source: draft-ietf-httpbis/latest-roy/p1-messaging.xml @ 425

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.05"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypertext
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate resource targets and
235   relationships between resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
239   between HTTP and MIME messages).
240</t>
241<t>
242   HTTP is a generic interface protocol for informations systems. It is
243   designed to hide the details of how a service is implemented by presenting
244   a uniform interface to clients that is independent of the types of
245   resources provided. Likewise, servers do not need to be aware of each
246   client's purpose: an HTTP request can be considered in isolation rather
247   than being associated with a specific type of client or a predetermined
248   sequence of application steps. The result is a protocol that can be used
249   effectively in many different contexts and for which implementations can
250   evolve independently over time.
251</t>
252<t>
253   HTTP is also designed for use as a generic protocol for translating
254   communication to and from other Internet information systems, such as
255   USENET news services via NNTP <xref target="RFC3977"/>,
256   file services via FTP <xref target="RFC959"/>,
257   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
258   HTTP proxies and gateways provide access to alternative information
259   services by translating their diverse protocols into a hypermedia
260   format that can be viewed and manipulated by clients in the same way
261   as HTTP services.
262</t>
263<t>
264   One consequence of HTTP flexibility is that we cannot define the protocol
265   in terms of how to implement it behind the interface. Instead, we are
266   limited to restricting the syntax of communication, defining the intent
267   of received communication, and the expected behavior of recipients. If
268   the communication is considered in isolation, then successful actions
269   should be reflected in the observable interface provided by servers.
270   However, since many clients are potentially acting in parallel and
271   perhaps at cross-purposes, it would be meaningless to require that such
272   behavior be observable.
273</t>
274<t>
275   This document is Part 1 of the seven-part specification of HTTP,
276   defining the protocol referred to as "HTTP/1.1" and obsoleting
277   <xref target="RFC2616"/>.
278   Part 1 defines the URI schemes specific to HTTP-based resources, overall
279   network operation, transport protocol connection management, and HTTP
280   message framing and forwarding requirements.
281   Our goal is to define all of the mechanisms necessary for HTTP message
282   handling that are independent of message semantics, thereby defining the
283   complete set of requirements for a message parser and transparent
284   message-forwarding intermediaries.
285</t>
286
287<section title="Requirements" anchor="intro.requirements">
288<t>
289   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
290   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
291   document are to be interpreted as described in <xref target="RFC2119"/>.
292</t>
293<t>
294   An implementation is not compliant if it fails to satisfy one or more
295   of the &MUST; or &REQUIRED; level requirements for the protocols it
296   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
297   level and all the &SHOULD; level requirements for its protocols is said
298   to be "unconditionally compliant"; one that satisfies all the &MUST;
299   level requirements but not all the &SHOULD; level requirements for its
300   protocols is said to be "conditionally compliant."
301</t>
302</section>
303
304<section title="Syntax Notation" anchor="notation">
305<iref primary="true" item="Grammar" subitem="ALPHA"/>
306<iref primary="true" item="Grammar" subitem="CHAR"/>
307<iref primary="true" item="Grammar" subitem="CR"/>
308<iref primary="true" item="Grammar" subitem="CRLF"/>
309<iref primary="true" item="Grammar" subitem="CTL"/>
310<iref primary="true" item="Grammar" subitem="DIGIT"/>
311<iref primary="true" item="Grammar" subitem="DQUOTE"/>
312<iref primary="true" item="Grammar" subitem="HEXDIG"/>
313<iref primary="true" item="Grammar" subitem="HTAB"/>
314<iref primary="true" item="Grammar" subitem="LF"/>
315<iref primary="true" item="Grammar" subitem="OCTET"/>
316<iref primary="true" item="Grammar" subitem="SP"/>
317<iref primary="true" item="Grammar" subitem="WSP"/>
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CHAR"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="HTAB"/>
328  <x:anchor-alias value="LF"/>
329  <x:anchor-alias value="OCTET"/>
330  <x:anchor-alias value="SP"/>
331  <x:anchor-alias value="WSP"/>
332   This specification uses the Augmented Backus-Naur Form (ABNF) notation
333   of <xref target="RFC5234"/>.  The following core rules are included by
334   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
335   ALPHA (letters), CHAR (any <xref target="USASCII"/> character,
336   excluding NUL), CR (carriage return), CRLF (CR LF), CTL (controls),
337   DIGIT (decimal 0-9), DQUOTE (double quote),
338   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab),
339   LF (line feed), OCTET (any 8-bit sequence of data), SP (space)
340   and WSP (white space).
341</t>
342
343<section title="ABNF Extensions" anchor="notation.abnf">
344<t>
345   Two extensions to the ABNF rules of <xref target="RFC5234"/> are used to
346   improve readability.<cref>The current plan is to remove these extensions prior
347   to the last call draft.</cref>
348</t>
349
350<section title="#rule">
351  <t>
352    A construct "#" is defined, similar to "*", for defining lists of
353    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
354    &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
355    (",") and &OPTIONAL; linear white space (OWS). This makes the usual
356    form of lists very easy; a rule such as
357    <figure><artwork type="example">
358 ( *<x:ref>OWS</x:ref> element *( *<x:ref>OWS</x:ref> "," *<x:ref>OWS</x:ref> element ))</artwork></figure>
359  </t>
360  <t>
361    can be shown as
362    <figure><artwork type="example">
363 1#element</artwork></figure>
364  </t>
365  <t>
366    Wherever this construct is used, null elements are allowed, but do
367    not contribute to the count of elements present. That is,
368    "(element), , (element) " is permitted, but counts as only two
369    elements. Therefore, where at least one element is required, at
370    least one non-null element &MUST; be present. Default values are 0
371    and infinity so that "#element" allows any number, including zero;
372    "1#element" requires at least one; and "1#2element" allows one or
373    two.
374  </t>
375</section>
376
377<section title="implied *LWS" anchor="implied.LWS">
378  <iref item="implied *LWS" primary="true"/>
379    <t>
380      The grammar described by this specification is word-based. Except
381      where noted otherwise, linear white space (LWS) can be included
382      between any two adjacent words (token or quoted-string), and
383      between adjacent words and separators, without changing the
384      interpretation of a field. At least one delimiter (LWS and/or
385      separators) &MUST; exist between any two tokens (for the definition
386      of "token" below), since they would otherwise be interpreted as a
387      single token.
388    </t>
389</section>
390</section>
391
392<section title="Basic Rules" anchor="basic.rules">
393<t anchor="rule.CRLF">
394  <x:anchor-alias value="CRLF"/>
395   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
396   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
397   tolerant applications). The end-of-line marker within an entity-body
398   is defined by its associated media type, as described in &media-types;.
399</t>
400<t anchor="rule.LWS">
401   All linear white space (LWS) in header field-values has the same semantics as SP. A
402   recipient &MAY; replace any such linear white space with a single SP before
403   interpreting the field value or forwarding the message downstream.
404</t>
405<t>
406   Historically, HTTP/1.1 header field values allow linear white space folding across
407   multiple lines. However, this specification deprecates its use; senders &MUST-NOT;
408   produce messages that include LWS folding (i.e., use the obs-fold rule), except
409   within the message/http media type (<xref target="internet.media.type.message.http"/>).
410   Receivers &SHOULD; still parse folded linear white space.
411</t>
412<t>
413   This specification uses three rules to denote the use of linear white space;
414   BWS ("Bad" White Space), OWS (Optional White Space), and RWS (Required White Space).
415</t>
416<t>
417   "Bad" white space is allowed by the BNF, but senders &SHOULD-NOT; produce it in messages.
418   Receivers &MUST; accept it in incoming messages.
419</t>
420<t>
421   Required white space is used when at least one linear white space character
422   is required to separate field tokens. In all such cases, a single SP character
423   &SHOULD; be used.
424</t>
425<t anchor="rule.whitespace">
426  <x:anchor-alias value="BWS"/>
427  <x:anchor-alias value="OWS"/>
428  <x:anchor-alias value="RWS"/>
429  <x:anchor-alias value="obs-fold"/>
430</t>
431<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"/>
432  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
433                 ; "optional" white space
434  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
435                 ; "required" white space
436  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
437                 ; "bad" white space
438  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
439</artwork></figure>
440<t anchor="rule.TEXT">
441  <x:anchor-alias value="TEXT"/>
442   The TEXT rule is only used for descriptive field contents and values
443   that are not intended to be interpreted by the message parser. Words
444   of *TEXT &MAY; contain characters from character sets other than ISO-8859-1
445   <xref target="ISO-8859-1"/> only when encoded according to the rules of
446   <xref target="RFC2047"/>.
447</t>
448<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TEXT"/>
449  <x:ref>TEXT</x:ref>           = %x20-7E / %x80-FF / <x:ref>OWS</x:ref>
450                 ; any <x:ref>OCTET</x:ref> except <x:ref>CTL</x:ref>s, but including <x:ref>OWS</x:ref>
451</artwork></figure>
452<t>
453   A CRLF is allowed in the definition of TEXT only as part of a header
454   field continuation. It is expected that the folding LWS will be
455   replaced with a single SP before interpretation of the TEXT value.
456</t>
457<t anchor="rule.token.separators">
458  <x:anchor-alias value="tchar"/>
459  <x:anchor-alias value="token"/>
460   Many HTTP/1.1 header field values consist of words separated by LWS
461   or special characters. These special characters &MUST; be in a quoted
462   string to be used within a parameter value (as defined in
463   <xref target="transfer.codings"/>).
464</t>
465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
466  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
467                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
468                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
469                 
470  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
471</artwork></figure>
472<t anchor="rule.comment">
473  <x:anchor-alias value="comment"/>
474  <x:anchor-alias value="ctext"/>
475   Comments can be included in some HTTP header fields by surrounding
476   the comment text with parentheses. Comments are only allowed in
477   fields containing "comment" as part of their field value definition.
478   In all other fields, parentheses are considered part of the field
479   value.
480</t>
481<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
482  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
483  <x:ref>ctext</x:ref>          = &lt;any <x:ref>TEXT</x:ref> excluding "(" and ")"&gt;
484</artwork></figure>
485<t anchor="rule.quoted-string">
486  <x:anchor-alias value="quoted-string"/>
487  <x:anchor-alias value="qdtext"/>
488   A string of text is parsed as a single word if it is quoted using
489   double-quote marks.
490</t>
491<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/>
492  <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>
493  <x:ref>qdtext</x:ref>         = &lt;any <x:ref>TEXT</x:ref> excluding <x:ref>DQUOTE</x:ref> and "\">
494</artwork></figure>
495<t anchor="rule.quoted-pair">
496  <x:anchor-alias value="quoted-pair"/>
497  <x:anchor-alias value="quoted-text"/>
498   The backslash character ("\") &MAY; be used as a single-character
499   quoting mechanism only within quoted-string and comment constructs.
500</t>
501<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
502  <x:ref>quoted-text</x:ref>    = %x01-09 /
503                   %x0B-0C /
504                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
505  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
506</artwork></figure>
507</section>
508
509<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
510  <x:anchor-alias value="request-header"/>
511  <x:anchor-alias value="response-header"/>
512  <x:anchor-alias value="accept-params"/>
513  <x:anchor-alias value="entity-body"/>
514  <x:anchor-alias value="entity-header"/>
515  <x:anchor-alias value="Cache-Control"/>
516  <x:anchor-alias value="Pragma"/>
517  <x:anchor-alias value="Warning"/>
518<t>
519  The ABNF rules below are defined in other parts:
520</t>
521<figure><!-- Part2--><artwork type="abnf2616">
522  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
523  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
524</artwork></figure>
525<figure><!-- Part3--><artwork type="abnf2616">
526  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
527  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
528  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
529</artwork></figure>
530<figure><!-- Part6--><artwork type="abnf2616">
531  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
532  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
533  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
534</artwork></figure>
535</section>
536
537</section>
538</section>
539
540<section title="HTTP architecture" anchor="architecture">
541<t>
542   HTTP was created with a specific architecture in mind, the World Wide Web,
543   and has evolved over time to support the scalability needs of a worldwide
544   hypertext system. Much of that architecture is reflected in the terminology
545   and syntax productions used to define HTTP.
546</t>
547
548<section title="Uniform Resource Identifiers" anchor="uri">
549<t>
550   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
551   throughout HTTP as the means for identifying resources. URI references
552   are used to target requests, redirect responses, and define relationships.
553   HTTP does not limit what a resource may be; it merely defines an interface
554   that can be used to interact with a resource via HTTP. More information on
555   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
556</t>
557  <x:anchor-alias value="URI"/>
558  <x:anchor-alias value="URI-reference"/>
559  <x:anchor-alias value="absolute-URI"/>
560  <x:anchor-alias value="relative-part"/>
561  <x:anchor-alias value="authority"/>
562  <x:anchor-alias value="fragment"/>
563  <x:anchor-alias value="path-abempty"/>
564  <x:anchor-alias value="path-absolute"/>
565  <x:anchor-alias value="port"/>
566  <x:anchor-alias value="query"/>
567  <x:anchor-alias value="uri-host"/>
568  <x:anchor-alias value="partial-URI"/>
569<t>
570   This specification adopts the definitions of "URI-reference",
571   "absolute-URI", "relative-part", "fragment", "port", "host",
572   "path-abempty", "path-absolute", "query", and "authority" from
573   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
574   protocol elements that allow a relative URI without a fragment.
575</t>
576<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"/>
577  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>>
578  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>>
579  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>>
580  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>>
581  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>>
582  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>>
583  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
584  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>>
585  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>>
586  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>>
587  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>>
588 
589  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
590</artwork></figure>
591<t>
592   Each protocol element in HTTP that allows a URI reference will indicate in
593   its ABNF production whether the element allows only a URI in absolute form
594   (absolute-URI), any relative reference (relative-ref), or some other subset
595   of the URI-reference grammar. Unless otherwise indicated, URI references
596   are parsed relative to the request target (the default base URI for both
597   the request and its corresponding response).
598</t>
599
600<section title="http URI scheme" anchor="http.uri">
601  <x:anchor-alias value="http-URI"/>
602  <iref item="http URI scheme" primary="true"/>
603  <iref item="URI scheme" subitem="http" primary="true"/>
604<t>
605   The "http" scheme is used to locate network resources via the HTTP
606   protocol. This section defines the syntax and semantics for identifiers
607   using the http or https URI schemes.
608</t>
609<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
610  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
611</artwork></figure>
612<t>
613   If the port is empty or not given, port 80 is assumed. The semantics
614   are that the identified resource is located at the server listening
615   for TCP connections on that port of that host, and the request-target
616   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
617   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
618   the path-absolute is not present in the URL, it &MUST; be given as "/" when
619   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
620   receives a host name which is not a fully qualified domain name, it
621   &MAY; add its domain to the host name it received. If a proxy receives
622   a fully qualified domain name, the proxy &MUST-NOT; change the host
623   name.
624</t>
625<t><list><t>
626  <iref item="https URI scheme"/>
627  <iref item="URI scheme" subitem="https"/>
628  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
629</t></list></t>
630</section>
631
632<section title="URI Comparison" anchor="uri.comparison">
633<t>
634   When comparing two URIs to decide if they match or not, a client
635   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
636   URIs, with these exceptions:
637  <list style="symbols">
638    <t>A port that is empty or not given is equivalent to the default
639        port for that URI-reference;</t>
640    <t>Comparisons of host names &MUST; be case-insensitive;</t>
641    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
642    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
643  </list>
644</t>
645<t>
646   Characters other than those in the "reserved" set (see
647   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
648   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
649</t>
650<t>
651   For example, the following three URIs are equivalent:
652</t>
653<figure><artwork type="example">
654   http://example.com:80/~smith/home.html
655   http://EXAMPLE.com/%7Esmith/home.html
656   http://EXAMPLE.com:/%7esmith/home.html
657</artwork></figure>
658</section>
659
660<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
661<t>
662</t>
663</section>
664</section>
665
666<section title="Overall Operation" anchor="intro.overall.operation">
667<t>
668   HTTP is a request/response protocol. A client sends a
669   request to the server in the form of a request method, URI, and
670   protocol version, followed by a MIME-like message containing request
671   modifiers, client information, and possible body content over a
672   connection with a server. The server responds with a status line,
673   including the message's protocol version and a success or error code,
674   followed by a MIME-like message containing server information, entity
675   metainformation, and possible entity-body content.
676</t>
677<t>
678   Most HTTP communication is initiated by a user agent and consists of
679   a request to be applied to a resource on some origin server. In the
680   simplest case, this may be accomplished via a single connection (v)
681   between the user agent (UA) and the origin server (O).
682</t>
683<figure><artwork type="drawing">
684       request chain ------------------------&gt;
685    UA -------------------v------------------- O
686       &lt;----------------------- response chain
687</artwork></figure>
688<t>
689   A more complicated situation occurs when one or more intermediaries
690   are present in the request/response chain. There are three common
691   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
692   forwarding agent, receiving requests for a URI in its absolute form,
693   rewriting all or part of the message, and forwarding the reformatted
694   request toward the server identified by the URI. A gateway is a
695   receiving agent, acting as a layer above some other server(s) and, if
696   necessary, translating the requests to the underlying server's
697   protocol. A tunnel acts as a relay point between two connections
698   without changing the messages; tunnels are used when the
699   communication needs to pass through an intermediary (such as a
700   firewall) even when the intermediary cannot understand the contents
701   of the messages.
702</t>
703<figure><artwork type="drawing">
704       request chain --------------------------------------&gt;
705    UA -----v----- A -----v----- B -----v----- C -----v----- O
706       &lt;------------------------------------- response chain
707</artwork></figure>
708<t>
709   The figure above shows three intermediaries (A, B, and C) between the
710   user agent and origin server. A request or response message that
711   travels the whole chain will pass through four separate connections.
712   This distinction is important because some HTTP communication options
713   may apply only to the connection with the nearest, non-tunnel
714   neighbor, only to the end-points of the chain, or to all connections
715   along the chain. Although the diagram is linear, each participant may
716   be engaged in multiple, simultaneous communications. For example, B
717   may be receiving requests from many clients other than A, and/or
718   forwarding requests to servers other than C, at the same time that it
719   is handling A's request.
720</t>
721<t>
722   Any party to the communication which is not acting as a tunnel may
723   employ an internal cache for handling requests. The effect of a cache
724   is that the request/response chain is shortened if one of the
725   participants along the chain has a cached response applicable to that
726   request. The following illustrates the resulting chain if B has a
727   cached copy of an earlier response from O (via C) for a request which
728   has not been cached by UA or A.
729</t>
730<figure><artwork type="drawing">
731          request chain ----------&gt;
732       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
733          &lt;--------- response chain
734</artwork></figure>
735<t>
736   Not all responses are usefully cacheable, and some requests may
737   contain modifiers which place special requirements on cache behavior.
738   HTTP requirements for cache behavior and cacheable responses are
739   defined in &caching;.
740</t>
741<t>
742   In fact, there are a wide variety of architectures and configurations
743   of caches and proxies currently being experimented with or deployed
744   across the World Wide Web. These systems include national hierarchies
745   of proxy caches to save transoceanic bandwidth, systems that
746   broadcast or multicast cache entries, organizations that distribute
747   subsets of cached data via CD-ROM, and so on. HTTP systems are used
748   in corporate intranets over high-bandwidth links, and for access via
749   PDAs with low-power radio links and intermittent connectivity. The
750   goal of HTTP/1.1 is to support the wide diversity of configurations
751   already deployed while introducing protocol constructs that meet the
752   needs of those who build web applications that require high
753   reliability and, failing that, at least reliable indications of
754   failure.
755</t>
756<t>
757   HTTP communication usually takes place over TCP/IP connections. The
758   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
759   not preclude HTTP from being implemented on top of any other protocol
760   on the Internet, or on other networks. HTTP only presumes a reliable
761   transport; any protocol that provides such guarantees can be used;
762   the mapping of the HTTP/1.1 request and response structures onto the
763   transport data units of the protocol in question is outside the scope
764   of this specification.
765</t>
766<t>
767   In HTTP/1.0, most implementations used a new connection for each
768   request/response exchange. In HTTP/1.1, a connection may be used for
769   one or more request/response exchanges, although connections may be
770   closed for a variety of reasons (see <xref target="persistent.connections"/>).
771</t>
772</section>
773
774<section title="Use of HTTP for proxy communication" anchor="http.proxy">
775<t>
776   Configured to use HTTP to proxy HTTP or other protocols.
777</t>
778</section>
779<section title="Interception of HTTP for access control" anchor="http.intercept">
780<t>
781   Interception of HTTP traffic for initiating access control.
782</t>
783</section>
784<section title="Use of HTTP by other protocols" anchor="http.others">
785<t>
786   Profiles of HTTP defined by other protocol.
787   Extensions of HTTP like WebDAV.
788</t>
789</section>
790<section title="Use of HTTP by media type specification" anchor="http.media">
791<t>
792   Instructions on composing HTTP requests via hypertext formats.
793</t>
794</section>
795</section>
796
797<section title="Protocol Parameters" anchor="protocol.parameters">
798
799<section title="HTTP Version" anchor="http.version">
800  <x:anchor-alias value="HTTP-Version"/>
801  <x:anchor-alias value="HTTP-Prot-Name"/>
802<t>
803   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
804   of the protocol. The protocol versioning policy is intended to allow
805   the sender to indicate the format of a message and its capacity for
806   understanding further HTTP communication, rather than the features
807   obtained via that communication. No change is made to the version
808   number for the addition of message components which do not affect
809   communication behavior or which only add to extensible field values.
810   The &lt;minor&gt; number is incremented when the changes made to the
811   protocol add features which do not change the general message parsing
812   algorithm, but which may add to the message semantics and imply
813   additional capabilities of the sender. The &lt;major&gt; number is
814   incremented when the format of a message within the protocol is
815   changed. See <xref target="RFC2145"/> for a fuller explanation.
816</t>
817<t>
818   The version of an HTTP message is indicated by an HTTP-Version field
819   in the first line of the message. HTTP-Version is case-sensitive.
820</t>
821<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
822  <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>
823  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
824</artwork></figure>
825<t>
826   Note that the major and minor numbers &MUST; be treated as separate
827   integers and that each &MAY; be incremented higher than a single digit.
828   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
829   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
830   &MUST-NOT; be sent.
831</t>
832<t>
833   An application that sends a request or response message that includes
834   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
835   with this specification. Applications that are at least conditionally
836   compliant with this specification &SHOULD; use an HTTP-Version of
837   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
838   not compatible with HTTP/1.0. For more details on when to send
839   specific HTTP-Version values, see <xref target="RFC2145"/>.
840</t>
841<t>
842   The HTTP version of an application is the highest HTTP version for
843   which the application is at least conditionally compliant.
844</t>
845<t>
846   Proxy and gateway applications need to be careful when forwarding
847   messages in protocol versions different from that of the application.
848   Since the protocol version indicates the protocol capability of the
849   sender, a proxy/gateway &MUST-NOT; send a message with a version
850   indicator which is greater than its actual version. If a higher
851   version request is received, the proxy/gateway &MUST; either downgrade
852   the request version, or respond with an error, or switch to tunnel
853   behavior.
854</t>
855<t>
856   Due to interoperability problems with HTTP/1.0 proxies discovered
857   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
858   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
859   they support. The proxy/gateway's response to that request &MUST; be in
860   the same major version as the request.
861</t>
862<t>
863  <list>
864    <t>
865      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
866      of header fields required or forbidden by the versions involved.
867    </t>
868  </list>
869</t>
870</section>
871
872<section title="Date/Time Formats" anchor="date.time.formats">
873<section title="Full Date" anchor="full.date">
874  <x:anchor-alias value="HTTP-date"/>
875  <x:anchor-alias value="obsolete-date"/>
876  <x:anchor-alias value="rfc1123-date"/>
877  <x:anchor-alias value="rfc850-date"/>
878  <x:anchor-alias value="asctime-date"/>
879  <x:anchor-alias value="date1"/>
880  <x:anchor-alias value="date2"/>
881  <x:anchor-alias value="date3"/>
882  <x:anchor-alias value="rfc1123-date"/>
883  <x:anchor-alias value="time"/>
884  <x:anchor-alias value="wkday"/>
885  <x:anchor-alias value="weekday"/>
886  <x:anchor-alias value="month"/>
887<t>
888   HTTP applications have historically allowed three different formats
889   for the representation of date/time stamps:
890</t>
891<figure><artwork type="example">
892   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
893   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
894   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
895</artwork></figure>
896<t>
897   The first format is preferred as an Internet standard and represents
898   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
899   other formats are described here only for
900   compatibility with obsolete implementations.
901   HTTP/1.1 clients and servers that parse the date value &MUST; accept
902   all three formats (for compatibility with HTTP/1.0), though they &MUST;
903   only generate the RFC 1123 format for representing HTTP-date values
904   in header fields. See <xref target="tolerant.applications"/> for further information.
905</t>
906<t><list><t>
907      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
908      accepting date values that may have been sent by non-HTTP
909      applications, as is sometimes the case when retrieving or posting
910      messages via proxies/gateways to SMTP or NNTP.
911</t></list></t>
912<t>
913   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
914   (GMT), without exception. For the purposes of HTTP, GMT is exactly
915   equal to UTC (Coordinated Universal Time). This is indicated in the
916   first two formats by the inclusion of "GMT" as the three-letter
917   abbreviation for time zone, and &MUST; be assumed when reading the
918   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
919   additional LWS beyond that specifically included as SP in the
920   grammar.
921</t>
922<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="obsolete-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/>
923  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
924  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref>
925  <x:ref>rfc1123-date</x:ref> = <x:ref>wkday</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
926  <x:ref>rfc850-date</x:ref>  = <x:ref>weekday</x:ref> "," <x:ref>SP</x:ref> date2 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
927  <x:ref>asctime-date</x:ref> = <x:ref>wkday</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
928  <x:ref>date1</x:ref>        = 2<x:ref>DIGIT</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
929                 ; day month year (e.g., 02 Jun 1982)
930  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
931                 ; day-month-year (e.g., 02-Jun-82)
932  <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> ))
933                 ; month day (e.g., Jun  2)
934  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
935                 ; 00:00:00 - 23:59:59
936  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
937               / s-Thu / s-Fri / s-Sat / s-Sun
938  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
939               / l-Thu / l-Fri / l-Sat / l-Sun
940  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
941               / s-May / s-Jun / s-Jul / s-Aug
942               / s-Sep / s-Oct / s-Nov / s-Dec
943               
944  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
945
946  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
947  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
948  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
949  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
950  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
951  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
952  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
953
954  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
955  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
956  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
957  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
958  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
959  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
960  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
961
962  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
963  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
964  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
965  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
966  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
967  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
968  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
969  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
970  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
971  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
972  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
973  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
974</artwork></figure>
975<t>
976      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
977      to their usage within the protocol stream. Clients and servers are
978      not required to use these formats for user presentation, request
979      logging, etc.
980</t>
981</section>
982</section>
983
984<section title="Transfer Codings" anchor="transfer.codings">
985  <x:anchor-alias value="parameter"/>
986  <x:anchor-alias value="transfer-coding"/>
987  <x:anchor-alias value="transfer-extension"/>
988<t>
989   Transfer-coding values are used to indicate an encoding
990   transformation that has been, can be, or may need to be applied to an
991   entity-body in order to ensure "safe transport" through the network.
992   This differs from a content coding in that the transfer-coding is a
993   property of the message, not of the original entity.
994</t>
995<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
996  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
997  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
998</artwork></figure>
999<t anchor="rule.parameter">
1000  <x:anchor-alias value="attribute"/>
1001  <x:anchor-alias value="parameter"/>
1002  <x:anchor-alias value="value"/>
1003   Parameters are in  the form of attribute/value pairs.
1004</t>
1005<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
1006  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
1007  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1008  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1009</artwork></figure>
1010<t>
1011   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1012   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1013   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1014</t>
1015<t>
1016   Whenever a transfer-coding is applied to a message-body, the set of
1017   transfer-codings &MUST; include "chunked", unless the message indicates it
1018   is terminated by closing the connection. When the "chunked" transfer-coding
1019   is used, it &MUST; be the last transfer-coding applied to the
1020   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1021   than once to a message-body. These rules allow the recipient to
1022   determine the transfer-length of the message (<xref target="message.length"/>).
1023</t>
1024<t>
1025   Transfer-codings are analogous to the Content-Transfer-Encoding
1026   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1027   binary data over a 7-bit transport service. However, safe transport
1028   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1029   the only unsafe characteristic of message-bodies is the difficulty in
1030   determining the exact body length (<xref target="message.length"/>), or the desire to
1031   encrypt data over a shared transport.
1032</t>
1033<t>
1034   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1035   transfer-coding value tokens. Initially, the registry contains the
1036   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1037   "gzip", "compress", and "deflate" (&content-codings;).
1038</t>
1039<t>
1040   New transfer-coding value tokens &SHOULD; be registered in the same way
1041   as new content-coding value tokens (&content-codings;).
1042</t>
1043<t>
1044   A server which receives an entity-body with a transfer-coding it does
1045   not understand &SHOULD; return 501 (Not Implemented), and close the
1046   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1047   client.
1048</t>
1049
1050<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1051  <x:anchor-alias value="chunk"/>
1052  <x:anchor-alias value="Chunked-Body"/>
1053  <x:anchor-alias value="chunk-data"/>
1054  <x:anchor-alias value="chunk-ext"/>
1055  <x:anchor-alias value="chunk-ext-name"/>
1056  <x:anchor-alias value="chunk-ext-val"/>
1057  <x:anchor-alias value="chunk-size"/>
1058  <x:anchor-alias value="last-chunk"/>
1059  <x:anchor-alias value="trailer-part"/>
1060<t>
1061   The chunked encoding modifies the body of a message in order to
1062   transfer it as a series of chunks, each with its own size indicator,
1063   followed by an &OPTIONAL; trailer containing entity-header fields. This
1064   allows dynamically produced content to be transferred along with the
1065   information necessary for the recipient to verify that it has
1066   received the full message.
1067</t>
1068<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"/>
1069  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1070                   <x:ref>last-chunk</x:ref>
1071                   <x:ref>trailer-part</x:ref>
1072                   <x:ref>CRLF</x:ref>
1073 
1074  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1075                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1076  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1077  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1078 
1079  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1080                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1081  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1082  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1083  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1084  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1085</artwork></figure>
1086<t>
1087   The chunk-size field is a string of hex digits indicating the size of
1088   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1089   zero, followed by the trailer, which is terminated by an empty line.
1090</t>
1091<t>
1092   The trailer allows the sender to include additional HTTP header
1093   fields at the end of the message. The Trailer header field can be
1094   used to indicate which header fields are included in a trailer (see
1095   <xref target="header.trailer"/>).
1096</t>
1097<t>
1098   A server using chunked transfer-coding in a response &MUST-NOT; use the
1099   trailer for any header fields unless at least one of the following is
1100   true:
1101  <list style="numbers">
1102    <t>the request included a TE header field that indicates "trailers" is
1103     acceptable in the transfer-coding of the  response, as described in
1104     <xref target="header.te"/>; or,</t>
1105
1106    <t>the server is the origin server for the response, the trailer
1107     fields consist entirely of optional metadata, and the recipient
1108     could use the message (in a manner acceptable to the origin server)
1109     without receiving this metadata.  In other words, the origin server
1110     is willing to accept the possibility that the trailer fields might
1111     be silently discarded along the path to the client.</t>
1112  </list>
1113</t>
1114<t>
1115   This requirement prevents an interoperability failure when the
1116   message is being received by an HTTP/1.1 (or later) proxy and
1117   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1118   compliance with the protocol would have necessitated a possibly
1119   infinite buffer on the proxy.
1120</t>
1121<t>
1122   A process for decoding the "chunked" transfer-coding
1123   can be represented in pseudo-code as:
1124</t>
1125<figure><artwork type="code">
1126  length := 0
1127  read chunk-size, chunk-ext (if any) and CRLF
1128  while (chunk-size &gt; 0) {
1129     read chunk-data and CRLF
1130     append chunk-data to entity-body
1131     length := length + chunk-size
1132     read chunk-size and CRLF
1133  }
1134  read entity-header
1135  while (entity-header not empty) {
1136     append entity-header to existing header fields
1137     read entity-header
1138  }
1139  Content-Length := length
1140  Remove "chunked" from Transfer-Encoding
1141</artwork></figure>
1142<t>
1143   All HTTP/1.1 applications &MUST; be able to receive and decode the
1144   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1145   they do not understand.
1146</t>
1147</section>
1148</section>
1149
1150<section title="Product Tokens" anchor="product.tokens">
1151  <x:anchor-alias value="product"/>
1152  <x:anchor-alias value="product-version"/>
1153<t>
1154   Product tokens are used to allow communicating applications to
1155   identify themselves by software name and version. Most fields using
1156   product tokens also allow sub-products which form a significant part
1157   of the application to be listed, separated by white space. By
1158   convention, the products are listed in order of their significance
1159   for identifying the application.
1160</t>
1161<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1162  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1163  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1164</artwork></figure>
1165<t>
1166   Examples:
1167</t>
1168<figure><artwork type="example">
1169    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1170    Server: Apache/0.8.4
1171</artwork></figure>
1172<t>
1173   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1174   used for advertising or other non-essential information. Although any
1175   token character &MAY; appear in a product-version, this token &SHOULD;
1176   only be used for a version identifier (i.e., successive versions of
1177   the same product &SHOULD; only differ in the product-version portion of
1178   the product value).
1179</t>
1180</section>
1181
1182</section>
1183
1184<section title="HTTP Message" anchor="http.message">
1185
1186<section title="Message Types" anchor="message.types">
1187  <x:anchor-alias value="generic-message"/>
1188  <x:anchor-alias value="HTTP-message"/>
1189  <x:anchor-alias value="start-line"/>
1190<t>
1191   HTTP messages consist of requests from client to server and responses
1192   from server to client.
1193</t>
1194<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1195  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1196</artwork></figure>
1197<t>
1198   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1199   message format of <xref target="RFC5322"/> for transferring entities (the payload
1200   of the message). Both types of message consist of a start-line, zero
1201   or more header fields (also known as "headers"), an empty line (i.e.,
1202   a line with nothing preceding the CRLF) indicating the end of the
1203   header fields, and possibly a message-body.
1204</t>
1205<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1206  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1207                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1208                    <x:ref>CRLF</x:ref>
1209                    [ <x:ref>message-body</x:ref> ]
1210  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1211</artwork></figure>
1212<t>
1213   In the interest of robustness, servers &SHOULD; ignore any empty
1214   line(s) received where a Request-Line is expected. In other words, if
1215   the server is reading the protocol stream at the beginning of a
1216   message and receives a CRLF first, it should ignore the CRLF.
1217</t>
1218<t>
1219   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1220   after a POST request. To restate what is explicitly forbidden by the
1221   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1222   extra CRLF.
1223</t>
1224</section>
1225
1226<section title="Message Headers" anchor="message.headers">
1227  <x:anchor-alias value="field-content"/>
1228  <x:anchor-alias value="field-name"/>
1229  <x:anchor-alias value="field-value"/>
1230  <x:anchor-alias value="message-header"/>
1231<t>
1232   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1233   request-header (&request-header-fields;), response-header (&response-header-fields;), and
1234   entity-header (&entity-header-fields;) fields, follow the same generic format as
1235   that given in <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1236   of a name followed by a colon (":") and the field value. Field names
1237   are case-insensitive. The field value &MAY; be preceded by any amount
1238   of LWS, though a single SP is preferred. Header fields can be
1239   extended over multiple lines by preceding each extra line with at
1240   least one SP or HTAB. Applications ought to follow "common form", where
1241   one is known or indicated, when generating HTTP constructs, since
1242   there might exist some implementations that fail to accept anything
1243   beyond the common forms.
1244</t>
1245<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"/>
1246  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" [ <x:ref>field-value</x:ref> ]
1247  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1248  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1249  <x:ref>field-content</x:ref>  = &lt;field content&gt;
1250</artwork></figure>
1251<t>
1252  <cref>whitespace between field-name and colon is an error and MUST NOT be accepted</cref>
1253</t>
1254<t>
1255   The field-content does not include any leading or trailing LWS:
1256   linear white space occurring before the first non-whitespace
1257   character of the field-value or after the last non-whitespace
1258   character of the field-value. Such leading or trailing LWS &MAY; be
1259   removed without changing the semantics of the field value. Any LWS
1260   that occurs between field-content &MAY; be replaced with a single SP
1261   before interpreting the field value or forwarding the message
1262   downstream.
1263</t>
1264<t>
1265   The order in which header fields with differing field names are
1266   received is not significant. However, it is "good practice" to send
1267   general-header fields first, followed by request-header or response-header
1268   fields, and ending with the entity-header fields.
1269</t>
1270<t>
1271   Multiple message-header fields with the same field-name &MAY; be
1272   present in a message if and only if the entire field-value for that
1273   header field is defined as a comma-separated list [i.e., #(values)].
1274   It &MUST; be possible to combine the multiple header fields into one
1275   "field-name: field-value" pair, without changing the semantics of the
1276   message, by appending each subsequent field-value to the first, each
1277   separated by a comma. The order in which header fields with the same
1278   field-name are received is therefore significant to the
1279   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1280   change the order of these field values when a message is forwarded.
1281</t>
1282<t>
1283  <list><t>
1284   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1285   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1286   can occur multiple times, but does not use the list syntax, and thus cannot
1287   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1288   for details.) Also note that the Set-Cookie2 header specified in
1289   <xref target="RFC2965"/> does not share this problem.
1290  </t></list>
1291</t>
1292 
1293</section>
1294
1295<section title="Message Body" anchor="message.body">
1296  <x:anchor-alias value="message-body"/>
1297<t>
1298   The message-body (if any) of an HTTP message is used to carry the
1299   entity-body associated with the request or response. The message-body
1300   differs from the entity-body only when a transfer-coding has been
1301   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1302</t>
1303<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1304  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1305               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1306</artwork></figure>
1307<t>
1308   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1309   applied by an application to ensure safe and proper transfer of the
1310   message. Transfer-Encoding is a property of the message, not of the
1311   entity, and thus &MAY; be added or removed by any application along the
1312   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1313   when certain transfer-codings may be used.)
1314</t>
1315<t>
1316   The rules for when a message-body is allowed in a message differ for
1317   requests and responses.
1318</t>
1319<t>
1320   The presence of a message-body in a request is signaled by the
1321   inclusion of a Content-Length or Transfer-Encoding header field in
1322   the request's message-headers. A message-body &MUST-NOT; be included in
1323   a request if the specification of the request method (&method;)
1324   explicitly disallows an entity-body in requests.
1325   When a request message contains both a message-body of non-zero
1326   length and a method that does not define any semantics for that
1327   request message-body, then an origin server &SHOULD; either ignore
1328   the message-body or respond with an appropriate error message
1329   (e.g., 413).  A proxy or gateway, when presented the same request,
1330   &SHOULD; either forward the request inbound with the message-body or
1331   ignore the message-body when determining a response.
1332</t>
1333<t>
1334   For response messages, whether or not a message-body is included with
1335   a message is dependent on both the request method and the response
1336   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1337   &MUST-NOT; include a message-body, even though the presence of entity-header
1338   fields might lead one to believe they do. All 1xx
1339   (informational), 204 (No Content), and 304 (Not Modified) responses
1340   &MUST-NOT; include a message-body. All other responses do include a
1341   message-body, although it &MAY; be of zero length.
1342</t>
1343</section>
1344
1345<section title="Message Length" anchor="message.length">
1346<t>
1347   The transfer-length of a message is the length of the message-body as
1348   it appears in the message; that is, after any transfer-codings have
1349   been applied. When a message-body is included with a message, the
1350   transfer-length of that body is determined by one of the following
1351   (in order of precedence):
1352</t>
1353<t>
1354  <list style="numbers">
1355    <x:lt><t>
1356     Any response message which "&MUST-NOT;" include a message-body (such
1357     as the 1xx, 204, and 304 responses and any response to a HEAD
1358     request) is always terminated by the first empty line after the
1359     header fields, regardless of the entity-header fields present in
1360     the message.
1361    </t></x:lt>
1362    <x:lt><t>
1363     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1364     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1365     is used, the transfer-length is defined by the use of this transfer-coding.
1366     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1367     is not present, the transfer-length is defined by the sender closing the connection.
1368    </t></x:lt>
1369    <x:lt><t>
1370     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1371     decimal value in OCTETs represents both the entity-length and the
1372     transfer-length. The Content-Length header field &MUST-NOT; be sent
1373     if these two lengths are different (i.e., if a Transfer-Encoding
1374     header field is present). If a message is received with both a
1375     Transfer-Encoding header field and a Content-Length header field,
1376     the latter &MUST; be ignored.
1377    </t></x:lt>
1378    <x:lt><t>
1379     If the message uses the media type "multipart/byteranges", and the
1380     transfer-length is not otherwise specified, then this self-delimiting
1381     media type defines the transfer-length. This media type
1382     &MUST-NOT; be used unless the sender knows that the recipient can parse
1383     it; the presence in a request of a Range header with multiple byte-range
1384     specifiers from a 1.1 client implies that the client can parse
1385     multipart/byteranges responses.
1386    <list style="empty"><t>
1387       A range header might be forwarded by a 1.0 proxy that does not
1388       understand multipart/byteranges; in this case the server &MUST;
1389       delimit the message using methods defined in items 1, 3 or 5 of
1390       this section.
1391    </t></list>
1392    </t></x:lt>
1393    <x:lt><t>
1394     By the server closing the connection. (Closing the connection
1395     cannot be used to indicate the end of a request body, since that
1396     would leave no possibility for the server to send back a response.)
1397    </t></x:lt>
1398  </list>
1399</t>
1400<t>
1401   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1402   containing a message-body &MUST; include a valid Content-Length header
1403   field unless the server is known to be HTTP/1.1 compliant. If a
1404   request contains a message-body and a Content-Length is not given,
1405   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1406   determine the length of the message, or with 411 (Length Required) if
1407   it wishes to insist on receiving a valid Content-Length.
1408</t>
1409<t>
1410   All HTTP/1.1 applications that receive entities &MUST; accept the
1411   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1412   to be used for messages when the message length cannot be determined
1413   in advance.
1414</t>
1415<t>
1416   Messages &MUST-NOT; include both a Content-Length header field and a
1417   transfer-coding. If the message does include a
1418   transfer-coding, the Content-Length &MUST; be ignored.
1419</t>
1420<t>
1421   When a Content-Length is given in a message where a message-body is
1422   allowed, its field value &MUST; exactly match the number of OCTETs in
1423   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1424   invalid length is received and detected.
1425</t>
1426</section>
1427
1428<section title="General Header Fields" anchor="general.header.fields">
1429  <x:anchor-alias value="general-header"/>
1430<t>
1431   There are a few header fields which have general applicability for
1432   both request and response messages, but which do not apply to the
1433   entity being transferred. These header fields apply only to the
1434   message being transmitted.
1435</t>
1436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1437  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1438                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1439                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1440                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1441                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1442                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1443                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1444                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1445                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1446</artwork></figure>
1447<t>
1448   General-header field names can be extended reliably only in
1449   combination with a change in the protocol version. However, new or
1450   experimental header fields may be given the semantics of general
1451   header fields if all parties in the communication recognize them to
1452   be general-header fields. Unrecognized header fields are treated as
1453   entity-header fields.
1454</t>
1455</section>
1456</section>
1457
1458<section title="Request" anchor="request">
1459  <x:anchor-alias value="Request"/>
1460<t>
1461   A request message from a client to a server includes, within the
1462   first line of that message, the method to be applied to the resource,
1463   the identifier of the resource, and the protocol version in use.
1464</t>
1465<!--                 Host                      ; should be moved here eventually -->
1466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1467  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1468                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1469                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1470                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1471                  <x:ref>CRLF</x:ref>
1472                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1473</artwork></figure>
1474
1475<section title="Request-Line" anchor="request-line">
1476  <x:anchor-alias value="Request-Line"/>
1477<t>
1478   The Request-Line begins with a method token, followed by the
1479   request-target and the protocol version, and ending with CRLF. The
1480   elements are separated by SP characters. No CR or LF is allowed
1481   except in the final CRLF sequence.
1482</t>
1483<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1484  <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>
1485</artwork></figure>
1486
1487<section title="Method" anchor="method">
1488  <x:anchor-alias value="Method"/>
1489<t>
1490   The Method  token indicates the method to be performed on the
1491   resource identified by the request-target. The method is case-sensitive.
1492</t>
1493<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1494  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1495</artwork></figure>
1496</section>
1497
1498<section title="request-target" anchor="request-target">
1499  <x:anchor-alias value="request-target"/>
1500<t>
1501   The request-target is a Uniform Resource Identifier (<xref target="uri"/>) and
1502   identifies the resource upon which to apply the request.
1503</t>
1504<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1505  <x:ref>request-target</x:ref>    = "*"
1506                 / <x:ref>absolute-URI</x:ref>
1507                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1508                 / <x:ref>authority</x:ref>
1509</artwork></figure>
1510<t>
1511   The four options for request-target are dependent on the nature of the
1512   request. The asterisk "*" means that the request does not apply to a
1513   particular resource, but to the server itself, and is only allowed
1514   when the method used does not necessarily apply to a resource. One
1515   example would be
1516</t>
1517<figure><artwork type="example">
1518    OPTIONS * HTTP/1.1
1519</artwork></figure>
1520<t>
1521   The absolute-URI form is &REQUIRED; when the request is being made to a
1522   proxy. The proxy is requested to forward the request or service it
1523   from a valid cache, and return the response. Note that the proxy &MAY;
1524   forward the request on to another proxy or directly to the server
1525   specified by the absolute-URI. In order to avoid request loops, a
1526   proxy &MUST; be able to recognize all of its server names, including
1527   any aliases, local variations, and the numeric IP address. An example
1528   Request-Line would be:
1529</t>
1530<figure><artwork type="example">
1531    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1532</artwork></figure>
1533<t>
1534   To allow for transition to absolute-URIs in all requests in future
1535   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1536   form in requests, even though HTTP/1.1 clients will only generate
1537   them in requests to proxies.
1538</t>
1539<t>
1540   The authority form is only used by the CONNECT method (&CONNECT;).
1541</t>
1542<t>
1543   The most common form of request-target is that used to identify a
1544   resource on an origin server or gateway. In this case the absolute
1545   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1546   the request-target, and the network location of the URI (authority) &MUST;
1547   be transmitted in a Host header field. For example, a client wishing
1548   to retrieve the resource above directly from the origin server would
1549   create a TCP connection to port 80 of the host "www.example.org" and send
1550   the lines:
1551</t>
1552<figure><artwork type="example">
1553    GET /pub/WWW/TheProject.html HTTP/1.1
1554    Host: www.example.org
1555</artwork></figure>
1556<t>
1557   followed by the remainder of the Request. Note that the absolute path
1558   cannot be empty; if none is present in the original URI, it &MUST; be
1559   given as "/" (the server root).
1560</t>
1561<t>
1562   The request-target is transmitted in the format specified in
1563   <xref target="http.uri"/>. If the request-target is encoded using the
1564   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1565   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1566   &MUST; decode the request-target in order to
1567   properly interpret the request. Servers &SHOULD; respond to invalid
1568   request-targets with an appropriate status code.
1569</t>
1570<t>
1571   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1572   received request-target when forwarding it to the next inbound server,
1573   except as noted above to replace a null path-absolute with "/".
1574</t>
1575<t>
1576  <list><t>
1577      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1578      meaning of the request when the origin server is improperly using
1579      a non-reserved URI character for a reserved purpose.  Implementors
1580      should be aware that some pre-HTTP/1.1 proxies have been known to
1581      rewrite the request-target.
1582  </t></list>
1583</t>
1584<t>
1585   HTTP does not place a pre-defined limit on the length of a request-target.
1586   A server &MUST; be prepared to receive URIs of unbounded length and
1587   respond with the 414 (URI too long) status if the received
1588   request-target would be longer than the server wishes to handle
1589   (see &status-414;).
1590</t>
1591<t>
1592   Various ad-hoc limitations on request-target length are found in practice.
1593   It is &RECOMMENDED; that all HTTP senders and recipients support
1594   request-target lengths of 8000 or more OCTETs.
1595</t>
1596</section>
1597</section>
1598
1599<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1600<t>
1601   The exact resource identified by an Internet request is determined by
1602   examining both the request-target and the Host header field.
1603</t>
1604<t>
1605   An origin server that does not allow resources to differ by the
1606   requested host &MAY; ignore the Host header field value when
1607   determining the resource identified by an HTTP/1.1 request. (But see
1608   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1609   for other requirements on Host support in HTTP/1.1.)
1610</t>
1611<t>
1612   An origin server that does differentiate resources based on the host
1613   requested (sometimes referred to as virtual hosts or vanity host
1614   names) &MUST; use the following rules for determining the requested
1615   resource on an HTTP/1.1 request:
1616  <list style="numbers">
1617    <t>If request-target is an absolute-URI, the host is part of the
1618     request-target. Any Host header field value in the request &MUST; be
1619     ignored.</t>
1620    <t>If the request-target is not an absolute-URI, and the request includes
1621     a Host header field, the host is determined by the Host header
1622     field value.</t>
1623    <t>If the host as determined by rule 1 or 2 is not a valid host on
1624     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1625  </list>
1626</t>
1627<t>
1628   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1629   attempt to use heuristics (e.g., examination of the URI path for
1630   something unique to a particular host) in order to determine what
1631   exact resource is being requested.
1632</t>
1633</section>
1634
1635</section>
1636
1637
1638<section title="Response" anchor="response">
1639  <x:anchor-alias value="Response"/>
1640<t>
1641   After receiving and interpreting a request message, a server responds
1642   with an HTTP response message.
1643</t>
1644<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1645  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1646                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1647                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1648                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1649                  <x:ref>CRLF</x:ref>
1650                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1651</artwork></figure>
1652
1653<section title="Status-Line" anchor="status-line">
1654  <x:anchor-alias value="Status-Line"/>
1655<t>
1656   The first line of a Response message is the Status-Line, consisting
1657   of the protocol version followed by a numeric status code and its
1658   associated textual phrase, with each element separated by SP
1659   characters. No CR or LF is allowed except in the final CRLF sequence.
1660</t>
1661<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1662  <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>
1663</artwork></figure>
1664
1665<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1666  <x:anchor-alias value="Reason-Phrase"/>
1667  <x:anchor-alias value="Status-Code"/>
1668<t>
1669   The Status-Code element is a 3-digit integer result code of the
1670   attempt to understand and satisfy the request. These codes are fully
1671   defined in &status-codes;.  The Reason Phrase exists for the sole
1672   purpose of providing a textual description associated with the numeric
1673   status code, out of deference to earlier Internet application protocols
1674   that were more frequently used with interactive text clients.
1675   A client &SHOULD; ignore the content of the Reason Phrase.
1676</t>
1677<t>
1678   The first digit of the Status-Code defines the class of response. The
1679   last two digits do not have any categorization role. There are 5
1680   values for the first digit:
1681  <list style="symbols">
1682    <t>
1683      1xx: Informational - Request received, continuing process
1684    </t>
1685    <t>
1686      2xx: Success - The action was successfully received,
1687        understood, and accepted
1688    </t>
1689    <t>
1690      3xx: Redirection - Further action must be taken in order to
1691        complete the request
1692    </t>
1693    <t>
1694      4xx: Client Error - The request contains bad syntax or cannot
1695        be fulfilled
1696    </t>
1697    <t>
1698      5xx: Server Error - The server failed to fulfill an apparently
1699        valid request
1700    </t>
1701  </list>
1702</t>
1703<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"/>
1704  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1705  <x:ref>Reason-Phrase</x:ref>  = *&lt;<x:ref>TEXT</x:ref>, excluding <x:ref>CR</x:ref>, <x:ref>LF</x:ref>&gt;
1706</artwork></figure>
1707</section>
1708</section>
1709
1710</section>
1711
1712
1713<section title="Connections" anchor="connections">
1714
1715<section title="Persistent Connections" anchor="persistent.connections">
1716
1717<section title="Purpose" anchor="persistent.purpose">
1718<t>
1719   Prior to persistent connections, a separate TCP connection was
1720   established to fetch each URL, increasing the load on HTTP servers
1721   and causing congestion on the Internet. The use of inline images and
1722   other associated data often require a client to make multiple
1723   requests of the same server in a short amount of time. Analysis of
1724   these performance problems and results from a prototype
1725   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1726   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1727   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1728   T/TCP <xref target="Tou1998"/>.
1729</t>
1730<t>
1731   Persistent HTTP connections have a number of advantages:
1732  <list style="symbols">
1733      <t>
1734        By opening and closing fewer TCP connections, CPU time is saved
1735        in routers and hosts (clients, servers, proxies, gateways,
1736        tunnels, or caches), and memory used for TCP protocol control
1737        blocks can be saved in hosts.
1738      </t>
1739      <t>
1740        HTTP requests and responses can be pipelined on a connection.
1741        Pipelining allows a client to make multiple requests without
1742        waiting for each response, allowing a single TCP connection to
1743        be used much more efficiently, with much lower elapsed time.
1744      </t>
1745      <t>
1746        Network congestion is reduced by reducing the number of packets
1747        caused by TCP opens, and by allowing TCP sufficient time to
1748        determine the congestion state of the network.
1749      </t>
1750      <t>
1751        Latency on subsequent requests is reduced since there is no time
1752        spent in TCP's connection opening handshake.
1753      </t>
1754      <t>
1755        HTTP can evolve more gracefully, since errors can be reported
1756        without the penalty of closing the TCP connection. Clients using
1757        future versions of HTTP might optimistically try a new feature,
1758        but if communicating with an older server, retry with old
1759        semantics after an error is reported.
1760      </t>
1761    </list>
1762</t>
1763<t>
1764   HTTP implementations &SHOULD; implement persistent connections.
1765</t>
1766</section>
1767
1768<section title="Overall Operation" anchor="persistent.overall">
1769<t>
1770   A significant difference between HTTP/1.1 and earlier versions of
1771   HTTP is that persistent connections are the default behavior of any
1772   HTTP connection. That is, unless otherwise indicated, the client
1773   &SHOULD; assume that the server will maintain a persistent connection,
1774   even after error responses from the server.
1775</t>
1776<t>
1777   Persistent connections provide a mechanism by which a client and a
1778   server can signal the close of a TCP connection. This signaling takes
1779   place using the Connection header field (<xref target="header.connection"/>). Once a close
1780   has been signaled, the client &MUST-NOT; send any more requests on that
1781   connection.
1782</t>
1783
1784<section title="Negotiation" anchor="persistent.negotiation">
1785<t>
1786   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1787   maintain a persistent connection unless a Connection header including
1788   the connection-token "close" was sent in the request. If the server
1789   chooses to close the connection immediately after sending the
1790   response, it &SHOULD; send a Connection header including the
1791   connection-token close.
1792</t>
1793<t>
1794   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1795   decide to keep it open based on whether the response from a server
1796   contains a Connection header with the connection-token close. In case
1797   the client does not want to maintain a connection for more than that
1798   request, it &SHOULD; send a Connection header including the
1799   connection-token close.
1800</t>
1801<t>
1802   If either the client or the server sends the close token in the
1803   Connection header, that request becomes the last one for the
1804   connection.
1805</t>
1806<t>
1807   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1808   maintained for HTTP versions less than 1.1 unless it is explicitly
1809   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1810   compatibility with HTTP/1.0 clients.
1811</t>
1812<t>
1813   In order to remain persistent, all messages on the connection &MUST;
1814   have a self-defined message length (i.e., one not defined by closure
1815   of the connection), as described in <xref target="message.length"/>.
1816</t>
1817</section>
1818
1819<section title="Pipelining" anchor="pipelining">
1820<t>
1821   A client that supports persistent connections &MAY; "pipeline" its
1822   requests (i.e., send multiple requests without waiting for each
1823   response). A server &MUST; send its responses to those requests in the
1824   same order that the requests were received.
1825</t>
1826<t>
1827   Clients which assume persistent connections and pipeline immediately
1828   after connection establishment &SHOULD; be prepared to retry their
1829   connection if the first pipelined attempt fails. If a client does
1830   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1831   persistent. Clients &MUST; also be prepared to resend their requests if
1832   the server closes the connection before sending all of the
1833   corresponding responses.
1834</t>
1835<t>
1836   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1837   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1838   premature termination of the transport connection could lead to
1839   indeterminate results. A client wishing to send a non-idempotent
1840   request &SHOULD; wait to send that request until it has received the
1841   response status for the previous request.
1842</t>
1843</section>
1844</section>
1845
1846<section title="Proxy Servers" anchor="persistent.proxy">
1847<t>
1848   It is especially important that proxies correctly implement the
1849   properties of the Connection header field as specified in <xref target="header.connection"/>.
1850</t>
1851<t>
1852   The proxy server &MUST; signal persistent connections separately with
1853   its clients and the origin servers (or other proxy servers) that it
1854   connects to. Each persistent connection applies to only one transport
1855   link.
1856</t>
1857<t>
1858   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1859   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1860   discussion of the problems with the Keep-Alive header implemented by
1861   many HTTP/1.0 clients).
1862</t>
1863</section>
1864
1865<section title="Practical Considerations" anchor="persistent.practical">
1866<t>
1867   Servers will usually have some time-out value beyond which they will
1868   no longer maintain an inactive connection. Proxy servers might make
1869   this a higher value since it is likely that the client will be making
1870   more connections through the same server. The use of persistent
1871   connections places no requirements on the length (or existence) of
1872   this time-out for either the client or the server.
1873</t>
1874<t>
1875   When a client or server wishes to time-out it &SHOULD; issue a graceful
1876   close on the transport connection. Clients and servers &SHOULD; both
1877   constantly watch for the other side of the transport close, and
1878   respond to it as appropriate. If a client or server does not detect
1879   the other side's close promptly it could cause unnecessary resource
1880   drain on the network.
1881</t>
1882<t>
1883   A client, server, or proxy &MAY; close the transport connection at any
1884   time. For example, a client might have started to send a new request
1885   at the same time that the server has decided to close the "idle"
1886   connection. From the server's point of view, the connection is being
1887   closed while it was idle, but from the client's point of view, a
1888   request is in progress.
1889</t>
1890<t>
1891   This means that clients, servers, and proxies &MUST; be able to recover
1892   from asynchronous close events. Client software &SHOULD; reopen the
1893   transport connection and retransmit the aborted sequence of requests
1894   without user interaction so long as the request sequence is
1895   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1896   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1897   human operator the choice of retrying the request(s). Confirmation by
1898   user-agent software with semantic understanding of the application
1899   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT;
1900   be repeated if the second sequence of requests fails.
1901</t>
1902<t>
1903   Servers &SHOULD; always respond to at least one request per connection,
1904   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1905   middle of transmitting a response, unless a network or client failure
1906   is suspected.
1907</t>
1908<t>
1909   Clients that use persistent connections &SHOULD; limit the number of
1910   simultaneous connections that they maintain to a given server. A
1911   single-user client &SHOULD-NOT; maintain more than 2 connections with
1912   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1913   another server or proxy, where N is the number of simultaneously
1914   active users. These guidelines are intended to improve HTTP response
1915   times and avoid congestion.
1916</t>
1917</section>
1918</section>
1919
1920<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1921
1922<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1923<t>
1924   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1925   flow control mechanisms to resolve temporary overloads, rather than
1926   terminating connections with the expectation that clients will retry.
1927   The latter technique can exacerbate network congestion.
1928</t>
1929</section>
1930
1931<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1932<t>
1933   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1934   the network connection for an error status while it is transmitting
1935   the request. If the client sees an error status, it &SHOULD;
1936   immediately cease transmitting the body. If the body is being sent
1937   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1938   empty trailer &MAY; be used to prematurely mark the end of the message.
1939   If the body was preceded by a Content-Length header, the client &MUST;
1940   close the connection.
1941</t>
1942</section>
1943
1944<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1945<t>
1946   The purpose of the 100 (Continue) status (see &status-100;) is to
1947   allow a client that is sending a request message with a request body
1948   to determine if the origin server is willing to accept the request
1949   (based on the request headers) before the client sends the request
1950   body. In some cases, it might either be inappropriate or highly
1951   inefficient for the client to send the body if the server will reject
1952   the message without looking at the body.
1953</t>
1954<t>
1955   Requirements for HTTP/1.1 clients:
1956  <list style="symbols">
1957    <t>
1958        If a client will wait for a 100 (Continue) response before
1959        sending the request body, it &MUST; send an Expect request-header
1960        field (&header-expect;) with the "100-continue" expectation.
1961    </t>
1962    <t>
1963        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1964        with the "100-continue" expectation if it does not intend
1965        to send a request body.
1966    </t>
1967  </list>
1968</t>
1969<t>
1970   Because of the presence of older implementations, the protocol allows
1971   ambiguous situations in which a client may send "Expect: 100-continue"
1972   without receiving either a 417 (Expectation Failed) status
1973   or a 100 (Continue) status. Therefore, when a client sends this
1974   header field to an origin server (possibly via a proxy) from which it
1975   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1976   for an indefinite period before sending the request body.
1977</t>
1978<t>
1979   Requirements for HTTP/1.1 origin servers:
1980  <list style="symbols">
1981    <t> Upon receiving a request which includes an Expect request-header
1982        field with the "100-continue" expectation, an origin server &MUST;
1983        either respond with 100 (Continue) status and continue to read
1984        from the input stream, or respond with a final status code. The
1985        origin server &MUST-NOT; wait for the request body before sending
1986        the 100 (Continue) response. If it responds with a final status
1987        code, it &MAY; close the transport connection or it &MAY; continue
1988        to read and discard the rest of the request.  It &MUST-NOT;
1989        perform the requested method if it returns a final status code.
1990    </t>
1991    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
1992        the request message does not include an Expect request-header
1993        field with the "100-continue" expectation, and &MUST-NOT; send a
1994        100 (Continue) response if such a request comes from an HTTP/1.0
1995        (or earlier) client. There is an exception to this rule: for
1996        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
1997        status in response to an HTTP/1.1 PUT or POST request that does
1998        not include an Expect request-header field with the "100-continue"
1999        expectation. This exception, the purpose of which is
2000        to minimize any client processing delays associated with an
2001        undeclared wait for 100 (Continue) status, applies only to
2002        HTTP/1.1 requests, and not to requests with any other HTTP-version
2003        value.
2004    </t>
2005    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2006        already received some or all of the request body for the
2007        corresponding request.
2008    </t>
2009    <t> An origin server that sends a 100 (Continue) response &MUST;
2010    ultimately send a final status code, once the request body is
2011        received and processed, unless it terminates the transport
2012        connection prematurely.
2013    </t>
2014    <t> If an origin server receives a request that does not include an
2015        Expect request-header field with the "100-continue" expectation,
2016        the request includes a request body, and the server responds
2017        with a final status code before reading the entire request body
2018        from the transport connection, then the server &SHOULD-NOT;  close
2019        the transport connection until it has read the entire request,
2020        or until the client closes the connection. Otherwise, the client
2021        might not reliably receive the response message. However, this
2022        requirement is not be construed as preventing a server from
2023        defending itself against denial-of-service attacks, or from
2024        badly broken client implementations.
2025      </t>
2026    </list>
2027</t>
2028<t>
2029   Requirements for HTTP/1.1 proxies:
2030  <list style="symbols">
2031    <t> If a proxy receives a request that includes an Expect request-header
2032        field with the "100-continue" expectation, and the proxy
2033        either knows that the next-hop server complies with HTTP/1.1 or
2034        higher, or does not know the HTTP version of the next-hop
2035        server, it &MUST; forward the request, including the Expect header
2036        field.
2037    </t>
2038    <t> If the proxy knows that the version of the next-hop server is
2039        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2040        respond with a 417 (Expectation Failed) status.
2041    </t>
2042    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2043        numbers received from recently-referenced next-hop servers.
2044    </t>
2045    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2046        request message was received from an HTTP/1.0 (or earlier)
2047        client and did not include an Expect request-header field with
2048        the "100-continue" expectation. This requirement overrides the
2049        general rule for forwarding of 1xx responses (see &status-1xx;).
2050    </t>
2051  </list>
2052</t>
2053</section>
2054
2055<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2056<t>
2057   If an HTTP/1.1 client sends a request which includes a request body,
2058   but which does not include an Expect request-header field with the
2059   "100-continue" expectation, and if the client is not directly
2060   connected to an HTTP/1.1 origin server, and if the client sees the
2061   connection close before receiving any status from the server, the
2062   client &SHOULD; retry the request.  If the client does retry this
2063   request, it &MAY; use the following "binary exponential backoff"
2064   algorithm to be assured of obtaining a reliable response:
2065  <list style="numbers">
2066    <t>
2067      Initiate a new connection to the server
2068    </t>
2069    <t>
2070      Transmit the request-headers
2071    </t>
2072    <t>
2073      Initialize a variable R to the estimated round-trip time to the
2074         server (e.g., based on the time it took to establish the
2075         connection), or to a constant value of 5 seconds if the round-trip
2076         time is not available.
2077    </t>
2078    <t>
2079       Compute T = R * (2**N), where N is the number of previous
2080         retries of this request.
2081    </t>
2082    <t>
2083       Wait either for an error response from the server, or for T
2084         seconds (whichever comes first)
2085    </t>
2086    <t>
2087       If no error response is received, after T seconds transmit the
2088         body of the request.
2089    </t>
2090    <t>
2091       If client sees that the connection is closed prematurely,
2092         repeat from step 1 until the request is accepted, an error
2093         response is received, or the user becomes impatient and
2094         terminates the retry process.
2095    </t>
2096  </list>
2097</t>
2098<t>
2099   If at any point an error status is received, the client
2100  <list style="symbols">
2101      <t>&SHOULD-NOT;  continue and</t>
2102
2103      <t>&SHOULD; close the connection if it has not completed sending the
2104        request message.</t>
2105    </list>
2106</t>
2107</section>
2108</section>
2109</section>
2110
2111
2112<section title="Header Field Definitions" anchor="header.fields">
2113<t>
2114   This section defines the syntax and semantics of HTTP/1.1 header fields
2115   related to message framing and transport protocols.
2116</t>
2117<t>
2118   For entity-header fields, both sender and recipient refer to either the
2119   client or the server, depending on who sends and who receives the entity.
2120</t>
2121
2122<section title="Connection" anchor="header.connection">
2123  <iref primary="true" item="Connection header" x:for-anchor=""/>
2124  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2125  <x:anchor-alias value="Connection"/>
2126  <x:anchor-alias value="connection-token"/>
2127  <x:anchor-alias value="Connection-v"/>
2128<t>
2129   The general-header field "Connection" allows the sender to specify
2130   options that are desired for that particular connection and &MUST-NOT;
2131   be communicated by proxies over further connections.
2132</t>
2133<t>
2134   The Connection header's value has the following grammar:
2135</t>
2136<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"/>
2137  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2138  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2139  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2140</artwork></figure>
2141<t>
2142   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2143   message is forwarded and, for each connection-token in this field,
2144   remove any header field(s) from the message with the same name as the
2145   connection-token. Connection options are signaled by the presence of
2146   a connection-token in the Connection header field, not by any
2147   corresponding additional header field(s), since the additional header
2148   field may not be sent if there are no parameters associated with that
2149   connection option.
2150</t>
2151<t>
2152   Message headers listed in the Connection header &MUST-NOT; include
2153   end-to-end headers, such as Cache-Control.
2154</t>
2155<t>
2156   HTTP/1.1 defines the "close" connection option for the sender to
2157   signal that the connection will be closed after completion of the
2158   response. For example,
2159</t>
2160<figure><artwork type="example">
2161  Connection: close
2162</artwork></figure>
2163<t>
2164   in either the request or the response header fields indicates that
2165   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2166   after the current request/response is complete.
2167</t>
2168<t>
2169   An HTTP/1.1 client that does not support persistent connections &MUST;
2170   include the "close" connection option in every request message.
2171</t>
2172<t>
2173   An HTTP/1.1 server that does not support persistent connections &MUST;
2174   include the "close" connection option in every response message that
2175   does not have a 1xx (informational) status code.
2176</t>
2177<t>
2178   A system receiving an HTTP/1.0 (or lower-version) message that
2179   includes a Connection header &MUST;, for each connection-token in this
2180   field, remove and ignore any header field(s) from the message with
2181   the same name as the connection-token. This protects against mistaken
2182   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2183</t>
2184</section>
2185
2186<section title="Content-Length" anchor="header.content-length">
2187  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2188  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2189  <x:anchor-alias value="Content-Length"/>
2190  <x:anchor-alias value="Content-Length-v"/>
2191<t>
2192   The entity-header field "Content-Length" indicates the size of the
2193   entity-body, in decimal number of OCTETs, sent to the recipient or,
2194   in the case of the HEAD method, the size of the entity-body that
2195   would have been sent had the request been a GET.
2196</t>
2197<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2198  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2199  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2200</artwork></figure>
2201<t>
2202   An example is
2203</t>
2204<figure><artwork type="example">
2205  Content-Length: 3495
2206</artwork></figure>
2207<t>
2208   Applications &SHOULD; use this field to indicate the transfer-length of
2209   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2210</t>
2211<t>
2212   Any Content-Length greater than or equal to zero is a valid value.
2213   <xref target="message.length"/> describes how to determine the length of a message-body
2214   if a Content-Length is not given.
2215</t>
2216<t>
2217   Note that the meaning of this field is significantly different from
2218   the corresponding definition in MIME, where it is an optional field
2219   used within the "message/external-body" content-type. In HTTP, it
2220   &SHOULD; be sent whenever the message's length can be determined prior
2221   to being transferred, unless this is prohibited by the rules in
2222   <xref target="message.length"/>.
2223</t>
2224</section>
2225
2226<section title="Date" anchor="header.date">
2227  <iref primary="true" item="Date header" x:for-anchor=""/>
2228  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2229  <x:anchor-alias value="Date"/>
2230  <x:anchor-alias value="Date-v"/>
2231<t>
2232   The general-header field "Date" represents the date and time at which
2233   the message was originated, having the same semantics as orig-date in
2234   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2235   HTTP-date, as described in <xref target="full.date"/>;
2236   it &MUST; be sent in rfc1123-date format.
2237</t>
2238<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2239  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2240  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2241</artwork></figure>
2242<t>
2243   An example is
2244</t>
2245<figure><artwork type="example">
2246  Date: Tue, 15 Nov 1994 08:12:31 GMT
2247</artwork></figure>
2248<t>
2249   Origin servers &MUST; include a Date header field in all responses,
2250   except in these cases:
2251  <list style="numbers">
2252      <t>If the response status code is 100 (Continue) or 101 (Switching
2253         Protocols), the response &MAY; include a Date header field, at
2254         the server's option.</t>
2255
2256      <t>If the response status code conveys a server error, e.g. 500
2257         (Internal Server Error) or 503 (Service Unavailable), and it is
2258         inconvenient or impossible to generate a valid Date.</t>
2259
2260      <t>If the server does not have a clock that can provide a
2261         reasonable approximation of the current time, its responses
2262         &MUST-NOT; include a Date header field. In this case, the rules
2263         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2264  </list>
2265</t>
2266<t>
2267   A received message that does not have a Date header field &MUST; be
2268   assigned one by the recipient if the message will be cached by that
2269   recipient or gatewayed via a protocol which requires a Date. An HTTP
2270   implementation without a clock &MUST-NOT; cache responses without
2271   revalidating them on every use. An HTTP cache, especially a shared
2272   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2273   clock with a reliable external standard.
2274</t>
2275<t>
2276   Clients &SHOULD; only send a Date header field in messages that include
2277   an entity-body, as in the case of the PUT and POST requests, and even
2278   then it is optional. A client without a clock &MUST-NOT; send a Date
2279   header field in a request.
2280</t>
2281<t>
2282   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2283   time subsequent to the generation of the message. It &SHOULD; represent
2284   the best available approximation of the date and time of message
2285   generation, unless the implementation has no means of generating a
2286   reasonably accurate date and time. In theory, the date ought to
2287   represent the moment just before the entity is generated. In
2288   practice, the date can be generated at any time during the message
2289   origination without affecting its semantic value.
2290</t>
2291
2292<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2293<t>
2294   Some origin server implementations might not have a clock available.
2295   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2296   values to a response, unless these values were associated
2297   with the resource by a system or user with a reliable clock. It &MAY;
2298   assign an Expires value that is known, at or before server
2299   configuration time, to be in the past (this allows "pre-expiration"
2300   of responses without storing separate Expires values for each
2301   resource).
2302</t>
2303</section>
2304</section>
2305
2306<section title="Host" anchor="header.host">
2307  <iref primary="true" item="Host header" x:for-anchor=""/>
2308  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2309  <x:anchor-alias value="Host"/>
2310  <x:anchor-alias value="Host-v"/>
2311<t>
2312   The request-header field "Host" specifies the Internet host and port
2313   number of the resource being requested, as obtained from the original
2314   URI given by the user or referring resource (generally an http URI,
2315   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2316   the naming authority of the origin server or gateway given by the
2317   original URL. This allows the origin server or gateway to
2318   differentiate between internally-ambiguous URLs, such as the root "/"
2319   URL of a server for multiple host names on a single IP address.
2320</t>
2321<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2322  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2323  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2324</artwork></figure>
2325<t>
2326   A "host" without any trailing port information implies the default
2327   port for the service requested (e.g., "80" for an HTTP URL). For
2328   example, a request on the origin server for
2329   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2330</t>
2331<figure><artwork type="example">
2332  GET /pub/WWW/ HTTP/1.1
2333  Host: www.example.org
2334</artwork></figure>
2335<t>
2336   A client &MUST; include a Host header field in all HTTP/1.1 request
2337   messages. If the requested URI does not include an Internet host
2338   name for the service being requested, then the Host header field &MUST;
2339   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2340   request message it forwards does contain an appropriate Host header
2341   field that identifies the service being requested by the proxy. All
2342   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2343   status code to any HTTP/1.1 request message which lacks a Host header
2344   field.
2345</t>
2346<t>
2347   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2348   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2349   for other requirements relating to Host.
2350</t>
2351</section>
2352
2353<section title="TE" anchor="header.te">
2354  <iref primary="true" item="TE header" x:for-anchor=""/>
2355  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2356  <x:anchor-alias value="TE"/>
2357  <x:anchor-alias value="TE-v"/>
2358  <x:anchor-alias value="t-codings"/>
2359<t>
2360   The request-header field "TE" indicates what extension transfer-codings
2361   it is willing to accept in the response and whether or not it is
2362   willing to accept trailer fields in a chunked transfer-coding. Its
2363   value may consist of the keyword "trailers" and/or a comma-separated
2364   list of extension transfer-coding names with optional accept
2365   parameters (as described in <xref target="transfer.codings"/>).
2366</t>
2367<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"/>
2368  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2369  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2370  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2371</artwork></figure>
2372<t>
2373   The presence of the keyword "trailers" indicates that the client is
2374   willing to accept trailer fields in a chunked transfer-coding, as
2375   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2376   transfer-coding values even though it does not itself represent a
2377   transfer-coding.
2378</t>
2379<t>
2380   Examples of its use are:
2381</t>
2382<figure><artwork type="example">
2383  TE: deflate
2384  TE:
2385  TE: trailers, deflate;q=0.5
2386</artwork></figure>
2387<t>
2388   The TE header field only applies to the immediate connection.
2389   Therefore, the keyword &MUST; be supplied within a Connection header
2390   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2391</t>
2392<t>
2393   A server tests whether a transfer-coding is acceptable, according to
2394   a TE field, using these rules:
2395  <list style="numbers">
2396    <x:lt>
2397      <t>The "chunked" transfer-coding is always acceptable. If the
2398         keyword "trailers" is listed, the client indicates that it is
2399         willing to accept trailer fields in the chunked response on
2400         behalf of itself and any downstream clients. The implication is
2401         that, if given, the client is stating that either all
2402         downstream clients are willing to accept trailer fields in the
2403         forwarded response, or that it will attempt to buffer the
2404         response on behalf of downstream recipients.
2405      </t><t>
2406         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2407         chunked response such that a client can be assured of buffering
2408         the entire response.</t>
2409    </x:lt>
2410    <x:lt>
2411      <t>If the transfer-coding being tested is one of the transfer-codings
2412         listed in the TE field, then it is acceptable unless it
2413         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2414         qvalue of 0 means "not acceptable.")</t>
2415    </x:lt>
2416    <x:lt>
2417      <t>If multiple transfer-codings are acceptable, then the
2418         acceptable transfer-coding with the highest non-zero qvalue is
2419         preferred.  The "chunked" transfer-coding always has a qvalue
2420         of 1.</t>
2421    </x:lt>
2422  </list>
2423</t>
2424<t>
2425   If the TE field-value is empty or if no TE field is present, the only
2426   transfer-coding  is "chunked". A message with no transfer-coding is
2427   always acceptable.
2428</t>
2429</section>
2430
2431<section title="Trailer" anchor="header.trailer">
2432  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2433  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2434  <x:anchor-alias value="Trailer"/>
2435  <x:anchor-alias value="Trailer-v"/>
2436<t>
2437   The general field "Trailer" indicates that the given set of
2438   header fields is present in the trailer of a message encoded with
2439   chunked transfer-coding.
2440</t>
2441<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2442  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2443  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2444</artwork></figure>
2445<t>
2446   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2447   message using chunked transfer-coding with a non-empty trailer. Doing
2448   so allows the recipient to know which header fields to expect in the
2449   trailer.
2450</t>
2451<t>
2452   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2453   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2454   trailer fields in a "chunked" transfer-coding.
2455</t>
2456<t>
2457   Message header fields listed in the Trailer header field &MUST-NOT;
2458   include the following header fields:
2459  <list style="symbols">
2460    <t>Transfer-Encoding</t>
2461    <t>Content-Length</t>
2462    <t>Trailer</t>
2463  </list>
2464</t>
2465</section>
2466
2467<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2468  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2469  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2470  <x:anchor-alias value="Transfer-Encoding"/>
2471  <x:anchor-alias value="Transfer-Encoding-v"/>
2472<t>
2473   The general-header "Transfer-Encoding" field indicates what (if any)
2474   type of transformation has been applied to the message body in order
2475   to safely transfer it between the sender and the recipient. This
2476   differs from the content-coding in that the transfer-coding is a
2477   property of the message, not of the entity.
2478</t>
2479<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2480  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2481                        <x:ref>Transfer-Encoding-v</x:ref>
2482  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2483</artwork></figure>
2484<t>
2485   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2486</t>
2487<figure><artwork type="example">
2488  Transfer-Encoding: chunked
2489</artwork></figure>
2490<t>
2491   If multiple encodings have been applied to an entity, the transfer-codings
2492   &MUST; be listed in the order in which they were applied.
2493   Additional information about the encoding parameters &MAY; be provided
2494   by other entity-header fields not defined by this specification.
2495</t>
2496<t>
2497   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2498   header.
2499</t>
2500</section>
2501
2502<section title="Upgrade" anchor="header.upgrade">
2503  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2504  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2505  <x:anchor-alias value="Upgrade"/>
2506  <x:anchor-alias value="Upgrade-v"/>
2507<t>
2508   The general-header "Upgrade" allows the client to specify what
2509   additional communication protocols it supports and would like to use
2510   if the server finds it appropriate to switch protocols. The server
2511   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2512   response to indicate which protocol(s) are being switched.
2513</t>
2514<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2515  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2516  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2517</artwork></figure>
2518<t>
2519   For example,
2520</t>
2521<figure><artwork type="example">
2522  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2523</artwork></figure>
2524<t>
2525   The Upgrade header field is intended to provide a simple mechanism
2526   for transition from HTTP/1.1 to some other, incompatible protocol. It
2527   does so by allowing the client to advertise its desire to use another
2528   protocol, such as a later version of HTTP with a higher major version
2529   number, even though the current request has been made using HTTP/1.1.
2530   This eases the difficult transition between incompatible protocols by
2531   allowing the client to initiate a request in the more commonly
2532   supported protocol while indicating to the server that it would like
2533   to use a "better" protocol if available (where "better" is determined
2534   by the server, possibly according to the nature of the method and/or
2535   resource being requested).
2536</t>
2537<t>
2538   The Upgrade header field only applies to switching application-layer
2539   protocols upon the existing transport-layer connection. Upgrade
2540   cannot be used to insist on a protocol change; its acceptance and use
2541   by the server is optional. The capabilities and nature of the
2542   application-layer communication after the protocol change is entirely
2543   dependent upon the new protocol chosen, although the first action
2544   after changing the protocol &MUST; be a response to the initial HTTP
2545   request containing the Upgrade header field.
2546</t>
2547<t>
2548   The Upgrade header field only applies to the immediate connection.
2549   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2550   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2551   HTTP/1.1 message.
2552</t>
2553<t>
2554   The Upgrade header field cannot be used to indicate a switch to a
2555   protocol on a different connection. For that purpose, it is more
2556   appropriate to use a 301, 302, 303, or 305 redirection response.
2557</t>
2558<t>
2559   This specification only defines the protocol name "HTTP" for use by
2560   the family of Hypertext Transfer Protocols, as defined by the HTTP
2561   version rules of <xref target="http.version"/> and future updates to this
2562   specification. Any token can be used as a protocol name; however, it
2563   will only be useful if both the client and server associate the name
2564   with the same protocol.
2565</t>
2566</section>
2567
2568<section title="Via" anchor="header.via">
2569  <iref primary="true" item="Via header" x:for-anchor=""/>
2570  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2571  <x:anchor-alias value="protocol-name"/>
2572  <x:anchor-alias value="protocol-version"/>
2573  <x:anchor-alias value="pseudonym"/>
2574  <x:anchor-alias value="received-by"/>
2575  <x:anchor-alias value="received-protocol"/>
2576  <x:anchor-alias value="Via"/>
2577  <x:anchor-alias value="Via-v"/>
2578<t>
2579   The general-header field "Via" &MUST; be used by gateways and proxies to
2580   indicate the intermediate protocols and recipients between the user
2581   agent and the server on requests, and between the origin server and
2582   the client on responses. It is analogous to the "Received" field defined in
2583   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2584   avoiding request loops, and identifying the protocol capabilities of
2585   all senders along the request/response chain.
2586</t>
2587<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"/>
2588  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2589  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2590                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2591  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2592  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2593  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2594  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2595  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2596</artwork></figure>
2597<t>
2598   The received-protocol indicates the protocol version of the message
2599   received by the server or client along each segment of the
2600   request/response chain. The received-protocol version is appended to
2601   the Via field value when the message is forwarded so that information
2602   about the protocol capabilities of upstream applications remains
2603   visible to all recipients.
2604</t>
2605<t>
2606   The protocol-name is optional if and only if it would be "HTTP". The
2607   received-by field is normally the host and optional port number of a
2608   recipient server or client that subsequently forwarded the message.
2609   However, if the real host is considered to be sensitive information,
2610   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2611   be assumed to be the default port of the received-protocol.
2612</t>
2613<t>
2614   Multiple Via field values represents each proxy or gateway that has
2615   forwarded the message. Each recipient &MUST; append its information
2616   such that the end result is ordered according to the sequence of
2617   forwarding applications.
2618</t>
2619<t>
2620   Comments &MAY; be used in the Via header field to identify the software
2621   of the recipient proxy or gateway, analogous to the User-Agent and
2622   Server header fields. However, all comments in the Via field are
2623   optional and &MAY; be removed by any recipient prior to forwarding the
2624   message.
2625</t>
2626<t>
2627   For example, a request message could be sent from an HTTP/1.0 user
2628   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2629   forward the request to a public proxy at p.example.net, which completes
2630   the request by forwarding it to the origin server at www.example.com.
2631   The request received by www.example.com would then have the following
2632   Via header field:
2633</t>
2634<figure><artwork type="example">
2635  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2636</artwork></figure>
2637<t>
2638   Proxies and gateways used as a portal through a network firewall
2639   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2640   the firewall region. This information &SHOULD; only be propagated if
2641   explicitly enabled. If not enabled, the received-by host of any host
2642   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2643   for that host.
2644</t>
2645<t>
2646   For organizations that have strong privacy requirements for hiding
2647   internal structures, a proxy &MAY; combine an ordered subsequence of
2648   Via header field entries with identical received-protocol values into
2649   a single such entry. For example,
2650</t>
2651<figure><artwork type="example">
2652  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2653</artwork></figure>
2654<t>
2655        could be collapsed to
2656</t>
2657<figure><artwork type="example">
2658  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2659</artwork></figure>
2660<t>
2661   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2662   under the same organizational control and the hosts have already been
2663   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2664   have different received-protocol values.
2665</t>
2666</section>
2667
2668</section>
2669
2670<section title="IANA Considerations" anchor="IANA.considerations">
2671<section title="Message Header Registration" anchor="message.header.registration">
2672<t>
2673   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2674   with the permanent registrations below (see <xref target="RFC3864"/>):
2675</t>
2676<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2677<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2678   <ttcol>Header Field Name</ttcol>
2679   <ttcol>Protocol</ttcol>
2680   <ttcol>Status</ttcol>
2681   <ttcol>Reference</ttcol>
2682
2683   <c>Connection</c>
2684   <c>http</c>
2685   <c>standard</c>
2686   <c>
2687      <xref target="header.connection"/>
2688   </c>
2689   <c>Content-Length</c>
2690   <c>http</c>
2691   <c>standard</c>
2692   <c>
2693      <xref target="header.content-length"/>
2694   </c>
2695   <c>Date</c>
2696   <c>http</c>
2697   <c>standard</c>
2698   <c>
2699      <xref target="header.date"/>
2700   </c>
2701   <c>Host</c>
2702   <c>http</c>
2703   <c>standard</c>
2704   <c>
2705      <xref target="header.host"/>
2706   </c>
2707   <c>TE</c>
2708   <c>http</c>
2709   <c>standard</c>
2710   <c>
2711      <xref target="header.te"/>
2712   </c>
2713   <c>Trailer</c>
2714   <c>http</c>
2715   <c>standard</c>
2716   <c>
2717      <xref target="header.trailer"/>
2718   </c>
2719   <c>Transfer-Encoding</c>
2720   <c>http</c>
2721   <c>standard</c>
2722   <c>
2723      <xref target="header.transfer-encoding"/>
2724   </c>
2725   <c>Upgrade</c>
2726   <c>http</c>
2727   <c>standard</c>
2728   <c>
2729      <xref target="header.upgrade"/>
2730   </c>
2731   <c>Via</c>
2732   <c>http</c>
2733   <c>standard</c>
2734   <c>
2735      <xref target="header.via"/>
2736   </c>
2737</texttable>
2738<!--(END)-->
2739<t>
2740   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2741</t>
2742</section>
2743
2744<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2745<t>
2746   The entry for the "http" URI Scheme in the registry located at
2747   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2748   should be updated to point to <xref target="http.uri"/> of this document
2749   (see <xref target="RFC4395"/>).
2750</t>
2751</section>
2752
2753<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2754<t>
2755   This document serves as the specification for the Internet media types
2756   "message/http" and "application/http". The following is to be registered with
2757   IANA (see <xref target="RFC4288"/>).
2758</t>
2759<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2760<iref item="Media Type" subitem="message/http" primary="true"/>
2761<iref item="message/http Media Type" primary="true"/>
2762<t>
2763   The message/http type can be used to enclose a single HTTP request or
2764   response message, provided that it obeys the MIME restrictions for all
2765   "message" types regarding line length and encodings.
2766</t>
2767<t>
2768  <list style="hanging" x:indent="12em">
2769    <t hangText="Type name:">
2770      message
2771    </t>
2772    <t hangText="Subtype name:">
2773      http
2774    </t>
2775    <t hangText="Required parameters:">
2776      none
2777    </t>
2778    <t hangText="Optional parameters:">
2779      version, msgtype
2780      <list style="hanging">
2781        <t hangText="version:">
2782          The HTTP-Version number of the enclosed message
2783          (e.g., "1.1"). If not present, the version can be
2784          determined from the first line of the body.
2785        </t>
2786        <t hangText="msgtype:">
2787          The message type -- "request" or "response". If not
2788          present, the type can be determined from the first
2789          line of the body.
2790        </t>
2791      </list>
2792    </t>
2793    <t hangText="Encoding considerations:">
2794      only "7bit", "8bit", or "binary" are permitted
2795    </t>
2796    <t hangText="Security considerations:">
2797      none
2798    </t>
2799    <t hangText="Interoperability considerations:">
2800      none
2801    </t>
2802    <t hangText="Published specification:">
2803      This specification (see <xref target="internet.media.type.message.http"/>).
2804    </t>
2805    <t hangText="Applications that use this media type:">
2806    </t>
2807    <t hangText="Additional information:">
2808      <list style="hanging">
2809        <t hangText="Magic number(s):">none</t>
2810        <t hangText="File extension(s):">none</t>
2811        <t hangText="Macintosh file type code(s):">none</t>
2812      </list>
2813    </t>
2814    <t hangText="Person and email address to contact for further information:">
2815      See Authors Section.
2816    </t>
2817                <t hangText="Intended usage:">
2818                  COMMON
2819    </t>
2820                <t hangText="Restrictions on usage:">
2821                  none
2822    </t>
2823    <t hangText="Author/Change controller:">
2824      IESG
2825    </t>
2826  </list>
2827</t>
2828</section>
2829<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2830<iref item="Media Type" subitem="application/http" primary="true"/>
2831<iref item="application/http Media Type" primary="true"/>
2832<t>
2833   The application/http type can be used to enclose a pipeline of one or more
2834   HTTP request or response messages (not intermixed).
2835</t>
2836<t>
2837  <list style="hanging" x:indent="12em">
2838    <t hangText="Type name:">
2839      application
2840    </t>
2841    <t hangText="Subtype name:">
2842      http
2843    </t>
2844    <t hangText="Required parameters:">
2845      none
2846    </t>
2847    <t hangText="Optional parameters:">
2848      version, msgtype
2849      <list style="hanging">
2850        <t hangText="version:">
2851          The HTTP-Version number of the enclosed messages
2852          (e.g., "1.1"). If not present, the version can be
2853          determined from the first line of the body.
2854        </t>
2855        <t hangText="msgtype:">
2856          The message type -- "request" or "response". If not
2857          present, the type can be determined from the first
2858          line of the body.
2859        </t>
2860      </list>
2861    </t>
2862    <t hangText="Encoding considerations:">
2863      HTTP messages enclosed by this type
2864      are in "binary" format; use of an appropriate
2865      Content-Transfer-Encoding is required when
2866      transmitted via E-mail.
2867    </t>
2868    <t hangText="Security considerations:">
2869      none
2870    </t>
2871    <t hangText="Interoperability considerations:">
2872      none
2873    </t>
2874    <t hangText="Published specification:">
2875      This specification (see <xref target="internet.media.type.application.http"/>).
2876    </t>
2877    <t hangText="Applications that use this media type:">
2878    </t>
2879    <t hangText="Additional information:">
2880      <list style="hanging">
2881        <t hangText="Magic number(s):">none</t>
2882        <t hangText="File extension(s):">none</t>
2883        <t hangText="Macintosh file type code(s):">none</t>
2884      </list>
2885    </t>
2886    <t hangText="Person and email address to contact for further information:">
2887      See Authors Section.
2888    </t>
2889                <t hangText="Intended usage:">
2890                  COMMON
2891    </t>
2892                <t hangText="Restrictions on usage:">
2893                  none
2894    </t>
2895    <t hangText="Author/Change controller:">
2896      IESG
2897    </t>
2898  </list>
2899</t>
2900</section>
2901</section>
2902
2903</section>
2904
2905<section title="Security Considerations" anchor="security.considerations">
2906<t>
2907   This section is meant to inform application developers, information
2908   providers, and users of the security limitations in HTTP/1.1 as
2909   described by this document. The discussion does not include
2910   definitive solutions to the problems revealed, though it does make
2911   some suggestions for reducing security risks.
2912</t>
2913
2914<section title="Personal Information" anchor="personal.information">
2915<t>
2916   HTTP clients are often privy to large amounts of personal information
2917   (e.g. the user's name, location, mail address, passwords, encryption
2918   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2919   leakage of this information.
2920   We very strongly recommend that a convenient interface be provided
2921   for the user to control dissemination of such information, and that
2922   designers and implementors be particularly careful in this area.
2923   History shows that errors in this area often create serious security
2924   and/or privacy problems and generate highly adverse publicity for the
2925   implementor's company.
2926</t>
2927</section>
2928
2929<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2930<t>
2931   A server is in the position to save personal data about a user's
2932   requests which might identify their reading patterns or subjects of
2933   interest. This information is clearly confidential in nature and its
2934   handling can be constrained by law in certain countries. People using
2935   HTTP to provide data are responsible for ensuring that
2936   such material is not distributed without the permission of any
2937   individuals that are identifiable by the published results.
2938</t>
2939</section>
2940
2941<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2942<t>
2943   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2944   the documents returned by HTTP requests to be only those that were
2945   intended by the server administrators. If an HTTP server translates
2946   HTTP URIs directly into file system calls, the server &MUST; take
2947   special care not to serve files that were not intended to be
2948   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2949   other operating systems use ".." as a path component to indicate a
2950   directory level above the current one. On such a system, an HTTP
2951   server &MUST; disallow any such construct in the request-target if it
2952   would otherwise allow access to a resource outside those intended to
2953   be accessible via the HTTP server. Similarly, files intended for
2954   reference only internally to the server (such as access control
2955   files, configuration files, and script code) &MUST; be protected from
2956   inappropriate retrieval, since they might contain sensitive
2957   information. Experience has shown that minor bugs in such HTTP server
2958   implementations have turned into security risks.
2959</t>
2960</section>
2961
2962<section title="DNS Spoofing" anchor="dns.spoofing">
2963<t>
2964   Clients using HTTP rely heavily on the Domain Name Service, and are
2965   thus generally prone to security attacks based on the deliberate
2966   mis-association of IP addresses and DNS names. Clients need to be
2967   cautious in assuming the continuing validity of an IP number/DNS name
2968   association.
2969</t>
2970<t>
2971   In particular, HTTP clients &SHOULD; rely on their name resolver for
2972   confirmation of an IP number/DNS name association, rather than
2973   caching the result of previous host name lookups. Many platforms
2974   already can cache host name lookups locally when appropriate, and
2975   they &SHOULD; be configured to do so. It is proper for these lookups to
2976   be cached, however, only when the TTL (Time To Live) information
2977   reported by the name server makes it likely that the cached
2978   information will remain useful.
2979</t>
2980<t>
2981   If HTTP clients cache the results of host name lookups in order to
2982   achieve a performance improvement, they &MUST; observe the TTL
2983   information reported by DNS.
2984</t>
2985<t>
2986   If HTTP clients do not observe this rule, they could be spoofed when
2987   a previously-accessed server's IP address changes. As network
2988   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
2989   possibility of this form of attack will grow. Observing this
2990   requirement thus reduces this potential security vulnerability.
2991</t>
2992<t>
2993   This requirement also improves the load-balancing behavior of clients
2994   for replicated servers using the same DNS name and reduces the
2995   likelihood of a user's experiencing failure in accessing sites which
2996   use that strategy.
2997</t>
2998</section>
2999
3000<section title="Proxies and Caching" anchor="attack.proxies">
3001<t>
3002   By their very nature, HTTP proxies are men-in-the-middle, and
3003   represent an opportunity for man-in-the-middle attacks. Compromise of
3004   the systems on which the proxies run can result in serious security
3005   and privacy problems. Proxies have access to security-related
3006   information, personal information about individual users and
3007   organizations, and proprietary information belonging to users and
3008   content providers. A compromised proxy, or a proxy implemented or
3009   configured without regard to security and privacy considerations,
3010   might be used in the commission of a wide range of potential attacks.
3011</t>
3012<t>
3013   Proxy operators should protect the systems on which proxies run as
3014   they would protect any system that contains or transports sensitive
3015   information. In particular, log information gathered at proxies often
3016   contains highly sensitive personal information, and/or information
3017   about organizations. Log information should be carefully guarded, and
3018   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3019</t>
3020<t>
3021   Proxy implementors should consider the privacy and security
3022   implications of their design and coding decisions, and of the
3023   configuration options they provide to proxy operators (especially the
3024   default configuration).
3025</t>
3026<t>
3027   Users of a proxy need to be aware that they are no trustworthier than
3028   the people who run the proxy; HTTP itself cannot solve this problem.
3029</t>
3030<t>
3031   The judicious use of cryptography, when appropriate, may suffice to
3032   protect against a broad range of security and privacy attacks. Such
3033   cryptography is beyond the scope of the HTTP/1.1 specification.
3034</t>
3035</section>
3036
3037<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3038<t>
3039   They exist. They are hard to defend against. Research continues.
3040   Beware.
3041</t>
3042</section>
3043</section>
3044
3045<section title="Acknowledgments" anchor="ack">
3046<t>
3047   HTTP has evolved considerably over the years. It has
3048   benefited from a large and active developer community--the many
3049   people who have participated on the www-talk mailing list--and it is
3050   that community which has been most responsible for the success of
3051   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3052   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3053   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3054   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3055   VanHeyningen deserve special recognition for their efforts in
3056   defining early aspects of the protocol.
3057</t>
3058<t>
3059   This document has benefited greatly from the comments of all those
3060   participating in the HTTP-WG. In addition to those already mentioned,
3061   the following individuals have contributed to this specification:
3062</t>
3063<t>
3064   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3065   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3066   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3067   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3068   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3069   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3070   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3071   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3072   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3073   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3074   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3075   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3076   Josh Cohen.
3077</t>
3078<t>
3079   Thanks to the "cave men" of Palo Alto. You know who you are.
3080</t>
3081<t>
3082   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3083   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3084   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3085   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3086   Larry Masinter for their help. And thanks go particularly to Jeff
3087   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3088</t>
3089<t>
3090   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3091   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3092   discovery of many of the problems that this document attempts to
3093   rectify.
3094</t>
3095<t>
3096   This specification makes heavy use of the augmented BNF and generic
3097   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3098   reuses many of the definitions provided by Nathaniel Borenstein and
3099   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3100   specification will help reduce past confusion over the relationship
3101   between HTTP and Internet mail message formats.
3102</t>
3103</section>
3104
3105</middle>
3106<back>
3107
3108<references title="Normative References">
3109
3110<reference anchor="ISO-8859-1">
3111  <front>
3112    <title>
3113     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3114    </title>
3115    <author>
3116      <organization>International Organization for Standardization</organization>
3117    </author>
3118    <date year="1998"/>
3119  </front>
3120  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3121</reference>
3122
3123<reference anchor="Part2">
3124  <front>
3125    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3126    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3127      <organization abbrev="Day Software">Day Software</organization>
3128      <address><email>fielding@gbiv.com</email></address>
3129    </author>
3130    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3131      <organization>One Laptop per Child</organization>
3132      <address><email>jg@laptop.org</email></address>
3133    </author>
3134    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3135      <organization abbrev="HP">Hewlett-Packard Company</organization>
3136      <address><email>JeffMogul@acm.org</email></address>
3137    </author>
3138    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3139      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3140      <address><email>henrikn@microsoft.com</email></address>
3141    </author>
3142    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3143      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3144      <address><email>LMM@acm.org</email></address>
3145    </author>
3146    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3147      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3148      <address><email>paulle@microsoft.com</email></address>
3149    </author>
3150    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3151      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3152      <address><email>timbl@w3.org</email></address>
3153    </author>
3154    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3155      <organization abbrev="W3C">World Wide Web Consortium</organization>
3156      <address><email>ylafon@w3.org</email></address>
3157    </author>
3158    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3159      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3160      <address><email>julian.reschke@greenbytes.de</email></address>
3161    </author>
3162    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3163  </front>
3164  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3165  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3166</reference>
3167
3168<reference anchor="Part3">
3169  <front>
3170    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3171    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3172      <organization abbrev="Day Software">Day Software</organization>
3173      <address><email>fielding@gbiv.com</email></address>
3174    </author>
3175    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3176      <organization>One Laptop per Child</organization>
3177      <address><email>jg@laptop.org</email></address>
3178    </author>
3179    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3180      <organization abbrev="HP">Hewlett-Packard Company</organization>
3181      <address><email>JeffMogul@acm.org</email></address>
3182    </author>
3183    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3184      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3185      <address><email>henrikn@microsoft.com</email></address>
3186    </author>
3187    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3188      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3189      <address><email>LMM@acm.org</email></address>
3190    </author>
3191    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3192      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3193      <address><email>paulle@microsoft.com</email></address>
3194    </author>
3195    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3196      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3197      <address><email>timbl@w3.org</email></address>
3198    </author>
3199    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3200      <organization abbrev="W3C">World Wide Web Consortium</organization>
3201      <address><email>ylafon@w3.org</email></address>
3202    </author>
3203    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3204      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3205      <address><email>julian.reschke@greenbytes.de</email></address>
3206    </author>
3207    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3208  </front>
3209  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3210  <x:source href="p3-payload.xml" basename="p3-payload"/>
3211</reference>
3212
3213<reference anchor="Part5">
3214  <front>
3215    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3216    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3217      <organization abbrev="Day Software">Day Software</organization>
3218      <address><email>fielding@gbiv.com</email></address>
3219    </author>
3220    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3221      <organization>One Laptop per Child</organization>
3222      <address><email>jg@laptop.org</email></address>
3223    </author>
3224    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3225      <organization abbrev="HP">Hewlett-Packard Company</organization>
3226      <address><email>JeffMogul@acm.org</email></address>
3227    </author>
3228    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3229      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3230      <address><email>henrikn@microsoft.com</email></address>
3231    </author>
3232    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3233      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3234      <address><email>LMM@acm.org</email></address>
3235    </author>
3236    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3237      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3238      <address><email>paulle@microsoft.com</email></address>
3239    </author>
3240    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3241      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3242      <address><email>timbl@w3.org</email></address>
3243    </author>
3244    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3245      <organization abbrev="W3C">World Wide Web Consortium</organization>
3246      <address><email>ylafon@w3.org</email></address>
3247    </author>
3248    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3249      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3250      <address><email>julian.reschke@greenbytes.de</email></address>
3251    </author>
3252    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3253  </front>
3254  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3255  <x:source href="p5-range.xml" basename="p5-range"/>
3256</reference>
3257
3258<reference anchor="Part6">
3259  <front>
3260    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3261    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3262      <organization abbrev="Day Software">Day Software</organization>
3263      <address><email>fielding@gbiv.com</email></address>
3264    </author>
3265    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3266      <organization>One Laptop per Child</organization>
3267      <address><email>jg@laptop.org</email></address>
3268    </author>
3269    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3270      <organization abbrev="HP">Hewlett-Packard Company</organization>
3271      <address><email>JeffMogul@acm.org</email></address>
3272    </author>
3273    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3274      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3275      <address><email>henrikn@microsoft.com</email></address>
3276    </author>
3277    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3278      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3279      <address><email>LMM@acm.org</email></address>
3280    </author>
3281    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3282      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3283      <address><email>paulle@microsoft.com</email></address>
3284    </author>
3285    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3286      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3287      <address><email>timbl@w3.org</email></address>
3288    </author>
3289    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3290      <organization abbrev="W3C">World Wide Web Consortium</organization>
3291      <address><email>ylafon@w3.org</email></address>
3292    </author>
3293    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3294      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3295      <address><email>julian.reschke@greenbytes.de</email></address>
3296    </author>
3297    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3298  </front>
3299  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3300  <x:source href="p6-cache.xml" basename="p6-cache"/>
3301</reference>
3302
3303<reference anchor="RFC5234">
3304  <front>
3305    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3306    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3307      <organization>Brandenburg InternetWorking</organization>
3308      <address>
3309      <postal>
3310      <street>675 Spruce Dr.</street>
3311      <city>Sunnyvale</city>
3312      <region>CA</region>
3313      <code>94086</code>
3314      <country>US</country></postal>
3315      <phone>+1.408.246.8253</phone>
3316      <email>dcrocker@bbiw.net</email></address> 
3317    </author>
3318    <author initials="P." surname="Overell" fullname="Paul Overell">
3319      <organization>THUS plc.</organization>
3320      <address>
3321      <postal>
3322      <street>1/2 Berkeley Square</street>
3323      <street>99 Berkely Street</street>
3324      <city>Glasgow</city>
3325      <code>G3 7HR</code>
3326      <country>UK</country></postal>
3327      <email>paul.overell@thus.net</email></address>
3328    </author>
3329    <date month="January" year="2008"/>
3330  </front>
3331  <seriesInfo name="STD" value="68"/>
3332  <seriesInfo name="RFC" value="5234"/>
3333</reference>
3334
3335<reference anchor="RFC2045">
3336  <front>
3337    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3338    <author initials="N." surname="Freed" fullname="Ned Freed">
3339      <organization>Innosoft International, Inc.</organization>
3340      <address><email>ned@innosoft.com</email></address>
3341    </author>
3342    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3343      <organization>First Virtual Holdings</organization>
3344      <address><email>nsb@nsb.fv.com</email></address>
3345    </author>
3346    <date month="November" year="1996"/>
3347  </front>
3348  <seriesInfo name="RFC" value="2045"/>
3349</reference>
3350
3351<reference anchor="RFC2047">
3352  <front>
3353    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3354    <author initials="K." surname="Moore" fullname="Keith Moore">
3355      <organization>University of Tennessee</organization>
3356      <address><email>moore@cs.utk.edu</email></address>
3357    </author>
3358    <date month="November" year="1996"/>
3359  </front>
3360  <seriesInfo name="RFC" value="2047"/>
3361</reference>
3362
3363<reference anchor="RFC2119">
3364  <front>
3365    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3366    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3367      <organization>Harvard University</organization>
3368      <address><email>sob@harvard.edu</email></address>
3369    </author>
3370    <date month="March" year="1997"/>
3371  </front>
3372  <seriesInfo name="BCP" value="14"/>
3373  <seriesInfo name="RFC" value="2119"/>
3374</reference>
3375
3376<reference anchor="RFC3986">
3377 <front>
3378  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3379  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3380    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3381    <address>
3382       <email>timbl@w3.org</email>
3383       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3384    </address>
3385  </author>
3386  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3387    <organization abbrev="Day Software">Day Software</organization>
3388    <address>
3389      <email>fielding@gbiv.com</email>
3390      <uri>http://roy.gbiv.com/</uri>
3391    </address>
3392  </author>
3393  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3394    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3395    <address>
3396      <email>LMM@acm.org</email>
3397      <uri>http://larry.masinter.net/</uri>
3398    </address>
3399  </author>
3400  <date month='January' year='2005'></date>
3401 </front>
3402 <seriesInfo name="RFC" value="3986"/>
3403 <seriesInfo name="STD" value="66"/>
3404</reference>
3405
3406<reference anchor="USASCII">
3407  <front>
3408    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3409    <author>
3410      <organization>American National Standards Institute</organization>
3411    </author>
3412    <date year="1986"/>
3413  </front>
3414  <seriesInfo name="ANSI" value="X3.4"/>
3415</reference>
3416
3417</references>
3418
3419<references title="Informative References">
3420
3421<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3422  <front>
3423    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3424    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3425      <organization/>
3426    </author>
3427    <author initials="J." surname="Gettys" fullname="J. Gettys">
3428      <organization/>
3429    </author>
3430    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3431      <organization/>
3432    </author>
3433    <author initials="H." surname="Lie" fullname="H. Lie">
3434      <organization/>
3435    </author>
3436    <author initials="C." surname="Lilley" fullname="C. Lilley">
3437      <organization/>
3438    </author>
3439    <date year="1997" month="September"/>
3440  </front>
3441  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3442</reference>
3443
3444<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3445  <front>
3446    <title>Improving HTTP Latency</title>
3447    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3448      <organization/>
3449    </author>
3450    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3451      <organization/>
3452    </author>
3453    <date year="1995" month="December"/>
3454  </front>
3455  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3456</reference>
3457
3458<reference anchor="RFC959">
3459  <front>
3460    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3461    <author initials="J." surname="Postel" fullname="J. Postel">
3462      <organization>Information Sciences Institute (ISI)</organization>
3463    </author>
3464    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3465      <organization/>
3466    </author>
3467    <date month="October" year="1985"/>
3468  </front>
3469  <seriesInfo name="STD" value="9"/>
3470  <seriesInfo name="RFC" value="959"/>
3471</reference>
3472
3473<reference anchor="RFC1123">
3474  <front>
3475    <title>Requirements for Internet Hosts - Application and Support</title>
3476    <author initials="R." surname="Braden" fullname="Robert Braden">
3477      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3478      <address><email>Braden@ISI.EDU</email></address>
3479    </author>
3480    <date month="October" year="1989"/>
3481  </front>
3482  <seriesInfo name="STD" value="3"/>
3483  <seriesInfo name="RFC" value="1123"/>
3484</reference>
3485
3486<reference anchor="RFC1305">
3487  <front>
3488    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3489    <author initials="D." surname="Mills" fullname="David L. Mills">
3490      <organization>University of Delaware, Electrical Engineering Department</organization>
3491      <address><email>mills@udel.edu</email></address>
3492    </author>
3493    <date month="March" year="1992"/>
3494  </front>
3495  <seriesInfo name="RFC" value="1305"/>
3496</reference>
3497
3498<reference anchor="RFC1436">
3499  <front>
3500    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3501    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3502      <organization>University of Minnesota, Computer and Information Services</organization>
3503      <address><email>fxa@boombox.micro.umn.edu</email></address>
3504    </author>
3505    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3506      <organization>University of Minnesota, Computer and Information Services</organization>
3507      <address><email>mpm@boombox.micro.umn.edu</email></address>
3508    </author>
3509    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3510      <organization>University of Minnesota, Computer and Information Services</organization>
3511      <address><email>lindner@boombox.micro.umn.edu</email></address>
3512    </author>
3513    <author initials="D." surname="Johnson" fullname="David Johnson">
3514      <organization>University of Minnesota, Computer and Information Services</organization>
3515      <address><email>dmj@boombox.micro.umn.edu</email></address>
3516    </author>
3517    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3518      <organization>University of Minnesota, Computer and Information Services</organization>
3519      <address><email>daniel@boombox.micro.umn.edu</email></address>
3520    </author>
3521    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3522      <organization>University of Minnesota, Computer and Information Services</organization>
3523      <address><email>alberti@boombox.micro.umn.edu</email></address>
3524    </author>
3525    <date month="March" year="1993"/>
3526  </front>
3527  <seriesInfo name="RFC" value="1436"/>
3528</reference>
3529
3530<reference anchor="RFC1900">
3531  <front>
3532    <title>Renumbering Needs Work</title>
3533    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3534      <organization>CERN, Computing and Networks Division</organization>
3535      <address><email>brian@dxcoms.cern.ch</email></address>
3536    </author>
3537    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3538      <organization>cisco Systems</organization>
3539      <address><email>yakov@cisco.com</email></address>
3540    </author>
3541    <date month="February" year="1996"/>
3542  </front>
3543  <seriesInfo name="RFC" value="1900"/>
3544</reference>
3545
3546<reference anchor="RFC1945">
3547  <front>
3548    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3549    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3550      <organization>MIT, Laboratory for Computer Science</organization>
3551      <address><email>timbl@w3.org</email></address>
3552    </author>
3553    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3554      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3555      <address><email>fielding@ics.uci.edu</email></address>
3556    </author>
3557    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3558      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3559      <address><email>frystyk@w3.org</email></address>
3560    </author>
3561    <date month="May" year="1996"/>
3562  </front>
3563  <seriesInfo name="RFC" value="1945"/>
3564</reference>
3565
3566<reference anchor="RFC2068">
3567  <front>
3568    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3569    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3570      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3571      <address><email>fielding@ics.uci.edu</email></address>
3572    </author>
3573    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3574      <organization>MIT Laboratory for Computer Science</organization>
3575      <address><email>jg@w3.org</email></address>
3576    </author>
3577    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3578      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3579      <address><email>mogul@wrl.dec.com</email></address>
3580    </author>
3581    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3582      <organization>MIT Laboratory for Computer Science</organization>
3583      <address><email>frystyk@w3.org</email></address>
3584    </author>
3585    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3586      <organization>MIT Laboratory for Computer Science</organization>
3587      <address><email>timbl@w3.org</email></address>
3588    </author>
3589    <date month="January" year="1997"/>
3590  </front>
3591  <seriesInfo name="RFC" value="2068"/>
3592</reference>
3593
3594<reference anchor='RFC2109'>
3595  <front>
3596    <title>HTTP State Management Mechanism</title>
3597    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3598      <organization>Bell Laboratories, Lucent Technologies</organization>
3599      <address><email>dmk@bell-labs.com</email></address>
3600    </author>
3601    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3602      <organization>Netscape Communications Corp.</organization>
3603      <address><email>montulli@netscape.com</email></address>
3604    </author>
3605    <date year='1997' month='February' />
3606  </front>
3607  <seriesInfo name='RFC' value='2109' />
3608</reference>
3609
3610<reference anchor="RFC2145">
3611  <front>
3612    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3613    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3614      <organization>Western Research Laboratory</organization>
3615      <address><email>mogul@wrl.dec.com</email></address>
3616    </author>
3617    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3618      <organization>Department of Information and Computer Science</organization>
3619      <address><email>fielding@ics.uci.edu</email></address>
3620    </author>
3621    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3622      <organization>MIT Laboratory for Computer Science</organization>
3623      <address><email>jg@w3.org</email></address>
3624    </author>
3625    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3626      <organization>W3 Consortium</organization>
3627      <address><email>frystyk@w3.org</email></address>
3628    </author>
3629    <date month="May" year="1997"/>
3630  </front>
3631  <seriesInfo name="RFC" value="2145"/>
3632</reference>
3633
3634<reference anchor="RFC2616">
3635  <front>
3636    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3637    <author initials="R." surname="Fielding" fullname="R. Fielding">
3638      <organization>University of California, Irvine</organization>
3639      <address><email>fielding@ics.uci.edu</email></address>
3640    </author>
3641    <author initials="J." surname="Gettys" fullname="J. Gettys">
3642      <organization>W3C</organization>
3643      <address><email>jg@w3.org</email></address>
3644    </author>
3645    <author initials="J." surname="Mogul" fullname="J. Mogul">
3646      <organization>Compaq Computer Corporation</organization>
3647      <address><email>mogul@wrl.dec.com</email></address>
3648    </author>
3649    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3650      <organization>MIT Laboratory for Computer Science</organization>
3651      <address><email>frystyk@w3.org</email></address>
3652    </author>
3653    <author initials="L." surname="Masinter" fullname="L. Masinter">
3654      <organization>Xerox Corporation</organization>
3655      <address><email>masinter@parc.xerox.com</email></address>
3656    </author>
3657    <author initials="P." surname="Leach" fullname="P. Leach">
3658      <organization>Microsoft Corporation</organization>
3659      <address><email>paulle@microsoft.com</email></address>
3660    </author>
3661    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3662      <organization>W3C</organization>
3663      <address><email>timbl@w3.org</email></address>
3664    </author>
3665    <date month="June" year="1999"/>
3666  </front>
3667  <seriesInfo name="RFC" value="2616"/>
3668</reference>
3669
3670<reference anchor='RFC2818'>
3671  <front>
3672    <title>HTTP Over TLS</title>
3673    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3674      <organization>RTFM, Inc.</organization>
3675      <address><email>ekr@rtfm.com</email></address>
3676    </author>
3677    <date year='2000' month='May' />
3678  </front>
3679  <seriesInfo name='RFC' value='2818' />
3680</reference>
3681
3682<reference anchor='RFC2965'>
3683  <front>
3684    <title>HTTP State Management Mechanism</title>
3685    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3686      <organization>Bell Laboratories, Lucent Technologies</organization>
3687      <address><email>dmk@bell-labs.com</email></address>
3688    </author>
3689    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3690      <organization>Epinions.com, Inc.</organization>
3691      <address><email>lou@montulli.org</email></address>
3692    </author>
3693    <date year='2000' month='October' />
3694  </front>
3695  <seriesInfo name='RFC' value='2965' />
3696</reference>
3697
3698<reference anchor='RFC3864'>
3699  <front>
3700    <title>Registration Procedures for Message Header Fields</title>
3701    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3702      <organization>Nine by Nine</organization>
3703      <address><email>GK-IETF@ninebynine.org</email></address>
3704    </author>
3705    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3706      <organization>BEA Systems</organization>
3707      <address><email>mnot@pobox.com</email></address>
3708    </author>
3709    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3710      <organization>HP Labs</organization>
3711      <address><email>JeffMogul@acm.org</email></address>
3712    </author>
3713    <date year='2004' month='September' />
3714  </front>
3715  <seriesInfo name='BCP' value='90' />
3716  <seriesInfo name='RFC' value='3864' />
3717</reference>
3718
3719<reference anchor='RFC3977'>
3720  <front>
3721    <title>Network News Transfer Protocol (NNTP)</title>
3722    <author initials='C.' surname='Feather' fullname='C. Feather'>
3723      <organization>THUS plc</organization>
3724      <address><email>clive@demon.net</email></address>
3725    </author>
3726    <date year='2006' month='October' />
3727  </front>
3728  <seriesInfo name="RFC" value="3977"/>
3729</reference>
3730
3731<reference anchor="RFC4288">
3732  <front>
3733    <title>Media Type Specifications and Registration Procedures</title>
3734    <author initials="N." surname="Freed" fullname="N. Freed">
3735      <organization>Sun Microsystems</organization>
3736      <address>
3737        <email>ned.freed@mrochek.com</email>
3738      </address>
3739    </author>
3740    <author initials="J." surname="Klensin" fullname="J. Klensin">
3741      <organization/>
3742      <address>
3743        <email>klensin+ietf@jck.com</email>
3744      </address>
3745    </author>
3746    <date year="2005" month="December"/>
3747  </front>
3748  <seriesInfo name="BCP" value="13"/>
3749  <seriesInfo name="RFC" value="4288"/>
3750</reference>
3751
3752<reference anchor='RFC4395'>
3753  <front>
3754    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3755    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3756      <organization>AT&amp;T Laboratories</organization>
3757      <address>
3758        <email>tony+urireg@maillennium.att.com</email>
3759      </address>
3760    </author>
3761    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3762      <organization>Qualcomm, Inc.</organization>
3763      <address>
3764        <email>hardie@qualcomm.com</email>
3765      </address>
3766    </author>
3767    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3768      <organization>Adobe Systems</organization>
3769      <address>
3770        <email>LMM@acm.org</email>
3771      </address>
3772    </author>
3773    <date year='2006' month='February' />
3774  </front>
3775  <seriesInfo name='BCP' value='115' />
3776  <seriesInfo name='RFC' value='4395' />
3777</reference>
3778
3779<reference anchor="RFC5322">
3780  <front>
3781    <title>Internet Message Format</title>
3782    <author initials="P." surname="Resnick" fullname="P. Resnick">
3783      <organization>Qualcomm Incorporated</organization>
3784    </author>
3785    <date year="2008" month="October"/>
3786  </front>
3787  <seriesInfo name="RFC" value="5322"/>
3788</reference>
3789
3790<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3791  <front>
3792    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3793    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3794      <organization/>
3795    </author>
3796    <date year="2001" month="November"/>
3797  </front>
3798  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3799</reference>
3800
3801<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3802  <front>
3803  <title>Analysis of HTTP Performance Problems</title>
3804  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3805    <organization/>
3806  </author>
3807  <date/>
3808  </front>
3809</reference>
3810
3811<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3812  <front>
3813  <title>Analysis of HTTP Performance</title>
3814  <author initials="J." surname="Touch" fullname="Joe Touch">
3815    <organization>USC/Information Sciences Institute</organization>
3816    <address><email>touch@isi.edu</email></address>
3817  </author>
3818  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3819    <organization>USC/Information Sciences Institute</organization>
3820    <address><email>johnh@isi.edu</email></address>
3821  </author>
3822  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3823    <organization>USC/Information Sciences Institute</organization>
3824    <address><email>katia@isi.edu</email></address>
3825  </author>
3826  <date year="1998" month="Aug"/>
3827  </front>
3828  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3829  <annotation>(original report dated Aug. 1996)</annotation>
3830</reference>
3831
3832<reference anchor="WAIS">
3833  <front>
3834    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3835    <author initials="F." surname="Davis" fullname="F. Davis">
3836      <organization>Thinking Machines Corporation</organization>
3837    </author>
3838    <author initials="B." surname="Kahle" fullname="B. Kahle">
3839      <organization>Thinking Machines Corporation</organization>
3840    </author>
3841    <author initials="H." surname="Morris" fullname="H. Morris">
3842      <organization>Thinking Machines Corporation</organization>
3843    </author>
3844    <author initials="J." surname="Salem" fullname="J. Salem">
3845      <organization>Thinking Machines Corporation</organization>
3846    </author>
3847    <author initials="T." surname="Shen" fullname="T. Shen">
3848      <organization>Thinking Machines Corporation</organization>
3849    </author>
3850    <author initials="R." surname="Wang" fullname="R. Wang">
3851      <organization>Thinking Machines Corporation</organization>
3852    </author>
3853    <author initials="J." surname="Sui" fullname="J. Sui">
3854      <organization>Thinking Machines Corporation</organization>
3855    </author>
3856    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3857      <organization>Thinking Machines Corporation</organization>
3858    </author>
3859    <date month="April" year="1990"/>
3860  </front>
3861  <seriesInfo name="Thinking Machines Corporation" value=""/>
3862</reference>
3863
3864</references>
3865
3866
3867<section title="Tolerant Applications" anchor="tolerant.applications">
3868<t>
3869   Although this document specifies the requirements for the generation
3870   of HTTP/1.1 messages, not all applications will be correct in their
3871   implementation. We therefore recommend that operational applications
3872   be tolerant of deviations whenever those deviations can be
3873   interpreted unambiguously.
3874</t>
3875<t>
3876   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3877   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3878   accept any amount of SP or HTAB characters between fields, even though
3879   only a single SP is required.
3880</t>
3881<t>
3882   The line terminator for message-header fields is the sequence CRLF.
3883   However, we recommend that applications, when parsing such headers,
3884   recognize a single LF as a line terminator and ignore the leading CR.
3885</t>
3886<t>
3887   The character set of an entity-body &SHOULD; be labeled as the lowest
3888   common denominator of the character codes used within that body, with
3889   the exception that not labeling the entity is preferred over labeling
3890   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3891</t>
3892<t>
3893   Additional rules for requirements on parsing and encoding of dates
3894   and other potential problems with date encodings include:
3895</t>
3896<t>
3897  <list style="symbols">
3898     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3899        which appears to be more than 50 years in the future is in fact
3900        in the past (this helps solve the "year 2000" problem).</t>
3901
3902     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3903        Expires date as earlier than the proper value, but &MUST-NOT;
3904        internally represent a parsed Expires date as later than the
3905        proper value.</t>
3906
3907     <t>All expiration-related calculations &MUST; be done in GMT. The
3908        local time zone &MUST-NOT; influence the calculation or comparison
3909        of an age or expiration time.</t>
3910
3911     <t>If an HTTP header incorrectly carries a date value with a time
3912        zone other than GMT, it &MUST; be converted into GMT using the
3913        most conservative possible conversion.</t>
3914  </list>
3915</t>
3916</section>
3917
3918<section title="Compatibility with Previous Versions" anchor="compatibility">
3919<t>
3920   HTTP has been in use by the World-Wide Web global information initiative
3921   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3922   was a simple protocol for hypertext data transfer across the Internet
3923   with only a single method and no metadata.
3924   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3925   methods and MIME-like messaging that could include metadata about the data
3926   transferred and modifiers on the request/response semantics. However,
3927   HTTP/1.0 did not sufficiently take into consideration the effects of
3928   hierarchical proxies, caching, the need for persistent connections, or
3929   name-based virtual hosts. The proliferation of incompletely-implemented
3930   applications calling themselves "HTTP/1.0" further necessitated a
3931   protocol version change in order for two communicating applications
3932   to determine each other's true capabilities.
3933</t>
3934<t>
3935   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3936   requirements that enable reliable implementations, adding only
3937   those new features that will either be safely ignored by an HTTP/1.0
3938   recipient or only sent when communicating with a party advertising
3939   compliance with HTTP/1.1.
3940</t>
3941<t>
3942   It is beyond the scope of a protocol specification to mandate
3943   compliance with previous versions. HTTP/1.1 was deliberately
3944   designed, however, to make supporting previous versions easy. It is
3945   worth noting that, at the time of composing this specification
3946   (1996), we would expect commercial HTTP/1.1 servers to:
3947  <list style="symbols">
3948     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3949        1.1 requests;</t>
3950
3951     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3952        1.1;</t>
3953
3954     <t>respond appropriately with a message in the same major version
3955        used by the client.</t>
3956  </list>
3957</t>
3958<t>
3959   And we would expect HTTP/1.1 clients to:
3960  <list style="symbols">
3961     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3962        responses;</t>
3963
3964     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3965        1.1.</t>
3966  </list>
3967</t>
3968<t>
3969   For most implementations of HTTP/1.0, each connection is established
3970   by the client prior to the request and closed by the server after
3971   sending the response. Some implementations implement the Keep-Alive
3972   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3973</t>
3974
3975<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3976<t>
3977   This section summarizes major differences between versions HTTP/1.0
3978   and HTTP/1.1.
3979</t>
3980
3981<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">
3982<t>
3983   The requirements that clients and servers support the Host request-header,
3984   report an error if the Host request-header (<xref target="header.host"/>) is
3985   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3986   are among the most important changes defined by this
3987   specification.
3988</t>
3989<t>
3990   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3991   addresses and servers; there was no other established mechanism for
3992   distinguishing the intended server of a request than the IP address
3993   to which that request was directed. The changes outlined above will
3994   allow the Internet, once older HTTP clients are no longer common, to
3995   support multiple Web sites from a single IP address, greatly
3996   simplifying large operational Web servers, where allocation of many
3997   IP addresses to a single host has created serious problems. The
3998   Internet will also be able to recover the IP addresses that have been
3999   allocated for the sole purpose of allowing special-purpose domain
4000   names to be used in root-level HTTP URLs. Given the rate of growth of
4001   the Web, and the number of servers already deployed, it is extremely
4002   important that all implementations of HTTP (including updates to
4003   existing HTTP/1.0 applications) correctly implement these
4004   requirements:
4005  <list style="symbols">
4006     <t>Both clients and servers &MUST; support the Host request-header.</t>
4007
4008     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4009
4010     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4011        request does not include a Host request-header.</t>
4012
4013     <t>Servers &MUST; accept absolute URIs.</t>
4014  </list>
4015</t>
4016</section>
4017</section>
4018
4019<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4020<t>
4021   Some clients and servers might wish to be compatible with some
4022   previous implementations of persistent connections in HTTP/1.0
4023   clients and servers. Persistent connections in HTTP/1.0 are
4024   explicitly negotiated as they are not the default behavior. HTTP/1.0
4025   experimental implementations of persistent connections are faulty,
4026   and the new facilities in HTTP/1.1 are designed to rectify these
4027   problems. The problem was that some existing 1.0 clients may be
4028   sending Keep-Alive to a proxy server that doesn't understand
4029   Connection, which would then erroneously forward it to the next
4030   inbound server, which would establish the Keep-Alive connection and
4031   result in a hung HTTP/1.0 proxy waiting for the close on the
4032   response. The result is that HTTP/1.0 clients must be prevented from
4033   using Keep-Alive when talking to proxies.
4034</t>
4035<t>
4036   However, talking to proxies is the most important use of persistent
4037   connections, so that prohibition is clearly unacceptable. Therefore,
4038   we need some other mechanism for indicating a persistent connection
4039   is desired, which is safe to use even when talking to an old proxy
4040   that ignores Connection. Persistent connections are the default for
4041   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4042   declaring non-persistence. See <xref target="header.connection"/>.
4043</t>
4044<t>
4045   The original HTTP/1.0 form of persistent connections (the Connection:
4046   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4047</t>
4048</section>
4049
4050<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4051<t>
4052   This specification has been carefully audited to correct and
4053   disambiguate key word usage; RFC 2068 had many problems in respect to
4054   the conventions laid out in <xref target="RFC2119"/>.
4055</t>
4056<t>
4057   Transfer-coding and message lengths all interact in ways that
4058   required fixing exactly when chunked encoding is used (to allow for
4059   transfer encoding that may not be self delimiting); it was important
4060   to straighten out exactly how message lengths are computed. (Sections
4061   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4062   <xref target="header.content-length" format="counter"/>,
4063   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4064</t>
4065<t>
4066   The use and interpretation of HTTP version numbers has been clarified
4067   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4068   version they support to deal with problems discovered in HTTP/1.0
4069   implementations (<xref target="http.version"/>)
4070</t>
4071<t>
4072   Transfer-coding had significant problems, particularly with
4073   interactions with chunked encoding. The solution is that transfer-codings
4074   become as full fledged as content-codings. This involves
4075   adding an IANA registry for transfer-codings (separate from content
4076   codings), a new header field (TE) and enabling trailer headers in the
4077   future. Transfer encoding is a major performance benefit, so it was
4078   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4079   interoperability problem that could have occurred due to interactions
4080   between authentication trailers, chunked encoding and HTTP/1.0
4081   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4082   and <xref target="header.te" format="counter"/>)
4083</t>
4084</section>
4085
4086<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4087<t>
4088  Rules about implicit linear white space between certain grammar productions
4089  have been removed; now it's only allowed when specifically pointed out
4090  in the ABNF.
4091  The CHAR rule does not allow the NUL character anymore (this affects
4092  the comment and quoted-string rules).  Furthermore, the quoted-pair
4093  rule does not allow escaping NUL, CR or LF anymore.
4094  (<xref target="basic.rules"/>)
4095</t>
4096<t>
4097  Clarify that HTTP-Version is case sensitive.
4098  (<xref target="http.version"/>)
4099</t>
4100<t>
4101  Remove reference to non-existant identity transfer-coding value tokens.
4102  (Sections <xref format="counter" target="transfer.codings"/> and
4103  <xref format="counter" target="message.length"/>)
4104</t>
4105<t>
4106  Clarification that the chunk length does not include
4107  the count of the octets in the chunk header and trailer.
4108  (<xref target="chunked.transfer.encoding"/>)
4109</t>
4110<t>
4111  Update use of abs_path production from RFC1808 to the path-absolute + query
4112  components of RFC3986.
4113  (<xref target="request-target"/>)
4114</t>
4115<t>
4116  Clarify exactly when close connection options must be sent.
4117  (<xref target="header.connection"/>)
4118</t>
4119</section>
4120</section>
4121
4122<section title="Terminology" anchor="terminology">
4123<t>
4124   This specification uses a number of terms to refer to the roles
4125   played by participants in, and objects of, the HTTP communication.
4126</t>
4127<t>
4128  <iref item="connection"/>
4129  <x:dfn>connection</x:dfn>
4130  <list>
4131    <t>
4132      A transport layer virtual circuit established between two programs
4133      for the purpose of communication.
4134    </t>
4135  </list>
4136</t>
4137<t>
4138  <iref item="message"/>
4139  <x:dfn>message</x:dfn>
4140  <list>
4141    <t>
4142      The basic unit of HTTP communication, consisting of a structured
4143      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4144      transmitted via the connection.
4145    </t>
4146  </list>
4147</t>
4148<t>
4149  <iref item="request"/>
4150  <x:dfn>request</x:dfn>
4151  <list>
4152    <t>
4153      An HTTP request message, as defined in <xref target="request"/>.
4154    </t>
4155  </list>
4156</t>
4157<t>
4158  <iref item="response"/>
4159  <x:dfn>response</x:dfn>
4160  <list>
4161    <t>
4162      An HTTP response message, as defined in <xref target="response"/>.
4163    </t>
4164  </list>
4165</t>
4166<t>
4167  <iref item="resource"/>
4168  <x:dfn>resource</x:dfn>
4169  <list>
4170    <t>
4171      A network data object or service that can be identified by a URI,
4172      as defined in <xref target="uri"/>. Resources may be available in multiple
4173      representations (e.g. multiple languages, data formats, size, and
4174      resolutions) or vary in other ways.
4175    </t>
4176  </list>
4177</t>
4178<t>
4179  <iref item="entity"/>
4180  <x:dfn>entity</x:dfn>
4181  <list>
4182    <t>
4183      The information transferred as the payload of a request or
4184      response. An entity consists of metainformation in the form of
4185      entity-header fields and content in the form of an entity-body, as
4186      described in &entity;.
4187    </t>
4188  </list>
4189</t>
4190<t>
4191  <iref item="representation"/>
4192  <x:dfn>representation</x:dfn>
4193  <list>
4194    <t>
4195      An entity included with a response that is subject to content
4196      negotiation, as described in &content.negotiation;. There may exist multiple
4197      representations associated with a particular response status.
4198    </t>
4199  </list>
4200</t>
4201<t>
4202  <iref item="content negotiation"/>
4203  <x:dfn>content negotiation</x:dfn>
4204  <list>
4205    <t>
4206      The mechanism for selecting the appropriate representation when
4207      servicing a request, as described in &content.negotiation;. The
4208      representation of entities in any response can be negotiated
4209      (including error responses).
4210    </t>
4211  </list>
4212</t>
4213<t>
4214  <iref item="variant"/>
4215  <x:dfn>variant</x:dfn>
4216  <list>
4217    <t>
4218      A resource may have one, or more than one, representation(s)
4219      associated with it at any given instant. Each of these
4220      representations is termed a `variant'.  Use of the term `variant'
4221      does not necessarily imply that the resource is subject to content
4222      negotiation.
4223    </t>
4224  </list>
4225</t>
4226<t>
4227  <iref item="client"/>
4228  <x:dfn>client</x:dfn>
4229  <list>
4230    <t>
4231      A program that establishes connections for the purpose of sending
4232      requests.
4233    </t>
4234  </list>
4235</t>
4236<t>
4237  <iref item="user agent"/>
4238  <x:dfn>user agent</x:dfn>
4239  <list>
4240    <t>
4241      The client which initiates a request. These are often browsers,
4242      editors, spiders (web-traversing robots), or other end user tools.
4243    </t>
4244  </list>
4245</t>
4246<t>
4247  <iref item="server"/>
4248  <x:dfn>server</x:dfn>
4249  <list>
4250    <t>
4251      An application program that accepts connections in order to
4252      service requests by sending back responses. Any given program may
4253      be capable of being both a client and a server; our use of these
4254      terms refers only to the role being performed by the program for a
4255      particular connection, rather than to the program's capabilities
4256      in general. Likewise, any server may act as an origin server,
4257      proxy, gateway, or tunnel, switching behavior based on the nature
4258      of each request.
4259    </t>
4260  </list>
4261</t>
4262<t>
4263  <iref item="origin server"/>
4264  <x:dfn>origin server</x:dfn>
4265  <list>
4266    <t>
4267      The server on which a given resource resides or is to be created.
4268    </t>
4269  </list>
4270</t>
4271<t>
4272  <iref item="proxy"/>
4273  <x:dfn>proxy</x:dfn>
4274  <list>
4275    <t>
4276      An intermediary program which acts as both a server and a client
4277      for the purpose of making requests on behalf of other clients.
4278      Requests are serviced internally or by passing them on, with
4279      possible translation, to other servers. A proxy &MUST; implement
4280      both the client and server requirements of this specification. A
4281      "transparent proxy" is a proxy that does not modify the request or
4282      response beyond what is required for proxy authentication and
4283      identification. A "non-transparent proxy" is a proxy that modifies
4284      the request or response in order to provide some added service to
4285      the user agent, such as group annotation services, media type
4286      transformation, protocol reduction, or anonymity filtering. Except
4287      where either transparent or non-transparent behavior is explicitly
4288      stated, the HTTP proxy requirements apply to both types of
4289      proxies.
4290    </t>
4291  </list>
4292</t>
4293<t>
4294  <iref item="gateway"/>
4295  <x:dfn>gateway</x:dfn>
4296  <list>
4297    <t>
4298      A server which acts as an intermediary for some other server.
4299      Unlike a proxy, a gateway receives requests as if it were the
4300      origin server for the requested resource; the requesting client
4301      may not be aware that it is communicating with a gateway.
4302    </t>
4303  </list>
4304</t>
4305<t>
4306  <iref item="tunnel"/>
4307  <x:dfn>tunnel</x:dfn>
4308  <list>
4309    <t>
4310      An intermediary program which is acting as a blind relay between
4311      two connections. Once active, a tunnel is not considered a party
4312      to the HTTP communication, though the tunnel may have been
4313      initiated by an HTTP request. The tunnel ceases to exist when both
4314      ends of the relayed connections are closed.
4315    </t>
4316  </list>
4317</t>
4318<t>
4319  <iref item="cache"/>
4320  <x:dfn>cache</x:dfn>
4321  <list>
4322    <t>
4323      A program's local store of response messages and the subsystem
4324      that controls its message storage, retrieval, and deletion. A
4325      cache stores cacheable responses in order to reduce the response
4326      time and network bandwidth consumption on future, equivalent
4327      requests. Any client or server may include a cache, though a cache
4328      cannot be used by a server that is acting as a tunnel.
4329    </t>
4330  </list>
4331</t>
4332<t>
4333  <iref item="cacheable"/>
4334  <x:dfn>cacheable</x:dfn>
4335  <list>
4336    <t>
4337      A response is cacheable if a cache is allowed to store a copy of
4338      the response message for use in answering subsequent requests. The
4339      rules for determining the cacheability of HTTP responses are
4340      defined in &caching;. Even if a resource is cacheable, there may
4341      be additional constraints on whether a cache can use the cached
4342      copy for a particular request.
4343    </t>
4344  </list>
4345</t>
4346<t>
4347  <iref item="upstream"/>
4348  <iref item="downstream"/>
4349  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4350  <list>
4351    <t>
4352      Upstream and downstream describe the flow of a message: all
4353      messages flow from upstream to downstream.
4354    </t>
4355  </list>
4356</t>
4357<t>
4358  <iref item="inbound"/>
4359  <iref item="outbound"/>
4360  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4361  <list>
4362    <t>
4363      Inbound and outbound refer to the request and response paths for
4364      messages: "inbound" means "traveling toward the origin server",
4365      and "outbound" means "traveling toward the user agent"
4366    </t>
4367  </list>
4368</t>
4369</section>
4370
4371<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4372
4373<section title="Since RFC2616">
4374<t>
4375  Extracted relevant partitions from <xref target="RFC2616"/>.
4376</t>
4377</section>
4378
4379<section title="Since draft-ietf-httpbis-p1-messaging-00">
4380<t>
4381  Closed issues:
4382  <list style="symbols">
4383    <t>
4384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4385      "HTTP Version should be case sensitive"
4386      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4387    </t>
4388    <t>
4389      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4390      "'unsafe' characters"
4391      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4392    </t>
4393    <t>
4394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4395      "Chunk Size Definition"
4396      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4397    </t>
4398    <t>
4399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4400      "Message Length"
4401      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4402    </t>
4403    <t>
4404      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4405      "Media Type Registrations"
4406      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4407    </t>
4408    <t>
4409      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4410      "URI includes query"
4411      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4412    </t>
4413    <t>
4414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4415      "No close on 1xx responses"
4416      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4417    </t>
4418    <t>
4419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4420      "Remove 'identity' token references"
4421      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4422    </t>
4423    <t>
4424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4425      "Import query BNF"
4426    </t>
4427    <t>
4428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4429      "qdtext BNF"
4430    </t>
4431    <t>
4432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4433      "Normative and Informative references"
4434    </t>
4435    <t>
4436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4437      "RFC2606 Compliance"
4438    </t>
4439    <t>
4440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4441      "RFC977 reference"
4442    </t>
4443    <t>
4444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4445      "RFC1700 references"
4446    </t>
4447    <t>
4448      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4449      "inconsistency in date format explanation"
4450    </t>
4451    <t>
4452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4453      "Date reference typo"
4454    </t>
4455    <t>
4456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4457      "Informative references"
4458    </t>
4459    <t>
4460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4461      "ISO-8859-1 Reference"
4462    </t>
4463    <t>
4464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4465      "Normative up-to-date references"
4466    </t>
4467  </list>
4468</t>
4469<t>
4470  Other changes:
4471  <list style="symbols">
4472    <t>
4473      Update media type registrations to use RFC4288 template.
4474    </t>
4475    <t>
4476      Use names of RFC4234 core rules DQUOTE and HTAB,
4477      fix broken ABNF for chunk-data
4478      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4479    </t>
4480  </list>
4481</t>
4482</section>
4483
4484<section title="Since draft-ietf-httpbis-p1-messaging-01">
4485<t>
4486  Closed issues:
4487  <list style="symbols">
4488    <t>
4489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4490      "Bodies on GET (and other) requests"
4491    </t>
4492    <t>
4493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4494      "Updating to RFC4288"
4495    </t>
4496    <t>
4497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4498      "Status Code and Reason Phrase"
4499    </t>
4500    <t>
4501      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4502      "rel_path not used"
4503    </t>
4504  </list>
4505</t>
4506<t>
4507  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4508  <list style="symbols">
4509    <t>
4510      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4511      "trailer-part").
4512    </t>
4513    <t>
4514      Avoid underscore character in rule names ("http_URL" ->
4515      "http-URL", "abs_path" -> "path-absolute").
4516    </t>
4517    <t>
4518      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4519      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4520      have to be updated when switching over to RFC3986.
4521    </t>
4522    <t>
4523      Synchronize core rules with RFC5234 (this includes a change to CHAR
4524      which now excludes NUL).
4525    </t>
4526    <t>
4527      Get rid of prose rules that span multiple lines.
4528    </t>
4529    <t>
4530      Get rid of unused rules LOALPHA and UPALPHA.
4531    </t>
4532    <t>
4533      Move "Product Tokens" section (back) into Part 1, as "token" is used
4534      in the definition of the Upgrade header.
4535    </t>
4536    <t>
4537      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4538    </t>
4539    <t>
4540      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4541    </t>
4542  </list>
4543</t>
4544</section>
4545
4546<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4547<t>
4548  Closed issues:
4549  <list style="symbols">
4550    <t>
4551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4552      "HTTP-date vs. rfc1123-date"
4553    </t>
4554    <t>
4555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4556      "WS in quoted-pair"
4557    </t>
4558  </list>
4559</t>
4560<t>
4561  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4562  <list style="symbols">
4563    <t>
4564      Reference RFC 3984, and update header registrations for headers defined
4565      in this document.
4566    </t>
4567  </list>
4568</t>
4569<t>
4570  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4571  <list style="symbols">
4572    <t>
4573      Replace string literals when the string really is case-sensitive (HTTP-Version).
4574    </t>
4575  </list>
4576</t>
4577</section>
4578
4579<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4580<t>
4581  Closed issues:
4582  <list style="symbols">
4583    <t>
4584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4585      "Connection closing"
4586    </t>
4587    <t>
4588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4589      "Move registrations and registry information to IANA Considerations"
4590    </t>
4591    <t>
4592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4593      "need new URL for PAD1995 reference"
4594    </t>
4595    <t>
4596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4597      "IANA Considerations: update HTTP URI scheme registration"
4598    </t>
4599    <t>
4600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4601      "Cite HTTPS URI scheme definition"
4602    </t>
4603    <t>
4604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4605      "List-type headers vs Set-Cookie"
4606    </t>
4607  </list>
4608</t>
4609<t>
4610  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4611  <list style="symbols">
4612    <t>
4613      Replace string literals when the string really is case-sensitive (HTTP-Date).
4614    </t>
4615    <t>
4616      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4617    </t>
4618  </list>
4619</t>
4620</section>
4621
4622<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4623<t>
4624  Closed issues:
4625  <list style="symbols">
4626    <t>
4627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4628      "Out-of-date reference for URIs"
4629    </t>
4630    <t>
4631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4632      "RFC 2822 is updated by RFC 5322"
4633    </t>
4634  </list>
4635</t>
4636<t>
4637  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4638  <list style="symbols">
4639    <t>
4640      Use "/" instead of "|" for alternatives.
4641    </t>
4642    <t>
4643      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4644    </t>
4645    <t>
4646      Only reference RFC 5234's core rules.
4647    </t>
4648    <t>
4649      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4650      whitespace ("OWS") and required whitespace ("RWS").
4651    </t>
4652    <t>
4653      Rewrite ABNFs to spell out whitespace rules, factor out
4654      header value format definitions.
4655    </t>
4656  </list>
4657</t>
4658</section>
4659
4660<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4661<t>
4662  Closed issues:
4663  <list style="symbols">
4664    <t>
4665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4666      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4667    </t>
4668    <t>
4669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4670      "RFC822 reference left in discussion of date formats"
4671    </t>
4672  </list>
4673</t>
4674</section>
4675
4676</section>
4677
4678</back>
4679</rfc>
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