code: func (g *rfc4122Generator) getHardwareAddr() ([]byte, error) {
  	var err error
  	g.hardwareAddrOnce.Do(func() {
  		if hwAddr, err := g.hwAddrFunc(); err == nil {
  			copy(g.hardwareAddr[:], hwAddr)
  			return
  		}
  
  		// Initialize hardwareAddr randomly in case
  		// of real network interfaces absence.
  		if _, err = io.ReadFull(g.rand, g.hardwareAddr[:]); err != nil {
  			return
  		}
  		// Set multicast bit as recommended by RFC 4122
  		g.hardwareAddr[0] |= 0x01
  	})
  	if err != nil {
  		return []byte{}, err
  	}
  	return g.hardwareAddr[:], nil
  }
docs: // Returns hardware address.