Application: use proper completablefuture for backend

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

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

@@ -19,7 +19,6 @@ import android.support.v7.app.AppCompatDelegate;
 import com.wireguard.android.backend.Backend;
 import com.wireguard.android.backend.GoBackend;
 import com.wireguard.android.backend.WgQuickBackend;
-import com.wireguard.android.configStore.ConfigStore;
 import com.wireguard.android.configStore.FileConfigStore;
 import com.wireguard.android.model.TunnelManager;
 import com.wireguard.android.util.AsyncWorker;
@@ -37,10 +36,8 @@ import java.io.File;
 import java.lang.ref.WeakReference;
 import java.security.cert.CertificateFactory;
 import java.security.cert.X509Certificate;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Objects;
-import java.util.concurrent.Executor;
+
+import java9.util.concurrent.CompletableFuture;
 
 
 @AcraCore(reportFormat = StringFormat.JSON,
@@ -59,10 +56,8 @@ public class Application extends android.app.Application {
     @SuppressWarnings("NullableProblems") private SharedPreferences sharedPreferences;
     @SuppressWarnings("NullableProblems") private ToolsInstaller toolsInstaller;
     @SuppressWarnings("NullableProblems") private TunnelManager tunnelManager;
-    @SuppressWarnings("NullableProblems") private Handler handler;
     @Nullable private Backend backend;
-    @Nullable private Collection<BackendCallback> haveBackendCallbacks = new ArrayList<>();
-    private final Object haveBackendCallbacksLock = new Object();
+    private final CompletableFuture<Backend> futureBackend = new CompletableFuture<>();
 
     public Application() {
         weakSelf = new WeakReference<>(this);
@@ -114,43 +109,26 @@ public class Application extends android.app.Application {
 
     public static Backend getBackend() {
         final Application app = get();
-        synchronized (app) {
+        synchronized (app.futureBackend) {
             if (app.backend == null) {
+                Backend backend = null;
                 if (new File("/sys/module/wireguard").exists()) {
                     try {
                         app.rootShell.start();
-                        app.backend = new WgQuickBackend(app.getApplicationContext());
-                    } catch (final Exception ignored) { }
-                }
-                if (app.backend == null)
-                    app.backend = new GoBackend(app.getApplicationContext());
-                synchronized (app.haveBackendCallbacksLock) {
-                    if (app.haveBackendCallbacks != null) {
-                        for (final BackendCallback callback : app.haveBackendCallbacks)
-                            app.handler.post(() -> callback.callback(app.backend));
-                        app.haveBackendCallbacks = null;
+                        backend = new WgQuickBackend(app.getApplicationContext());
+                    } catch (final Exception ignored) {
                     }
                 }
+                if (backend == null)
+                    backend = new GoBackend(app.getApplicationContext());
+                app.backend = backend;
             }
             return app.backend;
         }
     }
 
-    @FunctionalInterface
-    public interface BackendCallback {
-        void callback(final Backend backend);
-    }
-
-    public static void onHaveBackend(final BackendCallback callback) {
-        final Application app = get();
-        synchronized (app.haveBackendCallbacksLock) {
-            if (app.haveBackendCallbacks == null) {
-                Objects.requireNonNull(app.backend, "Backend still null in onHaveBackend call");
-                callback.callback(app.backend);
-            } else {
-                app.haveBackendCallbacks.add(callback);
-            }
-        }
+    public static CompletableFuture<Backend> getBackendAsync() {
+        return get().futureBackend;
     }
 
     public static RootShell getRootShell() {
@@ -173,11 +151,7 @@ public class Application extends android.app.Application {
     public void onCreate() {
         super.onCreate();
 
-        handler = new Handler(Looper.getMainLooper());
-        final Executor executor = AsyncTask.SERIAL_EXECUTOR;
-        final ConfigStore configStore = new FileConfigStore(getApplicationContext());
-
-        asyncWorker = new AsyncWorker(executor, handler);
+        asyncWorker = new AsyncWorker(AsyncTask.SERIAL_EXECUTOR, new Handler(Looper.getMainLooper()));
         rootShell = new RootShell(getApplicationContext());
         toolsInstaller = new ToolsInstaller(getApplicationContext());
 
@@ -186,16 +160,14 @@ public class Application extends android.app.Application {
                 sharedPreferences.getBoolean("dark_theme", false) ?
                         AppCompatDelegate.MODE_NIGHT_YES : AppCompatDelegate.MODE_NIGHT_NO);
 
-        tunnelManager = new TunnelManager(configStore);
-        asyncWorker.runAsync(Application::getBackend);
+        tunnelManager = new TunnelManager(new FileConfigStore(getApplicationContext()));
         tunnelManager.onCreate();
 
-        onHaveBackend(backend -> {
+        asyncWorker.supplyAsync(Application::getBackend).thenAccept(backend -> {
+            futureBackend.complete(backend);
             ACRA.getErrorReporter().putCustomData("backend", backend.getClass().getSimpleName());
-            getAsyncWorker().supplyAsync(backend::getVersion).whenComplete((version, exception) -> {
-                if (exception == null)
-                    ACRA.getErrorReporter().putCustomData("backendVersion", version);
-            });
+            asyncWorker.supplyAsync(backend::getVersion).thenAccept(version ->
+                    ACRA.getErrorReporter().putCustomData("backendVersion", version));
         });
     }
 }

app/src/main/java/com/wireguard/android/BootShutdownReceiver.java

@@ -20,7 +20,7 @@ public class BootShutdownReceiver extends BroadcastReceiver {
 
     @Override
     public void onReceive(final Context context, final Intent intent) {
-        Application.onHaveBackend(backend -> {
+        Application.getBackendAsync().thenAccept(backend -> {
             if (!(backend instanceof WgQuickBackend))
                 return;
             final String action = intent.getAction();

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

@@ -99,7 +99,7 @@ public class SettingsActivity extends ThemeChangeAwareActivity {
             for (final Preference pref : wgQuickOnlyPrefs)
                 pref.setVisible(false);
             final PreferenceScreen screen = getPreferenceScreen();
-            Application.onHaveBackend(backend -> {
+            Application.getBackendAsync().thenAccept(backend -> {
                 for (final Preference pref : wgQuickOnlyPrefs) {
                     if (backend instanceof WgQuickBackend)
                         pref.setVisible(true);

app/src/main/java/com/wireguard/android/fragment/BaseFragment.java

@@ -94,7 +94,7 @@ public abstract class BaseFragment extends Fragment implements OnSelectedTunnelC
         if (tunnel == null)
             return;
 
-        Application.onHaveBackend(backend -> {
+        Application.getBackendAsync().thenAccept(backend -> {
             if (backend instanceof GoBackend) {
                 final Intent intent = GoBackend.VpnService.prepare(view.getContext());
                 if (intent != null) {

app/src/main/java/com/wireguard/android/preference/VersionPreference.java

@@ -23,7 +23,7 @@ public class VersionPreference extends Preference {
     public VersionPreference(final Context context, final AttributeSet attrs) {
         super(context, attrs);
 
-        Application.onHaveBackend(backend -> {
+        Application.getBackendAsync().thenAccept(backend -> {
             versionSummary = getContext().getString(R.string.version_summary_checking, backend.getTypeName().toLowerCase());
             Application.getAsyncWorker().supplyAsync(backend::getVersion).whenComplete((version, exception) -> {
                 versionSummary = exception == null