http.go
func (req *Request) SetBodyStreamWriter(sw StreamWriter) {
	sr := NewStreamReader(sw)
	req.SetBodyStream(sr, -1)
}
func (req *Request) SetBodyStreamWriter(sw StreamWriter) {
	sr := NewStreamReader(sw)
	req.SetBodyStream(sr, -1)
}
// SetBodyStreamWriter registers the given sw for populating request body.
//
// This function may be used in the following cases:
//
//     * if request body is too big (more than 10MB).
//     * if request body is streamed from slow external sources.
//     * if request body must be streamed to the server in chunks
//     (aka `http client push` or `chunked transfer-encoding`).
//
// Note that GET and HEAD requests cannot have body.
//
/// See also SetBodyStream.