Expect HTTP request header indicates expectations
that need to be met by the server to handle the request successfully.
Expect: 100-continue, the server responds with:
100(Continue) if the information from the request header is insufficient to resolve the response and the client should proceed with sending the body.
417(Expectation Failed) if the server cannot meet the expectation
or any other status otherwise (e.g. a 4xx status for a client error, or a 2xx status if the request can be resolved successfully without further processing).
For example, the server may reject a request if its
No common browsers send the
Expect header, but some other clients such as
cURL do so by default.
A client sends a request with
Expect header and waits for the server to respond
before sending the message body.
PUT /somewhere/fun HTTP/1.1
The server checks the headers and generates the response.
The server sends
100 (Continue), which instructs the client to send the message body.
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