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324</style><link rel="Contents" href="#rfc.toc">
325      <link rel="Author" href="#rfc.authors">
326      <link rel="Copyright" href="#rfc.copyright">
327      <link rel="Index" href="#rfc.index">
328      <link rel="Chapter" title="1 Introduction" href="#rfc.section.1">
329      <link rel="Chapter" title="2 Product Tokens" href="#rfc.section.2">
330      <link rel="Chapter" title="3 Method" href="#rfc.section.3">
331      <link rel="Chapter" title="4 Request Header Fields" href="#rfc.section.4">
332      <link rel="Chapter" title="5 Status Code and Reason Phrase" href="#rfc.section.5">
333      <link rel="Chapter" title="6 Response Header Fields" href="#rfc.section.6">
334      <link rel="Chapter" title="7 Entity" href="#rfc.section.7">
335      <link rel="Chapter" title="8 Method Definitions" href="#rfc.section.8">
336      <link rel="Chapter" title="9 Status Code Definitions" href="#rfc.section.9">
337      <link rel="Chapter" title="10 Header Field Definitions" href="#rfc.section.10">
338      <link rel="Chapter" title="11 IANA Considerations" href="#rfc.section.11">
339      <link rel="Chapter" title="12 Security Considerations" href="#rfc.section.12">
340      <link rel="Chapter" title="13 Acknowledgments" href="#rfc.section.13">
341      <link rel="Chapter" href="#rfc.section.14" title="14 References">
342      <link rel="Appendix" title="A Changes from RFC 2068" href="#rfc.section.A">
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344      <link rel="schema.dct" href="http://purl.org/dc/terms/">
345      <meta name="dct.creator" content="Fielding, R.">
346      <meta name="dct.creator" content="Gettys, J.">
347      <meta name="dct.creator" content="Mogul, J.">
348      <meta name="dct.creator" content="Frystyk, H.">
349      <meta name="dct.creator" content="Masinter, L.">
350      <meta name="dct.creator" content="Leach, P.">
351      <meta name="dct.creator" content="Berners-Lee, T.">
352      <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p2-semantics-00">
353      <meta name="dct.issued" scheme="ISO8601" content="2007-12-20">
354      <meta name="dct.replaces" content="urn:ietf:rfc:2068">
355      <meta name="dct.replaces" content="urn:ietf:rfc:2616">
356      <meta name="dct.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.">
357      <meta name="description" 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.">
358   </head>
359   <body>
360      <table class="header">
361         <tbody>
362            <tr>
363               <td class="left">Network Working Group</td>
364               <td class="right">R. Fielding, Editor</td>
365            </tr>
366            <tr>
367               <td class="left">Internet-Draft</td>
368               <td class="right">Day Software</td>
369            </tr>
370            <tr>
371               <td class="left">Obsoletes: <a href="http://tools.ietf.org/html/rfc2068">2068</a>, <a href="http://tools.ietf.org/html/rfc2616">2616</a> (if approved)
372               </td>
373               <td class="right">J. Gettys</td>
374            </tr>
375            <tr>
376               <td class="left">Intended status: Standards Track</td>
377               <td class="right">One Laptop per Child</td>
378            </tr>
379            <tr>
380               <td class="left">Expires: June 22, 2008</td>
381               <td class="right">J. Mogul</td>
382            </tr>
383            <tr>
384               <td class="left"></td>
385               <td class="right">HP</td>
386            </tr>
387            <tr>
388               <td class="left"></td>
389               <td class="right">H. Frystyk</td>
390            </tr>
391            <tr>
392               <td class="left"></td>
393               <td class="right">Microsoft</td>
394            </tr>
395            <tr>
396               <td class="left"></td>
397               <td class="right">L. Masinter</td>
398            </tr>
399            <tr>
400               <td class="left"></td>
401               <td class="right">Adobe Systems</td>
402            </tr>
403            <tr>
404               <td class="left"></td>
405               <td class="right">P. Leach</td>
406            </tr>
407            <tr>
408               <td class="left"></td>
409               <td class="right">Microsoft</td>
410            </tr>
411            <tr>
412               <td class="left"></td>
413               <td class="right">T. Berners-Lee</td>
414            </tr>
415            <tr>
416               <td class="left"></td>
417               <td class="right">W3C/MIT</td>
418            </tr>
419            <tr>
420               <td class="left"></td>
421               <td class="right">December 20, 2007</td>
422            </tr>
423         </tbody>
424      </table>
425      <p class="title">HTTP/1.1, part 2: Message Semantics<br><span class="filename">draft-ietf-httpbis-p2-semantics-00</span></p>
426      <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1>
427      <p>By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she
428         is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section
429         6 of BCP 79.
430      </p>
431      <p>Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note
432         that other groups may also distribute working documents as Internet-Drafts.
433      </p>
434      <p>Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other
435         documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work
436         in progress”.
437      </p>
438      <p>The list of current Internet-Drafts can be accessed at <a href="http://www.ietf.org/ietf/1id-abstracts.txt">http://www.ietf.org/ietf/1id-abstracts.txt</a>.
439      </p>
440      <p>The list of Internet-Draft Shadow Directories can be accessed at <a href="http://www.ietf.org/shadow.html">http://www.ietf.org/shadow.html</a>.
441      </p>
442      <p>This Internet-Draft will expire on June 22, 2008.</p>
443      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
444      <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information
445         systems. HTTP has been in use by the World Wide Web global information initiative since 1990. This document is Part 2 of the
446         seven-part specification that defines the protocol referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616. Part
447         2 defines the semantics of HTTP messages as expressed by request methods, request-header fields, response status codes, and
448         response-header fields.
449      </p>
450      <h1 id="rfc.note.1"><a href="#rfc.note.1">Editorial Note (To be removed by RFC Editor)</a></h1>
451      <p>This version of the HTTP specification contains only minimal editorial changes from <a href="#RFC2616" id="rfc.xref.RFC2616.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a> (abstract, introductory paragraph, and authors' addresses). All other changes are due to partitioning the original into seven
452         mostly independent parts. The intent is for readers of future drafts to able to use draft 00 as the basis for comparison when
453         the WG makes later changes to the specification text. This draft will shortly be followed by draft 01 (containing the first
454         round of changes that have already been agreed to on the mailing list). There is no point in reviewing this draft other than
455         to verify that the partitioning has been done correctly. Roy T. Fielding, Yves Lafon, and Julian Reschke will be the editors
456         after draft 00 is submitted.
457      </p> 
458      <p>Discussion of this draft should take place on the HTTPBIS working group mailing list (ietf-http-wg@w3.org). The current issues
459         list is at &lt;<a href="http://www3.tools.ietf.org/wg/httpbis/trac/report/11">http://www3.tools.ietf.org/wg/httpbis/trac/report/11</a>&gt; and related documents (including fancy diffs) can be found at &lt;<a href="http://www3.tools.ietf.org/wg/httpbis/">http://www3.tools.ietf.org/wg/httpbis/</a>&gt;.
460      </p>
461      <hr class="noprint">
462      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
463      <ul class="toc">
464         <li>1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a></li>
465         <li>2.&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
466         <li>3.&nbsp;&nbsp;&nbsp;<a href="#method">Method</a></li>
467         <li>4.&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a></li>
468         <li>5.&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>
469         <li>6.&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a></li>
470         <li>7.&nbsp;&nbsp;&nbsp;<a href="#entity">Entity</a></li>
471         <li>8.&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul>
472               <li>8.1&nbsp;&nbsp;&nbsp;<a href="#safe.and.idempotent">Safe and Idempotent Methods</a><ul>
473                     <li>8.1.1&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li>
474                     <li>8.1.2&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li>
475                  </ul>
476               </li>
477               <li>8.2&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li>
478               <li>8.3&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li>
479               <li>8.4&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li>
480               <li>8.5&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li>
481               <li>8.6&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li>
482               <li>8.7&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li>
483               <li>8.8&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li>
484               <li>8.9&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a></li>
485            </ul>
486         </li>
487         <li>9.&nbsp;&nbsp;&nbsp;<a href="#status.codes">Status Code Definitions</a><ul>
488               <li>9.1&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul>
489                     <li>9.1.1&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li>
490                     <li>9.1.2&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li>
491                  </ul>
492               </li>
493               <li>9.2&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul>
494                     <li>9.2.1&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li>
495                     <li>9.2.2&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li>
496                     <li>9.2.3&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li>
497                     <li>9.2.4&nbsp;&nbsp;&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></li>
498                     <li>9.2.5&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li>
499                     <li>9.2.6&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li>
500                     <li>9.2.7&nbsp;&nbsp;&nbsp;<a href="#status.206">206 Partial Content</a></li>
501                  </ul>
502               </li>
503               <li>9.3&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul>
504                     <li>9.3.1&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li>
505                     <li>9.3.2&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li>
506                     <li>9.3.3&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li>
507                     <li>9.3.4&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li>
508                     <li>9.3.5&nbsp;&nbsp;&nbsp;<a href="#status.304">304 Not Modified</a></li>
509                     <li>9.3.6&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li>
510                     <li>9.3.7&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li>
511                     <li>9.3.8&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li>
512                  </ul>
513               </li>
514               <li>9.4&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul>
515                     <li>9.4.1&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li>
516                     <li>9.4.2&nbsp;&nbsp;&nbsp;<a href="#status.401">401 Unauthorized</a></li>
517                     <li>9.4.3&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li>
518                     <li>9.4.4&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li>
519                     <li>9.4.5&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li>
520                     <li>9.4.6&nbsp;&nbsp;&nbsp;<a href="#status.405">405 Method Not Allowed</a></li>
521                     <li>9.4.7&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li>
522                     <li>9.4.8&nbsp;&nbsp;&nbsp;<a href="#status.407">407 Proxy Authentication Required</a></li>
523                     <li>9.4.9&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li>
524                     <li>9.4.10&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li>
525                     <li>9.4.11&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li>
526                     <li>9.4.12&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li>
527                     <li>9.4.13&nbsp;&nbsp;&nbsp;<a href="#status.412">412 Precondition Failed</a></li>
528                     <li>9.4.14&nbsp;&nbsp;&nbsp;<a href="#status.413">413 Request Entity Too Large</a></li>
529                     <li>9.4.15&nbsp;&nbsp;&nbsp;<a href="#status.414">414 Request-URI Too Long</a></li>
530                     <li>9.4.16&nbsp;&nbsp;&nbsp;<a href="#status.415">415 Unsupported Media Type</a></li>
531                     <li>9.4.17&nbsp;&nbsp;&nbsp;<a href="#status.416">416 Requested Range Not Satisfiable</a></li>
532                     <li>9.4.18&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li>
533                  </ul>
534               </li>
535               <li>9.5&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul>
536                     <li>9.5.1&nbsp;&nbsp;&nbsp;<a href="#status.500">500 Internal Server Error</a></li>
537                     <li>9.5.2&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li>
538                     <li>9.5.3&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li>
539                     <li>9.5.4&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li>
540                     <li>9.5.5&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li>
541                     <li>9.5.6&nbsp;&nbsp;&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></li>
542                  </ul>
543               </li>
544            </ul>
545         </li>
546         <li>10.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul>
547               <li>10.1&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li>
548               <li>10.2&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li>
549               <li>10.3&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li>
550               <li>10.4&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li>
551               <li>10.5&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li>
552               <li>10.6&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li>
553               <li>10.7&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li>
554               <li>10.8&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li>
555               <li>10.9&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li>
556            </ul>
557         </li>
558         <li>11.&nbsp;&nbsp;&nbsp;<a href="#IANA.considerations">IANA Considerations</a></li>
559         <li>12.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
560               <li>12.1&nbsp;&nbsp;&nbsp;<a href="#security.sensitive">Transfer of Sensitive Information</a></li>
561               <li>12.2&nbsp;&nbsp;&nbsp;<a href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URI's</a></li>
562               <li>12.3&nbsp;&nbsp;&nbsp;<a href="#location.spoofing">Location Headers and Spoofing</a></li>
563            </ul>
564         </li>
565         <li>13.&nbsp;&nbsp;&nbsp;<a href="#ack">Acknowledgments</a></li>
566         <li>14.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a></li>
567         <li><a href="#rfc.authors">Authors' Addresses</a></li>
568         <li>A.&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li>
569         <li><a href="#rfc.index">Index</a></li>
570         <li><a href="#rfc.ipr">Intellectual Property and Copyright Statements</a></li>
571      </ul>
572      <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
573      <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
574         relevant sections of RFC 2616 with only minor edits.
575      </p>
576      <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,
577         URI, and protocol version, followed by a MIME-like message containing request modifiers, client information, and possible
578         body content over a connection with a server. The server responds with a status line, including the message's protocol version
579         and a success or error code, followed by a MIME-like message containing server information, entity metainformation, and possible
580         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>.
581      </p>
582      <h1 id="rfc.section.2"><a href="#rfc.section.2">2.</a>&nbsp;<a id="product.tokens" href="#product.tokens">Product Tokens</a></h1>
583      <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
584         using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white
585         space. By convention, the products are listed in order of their significance for identifying the application.
586      </p>
587      <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]
588    product-version = token
589</pre><p id="rfc.section.2.p.3">Examples:</p>
590      <div id="rfc.figure.u.2"></div><pre class="text">    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
591    Server: Apache/0.8.4
592</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).
593      </p>
594      <h1 id="rfc.section.3"><a href="#rfc.section.3">3.</a>&nbsp;<a id="method" href="#method">Method</a></h1>
595      <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>
596      <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>
597                   | "GET"                    ; <a href="#GET" id="rfc.xref.GET.1" title="GET">Section&nbsp;8.3</a>
598                   | "HEAD"                   ; <a href="#HEAD" id="rfc.xref.HEAD.1" title="HEAD">Section&nbsp;8.4</a>
599                   | "POST"                   ; <a href="#POST" id="rfc.xref.POST.1" title="POST">Section&nbsp;8.5</a>
600                   | "PUT"                    ; <a href="#PUT" id="rfc.xref.PUT.1" title="PUT">Section&nbsp;8.6</a>
601                   | "DELETE"                 ; <a href="#DELETE" id="rfc.xref.DELETE.1" title="DELETE">Section&nbsp;8.7</a>
602                   | "TRACE"                  ; <a href="#TRACE" id="rfc.xref.TRACE.1" title="TRACE">Section&nbsp;8.8</a>
603                   | "CONNECT"                ; <a href="#CONNECT" id="rfc.xref.CONNECT.1" title="CONNECT">Section&nbsp;8.9</a>
604                   | extension-method
605    extension-method = token
606</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
607         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
608         resource, and 501 (Not Implemented) if the method is unrecognized or not implemented by the origin server. The methods GET
609         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>.
610      </p>
611      <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>
612      <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,
613         to the server. These fields act as request modifiers, with semantics equivalent to the parameters on a programming language
614         method invocation.
615      </p>
616      <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>
617                   | 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>
618                   | 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>
619                   | 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>
620                   | 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>
621                   | Expect                   ; <a href="#header.expect" id="rfc.xref.header.expect.1" title="Expect">Section&nbsp;10.2</a>
622                   | From                     ; <a href="#header.from" id="rfc.xref.header.from.1" title="From">Section&nbsp;10.3</a>
623                   | 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>
624                   | 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>
625                   | 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>
626                   | 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>
627                   | 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>
628                   | 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>
629                   | Max-Forwards             ; <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.1" title="Max-Forwards">Section&nbsp;10.5</a>
630                   | 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>
631                   | 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>
632                   | Referer                  ; <a href="#header.referer" id="rfc.xref.header.referer.1" title="Referer">Section&nbsp;10.6</a>
633                   | 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>
634                   | User-Agent               ; <a href="#header.user-agent" id="rfc.xref.header.user-agent.1" title="User-Agent">Section&nbsp;10.9</a>
635</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
636         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.
637         Unrecognized header fields are treated as entity-header fields.
638      </p>
639      <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>
640      <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
641         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
642         by automata and the Reason-Phrase is intended for the human user. The client is not required to examine or display the Reason-Phrase.
643      </p>
644      <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,
645         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.
646      </p>
647      <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    =
648         "100"  ; <a href="#status.100" id="rfc.xref.status.100.1" title="100 Continue">Section&nbsp;9.1.1</a>: Continue
649       | "101"  ; <a href="#status.101" id="rfc.xref.status.101.1" title="101 Switching Protocols">Section&nbsp;9.1.2</a>: Switching Protocols
650       | "200"  ; <a href="#status.200" id="rfc.xref.status.200.1" title="200 OK">Section&nbsp;9.2.1</a>: OK
651       | "201"  ; <a href="#status.201" id="rfc.xref.status.201.1" title="201 Created">Section&nbsp;9.2.2</a>: Created
652       | "202"  ; <a href="#status.202" id="rfc.xref.status.202.1" title="202 Accepted">Section&nbsp;9.2.3</a>: Accepted
653       | "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
654       | "204"  ; <a href="#status.204" id="rfc.xref.status.204.1" title="204 No Content">Section&nbsp;9.2.5</a>: No Content
655       | "205"  ; <a href="#status.205" id="rfc.xref.status.205.1" title="205 Reset Content">Section&nbsp;9.2.6</a>: Reset Content
656       | "206"  ; <a href="#status.206" id="rfc.xref.status.206.1" title="206 Partial Content">Section&nbsp;9.2.7</a>: Partial Content
657       | "300"  ; <a href="#status.300" id="rfc.xref.status.300.1" title="300 Multiple Choices">Section&nbsp;9.3.1</a>: Multiple Choices
658       | "301"  ; <a href="#status.301" id="rfc.xref.status.301.1" title="301 Moved Permanently">Section&nbsp;9.3.2</a>: Moved Permanently
659       | "302"  ; <a href="#status.302" id="rfc.xref.status.302.1" title="302 Found">Section&nbsp;9.3.3</a>: Found
660       | "303"  ; <a href="#status.303" id="rfc.xref.status.303.1" title="303 See Other">Section&nbsp;9.3.4</a>: See Other
661       | "304"  ; <a href="#status.304" id="rfc.xref.status.304.1" title="304 Not Modified">Section&nbsp;9.3.5</a>: Not Modified
662       | "305"  ; <a href="#status.305" id="rfc.xref.status.305.1" title="305 Use Proxy">Section&nbsp;9.3.6</a>: Use Proxy
663       | "307"  ; <a href="#status.307" id="rfc.xref.status.307.1" title="307 Temporary Redirect">Section&nbsp;9.3.8</a>: Temporary Redirect
664       | "400"  ; <a href="#status.400" id="rfc.xref.status.400.1" title="400 Bad Request">Section&nbsp;9.4.1</a>: Bad Request
665       | "401"  ; <a href="#status.401" id="rfc.xref.status.401.1" title="401 Unauthorized">Section&nbsp;9.4.2</a>: Unauthorized
666       | "402"  ; <a href="#status.402" id="rfc.xref.status.402.1" title="402 Payment Required">Section&nbsp;9.4.3</a>: Payment Required
667       | "403"  ; <a href="#status.403" id="rfc.xref.status.403.1" title="403 Forbidden">Section&nbsp;9.4.4</a>: Forbidden
668       | "404"  ; <a href="#status.404" id="rfc.xref.status.404.1" title="404 Not Found">Section&nbsp;9.4.5</a>: Not Found
669       | "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
670       | "406"  ; <a href="#status.406" id="rfc.xref.status.406.1" title="406 Not Acceptable">Section&nbsp;9.4.7</a>: Not Acceptable
671       | "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
672       | "408"  ; <a href="#status.408" id="rfc.xref.status.408.1" title="408 Request Timeout">Section&nbsp;9.4.9</a>: Request Time-out
673       | "409"  ; <a href="#status.409" id="rfc.xref.status.409.1" title="409 Conflict">Section&nbsp;9.4.10</a>: Conflict
674       | "410"  ; <a href="#status.410" id="rfc.xref.status.410.1" title="410 Gone">Section&nbsp;9.4.11</a>: Gone
675       | "411"  ; <a href="#status.411" id="rfc.xref.status.411.1" title="411 Length Required">Section&nbsp;9.4.12</a>: Length Required
676       | "412"  ; <a href="#status.412" id="rfc.xref.status.412.1" title="412 Precondition Failed">Section&nbsp;9.4.13</a>: Precondition Failed
677       | "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
678       | "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
679       | "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
680       | "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
681       | "417"  ; <a href="#status.417" id="rfc.xref.status.417.1" title="417 Expectation Failed">Section&nbsp;9.4.18</a>: Expectation Failed
682       | "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
683       | "501"  ; <a href="#status.501" id="rfc.xref.status.501.1" title="501 Not Implemented">Section&nbsp;9.5.2</a>: Not Implemented
684       | "502"  ; <a href="#status.502" id="rfc.xref.status.502.1" title="502 Bad Gateway">Section&nbsp;9.5.3</a>: Bad Gateway
685       | "503"  ; <a href="#status.503" id="rfc.xref.status.503.1" title="503 Service Unavailable">Section&nbsp;9.5.4</a>: Service Unavailable
686       | "504"  ; <a href="#status.504" id="rfc.xref.status.504.1" title="504 Gateway Timeout">Section&nbsp;9.5.5</a>: Gateway Time-out
687       | "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
688       | extension-code
689
690   extension-code = 3DIGIT
691   Reason-Phrase  = *&lt;TEXT, excluding CR, LF&gt;
692</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,
693         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
694         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
695         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
696         which will explain the unusual status.
697      </p>
698      <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>
699      <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
700         Status-Line. These header fields give information about the server and about further access to the resource identified by
701         the Request-URI.
702      </p>
703      <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>
704                    | 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>
705                    | 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>
706                    | Location                ; <a href="#header.location" id="rfc.xref.header.location.1" title="Location">Section&nbsp;10.4</a>
707                    | 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>
708                    | Retry-After             ; <a href="#header.retry-after" id="rfc.xref.header.retry-after.1" title="Retry-After">Section&nbsp;10.7</a>
709                    | Server                  ; <a href="#header.server" id="rfc.xref.header.server.1" title="Server">Section&nbsp;10.8</a>
710                    | 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>
711                    | 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>
712</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
713         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
714         fields. Unrecognized header fields are treated as entity-header fields.
715      </p>
716      <h1 id="rfc.section.7"><a href="#rfc.section.7">7.</a>&nbsp;<a id="entity" href="#entity">Entity</a></h1>
717      <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
718         fields and an entity-body, although some responses will only include the entity-headers. HTTP entity-body and entity-header
719         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>.
720      </p>
721      <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
722         safe and proper transfer of the message.
723      </p>
724      <h1 id="rfc.section.8"><a href="#rfc.section.8">8.</a>&nbsp;<a id="method.definitions" href="#method.definitions">Method Definitions</a></h1>
725      <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
726         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.
727      </p>
728      <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>
729      <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>
730      <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
731         careful to allow the user to be aware of any actions they might take which may have an unexpected significance to themselves
732         or others.
733      </p>
734      <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
735         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
736         that a possibly unsafe action is being requested.
737      </p>
738      <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;
739         in fact, some dynamic resources consider that a feature. The important distinction here is that the user did not request the
740         side-effects, so therefore cannot be held accountable for them.
741      </p>
742      <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>
743      <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
744         &gt; 0 identical requests is the same as for a single request. The methods GET, HEAD, PUT and DELETE share this property. Also,
745         the methods OPTIONS and TRACE <em class="bcp14">SHOULD NOT</em> have side effects, and so are inherently idempotent.
746      </p>
747      <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
748         sequence are idempotent. (A sequence is idempotent if a single execution of the entire sequence always yields a result that
749         is not changed by a reexecution of all, or part, of that sequence.) For example, a sequence is non-idempotent if its result
750         depends on a value that is later modified in the same sequence.
751      </p>
752      <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
753         on the same set of resources).
754      </p>
755      <div id="rfc.iref.o.1"></div>
756      <div id="rfc.iref.m.1"></div>
757      <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a id="OPTIONS" href="#OPTIONS">OPTIONS</a></h2>
758      <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
759         chain identified by the Request-URI. This method allows the client to determine the options and/or requirements associated
760         with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
761      </p>
762      <p id="rfc.section.8.2.p.2">Responses to this method are not cacheable.</p>
763      <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
764         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
765         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.
766      </p>
767      <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
768         a specific resource. Since a server's communication options typically depend on the resource, the "*" request is only useful
769         as a "ping" or "no-op" type of method; it does nothing beyond allowing the client to test the capabilities of the server.
770         For example, this can be used to test a proxy for HTTP/1.1 compliance (or lack thereof).
771      </p>
772      <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
773         with that resource.
774      </p>
775      <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.,
776         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,
777         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".
778      </p>
779      <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
780         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
781         request <em class="bcp14">MUST NOT</em> include a Max-Forwards field.
782      </p>
783      <div id="rfc.iref.g.10"></div>
784      <div id="rfc.iref.m.2"></div>
785      <h2 id="rfc.section.8.3"><a href="#rfc.section.8.3">8.3</a>&nbsp;<a id="GET" href="#GET">GET</a></h2>
786      <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
787         refers to a data-producing process, it is the produced data which shall be returned as the entity in the response and not
788         the source text of the process, unless that text happens to be the output of the process.
789      </p>
790      <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,
791         If-Match, If-None-Match, or If-Range header field. A conditional GET method requests that the entity be transferred only under
792         the circumstances described by the conditional header field(s). The conditional GET method is intended to reduce unnecessary
793         network usage by allowing cached entities to be refreshed without requiring multiple requests or transferring data already
794         held by the client.
795      </p>
796      <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
797         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
798         without transferring data already held by the client.
799      </p>
800      <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>.
801      </p>
802      <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.
803      </p>
804      <div id="rfc.iref.h.1"></div>
805      <div id="rfc.iref.m.3"></div>
806      <h2 id="rfc.section.8.4"><a href="#rfc.section.8.4">8.4</a>&nbsp;<a id="HEAD" href="#HEAD">HEAD</a></h2>
807      <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
808         the entity implied by the request without transferring the entity-body itself. This method is often used for testing hypertext
809         links for validity, accessibility, and recent modification.
810      </p>
811      <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
812         from the current entity (as would be indicated by a change in Content-Length, Content-MD5, ETag or Last-Modified), then the
813         cache <em class="bcp14">MUST</em> treat the cache entry as stale.
814      </p>
815      <div id="rfc.iref.p.1"></div>
816      <div id="rfc.iref.m.4"></div>
817      <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a>&nbsp;<a id="POST" href="#POST">POST</a></h2>
818      <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 a new subordinate of
819         the resource identified by the Request-URI in the Request-Line. POST is designed to allow a uniform method to cover the following
820         functions:
821      </p>
822      <ul>
823         <li>Annotation of existing resources;</li>
824         <li>Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles;</li>
825         <li>Providing a block of data, such as the result of submitting a form, to a data-handling process;</li>
826         <li>Extending a database through an append operation.</li>
827      </ul>
828      <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.
829         The posted entity is subordinate to that URI in the same way that a file is subordinate to a directory containing it, a news
830         article is subordinate to a newsgroup to which it is posted, or a record is subordinate to a database.
831      </p>
832      <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
833         200 (OK) or 204 (No Content) is the appropriate response status, depending on whether or not the response includes an entity
834         that describes the result.
835      </p>
836      <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
837         header (see <a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section&nbsp;10.4</a>).
838      </p>
839      <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.
840         However, the 303 (See Other) response can be used to direct the user agent to retrieve a cacheable resource.
841      </p>
842      <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>.
843      </p>
844      <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.
845      </p>
846      <div id="rfc.iref.p.2"></div>
847      <div id="rfc.iref.m.5"></div>
848      <h2 id="rfc.section.8.6"><a href="#rfc.section.8.6">8.6</a>&nbsp;<a id="PUT" href="#PUT">PUT</a></h2>
849      <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
850         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
851         resource, and that URI is capable of being defined as a new resource by the requesting user agent, the origin server can create
852         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
853         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,
854         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.
855      </p>
856      <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.
857      </p>
858      <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
859         URI in a POST request identifies the resource that will handle the enclosed entity. That resource might be a data-accepting
860         process, a gateway to some other protocol, or a separate entity that accepts annotations. In contrast, the URI in a PUT request
861         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,
862         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.
863      </p>
864      <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
865         is separate from the URI identifying each particular version. In this case, a PUT request on a general URI might result in
866         several other URIs being defined by the origin server.
867      </p>
868      <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>
869      <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>.
870      </p>
871      <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.
872      </p>
873      <div id="rfc.iref.d.1"></div>
874      <div id="rfc.iref.m.6"></div>
875      <h2 id="rfc.section.8.7"><a href="#rfc.section.8.7">8.7</a>&nbsp;<a id="DELETE" href="#DELETE">DELETE</a></h2>
876      <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
877         has been carried out, even if the status code returned from the origin server indicates that the action has been completed
878         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
879         location.
880      </p>
881      <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,
882         or 204 (No Content) if the action has been enacted but the response does not include an entity.
883      </p>
884      <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.
885      </p>
886      <div id="rfc.iref.t.1"></div>
887      <div id="rfc.iref.m.7"></div>
888      <h2 id="rfc.section.8.8"><a href="#rfc.section.8.8">8.8</a>&nbsp;<a id="TRACE" href="#TRACE">TRACE</a></h2>
889      <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
890         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
891         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.
892      </p>
893      <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
894         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
895         client to limit the length of the request chain, which is useful for testing a chain of proxies forwarding messages in an
896         infinite loop.
897      </p>
898      <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.
899      </p>
900      <div id="rfc.iref.c.1"></div>
901      <div id="rfc.iref.m.8"></div>
902      <h2 id="rfc.section.8.9"><a href="#rfc.section.8.9">8.9</a>&nbsp;<a id="CONNECT" href="#CONNECT">CONNECT</a></h2>
903      <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.
904         SSL tunneling <a href="#Luo1998" id="rfc.xref.Luo1998.1"><cite title="Tunneling TCP based protocols through Web proxy servers">[Luo1998]</cite></a>).
905      </p>
906      <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>
907      <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
908         in the response.
909      </p>
910      <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>
911      <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
912         terminated by an empty line. There are no required headers for this class of status code. Since HTTP/1.0 did not define any
913         1xx status codes, servers <em class="bcp14">MUST NOT</em> send a 1xx response to an HTTP/1.0 client except under experimental conditions.
914      </p>
915      <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
916         (Continue) status message. Unexpected 1xx status responses <em class="bcp14">MAY</em> be ignored by a user agent.
917      </p>
918      <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
919         requested the generation of the 1xx response. (For example, if a proxy adds a "Expect: 100-continue" field when it forwards
920         a request, then it need not forward the corresponding 100 (Continue) response(s).)
921      </p>
922      <div id="rfc.iref.25"></div>
923      <div id="rfc.iref.s.1"></div>
924      <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>
925      <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
926         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
927         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.
928      </p>
929      <div id="rfc.iref.26"></div>
930      <div id="rfc.iref.s.2"></div>
931      <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>
932      <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
933         by the response's Upgrade header field immediately after the empty line which terminates the 101 response.
934      </p>
935      <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
936         older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use
937         such features.
938      </p>
939      <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>
940      <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>
941      <div id="rfc.iref.27"></div>
942      <div id="rfc.iref.s.3"></div>
943      <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>
944      <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
945         example:
946      </p>
947      <dl>
948         <dt>GET</dt>
949         <dd>an entity corresponding to the requested resource is sent in the response;</dd>
950         <dt>HEAD</dt>
951         <dd>the entity-header fields corresponding to the requested resource are sent in the response without any message-body;</dd>
952         <dt>POST</dt>
953         <dd>an entity describing or containing the result of the action;</dd>
954         <dt>TRACE</dt>
955         <dd>an entity containing the request message as received by the end server.</dd>
956      </dl>
957      <div id="rfc.iref.28"></div>
958      <div id="rfc.iref.s.4"></div>
959      <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>
960      <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
961         by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header
962         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
963         the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. The origin
964         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.
965      </p>
966      <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,
967         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>.
968      </p>
969      <div id="rfc.iref.29"></div>
970      <div id="rfc.iref.s.5"></div>
971      <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>
972      <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
973         be acted upon, as it might be disallowed when processing actually takes place. There is no facility for re-sending a status
974         code from an asynchronous operation such as this.
975      </p>
976      <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
977         (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the
978         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
979         user can expect the request to be fulfilled.
980      </p>
981      <div id="rfc.iref.30"></div>
982      <div id="rfc.iref.s.6"></div>
983      <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>
984      <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
985         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
986         result in a superset of the metainformation known by the origin server. Use of this response code is not required and is only
987         appropriate when the response would otherwise be 200 (OK).
988      </p>
989      <div id="rfc.iref.31"></div>
990      <div id="rfc.iref.s.7"></div>
991      <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>
992      <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.
993         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.
994      </p>
995      <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
996         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.
997      </p>
998      <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.
999      </p>
1000      <div id="rfc.iref.32"></div>
1001      <div id="rfc.iref.s.8"></div>
1002      <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>
1003      <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
1004         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
1005         another input action. The response <em class="bcp14">MUST NOT</em> include an entity.
1006      </p>
1007      <div id="rfc.iref.33"></div>
1008      <div id="rfc.iref.s.9"></div>
1009      <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>
1010      <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
1011         in <a href="#Part5" id="rfc.xref.Part5.6"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>.
1012      </p>
1013      <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>
1014      <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.
1015         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
1016         GET or HEAD. A client <em class="bcp14">SHOULD</em> detect infinite redirection loops, since such loops generate network traffic for each redirection.
1017      </p>
1018      <ul class="empty">
1019         <li> <b>Note:</b> previous versions of this specification recommended a maximum of five redirections. Content developers should be aware that
1020            there might be clients that implement such a fixed limitation.
1021         </li>
1022      </ul>
1023      <div id="rfc.iref.34"></div>
1024      <div id="rfc.iref.s.10"></div>
1025      <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>
1026      <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
1027         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
1028         location.
1029      </p>
1030      <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
1031         the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. Depending
1032         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.
1033      </p>
1034      <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.
1035      </p>
1036      <div id="rfc.iref.35"></div>
1037      <div id="rfc.iref.s.11"></div>
1038      <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>
1039      <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
1040         to one or more of the new references returned by the server, where possible. This response is cacheable unless indicated otherwise.
1041      </p>
1042      <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).
1043      </p>
1044      <p id="rfc.section.9.3.2.p.3">If the 301 status code is received in response to a request other than GET or HEAD, 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
1045         the request was issued.
1046      </p>
1047      <ul class="empty">
1048         <li> <b>Note:</b> When automatically redirecting a POST request after receiving a 301 status code, some existing HTTP/1.0 user agents will erroneously
1049            change it into a GET request.
1050         </li>
1051      </ul>
1052      <div id="rfc.iref.36"></div>
1053      <div id="rfc.iref.s.12"></div>
1054      <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>
1055      <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
1056         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
1057         header field.
1058      </p>
1059      <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).
1060      </p>
1061      <p id="rfc.section.9.3.3.p.3">If the 302 status code is received in response to a request other than GET or HEAD, 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
1062         the request was issued.
1063      </p>
1064      <ul class="empty">
1065         <li> <b>Note:</b> RFC 1945 and RFC 2068 specify that the client is not allowed to change the method on the redirected request. However, most
1066            existing user agent implementations treat 302 as if it were a 303 response, performing a GET on the Location field-value regardless
1067            of the original request method. The status codes 303 and 307 have been added for servers that wish to make unambiguously clear
1068            which kind of reaction is expected of the client.
1069         </li>
1070      </ul>
1071      <div id="rfc.iref.37"></div>
1072      <div id="rfc.iref.s.13"></div>
1073      <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>
1074      <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
1075         to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested
1076         resource. The 303 response <em class="bcp14">MUST NOT</em> be cached, but the response to the second (redirected) request might be cacheable.
1077      </p>
1078      <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).
1079      </p>
1080      <ul class="empty">
1081         <li> <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
1082            302 status code may be used instead, since most user agents react to a 302 response as described here for 303.
1083         </li>
1084      </ul>
1085      <div id="rfc.iref.38"></div>
1086      <div id="rfc.iref.s.14"></div>
1087      <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>
1088      <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,
1089         as defined in <a href="#Part4" id="rfc.xref.Part4.7"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>.
1090      </p>
1091      <div id="rfc.iref.39"></div>
1092      <div id="rfc.iref.s.15"></div>
1093      <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>
1094      <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
1095         expected to repeat this single request via the proxy. 305 responses <em class="bcp14">MUST</em> only be generated by origin servers.
1096      </p>
1097      <ul class="empty">
1098         <li> <b>Note:</b> RFC 2068 was not clear that 305 was intended to redirect a single request, and to be generated by origin servers only. Not
1099            observing these limitations has significant security consequences.
1100         </li>
1101      </ul>
1102      <div id="rfc.iref.40"></div>
1103      <div id="rfc.iref.s.16"></div>
1104      <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>
1105      <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>
1106      <div id="rfc.iref.41"></div>
1107      <div id="rfc.iref.s.17"></div>
1108      <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>
1109      <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
1110         header field.
1111      </p>
1112      <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
1113         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.
1114      </p>
1115      <p id="rfc.section.9.3.8.p.3">If the 307 status code is received in response to a request other than GET or HEAD, 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
1116         the request was issued.
1117      </p>
1118      <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>
1119      <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
1120         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.
1121         These status codes are applicable to any request method. User agents <em class="bcp14">SHOULD</em> display any included entity to the user.
1122      </p>
1123      <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
1124         the input connection. If the client continues sending data to the server after the close, the server's TCP stack will send
1125         a reset packet to the client, which may erase the client's unacknowledged input buffers before they can be read and interpreted
1126         by the HTTP application.
1127      </p>
1128      <div id="rfc.iref.42"></div>
1129      <div id="rfc.iref.s.18"></div>
1130      <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>
1131      <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.
1132      </p>
1133      <div id="rfc.iref.43"></div>
1134      <div id="rfc.iref.s.19"></div>
1135      <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>
1136      <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>).
1137      </p>
1138      <div id="rfc.iref.44"></div>
1139      <div id="rfc.iref.s.20"></div>
1140      <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>
1141      <p id="rfc.section.9.4.3.p.1">This code is reserved for future use.</p>
1142      <div id="rfc.iref.45"></div>
1143      <div id="rfc.iref.s.21"></div>
1144      <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>
1145      <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,
1146         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,
1147         the status code 404 (Not Found) can be used instead.
1148      </p>
1149      <div id="rfc.iref.46"></div>
1150      <div id="rfc.iref.s.22"></div>
1151      <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>
1152      <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
1153         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
1154         and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request
1155         has been refused, or when no other response is applicable.
1156      </p>
1157      <div id="rfc.iref.47"></div>
1158      <div id="rfc.iref.s.23"></div>
1159      <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>
1160      <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.
1161      </p>
1162      <div id="rfc.iref.48"></div>
1163      <div id="rfc.iref.s.24"></div>
1164      <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>
1165      <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
1166         not acceptable according to the accept headers sent in the request.
1167      </p>
1168      <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
1169         can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field.
1170         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.
1171      </p>
1172      <ul class="empty">
1173         <li> <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.
1174            In some cases, this may even be preferable to sending a 406 response. User agents are encouraged to inspect the headers of
1175            an incoming response to determine if it is acceptable.
1176         </li>
1177      </ul>
1178      <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.
1179      </p>
1180      <div id="rfc.iref.49"></div>
1181      <div id="rfc.iref.s.25"></div>
1182      <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>
1183      <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>).
1184      </p>
1185      <div id="rfc.iref.50"></div>
1186      <div id="rfc.iref.s.26"></div>
1187      <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>
1188      <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.
1189      </p>
1190      <div id="rfc.iref.51"></div>
1191      <div id="rfc.iref.s.27"></div>
1192      <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>
1193      <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
1194         situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response
1195         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
1196         enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.
1197      </p>
1198      <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
1199         being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might
1200         use the 409 response to indicate that it can't complete the request. In this case, the response entity would likely contain
1201         a list of the differences between the two versions in a format defined by the response Content-Type.
1202      </p>
1203      <div id="rfc.iref.52"></div>
1204      <div id="rfc.iref.s.28"></div>
1205      <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>
1206      <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
1207         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
1208         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.
1209      </p>
1210      <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
1211         is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event
1212         is common for limited-time, promotional services and for resources belonging to individuals no longer working at the server's
1213         site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time
1214         -- that is left to the discretion of the server owner.
1215      </p>
1216      <div id="rfc.iref.53"></div>
1217      <div id="rfc.iref.s.29"></div>
1218      <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>
1219      <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
1220         message.
1221      </p>
1222      <div id="rfc.iref.54"></div>
1223      <div id="rfc.iref.s.30"></div>
1224      <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>
1225      <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
1226         defined in <a href="#Part4" id="rfc.xref.Part4.8"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>.
1227      </p>
1228      <div id="rfc.iref.55"></div>
1229      <div id="rfc.iref.s.31"></div>
1230      <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>
1231      <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.
1232         The server <em class="bcp14">MAY</em> close the connection to prevent the client from continuing the request.
1233      </p>
1234      <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.
1235      </p>
1236      <div id="rfc.iref.56"></div>
1237      <div id="rfc.iref.s.32"></div>
1238      <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>
1239      <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
1240         rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query
1241         information, when the client has descended into a URI "black hole" of redirection (e.g., a redirected URI prefix that points
1242         to a suffix of itself), or when the server is under attack by a client attempting to exploit security holes present in some
1243         servers using fixed-length buffers for reading or manipulating the Request-URI.
1244      </p>
1245      <div id="rfc.iref.57"></div>
1246      <div id="rfc.iref.s.33"></div>
1247      <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>
1248      <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
1249         resource for the requested method.
1250      </p>
1251      <div id="rfc.iref.58"></div>
1252      <div id="rfc.iref.s.34"></div>
1253      <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>
1254      <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.
1255      </p>
1256      <div id="rfc.iref.59"></div>
1257      <div id="rfc.iref.s.35"></div>
1258      <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>
1259      <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
1260         not be met by the next-hop server.
1261      </p>
1262      <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>
1263      <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
1264         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.
1265         User agents <em class="bcp14">SHOULD</em> display any included entity to the user. These response codes are applicable to any request method.
1266      </p>
1267      <div id="rfc.iref.60"></div>
1268      <div id="rfc.iref.s.36"></div>
1269      <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>
1270      <p id="rfc.section.9.5.1.p.1">The server encountered an unexpected condition which prevented it from fulfilling the request.</p>
1271      <div id="rfc.iref.61"></div>
1272      <div id="rfc.iref.s.37"></div>
1273      <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>
1274      <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
1275         does not recognize the request method and is not capable of supporting it for any resource.
1276      </p>
1277      <div id="rfc.iref.62"></div>
1278      <div id="rfc.iref.s.38"></div>
1279      <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>
1280      <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
1281         to fulfill the request.
1282      </p>
1283      <div id="rfc.iref.63"></div>
1284      <div id="rfc.iref.s.39"></div>
1285      <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>
1286      <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
1287         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.
1288      </p>
1289      <ul class="empty">
1290         <li> <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
1291            to simply refuse the connection.
1292         </li>
1293      </ul>
1294      <div id="rfc.iref.64"></div>
1295      <div id="rfc.iref.s.40"></div>
1296      <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>
1297      <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
1298         URI (e.g. HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed to access in attempting to complete the request.
1299      </p>
1300      <ul class="empty">
1301         <li> <b>Note:</b> Note to implementors: some deployed proxies are known to return 400 or 500 when DNS lookups time out.
1302         </li>
1303      </ul>
1304      <div id="rfc.iref.65"></div>
1305      <div id="rfc.iref.s.41"></div>
1306      <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>
1307      <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
1308         is indicating that it is unable or unwilling to complete the request using the same major version as the client, as described
1309         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.
1310      </p>
1311      <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>
1312      <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
1313         and recipient refer to either the client or the server, depending on who sends and who receives the entity.
1314      </p>
1315      <div id="rfc.iref.a.1"></div>
1316      <div id="rfc.iref.h.2"></div>
1317      <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>
1318      <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
1319         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.
1320      </p>
1321      <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.11"></span>       Allow   = "Allow" ":" #Method
1322</pre><p id="rfc.section.10.1.p.3">Example of use:</p>
1323      <div id="rfc.figure.u.8"></div><pre class="text">       Allow: GET, HEAD, PUT
1324</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.
1325      </p>
1326      <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
1327         required to support these methods and <em class="bcp14">SHOULD</em> include an Allow header in the response giving the actual supported methods.
1328      </p>
1329      <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
1330         means of communicating with the origin server.
1331      </p>
1332      <div id="rfc.iref.e.1"></div>
1333      <div id="rfc.iref.h.3"></div>
1334      <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>
1335      <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>
1336      <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
1337
1338   expectation  =  "100-continue" | expectation-extension
1339   expectation-extension =  token [ "=" ( token | quoted-string )
1340                            *expect-params ]
1341   expect-params =  ";" token [ "=" ( token | quoted-string ) ]
1342</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
1343         the request, some other 4xx status.
1344      </p>
1345      <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
1346         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.
1347      </p>
1348      <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
1349         for quoted-string expectation-extensions.
1350      </p>
1351      <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
1352         request-header itself is end-to-end; it <em class="bcp14">MUST</em> be forwarded if the request is forwarded.
1353      </p>
1354      <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>
1355      <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.
1356      </p>
1357      <div id="rfc.iref.f.1"></div>
1358      <div id="rfc.iref.h.4"></div>
1359      <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>
1360      <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 RFC 822 <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 RFC 1123 <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a>:
1361      </p>
1362      <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.16"></span>    From   = "From" ":" mailbox
1363</pre><p id="rfc.section.10.3.p.3">An example is:</p>
1364      <div id="rfc.figure.u.11"></div><pre class="text">    From: webmaster@w3.org
1365</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
1366         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
1367         end.
1368      </p>
1369      <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
1370         issuer's address <em class="bcp14">SHOULD</em> be used.
1371      </p>
1372      <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
1373         security policy. It is strongly recommended that the user be able to disable, enable, and modify the value of this field at
1374         any time prior to a request.
1375      </p>
1376      <div id="rfc.iref.l.1"></div>
1377      <div id="rfc.iref.h.5"></div>
1378      <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>
1379      <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
1380         of the request or identification of a new resource. For 201 (Created) responses, the Location is that of the new resource
1381         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
1382         URI.
1383      </p>
1384      <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.17"></span>    Location       = "Location" ":" absoluteURI
1385</pre><p id="rfc.section.10.4.p.3">An example is:</p>
1386      <div id="rfc.figure.u.13"></div><pre class="text">    Location: http://www.w3.org/pub/WWW/People.html
1387</pre><p id="rfc.section.10.4.p.5"> </p>
1388      <ul class="empty">
1389         <li> <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.
1390            It is therefore possible for a response to contain header fields for both Location and Content-Location.
1391         </li>
1392      </ul>
1393      <div id="rfc.iref.m.9"></div>
1394      <div id="rfc.iref.h.6"></div>
1395      <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>
1396      <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
1397         useful when the client is attempting to trace a request chain which appears to be failing or looping in mid-chain.
1398      </p>
1399      <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.18"></span>    Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
1400</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>
1401      <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).
1402      </p>
1403      <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
1404         referred to as part of that method definition.
1405      </p>
1406      <div id="rfc.iref.r.1"></div>
1407      <div id="rfc.iref.h.7"></div>
1408      <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>
1409      <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
1410         from which the Request-URI was obtained (the "referrer", although the header field is misspelled.) The Referer request-header
1411         allows a server to generate lists of back-links to resources for interest, logging, optimized caching, etc. It also allows
1412         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.
1413      </p>
1414      <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.19"></span>    Referer        = "Referer" ":" ( absoluteURI | relativeURI )
1415</pre><p id="rfc.section.10.6.p.3">Example:</p>
1416      <div id="rfc.figure.u.16"></div><pre class="text">    Referer: http://www.w3.org/hypertext/DataSources/Overview.html
1417</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.
1418      </p>
1419      <div id="rfc.iref.r.2"></div>
1420      <div id="rfc.iref.h.8"></div>
1421      <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>
1422      <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
1423         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
1424         the redirected request. The value of this field can be either an HTTP-date or an integer number of seconds (in decimal) after
1425         the time of the response.
1426      </p>
1427      <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 )
1428</pre><p id="rfc.section.10.7.p.3">Two examples of its use are</p>
1429      <div id="rfc.figure.u.18"></div><pre class="text">    Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
1430    Retry-After: 120
1431</pre><p id="rfc.section.10.7.p.5">In the latter example, the delay is 2 minutes.</p>
1432      <div id="rfc.iref.s.42"></div>
1433      <div id="rfc.iref.h.9"></div>
1434      <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>
1435      <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.
1436         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
1437         for identifying the application.
1438      </p>
1439      <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.21"></span>    Server         = "Server" ":" 1*( product | comment )
1440</pre><p id="rfc.section.10.8.p.3">Example:</p>
1441      <div id="rfc.figure.u.20"></div><pre class="text">    Server: CERN/3.0 libwww/2.17
1442</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">SHOULD</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>).
1443      </p>
1444      <ul class="empty">
1445         <li> <b>Note:</b> Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks
1446            against software that is known to contain security holes. Server implementors are encouraged to make this field a configurable
1447            option.
1448         </li>
1449      </ul>
1450      <div id="rfc.iref.u.1"></div>
1451      <div id="rfc.iref.h.10"></div>
1452      <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>
1453      <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
1454         purposes, the tracing of protocol violations, and automated recognition of user agents for the sake of tailoring responses
1455         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
1456         product tokens are listed in order of their significance for identifying the application.
1457      </p>
1458      <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.22"></span>    User-Agent     = "User-Agent" ":" 1*( product | comment )
1459</pre><p id="rfc.section.10.9.p.3">Example:</p>
1460      <div id="rfc.figure.u.22"></div><pre class="text">    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1461</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>
1462      <p id="rfc.section.11.p.1">TBD.</p>
1463      <h1 id="rfc.section.12"><a href="#rfc.section.12">12.</a>&nbsp;<a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>
1464      <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
1465         as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does
1466         make some suggestions for reducing security risks.
1467      </p>
1468      <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>
1469      <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
1470         a priori method of determining the sensitivity of any particular piece of information within the context of any given request.
1471         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
1472         special mention in this context: Server, Via, Referer and From.
1473      </p>
1474      <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
1475         against software that is known to contain security holes. Implementors <em class="bcp14">SHOULD</em> make the Server header field a configurable option.
1476      </p>
1477      <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,
1478         they <em class="bcp14">SHOULD</em> remove, or replace with sanitized versions, any Via fields generated behind the firewall.
1479      </p>
1480      <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
1481         can be abused if user details are not separated from the information contained in the Referer. Even when the personal information
1482         has been removed, the Referer header might indicate a private document's URI whose publication would be inappropriate.
1483      </p>
1484      <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
1485         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.
1486      </p>
1487      <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
1488         of From and Referer information.
1489      </p>
1490      <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
1491         might be exploited. Unfortunately, this same information is often used for other valuable purposes for which HTTP currently
1492         has no better mechanism.
1493      </p>
1494      <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>
1495      <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
1496         recommended that the user be able to select whether or not the Referer field is sent. For example, a browser client could
1497         have a toggle switch for browsing openly/anonymously, which would respectively enable/disable the sending of Referer and From
1498         information.
1499      </p>
1500      <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.
1501      </p>
1502      <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.
1503         Many existing servers, proxies, and user agents will log the request URI in some place where it might be visible to third
1504         parties. Servers can use POST-based form submission instead
1505      </p>
1506      <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>
1507      <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
1508         to make sure that they do not attempt to invalidate resources over which they have no authority.
1509      </p>
1510      <h1 id="rfc.section.13"><a href="#rfc.section.13">13.</a>&nbsp;<a id="ack" href="#ack">Acknowledgments</a></h1>
1511      <p id="rfc.section.13.p.1">Based on an XML translation of RFC 2616 by Julian Reschke.</p>
1512      <h1 id="rfc.references"><a href="#rfc.section.14" id="rfc.section.14">14.</a> References
1513      </h1>
1514      <table>                     
1515         <tr>
1516            <td class="reference"><b id="Luo1998">[Luo1998]</b></td>
1517            <td class="top">Luotonen, A., “Tunneling TCP based protocols through Web proxy servers”, &nbsp;Work in Progress.</td>
1518         </tr>
1519         <tr>
1520            <td class="reference"><b id="Part1">[Part1]</b></td>
1521            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p1-messaging-00">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p1-messaging-00 (work in progress), December&nbsp;2007.
1522            </td>
1523         </tr>
1524         <tr>
1525            <td class="reference"><b id="Part3">[Part3]</b></td>
1526            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p3-payload-00">HTTP/1.1, part 3: Message Payload and Content Negotiation</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p3-payload-00 (work in progress), December&nbsp;2007.
1527            </td>
1528         </tr>
1529         <tr>
1530            <td class="reference"><b id="Part4">[Part4]</b></td>
1531            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-00">HTTP/1.1, part 4: Conditional Requests</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p4-conditional-00 (work in progress), December&nbsp;2007.
1532            </td>
1533         </tr>
1534         <tr>
1535            <td class="reference"><b id="Part5">[Part5]</b></td>
1536            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-00">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p5-range-00 (work in progress), December&nbsp;2007.
1537            </td>
1538         </tr>
1539         <tr>
1540            <td class="reference"><b id="Part6">[Part6]</b></td>
1541            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-00">HTTP/1.1, part 6: Caching</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p6-cache-00 (work in progress), December&nbsp;2007.
1542            </td>
1543         </tr>
1544         <tr>
1545            <td class="reference"><b id="Part7">[Part7]</b></td>
1546            <td class="top"><a href="mailto:fielding@gbiv.com" title="Day Software">Fielding, R., Ed.</a>, <a href="mailto:jg@laptop.org" title="One Laptop per Child">Gettys, J.</a>, <a href="mailto:JeffMogul@acm.org" title="Hewlett-Packard Company">Mogul, J.</a>, <a href="mailto:henrikn@microsoft.com" title="Microsoft Corporation">Frystyk, H.</a>, <a href="mailto:LMM@acm.org" title="Adobe Systems, Incorporated">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" title="World Wide Web Consortium">T. Berners-Lee</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p7-auth-00">HTTP/1.1, part 7: Authentication</a>”, Internet-Draft&nbsp;draft-ietf-httpbis-p7-auth-00 (work in progress), December&nbsp;2007.
1547            </td>
1548         </tr>
1549         <tr>
1550            <td class="reference"><b id="RFC1123">[RFC1123]</b></td>
1551            <td class="top"><a href="mailto:Braden@ISI.EDU" 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.
1552            </td>
1553         </tr>
1554         <tr>
1555            <td class="reference"><b id="RFC2068">[RFC2068]</b></td>
1556            <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine, Department of Information and Computer Science">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="MIT Laboratory for Computer Science">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Digital Equipment Corporation, Western Research Laboratory">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Nielsen, H.</a>, and <a href="mailto:timbl@w3.org" 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.
1557            </td>
1558         </tr>
1559         <tr>
1560            <td class="reference"><b id="RFC2616">[RFC2616]</b></td>
1561            <td class="top"><a href="mailto:fielding@ics.uci.edu" title="University of California, Irvine">Fielding, R.</a>, <a href="mailto:jg@w3.org" title="W3C">Gettys, J.</a>, <a href="mailto:mogul@wrl.dec.com" title="Compaq Computer Corporation">Mogul, J.</a>, <a href="mailto:frystyk@w3.org" title="MIT Laboratory for Computer Science">Frystyk, H.</a>, <a href="mailto:masinter@parc.xerox.com" title="Xerox Corporation">Masinter, L.</a>, <a href="mailto:paulle@microsoft.com" title="Microsoft Corporation">Leach, P.</a>, and <a href="mailto:timbl@w3.org" 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.
1562            </td>
1563         </tr>
1564         <tr>
1565            <td class="reference"><b id="RFC822">[RFC822]</b></td>
1566            <td class="top"><a href="mailto:DCrocker@UDel-Relay" title="University of Delaware, Dept. of Electrical Engineering">Crocker, D.</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.
1567            </td>
1568         </tr>
1569      </table>
1570      <div class="avoidbreak">
1571         <h1 id="rfc.authors"><a href="#rfc.authors">Authors' Addresses</a></h1>
1572         <address class="vcard"><span class="vcardline"><span class="fn">Roy T. Fielding</span>
1573               (editor)
1574               <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 href="mailto:fielding@gbiv.com"><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>
1575         <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 href="mailto:jg@laptop.org"><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>
1576         <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 href="mailto:JeffMogul@acm.org"><span class="email">JeffMogul@acm.org</span></a></span></address>
1577         <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 href="mailto:henrikn@microsoft.com"><span class="email">henrikn@microsoft.com</span></a></span></address>
1578         <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 href="mailto:LMM@acm.org"><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>
1579         <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 href="mailto:paulle@microsoft.com"><span class="email">paulle@microsoft.com</span></a></span></address>
1580         <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 href="mailto:timbl@w3.org"><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>
1581      </div>
1582      <h1 id="rfc.section.A" class="np"><a href="#rfc.section.A">A.</a>&nbsp;<a id="changes.from.rfc.2068" href="#changes.from.rfc.2068">Changes from RFC 2068</a></h1>
1583      <p id="rfc.section.A.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>).
1584      </p>
1585      <p id="rfc.section.A.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>).
1586      </p>
1587      <p id="rfc.section.A.p.3">Rewrite of message transmission requirements to make it much harder for implementors to get it wrong, as the consequences
1588         of errors here can have significant impact on the Internet, and to deal with the following problems:
1589      </p>
1590      <ol>
1591         <li>Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where this was incorrectly placing a requirement on the behavior of
1592            an implementation of a future version of HTTP/1.x
1593         </li>
1594         <li>Made it clear that user-agents should retry requests, not "clients" in general.</li>
1595         <li>Converted requirements for clients to ignore unexpected 100 (Continue) responses, and for proxies to forward 100 responses,
1596            into a general requirement for 1xx responses.
1597         </li>
1598         <li>Modified some TCP-specific language, to make it clearer that non-TCP transports are possible for HTTP.</li>
1599         <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.
1600         </li>
1601         <li>Allow, rather than require, a server to omit 100 (Continue) if it has already seen some of the request body.</li>
1602         <li>Allow servers to defend against denial-of-service attacks and broken clients.</li>
1603      </ol>
1604      <p id="rfc.section.A.p.4">This change adds the Expect header and 417 status code.</p>
1605      <p id="rfc.section.A.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>)
1606      </p>
1607      <p id="rfc.section.A.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 RFC 2068 <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>.
1608      </p>
1609      <h1 id="rfc.index"><a href="#rfc.index">Index</a></h1>
1610      <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>
1611      </p>
1612      <div class="print2col">
1613         <ul class="ind">
1614            <li><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul>
1615                  <li>100 Continue (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.100.1">5</a>, <a href="#rfc.iref.25"><b>9.1.1</b></a></li>
1616                  <li>101 Switching Protocols (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.101.1">5</a>, <a href="#rfc.iref.26"><b>9.1.2</b></a></li>
1617               </ul>
1618            </li>
1619            <li><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul>
1620                  <li>200 OK (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.200.1">5</a>, <a href="#rfc.iref.27"><b>9.2.1</b></a></li>
1621                  <li>201 Created (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.201.1">5</a>, <a href="#rfc.iref.28"><b>9.2.2</b></a>, <a href="#rfc.xref.status.201.2">A</a></li>
1622                  <li>202 Accepted (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.202.1">5</a>, <a href="#rfc.iref.29"><b>9.2.3</b></a></li>
1623                  <li>203 Non-Authoritative Information (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.203.1">5</a>, <a href="#rfc.iref.30"><b>9.2.4</b></a></li>
1624                  <li>204 No Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.204.1">5</a>, <a href="#rfc.iref.31"><b>9.2.5</b></a></li>
1625                  <li>205 Reset Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.205.1">5</a>, <a href="#rfc.iref.32"><b>9.2.6</b></a></li>
1626                  <li>206 Partial Content (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.206.1">5</a>, <a href="#rfc.iref.33"><b>9.2.7</b></a></li>
1627               </ul>
1628            </li>
1629            <li><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul>
1630                  <li>300 Multiple Choices (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.300.1">5</a>, <a href="#rfc.iref.34"><b>9.3.1</b></a></li>
1631                  <li>301 Moved Permanently (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.301.1">5</a>, <a href="#rfc.iref.35"><b>9.3.2</b></a></li>
1632                  <li>302 Found (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.302.1">5</a>, <a href="#rfc.iref.36"><b>9.3.3</b></a></li>
1633                  <li>303 See Other (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.303.1">5</a>, <a href="#rfc.iref.37"><b>9.3.4</b></a></li>
1634                  <li>304 Not Modified (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.304.1">5</a>, <a href="#rfc.iref.38"><b>9.3.5</b></a></li>
1635                  <li>305 Use Proxy (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.305.1">5</a>, <a href="#rfc.iref.39"><b>9.3.6</b></a></li>
1636                  <li>306 (Unused) (status code)&nbsp;&nbsp;<a href="#rfc.iref.40"><b>9.3.7</b></a></li>
1637                  <li>307 Temporary Redirect (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.307.1">5</a>, <a href="#rfc.iref.41"><b>9.3.8</b></a></li>
1638               </ul>
1639            </li>
1640            <li><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul>
1641                  <li>400 Bad Request (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.400.1">5</a>, <a href="#rfc.iref.42"><b>9.4.1</b></a></li>
1642                  <li>401 Unauthorized (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.401.1">5</a>, <a href="#rfc.iref.43"><b>9.4.2</b></a></li>
1643                  <li>402 Payment Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.402.1">5</a>, <a href="#rfc.iref.44"><b>9.4.3</b></a></li>
1644                  <li>403 Forbidden (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.403.1">5</a>, <a href="#rfc.iref.45"><b>9.4.4</b></a>, <a href="#rfc.xref.status.403.2">A</a></li>
1645                  <li>404 Not Found (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.404.1">5</a>, <a href="#rfc.iref.46"><b>9.4.5</b></a>, <a href="#rfc.xref.status.404.2">A</a></li>
1646                  <li>405 Method Not Allowed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.405.1">5</a>, <a href="#rfc.iref.47"><b>9.4.6</b></a></li>
1647                  <li>406 Not Acceptable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.406.1">5</a>, <a href="#rfc.iref.48"><b>9.4.7</b></a></li>
1648                  <li>407 Proxy Authentication Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.407.1">5</a>, <a href="#rfc.iref.49"><b>9.4.8</b></a></li>
1649                  <li>408 Request Timeout (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.408.1">5</a>, <a href="#rfc.iref.50"><b>9.4.9</b></a></li>
1650                  <li>409 Conflict (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.409.1">5</a>, <a href="#rfc.iref.51"><b>9.4.10</b></a></li>
1651                  <li>410 Gone (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.410.1">5</a>, <a href="#rfc.iref.52"><b>9.4.11</b></a>, <a href="#rfc.xref.status.410.2">A</a></li>
1652                  <li>411 Length Required (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.411.1">5</a>, <a href="#rfc.iref.53"><b>9.4.12</b></a></li>
1653                  <li>412 Precondition Failed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.412.1">5</a>, <a href="#rfc.iref.54"><b>9.4.13</b></a></li>
1654                  <li>413 Request Entity Too Large (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.413.1">5</a>, <a href="#rfc.iref.55"><b>9.4.14</b></a></li>
1655                  <li>414 Request-URI Too Long (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.414.1">5</a>, <a href="#rfc.iref.56"><b>9.4.15</b></a></li>
1656                  <li>415 Unsupported Media Type (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.415.1">5</a>, <a href="#rfc.iref.57"><b>9.4.16</b></a></li>
1657                  <li>416 Requested Range Not Satisfiable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.416.1">5</a>, <a href="#rfc.iref.58"><b>9.4.17</b></a></li>
1658                  <li>417 Expectation Failed (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.417.1">5</a>, <a href="#rfc.iref.59"><b>9.4.18</b></a></li>
1659               </ul>
1660            </li>
1661            <li><a id="rfc.index.5" href="#rfc.index.5"><b>5</b></a><ul>
1662                  <li>500 Internal Server Error (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.500.1">5</a>, <a href="#rfc.iref.60"><b>9.5.1</b></a></li>
1663                  <li>501 Not Implemented (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.501.1">5</a>, <a href="#rfc.iref.61"><b>9.5.2</b></a></li>
1664                  <li>502 Bad Gateway (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.502.1">5</a>, <a href="#rfc.iref.62"><b>9.5.3</b></a></li>
1665                  <li>503 Service Unavailable (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.503.1">5</a>, <a href="#rfc.iref.63"><b>9.5.4</b></a></li>
1666                  <li>504 Gateway Timeout (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.504.1">5</a>, <a href="#rfc.iref.64"><b>9.5.5</b></a>, <a href="#rfc.xref.status.504.2">A</a></li>
1667                  <li>505 HTTP Version Not Supported (status code)&nbsp;&nbsp;<a href="#rfc.xref.status.505.1">5</a>, <a href="#rfc.iref.65"><b>9.5.6</b></a></li>
1668               </ul>
1669            </li>
1670            <li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul>
1671                  <li>Allow header&nbsp;&nbsp;<a href="#rfc.xref.header.allow.1">3</a>, <a href="#rfc.iref.a.1"><b>10.1</b></a></li>
1672               </ul>
1673            </li>
1674            <li><a id="rfc.index.C" href="#rfc.index.C"><b>C</b></a><ul>
1675                  <li>CONNECT method&nbsp;&nbsp;<a href="#rfc.xref.CONNECT.1">3</a>, <a href="#rfc.iref.c.1"><b>8.9</b></a></li>
1676               </ul>
1677            </li>
1678            <li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul>
1679                  <li>DELETE method&nbsp;&nbsp;<a href="#rfc.xref.DELETE.1">3</a>, <a href="#rfc.iref.d.1"><b>8.7</b></a></li>
1680               </ul>
1681            </li>
1682            <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul>
1683                  <li>Expect header&nbsp;&nbsp;<a href="#rfc.xref.header.expect.1">4</a>, <a href="#rfc.xref.header.expect.2">9.4.18</a>, <a href="#rfc.iref.e.1"><b>10.2</b></a></li>
1684               </ul>
1685            </li>
1686            <li><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul>
1687                  <li>From header&nbsp;&nbsp;<a href="#rfc.xref.header.from.1">4</a>, <a href="#rfc.iref.f.1"><b>10.3</b></a></li>
1688               </ul>
1689            </li>
1690            <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul>
1691                  <li>GET method&nbsp;&nbsp;<a href="#rfc.xref.GET.1">3</a>, <a href="#rfc.iref.g.10"><b>8.3</b></a></li>
1692                  <li><tt>Grammar</tt>&nbsp;&nbsp;
1693                     <ul>
1694                        <li><tt>Allow</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.11"><b>10.1</b></a></li>
1695                        <li><tt>Expect</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.12"><b>10.2</b></a></li>
1696                        <li><tt>expect-params</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.15"><b>10.2</b></a></li>
1697                        <li><tt>expectation</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.13"><b>10.2</b></a></li>
1698                        <li><tt>expectation-extension</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.14"><b>10.2</b></a></li>
1699                        <li><tt>extension-code</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.7"><b>5</b></a></li>
1700                        <li><tt>extension-method</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.4"><b>3</b></a></li>
1701                        <li><tt>From</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.16"><b>10.3</b></a></li>
1702                        <li><tt>Location</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.17"><b>10.4</b></a></li>
1703                        <li><tt>Max-Forwards</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.18"><b>10.5</b></a></li>
1704                        <li><tt>Method</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.3"><b>3</b></a></li>
1705                        <li><tt>product</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.1"><b>2</b></a></li>
1706                        <li><tt>product-version</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.2"><b>2</b></a></li>
1707                        <li><tt>Reason-Phrase</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.8"><b>5</b></a></li>
1708                        <li><tt>Referer</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.19"><b>10.6</b></a></li>
1709                        <li><tt>request-header</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.5"><b>4</b></a></li>
1710                        <li><tt>response-header</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.9"><b>6</b></a></li>
1711                        <li><tt>Retry-After</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.20"><b>10.7</b></a></li>
1712                        <li><tt>Server</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.21"><b>10.8</b></a></li>
1713                        <li><tt>Status-Code</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.6"><b>5</b></a></li>
1714                        <li><tt>User-Agent</tt>&nbsp;&nbsp;<a href="#rfc.iref.g.22"><b>10.9</b></a></li>
1715                     </ul>
1716                  </li>
1717               </ul>
1718            </li>
1719            <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul>
1720                  <li>HEAD method&nbsp;&nbsp;<a href="#rfc.xref.HEAD.1">3</a>, <a href="#rfc.iref.h.1"><b>8.4</b></a></li>
1721                  <li>Headers&nbsp;&nbsp;
1722                     <ul>
1723                        <li>Allow&nbsp;&nbsp;<a href="#rfc.xref.header.allow.1">3</a>, <a href="#rfc.iref.h.2"><b>10.1</b></a></li>
1724                        <li>Expect&nbsp;&nbsp;<a href="#rfc.xref.header.expect.1">4</a>, <a href="#rfc.xref.header.expect.2">9.4.18</a>, <a href="#rfc.iref.h.3"><b>10.2</b></a></li>
1725                        <li>From&nbsp;&nbsp;<a href="#rfc.xref.header.from.1">4</a>, <a href="#rfc.iref.h.4"><b>10.3</b></a></li>
1726                        <li>Location&nbsp;&nbsp;<a href="#rfc.xref.header.location.1">6</a>, <a href="#rfc.xref.header.location.2">8.5</a>, <a href="#rfc.iref.h.5"><b>10.4</b></a></li>
1727                        <li>Max-Forwards&nbsp;&nbsp;<a href="#rfc.xref.header.max-forwards.1">4</a>, <a href="#rfc.xref.header.max-forwards.2">8.8</a>, <a href="#rfc.iref.h.6"><b>10.5</b></a></li>
1728                        <li>Referer&nbsp;&nbsp;<a href="#rfc.xref.header.referer.1">4</a>, <a href="#rfc.iref.h.7"><b>10.6</b></a></li>
1729                        <li>Retry-After&nbsp;&nbsp;<a href="#rfc.xref.header.retry-after.1">6</a>, <a href="#rfc.iref.h.8"><b>10.7</b></a></li>
1730                        <li>Server&nbsp;&nbsp;<a href="#rfc.xref.header.server.1">6</a>, <a href="#rfc.iref.h.9"><b>10.8</b></a>, <a href="#rfc.xref.header.server.2">12.1</a></li>
1731                        <li>User-Agent&nbsp;&nbsp;<a href="#rfc.xref.header.user-agent.1">4</a>, <a href="#rfc.iref.h.10"><b>10.9</b></a>, <a href="#rfc.xref.header.user-agent.2">12.1</a></li>
1732                     </ul>
1733                  </li>
1734               </ul>
1735            </li>
1736            <li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul>
1737                  <li>LINK method&nbsp;&nbsp;<a href="#rfc.iref.l.2"><b>A</b></a></li>
1738                  <li>Location header&nbsp;&nbsp;<a href="#rfc.xref.header.location.1">6</a>, <a href="#rfc.xref.header.location.2">8.5</a>, <a href="#rfc.iref.l.1"><b>10.4</b></a></li>
1739                  <li><em>Luo1998</em>&nbsp;&nbsp;<a href="#rfc.xref.Luo1998.1">8.9</a>, <a href="#Luo1998"><b>14</b></a></li>
1740               </ul>
1741            </li>
1742            <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul>
1743                  <li>Max-Forwards header&nbsp;&nbsp;<a href="#rfc.xref.header.max-forwards.1">4</a>, <a href="#rfc.xref.header.max-forwards.2">8.8</a>, <a href="#rfc.iref.m.9"><b>10.5</b></a></li>
1744                  <li>Methods&nbsp;&nbsp;
1745                     <ul>
1746                        <li>CONNECT&nbsp;&nbsp;<a href="#rfc.xref.CONNECT.1">3</a>, <a href="#rfc.iref.m.8"><b>8.9</b></a></li>
1747                        <li>DELETE&nbsp;&nbsp;<a href="#rfc.xref.DELETE.1">3</a>, <a href="#rfc.iref.m.6"><b>8.7</b></a></li>
1748                        <li>GET&nbsp;&nbsp;<a href="#rfc.xref.GET.1">3</a>, <a href="#rfc.iref.m.2"><b>8.3</b></a></li>
1749                        <li>HEAD&nbsp;&nbsp;<a href="#rfc.xref.HEAD.1">3</a>, <a href="#rfc.iref.m.3"><b>8.4</b></a></li>
1750                        <li>LINK&nbsp;&nbsp;<a href="#rfc.iref.m.11"><b>A</b></a></li>
1751                        <li>OPTIONS&nbsp;&nbsp;<a href="#rfc.xref.OPTIONS.1">3</a>, <a href="#rfc.iref.m.1"><b>8.2</b></a>, <a href="#rfc.xref.OPTIONS.2">10.5</a></li>
1752                        <li>PATCH&nbsp;&nbsp;<a href="#rfc.iref.m.10"><b>A</b></a></li>
1753                        <li>POST&nbsp;&nbsp;<a href="#rfc.xref.POST.1">3</a>, <a href="#rfc.iref.m.4"><b>8.5</b></a></li>
1754                        <li>PUT&nbsp;&nbsp;<a href="#rfc.xref.PUT.1">3</a>, <a href="#rfc.iref.m.5"><b>8.6</b></a></li>
1755                        <li>TRACE&nbsp;&nbsp;<a href="#rfc.xref.TRACE.1">3</a>, <a href="#rfc.iref.m.7"><b>8.8</b></a>, <a href="#rfc.xref.TRACE.2">10.5</a></li>
1756                        <li>UNLINK&nbsp;&nbsp;<a href="#rfc.iref.m.12"><b>A</b></a></li>
1757                     </ul>
1758                  </li>
1759               </ul>
1760            </li>
1761            <li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul>
1762                  <li>OPTIONS method&nbsp;&nbsp;<a href="#rfc.xref.OPTIONS.1">3</a>, <a href="#rfc.iref.o.1"><b>8.2</b></a>, <a href="#rfc.xref.OPTIONS.2">10.5</a></li>
1763               </ul>
1764            </li>
1765            <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
1766                  <li><em>Part1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">4</a>, <a href="#rfc.xref.Part1.2">4</a>, <a href="#rfc.xref.Part1.3">7</a>, <a href="#rfc.xref.Part1.4">8</a>, <a href="#rfc.xref.Part1.5">8.5</a>, <a href="#rfc.xref.Part1.6">8.6</a>, <a href="#rfc.xref.Part1.7">8.8</a>, <a href="#rfc.xref.Part1.8">9.1.1</a>, <a href="#rfc.xref.Part1.9">9.5.6</a>, <a href="#rfc.xref.Part1.10">10.2</a>, <a href="#rfc.xref.Part1.11">10.8</a>, <a href="#Part1"><b>14</b></a><ul>
1767                        <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.9">9.5.6</a></li>
1768                        <li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.3">7</a></li>
1769                        <li><em>Section 7.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.5">8.5</a>, <a href="#rfc.xref.Part1.6">8.6</a></li>
1770                        <li><em>Section 7.2.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.8">9.1.1</a>, <a href="#rfc.xref.Part1.10">10.2</a></li>
1771                        <li><em>Section 8.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.1">4</a>, <a href="#rfc.xref.Part1.4">8</a></li>
1772                        <li><em>Section 8.8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.2">4</a></li>
1773                        <li><em>Section 8.9</em>&nbsp;&nbsp;<a href="#rfc.xref.Part1.7">8.8</a>, <a href="#rfc.xref.Part1.11">10.8</a></li>
1774                     </ul>
1775                  </li>
1776                  <li><em>Part3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">1</a>, <a href="#rfc.xref.Part3.2">4</a>, <a href="#rfc.xref.Part3.3">4</a>, <a href="#rfc.xref.Part3.4">4</a>, <a href="#rfc.xref.Part3.5">4</a>, <a href="#rfc.xref.Part3.6">7</a>, <a href="#rfc.xref.Part3.7">9.3.1</a>, <a href="#rfc.xref.Part3.8">10.4</a>, <a href="#Part3"><b>14</b></a><ul>
1777                        <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.7">9.3.1</a></li>
1778                        <li><em>Section 5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.2">4</a></li>
1779                        <li><em>Section 5.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.3">4</a></li>
1780                        <li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.4">4</a></li>
1781                        <li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.5">4</a></li>
1782                        <li><em>Section 5.7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.8">10.4</a></li>
1783                        <li><em>Appendix A</em>&nbsp;&nbsp;<a href="#rfc.xref.Part3.1">1</a></li>
1784                     </ul>
1785                  </li>
1786                  <li><em>Part4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">4</a>, <a href="#rfc.xref.Part4.2">4</a>, <a href="#rfc.xref.Part4.3">4</a>, <a href="#rfc.xref.Part4.4">4</a>, <a href="#rfc.xref.Part4.5">6</a>, <a href="#rfc.xref.Part4.6">9.2.2</a>, <a href="#rfc.xref.Part4.7">9.3.5</a>, <a href="#rfc.xref.Part4.8">9.4.13</a>, <a href="#Part4"><b>14</b></a><ul>
1787                        <li><em>Section 6.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.5">6</a>, <a href="#rfc.xref.Part4.6">9.2.2</a></li>
1788                        <li><em>Section 6.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.1">4</a></li>
1789                        <li><em>Section 6.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.2">4</a></li>
1790                        <li><em>Section 6.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.3">4</a></li>
1791                        <li><em>Section 6.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part4.4">4</a></li>
1792                     </ul>
1793                  </li>
1794                  <li><em>Part5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">4</a>, <a href="#rfc.xref.Part5.2">4</a>, <a href="#rfc.xref.Part5.3">6</a>, <a href="#rfc.xref.Part5.4">8.3</a>, <a href="#rfc.xref.Part5.5">9.1.2</a>, <a href="#rfc.xref.Part5.6">9.2.7</a>, <a href="#rfc.xref.Part5.7">9.4.17</a>, <a href="#Part5"><b>14</b></a><ul>
1795                        <li><em>Section 5.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.3">6</a></li>
1796                        <li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.1">4</a></li>
1797                        <li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part5.2">4</a>, <a href="#rfc.xref.Part5.4">8.3</a>, <a href="#rfc.xref.Part5.5">9.1.2</a>, <a href="#rfc.xref.Part5.7">9.4.17</a></li>
1798                     </ul>
1799                  </li>
1800                  <li><em>Part6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">6</a>, <a href="#rfc.xref.Part6.2">6</a>, <a href="#rfc.xref.Part6.3">8.3</a>, <a href="#Part6"><b>14</b></a><ul>
1801                        <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.1">6</a></li>
1802                        <li><em>Section 3.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part6.2">6</a></li>
1803                     </ul>
1804                  </li>
1805                  <li><em>Part7</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">4</a>, <a href="#rfc.xref.Part7.2">4</a>, <a href="#rfc.xref.Part7.3">6</a>, <a href="#rfc.xref.Part7.4">6</a>, <a href="#rfc.xref.Part7.5">9.4.2</a>, <a href="#rfc.xref.Part7.6">9.4.8</a>, <a href="#Part7"><b>14</b></a><ul>
1806                        <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.1">4</a></li>
1807                        <li><em>Section 3.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.3">6</a></li>
1808                        <li><em>Section 3.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.2">4</a></li>
1809                        <li><em>Section 3.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part7.4">6</a></li>
1810                     </ul>
1811                  </li>
1812                  <li>PATCH method&nbsp;&nbsp;<a href="#rfc.iref.p.3"><b>A</b></a></li>
1813                  <li>POST method&nbsp;&nbsp;<a href="#rfc.xref.POST.1">3</a>, <a href="#rfc.iref.p.1"><b>8.5</b></a></li>
1814                  <li>PUT method&nbsp;&nbsp;<a href="#rfc.xref.PUT.1">3</a>, <a href="#rfc.iref.p.2"><b>8.6</b></a></li>
1815               </ul>
1816            </li>
1817            <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul>
1818                  <li>Referer header&nbsp;&nbsp;<a href="#rfc.xref.header.referer.1">4</a>, <a href="#rfc.iref.r.1"><b>10.6</b></a></li>
1819                  <li>Retry-After header&nbsp;&nbsp;<a href="#rfc.xref.header.retry-after.1">6</a>, <a href="#rfc.iref.r.2"><b>10.7</b></a></li>
1820                  <li><em>RFC1123</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC1123.1">10.3</a>, <a href="#RFC1123"><b>14</b></a></li>
1821                  <li><em>RFC2068</em>&nbsp;&nbsp;<a href="#RFC2068"><b>14</b></a>, <a href="#rfc.xref.RFC2068.1">A</a></li>
1822                  <li><em>RFC2616</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC2616.1">§</a>, <a href="#RFC2616"><b>14</b></a></li>
1823                  <li><em>RFC822</em>&nbsp;&nbsp;<a href="#rfc.xref.RFC822.1">10.3</a>, <a href="#RFC822"><b>14</b></a></li>
1824               </ul>
1825            </li>
1826            <li><a id="rfc.index.S" href="#rfc.index.S"><b>S</b></a><ul>
1827                  <li>Server header&nbsp;&nbsp;<a href="#rfc.xref.header.server.1">6</a>, <a href="#rfc.iref.s.42"><b>10.8</b></a>, <a href="#rfc.xref.header.server.2">12.1</a></li>
1828                  <li>Status Codes&nbsp;&nbsp;
1829                     <ul>
1830                        <li>100 Continue&nbsp;&nbsp;<a href="#rfc.xref.status.100.1">5</a>, <a href="#rfc.iref.s.1"><b>9.1.1</b></a></li>
1831                        <li>101 Switching Protocols&nbsp;&nbsp;<a href="#rfc.xref.status.101.1">5</a>, <a href="#rfc.iref.s.2"><b>9.1.2</b></a></li>
1832                        <li>200 OK&nbsp;&nbsp;<a href="#rfc.xref.status.200.1">5</a>, <a href="#rfc.iref.s.3"><b>9.2.1</b></a></li>
1833                        <li>201 Created&nbsp;&nbsp;<a href="#rfc.xref.status.201.1">5</a>, <a href="#rfc.iref.s.4"><b>9.2.2</b></a>, <a href="#rfc.xref.status.201.2">A</a></li>
1834                        <li>202 Accepted&nbsp;&nbsp;<a href="#rfc.xref.status.202.1">5</a>, <a href="#rfc.iref.s.5"><b>9.2.3</b></a></li>
1835                        <li>203 Non-Authoritative Information&nbsp;&nbsp;<a href="#rfc.xref.status.203.1">5</a>, <a href="#rfc.iref.s.6"><b>9.2.4</b></a></li>
1836                        <li>204 No Content&nbsp;&nbsp;<a href="#rfc.xref.status.204.1">5</a>, <a href="#rfc.iref.s.7"><b>9.2.5</b></a></li>
1837                        <li>205 Reset Content&nbsp;&nbsp;<a href="#rfc.xref.status.205.1">5</a>, <a href="#rfc.iref.s.8"><b>9.2.6</b></a></li>
1838                        <li>206 Partial Content&nbsp;&nbsp;<a href="#rfc.xref.status.206.1">5</a>, <a href="#rfc.iref.s.9"><b>9.2.7</b></a></li>
1839                        <li>300 Multiple Choices&nbsp;&nbsp;<a href="#rfc.xref.status.300.1">5</a>, <a href="#rfc.iref.s.10"><b>9.3.1</b></a></li>
1840                        <li>301 Moved Permanently&nbsp;&nbsp;<a href="#rfc.xref.status.301.1">5</a>, <a href="#rfc.iref.s.11"><b>9.3.2</b></a></li>
1841                        <li>302 Found&nbsp;&nbsp;<a href="#rfc.xref.status.302.1">5</a>, <a href="#rfc.iref.s.12"><b>9.3.3</b></a></li>
1842                        <li>303 See Other&nbsp;&nbsp;<a href="#rfc.xref.status.303.1">5</a>, <a href="#rfc.iref.s.13"><b>9.3.4</b></a></li>
1843                        <li>304 Not Modified&nbsp;&nbsp;<a href="#rfc.xref.status.304.1">5</a>, <a href="#rfc.iref.s.14"><b>9.3.5</b></a></li>
1844                        <li>305 Use Proxy&nbsp;&nbsp;<a href="#rfc.xref.status.305.1">5</a>, <a href="#rfc.iref.s.15"><b>9.3.6</b></a></li>
1845                        <li>306 (Unused)&nbsp;&nbsp;<a href="#rfc.iref.s.16"><b>9.3.7</b></a></li>
1846                        <li>307 Temporary Redirect&nbsp;&nbsp;<a href="#rfc.xref.status.307.1">5</a>, <a href="#rfc.iref.s.17"><b>9.3.8</b></a></li>
1847                        <li>400 Bad Request&nbsp;&nbsp;<a href="#rfc.xref.status.400.1">5</a>, <a href="#rfc.iref.s.18"><b>9.4.1</b></a></li>
1848                        <li>401 Unauthorized&nbsp;&nbsp;<a href="#rfc.xref.status.401.1">5</a>, <a href="#rfc.iref.s.19"><b>9.4.2</b></a></li>
1849                        <li>402 Payment Required&nbsp;&nbsp;<a href="#rfc.xref.status.402.1">5</a>, <a href="#rfc.iref.s.20"><b>9.4.3</b></a></li>
1850                        <li>403 Forbidden&nbsp;&nbsp;<a href="#rfc.xref.status.403.1">5</a>, <a href="#rfc.iref.s.21"><b>9.4.4</b></a>, <a href="#rfc.xref.status.403.2">A</a></li>
1851                        <li>404 Not Found&nbsp;&nbsp;<a href="#rfc.xref.status.404.1">5</a>, <a href="#rfc.iref.s.22"><b>9.4.5</b></a>, <a href="#rfc.xref.status.404.2">A</a></li>
1852                        <li>405 Method Not Allowed&nbsp;&nbsp;<a href="#rfc.xref.status.405.1">5</a>, <a href="#rfc.iref.s.23"><b>9.4.6</b></a></li>
1853                        <li>406 Not Acceptable&nbsp;&nbsp;<a href="#rfc.xref.status.406.1">5</a>, <a href="#rfc.iref.s.24"><b>9.4.7</b></a></li>
1854                        <li>407 Proxy Authentication Required&nbsp;&nbsp;<a href="#rfc.xref.status.407.1">5</a>, <a href="#rfc.iref.s.25"><b>9.4.8</b></a></li>
1855                        <li>408 Request Timeout&nbsp;&nbsp;<a href="#rfc.xref.status.408.1">5</a>, <a href="#rfc.iref.s.26"><b>9.4.9</b></a></li>
1856                        <li>409 Conflict&nbsp;&nbsp;<a href="#rfc.xref.status.409.1">5</a>, <a href="#rfc.iref.s.27"><b>9.4.10</b></a></li>
1857                        <li>410 Gone&nbsp;&nbsp;<a href="#rfc.xref.status.410.1">5</a>, <a href="#rfc.iref.s.28"><b>9.4.11</b></a>, <a href="#rfc.xref.status.410.2">A</a></li>
1858                        <li>411 Length Required&nbsp;&nbsp;<a href="#rfc.xref.status.411.1">5</a>, <a href="#rfc.iref.s.29"><b>9.4.12</b></a></li>
1859                        <li>412 Precondition Failed&nbsp;&nbsp;<a href="#rfc.xref.status.412.1">5</a>, <a href="#rfc.iref.s.30"><b>9.4.13</b></a></li>
1860                        <li>413 Request Entity Too Large&nbsp;&nbsp;<a href="#rfc.xref.status.413.1">5</a>, <a href="#rfc.iref.s.31"><b>9.4.14</b></a></li>
1861                        <li>414 Request-URI Too Long&nbsp;&nbsp;<a href="#rfc.xref.status.414.1">5</a>, <a href="#rfc.iref.s.32"><b>9.4.15</b></a></li>
1862                        <li>415 Unsupported Media Type&nbsp;&nbsp;<a href="#rfc.xref.status.415.1">5</a>, <a href="#rfc.iref.s.33"><b>9.4.16</b></a></li>
1863                        <li>416 Requested Range Not Satisfiable&nbsp;&nbsp;<a href="#rfc.xref.status.416.1">5</a>, <a href="#rfc.iref.s.34"><b>9.4.17</b></a></li>
1864                        <li>417 Expectation Failed&nbsp;&nbsp;<a href="#rfc.xref.status.417.1">5</a>, <a href="#rfc.iref.s.35"><b>9.4.18</b></a></li>
1865                        <li>500 Internal Server Error&nbsp;&nbsp;<a href="#rfc.xref.status.500.1">5</a>, <a href="#rfc.iref.s.36"><b>9.5.1</b></a></li>
1866                        <li>501 Not Implemented&nbsp;&nbsp;<a href="#rfc.xref.status.501.1">5</a>, <a href="#rfc.iref.s.37"><b>9.5.2</b></a></li>
1867                        <li>502 Bad Gateway&nbsp;&nbsp;<a href="#rfc.xref.status.502.1">5</a>, <a href="#rfc.iref.s.38"><b>9.5.3</b></a></li>
1868                        <li>503 Service Unavailable&nbsp;&nbsp;<a href="#rfc.xref.status.503.1">5</a>, <a href="#rfc.iref.s.39"><b>9.5.4</b></a></li>
1869                        <li>504 Gateway Timeout&nbsp;&nbsp;<a href="#rfc.xref.status.504.1">5</a>, <a href="#rfc.iref.s.40"><b>9.5.5</b></a>, <a href="#rfc.xref.status.504.2">A</a></li>
1870                        <li>505 HTTP Version Not Supported&nbsp;&nbsp;<a href="#rfc.xref.status.505.1">5</a>, <a href="#rfc.iref.s.41"><b>9.5.6</b></a></li>
1871                     </ul>
1872                  </li>
1873               </ul>
1874            </li>
1875            <li><a id="rfc.index.T" href="#rfc.index.T"><b>T</b></a><ul>
1876                  <li>TRACE method&nbsp;&nbsp;<a href="#rfc.xref.TRACE.1">3</a>, <a href="#rfc.iref.t.1"><b>8.8</b></a>, <a href="#rfc.xref.TRACE.2">10.5</a></li>
1877               </ul>
1878            </li>
1879            <li><a id="rfc.index.U" href="#rfc.index.U"><b>U</b></a><ul>
1880                  <li>UNLINK method&nbsp;&nbsp;<a href="#rfc.iref.u.2"><b>A</b></a></li>
1881                  <li>User-Agent header&nbsp;&nbsp;<a href="#rfc.xref.header.user-agent.1">4</a>, <a href="#rfc.iref.u.1"><b>10.9</b></a>, <a href="#rfc.xref.header.user-agent.2">12.1</a></li>
1882               </ul>
1883            </li>
1884         </ul>
1885      </div>
1886      <h1><a id="rfc.copyright" href="#rfc.copyright">Full Copyright Statement</a></h1>
1887      <p>Copyright © The IETF Trust (2007).</p>
1888      <p>This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the
1889         authors retain all their rights.
1890      </p>
1891      <p>This document and the information contained herein are provided on an “AS IS” basis and THE CONTRIBUTOR, THE ORGANIZATION
1892         HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE
1893         DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
1894         WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
1895      </p>
1896      <h1><a id="rfc.ipr" href="#rfc.ipr">Intellectual Property</a></h1>
1897      <p>The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might
1898         be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any
1899         license under such rights might or might not be available; nor does it represent that it has made any independent effort to
1900         identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and
1901         BCP 79.
1902      </p>
1903      <p>Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result
1904         of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users
1905         of this specification can be obtained from the IETF on-line IPR repository at <a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>.
1906      </p>
1907      <p>The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary
1908         rights that may cover technology that may be required to implement this standard. Please address the information to the IETF
1909         at <a href="mailto:ietf-ipr@ietf.org">ietf-ipr@ietf.org</a>.
1910      </p>
1911   </body>
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