# Constant hyper::header::EXPECT [−] [src]

    pub const EXPECT: HeaderName;

Indicates expectations that need to be fulfilled by the server in order to properly handle the request.

The only expectation defined in the specification is Expect: 100-continue, to which the server shall respond with:

- 100 if the information contained in the header is sufficient to cause an immediate success,

- 417 (Expectation Failed) if it cannot meet the expectation; or any other 4xx status otherwise.

For example, the server may reject a request if its Content-Length is too large.

No common browsers send the Expect header, but some other clients such as cURL do so by default.