source: draft-ietf-httpbis/latest/p3-payload.html @ 580

Last change on this file since 580 was 580, checked in by julian.reschke@…, 10 years ago

re-organize section on HTTP-date including ABNF, refer to RFC 5322 for semantics (related to #163)

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336       content: "INTERNET DRAFT"; 
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[573]339       content: "May 2009"; 
[52]340  } 
341  @top-center {
[120]342       content: "HTTP/1.1, Part 3"; 
[52]343  } 
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345       content: "Fielding, et al."; 
346  } 
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366</style><link rel="Contents" href="#rfc.toc">
367      <link rel="Author" href="#rfc.authors">
368      <link rel="Copyright" href="#rfc.copyright">
369      <link rel="Index" href="#rfc.index">
370      <link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
[424]371      <link rel="Chapter" title="2 Protocol Parameters" href="#rfc.section.2">
372      <link rel="Chapter" title="3 Entity" href="#rfc.section.3">
373      <link rel="Chapter" title="4 Content Negotiation" href="#rfc.section.4">
374      <link rel="Chapter" title="5 Header Field Definitions" href="#rfc.section.5">
375      <link rel="Chapter" title="6 IANA Considerations" href="#rfc.section.6">
376      <link rel="Chapter" title="7 Security Considerations" href="#rfc.section.7">
377      <link rel="Chapter" title="8 Acknowledgments" href="#rfc.section.8">
378      <link rel="Chapter" href="#rfc.section.9" title="9 References">
[52]379      <link rel="Appendix" title="A Differences Between HTTP Entities and RFC 2045 Entities" href="#rfc.section.A">
380      <link rel="Appendix" title="B Additional Features" href="#rfc.section.B">
[99]381      <link rel="Appendix" title="C Compatibility with Previous Versions" href="#rfc.section.C">
[421]382      <link rel="Appendix" title="D Collected ABNF" href="#rfc.section.D">
383      <link rel="Appendix" title="E Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.E">
[573]384      <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.432, 2009-04-09 13:16:17, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/">
[52]385      <link rel="schema.DC" href="http://purl.org/dc/elements/1.1/">
386      <meta name="DC.Creator" content="Fielding, R.">
387      <meta name="DC.Creator" content="Gettys, J.">
388      <meta name="DC.Creator" content="Mogul, J.">
389      <meta name="DC.Creator" content="Frystyk, H.">
390      <meta name="DC.Creator" content="Masinter, L.">
391      <meta name="DC.Creator" content="Leach, P.">
392      <meta name="DC.Creator" content="Berners-Lee, T.">
[95]393      <meta name="DC.Creator" content="Lafon, Y.">
394      <meta name="DC.Creator" content="Reschke, J. F.">
[52]395      <meta name="DC.Identifier" content="urn:ietf:id:draft-ietf-httpbis-p3-payload-latest">
[573]396      <meta name="DC.Date.Issued" scheme="ISO8601" content="2009-05">
[52]397      <meta name="DC.Relation.Replaces" content="urn:ietf:rfc:2616">
398      <meta name="DC.Description.Abstract" content="The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 3 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 3 defines HTTP message content, metadata, and content negotiation.">
399   </head>
400   <body>
401      <table summary="header information" class="header" border="0" cellpadding="1" cellspacing="1">
402         <tr>
[440]403            <td class="header left">HTTPbis Working Group</td>
[52]404            <td class="header right">R. Fielding, Editor</td>
405         </tr>
406         <tr>
407            <td class="header left">Internet Draft</td>
408            <td class="header right">Day Software</td>
409         </tr>
410         <tr>
411            <td class="header left">
412               &lt;draft-ietf-httpbis-p3-payload-latest&gt;
413               
414            </td>
415            <td class="header right">J. Gettys</td>
416         </tr>
417         <tr>
[150]418            <td class="header left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
[52]419            </td>
420            <td class="header right">One Laptop per Child</td>
421         </tr>
422         <tr>
423            <td class="header left">Intended status: Standards Track</td>
424            <td class="header right">J. Mogul</td>
425         </tr>
426         <tr>
[573]427            <td class="header left">Expires: November 2009</td>
[52]428            <td class="header right">HP</td>
429         </tr>
430         <tr>
431            <td class="header left"></td>
432            <td class="header right">H. Frystyk</td>
433         </tr>
434         <tr>
435            <td class="header left"></td>
436            <td class="header right">Microsoft</td>
437         </tr>
438         <tr>
439            <td class="header left"></td>
440            <td class="header right">L. Masinter</td>
441         </tr>
442         <tr>
443            <td class="header left"></td>
444            <td class="header right">Adobe Systems</td>
445         </tr>
446         <tr>
447            <td class="header left"></td>
448            <td class="header right">P. Leach</td>
449         </tr>
450         <tr>
451            <td class="header left"></td>
452            <td class="header right">Microsoft</td>
453         </tr>
454         <tr>
455            <td class="header left"></td>
456            <td class="header right">T. Berners-Lee</td>
457         </tr>
458         <tr>
459            <td class="header left"></td>
460            <td class="header right">W3C/MIT</td>
461         </tr>
462         <tr>
463            <td class="header left"></td>
[95]464            <td class="header right">Y. Lafon, Editor</td>
465         </tr>
466         <tr>
467            <td class="header left"></td>
468            <td class="header right">W3C</td>
469         </tr>
470         <tr>
471            <td class="header left"></td>
472            <td class="header right">J. F. Reschke, Editor</td>
473         </tr>
474         <tr>
475            <td class="header left"></td>
476            <td class="header right">greenbytes</td>
477         </tr>
478         <tr>
479            <td class="header left"></td>
[580]480            <td class="header right">May 10, 2009</td>
[52]481         </tr>
482      </table>
483      <p class="title">HTTP/1.1, part 3: Message Payload and Content Negotiation<br><span class="filename">draft-ietf-httpbis-p3-payload-latest</span></p>
484      <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1>
[446]485      <p>This Internet-Draft is submitted to IETF pursuant to, and in full conformance with, the provisions of BCP 78 and BCP 79. This
486         document may contain material from IETF Documents or IETF Contributions published or made publicly available before November
487         10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to
488         allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s)
489         controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative
490         works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate
491         it into languages other than English.
[52]492      </p>
493      <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note
494         that other groups may also distribute working documents as Internet-Drafts.
495      </p>
496      <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
497         documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
498         in progress”.
499      </p>
500      <p>The list of current Internet-Drafts can be accessed at &lt;<a href="http://www.ietf.org/ietf/1id-abstracts.txt">http://www.ietf.org/ietf/1id-abstracts.txt</a>&gt;.
501      </p>
502      <p>The list of Internet-Draft Shadow Directories can be accessed at &lt;<a href="http://www.ietf.org/shadow.html">http://www.ietf.org/shadow.html</a>&gt;.
503      </p>
[573]504      <p>This Internet-Draft will expire in November 2009.</p>
[446]505      <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
506      <p>Copyright © 2009 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
507      <p>This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date
508         of publication of this document (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>). Please review these documents carefully, as they describe your rights and restrictions with respect to this document.
509      </p>
[52]510      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> 
511      <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information
512         systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 3 of the
513         seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part
514         3 defines HTTP message content, metadata, and content negotiation.
515      </p> 
516      <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> 
517      <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org). The current issues
[324]518         list is at &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/report/11">http://tools.ietf.org/wg/httpbis/trac/report/11</a>&gt; and related documents (including fancy diffs) can be found at &lt;<a href="http://tools.ietf.org/wg/httpbis/">http://tools.ietf.org/wg/httpbis/</a>&gt;.
[153]519      </p> 
[547]520      <p>The changes in this draft are summarized in <a href="#changes.since.06" title="Since draft-ietf-httpbis-p3-payload-06">Appendix&nbsp;E.8</a>.
[52]521      </p> 
522      <hr class="noprint">
523      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
524      <ul class="toc">
[96]525         <li class="tocline0">1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul class="toc">
526               <li class="tocline1">1.1&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
[424]527               <li class="tocline1">1.2&nbsp;&nbsp;&nbsp;<a href="#notation">Syntax Notation</a><ul class="toc">
528                     <li class="tocline1">1.2.1&nbsp;&nbsp;&nbsp;<a href="#core.rules">Core Rules</a></li>
529                     <li class="tocline1">1.2.2&nbsp;&nbsp;&nbsp;<a href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></li>
530                  </ul>
531               </li>
[96]532            </ul>
533         </li>
[424]534         <li class="tocline0">2.&nbsp;&nbsp;&nbsp;<a href="#protocol.parameters">Protocol Parameters</a><ul class="toc">
535               <li class="tocline1">2.1&nbsp;&nbsp;&nbsp;<a href="#character.sets">Character Sets</a><ul class="toc">
536                     <li class="tocline1">2.1.1&nbsp;&nbsp;&nbsp;<a href="#missing.charset">Missing Charset</a></li>
[211]537                  </ul>
538               </li>
[424]539               <li class="tocline1">2.2&nbsp;&nbsp;&nbsp;<a href="#content.codings">Content Codings</a></li>
540               <li class="tocline1">2.3&nbsp;&nbsp;&nbsp;<a href="#media.types">Media Types</a><ul class="toc">
541                     <li class="tocline1">2.3.1&nbsp;&nbsp;&nbsp;<a href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></li>
542                     <li class="tocline1">2.3.2&nbsp;&nbsp;&nbsp;<a href="#multipart.types">Multipart Types</a></li>
[52]543                  </ul>
544               </li>
[457]545               <li class="tocline1">2.4&nbsp;&nbsp;&nbsp;<a href="#language.tags">Language Tags</a></li>
[52]546            </ul>
547         </li>
[424]548         <li class="tocline0">3.&nbsp;&nbsp;&nbsp;<a href="#entity">Entity</a><ul class="toc">
549               <li class="tocline1">3.1&nbsp;&nbsp;&nbsp;<a href="#entity.header.fields">Entity Header Fields</a></li>
550               <li class="tocline1">3.2&nbsp;&nbsp;&nbsp;<a href="#entity.body">Entity Body</a><ul class="toc">
551                     <li class="tocline1">3.2.1&nbsp;&nbsp;&nbsp;<a href="#type">Type</a></li>
552                     <li class="tocline1">3.2.2&nbsp;&nbsp;&nbsp;<a href="#entity.length">Entity Length</a></li>
[52]553                  </ul>
554               </li>
555            </ul>
556         </li>
[424]557         <li class="tocline0">4.&nbsp;&nbsp;&nbsp;<a href="#content.negotiation">Content Negotiation</a><ul class="toc">
558               <li class="tocline1">4.1&nbsp;&nbsp;&nbsp;<a href="#server-driven.negotiation">Server-driven Negotiation</a></li>
559               <li class="tocline1">4.2&nbsp;&nbsp;&nbsp;<a href="#agent-driven.negotiation">Agent-driven Negotiation</a></li>
560               <li class="tocline1">4.3&nbsp;&nbsp;&nbsp;<a href="#transparent.negotiation">Transparent Negotiation</a></li>
[52]561            </ul>
562         </li>
[424]563         <li class="tocline0">5.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul class="toc">
564               <li class="tocline1">5.1&nbsp;&nbsp;&nbsp;<a href="#header.accept">Accept</a></li>
565               <li class="tocline1">5.2&nbsp;&nbsp;&nbsp;<a href="#header.accept-charset">Accept-Charset</a></li>
566               <li class="tocline1">5.3&nbsp;&nbsp;&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></li>
567               <li class="tocline1">5.4&nbsp;&nbsp;&nbsp;<a href="#header.accept-language">Accept-Language</a></li>
568               <li class="tocline1">5.5&nbsp;&nbsp;&nbsp;<a href="#header.content-encoding">Content-Encoding</a></li>
569               <li class="tocline1">5.6&nbsp;&nbsp;&nbsp;<a href="#header.content-language">Content-Language</a></li>
570               <li class="tocline1">5.7&nbsp;&nbsp;&nbsp;<a href="#header.content-location">Content-Location</a></li>
571               <li class="tocline1">5.8&nbsp;&nbsp;&nbsp;<a href="#header.content-md5">Content-MD5</a></li>
572               <li class="tocline1">5.9&nbsp;&nbsp;&nbsp;<a href="#header.content-type">Content-Type</a></li>
[52]573            </ul>
574         </li>
[424]575         <li class="tocline0">6.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a><ul class="toc">
576               <li class="tocline1">6.1&nbsp;&nbsp;&nbsp;<a href="#message.header.registration">Message Header Registration</a></li>
[253]577            </ul>
578         </li>
[424]579         <li class="tocline0">7.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul class="toc">
580               <li class="tocline1">7.1&nbsp;&nbsp;&nbsp;<a href="#privacy.issues.connected.to.accept.headers">Privacy Issues Connected to Accept Headers</a></li>
581               <li class="tocline1">7.2&nbsp;&nbsp;&nbsp;<a href="#content-disposition.issues">Content-Disposition Issues</a></li>
[52]582            </ul>
583         </li>
[424]584         <li class="tocline0">8.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
585         <li class="tocline0">9.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a><ul class="toc">
586               <li class="tocline1">9.1&nbsp;&nbsp;&nbsp;<a href="#rfc.references.1">Normative References</a></li>
587               <li class="tocline1">9.2&nbsp;&nbsp;&nbsp;<a href="#rfc.references.2">Informative References</a></li>
[119]588            </ul>
589         </li>
[52]590         <li class="tocline0"><a href="#rfc.authors">Authors' Addresses</a></li>
591         <li class="tocline0">A.&nbsp;&nbsp;&nbsp;<a href="#differences.between.http.entities.and.rfc.2045.entities">Differences Between HTTP Entities and RFC 2045 Entities</a><ul class="toc">
592               <li class="tocline1">A.1&nbsp;&nbsp;&nbsp;<a href="#mime-version">MIME-Version</a></li>
593               <li class="tocline1">A.2&nbsp;&nbsp;&nbsp;<a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li>
[385]594               <li class="tocline1">A.3&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>
595               <li class="tocline1">A.4&nbsp;&nbsp;&nbsp;<a href="#introduction.of.content-encoding">Introduction of Content-Encoding</a></li>
596               <li class="tocline1">A.5&nbsp;&nbsp;&nbsp;<a href="#no.content-transfer-encoding">No Content-Transfer-Encoding</a></li>
597               <li class="tocline1">A.6&nbsp;&nbsp;&nbsp;<a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></li>
598               <li class="tocline1">A.7&nbsp;&nbsp;&nbsp;<a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li>
[52]599            </ul>
600         </li>
601         <li class="tocline0">B.&nbsp;&nbsp;&nbsp;<a href="#additional.features">Additional Features</a><ul class="toc">
602               <li class="tocline1">B.1&nbsp;&nbsp;&nbsp;<a href="#content-disposition">Content-Disposition</a></li>
603            </ul>
604         </li>
[99]605         <li class="tocline0">C.&nbsp;&nbsp;&nbsp;<a href="#compatibility">Compatibility with Previous Versions</a><ul class="toc">
606               <li class="tocline1">C.1&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li>
607               <li class="tocline1">C.2&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
608            </ul>
609         </li>
[421]610         <li class="tocline0">D.&nbsp;&nbsp;&nbsp;<a href="#collected.abnf">Collected ABNF</a></li>
611         <li class="tocline0">E.&nbsp;&nbsp;&nbsp;<a href="#change.log">Change Log (to be removed by RFC Editor before publication)</a><ul class="toc">
612               <li class="tocline1">E.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.1">Since RFC2616</a></li>
613               <li class="tocline1">E.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.2">Since draft-ietf-httpbis-p3-payload-00</a></li>
614               <li class="tocline1">E.3&nbsp;&nbsp;&nbsp;<a href="#rfc.section.E.3">Since draft-ietf-httpbis-p3-payload-01</a></li>
615               <li class="tocline1">E.4&nbsp;&nbsp;&nbsp;<a href="#changes.since.02">Since draft-ietf-httpbis-p3-payload-02</a></li>
616               <li class="tocline1">E.5&nbsp;&nbsp;&nbsp;<a href="#changes.since.03">Since draft-ietf-httpbis-p3-payload-03</a></li>
617               <li class="tocline1">E.6&nbsp;&nbsp;&nbsp;<a href="#changes.since.04">Since draft-ietf-httpbis-p3-payload-04</a></li>
618               <li class="tocline1">E.7&nbsp;&nbsp;&nbsp;<a href="#changes.since.05">Since draft-ietf-httpbis-p3-payload-05</a></li>
[547]619               <li class="tocline1">E.8&nbsp;&nbsp;&nbsp;<a href="#changes.since.06">Since draft-ietf-httpbis-p3-payload-06</a></li>
[115]620            </ul>
621         </li>
[52]622         <li class="tocline0"><a href="#rfc.index">Index</a></li>
623      </ul>
624      <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
[163]625      <p id="rfc.section.1.p.1">This document defines HTTP/1.1 message payloads (a.k.a., content), the associated metadata header fields that define how the
626         payload is intended to be interpreted by a recipient, the request header fields that may influence content selection, and
627         the various selection algorithms that are collectively referred to as HTTP content negotiation.
[52]628      </p>
[161]629      <p id="rfc.section.1.p.2">This document is currently disorganized in order to minimize the changes between drafts and enable reviewers to see the smaller
630         errata changes. The next draft will reorganize the sections to better reflect the content. In particular, the sections on
631         entities will be renamed payload and moved to the first half of the document, while the sections on content negotiation and
632         associated request header fields will be moved to the second half. The current mess reflects how widely dispersed these topics
633         and associated requirements had become in <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
634      </p>
[96]635      <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a id="intro.requirements" href="#intro.requirements">Requirements</a></h2>
636      <p id="rfc.section.1.1.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
637         in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.
638      </p>
639      <p id="rfc.section.1.1.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant."
640      </p>
[424]641      <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a id="notation" href="#notation">Syntax Notation</a></h2>
[543]642      <p id="rfc.section.1.2.p.1">This specification uses the ABNF syntax defined in <a href="p1-messaging.html#notation" title="Syntax Notation">Section 1.2</a> of <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> (which extends the syntax defined in <a href="#RFC5234" id="rfc.xref.RFC5234.1"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a> with a list rule). <a href="#collected.abnf" title="Collected ABNF">Appendix&nbsp;D</a> shows the collected ABNF, with the list rule expanded.
643      </p>
644      <p id="rfc.section.1.2.p.2">The following core rules are included by reference, as defined in <a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>, <a href="http://tools.ietf.org/html/rfc5234#appendix-B.1">Appendix B.1</a>: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG
[425]645         (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), VCHAR (any visible USASCII character),
646         and WSP (whitespace).
[205]647      </p>
[424]648      <h3 id="rfc.section.1.2.1"><a href="#rfc.section.1.2.1">1.2.1</a>&nbsp;<a id="core.rules" href="#core.rules">Core Rules</a></h3>
649      <p id="rfc.section.1.2.1.p.1">The core rules below are defined in <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a> of <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>:
650      </p>
[425]651      <div id="rfc.figure.u.1"></div><pre class="inline">  <a href="#core.rules" class="smpl">quoted-string</a>  = &lt;quoted-string, defined in <a href="#Part1" id="rfc.xref.Part1.3"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>&gt;
652  <a href="#core.rules" class="smpl">token</a>          = &lt;token, defined in <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>&gt;
653  <a href="#core.rules" class="smpl">OWS</a>            = &lt;OWS, defined in <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#basic.rules" title="Basic Rules">Section 1.2.2</a>&gt;
[424]654</pre><h3 id="rfc.section.1.2.2"><a href="#rfc.section.1.2.2">1.2.2</a>&nbsp;<a id="abnf.dependencies" href="#abnf.dependencies">ABNF Rules defined in other Parts of the Specification</a></h3>
655      <p id="rfc.section.1.2.2.p.1">The ABNF rules below are defined in other parts:</p>
[425]656      <div id="rfc.figure.u.2"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">absolute-URI</a>   = &lt;absolute-URI, defined in <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.1</a>&gt;
657  <a href="#abnf.dependencies" class="smpl">Content-Length</a> = &lt;Content-Length, defined in <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#header.content-length" title="Content-Length">Section 8.2</a>&gt;
658  <a href="#abnf.dependencies" class="smpl">message-header</a> = &lt;message-header, defined in <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#message.headers" title="Message Headers">Section 4.2</a>&gt;
659  <a href="#abnf.dependencies" class="smpl">partial-URI</a>    = &lt;partial-URI, defined in <a href="#Part1" id="rfc.xref.Part1.9"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#uri" title="Uniform Resource Identifiers">Section 2.1</a>&gt;
[457]660  <a href="#abnf.dependencies" class="smpl">qvalue</a>         = &lt;qvalue, defined in <a href="#Part1" id="rfc.xref.Part1.10"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#quality.values" title="Quality Values">Section 3.5</a>&gt;
[425]661</pre><div id="rfc.figure.u.3"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">Last-Modified</a>  = &lt;Last-Modified, defined in <a href="#Part4" id="rfc.xref.Part4.1"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 6.6</a>&gt;
662</pre><div id="rfc.figure.u.4"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">Content-Range</a>  = &lt;Content-Range, defined in <a href="#Part5" id="rfc.xref.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>, <a href="p5-range.html#header.content-range" title="Content-Range">Section 5.2</a>&gt;
[538]663</pre><div id="rfc.figure.u.5"></div><pre class="inline">  <a href="#abnf.dependencies" class="smpl">Expires</a>        = &lt;Expires, defined in <a href="#Part6" id="rfc.xref.Part6.1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.expires" title="Expires">Section 3.3</a>&gt;
[424]664</pre><h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="protocol.parameters" href="#protocol.parameters">Protocol Parameters</a></h1>
665      <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="character.sets" href="#character.sets">Character Sets</a></h2>
666      <p id="rfc.section.2.1.p.1">HTTP uses the same definition of the term "character set" as that described for MIME:</p>
667      <p id="rfc.section.2.1.p.2">The term "character set" is used in this document to refer to a method used with one or more tables to convert a sequence
[52]668         of octets into a sequence of characters. Note that unconditional conversion in the other direction is not required, in that
669         not all characters may be available in a given character set and a character set may provide more than one sequence of octets
670         to represent a particular character. This definition is intended to allow various kinds of character encoding, from simple
671         single-table mappings such as US-ASCII to complex table switching methods such as those that use ISO-2022's techniques. However,
672         the definition associated with a MIME character set name <em class="bcp14">MUST</em> fully specify the mapping to be performed from octets to characters. In particular, use of external profiling information
673         to determine the exact mapping is not permitted.
674      </p>
[563]675      <div class="note"> 
676         <p> <b>Note:</b> This use of the term "character set" is more commonly referred to as a "character encoding." However, since HTTP and MIME
[52]677            share the same registry, it is important that the terminology also be shared.
[563]678         </p> 
679      </div>
[229]680      <div id="rule.charset">
[424]681         <p id="rfc.section.2.1.p.4">  HTTP character sets are identified by case-insensitive tokens. The complete set of tokens is defined by the IANA Character
[229]682            Set registry (&lt;<a href="http://www.iana.org/assignments/character-sets">http://www.iana.org/assignments/character-sets</a>&gt;).
683         </p>
684      </div>
[425]685      <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.1"></span>  <a href="#rule.charset" class="smpl">charset</a> = <a href="#core.rules" class="smpl">token</a>
[424]686</pre><p id="rfc.section.2.1.p.6">Although HTTP allows an arbitrary token to be used as a charset value, any token that has a predefined value within the IANA
[92]687         Character Set registry <em class="bcp14">MUST</em> represent the character set defined by that registry. Applications <em class="bcp14">SHOULD</em> limit their use of character sets to those defined by the IANA registry.
[52]688      </p>
[424]689      <p id="rfc.section.2.1.p.7">HTTP uses charset in two contexts: within an Accept-Charset request header (in which the charset value is an unquoted token)
[115]690         and as the value of a parameter in a Content-Type header (within a request or response), in which case the parameter value
[92]691         of the charset parameter may be quoted.
[52]692      </p>
[424]693      <p id="rfc.section.2.1.p.8">Implementors should be aware of IETF character set requirements <a href="#RFC3629" id="rfc.xref.RFC3629.1"><cite title="UTF-8, a transformation format of ISO 10646">[RFC3629]</cite></a>  <a href="#RFC2277" id="rfc.xref.RFC2277.1"><cite title="IETF Policy on Character Sets and Languages">[RFC2277]</cite></a>.
[92]694      </p>
[424]695      <h3 id="rfc.section.2.1.1"><a href="#rfc.section.2.1.1">2.1.1</a>&nbsp;<a id="missing.charset" href="#missing.charset">Missing Charset</a></h3>
696      <p id="rfc.section.2.1.1.p.1">Some HTTP/1.0 software has interpreted a Content-Type header without charset parameter incorrectly to mean "recipient should
[211]697         guess." Senders wishing to defeat this behavior <em class="bcp14">MAY</em> include a charset parameter even when the charset is ISO-8859-1 (<a href="#ISO-8859-1" id="rfc.xref.ISO-8859-1.1"><cite title="Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1">[ISO-8859-1]</cite></a>) and <em class="bcp14">SHOULD</em> do so when it is known that it will not confuse the recipient.
698      </p>
[424]699      <p id="rfc.section.2.1.1.p.2">Unfortunately, some older HTTP/1.0 clients did not deal properly with an explicit charset parameter. HTTP/1.1 recipients <em class="bcp14">MUST</em> respect the charset label provided by the sender; and those user agents that have a provision to "guess" a charset <em class="bcp14">MUST</em> use the charset from the content-type field if they support that charset, rather than the recipient's preference, when initially
700         displaying a document. See <a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section&nbsp;2.3.1</a>.
[211]701      </p>
[424]702      <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="content.codings" href="#content.codings">Content Codings</a></h2>
703      <p id="rfc.section.2.2.p.1">Content coding values indicate an encoding transformation that has been or can be applied to an entity. Content codings are
[52]704         primarily used to allow a document to be compressed or otherwise usefully transformed without losing the identity of its underlying
705         media type and without loss of information. Frequently, the entity is stored in coded form, transmitted directly, and only
706         decoded by the recipient.
707      </p>
[425]708      <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.2"></span>  <a href="#content.codings" class="smpl">content-coding</a>   = <a href="#core.rules" class="smpl">token</a>
[424]709</pre><p id="rfc.section.2.2.p.3">All content-coding values are case-insensitive. HTTP/1.1 uses content-coding values in the Accept-Encoding (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.1" title="Accept-Encoding">Section&nbsp;5.3</a>) and Content-Encoding (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section&nbsp;5.5</a>) header fields. Although the value describes the content-coding, what is more important is that it indicates what decoding
[52]710         mechanism will be required to remove the encoding.
711      </p>
[424]712      <p id="rfc.section.2.2.p.4">The Internet Assigned Numbers Authority (IANA) acts as a registry for content-coding value tokens. Initially, the registry
[52]713         contains the following tokens:
714      </p>
[424]715      <p id="rfc.section.2.2.p.5">gzip<span id="rfc.iref.g.3"></span> 
[52]716      </p>
717      <dl class="empty">
[97]718         <dd>An encoding format produced by the file compression program "gzip" (GNU zip) as described in <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[RFC1952]</cite></a>. This format is a Lempel-Ziv coding (LZ77) with a 32 bit CRC.
[52]719         </dd>
720      </dl>
[424]721      <p id="rfc.section.2.2.p.6">compress<span id="rfc.iref.c.1"></span> 
[52]722      </p>
723      <dl class="empty">
724         <dd>The encoding format produced by the common UNIX file compression program "compress". This format is an adaptive Lempel-Ziv-Welch
725            coding (LZW).
726         </dd>
727         <dd>Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings.
728            Their use here is representative of historical practice, not good design. For compatibility with previous implementations
729            of HTTP, applications <em class="bcp14">SHOULD</em> consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress" respectively.
730         </dd>
731      </dl>
[424]732      <p id="rfc.section.2.2.p.7">deflate<span id="rfc.iref.d.1"></span> 
[52]733      </p>
734      <dl class="empty">
[97]735         <dd>The "zlib" format defined in <a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[RFC1950]</cite></a> in combination with the "deflate" compression mechanism described in <a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[RFC1951]</cite></a>.
[52]736         </dd>
737      </dl>
[424]738      <p id="rfc.section.2.2.p.8">identity<span id="rfc.iref.i.1"></span> 
[52]739      </p>
740      <dl class="empty">
741         <dd>The default (identity) encoding; the use of no transformation whatsoever. This content-coding is used only in the Accept-Encoding
742            header, and <em class="bcp14">SHOULD NOT</em> be used in the Content-Encoding header.
743         </dd>
744      </dl>
[424]745      <p id="rfc.section.2.2.p.9">New content-coding value tokens <em class="bcp14">SHOULD</em> be registered; to allow interoperability between clients and servers, specifications of the content coding algorithms needed
[52]746         to implement a new value <em class="bcp14">SHOULD</em> be publicly available and adequate for independent implementation, and conform to the purpose of content coding defined in
747         this section.
748      </p>
[424]749      <h2 id="rfc.section.2.3"><a href="#rfc.section.2.3">2.3</a>&nbsp;<a id="media.types" href="#media.types">Media Types</a></h2>
750      <p id="rfc.section.2.3.p.1">HTTP uses Internet Media Types <a href="#RFC2046" id="rfc.xref.RFC2046.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> in the Content-Type (<a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section&nbsp;5.9</a>) and Accept (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section&nbsp;5.1</a>) header fields in order to provide open and extensible data typing and type negotiation.
[52]751      </p>
[425]752      <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span>  <a href="#media.types" class="smpl">media-type</a> = <a href="#media.types" class="smpl">type</a> "/" <a href="#media.types" class="smpl">subtype</a> *( <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )
[424]753  <a href="#media.types" class="smpl">type</a>       = <a href="#core.rules" class="smpl">token</a>
754  <a href="#media.types" class="smpl">subtype</a>    = <a href="#core.rules" class="smpl">token</a>
[229]755</pre><div id="rule.parameter">
[424]756         <p id="rfc.section.2.3.p.3">      Parameters <em class="bcp14">MAY</em> follow the type/subtype in the form of attribute/value pairs.
[229]757         </p>
758      </div>
[425]759      <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span>  <a href="#rule.parameter" class="smpl">parameter</a>      = <a href="#rule.parameter" class="smpl">attribute</a> "=" <a href="#rule.parameter" class="smpl">value</a>
[424]760  <a href="#rule.parameter" class="smpl">attribute</a>      = <a href="#core.rules" class="smpl">token</a>
761  <a href="#rule.parameter" class="smpl">value</a>          = <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a>
762</pre><p id="rfc.section.2.3.p.5">The type, subtype, and parameter attribute names are case-insensitive. Parameter values might or might not be case-sensitive,
[370]763         depending on the semantics of the parameter name. The presence or absence of a parameter might be significant to the processing
764         of a media-type, depending on its definition within the media type registry.
[52]765      </p>
[424]766      <p id="rfc.section.2.3.p.6">A parameter value that matches the <a href="#core.rules" class="smpl">token</a> production may be transmitted as either a token or within a quoted-string. The quoted and unquoted values are equivalent.
[297]767      </p>
[424]768      <p id="rfc.section.2.3.p.7">Note that some older HTTP applications do not recognize media type parameters. When sending data to older HTTP applications,
[52]769         implementations <em class="bcp14">SHOULD</em> only use media type parameters when they are required by that type/subtype definition.
770      </p>
[424]771      <p id="rfc.section.2.3.p.8">Media-type values are registered with the Internet Assigned Number Authority (IANA). The media type registration process is
[152]772         outlined in <a href="#RFC4288" id="rfc.xref.RFC4288.1"><cite title="Media Type Specifications and Registration Procedures">[RFC4288]</cite></a>. Use of non-registered media types is discouraged.
[52]773      </p>
[424]774      <h3 id="rfc.section.2.3.1"><a href="#rfc.section.2.3.1">2.3.1</a>&nbsp;<a id="canonicalization.and.text.defaults" href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></h3>
775      <p id="rfc.section.2.3.1.p.1">Internet media types are registered with a canonical form. An entity-body transferred via HTTP messages <em class="bcp14">MUST</em> be represented in the appropriate canonical form prior to its transmission except for "text" types, as defined in the next
[52]776         paragraph.
777      </p>
[424]778      <p id="rfc.section.2.3.1.p.2">When in canonical form, media subtypes of the "text" type use CRLF as the text line break. HTTP relaxes this requirement and
[52]779         allows the transport of text media with plain CR or LF alone representing a line break when it is done consistently for an
780         entire entity-body. HTTP applications <em class="bcp14">MUST</em> accept CRLF, bare CR, and bare LF as being representative of a line break in text media received via HTTP. In addition, if
781         the text is represented in a character set that does not use octets 13 and 10 for CR and LF respectively, as is the case for
782         some multi-byte character sets, HTTP allows the use of whatever octet sequences are defined by that character set to represent
783         the equivalent of CR and LF for line breaks. This flexibility regarding line breaks applies only to text media in the entity-body;
784         a bare CR or LF <em class="bcp14">MUST NOT</em> be substituted for CRLF within any of the HTTP control structures (such as header fields and multipart boundaries).
785      </p>
[424]786      <p id="rfc.section.2.3.1.p.3">If an entity-body is encoded with a content-coding, the underlying data <em class="bcp14">MUST</em> be in a form defined above prior to being encoded.
[52]787      </p>
[424]788      <p id="rfc.section.2.3.1.p.4">The "charset" parameter is used with some media types to define the character set (<a href="#character.sets" title="Character Sets">Section&nbsp;2.1</a>) of the data. When no explicit charset parameter is provided by the sender, media subtypes of the "text" type are defined
[211]789         to have a default charset value of "ISO-8859-1" when received via HTTP. Data in character sets other than "ISO-8859-1" or
[424]790         its subsets <em class="bcp14">MUST</em> be labeled with an appropriate charset value. See <a href="#missing.charset" title="Missing Charset">Section&nbsp;2.1.1</a> for compatibility problems.
[52]791      </p>
[424]792      <h3 id="rfc.section.2.3.2"><a href="#rfc.section.2.3.2">2.3.2</a>&nbsp;<a id="multipart.types" href="#multipart.types">Multipart Types</a></h3>
793      <p id="rfc.section.2.3.2.p.1">MIME provides for a number of "multipart" types -- encapsulations of one or more entities within a single message-body. All
[152]794         multipart types share a common syntax, as defined in <a href="http://tools.ietf.org/html/rfc2046#section-5.1.1">Section 5.1.1</a> of <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a>, and <em class="bcp14">MUST</em> include a boundary parameter as part of the media type value. The message body is itself a protocol element and <em class="bcp14">MUST</em> therefore use only CRLF to represent line breaks between body-parts. Unlike in RFC 2046, the epilogue of any multipart message <em class="bcp14">MUST</em> be empty; HTTP applications <em class="bcp14">MUST NOT</em> transmit the epilogue (even if the original multipart contains an epilogue). These restrictions exist in order to preserve
[52]795         the self-delimiting nature of a multipart message-body, wherein the "end" of the message-body is indicated by the ending multipart
796         boundary.
797      </p>
[424]798      <p id="rfc.section.2.3.2.p.2">In general, HTTP treats a multipart message-body no differently than any other media type: strictly as payload. The one exception
[331]799         is the "multipart/byteranges" type (<a href="p5-range.html#internet.media.type.multipart.byteranges" title="Internet Media Type multipart/byteranges">Appendix A</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) when it appears in a 206 (Partial Content) response.  In all other cases, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. The MIME header fields within
800         each body-part of a multipart message-body do not have any significance to HTTP beyond that defined by their MIME semantics.
[52]801      </p>
[424]802      <p id="rfc.section.2.3.2.p.3">In general, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. If an application receives
[52]803         an unrecognized multipart subtype, the application <em class="bcp14">MUST</em> treat it as being equivalent to "multipart/mixed".
804      </p>
[563]805      <div class="note"> 
806         <p> <b>Note:</b> The "multipart/form-data" type has been specifically defined for carrying form data suitable for processing via the POST request
[129]807            method, as described in <a href="#RFC2388" id="rfc.xref.RFC2388.1"><cite title="Returning Values from Forms: multipart/form-data">[RFC2388]</cite></a>.
[563]808         </p> 
809      </div>
[457]810      <h2 id="rfc.section.2.4"><a href="#rfc.section.2.4">2.4</a>&nbsp;<a id="language.tags" href="#language.tags">Language Tags</a></h2>
811      <p id="rfc.section.2.4.p.1">A language tag identifies a natural language spoken, written, or otherwise conveyed by human beings for communication of information
[52]812         to other human beings. Computer languages are explicitly excluded. HTTP uses language tags within the Accept-Language and
813         Content-Language fields.
814      </p>
[457]815      <p id="rfc.section.2.4.p.2">The syntax and registry of HTTP language tags is the same as that defined by <a href="#RFC1766" id="rfc.xref.RFC1766.1"><cite title="Tags for the Identification of Languages">[RFC1766]</cite></a>. In summary, a language tag is composed of 1 or more parts: A primary language tag and a possibly empty series of subtags:
[52]816      </p>
[457]817      <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span>  <a href="#language.tags" class="smpl">language-tag</a>  = <a href="#language.tags" class="smpl">primary-tag</a> *( "-" <a href="#language.tags" class="smpl">subtag</a> )
[425]818  <a href="#language.tags" class="smpl">primary-tag</a>   = 1*8<a href="#notation" class="smpl">ALPHA</a>
819  <a href="#language.tags" class="smpl">subtag</a>        = 1*8<a href="#notation" class="smpl">ALPHA</a>
[457]820</pre><p id="rfc.section.2.4.p.4">White space is not allowed within the tag and all tags are case-insensitive. The name space of language tags is administered
[52]821         by the IANA. Example tags include:
822      </p>
[458]823      <div id="rfc.figure.u.11"></div><pre class="text">  en, en-US, en-cockney, i-cherokee, x-pig-latin
[457]824</pre><p id="rfc.section.2.4.p.6">where any two-letter primary-tag is an ISO-639 language abbreviation and any two-letter initial subtag is an ISO-3166 country
[52]825         code. (The last three tags above are not registered tags; all but the last are examples of tags which could be registered
826         in future.)
827      </p>
[424]828      <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="entity" href="#entity">Entity</a></h1>
829      <p id="rfc.section.3.p.1">Request and Response messages <em class="bcp14">MAY</em> transfer an entity if not otherwise restricted by the request method or response status code. An entity consists of entity-header
[52]830         fields and an entity-body, although some responses will only include the entity-headers.
831      </p>
[424]832      <p id="rfc.section.3.p.2">In this section, both sender and recipient refer to either the client or the server, depending on who sends and who receives
[52]833         the entity.
834      </p>
[424]835      <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="entity.header.fields" href="#entity.header.fields">Entity Header Fields</a></h2>
836      <p id="rfc.section.3.1.p.1">Entity-header fields define metainformation about the entity-body or, if no body is present, about the resource identified
[148]837         by the request.
[52]838      </p>
[457]839      <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span>  <a href="#entity.header.fields" class="smpl">entity-header</a>  = <a href="#header.content-encoding" class="smpl">Content-Encoding</a>         ; <a href="#header.content-encoding" id="rfc.xref.header.content-encoding.2" title="Content-Encoding">Section&nbsp;5.5</a>
[424]840                 / <a href="#header.content-language" class="smpl">Content-Language</a>         ; <a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section&nbsp;5.6</a>
[457]841                 / <a href="#abnf.dependencies" class="smpl">Content-Length</a>           ; <a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#header.content-length" title="Content-Length">Section 8.2</a>
[424]842                 / <a href="#header.content-location" class="smpl">Content-Location</a>         ; <a href="#header.content-location" id="rfc.xref.header.content-location.1" title="Content-Location">Section&nbsp;5.7</a>
843                 / <a href="#header.content-md5" class="smpl">Content-MD5</a>              ; <a href="#header.content-md5" id="rfc.xref.header.content-md5.1" title="Content-MD5">Section&nbsp;5.8</a>
844                 / <a href="#abnf.dependencies" class="smpl">Content-Range</a>            ; <a href="#Part5" id="rfc.xref.Part5.3"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>, <a href="p5-range.html#header.content-range" title="Content-Range">Section 5.2</a>
845                 / <a href="#header.content-type" class="smpl">Content-Type</a>             ; <a href="#header.content-type" id="rfc.xref.header.content-type.2" title="Content-Type">Section&nbsp;5.9</a>
[538]846                 / <a href="#abnf.dependencies" class="smpl">Expires</a>                  ; <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>, <a href="p6-cache.html#header.expires" title="Expires">Section 3.3</a>
[424]847                 / <a href="#abnf.dependencies" class="smpl">Last-Modified</a>            ; <a href="#Part4" id="rfc.xref.Part4.2"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 6.6</a>
[334]848                 / <a href="#entity.header.fields" class="smpl">extension-header</a>
[135]849 
[229]850  <a href="#entity.header.fields" class="smpl">extension-header</a> = <a href="#abnf.dependencies" class="smpl">message-header</a>
[424]851</pre><p id="rfc.section.3.1.p.3">The extension-header mechanism allows additional entity-header fields to be defined without changing the protocol, but these
[52]852         fields cannot be assumed to be recognizable by the recipient. Unrecognized header fields <em class="bcp14">SHOULD</em> be ignored by the recipient and <em class="bcp14">MUST</em> be forwarded by transparent proxies.
853      </p>
[424]854      <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="entity.body" href="#entity.body">Entity Body</a></h2>
855      <p id="rfc.section.3.2.p.1">The entity-body (if any) sent with an HTTP request or response is in a format and encoding defined by the entity-header fields.</p>
[457]856      <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.15"></span>  <a href="#entity.body" class="smpl">entity-body</a>    = *<a href="#notation" class="smpl">OCTET</a>
857</pre><p id="rfc.section.3.2.p.3">An entity-body is only present in a message when a message-body is present, as described in <a href="p1-messaging.html#message.body" title="Message Body">Section 4.3</a> of <a href="#Part1" id="rfc.xref.Part1.12"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>. The entity-body is obtained from the message-body by decoding any Transfer-Encoding that might have been applied to ensure
[52]858         safe and proper transfer of the message.
859      </p>
[424]860      <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;<a id="type" href="#type">Type</a></h3>
861      <p id="rfc.section.3.2.1.p.1">When an entity-body is included with a message, the data type of that body is determined via the header fields Content-Type
[52]862         and Content-Encoding. These define a two-layer, ordered encoding model:
863      </p>
[458]864      <div id="rfc.figure.u.14"></div><pre class="text">  entity-body := Content-Encoding( Content-Type( data ) )
[424]865</pre><p id="rfc.section.3.2.1.p.3">Content-Type specifies the media type of the underlying data. Content-Encoding may be used to indicate any additional content
[52]866         codings applied to the data, usually for the purpose of data compression, that are a property of the requested resource. There
867         is no default encoding.
868      </p>
[424]869      <p id="rfc.section.3.2.1.p.4">Any HTTP/1.1 message containing an entity-body <em class="bcp14">SHOULD</em> include a Content-Type header field defining the media type of that body. If and only if the media type is not given by a
[52]870         Content-Type field, the recipient <em class="bcp14">MAY</em> attempt to guess the media type via inspection of its content and/or the name extension(s) of the URI used to identify the
[572]871         resource. If the media type remains unknown, the recipient <em class="bcp14">SHOULD</em> treat it as type "application/octet-stream" (<a href="#RFC2046" id="rfc.xref.RFC2046.3"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a>, <a href="http://tools.ietf.org/html/rfc2046#section-4.5.1">Section 4.5.1</a>).
[52]872      </p>
[424]873      <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;<a id="entity.length" href="#entity.length">Entity Length</a></h3>
[457]874      <p id="rfc.section.3.2.2.p.1">The entity-length of a message is the length of the message-body before any transfer-codings have been applied. <a href="p1-messaging.html#message.length" title="Message Length">Section 4.4</a> of <a href="#Part1" id="rfc.xref.Part1.13"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> defines how the transfer-length of a message-body is determined.
[52]875      </p>
[424]876      <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="content.negotiation" href="#content.negotiation">Content Negotiation</a></h1>
877      <p id="rfc.section.4.p.1">Most HTTP responses include an entity which contains information for interpretation by a human user. Naturally, it is desirable
[52]878         to supply the user with the "best available" entity corresponding to the request. Unfortunately for servers and caches, not
879         all users have the same preferences for what is "best," and not all user agents are equally capable of rendering all entity
880         types. For that reason, HTTP has provisions for several mechanisms for "content negotiation" -- the process of selecting the
[563]881         best representation for a given response when there are multiple representations available.
[52]882      </p>
[563]883      <div class="note"> 
884         <p> <b>Note:</b> This is not called "format negotiation" because the alternate representations may be of the same media type, but use different
[52]885            capabilities of that type, be in different languages, etc.
[563]886         </p> 
887      </div>
888      <p id="rfc.section.4.p.3">Any response containing an entity-body <em class="bcp14">MAY</em> be subject to negotiation, including error responses.
[52]889      </p>
[563]890      <p id="rfc.section.4.p.4">There are two kinds of content negotiation which are possible in HTTP: server-driven and agent-driven negotiation. These two
[52]891         kinds of negotiation are orthogonal and thus may be used separately or in combination. One method of combination, referred
892         to as transparent negotiation, occurs when a cache uses the agent-driven negotiation information provided by the origin server
893         in order to provide server-driven negotiation for subsequent requests.
894      </p>
[424]895      <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="server-driven.negotiation" href="#server-driven.negotiation">Server-driven Negotiation</a></h2>
896      <p id="rfc.section.4.1.p.1">If the selection of the best representation for a response is made by an algorithm located at the server, it is called server-driven
[52]897         negotiation. Selection is based on the available representations of the response (the dimensions over which it can vary; e.g.
898         language, content-coding, etc.) and the contents of particular header fields in the request message or on other information
899         pertaining to the request (such as the network address of the client).
900      </p>
[424]901      <p id="rfc.section.4.1.p.2">Server-driven negotiation is advantageous when the algorithm for selecting from among the available representations is difficult
[52]902         to describe to the user agent, or when the server desires to send its "best guess" to the client along with the first response
903         (hoping to avoid the round-trip delay of a subsequent request if the "best guess" is good enough for the user). In order to
904         improve the server's guess, the user agent <em class="bcp14">MAY</em> include request header fields (Accept, Accept-Language, Accept-Encoding, etc.) which describe its preferences for such a response.
905      </p>
[424]906      <p id="rfc.section.4.1.p.3">Server-driven negotiation has disadvantages: </p>
[52]907      <ol>
908         <li>It is impossible for the server to accurately determine what might be "best" for any given user, since that would require
909            complete knowledge of both the capabilities of the user agent and the intended use for the response (e.g., does the user want
910            to view it on screen or print it on paper?).
911         </li>
912         <li>Having the user agent describe its capabilities in every request can be both very inefficient (given that only a small percentage
913            of responses have multiple representations) and a potential violation of the user's privacy.
914         </li>
915         <li>It complicates the implementation of an origin server and the algorithms for generating responses to a request.</li>
916         <li>It may limit a public cache's ability to use the same response for multiple user's requests.</li>
917      </ol>
[424]918      <p id="rfc.section.4.1.p.4">HTTP/1.1 includes the following request-header fields for enabling server-driven negotiation through description of user agent
919         capabilities and user preferences: Accept (<a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section&nbsp;5.1</a>), Accept-Charset (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.1" title="Accept-Charset">Section&nbsp;5.2</a>), Accept-Encoding (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.2" title="Accept-Encoding">Section&nbsp;5.3</a>), Accept-Language (<a href="#header.accept-language" id="rfc.xref.header.accept-language.1" title="Accept-Language">Section&nbsp;5.4</a>), and User-Agent (<a href="p2-semantics.html#header.user-agent" title="User-Agent">Section 9.9</a> of <a href="#Part2" id="rfc.xref.Part2.1"><cite title="HTTP/1.1, part 2: Message Semantics">[Part2]</cite></a>). However, an origin server is not limited to these dimensions and <em class="bcp14">MAY</em> vary the response based on any aspect of the request, including information outside the request-header fields or within extension
[52]920         header fields not defined by this specification.
921      </p>
[538]922      <p id="rfc.section.4.1.p.5">The Vary header field (<a href="p6-cache.html#header.vary" title="Vary">Section 3.5</a> of <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) can be used to express the parameters the server uses to select a representation that is subject to server-driven negotiation.
[52]923      </p>
[424]924      <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="agent-driven.negotiation" href="#agent-driven.negotiation">Agent-driven Negotiation</a></h2>
925      <p id="rfc.section.4.2.p.1">With agent-driven negotiation, selection of the best representation for a response is performed by the user agent after receiving
[52]926         an initial response from the origin server. Selection is based on a list of the available representations of the response
927         included within the header fields or entity-body of the initial response, with each representation identified by its own URI.
928         Selection from among the representations may be performed automatically (if the user agent is capable of doing so) or manually
929         by the user selecting from a generated (possibly hypertext) menu.
930      </p>
[424]931      <p id="rfc.section.4.2.p.2">Agent-driven negotiation is advantageous when the response would vary over commonly-used dimensions (such as type, language,
[52]932         or encoding), when the origin server is unable to determine a user agent's capabilities from examining the request, and generally
933         when public caches are used to distribute server load and reduce network usage.
934      </p>
[424]935      <p id="rfc.section.4.2.p.3">Agent-driven negotiation suffers from the disadvantage of needing a second request to obtain the best alternate representation.
[52]936         This second request is only efficient when caching is used. In addition, this specification does not define any mechanism
937         for supporting automatic selection, though it also does not prevent any such mechanism from being developed as an extension
938         and used within HTTP/1.1.
939      </p>
[424]940      <p id="rfc.section.4.2.p.4">HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable) status codes for enabling agent-driven negotiation when
[52]941         the server is unwilling or unable to provide a varying response using server-driven negotiation.
942      </p>
[424]943      <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a id="transparent.negotiation" href="#transparent.negotiation">Transparent Negotiation</a></h2>
944      <p id="rfc.section.4.3.p.1">Transparent negotiation is a combination of both server-driven and agent-driven negotiation. When a cache is supplied with
[52]945         a form of the list of available representations of the response (as in agent-driven negotiation) and the dimensions of variance
946         are completely understood by the cache, then the cache becomes capable of performing server-driven negotiation on behalf of
947         the origin server for subsequent requests on that resource.
948      </p>
[424]949      <p id="rfc.section.4.3.p.2">Transparent negotiation has the advantage of distributing the negotiation work that would otherwise be required of the origin
[52]950         server and also removing the second request delay of agent-driven negotiation when the cache is able to correctly guess the
951         right response.
952      </p>
[424]953      <p id="rfc.section.4.3.p.3">This specification does not define any mechanism for transparent negotiation, though it also does not prevent any such mechanism
[52]954         from being developed as an extension that could be used within HTTP/1.1.
955      </p>
[424]956      <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>
957      <p id="rfc.section.5.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to the payload of messages.</p>
958      <p id="rfc.section.5.p.2">For entity-header fields, both sender and recipient refer to either the client or the server, depending on who sends and who
[117]959         receives the entity.
[52]960      </p>
961      <div id="rfc.iref.a.1"></div>
962      <div id="rfc.iref.h.1"></div>
[424]963      <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a id="header.accept" href="#header.accept">Accept</a></h2>
964      <p id="rfc.section.5.1.p.1">The request-header field "Accept" can be used to specify certain media types which are acceptable for the response. Accept
[357]965         headers can be used to indicate that the request is specifically limited to a small set of desired types, as in the case of
966         a request for an in-line image.
[52]967      </p>
[457]968      <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span>  <a href="#header.accept" class="smpl">Accept</a>   = "Accept" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.accept" class="smpl">Accept-v</a>
[357]969  <a href="#header.accept" class="smpl">Accept-v</a> = #( <a href="#header.accept" class="smpl">media-range</a> [ <a href="#header.accept" class="smpl">accept-params</a> ] )
[135]970 
[229]971  <a href="#header.accept" class="smpl">media-range</a>    = ( "*/*"
[334]972                   / ( <a href="#media.types" class="smpl">type</a> "/" "*" )
973                   / ( <a href="#media.types" class="smpl">type</a> "/" <a href="#media.types" class="smpl">subtype</a> )
[424]974                   ) *( <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )
[457]975  <a href="#header.accept" class="smpl">accept-params</a>  = <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> "q=" <a href="#abnf.dependencies" class="smpl">qvalue</a> *( <a href="#header.accept" class="smpl">accept-ext</a> )
[424]976  <a href="#header.accept" class="smpl">accept-ext</a>     = <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> <a href="#core.rules" class="smpl">token</a>
977                   [ "=" ( <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a> ) ]
978</pre><p id="rfc.section.5.1.p.3">The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating
[52]979         all subtypes of that type. The media-range <em class="bcp14">MAY</em> include media type parameters that are applicable to that range.
980      </p>
[424]981      <p id="rfc.section.5.1.p.4">Each media-range <em class="bcp14">MAY</em> be followed by one or more accept-params, beginning with the "q" parameter for indicating a relative quality factor. The first
[52]982         "q" parameter (if any) separates the media-range parameter(s) from the accept-params. Quality factors allow the user or user
[563]983         agent to indicate the relative degree of preference for that media-range, using the qvalue scale from 0 to 1 (<a href="p1-messaging.html#quality.values" title="Quality Values">Section 3.5</a> of <a href="#Part1" id="rfc.xref.Part1.14"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). The default value is q=1.
[52]984      </p>
[563]985      <div class="note"> 
986         <p> <b>Note:</b> Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to historical practice.
[52]987            Although this prevents any media type parameter named "q" from being used with a media range, such an event is believed to
988            be unlikely given the lack of any "q" parameters in the IANA media type registry and the rare usage of any media type parameters
989            in Accept. Future media types are discouraged from registering any parameter named "q".
[563]990         </p> 
991      </div>
992      <p id="rfc.section.5.1.p.6">The example</p>
[457]993      <div id="rfc.figure.u.16"></div><pre class="text">  Accept: audio/*; q=0.2, audio/basic
[563]994</pre><p id="rfc.section.5.1.p.8"> <em class="bcp14">SHOULD</em> be interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80% mark-down in
[52]995         quality."
996      </p>
[563]997      <p id="rfc.section.5.1.p.9">If no Accept header field is present, then it is assumed that the client accepts all media types. If an Accept header field
[52]998         is present, and if the server cannot send a response which is acceptable according to the combined Accept field value, then
[137]999         the server <em class="bcp14">SHOULD</em> send a 406 (Not Acceptable) response.
[52]1000      </p>
[563]1001      <p id="rfc.section.5.1.p.10">A more elaborate example is</p>
[457]1002      <div id="rfc.figure.u.17"></div><pre class="text">  Accept: text/plain; q=0.5, text/html,
[357]1003          text/x-dvi; q=0.8, text/x-c
[563]1004</pre><p id="rfc.section.5.1.p.12">Verbally, this would be interpreted as "text/html and text/x-c are the preferred media types, but if they do not exist, then
[52]1005         send the text/x-dvi entity, and if that does not exist, send the text/plain entity."
1006      </p>
[563]1007      <p id="rfc.section.5.1.p.13">Media ranges can be overridden by more specific media ranges or specific media types. If more than one media range applies
[52]1008         to a given type, the most specific reference has precedence. For example,
1009      </p>
[457]1010      <div id="rfc.figure.u.18"></div><pre class="text">  Accept: text/*, text/html, text/html;level=1, */*
[563]1011</pre><p id="rfc.section.5.1.p.15">have the following precedence: </p>
[459]1012      <ol>
1013         <li>text/html;level=1</li>
1014         <li>text/html</li>
1015         <li>text/*</li>
1016         <li>*/*</li>
1017      </ol>
[563]1018      <p id="rfc.section.5.1.p.16">The media type quality factor associated with a given type is determined by finding the media range with the highest precedence
[52]1019         which matches that type. For example,
1020      </p>
[459]1021      <div id="rfc.figure.u.19"></div><pre class="text">  Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
[357]1022          text/html;level=2;q=0.4, */*;q=0.5
[563]1023</pre><p id="rfc.section.5.1.p.18">would cause the following values to be associated:</p>
[459]1024      <div id="rfc.table.u.1">
1025         <table summary="" class="tt full" cellpadding="3" cellspacing="0">
1026            <thead>
1027               <tr>
1028                  <th>Media Type</th>
1029                  <th>Quality Value</th>
1030               </tr>
1031            </thead>
1032            <tbody>
1033               <tr>
1034                  <td>text/html;level=1</td>
1035                  <td>1</td>
1036               </tr>
1037               <tr>
1038                  <td>text/html</td>
1039                  <td>0.7</td>
1040               </tr>
1041               <tr>
1042                  <td>text/plain</td>
1043                  <td>0.3</td>
1044               </tr>
1045               <tr>
1046                  <td>image/jpeg</td>
1047                  <td>0.5</td>
1048               </tr>
1049               <tr>
1050                  <td>text/html;level=2</td>
1051                  <td>0.4</td>
1052               </tr>
1053               <tr>
1054                  <td>text/html;level=3</td>
1055                  <td>0.7</td>
1056               </tr>
1057            </tbody>
1058         </table>
1059      </div>
[563]1060      <p id="rfc.section.5.1.p.19"> <b>Note:</b> A user agent might be provided with a default set of quality values for certain media ranges. However, unless the user agent
[52]1061         is a closed system which cannot interact with other rendering agents, this default set ought to be configurable by the user.
1062      </p>
1063      <div id="rfc.iref.a.2"></div>
1064      <div id="rfc.iref.h.2"></div>
[424]1065      <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a id="header.accept-charset" href="#header.accept-charset">Accept-Charset</a></h2>
1066      <p id="rfc.section.5.2.p.1">The request-header field "Accept-Charset" can be used to indicate what character sets are acceptable for the response. This
[52]1067         field allows clients capable of understanding more comprehensive or special-purpose character sets to signal that capability
1068         to a server which is capable of representing documents in those character sets.
1069      </p>
[459]1070      <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span>  <a href="#header.accept-charset" class="smpl">Accept-Charset</a>   = "Accept-Charset" ":" <a href="#core.rules" class="smpl">OWS</a>
[357]1071          <a href="#header.accept-charset" class="smpl">Accept-Charset-v</a>
[376]1072  <a href="#header.accept-charset" class="smpl">Accept-Charset-v</a> = 1#( ( <a href="#rule.charset" class="smpl">charset</a> / "*" )
[457]1073                         [ <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> "q=" <a href="#abnf.dependencies" class="smpl">qvalue</a> ] )
[424]1074</pre><p id="rfc.section.5.2.p.3">Character set values are described in <a href="#character.sets" title="Character Sets">Section&nbsp;2.1</a>. Each charset <em class="bcp14">MAY</em> be given an associated quality value which represents the user's preference for that charset. The default value is q=1. An
[52]1075         example is
1076      </p>
[459]1077      <div id="rfc.figure.u.21"></div><pre class="text">  Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
[424]1078</pre><p id="rfc.section.5.2.p.5">The special value "*", if present in the Accept-Charset field, matches every character set (including ISO-8859-1) which is
[52]1079         not mentioned elsewhere in the Accept-Charset field. If no "*" is present in an Accept-Charset field, then all character sets
1080         not explicitly mentioned get a quality value of 0, except for ISO-8859-1, which gets a quality value of 1 if not explicitly
1081         mentioned.
1082      </p>
[424]1083      <p id="rfc.section.5.2.p.6">If no Accept-Charset header is present, the default is that any character set is acceptable. If an Accept-Charset header is
[137]1084         present, and if the server cannot send a response which is acceptable according to the Accept-Charset header, then the server <em class="bcp14">SHOULD</em> send an error response with the 406 (Not Acceptable) status code, though the sending of an unacceptable response is also allowed.
[52]1085      </p>
1086      <div id="rfc.iref.a.3"></div>
1087      <div id="rfc.iref.h.3"></div>
[424]1088      <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a>&nbsp;<a id="header.accept-encoding" href="#header.accept-encoding">Accept-Encoding</a></h2>
1089      <p id="rfc.section.5.3.p.1">The request-header field "Accept-Encoding" is similar to Accept, but restricts the content-codings (<a href="#content.codings" title="Content Codings">Section&nbsp;2.2</a>) that are acceptable in the response.
[52]1090      </p>
[459]1091      <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.23"></span><span id="rfc.iref.g.24"></span><span id="rfc.iref.g.25"></span>  <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a>    = "Accept-Encoding" ":" <a href="#core.rules" class="smpl">OWS</a>
[357]1092                     <a href="#header.accept-encoding" class="smpl">Accept-Encoding-v</a>
1093  <a href="#header.accept-encoding" class="smpl">Accept-Encoding-v</a>  =
[457]1094                     #( <a href="#header.accept-encoding" class="smpl">codings</a> [ <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> "q=" <a href="#abnf.dependencies" class="smpl">qvalue</a> ] )
[357]1095  <a href="#header.accept-encoding" class="smpl">codings</a>            = ( <a href="#content.codings" class="smpl">content-coding</a> / "*" )
[424]1096</pre><p id="rfc.section.5.3.p.3">Each codings value <em class="bcp14">MAY</em> be given an associated quality value which represents the preference for that encoding. The default value is q=1.
[248]1097      </p>
[424]1098      <p id="rfc.section.5.3.p.4">Examples of its use are:</p>
[459]1099      <div id="rfc.figure.u.23"></div><pre class="text">  Accept-Encoding: compress, gzip
[357]1100  Accept-Encoding:
1101  Accept-Encoding: *
1102  Accept-Encoding: compress;q=0.5, gzip;q=1.0
1103  Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
[424]1104</pre><p id="rfc.section.5.3.p.6">A server tests whether a content-coding is acceptable, according to an Accept-Encoding field, using these rules: </p>
[97]1105      <ol>
1106         <li>If the content-coding is one of the content-codings listed in the Accept-Encoding field, then it is acceptable, unless it
[457]1107            is accompanied by a qvalue of 0. (As defined in <a href="p1-messaging.html#quality.values" title="Quality Values">Section 3.5</a> of <a href="#Part1" id="rfc.xref.Part1.15"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, a qvalue of 0 means "not acceptable.")
[97]1108         </li>
1109         <li>The special "*" symbol in an Accept-Encoding field matches any available content-coding not explicitly listed in the header
1110            field.
1111         </li>
1112         <li>If multiple content-codings are acceptable, then the acceptable content-coding with the highest non-zero qvalue is preferred.</li>
1113         <li>The "identity" content-coding is always acceptable, unless specifically refused because the Accept-Encoding field includes
1114            "identity;q=0", or because the field includes "*;q=0" and does not explicitly include the "identity" content-coding. If the
1115            Accept-Encoding field-value is empty, then only the "identity" encoding is acceptable.
1116         </li>
1117      </ol>
[424]1118      <p id="rfc.section.5.3.p.7">If an Accept-Encoding field is present in a request, and if the server cannot send a response which is acceptable according
[97]1119         to the Accept-Encoding header, then the server <em class="bcp14">SHOULD</em> send an error response with the 406 (Not Acceptable) status code.
1120      </p>
[424]1121      <p id="rfc.section.5.3.p.8">If no Accept-Encoding field is present in a request, the server <em class="bcp14">MAY</em> assume that the client will accept any content coding. In this case, if "identity" is one of the available content-codings,
[97]1122         then the server <em class="bcp14">SHOULD</em> use the "identity" content-coding, unless it has additional information that a different content-coding is meaningful to the
[563]1123         client.
[97]1124      </p>
[563]1125      <div class="note"> 
1126         <p> <b>Note:</b> If the request does not include an Accept-Encoding field, and if the "identity" content-coding is unavailable, then content-codings
[97]1127            commonly understood by HTTP/1.0 clients (i.e., "gzip" and "compress") are preferred; some older clients improperly display
1128            messages sent with other content-codings. The server might also make this decision based on information about the particular
1129            user-agent or client.
[563]1130         </p> 
1131      </div>
1132      <div class="note"> 
1133         <p> <b>Note:</b> Most HTTP/1.0 applications do not recognize or obey qvalues associated with content-codings. This means that qvalues will
[97]1134            not work and are not permitted with x-gzip or x-compress.
[563]1135         </p> 
1136      </div>
[97]1137      <div id="rfc.iref.a.4"></div>
1138      <div id="rfc.iref.h.4"></div>
[424]1139      <h2 id="rfc.section.5.4"><a href="#rfc.section.5.4">5.4</a>&nbsp;<a id="header.accept-language" href="#header.accept-language">Accept-Language</a></h2>
1140      <p id="rfc.section.5.4.p.1">The request-header field "Accept-Language" is similar to Accept, but restricts the set of natural languages that are preferred
[457]1141         as a response to the request. Language tags are defined in <a href="#language.tags" title="Language Tags">Section&nbsp;2.4</a>.
[97]1142      </p>
[459]1143      <div id="rfc.figure.u.24"></div><pre class="inline"><span id="rfc.iref.g.26"></span><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span>  <a href="#header.accept-language" class="smpl">Accept-Language</a>   = "Accept-Language" ":" <a href="#core.rules" class="smpl">OWS</a>
[357]1144                    <a href="#header.accept-language" class="smpl">Accept-Language-v</a>
1145  <a href="#header.accept-language" class="smpl">Accept-Language-v</a> =
[457]1146                    1#( <a href="#header.accept-language" class="smpl">language-range</a> [ <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> "q=" <a href="#abnf.dependencies" class="smpl">qvalue</a> ] )
[357]1147  <a href="#header.accept-language" class="smpl">language-range</a>    =
[303]1148            &lt;language-range, defined in <a href="#RFC4647" id="rfc.xref.RFC4647.1"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="http://tools.ietf.org/html/rfc4647#section-2.1">Section 2.1</a>&gt;
[424]1149</pre><p id="rfc.section.5.4.p.3">Each language-range can be given an associated quality value which represents an estimate of the user's preference for the
[303]1150         languages specified by that range. The quality value defaults to "q=1". For example,
[97]1151      </p>
[459]1152      <div id="rfc.figure.u.25"></div><pre class="text">  Accept-Language: da, en-gb;q=0.8, en;q=0.7
[424]1153</pre><p id="rfc.section.5.4.p.5">would mean: "I prefer Danish, but will accept British English and other types of English."</p>
1154      <p id="rfc.section.5.4.p.6">For matching, the "Basic Filtering" matching scheme, defined in <a href="http://tools.ietf.org/html/rfc4647#section-3.3.1">Section 3.3.1</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, is used:
[97]1155      </p>
[424]1156      <blockquote id="rfc.section.5.4.p.7" cite="http://tools.ietf.org/html/rfc4647#section-3.3.1"> 
[303]1157         <p>A language range matches a particular language tag if, in a case-insensitive comparison, it exactly equals the tag, or if
1158            it exactly equals a prefix of the tag such that the first character following the prefix is "-".
1159         </p> 
1160      </blockquote>
[424]1161      <p id="rfc.section.5.4.p.8">The special range "*", if present in the Accept-Language field, matches every tag not matched by any other range present in
[563]1162         the Accept-Language field.
[303]1163      </p>
[563]1164      <div class="note"> 
1165         <p> <b>Note:</b> This use of a prefix matching rule does not imply that language tags are assigned to languages in such a way that it is always
[97]1166            true that if a user understands a language with a certain tag, then this user will also understand all languages with tags
1167            for which this tag is a prefix. The prefix rule simply allows the use of prefix tags if this is the case.
[563]1168         </p> 
1169      </div>
1170      <p id="rfc.section.5.4.p.10">The language quality factor assigned to a language-tag by the Accept-Language field is the quality value of the longest language-range
[97]1171         in the field that matches the language-tag. If no language-range in the field matches the tag, the language quality factor
1172         assigned is 0. If no Accept-Language header is present in the request, the server <em class="bcp14">SHOULD</em> assume that all languages are equally acceptable. If an Accept-Language header is present, then all languages which are assigned
1173         a quality factor greater than 0 are acceptable.
1174      </p>
[563]1175      <p id="rfc.section.5.4.p.11">It might be contrary to the privacy expectations of the user to send an Accept-Language header with the complete linguistic
[424]1176         preferences of the user in every request. For a discussion of this issue, see <a href="#privacy.issues.connected.to.accept.headers" title="Privacy Issues Connected to Accept Headers">Section&nbsp;7.1</a>.
[97]1177      </p>
[563]1178      <p id="rfc.section.5.4.p.12">As intelligibility is highly dependent on the individual user, it is recommended that client applications make the choice
1179         of linguistic preference available to the user. If the choice is not made available, then the Accept-Language header field <em class="bcp14">MUST NOT</em> be given in the request.
[97]1180      </p>
[563]1181      <div class="note"> 
1182         <p> <b>Note:</b> When making the choice of linguistic preference available to the user, we remind implementors of the fact that users are not
[97]1183            familiar with the details of language matching as described above, and should provide appropriate guidance. As an example,
1184            users might assume that on selecting "en-gb", they will be served any kind of English document if British English is not available.
1185            A user agent might suggest in such a case to add "en" to get the best matching behavior.
[563]1186         </p> 
1187      </div>
[97]1188      <div id="rfc.iref.c.2"></div>
1189      <div id="rfc.iref.h.5"></div>
[424]1190      <h2 id="rfc.section.5.5"><a href="#rfc.section.5.5">5.5</a>&nbsp;<a id="header.content-encoding" href="#header.content-encoding">Content-Encoding</a></h2>
1191      <p id="rfc.section.5.5.p.1">The entity-header field "Content-Encoding" is used as a modifier to the media-type. When present, its value indicates what
[357]1192         additional content codings have been applied to the entity-body, and thus what decoding mechanisms must be applied in order
1193         to obtain the media-type referenced by the Content-Type header field. Content-Encoding is primarily used to allow a document
1194         to be compressed without losing the identity of its underlying media type.
[97]1195      </p>
[459]1196      <div id="rfc.figure.u.26"></div><pre class="inline"><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span>  <a href="#header.content-encoding" class="smpl">Content-Encoding</a>   = "Content-Encoding" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.content-encoding" class="smpl">Content-Encoding-v</a>
[357]1197  <a href="#header.content-encoding" class="smpl">Content-Encoding-v</a> = 1#<a href="#content.codings" class="smpl">content-coding</a>
[424]1198</pre><p id="rfc.section.5.5.p.3">Content codings are defined in <a href="#content.codings" title="Content Codings">Section&nbsp;2.2</a>. An example of its use is
[97]1199      </p>
[459]1200      <div id="rfc.figure.u.27"></div><pre class="text">  Content-Encoding: gzip
[424]1201</pre><p id="rfc.section.5.5.p.5">The content-coding is a characteristic of the entity identified by the request-target. Typically, the entity-body is stored
[391]1202         with this encoding and is only decoded before rendering or analogous usage. However, a non-transparent proxy <em class="bcp14">MAY</em> modify the content-coding if the new coding is known to be acceptable to the recipient, unless the "no-transform" cache-control
[97]1203         directive is present in the message.
1204      </p>
[424]1205      <p id="rfc.section.5.5.p.6">If the content-coding of an entity is not "identity", then the response <em class="bcp14">MUST</em> include a Content-Encoding entity-header (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.3" title="Content-Encoding">Section&nbsp;5.5</a>) that lists the non-identity content-coding(s) used.
[97]1206      </p>
[424]1207      <p id="rfc.section.5.5.p.7">If the content-coding of an entity in a request message is not acceptable to the origin server, the server <em class="bcp14">SHOULD</em> respond with a status code of 415 (Unsupported Media Type).
[97]1208      </p>
[424]1209      <p id="rfc.section.5.5.p.8">If multiple encodings have been applied to an entity, the content codings <em class="bcp14">MUST</em> be listed in the order in which they were applied. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other entity-header fields not defined by this specification.
[97]1210      </p>
1211      <div id="rfc.iref.c.3"></div>
1212      <div id="rfc.iref.h.6"></div>
[424]1213      <h2 id="rfc.section.5.6"><a href="#rfc.section.5.6">5.6</a>&nbsp;<a id="header.content-language" href="#header.content-language">Content-Language</a></h2>
1214      <p id="rfc.section.5.6.p.1">The entity-header field "Content-Language" describes the natural language(s) of the intended audience for the enclosed entity.
[97]1215         Note that this might not be equivalent to all the languages used within the entity-body.
1216      </p>
[459]1217      <div id="rfc.figure.u.28"></div><pre class="inline"><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span>  <a href="#header.content-language" class="smpl">Content-Language</a>   = "Content-Language" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.content-language" class="smpl">Content-Language-v</a>
[357]1218  <a href="#header.content-language" class="smpl">Content-Language-v</a> = 1#<a href="#language.tags" class="smpl">language-tag</a>
[457]1219</pre><p id="rfc.section.5.6.p.3">Language tags are defined in <a href="#language.tags" title="Language Tags">Section&nbsp;2.4</a>. The primary purpose of Content-Language is to allow a user to identify and differentiate entities according to the user's
[97]1220         own preferred language. Thus, if the body content is intended only for a Danish-literate audience, the appropriate field is
1221      </p>
[459]1222      <div id="rfc.figure.u.29"></div><pre class="text">  Content-Language: da
[424]1223</pre><p id="rfc.section.5.6.p.5">If no Content-Language is specified, the default is that the content is intended for all language audiences. This might mean
[97]1224         that the sender does not consider it to be specific to any natural language, or that the sender does not know for which language
1225         it is intended.
1226      </p>
[424]1227      <p id="rfc.section.5.6.p.6">Multiple languages <em class="bcp14">MAY</em> be listed for content that is intended for multiple audiences. For example, a rendition of the "Treaty of Waitangi," presented
[97]1228         simultaneously in the original Maori and English versions, would call for
1229      </p>
[459]1230      <div id="rfc.figure.u.30"></div><pre class="text">  Content-Language: mi, en
[424]1231</pre><p id="rfc.section.5.6.p.8">However, just because multiple languages are present within an entity does not mean that it is intended for multiple linguistic
[97]1232         audiences. An example would be a beginner's language primer, such as "A First Lesson in Latin," which is clearly intended
1233         to be used by an English-literate audience. In this case, the Content-Language would properly only include "en".
1234      </p>
[424]1235      <p id="rfc.section.5.6.p.9">Content-Language <em class="bcp14">MAY</em> be applied to any media type -- it is not limited to textual documents.
[97]1236      </p>
1237      <div id="rfc.iref.c.4"></div>
1238      <div id="rfc.iref.h.7"></div>
[424]1239      <h2 id="rfc.section.5.7"><a href="#rfc.section.5.7">5.7</a>&nbsp;<a id="header.content-location" href="#header.content-location">Content-Location</a></h2>
1240      <p id="rfc.section.5.7.p.1">The entity-header field "Content-Location" <em class="bcp14">MAY</em> be used to supply the resource location for the entity enclosed in the message when that entity is accessible from a location
[97]1241         separate from the requested resource's URI. A server <em class="bcp14">SHOULD</em> provide a Content-Location for the variant corresponding to the response entity; especially in the case where a resource has
1242         multiple entities associated with it, and those entities actually have separate locations by which they might be individually
1243         accessed, the server <em class="bcp14">SHOULD</em> provide a Content-Location for the particular variant which is returned.
1244      </p>
[459]1245      <div id="rfc.figure.u.31"></div><pre class="inline"><span id="rfc.iref.g.33"></span><span id="rfc.iref.g.34"></span>  <a href="#header.content-location" class="smpl">Content-Location</a>   = "Content-Location" ":" <a href="#core.rules" class="smpl">OWS</a>
[357]1246                    <a href="#header.content-location" class="smpl">Content-Location-v</a>
1247  <a href="#header.content-location" class="smpl">Content-Location-v</a> =
[391]1248                    <a href="#abnf.dependencies" class="smpl">absolute-URI</a> / <a href="#abnf.dependencies" class="smpl">partial-URI</a>
[424]1249</pre><p id="rfc.section.5.7.p.3">The value of Content-Location also defines the base URI for the entity.</p>
1250      <p id="rfc.section.5.7.p.4">The Content-Location value is not a replacement for the original requested URI; it is only a statement of the location of
[391]1251         the resource corresponding to this particular entity at the time of the request. Future requests <em class="bcp14">MAY</em> specify the Content-Location URI as the request-target if the desire is to identify the source of that particular entity.
[97]1252      </p>
[424]1253      <p id="rfc.section.5.7.p.5">A cache cannot assume that an entity with a Content-Location different from the URI used to retrieve it can be used to respond
[97]1254         to later requests on that Content-Location URI. However, the Content-Location can be used to differentiate between multiple
[538]1255         entities retrieved from a single requested resource, as described in <a href="p6-cache.html#caching.negotiated.responses" title="Caching Negotiated Responses">Section 2.6</a> of <a href="#Part6" id="rfc.xref.Part6.4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.
[97]1256      </p>
[424]1257      <p id="rfc.section.5.7.p.6">If the Content-Location is a relative URI, the relative URI is interpreted relative to the request-target.</p>
[577]1258      <p id="rfc.section.5.7.p.7">The meaning of the Content-Location header in requests is undefined; servers are free to ignore it in those cases.</p>
[97]1259      <div id="rfc.iref.c.5"></div>
1260      <div id="rfc.iref.h.8"></div>
[424]1261      <h2 id="rfc.section.5.8"><a href="#rfc.section.5.8">5.8</a>&nbsp;<a id="header.content-md5" href="#header.content-md5">Content-MD5</a></h2>
1262      <p id="rfc.section.5.8.p.1">The entity-header field "Content-MD5", as defined in <a href="#RFC1864" id="rfc.xref.RFC1864.1"><cite title="The Content-MD5 Header Field">[RFC1864]</cite></a>, is an MD5 digest of the entity-body for the purpose of providing an end-to-end message integrity check (MIC) of the entity-body.
[97]1263         (Note: a MIC is good for detecting accidental modification of the entity-body in transit, but is not proof against malicious
1264         attacks.)
1265      </p>
[459]1266      <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span>  <a href="#header.content-md5" class="smpl">Content-MD5</a>   = "Content-MD5" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.content-md5" class="smpl">Content-MD5-v</a>
[357]1267  <a href="#header.content-md5" class="smpl">Content-MD5-v</a> = &lt;base64 of 128 bit MD5 digest as per <a href="#RFC1864" id="rfc.xref.RFC1864.2"><cite title="The Content-MD5 Header Field">[RFC1864]</cite></a>&gt;
[424]1268</pre><p id="rfc.section.5.8.p.3">The Content-MD5 header field <em class="bcp14">MAY</em> be generated by an origin server or client to function as an integrity check of the entity-body. Only origin servers or clients <em class="bcp14">MAY</em> generate the Content-MD5 header field; proxies and gateways <em class="bcp14">MUST NOT</em> generate it, as this would defeat its value as an end-to-end integrity check. Any recipient of the entity-body, including
[97]1269         gateways and proxies, <em class="bcp14">MAY</em> check that the digest value in this header field matches that of the entity-body as received.
1270      </p>
[424]1271      <p id="rfc.section.5.8.p.4">The MD5 digest is computed based on the content of the entity-body, including any content-coding that has been applied, but
[97]1272         not including any transfer-encoding applied to the message-body. If the message is received with a transfer-encoding, that
1273         encoding <em class="bcp14">MUST</em> be removed prior to checking the Content-MD5 value against the received entity.
1274      </p>
[424]1275      <p id="rfc.section.5.8.p.5">This has the result that the digest is computed on the octets of the entity-body exactly as, and in the order that, they would
[97]1276         be sent if no transfer-encoding were being applied.
1277      </p>
[424]1278      <p id="rfc.section.5.8.p.6">HTTP extends RFC 1864 to permit the digest to be computed for MIME composite media-types (e.g., multipart/* and message/rfc822),
[97]1279         but this does not change how the digest is computed as defined in the preceding paragraph.
1280      </p>
[424]1281      <p id="rfc.section.5.8.p.7">There are several consequences of this. The entity-body for composite types <em class="bcp14">MAY</em> contain many body-parts, each with its own MIME and HTTP headers (including Content-MD5, Content-Transfer-Encoding, and Content-Encoding
[97]1282         headers). If a body-part has a Content-Transfer-Encoding or Content-Encoding header, it is assumed that the content of the
1283         body-part has had the encoding applied, and the body-part is included in the Content-MD5 digest as is -- i.e., after the application.
1284         The Transfer-Encoding header field is not allowed within body-parts.
1285      </p>
[563]1286      <p id="rfc.section.5.8.p.8">Conversion of all line breaks to CRLF <em class="bcp14">MUST NOT</em> be done before computing or checking the digest: the line break convention used in the text actually transmitted <em class="bcp14">MUST</em> be left unaltered when computing the digest.
[97]1287      </p>
[563]1288      <div class="note"> 
1289         <p> <b>Note:</b> while the definition of Content-MD5 is exactly the same for HTTP as in RFC 1864 for MIME entity-bodies, there are several
[97]1290            ways in which the application of Content-MD5 to HTTP entity-bodies differs from its application to MIME entity-bodies. One
1291            is that HTTP, unlike MIME, does not use Content-Transfer-Encoding, and does use Transfer-Encoding and Content-Encoding. Another
1292            is that HTTP more frequently uses binary content types than MIME, so it is worth noting that, in such cases, the byte order
1293            used to compute the digest is the transmission byte order defined for the type. Lastly, HTTP allows transmission of text types
1294            with any of several line break conventions and not just the canonical form using CRLF.
[563]1295         </p> 
1296      </div>
[97]1297      <div id="rfc.iref.c.6"></div>
1298      <div id="rfc.iref.h.9"></div>
[424]1299      <h2 id="rfc.section.5.9"><a href="#rfc.section.5.9">5.9</a>&nbsp;<a id="header.content-type" href="#header.content-type">Content-Type</a></h2>
1300      <p id="rfc.section.5.9.p.1">The entity-header field "Content-Type" indicates the media type of the entity-body sent to the recipient or, in the case of
[97]1301         the HEAD method, the media type that would have been sent had the request been a GET.
1302      </p>
[459]1303      <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.37"></span><span id="rfc.iref.g.38"></span>  <a href="#header.content-type" class="smpl">Content-Type</a>   = "Content-Type" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#header.content-type" class="smpl">Content-Type-v</a>
[357]1304  <a href="#header.content-type" class="smpl">Content-Type-v</a> = <a href="#media.types" class="smpl">media-type</a>
[424]1305</pre><p id="rfc.section.5.9.p.3">Media types are defined in <a href="#media.types" title="Media Types">Section&nbsp;2.3</a>. An example of the field is
[97]1306      </p>
[459]1307      <div id="rfc.figure.u.34"></div><pre class="text">  Content-Type: text/html; charset=ISO-8859-4
[424]1308</pre><p id="rfc.section.5.9.p.5">Further discussion of methods for identifying the media type of an entity is provided in <a href="#type" title="Type">Section&nbsp;3.2.1</a>.
[97]1309      </p>
[424]1310      <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
1311      <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="message.header.registration" href="#message.header.registration">Message Header Registration</a></h2>
1312      <p id="rfc.section.6.1.p.1">The Message Header Registry located at &lt;<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>&gt; should be updated with the permanent registrations below (see <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>):
[203]1313      </p>
[290]1314      <div id="rfc.table.1">
1315         <div id="iana.header.registration.table"></div>
[253]1316         <table summary="" class="tt full" cellpadding="3" cellspacing="0">
1317            <thead>
1318               <tr>
1319                  <th>Header Field Name</th>
1320                  <th>Protocol</th>
1321                  <th>Status</th>
1322                  <th>Reference</th>
1323               </tr>
1324            </thead>
1325            <tbody>
1326               <tr>
1327                  <td>Accept</td>
1328                  <td>http</td>
1329                  <td>standard</td>
[424]1330                  <td> <a href="#header.accept" id="rfc.xref.header.accept.3" title="Accept">Section&nbsp;5.1</a> 
[253]1331                  </td>
1332               </tr>
1333               <tr>
1334                  <td>Accept-Charset</td>
1335                  <td>http</td>
1336                  <td>standard</td>
[424]1337                  <td> <a href="#header.accept-charset" id="rfc.xref.header.accept-charset.2" title="Accept-Charset">Section&nbsp;5.2</a> 
[253]1338                  </td>
1339               </tr>
1340               <tr>
1341                  <td>Accept-Encoding</td>
1342                  <td>http</td>
1343                  <td>standard</td>
[424]1344                  <td> <a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.3" title="Accept-Encoding">Section&nbsp;5.3</a> 
[253]1345                  </td>
1346               </tr>
1347               <tr>
1348                  <td>Accept-Language</td>
1349                  <td>http</td>
1350                  <td>standard</td>
[424]1351                  <td> <a href="#header.accept-language" id="rfc.xref.header.accept-language.2" title="Accept-Language">Section&nbsp;5.4</a> 
[253]1352                  </td>
1353               </tr>
1354               <tr>
1355                  <td>Content-Disposition</td>
1356                  <td>http</td>
[291]1357                  <td></td>
[253]1358                  <td> <a href="#content-disposition" id="rfc.xref.content-disposition.1" title="Content-Disposition">Appendix&nbsp;B.1</a> 
1359                  </td>
1360               </tr>
1361               <tr>
1362                  <td>Content-Encoding</td>
1363                  <td>http</td>
1364                  <td>standard</td>
[424]1365                  <td> <a href="#header.content-encoding" id="rfc.xref.header.content-encoding.4" title="Content-Encoding">Section&nbsp;5.5</a> 
[253]1366                  </td>
1367               </tr>
1368               <tr>
1369                  <td>Content-Language</td>
1370                  <td>http</td>
1371                  <td>standard</td>
[424]1372                  <td> <a href="#header.content-language" id="rfc.xref.header.content-language.2" title="Content-Language">Section&nbsp;5.6</a> 
[253]1373                  </td>
1374               </tr>
1375               <tr>
1376                  <td>Content-Location</td>
1377                  <td>http</td>
1378                  <td>standard</td>
[424]1379                  <td> <a href="#header.content-location" id="rfc.xref.header.content-location.2" title="Content-Location">Section&nbsp;5.7</a> 
[253]1380                  </td>
1381               </tr>
1382               <tr>
1383                  <td>Content-MD5</td>
1384                  <td>http</td>
1385                  <td>standard</td>
[424]1386                  <td> <a href="#header.content-md5" id="rfc.xref.header.content-md5.2" title="Content-MD5">Section&nbsp;5.8</a> 
[253]1387                  </td>
1388               </tr>
1389               <tr>
1390                  <td>Content-Type</td>
1391                  <td>http</td>
1392                  <td>standard</td>
[424]1393                  <td> <a href="#header.content-type" id="rfc.xref.header.content-type.3" title="Content-Type">Section&nbsp;5.9</a> 
[253]1394                  </td>
1395               </tr>
[291]1396               <tr>
1397                  <td>MIME-Version</td>
1398                  <td>http</td>
1399                  <td></td>
1400                  <td> <a href="#mime-version" id="rfc.xref.mime-version.1" title="MIME-Version">Appendix&nbsp;A.1</a> 
1401                  </td>
1402               </tr>
[253]1403            </tbody>
1404         </table>
1405      </div>
[424]1406      <p id="rfc.section.6.1.p.2">The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>
1407      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
1408      <p id="rfc.section.7.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1
[97]1409         as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does
1410         make some suggestions for reducing security risks.
1411      </p>
[424]1412      <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="privacy.issues.connected.to.accept.headers" href="#privacy.issues.connected.to.accept.headers">Privacy Issues Connected to Accept Headers</a></h2>
1413      <p id="rfc.section.7.1.p.1">Accept request-headers can reveal information about the user to all servers which are accessed. The Accept-Language header
[97]1414         in particular can reveal information the user would consider to be of a private nature, because the understanding of particular
1415         languages is often strongly correlated to the membership of a particular ethnic group. User agents which offer the option
1416         to configure the contents of an Accept-Language header to be sent in every request are strongly encouraged to let the configuration
1417         process include a message which makes the user aware of the loss of privacy involved.
1418      </p>
[424]1419      <p id="rfc.section.7.1.p.2">An approach that limits the loss of privacy would be for a user agent to omit the sending of Accept-Language headers by default,
[97]1420         and to ask the user whether or not to start sending Accept-Language headers to a server if it detects, by looking for any
1421         Vary response-header fields generated by the server, that such sending could improve the quality of service.
1422      </p>
[424]1423      <p id="rfc.section.7.1.p.3">Elaborate user-customized accept header fields sent in every request, in particular if these include quality values, can be
[97]1424         used by servers as relatively reliable and long-lived user identifiers. Such user identifiers would allow content providers
1425         to do click-trail tracking, and would allow collaborating content providers to match cross-server click-trails or form submissions
1426         of individual users. Note that for many users not behind a proxy, the network address of the host running the user agent will
1427         also serve as a long-lived user identifier. In environments where proxies are used to enhance privacy, user agents ought to
1428         be conservative in offering accept header configuration options to end users. As an extreme privacy measure, proxies could
1429         filter the accept headers in relayed requests. General purpose user agents which provide a high degree of header configurability <em class="bcp14">SHOULD</em> warn users about the loss of privacy which can be involved.
1430      </p>
[424]1431      <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a id="content-disposition.issues" href="#content-disposition.issues">Content-Disposition Issues</a></h2>
1432      <p id="rfc.section.7.2.p.1"> <a href="#RFC2183" id="rfc.xref.RFC2183.1"><cite title="Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field">[RFC2183]</cite></a>, from which the often implemented Content-Disposition (see <a href="#content-disposition" id="rfc.xref.content-disposition.2" title="Content-Disposition">Appendix&nbsp;B.1</a>) header in HTTP is derived, has a number of very serious security considerations. Content-Disposition is not part of the
[269]1433         HTTP standard, but since it is widely implemented, we are documenting its use and risks for implementors. See <a href="http://tools.ietf.org/html/rfc2183#section-5">Section 5</a> of <a href="#RFC2183" id="rfc.xref.RFC2183.2"><cite title="Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field">[RFC2183]</cite></a> for details.
[97]1434      </p>
[424]1435      <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
1436      <h1 id="rfc.references"><a id="rfc.section.9" href="#rfc.section.9">9.</a> References
[97]1437      </h1>
[424]1438      <h2 id="rfc.references.1"><a href="#rfc.section.9.1" id="rfc.section.9.1">9.1</a> Normative References
[119]1439      </h2>
[425]1440      <table summary="Normative References">                               
[97]1441         <tr>
[121]1442            <td class="reference"><b id="ISO-8859-1">[ISO-8859-1]</b></td>
[446]1443            <td class="top">International Organization for Standardization, “Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1”, ISO/IEC&nbsp;8859-1:1998, 1998.</td>
[121]1444         </tr>
1445         <tr>
[97]1446            <td class="reference"><b id="Part1">[Part1]</b></td>
[573]1447            <td class="top"><a title="Day Software">Fielding, R., Ed.</a>, <a title="One Laptop per Child">Gettys, J.</a>, <a title="Hewlett-Packard Company">Mogul, J.</a>, <a title="Microsoft Corporation">Frystyk, H.</a>, <a title="Adobe Systems, Incorporated">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, <a title="World Wide Web Consortium">Berners-Lee, T.</a>, <a title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a title="greenbytes GmbH">J. F. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-latest">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p1-messaging-latest (work in progress), May&nbsp;2009.
[97]1448            </td>
1449         </tr>
1450         <tr>
1451            <td class="reference"><b id="Part2">[Part2]</b></td>
[573]1452            <td class="top"><a title="Day Software">Fielding, R., Ed.</a>, <a title="One Laptop per Child">Gettys, J.</a>, <a title="Hewlett-Packard Company">Mogul, J.</a>, <a title="Microsoft Corporation">Frystyk, H.</a>, <a title="Adobe Systems, Incorporated">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, <a title="World Wide Web Consortium">Berners-Lee, T.</a>, <a title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a title="greenbytes GmbH">J. F. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p2-semantics-latest">HTTP/1.1, part 2: Message Semantics</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p2-semantics-latest (work in progress), May&nbsp;2009.
[97]1453            </td>
1454         </tr>
1455         <tr>
1456            <td class="reference"><b id="Part4">[Part4]</b></td>
[573]1457            <td class="top"><a title="Day Software">Fielding, R., Ed.</a>, <a title="One Laptop per Child">Gettys, J.</a>, <a title="Hewlett-Packard Company">Mogul, J.</a>, <a title="Microsoft Corporation">Frystyk, H.</a>, <a title="Adobe Systems, Incorporated">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, <a title="World Wide Web Consortium">Berners-Lee, T.</a>, <a title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a title="greenbytes GmbH">J. F. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-latest">HTTP/1.1, part 4: Conditional Requests</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p4-conditional-latest (work in progress), May&nbsp;2009.
[97]1458            </td>
1459         </tr>
1460         <tr>
1461            <td class="reference"><b id="Part5">[Part5]</b></td>
[573]1462            <td class="top"><a title="Day Software">Fielding, R., Ed.</a>, <a title="One Laptop per Child">Gettys, J.</a>, <a title="Hewlett-Packard Company">Mogul, J.</a>, <a title="Microsoft Corporation">Frystyk, H.</a>, <a title="Adobe Systems, Incorporated">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, <a title="World Wide Web Consortium">Berners-Lee, T.</a>, <a title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a title="greenbytes GmbH">J. F. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-latest">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p5-range-latest (work in progress), May&nbsp;2009.
[97]1463            </td>
1464         </tr>
1465         <tr>
1466            <td class="reference"><b id="Part6">[Part6]</b></td>
[573]1467            <td class="top"><a title="Day Software">Fielding, R., Ed.</a>, <a title="One Laptop per Child">Gettys, J.</a>, <a title="Hewlett-Packard Company">Mogul, J.</a>, <a title="Microsoft Corporation">Frystyk, H.</a>, <a title="Adobe Systems, Incorporated">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, <a title="World Wide Web Consortium">Berners-Lee, T.</a>, <a title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a title="greenbytes GmbH">J. F. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-latest">HTTP/1.1, part 6: Caching</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p6-cache-latest (work in progress), May&nbsp;2009.
[97]1468            </td>
1469         </tr>
1470         <tr>
[132]1471            <td class="reference"><b id="RFC1766">[RFC1766]</b></td>
1472            <td class="top"><a title="UNINETT">Alvestrand, H.</a>, “<a href="http://tools.ietf.org/html/rfc1766">Tags for the Identification of Languages</a>”, RFC&nbsp;1766, March&nbsp;1995.
1473            </td>
1474         </tr>
1475         <tr>
[131]1476            <td class="reference"><b id="RFC1864">[RFC1864]</b></td>
1477            <td class="top"><a title="Carnegie Mellon University">Myers, J.</a> and <a title="Dover Beach Consulting, Inc.">M. Rose</a>, “<a href="http://tools.ietf.org/html/rfc1864">The Content-MD5 Header Field</a>”, RFC&nbsp;1864, October&nbsp;1995.
1478            </td>
1479         </tr>
1480         <tr>
[122]1481            <td class="reference"><b id="RFC1950">[RFC1950]</b></td>
[277]1482            <td class="top"><a title="Aladdin Enterprises">Deutsch, L.P.</a> and J-L. Gailly, “<a href="http://tools.ietf.org/html/rfc1950">ZLIB Compressed Data Format Specification version 3.3</a>”, RFC&nbsp;1950, May&nbsp;1996.<br>RFC 1950 is an Informational RFC, thus it may be less stable than this specification. On the other hand, this downward reference
1483               was present since the publication of RFC 2068 in 1997 (<a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>), therefore it is unlikely to cause problems in practice. See also <a href="#BCP97" id="rfc.xref.BCP97.1"><cite title="Handling Normative References to Standards-Track Documents">[BCP97]</cite></a>.
[122]1484            </td>
1485         </tr>
1486         <tr>
1487            <td class="reference"><b id="RFC1951">[RFC1951]</b></td>
[277]1488            <td class="top"><a title="Aladdin Enterprises">Deutsch, P.</a>, “<a href="http://tools.ietf.org/html/rfc1951">DEFLATE Compressed Data Format Specification version 1.3</a>”, RFC&nbsp;1951, May&nbsp;1996.<br>RFC 1951 is an Informational RFC, thus it may be less stable than this specification. On the other hand, this downward reference
1489               was present since the publication of RFC 2068 in 1997 (<a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>), therefore it is unlikely to cause problems in practice. See also <a href="#BCP97" id="rfc.xref.BCP97.2"><cite title="Handling Normative References to Standards-Track Documents">[BCP97]</cite></a>.
[122]1490            </td>
1491         </tr>
1492         <tr>
1493            <td class="reference"><b id="RFC1952">[RFC1952]</b></td>
[277]1494            <td class="top"><a title="Aladdin Enterprises">Deutsch, P.</a>, <a>Gailly, J-L.</a>, <a>Adler, M.</a>, <a>Deutsch, L.P.</a>, and <a>G. Randers-Pehrson</a>, “<a href="http://tools.ietf.org/html/rfc1952">GZIP file format specification version 4.3</a>”, RFC&nbsp;1952, May&nbsp;1996.<br>RFC 1952 is an Informational RFC, thus it may be less stable than this specification. On the other hand, this downward reference
1495               was present since the publication of RFC 2068 in 1997 (<a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>), therefore it is unlikely to cause problems in practice. See also <a href="#BCP97" id="rfc.xref.BCP97.3"><cite title="Handling Normative References to Standards-Track Documents">[BCP97]</cite></a>.
[122]1496            </td>
1497         </tr>
1498         <tr>
[131]1499            <td class="reference"><b id="RFC2045">[RFC2045]</b></td>
1500            <td class="top"><a title="Innosoft International, Inc.">Freed, N.</a> and <a title="First Virtual Holdings">N.S. Borenstein</a>, “<a href="http://tools.ietf.org/html/rfc2045">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</a>”, RFC&nbsp;2045, November&nbsp;1996.
1501            </td>
1502         </tr>
1503         <tr>
1504            <td class="reference"><b id="RFC2046">[RFC2046]</b></td>
1505            <td class="top"><a title="Innosoft International, Inc.">Freed, N.</a> and <a title="First Virtual Holdings">N. Borenstein</a>, “<a href="http://tools.ietf.org/html/rfc2046">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</a>”, RFC&nbsp;2046, November&nbsp;1996.
1506            </td>
1507         </tr>
1508         <tr>
[119]1509            <td class="reference"><b id="RFC2119">[RFC2119]</b></td>
1510            <td class="top"><a title="Harvard University">Bradner, S.</a>, “<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>”, BCP&nbsp;14, RFC&nbsp;2119, March&nbsp;1997.
1511            </td>
1512         </tr>
[303]1513         <tr>
1514            <td class="reference"><b id="RFC4647">[RFC4647]</b></td>
1515            <td class="top"><a title="Yahoo! Inc.">Phillips, A., Ed.</a> and <a title="Google">M. Davis, Ed.</a>, “<a href="http://tools.ietf.org/html/rfc4647">Matching of Language Tags</a>”, BCP&nbsp;47, RFC&nbsp;4647, September&nbsp;2006.
1516            </td>
1517         </tr>
[425]1518         <tr>
1519            <td class="reference"><b id="RFC5234">[RFC5234]</b></td>
1520            <td class="top"><a title="Brandenburg InternetWorking">Crocker, D., Ed.</a> and <a title="THUS plc.">P. Overell</a>, “<a href="http://tools.ietf.org/html/rfc5234">Augmented BNF for Syntax Specifications: ABNF</a>”, STD&nbsp;68, RFC&nbsp;5234, January&nbsp;2008.
1521            </td>
1522         </tr>
[119]1523      </table>
[424]1524      <h2 id="rfc.references.2"><a href="#rfc.section.9.2" id="rfc.section.9.2">9.2</a> Informative References
[119]1525      </h2>
[277]1526      <table summary="Informative References">                           
[119]1527         <tr>
[277]1528            <td class="reference"><b id="BCP97">[BCP97]</b></td>
1529            <td class="top"><a>Klensin, J.</a> and <a title="MIT">S. Hartman</a>, “<a href="http://tools.ietf.org/html/rfc4897">Handling Normative References to Standards-Track Documents</a>”, BCP&nbsp;97, RFC&nbsp;4897, June&nbsp;2007.
1530            </td>
1531         </tr>
1532         <tr>
[129]1533            <td class="reference"><b id="RFC1945">[RFC1945]</b></td>
1534            <td class="top"><a title="MIT, Laboratory for Computer Science">Berners-Lee, T.</a>, <a title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.T.</a>, and <a title="W3 Consortium, MIT Laboratory for Computer Science">H.F. Nielsen</a>, “<a href="http://tools.ietf.org/html/rfc1945">Hypertext Transfer Protocol -- HTTP/1.0</a>”, RFC&nbsp;1945, May&nbsp;1996.
[119]1535            </td>
1536         </tr>
1537         <tr>
[129]1538            <td class="reference"><b id="RFC2049">[RFC2049]</b></td>
1539            <td class="top"><a title="Innosoft International, Inc.">Freed, N.</a> and <a title="First Virtual Holdings">N.S. Borenstein</a>, “<a href="http://tools.ietf.org/html/rfc2049">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</a>”, RFC&nbsp;2049, November&nbsp;1996.
[97]1540            </td>
1541         </tr>
1542         <tr>
[129]1543            <td class="reference"><b id="RFC2068">[RFC2068]</b></td>
1544            <td class="top"><a title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, <a title="MIT Laboratory for Computer Science">Gettys, J.</a>, <a title="Digital Equipment Corporation, Western Research Laboratory">Mogul, J.</a>, <a title="MIT Laboratory for Computer Science">Nielsen, H.</a>, and <a title="MIT Laboratory for Computer Science">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2068">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2068, January&nbsp;1997.
[97]1545            </td>
1546         </tr>
1547         <tr>
[129]1548            <td class="reference"><b id="RFC2076">[RFC2076]</b></td>
1549            <td class="top"><a title="Stockholm University/KTH">Palme, J.</a>, “<a href="http://tools.ietf.org/html/rfc2076">Common Internet Message Headers</a>”, RFC&nbsp;2076, February&nbsp;1997.
[97]1550            </td>
1551         </tr>
1552         <tr>
[129]1553            <td class="reference"><b id="RFC2183">[RFC2183]</b></td>
1554            <td class="top"><a title="New Century Systems">Troost, R.</a>, <a title="QUALCOMM Incorporated">Dorner, S.</a>, and <a title="Department of Computer Science">K. Moore</a>, “<a href="http://tools.ietf.org/html/rfc2183">Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field</a>”, RFC&nbsp;2183, August&nbsp;1997.
[97]1555            </td>
1556         </tr>
1557         <tr>
[129]1558            <td class="reference"><b id="RFC2277">[RFC2277]</b></td>
1559            <td class="top"><a title="UNINETT">Alvestrand, H.T.</a>, “<a href="http://tools.ietf.org/html/rfc2277">IETF Policy on Character Sets and Languages</a>”, BCP&nbsp;18, RFC&nbsp;2277, January&nbsp;1998.
[97]1560            </td>
1561         </tr>
1562         <tr>
[129]1563            <td class="reference"><b id="RFC2388">[RFC2388]</b></td>
[446]1564            <td class="top"><a title="Xerox Palo Alto Research Center">Masinter, L.</a>, “<a href="http://tools.ietf.org/html/rfc2388">Returning Values from Forms: multipart/form-data</a>”, RFC&nbsp;2388, August&nbsp;1998.
[97]1565            </td>
1566         </tr>
1567         <tr>
[129]1568            <td class="reference"><b id="RFC2557">[RFC2557]</b></td>
1569            <td class="top"><a title="Stockholm University and KTH">Palme, F.</a>, <a title="Microsoft Corporation">Hopmann, A.</a>, <a title="Lotus Development Corporation">Shelness, N.</a>, and <a>E. Stefferud</a>, “<a href="http://tools.ietf.org/html/rfc2557">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</a>”, RFC&nbsp;2557, March&nbsp;1999.
[97]1570            </td>
1571         </tr>
1572         <tr>
[129]1573            <td class="reference"><b id="RFC2616">[RFC2616]</b></td>
1574            <td class="top"><a title="University of California, Irvine">Fielding, R.</a>, <a title="W3C">Gettys, J.</a>, <a title="Compaq Computer Corporation">Mogul, J.</a>, <a title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a title="Xerox Corporation">Masinter, L.</a>, <a title="Microsoft Corporation">Leach, P.</a>, and <a title="W3C">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/rfc2616">Hypertext Transfer Protocol -- HTTP/1.1</a>”, RFC&nbsp;2616, June&nbsp;1999.
[97]1575            </td>
1576         </tr>
1577         <tr>
[133]1578            <td class="reference"><b id="RFC3629">[RFC3629]</b></td>
1579            <td class="top"><a title="Alis Technologies">Yergeau, F.</a>, “<a href="http://tools.ietf.org/html/rfc3629">UTF-8, a transformation format of ISO 10646</a>”, RFC&nbsp;3629, STD&nbsp;63, November&nbsp;2003.
[97]1580            </td>
1581         </tr>
[200]1582         <tr>
[253]1583            <td class="reference"><b id="RFC3864">[RFC3864]</b></td>
1584            <td class="top"><a title="Nine by Nine">Klyne, G.</a>, <a title="BEA Systems">Nottingham, M.</a>, and <a title="HP Labs">J. Mogul</a>, “<a href="http://tools.ietf.org/html/rfc3864">Registration Procedures for Message Header Fields</a>”, BCP&nbsp;90, RFC&nbsp;3864, September&nbsp;2004.
1585            </td>
1586         </tr>
1587         <tr>
[200]1588            <td class="reference"><b id="RFC4288">[RFC4288]</b></td>
1589            <td class="top"><a title="Sun Microsystems">Freed, N.</a> and <a>J. Klensin</a>, “<a href="http://tools.ietf.org/html/rfc4288">Media Type Specifications and Registration Procedures</a>”, BCP&nbsp;13, RFC&nbsp;4288, December&nbsp;2005.
1590            </td>
1591         </tr>
[327]1592         <tr>
1593            <td class="reference"><b id="RFC5322">[RFC5322]</b></td>
1594            <td class="top">Resnick, P., “<a href="http://tools.ietf.org/html/rfc5322">Internet Message Format</a>”, RFC&nbsp;5322, October&nbsp;2008.
1595            </td>
1596         </tr>
[129]1597      </table>
[97]1598      <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1>
1599      <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span>
1600            (editor)
1601            <span class="n hidden"><span class="family-name">Fielding</span><span class="given-name">Roy T.</span></span></span><span class="org vcardline">Day Software</span><span class="adr"><span class="street-address vcardline">23 Corporate Plaza DR, Suite 280</span><span class="vcardline"><span class="locality">Newport Beach</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">92660</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline tel">Phone: <a href="tel:+1-949-706-5300"><span class="value">+1-949-706-5300</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:+1-949-706-5305"><span class="value">+1-949-706-5305</span></a></span><span class="vcardline">EMail: <a><span class="email">fielding@gbiv.com</span></a></span><span class="vcardline">URI: <a href="http://roy.gbiv.com/" class="url">http://roy.gbiv.com/</a></span></address>
1602      <address class="vcard"><span class="vcardline"><span class="fn">Jim Gettys</span><span class="n hidden"><span class="family-name">Gettys</span><span class="given-name">Jim</span></span></span><span class="org vcardline">One Laptop per Child</span><span class="adr"><span class="street-address vcardline">21 Oak Knoll Road</span><span class="vcardline"><span class="locality">Carlisle</span>, <span class="region">MA</span>&nbsp;<span class="postal-code">01741</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a><span class="email">jg@laptop.org</span></a></span><span class="vcardline">URI: <a href="http://www.laptop.org/" class="url">http://www.laptop.org/</a></span></address>
1603      <address class="vcard"><span class="vcardline"><span class="fn">Jeffrey C. Mogul</span><span class="n hidden"><span class="family-name">Mogul</span><span class="given-name">Jeffrey C.</span></span></span><span class="org vcardline">Hewlett-Packard Company</span><span class="adr"><span class="street-address vcardline">HP Labs, Large Scale Systems Group</span><span class="street-address vcardline">1501 Page Mill Road, MS 1177</span><span class="vcardline"><span class="locality">Palo Alto</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">94304</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a><span class="email">JeffMogul@acm.org</span></a></span></address>
1604      <address class="vcard"><span class="vcardline"><span class="fn">Henrik Frystyk Nielsen</span><span class="n hidden"><span class="family-name">Frystyk</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span>&nbsp;<span class="postal-code">98052</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a><span class="email">henrikn@microsoft.com</span></a></span></address>
1605      <address class="vcard"><span class="vcardline"><span class="fn">Larry Masinter</span><span class="n hidden"><span class="family-name">Masinter</span><span class="given-name">Larry</span></span></span><span class="org vcardline">Adobe Systems, Incorporated</span><span class="adr"><span class="street-address vcardline">345 Park Ave</span><span class="vcardline"><span class="locality">San Jose</span>, <span class="region">CA</span>&nbsp;<span class="postal-code">95110</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a><span class="email">LMM@acm.org</span></a></span><span class="vcardline">URI: <a href="http://larry.masinter.net/" class="url">http://larry.masinter.net/</a></span></address>
1606      <address class="vcard"><span class="vcardline"><span class="fn">Paul J. Leach</span><span class="n hidden"><span class="family-name">Leach</span><span class="given-name">Paul J.</span></span></span><span class="org vcardline">Microsoft Corporation</span><span class="adr"><span class="street-address vcardline">1 Microsoft Way</span><span class="vcardline"><span class="locality">Redmond</span>, <span class="region">WA</span>&nbsp;<span class="postal-code">98052</span></span></span><span class="vcardline">EMail: <a><span class="email">paulle@microsoft.com</span></a></span></address>
1607      <address class="vcard"><span class="vcardline"><span class="fn">Tim Berners-Lee</span><span class="n hidden"><span class="family-name">Berners-Lee</span><span class="given-name">Tim</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">MIT Computer Science and Artificial Intelligence Laboratory</span><span class="street-address vcardline">The Stata Center, Building 32</span><span class="street-address vcardline">32 Vassar Street</span><span class="vcardline"><span class="locality">Cambridge</span>, <span class="region">MA</span>&nbsp;<span class="postal-code">02139</span></span><span class="country-name vcardline">USA</span></span><span class="vcardline">EMail: <a><span class="email">timbl@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.w3.org/People/Berners-Lee/" class="url">http://www.w3.org/People/Berners-Lee/</a></span></address>
1608      <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span>
1609            (editor)
1610            <span class="n hidden"><span class="family-name">Lafon</span><span class="given-name">Yves</span></span></span><span class="org vcardline">World Wide Web Consortium</span><span class="adr"><span class="street-address vcardline">W3C / ERCIM</span><span class="street-address vcardline">2004, rte des Lucioles</span><span class="vcardline"><span class="locality">Sophia-Antipolis</span>, <span class="region">AM</span>&nbsp;<span class="postal-code">06902</span></span><span class="country-name vcardline">France</span></span><span class="vcardline">EMail: <a><span class="email">ylafon@w3.org</span></a></span><span class="vcardline">URI: <a href="http://www.raubacapeu.net/people/yves/" class="url">http://www.raubacapeu.net/people/yves/</a></span></address>
1611      <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span>
1612            (editor)
1613            <span class="n hidden"><span class="family-name">Reschke</span><span class="given-name">Julian F.</span></span></span><span class="org vcardline">greenbytes GmbH</span><span class="adr"><span class="street-address vcardline">Hafenweg 16</span><span class="vcardline"><span class="locality">Muenster</span>, <span class="region">NW</span>&nbsp;<span class="postal-code">48155</span></span><span class="country-name vcardline">Germany</span></span><span class="vcardline tel">Phone: <a href="tel:+492512807760"><span class="value">+49 251 2807760</span></a></span><span class="vcardline tel"><span class="type">Fax</span>: <a href="fax:+492512807761"><span class="value">+49 251 2807761</span></a></span><span class="vcardline">EMail: <a><span class="email">julian.reschke@greenbytes.de</span></a></span><span class="vcardline">URI: <a href="http://greenbytes.de/tech/webdav/" class="url">http://greenbytes.de/tech/webdav/</a></span></address>
1614      <h1 id="rfc.section.A"><a href="#rfc.section.A">A.</a>&nbsp;<a id="differences.between.http.entities.and.rfc.2045.entities" href="#differences.between.http.entities.and.rfc.2045.entities">Differences Between HTTP Entities and RFC 2045 Entities</a></h1>
[327]1615      <p id="rfc.section.A.p.1">HTTP/1.1 uses many of the constructs defined for Internet Mail (<a href="#RFC5322" id="rfc.xref.RFC5322.1"><cite title="Internet Message Format">[RFC5322]</cite></a>) and the Multipurpose Internet Mail Extensions (MIME <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>) to allow entities to be transmitted in an open variety of representations and with extensible mechanisms. However, RFC 2045
[97]1616         discusses mail, and HTTP has a few features that are different from those described in RFC 2045. These differences were carefully
1617         chosen to optimize performance over binary connections, to allow greater freedom in the use of new media types, to make date
1618         comparisons easier, and to acknowledge the practice of some early HTTP servers and clients.
1619      </p>
1620      <p id="rfc.section.A.p.2">This appendix describes specific areas where HTTP differs from RFC 2045. Proxies and gateways to strict MIME environments <em class="bcp14">SHOULD</em> be aware of these differences and provide the appropriate conversions where necessary. Proxies and gateways from MIME environments
1621         to HTTP also need to be aware of the differences because some conversions might be required.
1622      </p>
[291]1623      <div id="rfc.iref.m.1"></div>
1624      <div id="rfc.iref.h.10"></div>
[97]1625      <h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a>&nbsp;<a id="mime-version" href="#mime-version">MIME-Version</a></h2>
1626      <p id="rfc.section.A.1.p.1">HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages <em class="bcp14">MAY</em> include a single MIME-Version general-header field to indicate what version of the MIME protocol was used to construct the
1627         message. Use of the MIME-Version header field indicates that the message is in full compliance with the MIME protocol (as
[115]1628         defined in <a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a>). Proxies/gateways are responsible for ensuring full compliance (where possible) when exporting HTTP messages to strict MIME
[97]1629         environments.
1630      </p>
[459]1631      <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.39"></span><span id="rfc.iref.g.40"></span>  <a href="#mime-version" class="smpl">MIME-Version</a>   = "MIME-Version" ":" <a href="#core.rules" class="smpl">OWS</a> <a href="#mime-version" class="smpl">MIME-Version-v</a>
[425]1632  <a href="#mime-version" class="smpl">MIME-Version-v</a> = 1*<a href="#notation" class="smpl">DIGIT</a> "." 1*<a href="#notation" class="smpl">DIGIT</a>
[97]1633</pre><p id="rfc.section.A.1.p.3">MIME version "1.0" is the default for use in HTTP/1.1. However, HTTP/1.1 message parsing and semantics are defined by this
1634         document and not the MIME specification.
1635      </p>
1636      <h2 id="rfc.section.A.2"><a href="#rfc.section.A.2">A.2</a>&nbsp;<a id="conversion.to.canonical.form" href="#conversion.to.canonical.form">Conversion to Canonical Form</a></h2>
[572]1637      <p id="rfc.section.A.2.p.1"> <a href="#RFC2045" id="rfc.xref.RFC2045.3"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[RFC2045]</cite></a> requires that an Internet mail entity be converted to canonical form prior to being transferred, as described in <a href="http://tools.ietf.org/html/rfc2049#section-4">Section 4</a> of <a href="#RFC2049" id="rfc.xref.RFC2049.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples">[RFC2049]</cite></a>. <a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section&nbsp;2.3.1</a> of this document describes the forms allowed for subtypes of the "text" media type when transmitted over HTTP. <a href="#RFC2046" id="rfc.xref.RFC2046.4"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> requires that content with a type of "text" represent line breaks as CRLF and forbids the use of CR or LF outside of line
[97]1638         break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a line break within text content when a message is transmitted
1639         over HTTP.
1640      </p>
[424]1641      <p id="rfc.section.A.2.p.2">Where it is possible, a proxy or gateway from HTTP to a strict MIME environment <em class="bcp14">SHOULD</em> translate all line breaks within the text media types described in <a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section&nbsp;2.3.1</a> of this document to the RFC 2049 canonical form of CRLF. Note, however, that this might be complicated by the presence of
[97]1642         a Content-Encoding and by the fact that HTTP allows the use of some character sets which do not use octets 13 and 10 to represent
1643         CR and LF, as is the case for some multi-byte character sets.
1644      </p>
1645      <p id="rfc.section.A.2.p.3">Implementors should note that conversion will break any cryptographic checksums applied to the original content unless the
1646         original content is already in canonical form. Therefore, the canonical form is recommended for any content that uses such
1647         checksums in HTTP.
1648      </p>
[385]1649      <h2 id="rfc.section.A.3"><a href="#rfc.section.A.3">A.3</a>&nbsp;<a id="conversion.of.date.formats" href="#conversion.of.date.formats">Conversion of Date Formats</a></h2>
[580]1650      <p id="rfc.section.A.3.p.1">HTTP/1.1 uses a restricted set of date formats (<a href="p1-messaging.html#date.time.formats.full.date" title="Date/Time Formats: Full Date">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.16"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) to simplify the process of date comparison. Proxies and gateways from other protocols <em class="bcp14">SHOULD</em> ensure that any Date header field present in a message conforms to one of the HTTP/1.1 formats and rewrite the date if necessary.
[385]1651      </p>
1652      <h2 id="rfc.section.A.4"><a href="#rfc.section.A.4">A.4</a>&nbsp;<a id="introduction.of.content-encoding" href="#introduction.of.content-encoding">Introduction of Content-Encoding</a></h2>
1653      <p id="rfc.section.A.4.p.1">RFC 2045 does not include any concept equivalent to HTTP/1.1's Content-Encoding header field. Since this acts as a modifier
[97]1654         on the media type, proxies and gateways from HTTP to MIME-compliant protocols <em class="bcp14">MUST</em> either change the value of the Content-Type header field or decode the entity-body before forwarding the message. (Some experimental
1655         applications of Content-Type for Internet mail have used a media-type parameter of ";conversions=&lt;content-coding&gt;" to perform
1656         a function equivalent to Content-Encoding. However, this parameter is not part of RFC 2045).
1657      </p>
[385]1658      <h2 id="rfc.section.A.5"><a href="#rfc.section.A.5">A.5</a>&nbsp;<a id="no.content-transfer-encoding" href="#no.content-transfer-encoding">No Content-Transfer-Encoding</a></h2>
1659      <p id="rfc.section.A.5.p.1">HTTP does not use the Content-Transfer-Encoding field of RFC 2045. Proxies and gateways from MIME-compliant protocols to HTTP <em class="bcp14">MUST</em> remove any Content-Transfer-Encoding prior to delivering the response message to an HTTP client.
[97]1660      </p>
[385]1661      <p id="rfc.section.A.5.p.2">Proxies and gateways from HTTP to MIME-compliant protocols are responsible for ensuring that the message is in the correct
[97]1662         format and encoding for safe transport on that protocol, where "safe transport" is defined by the limitations of the protocol
1663         being used. Such a proxy or gateway <em class="bcp14">SHOULD</em> label the data with an appropriate Content-Transfer-Encoding if doing so will improve the likelihood of safe transport over
1664         the destination protocol.
1665      </p>
[385]1666      <h2 id="rfc.section.A.6"><a href="#rfc.section.A.6">A.6</a>&nbsp;<a id="introduction.of.transfer-encoding" href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></h2>
[457]1667      <p id="rfc.section.A.6.p.1">HTTP/1.1 introduces the Transfer-Encoding header field (<a href="p1-messaging.html#header.transfer-encoding" title="Transfer-Encoding">Section 8.7</a> of <a href="#Part1" id="rfc.xref.Part1.17"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>). Proxies/gateways <em class="bcp14">MUST</em> remove any transfer-coding prior to forwarding a message via a MIME-compliant protocol.
[97]1668      </p>
[385]1669      <h2 id="rfc.section.A.7"><a href="#rfc.section.A.7">A.7</a>&nbsp;<a id="mhtml.line.length" href="#mhtml.line.length">MHTML and Line Length Limitations</a></h2>
1670      <p id="rfc.section.A.7.p.1">HTTP implementations which share code with MHTML <a href="#RFC2557" id="rfc.xref.RFC2557.1"><cite title="MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)">[RFC2557]</cite></a> implementations need to be aware of MIME line length limitations. Since HTTP does not have this limitation, HTTP does not
[97]1671         fold long lines. MHTML messages being transported by HTTP follow all conventions of MHTML, including line length limitations
[424]1672         and folding, canonicalization, etc., since HTTP transports all message-bodies as payload (see <a href="#multipart.types" title="Multipart Types">Section&nbsp;2.3.2</a>) and does not interpret the content or any MIME header lines that might be contained therein.
[97]1673      </p>
1674      <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;<a id="additional.features" href="#additional.features">Additional Features</a></h1>
[122]1675      <p id="rfc.section.B.p.1"> <a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[RFC1945]</cite></a> and <a href="#RFC2068" id="rfc.xref.RFC2068.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> document protocol elements used by some existing HTTP implementations, but not consistently and correctly across most HTTP/1.1
[97]1676         applications. Implementors are advised to be aware of these features, but cannot rely upon their presence in, or interoperability
1677         with, other HTTP/1.1 applications. Some of these describe proposed experimental features, and some describe features that
1678         experimental deployment found lacking that are now addressed in the base HTTP/1.1 specification.
1679      </p>
1680      <p id="rfc.section.B.p.2">A number of other headers, such as Content-Disposition and Title, from SMTP and MIME are also often implemented (see <a href="#RFC2076" id="rfc.xref.RFC2076.1"><cite title="Common Internet Message Headers">[RFC2076]</cite></a>).
1681      </p>
[291]1682      <div id="rfc.iref.h.11"></div>
[97]1683      <div id="rfc.iref.c.7"></div>
1684      <h2 id="rfc.section.B.1"><a href="#rfc.section.B.1">B.1</a>&nbsp;<a id="content-disposition" href="#content-disposition">Content-Disposition</a></h2>
1685      <p id="rfc.section.B.1.p.1">The Content-Disposition response-header field has been proposed as a means for the origin server to suggest a default filename
1686         if the user requests that the content is saved to a file. This usage is derived from the definition of Content-Disposition
[269]1687         in <a href="#RFC2183" id="rfc.xref.RFC2183.3"><cite title="Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field">[RFC2183]</cite></a>.
[97]1688      </p>
[459]1689      <div id="rfc.figure.u.36"></div><pre class="inline"><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span><span id="rfc.iref.g.46"></span><span id="rfc.iref.g.47"></span>  <a href="#content-disposition" class="smpl">content-disposition</a> = "Content-Disposition" ":" <a href="#core.rules" class="smpl">OWS</a>
[357]1690                        <a href="#content-disposition" class="smpl">content-disposition-v</a>
[376]1691  <a href="#content-disposition" class="smpl">content-disposition-v</a> = <a href="#content-disposition" class="smpl">disposition-type</a>
[424]1692                          *( <a href="#core.rules" class="smpl">OWS</a> ";" <a href="#core.rules" class="smpl">OWS</a> <a href="#content-disposition" class="smpl">disposition-parm</a> )
[334]1693  <a href="#content-disposition" class="smpl">disposition-type</a> = "attachment" / <a href="#content-disposition" class="smpl">disp-extension-token</a>
1694  <a href="#content-disposition" class="smpl">disposition-parm</a> = <a href="#content-disposition" class="smpl">filename-parm</a> / <a href="#content-disposition" class="smpl">disp-extension-parm</a>
[424]1695  <a href="#content-disposition" class="smpl">filename-parm</a> = "filename" "=" <a href="#core.rules" class="smpl">quoted-string</a>
1696  <a href="#content-disposition" class="smpl">disp-extension-token</a> = <a href="#core.rules" class="smpl">token</a>
1697  <a href="#content-disposition" class="smpl">disp-extension-parm</a> = <a href="#core.rules" class="smpl">token</a> "=" ( <a href="#core.rules" class="smpl">token</a> / <a href="#core.rules" class="smpl">quoted-string</a> )
[97]1698</pre><p id="rfc.section.B.1.p.3">An example is</p>
[459]1699      <div id="rfc.figure.u.37"></div><pre class="text">  Content-Disposition: attachment; filename="fname.ext"
[97]1700</pre><p id="rfc.section.B.1.p.5">The receiving user agent <em class="bcp14">SHOULD NOT</em> respect any directory path information present in the filename-parm parameter, which is the only parameter believed to apply
1701         to HTTP implementations at this time. The filename <em class="bcp14">SHOULD</em> be treated as a terminal component only.
1702      </p>
1703      <p id="rfc.section.B.1.p.6">If this header is used in a response with the application/octet-stream content-type, the implied suggestion is that the user
1704         agent should not display the response, but directly enter a `save response as...' dialog.
1705      </p>
[424]1706      <p id="rfc.section.B.1.p.7">See <a href="#content-disposition.issues" title="Content-Disposition Issues">Section&nbsp;7.2</a> for Content-Disposition security issues.
[97]1707      </p>
[99]1708      <h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a>&nbsp;<a id="compatibility" href="#compatibility">Compatibility with Previous Versions</a></h1>
1709      <h2 id="rfc.section.C.1"><a href="#rfc.section.C.1">C.1</a>&nbsp;<a id="changes.from.rfc.2068" href="#changes.from.rfc.2068">Changes from RFC 2068</a></h2>
[138]1710      <p id="rfc.section.C.1.p.1">Transfer-coding and message lengths all interact in ways that required fixing exactly when chunked encoding is used (to allow
1711         for transfer encoding that may not be self delimiting); it was important to straighten out exactly how message lengths are
[457]1712         computed. (<a href="#entity.length" title="Entity Length">Section&nbsp;3.2.2</a>, see also <a href="#Part1" id="rfc.xref.Part1.18"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="#Part5" id="rfc.xref.Part5.4"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a> and <a href="#Part6" id="rfc.xref.Part6.5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).
[97]1713      </p>
[424]1714      <p id="rfc.section.C.1.p.2">Charset wildcarding is introduced to avoid explosion of character set names in accept headers. (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.3" title="Accept-Charset">Section&nbsp;5.2</a>)
[138]1715      </p>
1716      <p id="rfc.section.C.1.p.3">Content-Base was deleted from the specification: it was not implemented widely, and there is no simple, safe way to introduce
[129]1717         it without a robust extension mechanism. In addition, it is used in a similar, but not identical fashion in MHTML <a href="#RFC2557" id="rfc.xref.RFC2557.2"><cite title="MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)">[RFC2557]</cite></a>.
[97]1718      </p>
[424]1719      <p id="rfc.section.C.1.p.4">A content-coding of "identity" was introduced, to solve problems discovered in caching. (<a href="#content.codings" title="Content Codings">Section&nbsp;2.2</a>)
[97]1720      </p>
[457]1721      <p id="rfc.section.C.1.p.5">The Alternates<span id="rfc.iref.a.5"></span><span id="rfc.iref.h.12"></span>, Content-Version<span id="rfc.iref.c.8"></span><span id="rfc.iref.h.13"></span>, Derived-From<span id="rfc.iref.d.2"></span><span id="rfc.iref.h.14"></span>, Link<span id="rfc.iref.l.1"></span><span id="rfc.iref.h.15"></span>, URI<span id="rfc.iref.u.1"></span><span id="rfc.iref.h.16"></span>, Public<span id="rfc.iref.p.1"></span><span id="rfc.iref.h.17"></span> and Content-Base<span id="rfc.iref.c.9"></span><span id="rfc.iref.h.18"></span> header fields were defined in previous versions of this specification, but not commonly implemented. See <a href="http://tools.ietf.org/html/rfc2068#section-19.6.2">Section 19.6.2</a> of <a href="#RFC2068" id="rfc.xref.RFC2068.5"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>.
[97]1722      </p>
[99]1723      <h2 id="rfc.section.C.2"><a href="#rfc.section.C.2">C.2</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h2>
[424]1724      <p id="rfc.section.C.2.p.1">Clarify contexts that charset is used in. (<a href="#character.sets" title="Character Sets">Section&nbsp;2.1</a>)
[102]1725      </p>
[385]1726      <p id="rfc.section.C.2.p.2">Remove reference to non-existant identity transfer-coding value tokens. (<a href="#no.content-transfer-encoding" title="No Content-Transfer-Encoding">Appendix&nbsp;A.5</a>)
[104]1727      </p>
[421]1728      <h1 id="rfc.section.D"><a href="#rfc.section.D">D.</a>&nbsp;<a id="collected.abnf" href="#collected.abnf">Collected ABNF</a></h1>
[459]1729      <div id="rfc.figure.u.38"></div> <pre class="inline"><a href="#header.accept" class="smpl">Accept</a> = "Accept:" OWS Accept-v
[427]1730<a href="#header.accept-charset" class="smpl">Accept-Charset</a> = "Accept-Charset:" OWS Accept-Charset-v
1731<a href="#header.accept-charset" class="smpl">Accept-Charset-v</a> = *( "," OWS ) ( charset / "*" ) [ OWS ";" OWS "q="
[421]1732 qvalue ] *( OWS "," [ OWS ( charset / "*" ) [ OWS ";" OWS "q="
1733 qvalue ] ] )
[427]1734<a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> = "Accept-Encoding:" OWS Accept-Encoding-v
1735<a href="#header.accept-encoding" class="smpl">Accept-Encoding-v</a> = [ ( "," / ( codings [ OWS ";" OWS "q=" qvalue ] )
[421]1736 ) *( OWS "," [ OWS codings [ OWS ";" OWS "q=" qvalue ] ] ) ]
[427]1737<a href="#header.accept-language" class="smpl">Accept-Language</a> = "Accept-Language:" OWS Accept-Language-v
1738<a href="#header.accept-language" class="smpl">Accept-Language-v</a> = *( "," OWS ) language-range [ OWS ";" OWS "q="
[421]1739 qvalue ] *( OWS "," [ OWS language-range [ OWS ";" OWS "q=" qvalue ]
1740 ] )
[427]1741<a href="#header.accept" class="smpl">Accept-v</a> = [ ( "," / ( media-range [ accept-params ] ) ) *( OWS "," [
[421]1742 OWS media-range [ accept-params ] ] ) ]
[428]1743
[427]1744<a href="#header.content-encoding" class="smpl">Content-Encoding</a> = "Content-Encoding:" OWS Content-Encoding-v
1745<a href="#header.content-encoding" class="smpl">Content-Encoding-v</a> = *( "," OWS ) content-coding *( OWS "," [ OWS
[421]1746 content-coding ] )
[427]1747<a href="#header.content-language" class="smpl">Content-Language</a> = "Content-Language:" OWS Content-Language-v
1748<a href="#header.content-language" class="smpl">Content-Language-v</a> = *( "," OWS ) language-tag *( OWS "," [ OWS
[421]1749 language-tag ] )
[427]1750<a href="#abnf.dependencies" class="smpl">Content-Length</a> = &lt;Content-Length, defined in [Part1], Section 8.2&gt;
1751<a href="#header.content-location" class="smpl">Content-Location</a> = "Content-Location:" OWS Content-Location-v
1752<a href="#header.content-location" class="smpl">Content-Location-v</a> = absolute-URI / partial-URI
1753<a href="#header.content-md5" class="smpl">Content-MD5</a> = "Content-MD5:" OWS Content-MD5-v
1754<a href="#header.content-md5" class="smpl">Content-MD5-v</a> = &lt;base64 of 128 bit MD5 digest as per [RFC1864]&gt;
1755<a href="#abnf.dependencies" class="smpl">Content-Range</a> = &lt;Content-Range, defined in [Part5], Section 5.2&gt;
1756<a href="#header.content-type" class="smpl">Content-Type</a> = "Content-Type:" OWS Content-Type-v
1757<a href="#header.content-type" class="smpl">Content-Type-v</a> = media-type
1758
[538]1759<a href="#abnf.dependencies" class="smpl">Expires</a> = &lt;Expires, defined in [Part6], Section 3.3&gt;
[427]1760
1761<a href="#abnf.dependencies" class="smpl">Last-Modified</a> = &lt;Last-Modified, defined in [Part4], Section 6.6&gt;
1762
1763<a href="#mime-version" class="smpl">MIME-Version</a> = "MIME-Version:" OWS MIME-Version-v
1764<a href="#mime-version" class="smpl">MIME-Version-v</a> = 1*DIGIT "." 1*DIGIT
1765
1766<a href="#core.rules" class="smpl">OWS</a> = &lt;OWS, defined in [Part1], Section 1.2.2&gt;
1767
1768<a href="#abnf.dependencies" class="smpl">absolute-URI</a> = &lt;absolute-URI, defined in [Part1], Section 2.1&gt;
1769<a href="#header.accept" class="smpl">accept-ext</a> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
1770<a href="#header.accept" class="smpl">accept-params</a> = OWS ";" OWS "q=" qvalue *accept-ext
1771<a href="#rule.parameter" class="smpl">attribute</a> = token
1772
1773<a href="#rule.charset" class="smpl">charset</a> = token
1774<a href="#header.accept-encoding" class="smpl">codings</a> = ( content-coding / "*" )
1775<a href="#content.codings" class="smpl">content-coding</a> = token
1776<a href="#content-disposition" class="smpl">content-disposition</a> = "Content-Disposition:" OWS
[421]1777 content-disposition-v
[427]1778<a href="#content-disposition" class="smpl">content-disposition-v</a> = disposition-type *( OWS ";" OWS
[421]1779 disposition-parm )
[428]1780
[427]1781<a href="#content-disposition" class="smpl">disp-extension-parm</a> = token "=" ( token / quoted-string )
1782<a href="#content-disposition" class="smpl">disp-extension-token</a> = token
1783<a href="#content-disposition" class="smpl">disposition-parm</a> = filename-parm / disp-extension-parm
1784<a href="#content-disposition" class="smpl">disposition-type</a> = "attachment" / disp-extension-token
1785
1786<a href="#entity.body" class="smpl">entity-body</a> = *OCTET
1787<a href="#entity.header.fields" class="smpl">entity-header</a> = Content-Encoding / Content-Language / Content-Length
[421]1788 / Content-Location / Content-MD5 / Content-Range / Content-Type /
1789 Expires / Last-Modified / extension-header
[427]1790<a href="#entity.header.fields" class="smpl">extension-header</a> = message-header
1791
1792<a href="#content-disposition" class="smpl">filename-parm</a> = "filename=" quoted-string
1793
1794<a href="#header.accept-language" class="smpl">language-range</a> = &lt;language-range, defined in [RFC4647], Section 2.1&gt;
1795<a href="#language.tags" class="smpl">language-tag</a> = primary-tag *( "-" subtag )
1796
1797<a href="#header.accept" class="smpl">media-range</a> = ( "*/*" / ( type "/*" ) / ( type "/" subtype ) ) *( OWS
[421]1798 ";" OWS parameter )
[427]1799<a href="#media.types" class="smpl">media-type</a> = type "/" subtype *( OWS ";" OWS parameter )
1800<a href="#abnf.dependencies" class="smpl">message-header</a> = &lt;message-header, defined in [Part1], Section 4.2&gt;
1801
1802<a href="#rule.parameter" class="smpl">parameter</a> = attribute "=" value
1803<a href="#abnf.dependencies" class="smpl">partial-URI</a> = &lt;partial-URI, defined in [Part1], Section 2.1&gt;
1804<a href="#language.tags" class="smpl">primary-tag</a> = 1*8ALPHA
1805
1806<a href="#core.rules" class="smpl">quoted-string</a> = &lt;quoted-string, defined in [Part1], Section 1.2.2&gt;
[457]1807<a href="#abnf.dependencies" class="smpl">qvalue</a> = &lt;qvalue, defined in [Part1], Section 3.5&gt;
[427]1808
1809<a href="#language.tags" class="smpl">subtag</a> = 1*8ALPHA
1810<a href="#media.types" class="smpl">subtype</a> = token
1811
1812<a href="#core.rules" class="smpl">token</a> = &lt;token, defined in [Part1], Section 1.2.2&gt;
1813<a href="#media.types" class="smpl">type</a> = token
1814
1815<a href="#rule.parameter" class="smpl">value</a> = token / quoted-string
1816
[454]1817
[459]1818</pre> <div id="rfc.figure.u.39"></div>
[454]1819      <p>ABNF diagnostics:</p><pre class="inline">; Accept defined but not used
[421]1820; Accept-Charset defined but not used
1821; Accept-Encoding defined but not used
1822; Accept-Language defined but not used
1823; MIME-Version defined but not used
1824; content-disposition defined but not used
1825; entity-body defined but not used
1826; entity-header defined but not used
[454]1827</pre><h1 id="rfc.section.E"><a href="#rfc.section.E">E.</a>&nbsp;<a id="change.log" href="#change.log">Change Log (to be removed by RFC Editor before publication)</a></h1>
[421]1828      <h2 id="rfc.section.E.1"><a href="#rfc.section.E.1">E.1</a>&nbsp;Since RFC2616
[115]1829      </h2>
[421]1830      <p id="rfc.section.E.1.p.1">Extracted relevant partitions from <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
[115]1831      </p>
[421]1832      <h2 id="rfc.section.E.2"><a href="#rfc.section.E.2">E.2</a>&nbsp;Since draft-ietf-httpbis-p3-payload-00
[115]1833      </h2>
[421]1834      <p id="rfc.section.E.2.p.1">Closed issues: </p>
[116]1835      <ul>
[324]1836         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/8">http://tools.ietf.org/wg/httpbis/trac/ticket/8</a>&gt;: "Media Type Registrations" (&lt;<a href="http://purl.org/NET/http-errata#media-reg">http://purl.org/NET/http-errata#media-reg</a>&gt;)
[116]1837         </li>
[324]1838         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/14">http://tools.ietf.org/wg/httpbis/trac/ticket/14</a>&gt;: "Clarification regarding quoting of charset values" (&lt;<a href="http://purl.org/NET/http-errata#charactersets">http://purl.org/NET/http-errata#charactersets</a>&gt;)
[116]1839         </li>
[324]1840         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/16">http://tools.ietf.org/wg/httpbis/trac/ticket/16</a>&gt;: "Remove 'identity' token references" (&lt;<a href="http://purl.org/NET/http-errata#identity">http://purl.org/NET/http-errata#identity</a>&gt;)
[116]1841         </li>
[324]1842         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/25">http://tools.ietf.org/wg/httpbis/trac/ticket/25</a>&gt;: "Accept-Encoding BNF"
[126]1843         </li>
[324]1844         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/35">http://tools.ietf.org/wg/httpbis/trac/ticket/35</a>&gt;: "Normative and Informative references"
[152]1845         </li>
[324]1846         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/46">http://tools.ietf.org/wg/httpbis/trac/ticket/46</a>&gt;: "RFC1700 references"
[116]1847         </li>
[324]1848         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/55">http://tools.ietf.org/wg/httpbis/trac/ticket/55</a>&gt;: "Updating to RFC4288"
[200]1849         </li>
[324]1850         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/65">http://tools.ietf.org/wg/httpbis/trac/ticket/65</a>&gt;: "Informative references"
[129]1851         </li>
[324]1852         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/66">http://tools.ietf.org/wg/httpbis/trac/ticket/66</a>&gt;: "ISO-8859-1 Reference"
[123]1853         </li>
[324]1854         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/68">http://tools.ietf.org/wg/httpbis/trac/ticket/68</a>&gt;: "Encoding References Normative"
[122]1855         </li>
[324]1856         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/86">http://tools.ietf.org/wg/httpbis/trac/ticket/86</a>&gt;: "Normative up-to-date references"
[131]1857         </li>
[116]1858      </ul>
[421]1859      <h2 id="rfc.section.E.3"><a href="#rfc.section.E.3">E.3</a>&nbsp;Since draft-ietf-httpbis-p3-payload-01
[170]1860      </h2>
[421]1861      <p id="rfc.section.E.3.p.1">Ongoing work on ABNF conversion (&lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/36">http://tools.ietf.org/wg/httpbis/trac/ticket/36</a>&gt;):
[205]1862      </p>
1863      <ul>
1864         <li>Add explicit references to BNF syntax and rules imported from other parts of the specification.</li>
1865      </ul>
[421]1866      <h2 id="rfc.section.E.4"><a href="#rfc.section.E.4">E.4</a>&nbsp;<a id="changes.since.02" href="#changes.since.02">Since draft-ietf-httpbis-p3-payload-02</a></h2>
1867      <p id="rfc.section.E.4.p.1">Closed issues: </p>
[232]1868      <ul>
[324]1869         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/67">http://tools.ietf.org/wg/httpbis/trac/ticket/67</a>&gt;: "Quoting Charsets"
[251]1870         </li>
[324]1871         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/105">http://tools.ietf.org/wg/httpbis/trac/ticket/105</a>&gt;: "Classification for Allow header"
[232]1872         </li>
[324]1873         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/115">http://tools.ietf.org/wg/httpbis/trac/ticket/115</a>&gt;: "missing default for qvalue in description of Accept-Encoding"
[248]1874         </li>
[232]1875      </ul>
[421]1876      <p id="rfc.section.E.4.p.2">Ongoing work on IANA Message Header Registration (&lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/40">http://tools.ietf.org/wg/httpbis/trac/ticket/40</a>&gt;):
[253]1877      </p>
1878      <ul>
1879         <li>Reference RFC 3984, and update header registrations for headers defined in this document.</li>
1880      </ul>
[421]1881      <h2 id="rfc.section.E.5"><a href="#rfc.section.E.5">E.5</a>&nbsp;<a id="changes.since.03" href="#changes.since.03">Since draft-ietf-httpbis-p3-payload-03</a></h2>
1882      <p id="rfc.section.E.5.p.1">Closed issues: </p>
[269]1883      <ul>
[297]1884         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/67">http://tools.ietf.org/wg/httpbis/trac/ticket/67</a>&gt;: "Quoting Charsets"
1885         </li>
[303]1886         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/113">http://tools.ietf.org/wg/httpbis/trac/ticket/113</a>&gt;: "language tag matching (Accept-Language) vs RFC4647"
1887         </li>
[277]1888         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/121">http://tools.ietf.org/wg/httpbis/trac/ticket/121</a>&gt;: "RFC 1806 has been replaced by RFC2183"
[269]1889         </li>
1890      </ul>
[421]1891      <p id="rfc.section.E.5.p.2">Other changes: </p>
[277]1892      <ul>
1893         <li> &lt;<a href="http://tools.ietf.org/wg/httpbis/trac/ticket/68">http://tools.ietf.org/wg/httpbis/trac/ticket/68</a>&gt;: "Encoding References Normative" -- rephrase the annotation and reference <a href="#BCP97" id="rfc.xref.BCP97.4"><cite title="Handling Normative References to Standards-Track Documents">[BCP97]</cite></a>.
1894         </li>
1895      </ul>
[421]1896      <h2 id="rfc.section.E.6"><a href="#rfc.section.E.6">E.6</a>&nbsp;<a id="changes.since.04" href="#changes.since.04">Since draft-ietf-httpbis-p3-payload-04</a></h2>
1897      <p id="rfc.section.E.6.p.1"