code: func defaultHWAddrFunc() (net.HardwareAddr, error) {
  	ifaces, err := net.Interfaces()
  	if err != nil {
  		return []byte{}, err
  	}
  	for _, iface := range ifaces {
  		if len(iface.HardwareAddr) >= 6 {
  			return iface.HardwareAddr, nil
  		}
  	}
  	return []byte{}, fmt.Errorf("uuid: no HW address found")
  }
docs: // Returns hardware address.