Refined code and documentations.

if.go

@@ -52,6 +52,7 @@ func New(config Config) (ifce *Interface, err error) {
 // NewTAP creates a new TAP interface whose name is ifName. If ifName is empty, a
 // default name (tap0, tap1, ... ) will be assigned. ifName should not exceed
 // 16 bytes. TAP interfaces are not supported on darwin.
+// ifName cannot be specified on windows, you will need ifce.Name() to use some cmds.
 //
 // Note: this function is deprecated and will be removed from the library.
 // Please use New() instead.
@@ -61,6 +62,7 @@ func NewTAP(ifName string) (ifce *Interface, err error) {
 
 // NewTUN creates a new TUN interface whose name is ifName. If ifName is empty, a
 // default name (tap0, tap1, ... ) will be assigned. ifName should not exceed
+// ifName cannot be specified on windows, you will need ifce.Name() to use some cmds.
 //
 // Note: this function is deprecated and will be removed from the library.
 // Please use New() instead.

syscalls_windows.go

@@ -7,6 +7,7 @@
 package water
 
 import (
+	"bytes"
 	"errors"
 	"net"
 	"os"
@@ -17,7 +18,8 @@ import (
 
 var (
 	IfceNameNotFound  = errors.New("Failed to find the name of interface.")
-	TapDeviceNotFound = errors.New("Failed to find the tap device in registry.")
+	TapDeviceNotFound = errors.New("Failed to find the tap device with specified ComponentId in registry, TAP driver may not installed.")
+	RegistryOpenErr   = errors.New("Failed to open the adapter registry, TAP driver may not installed.")
 	// Device Control Codes
 	tap_win_ioctl_get_mac             = tap_control_code(1, 0)
 	tap_win_ioctl_get_version         = tap_control_code(2, 0)
@@ -31,6 +33,9 @@ var (
 	tap_ioctl_config_tun              = tap_control_code(10, 0)
 	// w32 api
 	file_device_unknown = uint32(0x00000022)
+	// Driver maker specified ComponentId
+	// ComponentId is defined here: https://github.com/OpenVPN/tap-windows6/blob/master/version.m4#L5
+	componentId = "tap0901"
 )
 
 func ctl_code(device_type, function, method, access uint32) uint32 {
@@ -41,39 +46,40 @@ func tap_control_code(request, method uint32) uint32 {
 	return ctl_code(file_device_unknown, request, method, 0)
 }
 
-// getdeviceid finds out a TAP device from registry, it requires privileged right.
+// getdeviceid finds out a TAP device from registry, it *may* requires privileged right to prevent some weird issue.
 func getdeviceid() (string, error) {
 	// TAP driver key location
 	regkey := `SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}`
-	k, err := registry.OpenKey(registry.LOCAL_MACHINE, regkey, registry.ALL_ACCESS)
+	k, err := registry.OpenKey(registry.LOCAL_MACHINE, regkey, registry.READ)
 	if err != nil {
-		return "", err
+		return "", RegistryOpenErr
 	}
 	defer k.Close()
-	// read all subkeys
+	// read all subkeys, it should not return an err here
 	keys, err := k.ReadSubKeyNames(-1)
 	if err != nil {
 		return "", err
 	}
-	// find the one with ComponentId == "tap0901"
+	// find the one matched ComponentId
 	for _, v := range keys {
-		key, err := registry.OpenKey(registry.LOCAL_MACHINE, regkey+"\\"+v, registry.ALL_ACCESS)
+		key, err := registry.OpenKey(registry.LOCAL_MACHINE, regkey+"\\"+v, registry.READ)
 		if err != nil {
 			continue
 		}
 		val, _, err := key.GetStringValue("ComponentId")
 		if err != nil {
-			goto next
+			key.Close()
+			continue
 		}
-		if val == "tap0901" {
+		if val == componentId {
 			val, _, err = key.GetStringValue("NetCfgInstanceId")
 			if err != nil {
-				goto next
+				key.Close()
+				continue
 			}
 			key.Close()
 			return val, nil
 		}
-	next:
 		key.Close()
 	}
 	return "", TapDeviceNotFound
@@ -82,7 +88,7 @@ func getdeviceid() (string, error) {
 // openDev find and open an interface.
 func openDev(isTAP bool) (ifce *Interface, err error) {
 	// ifName won't work
-	// find the device in registrym you need privileged right.
+	// find the device in registry.
 	deviceid, err := getdeviceid()
 	if err != nil {
 		return nil, err
@@ -135,22 +141,13 @@ func openDev(isTAP bool) (ifce *Interface, err error) {
 		return
 	}
 	// find the name of tap interface(u need it to set the ip or other command)
-	hwaddr_equal := func(a net.HardwareAddr, b []byte) bool {
-		for i := 0; i < 6; i++ {
-			if a[i] != b[i] {
-				return false
-			}
-		}
-		return true
-	}
-
 	ifces, err := net.Interfaces()
 	if err != nil {
 		return
 	}
 
 	for _, v := range ifces {
-		if hwaddr_equal(v.HardwareAddr[:6], mac[:6]) {
+		if bytes.Equal(v.HardwareAddr[:6], mac[:6]) {
 			ifce.name = v.Name
 			return
 		}