Ignore:
Timestamp:
Aug 25, 2012, 2:08:32 AM (7 years ago)
Author:
fielding@…
Message:

Begin plowing through p2 to properly explain what HTTP semantics are and why.
Rewrite introductory description of methods.
Rewrite definition of "safe" to be more operable and weaken the original
same-origin restrictions to be more consistent with modern UAs.

File:
1 edited

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  • draft-ietf-httpbis/latest/p1-messaging.html

    r1838 r1839  
    449449  }
    450450  @bottom-center {
    451        content: "Expires February 21, 2013";
     451       content: "Expires February 25, 2013";
    452452  }
    453453  @bottom-right {
     
    492492      <meta name="dct.creator" content="Reschke, J. F.">
    493493      <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-p1-messaging-latest">
    494       <meta name="dct.issued" scheme="ISO8601" content="2012-08-20">
     494      <meta name="dct.issued" scheme="ISO8601" content="2012-08-24">
    495495      <meta name="dct.replaces" content="urn:ietf:rfc:2145">
    496496      <meta name="dct.replaces" content="urn:ietf:rfc:2616">
     
    524524            </tr>
    525525            <tr>
    526                <td class="left">Expires: February 21, 2013</td>
     526               <td class="left">Expires: February 25, 2013</td>
    527527               <td class="right">greenbytes</td>
    528528            </tr>
    529529            <tr>
    530530               <td class="left"></td>
    531                <td class="right">August 20, 2012</td>
     531               <td class="right">August 24, 2012</td>
    532532            </tr>
    533533         </tbody>
     
    556556         in progress”.
    557557      </p>
    558       <p>This Internet-Draft will expire on February 21, 2013.</p>
     558      <p>This Internet-Draft will expire on February 25, 2013.</p>
    559559      <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    560560      <p>Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
     
    584584               <li><a href="#rfc.section.2.3">2.3</a>&nbsp;&nbsp;&nbsp;<a href="#intermediaries">Intermediaries</a></li>
    585585               <li><a href="#rfc.section.2.4">2.4</a>&nbsp;&nbsp;&nbsp;<a href="#caches">Caches</a></li>
    586                <li><a href="#rfc.section.2.5">2.5</a>&nbsp;&nbsp;&nbsp;<a href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></li>
     586               <li><a href="#rfc.section.2.5">2.5</a>&nbsp;&nbsp;&nbsp;<a href="#conformance">Conformance and Error Handling</a></li>
    587587               <li><a href="#rfc.section.2.6">2.6</a>&nbsp;&nbsp;&nbsp;<a href="#http.version">Protocol Versioning</a></li>
    588588               <li><a href="#rfc.section.2.7">2.7</a>&nbsp;&nbsp;&nbsp;<a href="#uri">Uniform Resource Identifiers</a><ul>
     
    776776         in this document are to be interpreted as described in <a href="#RFC2119" id="rfc.xref.RFC2119.1"><cite title="Key words for use in RFCs to Indicate Requirement Levels">[RFC2119]</cite></a>.
    777777      </p>
     778      <p id="rfc.section.1.1.p.2">Conformance criteria and considerations regarding error handling are defined in <a href="#conformance" title="Conformance and Error Handling">Section&nbsp;2.5</a>.
     779      </p>
    778780      <div id="rfc.iref.g.1"></div>
    779781      <div id="rfc.iref.g.2"></div>
     
    906908         or an intranet-to-Internet privacy filter. Such transformations are presumed to be desired by the client (or client organization)
    907909         that selected the proxy and are beyond the scope of this specification. However, when a proxy is not intended to transform
    908          a given message, we use the term "<dfn>non-transforming proxy</dfn>" to target requirements that preserve HTTP message semantics. See <a href="p2-semantics.html#status.203" title="203 Non-Authoritative Information">Section 4.4.4</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a> and <a href="p6-cache.html#header.warning" title="Warning">Section 7.6</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a> for status and warning codes related to transformations.
     910         a given message, we use the term "<dfn>non-transforming proxy</dfn>" to target requirements that preserve HTTP message semantics. See <a href="p2-semantics.html#status.203" title="203 Non-Authoritative Information">Section 5.4.4</a> of <a href="#Part2" id="rfc.xref.Part2.3"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a> and <a href="p6-cache.html#header.warning" title="Warning">Section 7.6</a> of <a href="#Part6" id="rfc.xref.Part6.2"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a> for status and warning codes related to transformations.
    909911      </p>
    910912      <p id="rfc.section.2.3.p.7"><span id="rfc.iref.g.13"></span><span id="rfc.iref.r.4"></span>  <span id="rfc.iref.a.1"></span> A "<dfn>gateway</dfn>" (a.k.a., "<dfn>reverse proxy</dfn>") is a receiving agent that acts as a layer above some other server(s) and translates the received requests to the underlying
     
    957959         on.
    958960      </p>
    959       <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a id="intro.conformance.and.error.handling" href="#intro.conformance.and.error.handling">Conformance and Error Handling</a></h2>
     961      <h2 id="rfc.section.2.5"><a href="#rfc.section.2.5">2.5</a>&nbsp;<a id="conformance" href="#conformance">Conformance and Error Handling</a></h2>
    960962      <p id="rfc.section.2.5.p.1">This specification targets conformance criteria according to the role of a participant in HTTP communication. Hence, HTTP
    961963         requirements are placed on senders, recipients, clients, servers, user agents, intermediaries, origin servers, proxies, gateways,
     
    10761078      </p>
    10771079      <p id="rfc.section.2.7.1.p.6">When an "http" URI is used within a context that calls for access to the indicated resource, a client <em class="bcp14">MAY</em> attempt access by resolving the host to an IP address, establishing a TCP connection to that address on the indicated port,
    1078          and sending an HTTP request message (<a href="#http.message" title="Message Format">Section&nbsp;3</a>) containing the URI's identifying data (<a href="#message.routing" title="Message Routing">Section&nbsp;5</a>) to the server. If the server responds to that request with a non-interim HTTP response message, as described in <a href="p2-semantics.html#status.codes" title="Status Codes">Section 4</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>, then that response is considered an authoritative answer to the client's request.
     1080         and sending an HTTP request message (<a href="#http.message" title="Message Format">Section&nbsp;3</a>) containing the URI's identifying data (<a href="#message.routing" title="Message Routing">Section&nbsp;5</a>) to the server. If the server responds to that request with a non-interim HTTP response message, as described in <a href="p2-semantics.html#status.codes" title="Response Status Codes">Section 5</a> of <a href="#Part2" id="rfc.xref.Part2.4"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>, then that response is considered an authoritative answer to the client's request.
    10791081      </p>
    10801082      <p id="rfc.section.2.7.1.p.7">Although HTTP is independent of the transport protocol, the "http" scheme is specific to TCP-based services because the name
     
    11741176      </div>
    11751177      <div id="rfc.figure.u.14"></div><pre class="inline"><span id="rfc.iref.g.29"></span>  <a href="#method" class="smpl">method</a>         = <a href="#rule.token.separators" class="smpl">token</a>
    1176 </pre><p id="rfc.section.3.1.1.p.6">The methods defined by this specification can be found in <a href="p2-semantics.html#methods" title="Methods">Section 2</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>, along with information regarding the HTTP method registry and considerations for defining new methods.
     1178</pre><p id="rfc.section.3.1.1.p.6">The methods defined by this specification can be found in <a href="p2-semantics.html#methods" title="Request Methods">Section 3</a> of <a href="#Part2" id="rfc.xref.Part2.5"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>, along with information regarding the HTTP method registry and considerations for defining new methods.
    11771179      </p>
    11781180      <div id="rfc.iref.r.6"></div>
     
    11871189      </p>
    11881190      <p id="rfc.section.3.1.1.p.10">HTTP does not place a pre-defined limit on the length of a request-line. A server that receives a method longer than any that
    1189          it implements <em class="bcp14">SHOULD</em> respond with either a <a href="p2-semantics.html#status.405" class="smpl">405 (Method Not Allowed)</a>, if it is an origin server, or a <a href="p2-semantics.html#status.501" class="smpl">501 (Not Implemented)</a> status code. A server <em class="bcp14">MUST</em> be prepared to receive URIs of unbounded length and respond with the <a href="p2-semantics.html#status.414" class="smpl">414 (URI Too Long)</a> status code if the received request-target would be longer than the server wishes to handle (see <a href="p2-semantics.html#status.414" title="414 URI Too Long">Section 4.6.12</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>).
     1191         it implements <em class="bcp14">SHOULD</em> respond with either a <a href="p2-semantics.html#status.405" class="smpl">405 (Method Not Allowed)</a>, if it is an origin server, or a <a href="p2-semantics.html#status.501" class="smpl">501 (Not Implemented)</a> status code. A server <em class="bcp14">MUST</em> be prepared to receive URIs of unbounded length and respond with the <a href="p2-semantics.html#status.414" class="smpl">414 (URI Too Long)</a> status code if the received request-target would be longer than the server wishes to handle (see <a href="p2-semantics.html#status.414" title="414 URI Too Long">Section 5.6.12</a> of <a href="#Part2" id="rfc.xref.Part2.6"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>).
    11901192      </p>
    11911193      <p id="rfc.section.3.1.1.p.11">Various ad-hoc limitations on request-line length are found in practice. It is <em class="bcp14">RECOMMENDED</em> that all HTTP senders and recipients support, at a minimum, request-line lengths of up to 8000 octets.
     
    12001202      <p id="rfc.section.3.1.2.p.4">The status-code element is a 3-digit integer code describing the result of the server's attempt to understand and satisfy
    12011203         the client's corresponding request. The rest of the response message is to be interpreted in light of the semantics defined
    1202          for that status code. See <a href="p2-semantics.html#status.codes" title="Status Codes">Section 4</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a> for information about the semantics of status codes, including the classes of status code (indicated by the first digit),
     1204         for that status code. See <a href="p2-semantics.html#status.codes" title="Response Status Codes">Section 5</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a> for information about the semantics of status codes, including the classes of status code (indicated by the first digit),
    12031205         the status codes defined by this specification, considerations for the definition of new status codes, and the IANA registry.
    12041206      </p>
     
    12211223                 ; see <a href="#field.parsing" title="Field Parsing">Section&nbsp;3.2.2</a>
    12221224</pre><p id="rfc.section.3.2.p.3">The field-name token labels the corresponding field-value as having the semantics defined by that header field. For example,
    1223          the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field is defined in <a href="p2-semantics.html#header.date" title="Date">Section 9.10</a> of <a href="#Part2" id="rfc.xref.Part2.8"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a> as containing the origination timestamp for the message in which it appears.
     1225         the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field is defined in <a href="p2-semantics.html#header.date" title="Date">Section 10.10</a> of <a href="#Part2" id="rfc.xref.Part2.8"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a> as containing the origination timestamp for the message in which it appears.
    12241226      </p>
    12251227      <p id="rfc.section.3.2.p.4">HTTP header fields are fully extensible: there is no limit on the introduction of new field names, each presumably defining
     
    12291231         them.
    12301232      </p>
    1231       <p id="rfc.section.3.2.p.5">New HTTP header fields <em class="bcp14">SHOULD</em> be registered with IANA according to the procedures in <a href="p2-semantics.html#considerations.for.creating.header.fields" title="Considerations for Creating Header Fields">Section 3.1</a> of <a href="#Part2" id="rfc.xref.Part2.9"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>. Unrecognized header fields <em class="bcp14">MUST</em> be forwarded by a proxy unless the field-name is listed in the <a href="#header.connection" class="smpl">Connection</a> header field (<a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section&nbsp;6.1</a>) or the proxy is specifically configured to block or otherwise transform such fields. Unrecognized header fields <em class="bcp14">SHOULD</em> be ignored by other recipients.
     1233      <p id="rfc.section.3.2.p.5">New HTTP header fields <em class="bcp14">SHOULD</em> be registered with IANA according to the procedures in <a href="p2-semantics.html#considerations.for.creating.header.fields" title="Considerations for Creating Header Fields">Section 4.5</a> of <a href="#Part2" id="rfc.xref.Part2.9"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>. Unrecognized header fields <em class="bcp14">MUST</em> be forwarded by a proxy unless the field-name is listed in the <a href="#header.connection" class="smpl">Connection</a> header field (<a href="#header.connection" id="rfc.xref.header.connection.3" title="Connection">Section&nbsp;6.1</a>) or the proxy is specifically configured to block or otherwise transform such fields. Unrecognized header fields <em class="bcp14">SHOULD</em> be ignored by other recipients.
    12321234      </p>
    12331235      <p id="rfc.section.3.2.p.6">The order in which header fields with differing field names are received is not significant. However, it is "good practice"
     
    13811383      <p id="rfc.section.3.3.1.p.6">If more than one Transfer-Encoding header field is present in a message, the multiple field-values <em class="bcp14">MUST</em> be combined into one field-value, according to the algorithm defined in <a href="#header.fields" title="Header Fields">Section&nbsp;3.2</a>, before determining the message body length.
    13821384      </p>
    1383       <p id="rfc.section.3.3.1.p.7">Unlike <a href="p2-semantics.html#header.content-encoding" class="smpl">Content-Encoding</a> (<a href="p2-semantics.html#content.codings" title="Content Codings">Section 5.4</a> of <a href="#Part2" id="rfc.xref.Part2.10"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>), Transfer-Encoding is a property of the message, not of the payload, and thus <em class="bcp14">MAY</em> be added or removed by any implementation along the request/response chain. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other header fields not defined by this specification.
     1385      <p id="rfc.section.3.3.1.p.7">Unlike <a href="p2-semantics.html#header.content-encoding" class="smpl">Content-Encoding</a> (<a href="p2-semantics.html#content.codings" title="Content Codings">Section 6.4</a> of <a href="#Part2" id="rfc.xref.Part2.10"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>), Transfer-Encoding is a property of the message, not of the payload, and thus <em class="bcp14">MAY</em> be added or removed by any implementation along the request/response chain. Additional information about the encoding parameters <em class="bcp14">MAY</em> be provided by other header fields not defined by this specification.
    13841386      </p>
    13851387      <p id="rfc.section.3.3.1.p.8">Transfer-Encoding <em class="bcp14">MAY</em> be sent in a response to a HEAD request or in a <a href="p4-conditional.html#status.304" class="smpl">304 (Not Modified)</a> response (<a href="p4-conditional.html#status.304" title="304 Not Modified">Section 4.1</a> of <a href="#Part4" id="rfc.xref.Part4.2"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>) to a GET request, neither of which includes a message body, to indicate that the origin server would have applied a transfer
     
    16611663         that a client can be assured of buffering the entire response.
    16621664      </p>
    1663       <p id="rfc.section.4.3.p.7">When multiple transfer-codings are acceptable, the client <em class="bcp14">MAY</em> rank the codings by preference using a "q" parameter (similar to the qvalues used in content negotiation fields, <a href="p2-semantics.html#quality.values" title="Quality Values">Section 8.3</a> of <a href="#Part2" id="rfc.xref.Part2.11"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). The rank value is a real number in the range 0 through 1, where 0.001 is the least preferred and 1 is the most preferred;
     1665      <p id="rfc.section.4.3.p.7">When multiple transfer-codings are acceptable, the client <em class="bcp14">MAY</em> rank the codings by preference using a "q" parameter (similar to the qvalues used in content negotiation fields, <a href="p2-semantics.html#quality.values" title="Quality Values">Section 9.3</a> of <a href="#Part2" id="rfc.xref.Part2.11"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). The rank value is a real number in the range 0 through 1, where 0.001 is the least preferred and 1 is the most preferred;
    16641666         a value of 0 means "not acceptable".
    16651667      </p>
     
    16851687         for client-side processing (<a href="#RFC3986" id="rfc.xref.RFC3986.18"><cite title="Uniform Resource Identifier (URI): Generic Syntax">[RFC3986]</cite></a>, <a href="http://tools.ietf.org/html/rfc3986#section-3.5">Section 3.5</a>).
    16861688      </p>
    1687       <p id="rfc.section.5.1.p.3">HTTP intermediaries obtain the request semantics and target URI from the request-line of an incoming request message.</p>
    16881689      <h2 id="rfc.section.5.2"><a href="#rfc.section.5.2">5.2</a>&nbsp;<a id="connecting.inbound" href="#connecting.inbound">Connecting Inbound</a></h2>
    16891690      <p id="rfc.section.5.2.p.1">Once the target URI is determined, a client needs to decide whether a network request is necessary to accomplish the desired
     
    17421743      </p>
    17431744      <div id="authority-form">
    1744          <p id="rfc.section.5.3.p.13"><span id="rfc.iref.a.3"></span> The authority-form of request-target is only used for CONNECT requests (<a href="p2-semantics.html#CONNECT" title="CONNECT">Section 2.3.8</a> of <a href="#Part2" id="rfc.xref.Part2.13"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). When making a CONNECT request to establish a tunnel through one or more proxies, a client <em class="bcp14">MUST</em> send only the target URI's authority component (excluding any userinfo) as the request-target. For example,
     1745         <p id="rfc.section.5.3.p.13"><span id="rfc.iref.a.3"></span> The authority-form of request-target is only used for CONNECT requests (<a href="p2-semantics.html#CONNECT" title="CONNECT">Section 3.3.8</a> of <a href="#Part2" id="rfc.xref.Part2.13"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). When making a CONNECT request to establish a tunnel through one or more proxies, a client <em class="bcp14">MUST</em> send only the target URI's authority component (excluding any userinfo) as the request-target. For example,
    17451746         </p>
    17461747      </div>
    17471748      <div id="rfc.figure.u.41"></div><pre class="text2">CONNECT www.example.com:80 HTTP/1.1
    17481749</pre><div id="asterisk-form">
    1749          <p id="rfc.section.5.3.p.15"><span id="rfc.iref.a.4"></span> The asterisk-form of request-target is only used for a server-wide OPTIONS request (<a href="p2-semantics.html#OPTIONS" title="OPTIONS">Section 2.3.1</a> of <a href="#Part2" id="rfc.xref.Part2.14"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). When a client wishes to request OPTIONS for the server as a whole, as opposed to a specific named resource of that server,
     1750         <p id="rfc.section.5.3.p.15"><span id="rfc.iref.a.4"></span> The asterisk-form of request-target is only used for a server-wide OPTIONS request (<a href="p2-semantics.html#OPTIONS" title="OPTIONS">Section 3.3.1</a> of <a href="#Part2" id="rfc.xref.Part2.14"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). When a client wishes to request OPTIONS for the server as a whole, as opposed to a specific named resource of that server,
    17501751            the client <em class="bcp14">MUST</em> send only "*" (%x2A) as the request-target. For example,
    17511752         </p>
     
    18931894      </p>
    18941895      <ul>
    1895          <li><a href="p2-semantics.html#header.allow" class="smpl">Allow</a> (<a href="p2-semantics.html#header.allow" title="Allow">Section 9.5</a> of <a href="#Part2" id="rfc.xref.Part2.16"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
    1896          </li>
    1897          <li><a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> (<a href="p2-semantics.html#header.content-location" title="Content-Location">Section 9.8</a> of <a href="#Part2" id="rfc.xref.Part2.17"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
     1896         <li><a href="p2-semantics.html#header.allow" class="smpl">Allow</a> (<a href="p2-semantics.html#header.allow" title="Allow">Section 10.5</a> of <a href="#Part2" id="rfc.xref.Part2.16"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
     1897         </li>
     1898         <li><a href="p2-semantics.html#header.content-location" class="smpl">Content-Location</a> (<a href="p2-semantics.html#header.content-location" title="Content-Location">Section 10.8</a> of <a href="#Part2" id="rfc.xref.Part2.17"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
    18981899         </li>
    18991900         <li>Content-MD5 (<a href="http://tools.ietf.org/html/rfc2616#section-14.15">Section 14.15</a> of <a href="#RFC2616" id="rfc.xref.RFC2616.3"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2616]</cite></a>)
     
    19031904         <li><a href="p4-conditional.html#header.last-modified" class="smpl">Last-Modified</a> (<a href="p4-conditional.html#header.last-modified" title="Last-Modified">Section 2.2</a> of <a href="#Part4" id="rfc.xref.Part4.5"><cite title="HTTP/1.1, part 4: Conditional Requests">[Part4]</cite></a>)
    19041905         </li>
    1905          <li><a href="p2-semantics.html#header.server" class="smpl">Server</a> (<a href="p2-semantics.html#header.server" title="Server">Section 9.17</a> of <a href="#Part2" id="rfc.xref.Part2.18"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
     1906         <li><a href="p2-semantics.html#header.server" class="smpl">Server</a> (<a href="p2-semantics.html#header.server" title="Server">Section 10.17</a> of <a href="#Part2" id="rfc.xref.Part2.18"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
    19061907         </li>
    19071908      </ul>
     
    19111912      </p>
    19121913      <ul>
    1913          <li><a href="p2-semantics.html#header.content-encoding" class="smpl">Content-Encoding</a> (<a href="p2-semantics.html#header.content-encoding" title="Content-Encoding">Section 9.6</a> of <a href="#Part2" id="rfc.xref.Part2.19"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
     1914         <li><a href="p2-semantics.html#header.content-encoding" class="smpl">Content-Encoding</a> (<a href="p2-semantics.html#header.content-encoding" title="Content-Encoding">Section 10.6</a> of <a href="#Part2" id="rfc.xref.Part2.19"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
    19141915         </li>
    19151916         <li><a href="p5-range.html#header.content-range" class="smpl">Content-Range</a> (<a href="p5-range.html#header.content-range" title="Content-Range">Section 5.2</a> of <a href="#Part5" id="rfc.xref.Part5.2"><cite title="HTTP/1.1, part 5: Range Requests">[Part5]</cite></a>)
    19161917         </li>
    1917          <li><a href="p2-semantics.html#header.content-type" class="smpl">Content-Type</a> (<a href="p2-semantics.html#header.content-type" title="Content-Type">Section 9.9</a> of <a href="#Part2" id="rfc.xref.Part2.20"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
     1918         <li><a href="p2-semantics.html#header.content-type" class="smpl">Content-Type</a> (<a href="p2-semantics.html#header.content-type" title="Content-Type">Section 10.9</a> of <a href="#Part2" id="rfc.xref.Part2.20"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>)
    19181919         </li>
    19191920      </ul>
     
    19281929      <p id="rfc.section.5.9.p.1">HTTP does not include a request identifier for associating a given request message with its corresponding one or more response
    19291930         messages. Hence, it relies on the order of response arrival to correspond exactly to the order in which requests are made
    1930          on the same connection. More than one response message per request only occurs when one or more informational responses (<a href="p2-semantics.html#status.1xx" class="smpl">1xx</a>, see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 4.3</a> of <a href="#Part2" id="rfc.xref.Part2.21"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) precede a final response to the same request.
     1931         on the same connection. More than one response message per request only occurs when one or more informational responses (<a href="p2-semantics.html#status.1xx" class="smpl">1xx</a>, see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 5.3</a> of <a href="#Part2" id="rfc.xref.Part2.21"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) precede a final response to the same request.
    19311932      </p>
    19321933      <p id="rfc.section.5.9.p.2">A client that uses persistent connections and sends more than one request per connection <em class="bcp14">MUST</em> maintain a list of outstanding requests in the order sent on that connection and <em class="bcp14">MUST</em> associate each received response message to the highest ordered request that has not yet received a final (non-<a href="p2-semantics.html#status.1xx" class="smpl">1xx</a>) response.
     
    20372038      <p id="rfc.section.6.2.2.1.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses.
    20382039      </p>
    2039       <p id="rfc.section.6.2.2.1.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent request methods or non-idempotent sequences of request methods (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 2.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.22"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to
     2040      <p id="rfc.section.6.2.2.1.p.3">Clients <em class="bcp14">SHOULD NOT</em> pipeline requests using non-idempotent request methods or non-idempotent sequences of request methods (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 3.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.22"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to
    20402041         send a non-idempotent request <em class="bcp14">SHOULD</em> wait to send that request until it has received the response status line for the previous request.
    20412042      </p>
    20422043      <h4 id="rfc.section.6.2.2.2"><a href="#rfc.section.6.2.2.2">6.2.2.2</a>&nbsp;<a id="persistent.retrying.requests" href="#persistent.retrying.requests">Retrying Requests</a></h4>
    20432044      <p id="rfc.section.6.2.2.2.p.1">Senders can close the transport connection at any time. Therefore, clients, servers, and proxies <em class="bcp14">MUST</em> be able to recover from asynchronous close events. Client software <em class="bcp14">MAY</em> reopen the transport connection and retransmit the aborted sequence of requests without user interaction so long as the request
    2044          sequence is idempotent (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 2.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.23"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). Non-idempotent request methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding
     2045         sequence is idempotent (see <a href="p2-semantics.html#idempotent.methods" title="Idempotent Methods">Section 3.1.2</a> of <a href="#Part2" id="rfc.xref.Part2.23"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>). Non-idempotent request methods or sequences <em class="bcp14">MUST NOT</em> be automatically retried, although user agents <em class="bcp14">MAY</em> offer a human operator the choice of retrying the request(s). Confirmation by user-agent software with semantic understanding
    20452046         of the application <em class="bcp14">MAY</em> substitute for user confirmation. The automatic retry <em class="bcp14">SHOULD NOT</em> be repeated if the second sequence of requests fails.
    20462047      </p>
     
    20932094      </p>
    20942095      <h2 id="rfc.section.6.3"><a href="#rfc.section.6.3">6.3</a>&nbsp;<a id="use.of.the.100.status" href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h2>
    2095       <p id="rfc.section.6.3.p.1">The purpose of the <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> status code (see <a href="p2-semantics.html#status.100" title="100 Continue">Section 4.3.1</a> of <a href="#Part2" id="rfc.xref.Part2.24"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing
     2096      <p id="rfc.section.6.3.p.1">The purpose of the <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> status code (see <a href="p2-semantics.html#status.100" title="100 Continue">Section 5.3.1</a> of <a href="#Part2" id="rfc.xref.Part2.24"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) is to allow a client that is sending a request message with a request body to determine if the origin server is willing
    20962097         to accept the request (based on the request header fields) before the client sends the request body. In some cases, it might
    20972098         either be inappropriate or highly inefficient for the client to send the body if the server will reject the message without
     
    21002101      <p id="rfc.section.6.3.p.2">Requirements for HTTP/1.1 clients: </p>
    21012102      <ul>
    2102          <li>If a client will wait for a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response before sending the request body, it <em class="bcp14">MUST</em> send an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 9.11</a> of <a href="#Part2" id="rfc.xref.Part2.25"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) with the "100-continue" expectation.
     2103         <li>If a client will wait for a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response before sending the request body, it <em class="bcp14">MUST</em> send an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 10.11</a> of <a href="#Part2" id="rfc.xref.Part2.25"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) with the "100-continue" expectation.
    21032104         </li>
    21042105         <li>A client <em class="bcp14">MUST NOT</em> send an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field with the "100-continue" expectation if it does not intend to send a request body.
     
    21382139         <li>Proxies <em class="bcp14">SHOULD</em> maintain a record of the HTTP version numbers received from recently-referenced next-hop servers.
    21392140         </li>
    2140          <li>A proxy <em class="bcp14">MUST NOT</em> forward a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response if the request message was received from an HTTP/1.0 (or earlier) client and did not include an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding of <a href="p2-semantics.html#status.1xx" class="smpl">1xx</a> responses (see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 4.3</a> of <a href="#Part2" id="rfc.xref.Part2.26"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>).
     2141         <li>A proxy <em class="bcp14">MUST NOT</em> forward a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response if the request message was received from an HTTP/1.0 (or earlier) client and did not include an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field with the "100-continue" expectation. This requirement overrides the general rule for forwarding of <a href="p2-semantics.html#status.1xx" class="smpl">1xx</a> responses (see <a href="p2-semantics.html#status.1xx" title="Informational 1xx">Section 5.3</a> of <a href="#Part2" id="rfc.xref.Part2.26"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>).
    21412142         </li>
    21422143      </ul>
     
    21692170      </p>
    21702171      <p id="rfc.section.6.4.p.8">The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it
    2171          is more appropriate to use a <a href="p2-semantics.html#status.3xx" class="smpl">3xx (Redirection)</a> response (<a href="p2-semantics.html#status.3xx" title="Redirection 3xx">Section 4.5</a> of <a href="#Part2" id="rfc.xref.Part2.27"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>).
     2172         is more appropriate to use a <a href="p2-semantics.html#status.3xx" class="smpl">3xx (Redirection)</a> response (<a href="p2-semantics.html#status.3xx" title="Redirection 3xx">Section 5.5</a> of <a href="#Part2" id="rfc.xref.Part2.27"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>).
    21722173      </p>
    21732174      <p id="rfc.section.6.4.p.9">Servers <em class="bcp14">MUST</em> include the "Upgrade" header field in <a href="p2-semantics.html#status.101" class="smpl">101 (Switching
     
    24332434         <li>Pointer to specification text</li>
    24342435      </ul>
    2435       <p id="rfc.section.7.4.p.3">Names of transfer codings <em class="bcp14">MUST NOT</em> overlap with names of content codings (<a href="p2-semantics.html#content.codings" title="Content Codings">Section 5.4</a> of <a href="#Part2" id="rfc.xref.Part2.28"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) unless the encoding transformation is identical, as is the case for the compression codings defined in <a href="#compression.codings" title="Compression Codings">Section&nbsp;4.2</a>.
     2436      <p id="rfc.section.7.4.p.3">Names of transfer codings <em class="bcp14">MUST NOT</em> overlap with names of content codings (<a href="p2-semantics.html#content.codings" title="Content Codings">Section 6.4</a> of <a href="#Part2" id="rfc.xref.Part2.28"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) unless the encoding transformation is identical, as is the case for the compression codings defined in <a href="#compression.codings" title="Compression Codings">Section&nbsp;4.2</a>.
    24362437      </p>
    24372438      <p id="rfc.section.7.4.p.4">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.RFC5226.1"><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 transfer coding defined in this section. Use of program names for the identification of encoding
     
    25892590         that most implementations will choose substantially higher limits.
    25902591      </p>
    2591       <p id="rfc.section.8.6.p.3">This specification also provides a way for servers to reject messages that have request-targets that are too long (<a href="p2-semantics.html#status.414" title="414 URI Too Long">Section 4.6.12</a> of <a href="#Part2" id="rfc.xref.Part2.29"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) or request entities that are too large (<a href="p2-semantics.html#status.4xx" title="Client Error 4xx">Section 4.6</a> of <a href="#Part2" id="rfc.xref.Part2.30"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>).
     2592      <p id="rfc.section.8.6.p.3">This specification also provides a way for servers to reject messages that have request-targets that are too long (<a href="p2-semantics.html#status.414" title="414 URI Too Long">Section 5.6.12</a> of <a href="#Part2" id="rfc.xref.Part2.29"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>) or request entities that are too large (<a href="p2-semantics.html#status.4xx" title="Client Error 4xx">Section 5.6</a> of <a href="#Part2" id="rfc.xref.Part2.30"><cite title="HTTP/1.1, part 2: Semantics and Payloads">[Part2]</cite></a>).
    25922593      </p>
    25932594      <p id="rfc.section.8.6.p.4">Other fields (including but not limited to request methods, response status phrases, header field-names, and body chunks) <em class="bcp14">SHOULD</em> be limited by implementations carefully, so as to not impede interoperability.
     
    36653666            <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul>
    36663667                  <li><em>Part2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.1">1</a>, <a href="#rfc.xref.Part2.2">2.1</a>, <a href="#rfc.xref.Part2.3">2.3</a>, <a href="#rfc.xref.Part2.4">2.7.1</a>, <a href="#rfc.xref.Part2.5">3.1.1</a>, <a href="#rfc.xref.Part2.6">3.1.1</a>, <a href="#rfc.xref.Part2.7">3.1.2</a>, <a href="#rfc.xref.Part2.8">3.2</a>, <a href="#rfc.xref.Part2.9">3.2</a>, <a href="#rfc.xref.Part2.10">3.3.1</a>, <a href="#rfc.xref.Part2.11">4.3</a>, <a href="#rfc.xref.Part2.12">5.1</a>, <a href="#rfc.xref.Part2.13">5.3</a>, <a href="#rfc.xref.Part2.14">5.3</a>, <a href="#rfc.xref.Part2.15">5.8</a>, <a href="#rfc.xref.Part2.16">5.8</a>, <a href="#rfc.xref.Part2.17">5.8</a>, <a href="#rfc.xref.Part2.18">5.8</a>, <a href="#rfc.xref.Part2.19">5.8</a>, <a href="#rfc.xref.Part2.20">5.8</a>, <a href="#rfc.xref.Part2.21">5.9</a>, <a href="#rfc.xref.Part2.22">6.2.2.1</a>, <a href="#rfc.xref.Part2.23">6.2.2.2</a>, <a href="#rfc.xref.Part2.24">6.3</a>, <a href="#rfc.xref.Part2.25">6.3</a>, <a href="#rfc.xref.Part2.26">6.3</a>, <a href="#rfc.xref.Part2.27">6.4</a>, <a href="#rfc.xref.Part2.28">7.4</a>, <a href="#rfc.xref.Part2.29">8.6</a>, <a href="#rfc.xref.Part2.30">8.6</a>, <a href="#Part2"><b>10.1</b></a><ul>
    3667                         <li><em>Section 2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.5">3.1.1</a></li>
    3668                         <li><em>Section 2.1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.22">6.2.2.1</a>, <a href="#rfc.xref.Part2.23">6.2.2.2</a></li>
    3669                         <li><em>Section 2.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.14">5.3</a></li>
    3670                         <li><em>Section 2.3.8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.13">5.3</a></li>
    3671                         <li><em>Section 3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.9">3.2</a></li>
    3672                         <li><em>Section 4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.4">2.7.1</a>, <a href="#rfc.xref.Part2.7">3.1.2</a></li>
    3673                         <li><em>Section 4.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.21">5.9</a>, <a href="#rfc.xref.Part2.26">6.3</a></li>
    3674                         <li><em>Section 4.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.24">6.3</a></li>
    3675                         <li><em>Section 4.4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.3">2.3</a></li>
    3676                         <li><em>Section 4.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.27">6.4</a></li>
    3677                         <li><em>Section 4.6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.30">8.6</a></li>
    3678                         <li><em>Section 4.6.12</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.6">3.1.1</a>, <a href="#rfc.xref.Part2.29">8.6</a></li>
    3679                         <li><em>Section 5.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.10">3.3.1</a>, <a href="#rfc.xref.Part2.28">7.4</a></li>
    3680                         <li><em>Section 8.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.11">4.3</a></li>
    3681                         <li><em>Section 9.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.16">5.8</a></li>
    3682                         <li><em>Section 9.6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.19">5.8</a></li>
    3683                         <li><em>Section 9.8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.17">5.8</a></li>
    3684                         <li><em>Section 9.9</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.20">5.8</a></li>
    3685                         <li><em>Section 9.10</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.8">3.2</a></li>
    3686                         <li><em>Section 9.11</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.25">6.3</a></li>
    3687                         <li><em>Section 9.17</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.18">5.8</a></li>
     3668                        <li><em>Section 3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.5">3.1.1</a></li>
     3669                        <li><em>Section 3.1.2</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.22">6.2.2.1</a>, <a href="#rfc.xref.Part2.23">6.2.2.2</a></li>
     3670                        <li><em>Section 3.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.14">5.3</a></li>
     3671                        <li><em>Section 3.3.8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.13">5.3</a></li>
     3672                        <li><em>Section 4.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.9">3.2</a></li>
     3673                        <li><em>Section 5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.4">2.7.1</a>, <a href="#rfc.xref.Part2.7">3.1.2</a></li>
     3674                        <li><em>Section 5.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.21">5.9</a>, <a href="#rfc.xref.Part2.26">6.3</a></li>
     3675                        <li><em>Section 5.3.1</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.24">6.3</a></li>
     3676                        <li><em>Section 5.4.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.3">2.3</a></li>
     3677                        <li><em>Section 5.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.27">6.4</a></li>
     3678                        <li><em>Section 5.6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.30">8.6</a></li>
     3679                        <li><em>Section 5.6.12</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.6">3.1.1</a>, <a href="#rfc.xref.Part2.29">8.6</a></li>
     3680                        <li><em>Section 6.4</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.10">3.3.1</a>, <a href="#rfc.xref.Part2.28">7.4</a></li>
     3681                        <li><em>Section 9.3</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.11">4.3</a></li>
     3682                        <li><em>Section 10.5</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.16">5.8</a></li>
     3683                        <li><em>Section 10.6</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.19">5.8</a></li>
     3684                        <li><em>Section 10.8</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.17">5.8</a></li>
     3685                        <li><em>Section 10.9</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.20">5.8</a></li>
     3686                        <li><em>Section 10.10</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.8">3.2</a></li>
     3687                        <li><em>Section 10.11</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.25">6.3</a></li>
     3688                        <li><em>Section 10.17</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.18">5.8</a></li>
    36883689                        <li><em>Appendix A</em>&nbsp;&nbsp;<a href="#rfc.xref.Part2.2">2.1</a></li>
    36893690                     </ul>
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