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 sufficient to cause immediate success
417(Expectation Failed) if the server cannot meet the expectation
or any other 4xx status otherwise.
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.
|Header type||Request header|
|Forbidden header name||yes|
There is only one defined expectation:
Informs recipients that the client is about to send a (presumably large) message body in this request and wishes to receive a
100(Continue) interim response.
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 Host: origin.example.com Content-Type: video/h264 Content-Length: 1234567890987 Expect: 100-continue
The server checks the headers and generates the response.
The server sends
100 (Continue), which instructs the client to send the message body.
|Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content (HTTP/1.1)|
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