code: func (v *VTY) write(s string) error {
  	b := []byte(s)
  	b = append(b, 0)
  	v.conn.SetWriteDeadline(time.Now().Add(v.writeTimeout))
  	for len(b) > 0 {
  		n, err := v.conn.Write(b[:])
  		if err != nil {
  			return fmt.Errorf("VTY write failed: %v", err)
  		}
  		b = b[n:]
  	}
  	return nil
  }
docs: // write writes a command string to the VTY socket. A command from a VTY
  // client is terminated with a single trailing NULL byte (0).