Changeset 1740 for draft-ietf-httpbis/latest/p1-messaging.html
- Timestamp:
- 08/07/12 18:15:03 (9 years ago)
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draft-ietf-httpbis/latest/p1-messaging.html
r1737 r1740 961 961 <p id="rfc.section.2.5.p.4">Unless noted otherwise, recipients <em class="bcp14">MUST</em> be able to parse all protocol elements matching the ABNF rules defined for them and <em class="bcp14">MAY</em> attempt to recover a usable protocol element from an invalid construct. HTTP does not define specific error handling mechanisms 962 962 except when they have a direct impact on security, since different applications of the protocol require different error handling 963 strategies. For example, a Web browser might wish to transparently recover from a response where the Location header field964 doesn't parse according to the ABNF, whereas a systems control client might consider any form of error recoveryto be dangerous.963 strategies. For example, a Web browser might wish to transparently recover from a response where the <a href="p2-semantics.html#header.location" class="smpl">Location</a> header field doesn't parse according to the ABNF, whereas a systems control client might consider any form of error recovery 964 to be dangerous. 965 965 </p> 966 966 <h2 id="rfc.section.2.6"><a href="#rfc.section.2.6">2.6</a> <a id="http.version" href="#http.version">Protocol Versioning</a></h2> … … 1001 1001 </p> 1002 1002 <p id="rfc.section.2.6.p.10">An HTTP client <em class="bcp14">MAY</em> send a lower request version if it is known that the server incorrectly implements the HTTP specification, but only after 1003 the client has attempted at least one normal request and determined from the response status or header fields (e.g., Server) 1004 that the server improperly handles higher request versions. 1003 the client has attempted at least one normal request and determined from the response status or header fields (e.g., <a href="p2-semantics.html#header.server" class="smpl">Server</a>) that the server improperly handles higher request versions. 1005 1004 </p> 1006 1005 <p id="rfc.section.2.6.p.11">An HTTP server <em class="bcp14">SHOULD</em> send a response version equal to the highest version to which the server is conformant and whose major version is less than … … 1011 1010 specification and is incapable of correctly processing later version responses, such as when a client fails to parse the version 1012 1011 number correctly or when an intermediary is known to blindly forward the HTTP-version even when it doesn't conform to the 1013 given minor version of the protocol. Such protocol downgrades <em class="bcp14">SHOULD NOT</em> be performed unless triggered by specific client attributes, such as when one or more of the request header fields (e.g., 1014 User-Agent) uniquely match the values sent by a client known to be in error. 1012 given minor version of the protocol. Such protocol downgrades <em class="bcp14">SHOULD NOT</em> be performed unless triggered by specific client attributes, such as when one or more of the request header fields (e.g., <a href="p2-semantics.html#header.user-agent" class="smpl">User-Agent</a>) uniquely match the values sent by a client known to be in error. 1015 1013 </p> 1016 1014 <p id="rfc.section.2.6.p.13">The intention of HTTP's versioning design is that the major number will only be incremented if an incompatible message syntax … … 1209 1207 ; see <a href="#field.parsing" title="Field Parsing">Section 3.2.2</a> 1210 1208 </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, 1211 the Dateheader field is defined in <a href="p2-semantics.html#header.date" title="Date">Section 9.10</a> of <a href="#Part2" id="rfc.xref.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a> as containing the origination timestamp for the message in which it appears.1209 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.Part2.7"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a> as containing the origination timestamp for the message in which it appears. 1212 1210 </p> 1213 1211 <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 … … 1220 1218 </p> 1221 1219 <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" 1222 to send header fields that contain control data first, such as Host on requests and Date on responses, so that implementations 1223 can decide when not to handle a message as early as possible. A server <em class="bcp14">MUST</em> wait until the entire header section is received before interpreting a request message, since later header fields might include 1220 to send header fields that contain control data first, such as <a href="#header.host" class="smpl">Host</a> on requests and <a href="p2-semantics.html#header.date" class="smpl">Date</a> on responses, so that implementations can decide when not to handle a message as early as possible. A server <em class="bcp14">MUST</em> wait until the entire header section is received before interpreting a request message, since later header fields might include 1224 1221 conditionals, authentication credentials, or deliberately misleading duplicate header fields that would impact request processing. 1225 1222 </p> … … 1402 1399 <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 3.2</a>, before determining the message body length. 1403 1400 </p> 1404 <p id="rfc.section.3.3.1.p.7">Unlike Content-Encoding(<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: Message Semantics, Payload and Content Negotiation">[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.1401 <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: Message Semantics, Payload and Content Negotiation">[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. 1405 1402 </p> 1406 1403 <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 … … 1950 1947 </li> 1951 1948 </ul> 1952 <p id="rfc.section.5.6.2.p.4">but it <em class="bcp14">MAY</em> add any of these fields if not already present. If an <a href="p6-cache.html#header.expires" class="smpl">Expires</a> header field is added, it <em class="bcp14">MUST</em> be given a field -value identical to that of the Dateheader field in that response.1949 <p id="rfc.section.5.6.2.p.4">but it <em class="bcp14">MAY</em> add any of these fields if not already present. If an <a href="p6-cache.html#header.expires" class="smpl">Expires</a> header field is added, it <em class="bcp14">MUST</em> be given a field value identical to that of the <a href="p2-semantics.html#header.date" class="smpl">Date</a> header field in that response. 1953 1950 </p> 1954 1951 <p id="rfc.section.5.6.2.p.5">A proxy <em class="bcp14">MUST NOT</em> modify or add any of the following fields in a message that contains the no-transform cache-control directive, or in any request: 1955 1952 </p> 1956 1953 <ul> 1957 <li>Content-Encoding</li> 1958 <li>Content-Range</li> 1959 <li>Content-Type</li> 1954 <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.Part2.15"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) 1955 </li> 1956 <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.Part5.1"><cite title="HTTP/1.1, part 5: Range Requests and Partial Responses">[Part5]</cite></a>) 1957 </li> 1958 <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.Part2.16"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) 1959 </li> 1960 1960 </ul> 1961 1961 <p id="rfc.section.5.6.2.p.6">A transforming proxy <em class="bcp14">MAY</em> modify or add these fields to a message that does not include no-transform, but if it does so, it <em class="bcp14">MUST</em> add a Warning 214 (Transformation applied) if one does not already appear in the message (see <a href="p6-cache.html#header.warning" title="Warning">Section 3.6</a> of <a href="#Part6" id="rfc.xref.Part6.7"><cite title="HTTP/1.1, part 6: Caching">[Part6]</cite></a>). … … 1966 1966 </p> 1967 1967 </div> 1968 <p id="rfc.section.5.6.2.p.8">A non-transforming proxy <em class="bcp14">MUST</em> preserve the message payload (<a href="#Part2" id="rfc.xref.Part2.1 5"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>), though it <em class="bcp14">MAY</em> change the message body through application or removal of a transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section 4</a>).1968 <p id="rfc.section.5.6.2.p.8">A non-transforming proxy <em class="bcp14">MUST</em> preserve the message payload (<a href="#Part2" id="rfc.xref.Part2.17"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>), though it <em class="bcp14">MAY</em> change the message body through application or removal of a transfer-coding (<a href="#transfer.codings" title="Transfer Codings">Section 4</a>). 1969 1969 </p> 1970 1970 <h2 id="rfc.section.5.7"><a href="#rfc.section.5.7">5.7</a> <a id="associating.response.to.request" href="#associating.response.to.request">Associating a Response to a Request</a></h2> 1971 1971 <p id="rfc.section.5.7.p.1">HTTP does not include a request identifier for associating a given request message with its corresponding one or more response 1972 1972 messages. Hence, it relies on the order of response arrival to correspond exactly to the order in which requests are made 1973 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.Part2.1 6"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) precede a final response to the same request.1973 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.Part2.18"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) precede a final response to the same request. 1974 1974 </p> 1975 1975 <p id="rfc.section.5.7.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. … … 2042 2042 <p id="rfc.section.6.2.p.5">Multiple Via field values represent each proxy or gateway that has forwarded the message. Each recipient <em class="bcp14">MUST</em> append its information such that the end result is ordered according to the sequence of forwarding applications. 2043 2043 </p> 2044 <p id="rfc.section.6.2.p.6">Comments <em class="bcp14">MAY</em> be used in the Via header field to identify the software of each recipient, analogous to the User-Agent and Server header 2045 fields. However, all comments in the Via field are optional and <em class="bcp14">MAY</em> be removed by any recipient prior to forwarding the message. 2044 <p id="rfc.section.6.2.p.6">Comments <em class="bcp14">MAY</em> be used in the Via header field to identify the software of each recipient, analogous to the <a href="p2-semantics.html#header.user-agent" class="smpl">User-Agent</a> and <a href="p2-semantics.html#header.server" class="smpl">Server</a> header fields. However, all comments in the Via field are optional and <em class="bcp14">MAY</em> be removed by any recipient prior to forwarding the message. 2046 2045 </p> 2047 2046 <p id="rfc.section.6.2.p.7">For example, a request message could be sent from an HTTP/1.0 user agent to an internal proxy code-named "fred", which uses … … 2119 2118 <p id="rfc.section.6.3.2.2.p.2">Clients which assume persistent connections and pipeline immediately after connection establishment <em class="bcp14">SHOULD</em> be prepared to retry their connection if the first pipelined attempt fails. If a client does such a retry, it <em class="bcp14">MUST NOT</em> pipeline before it knows the connection is persistent. Clients <em class="bcp14">MUST</em> also be prepared to resend their requests if the server closes the connection before sending all of the corresponding responses. 2120 2119 </p> 2121 <p id="rfc.section.6.3.2.2.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.Part2.1 7"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to2120 <p id="rfc.section.6.3.2.2.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.Part2.19"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>). Otherwise, a premature termination of the transport connection could lead to indeterminate results. A client wishing to 2122 2121 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. 2123 2122 </p> … … 2149 2148 <h3 id="rfc.section.6.3.4"><a href="#rfc.section.6.3.4">6.3.4</a> <a id="persistent.retrying.requests" href="#persistent.retrying.requests">Retrying Requests</a></h3> 2150 2149 <p id="rfc.section.6.3.4.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 2151 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. 18"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[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 understanding2150 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.Part2.20"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[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 2152 2151 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. 2153 2152 </p> … … 2162 2161 </p> 2163 2162 <h3 id="rfc.section.6.4.3"><a href="#rfc.section.6.4.3">6.4.3</a> <a id="use.of.the.100.status" href="#use.of.the.100.status">Use of the 100 (Continue) Status</a></h3> 2164 <p id="rfc.section.6.4.3.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. 19"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[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 willing2163 <p id="rfc.section.6.4.3.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.Part2.21"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[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 2165 2164 to accept the request (based on the request header fields) before the client sends the request body. In some cases, it might 2166 2165 either be inappropriate or highly inefficient for the client to send the body if the server will reject the message without … … 2169 2168 <p id="rfc.section.6.4.3.p.2">Requirements for HTTP/1.1 clients: </p> 2170 2169 <ul> 2171 <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 Expect header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 9.11</a> of <a href="#Part2" id="rfc.xref.Part2.20"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) with the "100-continue" expectation.2172 </li> 2173 <li>A client <em class="bcp14">MUST NOT</em> send an Expect header field (<a href="p2-semantics.html#header.expect" title="Expect">Section 9.11</a> of <a href="#Part2" id="rfc.xref.Part2.21"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>)with the "100-continue" expectation if it does not intend to send a request body.2170 <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.Part2.22"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) with the "100-continue" expectation. 2171 </li> 2172 <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. 2174 2173 </li> 2175 2174 </ul> … … 2180 2179 <p id="rfc.section.6.4.3.p.4">Requirements for HTTP/1.1 origin servers: </p> 2181 2180 <ul> 2182 <li>Upon receiving a request which includes an Expectheader field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> status code and continue to read from the input stream, or respond with a final status code. The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the request method if it returns a final status code.2183 </li> 2184 <li>An origin server <em class="bcp14">SHOULD NOT</em> send a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response if the request message does not include an Expectheader field with the "100-continue" expectation, and <em class="bcp14">MUST NOT</em> send a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this rule: for compatibility2181 <li>Upon receiving a request which includes an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field with the "100-continue" expectation, an origin server <em class="bcp14">MUST</em> either respond with <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> status code and continue to read from the input stream, or respond with a final status code. The origin server <em class="bcp14">MUST NOT</em> wait for the request body before sending the <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response. If it responds with a final status code, it <em class="bcp14">MAY</em> close the transport connection or it <em class="bcp14">MAY</em> continue to read and discard the rest of the request. It <em class="bcp14">MUST NOT</em> perform the request method if it returns a final status code. 2182 </li> 2183 <li>An origin server <em class="bcp14">SHOULD NOT</em> send a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response if the request message does not include an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field with the "100-continue" expectation, and <em class="bcp14">MUST NOT</em> send a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> response if such a request comes from an HTTP/1.0 (or earlier) client. There is an exception to this rule: for compatibility 2185 2184 with <a href="#RFC2068" id="rfc.xref.RFC2068.4"><cite title="Hypertext Transfer Protocol -- HTTP/1.1">[RFC2068]</cite></a>, a server <em class="bcp14">MAY</em> send a <a href="p2-semantics.html#status.100" class="smpl">100 (Continue)</a> status code in response to an HTTP/1.1 PUT or POST request that does not include an Expect header field with the "100-continue" 2186 2185 expectation. This exception, the purpose of which is to minimize any client processing delays associated with an undeclared … … 2192 2191 prematurely. 2193 2192 </li> 2194 <li>If an origin server receives a request that does not include an Expect header field with the "100-continue" expectation, the 2195 request includes a request body, and the server responds with a final status code before reading the entire request body from 2196 the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise, 2193 <li>If an origin server receives a request that does not include an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field with the "100-continue" expectation, the request includes a request body, and the server responds with a final 2194 status code before reading the entire request body from the transport connection, then the server <em class="bcp14">SHOULD NOT</em> close the transport connection until it has read the entire request, or until the client closes the connection. Otherwise, 2197 2195 the client might not reliably receive the response message. However, this requirement ought not be construed as preventing 2198 2196 a server from defending itself against denial-of-service attacks, or from badly broken client implementations. … … 2201 2199 <p id="rfc.section.6.4.3.p.5">Requirements for HTTP/1.1 proxies: </p> 2202 2200 <ul> 2203 <li>If a proxy receives a request that includes an Expect header field with the "100-continue" expectation, and the proxy either 2204 knows that the next-hop server complies with HTTP/1.1 or higher, or does not know the HTTP version of the next-hop server, 2205 it <em class="bcp14">MUST</em> forward the request, including the Expect header field. 2201 <li>If a proxy receives a request that includes an <a href="p2-semantics.html#header.expect" class="smpl">Expect</a> header field with the "100-continue" expectation, and the proxy either knows that the next-hop server complies with HTTP/1.1 2202 or higher, or does not know the HTTP version of the next-hop server, it <em class="bcp14">MUST</em> forward the request, including the Expect header field. 2206 2203 </li> 2207 2204 <li>If the proxy knows that the version of the next-hop server is HTTP/1.0 or lower, it <em class="bcp14">MUST NOT</em> forward the request, and it <em class="bcp14">MUST</em> respond with a <a href="p2-semantics.html#status.417" class="smpl">417 (Expectation Failed)</a> status code. … … 2209 2206 <li>Proxies <em class="bcp14">SHOULD</em> maintain a record of the HTTP version numbers received from recently-referenced next-hop servers. 2210 2207 </li> 2211 <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 Expect header field 2212 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.Part2.22"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>). 2208 <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.Part2.23"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>). 2213 2209 </li> 2214 2210 </ul> … … 2247 2243 </p> 2248 2244 <p id="rfc.section.6.5.p.8">The Upgrade header field cannot be used to indicate a switch to a protocol on a different connection. For that purpose, it 2249 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.Part2.2 3"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>).2245 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.Part2.24"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>). 2250 2246 </p> 2251 2247 <p id="rfc.section.6.5.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 … … 2511 2507 <li>Pointer to specification text</li> 2512 2508 </ul> 2513 <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.Part2.2 4"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) unless the encoding transformation is identical, as it is the case for the compression codings defined in <a href="#compression.codings" title="Compression Codings">Section 4.2</a>.2509 <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.Part2.25"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>) unless the encoding transformation is identical, as it is the case for the compression codings defined in <a href="#compression.codings" title="Compression Codings">Section 4.2</a>. 2514 2510 </p> 2515 2511 <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. … … 2671 2667 that most implementations will choose substantially higher limits. 2672 2668 </p> 2673 <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.Part2.2 5"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[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.Part2.26"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>).2669 <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.Part2.26"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[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.Part2.27"><cite title="HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation">[Part2]</cite></a>). 2674 2670 </p> 2675 2671 <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. … … 2716 2712 <h2 id="rfc.references.1"><a href="#rfc.section.10.1" id="rfc.section.10.1">10.1</a> Normative References 2717 2713 </h2> 2718 <table> 2714 <table> 2719 2715 <tr> 2720 2716 <td class="reference"><b id="ISO-8859-1">[ISO-8859-1]</b></td> … … 2729 2725 <td class="reference"><b id="Part4">[Part4]</b></td> 2730 2726 <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p4-conditional-latest">HTTP/1.1, part 4: Conditional Requests</a>”, Internet-Draft draft-ietf-httpbis-p4-conditional-latest (work in progress), July 2012. 2727 </td> 2728 </tr> 2729 <tr> 2730 <td class="reference"><b id="Part5">[Part5]</b></td> 2731 <td class="top"><a href="mailto:fielding@gbiv.com" title="Adobe Systems Incorporated">Fielding, R., Ed.</a>, <a href="mailto:ylafon@w3.org" title="World Wide Web Consortium">Lafon, Y., Ed.</a>, and <a href="mailto:julian.reschke@greenbytes.de" title="greenbytes GmbH">J. Reschke, Ed.</a>, “<a href="http://tools.ietf.org/html/draft-ietf-httpbis-p5-range-latest">HTTP/1.1, part 5: Range Requests and Partial Responses</a>”, Internet-Draft draft-ietf-httpbis-p5-range-latest (work in progress), July 2012. 2731 2732 </td> 2732 2733 </tr> … … 3733 3734 <li><a id="rfc.index.P" href="#rfc.index.P"><b>P</b></a><ul> 3734 3735 <li><em>Pad1995</em> <a href="#rfc.xref.Pad1995.1">6.3.1</a>, <a href="#Pad1995"><b>10.2</b></a></li> 3735 <li><em>Part2</em> <a href="#rfc.xref.Part2.1">1</a>, <a href="#rfc.xref.Part2.2">2.3</a>, <a href="#rfc.xref.Part2.3">2.7.1</a>, <a href="#rfc.xref.Part2.4">3.1.1</a>, <a href="#rfc.xref.Part2.5">3.1.1</a>, <a href="#rfc.xref.Part2.6">3.1.2</a>, <a href="#rfc.xref.Part2.7">3.2</a>, <a href="#rfc.xref.Part2.8">3.2</a>, <a href="#rfc.xref.Part2.9">3.3</a>, <a href="#rfc.xref.Part2.10">3.3.1</a>, <a href="#rfc.xref.Part2.11">4.3.1</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">5.6.2</a>, <a href="#rfc.xref.Part2.16">5. 7</a>, <a href="#rfc.xref.Part2.17">6.3.2.2</a>, <a href="#rfc.xref.Part2.18">6.3.4</a>, <a href="#rfc.xref.Part2.19">6.4.3</a>, <a href="#rfc.xref.Part2.20">6.4.3</a>, <a href="#rfc.xref.Part2.21">6.4.3</a>, <a href="#rfc.xref.Part2.22">6.4.3</a>, <a href="#rfc.xref.Part2.23">6.5</a>, <a href="#rfc.xref.Part2.24">7.4</a>, <a href="#rfc.xref.Part2.25">8.6</a>, <a href="#rfc.xref.Part2.26">8.6</a>, <a href="#Part2"><b>10.1</b></a><ul>3736 <li><em>Part2</em> <a href="#rfc.xref.Part2.1">1</a>, <a href="#rfc.xref.Part2.2">2.3</a>, <a href="#rfc.xref.Part2.3">2.7.1</a>, <a href="#rfc.xref.Part2.4">3.1.1</a>, <a href="#rfc.xref.Part2.5">3.1.1</a>, <a href="#rfc.xref.Part2.6">3.1.2</a>, <a href="#rfc.xref.Part2.7">3.2</a>, <a href="#rfc.xref.Part2.8">3.2</a>, <a href="#rfc.xref.Part2.9">3.3</a>, <a href="#rfc.xref.Part2.10">3.3.1</a>, <a href="#rfc.xref.Part2.11">4.3.1</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">5.6.2</a>, <a href="#rfc.xref.Part2.16">5.6.2</a>, <a href="#rfc.xref.Part2.17">5.6.2</a>, <a href="#rfc.xref.Part2.18">5.7</a>, <a href="#rfc.xref.Part2.19">6.3.2.2</a>, <a href="#rfc.xref.Part2.20">6.3.4</a>, <a href="#rfc.xref.Part2.21">6.4.3</a>, <a href="#rfc.xref.Part2.22">6.4.3</a>, <a href="#rfc.xref.Part2.23">6.4.3</a>, <a href="#rfc.xref.Part2.24">6.5</a>, <a href="#rfc.xref.Part2.25">7.4</a>, <a href="#rfc.xref.Part2.26">8.6</a>, <a href="#rfc.xref.Part2.27">8.6</a>, <a href="#Part2"><b>10.1</b></a><ul> 3736 3737 <li><em>Section 2</em> <a href="#rfc.xref.Part2.4">3.1.1</a></li> 3737 <li><em>Section 2.1.2</em> <a href="#rfc.xref.Part2.1 7">6.3.2.2</a>, <a href="#rfc.xref.Part2.18">6.3.4</a></li>3738 <li><em>Section 2.1.2</em> <a href="#rfc.xref.Part2.19">6.3.2.2</a>, <a href="#rfc.xref.Part2.20">6.3.4</a></li> 3738 3739 <li><em>Section 2.3.1</em> <a href="#rfc.xref.Part2.14">5.3</a></li> 3739 3740 <li><em>Section 2.3.8</em> <a href="#rfc.xref.Part2.13">5.3</a></li> 3740 3741 <li><em>Section 3.1</em> <a href="#rfc.xref.Part2.8">3.2</a></li> 3741 3742 <li><em>Section 4</em> <a href="#rfc.xref.Part2.3">2.7.1</a>, <a href="#rfc.xref.Part2.6">3.1.2</a>, <a href="#rfc.xref.Part2.9">3.3</a></li> 3742 <li><em>Section 4.3</em> <a href="#rfc.xref.Part2.1 6">5.7</a>, <a href="#rfc.xref.Part2.22">6.4.3</a></li>3743 <li><em>Section 4.3.1</em> <a href="#rfc.xref.Part2. 19">6.4.3</a></li>3743 <li><em>Section 4.3</em> <a href="#rfc.xref.Part2.18">5.7</a>, <a href="#rfc.xref.Part2.23">6.4.3</a></li> 3744 <li><em>Section 4.3.1</em> <a href="#rfc.xref.Part2.21">6.4.3</a></li> 3744 3745 <li><em>Section 4.4.4</em> <a href="#rfc.xref.Part2.2">2.3</a></li> 3745 <li><em>Section 4.5</em> <a href="#rfc.xref.Part2.2 3">6.5</a></li>3746 <li><em>Section 4.6</em> <a href="#rfc.xref.Part2.2 6">8.6</a></li>3747 <li><em>Section 4.6.12</em> <a href="#rfc.xref.Part2.5">3.1.1</a>, <a href="#rfc.xref.Part2.2 5">8.6</a></li>3748 <li><em>Section 5.4</em> <a href="#rfc.xref.Part2.10">3.3.1</a>, <a href="#rfc.xref.Part2.2 4">7.4</a></li>3746 <li><em>Section 4.5</em> <a href="#rfc.xref.Part2.24">6.5</a></li> 3747 <li><em>Section 4.6</em> <a href="#rfc.xref.Part2.27">8.6</a></li> 3748 <li><em>Section 4.6.12</em> <a href="#rfc.xref.Part2.5">3.1.1</a>, <a href="#rfc.xref.Part2.26">8.6</a></li> 3749 <li><em>Section 5.4</em> <a href="#rfc.xref.Part2.10">3.3.1</a>, <a href="#rfc.xref.Part2.25">7.4</a></li> 3749 3750 <li><em>Section 8</em> <a href="#rfc.xref.Part2.11">4.3.1</a></li> 3751 <li><em>Section 9.6</em> <a href="#rfc.xref.Part2.15">5.6.2</a></li> 3752 <li><em>Section 9.9</em> <a href="#rfc.xref.Part2.16">5.6.2</a></li> 3750 3753 <li><em>Section 9.10</em> <a href="#rfc.xref.Part2.7">3.2</a></li> 3751 <li><em>Section 9.11</em> <a href="#rfc.xref.Part2.2 0">6.4.3</a>, <a href="#rfc.xref.Part2.21">6.4.3</a></li>3754 <li><em>Section 9.11</em> <a href="#rfc.xref.Part2.22">6.4.3</a></li> 3752 3755 <li><em>Appendix A</em> <a href="#rfc.xref.Part2.1">1</a></li> 3753 3756 </ul> … … 3755 3758 <li><em>Part4</em> <a href="#rfc.xref.Part4.1">3.3</a>, <a href="#rfc.xref.Part4.2">3.3.1</a>, <a href="#rfc.xref.Part4.3">3.3.2</a>, <a href="#Part4"><b>10.1</b></a><ul> 3756 3759 <li><em>Section 4.1</em> <a href="#rfc.xref.Part4.1">3.3</a>, <a href="#rfc.xref.Part4.2">3.3.1</a>, <a href="#rfc.xref.Part4.3">3.3.2</a></li> 3760 </ul> 3761 </li> 3762 <li><em>Part5</em> <a href="#rfc.xref.Part5.1">5.6.2</a>, <a href="#Part5"><b>10.1</b></a><ul> 3763 <li><em>Section 5.2</em> <a href="#rfc.xref.Part5.1">5.6.2</a></li> 3757 3764 </ul> 3758 3765 </li>
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