Add IpcMessenger class

client/android/src/org/amnezia/vpn/IpcMessenger.kt

@@ -0,0 +1,42 @@
+package org.amnezia.vpn
+
+import android.os.DeadObjectException
+import android.os.Message
+import android.os.Messenger
+import android.os.RemoteException
+
+private const val TAG = "IpcMessenger"
+
+class IpcMessenger(
+    private val onDeadObjectException: () -> Unit = {},
+    private val onRemoteException: () -> Unit = {},
+    private val messengerName: String = "Unknown"
+) {
+    private var messenger: Messenger? = null
+
+    fun set(messenger: Messenger) {
+        this.messenger = messenger
+    }
+
+    fun reset() {
+        messenger = null
+    }
+
+    fun send(msg: () -> Message) = messenger?.sendMsg(msg())
+
+    fun <T> send(msg: T)
+        where T : Enum<T>, T : IpcMessage = messenger?.sendMsg(msg.packToMessage())
+
+    private fun Messenger.sendMsg(msg: Message) {
+        try {
+            send(msg)
+        } catch (e: DeadObjectException) {
+            Log.w(TAG, "$messengerName messenger is dead")
+            messenger = null
+            onDeadObjectException()
+        } catch (e: RemoteException) {
+            Log.w(TAG, "Sending a message to the $messengerName messenger failed: ${e.message}")
+            onRemoteException()
+        }
+    }
+}