Defines an interface to verify whether an incoming HTTP request meets the target server's expectations.
The Expect request-header field is used to indicate that particular server behaviors are required by the client.
Expect = "Expect" ":" 1#expectation expectation = "100-continue" | expectation-extension expectation-extension = token [ "=" ( token | quoted-string ) *expect-params ] expect-params = ";" token [ "=" ( token | quoted-string ) ]
A server that does not understand or is unable to comply with any of the expectation values in the Expect field of a request MUST respond with appropriate error status. The server MUST respond with a 417 (Expectation Failed) status if any of the expectations cannot be met or, if there are other problems with the request, some other 4xx status.