:anchor-alias value="chunk-ext-name"/>
1121  <x:anchor-alias value="chunk-ext-val"/>
1122  <x:anchor-alias value="chunk-size"/>
1123  <x:anchor-alias value="last-chunk"/>
1124  <x:anchor-alias value="trailer-part"/>
1125<t>
1126   The chunked encoding modifies the body of a message in order to
1127   transfer it as a series of chunks, each with its own size indicator,
1128   followed by an &OPTIONAL; trailer containing entity-header fields. This
1129   allows dynamically produced content to be transferred along with the
1130   information necessary for the recipient to verify that it has
1131   received the full message.
1132</t>
1133<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/>
1134  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1135                   <x:ref>last-chunk</x:ref>
1136                   <x:ref>trailer-part</x:ref>
1137                   <x:ref>CRLF</x:ref>
1138 
1139  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1140                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1141  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1142  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1143 
1144  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1145                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1146  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1147  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1148  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1149  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1150</artwork></figure>
1151<t>
1152   The chunk-size field is a string of hex digits indicating the size of
1153   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1154   zero, followed by the trailer, which is terminated by an empty line.
1155</t>
1156<t>
1157   The trailer allows the sender to include additional HTTP header
1158   fields at the end of the message. The Trailer header field can be
1159   used to indicate which header fields are included in a trailer (see
1160   <xref target="header.trailer"/>).
1161</t>
1162<t>
1163   A server using chunked transfer-coding in a response &MUST-NOT; use the
1164   trailer for any header fields unless at least one of the following is
1165   true:
1166  <list style="numbers">
1167    <t>the request included a TE header field that indicates "trailers" is
1168     acceptable in the transfer-coding of the  response, as described in
1169     <xref target="header.te"/>; or,</t>
1170
1171    <t>the server is the origin server for the response, the trailer
1172     fields consist entirely of optional metadata, and the recipient
1173     could use the message (in a manner acceptable to the origin server)
1174     without receiving this metadata.  In other words, the origin server
1175     is willing to accept the possibility that the trailer fields might
1176     be silently discarded along the path to the client.</t>
1177  </list>
1178</t>
1179<t>
1180   This requirement prevents an interoperability failure when the
1181   message is being received by an HTTP/1.1 (or later) proxy and
1182   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1183   compliance with the protocol would have necessitated a possibly
1184   infinite buffer on the proxy.
1185</t>
1186<t>
1187   A process for decoding the "chunked" transfer-coding
1188   can be represented in pseudo-code as:
1189</t>
1190<figure><artwork type="code">
1191  length := 0
1192  read chunk-size, chunk-ext (if any) and CRLF
1193  while (chunk-size &gt; 0) {
1194     read chunk-data and CRLF
1195     append chunk-data to entity-body
1196     length := length + chunk-size
1197     read chunk-size and CRLF
1198  }
1199  read entity-header
1200  while (entity-header not empty) {
1201     append entity-header to existing header fields
1202     read entity-header
1203  }
1204  Content-Length := length
1205  Remove "chunked" from Transfer-Encoding
1206</artwork></figure>
1207<t>
1208   All HTTP/1.1 applications &MUST; be able to receive and decode the
1209   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1210   they do not understand.
1211</t>
1212</section>
1213</section>
1214
1215<section title="Product Tokens" anchor="product.tokens">
1216  <x:anchor-alias value="product"/>
1217  <x:anchor-alias value="product-version"/>
1218<t>
1219   Product tokens are used to allow communicating applications to
1220   identify themselves by software name and version. Most fields using
1221   product tokens also allow sub-products which form a significant part
1222   of the application to be listed, separated by whitespace. By
1223   convention, the products are listed in order of their significance
1224   for identifying the application.
1225</t>
1226<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1227  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1228  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1229</artwork></figure>
1230<t>
1231   Examples:
1232</t>
1233<figure><artwork type="example">
1234  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1235  Server: Apache/0.8.4
1236</artwork></figure>
1237<t>
1238   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1239   used for advertising or other non-essential information. Although any
1240   token character &MAY; appear in a product-version, this token &SHOULD;
1241   only be used for a version identifier (i.e., successive versions of
1242   the same product &SHOULD; only differ in the product-version portion of
1243   the product value).
1244</t>
1245</section>
1246
1247<section title="Quality Values" anchor="quality.values">
1248  <x:anchor-alias value="qvalue"/>
1249<t>
1250   Both transfer codings (TE request header, <xref target="header.te"/>)
1251   and content negotiation (&content.negotiation;) use short "floating point"
1252   numbers to indicate the relative importance ("weight") of various
1253   negotiable parameters.  A weight is normalized to a real number in
1254   the range 0 through 1, where 0 is the minimum and 1 the maximum
1255   value. If a parameter has a quality value of 0, then content with
1256   this parameter is `not acceptable' for the client. HTTP/1.1
1257   applications &MUST-NOT; generate more than three digits after the
1258   decimal point. User configuration of these values &SHOULD; also be
1259   limited in this fashion.
1260</t>
1261<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1262  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1263                 / ( "1" [ "." 0*3("0") ] )
1264</artwork></figure>
1265<x:note>
1266  <t>
1267     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1268     relative degradation in desired quality.
1269  </t>
1270</x:note>
1271</section>
1272
1273</section>
1274
1275<section title="HTTP Message" anchor="http.message">
1276
1277<section title="Message Types" anchor="message.types">
1278  <x:anchor-alias value="generic-message"/>
1279  <x:anchor-alias value="HTTP-message"/>
1280  <x:anchor-alias value="start-line"/>
1281<t>
1282   HTTP messages consist of requests from client to server and responses
1283   from server to client.
1284</t>
1285<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1286  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1287</artwork></figure>
1288<t>
1289   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1290   message format of <xref target="RFC5322"/> for transferring entities (the payload
1291   of the message). Both types of message consist of a start-line, zero
1292   or more header fields (also known as "headers"), an empty line (i.e.,
1293   a line with nothing preceding the CRLF) indicating the end of the
1294   header fields, and possibly a message-body.
1295</t>
1296<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1297  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1298                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1299                    <x:ref>CRLF</x:ref>
1300                    [ <x:ref>message-body</x:ref> ]
1301  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1302</artwork></figure>
1303<t>
1304   In the interest of robustness, servers &SHOULD; ignore any empty
1305   line(s) received where a Request-Line is expected. In other words, if
1306   the server is reading the protocol stream at the beginning of a
1307   message and receives a CRLF first, it should ignore the CRLF.
1308</t>
1309<t>
1310   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1311   after a POST request. To restate what is explicitly forbidden by the
1312   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1313   extra CRLF.
1314</t>
1315<t>
1316   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1317   header field. The presence of whitespace might be an attempt to trick a
1318   noncompliant implementation of HTTP into ignoring that field or processing
1319   the next line as a new request, either of which may result in security
1320   issues when implementations within the request chain interpret the
1321   same message differently. HTTP/1.1 servers &MUST; reject such a message
1322   with a 400 (Bad Request) response.
1323</t>
1324</section>
1325
1326<section title="Message Headers" anchor="message.headers">
1327  <x:anchor-alias value="field-content"/>
1328  <x:anchor-alias value="field-name"/>
1329  <x:anchor-alias value="field-value"/>
1330  <x:anchor-alias value="message-header"/>
1331<t>
1332   HTTP header fields follow the same general format as Internet messages in
1333   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1334   of a name followed by a colon (":"), optional whitespace, and the field
1335   value. Field names are case-insensitive.
1336</t>
1337<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"/>
1338  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1339  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1340  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1341  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1342</artwork></figure>
1343<t>
1344   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1345   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1346   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1347   header field-values use only a subset of the US-ASCII charset
1348   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1349   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1350   (obs-text) octets in field-content as opaque data.
1351</t>
1352<t>
1353   No whitespace is allowed between the header field-name and colon. For
1354   security reasons, any request message received containing such whitespace
1355   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1356   whitespace in a response message &MUST; be removed.
1357</t>
1358<t>
1359   The field value &MAY; be preceded by optional whitespace; a single SP is
1360   preferred. The field-value does not include any leading or trailing white
1361   space: OWS occurring before the first non-whitespace character of the
1362   field-value or after the last non-whitespace character of the field-value
1363   is ignored and &MAY; be removed without changing the meaning of the header
1364   field.
1365</t>
1366<t>
1367   Historically, HTTP header field values could be extended over multiple
1368   lines by preceding each extra line with at least one space or horizontal
1369   tab character (line folding). This specification deprecates such line
1370   folding except within the message/http media type
1371   (<xref target="internet.media.type.message.http"/>).
1372   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1373   (i.e., that contain any field-content that matches the obs-fold rule) unless
1374   the message is intended for packaging within the message/http media type.
1375   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1376   obs-fold whitespace with a single SP prior to interpreting the field value
1377   or forwarding the message downstream.
1378</t>
1379<t anchor="rule.comment">
1380  <x:anchor-alias value="comment"/>
1381  <x:anchor-alias value="ctext"/>
1382   Comments can be included in some HTTP header fields by surrounding
1383   the comment text with parentheses. Comments are only allowed in
1384   fields containing "comment" as part of their field value definition.
1385   In all other fields, parentheses are considered part of the field
1386   value.
1387</t>
1388<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1389  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1390  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1391                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1392</artwork></figure>
1393<t>
1394   The order in which header fields with differing field names are
1395   received is not significant. However, it is "good practice" to send
1396   general-header fields first, followed by request-header or response-header
1397   fields, and ending with the entity-header fields.
1398</t>
1399<t>
1400   Multiple message-header fields with the same field-name &MAY; be
1401   present in a message if and only if the entire field-value for that
1402   header field is defined as a comma-separated list [i.e., #(values)].
1403   It &MUST; be possible to combine the multiple header fields into one
1404   "field-name: field-value" pair, without changing the semantics of the
1405   message, by appending each subsequent field-value to the first, each
1406   separated by a comma. The order in which header fields with the same
1407   field-name are received is therefore significant to the
1408   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1409   change the order of these field values when a message is forwarded.
1410</t>
1411<x:note>
1412  <t>
1413   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1414   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1415   can occur multiple times, but does not use the list syntax, and thus cannot
1416   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1417   for details.) Also note that the Set-Cookie2 header specified in
1418   <xref target="RFC2965"/> does not share this problem.
1419  </t>
1420</x:note>
1421 
1422</section>
1423
1424<section title="Message Body" anchor="message.body">
1425  <x:anchor-alias value="message-body"/>
1426<t>
1427   The message-body (if any) of an HTTP message is used to carry the
1428   entity-body associated with the request or response. The message-body
1429   differs from the entity-body only when a transfer-coding has been
1430   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1431</t>
1432<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1433  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1434               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1435</artwork></figure>
1436<t>
1437   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1438   applied by an application to ensure safe and proper transfer of the
1439   message. Transfer-Encoding is a property of the message, not of the
1440   entity, and thus &MAY; be added or removed by any application along the
1441   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1442   when certain transfer-codings may be used.)
1443</t>
1444<t>
1445   The rules for when a message-body is allowed in a message differ for
1446   requests and responses.
1447</t>
1448<t>
1449   The presence of a message-body in a request is signaled by the
1450   inclusion of a Content-Length or Transfer-Encoding header field in
1451   the request's message-headers.
1452   When a request message contains both a message-body of non-zero
1453   length and a method that does not define any semantics for that
1454   request message-body, then an origin server &SHOULD; either ignore
1455   the message-body or respond with an appropriate error message
1456   (e.g., 413).  A proxy or gateway, when presented the same request,
1457   &SHOULD; either forward the request inbound with the message-body or
1458   ignore the message-body when determining a response.
1459</t>
1460<t>
1461   For response messages, whether or not a message-body is included with
1462   a message is dependent on both the request method and the response
1463   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1464   &MUST-NOT; include a message-body, even though the presence of entity-header
1465   fields might lead one to believe they do. All 1xx
1466   (informational), 204 (No Content), and 304 (Not Modified) responses
1467   &MUST-NOT; include a message-body. All other responses do include a
1468   message-body, although it &MAY; be of zero length.
1469</t>
1470</section>
1471
1472<section title="Message Length" anchor="message.length">
1473<t>
1474   The transfer-length of a message is the length of the message-body as
1475   it appears in the message; that is, after any transfer-codings have
1476   been applied. When a message-body is included with a message, the
1477   transfer-length of that body is determined by one of the following
1478   (in order of precedence):
1479</t>
1480<t>
1481  <list style="numbers">
1482    <x:lt><t>
1483     Any response message which "&MUST-NOT;" include a message-body (such
1484     as the 1xx, 204, and 304 responses and any response to a HEAD
1485     request) is always terminated by the first empty line after the
1486     header fields, regardless of the entity-header fields present in
1487     the message.
1488    </t></x:lt>
1489    <x:lt><t>
1490     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1491     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1492     is used, the transfer-length is defined by the use of this transfer-coding.
1493     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1494     is not present, the transfer-length is defined by the sender closing the connection.
1495    </t></x:lt>
1496    <x:lt><t>
1497     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1498     value in OCTETs represents both the entity-length and the
1499     transfer-length. The Content-Length header field &MUST-NOT; be sent
1500     if these two lengths are different (i.e., if a Transfer-Encoding
1501     header field is present). If a message is received with both a
1502     Transfer-Encoding header field and a Content-Length header field,
1503     the latter &MUST; be ignored.
1504    </t></x:lt>
1505    <x:lt><t>
1506     If the message uses the media type "multipart/byteranges", and the
1507     transfer-length is not otherwise specified, then this self-delimiting
1508     media type defines the transfer-length. This media type
1509     &MUST-NOT; be used unless the sender knows that the recipient can parse
1510     it; the presence in a request of a Range header with multiple byte-range
1511     specifiers from a 1.1 client implies that the client can parse
1512     multipart/byteranges responses.
1513    <list style="empty"><t>
1514       A range header might be forwarded by a 1.0 proxy that does not
1515       understand multipart/byteranges; in this case the server &MUST;
1516       delimit the message using methods defined in items 1, 3 or 5 of
1517       this section.
1518    </t></list>
1519    </t></x:lt>
1520    <x:lt><t>
1521     By the server closing the connection. (Closing the connection
1522     cannot be used to indicate the end of a request body, since that
1523     would leave no possibility for the server to send back a response.)
1524    </t></x:lt>
1525  </list>
1526</t>
1527<t>
1528   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1529   containing a message-body &MUST; include a valid Content-Length header
1530   field unless the server is known to be HTTP/1.1 compliant. If a
1531   request contains a message-body and a Content-Length is not given,
1532   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1533   determine the length of the message, or with 411 (Length Required) if
1534   it wishes to insist on receiving a valid Content-Length.
1535</t>
1536<t>
1537   All HTTP/1.1 applications that receive entities &MUST; accept the
1538   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1539   to be used for messages when the message length cannot be determined
1540   in advance.
1541</t>
1542<t>
1543   Messages &MUST-NOT; include both a Content-Length header field and a
1544   transfer-coding. If the message does include a
1545   transfer-coding, the Content-Length &MUST; be ignored.
1546</t>
1547<t>
1548   When a Content-Length is given in a message where a message-body is
1549   allowed, its field value &MUST; exactly match the number of OCTETs in
1550   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1551   invalid length is received and detected.
1552</t>
1553</section>
1554
1555<section title="General Header Fields" anchor="general.header.fields">
1556  <x:anchor-alias value="general-header"/>
1557<t>
1558   There are a few header fields which have general applicability for
1559   both request and response messages, but which do not apply to the
1560   entity being transferred. These header fields apply only to the
1561   message being transmitted.
1562</t>
1563<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1564  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1565                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1566                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1567                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1568                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1569                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1570                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1571                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1572                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1573</artwork></figure>
1574<t>
1575   General-header field names can be extended reliably only in
1576   combination with a change in the protocol version. However, new or
1577   experimental header fields may be given the semantics of general
1578   header fields if all parties in the communication recognize them to
1579   be general-header fields. Unrecognized header fields are treated as
1580   entity-header fields.
1581</t>
1582</section>
1583</section>
1584
1585<section title="Request" anchor="request">
1586  <x:anchor-alias value="Request"/>
1587<t>
1588   A request message from a client to a server includes, within the
1589   first line of that message, the method to be applied to the resource,
1590   the identifier of the resource, and the protocol version in use.
1591</t>
1592<!--                 Host                      ; should be moved here eventually -->
1593<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1594  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1595                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1596                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1597                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1598                  <x:ref>CRLF</x:ref>
1599                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1600</artwork></figure>
1601
1602<section title="Request-Line" anchor="request-line">
1603  <x:anchor-alias value="Request-Line"/>
1604<t>
1605   The Request-Line begins with a method token, followed by the
1606   request-target and the protocol version, and ending with CRLF. The
1607   elements are separated by SP characters. No CR or LF is allowed
1608   except in the final CRLF sequence.
1609</t>
1610<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1611  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1612</artwork></figure>
1613
1614<section title="Method" anchor="method">
1615  <x:anchor-alias value="Method"/>
1616<t>
1617   The Method  token indicates the method to be performed on the
1618   resource identified by the request-target. The method is case-sensitive.
1619</t>
1620<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1621  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1622</artwork></figure>
1623</section>
1624
1625<section title="request-target" anchor="request-target">
1626  <x:anchor-alias value="request-target"/>
1627<t>
1628   The request-target
1629   identifies the resource upon which to apply the request.
1630</t>
1631<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1632  <x:ref>request-target</x:ref> = "*"
1633                 / <x:ref>absolute-URI</x:ref>
1634                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1635                 / <x:ref>authority</x:ref>
1636</artwork></figure>
1637<t>
1638   The four options for request-target are dependent on the nature of the
1639   request. The asterisk "*" means that the request does not apply to a
1640   particular resource, but to the server itself, and is only allowed
1641   when the method used does not necessarily apply to a resource. One
1642   example would be
1643</t>
1644<figure><artwork type="example">
1645  OPTIONS * HTTP/1.1
1646</artwork></figure>
1647<t>
1648   The absolute-URI form is &REQUIRED; when the request is being made to a
1649   proxy. The proxy is requested to forward the request or service it
1650   from a valid cache, and return the response. Note that the proxy &MAY;
1651   forward the request on to another proxy or directly to the server
1652   specified by the absolute-URI. In order to avoid request loops, a
1653   proxy &MUST; be able to recognize all of its server names, including
1654   any aliases, local variations, and the numeric IP address. An example
1655   Request-Line would be:
1656</t>
1657<figure><artwork type="example">
1658  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1659</artwork></figure>
1660<t>
1661   To allow for transition to absolute-URIs in all requests in future
1662   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1663   form in requests, even though HTTP/1.1 clients will only generate
1664   them in requests to proxies.
1665</t>
1666<t>
1667   The authority form is only used by the CONNECT method (&CONNECT;).
1668</t>
1669<t>
1670   The most common form of request-target is that used to identify a
1671   resource on an origin server or gateway. In this case the absolute
1672   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1673   the request-target, and the network location of the URI (authority) &MUST;
1674   be transmitted in a Host header field. For example, a client wishing
1675   to retrieve the resource above directly from the origin server would
1676   create a TCP connection to port 80 of the host "www.example.org" and send
1677   the lines:
1678</t>
1679<figure><artwork type="example">
1680  GET /pub/WWW/TheProject.html HTTP/1.1
1681  Host: www.example.org
1682</artwork></figure>
1683<t>
1684   followed by the remainder of the Request. Note that the absolute path
1685   cannot be empty; if none is present in the original URI, it &MUST; be
1686   given as "/" (the server root).
1687</t>
1688<t>
1689   If a proxy receives a request without any path in the request-target and
1690   the method specified is capable of supporting the asterisk form of
1691   request-target, then the last proxy on the request chain &MUST; forward the
1692   request with "*" as the final request-target.
1693</t>
1694<figure><preamble>   
1695   For example, the request
1696</preamble><artwork type="example">
1697  OPTIONS http://www.example.org:8001 HTTP/1.1
1698</artwork></figure>
1699<figure><preamble>   
1700  would be forwarded by the proxy as
1701</preamble><artwork type="example">
1702  OPTIONS * HTTP/1.1
1703  Host: www.example.org:8001
1704</artwork>
1705<postamble>
1706   after connecting to port 8001 of host "www.example.org".
1707</postamble>
1708</figure>
1709<t>
1710   The request-target is transmitted in the format specified in
1711   <xref target="http.uri"/>. If the request-target is percent-encoded
1712   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1713   &MUST; decode the request-target in order to
1714   properly interpret the request. Servers &SHOULD; respond to invalid
1715   request-targets with an appropriate status code.
1716</t>
1717<t>
1718   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1719   received request-target when forwarding it to the next inbound server,
1720   except as noted above to replace a null path-absolute with "/".
1721</t>
1722<x:note>
1723  <t>
1724    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1725    meaning of the request when the origin server is improperly using
1726    a non-reserved URI character for a reserved purpose.  Implementors
1727    should be aware that some pre-HTTP/1.1 proxies have been known to
1728    rewrite the request-target.
1729  </t>
1730</x:note>
1731<t>
1732   HTTP does not place a pre-defined limit on the length of a request-target.
1733   A server &MUST; be prepared to receive URIs of unbounded length and
1734   respond with the 414 (URI Too Long) status if the received
1735   request-target would be longer than the server wishes to handle
1736   (see &status-414;).
1737</t>
1738<t>
1739   Various ad-hoc limitations on request-target length are found in practice.
1740   It is &RECOMMENDED; that all HTTP senders and recipients support
1741   request-target lengths of 8000 or more OCTETs.
1742</t>
1743</section>
1744</section>
1745
1746<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1747<t>
1748   The exact resource identified by an Internet request is determined by
1749   examining both the request-target and the Host header field.
1750</t>
1751<t>
1752   An origin server that does not allow resources to differ by the
1753   requested host &MAY; ignore the Host header field value when
1754   determining the resource identified by an HTTP/1.1 request. (But see
1755   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1756   for other requirements on Host support in HTTP/1.1.)
1757</t>
1758<t>
1759   An origin server that does differentiate resources based on the host
1760   requested (sometimes referred to as virtual hosts or vanity host
1761   names) &MUST; use the following rules for determining the requested
1762   resource on an HTTP/1.1 request:
1763  <list style="numbers">
1764    <t>If request-target is an absolute-URI, the host is part of the
1765     request-target. Any Host header field value in the request &MUST; be
1766     ignored.</t>
1767    <t>If the request-target is not an absolute-URI, and the request includes
1768     a Host header field, the host is determined by the Host header
1769     field value.</t>
1770    <t>If the host as determined by rule 1 or 2 is not a valid host on
1771     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1772  </list>
1773</t>
1774<t>
1775   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1776   attempt to use heuristics (e.g., examination of the URI path for
1777   something unique to a particular host) in order to determine what
1778   exact resource is being requested.
1779</t>
1780</section>
1781
1782</section>
1783
1784
1785<section title="Response" anchor="response">
1786  <x:anchor-alias value="Response"/>
1787<t>
1788   After receiving and interpreting a request message, a server responds
1789   with an HTTP response message.
1790</t>
1791<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1792  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1793                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1794                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1795                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1796                  <x:ref>CRLF</x:ref>
1797                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1798</artwork></figure>
1799
1800<section title="Status-Line" anchor="status-line">
1801  <x:anchor-alias value="Status-Line"/>
1802<t>
1803   The first line of a Response message is the Status-Line, consisting
1804   of the protocol version followed by a numeric status code and its
1805   associated textual phrase, with each element separated by SP
1806   characters. No CR or LF is allowed except in the final CRLF sequence.
1807</t>
1808<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1809  <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>
1810</artwork></figure>
1811
1812<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1813  <x:anchor-alias value="Reason-Phrase"/>
1814  <x:anchor-alias value="Status-Code"/>
1815<t>
1816   The Status-Code element is a 3-digit integer result code of the
1817   attempt to understand and satisfy the request. These codes are fully
1818   defined in &status-codes;.  The Reason Phrase exists for the sole
1819   purpose of providing a textual description associated with the numeric
1820   status code, out of deference to earlier Internet application protocols
1821   that were more frequently used with interactive text clients.
1822   A client &SHOULD; ignore the content of the Reason Phrase.
1823</t>
1824<t>
1825   The first digit of the Status-Code defines the class of response. The
1826   last two digits do not have any categorization role. There are 5
1827   values for the first digit:
1828  <list style="symbols">
1829    <t>
1830      1xx: Informational - Request received, continuing process
1831    </t>
1832    <t>
1833      2xx: Success - The action was successfully received,
1834        understood, and accepted
1835    </t>
1836    <t>
1837      3xx: Redirection - Further action must be taken in order to
1838        complete the request
1839    </t>
1840    <t>
1841      4xx: Client Error - The request contains bad syntax or cannot
1842        be fulfilled
1843    </t>
1844    <t>
1845      5xx: Server Error - The server failed to fulfill an apparently
1846        valid request
1847    </t>
1848  </list>
1849</t>
1850<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"/>
1851  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1852  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1853</artwork></figure>
1854</section>
1855</section>
1856
1857</section>
1858
1859
1860<section title="Connections" anchor="connections">
1861
1862<section title="Persistent Connections" anchor="persistent.connections">
1863
1864<section title="Purpose" anchor="persistent.purpose">
1865<t>
1866   Prior to persistent connections, a separate TCP connection was
1867   established to fetch each URL, increasing the load on HTTP servers
1868   and causing congestion on the Internet. The use of inline images and
1869   other associated data often require a client to make multiple
1870   requests of the same server in a short amount of time. Analysis of
1871   these performance problems and results from a prototype
1872   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1873   measurements of actual HTTP/1.1 implementations show good
1874   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1875   T/TCP <xref target="Tou1998"/>.
1876</t>
1877<t>
1878   Persistent HTTP connections have a number of advantages:
1879  <list style="symbols">
1880      <t>
1881        By opening and closing fewer TCP connections, CPU time is saved
1882        in routers and hosts (clients, servers, proxies, gateways,
1883        tunnels, or caches), and memory used for TCP protocol control
1884        blocks can be saved in hosts.
1885      </t>
1886      <t>
1887        HTTP requests and responses can be pipelined on a connection.
1888        Pipelining allows a client to make multiple requests without
1889        waiting for each response, allowing a single TCP connection to
1890        be used much more efficiently, with much lower elapsed time.
1891      </t>
1892      <t>
1893        Network congestion is reduced by reducing the number of packets
1894        caused by TCP opens, and by allowing TCP sufficient time to
1895        determine the congestion state of the network.
1896      </t>
1897      <t>
1898        Latency on subsequent requests is reduced since there is no time
1899        spent in TCP's connection opening handshake.
1900      </t>
1901      <t>
1902        HTTP can evolve more gracefully, since errors can be reported
1903        without the penalty of closing the TCP connection. Clients using
1904        future versions of HTTP might optimistically try a new feature,
1905        but if communicating with an older server, retry with old
1906        semantics after an error is reported.
1907      </t>
1908    </list>
1909</t>
1910<t>
1911   HTTP implementations &SHOULD; implement persistent connections.
1912</t>
1913</section>
1914
1915<section title="Overall Operation" anchor="persistent.overall">
1916<t>
1917   A significant difference between HTTP/1.1 and earlier versions of
1918   HTTP is that persistent connections are the default behavior of any
1919   HTTP connection. That is, unless otherwise indicated, the client
1920   &SHOULD; assume that the server will maintain a persistent connection,
1921   even after error responses from the server.
1922</t>
1923<t>
1924   Persistent connections provide a mechanism by which a client and a
1925   server can signal the close of a TCP connection. This signaling takes
1926   place using the Connection header field (<xref target="header.connection"/>). Once a close
1927   has been signaled, the client &MUST-NOT; send any more requests on that
1928   connection.
1929</t>
1930
1931<section title="Negotiation" anchor="persistent.negotiation">
1932<t>
1933   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1934   maintain a persistent connection unless a Connection header including
1935   the connection-token "close" was sent in the request. If the server
1936   chooses to close the connection immediately after sending the
1937   response, it &SHOULD; send a Connection header including the
1938   connection-token close.
1939</t>
1940<t>
1941   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1942   decide to keep it open based on whether the response from a server
1943   contains a Connection header with the connection-token close. In case
1944   the client does not want to maintain a connection for more than that
1945   request, it &SHOULD; send a Connection header including the
1946   connection-token close.
1947</t>
1948<t>
1949   If either the client or the server sends the close token in the
1950   Connection header, that request becomes the last one for the
1951   connection.
1952</t>
1953<t>
1954   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1955   maintained for HTTP versions less than 1.1 unless it is explicitly
1956   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1957   compatibility with HTTP/1.0 clients.
1958</t>
1959<t>
1960   In order to remain persistent, all messages on the connection &MUST;
1961   have a self-defined message length (i.e., one not defined by closure
1962   of the connection), as described in <xref target="message.length"/>.
1963</t>
1964</section>
1965
1966<section title="Pipelining" anchor="pipelining">
1967<t>
1968   A client that supports persistent connections &MAY; "pipeline" its
1969   requests (i.e., send multiple requests without waiting for each
1970   response). A server &MUST; send its responses to those requests in the
1971   same order that the requests were received.
1972</t>
1973<t>
1974   Clients which assume persistent connections and pipeline immediately
1975   after connection establishment &SHOULD; be prepared to retry their
1976   connection if the first pipelined attempt fails. If a client does
1977   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1978   persistent. Clients &MUST; also be prepared to resend their requests if
1979   the server closes the connection before sending all of the
1980   corresponding responses.
1981</t>
1982<t>
1983   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1984   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1985   premature termination of the transport connection could lead to
1986   indeterminate results. A client wishing to send a non-idempotent
1987   request &SHOULD; wait to send that request until it has received the
1988   response status for the previous request.
1989</t>
1990</section>
1991</section>
1992
1993<section title="Proxy Servers" anchor="persistent.proxy">
1994<t>
1995   It is especially important that proxies correctly implement the
1996   properties of the Connection header field as specified in <xref target="header.connection"/>.
1997</t>
1998<t>
1999   The proxy server &MUST; signal persistent connections separately with
2000   its clients and the origin servers (or other proxy servers) that it
2001   connects to. Each persistent connection applies to only one transport
2002   link.
2003</t>
2004<t>
2005   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2006   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2007   for information and discussion of the problems with the Keep-Alive header
2008   implemented by many HTTP/1.0 clients).
2009</t>
2010</section>
2011
2012<section title="Practical Considerations" anchor="persistent.practical">
2013<t>
2014   Servers will usually have some time-out value beyond which they will
2015   no longer maintain an inactive connection. Proxy servers might make
2016   this a higher value since it is likely that the client will be making
2017   more connections through the same server. The use of persistent
2018   connections places no requirements on the length (or existence) of
2019   this time-out for either the client or the server.
2020</t>
2021<t>
2022   When a client or server wishes to time-out it &SHOULD; issue a graceful
2023   close on the transport connection. Clients and servers &SHOULD; both
2024   constantly watch for the other side of the transport close, and
2025   respond to it as appropriate. If a client or server does not detect
2026   the other side's close promptly it could cause unnecessary resource
2027   drain on the network.
2028</t>
2029<t>
2030   A client, server, or proxy &MAY; close the transport connection at any
2031   time. For example, a client might have started to send a new request
2032   at the same time that the server has decided to close the "idle"
2033   connection. From the server's point of view, the connection is being
2034   closed while it was idle, but from the client's point of view, a
2035   request is in progress.
2036</t>
2037<t>
2038   This means that clients, servers, and proxies &MUST; be able to recover
2039   from asynchronous close events. Client software &SHOULD; reopen the
2040   transport connection and retransmit the aborted sequence of requests
2041   without user interaction so long as the request sequence is
2042   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2043   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2044   human operator the choice of retrying the request(s). Confirmation by
2045   user-agent software with semantic understanding of the application
2046   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2047   be repeated if the second sequence of requests fails.
2048</t>
2049<t>
2050   Servers &SHOULD; always respond to at least one request per connection,
2051   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2052   middle of transmitting a response, unless a network or client failure
2053   is suspected.
2054</t>
2055<t>
2056   Clients that use persistent connections &SHOULD; limit the number of
2057   simultaneous connections that they maintain to a given server. A
2058   single-user client &SHOULD-NOT; maintain more than 2 connections with
2059   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
2060   another server or proxy, where N is the number of simultaneously
2061   active users. These guidelines are intended to improve HTTP response
2062   times and avoid congestion.
2063</t>
2064</section>
2065</section>
2066
2067<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2068
2069<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2070<t>
2071   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2072   flow control mechanisms to resolve temporary overloads, rather than
2073   terminating connections with the expectation that clients will retry.
2074   The latter technique can exacerbate network congestion.
2075</t>
2076</section>
2077
2078<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2079<t>
2080   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2081   the network connection for an error status while it is transmitting
2082   the request. If the client sees an error status, it &SHOULD;
2083   immediately cease transmitting the body. If the body is being sent
2084   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2085   empty trailer &MAY; be used to prematurely mark the end of the message.
2086   If the body was preceded by a Content-Length header, the client &MUST;
2087   close the connection.
2088</t>
2089</section>
2090
2091<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2092<t>
2093   The purpose of the 100 (Continue) status (see &status-100;) is to
2094   allow a client that is sending a request message with a request body
2095   to determine if the origin server is willing to accept the request
2096   (based on the request headers) before the client sends the request
2097   body. In some cases, it might either be inappropriate or highly
2098   inefficient for the client to send the body if the server will reject
2099   the message without looking at the body.
2100</t>
2101<t>
2102   Requirements for HTTP/1.1 clients:
2103  <list style="symbols">
2104    <t>
2105        If a client will wait for a 100 (Continue) response before
2106        sending the request body, it &MUST; send an Expect request-header
2107        field (&header-expect;) with the "100-continue" expectation.
2108    </t>
2109    <t>
2110        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2111        with the "100-continue" expectation if it does not intend
2112        to send a request body.
2113    </t>
2114  </list>
2115</t>
2116<t>
2117   Because of the presence of older implementations, the protocol allows
2118   ambiguous situations in which a client may send "Expect: 100-continue"
2119   without receiving either a 417 (Expectation Failed) status
2120   or a 100 (Continue) status. Therefore, when a client sends this
2121   header field to an origin server (possibly via a proxy) from which it
2122   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2123   for an indefinite period before sending the request body.
2124</t>
2125<t>
2126   Requirements for HTTP/1.1 origin servers:
2127  <list style="symbols">
2128    <t> Upon receiving a request which includes an Expect request-header
2129        field with the "100-continue" expectation, an origin server &MUST;
2130        either respond with 100 (Continue) status and continue to read
2131        from the input stream, or respond with a final status code. The
2132        origin server &MUST-NOT; wait for the request body before sending
2133        the 100 (Continue) response. If it responds with a final status
2134        code, it &MAY; close the transport connection or it &MAY; continue
2135        to read and discard the rest of the request.  It &MUST-NOT;
2136        perform the requested method if it returns a final status code.
2137    </t>
2138    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2139        the request message does not include an Expect request-header
2140        field with the "100-continue" expectation, and &MUST-NOT; send a
2141        100 (Continue) response if such a request comes from an HTTP/1.0
2142        (or earlier) client. There is an exception to this rule: for
2143        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2144        status in response to an HTTP/1.1 PUT or POST request that does
2145        not include an Expect request-header field with the "100-continue"
2146        expectation. This exception, the purpose of which is
2147        to minimize any client processing delays associated with an
2148        undeclared wait for 100 (Continue) status, applies only to
2149        HTTP/1.1 requests, and not to requests with any other HTTP-version
2150        value.
2151    </t>
2152    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2153        already received some or all of the request body for the
2154        corresponding request.
2155    </t>
2156    <t> An origin server that sends a 100 (Continue) response &MUST;
2157    ultimately send a final status code, once the request body is
2158        received and processed, unless it terminates the transport
2159        connection prematurely.
2160    </t>
2161    <t> If an origin server receives a request that does not include an
2162        Expect request-header field with the "100-continue" expectation,
2163        the request includes a request body, and the server responds
2164        with a final status code before reading the entire request body
2165        from the transport connection, then the server &SHOULD-NOT;  close
2166        the transport connection until it has read the entire request,
2167        or until the client closes the connection. Otherwise, the client
2168        might not reliably receive the response message. However, this
2169        requirement is not be construed as preventing a server from
2170        defending itself against denial-of-service attacks, or from
2171        badly broken client implementations.
2172      </t>
2173    </list>
2174</t>
2175<t>
2176   Requirements for HTTP/1.1 proxies:
2177  <list style="symbols">
2178    <t> If a proxy receives a request that includes an Expect request-header
2179        field with the "100-continue" expectation, and the proxy
2180        either knows that the next-hop server complies with HTTP/1.1 or
2181        higher, or does not know the HTTP version of the next-hop
2182        server, it &MUST; forward the request, including the Expect header
2183        field.
2184    </t>
2185    <t> If the proxy knows that the version of the next-hop server is
2186        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2187        respond with a 417 (Expectation Failed) status.
2188    </t>
2189    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2190        numbers received from recently-referenced next-hop servers.
2191    </t>
2192    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2193        request message was received from an HTTP/1.0 (or earlier)
2194        client and did not include an Expect request-header field with
2195        the "100-continue" expectation. This requirement overrides the
2196        general rule for forwarding of 1xx responses (see &status-1xx;).
2197    </t>
2198  </list>
2199</t>
2200</section>
2201
2202<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2203<t>
2204   If an HTTP/1.1 client sends a request which includes a request body,
2205   but which does not include an Expect request-header field with the
2206   "100-continue" expectation, and if the client is not directly
2207   connected to an HTTP/1.1 origin server, and if the client sees the
2208   connection close before receiving any status from the server, the
2209   client &SHOULD; retry the request.  If the client does retry this
2210   request, it &MAY; use the following "binary exponential backoff"
2211   algorithm to be assured of obtaining a reliable response:
2212  <list style="numbers">
2213    <t>
2214      Initiate a new connection to the server
2215    </t>
2216    <t>
2217      Transmit the request-headers
2218    </t>
2219    <t>
2220      Initialize a variable R to the estimated round-trip time to the
2221         server (e.g., based on the time it took to establish the
2222         connection), or to a constant value of 5 seconds if the round-trip
2223         time is not available.
2224    </t>
2225    <t>
2226       Compute T = R * (2**N), where N is the number of previous
2227         retries of this request.
2228    </t>
2229    <t>
2230       Wait either for an error response from the server, or for T
2231         seconds (whichever comes first)
2232    </t>
2233    <t>
2234       If no error response is received, after T seconds transmit the
2235         body of the request.
2236    </t>
2237    <t>
2238       If client sees that the connection is closed prematurely,
2239         repeat from step 1 until the request is accepted, an error
2240         response is received, or the user becomes impatient and
2241         terminates the retry process.
2242    </t>
2243  </list>
2244</t>
2245<t>
2246   If at any point an error status is received, the client
2247  <list style="symbols">
2248      <t>&SHOULD-NOT;  continue and</t>
2249
2250      <t>&SHOULD; close the connection if it has not completed sending the
2251        request message.</t>
2252    </list>
2253</t>
2254</section>
2255</section>
2256</section>
2257
2258
2259<section title="Header Field Definitions" anchor="header.fields">
2260<t>
2261   This section defines the syntax and semantics of HTTP/1.1 header fields
2262   related to message framing and transport protocols.
2263</t>
2264<t>
2265   For entity-header fields, both sender and recipient refer to either the
2266   client or the server, depending on who sends and who receives the entity.
2267</t>
2268
2269<section title="Connection" anchor="header.connection">
2270  <iref primary="true" item="Connection header" x:for-anchor=""/>
2271  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2272  <x:anchor-alias value="Connection"/>
2273  <x:anchor-alias value="connection-token"/>
2274  <x:anchor-alias value="Connection-v"/>
2275<t>
2276   The general-header field "Connection" allows the sender to specify
2277   options that are desired for that particular connection and &MUST-NOT;
2278   be communicated by proxies over further connections.
2279</t>
2280<t>
2281   The Connection header's value has the following grammar:
2282</t>
2283<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2284  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2285  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2286  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2287</artwork></figure>
2288<t>
2289   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2290   message is forwarded and, for each connection-token in this field,
2291   remove any header field(s) from the message with the same name as the
2292   connection-token. Connection options are signaled by the presence of
2293   a connection-token in the Connection header field, not by any
2294   corresponding additional header field(s), since the additional header
2295   field may not be sent if there are no parameters associated with that
2296   connection option.
2297</t>
2298<t>
2299   Message headers listed in the Connection header &MUST-NOT; include
2300   end-to-end headers, such as Cache-Control.
2301</t>
2302<t>
2303   HTTP/1.1 defines the "close" connection option for the sender to
2304   signal that the connection will be closed after completion of the
2305   response. For example,
2306</t>
2307<figure><artwork type="example">
2308  Connection: close
2309</artwork></figure>
2310<t>
2311   in either the request or the response header fields indicates that
2312   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2313   after the current request/response is complete.
2314</t>
2315<t>
2316   An HTTP/1.1 client that does not support persistent connections &MUST;
2317   include the "close" connection option in every request message.
2318</t>
2319<t>
2320   An HTTP/1.1 server that does not support persistent connections &MUST;
2321   include the "close" connection option in every response message that
2322   does not have a 1xx (informational) status code.
2323</t>
2324<t>
2325   A system receiving an HTTP/1.0 (or lower-version) message that
2326   includes a Connection header &MUST;, for each connection-token in this
2327   field, remove and ignore any header field(s) from the message with
2328   the same name as the connection-token. This protects against mistaken
2329   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2330</t>
2331</section>
2332
2333<section title="Content-Length" anchor="header.content-length">
2334  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2335  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2336  <x:anchor-alias value="Content-Length"/>
2337  <x:anchor-alias value="Content-Length-v"/>
2338<t>
2339   The entity-header field "Content-Length" indicates the size of the
2340   entity-body, in number of OCTETs, sent to the recipient or,
2341   in the case of the HEAD method, the size of the entity-body that
2342   would have been sent had the request been a GET.
2343</t>
2344<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2345  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2346  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2347</artwork></figure>
2348<t>
2349   An example is
2350</t>
2351<figure><artwork type="example">
2352  Content-Length: 3495
2353</artwork></figure>
2354<t>
2355   Applications &SHOULD; use this field to indicate the transfer-length of
2356   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2357</t>
2358<t>
2359   Any Content-Length greater than or equal to zero is a valid value.
2360   <xref target="message.length"/> describes how to determine the length of a message-body
2361   if a Content-Length is not given.
2362</t>
2363<t>
2364   Note that the meaning of this field is significantly different from
2365   the corresponding definition in MIME, where it is an optional field
2366   used within the "message/external-body" content-type. In HTTP, it
2367   &SHOULD; be sent whenever the message's length can be determined prior
2368   to being transferred, unless this is prohibited by the rules in
2369   <xref target="message.length"/>.
2370</t>
2371</section>
2372
2373<section title="Date" anchor="header.date">
2374  <iref primary="true" item="Date header" x:for-anchor=""/>
2375  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2376  <x:anchor-alias value="Date"/>
2377  <x:anchor-alias value="Date-v"/>
2378<t>
2379   The general-header field "Date" represents the date and time at which
2380   the message was originated, having the same semantics as orig-date in
2381   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2382   HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2383   it &MUST; be sent in rfc1123-date format.
2384</t>
2385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2386  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2387  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2388</artwork></figure>
2389<t>
2390   An example is
2391</t>
2392<figure><artwork type="example">
2393  Date: Tue, 15 Nov 1994 08:12:31 GMT
2394</artwork></figure>
2395<t>
2396   Origin servers &MUST; include a Date header field in all responses,
2397   except in these cases:
2398  <list style="numbers">
2399      <t>If the response status code is 100 (Continue) or 101 (Switching
2400         Protocols), the response &MAY; include a Date header field, at
2401         the server's option.</t>
2402
2403      <t>If the response status code conveys a server error, e.g. 500
2404         (Internal Server Error) or 503 (Service Unavailable), and it is
2405         inconvenient or impossible to generate a valid Date.</t>
2406
2407      <t>If the server does not have a clock that can provide a
2408         reasonable approximation of the current time, its responses
2409         &MUST-NOT; include a Date header field. In this case, the rules
2410         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2411  </list>
2412</t>
2413<t>
2414   A received message that does not have a Date header field &MUST; be
2415   assigned one by the recipient if the message will be cached by that
2416   recipient or gatewayed via a protocol which requires a Date. An HTTP
2417   implementation without a clock &MUST-NOT; cache responses without
2418   revalidating them on every use. An HTTP cache, especially a shared
2419   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2420   clock with a reliable external standard.
2421</t>
2422<t>
2423   Clients &SHOULD; only send a Date header field in messages that include
2424   an entity-body, as in the case of the PUT and POST requests, and even
2425   then it is optional. A client without a clock &MUST-NOT; send a Date
2426   header field in a request.
2427</t>
2428<t>
2429   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2430   time subsequent to the generation of the message. It &SHOULD; represent
2431   the best available approximation of the date and time of message
2432   generation, unless the implementation has no means of generating a
2433   reasonably accurate date and time. In theory, the date ought to
2434   represent the moment just before the entity is generated. In
2435   practice, the date can be generated at any time during the message
2436   origination without affecting its semantic value.
2437</t>
2438
2439<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2440<t>
2441   Some origin server implementations might not have a clock available.
2442   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2443   values to a response, unless these values were associated
2444   with the resource by a system or user with a reliable clock. It &MAY;
2445   assign an Expires value that is known, at or before server
2446   configuration time, to be in the past (this allows "pre-expiration"
2447   of responses without storing separate Expires values for each
2448   resource).
2449</t>
2450</section>
2451</section>
2452
2453<section title="Host" anchor="header.host">
2454  <iref primary="true" item="Host header" x:for-anchor=""/>
2455  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2456  <x:anchor-alias value="Host"/>
2457  <x:anchor-alias value="Host-v"/>
2458<t>
2459   The request-header field "Host" specifies the Internet host and port
2460   number of the resource being requested, as obtained from the original
2461   URI given by the user or referring resource (generally an http URI,
2462   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2463   the naming authority of the origin server or gateway given by the
2464   original URL. This allows the origin server or gateway to
2465   differentiate between internally-ambiguous URLs, such as the root "/"
2466   URL of a server for multiple host names on a single IP address.
2467</t>
2468<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2469  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2470  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2471</artwork></figure>
2472<t>
2473   A "host" without any trailing port information implies the default
2474   port for the service requested (e.g., "80" for an HTTP URL). For
2475   example, a request on the origin server for
2476   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2477</t>
2478<figure><artwork type="example">
2479  GET /pub/WWW/ HTTP/1.1
2480  Host: www.example.org
2481</artwork></figure>
2482<t>
2483   A client &MUST; include a Host header field in all HTTP/1.1 request
2484   messages. If the requested URI does not include an Internet host
2485   name for the service being requested, then the Host header field &MUST;
2486   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2487   request message it forwards does contain an appropriate Host header
2488   field that identifies the service being requested by the proxy. All
2489   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2490   status code to any HTTP/1.1 request message which lacks a Host header
2491   field.
2492</t>
2493<t>
2494   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2495   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2496   for other requirements relating to Host.
2497</t>
2498</section>
2499
2500<section title="TE" anchor="header.te">
2501  <iref primary="true" item="TE header" x:for-anchor=""/>
2502  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2503  <x:anchor-alias value="TE"/>
2504  <x:anchor-alias value="TE-v"/>
2505  <x:anchor-alias value="t-codings"/>
2506  <x:anchor-alias value="te-params"/>
2507  <x:anchor-alias value="te-ext"/>
2508<t>
2509   The request-header field "TE" indicates what extension transfer-codings
2510   it is willing to accept in the response and whether or not it is
2511   willing to accept trailer fields in a chunked transfer-coding. Its
2512   value may consist of the keyword "trailers" and/or a comma-separated
2513   list of extension transfer-coding names with optional accept
2514   parameters (as described in <xref target="transfer.codings"/>).
2515</t>
2516<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2517  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2518  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2519  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2520  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2521  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2522</artwork></figure>
2523<t>
2524   The presence of the keyword "trailers" indicates that the client is
2525   willing to accept trailer fields in a chunked transfer-coding, as
2526   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2527   transfer-coding values even though it does not itself represent a
2528   transfer-coding.
2529</t>
2530<t>
2531   Examples of its use are:
2532</t>
2533<figure><artwork type="example">
2534  TE: deflate
2535  TE:
2536  TE: trailers, deflate;q=0.5
2537</artwork></figure>
2538<t>
2539   The TE header field only applies to the immediate connection.
2540   Therefore, the keyword &MUST; be supplied within a Connection header
2541   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2542</t>
2543<t>
2544   A server tests whether a transfer-coding is acceptable, according to
2545   a TE field, using these rules:
2546  <list style="numbers">
2547    <x:lt>
2548      <t>The "chunked" transfer-coding is always acceptable. If the
2549         keyword "trailers" is listed, the client indicates that it is
2550         willing to accept trailer fields in the chunked response on
2551         behalf of itself and any downstream clients. The implication is
2552         that, if given, the client is stating that either all
2553         downstream clients are willing to accept trailer fields in the
2554         forwarded response, or that it will attempt to buffer the
2555         response on behalf of downstream recipients.
2556      </t><t>
2557         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2558         chunked response such that a client can be assured of buffering
2559         the entire response.</t>
2560    </x:lt>
2561    <x:lt>
2562      <t>If the transfer-coding being tested is one of the transfer-codings
2563         listed in the TE field, then it is acceptable unless it
2564         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2565         qvalue of 0 means "not acceptable.")</t>
2566    </x:lt>
2567    <x:lt>
2568      <t>If multiple transfer-codings are acceptable, then the
2569         acceptable transfer-coding with the highest non-zero qvalue is
2570         preferred.  The "chunked" transfer-coding always has a qvalue
2571         of 1.</t>
2572    </x:lt>
2573  </list>
2574</t>
2575<t>
2576   If the TE field-value is empty or if no TE field is present, the only
2577   transfer-coding is "chunked". A message with no transfer-coding is
2578   always acceptable.
2579</t>
2580</section>
2581
2582<section title="Trailer" anchor="header.trailer">
2583  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2584  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2585  <x:anchor-alias value="Trailer"/>
2586  <x:anchor-alias value="Trailer-v"/>
2587<t>
2588   The general field "Trailer" indicates that the given set of
2589   header fields is present in the trailer of a message encoded with
2590   chunked transfer-coding.
2591</t>
2592<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2593  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2594  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2595</artwork></figure>
2596<t>
2597   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2598   message using chunked transfer-coding with a non-empty trailer. Doing
2599   so allows the recipient to know which header fields to expect in the
2600   trailer.
2601</t>
2602<t>
2603   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2604   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2605   trailer fields in a "chunked" transfer-coding.
2606</t>
2607<t>
2608   Message header fields listed in the Trailer header field &MUST-NOT;
2609   include the following header fields:
2610  <list style="symbols">
2611    <t>Transfer-Encoding</t>
2612    <t>Content-Length</t>
2613    <t>Trailer</t>
2614  </list>
2615</t>
2616</section>
2617
2618<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2619  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2620  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2621  <x:anchor-alias value="Transfer-Encoding"/>
2622  <x:anchor-alias value="Transfer-Encoding-v"/>
2623<t>
2624   The general-header "Transfer-Encoding" field indicates what (if any)
2625   type of transformation has been applied to the message body in order
2626   to safely transfer it between the sender and the recipient. This
2627   differs from the content-coding in that the transfer-coding is a
2628   property of the message, not of the entity.
2629</t>
2630<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2631  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2632                        <x:ref>Transfer-Encoding-v</x:ref>
2633  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2634</artwork></figure>
2635<t>
2636   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2637</t>
2638<figure><artwork type="example">
2639  Transfer-Encoding: chunked
2640</artwork></figure>
2641<t>
2642   If multiple encodings have been applied to an entity, the transfer-codings
2643   &MUST; be listed in the order in which they were applied.
2644   Additional information about the encoding parameters &MAY; be provided
2645   by other entity-header fields not defined by this specification.
2646</t>
2647<t>
2648   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2649   header.
2650</t>
2651</section>
2652
2653<section title="Upgrade" anchor="header.upgrade">
2654  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2655  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2656  <x:anchor-alias value="Upgrade"/>
2657  <x:anchor-alias value="Upgrade-v"/>
2658<t>
2659   The general-header "Upgrade" allows the client to specify what
2660   additional communication protocols it supports and would like to use
2661   if the server finds it appropriate to switch protocols. The server
2662   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2663   response to indicate which protocol(s) are being switched.
2664</t>
2665<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2666  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2667  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2668</artwork></figure>
2669<t>
2670   For example,
2671</t>
2672<figure><artwork type="example">
2673  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2674</artwork></figure>
2675<t>
2676   The Upgrade header field is intended to provide a simple mechanism
2677   for transition from HTTP/1.1 to some other, incompatible protocol. It
2678   does so by allowing the client to advertise its desire to use another
2679   protocol, such as a later version of HTTP with a higher major version
2680   number, even though the current request has been made using HTTP/1.1.
2681   This eases the difficult transition between incompatible protocols by
2682   allowing the client to initiate a request in the more commonly
2683   supported protocol while indicating to the server that it would like
2684   to use a "better" protocol if available (where "better" is determined
2685   by the server, possibly according to the nature of the method and/or
2686   resource being requested).
2687</t>
2688<t>
2689   The Upgrade header field only applies to switching application-layer
2690   protocols upon the existing transport-layer connection. Upgrade
2691   cannot be used to insist on a protocol change; its acceptance and use
2692   by the server is optional. The capabilities and nature of the
2693   application-layer communication after the protocol change is entirely
2694   dependent upon the new protocol chosen, although the first action
2695   after changing the protocol &MUST; be a response to the initial HTTP
2696   request containing the Upgrade header field.
2697</t>
2698<t>
2699   The Upgrade header field only applies to the immediate connection.
2700   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2701   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2702   HTTP/1.1 message.
2703</t>
2704<t>
2705   The Upgrade header field cannot be used to indicate a switch to a
2706   protocol on a different connection. For that purpose, it is more
2707   appropriate to use a 301, 302, 303, or 305 redirection response.
2708</t>
2709<t>
2710   This specification only defines the protocol name "HTTP" for use by
2711   the family of Hypertext Transfer Protocols, as defined by the HTTP
2712   version rules of <xref target="http.version"/> and future updates to this
2713   specification. Any token can be used as a protocol name; however, it
2714   will only be useful if both the client and server associate the name
2715   with the same protocol.
2716</t>
2717</section>
2718
2719<section title="Via" anchor="header.via">
2720  <iref primary="true" item="Via header" x:for-anchor=""/>
2721  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2722  <x:anchor-alias value="protocol-name"/>
2723  <x:anchor-alias value="protocol-version"/>
2724  <x:anchor-alias value="pseudonym"/>
2725  <x:anchor-alias value="received-by"/>
2726  <x:anchor-alias value="received-protocol"/>
2727  <x:anchor-alias value="Via"/>
2728  <x:anchor-alias value="Via-v"/>
2729<t>
2730   The general-header field "Via" &MUST; be used by gateways and proxies to
2731   indicate the intermediate protocols and recipients between the user
2732   agent and the server on requests, and between the origin server and
2733   the client on responses. It is analogous to the "Received" field defined in
2734   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2735   avoiding request loops, and identifying the protocol capabilities of
2736   all senders along the request/response chain.
2737</t>
2738<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
2739  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2740  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2741                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2742  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2743  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2744  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2745  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2746  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2747</artwork></figure>
2748<t>
2749   The received-protocol indicates the protocol version of the message
2750   received by the server or client along each segment of the
2751   request/response chain. The received-protocol version is appended to
2752   the Via field value when the message is forwarded so that information
2753   about the protocol capabilities of upstream applications remains
2754   visible to all recipients.
2755</t>
2756<t>
2757   The protocol-name is optional if and only if it would be "HTTP". The
2758   received-by field is normally the host and optional port number of a
2759   recipient server or client that subsequently forwarded the message.
2760   However, if the real host is considered to be sensitive information,
2761   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2762   be assumed to be the default port of the received-protocol.
2763</t>
2764<t>
2765   Multiple Via field values represents each proxy or gateway that has
2766   forwarded the message. Each recipient &MUST; append its information
2767   such that the end result is ordered according to the sequence of
2768   forwarding applications.
2769</t>
2770<t>
2771   Comments &MAY; be used in the Via header field to identify the software
2772   of the recipient proxy or gateway, analogous to the User-Agent and
2773   Server header fields. However, all comments in the Via field are
2774   optional and &MAY; be removed by any recipient prior to forwarding the
2775   message.
2776</t>
2777<t>
2778   For example, a request message could be sent from an HTTP/1.0 user
2779   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2780   forward the request to a public proxy at p.example.net, which completes
2781   the request by forwarding it to the origin server at www.example.com.
2782   The request received by www.example.com would then have the following
2783   Via header field:
2784</t>
2785<figure><artwork type="example">
2786  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2787</artwork></figure>
2788<t>
2789   Proxies and gateways used as a portal through a network firewall
2790   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2791   the firewall region. This information &SHOULD; only be propagated if
2792   explicitly enabled. If not enabled, the received-by host of any host
2793   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2794   for that host.
2795</t>
2796<t>
2797   For organizations that have strong privacy requirements for hiding
2798   internal structures, a proxy &MAY; combine an ordered subsequence of
2799   Via header field entries with identical received-protocol values into
2800   a single such entry. For example,
2801</t>
2802<figure><artwork type="example">
2803  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2804</artwork></figure>
2805<t>
2806        could be collapsed to
2807</t>
2808<figure><artwork type="example">
2809  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2810</artwork></figure>
2811<t>
2812   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2813   under the same organizational control and the hosts have already been
2814   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2815   have different received-protocol values.
2816</t>
2817</section>
2818
2819</section>
2820
2821<section title="IANA Considerations" anchor="IANA.considerations">
2822<section title="Message Header Registration" anchor="message.header.registration">
2823<t>
2824   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2825   with the permanent registrations below (see <xref target="RFC3864"/>):
2826</t>
2827<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2828<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2829   <ttcol>Header Field Name</ttcol>
2830   <ttcol>Protocol</ttcol>
2831   <ttcol>Status</ttcol>
2832   <ttcol>Reference</ttcol>
2833
2834   <c>Connection</c>
2835   <c>http</c>
2836   <c>standard</c>
2837   <c>
2838      <xref target="header.connection"/>
2839   </c>
2840   <c>Content-Length</c>
2841   <c>http</c>
2842   <c>standard</c>
2843   <c>
2844      <xref target="header.content-length"/>
2845   </c>
2846   <c>Date</c>
2847   <c>http</c>
2848   <c>standard</c>
2849   <c>
2850      <xref target="header.date"/>
2851   </c>
2852   <c>Host</c>
2853   <c>http</c>
2854   <c>standard</c>
2855   <c>
2856      <xref target="header.host"/>
2857   </c>
2858   <c>TE</c>
2859   <c>http</c>
2860   <c>standard</c>
2861   <c>
2862      <xref target="header.te"/>
2863   </c>
2864   <c>Trailer</c>
2865   <c>http</c>
2866   <c>standard</c>
2867   <c>
2868      <xref target="header.trailer"/>
2869   </c>
2870   <c>Transfer-Encoding</c>
2871   <c>http</c>
2872   <c>standard</c>
2873   <c>
2874      <xref target="header.transfer-encoding"/>
2875   </c>
2876   <c>Upgrade</c>
2877   <c>http</c>
2878   <c>standard</c>
2879   <c>
2880      <xref target="header.upgrade"/>
2881   </c>
2882   <c>Via</c>
2883   <c>http</c>
2884   <c>standard</c>
2885   <c>
2886      <xref target="header.via"/>
2887   </c>
2888</texttable>
2889<!--(END)-->
2890<t>
2891   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2892</t>
2893</section>
2894
2895<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2896<t>
2897   The entry for the "http" URI Scheme in the registry located at
2898   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2899   should be updated to point to <xref target="http.uri"/> of this document
2900   (see <xref target="RFC4395"/>).
2901</t>
2902</section>
2903
2904<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2905<t>
2906   This document serves as the specification for the Internet media types
2907   "message/http" and "application/http". The following is to be registered with
2908   IANA (see <xref target="RFC4288"/>).
2909</t>
2910<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2911<iref item="Media Type" subitem="message/http" primary="true"/>
2912<iref item="message/http Media Type" primary="true"/>
2913<t>
2914   The message/http type can be used to enclose a single HTTP request or
2915   response message, provided that it obeys the MIME restrictions for all
2916   "message" types regarding line length and encodings.
2917</t>
2918<t>
2919  <list style="hanging" x:indent="12em">
2920    <t hangText="Type name:">
2921      message
2922    </t>
2923    <t hangText="Subtype name:">
2924      http
2925    </t>
2926    <t hangText="Required parameters:">
2927      none
2928    </t>
2929    <t hangText="Optional parameters:">
2930      version, msgtype
2931      <list style="hanging">
2932        <t hangText="version:">
2933          The HTTP-Version number of the enclosed message
2934          (e.g., "1.1"). If not present, the version can be
2935          determined from the first line of the body.
2936        </t>
2937        <t hangText="msgtype:">
2938          The message type -- "request" or "response". If not
2939          present, the type can be determined from the first
2940          line of the body.
2941        </t>
2942      </list>
2943    </t>
2944    <t hangText="Encoding considerations:">
2945      only "7bit", "8bit", or "binary" are permitted
2946    </t>
2947    <t hangText="Security considerations:">
2948      none
2949    </t>
2950    <t hangText="Interoperability considerations:">
2951      none
2952    </t>
2953    <t hangText="Published specification:">
2954      This specification (see <xref target="internet.media.type.message.http"/>).
2955    </t>
2956    <t hangText="Applications that use this media type:">
2957    </t>
2958    <t hangText="Additional information:">
2959      <list style="hanging">
2960        <t hangText="Magic number(s):">none</t>
2961        <t hangText="File extension(s):">none</t>
2962        <t hangText="Macintosh file type code(s):">none</t>
2963      </list>
2964    </t>
2965    <t hangText="Person and email address to contact for further information:">
2966      See Authors Section.
2967    </t>
2968    <t hangText="Intended usage:">
2969      COMMON
2970    </t>
2971    <t hangText="Restrictions on usage:">
2972      none
2973    </t>
2974    <t hangText="Author/Change controller:">
2975      IESG
2976    </t>
2977  </list>
2978</t>
2979</section>
2980<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2981<iref item="Media Type" subitem="application/http" primary="true"/>
2982<iref item="application/http Media Type" primary="true"/>
2983<t>
2984   The application/http type can be used to enclose a pipeline of one or more
2985   HTTP request or response messages (not intermixed).
2986</t>
2987<t>
2988  <list style="hanging" x:indent="12em">
2989    <t hangText="Type name:">
2990      application
2991    </t>
2992    <t hangText="Subtype name:">
2993      http
2994    </t>
2995    <t hangText="Required parameters:">
2996      none
2997    </t>
2998    <t hangText="Optional parameters:">
2999      version, msgtype
3000      <list style="hanging">
3001        <t hangText="version:">
3002          The HTTP-Version number of the enclosed messages
3003          (e.g., "1.1"). If not present, the version can be
3004          determined from the first line of the body.
3005        </t>
3006        <t hangText="msgtype:">
3007          The message type -- "request" or "response". If not
3008          present, the type can be determined from the first
3009          line of the body.
3010        </t>
3011      </list>
3012    </t>
3013    <t hangText="Encoding considerations:">
3014      HTTP messages enclosed by this type
3015      are in "binary" format; use of an appropriate
3016      Content-Transfer-Encoding is required when
3017      transmitted via E-mail.
3018    </t>
3019    <t hangText="Security considerations:">
3020      none
3021    </t>
3022    <t hangText="Interoperability considerations:">
3023      none
3024    </t>
3025    <t hangText="Published specification:">
3026      This specification (see <xref target="internet.media.type.application.http"/>).
3027    </t>
3028    <t hangText="Applications that use this media type:">
3029    </t>
3030    <t hangText="Additional information:">
3031      <list style="hanging">
3032        <t hangText="Magic number(s):">none</t>
3033        <t hangText="File extension(s):">none</t>
3034        <t hangText="Macintosh file type code(s):">none</t>
3035      </list>
3036    </t>
3037    <t hangText="Person and email address to contact for further information:">
3038      See Authors Section.
3039    </t>
3040    <t hangText="Intended usage:">
3041      COMMON
3042    </t>
3043    <t hangText="Restrictions on usage:">
3044      none
3045    </t>
3046    <t hangText="Author/Change controller:">
3047      IESG
3048    </t>
3049  </list>
3050</t>
3051</section>
3052</section>
3053
3054</section>
3055
3056<section title="Security Considerations" anchor="security.considerations">
3057<t>
3058   This section is meant to inform application developers, information
3059   providers, and users of the security limitations in HTTP/1.1 as
3060   described by this document. The discussion does not include
3061   definitive solutions to the problems revealed, though it does make
3062   some suggestions for reducing security risks.
3063</t>
3064
3065<section title="Personal Information" anchor="personal.information">
3066<t>
3067   HTTP clients are often privy to large amounts of personal information
3068   (e.g. the user's name, location, mail address, passwords, encryption
3069   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3070   leakage of this information.
3071   We very strongly recommend that a convenient interface be provided
3072   for the user to control dissemination of such information, and that
3073   designers and implementors be particularly careful in this area.
3074   History shows that errors in this area often create serious security
3075   and/or privacy problems and generate highly adverse publicity for the
3076   implementor's company.
3077</t>
3078</section>
3079
3080<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3081<t>
3082   A server is in the position to save personal data about a user's
3083   requests which might identify their reading patterns or subjects of
3084   interest. This information is clearly confidential in nature and its
3085   handling can be constrained by law in certain countries. People using
3086   HTTP to provide data are responsible for ensuring that
3087   such material is not distributed without the permission of any
3088   individuals that are identifiable by the published results.
3089</t>
3090</section>
3091
3092<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3093<t>
3094   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3095   the documents returned by HTTP requests to be only those that were
3096   intended by the server administrators. If an HTTP server translates
3097   HTTP URIs directly into file system calls, the server &MUST; take
3098   special care not to serve files that were not intended to be
3099   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3100   other operating systems use ".." as a path component to indicate a
3101   directory level above the current one. On such a system, an HTTP
3102   server &MUST; disallow any such construct in the request-target if it
3103   would otherwise allow access to a resource outside those intended to
3104   be accessible via the HTTP server. Similarly, files intended for
3105   reference only internally to the server (such as access control
3106   files, configuration files, and script code) &MUST; be protected from
3107   inappropriate retrieval, since they might contain sensitive
3108   information. Experience has shown that minor bugs in such HTTP server
3109   implementations have turned into security risks.
3110</t>
3111</section>
3112
3113<section title="DNS Spoofing" anchor="dns.spoofing">
3114<t>
3115   Clients using HTTP rely heavily on the Domain Name Service, and are
3116   thus generally prone to security attacks based on the deliberate
3117   mis-association of IP addresses and DNS names. Clients need to be
3118   cautious in assuming the continuing validity of an IP number/DNS name
3119   association.
3120</t>
3121<t>
3122   In particular, HTTP clients &SHOULD; rely on their name resolver for
3123   confirmation of an IP number/DNS name association, rather than
3124   caching the result of previous host name lookups. Many platforms
3125   already can cache host name lookups locally when appropriate, and
3126   they &SHOULD; be configured to do so. It is proper for these lookups to
3127   be cached, however, only when the TTL (Time To Live) information
3128   reported by the name server makes it likely that the cached
3129   information will remain useful.
3130</t>
3131<t>
3132   If HTTP clients cache the results of host name lookups in order to
3133   achieve a performance improvement, they &MUST; observe the TTL
3134   information reported by DNS.
3135</t>
3136<t>
3137   If HTTP clients do not observe this rule, they could be spoofed when
3138   a previously-accessed server's IP address changes. As network
3139   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3140   possibility of this form of attack will grow. Observing this
3141   requirement thus reduces this potential security vulnerability.
3142</t>
3143<t>
3144   This requirement also improves the load-balancing behavior of clients
3145   for replicated servers using the same DNS name and reduces the
3146   likelihood of a user's experiencing failure in accessing sites which
3147   use that strategy.
3148</t>
3149</section>
3150
3151<section title="Proxies and Caching" anchor="attack.proxies">
3152<t>
3153   By their very nature, HTTP proxies are men-in-the-middle, and
3154   represent an opportunity for man-in-the-middle attacks. Compromise of
3155   the systems on which the proxies run can result in serious security
3156   and privacy problems. Proxies have access to security-related
3157   information, personal information about individual users and
3158   organizations, and proprietary information belonging to users and
3159   content providers. A compromised proxy, or a proxy implemented or
3160   configured without regard to security and privacy considerations,
3161   might be used in the commission of a wide range of potential attacks.
3162</t>
3163<t>
3164   Proxy operators should protect the systems on which proxies run as
3165   they would protect any system that contains or transports sensitive
3166   information. In particular, log information gathered at proxies often
3167   contains highly sensitive personal information, and/or information
3168   about organizations. Log information should be carefully guarded, and
3169   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3170</t>
3171<t>
3172   Proxy implementors should consider the privacy and security
3173   implications of their design and coding decisions, and of the
3174   configuration options they provide to proxy operators (especially the
3175   default configuration).
3176</t>
3177<t>
3178   Users of a proxy need to be aware that they are no trustworthier than
3179   the people who run the proxy; HTTP itself cannot solve this problem.
3180</t>
3181<t>
3182   The judicious use of cryptography, when appropriate, may suffice to
3183   protect against a broad range of security and privacy attacks. Such
3184   cryptography is beyond the scope of the HTTP/1.1 specification.
3185</t>
3186</section>
3187
3188<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3189<t>
3190   They exist. They are hard to defend against. Research continues.
3191   Beware.
3192</t>
3193</section>
3194</section>
3195
3196<section title="Acknowledgments" anchor="ack">
3197<t>
3198   HTTP has evolved considerably over the years. It has
3199   benefited from a large and active developer community--the many
3200   people who have participated on the www-talk mailing list--and it is
3201   that community which has been most responsible for the success of
3202   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3203   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3204   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3205   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3206   VanHeyningen deserve special recognition for their efforts in
3207   defining early aspects of the protocol.
3208</t>
3209<t>
3210   This document has benefited greatly from the comments of all those
3211   participating in the HTTP-WG. In addition to those already mentioned,
3212   the following individuals have contributed to this specification:
3213</t>
3214<t>
3215   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3216   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3217   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3218   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3219   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3220   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3221   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3222   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3223   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3224   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3225   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3226   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3227   Josh Cohen.
3228</t>
3229<t>
3230   Thanks to the "cave men" of Palo Alto. You know who you are.
3231</t>
3232<t>
3233   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3234   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3235   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3236   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3237   Larry Masinter for their help. And thanks go particularly to Jeff
3238   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3239</t>
3240<t>
3241   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3242   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3243   discovery of many of the problems that this document attempts to
3244   rectify.
3245</t>
3246<t>
3247   This specification makes heavy use of the augmented BNF and generic
3248   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3249   reuses many of the definitions provided by Nathaniel Borenstein and
3250   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3251   specification will help reduce past confusion over the relationship
3252   between HTTP and Internet mail message formats.
3253</t>
3254</section>
3255
3256</middle>
3257<back>
3258
3259<references title="Normative References">
3260
3261<reference anchor="ISO-8859-1">
3262  <front>
3263    <title>
3264     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3265    </title>
3266    <author>
3267      <organization>International Organization for Standardization</organization>
3268    </author>
3269    <date year="1998"/>
3270  </front>
3271  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3272</reference>
3273
3274<reference anchor="Part2">
3275  <front>
3276    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3277    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3278      <organization abbrev="Day Software">Day Software</organization>
3279      <address><email>fielding@gbiv.com</email></address>
3280    </author>
3281    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3282      <organization>One Laptop per Child</organization>
3283      <address><email>jg@laptop.org</email></address>
3284    </author>
3285    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3286      <organization abbrev="HP">Hewlett-Packard Company</organization>
3287      <address><email>JeffMogul@acm.org</email></address>
3288    </author>
3289    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3290      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3291      <address><email>henrikn@microsoft.com</email></address>
3292    </author>
3293    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3294      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3295      <address><email>LMM@acm.org</email></address>
3296    </author>
3297    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3298      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3299      <address><email>paulle@microsoft.com</email></address>
3300    </author>
3301    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3302      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3303      <address><email>timbl@w3.org</email></address>
3304    </author>
3305    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3306      <organization abbrev="W3C">World Wide Web Consortium</organization>
3307      <address><email>ylafon@w3.org</email></address>
3308    </author>
3309    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3310      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3311      <address><email>julian.reschke@greenbytes.de</email></address>
3312    </author>
3313    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3314  </front>
3315  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3316  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3317</reference>
3318
3319<reference anchor="Part3">
3320  <front>
3321    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3322    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3323      <organization abbrev="Day Software">Day Software</organization>
3324      <address><email>fielding@gbiv.com</email></address>
3325    </author>
3326    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3327      <organization>One Laptop per Child</organization>
3328      <address><email>jg@laptop.org</email></address>
3329    </author>
3330    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3331      <organization abbrev="HP">Hewlett-Packard Company</organization>
3332      <address><email>JeffMogul@acm.org</email></address>
3333    </author>
3334    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3335      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3336      <address><email>henrikn@microsoft.com</email></address>
3337    </author>
3338    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3339      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3340      <address><email>LMM@acm.org</email></address>
3341    </author>
3342    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3343      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3344      <address><email>paulle@microsoft.com</email></address>
3345    </author>
3346    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3347      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3348      <address><email>timbl@w3.org</email></address>
3349    </author>
3350    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3351      <organization abbrev="W3C">World Wide Web Consortium</organization>
3352      <address><email>ylafon@w3.org</email></address>
3353    </author>
3354    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3355      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3356      <address><email>julian.reschke@greenbytes.de</email></address>
3357    </author>
3358    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3359  </front>
3360  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3361  <x:source href="p3-payload.xml" basename="p3-payload"/>
3362</reference>
3363
3364<reference anchor="Part5">
3365  <front>
3366    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3367    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3368      <organization abbrev="Day Software">Day Software</organization>
3369      <address><email>fielding@gbiv.com</email></address>
3370    </author>
3371    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3372      <organization>One Laptop per Child</organization>
3373      <address><email>jg@laptop.org</email></address>
3374    </author>
3375    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3376      <organization abbrev="HP">Hewlett-Packard Company</organization>
3377      <address><email>JeffMogul@acm.org</email></address>
3378    </author>
3379    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3380      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3381      <address><email>henrikn@microsoft.com</email></address>
3382    </author>
3383    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3384      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3385      <address><email>LMM@acm.org</email></address>
3386    </author>
3387    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3388      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3389      <address><email>paulle@microsoft.com</email></address>
3390    </author>
3391    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3392      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3393      <address><email>timbl@w3.org</email></address>
3394    </author>
3395    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3396      <organization abbrev="W3C">World Wide Web Consortium</organization>
3397      <address><email>ylafon@w3.org</email></address>
3398    </author>
3399    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3400      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3401      <address><email>julian.reschke@greenbytes.de</email></address>
3402    </author>
3403    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3404  </front>
3405  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3406  <x:source href="p5-range.xml" basename="p5-range"/>
3407</reference>
3408
3409<reference anchor="Part6">
3410  <front>
3411    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3412    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3413      <organization abbrev="Day Software">Day Software</organization>
3414      <address><email>fielding@gbiv.com</email></address>
3415    </author>
3416    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3417      <organization>One Laptop per Child</organization>
3418      <address><email>jg@laptop.org</email></address>
3419    </author>
3420    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3421      <organization abbrev="HP">Hewlett-Packard Company</organization>
3422      <address><email>JeffMogul@acm.org</email></address>
3423    </author>
3424    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3425      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3426      <address><email>henrikn@microsoft.com</email></address>
3427    </author>
3428    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3429      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3430      <address><email>LMM@acm.org</email></address>
3431    </author>
3432    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3433      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3434      <address><email>paulle@microsoft.com</email></address>
3435    </author>
3436    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3437      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3438      <address><email>timbl@w3.org</email></address>
3439    </author>
3440    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3441      <organization abbrev="W3C">World Wide Web Consortium</organization>
3442      <address><email>ylafon@w3.org</email></address>
3443    </author>
3444    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3445      <organization />
3446      <address><email>mnot@mnot.net</email></address>
3447    </author>
3448    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3449      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3450      <address><email>julian.reschke@greenbytes.de</email></address>
3451    </author>
3452    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3453  </front>
3454  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3455  <x:source href="p6-cache.xml" basename="p6-cache"/>
3456</reference>
3457
3458<reference anchor="RFC5234">
3459  <front>
3460    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3461    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3462      <organization>Brandenburg InternetWorking</organization>
3463      <address>
3464      <postal>
3465      <street>675 Spruce Dr.</street>
3466      <city>Sunnyvale</city>
3467      <region>CA</region>
3468      <code>94086</code>
3469      <country>US</country></postal>
3470      <phone>+1.408.246.8253</phone>
3471      <email>dcrocker@bbiw.net</email></address> 
3472    </author>
3473    <author initials="P." surname="Overell" fullname="Paul Overell">
3474      <organization>THUS plc.</organization>
3475      <address>
3476      <postal>
3477      <street>1/2 Berkeley Square</street>
3478      <street>99 Berkely Street</street>
3479      <city>Glasgow</city>
3480      <code>G3 7HR</code>
3481      <country>UK</country></postal>
3482      <email>paul.overell@thus.net</email></address>
3483    </author>
3484    <date month="January" year="2008"/>
3485  </front>
3486  <seriesInfo name="STD" value="68"/>
3487  <seriesInfo name="RFC" value="5234"/>
3488</reference>
3489
3490<reference anchor="RFC2119">
3491  <front>
3492    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3493    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3494      <organization>Harvard University</organization>
3495      <address><email>sob@harvard.edu</email></address>
3496    </author>
3497    <date month="March" year="1997"/>
3498  </front>
3499  <seriesInfo name="BCP" value="14"/>
3500  <seriesInfo name="RFC" value="2119"/>
3501</reference>
3502
3503<reference anchor="RFC3986">
3504 <front>
3505  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3506  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3507    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3508    <address>
3509       <email>timbl@w3.org</email>
3510       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3511    </address>
3512  </author>
3513  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3514    <organization abbrev="Day Software">Day Software</organization>
3515    <address>
3516      <email>fielding@gbiv.com</email>
3517      <uri>http://roy.gbiv.com/</uri>
3518    </address>
3519  </author>
3520  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3521    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3522    <address>
3523      <email>LMM@acm.org</email>
3524      <uri>http://larry.masinter.net/</uri>
3525    </address>
3526  </author>
3527  <date month='January' year='2005'></date>
3528 </front>
3529 <seriesInfo name="RFC" value="3986"/>
3530 <seriesInfo name="STD" value="66"/>
3531</reference>
3532
3533<reference anchor="USASCII">
3534  <front>
3535    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3536    <author>
3537      <organization>American National Standards Institute</organization>
3538    </author>
3539    <date year="1986"/>
3540  </front>
3541  <seriesInfo name="ANSI" value="X3.4"/>
3542</reference>
3543
3544</references>
3545
3546<references title="Informative References">
3547
3548<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3549  <front>
3550    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3551    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3552      <organization/>
3553    </author>
3554    <author initials="J." surname="Gettys" fullname="J. Gettys">
3555      <organization/>
3556    </author>
3557    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3558      <organization/>
3559    </author>
3560    <author initials="H." surname="Lie" fullname="H. Lie">
3561      <organization/>
3562    </author>
3563    <author initials="C." surname="Lilley" fullname="C. Lilley">
3564      <organization/>
3565    </author>
3566    <date year="1997" month="September"/>
3567  </front>
3568  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3569</reference>
3570
3571<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3572  <front>
3573    <title>Improving HTTP Latency</title>
3574    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3575      <organization/>
3576    </author>
3577    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3578      <organization/>
3579    </author>
3580    <date year="1995" month="December"/>
3581  </front>
3582  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3583</reference>
3584
3585<reference anchor="RFC1123">
3586  <front>
3587    <title>Requirements for Internet Hosts - Application and Support</title>
3588    <author initials="R." surname="Braden" fullname="Robert Braden">
3589      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3590      <address><email>Braden@ISI.EDU</email></address>
3591    </author>
3592    <date month="October" year="1989"/>
3593  </front>
3594  <seriesInfo name="STD" value="3"/>
3595  <seriesInfo name="RFC" value="1123"/>
3596</reference>
3597
3598<reference anchor="RFC1305">
3599  <front>
3600    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3601    <author initials="D." surname="Mills" fullname="David L. Mills">
3602      <organization>University of Delaware, Electrical Engineering Department</organization>
3603      <address><email>mills@udel.edu</email></address>
3604    </author>
3605    <date month="March" year="1992"/>
3606  </front>
3607  <seriesInfo name="RFC" value="1305"/>
3608</reference>
3609
3610<reference anchor="RFC1900">
3611  <front>
3612    <title>Renumbering Needs Work</title>
3613    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3614      <organization>CERN, Computing and Networks Division</organization>
3615      <address><email>brian@dxcoms.cern.ch</email></address>
3616    </author>
3617    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3618      <organization>cisco Systems</organization>
3619      <address><email>yakov@cisco.com</email></address>
3620    </author>
3621    <date month="February" year="1996"/>
3622  </front>
3623  <seriesInfo name="RFC" value="1900"/>
3624</reference>
3625
3626<reference anchor="RFC1945">
3627  <front>
3628    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3629    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3630      <organization>MIT, Laboratory for Computer Science</organization>
3631      <address><email>timbl@w3.org</email></address>
3632    </author>
3633    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3634      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3635      <address><email>fielding@ics.uci.edu</email></address>
3636    </author>
3637    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3638      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3639      <address><email>frystyk@w3.org</email></address>
3640    </author>
3641    <date month="May" year="1996"/>
3642  </front>
3643  <seriesInfo name="RFC" value="1945"/>
3644</reference>
3645
3646<reference anchor="RFC2045">
3647  <front>
3648    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3649    <author initials="N." surname="Freed" fullname="Ned Freed">
3650      <organization>Innosoft International, Inc.</organization>
3651      <address><email>ned@innosoft.com</email></address>
3652    </author>
3653    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3654      <organization>First Virtual Holdings</organization>
3655      <address><email>nsb@nsb.fv.com</email></address>
3656    </author>
3657    <date month="November" year="1996"/>
3658  </front>
3659  <seriesInfo name="RFC" value="2045"/>
3660</reference>
3661
3662<reference anchor="RFC2047">
3663  <front>
3664    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3665    <author initials="K." surname="Moore" fullname="Keith Moore">
3666      <organization>University of Tennessee</organization>
3667      <address><email>moore@cs.utk.edu</email></address>
3668    </author>
3669    <date month="November" year="1996"/>
3670  </front>
3671  <seriesInfo name="RFC" value="2047"/>
3672</reference>
3673
3674<reference anchor="RFC2068">
3675  <front>
3676    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3677    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3678      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3679      <address><email>fielding@ics.uci.edu</email></address>
3680    </author>
3681    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3682      <organization>MIT Laboratory for Computer Science</organization>
3683      <address><email>jg@w3.org</email></address>
3684    </author>
3685    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3686      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3687      <address><email>mogul@wrl.dec.com</email></address>
3688    </author>
3689    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3690      <organization>MIT Laboratory for Computer Science</organization>
3691      <address><email>frystyk@w3.org</email></address>
3692    </author>
3693    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3694      <organization>MIT Laboratory for Computer Science</organization>
3695      <address><email>timbl@w3.org</email></address>
3696    </author>
3697    <date month="January" year="1997"/>
3698  </front>
3699  <seriesInfo name="RFC" value="2068"/>
3700</reference>
3701
3702<reference anchor='RFC2109'>
3703  <front>
3704    <title>HTTP State Management Mechanism</title>
3705    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3706      <organization>Bell Laboratories, Lucent Technologies</organization>
3707      <address><email>dmk@bell-labs.com</email></address>
3708    </author>
3709    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3710      <organization>Netscape Communications Corp.</organization>
3711      <address><email>montulli@netscape.com</email></address>
3712    </author>
3713    <date year='1997' month='February' />
3714  </front>
3715  <seriesInfo name='RFC' value='2109' />
3716</reference>
3717
3718<reference anchor="RFC2145">
3719  <front>
3720    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3721    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3722      <organization>Western Research Laboratory</organization>
3723      <address><email>mogul@wrl.dec.com</email></address>
3724    </author>
3725    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3726      <organization>Department of Information and Computer Science</organization>
3727      <address><email>fielding@ics.uci.edu</email></address>
3728    </author>
3729    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3730      <organization>MIT Laboratory for Computer Science</organization>
3731      <address><email>jg@w3.org</email></address>
3732    </author>
3733    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3734      <organization>W3 Consortium</organization>
3735      <address><email>frystyk@w3.org</email></address>
3736    </author>
3737    <date month="May" year="1997"/>
3738  </front>
3739  <seriesInfo name="RFC" value="2145"/>
3740</reference>
3741
3742<reference anchor="RFC2616">
3743  <front>
3744    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3745    <author initials="R." surname="Fielding" fullname="R. Fielding">
3746      <organization>University of California, Irvine</organization>
3747      <address><email>fielding@ics.uci.edu</email></address>
3748    </author>
3749    <author initials="J." surname="Gettys" fullname="J. Gettys">
3750      <organization>W3C</organization>
3751      <address><email>jg@w3.org</email></address>
3752    </author>
3753    <author initials="J." surname="Mogul" fullname="J. Mogul">
3754      <organization>Compaq Computer Corporation</organization>
3755      <address><email>mogul@wrl.dec.com</email></address>
3756    </author>
3757    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3758      <organization>MIT Laboratory for Computer Science</organization>
3759      <address><email>frystyk@w3.org</email></address>
3760    </author>
3761    <author initials="L." surname="Masinter" fullname="L. Masinter">
3762      <organization>Xerox Corporation</organization>
3763      <address><email>masinter@parc.xerox.com</email></address>
3764    </author>
3765    <author initials="P." surname="Leach" fullname="P. Leach">
3766      <organization>Microsoft Corporation</organization>
3767      <address><email>paulle@microsoft.com</email></address>
3768    </author>
3769    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3770      <organization>W3C</organization>
3771      <address><email>timbl@w3.org</email></address>
3772    </author>
3773    <date month="June" year="1999"/>
3774  </front>
3775  <seriesInfo name="RFC" value="2616"/>
3776</reference>
3777
3778<reference anchor='RFC2818'>
3779  <front>
3780    <title>HTTP Over TLS</title>
3781    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3782      <organization>RTFM, Inc.</organization>
3783      <address><email>ekr@rtfm.com</email></address>
3784    </author>
3785    <date year='2000' month='May' />
3786  </front>
3787  <seriesInfo name='RFC' value='2818' />
3788</reference>
3789
3790<reference anchor='RFC2965'>
3791  <front>
3792    <title>HTTP State Management Mechanism</title>
3793    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3794      <organization>Bell Laboratories, Lucent Technologies</organization>
3795      <address><email>dmk@bell-labs.com</email></address>
3796    </author>
3797    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3798      <organization>Epinions.com, Inc.</organization>
3799      <address><email>lou@montulli.org</email></address>
3800    </author>
3801    <date year='2000' month='October' />
3802  </front>
3803  <seriesInfo name='RFC' value='2965' />
3804</reference>
3805
3806<reference anchor='RFC3864'>
3807  <front>
3808    <title>Registration Procedures for Message Header Fields</title>
3809    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3810      <organization>Nine by Nine</organization>
3811      <address><email>GK-IETF@ninebynine.org</email></address>
3812    </author>
3813    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3814      <organization>BEA Systems</organization>
3815      <address><email>mnot@pobox.com</email></address>
3816    </author>
3817    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3818      <organization>HP Labs</organization>
3819      <address><email>JeffMogul@acm.org</email></address>
3820    </author>
3821    <date year='2004' month='September' />
3822  </front>
3823  <seriesInfo name='BCP' value='90' />
3824  <seriesInfo name='RFC' value='3864' />
3825</reference>
3826
3827<reference anchor="RFC4288">
3828  <front>
3829    <title>Media Type Specifications and Registration Procedures</title>
3830    <author initials="N." surname="Freed" fullname="N. Freed">
3831      <organization>Sun Microsystems</organization>
3832      <address>
3833        <email>ned.freed@mrochek.com</email>
3834      </address>
3835    </author>
3836    <author initials="J." surname="Klensin" fullname="J. Klensin">
3837      <organization/>
3838      <address>
3839        <email>klensin+ietf@jck.com</email>
3840      </address>
3841    </author>
3842    <date year="2005" month="December"/>
3843  </front>
3844  <seriesInfo name="BCP" value="13"/>
3845  <seriesInfo name="RFC" value="4288"/>
3846</reference>
3847
3848<reference anchor='RFC4395'>
3849  <front>
3850    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3851    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3852      <organization>AT&amp;T Laboratories</organization>
3853      <address>
3854        <email>tony+urireg@maillennium.att.com</email>
3855      </address>
3856    </author>
3857    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3858      <organization>Qualcomm, Inc.</organization>
3859      <address>
3860        <email>hardie@qualcomm.com</email>
3861      </address>
3862    </author>
3863    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3864      <organization>Adobe Systems</organization>
3865      <address>
3866        <email>LMM@acm.org</email>
3867      </address>
3868    </author>
3869    <date year='2006' month='February' />
3870  </front>
3871  <seriesInfo name='BCP' value='115' />
3872  <seriesInfo name='RFC' value='4395' />
3873</reference>
3874
3875<reference anchor="RFC5322">
3876  <front>
3877    <title>Internet Message Format</title>
3878    <author initials="P." surname="Resnick" fullname="P. Resnick">
3879      <organization>Qualcomm Incorporated</organization>
3880    </author>
3881    <date year="2008" month="October"/>
3882  </front> 
3883  <seriesInfo name="RFC" value="5322"/>
3884</reference>
3885
3886<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3887  <front>
3888    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3889    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3890      <organization/>
3891    </author>
3892    <date year="2001" month="November"/>
3893  </front>
3894  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3895</reference>
3896
3897<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3898  <front>
3899  <title>Analysis of HTTP Performance Problems</title>
3900  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3901    <organization/>
3902  </author>
3903  <date/>
3904  </front>
3905</reference>
3906
3907<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3908  <front>
3909  <title>Analysis of HTTP Performance</title>
3910  <author initials="J." surname="Touch" fullname="Joe Touch">
3911    <organization>USC/Information Sciences Institute</organization>
3912    <address><email>touch@isi.edu</email></address>
3913  </author>
3914  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3915    <organization>USC/Information Sciences Institute</organization>
3916    <address><email>johnh@isi.edu</email></address>
3917  </author>
3918  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3919    <organization>USC/Information Sciences Institute</organization>
3920    <address><email>katia@isi.edu</email></address>
3921  </author>
3922  <date year="1998" month="Aug"/>
3923  </front>
3924  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3925  <annotation>(original report dated Aug. 1996)</annotation>
3926</reference>
3927
3928</references>
3929
3930
3931<section title="Tolerant Applications" anchor="tolerant.applications">
3932<t>
3933   Although this document specifies the requirements for the generation
3934   of HTTP/1.1 messages, not all applications will be correct in their
3935   implementation. We therefore recommend that operational applications
3936   be tolerant of deviations whenever those deviations can be
3937   interpreted unambiguously.
3938</t>
3939<t>
3940   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3941   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3942   accept any amount of WSP characters between fields, even though
3943   only a single SP is required.
3944</t>
3945<t>
3946   The line terminator for message-header fields is the sequence CRLF.
3947   However, we recommend that applications, when parsing such headers,
3948   recognize a single LF as a line terminator and ignore the leading CR.
3949</t>
3950<t>
3951   The character set of an entity-body &SHOULD; be labeled as the lowest
3952   common denominator of the character codes used within that body, with
3953   the exception that not labeling the entity is preferred over labeling
3954   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3955</t>
3956<t>
3957   Additional rules for requirements on parsing and encoding of dates
3958   and other potential problems with date encodings include:
3959</t>
3960<t>
3961  <list style="symbols">
3962     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3963        which appears to be more than 50 years in the future is in fact
3964        in the past (this helps solve the "year 2000" problem).</t>
3965
3966     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3967        Expires date as earlier than the proper value, but &MUST-NOT;
3968        internally represent a parsed Expires date as later than the
3969        proper value.</t>
3970
3971     <t>All expiration-related calculations &MUST; be done in GMT. The
3972        local time zone &MUST-NOT; influence the calculation or comparison
3973        of an age or expiration time.</t>
3974
3975     <t>If an HTTP header incorrectly carries a date value with a time
3976        zone other than GMT, it &MUST; be converted into GMT using the
3977        most conservative possible conversion.</t>
3978  </list>
3979</t>
3980</section>
3981
3982<section title="Compatibility with Previous Versions" anchor="compatibility">
3983<t>
3984   HTTP has been in use by the World-Wide Web global information initiative
3985   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3986   was a simple protocol for hypertext data transfer across the Internet
3987   with only a single method and no metadata.
3988   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3989   methods and MIME-like messaging that could include metadata about the data
3990   transferred and modifiers on the request/response semantics. However,
3991   HTTP/1.0 did not sufficiently take into consideration the effects of
3992   hierarchical proxies, caching, the need for persistent connections, or
3993   name-based virtual hosts. The proliferation of incompletely-implemented
3994   applications calling themselves "HTTP/1.0" further necessitated a
3995   protocol version change in order for two communicating applications
3996   to determine each other's true capabilities.
3997</t>
3998<t>
3999   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4000   requirements that enable reliable implementations, adding only
4001   those new features that will either be safely ignored by an HTTP/1.0
4002   recipient or only sent when communicating with a party advertising
4003   compliance with HTTP/1.1.
4004</t>
4005<t>
4006   It is beyond the scope of a protocol specification to mandate
4007   compliance with previous versions. HTTP/1.1 was deliberately
4008   designed, however, to make supporting previous versions easy. It is
4009   worth noting that, at the time of composing this specification
4010   (1996), we would expect commercial HTTP/1.1 servers to:
4011  <list style="symbols">
4012     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
4013        1.1 requests;</t>
4014
4015     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4016        1.1;</t>
4017
4018     <t>respond appropriately with a message in the same major version
4019        used by the client.</t>
4020  </list>
4021</t>
4022<t>
4023   And we would expect HTTP/1.1 clients to:
4024  <list style="symbols">
4025     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4026        responses;</t>
4027
4028     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4029        1.1.</t>
4030  </list>
4031</t>
4032<t>
4033   For most implementations of HTTP/1.0, each connection is established
4034   by the client prior to the request and closed by the server after
4035   sending the response. Some implementations implement the Keep-Alive
4036   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4037</t>
4038
4039<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4040<t>
4041   This section summarizes major differences between versions HTTP/1.0
4042   and HTTP/1.1.
4043</t>
4044
4045<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">
4046<t>
4047   The requirements that clients and servers support the Host request-header,
4048   report an error if the Host request-header (<xref target="header.host"/>) is
4049   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4050   are among the most important changes defined by this
4051   specification.
4052</t>
4053<t>
4054   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4055   addresses and servers; there was no other established mechanism for
4056   distinguishing the intended server of a request than the IP address
4057   to which that request was directed. The changes outlined above will
4058   allow the Internet, once older HTTP clients are no longer common, to
4059   support multiple Web sites from a single IP address, greatly
4060   simplifying large operational Web servers, where allocation of many
4061   IP addresses to a single host has created serious problems. The
4062   Internet will also be able to recover the IP addresses that have been
4063   allocated for the sole purpose of allowing special-purpose domain
4064   names to be used in root-level HTTP URLs. Given the rate of growth of
4065   the Web, and the number of servers already deployed, it is extremely
4066   important that all implementations of HTTP (including updates to
4067   existing HTTP/1.0 applications) correctly implement these
4068   requirements:
4069  <list style="symbols">
4070     <t>Both clients and servers &MUST; support the Host request-header.</t>
4071
4072     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4073
4074     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4075        request does not include a Host request-header.</t>
4076
4077     <t>Servers &MUST; accept absolute URIs.</t>
4078  </list>
4079</t>
4080</section>
4081</section>
4082
4083<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4084<t>
4085   Some clients and servers might wish to be compatible with some
4086   previous implementations of persistent connections in HTTP/1.0
4087   clients and servers. Persistent connections in HTTP/1.0 are
4088   explicitly negotiated as they are not the default behavior. HTTP/1.0
4089   experimental implementations of persistent connections are faulty,
4090   and the new facilities in HTTP/1.1 are designed to rectify these
4091   problems. The problem was that some existing 1.0 clients may be
4092   sending Keep-Alive to a proxy server that doesn't understand
4093   Connection, which would then erroneously forward it to the next
4094   inbound server, which would establish the Keep-Alive connection and
4095   result in a hung HTTP/1.0 proxy waiting for the close on the
4096   response. The result is that HTTP/1.0 clients must be prevented from
4097   using Keep-Alive when talking to proxies.
4098</t>
4099<t>
4100   However, talking to proxies is the most important use of persistent
4101   connections, so that prohibition is clearly unacceptable. Therefore,
4102   we need some other mechanism for indicating a persistent connection
4103   is desired, which is safe to use even when talking to an old proxy
4104   that ignores Connection. Persistent connections are the default for
4105   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4106   declaring non-persistence. See <xref target="header.connection"/>.
4107</t>
4108<t>
4109   The original HTTP/1.0 form of persistent connections (the Connection:
4110   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4111</t>
4112</section>
4113
4114<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4115<t>
4116   This specification has been carefully audited to correct and
4117   disambiguate key word usage; RFC 2068 had many problems in respect to
4118   the conventions laid out in <xref target="RFC2119"/>.
4119</t>
4120<t>
4121   Transfer-coding and message lengths all interact in ways that
4122   required fixing exactly when chunked encoding is used (to allow for
4123   transfer encoding that may not be self delimiting); it was important
4124   to straighten out exactly how message lengths are computed. (Sections
4125   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4126   <xref target="header.content-length" format="counter"/>,
4127   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4128</t>
4129<t>
4130   The use and interpretation of HTTP version numbers has been clarified
4131   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4132   version they support to deal with problems discovered in HTTP/1.0
4133   implementations (<xref target="http.version"/>)
4134</t>
4135<t>
4136   Quality Values of zero should indicate that "I don't want something"
4137   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4138</t>
4139<t>
4140   Transfer-coding had significant problems, particularly with
4141   interactions with chunked encoding. The solution is that transfer-codings
4142   become as full fledged as content-codings. This involves
4143   adding an IANA registry for transfer-codings (separate from content
4144   codings), a new header field (TE) and enabling trailer headers in the
4145   future. Transfer encoding is a major performance benefit, so it was
4146   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4147   interoperability problem that could have occurred due to interactions
4148   between authentication trailers, chunked encoding and HTTP/1.0
4149   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4150   and <xref target="header.te" format="counter"/>)
4151</t>
4152</section>
4153
4154<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4155<t>
4156  Empty list elements in list productions have been deprecated.
4157  (<xref target="notation.abnf"/>)
4158</t>
4159<t>
4160  Rules about implicit linear whitespace between certain grammar productions
4161  have been removed; now it's only allowed when specifically pointed out
4162  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4163  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4164  Non-ASCII content in header fields and reason phrase has been obsoleted and
4165  made opaque (the TEXT rule was removed)
4166  (<xref target="basic.rules"/>)
4167</t>
4168<t>
4169  Clarify that HTTP-Version is case sensitive.
4170  (<xref target="http.version"/>)
4171</t>
4172<t>
4173  Remove reference to non-existant identity transfer-coding value tokens.
4174  (Sections <xref format="counter" target="transfer.codings"/> and
4175  <xref format="counter" target="message.length"/>)
4176</t>
4177<t>
4178  Clarification that the chunk length does not include
4179  the count of the octets in the chunk header and trailer.
4180  (<xref target="chunked.transfer.encoding"/>)
4181</t>
4182<t>
4183  Require that invalid whitespace around field-names be rejected.
4184  (<xref target="message.headers"/>)
4185</t>
4186<t>
4187  Update use of abs_path production from RFC1808 to the path-absolute + query
4188  components of RFC3986.
4189  (<xref target="request-target"/>)
4190</t>
4191<t>
4192  Clarify exactly when close connection options must be sent.
4193  (<xref target="header.connection"/>)
4194</t>
4195</section>
4196</section>
4197
4198<section title="Terminology" anchor="terminology">
4199<t>
4200   This specification uses a number of terms to refer to the roles
4201   played by participants in, and objects of, the HTTP communication.
4202</t>
4203<t>
4204  <iref item="cache"/>
4205  <x:dfn>cache</x:dfn>
4206  <list>
4207    <t>
4208      A program's local store of response messages and the subsystem
4209      that controls its message storage, retrieval, and deletion. A
4210      cache stores cacheable responses in order to reduce the response
4211      time and network bandwidth consumption on future, equivalent
4212      requests. Any client or server may include a cache, though a cache
4213      cannot be used by a server that is acting as a tunnel.
4214    </t>
4215  </list>
4216</t>
4217<t>
4218  <iref item="cacheable"/>
4219  <x:dfn>cacheable</x:dfn>
4220  <list>
4221    <t>
4222      A response is cacheable if a cache is allowed to store a copy of
4223      the response message for use in answering subsequent requests. The
4224      rules for determining the cacheability of HTTP responses are
4225      defined in &caching;. Even if a resource is cacheable, there may
4226      be additional constraints on whether a cache can use the cached
4227      copy for a particular request.
4228    </t>
4229  </list>
4230</t>
4231<t>
4232  <iref item="client"/>
4233  <x:dfn>client</x:dfn>
4234  <list>
4235    <t>
4236      A program that establishes connections for the purpose of sending
4237      requests.
4238    </t>
4239  </list>
4240</t>
4241<t>
4242  <iref item="connection"/>
4243  <x:dfn>connection</x:dfn>
4244  <list>
4245    <t>
4246      A transport layer virtual circuit established between two programs
4247      for the purpose of communication.
4248    </t>
4249  </list>
4250</t>
4251<t>
4252  <iref item="content negotiation"/>
4253  <x:dfn>content negotiation</x:dfn>
4254  <list>
4255    <t>
4256      The mechanism for selecting the appropriate representation when
4257      servicing a request, as described in &content.negotiation;. The
4258      representation of entities in any response can be negotiated
4259      (including error responses).
4260    </t>
4261  </list>
4262</t>
4263<t>
4264  <iref item="entity"/>
4265  <x:dfn>entity</x:dfn>
4266  <list>
4267    <t>
4268      The information transferred as the payload of a request or
4269      response. An entity consists of metadata in the form of
4270      entity-header fields and content in the form of an entity-body, as
4271      described in &entity;.
4272    </t>
4273  </list>
4274</t>
4275<t>
4276  <iref item="gateway"/>
4277  <x:dfn>gateway</x:dfn>
4278  <list>
4279    <t>
4280      A server which acts as an intermediary for some other server.
4281      Unlike a proxy, a gateway receives requests as if it were the
4282      origin server for the requested resource; the requesting client
4283      may not be aware that it is communicating with a gateway.
4284    </t>
4285  </list>
4286</t>
4287<t>
4288  <iref item="inbound"/>
4289  <iref item="outbound"/>
4290  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4291  <list>
4292    <t>
4293      Inbound and outbound refer to the request and response paths for
4294      messages: "inbound" means "traveling toward the origin server",
4295      and "outbound" means "traveling toward the user agent"
4296    </t>
4297  </list>
4298</t>
4299<t>
4300  <iref item="message"/>
4301  <x:dfn>message</x:dfn>
4302  <list>
4303    <t>
4304      The basic unit of HTTP communication, consisting of a structured
4305      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4306      transmitted via the connection.
4307    </t>
4308  </list>
4309</t>
4310<t>
4311  <iref item="origin server"/>
4312  <x:dfn>origin server</x:dfn>
4313  <list>
4314    <t>
4315      The server on which a given resource resides or is to be created.
4316    </t>
4317  </list>
4318</t>
4319<t>
4320  <iref item="proxy"/>
4321  <x:dfn>proxy</x:dfn>
4322  <list>
4323    <t>
4324      An intermediary program which acts as both a server and a client
4325      for the purpose of making requests on behalf of other clients.
4326      Requests are serviced internally or by passing them on, with
4327      possible translation, to other servers. A proxy &MUST; implement
4328      both the client and server requirements of this specification. A
4329      "transparent proxy" is a proxy that does not modify the request or
4330      response beyond what is required for proxy authentication and
4331      identification. A "non-transparent proxy" is a proxy that modifies
4332      the request or response in order to provide some added service to
4333      the user agent, such as group annotation services, media type
4334      transformation, protocol reduction, or anonymity filtering. Except
4335      where either transparent or non-transparent behavior is explicitly
4336      stated, the HTTP proxy requirements apply to both types of
4337      proxies.
4338    </t>
4339  </list>
4340</t>
4341<t>
4342  <iref item="request"/>
4343  <x:dfn>request</x:dfn>
4344  <list>
4345    <t>
4346      An HTTP request message, as defined in <xref target="request"/>.
4347    </t>
4348  </list>
4349</t>
4350<t>
4351  <iref item="response"/>
4352  <x:dfn>response</x:dfn>
4353  <list>
4354    <t>
4355      An HTTP response message, as defined in <xref target="response"/>.
4356    </t>
4357  </list>
4358</t>
4359<t>
4360  <iref item="representation"/>
4361  <x:dfn>representation</x:dfn>
4362  <list>
4363    <t>
4364      An entity included with a response that is subject to content
4365      negotiation, as described in &content.negotiation;. There may exist multiple
4366      representations associated with a particular response status.
4367    </t>
4368  </list>
4369</t>
4370<t>
4371  <iref item="server"/>
4372  <x:dfn>server</x:dfn>
4373  <list>
4374    <t>
4375      An application program that accepts connections in order to
4376      service requests by sending back responses. Any given program may
4377      be capable of being both a client and a server; our use of these
4378      terms refers only to the role being performed by the program for a
4379      particular connection, rather than to the program's capabilities
4380      in general. Likewise, any server may act as an origin server,
4381      proxy, gateway, or tunnel, switching behavior based on the nature
4382      of each request.
4383    </t>
4384  </list>
4385</t>
4386<t>
4387  <iref item="tunnel"/>
4388  <x:dfn>tunnel</x:dfn>
4389  <list>
4390    <t>
4391      An intermediary program which is acting as a blind relay between
4392      two connections. Once active, a tunnel is not considered a party
4393      to the HTTP communication, though the tunnel may have been
4394      initiated by an HTTP request. The tunnel ceases to exist when both
4395      ends of the relayed connections are closed.
4396    </t>
4397  </list>
4398</t>
4399<t>
4400  <iref item="upstream"/>
4401  <iref item="downstream"/>
4402  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4403  <list>
4404    <t>
4405      Upstream and downstream describe the flow of a message: all
4406      messages flow from upstream to downstream.
4407    </t>
4408  </list>
4409</t>
4410<t>
4411  <iref item="user agent"/>
4412  <x:dfn>user agent</x:dfn>
4413  <list>
4414    <t>
4415      The client which initiates a request. These are often browsers,
4416      editors, spiders (web-traversing robots), or other end user tools.
4417    </t>
4418  </list>
4419</t>
4420<t>
4421  <iref item="variant"/>
4422  <x:dfn>variant</x:dfn>
4423  <list>
4424    <t>
4425      A resource may have one, or more than one, representation(s)
4426      associated with it at any given instant. Each of these
4427      representations is termed a `variant'.  Use of the term `variant'
4428      does not necessarily imply that the resource is subject to content
4429      negotiation.
4430    </t>
4431  </list>
4432</t>
4433</section>
4434
4435<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4436<figure>
4437<artwork type="abnf" name="p1-messaging.parsed-abnf">
4438<x:ref>BWS</x:ref> = OWS
4439
4440<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4441<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4442<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4443<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4444 connection-token ] )
4445<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4446<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4447
4448<x:ref>Date</x:ref> = "Date:" OWS Date-v
4449<x:ref>Date-v</x:ref> = HTTP-date
4450
4451<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4452
4453<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4454<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4455<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4456<x:ref>HTTP-message</x:ref> = Request / Response
4457<x:ref>Host</x:ref> = "Host:" OWS Host-v
4458<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4459
4460<x:ref>Method</x:ref> = token
4461
4462<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4463
4464<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4465
4466<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4467<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4468<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4469 entity-header ) CRLF ) CRLF [ message-body ]
4470<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4471<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4472 entity-header ) CRLF ) CRLF [ message-body ]
4473
4474<x:ref>Status-Code</x:ref> = 3DIGIT
4475<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4476
4477<x:ref>TE</x:ref> = "TE:" OWS TE-v
4478<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4479<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4480<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4481<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4482<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4483 transfer-coding ] )
4484
4485<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4486<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4487<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4488<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4489
4490<x:ref>Via</x:ref> = "Via:" OWS Via-v
4491<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4492 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4493 ] )
4494
4495<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4496
4497<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4498<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4499<x:ref>attribute</x:ref> = token
4500<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4501
4502<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4503<x:ref>chunk-data</x:ref> = 1*OCTET
4504<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4505<x:ref>chunk-ext-name</x:ref> = token
4506<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4507<x:ref>chunk-size</x:ref> = 1*HEXDIG
4508<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4509<x:ref>connection-token</x:ref> = token
4510<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4511 / %x2A-5B ; '*'-'['
4512 / %x5D-7E ; ']'-'~'
4513 / obs-text
4514
4515<x:ref>date1</x:ref> = day SP month SP year
4516<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4517<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4518<x:ref>day</x:ref> = 2DIGIT
4519<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4520 / %x54.75.65 ; Tue
4521 / %x57.65.64 ; Wed
4522 / %x54.68.75 ; Thu
4523 / %x46.72.69 ; Fri
4524 / %x53.61.74 ; Sat
4525 / %x53.75.6E ; Sun
4526<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4527 / %x54.75.65.73.64.61.79 ; Tuesday
4528 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4529 / %x54.68.75.72.73.64.61.79 ; Thursday
4530 / %x46.72.69.64.61.79 ; Friday
4531 / %x53.61.74.75.72.64.61.79 ; Saturday
4532 / %x53.75.6E.64.61.79 ; Sunday
4533
4534<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4535<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4536
4537<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4538<x:ref>field-name</x:ref> = token
4539<x:ref>field-value</x:ref> = *( field-content / OWS )
4540<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4541
4542<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4543 / Transfer-Encoding / Upgrade / Via / Warning
4544<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4545 message-body ]
4546
4547<x:ref>hour</x:ref> = 2DIGIT
4548<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4549
4550<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4551
4552<x:ref>message-body</x:ref> = entity-body /
4553 &lt;entity-body encoded as per Transfer-Encoding&gt;
4554<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4555<x:ref>minute</x:ref> = 2DIGIT
4556<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4557 / %x46.65.62 ; Feb
4558 / %x4D.61.72 ; Mar
4559 / %x41.70.72 ; Apr
4560 / %x4D.61.79 ; May
4561 / %x4A.75.6E ; Jun
4562 / %x4A.75.6C ; Jul
4563 / %x41.75.67 ; Aug
4564 / %x53.65.70 ; Sep
4565 / %x4F.63.74 ; Oct
4566 / %x4E.6F.76 ; Nov
4567 / %x44.65.63 ; Dec
4568
4569<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4570<x:ref>obs-fold</x:ref> = CRLF
4571<x:ref>obs-text</x:ref> = %x80-FF
4572
4573<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4574<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4575<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4576<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4577<x:ref>product</x:ref> = token [ "/" product-version ]
4578<x:ref>product-version</x:ref> = token
4579<x:ref>protocol-name</x:ref> = token
4580<x:ref>protocol-version</x:ref> = token
4581<x:ref>pseudonym</x:ref> = token
4582
4583<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4584 / %x5D-7E ; ']'-'~'
4585 / obs-text
4586<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4587<x:ref>quoted-pair</x:ref> = "\" quoted-text
4588<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4589<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4590<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4591
4592<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4593<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4594<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4595<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4596<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4597 / authority
4598<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4599<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4600<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4601
4602<x:ref>second</x:ref> = 2DIGIT
4603<x:ref>start-line</x:ref> = Request-Line / Status-Line
4604
4605<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4606<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4607 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4608<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4609<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4610<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4611<x:ref>token</x:ref> = 1*tchar
4612<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4613<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4614<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
4615<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
4616
4617<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4618
4619<x:ref>value</x:ref> = token / quoted-string
4620
4621<x:ref>year</x:ref> = 4DIGIT
4622</artwork>
4623</figure>
4624<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4625; Chunked-Body defined but not used
4626; Content-Length defined but not used
4627; HTTP-message defined but not used
4628; Host defined but not used
4629; TE defined but not used
4630; URI defined but not used
4631; URI-reference defined but not used
4632; fragment defined but not used
4633; generic-message defined but not used
4634; http-URI defined but not used
4635; https-URI defined but not used
4636; partial-URI defined but not used
4637</artwork></figure></section>
4638
4639<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4640
4641<section title="Since RFC2616">
4642<t>
4643  Extracted relevant partitions from <xref target="RFC2616"/>.
4644</t>
4645</section>
4646
4647<section title="Since draft-ietf-httpbis-p1-messaging-00">
4648<t>
4649  Closed issues:
4650  <list style="symbols"> 
4651    <t>
4652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4653      "HTTP Version should be case sensitive"
4654      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4655    </t>
4656    <t>
4657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4658      "'unsafe' characters"
4659      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4660    </t>
4661    <t>
4662      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4663      "Chunk Size Definition"
4664      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4665    </t>
4666    <t>
4667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4668      "Message Length"
4669      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4670    </t>
4671    <t>
4672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4673      "Media Type Registrations"
4674      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4675    </t>
4676    <t>
4677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4678      "URI includes query"
4679      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4680    </t>
4681    <t>
4682      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4683      "No close on 1xx responses"
4684      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4685    </t>
4686    <t>
4687      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4688      "Remove 'identity' token references"
4689      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4690    </t>
4691    <t>
4692      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4693      "Import query BNF"
4694    </t>
4695    <t>
4696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4697      "qdtext BNF"
4698    </t>
4699    <t>
4700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4701      "Normative and Informative references"
4702    </t>
4703    <t>
4704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4705      "RFC2606 Compliance"
4706    </t>
4707    <t>
4708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4709      "RFC977 reference"
4710    </t>
4711    <t>
4712      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4713      "RFC1700 references"
4714    </t>
4715    <t>
4716      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4717      "inconsistency in date format explanation"
4718    </t>
4719    <t>
4720      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4721      "Date reference typo"
4722    </t>
4723    <t>
4724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4725      "Informative references"
4726    </t>
4727    <t>
4728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4729      "ISO-8859-1 Reference"
4730    </t>
4731    <t>
4732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4733      "Normative up-to-date references"
4734    </t>
4735  </list>
4736</t>
4737<t>
4738  Other changes:
4739  <list style="symbols"> 
4740    <t>
4741      Update media type registrations to use RFC4288 template.
4742    </t>
4743    <t>
4744      Use names of RFC4234 core rules DQUOTE and WSP,
4745      fix broken ABNF for chunk-data
4746      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4747    </t>
4748  </list>
4749</t>
4750</section>
4751
4752<section title="Since draft-ietf-httpbis-p1-messaging-01">
4753<t>
4754  Closed issues:
4755  <list style="symbols"> 
4756    <t>
4757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4758      "Bodies on GET (and other) requests"
4759    </t>
4760    <t>
4761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4762      "Updating to RFC4288"
4763    </t>
4764    <t>
4765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4766      "Status Code and Reason Phrase"
4767    </t>
4768    <t>
4769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4770      "rel_path not used"
4771    </t>
4772  </list>
4773</t>
4774<t>
4775  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4776  <list style="symbols"> 
4777    <t>
4778      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4779      "trailer-part").
4780    </t>
4781    <t>
4782      Avoid underscore character in rule names ("http_URL" ->
4783      "http-URL", "abs_path" -> "path-absolute").
4784    </t>
4785    <t>
4786      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4787      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4788      have to be updated when switching over to RFC3986.
4789    </t>
4790    <t>
4791      Synchronize core rules with RFC5234.
4792    </t>
4793    <t>
4794      Get rid of prose rules that span multiple lines.
4795    </t>
4796    <t>
4797      Get rid of unused rules LOALPHA and UPALPHA.
4798    </t>
4799    <t>
4800      Move "Product Tokens" section (back) into Part 1, as "token" is used
4801      in the definition of the Upgrade header.
4802    </t>
4803    <t>
4804      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4805    </t>
4806    <t>
4807      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4808    </t>
4809  </list>
4810</t>
4811</section>
4812
4813<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4814<t>
4815  Closed issues:
4816  <list style="symbols"> 
4817    <t>
4818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4819      "HTTP-date vs. rfc1123-date"
4820    </t>
4821    <t>
4822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4823      "WS in quoted-pair"
4824    </t>
4825  </list>
4826</t>
4827<t>
4828  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4829  <list style="symbols"> 
4830    <t>
4831      Reference RFC 3984, and update header registrations for headers defined
4832      in this document.
4833    </t>
4834  </list>
4835</t>
4836<t>
4837  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4838  <list style="symbols"> 
4839    <t>
4840      Replace string literals when the string really is case-sensitive (HTTP-Version).
4841    </t>
4842  </list>
4843</t>
4844</section>
4845
4846<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4847<t>
4848  Closed issues:
4849  <list style="symbols"> 
4850    <t>
4851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4852      "Connection closing"
4853    </t>
4854    <t>
4855      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4856      "Move registrations and registry information to IANA Considerations"
4857    </t>
4858    <t>
4859      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4860      "need new URL for PAD1995 reference"
4861    </t>
4862    <t>
4863      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4864      "IANA Considerations: update HTTP URI scheme registration"
4865    </t>
4866    <t>
4867      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4868      "Cite HTTPS URI scheme definition"
4869    </t>
4870    <t>
4871      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4872      "List-type headers vs Set-Cookie"
4873    </t>
4874  </list>
4875</t>
4876<t>
4877  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4878  <list style="symbols"> 
4879    <t>
4880      Replace string literals when the string really is case-sensitive (HTTP-Date).
4881    </t>
4882    <t>
4883      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4884    </t>
4885  </list>
4886</t>
4887</section>
4888
4889<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4890<t>
4891  Closed issues:
4892  <list style="symbols"> 
4893    <t>
4894      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4895      "Out-of-date reference for URIs"
4896    </t>
4897    <t>
4898      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4899      "RFC 2822 is updated by RFC 5322"
4900    </t>
4901  </list>
4902</t>
4903<t>
4904  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4905  <list style="symbols"> 
4906    <t>
4907      Use "/" instead of "|" for alternatives.
4908    </t>
4909    <t>
4910      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4911    </t>
4912    <t>
4913      Only reference RFC 5234's core rules.
4914    </t>
4915    <t>
4916      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4917      whitespace ("OWS") and required whitespace ("RWS").
4918    </t>
4919    <t>
4920      Rewrite ABNFs to spell out whitespace rules, factor out
4921      header value format definitions.
4922    </t>
4923  </list>
4924</t>
4925</section>
4926
4927<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4928<t>
4929  Closed issues:
4930  <list style="symbols"> 
4931    <t>
4932      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4933      "Header LWS"
4934    </t>
4935    <t>
4936      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4937      "Sort 1.3 Terminology"
4938    </t>
4939    <t>
4940      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4941      "RFC2047 encoded words"
4942    </t>
4943    <t>
4944      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4945      "Character Encodings in TEXT"
4946    </t>
4947    <t>
4948      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4949      "Line Folding"
4950    </t>
4951    <t>
4952      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4953      "OPTIONS * and proxies"
4954    </t>
4955    <t>
4956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4957      "Reason-Phrase BNF"
4958    </t>
4959    <t>
4960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4961      "Use of TEXT"
4962    </t>
4963    <t>
4964      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4965      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4966    </t>
4967    <t>
4968      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4969      "RFC822 reference left in discussion of date formats"
4970    </t>
4971  </list>
4972</t>
4973<t>
4974  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4975  <list style="symbols"> 
4976    <t>
4977      Rewrite definition of list rules, deprecate empty list elements.
4978    </t>
4979    <t>
4980      Add appendix containing collected and expanded ABNF.
4981    </t>
4982  </list>
4983</t>
4984<t>
4985  Other changes:
4986  <list style="symbols"> 
4987    <t>
4988      Rewrite introduction; add mostly new Architecture Section.
4989    </t>
4990    <t>
4991      Move definition of quality values from Part 3 into Part 1;
4992      make TE request header grammar independent of accept-params (defined in Part 3).
4993    </t>
4994  </list>
4995</t>
4996</section>
4997
4998<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4999<t>
5000  Closed issues:
5001  <list style="symbols"> 
5002    <t>
5003      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5004      "base for numeric protocol elements"
5005    </t>
5006    <t>
5007      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5008      "comment ABNF"
5009    </t>
5010  </list>
5011</t>
5012<t>
5013  Partly resolved issues:
5014  <list style="symbols"> 
5015    <t>
5016      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5017      "205 Bodies" (took out language that implied that there may be
5018      methods for which a request body MUST NOT be included)
5019    </t>
5020    <t>
5021      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5022      "editorial improvements around HTTP-date"
5023    </t>
5024  </list>
5025</t>
5026</section>
5027
5028<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5029<t>
5030  None.
5031</t>
5032</section>
5033
5034</section>
5035
5036</back>
5037</rfc>
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