code: func (r *Response) Write(b []byte) (n int, err error) {
  	n, err = r.ResponseWriter.Write(b)
  	r.size += int64(n)
  	return n, err
  }
docs: // Write writes the data to the connection as part of an HTTP reply.
  // If WriteHeader has not yet been called, Write calls WriteHeader(http.StatusOK)
  // before writing the data.  If the Header does not contain a
  // Content-Type line, Write adds a Content-Type set to the result of passing
  // the initial 512 bytes of written data to DetectContentType.