WgQuickBackend: by default use single-tunnel mode like GoBackend, but add option

Note that this currently doesn't play well with people activating
wg-quick tunnels from outside the app. Those tunnels won't be
deactivated. But presumably that's desired behavior anyway, considering
people are mucking around at the command line.

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

tunnel/src/main/java/com/wireguard/android/backend/WgQuickBackend.java

@@ -9,6 +9,7 @@ import androidx.annotation.Nullable;
 
 import android.content.Context;
 import android.util.Log;
+import android.util.Pair;
 
 import com.wireguard.android.backend.BackendException.Reason;
 import com.wireguard.android.backend.Tunnel.State;
@@ -23,6 +24,7 @@ import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -44,6 +46,7 @@ public final class WgQuickBackend implements Backend {
     private final ToolsInstaller toolsInstaller;
     private final File localTemporaryDir;
     private final Map<Tunnel, Config> runningConfigs = new HashMap<>();
+    private boolean multipleTunnels;
 
     public WgQuickBackend(final Context context, final RootShell rootShell, final ToolsInstaller toolsInstaller) {
         localTemporaryDir = new File(context.getCacheDir(), "tmp");
@@ -51,6 +54,10 @@ public final class WgQuickBackend implements Backend {
         this.toolsInstaller = toolsInstaller;
     }
 
+    public void setMultipleTunnels(boolean on) {
+        multipleTunnels = on;
+    }
+
     @Override
     public Set<String> getRunningTunnelNames() {
         final List<String> output = new ArrayList<>();
@@ -106,6 +113,7 @@ public final class WgQuickBackend implements Backend {
     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);
+        final Map<Tunnel, Config> runningConfigsSnapshot = new HashMap<>(runningConfigs);
 
         if (state == State.TOGGLE)
             state = originalState == State.UP ? State.DOWN : State.UP;
@@ -114,13 +122,37 @@ public final class WgQuickBackend implements Backend {
             return originalState;
         if (state == State.UP) {
             toolsInstaller.ensureToolsAvailable();
+            if (!multipleTunnels && originalState == State.DOWN) {
+                final List<Pair<Tunnel, Config>> rewind = new LinkedList<>();
+                try {
+                    for (final Map.Entry<Tunnel, Config> entry : runningConfigsSnapshot.entrySet()) {
+                        setStateInternal(entry.getKey(), entry.getValue(), State.DOWN);
+                        rewind.add(Pair.create(entry.getKey(), entry.getValue()));
+                    }
+                } catch (final Exception e) {
+                    try {
+                        for (final Pair<Tunnel, Config> entry : rewind) {
+                            setStateInternal(entry.first, entry.second, State.UP);
+                        }
+                    } catch (final Exception ignored) { }
+                    throw e;
+                }
+            }
             if (originalState == State.UP)
                 setStateInternal(tunnel, originalConfig == null ? config : originalConfig, State.DOWN);
             try {
                 setStateInternal(tunnel, config, State.UP);
-            } catch(final Exception e) {
+            } catch (final Exception e) {
-                if (originalState == State.UP && originalConfig != null)
+                try {
+                    if (originalState == State.UP && originalConfig != null) {
                         setStateInternal(tunnel, originalConfig, State.UP);
+                    }
+                    if (!multipleTunnels && originalState == State.DOWN) {
+                        for (final Map.Entry<Tunnel, Config> entry : runningConfigsSnapshot.entrySet()) {
+                            setStateInternal(entry.getKey(), entry.getValue(), State.UP);
+                        }
+                    }
+                } catch (final Exception ignored) { }
                 throw e;
             }
         } else if (state == State.DOWN) {

ui/src/main/java/com/wireguard/android/Application.java

@@ -35,7 +35,7 @@ import java.util.Locale;
 
 import java9.util.concurrent.CompletableFuture;
 
-public class Application extends android.app.Application {
+public class Application extends android.app.Application implements SharedPreferences.OnSharedPreferenceChangeListener {
     private static final String TAG = "WireGuard/" + Application.class.getSimpleName();
     public static final String USER_AGENT;
 
@@ -86,7 +86,9 @@ public class Application extends android.app.Application {
                     try {
                         if (!didStartRootShell)
                             app.rootShell.start();
-                        backend = new WgQuickBackend(app.getApplicationContext(), app.rootShell, app.toolsInstaller);
+                        WgQuickBackend wgQuickBackend = new WgQuickBackend(app.getApplicationContext(), app.rootShell, app.toolsInstaller);
+                        wgQuickBackend.setMultipleTunnels(app.sharedPreferences.getBoolean("multiple_tunnels", false));
+                        backend = wgQuickBackend;
                     } catch (final Exception ignored) {
                     }
                 }
@@ -167,5 +169,19 @@ public class Application extends android.app.Application {
         tunnelManager.onCreate();
 
         asyncWorker.supplyAsync(Application::getBackend).thenAccept(futureBackend::complete);
+
+        sharedPreferences.registerOnSharedPreferenceChangeListener(this);
+    }
+
+    @Override
+    public void onTerminate() {
+        sharedPreferences.unregisterOnSharedPreferenceChangeListener(this);
+        super.onTerminate();
+    }
+
+    @Override
+    public void onSharedPreferenceChanged(final SharedPreferences sharedPreferences, final String key) {
+        if ("multiple_tunnels".equals(key) && backend != null && backend instanceof WgQuickBackend)
+            ((WgQuickBackend)backend).setMultipleTunnels(sharedPreferences.getBoolean(key, false));
     }
 }

ui/src/main/java/com/wireguard/android/activity/SettingsActivity.java

@@ -99,7 +99,8 @@ public class SettingsActivity extends ThemeChangeAwareActivity {
 
             final Preference wgQuickOnlyPrefs[] = {
                     getPreferenceManager().findPreference("tools_installer"),
-                    getPreferenceManager().findPreference("restore_on_boot")
+                    getPreferenceManager().findPreference("restore_on_boot"),
+                    getPreferenceManager().findPreference("multiple_tunnels")
             };
             for (final Preference pref : wgQuickOnlyPrefs)
                 pref.setVisible(false);

ui/src/main/res/values/strings.xml

@@ -104,6 +104,9 @@
     <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_title">Allow multiple simultaneous tunnels</string>
+    <string name="multiple_tunnels_summary_on">Multiple tunnels may be turned on simultaneously</string>
+    <string name="multiple_tunnels_summary_off">Turning on one tunnel will turn off others</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>

ui/src/main/res/xml/preferences.xml

@@ -8,6 +8,12 @@
         android:title="@string/restore_on_boot_title" />
     <com.wireguard.android.preference.ModuleDownloaderPreference android:key="module_downloader" />
     <com.wireguard.android.preference.ToolsInstallerPreference android:key="tools_installer" />
+    <CheckBoxPreference
+        android:defaultValue="false"
+        android:key="multiple_tunnels"
+        android:summaryOff="@string/multiple_tunnels_summary_off"
+        android:summaryOn="@string/multiple_tunnels_summary_on"
+        android:title="@string/multiple_tunnels_title" />
     <com.wireguard.android.preference.ZipExporterPreference />
     <com.wireguard.android.preference.LogExporterPreference />
     <CheckBoxPreference