code: func (nc *Conn) readOp(c *control) error {
  	br := bufio.NewReaderSize(nc.conn, defaultBufSize)
  	line, err := br.ReadString('\n')
  	if err != nil {
  		return err
  	}
  	parseControl(line, c)
  	return nil
  }
docs: // Read a control line and process the intended op.