tun: allow darwin to auto assign names

main.go

@@ -115,13 +115,6 @@ func main() {
 		return LogLevelInfo
 	}()
 
-	logger := NewLogger(
-		logLevel,
-		fmt.Sprintf("(%s) ", interfaceName),
-	)
-
-	logger.Debug.Println("Debug log enabled")
-
 	// open TUN device (or use supplied fd)
 
 	tun, err := func() (TUNDevice, error) {
@@ -141,6 +134,21 @@ func main() {
 		return CreateTUNFromFile(file)
 	}()
 
+	if err == nil {
+		realInterfaceName, err2 := tun.Name()
+		if err2 == nil {
+			interfaceName = realInterfaceName
+		}
+	}
+
+	logger := NewLogger(
+		logLevel,
+		fmt.Sprintf("(%s) ", interfaceName),
+	)
+
+	logger.Debug.Println("Debug log enabled")
+
+
 	if err != nil {
 		logger.Error.Println("Failed to create TUN device:", err)
 		os.Exit(ExitSetupFailed)

tun_darwin.go

@@ -46,9 +46,11 @@ var sockaddrCtlSize uintptr = 32
 
 func CreateTUN(name string) (TUNDevice, error) {
 	ifIndex := -1
-	fmt.Sscanf(name, "utun%d", &ifIndex)
-	if ifIndex < 0 {
-		return nil, fmt.Errorf("error parsing interface name %s, must be utun[0-9]+", name)
+	if (name != "utun") {
+		fmt.Sscanf(name, "utun%d", &ifIndex)
+		if ifIndex < 0 {
+			return nil, fmt.Errorf("Interface name must be utun[0-9]*")
+		}
 	}
 
 	fd, err := unix.Socket(unix.AF_SYSTEM, unix.SOCK_DGRAM, 2)