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330</style><link rel="Contents" href="#rfc.toc">
331      <link rel="Author" href="#rfc.authors">
332      <link rel="Copyright" href="#rfc.copyright">
333      <link rel="Index" href="#rfc.index">
334      <link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
335      <link rel="Chapter" title="2 Product Tokens" href="#rfc.section.2">
336      <link rel="Chapter" title="3 Method" href="#rfc.section.3">
337      <link rel="Chapter" title="4 Request Header Fields" href="#rfc.section.4">
338      <link rel="Chapter" title="5 Status Code and Reason Phrase" href="#rfc.section.5">
339      <link rel="Chapter" title="6 Response Header Fields" href="#rfc.section.6">
340      <link rel="Chapter" title="7 Entity" href="#rfc.section.7">
341      <link rel="Chapter" title="8 Method Definitions" href="#rfc.section.8">
342      <link rel="Chapter" title="9 Status Code Definitions" href="#rfc.section.9">
343      <link rel="Chapter" title="10 Header Field Definitions" href="#rfc.section.10">
344      <link rel="Chapter" title="11 IANA Considerations" href="#rfc.section.11">
345      <link rel="Chapter" title="12 Security Considerations" href="#rfc.section.12">
346      <link rel="Chapter" title="13 Acknowledgments" href="#rfc.section.13">
347      <link rel="Chapter" href="#rfc.section.14" title="14 References">
[99]348      <link rel="Appendix" title="A Compatibility with Previous Versions" href="#rfc.section.A">
[115]349      <link rel="Appendix" title="B Change Log (to be removed by RFC Editor before publication)" href="#rfc.section.B">
[52]350      <meta name="generator" content="http://greenbytes.de/tech/webdav/rfc2629.xslt, Revision 1.353, 2007/12/11 23:20:44, XSLT vendor: SAXON 8.9 from Saxonica http://www.saxonica.com/">
351      <link rel="schema.DC" href="http://purl.org/dc/elements/1.1/">
352      <meta name="DC.Creator" content="Fielding, R.">
353      <meta name="DC.Creator" content="Gettys, J.">
354      <meta name="DC.Creator" content="Mogul, J.">
355      <meta name="DC.Creator" content="Frystyk, H.">
356      <meta name="DC.Creator" content="Masinter, L.">
357      <meta name="DC.Creator" content="Leach, P.">
358      <meta name="DC.Creator" content="Berners-Lee, T.">
[95]359      <meta name="DC.Creator" content="Lafon, Y.">
360      <meta name="DC.Creator" content="Reschke, J. F.">
[52]361      <meta name="DC.Identifier" content="urn:ietf:id:draft-ietf-httpbis-p2-semantics-latest">
362      <meta name="DC.Date.Issued" scheme="ISO8601" content="2007-12">
363      <meta name="DC.Relation.Replaces" content="urn:ietf:rfc:2068">
364      <meta name="DC.Relation.Replaces" content="urn:ietf:rfc:2616">
365      <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 2 of the seven-part specification that defines the protocol referred to as &#34;HTTP/1.1&#34; and, taken together, obsoletes RFC 2616. Part 2 defines the semantics of HTTP messages as expressed by request methods, request-header fields, response status codes, and response-header fields.">
366   </head>
367   <body>
368      <table summary="header information" class="header" border="0" cellpadding="1" cellspacing="1">
369         <tr>
370            <td class="header left">Network Working Group</td>
371            <td class="header right">R. Fielding, Editor</td>
372         </tr>
373         <tr>
374            <td class="header left">Internet Draft</td>
375            <td class="header right">Day Software</td>
376         </tr>
377         <tr>
378            <td class="header left">
379               &lt;draft-ietf-httpbis-p2-semantics-latest&gt;
380               
381            </td>
382            <td class="header right">J. Gettys</td>
383         </tr>
384         <tr>
385            <td class="header left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2068">2068</a>,
386               <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
387            </td>
388            <td class="header right">One Laptop per Child</td>
389         </tr>
390         <tr>
391            <td class="header left">Intended status: Standards Track</td>
392            <td class="header right">J. Mogul</td>
393         </tr>
394         <tr>
395            <td class="header left">Expires: June 2008</td>
396            <td class="header right">HP</td>
397         </tr>
398         <tr>
399            <td class="header left"></td>
400            <td class="header right">H. Frystyk</td>
401         </tr>
402         <tr>
403            <td class="header left"></td>
404            <td class="header right">Microsoft</td>
405         </tr>
406         <tr>
407            <td class="header left"></td>
408            <td class="header right">L. Masinter</td>
409         </tr>
410         <tr>
411            <td class="header left"></td>
412            <td class="header right">Adobe Systems</td>
413         </tr>
414         <tr>
415            <td class="header left"></td>
416            <td class="header right">P. Leach</td>
417         </tr>
418         <tr>
419            <td class="header left"></td>
420            <td class="header right">Microsoft</td>
421         </tr>
422         <tr>
423            <td class="header left"></td>
424            <td class="header right">T. Berners-Lee</td>
425         </tr>
426         <tr>
427            <td class="header left"></td>
428            <td class="header right">W3C/MIT</td>
429         </tr>
430         <tr>
431            <td class="header left"></td>
[95]432            <td class="header right">Y. Lafon, Editor</td>
433         </tr>
434         <tr>
435            <td class="header left"></td>
436            <td class="header right">W3C</td>
437         </tr>
438         <tr>
439            <td class="header left"></td>
440            <td class="header right">J. F. Reschke, Editor</td>
441         </tr>
442         <tr>
443            <td class="header left"></td>
444            <td class="header right">greenbytes</td>
445         </tr>
446         <tr>
447            <td class="header left"></td>
[52]448            <td class="header right">December 2007</td>
449         </tr>
450      </table>
451      <p class="title">HTTP/1.1, part 2: Message Semantics<br><span class="filename">draft-ietf-httpbis-p2-semantics-latest</span></p>
452      <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1>
453      <p>By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she
454         is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section
455         6 of BCP 79.
456      </p>
457      <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note
458         that other groups may also distribute working documents as Internet-Drafts.
459      </p>
460      <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
461         documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
462         in progress”.
463      </p>
464      <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;.
465      </p>
466      <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;.
467      </p>
468      <p>This Internet-Draft will expire in June 2008.</p>
469      <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
470      <p>Copyright © The IETF Trust (2007). All Rights Reserved.</p>
471      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1> 
472      <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information
473         systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 2 of the
474         seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part
475         2 defines the semantics of HTTP messages as expressed by request methods, request-header fields, response status codes, and
476         response-header fields.
477      </p> 
478      <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1> 
479      <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org). The current issues
[113]480         list is at &lt;<a href="http://www.tools.ietf.org/wg/httpbis/trac/report/11">http://www.tools.ietf.org/wg/httpbis/trac/report/11</a>&gt; and related documents (including fancy diffs) can be found at &lt;<a href="http://www.tools.ietf.org/wg/httpbis/">http://www.tools.ietf.org/wg/httpbis/</a>&gt;.
[52]481      </p> 
482      <hr class="noprint">
483      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
484      <ul class="toc">
[96]485         <li class="tocline0">1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul class="toc">
486               <li class="tocline1">1.1&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
487            </ul>
488         </li>
[52]489         <li class="tocline0">2.&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
490         <li class="tocline0">3.&nbsp;&nbsp;&nbsp;<a href="#method">Method</a></li>
491         <li class="tocline0">4.&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a></li>
492         <li class="tocline0">5.&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>
493         <li class="tocline0">6.&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a></li>
494         <li class="tocline0">7.&nbsp;&nbsp;&nbsp;<a href="#entity">Entity</a></li>
495         <li class="tocline0">8.&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul class="toc">
496               <li class="tocline1">8.1&nbsp;&nbsp;&nbsp;<a href="#safe.and.idempotent">Safe and Idempotent Methods</a><ul class="toc">
497                     <li class="tocline1">8.1.1&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li>
498                     <li class="tocline1">8.1.2&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li>
499                  </ul>
500               </li>
501               <li class="tocline1">8.2&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li>
502               <li class="tocline1">8.3&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li>
503               <li class="tocline1">8.4&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li>
504               <li class="tocline1">8.5&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li>
505               <li class="tocline1">8.6&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li>
506               <li class="tocline1">8.7&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li>
507               <li class="tocline1">8.8&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li>
508               <li class="tocline1">8.9&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a></li>
509            </ul>
510         </li>
511         <li class="tocline0">9.&nbsp;&nbsp;&nbsp;<a href="#status.codes">Status Code Definitions</a><ul class="toc">
512               <li class="tocline1">9.1&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul class="toc">
513                     <li class="tocline1">9.1.1&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li>
514                     <li class="tocline1">9.1.2&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li>
515                  </ul>
516               </li>
517               <li class="tocline1">9.2&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul class="toc">
518                     <li class="tocline1">9.2.1&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li>
519                     <li class="tocline1">9.2.2&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li>
520                     <li class="tocline1">9.2.3&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li>
521                     <li class="tocline1">9.2.4&nbsp;&nbsp;&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></li>
522                     <li class="tocline1">9.2.5&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li>
523                     <li class="tocline1">9.2.6&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li>
524                     <li class="tocline1">9.2.7&nbsp;&nbsp;&nbsp;<a href="#status.206">206 Partial Content</a></li>
525                  </ul>
526               </li>
527               <li class="tocline1">9.3&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul class="toc">
528                     <li class="tocline1">9.3.1&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li>
529                     <li class="tocline1">9.3.2&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li>
530                     <li class="tocline1">9.3.3&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li>
531                     <li class="tocline1">9.3.4&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li>
532                     <li class="tocline1">9.3.5&nbsp;&nbsp;&nbsp;<a href="#status.304">304 Not Modified</a></li>
533                     <li class="tocline1">9.3.6&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li>
534                     <li class="tocline1">9.3.7&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li>
535                     <li class="tocline1">9.3.8&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li>
536                  </ul>
537               </li>
538               <li class="tocline1">9.4&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul class="toc">
539                     <li class="tocline1">9.4.1&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li>
540                     <li class="tocline1">9.4.2&nbsp;&nbsp;&nbsp;<a href="#status.401">401 Unauthorized</a></li>
541                     <li class="tocline1">9.4.3&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li>
542                     <li class="tocline1">9.4.4&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li>
543                     <li class="tocline1">9.4.5&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li>
544                     <li class="tocline1">9.4.6&nbsp;&nbsp;&nbsp;<a href="#status.405">405 Method Not Allowed</a></li>
545                     <li class="tocline1">9.4.7&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li>
546                     <li class="tocline1">9.4.8&nbsp;&nbsp;&nbsp;<a href="#status.407">407 Proxy Authentication Required</a></li>
547                     <li class="tocline1">9.4.9&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li>
548                     <li class="tocline1">9.4.10&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li>
549                     <li class="tocline1">9.4.11&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li>
550                     <li class="tocline1">9.4.12&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li>
551                     <li class="tocline1">9.4.13&nbsp;&nbsp;&nbsp;<a href="#status.412">412 Precondition Failed</a></li>
552                     <li class="tocline1">9.4.14&nbsp;&nbsp;&nbsp;<a href="#status.413">413 Request Entity Too Large</a></li>
553                     <li class="tocline1">9.4.15&nbsp;&nbsp;&nbsp;<a href="#status.414">414 Request-URI Too Long</a></li>
554                     <li class="tocline1">9.4.16&nbsp;&nbsp;&nbsp;<a href="#status.415">415 Unsupported Media Type</a></li>
555                     <li class="tocline1">9.4.17&nbsp;&nbsp;&nbsp;<a href="#status.416">416 Requested Range Not Satisfiable</a></li>
556                     <li class="tocline1">9.4.18&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li>
557                  </ul>
558               </li>
559               <li class="tocline1">9.5&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul class="toc">
560                     <li class="tocline1">9.5.1&nbsp;&nbsp;&nbsp;<a href="#status.500">500 Internal Server Error</a></li>
561                     <li class="tocline1">9.5.2&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li>
562                     <li class="tocline1">9.5.3&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li>
563                     <li class="tocline1">9.5.4&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li>
564                     <li class="tocline1">9.5.5&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li>
565                     <li class="tocline1">9.5.6&nbsp;&nbsp;&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></li>
566                  </ul>
567               </li>
568            </ul>
569         </li>
570         <li class="tocline0">10.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul class="toc">
571               <li class="tocline1">10.1&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li>
572               <li class="tocline1">10.2&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li>
573               <li class="tocline1">10.3&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li>
574               <li class="tocline1">10.4&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li>
575               <li class="tocline1">10.5&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li>
576               <li class="tocline1">10.6&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li>
577               <li class="tocline1">10.7&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li>
578               <li class="tocline1">10.8&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li>
579               <li class="tocline1">10.9&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li>
580            </ul>
581         </li>
582         <li class="tocline0">11.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a></li>
583         <li class="tocline0">12.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul class="toc">
584               <li class="tocline1">12.1&nbsp;&nbsp;&nbsp;<a href="#security.sensitive">Transfer of Sensitive Information</a></li>
585               <li class="tocline1">12.2&nbsp;&nbsp;&nbsp;<a href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URI's</a></li>
586               <li class="tocline1">12.3&nbsp;&nbsp;&nbsp;<a href="#location.spoofing">Location Headers and Spoofing</a></li>
587            </ul>
588         </li>
589         <li class="tocline0">13.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
590         <li class="tocline0">14.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a></li>
591         <li class="tocline0"><a href="#rfc.authors">Authors' Addresses</a></li>
[99]592         <li class="tocline0">A.&nbsp;&nbsp;&nbsp;<a href="#compatibility">Compatibility with Previous Versions</a><ul class="toc">
593               <li class="tocline1">A.1&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li>
594               <li class="tocline1">A.2&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2616">Changes from RFC 2616</a></li>
595            </ul>
596         </li>
[115]597         <li class="tocline0">B.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.B">Change Log (to be removed by RFC Editor before publication)</a><ul class="toc">
598               <li class="tocline1">B.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.B.1">Since RFC2616</a></li>
599               <li class="tocline1">B.2&nbsp;&nbsp;&nbsp;<a href="#rfc.section.B.2">Since draft-ietf-httpbis-p2-semantics-00</a></li>
600            </ul>
601         </li>
[52]602         <li class="tocline0"><a href="#rfc.ipr">Intellectual Property and Copyright Statements</a></li>
603         <li class="tocline0"><a href="#rfc.index">Index</a></li>
604      </ul>
605      <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
606      <p id="rfc.section.1.p.1">This document will define aspects of HTTP related to request and response semantics. Right now it only includes the extracted
607         relevant sections of RFC 2616 with only minor edits.
608      </p>
609      <p id="rfc.section.1.p.2">The HTTP protocol is a request/response protocol. A client sends a request to the server in the form of a request method,
610         URI, and protocol version, followed by a MIME-like message containing request modifiers, client information, and possible
611         body content over a connection with a server. The server responds with a status line, including the message's protocol version
612         and a success or error code, followed by a MIME-like message containing server information, entity metainformation, and possible
613         entity-body content. The relationship between HTTP and MIME is described in <a href="p3-payload.html#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix A</a> of <a href="#Part3" id="rfc.xref.Part3.1"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
614      </p>
[96]615      <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>
616      <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"
617         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>.
618      </p>
619      <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."
620      </p>
[52]621      <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="product.tokens" href="#product.tokens">Product Tokens</a></h1>
622      <p id="rfc.section.2.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields
623         using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white
624         space. By convention, the products are listed in order of their significance for identifying the application.
625      </p>
626      <div id="rfc.figure.u.1"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span>    product         = token ["/" product-version]
627    product-version = token
628</pre><p id="rfc.section.2.p.3">Examples:</p>
629      <div id="rfc.figure.u.2"></div><pre class="text">    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
630    Server: Apache/0.8.4
631</pre><p id="rfc.section.2.p.5">Product tokens <em class="bcp14">SHOULD</em> be short and to the point. They <em class="bcp14">MUST NOT</em> be used for advertising or other non-essential information. Although any token character <em class="bcp14">MAY</em> appear in a product-version, this token <em class="bcp14">SHOULD</em> only be used for a version identifier (i.e., successive versions of the same product <em class="bcp14">SHOULD</em> only differ in the product-version portion of the product value).
632      </p>
633      <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="method" href="#method">Method</a></h1>
634      <p id="rfc.section.3.p.1">The Method token indicates the method to be performed on the resource identified by the Request-URI. The method is case-sensitive.</p>
635      <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span>    Method         = "OPTIONS"                ; <a href="#OPTIONS" id="rfc.xref.OPTIONS.1" title="OPTIONS">Section&nbsp;8.2</a>
636                   | "GET"                    ; <a href="#GET" id="rfc.xref.GET.1" title="GET">Section&nbsp;8.3</a>
637                   | "HEAD"                   ; <a href="#HEAD" id="rfc.xref.HEAD.1" title="HEAD">Section&nbsp;8.4</a>
638                   | "POST"                   ; <a href="#POST" id="rfc.xref.POST.1" title="POST">Section&nbsp;8.5</a>
639                   | "PUT"                    ; <a href="#PUT" id="rfc.xref.PUT.1" title="PUT">Section&nbsp;8.6</a>
640                   | "DELETE"                 ; <a href="#DELETE" id="rfc.xref.DELETE.1" title="DELETE">Section&nbsp;8.7</a>
641                   | "TRACE"                  ; <a href="#TRACE" id="rfc.xref.TRACE.1" title="TRACE">Section&nbsp;8.8</a>
642                   | "CONNECT"                ; <a href="#CONNECT" id="rfc.xref.CONNECT.1" title="CONNECT">Section&nbsp;8.9</a>
643                   | extension-method
644    extension-method = token
645</pre><p id="rfc.section.3.p.3">The list of methods allowed by a resource can be specified in an Allow header field (<a href="#header.allow" id="rfc.xref.header.allow.1" title="Allow">Section&nbsp;10.1</a>). The return code of the response always notifies the client whether a method is currently allowed on a resource, since the
646         set of allowed methods can change dynamically. An origin server <em class="bcp14">SHOULD</em> return the status code 405 (Method Not Allowed) if the method is known by the origin server but not allowed for the requested
647         resource, and 501 (Not Implemented) if the method is unrecognized or not implemented by the origin server. The methods GET
648         and HEAD <em class="bcp14">MUST</em> be supported by all general-purpose servers. All other methods are <em class="bcp14">OPTIONAL</em>; however, if the above methods are implemented, they <em class="bcp14">MUST</em> be implemented with the same semantics as those specified in <a href="#method.definitions" title="Method Definitions">Section&nbsp;8</a>.
649      </p>
650      <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a>&nbsp;<a id="request.header.fields" href="#request.header.fields">Request Header Fields</a></h1>
651      <p id="rfc.section.4.p.1">The request-header fields allow the client to pass additional information about the request, and about the client itself,
652         to the server. These fields act as request modifiers, with semantics equivalent to the parameters on a programming language
653         method invocation.
654      </p>
655      <div id="rfc.figure.u.4"></div><pre class="inline"><span id="rfc.iref.g.5"></span>    request-header = Accept                   ; <a href="#Part3" id="rfc.xref.Part3.2"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="p3-payload.html#header.accept" title="Accept">Section 5.1</a>
656                   | Accept-Charset           ; <a href="#Part3" id="rfc.xref.Part3.3"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="p3-payload.html#header.accept-charset" title="Accept-Charset">Section 5.2</a>
657                   | Accept-Encoding          ; <a href="#Part3" id="rfc.xref.Part3.4"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="p3-payload.html#header.accept-encoding" title="Accept-Encoding">Section 5.3</a>
658                   | Accept-Language          ; <a href="#Part3" id="rfc.xref.Part3.5"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>, <a href="p3-payload.html#header.accept-language" title="Accept-Language">Section 5.4</a>
659                   | Authorization            ; <a href="#Part7" id="rfc.xref.Part7.1"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>, <a href="p7-auth.html#header.authorization" title="Authorization">Section 3.1</a>
660                   | Expect                   ; <a href="#header.expect" id="rfc.xref.header.expect.1" title="Expect">Section&nbsp;10.2</a>
661                   | From                     ; <a href="#header.from" id="rfc.xref.header.from.1" title="From">Section&nbsp;10.3</a>
662                   | Host                     ; <a href="#Part1" id="rfc.xref.Part1.1"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#header.host" title="Host">Section 8.4</a>
[60]663                   | If-Match                 ; <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.if-match" title="If-Match">Section 6.2</a>
664                   | If-Modified-Since        ; <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.if-modified-since" title="If-Modified-Since">Section 6.3</a>
665                   | If-None-Match            ; <a href="#Part4" id="rfc.xref.Part4.3"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p4-conditional.html#header.if-none-match" title="If-None-Match">Section 6.4</a>
[52]666                   | If-Range                 ; <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.if-range" title="If-Range">Section 5.3</a>
[60]667                   | If-Unmodified-Since      ; <a href="#Part4" id="rfc.xref.Part4.4"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p4-conditional.html#header.if-unmodified-since" title="If-Unmodified-Since">Section 6.5</a>
[52]668                   | Max-Forwards             ; <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.1" title="Max-Forwards">Section&nbsp;10.5</a>
669                   | Proxy-Authorization      ; <a href="#Part7" id="rfc.xref.Part7.2"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>, <a href="p7-auth.html#header.proxy-authorization" title="Proxy-Authorization">Section 3.3</a>
670                   | Range                    ; <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>, <a href="p5-range.html#header.range" title="Range">Section 5.4</a>
671                   | Referer                  ; <a href="#header.referer" id="rfc.xref.header.referer.1" title="Referer">Section&nbsp;10.6</a>
672                   | TE                       ; <a href="#Part1" id="rfc.xref.Part1.2"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, <a href="p1-messaging.html#header.upgrade" title="Upgrade">Section 8.8</a>
673                   | User-Agent               ; <a href="#header.user-agent" id="rfc.xref.header.user-agent.1" title="User-Agent">Section&nbsp;10.9</a>
674</pre><p id="rfc.section.4.p.3">Request-header field names can be extended reliably only in combination with a change in the protocol version. However, new
675         or experimental header fields <em class="bcp14">MAY</em> be given the semantics of request-header fields if all parties in the communication recognize them to be request-header fields.
676         Unrecognized header fields are treated as entity-header fields.
677      </p>
678      <h1 id="rfc.section.5"><a href="#rfc.section.5">5.</a>&nbsp;<a id="status.code.and.reason.phrase" href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h1>
679      <p id="rfc.section.5.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes
680         are fully defined in <a href="#status.codes" title="Status Code Definitions">Section&nbsp;9</a>. The Reason-Phrase is intended to give a short textual description of the Status-Code. The Status-Code is intended for use
681         by automata and the Reason-Phrase is intended for the human user. The client is not required to examine or display the Reason-Phrase.
682      </p>
683      <p id="rfc.section.5.p.2">The individual values of the numeric status codes defined for HTTP/1.1, and an example set of corresponding Reason-Phrase's,
684         are presented below. The reason phrases listed here are only recommendations -- they <em class="bcp14">MAY</em> be replaced by local equivalents without affecting the protocol.
685      </p>
686      <div id="rfc.figure.u.5"></div><pre class="inline"><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span>   Status-Code    =
687         "100"  ; <a href="#status.100" id="rfc.xref.status.100.1" title="100 Continue">Section&nbsp;9.1.1</a>: Continue
688       | "101"  ; <a href="#status.101" id="rfc.xref.status.101.1" title="101 Switching Protocols">Section&nbsp;9.1.2</a>: Switching Protocols
689       | "200"  ; <a href="#status.200" id="rfc.xref.status.200.1" title="200 OK">Section&nbsp;9.2.1</a>: OK
690       | "201"  ; <a href="#status.201" id="rfc.xref.status.201.1" title="201 Created">Section&nbsp;9.2.2</a>: Created
691       | "202"  ; <a href="#status.202" id="rfc.xref.status.202.1" title="202 Accepted">Section&nbsp;9.2.3</a>: Accepted
692       | "203"  ; <a href="#status.203" id="rfc.xref.status.203.1" title="203 Non-Authoritative Information">Section&nbsp;9.2.4</a>: Non-Authoritative Information
693       | "204"  ; <a href="#status.204" id="rfc.xref.status.204.1" title="204 No Content">Section&nbsp;9.2.5</a>: No Content
694       | "205"  ; <a href="#status.205" id="rfc.xref.status.205.1" title="205 Reset Content">Section&nbsp;9.2.6</a>: Reset Content
695       | "206"  ; <a href="#status.206" id="rfc.xref.status.206.1" title="206 Partial Content">Section&nbsp;9.2.7</a>: Partial Content
696       | "300"  ; <a href="#status.300" id="rfc.xref.status.300.1" title="300 Multiple Choices">Section&nbsp;9.3.1</a>: Multiple Choices
697       | "301"  ; <a href="#status.301" id="rfc.xref.status.301.1" title="301 Moved Permanently">Section&nbsp;9.3.2</a>: Moved Permanently
698       | "302"  ; <a href="#status.302" id="rfc.xref.status.302.1" title="302 Found">Section&nbsp;9.3.3</a>: Found
699       | "303"  ; <a href="#status.303" id="rfc.xref.status.303.1" title="303 See Other">Section&nbsp;9.3.4</a>: See Other
700       | "304"  ; <a href="#status.304" id="rfc.xref.status.304.1" title="304 Not Modified">Section&nbsp;9.3.5</a>: Not Modified
701       | "305"  ; <a href="#status.305" id="rfc.xref.status.305.1" title="305 Use Proxy">Section&nbsp;9.3.6</a>: Use Proxy
702       | "307"  ; <a href="#status.307" id="rfc.xref.status.307.1" title="307 Temporary Redirect">Section&nbsp;9.3.8</a>: Temporary Redirect
703       | "400"  ; <a href="#status.400" id="rfc.xref.status.400.1" title="400 Bad Request">Section&nbsp;9.4.1</a>: Bad Request
704       | "401"  ; <a href="#status.401" id="rfc.xref.status.401.1" title="401 Unauthorized">Section&nbsp;9.4.2</a>: Unauthorized
705       | "402"  ; <a href="#status.402" id="rfc.xref.status.402.1" title="402 Payment Required">Section&nbsp;9.4.3</a>: Payment Required
706       | "403"  ; <a href="#status.403" id="rfc.xref.status.403.1" title="403 Forbidden">Section&nbsp;9.4.4</a>: Forbidden
707       | "404"  ; <a href="#status.404" id="rfc.xref.status.404.1" title="404 Not Found">Section&nbsp;9.4.5</a>: Not Found
708       | "405"  ; <a href="#status.405" id="rfc.xref.status.405.1" title="405 Method Not Allowed">Section&nbsp;9.4.6</a>: Method Not Allowed
709       | "406"  ; <a href="#status.406" id="rfc.xref.status.406.1" title="406 Not Acceptable">Section&nbsp;9.4.7</a>: Not Acceptable
710       | "407"  ; <a href="#status.407" id="rfc.xref.status.407.1" title="407 Proxy Authentication Required">Section&nbsp;9.4.8</a>: Proxy Authentication Required
711       | "408"  ; <a href="#status.408" id="rfc.xref.status.408.1" title="408 Request Timeout">Section&nbsp;9.4.9</a>: Request Time-out
712       | "409"  ; <a href="#status.409" id="rfc.xref.status.409.1" title="409 Conflict">Section&nbsp;9.4.10</a>: Conflict
713       | "410"  ; <a href="#status.410" id="rfc.xref.status.410.1" title="410 Gone">Section&nbsp;9.4.11</a>: Gone
714       | "411"  ; <a href="#status.411" id="rfc.xref.status.411.1" title="411 Length Required">Section&nbsp;9.4.12</a>: Length Required
715       | "412"  ; <a href="#status.412" id="rfc.xref.status.412.1" title="412 Precondition Failed">Section&nbsp;9.4.13</a>: Precondition Failed
716       | "413"  ; <a href="#status.413" id="rfc.xref.status.413.1" title="413 Request Entity Too Large">Section&nbsp;9.4.14</a>: Request Entity Too Large
717       | "414"  ; <a href="#status.414" id="rfc.xref.status.414.1" title="414 Request-URI Too Long">Section&nbsp;9.4.15</a>: Request-URI Too Large
718       | "415"  ; <a href="#status.415" id="rfc.xref.status.415.1" title="415 Unsupported Media Type">Section&nbsp;9.4.16</a>: Unsupported Media Type
719       | "416"  ; <a href="#status.416" id="rfc.xref.status.416.1" title="416 Requested Range Not Satisfiable">Section&nbsp;9.4.17</a>: Requested range not satisfiable
720       | "417"  ; <a href="#status.417" id="rfc.xref.status.417.1" title="417 Expectation Failed">Section&nbsp;9.4.18</a>: Expectation Failed
721       | "500"  ; <a href="#status.500" id="rfc.xref.status.500.1" title="500 Internal Server Error">Section&nbsp;9.5.1</a>: Internal Server Error
722       | "501"  ; <a href="#status.501" id="rfc.xref.status.501.1" title="501 Not Implemented">Section&nbsp;9.5.2</a>: Not Implemented
723       | "502"  ; <a href="#status.502" id="rfc.xref.status.502.1" title="502 Bad Gateway">Section&nbsp;9.5.3</a>: Bad Gateway
724       | "503"  ; <a href="#status.503" id="rfc.xref.status.503.1" title="503 Service Unavailable">Section&nbsp;9.5.4</a>: Service Unavailable
725       | "504"  ; <a href="#status.504" id="rfc.xref.status.504.1" title="504 Gateway Timeout">Section&nbsp;9.5.5</a>: Gateway Time-out
726       | "505"  ; <a href="#status.505" id="rfc.xref.status.505.1" title="505 HTTP Version Not Supported">Section&nbsp;9.5.6</a>: HTTP Version not supported
727       | extension-code
728
729   extension-code = 3DIGIT
730   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
731</pre><p id="rfc.section.5.p.4">HTTP status codes are extensible. HTTP applications are not required to understand the meaning of all registered status codes,
732         though such understanding is obviously desirable. However, applications <em class="bcp14">MUST</em> understand the class of any status code, as indicated by the first digit, and treat any unrecognized response as being equivalent
733         to the x00 status code of that class, with the exception that an unrecognized response <em class="bcp14">MUST NOT</em> be cached. For example, if an unrecognized status code of 431 is received by the client, it can safely assume that there was
734         something wrong with its request and treat the response as if it had received a 400 status code. In such cases, user agents <em class="bcp14">SHOULD</em> present to the user the entity returned with the response, since that entity is likely to include human-readable information
735         which will explain the unusual status.
736      </p>
737      <h1 id="rfc.section.6"><a href="#rfc.section.6">6.</a>&nbsp;<a id="response.header.fields" href="#response.header.fields">Response Header Fields</a></h1>
738      <p id="rfc.section.6.p.1">The response-header fields allow the server to pass additional information about the response which cannot be placed in the
739         Status-Line. These header fields give information about the server and about further access to the resource identified by
740         the Request-URI.
741      </p>
742      <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.9"></span>    response-header = Accept-Ranges           ; <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.accept-ranges" title="Accept-Ranges">Section 5.1</a>
743                    | Age                     ; <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.age" title="Age">Section 3.1</a>
[60]744                    | ETag                    ; <a href="#Part4" id="rfc.xref.Part4.5"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>, <a href="p4-conditional.html#header.etag" title="ETag">Section 6.1</a>
[52]745                    | Location                ; <a href="#header.location" id="rfc.xref.header.location.1" title="Location">Section&nbsp;10.4</a>
746                    | Proxy-Authenticate      ; <a href="#Part7" id="rfc.xref.Part7.3"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>, <a href="p7-auth.html#header.proxy-authenticate" title="Proxy-Authenticate">Section 3.2</a>
747                    | Retry-After             ; <a href="#header.retry-after" id="rfc.xref.header.retry-after.1" title="Retry-After">Section&nbsp;10.7</a>
748                    | Server                  ; <a href="#header.server" id="rfc.xref.header.server.1" title="Server">Section&nbsp;10.8</a>
749                    | Vary                    ; <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.vary" title="Vary">Section 3.5</a>
750                    | WWW-Authenticate        ; <a href="#Part7" id="rfc.xref.Part7.4"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>, <a href="p7-auth.html#header.www-authenticate" title="WWW-Authenticate">Section 3.4</a>
751</pre><p id="rfc.section.6.p.3">Response-header field names can be extended reliably only in combination with a change in the protocol version. However, new
752         or experimental header fields <em class="bcp14">MAY</em> be given the semantics of response-header fields if all parties in the communication recognize them to be response-header
753         fields. Unrecognized header fields are treated as entity-header fields.
754      </p>
755      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="entity" href="#entity">Entity</a></h1>
756      <p id="rfc.section.7.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
757         fields and an entity-body, although some responses will only include the entity-headers. HTTP entity-body and entity-header
758         fields are defined in <a href="#Part3" id="rfc.xref.Part3.6"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>.
759      </p>
760      <p id="rfc.section.7.p.2">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.Part1.3"><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
761         safe and proper transfer of the message.
762      </p>
763      <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="method.definitions" href="#method.definitions">Method Definitions</a></h1>
764      <p id="rfc.section.8.p.1">The set of common methods for HTTP/1.1 is defined below. Although this set can be expanded, additional methods cannot be assumed
765         to share the same semantics for separately extended clients and servers. The Host request-header field (<a href="p1-messaging.html#header.host" title="Host">Section 8.4</a> of <a href="#Part1" id="rfc.xref.Part1.4"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) <em class="bcp14">MUST</em> accompany all HTTP/1.1 requests.
766      </p>
767      <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a id="safe.and.idempotent" href="#safe.and.idempotent">Safe and Idempotent Methods</a></h2>
768      <h3 id="rfc.section.8.1.1"><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;<a id="safe.methods" href="#safe.methods">Safe Methods</a></h3>
769      <p id="rfc.section.8.1.1.p.1">Implementors should be aware that the software represents the user in their interactions over the Internet, and should be
770         careful to allow the user to be aware of any actions they might take which may have an unexpected significance to themselves
771         or others.
772      </p>
773      <p id="rfc.section.8.1.1.p.2">In particular, the convention has been established that the GET and HEAD methods <em class="bcp14">SHOULD NOT</em> have the significance of taking an action other than retrieval. These methods ought to be considered "safe". This allows user
774         agents to represent other methods, such as POST, PUT and DELETE, in a special way, so that the user is made aware of the fact
775         that a possibly unsafe action is being requested.
776      </p>
777      <p id="rfc.section.8.1.1.p.3">Naturally, it is not possible to ensure that the server does not generate side-effects as a result of performing a GET request;
778         in fact, some dynamic resources consider that a feature. The important distinction here is that the user did not request the
779         side-effects, so therefore cannot be held accountable for them.
780      </p>
781      <h3 id="rfc.section.8.1.2"><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;<a id="idempotent.methods" href="#idempotent.methods">Idempotent Methods</a></h3>
782      <p id="rfc.section.8.1.2.p.1">Methods can also have the property of "idempotence" in that (aside from error or expiration issues) the side-effects of N
783         &gt; 0 identical requests is the same as for a single request. The methods GET, HEAD, PUT and DELETE share this property. Also,
784         the methods OPTIONS and TRACE <em class="bcp14">SHOULD NOT</em> have side effects, and so are inherently idempotent.
785      </p>
786      <p id="rfc.section.8.1.2.p.2">However, it is possible that a sequence of several requests is non-idempotent, even if all of the methods executed in that
787         sequence are idempotent. (A sequence is idempotent if a single execution of the entire sequence always yields a result that
788         is not changed by a reexecution of all, or part, of that sequence.) For example, a sequence is non-idempotent if its result
789         depends on a value that is later modified in the same sequence.
790      </p>
791      <p id="rfc.section.8.1.2.p.3">A sequence that never has side effects is idempotent, by definition (provided that no concurrent operations are being executed
792         on the same set of resources).
793      </p>
794      <div id="rfc.iref.o.1"></div>
795      <div id="rfc.iref.m.1"></div>
796      <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a id="OPTIONS" href="#OPTIONS">OPTIONS</a></h2>
797      <p id="rfc.section.8.2.p.1">The OPTIONS method represents a request for information about the communication options available on the request/response
798         chain identified by the Request-URI. This method allows the client to determine the options and/or requirements associated
799         with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
800      </p>
801      <p id="rfc.section.8.2.p.2">Responses to this method are not cacheable.</p>
802      <p id="rfc.section.8.2.p.3">If the OPTIONS request includes an entity-body (as indicated by the presence of Content-Length or Transfer-Encoding), then
803         the media type <em class="bcp14">MUST</em> be indicated by a Content-Type field. Although this specification does not define any use for such a body, future extensions
804         to HTTP might use the OPTIONS body to make more detailed queries on the server. A server that does not support such an extension <em class="bcp14">MAY</em> discard the request body.
805      </p>
806      <p id="rfc.section.8.2.p.4">If the Request-URI is an asterisk ("*"), the OPTIONS request is intended to apply to the server in general rather than to
807         a specific resource. Since a server's communication options typically depend on the resource, the "*" request is only useful
808         as a "ping" or "no-op" type of method; it does nothing beyond allowing the client to test the capabilities of the server.
809         For example, this can be used to test a proxy for HTTP/1.1 compliance (or lack thereof).
810      </p>
811      <p id="rfc.section.8.2.p.5">If the Request-URI is not an asterisk, the OPTIONS request applies only to the options that are available when communicating
812         with that resource.
813      </p>
814      <p id="rfc.section.8.2.p.6">A 200 response <em class="bcp14">SHOULD</em> include any header fields that indicate optional features implemented by the server and applicable to that resource (e.g.,
815         Allow), possibly including extensions not defined by this specification. The response body, if any, <em class="bcp14">SHOULD</em> also include information about the communication options. The format for such a body is not defined by this specification,
816         but might be defined by future extensions to HTTP. Content negotiation <em class="bcp14">MAY</em> be used to select the appropriate response format. If no response body is included, the response <em class="bcp14">MUST</em> include a Content-Length field with a field-value of "0".
817      </p>
818      <p id="rfc.section.8.2.p.7">The Max-Forwards request-header field <em class="bcp14">MAY</em> be used to target a specific proxy in the request chain. When a proxy receives an OPTIONS request on an absoluteURI for which
819         request forwarding is permitted, the proxy <em class="bcp14">MUST</em> check for a Max-Forwards field. If the Max-Forwards field-value is zero ("0"), the proxy <em class="bcp14">MUST NOT</em> forward the message; instead, the proxy <em class="bcp14">SHOULD</em> respond with its own communication options. If the Max-Forwards field-value is an integer greater than zero, the proxy <em class="bcp14">MUST</em> decrement the field-value when it forwards the request. If no Max-Forwards field is present in the request, then the forwarded
820         request <em class="bcp14">MUST NOT</em> include a Max-Forwards field.
821      </p>
822      <div id="rfc.iref.g.10"></div>
823      <div id="rfc.iref.m.2"></div>
824      <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a id="GET" href="#GET">GET</a></h2>
825      <p id="rfc.section.8.3.p.1">The GET method means retrieve whatever information (in the form of an entity) is identified by the Request-URI. If the Request-URI
826         refers to a data-producing process, it is the produced data which shall be returned as the entity in the response and not
827         the source text of the process, unless that text happens to be the output of the process.
828      </p>
829      <p id="rfc.section.8.3.p.2">The semantics of the GET method change to a "conditional GET" if the request message includes an If-Modified-Since, If-Unmodified-Since,
830         If-Match, If-None-Match, or If-Range header field. A conditional GET method requests that the entity be transferred only under
831         the circumstances described by the conditional header field(s). The conditional GET method is intended to reduce unnecessary
832         network usage by allowing cached entities to be refreshed without requiring multiple requests or transferring data already
833         held by the client.
834      </p>
835      <p id="rfc.section.8.3.p.3">The semantics of the GET method change to a "partial GET" if the request message includes a Range header field. A partial
836         GET requests that only part of the entity be transferred, as described in <a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.4"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>. The partial GET method is intended to reduce unnecessary network usage by allowing partially-retrieved entities to be completed
837         without transferring data already held by the client.
838      </p>
839      <p id="rfc.section.8.3.p.4">The response to a GET request is cacheable if and only if it meets the requirements for HTTP caching described in <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.
840      </p>
841      <p id="rfc.section.8.3.p.5">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URI's">Section&nbsp;12.2</a> for security considerations when used for forms.
842      </p>
843      <div id="rfc.iref.h.1"></div>
844      <div id="rfc.iref.m.3"></div>
845      <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a id="HEAD" href="#HEAD">HEAD</a></h2>
846      <p id="rfc.section.8.4.p.1">The HEAD method is identical to GET except that the server <em class="bcp14">MUST NOT</em> return a message-body in the response. The metainformation contained in the HTTP headers in response to a HEAD request <em class="bcp14">SHOULD</em> be identical to the information sent in response to a GET request. This method can be used for obtaining metainformation about
847         the entity implied by the request without transferring the entity-body itself. This method is often used for testing hypertext
848         links for validity, accessibility, and recent modification.
849      </p>
850      <p id="rfc.section.8.4.p.2">The response to a HEAD request <em class="bcp14">MAY</em> be cacheable in the sense that the information contained in the response <em class="bcp14">MAY</em> be used to update a previously cached entity from that resource. If the new field values indicate that the cached entity differs
851         from the current entity (as would be indicated by a change in Content-Length, Content-MD5, ETag or Last-Modified), then the
852         cache <em class="bcp14">MUST</em> treat the cache entry as stale.
853      </p>
854      <div id="rfc.iref.p.1"></div>
855      <div id="rfc.iref.m.4"></div>
856      <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a>&nbsp;<a id="POST" href="#POST">POST</a></h2>
[92]857      <p id="rfc.section.8.5.p.1">The POST method is used to request that the origin server accept the entity enclosed in the request as data to be processed
858         by the resource identified by the Request-URI in the Request-Line. POST is designed to allow a uniform method to cover the
859         following functions:
[52]860      </p>
861      <ul>
862         <li>Annotation of existing resources;</li>
863         <li>Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles;</li>
864         <li>Providing a block of data, such as the result of submitting a form, to a data-handling process;</li>
865         <li>Extending a database through an append operation.</li>
866      </ul>
[92]867      <p id="rfc.section.8.5.p.2">The actual function performed by the POST method is determined by the server and is usually dependent on the Request-URI.</p>
[52]868      <p id="rfc.section.8.5.p.3">The action performed by the POST method might not result in a resource that can be identified by a URI. In this case, either
869         200 (OK) or 204 (No Content) is the appropriate response status, depending on whether or not the response includes an entity
870         that describes the result.
871      </p>
872      <p id="rfc.section.8.5.p.4">If a resource has been created on the origin server, the response <em class="bcp14">SHOULD</em> be 201 (Created) and contain an entity which describes the status of the request and refers to the new resource, and a Location
873         header (see <a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section&nbsp;10.4</a>).
874      </p>
875      <p id="rfc.section.8.5.p.5">Responses to this method are not cacheable, unless the response includes appropriate Cache-Control or Expires header fields.
876         However, the 303 (See Other) response can be used to direct the user agent to retrieve a cacheable resource.
877      </p>
878      <p id="rfc.section.8.5.p.6">POST requests <em class="bcp14">MUST</em> obey the message transmission requirements set out in <a href="p1-messaging.html#message.transmission.requirements" title="Message Transmission Requirements">Section 7.2</a> of <a href="#Part1" id="rfc.xref.Part1.5"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
879      </p>
880      <p id="rfc.section.8.5.p.7">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URI's">Section&nbsp;12.2</a> for security considerations.
881      </p>
882      <div id="rfc.iref.p.2"></div>
883      <div id="rfc.iref.m.5"></div>
884      <h2 id="rfc.section.8.6"><a href="#rfc.section.8.6">8.6</a>&nbsp;<a id="PUT" href="#PUT">PUT</a></h2>
885      <p id="rfc.section.8.6.p.1">The PUT method requests that the enclosed entity be stored under the supplied Request-URI. If the Request-URI refers to an
886         already existing resource, the enclosed entity <em class="bcp14">SHOULD</em> be considered as a modified version of the one residing on the origin server. If the Request-URI does not point to an existing
887         resource, and that URI is capable of being defined as a new resource by the requesting user agent, the origin server can create
888         the resource with that URI. If a new resource is created, the origin server <em class="bcp14">MUST</em> inform the user agent via the 201 (Created) response. If an existing resource is modified, either the 200 (OK) or 204 (No
889         Content) response codes <em class="bcp14">SHOULD</em> be sent to indicate successful completion of the request. If the resource could not be created or modified with the Request-URI,
890         an appropriate error response <em class="bcp14">SHOULD</em> be given that reflects the nature of the problem. The recipient of the entity <em class="bcp14">MUST NOT</em> ignore any Content-* (e.g. Content-Range) headers that it does not understand or implement and <em class="bcp14">MUST</em> return a 501 (Not Implemented) response in such cases.
891      </p>
892      <p id="rfc.section.8.6.p.2">If the request passes through a cache and the Request-URI identifies one or more currently cached entities, those entries <em class="bcp14">SHOULD</em> be treated as stale. Responses to this method are not cacheable.
893      </p>
894      <p id="rfc.section.8.6.p.3">The fundamental difference between the POST and PUT requests is reflected in the different meaning of the Request-URI. The
895         URI in a POST request identifies the resource that will handle the enclosed entity. That resource might be a data-accepting
896         process, a gateway to some other protocol, or a separate entity that accepts annotations. In contrast, the URI in a PUT request
897         identifies the entity enclosed with the request -- the user agent knows what URI is intended and the server <em class="bcp14">MUST NOT</em> attempt to apply the request to some other resource. If the server desires that the request be applied to a different URI,
898         it <em class="bcp14">MUST</em> send a 301 (Moved Permanently) response; the user agent <em class="bcp14">MAY</em> then make its own decision regarding whether or not to redirect the request.
899      </p>
900      <p id="rfc.section.8.6.p.4">A single resource <em class="bcp14">MAY</em> be identified by many different URIs. For example, an article might have a URI for identifying "the current version" which
901         is separate from the URI identifying each particular version. In this case, a PUT request on a general URI might result in
902         several other URIs being defined by the origin server.
903      </p>
904      <p id="rfc.section.8.6.p.5">HTTP/1.1 does not define how a PUT method affects the state of an origin server.</p>
905      <p id="rfc.section.8.6.p.6">PUT requests <em class="bcp14">MUST</em> obey the message transmission requirements set out in <a href="p1-messaging.html#message.transmission.requirements" title="Message Transmission Requirements">Section 7.2</a> of <a href="#Part1" id="rfc.xref.Part1.6"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>.
906      </p>
907      <p id="rfc.section.8.6.p.7">Unless otherwise specified for a particular entity-header, the entity-headers in the PUT request <em class="bcp14">SHOULD</em> be applied to the resource created or modified by the PUT.
908      </p>
909      <div id="rfc.iref.d.1"></div>
910      <div id="rfc.iref.m.6"></div>
911      <h2 id="rfc.section.8.7"><a href="#rfc.section.8.7">8.7</a>&nbsp;<a id="DELETE" href="#DELETE">DELETE</a></h2>
912      <p id="rfc.section.8.7.p.1">The DELETE method requests that the origin server delete the resource identified by the Request-URI. This method <em class="bcp14">MAY</em> be overridden by human intervention (or other means) on the origin server. The client cannot be guaranteed that the operation
913         has been carried out, even if the status code returned from the origin server indicates that the action has been completed
914         successfully. However, the server <em class="bcp14">SHOULD NOT</em> indicate success unless, at the time the response is given, it intends to delete the resource or move it to an inaccessible
915         location.
916      </p>
917      <p id="rfc.section.8.7.p.2">A successful response <em class="bcp14">SHOULD</em> be 200 (OK) if the response includes an entity describing the status, 202 (Accepted) if the action has not yet been enacted,
918         or 204 (No Content) if the action has been enacted but the response does not include an entity.
919      </p>
920      <p id="rfc.section.8.7.p.3">If the request passes through a cache and the Request-URI identifies one or more currently cached entities, those entries <em class="bcp14">SHOULD</em> be treated as stale. Responses to this method are not cacheable.
921      </p>
922      <div id="rfc.iref.t.1"></div>
923      <div id="rfc.iref.m.7"></div>
924      <h2 id="rfc.section.8.8"><a href="#rfc.section.8.8">8.8</a>&nbsp;<a id="TRACE" href="#TRACE">TRACE</a></h2>
925      <p id="rfc.section.8.8.p.1">The TRACE method is used to invoke a remote, application-layer loop-back of the request message. The final recipient of the
926         request <em class="bcp14">SHOULD</em> reflect the message received back to the client as the entity-body of a 200 (OK) response. The final recipient is either the
927         origin server or the first proxy or gateway to receive a Max-Forwards value of zero (0) in the request (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.2" title="Max-Forwards">Section&nbsp;10.5</a>). A TRACE request <em class="bcp14">MUST NOT</em> include an entity.
928      </p>
929      <p id="rfc.section.8.8.p.2">TRACE allows the client to see what is being received at the other end of the request chain and use that data for testing
930         or diagnostic information. The value of the Via header field (<a href="p1-messaging.html#header.via" title="Via">Section 8.9</a> of <a href="#Part1" id="rfc.xref.Part1.7"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>) is of particular interest, since it acts as a trace of the request chain. Use of the Max-Forwards header field allows the
931         client to limit the length of the request chain, which is useful for testing a chain of proxies forwarding messages in an
932         infinite loop.
933      </p>
934      <p id="rfc.section.8.8.p.3">If the request is valid, the response <em class="bcp14">SHOULD</em> contain the entire request message in the entity-body, with a Content-Type of "message/http". Responses to this method <em class="bcp14">MUST NOT</em> be cached.
935      </p>
936      <div id="rfc.iref.c.1"></div>
937      <div id="rfc.iref.m.8"></div>
938      <h2 id="rfc.section.8.9"><a href="#rfc.section.8.9">8.9</a>&nbsp;<a id="CONNECT" href="#CONNECT">CONNECT</a></h2>
939      <p id="rfc.section.8.9.p.1">This specification reserves the method name CONNECT for use with a proxy that can dynamically switch to being a tunnel (e.g.
940         SSL tunneling <a href="#Luo1998" id="rfc.xref.Luo1998.1"><cite title="Tunneling TCP based protocols through Web proxy servers">[Luo1998]</cite></a>).
941      </p>
942      <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;<a id="status.codes" href="#status.codes">Status Code Definitions</a></h1>
943      <p id="rfc.section.9.p.1">Each Status-Code is described below, including a description of which method(s) it can follow and any metainformation required
944         in the response.
945      </p>
946      <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a id="status.1xx" href="#status.1xx">Informational 1xx</a></h2>
947      <p id="rfc.section.9.1.p.1">This class of status code indicates a provisional response, consisting only of the Status-Line and optional headers, and is
948         terminated by an empty line. There are no required headers for this class of status code. Since HTTP/1.0 did not define any
949         1xx status codes, servers <em class="bcp14">MUST NOT</em> send a 1xx response to an HTTP/1.0 client except under experimental conditions.
950      </p>
951      <p id="rfc.section.9.1.p.2">A client <em class="bcp14">MUST</em> be prepared to accept one or more 1xx status responses prior to a regular response, even if the client does not expect a 100
952         (Continue) status message. Unexpected 1xx status responses <em class="bcp14">MAY</em> be ignored by a user agent.
953      </p>
954      <p id="rfc.section.9.1.p.3">Proxies <em class="bcp14">MUST</em> forward 1xx responses, unless the connection between the proxy and its client has been closed, or unless the proxy itself
955         requested the generation of the 1xx response. (For example, if a proxy adds a "Expect: 100-continue" field when it forwards
956         a request, then it need not forward the corresponding 100 (Continue) response(s).)
957      </p>
958      <div id="rfc.iref.25"></div>
959      <div id="rfc.iref.s.1"></div>
960      <h3 id="rfc.section.9.1.1"><a href="#rfc.section.9.1.1">9.1.1</a>&nbsp;<a id="status.100" href="#status.100">100 Continue</a></h3>
961      <p id="rfc.section.9.1.1.p.1">The client <em class="bcp14">SHOULD</em> continue with its request. This interim response is used to inform the client that the initial part of the request has been
962         received and has not yet been rejected by the server. The client <em class="bcp14">SHOULD</em> continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The
963         server <em class="bcp14">MUST</em> send a final response after the request has been completed. See <a href="p1-messaging.html#use.of.the.100.status" title="Use of the 100 (Continue) Status">Section 7.2.3</a> of <a href="#Part1" id="rfc.xref.Part1.8"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for detailed discussion of the use and handling of this status code.
964      </p>
965      <div id="rfc.iref.26"></div>
966      <div id="rfc.iref.s.2"></div>
967      <h3 id="rfc.section.9.1.2"><a href="#rfc.section.9.1.2">9.1.2</a>&nbsp;<a id="status.101" href="#status.101">101 Switching Protocols</a></h3>
968      <p id="rfc.section.9.1.2.p.1">The server understands and is willing to comply with the client's request, via the Upgrade message header field (<a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.5"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>), for a change in the application protocol being used on this connection. The server will switch protocols to those defined
969         by the response's Upgrade header field immediately after the empty line which terminates the 101 response.
970      </p>
971      <p id="rfc.section.9.1.2.p.2">The protocol <em class="bcp14">SHOULD</em> be switched only when it is advantageous to do so. For example, switching to a newer version of HTTP is advantageous over
972         older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use
973         such features.
974      </p>
975      <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a id="status.2xx" href="#status.2xx">Successful 2xx</a></h2>
976      <p id="rfc.section.9.2.p.1">This class of status code indicates that the client's request was successfully received, understood, and accepted.</p>
977      <div id="rfc.iref.27"></div>
978      <div id="rfc.iref.s.3"></div>
979      <h3 id="rfc.section.9.2.1"><a href="#rfc.section.9.2.1">9.2.1</a>&nbsp;<a id="status.200" href="#status.200">200 OK</a></h3>
980      <p id="rfc.section.9.2.1.p.1">The request has succeeded. The information returned with the response is dependent on the method used in the request, for
981         example:
982      </p>
983      <dl>
984         <dt>GET</dt>
985         <dd>an entity corresponding to the requested resource is sent in the response;</dd>
986         <dt>HEAD</dt>
987         <dd>the entity-header fields corresponding to the requested resource are sent in the response without any message-body;</dd>
988         <dt>POST</dt>
989         <dd>an entity describing or containing the result of the action;</dd>
990         <dt>TRACE</dt>
991         <dd>an entity containing the request message as received by the end server.</dd>
992      </dl>
993      <div id="rfc.iref.28"></div>
994      <div id="rfc.iref.s.4"></div>
995      <h3 id="rfc.section.9.2.2"><a href="#rfc.section.9.2.2">9.2.2</a>&nbsp;<a id="status.201" href="#status.201">201 Created</a></h3>
996      <p id="rfc.section.9.2.2.p.1">The request has been fulfilled and resulted in a new resource being created. The newly created resource can be referenced
997         by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header
998         field. The response <em class="bcp14">SHOULD</em> include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose
999         the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. The origin
1000         server <em class="bcp14">MUST</em> create the resource before returning the 201 status code. If the action cannot be carried out immediately, the server <em class="bcp14">SHOULD</em> respond with 202 (Accepted) response instead.
1001      </p>
1002      <p id="rfc.section.9.2.2.p.2">A 201 response <em class="bcp14">MAY</em> contain an ETag response header field indicating the current value of the entity tag for the requested variant just created,
[60]1003         see <a href="p4-conditional.html#header.etag" title="ETag">Section 6.1</a> of <a href="#Part4" id="rfc.xref.Part4.6"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>.
[52]1004      </p>
1005      <div id="rfc.iref.29"></div>
1006      <div id="rfc.iref.s.5"></div>
1007      <h3 id="rfc.section.9.2.3"><a href="#rfc.section.9.2.3">9.2.3</a>&nbsp;<a id="status.202" href="#status.202">202 Accepted</a></h3>
1008      <p id="rfc.section.9.2.3.p.1">The request has been accepted for processing, but the processing has not been completed. The request might or might not eventually
1009         be acted upon, as it might be disallowed when processing actually takes place. There is no facility for re-sending a status
1010         code from an asynchronous operation such as this.
1011      </p>
1012      <p id="rfc.section.9.2.3.p.2">The 202 response is intentionally non-committal. Its purpose is to allow a server to accept a request for some other process
1013         (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the
1014         server persist until the process is completed. The entity returned with this response <em class="bcp14">SHOULD</em> include an indication of the request's current status and either a pointer to a status monitor or some estimate of when the
1015         user can expect the request to be fulfilled.
1016      </p>
1017      <div id="rfc.iref.30"></div>
1018      <div id="rfc.iref.s.6"></div>
1019      <h3 id="rfc.section.9.2.4"><a href="#rfc.section.9.2.4">9.2.4</a>&nbsp;<a id="status.203" href="#status.203">203 Non-Authoritative Information</a></h3>
1020      <p id="rfc.section.9.2.4.p.1">The returned metainformation in the entity-header is not the definitive set as available from the origin server, but is gathered
1021         from a local or a third-party copy. The set presented <em class="bcp14">MAY</em> be a subset or superset of the original version. For example, including local annotation information about the resource might
1022         result in a superset of the metainformation known by the origin server. Use of this response code is not required and is only
1023         appropriate when the response would otherwise be 200 (OK).
1024      </p>
1025      <div id="rfc.iref.31"></div>
1026      <div id="rfc.iref.s.7"></div>
1027      <h3 id="rfc.section.9.2.5"><a href="#rfc.section.9.2.5">9.2.5</a>&nbsp;<a id="status.204" href="#status.204">204 No Content</a></h3>
1028      <p id="rfc.section.9.2.5.p.1">The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation.
1029         The response <em class="bcp14">MAY</em> include new or updated metainformation in the form of entity-headers, which if present <em class="bcp14">SHOULD</em> be associated with the requested variant.
1030      </p>
1031      <p id="rfc.section.9.2.5.p.2">If the client is a user agent, it <em class="bcp14">SHOULD NOT</em> change its document view from that which caused the request to be sent. This response is primarily intended to allow input
1032         for actions to take place without causing a change to the user agent's active document view, although any new or updated metainformation <em class="bcp14">SHOULD</em> be applied to the document currently in the user agent's active view.
1033      </p>
1034      <p id="rfc.section.9.2.5.p.3">The 204 response <em class="bcp14">MUST NOT</em> include a message-body, and thus is always terminated by the first empty line after the header fields.
1035      </p>
1036      <div id="rfc.iref.32"></div>
1037      <div id="rfc.iref.s.8"></div>
1038      <h3 id="rfc.section.9.2.6"><a href="#rfc.section.9.2.6">9.2.6</a>&nbsp;<a id="status.205" href="#status.205">205 Reset Content</a></h3>
1039      <p id="rfc.section.9.2.6.p.1">The server has fulfilled the request and the user agent <em class="bcp14">SHOULD</em> reset the document view which caused the request to be sent. This response is primarily intended to allow input for actions
1040         to take place via user input, followed by a clearing of the form in which the input is given so that the user can easily initiate
1041         another input action. The response <em class="bcp14">MUST NOT</em> include an entity.
1042      </p>
1043      <div id="rfc.iref.33"></div>
1044      <div id="rfc.iref.s.9"></div>
1045      <h3 id="rfc.section.9.2.7"><a href="#rfc.section.9.2.7">9.2.7</a>&nbsp;<a id="status.206" href="#status.206">206 Partial Content</a></h3>
1046      <p id="rfc.section.9.2.7.p.1">The server has fulfilled the partial GET request for the resource and the enclosed entity is a partial representation as defined
1047         in <a href="#Part5" id="rfc.xref.Part5.6"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>.
1048      </p>
1049      <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a id="status.3xx" href="#status.3xx">Redirection 3xx</a></h2>
1050      <p id="rfc.section.9.3.p.1">This class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request.
1051         The action required <em class="bcp14">MAY</em> be carried out by the user agent without interaction with the user if and only if the method used in the second request is
1052         GET or HEAD. A client <em class="bcp14">SHOULD</em> detect infinite redirection loops, since such loops generate network traffic for each redirection.
1053      </p>
1054      <dl class="empty">
1055         <dd> <b>Note:</b> previous versions of this specification recommended a maximum of five redirections. Content developers should be aware that
1056            there might be clients that implement such a fixed limitation.
1057         </dd>
1058      </dl>
1059      <div id="rfc.iref.34"></div>
1060      <div id="rfc.iref.s.10"></div>
1061      <h3 id="rfc.section.9.3.1"><a href="#rfc.section.9.3.1">9.3.1</a>&nbsp;<a id="status.300" href="#status.300">300 Multiple Choices</a></h3>
1062      <p id="rfc.section.9.3.1.p.1">The requested resource corresponds to any one of a set of representations, each with its own specific location, and agent-driven
1063         negotiation information (<a href="p3-payload.html#content.negotiation" title="Content Negotiation">Section 4</a> of <a href="#Part3" id="rfc.xref.Part3.7"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) is being provided so that the user (or user agent) can select a preferred representation and redirect its request to that
1064         location.
1065      </p>
1066      <p id="rfc.section.9.3.1.p.2">Unless it was a HEAD request, the response <em class="bcp14">SHOULD</em> include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose
1067         the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. Depending
1068         upon the format and the capabilities of the user agent, selection of the most appropriate choice <em class="bcp14">MAY</em> be performed automatically. However, this specification does not define any standard for such automatic selection.
1069      </p>
1070      <p id="rfc.section.9.3.1.p.3">If the server has a preferred choice of representation, it <em class="bcp14">SHOULD</em> include the specific URI for that representation in the Location field; user agents <em class="bcp14">MAY</em> use the Location field value for automatic redirection. This response is cacheable unless indicated otherwise.
1071      </p>
1072      <div id="rfc.iref.35"></div>
1073      <div id="rfc.iref.s.11"></div>
1074      <h3 id="rfc.section.9.3.2"><a href="#rfc.section.9.3.2">9.3.2</a>&nbsp;<a id="status.301" href="#status.301">301 Moved Permanently</a></h3>
1075      <p id="rfc.section.9.3.2.p.1">The requested resource has been assigned a new permanent URI and any future references to this resource <em class="bcp14">SHOULD</em> use one of the returned URIs. Clients with link editing capabilities ought to automatically re-link references to the Request-URI
1076         to one or more of the new references returned by the server, where possible. This response is cacheable unless indicated otherwise.
1077      </p>
1078      <p id="rfc.section.9.3.2.p.2">The new permanent URI <em class="bcp14">SHOULD</em> be given by the Location field in the response. Unless the request method was HEAD, the entity of the response <em class="bcp14">SHOULD</em> contain a short hypertext note with a hyperlink to the new URI(s).
1079      </p>
[96]1080      <p id="rfc.section.9.3.2.p.3">If the 301 status code is received in response to a request method that is known to be "safe", as defined in <a href="#safe.methods" title="Safe Methods">Section&nbsp;8.1.1</a>, then the request <em class="bcp14">MAY</em> be automatically redirected by the user agent without confirmation. Otherwise, the user agent <em class="bcp14">MUST NOT</em> automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which
[52]1081         the request was issued.
1082      </p>
1083      <dl class="empty">
1084         <dd> <b>Note:</b> When automatically redirecting a POST request after receiving a 301 status code, some existing HTTP/1.0 user agents will erroneously
1085            change it into a GET request.
1086         </dd>
1087      </dl>
1088      <div id="rfc.iref.36"></div>
1089      <div id="rfc.iref.s.12"></div>
1090      <h3 id="rfc.section.9.3.3"><a href="#rfc.section.9.3.3">9.3.3</a>&nbsp;<a id="status.302" href="#status.302">302 Found</a></h3>
1091      <p id="rfc.section.9.3.3.p.1">The requested resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the
1092         client <em class="bcp14">SHOULD</em> continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires
1093         header field.
1094      </p>
1095      <p id="rfc.section.9.3.3.p.2">The temporary URI <em class="bcp14">SHOULD</em> be given by the Location field in the response. Unless the request method was HEAD, the entity of the response <em class="bcp14">SHOULD</em> contain a short hypertext note with a hyperlink to the new URI(s).
1096      </p>
[96]1097      <p id="rfc.section.9.3.3.p.3">If the 302 status code is received in response to a request method that is known to be "safe", as defined in <a href="#safe.methods" title="Safe Methods">Section&nbsp;8.1.1</a>, then the request <em class="bcp14">MAY</em> be automatically redirected by the user agent without confirmation. Otherwise, the user agent <em class="bcp14">MUST NOT</em> automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which
[52]1098         the request was issued.
1099      </p>
1100      <dl class="empty">
[97]1101         <dd> <b>Note:</b>  <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.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> specify that the client is not allowed to change the method on the redirected request. However, most existing user agent implementations
1102            treat 302 as if it were a 303 response, performing a GET on the Location field-value regardless of the original request method.
1103            The status codes 303 and 307 have been added for servers that wish to make unambiguously clear which kind of reaction is expected
1104            of the client.
[52]1105         </dd>
1106      </dl>
1107      <div id="rfc.iref.37"></div>
1108      <div id="rfc.iref.s.13"></div>
1109      <h3 id="rfc.section.9.3.4"><a href="#rfc.section.9.3.4">9.3.4</a>&nbsp;<a id="status.303" href="#status.303">303 See Other</a></h3>
1110      <p id="rfc.section.9.3.4.p.1">The response to the request can be found under a different URI and <em class="bcp14">SHOULD</em> be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script
1111         to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested
1112         resource. The 303 response <em class="bcp14">MUST NOT</em> be cached, but the response to the second (redirected) request might be cacheable.
1113      </p>
1114      <p id="rfc.section.9.3.4.p.2">The different URI <em class="bcp14">SHOULD</em> be given by the Location field in the response. Unless the request method was HEAD, the entity of the response <em class="bcp14">SHOULD</em> contain a short hypertext note with a hyperlink to the new URI(s).
1115      </p>
1116      <dl class="empty">
1117         <dd> <b>Note:</b> Many pre-HTTP/1.1 user agents do not understand the 303 status. When interoperability with such clients is a concern, the
1118            302 status code may be used instead, since most user agents react to a 302 response as described here for 303.
1119         </dd>
1120      </dl>
1121      <div id="rfc.iref.38"></div>
1122      <div id="rfc.iref.s.14"></div>
1123      <h3 id="rfc.section.9.3.5"><a href="#rfc.section.9.3.5">9.3.5</a>&nbsp;<a id="status.304" href="#status.304">304 Not Modified</a></h3>
1124      <p id="rfc.section.9.3.5.p.1">The response to the request has not been modified since the conditions indicated by the client's conditional GET request,
1125         as defined in <a href="#Part4" id="rfc.xref.Part4.7"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>.
1126      </p>
1127      <div id="rfc.iref.39"></div>
1128      <div id="rfc.iref.s.15"></div>
1129      <h3 id="rfc.section.9.3.6"><a href="#rfc.section.9.3.6">9.3.6</a>&nbsp;<a id="status.305" href="#status.305">305 Use Proxy</a></h3>
1130      <p id="rfc.section.9.3.6.p.1">The requested resource <em class="bcp14">MUST</em> be accessed through the proxy given by the Location field. The Location field gives the URI of the proxy. The recipient is
1131         expected to repeat this single request via the proxy. 305 responses <em class="bcp14">MUST</em> only be generated by origin servers.
1132      </p>
1133      <dl class="empty">
[97]1134         <dd> <b>Note:</b>  <a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a> was not clear that 305 was intended to redirect a single request, and to be generated by origin servers only. Not observing
1135            these limitations has significant security consequences.
[52]1136         </dd>
1137      </dl>
1138      <div id="rfc.iref.40"></div>
1139      <div id="rfc.iref.s.16"></div>
1140      <h3 id="rfc.section.9.3.7"><a href="#rfc.section.9.3.7">9.3.7</a>&nbsp;<a id="status.306" href="#status.306">306 (Unused)</a></h3>
1141      <p id="rfc.section.9.3.7.p.1">The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved.</p>
1142      <div id="rfc.iref.41"></div>
1143      <div id="rfc.iref.s.17"></div>
1144      <h3 id="rfc.section.9.3.8"><a href="#rfc.section.9.3.8">9.3.8</a>&nbsp;<a id="status.307" href="#status.307">307 Temporary Redirect</a></h3>
1145      <p id="rfc.section.9.3.8.p.1">The requested resource resides temporarily under a different URI. Since the redirection <em class="bcp14">MAY</em> be altered on occasion, the client <em class="bcp14">SHOULD</em> continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires
1146         header field.
1147      </p>
1148      <p id="rfc.section.9.3.8.p.2">The temporary URI <em class="bcp14">SHOULD</em> be given by the Location field in the response. Unless the request method was HEAD, the entity of the response <em class="bcp14">SHOULD</em> contain a short hypertext note with a hyperlink to the new URI(s) , since many pre-HTTP/1.1 user agents do not understand
1149         the 307 status. Therefore, the note <em class="bcp14">SHOULD</em> contain the information necessary for a user to repeat the original request on the new URI.
1150      </p>
[96]1151      <p id="rfc.section.9.3.8.p.3">If the 307 status code is received in response to a request method that is known to be "safe", as defined in <a href="#safe.methods" title="Safe Methods">Section&nbsp;8.1.1</a>, then the request <em class="bcp14">MAY</em> be automatically redirected by the user agent without confirmation. Otherwise, the user agent <em class="bcp14">MUST NOT</em> automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which
[52]1152         the request was issued.
1153      </p>
1154      <h2 id="rfc.section.9.4"><a href="#rfc.section.9.4">9.4</a>&nbsp;<a id="status.4xx" href="#status.4xx">Client Error 4xx</a></h2>
1155      <p id="rfc.section.9.4.p.1">The 4xx class of status code is intended for cases in which the client seems to have erred. Except when responding to a HEAD
1156         request, the server <em class="bcp14">SHOULD</em> include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
1157         These status codes are applicable to any request method. User agents <em class="bcp14">SHOULD</em> display any included entity to the user.
1158      </p>
1159      <p id="rfc.section.9.4.p.2">If the client is sending data, a server implementation using TCP <em class="bcp14">SHOULD</em> be careful to ensure that the client acknowledges receipt of the packet(s) containing the response, before the server closes
1160         the input connection. If the client continues sending data to the server after the close, the server's TCP stack will send
1161         a reset packet to the client, which may erase the client's unacknowledged input buffers before they can be read and interpreted
1162         by the HTTP application.
1163      </p>
1164      <div id="rfc.iref.42"></div>
1165      <div id="rfc.iref.s.18"></div>
1166      <h3 id="rfc.section.9.4.1"><a href="#rfc.section.9.4.1">9.4.1</a>&nbsp;<a id="status.400" href="#status.400">400 Bad Request</a></h3>
1167      <p id="rfc.section.9.4.1.p.1">The request could not be understood by the server due to malformed syntax. The client <em class="bcp14">SHOULD NOT</em> repeat the request without modifications.
1168      </p>
1169      <div id="rfc.iref.43"></div>
1170      <div id="rfc.iref.s.19"></div>
1171      <h3 id="rfc.section.9.4.2"><a href="#rfc.section.9.4.2">9.4.2</a>&nbsp;<a id="status.401" href="#status.401">401 Unauthorized</a></h3>
1172      <p id="rfc.section.9.4.2.p.1">The request requires user authentication (see <a href="#Part7" id="rfc.xref.Part7.5"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>).
1173      </p>
1174      <div id="rfc.iref.44"></div>
1175      <div id="rfc.iref.s.20"></div>
1176      <h3 id="rfc.section.9.4.3"><a href="#rfc.section.9.4.3">9.4.3</a>&nbsp;<a id="status.402" href="#status.402">402 Payment Required</a></h3>
1177      <p id="rfc.section.9.4.3.p.1">This code is reserved for future use.</p>
1178      <div id="rfc.iref.45"></div>
1179      <div id="rfc.iref.s.21"></div>
1180      <h3 id="rfc.section.9.4.4"><a href="#rfc.section.9.4.4">9.4.4</a>&nbsp;<a id="status.403" href="#status.403">403 Forbidden</a></h3>
1181      <p id="rfc.section.9.4.4.p.1">The server understood the request, but is refusing to fulfill it. Authorization will not help and the request <em class="bcp14">SHOULD NOT</em> be repeated. If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled,
1182         it <em class="bcp14">SHOULD</em> describe the reason for the refusal in the entity. If the server does not wish to make this information available to the client,
1183         the status code 404 (Not Found) can be used instead.
1184      </p>
1185      <div id="rfc.iref.46"></div>
1186      <div id="rfc.iref.s.22"></div>
1187      <h3 id="rfc.section.9.4.5"><a href="#rfc.section.9.4.5">9.4.5</a>&nbsp;<a id="status.404" href="#status.404">404 Not Found</a></h3>
1188      <p id="rfc.section.9.4.5.p.1">The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or
1189         permanent. The 410 (Gone) status code <em class="bcp14">SHOULD</em> be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable
1190         and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request
1191         has been refused, or when no other response is applicable.
1192      </p>
1193      <div id="rfc.iref.47"></div>
1194      <div id="rfc.iref.s.23"></div>
1195      <h3 id="rfc.section.9.4.6"><a href="#rfc.section.9.4.6">9.4.6</a>&nbsp;<a id="status.405" href="#status.405">405 Method Not Allowed</a></h3>
1196      <p id="rfc.section.9.4.6.p.1">The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response <em class="bcp14">MUST</em> include an Allow header containing a list of valid methods for the requested resource.
1197      </p>
1198      <div id="rfc.iref.48"></div>
1199      <div id="rfc.iref.s.24"></div>
1200      <h3 id="rfc.section.9.4.7"><a href="#rfc.section.9.4.7">9.4.7</a>&nbsp;<a id="status.406" href="#status.406">406 Not Acceptable</a></h3>
1201      <p id="rfc.section.9.4.7.p.1">The resource identified by the request is only capable of generating response entities which have content characteristics
1202         not acceptable according to the accept headers sent in the request.
1203      </p>
1204      <p id="rfc.section.9.4.7.p.2">Unless it was a HEAD request, the response <em class="bcp14">SHOULD</em> include an entity containing a list of available entity characteristics and location(s) from which the user or user agent
1205         can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field.
1206         Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice <em class="bcp14">MAY</em> be performed automatically. However, this specification does not define any standard for such automatic selection.
1207      </p>
1208      <dl class="empty">
1209         <dd> <b>Note:</b> HTTP/1.1 servers are allowed to return responses which are not acceptable according to the accept headers sent in the request.
1210            In some cases, this may even be preferable to sending a 406 response. User agents are encouraged to inspect the headers of
1211            an incoming response to determine if it is acceptable.
1212         </dd>
1213      </dl>
1214      <p id="rfc.section.9.4.7.p.3">If the response could be unacceptable, a user agent <em class="bcp14">SHOULD</em> temporarily stop receipt of more data and query the user for a decision on further actions.
1215      </p>
1216      <div id="rfc.iref.49"></div>
1217      <div id="rfc.iref.s.25"></div>
1218      <h3 id="rfc.section.9.4.8"><a href="#rfc.section.9.4.8">9.4.8</a>&nbsp;<a id="status.407" href="#status.407">407 Proxy Authentication Required</a></h3>
1219      <p id="rfc.section.9.4.8.p.1">This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy (see <a href="#Part7" id="rfc.xref.Part7.6"><cite title="HTTP/1.1, part 7: Authentication">[Part7]</cite></a>).
1220      </p>
1221      <div id="rfc.iref.50"></div>
1222      <div id="rfc.iref.s.26"></div>
1223      <h3 id="rfc.section.9.4.9"><a href="#rfc.section.9.4.9">9.4.9</a>&nbsp;<a id="status.408" href="#status.408">408 Request Timeout</a></h3>
1224      <p id="rfc.section.9.4.9.p.1">The client did not produce a request within the time that the server was prepared to wait. The client <em class="bcp14">MAY</em> repeat the request without modifications at any later time.
1225      </p>
1226      <div id="rfc.iref.51"></div>
1227      <div id="rfc.iref.s.27"></div>
1228      <h3 id="rfc.section.9.4.10"><a href="#rfc.section.9.4.10">9.4.10</a>&nbsp;<a id="status.409" href="#status.409">409 Conflict</a></h3>
1229      <p id="rfc.section.9.4.10.p.1">The request could not be completed due to a conflict with the current state of the resource. This code is only allowed in
1230         situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response
1231         body <em class="bcp14">SHOULD</em> include enough information for the user to recognize the source of the conflict. Ideally, the response entity would include
1232         enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.
1233      </p>
1234      <p id="rfc.section.9.4.10.p.2">Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the entity
1235         being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might
1236         use the 409 response to indicate that it can't complete the request. In this case, the response entity would likely contain
1237         a list of the differences between the two versions in a format defined by the response Content-Type.
1238      </p>
1239      <div id="rfc.iref.52"></div>
1240      <div id="rfc.iref.s.28"></div>
1241      <h3 id="rfc.section.9.4.11"><a href="#rfc.section.9.4.11">9.4.11</a>&nbsp;<a id="status.410" href="#status.410">410 Gone</a></h3>
1242      <p id="rfc.section.9.4.11.p.1">The requested resource is no longer available at the server and no forwarding address is known. This condition is expected
1243         to be considered permanent. Clients with link editing capabilities <em class="bcp14">SHOULD</em> delete references to the Request-URI after user approval. If the server does not know, or has no facility to determine, whether
1244         or not the condition is permanent, the status code 404 (Not Found) <em class="bcp14">SHOULD</em> be used instead. This response is cacheable unless indicated otherwise.
1245      </p>
1246      <p id="rfc.section.9.4.11.p.2">The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource
1247         is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event
1248         is common for limited-time, promotional services and for resources belonging to individuals no longer working at the server's
1249         site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time
1250         -- that is left to the discretion of the server owner.
1251      </p>
1252      <div id="rfc.iref.53"></div>
1253      <div id="rfc.iref.s.29"></div>
1254      <h3 id="rfc.section.9.4.12"><a href="#rfc.section.9.4.12">9.4.12</a>&nbsp;<a id="status.411" href="#status.411">411 Length Required</a></h3>
1255      <p id="rfc.section.9.4.12.p.1">The server refuses to accept the request without a defined Content-Length. The client <em class="bcp14">MAY</em> repeat the request if it adds a valid Content-Length header field containing the length of the message-body in the request
1256         message.
1257      </p>
1258      <div id="rfc.iref.54"></div>
1259      <div id="rfc.iref.s.30"></div>
1260      <h3 id="rfc.section.9.4.13"><a href="#rfc.section.9.4.13">9.4.13</a>&nbsp;<a id="status.412" href="#status.412">412 Precondition Failed</a></h3>
1261      <p id="rfc.section.9.4.13.p.1">The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server, as
1262         defined in <a href="#Part4" id="rfc.xref.Part4.8"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>.
1263      </p>
1264      <div id="rfc.iref.55"></div>
1265      <div id="rfc.iref.s.31"></div>
1266      <h3 id="rfc.section.9.4.14"><a href="#rfc.section.9.4.14">9.4.14</a>&nbsp;<a id="status.413" href="#status.413">413 Request Entity Too Large</a></h3>
1267      <p id="rfc.section.9.4.14.p.1">The server is refusing to process a request because the request entity is larger than the server is willing or able to process.
1268         The server <em class="bcp14">MAY</em> close the connection to prevent the client from continuing the request.
1269      </p>
1270      <p id="rfc.section.9.4.14.p.2">If the condition is temporary, the server <em class="bcp14">SHOULD</em> include a Retry-After header field to indicate that it is temporary and after what time the client <em class="bcp14">MAY</em> try again.
1271      </p>
1272      <div id="rfc.iref.56"></div>
1273      <div id="rfc.iref.s.32"></div>
1274      <h3 id="rfc.section.9.4.15"><a href="#rfc.section.9.4.15">9.4.15</a>&nbsp;<a id="status.414" href="#status.414">414 Request-URI Too Long</a></h3>
1275      <p id="rfc.section.9.4.15.p.1">The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret. This
1276         rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query
1277         information, when the client has descended into a URI "black hole" of redirection (e.g., a redirected URI prefix that points
1278         to a suffix of itself), or when the server is under attack by a client attempting to exploit security holes present in some
1279         servers using fixed-length buffers for reading or manipulating the Request-URI.
1280      </p>
1281      <div id="rfc.iref.57"></div>
1282      <div id="rfc.iref.s.33"></div>
1283      <h3 id="rfc.section.9.4.16"><a href="#rfc.section.9.4.16">9.4.16</a>&nbsp;<a id="status.415" href="#status.415">415 Unsupported Media Type</a></h3>
1284      <p id="rfc.section.9.4.16.p.1">The server is refusing to service the request because the entity of the request is in a format not supported by the requested
1285         resource for the requested method.
1286      </p>
1287      <div id="rfc.iref.58"></div>
1288      <div id="rfc.iref.s.34"></div>
1289      <h3 id="rfc.section.9.4.17"><a href="#rfc.section.9.4.17">9.4.17</a>&nbsp;<a id="status.416" href="#status.416">416 Requested Range Not Satisfiable</a></h3>
1290      <p id="rfc.section.9.4.17.p.1">The request included a Range request-header field (<a href="p5-range.html#header.range" title="Range">Section 5.4</a> of <a href="#Part5" id="rfc.xref.Part5.7"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) and none of the range-specifier values in this field overlap the current extent of the selected resource.
1291      </p>
1292      <div id="rfc.iref.59"></div>
1293      <div id="rfc.iref.s.35"></div>
1294      <h3 id="rfc.section.9.4.18"><a href="#rfc.section.9.4.18">9.4.18</a>&nbsp;<a id="status.417" href="#status.417">417 Expectation Failed</a></h3>
1295      <p id="rfc.section.9.4.18.p.1">The expectation given in an Expect request-header field (see <a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section&nbsp;10.2</a>) could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could
1296         not be met by the next-hop server.
1297      </p>
1298      <h2 id="rfc.section.9.5"><a href="#rfc.section.9.5">9.5</a>&nbsp;<a id="status.5xx" href="#status.5xx">Server Error 5xx</a></h2>
1299      <p id="rfc.section.9.5.p.1">Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has erred or is incapable
1300         of performing the request. Except when responding to a HEAD request, the server <em class="bcp14">SHOULD</em> include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition.
1301         User agents <em class="bcp14">SHOULD</em> display any included entity to the user. These response codes are applicable to any request method.
1302      </p>
1303      <div id="rfc.iref.60"></div>
1304      <div id="rfc.iref.s.36"></div>
1305      <h3 id="rfc.section.9.5.1"><a href="#rfc.section.9.5.1">9.5.1</a>&nbsp;<a id="status.500" href="#status.500">500 Internal Server Error</a></h3>
1306      <p id="rfc.section.9.5.1.p.1">The server encountered an unexpected condition which prevented it from fulfilling the request.</p>
1307      <div id="rfc.iref.61"></div>
1308      <div id="rfc.iref.s.37"></div>
1309      <h3 id="rfc.section.9.5.2"><a href="#rfc.section.9.5.2">9.5.2</a>&nbsp;<a id="status.501" href="#status.501">501 Not Implemented</a></h3>
1310      <p id="rfc.section.9.5.2.p.1">The server does not support the functionality required to fulfill the request. This is the appropriate response when the server
1311         does not recognize the request method and is not capable of supporting it for any resource.
1312      </p>
1313      <div id="rfc.iref.62"></div>
1314      <div id="rfc.iref.s.38"></div>
1315      <h3 id="rfc.section.9.5.3"><a href="#rfc.section.9.5.3">9.5.3</a>&nbsp;<a id="status.502" href="#status.502">502 Bad Gateway</a></h3>
1316      <p id="rfc.section.9.5.3.p.1">The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting
1317         to fulfill the request.
1318      </p>
1319      <div id="rfc.iref.63"></div>
1320      <div id="rfc.iref.s.39"></div>
1321      <h3 id="rfc.section.9.5.4"><a href="#rfc.section.9.5.4">9.5.4</a>&nbsp;<a id="status.503" href="#status.503">503 Service Unavailable</a></h3>
1322      <p id="rfc.section.9.5.4.p.1">The server is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication
1323         is that this is a temporary condition which will be alleviated after some delay. If known, the length of the delay <em class="bcp14">MAY</em> be indicated in a Retry-After header. If no Retry-After is given, the client <em class="bcp14">SHOULD</em> handle the response as it would for a 500 response.
1324      </p>
1325      <dl class="empty">
1326         <dd> <b>Note:</b> The existence of the 503 status code does not imply that a server must use it when becoming overloaded. Some servers may wish
1327            to simply refuse the connection.
1328         </dd>
1329      </dl>
1330      <div id="rfc.iref.64"></div>
1331      <div id="rfc.iref.s.40"></div>
1332      <h3 id="rfc.section.9.5.5"><a href="#rfc.section.9.5.5">9.5.5</a>&nbsp;<a id="status.504" href="#status.504">504 Gateway Timeout</a></h3>
1333      <p id="rfc.section.9.5.5.p.1">The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server specified by the
1334         URI (e.g. HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed to access in attempting to complete the request.
1335      </p>
1336      <dl class="empty">
1337         <dd> <b>Note:</b> Note to implementors: some deployed proxies are known to return 400 or 500 when DNS lookups time out.
1338         </dd>
1339      </dl>
1340      <div id="rfc.iref.65"></div>
1341      <div id="rfc.iref.s.41"></div>
1342      <h3 id="rfc.section.9.5.6"><a href="#rfc.section.9.5.6">9.5.6</a>&nbsp;<a id="status.505" href="#status.505">505 HTTP Version Not Supported</a></h3>
1343      <p id="rfc.section.9.5.6.p.1">The server does not support, or refuses to support, the HTTP protocol version that was used in the request message. The server
1344         is indicating that it is unable or unwilling to complete the request using the same major version as the client, as described
1345         in <a href="p1-messaging.html#http.version" title="HTTP Version">Section 3.1</a> of <a href="#Part1" id="rfc.xref.Part1.9"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>, other than with this error message. The response <em class="bcp14">SHOULD</em> contain an entity describing why that version is not supported and what other protocols are supported by that server.
1346      </p>
1347      <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a>&nbsp;<a id="header.fields" href="#header.fields">Header Field Definitions</a></h1>
1348      <p id="rfc.section.10.p.1">This section defines the syntax and semantics of all standard HTTP/1.1 header fields. For entity-header fields, both sender
1349         and recipient refer to either the client or the server, depending on who sends and who receives the entity.
1350      </p>
1351      <div id="rfc.iref.a.1"></div>
1352      <div id="rfc.iref.h.2"></div>
1353      <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a>&nbsp;<a id="header.allow" href="#header.allow">Allow</a></h2>
1354      <p id="rfc.section.10.1.p.1">The Allow entity-header field lists the set of methods supported by the resource identified by the Request-URI. The purpose
1355         of this field is strictly to inform the recipient of valid methods associated with the resource. An Allow header field <em class="bcp14">MUST</em> be present in a 405 (Method Not Allowed) response.
1356      </p>
1357      <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.11"></span>       Allow   = "Allow" ":" #Method
1358</pre><p id="rfc.section.10.1.p.3">Example of use:</p>
1359      <div id="rfc.figure.u.8"></div><pre class="text">       Allow: GET, HEAD, PUT
1360</pre><p id="rfc.section.10.1.p.5">This field cannot prevent a client from trying other methods. However, the indications given by the Allow header field value <em class="bcp14">SHOULD</em> be followed. The actual set of allowed methods is defined by the origin server at the time of each request.
1361      </p>
1362      <p id="rfc.section.10.1.p.6">The Allow header field <em class="bcp14">MAY</em> be provided with a PUT request to recommend the methods to be supported by the new or modified resource. The server is not
1363         required to support these methods and <em class="bcp14">SHOULD</em> include an Allow header in the response giving the actual supported methods.
1364      </p>
1365      <p id="rfc.section.10.1.p.7">A proxy <em class="bcp14">MUST NOT</em> modify the Allow header field even if it does not understand all the methods specified, since the user agent might have other
1366         means of communicating with the origin server.
1367      </p>
1368      <div id="rfc.iref.e.1"></div>
1369      <div id="rfc.iref.h.3"></div>
1370      <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a>&nbsp;<a id="header.expect" href="#header.expect">Expect</a></h2>
1371      <p id="rfc.section.10.2.p.1">The Expect request-header field is used to indicate that particular server behaviors are required by the client.</p>
1372      <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.12"></span><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span>   Expect       =  "Expect" ":" 1#expectation
1373
1374   expectation  =  "100-continue" | expectation-extension
1375   expectation-extension =  token [ "=" ( token | quoted-string )
1376                            *expect-params ]
1377   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1378</pre><p id="rfc.section.10.2.p.3">A server that does not understand or is unable to comply with any of the expectation values in the Expect field of a request <em class="bcp14">MUST</em> respond with appropriate error status. The server <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status if any of the expectations cannot be met or, if there are other problems with
1379         the request, some other 4xx status.
1380      </p>
1381      <p id="rfc.section.10.2.p.4">This header field is defined with extensible syntax to allow for future extensions. If a server receives a request containing
1382         an Expect field that includes an expectation-extension that it does not support, it <em class="bcp14">MUST</em> respond with a 417 (Expectation Failed) status.
1383      </p>
1384      <p id="rfc.section.10.2.p.5">Comparison of expectation values is case-insensitive for unquoted tokens (including the 100-continue token), and is case-sensitive
1385         for quoted-string expectation-extensions.
1386      </p>
1387      <p id="rfc.section.10.2.p.6">The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy <em class="bcp14">MUST</em> return a 417 (Expectation Failed) status if it receives a request with an expectation that it cannot meet. However, the Expect
1388         request-header itself is end-to-end; it <em class="bcp14">MUST</em> be forwarded if the request is forwarded.
1389      </p>
1390      <p id="rfc.section.10.2.p.7">Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect header.</p>
1391      <p id="rfc.section.10.2.p.8">See <a href="p1-messaging.html#use.of.the.100.status" title="Use of the 100 (Continue) Status">Section 7.2.3</a> of <a href="#Part1" id="rfc.xref.Part1.10"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a> for the use of the 100 (continue) status.
1392      </p>
1393      <div id="rfc.iref.f.1"></div>
1394      <div id="rfc.iref.h.4"></div>
1395      <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a>&nbsp;<a id="header.from" href="#header.from">From</a></h2>
[97]1396      <p id="rfc.section.10.3.p.1">The From request-header field, if given, <em class="bcp14">SHOULD</em> contain an Internet e-mail address for the human user who controls the requesting user agent. The address <em class="bcp14">SHOULD</em> be machine-usable, as defined by "mailbox" in <a href="#RFC822" id="rfc.xref.RFC822.1"><cite title="Standard for the format of ARPA Internet text messages">[RFC822]</cite></a> as updated by <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a>:
[52]1397      </p>
1398      <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.16"></span>    From   = "From" ":" mailbox
1399</pre><p id="rfc.section.10.3.p.3">An example is:</p>
[92]1400      <div id="rfc.figure.u.11"></div><pre class="text">    From: webmaster@example.org
[52]1401</pre><p id="rfc.section.10.3.p.5">This header field <em class="bcp14">MAY</em> be used for logging purposes and as a means for identifying the source of invalid or unwanted requests. It <em class="bcp14">SHOULD NOT</em> be used as an insecure form of access protection. The interpretation of this field is that the request is being performed
1402         on behalf of the person given, who accepts responsibility for the method performed. In particular, robot agents <em class="bcp14">SHOULD</em> include this header so that the person responsible for running the robot can be contacted if problems occur on the receiving
1403         end.
1404      </p>
1405      <p id="rfc.section.10.3.p.6">The Internet e-mail address in this field <em class="bcp14">MAY</em> be separate from the Internet host which issued the request. For example, when a request is passed through a proxy the original
1406         issuer's address <em class="bcp14">SHOULD</em> be used.
1407      </p>
1408      <p id="rfc.section.10.3.p.7">The client <em class="bcp14">SHOULD NOT</em> send the From header field without the user's approval, as it might conflict with the user's privacy interests or their site's
1409         security policy. It is strongly recommended that the user be able to disable, enable, and modify the value of this field at
1410         any time prior to a request.
1411      </p>
1412      <div id="rfc.iref.l.1"></div>
1413      <div id="rfc.iref.h.5"></div>
1414      <h2 id="rfc.section.10.4"><a href="#rfc.section.10.4">10.4</a>&nbsp;<a id="header.location" href="#header.location">Location</a></h2>
1415      <p id="rfc.section.10.4.p.1">The Location response-header field is used to redirect the recipient to a location other than the Request-URI for completion
1416         of the request or identification of a new resource. For 201 (Created) responses, the Location is that of the new resource
1417         which was created by the request. For 3xx responses, the location <em class="bcp14">SHOULD</em> indicate the server's preferred URI for automatic redirection to the resource. The field value consists of a single absolute
1418         URI.
1419      </p>
[92]1420      <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.17"></span>    Location       = "Location" ":" absoluteURI [ "#" fragment ]
[52]1421</pre><p id="rfc.section.10.4.p.3">An example is:</p>
[92]1422      <div id="rfc.figure.u.13"></div><pre class="text">    Location: http://www.example.org/pub/WWW/People.html
[52]1423</pre><p id="rfc.section.10.4.p.5"> </p>
1424      <dl class="empty">
1425         <dd> <b>Note:</b> The Content-Location header field (<a href="p3-payload.html#header.content-location" title="Content-Location">Section 5.7</a> of <a href="#Part3" id="rfc.xref.Part3.8"><cite title="HTTP/1.1, part 3: Message Payload and Content Negotiation">[Part3]</cite></a>) differs from Location in that the Content-Location identifies the original location of the entity enclosed in the request.
1426            It is therefore possible for a response to contain header fields for both Location and Content-Location.
1427         </dd>
1428      </dl>
[114]1429      <p id="rfc.section.10.4.p.6">There are circumstances in which a fragment identifier in a Location URL would not be appropriate: </p>
1430      <ul>
1431         <li>With a 201 Created response, because in this usage the Location header specifies the URL for the entire created resource.</li>
1432         <li>With a 300 Multiple Choices, since the choice decision is intended to be made on resource characteristics and not fragment
1433            characteristics.
1434         </li>
1435         <li>With 305 Use Proxy.</li>
1436      </ul>
[52]1437      <div id="rfc.iref.m.9"></div>
1438      <div id="rfc.iref.h.6"></div>
1439      <h2 id="rfc.section.10.5"><a href="#rfc.section.10.5">10.5</a>&nbsp;<a id="header.max-forwards" href="#header.max-forwards">Max-Forwards</a></h2>
1440      <p id="rfc.section.10.5.p.1">The Max-Forwards request-header field provides a mechanism with the TRACE (<a href="#TRACE" id="rfc.xref.TRACE.2" title="TRACE">Section&nbsp;8.8</a>) and OPTIONS (<a href="#OPTIONS" id="rfc.xref.OPTIONS.2" title="OPTIONS">Section&nbsp;8.2</a>) methods to limit the number of proxies or gateways that can forward the request to the next inbound server. This can be
1441         useful when the client is attempting to trace a request chain which appears to be failing or looping in mid-chain.
1442      </p>
1443      <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.18"></span>    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1444</pre><p id="rfc.section.10.5.p.3">The Max-Forwards value is a decimal integer indicating the remaining number of times this request message may be forwarded.</p>
1445      <p id="rfc.section.10.5.p.4">Each proxy or gateway recipient of a TRACE or OPTIONS request containing a Max-Forwards header field <em class="bcp14">MUST</em> check and update its value prior to forwarding the request. If the received value is zero (0), the recipient <em class="bcp14">MUST NOT</em> forward the request; instead, it <em class="bcp14">MUST</em> respond as the final recipient. If the received Max-Forwards value is greater than zero, then the forwarded message <em class="bcp14">MUST</em> contain an updated Max-Forwards field with a value decremented by one (1).
1446      </p>
1447      <p id="rfc.section.10.5.p.5">The Max-Forwards header field <em class="bcp14">MAY</em> be ignored for all other methods defined by this specification and for any extension methods for which it is not explicitly
1448         referred to as part of that method definition.
1449      </p>
1450      <div id="rfc.iref.r.1"></div>
1451      <div id="rfc.iref.h.7"></div>
1452      <h2 id="rfc.section.10.6"><a href="#rfc.section.10.6">10.6</a>&nbsp;<a id="header.referer" href="#header.referer">Referer</a></h2>
1453      <p id="rfc.section.10.6.p.1">The Referer[sic] request-header field allows the client to specify, for the server's benefit, the address (URI) of the resource
1454         from which the Request-URI was obtained (the "referrer", although the header field is misspelled.) The Referer request-header
1455         allows a server to generate lists of back-links to resources for interest, logging, optimized caching, etc. It also allows
1456         obsolete or mistyped links to be traced for maintenance. The Referer field <em class="bcp14">MUST NOT</em> be sent if the Request-URI was obtained from a source that does not have its own URI, such as input from the user keyboard.
1457      </p>
1458      <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.19"></span>    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1459</pre><p id="rfc.section.10.6.p.3">Example:</p>
[92]1460      <div id="rfc.figure.u.16"></div><pre class="text">    Referer: http://www.example.org/hypertext/Overview.html
[52]1461</pre><p id="rfc.section.10.6.p.5">If the field value is a relative URI, it <em class="bcp14">SHOULD</em> be interpreted relative to the Request-URI. The URI <em class="bcp14">MUST NOT</em> include a fragment. See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URI's">Section&nbsp;12.2</a> for security considerations.
1462      </p>
1463      <div id="rfc.iref.r.2"></div>
1464      <div id="rfc.iref.h.8"></div>
1465      <h2 id="rfc.section.10.7"><a href="#rfc.section.10.7">10.7</a>&nbsp;<a id="header.retry-after" href="#header.retry-after">Retry-After</a></h2>
1466      <p id="rfc.section.10.7.p.1">The Retry-After response-header field can be used with a 503 (Service Unavailable) response to indicate how long the service
1467         is expected to be unavailable to the requesting client. This field <em class="bcp14">MAY</em> also be used with any 3xx (Redirection) response to indicate the minimum time the user-agent is asked wait before issuing
1468         the redirected request. The value of this field can be either an HTTP-date or an integer number of seconds (in decimal) after
1469         the time of the response.
1470      </p>
1471      <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.20"></span>    Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
1472</pre><p id="rfc.section.10.7.p.3">Two examples of its use are</p>
1473      <div id="rfc.figure.u.18"></div><pre class="text">    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1474    Retry-After: 120
1475</pre><p id="rfc.section.10.7.p.5">In the latter example, the delay is 2 minutes.</p>
1476      <div id="rfc.iref.s.42"></div>
1477      <div id="rfc.iref.h.9"></div>
1478      <h2 id="rfc.section.10.8"><a href="#rfc.section.10.8">10.8</a>&nbsp;<a id="header.server" href="#header.server">Server</a></h2>
1479      <p id="rfc.section.10.8.p.1">The Server response-header field contains information about the software used by the origin server to handle the request.
1480         The field can contain multiple product tokens (<a href="#product.tokens" title="Product Tokens">Section&nbsp;2</a>) and comments identifying the server and any significant subproducts. The product tokens are listed in order of their significance
1481         for identifying the application.
1482      </p>
1483      <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.21"></span>    Server         = "Server" ":" 1*( product | comment )
1484</pre><p id="rfc.section.10.8.p.3">Example:</p>
1485      <div id="rfc.figure.u.20"></div><pre class="text">    Server: CERN/3.0 libwww/2.17
[92]1486</pre><p id="rfc.section.10.8.p.5">If the response is being forwarded through a proxy, the proxy application <em class="bcp14">MUST NOT</em> modify the Server response-header. Instead, it <em class="bcp14">MUST</em> include a Via field (as described in <a href="p1-messaging.html#header.via" title="Via">Section 8.9</a> of <a href="#Part1" id="rfc.xref.Part1.11"><cite title="HTTP/1.1, part 1: URIs, Connections, and Message Parsing">[Part1]</cite></a>).
[52]1487      </p>
1488      <dl class="empty">
1489         <dd> <b>Note:</b> Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks
1490            against software that is known to contain security holes. Server implementors are encouraged to make this field a configurable
1491            option.
1492         </dd>
1493      </dl>
1494      <div id="rfc.iref.u.1"></div>
1495      <div id="rfc.iref.h.10"></div>
1496      <h2 id="rfc.section.10.9"><a href="#rfc.section.10.9">10.9</a>&nbsp;<a id="header.user-agent" href="#header.user-agent">User-Agent</a></h2>
1497      <p id="rfc.section.10.9.p.1">The User-Agent request-header field contains information about the user agent originating the request. This is for statistical
1498         purposes, the tracing of protocol violations, and automated recognition of user agents for the sake of tailoring responses
1499         to avoid particular user agent limitations. User agents <em class="bcp14">SHOULD</em> include this field with requests. The field can contain multiple product tokens (<a href="#product.tokens" title="Product Tokens">Section&nbsp;2</a>) and comments identifying the agent and any subproducts which form a significant part of the user agent. By convention, the
1500         product tokens are listed in order of their significance for identifying the application.
1501      </p>
1502      <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.22"></span>    User-Agent     = "User-Agent" ":" 1*( product | comment )
1503</pre><p id="rfc.section.10.9.p.3">Example:</p>
1504      <div id="rfc.figure.u.22"></div><pre class="text">    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1505</pre><h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a>&nbsp;<a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>
1506      <p id="rfc.section.11.p.1">TBD.</p>
1507      <h1 id="rfc.section.12"><a href="#rfc.section.12">12.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
1508      <p id="rfc.section.12.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1
1509         as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does
1510         make some suggestions for reducing security risks.
1511      </p>
1512      <h2 id="rfc.section.12.1"><a href="#rfc.section.12.1">12.1</a>&nbsp;<a id="security.sensitive" href="#security.sensitive">Transfer of Sensitive Information</a></h2>
1513      <p id="rfc.section.12.1.p.1">Like any generic data transfer protocol, HTTP cannot regulate the content of the data that is transferred, nor is there any
1514         a priori method of determining the sensitivity of any particular piece of information within the context of any given request.
1515         Therefore, applications <em class="bcp14">SHOULD</em> supply as much control over this information as possible to the provider of that information. Four header fields are worth
1516         special mention in this context: Server, Via, Referer and From.
1517      </p>
1518      <p id="rfc.section.12.1.p.2">Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks
1519         against software that is known to contain security holes. Implementors <em class="bcp14">SHOULD</em> make the Server header field a configurable option.
1520      </p>
1521      <p id="rfc.section.12.1.p.3">Proxies which serve as a portal through a network firewall <em class="bcp14">SHOULD</em> take special precautions regarding the transfer of header information that identifies the hosts behind the firewall. In particular,
1522         they <em class="bcp14">SHOULD</em> remove, or replace with sanitized versions, any Via fields generated behind the firewall.
1523      </p>
1524      <p id="rfc.section.12.1.p.4">The Referer header allows reading patterns to be studied and reverse links drawn. Although it can be very useful, its power
1525         can be abused if user details are not separated from the information contained in the Referer. Even when the personal information
1526         has been removed, the Referer header might indicate a private document's URI whose publication would be inappropriate.
1527      </p>
1528      <p id="rfc.section.12.1.p.5">The information sent in the From field might conflict with the user's privacy interests or their site's security policy, and
1529         hence it <em class="bcp14">SHOULD NOT</em> be transmitted without the user being able to disable, enable, and modify the contents of the field. The user <em class="bcp14">MUST</em> be able to set the contents of this field within a user preference or application defaults configuration.
1530      </p>
1531      <p id="rfc.section.12.1.p.6">We suggest, though do not require, that a convenient toggle interface be provided for the user to enable or disable the sending
1532         of From and Referer information.
1533      </p>
1534      <p id="rfc.section.12.1.p.7">The User-Agent (<a href="#header.user-agent" id="rfc.xref.header.user-agent.2" title="User-Agent">Section&nbsp;10.9</a>) or Server (<a href="#header.server" id="rfc.xref.header.server.2" title="Server">Section&nbsp;10.8</a>) header fields can sometimes be used to determine that a specific client or server have a particular security hole which
1535         might be exploited. Unfortunately, this same information is often used for other valuable purposes for which HTTP currently
1536         has no better mechanism.
1537      </p>
1538      <h2 id="rfc.section.12.2"><a href="#rfc.section.12.2">12.2</a>&nbsp;<a id="encoding.sensitive.information.in.uris" href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URI's</a></h2>
1539      <p id="rfc.section.12.2.p.1">Because the source of a link might be private information or might reveal an otherwise private information source, it is strongly
1540         recommended that the user be able to select whether or not the Referer field is sent. For example, a browser client could
1541         have a toggle switch for browsing openly/anonymously, which would respectively enable/disable the sending of Referer and From
1542         information.
1543      </p>
1544      <p id="rfc.section.12.2.p.2">Clients <em class="bcp14">SHOULD NOT</em> include a Referer header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol.
1545      </p>
1546      <p id="rfc.section.12.2.p.3">Authors of services which use the HTTP protocol <em class="bcp14">SHOULD NOT</em> use GET based forms for the submission of sensitive data, because this will cause this data to be encoded in the Request-URI.
1547         Many existing servers, proxies, and user agents will log the request URI in some place where it might be visible to third
1548         parties. Servers can use POST-based form submission instead
1549      </p>
1550      <h2 id="rfc.section.12.3"><a href="#rfc.section.12.3">12.3</a>&nbsp;<a id="location.spoofing" href="#location.spoofing">Location Headers and Spoofing</a></h2>
1551      <p id="rfc.section.12.3.p.1">If a single server supports multiple organizations that do not trust one another, then it <em class="bcp14">MUST</em> check the values of Location and Content-Location headers in responses that are generated under control of said organizations
1552         to make sure that they do not attempt to invalidate resources over which they have no authority.
1553      </p>
1554      <h1 id="rfc.section.13"><a href="#rfc.section.13">13.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
1555      <h1 id="rfc.references"><a href="#rfc.section.14" id="rfc.section.14">14.</a> References
1556      </h1>
[97]1557      <table summary="References">                         
[52]1558         <tr>
1559            <td class="reference"><b id="Luo1998">[Luo1998]</b></td>
1560            <td class="top">Luotonen, A., “Tunneling TCP based protocols through Web proxy servers”, &nbsp;Work in Progress.</td>
1561         </tr>
1562         <tr>
1563            <td class="reference"><b id="Part1">[Part1]</b></td>
[95]1564            <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), December&nbsp;2007.
[52]1565            </td>
1566         </tr>
1567         <tr>
1568            <td class="reference"><b id="Part3">[Part3]</b></td>
[95]1569            <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-p3-payload-latest">HTTP/1.1, part 3: Message Payload and Content Negotiation</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p3-payload-latest (work in progress), December&nbsp;2007.
[52]1570            </td>
1571         </tr>
1572         <tr>
1573            <td class="reference"><b id="Part4">[Part4]</b></td>
[95]1574            <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), December&nbsp;2007.
[52]1575            </td>
1576         </tr>
1577         <tr>
1578            <td class="reference"><b id="Part5">[Part5]</b></td>
[95]1579            <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), December&nbsp;2007.
[52]1580            </td>
1581         </tr>
1582         <tr>
1583            <td class="reference"><b id="Part6">[Part6]</b></td>
[95]1584            <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), December&nbsp;2007.
[52]1585            </td>
1586         </tr>
1587         <tr>
1588            <td class="reference"><b id="Part7">[Part7]</b></td>
[95]1589            <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-p7-auth-latest">HTTP/1.1, part 7: Authentication</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p7-auth-latest (work in progress), December&nbsp;2007.
[52]1590            </td>
1591         </tr>
1592         <tr>
1593            <td class="reference"><b id="RFC1123">[RFC1123]</b></td>
1594            <td class="top"><a title="University of Southern California (USC), Information Sciences Institute">Braden, R.</a>, “<a href="http://tools.ietf.org/html/rfc1123">Requirements for Internet Hosts - Application and Support</a>”, STD&nbsp;3, RFC&nbsp;1123, October&nbsp;1989.
1595            </td>
1596         </tr>
1597         <tr>
[97]1598            <td class="reference"><b id="RFC1945">[RFC1945]</b></td>
1599            <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.
1600            </td>
1601         </tr>
1602         <tr>
[52]1603            <td class="reference"><b id="RFC2068">[RFC2068]</b></td>
1604            <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.
1605            </td>
1606         </tr>
1607         <tr>
[96]1608            <td class="reference"><b id="RFC2119">[RFC2119]</b></td>
1609            <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.
1610            </td>
1611         </tr>
1612         <tr>
[52]1613            <td class="reference"><b id="RFC2616">[RFC2616]</b></td>
1614            <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.
1615            </td>
1616         </tr>
1617         <tr>
1618            <td class="reference"><b id="RFC822">[RFC822]</b></td>
1619            <td class="top"><a title="University of Delaware, Dept. of Electrical Engineering">Crocker, D.H.</a>, “<a href="http://tools.ietf.org/html/rfc822">Standard for the format of ARPA Internet text messages</a>”, STD&nbsp;11, RFC&nbsp;822, August&nbsp;1982.
1620            </td>
1621         </tr>
1622      </table>
1623      <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1>
1624      <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span>
1625            (editor)
1626            <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>
1627      <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>
1628      <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>
1629      <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>
1630      <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>
1631      <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>
1632      <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>
[95]1633      <address class="vcard"><span class="vcardline"><span class="fn">Yves Lafon</span>
1634            (editor)
1635            <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>
1636      <address class="vcard"><span class="vcardline"><span class="fn">Julian F. Reschke</span>
1637            (editor)
1638            <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>
[99]1639      <h1 id="rfc.section.A"><a href="#rfc.section.A">A.</a>&nbsp;<a id="compatibility" href="#compatibility">Compatibility with Previous Versions</a></h1>
1640      <h2 id="rfc.section.A.1"><a href="#rfc.section.A.1">A.1</a>&nbsp;<a id="changes.from.rfc.2068" href="#changes.from.rfc.2068">Changes from RFC 2068</a></h2>
1641      <p id="rfc.section.A.1.p.1">Clarified which error code should be used for inbound server failures (e.g. DNS failures). (<a href="#status.504" id="rfc.xref.status.504.2" title="504 Gateway Timeout">Section&nbsp;9.5.5</a>).
[52]1642      </p>
[99]1643      <p id="rfc.section.A.1.p.2">CREATE had a race that required an Etag be sent when a resource is first created. (<a href="#status.201" id="rfc.xref.status.201.2" title="201 Created">Section&nbsp;9.2.2</a>).
[52]1644      </p>
[99]1645      <p id="rfc.section.A.1.p.3">Rewrite of message transmission requirements to make it much harder for implementors to get it wrong, as the consequences
[52]1646         of errors here can have significant impact on the Internet, and to deal with the following problems:
1647      </p>
1648      <ol>
1649         <li>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where this was incorrectly placing a requirement on the behavior of
1650            an implementation of a future version of HTTP/1.x
1651         </li>
1652         <li>Made it clear that user-agents should retry requests, not "clients" in general.</li>
1653         <li>Converted requirements for clients to ignore unexpected 100 (Continue) responses, and for proxies to forward 100 responses,
1654            into a general requirement for 1xx responses.
1655         </li>
1656         <li>Modified some TCP-specific language, to make it clearer that non-TCP transports are possible for HTTP.</li>
1657         <li>Require that the origin server <em class="bcp14">MUST NOT</em> wait for the request body before it sends a required 100 (Continue) response.
1658         </li>
1659         <li>Allow, rather than require, a server to omit 100 (Continue) if it has already seen some of the request body.</li>
1660         <li>Allow servers to defend against denial-of-service attacks and broken clients.</li>
1661      </ol>
[99]1662      <p id="rfc.section.A.1.p.4">This change adds the Expect header and 417 status code.</p>
1663      <p id="rfc.section.A.1.p.5">Clean up confusion between 403 and 404 responses. (Section <a href="#status.403" id="rfc.xref.status.403.2" title="403 Forbidden">9.4.4</a>, <a href="#status.404" id="rfc.xref.status.404.2" title="404 Not Found">9.4.5</a>, and <a href="#status.410" id="rfc.xref.status.410.2" title="410 Gone">9.4.11</a>)
[52]1664      </p>
[99]1665      <p id="rfc.section.A.1.p.6">The PATCH<span id="rfc.iref.p.3"></span><span id="rfc.iref.m.10"></span>, LINK<span id="rfc.iref.l.2"></span><span id="rfc.iref.m.11"></span>, UNLINK<span id="rfc.iref.u.2"></span><span id="rfc.iref.m.12"></span> methods were defined but not commonly implemented in previous versions of this specification. See <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>.
[52]1666      </p>
[99]1667      <h2 id="rfc.section.A.2"><a href="#rfc.section.A.2">A.2</a>&nbsp;<a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h2>
[108]1668      <p id="rfc.section.A.2.p.1">Clarify definition of POST. (<a href="#POST" id="rfc.xref.POST.2" title="POST">Section&nbsp;8.5</a>)
1669      </p>
[109]1670      <p id="rfc.section.A.2.p.2">Failed to consider that there are many other request methods that are safe to automatically redirect, and further that the
1671         user agent is able to make that determination based on the request method semantics. (Sections <a href="#status.301" id="rfc.xref.status.301.2" title="301 Moved Permanently">9.3.2</a>, <a href="#status.302" id="rfc.xref.status.302.2" title="302 Found">9.3.3</a> and <a href="#status.307" id="rfc.xref.status.307.2" title="307 Temporary Redirect">9.3.8</a> )
1672      </p>
[114]1673      <p id="rfc.section.A.2.p.3">Correct syntax of Location header to allow fragment, as referred symbol wasn't what was expected, and add some clarifications
1674         as to when it would not be appropriate. (<a href="#header.location" id="rfc.xref.header.location.3" title="Location">Section&nbsp;10.4</a>)
1675      </p>
1676      <p id="rfc.section.A.2.p.4">In the description of the Server header, the Via field was described as a SHOULD. The requirement was and is stated correctly
[112]1677         in the description of the Via header in <a href="p1-messaging.html#header.via" title="Via">Section 8.9</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>. (<a href="#header.server" id="rfc.xref.header.server.3" title="Server">Section&nbsp;10.8</a>)
1678      </p>
[115]1679      <h1 id="rfc.section.B"><a href="#rfc.section.B">B.</a>&nbsp;Change Log (to be removed by RFC Editor before publication)
1680      </h1>
1681      <h2 id="rfc.section.B.1"><a href="#rfc.section.B.1">B.1</a>&nbsp;Since RFC2616
1682      </h2>
1683      <p id="rfc.section.B.1.p.1">Extracted relevant partitions from <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>.
1684      </p>
1685      <h2 id="rfc.section.B.2"><a href="#rfc.section.B.2">B.2</a>&nbsp;Since draft-ietf-httpbis-p2-semantics-00
1686      </h2>
[116]1687      <p id="rfc.section.B.2.p.1">Closed issues: </p>
1688      <ul>
1689         <li> &lt;<a href="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5">http://www3.tools.ietf.org/wg/httpbis/trac/ticket/5</a>&gt;: "Via is a MUST" (&lt;<a href="http://purl.org/NET/http-errata#via-must">http://purl.org/NET/http-errata#via-must</a>&gt;)
1690         </li>
1691         <li> &lt;<a href="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6">http://www3.tools.ietf.org/wg/httpbis/trac/ticket/6</a>&gt;: "Fragments allowed in Location" (&lt;<a href="http://purl.org/NET/http-errata#location-fragments">http://purl.org/NET/http-errata#location-fragments</a>&gt;)
1692         </li>
1693         <li> &lt;<a href="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10">http://www3.tools.ietf.org/wg/httpbis/trac/ticket/10</a>&gt;: "Safe Methods vs Redirection" (&lt;<a href="http://purl.org/NET/http-errata#saferedirect">http://purl.org/NET/http-errata#saferedirect</a>&gt;)
1694         </li>
1695         <li> &lt;<a href="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17">http://www3.tools.ietf.org/wg/httpbis/trac/ticket/17</a>&gt;: "Revise description of the POST method" (&lt;<a href="http://purl.org/NET/http-errata#post">http://purl.org/NET/http-errata#post</a>&gt;)
1696         </li>
1697         <li> &lt;<a href="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42">http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42</a>&gt;: "RFC2606 Compliance"
1698         </li>
1699      </ul>
1700      <p id="rfc.section.B.2.p.2">Other changes: </p>
1701      <ul>
1702         <li>Move definitions of 304 and 412 condition codes to <a href="#Part4" id="rfc.xref.Part4.9"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a> 
1703         </li>
1704      </ul>
[52]1705      <h1><a id="rfc.copyright" href="#rfc.copyright">Full Copyright Statement</a></h1>
1706      <p>Copyright © The IETF Trust (2007).</p>
1707      <p>This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the
1708         authors retain all their rights.
1709      </p>
1710      <p>This document and the information contained herein are provided on an “AS IS” basis and THE CONTRIBUTOR, THE ORGANIZATION
1711         HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE
1712         DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
1713         WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
1714      </p>
1715      <h1><a id="rfc.ipr" href="#rfc.ipr">Intellectual Property</a></h1>
1716      <p>The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might
1717         be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any
1718         license under such rights might or might not be available; nor does it represent that it has made any independent effort to
1719         identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and
1720         BCP 79.
1721      </p>
1722      <p>Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result
1723         of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users
1724         of this specification can be obtained from the IETF on-line IPR repository at &lt;<a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>&gt;.
1725      </p>
1726      <p>The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary
1727         rights that may cover technology that may be required to implement this standard. Please address the information to the IETF
1728         at <a href="mailto:ietf-ipr@ietf.org">ietf-ipr@ietf.org</a>.
1729      </p>
1730      <h1>Acknowledgement</h1>
1731      <p>Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA).</p>
1732      <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1>
1733      <p class="noprint"><a href="#rfc.index.1">1</a> <a href="#rfc.index.2">2</a> <a href="#rfc.index.3">3</a> <a href="#rfc.index.4">4</a> <a href="#rfc.index.5">5</a> <a href="#rfc.index.A">A</a> <a href="#rfc.index.C">C</a> <a href="#rfc.index.D">D</a> <a href="#rfc.index.E">E</a> <a href="#rfc.index.F">F</a> <a href="#rfc.index.G">G</a> <a href="#rfc.index.H">H</a> <a href="#rfc.index.L">L</a> <a href="#rfc.index.M">M</a> <a href="#rfc.index.O">O</a> <a href="#rfc.index.P">P</a> <a href="#rfc.index.R">R</a> <a href="#rfc.index.S">S</a> <a href="#rfc.index.T">T</a> <a href="#rfc.index.U">U</a> 
1734      </p>
1735      <div class="print2col">
1736         <ul class="ind">
1737            <li class="indline0"><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul class="ind">
1738                  <li class="indline1">100 Continue (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.100.1">5</a>, <a class="iref" href="#rfc.iref.25"><b>9.1.1</b></a></li>
1739                  <li class="indline1">101 Switching Protocols (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.101.1">5</a>, <a class="iref" href="#rfc.iref.26"><b>9.1.2</b></a></li>
1740               </ul>
1741            </li>
1742            <li class="indline0"><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul class="ind">
1743                  <li class="indline1">200 OK (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.200.1">5</a>, <a class="iref" href="#rfc.iref.27"><b>9.2.1</b></a></li>
[99]1744                  <li class="indline1">201 Created (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.201.1">5</a>, <a class="iref" href="#rfc.iref.28"><b>9.2.2</b></a>, <a class="iref" href="#rfc.xref.status.201.2">A.1</a></li>
[52]1745                  <li class="indline1">202 Accepted (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.202.1">5</a>, <a class="iref" href="#rfc.iref.29"><b>9.2.3</b></a></li>
1746                  <li class="indline1">203 Non-Authoritative Information (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.203.1">5</a>, <a class="iref" href="#rfc.iref.30"><b>9.2.4</b></a></li>
1747                  <li class="indline1">204 No Content (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.204.1">5</a>, <a class="iref" href="#rfc.iref.31"><b>9.2.5</b></a></li>
1748                  <li class="indline1">205 Reset Content (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.205.1">5</a>, <a class="iref" href="#rfc.iref.32"><b>9.2.6</b></a></li>
1749                  <li class="indline1">206 Partial Content (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.206.1">5</a>, <a class="iref" href="#rfc.iref.33"><b>9.2.7</b></a></li>
1750               </ul>
1751            </li>
1752            <li class="indline0"><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul class="ind">
1753                  <li class="indline1">300 Multiple Choices (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.300.1">5</a>, <a class="iref" href="#rfc.iref.34"><b>9.3.1</b></a></li>
[109]1754                  <li class="indline1">301 Moved Permanently (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.301.1">5</a>, <a class="iref" href="#rfc.iref.35"><b>9.3.2</b></a>, <a class="iref" href="#rfc.xref.status.301.2">A.2</a></li>
1755                  <li class="indline1">302 Found (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.302.1">5</a>, <a class="iref" href="#rfc.iref.36"><b>9.3.3</b></a>, <a class="iref" href="#rfc.xref.status.302.2">A.2</a></li>
[52]1756                  <li class="indline1">303 See Other (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.303.1">5</a>, <a class="iref" href="#rfc.iref.37"><b>9.3.4</b></a></li>
1757                  <li class="indline1">304 Not Modified (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.304.1">5</a>, <a class="iref" href="#rfc.iref.38"><b>9.3.5</b></a></li>
1758                  <li class="indline1">305 Use Proxy (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.305.1">5</a>, <a class="iref" href="#rfc.iref.39"><b>9.3.6</b></a></li>
1759                  <li class="indline1">306 (Unused) (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.iref.40"><b>9.3.7</b></a></li>
[109]1760                  <li class="indline1">307 Temporary Redirect (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.307.1">5</a>, <a class="iref" href="#rfc.iref.41"><b>9.3.8</b></a>, <a class="iref" href="#rfc.xref.status.307.2">A.2</a></li>
[52]1761               </ul>
1762            </li>
1763            <li class="indline0"><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul class="ind">
1764                  <li class="indline1">400 Bad Request (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.400.1">5</a>, <a class="iref" href="#rfc.iref.42"><b>9.4.1</b></a></li>
1765                  <li class="indline1">401 Unauthorized (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.401.1">5</a>, <a class="iref" href="#rfc.iref.43"><b>9.4.2</b></a></li>
1766                  <li class="indline1">402 Payment Required (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.402.1">5</a>, <a class="iref" href="#rfc.iref.44"><b>9.4.3</b></a></li>
[99]1767                  <li class="indline1">403 Forbidden (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.403.1">5</a>, <a class="iref" href="#rfc.iref.45"><b>9.4.4</b></a>, <a class="iref" href="#rfc.xref.status.403.2">A.1</a></li>
1768                  <li class="indline1">404 Not Found (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.404.1">5</a>, <a class="iref" href="#rfc.iref.46"><b>9.4.5</b></a>, <a class="iref" href="#rfc.xref.status.404.2">A.1</a></li>
[52]1769                  <li class="indline1">405 Method Not Allowed (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.405.1">5</a>, <a class="iref" href="#rfc.iref.47"><b>9.4.6</b></a></li>
1770                  <li class="indline1">406 Not Acceptable (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.406.1">5</a>, <a class="iref" href="#rfc.iref.48"><b>9.4.7</b></a></li>
1771                  <li class="indline1">407 Proxy Authentication Required (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.407.1">5</a>, <a class="iref" href="#rfc.iref.49"><b>9.4.8</b></a></li>
1772                  <li class="indline1">408 Request Timeout (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.408.1">5</a>, <a class="iref" href="#rfc.iref.50"><b>9.4.9</b></a></li>
1773                  <li class="indline1">409 Conflict (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.409.1">5</a>, <a class="iref" href="#rfc.iref.51"><b>9.4.10</b></a></li>
[99]1774                  <li class="indline1">410 Gone (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.410.1">5</a>, <a class="iref" href="#rfc.iref.52"><b>9.4.11</b></a>, <a class="iref" href="#rfc.xref.status.410.2">A.1</a></li>
[52]1775                  <li class="indline1">411 Length Required (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.411.1">5</a>, <a class="iref" href="#rfc.iref.53"><b>9.4.12</b></a></li>
1776                  <li class="indline1">412 Precondition Failed (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.412.1">5</a>, <a class="iref" href="#rfc.iref.54"><b>9.4.13</b></a></li>
1777                  <li class="indline1">413 Request Entity Too Large (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.413.1">5</a>, <a class="iref" href="#rfc.iref.55"><b>9.4.14</b></a></li>
1778                  <li class="indline1">414 Request-URI Too Long (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.414.1">5</a>, <a class="iref" href="#rfc.iref.56"><b>9.4.15</b></a></li>
1779                  <li class="indline1">415 Unsupported Media Type (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.415.1">5</a>, <a class="iref" href="#rfc.iref.57"><b>9.4.16</b></a></li>
1780                  <li class="indline1">416 Requested Range Not Satisfiable (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.416.1">5</a>, <a class="iref" href="#rfc.iref.58"><b>9.4.17</b></a></li>
1781                  <li class="indline1">417 Expectation Failed (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.417.1">5</a>, <a class="iref" href="#rfc.iref.59"><b>9.4.18</b></a></li>
1782               </ul>
1783            </li>
1784            <li class="indline0"><a id="rfc.index.5" href="#rfc.index.5"><b>5</b></a><ul class="ind">
1785                  <li class="indline1">500 Internal Server Error (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.500.1">5</a>, <a class="iref" href="#rfc.iref.60"><b>9.5.1</b></a></li>
1786                  <li class="indline1">501 Not Implemented (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.501.1">5</a>, <a class="iref" href="#rfc.iref.61"><b>9.5.2</b></a></li>
1787                  <li class="indline1">502 Bad Gateway (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.502.1">5</a>, <a class="iref" href="#rfc.iref.62"><b>9.5.3</b></a></li>
1788                  <li class="indline1">503 Service Unavailable (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.503.1">5</a>, <a class="iref" href="#rfc.iref.63"><b>9.5.4</b></a></li>
[99]1789                  <li class="indline1">504 Gateway Timeout (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.504.1">5</a>, <a class="iref" href="#rfc.iref.64"><b>9.5.5</b></a>, <a class="iref" href="#rfc.xref.status.504.2">A.1</a></li>
[52]1790                  <li class="indline1">505 HTTP Version Not Supported (status code)&nbsp;&nbsp;<a class="iref" href="#rfc.xref.status.505.1">5</a>, <a class="iref" href="#rfc.iref.65"><b>9.5.6</b></a></li>
1791               </ul>
1792            </li>
1793            <li class="indline0"><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul class="ind">
1794                  <li class="indline1">Allow header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.allow.1">3</a>, <a class="iref" href="#rfc.iref.a.1"><b>10.1</b></a></li>
1795               </ul>
1796            </li>
1797            <li class="indline0"><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul class="ind">
1798                  <li class="indline1">CONNECT method&nbsp;&nbsp;<a class="iref" href="#rfc.xref.CONNECT.1">3</a>, <a class="iref" href="#rfc.iref.c.1"><b>8.9</b></a></li>
1799               </ul>
1800            </li>
1801            <li class="indline0"><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul class="ind">
1802                  <li class="indline1">DELETE method&nbsp;&nbsp;<a class="iref" href="#rfc.xref.DELETE.1">3</a>, <a class="iref" href="#rfc.iref.d.1"><b>8.7</b></a></li>
1803               </ul>
1804            </li>
1805            <li class="indline0"><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul class="ind">
1806                  <li class="indline1">Expect header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.expect.1">4</a>, <a class="iref" href="#rfc.xref.header.expect.2">9.4.18</a>, <a class="iref" href="#rfc.iref.e.1"><b>10.2</b></a></li>
1807               </ul>
1808            </li>
1809            <li class="indline0"><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul class="ind">
1810                  <li class="indline1">From header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.from.1">4</a>, <a class="iref" href="#rfc.iref.f.1"><b>10.3</b></a></li>
1811               </ul>
1812            </li>
1813            <li class="indline0"><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul class="ind">
1814                  <li class="indline1">GET method&nbsp;&nbsp;<a class="iref" href="#rfc.xref.GET.1">3</a>, <a class="iref" href="#rfc.iref.g.10"><b>8.3</b></a></li>
1815                  <li class="indline1"><tt>Grammar</tt>&nbsp;&nbsp;
1816                     <ul class="ind">
1817                        <li class="indline1"><tt>Allow</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.11"><b>10.1</b></a></li>
1818                        <li class="indline1"><tt>Expect</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.12"><b>10.2</b></a></li>
1819                        <li class="indline1"><tt>expect-params</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.15"><b>10.2</b></a></li>
1820                        <li class="indline1"><tt>expectation</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.13"><b>10.2</b></a></li>
1821                        <li class="indline1"><tt>expectation-extension</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.14"><b>10.2</b></a></li>
1822                        <li class="indline1"><tt>extension-code</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.7"><b>5</b></a></li>
1823                        <li class="indline1"><tt>extension-method</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.4"><b>3</b></a></li>
1824                        <li class="indline1"><tt>From</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.16"><b>10.3</b></a></li>
1825                        <li class="indline1"><tt>Location</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.17"><b>10.4</b></a></li>
1826                        <li class="indline1"><tt>Max-Forwards</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.18"><b>10.5</b></a></li>
1827                        <li class="indline1"><tt>Method</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.3"><b>3</b></a></li>
1828                        <li class="indline1"><tt>product</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.1"><b>2</b></a></li>
1829                        <li class="indline1"><tt>product-version</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.2"><b>2</b></a></li>
1830                        <li class="indline1"><tt>Reason-Phrase</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.8"><b>5</b></a></li>
1831                        <li class="indline1"><tt>Referer</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.19"><b>10.6</b></a></li>
1832                        <li class="indline1"><tt>request-header</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.5"><b>4</b></a></li>
1833                        <li class="indline1"><tt>response-header</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.9"><b>6</b></a></li>
1834                        <li class="indline1"><tt>Retry-After</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.20"><b>10.7</b></a></li>
1835                        <li class="indline1"><tt>Server</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.21"><b>10.8</b></a></li>
1836                        <li class="indline1"><tt>Status-Code</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.6"><b>5</b></a></li>
1837                        <li class="indline1"><tt>User-Agent</tt>&nbsp;&nbsp;<a class="iref" href="#rfc.iref.g.22"><b>10.9</b></a></li>
1838                     </ul>
1839                  </li>
1840               </ul>
1841            </li>
1842            <li class="indline0"><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul class="ind">
1843                  <li class="indline1">HEAD method&nbsp;&nbsp;<a class="iref" href="#rfc.xref.HEAD.1">3</a>, <a class="iref" href="#rfc.iref.h.1"><b>8.4</b></a></li>
1844                  <li class="indline1">Headers&nbsp;&nbsp;
1845                     <ul class="ind">
1846                        <li class="indline1">Allow&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.allow.1">3</a>, <a class="iref" href="#rfc.iref.h.2"><b>10.1</b></a></li>
1847                        <li class="indline1">Expect&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.expect.1">4</a>, <a class="iref" href="#rfc.xref.header.expect.2">9.4.18</a>, <a class="iref" href="#rfc.iref.h.3"><b>10.2</b></a></li>
1848                        <li class="indline1">From&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.from.1">4</a>, <a class="iref" href="#rfc.iref.h.4"><b>10.3</b></a></li>
[114]1849                        <li class="indline1">Location&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.location.1">6</a>, <a class="iref" href="#rfc.xref.header.location.2">8.5</a>, <a class="iref" href="#rfc.iref.h.5"><b>10.4</b></a>, <a class="iref" href="#rfc.xref.header.location.3">A.2</a></li>
[52]1850                        <li class="indline1">Max-Forwards&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.max-forwards.1">4</a>, <a class="iref" href="#rfc.xref.header.max-forwards.2">8.8</a>, <a class="iref" href="#rfc.iref.h.6"><b>10.5</b></a></li>
1851                        <li class="indline1">Referer&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.referer.1">4</a>, <a class="iref" href="#rfc.iref.h.7"><b>10.6</b></a></li>
1852                        <li class="indline1">Retry-After&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.retry-after.1">6</a>, <a class="iref" href="#rfc.iref.h.8"><b>10.7</b></a></li>
[112]1853                        <li class="indline1">Server&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.server.1">6</a>, <a class="iref" href="#rfc.iref.h.9"><b>10.8</b></a>, <a class="iref" href="#rfc.xref.header.server.2">12.1</a>, <a class="iref" href="#rfc.xref.header.server.3">A.2</a></li>
[52]1854                        <li class="indline1">User-Agent&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.user-agent.1">4</a>, <a class="iref" href="#rfc.iref.h.10"><b>10.9</b></a>, <a class="iref" href="#rfc.xref.header.user-agent.2">12.1</a></li>
1855                     </ul>
1856                  </li>
1857               </ul>
1858            </li>
1859            <li class="indline0"><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul class="ind">
[99]1860                  <li class="indline1">LINK method&nbsp;&nbsp;<a class="iref" href="#rfc.iref.l.2"><b>A.1</b></a></li>
[114]1861                  <li class="indline1">Location header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.location.1">6</a>, <a class="iref" href="#rfc.xref.header.location.2">8.5</a>, <a class="iref" href="#rfc.iref.l.1"><b>10.4</b></a>, <a class="iref" href="#rfc.xref.header.location.3">A.2</a></li>
[52]1862                  <li class="indline1"><em>Luo1998</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Luo1998.1">8.9</a>, <a class="iref" href="#Luo1998"><b>14</b></a></li>
1863               </ul>
1864            </li>
1865            <li class="indline0"><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul class="ind">
1866                  <li class="indline1">Max-Forwards header&nbsp;&nbsp;<a class="iref" href="#rfc.xref.header.max-forwards.1">4</a>, <a class="iref" href="#rfc.xref.header.max-forwards.2">8.8</a>, <a class="iref" href="#rfc.iref.m.9"><b>10.5</b></a></li>
1867                  <li class="indline1">Methods&nbsp;&nbsp;
1868                     <ul class="ind">
1869                        <li class="indline1">CONNECT&nbsp;&nbsp;<a class="iref" href="#rfc.xref.CONNECT.1">3</a>, <a class="iref" href="#rfc.iref.m.8"><b>8.9</b></a></li>
1870                        <li class="indline1">DELETE&nbsp;&nbsp;<a class="iref" href="#rfc.xref.DELETE.1">3</a>, <a class="iref" href="#rfc.iref.m.6"><b>8.7</b></a></li>
1871                        <li class="indline1">GET&nbsp;&nbsp;<a class="iref" href="#rfc.xref.GET.1">3</a>, <a class="iref" href="#rfc.iref.m.2"><b>8.3</b></a></li>
1872                        <li class="indline1">HEAD&nbsp;&nbsp;<a class="iref" href="#rfc.xref.HEAD.1">3</a>, <a class="iref" href="#rfc.iref.m.3"><b>8.4</b></a></li>
[99]1873                        <li class="indline1">LINK&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.11"><b>A.1</b></a></li>
[52]1874                        <li class="indline1">OPTIONS&nbsp;&nbsp;<a class="iref" href="#rfc.xref.OPTIONS.1">3</a>, <a class="iref" href="#rfc.iref.m.1"><b>8.2</b></a>, <a class="iref" href="#rfc.xref.OPTIONS.2">10.5</a></li>
[99]1875                        <li class="indline1">PATCH&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.10"><b>A.1</b></a></li>
[108]1876                        <li class="indline1">POST&nbsp;&nbsp;<a class="iref" href="#rfc.xref.POST.1">3</a>, <a class="iref" href="#rfc.iref.m.4"><b>8.5</b></a>, <a class="iref" href="#rfc.xref.POST.2">A.2</a></li>
[52]1877                        <li class="indline1">PUT&nbsp;&nbsp;<a class="iref" href="#rfc.xref.PUT.1">3</a>, <a class="iref" href="#rfc.iref.m.5"><b>8.6</b></a></li>
1878                        <li class="indline1">TRACE&nbsp;&nbsp;<a class="iref" href="#rfc.xref.TRACE.1">3</a>, <a class="iref" href="#rfc.iref.m.7"><b>8.8</b></a>, <a class="iref" href="#rfc.xref.TRACE.2">10.5</a></li>
[99]1879                        <li class="indline1">UNLINK&nbsp;&nbsp;<a class="iref" href="#rfc.iref.m.12"><b>A.1</b></a></li>
[52]1880                     </ul>
1881                  </li>
1882               </ul>
1883            </li>
1884            <li class="indline0"><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul class="ind">
1885                  <li class="indline1">OPTIONS method&nbsp;&nbsp;<a class="iref" href="#rfc.xref.OPTIONS.1">3</a>, <a class="iref" href="#rfc.iref.o.1"><b>8.2</b></a>, <a class="iref" href="#rfc.xref.OPTIONS.2">10.5</a></li>
1886               </ul>
1887            </li>
1888            <li class="indline0"><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul class="ind">
[112]1889                  <li class="indline1"><em>Part1</em>&nbsp;&nbsp;<a class="iref" href="#rfc.xref.Part1.1">4</a>, <a class="iref" href="#rfc.xref.Part1.2">4</a>, <a class="iref" href="#rfc.xref.Part1.3">7</a>, <a class="iref" href="#rfc.xref.Part1.4">8</a>, <a class="iref" href="#rfc.xref.Part1.5">8.5</a>, <a class="iref" href="#rfc.xref.Part1.6">8.6</a>, <a class="iref" href="#rfc.xref.Part1.7">8.8</a>, <a class="iref" href="#rfc.xref.Part1.8">9.1.1</a>, <a class="iref" href="#rfc.xref.Part1.9"