code: func (req *Request) SetBodyStream(bodyStream io.Reader, bodySize int) {
  	req.ResetBody()
  	req.bodyStream = bodyStream
  	req.Header.SetContentLength(bodySize)
  }
docs: // 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.