Changeset 1854
- Timestamp:
- 03/09/12 05:54:40 (10 years ago)
- Location:
- draft-ietf-httpbis/latest
- Files:
-
- 2 edited
Legend:
- Unmodified
- Added
- Removed
-
draft-ietf-httpbis/latest/p2-semantics.html
r1853 r1854 480 480 <link rel="Chapter" title="8 Protocol Parameters" href="#rfc.section.8"> 481 481 <link rel="Chapter" title="9 Payload" href="#rfc.section.9"> 482 <link rel="Chapter" title="10 Content Negotiation" href="#rfc.section.10"> 483 <link rel="Chapter" title="11 Header Field Definitions" href="#rfc.section.11"> 484 <link rel="Chapter" title="12 IANA Considerations" href="#rfc.section.12"> 485 <link rel="Chapter" title="13 Security Considerations" href="#rfc.section.13"> 486 <link rel="Chapter" title="14 Acknowledgments" href="#rfc.section.14"> 487 <link rel="Chapter" href="#rfc.section.15" title="15 References"> 482 <link rel="Chapter" title="10 Header Field Definitions" href="#rfc.section.10"> 483 <link rel="Chapter" title="11 IANA Considerations" href="#rfc.section.11"> 484 <link rel="Chapter" title="12 Security Considerations" href="#rfc.section.12"> 485 <link rel="Chapter" title="13 Acknowledgments" href="#rfc.section.13"> 486 <link rel="Chapter" href="#rfc.section.14" title="14 References"> 488 487 <link rel="Appendix" title="A Differences between HTTP and MIME" href="#rfc.section.A"> 489 488 <link rel="Appendix" title="B Additional Features" href="#rfc.section.B"> … … 591 590 <li><a href="#rfc.section.3.2">3.2</a> <a href="#representation.header.fields">Representation Header Fields</a></li> 592 591 <li><a href="#rfc.section.3.3">3.3</a> <a href="#representation.data">Representation Data</a></li> 592 <li><a href="#rfc.section.3.4">3.4</a> <a href="#content.negotiation">Content Negotiation</a><ul> 593 <li><a href="#rfc.section.3.4.1">3.4.1</a> <a href="#server-driven.negotiation">Server-driven Negotiation</a></li> 594 <li><a href="#rfc.section.3.4.2">3.4.2</a> <a href="#agent-driven.negotiation">Agent-driven Negotiation</a></li> 595 <li><a href="#rfc.section.3.4.3">3.4.3</a> <a href="#quality.values">Quality Values</a></li> 596 </ul> 597 </li> 593 598 </ul> 594 599 </li> … … 696 701 </ul> 697 702 </li> 698 <li><a href="#rfc.section.10">10.</a> <a href="#content.negotiation">Content Negotiation</a><ul> 699 <li><a href="#rfc.section.10.1">10.1</a> <a href="#server-driven.negotiation">Server-driven Negotiation</a></li> 700 <li><a href="#rfc.section.10.2">10.2</a> <a href="#agent-driven.negotiation">Agent-driven Negotiation</a></li> 701 <li><a href="#rfc.section.10.3">10.3</a> <a href="#quality.values">Quality Values</a></li> 703 <li><a href="#rfc.section.10">10.</a> <a href="#header.field.definitions">Header Field Definitions</a><ul> 704 <li><a href="#rfc.section.10.1">10.1</a> <a href="#header.accept">Accept</a></li> 705 <li><a href="#rfc.section.10.2">10.2</a> <a href="#header.accept-charset">Accept-Charset</a></li> 706 <li><a href="#rfc.section.10.3">10.3</a> <a href="#header.accept-encoding">Accept-Encoding</a></li> 707 <li><a href="#rfc.section.10.4">10.4</a> <a href="#header.accept-language">Accept-Language</a></li> 708 <li><a href="#rfc.section.10.5">10.5</a> <a href="#header.allow">Allow</a></li> 709 <li><a href="#rfc.section.10.6">10.6</a> <a href="#header.content-encoding">Content-Encoding</a></li> 710 <li><a href="#rfc.section.10.7">10.7</a> <a href="#header.content-language">Content-Language</a></li> 711 <li><a href="#rfc.section.10.8">10.8</a> <a href="#header.content-location">Content-Location</a></li> 712 <li><a href="#rfc.section.10.9">10.9</a> <a href="#header.content-type">Content-Type</a></li> 713 <li><a href="#rfc.section.10.10">10.10</a> <a href="#header.date">Date</a></li> 714 <li><a href="#rfc.section.10.11">10.11</a> <a href="#header.expect">Expect</a></li> 715 <li><a href="#rfc.section.10.12">10.12</a> <a href="#header.from">From</a></li> 716 <li><a href="#rfc.section.10.13">10.13</a> <a href="#header.location">Location</a></li> 717 <li><a href="#rfc.section.10.14">10.14</a> <a href="#header.max-forwards">Max-Forwards</a></li> 718 <li><a href="#rfc.section.10.15">10.15</a> <a href="#header.referer">Referer</a></li> 719 <li><a href="#rfc.section.10.16">10.16</a> <a href="#header.retry-after">Retry-After</a></li> 720 <li><a href="#rfc.section.10.17">10.17</a> <a href="#header.server">Server</a></li> 721 <li><a href="#rfc.section.10.18">10.18</a> <a href="#header.user-agent">User-Agent</a></li> 702 722 </ul> 703 723 </li> 704 <li><a href="#rfc.section.11">11.</a> <a href="#header.field.definitions">Header Field Definitions</a><ul> 705 <li><a href="#rfc.section.11.1">11.1</a> <a href="#header.accept">Accept</a></li> 706 <li><a href="#rfc.section.11.2">11.2</a> <a href="#header.accept-charset">Accept-Charset</a></li> 707 <li><a href="#rfc.section.11.3">11.3</a> <a href="#header.accept-encoding">Accept-Encoding</a></li> 708 <li><a href="#rfc.section.11.4">11.4</a> <a href="#header.accept-language">Accept-Language</a></li> 709 <li><a href="#rfc.section.11.5">11.5</a> <a href="#header.allow">Allow</a></li> 710 <li><a href="#rfc.section.11.6">11.6</a> <a href="#header.content-encoding">Content-Encoding</a></li> 711 <li><a href="#rfc.section.11.7">11.7</a> <a href="#header.content-language">Content-Language</a></li> 712 <li><a href="#rfc.section.11.8">11.8</a> <a href="#header.content-location">Content-Location</a></li> 713 <li><a href="#rfc.section.11.9">11.9</a> <a href="#header.content-type">Content-Type</a></li> 714 <li><a href="#rfc.section.11.10">11.10</a> <a href="#header.date">Date</a></li> 715 <li><a href="#rfc.section.11.11">11.11</a> <a href="#header.expect">Expect</a></li> 716 <li><a href="#rfc.section.11.12">11.12</a> <a href="#header.from">From</a></li> 717 <li><a href="#rfc.section.11.13">11.13</a> <a href="#header.location">Location</a></li> 718 <li><a href="#rfc.section.11.14">11.14</a> <a href="#header.max-forwards">Max-Forwards</a></li> 719 <li><a href="#rfc.section.11.15">11.15</a> <a href="#header.referer">Referer</a></li> 720 <li><a href="#rfc.section.11.16">11.16</a> <a href="#header.retry-after">Retry-After</a></li> 721 <li><a href="#rfc.section.11.17">11.17</a> <a href="#header.server">Server</a></li> 722 <li><a href="#rfc.section.11.18">11.18</a> <a href="#header.user-agent">User-Agent</a></li> 723 </ul> 724 </li> 725 <li><a href="#rfc.section.12">12.</a> <a href="#IANA.considerations">IANA Considerations</a><ul> 726 <li><a href="#rfc.section.12.1">12.1</a> <a href="#method.registry">Method Registry</a><ul> 727 <li><a href="#rfc.section.12.1.1">12.1.1</a> <a href="#method.procedure">Procedure</a></li> 728 <li><a href="#rfc.section.12.1.2">12.1.2</a> <a href="#considerations.for.new.methods">Considerations for New Methods</a></li> 729 <li><a href="#rfc.section.12.1.3">12.1.3</a> <a href="#method.registration">Registrations</a></li> 724 <li><a href="#rfc.section.11">11.</a> <a href="#IANA.considerations">IANA Considerations</a><ul> 725 <li><a href="#rfc.section.11.1">11.1</a> <a href="#method.registry">Method Registry</a><ul> 726 <li><a href="#rfc.section.11.1.1">11.1.1</a> <a href="#method.procedure">Procedure</a></li> 727 <li><a href="#rfc.section.11.1.2">11.1.2</a> <a href="#considerations.for.new.methods">Considerations for New Methods</a></li> 728 <li><a href="#rfc.section.11.1.3">11.1.3</a> <a href="#method.registration">Registrations</a></li> 730 729 </ul> 731 730 </li> 732 <li><a href="#rfc.section.1 2.2">12.2</a> <a href="#status.code.registry">Status Code Registry</a><ul>733 <li><a href="#rfc.section.1 2.2.1">12.2.1</a> <a href="#status.code.procedure">Procedure</a></li>734 <li><a href="#rfc.section.1 2.2.2">12.2.2</a> <a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></li>735 <li><a href="#rfc.section.1 2.2.3">12.2.3</a> <a href="#status.code.registration">Registrations</a></li>731 <li><a href="#rfc.section.11.2">11.2</a> <a href="#status.code.registry">Status Code Registry</a><ul> 732 <li><a href="#rfc.section.11.2.1">11.2.1</a> <a href="#status.code.procedure">Procedure</a></li> 733 <li><a href="#rfc.section.11.2.2">11.2.2</a> <a href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></li> 734 <li><a href="#rfc.section.11.2.3">11.2.3</a> <a href="#status.code.registration">Registrations</a></li> 736 735 </ul> 737 736 </li> 738 <li><a href="#rfc.section.1 2.3">12.3</a> <a href="#header.field.registry">Header Field Registry</a><ul>739 <li><a href="#rfc.section.1 2.3.1">12.3.1</a> <a href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></li>740 <li><a href="#rfc.section.1 2.3.2">12.3.2</a> <a href="#header.field.registration">Registrations</a></li>737 <li><a href="#rfc.section.11.3">11.3</a> <a href="#header.field.registry">Header Field Registry</a><ul> 738 <li><a href="#rfc.section.11.3.1">11.3.1</a> <a href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></li> 739 <li><a href="#rfc.section.11.3.2">11.3.2</a> <a href="#header.field.registration">Registrations</a></li> 741 740 </ul> 742 741 </li> 743 <li><a href="#rfc.section.1 2.4">12.4</a> <a href="#content.coding.registry">Content Coding Registry</a><ul>744 <li><a href="#rfc.section.1 2.4.1">12.4.1</a> <a href="#content.coding.procedure">Procedure</a></li>745 <li><a href="#rfc.section.1 2.4.2">12.4.2</a> <a href="#content.coding.registration">Registrations</a></li>742 <li><a href="#rfc.section.11.4">11.4</a> <a href="#content.coding.registry">Content Coding Registry</a><ul> 743 <li><a href="#rfc.section.11.4.1">11.4.1</a> <a href="#content.coding.procedure">Procedure</a></li> 744 <li><a href="#rfc.section.11.4.2">11.4.2</a> <a href="#content.coding.registration">Registrations</a></li> 746 745 </ul> 747 746 </li> 748 747 </ul> 749 748 </li> 750 <li><a href="#rfc.section.1 3">13.</a> <a href="#security.considerations">Security Considerations</a><ul>751 <li><a href="#rfc.section.1 3.1">13.1</a> <a href="#security.sensitive">Transfer of Sensitive Information</a></li>752 <li><a href="#rfc.section.1 3.2">13.2</a> <a href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URIs</a></li>753 <li><a href="#rfc.section.1 3.3">13.3</a> <a href="#location.spoofing-leakage">Location Header Fields: Spoofing and Information Leakage</a></li>754 <li><a href="#rfc.section.1 3.4">13.4</a> <a href="#rfc.section.13.4">Security Considerations for CONNECT</a></li>755 <li><a href="#rfc.section.1 3.5">13.5</a> <a href="#privacy.issues.connected.to.accept.header.fields">Privacy Issues Connected to Accept Header Fields</a></li>749 <li><a href="#rfc.section.12">12.</a> <a href="#security.considerations">Security Considerations</a><ul> 750 <li><a href="#rfc.section.12.1">12.1</a> <a href="#security.sensitive">Transfer of Sensitive Information</a></li> 751 <li><a href="#rfc.section.12.2">12.2</a> <a href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URIs</a></li> 752 <li><a href="#rfc.section.12.3">12.3</a> <a href="#location.spoofing-leakage">Location Header Fields: Spoofing and Information Leakage</a></li> 753 <li><a href="#rfc.section.12.4">12.4</a> <a href="#rfc.section.12.4">Security Considerations for CONNECT</a></li> 754 <li><a href="#rfc.section.12.5">12.5</a> <a href="#privacy.issues.connected.to.accept.header.fields">Privacy Issues Connected to Accept Header Fields</a></li> 756 755 </ul> 757 756 </li> 758 <li><a href="#rfc.section.1 4">14.</a> <a href="#acks">Acknowledgments</a></li>759 <li><a href="#rfc.section.1 5">15.</a> <a href="#rfc.references">References</a><ul>760 <li><a href="#rfc.section.1 5.1">15.1</a> <a href="#rfc.references.1">Normative References</a></li>761 <li><a href="#rfc.section.1 5.2">15.2</a> <a href="#rfc.references.2">Informative References</a></li>757 <li><a href="#rfc.section.13">13.</a> <a href="#acks">Acknowledgments</a></li> 758 <li><a href="#rfc.section.14">14.</a> <a href="#rfc.references">References</a><ul> 759 <li><a href="#rfc.section.14.1">14.1</a> <a href="#rfc.references.1">Normative References</a></li> 760 <li><a href="#rfc.section.14.2">14.2</a> <a href="#rfc.references.2">Informative References</a></li> 762 761 </ul> 763 762 </li> … … 913 912 <tr> 914 913 <td class="left">Content-Encoding</td> 915 <td class="left"><a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section 1 1.6</a></td>914 <td class="left"><a href="#header.content-encoding" id="rfc.xref.header.content-encoding.1" title="Content-Encoding">Section 10.6</a></td> 916 915 </tr> 917 916 <tr> 918 917 <td class="left">Content-Language</td> 919 <td class="left"><a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section 1 1.7</a></td>918 <td class="left"><a href="#header.content-language" id="rfc.xref.header.content-language.1" title="Content-Language">Section 10.7</a></td> 920 919 </tr> 921 920 <tr> 922 921 <td class="left">Content-Location</td> 923 <td class="left"><a href="#header.content-location" id="rfc.xref.header.content-location.1" title="Content-Location">Section 1 1.8</a></td>922 <td class="left"><a href="#header.content-location" id="rfc.xref.header.content-location.1" title="Content-Location">Section 10.8</a></td> 924 923 </tr> 925 924 <tr> 926 925 <td class="left">Content-Type</td> 927 <td class="left"><a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section 1 1.9</a></td>926 <td class="left"><a href="#header.content-type" id="rfc.xref.header.content-type.1" title="Content-Type">Section 10.9</a></td> 928 927 </tr> 929 928 <tr> … … 985 984 defined by the <a href="#header.content-type" class="smpl">Content-Type</a> header field. 986 985 </p> 986 <h2 id="rfc.section.3.4"><a href="#rfc.section.3.4">3.4</a> <a id="content.negotiation" href="#content.negotiation">Content Negotiation</a></h2> 987 <p id="rfc.section.3.4.p.1">HTTP responses include a representation which contains information for interpretation, whether by a human user or for further 988 processing. Often, the server has different ways of representing the same information; for example, in different formats, 989 languages, or using different character encodings. 990 </p> 991 <p id="rfc.section.3.4.p.2">HTTP clients and their users might have different or variable capabilities, characteristics or preferences which would influence 992 which representation, among those available from the server, would be best for the server to deliver. For this reason, HTTP 993 provides mechanisms for "content negotiation" — a process of allowing selection of a representation of a given resource, when 994 more than one is available. 995 </p> 996 <p id="rfc.section.3.4.p.3">This specification defines two patterns of content negotiation; "server-driven", where the server selects the representation 997 based upon the client's stated preferences, and "agent-driven" negotiation, where the server provides a list of representations 998 for the client to choose from, based upon their metadata. In addition, there are other patterns: some applications use an 999 "active content" pattern, where the server returns active content which runs on the client and, based on client available 1000 parameters, selects additional resources to invoke. "Transparent Content Negotiation" (<a href="#RFC2295" id="rfc.xref.RFC2295.1"><cite title="Transparent Content Negotiation in HTTP">[RFC2295]</cite></a>) has also been proposed. 1001 </p> 1002 <p id="rfc.section.3.4.p.4">These patterns are all widely used, and have trade-offs in applicability and practicality. In particular, when the number 1003 of preferences or capabilities to be expressed by a client are large (such as when many different formats are supported by 1004 a user-agent), server-driven negotiation becomes unwieldy, and might not be appropriate. Conversely, when the number of representations 1005 to choose from is very large, agent-driven negotiation might not be appropriate. 1006 </p> 1007 <p id="rfc.section.3.4.p.5">Note that, in all cases, the supplier of representations has the responsibility for determining which representations might 1008 be considered to be the "same information". 1009 </p> 1010 <h3 id="rfc.section.3.4.1"><a href="#rfc.section.3.4.1">3.4.1</a> <a id="server-driven.negotiation" href="#server-driven.negotiation">Server-driven Negotiation</a></h3> 1011 <p id="rfc.section.3.4.1.p.1">If the selection of the best representation for a response is made by an algorithm located at the server, it is called server-driven 1012 negotiation. Selection is based on the available representations of the response (the dimensions over which it can vary; e.g., 1013 language, content-coding, etc.) and the contents of particular header fields in the request message or on other information 1014 pertaining to the request (such as the network address of the client). 1015 </p> 1016 <p id="rfc.section.3.4.1.p.2">Server-driven negotiation is advantageous when the algorithm for selecting from among the available representations is difficult 1017 to describe to the user agent, or when the server desires to send its "best guess" to the client along with the first response 1018 (hoping to avoid the round-trip delay of a subsequent request if the "best guess" is good enough for the user). In order to 1019 improve the server's guess, the user agent <em class="bcp14">MAY</em> include request header fields (<a href="#header.accept" class="smpl">Accept</a>, <a href="#header.accept-language" class="smpl">Accept-Language</a>, <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a>, etc.) which describe its preferences for such a response. 1020 </p> 1021 <p id="rfc.section.3.4.1.p.3">Server-driven negotiation has disadvantages: </p> 1022 <ol> 1023 <li>It is impossible for the server to accurately determine what might be "best" for any given user, since that would require 1024 complete knowledge of both the capabilities of the user agent and the intended use for the response (e.g., does the user want 1025 to view it on screen or print it on paper?). 1026 </li> 1027 <li>Having the user agent describe its capabilities in every request can be both very inefficient (given that only a small percentage 1028 of responses have multiple representations) and a potential violation of the user's privacy. 1029 </li> 1030 <li>It complicates the implementation of an origin server and the algorithms for generating responses to a request.</li> 1031 <li>It might limit a public cache's ability to use the same response for multiple user's requests.</li> 1032 </ol> 1033 <p id="rfc.section.3.4.1.p.4">Server-driven negotiation allows the user agent to specify its preferences, but it cannot expect responses to always honor 1034 them. For example, the origin server might not implement server-driven negotiation, or it might decide that sending a response 1035 that doesn't conform to them is better than sending a <a href="#status.406" class="smpl">406 1036 (Not Acceptable)</a> response. 1037 </p> 1038 <p id="rfc.section.3.4.1.p.5">HTTP/1.1 includes the following header fields for enabling server-driven negotiation through description of user agent capabilities 1039 and user preferences: <a href="#header.accept" class="smpl">Accept</a> (<a href="#header.accept" id="rfc.xref.header.accept.1" title="Accept">Section 10.1</a>), <a href="#header.accept-charset" class="smpl">Accept-Charset</a> (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.1" title="Accept-Charset">Section 10.2</a>), <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.1" title="Accept-Encoding">Section 10.3</a>), <a href="#header.accept-language" class="smpl">Accept-Language</a> (<a href="#header.accept-language" id="rfc.xref.header.accept-language.1" title="Accept-Language">Section 10.4</a>), and <a href="#header.user-agent" class="smpl">User-Agent</a> (<a href="#header.user-agent" id="rfc.xref.header.user-agent.1" title="User-Agent">Section 10.18</a>). However, an origin server is not limited to these dimensions and <em class="bcp14">MAY</em> vary the response based on any aspect of the request, including aspects of the connection (e.g., IP address) or information 1040 within extension header fields not defined by this specification. 1041 </p> 1042 <div class="note" id="rfc.section.3.4.1.p.6"> 1043 <p> <b>Note:</b> In practice, <a href="#header.user-agent" class="smpl">User-Agent</a> based negotiation is fragile, because new clients might not be recognized. 1044 </p> 1045 </div> 1046 <p id="rfc.section.3.4.1.p.7">The <a href="p6-cache.html#header.vary" class="smpl">Vary</a> header field (<a href="p6-cache.html#header.vary" title="Vary">Section 7.5</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) can be used to express the parameters the server uses to select a representation that is subject to server-driven negotiation. 1047 </p> 1048 <h3 id="rfc.section.3.4.2"><a href="#rfc.section.3.4.2">3.4.2</a> <a id="agent-driven.negotiation" href="#agent-driven.negotiation">Agent-driven Negotiation</a></h3> 1049 <p id="rfc.section.3.4.2.p.1">With agent-driven negotiation, selection of the best representation for a response is performed by the user agent after receiving 1050 an initial response from the origin server. Selection is based on a list of the available representations of the response 1051 included within the header fields or body of the initial response, with each representation identified by its own URI. Selection 1052 from among the representations can be performed automatically (if the user agent is capable of doing so) or manually by the 1053 user selecting from a generated (possibly hypertext) menu. 1054 </p> 1055 <p id="rfc.section.3.4.2.p.2">Agent-driven negotiation is advantageous when the response would vary over commonly-used dimensions (such as type, language, 1056 or encoding), when the origin server is unable to determine a user agent's capabilities from examining the request, and generally 1057 when public caches are used to distribute server load and reduce network usage. 1058 </p> 1059 <p id="rfc.section.3.4.2.p.3">Agent-driven negotiation suffers from the disadvantage of needing a second request to obtain the best alternate representation. 1060 This second request is only efficient when caching is used. In addition, this specification does not define any mechanism 1061 for supporting automatic selection, though it also does not prevent any such mechanism from being developed as an extension 1062 and used within HTTP/1.1. 1063 </p> 1064 <p id="rfc.section.3.4.2.p.4">This specification defines the <a href="#status.300" class="smpl">300 (Multiple Choices)</a> and <a href="#status.406" class="smpl">406 (Not Acceptable)</a> status codes for enabling agent-driven negotiation when the server is unwilling or unable to provide a varying response using 1065 server-driven negotiation. 1066 </p> 1067 <h3 id="rfc.section.3.4.3"><a href="#rfc.section.3.4.3">3.4.3</a> <a id="quality.values" href="#quality.values">Quality Values</a></h3> 1068 <p id="rfc.section.3.4.3.p.1">Many of the request header fields for server-driven content negotiation use a common parameter, named "q", to assign a relative 1069 "weight" to the preference for that associated kind of content. This weight is referred to as a "quality value" (or "qvalue") 1070 because the same parameter name is often used within server configurations to assign a weight to the relative quality of the 1071 various representations that can be selected for a resource. 1072 </p> 1073 <p id="rfc.section.3.4.3.p.2">The weight is normalized to a real number in the range 0 through 1, where 0.001 is the least preferred and 1 is the most preferred; 1074 a value of 0 means "not acceptable". If no "q" parameter is present, the default weight is 1. 1075 </p> 1076 <div id="rfc.figure.u.2"></div><pre class="inline"><span id="rfc.iref.g.1"></span><span id="rfc.iref.g.2"></span> <a href="#quality.values" class="smpl">weight</a> = <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> "q=" <a href="#quality.values" class="smpl">qvalue</a> 1077 <a href="#quality.values" class="smpl">qvalue</a> = ( "0" [ "." 0*3<a href="#imported.abnf" class="smpl">DIGIT</a> ] ) 1078 / ( "1" [ "." 0*3("0") ] ) 1079 </pre><p id="rfc.section.3.4.3.p.4">A sender of qvalue <em class="bcp14">MUST NOT</em> generate more than three digits after the decimal point. User configuration of these values ought to be limited in the same 1080 fashion. 1081 </p> 987 1082 <h1 id="rfc.section.4"><a href="#rfc.section.4">4.</a> <a id="methods" href="#methods">Request Methods</a></h1> 988 1083 <h2 id="rfc.section.4.1"><a href="#rfc.section.4.1">4.1</a> <a id="method.overview" href="#method.overview">Overview</a></h2> … … 990 1085 this request and what is expected by the client as a successful result. The request semantics <em class="bcp14">MAY</em> be further specialized by the semantics of some header fields when present in a request (<a href="#request.header.fields" title="Request Header Fields">Section 5</a>) if those additional semantics do not conflict with the method. 991 1086 </p> 992 <div id="rfc.figure.u. 2"></div><pre class="inline"><span id="rfc.iref.g.1"></span> <a href="#method.overview" class="smpl">method</a> = <a href="#imported.abnf" class="smpl">token</a>1087 <div id="rfc.figure.u.3"></div><pre class="inline"><span id="rfc.iref.g.3"></span> <a href="#method.overview" class="smpl">method</a> = <a href="#imported.abnf" class="smpl">token</a> 993 1088 </pre><p id="rfc.section.4.1.p.3">HTTP was originally designed to be usable as an interface to distributed object systems. The request method was envisioned 994 1089 as applying semantics to a target resource in much the same way as invoking a defined method on an identified object would … … 1060 1155 </p> 1061 1156 <p id="rfc.section.4.1.p.7">Additional methods <em class="bcp14">MAY</em> be used in HTTP; many have already been standardized outside the scope of this specification and registered within the HTTP 1062 Method Registry maintained by IANA, as defined in <a href="#method.registry" title="Method Registry">Section 1 2.1</a>.1063 </p> 1064 <p id="rfc.section.4.1.p.8">The set of methods allowed by a target resource can be listed in an <a href="#header.allow" class="smpl">Allow</a> header field (<a href="#header.allow" id="rfc.xref.header.allow.1" title="Allow">Section 1 1.5</a>). However, the set of allowed methods can change dynamically. When a request message is received that is unrecognized or1157 Method Registry maintained by IANA, as defined in <a href="#method.registry" title="Method Registry">Section 11.1</a>. 1158 </p> 1159 <p id="rfc.section.4.1.p.8">The set of methods allowed by a target resource can be listed in an <a href="#header.allow" class="smpl">Allow</a> header field (<a href="#header.allow" id="rfc.xref.header.allow.1" title="Allow">Section 10.5</a>). However, the set of allowed methods can change dynamically. When a request message is received that is unrecognized or 1065 1160 not implemented by an origin server, the origin server <em class="bcp14">SHOULD</em> respond with the <a href="#status.501" class="smpl">501 (Not Implemented)</a> status code. When a request message is received that is known by an origin server but not allowed for the target resource, 1066 1161 the origin server <em class="bcp14">SHOULD</em> respond with the <a href="#status.405" class="smpl">405 (Method Not Allowed)</a> status code. … … 1115 1210 are defined to be cacheable. In general, safe methods that do not depend on a current or authoritative response are cacheable, 1116 1211 though the overwhelming majority of caches only support GET and HEAD. HTTP requirements for cache behavior and cacheable responses 1117 are defined in <a href="#Part6" id="rfc.xref.Part6. 2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.1212 are defined in <a href="#Part6" id="rfc.xref.Part6.3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. 1118 1213 </p> 1119 1214 <h2 id="rfc.section.4.3"><a href="#rfc.section.4.3">4.3</a> <a id="method.definitions" href="#method.definitions">Method Definitions</a></h2> 1120 1215 <h3 id="rfc.section.4.3.1"><a href="#rfc.section.4.3.1">4.3.1</a> <a id="GET" href="#GET">GET</a></h3> 1121 <div id="rfc.iref.g. 2"></div>1216 <div id="rfc.iref.g.4"></div> 1122 1217 <div id="rfc.iref.m.1"></div> 1123 1218 <p id="rfc.section.4.3.1.p.1">The GET method requests transfer of a current representation of the target resource.</p> … … 1135 1230 to reject the request. 1136 1231 </p> 1137 <p id="rfc.section.4.3.1.p.6">The response to a GET request is cacheable and <em class="bcp14">MAY</em> be used to satisfy subsequent GET and HEAD requests (see <a href="#Part6" id="rfc.xref.Part6. 3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).1138 </p> 1139 <p id="rfc.section.4.3.1.p.7">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URIs">Section 1 3.2</a> for security considerations when used for forms.1232 <p id="rfc.section.4.3.1.p.6">The response to a GET request is cacheable and <em class="bcp14">MAY</em> be used to satisfy subsequent GET and HEAD requests (see <a href="#Part6" id="rfc.xref.Part6.4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>). 1233 </p> 1234 <p id="rfc.section.4.3.1.p.7">See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URIs">Section 12.2</a> for security considerations when used for forms. 1140 1235 </p> 1141 1236 <h3 id="rfc.section.4.3.2"><a href="#rfc.section.4.3.2">4.3.2</a> <a id="HEAD" href="#HEAD">HEAD</a></h3> … … 1146 1241 hypertext links for validity, accessibility, and recent modification. 1147 1242 </p> 1148 <p id="rfc.section.4.3.2.p.2">The response to a HEAD request is cacheable and <em class="bcp14">MAY</em> be used to satisfy a subsequent HEAD request. It also has potential side effects on previously stored responses to GET; see <a href="p6-cache.html#head.effects" title="Updating Caches with HEAD Responses">Section 5</a> of <a href="#Part6" id="rfc.xref.Part6. 4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>.1243 <p id="rfc.section.4.3.2.p.2">The response to a HEAD request is cacheable and <em class="bcp14">MAY</em> be used to satisfy a subsequent HEAD request. It also has potential side effects on previously stored responses to GET; see <a href="p6-cache.html#head.effects" title="Updating Caches with HEAD Responses">Section 5</a> of <a href="#Part6" id="rfc.xref.Part6.5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>. 1149 1244 </p> 1150 1245 <p id="rfc.section.4.3.2.p.3">Bodies on HEAD requests have no defined semantics. Note that sending a body on a HEAD request might cause some existing implementations … … 1169 1264 the result. 1170 1265 </p> 1171 <p id="rfc.section.4.3.3.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 a representation which describes the status of the request and refers to the new resource, and a <a href="#header.location" class="smpl">Location</a> header field (see <a href="#header.location" id="rfc.xref.header.location.1" title="Location">Section 1 1.13</a>).1172 </p> 1173 <p id="rfc.section.4.3.3.p.5">Responses to POST requests are only cacheable when they include explicit freshness information (see <a href="p6-cache.html#calculating.freshness.lifetime" title="Calculating Freshness Lifetime">Section 4.1.1</a> of <a href="#Part6" id="rfc.xref.Part6. 5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>). A cached POST response with a <a href="#header.content-location" class="smpl">Content-Location</a> header field (see <a href="#header.content-location" id="rfc.xref.header.content-location.2" title="Content-Location">Section 11.8</a>) whose value is the effective Request URI <em class="bcp14">MAY</em> be used to satisfy subsequent GET and HEAD requests.1266 <p id="rfc.section.4.3.3.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 a representation which describes the status of the request and refers to the new resource, and a <a href="#header.location" class="smpl">Location</a> header field (see <a href="#header.location" id="rfc.xref.header.location.1" title="Location">Section 10.13</a>). 1267 </p> 1268 <p id="rfc.section.4.3.3.p.5">Responses to POST requests are only cacheable when they include explicit freshness information (see <a href="p6-cache.html#calculating.freshness.lifetime" title="Calculating Freshness Lifetime">Section 4.1.1</a> of <a href="#Part6" id="rfc.xref.Part6.6"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>). A cached POST response with a <a href="#header.content-location" class="smpl">Content-Location</a> header field (see <a href="#header.content-location" id="rfc.xref.header.content-location.2" title="Content-Location">Section 10.8</a>) whose value is the effective Request URI <em class="bcp14">MAY</em> be used to satisfy subsequent GET and HEAD requests. 1174 1269 </p> 1175 1270 <p id="rfc.section.4.3.3.p.6">Note that POST caching is not widely implemented. 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 representation of the resource. … … 1237 1332 </p> 1238 1333 <p id="rfc.section.4.3.4.p.11">Responses to the PUT method are not cacheable. If a PUT request passes through a cache that has one or more stored responses 1239 for the effective request URI, those stored responses will be invalidated (see <a href="p6-cache.html#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 6</a> of <a href="#Part6" id="rfc.xref.Part6. 6"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).1334 for the effective request URI, those stored responses will be invalidated (see <a href="p6-cache.html#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 6</a> of <a href="#Part6" id="rfc.xref.Part6.7"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>). 1240 1335 </p> 1241 1336 <h3 id="rfc.section.4.3.5"><a href="#rfc.section.4.3.5">4.3.5</a> <a id="DELETE" href="#DELETE">DELETE</a></h3> … … 1253 1348 </p> 1254 1349 <p id="rfc.section.4.3.5.p.4">Responses to the DELETE method are not cacheable. If a DELETE request passes through a cache that has one or more stored responses 1255 for the effective request URI, those stored responses will be invalidated (see <a href="p6-cache.html#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 6</a> of <a href="#Part6" id="rfc.xref.Part6. 7"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).1350 for the effective request URI, those stored responses will be invalidated (see <a href="p6-cache.html#invalidation.after.updates.or.deletions" title="Request Methods that Invalidate">Section 6</a> of <a href="#Part6" id="rfc.xref.Part6.8"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>). 1256 1351 </p> 1257 1352 <div id="rfc.iref.c.3"></div> … … 1264 1359 For example, 1265 1360 </p> 1266 <div id="rfc.figure.u. 3"></div><pre class="text2">CONNECT server.example.com:80 HTTP/1.11361 <div id="rfc.figure.u.4"></div><pre class="text2">CONNECT server.example.com:80 HTTP/1.1 1267 1362 Host: server.example.com:80 1268 1363 … … 1277 1372 </p> 1278 1373 <p id="rfc.section.4.3.6.p.7">Proxy authentication might be used to establish the authority to create a tunnel:</p> 1279 <div id="rfc.figure.u. 4"></div><pre class="text2">CONNECT server.example.com:80 HTTP/1.11374 <div id="rfc.figure.u.5"></div><pre class="text2">CONNECT server.example.com:80 HTTP/1.1 1280 1375 Host: server.example.com:80 1281 1376 Proxy-Authorization: basic aGVsbG86d29ybGQ= … … 1318 1413 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 <a href="p1-messaging.html#header.content-length" class="smpl">Content-Length</a> field with a field-value of "0". 1319 1414 </p> 1320 <p id="rfc.section.4.3.7.p.7">The <a href="#header.max-forwards" class="smpl">Max-Forwards</a> header field <em class="bcp14">MAY</em> be used to target a specific proxy in the request chain (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.1" title="Max-Forwards">Section 1 1.14</a>). If no Max-Forwards field is present in the request, then the forwarded request <em class="bcp14">MUST NOT</em> include a Max-Forwards field.1415 <p id="rfc.section.4.3.7.p.7">The <a href="#header.max-forwards" class="smpl">Max-Forwards</a> header field <em class="bcp14">MAY</em> be used to target a specific proxy in the request chain (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.1" title="Max-Forwards">Section 10.14</a>). If no Max-Forwards field is present in the request, then the forwarded request <em class="bcp14">MUST NOT</em> include a Max-Forwards field. 1321 1416 </p> 1322 1417 <h3 id="rfc.section.4.3.8"><a href="#rfc.section.4.3.8">4.3.8</a> <a id="TRACE" href="#TRACE">TRACE</a></h3> 1323 1418 <div id="rfc.iref.t.1"></div> 1324 1419 <div id="rfc.iref.m.8"></div> 1325 <p id="rfc.section.4.3.8.p.1">The TRACE method requests a remote, application-layer loop-back of the request message. The final recipient of the request <em class="bcp14">SHOULD</em> reflect the message received back to the client as the message 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 to receive a <a href="#header.max-forwards" class="smpl">Max-Forwards</a> value of zero (0) in the request (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.2" title="Max-Forwards">Section 1 1.14</a>). A TRACE request <em class="bcp14">MUST NOT</em> include a message body.1420 <p id="rfc.section.4.3.8.p.1">The TRACE method requests a remote, application-layer loop-back of the request message. The final recipient of the request <em class="bcp14">SHOULD</em> reflect the message received back to the client as the message 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 to receive a <a href="#header.max-forwards" class="smpl">Max-Forwards</a> value of zero (0) in the request (see <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.2" title="Max-Forwards">Section 10.14</a>). A TRACE request <em class="bcp14">MUST NOT</em> include a message body. 1326 1421 </p> 1327 1422 <p id="rfc.section.4.3.8.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 … … 1354 1449 <tr> 1355 1450 <td class="left">Max-Forwards</td> 1356 <td class="left"><a href="#header.max-forwards" id="rfc.xref.header.max-forwards.3" title="Max-Forwards">Section 1 1.14</a></td>1451 <td class="left"><a href="#header.max-forwards" id="rfc.xref.header.max-forwards.3" title="Max-Forwards">Section 10.14</a></td> 1357 1452 </tr> 1358 1453 <tr> 1359 1454 <td class="left">Expect</td> 1360 <td class="left"><a href="#header.expect" id="rfc.xref.header.expect.1" title="Expect">Section 1 1.11</a></td>1455 <td class="left"><a href="#header.expect" id="rfc.xref.header.expect.1" title="Expect">Section 10.11</a></td> 1361 1456 </tr> 1362 1457 <tr> … … 1416 1511 <tr> 1417 1512 <td class="left">Accept</td> 1418 <td class="left"><a href="#header.accept" id="rfc.xref.header.accept. 1" title="Accept">Section 11.1</a></td>1513 <td class="left"><a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section 10.1</a></td> 1419 1514 </tr> 1420 1515 <tr> 1421 1516 <td class="left">Accept-Charset</td> 1422 <td class="left"><a href="#header.accept-charset" id="rfc.xref.header.accept-charset. 1" title="Accept-Charset">Section 11.2</a></td>1517 <td class="left"><a href="#header.accept-charset" id="rfc.xref.header.accept-charset.2" title="Accept-Charset">Section 10.2</a></td> 1423 1518 </tr> 1424 1519 <tr> 1425 1520 <td class="left">Accept-Encoding</td> 1426 <td class="left"><a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding. 1" title="Accept-Encoding">Section 11.3</a></td>1521 <td class="left"><a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.2" title="Accept-Encoding">Section 10.3</a></td> 1427 1522 </tr> 1428 1523 <tr> 1429 1524 <td class="left">Accept-Language</td> 1430 <td class="left"><a href="#header.accept-language" id="rfc.xref.header.accept-language. 1" title="Accept-Language">Section 11.4</a></td>1525 <td class="left"><a href="#header.accept-language" id="rfc.xref.header.accept-language.2" title="Accept-Language">Section 10.4</a></td> 1431 1526 </tr> 1432 1527 </tbody> … … 1466 1561 <tr> 1467 1562 <td class="left">From</td> 1468 <td class="left"><a href="#header.from" id="rfc.xref.header.from.1" title="From">Section 1 1.12</a></td>1563 <td class="left"><a href="#header.from" id="rfc.xref.header.from.1" title="From">Section 10.12</a></td> 1469 1564 </tr> 1470 1565 <tr> 1471 1566 <td class="left">Referer</td> 1472 <td class="left"><a href="#header.referer" id="rfc.xref.header.referer.1" title="Referer">Section 1 1.15</a></td>1567 <td class="left"><a href="#header.referer" id="rfc.xref.header.referer.1" title="Referer">Section 10.15</a></td> 1473 1568 </tr> 1474 1569 <tr> … … 1478 1573 <tr> 1479 1574 <td class="left">User-Agent</td> 1480 <td class="left"><a href="#header.user-agent" id="rfc.xref.header.user-agent. 1" title="User-Agent">Section 11.18</a></td>1575 <td class="left"><a href="#header.user-agent" id="rfc.xref.header.user-agent.2" title="User-Agent">Section 10.18</a></td> 1481 1576 </tr> 1482 1577 </tbody> … … 1506 1601 </li> 1507 1602 </ul> 1508 <p id="rfc.section.6.p.4">For most status codes the response can carry a payload, in which case a <a href="#header.content-type" class="smpl">Content-Type</a> header field indicates the payload's media type (<a href="#header.content-type" id="rfc.xref.header.content-type.2" title="Content-Type">Section 1 1.9</a>).1603 <p id="rfc.section.6.p.4">For most status codes the response can carry a payload, in which case a <a href="#header.content-type" class="smpl">Content-Type</a> header field indicates the payload's media type (<a href="#header.content-type" id="rfc.xref.header.content-type.2" title="Content-Type">Section 10.9</a>). 1509 1604 </p> 1510 1605 <h2 id="rfc.section.6.1"><a href="#rfc.section.6.1">6.1</a> <a id="overview.of.status.codes" href="#overview.of.status.codes">Overview of Status Codes</a></h2> … … 1732 1827 <p id="rfc.section.6.1.p.2">Note that this list is not exhaustive — it does not include extension status codes defined in other specifications.</p> 1733 1828 <h2 id="rfc.section.6.2"><a href="#rfc.section.6.2">6.2</a> <a id="status.1xx" href="#status.1xx">Informational 1xx</a></h2> 1734 <div id="rfc.iref.2 3"></div>1829 <div id="rfc.iref.25"></div> 1735 1830 <div id="rfc.iref.s.3"></div> 1736 1831 <p id="rfc.section.6.2.p.1">This class of status code indicates a provisional response, consisting only of the status-line and optional header fields, … … 1745 1840 a request, then it need not forward the corresponding <a href="#status.100" class="smpl">100 (Continue)</a> response(s).) 1746 1841 </p> 1747 <div id="rfc.iref.2 4"></div>1842 <div id="rfc.iref.26"></div> 1748 1843 <div id="rfc.iref.s.4"></div> 1749 1844 <h3 id="rfc.section.6.2.1"><a href="#rfc.section.6.2.1">6.2.1</a> <a id="status.100" href="#status.100">100 Continue</a></h3> … … 1752 1847 server <em class="bcp14">MUST</em> send a final response after the request has been completed. See <a href="p1-messaging.html#use.of.the.100.status" title="Use of the 100 (Continue) Status">Section 6.3</a> of <a href="#Part1" id="rfc.xref.Part1.15"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a> for detailed discussion of the use and handling of this status code. 1753 1848 </p> 1754 <div id="rfc.iref.2 5"></div>1849 <div id="rfc.iref.27"></div> 1755 1850 <div id="rfc.iref.s.5"></div> 1756 1851 <h3 id="rfc.section.6.2.2"><a href="#rfc.section.6.2.2">6.2.2</a> <a id="status.101" href="#status.101">101 Switching Protocols</a></h3> … … 1763 1858 </p> 1764 1859 <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a> <a id="status.2xx" href="#status.2xx">Successful 2xx</a></h2> 1765 <div id="rfc.iref.2 6"></div>1860 <div id="rfc.iref.28"></div> 1766 1861 <div id="rfc.iref.s.6"></div> 1767 1862 <p id="rfc.section.6.3.p.1">This class of status code indicates that the client's request was successfully received, understood, and accepted.</p> 1768 <div id="rfc.iref.2 7"></div>1863 <div id="rfc.iref.29"></div> 1769 1864 <div id="rfc.iref.s.7"></div> 1770 1865 <h3 id="rfc.section.6.3.1"><a href="#rfc.section.6.3.1">6.3.1</a> <a id="status.200" href="#status.200">200 OK</a></h3> … … 1780 1875 <dd>a representation containing the request message as received by the end server.</dd> 1781 1876 </dl> 1782 <p id="rfc.section.6.3.1.p.2">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6. 8"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 200 responses.1783 </p> 1784 <div id="rfc.iref. 28"></div>1877 <p id="rfc.section.6.3.1.p.2">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.9"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 200 responses. 1878 </p> 1879 <div id="rfc.iref.30"></div> 1785 1880 <div id="rfc.iref.s.8"></div> 1786 1881 <h3 id="rfc.section.6.3.2"><a href="#rfc.section.6.3.2">6.3.2</a> <a id="status.201" href="#status.201">201 Created</a></h3> … … 1795 1890 the <a href="#header.location" class="smpl">Location</a> header field or, in case the Location header field was omitted, by the Effective Request URI (see <a href="p4-conditional.html#header.etag" title="ETag">Section 2.3</a> of <a href="#Part4" id="rfc.xref.Part4.12"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>). 1796 1891 </p> 1797 <div id="rfc.iref. 29"></div>1892 <div id="rfc.iref.31"></div> 1798 1893 <div id="rfc.iref.s.9"></div> 1799 1894 <h3 id="rfc.section.6.3.3"><a href="#rfc.section.6.3.3">6.3.3</a> <a id="status.202" href="#status.202">202 Accepted</a></h3> … … 1807 1902 user can expect the request to be fulfilled. 1808 1903 </p> 1809 <div id="rfc.iref.3 0"></div>1904 <div id="rfc.iref.32"></div> 1810 1905 <div id="rfc.iref.s.10"></div> 1811 1906 <h3 id="rfc.section.6.3.4"><a href="#rfc.section.6.3.4">6.3.4</a> <a id="status.203" href="#status.203">203 Non-Authoritative Information</a></h3> 1812 <p id="rfc.section.6.3.4.p.1">The representation in the response has been transformed or otherwise modified by a transforming proxy (<a href="p1-messaging.html#intermediaries" title="Intermediaries">Section 2.3</a> of <a href="#Part1" id="rfc.xref.Part1.17"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). Note that the behavior of transforming intermediaries is controlled by the no-transform Cache-Control directive (<a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 7.2</a> of <a href="#Part6" id="rfc.xref.Part6. 9"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>).1907 <p id="rfc.section.6.3.4.p.1">The representation in the response has been transformed or otherwise modified by a transforming proxy (<a href="p1-messaging.html#intermediaries" title="Intermediaries">Section 2.3</a> of <a href="#Part1" id="rfc.xref.Part1.17"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). Note that the behavior of transforming intermediaries is controlled by the no-transform Cache-Control directive (<a href="p6-cache.html#header.cache-control" title="Cache-Control">Section 7.2</a> of <a href="#Part6" id="rfc.xref.Part6.10"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>). 1813 1908 </p> 1814 1909 <p id="rfc.section.6.3.4.p.2">This status code is only appropriate when the response status code would have been <a href="#status.200" class="smpl">200 (OK)</a> otherwise. When the status code before transformation would have been different, the 214 Transformation Applied warn-code 1815 (<a href="p6-cache.html#header.warning" title="Warning">Section 7.6</a> of <a href="#Part6" id="rfc.xref.Part6.1 0"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) is appropriate.1816 </p> 1817 <p id="rfc.section.6.3.4.p.3">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.1 1"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 203 responses.1818 </p> 1819 <div id="rfc.iref.3 1"></div>1910 (<a href="p6-cache.html#header.warning" title="Warning">Section 7.6</a> of <a href="#Part6" id="rfc.xref.Part6.11"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) is appropriate. 1911 </p> 1912 <p id="rfc.section.6.3.4.p.3">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.12"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 203 responses. 1913 </p> 1914 <div id="rfc.iref.33"></div> 1820 1915 <div id="rfc.iref.s.11"></div> 1821 1916 <h3 id="rfc.section.6.3.5"><a href="#rfc.section.6.3.5">6.3.5</a> <a id="status.204" href="#status.204">204 No Content</a></h3> … … 1838 1933 <p id="rfc.section.6.3.5.p.5">The 204 response <em class="bcp14">MUST NOT</em> include a message body, and thus is always terminated by the first empty line after the header fields. 1839 1934 </p> 1840 <div id="rfc.iref.3 2"></div>1935 <div id="rfc.iref.34"></div> 1841 1936 <div id="rfc.iref.s.12"></div> 1842 1937 <h3 id="rfc.section.6.3.6"><a href="#rfc.section.6.3.6">6.3.6</a> <a id="status.205" href="#status.205">205 Reset Content</a></h3> … … 1848 1943 </p> 1849 1944 <h2 id="rfc.section.6.4"><a href="#rfc.section.6.4">6.4</a> <a id="status.3xx" href="#status.3xx">Redirection 3xx</a></h2> 1850 <div id="rfc.iref.3 3"></div>1945 <div id="rfc.iref.35"></div> 1851 1946 <div id="rfc.iref.s.13"></div> 1852 1947 <p id="rfc.section.6.4.p.1">This class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request. … … 1868 1963 </li> 1869 1964 <li> 1870 <p>Redirection offering a choice of matching resources for use by agent-driven content negotiation (<a href="#agent-driven.negotiation" title="Agent-driven Negotiation">Section 10.2</a>). This is status code <a href="#status.300" class="smpl">300 (Multiple Choices)</a>.1965 <p>Redirection offering a choice of matching resources for use by agent-driven content negotiation (<a href="#agent-driven.negotiation" title="Agent-driven Negotiation">Section 3.4.2</a>). This is status code <a href="#status.300" class="smpl">300 (Multiple Choices)</a>. 1871 1966 </p> 1872 1967 </li> … … 1883 1978 </p> 1884 1979 </div> 1885 <p id="rfc.section.6.4.p.4">A <a href="#header.location" class="smpl">Location</a> header field on a 3xx response indicates that a client <em class="bcp14">MAY</em> automatically redirect to the URI provided; see <a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section 1 1.13</a>.1980 <p id="rfc.section.6.4.p.4">A <a href="#header.location" class="smpl">Location</a> header field on a 3xx response indicates that a client <em class="bcp14">MAY</em> automatically redirect to the URI provided; see <a href="#header.location" id="rfc.xref.header.location.2" title="Location">Section 10.13</a>. 1886 1981 </p> 1887 1982 <p id="rfc.section.6.4.p.5">Note that for methods not known to be "safe", as defined in <a href="#safe.methods" title="Safe Methods">Section 4.2.1</a>, automatic redirection needs to done with care, since the redirect might change the conditions under which the request was … … 1894 1989 </p> 1895 1990 </div> 1896 <div id="rfc.iref.3 4"></div>1991 <div id="rfc.iref.36"></div> 1897 1992 <div id="rfc.iref.s.14"></div> 1898 1993 <h3 id="rfc.section.6.4.1"><a href="#rfc.section.6.4.1">6.4.1</a> <a id="status.300" href="#status.300">300 Multiple Choices</a></h3> 1899 1994 <p id="rfc.section.6.4.1.p.1">The target resource has more than one representation, each with its own specific location, and agent-driven negotiation information 1900 (<a href="#content.negotiation" title="Content Negotiation">Section 10</a>) is being provided so that the user (or user agent) can select a preferred representation by redirecting its request to that1995 (<a href="#content.negotiation" title="Content Negotiation">Section 3.4</a>) is being provided so that the user (or user agent) can select a preferred representation by redirecting its request to that 1901 1996 location. 1902 1997 </p> … … 1907 2002 <p id="rfc.section.6.4.1.p.3">If the server has a preferred choice of representation, it <em class="bcp14">SHOULD</em> include the specific URI for that representation in the <a href="#header.location" class="smpl">Location</a> field; user agents <em class="bcp14">MAY</em> use the Location field value for automatic redirection. 1908 2003 </p> 1909 <p id="rfc.section.6.4.1.p.4">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.1 2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 300 responses.1910 </p> 1911 <div id="rfc.iref.3 5"></div>2004 <p id="rfc.section.6.4.1.p.4">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.13"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 300 responses. 2005 </p> 2006 <div id="rfc.iref.37"></div> 1912 2007 <div id="rfc.iref.s.15"></div> 1913 2008 <h3 id="rfc.section.6.4.2"><a href="#rfc.section.6.4.2">6.4.2</a> <a id="status.301" href="#status.301">301 Moved Permanently</a></h3> … … 1915 2010 request URI to one or more of the new references returned by the server, where possible. 1916 2011 </p> 1917 <p id="rfc.section.6.4.2.p.2">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.1 3"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 301 responses.2012 <p id="rfc.section.6.4.2.p.2">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.14"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 301 responses. 1918 2013 </p> 1919 2014 <p id="rfc.section.6.4.2.p.3">The new permanent URI <em class="bcp14">SHOULD</em> be given by the <a href="#header.location" class="smpl">Location</a> field in the response. A response payload can contain a short hypertext note with a hyperlink to the new URI(s). … … 1923 2018 </p> 1924 2019 </div> 1925 <div id="rfc.iref.3 6"></div>2020 <div id="rfc.iref.38"></div> 1926 2021 <div id="rfc.iref.s.16"></div> 1927 2022 <h3 id="rfc.section.6.4.3"><a href="#rfc.section.6.4.3">6.4.3</a> <a id="status.302" href="#status.302">302 Found</a></h3> … … 1934 2029 </p> 1935 2030 </div> 1936 <div id="rfc.iref.3 7"></div>2031 <div id="rfc.iref.39"></div> 1937 2032 <div id="rfc.iref.s.17"></div> 1938 2033 <h3 id="rfc.section.6.4.4"><a href="#rfc.section.6.4.4">6.4.4</a> <a id="status.303" href="#status.303">303 See Other</a></h3> … … 1955 2050 <p id="rfc.section.6.4.4.p.4">Except for responses to a HEAD request, the representation of a 303 response <em class="bcp14">SHOULD</em> contain a short hypertext note with a hyperlink to the <a href="#header.location" class="smpl">Location</a> URI. 1956 2051 </p> 1957 <div id="rfc.iref. 38"></div>2052 <div id="rfc.iref.40"></div> 1958 2053 <div id="rfc.iref.s.18"></div> 1959 2054 <h3 id="rfc.section.6.4.5"><a href="#rfc.section.6.4.5">6.4.5</a> <a id="status.305" href="#status.305">305 Use Proxy</a></h3> 1960 2055 <p id="rfc.section.6.4.5.p.1">The 305 status code was defined in a previous version of this specification (see <a href="#changes.from.rfc.2616" title="Changes from RFC 2616">Appendix C</a>), and is now deprecated. 1961 2056 </p> 1962 <div id="rfc.iref. 39"></div>2057 <div id="rfc.iref.41"></div> 1963 2058 <div id="rfc.iref.s.19"></div> 1964 2059 <h3 id="rfc.section.6.4.6"><a href="#rfc.section.6.4.6">6.4.6</a> <a id="status.306" href="#status.306">306 (Unused)</a></h3> 1965 2060 <p id="rfc.section.6.4.6.p.1">The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved.</p> 1966 <div id="rfc.iref.4 0"></div>2061 <div id="rfc.iref.42"></div> 1967 2062 <div id="rfc.iref.s.20"></div> 1968 2063 <h3 id="rfc.section.6.4.7"><a href="#rfc.section.6.4.7">6.4.7</a> <a id="status.307" href="#status.307">307 Temporary Redirect</a></h3> … … 1978 2073 </div> 1979 2074 <h2 id="rfc.section.6.5"><a href="#rfc.section.6.5">6.5</a> <a id="status.4xx" href="#status.4xx">Client Error 4xx</a></h2> 1980 <div id="rfc.iref.4 1"></div>2075 <div id="rfc.iref.43"></div> 1981 2076 <div id="rfc.iref.s.21"></div> 1982 2077 <p id="rfc.section.6.5.p.1">The 4xx class of status code is intended for cases in which the client seems to have erred. Except when responding to a HEAD … … 1984 2079 These status codes are applicable to any request method. User agents <em class="bcp14">SHOULD</em> display any included representation to the user. 1985 2080 </p> 1986 <div id="rfc.iref.4 2"></div>2081 <div id="rfc.iref.44"></div> 1987 2082 <div id="rfc.iref.s.22"></div> 1988 2083 <h3 id="rfc.section.6.5.1"><a href="#rfc.section.6.5.1">6.5.1</a> <a id="status.400" href="#status.400">400 Bad Request</a></h3> 1989 2084 <p id="rfc.section.6.5.1.p.1">The server cannot or will not process the request, due to a client error (e.g., malformed syntax).</p> 1990 <div id="rfc.iref.4 3"></div>2085 <div id="rfc.iref.45"></div> 1991 2086 <div id="rfc.iref.s.23"></div> 1992 2087 <h3 id="rfc.section.6.5.2"><a href="#rfc.section.6.5.2">6.5.2</a> <a id="status.402" href="#status.402">402 Payment Required</a></h3> 1993 2088 <p id="rfc.section.6.5.2.p.1">This code is reserved for future use.</p> 1994 <div id="rfc.iref.4 4"></div>2089 <div id="rfc.iref.46"></div> 1995 2090 <div id="rfc.iref.s.24"></div> 1996 2091 <h3 id="rfc.section.6.5.3"><a href="#rfc.section.6.5.3">6.5.3</a> <a id="status.403" href="#status.403">403 Forbidden</a></h3> … … 2002 2097 (Not Found)</a> <em class="bcp14">MAY</em> be used instead. 2003 2098 </p> 2004 <div id="rfc.iref.4 5"></div>2099 <div id="rfc.iref.47"></div> 2005 2100 <div id="rfc.iref.s.25"></div> 2006 2101 <h3 id="rfc.section.6.5.4"><a href="#rfc.section.6.5.4">6.5.4</a> <a id="status.404" href="#status.404">404 Not Found</a></h3> … … 2010 2105 has been refused, or when no other response is applicable. 2011 2106 </p> 2012 <div id="rfc.iref.4 6"></div>2107 <div id="rfc.iref.48"></div> 2013 2108 <div id="rfc.iref.s.26"></div> 2014 2109 <h3 id="rfc.section.6.5.5"><a href="#rfc.section.6.5.5">6.5.5</a> <a id="status.405" href="#status.405">405 Method Not Allowed</a></h3> 2015 2110 <p id="rfc.section.6.5.5.p.1">The method specified in the request-line is not allowed for the target resource. The response <em class="bcp14">MUST</em> include an <a href="#header.allow" class="smpl">Allow</a> header field containing a list of valid methods for the requested resource. 2016 2111 </p> 2017 <div id="rfc.iref.4 7"></div>2112 <div id="rfc.iref.49"></div> 2018 2113 <div id="rfc.iref.s.27"></div> 2019 2114 <h3 id="rfc.section.6.5.6"><a href="#rfc.section.6.5.6">6.5.6</a> <a id="status.406" href="#status.406">406 Not Acceptable</a></h3> … … 2033 2128 <p id="rfc.section.6.5.6.p.4">If the response could be unacceptable, a user agent <em class="bcp14">SHOULD</em> temporarily stop receipt of more data and query the user for a decision on further actions. 2034 2129 </p> 2035 <div id="rfc.iref. 48"></div>2130 <div id="rfc.iref.50"></div> 2036 2131 <div id="rfc.iref.s.28"></div> 2037 2132 <h3 id="rfc.section.6.5.7"><a href="#rfc.section.6.5.7">6.5.7</a> <a id="status.408" href="#status.408">408 Request Timeout</a></h3> 2038 2133 <p id="rfc.section.6.5.7.p.1">The client did not produce a request within the time that the server was prepared to wait. The client <em class="bcp14">MAY</em> repeat the request without modifications at any later time. 2039 2134 </p> 2040 <div id="rfc.iref. 49"></div>2135 <div id="rfc.iref.51"></div> 2041 2136 <div id="rfc.iref.s.29"></div> 2042 2137 <h3 id="rfc.section.6.5.8"><a href="#rfc.section.6.5.8">6.5.8</a> <a id="status.409" href="#status.409">409 Conflict</a></h3> … … 2051 2146 contain a list of the differences between the two versions. 2052 2147 </p> 2053 <div id="rfc.iref.5 0"></div>2148 <div id="rfc.iref.52"></div> 2054 2149 <div id="rfc.iref.s.30"></div> 2055 2150 <h3 id="rfc.section.6.5.9"><a href="#rfc.section.6.5.9">6.5.9</a> <a id="status.410" href="#status.410">410 Gone</a></h3> … … 2064 2159 — that is left to the discretion of the server owner. 2065 2160 </p> 2066 <p id="rfc.section.6.5.9.p.3">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.1 4"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 410 responses.2067 </p> 2068 <div id="rfc.iref.5 1"></div>2161 <p id="rfc.section.6.5.9.p.3">Caches <em class="bcp14">MAY</em> use a heuristic (see <a href="p6-cache.html#heuristic.freshness" title="Calculating Heuristic Freshness">Section 4.1.2</a> of <a href="#Part6" id="rfc.xref.Part6.15"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) to determine freshness for 410 responses. 2162 </p> 2163 <div id="rfc.iref.53"></div> 2069 2164 <div id="rfc.iref.s.31"></div> 2070 2165 <h3 id="rfc.section.6.5.10"><a href="#rfc.section.6.5.10">6.5.10</a> <a id="status.411" href="#status.411">411 Length Required</a></h3> … … 2072 2167 message. 2073 2168 </p> 2074 <div id="rfc.iref.5 2"></div>2169 <div id="rfc.iref.54"></div> 2075 2170 <div id="rfc.iref.s.32"></div> 2076 2171 <h3 id="rfc.section.6.5.11"><a href="#rfc.section.6.5.11">6.5.11</a> <a id="status.413" href="#status.413">413 Request Representation Too Large</a></h3> … … 2080 2175 <p id="rfc.section.6.5.11.p.2">If the condition is temporary, the server <em class="bcp14">SHOULD</em> include a <a href="#header.retry-after" class="smpl">Retry-After</a> header field to indicate that it is temporary and after what time the client <em class="bcp14">MAY</em> try again. 2081 2176 </p> 2082 <div id="rfc.iref.5 3"></div>2177 <div id="rfc.iref.55"></div> 2083 2178 <div id="rfc.iref.s.33"></div> 2084 2179 <h3 id="rfc.section.6.5.12"><a href="#rfc.section.6.5.12">6.5.12</a> <a id="status.414" href="#status.414">414 URI Too Long</a></h3> … … 2089 2184 in some servers using fixed-length buffers for reading or manipulating the request-target. 2090 2185 </p> 2091 <div id="rfc.iref.5 4"></div>2186 <div id="rfc.iref.56"></div> 2092 2187 <div id="rfc.iref.s.34"></div> 2093 2188 <h3 id="rfc.section.6.5.13"><a href="#rfc.section.6.5.13">6.5.13</a> <a id="status.415" href="#status.415">415 Unsupported Media Type</a></h3> … … 2095 2190 on the target resource. 2096 2191 </p> 2097 <div id="rfc.iref.5 5"></div>2192 <div id="rfc.iref.57"></div> 2098 2193 <div id="rfc.iref.s.35"></div> 2099 2194 <h3 id="rfc.section.6.5.14"><a href="#rfc.section.6.5.14">6.5.14</a> <a id="status.417" href="#status.417">417 Expectation Failed</a></h3> 2100 <p id="rfc.section.6.5.14.p.1">The expectation given in an <a href="#header.expect" class="smpl">Expect</a> header field (see <a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section 1 1.11</a>) could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could2195 <p id="rfc.section.6.5.14.p.1">The expectation given in an <a href="#header.expect" class="smpl">Expect</a> header field (see <a href="#header.expect" id="rfc.xref.header.expect.2" title="Expect">Section 10.11</a>) could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could 2101 2196 not be met by the next-hop server. 2102 2197 </p> 2103 <div id="rfc.iref.5 6"></div>2198 <div id="rfc.iref.58"></div> 2104 2199 <div id="rfc.iref.s.36"></div> 2105 2200 <h3 id="rfc.section.6.5.15"><a href="#rfc.section.6.5.15">6.5.15</a> <a id="status.426" href="#status.426">426 Upgrade Required</a></h3> 2106 2201 <p id="rfc.section.6.5.15.p.1">The request can not be completed without a prior protocol upgrade. This response <em class="bcp14">MUST</em> include an <a href="p1-messaging.html#header.upgrade" class="smpl">Upgrade</a> header field (<a href="p1-messaging.html#header.upgrade" title="Upgrade">Section 6.4</a> of <a href="#Part1" id="rfc.xref.Part1.19"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>) specifying the required protocols. 2107 2202 </p> 2108 <div id="rfc.figure.u. 5"></div>2203 <div id="rfc.figure.u.6"></div> 2109 2204 <p>Example:</p> <pre class="text">HTTP/1.1 426 Upgrade Required 2110 2205 Upgrade: HTTP/3.0 … … 2118 2213 </p> 2119 2214 <h2 id="rfc.section.6.6"><a href="#rfc.section.6.6">6.6</a> <a id="status.5xx" href="#status.5xx">Server Error 5xx</a></h2> 2120 <div id="rfc.iref.5 7"></div>2215 <div id="rfc.iref.59"></div> 2121 2216 <div id="rfc.iref.s.37"></div> 2122 2217 <p id="rfc.section.6.6.p.1">Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has erred or is incapable … … 2124 2219 User agents <em class="bcp14">SHOULD</em> display any included representation to the user. These response codes are applicable to any request method. 2125 2220 </p> 2126 <div id="rfc.iref. 58"></div>2221 <div id="rfc.iref.60"></div> 2127 2222 <div id="rfc.iref.s.38"></div> 2128 2223 <h3 id="rfc.section.6.6.1"><a href="#rfc.section.6.6.1">6.6.1</a> <a id="status.500" href="#status.500">500 Internal Server Error</a></h3> 2129 2224 <p id="rfc.section.6.6.1.p.1">The server encountered an unexpected condition which prevented it from fulfilling the request.</p> 2130 <div id="rfc.iref. 59"></div>2225 <div id="rfc.iref.61"></div> 2131 2226 <div id="rfc.iref.s.39"></div> 2132 2227 <h3 id="rfc.section.6.6.2"><a href="#rfc.section.6.6.2">6.6.2</a> <a id="status.501" href="#status.501">501 Not Implemented</a></h3> … … 2134 2229 does not recognize the request method and is not capable of supporting it for any resource. 2135 2230 </p> 2136 <div id="rfc.iref.6 0"></div>2231 <div id="rfc.iref.62"></div> 2137 2232 <div id="rfc.iref.s.40"></div> 2138 2233 <h3 id="rfc.section.6.6.3"><a href="#rfc.section.6.6.3">6.6.3</a> <a id="status.502" href="#status.502">502 Bad Gateway</a></h3> … … 2140 2235 to fulfill the request. 2141 2236 </p> 2142 <div id="rfc.iref.6 1"></div>2237 <div id="rfc.iref.63"></div> 2143 2238 <div id="rfc.iref.s.41"></div> 2144 2239 <h3 id="rfc.section.6.6.4"><a href="#rfc.section.6.6.4">6.6.4</a> <a id="status.503" href="#status.503">503 Service Unavailable</a></h3> 2145 2240 <p id="rfc.section.6.6.4.p.1">The server is currently unable to handle the request due to a temporary overloading or maintenance of the server.</p> 2146 2241 <p id="rfc.section.6.6.4.p.2">The implication is that this is a temporary condition which will be alleviated after some delay. If known, the length of the 2147 delay <em class="bcp14">MAY</em> be indicated in a <a href="#header.retry-after" class="smpl">Retry-After</a> header field (<a href="#header.retry-after" id="rfc.xref.header.retry-after.1" title="Retry-After">Section 1 1.16</a>). If no Retry-After is given, the client <em class="bcp14">SHOULD</em> handle the response as it would for a <a href="#status.500" class="smpl">500 (Internal2242 delay <em class="bcp14">MAY</em> be indicated in a <a href="#header.retry-after" class="smpl">Retry-After</a> header field (<a href="#header.retry-after" id="rfc.xref.header.retry-after.1" title="Retry-After">Section 10.16</a>). If no Retry-After is given, the client <em class="bcp14">SHOULD</em> handle the response as it would for a <a href="#status.500" class="smpl">500 (Internal 2148 2243 Server Error)</a> response. 2149 2244 </p> … … 2153 2248 </p> 2154 2249 </div> 2155 <div id="rfc.iref.6 2"></div>2250 <div id="rfc.iref.64"></div> 2156 2251 <div id="rfc.iref.s.42"></div> 2157 2252 <h3 id="rfc.section.6.6.5"><a href="#rfc.section.6.6.5">6.6.5</a> <a id="status.504" href="#status.504">504 Gateway Timeout</a></h3> … … 2164 2259 </p> 2165 2260 </div> 2166 <div id="rfc.iref.6 3"></div>2261 <div id="rfc.iref.65"></div> 2167 2262 <div id="rfc.iref.s.43"></div> 2168 2263 <h3 id="rfc.section.6.6.6"><a href="#rfc.section.6.6.6">6.6.6</a> <a id="status.505" href="#status.505">505 HTTP Version Not Supported</a></h3> … … 2190 2285 <tr> 2191 2286 <td class="left">Age</td> 2192 <td class="left"><a href="p6-cache.html#header.age" title="Age">Section 7.1</a> of <a href="#Part6" id="rfc.xref.Part6.1 5"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a></td>2287 <td class="left"><a href="p6-cache.html#header.age" title="Age">Section 7.1</a> of <a href="#Part6" id="rfc.xref.Part6.16"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a></td> 2193 2288 </tr> 2194 2289 <tr> 2195 2290 <td class="left">Allow</td> 2196 <td class="left"><a href="#header.allow" id="rfc.xref.header.allow.2" title="Allow">Section 1 1.5</a></td>2291 <td class="left"><a href="#header.allow" id="rfc.xref.header.allow.2" title="Allow">Section 10.5</a></td> 2197 2292 </tr> 2198 2293 <tr> 2199 2294 <td class="left">Date</td> 2200 <td class="left"><a href="#header.date" id="rfc.xref.header.date.1" title="Date">Section 1 1.10</a></td>2295 <td class="left"><a href="#header.date" id="rfc.xref.header.date.1" title="Date">Section 10.10</a></td> 2201 2296 </tr> 2202 2297 <tr> … … 2206 2301 <tr> 2207 2302 <td class="left">Location</td> 2208 <td class="left"><a href="#header.location" id="rfc.xref.header.location.3" title="Location">Section 1 1.13</a></td>2303 <td class="left"><a href="#header.location" id="rfc.xref.header.location.3" title="Location">Section 10.13</a></td> 2209 2304 </tr> 2210 2305 <tr> … … 2214 2309 <tr> 2215 2310 <td class="left">Retry-After</td> 2216 <td class="left"><a href="#header.retry-after" id="rfc.xref.header.retry-after.2" title="Retry-After">Section 1 1.16</a></td>2311 <td class="left"><a href="#header.retry-after" id="rfc.xref.header.retry-after.2" title="Retry-After">Section 10.16</a></td> 2217 2312 </tr> 2218 2313 <tr> 2219 2314 <td class="left">Server</td> 2220 <td class="left"><a href="#header.server" id="rfc.xref.header.server.1" title="Server">Section 1 1.17</a></td>2315 <td class="left"><a href="#header.server" id="rfc.xref.header.server.1" title="Server">Section 10.17</a></td> 2221 2316 </tr> 2222 2317 <tr> 2223 2318 <td class="left">Vary</td> 2224 <td class="left"><a href="p6-cache.html#header.vary" title="Vary">Section 7.5</a> of <a href="#Part6" id="rfc.xref.Part6.1 6"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a></td>2319 <td class="left"><a href="p6-cache.html#header.vary" title="Vary">Section 7.5</a> of <a href="#Part6" id="rfc.xref.Part6.17"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a></td> 2225 2320 </tr> 2226 2321 <tr> … … 2236 2331 a fixed-length subset of that defined by <a href="#RFC1123" id="rfc.xref.RFC1123.1"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a>: 2237 2332 </p> 2238 <div id="rfc.figure.u. 6"></div><pre class="text">Sun, 06 Nov 1994 08:49:37 GMT ; RFC 11232333 <div id="rfc.figure.u.7"></div><pre class="text">Sun, 06 Nov 1994 08:49:37 GMT ; RFC 1123 2239 2334 </pre><p id="rfc.section.8.1.p.3">The other formats are described here only for compatibility with obsolete implementations.</p> 2240 <div id="rfc.figure.u. 7"></div><pre class="text">Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format2335 <div id="rfc.figure.u.8"></div><pre class="text">Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format 2241 2336 Sun Nov 6 08:49:37 1994 ; ANSI C's asctime() format 2242 2337 </pre><p id="rfc.section.8.1.p.5">HTTP/1.1 clients and servers that parse a 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. … … 2246 2341 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 whitespace beyond that specifically included as SP in the grammar. 2247 2342 </p> 2248 <div id="rfc.figure.u. 8"></div><pre class="inline"><span id="rfc.iref.g.3"></span> <a href="#http.date" class="smpl">HTTP-date</a> = <a href="#preferred.date.format" class="smpl">rfc1123-date</a> / <a href="#obsolete.date.formats" class="smpl">obs-date</a>2343 <div id="rfc.figure.u.9"></div><pre class="inline"><span id="rfc.iref.g.5"></span> <a href="#http.date" class="smpl">HTTP-date</a> = <a href="#preferred.date.format" class="smpl">rfc1123-date</a> / <a href="#obsolete.date.formats" class="smpl">obs-date</a> 2249 2344 </pre><div id="preferred.date.format"> 2250 2345 <p id="rfc.section.8.1.p.8"> Preferred format:</p> 2251 2346 </div> 2252 <div id="rfc.figure.u. 9"></div><pre class="inline"><span id="rfc.iref.g.4"></span><span id="rfc.iref.g.5"></span><span id="rfc.iref.g.6"></span><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><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span> <a href="#preferred.date.format" class="smpl">rfc1123-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> "," <a href="#imported.abnf" class="smpl">SP</a> date1 <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>2347 <div id="rfc.figure.u.10"></div><pre class="inline"><span id="rfc.iref.g.6"></span><span id="rfc.iref.g.7"></span><span id="rfc.iref.g.8"></span><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><span id="rfc.iref.g.13"></span><span id="rfc.iref.g.14"></span><span id="rfc.iref.g.15"></span><span id="rfc.iref.g.16"></span><span id="rfc.iref.g.17"></span> <a href="#preferred.date.format" class="smpl">rfc1123-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> "," <a href="#imported.abnf" class="smpl">SP</a> date1 <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a> 2253 2348 ; fixed length subset of the format defined in 2254 2349 ; <a href="http://tools.ietf.org/html/rfc1123#section-5.2.14">Section 5.2.14</a> of <a href="#RFC1123" id="rfc.xref.RFC1123.2"><cite title="Requirements for Internet Hosts - Application and Support">[RFC1123]</cite></a> … … 2293 2388 <p id="rfc.section.8.1.p.11"> Obsolete formats:</p> 2294 2389 </div> 2295 <div id="rfc.figure.u.1 0"></div><pre class="inline"><span id="rfc.iref.g.16"></span> <a href="#obsolete.date.formats" class="smpl">obs-date</a> = <a href="#obsolete.date.formats" class="smpl">rfc850-date</a> / <a href="#obsolete.date.formats" class="smpl">asctime-date</a>2296 </pre><div id="rfc.figure.u.1 1"></div><pre class="inline"><span id="rfc.iref.g.17"></span> <a href="#obsolete.date.formats" class="smpl">rfc850-date</a> = <a href="#obsolete.date.formats" class="smpl">day-name-l</a> "," <a href="#imported.abnf" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date2</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a>2390 <div id="rfc.figure.u.11"></div><pre class="inline"><span id="rfc.iref.g.18"></span> <a href="#obsolete.date.formats" class="smpl">obs-date</a> = <a href="#obsolete.date.formats" class="smpl">rfc850-date</a> / <a href="#obsolete.date.formats" class="smpl">asctime-date</a> 2391 </pre><div id="rfc.figure.u.12"></div><pre class="inline"><span id="rfc.iref.g.19"></span> <a href="#obsolete.date.formats" class="smpl">rfc850-date</a> = <a href="#obsolete.date.formats" class="smpl">day-name-l</a> "," <a href="#imported.abnf" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date2</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">GMT</a> 2297 2392 <a href="#obsolete.date.formats" class="smpl">date2</a> = <a href="#preferred.date.format" class="smpl">day</a> "-" <a href="#preferred.date.format" class="smpl">month</a> "-" 2<a href="#imported.abnf" class="smpl">DIGIT</a> 2298 2393 ; day-month-year (e.g., 02-Jun-82) … … 2305 2400 / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive 2306 2401 / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive 2307 </pre><div id="rfc.figure.u.1 2"></div><pre class="inline"><span id="rfc.iref.g.18"></span> <a href="#obsolete.date.formats" class="smpl">asctime-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date3</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">year</a>2402 </pre><div id="rfc.figure.u.13"></div><pre class="inline"><span id="rfc.iref.g.20"></span> <a href="#obsolete.date.formats" class="smpl">asctime-date</a> = <a href="#preferred.date.format" class="smpl">day-name</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#obsolete.date.formats" class="smpl">date3</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">time-of-day</a> <a href="#imported.abnf" class="smpl">SP</a> <a href="#preferred.date.format" class="smpl">year</a> 2308 2403 <a href="#obsolete.date.formats" class="smpl">date3</a> = <a href="#preferred.date.format" class="smpl">month</a> <a href="#imported.abnf" class="smpl">SP</a> ( 2<a href="#imported.abnf" class="smpl">DIGIT</a> / ( <a href="#imported.abnf" class="smpl">SP</a> 1<a href="#imported.abnf" class="smpl">DIGIT</a> )) 2309 2404 ; month day (e.g., Jun 2) … … 2323 2418 By convention, the products are listed in order of their significance for identifying the application. 2324 2419 </p> 2325 <div id="rfc.figure.u.1 3"></div><pre class="inline"><span id="rfc.iref.g.19"></span><span id="rfc.iref.g.20"></span> <a href="#product.tokens" class="smpl">product</a> = <a href="#imported.abnf" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>]2420 <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.21"></span><span id="rfc.iref.g.22"></span> <a href="#product.tokens" class="smpl">product</a> = <a href="#imported.abnf" class="smpl">token</a> ["/" <a href="#product.tokens" class="smpl">product-version</a>] 2326 2421 <a href="#product.tokens" class="smpl">product-version</a> = <a href="#imported.abnf" class="smpl">token</a> 2327 2422 </pre><p id="rfc.section.8.2.p.3">Examples:</p> 2328 <div id="rfc.figure.u.1 4"></div><pre class="text"> User-Agent: CERN-LineMode/2.15 libwww/2.17b32423 <div id="rfc.figure.u.15"></div><pre class="text"> User-Agent: CERN-LineMode/2.15 libwww/2.17b3 2329 2424 Server: Apache/0.8.4 2330 2425 </pre><p id="rfc.section.8.2.p.5">Product tokens <em class="bcp14">SHOULD</em> be short and to the point. They <em class="bcp14">MUST NOT</em> be used for advertising or other non-essential information. Although any token octet <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). … … 2337 2432 </p> 2338 2433 </div> 2339 <div id="rfc.figure.u.1 5"></div><pre class="inline"><span id="rfc.iref.g.21"></span> <a href="#rule.charset" class="smpl">charset</a> = <a href="#imported.abnf" class="smpl">token</a>2434 <div id="rfc.figure.u.16"></div><pre class="inline"><span id="rfc.iref.g.23"></span> <a href="#rule.charset" class="smpl">charset</a> = <a href="#imported.abnf" class="smpl">token</a> 2340 2435 </pre><p id="rfc.section.8.3.p.4">Although HTTP allows an arbitrary token to be used as a charset value, any token that has a predefined value within the IANA 2341 2436 Character Set registry <em class="bcp14">MUST</em> represent the character encoding defined by that registry. Applications <em class="bcp14">SHOULD</em> limit their use of character encodings to those defined within the IANA registry. … … 2351 2446 directly, and only decoded by the recipient. 2352 2447 </p> 2353 <div id="rfc.figure.u.1 6"></div><pre class="inline"><span id="rfc.iref.g.22"></span> <a href="#content.codings" class="smpl">content-coding</a> = <a href="#imported.abnf" class="smpl">token</a>2354 </pre><p id="rfc.section.8.4.p.3">All content-coding values are case-insensitive. HTTP/1.1 uses content-coding values in the <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding. 2" title="Accept-Encoding">Section 11.3</a>) and <a href="#header.content-encoding" class="smpl">Content-Encoding</a> (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.2" title="Content-Encoding">Section 11.6</a>) header fields. Although the value describes the content-coding, what is more important is that it indicates what decoding2448 <div id="rfc.figure.u.17"></div><pre class="inline"><span id="rfc.iref.g.24"></span> <a href="#content.codings" class="smpl">content-coding</a> = <a href="#imported.abnf" class="smpl">token</a> 2449 </pre><p id="rfc.section.8.4.p.3">All content-coding values are case-insensitive. HTTP/1.1 uses content-coding values in the <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.3" title="Accept-Encoding">Section 10.3</a>) and <a href="#header.content-encoding" class="smpl">Content-Encoding</a> (<a href="#header.content-encoding" id="rfc.xref.header.content-encoding.2" title="Content-Encoding">Section 10.6</a>) header fields. Although the value describes the content-coding, what is more important is that it indicates what decoding 2355 2450 mechanism will be required to remove the encoding. 2356 2451 </p> … … 2367 2462 </li> 2368 2463 </ul> 2369 <p id="rfc.section.8.4.p.6">gzip<span id="rfc.iref.g.2 3"></span><span id="rfc.iref.c.7"></span>2464 <p id="rfc.section.8.4.p.6">gzip<span id="rfc.iref.g.25"></span><span id="rfc.iref.c.7"></span> 2370 2465 </p> 2371 2466 <ul class="empty"> … … 2374 2469 </ul> 2375 2470 <h2 id="rfc.section.8.5"><a href="#rfc.section.8.5">8.5</a> <a id="media.types" href="#media.types">Media Types</a></h2> 2376 <p id="rfc.section.8.5.p.1">HTTP uses Internet Media Types <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> in the <a href="#header.content-type" class="smpl">Content-Type</a> (<a href="#header.content-type" id="rfc.xref.header.content-type.3" title="Content-Type">Section 1 1.9</a>) and <a href="#header.accept" class="smpl">Accept</a> (<a href="#header.accept" id="rfc.xref.header.accept.2" title="Accept">Section 11.1</a>) header fields in order to provide open and extensible data typing and type negotiation.2377 </p> 2378 <div id="rfc.figure.u.1 7"></div><pre class="inline"><span id="rfc.iref.g.24"></span><span id="rfc.iref.g.25"></span><span id="rfc.iref.g.26"></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="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> )2471 <p id="rfc.section.8.5.p.1">HTTP uses Internet Media Types <a href="#RFC2046" id="rfc.xref.RFC2046.2"><cite title="Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types">[RFC2046]</cite></a> in the <a href="#header.content-type" class="smpl">Content-Type</a> (<a href="#header.content-type" id="rfc.xref.header.content-type.3" title="Content-Type">Section 10.9</a>) and <a href="#header.accept" class="smpl">Accept</a> (<a href="#header.accept" id="rfc.xref.header.accept.3" title="Accept">Section 10.1</a>) header fields in order to provide open and extensible data typing and type negotiation. 2472 </p> 2473 <div id="rfc.figure.u.18"></div><pre class="inline"><span id="rfc.iref.g.26"></span><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span> <a href="#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="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#rule.parameter" class="smpl">parameter</a> ) 2379 2474 <a href="#media.types" class="smpl">type</a> = <a href="#imported.abnf" class="smpl">token</a> 2380 2475 <a href="#media.types" class="smpl">subtype</a> = <a href="#imported.abnf" class="smpl">token</a> … … 2383 2478 </p> 2384 2479 </div> 2385 <div id="rfc.figure.u.1 8"></div><pre class="inline"><span id="rfc.iref.g.27"></span><span id="rfc.iref.g.28"></span><span id="rfc.iref.g.29"></span> <a href="#rule.parameter" class="smpl">parameter</a> = <a href="#rule.parameter" class="smpl">attribute</a> "=" <a href="#rule.parameter" class="smpl">value</a>2480 <div id="rfc.figure.u.19"></div><pre class="inline"><span id="rfc.iref.g.29"></span><span id="rfc.iref.g.30"></span><span id="rfc.iref.g.31"></span> <a href="#rule.parameter" class="smpl">parameter</a> = <a href="#rule.parameter" class="smpl">attribute</a> "=" <a href="#rule.parameter" class="smpl">value</a> 2386 2481 <a href="#rule.parameter" class="smpl">attribute</a> = <a href="#imported.abnf" class="smpl">token</a> 2387 2482 <a href="#rule.parameter" class="smpl">value</a> = <a href="#imported.abnf" class="smpl">word</a> … … 2433 2528 of subtags: 2434 2529 </p> 2435 <div id="rfc.figure.u. 19"></div><pre class="inline"><span id="rfc.iref.g.30"></span> <a href="#language.tags" class="smpl">language-tag</a> = <Language-Tag, defined in <a href="#RFC5646" id="rfc.xref.RFC5646.2"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a>, <a href="http://tools.ietf.org/html/rfc5646#section-2.1">Section 2.1</a>>2530 <div id="rfc.figure.u.20"></div><pre class="inline"><span id="rfc.iref.g.32"></span> <a href="#language.tags" class="smpl">language-tag</a> = <Language-Tag, defined in <a href="#RFC5646" id="rfc.xref.RFC5646.2"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a>, <a href="http://tools.ietf.org/html/rfc5646#section-2.1">Section 2.1</a>> 2436 2531 </pre><p id="rfc.section.8.6.p.4">White space is not allowed within the tag and all tags are case-insensitive. The name space of language subtags is administered 2437 2532 by the IANA (see <<a href="http://www.iana.org/assignments/language-subtag-registry">http://www.iana.org/assignments/language-subtag-registry</a>>). 2438 2533 </p> 2439 <div id="rfc.figure.u.2 0"></div>2534 <div id="rfc.figure.u.21"></div> 2440 2535 <p>Example tags include:</p> <pre class="text"> en, en-US, es-419, az-Arab, x-pig-latin, man-Nkoo-GN 2441 2536 </pre> <p id="rfc.section.8.6.p.6">See <a href="#RFC5646" id="rfc.xref.RFC5646.3"><cite title="Tags for Identifying Languages">[RFC5646]</cite></a> for further information. … … 2478 2573 <p id="rfc.section.9.2.p.1">A payload body is only present in a message when a message body is present, as described in <a href="p1-messaging.html#message.body" title="Message Body">Section 3.3</a> of <a href="#Part1" id="rfc.xref.Part1.26"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>. The payload body is obtained from the message body by decoding any <a href="p1-messaging.html#header.transfer-encoding" class="smpl">Transfer-Encoding</a> that might have been applied to ensure safe and proper transfer of the message. 2479 2574 </p> 2480 <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a> <a id="content.negotiation" href="#content.negotiation">Content Negotiation</a></h1> 2481 <p id="rfc.section.10.p.1">HTTP responses include a representation which contains information for interpretation, whether by a human user or for further 2482 processing. Often, the server has different ways of representing the same information; for example, in different formats, 2483 languages, or using different character encodings. 2484 </p> 2485 <p id="rfc.section.10.p.2">HTTP clients and their users might have different or variable capabilities, characteristics or preferences which would influence 2486 which representation, among those available from the server, would be best for the server to deliver. For this reason, HTTP 2487 provides mechanisms for "content negotiation" — a process of allowing selection of a representation of a given resource, when 2488 more than one is available. 2489 </p> 2490 <p id="rfc.section.10.p.3">This specification defines two patterns of content negotiation; "server-driven", where the server selects the representation 2491 based upon the client's stated preferences, and "agent-driven" negotiation, where the server provides a list of representations 2492 for the client to choose from, based upon their metadata. In addition, there are other patterns: some applications use an 2493 "active content" pattern, where the server returns active content which runs on the client and, based on client available 2494 parameters, selects additional resources to invoke. "Transparent Content Negotiation" (<a href="#RFC2295" id="rfc.xref.RFC2295.1"><cite title="Transparent Content Negotiation in HTTP">[RFC2295]</cite></a>) has also been proposed. 2495 </p> 2496 <p id="rfc.section.10.p.4">These patterns are all widely used, and have trade-offs in applicability and practicality. In particular, when the number 2497 of preferences or capabilities to be expressed by a client are large (such as when many different formats are supported by 2498 a user-agent), server-driven negotiation becomes unwieldy, and might not be appropriate. Conversely, when the number of representations 2499 to choose from is very large, agent-driven negotiation might not be appropriate. 2500 </p> 2501 <p id="rfc.section.10.p.5">Note that, in all cases, the supplier of representations has the responsibility for determining which representations might 2502 be considered to be the "same information". 2503 </p> 2504 <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a> <a id="server-driven.negotiation" href="#server-driven.negotiation">Server-driven Negotiation</a></h2> 2505 <p id="rfc.section.10.1.p.1">If the selection of the best representation for a response is made by an algorithm located at the server, it is called server-driven 2506 negotiation. Selection is based on the available representations of the response (the dimensions over which it can vary; e.g., 2507 language, content-coding, etc.) and the contents of particular header fields in the request message or on other information 2508 pertaining to the request (such as the network address of the client). 2509 </p> 2510 <p id="rfc.section.10.1.p.2">Server-driven negotiation is advantageous when the algorithm for selecting from among the available representations is difficult 2511 to describe to the user agent, or when the server desires to send its "best guess" to the client along with the first response 2512 (hoping to avoid the round-trip delay of a subsequent request if the "best guess" is good enough for the user). In order to 2513 improve the server's guess, the user agent <em class="bcp14">MAY</em> include request header fields (<a href="#header.accept" class="smpl">Accept</a>, <a href="#header.accept-language" class="smpl">Accept-Language</a>, <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a>, etc.) which describe its preferences for such a response. 2514 </p> 2515 <p id="rfc.section.10.1.p.3">Server-driven negotiation has disadvantages: </p> 2516 <ol> 2517 <li>It is impossible for the server to accurately determine what might be "best" for any given user, since that would require 2518 complete knowledge of both the capabilities of the user agent and the intended use for the response (e.g., does the user want 2519 to view it on screen or print it on paper?). 2520 </li> 2521 <li>Having the user agent describe its capabilities in every request can be both very inefficient (given that only a small percentage 2522 of responses have multiple representations) and a potential violation of the user's privacy. 2523 </li> 2524 <li>It complicates the implementation of an origin server and the algorithms for generating responses to a request.</li> 2525 <li>It might limit a public cache's ability to use the same response for multiple user's requests.</li> 2526 </ol> 2527 <p id="rfc.section.10.1.p.4">Server-driven negotiation allows the user agent to specify its preferences, but it cannot expect responses to always honor 2528 them. For example, the origin server might not implement server-driven negotiation, or it might decide that sending a response 2529 that doesn't conform to them is better than sending a <a href="#status.406" class="smpl">406 2530 (Not Acceptable)</a> response. 2531 </p> 2532 <p id="rfc.section.10.1.p.5">HTTP/1.1 includes the following header fields for enabling server-driven negotiation through description of user agent capabilities 2533 and user preferences: <a href="#header.accept" class="smpl">Accept</a> (<a href="#header.accept" id="rfc.xref.header.accept.3" title="Accept">Section 11.1</a>), <a href="#header.accept-charset" class="smpl">Accept-Charset</a> (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.2" title="Accept-Charset">Section 11.2</a>), <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> (<a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.3" title="Accept-Encoding">Section 11.3</a>), <a href="#header.accept-language" class="smpl">Accept-Language</a> (<a href="#header.accept-language" id="rfc.xref.header.accept-language.2" title="Accept-Language">Section 11.4</a>), and <a href="#header.user-agent" class="smpl">User-Agent</a> (<a href="#header.user-agent" id="rfc.xref.header.user-agent.2" title="User-Agent">Section 11.18</a>). However, an origin server is not limited to these dimensions and <em class="bcp14">MAY</em> vary the response based on any aspect of the request, including aspects of the connection (e.g., IP address) or information 2534 within extension header fields not defined by this specification. 2535 </p> 2536 <div class="note" id="rfc.section.10.1.p.6"> 2537 <p> <b>Note:</b> In practice, <a href="#header.user-agent" class="smpl">User-Agent</a> based negotiation is fragile, because new clients might not be recognized. 2538 </p> 2539 </div> 2540 <p id="rfc.section.10.1.p.7">The <a href="p6-cache.html#header.vary" class="smpl">Vary</a> header field (<a href="p6-cache.html#header.vary" title="Vary">Section 7.5</a> of <a href="#Part6" id="rfc.xref.Part6.17"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>) can be used to express the parameters the server uses to select a representation that is subject to server-driven negotiation. 2541 </p> 2542 <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a> <a id="agent-driven.negotiation" href="#agent-driven.negotiation">Agent-driven Negotiation</a></h2> 2543 <p id="rfc.section.10.2.p.1">With agent-driven negotiation, selection of the best representation for a response is performed by the user agent after receiving 2544 an initial response from the origin server. Selection is based on a list of the available representations of the response 2545 included within the header fields or body of the initial response, with each representation identified by its own URI. Selection 2546 from among the representations can be performed automatically (if the user agent is capable of doing so) or manually by the 2547 user selecting from a generated (possibly hypertext) menu. 2548 </p> 2549 <p id="rfc.section.10.2.p.2">Agent-driven negotiation is advantageous when the response would vary over commonly-used dimensions (such as type, language, 2550 or encoding), when the origin server is unable to determine a user agent's capabilities from examining the request, and generally 2551 when public caches are used to distribute server load and reduce network usage. 2552 </p> 2553 <p id="rfc.section.10.2.p.3">Agent-driven negotiation suffers from the disadvantage of needing a second request to obtain the best alternate representation. 2554 This second request is only efficient when caching is used. In addition, this specification does not define any mechanism 2555 for supporting automatic selection, though it also does not prevent any such mechanism from being developed as an extension 2556 and used within HTTP/1.1. 2557 </p> 2558 <p id="rfc.section.10.2.p.4">This specification defines the <a href="#status.300" class="smpl">300 (Multiple Choices)</a> and <a href="#status.406" class="smpl">406 (Not Acceptable)</a> status codes for enabling agent-driven negotiation when the server is unwilling or unable to provide a varying response using 2559 server-driven negotiation. 2560 </p> 2561 <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a> <a id="quality.values" href="#quality.values">Quality Values</a></h2> 2562 <p id="rfc.section.10.3.p.1">Many of the request header fields for server-driven content negotiation use a common parameter, named "q", to assign a relative 2563 "weight" to the preference for that associated kind of content. This weight is referred to as a "quality value" (or "qvalue") 2564 because the same parameter name is often used within server configurations to assign a weight to the relative quality of the 2565 various representations that can be selected for a resource. 2566 </p> 2567 <p id="rfc.section.10.3.p.2">The weight is normalized to a real number in the range 0 through 1, where 0.001 is the least preferred and 1 is the most preferred; 2568 a value of 0 means "not acceptable". If no "q" parameter is present, the default weight is 1. 2569 </p> 2570 <div id="rfc.figure.u.21"></div><pre class="inline"><span id="rfc.iref.g.31"></span><span id="rfc.iref.g.32"></span> <a href="#quality.values" class="smpl">weight</a> = <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> "q=" <a href="#quality.values" class="smpl">qvalue</a> 2571 <a href="#quality.values" class="smpl">qvalue</a> = ( "0" [ "." 0*3<a href="#imported.abnf" class="smpl">DIGIT</a> ] ) 2572 / ( "1" [ "." 0*3("0") ] ) 2573 </pre><p id="rfc.section.10.3.p.4">A sender of qvalue <em class="bcp14">MUST NOT</em> generate more than three digits after the decimal point. User configuration of these values ought to be limited in the same 2574 fashion. 2575 </p> 2576 <h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a> <a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1> 2577 <p id="rfc.section.11.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to request and response semantics and to the 2575 <h1 id="rfc.section.10"><a href="#rfc.section.10">10.</a> <a id="header.field.definitions" href="#header.field.definitions">Header Field Definitions</a></h1> 2576 <p id="rfc.section.10.p.1">This section defines the syntax and semantics of HTTP/1.1 header fields related to request and response semantics and to the 2578 2577 payload of messages. 2579 2578 </p> 2580 2579 <div id="rfc.iref.a.1"></div> 2581 2580 <div id="rfc.iref.h.2"></div> 2582 <h2 id="rfc.section.1 1.1"><a href="#rfc.section.11.1">11.1</a> <a id="header.accept" href="#header.accept">Accept</a></h2>2583 <p id="rfc.section.1 1.1.p.1">The "Accept" header field can be used by user agents to specify response media types that are acceptable. Accept header fields2581 <h2 id="rfc.section.10.1"><a href="#rfc.section.10.1">10.1</a> <a id="header.accept" href="#header.accept">Accept</a></h2> 2582 <p id="rfc.section.10.1.p.1">The "Accept" header field can be used by user agents to specify response media types that are acceptable. Accept header fields 2584 2583 can be used to indicate that the request is specifically limited to a small set of desired types, as in the case of a request 2585 2584 for an in-line image. … … 2593 2592 <a href="#header.accept" class="smpl">accept-params</a> = <a href="#quality.values" class="smpl">weight</a> *( <a href="#header.accept" class="smpl">accept-ext</a> ) 2594 2593 <a href="#header.accept" class="smpl">accept-ext</a> = <a href="#imported.abnf" class="smpl">OWS</a> ";" <a href="#imported.abnf" class="smpl">OWS</a> <a href="#imported.abnf" class="smpl">token</a> [ "=" <a href="#imported.abnf" class="smpl">word</a> ] 2595 </pre><p id="rfc.section.1 1.1.p.3">The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating2594 </pre><p id="rfc.section.10.1.p.3">The asterisk "*" character is used to group media types into ranges, with "*/*" indicating all media types and "type/*" indicating 2596 2595 all subtypes of that type. The media-range <em class="bcp14">MAY</em> include media type parameters that are applicable to that range. 2597 2596 </p> 2598 <p id="rfc.section.1 1.1.p.4">Each media-range <em class="bcp14">MAY</em> be followed by one or more accept-params, beginning with the "q" parameter for indicating a relative weight, as defined in <a href="#quality.values" title="Quality Values">Section 10.3</a>. The first "q" parameter (if any) separates the media-range parameter(s) from the accept-params.2599 </p> 2600 <div class="note" id="rfc.section.1 1.1.p.5">2597 <p id="rfc.section.10.1.p.4">Each media-range <em class="bcp14">MAY</em> be followed by one or more accept-params, beginning with the "q" parameter for indicating a relative weight, as defined in <a href="#quality.values" title="Quality Values">Section 3.4.3</a>. The first "q" parameter (if any) separates the media-range parameter(s) from the accept-params. 2598 </p> 2599 <div class="note" id="rfc.section.10.1.p.5"> 2601 2600 <p> <b>Note:</b> Use of the "q" parameter name to separate media type parameters from Accept extension parameters is due to historical practice. 2602 2601 Although this prevents any media type parameter named "q" from being used with a media range, such an event is believed to … … 2605 2604 </p> 2606 2605 </div> 2607 <p id="rfc.section.1 1.1.p.6">The example</p>2606 <p id="rfc.section.10.1.p.6">The example</p> 2608 2607 <div id="rfc.figure.u.23"></div><pre class="text"> Accept: audio/*; q=0.2, audio/basic 2609 </pre><p id="rfc.section.1 1.1.p.8"> <em class="bcp14">SHOULD</em> be interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80% mark-down in2608 </pre><p id="rfc.section.10.1.p.8"> <em class="bcp14">SHOULD</em> be interpreted as "I prefer audio/basic, but send me any audio type if it is the best available after an 80% mark-down in 2610 2609 quality". 2611 2610 </p> 2612 <p id="rfc.section.1 1.1.p.9">A request without any Accept header field implies that the user agent will accept any media type in response. If an Accept2611 <p id="rfc.section.10.1.p.9">A request without any Accept header field implies that the user agent will accept any media type in response. If an Accept 2613 2612 header field is present in a request and none of the available representations for the response have a media type that is 2614 2613 listed as acceptable, the origin server <em class="bcp14">MAY</em> either honor the Accept header field by sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response or disregard the Accept header field by treating the response as if it is not subject to content negotiation. 2615 2614 </p> 2616 <p id="rfc.section.1 1.1.p.10">A more elaborate example is</p>2615 <p id="rfc.section.10.1.p.10">A more elaborate example is</p> 2617 2616 <div id="rfc.figure.u.24"></div><pre class="text"> Accept: text/plain; q=0.5, text/html, 2618 2617 text/x-dvi; q=0.8, text/x-c 2619 </pre><p id="rfc.section.1 1.1.p.12">Verbally, this would be interpreted as "text/html and text/x-c are the preferred media types, but if they do not exist, then2618 </pre><p id="rfc.section.10.1.p.12">Verbally, this would be interpreted as "text/html and text/x-c are the preferred media types, but if they do not exist, then 2620 2619 send the text/x-dvi representation, and if that does not exist, send the text/plain representation". 2621 2620 </p> 2622 <p id="rfc.section.1 1.1.p.13">Media ranges can be overridden by more specific media ranges or specific media types. If more than one media range applies2621 <p id="rfc.section.10.1.p.13">Media ranges can be overridden by more specific media ranges or specific media types. If more than one media range applies 2623 2622 to a given type, the most specific reference has precedence. For example, 2624 2623 </p> 2625 2624 <div id="rfc.figure.u.25"></div><pre class="text"> Accept: text/*, text/plain, text/plain;format=flowed, */* 2626 </pre><p id="rfc.section.1 1.1.p.15">have the following precedence: </p>2625 </pre><p id="rfc.section.10.1.p.15">have the following precedence: </p> 2627 2626 <ol> 2628 2627 <li>text/plain;format=flowed</li> … … 2631 2630 <li>*/*</li> 2632 2631 </ol> 2633 <p id="rfc.section.1 1.1.p.16">The media type quality factor associated with a given type is determined by finding the media range with the highest precedence2632 <p id="rfc.section.10.1.p.16">The media type quality factor associated with a given type is determined by finding the media range with the highest precedence 2634 2633 which matches that type. For example, 2635 2634 </p> 2636 2635 <div id="rfc.figure.u.26"></div><pre class="text"> Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1, 2637 2636 text/html;level=2;q=0.4, */*;q=0.5 2638 </pre><p id="rfc.section.1 1.1.p.18">would cause the following values to be associated:</p>2637 </pre><p id="rfc.section.10.1.p.18">would cause the following values to be associated:</p> 2639 2638 <div id="rfc.table.u.11"> 2640 2639 <table class="tt full left" cellpadding="3" cellspacing="0"> … … 2673 2672 </table> 2674 2673 </div> 2675 <p id="rfc.section.1 1.1.p.19"> <b>Note:</b> A user agent might be provided with a default set of quality values for certain media ranges. However, unless the user agent2674 <p id="rfc.section.10.1.p.19"> <b>Note:</b> A user agent might be provided with a default set of quality values for certain media ranges. However, unless the user agent 2676 2675 is a closed system which cannot interact with other rendering agents, this default set ought to be configurable by the user. 2677 2676 </p> 2678 2677 <div id="rfc.iref.a.2"></div> 2679 2678 <div id="rfc.iref.h.3"></div> 2680 <h2 id="rfc.section.1 1.2"><a href="#rfc.section.11.2">11.2</a> <a id="header.accept-charset" href="#header.accept-charset">Accept-Charset</a></h2>2681 <p id="rfc.section.1 1.2.p.1">The "Accept-Charset" header field can be used by user agents to indicate what character encodings are acceptable in a response2679 <h2 id="rfc.section.10.2"><a href="#rfc.section.10.2">10.2</a> <a id="header.accept-charset" href="#header.accept-charset">Accept-Charset</a></h2> 2680 <p id="rfc.section.10.2.p.1">The "Accept-Charset" header field can be used by user agents to indicate what character encodings are acceptable in a response 2682 2681 payload. This field allows clients capable of understanding more comprehensive or special-purpose character encodings to signal 2683 2682 that capability to a server which is capable of representing documents in those character encodings. 2684 2683 </p> 2685 2684 <div id="rfc.figure.u.27"></div><pre class="inline"><span id="rfc.iref.g.37"></span> <a href="#header.accept-charset" class="smpl">Accept-Charset</a> = 1#( ( <a href="#rule.charset" class="smpl">charset</a> / "*" ) [ <a href="#quality.values" class="smpl">weight</a> ] ) 2686 </pre><p id="rfc.section.1 1.2.p.3">Character encoding values (a.k.a., charsets) are described in <a href="#character.sets" title="Character Encodings (charset)">Section 8.3</a>. Each charset <em class="bcp14">MAY</em> be given an associated quality value which represents the user's preference for that charset, as defined in <a href="#quality.values" title="Quality Values">Section 10.3</a>. An example is2685 </pre><p id="rfc.section.10.2.p.3">Character encoding values (a.k.a., charsets) are described in <a href="#character.sets" title="Character Encodings (charset)">Section 8.3</a>. Each charset <em class="bcp14">MAY</em> be given an associated quality value which represents the user's preference for that charset, as defined in <a href="#quality.values" title="Quality Values">Section 3.4.3</a>. An example is 2687 2686 </p> 2688 2687 <div id="rfc.figure.u.28"></div><pre class="text"> Accept-Charset: iso-8859-5, unicode-1-1;q=0.8 2689 </pre><p id="rfc.section.1 1.2.p.5">The special value "*", if present in the Accept-Charset field, matches every character encoding which is not mentioned elsewhere2688 </pre><p id="rfc.section.10.2.p.5">The special value "*", if present in the Accept-Charset field, matches every character encoding which is not mentioned elsewhere 2690 2689 in the Accept-Charset field. If no "*" is present in an Accept-Charset field, then any character encodings not explicitly 2691 2690 mentioned in the field are considered "not acceptable" to the client. 2692 2691 </p> 2693 <p id="rfc.section.1 1.2.p.6">A request without any Accept-Charset header field implies that the user agent will accept any character encoding in response.</p>2694 <p id="rfc.section.1 1.2.p.7">If an Accept-Charset header field is present in a request and none of the available representations for the response have2692 <p id="rfc.section.10.2.p.6">A request without any Accept-Charset header field implies that the user agent will accept any character encoding in response.</p> 2693 <p id="rfc.section.10.2.p.7">If an Accept-Charset header field is present in a request and none of the available representations for the response have 2695 2694 a character encoding that is listed as acceptable, the origin server <em class="bcp14">MAY</em> either honor the Accept-Charset header field by sending a <a href="#status.406" class="smpl">406 (Not Acceptable)</a> response or disregard the Accept-Charset header field by treating the response as if it is not subject to content negotiation. 2696 2695 </p> 2697 2696 <div id="rfc.iref.a.3"></div> 2698 2697 <div id="rfc.iref.h.4"></div> 2699 <h2 id="rfc.section.1 1.3"><a href="#rfc.section.11.3">11.3</a> <a id="header.accept-encoding" href="#header.accept-encoding">Accept-Encoding</a></h2>2700 <p id="rfc.section.1 1.3.p.1">The "Accept-Encoding" header field can be used by user agents to indicate what response content-codings (<a href="#content.codings" title="Content Codings">Section 8.4</a>) are acceptable in the response. An "identity" token is used as a synonym for "no encoding" in order to communicate when2698 <h2 id="rfc.section.10.3"><a href="#rfc.section.10.3">10.3</a> <a id="header.accept-encoding" href="#header.accept-encoding">Accept-Encoding</a></h2> 2699 <p id="rfc.section.10.3.p.1">The "Accept-Encoding" header field can be used by user agents to indicate what response content-codings (<a href="#content.codings" title="Content Codings">Section 8.4</a>) are acceptable in the response. An "identity" token is used as a synonym for "no encoding" in order to communicate when 2701 2700 no encoding is preferred. 2702 2701 </p> 2703 2702 <div id="rfc.figure.u.29"></div><pre class="inline"><span id="rfc.iref.g.38"></span><span id="rfc.iref.g.39"></span> <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> = #( <a href="#header.accept-encoding" class="smpl">codings</a> [ <a href="#quality.values" class="smpl">weight</a> ] ) 2704 2703 <a href="#header.accept-encoding" class="smpl">codings</a> = <a href="#content.codings" class="smpl">content-coding</a> / "identity" / "*" 2705 </pre><p id="rfc.section.1 1.3.p.3">Each codings value <em class="bcp14">MAY</em> be given an associated quality value which represents the preference for that encoding, as defined in <a href="#quality.values" title="Quality Values">Section 10.3</a>.2706 </p> 2707 <p id="rfc.section.1 1.3.p.4">For example,</p>2704 </pre><p id="rfc.section.10.3.p.3">Each codings value <em class="bcp14">MAY</em> be given an associated quality value which represents the preference for that encoding, as defined in <a href="#quality.values" title="Quality Values">Section 3.4.3</a>. 2705 </p> 2706 <p id="rfc.section.10.3.p.4">For example,</p> 2708 2707 <div id="rfc.figure.u.30"></div><pre class="text"> Accept-Encoding: compress, gzip 2709 2708 Accept-Encoding: … … 2711 2710 Accept-Encoding: compress;q=0.5, gzip;q=1.0 2712 2711 Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0 2713 </pre><p id="rfc.section.1 1.3.p.6">A server tests whether a content-coding for a given representation is acceptable, according to an Accept-Encoding field, using2712 </pre><p id="rfc.section.10.3.p.6">A server tests whether a content-coding for a given representation is acceptable, according to an Accept-Encoding field, using 2714 2713 these rules: 2715 2714 </p> … … 2722 2721 </li> 2723 2722 <li>If the representation's content-coding is one of the content-codings listed in the Accept-Encoding field, then it is acceptable 2724 unless it is accompanied by a qvalue of 0. (As defined in <a href="#quality.values" title="Quality Values">Section 10.3</a>, a qvalue of 0 means "not acceptable".)2723 unless it is accompanied by a qvalue of 0. (As defined in <a href="#quality.values" title="Quality Values">Section 3.4.3</a>, a qvalue of 0 means "not acceptable".) 2725 2724 </li> 2726 2725 <li>If multiple content-codings are acceptable, then the acceptable content-coding with the highest non-zero qvalue is preferred.</li> 2727 2726 </ol> 2728 <p id="rfc.section.1 1.3.p.7">An Accept-Encoding header field with a combined field-value that is empty implies that the user agent does not want any content-coding2727 <p id="rfc.section.10.3.p.7">An Accept-Encoding header field with a combined field-value that is empty implies that the user agent does not want any content-coding 2729 2728 in response. If an Accept-Encoding header field is present in a request and none of the available representations for the 2730 2729 response have a content-coding that is listed as acceptable, the origin server <em class="bcp14">SHOULD</em> send a response without any content-coding. 2731 2730 </p> 2732 <p id="rfc.section.1 1.3.p.8">A request without an Accept-Encoding header field implies that the user agent will accept any content-coding in response.</p>2733 <div class="note" id="rfc.section.1 1.3.p.9">2731 <p id="rfc.section.10.3.p.8">A request without an Accept-Encoding header field implies that the user agent will accept any content-coding in response.</p> 2732 <div class="note" id="rfc.section.10.3.p.9"> 2734 2733 <p> <b>Note:</b> Most HTTP/1.0 applications do not recognize or obey qvalues associated with content-codings. This means that qvalues will 2735 2734 not work and are not permitted with x-gzip or x-compress. … … 2738 2737 <div id="rfc.iref.a.4"></div> 2739 2738 <div id="rfc.iref.h.5"></div> 2740 <h2 id="rfc.section.1 1.4"><a href="#rfc.section.11.4">11.4</a> <a id="header.accept-language" href="#header.accept-language">Accept-Language</a></h2>2741 <p id="rfc.section.1 1.4.p.1">The "Accept-Language" header field can be used by user agents to indicate the set of natural languages that are preferred2739 <h2 id="rfc.section.10.4"><a href="#rfc.section.10.4">10.4</a> <a id="header.accept-language" href="#header.accept-language">Accept-Language</a></h2> 2740 <p id="rfc.section.10.4.p.1">The "Accept-Language" header field can be used by user agents to indicate the set of natural languages that are preferred 2742 2741 in the response. Language tags are defined in <a href="#language.tags" title="Language Tags">Section 8.6</a>. 2743 2742 </p> … … 2745 2744 <a href="#header.accept-language" class="smpl">language-range</a> = 2746 2745 <language-range, defined in <a href="#RFC4647" id="rfc.xref.RFC4647.1"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="http://tools.ietf.org/html/rfc4647#section-2.1">Section 2.1</a>> 2747 </pre><p id="rfc.section.1 1.4.p.3">Each language-range can be given an associated quality value which represents an estimate of the user's preference for the2748 languages specified by that range, as defined in <a href="#quality.values" title="Quality Values">Section 10.3</a>. For example,2746 </pre><p id="rfc.section.10.4.p.3">Each language-range can be given an associated quality value which represents an estimate of the user's preference for the 2747 languages specified by that range, as defined in <a href="#quality.values" title="Quality Values">Section 3.4.3</a>. For example, 2749 2748 </p> 2750 2749 <div id="rfc.figure.u.32"></div><pre class="text"> Accept-Language: da, en-gb;q=0.8, en;q=0.7 2751 </pre><p id="rfc.section.1 1.4.p.5">would mean: "I prefer Danish, but will accept British English and other types of English". (see also <a href="http://tools.ietf.org/html/rfc4647#section-2.3">Section 2.3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>)2752 </p> 2753 <p id="rfc.section.1 1.4.p.6">For matching, <a href="http://tools.ietf.org/html/rfc4647#section-3">Section 3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.3"><cite title="Matching of Language Tags">[RFC4647]</cite></a> defines several matching schemes. Implementations can offer the most appropriate matching scheme for their requirements.2754 </p> 2755 <div class="note" id="rfc.section.1 1.4.p.7">2750 </pre><p id="rfc.section.10.4.p.5">would mean: "I prefer Danish, but will accept British English and other types of English". (see also <a href="http://tools.ietf.org/html/rfc4647#section-2.3">Section 2.3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.2"><cite title="Matching of Language Tags">[RFC4647]</cite></a>) 2751 </p> 2752 <p id="rfc.section.10.4.p.6">For matching, <a href="http://tools.ietf.org/html/rfc4647#section-3">Section 3</a> of <a href="#RFC4647" id="rfc.xref.RFC4647.3"><cite title="Matching of Language Tags">[RFC4647]</cite></a> defines several matching schemes. Implementations can offer the most appropriate matching scheme for their requirements. 2753 </p> 2754 <div class="note" id="rfc.section.10.4.p.7"> 2756 2755 <p> <b>Note:</b> The "Basic Filtering" scheme (<a href="#RFC4647" id="rfc.xref.RFC4647.4"><cite title="Matching of Language Tags">[RFC4647]</cite></a>, <a href="http://tools.ietf.org/html/rfc4647#section-3.3.1">Section 3.3.1</a>) is identical to the matching scheme that was previously defined in <a href="http://tools.ietf.org/html/rfc2616#section-14.4">Section 14.4</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.2"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>. 2757 2756 </p> 2758 2757 </div> 2759 <p id="rfc.section.1 1.4.p.8">It might be contrary to the privacy expectations of the user to send an Accept-Language header field with the complete linguistic2760 preferences of the user in every request. For a discussion of this issue, see <a href="#privacy.issues.connected.to.accept.header.fields" title="Privacy Issues Connected to Accept Header Fields">Section 1 3.5</a>.2761 </p> 2762 <p id="rfc.section.1 1.4.p.9">As intelligibility is highly dependent on the individual user, it is recommended that client applications make the choice2758 <p id="rfc.section.10.4.p.8">It might be contrary to the privacy expectations of the user to send an Accept-Language header field with the complete linguistic 2759 preferences of the user in every request. For a discussion of this issue, see <a href="#privacy.issues.connected.to.accept.header.fields" title="Privacy Issues Connected to Accept Header Fields">Section 12.5</a>. 2760 </p> 2761 <p id="rfc.section.10.4.p.9">As intelligibility is highly dependent on the individual user, it is recommended that client applications make the choice 2763 2762 of linguistic preference available to the user. If the choice is not made available, then the Accept-Language header field <em class="bcp14">MUST NOT</em> be given in the request. 2764 2763 </p> 2765 <div class="note" id="rfc.section.1 1.4.p.10">2764 <div class="note" id="rfc.section.10.4.p.10"> 2766 2765 <p> <b>Note:</b> When making the choice of linguistic preference available to the user, we remind implementers of the fact that users are not 2767 2766 familiar with the details of language matching as described above, and ought to be provided appropriate guidance. As an example, … … 2772 2771 <div id="rfc.iref.a.5"></div> 2773 2772 <div id="rfc.iref.h.6"></div> 2774 <h2 id="rfc.section.1 1.5"><a href="#rfc.section.11.5">11.5</a> <a id="header.allow" href="#header.allow">Allow</a></h2>2775 <p id="rfc.section.1 1.5.p.1">The "Allow" header field lists the set of methods advertised as supported by the target resource. The purpose of this field2773 <h2 id="rfc.section.10.5"><a href="#rfc.section.10.5">10.5</a> <a id="header.allow" href="#header.allow">Allow</a></h2> 2774 <p id="rfc.section.10.5.p.1">The "Allow" header field lists the set of methods advertised as supported by the target resource. The purpose of this field 2776 2775 is strictly to inform the recipient of valid request methods associated with the resource. 2777 2776 </p> 2778 2777 <div id="rfc.figure.u.33"></div><pre class="inline"><span id="rfc.iref.g.42"></span> <a href="#header.allow" class="smpl">Allow</a> = #<a href="#method.overview" class="smpl">method</a> 2779 </pre><p id="rfc.section.1 1.5.p.3">Example of use:</p>2778 </pre><p id="rfc.section.10.5.p.3">Example of use:</p> 2780 2779 <div id="rfc.figure.u.34"></div><pre class="text"> Allow: GET, HEAD, PUT 2781 </pre><p id="rfc.section.1 1.5.p.5">The actual set of allowed methods is defined by the origin server at the time of each request.</p>2782 <p id="rfc.section.1 1.5.p.6">A proxy <em class="bcp14">MUST NOT</em> modify the Allow header field — it does not need to understand all the methods specified in order to handle them according2780 </pre><p id="rfc.section.10.5.p.5">The actual set of allowed methods is defined by the origin server at the time of each request.</p> 2781 <p id="rfc.section.10.5.p.6">A proxy <em class="bcp14">MUST NOT</em> modify the Allow header field — it does not need to understand all the methods specified in order to handle them according 2783 2782 to the generic message handling rules. 2784 2783 </p> 2785 2784 <div id="rfc.iref.c.8"></div> 2786 2785 <div id="rfc.iref.h.7"></div> 2787 <h2 id="rfc.section.1 1.6"><a href="#rfc.section.11.6">11.6</a> <a id="header.content-encoding" href="#header.content-encoding">Content-Encoding</a></h2>2788 <p id="rfc.section.1 1.6.p.1">The "Content-Encoding" header field indicates what content-codings have been applied to the representation beyond those inherent2786 <h2 id="rfc.section.10.6"><a href="#rfc.section.10.6">10.6</a> <a id="header.content-encoding" href="#header.content-encoding">Content-Encoding</a></h2> 2787 <p id="rfc.section.10.6.p.1">The "Content-Encoding" header field indicates what content-codings have been applied to the representation beyond those inherent 2789 2788 in the media type, and thus what decoding mechanisms have to be applied in order to obtain the media-type referenced by the <a href="#header.content-type" class="smpl">Content-Type</a> header field. Content-Encoding is primarily used to allow a representation to be compressed without losing the identity of 2790 2789 its underlying media type. 2791 2790 </p> 2792 2791 <div id="rfc.figure.u.35"></div><pre class="inline"><span id="rfc.iref.g.43"></span> <a href="#header.content-encoding" class="smpl">Content-Encoding</a> = 1#<a href="#content.codings" class="smpl">content-coding</a> 2793 </pre><p id="rfc.section.1 1.6.p.3">Content codings are defined in <a href="#content.codings" title="Content Codings">Section 8.4</a>. An example of its use is2792 </pre><p id="rfc.section.10.6.p.3">Content codings are defined in <a href="#content.codings" title="Content Codings">Section 8.4</a>. An example of its use is 2794 2793 </p> 2795 2794 <div id="rfc.figure.u.36"></div><pre class="text"> Content-Encoding: gzip 2796 </pre><p id="rfc.section.1 1.6.p.5">The content-coding is a characteristic of the representation. Typically, the representation body is stored with this encoding2795 </pre><p id="rfc.section.10.6.p.5">The content-coding is a characteristic of the representation. Typically, the representation body is stored with this encoding 2797 2796 and is only decoded before rendering or analogous usage. However, a transforming proxy <em class="bcp14">MAY</em> modify the content-coding if the new coding is known to be acceptable to the recipient, unless the "no-transform" cache-control 2798 2797 directive is present in the message. 2799 2798 </p> 2800 <p id="rfc.section.1 1.6.p.6">If the media type includes an inherent encoding, such as a data format that is always compressed, then that encoding would2799 <p id="rfc.section.10.6.p.6">If the media type includes an inherent encoding, such as a data format that is always compressed, then that encoding would 2801 2800 not be restated as a Content-Encoding even if it happens to be the same algorithm as one of the content-codings. Such a content-coding 2802 2801 would only be listed if, for some bizarre reason, it is applied a second time to form the representation. Likewise, an origin … … 2805 2804 as ..." dialog instead of automatic decompression and rendering of content). 2806 2805 </p> 2807 <p id="rfc.section.1 1.6.p.7">A representation that has a content-coding applied to it <em class="bcp14">MUST</em> include a Content-Encoding header field that lists the content-coding(s) applied.2808 </p> 2809 <p id="rfc.section.1 1.6.p.8">If multiple encodings have been applied to a representation, the content codings <em class="bcp14">MUST</em> be listed in the order in which they were applied. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other header fields not defined by this specification.2810 </p> 2811 <p id="rfc.section.1 1.6.p.9">If the content-coding of a representation in a request message is not acceptable to the origin server, the server <em class="bcp14">SHOULD</em> respond with a status code of 415 (Unsupported Media Type).2806 <p id="rfc.section.10.6.p.7">A representation that has a content-coding applied to it <em class="bcp14">MUST</em> include a Content-Encoding header field that lists the content-coding(s) applied. 2807 </p> 2808 <p id="rfc.section.10.6.p.8">If multiple encodings have been applied to a representation, the content codings <em class="bcp14">MUST</em> be listed in the order in which they were applied. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other header fields not defined by this specification. 2809 </p> 2810 <p id="rfc.section.10.6.p.9">If the content-coding of a representation in a request message is not acceptable to the origin server, the server <em class="bcp14">SHOULD</em> respond with a status code of 415 (Unsupported Media Type). 2812 2811 </p> 2813 2812 <div id="rfc.iref.c.9"></div> 2814 2813 <div id="rfc.iref.h.8"></div> 2815 <h2 id="rfc.section.1 1.7"><a href="#rfc.section.11.7">11.7</a> <a id="header.content-language" href="#header.content-language">Content-Language</a></h2>2816 <p id="rfc.section.1 1.7.p.1">The "Content-Language" header field describes the natural language(s) of the intended audience for the representation. Note2814 <h2 id="rfc.section.10.7"><a href="#rfc.section.10.7">10.7</a> <a id="header.content-language" href="#header.content-language">Content-Language</a></h2> 2815 <p id="rfc.section.10.7.p.1">The "Content-Language" header field describes the natural language(s) of the intended audience for the representation. Note 2817 2816 that this might not be equivalent to all the languages used within the representation. 2818 2817 </p> 2819 2818 <div id="rfc.figure.u.37"></div><pre class="inline"><span id="rfc.iref.g.44"></span> <a href="#header.content-language" class="smpl">Content-Language</a> = 1#<a href="#language.tags" class="smpl">language-tag</a> 2820 </pre><p id="rfc.section.1 1.7.p.3">Language tags are defined in <a href="#language.tags" title="Language Tags">Section 8.6</a>. The primary purpose of Content-Language is to allow a user to identify and differentiate representations according to the2819 </pre><p id="rfc.section.10.7.p.3">Language tags are defined in <a href="#language.tags" title="Language Tags">Section 8.6</a>. The primary purpose of Content-Language is to allow a user to identify and differentiate representations according to the 2821 2820 user's own preferred language. Thus, if the body content is intended only for a Danish-literate audience, the appropriate 2822 2821 field is 2823 2822 </p> 2824 2823 <div id="rfc.figure.u.38"></div><pre class="text"> Content-Language: da 2825 </pre><p id="rfc.section.1 1.7.p.5">If no Content-Language is specified, the default is that the content is intended for all language audiences. This might mean2824 </pre><p id="rfc.section.10.7.p.5">If no Content-Language is specified, the default is that the content is intended for all language audiences. This might mean 2826 2825 that the sender does not consider it to be specific to any natural language, or that the sender does not know for which language 2827 2826 it is intended. 2828 2827 </p> 2829 <p id="rfc.section.1 1.7.p.6">Multiple languages <em class="bcp14">MAY</em> be listed for content that is intended for multiple audiences. For example, a rendition of the "Treaty of Waitangi", presented2828 <p id="rfc.section.10.7.p.6">Multiple languages <em class="bcp14">MAY</em> be listed for content that is intended for multiple audiences. For example, a rendition of the "Treaty of Waitangi", presented 2830 2829 simultaneously in the original Maori and English versions, would call for 2831 2830 </p> 2832 2831 <div id="rfc.figure.u.39"></div><pre class="text"> Content-Language: mi, en 2833 </pre><p id="rfc.section.1 1.7.p.8">However, just because multiple languages are present within a representation does not mean that it is intended for multiple2832 </pre><p id="rfc.section.10.7.p.8">However, just because multiple languages are present within a representation does not mean that it is intended for multiple 2834 2833 linguistic audiences. An example would be a beginner's language primer, such as "A First Lesson in Latin", which is clearly 2835 2834 intended to be used by an English-literate audience. In this case, the Content-Language would properly only include "en". 2836 2835 </p> 2837 <p id="rfc.section.1 1.7.p.9">Content-Language <em class="bcp14">MAY</em> be applied to any media type — it is not limited to textual documents.2836 <p id="rfc.section.10.7.p.9">Content-Language <em class="bcp14">MAY</em> be applied to any media type — it is not limited to textual documents. 2838 2837 </p> 2839 2838 <div id="rfc.iref.c.10"></div> 2840 2839 <div id="rfc.iref.h.9"></div> 2841 <h2 id="rfc.section.1 1.8"><a href="#rfc.section.11.8">11.8</a> <a id="header.content-location" href="#header.content-location">Content-Location</a></h2>2842 <p id="rfc.section.1 1.8.p.1">The "Content-Location" header field supplies a URI that can be used as a specific identifier for the representation in this2840 <h2 id="rfc.section.10.8"><a href="#rfc.section.10.8">10.8</a> <a id="header.content-location" href="#header.content-location">Content-Location</a></h2> 2841 <p id="rfc.section.10.8.p.1">The "Content-Location" header field supplies a URI that can be used as a specific identifier for the representation in this 2843 2842 message. In other words, if one were to perform a GET on this URI at the time of this message's generation, then a <a href="#status.200" class="smpl">200 (OK)</a> response would contain the same representation that is enclosed as payload in this message. 2844 2843 </p> 2845 2844 <div id="rfc.figure.u.40"></div><pre class="inline"><span id="rfc.iref.g.45"></span> <a href="#header.content-location" class="smpl">Content-Location</a> = <a href="#imported.abnf" class="smpl">absolute-URI</a> / <a href="#imported.abnf" class="smpl">partial-URI</a> 2846 </pre><p id="rfc.section.1 1.8.p.3">The Content-Location value is not a replacement for the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#Part1" id="rfc.xref.Part1.27"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). It is representation metadata. It has the same syntax and semantics as the header field of the same name defined for MIME2845 </pre><p id="rfc.section.10.8.p.3">The Content-Location value is not a replacement for the effective Request URI (<a href="p1-messaging.html#effective.request.uri" title="Effective Request URI">Section 5.5</a> of <a href="#Part1" id="rfc.xref.Part1.27"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). It is representation metadata. It has the same syntax and semantics as the header field of the same name defined for MIME 2847 2846 body parts in <a href="http://tools.ietf.org/html/rfc2557#section-4">Section 4</a> of <a href="#RFC2557" id="rfc.xref.RFC2557.1"><cite title="MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)">[RFC2557]</cite></a>. However, its appearance in an HTTP message has some special implications for HTTP recipients. 2848 2847 </p> 2849 <p id="rfc.section.1 1.8.p.4">If Content-Location is included in a response message and its value is the same as the effective request URI, then the response2848 <p id="rfc.section.10.8.p.4">If Content-Location is included in a response message and its value is the same as the effective request URI, then the response 2850 2849 payload <em class="bcp14">SHOULD</em> be considered a current representation of that resource. For a GET or HEAD request, this is the same as the default semantics 2851 2850 when no Content-Location is provided by the server. For a state-changing request like PUT or POST, it implies that the server's … … 2854 2853 need for a subsequent GET request. 2855 2854 </p> 2856 <p id="rfc.section.1 1.8.p.5">If Content-Location is included in a response message and its value differs from the effective request URI, then the origin2855 <p id="rfc.section.10.8.p.5">If Content-Location is included in a response message and its value differs from the effective request URI, then the origin 2857 2856 server is informing recipients that this representation has its own, presumably more specific, identifier. For a GET or HEAD 2858 2857 request, this is an indication that the effective request URI identifies a resource that is subject to content negotiation … … 2862 2861 the payload of the <a href="#status.200" class="smpl">200 (OK)</a> response; the Content-Location value provides an identifier for retrieving a copy of that same receipt in the future. 2863 2862 </p> 2864 <p id="rfc.section.1 1.8.p.6">If Content-Location is included in a request message, then it <em class="bcp14">MAY</em> be interpreted by the origin server as an indication of where the user agent originally obtained the content of the enclosed2863 <p id="rfc.section.10.8.p.6">If Content-Location is included in a request message, then it <em class="bcp14">MAY</em> be interpreted by the origin server as an indication of where the user agent originally obtained the content of the enclosed 2865 2864 representation (prior to any subsequent modification of the content by that user agent). In other words, the user agent is 2866 2865 providing the same representation metadata that it received with the original representation. However, such interpretation <em class="bcp14">MUST NOT</em> be used to alter the semantics of the method requested by the client. For example, if a client makes a PUT request on a negotiated … … 2870 2869 latter semantics, it would have applied the PUT directly to the Content-Location URI. 2871 2870 </p> 2872 <p id="rfc.section.1 1.8.p.7">A Content-Location field received in a request message is transitory information that <em class="bcp14">SHOULD NOT</em> be saved with other representation metadata for use in later responses. The Content-Location's value might be saved for use2871 <p id="rfc.section.10.8.p.7">A Content-Location field received in a request message is transitory information that <em class="bcp14">SHOULD NOT</em> be saved with other representation metadata for use in later responses. The Content-Location's value might be saved for use 2873 2872 in other contexts, such as within source links or other metadata. 2874 2873 </p> 2875 <p id="rfc.section.1 1.8.p.8">A cache cannot assume that a representation with a Content-Location different from the URI used to retrieve it can be used2874 <p id="rfc.section.10.8.p.8">A cache cannot assume that a representation with a Content-Location different from the URI used to retrieve it can be used 2876 2875 to respond to later requests on that Content-Location URI. 2877 2876 </p> 2878 <p id="rfc.section.1 1.8.p.9">If the Content-Location value is a partial URI, the partial URI is interpreted relative to the effective request URI.</p>2877 <p id="rfc.section.10.8.p.9">If the Content-Location value is a partial URI, the partial URI is interpreted relative to the effective request URI.</p> 2879 2878 <div id="rfc.iref.c.11"></div> 2880 2879 <div id="rfc.iref.h.10"></div> 2881 <h2 id="rfc.section.1 1.9"><a href="#rfc.section.11.9">11.9</a> <a id="header.content-type" href="#header.content-type">Content-Type</a></h2>2882 <p id="rfc.section.1 1.9.p.1">The "Content-Type" header field indicates the media type of the representation. In the case of responses to the HEAD method,2880 <h2 id="rfc.section.10.9"><a href="#rfc.section.10.9">10.9</a> <a id="header.content-type" href="#header.content-type">Content-Type</a></h2> 2881 <p id="rfc.section.10.9.p.1">The "Content-Type" header field indicates the media type of the representation. In the case of responses to the HEAD method, 2883 2882 the media type is that which would have been sent had the request been a GET. 2884 2883 </p> 2885 2884 <div id="rfc.figure.u.41"></div><pre class="inline"><span id="rfc.iref.g.46"></span> <a href="#header.content-type" class="smpl">Content-Type</a> = <a href="#media.types" class="smpl">media-type</a> 2886 </pre><p id="rfc.section.1 1.9.p.3">Media types are defined in <a href="#media.types" title="Media Types">Section 8.5</a>. An example of the field is2885 </pre><p id="rfc.section.10.9.p.3">Media types are defined in <a href="#media.types" title="Media Types">Section 8.5</a>. An example of the field is 2887 2886 </p> 2888 2887 <div id="rfc.figure.u.42"></div><pre class="text"> Content-Type: text/html; charset=ISO-8859-4 2889 </pre><p id="rfc.section.1 1.9.p.5">Further discussion of Content-Type is provided in <a href="#representation.data" title="Representation Data">Section 3.3</a>.2888 </pre><p id="rfc.section.10.9.p.5">Further discussion of Content-Type is provided in <a href="#representation.data" title="Representation Data">Section 3.3</a>. 2890 2889 </p> 2891 2890 <div id="rfc.iref.d.3"></div> 2892 2891 <div id="rfc.iref.h.11"></div> 2893 <h2 id="rfc.section.1 1.10"><a href="#rfc.section.11.10">11.10</a> <a id="header.date" href="#header.date">Date</a></h2>2894 <p id="rfc.section.1 1.10.p.1">The "Date" header field represents the date and time at which the message was originated, having the same semantics as the2892 <h2 id="rfc.section.10.10"><a href="#rfc.section.10.10">10.10</a> <a id="header.date" href="#header.date">Date</a></h2> 2893 <p id="rfc.section.10.10.p.1">The "Date" header field represents the date and time at which the message was originated, having the same semantics as the 2895 2894 Origination Date Field (orig-date) defined in <a href="http://tools.ietf.org/html/rfc5322#section-3.6.1">Section 3.6.1</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.2"><cite title="Internet Message Format">[RFC5322]</cite></a>. The field value is an HTTP-date, as defined in <a href="#http.date" title="Date/Time Formats">Section 8.1</a>; it <em class="bcp14">MUST</em> be sent in rfc1123-date format. 2896 2895 </p> 2897 2896 <div id="rfc.figure.u.43"></div><pre class="inline"><span id="rfc.iref.g.47"></span> <a href="#header.date" class="smpl">Date</a> = <a href="#http.date" class="smpl">HTTP-date</a> 2898 </pre><p id="rfc.section.1 1.10.p.3">An example is</p>2897 </pre><p id="rfc.section.10.10.p.3">An example is</p> 2899 2898 <div id="rfc.figure.u.44"></div><pre class="text"> Date: Tue, 15 Nov 1994 08:12:31 GMT 2900 </pre><p id="rfc.section.1 1.10.p.5">Origin servers <em class="bcp14">MUST</em> include a Date header field in all responses, except in these cases:2899 </pre><p id="rfc.section.10.10.p.5">Origin servers <em class="bcp14">MUST</em> include a Date header field in all responses, except in these cases: 2901 2900 </p> 2902 2901 <ol> … … 2909 2908 </li> 2910 2909 </ol> 2911 <p id="rfc.section.1 1.10.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient.2912 </p> 2913 <p id="rfc.section.1 1.10.p.7">Clients can use the Date header field as well; in order to keep request messages small, they are advised not to include it2910 <p id="rfc.section.10.10.p.6">A received message that does not have a Date header field <em class="bcp14">MUST</em> be assigned one by the recipient if the message will be cached by that recipient. 2911 </p> 2912 <p id="rfc.section.10.10.p.7">Clients can use the Date header field as well; in order to keep request messages small, they are advised not to include it 2914 2913 when it doesn't convey any useful information (as is usually the case for requests that do not contain a payload). 2915 2914 </p> 2916 <p id="rfc.section.1 1.10.p.8">The HTTP-date sent in a Date header field <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means2915 <p id="rfc.section.10.10.p.8">The HTTP-date sent in a Date header field <em class="bcp14">SHOULD NOT</em> represent a date and time subsequent to the generation of the message. It <em class="bcp14">SHOULD</em> represent the best available approximation of the date and time of message generation, unless the implementation has no means 2917 2916 of generating a reasonably accurate date and time. In theory, the date ought to represent the moment just before the payload 2918 2917 is generated. In practice, the date can be generated at any time during the message origination without affecting its semantic … … 2921 2920 <div id="rfc.iref.e.1"></div> 2922 2921 <div id="rfc.iref.h.12"></div> 2923 <h2 id="rfc.section.1 1.11"><a href="#rfc.section.11.11">11.11</a> <a id="header.expect" href="#header.expect">Expect</a></h2>2924 <p id="rfc.section.1 1.11.p.1">The "Expect" header field is used to indicate that particular server behaviors are required by the client.</p>2922 <h2 id="rfc.section.10.11"><a href="#rfc.section.10.11">10.11</a> <a id="header.expect" href="#header.expect">Expect</a></h2> 2923 <p id="rfc.section.10.11.p.1">The "Expect" header field is used to indicate that particular server behaviors are required by the client.</p> 2925 2924 <div id="rfc.figure.u.45"></div><pre class="inline"><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> <a href="#header.expect" class="smpl">Expect</a> = 1#<a href="#header.expect" class="smpl">expectation</a> 2926 2925 … … 2931 2930 <a href="#header.expect" class="smpl">expect-name</a> = <a href="#imported.abnf" class="smpl">token</a> 2932 2931 <a href="#header.expect" class="smpl">expect-value</a> = <a href="#imported.abnf" class="smpl">token</a> / <a href="#imported.abnf" class="smpl">quoted-string</a> 2933 </pre><p id="rfc.section.1 1.11.p.3">If all received Expect header field(s) are syntactically valid but contain an expectation that the recipient does not understand2932 </pre><p id="rfc.section.10.11.p.3">If all received Expect header field(s) are syntactically valid but contain an expectation that the recipient does not understand 2934 2933 or cannot comply with, the recipient <em class="bcp14">MUST</em> respond with a <a href="#status.417" class="smpl">417 (Expectation Failed)</a> status code. A recipient of a syntactically invalid Expectation header field <em class="bcp14">MUST</em> respond with a <a href="#status.4xx" class="smpl">4xx</a> status code other than 417. 2935 2934 </p> 2936 <p id="rfc.section.1 1.11.p.4">The only expectation defined by this specification is:</p>2937 <p id="rfc.section.1 1.11.p.5"><span id="rfc.iref.142"></span><span id="rfc.iref.e.2"></span> 100-continue2935 <p id="rfc.section.10.11.p.4">The only expectation defined by this specification is:</p> 2936 <p id="rfc.section.10.11.p.5"><span id="rfc.iref.142"></span><span id="rfc.iref.e.2"></span> 100-continue 2938 2937 </p> 2939 2938 <ul class="empty"> … … 2941 2940 </li> 2942 2941 </ul> 2943 <p id="rfc.section.1 1.11.p.6">Comparison is case-insensitive for names (expect-name), and case-sensitive for values (expect-value).</p>2944 <p id="rfc.section.1 1.11.p.7">The Expect mechanism is hop-by-hop: the above requirements apply to any server, including proxies. However, the Expect header2942 <p id="rfc.section.10.11.p.6">Comparison is case-insensitive for names (expect-name), and case-sensitive for values (expect-value).</p> 2943 <p id="rfc.section.10.11.p.7">The Expect mechanism is hop-by-hop: the above requirements apply to any server, including proxies. However, the Expect header 2945 2944 field itself is end-to-end; it <em class="bcp14">MUST</em> be forwarded if the request is forwarded. 2946 2945 </p> 2947 <p id="rfc.section.1 1.11.p.8">Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect header field.</p>2946 <p id="rfc.section.10.11.p.8">Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect header field.</p> 2948 2947 <div id="rfc.iref.f.1"></div> 2949 2948 <div id="rfc.iref.h.13"></div> 2950 <h2 id="rfc.section.1 1.12"><a href="#rfc.section.11.12">11.12</a> <a id="header.from" href="#header.from">From</a></h2>2951 <p id="rfc.section.1 1.12.p.1">The "From" header field, if given, <em class="bcp14">SHOULD</em> contain an Internet e-mail address for the human user who controls the requesting user agent. The address <em class="bcp14">SHOULD</em> be machine-usable, as defined by "mailbox" in <a href="http://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>:2949 <h2 id="rfc.section.10.12"><a href="#rfc.section.10.12">10.12</a> <a id="header.from" href="#header.from">From</a></h2> 2950 <p id="rfc.section.10.12.p.1">The "From" header field, if given, <em class="bcp14">SHOULD</em> contain an Internet e-mail address for the human user who controls the requesting user agent. The address <em class="bcp14">SHOULD</em> be machine-usable, as defined by "mailbox" in <a href="http://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a> of <a href="#RFC5322" id="rfc.xref.RFC5322.3"><cite title="Internet Message Format">[RFC5322]</cite></a>: 2952 2951 </p> 2953 2952 <div id="rfc.figure.u.46"></div><pre class="inline"><span id="rfc.iref.g.53"></span> <a href="#header.from" class="smpl">From</a> = <a href="#header.from" class="smpl">mailbox</a> 2954 2953 2955 2954 <a href="#header.from" class="smpl">mailbox</a> = <mailbox, defined in <a href="#RFC5322" id="rfc.xref.RFC5322.4"><cite title="Internet Message Format">[RFC5322]</cite></a>, <a href="http://tools.ietf.org/html/rfc5322#section-3.4">Section 3.4</a>> 2956 </pre><p id="rfc.section.1 1.12.p.3">An example is:</p>2955 </pre><p id="rfc.section.10.12.p.3">An example is:</p> 2957 2956 <div id="rfc.figure.u.47"></div><pre class="text"> From: webmaster@example.org 2958 </pre><p id="rfc.section.1 1.12.p.5">This header field <em class="bcp14">MAY</em> be used for logging purposes and as a means for identifying the source of invalid or unwanted requests. It <em class="bcp14">SHOULD NOT</em> be used as an insecure form of access protection. The interpretation of this field is that the request is being performed2957 </pre><p id="rfc.section.10.12.p.5">This header field <em class="bcp14">MAY</em> be used for logging purposes and as a means for identifying the source of invalid or unwanted requests. It <em class="bcp14">SHOULD NOT</em> be used as an insecure form of access protection. The interpretation of this field is that the request is being performed 2959 2958 on behalf of the person given, who accepts responsibility for the method performed. In particular, robot agents <em class="bcp14">SHOULD</em> include this header field so that the person responsible for running the robot can be contacted if problems occur on the receiving 2960 2959 end. 2961 2960 </p> 2962 <p id="rfc.section.1 1.12.p.6">The Internet e-mail address in this field <em class="bcp14">MAY</em> be separate from the Internet host which issued the request. For example, when a request is passed through a proxy the original2961 <p id="rfc.section.10.12.p.6">The Internet e-mail address in this field <em class="bcp14">MAY</em> be separate from the Internet host which issued the request. For example, when a request is passed through a proxy the original 2963 2962 issuer's address <em class="bcp14">SHOULD</em> be used. 2964 2963 </p> 2965 <p id="rfc.section.1 1.12.p.7">The client <em class="bcp14">SHOULD NOT</em> send the From header field without the user's approval, as it might conflict with the user's privacy interests or their site's2964 <p id="rfc.section.10.12.p.7">The client <em class="bcp14">SHOULD NOT</em> send the From header field without the user's approval, as it might conflict with the user's privacy interests or their site's 2966 2965 security policy. It is strongly recommended that the user be able to disable, enable, and modify the value of this field at 2967 2966 any time prior to a request. … … 2969 2968 <div id="rfc.iref.l.1"></div> 2970 2969 <div id="rfc.iref.h.14"></div> 2971 <h2 id="rfc.section.1 1.13"><a href="#rfc.section.11.13">11.13</a> <a id="header.location" href="#header.location">Location</a></h2>2972 <p id="rfc.section.1 1.13.p.1">The "Location" header field <em class="bcp14">MAY</em> be sent in responses to refer to a specific resource in accordance with the semantics of the status code.2970 <h2 id="rfc.section.10.13"><a href="#rfc.section.10.13">10.13</a> <a id="header.location" href="#header.location">Location</a></h2> 2971 <p id="rfc.section.10.13.p.1">The "Location" header field <em class="bcp14">MAY</em> be sent in responses to refer to a specific resource in accordance with the semantics of the status code. 2973 2972 </p> 2974 2973 <div id="rfc.figure.u.48"></div><pre class="inline"><span id="rfc.iref.g.54"></span> <a href="#header.location" class="smpl">Location</a> = <a href="#imported.abnf" class="smpl">URI-reference</a> 2975 </pre><p id="rfc.section.1 1.13.p.3">For <a href="#status.201" class="smpl">201 (Created)</a> responses, the Location is the URI of the new resource which was created by the request. For <a href="#status.3xx" class="smpl">3xx (Redirection)</a> responses, the location <em class="bcp14">SHOULD</em> indicate the server's preferred URI for automatic redirection to the resource.2976 </p> 2977 <p id="rfc.section.1 1.13.p.4">The field value consists of a single URI-reference. When it has the form of a relative reference (<a href="#RFC3986" id="rfc.xref.RFC3986.1"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.2">Section 4.2</a>), the final value is computed by resolving it against the effective request URI (<a href="#RFC3986" id="rfc.xref.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-5">Section 5</a>). If the original URI, as navigated to by the user agent, did contain a fragment identifier, and the final value does not,2974 </pre><p id="rfc.section.10.13.p.3">For <a href="#status.201" class="smpl">201 (Created)</a> responses, the Location is the URI of the new resource which was created by the request. For <a href="#status.3xx" class="smpl">3xx (Redirection)</a> responses, the location <em class="bcp14">SHOULD</em> indicate the server's preferred URI for automatic redirection to the resource. 2975 </p> 2976 <p id="rfc.section.10.13.p.4">The field value consists of a single URI-reference. When it has the form of a relative reference (<a href="#RFC3986" id="rfc.xref.RFC3986.1"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-4.2">Section 4.2</a>), the final value is computed by resolving it against the effective request URI (<a href="#RFC3986" id="rfc.xref.RFC3986.2"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-5">Section 5</a>). If the original URI, as navigated to by the user agent, did contain a fragment identifier, and the final value does not, 2978 2977 then the original URI's fragment identifier is added to the final value. 2979 2978 </p> … … 2984 2983 <p>An original URI "http://www.example.org/index.html#larry", combined with a field value given as:</p> <pre class="text"> Location: http://www.example.net/index.html 2985 2984 </pre> <p>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</p> 2986 <div class="note" id="rfc.section.1 1.13.p.7">2985 <div class="note" id="rfc.section.10.13.p.7"> 2987 2986 <p> <b>Note:</b> Some recipients attempt to recover from Location fields that are not valid URI references. This specification does not mandate 2988 2987 or define such processing, but does allow it. 2989 2988 </p> 2990 2989 </div> 2991 <p id="rfc.section.1 1.13.p.8">There are circumstances in which a fragment identifier in a Location URI would not be appropriate. For instance, when it appears2990 <p id="rfc.section.10.13.p.8">There are circumstances in which a fragment identifier in a Location URI would not be appropriate. For instance, when it appears 2992 2991 in a <a href="#status.201" class="smpl">201 2993 2992 (Created)</a> response, where the Location header field specifies the URI for the entire created resource. 2994 2993 </p> 2995 <div class="note" id="rfc.section.1 1.13.p.9">2996 <p> <b>Note:</b> The <a href="#header.content-location" class="smpl">Content-Location</a> header field (<a href="#header.content-location" id="rfc.xref.header.content-location.3" title="Content-Location">Section 1 1.8</a>) differs from Location in that the Content-Location identifies the most specific resource corresponding to the enclosed representation.2994 <div class="note" id="rfc.section.10.13.p.9"> 2995 <p> <b>Note:</b> The <a href="#header.content-location" class="smpl">Content-Location</a> header field (<a href="#header.content-location" id="rfc.xref.header.content-location.3" title="Content-Location">Section 10.8</a>) differs from Location in that the Content-Location identifies the most specific resource corresponding to the enclosed representation. 2997 2996 It is therefore possible for a response to contain header fields for both Location and Content-Location. 2998 2997 </p> … … 3000 2999 <div id="rfc.iref.m.9"></div> 3001 3000 <div id="rfc.iref.h.15"></div> 3002 <h2 id="rfc.section.1 1.14"><a href="#rfc.section.11.14">11.14</a> <a id="header.max-forwards" href="#header.max-forwards">Max-Forwards</a></h2>3003 <p id="rfc.section.1 1.14.p.1">The "Max-Forwards" header field provides a mechanism with the TRACE (<a href="#TRACE" id="rfc.xref.TRACE.2" title="TRACE">Section 4.3.8</a>) and OPTIONS (<a href="#OPTIONS" id="rfc.xref.OPTIONS.2" title="OPTIONS">Section 4.3.7</a>) methods to limit the number of times that the request is forwarded by proxies. This can be useful when the client is attempting3001 <h2 id="rfc.section.10.14"><a href="#rfc.section.10.14">10.14</a> <a id="header.max-forwards" href="#header.max-forwards">Max-Forwards</a></h2> 3002 <p id="rfc.section.10.14.p.1">The "Max-Forwards" header field provides a mechanism with the TRACE (<a href="#TRACE" id="rfc.xref.TRACE.2" title="TRACE">Section 4.3.8</a>) and OPTIONS (<a href="#OPTIONS" id="rfc.xref.OPTIONS.2" title="OPTIONS">Section 4.3.7</a>) methods to limit the number of times that the request is forwarded by proxies. This can be useful when the client is attempting 3004 3003 to trace a request which appears to be failing or looping mid-chain. 3005 3004 </p> 3006 3005 <div id="rfc.figure.u.51"></div><pre class="inline"><span id="rfc.iref.g.55"></span> <a href="#header.max-forwards" class="smpl">Max-Forwards</a> = 1*<a href="#imported.abnf" class="smpl">DIGIT</a> 3007 </pre><p id="rfc.section.1 1.14.p.3">The Max-Forwards value is a decimal integer indicating the remaining number of times this request message can be forwarded.</p>3008 <p id="rfc.section.1 1.14.p.4">Each recipient of a TRACE or OPTIONS request containing a Max-Forwards header field <em class="bcp14">MUST</em> check and update its value prior to forwarding the request. If the received value is zero (0), the recipient <em class="bcp14">MUST NOT</em> forward the request; instead, it <em class="bcp14">MUST</em> respond as the final recipient. If the received Max-Forwards value is greater than zero, then the forwarded message <em class="bcp14">MUST</em> contain an updated Max-Forwards field with a value decremented by one (1).3009 </p> 3010 <p id="rfc.section.1 1.14.p.5">The Max-Forwards header field <em class="bcp14">MAY</em> be ignored for all other request methods.3006 </pre><p id="rfc.section.10.14.p.3">The Max-Forwards value is a decimal integer indicating the remaining number of times this request message can be forwarded.</p> 3007 <p id="rfc.section.10.14.p.4">Each recipient of a TRACE or OPTIONS request containing a Max-Forwards header field <em class="bcp14">MUST</em> check and update its value prior to forwarding the request. If the received value is zero (0), the recipient <em class="bcp14">MUST NOT</em> forward the request; instead, it <em class="bcp14">MUST</em> respond as the final recipient. If the received Max-Forwards value is greater than zero, then the forwarded message <em class="bcp14">MUST</em> contain an updated Max-Forwards field with a value decremented by one (1). 3008 </p> 3009 <p id="rfc.section.10.14.p.5">The Max-Forwards header field <em class="bcp14">MAY</em> be ignored for all other request methods. 3011 3010 </p> 3012 3011 <div id="rfc.iref.r.2"></div> 3013 3012 <div id="rfc.iref.h.16"></div> 3014 <h2 id="rfc.section.1 1.15"><a href="#rfc.section.11.15">11.15</a> <a id="header.referer" href="#header.referer">Referer</a></h2>3015 <p id="rfc.section.1 1.15.p.1">The "Referer" [sic] header field allows the client to specify the URI of the resource from which the target URI was obtained3013 <h2 id="rfc.section.10.15"><a href="#rfc.section.10.15">10.15</a> <a id="header.referer" href="#header.referer">Referer</a></h2> 3014 <p id="rfc.section.10.15.p.1">The "Referer" [sic] header field allows the client to specify the URI of the resource from which the target URI was obtained 3016 3015 (the "referrer", although the header field is misspelled.). 3017 3016 </p> 3018 <p id="rfc.section.1 1.15.p.2">The Referer header field allows servers to generate lists of back-links to resources for interest, logging, optimized caching,3017 <p id="rfc.section.10.15.p.2">The Referer header field allows servers to generate lists of back-links to resources for interest, logging, optimized caching, 3019 3018 etc. It also allows obsolete or mistyped links to be traced for maintenance. Some servers use Referer as a means of controlling 3020 3019 where they allow links from (so-called "deep linking"), but legitimate requests do not always contain a Referer header field. 3021 3020 </p> 3022 <p id="rfc.section.1 1.15.p.3">If the target URI was obtained from a source that does not have its own URI (e.g., input from the user keyboard), the Referer3021 <p id="rfc.section.10.15.p.3">If the target URI was obtained from a source that does not have its own URI (e.g., input from the user keyboard), the Referer 3023 3022 field <em class="bcp14">MUST</em> either be sent with the value "about:blank", or not be sent at all. Note that this requirement does not apply to sources with 3024 3023 non-HTTP URIs (e.g., FTP). 3025 3024 </p> 3026 3025 <div id="rfc.figure.u.52"></div><pre class="inline"><span id="rfc.iref.g.56"></span> <a href="#header.referer" class="smpl">Referer</a> = <a href="#imported.abnf" class="smpl">absolute-URI</a> / <a href="#imported.abnf" class="smpl">partial-URI</a> 3027 </pre><p id="rfc.section.1 1.15.p.5">Example:</p>3026 </pre><p id="rfc.section.10.15.p.5">Example:</p> 3028 3027 <div id="rfc.figure.u.53"></div><pre class="text"> Referer: http://www.example.org/hypertext/Overview.html 3029 </pre><p id="rfc.section.1 1.15.p.7">If the field value is a relative URI, it <em class="bcp14">SHOULD</em> be interpreted relative to the effective request URI. The URI <em class="bcp14">MUST NOT</em> include a fragment. See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URIs">Section 13.2</a> for security considerations.3028 </pre><p id="rfc.section.10.15.p.7">If the field value is a relative URI, it <em class="bcp14">SHOULD</em> be interpreted relative to the effective request URI. The URI <em class="bcp14">MUST NOT</em> include a fragment. See <a href="#encoding.sensitive.information.in.uris" title="Encoding Sensitive Information in URIs">Section 12.2</a> for security considerations. 3030 3029 </p> 3031 3030 <div id="rfc.iref.r.3"></div> 3032 3031 <div id="rfc.iref.h.17"></div> 3033 <h2 id="rfc.section.1 1.16"><a href="#rfc.section.11.16">11.16</a> <a id="header.retry-after" href="#header.retry-after">Retry-After</a></h2>3034 <p id="rfc.section.1 1.16.p.1">The header "Retry-After" field can be used with a <a href="#status.503" class="smpl">503 (Service3032 <h2 id="rfc.section.10.16"><a href="#rfc.section.10.16">10.16</a> <a id="header.retry-after" href="#header.retry-after">Retry-After</a></h2> 3033 <p id="rfc.section.10.16.p.1">The header "Retry-After" field can be used with a <a href="#status.503" class="smpl">503 (Service 3035 3034 Unavailable)</a> response to indicate how long the service is expected to be unavailable to the requesting client. This field <em class="bcp14">MAY</em> also be used with any <a href="#status.3xx" class="smpl">3xx (Redirection)</a> response to indicate the minimum time the user-agent is asked to wait before issuing the redirected request. 3036 3035 </p> 3037 <p id="rfc.section.1 1.16.p.2">The value of this field can be either an HTTP-date or an integer number of seconds (in decimal) after the time of the response.</p>3036 <p id="rfc.section.10.16.p.2">The value of this field can be either an HTTP-date or an integer number of seconds (in decimal) after the time of the response.</p> 3038 3037 <div id="rfc.figure.u.54"></div><pre class="inline"><span id="rfc.iref.g.57"></span> <a href="#header.retry-after" class="smpl">Retry-After</a> = <a href="#http.date" class="smpl">HTTP-date</a> / <a href="#rule.delta-seconds" class="smpl">delta-seconds</a> 3039 3038 </pre><div id="rule.delta-seconds"> 3040 <p id="rfc.section.1 1.16.p.4"> Time spans are non-negative decimal integers, representing time in seconds.</p>3039 <p id="rfc.section.10.16.p.4"> Time spans are non-negative decimal integers, representing time in seconds.</p> 3041 3040 </div> 3042 3041 <div id="rfc.figure.u.55"></div><pre class="inline"><span id="rfc.iref.g.58"></span> <a href="#rule.delta-seconds" class="smpl">delta-seconds</a> = 1*<a href="#imported.abnf" class="smpl">DIGIT</a> 3043 </pre><p id="rfc.section.1 1.16.p.6">Two examples of its use are</p>3042 </pre><p id="rfc.section.10.16.p.6">Two examples of its use are</p> 3044 3043 <div id="rfc.figure.u.56"></div><pre class="text"> Retry-After: Fri, 31 Dec 1999 23:59:59 GMT 3045 3044 Retry-After: 120 3046 </pre><p id="rfc.section.1 1.16.p.8">In the latter example, the delay is 2 minutes.</p>3045 </pre><p id="rfc.section.10.16.p.8">In the latter example, the delay is 2 minutes.</p> 3047 3046 <div id="rfc.iref.s.44"></div> 3048 3047 <div id="rfc.iref.h.18"></div> 3049 <h2 id="rfc.section.1 1.17"><a href="#rfc.section.11.17">11.17</a> <a id="header.server" href="#header.server">Server</a></h2>3050 <p id="rfc.section.1 1.17.p.1">The "Server" header field contains information about the software used by the origin server to handle the request.</p>3051 <p id="rfc.section.1 1.17.p.2">The field can contain multiple product tokens (<a href="#product.tokens" title="Product Tokens">Section 8.2</a>) and comments (<a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.29"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>) identifying the server and any significant subproducts. The product tokens are listed in order of their significance for3048 <h2 id="rfc.section.10.17"><a href="#rfc.section.10.17">10.17</a> <a id="header.server" href="#header.server">Server</a></h2> 3049 <p id="rfc.section.10.17.p.1">The "Server" header field contains information about the software used by the origin server to handle the request.</p> 3050 <p id="rfc.section.10.17.p.2">The field can contain multiple product tokens (<a href="#product.tokens" title="Product Tokens">Section 8.2</a>) and comments (<a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.29"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>) identifying the server and any significant subproducts. The product tokens are listed in order of their significance for 3052 3051 identifying the application. 3053 3052 </p> 3054 3053 <div id="rfc.figure.u.57"></div><pre class="inline"><span id="rfc.iref.g.59"></span> <a href="#header.server" class="smpl">Server</a> = <a href="#product.tokens" class="smpl">product</a> *( <a href="#imported.abnf" class="smpl">RWS</a> ( <a href="#product.tokens" class="smpl">product</a> / <a href="#imported.abnf" class="smpl">comment</a> ) ) 3055 </pre><p id="rfc.section.1 1.17.p.4">Example:</p>3054 </pre><p id="rfc.section.10.17.p.4">Example:</p> 3056 3055 <div id="rfc.figure.u.58"></div><pre class="text"> Server: CERN/3.0 libwww/2.17 3057 </pre><p id="rfc.section.1 1.17.p.6">If the response is being forwarded through a proxy, the proxy application <em class="bcp14">MUST NOT</em> modify the <a href="#header.server" class="smpl">Server</a> header field. Instead, it <em class="bcp14">MUST</em> include a <a href="p1-messaging.html#header.via" class="smpl">Via</a> field (as described in <a href="p1-messaging.html#header.via" title="Via">Section 5.7</a> of <a href="#Part1" id="rfc.xref.Part1.30"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>).3058 </p> 3059 <div class="note" id="rfc.section.1 1.17.p.7">3056 </pre><p id="rfc.section.10.17.p.6">If the response is being forwarded through a proxy, the proxy application <em class="bcp14">MUST NOT</em> modify the <a href="#header.server" class="smpl">Server</a> header field. Instead, it <em class="bcp14">MUST</em> include a <a href="p1-messaging.html#header.via" class="smpl">Via</a> field (as described in <a href="p1-messaging.html#header.via" title="Via">Section 5.7</a> of <a href="#Part1" id="rfc.xref.Part1.30"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). 3057 </p> 3058 <div class="note" id="rfc.section.10.17.p.7"> 3060 3059 <p> <b>Note:</b> Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks 3061 3060 against software that is known to contain security holes. Server implementers are encouraged to make this field a configurable … … 3065 3064 <div id="rfc.iref.u.1"></div> 3066 3065 <div id="rfc.iref.h.19"></div> 3067 <h2 id="rfc.section.1 1.18"><a href="#rfc.section.11.18">11.18</a> <a id="header.user-agent" href="#header.user-agent">User-Agent</a></h2>3068 <p id="rfc.section.1 1.18.p.1">The "User-Agent" header field contains information about the user agent originating the request. User agents <em class="bcp14">SHOULD</em> include this field with requests.3069 </p> 3070 <p id="rfc.section.1 1.18.p.2">Typically, it is used for statistical purposes, the tracing of protocol violations, and tailoring responses to avoid particular3066 <h2 id="rfc.section.10.18"><a href="#rfc.section.10.18">10.18</a> <a id="header.user-agent" href="#header.user-agent">User-Agent</a></h2> 3067 <p id="rfc.section.10.18.p.1">The "User-Agent" header field contains information about the user agent originating the request. User agents <em class="bcp14">SHOULD</em> include this field with requests. 3068 </p> 3069 <p id="rfc.section.10.18.p.2">Typically, it is used for statistical purposes, the tracing of protocol violations, and tailoring responses to avoid particular 3071 3070 user agent limitations. 3072 3071 </p> 3073 <p id="rfc.section.1 1.18.p.3">The field can contain multiple product tokens (<a href="#product.tokens" title="Product Tokens">Section 8.2</a>) and comments (<a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.31"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>) identifying the agent and its significant subproducts. By convention, the product tokens are listed in order of their significance3072 <p id="rfc.section.10.18.p.3">The field can contain multiple product tokens (<a href="#product.tokens" title="Product Tokens">Section 8.2</a>) and comments (<a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.31"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>) identifying the agent and its significant subproducts. By convention, the product tokens are listed in order of their significance 3074 3073 for identifying the application. 3075 3074 </p> 3076 <p id="rfc.section.1 1.18.p.4">Because this field is usually sent on every request a user agent makes, implementations are encouraged not to include needlessly3075 <p id="rfc.section.10.18.p.4">Because this field is usually sent on every request a user agent makes, implementations are encouraged not to include needlessly 3077 3076 fine-grained detail, and to limit (or even prohibit) the addition of subproducts by third parties. Overly long and detailed 3078 3077 User-Agent field values make requests larger and can also be used to identify ("fingerprint") the user against their wishes. 3079 3078 </p> 3080 <p id="rfc.section.1 1.18.p.5">Likewise, implementations are encouraged not to use the product tokens of other implementations in order to declare compatibility3079 <p id="rfc.section.10.18.p.5">Likewise, implementations are encouraged not to use the product tokens of other implementations in order to declare compatibility 3081 3080 with them, as this circumvents the purpose of the field. Finally, they are encouraged not to use comments to identify products; 3082 3081 doing so makes the field value more difficult to parse. 3083 3082 </p> 3084 3083 <div id="rfc.figure.u.59"></div><pre class="inline"><span id="rfc.iref.g.60"></span> <a href="#header.user-agent" class="smpl">User-Agent</a> = <a href="#product.tokens" class="smpl">product</a> *( <a href="#imported.abnf" class="smpl">RWS</a> ( <a href="#product.tokens" class="smpl">product</a> / <a href="#imported.abnf" class="smpl">comment</a> ) ) 3085 </pre><p id="rfc.section.1 1.18.p.7">Example:</p>3084 </pre><p id="rfc.section.10.18.p.7">Example:</p> 3086 3085 <div id="rfc.figure.u.60"></div><pre class="text"> User-Agent: CERN-LineMode/2.15 libwww/2.17b3 3087 </pre><h1 id="rfc.section.1 2"><a href="#rfc.section.12">12.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1>3088 <h2 id="rfc.section.1 2.1"><a href="#rfc.section.12.1">12.1</a> <a id="method.registry" href="#method.registry">Method Registry</a></h2>3089 <p id="rfc.section.1 2.1.p.1">The HTTP Method Registry defines the name space for the request method token (<a href="#methods" title="Request Methods">Section 4</a>). The method registry is maintained at <<a href="http://www.iana.org/assignments/http-methods">http://www.iana.org/assignments/http-methods</a>>.3090 </p> 3091 <h3 id="rfc.section.1 2.1.1"><a href="#rfc.section.12.1.1">12.1.1</a> <a id="method.procedure" href="#method.procedure">Procedure</a></h3>3092 <p id="rfc.section.1 2.1.1.p.1">HTTP method registrations <em class="bcp14">MUST</em> include the following fields:3086 </pre><h1 id="rfc.section.11"><a href="#rfc.section.11">11.</a> <a id="IANA.considerations" href="#IANA.considerations">IANA Considerations</a></h1> 3087 <h2 id="rfc.section.11.1"><a href="#rfc.section.11.1">11.1</a> <a id="method.registry" href="#method.registry">Method Registry</a></h2> 3088 <p id="rfc.section.11.1.p.1">The HTTP Method Registry defines the name space for the request method token (<a href="#methods" title="Request Methods">Section 4</a>). The method registry is maintained at <<a href="http://www.iana.org/assignments/http-methods">http://www.iana.org/assignments/http-methods</a>>. 3089 </p> 3090 <h3 id="rfc.section.11.1.1"><a href="#rfc.section.11.1.1">11.1.1</a> <a id="method.procedure" href="#method.procedure">Procedure</a></h3> 3091 <p id="rfc.section.11.1.1.p.1">HTTP method registrations <em class="bcp14">MUST</em> include the following fields: 3093 3092 </p> 3094 3093 <ul> … … 3101 3100 <li>Pointer to specification text</li> 3102 3101 </ul> 3103 <p id="rfc.section.1 2.1.1.p.2">Values to be added to this name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).3104 </p> 3105 <h3 id="rfc.section.1 2.1.2"><a href="#rfc.section.12.1.2">12.1.2</a> <a id="considerations.for.new.methods" href="#considerations.for.new.methods">Considerations for New Methods</a></h3>3106 <p id="rfc.section.1 2.1.2.p.1">Standardized HTTP methods are generic; that is, they are potentially applicable to any resource, not just one particular media3102 <p id="rfc.section.11.1.1.p.2">Values to be added to this name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.1"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>). 3103 </p> 3104 <h3 id="rfc.section.11.1.2"><a href="#rfc.section.11.1.2">11.1.2</a> <a id="considerations.for.new.methods" href="#considerations.for.new.methods">Considerations for New Methods</a></h3> 3105 <p id="rfc.section.11.1.2.p.1">Standardized HTTP methods are generic; that is, they are potentially applicable to any resource, not just one particular media 3107 3106 type, kind of resource, or application. As such, it is preferred that new HTTP methods be registered in a document that isn't 3108 3107 specific to a single application or data format, since orthogonal technologies deserve orthogonal specification. 3109 3108 </p> 3110 <p id="rfc.section.1 2.1.2.p.2">Since HTTP message parsing (<a href="p1-messaging.html#message.body" title="Message Body">Section 3.3</a> of <a href="#Part1" id="rfc.xref.Part1.32"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>) is independent of method semantics (aside from responses to HEAD), definitions of new HTTP methods cannot change the parsing3109 <p id="rfc.section.11.1.2.p.2">Since HTTP message parsing (<a href="p1-messaging.html#message.body" title="Message Body">Section 3.3</a> of <a href="#Part1" id="rfc.xref.Part1.32"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>) is independent of method semantics (aside from responses to HEAD), definitions of new HTTP methods cannot change the parsing 3111 3110 algorithm or prohibit the presence of a message body on either the request or the response message. Definitions of new methods 3112 3111 can specify that only zero-length bodies are allowed, which would imply that each such messages would be required to contain 3113 3112 a Content-Length header field with a value of "0". 3114 3113 </p> 3115 <p id="rfc.section.1 2.1.2.p.3">New method definitions need to indicate whether they are safe (<a href="#safe.methods" title="Safe Methods">Section 4.2.1</a>), idempotent (<a href="#idempotent.methods" title="Idempotent Methods">Section 4.2.2</a>), cacheable (<a href="#cacheable.methods" title="Cacheable Methods">Section 4.2.3</a>), and what semantics are to be associated with the request body if any is present in the request. If a method is cacheable,3114 <p id="rfc.section.11.1.2.p.3">New method definitions need to indicate whether they are safe (<a href="#safe.methods" title="Safe Methods">Section 4.2.1</a>), idempotent (<a href="#idempotent.methods" title="Idempotent Methods">Section 4.2.2</a>), cacheable (<a href="#cacheable.methods" title="Cacheable Methods">Section 4.2.3</a>), and what semantics are to be associated with the request body if any is present in the request. If a method is cacheable, 3116 3115 the method definition ought to describe how, and under what conditions, a cache can store a response and use it to satisfy 3117 3116 a subsequent request. 3118 3117 </p> 3119 <h3 id="rfc.section.1 2.1.3"><a href="#rfc.section.12.1.3">12.1.3</a> <a id="method.registration" href="#method.registration">Registrations</a></h3>3120 <p id="rfc.section.1 2.1.3.p.1">The HTTP Method Registry shall be populated with the registrations below:</p>3118 <h3 id="rfc.section.11.1.3"><a href="#rfc.section.11.1.3">11.1.3</a> <a id="method.registration" href="#method.registration">Registrations</a></h3> 3119 <p id="rfc.section.11.1.3.p.1">The HTTP Method Registry shall be populated with the registrations below:</p> 3121 3120 <div id="rfc.table.2"> 3122 3121 <div id="iana.method.registration.table"></div> … … 3190 3189 </table> 3191 3190 </div> 3192 <h2 id="rfc.section.1 2.2"><a href="#rfc.section.12.2">12.2</a> <a id="status.code.registry" href="#status.code.registry">Status Code Registry</a></h2>3193 <p id="rfc.section.1 2.2.p.1">The HTTP Status Code Registry defines the name space for the response status-code token (<a href="#status.codes" title="Response Status Codes">Section 6</a>). The status code registry is maintained at <<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>>.3194 </p> 3195 <p id="rfc.section.1 2.2.p.2">This section replaces the registration procedure for HTTP Status Codes previously defined in <a href="http://tools.ietf.org/html/rfc2817#section-7.1">Section 7.1</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.1"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>.3196 </p> 3197 <h3 id="rfc.section.1 2.2.1"><a href="#rfc.section.12.2.1">12.2.1</a> <a id="status.code.procedure" href="#status.code.procedure">Procedure</a></h3>3198 <p id="rfc.section.1 2.2.1.p.1">Values to be added to the HTTP status code name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>).3199 </p> 3200 <h3 id="rfc.section.1 2.2.2"><a href="#rfc.section.12.2.2">12.2.2</a> <a id="considerations.for.new.status.codes" href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></h3>3201 <p id="rfc.section.1 2.2.2.p.1">When it is necessary to express new semantics for a HTTP response that aren't specific to a single application or media type,3191 <h2 id="rfc.section.11.2"><a href="#rfc.section.11.2">11.2</a> <a id="status.code.registry" href="#status.code.registry">Status Code Registry</a></h2> 3192 <p id="rfc.section.11.2.p.1">The HTTP Status Code Registry defines the name space for the response status-code token (<a href="#status.codes" title="Response Status Codes">Section 6</a>). The status code registry is maintained at <<a href="http://www.iana.org/assignments/http-status-codes">http://www.iana.org/assignments/http-status-codes</a>>. 3193 </p> 3194 <p id="rfc.section.11.2.p.2">This section replaces the registration procedure for HTTP Status Codes previously defined in <a href="http://tools.ietf.org/html/rfc2817#section-7.1">Section 7.1</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.1"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>. 3195 </p> 3196 <h3 id="rfc.section.11.2.1"><a href="#rfc.section.11.2.1">11.2.1</a> <a id="status.code.procedure" href="#status.code.procedure">Procedure</a></h3> 3197 <p id="rfc.section.11.2.1.p.1">Values to be added to the HTTP status code name space require IETF Review (see <a href="#RFC5226" id="rfc.xref.RFC5226.2"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>, <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a>). 3198 </p> 3199 <h3 id="rfc.section.11.2.2"><a href="#rfc.section.11.2.2">11.2.2</a> <a id="considerations.for.new.status.codes" href="#considerations.for.new.status.codes">Considerations for New Status Codes</a></h3> 3200 <p id="rfc.section.11.2.2.p.1">When it is necessary to express new semantics for a HTTP response that aren't specific to a single application or media type, 3202 3201 and currently defined status codes are inadequate, a new status code can be registered. 3203 3202 </p> 3204 <p id="rfc.section.1 2.2.2.p.2">HTTP status codes are generic; that is, they are potentially applicable to any resource, not just one particular media type,3203 <p id="rfc.section.11.2.2.p.2">HTTP status codes are generic; that is, they are potentially applicable to any resource, not just one particular media type, 3205 3204 "type" of resource, or application. As such, it is preferred that new HTTP status codes be registered in a document that isn't 3206 3205 specific to a single application, so that this is clear. 3207 3206 </p> 3208 <p id="rfc.section.1 2.2.2.p.3">Definitions of new HTTP status codes typically explain the request conditions that produce a response containing the status3207 <p id="rfc.section.11.2.2.p.3">Definitions of new HTTP status codes typically explain the request conditions that produce a response containing the status 3209 3208 code (e.g., combinations of request header fields and/or method(s)), along with any interactions with response header fields 3210 3209 (e.g., those that are required, those that modify the semantics of the response). 3211 3210 </p> 3212 <p id="rfc.section.1 2.2.2.p.4">New HTTP status codes are required to fall under one of the categories defined in <a href="#status.codes" title="Response Status Codes">Section 6</a>. To allow existing parsers to properly handle them, new status codes cannot disallow a response body, although they can mandate3211 <p id="rfc.section.11.2.2.p.4">New HTTP status codes are required to fall under one of the categories defined in <a href="#status.codes" title="Response Status Codes">Section 6</a>. To allow existing parsers to properly handle them, new status codes cannot disallow a response body, although they can mandate 3213 3212 a zero-length response body. They can require the presence of one or more particular HTTP response header field(s). 3214 3213 </p> 3215 <p id="rfc.section.1 2.2.2.p.5">Likewise, their definitions can specify that caches are allowed to use heuristics to determine their freshness (see <a href="#Part6" id="rfc.xref.Part6.18"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>; by default, it is not allowed), and can define how to determine the resource which they carry a representation for (see <a href="#identifying.response.associated.with.representation" title="Identifying the Resource Associated with a Representation">Section 3.1</a>; by default, it is anonymous).3216 </p> 3217 <h3 id="rfc.section.1 2.2.3"><a href="#rfc.section.12.2.3">12.2.3</a> <a id="status.code.registration" href="#status.code.registration">Registrations</a></h3>3218 <p id="rfc.section.1 2.2.3.p.1">The HTTP Status Code Registry shall be updated with the registrations below:</p>3214 <p id="rfc.section.11.2.2.p.5">Likewise, their definitions can specify that caches are allowed to use heuristics to determine their freshness (see <a href="#Part6" id="rfc.xref.Part6.18"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>; by default, it is not allowed), and can define how to determine the resource which they carry a representation for (see <a href="#identifying.response.associated.with.representation" title="Identifying the Resource Associated with a Representation">Section 3.1</a>; by default, it is anonymous). 3215 </p> 3216 <h3 id="rfc.section.11.2.3"><a href="#rfc.section.11.2.3">11.2.3</a> <a id="status.code.registration" href="#status.code.registration">Registrations</a></h3> 3217 <p id="rfc.section.11.2.3.p.1">The HTTP Status Code Registry shall be updated with the registrations below:</p> 3219 3218 <div id="rfc.table.3"> 3220 3219 <div id="iana.status.code.registration.table"></div> … … 3447 3446 </table> 3448 3447 </div> 3449 <h2 id="rfc.section.1 2.3"><a href="#rfc.section.12.3">12.3</a> <a id="header.field.registry" href="#header.field.registry">Header Field Registry</a></h2>3450 <p id="rfc.section.1 2.3.p.1">HTTP header fields are registered within the Message Header Field Registry located at <<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>>, as defined by <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>.3451 </p> 3452 <h3 id="rfc.section.1 2.3.1"><a href="#rfc.section.12.3.1">12.3.1</a> <a id="considerations.for.new.header.fields" href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></h3>3453 <p id="rfc.section.1 2.3.1.p.1">Header fields are key:value pairs that can be used to communicate data about the message, its payload, the target resource,3448 <h2 id="rfc.section.11.3"><a href="#rfc.section.11.3">11.3</a> <a id="header.field.registry" href="#header.field.registry">Header Field Registry</a></h2> 3449 <p id="rfc.section.11.3.p.1">HTTP header fields are registered within the Message Header Field Registry located at <<a href="http://www.iana.org/assignments/message-headers/message-header-index.html">http://www.iana.org/assignments/message-headers/message-header-index.html</a>>, as defined by <a href="#RFC3864" id="rfc.xref.RFC3864.1"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>. 3450 </p> 3451 <h3 id="rfc.section.11.3.1"><a href="#rfc.section.11.3.1">11.3.1</a> <a id="considerations.for.new.header.fields" href="#considerations.for.new.header.fields">Considerations for New Header Fields</a></h3> 3452 <p id="rfc.section.11.3.1.p.1">Header fields are key:value pairs that can be used to communicate data about the message, its payload, the target resource, 3454 3453 or the connection (i.e., control data). See <a href="p1-messaging.html#header.fields" title="Header Fields">Section 3.2</a> of <a href="#Part1" id="rfc.xref.Part1.33"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a> for a general definition of header field syntax in HTTP messages. 3455 3454 </p> 3456 <p id="rfc.section.1 2.3.1.p.2">The requirements for header field names are defined in <a href="http://tools.ietf.org/html/rfc3864#section-4.1">Section 4.1</a> of <a href="#RFC3864" id="rfc.xref.RFC3864.2"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>. Authors of specifications defining new fields are advised to keep the name as short as practical, and not to prefix them3455 <p id="rfc.section.11.3.1.p.2">The requirements for header field names are defined in <a href="http://tools.ietf.org/html/rfc3864#section-4.1">Section 4.1</a> of <a href="#RFC3864" id="rfc.xref.RFC3864.2"><cite title="Registration Procedures for Message Header Fields">[RFC3864]</cite></a>. Authors of specifications defining new fields are advised to keep the name as short as practical, and not to prefix them 3457 3456 with "X-" if they are to be registered (either immediately or in the future). 3458 3457 </p> 3459 <p id="rfc.section.1 2.3.1.p.3">New header field values typically have their syntax defined using ABNF (<a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>), using the extension defined in <a href="p1-messaging.html#abnf.extension" title="ABNF list extension: #rule">Appendix B</a> of <a href="#Part1" id="rfc.xref.Part1.34"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a> as necessary, and are usually constrained to the range of ASCII characters. Header fields needing a greater range of characters3458 <p id="rfc.section.11.3.1.p.3">New header field values typically have their syntax defined using ABNF (<a href="#RFC5234" id="rfc.xref.RFC5234.2"><cite title="Augmented BNF for Syntax Specifications: ABNF">[RFC5234]</cite></a>), using the extension defined in <a href="p1-messaging.html#abnf.extension" title="ABNF list extension: #rule">Appendix B</a> of <a href="#Part1" id="rfc.xref.Part1.34"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a> as necessary, and are usually constrained to the range of ASCII characters. Header fields needing a greater range of characters 3460 3459 can use an encoding such as the one defined in <a href="#RFC5987" id="rfc.xref.RFC5987.1"><cite title="Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters">[RFC5987]</cite></a>. 3461 3460 </p> 3462 <p id="rfc.section.1 2.3.1.p.4">Because commas (",") are used as a generic delimiter between field-values, they need to be treated with care if they are allowed3461 <p id="rfc.section.11.3.1.p.4">Because commas (",") are used as a generic delimiter between field-values, they need to be treated with care if they are allowed 3463 3462 in the field-value's payload. Typically, components that might contain a comma are protected with double-quotes using the 3464 3463 quoted-string ABNF production (<a href="p1-messaging.html#field.components" title="Field value components">Section 3.2.4</a> of <a href="#Part1" id="rfc.xref.Part1.35"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). 3465 3464 </p> 3466 <p id="rfc.section.1 2.3.1.p.5">For example, a textual date and a URI (either of which might contain a comma) could be safely carried in field-values like3465 <p id="rfc.section.11.3.1.p.5">For example, a textual date and a URI (either of which might contain a comma) could be safely carried in field-values like 3467 3466 these: 3468 3467 </p> … … 3470 3469 "http://without-a-comma.example.com/" 3471 3470 Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005" 3472 </pre><p id="rfc.section.1 2.3.1.p.7">Note that double-quote delimiters almost always are used with the quoted-string production; using a different syntax inside3471 </pre><p id="rfc.section.11.3.1.p.7">Note that double-quote delimiters almost always are used with the quoted-string production; using a different syntax inside 3473 3472 double-quotes will likely cause unnecessary confusion. 3474 3473 </p> 3475 <p id="rfc.section.1 2.3.1.p.8">Many header fields use a format including (case-insensitively) named parameters (for instance, <a href="#header.content-type" class="smpl">Content-Type</a>, defined in <a href="#header.content-type" id="rfc.xref.header.content-type.4" title="Content-Type">Section 11.9</a>). Allowing both unquoted (token) and quoted (quoted-string) syntax for the parameter value enables recipients to use existing3474 <p id="rfc.section.11.3.1.p.8">Many header fields use a format including (case-insensitively) named parameters (for instance, <a href="#header.content-type" class="smpl">Content-Type</a>, defined in <a href="#header.content-type" id="rfc.xref.header.content-type.4" title="Content-Type">Section 10.9</a>). Allowing both unquoted (token) and quoted (quoted-string) syntax for the parameter value enables recipients to use existing 3476 3475 parser components. When allowing both forms, the meaning of a parameter value ought to be independent of the syntax used for 3477 3476 it (for an example, see the notes on parameter handling for media types in <a href="#media.types" title="Media Types">Section 8.5</a>). 3478 3477 </p> 3479 <p id="rfc.section.1 2.3.1.p.9">Authors of specifications defining new header fields are advised to consider documenting: </p>3478 <p id="rfc.section.11.3.1.p.9">Authors of specifications defining new header fields are advised to consider documenting: </p> 3480 3479 <ul> 3481 3480 <li> … … 3514 3513 </li> 3515 3514 </ul> 3516 <h3 id="rfc.section.1 2.3.2"><a href="#rfc.section.12.3.2">12.3.2</a> <a id="header.field.registration" href="#header.field.registration">Registrations</a></h3>3517 <p id="rfc.section.1 2.3.2.p.1">The Message Header Field Registry shall be updated with the following permanent registrations:</p>3515 <h3 id="rfc.section.11.3.2"><a href="#rfc.section.11.3.2">11.3.2</a> <a id="header.field.registration" href="#header.field.registration">Registrations</a></h3> 3516 <p id="rfc.section.11.3.2.p.1">The Message Header Field Registry shall be updated with the following permanent registrations:</p> 3518 3517 <div id="rfc.table.4"> 3519 3518 <div id="iana.header.registration.table"></div> … … 3532 3531 <td class="left">http</td> 3533 3532 <td class="left">standard</td> 3534 <td class="left"> <a href="#header.accept" id="rfc.xref.header.accept.4" title="Accept">Section 1 1.1</a>3533 <td class="left"> <a href="#header.accept" id="rfc.xref.header.accept.4" title="Accept">Section 10.1</a> 3535 3534 </td> 3536 3535 </tr> … … 3539 3538 <td class="left">http</td> 3540 3539 <td class="left">standard</td> 3541 <td class="left"> <a href="#header.accept-charset" id="rfc.xref.header.accept-charset.3" title="Accept-Charset">Section 1 1.2</a>3540 <td class="left"> <a href="#header.accept-charset" id="rfc.xref.header.accept-charset.3" title="Accept-Charset">Section 10.2</a> 3542 3541 </td> 3543 3542 </tr> … … 3546 3545 <td class="left">http</td> 3547 3546 <td class="left">standard</td> 3548 <td class="left"> <a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.4" title="Accept-Encoding">Section 1 1.3</a>3547 <td class="left"> <a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.4" title="Accept-Encoding">Section 10.3</a> 3549 3548 </td> 3550 3549 </tr> … … 3553 3552 <td class="left">http</td> 3554 3553 <td class="left">standard</td> 3555 <td class="left"> <a href="#header.accept-language" id="rfc.xref.header.accept-language.3" title="Accept-Language">Section 1 1.4</a>3554 <td class="left"> <a href="#header.accept-language" id="rfc.xref.header.accept-language.3" title="Accept-Language">Section 10.4</a> 3556 3555 </td> 3557 3556 </tr> … … 3560 3559 <td class="left">http</td> 3561 3560 <td class="left">standard</td> 3562 <td class="left"> <a href="#header.allow" id="rfc.xref.header.allow.3" title="Allow">Section 1 1.5</a>3561 <td class="left"> <a href="#header.allow" id="rfc.xref.header.allow.3" title="Allow">Section 10.5</a> 3563 3562 </td> 3564 3563 </tr> … … 3567 3566 <td class="left">http</td> 3568 3567 <td class="left">standard</td> 3569 <td class="left"> <a href="#header.content-encoding" id="rfc.xref.header.content-encoding.3" title="Content-Encoding">Section 1 1.6</a>3568 <td class="left"> <a href="#header.content-encoding" id="rfc.xref.header.content-encoding.3" title="Content-Encoding">Section 10.6</a> 3570 3569 </td> 3571 3570 </tr> … … 3574 3573 <td class="left">http</td> 3575 3574 <td class="left">standard</td> 3576 <td class="left"> <a href="#header.content-language" id="rfc.xref.header.content-language.2" title="Content-Language">Section 1 1.7</a>3575 <td class="left"> <a href="#header.content-language" id="rfc.xref.header.content-language.2" title="Content-Language">Section 10.7</a> 3577 3576 </td> 3578 3577 </tr> … … 3581 3580 <td class="left">http</td> 3582 3581 <td class="left">standard</td> 3583 <td class="left"> <a href="#header.content-location" id="rfc.xref.header.content-location.4" title="Content-Location">Section 1 1.8</a>3582 <td class="left"> <a href="#header.content-location" id="rfc.xref.header.content-location.4" title="Content-Location">Section 10.8</a> 3584 3583 </td> 3585 3584 </tr> … … 3588 3587 <td class="left">http</td> 3589 3588 <td class="left">standard</td> 3590 <td class="left"> <a href="#header.content-type" id="rfc.xref.header.content-type.5" title="Content-Type">Section 1 1.9</a>3589 <td class="left"> <a href="#header.content-type" id="rfc.xref.header.content-type.5" title="Content-Type">Section 10.9</a> 3591 3590 </td> 3592 3591 </tr> … … 3595 3594 <td class="left">http</td> 3596 3595 <td class="left">standard</td> 3597 <td class="left"> <a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section 1 1.10</a>3596 <td class="left"> <a href="#header.date" id="rfc.xref.header.date.2" title="Date">Section 10.10</a> 3598 3597 </td> 3599 3598 </tr> … … 3602 3601 <td class="left">http</td> 3603 3602 <td class="left">standard</td> 3604 <td class="left"> <a href="#header.expect" id="rfc.xref.header.expect.3" title="Expect">Section 1 1.11</a>3603 <td class="left"> <a href="#header.expect" id="rfc.xref.header.expect.3" title="Expect">Section 10.11</a> 3605 3604 </td> 3606 3605 </tr> … … 3609 3608 <td class="left">http</td> 3610 3609 <td class="left">standard</td> 3611 <td class="left"> <a href="#header.from" id="rfc.xref.header.from.2" title="From">Section 1 1.12</a>3610 <td class="left"> <a href="#header.from" id="rfc.xref.header.from.2" title="From">Section 10.12</a> 3612 3611 </td> 3613 3612 </tr> … … 3616 3615 <td class="left">http</td> 3617 3616 <td class="left">standard</td> 3618 <td class="left"> <a href="#header.location" id="rfc.xref.header.location.4" title="Location">Section 1 1.13</a>3617 <td class="left"> <a href="#header.location" id="rfc.xref.header.location.4" title="Location">Section 10.13</a> 3619 3618 </td> 3620 3619 </tr> … … 3630 3629 <td class="left">http</td> 3631 3630 <td class="left">standard</td> 3632 <td class="left"> <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.4" title="Max-Forwards">Section 1 1.14</a>3631 <td class="left"> <a href="#header.max-forwards" id="rfc.xref.header.max-forwards.4" title="Max-Forwards">Section 10.14</a> 3633 3632 </td> 3634 3633 </tr> … … 3637 3636 <td class="left">http</td> 3638 3637 <td class="left">standard</td> 3639 <td class="left"> <a href="#header.referer" id="rfc.xref.header.referer.2" title="Referer">Section 1 1.15</a>3638 <td class="left"> <a href="#header.referer" id="rfc.xref.header.referer.2" title="Referer">Section 10.15</a> 3640 3639 </td> 3641 3640 </tr> … … 3644 3643 <td class="left">http</td> 3645 3644 <td class="left">standard</td> 3646 <td class="left"> <a href="#header.retry-after" id="rfc.xref.header.retry-after.3" title="Retry-After">Section 1 1.16</a>3645 <td class="left"> <a href="#header.retry-after" id="rfc.xref.header.retry-after.3" title="Retry-After">Section 10.16</a> 3647 3646 </td> 3648 3647 </tr> … … 3651 3650 <td class="left">http</td> 3652 3651 <td class="left">standard</td> 3653 <td class="left"> <a href="#header.server" id="rfc.xref.header.server.2" title="Server">Section 1 1.17</a>3652 <td class="left"> <a href="#header.server" id="rfc.xref.header.server.2" title="Server">Section 10.17</a> 3654 3653 </td> 3655 3654 </tr> … … 3658 3657 <td class="left">http</td> 3659 3658 <td class="left">standard</td> 3660 <td class="left"> <a href="#header.user-agent" id="rfc.xref.header.user-agent.3" title="User-Agent">Section 1 1.18</a>3659 <td class="left"> <a href="#header.user-agent" id="rfc.xref.header.user-agent.3" title="User-Agent">Section 10.18</a> 3661 3660 </td> 3662 3661 </tr> … … 3664 3663 </table> 3665 3664 </div> 3666 <p id="rfc.section.1 2.3.2.p.2">The change controller for the above registrations is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p>3667 <h2 id="rfc.section.1 2.4"><a href="#rfc.section.12.4">12.4</a> <a id="content.coding.registry" href="#content.coding.registry">Content Coding Registry</a></h2>3668 <p id="rfc.section.1 2.4.p.1">The HTTP Content Coding Registry defines the name space for content coding names (<a href="p1-messaging.html#compression.codings" title="Compression Codings">Section 4.2</a> of <a href="#Part1" id="rfc.xref.Part1.39"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). The content coding registry is maintained at <<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>>.3669 </p> 3670 <h3 id="rfc.section.1 2.4.1"><a href="#rfc.section.12.4.1">12.4.1</a> <a id="content.coding.procedure" href="#content.coding.procedure">Procedure</a></h3>3671 <p id="rfc.section.1 2.4.1.p.1">Content Coding registrations <em class="bcp14">MUST</em> include the following fields:3665 <p id="rfc.section.11.3.2.p.2">The change controller for the above registrations is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".</p> 3666 <h2 id="rfc.section.11.4"><a href="#rfc.section.11.4">11.4</a> <a id="content.coding.registry" href="#content.coding.registry">Content Coding Registry</a></h2> 3667 <p id="rfc.section.11.4.p.1">The HTTP Content Coding Registry defines the name space for content coding names (<a href="p1-messaging.html#compression.codings" title="Compression Codings">Section 4.2</a> of <a href="#Part1" id="rfc.xref.Part1.39"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). The content coding registry is maintained at <<a href="http://www.iana.org/assignments/http-parameters">http://www.iana.org/assignments/http-parameters</a>>. 3668 </p> 3669 <h3 id="rfc.section.11.4.1"><a href="#rfc.section.11.4.1">11.4.1</a> <a id="content.coding.procedure" href="#content.coding.procedure">Procedure</a></h3> 3670 <p id="rfc.section.11.4.1.p.1">Content Coding registrations <em class="bcp14">MUST</em> include the following fields: 3672 3671 </p> 3673 3672 <ul> … … 3676 3675 <li>Pointer to specification text</li> 3677 3676 </ul> 3678 <p id="rfc.section.1 2.4.1.p.2">Names of content codings <em class="bcp14">MUST NOT</em> overlap with names of transfer codings (<a href="p1-messaging.html#transfer.codings" title="Transfer Codings">Section 4</a> of <a href="#Part1" id="rfc.xref.Part1.40"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>), unless the encoding transformation is identical (as is the case for the compression codings defined in <a href="p1-messaging.html#compression.codings" title="Compression Codings">Section 4.2</a> of <a href="#Part1" id="rfc.xref.Part1.41"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>).3679 </p> 3680 <p id="rfc.section.1 2.4.1.p.3">Values to be added to this name space require IETF Review (see <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a> of <a href="#RFC5226" id="rfc.xref.RFC5226.3"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>), and <em class="bcp14">MUST</em> conform to the purpose of content coding defined in this section.3681 </p> 3682 <h3 id="rfc.section.1 2.4.2"><a href="#rfc.section.12.4.2">12.4.2</a> <a id="content.coding.registration" href="#content.coding.registration">Registrations</a></h3>3683 <p id="rfc.section.1 2.4.2.p.1">The HTTP Content Codings Registry shall be updated with the registrations below:</p>3677 <p id="rfc.section.11.4.1.p.2">Names of content codings <em class="bcp14">MUST NOT</em> overlap with names of transfer codings (<a href="p1-messaging.html#transfer.codings" title="Transfer Codings">Section 4</a> of <a href="#Part1" id="rfc.xref.Part1.40"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>), unless the encoding transformation is identical (as is the case for the compression codings defined in <a href="p1-messaging.html#compression.codings" title="Compression Codings">Section 4.2</a> of <a href="#Part1" id="rfc.xref.Part1.41"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>). 3678 </p> 3679 <p id="rfc.section.11.4.1.p.3">Values to be added to this name space require IETF Review (see <a href="http://tools.ietf.org/html/rfc5226#section-4.1">Section 4.1</a> of <a href="#RFC5226" id="rfc.xref.RFC5226.3"><cite title="Guidelines for Writing an IANA Considerations Section in RFCs">[RFC5226]</cite></a>), and <em class="bcp14">MUST</em> conform to the purpose of content coding defined in this section. 3680 </p> 3681 <h3 id="rfc.section.11.4.2"><a href="#rfc.section.11.4.2">11.4.2</a> <a id="content.coding.registration" href="#content.coding.registration">Registrations</a></h3> 3682 <p id="rfc.section.11.4.2.p.1">The HTTP Content Codings Registry shall be updated with the registrations below:</p> 3684 3683 <div id="rfc.table.5"> 3685 3684 <div id="iana.content.coding.registration.table"></div> … … 3716 3715 <td class="left">reserved (synonym for "no encoding" in <a href="#header.accept-encoding" class="smpl">Accept-Encoding</a> header field) 3717 3716 </td> 3718 <td class="left"> <a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.5" title="Accept-Encoding">Section 1 1.3</a>3717 <td class="left"> <a href="#header.accept-encoding" id="rfc.xref.header.accept-encoding.5" title="Accept-Encoding">Section 10.3</a> 3719 3718 </td> 3720 3719 </tr> … … 3722 3721 </table> 3723 3722 </div> 3724 <h1 id="rfc.section.1 3"><a href="#rfc.section.13">13.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1>3725 <p id="rfc.section.1 3.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.13723 <h1 id="rfc.section.12"><a href="#rfc.section.12">12.</a> <a id="security.considerations" href="#security.considerations">Security Considerations</a></h1> 3724 <p id="rfc.section.12.p.1">This section is meant to inform application developers, information providers, and users of the security limitations in HTTP/1.1 3726 3725 as described by this document. The discussion does not include definitive solutions to the problems revealed, though it does 3727 3726 make some suggestions for reducing security risks. 3728 3727 </p> 3729 <h2 id="rfc.section.1 3.1"><a href="#rfc.section.13.1">13.1</a> <a id="security.sensitive" href="#security.sensitive">Transfer of Sensitive Information</a></h2>3730 <p id="rfc.section.1 3.1.p.1">Like any generic data transfer protocol, HTTP cannot regulate the content of the data that is transferred, nor is there any3728 <h2 id="rfc.section.12.1"><a href="#rfc.section.12.1">12.1</a> <a id="security.sensitive" href="#security.sensitive">Transfer of Sensitive Information</a></h2> 3729 <p id="rfc.section.12.1.p.1">Like any generic data transfer protocol, HTTP cannot regulate the content of the data that is transferred, nor is there any 3731 3730 a priori method of determining the sensitivity of any particular piece of information within the context of any given request. 3732 3731 Therefore, applications <em class="bcp14">SHOULD</em> supply as much control over this information as possible to the provider of that information. Four header fields are worth 3733 3732 special mention in this context: <a href="#header.server" class="smpl">Server</a>, <a href="p1-messaging.html#header.via" class="smpl">Via</a>, <a href="#header.referer" class="smpl">Referer</a> and <a href="#header.from" class="smpl">From</a>. 3734 3733 </p> 3735 <p id="rfc.section.1 3.1.p.2">Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks3734 <p id="rfc.section.12.1.p.2">Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks 3736 3735 against software that is known to contain security holes. Implementers <em class="bcp14">SHOULD</em> make the <a href="#header.server" class="smpl">Server</a> header field a configurable option. 3737 3736 </p> 3738 <p id="rfc.section.1 3.1.p.3">Proxies which serve as a portal through a network firewall <em class="bcp14">SHOULD</em> take special precautions regarding the transfer of header information that identifies the hosts behind the firewall. In particular,3737 <p id="rfc.section.12.1.p.3">Proxies which serve as a portal through a network firewall <em class="bcp14">SHOULD</em> take special precautions regarding the transfer of header information that identifies the hosts behind the firewall. In particular, 3739 3738 they <em class="bcp14">SHOULD</em> remove, or replace with sanitized versions, any <a href="p1-messaging.html#header.via" class="smpl">Via</a> fields generated behind the firewall. 3740 3739 </p> 3741 <p id="rfc.section.1 3.1.p.4">The <a href="#header.referer" class="smpl">Referer</a> header field allows reading patterns to be studied and reverse links drawn. Although it can be very useful, its power can3740 <p id="rfc.section.12.1.p.4">The <a href="#header.referer" class="smpl">Referer</a> header field allows reading patterns to be studied and reverse links drawn. Although it can be very useful, its power can 3742 3741 be abused if user details are not separated from the information contained in the Referer. Even when the personal information 3743 3742 has been removed, the Referer header field might indicate a private document's URI whose publication would be inappropriate. 3744 3743 </p> 3745 <p id="rfc.section.1 3.1.p.5">The information sent in the <a href="#header.from" class="smpl">From</a> field might conflict with the user's privacy interests or their site's security policy, and hence it <em class="bcp14">SHOULD NOT</em> be transmitted without the user being able to disable, enable, and modify the contents of the field. The user <em class="bcp14">MUST</em> be able to set the contents of this field within a user preference or application defaults configuration.3746 </p> 3747 <p id="rfc.section.1 3.1.p.6">We suggest, though do not require, that a convenient toggle interface be provided for the user to enable or disable the sending3744 <p id="rfc.section.12.1.p.5">The information sent in the <a href="#header.from" class="smpl">From</a> field might conflict with the user's privacy interests or their site's security policy, and hence it <em class="bcp14">SHOULD NOT</em> be transmitted without the user being able to disable, enable, and modify the contents of the field. The user <em class="bcp14">MUST</em> be able to set the contents of this field within a user preference or application defaults configuration. 3745 </p> 3746 <p id="rfc.section.12.1.p.6">We suggest, though do not require, that a convenient toggle interface be provided for the user to enable or disable the sending 3748 3747 of <a href="#header.from" class="smpl">From</a> and <a href="#header.referer" class="smpl">Referer</a> information. 3749 3748 </p> 3750 <p id="rfc.section.1 3.1.p.7">The <a href="#header.user-agent" class="smpl">User-Agent</a> (<a href="#header.user-agent" id="rfc.xref.header.user-agent.4" title="User-Agent">Section 11.18</a>) or <a href="#header.server" class="smpl">Server</a> (<a href="#header.server" id="rfc.xref.header.server.3" title="Server">Section 11.17</a>) header fields can sometimes be used to determine that a specific client or server has a particular security hole which might3749 <p id="rfc.section.12.1.p.7">The <a href="#header.user-agent" class="smpl">User-Agent</a> (<a href="#header.user-agent" id="rfc.xref.header.user-agent.4" title="User-Agent">Section 10.18</a>) or <a href="#header.server" class="smpl">Server</a> (<a href="#header.server" id="rfc.xref.header.server.3" title="Server">Section 10.17</a>) header fields can sometimes be used to determine that a specific client or server has a particular security hole which might 3751 3750 be exploited. Unfortunately, this same information is often used for other valuable purposes for which HTTP currently has 3752 3751 no better mechanism. 3753 3752 </p> 3754 <p id="rfc.section.1 3.1.p.8">Furthermore, the <a href="#header.user-agent" class="smpl">User-Agent</a> header field might contain enough entropy to be used, possibly in conjunction with other material, to uniquely identify the3753 <p id="rfc.section.12.1.p.8">Furthermore, the <a href="#header.user-agent" class="smpl">User-Agent</a> header field might contain enough entropy to be used, possibly in conjunction with other material, to uniquely identify the 3755 3754 user. 3756 3755 </p> 3757 <p id="rfc.section.1 3.1.p.9">Some request methods, like TRACE (<a href="#TRACE" id="rfc.xref.TRACE.4" title="TRACE">Section 4.3.8</a>), expose information that was sent in request header fields within the body of their response. Clients <em class="bcp14">SHOULD</em> be careful with sensitive information, like Cookies, Authorization credentials, and other header fields that might be used3756 <p id="rfc.section.12.1.p.9">Some request methods, like TRACE (<a href="#TRACE" id="rfc.xref.TRACE.4" title="TRACE">Section 4.3.8</a>), expose information that was sent in request header fields within the body of their response. Clients <em class="bcp14">SHOULD</em> be careful with sensitive information, like Cookies, Authorization credentials, and other header fields that might be used 3758 3757 to collect data from the client. 3759 3758 </p> 3760 <h2 id="rfc.section.1 3.2"><a href="#rfc.section.13.2">13.2</a> <a id="encoding.sensitive.information.in.uris" href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URIs</a></h2>3761 <p id="rfc.section.1 3.2.p.1">Because the source of a link might be private information or might reveal an otherwise private information source, it is strongly3759 <h2 id="rfc.section.12.2"><a href="#rfc.section.12.2">12.2</a> <a id="encoding.sensitive.information.in.uris" href="#encoding.sensitive.information.in.uris">Encoding Sensitive Information in URIs</a></h2> 3760 <p id="rfc.section.12.2.p.1">Because the source of a link might be private information or might reveal an otherwise private information source, it is strongly 3762 3761 recommended that the user be able to select whether or not the <a href="#header.referer" class="smpl">Referer</a> field is sent. For example, a browser client could have a toggle switch for browsing openly/anonymously, which would respectively 3763 3762 enable/disable the sending of Referer and From information. 3764 3763 </p> 3765 <p id="rfc.section.1 3.2.p.2">Clients <em class="bcp14">SHOULD NOT</em> include a <a href="#header.referer" class="smpl">Referer</a> header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol.3766 </p> 3767 <p id="rfc.section.1 3.2.p.3">Authors of services <em class="bcp14">SHOULD NOT</em> use GET-based forms for the submission of sensitive data because that data will be placed in the request-target. Many existing3764 <p id="rfc.section.12.2.p.2">Clients <em class="bcp14">SHOULD NOT</em> include a <a href="#header.referer" class="smpl">Referer</a> header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol. 3765 </p> 3766 <p id="rfc.section.12.2.p.3">Authors of services <em class="bcp14">SHOULD NOT</em> use GET-based forms for the submission of sensitive data because that data will be placed in the request-target. Many existing 3768 3767 servers, proxies, and user agents log or display the request-target in places where it might be visible to third parties. 3769 3768 Such services can use POST-based form submission instead. 3770 3769 </p> 3771 <h2 id="rfc.section.1 3.3"><a href="#rfc.section.13.3">13.3</a> <a id="location.spoofing-leakage" href="#location.spoofing-leakage">Location Header Fields: Spoofing and Information Leakage</a></h2>3772 <p id="rfc.section.1 3.3.p.1">If a single server supports multiple organizations that do not trust one another, then it <em class="bcp14">MUST</em> check the values of <a href="#header.location" class="smpl">Location</a> and <a href="#header.content-location" class="smpl">Content-Location</a> header fields in responses that are generated under control of said organizations to make sure that they do not attempt to3770 <h2 id="rfc.section.12.3"><a href="#rfc.section.12.3">12.3</a> <a id="location.spoofing-leakage" href="#location.spoofing-leakage">Location Header Fields: Spoofing and Information Leakage</a></h2> 3771 <p id="rfc.section.12.3.p.1">If a single server supports multiple organizations that do not trust one another, then it <em class="bcp14">MUST</em> check the values of <a href="#header.location" class="smpl">Location</a> and <a href="#header.content-location" class="smpl">Content-Location</a> header fields in responses that are generated under control of said organizations to make sure that they do not attempt to 3773 3772 invalidate resources over which they have no authority. 3774 3773 </p> 3775 <p id="rfc.section.1 3.3.p.2">Furthermore, appending the fragment identifier from one URI to another one obtained from a <a href="#header.location" class="smpl">Location</a> header field might leak confidential information to the target server — although the fragment identifier is not transmitted3774 <p id="rfc.section.12.3.p.2">Furthermore, appending the fragment identifier from one URI to another one obtained from a <a href="#header.location" class="smpl">Location</a> header field might leak confidential information to the target server — although the fragment identifier is not transmitted 3776 3775 in the final request, it might be visible to the user agent through other means, such as scripting. 3777 3776 </p> 3778 <h2 id="rfc.section.1 3.4"><a href="#rfc.section.13.4">13.4</a> Security Considerations for CONNECT3777 <h2 id="rfc.section.12.4"><a href="#rfc.section.12.4">12.4</a> Security Considerations for CONNECT 3779 3778 </h2> 3780 <p id="rfc.section.1 3.4.p.1">Since tunneled data is opaque to the proxy, there are additional risks to tunneling to other well-known or reserved ports.3779 <p id="rfc.section.12.4.p.1">Since tunneled data is opaque to the proxy, there are additional risks to tunneling to other well-known or reserved ports. 3781 3780 A HTTP client CONNECTing to port 25 could relay spam via SMTP, for example. As such, proxies <em class="bcp14">SHOULD</em> restrict CONNECT access to a small number of known ports. 3782 3781 </p> 3783 <h2 id="rfc.section.1 3.5"><a href="#rfc.section.13.5">13.5</a> <a id="privacy.issues.connected.to.accept.header.fields" href="#privacy.issues.connected.to.accept.header.fields">Privacy Issues Connected to Accept Header Fields</a></h2>3784 <p id="rfc.section.1 3.5.p.1">Accept header fields can reveal information about the user to all servers which are accessed. The <a href="#header.accept-language" class="smpl">Accept-Language</a> header field in particular can reveal information the user would consider to be of a private nature, because the understanding3782 <h2 id="rfc.section.12.5"><a href="#rfc.section.12.5">12.5</a> <a id="privacy.issues.connected.to.accept.header.fields" href="#privacy.issues.connected.to.accept.header.fields">Privacy Issues Connected to Accept Header Fields</a></h2> 3783 <p id="rfc.section.12.5.p.1">Accept header fields can reveal information about the user to all servers which are accessed. The <a href="#header.accept-language" class="smpl">Accept-Language</a> header field in particular can reveal information the user would consider to be of a private nature, because the understanding 3785 3784 of particular languages is often strongly correlated to the membership of a particular ethnic group. User agents which offer 3786 3785 the option to configure the contents of an Accept-Language header field to be sent in every request are strongly encouraged 3787 3786 to let the configuration process include a message which makes the user aware of the loss of privacy involved. 3788 3787 </p> 3789 <p id="rfc.section.1 3.5.p.2">An approach that limits the loss of privacy would be for a user agent to omit the sending of Accept-Language header fields3788 <p id="rfc.section.12.5.p.2">An approach that limits the loss of privacy would be for a user agent to omit the sending of Accept-Language header fields 3790 3789 by default, and to ask the user whether or not to start sending Accept-Language header fields to a server if it detects, by 3791 3790 looking for any <a href="p6-cache.html#header.vary" class="smpl">Vary</a> header fields generated by the server, that such sending could improve the quality of service. 3792 3791 </p> 3793 <p id="rfc.section.1 3.5.p.3">Elaborate user-customized accept header fields sent in every request, in particular if these include quality values, can be3792 <p id="rfc.section.12.5.p.3">Elaborate user-customized accept header fields sent in every request, in particular if these include quality values, can be 3794 3793 used by servers as relatively reliable and long-lived user identifiers. Such user identifiers would allow content providers 3795 3794 to do click-trail tracking, and would allow collaborating content providers to match cross-server click-trails or form submissions … … 3800 3799 field configurability <em class="bcp14">SHOULD</em> warn users about the loss of privacy which can be involved. 3801 3800 </p> 3802 <h1 id="rfc.section.1 4"><a href="#rfc.section.14">14.</a> <a id="acks" href="#acks">Acknowledgments</a></h1>3803 <p id="rfc.section.1 4.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 9</a> of <a href="#Part1" id="rfc.xref.Part1.45"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>.3804 </p> 3805 <h1 id="rfc.references"><a id="rfc.section.1 5" href="#rfc.section.15">15.</a> References3801 <h1 id="rfc.section.13"><a href="#rfc.section.13">13.</a> <a id="acks" href="#acks">Acknowledgments</a></h1> 3802 <p id="rfc.section.13.p.1">See <a href="p1-messaging.html#acks" title="Acknowledgments">Section 9</a> of <a href="#Part1" id="rfc.xref.Part1.45"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>. 3803 </p> 3804 <h1 id="rfc.references"><a id="rfc.section.14" href="#rfc.section.14">14.</a> References 3806 3805 </h1> 3807 <h2 id="rfc.references.1"><a href="#rfc.section.1 5.1" id="rfc.section.15.1">15.1</a> Normative References3806 <h2 id="rfc.references.1"><a href="#rfc.section.14.1" id="rfc.section.14.1">14.1</a> Normative References 3808 3807 </h2> 3809 3808 <table> … … 3884 3883 </tr> 3885 3884 </table> 3886 <h2 id="rfc.references.2"><a href="#rfc.section.1 5.2" id="rfc.section.15.2">15.2</a> Informative References3885 <h2 id="rfc.references.2"><a href="#rfc.section.14.2" id="rfc.section.14.2">14.2</a> Informative References 3887 3886 </h2> 3888 3887 <table> … … 4075 4074 </p> 4076 4075 <h1 id="rfc.section.C"><a href="#rfc.section.C">C.</a> <a id="changes.from.rfc.2616" href="#changes.from.rfc.2616">Changes from RFC 2616</a></h1> 4077 <p id="rfc.section.C.p.1">Introduce Method Registry. (<a href="#method.registry" title="Method Registry">Section 1 2.1</a>)4076 <p id="rfc.section.C.p.1">Introduce Method Registry. (<a href="#method.registry" title="Method Registry">Section 11.1</a>) 4078 4077 </p> 4079 4078 <p id="rfc.section.C.p.2">Clarify definition of POST. (<a href="#POST" id="rfc.xref.POST.3" title="POST">Section 4.3.3</a>) … … 4083 4082 <p id="rfc.section.C.p.4">Take over definition of CONNECT method from <a href="#RFC2817" id="rfc.xref.RFC2817.2"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>. (<a href="#CONNECT" id="rfc.xref.CONNECT.3" title="CONNECT">Section 4.3.6</a>) 4084 4083 </p> 4085 <p id="rfc.section.C.p.5">Take over the Status Code Registry, previously defined in <a href="http://tools.ietf.org/html/rfc2817#section-7.1">Section 7.1</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.3"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>. (<a href="#status.code.registry" title="Status Code Registry">Section 1 2.2</a>)4084 <p id="rfc.section.C.p.5">Take over the Status Code Registry, previously defined in <a href="http://tools.ietf.org/html/rfc2817#section-7.1">Section 7.1</a> of <a href="#RFC2817" id="rfc.xref.RFC2817.3"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>. (<a href="#status.code.registry" title="Status Code Registry">Section 11.2</a>) 4086 4085 </p> 4087 4086 <p id="rfc.section.C.p.6">Broadened the definition of <a href="#status.203" class="smpl">203 (Non-Authoritative Information)</a> to include cases of payload transformations as well. (<a href="#status.203" id="rfc.xref.status.203.3" title="203 Non-Authoritative Information">Section 6.3.4</a>) … … 4099 4098 <p id="rfc.section.C.p.10">Define status <a href="#status.426" class="smpl">426 (Upgrade Required)</a> (this was incorporated from <a href="#RFC2817" id="rfc.xref.RFC2817.4"><cite title="Upgrading to TLS Within HTTP/1.1">[RFC2817]</cite></a>). (<a href="#status.426" id="rfc.xref.status.426.3" title="426 Upgrade Required">Section 6.5.15</a>) 4100 4099 </p> 4101 <p id="rfc.section.C.p.11">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section 1 1</a>)4100 <p id="rfc.section.C.p.11">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section 10</a>) 4102 4101 </p> 4103 4102 <p id="rfc.section.C.p.12">Reclassify "<a href="#header.allow" class="smpl">Allow</a>" as response header field, removing the option to specify it in a PUT request. Relax the server requirement on the contents 4104 of the Allow header field and remove requirement on clients to always trust the header field value. (<a href="#header.allow" id="rfc.xref.header.allow.4" title="Allow">Section 1 1.5</a>)4103 of the Allow header field and remove requirement on clients to always trust the header field value. (<a href="#header.allow" id="rfc.xref.header.allow.4" title="Allow">Section 10.5</a>) 4105 4104 </p> 4106 4105 <p id="rfc.section.C.p.13">The ABNF for the <a href="#header.expect" class="smpl">Expect</a> header field has been both fixed (allowing parameters for value-less expectations as well) and simplified (allowing trailing 4107 semicolons after "100-continue" when they were invalid before). (<a href="#header.expect" id="rfc.xref.header.expect.4" title="Expect">Section 1 1.11</a>)4106 semicolons after "100-continue" when they were invalid before). (<a href="#header.expect" id="rfc.xref.header.expect.4" title="Expect">Section 10.11</a>) 4108 4107 </p> 4109 4108 <p id="rfc.section.C.p.14">Correct syntax of <a href="#header.location" class="smpl">Location</a> header field to allow URI references (including relative references and fragments), as referred symbol "absoluteURI" wasn't 4110 what was expected, and add some clarifications as to when use of fragments would not be appropriate. (<a href="#header.location" id="rfc.xref.header.location.5" title="Location">Section 1 1.13</a>)4111 </p> 4112 <p id="rfc.section.C.p.15">Restrict <a href="#header.max-forwards" class="smpl">Max-Forwards</a> header field to OPTIONS and TRACE (previously, extension methods could have used it as well). (<a href="#header.max-forwards" id="rfc.xref.header.max-forwards.5" title="Max-Forwards">Section 1 1.14</a>)4113 </p> 4114 <p id="rfc.section.C.p.16">Allow <a href="#header.referer" class="smpl">Referer</a> field value of "about:blank" as alternative to not specifying it. (<a href="#header.referer" id="rfc.xref.header.referer.3" title="Referer">Section 1 1.15</a>)4115 </p> 4116 <p id="rfc.section.C.p.17">In the description of the <a href="#header.server" class="smpl">Server</a> header field, the <a href="p1-messaging.html#header.via" class="smpl">Via</a> field was described as a SHOULD. The requirement was and is stated correctly in the description of the Via header field in <a href="p1-messaging.html#header.via" title="Via">Section 5.7</a> of <a href="#Part1" id="rfc.xref.Part1.46"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>. (<a href="#header.server" id="rfc.xref.header.server.4" title="Server">Section 1 1.17</a>)4109 what was expected, and add some clarifications as to when use of fragments would not be appropriate. (<a href="#header.location" id="rfc.xref.header.location.5" title="Location">Section 10.13</a>) 4110 </p> 4111 <p id="rfc.section.C.p.15">Restrict <a href="#header.max-forwards" class="smpl">Max-Forwards</a> header field to OPTIONS and TRACE (previously, extension methods could have used it as well). (<a href="#header.max-forwards" id="rfc.xref.header.max-forwards.5" title="Max-Forwards">Section 10.14</a>) 4112 </p> 4113 <p id="rfc.section.C.p.16">Allow <a href="#header.referer" class="smpl">Referer</a> field value of "about:blank" as alternative to not specifying it. (<a href="#header.referer" id="rfc.xref.header.referer.3" title="Referer">Section 10.15</a>) 4114 </p> 4115 <p id="rfc.section.C.p.17">In the description of the <a href="#header.server" class="smpl">Server</a> header field, the <a href="p1-messaging.html#header.via" class="smpl">Via</a> field was described as a SHOULD. The requirement was and is stated correctly in the description of the Via header field in <a href="p1-messaging.html#header.via" title="Via">Section 5.7</a> of <a href="#Part1" id="rfc.xref.Part1.46"><cite title="HTTP/1.1, part 1: Message Routing and Syntax"">[Part1]</cite></a>. (<a href="#header.server" id="rfc.xref.header.server.4" title="Server">Section 10.17</a>) 4117 4116 </p> 4118 4117 <p id="rfc.section.C.p.18">Clarify contexts that charset is used in. (<a href="#character.sets" title="Character Encodings (charset)">Section 8.3</a>) 4119 4118 </p> 4120 <p id="rfc.section.C.p.19">Registration of Content Codings now requires IETF Review (<a href="#content.coding.registry" title="Content Coding Registry">Section 1 2.4</a>)4119 <p id="rfc.section.C.p.19">Registration of Content Codings now requires IETF Review (<a href="#content.coding.registry" title="Content Coding Registry">Section 11.4</a>) 4121 4120 </p> 4122 4121 <p id="rfc.section.C.p.20">Remove the default character encoding of "ISO-8859-1" for text media types; the default now is whatever the media type definition 4123 4122 says. (<a href="#canonicalization.and.text.defaults" title="Canonicalization and Text Defaults">Section 8.5.1</a>) 4124 4123 </p> 4125 <p id="rfc.section.C.p.21">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section 1 1</a>)4124 <p id="rfc.section.C.p.21">Change ABNF productions for header fields to only define the field value. (<a href="#header.field.definitions" title="Header Field Definitions">Section 10</a>) 4126 4125 </p> 4127 4126 <p id="rfc.section.C.p.22">Remove definition of Content-MD5 header field because it was inconsistently implemented with respect to partial responses, 4128 and also because of known deficiencies in the hash algorithm itself (see <a href="#RFC6151" id="rfc.xref.RFC6151.1"><cite title="Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms">[RFC6151]</cite></a> for details). (<a href="#header.field.definitions" title="Header Field Definitions">Section 1 1</a>)4129 </p> 4130 <p id="rfc.section.C.p.23">Remove ISO-8859-1 special-casing in <a href="#header.accept-charset" class="smpl">Accept-Charset</a>. (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.4" title="Accept-Charset">Section 1 1.2</a>)4127 and also because of known deficiencies in the hash algorithm itself (see <a href="#RFC6151" id="rfc.xref.RFC6151.1"><cite title="Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms">[RFC6151]</cite></a> for details). (<a href="#header.field.definitions" title="Header Field Definitions">Section 10</a>) 4128 </p> 4129 <p id="rfc.section.C.p.23">Remove ISO-8859-1 special-casing in <a href="#header.accept-charset" class="smpl">Accept-Charset</a>. (<a href="#header.accept-charset" id="rfc.xref.header.accept-charset.4" title="Accept-Charset">Section 10.2</a>) 4131 4130 </p> 4132 4131 <p id="rfc.section.C.p.24">Remove base URI setting semantics for <a href="#header.content-location" class="smpl">Content-Location</a> due to poor implementation support, which was caused by too many broken servers emitting bogus Content-Location header fields, 4133 and also the potentially undesirable effect of potentially breaking relative links in content-negotiated resources. (<a href="#header.content-location" id="rfc.xref.header.content-location.5" title="Content-Location">Section 1 1.8</a>)4132 and also the potentially undesirable effect of potentially breaking relative links in content-negotiated resources. (<a href="#header.content-location" id="rfc.xref.header.content-location.5" title="Content-Location">Section 10.8</a>) 4134 4133 </p> 4135 4134 <p id="rfc.section.C.p.25">Remove reference to non-existant identity transfer-coding value tokens. (<a href="#no.content-transfer-encoding" id="rfc.xref.no.content-transfer-encoding.1" title="No Content-Transfer-Encoding">Appendix A.5</a>) … … 4860 4859 <ul class="ind"> 4861 4860 <li><a id="rfc.index.1" href="#rfc.index.1"><b>1</b></a><ul> 4862 <li>100 Continue (status code) <a href="#rfc.xref.status.100.1">6.1</a>, <a href="#rfc.iref.2 4"><b>6.2.1</b></a>, <a href="#rfc.xref.status.100.2">12.2.3</a></li>4863 <li>100-continue (expect value) <a href="#rfc.iref.142"><b>1 1.11</b></a></li>4864 <li>101 Switching Protocols (status code) <a href="#rfc.xref.status.101.1">6.1</a>, <a href="#rfc.iref.2 5"><b>6.2.2</b></a>, <a href="#rfc.xref.status.101.2">12.2.3</a></li>4865 <li>1xx Informational (status code class) <a href="#rfc.iref.2 3"><b>6.2</b></a></li>4861 <li>100 Continue (status code) <a href="#rfc.xref.status.100.1">6.1</a>, <a href="#rfc.iref.26"><b>6.2.1</b></a>, <a href="#rfc.xref.status.100.2">11.2.3</a></li> 4862 <li>100-continue (expect value) <a href="#rfc.iref.142"><b>10.11</b></a></li> 4863 <li>101 Switching Protocols (status code) <a href="#rfc.xref.status.101.1">6.1</a>, <a href="#rfc.iref.27"><b>6.2.2</b></a>, <a href="#rfc.xref.status.101.2">11.2.3</a></li> 4864 <li>1xx Informational (status code class) <a href="#rfc.iref.25"><b>6.2</b></a></li> 4866 4865 </ul> 4867 4866 </li> 4868 4867 <li><a id="rfc.index.2" href="#rfc.index.2"><b>2</b></a><ul> 4869 <li>200 OK (status code) <a href="#rfc.xref.status.200.1">6.1</a>, <a href="#rfc.iref.2 7"><b>6.3.1</b></a>, <a href="#rfc.xref.status.200.2">12.2.3</a></li>4870 <li>201 Created (status code) <a href="#rfc.xref.status.201.1">6.1</a>, <a href="#rfc.iref. 28"><b>6.3.2</b></a>, <a href="#rfc.xref.status.201.2">12.2.3</a></li>4871 <li>202 Accepted (status code) <a href="#rfc.xref.status.202.1">6.1</a>, <a href="#rfc.iref. 29"><b>6.3.3</b></a>, <a href="#rfc.xref.status.202.2">12.2.3</a></li>4872 <li>203 Non-Authoritative Information (status code) <a href="#rfc.xref.status.203.1">6.1</a>, <a href="#rfc.iref.3 0"><b>6.3.4</b></a>, <a href="#rfc.xref.status.203.2">12.2.3</a>, <a href="#rfc.xref.status.203.3">C</a></li>4873 <li>204 No Content (status code) <a href="#rfc.xref.status.204.1">6.1</a>, <a href="#rfc.iref.3 1"><b>6.3.5</b></a>, <a href="#rfc.xref.status.204.2">12.2.3</a></li>4874 <li>205 Reset Content (status code) <a href="#rfc.xref.status.205.1">6.1</a>, <a href="#rfc.iref.3 2"><b>6.3.6</b></a>, <a href="#rfc.xref.status.205.2">12.2.3</a></li>4875 <li>2xx Successful (status code class) <a href="#rfc.iref.2 6"><b>6.3</b></a></li>4868 <li>200 OK (status code) <a href="#rfc.xref.status.200.1">6.1</a>, <a href="#rfc.iref.29"><b>6.3.1</b></a>, <a href="#rfc.xref.status.200.2">11.2.3</a></li> 4869 <li>201 Created (status code) <a href="#rfc.xref.status.201.1">6.1</a>, <a href="#rfc.iref.30"><b>6.3.2</b></a>, <a href="#rfc.xref.status.201.2">11.2.3</a></li> 4870 <li>202 Accepted (status code) <a href="#rfc.xref.status.202.1">6.1</a>, <a href="#rfc.iref.31"><b>6.3.3</b></a>, <a href="#rfc.xref.status.202.2">11.2.3</a></li> 4871 <li>203 Non-Authoritative Information (status code) <a href="#rfc.xref.status.203.1">6.1</a>, <a href="#rfc.iref.32"><b>6.3.4</b></a>, <a href="#rfc.xref.status.203.2">11.2.3</a>, <a href="#rfc.xref.status.203.3">C</a></li> 4872 <li>204 No Content (status code) <a href="#rfc.xref.status.204.1">6.1</a>, <a href="#rfc.iref.33"><b>6.3.5</b></a>, <a href="#rfc.xref.status.204.2">11.2.3</a></li> 4873 <li>205 Reset Content (status code) <a href="#rfc.xref.status.205.1">6.1</a>, <a href="#rfc.iref.34"><b>6.3.6</b></a>, <a href="#rfc.xref.status.205.2">11.2.3</a></li> 4874 <li>2xx Successful (status code class) <a href="#rfc.iref.28"><b>6.3</b></a></li> 4876 4875 </ul> 4877 4876 </li> 4878 4877 <li><a id="rfc.index.3" href="#rfc.index.3"><b>3</b></a><ul> 4879 <li>300 Multiple Choices (status code) <a href="#rfc.xref.status.300.1">6.1</a>, <a href="#rfc.iref.3 4"><b>6.4.1</b></a>, <a href="#rfc.xref.status.300.2">12.2.3</a></li>4880 <li>301 Moved Permanently (status code) <a href="#rfc.xref.status.301.1">6.1</a>, <a href="#rfc.iref.3 5"><b>6.4.2</b></a>, <a href="#rfc.xref.status.301.2">12.2.3</a>, <a href="#rfc.xref.status.301.3">C</a></li>4881 <li>302 Found (status code) <a href="#rfc.xref.status.302.1">6.1</a>, <a href="#rfc.iref.3 6"><b>6.4.3</b></a>, <a href="#rfc.xref.status.302.2">12.2.3</a>, <a href="#rfc.xref.status.302.3">C</a></li>4882 <li>303 See Other (status code) <a href="#rfc.xref.status.303.1">6.1</a>, <a href="#rfc.iref.3 7"><b>6.4.4</b></a>, <a href="#rfc.xref.status.303.2">12.2.3</a></li>4883 <li>305 Use Proxy (status code) <a href="#rfc.xref.status.305.1">6.1</a>, <a href="#rfc.iref. 38"><b>6.4.5</b></a>, <a href="#rfc.xref.status.305.2">12.2.3</a>, <a href="#rfc.xref.status.305.3">C</a></li>4884 <li>306 (Unused) (status code) <a href="#rfc.iref. 39"><b>6.4.6</b></a>, <a href="#rfc.xref.status.306.1">12.2.3</a></li>4885 <li>307 Temporary Redirect (status code) <a href="#rfc.xref.status.307.1">6.1</a>, <a href="#rfc.iref.4 0"><b>6.4.7</b></a>, <a href="#rfc.xref.status.307.2">12.2.3</a>, <a href="#rfc.xref.status.307.3">C</a></li>4886 <li>3xx Redirection (status code class) <a href="#rfc.iref.3 3"><b>6.4</b></a>, <a href="#rfc.xref.status.3xx.1">C</a></li>4878 <li>300 Multiple Choices (status code) <a href="#rfc.xref.status.300.1">6.1</a>, <a href="#rfc.iref.36"><b>6.4.1</b></a>, <a href="#rfc.xref.status.300.2">11.2.3</a></li> 4879 <li>301 Moved Permanently (status code) <a href="#rfc.xref.status.301.1">6.1</a>, <a href="#rfc.iref.37"><b>6.4.2</b></a>, <a href="#rfc.xref.status.301.2">11.2.3</a>, <a href="#rfc.xref.status.301.3">C</a></li> 4880 <li>302 Found (status code) <a href="#rfc.xref.status.302.1">6.1</a>, <a href="#rfc.iref.38"><b>6.4.3</b></a>, <a href="#rfc.xref.status.302.2">11.2.3</a>, <a href="#rfc.xref.status.302.3">C</a></li> 4881 <li>303 See Other (status code) <a href="#rfc.xref.status.303.1">6.1</a>, <a href="#rfc.iref.39"><b>6.4.4</b></a>, <a href="#rfc.xref.status.303.2">11.2.3</a></li> 4882 <li>305 Use Proxy (status code) <a href="#rfc.xref.status.305.1">6.1</a>, <a href="#rfc.iref.40"><b>6.4.5</b></a>, <a href="#rfc.xref.status.305.2">11.2.3</a>, <a href="#rfc.xref.status.305.3">C</a></li> 4883 <li>306 (Unused) (status code) <a href="#rfc.iref.41"><b>6.4.6</b></a>, <a href="#rfc.xref.status.306.1">11.2.3</a></li> 4884 <li>307 Temporary Redirect (status code) <a href="#rfc.xref.status.307.1">6.1</a>, <a href="#rfc.iref.42"><b>6.4.7</b></a>, <a href="#rfc.xref.status.307.2">11.2.3</a>, <a href="#rfc.xref.status.307.3">C</a></li> 4885 <li>3xx Redirection (status code class) <a href="#rfc.iref.35"><b>6.4</b></a>, <a href="#rfc.xref.status.3xx.1">C</a></li> 4887 4886 </ul> 4888 4887 </li> 4889 4888 <li><a id="rfc.index.4" href="#rfc.index.4"><b>4</b></a><ul> 4890 <li>400 Bad Request (status code) <a href="#rfc.xref.status.400.1">6.1</a>, <a href="#rfc.iref.4 2"><b>6.5.1</b></a>, <a href="#rfc.xref.status.400.2">12.2.3</a></li>4891 <li>402 Payment Required (status code) <a href="#rfc.xref.status.402.1">6.1</a>, <a href="#rfc.iref.4 3"><b>6.5.2</b></a>, <a href="#rfc.xref.status.402.2">12.2.3</a></li>4892 <li>403 Forbidden (status code) <a href="#rfc.xref.status.403.1">6.1</a>, <a href="#rfc.iref.4 4"><b>6.5.3</b></a>, <a href="#rfc.xref.status.403.2">12.2.3</a></li>4893 <li>404 Not Found (status code) <a href="#rfc.xref.status.404.1">6.1</a>, <a href="#rfc.iref.4 5"><b>6.5.4</b></a>, <a href="#rfc.xref.status.404.2">12.2.3</a></li>4894 <li>405 Method Not Allowed (status code) <a href="#rfc.xref.status.405.1">6.1</a>, <a href="#rfc.iref.4 6"><b>6.5.5</b></a>, <a href="#rfc.xref.status.405.2">12.2.3</a></li>4895 <li>406 Not Acceptable (status code) <a href="#rfc.xref.status.406.1">6.1</a>, <a href="#rfc.iref.4 7"><b>6.5.6</b></a>, <a href="#rfc.xref.status.406.2">12.2.3</a></li>4896 <li>408 Request Timeout (status code) <a href="#rfc.xref.status.408.1">6.1</a>, <a href="#rfc.iref. 48"><b>6.5.7</b></a>, <a href="#rfc.xref.status.408.2">12.2.3</a></li>4897 <li>409 Conflict (status code) <a href="#rfc.xref.status.409.1">6.1</a>, <a href="#rfc.iref. 49"><b>6.5.8</b></a>, <a href="#rfc.xref.status.409.2">12.2.3</a></li>4898 <li>410 Gone (status code) <a href="#rfc.xref.status.410.1">6.1</a>, <a href="#rfc.iref.5 0"><b>6.5.9</b></a>, <a href="#rfc.xref.status.410.2">12.2.3</a></li>4899 <li>411 Length Required (status code) <a href="#rfc.xref.status.411.1">6.1</a>, <a href="#rfc.iref.5 1"><b>6.5.10</b></a>, <a href="#rfc.xref.status.411.2">12.2.3</a></li>4900 <li>413 Request Representation Too Large (status code) <a href="#rfc.xref.status.413.1">6.1</a>, <a href="#rfc.iref.5 2"><b>6.5.11</b></a>, <a href="#rfc.xref.status.413.2">12.2.3</a></li>4901 <li>414 URI Too Long (status code) <a href="#rfc.xref.status.414.1">6.1</a>, <a href="#rfc.iref.5 3"><b>6.5.12</b></a>, <a href="#rfc.xref.status.414.2">12.2.3</a></li>4902 <li>415 Unsupported Media Type (status code) <a href="#rfc.xref.status.415.1">6.1</a>, <a href="#rfc.iref.5 4"><b>6.5.13</b></a>, <a href="#rfc.xref.status.415.2">12.2.3</a></li>4903 <li>417 Expectation Failed (status code) <a href="#rfc.xref.status.417.1">6.1</a>, <a href="#rfc.iref.5 5"><b>6.5.14</b></a>, <a href="#rfc.xref.status.417.2">12.2.3</a></li>4904 <li>426 Upgrade Required (status code) <a href="#rfc.xref.status.426.1">6.1</a>, <a href="#rfc.iref.5 6"><b>6.5.15</b></a>, <a href="#rfc.xref.status.426.2">12.2.3</a>, <a href="#rfc.xref.status.426.3">C</a></li>4905 <li>4xx Client Error (status code class) <a href="#rfc.iref.4 1"><b>6.5</b></a></li>4889 <li>400 Bad Request (status code) <a href="#rfc.xref.status.400.1">6.1</a>, <a href="#rfc.iref.44"><b>6.5.1</b></a>, <a href="#rfc.xref.status.400.2">11.2.3</a></li> 4890 <li>402 Payment Required (status code) <a href="#rfc.xref.status.402.1">6.1</a>, <a href="#rfc.iref.45"><b>6.5.2</b></a>, <a href="#rfc.xref.status.402.2">11.2.3</a></li> 4891 <li>403 Forbidden (status code) <a href="#rfc.xref.status.403.1">6.1</a>, <a href="#rfc.iref.46"><b>6.5.3</b></a>, <a href="#rfc.xref.status.403.2">11.2.3</a></li> 4892 <li>404 Not Found (status code) <a href="#rfc.xref.status.404.1">6.1</a>, <a href="#rfc.iref.47"><b>6.5.4</b></a>, <a href="#rfc.xref.status.404.2">11.2.3</a></li> 4893 <li>405 Method Not Allowed (status code) <a href="#rfc.xref.status.405.1">6.1</a>, <a href="#rfc.iref.48"><b>6.5.5</b></a>, <a href="#rfc.xref.status.405.2">11.2.3</a></li> 4894 <li>406 Not Acceptable (status code) <a href="#rfc.xref.status.406.1">6.1</a>, <a href="#rfc.iref.49"><b>6.5.6</b></a>, <a href="#rfc.xref.status.406.2">11.2.3</a></li> 4895 <li>408 Request Timeout (status code) <a href="#rfc.xref.status.408.1">6.1</a>, <a href="#rfc.iref.50"><b>6.5.7</b></a>, <a href="#rfc.xref.status.408.2">11.2.3</a></li> 4896 <li>409 Conflict (status code) <a href="#rfc.xref.status.409.1">6.1</a>, <a href="#rfc.iref.51"><b>6.5.8</b></a>, <a href="#rfc.xref.status.409.2">11.2.3</a></li> 4897 <li>410 Gone (status code) <a href="#rfc.xref.status.410.1">6.1</a>, <a href="#rfc.iref.52"><b>6.5.9</b></a>, <a href="#rfc.xref.status.410.2">11.2.3</a></li> 4898 <li>411 Length Required (status code) <a href="#rfc.xref.status.411.1">6.1</a>, <a href="#rfc.iref.53"><b>6.5.10</b></a>, <a href="#rfc.xref.status.411.2">11.2.3</a></li> 4899 <li>413 Request Representation Too Large (status code) <a href="#rfc.xref.status.413.1">6.1</a>, <a href="#rfc.iref.54"><b>6.5.11</b></a>, <a href="#rfc.xref.status.413.2">11.2.3</a></li> 4900 <li>414 URI Too Long (status code) <a href="#rfc.xref.status.414.1">6.1</a>, <a href="#rfc.iref.55"><b>6.5.12</b></a>, <a href="#rfc.xref.status.414.2">11.2.3</a></li> 4901 <li>415 Unsupported Media Type (status code) <a href="#rfc.xref.status.415.1">6.1</a>, <a href="#rfc.iref.56"><b>6.5.13</b></a>, <a href="#rfc.xref.status.415.2">11.2.3</a></li> 4902 <li>417 Expectation Failed (status code) <a href="#rfc.xref.status.417.1">6.1</a>, <a href="#rfc.iref.57"><b>6.5.14</b></a>, <a href="#rfc.xref.status.417.2">11.2.3</a></li> 4903 <li>426 Upgrade Required (status code) <a href="#rfc.xref.status.426.1">6.1</a>, <a href="#rfc.iref.58"><b>6.5.15</b></a>, <a href="#rfc.xref.status.426.2">11.2.3</a>, <a href="#rfc.xref.status.426.3">C</a></li> 4904 <li>4xx Client Error (status code class) <a href="#rfc.iref.43"><b>6.5</b></a></li> 4906 4905 </ul> 4907 4906 </li> 4908 4907 <li><a id="rfc.index.5" href="#rfc.index.5"><b>5</b></a><ul> 4909 <li>500 Internal Server Error (status code) <a href="#rfc.xref.status.500.1">6.1</a>, <a href="#rfc.iref. 58"><b>6.6.1</b></a>, <a href="#rfc.xref.status.500.2">12.2.3</a></li>4910 <li>501 Not Implemented (status code) <a href="#rfc.xref.status.501.1">6.1</a>, <a href="#rfc.iref. 59"><b>6.6.2</b></a>, <a href="#rfc.xref.status.501.2">12.2.3</a></li>4911 <li>502 Bad Gateway (status code) <a href="#rfc.xref.status.502.1">6.1</a>, <a href="#rfc.iref.6 0"><b>6.6.3</b></a>, <a href="#rfc.xref.status.502.2">12.2.3</a></li>4912 <li>503 Service Unavailable (status code) <a href="#rfc.xref.status.503.1">6.1</a>, <a href="#rfc.iref.6 1"><b>6.6.4</b></a>, <a href="#rfc.xref.status.503.2">12.2.3</a></li>4913 <li>504 Gateway Timeout (status code) <a href="#rfc.xref.status.504.1">6.1</a>, <a href="#rfc.iref.6 2"><b>6.6.5</b></a>, <a href="#rfc.xref.status.504.2">12.2.3</a></li>4914 <li>505 HTTP Version Not Supported (status code) <a href="#rfc.xref.status.505.1">6.1</a>, <a href="#rfc.iref.6 3"><b>6.6.6</b></a>, <a href="#rfc.xref.status.505.2">12.2.3</a></li>4915 <li>5xx Server Error (status code class) <a href="#rfc.iref.5 7"><b>6.6</b></a></li>4908 <li>500 Internal Server Error (status code) <a href="#rfc.xref.status.500.1">6.1</a>, <a href="#rfc.iref.60"><b>6.6.1</b></a>, <a href="#rfc.xref.status.500.2">11.2.3</a></li> 4909 <li>501 Not Implemented (status code) <a href="#rfc.xref.status.501.1">6.1</a>, <a href="#rfc.iref.61"><b>6.6.2</b></a>, <a href="#rfc.xref.status.501.2">11.2.3</a></li> 4910 <li>502 Bad Gateway (status code) <a href="#rfc.xref.status.502.1">6.1</a>, <a href="#rfc.iref.62"><b>6.6.3</b></a>, <a href="#rfc.xref.status.502.2">11.2.3</a></li> 4911 <li>503 Service Unavailable (status code) <a href="#rfc.xref.status.503.1">6.1</a>, <a href="#rfc.iref.63"><b>6.6.4</b></a>, <a href="#rfc.xref.status.503.2">11.2.3</a></li> 4912 <li>504 Gateway Timeout (status code) <a href="#rfc.xref.status.504.1">6.1</a>, <a href="#rfc.iref.64"><b>6.6.5</b></a>, <a href="#rfc.xref.status.504.2">11.2.3</a></li> 4913 <li>505 HTTP Version Not Supported (status code) <a href="#rfc.xref.status.505.1">6.1</a>, <a href="#rfc.iref.65"><b>6.6.6</b></a>, <a href="#rfc.xref.status.505.2">11.2.3</a></li> 4914 <li>5xx Server Error (status code class) <a href="#rfc.iref.59"><b>6.6</b></a></li> 4916 4915 </ul> 4917 4916 </li> 4918 4917 <li><a id="rfc.index.A" href="#rfc.index.A"><b>A</b></a><ul> 4919 <li>Accept header field <a href="#rfc.xref.header.accept.1"> 5.3</a>, <a href="#rfc.xref.header.accept.2">8.5</a>, <a href="#rfc.xref.header.accept.3">10.1</a>, <a href="#rfc.iref.a.1"><b>11.1</b></a>, <a href="#rfc.xref.header.accept.4">12.3.2</a></li>4920 <li>Accept-Charset header field <a href="#rfc.xref.header.accept-charset.1"> 5.3</a>, <a href="#rfc.xref.header.accept-charset.2">10.1</a>, <a href="#rfc.iref.a.2"><b>11.2</b></a>, <a href="#rfc.xref.header.accept-charset.3">12.3.2</a>, <a href="#rfc.xref.header.accept-charset.4">C</a></li>4921 <li>Accept-Encoding header field <a href="#rfc.xref.header.accept-encoding.1"> 5.3</a>, <a href="#rfc.xref.header.accept-encoding.2">8.4</a>, <a href="#rfc.xref.header.accept-encoding.3">10.1</a>, <a href="#rfc.iref.a.3"><b>11.3</b></a>, <a href="#rfc.xref.header.accept-encoding.4">12.3.2</a>, <a href="#rfc.xref.header.accept-encoding.5">12.4.2</a></li>4922 <li>Accept-Language header field <a href="#rfc.xref.header.accept-language.1"> 5.3</a>, <a href="#rfc.xref.header.accept-language.2">10.1</a>, <a href="#rfc.iref.a.4"><b>11.4</b></a>, <a href="#rfc.xref.header.accept-language.3">12.3.2</a></li>4923 <li>Allow header field <a href="#rfc.xref.header.allow.1">4.1</a>, <a href="#rfc.xref.header.allow.2">7</a>, <a href="#rfc.iref.a.5"><b>1 1.5</b></a>, <a href="#rfc.xref.header.allow.3">12.3.2</a>, <a href="#rfc.xref.header.allow.4">C</a></li>4918 <li>Accept header field <a href="#rfc.xref.header.accept.1">3.4.1</a>, <a href="#rfc.xref.header.accept.2">5.3</a>, <a href="#rfc.xref.header.accept.3">8.5</a>, <a href="#rfc.iref.a.1"><b>10.1</b></a>, <a href="#rfc.xref.header.accept.4">11.3.2</a></li> 4919 <li>Accept-Charset header field <a href="#rfc.xref.header.accept-charset.1">3.4.1</a>, <a href="#rfc.xref.header.accept-charset.2">5.3</a>, <a href="#rfc.iref.a.2"><b>10.2</b></a>, <a href="#rfc.xref.header.accept-charset.3">11.3.2</a>, <a href="#rfc.xref.header.accept-charset.4">C</a></li> 4920 <li>Accept-Encoding header field <a href="#rfc.xref.header.accept-encoding.1">3.4.1</a>, <a href="#rfc.xref.header.accept-encoding.2">5.3</a>, <a href="#rfc.xref.header.accept-encoding.3">8.4</a>, <a href="#rfc.iref.a.3"><b>10.3</b></a>, <a href="#rfc.xref.header.accept-encoding.4">11.3.2</a>, <a href="#rfc.xref.header.accept-encoding.5">11.4.2</a></li> 4921 <li>Accept-Language header field <a href="#rfc.xref.header.accept-language.1">3.4.1</a>, <a href="#rfc.xref.header.accept-language.2">5.3</a>, <a href="#rfc.iref.a.4"><b>10.4</b></a>, <a href="#rfc.xref.header.accept-language.3">11.3.2</a></li> 4922 <li>Allow header field <a href="#rfc.xref.header.allow.1">4.1</a>, <a href="#rfc.xref.header.allow.2">7</a>, <a href="#rfc.iref.a.5"><b>10.5</b></a>, <a href="#rfc.xref.header.allow.3">11.3.2</a>, <a href="#rfc.xref.header.allow.4">C</a></li> 4924 4923 </ul> 4925 4924 </li> … … 4934 4933 </li> 4935 4934 <li>compress (Coding Format) <a href="#rfc.iref.c.4">8.4</a></li> 4936 <li>CONNECT method <a href="#rfc.xref.CONNECT.1">4.1</a>, <a href="#rfc.iref.c.3"><b>4.3.6</b></a>, <a href="#rfc.xref.CONNECT.2">1 2.1.3</a>, <a href="#rfc.xref.CONNECT.3">C</a></li>4935 <li>CONNECT method <a href="#rfc.xref.CONNECT.1">4.1</a>, <a href="#rfc.iref.c.3"><b>4.3.6</b></a>, <a href="#rfc.xref.CONNECT.2">11.1.3</a>, <a href="#rfc.xref.CONNECT.3">C</a></li> 4937 4936 <li>content negotiation <a href="#rfc.iref.c.1">1</a></li> 4938 <li>Content-Encoding header field <a href="#rfc.xref.header.content-encoding.1">3.2</a>, <a href="#rfc.xref.header.content-encoding.2">8.4</a>, <a href="#rfc.iref.c.8"><b>1 1.6</b></a>, <a href="#rfc.xref.header.content-encoding.3">12.3.2</a></li>4939 <li>Content-Language header field <a href="#rfc.xref.header.content-language.1">3.2</a>, <a href="#rfc.iref.c.9"><b>1 1.7</b></a>, <a href="#rfc.xref.header.content-language.2">12.3.2</a></li>4940 <li>Content-Location header field <a href="#rfc.xref.header.content-location.1">3.2</a>, <a href="#rfc.xref.header.content-location.2">4.3.3</a>, <a href="#rfc.iref.c.10"><b>1 1.8</b></a>, <a href="#rfc.xref.header.content-location.3">11.13</a>, <a href="#rfc.xref.header.content-location.4">12.3.2</a>, <a href="#rfc.xref.header.content-location.5">C</a></li>4937 <li>Content-Encoding header field <a href="#rfc.xref.header.content-encoding.1">3.2</a>, <a href="#rfc.xref.header.content-encoding.2">8.4</a>, <a href="#rfc.iref.c.8"><b>10.6</b></a>, <a href="#rfc.xref.header.content-encoding.3">11.3.2</a></li> 4938 <li>Content-Language header field <a href="#rfc.xref.header.content-language.1">3.2</a>, <a href="#rfc.iref.c.9"><b>10.7</b></a>, <a href="#rfc.xref.header.content-language.2">11.3.2</a></li> 4939 <li>Content-Location header field <a href="#rfc.xref.header.content-location.1">3.2</a>, <a href="#rfc.xref.header.content-location.2">4.3.3</a>, <a href="#rfc.iref.c.10"><b>10.8</b></a>, <a href="#rfc.xref.header.content-location.3">10.13</a>, <a href="#rfc.xref.header.content-location.4">11.3.2</a>, <a href="#rfc.xref.header.content-location.5">C</a></li> 4941 4940 <li>Content-Transfer-Encoding header field <a href="#rfc.iref.c.12">A.5</a>, <a href="#rfc.xref.no.content-transfer-encoding.1">C</a></li> 4942 <li>Content-Type header field <a href="#rfc.xref.header.content-type.1">3.2</a>, <a href="#rfc.xref.header.content-type.2">6</a>, <a href="#rfc.xref.header.content-type.3">8.5</a>, <a href="#rfc.iref.c.11"><b>1 1.9</b></a>, <a href="#rfc.xref.header.content-type.4">12.3.1</a>, <a href="#rfc.xref.header.content-type.5">12.3.2</a></li>4941 <li>Content-Type header field <a href="#rfc.xref.header.content-type.1">3.2</a>, <a href="#rfc.xref.header.content-type.2">6</a>, <a href="#rfc.xref.header.content-type.3">8.5</a>, <a href="#rfc.iref.c.11"><b>10.9</b></a>, <a href="#rfc.xref.header.content-type.4">11.3.1</a>, <a href="#rfc.xref.header.content-type.5">11.3.2</a></li> 4943 4942 </ul> 4944 4943 </li> 4945 4944 <li><a id="rfc.index.D" href="#rfc.index.D"><b>D</b></a><ul> 4946 <li>Date header field <a href="#rfc.xref.header.date.1">7</a>, <a href="#rfc.iref.d.3"><b>1 1.10</b></a>, <a href="#rfc.xref.header.date.2">12.3.2</a></li>4945 <li>Date header field <a href="#rfc.xref.header.date.1">7</a>, <a href="#rfc.iref.d.3"><b>10.10</b></a>, <a href="#rfc.xref.header.date.2">11.3.2</a></li> 4947 4946 <li>deflate (Coding Format) <a href="#rfc.iref.d.2">8.4</a></li> 4948 <li>DELETE method <a href="#rfc.xref.DELETE.1">4.1</a>, <a href="#rfc.iref.d.1"><b>4.3.5</b></a>, <a href="#rfc.xref.DELETE.2">1 2.1.3</a></li>4947 <li>DELETE method <a href="#rfc.xref.DELETE.1">4.1</a>, <a href="#rfc.iref.d.1"><b>4.3.5</b></a>, <a href="#rfc.xref.DELETE.2">11.1.3</a></li> 4949 4948 </ul> 4950 4949 </li> 4951 4950 <li><a id="rfc.index.E" href="#rfc.index.E"><b>E</b></a><ul> 4952 <li>Expect header field <a href="#rfc.xref.header.expect.1">5.1</a>, <a href="#rfc.xref.header.expect.2">6.5.14</a>, <a href="#rfc.iref.e.1"><b>1 1.11</b></a>, <a href="#rfc.xref.header.expect.3">12.3.2</a>, <a href="#rfc.xref.header.expect.4">C</a></li>4951 <li>Expect header field <a href="#rfc.xref.header.expect.1">5.1</a>, <a href="#rfc.xref.header.expect.2">6.5.14</a>, <a href="#rfc.iref.e.1"><b>10.11</b></a>, <a href="#rfc.xref.header.expect.3">11.3.2</a>, <a href="#rfc.xref.header.expect.4">C</a></li> 4953 4952 <li>Expect Values 4954 4953 <ul> 4955 <li>100-continue <a href="#rfc.iref.e.2"><b>1 1.11</b></a></li>4954 <li>100-continue <a href="#rfc.iref.e.2"><b>10.11</b></a></li> 4956 4955 </ul> 4957 4956 </li> … … 4959 4958 </li> 4960 4959 <li><a id="rfc.index.F" href="#rfc.index.F"><b>F</b></a><ul> 4961 <li>From header field <a href="#rfc.xref.header.from.1">5.5</a>, <a href="#rfc.iref.f.1"><b>1 1.12</b></a>, <a href="#rfc.xref.header.from.2">12.3.2</a></li>4960 <li>From header field <a href="#rfc.xref.header.from.1">5.5</a>, <a href="#rfc.iref.f.1"><b>10.12</b></a>, <a href="#rfc.xref.header.from.2">11.3.2</a></li> 4962 4961 </ul> 4963 4962 </li> 4964 4963 <li><a id="rfc.index.G" href="#rfc.index.G"><b>G</b></a><ul> 4965 <li>GET method <a href="#rfc.xref.GET.1">4.1</a>, <a href="#rfc.iref.g. 2"><b>4.3.1</b></a>, <a href="#rfc.xref.GET.2">12.1.3</a></li>4964 <li>GET method <a href="#rfc.xref.GET.1">4.1</a>, <a href="#rfc.iref.g.4"><b>4.3.1</b></a>, <a href="#rfc.xref.GET.2">11.1.3</a></li> 4966 4965 <li><tt>Grammar</tt> 4967 4966 <ul> 4968 <li><tt>Accept</tt> <a href="#rfc.iref.g.33"><b>1 1.1</b></a></li>4969 <li><tt>Accept-Charset</tt> <a href="#rfc.iref.g.37"><b>1 1.2</b></a></li>4970 <li><tt>Accept-Encoding</tt> <a href="#rfc.iref.g.38"><b>1 1.3</b></a></li>4971 <li><tt>accept-ext</tt> <a href="#rfc.iref.g.36"><b>1 1.1</b></a></li>4972 <li><tt>Accept-Language</tt> <a href="#rfc.iref.g.40"><b>1 1.4</b></a></li>4973 <li><tt>accept-params</tt> <a href="#rfc.iref.g.35"><b>1 1.1</b></a></li>4974 <li><tt>Allow</tt> <a href="#rfc.iref.g.42"><b>1 1.5</b></a></li>4975 <li><tt>asctime-date</tt> <a href="#rfc.iref.g. 18"><b>8.1</b></a></li>4976 <li><tt>attribute</tt> <a href="#rfc.iref.g. 28"><b>8.5</b></a></li>4977 <li><tt>charset</tt> <a href="#rfc.iref.g.2 1"><b>8.3</b></a></li>4978 <li><tt>codings</tt> <a href="#rfc.iref.g.39"><b>1 1.3</b></a></li>4979 <li><tt>content-coding</tt> <a href="#rfc.iref.g.2 2"><b>8.4</b></a></li>4980 <li><tt>Content-Encoding</tt> <a href="#rfc.iref.g.43"><b>1 1.6</b></a></li>4981 <li><tt>Content-Language</tt> <a href="#rfc.iref.g.44"><b>1 1.7</b></a></li>4982 <li><tt>Content-Location</tt> <a href="#rfc.iref.g.45"><b>1 1.8</b></a></li>4983 <li><tt>Content-Type</tt> <a href="#rfc.iref.g.46"><b>1 1.9</b></a></li>4984 <li><tt>Date</tt> <a href="#rfc.iref.g.47"><b>1 1.10</b></a></li>4985 <li><tt>date1</tt> <a href="#rfc.iref.g. 5"><b>8.1</b></a></li>4986 <li><tt>day</tt> <a href="#rfc.iref.g.1 2"><b>8.1</b></a></li>4987 <li><tt>day-name</tt> <a href="#rfc.iref.g.1 0"><b>8.1</b></a></li>4988 <li><tt>day-name-l</tt> <a href="#rfc.iref.g.1 1"><b>8.1</b></a></li>4989 <li><tt>delta-seconds</tt> <a href="#rfc.iref.g.58"><b>1 1.16</b></a></li>4990 <li><tt>Expect</tt> <a href="#rfc.iref.g.48"><b>1 1.11</b></a></li>4991 <li><tt>expect-name</tt> <a href="#rfc.iref.g.52"><b>1 1.11</b></a></li>4992 <li><tt>expect-param</tt> <a href="#rfc.iref.g.50"><b>1 1.11</b></a></li>4993 <li><tt>expect-value</tt> <a href="#rfc.iref.g.51"><b>1 1.11</b></a></li>4994 <li><tt>expectation</tt> <a href="#rfc.iref.g.49"><b>1 1.11</b></a></li>4995 <li><tt>From</tt> <a href="#rfc.iref.g.53"><b>1 1.12</b></a></li>4996 <li><tt>GMT</tt> <a href="#rfc.iref.g.1 5"><b>8.1</b></a></li>4997 <li><tt>hour</tt> <a href="#rfc.iref.g. 7"><b>8.1</b></a></li>4998 <li><tt>HTTP-date</tt> <a href="#rfc.iref.g. 3"><b>8.1</b></a></li>4999 <li><tt>language-range</tt> <a href="#rfc.iref.g.41"><b>1 1.4</b></a></li>5000 <li><tt>language-tag</tt> <a href="#rfc.iref.g.3 0"><b>8.6</b></a></li>5001 <li><tt>Location</tt> <a href="#rfc.iref.g.54"><b>1 1.13</b></a></li>5002 <li><tt>Max-Forwards</tt> <a href="#rfc.iref.g.55"><b>1 1.14</b></a></li>5003 <li><tt>media-range</tt> <a href="#rfc.iref.g.34"><b>1 1.1</b></a></li>5004 <li><tt>media-type</tt> <a href="#rfc.iref.g.2 4"><b>8.5</b></a></li>5005 <li><tt>method</tt> <a href="#rfc.iref.g. 1"><b>4.1</b></a></li>4967 <li><tt>Accept</tt> <a href="#rfc.iref.g.33"><b>10.1</b></a></li> 4968 <li><tt>Accept-Charset</tt> <a href="#rfc.iref.g.37"><b>10.2</b></a></li> 4969 <li><tt>Accept-Encoding</tt> <a href="#rfc.iref.g.38"><b>10.3</b></a></li> 4970 <li><tt>accept-ext</tt> <a href="#rfc.iref.g.36"><b>10.1</b></a></li> 4971 <li><tt>Accept-Language</tt> <a href="#rfc.iref.g.40"><b>10.4</b></a></li> 4972 <li><tt>accept-params</tt> <a href="#rfc.iref.g.35"><b>10.1</b></a></li> 4973 <li><tt>Allow</tt> <a href="#rfc.iref.g.42"><b>10.5</b></a></li> 4974 <li><tt>asctime-date</tt> <a href="#rfc.iref.g.20"><b>8.1</b></a></li> 4975 <li><tt>attribute</tt> <a href="#rfc.iref.g.30"><b>8.5</b></a></li> 4976 <li><tt>charset</tt> <a href="#rfc.iref.g.23"><b>8.3</b></a></li> 4977 <li><tt>codings</tt> <a href="#rfc.iref.g.39"><b>10.3</b></a></li> 4978 <li><tt>content-coding</tt> <a href="#rfc.iref.g.24"><b>8.4</b></a></li> 4979 <li><tt>Content-Encoding</tt> <a href="#rfc.iref.g.43"><b>10.6</b></a></li> 4980 <li><tt>Content-Language</tt> <a href="#rfc.iref.g.44"><b>10.7</b></a></li> 4981 <li><tt>Content-Location</tt> <a href="#rfc.iref.g.45"><b>10.8</b></a></li> 4982 <li><tt>Content-Type</tt> <a href="#rfc.iref.g.46"><b>10.9</b></a></li> 4983 <li><tt>Date</tt> <a href="#rfc.iref.g.47"><b>10.10</b></a></li> 4984 <li><tt>date1</tt> <a href="#rfc.iref.g.7"><b>8.1</b></a></li> 4985 <li><tt>day</tt> <a href="#rfc.iref.g.14"><b>8.1</b></a></li> 4986 <li><tt>day-name</tt> <a href="#rfc.iref.g.12"><b>8.1</b></a></li> 4987 <li><tt>day-name-l</tt> <a href="#rfc.iref.g.13"><b>8.1</b></a></li> 4988 <li><tt>delta-seconds</tt> <a href="#rfc.iref.g.58"><b>10.16</b></a></li> 4989 <li><tt>Expect</tt> <a href="#rfc.iref.g.48"><b>10.11</b></a></li> 4990 <li><tt>expect-name</tt> <a href="#rfc.iref.g.52"><b>10.11</b></a></li> 4991 <li><tt>expect-param</tt> <a href="#rfc.iref.g.50"><b>10.11</b></a></li> 4992 <li><tt>expect-value</tt> <a href="#rfc.iref.g.51"><b>10.11</b></a></li> 4993 <li><tt>expectation</tt> <a href="#rfc.iref.g.49"><b>10.11</b></a></li> 4994 <li><tt>From</tt> <a href="#rfc.iref.g.53"><b>10.12</b></a></li> 4995 <li><tt>GMT</tt> <a href="#rfc.iref.g.17"><b>8.1</b></a></li> 4996 <li><tt>hour</tt> <a href="#rfc.iref.g.9"><b>8.1</b></a></li> 4997 <li><tt>HTTP-date</tt> <a href="#rfc.iref.g.5"><b>8.1</b></a></li> 4998 <li><tt>language-range</tt> <a href="#rfc.iref.g.41"><b>10.4</b></a></li> 4999 <li><tt>language-tag</tt> <a href="#rfc.iref.g.32"><b>8.6</b></a></li> 5000 <li><tt>Location</tt> <a href="#rfc.iref.g.54"><b>10.13</b></a></li> 5001 <li><tt>Max-Forwards</tt> <a href="#rfc.iref.g.55"><b>10.14</b></a></li> 5002 <li><tt>media-range</tt> <a href="#rfc.iref.g.34"><b>10.1</b></a></li> 5003 <li><tt>media-type</tt> <a href="#rfc.iref.g.26"><b>8.5</b></a></li> 5004 <li><tt>method</tt> <a href="#rfc.iref.g.3"><b>4.1</b></a></li> 5006 5005 <li><tt>MIME-Version</tt> <a href="#rfc.iref.g.61"><b>A.1</b></a></li> 5007 <li><tt>minute</tt> <a href="#rfc.iref.g. 8"><b>8.1</b></a></li>5008 <li><tt>month</tt> <a href="#rfc.iref.g.1 3"><b>8.1</b></a></li>5009 <li><tt>obs-date</tt> <a href="#rfc.iref.g.1 6"><b>8.1</b></a></li>5010 <li><tt>parameter</tt> <a href="#rfc.iref.g.2 7"><b>8.5</b></a></li>5011 <li><tt>product</tt> <a href="#rfc.iref.g. 19"><b>8.2</b></a></li>5012 <li><tt>product-version</tt> <a href="#rfc.iref.g.2 0"><b>8.2</b></a></li>5013 <li><tt>qvalue</tt> <a href="#rfc.iref.g. 32"><b>10.3</b></a></li>5014 <li><tt>Referer</tt> <a href="#rfc.iref.g.56"><b>1 1.15</b></a></li>5015 <li><tt>Retry-After</tt> <a href="#rfc.iref.g.57"><b>1 1.16</b></a></li>5016 <li><tt>rfc1123-date</tt> <a href="#rfc.iref.g. 4"><b>8.1</b></a></li>5017 <li><tt>rfc850-date</tt> <a href="#rfc.iref.g.1 7"><b>8.1</b></a></li>5018 <li><tt>second</tt> <a href="#rfc.iref.g. 9"><b>8.1</b></a></li>5019 <li><tt>Server</tt> <a href="#rfc.iref.g.59"><b>1 1.17</b></a></li>5020 <li><tt>subtype</tt> <a href="#rfc.iref.g.2 6"><b>8.5</b></a></li>5021 <li><tt>time-of-day</tt> <a href="#rfc.iref.g. 6"><b>8.1</b></a></li>5022 <li><tt>type</tt> <a href="#rfc.iref.g.2 5"><b>8.5</b></a></li>5023 <li><tt>User-Agent</tt> <a href="#rfc.iref.g.60"><b>1 1.18</b></a></li>5024 <li><tt>value</tt> <a href="#rfc.iref.g. 29"><b>8.5</b></a></li>5025 <li><tt>weight</tt> <a href="#rfc.iref.g. 31"><b>10.3</b></a></li>5026 <li><tt>year</tt> <a href="#rfc.iref.g.1 4"><b>8.1</b></a></li>5006 <li><tt>minute</tt> <a href="#rfc.iref.g.10"><b>8.1</b></a></li> 5007 <li><tt>month</tt> <a href="#rfc.iref.g.15"><b>8.1</b></a></li> 5008 <li><tt>obs-date</tt> <a href="#rfc.iref.g.18"><b>8.1</b></a></li> 5009 <li><tt>parameter</tt> <a href="#rfc.iref.g.29"><b>8.5</b></a></li> 5010 <li><tt>product</tt> <a href="#rfc.iref.g.21"><b>8.2</b></a></li> 5011 <li><tt>product-version</tt> <a href="#rfc.iref.g.22"><b>8.2</b></a></li> 5012 <li><tt>qvalue</tt> <a href="#rfc.iref.g.2"><b>3.4.3</b></a></li> 5013 <li><tt>Referer</tt> <a href="#rfc.iref.g.56"><b>10.15</b></a></li> 5014 <li><tt>Retry-After</tt> <a href="#rfc.iref.g.57"><b>10.16</b></a></li> 5015 <li><tt>rfc1123-date</tt> <a href="#rfc.iref.g.6"><b>8.1</b></a></li> 5016 <li><tt>rfc850-date</tt> <a href="#rfc.iref.g.19"><b>8.1</b></a></li> 5017 <li><tt>second</tt> <a href="#rfc.iref.g.11"><b>8.1</b></a></li> 5018 <li><tt>Server</tt> <a href="#rfc.iref.g.59"><b>10.17</b></a></li> 5019 <li><tt>subtype</tt> <a href="#rfc.iref.g.28"><b>8.5</b></a></li> 5020 <li><tt>time-of-day</tt> <a href="#rfc.iref.g.8"><b>8.1</b></a></li> 5021 <li><tt>type</tt> <a href="#rfc.iref.g.27"><b>8.5</b></a></li> 5022 <li><tt>User-Agent</tt> <a href="#rfc.iref.g.60"><b>10.18</b></a></li> 5023 <li><tt>value</tt> <a href="#rfc.iref.g.31"><b>8.5</b></a></li> 5024 <li><tt>weight</tt> <a href="#rfc.iref.g.1"><b>3.4.3</b></a></li> 5025 <li><tt>year</tt> <a href="#rfc.iref.g.16"><b>8.1</b></a></li> 5027 5026 </ul> 5028 5027 </li> 5029 <li>gzip (Coding Format) <a href="#rfc.iref.g.2 3">8.4</a></li>5028 <li>gzip (Coding Format) <a href="#rfc.iref.g.25">8.4</a></li> 5030 5029 </ul> 5031 5030 </li> 5032 5031 <li><a id="rfc.index.H" href="#rfc.index.H"><b>H</b></a><ul> 5033 <li>HEAD method <a href="#rfc.xref.HEAD.1">4.1</a>, <a href="#rfc.iref.h.1"><b>4.3.2</b></a>, <a href="#rfc.xref.HEAD.2">1 2.1.3</a></li>5032 <li>HEAD method <a href="#rfc.xref.HEAD.1">4.1</a>, <a href="#rfc.iref.h.1"><b>4.3.2</b></a>, <a href="#rfc.xref.HEAD.2">11.1.3</a></li> 5034 5033 <li>Header Fields 5035 5034 <ul> 5036 <li>Accept <a href="#rfc.xref.header.accept.1"> 5.3</a>, <a href="#rfc.xref.header.accept.2">8.5</a>, <a href="#rfc.xref.header.accept.3">10.1</a>, <a href="#rfc.iref.h.2"><b>11.1</b></a>, <a href="#rfc.xref.header.accept.4">12.3.2</a></li>5037 <li>Accept-Charset <a href="#rfc.xref.header.accept-charset.1"> 5.3</a>, <a href="#rfc.xref.header.accept-charset.2">10.1</a>, <a href="#rfc.iref.h.3"><b>11.2</b></a>, <a href="#rfc.xref.header.accept-charset.3">12.3.2</a>, <a href="#rfc.xref.header.accept-charset.4">C</a></li>5038 <li>Accept-Encoding <a href="#rfc.xref.header.accept-encoding.1"> 5.3</a>, <a href="#rfc.xref.header.accept-encoding.2">8.4</a>, <a href="#rfc.xref.header.accept-encoding.3">10.1</a>, <a href="#rfc.iref.h.4"><b>11.3</b></a>, <a href="#rfc.xref.header.accept-encoding.4">12.3.2</a>, <a href="#rfc.xref.header.accept-encoding.5">12.4.2</a></li>5039 <li>Accept-Language <a href="#rfc.xref.header.accept-language.1"> 5.3</a>, <a href="#rfc.xref.header.accept-language.2">10.1</a>, <a href="#rfc.iref.h.5"><b>11.4</b></a>, <a href="#rfc.xref.header.accept-language.3">12.3.2</a></li>5040 <li>Allow <a href="#rfc.xref.header.allow.1">4.1</a>, <a href="#rfc.xref.header.allow.2">7</a>, <a href="#rfc.iref.h.6"><b>1 1.5</b></a>, <a href="#rfc.xref.header.allow.3">12.3.2</a>, <a href="#rfc.xref.header.allow.4">C</a></li>5041 <li>Content-Encoding <a href="#rfc.xref.header.content-encoding.1">3.2</a>, <a href="#rfc.xref.header.content-encoding.2">8.4</a>, <a href="#rfc.iref.h.7"><b>1 1.6</b></a>, <a href="#rfc.xref.header.content-encoding.3">12.3.2</a></li>5042 <li>Content-Language <a href="#rfc.xref.header.content-language.1">3.2</a>, <a href="#rfc.iref.h.8"><b>1 1.7</b></a>, <a href="#rfc.xref.header.content-language.2">12.3.2</a></li>5043 <li>Content-Location <a href="#rfc.xref.header.content-location.1">3.2</a>, <a href="#rfc.xref.header.content-location.2">4.3.3</a>, <a href="#rfc.iref.h.9"><b>1 1.8</b></a>, <a href="#rfc.xref.header.content-location.3">11.13</a>, <a href="#rfc.xref.header.content-location.4">12.3.2</a>, <a href="#rfc.xref.header.content-location.5">C</a></li>5035 <li>Accept <a href="#rfc.xref.header.accept.1">3.4.1</a>, <a href="#rfc.xref.header.accept.2">5.3</a>, <a href="#rfc.xref.header.accept.3">8.5</a>, <a href="#rfc.iref.h.2"><b>10.1</b></a>, <a href="#rfc.xref.header.accept.4">11.3.2</a></li> 5036 <li>Accept-Charset <a href="#rfc.xref.header.accept-charset.1">3.4.1</a>, <a href="#rfc.xref.header.accept-charset.2">5.3</a>, <a href="#rfc.iref.h.3"><b>10.2</b></a>, <a href="#rfc.xref.header.accept-charset.3">11.3.2</a>, <a href="#rfc.xref.header.accept-charset.4">C</a></li> 5037 <li>Accept-Encoding <a href="#rfc.xref.header.accept-encoding.1">3.4.1</a>, <a href="#rfc.xref.header.accept-encoding.2">5.3</a>, <a href="#rfc.xref.header.accept-encoding.3">8.4</a>, <a href="#rfc.iref.h.4"><b>10.3</b></a>, <a href="#rfc.xref.header.accept-encoding.4">11.3.2</a>, <a href="#rfc.xref.header.accept-encoding.5">11.4.2</a></li> 5038 <li>Accept-Language <a href="#rfc.xref.header.accept-language.1">3.4.1</a>, <a href="#rfc.xref.header.accept-language.2">5.3</a>, <a href="#rfc.iref.h.5"><b>10.4</b></a>, <a href="#rfc.xref.header.accept-language.3">11.3.2</a></li> 5039 <li>Allow <a href="#rfc.xref.header.allow.1">4.1</a>, <a href="#rfc.xref.header.allow.2">7</a>, <a href="#rfc.iref.h.6"><b>10.5</b></a>, <a href="#rfc.xref.header.allow.3">11.3.2</a>, <a href="#rfc.xref.header.allow.4">C</a></li> 5040 <li>Content-Encoding <a href="#rfc.xref.header.content-encoding.1">3.2</a>, <a href="#rfc.xref.header.content-encoding.2">8.4</a>, <a href="#rfc.iref.h.7"><b>10.6</b></a>, <a href="#rfc.xref.header.content-encoding.3">11.3.2</a></li> 5041 <li>Content-Language <a href="#rfc.xref.header.content-language.1">3.2</a>, <a href="#rfc.iref.h.8"><b>10.7</b></a>, <a href="#rfc.xref.header.content-language.2">11.3.2</a></li> 5042 <li>Content-Location <a href="#rfc.xref.header.content-location.1">3.2</a>, <a href="#rfc.xref.header.content-location.2">4.3.3</a>, <a href="#rfc.iref.h.9"><b>10.8</b></a>, <a href="#rfc.xref.header.content-location.3">10.13</a>, <a href="#rfc.xref.header.content-location.4">11.3.2</a>, <a href="#rfc.xref.header.content-location.5">C</a></li> 5044 5043 <li>Content-Transfer-Encoding <a href="#rfc.iref.h.21">A.5</a>, <a href="#rfc.xref.no.content-transfer-encoding.1">C</a></li> 5045 <li>Content-Type <a href="#rfc.xref.header.content-type.1">3.2</a>, <a href="#rfc.xref.header.content-type.2">6</a>, <a href="#rfc.xref.header.content-type.3">8.5</a>, <a href="#rfc.iref.h.10"><b>1 1.9</b></a>, <a href="#rfc.xref.header.content-type.4">12.3.1</a>, <a href="#rfc.xref.header.content-type.5">12.3.2</a></li>5046 <li>Date <a href="#rfc.xref.header.date.1">7</a>, <a href="#rfc.iref.h.11"><b>1 1.10</b></a>, <a href="#rfc.xref.header.date.2">12.3.2</a></li>5047 <li>Expect <a href="#rfc.xref.header.expect.1">5.1</a>, <a href="#rfc.xref.header.expect.2">6.5.14</a>, <a href="#rfc.iref.h.12"><b>1 1.11</b></a>, <a href="#rfc.xref.header.expect.3">12.3.2</a>, <a href="#rfc.xref.header.expect.4">C</a></li>5048 <li>From <a href="#rfc.xref.header.from.1">5.5</a>, <a href="#rfc.iref.h.13"><b>1 1.12</b></a>, <a href="#rfc.xref.header.from.2">12.3.2</a></li>5049 <li>Location <a href="#rfc.xref.header.location.1">4.3.3</a>, <a href="#rfc.xref.header.location.2">6.4</a>, <a href="#rfc.xref.header.location.3">7</a>, <a href="#rfc.iref.h.14"><b>1 1.13</b></a>, <a href="#rfc.xref.header.location.4">12.3.2</a>, <a href="#rfc.xref.header.location.5">C</a></li>5050 <li>Max-Forwards <a href="#rfc.xref.header.max-forwards.1">4.3.7</a>, <a href="#rfc.xref.header.max-forwards.2">4.3.8</a>, <a href="#rfc.xref.header.max-forwards.3">5.1</a>, <a href="#rfc.iref.h.15"><b>1 1.14</b></a>, <a href="#rfc.xref.header.max-forwards.4">12.3.2</a>, <a href="#rfc.xref.header.max-forwards.5">C</a></li>5051 <li>MIME-Version <a href="#rfc.xref.mime-version.1">1 2.3.2</a>, <a href="#rfc.iref.h.20"><b>A.1</b></a></li>5052 <li>Referer <a href="#rfc.xref.header.referer.1">5.5</a>, <a href="#rfc.iref.h.16"><b>1 1.15</b></a>, <a href="#rfc.xref.header.referer.2">12.3.2</a>, <a href="#rfc.xref.header.referer.3">C</a></li>5053 <li>Retry-After <a href="#rfc.xref.header.retry-after.1">6.6.4</a>, <a href="#rfc.xref.header.retry-after.2">7</a>, <a href="#rfc.iref.h.17"><b>1 1.16</b></a>, <a href="#rfc.xref.header.retry-after.3">12.3.2</a></li>5054 <li>Server <a href="#rfc.xref.header.server.1">7</a>, <a href="#rfc.iref.h.18"><b>1 1.17</b></a>, <a href="#rfc.xref.header.server.2">12.3.2</a>, <a href="#rfc.xref.header.server.3">13.1</a>, <a href="#rfc.xref.header.server.4">C</a></li>5055 <li>User-Agent <a href="#rfc.xref.header.user-agent.1"> 5.5</a>, <a href="#rfc.xref.header.user-agent.2">10.1</a>, <a href="#rfc.iref.h.19"><b>11.18</b></a>, <a href="#rfc.xref.header.user-agent.3">12.3.2</a>, <a href="#rfc.xref.header.user-agent.4">13.1</a></li>5044 <li>Content-Type <a href="#rfc.xref.header.content-type.1">3.2</a>, <a href="#rfc.xref.header.content-type.2">6</a>, <a href="#rfc.xref.header.content-type.3">8.5</a>, <a href="#rfc.iref.h.10"><b>10.9</b></a>, <a href="#rfc.xref.header.content-type.4">11.3.1</a>, <a href="#rfc.xref.header.content-type.5">11.3.2</a></li> 5045 <li>Date <a href="#rfc.xref.header.date.1">7</a>, <a href="#rfc.iref.h.11"><b>10.10</b></a>, <a href="#rfc.xref.header.date.2">11.3.2</a></li> 5046 <li>Expect <a href="#rfc.xref.header.expect.1">5.1</a>, <a href="#rfc.xref.header.expect.2">6.5.14</a>, <a href="#rfc.iref.h.12"><b>10.11</b></a>, <a href="#rfc.xref.header.expect.3">11.3.2</a>, <a href="#rfc.xref.header.expect.4">C</a></li> 5047 <li>From <a href="#rfc.xref.header.from.1">5.5</a>, <a href="#rfc.iref.h.13"><b>10.12</b></a>, <a href="#rfc.xref.header.from.2">11.3.2</a></li> 5048 <li>Location <a href="#rfc.xref.header.location.1">4.3.3</a>, <a href="#rfc.xref.header.location.2">6.4</a>, <a href="#rfc.xref.header.location.3">7</a>, <a href="#rfc.iref.h.14"><b>10.13</b></a>, <a href="#rfc.xref.header.location.4">11.3.2</a>, <a href="#rfc.xref.header.location.5">C</a></li> 5049 <li>Max-Forwards <a href="#rfc.xref.header.max-forwards.1">4.3.7</a>, <a href="#rfc.xref.header.max-forwards.2">4.3.8</a>, <a href="#rfc.xref.header.max-forwards.3">5.1</a>, <a href="#rfc.iref.h.15"><b>10.14</b></a>, <a href="#rfc.xref.header.max-forwards.4">11.3.2</a>, <a href="#rfc.xref.header.max-forwards.5">C</a></li> 5050 <li>MIME-Version <a href="#rfc.xref.mime-version.1">11.3.2</a>, <a href="#rfc.iref.h.20"><b>A.1</b></a></li> 5051 <li>Referer <a href="#rfc.xref.header.referer.1">5.5</a>, <a href="#rfc.iref.h.16"><b>10.15</b></a>, <a href="#rfc.xref.header.referer.2">11.3.2</a>, <a href="#rfc.xref.header.referer.3">C</a></li> 5052 <li>Retry-After <a href="#rfc.xref.header.retry-after.1">6.6.4</a>, <a href="#rfc.xref.header.retry-after.2">7</a>, <a href="#rfc.iref.h.17"><b>10.16</b></a>, <a href="#rfc.xref.header.retry-after.3">11.3.2</a></li> 5053 <li>Server <a href="#rfc.xref.header.server.1">7</a>, <a href="#rfc.iref.h.18"><b>10.17</b></a>, <a href="#rfc.xref.header.server.2">11.3.2</a>, <a href="#rfc.xref.header.server.3">12.1</a>, <a href="#rfc.xref.header.server.4">C</a></li> 5054 <li>User-Agent <a href="#rfc.xref.header.user-agent.1">3.4.1</a>, <a href="#rfc.xref.header.user-agent.2">5.5</a>, <a href="#rfc.iref.h.19"><b>10.18</b></a>, <a href="#rfc.xref.header.user-agent.3">11.3.2</a>, <a href="#rfc.xref.header.user-agent.4">12.1</a></li> 5056 5055 </ul> 5057 5056 </li> … … 5063 5062 </li> 5064 5063 <li><a id="rfc.index.L" href="#rfc.index.L"><b>L</b></a><ul> 5065 <li>Location header field <a href="#rfc.xref.header.location.1">4.3.3</a>, <a href="#rfc.xref.header.location.2">6.4</a>, <a href="#rfc.xref.header.location.3">7</a>, <a href="#rfc.iref.l.1"><b>1 1.13</b></a>, <a href="#rfc.xref.header.location.4">12.3.2</a>, <a href="#rfc.xref.header.location.5">C</a></li>5064 <li>Location header field <a href="#rfc.xref.header.location.1">4.3.3</a>, <a href="#rfc.xref.header.location.2">6.4</a>, <a href="#rfc.xref.header.location.3">7</a>, <a href="#rfc.iref.l.1"><b>10.13</b></a>, <a href="#rfc.xref.header.location.4">11.3.2</a>, <a href="#rfc.xref.header.location.5">C</a></li> 5066 5065 </ul> 5067 5066 </li> 5068 5067 <li><a id="rfc.index.M" href="#rfc.index.M"><b>M</b></a><ul> 5069 <li>Max-Forwards header field <a href="#rfc.xref.header.max-forwards.1">4.3.7</a>, <a href="#rfc.xref.header.max-forwards.2">4.3.8</a>, <a href="#rfc.xref.header.max-forwards.3">5.1</a>, <a href="#rfc.iref.m.9"><b>1 1.14</b></a>, <a href="#rfc.xref.header.max-forwards.4">12.3.2</a>, <a href="#rfc.xref.header.max-forwards.5">C</a></li>5068 <li>Max-Forwards header field <a href="#rfc.xref.header.max-forwards.1">4.3.7</a>, <a href="#rfc.xref.header.max-forwards.2">4.3.8</a>, <a href="#rfc.xref.header.max-forwards.3">5.1</a>, <a href="#rfc.iref.m.9"><b>10.14</b></a>, <a href="#rfc.xref.header.max-forwards.4">11.3.2</a>, <a href="#rfc.xref.header.max-forwards.5">C</a></li> 5070 5069 <li>Methods 5071 5070 <ul> 5072 <li>CONNECT <a href="#rfc.xref.CONNECT.1">4.1</a>, <a href="#rfc.iref.m.6"><b>4.3.6</b></a>, <a href="#rfc.xref.CONNECT.2">1 2.1.3</a>, <a href="#rfc.xref.CONNECT.3">C</a></li>5073 <li>DELETE <a href="#rfc.xref.DELETE.1">4.1</a>, <a href="#rfc.iref.m.5"><b>4.3.5</b></a>, <a href="#rfc.xref.DELETE.2">1 2.1.3</a></li>5074 <li>GET <a href="#rfc.xref.GET.1">4.1</a>, <a href="#rfc.iref.m.1"><b>4.3.1</b></a>, <a href="#rfc.xref.GET.2">1 2.1.3</a></li>5075 <li>HEAD <a href="#rfc.xref.HEAD.1">4.1</a>, <a href="#rfc.iref.m.2"><b>4.3.2</b></a>, <a href="#rfc.xref.HEAD.2">1 2.1.3</a></li>5076 <li>OPTIONS <a href="#rfc.xref.OPTIONS.1">4.1</a>, <a href="#rfc.iref.m.7"><b>4.3.7</b></a>, <a href="#rfc.xref.OPTIONS.2">1 1.14</a>, <a href="#rfc.xref.OPTIONS.3">12.1.3</a></li>5077 <li>POST <a href="#rfc.xref.POST.1">4.1</a>, <a href="#rfc.iref.m.3"><b>4.3.3</b></a>, <a href="#rfc.xref.POST.2">1 2.1.3</a>, <a href="#rfc.xref.POST.3">C</a></li>5078 <li>PUT <a href="#rfc.xref.PUT.1">4.1</a>, <a href="#rfc.iref.m.4"><b>4.3.4</b></a>, <a href="#rfc.xref.PUT.2">1 2.1.3</a>, <a href="#rfc.xref.PUT.3">C</a></li>5079 <li>TRACE <a href="#rfc.xref.TRACE.1">4.1</a>, <a href="#rfc.iref.m.8"><b>4.3.8</b></a>, <a href="#rfc.xref.TRACE.2">1 1.14</a>, <a href="#rfc.xref.TRACE.3">12.1.3</a>, <a href="#rfc.xref.TRACE.4">13.1</a></li>5071 <li>CONNECT <a href="#rfc.xref.CONNECT.1">4.1</a>, <a href="#rfc.iref.m.6"><b>4.3.6</b></a>, <a href="#rfc.xref.CONNECT.2">11.1.3</a>, <a href="#rfc.xref.CONNECT.3">C</a></li> 5072 <li>DELETE <a href="#rfc.xref.DELETE.1">4.1</a>, <a href="#rfc.iref.m.5"><b>4.3.5</b></a>, <a href="#rfc.xref.DELETE.2">11.1.3</a></li> 5073 <li>GET <a href="#rfc.xref.GET.1">4.1</a>, <a href="#rfc.iref.m.1"><b>4.3.1</b></a>, <a href="#rfc.xref.GET.2">11.1.3</a></li> 5074 <li>HEAD <a href="#rfc.xref.HEAD.1">4.1</a>, <a href="#rfc.iref.m.2"><b>4.3.2</b></a>, <a href="#rfc.xref.HEAD.2">11.1.3</a></li> 5075 <li>OPTIONS <a href="#rfc.xref.OPTIONS.1">4.1</a>, <a href="#rfc.iref.m.7"><b>4.3.7</b></a>, <a href="#rfc.xref.OPTIONS.2">10.14</a>, <a href="#rfc.xref.OPTIONS.3">11.1.3</a></li> 5076 <li>POST <a href="#rfc.xref.POST.1">4.1</a>, <a href="#rfc.iref.m.3"><b>4.3.3</b></a>, <a href="#rfc.xref.POST.2">11.1.3</a>, <a href="#rfc.xref.POST.3">C</a></li> 5077 <li>PUT <a href="#rfc.xref.PUT.1">4.1</a>, <a href="#rfc.iref.m.4"><b>4.3.4</b></a>, <a href="#rfc.xref.PUT.2">11.1.3</a>, <a href="#rfc.xref.PUT.3">C</a></li> 5078 <li>TRACE <a href="#rfc.xref.TRACE.1">4.1</a>, <a href="#rfc.iref.m.8"><b>4.3.8</b></a>, <a href="#rfc.xref.TRACE.2">10.14</a>, <a href="#rfc.xref.TRACE.3">11.1.3</a>, <a href="#rfc.xref.TRACE.4">12.1</a></li> 5080 5079 </ul> 5081 5080 </li> 5082 <li>MIME-Version header field <a href="#rfc.xref.mime-version.1">1 2.3.2</a>, <a href="#rfc.iref.m.10"><b>A.1</b></a></li>5081 <li>MIME-Version header field <a href="#rfc.xref.mime-version.1">11.3.2</a>, <a href="#rfc.iref.m.10"><b>A.1</b></a></li> 5083 5082 </ul> 5084 5083 </li> 5085 5084 <li><a id="rfc.index.O" href="#rfc.index.O"><b>O</b></a><ul> 5086 <li>OPTIONS method <a href="#rfc.xref.OPTIONS.1">4.1</a>, <a href="#rfc.iref.o.1"><b>4.3.7</b></a>, <a href="#rfc.xref.OPTIONS.2">1 1.14</a>, <a href="#rfc.xref.OPTIONS.3">12.1.3</a></li>5085 <li>OPTIONS method <a href="#rfc.xref.OPTIONS.1">4.1</a>, <a href="#rfc.iref.o.1"><b>4.3.7</b></a>, <a href="#rfc.xref.OPTIONS.2">10.14</a>, <a href="#rfc.xref.OPTIONS.3">11.1.3</a></li> 5087 5086 </ul> 5088 5087 </li> 5089 5088 <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul> 5090 <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1</a>, <a href="#rfc.xref.Part1.2">1.1</a>, <a href="#rfc.xref.Part1.3">1.2</a>, <a href="#rfc.xref.Part1.4">2</a>, <a href="#rfc.xref.Part1.5">2</a>, <a href="#rfc.xref.Part1.6">2</a>, <a href="#rfc.xref.Part1.7">3</a>, <a href="#rfc.xref.Part1.8">3.1</a>, <a href="#rfc.xref.Part1.9">4.3.6</a>, <a href="#rfc.xref.Part1.10">4.3.7</a>, <a href="#rfc.xref.Part1.11">4.3.8</a>, <a href="#rfc.xref.Part1.12">4.3.8</a>, <a href="#rfc.xref.Part1.13">5.1</a>, <a href="#rfc.xref.Part1.14">5.5</a>, <a href="#rfc.xref.Part1.15">6.2.1</a>, <a href="#rfc.xref.Part1.16">6.2.2</a>, <a href="#rfc.xref.Part1.17">6.3.4</a>, <a href="#rfc.xref.Part1.18">6.3.6</a>, <a href="#rfc.xref.Part1.19">6.5.15</a>, <a href="#rfc.xref.Part1.20">6.6.6</a>, <a href="#rfc.xref.Part1.21">7</a>, <a href="#rfc.xref.Part1.22">8.4</a>, <a href="#rfc.xref.Part1.23">8.4</a>, <a href="#rfc.xref.Part1.24">8.4</a>, <a href="#rfc.xref.Part1.25">9.1</a>, <a href="#rfc.xref.Part1.26">9.2</a>, <a href="#rfc.xref.Part1.27">1 1.8</a>, <a href="#rfc.xref.Part1.28">11.11</a>, <a href="#rfc.xref.Part1.29">11.17</a>, <a href="#rfc.xref.Part1.30">11.17</a>, <a href="#rfc.xref.Part1.31">11.18</a>, <a href="#rfc.xref.Part1.32">12.1.2</a>, <a href="#rfc.xref.Part1.33">12.3.1</a>, <a href="#rfc.xref.Part1.34">12.3.1</a>, <a href="#rfc.xref.Part1.35">12.3.1</a>, <a href="#rfc.xref.Part1.36">12.3.1</a>, <a href="#rfc.xref.Part1.37">12.3.1</a>, <a href="#rfc.xref.Part1.38">12.3.1</a>, <a href="#rfc.xref.Part1.39">12.4</a>, <a href="#rfc.xref.Part1.40">12.4.1</a>, <a href="#rfc.xref.Part1.41">12.4.1</a>, <a href="#rfc.xref.Part1.42">12.4.2</a>, <a href="#rfc.xref.Part1.43">12.4.2</a>, <a href="#rfc.xref.Part1.44">12.4.2</a>, <a href="#rfc.xref.Part1.45">14</a>, <a href="#Part1"><b>15.1</b></a>, <a href="#rfc.xref.Part1.46">C</a>, <a href="#rfc.xref.Part1.47">D</a>, <a href="#rfc.xref.Part1.48">D</a>, <a href="#rfc.xref.Part1.49">D</a>, <a href="#rfc.xref.Part1.50">D</a>, <a href="#rfc.xref.Part1.51">D</a>, <a href="#rfc.xref.Part1.52">D</a>, <a href="#rfc.xref.Part1.53">D</a>, <a href="#rfc.xref.Part1.54">D</a>, <a href="#rfc.xref.Part1.55">D</a>, <a href="#rfc.xref.Part1.56">D</a>, <a href="#rfc.xref.Part1.57">D</a><ul>5089 <li><em>Part1</em> <a href="#rfc.xref.Part1.1">1</a>, <a href="#rfc.xref.Part1.2">1.1</a>, <a href="#rfc.xref.Part1.3">1.2</a>, <a href="#rfc.xref.Part1.4">2</a>, <a href="#rfc.xref.Part1.5">2</a>, <a href="#rfc.xref.Part1.6">2</a>, <a href="#rfc.xref.Part1.7">3</a>, <a href="#rfc.xref.Part1.8">3.1</a>, <a href="#rfc.xref.Part1.9">4.3.6</a>, <a href="#rfc.xref.Part1.10">4.3.7</a>, <a href="#rfc.xref.Part1.11">4.3.8</a>, <a href="#rfc.xref.Part1.12">4.3.8</a>, <a href="#rfc.xref.Part1.13">5.1</a>, <a href="#rfc.xref.Part1.14">5.5</a>, <a href="#rfc.xref.Part1.15">6.2.1</a>, <a href="#rfc.xref.Part1.16">6.2.2</a>, <a href="#rfc.xref.Part1.17">6.3.4</a>, <a href="#rfc.xref.Part1.18">6.3.6</a>, <a href="#rfc.xref.Part1.19">6.5.15</a>, <a href="#rfc.xref.Part1.20">6.6.6</a>, <a href="#rfc.xref.Part1.21">7</a>, <a href="#rfc.xref.Part1.22">8.4</a>, <a href="#rfc.xref.Part1.23">8.4</a>, <a href="#rfc.xref.Part1.24">8.4</a>, <a href="#rfc.xref.Part1.25">9.1</a>, <a href="#rfc.xref.Part1.26">9.2</a>, <a href="#rfc.xref.Part1.27">10.8</a>, <a href="#rfc.xref.Part1.28">10.11</a>, <a href="#rfc.xref.Part1.29">10.17</a>, <a href="#rfc.xref.Part1.30">10.17</a>, <a href="#rfc.xref.Part1.31">10.18</a>, <a href="#rfc.xref.Part1.32">11.1.2</a>, <a href="#rfc.xref.Part1.33">11.3.1</a>, <a href="#rfc.xref.Part1.34">11.3.1</a>, <a href="#rfc.xref.Part1.35">11.3.1</a>, <a href="#rfc.xref.Part1.36">11.3.1</a>, <a href="#rfc.xref.Part1.37">11.3.1</a>, <a href="#rfc.xref.Part1.38">11.3.1</a>, <a href="#rfc.xref.Part1.39">11.4</a>, <a href="#rfc.xref.Part1.40">11.4.1</a>, <a href="#rfc.xref.Part1.41">11.4.1</a>, <a href="#rfc.xref.Part1.42">11.4.2</a>, <a href="#rfc.xref.Part1.43">11.4.2</a>, <a href="#rfc.xref.Part1.44">11.4.2</a>, <a href="#rfc.xref.Part1.45">13</a>, <a href="#Part1"><b>14.1</b></a>, <a href="#rfc.xref.Part1.46">C</a>, <a href="#rfc.xref.Part1.47">D</a>, <a href="#rfc.xref.Part1.48">D</a>, <a href="#rfc.xref.Part1.49">D</a>, <a href="#rfc.xref.Part1.50">D</a>, <a href="#rfc.xref.Part1.51">D</a>, <a href="#rfc.xref.Part1.52">D</a>, <a href="#rfc.xref.Part1.53">D</a>, <a href="#rfc.xref.Part1.54">D</a>, <a href="#rfc.xref.Part1.55">D</a>, <a href="#rfc.xref.Part1.56">D</a>, <a href="#rfc.xref.Part1.57">D</a><ul> 5091 5090 <li><em>Section 1.2</em> <a href="#rfc.xref.Part1.3">1.2</a></li> 5092 5091 <li><em>Section 2.3</em> <a href="#rfc.xref.Part1.17">6.3.4</a></li> … … 5094 5093 <li><em>Section 2.6</em> <a href="#rfc.xref.Part1.20">6.6.6</a></li> 5095 5094 <li><em>Section 2.7</em> <a href="#rfc.xref.Part1.4">2</a>, <a href="#rfc.xref.Part1.54">D</a>, <a href="#rfc.xref.Part1.56">D</a>, <a href="#rfc.xref.Part1.57">D</a></li> 5096 <li><em>Section 3.2</em> <a href="#rfc.xref.Part1.29">1 1.17</a>, <a href="#rfc.xref.Part1.31">11.18</a>, <a href="#rfc.xref.Part1.33">12.3.1</a>, <a href="#rfc.xref.Part1.36">12.3.1</a></li>5095 <li><em>Section 3.2</em> <a href="#rfc.xref.Part1.29">10.17</a>, <a href="#rfc.xref.Part1.31">10.18</a>, <a href="#rfc.xref.Part1.33">11.3.1</a>, <a href="#rfc.xref.Part1.36">11.3.1</a></li> 5097 5096 <li><em>Section 3.2.1</em> <a href="#rfc.xref.Part1.48">D</a>, <a href="#rfc.xref.Part1.49">D</a>, <a href="#rfc.xref.Part1.50">D</a></li> 5098 <li><em>Section 3.2.4</em> <a href="#rfc.xref.Part1.35">1 2.3.1</a>, <a href="#rfc.xref.Part1.51">D</a>, <a href="#rfc.xref.Part1.52">D</a>, <a href="#rfc.xref.Part1.53">D</a>, <a href="#rfc.xref.Part1.55">D</a></li>5099 <li><em>Section 3.3</em> <a href="#rfc.xref.Part1.7">3</a>, <a href="#rfc.xref.Part1.18">6.3.6</a>, <a href="#rfc.xref.Part1.26">9.2</a>, <a href="#rfc.xref.Part1.32">1 2.1.2</a></li>5097 <li><em>Section 3.2.4</em> <a href="#rfc.xref.Part1.35">11.3.1</a>, <a href="#rfc.xref.Part1.51">D</a>, <a href="#rfc.xref.Part1.52">D</a>, <a href="#rfc.xref.Part1.53">D</a>, <a href="#rfc.xref.Part1.55">D</a></li> 5098 <li><em>Section 3.3</em> <a href="#rfc.xref.Part1.7">3</a>, <a href="#rfc.xref.Part1.18">6.3.6</a>, <a href="#rfc.xref.Part1.26">9.2</a>, <a href="#rfc.xref.Part1.32">11.1.2</a></li> 5100 5099 <li><em>Section 3.3.2</em> <a href="#rfc.xref.Part1.25">9.1</a></li> 5101 <li><em>Section 4</em> <a href="#rfc.xref.Part1.40">1 2.4.1</a></li>5102 <li><em>Section 4.1</em> <a href="#rfc.xref.Part1.38">1 2.3.1</a></li>5103 <li><em>Section 4.2.1</em> <a href="#rfc.xref.Part1.22">8.4</a>, <a href="#rfc.xref.Part1.42">1 2.4.2</a></li>5104 <li><em>Section 4.2</em> <a href="#rfc.xref.Part1.39">1 2.4</a>, <a href="#rfc.xref.Part1.41">12.4.1</a></li>5105 <li><em>Section 4.2.2</em> <a href="#rfc.xref.Part1.23">8.4</a>, <a href="#rfc.xref.Part1.43">1 2.4.2</a></li>5106 <li><em>Section 4.2.3</em> <a href="#rfc.xref.Part1.24">8.4</a>, <a href="#rfc.xref.Part1.44">1 2.4.2</a></li>5100 <li><em>Section 4</em> <a href="#rfc.xref.Part1.40">11.4.1</a></li> 5101 <li><em>Section 4.1</em> <a href="#rfc.xref.Part1.38">11.3.1</a></li> 5102 <li><em>Section 4.2.1</em> <a href="#rfc.xref.Part1.22">8.4</a>, <a href="#rfc.xref.Part1.42">11.4.2</a></li> 5103 <li><em>Section 4.2</em> <a href="#rfc.xref.Part1.39">11.4</a>, <a href="#rfc.xref.Part1.41">11.4.1</a></li> 5104 <li><em>Section 4.2.2</em> <a href="#rfc.xref.Part1.23">8.4</a>, <a href="#rfc.xref.Part1.43">11.4.2</a></li> 5105 <li><em>Section 4.2.3</em> <a href="#rfc.xref.Part1.24">8.4</a>, <a href="#rfc.xref.Part1.44">11.4.2</a></li> 5107 5106 <li><em>Section 4.3</em> <a href="#rfc.xref.Part1.14">5.5</a></li> 5108 5107 <li><em>Section 5.3</em> <a href="#rfc.xref.Part1.5">2</a>, <a href="#rfc.xref.Part1.9">4.3.6</a>, <a href="#rfc.xref.Part1.10">4.3.7</a></li> 5109 5108 <li><em>Section 5.4</em> <a href="#rfc.xref.Part1.13">5.1</a></li> 5110 <li><em>Section 5.5</em> <a href="#rfc.xref.Part1.6">2</a>, <a href="#rfc.xref.Part1.8">3.1</a>, <a href="#rfc.xref.Part1.21">7</a>, <a href="#rfc.xref.Part1.27">1 1.8</a></li>5111 <li><em>Section 5.7</em> <a href="#rfc.xref.Part1.11">4.3.8</a>, <a href="#rfc.xref.Part1.30">1 1.17</a>, <a href="#rfc.xref.Part1.46">C</a></li>5112 <li><em>Section 6.1</em> <a href="#rfc.xref.Part1.37">1 2.3.1</a></li>5113 <li><em>Section 6.3</em> <a href="#rfc.xref.Part1.15">6.2.1</a>, <a href="#rfc.xref.Part1.28">1 1.11</a></li>5109 <li><em>Section 5.5</em> <a href="#rfc.xref.Part1.6">2</a>, <a href="#rfc.xref.Part1.8">3.1</a>, <a href="#rfc.xref.Part1.21">7</a>, <a href="#rfc.xref.Part1.27">10.8</a></li> 5110 <li><em>Section 5.7</em> <a href="#rfc.xref.Part1.11">4.3.8</a>, <a href="#rfc.xref.Part1.30">10.17</a>, <a href="#rfc.xref.Part1.46">C</a></li> 5111 <li><em>Section 6.1</em> <a href="#rfc.xref.Part1.37">11.3.1</a></li> 5112 <li><em>Section 6.3</em> <a href="#rfc.xref.Part1.15">6.2.1</a>, <a href="#rfc.xref.Part1.28">10.11</a></li> 5114 5113 <li><em>Section 6.4</em> <a href="#rfc.xref.Part1.16">6.2.2</a>, <a href="#rfc.xref.Part1.19">6.5.15</a></li> 5115 5114 <li><em>Section 7.3.1</em> <a href="#rfc.xref.Part1.12">4.3.8</a></li> 5116 <li><em>Section 9</em> <a href="#rfc.xref.Part1.45">1 4</a></li>5117 <li><em>Appendix B</em> <a href="#rfc.xref.Part1.34">1 2.3.1</a></li>5115 <li><em>Section 9</em> <a href="#rfc.xref.Part1.45">13</a></li> 5116 <li><em>Appendix B</em> <a href="#rfc.xref.Part1.34">11.3.1</a></li> 5118 5117 </ul> 5119 5118 </li> 5120 <li><em>Part4</em> <a href="#rfc.xref.Part4.1">3.2</a>, <a href="#rfc.xref.Part4.2">3.2</a>, <a href="#rfc.xref.Part4.3">4.3.1</a>, <a href="#rfc.xref.Part4.4">5.2</a>, <a href="#rfc.xref.Part4.5">5.2</a>, <a href="#rfc.xref.Part4.6">5.2</a>, <a href="#rfc.xref.Part4.7">5.2</a>, <a href="#rfc.xref.Part4.8">5.2</a>, <a href="#rfc.xref.Part4.9">6.1</a>, <a href="#rfc.xref.Part4.10">6.1</a>, <a href="#rfc.xref.Part4.11">6.1</a>, <a href="#rfc.xref.Part4.12">6.3.2</a>, <a href="#rfc.xref.Part4.13">6.4</a>, <a href="#rfc.xref.Part4.14">7</a>, <a href="#Part4"><b>1 5.1</b></a>, <a href="#rfc.xref.Part4.15">F.2</a><ul>5119 <li><em>Part4</em> <a href="#rfc.xref.Part4.1">3.2</a>, <a href="#rfc.xref.Part4.2">3.2</a>, <a href="#rfc.xref.Part4.3">4.3.1</a>, <a href="#rfc.xref.Part4.4">5.2</a>, <a href="#rfc.xref.Part4.5">5.2</a>, <a href="#rfc.xref.Part4.6">5.2</a>, <a href="#rfc.xref.Part4.7">5.2</a>, <a href="#rfc.xref.Part4.8">5.2</a>, <a href="#rfc.xref.Part4.9">6.1</a>, <a href="#rfc.xref.Part4.10">6.1</a>, <a href="#rfc.xref.Part4.11">6.1</a>, <a href="#rfc.xref.Part4.12">6.3.2</a>, <a href="#rfc.xref.Part4.13">6.4</a>, <a href="#rfc.xref.Part4.14">7</a>, <a href="#Part4"><b>14.1</b></a>, <a href="#rfc.xref.Part4.15">F.2</a><ul> 5121 5120 <li><em>Section 2.2</em> <a href="#rfc.xref.Part4.2">3.2</a></li> 5122 5121 <li><em>Section 2.3</em> <a href="#rfc.xref.Part4.1">3.2</a>, <a href="#rfc.xref.Part4.12">6.3.2</a>, <a href="#rfc.xref.Part4.14">7</a></li> … … 5130 5129 </ul> 5131 5130 </li> 5132 <li><em>Part5</em> <a href="#rfc.xref.Part5.1">4.3.1</a>, <a href="#rfc.xref.Part5.2">4.3.1</a>, <a href="#rfc.xref.Part5.3">4.3.4</a>, <a href="#rfc.xref.Part5.4">5.1</a>, <a href="#rfc.xref.Part5.5">5.2</a>, <a href="#rfc.xref.Part5.6">6.1</a>, <a href="#rfc.xref.Part5.7">6.1</a>, <a href="#rfc.xref.Part5.8">6.1</a>, <a href="#rfc.xref.Part5.9">7</a>, <a href="#rfc.xref.Part5.10">9.1</a>, <a href="#Part5"><b>1 5.1</b></a><ul>5131 <li><em>Part5</em> <a href="#rfc.xref.Part5.1">4.3.1</a>, <a href="#rfc.xref.Part5.2">4.3.1</a>, <a href="#rfc.xref.Part5.3">4.3.4</a>, <a href="#rfc.xref.Part5.4">5.1</a>, <a href="#rfc.xref.Part5.5">5.2</a>, <a href="#rfc.xref.Part5.6">6.1</a>, <a href="#rfc.xref.Part5.7">6.1</a>, <a href="#rfc.xref.Part5.8">6.1</a>, <a href="#rfc.xref.Part5.9">7</a>, <a href="#rfc.xref.Part5.10">9.1</a>, <a href="#Part5"><b>14.1</b></a><ul> 5133 5132 <li><em>Section 3</em> <a href="#rfc.xref.Part5.6">6.1</a></li> 5134 5133 <li><em>Section 3.1</em> <a href="#rfc.xref.Part5.7">6.1</a></li> … … 5140 5139 </ul> 5141 5140 </li> 5142 <li><em>Part6</em> <a href="#rfc.xref.Part6.1">3.2</a>, <a href="#rfc.xref.Part6.2"> 4.2.3</a>, <a href="#rfc.xref.Part6.3">4.3.1</a>, <a href="#rfc.xref.Part6.4">4.3.2</a>, <a href="#rfc.xref.Part6.5">4.3.3</a>, <a href="#rfc.xref.Part6.6">4.3.4</a>, <a href="#rfc.xref.Part6.7">4.3.5</a>, <a href="#rfc.xref.Part6.8">6.3.1</a>, <a href="#rfc.xref.Part6.9">6.3.4</a>, <a href="#rfc.xref.Part6.10">6.3.4</a>, <a href="#rfc.xref.Part6.11">6.3.4</a>, <a href="#rfc.xref.Part6.12">6.4.1</a>, <a href="#rfc.xref.Part6.13">6.4.2</a>, <a href="#rfc.xref.Part6.14">6.5.9</a>, <a href="#rfc.xref.Part6.15">7</a>, <a href="#rfc.xref.Part6.16">7</a>, <a href="#rfc.xref.Part6.17">10.1</a>, <a href="#rfc.xref.Part6.18">12.2.2</a>, <a href="#rfc.xref.Part6.19">12.3.1</a>, <a href="#Part6"><b>15.1</b></a><ul>5143 <li><em>Section 4.1.1</em> <a href="#rfc.xref.Part6. 5">4.3.3</a></li>5144 <li><em>Section 4.1.2</em> <a href="#rfc.xref.Part6. 8">6.3.1</a>, <a href="#rfc.xref.Part6.11">6.3.4</a>, <a href="#rfc.xref.Part6.12">6.4.1</a>, <a href="#rfc.xref.Part6.13">6.4.2</a>, <a href="#rfc.xref.Part6.14">6.5.9</a></li>5145 <li><em>Section 5</em> <a href="#rfc.xref.Part6. 4">4.3.2</a></li>5146 <li><em>Section 6</em> <a href="#rfc.xref.Part6. 6">4.3.4</a>, <a href="#rfc.xref.Part6.7">4.3.5</a></li>5147 <li><em>Section 7.1</em> <a href="#rfc.xref.Part6.1 5">7</a></li>5148 <li><em>Section 7.2</em> <a href="#rfc.xref.Part6. 9">6.3.4</a></li>5141 <li><em>Part6</em> <a href="#rfc.xref.Part6.1">3.2</a>, <a href="#rfc.xref.Part6.2">3.4.1</a>, <a href="#rfc.xref.Part6.3">4.2.3</a>, <a href="#rfc.xref.Part6.4">4.3.1</a>, <a href="#rfc.xref.Part6.5">4.3.2</a>, <a href="#rfc.xref.Part6.6">4.3.3</a>, <a href="#rfc.xref.Part6.7">4.3.4</a>, <a href="#rfc.xref.Part6.8">4.3.5</a>, <a href="#rfc.xref.Part6.9">6.3.1</a>, <a href="#rfc.xref.Part6.10">6.3.4</a>, <a href="#rfc.xref.Part6.11">6.3.4</a>, <a href="#rfc.xref.Part6.12">6.3.4</a>, <a href="#rfc.xref.Part6.13">6.4.1</a>, <a href="#rfc.xref.Part6.14">6.4.2</a>, <a href="#rfc.xref.Part6.15">6.5.9</a>, <a href="#rfc.xref.Part6.16">7</a>, <a href="#rfc.xref.Part6.17">7</a>, <a href="#rfc.xref.Part6.18">11.2.2</a>, <a href="#rfc.xref.Part6.19">11.3.1</a>, <a href="#Part6"><b>14.1</b></a><ul> 5142 <li><em>Section 4.1.1</em> <a href="#rfc.xref.Part6.6">4.3.3</a></li> 5143 <li><em>Section 4.1.2</em> <a href="#rfc.xref.Part6.9">6.3.1</a>, <a href="#rfc.xref.Part6.12">6.3.4</a>, <a href="#rfc.xref.Part6.13">6.4.1</a>, <a href="#rfc.xref.Part6.14">6.4.2</a>, <a href="#rfc.xref.Part6.15">6.5.9</a></li> 5144 <li><em>Section 5</em> <a href="#rfc.xref.Part6.5">4.3.2</a></li> 5145 <li><em>Section 6</em> <a href="#rfc.xref.Part6.7">4.3.4</a>, <a href="#rfc.xref.Part6.8">4.3.5</a></li> 5146 <li><em>Section 7.1</em> <a href="#rfc.xref.Part6.16">7</a></li> 5147 <li><em>Section 7.2</em> <a href="#rfc.xref.Part6.10">6.3.4</a></li> 5149 5148 <li><em>Section 7.3</em> <a href="#rfc.xref.Part6.1">3.2</a></li> 5150 <li><em>Section 7.5</em> <a href="#rfc.xref.Part6. 16">7</a>, <a href="#rfc.xref.Part6.17">10.1</a></li>5151 <li><em>Section 7.6</em> <a href="#rfc.xref.Part6.1 0">6.3.4</a></li>5149 <li><em>Section 7.5</em> <a href="#rfc.xref.Part6.2">3.4.1</a>, <a href="#rfc.xref.Part6.17">7</a></li> 5150 <li><em>Section 7.6</em> <a href="#rfc.xref.Part6.11">6.3.4</a></li> 5152 5151 </ul> 5153 5152 </li> 5154 <li><em>Part7</em> <a href="#rfc.xref.Part7.1">5.4</a>, <a href="#rfc.xref.Part7.2">5.4</a>, <a href="#rfc.xref.Part7.3">6.1</a>, <a href="#rfc.xref.Part7.4">6.1</a>, <a href="#rfc.xref.Part7.5">6.1</a>, <a href="#rfc.xref.Part7.6">7</a>, <a href="#rfc.xref.Part7.7">7</a>, <a href="#Part7"><b>1 5.1</b></a><ul>5153 <li><em>Part7</em> <a href="#rfc.xref.Part7.1">5.4</a>, <a href="#rfc.xref.Part7.2">5.4</a>, <a href="#rfc.xref.Part7.3">6.1</a>, <a href="#rfc.xref.Part7.4">6.1</a>, <a href="#rfc.xref.Part7.5">6.1</a>, <a href="#rfc.xref.Part7.6">7</a>, <a href="#rfc.xref.Part7.7">7</a>, <a href="#Part7"><b>14.1</b></a><ul> 5155 5154 <li><em>Section 3</em> <a href="#rfc.xref.Part7.3">6.1</a></li> 5156 5155 <li><em>Section 3.1</em> <a href="#rfc.xref.Part7.4">6.1</a></li> … … 5163 5162 </li> 5164 5163 <li>payload <a href="#rfc.iref.p.3">9</a></li> 5165 <li>POST method <a href="#rfc.xref.POST.1">4.1</a>, <a href="#rfc.iref.p.1"><b>4.3.3</b></a>, <a href="#rfc.xref.POST.2">1 2.1.3</a>, <a href="#rfc.xref.POST.3">C</a></li>5166 <li>PUT method <a href="#rfc.xref.PUT.1">4.1</a>, <a href="#rfc.iref.p.2"><b>4.3.4</b></a>, <a href="#rfc.xref.PUT.2">1 2.1.3</a>, <a href="#rfc.xref.PUT.3">C</a></li>5164 <li>POST method <a href="#rfc.xref.POST.1">4.1</a>, <a href="#rfc.iref.p.1"><b>4.3.3</b></a>, <a href="#rfc.xref.POST.2">11.1.3</a>, <a href="#rfc.xref.POST.3">C</a></li> 5165 <li>PUT method <a href="#rfc.xref.PUT.1">4.1</a>, <a href="#rfc.iref.p.2"><b>4.3.4</b></a>, <a href="#rfc.xref.PUT.2">11.1.3</a>, <a href="#rfc.xref.PUT.3">C</a></li> 5167 5166 </ul> 5168 5167 </li> 5169 5168 <li><a id="rfc.index.R" href="#rfc.index.R"><b>R</b></a><ul> 5170 <li>Referer header field <a href="#rfc.xref.header.referer.1">5.5</a>, <a href="#rfc.iref.r.2"><b>1 1.15</b></a>, <a href="#rfc.xref.header.referer.2">12.3.2</a>, <a href="#rfc.xref.header.referer.3">C</a></li>5169 <li>Referer header field <a href="#rfc.xref.header.referer.1">5.5</a>, <a href="#rfc.iref.r.2"><b>10.15</b></a>, <a href="#rfc.xref.header.referer.2">11.3.2</a>, <a href="#rfc.xref.header.referer.3">C</a></li> 5171 5170 <li>representation <a href="#rfc.iref.r.1">3</a></li> 5172 <li><em>REST</em> <a href="#rfc.xref.REST.1">4.1</a>, <a href="#REST"><b>1 5.2</b></a></li>5173 <li>Retry-After header field <a href="#rfc.xref.header.retry-after.1">6.6.4</a>, <a href="#rfc.xref.header.retry-after.2">7</a>, <a href="#rfc.iref.r.3"><b>1 1.16</b></a>, <a href="#rfc.xref.header.retry-after.3">12.3.2</a></li>5174 <li><em>RFC1123</em> <a href="#rfc.xref.RFC1123.1">8.1</a>, <a href="#rfc.xref.RFC1123.2">8.1</a>, <a href="#RFC1123"><b>1 5.2</b></a><ul>5171 <li><em>REST</em> <a href="#rfc.xref.REST.1">4.1</a>, <a href="#REST"><b>14.2</b></a></li> 5172 <li>Retry-After header field <a href="#rfc.xref.header.retry-after.1">6.6.4</a>, <a href="#rfc.xref.header.retry-after.2">7</a>, <a href="#rfc.iref.r.3"><b>10.16</b></a>, <a href="#rfc.xref.header.retry-after.3">11.3.2</a></li> 5173 <li><em>RFC1123</em> <a href="#rfc.xref.RFC1123.1">8.1</a>, <a href="#rfc.xref.RFC1123.2">8.1</a>, <a href="#RFC1123"><b>14.2</b></a><ul> 5175 5174 <li><em>Section 5.2.14</em> <a href="#rfc.xref.RFC1123.2">8.1</a></li> 5176 5175 </ul> 5177 5176 </li> 5178 <li><em>RFC1945</em> <a href="#rfc.xref.RFC1945.1">6.4</a>, <a href="#RFC1945"><b>1 5.2</b></a>, <a href="#rfc.xref.RFC1945.2">B</a><ul>5177 <li><em>RFC1945</em> <a href="#rfc.xref.RFC1945.1">6.4</a>, <a href="#RFC1945"><b>14.2</b></a>, <a href="#rfc.xref.RFC1945.2">B</a><ul> 5179 5178 <li><em>Section 9.3</em> <a href="#rfc.xref.RFC1945.1">6.4</a></li> 5180 5179 </ul> 5181 5180 </li> 5182 <li><em>RFC1950</em> <a href="#rfc.xref.RFC1950.1">1 2.4.2</a>, <a href="#RFC1950"><b>15.1</b></a></li>5183 <li><em>RFC1951</em> <a href="#rfc.xref.RFC1951.1">1 2.4.2</a>, <a href="#RFC1951"><b>15.1</b></a></li>5184 <li><em>RFC1952</em> <a href="#rfc.xref.RFC1952.1">1 2.4.2</a>, <a href="#RFC1952"><b>15.1</b></a></li>5185 <li><em>RFC2045</em> <a href="#RFC2045"><b>1 5.1</b></a>, <a href="#rfc.xref.RFC2045.1">A</a>, <a href="#rfc.xref.RFC2045.2">A.1</a></li>5186 <li><em>RFC2046</em> <a href="#rfc.xref.RFC2046.1">3.3</a>, <a href="#rfc.xref.RFC2046.2">8.5</a>, <a href="#rfc.xref.RFC2046.3">8.5.2</a>, <a href="#RFC2046"><b>1 5.1</b></a>, <a href="#rfc.xref.RFC2046.4">A.2</a><ul>5181 <li><em>RFC1950</em> <a href="#rfc.xref.RFC1950.1">11.4.2</a>, <a href="#RFC1950"><b>14.1</b></a></li> 5182 <li><em>RFC1951</em> <a href="#rfc.xref.RFC1951.1">11.4.2</a>, <a href="#RFC1951"><b>14.1</b></a></li> 5183 <li><em>RFC1952</em> <a href="#rfc.xref.RFC1952.1">11.4.2</a>, <a href="#RFC1952"><b>14.1</b></a></li> 5184 <li><em>RFC2045</em> <a href="#RFC2045"><b>14.1</b></a>, <a href="#rfc.xref.RFC2045.1">A</a>, <a href="#rfc.xref.RFC2045.2">A.1</a></li> 5185 <li><em>RFC2046</em> <a href="#rfc.xref.RFC2046.1">3.3</a>, <a href="#rfc.xref.RFC2046.2">8.5</a>, <a href="#rfc.xref.RFC2046.3">8.5.2</a>, <a href="#RFC2046"><b>14.1</b></a>, <a href="#rfc.xref.RFC2046.4">A.2</a><ul> 5187 5186 <li><em>Section 4.5.1</em> <a href="#rfc.xref.RFC2046.1">3.3</a></li> 5188 5187 <li><em>Section 5.1.1</em> <a href="#rfc.xref.RFC2046.3">8.5.2</a></li> 5189 5188 </ul> 5190 5189 </li> 5191 <li><em>RFC2049</em> <a href="#RFC2049"><b>1 5.2</b></a>, <a href="#rfc.xref.RFC2049.1">A.2</a><ul>5190 <li><em>RFC2049</em> <a href="#RFC2049"><b>14.2</b></a>, <a href="#rfc.xref.RFC2049.1">A.2</a><ul> 5192 5191 <li><em>Section 4</em> <a href="#rfc.xref.RFC2049.1">A.2</a></li> 5193 5192 </ul> 5194 5193 </li> 5195 <li><em>RFC2068</em> <a href="#rfc.xref.RFC2068.1">6.4</a>, <a href="#rfc.xref.RFC2068.2">6.4</a>, <a href="#RFC2068"><b>1 5.2</b></a>, <a href="#rfc.xref.RFC2068.3">B</a><ul>5194 <li><em>RFC2068</em> <a href="#rfc.xref.RFC2068.1">6.4</a>, <a href="#rfc.xref.RFC2068.2">6.4</a>, <a href="#RFC2068"><b>14.2</b></a>, <a href="#rfc.xref.RFC2068.3">B</a><ul> 5196 5195 <li><em>Section 10.3</em> <a href="#rfc.xref.RFC2068.2">6.4</a></li> 5197 5196 <li><em>Section 10.3.4</em> <a href="#rfc.xref.RFC2068.1">6.4</a></li> 5198 5197 </ul> 5199 5198 </li> 5200 <li><em>RFC2076</em> <a href="#RFC2076"><b>1 5.2</b></a>, <a href="#rfc.xref.RFC2076.1">B</a></li>5201 <li><em>RFC2119</em> <a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>1 5.1</b></a></li>5202 <li><em>RFC2277</em> <a href="#rfc.xref.RFC2277.1">8.3</a>, <a href="#RFC2277"><b>1 5.2</b></a></li>5203 <li><em>RFC2295</em> <a href="#rfc.xref.RFC2295.1"> 10</a>, <a href="#RFC2295"><b>15.2</b></a></li>5204 <li><em>RFC2388</em> <a href="#rfc.xref.RFC2388.1">8.5.2</a>, <a href="#RFC2388"><b>1 5.2</b></a></li>5205 <li><em>RFC2557</em> <a href="#rfc.xref.RFC2557.1">1 1.8</a>, <a href="#RFC2557"><b>15.2</b></a>, <a href="#rfc.xref.RFC2557.2">A.6</a><ul>5206 <li><em>Section 4</em> <a href="#rfc.xref.RFC2557.1">1 1.8</a></li>5199 <li><em>RFC2076</em> <a href="#RFC2076"><b>14.2</b></a>, <a href="#rfc.xref.RFC2076.1">B</a></li> 5200 <li><em>RFC2119</em> <a href="#rfc.xref.RFC2119.1">1.1</a>, <a href="#RFC2119"><b>14.1</b></a></li> 5201 <li><em>RFC2277</em> <a href="#rfc.xref.RFC2277.1">8.3</a>, <a href="#RFC2277"><b>14.2</b></a></li> 5202 <li><em>RFC2295</em> <a href="#rfc.xref.RFC2295.1">3.4</a>, <a href="#RFC2295"><b>14.2</b></a></li> 5203 <li><em>RFC2388</em> <a href="#rfc.xref.RFC2388.1">8.5.2</a>, <a href="#RFC2388"><b>14.2</b></a></li> 5204 <li><em>RFC2557</em> <a href="#rfc.xref.RFC2557.1">10.8</a>, <a href="#RFC2557"><b>14.2</b></a>, <a href="#rfc.xref.RFC2557.2">A.6</a><ul> 5205 <li><em>Section 4</em> <a href="#rfc.xref.RFC2557.1">10.8</a></li> 5207 5206 </ul> 5208 5207 </li> 5209 <li><em>RFC2616</em> <a href="#rfc.xref.RFC2616.1">6.4</a>, <a href="#rfc.xref.RFC2616.2">1 1.4</a>, <a href="#RFC2616"><b>15.2</b></a>, <a href="#rfc.xref.RFC2616.3">F.1</a><ul>5208 <li><em>RFC2616</em> <a href="#rfc.xref.RFC2616.1">6.4</a>, <a href="#rfc.xref.RFC2616.2">10.4</a>, <a href="#RFC2616"><b>14.2</b></a>, <a href="#rfc.xref.RFC2616.3">F.1</a><ul> 5210 5209 <li><em>Section 10.3.8</em> <a href="#rfc.xref.RFC2616.1">6.4</a></li> 5211 <li><em>Section 14.4</em> <a href="#rfc.xref.RFC2616.2">1 1.4</a></li>5210 <li><em>Section 14.4</em> <a href="#rfc.xref.RFC2616.2">10.4</a></li> 5212 5211 </ul> 5213 5212 </li> 5214 <li><em>RFC2817</em> <a href="#rfc.xref.RFC2817.1">1 2.2</a>, <a href="#RFC2817"><b>15.2</b></a>, <a href="#rfc.xref.RFC2817.2">C</a>, <a href="#rfc.xref.RFC2817.3">C</a>, <a href="#rfc.xref.RFC2817.4">C</a><ul>5215 <li><em>Section 7.1</em> <a href="#rfc.xref.RFC2817.1">1 2.2</a>, <a href="#rfc.xref.RFC2817.3">C</a></li>5213 <li><em>RFC2817</em> <a href="#rfc.xref.RFC2817.1">11.2</a>, <a href="#RFC2817"><b>14.2</b></a>, <a href="#rfc.xref.RFC2817.2">C</a>, <a href="#rfc.xref.RFC2817.3">C</a>, <a href="#rfc.xref.RFC2817.4">C</a><ul> 5214 <li><em>Section 7.1</em> <a href="#rfc.xref.RFC2817.1">11.2</a>, <a href="#rfc.xref.RFC2817.3">C</a></li> 5216 5215 </ul> 5217 5216 </li> 5218 <li><em>RFC3629</em> <a href="#rfc.xref.RFC3629.1">8.3</a>, <a href="#RFC3629"><b>1 5.2</b></a></li>5219 <li><em>RFC3864</em> <a href="#rfc.xref.RFC3864.1">1 2.3</a>, <a href="#rfc.xref.RFC3864.2">12.3.1</a>, <a href="#RFC3864"><b>15.2</b></a><ul>5220 <li><em>Section 4.1</em> <a href="#rfc.xref.RFC3864.2">1 2.3.1</a></li>5217 <li><em>RFC3629</em> <a href="#rfc.xref.RFC3629.1">8.3</a>, <a href="#RFC3629"><b>14.2</b></a></li> 5218 <li><em>RFC3864</em> <a href="#rfc.xref.RFC3864.1">11.3</a>, <a href="#rfc.xref.RFC3864.2">11.3.1</a>, <a href="#RFC3864"><b>14.2</b></a><ul> 5219 <li><em>Section 4.1</em> <a href="#rfc.xref.RFC3864.2">11.3.1</a></li> 5221 5220 </ul> 5222 5221 </li> 5223 <li><em>RFC3986</em> <a href="#rfc.xref.RFC3986.1">1 1.13</a>, <a href="#rfc.xref.RFC3986.2">11.13</a>, <a href="#RFC3986"><b>15.1</b></a><ul>5224 <li><em>Section 4.2</em> <a href="#rfc.xref.RFC3986.1">1 1.13</a></li>5225 <li><em>Section 5</em> <a href="#rfc.xref.RFC3986.2">1 1.13</a></li>5222 <li><em>RFC3986</em> <a href="#rfc.xref.RFC3986.1">10.13</a>, <a href="#rfc.xref.RFC3986.2">10.13</a>, <a href="#RFC3986"><b>14.1</b></a><ul> 5223 <li><em>Section 4.2</em> <a href="#rfc.xref.RFC3986.1">10.13</a></li> 5224 <li><em>Section 5</em> <a href="#rfc.xref.RFC3986.2">10.13</a></li> 5226 5225 </ul> 5227 5226 </li> 5228 <li><em>RFC4288</em> <a href="#rfc.xref.RFC4288.1">8.5</a>, <a href="#RFC4288"><b>1 5.2</b></a></li>5229 <li><em>RFC4647</em> <a href="#rfc.xref.RFC4647.1">1 1.4</a>, <a href="#rfc.xref.RFC4647.2">11.4</a>, <a href="#rfc.xref.RFC4647.3">11.4</a>, <a href="#rfc.xref.RFC4647.4">11.4</a>, <a href="#RFC4647"><b>15.1</b></a><ul>5230 <li><em>Section 2.1</em> <a href="#rfc.xref.RFC4647.1">1 1.4</a></li>5231 <li><em>Section 2.3</em> <a href="#rfc.xref.RFC4647.2">1 1.4</a></li>5232 <li><em>Section 3</em> <a href="#rfc.xref.RFC4647.3">1 1.4</a></li>5233 <li><em>Section 3.3.1</em> <a href="#rfc.xref.RFC4647.4">1 1.4</a></li>5227 <li><em>RFC4288</em> <a href="#rfc.xref.RFC4288.1">8.5</a>, <a href="#RFC4288"><b>14.2</b></a></li> 5228 <li><em>RFC4647</em> <a href="#rfc.xref.RFC4647.1">10.4</a>, <a href="#rfc.xref.RFC4647.2">10.4</a>, <a href="#rfc.xref.RFC4647.3">10.4</a>, <a href="#rfc.xref.RFC4647.4">10.4</a>, <a href="#RFC4647"><b>14.1</b></a><ul> 5229 <li><em>Section 2.1</em> <a href="#rfc.xref.RFC4647.1">10.4</a></li> 5230 <li><em>Section 2.3</em> <a href="#rfc.xref.RFC4647.2">10.4</a></li> 5231 <li><em>Section 3</em> <a href="#rfc.xref.RFC4647.3">10.4</a></li> 5232 <li><em>Section 3.3.1</em> <a href="#rfc.xref.RFC4647.4">10.4</a></li> 5234 5233 </ul> 5235 5234 </li> 5236 <li><em>RFC5226</em> <a href="#rfc.xref.RFC5226.1">1 2.1.1</a>, <a href="#rfc.xref.RFC5226.2">12.2.1</a>, <a href="#rfc.xref.RFC5226.3">12.4.1</a>, <a href="#RFC5226"><b>15.2</b></a><ul>5237 <li><em>Section 4.1</em> <a href="#rfc.xref.RFC5226.1">1 2.1.1</a>, <a href="#rfc.xref.RFC5226.2">12.2.1</a>, <a href="#rfc.xref.RFC5226.3">12.4.1</a></li>5235 <li><em>RFC5226</em> <a href="#rfc.xref.RFC5226.1">11.1.1</a>, <a href="#rfc.xref.RFC5226.2">11.2.1</a>, <a href="#rfc.xref.RFC5226.3">11.4.1</a>, <a href="#RFC5226"><b>14.2</b></a><ul> 5236 <li><em>Section 4.1</em> <a href="#rfc.xref.RFC5226.1">11.1.1</a>, <a href="#rfc.xref.RFC5226.2">11.2.1</a>, <a href="#rfc.xref.RFC5226.3">11.4.1</a></li> 5238 5237 </ul> 5239 5238 </li> 5240 <li><em>RFC5234</em> <a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">1 2.3.1</a>, <a href="#RFC5234"><b>15.1</b></a>, <a href="#rfc.xref.RFC5234.3">D</a><ul>5239 <li><em>RFC5234</em> <a href="#rfc.xref.RFC5234.1">1.2</a>, <a href="#rfc.xref.RFC5234.2">11.3.1</a>, <a href="#RFC5234"><b>14.1</b></a>, <a href="#rfc.xref.RFC5234.3">D</a><ul> 5241 5240 <li><em>Appendix B.1</em> <a href="#rfc.xref.RFC5234.3">D</a></li> 5242 5241 </ul> 5243 5242 </li> 5244 <li><em>RFC5322</em> <a href="#rfc.xref.RFC5322.1">8.1</a>, <a href="#rfc.xref.RFC5322.2">1 1.10</a>, <a href="#rfc.xref.RFC5322.3">11.12</a>, <a href="#rfc.xref.RFC5322.4">11.12</a>, <a href="#RFC5322"><b>15.2</b></a>, <a href="#rfc.xref.RFC5322.5">A</a><ul>5243 <li><em>RFC5322</em> <a href="#rfc.xref.RFC5322.1">8.1</a>, <a href="#rfc.xref.RFC5322.2">10.10</a>, <a href="#rfc.xref.RFC5322.3">10.12</a>, <a href="#rfc.xref.RFC5322.4">10.12</a>, <a href="#RFC5322"><b>14.2</b></a>, <a href="#rfc.xref.RFC5322.5">A</a><ul> 5245 5244 <li><em>Section 3.3</em> <a href="#rfc.xref.RFC5322.1">8.1</a></li> 5246 <li><em>Section 3.4</em> <a href="#rfc.xref.RFC5322.3">1 1.12</a>, <a href="#rfc.xref.RFC5322.4">11.12</a></li>5247 <li><em>Section 3.6.1</em> <a href="#rfc.xref.RFC5322.2">1 1.10</a></li>5245 <li><em>Section 3.4</em> <a href="#rfc.xref.RFC5322.3">10.12</a>, <a href="#rfc.xref.RFC5322.4">10.12</a></li> 5246 <li><em>Section 3.6.1</em> <a href="#rfc.xref.RFC5322.2">10.10</a></li> 5248 5247 </ul> 5249 5248 </li> 5250 <li><em>RFC5646</em> <a href="#rfc.xref.RFC5646.1">8.6</a>, <a href="#rfc.xref.RFC5646.2">8.6</a>, <a href="#rfc.xref.RFC5646.3">8.6</a>, <a href="#RFC5646"><b>1 5.1</b></a><ul>5249 <li><em>RFC5646</em> <a href="#rfc.xref.RFC5646.1">8.6</a>, <a href="#rfc.xref.RFC5646.2">8.6</a>, <a href="#rfc.xref.RFC5646.3">8.6</a>, <a href="#RFC5646"><b>14.1</b></a><ul> 5251 5250 <li><em>Section 2.1</em> <a href="#rfc.xref.RFC5646.2">8.6</a></li> 5252 5251 </ul> 5253 5252 </li> 5254 <li><em>RFC5789</em> <a href="#rfc.xref.RFC5789.1">4.3.4</a>, <a href="#RFC5789"><b>1 5.2</b></a></li>5255 <li><em>RFC5987</em> <a href="#rfc.xref.RFC5987.1">1 2.3.1</a>, <a href="#RFC5987"><b>15.2</b></a></li>5256 <li><em>RFC6151</em> <a href="#RFC6151"><b>1 5.2</b></a>, <a href="#rfc.xref.RFC6151.1">C</a></li>5257 <li><em>RFC6266</em> <a href="#RFC6266"><b>1 5.2</b></a>, <a href="#rfc.xref.RFC6266.1">B</a>, <a href="#rfc.xref.RFC6266.2">C</a></li>5253 <li><em>RFC5789</em> <a href="#rfc.xref.RFC5789.1">4.3.4</a>, <a href="#RFC5789"><b>14.2</b></a></li> 5254 <li><em>RFC5987</em> <a href="#rfc.xref.RFC5987.1">11.3.1</a>, <a href="#RFC5987"><b>14.2</b></a></li> 5255 <li><em>RFC6151</em> <a href="#RFC6151"><b>14.2</b></a>, <a href="#rfc.xref.RFC6151.1">C</a></li> 5256 <li><em>RFC6266</em> <a href="#RFC6266"><b>14.2</b></a>, <a href="#rfc.xref.RFC6266.1">B</a>, <a href="#rfc.xref.RFC6266.2">C</a></li> 5258 5257 </ul> 5259 5258 </li> … … 5261 5260 <li>safe <a href="#rfc.iref.s.2"><b>4.2.1</b></a></li> 5262 5261 <li>selected representation <a href="#rfc.iref.s.1"><b>3.2</b></a></li> 5263 <li>Server header field <a href="#rfc.xref.header.server.1">7</a>, <a href="#rfc.iref.s.44"><b>1 1.17</b></a>, <a href="#rfc.xref.header.server.2">12.3.2</a>, <a href="#rfc.xref.header.server.3">13.1</a>, <a href="#rfc.xref.header.server.4">C</a></li>5262 <li>Server header field <a href="#rfc.xref.header.server.1">7</a>, <a href="#rfc.iref.s.44"><b>10.17</b></a>, <a href="#rfc.xref.header.server.2">11.3.2</a>, <a href="#rfc.xref.header.server.3">12.1</a>, <a href="#rfc.xref.header.server.4">C</a></li> 5264 5263 <li>Status Codes 5265 5264 <ul> 5266 <li>100 Continue <a href="#rfc.xref.status.100.1">6.1</a>, <a href="#rfc.iref.s.4"><b>6.2.1</b></a>, <a href="#rfc.xref.status.100.2">1 2.2.3</a></li>5267 <li>101 Switching Protocols <a href="#rfc.xref.status.101.1">6.1</a>, <a href="#rfc.iref.s.5"><b>6.2.2</b></a>, <a href="#rfc.xref.status.101.2">1 2.2.3</a></li>5268 <li>200 OK <a href="#rfc.xref.status.200.1">6.1</a>, <a href="#rfc.iref.s.7"><b>6.3.1</b></a>, <a href="#rfc.xref.status.200.2">1 2.2.3</a></li>5269 <li>201 Created <a href="#rfc.xref.status.201.1">6.1</a>, <a href="#rfc.iref.s.8"><b>6.3.2</b></a>, <a href="#rfc.xref.status.201.2">1 2.2.3</a></li>5270 <li>202 Accepted <a href="#rfc.xref.status.202.1">6.1</a>, <a href="#rfc.iref.s.9"><b>6.3.3</b></a>, <a href="#rfc.xref.status.202.2">1 2.2.3</a></li>5271 <li>203 Non-Authoritative Information <a href="#rfc.xref.status.203.1">6.1</a>, <a href="#rfc.iref.s.10"><b>6.3.4</b></a>, <a href="#rfc.xref.status.203.2">1 2.2.3</a>, <a href="#rfc.xref.status.203.3">C</a></li>5272 <li>204 No Content <a href="#rfc.xref.status.204.1">6.1</a>, <a href="#rfc.iref.s.11"><b>6.3.5</b></a>, <a href="#rfc.xref.status.204.2">1 2.2.3</a></li>5273 <li>205 Reset Content <a href="#rfc.xref.status.205.1">6.1</a>, <a href="#rfc.iref.s.12"><b>6.3.6</b></a>, <a href="#rfc.xref.status.205.2">1 2.2.3</a></li>5274 <li>300 Multiple Choices <a href="#rfc.xref.status.300.1">6.1</a>, <a href="#rfc.iref.s.14"><b>6.4.1</b></a>, <a href="#rfc.xref.status.300.2">1 2.2.3</a></li>5275 <li>301 Moved Permanently <a href="#rfc.xref.status.301.1">6.1</a>, <a href="#rfc.iref.s.15"><b>6.4.2</b></a>, <a href="#rfc.xref.status.301.2">1 2.2.3</a>, <a href="#rfc.xref.status.301.3">C</a></li>5276 <li>302 Found <a href="#rfc.xref.status.302.1">6.1</a>, <a href="#rfc.iref.s.16"><b>6.4.3</b></a>, <a href="#rfc.xref.status.302.2">1 2.2.3</a>, <a href="#rfc.xref.status.302.3">C</a></li>5277 <li>303 See Other <a href="#rfc.xref.status.303.1">6.1</a>, <a href="#rfc.iref.s.17"><b>6.4.4</b></a>, <a href="#rfc.xref.status.303.2">1 2.2.3</a></li>5278 <li>305 Use Proxy <a href="#rfc.xref.status.305.1">6.1</a>, <a href="#rfc.iref.s.18"><b>6.4.5</b></a>, <a href="#rfc.xref.status.305.2">1 2.2.3</a>, <a href="#rfc.xref.status.305.3">C</a></li>5279 <li>306 (Unused) <a href="#rfc.iref.s.19"><b>6.4.6</b></a>, <a href="#rfc.xref.status.306.1">1 2.2.3</a></li>5280 <li>307 Temporary Redirect <a href="#rfc.xref.status.307.1">6.1</a>, <a href="#rfc.iref.s.20"><b>6.4.7</b></a>, <a href="#rfc.xref.status.307.2">1 2.2.3</a>, <a href="#rfc.xref.status.307.3">C</a></li>5281 <li>400 Bad Request <a href="#rfc.xref.status.400.1">6.1</a>, <a href="#rfc.iref.s.22"><b>6.5.1</b></a>, <a href="#rfc.xref.status.400.2">1 2.2.3</a></li>5282 <li>402 Payment Required <a href="#rfc.xref.status.402.1">6.1</a>, <a href="#rfc.iref.s.23"><b>6.5.2</b></a>, <a href="#rfc.xref.status.402.2">1 2.2.3</a></li>5283 <li>403 Forbidden <a href="#rfc.xref.status.403.1">6.1</a>, <a href="#rfc.iref.s.24"><b>6.5.3</b></a>, <a href="#rfc.xref.status.403.2">1 2.2.3</a></li>5284 <li>404 Not Found <a href="#rfc.xref.status.404.1">6.1</a>, <a href="#rfc.iref.s.25"><b>6.5.4</b></a>, <a href="#rfc.xref.status.404.2">1 2.2.3</a></li>5285 <li>405 Method Not Allowed <a href="#rfc.xref.status.405.1">6.1</a>, <a href="#rfc.iref.s.26"><b>6.5.5</b></a>, <a href="#rfc.xref.status.405.2">1 2.2.3</a></li>5286 <li>406 Not Acceptable <a href="#rfc.xref.status.406.1">6.1</a>, <a href="#rfc.iref.s.27"><b>6.5.6</b></a>, <a href="#rfc.xref.status.406.2">1 2.2.3</a></li>5287 <li>408 Request Timeout <a href="#rfc.xref.status.408.1">6.1</a>, <a href="#rfc.iref.s.28"><b>6.5.7</b></a>, <a href="#rfc.xref.status.408.2">1 2.2.3</a></li>5288 <li>409 Conflict <a href="#rfc.xref.status.409.1">6.1</a>, <a href="#rfc.iref.s.29"><b>6.5.8</b></a>, <a href="#rfc.xref.status.409.2">1 2.2.3</a></li>5289 <li>410 Gone <a href="#rfc.xref.status.410.1">6.1</a>, <a href="#rfc.iref.s.30"><b>6.5.9</b></a>, <a href="#rfc.xref.status.410.2">1 2.2.3</a></li>5290 <li>411 Length Required <a href="#rfc.xref.status.411.1">6.1</a>, <a href="#rfc.iref.s.31"><b>6.5.10</b></a>, <a href="#rfc.xref.status.411.2">1 2.2.3</a></li>5291 <li>413 Request Representation Too Large <a href="#rfc.xref.status.413.1">6.1</a>, <a href="#rfc.iref.s.32"><b>6.5.11</b></a>, <a href="#rfc.xref.status.413.2">1 2.2.3</a></li>5292 <li>414 URI Too Long <a href="#rfc.xref.status.414.1">6.1</a>, <a href="#rfc.iref.s.33"><b>6.5.12</b></a>, <a href="#rfc.xref.status.414.2">1 2.2.3</a></li>5293 <li>415 Unsupported Media Type <a href="#rfc.xref.status.415.1">6.1</a>, <a href="#rfc.iref.s.34"><b>6.5.13</b></a>, <a href="#rfc.xref.status.415.2">1 2.2.3</a></li>5294 <li>417 Expectation Failed <a href="#rfc.xref.status.417.1">6.1</a>, <a href="#rfc.iref.s.35"><b>6.5.14</b></a>, <a href="#rfc.xref.status.417.2">1 2.2.3</a></li>5295 <li>426 Upgrade Required <a href="#rfc.xref.status.426.1">6.1</a>, <a href="#rfc.iref.s.36"><b>6.5.15</b></a>, <a href="#rfc.xref.status.426.2">1 2.2.3</a>, <a href="#rfc.xref.status.426.3">C</a></li>5296 <li>500 Internal Server Error <a href="#rfc.xref.status.500.1">6.1</a>, <a href="#rfc.iref.s.38"><b>6.6.1</b></a>, <a href="#rfc.xref.status.500.2">1 2.2.3</a></li>5297 <li>501 Not Implemented <a href="#rfc.xref.status.501.1">6.1</a>, <a href="#rfc.iref.s.39"><b>6.6.2</b></a>, <a href="#rfc.xref.status.501.2">1 2.2.3</a></li>5298 <li>502 Bad Gateway <a href="#rfc.xref.status.502.1">6.1</a>, <a href="#rfc.iref.s.40"><b>6.6.3</b></a>, <a href="#rfc.xref.status.502.2">1 2.2.3</a></li>5299 <li>503 Service Unavailable <a href="#rfc.xref.status.503.1">6.1</a>, <a href="#rfc.iref.s.41"><b>6.6.4</b></a>, <a href="#rfc.xref.status.503.2">1 2.2.3</a></li>5300 <li>504 Gateway Timeout <a href="#rfc.xref.status.504.1">6.1</a>, <a href="#rfc.iref.s.42"><b>6.6.5</b></a>, <a href="#rfc.xref.status.504.2">1 2.2.3</a></li>5301 <li>505 HTTP Version Not Supported <a href="#rfc.xref.status.505.1">6.1</a>, <a href="#rfc.iref.s.43"><b>6.6.6</b></a>, <a href="#rfc.xref.status.505.2">1 2.2.3</a></li>5265 <li>100 Continue <a href="#rfc.xref.status.100.1">6.1</a>, <a href="#rfc.iref.s.4"><b>6.2.1</b></a>, <a href="#rfc.xref.status.100.2">11.2.3</a></li> 5266 <li>101 Switching Protocols <a href="#rfc.xref.status.101.1">6.1</a>, <a href="#rfc.iref.s.5"><b>6.2.2</b></a>, <a href="#rfc.xref.status.101.2">11.2.3</a></li> 5267 <li>200 OK <a href="#rfc.xref.status.200.1">6.1</a>, <a href="#rfc.iref.s.7"><b>6.3.1</b></a>, <a href="#rfc.xref.status.200.2">11.2.3</a></li> 5268 <li>201 Created <a href="#rfc.xref.status.201.1">6.1</a>, <a href="#rfc.iref.s.8"><b>6.3.2</b></a>, <a href="#rfc.xref.status.201.2">11.2.3</a></li> 5269 <li>202 Accepted <a href="#rfc.xref.status.202.1">6.1</a>, <a href="#rfc.iref.s.9"><b>6.3.3</b></a>, <a href="#rfc.xref.status.202.2">11.2.3</a></li> 5270 <li>203 Non-Authoritative Information <a href="#rfc.xref.status.203.1">6.1</a>, <a href="#rfc.iref.s.10"><b>6.3.4</b></a>, <a href="#rfc.xref.status.203.2">11.2.3</a>, <a href="#rfc.xref.status.203.3">C</a></li> 5271 <li>204 No Content <a href="#rfc.xref.status.204.1">6.1</a>, <a href="#rfc.iref.s.11"><b>6.3.5</b></a>, <a href="#rfc.xref.status.204.2">11.2.3</a></li> 5272 <li>205 Reset Content <a href="#rfc.xref.status.205.1">6.1</a>, <a href="#rfc.iref.s.12"><b>6.3.6</b></a>, <a href="#rfc.xref.status.205.2">11.2.3</a></li> 5273 <li>300 Multiple Choices <a href="#rfc.xref.status.300.1">6.1</a>, <a href="#rfc.iref.s.14"><b>6.4.1</b></a>, <a href="#rfc.xref.status.300.2">11.2.3</a></li> 5274 <li>301 Moved Permanently <a href="#rfc.xref.status.301.1">6.1</a>, <a href="#rfc.iref.s.15"><b>6.4.2</b></a>, <a href="#rfc.xref.status.301.2">11.2.3</a>, <a href="#rfc.xref.status.301.3">C</a></li> 5275 <li>302 Found <a href="#rfc.xref.status.302.1">6.1</a>, <a href="#rfc.iref.s.16"><b>6.4.3</b></a>, <a href="#rfc.xref.status.302.2">11.2.3</a>, <a href="#rfc.xref.status.302.3">C</a></li> 5276 <li>303 See Other <a href="#rfc.xref.status.303.1">6.1</a>, <a href="#rfc.iref.s.17"><b>6.4.4</b></a>, <a href="#rfc.xref.status.303.2">11.2.3</a></li> 5277 <li>305 Use Proxy <a href="#rfc.xref.status.305.1">6.1</a>, <a href="#rfc.iref.s.18"><b>6.4.5</b></a>, <a href="#rfc.xref.status.305.2">11.2.3</a>, <a href="#rfc.xref.status.305.3">C</a></li> 5278 <li>306 (Unused) <a href="#rfc.iref.s.19"><b>6.4.6</b></a>, <a href="#rfc.xref.status.306.1">11.2.3</a></li> 5279 <li>307 Temporary Redirect <a href="#rfc.xref.status.307.1">6.1</a>, <a href="#rfc.iref.s.20"><b>6.4.7</b></a>, <a href="#rfc.xref.status.307.2">11.2.3</a>, <a href="#rfc.xref.status.307.3">C</a></li> 5280 <li>400 Bad Request <a href="#rfc.xref.status.400.1">6.1</a>, <a href="#rfc.iref.s.22"><b>6.5.1</b></a>, <a href="#rfc.xref.status.400.2">11.2.3</a></li> 5281 <li>402 Payment Required <a href="#rfc.xref.status.402.1">6.1</a>, <a href="#rfc.iref.s.23"><b>6.5.2</b></a>, <a href="#rfc.xref.status.402.2">11.2.3</a></li> 5282 <li>403 Forbidden <a href="#rfc.xref.status.403.1">6.1</a>, <a href="#rfc.iref.s.24"><b>6.5.3</b></a>, <a href="#rfc.xref.status.403.2">11.2.3</a></li> 5283 <li>404 Not Found <a href="#rfc.xref.status.404.1">6.1</a>, <a href="#rfc.iref.s.25"><b>6.5.4</b></a>, <a href="#rfc.xref.status.404.2">11.2.3</a></li> 5284 <li>405 Method Not Allowed <a href="#rfc.xref.status.405.1">6.1</a>, <a href="#rfc.iref.s.26"><b>6.5.5</b></a>, <a href="#rfc.xref.status.405.2">11.2.3</a></li> 5285 <li>406 Not Acceptable <a href="#rfc.xref.status.406.1">6.1</a>, <a href="#rfc.iref.s.27"><b>6.5.6</b></a>, <a href="#rfc.xref.status.406.2">11.2.3</a></li> 5286 <li>408 Request Timeout <a href="#rfc.xref.status.408.1">6.1</a>, <a href="#rfc.iref.s.28"><b>6.5.7</b></a>, <a href="#rfc.xref.status.408.2">11.2.3</a></li> 5287 <li>409 Conflict <a href="#rfc.xref.status.409.1">6.1</a>, <a href="#rfc.iref.s.29"><b>6.5.8</b></a>, <a href="#rfc.xref.status.409.2">11.2.3</a></li> 5288 <li>410 Gone <a href="#rfc.xref.status.410.1">6.1</a>, <a href="#rfc.iref.s.30"><b>6.5.9</b></a>, <a href="#rfc.xref.status.410.2">11.2.3</a></li> 5289 <li>411 Length Required <a href="#rfc.xref.status.411.1">6.1</a>, <a href="#rfc.iref.s.31"><b>6.5.10</b></a>, <a href="#rfc.xref.status.411.2">11.2.3</a></li> 5290 <li>413 Request Representation Too Large <a href="#rfc.xref.status.413.1">6.1</a>, <a href="#rfc.iref.s.32"><b>6.5.11</b></a>, <a href="#rfc.xref.status.413.2">11.2.3</a></li> 5291 <li>414 URI Too Long <a href="#rfc.xref.status.414.1">6.1</a>, <a href="#rfc.iref.s.33"><b>6.5.12</b></a>, <a href="#rfc.xref.status.414.2">11.2.3</a></li> 5292 <li>415 Unsupported Media Type <a href="#rfc.xref.status.415.1">6.1</a>, <a href="#rfc.iref.s.34"><b>6.5.13</b></a>, <a href="#rfc.xref.status.415.2">11.2.3</a></li> 5293 <li>417 Expectation Failed <a href="#rfc.xref.status.417.1">6.1</a>, <a href="#rfc.iref.s.35"><b>6.5.14</b></a>, <a href="#rfc.xref.status.417.2">11.2.3</a></li> 5294 <li>426 Upgrade Required <a href="#rfc.xref.status.426.1">6.1</a>, <a href="#rfc.iref.s.36"><b>6.5.15</b></a>, <a href="#rfc.xref.status.426.2">11.2.3</a>, <a href="#rfc.xref.status.426.3">C</a></li> 5295 <li>500 Internal Server Error <a href="#rfc.xref.status.500.1">6.1</a>, <a href="#rfc.iref.s.38"><b>6.6.1</b></a>, <a href="#rfc.xref.status.500.2">11.2.3</a></li> 5296 <li>501 Not Implemented <a href="#rfc.xref.status.501.1">6.1</a>, <a href="#rfc.iref.s.39"><b>6.6.2</b></a>, <a href="#rfc.xref.status.501.2">11.2.3</a></li> 5297 <li>502 Bad Gateway <a href="#rfc.xref.status.502.1">6.1</a>, <a href="#rfc.iref.s.40"><b>6.6.3</b></a>, <a href="#rfc.xref.status.502.2">11.2.3</a></li> 5298 <li>503 Service Unavailable <a href="#rfc.xref.status.503.1">6.1</a>, <a href="#rfc.iref.s.41"><b>6.6.4</b></a>, <a href="#rfc.xref.status.503.2">11.2.3</a></li> 5299 <li>504 Gateway Timeout <a href="#rfc.xref.status.504.1">6.1</a>, <a href="#rfc.iref.s.42"><b>6.6.5</b></a>, <a href="#rfc.xref.status.504.2">11.2.3</a></li> 5300 <li>505 HTTP Version Not Supported <a href="#rfc.xref.status.505.1">6.1</a>, <a href="#rfc.iref.s.43"><b>6.6.6</b></a>, <a href="#rfc.xref.status.505.2">11.2.3</a></li> 5302 5301 </ul> 5303 5302 </li> … … 5311 5310 </ul> 5312 5311 </li> 5313 <li><em>status-308</em> <a href="#rfc.xref.status-308.1">6.4.7</a>, <a href="#status-308"><b>1 5.2</b></a></li>5312 <li><em>status-308</em> <a href="#rfc.xref.status-308.1">6.4.7</a>, <a href="#status-308"><b>14.2</b></a></li> 5314 5313 </ul> 5315 5314 </li> 5316 5315 <li><a id="rfc.index.T" href="#rfc.index.T"><b>T</b></a><ul> 5317 <li>TRACE method <a href="#rfc.xref.TRACE.1">4.1</a>, <a href="#rfc.iref.t.1"><b>4.3.8</b></a>, <a href="#rfc.xref.TRACE.2">1 1.14</a>, <a href="#rfc.xref.TRACE.3">12.1.3</a>, <a href="#rfc.xref.TRACE.4">13.1</a></li>5316 <li>TRACE method <a href="#rfc.xref.TRACE.1">4.1</a>, <a href="#rfc.iref.t.1"><b>4.3.8</b></a>, <a href="#rfc.xref.TRACE.2">10.14</a>, <a href="#rfc.xref.TRACE.3">11.1.3</a>, <a href="#rfc.xref.TRACE.4">12.1</a></li> 5318 5317 </ul> 5319 5318 </li> 5320 5319 <li><a id="rfc.index.U" href="#rfc.index.U"><b>U</b></a><ul> 5321 <li>User-Agent header field <a href="#rfc.xref.header.user-agent.1"> 5.5</a>, <a href="#rfc.xref.header.user-agent.2">10.1</a>, <a href="#rfc.iref.u.1"><b>11.18</b></a>, <a href="#rfc.xref.header.user-agent.3">12.3.2</a>, <a href="#rfc.xref.header.user-agent.4">13.1</a></li>5320 <li>User-Agent header field <a href="#rfc.xref.header.user-agent.1">3.4.1</a>, <a href="#rfc.xref.header.user-agent.2">5.5</a>, <a href="#rfc.iref.u.1"><b>10.18</b></a>, <a href="#rfc.xref.header.user-agent.3">11.3.2</a>, <a href="#rfc.xref.header.user-agent.4">12.1</a></li> 5322 5321 </ul> 5323 5322 </li> -
draft-ietf-httpbis/latest/p2-semantics.xml
r1853 r1854 461 461 </t> 462 462 </section> 463 464 <section title="Content Negotiation" anchor="content.negotiation"> 465 <t> 466 HTTP responses include a representation which contains information for 467 interpretation, whether by a human user or for further processing. 468 Often, the server has different ways of representing the 469 same information; for example, in different formats, languages, 470 or using different character encodings. 471 </t> 472 <t> 473 HTTP clients and their users might have different or variable 474 capabilities, characteristics or preferences which would influence 475 which representation, among those available from the server, 476 would be best for the server to deliver. For this reason, HTTP 477 provides mechanisms for "content negotiation" — a process of 478 allowing selection of a representation of a given resource, 479 when more than one is available. 480 </t> 481 <t> 482 This specification defines two patterns of content negotiation; 483 "server-driven", where the server selects the representation based 484 upon the client's stated preferences, and "agent-driven" negotiation, 485 where the server provides a list of representations for the client to 486 choose from, based upon their metadata. In addition, there are 487 other patterns: some applications use an "active content" pattern, 488 where the server returns active content which runs on the client 489 and, based on client available parameters, selects additional 490 resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>) 491 has also been proposed. 492 </t> 493 <t> 494 These patterns are all widely used, and have trade-offs in applicability 495 and practicality. In particular, when the number of preferences or 496 capabilities to be expressed by a client are large (such as when many 497 different formats are supported by a user-agent), server-driven 498 negotiation becomes unwieldy, and might not be appropriate. Conversely, 499 when the number of representations to choose from is very large, 500 agent-driven negotiation might not be appropriate. 501 </t> 502 <t> 503 Note that, in all cases, the supplier of representations has the 504 responsibility for determining which representations might be 505 considered to be the "same information". 506 </t> 507 508 <section title="Server-driven Negotiation" anchor="server-driven.negotiation"> 509 <t> 510 If the selection of the best representation for a response is made by 511 an algorithm located at the server, it is called server-driven 512 negotiation. Selection is based on the available representations of 513 the response (the dimensions over which it can vary; e.g., language, 514 content-coding, etc.) and the contents of particular header fields in 515 the request message or on other information pertaining to the request 516 (such as the network address of the client). 517 </t> 518 <t> 519 Server-driven negotiation is advantageous when the algorithm for 520 selecting from among the available representations is difficult to 521 describe to the user agent, or when the server desires to send its 522 "best guess" to the client along with the first response (hoping to 523 avoid the round-trip delay of a subsequent request if the "best 524 guess" is good enough for the user). In order to improve the server's 525 guess, the user agent &MAY; include request header fields (<x:ref>Accept</x:ref>, 526 <x:ref>Accept-Language</x:ref>, <x:ref>Accept-Encoding</x:ref>, etc.) which describe its 527 preferences for such a response. 528 </t> 529 <t> 530 Server-driven negotiation has disadvantages: 531 <list style="numbers"> 532 <t> 533 It is impossible for the server to accurately determine what 534 might be "best" for any given user, since that would require 535 complete knowledge of both the capabilities of the user agent 536 and the intended use for the response (e.g., does the user want 537 to view it on screen or print it on paper?). 538 </t> 539 <t> 540 Having the user agent describe its capabilities in every 541 request can be both very inefficient (given that only a small 542 percentage of responses have multiple representations) and a 543 potential violation of the user's privacy. 544 </t> 545 <t> 546 It complicates the implementation of an origin server and the 547 algorithms for generating responses to a request. 548 </t> 549 <t> 550 It might limit a public cache's ability to use the same response 551 for multiple user's requests. 552 </t> 553 </list> 554 </t> 555 <t> 556 Server-driven negotiation allows the user agent to specify its preferences, 557 but it cannot expect responses to always honor them. For example, the origin 558 server might not implement server-driven negotiation, or it might decide that 559 sending a response that doesn't conform to them is better than sending a <x:ref>406 560 (Not Acceptable)</x:ref> response. 561 </t> 562 <t> 563 HTTP/1.1 includes the following header fields for enabling 564 server-driven negotiation through description of user agent 565 capabilities and user preferences: <x:ref>Accept</x:ref> 566 (<xref target="header.accept"/>), <x:ref>Accept-Charset</x:ref> 567 (<xref target="header.accept-charset"/>), <x:ref>Accept-Encoding</x:ref> 568 (<xref target="header.accept-encoding"/>), <x:ref>Accept-Language</x:ref> 569 (<xref target="header.accept-language"/>), and <x:ref>User-Agent</x:ref> 570 (&header-user-agent;). 571 However, an origin server is not limited to these dimensions and &MAY; vary 572 the response based on any aspect of the request, including aspects 573 of the connection (e.g., IP address) or information within extension 574 header fields not defined by this specification. 575 </t> 576 <x:note> 577 <t> 578 &Note; In practice, <x:ref>User-Agent</x:ref> based negotiation is fragile, 579 because new clients might not be recognized. 580 </t> 581 </x:note> 582 <t> 583 The <x:ref>Vary</x:ref> header field (&header-vary;) can be used to express 584 the parameters the server uses to select a representation that is subject to 585 server-driven negotiation. 586 </t> 587 </section> 588 589 <section title="Agent-driven Negotiation" anchor="agent-driven.negotiation"> 590 <t> 591 With agent-driven negotiation, selection of the best representation 592 for a response is performed by the user agent after receiving an 593 initial response from the origin server. Selection is based on a list 594 of the available representations of the response included within the 595 header fields or body of the initial response, with each 596 representation identified by its own URI. Selection from among the 597 representations can be performed automatically (if the user agent is 598 capable of doing so) or manually by the user selecting from a 599 generated (possibly hypertext) menu. 600 </t> 601 <t> 602 Agent-driven negotiation is advantageous when the response would vary 603 over commonly-used dimensions (such as type, language, or encoding), 604 when the origin server is unable to determine a user agent's 605 capabilities from examining the request, and generally when public 606 caches are used to distribute server load and reduce network usage. 607 </t> 608 <t> 609 Agent-driven negotiation suffers from the disadvantage of needing a 610 second request to obtain the best alternate representation. This 611 second request is only efficient when caching is used. In addition, 612 this specification does not define any mechanism for supporting 613 automatic selection, though it also does not prevent any such 614 mechanism from being developed as an extension and used within 615 HTTP/1.1. 616 </t> 617 <t> 618 This specification defines the <x:ref>300 (Multiple Choices)</x:ref> and 619 <x:ref>406 (Not Acceptable)</x:ref> status codes for enabling agent-driven 620 negotiation when the server is unwilling or unable to provide a varying 621 response using server-driven negotiation. 622 </t> 623 </section> 624 625 <section title="Quality Values" anchor="quality.values"> 626 <x:anchor-alias value="weight"/> 627 <x:anchor-alias value="qvalue"/> 628 <t> 629 Many of the request header fields for server-driven content negotiation 630 use a common parameter, named "q", to assign a relative "weight" to the 631 preference for that associated kind of content. 632 This weight is referred to as a "quality value" (or "qvalue") because 633 the same parameter name is often used within server configurations to 634 assign a weight to the relative quality of the various representations 635 that can be selected for a resource. 636 </t> 637 <t> 638 The weight is normalized to a real number in the range 0 through 1, 639 where 0.001 is the least preferred and 1 is the most preferred; 640 a value of 0 means "not acceptable". If no "q" parameter is present, 641 the default weight is 1. 642 </t> 643 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="weight"/><iref primary="true" item="Grammar" subitem="qvalue"/> 644 <x:ref>weight</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> 645 <x:ref>qvalue</x:ref> = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] ) 646 / ( "1" [ "." 0*3("0") ] ) 647 </artwork></figure> 648 <t> 649 A sender of qvalue &MUST-NOT; generate more than three digits after the 650 decimal point. User configuration of these values ought to be limited in 651 the same fashion. 652 </t> 653 </section> 654 </section> 463 655 </section> 464 656 … … 2688 2880 from the message body by decoding any <x:ref>Transfer-Encoding</x:ref> that 2689 2881 might have been applied to ensure safe and proper transfer of the message. 2690 </t>2691 </section>2692 </section>2693 2694 <section title="Content Negotiation" anchor="content.negotiation">2695 <t>2696 HTTP responses include a representation which contains information for2697 interpretation, whether by a human user or for further processing.2698 Often, the server has different ways of representing the2699 same information; for example, in different formats, languages,2700 or using different character encodings.2701 </t>2702 <t>2703 HTTP clients and their users might have different or variable2704 capabilities, characteristics or preferences which would influence2705 which representation, among those available from the server,2706 would be best for the server to deliver. For this reason, HTTP2707 provides mechanisms for "content negotiation" — a process of2708 allowing selection of a representation of a given resource,2709 when more than one is available.2710 </t>2711 <t>2712 This specification defines two patterns of content negotiation;2713 "server-driven", where the server selects the representation based2714 upon the client's stated preferences, and "agent-driven" negotiation,2715 where the server provides a list of representations for the client to2716 choose from, based upon their metadata. In addition, there are2717 other patterns: some applications use an "active content" pattern,2718 where the server returns active content which runs on the client2719 and, based on client available parameters, selects additional2720 resources to invoke. "Transparent Content Negotiation" (<xref target="RFC2295"/>)2721 has also been proposed.2722 </t>2723 <t>2724 These patterns are all widely used, and have trade-offs in applicability2725 and practicality. In particular, when the number of preferences or2726 capabilities to be expressed by a client are large (such as when many2727 different formats are supported by a user-agent), server-driven2728 negotiation becomes unwieldy, and might not be appropriate. Conversely,2729 when the number of representations to choose from is very large,2730 agent-driven negotiation might not be appropriate.2731 </t>2732 <t>2733 Note that, in all cases, the supplier of representations has the2734 responsibility for determining which representations might be2735 considered to be the "same information".2736 </t>2737 2738 <section title="Server-driven Negotiation" anchor="server-driven.negotiation">2739 <t>2740 If the selection of the best representation for a response is made by2741 an algorithm located at the server, it is called server-driven2742 negotiation. Selection is based on the available representations of2743 the response (the dimensions over which it can vary; e.g., language,2744 content-coding, etc.) and the contents of particular header fields in2745 the request message or on other information pertaining to the request2746 (such as the network address of the client).2747 </t>2748 <t>2749 Server-driven negotiation is advantageous when the algorithm for2750 selecting from among the available representations is difficult to2751 describe to the user agent, or when the server desires to send its2752 "best guess" to the client along with the first response (hoping to2753 avoid the round-trip delay of a subsequent request if the "best2754 guess" is good enough for the user). In order to improve the server's2755 guess, the user agent &MAY; include request header fields (<x:ref>Accept</x:ref>,2756 <x:ref>Accept-Language</x:ref>, <x:ref>Accept-Encoding</x:ref>, etc.) which describe its2757 preferences for such a response.2758 </t>2759 <t>2760 Server-driven negotiation has disadvantages:2761 <list style="numbers">2762 <t>2763 It is impossible for the server to accurately determine what2764 might be "best" for any given user, since that would require2765 complete knowledge of both the capabilities of the user agent2766 and the intended use for the response (e.g., does the user want2767 to view it on screen or print it on paper?).2768 </t>2769 <t>2770 Having the user agent describe its capabilities in every2771 request can be both very inefficient (given that only a small2772 percentage of responses have multiple representations) and a2773 potential violation of the user's privacy.2774 </t>2775 <t>2776 It complicates the implementation of an origin server and the2777 algorithms for generating responses to a request.2778 </t>2779 <t>2780 It might limit a public cache's ability to use the same response2781 for multiple user's requests.2782 </t>2783 </list>2784 </t>2785 <t>2786 Server-driven negotiation allows the user agent to specify its preferences,2787 but it cannot expect responses to always honor them. For example, the origin2788 server might not implement server-driven negotiation, or it might decide that2789 sending a response that doesn't conform to them is better than sending a <x:ref>4062790 (Not Acceptable)</x:ref> response.2791 </t>2792 <t>2793 HTTP/1.1 includes the following header fields for enabling2794 server-driven negotiation through description of user agent2795 capabilities and user preferences: <x:ref>Accept</x:ref>2796 (<xref target="header.accept"/>), <x:ref>Accept-Charset</x:ref>2797 (<xref target="header.accept-charset"/>), <x:ref>Accept-Encoding</x:ref>2798 (<xref target="header.accept-encoding"/>), <x:ref>Accept-Language</x:ref>2799 (<xref target="header.accept-language"/>), and <x:ref>User-Agent</x:ref>2800 (&header-user-agent;).2801 However, an origin server is not limited to these dimensions and &MAY; vary2802 the response based on any aspect of the request, including aspects2803 of the connection (e.g., IP address) or information within extension2804 header fields not defined by this specification.2805 </t>2806 <x:note>2807 <t>2808 &Note; In practice, <x:ref>User-Agent</x:ref> based negotiation is fragile,2809 because new clients might not be recognized.2810 </t>2811 </x:note>2812 <t>2813 The <x:ref>Vary</x:ref> header field (&header-vary;) can be used to express2814 the parameters the server uses to select a representation that is subject to2815 server-driven negotiation.2816 </t>2817 </section>2818 2819 <section title="Agent-driven Negotiation" anchor="agent-driven.negotiation">2820 <t>2821 With agent-driven negotiation, selection of the best representation2822 for a response is performed by the user agent after receiving an2823 initial response from the origin server. Selection is based on a list2824 of the available representations of the response included within the2825 header fields or body of the initial response, with each2826 representation identified by its own URI. Selection from among the2827 representations can be performed automatically (if the user agent is2828 capable of doing so) or manually by the user selecting from a2829 generated (possibly hypertext) menu.2830 </t>2831 <t>2832 Agent-driven negotiation is advantageous when the response would vary2833 over commonly-used dimensions (such as type, language, or encoding),2834 when the origin server is unable to determine a user agent's2835 capabilities from examining the request, and generally when public2836 caches are used to distribute server load and reduce network usage.2837 </t>2838 <t>2839 Agent-driven negotiation suffers from the disadvantage of needing a2840 second request to obtain the best alternate representation. This2841 second request is only efficient when caching is used. In addition,2842 this specification does not define any mechanism for supporting2843 automatic selection, though it also does not prevent any such2844 mechanism from being developed as an extension and used within2845 HTTP/1.1.2846 </t>2847 <t>2848 This specification defines the <x:ref>300 (Multiple Choices)</x:ref> and2849 <x:ref>406 (Not Acceptable)</x:ref> status codes for enabling agent-driven2850 negotiation when the server is unwilling or unable to provide a varying2851 response using server-driven negotiation.2852 </t>2853 </section>2854 2855 <section title="Quality Values" anchor="quality.values">2856 <x:anchor-alias value="weight"/>2857 <x:anchor-alias value="qvalue"/>2858 <t>2859 Many of the request header fields for server-driven content negotiation2860 use a common parameter, named "q", to assign a relative "weight" to the2861 preference for that associated kind of content.2862 This weight is referred to as a "quality value" (or "qvalue") because2863 the same parameter name is often used within server configurations to2864 assign a weight to the relative quality of the various representations2865 that can be selected for a resource.2866 </t>2867 <t>2868 The weight is normalized to a real number in the range 0 through 1,2869 where 0.001 is the least preferred and 1 is the most preferred;2870 a value of 0 means "not acceptable". If no "q" parameter is present,2871 the default weight is 1.2872 </t>2873 <figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="weight"/><iref primary="true" item="Grammar" subitem="qvalue"/>2874 <x:ref>weight</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref>2875 <x:ref>qvalue</x:ref> = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )2876 / ( "1" [ "." 0*3("0") ] )2877 </artwork></figure>2878 <t>2879 A sender of qvalue &MUST-NOT; generate more than three digits after the2880 decimal point. User configuration of these values ought to be limited in2881 the same fashion.2882 2882 </t> 2883 2883 </section>
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