tap: make net parameter optional (#472)

tuntap_linux.go

@@ -74,10 +74,14 @@ func createTun(cfg TunConfig) (conn net.Conn, itf *net.Interface, err error) {
 }
 
 func createTap(cfg TapConfig) (conn net.Conn, itf *net.Interface, err error) {
-	ip, ipNet, err := net.ParseCIDR(cfg.Addr)
+	var ip net.IP
+	var ipNet *net.IPNet
+	if cfg.Addr != "" {
+		ip, ipNet, err = net.ParseCIDR(cfg.Addr)
 		if err != nil {
 			return
 		}
+	}
 
 	ifce, err := water.New(water.Config{
 		DeviceType: water.TAP,
@@ -106,12 +110,14 @@ func createTap(cfg TapConfig) (conn net.Conn, itf *net.Interface, err error) {
 		return
 	}
 
+	if cfg.Addr != "" {
 		cmd = fmt.Sprintf("ip address add %s dev %s", cfg.Addr, ifce.Name())
 		log.Log("[tap]", cmd)
 		if er := link.SetLinkIp(ip, ipNet); er != nil {
 			err = fmt.Errorf("%s: %v", cmd, er)
 			return
 		}
+	}
 
 	cmd = fmt.Sprintf("ip link set dev %s up", ifce.Name())
 	log.Log("[tap]", cmd)

tuntap_unix.go

@@ -55,10 +55,7 @@ func createTun(cfg TunConfig) (conn net.Conn, itf *net.Interface, err error) {
 }
 
 func createTap(cfg TapConfig) (conn net.Conn, itf *net.Interface, err error) {
-	ip, _, err := net.ParseCIDR(cfg.Addr)
+	ip, _, _ := net.ParseCIDR(cfg.Addr)
-	if err != nil {
-		return
-	}
 
 	ifce, err := water.New(water.Config{
 		DeviceType: water.TAP,
@@ -72,7 +69,12 @@ func createTap(cfg TapConfig) (conn net.Conn, itf *net.Interface, err error) {
 		mtu = DefaultMTU
 	}
 
-	cmd := fmt.Sprintf("ifconfig %s inet %s mtu %d up", ifce.Name(), cfg.Addr, mtu)
+	var cmd string
+	if cfg.Addr != "" {
+		cmd = fmt.Sprintf("ifconfig %s inet %s mtu %d up", ifce.Name(), cfg.Addr, mtu)
+	} else {
+		cmd = fmt.Sprintf("ifconfig %s mtu %d up", ifce.Name(), mtu)
+	}
 	log.Log("[tap]", cmd)
 	args := strings.Split(cmd, " ")
 	if er := exec.Command(args[0], args[1:]...).Run(); er != nil {

tuntap_windows.go

@@ -55,10 +55,7 @@ func createTun(cfg TunConfig) (conn net.Conn, itf *net.Interface, err error) {
 }
 
 func createTap(cfg TapConfig) (conn net.Conn, itf *net.Interface, err error) {
-	ip, ipNet, err := net.ParseCIDR(cfg.Addr)
+	ip, ipNet, _ := net.ParseCIDR(cfg.Addr)
-	if err != nil {
-		return
-	}
 
 	ifce, err := water.New(water.Config{
 		DeviceType: water.TAP,
@@ -72,6 +69,7 @@ func createTap(cfg TapConfig) (conn net.Conn, itf *net.Interface, err error) {
 		return
 	}
 
+	if ip != nil && ipNet != nil {
 		cmd := fmt.Sprintf("netsh interface ip set address name=%s "+
 			"source=static addr=%s mask=%s gateway=none",
 			ifce.Name(), ip.String(), ipMask(ipNet.Mask))
@@ -81,6 +79,7 @@ func createTap(cfg TapConfig) (conn net.Conn, itf *net.Interface, err error) {
 			err = fmt.Errorf("%s: %v", cmd, er)
 			return
 		}
+	}
 
 	if err = addTapRoutes(ifce.Name(), cfg.Gateway, cfg.Routes...); err != nil {
 		return