Feature/dns client configuration (#563)

Added host configurators for Linux, Windows, and macOS.

The host configurator will update the peer system configuration
 directing DNS queries according to its capabilities.

Some Linux distributions don't support split (match) DNS or custom ports,
 and that will be reported to our management system in another PR

iface/iface.go

@@ -73,13 +73,15 @@ func parseAddress(address string) (WGAddress, error) {
 func (w *WGIface) Close() error {
 	w.mu.Lock()
 	defer w.mu.Unlock()
-
+	if w.Interface == nil {
+		return nil
+	}
 	err := w.Interface.Close()
 	if err != nil {
 		return err
 	}
 
-	if runtime.GOOS == "darwin" {
+	if runtime.GOOS != "windows" {
 		sockPath := "/var/run/wireguard/" + w.Name + ".sock"
 		if _, statErr := os.Stat(sockPath); statErr == nil {
 			statErr = os.Remove(sockPath)

iface/iface_unix.go

@@ -75,3 +75,8 @@ func (w *WGIface) UpdateAddr(newAddr string) error {
 	w.Address = addr
 	return w.assignAddr()
 }
+
+// GetInterfaceGUIDString returns an interface GUID. This is useful on Windows only
+func (w *WGIface) GetInterfaceGUIDString() (string, error) {
+	return "", nil
+}

iface/iface_windows.go

@@ -58,6 +58,20 @@ func (w *WGIface) UpdateAddr(newAddr string) error {
 	return w.assignAddr(luid)
 }
 
+// GetInterfaceGUIDString returns an interface GUID string
+func (w *WGIface) GetInterfaceGUIDString() (string, error) {
+	if w.Interface == nil {
+		return "", fmt.Errorf("interface has not been initialized yet")
+	}
+	windowsDevice := w.Interface.(*driver.Adapter)
+	luid := windowsDevice.LUID()
+	guid, err := luid.GUID()
+	if err != nil {
+		return "", err
+	}
+	return guid.String(), nil
+}
+
 // WireguardModuleIsLoaded check if we can load wireguard mod (linux only)
 func WireguardModuleIsLoaded() bool {
 	return false