code: func NewListener(net, laddr string) (net.Listener, error) {
  	switch net {
  	case "unix":
  		return newUnixListener(laddr)
  	case "tcp", "": // an empty net means tcp
  		return newTCPListener(laddr)
  	default:
  		return nil, fmt.Errorf("unknown address type %s", net)
  	}
  }
docs: // NewListener announces on laddr and net. Accepted values of the net are
  // 'unix' and 'tcp'