Remove fallback DNS

mobile/src/main/java/be/mygod/vpnhotspot/RoutingManager.kt

@@ -0,0 +1,60 @@
+package be.mygod.vpnhotspot
+
+import be.mygod.vpnhotspot.App.Companion.app
+import be.mygod.vpnhotspot.net.Routing
+import be.mygod.vpnhotspot.widget.SmartSnackbar
+import timber.log.Timber
+
+abstract class RoutingManager(private val caller: Any, val downstream: String) {
+    companion object {
+        private const val KEY_MASQUERADE_MODE = "service.masqueradeMode"
+        var masqueradeMode: Routing.MasqueradeMode
+            get() {
+                app.pref.getString(KEY_MASQUERADE_MODE, null)?.let { return Routing.MasqueradeMode.valueOf(it) }
+                return if (app.pref.getBoolean("service.masquerade", true)) // legacy settings
+                    Routing.MasqueradeMode.Simple else Routing.MasqueradeMode.None
+            }
+            set(value) = app.pref.edit().putString(KEY_MASQUERADE_MODE, value.name).apply()
+    }
+
+    class LocalOnly(caller: Any, downstream: String) : RoutingManager(caller, downstream) {
+        override fun Routing.configure() {
+            ipForward() // local only interfaces need to enable ip_forward
+            forward()
+            masquerade(masqueradeMode)
+            commit(true)
+        }
+    }
+
+    var routing: Routing? = null
+
+    init {
+        app.onPreCleanRoutings[this] = { routing?.stop() }
+        app.onRoutingsCleaned[this] = { initRouting() }
+    }
+
+    fun initRouting() = try {
+        routing = Routing(caller, downstream).apply {
+            try {
+                configure()
+            } catch (e: Exception) {
+                revert()
+                throw e
+            }
+        }
+        true
+    } catch (e: Exception) {
+        SmartSnackbar.make(e).show()
+        Timber.w(e)
+        routing = null
+        false
+    }
+
+    protected abstract fun Routing.configure()
+
+    fun stop() {
+        app.onPreCleanRoutings -= this
+        app.onRoutingsCleaned -= this
+        routing?.revert()
+    }
+}