backend: do not depend on anything except config

This is likely broken but should make for a good starting point.

It also should hopefully handle stopping tunnels before starting new
ones, in the case of the GoBackend. Again, untested.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

28 files changed, 378 insertions, 274 deletions

diff --git a/app/src/main/java/com/wireguard/android/Application.java b/app/src/main/java/com/wireguard/android/Application.java
index 9b40fcd6..0fd00874 100644
--- a/app/src/main/java/com/wireguard/android/Application.java
+++ b/app/src/main/java/com/wireguard/android/Application.java
@@ -5,6 +5,7 @@
 
 package com.wireguard.android;
 
+import android.app.PendingIntent;
 import android.content.Context;
 import android.content.Intent;
 import android.content.SharedPreferences;
@@ -19,12 +20,14 @@ import androidx.preference.PreferenceManager;
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.AppCompatDelegate;
 
+import com.wireguard.android.activity.MainActivity;
 import com.wireguard.android.backend.Backend;
 import com.wireguard.android.backend.GoBackend;
 import com.wireguard.android.backend.WgQuickBackend;
 import com.wireguard.android.configStore.FileConfigStore;
 import com.wireguard.android.model.TunnelManager;
 import com.wireguard.android.util.AsyncWorker;
+import com.wireguard.android.util.ExceptionLoggers;
 import com.wireguard.android.util.ModuleLoader;
 import com.wireguard.android.util.RootShell;
 import com.wireguard.android.util.ToolsInstaller;
@@ -89,8 +92,16 @@ public class Application extends android.app.Application {
                     } catch (final Exception ignored) {
                     }
                 }
-                if (backend == null)
-                    backend = new GoBackend(app.getApplicationContext());
+                if (backend == null) {
+                    final Context context = app.getApplicationContext();
+                    final Intent configureIntent = new Intent(context, MainActivity.class);
+                    configureIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
+                    final PendingIntent pendingConfigureIntent = PendingIntent.getActivity(context, 0, configureIntent, 0);
+                    backend = new GoBackend(context, pendingConfigureIntent);
+                    GoBackend.setAlwaysOnCallback(() -> {
+                        get().tunnelManager.restoreState(true).whenComplete(ExceptionLoggers.D);
+                    });
+                }
                 app.backend = backend;
             }
             return app.backend;
diff --git a/app/src/main/java/com/wireguard/android/QuickTileService.java b/app/src/main/java/com/wireguard/android/QuickTileService.java
index 8909beec..66aecec3 100644
--- a/app/src/main/java/com/wireguard/android/QuickTileService.java
+++ b/app/src/main/java/com/wireguard/android/QuickTileService.java
@@ -21,8 +21,8 @@ import android.util.Log;
 
 import com.wireguard.android.activity.MainActivity;
 import com.wireguard.android.activity.TunnelToggleActivity;
-import com.wireguard.android.model.Tunnel;
-import com.wireguard.android.model.Tunnel.State;
+import com.wireguard.android.backend.Tunnel.State;
+import com.wireguard.android.model.ObservableTunnel;
 import com.wireguard.android.widget.SlashDrawable;
 
 import java.util.Objects;
@@ -41,7 +41,7 @@ public class QuickTileService extends TileService {
     private final OnTunnelChangedCallback onTunnelChangedCallback = new OnTunnelChangedCallback();
     @Nullable private Icon iconOff;
     @Nullable private Icon iconOn;
-    @Nullable private Tunnel tunnel;
+    @Nullable private ObservableTunnel tunnel;
 
     /* This works around an annoying unsolved frameworks bug some people are hitting. */
     @Override
@@ -121,7 +121,7 @@ public class QuickTileService extends TileService {
 
     private void updateTile() {
         // Update the tunnel.
-        final Tunnel newTunnel = Application.getTunnelManager().getLastUsedTunnel();
+        final ObservableTunnel newTunnel = Application.getTunnelManager().getLastUsedTunnel();
         if (newTunnel != tunnel) {
             if (tunnel != null)
                 tunnel.removeOnPropertyChangedCallback(onStateChangedCallback);
@@ -135,7 +135,7 @@ public class QuickTileService extends TileService {
         final Tile tile = getQsTile();
         if (tunnel != null) {
             label = tunnel.getName();
-            state = tunnel.getState() == Tunnel.State.UP ? Tile.STATE_ACTIVE : Tile.STATE_INACTIVE;
+            state = tunnel.getState() == State.UP ? Tile.STATE_ACTIVE : Tile.STATE_INACTIVE;
         } else {
             label = getString(R.string.app_name);
             state = Tile.STATE_INACTIVE;
diff --git a/app/src/main/java/com/wireguard/android/activity/BaseActivity.java b/app/src/main/java/com/wireguard/android/activity/BaseActivity.java
index b27ca6dd..8ec58ee8 100644
--- a/app/src/main/java/com/wireguard/android/activity/BaseActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/BaseActivity.java
@@ -11,7 +11,7 @@ import android.os.Bundle;
 import androidx.annotation.Nullable;
 
 import com.wireguard.android.Application;
-import com.wireguard.android.model.Tunnel;
+import com.wireguard.android.model.ObservableTunnel;
 
 import java.util.Objects;
 
@@ -23,14 +23,14 @@ public abstract class BaseActivity extends ThemeChangeAwareActivity {
     private static final String KEY_SELECTED_TUNNEL = "selected_tunnel";
 
     private final SelectionChangeRegistry selectionChangeRegistry = new SelectionChangeRegistry();
-    @Nullable private Tunnel selectedTunnel;
+    @Nullable private ObservableTunnel selectedTunnel;
 
     public void addOnSelectedTunnelChangedListener(final OnSelectedTunnelChangedListener listener) {
         selectionChangeRegistry.add(listener);
     }
 
     @Nullable
-    public Tunnel getSelectedTunnel() {
+    public ObservableTunnel getSelectedTunnel() {
         return selectedTunnel;
     }
 
@@ -60,15 +60,15 @@ public abstract class BaseActivity extends ThemeChangeAwareActivity {
         super.onSaveInstanceState(outState);
     }
 
-    protected abstract void onSelectedTunnelChanged(@Nullable Tunnel oldTunnel, @Nullable Tunnel newTunnel);
+    protected abstract void onSelectedTunnelChanged(@Nullable ObservableTunnel oldTunnel, @Nullable ObservableTunnel newTunnel);
 
     public void removeOnSelectedTunnelChangedListener(
             final OnSelectedTunnelChangedListener listener) {
         selectionChangeRegistry.remove(listener);
     }
 
-    public void setSelectedTunnel(@Nullable final Tunnel tunnel) {
-        final Tunnel oldTunnel = selectedTunnel;
+    public void setSelectedTunnel(@Nullable final ObservableTunnel tunnel) {
+        final ObservableTunnel oldTunnel = selectedTunnel;
         if (Objects.equals(oldTunnel, tunnel))
             return;
         selectedTunnel = tunnel;
@@ -77,21 +77,21 @@ public abstract class BaseActivity extends ThemeChangeAwareActivity {
     }
 
     public interface OnSelectedTunnelChangedListener {
-        void onSelectedTunnelChanged(@Nullable Tunnel oldTunnel, @Nullable Tunnel newTunnel);
+        void onSelectedTunnelChanged(@Nullable ObservableTunnel oldTunnel, @Nullable ObservableTunnel newTunnel);
     }
 
     private static final class SelectionChangeNotifier
-            extends NotifierCallback<OnSelectedTunnelChangedListener, Tunnel, Tunnel> {
+            extends NotifierCallback<OnSelectedTunnelChangedListener, ObservableTunnel, ObservableTunnel> {
         @Override
         public void onNotifyCallback(final OnSelectedTunnelChangedListener listener,
-                                     final Tunnel oldTunnel, final int ignored,
-                                     final Tunnel newTunnel) {
+                                     final ObservableTunnel oldTunnel, final int ignored,
+                                     final ObservableTunnel newTunnel) {
             listener.onSelectedTunnelChanged(oldTunnel, newTunnel);
         }
     }
 
     private static final class SelectionChangeRegistry
-            extends CallbackRegistry<OnSelectedTunnelChangedListener, Tunnel, Tunnel> {
+            extends CallbackRegistry<OnSelectedTunnelChangedListener, ObservableTunnel, ObservableTunnel> {
         private SelectionChangeRegistry() {
             super(new SelectionChangeNotifier());
         }
diff --git a/app/src/main/java/com/wireguard/android/activity/MainActivity.java b/app/src/main/java/com/wireguard/android/activity/MainActivity.java
index c86669ba..5c9084d0 100644
--- a/app/src/main/java/com/wireguard/android/activity/MainActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/MainActivity.java
@@ -21,7 +21,7 @@ import android.widget.LinearLayout;
 import com.wireguard.android.R;
 import com.wireguard.android.fragment.TunnelDetailFragment;
 import com.wireguard.android.fragment.TunnelEditorFragment;
-import com.wireguard.android.model.Tunnel;
+import com.wireguard.android.model.ObservableTunnel;
 
 import java.util.List;
 
@@ -117,8 +117,8 @@ public class MainActivity extends BaseActivity
     }
 
     @Override
-    protected void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel,
-                                           @Nullable final Tunnel newTunnel) {
+    protected void onSelectedTunnelChanged(@Nullable final ObservableTunnel oldTunnel,
+                                           @Nullable final ObservableTunnel newTunnel) {
         final FragmentManager fragmentManager = getSupportFragmentManager();
         final int backStackEntries = fragmentManager.getBackStackEntryCount();
         if (newTunnel == null) {
diff --git a/app/src/main/java/com/wireguard/android/activity/TunnelCreatorActivity.java b/app/src/main/java/com/wireguard/android/activity/TunnelCreatorActivity.java
index 08ea8e7e..c87ec537 100644
--- a/app/src/main/java/com/wireguard/android/activity/TunnelCreatorActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/TunnelCreatorActivity.java
@@ -9,7 +9,7 @@ import android.os.Bundle;
 import androidx.annotation.Nullable;
 
 import com.wireguard.android.fragment.TunnelEditorFragment;
-import com.wireguard.android.model.Tunnel;
+import com.wireguard.android.model.ObservableTunnel;
 
 /**
  * Standalone activity for creating tunnels.
@@ -28,7 +28,7 @@ public class TunnelCreatorActivity extends BaseActivity {
     }
 
     @Override
-    protected void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel, @Nullable final Tunnel newTunnel) {
+    protected void onSelectedTunnelChanged(@Nullable final ObservableTunnel oldTunnel, @Nullable final ObservableTunnel newTunnel) {
         finish();
     }
 }
diff --git a/app/src/main/java/com/wireguard/android/activity/TunnelToggleActivity.java b/app/src/main/java/com/wireguard/android/activity/TunnelToggleActivity.java
index 69c995fe..09a34bf7 100644
--- a/app/src/main/java/com/wireguard/android/activity/TunnelToggleActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/TunnelToggleActivity.java
@@ -19,8 +19,8 @@ import android.widget.Toast;
 import com.wireguard.android.Application;
 import com.wireguard.android.QuickTileService;
 import com.wireguard.android.R;
-import com.wireguard.android.model.Tunnel;
-import com.wireguard.android.model.Tunnel.State;
+import com.wireguard.android.model.ObservableTunnel;
+import com.wireguard.android.backend.Tunnel.State;
 import com.wireguard.android.util.ErrorMessages;
 
 @RequiresApi(Build.VERSION_CODES.N)
@@ -30,7 +30,7 @@ public class TunnelToggleActivity extends AppCompatActivity {
     @Override
     protected void onCreate(@Nullable final Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
-        final Tunnel tunnel = Application.getTunnelManager().getLastUsedTunnel();
+        final ObservableTunnel tunnel = Application.getTunnelManager().getLastUsedTunnel();
         if (tunnel == null)
             return;
         tunnel.setState(State.TOGGLE).whenComplete((v, t) -> {
diff --git a/app/src/main/java/com/wireguard/android/backend/Backend.java b/app/src/main/java/com/wireguard/android/backend/Backend.java
index a25bfd04..7569b5fa 100644
--- a/app/src/main/java/com/wireguard/android/backend/Backend.java
+++ b/app/src/main/java/com/wireguard/android/backend/Backend.java
@@ -5,43 +5,32 @@
 
 package com.wireguard.android.backend;
 
-import com.wireguard.android.model.Tunnel;
-import com.wireguard.android.model.Tunnel.State;
-import com.wireguard.android.model.Tunnel.Statistics;
 import com.wireguard.config.Config;
 
+import java.util.Collection;
 import java.util.Set;
 
+import androidx.annotation.Nullable;
+
 /**
  * Interface for implementations of the WireGuard secure network tunnel.
  */
 
 public interface Backend {
     /**
-     * Update the volatile configuration of a running tunnel and return the resulting configuration.
-     * If the tunnel is not up, return the configuration that would result (if known), or else
-     * simply return the given configuration.
-     *
-     * @param tunnel The tunnel to apply the configuration to.
-     * @param config The new configuration for this tunnel.
-     * @return The updated configuration of the tunnel.
-     */
-    Config applyConfig(Tunnel tunnel, Config config) throws Exception;
-
-    /**
-     * Enumerate the names of currently-running tunnels.
+     * Enumerate names of currently-running tunnels.
      *
      * @return The set of running tunnel names.
      */
-    Set<String> enumerate();
+    Set<String> getRunningTunnelNames();
 
     /**
-     * Get the actual state of a tunnel.
+     * Get the state of a tunnel.
      *
      * @param tunnel The tunnel to examine the state of.
      * @return The state of the tunnel.
      */
-    State getState(Tunnel tunnel) throws Exception;
+    Tunnel.State getState(Tunnel tunnel) throws Exception;
 
     /**
      * Get statistics about traffic and errors on this tunnel. If the tunnel is not running, the
@@ -68,12 +57,32 @@ public interface Backend {
     String getVersion() throws Exception;
 
     /**
-     * Set the state of a tunnel.
+     * Set the state of a tunnel, updating it's configuration. If the tunnel is already up, config
+     * may update the running configuration; config may be null when setting the tunnel down.
      *
      * @param tunnel The tunnel to control the state of.
      * @param state  The new state for this tunnel. Must be {@code UP}, {@code DOWN}, or
      *               {@code TOGGLE}.
+     * @param config The configuration for this tunnel, may be null if state is {@code DOWN}.
      * @return The updated state of the tunnel.
      */
-    State setState(Tunnel tunnel, State state) throws Exception;
+    Tunnel.State setState(Tunnel tunnel, Tunnel.State state, @Nullable Config config) throws Exception;
+
+    interface TunnelStateChangeNotificationReceiver {
+        void tunnelStateChange(Tunnel tunnel, Tunnel.State state);
+    }
+
+    /**
+     * Register a state change notification callback.
+     *
+     * @param receiver The receiver object to receive the notification.
+     */
+    void registerStateChangeNotification(TunnelStateChangeNotificationReceiver receiver);
+
+    /**
+     * Unregister a state change notification callback.
+     *
+     * @param receiver The receiver object to no longer receive the notification.
+     */
+    void unregisterStateChangeNotification(TunnelStateChangeNotificationReceiver receiver);
 }
diff --git a/app/src/main/java/com/wireguard/android/backend/GoBackend.java b/app/src/main/java/com/wireguard/android/backend/GoBackend.java
index ad45c933..6bbf5a3b 100644
--- a/app/src/main/java/com/wireguard/android/backend/GoBackend.java
+++ b/app/src/main/java/com/wireguard/android/backend/GoBackend.java
@@ -16,10 +16,7 @@ import android.util.Log;
 
 import com.wireguard.android.Application;
 import com.wireguard.android.R;
-import com.wireguard.android.activity.MainActivity;
-import com.wireguard.android.model.Tunnel;
-import com.wireguard.android.model.Tunnel.State;
-import com.wireguard.android.model.Tunnel.Statistics;
+import com.wireguard.android.backend.Tunnel.State;
 import com.wireguard.android.util.ExceptionLoggers;
 import com.wireguard.android.util.SharedLibraryLoader;
 import com.wireguard.config.Config;
@@ -30,6 +27,7 @@ import com.wireguard.crypto.KeyFormatException;
 
 import java.net.InetAddress;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
@@ -40,14 +38,26 @@ import java9.util.concurrent.CompletableFuture;
 public final class GoBackend implements Backend {
     private static final String TAG = "WireGuard/" + GoBackend.class.getSimpleName();
     private static CompletableFuture<VpnService> vpnService = new CompletableFuture<>();
+    public interface AlwaysOnCallback {
+        void alwaysOnTriggered();
+    }
+    @Nullable private static AlwaysOnCallback alwaysOnCallback;
+    public static void setAlwaysOnCallback(AlwaysOnCallback cb) {
+        alwaysOnCallback = cb;
+    }
 
     private final Context context;
+    private final PendingIntent configurationIntent;
     @Nullable private Tunnel currentTunnel;
+    @Nullable private Config currentConfig;
     private int currentTunnelHandle = -1;
 
-    public GoBackend(final Context context) {
+    private final Set<TunnelStateChangeNotificationReceiver> notifiers = new HashSet<>();
+
+    public GoBackend(final Context context, final PendingIntent configurationIntent) {
         SharedLibraryLoader.loadSharedLibrary(context, "wg-go");
         this.context = context;
+        this.configurationIntent = configurationIntent;
     }
 
     private static native String wgGetConfig(int handle);
@@ -63,23 +73,7 @@ public final class GoBackend implements Backend {
     private static native String wgVersion();
 
     @Override
-    public Config applyConfig(final Tunnel tunnel, final Config config) throws Exception {
-        if (tunnel.getState() == State.UP) {
-            // Restart the tunnel to apply the new config.
-            setStateInternal(tunnel, tunnel.getConfig(), State.DOWN);
-            try {
-                setStateInternal(tunnel, config, State.UP);
-            } catch (final Exception e) {
-                // The new configuration didn't work, so try to go back to the old one.
-                setStateInternal(tunnel, tunnel.getConfig(), State.UP);
-                throw e;
-            }
-        }
-        return config;
-    }
-
-    @Override
-    public Set<String> enumerate() {
+    public Set<String> getRunningTunnelNames() {
         if (currentTunnel != null) {
             final Set<String> runningTunnels = new ArraySet<>();
             runningTunnels.add(currentTunnel.getName());
@@ -147,25 +141,36 @@ public final class GoBackend implements Backend {
     }
 
     @Override
-    public State setState(final Tunnel tunnel, State state) throws Exception {
+    public State setState(final Tunnel tunnel, State state, @Nullable final Config config) throws Exception {
         final State originalState = getState(tunnel);
+
         if (state == State.TOGGLE)
             state = originalState == State.UP ? State.DOWN : State.UP;
-        if (state == originalState)
+        if (state == originalState && tunnel == currentTunnel && config == currentConfig)
             return originalState;
-        if (state == State.UP && currentTunnel != null)
-            throw new IllegalStateException(context.getString(R.string.multiple_tunnels_error));
-        Log.d(TAG, "Changing tunnel " + tunnel.getName() + " to state " + state);
-        setStateInternal(tunnel, tunnel.getConfig(), state);
+        if (state == State.UP) {
+            final Config originalConfig = currentConfig;
+            final Tunnel originalTunnel = currentTunnel;
+            if (currentTunnel != null)
+                setStateInternal(currentTunnel, null, State.DOWN);
+            try {
+                setStateInternal(tunnel, config, state);
+            } catch(final Exception e) {
+                if (originalTunnel != null)
+                    setStateInternal(originalTunnel, originalConfig, State.UP);
+                throw e;
+            }
+        } else if (state == State.DOWN && tunnel == currentTunnel) {
+            setStateInternal(tunnel, null, State.DOWN);
+        }
         return getState(tunnel);
     }
 
     private void setStateInternal(final Tunnel tunnel, @Nullable final Config config, final State state)
             throws Exception {
+        Log.i(TAG, "Bringing tunnel " + tunnel.getName() + " " + state);
 
         if (state == State.UP) {
-            Log.i(TAG, "Bringing tunnel up");
-
             Objects.requireNonNull(config, context.getString(R.string.no_config_error));
 
             if (VpnService.prepare(context) != null)
@@ -180,6 +185,7 @@ public final class GoBackend implements Backend {
             } catch (final TimeoutException e) {
                 throw new Exception(context.getString(R.string.vpn_start_error), e);
             }
+            service.setOwner(this);
 
             if (currentTunnelHandle != -1) {
                 Log.w(TAG, "Tunnel already up");
@@ -193,9 +199,7 @@ public final class GoBackend implements Backend {
             final VpnService.Builder builder = service.getBuilder();
             builder.setSession(tunnel.getName());
 
-            final Intent configureIntent = new Intent(context, MainActivity.class);
-            configureIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
-            builder.setConfigureIntent(PendingIntent.getActivity(context, 0, configureIntent, 0));
+            builder.setConfigureIntent(configurationIntent);
 
             for (final String excludedApplication : config.getInterface().getExcludedApplications())
                 builder.addDisallowedApplication(excludedApplication);
@@ -229,12 +233,11 @@ public final class GoBackend implements Backend {
                 throw new Exception(context.getString(R.string.tunnel_on_error, currentTunnelHandle));
 
             currentTunnel = tunnel;
+            currentConfig = config;
 
             service.protect(wgGetSocketV4(currentTunnelHandle));
             service.protect(wgGetSocketV6(currentTunnelHandle));
         } else {
-            Log.i(TAG, "Bringing tunnel down");
-
             if (currentTunnelHandle == -1) {
                 Log.w(TAG, "Tunnel already down");
                 return;
@@ -243,7 +246,11 @@ public final class GoBackend implements Backend {
             wgTurnOff(currentTunnelHandle);
             currentTunnel = null;
             currentTunnelHandle = -1;
+            currentConfig = null;
         }
+
+        for (final TunnelStateChangeNotificationReceiver notifier : notifiers)
+            notifier.tunnelStateChange(tunnel, state);
     }
 
     private void startVpnService() {
@@ -251,7 +258,23 @@ public final class GoBackend implements Backend {
         context.startService(new Intent(context, VpnService.class));
     }
 
+    @Override
+    public void registerStateChangeNotification(final TunnelStateChangeNotificationReceiver receiver) {
+        notifiers.add(receiver);
+    }
+
+    @Override
+    public void unregisterStateChangeNotification(final TunnelStateChangeNotificationReceiver receiver) {
+        notifiers.remove(receiver);
+    }
+
     public static class VpnService extends android.net.VpnService {
+        @Nullable private GoBackend owner;
+
+        public void setOwner(final GoBackend owner) {
+            this.owner = owner;
+        }
+
         public Builder getBuilder() {
             return new Builder();
         }
@@ -264,13 +287,18 @@ public final class GoBackend implements Backend {
 
         @Override
         public void onDestroy() {
-            Application.getTunnelManager().getTunnels().thenAccept(tunnels -> {
-                for (final Tunnel tunnel : tunnels) {
-                    if (tunnel != null && tunnel.getState() != State.DOWN)
-                        tunnel.setState(State.DOWN);
+            if (owner != null) {
+                final Tunnel tunnel = owner.currentTunnel;
+                if (tunnel != null) {
+                    if (owner.currentTunnelHandle != -1)
+                        wgTurnOff(owner.currentTunnelHandle);
+                    owner.currentTunnel = null;
+                    owner.currentTunnelHandle = -1;
+                    owner.currentConfig = null;
+                    for (final TunnelStateChangeNotificationReceiver notifier : owner.notifiers)
+                        notifier.tunnelStateChange(tunnel, State.DOWN);
                 }
-            });
-
+            }
             vpnService = vpnService.newIncompleteFuture();
             super.onDestroy();
         }
@@ -280,10 +308,10 @@ public final class GoBackend implements Backend {
             vpnService.complete(this);
             if (intent == null || intent.getComponent() == null || !intent.getComponent().getPackageName().equals(getPackageName())) {
                 Log.d(TAG, "Service started by Always-on VPN feature");
-                Application.getTunnelManager().restoreState(true).whenComplete(ExceptionLoggers.D);
+                if (alwaysOnCallback != null)
+                    alwaysOnCallback.alwaysOnTriggered();
             }
             return super.onStartCommand(intent, flags, startId);
         }
-
     }
 }
diff --git a/app/src/main/java/com/wireguard/android/backend/Statistics.java b/app/src/main/java/com/wireguard/android/backend/Statistics.java
new file mode 100644
index 00000000..2ca87d23
--- /dev/null
+++ b/app/src/main/java/com/wireguard/android/backend/Statistics.java
@@ -0,0 +1,62 @@
+/*
+ * Copyright © 2020 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.backend;
+
+import android.os.SystemClock;
+import android.util.Pair;
+
+import com.wireguard.crypto.Key;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class Statistics {
+    private long lastTouched = SystemClock.elapsedRealtime();
+    private final Map<Key, Pair<Long, Long>> peerBytes = new HashMap<>();
+
+    Statistics() { }
+
+    void add(final Key key, final long rx, final long tx) {
+        peerBytes.put(key, Pair.create(rx, tx));
+        lastTouched = SystemClock.elapsedRealtime();
+    }
+
+    public boolean isStale() {
+        return SystemClock.elapsedRealtime() - lastTouched > 900;
+    }
+
+    public Key[] peers() {
+        return peerBytes.keySet().toArray(new Key[0]);
+    }
+
+    public long peerRx(final Key peer) {
+        if (!peerBytes.containsKey(peer))
+            return 0;
+        return peerBytes.get(peer).first;
+    }
+
+    public long peerTx(final Key peer) {
+        if (!peerBytes.containsKey(peer))
+            return 0;
+        return peerBytes.get(peer).second;
+    }
+
+    public long totalRx() {
+        long rx = 0;
+        for (final Pair<Long, Long> val : peerBytes.values()) {
+            rx += val.first;
+        }
+        return rx;
+    }
+
+    public long totalTx() {
+        long tx = 0;
+        for (final Pair<Long, Long> val : peerBytes.values()) {
+            tx += val.second;
+        }
+        return tx;
+    }
+}
diff --git a/app/src/main/java/com/wireguard/android/backend/Tunnel.java b/app/src/main/java/com/wireguard/android/backend/Tunnel.java
new file mode 100644
index 00000000..86661355
--- /dev/null
+++ b/app/src/main/java/com/wireguard/android/backend/Tunnel.java
@@ -0,0 +1,33 @@
+/*
+ * Copyright © 2020 WireGuard LLC. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.android.backend;
+
+import java.util.regex.Pattern;
+
+/**
+ * Represents a WireGuard tunnel.
+ */
+
+public interface Tunnel {
+    enum State {
+        DOWN,
+        TOGGLE,
+        UP;
+
+        public static State of(final boolean running) {
+            return running ? UP : DOWN;
+        }
+    }
+
+    int NAME_MAX_LENGTH = 15;
+    Pattern NAME_PATTERN = Pattern.compile("[a-zA-Z0-9_=+.-]{1,15}");
+
+    static boolean isNameInvalid(final CharSequence name) {
+        return !NAME_PATTERN.matcher(name).matches();
+    }
+
+    String getName();
+}
diff --git a/app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java b/app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java
index 99b90af2..e04e6658 100644
--- a/app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java
+++ b/app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java
@@ -11,9 +11,7 @@ import android.util.Log;
 
 import com.wireguard.android.Application;
 import com.wireguard.android.R;
-import com.wireguard.android.model.Tunnel;
-import com.wireguard.android.model.Tunnel.State;
-import com.wireguard.android.model.Tunnel.Statistics;
+import com.wireguard.android.backend.Tunnel.State;
 import com.wireguard.config.Config;
 import com.wireguard.crypto.Key;
 
@@ -23,10 +21,13 @@ import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
+import java.util.HashMap;
 
 import java9.util.stream.Collectors;
 import java9.util.stream.Stream;
@@ -40,6 +41,8 @@ public final class WgQuickBackend implements Backend {
 
     private final File localTemporaryDir;
     private final Context context;
+    private final Map<Tunnel, Config> runningConfigs = new HashMap<>();
+    private final Set<TunnelStateChangeNotificationReceiver> notifiers = new HashSet<>();
 
     public WgQuickBackend(final Context context) {
         localTemporaryDir = new File(context.getCacheDir(), "tmp");
@@ -47,23 +50,7 @@ public final class WgQuickBackend implements Backend {
     }
 
     @Override
-    public Config applyConfig(final Tunnel tunnel, final Config config) throws Exception {
-        if (tunnel.getState() == State.UP) {
-            // Restart the tunnel to apply the new config.
-            setStateInternal(tunnel, tunnel.getConfig(), State.DOWN);
-            try {
-                setStateInternal(tunnel, config, State.UP);
-            } catch (final Exception e) {
-                // The new configuration didn't work, so try to go back to the old one.
-                setStateInternal(tunnel, tunnel.getConfig(), State.UP);
-                throw e;
-            }
-        }
-        return config;
-    }
-
-    @Override
-    public Set<String> enumerate() {
+    public Set<String> getRunningTunnelNames() {
         final List<String> output = new ArrayList<>();
         // Don't throw an exception here or nothing will show up in the UI.
         try {
@@ -80,7 +67,7 @@ public final class WgQuickBackend implements Backend {
 
     @Override
     public State getState(final Tunnel tunnel) {
-        return enumerate().contains(tunnel.getName()) ? State.UP : State.DOWN;
+        return getRunningTunnelNames().contains(tunnel.getName()) ? State.UP : State.DOWN;
     }
 
     @Override
@@ -120,20 +107,36 @@ public final class WgQuickBackend implements Backend {
     }
 
     @Override
-    public State setState(final Tunnel tunnel, State state) throws Exception {
+    public State setState(final Tunnel tunnel, State state, @Nullable final Config config) throws Exception {
         final State originalState = getState(tunnel);
+        final Config originalConfig = runningConfigs.get(tunnel);
+
         if (state == State.TOGGLE)
             state = originalState == State.UP ? State.DOWN : State.UP;
-        if (state == originalState)
+        if ((state == State.UP && originalState == State.UP && originalConfig != null && originalConfig == config) ||
+                (state == State.DOWN && originalState == State.DOWN))
             return originalState;
-        Log.d(TAG, "Changing tunnel " + tunnel.getName() + " to state " + state);
-        Application.getToolsInstaller().ensureToolsAvailable();
-        setStateInternal(tunnel, tunnel.getConfig(), state);
-        return getState(tunnel);
+        if (state == State.UP) {
+            Application.getToolsInstaller().ensureToolsAvailable();
+            if (originalState == State.UP)
+                setStateInternal(tunnel, originalConfig == null ? config : originalConfig, State.DOWN);
+            try {
+                setStateInternal(tunnel, config, State.UP);
+            } catch(final Exception e) {
+                if (originalState == State.UP && originalConfig != null)
+                    setStateInternal(tunnel, originalConfig, State.UP);
+                throw e;
+            }
+        } else if (state == State.DOWN) {
+            setStateInternal(tunnel, originalConfig == null ? config : originalConfig, State.DOWN);
+        }
+        return state;
     }
 
     private void setStateInternal(final Tunnel tunnel, @Nullable final Config config, final State state) throws Exception {
-        Objects.requireNonNull(config, "Trying to set state with a null config");
+        Log.i(TAG, "Bringing tunnel " + tunnel.getName() + " " + state);
+
+        Objects.requireNonNull(config, "Trying to set state up with a null config");
 
         final File tempFile = new File(localTemporaryDir, tunnel.getName() + ".conf");
         try (final FileOutputStream stream = new FileOutputStream(tempFile, false)) {
@@ -148,5 +151,23 @@ public final class WgQuickBackend implements Backend {
         tempFile.delete();
         if (result != 0)
             throw new Exception(context.getString(R.string.tunnel_config_error, result));
+
+        if (state == State.UP)
+            runningConfigs.put(tunnel, config);
+        else
+            runningConfigs.remove(tunnel);
+
+        for (final TunnelStateChangeNotificationReceiver notifier : notifiers)
+            notifier.tunnelStateChange(tunnel, state);
+    }
+
+    @Override
+    public void registerStateChangeNotification(final TunnelStateChangeNotificationReceiver receiver) {
+        notifiers.add(receiver);
+    }
+
+    @Override
+    public void unregisterStateChangeNotification(final TunnelStateChangeNotificationReceiver receiver) {
+        notifiers.remove(receiver);
     }
 }
diff --git a/app/src/main/java/com/wireguard/android/fragment/BaseFragment.java b/app/src/main/java/com/wireguard/android/fragment/BaseFragment.java
index 00e26348..11af26e4 100644
--- a/app/src/main/java/com/wireguard/android/fragment/BaseFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/BaseFragment.java
@@ -23,8 +23,8 @@ import com.wireguard.android.activity.BaseActivity.OnSelectedTunnelChangedListen
 import com.wireguard.android.backend.GoBackend;
 import com.wireguard.android.databinding.TunnelDetailFragmentBinding;
 import com.wireguard.android.databinding.TunnelListItemBinding;
-import com.wireguard.android.model.Tunnel;
-import com.wireguard.android.model.Tunnel.State;
+import com.wireguard.android.model.ObservableTunnel;
+import com.wireguard.android.backend.Tunnel.State;
 import com.wireguard.android.util.ErrorMessages;
 
 /**
@@ -36,11 +36,11 @@ public abstract class BaseFragment extends Fragment implements OnSelectedTunnelC
     private static final int REQUEST_CODE_VPN_PERMISSION = 23491;
     private static final String TAG = "WireGuard/" + BaseFragment.class.getSimpleName();
     @Nullable private BaseActivity activity;
-    @Nullable private Tunnel pendingTunnel;
+    @Nullable private ObservableTunnel pendingTunnel;
     @Nullable private Boolean pendingTunnelUp;
 
     @Nullable
-    protected Tunnel getSelectedTunnel() {
+    protected ObservableTunnel getSelectedTunnel() {
         return activity != null ? activity.getSelectedTunnel() : null;
     }
 
@@ -75,14 +75,14 @@ public abstract class BaseFragment extends Fragment implements OnSelectedTunnelC
         super.onDetach();
     }
 
-    protected void setSelectedTunnel(@Nullable final Tunnel tunnel) {
+    protected void setSelectedTunnel(@Nullable final ObservableTunnel tunnel) {
         if (activity != null)
             activity.setSelectedTunnel(tunnel);
     }
 
     public void setTunnelState(final View view, final boolean checked) {
         final ViewDataBinding binding = DataBindingUtil.findBinding(view);
-        final Tunnel tunnel;
+        final ObservableTunnel tunnel;
         if (binding instanceof TunnelDetailFragmentBinding)
             tunnel = ((TunnelDetailFragmentBinding) binding).getTunnel();
         else if (binding instanceof TunnelListItemBinding)
@@ -107,7 +107,7 @@ public abstract class BaseFragment extends Fragment implements OnSelectedTunnelC
         });
     }
 
-    private void setTunnelStateWithPermissionsResult(final Tunnel tunnel, final boolean checked) {
+    private void setTunnelStateWithPermissionsResult(final ObservableTunnel tunnel, final boolean checked) {
         tunnel.setState(State.of(checked)).whenComplete((state, throwable) -> {
             if (throwable == null)
                 return;
diff --git a/app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java b/app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java
index 57e0d8ea..89fe6c77 100644
--- a/app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java
@@ -18,8 +18,8 @@ import android.view.ViewGroup;
 import com.wireguard.android.R;
 import com.wireguard.android.databinding.TunnelDetailFragmentBinding;
 import com.wireguard.android.databinding.TunnelDetailPeerBinding;
-import com.wireguard.android.model.Tunnel;
-import com.wireguard.android.model.Tunnel.State;
+import com.wireguard.android.model.ObservableTunnel;
+import com.wireguard.android.backend.Tunnel.State;
 import com.wireguard.android.ui.EdgeToEdge;
 import com.wireguard.crypto.Key;
 
@@ -85,7 +85,7 @@ public class TunnelDetailFragment extends BaseFragment {
     }
 
     @Override
-    public void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel, @Nullable final Tunnel newTunnel) {
+    public void onSelectedTunnelChanged(@Nullable final ObservableTunnel oldTunnel, @Nullable final ObservableTunnel newTunnel) {
         if (binding == null)
             return;
         binding.setTunnel(newTunnel);
@@ -123,7 +123,7 @@ public class TunnelDetailFragment extends BaseFragment {
     private void updateStats() {
         if (binding == null || !isResumed())
             return;
-        final Tunnel tunnel = binding.getTunnel();
+        final ObservableTunnel tunnel = binding.getTunnel();
         if (tunnel == null)
             return;
         final State state = tunnel.getState();
diff --git a/app/src/main/java/com/wireguard/android/fragment/TunnelEditorFragment.java b/app/src/main/java/com/wireguard/android/fragment/TunnelEditorFragment.java
index a93fabf6..b342d5a8 100644
--- a/app/src/main/java/com/wireguard/android/fragment/TunnelEditorFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/TunnelEditorFragment.java
@@ -11,7 +11,7 @@ import androidx.databinding.ObservableList;
 import android.os.Bundle;
 import androidx.annotation.Nullable;
 import com.google.android.material.snackbar.Snackbar;
-import androidx.fragment.app.FragmentManager;
+
 import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.Menu;
@@ -26,7 +26,7 @@ import com.wireguard.android.Application;
 import com.wireguard.android.R;
 import com.wireguard.android.databinding.TunnelEditorFragmentBinding;
 import com.wireguard.android.fragment.AppListDialogFragment.AppExclusionListener;
-import com.wireguard.android.model.Tunnel;
+import com.wireguard.android.model.ObservableTunnel;
 import com.wireguard.android.model.TunnelManager;
 import com.wireguard.android.ui.EdgeToEdge;
 import com.wireguard.android.util.ErrorMessages;
@@ -47,7 +47,7 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
     private static final String TAG = "WireGuard/" + TunnelEditorFragment.class.getSimpleName();
 
     @Nullable private TunnelEditorFragmentBinding binding;
-    @Nullable private Tunnel tunnel;
+    @Nullable private ObservableTunnel tunnel;
 
     private void onConfigLoaded(final Config config) {
         if (binding != null) {
@@ -55,7 +55,7 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
         }
     }
 
-    private void onConfigSaved(final Tunnel savedTunnel,
+    private void onConfigSaved(final ObservableTunnel savedTunnel,
                                @Nullable final Throwable throwable) {
         final String message;
         if (throwable == null) {
@@ -126,7 +126,7 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
         getActivity().runOnUiThread(() -> {
             // TODO(smaeul): Remove this hack when fixing the Config ViewModel
             // The selected tunnel has to actually change, but we have to remember this one.
-            final Tunnel savedTunnel = tunnel;
+            final ObservableTunnel savedTunnel = tunnel;
             if (savedTunnel == getSelectedTunnel())
                 setSelectedTunnel(null);
             setSelectedTunnel(savedTunnel);
@@ -187,8 +187,8 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
     }
 
     @Override
-    public void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel,
-                                        @Nullable final Tunnel newTunnel) {
+    public void onSelectedTunnelChanged(@Nullable final ObservableTunnel oldTunnel,
+                                        @Nullable final ObservableTunnel newTunnel) {
         tunnel = newTunnel;
         if (binding == null)
             return;
@@ -201,7 +201,7 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
         }
     }
 
-    private void onTunnelCreated(final Tunnel newTunnel, @Nullable final Throwable throwable) {
+    private void onTunnelCreated(final ObservableTunnel newTunnel, @Nullable final Throwable throwable) {
         final String message;
         if (throwable == null) {
             tunnel = newTunnel;
@@ -219,7 +219,7 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
         }
     }
 
-    private void onTunnelRenamed(final Tunnel renamedTunnel, final Config newConfig,
+    private void onTunnelRenamed(final ObservableTunnel renamedTunnel, final Config newConfig,
                                  @Nullable final Throwable throwable) {
         final String message;
         if (throwable == null) {
diff --git a/app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java b/app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java
index fe8a3da1..21618e60 100644
--- a/app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java
@@ -17,7 +17,7 @@ import android.provider.OpenableColumns;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import com.google.android.material.snackbar.Snackbar;
-import androidx.fragment.app.FragmentManager;
+
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.appcompat.view.ActionMode;
 import androidx.recyclerview.widget.RecyclerView;
@@ -36,7 +36,7 @@ import com.wireguard.android.activity.TunnelCreatorActivity;
 import com.wireguard.android.databinding.ObservableKeyedRecyclerViewAdapter;
 import com.wireguard.android.databinding.TunnelListFragmentBinding;
 import com.wireguard.android.databinding.TunnelListItemBinding;
-import com.wireguard.android.model.Tunnel;
+import com.wireguard.android.model.ObservableTunnel;
 import com.wireguard.android.ui.EdgeToEdge;
 import com.wireguard.android.util.ErrorMessages;
 import com.wireguard.android.widget.MultiselectableRelativeLayout;
@@ -91,7 +91,7 @@ public class TunnelListFragment extends BaseFragment {
             return;
         final ContentResolver contentResolver = activity.getContentResolver();
 
-        final Collection<CompletableFuture<Tunnel>> futureTunnels = new ArrayList<>();
+        final Collection<CompletableFuture<ObservableTunnel>> futureTunnels = new ArrayList<>();
         final List<Throwable> throwables = new ArrayList<>();
         Application.getAsyncWorker().supplyAsync(() -> {
             final String[] columns = {OpenableColumns.DISPLAY_NAME};
@@ -161,9 +161,9 @@ public class TunnelListFragment extends BaseFragment {
                 onTunnelImportFinished(Collections.emptyList(), Collections.singletonList(exception));
             } else {
                 future.whenComplete((ignored1, ignored2) -> {
-                    final List<Tunnel> tunnels = new ArrayList<>(futureTunnels.size());
-                    for (final CompletableFuture<Tunnel> futureTunnel : futureTunnels) {
-                        Tunnel tunnel = null;
+                    final List<ObservableTunnel> tunnels = new ArrayList<>(futureTunnels.size());
+                    for (final CompletableFuture<ObservableTunnel> futureTunnel : futureTunnels) {
+                        ObservableTunnel tunnel = null;
                         try {
                             tunnel = futureTunnel.getNow(null);
                         } catch (final Exception e) {
@@ -250,7 +250,7 @@ public class TunnelListFragment extends BaseFragment {
     }
 
     @Override
-    public void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel, @Nullable final Tunnel newTunnel) {
+    public void onSelectedTunnelChanged(@Nullable final ObservableTunnel oldTunnel, @Nullable final ObservableTunnel newTunnel) {
         if (binding == null)
             return;
         Application.getTunnelManager().getTunnels().thenAccept(tunnels -> {
@@ -281,7 +281,7 @@ public class TunnelListFragment extends BaseFragment {
         showSnackbar(message);
     }
 
-    private void onTunnelImportFinished(final List<Tunnel> tunnels, final Collection<Throwable> throwables) {
+    private void onTunnelImportFinished(final List<ObservableTunnel> tunnels, final Collection<Throwable> throwables) {
         String message = null;
 
         for (final Throwable throwable : throwables) {
@@ -315,7 +315,7 @@ public class TunnelListFragment extends BaseFragment {
 
         binding.setFragment(this);
         Application.getTunnelManager().getTunnels().thenAccept(binding::setTunnels);
-        binding.setRowConfigurationHandler((ObservableKeyedRecyclerViewAdapter.RowConfigurationHandler<TunnelListItemBinding, Tunnel>) (binding, tunnel, position) -> {
+        binding.setRowConfigurationHandler((ObservableKeyedRecyclerViewAdapter.RowConfigurationHandler<TunnelListItemBinding, ObservableTunnel>) (binding, tunnel, position) -> {
             binding.setFragment(this);
             binding.getRoot().setOnClickListener(clicked -> {
                 if (actionMode == null) {
@@ -336,7 +336,7 @@ public class TunnelListFragment extends BaseFragment {
         });
     }
 
-    private MultiselectableRelativeLayout viewForTunnel(final Tunnel tunnel, final List tunnels) {
+    private MultiselectableRelativeLayout viewForTunnel(final ObservableTunnel tunnel, final List tunnels) {
         return (MultiselectableRelativeLayout) binding.tunnelList.findViewHolderForAdapterPosition(tunnels.indexOf(tunnel)).itemView;
     }
 
@@ -355,12 +355,12 @@ public class TunnelListFragment extends BaseFragment {
                 case R.id.menu_action_delete:
                     final Iterable<Integer> copyCheckedItems = new HashSet<>(checkedItems);
                     Application.getTunnelManager().getTunnels().thenAccept(tunnels -> {
-                        final Collection<Tunnel> tunnelsToDelete = new ArrayList<>();
+                        final Collection<ObservableTunnel> tunnelsToDelete = new ArrayList<>();
                         for (final Integer position : copyCheckedItems)
                             tunnelsToDelete.add(tunnels.get(position));
 
                         final CompletableFuture[] futures = StreamSupport.stream(tunnelsToDelete)
-                                .map(Tunnel::delete)
+                                .map(ObservableTunnel::delete)
                                 .toArray(CompletableFuture[]::new);
                         CompletableFuture.allOf(futures)
                                 .thenApply(x -> futures.length)
diff --git a/app/src/main/java/com/wireguard/android/model/Tunnel.java b/app/src/main/java/com/wireguard/android/model/ObservableTunnel.java
index 87b607d0..826a6a2a 100644
--- a/app/src/main/java/com/wireguard/android/model/Tunnel.java
+++ b/app/src/main/java/com/wireguard/android/model/ObservableTunnel.java
@@ -5,23 +5,17 @@
 
 package com.wireguard.android.model;
 
-import android.os.SystemClock;
-import android.util.Pair;
-
 import androidx.databinding.BaseObservable;
 import androidx.databinding.Bindable;
 import androidx.annotation.Nullable;
 
 import com.wireguard.android.BR;
+import com.wireguard.android.backend.Statistics;
+import com.wireguard.android.backend.Tunnel;
 import com.wireguard.android.util.ExceptionLoggers;
 import com.wireguard.config.Config;
-import com.wireguard.crypto.Key;
 import com.wireguard.util.Keyed;
 
-import java.util.HashMap;
-import java.util.Map;
-import java.util.regex.Pattern;
-
 import java9.util.concurrent.CompletableFuture;
 import java9.util.concurrent.CompletionStage;
 
@@ -29,28 +23,21 @@ import java9.util.concurrent.CompletionStage;
  * Encapsulates the volatile and nonvolatile state of a WireGuard tunnel.
  */
 
-public class Tunnel extends BaseObservable implements Keyed<String> {
-    public static final int NAME_MAX_LENGTH = 15;
-    private static final Pattern NAME_PATTERN = Pattern.compile("[a-zA-Z0-9_=+.-]{1,15}");
-
+public class ObservableTunnel extends BaseObservable implements Keyed<String>, Tunnel {
     private final TunnelManager manager;
     @Nullable private Config config;
-    private String name;
     private State state;
+    private String name;
     @Nullable private Statistics statistics;
 
-    Tunnel(final TunnelManager manager, final String name,
+    ObservableTunnel(final TunnelManager manager, final String name,
            @Nullable final Config config, final State state) {
-        this.manager = manager;
         this.name = name;
+        this.manager = manager;
         this.config = config;
         this.state = state;
     }
 
-    public static boolean isNameInvalid(final CharSequence name) {
-        return !NAME_PATTERN.matcher(name).matches();
-    }
-
     public CompletionStage<Void> delete() {
         return manager.delete(this);
     }
@@ -74,6 +61,7 @@ public class Tunnel extends BaseObservable implements Keyed<String> {
         return name;
     }
 
+    @Override
     @Bindable
     public String getName() {
         return name;
@@ -146,60 +134,4 @@ public class Tunnel extends BaseObservable implements Keyed<String> {
             return manager.setTunnelState(this, state);
         return CompletableFuture.completedFuture(this.state);
     }
-
-    public enum State {
-        DOWN,
-        TOGGLE,
-        UP;
-
-        public static State of(final boolean running) {
-            return running ? UP : DOWN;
-        }
-    }
-
-    public static class Statistics extends BaseObservable {
-        private long lastTouched = SystemClock.elapsedRealtime();
-        private final Map<Key, Pair<Long, Long>> peerBytes = new HashMap<>();
-
-        public void add(final Key key, final long rx, final long tx) {
-            peerBytes.put(key, Pair.create(rx, tx));
-            lastTouched = SystemClock.elapsedRealtime();
-        }
-
-        private boolean isStale() {
-            return SystemClock.elapsedRealtime() - lastTouched > 900;
-        }
-
-        public Key[] peers() {
-            return peerBytes.keySet().toArray(new Key[0]);
-        }
-
-        public long peerRx(final Key peer) {
-            if (!peerBytes.containsKey(peer))
-                return 0;
-            return peerBytes.get(peer).first;
-        }
-
-        public long peerTx(final Key peer) {
-            if (!peerBytes.containsKey(peer))
-                return 0;
-            return peerBytes.get(peer).second;
-        }
-
-        public long totalRx() {
-            long rx = 0;
-            for (final Pair<Long, Long> val : peerBytes.values()) {
-                rx += val.first;
-            }
-            return rx;
-        }
-
-        public long totalTx() {
-            long tx = 0;
-            for (final Pair<Long, Long> val : peerBytes.values()) {
-                tx += val.second;
-            }
-            return tx;
-        }
-    }
 }
diff --git a/app/src/main/java/com/wireguard/android/model/TunnelManager.java b/app/src/main/java/com/wireguard/android/model/TunnelManager.java
index 2deea6df..e7bb9cd5 100644
--- a/app/src/main/java/com/wireguard/android/model/TunnelManager.java
+++ b/app/src/main/java/com/wireguard/android/model/TunnelManager.java
@@ -15,9 +15,11 @@ import androidx.annotation.Nullable;
 import com.wireguard.android.Application;
 import com.wireguard.android.BR;
 import com.wireguard.android.R;
+import com.wireguard.android.backend.Backend.TunnelStateChangeNotificationReceiver;
 import com.wireguard.android.configStore.ConfigStore;
-import com.wireguard.android.model.Tunnel.State;
-import com.wireguard.android.model.Tunnel.Statistics;
+import com.wireguard.android.backend.Tunnel;
+import com.wireguard.android.backend.Tunnel.State;
+import com.wireguard.android.backend.Statistics;
 import com.wireguard.android.util.ExceptionLoggers;
 import com.wireguard.android.util.ObservableSortedKeyedArrayList;
 import com.wireguard.android.util.ObservableSortedKeyedList;
@@ -38,42 +40,49 @@ import java9.util.stream.StreamSupport;
  * Maintains and mediates changes to the set of available WireGuard tunnels,
  */
 
-public final class TunnelManager extends BaseObservable {
+public final class TunnelManager extends BaseObservable implements TunnelStateChangeNotificationReceiver {
     private static final Comparator<String> COMPARATOR = Comparators.<String>thenComparing(
             String.CASE_INSENSITIVE_ORDER, Comparators.naturalOrder());
     private static final String KEY_LAST_USED_TUNNEL = "last_used_tunnel";
     private static final String KEY_RESTORE_ON_BOOT = "restore_on_boot";
     private static final String KEY_RUNNING_TUNNELS = "enabled_configs";
 
-    private final CompletableFuture<ObservableSortedKeyedList<String, Tunnel>> completableTunnels = new CompletableFuture<>();
+    private final CompletableFuture<ObservableSortedKeyedList<String, ObservableTunnel>> completableTunnels = new CompletableFuture<>();
     private final ConfigStore configStore;
     private final Context context = Application.get();
     private final ArrayList<CompletableFuture<Void>> delayedLoadRestoreTunnels = new ArrayList<>();
-    private final ObservableSortedKeyedList<String, Tunnel> tunnels = new ObservableSortedKeyedArrayList<>(COMPARATOR);
+    private final ObservableSortedKeyedList<String, ObservableTunnel> tunnels = new ObservableSortedKeyedArrayList<>(COMPARATOR);
     private boolean haveLoaded;
-    @Nullable private Tunnel lastUsedTunnel;
+    @Nullable private ObservableTunnel lastUsedTunnel;
 
     public TunnelManager(final ConfigStore configStore) {
         this.configStore = configStore;
+        Application.getBackendAsync().thenAccept(backend -> backend.registerStateChangeNotification(this));
     }
 
-    static CompletionStage<State> getTunnelState(final Tunnel tunnel) {
+    @Override
+    protected void finalize() throws Throwable {
+        Application.getBackendAsync().thenAccept(backend -> backend.unregisterStateChangeNotification(this));
+        super.finalize();
+    }
+
+    static CompletionStage<State> getTunnelState(final ObservableTunnel tunnel) {
         return Application.getAsyncWorker().supplyAsync(() -> Application.getBackend().getState(tunnel))
                 .thenApply(tunnel::onStateChanged);
     }
 
-    static CompletionStage<Statistics> getTunnelStatistics(final Tunnel tunnel) {
+    static CompletionStage<Statistics> getTunnelStatistics(final ObservableTunnel tunnel) {
         return Application.getAsyncWorker().supplyAsync(() -> Application.getBackend().getStatistics(tunnel))
                 .thenApply(tunnel::onStatisticsChanged);
     }
 
-    private Tunnel addToList(final String name, @Nullable final Config config, final State state) {
-        final Tunnel tunnel = new Tunnel(this, name, config, state);
+    private ObservableTunnel addToList(final String name, @Nullable final Config config, final State state) {
+        final ObservableTunnel tunnel = new ObservableTunnel(this, name, config, state);
         tunnels.add(tunnel);
         return tunnel;
     }
 
-    public CompletionStage<Tunnel> create(final String name, @Nullable final Config config) {
+    public CompletionStage<ObservableTunnel> create(final String name, @Nullable final Config config) {
         if (Tunnel.isNameInvalid(name))
             return CompletableFuture.failedFuture(new IllegalArgumentException(context.getString(R.string.tunnel_error_invalid_name)));
         if (tunnels.containsKey(name)) {
@@ -84,7 +93,7 @@ public final class TunnelManager extends BaseObservable {
                 .thenApply(savedConfig -> addToList(name, savedConfig, State.DOWN));
     }
 
-    CompletionStage<Void> delete(final Tunnel tunnel) {
+    CompletionStage<Void> delete(final ObservableTunnel tunnel) {
         final State originalState = tunnel.getState();
         final boolean wasLastUsed = tunnel == lastUsedTunnel;
         // Make sure nothing touches the tunnel.
@@ -93,12 +102,12 @@ public final class TunnelManager extends BaseObservable {
         tunnels.remove(tunnel);
         return Application.getAsyncWorker().runAsync(() -> {
             if (originalState == State.UP)
-                Application.getBackend().setState(tunnel, State.DOWN);
+                Application.getBackend().setState(tunnel, State.DOWN, null);
             try {
                 configStore.delete(tunnel.getName());
             } catch (final Exception e) {
                 if (originalState == State.UP)
-                    Application.getBackend().setState(tunnel, State.UP);
+                    Application.getBackend().setState(tunnel, State.UP, tunnel.getConfig());
                 // Re-throw the exception to fail the completion.
                 throw e;
             }
@@ -114,22 +123,22 @@ public final class TunnelManager extends BaseObservable {
 
     @Bindable
     @Nullable
-    public Tunnel getLastUsedTunnel() {
+    public ObservableTunnel getLastUsedTunnel() {
         return lastUsedTunnel;
     }
 
-    CompletionStage<Config> getTunnelConfig(final Tunnel tunnel) {
+    CompletionStage<Config> getTunnelConfig(final ObservableTunnel tunnel) {
         return Application.getAsyncWorker().supplyAsync(() -> configStore.load(tunnel.getName()))
                 .thenApply(tunnel::onConfigChanged);
     }
 
-    public CompletableFuture<ObservableSortedKeyedList<String, Tunnel>> getTunnels() {
+    public CompletableFuture<ObservableSortedKeyedList<String, ObservableTunnel>> getTunnels() {
         return completableTunnels;
     }
 
     public void onCreate() {
         Application.getAsyncWorker().supplyAsync(configStore::enumerate)
-                .thenAcceptBoth(Application.getAsyncWorker().supplyAsync(() -> Application.getBackend().enumerate()), this::onTunnelsLoaded)
+                .thenAcceptBoth(Application.getAsyncWorker().supplyAsync(() -> Application.getBackend().getRunningTunnelNames()), this::onTunnelsLoaded)
                 .whenComplete(ExceptionLoggers.E);
     }
 
@@ -159,9 +168,9 @@ public final class TunnelManager extends BaseObservable {
     }
 
     public void refreshTunnelStates() {
-        Application.getAsyncWorker().supplyAsync(() -> Application.getBackend().enumerate())
+        Application.getAsyncWorker().supplyAsync(() -> Application.getBackend().getRunningTunnelNames())
                 .thenAccept(running -> {
-                    for (final Tunnel tunnel : tunnels)
+                    for (final ObservableTunnel tunnel : tunnels)
                         tunnel.onStateChanged(running.contains(tunnel.getName()) ? State.UP : State.DOWN);
                 })
                 .whenComplete(ExceptionLoggers.E);
@@ -189,12 +198,12 @@ public final class TunnelManager extends BaseObservable {
     public void saveState() {
         final Set<String> runningTunnels = StreamSupport.stream(tunnels)
                 .filter(tunnel -> tunnel.getState() == State.UP)
-                .map(Tunnel::getName)
+                .map(ObservableTunnel::getName)
                 .collect(Collectors.toUnmodifiableSet());
         Application.getSharedPreferences().edit().putStringSet(KEY_RUNNING_TUNNELS, runningTunnels).apply();
     }
 
-    private void setLastUsedTunnel(@Nullable final Tunnel tunnel) {
+    private void setLastUsedTunnel(@Nullable final ObservableTunnel tunnel) {
         if (tunnel == lastUsedTunnel)
             return;
         lastUsedTunnel = tunnel;
@@ -205,14 +214,14 @@ public final class TunnelManager extends BaseObservable {
             Application.getSharedPreferences().edit().remove(KEY_LAST_USED_TUNNEL).apply();
     }
 
-    CompletionStage<Config> setTunnelConfig(final Tunnel tunnel, final Config config) {
+    CompletionStage<Config> setTunnelConfig(final ObservableTunnel tunnel, final Config config) {
         return Application.getAsyncWorker().supplyAsync(() -> {
-            final Config appliedConfig = Application.getBackend().applyConfig(tunnel, config);
-            return configStore.save(tunnel.getName(), appliedConfig);
+            Application.getBackend().setState(tunnel, tunnel.getState(), config);
+            return configStore.save(tunnel.getName(), config);
         }).thenApply(tunnel::onConfigChanged);
     }
 
-    CompletionStage<String> setTunnelName(final Tunnel tunnel, final String name) {
+    CompletionStage<String> setTunnelName(final ObservableTunnel tunnel, final String name) {
         if (Tunnel.isNameInvalid(name))
             return CompletableFuture.failedFuture(new IllegalArgumentException(context.getString(R.string.tunnel_error_invalid_name)));
         if (tunnels.containsKey(name)) {
@@ -227,11 +236,11 @@ public final class TunnelManager extends BaseObservable {
         tunnels.remove(tunnel);
         return Application.getAsyncWorker().supplyAsync(() -> {
             if (originalState == State.UP)
-                Application.getBackend().setState(tunnel, State.DOWN);
+                Application.getBackend().setState(tunnel, State.DOWN, null);
             configStore.rename(tunnel.getName(), name);
             final String newName = tunnel.onNameChanged(name);
             if (originalState == State.UP)
-                Application.getBackend().setState(tunnel, State.UP);
+                Application.getBackend().setState(tunnel, State.UP, tunnel.getConfig());
             return newName;
         }).whenComplete((newName, e) -> {
             // On failure, we don't know what state the tunnel might be in. Fix that.
@@ -244,10 +253,10 @@ public final class TunnelManager extends BaseObservable {
         });
     }
 
-    CompletionStage<State> setTunnelState(final Tunnel tunnel, final State state) {
+    CompletionStage<State> setTunnelState(final ObservableTunnel tunnel, final State state) {
         // Ensure the configuration is loaded before trying to use it.
-        return tunnel.getConfigAsync().thenCompose(x ->
-                Application.getAsyncWorker().supplyAsync(() -> Application.getBackend().setState(tunnel, state))
+        return tunnel.getConfigAsync().thenCompose(config ->
+                Application.getAsyncWorker().supplyAsync(() -> Application.getBackend().setState(tunnel, state, config))
         ).whenComplete((newState, e) -> {
             // Ensure onStateChanged is always called (failure or not), and with the correct state.
             tunnel.onStateChanged(e == null ? newState : tunnel.getState());
@@ -257,6 +266,11 @@ public final class TunnelManager extends BaseObservable {
         });
     }
 
+    @Override
+    public void tunnelStateChange(final Tunnel tunnel, final State state) {
+        ((ObservableTunnel)tunnel).onStateChanged(state);
+    }
+
     public static final class IntentReceiver extends BroadcastReceiver {
         @Override
         public void onReceive(final Context context, @Nullable final Intent intent) {
@@ -290,7 +304,7 @@ public final class TunnelManager extends BaseObservable {
             if (tunnelName == null)
                 return;
             manager.getTunnels().thenAccept(tunnels -> {
-                final Tunnel tunnel = tunnels.get(tunnelName);
+                final ObservableTunnel tunnel = tunnels.get(tunnelName);
                 if (tunnel == null)
                     return;
                 manager.setTunnelState(tunnel, state);
diff --git a/app/src/main/java/com/wireguard/android/preference/ZipExporterPreference.java b/app/src/main/java/com/wireguard/android/preference/ZipExporterPreference.java
index efda91bb..3af412a5 100644
--- a/app/src/main/java/com/wireguard/android/preference/ZipExporterPreference.java
+++ b/app/src/main/java/com/wireguard/android/preference/ZipExporterPreference.java
@@ -16,7 +16,7 @@ import android.util.Log;
 
 import com.wireguard.android.Application;
 import com.wireguard.android.R;
-import com.wireguard.android.model.Tunnel;
+import com.wireguard.android.model.ObservableTunnel;
 import com.wireguard.android.util.DownloadsFileSaver;
 import com.wireguard.android.util.DownloadsFileSaver.DownloadsFile;
 import com.wireguard.android.util.ErrorMessages;
@@ -48,9 +48,9 @@ public class ZipExporterPreference extends Preference {
         Application.getTunnelManager().getTunnels().thenAccept(this::exportZip);
     }
 
-    private void exportZip(final List<Tunnel> tunnels) {
+    private void exportZip(final List<ObservableTunnel> tunnels) {
         final List<CompletableFuture<Config>> futureConfigs = new ArrayList<>(tunnels.size());
-        for (final Tunnel tunnel : tunnels)
+        for (final ObservableTunnel tunnel : tunnels)
             futureConfigs.add(tunnel.getConfigAsync().toCompletableFuture());
         if (futureConfigs.isEmpty()) {
             exportZipComplete(null, new IllegalArgumentException(
diff --git a/app/src/main/java/com/wireguard/android/widget/NameInputFilter.java b/app/src/main/java/com/wireguard/android/widget/NameInputFilter.java
index 07759a18..030be25a 100644
--- a/app/src/main/java/com/wireguard/android/widget/NameInputFilter.java
+++ b/app/src/main/java/com/wireguard/android/widget/NameInputFilter.java
@@ -10,7 +10,7 @@ import android.text.InputFilter;
 import android.text.SpannableStringBuilder;
 import android.text.Spanned;
 
-import com.wireguard.android.model.Tunnel;
+import com.wireguard.android.backend.Tunnel;
 
 /**
  * InputFilter for entering WireGuard configuration names (Linux interface names).
diff --git a/app/src/main/res/layout/tunnel_detail_fragment.xml b/app/src/main/res/layout/tunnel_detail_fragment.xml
index 40a79eb7..463f8b80 100644
--- a/app/src/main/res/layout/tunnel_detail_fragment.xml
+++ b/app/src/main/res/layout/tunnel_detail_fragment.xml
@@ -5,7 +5,7 @@
 
     <data>
 
-        <import type="com.wireguard.android.model.Tunnel.State" />
+        <import type="com.wireguard.android.backend.Tunnel.State" />
 
         <import type="com.wireguard.android.util.ClipboardUtils" />
 
@@ -15,7 +15,7 @@
 
         <variable
             name="tunnel"
-            type="com.wireguard.android.model.Tunnel" />
+            type="com.wireguard.android.model.ObservableTunnel" />
 
         <variable
             name="config"
diff --git a/app/src/main/res/layout/tunnel_list_fragment.xml b/app/src/main/res/layout/tunnel_list_fragment.xml
index c4247019..c8144dbb 100644
--- a/app/src/main/res/layout/tunnel_list_fragment.xml
+++ b/app/src/main/res/layout/tunnel_list_fragment.xml
@@ -5,7 +5,7 @@
 
     <data>
 
-        <import type="com.wireguard.android.model.Tunnel" />
+        <import type="com.wireguard.android.model.ObservableTunnel" />
 
         <variable
             name="fragment"
@@ -17,7 +17,7 @@
 
         <variable
             name="tunnels"
-            type="com.wireguard.android.util.ObservableKeyedList&lt;String, Tunnel&gt;" />
+            type="com.wireguard.android.util.ObservableKeyedList&lt;String, ObservableTunnel&gt;" />
     </data>
 
     <androidx.coordinatorlayout.widget.CoordinatorLayout
diff --git a/app/src/main/res/layout/tunnel_list_item.xml b/app/src/main/res/layout/tunnel_list_item.xml
index 1cca9453..04c0f51e 100644
--- a/app/src/main/res/layout/tunnel_list_item.xml
+++ b/app/src/main/res/layout/tunnel_list_item.xml
@@ -5,13 +5,13 @@
 
     <data>
 
-        <import type="com.wireguard.android.model.Tunnel" />
+        <import type="com.wireguard.android.model.ObservableTunnel" />
 
-        <import type="com.wireguard.android.model.Tunnel.State" />
+        <import type="com.wireguard.android.backend.Tunnel.State" />
 
         <variable
             name="collection"
-            type="com.wireguard.android.util.ObservableKeyedList&lt;String, Tunnel&gt;" />
+            type="com.wireguard.android.util.ObservableKeyedList&lt;String, ObservableTunnel&gt;" />
 
         <variable
             name="key"
@@ -19,7 +19,7 @@
 
         <variable
             name="item"
-            type="com.wireguard.android.model.Tunnel" />
+            type="com.wireguard.android.model.ObservableTunnel" />
 
         <variable
             name="fragment"
diff --git a/app/src/main/res/values-hi/strings.xml b/app/src/main/res/values-hi/strings.xml
index 46785bc1..a9f01861 100644
--- a/app/src/main/res/values-hi/strings.xml
+++ b/app/src/main/res/values-hi/strings.xml
@@ -104,7 +104,6 @@
     <string name="module_installer_working">डाउनलोड कर रहा है और स्थापित कर रहा है…</string>
     <string name="module_installer_error">कुछ गलत हो गया। कृपया पुन: प्रयास करें</string>
     <string name="mtu">MTU</string>
-    <string name="multiple_tunnels_error">एक समय में केवल एक यूजरस्पेस टनल ही चल सकता है</string>
     <string name="name">नाम</string>
     <string name="no_config_error">बिना किसी कॉन्फ़िगरेशन के एक टनल को लाने की कोशिश करना</string>
     <string name="no_configs_error">कोई कॉन्फ़िगरेशन नहीं मिला</string>
diff --git a/app/src/main/res/values-it/strings.xml b/app/src/main/res/values-it/strings.xml
index a7bd29cb..b76c39cd 100644
--- a/app/src/main/res/values-it/strings.xml
+++ b/app/src/main/res/values-it/strings.xml
@@ -104,7 +104,6 @@
     <string name="module_installer_working">Scaricamento e installazione…</string>
     <string name="module_installer_error">Qualcosa è andato storto. Riprova</string>
     <string name="mtu">MTU</string>
-    <string name="multiple_tunnels_error">Può essere attivo solo un tunnel su spazio utente alla volta</string>
     <string name="name">Nome</string>
     <string name="no_config_error">Tentativo di attivare un tunnel senza configurazione</string>
     <string name="no_configs_error">Nessuna configurazione trovata</string>
diff --git a/app/src/main/res/values-ja/strings.xml b/app/src/main/res/values-ja/strings.xml
index 16cd165e..22d1b72f 100644
--- a/app/src/main/res/values-ja/strings.xml
+++ b/app/src/main/res/values-ja/strings.xml
@@ -98,7 +98,6 @@
     <string name="module_installer_working">ダウンロードしてインストールしています…</string>
     <string name="module_installer_error">失敗しました. 再度実行してみてください</string>
     <string name="mtu">MTU</string>
-    <string name="multiple_tunnels_error">同時に実行できるユーザースペーストンネルは1つだけです</string>
     <string name="name">名前</string>
     <string name="no_config_error">未設定のままトンネルを起動しようとしています</string>
     <string name="no_configs_error">設定が見つかりません</string>
diff --git a/app/src/main/res/values-ru/strings.xml b/app/src/main/res/values-ru/strings.xml
index 0add655c..c8f1b8aa 100644
--- a/app/src/main/res/values-ru/strings.xml
+++ b/app/src/main/res/values-ru/strings.xml
@@ -104,7 +104,6 @@
     <string name="module_installer_working">Скачивание и установка…</string>
     <string name="module_installer_error">Что-то пошло не так. Пожалуйста, попробуйте еще раз</string>
     <string name="mtu">MTU</string>
-    <string name="multiple_tunnels_error">Только один пользовательский туннель может работать одновременно</string>
     <string name="name">Имя</string>
     <string name="no_config_error">Попытка поднять туннель без конфигурации</string>
     <string name="no_configs_error">Конфигурации не найдены</string>
diff --git a/app/src/main/res/values-zh-rCN/strings.xml b/app/src/main/res/values-zh-rCN/strings.xml
index 26ca0232..8f7ab987 100644
--- a/app/src/main/res/values-zh-rCN/strings.xml
+++ b/app/src/main/res/values-zh-rCN/strings.xml
@@ -98,7 +98,6 @@
     <string name="module_installer_working">正在下载安装...</string>
     <string name="module_installer_error">发生错误，请重试</string>
     <string name="mtu">MTU</string>
-    <string name="multiple_tunnels_error">用户空间内一次只能建立一个连接</string>
     <string name="name">名称</string>
     <string name="no_config_error">尝试在无配置情况下建立连接</string>
     <string name="no_configs_error">未找到配置</string>
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 91bbf0f1..45964eec 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -104,7 +104,6 @@
     <string name="module_installer_working">Downloading and installing…</string>
     <string name="module_installer_error">Something went wrong. Please try again</string>
     <string name="mtu">MTU</string>
-    <string name="multiple_tunnels_error">Only one userspace tunnel can run at a time</string>
     <string name="name">Name</string>
     <string name="no_config_error">Trying to bring up a tunnel with no config</string>
     <string name="no_configs_error">No configurations found</string>