Current http client doesn't support Expect: 100-continue request
header(RFC2616-8/RFC7231-5.1.1). So even if the client have the header,
the head of the request body is consumed prematurely.
Those are my intentions to avoid premature consuming body in this change.
- If http.Request header contains body and Expect: 100-continue
header, it blocks sending body until it gets the first response.
- If the first status code to the request were 100, the request
starts sending body. Otherwise, sending body will be cancelled.
- Tranport.ExpectContinueTimeout specifies the amount of the time to
wait for the first response.