http.go
func (req *Request) SetBodyStream(bodyStream io.Reader, bodySize int) {
	req.ResetBody()
	req.bodyStream = bodyStream
	req.Header.SetContentLength(bodySize)
}
func (req *Request) SetBodyStream(bodyStream io.Reader, bodySize int) {
	req.ResetBody()
	req.bodyStream = bodyStream
	req.Header.SetContentLength(bodySize)
}
// SetBodyStream sets request body stream and, optionally body size.
//
// If bodySize is >= 0, then the bodyStream must provide exactly bodySize bytes
// before returning io.EOF.
//
// If bodySize < 0, then bodyStream is read until io.EOF.
//
// bodyStream.Close() is called after finishing reading all body data
// if it implements io.Closer.
//
// Note that GET and HEAD requests cannot have body.
//
// See also SetBodyStreamWriter.