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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<!DOCTYPE rfc
17  PUBLIC "" "rfc2629.dtd">
18<rfc obsoletes="2616" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-06">
19<front>
20
21  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
22
23  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
24    <organization abbrev="Day Software">Day Software</organization>
25    <address>
26      <postal>
27        <street>23 Corporate Plaza DR, Suite 280</street>
28        <city>Newport Beach</city>
29        <region>CA</region>
30        <code>92660</code>
31        <country>USA</country>
32      </postal>
33      <phone>+1-949-706-5300</phone>
34      <facsimile>+1-949-706-5305</facsimile>
35      <email>fielding@gbiv.com</email>
36      <uri>http://roy.gbiv.com/</uri>
37    </address>
38  </author>
39
40  <author initials="J." surname="Gettys" fullname="Jim Gettys">
41    <organization>One Laptop per Child</organization>
42    <address>
43      <postal>
44        <street>21 Oak Knoll Road</street>
45        <city>Carlisle</city>
46        <region>MA</region>
47        <code>01741</code>
48        <country>USA</country>
49      </postal>
50      <email>jg@laptop.org</email>
51      <uri>http://www.laptop.org/</uri>
52    </address>
53  </author>
54 
55  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
56    <organization abbrev="HP">Hewlett-Packard Company</organization>
57    <address>
58      <postal>
59        <street>HP Labs, Large Scale Systems Group</street>
60        <street>1501 Page Mill Road, MS 1177</street>
61        <city>Palo Alto</city>
62        <region>CA</region>
63        <code>94304</code>
64        <country>USA</country>
65      </postal>
66      <email>JeffMogul@acm.org</email>
67    </address>
68  </author>
69
70  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
71    <organization abbrev="Microsoft">Microsoft Corporation</organization>
72    <address>
73      <postal>
74        <street>1 Microsoft Way</street>
75        <city>Redmond</city>
76        <region>WA</region>
77        <code>98052</code>
78        <country>USA</country>
79      </postal>
80      <email>henrikn@microsoft.com</email>
81    </address>
82  </author>
83
84  <author initials="L." surname="Masinter" fullname="Larry Masinter">
85    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
86    <address>
87      <postal>
88        <street>345 Park Ave</street>
89        <city>San Jose</city>
90        <region>CA</region>
91        <code>95110</code>
92        <country>USA</country>
93      </postal>
94      <email>LMM@acm.org</email>
95      <uri>http://larry.masinter.net/</uri>
96    </address>
97  </author>
98 
99  <author initials="P." surname="Leach" fullname="Paul J. Leach">
100    <organization abbrev="Microsoft">Microsoft Corporation</organization>
101    <address>
102      <postal>
103        <street>1 Microsoft Way</street>
104        <city>Redmond</city>
105        <region>WA</region>
106        <code>98052</code>
107      </postal>
108      <email>paulle@microsoft.com</email>
109    </address>
110  </author>
111   
112  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
113    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
114    <address>
115      <postal>
116        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
117        <street>The Stata Center, Building 32</street>
118        <street>32 Vassar Street</street>
119        <city>Cambridge</city>
120        <region>MA</region>
121        <code>02139</code>
122        <country>USA</country>
123      </postal>
124      <email>timbl@w3.org</email>
125      <uri>http://www.w3.org/People/Berners-Lee/</uri>
126    </address>
127  </author>
128
129  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
130    <organization abbrev="W3C">World Wide Web Consortium</organization>
131    <address>
132      <postal>
133        <street>W3C / ERCIM</street>
134        <street>2004, rte des Lucioles</street>
135        <city>Sophia-Antipolis</city>
136        <region>AM</region>
137        <code>06902</code>
138        <country>France</country>
139      </postal>
140      <email>ylafon@w3.org</email>
141      <uri>http://www.raubacapeu.net/people/yves/</uri>
142    </address>
143  </author>
144
145  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
146    <organization abbrev="greenbytes">greenbytes GmbH</organization>
147    <address>
148      <postal>
149        <street>Hafenweg 16</street>
150        <city>Muenster</city><region>NW</region><code>48155</code>
151        <country>Germany</country>
152      </postal>
153      <phone>+49 251 2807760</phone>   
154      <facsimile>+49 251 2807761</facsimile>   
155      <email>julian.reschke@greenbytes.de</email>       
156      <uri>http://greenbytes.de/tech/webdav/</uri>     
157    </address>
158  </author>
159
160  <date month="March" year="2009" day="9"/>
161  <workgroup>HTTPbis Working Group</workgroup>
162
163<abstract>
164<t>
165   The Hypertext Transfer Protocol (HTTP) is an application-level
166   protocol for distributed, collaborative, hypertext information
167   systems. HTTP has been in use by the World Wide Web global information
168   initiative since 1990. This document is Part 1 of the seven-part specification
169   that defines the protocol referred to as "HTTP/1.1" and, taken together,
170   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
171   its associated terminology, defines the "http" and "https" Uniform
172   Resource Identifier (URI) schemes, defines the generic message syntax
173   and parsing requirements for HTTP message frames, and describes
174   general security concerns for implementations.
175</t>
176</abstract>
177
178<note title="Editorial Note (To be removed by RFC Editor)">
179  <t>
180    Discussion of this draft should take place on the HTTPBIS working group
181    mailing list (ietf-http-wg@w3.org). The current issues list is
182    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
183    and related documents (including fancy diffs) can be found at
184    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
185  </t>
186  <t>
187    The changes in this draft are summarized in <xref target="changes.since.05"/>.
188  </t>
189</note>
190</front>
191<middle>
192<section title="Introduction" anchor="introduction">
193<t>
194   The Hypertext Transfer Protocol (HTTP) is an application-level
195   request/response protocol that uses extensible semantics and MIME-like
196   message payloads for flexible interaction with network-based hypertext
197   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
198   standard <xref target="RFC3986"/> to indicate request targets and
199   relationships between resources.
200   Messages are passed in a format similar to that used by Internet mail
201   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
202   (MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part3"/> for the differences
203   between HTTP and MIME messages).
204</t>
205<t>
206   HTTP is a generic interface protocol for information systems. It is
207   designed to hide the details of how a service is implemented by presenting
208   a uniform interface to clients that is independent of the types of
209   resources provided. Likewise, servers do not need to be aware of each
210   client's purpose: an HTTP request can be considered in isolation rather
211   than being associated with a specific type of client or a predetermined
212   sequence of application steps. The result is a protocol that can be used
213   effectively in many different contexts and for which implementations can
214   evolve independently over time.
215</t>
216<t>
217   HTTP is also designed for use as a generic protocol for translating
218   communication to and from other Internet information systems.
219   HTTP proxies and gateways provide access to alternative information
220   services by translating their diverse protocols into a hypertext
221   format that can be viewed and manipulated by clients in the same way
222   as HTTP services.
223</t>
224<t>
225   One consequence of HTTP flexibility is that the protocol cannot be
226   defined in terms of what occurs behind the interface. Instead, we
227   are limited to defining the syntax of communication, the intent
228   of received communication, and the expected behavior of recipients.
229   If the communication is considered in isolation, then successful
230   actions should be reflected in corresponding changes to the
231   observable interface provided by servers. However, since multiple
232   clients may act in parallel and perhaps at cross-purposes, we
233   cannot require that such changes be observable beyond the scope
234   of a single response.
235</t>
236<t>
237   This document is Part 1 of the seven-part specification of HTTP,
238   defining the protocol referred to as "HTTP/1.1" and obsoleting
239   <xref target="RFC2616"/>.
240   Part 1 describes the architectural elements that are used or
241   referred to in HTTP and defines the URI schemes specific to
242   HTTP-based resources, overall network operation, connection
243   management, and HTTP message framing and forwarding requirements.
244   Our goal is to define all of the mechanisms necessary for HTTP message
245   handling that are independent of message semantics, thereby defining the
246   complete set of requirements for message parsers and
247   message-forwarding intermediaries.
248</t>
249
250<section title="Requirements" anchor="intro.requirements">
251<t>
252   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
253   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
254   document are to be interpreted as described in <xref target="RFC2119"/>.
255</t>
256<t>
257   An implementation is not compliant if it fails to satisfy one or more
258   of the MUST or REQUIRED level requirements for the protocols it
259   implements. An implementation that satisfies all the MUST or REQUIRED
260   level and all the SHOULD level requirements for its protocols is said
261   to be "unconditionally compliant"; one that satisfies all the MUST
262   level requirements but not all the SHOULD level requirements for its
263   protocols is said to be "conditionally compliant."
264</t>
265</section>
266
267<section title="Syntax Notation" anchor="notation">
268<iref primary="true" item="Grammar" subitem="ALPHA"/>
269<iref primary="true" item="Grammar" subitem="CR"/>
270<iref primary="true" item="Grammar" subitem="CRLF"/>
271<iref primary="true" item="Grammar" subitem="CTL"/>
272<iref primary="true" item="Grammar" subitem="DIGIT"/>
273<iref primary="true" item="Grammar" subitem="DQUOTE"/>
274<iref primary="true" item="Grammar" subitem="HEXDIG"/>
275<iref primary="true" item="Grammar" subitem="LF"/>
276<iref primary="true" item="Grammar" subitem="OCTET"/>
277<iref primary="true" item="Grammar" subitem="SP"/>
278<iref primary="true" item="Grammar" subitem="VCHAR"/>
279<iref primary="true" item="Grammar" subitem="WSP"/>
280<t>
281   This specification uses the Augmented Backus-Naur Form (ABNF) notation
282   of <xref target="RFC5234"/>.
283</t>
284<t anchor="core.rules">
285 
286 
287 
288 
289 
290 
291 
292 
293 
294 
295 
296 
297   The following core rules are included by
298   reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
299   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
300   DIGIT (decimal 0-9), DQUOTE (double quote),
301   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
302   OCTET (any 8-bit sequence of data), SP (space),
303   VCHAR (any visible <xref target="USASCII"/> character),
304   and WSP (whitespace).
305</t>
306
307<section title="ABNF Extension: #rule" anchor="notation.abnf">
308  <t>
309    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
310    improve readability.
311  </t>
312  <t>
313    A construct "#" is defined, similar to "*", for defining lists of
314    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
315    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
316    (",") and optional whitespace (OWS).   
317  </t>
318  <figure><preamble>
319    Thus,
320</preamble><artwork type="example"><![CDATA[
321  1#element => element *( OWS "," OWS element )
322]]></artwork></figure>
323  <figure><preamble>
324    and:
325</preamble><artwork type="example"><![CDATA[
326  #element => [ 1#element ]
327]]></artwork></figure>
328  <figure><preamble>
329    and for n &gt;= 1 and m &gt; 1:
330</preamble><artwork type="example"><![CDATA[
331  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
332]]></artwork></figure>
333  <t>
334    For compatibility with legacy list rules, recipients SHOULD accept empty
335    list elements. In other words, consumers would follow the list productions:
336  </t>
337<figure><artwork type="example"><![CDATA[
338  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
339 
340  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
341]]></artwork></figure> 
342<t>
343  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
344  expanded as explained above.
345</t>
346</section>
347
348<section title="Basic Rules" anchor="basic.rules">
349<t anchor="rule.CRLF">
350 
351   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
352   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
353   tolerant applications). The end-of-line marker within an entity-body
354   is defined by its associated media type, as described in Section 2.3 of <xref target="Part3"/>.
355</t>
356<t anchor="rule.LWS">
357   This specification uses three rules to denote the use of linear
358   whitespace: OWS (optional whitespace), RWS (required whitespace), and
359   BWS ("bad" whitespace).
360</t>
361<t>
362   The OWS rule is used where zero or more linear whitespace characters may
363   appear. OWS SHOULD either not be produced or be produced as a single SP
364   character. Multiple OWS characters that occur within field-content SHOULD
365   be replaced with a single SP before interpreting the field value or
366   forwarding the message downstream.
367</t>
368<t>
369   RWS is used when at least one linear whitespace character is required to
370   separate field tokens. RWS SHOULD be produced as a single SP character.
371   Multiple RWS characters that occur within field-content SHOULD be
372   replaced with a single SP before interpreting the field value or
373   forwarding the message downstream.
374</t>
375<t>
376   BWS is used where the grammar allows optional whitespace for historical
377   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
378   recipients MUST accept such bad optional whitespace and remove it before
379   interpreting the field value or forwarding the message downstream.
380</t>
381<t anchor="rule.whitespace">
382 
383 
384 
385 
386</t>
387<figure><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/><artwork type="abnf2616"><![CDATA[
388  OWS            = *( [ obs-fold ] WSP )
389                 ; "optional" whitespace
390  RWS            = 1*( [ obs-fold ] WSP )
391                 ; "required" whitespace
392  BWS            = OWS
393                 ; "bad" whitespace
394  obs-fold       = CRLF
395                 ; see Section 4.2
396]]></artwork></figure>
397<t anchor="rule.token.separators">
398 
399 
400   Many HTTP/1.1 header field values consist of words separated by whitespace
401   or special characters. These special characters MUST be in a quoted
402   string to be used within a parameter value (as defined in
403   <xref target="transfer.codings"/>).
404</t>
405<figure><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><artwork type="abnf2616"><![CDATA[
406  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
407                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
408                 / DIGIT / ALPHA
409                 
410  token          = 1*tchar
411]]></artwork></figure>
412<t anchor="rule.quoted-string">
413 
414 
415 
416   A string of text is parsed as a single word if it is quoted using
417   double-quote marks.
418</t>
419<figure><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/><artwork type="abnf2616"><![CDATA[
420  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
421  qdtext         = *( OWS / %x21 / %x23-5B / %x5D-7E / obs-text )
422  obs-text       = %x80-FF
423]]></artwork></figure>
424<t anchor="rule.quoted-pair">
425 
426 
427   The backslash character ("\") MAY be used as a single-character
428   quoting mechanism only within quoted-string and comment constructs.
429</t>
430<figure><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
431  quoted-text    = %x01-09 /
432                   %x0B-0C /
433                   %x0E-FF ; Characters excluding NUL, CR and LF
434  quoted-pair    = "\" quoted-text
435]]></artwork></figure>
436</section>
437
438<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
439 
440 
441 
442 
443 
444 
445 
446<t>
447  The ABNF rules below are defined in other parts:
448</t>
449<figure><!-- Part2--><artwork type="abnf2616"><![CDATA[
450  request-header  = <request-header, defined in [Part2], Section 3>
451  response-header = <response-header, defined in [Part2], Section 5>
452]]></artwork></figure>
453<figure><!-- Part3--><artwork type="abnf2616"><![CDATA[
454  entity-body     = <entity-body, defined in [Part3], Section 3.2>
455  entity-header   = <entity-header, defined in [Part3], Section 3.1>
456]]></artwork></figure>
457<figure><!-- Part6--><artwork type="abnf2616"><![CDATA[
458  Cache-Control   = <Cache-Control, defined in [Part6], Section 3.4>
459  Pragma          = <Pragma, defined in [Part6], Section 3.4>
460  Warning         = <Warning, defined in [Part6], Section 3.6>
461]]></artwork></figure>
462</section>
463
464</section>
465</section>
466
467<section title="HTTP architecture" anchor="architecture">
468<t>
469   HTTP was created with a specific architecture in mind, the World Wide Web,
470   and has evolved over time to support the scalability needs of a worldwide
471   hypertext system. Much of that architecture is reflected in the terminology
472   and syntax productions used to define HTTP.
473</t>
474
475<section title="Uniform Resource Identifiers" anchor="uri">
476<t>
477   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
478   throughout HTTP as the means for identifying resources. URI references
479   are used to target requests, redirect responses, and define relationships.
480   HTTP does not limit what a resource may be; it merely defines an interface
481   that can be used to interact with a resource via HTTP. More information on
482   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
483</t>
484 
485 
486 
487 
488 
489 
490 
491 
492 
493 
494 
495 
496<t>
497   This specification adopts the definitions of "URI-reference",
498   "absolute-URI", "relative-part", "fragment", "port", "host",
499   "path-abempty", "path-absolute", "query", and "authority" from
500   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
501   protocol elements that allow a relative URI without a fragment.
502</t>
503<figure><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"/><artwork type="abnf2616"><![CDATA[
504  URI           = <URI, defined in [RFC3986], Section 3>
505  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
506  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
507  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
508  authority     = <authority, defined in [RFC3986], Section 3.2>
509  fragment      = <fragment, defined in [RFC3986], Section 3.5>
510  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
511  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
512  port          = <port, defined in [RFC3986], Section 3.2.3>
513  query         = <query, defined in [RFC3986], Section 3.4>
514  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
515 
516  partial-URI   = relative-part [ "?" query ]
517]]></artwork></figure>
518<t>
519   Each protocol element in HTTP that allows a URI reference will indicate in
520   its ABNF production whether the element allows only a URI in absolute form
521   (absolute-URI), any relative reference (relative-ref), or some other subset
522   of the URI-reference grammar. Unless otherwise indicated, URI references
523   are parsed relative to the request target (the default base URI for both
524   the request and its corresponding response).
525</t>
526
527<section title="http URI scheme" anchor="http.uri">
528 
529  <iref item="http URI scheme" primary="true"/>
530  <iref item="URI scheme" subitem="http" primary="true"/>
531<t>
532   The "http" scheme is used to locate network resources via the HTTP
533   protocol.
534</t>
535<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
536  http-URI = "http:" "//" authority path-abempty [ "?" query ]
537]]></artwork></figure>
538<t>
539   If the port is empty or not given, port 80 is assumed. The semantics
540   are that the identified resource is located at the server listening
541   for TCP connections on that port of that host, and the request-target
542   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
543   in URLs SHOULD be avoided whenever possible (see <xref target="RFC1900"/>). If
544   the path-absolute is not present in the URL, it MUST be given as "/" when
545   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
546   receives a host name which is not a fully qualified domain name, it
547   MAY add its domain to the host name it received. If a proxy receives
548   a fully qualified domain name, the proxy MUST NOT change the host
549   name.
550</t>
551</section>
552
553<section title="https URI scheme" anchor="https.uri">
554   <iref item="https URI scheme"/>
555   <iref item="URI scheme" subitem="https"/>
556<t>
557   <cref>TBD: Define and explain purpose of https scheme.</cref>
558</t>
559<t><list><t>
560  Note: the "https" scheme is defined in <xref target="RFC2818"/>.
561</t></list></t>
562</section>
563
564<section title="URI Comparison" anchor="uri.comparison">
565<t>
566   When comparing two URIs to decide if they match or not, a client
567   SHOULD use a case-sensitive octet-by-octet comparison of the entire
568   URIs, with these exceptions:
569  <list style="symbols">
570    <t>A port that is empty or not given is equivalent to the default
571        port for that URI-reference;</t>
572    <t>Comparisons of host names MUST be case-insensitive;</t>
573    <t>Comparisons of scheme names MUST be case-insensitive;</t>
574    <t>An empty path-absolute is equivalent to a path-absolute of "/".</t>
575    <t>Characters other than those in the "reserved" set are equivalent to their
576       percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1).
577    </t>
578  </list>
579</t>
580<t>
581   For example, the following three URIs are equivalent:
582</t>
583<figure><artwork type="example"><![CDATA[
584   http://example.com:80/~smith/home.html
585   http://EXAMPLE.com/%7Esmith/home.html
586   http://EXAMPLE.com:/%7esmith/home.html
587]]></artwork></figure>
588</section>
589
590<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
591<t>
592</t>
593</section>
594</section>
595
596<section title="Overall Operation" anchor="intro.overall.operation">
597<t>
598   HTTP is a request/response protocol. A client sends a
599   request to the server in the form of a request method, URI, and
600   protocol version, followed by a MIME-like message containing request
601   modifiers, client information, and possible body content over a
602   connection with a server. The server responds with a status line,
603   including the message's protocol version and a success or error code,
604   followed by a MIME-like message containing server information, entity
605   metainformation, and possible entity-body content.
606</t>
607<t>
608   Most HTTP communication is initiated by a user agent and consists of
609   a request to be applied to a resource on some origin server. In the
610   simplest case, this may be accomplished via a single connection (v)
611   between the user agent (UA) and the origin server (O).
612</t>
613<figure><artwork type="drawing"><![CDATA[
614       request chain ------------------------>
615    UA -------------------v------------------- O
616       <----------------------- response chain
617]]></artwork></figure>
618<t>
619   A more complicated situation occurs when one or more intermediaries
620   are present in the request/response chain. There are three common
621   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
622   forwarding agent, receiving requests for a URI in its absolute form,
623   rewriting all or part of the message, and forwarding the reformatted
624   request toward the server identified by the URI. A gateway is a
625   receiving agent, acting as a layer above some other server(s) and, if
626   necessary, translating the requests to the underlying server's
627   protocol. A tunnel acts as a relay point between two connections
628   without changing the messages; tunnels are used when the
629   communication needs to pass through an intermediary (such as a
630   firewall) even when the intermediary cannot understand the contents
631   of the messages.
632</t>
633<figure><artwork type="drawing"><![CDATA[
634       request chain -------------------------------------->
635    UA -----v----- A -----v----- B -----v----- C -----v----- O
636       <------------------------------------- response chain
637]]></artwork></figure>
638<t>
639   The figure above shows three intermediaries (A, B, and C) between the
640   user agent and origin server. A request or response message that
641   travels the whole chain will pass through four separate connections.
642   This distinction is important because some HTTP communication options
643   may apply only to the connection with the nearest, non-tunnel
644   neighbor, only to the end-points of the chain, or to all connections
645   along the chain. Although the diagram is linear, each participant may
646   be engaged in multiple, simultaneous communications. For example, B
647   may be receiving requests from many clients other than A, and/or
648   forwarding requests to servers other than C, at the same time that it
649   is handling A's request.
650</t>
651<t>
652   Any party to the communication which is not acting as a tunnel may
653   employ an internal cache for handling requests. The effect of a cache
654   is that the request/response chain is shortened if one of the
655   participants along the chain has a cached response applicable to that
656   request. The following illustrates the resulting chain if B has a
657   cached copy of an earlier response from O (via C) for a request which
658   has not been cached by UA or A.
659</t>
660<figure><artwork type="drawing"><![CDATA[
661          request chain ---------->
662       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
663          <--------- response chain
664]]></artwork></figure>
665<t>
666   Not all responses are usefully cacheable, and some requests may
667   contain modifiers which place special requirements on cache behavior.
668   HTTP requirements for cache behavior and cacheable responses are
669   defined in Section 1 of <xref target="Part6"/>.
670</t>
671<t>
672   In fact, there are a wide variety of architectures and configurations
673   of caches and proxies currently being experimented with or deployed
674   across the World Wide Web. These systems include national hierarchies
675   of proxy caches to save transoceanic bandwidth, systems that
676   broadcast or multicast cache entries, organizations that distribute
677   subsets of cached data via CD-ROM, and so on. HTTP systems are used
678   in corporate intranets over high-bandwidth links, and for access via
679   PDAs with low-power radio links and intermittent connectivity. The
680   goal of HTTP/1.1 is to support the wide diversity of configurations
681   already deployed while introducing protocol constructs that meet the
682   needs of those who build web applications that require high
683   reliability and, failing that, at least reliable indications of
684   failure.
685</t>
686<t>
687   HTTP communication usually takes place over TCP/IP connections. The
688   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
689   not preclude HTTP from being implemented on top of any other protocol
690   on the Internet, or on other networks. HTTP only presumes a reliable
691   transport; any protocol that provides such guarantees can be used;
692   the mapping of the HTTP/1.1 request and response structures onto the
693   transport data units of the protocol in question is outside the scope
694   of this specification.
695</t>
696<t>
697   In HTTP/1.0, most implementations used a new connection for each
698   request/response exchange. In HTTP/1.1, a connection may be used for
699   one or more request/response exchanges, although connections may be
700   closed for a variety of reasons (see <xref target="persistent.connections"/>).
701</t>
702</section>
703
704<section title="Use of HTTP for proxy communication" anchor="http.proxy">
705<t>
706   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
707</t>
708</section>
709<section title="Interception of HTTP for access control" anchor="http.intercept">
710<t>
711   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
712</t>
713</section>
714<section title="Use of HTTP by other protocols" anchor="http.others">
715<t>
716   <cref>TBD: Profiles of HTTP defined by other protocol.
717   Extensions of HTTP like WebDAV.</cref>
718</t>
719</section>
720<section title="Use of HTTP by media type specification" anchor="http.media">
721<t>
722   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
723</t>
724</section>
725</section>
726
727<section title="Protocol Parameters" anchor="protocol.parameters">
728
729<section title="HTTP Version" anchor="http.version">
730 
731 
732<t>
733   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
734   of the protocol. The protocol versioning policy is intended to allow
735   the sender to indicate the format of a message and its capacity for
736   understanding further HTTP communication, rather than the features
737   obtained via that communication. No change is made to the version
738   number for the addition of message components which do not affect
739   communication behavior or which only add to extensible field values.
740   The &lt;minor&gt; number is incremented when the changes made to the
741   protocol add features which do not change the general message parsing
742   algorithm, but which may add to the message semantics and imply
743   additional capabilities of the sender. The &lt;major&gt; number is
744   incremented when the format of a message within the protocol is
745   changed. See <xref target="RFC2145"/> for a fuller explanation.
746</t>
747<t>
748   The version of an HTTP message is indicated by an HTTP-Version field
749   in the first line of the message. HTTP-Version is case-sensitive.
750</t>
751<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
752  HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
753  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
754]]></artwork></figure>
755<t>
756   Note that the major and minor numbers MUST be treated as separate
757   integers and that each MAY be incremented higher than a single digit.
758   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
759   lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
760   MUST NOT be sent.
761</t>
762<t>
763   An application that sends a request or response message that includes
764   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
765   with this specification. Applications that are at least conditionally
766   compliant with this specification SHOULD use an HTTP-Version of
767   "HTTP/1.1" in their messages, and MUST do so for any message that is
768   not compatible with HTTP/1.0. For more details on when to send
769   specific HTTP-Version values, see <xref target="RFC2145"/>.
770</t>
771<t>
772   The HTTP version of an application is the highest HTTP version for
773   which the application is at least conditionally compliant.
774</t>
775<t>
776   Proxy and gateway applications need to be careful when forwarding
777   messages in protocol versions different from that of the application.
778   Since the protocol version indicates the protocol capability of the
779   sender, a proxy/gateway MUST NOT send a message with a version
780   indicator which is greater than its actual version. If a higher
781   version request is received, the proxy/gateway MUST either downgrade
782   the request version, or respond with an error, or switch to tunnel
783   behavior.
784</t>
785<t>
786   Due to interoperability problems with HTTP/1.0 proxies discovered
787   since the publication of <xref target="RFC2068"/>, caching proxies MUST, gateways
788   MAY, and tunnels MUST NOT upgrade the request to the highest version
789   they support. The proxy/gateway's response to that request MUST be in
790   the same major version as the request.
791</t>
792<t>
793  <list>
794    <t>
795      Note: Converting between versions of HTTP may involve modification
796      of header fields required or forbidden by the versions involved.
797    </t>
798  </list>
799</t>
800</section>
801
802<section title="Date/Time Formats" anchor="date.time.formats">
803<section title="Full Date" anchor="full.date">
804 
805 
806 
807 
808 
809 
810 
811 
812 
813 
814 
815 
816 
817<t>
818   HTTP applications have historically allowed three different formats
819   for the representation of date/time stamps:
820</t>
821<figure><artwork type="example"><![CDATA[
822  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
823  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
824  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
825]]></artwork></figure>
826<t>
827   The first format is preferred as an Internet standard and represents
828   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
829   other formats are described here only for
830   compatibility with obsolete implementations.
831   HTTP/1.1 clients and servers that parse the date value MUST accept
832   all three formats (for compatibility with HTTP/1.0), though they MUST
833   only generate the RFC 1123 format for representing HTTP-date values
834   in header fields. See <xref target="tolerant.applications"/> for further information.
835</t>
836<t><list><t>
837      Note: Recipients of date values are encouraged to be robust in
838      accepting date values that may have been sent by non-HTTP
839      applications, as is sometimes the case when retrieving or posting
840      messages via proxies/gateways to SMTP or NNTP.
841</t></list></t>
842<t>
843   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
844   (GMT), without exception. For the purposes of HTTP, GMT is exactly
845   equal to UTC (Coordinated Universal Time). This is indicated in the
846   first two formats by the inclusion of "GMT" as the three-letter
847   abbreviation for time zone, and MUST be assumed when reading the
848   asctime format. HTTP-date is case sensitive and MUST NOT include
849   additional whitespace beyond that specifically included as SP in the
850   grammar.
851</t>
852<figure><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"/><artwork type="abnf2616"><![CDATA[
853  HTTP-date    = rfc1123-date / obsolete-date
854  obsolete-date = rfc850-date / asctime-date
855  rfc1123-date = wkday "," SP date1 SP time SP GMT
856  rfc850-date  = weekday "," SP date2 SP time SP GMT
857  asctime-date = wkday SP date3 SP time SP 4DIGIT
858  date1        = 2DIGIT SP month SP 4DIGIT
859                 ; day month year (e.g., 02 Jun 1982)
860  date2        = 2DIGIT "-" month "-" 2DIGIT
861                 ; day-month-year (e.g., 02-Jun-82)
862  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
863                 ; month day (e.g., Jun  2)
864  time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
865                 ; 00:00:00 - 23:59:59
866  wkday        = s-Mon / s-Tue / s-Wed
867               / s-Thu / s-Fri / s-Sat / s-Sun
868  weekday      = l-Mon / l-Tue / l-Wed
869               / l-Thu / l-Fri / l-Sat / l-Sun
870  month        = s-Jan / s-Feb / s-Mar / s-Apr
871               / s-May / s-Jun / s-Jul / s-Aug
872               / s-Sep / s-Oct / s-Nov / s-Dec
873               
874  GMT   = %x47.4D.54 ; "GMT", case-sensitive
875
876  s-Mon = %x4D.6F.6E ; "Mon", case-sensitive
877  s-Tue = %x54.75.65 ; "Tue", case-sensitive
878  s-Wed = %x57.65.64 ; "Wed", case-sensitive
879  s-Thu = %x54.68.75 ; "Thu", case-sensitive
880  s-Fri = %x46.72.69 ; "Fri", case-sensitive
881  s-Sat = %x53.61.74 ; "Sat", case-sensitive
882  s-Sun = %x53.75.6E ; "Sun", case-sensitive
883
884  l-Mon = %x4D.6F.6E.64.61.79          ; "Monday", case-sensitive
885  l-Tue = %x54.75.65.73.64.61.79       ; "Tuesday", case-sensitive
886  l-Wed = %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
887  l-Thu = %x54.68.75.72.73.64.61.79    ; "Thursday", case-sensitive
888  l-Fri = %x46.72.69.64.61.79          ; "Friday", case-sensitive
889  l-Sat = %x53.61.74.75.72.64.61.79    ; "Saturday", case-sensitive
890  l-Sun = %x53.75.6E.64.61.79          ; "Sunday", case-sensitive
891
892  s-Jan = %x4A.61.6E ; "Jan", case-sensitive
893  s-Feb = %x46.65.62 ; "Feb", case-sensitive
894  s-Mar = %x4D.61.72 ; "Mar", case-sensitive
895  s-Apr = %x41.70.72 ; "Apr", case-sensitive
896  s-May = %x4D.61.79 ; "May", case-sensitive
897  s-Jun = %x4A.75.6E ; "Jun", case-sensitive
898  s-Jul = %x4A.75.6C ; "Jul", case-sensitive
899  s-Aug = %x41.75.67 ; "Aug", case-sensitive
900  s-Sep = %x53.65.70 ; "Sep", case-sensitive
901  s-Oct = %x4F.63.74 ; "Oct", case-sensitive
902  s-Nov = %x4E.6F.76 ; "Nov", case-sensitive
903  s-Dec = %x44.65.63 ; "Dec", case-sensitive
904]]></artwork></figure>
905<t>
906      Note: HTTP requirements for the date/time stamp format apply only
907      to their usage within the protocol stream. Clients and servers are
908      not required to use these formats for user presentation, request
909      logging, etc.
910</t>
911</section>
912</section>
913
914<section title="Transfer Codings" anchor="transfer.codings">
915 
916 
917 
918<t>
919   Transfer-coding values are used to indicate an encoding
920   transformation that has been, can be, or may need to be applied to an
921   entity-body in order to ensure "safe transport" through the network.
922   This differs from a content coding in that the transfer-coding is a
923   property of the message, not of the original entity.
924</t>
925<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
926  transfer-coding         = "chunked" / transfer-extension
927  transfer-extension      = token *( OWS ";" OWS parameter )
928]]></artwork></figure>
929<t anchor="rule.parameter">
930 
931 
932 
933   Parameters are in  the form of attribute/value pairs.
934</t>
935<figure><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><artwork type="abnf2616"><![CDATA[
936  parameter               = attribute BWS "=" BWS value
937  attribute               = token
938  value                   = token / quoted-string
939]]></artwork></figure>
940<t>
941   All transfer-coding values are case-insensitive. HTTP/1.1 uses
942   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
943   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
944</t>
945<t>
946   Whenever a transfer-coding is applied to a message-body, the set of
947   transfer-codings MUST include "chunked", unless the message indicates it
948   is terminated by closing the connection. When the "chunked" transfer-coding
949   is used, it MUST be the last transfer-coding applied to the
950   message-body. The "chunked" transfer-coding MUST NOT be applied more
951   than once to a message-body. These rules allow the recipient to
952   determine the transfer-length of the message (<xref target="message.length"/>).
953</t>
954<t>
955   Transfer-codings are analogous to the Content-Transfer-Encoding
956   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
957   binary data over a 7-bit transport service. However, safe transport
958   has a different focus for an 8bit-clean transfer protocol. In HTTP,
959   the only unsafe characteristic of message-bodies is the difficulty in
960   determining the exact body length (<xref target="message.length"/>), or the desire to
961   encrypt data over a shared transport.
962</t>
963<t>
964   The Internet Assigned Numbers Authority (IANA) acts as a registry for
965   transfer-coding value tokens. Initially, the registry contains the
966   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
967   "gzip", "compress", and "deflate" (Section 2.2 of <xref target="Part3"/>).
968</t>
969<t>
970   New transfer-coding value tokens SHOULD be registered in the same way
971   as new content-coding value tokens (Section 2.2 of <xref target="Part3"/>).
972</t>
973<t>
974   A server which receives an entity-body with a transfer-coding it does
975   not understand SHOULD return 501 (Not Implemented), and close the
976   connection. A server MUST NOT send transfer-codings to an HTTP/1.0
977   client.
978</t>
979
980<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
981 
982 
983 
984 
985 
986 
987 
988 
989 
990<t>
991   The chunked encoding modifies the body of a message in order to
992   transfer it as a series of chunks, each with its own size indicator,
993   followed by an OPTIONAL trailer containing entity-header fields. This
994   allows dynamically produced content to be transferred along with the
995   information necessary for the recipient to verify that it has
996   received the full message.
997</t>
998<figure><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"/><artwork type="abnf2616"><![CDATA[
999  Chunked-Body   = *chunk
1000                   last-chunk
1001                   trailer-part
1002                   CRLF
1003 
1004  chunk          = chunk-size *WSP [ chunk-ext ] CRLF
1005                   chunk-data CRLF
1006  chunk-size     = 1*HEXDIG
1007  last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF
1008 
1009  chunk-ext      = *( ";" *WSP chunk-ext-name
1010                      [ "=" chunk-ext-val ] *WSP )
1011  chunk-ext-name = token
1012  chunk-ext-val  = token / quoted-string
1013  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
1014  trailer-part   = *( entity-header CRLF )
1015]]></artwork></figure>
1016<t>
1017   The chunk-size field is a string of hex digits indicating the size of
1018   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1019   zero, followed by the trailer, which is terminated by an empty line.
1020</t>
1021<t>
1022   The trailer allows the sender to include additional HTTP header
1023   fields at the end of the message. The Trailer header field can be
1024   used to indicate which header fields are included in a trailer (see
1025   <xref target="header.trailer"/>).
1026</t>
1027<t>
1028   A server using chunked transfer-coding in a response MUST NOT use the
1029   trailer for any header fields unless at least one of the following is
1030   true:
1031  <list style="numbers">
1032    <t>the request included a TE header field that indicates "trailers" is
1033     acceptable in the transfer-coding of the  response, as described in
1034     <xref target="header.te"/>; or,</t>
1035
1036    <t>the server is the origin server for the response, the trailer
1037     fields consist entirely of optional metadata, and the recipient
1038     could use the message (in a manner acceptable to the origin server)
1039     without receiving this metadata.  In other words, the origin server
1040     is willing to accept the possibility that the trailer fields might
1041     be silently discarded along the path to the client.</t>
1042  </list>
1043</t>
1044<t>
1045   This requirement prevents an interoperability failure when the
1046   message is being received by an HTTP/1.1 (or later) proxy and
1047   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1048   compliance with the protocol would have necessitated a possibly
1049   infinite buffer on the proxy.
1050</t>
1051<t>
1052   A process for decoding the "chunked" transfer-coding
1053   can be represented in pseudo-code as:
1054</t>
1055<figure><artwork type="code"><![CDATA[
1056  length := 0
1057  read chunk-size, chunk-ext (if any) and CRLF
1058  while (chunk-size > 0) {
1059     read chunk-data and CRLF
1060     append chunk-data to entity-body
1061     length := length + chunk-size
1062     read chunk-size and CRLF
1063  }
1064  read entity-header
1065  while (entity-header not empty) {
1066     append entity-header to existing header fields
1067     read entity-header
1068  }
1069  Content-Length := length
1070  Remove "chunked" from Transfer-Encoding
1071]]></artwork></figure>
1072<t>
1073   All HTTP/1.1 applications MUST be able to receive and decode the
1074   "chunked" transfer-coding, and MUST ignore chunk-ext extensions
1075   they do not understand.
1076</t>
1077</section>
1078</section>
1079
1080<section title="Product Tokens" anchor="product.tokens">
1081 
1082 
1083<t>
1084   Product tokens are used to allow communicating applications to
1085   identify themselves by software name and version. Most fields using
1086   product tokens also allow sub-products which form a significant part
1087   of the application to be listed, separated by whitespace. By
1088   convention, the products are listed in order of their significance
1089   for identifying the application.
1090</t>
1091<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
1092  product         = token ["/" product-version]
1093  product-version = token
1094]]></artwork></figure>
1095<t>
1096   Examples:
1097</t>
1098<figure><artwork type="example"><![CDATA[
1099  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1100  Server: Apache/0.8.4
1101]]></artwork></figure>
1102<t>
1103   Product tokens SHOULD be short and to the point. They MUST NOT be
1104   used for advertising or other non-essential information. Although any
1105   token character MAY appear in a product-version, this token SHOULD
1106   only be used for a version identifier (i.e., successive versions of
1107   the same product SHOULD only differ in the product-version portion of
1108   the product value).
1109</t>
1110</section>
1111
1112<section title="Quality Values" anchor="quality.values">
1113 
1114<t>
1115   Both transfer codings (TE request header, <xref target="header.te"/>)
1116   and content negotiation (Section 4 of <xref target="Part3"/>) use short "floating point"
1117   numbers to indicate the relative importance ("weight") of various
1118   negotiable parameters.  A weight is normalized to a real number in
1119   the range 0 through 1, where 0 is the minimum and 1 the maximum
1120   value. If a parameter has a quality value of 0, then content with
1121   this parameter is `not acceptable' for the client. HTTP/1.1
1122   applications MUST NOT generate more than three digits after the
1123   decimal point. User configuration of these values SHOULD also be
1124   limited in this fashion.
1125</t>
1126<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
1127  qvalue         = ( "0" [ "." 0*3DIGIT ] )
1128                 / ( "1" [ "." 0*3("0") ] )
1129]]></artwork></figure>
1130<t><list>
1131  <t>
1132     Note: "Quality values" is a misnomer, since these values merely represent
1133     relative degradation in desired quality.
1134  </t>
1135</list></t>
1136</section>
1137
1138</section>
1139
1140<section title="HTTP Message" anchor="http.message">
1141
1142<section title="Message Types" anchor="message.types">
1143 
1144 
1145 
1146<t>
1147   HTTP messages consist of requests from client to server and responses
1148   from server to client.
1149</t>
1150<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1151  HTTP-message   = Request / Response     ; HTTP/1.1 messages
1152]]></artwork></figure>
1153<t>
1154   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1155   message format of <xref target="RFC5322"/> for transferring entities (the payload
1156   of the message). Both types of message consist of a start-line, zero
1157   or more header fields (also known as "headers"), an empty line (i.e.,
1158   a line with nothing preceding the CRLF) indicating the end of the
1159   header fields, and possibly a message-body.
1160</t>
1161<figure><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/><artwork type="abnf2616"><![CDATA[
1162  generic-message = start-line
1163                    *( message-header CRLF )
1164                    CRLF
1165                    [ message-body ]
1166  start-line      = Request-Line / Status-Line
1167]]></artwork></figure>
1168<t>
1169   In the interest of robustness, servers SHOULD ignore any empty
1170   line(s) received where a Request-Line is expected. In other words, if
1171   the server is reading the protocol stream at the beginning of a
1172   message and receives a CRLF first, it should ignore the CRLF.
1173</t>
1174<t>
1175   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1176   after a POST request. To restate what is explicitly forbidden by the
1177   BNF, an HTTP/1.1 client MUST NOT preface or follow a request with an
1178   extra CRLF.
1179</t>
1180<t>
1181   Whitespace (WSP) MUST NOT be sent between the start-line and the first
1182   header field. The presence of whitespace might be an attempt to trick a
1183   noncompliant implementation of HTTP into ignoring that field or processing
1184   the next line as a new request, either of which may result in security
1185   issues when implementations within the request chain interpret the
1186   same message differently. HTTP/1.1 servers MUST reject such a message
1187   with a 400 (Bad Request) response.
1188</t>
1189</section>
1190
1191<section title="Message Headers" anchor="message.headers">
1192 
1193 
1194 
1195 
1196<t>
1197   HTTP header fields follow the same general format as Internet messages in
1198   Section 2.1 of <xref target="RFC5322"/>. Each header field consists
1199   of a name followed by a colon (":"), optional whitespace, and the field
1200   value. Field names are case-insensitive.
1201</t>
1202<figure><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"/><artwork type="abnf2616"><![CDATA[
1203  message-header = field-name ":" OWS [ field-value ] OWS
1204  field-name     = token
1205  field-value    = *( field-content / OWS )
1206  field-content  = *( WSP / VCHAR / obs-text )
1207]]></artwork></figure>
1208<t>
1209   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1210   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1211   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1212   header field-values use only a subset of the US-ASCII charset
1213   <xref target="USASCII"/>. Newly defined header fields SHOULD constrain
1214   their field-values to US-ASCII characters. Recipients SHOULD treat other
1215   (obs-text) octets in field-content as opaque data.
1216</t>
1217<t>
1218   No whitespace is allowed between the header field-name and colon. For
1219   security reasons, any request message received containing such whitespace
1220   MUST be rejected with a response code of 400 (Bad Request) and any such
1221   whitespace in a response message MUST be removed.
1222</t>
1223<t>
1224   The field value MAY be preceded by optional whitespace; a single SP is
1225   preferred. The field-value does not include any leading or trailing white
1226   space: OWS occurring before the first non-whitespace character of the
1227   field-value or after the last non-whitespace character of the field-value
1228   is ignored and MAY be removed without changing the meaning of the header
1229   field.
1230</t>
1231<t>
1232   Historically, HTTP header field values could be extended over multiple
1233   lines by preceding each extra line with at least one space or horizontal
1234   tab character (line folding). This specification deprecates such line
1235   folding except within the message/http media type
1236   (<xref target="internet.media.type.message.http"/>).
1237   HTTP/1.1 senders MUST NOT produce messages that include line folding
1238   (i.e., that contain any field-content that matches the obs-fold rule) unless
1239   the message is intended for packaging within the message/http media type.
1240   HTTP/1.1 recipients SHOULD accept line folding and replace any embedded
1241   obs-fold whitespace with a single SP prior to interpreting the field value
1242   or forwarding the message downstream.
1243</t>
1244<t anchor="rule.comment">
1245 
1246 
1247   Comments can be included in some HTTP header fields by surrounding
1248   the comment text with parentheses. Comments are only allowed in
1249   fields containing "comment" as part of their field value definition.
1250   In all other fields, parentheses are considered part of the field
1251   value.
1252</t>
1253<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1254  comment        = "(" *( ctext / quoted-pair / comment ) ")"
1255  ctext          = *( OWS / %x21-27 / %x2A-7E / obs-text )
1256]]></artwork></figure>
1257<t>
1258   The order in which header fields with differing field names are
1259   received is not significant. However, it is "good practice" to send
1260   general-header fields first, followed by request-header or response-header
1261   fields, and ending with the entity-header fields.
1262</t>
1263<t>
1264   Multiple message-header fields with the same field-name MAY be
1265   present in a message if and only if the entire field-value for that
1266   header field is defined as a comma-separated list [i.e., #(values)].
1267   It MUST be possible to combine the multiple header fields into one
1268   "field-name: field-value" pair, without changing the semantics of the
1269   message, by appending each subsequent field-value to the first, each
1270   separated by a comma. The order in which header fields with the same
1271   field-name are received is therefore significant to the
1272   interpretation of the combined field value, and thus a proxy MUST NOT
1273   change the order of these field values when a message is forwarded.
1274</t>
1275<t>
1276  <list><t>
1277   Note: the "Set-Cookie" header as implemented in
1278   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1279   can occur multiple times, but does not use the list syntax, and thus cannot
1280   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1281   for details.) Also note that the Set-Cookie2 header specified in
1282   <xref target="RFC2965"/> does not share this problem.
1283  </t></list>
1284</t>
1285 
1286</section>
1287
1288<section title="Message Body" anchor="message.body">
1289 
1290<t>
1291   The message-body (if any) of an HTTP message is used to carry the
1292   entity-body associated with the request or response. The message-body
1293   differs from the entity-body only when a transfer-coding has been
1294   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1295</t>
1296<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1297  message-body = entity-body
1298               / <entity-body encoded as per Transfer-Encoding>
1299]]></artwork></figure>
1300<t>
1301   Transfer-Encoding MUST be used to indicate any transfer-codings
1302   applied by an application to ensure safe and proper transfer of the
1303   message. Transfer-Encoding is a property of the message, not of the
1304   entity, and thus MAY be added or removed by any application along the
1305   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1306   when certain transfer-codings may be used.)
1307</t>
1308<t>
1309   The rules for when a message-body is allowed in a message differ for
1310   requests and responses.
1311</t>
1312<t>
1313   The presence of a message-body in a request is signaled by the
1314   inclusion of a Content-Length or Transfer-Encoding header field in
1315   the request's message-headers. A message-body MUST NOT be included in
1316   a request if the specification of the request method (Section 2 of <xref target="Part2"/>)
1317   explicitly disallows an entity-body in requests.
1318   When a request message contains both a message-body of non-zero
1319   length and a method that does not define any semantics for that
1320   request message-body, then an origin server SHOULD either ignore
1321   the message-body or respond with an appropriate error message
1322   (e.g., 413).  A proxy or gateway, when presented the same request,
1323   SHOULD either forward the request inbound with the message-body or
1324   ignore the message-body when determining a response.
1325</t>
1326<t>
1327   For response messages, whether or not a message-body is included with
1328   a message is dependent on both the request method and the response
1329   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1330   MUST NOT include a message-body, even though the presence of entity-header
1331   fields might lead one to believe they do. All 1xx
1332   (informational), 204 (No Content), and 304 (Not Modified) responses
1333   MUST NOT include a message-body. All other responses do include a
1334   message-body, although it MAY be of zero length.
1335</t>
1336</section>
1337
1338<section title="Message Length" anchor="message.length">
1339<t>
1340   The transfer-length of a message is the length of the message-body as
1341   it appears in the message; that is, after any transfer-codings have
1342   been applied. When a message-body is included with a message, the
1343   transfer-length of that body is determined by one of the following
1344   (in order of precedence):
1345</t>
1346<t>
1347  <list style="numbers">
1348    <t>
1349     Any response message which "MUST NOT" include a message-body (such
1350     as the 1xx, 204, and 304 responses and any response to a HEAD
1351     request) is always terminated by the first empty line after the
1352     header fields, regardless of the entity-header fields present in
1353     the message.
1354    </t>
1355    <t>
1356     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1357     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1358     is used, the transfer-length is defined by the use of this transfer-coding.
1359     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1360     is not present, the transfer-length is defined by the sender closing the connection.
1361    </t>
1362    <t>
1363     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1364     decimal value in OCTETs represents both the entity-length and the
1365     transfer-length. The Content-Length header field MUST NOT be sent
1366     if these two lengths are different (i.e., if a Transfer-Encoding
1367     header field is present). If a message is received with both a
1368     Transfer-Encoding header field and a Content-Length header field,
1369     the latter MUST be ignored.
1370    </t>
1371    <t>
1372     If the message uses the media type "multipart/byteranges", and the
1373     transfer-length is not otherwise specified, then this self-delimiting
1374     media type defines the transfer-length. This media type
1375     MUST NOT be used unless the sender knows that the recipient can parse
1376     it; the presence in a request of a Range header with multiple byte-range
1377     specifiers from a 1.1 client implies that the client can parse
1378     multipart/byteranges responses.
1379    <list style="empty"><t>
1380       A range header might be forwarded by a 1.0 proxy that does not
1381       understand multipart/byteranges; in this case the server MUST
1382       delimit the message using methods defined in items 1, 3 or 5 of
1383       this section.
1384    </t></list>
1385    </t>
1386    <t>
1387     By the server closing the connection. (Closing the connection
1388     cannot be used to indicate the end of a request body, since that
1389     would leave no possibility for the server to send back a response.)
1390    </t>
1391  </list>
1392</t>
1393<t>
1394   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1395   containing a message-body MUST include a valid Content-Length header
1396   field unless the server is known to be HTTP/1.1 compliant. If a
1397   request contains a message-body and a Content-Length is not given,
1398   the server SHOULD respond with 400 (Bad Request) if it cannot
1399   determine the length of the message, or with 411 (Length Required) if
1400   it wishes to insist on receiving a valid Content-Length.
1401</t>
1402<t>
1403   All HTTP/1.1 applications that receive entities MUST accept the
1404   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1405   to be used for messages when the message length cannot be determined
1406   in advance.
1407</t>
1408<t>
1409   Messages MUST NOT include both a Content-Length header field and a
1410   transfer-coding. If the message does include a
1411   transfer-coding, the Content-Length MUST be ignored.
1412</t>
1413<t>
1414   When a Content-Length is given in a message where a message-body is
1415   allowed, its field value MUST exactly match the number of OCTETs in
1416   the message-body. HTTP/1.1 user agents MUST notify the user when an
1417   invalid length is received and detected.
1418</t>
1419</section>
1420
1421<section title="General Header Fields" anchor="general.header.fields">
1422 
1423<t>
1424   There are a few header fields which have general applicability for
1425   both request and response messages, but which do not apply to the
1426   entity being transferred. These header fields apply only to the
1427   message being transmitted.
1428</t>
1429<figure><iref primary="true" item="Grammar" subitem="general-header"/><artwork type="abnf2616"><![CDATA[
1430  general-header = Cache-Control            ; [Part6], Section 3.2
1431                 / Connection               ; Section 8.1
1432                 / Date                     ; Section 8.3
1433                 / Pragma                   ; [Part6], Section 3.4
1434                 / Trailer                  ; Section 8.6
1435                 / Transfer-Encoding        ; Section 8.7
1436                 / Upgrade                  ; Section 8.8
1437                 / Via                      ; Section 8.9
1438                 / Warning                  ; [Part6], Section 3.6
1439]]></artwork></figure>
1440<t>
1441   General-header field names can be extended reliably only in
1442   combination with a change in the protocol version. However, new or
1443   experimental header fields may be given the semantics of general
1444   header fields if all parties in the communication recognize them to
1445   be general-header fields. Unrecognized header fields are treated as
1446   entity-header fields.
1447</t>
1448</section>
1449</section>
1450
1451<section title="Request" anchor="request">
1452 
1453<t>
1454   A request message from a client to a server includes, within the
1455   first line of that message, the method to be applied to the resource,
1456   the identifier of the resource, and the protocol version in use.
1457</t>
1458<!--                 Host                      ; should be moved here eventually -->
1459<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1460  Request       = Request-Line              ; Section 5.1
1461                  *(( general-header        ; Section 4.5
1462                   / request-header         ; [Part2], Section 3
1463                   / entity-header ) CRLF )  ; [Part3], Section 3.1
1464                  CRLF
1465                  [ message-body ]          ; Section 4.3
1466]]></artwork></figure>
1467
1468<section title="Request-Line" anchor="request-line">
1469 
1470<t>
1471   The Request-Line begins with a method token, followed by the
1472   request-target and the protocol version, and ending with CRLF. The
1473   elements are separated by SP characters. No CR or LF is allowed
1474   except in the final CRLF sequence.
1475</t>
1476<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1477  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1478]]></artwork></figure>
1479
1480<section title="Method" anchor="method">
1481 
1482<t>
1483   The Method  token indicates the method to be performed on the
1484   resource identified by the request-target. The method is case-sensitive.
1485</t>
1486<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
1487  Method         = token
1488]]></artwork></figure>
1489</section>
1490
1491<section title="request-target" anchor="request-target">
1492 
1493<t>
1494   The request-target
1495   identifies the resource upon which to apply the request.
1496</t>
1497<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1498  request-target = "*"
1499                 / absolute-URI
1500                 / ( path-absolute [ "?" query ] )
1501                 / authority
1502]]></artwork></figure>
1503<t>
1504   The four options for request-target are dependent on the nature of the
1505   request. The asterisk "*" means that the request does not apply to a
1506   particular resource, but to the server itself, and is only allowed
1507   when the method used does not necessarily apply to a resource. One
1508   example would be
1509</t>
1510<figure><artwork type="example"><![CDATA[
1511  OPTIONS * HTTP/1.1
1512]]></artwork></figure>
1513<t>
1514   The absolute-URI form is REQUIRED when the request is being made to a
1515   proxy. The proxy is requested to forward the request or service it
1516   from a valid cache, and return the response. Note that the proxy MAY
1517   forward the request on to another proxy or directly to the server
1518   specified by the absolute-URI. In order to avoid request loops, a
1519   proxy MUST be able to recognize all of its server names, including
1520   any aliases, local variations, and the numeric IP address. An example
1521   Request-Line would be:
1522</t>
1523<figure><artwork type="example"><![CDATA[
1524  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1525]]></artwork></figure>
1526<t>
1527   To allow for transition to absolute-URIs in all requests in future
1528   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1529   form in requests, even though HTTP/1.1 clients will only generate
1530   them in requests to proxies.
1531</t>
1532<t>
1533   The authority form is only used by the CONNECT method (Section 7.9 of <xref target="Part2"/>).
1534</t>
1535<t>
1536   The most common form of request-target is that used to identify a
1537   resource on an origin server or gateway. In this case the absolute
1538   path of the URI MUST be transmitted (see <xref target="http.uri"/>, path-absolute) as
1539   the request-target, and the network location of the URI (authority) MUST
1540   be transmitted in a Host header field. For example, a client wishing
1541   to retrieve the resource above directly from the origin server would
1542   create a TCP connection to port 80 of the host "www.example.org" and send
1543   the lines:
1544</t>
1545<figure><artwork type="example"><![CDATA[
1546  GET /pub/WWW/TheProject.html HTTP/1.1
1547  Host: www.example.org
1548]]></artwork></figure>
1549<t>
1550   followed by the remainder of the Request. Note that the absolute path
1551   cannot be empty; if none is present in the original URI, it MUST be
1552   given as "/" (the server root).
1553</t>
1554<t>
1555   If a proxy receives a request without any path in the request-target and
1556   the method specified is capable of supporting the asterisk form of
1557   request-target, then the last proxy on the request chain MUST forward the
1558   request with "*" as the final request-target.
1559</t>
1560<figure><preamble>   
1561   For example, the request
1562</preamble><artwork type="example"><![CDATA[
1563  OPTIONS http://www.example.org:8001 HTTP/1.1
1564]]></artwork></figure>
1565<figure><preamble>   
1566  would be forwarded by the proxy as
1567</preamble><artwork type="example"><![CDATA[
1568  OPTIONS * HTTP/1.1
1569  Host: www.example.org:8001
1570]]></artwork>
1571<postamble>
1572   after connecting to port 8001 of host "www.example.org".
1573</postamble>
1574</figure>
1575<t>
1576   The request-target is transmitted in the format specified in
1577   <xref target="http.uri"/>. If the request-target is percent-encoded
1578   (<xref target="RFC3986"/>, Section 2.1), the origin server
1579   MUST decode the request-target in order to
1580   properly interpret the request. Servers SHOULD respond to invalid
1581   request-targets with an appropriate status code.
1582</t>
1583<t>
1584   A transparent proxy MUST NOT rewrite the "path-absolute" part of the
1585   received request-target when forwarding it to the next inbound server,
1586   except as noted above to replace a null path-absolute with "/".
1587</t>
1588<t>
1589  <list><t>
1590      Note: The "no rewrite" rule prevents the proxy from changing the
1591      meaning of the request when the origin server is improperly using
1592      a non-reserved URI character for a reserved purpose.  Implementors
1593      should be aware that some pre-HTTP/1.1 proxies have been known to
1594      rewrite the request-target.
1595  </t></list>
1596</t>
1597<t>
1598   HTTP does not place a pre-defined limit on the length of a request-target.
1599   A server MUST be prepared to receive URIs of unbounded length and
1600   respond with the 414 (URI Too Long) status if the received
1601   request-target would be longer than the server wishes to handle
1602   (see Section 8.4.15 of <xref target="Part2"/>).
1603</t>
1604<t>
1605   Various ad-hoc limitations on request-target length are found in practice.
1606   It is RECOMMENDED that all HTTP senders and recipients support
1607   request-target lengths of 8000 or more OCTETs.
1608</t>
1609</section>
1610</section>
1611
1612<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1613<t>
1614   The exact resource identified by an Internet request is determined by
1615   examining both the request-target and the Host header field.
1616</t>
1617<t>
1618   An origin server that does not allow resources to differ by the
1619   requested host MAY ignore the Host header field value when
1620   determining the resource identified by an HTTP/1.1 request. (But see
1621   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1622   for other requirements on Host support in HTTP/1.1.)
1623</t>
1624<t>
1625   An origin server that does differentiate resources based on the host
1626   requested (sometimes referred to as virtual hosts or vanity host
1627   names) MUST use the following rules for determining the requested
1628   resource on an HTTP/1.1 request:
1629  <list style="numbers">
1630    <t>If request-target is an absolute-URI, the host is part of the
1631     request-target. Any Host header field value in the request MUST be
1632     ignored.</t>
1633    <t>If the request-target is not an absolute-URI, and the request includes
1634     a Host header field, the host is determined by the Host header
1635     field value.</t>
1636    <t>If the host as determined by rule 1 or 2 is not a valid host on
1637     the server, the response MUST be a 400 (Bad Request) error message.</t>
1638  </list>
1639</t>
1640<t>
1641   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1642   attempt to use heuristics (e.g., examination of the URI path for
1643   something unique to a particular host) in order to determine what
1644   exact resource is being requested.
1645</t>
1646</section>
1647
1648</section>
1649
1650
1651<section title="Response" anchor="response">
1652 
1653<t>
1654   After receiving and interpreting a request message, a server responds
1655   with an HTTP response message.
1656</t>
1657<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1658  Response      = Status-Line               ; Section 6.1
1659                  *(( general-header        ; Section 4.5
1660                   / response-header        ; [Part2], Section 5
1661                   / entity-header ) CRLF )  ; [Part3], Section 3.1
1662                  CRLF
1663                  [ message-body ]          ; Section 4.3
1664]]></artwork></figure>
1665
1666<section title="Status-Line" anchor="status-line">
1667 
1668<t>
1669   The first line of a Response message is the Status-Line, consisting
1670   of the protocol version followed by a numeric status code and its
1671   associated textual phrase, with each element separated by SP
1672   characters. No CR or LF is allowed except in the final CRLF sequence.
1673</t>
1674<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1675  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1676]]></artwork></figure>
1677
1678<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1679 
1680 
1681<t>
1682   The Status-Code element is a 3-digit integer result code of the
1683   attempt to understand and satisfy the request. These codes are fully
1684   defined in Section 8 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1685   purpose of providing a textual description associated with the numeric
1686   status code, out of deference to earlier Internet application protocols
1687   that were more frequently used with interactive text clients.
1688   A client SHOULD ignore the content of the Reason Phrase.
1689</t>
1690<t>
1691   The first digit of the Status-Code defines the class of response. The
1692   last two digits do not have any categorization role. There are 5
1693   values for the first digit:
1694  <list style="symbols">
1695    <t>
1696      1xx: Informational - Request received, continuing process
1697    </t>
1698    <t>
1699      2xx: Success - The action was successfully received,
1700        understood, and accepted
1701    </t>
1702    <t>
1703      3xx: Redirection - Further action must be taken in order to
1704        complete the request
1705    </t>
1706    <t>
1707      4xx: Client Error - The request contains bad syntax or cannot
1708        be fulfilled
1709    </t>
1710    <t>
1711      5xx: Server Error - The server failed to fulfill an apparently
1712        valid request
1713    </t>
1714  </list>
1715</t>
1716<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1717  Status-Code    = 3DIGIT
1718  Reason-Phrase  = *( WSP / VCHAR / obs-text )
1719]]></artwork></figure>
1720</section>
1721</section>
1722
1723</section>
1724
1725
1726<section title="Connections" anchor="connections">
1727
1728<section title="Persistent Connections" anchor="persistent.connections">
1729
1730<section title="Purpose" anchor="persistent.purpose">
1731<t>
1732   Prior to persistent connections, a separate TCP connection was
1733   established to fetch each URL, increasing the load on HTTP servers
1734   and causing congestion on the Internet. The use of inline images and
1735   other associated data often require a client to make multiple
1736   requests of the same server in a short amount of time. Analysis of
1737   these performance problems and results from a prototype
1738   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1739   measurements of actual HTTP/1.1 (RFC 2068) implementations show good
1740   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1741   T/TCP <xref target="Tou1998"/>.
1742</t>
1743<t>
1744   Persistent HTTP connections have a number of advantages:
1745  <list style="symbols">
1746      <t>
1747        By opening and closing fewer TCP connections, CPU time is saved
1748        in routers and hosts (clients, servers, proxies, gateways,
1749        tunnels, or caches), and memory used for TCP protocol control
1750        blocks can be saved in hosts.
1751      </t>
1752      <t>
1753        HTTP requests and responses can be pipelined on a connection.
1754        Pipelining allows a client to make multiple requests without
1755        waiting for each response, allowing a single TCP connection to
1756        be used much more efficiently, with much lower elapsed time.
1757      </t>
1758      <t>
1759        Network congestion is reduced by reducing the number of packets
1760        caused by TCP opens, and by allowing TCP sufficient time to
1761        determine the congestion state of the network.
1762      </t>
1763      <t>
1764        Latency on subsequent requests is reduced since there is no time
1765        spent in TCP's connection opening handshake.
1766      </t>
1767      <t>
1768        HTTP can evolve more gracefully, since errors can be reported
1769        without the penalty of closing the TCP connection. Clients using
1770        future versions of HTTP might optimistically try a new feature,
1771        but if communicating with an older server, retry with old
1772        semantics after an error is reported.
1773      </t>
1774    </list>
1775</t>
1776<t>
1777   HTTP implementations SHOULD implement persistent connections.
1778</t>
1779</section>
1780
1781<section title="Overall Operation" anchor="persistent.overall">
1782<t>
1783   A significant difference between HTTP/1.1 and earlier versions of
1784   HTTP is that persistent connections are the default behavior of any
1785   HTTP connection. That is, unless otherwise indicated, the client
1786   SHOULD assume that the server will maintain a persistent connection,
1787   even after error responses from the server.
1788</t>
1789<t>
1790   Persistent connections provide a mechanism by which a client and a
1791   server can signal the close of a TCP connection. This signaling takes
1792   place using the Connection header field (<xref target="header.connection"/>). Once a close
1793   has been signaled, the client MUST NOT send any more requests on that
1794   connection.
1795</t>
1796
1797<section title="Negotiation" anchor="persistent.negotiation">
1798<t>
1799   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
1800   maintain a persistent connection unless a Connection header including
1801   the connection-token "close" was sent in the request. If the server
1802   chooses to close the connection immediately after sending the
1803   response, it SHOULD send a Connection header including the
1804   connection-token close.
1805</t>
1806<t>
1807   An HTTP/1.1 client MAY expect a connection to remain open, but would
1808   decide to keep it open based on whether the response from a server
1809   contains a Connection header with the connection-token close. In case
1810   the client does not want to maintain a connection for more than that
1811   request, it SHOULD send a Connection header including the
1812   connection-token close.
1813</t>
1814<t>
1815   If either the client or the server sends the close token in the
1816   Connection header, that request becomes the last one for the
1817   connection.
1818</t>
1819<t>
1820   Clients and servers SHOULD NOT  assume that a persistent connection is
1821   maintained for HTTP versions less than 1.1 unless it is explicitly
1822   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1823   compatibility with HTTP/1.0 clients.
1824</t>
1825<t>
1826   In order to remain persistent, all messages on the connection MUST
1827   have a self-defined message length (i.e., one not defined by closure
1828   of the connection), as described in <xref target="message.length"/>.
1829</t>
1830</section>
1831
1832<section title="Pipelining" anchor="pipelining">
1833<t>
1834   A client that supports persistent connections MAY "pipeline" its
1835   requests (i.e., send multiple requests without waiting for each
1836   response). A server MUST send its responses to those requests in the
1837   same order that the requests were received.
1838</t>
1839<t>
1840   Clients which assume persistent connections and pipeline immediately
1841   after connection establishment SHOULD be prepared to retry their
1842   connection if the first pipelined attempt fails. If a client does
1843   such a retry, it MUST NOT pipeline before it knows the connection is
1844   persistent. Clients MUST also be prepared to resend their requests if
1845   the server closes the connection before sending all of the
1846   corresponding responses.
1847</t>
1848<t>
1849   Clients SHOULD NOT  pipeline requests using non-idempotent methods or
1850   non-idempotent sequences of methods (see Section 7.1.2 of <xref target="Part2"/>). Otherwise, a
1851   premature termination of the transport connection could lead to
1852   indeterminate results. A client wishing to send a non-idempotent
1853   request SHOULD wait to send that request until it has received the
1854   response status for the previous request.
1855</t>
1856</section>
1857</section>
1858
1859<section title="Proxy Servers" anchor="persistent.proxy">
1860<t>
1861   It is especially important that proxies correctly implement the
1862   properties of the Connection header field as specified in <xref target="header.connection"/>.
1863</t>
1864<t>
1865   The proxy server MUST signal persistent connections separately with
1866   its clients and the origin servers (or other proxy servers) that it
1867   connects to. Each persistent connection applies to only one transport
1868   link.
1869</t>
1870<t>
1871   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
1872   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1873   discussion of the problems with the Keep-Alive header implemented by
1874   many HTTP/1.0 clients).
1875</t>
1876</section>
1877
1878<section title="Practical Considerations" anchor="persistent.practical">
1879<t>
1880   Servers will usually have some time-out value beyond which they will
1881   no longer maintain an inactive connection. Proxy servers might make
1882   this a higher value since it is likely that the client will be making
1883   more connections through the same server. The use of persistent
1884   connections places no requirements on the length (or existence) of
1885   this time-out for either the client or the server.
1886</t>
1887<t>
1888   When a client or server wishes to time-out it SHOULD issue a graceful
1889   close on the transport connection. Clients and servers SHOULD both
1890   constantly watch for the other side of the transport close, and
1891   respond to it as appropriate. If a client or server does not detect
1892   the other side's close promptly it could cause unnecessary resource
1893   drain on the network.
1894</t>
1895<t>
1896   A client, server, or proxy MAY close the transport connection at any
1897   time. For example, a client might have started to send a new request
1898   at the same time that the server has decided to close the "idle"
1899   connection. From the server's point of view, the connection is being
1900   closed while it was idle, but from the client's point of view, a
1901   request is in progress.
1902</t>
1903<t>
1904   This means that clients, servers, and proxies MUST be able to recover
1905   from asynchronous close events. Client software SHOULD reopen the
1906   transport connection and retransmit the aborted sequence of requests
1907   without user interaction so long as the request sequence is
1908   idempotent (see Section 7.1.2 of <xref target="Part2"/>). Non-idempotent methods or sequences
1909   MUST NOT be automatically retried, although user agents MAY offer a
1910   human operator the choice of retrying the request(s). Confirmation by
1911   user-agent software with semantic understanding of the application
1912   MAY substitute for user confirmation. The automatic retry SHOULD NOT
1913   be repeated if the second sequence of requests fails.
1914</t>
1915<t>
1916   Servers SHOULD always respond to at least one request per connection,
1917   if at all possible. Servers SHOULD NOT  close a connection in the
1918   middle of transmitting a response, unless a network or client failure
1919   is suspected.
1920</t>
1921<t>
1922   Clients that use persistent connections SHOULD limit the number of
1923   simultaneous connections that they maintain to a given server. A
1924   single-user client SHOULD NOT maintain more than 2 connections with
1925   any server or proxy. A proxy SHOULD use up to 2*N connections to
1926   another server or proxy, where N is the number of simultaneously
1927   active users. These guidelines are intended to improve HTTP response
1928   times and avoid congestion.
1929</t>
1930</section>
1931</section>
1932
1933<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1934
1935<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1936<t>
1937   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
1938   flow control mechanisms to resolve temporary overloads, rather than
1939   terminating connections with the expectation that clients will retry.
1940   The latter technique can exacerbate network congestion.
1941</t>
1942</section>
1943
1944<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1945<t>
1946   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
1947   the network connection for an error status while it is transmitting
1948   the request. If the client sees an error status, it SHOULD
1949   immediately cease transmitting the body. If the body is being sent
1950   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1951   empty trailer MAY be used to prematurely mark the end of the message.
1952   If the body was preceded by a Content-Length header, the client MUST
1953   close the connection.
1954</t>
1955</section>
1956
1957<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1958<t>
1959   The purpose of the 100 (Continue) status (see Section 8.1.1 of <xref target="Part2"/>) is to
1960   allow a client that is sending a request message with a request body
1961   to determine if the origin server is willing to accept the request
1962   (based on the request headers) before the client sends the request
1963   body. In some cases, it might either be inappropriate or highly
1964   inefficient for the client to send the body if the server will reject
1965   the message without looking at the body.
1966</t>
1967<t>
1968   Requirements for HTTP/1.1 clients:
1969  <list style="symbols">
1970    <t>
1971        If a client will wait for a 100 (Continue) response before
1972        sending the request body, it MUST send an Expect request-header
1973        field (Section 9.2 of <xref target="Part2"/>) with the "100-continue" expectation.
1974    </t>
1975    <t>
1976        A client MUST NOT send an Expect request-header field (Section 9.2 of <xref target="Part2"/>)
1977        with the "100-continue" expectation if it does not intend
1978        to send a request body.
1979    </t>
1980  </list>
1981</t>
1982<t>
1983   Because of the presence of older implementations, the protocol allows
1984   ambiguous situations in which a client may send "Expect: 100-continue"
1985   without receiving either a 417 (Expectation Failed) status
1986   or a 100 (Continue) status. Therefore, when a client sends this
1987   header field to an origin server (possibly via a proxy) from which it
1988   has never seen a 100 (Continue) status, the client SHOULD NOT  wait
1989   for an indefinite period before sending the request body.
1990</t>
1991<t>
1992   Requirements for HTTP/1.1 origin servers:
1993  <list style="symbols">
1994    <t> Upon receiving a request which includes an Expect request-header
1995        field with the "100-continue" expectation, an origin server MUST
1996        either respond with 100 (Continue) status and continue to read
1997        from the input stream, or respond with a final status code. The
1998        origin server MUST NOT wait for the request body before sending
1999        the 100 (Continue) response. If it responds with a final status
2000        code, it MAY close the transport connection or it MAY continue
2001        to read and discard the rest of the request.  It MUST NOT
2002        perform the requested method if it returns a final status code.
2003    </t>
2004    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2005        the request message does not include an Expect request-header
2006        field with the "100-continue" expectation, and MUST NOT send a
2007        100 (Continue) response if such a request comes from an HTTP/1.0
2008        (or earlier) client. There is an exception to this rule: for
2009        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2010        status in response to an HTTP/1.1 PUT or POST request that does
2011        not include an Expect request-header field with the "100-continue"
2012        expectation. This exception, the purpose of which is
2013        to minimize any client processing delays associated with an
2014        undeclared wait for 100 (Continue) status, applies only to
2015        HTTP/1.1 requests, and not to requests with any other HTTP-version
2016        value.
2017    </t>
2018    <t> An origin server MAY omit a 100 (Continue) response if it has
2019        already received some or all of the request body for the
2020        corresponding request.
2021    </t>
2022    <t> An origin server that sends a 100 (Continue) response MUST
2023    ultimately send a final status code, once the request body is
2024        received and processed, unless it terminates the transport
2025        connection prematurely.
2026    </t>
2027    <t> If an origin server receives a request that does not include an
2028        Expect request-header field with the "100-continue" expectation,
2029        the request includes a request body, and the server responds
2030        with a final status code before reading the entire request body
2031        from the transport connection, then the server SHOULD NOT  close
2032        the transport connection until it has read the entire request,
2033        or until the client closes the connection. Otherwise, the client
2034        might not reliably receive the response message. However, this
2035        requirement is not be construed as preventing a server from
2036        defending itself against denial-of-service attacks, or from
2037        badly broken client implementations.
2038      </t>
2039    </list>
2040</t>
2041<t>
2042   Requirements for HTTP/1.1 proxies:
2043  <list style="symbols">
2044    <t> If a proxy receives a request that includes an Expect request-header
2045        field with the "100-continue" expectation, and the proxy
2046        either knows that the next-hop server complies with HTTP/1.1 or
2047        higher, or does not know the HTTP version of the next-hop
2048        server, it MUST forward the request, including the Expect header
2049        field.
2050    </t>
2051    <t> If the proxy knows that the version of the next-hop server is
2052        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2053        respond with a 417 (Expectation Failed) status.
2054    </t>
2055    <t> Proxies SHOULD maintain a cache recording the HTTP version
2056        numbers received from recently-referenced next-hop servers.
2057    </t>
2058    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2059        request message was received from an HTTP/1.0 (or earlier)
2060        client and did not include an Expect request-header field with
2061        the "100-continue" expectation. This requirement overrides the
2062        general rule for forwarding of 1xx responses (see Section 8.1 of <xref target="Part2"/>).
2063    </t>
2064  </list>
2065</t>
2066</section>
2067
2068<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2069<t>
2070   If an HTTP/1.1 client sends a request which includes a request body,
2071   but which does not include an Expect request-header field with the
2072   "100-continue" expectation, and if the client is not directly
2073   connected to an HTTP/1.1 origin server, and if the client sees the
2074   connection close before receiving any status from the server, the
2075   client SHOULD retry the request.  If the client does retry this
2076   request, it MAY use the following "binary exponential backoff"
2077   algorithm to be assured of obtaining a reliable response:
2078  <list style="numbers">
2079    <t>
2080      Initiate a new connection to the server
2081    </t>
2082    <t>
2083      Transmit the request-headers
2084    </t>
2085    <t>
2086      Initialize a variable R to the estimated round-trip time to the
2087         server (e.g., based on the time it took to establish the
2088         connection), or to a constant value of 5 seconds if the round-trip
2089         time is not available.
2090    </t>
2091    <t>
2092       Compute T = R * (2**N), where N is the number of previous
2093         retries of this request.
2094    </t>
2095    <t>
2096       Wait either for an error response from the server, or for T
2097         seconds (whichever comes first)
2098    </t>
2099    <t>
2100       If no error response is received, after T seconds transmit the
2101         body of the request.
2102    </t>
2103    <t>
2104       If client sees that the connection is closed prematurely,
2105         repeat from step 1 until the request is accepted, an error
2106         response is received, or the user becomes impatient and
2107         terminates the retry process.
2108    </t>
2109  </list>
2110</t>
2111<t>
2112   If at any point an error status is received, the client
2113  <list style="symbols">
2114      <t>SHOULD NOT  continue and</t>
2115
2116      <t>SHOULD close the connection if it has not completed sending the
2117        request message.</t>
2118    </list>
2119</t>
2120</section>
2121</section>
2122</section>
2123
2124
2125<section title="Header Field Definitions" anchor="header.fields">
2126<t>
2127   This section defines the syntax and semantics of HTTP/1.1 header fields
2128   related to message framing and transport protocols.
2129</t>
2130<t>
2131   For entity-header fields, both sender and recipient refer to either the
2132   client or the server, depending on who sends and who receives the entity.
2133</t>
2134
2135<section title="Connection" anchor="header.connection">
2136  <iref primary="true" item="Connection header"/>
2137  <iref primary="true" item="Headers" subitem="Connection"/>
2138 
2139 
2140 
2141<t>
2142   The general-header field "Connection" allows the sender to specify
2143   options that are desired for that particular connection and MUST NOT
2144   be communicated by proxies over further connections.
2145</t>
2146<t>
2147   The Connection header's value has the following grammar:
2148</t>
2149<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
2150  Connection       = "Connection" ":" OWS Connection-v
2151  Connection-v     = 1#connection-token
2152  connection-token = token
2153]]></artwork></figure>
2154<t>
2155   HTTP/1.1 proxies MUST parse the Connection header field before a
2156   message is forwarded and, for each connection-token in this field,
2157   remove any header field(s) from the message with the same name as the
2158   connection-token. Connection options are signaled by the presence of
2159   a connection-token in the Connection header field, not by any
2160   corresponding additional header field(s), since the additional header
2161   field may not be sent if there are no parameters associated with that
2162   connection option.
2163</t>
2164<t>
2165   Message headers listed in the Connection header MUST NOT include
2166   end-to-end headers, such as Cache-Control.
2167</t>
2168<t>
2169   HTTP/1.1 defines the "close" connection option for the sender to
2170   signal that the connection will be closed after completion of the
2171   response. For example,
2172</t>
2173<figure><artwork type="example"><![CDATA[
2174  Connection: close
2175]]></artwork></figure>
2176<t>
2177   in either the request or the response header fields indicates that
2178   the connection SHOULD NOT  be considered `persistent' (<xref target="persistent.connections"/>)
2179   after the current request/response is complete.
2180</t>
2181<t>
2182   An HTTP/1.1 client that does not support persistent connections MUST
2183   include the "close" connection option in every request message.
2184</t>
2185<t>
2186   An HTTP/1.1 server that does not support persistent connections MUST
2187   include the "close" connection option in every response message that
2188   does not have a 1xx (informational) status code.
2189</t>
2190<t>
2191   A system receiving an HTTP/1.0 (or lower-version) message that
2192   includes a Connection header MUST, for each connection-token in this
2193   field, remove and ignore any header field(s) from the message with
2194   the same name as the connection-token. This protects against mistaken
2195   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2196</t>
2197</section>
2198
2199<section title="Content-Length" anchor="header.content-length">
2200  <iref primary="true" item="Content-Length header"/>
2201  <iref primary="true" item="Headers" subitem="Content-Length"/>
2202 
2203 
2204<t>
2205   The entity-header field "Content-Length" indicates the size of the
2206   entity-body, in decimal number of OCTETs, sent to the recipient or,
2207   in the case of the HEAD method, the size of the entity-body that
2208   would have been sent had the request been a GET.
2209</t>
2210<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/><artwork type="abnf2616"><![CDATA[
2211  Content-Length   = "Content-Length" ":" OWS 1*Content-Length-v
2212  Content-Length-v = 1*DIGIT
2213]]></artwork></figure>
2214<t>
2215   An example is
2216</t>
2217<figure><artwork type="example"><![CDATA[
2218  Content-Length: 3495
2219]]></artwork></figure>
2220<t>
2221   Applications SHOULD use this field to indicate the transfer-length of
2222   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2223</t>
2224<t>
2225   Any Content-Length greater than or equal to zero is a valid value.
2226   <xref target="message.length"/> describes how to determine the length of a message-body
2227   if a Content-Length is not given.
2228</t>
2229<t>
2230   Note that the meaning of this field is significantly different from
2231   the corresponding definition in MIME, where it is an optional field
2232   used within the "message/external-body" content-type. In HTTP, it
2233   SHOULD be sent whenever the message's length can be determined prior
2234   to being transferred, unless this is prohibited by the rules in
2235   <xref target="message.length"/>.
2236</t>
2237</section>
2238
2239<section title="Date" anchor="header.date">
2240  <iref primary="true" item="Date header"/>
2241  <iref primary="true" item="Headers" subitem="Date"/>
2242 
2243 
2244<t>
2245   The general-header field "Date" represents the date and time at which
2246   the message was originated, having the same semantics as orig-date in
2247   Section 3.6.1 of <xref target="RFC5322"/>. The field value is an
2248   HTTP-date, as described in <xref target="full.date"/>;
2249   it MUST be sent in rfc1123-date format.
2250</t>
2251<figure><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/><artwork type="abnf2616"><![CDATA[
2252  Date   = "Date" ":" OWS Date-v
2253  Date-v = HTTP-date
2254]]></artwork></figure>
2255<t>
2256   An example is
2257</t>
2258<figure><artwork type="example"><![CDATA[
2259  Date: Tue, 15 Nov 1994 08:12:31 GMT
2260]]></artwork></figure>
2261<t>
2262   Origin servers MUST include a Date header field in all responses,
2263   except in these cases:
2264  <list style="numbers">
2265      <t>If the response status code is 100 (Continue) or 101 (Switching
2266         Protocols), the response MAY include a Date header field, at
2267         the server's option.</t>
2268
2269      <t>If the response status code conveys a server error, e.g. 500
2270         (Internal Server Error) or 503 (Service Unavailable), and it is
2271         inconvenient or impossible to generate a valid Date.</t>
2272
2273      <t>If the server does not have a clock that can provide a
2274         reasonable approximation of the current time, its responses
2275         MUST NOT include a Date header field. In this case, the rules
2276         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
2277  </list>
2278</t>
2279<t>
2280   A received message that does not have a Date header field MUST be
2281   assigned one by the recipient if the message will be cached by that
2282   recipient or gatewayed via a protocol which requires a Date. An HTTP
2283   implementation without a clock MUST NOT cache responses without
2284   revalidating them on every use. An HTTP cache, especially a shared
2285   cache, SHOULD use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2286   clock with a reliable external standard.
2287</t>
2288<t>
2289   Clients SHOULD only send a Date header field in messages that include
2290   an entity-body, as in the case of the PUT and POST requests, and even
2291   then it is optional. A client without a clock MUST NOT send a Date
2292   header field in a request.
2293</t>
2294<t>
2295   The HTTP-date sent in a Date header SHOULD NOT  represent a date and
2296   time subsequent to the generation of the message. It SHOULD represent
2297   the best available approximation of the date and time of message
2298   generation, unless the implementation has no means of generating a
2299   reasonably accurate date and time. In theory, the date ought to
2300   represent the moment just before the entity is generated. In
2301   practice, the date can be generated at any time during the message
2302   origination without affecting its semantic value.
2303</t>
2304
2305<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2306<t>
2307   Some origin server implementations might not have a clock available.
2308   An origin server without a clock MUST NOT assign Expires or Last-Modified
2309   values to a response, unless these values were associated
2310   with the resource by a system or user with a reliable clock. It MAY
2311   assign an Expires value that is known, at or before server
2312   configuration time, to be in the past (this allows "pre-expiration"
2313   of responses without storing separate Expires values for each
2314   resource).
2315</t>
2316</section>
2317</section>
2318
2319<section title="Host" anchor="header.host">
2320  <iref primary="true" item="Host header"/>
2321  <iref primary="true" item="Headers" subitem="Host"/>
2322 
2323 
2324<t>
2325   The request-header field "Host" specifies the Internet host and port
2326   number of the resource being requested, as obtained from the original
2327   URI given by the user or referring resource (generally an http URI,
2328   as described in <xref target="http.uri"/>). The Host field value MUST represent
2329   the naming authority of the origin server or gateway given by the
2330   original URL. This allows the origin server or gateway to
2331   differentiate between internally-ambiguous URLs, such as the root "/"
2332   URL of a server for multiple host names on a single IP address.
2333</t>
2334<figure><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/><artwork type="abnf2616"><![CDATA[
2335  Host   = "Host" ":" OWS Host-v
2336  Host-v = uri-host [ ":" port ] ; Section 2.1.1
2337]]></artwork></figure>
2338<t>
2339   A "host" without any trailing port information implies the default
2340   port for the service requested (e.g., "80" for an HTTP URL). For
2341   example, a request on the origin server for
2342   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2343</t>
2344<figure><artwork type="example"><![CDATA[
2345  GET /pub/WWW/ HTTP/1.1
2346  Host: www.example.org
2347]]></artwork></figure>
2348<t>
2349   A client MUST include a Host header field in all HTTP/1.1 request
2350   messages. If the requested URI does not include an Internet host
2351   name for the service being requested, then the Host header field MUST
2352   be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
2353   request message it forwards does contain an appropriate Host header
2354   field that identifies the service being requested by the proxy. All
2355   Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
2356   status code to any HTTP/1.1 request message which lacks a Host header
2357   field.
2358</t>
2359<t>
2360   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2361   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2362   for other requirements relating to Host.
2363</t>
2364</section>
2365
2366<section title="TE" anchor="header.te">
2367  <iref primary="true" item="TE header"/>
2368  <iref primary="true" item="Headers" subitem="TE"/>
2369 
2370 
2371 
2372 
2373 
2374<t>
2375   The request-header field "TE" indicates what extension transfer-codings
2376   it is willing to accept in the response and whether or not it is
2377   willing to accept trailer fields in a chunked transfer-coding. Its
2378   value may consist of the keyword "trailers" and/or a comma-separated
2379   list of extension transfer-coding names with optional accept
2380   parameters (as described in <xref target="transfer.codings"/>).
2381</t>
2382<figure><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/><artwork type="abnf2616"><![CDATA[
2383  TE        = "TE" ":" OWS TE-v
2384  TE-v      = #t-codings
2385  t-codings = "trailers" / ( transfer-extension [ te-params ] )
2386  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
2387  te-ext    = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2388]]></artwork></figure>
2389<t>
2390   The presence of the keyword "trailers" indicates that the client is
2391   willing to accept trailer fields in a chunked transfer-coding, as
2392   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2393   transfer-coding values even though it does not itself represent a
2394   transfer-coding.
2395</t>
2396<t>
2397   Examples of its use are:
2398</t>
2399<figure><artwork type="example"><![CDATA[
2400  TE: deflate
2401  TE:
2402  TE: trailers, deflate;q=0.5
2403]]></artwork></figure>
2404<t>
2405   The TE header field only applies to the immediate connection.
2406   Therefore, the keyword MUST be supplied within a Connection header
2407   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2408</t>
2409<t>
2410   A server tests whether a transfer-coding is acceptable, according to
2411   a TE field, using these rules:
2412  <list style="numbers">
2413    <t>The "chunked" transfer-coding is always acceptable. If the
2414         keyword "trailers" is listed, the client indicates that it is
2415         willing to accept trailer fields in the chunked response on
2416         behalf of itself and any downstream clients. The implication is
2417         that, if given, the client is stating that either all
2418         downstream clients are willing to accept trailer fields in the
2419         forwarded response, or that it will attempt to buffer the
2420         response on behalf of downstream recipients.
2421      <vspace blankLines="1"/>
2422         Note: HTTP/1.1 does not define any means to limit the size of a
2423         chunked response such that a client can be assured of buffering
2424         the entire response.</t>
2425    <t>If the transfer-coding being tested is one of the transfer-codings
2426         listed in the TE field, then it is acceptable unless it
2427         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2428         qvalue of 0 means "not acceptable.")</t>
2429    <t>If multiple transfer-codings are acceptable, then the
2430         acceptable transfer-coding with the highest non-zero qvalue is
2431         preferred.  The "chunked" transfer-coding always has a qvalue
2432         of 1.</t>
2433  </list>
2434</t>
2435<t>
2436   If the TE field-value is empty or if no TE field is present, the only
2437   transfer-coding is "chunked". A message with no transfer-coding is
2438   always acceptable.
2439</t>
2440</section>
2441
2442<section title="Trailer" anchor="header.trailer">
2443  <iref primary="true" item="Trailer header"/>
2444  <iref primary="true" item="Headers" subitem="Trailer"/>
2445 
2446 
2447<t>
2448   The general field "Trailer" indicates that the given set of
2449   header fields is present in the trailer of a message encoded with
2450   chunked transfer-coding.
2451</t>
2452<figure><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/><artwork type="abnf2616"><![CDATA[
2453  Trailer   = "Trailer" ":" OWS Trailer-v
2454  Trailer-v = 1#field-name
2455]]></artwork></figure>
2456<t>
2457   An HTTP/1.1 message SHOULD include a Trailer header field in a
2458   message using chunked transfer-coding with a non-empty trailer. Doing
2459   so allows the recipient to know which header fields to expect in the
2460   trailer.
2461</t>
2462<t>
2463   If no Trailer header field is present, the trailer SHOULD NOT  include
2464   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2465   trailer fields in a "chunked" transfer-coding.
2466</t>
2467<t>
2468   Message header fields listed in the Trailer header field MUST NOT
2469   include the following header fields:
2470  <list style="symbols">
2471    <t>Transfer-Encoding</t>
2472    <t>Content-Length</t>
2473    <t>Trailer</t>
2474  </list>
2475</t>
2476</section>
2477
2478<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2479  <iref primary="true" item="Transfer-Encoding header"/>
2480  <iref primary="true" item="Headers" subitem="Transfer-Encoding"/>
2481 
2482 
2483<t>
2484   The general-header "Transfer-Encoding" field indicates what (if any)
2485   type of transformation has been applied to the message body in order
2486   to safely transfer it between the sender and the recipient. This
2487   differs from the content-coding in that the transfer-coding is a
2488   property of the message, not of the entity.
2489</t>
2490<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/><artwork type="abnf2616"><![CDATA[
2491  Transfer-Encoding   = "Transfer-Encoding" ":" OWS
2492                        Transfer-Encoding-v
2493  Transfer-Encoding-v = 1#transfer-coding
2494]]></artwork></figure>
2495<t>
2496   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2497</t>
2498<figure><artwork type="example"><![CDATA[
2499  Transfer-Encoding: chunked
2500]]></artwork></figure>
2501<t>
2502   If multiple encodings have been applied to an entity, the transfer-codings
2503   MUST be listed in the order in which they were applied.
2504   Additional information about the encoding parameters MAY be provided
2505   by other entity-header fields not defined by this specification.
2506</t>
2507<t>
2508   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2509   header.
2510</t>
2511</section>
2512
2513<section title="Upgrade" anchor="header.upgrade">
2514  <iref primary="true" item="Upgrade header"/>
2515  <iref primary="true" item="Headers" subitem="Upgrade"/>
2516 
2517 
2518<t>
2519   The general-header "Upgrade" allows the client to specify what
2520   additional communication protocols it supports and would like to use
2521   if the server finds it appropriate to switch protocols. The server
2522   MUST use the Upgrade header field within a 101 (Switching Protocols)
2523   response to indicate which protocol(s) are being switched.
2524</t>
2525<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/><artwork type="abnf2616"><![CDATA[
2526  Upgrade   = "Upgrade" ":" OWS Upgrade-v
2527  Upgrade-v = 1#product
2528]]></artwork></figure>
2529<t>
2530   For example,
2531</t>
2532<figure><artwork type="example"><![CDATA[
2533  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2534]]></artwork></figure>
2535<t>
2536   The Upgrade header field is intended to provide a simple mechanism
2537   for transition from HTTP/1.1 to some other, incompatible protocol. It
2538   does so by allowing the client to advertise its desire to use another
2539   protocol, such as a later version of HTTP with a higher major version
2540   number, even though the current request has been made using HTTP/1.1.
2541   This eases the difficult transition between incompatible protocols by
2542   allowing the client to initiate a request in the more commonly
2543   supported protocol while indicating to the server that it would like
2544   to use a "better" protocol if available (where "better" is determined
2545   by the server, possibly according to the nature of the method and/or
2546   resource being requested).
2547</t>
2548<t>
2549   The Upgrade header field only applies to switching application-layer
2550   protocols upon the existing transport-layer connection. Upgrade
2551   cannot be used to insist on a protocol change; its acceptance and use
2552   by the server is optional. The capabilities and nature of the
2553   application-layer communication after the protocol change is entirely
2554   dependent upon the new protocol chosen, although the first action
2555   after changing the protocol MUST be a response to the initial HTTP
2556   request containing the Upgrade header field.
2557</t>
2558<t>
2559   The Upgrade header field only applies to the immediate connection.
2560   Therefore, the upgrade keyword MUST be supplied within a Connection
2561   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2562   HTTP/1.1 message.
2563</t>
2564<t>
2565   The Upgrade header field cannot be used to indicate a switch to a
2566   protocol on a different connection. For that purpose, it is more
2567   appropriate to use a 301, 302, 303, or 305 redirection response.
2568</t>
2569<t>
2570   This specification only defines the protocol name "HTTP" for use by
2571   the family of Hypertext Transfer Protocols, as defined by the HTTP
2572   version rules of <xref target="http.version"/> and future updates to this
2573   specification. Any token can be used as a protocol name; however, it
2574   will only be useful if both the client and server associate the name
2575   with the same protocol.
2576</t>
2577</section>
2578
2579<section title="Via" anchor="header.via">
2580  <iref primary="true" item="Via header"/>
2581  <iref primary="true" item="Headers" subitem="Via"/>
2582 
2583 
2584 
2585 
2586 
2587 
2588 
2589<t>
2590   The general-header field "Via" MUST be used by gateways and proxies to
2591   indicate the intermediate protocols and recipients between the user
2592   agent and the server on requests, and between the origin server and
2593   the client on responses. It is analogous to the "Received" field defined in
2594   Section 3.6.7 of <xref target="RFC5322"/> and is intended to be used for tracking message forwards,
2595   avoiding request loops, and identifying the protocol capabilities of
2596   all senders along the request/response chain.
2597</t>
2598<figure><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"/><artwork type="abnf2616"><![CDATA[
2599  Via               = "Via" ":" OWS Via-v
2600  Via-v             = 1#( received-protocol RWS received-by
2601                          [ RWS comment ] )
2602  received-protocol = [ protocol-name "/" ] protocol-version
2603  protocol-name     = token
2604  protocol-version  = token
2605  received-by       = ( uri-host [ ":" port ] ) / pseudonym
2606  pseudonym         = token
2607]]></artwork></figure>
2608<t>
2609   The received-protocol indicates the protocol version of the message
2610   received by the server or client along each segment of the
2611   request/response chain. The received-protocol version is appended to
2612   the Via field value when the message is forwarded so that information
2613   about the protocol capabilities of upstream applications remains
2614   visible to all recipients.
2615</t>
2616<t>
2617   The protocol-name is optional if and only if it would be "HTTP". The
2618   received-by field is normally the host and optional port number of a
2619   recipient server or client that subsequently forwarded the message.
2620   However, if the real host is considered to be sensitive information,
2621   it MAY be replaced by a pseudonym. If the port is not given, it MAY
2622   be assumed to be the default port of the received-protocol.
2623</t>
2624<t>
2625   Multiple Via field values represents each proxy or gateway that has
2626   forwarded the message. Each recipient MUST append its information
2627   such that the end result is ordered according to the sequence of
2628   forwarding applications.
2629</t>
2630<t>
2631   Comments MAY be used in the Via header field to identify the software
2632   of the recipient proxy or gateway, analogous to the User-Agent and
2633   Server header fields. However, all comments in the Via field are
2634   optional and MAY be removed by any recipient prior to forwarding the
2635   message.
2636</t>
2637<t>
2638   For example, a request message could be sent from an HTTP/1.0 user
2639   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2640   forward the request to a public proxy at p.example.net, which completes
2641   the request by forwarding it to the origin server at www.example.com.
2642   The request received by www.example.com would then have the following
2643   Via header field:
2644</t>
2645<figure><artwork type="example"><![CDATA[
2646  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2647]]></artwork></figure>
2648<t>
2649   Proxies and gateways used as a portal through a network firewall
2650   SHOULD NOT, by default, forward the names and ports of hosts within
2651   the firewall region. This information SHOULD only be propagated if
2652   explicitly enabled. If not enabled, the received-by host of any host
2653   behind the firewall SHOULD be replaced by an appropriate pseudonym
2654   for that host.
2655</t>
2656<t>
2657   For organizations that have strong privacy requirements for hiding
2658   internal structures, a proxy MAY combine an ordered subsequence of
2659   Via header field entries with identical received-protocol values into
2660   a single such entry. For example,
2661</t>
2662<figure><artwork type="example"><![CDATA[
2663  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2664]]></artwork></figure>
2665<t>
2666        could be collapsed to
2667</t>
2668<figure><artwork type="example"><![CDATA[
2669  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2670]]></artwork></figure>
2671<t>
2672   Applications SHOULD NOT  combine multiple entries unless they are all
2673   under the same organizational control and the hosts have already been
2674   replaced by pseudonyms. Applications MUST NOT combine entries which
2675   have different received-protocol values.
2676</t>
2677</section>
2678
2679</section>
2680
2681<section title="IANA Considerations" anchor="IANA.considerations">
2682<section title="Message Header Registration" anchor="message.header.registration">
2683<t>
2684   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2685   with the permanent registrations below (see <xref target="RFC3864"/>):
2686</t>
2687<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2688<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2689   <ttcol>Header Field Name</ttcol>
2690   <ttcol>Protocol</ttcol>
2691   <ttcol>Status</ttcol>
2692   <ttcol>Reference</ttcol>
2693
2694   <c>Connection</c>
2695   <c>http</c>
2696   <c>standard</c>
2697   <c>
2698      <xref target="header.connection"/>
2699   </c>
2700   <c>Content-Length</c>
2701   <c>http</c>
2702   <c>standard</c>
2703   <c>
2704      <xref target="header.content-length"/>
2705   </c>
2706   <c>Date</c>
2707   <c>http</c>
2708   <c>standard</c>
2709   <c>
2710      <xref target="header.date"/>
2711   </c>
2712   <c>Host</c>
2713   <c>http</c>
2714   <c>standard</c>
2715   <c>
2716      <xref target="header.host"/>
2717   </c>
2718   <c>TE</c>
2719   <c>http</c>
2720   <c>standard</c>
2721   <c>
2722      <xref target="header.te"/>
2723   </c>
2724   <c>Trailer</c>
2725   <c>http</c>
2726   <c>standard</c>
2727   <c>
2728      <xref target="header.trailer"/>
2729   </c>
2730   <c>Transfer-Encoding</c>
2731   <c>http</c>
2732   <c>standard</c>
2733   <c>
2734      <xref target="header.transfer-encoding"/>
2735   </c>
2736   <c>Upgrade</c>
2737   <c>http</c>
2738   <c>standard</c>
2739   <c>
2740      <xref target="header.upgrade"/>
2741   </c>
2742   <c>Via</c>
2743   <c>http</c>
2744   <c>standard</c>
2745   <c>
2746      <xref target="header.via"/>
2747   </c>
2748</texttable>
2749<!--(END)-->
2750<t>
2751   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2752</t>
2753</section>
2754
2755<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2756<t>
2757   The entry for the "http" URI Scheme in the registry located at
2758   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2759   should be updated to point to <xref target="http.uri"/> of this document
2760   (see <xref target="RFC4395"/>).
2761</t>
2762</section>
2763
2764<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2765<t>
2766   This document serves as the specification for the Internet media types
2767   "message/http" and "application/http". The following is to be registered with
2768   IANA (see <xref target="RFC4288"/>).
2769</t>
2770<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2771<iref item="Media Type" subitem="message/http" primary="true"/>
2772<iref item="message/http Media Type" primary="true"/>
2773<t>
2774   The message/http type can be used to enclose a single HTTP request or
2775   response message, provided that it obeys the MIME restrictions for all
2776   "message" types regarding line length and encodings.
2777</t>
2778<t>
2779  <list style="hanging">
2780    <t hangText="Type name:">
2781      message
2782    </t>
2783    <t hangText="Subtype name:">
2784      http
2785    </t>
2786    <t hangText="Required parameters:">
2787      none
2788    </t>
2789    <t hangText="Optional parameters:">
2790      version, msgtype
2791      <list style="hanging">
2792        <t hangText="version:">
2793          The HTTP-Version number of the enclosed message
2794          (e.g., "1.1"). If not present, the version can be
2795          determined from the first line of the body.
2796        </t>
2797        <t hangText="msgtype:">
2798          The message type -- "request" or "response". If not
2799          present, the type can be determined from the first
2800          line of the body.
2801        </t>
2802      </list>
2803    </t>
2804    <t hangText="Encoding considerations:">
2805      only "7bit", "8bit", or "binary" are permitted
2806    </t>
2807    <t hangText="Security considerations:">
2808      none
2809    </t>
2810    <t hangText="Interoperability considerations:">
2811      none
2812    </t>
2813    <t hangText="Published specification:">
2814      This specification (see <xref target="internet.media.type.message.http"/>).
2815    </t>
2816    <t hangText="Applications that use this media type:">
2817    </t>
2818    <t hangText="Additional information:">
2819      <list style="hanging">
2820        <t hangText="Magic number(s):">none</t>
2821        <t hangText="File extension(s):">none</t>
2822        <t hangText="Macintosh file type code(s):">none</t>
2823      </list>
2824    </t>
2825    <t hangText="Person and email address to contact for further information:">
2826      See Authors Section.
2827    </t>
2828                <t hangText="Intended usage:">
2829                  COMMON
2830    </t>
2831                <t hangText="Restrictions on usage:">
2832                  none
2833    </t>
2834    <t hangText="Author/Change controller:">
2835      IESG
2836    </t>
2837  </list>
2838</t>
2839</section>
2840<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2841<iref item="Media Type" subitem="application/http" primary="true"/>
2842<iref item="application/http Media Type" primary="true"/>
2843<t>
2844   The application/http type can be used to enclose a pipeline of one or more
2845   HTTP request or response messages (not intermixed).
2846</t>
2847<t>
2848  <list style="hanging">
2849    <t hangText="Type name:">
2850      application
2851    </t>
2852    <t hangText="Subtype name:">
2853      http
2854    </t>
2855    <t hangText="Required parameters:">
2856      none
2857    </t>
2858    <t hangText="Optional parameters:">
2859      version, msgtype
2860      <list style="hanging">
2861        <t hangText="version:">
2862          The HTTP-Version number of the enclosed messages
2863          (e.g., "1.1"). If not present, the version can be
2864          determined from the first line of the body.
2865        </t>
2866        <t hangText="msgtype:">
2867          The message type -- "request" or "response". If not
2868          present, the type can be determined from the first
2869          line of the body.
2870        </t>
2871      </list>
2872    </t>
2873    <t hangText="Encoding considerations:">
2874      HTTP messages enclosed by this type
2875      are in "binary" format; use of an appropriate
2876      Content-Transfer-Encoding is required when
2877      transmitted via E-mail.
2878    </t>
2879    <t hangText="Security considerations:">
2880      none
2881    </t>
2882    <t hangText="Interoperability considerations:">
2883      none
2884    </t>
2885    <t hangText="Published specification:">
2886      This specification (see <xref target="internet.media.type.application.http"/>).
2887    </t>
2888    <t hangText="Applications that use this media type:">
2889    </t>
2890    <t hangText="Additional information:">
2891      <list style="hanging">
2892        <t hangText="Magic number(s):">none</t>
2893        <t hangText="File extension(s):">none</t>
2894        <t hangText="Macintosh file type code(s):">none</t>
2895      </list>
2896    </t>
2897    <t hangText="Person and email address to contact for further information:">
2898      See Authors Section.
2899    </t>
2900                <t hangText="Intended usage:">
2901                  COMMON
2902    </t>
2903                <t hangText="Restrictions on usage:">
2904                  none
2905    </t>
2906    <t hangText="Author/Change controller:">
2907      IESG
2908    </t>
2909  </list>
2910</t>
2911</section>
2912</section>
2913
2914</section>
2915
2916<section title="Security Considerations" anchor="security.considerations">
2917<t>
2918   This section is meant to inform application developers, information
2919   providers, and users of the security limitations in HTTP/1.1 as
2920   described by this document. The discussion does not include
2921   definitive solutions to the problems revealed, though it does make
2922   some suggestions for reducing security risks.
2923</t>
2924
2925<section title="Personal Information" anchor="personal.information">
2926<t>
2927   HTTP clients are often privy to large amounts of personal information
2928   (e.g. the user's name, location, mail address, passwords, encryption
2929   keys, etc.), and SHOULD be very careful to prevent unintentional
2930   leakage of this information.
2931   We very strongly recommend that a convenient interface be provided
2932   for the user to control dissemination of such information, and that
2933   designers and implementors be particularly careful in this area.
2934   History shows that errors in this area often create serious security
2935   and/or privacy problems and generate highly adverse publicity for the
2936   implementor's company.
2937</t>
2938</section>
2939
2940<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2941<t>
2942   A server is in the position to save personal data about a user's
2943   requests which might identify their reading patterns or subjects of
2944   interest. This information is clearly confidential in nature and its
2945   handling can be constrained by law in certain countries. People using
2946   HTTP to provide data are responsible for ensuring that
2947   such material is not distributed without the permission of any
2948   individuals that are identifiable by the published results.
2949</t>
2950</section>
2951
2952<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2953<t>
2954   Implementations of HTTP origin servers SHOULD be careful to restrict
2955   the documents returned by HTTP requests to be only those that were
2956   intended by the server administrators. If an HTTP server translates
2957   HTTP URIs directly into file system calls, the server MUST take
2958   special care not to serve files that were not intended to be
2959   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2960   other operating systems use ".." as a path component to indicate a
2961   directory level above the current one. On such a system, an HTTP
2962   server MUST disallow any such construct in the request-target if it
2963   would otherwise allow access to a resource outside those intended to
2964   be accessible via the HTTP server. Similarly, files intended for
2965   reference only internally to the server (such as access control
2966   files, configuration files, and script code) MUST be protected from
2967   inappropriate retrieval, since they might contain sensitive
2968   information. Experience has shown that minor bugs in such HTTP server
2969   implementations have turned into security risks.
2970</t>
2971</section>
2972
2973<section title="DNS Spoofing" anchor="dns.spoofing">
2974<t>
2975   Clients using HTTP rely heavily on the Domain Name Service, and are
2976   thus generally prone to security attacks based on the deliberate
2977   mis-association of IP addresses and DNS names. Clients need to be
2978   cautious in assuming the continuing validity of an IP number/DNS name
2979   association.
2980</t>
2981<t>
2982   In particular, HTTP clients SHOULD rely on their name resolver for
2983   confirmation of an IP number/DNS name association, rather than
2984   caching the result of previous host name lookups. Many platforms
2985   already can cache host name lookups locally when appropriate, and
2986   they SHOULD be configured to do so. It is proper for these lookups to
2987   be cached, however, only when the TTL (Time To Live) information
2988   reported by the name server makes it likely that the cached
2989   information will remain useful.
2990</t>
2991<t>
2992   If HTTP clients cache the results of host name lookups in order to
2993   achieve a performance improvement, they MUST observe the TTL
2994   information reported by DNS.
2995</t>
2996<t>
2997   If HTTP clients do not observe this rule, they could be spoofed when
2998   a previously-accessed server's IP address changes. As network
2999   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3000   possibility of this form of attack will grow. Observing this
3001   requirement thus reduces this potential security vulnerability.
3002</t>
3003<t>
3004   This requirement also improves the load-balancing behavior of clients
3005   for replicated servers using the same DNS name and reduces the
3006   likelihood of a user's experiencing failure in accessing sites which
3007   use that strategy.
3008</t>
3009</section>
3010
3011<section title="Proxies and Caching" anchor="attack.proxies">
3012<t>
3013   By their very nature, HTTP proxies are men-in-the-middle, and
3014   represent an opportunity for man-in-the-middle attacks. Compromise of
3015   the systems on which the proxies run can result in serious security
3016   and privacy problems. Proxies have access to security-related
3017   information, personal information about individual users and
3018   organizations, and proprietary information belonging to users and
3019   content providers. A compromised proxy, or a proxy implemented or
3020   configured without regard to security and privacy considerations,
3021   might be used in the commission of a wide range of potential attacks.
3022</t>
3023<t>
3024   Proxy operators should protect the systems on which proxies run as
3025   they would protect any system that contains or transports sensitive
3026   information. In particular, log information gathered at proxies often
3027   contains highly sensitive personal information, and/or information
3028   about organizations. Log information should be carefully guarded, and
3029   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3030</t>
3031<t>
3032   Proxy implementors should consider the privacy and security
3033   implications of their design and coding decisions, and of the
3034   configuration options they provide to proxy operators (especially the
3035   default configuration).
3036</t>
3037<t>
3038   Users of a proxy need to be aware that they are no trustworthier than
3039   the people who run the proxy; HTTP itself cannot solve this problem.
3040</t>
3041<t>
3042   The judicious use of cryptography, when appropriate, may suffice to
3043   protect against a broad range of security and privacy attacks. Such
3044   cryptography is beyond the scope of the HTTP/1.1 specification.
3045</t>
3046</section>
3047
3048<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3049<t>
3050   They exist. They are hard to defend against. Research continues.
3051   Beware.
3052</t>
3053</section>
3054</section>
3055
3056<section title="Acknowledgments" anchor="ack">
3057<t>
3058   HTTP has evolved considerably over the years. It has
3059   benefited from a large and active developer community--the many
3060   people who have participated on the www-talk mailing list--and it is
3061   that community which has been most responsible for the success of
3062   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3063   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3064   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3065   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3066   VanHeyningen deserve special recognition for their efforts in
3067   defining early aspects of the protocol.
3068</t>
3069<t>
3070   This document has benefited greatly from the comments of all those
3071   participating in the HTTP-WG. In addition to those already mentioned,
3072   the following individuals have contributed to this specification:
3073</t>
3074<t>
3075   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3076   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3077   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3078   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3079   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3080   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3081   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3082   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3083   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3084   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3085   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3086   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3087   Josh Cohen.
3088</t>
3089<t>
3090   Thanks to the "cave men" of Palo Alto. You know who you are.
3091</t>
3092<t>
3093   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3094   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3095   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3096   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3097   Larry Masinter for their help. And thanks go particularly to Jeff
3098   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3099</t>
3100<t>
3101   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3102   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3103   discovery of many of the problems that this document attempts to
3104   rectify.
3105</t>
3106<t>
3107   This specification makes heavy use of the augmented BNF and generic
3108   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3109   reuses many of the definitions provided by Nathaniel Borenstein and
3110   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3111   specification will help reduce past confusion over the relationship
3112   between HTTP and Internet mail message formats.
3113</t>
3114</section>
3115
3116</middle>
3117<back>
3118
3119<references title="Normative References">
3120
3121<reference anchor="ISO-8859-1">
3122  <front>
3123    <title>
3124     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3125    </title>
3126    <author>
3127      <organization>International Organization for Standardization</organization>
3128    </author>
3129    <date year="1998"/>
3130  </front>
3131  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3132</reference>
3133
3134<reference anchor="Part2">
3135  <front>
3136    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3137    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3138      <organization abbrev="Day Software">Day Software</organization>
3139      <address><email>fielding@gbiv.com</email></address>
3140    </author>
3141    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3142      <organization>One Laptop per Child</organization>
3143      <address><email>jg@laptop.org</email></address>
3144    </author>
3145    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3146      <organization abbrev="HP">Hewlett-Packard Company</organization>
3147      <address><email>JeffMogul@acm.org</email></address>
3148    </author>
3149    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3150      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3151      <address><email>henrikn@microsoft.com</email></address>
3152    </author>
3153    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3154      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3155      <address><email>LMM@acm.org</email></address>
3156    </author>
3157    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3158      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3159      <address><email>paulle@microsoft.com</email></address>
3160    </author>
3161    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3162      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3163      <address><email>timbl@w3.org</email></address>
3164    </author>
3165    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3166      <organization abbrev="W3C">World Wide Web Consortium</organization>
3167      <address><email>ylafon@w3.org</email></address>
3168    </author>
3169    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3170      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3171      <address><email>julian.reschke@greenbytes.de</email></address>
3172    </author>
3173    <date month="March" year="2009"/>
3174  </front>
3175  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-06"/>
3176 
3177</reference>
3178
3179<reference anchor="Part3">
3180  <front>
3181    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3182    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3183      <organization abbrev="Day Software">Day Software</organization>
3184      <address><email>fielding@gbiv.com</email></address>
3185    </author>
3186    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3187      <organization>One Laptop per Child</organization>
3188      <address><email>jg@laptop.org</email></address>
3189    </author>
3190    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3191      <organization abbrev="HP">Hewlett-Packard Company</organization>
3192      <address><email>JeffMogul@acm.org</email></address>
3193    </author>
3194    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3195      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3196      <address><email>henrikn@microsoft.com</email></address>
3197    </author>
3198    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3199      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3200      <address><email>LMM@acm.org</email></address>
3201    </author>
3202    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3203      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3204      <address><email>paulle@microsoft.com</email></address>
3205    </author>
3206    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3207      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3208      <address><email>timbl@w3.org</email></address>
3209    </author>
3210    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3211      <organization abbrev="W3C">World Wide Web Consortium</organization>
3212      <address><email>ylafon@w3.org</email></address>
3213    </author>
3214    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3215      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3216      <address><email>julian.reschke@greenbytes.de</email></address>
3217    </author>
3218    <date month="March" year="2009"/>
3219  </front>
3220  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-06"/>
3221 
3222</reference>
3223
3224<reference anchor="Part5">
3225  <front>
3226    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3227    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3228      <organization abbrev="Day Software">Day Software</organization>
3229      <address><email>fielding@gbiv.com</email></address>
3230    </author>
3231    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3232      <organization>One Laptop per Child</organization>
3233      <address><email>jg@laptop.org</email></address>
3234    </author>
3235    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3236      <organization abbrev="HP">Hewlett-Packard Company</organization>
3237      <address><email>JeffMogul@acm.org</email></address>
3238    </author>
3239    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3240      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3241      <address><email>henrikn@microsoft.com</email></address>
3242    </author>
3243    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3244      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3245      <address><email>LMM@acm.org</email></address>
3246    </author>
3247    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3248      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3249      <address><email>paulle@microsoft.com</email></address>
3250    </author>
3251    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3252      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3253      <address><email>timbl@w3.org</email></address>
3254    </author>
3255    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3256      <organization abbrev="W3C">World Wide Web Consortium</organization>
3257      <address><email>ylafon@w3.org</email></address>
3258    </author>
3259    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3260      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3261      <address><email>julian.reschke@greenbytes.de</email></address>
3262    </author>
3263    <date month="March" year="2009"/>
3264  </front>
3265  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-06"/>
3266 
3267</reference>
3268
3269<reference anchor="Part6">
3270  <front>
3271    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3272    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3273      <organization abbrev="Day Software">Day Software</organization>
3274      <address><email>fielding@gbiv.com</email></address>
3275    </author>
3276    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3277      <organization>One Laptop per Child</organization>
3278      <address><email>jg@laptop.org</email></address>
3279    </author>
3280    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3281      <organization abbrev="HP">Hewlett-Packard Company</organization>
3282      <address><email>JeffMogul@acm.org</email></address>
3283    </author>
3284    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3285      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3286      <address><email>henrikn@microsoft.com</email></address>
3287    </author>
3288    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3289      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3290      <address><email>LMM@acm.org</email></address>
3291    </author>
3292    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3293      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3294      <address><email>paulle@microsoft.com</email></address>
3295    </author>
3296    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3297      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3298      <address><email>timbl@w3.org</email></address>
3299    </author>
3300    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3301      <organization abbrev="W3C">World Wide Web Consortium</organization>
3302      <address><email>ylafon@w3.org</email></address>
3303    </author>
3304    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3305      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3306      <address><email>julian.reschke@greenbytes.de</email></address>
3307    </author>
3308    <date month="March" year="2009"/>
3309  </front>
3310  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-06"/>
3311 
3312</reference>
3313
3314<reference anchor="RFC5234">
3315  <front>
3316    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3317    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3318      <organization>Brandenburg InternetWorking</organization>
3319      <address>
3320      <postal>
3321      <street>675 Spruce Dr.</street>
3322      <city>Sunnyvale</city>
3323      <region>CA</region>
3324      <code>94086</code>
3325      <country>US</country></postal>
3326      <phone>+1.408.246.8253</phone>
3327      <email>dcrocker@bbiw.net</email></address> 
3328    </author>
3329    <author initials="P." surname="Overell" fullname="Paul Overell">
3330      <organization>THUS plc.</organization>
3331      <address>
3332      <postal>
3333      <street>1/2 Berkeley Square</street>
3334      <street>99 Berkely Street</street>
3335      <city>Glasgow</city>
3336      <code>G3 7HR</code>
3337      <country>UK</country></postal>
3338      <email>paul.overell@thus.net</email></address>
3339    </author>
3340    <date month="January" year="2008"/>
3341  </front>
3342  <seriesInfo name="STD" value="68"/>
3343  <seriesInfo name="RFC" value="5234"/>
3344</reference>
3345
3346<reference anchor="RFC2119">
3347  <front>
3348    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3349    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3350      <organization>Harvard University</organization>
3351      <address><email>sob@harvard.edu</email></address>
3352    </author>
3353    <date month="March" year="1997"/>
3354  </front>
3355  <seriesInfo name="BCP" value="14"/>
3356  <seriesInfo name="RFC" value="2119"/>
3357</reference>
3358
3359<reference anchor="RFC3986">
3360 <front>
3361  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
3362  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3363    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3364    <address>
3365       <email>timbl@w3.org</email>
3366       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3367    </address>
3368  </author>
3369  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3370    <organization abbrev="Day Software">Day Software</organization>
3371    <address>
3372      <email>fielding@gbiv.com</email>
3373      <uri>http://roy.gbiv.com/</uri>
3374    </address>
3375  </author>
3376  <author initials="L." surname="Masinter" fullname="Larry Masinter">
3377    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3378    <address>
3379      <email>LMM@acm.org</email>
3380      <uri>http://larry.masinter.net/</uri>
3381    </address>
3382  </author>
3383  <date month="January" year="2005"/>
3384 </front>
3385 <seriesInfo name="RFC" value="3986"/>
3386 <seriesInfo name="STD" value="66"/>
3387</reference>
3388
3389<reference anchor="USASCII">
3390  <front>
3391    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3392    <author>
3393      <organization>American National Standards Institute</organization>
3394    </author>
3395    <date year="1986"/>
3396  </front>
3397  <seriesInfo name="ANSI" value="X3.4"/>
3398</reference>
3399
3400</references>
3401
3402<references title="Informative References">
3403
3404<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3405  <front>
3406    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3407    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3408      <organization/>
3409    </author>
3410    <author initials="J." surname="Gettys" fullname="J. Gettys">
3411      <organization/>
3412    </author>
3413    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3414      <organization/>
3415    </author>
3416    <author initials="H." surname="Lie" fullname="H. Lie">
3417      <organization/>
3418    </author>
3419    <author initials="C." surname="Lilley" fullname="C. Lilley">
3420      <organization/>
3421    </author>
3422    <date year="1997" month="September"/>
3423  </front>
3424  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3425</reference>
3426
3427<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3428  <front>
3429    <title>Improving HTTP Latency</title>
3430    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3431      <organization/>
3432    </author>
3433    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3434      <organization/>
3435    </author>
3436    <date year="1995" month="December"/>
3437  </front>
3438  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3439</reference>
3440
3441<reference anchor="RFC1123">
3442  <front>
3443    <title>Requirements for Internet Hosts - Application and Support</title>
3444    <author initials="R." surname="Braden" fullname="Robert Braden">
3445      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3446      <address><email>Braden@ISI.EDU</email></address>
3447    </author>
3448    <date month="October" year="1989"/>
3449  </front>
3450  <seriesInfo name="STD" value="3"/>
3451  <seriesInfo name="RFC" value="1123"/>
3452</reference>
3453
3454<reference anchor="RFC1305">
3455  <front>
3456    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3457    <author initials="D." surname="Mills" fullname="David L. Mills">
3458      <organization>University of Delaware, Electrical Engineering Department</organization>
3459      <address><email>mills@udel.edu</email></address>
3460    </author>
3461    <date month="March" year="1992"/>
3462  </front>
3463  <seriesInfo name="RFC" value="1305"/>
3464</reference>
3465
3466<reference anchor="RFC1900">
3467  <front>
3468    <title>Renumbering Needs Work</title>
3469    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3470      <organization>CERN, Computing and Networks Division</organization>
3471      <address><email>brian@dxcoms.cern.ch</email></address>
3472    </author>
3473    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3474      <organization>cisco Systems</organization>
3475      <address><email>yakov@cisco.com</email></address>
3476    </author>
3477    <date month="February" year="1996"/>
3478  </front>
3479  <seriesInfo name="RFC" value="1900"/>
3480</reference>
3481
3482<reference anchor="RFC1945">
3483  <front>
3484    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3485    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3486      <organization>MIT, Laboratory for Computer Science</organization>
3487      <address><email>timbl@w3.org</email></address>
3488    </author>
3489    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3490      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3491      <address><email>fielding@ics.uci.edu</email></address>
3492    </author>
3493    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3494      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3495      <address><email>frystyk@w3.org</email></address>
3496    </author>
3497    <date month="May" year="1996"/>
3498  </front>
3499  <seriesInfo name="RFC" value="1945"/>
3500</reference>
3501
3502<reference anchor="RFC2045">
3503  <front>
3504    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3505    <author initials="N." surname="Freed" fullname="Ned Freed">
3506      <organization>Innosoft International, Inc.</organization>
3507      <address><email>ned@innosoft.com</email></address>
3508    </author>
3509    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3510      <organization>First Virtual Holdings</organization>
3511      <address><email>nsb@nsb.fv.com</email></address>
3512    </author>
3513    <date month="November" year="1996"/>
3514  </front>
3515  <seriesInfo name="RFC" value="2045"/>
3516</reference>
3517
3518<reference anchor="RFC2047">
3519  <front>
3520    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3521    <author initials="K." surname="Moore" fullname="Keith Moore">
3522      <organization>University of Tennessee</organization>
3523      <address><email>moore@cs.utk.edu</email></address>
3524    </author>
3525    <date month="November" year="1996"/>
3526  </front>
3527  <seriesInfo name="RFC" value="2047"/>
3528</reference>
3529
3530<reference anchor="RFC2068">
3531  <front>
3532    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3533    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3534      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3535      <address><email>fielding@ics.uci.edu</email></address>
3536    </author>
3537    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3538      <organization>MIT Laboratory for Computer Science</organization>
3539      <address><email>jg@w3.org</email></address>
3540    </author>
3541    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3542      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3543      <address><email>mogul@wrl.dec.com</email></address>
3544    </author>
3545    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3546      <organization>MIT Laboratory for Computer Science</organization>
3547      <address><email>frystyk@w3.org</email></address>
3548    </author>
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    <date month="January" year="1997"/>
3554  </front>
3555  <seriesInfo name="RFC" value="2068"/>
3556</reference>
3557
3558<reference anchor="RFC2109">
3559  <front>
3560    <title>HTTP State Management Mechanism</title>
3561    <author initials="D.M." surname="Kristol" fullname="David M. Kristol">
3562      <organization>Bell Laboratories, Lucent Technologies</organization>
3563      <address><email>dmk@bell-labs.com</email></address>
3564    </author>
3565    <author initials="L." surname="Montulli" fullname="Lou Montulli">
3566      <organization>Netscape Communications Corp.</organization>
3567      <address><email>montulli@netscape.com</email></address>
3568    </author>
3569    <date year="1997" month="February"/>
3570  </front>
3571  <seriesInfo name="RFC" value="2109"/>
3572</reference>
3573
3574<reference anchor="RFC2145">
3575  <front>
3576    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3577    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3578      <organization>Western Research Laboratory</organization>
3579      <address><email>mogul@wrl.dec.com</email></address>
3580    </author>
3581    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3582      <organization>Department of Information and Computer Science</organization>
3583      <address><email>fielding@ics.uci.edu</email></address>
3584    </author>
3585    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3586      <organization>MIT Laboratory for Computer Science</organization>
3587      <address><email>jg@w3.org</email></address>
3588    </author>
3589    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3590      <organization>W3 Consortium</organization>
3591      <address><email>frystyk@w3.org</email></address>
3592    </author>
3593    <date month="May" year="1997"/>
3594  </front>
3595  <seriesInfo name="RFC" value="2145"/>
3596</reference>
3597
3598<reference anchor="RFC2616">
3599  <front>
3600    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3601    <author initials="R." surname="Fielding" fullname="R. Fielding">
3602      <organization>University of California, Irvine</organization>
3603      <address><email>fielding@ics.uci.edu</email></address>
3604    </author>
3605    <author initials="J." surname="Gettys" fullname="J. Gettys">
3606      <organization>W3C</organization>
3607      <address><email>jg@w3.org</email></address>
3608    </author>
3609    <author initials="J." surname="Mogul" fullname="J. Mogul">
3610      <organization>Compaq Computer Corporation</organization>
3611      <address><email>mogul@wrl.dec.com</email></address>
3612    </author>
3613    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3614      <organization>MIT Laboratory for Computer Science</organization>
3615      <address><email>frystyk@w3.org</email></address>
3616    </author>
3617    <author initials="L." surname="Masinter" fullname="L. Masinter">
3618      <organization>Xerox Corporation</organization>
3619      <address><email>masinter@parc.xerox.com</email></address>
3620    </author>
3621    <author initials="P." surname="Leach" fullname="P. Leach">
3622      <organization>Microsoft Corporation</organization>
3623      <address><email>paulle@microsoft.com</email></address>
3624    </author>
3625    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3626      <organization>W3C</organization>
3627      <address><email>timbl@w3.org</email></address>
3628    </author>
3629    <date month="June" year="1999"/>
3630  </front>
3631  <seriesInfo name="RFC" value="2616"/>
3632</reference>
3633
3634<reference anchor="RFC2818">
3635  <front>
3636    <title>HTTP Over TLS</title>
3637    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
3638      <organization>RTFM, Inc.</organization>
3639      <address><email>ekr@rtfm.com</email></address>
3640    </author>
3641    <date year="2000" month="May"/>
3642  </front>
3643  <seriesInfo name="RFC" value="2818"/>
3644</reference>
3645
3646<reference anchor="RFC2965">
3647  <front>
3648    <title>HTTP State Management Mechanism</title>
3649    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
3650      <organization>Bell Laboratories, Lucent Technologies</organization>
3651      <address><email>dmk@bell-labs.com</email></address>
3652    </author>
3653    <author initials="L." surname="Montulli" fullname="Lou Montulli">
3654      <organization>Epinions.com, Inc.</organization>
3655      <address><email>lou@montulli.org</email></address>
3656    </author>
3657    <date year="2000" month="October"/>
3658  </front>
3659  <seriesInfo name="RFC" value="2965"/>
3660</reference>
3661
3662<reference anchor="RFC3864">
3663  <front>
3664    <title>Registration Procedures for Message Header Fields</title>
3665    <author initials="G." surname="Klyne" fullname="G. Klyne">
3666      <organization>Nine by Nine</organization>
3667      <address><email>GK-IETF@ninebynine.org</email></address>
3668    </author>
3669    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
3670      <organization>BEA Systems</organization>
3671      <address><email>mnot@pobox.com</email></address>
3672    </author>
3673    <author initials="J." surname="Mogul" fullname="J. Mogul">
3674      <organization>HP Labs</organization>
3675      <address><email>JeffMogul@acm.org</email></address>
3676    </author>
3677    <date year="2004" month="September"/>
3678  </front>
3679  <seriesInfo name="BCP" value="90"/>
3680  <seriesInfo name="RFC" value="3864"/>
3681</reference>
3682
3683<reference anchor="RFC4288">
3684  <front>
3685    <title>Media Type Specifications and Registration Procedures</title>
3686    <author initials="N." surname="Freed" fullname="N. Freed">
3687      <organization>Sun Microsystems</organization>
3688      <address>
3689        <email>ned.freed@mrochek.com</email>
3690      </address>
3691    </author>
3692    <author initials="J." surname="Klensin" fullname="J. Klensin">
3693      <organization/>
3694      <address>
3695        <email>klensin+ietf@jck.com</email>
3696      </address>
3697    </author>
3698    <date year="2005" month="December"/>
3699  </front>
3700  <seriesInfo name="BCP" value="13"/>
3701  <seriesInfo name="RFC" value="4288"/>
3702</reference>
3703
3704<reference anchor="RFC4395">
3705  <front>
3706    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3707    <author initials="T." surname="Hansen" fullname="T. Hansen">
3708      <organization>AT&amp;T Laboratories</organization>
3709      <address>
3710        <email>tony+urireg@maillennium.att.com</email>
3711      </address>
3712    </author>
3713    <author initials="T." surname="Hardie" fullname="T. Hardie">
3714      <organization>Qualcomm, Inc.</organization>
3715      <address>
3716        <email>hardie@qualcomm.com</email>
3717      </address>
3718    </author>
3719    <author initials="L." surname="Masinter" fullname="L. Masinter">
3720      <organization>Adobe Systems</organization>
3721      <address>
3722        <email>LMM@acm.org</email>
3723      </address>
3724    </author>
3725    <date year="2006" month="February"/>
3726  </front>
3727  <seriesInfo name="BCP" value="115"/>
3728  <seriesInfo name="RFC" value="4395"/>
3729</reference>
3730
3731<reference anchor="RFC5322">
3732  <front>
3733    <title>Internet Message Format</title>
3734    <author initials="P." surname="Resnick" fullname="P. Resnick">
3735      <organization>Qualcomm Incorporated</organization>
3736    </author>
3737    <date year="2008" month="October"/>
3738  </front> 
3739  <seriesInfo name="RFC" value="5322"/>
3740</reference>
3741
3742<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3743  <front>
3744    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3745    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3746      <organization/>
3747    </author>
3748    <date year="2001" month="November"/>
3749  </front>
3750  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3751</reference>
3752
3753<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3754  <front>
3755  <title>Analysis of HTTP Performance Problems</title>
3756  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3757    <organization/>
3758  </author>
3759  <date/>
3760  </front>
3761</reference>
3762
3763<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3764  <front>
3765  <title>Analysis of HTTP Performance</title>
3766  <author initials="J." surname="Touch" fullname="Joe Touch">
3767    <organization>USC/Information Sciences Institute</organization>
3768    <address><email>touch@isi.edu</email></address>
3769  </author>
3770  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3771    <organization>USC/Information Sciences Institute</organization>
3772    <address><email>johnh@isi.edu</email></address>
3773  </author>
3774  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3775    <organization>USC/Information Sciences Institute</organization>
3776    <address><email>katia@isi.edu</email></address>
3777  </author>
3778  <date year="1998" month="Aug"/>
3779  </front>
3780  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3781  <annotation>(original report dated Aug. 1996)</annotation>
3782</reference>
3783
3784</references>
3785
3786
3787<section title="Tolerant Applications" anchor="tolerant.applications">
3788<t>
3789   Although this document specifies the requirements for the generation
3790   of HTTP/1.1 messages, not all applications will be correct in their
3791   implementation. We therefore recommend that operational applications
3792   be tolerant of deviations whenever those deviations can be
3793   interpreted unambiguously.
3794</t>
3795<t>
3796   Clients SHOULD be tolerant in parsing the Status-Line and servers
3797   tolerant when parsing the Request-Line. In particular, they SHOULD
3798   accept any amount of WSP characters between fields, even though
3799   only a single SP is required.
3800</t>
3801<t>
3802   The line terminator for message-header fields is the sequence CRLF.
3803   However, we recommend that applications, when parsing such headers,
3804   recognize a single LF as a line terminator and ignore the leading CR.
3805</t>
3806<t>
3807   The character set of an entity-body SHOULD be labeled as the lowest
3808   common denominator of the character codes used within that body, with
3809   the exception that not labeling the entity is preferred over labeling
3810   the entity with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
3811</t>
3812<t>
3813   Additional rules for requirements on parsing and encoding of dates
3814   and other potential problems with date encodings include:
3815</t>
3816<t>
3817  <list style="symbols">
3818     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
3819        which appears to be more than 50 years in the future is in fact
3820        in the past (this helps solve the "year 2000" problem).</t>
3821
3822     <t>An HTTP/1.1 implementation MAY internally represent a parsed
3823        Expires date as earlier than the proper value, but MUST NOT
3824        internally represent a parsed Expires date as later than the
3825        proper value.</t>
3826
3827     <t>All expiration-related calculations MUST be done in GMT. The
3828        local time zone MUST NOT influence the calculation or comparison
3829        of an age or expiration time.</t>
3830
3831     <t>If an HTTP header incorrectly carries a date value with a time
3832        zone other than GMT, it MUST be converted into GMT using the
3833        most conservative possible conversion.</t>
3834  </list>
3835</t>
3836</section>
3837
3838<section title="Compatibility with Previous Versions" anchor="compatibility">
3839<t>
3840   HTTP has been in use by the World-Wide Web global information initiative
3841   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3842   was a simple protocol for hypertext data transfer across the Internet
3843   with only a single method and no metadata.
3844   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3845   methods and MIME-like messaging that could include metadata about the data
3846   transferred and modifiers on the request/response semantics. However,
3847   HTTP/1.0 did not sufficiently take into consideration the effects of
3848   hierarchical proxies, caching, the need for persistent connections, or
3849   name-based virtual hosts. The proliferation of incompletely-implemented
3850   applications calling themselves "HTTP/1.0" further necessitated a
3851   protocol version change in order for two communicating applications
3852   to determine each other's true capabilities.
3853</t>
3854<t>
3855   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3856   requirements that enable reliable implementations, adding only
3857   those new features that will either be safely ignored by an HTTP/1.0
3858   recipient or only sent when communicating with a party advertising
3859   compliance with HTTP/1.1.
3860</t>
3861<t>
3862   It is beyond the scope of a protocol specification to mandate
3863   compliance with previous versions. HTTP/1.1 was deliberately
3864   designed, however, to make supporting previous versions easy. It is
3865   worth noting that, at the time of composing this specification
3866   (1996), we would expect commercial HTTP/1.1 servers to:
3867  <list style="symbols">
3868     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3869        1.1 requests;</t>
3870
3871     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3872        1.1;</t>
3873
3874     <t>respond appropriately with a message in the same major version
3875        used by the client.</t>
3876  </list>
3877</t>
3878<t>
3879   And we would expect HTTP/1.1 clients to:
3880  <list style="symbols">
3881     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3882        responses;</t>
3883
3884     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3885        1.1.</t>
3886  </list>
3887</t>
3888<t>
3889   For most implementations of HTTP/1.0, each connection is established
3890   by the client prior to the request and closed by the server after
3891   sending the response. Some implementations implement the Keep-Alive
3892   version of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
3893</t>
3894
3895<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3896<t>
3897   This section summarizes major differences between versions HTTP/1.0
3898   and HTTP/1.1.
3899</t>
3900
3901<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">
3902<t>
3903   The requirements that clients and servers support the Host request-header,
3904   report an error if the Host request-header (<xref target="header.host"/>) is
3905   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3906   are among the most important changes defined by this
3907   specification.
3908</t>
3909<t>
3910   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3911   addresses and servers; there was no other established mechanism for
3912   distinguishing the intended server of a request than the IP address
3913   to which that request was directed. The changes outlined above will
3914   allow the Internet, once older HTTP clients are no longer common, to
3915   support multiple Web sites from a single IP address, greatly
3916   simplifying large operational Web servers, where allocation of many
3917   IP addresses to a single host has created serious problems. The
3918   Internet will also be able to recover the IP addresses that have been
3919   allocated for the sole purpose of allowing special-purpose domain
3920   names to be used in root-level HTTP URLs. Given the rate of growth of
3921   the Web, and the number of servers already deployed, it is extremely
3922   important that all implementations of HTTP (including updates to
3923   existing HTTP/1.0 applications) correctly implement these
3924   requirements:
3925  <list style="symbols">
3926     <t>Both clients and servers MUST support the Host request-header.</t>
3927
3928     <t>A client that sends an HTTP/1.1 request MUST send a Host header.</t>
3929
3930     <t>Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
3931        request does not include a Host request-header.</t>
3932
3933     <t>Servers MUST accept absolute URIs.</t>
3934  </list>
3935</t>
3936</section>
3937</section>
3938
3939<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3940<t>
3941   Some clients and servers might wish to be compatible with some
3942   previous implementations of persistent connections in HTTP/1.0
3943   clients and servers. Persistent connections in HTTP/1.0 are
3944   explicitly negotiated as they are not the default behavior. HTTP/1.0
3945   experimental implementations of persistent connections are faulty,
3946   and the new facilities in HTTP/1.1 are designed to rectify these
3947   problems. The problem was that some existing 1.0 clients may be
3948   sending Keep-Alive to a proxy server that doesn't understand
3949   Connection, which would then erroneously forward it to the next
3950   inbound server, which would establish the Keep-Alive connection and
3951   result in a hung HTTP/1.0 proxy waiting for the close on the
3952   response. The result is that HTTP/1.0 clients must be prevented from
3953   using Keep-Alive when talking to proxies.
3954</t>
3955<t>
3956   However, talking to proxies is the most important use of persistent
3957   connections, so that prohibition is clearly unacceptable. Therefore,
3958   we need some other mechanism for indicating a persistent connection
3959   is desired, which is safe to use even when talking to an old proxy
3960   that ignores Connection. Persistent connections are the default for
3961   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
3962   declaring non-persistence. See <xref target="header.connection"/>.
3963</t>
3964<t>
3965   The original HTTP/1.0 form of persistent connections (the Connection:
3966   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
3967</t>
3968</section>
3969
3970<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
3971<t>
3972   This specification has been carefully audited to correct and
3973   disambiguate key word usage; RFC 2068 had many problems in respect to
3974   the conventions laid out in <xref target="RFC2119"/>.
3975</t>
3976<t>
3977   Transfer-coding and message lengths all interact in ways that
3978   required fixing exactly when chunked encoding is used (to allow for
3979   transfer encoding that may not be self delimiting); it was important
3980   to straighten out exactly how message lengths are computed. (Sections
3981   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
3982   <xref target="header.content-length" format="counter"/>,
3983   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
3984</t>
3985<t>
3986   The use and interpretation of HTTP version numbers has been clarified
3987   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
3988   version they support to deal with problems discovered in HTTP/1.0
3989   implementations (<xref target="http.version"/>)
3990</t>
3991<t>
3992   Quality Values of zero should indicate that "I don't want something"
3993   to allow clients to refuse a representation. (<xref target="quality.values"/>)
3994</t>
3995<t>
3996   Transfer-coding had significant problems, particularly with
3997   interactions with chunked encoding. The solution is that transfer-codings
3998   become as full fledged as content-codings. This involves
3999   adding an IANA registry for transfer-codings (separate from content
4000   codings), a new header field (TE) and enabling trailer headers in the
4001   future. Transfer encoding is a major performance benefit, so it was
4002   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4003   interoperability problem that could have occurred due to interactions
4004   between authentication trailers, chunked encoding and HTTP/1.0
4005   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4006   and <xref target="header.te" format="counter"/>)
4007</t>
4008</section>
4009
4010<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4011<t>
4012  Empty list elements in list productions have been deprecated.
4013  (<xref target="notation.abnf"/>)
4014</t>
4015<t>
4016  Rules about implicit linear whitespace between certain grammar productions
4017  have been removed; now it's only allowed when specifically pointed out
4018  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4019  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4020  Non-ASCII content in header fields and reason phrase has been obsoleted and
4021  made opaque (the TEXT rule was removed)
4022  (<xref target="basic.rules"/>)
4023</t>
4024<t>
4025  Clarify that HTTP-Version is case sensitive.
4026  (<xref target="http.version"/>)
4027</t>
4028<t>
4029  Remove reference to non-existant identity transfer-coding value tokens.
4030  (Sections <xref format="counter" target="transfer.codings"/> and
4031  <xref format="counter" target="message.length"/>)
4032</t>
4033<t>
4034  Clarification that the chunk length does not include
4035  the count of the octets in the chunk header and trailer.
4036  (<xref target="chunked.transfer.encoding"/>)
4037</t>
4038<t>
4039  Require that invalid whitespace around field-names be rejected.
4040  (<xref target="message.headers"/>)
4041</t>
4042<t>
4043  Update use of abs_path production from RFC1808 to the path-absolute + query
4044  components of RFC3986.
4045  (<xref target="request-target"/>)
4046</t>
4047<t>
4048  Clarify exactly when close connection options must be sent.
4049  (<xref target="header.connection"/>)
4050</t>
4051</section>
4052</section>
4053
4054<section title="Terminology" anchor="terminology">
4055<t>
4056   This specification uses a number of terms to refer to the roles
4057   played by participants in, and objects of, the HTTP communication.
4058</t>
4059<t>
4060  <iref item="cache"/>
4061  <?rfc needLines="4"?>cache
4062  <list>
4063    <t>
4064      A program's local store of response messages and the subsystem
4065      that controls its message storage, retrieval, and deletion. A
4066      cache stores cacheable responses in order to reduce the response
4067      time and network bandwidth consumption on future, equivalent
4068      requests. Any client or server may include a cache, though a cache
4069      cannot be used by a server that is acting as a tunnel.
4070    </t>
4071  </list>
4072</t>
4073<t>
4074  <iref item="cacheable"/>
4075  <?rfc needLines="4"?>cacheable
4076  <list>
4077    <t>
4078      A response is cacheable if a cache is allowed to store a copy of
4079      the response message for use in answering subsequent requests. The
4080      rules for determining the cacheability of HTTP responses are
4081      defined in Section 1 of <xref target="Part6"/>. Even if a resource is cacheable, there may
4082      be additional constraints on whether a cache can use the cached
4083      copy for a particular request.
4084    </t>
4085  </list>
4086</t>
4087<t>
4088  <iref item="client"/>
4089  <?rfc needLines="4"?>client
4090  <list>
4091    <t>
4092      A program that establishes connections for the purpose of sending
4093      requests.
4094    </t>
4095  </list>
4096</t>
4097<t>
4098  <iref item="connection"/>
4099  <?rfc needLines="4"?>connection
4100  <list>
4101    <t>
4102      A transport layer virtual circuit established between two programs
4103      for the purpose of communication.
4104    </t>
4105  </list>
4106</t>
4107<t>
4108  <iref item="content negotiation"/>
4109  <?rfc needLines="4"?>content negotiation
4110  <list>
4111    <t>
4112      The mechanism for selecting the appropriate representation when
4113      servicing a request, as described in Section 4 of <xref target="Part3"/>. The
4114      representation of entities in any response can be negotiated
4115      (including error responses).
4116    </t>
4117  </list>
4118</t>
4119<t>
4120  <iref item="entity"/>
4121  <?rfc needLines="4"?>entity
4122  <list>
4123    <t>
4124      The information transferred as the payload of a request or
4125      response. An entity consists of metainformation in the form of
4126      entity-header fields and content in the form of an entity-body, as
4127      described in Section 3 of <xref target="Part3"/>.
4128    </t>
4129  </list>
4130</t>
4131<t>
4132  <iref item="gateway"/>
4133  <?rfc needLines="4"?>gateway
4134  <list>
4135    <t>
4136      A server which acts as an intermediary for some other server.
4137      Unlike a proxy, a gateway receives requests as if it were the
4138      origin server for the requested resource; the requesting client
4139      may not be aware that it is communicating with a gateway.
4140    </t>
4141  </list>
4142</t>
4143<t>
4144  <iref item="inbound"/>
4145  <iref item="outbound"/>
4146  <?rfc needLines="4"?>inbound/outbound
4147  <list>
4148    <t>
4149      Inbound and outbound refer to the request and response paths for
4150      messages: "inbound" means "traveling toward the origin server",
4151      and "outbound" means "traveling toward the user agent"
4152    </t>
4153  </list>
4154</t>
4155<t>
4156  <iref item="message"/>
4157  <?rfc needLines="4"?>message
4158  <list>
4159    <t>
4160      The basic unit of HTTP communication, consisting of a structured
4161      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4162      transmitted via the connection.
4163    </t>
4164  </list>
4165</t>
4166<t>
4167  <iref item="origin server"/>
4168  <?rfc needLines="4"?>origin server
4169  <list>
4170    <t>
4171      The server on which a given resource resides or is to be created.
4172    </t>
4173  </list>
4174</t>
4175<t>
4176  <iref item="proxy"/>
4177  <?rfc needLines="4"?>proxy
4178  <list>
4179    <t>
4180      An intermediary program which acts as both a server and a client
4181      for the purpose of making requests on behalf of other clients.
4182      Requests are serviced internally or by passing them on, with
4183      possible translation, to other servers. A proxy MUST implement
4184      both the client and server requirements of this specification. A
4185      "transparent proxy" is a proxy that does not modify the request or
4186      response beyond what is required for proxy authentication and
4187      identification. A "non-transparent proxy" is a proxy that modifies
4188      the request or response in order to provide some added service to
4189      the user agent, such as group annotation services, media type
4190      transformation, protocol reduction, or anonymity filtering. Except
4191      where either transparent or non-transparent behavior is explicitly
4192      stated, the HTTP proxy requirements apply to both types of
4193      proxies.
4194    </t>
4195  </list>
4196</t>
4197<t>
4198  <iref item="request"/>
4199  <?rfc needLines="4"?>request
4200  <list>
4201    <t>
4202      An HTTP request message, as defined in <xref target="request"/>.
4203    </t>
4204  </list>
4205</t>
4206<t>
4207  <iref item="resource"/>
4208  <?rfc needLines="4"?>resource
4209  <list>
4210    <t>
4211      A network data object or service that can be identified by a URI,
4212      as defined in <xref target="uri"/>. Resources may be available in multiple
4213      representations (e.g. multiple languages, data formats, size, and
4214      resolutions) or vary in other ways.
4215    </t>
4216  </list>
4217</t>
4218<t>
4219  <iref item="response"/>
4220  <?rfc needLines="4"?>response
4221  <list>
4222    <t>
4223      An HTTP response message, as defined in <xref target="response"/>.
4224    </t>
4225  </list>
4226</t>
4227<t>
4228  <iref item="representation"/>
4229  <?rfc needLines="4"?>representation
4230  <list>
4231    <t>
4232      An entity included with a response that is subject to content
4233      negotiation, as described in Section 4 of <xref target="Part3"/>. There may exist multiple
4234      representations associated with a particular response status.
4235    </t>
4236  </list>
4237</t>
4238<t>
4239  <iref item="server"/>
4240  <?rfc needLines="4"?>server
4241  <list>
4242    <t>
4243      An application program that accepts connections in order to
4244      service requests by sending back responses. Any given program may
4245      be capable of being both a client and a server; our use of these
4246      terms refers only to the role being performed by the program for a
4247      particular connection, rather than to the program's capabilities
4248      in general. Likewise, any server may act as an origin server,
4249      proxy, gateway, or tunnel, switching behavior based on the nature
4250      of each request.
4251    </t>
4252  </list>
4253</t>
4254<t>
4255  <iref item="tunnel"/>
4256  <?rfc needLines="4"?>tunnel
4257  <list>
4258    <t>
4259      An intermediary program which is acting as a blind relay between
4260      two connections. Once active, a tunnel is not considered a party
4261      to the HTTP communication, though the tunnel may have been
4262      initiated by an HTTP request. The tunnel ceases to exist when both
4263      ends of the relayed connections are closed.
4264    </t>
4265  </list>
4266</t>
4267<t>
4268  <iref item="upstream"/>
4269  <iref item="downstream"/>
4270  <?rfc needLines="4"?>upstream/downstream
4271  <list>
4272    <t>
4273      Upstream and downstream describe the flow of a message: all
4274      messages flow from upstream to downstream.
4275    </t>
4276  </list>
4277</t>
4278<t>
4279  <iref item="user agent"/>
4280  <?rfc needLines="4"?>user agent
4281  <list>
4282    <t>
4283      The client which initiates a request. These are often browsers,
4284      editors, spiders (web-traversing robots), or other end user tools.
4285    </t>
4286  </list>
4287</t>
4288<t>
4289  <iref item="variant"/>
4290  <?rfc needLines="4"?>variant
4291  <list>
4292    <t>
4293      A resource may have one, or more than one, representation(s)
4294      associated with it at any given instant. Each of these
4295      representations is termed a `variant'.  Use of the term `variant'
4296      does not necessarily imply that the resource is subject to content
4297      negotiation.
4298    </t>
4299  </list>
4300</t>
4301</section>
4302
4303<section title="Collected ABNF" anchor="collected.abnf">
4304<figure>
4305<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
4306BWS = OWS
4307
4308Cache-Control = <Cache-Control, defined in [Part6], Section 3.4>
4309Chunked-Body = *chunk last-chunk trailer-part CRLF
4310Connection = "Connection:" OWS Connection-v
4311Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
4312 connection-token ] )
4313Content-Length = "Content-Length:" OWS 1*Content-Length-v
4314Content-Length-v = 1*DIGIT
4315
4316Date = "Date:" OWS Date-v
4317Date-v = HTTP-date
4318
4319GMT = %x47.4D.54
4320
4321HTTP-Prot-Name = %x48.54.54.50
4322HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4323HTTP-date = rfc1123-date / obsolete-date
4324HTTP-message = Request / Response
4325Host = "Host:" OWS Host-v
4326Host-v = uri-host [ ":" port ]
4327
4328Method = token
4329
4330OWS = *( [ obs-fold ] WSP )
4331
4332Pragma = <Pragma, defined in [Part6], Section 3.4>
4333
4334RWS = 1*( [ obs-fold ] WSP )
4335Reason-Phrase = *( WSP / VCHAR / obs-text )
4336Request = Request-Line *( ( general-header / request-header /
4337 entity-header ) CRLF ) CRLF [ message-body ]
4338Request-Line = Method SP request-target SP HTTP-Version CRLF
4339Response = Status-Line *( ( general-header / response-header /
4340 entity-header ) CRLF ) CRLF [ message-body ]
4341
4342Status-Code = 3DIGIT
4343Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4344
4345TE = "TE:" OWS TE-v
4346TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4347Trailer = "Trailer:" OWS Trailer-v
4348Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4349Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
4350Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4351 transfer-coding ] )
4352
4353URI = <URI, defined in [RFC3986], Section 3>
4354URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
4355Upgrade = "Upgrade:" OWS Upgrade-v
4356Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )
4357
4358Via = "Via:" OWS Via-v
4359Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4360 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4361 ] )
4362
4363Warning = <Warning, defined in [Part6], Section 3.6>
4364
4365absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
4366asctime-date = wkday SP date3 SP time SP 4DIGIT
4367attribute = token
4368authority = <authority, defined in [RFC3986], Section 3.2>
4369
4370chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4371chunk-data = 1*OCTET
4372chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4373chunk-ext-name = token
4374chunk-ext-val = token / quoted-string
4375chunk-size = 1*HEXDIG
4376comment = "(" *( ctext / quoted-pair / comment ) ")"
4377connection-token = token
4378ctext = *( OWS / %x21-27 / %x2A-7E / obs-text )
4379
4380date1 = 2DIGIT SP month SP 4DIGIT
4381date2 = 2DIGIT "-" month "-" 2DIGIT
4382date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
4383
4384entity-body = <entity-body, defined in [Part3], Section 3.2>
4385entity-header = <entity-header, defined in [Part3], Section 3.1>
4386
4387field-content = *( WSP / VCHAR / obs-text )
4388field-name = token
4389field-value = *( field-content / OWS )
4390fragment = <fragment, defined in [RFC3986], Section 3.5>
4391
4392general-header = Cache-Control / Connection / Date / Pragma / Trailer
4393 / Transfer-Encoding / Upgrade / Via / Warning
4394generic-message = start-line *( message-header CRLF ) CRLF [
4395 message-body ]
4396
4397http-URI = "http://" authority path-abempty [ "?" query ]
4398
4399l-Fri = %x46.72.69.64.61.79
4400l-Mon = %x4D.6F.6E.64.61.79
4401l-Sat = %x53.61.74.75.72.64.61.79
4402l-Sun = %x53.75.6E.64.61.79
4403l-Thu = %x54.68.75.72.73.64.61.79
4404l-Tue = %x54.75.65.73.64.61.79
4405l-Wed = %x57.65.64.6E.65.73.64.61.79
4406last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
4407
4408message-body = entity-body /
4409 <entity-body encoded as per Transfer-Encoding>
4410message-header = field-name ":" OWS [ field-value ] OWS
4411month = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4412 / s-Sep / s-Oct / s-Nov / s-Dec
4413
4414obs-fold = CRLF
4415obs-text = %x80-FF
4416obsolete-date = rfc850-date / asctime-date
4417
4418parameter = attribute BWS "=" BWS value
4419partial-URI = relative-part [ "?" query ]
4420path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
4421path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
4422port = <port, defined in [RFC3986], Section 3.2.3>
4423product = token [ "/" product-version ]
4424product-version = token
4425protocol-name = token
4426protocol-version = token
4427pseudonym = token
4428
4429qdtext = *( OWS / "!" / %x23-5B / %x5D-7E / obs-text )
4430query = <query, defined in [RFC3986], Section 3.4>
4431quoted-pair = "\" quoted-text
4432quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4433quoted-text = %x01-09 / %x0B-0C / %x0E-FF
4434qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4435
4436received-by = ( uri-host [ ":" port ] ) / pseudonym
4437received-protocol = [ protocol-name "/" ] protocol-version
4438relative-part = <relative-part, defined in [RFC3986], Section 4.2>
4439request-header = <request-header, defined in [Part2], Section 3>
4440request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4441 / authority
4442response-header = <response-header, defined in [Part2], Section 5>
4443rfc1123-date = wkday "," SP date1 SP time SP GMT
4444rfc850-date = weekday "," SP date2 SP time SP GMT
4445
4446s-Apr = %x41.70.72
4447s-Aug = %x41.75.67
4448s-Dec = %x44.65.63
4449s-Feb = %x46.65.62
4450s-Fri = %x46.72.69
4451s-Jan = %x4A.61.6E
4452s-Jul = %x4A.75.6C
4453s-Jun = %x4A.75.6E
4454s-Mar = %x4D.61.72
4455s-May = %x4D.61.79
4456s-Mon = %x4D.6F.6E
4457s-Nov = %x4E.6F.76
4458s-Oct = %x4F.63.74
4459s-Sat = %x53.61.74
4460s-Sep = %x53.65.70
4461s-Sun = %x53.75.6E
4462s-Thu = %x54.68.75
4463s-Tue = %x54.75.65
4464s-Wed = %x57.65.64
4465start-line = Request-Line / Status-Line
4466
4467t-codings = "trailers" / ( transfer-extension [ te-params ] )
4468tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
4469 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4470te-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4471te-params = OWS ";" OWS "q=" qvalue *te-ext
4472time = 2DIGIT ":" 2DIGIT ":" 2DIGIT
4473token = 1*tchar
4474trailer-part = *( entity-header CRLF )
4475transfer-coding = "chunked" / transfer-extension
4476transfer-extension = token *( OWS ";" OWS parameter )
4477
4478uri-host = <host, defined in [RFC3986], Section 3.2.2>
4479
4480value = token / quoted-string
4481
4482weekday = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4483wkday = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4484
4485
4486]]></artwork>
4487</figure>
4488<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
4489; Chunked-Body defined but not used
4490; Content-Length defined but not used
4491; HTTP-message defined but not used
4492; Host defined but not used
4493; TE defined but not used
4494; URI defined but not used
4495; URI-reference defined but not used
4496; fragment defined but not used
4497; generic-message defined but not used
4498; http-URI defined but not used
4499; partial-URI defined but not used
4500]]></artwork></figure></section>
4501
4502<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4503
4504<section title="Since RFC2616">
4505<t>
4506  Extracted relevant partitions from <xref target="RFC2616"/>.
4507</t>
4508</section>
4509
4510<section title="Since draft-ietf-httpbis-p1-messaging-00">
4511<t>
4512  Closed issues:
4513  <list style="symbols"> 
4514    <t>
4515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4516      "HTTP Version should be case sensitive"
4517      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4518    </t>
4519    <t>
4520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4521      "'unsafe' characters"
4522      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4523    </t>
4524    <t>
4525      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4526      "Chunk Size Definition"
4527      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4528    </t>
4529    <t>
4530      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4531      "Message Length"
4532      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4533    </t>
4534    <t>
4535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4536      "Media Type Registrations"
4537      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4538    </t>
4539    <t>
4540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4541      "URI includes query"
4542      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4543    </t>
4544    <t>
4545      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4546      "No close on 1xx responses"
4547      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4548    </t>
4549    <t>
4550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4551      "Remove 'identity' token references"
4552      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4553    </t>
4554    <t>
4555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4556      "Import query BNF"
4557    </t>
4558    <t>
4559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4560      "qdtext BNF"
4561    </t>
4562    <t>
4563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4564      "Normative and Informative references"
4565    </t>
4566    <t>
4567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4568      "RFC2606 Compliance"
4569    </t>
4570    <t>
4571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4572      "RFC977 reference"
4573    </t>
4574    <t>
4575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4576      "RFC1700 references"
4577    </t>
4578    <t>
4579      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4580      "inconsistency in date format explanation"
4581    </t>
4582    <t>
4583      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4584      "Date reference typo"
4585    </t>
4586    <t>
4587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4588      "Informative references"
4589    </t>
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4592      "ISO-8859-1 Reference"
4593    </t>
4594    <t>
4595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4596      "Normative up-to-date references"
4597    </t>
4598  </list>
4599</t>
4600<t>
4601  Other changes:
4602  <list style="symbols"> 
4603    <t>
4604      Update media type registrations to use RFC4288 template.
4605    </t>
4606    <t>
4607      Use names of RFC4234 core rules DQUOTE and WSP,
4608      fix broken ABNF for chunk-data
4609      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4610    </t>
4611  </list>
4612</t>
4613</section>
4614
4615<section title="Since draft-ietf-httpbis-p1-messaging-01">
4616<t>
4617  Closed issues:
4618  <list style="symbols"> 
4619    <t>
4620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4621      "Bodies on GET (and other) requests"
4622    </t>
4623    <t>
4624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4625      "Updating to RFC4288"
4626    </t>
4627    <t>
4628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4629      "Status Code and Reason Phrase"
4630    </t>
4631    <t>
4632      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4633      "rel_path not used"
4634    </t>
4635  </list>
4636</t>
4637<t>
4638  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4639  <list style="symbols"> 
4640    <t>
4641      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
4642      "trailer-part").
4643    </t>
4644    <t>
4645      Avoid underscore character in rule names ("http_URL" -&gt;
4646      "http-URL", "abs_path" -&gt; "path-absolute").
4647    </t>
4648    <t>
4649      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4650      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4651      have to be updated when switching over to RFC3986.
4652    </t>
4653    <t>
4654      Synchronize core rules with RFC5234.
4655    </t>
4656    <t>
4657      Get rid of prose rules that span multiple lines.
4658    </t>
4659    <t>
4660      Get rid of unused rules LOALPHA and UPALPHA.
4661    </t>
4662    <t>
4663      Move "Product Tokens" section (back) into Part 1, as "token" is used
4664      in the definition of the Upgrade header.
4665    </t>
4666    <t>
4667      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4668    </t>
4669    <t>
4670      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4671    </t>
4672  </list>
4673</t>
4674</section>
4675
4676<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4677<t>
4678  Closed issues:
4679  <list style="symbols"> 
4680    <t>
4681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4682      "HTTP-date vs. rfc1123-date"
4683    </t>
4684    <t>
4685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4686      "WS in quoted-pair"
4687    </t>
4688  </list>
4689</t>
4690<t>
4691  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4692  <list style="symbols"> 
4693    <t>
4694      Reference RFC 3984, and update header registrations for headers defined
4695      in this document.
4696    </t>
4697  </list>
4698</t>
4699<t>
4700  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4701  <list style="symbols"> 
4702    <t>
4703      Replace string literals when the string really is case-sensitive (HTTP-Version).
4704    </t>
4705  </list>
4706</t>
4707</section>
4708
4709<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4710<t>
4711  Closed issues:
4712  <list style="symbols"> 
4713    <t>
4714      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4715      "Connection closing"
4716    </t>
4717    <t>
4718      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4719      "Move registrations and registry information to IANA Considerations"
4720    </t>
4721    <t>
4722      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4723      "need new URL for PAD1995 reference"
4724    </t>
4725    <t>
4726      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4727      "IANA Considerations: update HTTP URI scheme registration"
4728    </t>
4729    <t>
4730      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4731      "Cite HTTPS URI scheme definition"
4732    </t>
4733    <t>
4734      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4735      "List-type headers vs Set-Cookie"
4736    </t>
4737  </list>
4738</t>
4739<t>
4740  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4741  <list style="symbols"> 
4742    <t>
4743      Replace string literals when the string really is case-sensitive (HTTP-Date).
4744    </t>
4745    <t>
4746      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4747    </t>
4748  </list>
4749</t>
4750</section>
4751
4752<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4753<t>
4754  Closed issues:
4755  <list style="symbols"> 
4756    <t>
4757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4758      "Out-of-date reference for URIs"
4759    </t>
4760    <t>
4761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4762      "RFC 2822 is updated by RFC 5322"
4763    </t>
4764  </list>
4765</t>
4766<t>
4767  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4768  <list style="symbols"> 
4769    <t>
4770      Use "/" instead of "|" for alternatives.
4771    </t>
4772    <t>
4773      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4774    </t>
4775    <t>
4776      Only reference RFC 5234's core rules.
4777    </t>
4778    <t>
4779      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4780      whitespace ("OWS") and required whitespace ("RWS").
4781    </t>
4782    <t>
4783      Rewrite ABNFs to spell out whitespace rules, factor out
4784      header value format definitions.
4785    </t>
4786  </list>
4787</t>
4788</section>
4789
4790<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4791<t>
4792  Closed issues:
4793  <list style="symbols"> 
4794    <t>
4795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4796      "Header LWS"
4797    </t>
4798    <t>
4799      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4800      "Sort 1.3 Terminology"
4801    </t>
4802    <t>
4803      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4804      "RFC2047 encoded words"
4805    </t>
4806    <t>
4807      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4808      "Character Encodings in TEXT"
4809    </t>
4810    <t>
4811      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4812      "Line Folding"
4813    </t>
4814    <t>
4815      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4816      "OPTIONS * and proxies"
4817    </t>
4818    <t>
4819      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4820      "Reason-Phrase BNF"
4821    </t>
4822    <t>
4823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4824      "Use of TEXT"
4825    </t>
4826    <t>
4827      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4828      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4829    </t>
4830    <t>
4831      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4832      "RFC822 reference left in discussion of date formats"
4833    </t>
4834  </list>
4835</t>
4836<t>
4837  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4838  <list style="symbols"> 
4839    <t>
4840      Rewrite definition of list rules, deprecate empty list elements.
4841    </t>
4842    <t>
4843      Add appendix containing collected and expanded ABNF.
4844    </t>
4845  </list>
4846</t>
4847<t>
4848  Other changes:
4849  <list style="symbols"> 
4850    <t>
4851      Rewrite introduction; add mostly new Architecture Section.
4852    </t>
4853    <t>
4854      Move definition of quality values from Part 3 into Part 1;
4855      make TE request header grammar independent of accept-params (defined in Part 3).
4856    </t>
4857  </list>
4858</t>
4859</section>
4860
4861</section>
4862
4863</back>
4864</rfc>
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