Ignore:
Timestamp:
20/01/14 07:43:53 (8 years ago)
Author:
julian.reschke@…
Message:

update rfc2617.xml (ABNF alignment was off from published version), regen all HTML

File:
1 edited

Legend:

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  • draft-ietf-httpbis/orig/rfc2616.html

    r1305 r2564  
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    300        content: "RFC 2616"; 
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     288       content: "RFC 2616";
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    303        content: "June 1999"; 
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    354342      <link rel="Help" title="RFC-Editor's Status Page" href="http://www.rfc-editor.org/info/rfc2616">
    355343      <link rel="Help" title="Additional Information on tools.ietf.org" href="http://tools.ietf.org/html/rfc2616">
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    357345      <link rel="schema.dct" href="http://purl.org/dc/terms/">
    358346      <meta name="dct.creator" content="Fielding, R.">
     
    436424      </table>
    437425      <p class="title">Hypertext Transfer Protocol -- HTTP/1.1</p>
    438       <h1><a id="rfc.status" href="#rfc.status">Status of this Memo</a></h1>
    439       <p>This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions
    440          for improvements. Please refer to the current edition of the “Internet Official Protocol Standards” (STD 1) for the standardization
    441          state and status of this protocol. Distribution of this memo is unlimited.
    442       </p>
    443       <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    444       <p>Copyright © The Internet Society (1999). All Rights Reserved.</p>
    445       <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
     426      <div id="rfc.status">
     427         <h1><a href="#rfc.status">Status of this Memo</a></h1>
     428         <p>This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions
     429            for improvements. Please refer to the current edition of the “Internet Official Protocol Standards” (STD 1) for the standardization
     430            state and status of this protocol. Distribution of this memo is unlimited.
     431         </p>
     432      </div>
     433      <div id="rfc.copyrightnotice">
     434         <h1><a href="#rfc.copyrightnotice">Copyright Notice</a></h1>
     435         <p>Copyright © The Internet Society (1999). All Rights Reserved.</p>
     436      </div>
     437      <h1 id="rfc.abstract"><a href="#rfc.abstract">Abstract</a></h1>
    446438      <p>The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information
    447439         systems. It is a generic, stateless, protocol which can be used for many tasks beyond its use for hypertext, such as name
    448440         servers and distributed object management systems, through extension of its request methods, error codes and headers <a href="#RFC2324" id="rfc.xref.RFC2324.1"><cite title="Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)">[47]</cite></a>. A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built independently of the
    449441         data being transferred.
    450       </p> 
     442      </p>
    451443      <p>HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol
    452444         referred to as "HTTP/1.1", and is an update to RFC 2068 <a href="#RFC2068" id="rfc.xref.RFC2068.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[33]</cite></a>.
    453       </p> 
     445      </p>
    454446      <hr class="noprint">
    455447      <h1 class="np" id="rfc.toc"><a href="#rfc.toc">Table of Contents</a></h1>
    456448      <ul class="toc">
    457          <li>1.&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
    458                <li>1.1&nbsp;&nbsp;&nbsp;<a href="#intro.purpose">Purpose</a></li>
    459                <li>1.2&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
    460                <li>1.3&nbsp;&nbsp;&nbsp;<a href="#intro.terminology">Terminology</a></li>
    461                <li>1.4&nbsp;&nbsp;&nbsp;<a href="#intro.overall.operation">Overall Operation</a></li>
     449         <li><a href="#rfc.section.1">1.</a>&nbsp;&nbsp;&nbsp;<a href="#introduction">Introduction</a><ul>
     450               <li><a href="#rfc.section.1.1">1.1</a>&nbsp;&nbsp;&nbsp;<a href="#intro.purpose">Purpose</a></li>
     451               <li><a href="#rfc.section.1.2">1.2</a>&nbsp;&nbsp;&nbsp;<a href="#intro.requirements">Requirements</a></li>
     452               <li><a href="#rfc.section.1.3">1.3</a>&nbsp;&nbsp;&nbsp;<a href="#intro.terminology">Terminology</a></li>
     453               <li><a href="#rfc.section.1.4">1.4</a>&nbsp;&nbsp;&nbsp;<a href="#intro.overall.operation">Overall Operation</a></li>
    462454            </ul>
    463455         </li>
    464          <li>2.&nbsp;&nbsp;&nbsp;<a href="#notation">Notational Conventions and Generic Grammar</a><ul>
    465                <li>2.1&nbsp;&nbsp;&nbsp;<a href="#notation.abnf">Augmented BNF</a></li>
    466                <li>2.2&nbsp;&nbsp;&nbsp;<a href="#basic.rules">Basic Rules</a></li>
     456         <li><a href="#rfc.section.2">2.</a>&nbsp;&nbsp;&nbsp;<a href="#notation">Notational Conventions and Generic Grammar</a><ul>
     457               <li><a href="#rfc.section.2.1">2.1</a>&nbsp;&nbsp;&nbsp;<a href="#notation.abnf">Augmented BNF</a></li>
     458               <li><a href="#rfc.section.2.2">2.2</a>&nbsp;&nbsp;&nbsp;<a href="#basic.rules">Basic Rules</a></li>
    467459            </ul>
    468460         </li>
    469          <li>3.&nbsp;&nbsp;&nbsp;<a href="#protocol.parameters">Protocol Parameters</a><ul>
    470                <li>3.1&nbsp;&nbsp;&nbsp;<a href="#http.version">HTTP Version</a></li>
    471                <li>3.2&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul>
    472                      <li>3.2.1&nbsp;&nbsp;&nbsp;<a href="#general.syntax">General Syntax</a></li>
    473                      <li>3.2.2&nbsp;&nbsp;&nbsp;<a href="#http.url">http URL</a></li>
    474                      <li>3.2.3&nbsp;&nbsp;&nbsp;<a href="#uri.comparison">URI Comparison</a></li>
     461         <li><a href="#rfc.section.3">3.</a>&nbsp;&nbsp;&nbsp;<a href="#protocol.parameters">Protocol Parameters</a><ul>
     462               <li><a href="#rfc.section.3.1">3.1</a>&nbsp;&nbsp;&nbsp;<a href="#http.version">HTTP Version</a></li>
     463               <li><a href="#rfc.section.3.2">3.2</a>&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul>
     464                     <li><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#general.syntax">General Syntax</a></li>
     465                     <li><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#http.url">http URL</a></li>
     466                     <li><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#uri.comparison">URI Comparison</a></li>
    475467                  </ul>
    476468               </li>
    477                <li>3.3&nbsp;&nbsp;&nbsp;<a href="#date.time.formats">Date/Time Formats</a><ul>
    478                      <li>3.3.1&nbsp;&nbsp;&nbsp;<a href="#full.date">Full Date</a></li>
    479                      <li>3.3.2&nbsp;&nbsp;&nbsp;<a href="#delta.seconds">Delta Seconds</a></li>
     469               <li><a href="#rfc.section.3.3">3.3</a>&nbsp;&nbsp;&nbsp;<a href="#date.time.formats">Date/Time Formats</a><ul>
     470                     <li><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#full.date">Full Date</a></li>
     471                     <li><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#delta.seconds">Delta Seconds</a></li>
    480472                  </ul>
    481473               </li>
    482                <li>3.4&nbsp;&nbsp;&nbsp;<a href="#character.sets">Character Sets</a><ul>
    483                      <li>3.4.1&nbsp;&nbsp;&nbsp;<a href="#missing.charset">Missing Charset</a></li>
     474               <li><a href="#rfc.section.3.4">3.4</a>&nbsp;&nbsp;&nbsp;<a href="#character.sets">Character Sets</a><ul>
     475                     <li><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#missing.charset">Missing Charset</a></li>
    484476                  </ul>
    485477               </li>
    486                <li>3.5&nbsp;&nbsp;&nbsp;<a href="#content.codings">Content Codings</a></li>
    487                <li>3.6&nbsp;&nbsp;&nbsp;<a href="#transfer.codings">Transfer Codings</a><ul>
    488                      <li>3.6.1&nbsp;&nbsp;&nbsp;<a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></li>
     478               <li><a href="#rfc.section.3.5">3.5</a>&nbsp;&nbsp;&nbsp;<a href="#content.codings">Content Codings</a></li>
     479               <li><a href="#rfc.section.3.6">3.6</a>&nbsp;&nbsp;&nbsp;<a href="#transfer.codings">Transfer Codings</a><ul>
     480                     <li><a href="#rfc.section.3.6.1">3.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></li>
    489481                  </ul>
    490482               </li>
    491                <li>3.7&nbsp;&nbsp;&nbsp;<a href="#media.types">Media Types</a><ul>
    492                      <li>3.7.1&nbsp;&nbsp;&nbsp;<a href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></li>
    493                      <li>3.7.2&nbsp;&nbsp;&nbsp;<a href="#multipart.types">Multipart Types</a></li>
     483               <li><a href="#rfc.section.3.7">3.7</a>&nbsp;&nbsp;&nbsp;<a href="#media.types">Media Types</a><ul>
     484                     <li><a href="#rfc.section.3.7.1">3.7.1</a>&nbsp;&nbsp;&nbsp;<a href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></li>
     485                     <li><a href="#rfc.section.3.7.2">3.7.2</a>&nbsp;&nbsp;&nbsp;<a href="#multipart.types">Multipart Types</a></li>
    494486                  </ul>
    495487               </li>
    496                <li>3.8&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
    497                <li>3.9&nbsp;&nbsp;&nbsp;<a href="#quality.values">Quality Values</a></li>
    498                <li>3.10&nbsp;&nbsp;&nbsp;<a href="#language.tags">Language Tags</a></li>
    499                <li>3.11&nbsp;&nbsp;&nbsp;<a href="#entity.tags">Entity Tags</a></li>
    500                <li>3.12&nbsp;&nbsp;&nbsp;<a href="#range.units">Range Units</a></li>
     488               <li><a href="#rfc.section.3.8">3.8</a>&nbsp;&nbsp;&nbsp;<a href="#product.tokens">Product Tokens</a></li>
     489               <li><a href="#rfc.section.3.9">3.9</a>&nbsp;&nbsp;&nbsp;<a href="#quality.values">Quality Values</a></li>
     490               <li><a href="#rfc.section.3.10">3.10</a>&nbsp;&nbsp;&nbsp;<a href="#language.tags">Language Tags</a></li>
     491               <li><a href="#rfc.section.3.11">3.11</a>&nbsp;&nbsp;&nbsp;<a href="#entity.tags">Entity Tags</a></li>
     492               <li><a href="#rfc.section.3.12">3.12</a>&nbsp;&nbsp;&nbsp;<a href="#range.units">Range Units</a></li>
    501493            </ul>
    502494         </li>
    503          <li>4.&nbsp;&nbsp;&nbsp;<a href="#http.message">HTTP Message</a><ul>
    504                <li>4.1&nbsp;&nbsp;&nbsp;<a href="#message.types">Message Types</a></li>
    505                <li>4.2&nbsp;&nbsp;&nbsp;<a href="#message.headers">Message Headers</a></li>
    506                <li>4.3&nbsp;&nbsp;&nbsp;<a href="#message.body">Message Body</a></li>
    507                <li>4.4&nbsp;&nbsp;&nbsp;<a href="#message.length">Message Length</a></li>
    508                <li>4.5&nbsp;&nbsp;&nbsp;<a href="#general.header.fields">General Header Fields</a></li>
     495         <li><a href="#rfc.section.4">4.</a>&nbsp;&nbsp;&nbsp;<a href="#http.message">HTTP Message</a><ul>
     496               <li><a href="#rfc.section.4.1">4.1</a>&nbsp;&nbsp;&nbsp;<a href="#message.types">Message Types</a></li>
     497               <li><a href="#rfc.section.4.2">4.2</a>&nbsp;&nbsp;&nbsp;<a href="#message.headers">Message Headers</a></li>
     498               <li><a href="#rfc.section.4.3">4.3</a>&nbsp;&nbsp;&nbsp;<a href="#message.body">Message Body</a></li>
     499               <li><a href="#rfc.section.4.4">4.4</a>&nbsp;&nbsp;&nbsp;<a href="#message.length">Message Length</a></li>
     500               <li><a href="#rfc.section.4.5">4.5</a>&nbsp;&nbsp;&nbsp;<a href="#general.header.fields">General Header Fields</a></li>
    509501            </ul>
    510502         </li>
    511          <li>5.&nbsp;&nbsp;&nbsp;<a href="#request">Request</a><ul>
    512                <li>5.1&nbsp;&nbsp;&nbsp;<a href="#request-line">Request-Line</a><ul>
    513                      <li>5.1.1&nbsp;&nbsp;&nbsp;<a href="#method">Method</a></li>
    514                      <li>5.1.2&nbsp;&nbsp;&nbsp;<a href="#request-uri">Request-URI</a></li>
     503         <li><a href="#rfc.section.5">5.</a>&nbsp;&nbsp;&nbsp;<a href="#request">Request</a><ul>
     504               <li><a href="#rfc.section.5.1">5.1</a>&nbsp;&nbsp;&nbsp;<a href="#request-line">Request-Line</a><ul>
     505                     <li><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#method">Method</a></li>
     506                     <li><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#request-uri">Request-URI</a></li>
    515507                  </ul>
    516508               </li>
    517                <li>5.2&nbsp;&nbsp;&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></li>
    518                <li>5.3&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a></li>
     509               <li><a href="#rfc.section.5.2">5.2</a>&nbsp;&nbsp;&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></li>
     510               <li><a href="#rfc.section.5.3">5.3</a>&nbsp;&nbsp;&nbsp;<a href="#request.header.fields">Request Header Fields</a></li>
    519511            </ul>
    520512         </li>
    521          <li>6.&nbsp;&nbsp;&nbsp;<a href="#response">Response</a><ul>
    522                <li>6.1&nbsp;&nbsp;&nbsp;<a href="#status-line">Status-Line</a><ul>
    523                      <li>6.1.1&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>
     513         <li><a href="#rfc.section.6">6.</a>&nbsp;&nbsp;&nbsp;<a href="#response">Response</a><ul>
     514               <li><a href="#rfc.section.6.1">6.1</a>&nbsp;&nbsp;&nbsp;<a href="#status-line">Status-Line</a><ul>
     515                     <li><a href="#rfc.section.6.1.1">6.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></li>
    524516                  </ul>
    525517               </li>
    526                <li>6.2&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a></li>
     518               <li><a href="#rfc.section.6.2">6.2</a>&nbsp;&nbsp;&nbsp;<a href="#response.header.fields">Response Header Fields</a></li>
    527519            </ul>
    528520         </li>
    529          <li>7.&nbsp;&nbsp;&nbsp;<a href="#entity">Entity</a><ul>
    530                <li>7.1&nbsp;&nbsp;&nbsp;<a href="#entity.header.fields">Entity Header Fields</a></li>
    531                <li>7.2&nbsp;&nbsp;&nbsp;<a href="#entity.body">Entity Body</a><ul>
    532                      <li>7.2.1&nbsp;&nbsp;&nbsp;<a href="#type">Type</a></li>
    533                      <li>7.2.2&nbsp;&nbsp;&nbsp;<a href="#entity.length">Entity Length</a></li>
     521         <li><a href="#rfc.section.7">7.</a>&nbsp;&nbsp;&nbsp;<a href="#entity">Entity</a><ul>
     522               <li><a href="#rfc.section.7.1">7.1</a>&nbsp;&nbsp;&nbsp;<a href="#entity.header.fields">Entity Header Fields</a></li>
     523               <li><a href="#rfc.section.7.2">7.2</a>&nbsp;&nbsp;&nbsp;<a href="#entity.body">Entity Body</a><ul>
     524                     <li><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#type">Type</a></li>
     525                     <li><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#entity.length">Entity Length</a></li>
    534526                  </ul>
    535527               </li>
    536528            </ul>
    537529         </li>
    538          <li>8.&nbsp;&nbsp;&nbsp;<a href="#connections">Connections</a><ul>
    539                <li>8.1&nbsp;&nbsp;&nbsp;<a href="#persistent.connections">Persistent Connections</a><ul>
    540                      <li>8.1.1&nbsp;&nbsp;&nbsp;<a href="#persistent.purpose">Purpose</a></li>
    541                      <li>8.1.2&nbsp;&nbsp;&nbsp;<a href="#persistent.overall">Overall Operation</a><ul>
    542                            <li>8.1.2.1&nbsp;&nbsp;&nbsp;<a href="#persistent.negotiation">Negotiation</a></li>
    543                            <li>8.1.2.2&nbsp;&nbsp;&nbsp;<a href="#pipelining">Pipelining</a></li>
     530         <li><a href="#rfc.section.8">8.</a>&nbsp;&nbsp;&nbsp;<a href="#connections">Connections</a><ul>
     531               <li><a href="#rfc.section.8.1">8.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.connections">Persistent Connections</a><ul>
     532                     <li><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.purpose">Purpose</a></li>
     533                     <li><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.overall">Overall Operation</a><ul>
     534                           <li><a href="#rfc.section.8.1.2.1">8.1.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.negotiation">Negotiation</a></li>
     535                           <li><a href="#rfc.section.8.1.2.2">8.1.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#pipelining">Pipelining</a></li>
    544536                        </ul>
    545537                     </li>
    546                      <li>8.1.3&nbsp;&nbsp;&nbsp;<a href="#persistent.proxy">Proxy Servers</a></li>
    547                      <li>8.1.4&nbsp;&nbsp;&nbsp;<a href="#persistent.practical">Practical Considerations</a></li>
     538                     <li><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.proxy">Proxy Servers</a></li>
     539                     <li><a href="#rfc.section.8.1.4">8.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.practical">Practical Considerations</a></li>
    548540                  </ul>
    549541               </li>
    550                <li>8.2&nbsp;&nbsp;&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a><ul>
    551                      <li>8.2.1&nbsp;&nbsp;&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></li>
    552                      <li>8.2.2&nbsp;&nbsp;&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></li>
    553                      <li>8.2.3&nbsp;&nbsp;&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></li>
    554                      <li>8.2.4&nbsp;&nbsp;&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></li>
     542               <li><a href="#rfc.section.8.2">8.2</a>&nbsp;&nbsp;&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a><ul>
     543                     <li><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></li>
     544                     <li><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></li>
     545                     <li><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></li>
     546                     <li><a href="#rfc.section.8.2.4">8.2.4</a>&nbsp;&nbsp;&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></li>
    555547                  </ul>
    556548               </li>
    557549            </ul>
    558550         </li>
    559          <li>9.&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul>
    560                <li>9.1&nbsp;&nbsp;&nbsp;<a href="#safe.and.idempotent">Safe and Idempotent Methods</a><ul>
    561                      <li>9.1.1&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li>
    562                      <li>9.1.2&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li>
     551         <li><a href="#rfc.section.9">9.</a>&nbsp;&nbsp;&nbsp;<a href="#method.definitions">Method Definitions</a><ul>
     552               <li><a href="#rfc.section.9.1">9.1</a>&nbsp;&nbsp;&nbsp;<a href="#safe.and.idempotent">Safe and Idempotent Methods</a><ul>
     553                     <li><a href="#rfc.section.9.1.1">9.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#safe.methods">Safe Methods</a></li>
     554                     <li><a href="#rfc.section.9.1.2">9.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></li>
    563555                  </ul>
    564556               </li>
    565                <li>9.2&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li>
    566                <li>9.3&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li>
    567                <li>9.4&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li>
    568                <li>9.5&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li>
    569                <li>9.6&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li>
    570                <li>9.7&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li>
    571                <li>9.8&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li>
    572                <li>9.9&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a></li>
     557               <li><a href="#rfc.section.9.2">9.2</a>&nbsp;&nbsp;&nbsp;<a href="#OPTIONS">OPTIONS</a></li>
     558               <li><a href="#rfc.section.9.3">9.3</a>&nbsp;&nbsp;&nbsp;<a href="#GET">GET</a></li>
     559               <li><a href="#rfc.section.9.4">9.4</a>&nbsp;&nbsp;&nbsp;<a href="#HEAD">HEAD</a></li>
     560               <li><a href="#rfc.section.9.5">9.5</a>&nbsp;&nbsp;&nbsp;<a href="#POST">POST</a></li>
     561               <li><a href="#rfc.section.9.6">9.6</a>&nbsp;&nbsp;&nbsp;<a href="#PUT">PUT</a></li>
     562               <li><a href="#rfc.section.9.7">9.7</a>&nbsp;&nbsp;&nbsp;<a href="#DELETE">DELETE</a></li>
     563               <li><a href="#rfc.section.9.8">9.8</a>&nbsp;&nbsp;&nbsp;<a href="#TRACE">TRACE</a></li>
     564               <li><a href="#rfc.section.9.9">9.9</a>&nbsp;&nbsp;&nbsp;<a href="#CONNECT">CONNECT</a></li>
    573565            </ul>
    574566         </li>
    575          <li>10.&nbsp;&nbsp;&nbsp;<a href="#status.codes">Status Code Definitions</a><ul>
    576                <li>10.1&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul>
    577                      <li>10.1.1&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li>
    578                      <li>10.1.2&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li>
     567         <li><a href="#rfc.section.10">10.</a>&nbsp;&nbsp;&nbsp;<a href="#status.codes">Status Code Definitions</a><ul>
     568               <li><a href="#rfc.section.10.1">10.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.1xx">Informational 1xx</a><ul>
     569                     <li><a href="#rfc.section.10.1.1">10.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.100">100 Continue</a></li>
     570                     <li><a href="#rfc.section.10.1.2">10.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.101">101 Switching Protocols</a></li>
    579571                  </ul>
    580572               </li>
    581                <li>10.2&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul>
    582                      <li>10.2.1&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li>
    583                      <li>10.2.2&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li>
    584                      <li>10.2.3&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li>
    585                      <li>10.2.4&nbsp;&nbsp;&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></li>
    586                      <li>10.2.5&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li>
    587                      <li>10.2.6&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li>
    588                      <li>10.2.7&nbsp;&nbsp;&nbsp;<a href="#status.206">206 Partial Content</a></li>
     573               <li><a href="#rfc.section.10.2">10.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.2xx">Successful 2xx</a><ul>
     574                     <li><a href="#rfc.section.10.2.1">10.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.200">200 OK</a></li>
     575                     <li><a href="#rfc.section.10.2.2">10.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.201">201 Created</a></li>
     576                     <li><a href="#rfc.section.10.2.3">10.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.202">202 Accepted</a></li>
     577                     <li><a href="#rfc.section.10.2.4">10.2.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.203">203 Non-Authoritative Information</a></li>
     578                     <li><a href="#rfc.section.10.2.5">10.2.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.204">204 No Content</a></li>
     579                     <li><a href="#rfc.section.10.2.6">10.2.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.205">205 Reset Content</a></li>
     580                     <li><a href="#rfc.section.10.2.7">10.2.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.206">206 Partial Content</a></li>
    589581                  </ul>
    590582               </li>
    591                <li>10.3&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul>
    592                      <li>10.3.1&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li>
    593                      <li>10.3.2&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li>
    594                      <li>10.3.3&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li>
    595                      <li>10.3.4&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li>
    596                      <li>10.3.5&nbsp;&nbsp;&nbsp;<a href="#status.304">304 Not Modified</a></li>
    597                      <li>10.3.6&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li>
    598                      <li>10.3.7&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li>
    599                      <li>10.3.8&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li>
     583               <li><a href="#rfc.section.10.3">10.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.3xx">Redirection 3xx</a><ul>
     584                     <li><a href="#rfc.section.10.3.1">10.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.300">300 Multiple Choices</a></li>
     585                     <li><a href="#rfc.section.10.3.2">10.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.301">301 Moved Permanently</a></li>
     586                     <li><a href="#rfc.section.10.3.3">10.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.302">302 Found</a></li>
     587                     <li><a href="#rfc.section.10.3.4">10.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.303">303 See Other</a></li>
     588                     <li><a href="#rfc.section.10.3.5">10.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.304">304 Not Modified</a></li>
     589                     <li><a href="#rfc.section.10.3.6">10.3.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.305">305 Use Proxy</a></li>
     590                     <li><a href="#rfc.section.10.3.7">10.3.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.306">306 (Unused)</a></li>
     591                     <li><a href="#rfc.section.10.3.8">10.3.8</a>&nbsp;&nbsp;&nbsp;<a href="#status.307">307 Temporary Redirect</a></li>
    600592                  </ul>
    601593               </li>
    602                <li>10.4&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul>
    603                      <li>10.4.1&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li>
    604                      <li>10.4.2&nbsp;&nbsp;&nbsp;<a href="#status.401">401 Unauthorized</a></li>
    605                      <li>10.4.3&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li>
    606                      <li>10.4.4&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li>
    607                      <li>10.4.5&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li>
    608                      <li>10.4.6&nbsp;&nbsp;&nbsp;<a href="#status.405">405 Method Not Allowed</a></li>
    609                      <li>10.4.7&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li>
    610                      <li>10.4.8&nbsp;&nbsp;&nbsp;<a href="#status.407">407 Proxy Authentication Required</a></li>
    611                      <li>10.4.9&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li>
    612                      <li>10.4.10&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li>
    613                      <li>10.4.11&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li>
    614                      <li>10.4.12&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li>
    615                      <li>10.4.13&nbsp;&nbsp;&nbsp;<a href="#status.412">412 Precondition Failed</a></li>
    616                      <li>10.4.14&nbsp;&nbsp;&nbsp;<a href="#status.413">413 Request Entity Too Large</a></li>
    617                      <li>10.4.15&nbsp;&nbsp;&nbsp;<a href="#status.414">414 Request-URI Too Long</a></li>
    618                      <li>10.4.16&nbsp;&nbsp;&nbsp;<a href="#status.415">415 Unsupported Media Type</a></li>
    619                      <li>10.4.17&nbsp;&nbsp;&nbsp;<a href="#status.416">416 Requested Range Not Satisfiable</a></li>
    620                      <li>10.4.18&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li>
     594               <li><a href="#rfc.section.10.4">10.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.4xx">Client Error 4xx</a><ul>
     595                     <li><a href="#rfc.section.10.4.1">10.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.400">400 Bad Request</a></li>
     596                     <li><a href="#rfc.section.10.4.2">10.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.401">401 Unauthorized</a></li>
     597                     <li><a href="#rfc.section.10.4.3">10.4.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.402">402 Payment Required</a></li>
     598                     <li><a href="#rfc.section.10.4.4">10.4.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.403">403 Forbidden</a></li>
     599                     <li><a href="#rfc.section.10.4.5">10.4.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.404">404 Not Found</a></li>
     600                     <li><a href="#rfc.section.10.4.6">10.4.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.405">405 Method Not Allowed</a></li>
     601                     <li><a href="#rfc.section.10.4.7">10.4.7</a>&nbsp;&nbsp;&nbsp;<a href="#status.406">406 Not Acceptable</a></li>
     602                     <li><a href="#rfc.section.10.4.8">10.4.8</a>&nbsp;&nbsp;&nbsp;<a href="#status.407">407 Proxy Authentication Required</a></li>
     603                     <li><a href="#rfc.section.10.4.9">10.4.9</a>&nbsp;&nbsp;&nbsp;<a href="#status.408">408 Request Timeout</a></li>
     604                     <li><a href="#rfc.section.10.4.10">10.4.10</a>&nbsp;&nbsp;&nbsp;<a href="#status.409">409 Conflict</a></li>
     605                     <li><a href="#rfc.section.10.4.11">10.4.11</a>&nbsp;&nbsp;&nbsp;<a href="#status.410">410 Gone</a></li>
     606                     <li><a href="#rfc.section.10.4.12">10.4.12</a>&nbsp;&nbsp;&nbsp;<a href="#status.411">411 Length Required</a></li>
     607                     <li><a href="#rfc.section.10.4.13">10.4.13</a>&nbsp;&nbsp;&nbsp;<a href="#status.412">412 Precondition Failed</a></li>
     608                     <li><a href="#rfc.section.10.4.14">10.4.14</a>&nbsp;&nbsp;&nbsp;<a href="#status.413">413 Request Entity Too Large</a></li>
     609                     <li><a href="#rfc.section.10.4.15">10.4.15</a>&nbsp;&nbsp;&nbsp;<a href="#status.414">414 Request-URI Too Long</a></li>
     610                     <li><a href="#rfc.section.10.4.16">10.4.16</a>&nbsp;&nbsp;&nbsp;<a href="#status.415">415 Unsupported Media Type</a></li>
     611                     <li><a href="#rfc.section.10.4.17">10.4.17</a>&nbsp;&nbsp;&nbsp;<a href="#status.416">416 Requested Range Not Satisfiable</a></li>
     612                     <li><a href="#rfc.section.10.4.18">10.4.18</a>&nbsp;&nbsp;&nbsp;<a href="#status.417">417 Expectation Failed</a></li>
    621613                  </ul>
    622614               </li>
    623                <li>10.5&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul>
    624                      <li>10.5.1&nbsp;&nbsp;&nbsp;<a href="#status.500">500 Internal Server Error</a></li>
    625                      <li>10.5.2&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li>
    626                      <li>10.5.3&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li>
    627                      <li>10.5.4&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li>
    628                      <li>10.5.5&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li>
    629                      <li>10.5.6&nbsp;&nbsp;&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></li>
     615               <li><a href="#rfc.section.10.5">10.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.5xx">Server Error 5xx</a><ul>
     616                     <li><a href="#rfc.section.10.5.1">10.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#status.500">500 Internal Server Error</a></li>
     617                     <li><a href="#rfc.section.10.5.2">10.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#status.501">501 Not Implemented</a></li>
     618                     <li><a href="#rfc.section.10.5.3">10.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#status.502">502 Bad Gateway</a></li>
     619                     <li><a href="#rfc.section.10.5.4">10.5.4</a>&nbsp;&nbsp;&nbsp;<a href="#status.503">503 Service Unavailable</a></li>
     620                     <li><a href="#rfc.section.10.5.5">10.5.5</a>&nbsp;&nbsp;&nbsp;<a href="#status.504">504 Gateway Timeout</a></li>
     621                     <li><a href="#rfc.section.10.5.6">10.5.6</a>&nbsp;&nbsp;&nbsp;<a href="#status.505">505 HTTP Version Not Supported</a></li>
    630622                  </ul>
    631623               </li>
    632624            </ul>
    633625         </li>
    634          <li>11.&nbsp;&nbsp;&nbsp;<a href="#access.authentication">Access Authentication</a></li>
    635          <li>12.&nbsp;&nbsp;&nbsp;<a href="#content.negotiation">Content Negotiation</a><ul>
    636                <li>12.1&nbsp;&nbsp;&nbsp;<a href="#server-driven.negotiation">Server-driven Negotiation</a></li>
    637                <li>12.2&nbsp;&nbsp;&nbsp;<a href="#agent-driven.negotiation">Agent-driven Negotiation</a></li>
    638                <li>12.3&nbsp;&nbsp;&nbsp;<a href="#transparent.negotiation">Transparent Negotiation</a></li>
     626         <li><a href="#rfc.section.11">11.</a>&nbsp;&nbsp;&nbsp;<a href="#access.authentication">Access Authentication</a></li>
     627         <li><a href="#rfc.section.12">12.</a>&nbsp;&nbsp;&nbsp;<a href="#content.negotiation">Content Negotiation</a><ul>
     628               <li><a href="#rfc.section.12.1">12.1</a>&nbsp;&nbsp;&nbsp;<a href="#server-driven.negotiation">Server-driven Negotiation</a></li>
     629               <li><a href="#rfc.section.12.2">12.2</a>&nbsp;&nbsp;&nbsp;<a href="#agent-driven.negotiation">Agent-driven Negotiation</a></li>
     630               <li><a href="#rfc.section.12.3">12.3</a>&nbsp;&nbsp;&nbsp;<a href="#transparent.negotiation">Transparent Negotiation</a></li>
    639631            </ul>
    640632         </li>
    641          <li>13.&nbsp;&nbsp;&nbsp;<a href="#caching">Caching in HTTP</a><ul>
    642                <li>13.1&nbsp;&nbsp;&nbsp;<a href="#rfc.section.13.1"></a><ul>
    643                      <li>13.1.1&nbsp;&nbsp;&nbsp;<a href="#cache.correctness">Cache Correctness</a></li>
    644                      <li>13.1.2&nbsp;&nbsp;&nbsp;<a href="#warnings">Warnings</a></li>
    645                      <li>13.1.3&nbsp;&nbsp;&nbsp;<a href="#cache-control.mechanisms">Cache-control Mechanisms</a></li>
    646                      <li>13.1.4&nbsp;&nbsp;&nbsp;<a href="#explicit.ua.warnings">Explicit User Agent Warnings</a></li>
    647                      <li>13.1.5&nbsp;&nbsp;&nbsp;<a href="#exceptions.to.the.rules.and.warnings">Exceptions to the Rules and Warnings</a></li>
    648                      <li>13.1.6&nbsp;&nbsp;&nbsp;<a href="#client-controlled.behavior">Client-controlled Behavior</a></li>
     633         <li><a href="#rfc.section.13">13.</a>&nbsp;&nbsp;&nbsp;<a href="#caching">Caching in HTTP</a><ul>
     634               <li><a href="#rfc.section.13.1">13.1</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.13.1"></a><ul>
     635                     <li><a href="#rfc.section.13.1.1">13.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#cache.correctness">Cache Correctness</a></li>
     636                     <li><a href="#rfc.section.13.1.2">13.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#warnings">Warnings</a></li>
     637                     <li><a href="#rfc.section.13.1.3">13.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#cache-control.mechanisms">Cache-control Mechanisms</a></li>
     638                     <li><a href="#rfc.section.13.1.4">13.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#explicit.ua.warnings">Explicit User Agent Warnings</a></li>
     639                     <li><a href="#rfc.section.13.1.5">13.1.5</a>&nbsp;&nbsp;&nbsp;<a href="#exceptions.to.the.rules.and.warnings">Exceptions to the Rules and Warnings</a></li>
     640                     <li><a href="#rfc.section.13.1.6">13.1.6</a>&nbsp;&nbsp;&nbsp;<a href="#client-controlled.behavior">Client-controlled Behavior</a></li>
    649641                  </ul>
    650642               </li>
    651                <li>13.2&nbsp;&nbsp;&nbsp;<a href="#expiration.model">Expiration Model</a><ul>
    652                      <li>13.2.1&nbsp;&nbsp;&nbsp;<a href="#server-specified.expiration">Server-Specified Expiration</a></li>
    653                      <li>13.2.2&nbsp;&nbsp;&nbsp;<a href="#heuristic.expiration">Heuristic Expiration</a></li>
    654                      <li>13.2.3&nbsp;&nbsp;&nbsp;<a href="#age.calculations">Age Calculations</a></li>
    655                      <li>13.2.4&nbsp;&nbsp;&nbsp;<a href="#expiration.calculations">Expiration Calculations</a></li>
    656                      <li>13.2.5&nbsp;&nbsp;&nbsp;<a href="#disambiguating.expiration.values">Disambiguating Expiration Values</a></li>
    657                      <li>13.2.6&nbsp;&nbsp;&nbsp;<a href="#disambiguating.multiple.responses">Disambiguating Multiple Responses</a></li>
     643               <li><a href="#rfc.section.13.2">13.2</a>&nbsp;&nbsp;&nbsp;<a href="#expiration.model">Expiration Model</a><ul>
     644                     <li><a href="#rfc.section.13.2.1">13.2.1</a>&nbsp;&nbsp;&nbsp;<a href="#server-specified.expiration">Server-Specified Expiration</a></li>
     645                     <li><a href="#rfc.section.13.2.2">13.2.2</a>&nbsp;&nbsp;&nbsp;<a href="#heuristic.expiration">Heuristic Expiration</a></li>
     646                     <li><a href="#rfc.section.13.2.3">13.2.3</a>&nbsp;&nbsp;&nbsp;<a href="#age.calculations">Age Calculations</a></li>
     647                     <li><a href="#rfc.section.13.2.4">13.2.4</a>&nbsp;&nbsp;&nbsp;<a href="#expiration.calculations">Expiration Calculations</a></li>
     648                     <li><a href="#rfc.section.13.2.5">13.2.5</a>&nbsp;&nbsp;&nbsp;<a href="#disambiguating.expiration.values">Disambiguating Expiration Values</a></li>
     649                     <li><a href="#rfc.section.13.2.6">13.2.6</a>&nbsp;&nbsp;&nbsp;<a href="#disambiguating.multiple.responses">Disambiguating Multiple Responses</a></li>
    658650                  </ul>
    659651               </li>
    660                <li>13.3&nbsp;&nbsp;&nbsp;<a href="#validation.model">Validation Model</a><ul>
    661                      <li>13.3.1&nbsp;&nbsp;&nbsp;<a href="#last-modified.dates">Last-Modified Dates</a></li>
    662                      <li>13.3.2&nbsp;&nbsp;&nbsp;<a href="#entity.tag.cache.validators">Entity Tag Cache Validators</a></li>
    663                      <li>13.3.3&nbsp;&nbsp;&nbsp;<a href="#weak.and.strong.validators">Weak and Strong Validators</a></li>
    664                      <li>13.3.4&nbsp;&nbsp;&nbsp;<a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></li>
    665                      <li>13.3.5&nbsp;&nbsp;&nbsp;<a href="#non-validating.conditionals">Non-validating Conditionals</a></li>
     652               <li><a href="#rfc.section.13.3">13.3</a>&nbsp;&nbsp;&nbsp;<a href="#validation.model">Validation Model</a><ul>
     653                     <li><a href="#rfc.section.13.3.1">13.3.1</a>&nbsp;&nbsp;&nbsp;<a href="#last-modified.dates">Last-Modified Dates</a></li>
     654                     <li><a href="#rfc.section.13.3.2">13.3.2</a>&nbsp;&nbsp;&nbsp;<a href="#entity.tag.cache.validators">Entity Tag Cache Validators</a></li>
     655                     <li><a href="#rfc.section.13.3.3">13.3.3</a>&nbsp;&nbsp;&nbsp;<a href="#weak.and.strong.validators">Weak and Strong Validators</a></li>
     656                     <li><a href="#rfc.section.13.3.4">13.3.4</a>&nbsp;&nbsp;&nbsp;<a href="#rules.for.when.to.use.entity.tags.and.last-modified.dates">Rules for When to Use Entity Tags and Last-Modified Dates</a></li>
     657                     <li><a href="#rfc.section.13.3.5">13.3.5</a>&nbsp;&nbsp;&nbsp;<a href="#non-validating.conditionals">Non-validating Conditionals</a></li>
    666658                  </ul>
    667659               </li>
    668                <li>13.4&nbsp;&nbsp;&nbsp;<a href="#response.cacheability">Response Cacheability</a></li>
    669                <li>13.5&nbsp;&nbsp;&nbsp;<a href="#constructing.responses.from.caches">Constructing Responses From Caches</a><ul>
    670                      <li>13.5.1&nbsp;&nbsp;&nbsp;<a href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></li>
    671                      <li>13.5.2&nbsp;&nbsp;&nbsp;<a href="#non-modifiable.headers">Non-modifiable Headers</a></li>
    672                      <li>13.5.3&nbsp;&nbsp;&nbsp;<a href="#combining.headers">Combining Headers</a></li>
    673                      <li>13.5.4&nbsp;&nbsp;&nbsp;<a href="#combining.byte.ranges">Combining Byte Ranges</a></li>
     660               <li><a href="#rfc.section.13.4">13.4</a>&nbsp;&nbsp;&nbsp;<a href="#response.cacheability">Response Cacheability</a></li>
     661               <li><a href="#rfc.section.13.5">13.5</a>&nbsp;&nbsp;&nbsp;<a href="#constructing.responses.from.caches">Constructing Responses From Caches</a><ul>
     662                     <li><a href="#rfc.section.13.5.1">13.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#end-to-end.and.hop-by-hop.headers">End-to-end and Hop-by-hop Headers</a></li>
     663                     <li><a href="#rfc.section.13.5.2">13.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#non-modifiable.headers">Non-modifiable Headers</a></li>
     664                     <li><a href="#rfc.section.13.5.3">13.5.3</a>&nbsp;&nbsp;&nbsp;<a href="#combining.headers">Combining Headers</a></li>
     665                     <li><a href="#rfc.section.13.5.4">13.5.4</a>&nbsp;&nbsp;&nbsp;<a href="#combining.byte.ranges">Combining Byte Ranges</a></li>
    674666                  </ul>
    675667               </li>
    676                <li>13.6&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li>
    677                <li>13.7&nbsp;&nbsp;&nbsp;<a href="#shared.and.non-shared.caches">Shared and Non-Shared Caches</a></li>
    678                <li>13.8&nbsp;&nbsp;&nbsp;<a href="#errors.or.incomplete.response.cache.behavior">Errors or Incomplete Response Cache Behavior</a></li>
    679                <li>13.9&nbsp;&nbsp;&nbsp;<a href="#side.effects.of.get.and.head">Side Effects of GET and HEAD</a></li>
    680                <li>13.10&nbsp;&nbsp;&nbsp;<a href="#invalidation.after.updates.or.deletions">Invalidation After Updates or Deletions</a></li>
    681                <li>13.11&nbsp;&nbsp;&nbsp;<a href="#write-through.mandatory">Write-Through Mandatory</a></li>
    682                <li>13.12&nbsp;&nbsp;&nbsp;<a href="#cache.replacement">Cache Replacement</a></li>
    683                <li>13.13&nbsp;&nbsp;&nbsp;<a href="#history.lists">History Lists</a></li>
     668               <li><a href="#rfc.section.13.6">13.6</a>&nbsp;&nbsp;&nbsp;<a href="#caching.negotiated.responses">Caching Negotiated Responses</a></li>
     669               <li><a href="#rfc.section.13.7">13.7</a>&nbsp;&nbsp;&nbsp;<a href="#shared.and.non-shared.caches">Shared and Non-Shared Caches</a></li>
     670               <li><a href="#rfc.section.13.8">13.8</a>&nbsp;&nbsp;&nbsp;<a href="#errors.or.incomplete.response.cache.behavior">Errors or Incomplete Response Cache Behavior</a></li>
     671               <li><a href="#rfc.section.13.9">13.9</a>&nbsp;&nbsp;&nbsp;<a href="#side.effects.of.get.and.head">Side Effects of GET and HEAD</a></li>
     672               <li><a href="#rfc.section.13.10">13.10</a>&nbsp;&nbsp;&nbsp;<a href="#invalidation.after.updates.or.deletions">Invalidation After Updates or Deletions</a></li>
     673               <li><a href="#rfc.section.13.11">13.11</a>&nbsp;&nbsp;&nbsp;<a href="#write-through.mandatory">Write-Through Mandatory</a></li>
     674               <li><a href="#rfc.section.13.12">13.12</a>&nbsp;&nbsp;&nbsp;<a href="#cache.replacement">Cache Replacement</a></li>
     675               <li><a href="#rfc.section.13.13">13.13</a>&nbsp;&nbsp;&nbsp;<a href="#history.lists">History Lists</a></li>
    684676            </ul>
    685677         </li>
    686          <li>14.&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul>
    687                <li>14.1&nbsp;&nbsp;&nbsp;<a href="#header.accept">Accept</a></li>
    688                <li>14.2&nbsp;&nbsp;&nbsp;<a href="#header.accept-charset">Accept-Charset</a></li>
    689                <li>14.3&nbsp;&nbsp;&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></li>
    690                <li>14.4&nbsp;&nbsp;&nbsp;<a href="#header.accept-language">Accept-Language</a></li>
    691                <li>14.5&nbsp;&nbsp;&nbsp;<a href="#header.accept-ranges">Accept-Ranges</a></li>
    692                <li>14.6&nbsp;&nbsp;&nbsp;<a href="#header.age">Age</a></li>
    693                <li>14.7&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li>
    694                <li>14.8&nbsp;&nbsp;&nbsp;<a href="#header.authorization">Authorization</a></li>
    695                <li>14.9&nbsp;&nbsp;&nbsp;<a href="#header.cache-control">Cache-Control</a><ul>
    696                      <li>14.9.1&nbsp;&nbsp;&nbsp;<a href="#what.is.cacheable">What is Cacheable</a></li>
    697                      <li>14.9.2&nbsp;&nbsp;&nbsp;<a href="#what.may.be.stored.by.caches">What May be Stored by Caches</a></li>
    698                      <li>14.9.3&nbsp;&nbsp;&nbsp;<a href="#modifications.of.the.basic.expiration.mechanism">Modifications of the Basic Expiration Mechanism</a></li>
    699                      <li>14.9.4&nbsp;&nbsp;&nbsp;<a href="#cache.revalidation.and.reload.controls">Cache Revalidation and Reload Controls</a></li>
    700                      <li>14.9.5&nbsp;&nbsp;&nbsp;<a href="#no-transform.directive">No-Transform Directive</a></li>
    701                      <li>14.9.6&nbsp;&nbsp;&nbsp;<a href="#cache.control.extensions">Cache Control Extensions</a></li>
     678         <li><a href="#rfc.section.14">14.</a>&nbsp;&nbsp;&nbsp;<a href="#header.fields">Header Field Definitions</a><ul>
     679               <li><a href="#rfc.section.14.1">14.1</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept">Accept</a></li>
     680               <li><a href="#rfc.section.14.2">14.2</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-charset">Accept-Charset</a></li>
     681               <li><a href="#rfc.section.14.3">14.3</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-encoding">Accept-Encoding</a></li>
     682               <li><a href="#rfc.section.14.4">14.4</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-language">Accept-Language</a></li>
     683               <li><a href="#rfc.section.14.5">14.5</a>&nbsp;&nbsp;&nbsp;<a href="#header.accept-ranges">Accept-Ranges</a></li>
     684               <li><a href="#rfc.section.14.6">14.6</a>&nbsp;&nbsp;&nbsp;<a href="#header.age">Age</a></li>
     685               <li><a href="#rfc.section.14.7">14.7</a>&nbsp;&nbsp;&nbsp;<a href="#header.allow">Allow</a></li>
     686               <li><a href="#rfc.section.14.8">14.8</a>&nbsp;&nbsp;&nbsp;<a href="#header.authorization">Authorization</a></li>
     687               <li><a href="#rfc.section.14.9">14.9</a>&nbsp;&nbsp;&nbsp;<a href="#header.cache-control">Cache-Control</a><ul>
     688                     <li><a href="#rfc.section.14.9.1">14.9.1</a>&nbsp;&nbsp;&nbsp;<a href="#what.is.cacheable">What is Cacheable</a></li>
     689                     <li><a href="#rfc.section.14.9.2">14.9.2</a>&nbsp;&nbsp;&nbsp;<a href="#what.may.be.stored.by.caches">What May be Stored by Caches</a></li>
     690                     <li><a href="#rfc.section.14.9.3">14.9.3</a>&nbsp;&nbsp;&nbsp;<a href="#modifications.of.the.basic.expiration.mechanism">Modifications of the Basic Expiration Mechanism</a></li>
     691                     <li><a href="#rfc.section.14.9.4">14.9.4</a>&nbsp;&nbsp;&nbsp;<a href="#cache.revalidation.and.reload.controls">Cache Revalidation and Reload Controls</a></li>
     692                     <li><a href="#rfc.section.14.9.5">14.9.5</a>&nbsp;&nbsp;&nbsp;<a href="#no-transform.directive">No-Transform Directive</a></li>
     693                     <li><a href="#rfc.section.14.9.6">14.9.6</a>&nbsp;&nbsp;&nbsp;<a href="#cache.control.extensions">Cache Control Extensions</a></li>
    702694                  </ul>
    703695               </li>
    704                <li>14.10&nbsp;&nbsp;&nbsp;<a href="#header.connection">Connection</a></li>
    705                <li>14.11&nbsp;&nbsp;&nbsp;<a href="#header.content-encoding">Content-Encoding</a></li>
    706                <li>14.12&nbsp;&nbsp;&nbsp;<a href="#header.content-language">Content-Language</a></li>
    707                <li>14.13&nbsp;&nbsp;&nbsp;<a href="#header.content-length">Content-Length</a></li>
    708                <li>14.14&nbsp;&nbsp;&nbsp;<a href="#header.content-location">Content-Location</a></li>
    709                <li>14.15&nbsp;&nbsp;&nbsp;<a href="#header.content-md5">Content-MD5</a></li>
    710                <li>14.16&nbsp;&nbsp;&nbsp;<a href="#header.content-range">Content-Range</a></li>
    711                <li>14.17&nbsp;&nbsp;&nbsp;<a href="#header.content-type">Content-Type</a></li>
    712                <li>14.18&nbsp;&nbsp;&nbsp;<a href="#header.date">Date</a><ul>
    713                      <li>14.18.1&nbsp;&nbsp;&nbsp;<a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></li>
     696               <li><a href="#rfc.section.14.10">14.10</a>&nbsp;&nbsp;&nbsp;<a href="#header.connection">Connection</a></li>
     697               <li><a href="#rfc.section.14.11">14.11</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-encoding">Content-Encoding</a></li>
     698               <li><a href="#rfc.section.14.12">14.12</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-language">Content-Language</a></li>
     699               <li><a href="#rfc.section.14.13">14.13</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-length">Content-Length</a></li>
     700               <li><a href="#rfc.section.14.14">14.14</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-location">Content-Location</a></li>
     701               <li><a href="#rfc.section.14.15">14.15</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-md5">Content-MD5</a></li>
     702               <li><a href="#rfc.section.14.16">14.16</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-range">Content-Range</a></li>
     703               <li><a href="#rfc.section.14.17">14.17</a>&nbsp;&nbsp;&nbsp;<a href="#header.content-type">Content-Type</a></li>
     704               <li><a href="#rfc.section.14.18">14.18</a>&nbsp;&nbsp;&nbsp;<a href="#header.date">Date</a><ul>
     705                     <li><a href="#rfc.section.14.18.1">14.18.1</a>&nbsp;&nbsp;&nbsp;<a href="#clockless.origin.server.operation">Clockless Origin Server Operation</a></li>
    714706                  </ul>
    715707               </li>
    716                <li>14.19&nbsp;&nbsp;&nbsp;<a href="#header.etag">ETag</a></li>
    717                <li>14.20&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li>
    718                <li>14.21&nbsp;&nbsp;&nbsp;<a href="#header.expires">Expires</a></li>
    719                <li>14.22&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li>
    720                <li>14.23&nbsp;&nbsp;&nbsp;<a href="#header.host">Host</a></li>
    721                <li>14.24&nbsp;&nbsp;&nbsp;<a href="#header.if-match">If-Match</a></li>
    722                <li>14.25&nbsp;&nbsp;&nbsp;<a href="#header.if-modified-since">If-Modified-Since</a></li>
    723                <li>14.26&nbsp;&nbsp;&nbsp;<a href="#header.if-none-match">If-None-Match</a></li>
    724                <li>14.27&nbsp;&nbsp;&nbsp;<a href="#header.if-range">If-Range</a></li>
    725                <li>14.28&nbsp;&nbsp;&nbsp;<a href="#header.if-unmodified-since">If-Unmodified-Since</a></li>
    726                <li>14.29&nbsp;&nbsp;&nbsp;<a href="#header.last-modified">Last-Modified</a></li>
    727                <li>14.30&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li>
    728                <li>14.31&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li>
    729                <li>14.32&nbsp;&nbsp;&nbsp;<a href="#header.pragma">Pragma</a></li>
    730                <li>14.33&nbsp;&nbsp;&nbsp;<a href="#header.proxy-authenticate">Proxy-Authenticate</a></li>
    731                <li>14.34&nbsp;&nbsp;&nbsp;<a href="#header.proxy-authorization">Proxy-Authorization</a></li>
    732                <li>14.35&nbsp;&nbsp;&nbsp;<a href="#header.range">Range</a><ul>
    733                      <li>14.35.1&nbsp;&nbsp;&nbsp;<a href="#byte.ranges">Byte Ranges</a></li>
    734                      <li>14.35.2&nbsp;&nbsp;&nbsp;<a href="#range.retrieval.requests">Range Retrieval Requests</a></li>
     708               <li><a href="#rfc.section.14.19">14.19</a>&nbsp;&nbsp;&nbsp;<a href="#header.etag">ETag</a></li>
     709               <li><a href="#rfc.section.14.20">14.20</a>&nbsp;&nbsp;&nbsp;<a href="#header.expect">Expect</a></li>
     710               <li><a href="#rfc.section.14.21">14.21</a>&nbsp;&nbsp;&nbsp;<a href="#header.expires">Expires</a></li>
     711               <li><a href="#rfc.section.14.22">14.22</a>&nbsp;&nbsp;&nbsp;<a href="#header.from">From</a></li>
     712               <li><a href="#rfc.section.14.23">14.23</a>&nbsp;&nbsp;&nbsp;<a href="#header.host">Host</a></li>
     713               <li><a href="#rfc.section.14.24">14.24</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-match">If-Match</a></li>
     714               <li><a href="#rfc.section.14.25">14.25</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-modified-since">If-Modified-Since</a></li>
     715               <li><a href="#rfc.section.14.26">14.26</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-none-match">If-None-Match</a></li>
     716               <li><a href="#rfc.section.14.27">14.27</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-range">If-Range</a></li>
     717               <li><a href="#rfc.section.14.28">14.28</a>&nbsp;&nbsp;&nbsp;<a href="#header.if-unmodified-since">If-Unmodified-Since</a></li>
     718               <li><a href="#rfc.section.14.29">14.29</a>&nbsp;&nbsp;&nbsp;<a href="#header.last-modified">Last-Modified</a></li>
     719               <li><a href="#rfc.section.14.30">14.30</a>&nbsp;&nbsp;&nbsp;<a href="#header.location">Location</a></li>
     720               <li><a href="#rfc.section.14.31">14.31</a>&nbsp;&nbsp;&nbsp;<a href="#header.max-forwards">Max-Forwards</a></li>
     721               <li><a href="#rfc.section.14.32">14.32</a>&nbsp;&nbsp;&nbsp;<a href="#header.pragma">Pragma</a></li>
     722               <li><a href="#rfc.section.14.33">14.33</a>&nbsp;&nbsp;&nbsp;<a href="#header.proxy-authenticate">Proxy-Authenticate</a></li>
     723               <li><a href="#rfc.section.14.34">14.34</a>&nbsp;&nbsp;&nbsp;<a href="#header.proxy-authorization">Proxy-Authorization</a></li>
     724               <li><a href="#rfc.section.14.35">14.35</a>&nbsp;&nbsp;&nbsp;<a href="#header.range">Range</a><ul>
     725                     <li><a href="#rfc.section.14.35.1">14.35.1</a>&nbsp;&nbsp;&nbsp;<a href="#byte.ranges">Byte Ranges</a></li>
     726                     <li><a href="#rfc.section.14.35.2">14.35.2</a>&nbsp;&nbsp;&nbsp;<a href="#range.retrieval.requests">Range Retrieval Requests</a></li>
    735727                  </ul>
    736728               </li>
    737                <li>14.36&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li>
    738                <li>14.37&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li>
    739                <li>14.38&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li>
    740                <li>14.39&nbsp;&nbsp;&nbsp;<a href="#header.te">TE</a></li>
    741                <li>14.40&nbsp;&nbsp;&nbsp;<a href="#header.trailer">Trailer</a></li>
    742                <li>14.41&nbsp;&nbsp;&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></li>
    743                <li>14.42&nbsp;&nbsp;&nbsp;<a href="#header.upgrade">Upgrade</a></li>
    744                <li>14.43&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li>
    745                <li>14.44&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li>
    746                <li>14.45&nbsp;&nbsp;&nbsp;<a href="#header.via">Via</a></li>
    747                <li>14.46&nbsp;&nbsp;&nbsp;<a href="#header.warning">Warning</a></li>
    748                <li>14.47&nbsp;&nbsp;&nbsp;<a href="#header.www-authenticate">WWW-Authenticate</a></li>
     729               <li><a href="#rfc.section.14.36">14.36</a>&nbsp;&nbsp;&nbsp;<a href="#header.referer">Referer</a></li>
     730               <li><a href="#rfc.section.14.37">14.37</a>&nbsp;&nbsp;&nbsp;<a href="#header.retry-after">Retry-After</a></li>
     731               <li><a href="#rfc.section.14.38">14.38</a>&nbsp;&nbsp;&nbsp;<a href="#header.server">Server</a></li>
     732               <li><a href="#rfc.section.14.39">14.39</a>&nbsp;&nbsp;&nbsp;<a href="#header.te">TE</a></li>
     733               <li><a href="#rfc.section.14.40">14.40</a>&nbsp;&nbsp;&nbsp;<a href="#header.trailer">Trailer</a></li>
     734               <li><a href="#rfc.section.14.41">14.41</a>&nbsp;&nbsp;&nbsp;<a href="#header.transfer-encoding">Transfer-Encoding</a></li>
     735               <li><a href="#rfc.section.14.42">14.42</a>&nbsp;&nbsp;&nbsp;<a href="#header.upgrade">Upgrade</a></li>
     736               <li><a href="#rfc.section.14.43">14.43</a>&nbsp;&nbsp;&nbsp;<a href="#header.user-agent">User-Agent</a></li>
     737               <li><a href="#rfc.section.14.44">14.44</a>&nbsp;&nbsp;&nbsp;<a href="#header.vary">Vary</a></li>
     738               <li><a href="#rfc.section.14.45">14.45</a>&nbsp;&nbsp;&nbsp;<a href="#header.via">Via</a></li>
     739               <li><a href="#rfc.section.14.46">14.46</a>&nbsp;&nbsp;&nbsp;<a href="#header.warning">Warning</a></li>
     740               <li><a href="#rfc.section.14.47">14.47</a>&nbsp;&nbsp;&nbsp;<a href="#header.www-authenticate">WWW-Authenticate</a></li>
    749741            </ul>
    750742         </li>
    751          <li>15.&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
    752                <li>15.1&nbsp;&nbsp;&nbsp;<a href="#personal.information">Personal Information</a><ul>
    753                      <li>15.1.1&nbsp;&nbsp;&nbsp;<a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></li>
    754                      <li>15.1.2&nbsp;&nbsp;&nbsp;<a href="#security.sensitive">Transfer of Sensitive Information</a></li>
    755                      <li>15.1.3&nbsp;&nbsp;&nbsp;<a href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URI's</a></li>
    756                      <li>15.1.4&nbsp;&nbsp;&nbsp;<a href="#privacy.issues.connected.to.accept.headers">Privacy Issues Connected to Accept Headers</a></li>
     743         <li><a href="#rfc.section.15">15.</a>&nbsp;&nbsp;&nbsp;<a href="#security.considerations">Security Considerations</a><ul>
     744               <li><a href="#rfc.section.15.1">15.1</a>&nbsp;&nbsp;&nbsp;<a href="#personal.information">Personal Information</a><ul>
     745                     <li><a href="#rfc.section.15.1.1">15.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#abuse.of.server.log.information">Abuse of Server Log Information</a></li>
     746                     <li><a href="#rfc.section.15.1.2">15.1.2</a>&nbsp;&nbsp;&nbsp;<a href="#security.sensitive">Transfer of Sensitive Information</a></li>
     747                     <li><a href="#rfc.section.15.1.3">15.1.3</a>&nbsp;&nbsp;&nbsp;<a href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URI's</a></li>
     748                     <li><a href="#rfc.section.15.1.4">15.1.4</a>&nbsp;&nbsp;&nbsp;<a href="#privacy.issues.connected.to.accept.headers">Privacy Issues Connected to Accept Headers</a></li>
    757749                  </ul>
    758750               </li>
    759                <li>15.2&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based On File and Path Names</a></li>
    760                <li>15.3&nbsp;&nbsp;&nbsp;<a href="#dns.spoofing">DNS Spoofing</a></li>
    761                <li>15.4&nbsp;&nbsp;&nbsp;<a href="#location.spoofing">Location Headers and Spoofing</a></li>
    762                <li>15.5&nbsp;&nbsp;&nbsp;<a href="#content-disposition.issues">Content-Disposition Issues</a></li>
    763                <li>15.6&nbsp;&nbsp;&nbsp;<a href="#auth.credentials.and.idle.clients">Authentication Credentials and Idle Clients</a></li>
    764                <li>15.7&nbsp;&nbsp;&nbsp;<a href="#attack.proxies">Proxies and Caching</a><ul>
    765                      <li>15.7.1&nbsp;&nbsp;&nbsp;<a href="#attack.DoS">Denial of Service Attacks on Proxies</a></li>
     751               <li><a href="#rfc.section.15.2">15.2</a>&nbsp;&nbsp;&nbsp;<a href="#attack.pathname">Attacks Based On File and Path Names</a></li>
     752               <li><a href="#rfc.section.15.3">15.3</a>&nbsp;&nbsp;&nbsp;<a href="#dns.spoofing">DNS Spoofing</a></li>
     753               <li><a href="#rfc.section.15.4">15.4</a>&nbsp;&nbsp;&nbsp;<a href="#location.spoofing">Location Headers and Spoofing</a></li>
     754               <li><a href="#rfc.section.15.5">15.5</a>&nbsp;&nbsp;&nbsp;<a href="#content-disposition.issues">Content-Disposition Issues</a></li>
     755               <li><a href="#rfc.section.15.6">15.6</a>&nbsp;&nbsp;&nbsp;<a href="#auth.credentials.and.idle.clients">Authentication Credentials and Idle Clients</a></li>
     756               <li><a href="#rfc.section.15.7">15.7</a>&nbsp;&nbsp;&nbsp;<a href="#attack.proxies">Proxies and Caching</a><ul>
     757                     <li><a href="#rfc.section.15.7.1">15.7.1</a>&nbsp;&nbsp;&nbsp;<a href="#attack.DoS">Denial of Service Attacks on Proxies</a></li>
    766758                  </ul>
    767759               </li>
    768760            </ul>
    769761         </li>
    770          <li>16.&nbsp;&nbsp;&nbsp;<a href="#acknowledgments">Acknowledgments</a></li>
    771          <li>17.&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a></li>
    772          <li>18.&nbsp;&nbsp;&nbsp;<a href="#rfc.authors">Authors' Addresses</a></li>
    773          <li>19.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.19">Appendices</a><ul>
    774                <li>19.1&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.http">Internet Media Type message/http and application/http</a></li>
    775                <li>19.2&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.multipart.byteranges">Internet Media Type multipart/byteranges</a></li>
    776                <li>19.3&nbsp;&nbsp;&nbsp;<a href="#tolerant.applications">Tolerant Applications</a></li>
    777                <li>19.4&nbsp;&nbsp;&nbsp;<a href="#differences.between.http.entities.and.rfc.2045.entities">Differences Between HTTP Entities and RFC 2045 Entities</a><ul>
    778                      <li>19.4.1&nbsp;&nbsp;&nbsp;<a href="#mime-version">MIME-Version</a></li>
    779                      <li>19.4.2&nbsp;&nbsp;&nbsp;<a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li>
    780                      <li>19.4.3&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>
    781                      <li>19.4.4&nbsp;&nbsp;&nbsp;<a href="#introduction.of.content-encoding">Introduction of Content-Encoding</a></li>
    782                      <li>19.4.5&nbsp;&nbsp;&nbsp;<a href="#no.content-transfer-encoding">No Content-Transfer-Encoding</a></li>
    783                      <li>19.4.6&nbsp;&nbsp;&nbsp;<a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></li>
    784                      <li>19.4.7&nbsp;&nbsp;&nbsp;<a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li>
     762         <li><a href="#rfc.section.16">16.</a>&nbsp;&nbsp;&nbsp;<a href="#acknowledgments">Acknowledgments</a></li>
     763         <li><a href="#rfc.section.17">17.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.references">References</a></li>
     764         <li><a href="#rfc.section.18">18.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.authors">Authors' Addresses</a></li>
     765         <li><a href="#rfc.section.19">19.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.19">Appendices</a><ul>
     766               <li><a href="#rfc.section.19.1">19.1</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.http">Internet Media Type message/http and application/http</a></li>
     767               <li><a href="#rfc.section.19.2">19.2</a>&nbsp;&nbsp;&nbsp;<a href="#internet.media.type.multipart.byteranges">Internet Media Type multipart/byteranges</a></li>
     768               <li><a href="#rfc.section.19.3">19.3</a>&nbsp;&nbsp;&nbsp;<a href="#tolerant.applications">Tolerant Applications</a></li>
     769               <li><a href="#rfc.section.19.4">19.4</a>&nbsp;&nbsp;&nbsp;<a href="#differences.between.http.entities.and.rfc.2045.entities">Differences Between HTTP Entities and RFC 2045 Entities</a><ul>
     770                     <li><a href="#rfc.section.19.4.1">19.4.1</a>&nbsp;&nbsp;&nbsp;<a href="#mime-version">MIME-Version</a></li>
     771                     <li><a href="#rfc.section.19.4.2">19.4.2</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.to.canonical.form">Conversion to Canonical Form</a></li>
     772                     <li><a href="#rfc.section.19.4.3">19.4.3</a>&nbsp;&nbsp;&nbsp;<a href="#conversion.of.date.formats">Conversion of Date Formats</a></li>
     773                     <li><a href="#rfc.section.19.4.4">19.4.4</a>&nbsp;&nbsp;&nbsp;<a href="#introduction.of.content-encoding">Introduction of Content-Encoding</a></li>
     774                     <li><a href="#rfc.section.19.4.5">19.4.5</a>&nbsp;&nbsp;&nbsp;<a href="#no.content-transfer-encoding">No Content-Transfer-Encoding</a></li>
     775                     <li><a href="#rfc.section.19.4.6">19.4.6</a>&nbsp;&nbsp;&nbsp;<a href="#introduction.of.transfer-encoding">Introduction of Transfer-Encoding</a></li>
     776                     <li><a href="#rfc.section.19.4.7">19.4.7</a>&nbsp;&nbsp;&nbsp;<a href="#mhtml.line.length">MHTML and Line Length Limitations</a></li>
    785777                  </ul>
    786778               </li>
    787                <li>19.5&nbsp;&nbsp;&nbsp;<a href="#additional.features">Additional Features</a><ul>
    788                      <li>19.5.1&nbsp;&nbsp;&nbsp;<a href="#content-disposition">Content-Disposition</a></li>
     779               <li><a href="#rfc.section.19.5">19.5</a>&nbsp;&nbsp;&nbsp;<a href="#additional.features">Additional Features</a><ul>
     780                     <li><a href="#rfc.section.19.5.1">19.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#content-disposition">Content-Disposition</a></li>
    789781                  </ul>
    790782               </li>
    791                <li>19.6&nbsp;&nbsp;&nbsp;<a href="#compatibility">Compatibility with Previous Versions</a><ul>
    792                      <li>19.6.1&nbsp;&nbsp;&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul>
    793                            <li>19.6.1.1&nbsp;&nbsp;&nbsp;<a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></li>
     783               <li><a href="#rfc.section.19.6">19.6</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility">Compatibility with Previous Versions</a><ul>
     784                     <li><a href="#rfc.section.19.6.1">19.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.1.0">Changes from HTTP/1.0</a><ul>
     785                           <li><a href="#rfc.section.19.6.1.1">19.6.1.1</a>&nbsp;&nbsp;&nbsp;<a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses</a></li>
    794786                        </ul>
    795787                     </li>
    796                      <li>19.6.2&nbsp;&nbsp;&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></li>
    797                      <li>19.6.3&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li>
     788                     <li><a href="#rfc.section.19.6.2">19.6.2</a>&nbsp;&nbsp;&nbsp;<a href="#compatibility.with.http.1.0.persistent.connections">Compatibility with HTTP/1.0 Persistent Connections</a></li>
     789                     <li><a href="#rfc.section.19.6.3">19.6.3</a>&nbsp;&nbsp;&nbsp;<a href="#changes.from.rfc.2068">Changes from RFC 2068</a></li>
    798790                  </ul>
    799791               </li>
    800792            </ul>
    801793         </li>
    802          <li>20.&nbsp;&nbsp;&nbsp;<a href="#rfc.section.20">Index</a></li>
     794         <li><a href="#rfc.section.20">20.</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.20">Index</a></li>
    803795         <li><a href="#rfc.index">Index</a></li>
    804796         <li><a href="#rfc.ipr">Intellectual Property and Copyright Statements</a></li>
    805797      </ul>
    806798      <hr class="noprint">
    807       <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a id="introduction" href="#introduction">Introduction</a></h1>
    808       <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a id="intro.purpose" href="#intro.purpose">Purpose</a></h2>
    809       <p id="rfc.section.1.1.p.1">The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information
    810          systems. HTTP has been in use by the World-Wide Web global information initiative since 1990. The first version of HTTP, referred
    811          to as HTTP/0.9, was a simple protocol for raw data transfer across the Internet. HTTP/1.0, as defined by RFC 1945 <a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[6]</cite></a>, improved the protocol by allowing messages to be in the format of MIME-like messages, containing metainformation about the
    812          data transferred and modifiers on the request/response semantics. However, HTTP/1.0 does not sufficiently take into consideration
    813          the effects of hierarchical proxies, caching, the need for persistent connections, or virtual hosts. In addition, the proliferation
    814          of incompletely-implemented applications calling themselves "HTTP/1.0" has necessitated a protocol version change in order
    815          for two communicating applications to determine each other's true capabilities.
    816       </p>
    817       <p id="rfc.section.1.1.p.2">This specification defines the protocol referred to as "HTTP/1.1". This protocol includes more stringent requirements than
    818          HTTP/1.0 in order to ensure reliable implementation of its features.
    819       </p>
    820       <p id="rfc.section.1.1.p.3">Practical information systems require more functionality than simple retrieval, including search, front-end update, and annotation.
    821          HTTP allows an open-ended set of methods and headers that indicate the purpose of a request <a href="#RFC2324" id="rfc.xref.RFC2324.2"><cite title="Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)">[47]</cite></a>. It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) <a href="#RFC1630" id="rfc.xref.RFC1630.1"><cite title="Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web">[3]</cite></a>, as a location (URL) <a href="#RFC1738" id="rfc.xref.RFC1738.1"><cite title="Uniform Resource Locators (URL)">[4]</cite></a> or name (URN) <a href="#RFC1737" id="rfc.xref.RFC1737.1"><cite title="Functional Requirements for Uniform Resource Names">[20]</cite></a>, for indicating the resource to which a method is to be applied. Messages are passed in a format similar to that used by
    822          Internet mail <a href="#RFC822" id="rfc.xref.RFC822.1"><cite title="Standard for the format of ARPA Internet text messages">[9]</cite></a> as defined by the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[7]</cite></a>.
    823       </p>
    824       <p id="rfc.section.1.1.p.4">HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet systems,
    825          including those supported by the SMTP <a href="#RFC821" id="rfc.xref.RFC821.1"><cite title="Simple Mail Transfer Protocol">[16]</cite></a>, NNTP <a href="#RFC977" id="rfc.xref.RFC977.1"><cite title="Network News Transfer Protocol">[13]</cite></a>, FTP <a href="#RFC959" id="rfc.xref.RFC959.1"><cite title="File Transfer Protocol">[18]</cite></a>, Gopher <a href="#RFC1436" id="rfc.xref.RFC1436.1"><cite title="The Internet Gopher Protocol (a distributed document search and retrieval protocol)">[2]</cite></a>, and WAIS <a href="#WAIS" id="rfc.xref.WAIS.1"><cite title="WAIS Interface Protocol Prototype Functional Specification (v1.5)">[10]</cite></a> protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse applications.
    826       </p>
    827       <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a id="intro.requirements" href="#intro.requirements">Requirements</a></h2>
    828       <p id="rfc.section.1.2.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
    829          in this document are to be interpreted as described in RFC 2119 <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[34]</cite></a>.
    830       </p>
    831       <p id="rfc.section.1.2.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant."
    832       </p>
    833       <h2 id="rfc.section.1.3"><a href="#rfc.section.1.3">1.3</a>&nbsp;<a id="intro.terminology" href="#intro.terminology">Terminology</a></h2>
    834       <p id="rfc.section.1.3.p.1">This specification uses a number of terms to refer to the roles played by participants in, and objects of, the HTTP communication.</p>
    835       <p id="rfc.section.1.3.p.2"> <span id="rfc.iref.c.1"></span>  <dfn>connection</dfn> 
    836       </p>
    837       <ul class="empty">
    838          <li>A transport layer virtual circuit established between two programs for the purpose of communication.</li>
    839       </ul>
    840       <p id="rfc.section.1.3.p.3"> <span id="rfc.iref.m.1"></span>  <dfn>message</dfn> 
    841       </p>
    842       <ul class="empty">
    843          <li>The basic unit of HTTP communication, consisting of a structured sequence of octets matching the syntax defined in <a href="#http.message" title="HTTP Message">Section&nbsp;4</a> and transmitted via the connection.
    844          </li>
    845       </ul>
    846       <p id="rfc.section.1.3.p.4"> <span id="rfc.iref.r.1"></span>  <dfn>request</dfn> 
    847       </p>
    848       <ul class="empty">
    849          <li>An HTTP request message, as defined in <a href="#request" title="Request">Section&nbsp;5</a>.
    850          </li>
    851       </ul>
    852       <p id="rfc.section.1.3.p.5"> <span id="rfc.iref.r.2"></span>  <dfn>response</dfn> 
    853       </p>
    854       <ul class="empty">
    855          <li>An HTTP response message, as defined in <a href="#response" title="Response">Section&nbsp;6</a>.
    856          </li>
    857       </ul>
    858       <p id="rfc.section.1.3.p.6"> <span id="rfc.iref.r.3"></span>  <dfn>resource</dfn> 
    859       </p>
    860       <ul class="empty">
    861          <li>A network data object or service that can be identified by a URI, as defined in <a href="#uri" title="Uniform Resource Identifiers">Section&nbsp;3.2</a>. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or
    862             vary in other ways.
    863          </li>
    864       </ul>
    865       <p id="rfc.section.1.3.p.7"> <span id="rfc.iref.e.1"></span>  <dfn>entity</dfn> 
    866       </p>
    867       <ul class="empty">
    868          <li>The information transferred as the payload of a request or response. An entity consists of metainformation in the form of
    869             entity-header fields and content in the form of an entity-body, as described in <a href="#entity" title="Entity">Section&nbsp;7</a>.
    870          </li>
    871       </ul>
    872       <p id="rfc.section.1.3.p.8"> <span id="rfc.iref.r.4"></span>  <dfn>representation</dfn> 
    873       </p>
    874       <ul class="empty">
    875          <li>An entity included with a response that is subject to content negotiation, as described in <a href="#content.negotiation" title="Content Negotiation">Section&nbsp;12</a>. There may exist multiple representations associated with a particular response status.
    876          </li>
    877       </ul>
    878       <p id="rfc.section.1.3.p.9"> <span id="rfc.iref.c.2"></span>  <dfn>content negotiation</dfn> 
    879       </p>
    880       <ul class="empty">
    881          <li>The mechanism for selecting the appropriate representation when servicing a request, as described in <a href="#content.negotiation" title="Content Negotiation">Section&nbsp;12</a>. The representation of entities in any response can be negotiated (including error responses).
    882          </li>
    883       </ul>
    884       <p id="rfc.section.1.3.p.10"> <span id="rfc.iref.v.1"></span>  <dfn>variant</dfn> 
    885       </p>
    886       <ul class="empty">
    887          <li>A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations
    888             is termed a `varriant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation.
    889          </li>
    890       </ul>
    891       <p id="rfc.section.1.3.p.11"> <span id="rfc.iref.c.3"></span>  <dfn>client</dfn> 
    892       </p>
    893       <ul class="empty">
    894          <li>A program that establishes connections for the purpose of sending requests.</li>
    895       </ul>
    896       <p id="rfc.section.1.3.p.12"> <span id="rfc.iref.u.1"></span>  <dfn>user agent</dfn> 
    897       </p>
    898       <ul class="empty">
    899          <li>The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user
    900             tools.
    901          </li>
    902       </ul>
    903       <p id="rfc.section.1.3.p.13"> <span id="rfc.iref.s.1"></span>  <dfn>server</dfn> 
    904       </p>
    905       <ul class="empty">
    906          <li>An application program that accepts connections in order to service requests by sending back responses. Any given program
    907             may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the
    908             program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as
    909             an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request.
    910          </li>
    911       </ul>
    912       <p id="rfc.section.1.3.p.14"> <span id="rfc.iref.o.1"></span>  <dfn>origin server</dfn> 
    913       </p>
    914       <ul class="empty">
    915          <li>The server on which a given resource resides or is to be created.</li>
    916       </ul>
    917       <p id="rfc.section.1.3.p.15"> <span id="rfc.iref.p.1"></span>  <dfn>proxy</dfn> 
    918       </p>
    919       <ul class="empty">
    920          <li>An intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients.
    921             Requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy <em class="bcp14">MUST</em> implement both the client and server requirements of this specification. A "transparent proxy" is a proxy that does not modify
    922             the request or response beyond what is required for proxy authentication and identification. A "non-transparent proxy" is
    923             a proxy that modifies the request or response in order to provide some added service to the user agent, such as group annotation
    924             services, media type transformation, protocol reduction, or anonymity filtering. Except where either transparent or non-transparent
    925             behavior is explicitly stated, the HTTP proxy requirements apply to both types of proxies.
    926          </li>
    927       </ul>
    928       <p id="rfc.section.1.3.p.16"> <span id="rfc.iref.g.1"></span>  <dfn>gateway</dfn> 
    929       </p>
    930       <ul class="empty">
    931          <li>A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the
    932             origin server for the requested resource; the requesting client may not be aware that it is communicating with a gateway.
    933          </li>
    934       </ul>
    935       <p id="rfc.section.1.3.p.17"> <span id="rfc.iref.t.1"></span>  <dfn>tunnel</dfn> 
    936       </p>
    937       <ul class="empty">
    938          <li>An intermediary program which is acting as a blind relay between two connections. Once active, a tunnel is not considered
    939             a party to the HTTP communication, though the tunnel may have been initiated by an HTTP request. The tunnel ceases to exist
    940             when both ends of the relayed connections are closed.
    941          </li>
    942       </ul>
    943       <p id="rfc.section.1.3.p.18"> <span id="rfc.iref.c.4"></span>  <dfn>cache</dfn> 
    944       </p>
    945       <ul class="empty">
    946          <li>A program's local store of response messages and the subsystem that controls its message storage, retrieval, and deletion.
    947             A cache stores cacheable responses in order to reduce the response time and network bandwidth consumption on future, equivalent
    948             requests. Any client or server may include a cache, though a cache cannot be used by a server that is acting as a tunnel.
    949          </li>
    950       </ul>
    951       <p id="rfc.section.1.3.p.19"> <span id="rfc.iref.c.5"></span>  <dfn>cacheable</dfn> 
    952       </p>
    953       <ul class="empty">
    954          <li>A response is cacheable if a cache is allowed to store a copy of the response message for use in answering subsequent requests.
    955             The rules for determining the cacheability of HTTP responses are defined in <a href="#caching" title="Caching in HTTP">Section&nbsp;13</a>. Even if a resource is cacheable, there may be additional constraints on whether a cache can use the cached copy for a particular
    956             request.
    957          </li>
    958       </ul>
    959       <p id="rfc.section.1.3.p.20"> <span id="rfc.iref.f.1"></span>  <dfn>first-hand</dfn> 
    960       </p>
    961       <ul class="empty">
    962          <li>A response is first-hand if it comes directly and without unnecessary delay from the origin server, perhaps via one or more
    963             proxies. A response is also first-hand if its validity has just been checked directly with the origin server.
    964          </li>
    965       </ul>
    966       <p id="rfc.section.1.3.p.21"> <span id="rfc.iref.e.2"></span>  <dfn>explicit expiration time</dfn> 
    967       </p>
    968       <ul class="empty">
    969          <li>The time at which the origin server intends that an entity should no longer be returned by a cache without further validation.</li>
    970       </ul>
    971       <p id="rfc.section.1.3.p.22"> <span id="rfc.iref.h.1"></span>  <dfn>heuristic expiration time</dfn> 
    972       </p>
    973       <ul class="empty">
    974          <li>An expiration time assigned by a cache when no explicit expiration time is available.</li>
    975       </ul>
    976       <p id="rfc.section.1.3.p.23"> <span id="rfc.iref.a.1"></span>  <dfn>age</dfn> 
    977       </p>
    978       <ul class="empty">
    979          <li>The age of a response is the time since it was sent by, or successfully validated with, the origin server.</li>
    980       </ul>
    981       <p id="rfc.section.1.3.p.24"> <span id="rfc.iref.f.2"></span>  <dfn>freshness lifetime</dfn> 
    982       </p>
    983       <ul class="empty">
    984          <li>The length of time between the generation of a response and its expiration time.</li>
    985       </ul>
    986       <p id="rfc.section.1.3.p.25"> <span id="rfc.iref.f.3"></span>  <dfn>fresh</dfn> 
    987       </p>
    988       <ul class="empty">
    989          <li>A response is fresh if its age has not yet exceeded its freshness lifetime.</li>
    990       </ul>
    991       <p id="rfc.section.1.3.p.26"> <span id="rfc.iref.s.2"></span>  <dfn>stale</dfn> 
    992       </p>
    993       <ul class="empty">
    994          <li>A response is stale if its age has passed its freshness lifetime.</li>
    995       </ul>
    996       <p id="rfc.section.1.3.p.27"> <span id="rfc.iref.s.3"></span>  <dfn>semantically transparent</dfn> 
    997       </p>
    998       <ul class="empty">
    999          <li>A cache behaves in a "semantically transparent" manner, with respect to a particular response, when its use affects neither
    1000             the requesting client nor the origin server, except to improve performance. When a cache is semantically transparent, the
    1001             client receives exactly the same response (except for hop-by-hop headers) that it would have received had its request been
    1002             handled directly by the origin server.
    1003          </li>
    1004       </ul>
    1005       <p id="rfc.section.1.3.p.28"> <span id="rfc.iref.v.2"></span>  <dfn>validator</dfn> 
    1006       </p>
    1007       <ul class="empty">
    1008          <li>A protocol element (e.g., an entity tag or a Last-Modified time) that is used to find out whether a cache entry is an equivalent
    1009             copy of an entity.
    1010          </li>
    1011       </ul>
    1012       <p id="rfc.section.1.3.p.29"> <span id="rfc.iref.u.2"></span>  <span id="rfc.iref.d.1"></span>  <dfn>upstream</dfn>/<dfn>downstream</dfn> 
    1013       </p>
    1014       <ul class="empty">
    1015          <li>Upstream and downstream describe the flow of a message: all messages flow from upstream to downstream.</li>
    1016       </ul>
    1017       <p id="rfc.section.1.3.p.30"> <span id="rfc.iref.i.1"></span>  <span id="rfc.iref.o.2"></span>  <dfn>inbound</dfn>/<dfn>outbound</dfn> 
    1018       </p>
    1019       <ul class="empty">
    1020          <li>Inbound and outbound refer to the request and response paths for messages: "inbound" means "traveling toward the origin server",
    1021             and "outbound" means "traveling toward the user agent"
    1022          </li>
    1023       </ul>
    1024       <h2 id="rfc.section.1.4"><a href="#rfc.section.1.4">1.4</a>&nbsp;<a id="intro.overall.operation" href="#intro.overall.operation">Overall Operation</a></h2>
    1025       <p id="rfc.section.1.4.p.1">The HTTP protocol is a request/response protocol. A client sends a request to the server in the form of a request method,
    1026          URI, and protocol version, followed by a MIME-like message containing request modifiers, client information, and possible
    1027          body content over a connection with a server. The server responds with a status line, including the message's protocol version
    1028          and a success or error code, followed by a MIME-like message containing server information, entity metainformation, and possible
    1029          entity-body content. The relationship between HTTP and MIME is described in <a href="#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix&nbsp;19.4</a>.
    1030       </p>
    1031       <p id="rfc.section.1.4.p.2">Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin
    1032          server. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the origin
    1033          server (O).
    1034       </p>
    1035       <div id="rfc.figure.u.1"></div><pre class="drawing">       request chain ------------------------&gt;
     799      <div id="introduction">
     800         <h1 id="rfc.section.1" class="np"><a href="#rfc.section.1">1.</a>&nbsp;<a href="#introduction">Introduction</a></h1>
     801         <div id="intro.purpose">
     802            <h2 id="rfc.section.1.1"><a href="#rfc.section.1.1">1.1</a>&nbsp;<a href="#intro.purpose">Purpose</a></h2>
     803            <p id="rfc.section.1.1.p.1">The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information
     804               systems. HTTP has been in use by the World-Wide Web global information initiative since 1990. The first version of HTTP, referred
     805               to as HTTP/0.9, was a simple protocol for raw data transfer across the Internet. HTTP/1.0, as defined by RFC 1945 <a href="#RFC1945" id="rfc.xref.RFC1945.1"><cite title="Hypertext Transfer Protocol -- HTTP/1.0">[6]</cite></a>, improved the protocol by allowing messages to be in the format of MIME-like messages, containing metainformation about the
     806               data transferred and modifiers on the request/response semantics. However, HTTP/1.0 does not sufficiently take into consideration
     807               the effects of hierarchical proxies, caching, the need for persistent connections, or virtual hosts. In addition, the proliferation
     808               of incompletely-implemented applications calling themselves "HTTP/1.0" has necessitated a protocol version change in order
     809               for two communicating applications to determine each other's true capabilities.
     810            </p>
     811            <p id="rfc.section.1.1.p.2">This specification defines the protocol referred to as "HTTP/1.1". This protocol includes more stringent requirements than
     812               HTTP/1.0 in order to ensure reliable implementation of its features.
     813            </p>
     814            <p id="rfc.section.1.1.p.3">Practical information systems require more functionality than simple retrieval, including search, front-end update, and annotation.
     815               HTTP allows an open-ended set of methods and headers that indicate the purpose of a request <a href="#RFC2324" id="rfc.xref.RFC2324.2"><cite title="Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)">[47]</cite></a>. It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) <a href="#RFC1630" id="rfc.xref.RFC1630.1"><cite title="Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web">[3]</cite></a>, as a location (URL) <a href="#RFC1738" id="rfc.xref.RFC1738.1"><cite title="Uniform Resource Locators (URL)">[4]</cite></a> or name (URN) <a href="#RFC1737" id="rfc.xref.RFC1737.1"><cite title="Functional Requirements for Uniform Resource Names">[20]</cite></a>, for indicating the resource to which a method is to be applied. Messages are passed in a format similar to that used by
     816               Internet mail <a href="#RFC822" id="rfc.xref.RFC822.1"><cite title="Standard for the format of ARPA Internet text messages">[9]</cite></a> as defined by the Multipurpose Internet Mail Extensions (MIME) <a href="#RFC2045" id="rfc.xref.RFC2045.1"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[7]</cite></a>.
     817            </p>
     818            <p id="rfc.section.1.1.p.4">HTTP is also used as a generic protocol for communication between user agents and proxies/gateways to other Internet systems,
     819               including those supported by the SMTP <a href="#RFC821" id="rfc.xref.RFC821.1"><cite title="Simple Mail Transfer Protocol">[16]</cite></a>, NNTP <a href="#RFC977" id="rfc.xref.RFC977.1"><cite title="Network News Transfer Protocol">[13]</cite></a>, FTP <a href="#RFC959" id="rfc.xref.RFC959.1"><cite title="File Transfer Protocol">[18]</cite></a>, Gopher <a href="#RFC1436" id="rfc.xref.RFC1436.1"><cite title="The Internet Gopher Protocol (a distributed document search and retrieval protocol)">[2]</cite></a>, and WAIS <a href="#WAIS" id="rfc.xref.WAIS.1"><cite title="WAIS Interface Protocol Prototype Functional Specification (v1.5)">[10]</cite></a> protocols. In this way, HTTP allows basic hypermedia access to resources available from diverse applications.
     820            </p>
     821         </div>
     822         <div id="intro.requirements">
     823            <h2 id="rfc.section.1.2"><a href="#rfc.section.1.2">1.2</a>&nbsp;<a href="#intro.requirements">Requirements</a></h2>
     824            <p id="rfc.section.1.2.p.1">The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
     825               in this document are to be interpreted as described in RFC 2119 <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[34]</cite></a>.
     826            </p>
     827            <p id="rfc.section.1.2.p.2">An implementation is not compliant if it fails to satisfy one or more of the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level requirements for the protocols it implements. An implementation that satisfies all the <em class="bcp14">MUST</em> or <em class="bcp14">REQUIRED</em> level and all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the <em class="bcp14">MUST</em> level requirements but not all the <em class="bcp14">SHOULD</em> level requirements for its protocols is said to be "conditionally compliant."
     828            </p>
     829         </div>
     830         <div id="intro.terminology">
     831            <h2 id="rfc.section.1.3"><a href="#rfc.section.1.3">1.3</a>&nbsp;<a href="#intro.terminology">Terminology</a></h2>
     832            <p id="rfc.section.1.3.p.1">This specification uses a number of terms to refer to the roles played by participants in, and objects of, the HTTP communication.</p>
     833            <p id="rfc.section.1.3.p.2"><span id="rfc.iref.c.1"></span> <dfn>connection</dfn>
     834            </p>
     835            <ul class="empty">
     836               <li>A transport layer virtual circuit established between two programs for the purpose of communication.</li>
     837            </ul>
     838            <p id="rfc.section.1.3.p.3"><span id="rfc.iref.m.1"></span> <dfn>message</dfn>
     839            </p>
     840            <ul class="empty">
     841               <li>The basic unit of HTTP communication, consisting of a structured sequence of octets matching the syntax defined in <a href="#http.message" title="HTTP Message">Section&nbsp;4</a> and transmitted via the connection.
     842               </li>
     843            </ul>
     844            <p id="rfc.section.1.3.p.4"><span id="rfc.iref.r.1"></span> <dfn>request</dfn>
     845            </p>
     846            <ul class="empty">
     847               <li>An HTTP request message, as defined in <a href="#request" title="Request">Section&nbsp;5</a>.
     848               </li>
     849            </ul>
     850            <p id="rfc.section.1.3.p.5"><span id="rfc.iref.r.2"></span> <dfn>response</dfn>
     851            </p>
     852            <ul class="empty">
     853               <li>An HTTP response message, as defined in <a href="#response" title="Response">Section&nbsp;6</a>.
     854               </li>
     855            </ul>
     856            <p id="rfc.section.1.3.p.6"><span id="rfc.iref.r.3"></span> <dfn>resource</dfn>
     857            </p>
     858            <ul class="empty">
     859               <li>A network data object or service that can be identified by a URI, as defined in <a href="#uri" title="Uniform Resource Identifiers">Section&nbsp;3.2</a>. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or
     860                  vary in other ways.
     861               </li>
     862            </ul>
     863            <p id="rfc.section.1.3.p.7"><span id="rfc.iref.e.1"></span> <dfn>entity</dfn>
     864            </p>
     865            <ul class="empty">
     866               <li>The information transferred as the payload of a request or response. An entity consists of metainformation in the form of
     867                  entity-header fields and content in the form of an entity-body, as described in <a href="#entity" title="Entity">Section&nbsp;7</a>.
     868               </li>
     869            </ul>
     870            <p id="rfc.section.1.3.p.8"><span id="rfc.iref.r.4"></span> <dfn>representation</dfn>
     871            </p>
     872            <ul class="empty">
     873               <li>An entity included with a response that is subject to content negotiation, as described in <a href="#content.negotiation" title="Content Negotiation">Section&nbsp;12</a>. There may exist multiple representations associated with a particular response status.
     874               </li>
     875            </ul>
     876            <p id="rfc.section.1.3.p.9"><span id="rfc.iref.c.2"></span> <dfn>content negotiation</dfn>
     877            </p>
     878            <ul class="empty">
     879               <li>The mechanism for selecting the appropriate representation when servicing a request, as described in <a href="#content.negotiation" title="Content Negotiation">Section&nbsp;12</a>. The representation of entities in any response can be negotiated (including error responses).
     880               </li>
     881            </ul>
     882            <p id="rfc.section.1.3.p.10"><span id="rfc.iref.v.1"></span> <dfn>variant</dfn>
     883            </p>
     884            <ul class="empty">
     885               <li>A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations
     886                  is termed a `varriant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation.
     887               </li>
     888            </ul>
     889            <p id="rfc.section.1.3.p.11"><span id="rfc.iref.c.3"></span> <dfn>client</dfn>
     890            </p>
     891            <ul class="empty">
     892               <li>A program that establishes connections for the purpose of sending requests.</li>
     893            </ul>
     894            <p id="rfc.section.1.3.p.12"><span id="rfc.iref.u.1"></span> <dfn>user agent</dfn>
     895            </p>
     896            <ul class="empty">
     897               <li>The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user
     898                  tools.
     899               </li>
     900            </ul>
     901            <p id="rfc.section.1.3.p.13"><span id="rfc.iref.s.1"></span> <dfn>server</dfn>
     902            </p>
     903            <ul class="empty">
     904               <li>An application program that accepts connections in order to service requests by sending back responses. Any given program
     905                  may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the
     906                  program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as
     907                  an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request.
     908               </li>
     909            </ul>
     910            <p id="rfc.section.1.3.p.14"><span id="rfc.iref.o.1"></span> <dfn>origin server</dfn>
     911            </p>
     912            <ul class="empty">
     913               <li>The server on which a given resource resides or is to be created.</li>
     914            </ul>
     915            <p id="rfc.section.1.3.p.15"><span id="rfc.iref.p.1"></span> <dfn>proxy</dfn>
     916            </p>
     917            <ul class="empty">
     918               <li>An intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients.
     919                  Requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy <em class="bcp14">MUST</em> implement both the client and server requirements of this specification. A "transparent proxy" is a proxy that does not modify
     920                  the request or response beyond what is required for proxy authentication and identification. A "non-transparent proxy" is
     921                  a proxy that modifies the request or response in order to provide some added service to the user agent, such as group annotation
     922                  services, media type transformation, protocol reduction, or anonymity filtering. Except where either transparent or non-transparent
     923                  behavior is explicitly stated, the HTTP proxy requirements apply to both types of proxies.
     924               </li>
     925            </ul>
     926            <p id="rfc.section.1.3.p.16"><span id="rfc.iref.g.1"></span> <dfn>gateway</dfn>
     927            </p>
     928            <ul class="empty">
     929               <li>A server which acts as an intermediary for some other server. Unlike a proxy, a gateway receives requests as if it were the
     930                  origin server for the requested resource; the requesting client may not be aware that it is communicating with a gateway.
     931               </li>
     932            </ul>
     933            <p id="rfc.section.1.3.p.17"><span id="rfc.iref.t.1"></span> <dfn>tunnel</dfn>
     934            </p>
     935            <ul class="empty">
     936               <li>An intermediary program which is acting as a blind relay between two connections. Once active, a tunnel is not considered
     937                  a party to the HTTP communication, though the tunnel may have been initiated by an HTTP request. The tunnel ceases to exist
     938                  when both ends of the relayed connections are closed.
     939               </li>
     940            </ul>
     941            <p id="rfc.section.1.3.p.18"><span id="rfc.iref.c.4"></span> <dfn>cache</dfn>
     942            </p>
     943            <ul class="empty">
     944               <li>A program's local store of response messages and the subsystem that controls its message storage, retrieval, and deletion.
     945                  A cache stores cacheable responses in order to reduce the response time and network bandwidth consumption on future, equivalent
     946                  requests. Any client or server may include a cache, though a cache cannot be used by a server that is acting as a tunnel.
     947               </li>
     948            </ul>
     949            <p id="rfc.section.1.3.p.19"><span id="rfc.iref.c.5"></span> <dfn>cacheable</dfn>
     950            </p>
     951            <ul class="empty">
     952               <li>A response is cacheable if a cache is allowed to store a copy of the response message for use in answering subsequent requests.
     953                  The rules for determining the cacheability of HTTP responses are defined in <a href="#caching" title="Caching in HTTP">Section&nbsp;13</a>. Even if a resource is cacheable, there may be additional constraints on whether a cache can use the cached copy for a particular
     954                  request.
     955               </li>
     956            </ul>
     957            <p id="rfc.section.1.3.p.20"><span id="rfc.iref.f.1"></span> <dfn>first-hand</dfn>
     958            </p>
     959            <ul class="empty">
     960               <li>A response is first-hand if it comes directly and without unnecessary delay from the origin server, perhaps via one or more
     961                  proxies. A response is also first-hand if its validity has just been checked directly with the origin server.
     962               </li>
     963            </ul>
     964            <p id="rfc.section.1.3.p.21"><span id="rfc.iref.e.2"></span> <dfn>explicit expiration time</dfn>
     965            </p>
     966            <ul class="empty">
     967               <li>The time at which the origin server intends that an entity should no longer be returned by a cache without further validation.</li>
     968            </ul>
     969            <p id="rfc.section.1.3.p.22"><span id="rfc.iref.h.1"></span> <dfn>heuristic expiration time</dfn>
     970            </p>
     971            <ul class="empty">
     972               <li>An expiration time assigned by a cache when no explicit expiration time is available.</li>
     973            </ul>
     974            <p id="rfc.section.1.3.p.23"><span id="rfc.iref.a.1"></span> <dfn>age</dfn>
     975            </p>
     976            <ul class="empty">
     977               <li>The age of a response is the time since it was sent by, or successfully validated with, the origin server.</li>
     978            </ul>
     979            <p id="rfc.section.1.3.p.24"><span id="rfc.iref.f.2"></span> <dfn>freshness lifetime</dfn>
     980            </p>
     981            <ul class="empty">
     982               <li>The length of time between the generation of a response and its expiration time.</li>
     983            </ul>
     984            <p id="rfc.section.1.3.p.25"><span id="rfc.iref.f.3"></span> <dfn>fresh</dfn>
     985            </p>
     986            <ul class="empty">
     987               <li>A response is fresh if its age has not yet exceeded its freshness lifetime.</li>
     988            </ul>
     989            <p id="rfc.section.1.3.p.26"><span id="rfc.iref.s.2"></span> <dfn>stale</dfn>
     990            </p>
     991            <ul class="empty">
     992               <li>A response is stale if its age has passed its freshness lifetime.</li>
     993            </ul>
     994            <p id="rfc.section.1.3.p.27"><span id="rfc.iref.s.3"></span> <dfn>semantically transparent</dfn>
     995            </p>
     996            <ul class="empty">
     997               <li>A cache behaves in a "semantically transparent" manner, with respect to a particular response, when its use affects neither
     998                  the requesting client nor the origin server, except to improve performance. When a cache is semantically transparent, the
     999                  client receives exactly the same response (except for hop-by-hop headers) that it would have received had its request been
     1000                  handled directly by the origin server.
     1001               </li>
     1002            </ul>
     1003            <p id="rfc.section.1.3.p.28"><span id="rfc.iref.v.2"></span> <dfn>validator</dfn>
     1004            </p>
     1005            <ul class="empty">
     1006               <li>A protocol element (e.g., an entity tag or a Last-Modified time) that is used to find out whether a cache entry is an equivalent
     1007                  copy of an entity.
     1008               </li>
     1009            </ul>
     1010            <p id="rfc.section.1.3.p.29"><span id="rfc.iref.u.2"></span> <span id="rfc.iref.d.1"></span> <dfn>upstream</dfn>/<dfn>downstream</dfn>
     1011            </p>
     1012            <ul class="empty">
     1013               <li>Upstream and downstream describe the flow of a message: all messages flow from upstream to downstream.</li>
     1014            </ul>
     1015            <p id="rfc.section.1.3.p.30"><span id="rfc.iref.i.1"></span> <span id="rfc.iref.o.2"></span> <dfn>inbound</dfn>/<dfn>outbound</dfn>
     1016            </p>
     1017            <ul class="empty">
     1018               <li>Inbound and outbound refer to the request and response paths for messages: "inbound" means "traveling toward the origin server",
     1019                  and "outbound" means "traveling toward the user agent"
     1020               </li>
     1021            </ul>
     1022         </div>
     1023         <div id="intro.overall.operation">
     1024            <h2 id="rfc.section.1.4"><a href="#rfc.section.1.4">1.4</a>&nbsp;<a href="#intro.overall.operation">Overall Operation</a></h2>
     1025            <p id="rfc.section.1.4.p.1">The HTTP protocol is a request/response protocol. A client sends a request to the server in the form of a request method,
     1026               URI, and protocol version, followed by a MIME-like message containing request modifiers, client information, and possible
     1027               body content over a connection with a server. The server responds with a status line, including the message's protocol version
     1028               and a success or error code, followed by a MIME-like message containing server information, entity metainformation, and possible
     1029               entity-body content. The relationship between HTTP and MIME is described in <a href="#differences.between.http.entities.and.rfc.2045.entities" title="Differences Between HTTP Entities and RFC 2045 Entities">Appendix&nbsp;19.4</a>.
     1030            </p>
     1031            <p id="rfc.section.1.4.p.2">Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin
     1032               server. In the simplest case, this may be accomplished via a single connection (v) between the user agent (UA) and the origin
     1033               server (O).
     1034            </p>
     1035            <div id="rfc.figure.u.1"></div><pre class="drawing">       request chain ------------------------&gt;
    10361036    UA -------------------v------------------- O
    10371037       &lt;----------------------- response chain
    10381038</pre><p id="rfc.section.1.4.p.4">A more complicated situation occurs when one or more intermediaries are present in the request/response chain. There are three
    1039          common forms of intermediary: proxy, gateway, and tunnel. A proxy is a forwarding agent, receiving requests for a URI in its
    1040          absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server identified by
    1041          the URI. A gateway is a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests
    1042          to the underlying server's protocol. A tunnel acts as a relay point between two connections without changing the messages;
    1043          tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary
    1044          cannot understand the contents of the messages.
    1045       </p>
    1046       <div id="rfc.figure.u.2"></div><pre class="drawing">       request chain --------------------------------------&gt;
     1039               common forms of intermediary: proxy, gateway, and tunnel. A proxy is a forwarding agent, receiving requests for a URI in its
     1040               absolute form, rewriting all or part of the message, and forwarding the reformatted request toward the server identified by
     1041               the URI. A gateway is a receiving agent, acting as a layer above some other server(s) and, if necessary, translating the requests
     1042               to the underlying server's protocol. A tunnel acts as a relay point between two connections without changing the messages;
     1043               tunnels are used when the communication needs to pass through an intermediary (such as a firewall) even when the intermediary
     1044               cannot understand the contents of the messages.
     1045            </p>
     1046            <div id="rfc.figure.u.2"></div><pre class="drawing">       request chain --------------------------------------&gt;
    10471047    UA -----v----- A -----v----- B -----v----- C -----v----- O
    10481048       &lt;------------------------------------- response chain
    10491049</pre><p id="rfc.section.1.4.p.6">The figure above shows three intermediaries (A, B, and C) between the user agent and origin server. A request or response
    1050          message that travels the whole chain will pass through four separate connections. This distinction is important because some
    1051          HTTP communication options may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points
    1052          of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple,
    1053          simultaneous communications. For example, B may be receiving requests from many clients other than A, and/or forwarding requests
    1054          to servers other than C, at the same time that it is handling A's request.
    1055       </p>
    1056       <p id="rfc.section.1.4.p.7">Any party to the communication which is not acting as a tunnel may employ an internal cache for handling requests. The effect
    1057          of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached response
    1058          applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response from
    1059          O (via C) for a request which has not been cached by UA or A.
    1060       </p>
    1061       <div id="rfc.figure.u.3"></div><pre class="drawing">          request chain ----------&gt;
     1050               message that travels the whole chain will pass through four separate connections. This distinction is important because some
     1051               HTTP communication options may apply only to the connection with the nearest, non-tunnel neighbor, only to the end-points
     1052               of the chain, or to all connections along the chain. Although the diagram is linear, each participant may be engaged in multiple,
     1053               simultaneous communications. For example, B may be receiving requests from many clients other than A, and/or forwarding requests
     1054               to servers other than C, at the same time that it is handling A's request.
     1055            </p>
     1056            <p id="rfc.section.1.4.p.7">Any party to the communication which is not acting as a tunnel may employ an internal cache for handling requests. The effect
     1057               of a cache is that the request/response chain is shortened if one of the participants along the chain has a cached response
     1058               applicable to that request. The following illustrates the resulting chain if B has a cached copy of an earlier response from
     1059               O (via C) for a request which has not been cached by UA or A.
     1060            </p>
     1061            <div id="rfc.figure.u.3"></div><pre class="drawing">          request chain ----------&gt;
    10621062       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
    10631063          &lt;--------- response chain
    10641064</pre><p id="rfc.section.1.4.p.9">Not all responses are usefully cacheable, and some requests may contain modifiers which place special requirements on cache
    1065          behavior. HTTP requirements for cache behavior and cacheable responses are defined in <a href="#caching" title="Caching in HTTP">Section&nbsp;13</a>.
    1066       </p>
    1067       <p id="rfc.section.1.4.p.10">In fact, there are a wide variety of architectures and configurations of caches and proxies currently being experimented with
    1068          or deployed across the World Wide Web. These systems include national hierarchies of proxy caches to save transoceanic bandwidth,
    1069          systems that broadcast or multicast cache entries, organizations that distribute subsets of cached data via CD-ROM, and so
    1070          on. HTTP systems are used in corporate intranets over high-bandwidth links, and for access via PDAs with low-power radio links
    1071          and intermittent connectivity. The goal of HTTP/1.1 is to support the wide diversity of configurations already deployed while
    1072          introducing protocol constructs that meet the needs of those who build web applications that require high reliability and,
    1073          failing that, at least reliable indications of failure.
    1074       </p>
    1075       <p id="rfc.section.1.4.p.11">HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 <a href="#RFC1700" id="rfc.xref.RFC1700.1"><cite title="Assigned Numbers">[19]</cite></a>, but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet,
    1076          or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the
    1077          mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside
    1078          the scope of this specification.
    1079       </p>
    1080       <p id="rfc.section.1.4.p.12">In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection may
    1081          be used for one or more request/response exchanges, although connections may be closed for a variety of reasons (see <a href="#persistent.connections" title="Persistent Connections">Section&nbsp;8.1</a>).
    1082       </p>
     1065               behavior. HTTP requirements for cache behavior and cacheable responses are defined in <a href="#caching" title="Caching in HTTP">Section&nbsp;13</a>.
     1066            </p>
     1067            <p id="rfc.section.1.4.p.10">In fact, there are a wide variety of architectures and configurations of caches and proxies currently being experimented with
     1068               or deployed across the World Wide Web. These systems include national hierarchies of proxy caches to save transoceanic bandwidth,
     1069               systems that broadcast or multicast cache entries, organizations that distribute subsets of cached data via CD-ROM, and so
     1070               on. HTTP systems are used in corporate intranets over high-bandwidth links, and for access via PDAs with low-power radio links
     1071               and intermittent connectivity. The goal of HTTP/1.1 is to support the wide diversity of configurations already deployed while
     1072               introducing protocol constructs that meet the needs of those who build web applications that require high reliability and,
     1073               failing that, at least reliable indications of failure.
     1074            </p>
     1075            <p id="rfc.section.1.4.p.11">HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80 <a href="#RFC1700" id="rfc.xref.RFC1700.1"><cite title="Assigned Numbers">[19]</cite></a>, but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet,
     1076               or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the
     1077               mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside
     1078               the scope of this specification.
     1079            </p>
     1080            <p id="rfc.section.1.4.p.12">In HTTP/1.0, most implementations used a new connection for each request/response exchange. In HTTP/1.1, a connection may
     1081               be used for one or more request/response exchanges, although connections may be closed for a variety of reasons (see <a href="#persistent.connections" title="Persistent Connections">Section&nbsp;8.1</a>).
     1082            </p>
     1083         </div>
     1084      </div>
    10831085      <hr class="noprint">
    1084       <h1 id="rfc.section.2" class="np"><a href="#rfc.section.2">2.</a>&nbsp;<a id="notation" href="#notation">Notational Conventions and Generic Grammar</a></h1>
    1085       <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a id="notation.abnf" href="#notation.abnf">Augmented BNF</a></h2>
    1086       <p id="rfc.section.2.1.p.1">All of the mechanisms specified in this document are described in both prose and an augmented Backus-Naur Form (BNF) similar
    1087          to that used by RFC 822 <a href="#RFC822" id="rfc.xref.RFC822.2"><cite title="Standard for the format of ARPA Internet text messages">[9]</cite></a>. Implementors will need to be familiar with the notation in order to understand this specification. The augmented BNF includes
    1088          the following constructs:
    1089       </p>
    1090       <p id="rfc.section.2.1.p.2">name = definition </p>
    1091       <ul class="empty">
    1092          <li>The name of a rule is simply the name itself (without any enclosing "&lt;" and "&gt;") and is separated from its definition by the
    1093             equal "=" character. White space is only significant in that indentation of continuation lines is used to indicate a rule
    1094             definition that spans more than one line. Certain basic rules are in uppercase, such as <a href="#basic.rules" class="smpl" id="rfc.extref.s.1">SP</a>, <a href="#basic.rules.lws" class="smpl" id="rfc.extref.l.1">LWS</a>, <a href="#basic.rules" class="smpl" id="rfc.extref.h.1">HT</a>, <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.1">CRLF</a>, <a href="#basic.rules" class="smpl" id="rfc.extref.d.1">DIGIT</a>, <a href="#basic.rules" class="smpl" id="rfc.extref.a.1">ALPHA</a>, etc. Angle brackets are used within definitions whenever their presence will facilitate discerning the use of rule names.
    1095          </li>
    1096       </ul>
    1097       <p id="rfc.section.2.1.p.3">"literal" </p>
    1098       <ul class="empty">
    1099          <li>Quotation marks surround literal text. Unless stated otherwise, the text is case-insensitive.</li>
    1100       </ul>
    1101       <p id="rfc.section.2.1.p.4">rule1 | rule2 </p>
    1102       <ul class="empty">
    1103          <li>Elements separated by a bar ("|") are alternatives, e.g., "yes | no" will accept yes or no.</li>
    1104       </ul>
    1105       <p id="rfc.section.2.1.p.5">(rule1 rule2) </p>
    1106       <ul class="empty">
    1107          <li>Elements enclosed in parentheses are treated as a single element. Thus, "(elem (foo | bar) elem)" allows the token sequences
    1108             "elem foo elem" and "elem bar elem".
    1109          </li>
    1110       </ul>
    1111       <p id="rfc.section.2.1.p.6">*rule </p>
    1112       <ul class="empty">
    1113          <li>The character "*" preceding an element indicates repetition. The full form is "&lt;n&gt;*&lt;m&gt;element" indicating at least &lt;n&gt; and
    1114             at most &lt;m&gt; occurrences of element. Default values are 0 and infinity so that "*(element)" allows any number, including zero;
    1115             "1*element" requires at least one; and "1*2element" allows one or two.
    1116          </li>
    1117       </ul>
    1118       <p id="rfc.section.2.1.p.7">[rule] </p>
    1119       <ul class="empty">
    1120          <li>Square brackets enclose optional elements; "[foo bar]" is equivalent to "*1(foo bar)".</li>
    1121       </ul>
    1122       <p id="rfc.section.2.1.p.8">N rule </p>
    1123       <ul class="empty">
    1124          <li>Specific repetition: "&lt;n&gt;(element)" is equivalent to "&lt;n&gt;*&lt;n&gt;(element)"; that is, exactly &lt;n&gt; occurrences of (element). Thus
    1125             2DIGIT is a 2-digit number, and 3ALPHA is a string of three alphabetic characters.
    1126          </li>
    1127       </ul>
    1128       <p id="rfc.section.2.1.p.9">#rule </p>
    1129       <ul class="empty">
    1130          <li>A construct "#" is defined, similar to "*", for defining lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at
    1131             least &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas (",") and <em class="bcp14">OPTIONAL</em> linear white space (LWS). This makes the usual form of lists very easy; a rule such as
    1132             <div id="rfc.figure.u.4"></div><pre class="text">   ( *LWS element *( *LWS "," *LWS element ))
     1086      <div id="notation">
     1087         <h1 id="rfc.section.2" class="np"><a href="#rfc.section.2">2.</a>&nbsp;<a href="#notation">Notational Conventions and Generic Grammar</a></h1>
     1088         <div id="notation.abnf">
     1089            <h2 id="rfc.section.2.1"><a href="#rfc.section.2.1">2.1</a>&nbsp;<a href="#notation.abnf">Augmented BNF</a></h2>
     1090            <p id="rfc.section.2.1.p.1">All of the mechanisms specified in this document are described in both prose and an augmented Backus-Naur Form (BNF) similar
     1091               to that used by RFC 822 <a href="#RFC822" id="rfc.xref.RFC822.2"><cite title="Standard for the format of ARPA Internet text messages">[9]</cite></a>. Implementors will need to be familiar with the notation in order to understand this specification. The augmented BNF includes
     1092               the following constructs:
     1093            </p>
     1094            <p id="rfc.section.2.1.p.2">name = definition </p>
     1095            <ul class="empty">
     1096               <li>The name of a rule is simply the name itself (without any enclosing "&lt;" and "&gt;") and is separated from its definition by the
     1097                  equal "=" character. White space is only significant in that indentation of continuation lines is used to indicate a rule
     1098                  definition that spans more than one line. Certain basic rules are in uppercase, such as <a href="#basic.rules" class="smpl" id="rfc.extref.s.1">SP</a>, <a href="#basic.rules.lws" class="smpl" id="rfc.extref.l.1">LWS</a>, <a href="#basic.rules" class="smpl" id="rfc.extref.h.1">HT</a>, <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.1">CRLF</a>, <a href="#basic.rules" class="smpl" id="rfc.extref.d.1">DIGIT</a>, <a href="#basic.rules" class="smpl" id="rfc.extref.a.1">ALPHA</a>, etc. Angle brackets are used within definitions whenever their presence will facilitate discerning the use of rule names.
     1099               </li>
     1100            </ul>
     1101            <p id="rfc.section.2.1.p.3">"literal" </p>
     1102            <ul class="empty">
     1103               <li>Quotation marks surround literal text. Unless stated otherwise, the text is case-insensitive.</li>
     1104            </ul>
     1105            <p id="rfc.section.2.1.p.4">rule1 | rule2 </p>
     1106            <ul class="empty">
     1107               <li>Elements separated by a bar ("|") are alternatives, e.g., "yes | no" will accept yes or no.</li>
     1108            </ul>
     1109            <p id="rfc.section.2.1.p.5">(rule1 rule2) </p>
     1110            <ul class="empty">
     1111               <li>Elements enclosed in parentheses are treated as a single element. Thus, "(elem (foo | bar) elem)" allows the token sequences
     1112                  "elem foo elem" and "elem bar elem".
     1113               </li>
     1114            </ul>
     1115            <p id="rfc.section.2.1.p.6">*rule </p>
     1116            <ul class="empty">
     1117               <li>The character "*" preceding an element indicates repetition. The full form is "&lt;n&gt;*&lt;m&gt;element" indicating at least &lt;n&gt; and
     1118                  at most &lt;m&gt; occurrences of element. Default values are 0 and infinity so that "*(element)" allows any number, including zero;
     1119                  "1*element" requires at least one; and "1*2element" allows one or two.
     1120               </li>
     1121            </ul>
     1122            <p id="rfc.section.2.1.p.7">[rule] </p>
     1123            <ul class="empty">
     1124               <li>Square brackets enclose optional elements; "[foo bar]" is equivalent to "*1(foo bar)".</li>
     1125            </ul>
     1126            <p id="rfc.section.2.1.p.8">N rule </p>
     1127            <ul class="empty">
     1128               <li>Specific repetition: "&lt;n&gt;(element)" is equivalent to "&lt;n&gt;*&lt;n&gt;(element)"; that is, exactly &lt;n&gt; occurrences of (element). Thus
     1129                  2DIGIT is a 2-digit number, and 3ALPHA is a string of three alphabetic characters.
     1130               </li>
     1131            </ul>
     1132            <p id="rfc.section.2.1.p.9">#rule </p>
     1133            <ul class="empty">
     1134               <li>A construct "#" is defined, similar to "*", for defining lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at
     1135                  least &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas (",") and <em class="bcp14">OPTIONAL</em> linear white space (LWS). This makes the usual form of lists very easy; a rule such as
     1136                  <div id="rfc.figure.u.4"></div><pre class="text">   ( *LWS element *( *LWS "," *LWS element ))
    11331137</pre> </li>
    1134          <li>can be shown as
    1135             <div id="rfc.figure.u.5"></div><pre class="text">   1#element
     1138               <li>can be shown as
     1139                  <div id="rfc.figure.u.5"></div><pre class="text">   1#element
    11361140</pre> </li>
    1137          <li>Wherever this construct is used, null elements are allowed, but do not contribute to the count of elements present. That is,
    1138             "(element), , (element) " is permitted, but counts as only two elements. Therefore, where at least one element is required,
    1139             at least one non-null element <em class="bcp14">MUST</em> be present. Default values are 0 and infinity so that "#element" allows any number, including zero; "1#element" requires at
    1140             least one; and "1#2element" allows one or two.
    1141          </li>
    1142       </ul>
    1143       <p id="rfc.section.2.1.p.10">; comment </p>
    1144       <ul class="empty">
    1145          <li>A semi-colon, set off some distance to the right of rule text, starts a comment that continues to the end of line. This is
    1146             a simple way of including useful notes in parallel with the specifications.
    1147          </li>
    1148       </ul>
    1149       <div id="implied.LWS">
    1150          <p id="rfc.section.2.1.p.11">implied *LWS </p>
    1151          <ul class="empty">
    1152             <li>The grammar described by this specification is word-based. Except where noted otherwise, linear white space (LWS) can be included
    1153                between any two adjacent words (token or quoted-string), and between adjacent words and separators, without changing the interpretation
    1154                of a field. At least one delimiter (LWS and/or separators) <em class="bcp14">MUST</em> exist between any two tokens (for the definition of "token" below), since they would otherwise be interpreted as a single
    1155                token.
    1156             </li>
    1157          </ul>
    1158       </div>
    1159       <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a id="basic.rules" href="#basic.rules">Basic Rules</a></h2>
    1160       <p id="rfc.section.2.2.p.1">The following rules are used throughout this specification to describe basic parsing constructs. The US-ASCII coded character
    1161          set is defined by ANSI X3.4-1986 <a href="#USASCII" id="rfc.xref.USASCII.1"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[21]</cite></a>.
    1162       </p>
    1163       <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span>    <a href="#basic.rules" class="smpl" id="rfc.extref.o.1">OCTET</a>          = &lt;any 8-bit sequence of data&gt;
     1141               <li>Wherever this construct is used, null elements are allowed, but do not contribute to the count of elements present. That is,
     1142                  "(element), , (element) " is permitted, but counts as only two elements. Therefore, where at least one element is required,
     1143                  at least one non-null element <em class="bcp14">MUST</em> be present. Default values are 0 and infinity so that "#element" allows any number, including zero; "1#element" requires at
     1144                  least one; and "1#2element" allows one or two.
     1145               </li>
     1146            </ul>
     1147            <p id="rfc.section.2.1.p.10">; comment </p>
     1148            <ul class="empty">
     1149               <li>A semi-colon, set off some distance to the right of rule text, starts a comment that continues to the end of line. This is
     1150                  a simple way of including useful notes in parallel with the specifications.
     1151               </li>
     1152            </ul>
     1153            <div id="implied.LWS">
     1154               <p id="rfc.section.2.1.p.11">implied *LWS </p>
     1155               <ul class="empty">
     1156                  <li>The grammar described by this specification is word-based. Except where noted otherwise, linear white space (LWS) can be included
     1157                     between any two adjacent words (token or quoted-string), and between adjacent words and separators, without changing the interpretation
     1158                     of a field. At least one delimiter (LWS and/or separators) <em class="bcp14">MUST</em> exist between any two tokens (for the definition of "token" below), since they would otherwise be interpreted as a single
     1159                     token.
     1160                  </li>
     1161               </ul>
     1162            </div>
     1163         </div>
     1164         <div id="basic.rules">
     1165            <h2 id="rfc.section.2.2"><a href="#rfc.section.2.2">2.2</a>&nbsp;<a href="#basic.rules">Basic Rules</a></h2>
     1166            <p id="rfc.section.2.2.p.1">The following rules are used throughout this specification to describe basic parsing constructs. The US-ASCII coded character
     1167               set is defined by ANSI X3.4-1986 <a href="#USASCII" id="rfc.xref.USASCII.1"><cite title="Coded Character Set -- 7-bit American Standard Code for Information Interchange">[21]</cite></a>.
     1168            </p>
     1169            <div id="rfc.figure.u.6"></div><pre class="inline"><span id="rfc.iref.g.2"></span><span id="rfc.iref.g.3"></span><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span><span id="rfc.iref.g.9"></span><span id="rfc.iref.g.10"></span><span id="rfc.iref.g.11"></span><span id="rfc.iref.g.12"></span>    <a href="#basic.rules" class="smpl" id="rfc.extref.o.1">OCTET</a>          = &lt;any 8-bit sequence of data&gt;
    11641170    <a href="#basic.rules" class="smpl" id="rfc.extref.c.2">CHAR</a>           = &lt;any US-ASCII character (octets 0 - 127)&gt;
    11651171    <a href="#basic.rules" class="smpl" id="rfc.extref.u.1">UPALPHA</a>        = &lt;any US-ASCII uppercase letter "A".."Z"&gt;
     
    11751181    &lt;"&gt;            = &lt;US-ASCII double-quote mark (34)&gt;
    11761182</pre><div id="basic.rules.crlf">
    1177          <p id="rfc.section.2.2.p.3"> HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements except the entity-body (see <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;19.3</a> for tolerant applications). The end-of-line marker within an entity-body is defined by its associated media type, as described
    1178             in <a href="#media.types" title="Media Types">Section&nbsp;3.7</a>.
    1179          </p>
    1180       </div>
    1181       <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.13"></span>    <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.5">CRLF</a>           = <a href="#basic.rules" class="smpl" id="rfc.extref.c.6">CR</a> <a href="#basic.rules" class="smpl" id="rfc.extref.l.5">LF</a>
     1183               <p id="rfc.section.2.2.p.3"> HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all protocol elements except the entity-body (see <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;19.3</a> for tolerant applications). The end-of-line marker within an entity-body is defined by its associated media type, as described
     1184                  in <a href="#media.types" title="Media Types">Section&nbsp;3.7</a>.
     1185               </p>
     1186            </div>
     1187            <div id="rfc.figure.u.7"></div><pre class="inline"><span id="rfc.iref.g.13"></span>    <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.5">CRLF</a>           = <a href="#basic.rules" class="smpl" id="rfc.extref.c.6">CR</a> <a href="#basic.rules" class="smpl" id="rfc.extref.l.5">LF</a>
    11821188</pre><div id="basic.rules.lws">
    1183          <p id="rfc.section.2.2.p.5"> HTTP/1.1 header field values can be folded onto multiple lines if the continuation line begins with a space or horizontal
    1184             tab. All linear white space, including folding, has the same semantics as SP. A recipient <em class="bcp14">MAY</em> replace any linear white space with a single SP before interpreting the field value or forwarding the message downstream.
    1185          </p>
    1186       </div>
    1187       <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.14"></span>    <a href="#basic.rules.lws" class="smpl" id="rfc.extref.l.6">LWS</a>            = [<a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.7">CRLF</a>] 1*( <a href="#basic.rules" class="smpl" id="rfc.extref.s.3">SP</a> | <a href="#basic.rules" class="smpl" id="rfc.extref.h.3">HT</a> )
     1189               <p id="rfc.section.2.2.p.5"> HTTP/1.1 header field values can be folded onto multiple lines if the continuation line begins with a space or horizontal
     1190                  tab. All linear white space, including folding, has the same semantics as SP. A recipient <em class="bcp14">MAY</em> replace any linear white space with a single SP before interpreting the field value or forwarding the message downstream.
     1191               </p>
     1192            </div>
     1193            <div id="rfc.figure.u.8"></div><pre class="inline"><span id="rfc.iref.g.14"></span>    <a href="#basic.rules.lws" class="smpl" id="rfc.extref.l.6">LWS</a>            = [<a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.7">CRLF</a>] 1*( <a href="#basic.rules" class="smpl" id="rfc.extref.s.3">SP</a> | <a href="#basic.rules" class="smpl" id="rfc.extref.h.3">HT</a> )
    11881194</pre><div id="basic.rules.text">
    1189          <p id="rfc.section.2.2.p.7"> The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message
    1190             parser. Words of *TEXT <em class="bcp14">MAY</em> contain characters from character sets other than ISO-8859-1 <a href="#ISO-8859" id="rfc.xref.ISO-8859.1"><cite title="Information technology - 8-bit single byte coded graphic - character sets">[22]</cite></a> only when encoded according to the rules of RFC 2047 <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[14]</cite></a>.
    1191          </p>
    1192       </div>
    1193       <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.15"></span>    <a href="#basic.rules.text" class="smpl" id="rfc.extref.t.1">TEXT</a>           = &lt;any <a href="#basic.rules" class="smpl" id="rfc.extref.o.2">OCTET</a> except <a href="#basic.rules" class="smpl" id="rfc.extref.c.8">CTL</a>s,
     1195               <p id="rfc.section.2.2.p.7"> The TEXT rule is only used for descriptive field contents and values that are not intended to be interpreted by the message
     1196                  parser. Words of *TEXT <em class="bcp14">MAY</em> contain characters from character sets other than ISO-8859-1 <a href="#ISO-8859" id="rfc.xref.ISO-8859.1"><cite title="Information technology - 8-bit single byte coded graphic - character sets">[22]</cite></a> only when encoded according to the rules of RFC 2047 <a href="#RFC2047" id="rfc.xref.RFC2047.1"><cite title="MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text">[14]</cite></a>.
     1197               </p>
     1198            </div>
     1199            <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.15"></span>    <a href="#basic.rules.text" class="smpl" id="rfc.extref.t.1">TEXT</a>           = &lt;any <a href="#basic.rules" class="smpl" id="rfc.extref.o.2">OCTET</a> except <a href="#basic.rules" class="smpl" id="rfc.extref.c.8">CTL</a>s,
    11941200                     but including <a href="#basic.rules.lws" class="smpl" id="rfc.extref.l.7">LWS</a>&gt;
    11951201</pre><p id="rfc.section.2.2.p.9">A CRLF is allowed in the definition of TEXT only as part of a header field continuation. It is expected that the folding LWS
    1196          will be replaced with a single SP before interpretation of the TEXT value.
    1197       </p>
    1198       <div id="basic.rules.hex">
    1199          <p id="rfc.section.2.2.p.10"> Hexadecimal numeric characters are used in several protocol elements.</p>
    1200       </div>
    1201       <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.16"></span>    <a href="#basic.rules.hex" class="smpl" id="rfc.extref.h.4">HEX</a>            = "A" | "B" | "C" | "D" | "E" | "F"
     1202               will be replaced with a single SP before interpretation of the TEXT value.
     1203            </p>
     1204            <div id="basic.rules.hex">
     1205               <p id="rfc.section.2.2.p.10"> Hexadecimal numeric characters are used in several protocol elements.</p>
     1206            </div>
     1207            <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.16"></span>    <a href="#basic.rules.hex" class="smpl" id="rfc.extref.h.4">HEX</a>            = "A" | "B" | "C" | "D" | "E" | "F"
    12021208                   | "a" | "b" | "c" | "d" | "e" | "f" | <a href="#basic.rules" class="smpl" id="rfc.extref.d.3">DIGIT</a>
    12031209</pre><div id="basic.rules.token">
    1204          <p id="rfc.section.2.2.p.12">    Many HTTP/1.1 header field values consist of words separated by LWS or special characters. These special characters <em class="bcp14">MUST</em> be in a quoted string to be used within a parameter value (as defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>).
    1205          </p>
    1206       </div>
    1207       <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span>    <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.2">token</a>          = 1*&lt;any <a href="#basic.rules" class="smpl" id="rfc.extref.c.9">CHAR</a> except <a href="#basic.rules" class="smpl" id="rfc.extref.c.10">CTL</a>s or <a href="#basic.rules.token" class="smpl" id="rfc.extref.s.4">separators</a>&gt;
     1210               <p id="rfc.section.2.2.p.12">  Many HTTP/1.1 header field values consist of words separated by LWS or special characters. These special characters <em class="bcp14">MUST</em> be in a quoted string to be used within a parameter value (as defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>).
     1211               </p>
     1212            </div>
     1213            <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.17"></span><span id="rfc.iref.g.18"></span>    <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.2">token</a>          = 1*&lt;any <a href="#basic.rules" class="smpl" id="rfc.extref.c.9">CHAR</a> except <a href="#basic.rules" class="smpl" id="rfc.extref.c.10">CTL</a>s or <a href="#basic.rules.token" class="smpl" id="rfc.extref.s.4">separators</a>&gt;
    12081214    <a href="#basic.rules.token" class="smpl" id="rfc.extref.s.5">separators</a>     = "(" | ")" | "&lt;" | "&gt;" | "@"
    12091215                   | "," | ";" | ":" | "\" | &lt;"&gt;
     
    12111217                   | "{" | "}" | <a href="#basic.rules" class="smpl" id="rfc.extref.s.6">SP</a> | <a href="#basic.rules" class="smpl" id="rfc.extref.h.5">HT</a>
    12121218</pre><div id="basic.rules.comment">
    1213          <p id="rfc.section.2.2.p.14">    Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed
    1214             in fields containing "comment" as part of their field value definition. In all other fields, parentheses are considered part
    1215             of the field value.
    1216          </p>
    1217       </div>
    1218       <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span>    <a href="#basic.rules.comment" class="smpl" id="rfc.extref.c.11">comment</a>        = "(" *( <a href="#basic.rules.comment" class="smpl" id="rfc.extref.c.12">ctext</a> | <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.1">quoted-pair</a> | <a href="#basic.rules.comment" class="smpl" id="rfc.extref.c.13">comment</a> ) ")"
     1219               <p id="rfc.section.2.2.p.14">  Comments can be included in some HTTP header fields by surrounding the comment text with parentheses. Comments are only allowed
     1220                  in fields containing "comment" as part of their field value definition. In all other fields, parentheses are considered part
     1221                  of the field value.
     1222               </p>
     1223            </div>
     1224            <div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span>    <a href="#basic.rules.comment" class="smpl" id="rfc.extref.c.11">comment</a>        = "(" *( <a href="#basic.rules.comment" class="smpl" id="rfc.extref.c.12">ctext</a> | <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.1">quoted-pair</a> | <a href="#basic.rules.comment" class="smpl" id="rfc.extref.c.13">comment</a> ) ")"
    12191225    <a href="#basic.rules.comment" class="smpl" id="rfc.extref.c.14">ctext</a>          = &lt;any <a href="#basic.rules.text" class="smpl" id="rfc.extref.t.3">TEXT</a> excluding "(" and ")"&gt;
    12201226</pre><div id="basic.rules.quoted-string">
    1221          <p id="rfc.section.2.2.p.16">      A string of text is parsed as a single word if it is quoted using double-quote marks.</p>
    1222       </div>
    1223       <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span>    <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.2">quoted-string</a>  = ( &lt;"&gt; *(<a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.3">qdtext</a> | <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.4">quoted-pair</a> ) &lt;"&gt; )
     1227               <p id="rfc.section.2.2.p.16">   A string of text is parsed as a single word if it is quoted using double-quote marks.</p>
     1228            </div>
     1229            <div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span>    <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.2">quoted-string</a>  = ( &lt;"&gt; *(<a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.3">qdtext</a> | <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.4">quoted-pair</a> ) &lt;"&gt; )
    12241230    <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.5">qdtext</a>         = &lt;any <a href="#basic.rules.text" class="smpl" id="rfc.extref.t.4">TEXT</a> except &lt;"&gt;&gt;
    12251231</pre><p id="rfc.section.2.2.p.18">The backslash character ("\") <em class="bcp14">MAY</em> be used as a single-character quoting mechanism only within quoted-string and comment constructs.
    1226       </p>
    1227       <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.23"></span>    <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.6">quoted-pair</a>    = "\" <a href="#basic.rules" class="smpl" id="rfc.extref.c.15">CHAR</a>
    1228 </pre><hr class="noprint">
    1229       <h1 id="rfc.section.3" class="np"><a href="#rfc.section.3">3.</a>&nbsp;<a id="protocol.parameters" href="#protocol.parameters">Protocol Parameters</a></h1>
    1230       <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a id="http.version" href="#http.version">HTTP Version</a></h2>
    1231       <p id="rfc.section.3.1.p.1">HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended
    1232          to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather
    1233          than the features obtained via that communication. No change is made to the version number for the addition of message components
    1234          which do not affect communication behavior or which only add to extensible field values. The &lt;minor&gt; number is incremented
    1235          when the changes made to the protocol add features which do not change the general message parsing algorithm, but which may
    1236          add to the message semantics and imply additional capabilities of the sender. The &lt;major&gt; number is incremented when the format
    1237          of a message within the protocol is changed. See RFC 2145 <a href="#RFC2145" id="rfc.xref.RFC2145.1"><cite title="Use and Interpretation of HTTP Version Numbers">[36]</cite></a> for a fuller explanation.
    1238       </p>
    1239       <p id="rfc.section.3.1.p.2">The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message.</p>
    1240       <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.24"></span>       <a href="#http.version" class="smpl" id="rfc.extref.h.6">HTTP-Version</a>   = "HTTP" "/" 1*<a href="#basic.rules" class="smpl" id="rfc.extref.d.4">DIGIT</a> "." 1*<a href="#basic.rules" class="smpl" id="rfc.extref.d.5">DIGIT</a>
     1232            </p>
     1233            <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.23"></span>    <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.6">quoted-pair</a>    = "\" <a href="#basic.rules" class="smpl" id="rfc.extref.c.15">CHAR</a>
     1234</pre></div>
     1235      </div>
     1236      <hr class="noprint">
     1237      <div id="protocol.parameters">
     1238         <h1 id="rfc.section.3" class="np"><a href="#rfc.section.3">3.</a>&nbsp;<a href="#protocol.parameters">Protocol Parameters</a></h1>
     1239         <div id="http.version">
     1240            <h2 id="rfc.section.3.1"><a href="#rfc.section.3.1">3.1</a>&nbsp;<a href="#http.version">HTTP Version</a></h2>
     1241            <p id="rfc.section.3.1.p.1">HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions of the protocol. The protocol versioning policy is intended
     1242               to allow the sender to indicate the format of a message and its capacity for understanding further HTTP communication, rather
     1243               than the features obtained via that communication. No change is made to the version number for the addition of message components
     1244               which do not affect communication behavior or which only add to extensible field values. The &lt;minor&gt; number is incremented
     1245               when the changes made to the protocol add features which do not change the general message parsing algorithm, but which may
     1246               add to the message semantics and imply additional capabilities of the sender. The &lt;major&gt; number is incremented when the format
     1247               of a message within the protocol is changed. See RFC 2145 <a href="#RFC2145" id="rfc.xref.RFC2145.1"><cite title="Use and Interpretation of HTTP Version Numbers">[36]</cite></a> for a fuller explanation.
     1248            </p>
     1249            <p id="rfc.section.3.1.p.2">The version of an HTTP message is indicated by an HTTP-Version field in the first line of the message.</p>
     1250            <div id="rfc.figure.u.15"></div><pre class="inline"><span id="rfc.iref.g.24"></span>       <a href="#http.version" class="smpl" id="rfc.extref.h.6">HTTP-Version</a>   = "HTTP" "/" 1*<a href="#basic.rules" class="smpl" id="rfc.extref.d.4">DIGIT</a> "." 1*<a href="#basic.rules" class="smpl" id="rfc.extref.d.5">DIGIT</a>
    12411251</pre><p id="rfc.section.3.1.p.4">Note that the major and minor numbers <em class="bcp14">MUST</em> be treated as separate integers and that each <em class="bcp14">MAY</em> be incremented higher than a single digit. Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is lower than HTTP/12.3.
    1242          Leading zeros <em class="bcp14">MUST</em> be ignored by recipients and <em class="bcp14">MUST NOT</em> be sent.
    1243       </p>
    1244       <p id="rfc.section.3.1.p.5">An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" <em class="bcp14">MUST</em> be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this
    1245          specification <em class="bcp14">SHOULD</em> use an HTTP-Version of "HTTP/1.1" in their messages, and <em class="bcp14">MUST</em> do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values,
    1246          see RFC 2145 <a href="#RFC2145" id="rfc.xref.RFC2145.2"><cite title="Use and Interpretation of HTTP Version Numbers">[36]</cite></a>.
    1247       </p>
    1248       <p id="rfc.section.3.1.p.6">The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.</p>
    1249       <p id="rfc.section.3.1.p.7">Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the
    1250          application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway <em class="bcp14">MUST NOT</em> send a message with a version indicator which is greater than its actual version. If a higher version request is received,
    1251          the proxy/gateway <em class="bcp14">MUST</em> either downgrade the request version, or respond with an error, or switch to tunnel behavior.
    1252       </p>
    1253       <p id="rfc.section.3.1.p.8">Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of RFC 2068 <a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[33]</cite></a>, caching proxies <em class="bcp14">MUST</em>, gateways <em class="bcp14">MAY</em>, and tunnels <em class="bcp14">MUST NOT</em> upgrade the request to the highest version they support. The proxy/gateway's response to that request <em class="bcp14">MUST</em> be in the same major version as the request.
    1254       </p>
    1255       <p id="rfc.section.3.1.p.9"> </p>
    1256       <ul class="empty">
    1257          <li> <b>Note:</b> Converting between versions of HTTP may involve modification of header fields required or forbidden by the versions involved.
    1258          </li>
    1259       </ul>
    1260       <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a id="uri" href="#uri">Uniform Resource Identifiers</a></h2>
    1261       <p id="rfc.section.3.2.p.1">URIs have been known by many names: WWW addresses, Universal Document Identifiers, Universal Resource Identifiers <a href="#RFC1630" id="rfc.xref.RFC1630.2"><cite title="Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web">[3]</cite></a>, and finally the combination of Uniform Resource Locators (URL) <a href="#RFC1738" id="rfc.xref.RFC1738.2"><cite title="Uniform Resource Locators (URL)">[4]</cite></a> and Names (URN) <a href="#RFC1737" id="rfc.xref.RFC1737.2"><cite title="Functional Requirements for Uniform Resource Names">[20]</cite></a>. As far as HTTP is concerned, Uniform Resource Identifiers are simply formatted strings which identify--via name, location,
    1262          or any other characteristic--a resource.
    1263       </p>
    1264       <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;<a id="general.syntax" href="#general.syntax">General Syntax</a></h3>
    1265       <p id="rfc.section.3.2.1.p.1">URIs in HTTP can be represented in absolute form or relative to some known base URI <a href="#RFC1808" id="rfc.xref.RFC1808.1"><cite title="Relative Uniform Resource Locators">[11]</cite></a>, depending upon the context of their use. The two forms are differentiated by the fact that absolute URIs always begin with
    1266          a scheme name followed by a colon. For definitive information on URL syntax and semantics, see "Uniform Resource Identifiers
    1267          (URI): Generic Syntax and Semantics," RFC 2396 <a href="#RFC2396" id="rfc.xref.RFC2396.1"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[42]</cite></a> (which replaces RFCs 1738 <a href="#RFC1738" id="rfc.xref.RFC1738.3"><cite title="Uniform Resource Locators (URL)">[4]</cite></a> and RFC 1808 <a href="#RFC1808" id="rfc.xref.RFC1808.2"><cite title="Relative Uniform Resource Locators">[11]</cite></a>). This specification adopts the definitions of "URI-reference", "absoluteURI", "relativeURI", "port", "host","abs_path",
    1268          "rel_path", and "authority" from that specification.
    1269       </p>
    1270       <p id="rfc.section.3.2.1.p.2">The HTTP protocol does not place any a priori limit on the length of a URI. Servers <em class="bcp14">MUST</em> be able to handle the URI of any resource they serve, and <em class="bcp14">SHOULD</em> be able to handle URIs of unbounded length if they provide GET-based forms that could generate such URIs. A server <em class="bcp14">SHOULD</em> return <a href="#status.414" class="smpl">414 (Request-URI Too Long)</a> status if a URI is longer than the server can handle (see <a href="#status.414" id="rfc.xref.status.414.1" title="414 Request-URI Too Long">Section&nbsp;10.4.15</a>).
    1271       </p>
    1272       <p id="rfc.section.3.2.1.p.3"> </p>
    1273       <ul class="empty">
    1274          <li> <b>Note:</b> Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations
    1275             might not properly support these lengths.
    1276          </li>
    1277       </ul>
    1278       <div id="rfc.iref.h.2"></div>
    1279       <div id="rfc.iref.u.3"></div>
    1280       <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;<a id="http.url" href="#http.url">http URL</a></h3>
    1281       <p id="rfc.section.3.2.2.p.1">The "http" scheme is used to locate network resources via the HTTP protocol. This section defines the scheme-specific syntax
    1282          and semantics for http URLs.
    1283       </p>
    1284       <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.25"></span>http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]
     1252               Leading zeros <em class="bcp14">MUST</em> be ignored by recipients and <em class="bcp14">MUST NOT</em> be sent.
     1253            </p>
     1254            <p id="rfc.section.3.1.p.5">An application that sends a request or response message that includes HTTP-Version of "HTTP/1.1" <em class="bcp14">MUST</em> be at least conditionally compliant with this specification. Applications that are at least conditionally compliant with this
     1255               specification <em class="bcp14">SHOULD</em> use an HTTP-Version of "HTTP/1.1" in their messages, and <em class="bcp14">MUST</em> do so for any message that is not compatible with HTTP/1.0. For more details on when to send specific HTTP-Version values,
     1256               see RFC 2145 <a href="#RFC2145" id="rfc.xref.RFC2145.2"><cite title="Use and Interpretation of HTTP Version Numbers">[36]</cite></a>.
     1257            </p>
     1258            <p id="rfc.section.3.1.p.6">The HTTP version of an application is the highest HTTP version for which the application is at least conditionally compliant.</p>
     1259            <p id="rfc.section.3.1.p.7">Proxy and gateway applications need to be careful when forwarding messages in protocol versions different from that of the
     1260               application. Since the protocol version indicates the protocol capability of the sender, a proxy/gateway <em class="bcp14">MUST NOT</em> send a message with a version indicator which is greater than its actual version. If a higher version request is received,
     1261               the proxy/gateway <em class="bcp14">MUST</em> either downgrade the request version, or respond with an error, or switch to tunnel behavior.
     1262            </p>
     1263            <p id="rfc.section.3.1.p.8">Due to interoperability problems with HTTP/1.0 proxies discovered since the publication of RFC 2068 <a href="#RFC2068" id="rfc.xref.RFC2068.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[33]</cite></a>, caching proxies <em class="bcp14">MUST</em>, gateways <em class="bcp14">MAY</em>, and tunnels <em class="bcp14">MUST NOT</em> upgrade the request to the highest version they support. The proxy/gateway's response to that request <em class="bcp14">MUST</em> be in the same major version as the request.
     1264            </p>
     1265            <p id="rfc.section.3.1.p.9"></p>
     1266            <ul class="empty">
     1267               <li><b>Note:</b> Converting between versions of HTTP may involve modification of header fields required or forbidden by the versions involved.
     1268               </li>
     1269            </ul>
     1270         </div>
     1271         <div id="uri">
     1272            <h2 id="rfc.section.3.2"><a href="#rfc.section.3.2">3.2</a>&nbsp;<a href="#uri">Uniform Resource Identifiers</a></h2>
     1273            <p id="rfc.section.3.2.p.1">URIs have been known by many names: WWW addresses, Universal Document Identifiers, Universal Resource Identifiers <a href="#RFC1630" id="rfc.xref.RFC1630.2"><cite title="Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web">[3]</cite></a>, and finally the combination of Uniform Resource Locators (URL) <a href="#RFC1738" id="rfc.xref.RFC1738.2"><cite title="Uniform Resource Locators (URL)">[4]</cite></a> and Names (URN) <a href="#RFC1737" id="rfc.xref.RFC1737.2"><cite title="Functional Requirements for Uniform Resource Names">[20]</cite></a>. As far as HTTP is concerned, Uniform Resource Identifiers are simply formatted strings which identify--via name, location,
     1274               or any other characteristic--a resource.
     1275            </p>
     1276            <div id="general.syntax">
     1277               <h3 id="rfc.section.3.2.1"><a href="#rfc.section.3.2.1">3.2.1</a>&nbsp;<a href="#general.syntax">General Syntax</a></h3>
     1278               <p id="rfc.section.3.2.1.p.1">URIs in HTTP can be represented in absolute form or relative to some known base URI <a href="#RFC1808" id="rfc.xref.RFC1808.1"><cite title="Relative Uniform Resource Locators">[11]</cite></a>, depending upon the context of their use. The two forms are differentiated by the fact that absolute URIs always begin with
     1279                  a scheme name followed by a colon. For definitive information on URL syntax and semantics, see "Uniform Resource Identifiers
     1280                  (URI): Generic Syntax and Semantics," RFC 2396 <a href="#RFC2396" id="rfc.xref.RFC2396.1"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[42]</cite></a> (which replaces RFCs 1738 <a href="#RFC1738" id="rfc.xref.RFC1738.3"><cite title="Uniform Resource Locators (URL)">[4]</cite></a> and RFC 1808 <a href="#RFC1808" id="rfc.xref.RFC1808.2"><cite title="Relative Uniform Resource Locators">[11]</cite></a>). This specification adopts the definitions of "URI-reference", "absoluteURI", "relativeURI", "port", "host","abs_path",
     1281                  "rel_path", and "authority" from that specification.
     1282               </p>
     1283               <p id="rfc.section.3.2.1.p.2">The HTTP protocol does not place any a priori limit on the length of a URI. Servers <em class="bcp14">MUST</em> be able to handle the URI of any resource they serve, and <em class="bcp14">SHOULD</em> be able to handle URIs of unbounded length if they provide GET-based forms that could generate such URIs. A server <em class="bcp14">SHOULD</em> return <a href="#status.414" class="smpl">414 (Request-URI Too Long)</a> status if a URI is longer than the server can handle (see <a href="#status.414" id="rfc.xref.status.414.1" title="414 Request-URI Too Long">Section&nbsp;10.4.15</a>).
     1284               </p>
     1285               <p id="rfc.section.3.2.1.p.3"></p>
     1286               <ul class="empty">
     1287                  <li><b>Note:</b> Servers ought to be cautious about depending on URI lengths above 255 bytes, because some older client or proxy implementations
     1288                     might not properly support these lengths.
     1289                  </li>
     1290               </ul>
     1291            </div>
     1292            <div id="http.url">
     1293               <div id="rfc.iref.h.2"></div>
     1294               <div id="rfc.iref.u.3"></div>
     1295               <h3 id="rfc.section.3.2.2"><a href="#rfc.section.3.2.2">3.2.2</a>&nbsp;<a href="#http.url">http URL</a></h3>
     1296               <p id="rfc.section.3.2.2.p.1">The "http" scheme is used to locate network resources via the HTTP protocol. This section defines the scheme-specific syntax
     1297                  and semantics for http URLs.
     1298               </p>
     1299               <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.25"></span>http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]
    12851300</pre><p id="rfc.section.3.2.2.p.3">If the port is empty or not given, port 80 is assumed. The semantics are that the identified resource is located at the server
    1286          listening for TCP connections on that port of that host, and the Request-URI for the resource is abs_path (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>). The use of IP addresses in URLs <em class="bcp14">SHOULD</em> be avoided whenever possible (see RFC 1900 <a href="#RFC1900" id="rfc.xref.RFC1900.1"><cite title="Renumbering Needs Work">[24]</cite></a>). If the abs_path is not present in the URL, it <em class="bcp14">MUST</em> be given as "/" when used as a Request-URI for a resource (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>). If a proxy receives a host name which is not a fully qualified domain name, it <em class="bcp14">MAY</em> add its domain to the host name it received. If a proxy receives a fully qualified domain name, the proxy <em class="bcp14">MUST NOT</em> change the host name.
    1287       </p>
    1288       <h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;<a id="uri.comparison" href="#uri.comparison">URI Comparison</a></h3>
    1289       <p id="rfc.section.3.2.3.p.1">When comparing two URIs to decide if they match or not, a client <em class="bcp14">SHOULD</em> use a case-sensitive octet-by-octet comparison of the entire URIs, with these exceptions:
    1290       </p>
    1291       <ul>
    1292          <li>A port that is empty or not given is equivalent to the default port for that URI-reference;</li>
    1293          <li>Comparisons of host names <em class="bcp14">MUST</em> be case-insensitive;
    1294          </li>
    1295          <li>Comparisons of scheme names <em class="bcp14">MUST</em> be case-insensitive;
    1296          </li>
    1297          <li>An empty abs_path is equivalent to an abs_path of "/".</li>
    1298       </ul>
    1299       <p id="rfc.section.3.2.3.p.2">Characters other than those in the "reserved" and "unsafe" sets (see RFC 2396 <a href="#RFC2396" id="rfc.xref.RFC2396.2"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[42]</cite></a>) are equivalent to their ""%" HEX HEX" encoding.
    1300       </p>
    1301       <p id="rfc.section.3.2.3.p.3">For example, the following three URIs are equivalent:</p>
    1302       <div id="rfc.figure.u.17"></div><pre class="text">   http://abc.com:80/~smith/home.html
     1301                  listening for TCP connections on that port of that host, and the Request-URI for the resource is abs_path (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>). The use of IP addresses in URLs <em class="bcp14">SHOULD</em> be avoided whenever possible (see RFC 1900 <a href="#RFC1900" id="rfc.xref.RFC1900.1"><cite title="Renumbering Needs Work">[24]</cite></a>). If the abs_path is not present in the URL, it <em class="bcp14">MUST</em> be given as "/" when used as a Request-URI for a resource (<a href="#request-uri" title="Request-URI">Section&nbsp;5.1.2</a>). If a proxy receives a host name which is not a fully qualified domain name, it <em class="bcp14">MAY</em> add its domain to the host name it received. If a proxy receives a fully qualified domain name, the proxy <em class="bcp14">MUST NOT</em> change the host name.
     1302               </p>
     1303            </div>
     1304            <div id="uri.comparison">
     1305               <h3 id="rfc.section.3.2.3"><a href="#rfc.section.3.2.3">3.2.3</a>&nbsp;<a href="#uri.comparison">URI Comparison</a></h3>
     1306               <p id="rfc.section.3.2.3.p.1">When comparing two URIs to decide if they match or not, a client <em class="bcp14">SHOULD</em> use a case-sensitive octet-by-octet comparison of the entire URIs, with these exceptions:
     1307               </p>
     1308               <ul>
     1309                  <li>A port that is empty or not given is equivalent to the default port for that URI-reference;</li>
     1310                  <li>Comparisons of host names <em class="bcp14">MUST</em> be case-insensitive;
     1311                  </li>
     1312                  <li>Comparisons of scheme names <em class="bcp14">MUST</em> be case-insensitive;
     1313                  </li>
     1314                  <li>An empty abs_path is equivalent to an abs_path of "/".</li>
     1315               </ul>
     1316               <p id="rfc.section.3.2.3.p.2">Characters other than those in the "reserved" and "unsafe" sets (see RFC 2396 <a href="#RFC2396" id="rfc.xref.RFC2396.2"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[42]</cite></a>) are equivalent to their ""%" HEX HEX" encoding.
     1317               </p>
     1318               <p id="rfc.section.3.2.3.p.3">For example, the following three URIs are equivalent:</p>
     1319               <div id="rfc.figure.u.17"></div><pre class="text">   http://abc.com:80/~smith/home.html
    13031320   http://ABC.com/%7Esmith/home.html
    13041321   http://ABC.com:/%7esmith/home.html
    1305 </pre><h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a id="date.time.formats" href="#date.time.formats">Date/Time Formats</a></h2>
    1306       <h3 id="rfc.section.3.3.1"><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;<a id="full.date" href="#full.date">Full Date</a></h3>
    1307       <p id="rfc.section.3.3.1.p.1">HTTP applications have historically allowed three different formats for the representation of date/time stamps:</p>
    1308       <div id="rfc.figure.u.18"></div><pre class="text">   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
     1322</pre></div>
     1323         </div>
     1324         <div id="date.time.formats">
     1325            <h2 id="rfc.section.3.3"><a href="#rfc.section.3.3">3.3</a>&nbsp;<a href="#date.time.formats">Date/Time Formats</a></h2>
     1326            <div id="full.date">
     1327               <h3 id="rfc.section.3.3.1"><a href="#rfc.section.3.3.1">3.3.1</a>&nbsp;<a href="#full.date">Full Date</a></h3>
     1328               <p id="rfc.section.3.3.1.p.1">HTTP applications have historically allowed three different formats for the representation of date/time stamps:</p>
     1329               <div id="rfc.figure.u.18"></div><pre class="text">   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
    13091330   Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
    13101331   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
    13111332</pre><p id="rfc.section.3.3.1.p.3">The first format is preferred as an Internet standard and represents a fixed-length subset of that defined by RFC 1123 <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[8]</cite></a> (an update to RFC 822 <a href="#RFC822" id="rfc.xref.RFC822.3"><cite title="Standard for the format of ARPA Internet text messages">[9]</cite></a>). The second format is in common use, but is based on the obsolete RFC 850 <a href="#RFC1036" id="rfc.xref.RFC1036.1"><cite title="Standard for interchange of USENET messages">[12]</cite></a> date format and lacks a four-digit year. HTTP/1.1 clients and servers that parse the date value <em class="bcp14">MUST</em> accept all three formats (for compatibility with HTTP/1.0), though they <em class="bcp14">MUST</em> only generate the RFC 1123 format for representing HTTP-date values in header fields. See <a href="#tolerant.applications" title="Tolerant Applications">Appendix&nbsp;19.3</a> for further information.
    1312       </p>
    1313       <ul class="empty">
    1314          <li> <b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that may have been sent by non-HTTP applications,
    1315             as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP.
    1316          </li>
    1317       </ul>
    1318       <p id="rfc.section.3.3.1.p.5">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated
    1319          Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for
    1320          time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional LWS beyond that specifically included as SP in the grammar.
    1321       </p>
    1322       <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.26"></span><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span><span id="rfc.iref.g.33"></span><span id="rfc.iref.g.34"></span><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span>    <a href="#full.date" class="smpl" id="rfc.extref.h.7">HTTP-date</a>    = rfc1123-date | rfc850-date | asctime-date
     1333               </p>
     1334               <ul class="empty">
     1335                  <li><b>Note:</b> Recipients of date values are encouraged to be robust in accepting date values that may have been sent by non-HTTP applications,
     1336                     as is sometimes the case when retrieving or posting messages via proxies/gateways to SMTP or NNTP.
     1337                  </li>
     1338               </ul>
     1339               <p id="rfc.section.3.3.1.p.5">All HTTP date/time stamps <em class="bcp14">MUST</em> be represented in Greenwich Mean Time (GMT), without exception. For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated
     1340                  Universal Time). This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for
     1341                  time zone, and <em class="bcp14">MUST</em> be assumed when reading the asctime format. HTTP-date is case sensitive and <em class="bcp14">MUST NOT</em> include additional LWS beyond that specifically included as SP in the grammar.
     1342               </p>
     1343               <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.26"></span><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span><span id="rfc.iref.g.33"></span><span id="rfc.iref.g.34"></span><span id="rfc.iref.g.35"></span><span id="rfc.iref.g.36"></span>    <a href="#full.date" class="smpl" id="rfc.extref.h.7">HTTP-date</a>    = rfc1123-date | rfc850-date | asctime-date
    13231344    rfc1123-date = wkday "," <a href="#basic.rules" class="smpl" id="rfc.extref.s.7">SP</a> date1 <a href="#basic.rules" class="smpl" id="rfc.extref.s.8">SP</a> time <a href="#basic.rules" class="smpl" id="rfc.extref.s.9">SP</a> "GMT"
    13241345    rfc850-date  = weekday "," <a href="#basic.rules" class="smpl" id="rfc.extref.s.10">SP</a> date2 <a href="#basic.rules" class="smpl" id="rfc.extref.s.11">SP</a> time <a href="#basic.rules" class="smpl" id="rfc.extref.s.12">SP</a> "GMT"
     
    13391360                 | "May" | "Jun" | "Jul" | "Aug"
    13401361                 | "Sep" | "Oct" | "Nov" | "Dec"
    1341 </pre><p id="rfc.section.3.3.1.p.7"> <b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers
    1342          are not required to use these formats for user presentation, request logging, etc.
    1343       </p>
    1344       <h3 id="rfc.section.3.3.2"><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;<a id="delta.seconds" href="#delta.seconds">Delta Seconds</a></h3>
    1345       <p id="rfc.section.3.3.2.p.1">Some HTTP header fields allow a time value to be specified as an integer number of seconds, represented in decimal, after
    1346          the time that the message was received.
    1347       </p>
    1348       <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.37"></span>    <a href="#delta.seconds" class="smpl">delta-seconds</a>  = 1*<a href="#basic.rules" class="smpl" id="rfc.extref.d.17">DIGIT</a>
    1349 </pre><h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a id="character.sets" href="#character.sets">Character Sets</a></h2>
    1350       <p id="rfc.section.3.4.p.1">HTTP uses the same definition of the term "character set" as that described for MIME:</p>
    1351       <p id="rfc.section.3.4.p.2">The term "character set" is used in this document to refer to a method used with one or more tables to convert a sequence
    1352          of octets into a sequence of characters. Note that unconditional conversion in the other direction is not required, in that
    1353          not all characters may be available in a given character set and a character set may provide more than one sequence of octets
    1354          to represent a particular character. This definition is intended to allow various kinds of character encoding, from simple
    1355          single-table mappings such as US-ASCII to complex table switching methods such as those that use ISO-2022's techniques. However,
    1356          the definition associated with a MIME character set name <em class="bcp14">MUST</em> fully specify the mapping to be performed from octets to characters. In particular, use of external profiling information
    1357          to determine the exact mapping is not permitted.
    1358       </p>
    1359       <ul class="empty">
    1360          <li> <b>Note:</b> This use of the term "character set" is more commonly referred to as a "character encoding." However, since HTTP and MIME
    1361             share the same registry, it is important that the terminology also be shared.
    1362          </li>
    1363       </ul>
    1364       <div id="charset">
    1365          <p id="rfc.section.3.4.p.4">  HTTP character sets are identified by case-insensitive tokens. The complete set of tokens is defined by the IANA Character
    1366             Set registry <a href="#RFC1700" id="rfc.xref.RFC1700.2"><cite title="Assigned Numbers">[19]</cite></a>.
    1367          </p>
    1368       </div>
    1369       <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.38"></span>    <a href="#charset" class="smpl">charset</a> = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.5">token</a>
     1362</pre><p id="rfc.section.3.3.1.p.7"><b>Note:</b> HTTP requirements for the date/time stamp format apply only to their usage within the protocol stream. Clients and servers
     1363                  are not required to use these formats for user presentation, request logging, etc.
     1364               </p>
     1365            </div>
     1366            <div id="delta.seconds">
     1367               <h3 id="rfc.section.3.3.2"><a href="#rfc.section.3.3.2">3.3.2</a>&nbsp;<a href="#delta.seconds">Delta Seconds</a></h3>
     1368               <p id="rfc.section.3.3.2.p.1">Some HTTP header fields allow a time value to be specified as an integer number of seconds, represented in decimal, after
     1369                  the time that the message was received.
     1370               </p>
     1371               <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.37"></span>    <a href="#delta.seconds" class="smpl">delta-seconds</a>  = 1*<a href="#basic.rules" class="smpl" id="rfc.extref.d.17">DIGIT</a>
     1372</pre></div>
     1373         </div>
     1374         <div id="character.sets">
     1375            <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a>&nbsp;<a href="#character.sets">Character Sets</a></h2>
     1376            <p id="rfc.section.3.4.p.1">HTTP uses the same definition of the term "character set" as that described for MIME:</p>
     1377            <p id="rfc.section.3.4.p.2">The term "character set" is used in this document to refer to a method used with one or more tables to convert a sequence
     1378               of octets into a sequence of characters. Note that unconditional conversion in the other direction is not required, in that
     1379               not all characters may be available in a given character set and a character set may provide more than one sequence of octets
     1380               to represent a particular character. This definition is intended to allow various kinds of character encoding, from simple
     1381               single-table mappings such as US-ASCII to complex table switching methods such as those that use ISO-2022's techniques. However,
     1382               the definition associated with a MIME character set name <em class="bcp14">MUST</em> fully specify the mapping to be performed from octets to characters. In particular, use of external profiling information
     1383               to determine the exact mapping is not permitted.
     1384            </p>
     1385            <ul class="empty">
     1386               <li><b>Note:</b> This use of the term "character set" is more commonly referred to as a "character encoding." However, since HTTP and MIME
     1387                  share the same registry, it is important that the terminology also be shared.
     1388               </li>
     1389            </ul>
     1390            <div id="charset">
     1391               <p id="rfc.section.3.4.p.4"> HTTP character sets are identified by case-insensitive tokens. The complete set of tokens is defined by the IANA Character
     1392                  Set registry <a href="#RFC1700" id="rfc.xref.RFC1700.2"><cite title="Assigned Numbers">[19]</cite></a>.
     1393               </p>
     1394            </div>
     1395            <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.38"></span>    <a href="#charset" class="smpl">charset</a> = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.5">token</a>
    13701396</pre><p id="rfc.section.3.4.p.6">Although HTTP allows an arbitrary token to be used as a charset value, any token that has a predefined value within the IANA
    1371          Character Set registry <a href="#RFC1700" id="rfc.xref.RFC1700.3"><cite title="Assigned Numbers">[19]</cite></a>  <em class="bcp14">MUST</em> represent the character set defined by that registry. Applications <em class="bcp14">SHOULD</em> limit their use of character sets to those defined by the IANA registry.
    1372       </p>
    1373       <p id="rfc.section.3.4.p.7">Implementors should be aware of IETF character set requirements <a href="#RFC2279" id="rfc.xref.RFC2279.1"><cite title="UTF-8, a transformation format of ISO 10646">[38]</cite></a>  <a href="#RFC2277" id="rfc.xref.RFC2277.1"><cite title="IETF Policy on Character Sets and Languages">[41]</cite></a>.
    1374       </p>
    1375       <h3 id="rfc.section.3.4.1"><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;<a id="missing.charset" href="#missing.charset">Missing Charset</a></h3>
    1376       <p id="rfc.section.3.4.1.p.1">Some HTTP/1.0 software has interpreted a Content-Type header without charset parameter incorrectly to mean "recipient should
    1377          guess." Senders wishing to defeat this behavior <em class="bcp14">MAY</em> include a charset parameter even when the charset is ISO-8859-1 and <em class="bcp14">SHOULD</em> do so when it is known that it will not confuse the recipient.
    1378       </p>
    1379       <p id="rfc.section.3.4.1.p.2">Unfortunately, some older HTTP/1.0 clients did not deal properly with an explicit charset parameter. HTTP/1.1 recipients <em class="bcp14">MUST</em> respect the charset label provided by the sender; and those user agents that have a provision to "guess" a charset <em class="bcp14">MUST</em> use the charset from the content-type field if they support that charset, rather than the recipient's preference, when initially
    1380          displaying a document. See <a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section&nbsp;3.7.1</a>.
    1381       </p>
    1382       <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a id="content.codings" href="#content.codings">Content Codings</a></h2>
    1383       <div id="rfc.iref.c.6"></div>
    1384       <p id="rfc.section.3.5.p.1">Content coding values indicate an encoding transformation that has been or can be applied to an entity. Content codings are
    1385          primarily used to allow a document to be compressed or otherwise usefully transformed without losing the identity of its underlying
    1386          media type and without loss of information. Frequently, the entity is stored in coded form, transmitted directly, and only
    1387          decoded by the recipient.
    1388       </p>
    1389       <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.39"></span>    <a href="#content.codings" class="smpl">content-coding</a>   = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.6">token</a>
     1397               Character Set registry <a href="#RFC1700" id="rfc.xref.RFC1700.3"><cite title="Assigned Numbers">[19]</cite></a> <em class="bcp14">MUST</em> represent the character set defined by that registry. Applications <em class="bcp14">SHOULD</em> limit their use of character sets to those defined by the IANA registry.
     1398            </p>
     1399            <p id="rfc.section.3.4.p.7">Implementors should be aware of IETF character set requirements <a href="#RFC2279" id="rfc.xref.RFC2279.1"><cite title="UTF-8, a transformation format of ISO 10646">[38]</cite></a> <a href="#RFC2277" id="rfc.xref.RFC2277.1"><cite title="IETF Policy on Character Sets and Languages">[41]</cite></a>.
     1400            </p>
     1401            <div id="missing.charset">
     1402               <h3 id="rfc.section.3.4.1"><a href="#rfc.section.3.4.1">3.4.1</a>&nbsp;<a href="#missing.charset">Missing Charset</a></h3>
     1403               <p id="rfc.section.3.4.1.p.1">Some HTTP/1.0 software has interpreted a Content-Type header without charset parameter incorrectly to mean "recipient should
     1404                  guess." Senders wishing to defeat this behavior <em class="bcp14">MAY</em> include a charset parameter even when the charset is ISO-8859-1 and <em class="bcp14">SHOULD</em> do so when it is known that it will not confuse the recipient.
     1405               </p>
     1406               <p id="rfc.section.3.4.1.p.2">Unfortunately, some older HTTP/1.0 clients did not deal properly with an explicit charset parameter. HTTP/1.1 recipients <em class="bcp14">MUST</em> respect the charset label provided by the sender; and those user agents that have a provision to "guess" a charset <em class="bcp14">MUST</em> use the charset from the content-type field if they support that charset, rather than the recipient's preference, when initially
     1407                  displaying a document. See <a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section&nbsp;3.7.1</a>.
     1408               </p>
     1409            </div>
     1410         </div>
     1411         <div id="content.codings">
     1412            <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a href="#content.codings">Content Codings</a></h2>
     1413            <div id="rfc.iref.c.6"></div>
     1414            <p id="rfc.section.3.5.p.1">Content coding values indicate an encoding transformation that has been or can be applied to an entity. Content codings are
     1415               primarily used to allow a document to be compressed or otherwise usefully transformed without losing the identity of its underlying
     1416               media type and without loss of information. Frequently, the entity is stored in coded form, transmitted directly, and only
     1417               decoded by the recipient.
     1418            </p>
     1419            <div id="rfc.figure.u.22"></div><pre class="inline"><span id="rfc.iref.g.39"></span>    <a href="#content.codings" class="smpl">content-coding</a>   = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.6">token</a>
    13901420</pre><p id="rfc.section.3.5.p.3">All content-coding values are case-insensitive. HTTP/1.1 uses content-coding values in the Accept-Encoding (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.1" title="Accept-Encoding">Section&nbsp;14.3</a>) and Content-Encoding (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section&nbsp;14.11</a>) header fields. Although the value describes the content-coding, what is more important is that it indicates what decoding
    1391          mechanism will be required to remove the encoding.
    1392       </p>
    1393       <p id="rfc.section.3.5.p.4">The Internet Assigned Numbers Authority (IANA) acts as a registry for content-coding value tokens. Initially, the registry
    1394          contains the following tokens:
    1395       </p>
    1396       <p id="rfc.section.3.5.p.5">gzip<span id="rfc.iref.g.40"></span><span id="rfc.iref.c.7"></span> 
    1397       </p>
    1398       <ul class="empty">
    1399          <li>An encoding format produced by the file compression program "gzip" (GNU zip) as described in RFC 1952 <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[25]</cite></a>. This format is a Lempel-Ziv coding (LZ77) with a 32 bit CRC.
    1400          </li>
    1401       </ul>
    1402       <p id="rfc.section.3.5.p.6">compress<span id="rfc.iref.c.8"></span><span id="rfc.iref.c.9"></span> 
    1403       </p>
    1404       <ul class="empty">
    1405          <li>The encoding format produced by the common UNIX file compression program "compress". This format is an adaptive Lempel-Ziv-Welch
    1406             coding (LZW).
    1407          </li>
    1408          <li>Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings.
    1409             Their use here is representative of historical practice, not good design. For compatibility with previous implementations
    1410             of HTTP, applications <em class="bcp14">SHOULD</em> consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress" respectively.
    1411          </li>
    1412       </ul>
    1413       <p id="rfc.section.3.5.p.7">deflate<span id="rfc.iref.d.2"></span><span id="rfc.iref.c.10"></span> 
    1414       </p>
    1415       <ul class="empty">
    1416          <li>The "zlib" format defined in RFC 1950 <a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[31]</cite></a> in combination with the "deflate" compression mechanism described in RFC 1951 <a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[29]</cite></a>.
    1417          </li>
    1418       </ul>
    1419       <p id="rfc.section.3.5.p.8">identity<span id="rfc.iref.i.2"></span><span id="rfc.iref.c.11"></span> 
    1420       </p>
    1421       <ul class="empty">
    1422          <li>The default (identity) encoding; the use of no transformation whatsoever. This content-coding is used only in the Accept-Encoding
    1423             header, and <em class="bcp14">SHOULD NOT</em> be used in the Content-Encoding header.
    1424          </li>
    1425       </ul>
    1426       <p id="rfc.section.3.5.p.9">New content-coding value tokens <em class="bcp14">SHOULD</em> be registered; to allow interoperability between clients and servers, specifications of the content coding algorithms needed
    1427          to implement a new value <em class="bcp14">SHOULD</em> be publicly available and adequate for independent implementation, and conform to the purpose of content coding defined in
    1428          this section.
    1429       </p>
    1430       <h2 id="rfc.section.3.6"><a href="#rfc.section.3.6">3.6</a>&nbsp;<a id="transfer.codings" href="#transfer.codings">Transfer Codings</a></h2>
    1431       <p id="rfc.section.3.6.p.1">Transfer-coding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to
    1432          an entity-body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer-coding
    1433          is a property of the message, not of the original entity.
    1434       </p>
    1435       <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span>    <a href="#transfer.codings" class="smpl">transfer-coding</a>         = "chunked" | transfer-extension
     1421               mechanism will be required to remove the encoding.
     1422            </p>
     1423            <p id="rfc.section.3.5.p.4">The Internet Assigned Numbers Authority (IANA) acts as a registry for content-coding value tokens. Initially, the registry
     1424               contains the following tokens:
     1425            </p>
     1426            <p id="rfc.section.3.5.p.5">gzip<span id="rfc.iref.g.40"></span><span id="rfc.iref.c.7"></span>
     1427            </p>
     1428            <ul class="empty">
     1429               <li>An encoding format produced by the file compression program "gzip" (GNU zip) as described in RFC 1952 <a href="#RFC1952" id="rfc.xref.RFC1952.1"><cite title="GZIP file format specification version 4.3">[25]</cite></a>. This format is a Lempel-Ziv coding (LZ77) with a 32 bit CRC.
     1430               </li>
     1431            </ul>
     1432            <p id="rfc.section.3.5.p.6">compress<span id="rfc.iref.c.8"></span><span id="rfc.iref.c.9"></span>
     1433            </p>
     1434            <ul class="empty">
     1435               <li>The encoding format produced by the common UNIX file compression program "compress". This format is an adaptive Lempel-Ziv-Welch
     1436                  coding (LZW).
     1437               </li>
     1438               <li>Use of program names for the identification of encoding formats is not desirable and is discouraged for future encodings.
     1439                  Their use here is representative of historical practice, not good design. For compatibility with previous implementations
     1440                  of HTTP, applications <em class="bcp14">SHOULD</em> consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress" respectively.
     1441               </li>
     1442            </ul>
     1443            <p id="rfc.section.3.5.p.7">deflate<span id="rfc.iref.d.2"></span><span id="rfc.iref.c.10"></span>
     1444            </p>
     1445            <ul class="empty">
     1446               <li>The "zlib" format defined in RFC 1950 <a href="#RFC1950" id="rfc.xref.RFC1950.1"><cite title="ZLIB Compressed Data Format Specification version 3.3">[31]</cite></a> in combination with the "deflate" compression mechanism described in RFC 1951 <a href="#RFC1951" id="rfc.xref.RFC1951.1"><cite title="DEFLATE Compressed Data Format Specification version 1.3">[29]</cite></a>.
     1447               </li>
     1448            </ul>
     1449            <p id="rfc.section.3.5.p.8">identity<span id="rfc.iref.i.2"></span><span id="rfc.iref.c.11"></span>
     1450            </p>
     1451            <ul class="empty">
     1452               <li>The default (identity) encoding; the use of no transformation whatsoever. This content-coding is used only in the Accept-Encoding
     1453                  header, and <em class="bcp14">SHOULD NOT</em> be used in the Content-Encoding header.
     1454               </li>
     1455            </ul>
     1456            <p id="rfc.section.3.5.p.9">New content-coding value tokens <em class="bcp14">SHOULD</em> be registered; to allow interoperability between clients and servers, specifications of the content coding algorithms needed
     1457               to implement a new value <em class="bcp14">SHOULD</em> be publicly available and adequate for independent implementation, and conform to the purpose of content coding defined in
     1458               this section.
     1459            </p>
     1460         </div>
     1461         <div id="transfer.codings">
     1462            <h2 id="rfc.section.3.6"><a href="#rfc.section.3.6">3.6</a>&nbsp;<a href="#transfer.codings">Transfer Codings</a></h2>
     1463            <p id="rfc.section.3.6.p.1">Transfer-coding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to
     1464               an entity-body in order to ensure "safe transport" through the network. This differs from a content coding in that the transfer-coding
     1465               is a property of the message, not of the original entity.
     1466            </p>
     1467            <div id="rfc.figure.u.23"></div><pre class="inline"><span id="rfc.iref.g.41"></span><span id="rfc.iref.g.42"></span>    <a href="#transfer.codings" class="smpl">transfer-coding</a>         = "chunked" | transfer-extension
    14361468    transfer-extension      = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.8">token</a> *( ";" <a href="#rule.parameter" class="smpl">parameter</a> )
    14371469</pre><div id="rule.parameter">
    1438          <p id="rfc.section.3.6.p.3"> Parameters are in the form of attribute/value pairs.</p>
    1439       </div>
    1440       <div id="rfc.figure.u.24"></div><pre class="inline"><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span>    <a href="#rule.parameter" class="smpl">parameter</a>               = attribute "=" value
     1470               <p id="rfc.section.3.6.p.3"> Parameters are in the form of attribute/value pairs.</p>
     1471            </div>
     1472            <div id="rfc.figure.u.24"></div><pre class="inline"><span id="rfc.iref.g.43"></span><span id="rfc.iref.g.44"></span><span id="rfc.iref.g.45"></span>    <a href="#rule.parameter" class="smpl">parameter</a>               = attribute "=" value
    14411473    attribute               = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.9">token</a>
    14421474    value                   = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.10">token</a> | <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.7">quoted-string</a>
    14431475</pre><p id="rfc.section.3.6.p.5">All transfer-coding values are case-insensitive. HTTP/1.1 uses transfer-coding values in the TE header field (<a href="#header.te" id="rfc.xref.header.te.1" title="TE">Section&nbsp;14.39</a>) and in the Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.1" title="Transfer-Encoding">Section&nbsp;14.41</a>).
    1444       </p>
    1445       <p id="rfc.section.3.6.p.6">Whenever a transfer-coding is applied to a message-body, the set of transfer-codings <em class="bcp14">MUST</em> include "chunked", unless the message is terminated by closing the connection. When the "chunked" transfer-coding is used,
    1446          it <em class="bcp14">MUST</em> be the last transfer-coding applied to the message-body. The "chunked" transfer-coding <em class="bcp14">MUST NOT</em> be applied more than once to a message-body. These rules allow the recipient to determine the transfer-length of the message
    1447          (<a href="#message.length" title="Message Length">Section&nbsp;4.4</a>).
    1448       </p>
    1449       <p id="rfc.section.3.6.p.7">Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME <a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[7]</cite></a>, which were designed to enable safe transport of binary data over a 7-bit transport service. However, safe transport has
    1450          a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic of message-bodies is the difficulty
    1451          in determining the exact body length (<a href="#entity.length" title="Entity Length">Section&nbsp;7.2.2</a>), or the desire to encrypt data over a shared transport.
    1452       </p>
    1453       <p id="rfc.section.3.6.p.8">The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. Initially, the registry
    1454          contains the following tokens: "chunked" (<a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.6.1</a>), "identity" (section 3.6.2), "gzip" (<a href="#content.codings" title="Content Codings">Section&nbsp;3.5</a>), "compress" (<a href="#content.codings" title="Content Codings">Section&nbsp;3.5</a>), and "deflate" (<a href="#content.codings" title="Content Codings">Section&nbsp;3.5</a>).
    1455       </p>
    1456       <p id="rfc.section.3.6.p.9">New transfer-coding value tokens <em class="bcp14">SHOULD</em> be registered in the same way as new content-coding value tokens (<a href="#content.codings" title="Content Codings">Section&nbsp;3.5</a>).
    1457       </p>
    1458       <p id="rfc.section.3.6.p.10">A server which receives an entity-body with a transfer-coding it does not understand <em class="bcp14">SHOULD</em> return <a href="#status.501" class="smpl">501 (Unimplemented)</a>, and close the connection. A server <em class="bcp14">MUST NOT</em> send transfer-codings to an HTTP/1.0 client.
    1459       </p>
    1460       <h3 id="rfc.section.3.6.1"><a href="#rfc.section.3.6.1">3.6.1</a>&nbsp;<a id="chunked.transfer.encoding" href="#chunked.transfer.encoding">Chunked Transfer Coding</a></h3>
    1461       <p id="rfc.section.3.6.1.p.1">The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size
    1462          indicator, followed by an <em class="bcp14">OPTIONAL</em> trailer containing entity-header fields. This allows dynamically produced content to be transferred along with the information
    1463          necessary for the recipient to verify that it has received the full message.
    1464       </p>
    1465       <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.46"></span><span id="rfc.iref.g.47"></span><span id="rfc.iref.g.48"></span><span id="rfc.iref.g.49"></span><span id="rfc.iref.g.50"></span><span id="rfc.iref.g.51"></span><span id="rfc.iref.g.52"></span><span id="rfc.iref.g.53"></span><span id="rfc.iref.g.54"></span>    Chunked-Body   = *chunk
     1476            </p>
     1477            <p id="rfc.section.3.6.p.6">Whenever a transfer-coding is applied to a message-body, the set of transfer-codings <em class="bcp14">MUST</em> include "chunked", unless the message is terminated by closing the connection. When the "chunked" transfer-coding is used,
     1478               it <em class="bcp14">MUST</em> be the last transfer-coding applied to the message-body. The "chunked" transfer-coding <em class="bcp14">MUST NOT</em> be applied more than once to a message-body. These rules allow the recipient to determine the transfer-length of the message
     1479               (<a href="#message.length" title="Message Length">Section&nbsp;4.4</a>).
     1480            </p>
     1481            <p id="rfc.section.3.6.p.7">Transfer-codings are analogous to the Content-Transfer-Encoding values of MIME <a href="#RFC2045" id="rfc.xref.RFC2045.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies">[7]</cite></a>, which were designed to enable safe transport of binary data over a 7-bit transport service. However, safe transport has
     1482               a different focus for an 8bit-clean transfer protocol. In HTTP, the only unsafe characteristic of message-bodies is the difficulty
     1483               in determining the exact body length (<a href="#entity.length" title="Entity Length">Section&nbsp;7.2.2</a>), or the desire to encrypt data over a shared transport.
     1484            </p>
     1485            <p id="rfc.section.3.6.p.8">The Internet Assigned Numbers Authority (IANA) acts as a registry for transfer-coding value tokens. Initially, the registry
     1486               contains the following tokens: "chunked" (<a href="#chunked.transfer.encoding" title="Chunked Transfer Coding">Section&nbsp;3.6.1</a>), "identity" (section 3.6.2), "gzip" (<a href="#content.codings" title="Content Codings">Section&nbsp;3.5</a>), "compress" (<a href="#content.codings" title="Content Codings">Section&nbsp;3.5</a>), and "deflate" (<a href="#content.codings" title="Content Codings">Section&nbsp;3.5</a>).
     1487            </p>
     1488            <p id="rfc.section.3.6.p.9">New transfer-coding value tokens <em class="bcp14">SHOULD</em> be registered in the same way as new content-coding value tokens (<a href="#content.codings" title="Content Codings">Section&nbsp;3.5</a>).
     1489            </p>
     1490            <p id="rfc.section.3.6.p.10">A server which receives an entity-body with a transfer-coding it does not understand <em class="bcp14">SHOULD</em> return <a href="#status.501" class="smpl">501 (Unimplemented)</a>, and close the connection. A server <em class="bcp14">MUST NOT</em> send transfer-codings to an HTTP/1.0 client.
     1491            </p>
     1492            <div id="chunked.transfer.encoding">
     1493               <h3 id="rfc.section.3.6.1"><a href="#rfc.section.3.6.1">3.6.1</a>&nbsp;<a href="#chunked.transfer.encoding">Chunked Transfer Coding</a></h3>
     1494               <p id="rfc.section.3.6.1.p.1">The chunked encoding modifies the body of a message in order to transfer it as a series of chunks, each with its own size
     1495                  indicator, followed by an <em class="bcp14">OPTIONAL</em> trailer containing entity-header fields. This allows dynamically produced content to be transferred along with the information
     1496                  necessary for the recipient to verify that it has received the full message.
     1497               </p>
     1498               <div id="rfc.figure.u.25"></div><pre class="inline"><span id="rfc.iref.g.46"></span><span id="rfc.iref.g.47"></span><span id="rfc.iref.g.48"></span><span id="rfc.iref.g.49"></span><span id="rfc.iref.g.50"></span><span id="rfc.iref.g.51"></span><span id="rfc.iref.g.52"></span><span id="rfc.iref.g.53"></span><span id="rfc.iref.g.54"></span>    Chunked-Body   = *chunk
    14661499                     last-chunk
    14671500                     trailer
     
    14791512    trailer        = *(<a href="#entity.header.fields" class="smpl">entity-header</a> <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.22">CRLF</a>)
    14801513</pre><p id="rfc.section.3.6.1.p.3">The chunk-size field is a string of hex digits indicating the size of the chunk. The chunked encoding is ended by any chunk
    1481          whose size is zero, followed by the trailer, which is terminated by an empty line.
    1482       </p>
    1483       <p id="rfc.section.3.6.1.p.4">The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer header field
    1484          can be used to indicate which header fields are included in a trailer (see <a href="#header.trailer" id="rfc.xref.header.trailer.1" title="Trailer">Section&nbsp;14.40</a>).
    1485       </p>
    1486       <p id="rfc.section.3.6.1.p.5">A server using chunked transfer-coding in a response <em class="bcp14">MUST NOT</em> use the trailer for any header fields unless at least one of the following is true:
    1487       </p>
    1488       <ol>
    1489          <li>the request included a TE header field that indicates "trailers" is acceptable in the transfer-coding of the response, as
    1490             described in <a href="#header.te" id="rfc.xref.header.te.2" title="TE">Section&nbsp;14.39</a>; or,
    1491          </li>
    1492          <li>the server is the origin server for the response, the trailer fields consist entirely of optional metadata, and the recipient
    1493             could use the message (in a manner acceptable to the origin server) without receiving this metadata. In other words, the origin
    1494             server is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client.
    1495          </li>
    1496       </ol>
    1497       <p id="rfc.section.3.6.1.p.6">This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) proxy and
    1498          forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly
    1499          infinite buffer on the proxy.
    1500       </p>
    1501       <p id="rfc.section.3.6.1.p.7">An example process for decoding a Chunked-Body is presented in <a href="#introduction.of.transfer-encoding" title="Introduction of Transfer-Encoding">Appendix&nbsp;19.4.6</a>.
    1502       </p>
    1503       <p id="rfc.section.3.6.1.p.8">All HTTP/1.1 applications <em class="bcp14">MUST</em> be able to receive and decode the "chunked" transfer-coding, and <em class="bcp14">MUST</em> ignore chunk-extension extensions they do not understand.
    1504       </p>
    1505       <h2 id="rfc.section.3.7"><a href="#rfc.section.3.7">3.7</a>&nbsp;<a id="media.types" href="#media.types">Media Types</a></h2>
    1506       <p id="rfc.section.3.7.p.1">HTTP uses Internet Media Types <a href="#RFC1590" id="rfc.xref.RFC1590.1"><cite title="Media Type Registration Procedure">[17]</cite></a> in the Content-Type (<a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section&nbsp;14.17</a>) and Accept (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section&nbsp;14.1</a>) header fields in order to provide open and extensible data typing and type negotiation.
    1507       </p>
    1508       <div id="rfc.figure.u.26"></div><pre class="inline"><span id="rfc.iref.g.55"></span><span id="rfc.iref.g.56"></span><span id="rfc.iref.g.57"></span>    <a href="#media.types" class="smpl">media-type</a>     = <a href="#media.types" class="smpl">type</a> "/" <a href="#media.types" class="smpl">subtype</a> *( ";" <a href="#rule.parameter" class="smpl">parameter</a> )
     1514                  whose size is zero, followed by the trailer, which is terminated by an empty line.
     1515               </p>
     1516               <p id="rfc.section.3.6.1.p.4">The trailer allows the sender to include additional HTTP header fields at the end of the message. The Trailer header field
     1517                  can be used to indicate which header fields are included in a trailer (see <a href="#header.trailer" id="rfc.xref.header.trailer.1" title="Trailer">Section&nbsp;14.40</a>).
     1518               </p>
     1519               <p id="rfc.section.3.6.1.p.5">A server using chunked transfer-coding in a response <em class="bcp14">MUST NOT</em> use the trailer for any header fields unless at least one of the following is true:
     1520               </p>
     1521               <ol>
     1522                  <li>the request included a TE header field that indicates "trailers" is acceptable in the transfer-coding of the response, as
     1523                     described in <a href="#header.te" id="rfc.xref.header.te.2" title="TE">Section&nbsp;14.39</a>; or,
     1524                  </li>
     1525                  <li>the server is the origin server for the response, the trailer fields consist entirely of optional metadata, and the recipient
     1526                     could use the message (in a manner acceptable to the origin server) without receiving this metadata. In other words, the origin
     1527                     server is willing to accept the possibility that the trailer fields might be silently discarded along the path to the client.
     1528                  </li>
     1529               </ol>
     1530               <p id="rfc.section.3.6.1.p.6">This requirement prevents an interoperability failure when the message is being received by an HTTP/1.1 (or later) proxy and
     1531                  forwarded to an HTTP/1.0 recipient. It avoids a situation where compliance with the protocol would have necessitated a possibly
     1532                  infinite buffer on the proxy.
     1533               </p>
     1534               <p id="rfc.section.3.6.1.p.7">An example process for decoding a Chunked-Body is presented in <a href="#introduction.of.transfer-encoding" title="Introduction of Transfer-Encoding">Appendix&nbsp;19.4.6</a>.
     1535               </p>
     1536               <p id="rfc.section.3.6.1.p.8">All HTTP/1.1 applications <em class="bcp14">MUST</em> be able to receive and decode the "chunked" transfer-coding, and <em class="bcp14">MUST</em> ignore chunk-extension extensions they do not understand.
     1537               </p>
     1538            </div>
     1539         </div>
     1540         <div id="media.types">
     1541            <h2 id="rfc.section.3.7"><a href="#rfc.section.3.7">3.7</a>&nbsp;<a href="#media.types">Media Types</a></h2>
     1542            <p id="rfc.section.3.7.p.1">HTTP uses Internet Media Types <a href="#RFC1590" id="rfc.xref.RFC1590.1"><cite title="Media Type Registration Procedure">[17]</cite></a> in the Content-Type (<a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section&nbsp;14.17</a>) and Accept (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section&nbsp;14.1</a>) header fields in order to provide open and extensible data typing and type negotiation.
     1543            </p>
     1544            <div id="rfc.figure.u.26"></div><pre class="inline"><span id="rfc.iref.g.55"></span><span id="rfc.iref.g.56"></span><span id="rfc.iref.g.57"></span>    <a href="#media.types" class="smpl">media-type</a>     = <a href="#media.types" class="smpl">type</a> "/" <a href="#media.types" class="smpl">subtype</a> *( ";" <a href="#rule.parameter" class="smpl">parameter</a> )
    15091545    <a href="#media.types" class="smpl">type</a>           = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.15">token</a>
    15101546    <a href="#media.types" class="smpl">subtype</a>        = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.16">token</a>
    15111547</pre><p id="rfc.section.3.7.p.3">Parameters <em class="bcp14">MAY</em> follow the type/subtype in the form of attribute/value pairs (as defined in <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>).
    1512       </p>
    1513       <p id="rfc.section.3.7.p.4">The type, subtype, and parameter attribute names are case-insensitive. Parameter values might or might not be case-sensitive,
    1514          depending on the semantics of the parameter name. Linear white space (LWS) <em class="bcp14">MUST NOT</em> be used between the type and subtype, nor between an attribute and its value. The presence or absence of a parameter might
    1515          be significant to the processing of a media-type, depending on its definition within the media type registry.
    1516       </p>
    1517       <p id="rfc.section.3.7.p.5">Note that some older HTTP applications do not recognize media type parameters. When sending data to older HTTP applications,
    1518          implementations <em class="bcp14">SHOULD</em> only use media type parameters when they are required by that type/subtype definition.
    1519       </p>
    1520       <p id="rfc.section.3.7.p.6">Media-type values are registered with the Internet Assigned Number Authority (IANA <a href="#RFC1700" id="rfc.xref.RFC1700.4"><cite title="Assigned Numbers">[19]</cite></a>). The media type registration process is outlined in RFC 1590 <a href="#RFC1590" id="rfc.xref.RFC1590.2"><cite title="Media Type Registration Procedure">[17]</cite></a>. Use of non-registered media types is discouraged.
    1521       </p>
    1522       <h3 id="rfc.section.3.7.1"><a href="#rfc.section.3.7.1">3.7.1</a>&nbsp;<a id="canonicalization.and.text.defaults" href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></h3>
    1523       <p id="rfc.section.3.7.1.p.1">Internet media types are registered with a canonical form. An entity-body transferred via HTTP messages <em class="bcp14">MUST</em> be represented in the appropriate canonical form prior to its transmission except for "text" types, as defined in the next
    1524          paragraph.
    1525       </p>
    1526       <p id="rfc.section.3.7.1.p.2">When in canonical form, media subtypes of the "text" type use CRLF as the text line break. HTTP relaxes this requirement and
    1527          allows the transport of text media with plain CR or LF alone representing a line break when it is done consistently for an
    1528          entire entity-body. HTTP applications <em class="bcp14">MUST</em> accept CRLF, bare CR, and bare LF as being representative of a line break in text media received via HTTP. In addition, if
    1529          the text is represented in a character set that does not use octets 13 and 10 for CR and LF respectively, as is the case for
    1530          some multi-byte character sets, HTTP allows the use of whatever octet sequences are defined by that character set to represent
    1531          the equivalent of CR and LF for line breaks. This flexibility regarding line breaks applies only to text media in the entity-body;
    1532          a bare CR or LF <em class="bcp14">MUST NOT</em> be substituted for CRLF within any of the HTTP control structures (such as header fields and multipart boundaries).
    1533       </p>
    1534       <p id="rfc.section.3.7.1.p.3">If an entity-body is encoded with a content-coding, the underlying data <em class="bcp14">MUST</em> be in a form defined above prior to being encoded.
    1535       </p>
    1536       <p id="rfc.section.3.7.1.p.4">The "charset" parameter is used with some media types to define the character set (<a href="#character.sets" title="Character Sets">Section&nbsp;3.4</a>) of the data. When no explicit charset parameter is provided by the sender, media subtypes of the "text" type are defined
    1537          to have a default charset value of "ISO-8859-1" when received via HTTP. Data in character sets other than "ISO-8859-1" or
    1538          its subsets <em class="bcp14">MUST</em> be labeled with an appropriate charset value. See <a href="#missing.charset" title="Missing Charset">Section&nbsp;3.4.1</a> for compatibility problems.
    1539       </p>
    1540       <h3 id="rfc.section.3.7.2"><a href="#rfc.section.3.7.2">3.7.2</a>&nbsp;<a id="multipart.types" href="#multipart.types">Multipart Types</a></h3>
    1541       <p id="rfc.section.3.7.2.p.1">MIME provides for a number of "multipart" types -- encapsulations of one or more entities within a single message-body. All
    1542          multipart types share a common syntax, as defined in section <a href="http://tools.ietf.org/html/rfc2046#section-5.1.1" id="rfc.xref.RFC2046.1">5.1.1</a> of RFC 2046 <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[40]</cite></a>, and <em class="bcp14">MUST</em> include a boundary parameter as part of the media type value. The message body is itself a protocol element and <em class="bcp14">MUST</em> therefore use only CRLF to represent line breaks between body-parts. Unlike in RFC 2046, the epilogue of any multipart message <em class="bcp14">MUST</em> be empty; HTTP applications <em class="bcp14">MUST NOT</em> transmit the epilogue (even if the original multipart contains an epilogue). These restrictions exist in order to preserve
    1543          the self-delimiting nature of a multipart message-body, wherein the "end" of the message-body is indicated by the ending multipart
    1544          boundary.
    1545       </p>
    1546       <p id="rfc.section.3.7.2.p.2">In general, HTTP treats a multipart message-body no differently than any other media type: strictly as payload. The one exception
    1547          is the "multipart/byteranges" type (<a href="#internet.media.type.multipart.byteranges" title="Internet Media Type multipart/byteranges">Appendix&nbsp;19.2</a>) when it appears in a 206 (Partial Content) response, which will be interpreted by some HTTP caching mechanisms as described
    1548          in sections <a href="#combining.byte.ranges" title="Combining Byte Ranges">13.5.4</a> and <a href="#header.content-range" id="rfc.xref.header.content-range.1" title="Content-Range">14.16</a>. In all other cases, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. The MIME header fields within
    1549          each body-part of a multipart message-body do not have any significance to HTTP beyond that defined by their MIME semantics.
    1550       </p>
    1551       <p id="rfc.section.3.7.2.p.3">In general, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. If an application receives
    1552          an unrecognized multipart subtype, the application <em class="bcp14">MUST</em> treat it as being equivalent to "multipart/mixed".
    1553       </p>
    1554       <ul class="empty">
    1555          <li> <b>Note:</b> The "multipart/form-data" type has been specifically defined for carrying form data suitable for processing via the POST request
    1556             method, as described in RFC 1867 <a href="#RFC1867" id="rfc.xref.RFC1867.1"><cite title="Form-based File Upload in HTML">[15]</cite></a>.
    1557          </li>
    1558       </ul>
    1559       <h2 id="rfc.section.3.8"><a href="#rfc.section.3.8">3.8</a>&nbsp;<a id="product.tokens" href="#product.tokens">Product Tokens</a></h2>
    1560       <p id="rfc.section.3.8.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields
    1561          using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white
    1562          space. By convention, the products are listed in order of their significance for identifying the application.
    1563       </p>
    1564       <div id="rfc.figure.u.27"></div><pre class="inline"><span id="rfc.iref.g.58"></span><span id="rfc.iref.g.59"></span>    <a href="#product.tokens" class="smpl">product</a>         = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.17">token</a> ["/" product-version]
     1548            </p>
     1549            <p id="rfc.section.3.7.p.4">The type, subtype, and parameter attribute names are case-insensitive. Parameter values might or might not be case-sensitive,
     1550               depending on the semantics of the parameter name. Linear white space (LWS) <em class="bcp14">MUST NOT</em> be used between the type and subtype, nor between an attribute and its value. The presence or absence of a parameter might
     1551               be significant to the processing of a media-type, depending on its definition within the media type registry.
     1552            </p>
     1553            <p id="rfc.section.3.7.p.5">Note that some older HTTP applications do not recognize media type parameters. When sending data to older HTTP applications,
     1554               implementations <em class="bcp14">SHOULD</em> only use media type parameters when they are required by that type/subtype definition.
     1555            </p>
     1556            <p id="rfc.section.3.7.p.6">Media-type values are registered with the Internet Assigned Number Authority (IANA <a href="#RFC1700" id="rfc.xref.RFC1700.4"><cite title="Assigned Numbers">[19]</cite></a>). The media type registration process is outlined in RFC 1590 <a href="#RFC1590" id="rfc.xref.RFC1590.2"><cite title="Media Type Registration Procedure">[17]</cite></a>. Use of non-registered media types is discouraged.
     1557            </p>
     1558            <div id="canonicalization.and.text.defaults">
     1559               <h3 id="rfc.section.3.7.1"><a href="#rfc.section.3.7.1">3.7.1</a>&nbsp;<a href="#canonicalization.and.text.defaults">Canonicalization and Text Defaults</a></h3>
     1560               <p id="rfc.section.3.7.1.p.1">Internet media types are registered with a canonical form. An entity-body transferred via HTTP messages <em class="bcp14">MUST</em> be represented in the appropriate canonical form prior to its transmission except for "text" types, as defined in the next
     1561                  paragraph.
     1562               </p>
     1563               <p id="rfc.section.3.7.1.p.2">When in canonical form, media subtypes of the "text" type use CRLF as the text line break. HTTP relaxes this requirement and
     1564                  allows the transport of text media with plain CR or LF alone representing a line break when it is done consistently for an
     1565                  entire entity-body. HTTP applications <em class="bcp14">MUST</em> accept CRLF, bare CR, and bare LF as being representative of a line break in text media received via HTTP. In addition, if
     1566                  the text is represented in a character set that does not use octets 13 and 10 for CR and LF respectively, as is the case for
     1567                  some multi-byte character sets, HTTP allows the use of whatever octet sequences are defined by that character set to represent
     1568                  the equivalent of CR and LF for line breaks. This flexibility regarding line breaks applies only to text media in the entity-body;
     1569                  a bare CR or LF <em class="bcp14">MUST NOT</em> be substituted for CRLF within any of the HTTP control structures (such as header fields and multipart boundaries).
     1570               </p>
     1571               <p id="rfc.section.3.7.1.p.3">If an entity-body is encoded with a content-coding, the underlying data <em class="bcp14">MUST</em> be in a form defined above prior to being encoded.
     1572               </p>
     1573               <p id="rfc.section.3.7.1.p.4">The "charset" parameter is used with some media types to define the character set (<a href="#character.sets" title="Character Sets">Section&nbsp;3.4</a>) of the data. When no explicit charset parameter is provided by the sender, media subtypes of the "text" type are defined
     1574                  to have a default charset value of "ISO-8859-1" when received via HTTP. Data in character sets other than "ISO-8859-1" or
     1575                  its subsets <em class="bcp14">MUST</em> be labeled with an appropriate charset value. See <a href="#missing.charset" title="Missing Charset">Section&nbsp;3.4.1</a> for compatibility problems.
     1576               </p>
     1577            </div>
     1578            <div id="multipart.types">
     1579               <h3 id="rfc.section.3.7.2"><a href="#rfc.section.3.7.2">3.7.2</a>&nbsp;<a href="#multipart.types">Multipart Types</a></h3>
     1580               <p id="rfc.section.3.7.2.p.1">MIME provides for a number of "multipart" types -- encapsulations of one or more entities within a single message-body. All
     1581                  multipart types share a common syntax, as defined in section <a href="http://tools.ietf.org/html/rfc2046#section-5.1.1" id="rfc.xref.RFC2046.1">5.1.1</a> of RFC 2046 <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[40]</cite></a>, and <em class="bcp14">MUST</em> include a boundary parameter as part of the media type value. The message body is itself a protocol element and <em class="bcp14">MUST</em> therefore use only CRLF to represent line breaks between body-parts. Unlike in RFC 2046, the epilogue of any multipart message <em class="bcp14">MUST</em> be empty; HTTP applications <em class="bcp14">MUST NOT</em> transmit the epilogue (even if the original multipart contains an epilogue). These restrictions exist in order to preserve
     1582                  the self-delimiting nature of a multipart message-body, wherein the "end" of the message-body is indicated by the ending multipart
     1583                  boundary.
     1584               </p>
     1585               <p id="rfc.section.3.7.2.p.2">In general, HTTP treats a multipart message-body no differently than any other media type: strictly as payload. The one exception
     1586                  is the "multipart/byteranges" type (<a href="#internet.media.type.multipart.byteranges" title="Internet Media Type multipart/byteranges">Appendix&nbsp;19.2</a>) when it appears in a 206 (Partial Content) response, which will be interpreted by some HTTP caching mechanisms as described
     1587                  in sections <a href="#combining.byte.ranges" title="Combining Byte Ranges">13.5.4</a> and <a href="#header.content-range" id="rfc.xref.header.content-range.1" title="Content-Range">14.16</a>. In all other cases, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. The MIME header fields within
     1588                  each body-part of a multipart message-body do not have any significance to HTTP beyond that defined by their MIME semantics.
     1589               </p>
     1590               <p id="rfc.section.3.7.2.p.3">In general, an HTTP user agent <em class="bcp14">SHOULD</em> follow the same or similar behavior as a MIME user agent would upon receipt of a multipart type. If an application receives
     1591                  an unrecognized multipart subtype, the application <em class="bcp14">MUST</em> treat it as being equivalent to "multipart/mixed".
     1592               </p>
     1593               <ul class="empty">
     1594                  <li><b>Note:</b> The "multipart/form-data" type has been specifically defined for carrying form data suitable for processing via the POST request
     1595                     method, as described in RFC 1867 <a href="#RFC1867" id="rfc.xref.RFC1867.1"><cite title="Form-based File Upload in HTML">[15]</cite></a>.
     1596                  </li>
     1597               </ul>
     1598            </div>
     1599         </div>
     1600         <div id="product.tokens">
     1601            <h2 id="rfc.section.3.8"><a href="#rfc.section.3.8">3.8</a>&nbsp;<a href="#product.tokens">Product Tokens</a></h2>
     1602            <p id="rfc.section.3.8.p.1">Product tokens are used to allow communicating applications to identify themselves by software name and version. Most fields
     1603               using product tokens also allow sub-products which form a significant part of the application to be listed, separated by white
     1604               space. By convention, the products are listed in order of their significance for identifying the application.
     1605            </p>
     1606            <div id="rfc.figure.u.27"></div><pre class="inline"><span id="rfc.iref.g.58"></span><span id="rfc.iref.g.59"></span>    <a href="#product.tokens" class="smpl">product</a>         = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.17">token</a> ["/" product-version]
    15651607    product-version = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.18">token</a>
    15661608</pre><p id="rfc.section.3.8.p.3">Examples:</p>
    1567       <div id="rfc.figure.u.28"></div><pre class="text">    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
     1609            <div id="rfc.figure.u.28"></div><pre class="text">    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
    15681610    Server: Apache/0.8.4
    15691611</pre><p id="rfc.section.3.8.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).
    1570       </p>
    1571       <h2 id="rfc.section.3.9"><a href="#rfc.section.3.9">3.9</a>&nbsp;<a id="quality.values" href="#quality.values">Quality Values</a></h2>
    1572       <p id="rfc.section.3.9.p.1">HTTP content negotiation (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;12</a>) uses short "floating point" numbers to indicate the relative importance ("weight") of various negotiable parameters. A weight
    1573          is normalized to a real number in the range 0 through 1, where 0 is the minimum and 1 the maximum value. If a parameter has
    1574          a quality value of 0, then content with this parameter is `not acceptable' for the client. HTTP/1.1 applications <em class="bcp14">MUST NOT</em> generate more than three digits after the decimal point. User configuration of these values <em class="bcp14">SHOULD</em> also be limited in this fashion.
    1575       </p>
    1576       <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.60"></span>    <a href="#quality.values" class="smpl">qvalue</a>         = ( "0" [ "." 0*3<a href="#basic.rules" class="smpl" id="rfc.extref.d.18">DIGIT</a> ] )
     1612            </p>
     1613         </div>
     1614         <div id="quality.values">
     1615            <h2 id="rfc.section.3.9"><a href="#rfc.section.3.9">3.9</a>&nbsp;<a href="#quality.values">Quality Values</a></h2>
     1616            <p id="rfc.section.3.9.p.1">HTTP content negotiation (<a href="#content.negotiation" title="Content Negotiation">Section&nbsp;12</a>) uses short "floating point" numbers to indicate the relative importance ("weight") of various negotiable parameters. A weight
     1617               is normalized to a real number in the range 0 through 1, where 0 is the minimum and 1 the maximum value. If a parameter has
     1618               a quality value of 0, then content with this parameter is `not acceptable' for the client. HTTP/1.1 applications <em class="bcp14">MUST NOT</em> generate more than three digits after the decimal point. User configuration of these values <em class="bcp14">SHOULD</em> also be limited in this fashion.
     1619            </p>
     1620            <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.60"></span>    <a href="#quality.values" class="smpl">qvalue</a>         = ( "0" [ "." 0*3<a href="#basic.rules" class="smpl" id="rfc.extref.d.18">DIGIT</a> ] )
    15771621                   | ( "1" [ "." 0*3("0") ] )
    15781622</pre><p id="rfc.section.3.9.p.3">"Quality values" is a misnomer, since these values merely represent relative degradation in desired quality.</p>
    1579       <h2 id="rfc.section.3.10"><a href="#rfc.section.3.10">3.10</a>&nbsp;<a id="language.tags" href="#language.tags">Language Tags</a></h2>
    1580       <p id="rfc.section.3.10.p.1">A language tag identifies a natural language spoken, written, or otherwise conveyed by human beings for communication of information
    1581          to other human beings. Computer languages are explicitly excluded. HTTP uses language tags within the Accept-Language and
    1582          Content-Language fields.
    1583       </p>
    1584       <p id="rfc.section.3.10.p.2">The syntax and registry of HTTP language tags is the same as that defined by RFC 1766 <a href="#RFC1766" id="rfc.xref.RFC1766.1"><cite title="Tags for the Identification of Languages">[1]</cite></a>. In summary, a language tag is composed of 1 or more parts: A primary language tag and a possibly empty series of subtags:
    1585       </p>
    1586       <div id="rfc.figure.u.30"></div><pre class="inline"><span id="rfc.iref.g.61"></span><span id="rfc.iref.g.62"></span><span id="rfc.iref.g.63"></span>     <a href="#language.tags" class="smpl">language-tag</a>  = primary-tag *( "-" subtag )
     1623         </div>
     1624         <div id="language.tags">
     1625            <h2 id="rfc.section.3.10"><a href="#rfc.section.3.10">3.10</a>&nbsp;<a href="#language.tags">Language Tags</a></h2>
     1626            <p id="rfc.section.3.10.p.1">A language tag identifies a natural language spoken, written, or otherwise conveyed by human beings for communication of information
     1627               to other human beings. Computer languages are explicitly excluded. HTTP uses language tags within the Accept-Language and
     1628               Content-Language fields.
     1629            </p>
     1630            <p id="rfc.section.3.10.p.2">The syntax and registry of HTTP language tags is the same as that defined by RFC 1766 <a href="#RFC1766" id="rfc.xref.RFC1766.1"><cite title="Tags for the Identification of Languages">[1]</cite></a>. In summary, a language tag is composed of 1 or more parts: A primary language tag and a possibly empty series of subtags:
     1631            </p>
     1632            <div id="rfc.figure.u.30"></div><pre class="inline"><span id="rfc.iref.g.61"></span><span id="rfc.iref.g.62"></span><span id="rfc.iref.g.63"></span>     <a href="#language.tags" class="smpl">language-tag</a>  = primary-tag *( "-" subtag )
    15871633     primary-tag   = 1*8<a href="#basic.rules" class="smpl" id="rfc.extref.a.3">ALPHA</a>
    15881634     subtag        = 1*8<a href="#basic.rules" class="smpl" id="rfc.extref.a.4">ALPHA</a>
    15891635</pre><p id="rfc.section.3.10.p.4">White space is not allowed within the tag and all tags are case-insensitive. The name space of language tags is administered
    1590          by the IANA. Example tags include:
    1591       </p>
    1592       <div id="rfc.figure.u.31"></div><pre class="text">    en, en-US, en-cockney, i-cherokee, x-pig-latin
     1636               by the IANA. Example tags include:
     1637            </p>
     1638            <div id="rfc.figure.u.31"></div><pre class="text">    en, en-US, en-cockney, i-cherokee, x-pig-latin
    15931639</pre><p id="rfc.section.3.10.p.6">where any two-letter primary-tag is an ISO-639 language abbreviation and any two-letter initial subtag is an ISO-3166 country
    1594          code. (The last three tags above are not registered tags; all but the last are examples of tags which could be registered
    1595          in future.)
    1596       </p>
    1597       <h2 id="rfc.section.3.11"><a href="#rfc.section.3.11">3.11</a>&nbsp;<a id="entity.tags" href="#entity.tags">Entity Tags</a></h2>
    1598       <p id="rfc.section.3.11.p.1">Entity tags are used for comparing two or more entities from the same requested resource. HTTP/1.1 uses entity tags in the
    1599          ETag (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section&nbsp;14.19</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section&nbsp;14.24</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section&nbsp;14.26</a>), and If-Range (<a href="#header.if-range" id="rfc.xref.header.if-range.1" title="If-Range">Section&nbsp;14.27</a>) header fields. The definition of how they are used and compared as cache validators is in <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;13.3.3</a>. An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator.
    1600       </p>
    1601       <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.64"></span><span id="rfc.iref.g.65"></span><span id="rfc.iref.g.66"></span>   <a href="#entity.tags" class="smpl">entity-tag</a> = [ weak ] opaque-tag
     1640               code. (The last three tags above are not registered tags; all but the last are examples of tags which could be registered
     1641               in future.)
     1642            </p>
     1643         </div>
     1644         <div id="entity.tags">
     1645            <h2 id="rfc.section.3.11"><a href="#rfc.section.3.11">3.11</a>&nbsp;<a href="#entity.tags">Entity Tags</a></h2>
     1646            <p id="rfc.section.3.11.p.1">Entity tags are used for comparing two or more entities from the same requested resource. HTTP/1.1 uses entity tags in the
     1647               ETag (<a href="#header.etag" id="rfc.xref.header.etag.1" title="ETag">Section&nbsp;14.19</a>), If-Match (<a href="#header.if-match" id="rfc.xref.header.if-match.1" title="If-Match">Section&nbsp;14.24</a>), If-None-Match (<a href="#header.if-none-match" id="rfc.xref.header.if-none-match.1" title="If-None-Match">Section&nbsp;14.26</a>), and If-Range (<a href="#header.if-range" id="rfc.xref.header.if-range.1" title="If-Range">Section&nbsp;14.27</a>) header fields. The definition of how they are used and compared as cache validators is in <a href="#weak.and.strong.validators" title="Weak and Strong Validators">Section&nbsp;13.3.3</a>. An entity tag consists of an opaque quoted string, possibly prefixed by a weakness indicator.
     1648            </p>
     1649            <div id="rfc.figure.u.32"></div><pre class="inline"><span id="rfc.iref.g.64"></span><span id="rfc.iref.g.65"></span><span id="rfc.iref.g.66"></span>   <a href="#entity.tags" class="smpl">entity-tag</a> = [ weak ] opaque-tag
    16021650   weak       = "W/"
    16031651   opaque-tag = <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.10">quoted-string</a>
    16041652</pre><p id="rfc.section.3.11.p.3">A "strong entity tag" <em class="bcp14">MAY</em> be shared by two entities of a resource only if they are equivalent by octet equality.
    1605       </p>
    1606       <p id="rfc.section.3.11.p.4">A "weak entity tag," indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two entities of a resource only if the entities are equivalent and could be substituted for each other with no
    1607          significant change in semantics. A weak entity tag can only be used for weak comparison.
    1608       </p>
    1609       <p id="rfc.section.3.11.p.5">An entity tag <em class="bcp14">MUST</em> be unique across all versions of all entities associated with a particular resource. A given entity tag value <em class="bcp14">MAY</em> be used for entities obtained by requests on different URIs. The use of the same entity tag value in conjunction with entities
    1610          obtained by requests on different URIs does not imply the equivalence of those entities.
    1611       </p>
    1612       <h2 id="rfc.section.3.12"><a href="#rfc.section.3.12">3.12</a>&nbsp;<a id="range.units" href="#range.units">Range Units</a></h2>
    1613       <p id="rfc.section.3.12.p.1">HTTP/1.1 allows a client to request that only part (a range of) the response entity be included within the response. HTTP/1.1
    1614          uses range units in the Range (<a href="#header.range" id="rfc.xref.header.range.1" title="Range">Section&nbsp;14.35</a>) and Content-Range (<a href="#header.content-range" id="rfc.xref.header.content-range.2" title="Content-Range">Section&nbsp;14.16</a>) header fields. An entity can be broken down into subranges according to various structural units.
    1615       </p>
    1616       <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.67"></span><span id="rfc.iref.g.68"></span><span id="rfc.iref.g.69"></span>   <a href="#range.units" class="smpl">range-unit</a>       = bytes-unit | other-range-unit
     1653            </p>
     1654            <p id="rfc.section.3.11.p.4">A "weak entity tag," indicated by the "W/" prefix, <em class="bcp14">MAY</em> be shared by two entities of a resource only if the entities are equivalent and could be substituted for each other with no
     1655               significant change in semantics. A weak entity tag can only be used for weak comparison.
     1656            </p>
     1657            <p id="rfc.section.3.11.p.5">An entity tag <em class="bcp14">MUST</em> be unique across all versions of all entities associated with a particular resource. A given entity tag value <em class="bcp14">MAY</em> be used for entities obtained by requests on different URIs. The use of the same entity tag value in conjunction with entities
     1658               obtained by requests on different URIs does not imply the equivalence of those entities.
     1659            </p>
     1660         </div>
     1661         <div id="range.units">
     1662            <h2 id="rfc.section.3.12"><a href="#rfc.section.3.12">3.12</a>&nbsp;<a href="#range.units">Range Units</a></h2>
     1663            <p id="rfc.section.3.12.p.1">HTTP/1.1 allows a client to request that only part (a range of) the response entity be included within the response. HTTP/1.1
     1664               uses range units in the Range (<a href="#header.range" id="rfc.xref.header.range.1" title="Range">Section&nbsp;14.35</a>) and Content-Range (<a href="#header.content-range" id="rfc.xref.header.content-range.2" title="Content-Range">Section&nbsp;14.16</a>) header fields. An entity can be broken down into subranges according to various structural units.
     1665            </p>
     1666            <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.67"></span><span id="rfc.iref.g.68"></span><span id="rfc.iref.g.69"></span>   <a href="#range.units" class="smpl">range-unit</a>       = bytes-unit | other-range-unit
    16171667   bytes-unit       = "bytes"
    16181668   other-range-unit = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.19">token</a>
    16191669</pre><p id="rfc.section.3.12.p.3">The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1 implementations <em class="bcp14">MAY</em> ignore ranges specified using other units.
    1620       </p>
    1621       <p id="rfc.section.3.12.p.4">HTTP/1.1 has been designed to allow implementations of applications that do not depend on knowledge of ranges.</p>
     1670            </p>
     1671            <p id="rfc.section.3.12.p.4">HTTP/1.1 has been designed to allow implementations of applications that do not depend on knowledge of ranges.</p>
     1672         </div>
     1673      </div>
    16221674      <hr class="noprint">
    1623       <h1 id="rfc.section.4" class="np"><a href="#rfc.section.4">4.</a>&nbsp;<a id="http.message" href="#http.message">HTTP Message</a></h1>
    1624       <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a id="message.types" href="#message.types">Message Types</a></h2>
    1625       <p id="rfc.section.4.1.p.1">HTTP messages consist of requests from client to server and responses from server to client.</p>
    1626       <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.70"></span>    HTTP-message   = <a href="#request" class="smpl">Request</a> | <a href="#response" class="smpl">Response</a>     ; HTTP/1.1 messages
     1675      <div id="http.message">
     1676         <h1 id="rfc.section.4" class="np"><a href="#rfc.section.4">4.</a>&nbsp;<a href="#http.message">HTTP Message</a></h1>
     1677         <div id="message.types">
     1678            <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a>&nbsp;<a href="#message.types">Message Types</a></h2>
     1679            <p id="rfc.section.4.1.p.1">HTTP messages consist of requests from client to server and responses from server to client.</p>
     1680            <div id="rfc.figure.u.34"></div><pre class="inline"><span id="rfc.iref.g.70"></span>    HTTP-message   = <a href="#request" class="smpl">Request</a> | <a href="#response" class="smpl">Response</a>     ; HTTP/1.1 messages
    16271681</pre><p id="rfc.section.4.1.p.3">Request (<a href="#request" title="Request">Section&nbsp;5</a>) and Response (<a href="#response" title="Response">Section&nbsp;6</a>) messages use the generic message format of RFC 822 <a href="#RFC822" id="rfc.xref.RFC822.4"><cite title="Standard for the format of ARPA Internet text messages">[9]</cite></a> for transferring entities (the payload of the message). Both types of message consist of a start-line, zero or more header
    1628          fields (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header
    1629          fields, and possibly a message-body.
    1630       </p>
    1631       <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.71"></span><span id="rfc.iref.g.72"></span>     generic-message = start-line
     1682               fields (also known as "headers"), an empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header
     1683               fields, and possibly a message-body.
     1684            </p>
     1685            <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.71"></span><span id="rfc.iref.g.72"></span>     generic-message = start-line
    16321686                       *(<a href="#message.headers" class="smpl">message-header</a> <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.23">CRLF</a>)
    16331687                       <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.24">CRLF</a>
     
    16351689     start-line      = <a href="#request-line" class="smpl">Request-Line</a> | <a href="#status-line" class="smpl">Status-Line</a>
    16361690</pre><p id="rfc.section.4.1.p.5">In the interest of robustness, servers <em class="bcp14">SHOULD</em> ignore any empty line(s) received where a Request-Line is expected. In other words, if the server is reading the protocol
    1637          stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF.
    1638       </p>
    1639       <p id="rfc.section.4.1.p.6">Certain buggy HTTP/1.0 client implementations generate extra CRLF's after a POST request. To restate what is explicitly forbidden
    1640          by the BNF, an HTTP/1.1 client <em class="bcp14">MUST NOT</em> preface or follow a request with an extra CRLF.
    1641       </p>
    1642       <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a id="message.headers" href="#message.headers">Message Headers</a></h2>
    1643       <p id="rfc.section.4.2.p.1">HTTP header fields, which include general-header (<a href="#general.header.fields" title="General Header Fields">Section&nbsp;4.5</a>), request-header (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5.3</a>), response-header (<a href="#response.header.fields" title="Response Header Fields">Section&nbsp;6.2</a>), and entity-header (<a href="#entity.header.fields" title="Entity Header Fields">Section&nbsp;7.1</a>) fields, follow the same generic format as that given in <a href="http://tools.ietf.org/html/rfc822#section-3.1" id="rfc.xref.RFC822.5">Section 3.1</a> of RFC 822 <a href="#RFC822" id="rfc.xref.RFC822.6"><cite title="Standard for the format of ARPA Internet text messages">[9]</cite></a>. Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The
    1644          field value <em class="bcp14">MAY</em> be preceded by any amount of LWS, though a single SP is preferred. Header fields can be extended over multiple lines by preceding
    1645          each extra line with at least one SP or HT. Applications ought to follow "common form", where one is known or indicated, when
    1646          generating HTTP constructs, since there might exist some implementations that fail to accept anything beyond the common forms.
    1647       </p>
    1648       <div id="rfc.figure.u.36"></div><pre class="inline"><span id="rfc.iref.g.73"></span><span id="rfc.iref.g.74"></span><span id="rfc.iref.g.75"></span><span id="rfc.iref.g.76"></span>    <a href="#message.headers" class="smpl">message-header</a> = <a href="#message.headers" class="smpl">field-name</a> ":" [ field-value ]
     1691               stream at the beginning of a message and receives a CRLF first, it should ignore the CRLF.
     1692            </p>
     1693            <p id="rfc.section.4.1.p.6">Certain buggy HTTP/1.0 client implementations generate extra CRLF's after a POST request. To restate what is explicitly forbidden
     1694               by the BNF, an HTTP/1.1 client <em class="bcp14">MUST NOT</em> preface or follow a request with an extra CRLF.
     1695            </p>
     1696         </div>
     1697         <div id="message.headers">
     1698            <h2 id="rfc.section.4.2"><a href="#rfc.section.4.2">4.2</a>&nbsp;<a href="#message.headers">Message Headers</a></h2>
     1699            <p id="rfc.section.4.2.p.1">HTTP header fields, which include general-header (<a href="#general.header.fields" title="General Header Fields">Section&nbsp;4.5</a>), request-header (<a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5.3</a>), response-header (<a href="#response.header.fields" title="Response Header Fields">Section&nbsp;6.2</a>), and entity-header (<a href="#entity.header.fields" title="Entity Header Fields">Section&nbsp;7.1</a>) fields, follow the same generic format as that given in <a href="http://tools.ietf.org/html/rfc822#section-3.1" id="rfc.xref.RFC822.5">Section 3.1</a> of RFC 822 <a href="#RFC822" id="rfc.xref.RFC822.6"><cite title="Standard for the format of ARPA Internet text messages">[9]</cite></a>. Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The
     1700               field value <em class="bcp14">MAY</em> be preceded by any amount of LWS, though a single SP is preferred. Header fields can be extended over multiple lines by preceding
     1701               each extra line with at least one SP or HT. Applications ought to follow "common form", where one is known or indicated, when
     1702               generating HTTP constructs, since there might exist some implementations that fail to accept anything beyond the common forms.
     1703            </p>
     1704            <div id="rfc.figure.u.36"></div><pre class="inline"><span id="rfc.iref.g.73"></span><span id="rfc.iref.g.74"></span><span id="rfc.iref.g.75"></span><span id="rfc.iref.g.76"></span>    <a href="#message.headers" class="smpl">message-header</a> = <a href="#message.headers" class="smpl">field-name</a> ":" [ field-value ]
    16491705    <a href="#message.headers" class="smpl">field-name</a>     = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.20">token</a>
    16501706    field-value    = *( field-content | <a href="#basic.rules.lws" class="smpl" id="rfc.extref.l.9">LWS</a> )
     
    16531709                     of <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.22">token</a>, <a href="#basic.rules.token" class="smpl" id="rfc.extref.s.23">separators</a>, and <a href="#basic.rules.quoted-string" class="smpl" id="rfc.extref.q.11">quoted-string</a>&gt;
    16541710</pre><p id="rfc.section.4.2.p.3">The field-content does not include any leading or trailing LWS: linear white space occurring before the first non-whitespace
    1655          character of the field-value or after the last non-whitespace character of the field-value. Such leading or trailing LWS <em class="bcp14">MAY</em> be removed without changing the semantics of the field value. Any LWS that occurs between field-content <em class="bcp14">MAY</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream.
    1656       </p>
    1657       <p id="rfc.section.4.2.p.4">The order in which header fields with differing field names are received is not significant. However, it is "good practice"
    1658          to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header
    1659          fields.
    1660       </p>
    1661       <p id="rfc.section.4.2.p.5">Multiple message-header fields with the same field-name <em class="bcp14">MAY</em> be present in a message if and only if the entire field-value for that header field is defined as a comma-separated list [i.e.,
    1662          #(values)]. It <em class="bcp14">MUST</em> be possible to combine the multiple header fields into one "field-name: field-value" pair, without changing the semantics
    1663          of the message, by appending each subsequent field-value to the first, each separated by a comma. The order in which header
    1664          fields with the same field-name are received is therefore significant to the interpretation of the combined field value, and
    1665          thus a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when a message is forwarded.
    1666       </p>
    1667       <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a id="message.body" href="#message.body">Message Body</a></h2>
    1668       <p id="rfc.section.4.3.p.1">The message-body (if any) of an HTTP message is used to carry the entity-body associated with the request or response. The
    1669          message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding
    1670          header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.2" title="Transfer-Encoding">Section&nbsp;14.41</a>).
    1671       </p>
    1672       <div id="rfc.figure.u.37"></div><pre class="inline"><span id="rfc.iref.g.77"></span>    <a href="#message.body" class="smpl">message-body</a> = <a href="#entity.body" class="smpl">entity-body</a>
     1711               character of the field-value or after the last non-whitespace character of the field-value. Such leading or trailing LWS <em class="bcp14">MAY</em> be removed without changing the semantics of the field value. Any LWS that occurs between field-content <em class="bcp14">MAY</em> be replaced with a single SP before interpreting the field value or forwarding the message downstream.
     1712            </p>
     1713            <p id="rfc.section.4.2.p.4">The order in which header fields with differing field names are received is not significant. However, it is "good practice"
     1714               to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header
     1715               fields.
     1716            </p>
     1717            <p id="rfc.section.4.2.p.5">Multiple message-header fields with the same field-name <em class="bcp14">MAY</em> be present in a message if and only if the entire field-value for that header field is defined as a comma-separated list [i.e.,
     1718               #(values)]. It <em class="bcp14">MUST</em> be possible to combine the multiple header fields into one "field-name: field-value" pair, without changing the semantics
     1719               of the message, by appending each subsequent field-value to the first, each separated by a comma. The order in which header
     1720               fields with the same field-name are received is therefore significant to the interpretation of the combined field value, and
     1721               thus a proxy <em class="bcp14">MUST NOT</em> change the order of these field values when a message is forwarded.
     1722            </p>
     1723         </div>
     1724         <div id="message.body">
     1725            <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a>&nbsp;<a href="#message.body">Message Body</a></h2>
     1726            <p id="rfc.section.4.3.p.1">The message-body (if any) of an HTTP message is used to carry the entity-body associated with the request or response. The
     1727               message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding
     1728               header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.2" title="Transfer-Encoding">Section&nbsp;14.41</a>).
     1729            </p>
     1730            <div id="rfc.figure.u.37"></div><pre class="inline"><span id="rfc.iref.g.77"></span>    <a href="#message.body" class="smpl">message-body</a> = <a href="#entity.body" class="smpl">entity-body</a>
    16731731                 | &lt;<a href="#entity.body" class="smpl">entity-body</a> encoded as per Transfer-Encoding&gt;
    16741732</pre><p id="rfc.section.4.3.p.3">Transfer-Encoding <em class="bcp14">MUST</em> be used to indicate any transfer-codings applied by an application to ensure safe and proper transfer of the message. Transfer-Encoding
    1675          is a property of the message, not of the entity, and thus <em class="bcp14">MAY</em> be added or removed by any application along the request/response chain. (However, <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a> places restrictions on when certain transfer-codings may be used.)
    1676       </p>
    1677       <p id="rfc.section.4.3.p.4">The rules for when a message-body is allowed in a message differ for requests and responses.</p>
    1678       <p id="rfc.section.4.3.p.5">The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field
    1679          in the request's message-headers. A message-body <em class="bcp14">MUST NOT</em> be included in a request if the specification of the request method (<a href="#method" title="Method">Section&nbsp;5.1.1</a>) does not allow sending an entity-body in requests. A server <em class="bcp14">SHOULD</em> read and forward a message-body on any request; if the request method does not include defined semantics for an entity-body,
    1680          then the message-body <em class="bcp14">SHOULD</em> be ignored when handling the request.
    1681       </p>
    1682       <p id="rfc.section.4.3.p.6">For response messages, whether or not a message-body is included with a message is dependent on both the request method and
    1683          the response status code (<a href="#status.code.and.reason.phrase" title="Status Code and Reason Phrase">Section&nbsp;6.1.1</a>). All responses to the HEAD request method <em class="bcp14">MUST NOT</em> include a message-body, even though the presence of entity-header fields might lead one to believe they do. All 1xx (informational), <a href="#status.204" class="smpl">204 (no content)</a>, and <a href="#status.304" class="smpl">304 (not modified)</a> responses <em class="bcp14">MUST NOT</em> include a message-body. All other responses do include a message-body, although it <em class="bcp14">MAY</em> be of zero length.
    1684       </p>
    1685       <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a>&nbsp;<a id="message.length" href="#message.length">Message Length</a></h2>
    1686       <p id="rfc.section.4.4.p.1">The transfer-length of a message is the length of the message-body as it appears in the message; that is, after any transfer-codings
    1687          have been applied. When a message-body is included with a message, the transfer-length of that body is determined by one of
    1688          the following (in order of precedence):
    1689       </p>
    1690       <p id="rfc.section.4.4.p.2"> </p>
    1691       <ol>
    1692          <li>
    1693             <p>Any response message which "<em class="bcp14">MUST NOT</em>" include a message-body (such as the 1xx, 204, and 304 responses and any response to a HEAD request) is always terminated
    1694                by the first empty line after the header fields, regardless of the entity-header fields present in the message.
    1695             </p>
    1696          </li>
    1697          <li>
    1698             <p>If a Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.3" title="Transfer-Encoding">Section&nbsp;14.41</a>) is present and has any value other than "identity", then the transfer-length is defined by use of the "chunked" transfer-coding
    1699                (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>), unless the message is terminated by closing the connection.
    1700             </p>
    1701          </li>
    1702          <li>
    1703             <p>If a Content-Length header field (<a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section&nbsp;14.13</a>) is present, its decimal value in <a href="#basic.rules" class="smpl" id="rfc.extref.o.5">OCTET</a>s represents both the entity-length and the transfer-length. The Content-Length header field <em class="bcp14">MUST NOT</em> be sent if these two lengths are different (i.e., if a Transfer-Encoding header field is present). If a message is received
    1704                with both a Transfer-Encoding header field and a Content-Length header field, the latter <em class="bcp14">MUST</em> be ignored.
    1705             </p>
    1706          </li>
    1707          <li>
    1708             <p>If the message uses the media type "multipart/byteranges", and the ransfer-length is not otherwise specified, then this self-elimiting
    1709                media type defines the transfer-length. This media type UST NOT be used unless the sender knows that the recipient can arse
    1710                it; the presence in a request of a Range header with ultiple byte-range specifiers from a 1.1 client implies that the lient
    1711                can parse multipart/byteranges responses.
    1712             </p>
    1713             <ul class="empty">
    1714                <li>A range header might be forwarded by a 1.0 proxy that does not understand multipart/byteranges; in this case the server <em class="bcp14">MUST</em> delimit the message using methods defined in items 1, 3 or 5 of this section.
    1715                </li>
    1716             </ul>
    1717          </li>
    1718          <li>
    1719             <p>By the server closing the connection. (Closing the connection cannot be used to indicate the end of a request body, since
    1720                that would leave no possibility for the server to send back a response.)
    1721             </p>
    1722          </li>
    1723       </ol>
    1724       <p id="rfc.section.4.4.p.3">For compatibility with HTTP/1.0 applications, HTTP/1.1 requests containing a message-body <em class="bcp14">MUST</em> include a valid Content-Length header field unless the server is known to be HTTP/1.1 compliant. If a request contains a message-body
    1725          and a Content-Length is not given, the server <em class="bcp14">SHOULD</em> respond with <a href="#status.400" class="smpl">400 (bad request)</a> if it cannot determine the length of the message, or with <a href="#status.411" class="smpl">411 (length required)</a> if it wishes to insist on receiving a valid Content-Length.
    1726       </p>
    1727       <p id="rfc.section.4.4.p.4">All HTTP/1.1 applications that receive entities <em class="bcp14">MUST</em> accept the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>), thus allowing this mechanism to be used for messages when the message length cannot be determined in advance.
    1728       </p>
    1729       <p id="rfc.section.4.4.p.5">Messages <em class="bcp14">MUST NOT</em> include both a Content-Length header field and a non-identity transfer-coding. If the message does include a non-identity
    1730          transfer-coding, the Content-Length <em class="bcp14">MUST</em> be ignored.
    1731       </p>
    1732       <p id="rfc.section.4.4.p.6">When a Content-Length is given in a message where a message-body is allowed, its field value <em class="bcp14">MUST</em> exactly match the number of <a href="#basic.rules" class="smpl" id="rfc.extref.o.6">OCTET</a>s in the message-body. HTTP/1.1 user agents <em class="bcp14">MUST</em> notify the user when an invalid length is received and detected.
    1733       </p>
    1734       <h2 id="rfc.section.4.5"><a href="#rfc.section.4.5">4.5</a>&nbsp;<a id="general.header.fields" href="#general.header.fields">General Header Fields</a></h2>
    1735       <p id="rfc.section.4.5.p.1">There are a few header fields which have general applicability for both request and response messages, but which do not apply
    1736          to the entity being transferred. These header fields apply only to the message being transmitted.
    1737       </p>
    1738       <div id="rfc.figure.u.38"></div><pre class="inline"><span id="rfc.iref.g.78"></span>    <a href="#general.header.fields" class="smpl">general-header</a> = Cache-Control            ; <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section&nbsp;14.9</a>
     1733               is a property of the message, not of the entity, and thus <em class="bcp14">MAY</em> be added or removed by any application along the request/response chain. (However, <a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a> places restrictions on when certain transfer-codings may be used.)
     1734            </p>
     1735            <p id="rfc.section.4.3.p.4">The rules for when a message-body is allowed in a message differ for requests and responses.</p>
     1736            <p id="rfc.section.4.3.p.5">The presence of a message-body in a request is signaled by the inclusion of a Content-Length or Transfer-Encoding header field
     1737               in the request's message-headers. A message-body <em class="bcp14">MUST NOT</em> be included in a request if the specification of the request method (<a href="#method" title="Method">Section&nbsp;5.1.1</a>) does not allow sending an entity-body in requests. A server <em class="bcp14">SHOULD</em> read and forward a message-body on any request; if the request method does not include defined semantics for an entity-body,
     1738               then the message-body <em class="bcp14">SHOULD</em> be ignored when handling the request.
     1739            </p>
     1740            <p id="rfc.section.4.3.p.6">For response messages, whether or not a message-body is included with a message is dependent on both the request method and
     1741               the response status code (<a href="#status.code.and.reason.phrase" title="Status Code and Reason Phrase">Section&nbsp;6.1.1</a>). All responses to the HEAD request method <em class="bcp14">MUST NOT</em> include a message-body, even though the presence of entity-header fields might lead one to believe they do. All 1xx (informational), <a href="#status.204" class="smpl">204 (no content)</a>, and <a href="#status.304" class="smpl">304 (not modified)</a> responses <em class="bcp14">MUST NOT</em> include a message-body. All other responses do include a message-body, although it <em class="bcp14">MAY</em> be of zero length.
     1742            </p>
     1743         </div>
     1744         <div id="message.length">
     1745            <h2 id="rfc.section.4.4"><a href="#rfc.section.4.4">4.4</a>&nbsp;<a href="#message.length">Message Length</a></h2>
     1746            <p id="rfc.section.4.4.p.1">The transfer-length of a message is the length of the message-body as it appears in the message; that is, after any transfer-codings
     1747               have been applied. When a message-body is included with a message, the transfer-length of that body is determined by one of
     1748               the following (in order of precedence):
     1749            </p>
     1750            <p id="rfc.section.4.4.p.2"></p>
     1751            <ol>
     1752               <li>
     1753                  <p>Any response message which "<em class="bcp14">MUST NOT</em>" include a message-body (such as the 1xx, 204, and 304 responses and any response to a HEAD request) is always terminated
     1754                     by the first empty line after the header fields, regardless of the entity-header fields present in the message.
     1755                  </p>
     1756               </li>
     1757               <li>
     1758                  <p>If a Transfer-Encoding header field (<a href="#header.transfer-encoding" id="rfc.xref.header.transfer-encoding.3" title="Transfer-Encoding">Section&nbsp;14.41</a>) is present and has any value other than "identity", then the transfer-length is defined by use of the "chunked" transfer-coding
     1759                     (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>), unless the message is terminated by closing the connection.
     1760                  </p>
     1761               </li>
     1762               <li>
     1763                  <p>If a Content-Length header field (<a href="#header.content-length" id="rfc.xref.header.content-length.1" title="Content-Length">Section&nbsp;14.13</a>) is present, its decimal value in <a href="#basic.rules" class="smpl" id="rfc.extref.o.5">OCTET</a>s represents both the entity-length and the transfer-length. The Content-Length header field <em class="bcp14">MUST NOT</em> be sent if these two lengths are different (i.e., if a Transfer-Encoding header field is present). If a message is received
     1764                     with both a Transfer-Encoding header field and a Content-Length header field, the latter <em class="bcp14">MUST</em> be ignored.
     1765                  </p>
     1766               </li>
     1767               <li>
     1768                  <p>If the message uses the media type "multipart/byteranges", and the ransfer-length is not otherwise specified, then this self-elimiting
     1769                     media type defines the transfer-length. This media type UST NOT be used unless the sender knows that the recipient can arse
     1770                     it; the presence in a request of a Range header with ultiple byte-range specifiers from a 1.1 client implies that the lient
     1771                     can parse multipart/byteranges responses.
     1772                  </p>
     1773                  <ul class="empty">
     1774                     <li>A range header might be forwarded by a 1.0 proxy that does not understand multipart/byteranges; in this case the server <em class="bcp14">MUST</em> delimit the message using methods defined in items 1, 3 or 5 of this section.
     1775                     </li>
     1776                  </ul>
     1777               </li>
     1778               <li>
     1779                  <p>By the server closing the connection. (Closing the connection cannot be used to indicate the end of a request body, since
     1780                     that would leave no possibility for the server to send back a response.)
     1781                  </p>
     1782               </li>
     1783            </ol>
     1784            <p id="rfc.section.4.4.p.3">For compatibility with HTTP/1.0 applications, HTTP/1.1 requests containing a message-body <em class="bcp14">MUST</em> include a valid Content-Length header field unless the server is known to be HTTP/1.1 compliant. If a request contains a message-body
     1785               and a Content-Length is not given, the server <em class="bcp14">SHOULD</em> respond with <a href="#status.400" class="smpl">400 (bad request)</a> if it cannot determine the length of the message, or with <a href="#status.411" class="smpl">411 (length required)</a> if it wishes to insist on receiving a valid Content-Length.
     1786            </p>
     1787            <p id="rfc.section.4.4.p.4">All HTTP/1.1 applications that receive entities <em class="bcp14">MUST</em> accept the "chunked" transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>), thus allowing this mechanism to be used for messages when the message length cannot be determined in advance.
     1788            </p>
     1789            <p id="rfc.section.4.4.p.5">Messages <em class="bcp14">MUST NOT</em> include both a Content-Length header field and a non-identity transfer-coding. If the message does include a non-identity
     1790               transfer-coding, the Content-Length <em class="bcp14">MUST</em> be ignored.
     1791            </p>
     1792            <p id="rfc.section.4.4.p.6">When a Content-Length is given in a message where a message-body is allowed, its field value <em class="bcp14">MUST</em> exactly match the number of <a href="#basic.rules" class="smpl" id="rfc.extref.o.6">OCTET</a>s in the message-body. HTTP/1.1 user agents <em class="bcp14">MUST</em> notify the user when an invalid length is received and detected.
     1793            </p>
     1794         </div>
     1795         <div id="general.header.fields">
     1796            <h2 id="rfc.section.4.5"><a href="#rfc.section.4.5">4.5</a>&nbsp;<a href="#general.header.fields">General Header Fields</a></h2>
     1797            <p id="rfc.section.4.5.p.1">There are a few header fields which have general applicability for both request and response messages, but which do not apply
     1798               to the entity being transferred. These header fields apply only to the message being transmitted.
     1799            </p>
     1800            <div id="rfc.figure.u.38"></div><pre class="inline"><span id="rfc.iref.g.78"></span>    <a href="#general.header.fields" class="smpl">general-header</a> = Cache-Control            ; <a href="#header.cache-control" id="rfc.xref.header.cache-control.1" title="Cache-Control">Section&nbsp;14.9</a>
    17391801                   | Connection               ; <a href="#header.connection" id="rfc.xref.header.connection.1" title="Connection">Section&nbsp;14.10</a>
    17401802                   | Date                     ; <a href="#header.date" id="rfc.xref.header.date.1" title="Date">Section&nbsp;14.18</a>
     
    17461808                   | Warning                  ; <a href="#header.warning" id="rfc.xref.header.warning.1" title="Warning">Section&nbsp;14.46</a>
    17471809</pre><p id="rfc.section.4.5.p.3">General-header field names can be extended reliably only in combination with a change in the protocol version. However, new
    1748          or experimental header fields may be given the semantics of general header fields if all parties in the communication recognize
    1749          them to be general-header fields. Unrecognized header fields are treated as entity-header fields.
    1750       </p>
     1810               or experimental header fields may be given the semantics of general header fields if all parties in the communication recognize
     1811               them to be general-header fields. Unrecognized header fields are treated as entity-header fields.
     1812            </p>
     1813         </div>
     1814      </div>
    17511815      <hr class="noprint">
    1752       <h1 id="rfc.section.5" class="np"><a href="#rfc.section.5">5.</a>&nbsp;<a id="request" href="#request">Request</a></h1>
    1753       <p id="rfc.section.5.p.1">A request message from a client to a server includes, within the first line of that message, the method to be applied to the
    1754          resource, the identifier of the resource, and the protocol version in use.
    1755       </p>
    1756       <div id="rfc.figure.u.39"></div><pre class="inline"><span id="rfc.iref.g.79"></span>     <a href="#request" class="smpl">Request</a>       = <a href="#request-line" class="smpl">Request-Line</a>              ; <a href="#request-line" title="Request-Line">Section&nbsp;5.1</a>
     1816      <div id="request">
     1817         <h1 id="rfc.section.5" class="np"><a href="#rfc.section.5">5.</a>&nbsp;<a href="#request">Request</a></h1>
     1818         <p id="rfc.section.5.p.1">A request message from a client to a server includes, within the first line of that message, the method to be applied to the
     1819            resource, the identifier of the resource, and the protocol version in use.
     1820         </p>
     1821         <div id="rfc.figure.u.39"></div><pre class="inline"><span id="rfc.iref.g.79"></span>     <a href="#request" class="smpl">Request</a>       = <a href="#request-line" class="smpl">Request-Line</a>              ; <a href="#request-line" title="Request-Line">Section&nbsp;5.1</a>
    17571822                     *(( <a href="#general.header.fields" class="smpl">general-header</a>        ; <a href="#general.header.fields" title="General Header Fields">Section&nbsp;4.5</a>
    17581823                      | <a href="#request.header.fields" class="smpl">request-header</a>         ; <a href="#request.header.fields" title="Request Header Fields">Section&nbsp;5.3</a>
     
    17601825                     <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.26">CRLF</a>
    17611826                     [ <a href="#message.body" class="smpl">message-body</a> ]          ; <a href="#message.body" title="Message Body">Section&nbsp;4.3</a>
    1762 </pre><h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a id="request-line" href="#request-line">Request-Line</a></h2>
    1763       <p id="rfc.section.5.1.p.1">The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The
    1764          elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence.
    1765       </p>
    1766       <div id="rfc.figure.u.40"></div><pre class="inline"><span id="rfc.iref.g.80"></span>     <a href="#request-line" class="smpl">Request-Line</a>   = <a href="#method" class="smpl">Method</a> <a href="#basic.rules" class="smpl" id="rfc.extref.s.24">SP</a> <a href="#request-uri" class="smpl">Request-URI</a> <a href="#basic.rules" class="smpl" id="rfc.extref.s.25">SP</a> <a href="#http.version" class="smpl" id="rfc.extref.h.9">HTTP-Version</a> <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.27">CRLF</a>
    1767 </pre><h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;<a id="method" href="#method">Method</a></h3>
    1768       <p id="rfc.section.5.1.1.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>
    1769       <div id="rfc.figure.u.41"></div><pre class="inline"><span id="rfc.iref.g.81"></span><span id="rfc.iref.g.82"></span>    Method         = "OPTIONS"                ; <a href="#OPTIONS" id="rfc.xref.OPTIONS.1" title="OPTIONS">Section&nbsp;9.2</a>
     1827</pre><div id="request-line">
     1828            <h2 id="rfc.section.5.1"><a href="#rfc.section.5.1">5.1</a>&nbsp;<a href="#request-line">Request-Line</a></h2>
     1829            <p id="rfc.section.5.1.p.1">The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The
     1830               elements are separated by SP characters. No CR or LF is allowed except in the final CRLF sequence.
     1831            </p>
     1832            <div id="rfc.figure.u.40"></div><pre class="inline"><span id="rfc.iref.g.80"></span>     <a href="#request-line" class="smpl">Request-Line</a>   = <a href="#method" class="smpl">Method</a> <a href="#basic.rules" class="smpl" id="rfc.extref.s.24">SP</a> <a href="#request-uri" class="smpl">Request-URI</a> <a href="#basic.rules" class="smpl" id="rfc.extref.s.25">SP</a> <a href="#http.version" class="smpl" id="rfc.extref.h.9">HTTP-Version</a> <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.27">CRLF</a>
     1833</pre><div id="method">
     1834               <h3 id="rfc.section.5.1.1"><a href="#rfc.section.5.1.1">5.1.1</a>&nbsp;<a href="#method">Method</a></h3>
     1835               <p id="rfc.section.5.1.1.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>
     1836               <div id="rfc.figure.u.41"></div><pre class="inline"><span id="rfc.iref.g.81"></span><span id="rfc.iref.g.82"></span>    Method         = "OPTIONS"                ; <a href="#OPTIONS" id="rfc.xref.OPTIONS.1" title="OPTIONS">Section&nbsp;9.2</a>
    17701837                   | "GET"                    ; <a href="#GET" id="rfc.xref.GET.1" title="GET">Section&nbsp;9.3</a>
    17711838                   | "HEAD"                   ; <a href="#HEAD" id="rfc.xref.HEAD.1" title="HEAD">Section&nbsp;9.4</a>
     
    17781845    extension-method = <a href="#basic.rules.token" class="smpl" id="rfc.extref.t.23">token</a>
    17791846</pre><p id="rfc.section.5.1.1.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;14.7</a>). The return code of the response always notifies the client whether a method is currently allowed on a resource, since the
    1780          set of allowed methods can change dynamically. An origin server <em class="bcp14">SHOULD</em> return the status code <a href="#status.405" class="smpl">405 (Method Not Allowed)</a> if the method is known by the origin server but not allowed for the requested resource, and <a href="#status.501" class="smpl">501 (Not Implemented)</a> if the method is unrecognized or not implemented by the origin server. The methods GET 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;9</a>.
    1781       </p>
    1782       <h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;<a id="request-uri" href="#request-uri">Request-URI</a></h3>
    1783       <p id="rfc.section.5.1.2.p.1">The Request-URI is a Uniform Resource Identifier (<a href="#uri" title="Uniform Resource Identifiers">Section&nbsp;3.2</a>) and identifies the resource upon which to apply the request.
    1784       </p>
    1785       <div id="rfc.figure.u.42"></div><pre class="inline"><span id="rfc.iref.g.83"></span>    <a href="#request-uri" class="smpl">Request-URI</a>    = "*" | <a href="#general.syntax" class="smpl">absoluteURI</a> | abs_path | authority
     1847                  set of allowed methods can change dynamically. An origin server <em class="bcp14">SHOULD</em> return the status code <a href="#status.405" class="smpl">405 (Method Not Allowed)</a> if the method is known by the origin server but not allowed for the requested resource, and <a href="#status.501" class="smpl">501 (Not Implemented)</a> if the method is unrecognized or not implemented by the origin server. The methods GET 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;9</a>.
     1848               </p>
     1849            </div>
     1850            <div id="request-uri">
     1851               <h3 id="rfc.section.5.1.2"><a href="#rfc.section.5.1.2">5.1.2</a>&nbsp;<a href="#request-uri">Request-URI</a></h3>
     1852               <p id="rfc.section.5.1.2.p.1">The Request-URI is a Uniform Resource Identifier (<a href="#uri" title="Uniform Resource Identifiers">Section&nbsp;3.2</a>) and identifies the resource upon which to apply the request.
     1853               </p>
     1854               <div id="rfc.figure.u.42"></div><pre class="inline"><span id="rfc.iref.g.83"></span>    <a href="#request-uri" class="smpl">Request-URI</a>    = "*" | <a href="#general.syntax" class="smpl">absoluteURI</a> | abs_path | authority
    17861855</pre><p id="rfc.section.5.1.2.p.3">The four options for Request-URI are dependent on the nature of the request. The asterisk "*" means that the request does
    1787          not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily
    1788          apply to a resource. One example would be
    1789       </p>
    1790       <div id="rfc.figure.u.43"></div><pre class="text">    OPTIONS * HTTP/1.1
     1856                  not apply to a particular resource, but to the server itself, and is only allowed when the method used does not necessarily
     1857                  apply to a resource. One example would be
     1858               </p>
     1859               <div id="rfc.figure.u.43"></div><pre class="text">    OPTIONS * HTTP/1.1
    17911860</pre><p id="rfc.section.5.1.2.p.5">The absoluteURI form is <em class="bcp14">REQUIRED</em> when the request is being made to a proxy. The proxy is requested to forward the request or service it from a valid cache,
    1792          and return the response. Note that the proxy <em class="bcp14">MAY</em> forward the request on to another proxy or directly to the server specified by the absoluteURI. In order to avoid request
    1793          loops, a proxy <em class="bcp14">MUST</em> be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example
    1794          Request-Line would be:
    1795       </p>
    1796       <div id="rfc.figure.u.44"></div><pre class="text">    GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1
     1861                  and return the response. Note that the proxy <em class="bcp14">MAY</em> forward the request on to another proxy or directly to the server specified by the absoluteURI. In order to avoid request
     1862                  loops, a proxy <em class="bcp14">MUST</em> be able to recognize all of its server names, including any aliases, local variations, and the numeric IP address. An example
     1863                  Request-Line would be:
     1864               </p>
     1865               <div id="rfc.figure.u.44"></div><pre class="text">    GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1
    17971866</pre><p id="rfc.section.5.1.2.p.7">To allow for transition to absoluteURIs in all requests in future versions of HTTP, all HTTP/1.1 servers <em class="bcp14">MUST</em> accept the absoluteURI form in requests, even though HTTP/1.1 clients will only generate them in requests to proxies.
    1798       </p>
    1799       <p id="rfc.section.5.1.2.p.8">The authority form is only used by the CONNECT method (<a href="#CONNECT" id="rfc.xref.CONNECT.2" title="CONNECT">Section&nbsp;9.9</a>).
    1800       </p>
    1801       <p id="rfc.section.5.1.2.p.9">The most common form of Request-URI is that used to identify a resource on an origin server or gateway. In this case the absolute
    1802          path of the URI <em class="bcp14">MUST</em> be transmitted (see <a href="#general.syntax" title="General Syntax">Section&nbsp;3.2.1</a>, abs_path) as the Request-URI, and the network location of the URI (authority) <em class="bcp14">MUST</em> be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin
    1803          server would create a TCP connection to port 80 of the host "www.w3.org" and send the lines:
    1804       </p>
    1805       <div id="rfc.figure.u.45"></div><pre class="text">    GET /pub/WWW/TheProject.html HTTP/1.1
     1867               </p>
     1868               <p id="rfc.section.5.1.2.p.8">The authority form is only used by the CONNECT method (<a href="#CONNECT" id="rfc.xref.CONNECT.2" title="CONNECT">Section&nbsp;9.9</a>).
     1869               </p>
     1870               <p id="rfc.section.5.1.2.p.9">The most common form of Request-URI is that used to identify a resource on an origin server or gateway. In this case the absolute
     1871                  path of the URI <em class="bcp14">MUST</em> be transmitted (see <a href="#general.syntax" title="General Syntax">Section&nbsp;3.2.1</a>, abs_path) as the Request-URI, and the network location of the URI (authority) <em class="bcp14">MUST</em> be transmitted in a Host header field. For example, a client wishing to retrieve the resource above directly from the origin
     1872                  server would create a TCP connection to port 80 of the host "www.w3.org" and send the lines:
     1873               </p>
     1874               <div id="rfc.figure.u.45"></div><pre class="text">    GET /pub/WWW/TheProject.html HTTP/1.1
    18061875    Host: www.w3.org
    18071876</pre><p id="rfc.section.5.1.2.p.11">followed by the remainder of the Request. Note that the absolute path cannot be empty; if none is present in the original
    1808          URI, it <em class="bcp14">MUST</em> be given as "/" (the server root).
    1809       </p>
    1810       <p id="rfc.section.5.1.2.p.12">The Request-URI is transmitted in the format specified in <a href="#general.syntax" title="General Syntax">Section&nbsp;3.2.1</a>. If the Request-URI is encoded using the "% HEX HEX" encoding <a href="#RFC2396" id="rfc.xref.RFC2396.3"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[42]</cite></a>, the origin server <em class="bcp14">MUST</em> decode the Request-URI in order to properly interpret the request. Servers <em class="bcp14">SHOULD</em> respond to invalid Request-URIs with an appropriate status code.
    1811       </p>
    1812       <p id="rfc.section.5.1.2.p.13">A transparent proxy <em class="bcp14">MUST NOT</em> rewrite the "abs_path" part of the received Request-URI when forwarding it to the next inbound server, except as noted above
    1813          to replace a null abs_path with "/".
    1814       </p>
    1815       <p id="rfc.section.5.1.2.p.14"> </p>
    1816       <ul class="empty">
    1817          <li> <b>Note:</b> The "no rewrite" rule prevents the proxy from changing the meaning of the request when the origin server is improperly using
    1818             a non-reserved URI character for a reserved purpose. Implementors should be aware that some pre-HTTP/1.1 proxies have been
    1819             known to rewrite the Request-URI.
    1820          </li>
    1821       </ul>
    1822       <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a id="the.resource.identified.by.a.request" href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></h2>
    1823       <p id="rfc.section.5.2.p.1">The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.</p>
    1824       <p id="rfc.section.5.2.p.2">An origin server that does not allow resources to differ by the requested host <em class="bcp14">MAY</em> ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">Appendix&nbsp;19.6.1.1</a> for other requirements on Host support in HTTP/1.1.)
    1825       </p>
    1826       <p id="rfc.section.5.2.p.3">An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or
    1827          vanity host names) <em class="bcp14">MUST</em> use the following rules for determining the requested resource on an HTTP/1.1 request:
    1828       </p>
    1829       <ol>
    1830          <li>If Request-URI is an absoluteURI, the host is part of the Request-URI. Any Host header field value in the request <em class="bcp14">MUST</em> be ignored.
    1831          </li>
    1832          <li>If the Request-URI is not an absoluteURI, and the request includes a Host header field, the host is determined by the Host
    1833             header field value.
    1834          </li>
    1835          <li>If the host as determined by rule 1 or 2 is not a valid host on the server, the response <em class="bcp14">MUST</em> be a <a href="#status.400" class="smpl">400 (Bad Request)</a> error message.
    1836          </li>
    1837       </ol>
    1838       <p id="rfc.section.5.2.p.4">Recipients of an HTTP/1.0 request that lacks a Host header field <em class="bcp14">MAY</em> attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine
    1839          what exact resource is being requested.
    1840       </p>
    1841       <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a>&nbsp;<a id="request.header.fields" href="#request.header.fields">Request Header Fields</a></h2>
    1842       <p id="rfc.section.5.3.p.1">The request-header fields allow the client to pass additional information about the request, and about the client itself,
    1843          to the server. These fields act as request modifiers, with semantics equivalent to the parameters on a programming language
    1844          method invocation.
    1845       </p>
    1846       <div id="rfc.figure.u.46"></div><pre class="inline"><span id="rfc.iref.g.84"></span>    <a href="#request.header.fields" class="smpl">request-header</a> = Accept                   ; <a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section&nbsp;14.1</a>
     1877                  URI, it <em class="bcp14">MUST</em> be given as "/" (the server root).
     1878               </p>
     1879               <p id="rfc.section.5.1.2.p.12">The Request-URI is transmitted in the format specified in <a href="#general.syntax" title="General Syntax">Section&nbsp;3.2.1</a>. If the Request-URI is encoded using the "% HEX HEX" encoding <a href="#RFC2396" id="rfc.xref.RFC2396.3"><cite title="Uniform Resource Identifiers (URI): Generic Syntax">[42]</cite></a>, the origin server <em class="bcp14">MUST</em> decode the Request-URI in order to properly interpret the request. Servers <em class="bcp14">SHOULD</em> respond to invalid Request-URIs with an appropriate status code.
     1880               </p>
     1881               <p id="rfc.section.5.1.2.p.13">A transparent proxy <em class="bcp14">MUST NOT</em> rewrite the "abs_path" part of the received Request-URI when forwarding it to the next inbound server, except as noted above
     1882                  to replace a null abs_path with "/".
     1883               </p>
     1884               <p id="rfc.section.5.1.2.p.14"></p>
     1885               <ul class="empty">
     1886                  <li><b>Note:</b> The "no rewrite" rule prevents the proxy from changing the meaning of the request when the origin server is improperly using
     1887                     a non-reserved URI character for a reserved purpose. Implementors should be aware that some pre-HTTP/1.1 proxies have been
     1888                     known to rewrite the Request-URI.
     1889                  </li>
     1890               </ul>
     1891            </div>
     1892         </div>
     1893         <div id="the.resource.identified.by.a.request">
     1894            <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a href="#the.resource.identified.by.a.request">The Resource Identified by a Request</a></h2>
     1895            <p id="rfc.section.5.2.p.1">The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.</p>
     1896            <p id="rfc.section.5.2.p.2">An origin server that does not allow resources to differ by the requested host <em class="bcp14">MAY</em> ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see <a href="#changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses">Appendix&nbsp;19.6.1.1</a> for other requirements on Host support in HTTP/1.1.)
     1897            </p>
     1898            <p id="rfc.section.5.2.p.3">An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or
     1899               vanity host names) <em class="bcp14">MUST</em> use the following rules for determining the requested resource on an HTTP/1.1 request:
     1900            </p>
     1901            <ol>
     1902               <li>If Request-URI is an absoluteURI, the host is part of the Request-URI. Any Host header field value in the request <em class="bcp14">MUST</em> be ignored.
     1903               </li>
     1904               <li>If the Request-URI is not an absoluteURI, and the request includes a Host header field, the host is determined by the Host
     1905                  header field value.
     1906               </li>
     1907               <li>If the host as determined by rule 1 or 2 is not a valid host on the server, the response <em class="bcp14">MUST</em> be a <a href="#status.400" class="smpl">400 (Bad Request)</a> error message.
     1908               </li>
     1909            </ol>
     1910            <p id="rfc.section.5.2.p.4">Recipients of an HTTP/1.0 request that lacks a Host header field <em class="bcp14">MAY</em> attempt to use heuristics (e.g., examination of the URI path for something unique to a particular host) in order to determine
     1911               what exact resource is being requested.
     1912            </p>
     1913         </div>
     1914         <div id="request.header.fields">
     1915            <h2 id="rfc.section.5.3"><a href="#rfc.section.5.3">5.3</a>&nbsp;<a href="#request.header.fields">Request Header Fields</a></h2>
     1916            <p id="rfc.section.5.3.p.1">The request-header fields allow the client to pass additional information about the request, and about the client itself,
     1917               to the server. These fields act as request modifiers, with semantics equivalent to the parameters on a programming language
     1918               method invocation.
     1919            </p>
     1920            <div id="rfc.figure.u.46"></div><pre class="inline"><span id="rfc.iref.g.84"></span>    <a href="#request.header.fields" class="smpl">request-header</a> = Accept                   ; <a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section&nbsp;14.1</a>
    18471921                   | Accept-Charset           ; <a href="#header.accept-charset" id="rfc.xref.header.accept-charset.1" title="Accept-Charset">Section&nbsp;14.2</a>
    18481922                   | Accept-Encoding          ; <a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.2" title="Accept-Encoding">Section&nbsp;14.3</a>
     
    18641938                   | User-Agent               ; <a href="#header.user-agent" id="rfc.xref.header.user-agent.1" title="User-Agent">Section&nbsp;14.43</a>
    18651939</pre><p id="rfc.section.5.3.p.3">Request-header field names can be extended reliably only in combination with a change in the protocol version. However, new
    1866          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.
    1867          Unrecognized header fields are treated as entity-header fields.
    1868       </p>
     1940               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.
     1941               Unrecognized header fields are treated as entity-header fields.
     1942            </p>
     1943         </div>
     1944      </div>
    18691945      <hr class="noprint">
    1870       <h1 id="rfc.section.6" class="np"><a href="#rfc.section.6">6.</a>&nbsp;<a id="response" href="#response">Response</a></h1>
    1871       <p id="rfc.section.6.p.1">After receiving and interpreting a request message, a server responds with an HTTP response message.</p>
    1872       <div id="rfc.figure.u.47"></div><pre class="inline"><span id="rfc.iref.g.85"></span>    <a href="#response" class="smpl">Response</a>      = <a href="#status-line" class="smpl">Status-Line</a>               ; <a href="#status-line" title="Status-Line">Section&nbsp;6.1</a>
     1946      <div id="response">
     1947         <h1 id="rfc.section.6" class="np"><a href="#rfc.section.6">6.</a>&nbsp;<a href="#response">Response</a></h1>
     1948         <p id="rfc.section.6.p.1">After receiving and interpreting a request message, a server responds with an HTTP response message.</p>
     1949         <div id="rfc.figure.u.47"></div><pre class="inline"><span id="rfc.iref.g.85"></span>    <a href="#response" class="smpl">Response</a>      = <a href="#status-line" class="smpl">Status-Line</a>               ; <a href="#status-line" title="Status-Line">Section&nbsp;6.1</a>
    18731950                    *(( <a href="#general.header.fields" class="smpl">general-header</a>        ; <a href="#general.header.fields" title="General Header Fields">Section&nbsp;4.5</a>
    18741951                     | <a href="#response.header.fields" class="smpl">response-header</a>        ; <a href="#response.header.fields" title="Response Header Fields">Section&nbsp;6.2</a>
     
    18761953                    <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.29">CRLF</a>
    18771954                    [ <a href="#message.body" class="smpl">message-body</a> ]          ; <a href="#entity.body" title="Entity Body">Section&nbsp;7.2</a>
    1878 </pre><h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a id="status-line" href="#status-line">Status-Line</a></h2>
    1879       <p id="rfc.section.6.1.p.1">The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code
    1880          and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final
    1881          CRLF sequence.
    1882       </p>
    1883       <div id="rfc.figure.u.48"></div><pre class="inline"><span id="rfc.iref.g.86"></span>    <a href="#status-line" class="smpl">Status-Line</a> = <a href="#http.version" class="smpl" id="rfc.extref.h.10">HTTP-Version</a> <a href="#basic.rules" class="smpl" id="rfc.extref.s.28">SP</a> <a href="#status.code.and.reason.phrase.codes" class="smpl">Status-Code</a> <a href="#basic.rules" class="smpl" id="rfc.extref.s.30">SP</a> <a href="#status.code.and.reason.phrase.codes" class="smpl">Reason-Phrase</a> <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.30">CRLF</a>
    1884 </pre><h3 id="rfc.section.6.1.1"><a href="#rfc.section.6.1.1">6.1.1</a>&nbsp;<a id="status.code.and.reason.phrase" href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h3>
    1885       <p id="rfc.section.6.1.1.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes
    1886          are fully defined in <a href="#status.codes" title="Status Code Definitions">Section&nbsp;10</a>. The Reason-Phrase is intended to give a short textual description of the Status-Code. The Status-Code is intended for use
    1887          by automata and the Reason-Phrase is intended for the human user. The client is not required to examine or display the Reason-Phrase.
    1888       </p>
    1889       <p id="rfc.section.6.1.1.p.2">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role.
    1890          There are 5 values for the first digit:
    1891       </p>
    1892       <ul>
    1893          <li>1xx: Informational - Request received, continuing process</li>
    1894          <li>2xx: Success - The action was successfully received, understood, and accepted</li>
    1895          <li>3xx: Redirection - Further action must be taken in order to complete the request</li>
    1896          <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li>
    1897          <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li>
    1898       </ul>
    1899       <div id="status.code.and.reason.phrase.codes">
    1900          <p id="rfc.section.6.1.1.p.3">    The individual values of the numeric status codes defined for HTTP/1.1, and an example set of corresponding Reason-Phrase's,
    1901             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.
    1902          </p>
    1903       </div>
    1904       <div id="rfc.figure.u.49"></div><pre class="inline"><span id="rfc.iref.g.87"></span><span id="rfc.iref.g.88"></span><span id="rfc.iref.g.89"></span>   <a href="#status.code.and.reason.phrase.codes" class="smpl">Status-Code</a>    =
     1955</pre><div id="status-line">
     1956            <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a>&nbsp;<a href="#status-line">Status-Line</a></h2>
     1957            <p id="rfc.section.6.1.p.1">The first line of a Response message is the Status-Line, consisting of the protocol version followed by a numeric status code
     1958               and its associated textual phrase, with each element separated by SP characters. No CR or LF is allowed except in the final
     1959               CRLF sequence.
     1960            </p>
     1961            <div id="rfc.figure.u.48"></div><pre class="inline"><span id="rfc.iref.g.86"></span>    <a href="#status-line" class="smpl">Status-Line</a> = <a href="#http.version" class="smpl" id="rfc.extref.h.10">HTTP-Version</a> <a href="#basic.rules" class="smpl" id="rfc.extref.s.28">SP</a> <a href="#status.code.and.reason.phrase.codes" class="smpl">Status-Code</a> <a href="#basic.rules" class="smpl" id="rfc.extref.s.30">SP</a> <a href="#status.code.and.reason.phrase.codes" class="smpl">Reason-Phrase</a> <a href="#basic.rules.crlf" class="smpl" id="rfc.extref.c.30">CRLF</a>
     1962</pre><div id="status.code.and.reason.phrase">
     1963               <h3 id="rfc.section.6.1.1"><a href="#rfc.section.6.1.1">6.1.1</a>&nbsp;<a href="#status.code.and.reason.phrase">Status Code and Reason Phrase</a></h3>
     1964               <p id="rfc.section.6.1.1.p.1">The Status-Code element is a 3-digit integer result code of the attempt to understand and satisfy the request. These codes
     1965                  are fully defined in <a href="#status.codes" title="Status Code Definitions">Section&nbsp;10</a>. The Reason-Phrase is intended to give a short textual description of the Status-Code. The Status-Code is intended for use
     1966                  by automata and the Reason-Phrase is intended for the human user. The client is not required to examine or display the Reason-Phrase.
     1967               </p>
     1968               <p id="rfc.section.6.1.1.p.2">The first digit of the Status-Code defines the class of response. The last two digits do not have any categorization role.
     1969                  There are 5 values for the first digit:
     1970               </p>
     1971               <ul>
     1972                  <li>1xx: Informational - Request received, continuing process</li>
     1973                  <li>2xx: Success - The action was successfully received, understood, and accepted</li>
     1974                  <li>3xx: Redirection - Further action must be taken in order to complete the request</li>
     1975                  <li>4xx: Client Error - The request contains bad syntax or cannot be fulfilled</li>
     1976                  <li>5xx: Server Error - The server failed to fulfill an apparently valid request</li>
     1977               </ul>
     1978               <div id="status.code.and.reason.phrase.codes">
     1979                  <p id="rfc.section.6.1.1.p.3">  The individual values of the numeric status codes defined for HTTP/1.1, and an example set of corresponding Reason-Phrase's,
     1980                     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.
     1981                  </p>
     1982               </div>
     1983               <div id="rfc.figure.u.49"></div><pre class="inline"><span id="rfc.iref.g.87"></span><span id="rfc.iref.g.88"></span><span id="rfc.iref.g.89"></span>   <a href="#status.code.and.reason.phrase.codes" class="smpl">Status-Code</a>    =
    19051984         "100"  ; <a href="#status.100" id="rfc.xref.status.100.1" title="100 Continue">Section&nbsp;10.1.1</a>: Continue
    19061985       | "101"  ; <a href="#status.101" id="rfc.xref.status.101.1" title="101 Switching Protocols">Section&nbsp;10.1.2</a>: Switching Protocols
     
    19482027   <a href="#status.code.and.reason.phrase.codes" class="smpl">Reason-Phrase</a>  = *&lt;<a href="#basic.rules.text" class="smpl" id="rfc.extref.t.24">TEXT</a>, excluding <a href="#basic.rules" class="smpl" id="rfc.extref.c.31">CR</a>, <a href="#basic.rules" class="smpl" id="rfc.extref.l.10">LF</a>&gt;
    19492028</pre><p id="rfc.section.6.1.1.p.5">HTTP status codes are extensible. HTTP applications are not required to understand the meaning of all registered status codes,
    1950          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
    1951          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
    1952          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
    1953          which will explain the unusual status.
    1954       </p>
    1955       <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a id="response.header.fields" href="#response.header.fields">Response Header Fields</a></h2>
    1956       <p id="rfc.section.6.2.p.1">The response-header fields allow the server to pass additional information about the response which cannot be placed in the
    1957          Status-Line. These header fields give information about the server and about further access to the resource identified by
    1958          the Request-URI.
    1959       </p>
    1960       <div id="rfc.figure.u.50"></div><pre class="inline"><span id="rfc.iref.g.90"></span>    <a href="#response.header.fields" class="smpl">response-header</a> = Accept-Ranges           ; <a href="#header.accept-ranges" id="rfc.xref.header.accept-ranges.1" title="Accept-Ranges">Section&nbsp;14.5</a>
     2029                  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
     2030                  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
     2031                  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
     2032                  which will explain the unusual status.
     2033               </p>
     2034            </div>
     2035         </div>
     2036         <div id="response.header.fields">
     2037            <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a>&nbsp;<a href="#response.header.fields">Response Header Fields</a></h2>
     2038            <p id="rfc.section.6.2.p.1">The response-header fields allow the server to pass additional information about the response which cannot be placed in the
     2039               Status-Line. These header fields give information about the server and about further access to the resource identified by
     2040               the Request-URI.
     2041            </p>
     2042            <div id="rfc.figure.u.50"></div><pre class="inline"><span id="rfc.iref.g.90"></span>    <a href="#response.header.fields" class="smpl">response-header</a> = Accept-Ranges           ; <a href="#header.accept-ranges" id="rfc.xref.header.accept-ranges.1" title="Accept-Ranges">Section&nbsp;14.5</a>
    19612043                    | Age                     ; <a href="#header.age" id="rfc.xref.header.age.1" title="Age">Section&nbsp;14.6</a>
    19622044                    | ETag                    ; <a href="#header.etag" id="rfc.xref.header.etag.2" title="ETag">Section&nbsp;14.19</a>
     
    19682050                    | WWW-Authenticate        ; <a href="#header.www-authenticate" id="rfc.xref.header.www-authenticate.1" title="WWW-Authenticate">Section&nbsp;14.47</a>
    19692051</pre><p id="rfc.section.6.2.p.3">Response-header field names can be extended reliably only in combination with a change in the protocol version. However, new
    1970          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
    1971          fields. Unrecognized header fields are treated as entity-header fields.
    1972       </p>
     2052               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
     2053               fields. Unrecognized header fields are treated as entity-header fields.
     2054            </p>
     2055         </div>
     2056      </div>
    19732057      <hr class="noprint">
    1974       <h1 id="rfc.section.7" class="np"><a href="#rfc.section.7">7.</a>&nbsp;<a id="entity" href="#entity">Entity</a></h1>
    1975       <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
    1976          fields and an entity-body, although some responses will only include the entity-headers.
    1977       </p>
    1978       <p id="rfc.section.7.p.2">In this section, both sender and recipient refer to either the client or the server, depending on who sends and who receives
    1979          the entity.
    1980       </p>
    1981       <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a id="entity.header.fields" href="#entity.header.fields">Entity Header Fields</a></h2>
    1982       <p id="rfc.section.7.1.p.1">Entity-header fields define metainformation about the entity-body or, if no body is present, about the resource identified
    1983          by the request. Some of this metainformation is <em class="bcp14">OPTIONAL</em>; some might be <em class="bcp14">REQUIRED</em> by portions of this specification.
    1984       </p>
    1985       <div id="rfc.figure.u.51"></div><pre class="inline"><span id="rfc.iref.g.91"></span><span id="rfc.iref.g.92"></span>    <a href="#entity.header.fields" class="smpl">entity-header</a>  = Allow                    ; <a href="#header.allow" id="rfc.xref.header.allow.2" title="Allow">Section&nbsp;14.7</a>
     2058      <div id="entity">
     2059         <h1 id="rfc.section.7" class="np"><a href="#rfc.section.7">7.</a>&nbsp;<a href="#entity">Entity</a></h1>
     2060         <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
     2061            fields and an entity-body, although some responses will only include the entity-headers.
     2062         </p>
     2063         <p id="rfc.section.7.p.2">In this section, both sender and recipient refer to either the client or the server, depending on who sends and who receives
     2064            the entity.
     2065         </p>
     2066         <div id="entity.header.fields">
     2067            <h2 id="rfc.section.7.1"><a href="#rfc.section.7.1">7.1</a>&nbsp;<a href="#entity.header.fields">Entity Header Fields</a></h2>
     2068            <p id="rfc.section.7.1.p.1">Entity-header fields define metainformation about the entity-body or, if no body is present, about the resource identified
     2069               by the request. Some of this metainformation is <em class="bcp14">OPTIONAL</em>; some might be <em class="bcp14">REQUIRED</em> by portions of this specification.
     2070            </p>
     2071            <div id="rfc.figure.u.51"></div><pre class="inline"><span id="rfc.iref.g.91"></span><span id="rfc.iref.g.92"></span>    <a href="#entity.header.fields" class="smpl">entity-header</a>  = Allow                    ; <a href="#header.allow" id="rfc.xref.header.allow.2" title="Allow">Section&nbsp;14.7</a>
    19862072                   | Content-Encoding         ; <a href="#header.content-encoding" id="rfc.xref.header.content-encoding.2" title="Content-Encoding">Section&nbsp;14.11</a>
    19872073                   | Content-Language         ; <a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section&nbsp;14.12</a>
     
    19972083    extension-header = <a href="#message.headers" class="smpl">message-header</a>
    19982084</pre><p id="rfc.section.7.1.p.3">The extension-header mechanism allows additional entity-header fields to be defined without changing the protocol, but these
    1999          fields cannot be assumed to be recognizable by the recipient. Unrecognized header fields <em class="bcp14">SHOULD</em> be ignored by the recipient and <em class="bcp14">MUST</em> be forwarded by transparent proxies.
    2000       </p>
    2001       <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a id="entity.body" href="#entity.body">Entity Body</a></h2>
    2002       <p id="rfc.section.7.2.p.1">The entity-body (if any) sent with an HTTP request or response is in a format and encoding defined by the entity-header fields.</p>
    2003       <div id="rfc.figure.u.52"></div><pre class="inline"><span id="rfc.iref.g.93"></span>    <a href="#entity.body" class="smpl">entity-body</a>    = *<a href="#basic.rules" class="smpl" id="rfc.extref.o.7">OCTET</a>
     2085               fields cannot be assumed to be recognizable by the recipient. Unrecognized header fields <em class="bcp14">SHOULD</em> be ignored by the recipient and <em class="bcp14">MUST</em> be forwarded by transparent proxies.
     2086            </p>
     2087         </div>
     2088         <div id="entity.body">
     2089            <h2 id="rfc.section.7.2"><a href="#rfc.section.7.2">7.2</a>&nbsp;<a href="#entity.body">Entity Body</a></h2>
     2090            <p id="rfc.section.7.2.p.1">The entity-body (if any) sent with an HTTP request or response is in a format and encoding defined by the entity-header fields.</p>
     2091            <div id="rfc.figure.u.52"></div><pre class="inline"><span id="rfc.iref.g.93"></span>    <a href="#entity.body" class="smpl">entity-body</a>    = *<a href="#basic.rules" class="smpl" id="rfc.extref.o.7">OCTET</a>
    20042092</pre><p id="rfc.section.7.2.p.3">An entity-body is only present in a message when a message-body is present, as described in <a href="#message.body" title="Message Body">Section&nbsp;4.3</a>. The entity-body is obtained from the message-body by decoding any Transfer-Encoding that might have been applied to ensure
    2005          safe and proper transfer of the message.
    2006       </p>
    2007       <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;<a id="type" href="#type">Type</a></h3>
    2008       <p id="rfc.section.7.2.1.p.1">When an entity-body is included with a message, the data type of that body is determined via the header fields Content-Type
    2009          and Content-Encoding. These define a two-layer, ordered encoding model:
    2010       </p>
    2011       <div id="rfc.figure.u.53"></div><pre class="text">    entity-body := Content-Encoding( Content-Type( data ) )
     2093               safe and proper transfer of the message.
     2094            </p>
     2095            <div id="type">
     2096               <h3 id="rfc.section.7.2.1"><a href="#rfc.section.7.2.1">7.2.1</a>&nbsp;<a href="#type">Type</a></h3>
     2097               <p id="rfc.section.7.2.1.p.1">When an entity-body is included with a message, the data type of that body is determined via the header fields Content-Type
     2098                  and Content-Encoding. These define a two-layer, ordered encoding model:
     2099               </p>
     2100               <div id="rfc.figure.u.53"></div><pre class="text">    entity-body := Content-Encoding( Content-Type( data ) )
    20122101</pre><p id="rfc.section.7.2.1.p.3">Content-Type specifies the media type of the underlying data. Content-Encoding may be used to indicate any additional content
    2013          codings applied to the data, usually for the purpose of data compression, that are a property of the requested resource. There
    2014          is no default encoding.
    2015       </p>
    2016       <p id="rfc.section.7.2.1.p.4">Any HTTP/1.1 message containing an entity-body <em class="bcp14">SHOULD</em> include a Content-Type header field defining the media type of that body. If and only if the media type is not given by a
    2017          Content-Type field, the recipient <em class="bcp14">MAY</em> attempt to guess the media type via inspection of its content and/or the name extension(s) of the URI used to identify the
    2018          resource. If the media type remains unknown, the recipient <em class="bcp14">SHOULD</em> treat it as type "application/octet-stream".
    2019       </p>
    2020       <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;<a id="entity.length" href="#entity.length">Entity Length</a></h3>
    2021       <p id="rfc.section.7.2.2.p.1">The entity-length of a message is the length of the message-body before any transfer-codings have been applied. <a href="#message.length" title="Message Length">Section&nbsp;4.4</a> defines how the transfer-length of a message-body is determined.
    2022       </p>
     2102                  codings applied to the data, usually for the purpose of data compression, that are a property of the requested resource. There
     2103                  is no default encoding.
     2104               </p>
     2105               <p id="rfc.section.7.2.1.p.4">Any HTTP/1.1 message containing an entity-body <em class="bcp14">SHOULD</em> include a Content-Type header field defining the media type of that body. If and only if the media type is not given by a
     2106                  Content-Type field, the recipient <em class="bcp14">MAY</em> attempt to guess the media type via inspection of its content and/or the name extension(s) of the URI used to identify the
     2107                  resource. If the media type remains unknown, the recipient <em class="bcp14">SHOULD</em> treat it as type "application/octet-stream".
     2108               </p>
     2109            </div>
     2110            <div id="entity.length">
     2111               <h3 id="rfc.section.7.2.2"><a href="#rfc.section.7.2.2">7.2.2</a>&nbsp;<a href="#entity.length">Entity Length</a></h3>
     2112               <p id="rfc.section.7.2.2.p.1">The entity-length of a message is the length of the message-body before any transfer-codings have been applied. <a href="#message.length" title="Message Length">Section&nbsp;4.4</a> defines how the transfer-length of a message-body is determined.
     2113               </p>
     2114            </div>
     2115         </div>
     2116      </div>
    20232117      <hr class="noprint">
    2024       <h1 id="rfc.section.8" class="np"><a href="#rfc.section.8">8.</a>&nbsp;<a id="connections" href="#connections">Connections</a></h1>
    2025       <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a id="persistent.connections" href="#persistent.connections">Persistent Connections</a></h2>
    2026       <h3 id="rfc.section.8.1.1"><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;<a id="persistent.purpose" href="#persistent.purpose">Purpose</a></h3>
    2027       <p id="rfc.section.8.1.1.p.1">Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP
    2028          servers and causing congestion on the Internet. The use of inline images and other associated data often require a client
    2029          to make multiple requests of the same server in a short amount of time. Analysis of these performance problems and results
    2030          from a prototype implementation are available <a href="#Pad1995" id="rfc.xref.Pad1995.1"><cite title="Improving HTTP Latency">[26]</cite></a>  <a href="#Spe" id="rfc.xref.Spe.1"><cite title="Analysis of HTTP Performance Problems">[30]</cite></a>. Implementation experience and measurements of actual HTTP/1.1 (RFC 2068) implementations show good results <a href="#Nie1997" id="rfc.xref.Nie1997.1"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[39]</cite></a>. Alternatives have also been explored, for example, T/TCP <a href="#Tou1998" id="rfc.xref.Tou1998.1"><cite title="Analysis of HTTP Performance">[27]</cite></a>.
    2031       </p>
    2032       <p id="rfc.section.8.1.1.p.2">Persistent HTTP connections have a number of advantages: </p>
    2033       <ul>
    2034          <li>By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways,
    2035             tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts.
    2036          </li>
    2037          <li>HTTP requests and responses can be pipelined on a connection. Pipelining allows a client to make multiple requests without
    2038             waiting for each response, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time.
    2039          </li>
    2040          <li>Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to
    2041             determine the congestion state of the network.
    2042          </li>
    2043          <li>Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.</li>
    2044          <li>HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using
    2045             future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old
    2046             semantics after an error is reported.
    2047          </li>
    2048       </ul>
    2049       <p id="rfc.section.8.1.1.p.3">HTTP implementations <em class="bcp14">SHOULD</em> implement persistent connections.
    2050       </p>
    2051       <h3 id="rfc.section.8.1.2"><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;<a id="persistent.overall" href="#persistent.overall">Overall Operation</a></h3>
    2052       <p id="rfc.section.8.1.2.p.1">A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior
    2053          of any HTTP connection. That is, unless otherwise indicated, the client <em class="bcp14">SHOULD</em> assume that the server will maintain a persistent connection, even after error responses from the server.
    2054       </p>
    2055       <p id="rfc.section.8.1.2.p.2">Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling
    2056          takes place using the Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.2" title="Connection">Section&nbsp;14.10</a>). Once a close has been signaled, the client <em class="bcp14">MUST NOT</em> send any more requests on that connection.
    2057       </p>
    2058       <h4 id="rfc.section.8.1.2.1"><a href="#rfc.section.8.1.2.1">8.1.2.1</a>&nbsp;<a id="persistent.negotiation" href="#persistent.negotiation">Negotiation</a></h4>
    2059       <p id="rfc.section.8.1.2.1.p.1">An HTTP/1.1 server <em class="bcp14">MAY</em> assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token
    2060          "close" was sent in the request. If the server chooses to close the connection immediately after sending the response, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
    2061       </p>
    2062       <p id="rfc.section.8.1.2.1.p.2">An HTTP/1.1 client <em class="bcp14">MAY</em> expect a connection to remain open, but would decide to keep it open based on whether the response from a server contains
    2063          a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than
    2064          that request, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
    2065       </p>
    2066       <p id="rfc.section.8.1.2.1.p.3">If either the client or the server sends the close token in the Connection header, that request becomes the last one for the
    2067          connection.
    2068       </p>
    2069       <p id="rfc.section.8.1.2.1.p.4">Clients and servers <em class="bcp14">SHOULD NOT</em> assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;19.6.2</a> for more information on backward compatibility with HTTP/1.0 clients.
    2070       </p>
    2071       <p id="rfc.section.8.1.2.1.p.5">In order to remain persistent, all messages on the connection <em class="bcp14">MUST</em> have a self-defined message length (i.e., one not defined by closure of the connection), as described in <a href="#message.length" title="Message Length">Section&nbsp;4.4</a>.
    2072       </p>
    2073       <h4 id="rfc.section.8.1.2.2"><a href="#rfc.section.8.1.2.2">8.1.2.2</a>&nbsp;<a id="pipelining" href="#pipelining">Pipelining</a></h4>
    2074       <p id="rfc.section.8.1.2.2.p.1">A client that supports persistent connections <em class="bcp14">MAY</em> "pipeline" its requests (i.e., send multiple requests without waiting for each response). A server <em class="bcp14">MUST</em> send its responses to those requests in the same order that the requests were received.
    2075       </p>
    2076       <p id="rfc.section.8.1.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses.
    2077       </p>
    2078       <p id="rfc.section.8.1.2.2.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent methods or non-idempotent sequences of methods (see <a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;9.1.2</a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to
    2079          send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status for the previous request.
    2080       </p>
    2081       <h3 id="rfc.section.8.1.3"><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;<a id="persistent.proxy" href="#persistent.proxy">Proxy Servers</a></h3>
    2082       <p id="rfc.section.8.1.3.p.1">It is especially important that proxies correctly implement the properties of the Connection header field as specified in <a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section&nbsp;14.10</a>.
    2083       </p>
    2084       <p id="rfc.section.8.1.3.p.2">The proxy server <em class="bcp14">MUST</em> signal persistent connections separately with its clients and the origin servers (or other proxy servers) that it connects
    2085          to. Each persistent connection applies to only one transport link.
    2086       </p>
    2087       <p id="rfc.section.8.1.3.p.3">A proxy server <em class="bcp14">MUST NOT</em> establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see RFC 2068 <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[33]</cite></a> for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients).
    2088       </p>
    2089       <h3 id="rfc.section.8.1.4"><a href="#rfc.section.8.1.4">8.1.4</a>&nbsp;<a id="persistent.practical" href="#persistent.practical">Practical Considerations</a></h3>
    2090       <p id="rfc.section.8.1.4.p.1">Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. Proxy servers
    2091          might make this a higher value since it is likely that the client will be making more connections through the same server.
    2092          The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client
    2093          or the server.
    2094       </p>
    2095       <p id="rfc.section.8.1.4.p.2">When a client or server wishes to time-out it <em class="bcp14">SHOULD</em> issue a graceful close on the transport connection. Clients and servers <em class="bcp14">SHOULD</em> both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does
    2096          not detect the other side's close promptly it could cause unnecessary resource drain on the network.
    2097       </p>
    2098       <p id="rfc.section.8.1.4.p.3">A client, server, or proxy <em class="bcp14">MAY</em> close the transport connection at any time. For example, a client might have started to send a new request at the same time
    2099          that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed
    2100          while it was idle, but from the client's point of view, a request is in progress.
    2101       </p>
    2102       <p id="rfc.section.8.1.4.p.4">This means that clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">SHOULD</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request
    2103          sequence is idempotent (see <a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;9.1.2</a>). Non-idempotent methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding
    2104          of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails.
    2105       </p>
    2106       <p id="rfc.section.8.1.4.p.5">Servers <em class="bcp14">SHOULD</em> always respond to at least one request per connection, if at all possible. Servers <em class="bcp14">SHOULD NOT</em> close a connection in the middle of transmitting a response, unless a network or client failure is suspected.
    2107       </p>
    2108       <p id="rfc.section.8.1.4.p.6">Clients that use persistent connections <em class="bcp14">SHOULD</em> limit the number of simultaneous connections that they maintain to a given server. A single-user client <em class="bcp14">SHOULD NOT</em> maintain more than 2 connections with any server or proxy. A proxy <em class="bcp14">SHOULD</em> use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines
    2109          are intended to improve HTTP response times and avoid congestion.
    2110       </p>
    2111       <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a id="message.transmission.requirements" href="#message.transmission.requirements">Message Transmission Requirements</a></h2>
    2112       <h3 id="rfc.section.8.2.1"><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;<a id="persistent.flow" href="#persistent.flow">Persistent Connections and Flow Control</a></h3>
    2113       <p id="rfc.section.8.2.1.p.1">HTTP/1.1 servers <em class="bcp14">SHOULD</em> maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating
    2114          connections with the expectation that clients will retry. The latter technique can exacerbate network congestion.
    2115       </p>
    2116       <h3 id="rfc.section.8.2.2"><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;<a id="persistent.monitor" href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></h3>
    2117       <p id="rfc.section.8.2.2.p.1">An HTTP/1.1 (or later) client sending a message-body <em class="bcp14">SHOULD</em> monitor the network connection for an error status while it is transmitting the request. If the client sees an error status,
    2118          it <em class="bcp14">SHOULD</em> immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>), a zero length chunk and empty trailer <em class="bcp14">MAY</em> be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client <em class="bcp14">MUST</em> close the connection.
    2119       </p>
    2120       <h3 id="rfc.section.8.2.3"><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;<a id="use.of.the.100.status" href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3>
    2121       <p id="rfc.section.8.2.3.p.1">The purpose of the <a href="#status.100" class="smpl">100 (Continue)</a> status (see <a href="#status.100" id="rfc.xref.status.100.2" title="100 Continue">Section&nbsp;10.1.1</a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing
    2122          to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either
    2123          be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking
    2124          at the body.
    2125       </p>
    2126       <p id="rfc.section.8.2.3.p.2">Requirements for HTTP/1.1 clients: </p>
    2127       <ul>
    2128          <li>If a client will wait for a <a href="#status.100" class="smpl">100 (Continue)</a> response before sending the request body, it <em class="bcp14">MUST</em> send an Expect request-header field (<a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section&nbsp;14.20</a>) with the "100-continue" expectation.
    2129          </li>
    2130          <li>A client <em class="bcp14">MUST NOT</em> send an Expect request-header field (<a href="#header.expect" id="rfc.xref.header.expect.3" title="Expect">Section&nbsp;14.20</a>) with the "100-continue" expectation if it does not intend to send a request body.
    2131          </li>
    2132       </ul>
    2133       <p id="rfc.section.8.2.3.p.3">Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect:
    2134          100-continue" without receiving either a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status or a <a href="#status.100" class="smpl">100 (Continue)</a> status. Therefore, when a client sends this header field to an origin server (possibly via a proxy) from which it has never
    2135          seen a <a href="#status.100" class="smpl">100 (Continue)</a> status, the client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the request body.
    2136       </p>
    2137       <p id="rfc.section.8.2.3.p.4">Requirements for HTTP/1.1 origin servers: </p>
    2138       <ul>
    2139          <li>Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with <a href="#status.100" class="smpl">100 (Continue)</a> status and continue to read from the input stream, or respond with a final status code. The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the <a href="#status.100" class="smpl">100 (Continue)</a> response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the requested method if it returns a final status code.
    2140          </li>
    2141          <li>An origin server <em class="bcp14">SHOULD NOT</em> send a <a href="#status.100" class="smpl">100 (Continue)</a> response if the request message does not include an Expect request-header field with the "100-continue" expectation, and <em class="bcp14">MUST NOT</em> send a <a href="#status.100" class="smpl">100 (Continue)</a> response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this rule: for compatibility
    2142             with RFC 2068, a server <em class="bcp14">MAY</em> send a <a href="#status.100" class="smpl">100 (Continue)</a> status in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header field with the "100-continue"
    2143             expectation. This exception, the purpose of which is to minimize any client processing delays associated with an undeclared
    2144             wait for <a href="#status.100" class="smpl">100 (Continue)</a> status, applies only to HTTP/1.1 requests, and not to requests with any other HTTP-version value.
    2145          </li>
    2146          <li>An origin server <em class="bcp14">MAY</em> omit a <a href="#status.100" class="smpl">100 (Continue)</a> response if it has already received some or all of the request body for the corresponding request.
    2147          </li>
    2148          <li>An origin server that sends a <a href="#status.100" class="smpl">100 (Continue)</a> response <em class="bcp14">MUST</em> ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection
    2149             prematurely.
    2150          </li>
    2151          <li>If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation,
    2152             the request includes a request body, and the server responds with a final status code before reading the entire request body
    2153             from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise,
    2154             the client might not reliably receive the response message. However, this requirement is not be construed as preventing a
    2155             server from defending itself against denial-of-service attacks, or from badly broken client implementations.
    2156          </li>
    2157       </ul>
    2158       <p id="rfc.section.8.2.3.p.5">Requirements for HTTP/1.1 proxies: </p>
    2159       <ul>
    2160          <li>If a proxy receives a request that includes an Expect request-header field with the "100-continue" expectation, and the proxy
    2161             either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop
    2162             server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field.
    2163          </li>
    2164          <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status.
    2165          </li>
    2166          <li>Proxies <em class="bcp14">SHOULD</em> maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers.
    2167          </li>
    2168          <li>A proxy <em class="bcp14">MUST NOT</em> forward a <a href="#status.100" class="smpl">100 (Continue)</a> response if the request message was received from an HTTP/1.0 (or earlier) client and did not include an Expect request-header
    2169             field with the "100-continue" expectation. This requirement overrides the general rule for forwarding of 1xx responses (see <a href="#status.1xx" title="Informational 1xx">Section&nbsp;10.1</a>).
    2170          </li>
    2171       </ul>
    2172       <h3 id="rfc.section.8.2.4"><a href="#rfc.section.8.2.4">8.2.4</a>&nbsp;<a id="connection.premature" href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></h3>
    2173       <p id="rfc.section.8.2.4.p.1">If an HTTP/1.1 client sends a request which includes a request body, but which does not include an Expect request-header field
    2174          with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 origin server, and if the
    2175          client sees the connection close before receiving any status from the server, the client <em class="bcp14">SHOULD</em> retry the request. If the client does retry this request, it <em class="bcp14">MAY</em> use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable response:
    2176       </p>
    2177       <ol>
    2178          <li>Initiate a new connection to the server</li>
    2179          <li>Transmit the request-headers</li>
    2180          <li>Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection),
    2181             or to a constant value of 5 seconds if the round-trip time is not available.
    2182          </li>
    2183          <li>Compute T = R * (2**N), where N is the number of previous retries of this request.</li>
    2184          <li>Wait either for an error response from the server, or for T seconds (whichever comes first)</li>
    2185          <li>If no error response is received, after T seconds transmit the body of the request.</li>
    2186          <li>If client sees that the connection is closed prematurely, repeat from step 1 until the request is accepted, an error response
    2187             is received, or the user becomes impatient and terminates the retry process.
    2188          </li>
    2189       </ol>
    2190       <p id="rfc.section.8.2.4.p.2">If at any point an error status is received, the client </p>
    2191       <ul>
    2192          <li><em class="bcp14">SHOULD NOT</em> continue and
    2193          </li>
    2194          <li><em class="bcp14">SHOULD</em> close the connection if it has not completed sending the request message.
    2195          </li>
    2196       </ul>
     2118      <div id="connections">
     2119         <h1 id="rfc.section.8" class="np"><a href="#rfc.section.8">8.</a>&nbsp;<a href="#connections">Connections</a></h1>
     2120         <div id="persistent.connections">
     2121            <h2 id="rfc.section.8.1"><a href="#rfc.section.8.1">8.1</a>&nbsp;<a href="#persistent.connections">Persistent Connections</a></h2>
     2122            <div id="persistent.purpose">
     2123               <h3 id="rfc.section.8.1.1"><a href="#rfc.section.8.1.1">8.1.1</a>&nbsp;<a href="#persistent.purpose">Purpose</a></h3>
     2124               <p id="rfc.section.8.1.1.p.1">Prior to persistent connections, a separate TCP connection was established to fetch each URL, increasing the load on HTTP
     2125                  servers and causing congestion on the Internet. The use of inline images and other associated data often require a client
     2126                  to make multiple requests of the same server in a short amount of time. Analysis of these performance problems and results
     2127                  from a prototype implementation are available <a href="#Pad1995" id="rfc.xref.Pad1995.1"><cite title="Improving HTTP Latency">[26]</cite></a> <a href="#Spe" id="rfc.xref.Spe.1"><cite title="Analysis of HTTP Performance Problems">[30]</cite></a>. Implementation experience and measurements of actual HTTP/1.1 (RFC 2068) implementations show good results <a href="#Nie1997" id="rfc.xref.Nie1997.1"><cite title="Network Performance Effects of HTTP/1.1, CSS1, and PNG">[39]</cite></a>. Alternatives have also been explored, for example, T/TCP <a href="#Tou1998" id="rfc.xref.Tou1998.1"><cite title="Analysis of HTTP Performance">[27]</cite></a>.
     2128               </p>
     2129               <p id="rfc.section.8.1.1.p.2">Persistent HTTP connections have a number of advantages: </p>
     2130               <ul>
     2131                  <li>By opening and closing fewer TCP connections, CPU time is saved in routers and hosts (clients, servers, proxies, gateways,
     2132                     tunnels, or caches), and memory used for TCP protocol control blocks can be saved in hosts.
     2133                  </li>
     2134                  <li>HTTP requests and responses can be pipelined on a connection. Pipelining allows a client to make multiple requests without
     2135                     waiting for each response, allowing a single TCP connection to be used much more efficiently, with much lower elapsed time.
     2136                  </li>
     2137                  <li>Network congestion is reduced by reducing the number of packets caused by TCP opens, and by allowing TCP sufficient time to
     2138                     determine the congestion state of the network.
     2139                  </li>
     2140                  <li>Latency on subsequent requests is reduced since there is no time spent in TCP's connection opening handshake.</li>
     2141                  <li>HTTP can evolve more gracefully, since errors can be reported without the penalty of closing the TCP connection. Clients using
     2142                     future versions of HTTP might optimistically try a new feature, but if communicating with an older server, retry with old
     2143                     semantics after an error is reported.
     2144                  </li>
     2145               </ul>
     2146               <p id="rfc.section.8.1.1.p.3">HTTP implementations <em class="bcp14">SHOULD</em> implement persistent connections.
     2147               </p>
     2148            </div>
     2149            <div id="persistent.overall">
     2150               <h3 id="rfc.section.8.1.2"><a href="#rfc.section.8.1.2">8.1.2</a>&nbsp;<a href="#persistent.overall">Overall Operation</a></h3>
     2151               <p id="rfc.section.8.1.2.p.1">A significant difference between HTTP/1.1 and earlier versions of HTTP is that persistent connections are the default behavior
     2152                  of any HTTP connection. That is, unless otherwise indicated, the client <em class="bcp14">SHOULD</em> assume that the server will maintain a persistent connection, even after error responses from the server.
     2153               </p>
     2154               <p id="rfc.section.8.1.2.p.2">Persistent connections provide a mechanism by which a client and a server can signal the close of a TCP connection. This signaling
     2155                  takes place using the Connection header field (<a href="#header.connection" id="rfc.xref.header.connection.2" title="Connection">Section&nbsp;14.10</a>). Once a close has been signaled, the client <em class="bcp14">MUST NOT</em> send any more requests on that connection.
     2156               </p>
     2157               <div id="persistent.negotiation">
     2158                  <h4 id="rfc.section.8.1.2.1"><a href="#rfc.section.8.1.2.1">8.1.2.1</a>&nbsp;<a href="#persistent.negotiation">Negotiation</a></h4>
     2159                  <p id="rfc.section.8.1.2.1.p.1">An HTTP/1.1 server <em class="bcp14">MAY</em> assume that a HTTP/1.1 client intends to maintain a persistent connection unless a Connection header including the connection-token
     2160                     "close" was sent in the request. If the server chooses to close the connection immediately after sending the response, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
     2161                  </p>
     2162                  <p id="rfc.section.8.1.2.1.p.2">An HTTP/1.1 client <em class="bcp14">MAY</em> expect a connection to remain open, but would decide to keep it open based on whether the response from a server contains
     2163                     a Connection header with the connection-token close. In case the client does not want to maintain a connection for more than
     2164                     that request, it <em class="bcp14">SHOULD</em> send a Connection header including the connection-token close.
     2165                  </p>
     2166                  <p id="rfc.section.8.1.2.1.p.3">If either the client or the server sends the close token in the Connection header, that request becomes the last one for the
     2167                     connection.
     2168                  </p>
     2169                  <p id="rfc.section.8.1.2.1.p.4">Clients and servers <em class="bcp14">SHOULD NOT</em> assume that a persistent connection is maintained for HTTP versions less than 1.1 unless it is explicitly signaled. See <a href="#compatibility.with.http.1.0.persistent.connections" title="Compatibility with HTTP/1.0 Persistent Connections">Appendix&nbsp;19.6.2</a> for more information on backward compatibility with HTTP/1.0 clients.
     2170                  </p>
     2171                  <p id="rfc.section.8.1.2.1.p.5">In order to remain persistent, all messages on the connection <em class="bcp14">MUST</em> have a self-defined message length (i.e., one not defined by closure of the connection), as described in <a href="#message.length" title="Message Length">Section&nbsp;4.4</a>.
     2172                  </p>
     2173               </div>
     2174               <div id="pipelining">
     2175                  <h4 id="rfc.section.8.1.2.2"><a href="#rfc.section.8.1.2.2">8.1.2.2</a>&nbsp;<a href="#pipelining">Pipelining</a></h4>
     2176                  <p id="rfc.section.8.1.2.2.p.1">A client that supports persistent connections <em class="bcp14">MAY</em> "pipeline" its requests (i.e., send multiple requests without waiting for each response). A server <em class="bcp14">MUST</em> send its responses to those requests in the same order that the requests were received.
     2177                  </p>
     2178                  <p id="rfc.section.8.1.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses.
     2179                  </p>
     2180                  <p id="rfc.section.8.1.2.2.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent methods or non-idempotent sequences of methods (see <a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;9.1.2</a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to
     2181                     send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status for the previous request.
     2182                  </p>
     2183               </div>
     2184            </div>
     2185            <div id="persistent.proxy">
     2186               <h3 id="rfc.section.8.1.3"><a href="#rfc.section.8.1.3">8.1.3</a>&nbsp;<a href="#persistent.proxy">Proxy Servers</a></h3>
     2187               <p id="rfc.section.8.1.3.p.1">It is especially important that proxies correctly implement the properties of the Connection header field as specified in <a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section&nbsp;14.10</a>.
     2188               </p>
     2189               <p id="rfc.section.8.1.3.p.2">The proxy server <em class="bcp14">MUST</em> signal persistent connections separately with its clients and the origin servers (or other proxy servers) that it connects
     2190                  to. Each persistent connection applies to only one transport link.
     2191               </p>
     2192               <p id="rfc.section.8.1.3.p.3">A proxy server <em class="bcp14">MUST NOT</em> establish a HTTP/1.1 persistent connection with an HTTP/1.0 client (but see RFC 2068 <a href="#RFC2068" id="rfc.xref.RFC2068.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[33]</cite></a> for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients).
     2193               </p>
     2194            </div>
     2195            <div id="persistent.practical">
     2196               <h3 id="rfc.section.8.1.4"><a href="#rfc.section.8.1.4">8.1.4</a>&nbsp;<a href="#persistent.practical">Practical Considerations</a></h3>
     2197               <p id="rfc.section.8.1.4.p.1">Servers will usually have some time-out value beyond which they will no longer maintain an inactive connection. Proxy servers
     2198                  might make this a higher value since it is likely that the client will be making more connections through the same server.
     2199                  The use of persistent connections places no requirements on the length (or existence) of this time-out for either the client
     2200                  or the server.
     2201               </p>
     2202               <p id="rfc.section.8.1.4.p.2">When a client or server wishes to time-out it <em class="bcp14">SHOULD</em> issue a graceful close on the transport connection. Clients and servers <em class="bcp14">SHOULD</em> both constantly watch for the other side of the transport close, and respond to it as appropriate. If a client or server does
     2203                  not detect the other side's close promptly it could cause unnecessary resource drain on the network.
     2204               </p>
     2205               <p id="rfc.section.8.1.4.p.3">A client, server, or proxy <em class="bcp14">MAY</em> close the transport connection at any time. For example, a client might have started to send a new request at the same time
     2206                  that the server has decided to close the "idle" connection. From the server's point of view, the connection is being closed
     2207                  while it was idle, but from the client's point of view, a request is in progress.
     2208               </p>
     2209               <p id="rfc.section.8.1.4.p.4">This means that clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">SHOULD</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request
     2210                  sequence is idempotent (see <a href="#idempotent.methods" title="Idempotent Methods">Section&nbsp;9.1.2</a>). Non-idempotent methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding
     2211                  of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails.
     2212               </p>
     2213               <p id="rfc.section.8.1.4.p.5">Servers <em class="bcp14">SHOULD</em> always respond to at least one request per connection, if at all possible. Servers <em class="bcp14">SHOULD NOT</em> close a connection in the middle of transmitting a response, unless a network or client failure is suspected.
     2214               </p>
     2215               <p id="rfc.section.8.1.4.p.6">Clients that use persistent connections <em class="bcp14">SHOULD</em> limit the number of simultaneous connections that they maintain to a given server. A single-user client <em class="bcp14">SHOULD NOT</em> maintain more than 2 connections with any server or proxy. A proxy <em class="bcp14">SHOULD</em> use up to 2*N connections to another server or proxy, where N is the number of simultaneously active users. These guidelines
     2216                  are intended to improve HTTP response times and avoid congestion.
     2217               </p>
     2218            </div>
     2219         </div>
     2220         <div id="message.transmission.requirements">
     2221            <h2 id="rfc.section.8.2"><a href="#rfc.section.8.2">8.2</a>&nbsp;<a href="#message.transmission.requirements">Message Transmission Requirements</a></h2>
     2222            <div id="persistent.flow">
     2223               <h3 id="rfc.section.8.2.1"><a href="#rfc.section.8.2.1">8.2.1</a>&nbsp;<a href="#persistent.flow">Persistent Connections and Flow Control</a></h3>
     2224               <p id="rfc.section.8.2.1.p.1">HTTP/1.1 servers <em class="bcp14">SHOULD</em> maintain persistent connections and use TCP's flow control mechanisms to resolve temporary overloads, rather than terminating
     2225                  connections with the expectation that clients will retry. The latter technique can exacerbate network congestion.
     2226               </p>
     2227            </div>
     2228            <div id="persistent.monitor">
     2229               <h3 id="rfc.section.8.2.2"><a href="#rfc.section.8.2.2">8.2.2</a>&nbsp;<a href="#persistent.monitor">Monitoring Connections for Error Status Messages</a></h3>
     2230               <p id="rfc.section.8.2.2.p.1">An HTTP/1.1 (or later) client sending a message-body <em class="bcp14">SHOULD</em> monitor the network connection for an error status while it is transmitting the request. If the client sees an error status,
     2231                  it <em class="bcp14">SHOULD</em> immediately cease transmitting the body. If the body is being sent using a "chunked" encoding (<a href="#transfer.codings" title="Transfer Codings">Section&nbsp;3.6</a>), a zero length chunk and empty trailer <em class="bcp14">MAY</em> be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client <em class="bcp14">MUST</em> close the connection.
     2232               </p>
     2233            </div>
     2234            <div id="use.of.the.100.status">
     2235               <h3 id="rfc.section.8.2.3"><a href="#rfc.section.8.2.3">8.2.3</a>&nbsp;<a href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3>
     2236               <p id="rfc.section.8.2.3.p.1">The purpose of the <a href="#status.100" class="smpl">100 (Continue)</a> status (see <a href="#status.100" id="rfc.xref.status.100.2" title="100 Continue">Section&nbsp;10.1.1</a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing
     2237                  to accept the request (based on the request headers) before the client sends the request body. In some cases, it might either
     2238                  be inappropriate or highly inefficient for the client to send the body if the server will reject the message without looking
     2239                  at the body.
     2240               </p>
     2241               <p id="rfc.section.8.2.3.p.2">Requirements for HTTP/1.1 clients: </p>
     2242               <ul>
     2243                  <li>If a client will wait for a <a href="#status.100" class="smpl">100 (Continue)</a> response before sending the request body, it <em class="bcp14">MUST</em> send an Expect request-header field (<a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section&nbsp;14.20</a>) with the "100-continue" expectation.
     2244                  </li>
     2245                  <li>A client <em class="bcp14">MUST NOT</em> send an Expect request-header field (<a href="#header.expect" id="rfc.xref.header.expect.3" title="Expect">Section&nbsp;14.20</a>) with the "100-continue" expectation if it does not intend to send a request body.
     2246                  </li>
     2247               </ul>
     2248               <p id="rfc.section.8.2.3.p.3">Because of the presence of older implementations, the protocol allows ambiguous situations in which a client may send "Expect:
     2249                  100-continue" without receiving either a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status or a <a href="#status.100" class="smpl">100 (Continue)</a> status. Therefore, when a client sends this header field to an origin server (possibly via a proxy) from which it has never
     2250                  seen a <a href="#status.100" class="smpl">100 (Continue)</a> status, the client <em class="bcp14">SHOULD NOT</em> wait for an indefinite period before sending the request body.
     2251               </p>
     2252               <p id="rfc.section.8.2.3.p.4">Requirements for HTTP/1.1 origin servers: </p>
     2253               <ul>
     2254                  <li>Upon receiving a request which includes an Expect request-header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with <a href="#status.100" class="smpl">100 (Continue)</a> status and continue to read from the input stream, or respond with a final status code. The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the <a href="#status.100" class="smpl">100 (Continue)</a> response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the requested method if it returns a final status code.
     2255                  </li>
     2256                  <li>An origin server <em class="bcp14">SHOULD NOT</em> send a <a href="#status.100" class="smpl">100 (Continue)</a> response if the request message does not include an Expect request-header field with the "100-continue" expectation, and <em class="bcp14">MUST NOT</em> send a <a href="#status.100" class="smpl">100 (Continue)</a> response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this rule: for compatibility
     2257                     with RFC 2068, a server <em class="bcp14">MAY</em> send a <a href="#status.100" class="smpl">100 (Continue)</a> status in response to an HTTP/1.1 PUT or POST request that does not include an Expect request-header field with the "100-continue"
     2258                     expectation. This exception, the purpose of which is to minimize any client processing delays associated with an undeclared
     2259                     wait for <a href="#status.100" class="smpl">100 (Continue)</a> status, applies only to HTTP/1.1 requests, and not to requests with any other HTTP-version value.
     2260                  </li>
     2261                  <li>An origin server <em class="bcp14">MAY</em> omit a <a href="#status.100" class="smpl">100 (Continue)</a> response if it has already received some or all of the request body for the corresponding request.
     2262                  </li>
     2263                  <li>An origin server that sends a <a href="#status.100" class="smpl">100 (Continue)</a> response <em class="bcp14">MUST</em> ultimately send a final status code, once the request body is received and processed, unless it terminates the transport connection
     2264                     prematurely.
     2265                  </li>
     2266                  <li>If an origin server receives a request that does not include an Expect request-header field with the "100-continue" expectation,
     2267                     the request includes a request body, and the server responds with a final status code before reading the entire request body
     2268                     from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise,
     2269                     the client might not reliably receive the response message. However, this requirement is not be construed as preventing a
     2270                     server from defending itself against denial-of-service attacks, or from badly broken client implementations.
     2271                  </li>
     2272               </ul>
     2273               <p id="rfc.section.8.2.3.p.5">Requirements for HTTP/1.1 proxies: </p>
     2274               <ul>
     2275                  <li>If a proxy receives a request that includes an Expect request-header field with the "100-continue" expectation, and the proxy
     2276                     either knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop
     2277                     server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field.
     2278                  </li>
     2279                  <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status.
     2280                  </li>
     2281                  <li>Proxies <em class="bcp14">SHOULD</em> maintain a cache recording the HTTP version numbers received from recently-referenced next-hop servers.
     2282                  </li>
     2283                  <li>A proxy <em class="bcp14">MUST NOT</em> forward a <a href="#status.100" class="smpl">100 (Continue)</a> response if the request message was received from an HTTP/1.0 (or earlier) client and did not include an Expect request-header
     2284                     field with the "100-continue" expectation. This requirement overrides the general rule for forwarding of 1xx responses (see <a href="#status.1xx" title="Informational 1xx">Section&nbsp;10.1</a>).
     2285                  </li>
     2286               </ul>
     2287            </div>
     2288            <div id="connection.premature">
     2289               <h3 id="rfc.section.8.2.4"><a href="#rfc.section.8.2.4">8.2.4</a>&nbsp;<a href="#connection.premature">Client Behavior if Server Prematurely Closes Connection</a></h3>
     2290               <p id="rfc.section.8.2.4.p.1">If an HTTP/1.1 client sends a request which includes a request body, but which does not include an Expect request-header field
     2291                  with the "100-continue" expectation, and if the client is not directly connected to an HTTP/1.1 origin server, and if the
     2292                  client sees the connection close before receiving any status from the server, the client <em class="bcp14">SHOULD</em> retry the request. If the client does retry this request, it <em class="bcp14">MAY</em> use the following "binary exponential backoff" algorithm to be assured of obtaining a reliable response:
     2293               </p>
     2294               <ol>
     2295                  <li>Initiate a new connection to the server</li>
     2296                  <li>Transmit the request-headers</li>
     2297                  <li>Initialize a variable R to the estimated round-trip time to the server (e.g., based on the time it took to establish the connection),
     2298                     or to a constant value of 5 seconds if the round-trip time is not available.
     2299                  </li>
     2300                  <li>Compute T = R * (2**N), where N is the number of previous retries of this request.</li>
     2301                  <li>Wait either for an error response from the server, or for T seconds (whichever comes first)</li>
     2302                  <li>If no error response is received, after T seconds transmit the body of the request.</li>
     2303                  <li>If client sees that the connection is closed prematurely, repeat from step 1 until the request is accepted, an error response
     2304                     is received, or the user becomes impatient and terminates the retry process.
     2305                  </li>
     2306               </ol>
     2307               <p id="rfc.section.8.2.4.p.2">If at any point an error status is received, the client </p>
     2308               <ul>
     2309                  <li><em class="bcp14">SHOULD NOT</em> continue and
     2310                  </li>
     2311                  <li><em class="bcp14">SHOULD</em> close the connection if it has not completed sending the request message.
     2312                  </li>
     2313               </ul>
     2314            </div>
     2315         </div>
     2316      </div>
    21972317      <hr class="noprint">
    2198       <h1 id="rfc.section.9" class="np"><a href="#rfc.section.9">9.</a>&nbsp;<a id="method.definitions" href="#method.definitions">Method Definitions</a></h1>
    2199       <p id="rfc.section.9.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
    2200          to share the same semantics for separately extended clients and servers.
    2201       </p>
    2202       <p id="rfc.section.9.p.2">The Host request-header field (<a href="#header.host" id="rfc.xref.header.host.2" title="Host">Section&nbsp;14.23</a>) <em class="bcp14">MUST</em> accompany all HTTP/1.1 requests.
    2203       </p>
    2204       <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a id="safe.and.idempotent" href="#safe.and.idempotent">Safe and Idempotent Methods</a></h2>
    2205       <h3 id="rfc.section.9.1.1"><a href="#rfc.section.9.1.1">9.1.1</a>&nbsp;<a id="safe.methods" href="#safe.methods">Safe Methods</a></h3>
    2206       <p id="rfc.section.9.1.1.p.1">Implementors should be aware that the software represents the user in their interactions over the Internet, and should be
    2207          careful to allow the user to be aware of any actions they might take which may have an unexpected significance to themselves
    2208          or others.
    2209       </p>
    2210       <p id="rfc.section.9.1.1.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
    2211          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
    2212          that a possibly unsafe action is being requested.
    2213       </p>
    2214       <p id="rfc.section.9.1.1.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;
    2215          in fact, some dynamic resources consider that a feature. The important distinction here is that the user did not request the
    2216          side-effects, so therefore cannot be held accountable for them.
    2217       </p>
    2218       <h3 id="rfc.section.9.1.2"><a href="#rfc.section.9.1.2">9.1.2</a>&nbsp;<a id="idempotent.methods" href="#idempotent.methods">Idempotent Methods</a></h3>
    2219       <p id="rfc.section.9.1.2.p.1">Methods can also have the property of "idempotence" in that (aside from error or expiration issues) the side-effects of N
    2220          &gt; 0 identical requests is the same as for a single request. The methods GET, HEAD, PUT and DELETE share this property. Also,
    2221          the methods OPTIONS and TRACE <em class="bcp14">SHOULD NOT</em> have side effects, and so are inherently idempotent.
    2222       </p>
    2223       <p id="rfc.section.9.1.2.p.2">However, it is possible that a sequence of several requests is non-idempotent, even if all of the methods executed in that
    2224          sequence are idempotent. (A sequence is idempotent if a single execution of the entire sequence always yields a result that
    2225          is not changed by a reexecution of all, or part, of that sequence.) For example, a sequence is non-idempotent if its result
    2226          depends on a value that is later modified in the same sequence.
    2227       </p>
    2228       <p id="rfc.section.9.1.2.p.3">A sequence that never has side effects is idempotent, by definition (provided that no concurrent operations are being executed
    2229          on the same set of resources).
    2230       </p>
    2231       <div id="rfc.iref.o.3"></div>
    2232       <div id="rfc.iref.m.2"></div>
    2233       <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a id="OPTIONS" href="#OPTIONS">OPTIONS</a></h2>
    2234       <p id="rfc.section.9.2.p.1">The OPTIONS method represents a request for information about the communication options available on the request/response
    2235          chain identified by the Request-URI. This method allows the client to determine the options and/or requirements associated
    2236          with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
    2237       </p>
    2238       <p id="rfc.section.9.2.p.2">Responses to this method are not cacheable.</p>
    2239       <p id="rfc.section.9.2.p.3">If the OPTIONS request includes an entity-body (as indicated by the presence of Content-Length or Transfer-Encoding), then
    2240          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
    2241          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.
    2242       </p>
    2243       <p id="rfc.section.9.2.p.4">If the Request-URI is an asterisk ("*"), the OPTIONS request is intended to apply to the server in general rather than to
    2244          a specific resource. Since a server's communication options typically depend on the resource, the "*" request is only useful
    2245          as a "ping" or "no-op" type of method; it does nothing beyond allowing the client to test the capabilities of the server.
    2246          For example, this can be used to test a proxy for HTTP/1.1 compliance (or lack thereof).
    2247       </p>
    2248       <p id="rfc.section.9.2.p.5">If the Request-URI is not an asterisk, the OPTIONS request applies only to the options that are available when communicating
    2249          with that resource.
    2250       </p>
    2251       <p id="rfc.section.9.2.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.,
    2252          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,
    2253          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".
    2254       </p>
    2255       <p id="rfc.section.9.2.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
    2256          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
    2257          request <em class="bcp14">MUST NOT</em> include a Max-Forwards field.
    2258       </p>
    2259       <div id="rfc.iref.g.94"></div>
    2260       <div id="rfc.iref.m.3"></div>
    2261       <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a id="GET" href="#GET">GET</a></h2>
    2262       <p id="rfc.section.9.3.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
    2263          refers to a data-producing process, it is the produced data which shall be returned as the entity in the response and not
    2264          the source text of the process, unless that text happens to be the output of the process.
    2265       </p>
    2266       <p id="rfc.section.9.3.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,
    2267          If-Match, If-None-Match, or If-Range header field. A conditional GET method requests that the entity be transferred only under
    2268          the circumstances described by the conditional header field(s). The conditional GET method is intended to reduce unnecessary
    2269          network usage by allowing cached entities to be refreshed without requiring multiple requests or transferring data already
    2270          held by the client.
    2271       </p>
    2272       <p id="rfc.section.9.3.p.3">The semantics of the GET method change to a "partial GET" if the request message includes a Range header field. A partial
    2273          GET requests that only part of the entity be transferred, as described in <a href="#header.range" id="rfc.xref.header.range.3" title="Range">Section&nbsp;14.35</a>. The partial GET method is intended to reduce unnecessary network usage by allowing partially-retrieved entities to be completed
    2274          without transferring data already held by the client.
    2275       </p>
    2276       <p id="rfc.section.9.3.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="#caching" title="Caching in HTTP">Section&nbsp;13</a>.
    2277       </p>
    2278       <p id="rfc.section.9.3.p.5">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URI's">Section&nbsp;15.1.3</a> for security considerations when used for forms.
    2279       </p>
    2280       <div id="rfc.iref.h.3"></div>
    2281       <div id="rfc.iref.m.4"></div>
    2282       <h2 id="rfc.section.9.4"><a href="#rfc.section.9.4">9.4</a>&nbsp;<a id="HEAD" href="#HEAD">HEAD</a></h2>
    2283       <p id="rfc.section.9.4.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
    2284          the entity implied by the request without transferring the entity-body itself. This method is often used for testing hypertext
    2285          links for validity, accessibility, and recent modification.
    2286       </p>
    2287       <p id="rfc.section.9.4.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
    2288          from the current entity (as would be indicated by a change in Content-Length, Content-MD5, ETag or Last-Modified), then the
    2289          cache <em class="bcp14">MUST</em> treat the cache entry as stale.
    2290       </p>
    2291       <div id="rfc.iref.p.2"></div>
    2292       <div id="rfc.iref.m.5"></div>
    2293       <h2 id="rfc.section.9.5"><a href="#rfc.section.9.5">9.5</a>&nbsp;<a id="POST" href="#POST">POST</a></h2>
    2294       <p id="rfc.section.9.5.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
    2295          the resource identified by the Request-URI in the Request-Line. POST is designed to allow a uniform method to cover the following
    2296          functions:
    2297       </p>
    2298       <ul>
    2299          <li>Annotation of existing resources;</li>
    2300          <li>Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles;</li>
    2301          <li>Providing a block of data, such as the result of submitting a form, to a data-handling process;</li>
    2302          <li>Extending a database through an append operation.</li>
    2303       </ul>
    2304       <p id="rfc.section.9.5.p.2">The actual function performed by the POST method is determined by the server and is usually dependent on the Request-URI.
    2305          The posted entity is subordinate to that URI in the same way that a file is subordinate to a directory containing it, a news
    2306          article is subordinate to a newsgroup to which it is posted, or a record is subordinate to a database.
    2307       </p>
    2308       <p id="rfc.section.9.5.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 <a href="#status.200" class="smpl">200 (OK)</a> or <a href="#status.204" class="smpl">204 (No Content)</a> is the appropriate response status, depending on whether or not the response includes an entity that describes the result.
    2309       </p>
    2310       <p id="rfc.section.9.5.p.4">If a resource has been created on the origin server, the response <em class="bcp14">SHOULD</em> be <a href="#status.201" class="smpl">201 (Created)</a> and contain an entity which describes the status of the request and refers to the new resource, and a Location header (see <a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section&nbsp;14.30</a>).
    2311       </p>
    2312       <p id="rfc.section.9.5.p.5">Responses to this method are not cacheable, unless the response includes appropriate Cache-Control or Expires header fields.
    2313          However, the <a href="#status.303" class="smpl">303 (See Other)</a> response can be used to direct the user agent to retrieve a cacheable resource.
    2314       </p>
    2315       <p id="rfc.section.9.5.p.6">POST requests <em class="bcp14">MUST</em> obey the message transmission requirements set out in <a href="#message.transmission.requirements" title="Message Transmission Requirements">Section&nbsp;8.2</a>.
    2316       </p>
    2317       <p id="rfc.section.9.5.p.7">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URI's">Section&nbsp;15.1.3</a> for security considerations.
    2318       </p>
    2319       <div id="rfc.iref.p.3"></div>
    2320       <div id="rfc.iref.m.6"></div>
    2321       <h2 id="rfc.section.9.6"><a href="#rfc.section.9.6">9.6</a>&nbsp;<a id="PUT" href="#PUT">PUT</a></h2>
    2322       <p id="rfc.section.9.6.p.1">The PUT method requests that the enclosed entity be stored under the supplied Request-URI. If the Request-URI refers to an
    2323          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
    2324          resource, and that URI is capable of being defined as a new resource by the requesting user agent, the origin server can create
    2325          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 <a href="#status.201" class="smpl">201 (Created)</a> response. If an existing resource is modified, either the <a href="#status.200" class="smpl">200 (OK)</a> or <a href="#status.204" class="smpl">204 (No Content)</a> 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,
    2326          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 <a href="#status.501" class="smpl">501 (Not Implemented)</a> response in such cases.
    2327       </p>
    2328       <p id="rfc.section.9.6.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.
    2329       </p>
    2330       <p id="rfc.section.9.6.p.3">The fundamental difference between the POST and PUT requests is reflected in the different meaning of the Request-URI. The
    2331          URI in a POST request identifies the resource that will handle the enclosed entity. That resource might be a data-accepting
    2332          process, a gateway to some other protocol, or a separate entity that accepts annotations. In contrast, the URI in a PUT request
    2333          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,
    2334          it <em class="bcp14">MUST</em> send a <a href="#status.301" class="smpl">301 (Moved Permanently)</a> response; the user agent <em class="bcp14">MAY</em> then make its own decision regarding whether or not to redirect the request.
    2335       </p>
    2336       <p id="rfc.section.9.6.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
    2337          is separate from the URI identifying each particular version. In this case, a PUT request on a general URI might result in
    2338          several other URIs being defined by the origin server.
    2339       </p>
    2340       <p id="rfc.section.9.6.p.5">HTTP/1.1 does not define how a PUT method affects the state of an origin server.</p>
    2341       <p id="rfc.section.9.6.p.6">PUT requests <em class="bcp14">MUST</em> obey the message transmission requirements set out in <a href="#message.transmission.requirements" title="Message Transmission Requirements">Section&nbsp;8.2</a>.
    2342       </p>
    2343       <p id="rfc.section.9.6.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.
    2344       </p>
    2345       <div id="rfc.iref.d.3"></div>
    2346       <div id="rfc.iref.m.7"></div>
    2347       <h2 id="rfc.section.9.7"><a href="#rfc.section.9.7">9.7</a>&nbsp;<a id="DELETE" href="#DELETE">DELETE</a></h2>
    2348       <p id="rfc.section.9.7.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
    2349          has been carried out, even if the status code returned from the origin server indicates that the action has been completed
    2350          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
    2351          location.
    2352       </p>
    2353       <p id="rfc.section.9.7.p.2">A successful response <em class="bcp14">SHOULD</em> be <a href="#status.200" class="smpl">200 (OK)</a> if the response includes an entity describing the status, <a href="#status.202" class="smpl">202 (Accepted)</a> if the action has not yet been enacted, or <a href="#status.204" class="smpl">204 (No Content)</a> if the action has been enacted but the response does not include an entity.
    2354       </p>
    2355       <p id="rfc.section.9.7.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.
    2356       </p>
    2357       <div id="rfc.iref.t.2"></div>
    2358       <div id="rfc.iref.m.8"></div>
    2359       <h2 id="rfc.section.9.8"><a href="#rfc.section.9.8">9.8</a>&nbsp;<a id="TRACE" href="#TRACE">TRACE</a></h2>
    2360       <p id="rfc.section.9.8.p.1">The TRACE method is used to invoke a remote, application-layer loop-back of the request message. The final recipient of the
    2361          request <em class="bcp14">SHOULD</em> reflect the message received back to the client as the entity-body of a <a href="#status.200" class="smpl">200 (OK)</a> response. The final recipient is either the origin server or the first proxy or gateway to receive a Max-Forwards value of
    2362          zero (0) in the request (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.2" title="Max-Forwards">Section&nbsp;14.31</a>). A TRACE request <em class="bcp14">MUST NOT</em> include an entity.
    2363       </p>
    2364       <p id="rfc.section.9.8.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
    2365          or diagnostic information. The value of the Via header field (<a href="#header.via" id="rfc.xref.header.via.2" title="Via">Section&nbsp;14.45</a>) is of particular interest, since it acts as a trace of the request chain. Use of the Max-Forwards header field allows the
    2366          client to limit the length of the request chain, which is useful for testing a chain of proxies forwarding messages in an
    2367          infinite loop.
    2368       </p>
    2369       <p id="rfc.section.9.8.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.
    2370       </p>
    2371       <div id="rfc.iref.c.12"></div>
    2372       <div id="rfc.iref.m.9"></div>
    2373       <h2 id="rfc.section.9.9"><a href="#rfc.section.9.9">9.9</a>&nbsp;<a id="CONNECT" href="#CONNECT">CONNECT</a></h2>
    2374       <p id="rfc.section.9.9.p.1">This specification reserves the method name CONNECT for use with a proxy that can dynamically switch to being a tunnel (e.g.
    2375          SSL tunneling <a href="#Luo1998" id="rfc.xref.Luo1998.1"><cite title="Tunneling TCP based protocols through Web proxy servers">[44]</cite></a>).
    2376       </p>
     2318      <div id="method.definitions">
     2319         <h1 id="rfc.section.9" class="np"><a href="#rfc.section.9">9.</a>&nbsp;<a href="#method.definitions">Method Definitions</a></h1>
     2320         <p id="rfc.section.9.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
     2321            to share the same semantics for separately extended clients and servers.
     2322         </p>
     2323         <p id="rfc.section.9.p.2">The Host request-header field (<a href="#header.host" id="rfc.xref.header.host.2" title="Host">Section&nbsp;14.23</a>) <em class="bcp14">MUST</em> accompany all HTTP/1.1 requests.
     2324         </p>
     2325         <div id="safe.and.idempotent">
     2326            <h2 id="rfc.section.9.1"><a href="#rfc.section.9.1">9.1</a>&nbsp;<a href="#safe.and.idempotent">Safe and Idempotent Methods</a></h2>
     2327            <div id="safe.methods">
     2328               <h3 id="rfc.section.9.1.1"><a href="#rfc.section.9.1.1">9.1.1</a>&nbsp;<a href="#safe.methods">Safe Methods</a></h3>
     2329               <p id="rfc.section.9.1.1.p.1">Implementors should be aware that the software represents the user in their interactions over the Internet, and should be
     2330                  careful to allow the user to be aware of any actions they might take which may have an unexpected significance to themselves
     2331                  or others.
     2332               </p>
     2333               <p id="rfc.section.9.1.1.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
     2334                  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
     2335                  that a possibly unsafe action is being requested.
     2336               </p>
     2337               <p id="rfc.section.9.1.1.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;
     2338                  in fact, some dynamic resources consider that a feature. The important distinction here is that the user did not request the
     2339                  side-effects, so therefore cannot be held accountable for them.
     2340               </p>
     2341            </div>
     2342            <div id="idempotent.methods">
     2343               <h3 id="rfc.section.9.1.2"><a href="#rfc.section.9.1.2">9.1.2</a>&nbsp;<a href="#idempotent.methods">Idempotent Methods</a></h3>
     2344               <p id="rfc.section.9.1.2.p.1">Methods can also have the property of "idempotence" in that (aside from error or expiration issues) the side-effects of N
     2345                  &gt; 0 identical requests is the same as for a single request. The methods GET, HEAD, PUT and DELETE share this property. Also,
     2346                  the methods OPTIONS and TRACE <em class="bcp14">SHOULD NOT</em> have side effects, and so are inherently idempotent.
     2347               </p>
     2348               <p id="rfc.section.9.1.2.p.2">However, it is possible that a sequence of several requests is non-idempotent, even if all of the methods executed in that
     2349                  sequence are idempotent. (A sequence is idempotent if a single execution of the entire sequence always yields a result that
     2350                  is not changed by a reexecution of all, or part, of that sequence.) For example, a sequence is non-idempotent if its result
     2351                  depends on a value that is later modified in the same sequence.
     2352               </p>
     2353               <p id="rfc.section.9.1.2.p.3">A sequence that never has side effects is idempotent, by definition (provided that no concurrent operations are being executed
     2354                  on the same set of resources).
     2355               </p>
     2356            </div>
     2357         </div>
     2358         <div id="OPTIONS">
     2359            <div id="rfc.iref.o.3"></div>
     2360            <div id="rfc.iref.m.2"></div>
     2361            <h2 id="rfc.section.9.2"><a href="#rfc.section.9.2">9.2</a>&nbsp;<a href="#OPTIONS">OPTIONS</a></h2>
     2362            <p id="rfc.section.9.2.p.1">The OPTIONS method represents a request for information about the communication options available on the request/response
     2363               chain identified by the Request-URI. This method allows the client to determine the options and/or requirements associated
     2364               with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
     2365            </p>
     2366            <p id="rfc.section.9.2.p.2">Responses to this method are not cacheable.</p>
     2367            <p id="rfc.section.9.2.p.3">If the OPTIONS request includes an entity-body (as indicated by the presence of Content-Length or Transfer-Encoding), then
     2368               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
     2369               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.
     2370            </p>
     2371            <p id="rfc.section.9.2.p.4">If the Request-URI is an asterisk ("*"), the OPTIONS request is intended to apply to the server in general rather than to
     2372               a specific resource. Since a server's communication options typically depend on the resource, the "*" request is only useful
     2373               as a "ping" or "no-op" type of method; it does nothing beyond allowing the client to test the capabilities of the server.
     2374               For example, this can be used to test a proxy for HTTP/1.1 compliance (or lack thereof).
     2375            </p>
     2376            <p id="rfc.section.9.2.p.5">If the Request-URI is not an asterisk, the OPTIONS request applies only to the options that are available when communicating
     2377               with that resource.
     2378            </p>
     2379            <p id="rfc.section.9.2.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.,
     2380               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,
     2381               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".
     2382            </p>
     2383            <p id="rfc.section.9.2.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
     2384               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
     2385               request <em class="bcp14">MUST NOT</em> include a Max-Forwards field.
     2386            </p>
     2387         </div>
     2388         <div id="GET">
     2389            <div id="rfc.iref.g.94"></div>
     2390            <div id="rfc.iref.m.3"></div>
     2391            <h2 id="rfc.section.9.3"><a href="#rfc.section.9.3">9.3</a>&nbsp;<a href="#GET">GET</a></h2>
     2392            <p id="rfc.section.9.3.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
     2393               refers to a data-producing process, it is the produced data which shall be returned as the entity in the response and not
     2394               the source text of the process, unless that text happens to be the output of the process.
     2395            </p>
     2396            <p id="rfc.section.9.3.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,
     2397               If-Match, If-None-Match, or If-Range header field. A conditional GET method requests that the entity be transferred only under
     2398               the circumstances described by the conditional header field(s). The conditional GET method is intended to reduce unnecessary
     2399               network usage by allowing cached entities to be refreshed without requiring multiple requests or transferring data already
     2400               held by the client.
     2401            </p>
     2402            <p id="rfc.section.9.3.p.3">The semantics of the GET method change to a "partial GET" if the request message includes a Range header field. A partial
     2403               GET requests that only part of the entity be transferred, as described in <a href="#header.range" id="rfc.xref.header.range.3" title="Range">Section&nbsp;14.35</a>. The partial GET method is intended to reduce unnecessary network usage by allowing partially-retrieved entities to be completed
     2404               without transferring data already held by the client.
     2405            </p>
     2406            <p id="rfc.section.9.3.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="#caching" title="Caching in HTTP">Section&nbsp;13</a>.
     2407            </p>
     2408            <p id="rfc.section.9.3.p.5">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URI's">Section&nbsp;15.1.3</a> for security considerations when used for forms.
     2409            </p>
     2410         </div>
     2411         <div id="HEAD">
     2412            <div id="rfc.iref.h.3"></div>
     2413            <div id="rfc.iref.m.4"></div>
     2414            <h2 id="rfc.section.9.4"><a href="#rfc.section.9.4">9.4</a>&nbsp;<a href="#HEAD">HEAD</a></h2>
     2415            <p id="rfc.section.9.4.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
     2416               the entity implied by the request without transferring the entity-body itself. This method is often used for testing hypertext
     2417               links for validity, accessibility, and recent modification.
     2418            </p>
     2419            <p id="rfc.section.9.4.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
     2420               from the current entity (as would be indicated by a change in Content-Length, Content-MD5, ETag or Last-Modified), then the
     2421               cache <em class="bcp14">MUST</em> treat the cache entry as stale.
     2422            </p>
     2423         </div>
     2424         <div id="POST">
     2425            <div id="rfc.iref.p.2"></div>
     2426            <div id="rfc.iref.m.5"></div>
     2427            <h2 id="rfc.section.9.5"><a href="#rfc.section.9.5">9.5</a>&nbsp;<a href="#POST">POST</a></h2>
     2428            <p id="rfc.section.9.5.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
     2429               the resource identified by the Request-URI in the Request-Line. POST is designed to allow a uniform method to cover the following
     2430               functions:
     2431            </p>
     2432            <ul>
     2433               <li>Annotation of existing resources;</li>
     2434               <li>Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles;</li>
     2435               <li>Providing a block of data, such as the result of submitting a form, to a data-handling process;</li>
     2436               <li>Extending a database through an append operation.</li>
     2437            </ul>
     2438            <p id="rfc.section.9.5.p.2">The actual function performed by the POST method is determined by the server and is usually dependent on the Request-URI.
     2439               The posted entity is subordinate to that URI in the same way that a file is subordinate to a directory containing it, a news
     2440               article is subordinate to a newsgroup to which it is posted, or a record is subordinate to a database.
     2441            </p>
     2442            <p id="rfc.section.9.5.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 <a href="#status.200" class="smpl">200 (OK)</a> or <a href="#status.204" class="smpl">204 (No Content)</a> is the appropriate response status, depending on whether or not the response includes an entity that describes the result.
     2443            </p>
     2444            <p id="rfc.section.9.5.p.4">If a resource has been created on the origin server, the response <em class="bcp14">SHOULD</em> be <a href="#status.201" class="smpl">201 (Created)</a> and contain an entity which describes the status of the request and refers to the new resource, and a Location header (see <a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section&nbsp;14.30</a>).
     2445            </p>
     2446            <p id="rfc.section.9.5.p.5">Responses to this method are not cacheable, unless the response includes appropriate Cache-Control or Expires header fields.
     2447               However, the <a href="#status.303" class="smpl">303 (See Other)</a> response can be used to direct the user agent to retrieve a cacheable resource.
     2448            </p>
     2449            <p id="rfc.section.9.5.p.6">POST requests <em class="bcp14">MUST</em> obey the message transmission requirements set out in <a href="#message.transmission.requirements" title="Message Transmission Requirements">Section&nbsp;8.2</a>.
     2450            </p>
     2451            <p id="rfc.section.9.5.p.7">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URI's">Section&nbsp;15.1.3</a> for security considerations.<