code: func proxy(dst io.Writer, src io.Reader, errCh chan error) {
  	_, err := io.Copy(dst, src)
  	if tcpConn, ok := dst.(closeWriter); ok {
  		tcpConn.CloseWrite()
  	}
  	errCh <- err
  }
docs: // proxy is used to suffle data from src to destination, and sends errors
  // down a dedicated channel