Split ConditionManager into API-specific versions

* On API 29+ we need the location permission to start the hotspot, while
  on lower API levels, we don't. In order to handle permissions and
  other conditions in a clear manner depending the API level of the
  device the app is running on, have separate extensions of the base
  ConditionManager class.
* Take special care to handle situations gracefully where the Wifi is
  disabled and the user tries to start the hotspot. We cannot simply
  rely on Wifi being enabled as a sufficient condition that allows us to
  start the hotspot. We need to wait for WifiP2p to be available. While
  it is tricky to obtain that state (it involves registering a broadcast
  receiver for the WIFI_P2P_STATE_CHANGED_ACTION broadcast, keeping
  track of changes there and even then things are still ugly. It can
  happen that WifiP2p is available *before* Wifi is. Also it can happen
  that WifiP2p never becomes available because some other application
  has already opened a hotspot. Instead of checking that state, we now
  just try (and retry repeatedly after a delay) to start the hotspot
  (and the WifiP2p framework) hoping that is becomes availabe within a
  reasonable amount of time after Wifi has been detected to be on.
  Currently we try 5 times with a delay of 1 second.
* Improve the behavior of disabling and re-enabling the 'start hotspot'
  button, so that it becomes impossible to double-tap it, but still
  making sure that the button get re-enabled as soon as the UI is back
  in a state where the user should be able to tap the button again.

briar-android/src/main/java/org/briarproject/briar/android/hotspot/ConditionManager.java

@@ -1,171 +1,53 @@
 package org.briarproject.briar.android.hotspot;
 
-import android.content.DialogInterface.OnClickListener;
-import android.content.Intent;
 import android.net.wifi.WifiManager;
-import android.provider.Settings;
 
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.briar.R;
-
-import androidx.activity.result.ActivityResult;
-import androidx.activity.result.ActivityResultLauncher;
-import androidx.annotation.Nullable;
-import androidx.annotation.StringRes;
-import androidx.appcompat.app.AlertDialog;
+import androidx.core.util.Consumer;
 import androidx.fragment.app.FragmentActivity;
 
-import static android.Manifest.permission.ACCESS_FINE_LOCATION;
 import static android.content.Context.WIFI_SERVICE;
-import static android.os.Build.VERSION.SDK_INT;
-import static androidx.core.app.ActivityCompat.shouldShowRequestPermissionRationale;
-import static org.briarproject.briar.android.util.UiUtils.getGoToSettingsListener;
 
 /**
- * This class ensures that the conditions to open a hotspot are fulfilled.
- * <p>
- * Be sure to call {@link #onRequestPermissionResult(Boolean)} and
- * {@link #onRequestWifiEnabledResult()} when you get the
- * {@link ActivityResult}.
- * <p>
- * As soon as {@link #checkAndRequestConditions()} returns true,
- * all conditions are fulfilled.
+ * Abstract base class for the ConditionManagers that ensure that the conditions
+ * to open a hotspot are fulfilled. There are different extensions of this for
+ * API levels lower than 29 and 29+.
  */
-@NotNullByDefault
-class ConditionManager {
+abstract class ConditionManager {
 
-	private enum Permission {
+	enum Permission {
 		UNKNOWN, GRANTED, SHOW_RATIONALE, PERMANENTLY_DENIED
 	}
 
-	private Permission locationPermission = Permission.UNKNOWN;
-	private Permission wifiSetting = Permission.SHOW_RATIONALE;
+	protected final Consumer<Boolean> permissionUpdateCallback;
+	protected FragmentActivity ctx;
+	protected WifiManager wifiManager;
 
-	private final FragmentActivity ctx;
-	private final WifiManager wifiManager;
-	private final ActivityResultLauncher<String> locationRequest;
-	private final ActivityResultLauncher<Intent> wifiRequest;
+	ConditionManager(Consumer<Boolean> permissionUpdateCallback) {
+		this.permissionUpdateCallback = permissionUpdateCallback;
+	}
 
-	ConditionManager(FragmentActivity ctx,
-			ActivityResultLauncher<String> locationRequest,
-			ActivityResultLauncher<Intent> wifiRequest) {
+	/**
+	 * Pass a FragmentActivity context here during `onCreateView()`.
+	 */
+	void init(FragmentActivity ctx) {
 		this.ctx = ctx;
 		this.wifiManager = (WifiManager) ctx.getApplicationContext()
 				.getSystemService(WIFI_SERVICE);
-		this.locationRequest = locationRequest;
-		this.wifiRequest = wifiRequest;
 	}
 
 	/**
-	 * Call this to reset state when UI starts,
-	 * because state might have changed.
+	 * Call this during onStart() in the fragment where the ConditionManager
+	 * is used.
 	 */
-	void resetPermissions() {
-		locationPermission = Permission.UNKNOWN;
-		wifiSetting = Permission.SHOW_RATIONALE;
-	}
-
-	/**
-	 * This makes a request for location permission.
-	 * If {@link #checkAndRequestConditions()} returns true, you can continue.
-	 */
-	void startConditionChecks() {
-		locationRequest.launch(ACCESS_FINE_LOCATION);
-	}
+	abstract void onStart();
 
 	/**
+	 * Check if all required conditions are met such that the hotspot can be
+	 * started. If any precondition is not met yet, bring up relevant dialogs
+	 * asking the user to grant relevant permissions or take relevant actions.
+	 *
 	 * @return true if conditions are fulfilled and flow can continue.
 	 */
-	boolean checkAndRequestConditions() {
-		if (areEssentialPermissionsGranted()) return true;
-
-		// If an essential permission has been permanently denied, ask the
-		// user to change the setting
-		if (locationPermission == Permission.PERMANENTLY_DENIED) {
-			showDenialDialog(R.string.permission_location_title,
-					R.string.permission_hotspot_location_denied_body,
-					getGoToSettingsListener(ctx));
-			return false;
-		}
-		if (wifiSetting == Permission.PERMANENTLY_DENIED) {
-			showDenialDialog(R.string.wifi_settings_title,
-					R.string.wifi_settings_request_denied_body,
-					(d, w) -> requestEnableWiFi());
-			return false;
-		}
-
-		// Should we show the rationale for location permission or Wi-Fi?
-		if (locationPermission == Permission.SHOW_RATIONALE) {
-			showRationale(R.string.permission_location_title,
-					R.string.permission_hotspot_location_request_body,
-					this::requestPermissions);
-		} else if (wifiSetting == Permission.SHOW_RATIONALE) {
-			showRationale(R.string.wifi_settings_title,
-					R.string.wifi_settings_request_enable_body,
-					this::requestEnableWiFi);
-		}
-		return false;
-	}
-
-	void onRequestPermissionResult(@Nullable Boolean granted) {
-		if (granted != null && granted) {
-			locationPermission = Permission.GRANTED;
-		} else if (shouldShowRequestPermissionRationale(ctx,
-				ACCESS_FINE_LOCATION)) {
-			locationPermission = Permission.SHOW_RATIONALE;
-		} else {
-			locationPermission = Permission.PERMANENTLY_DENIED;
-		}
-	}
-
-	void onRequestWifiEnabledResult() {
-		wifiSetting = wifiManager.isWifiEnabled() ? Permission.GRANTED :
-				Permission.PERMANENTLY_DENIED;
-	}
-
-	private boolean areEssentialPermissionsGranted() {
-		if (SDK_INT < 29) {
-			if (!wifiManager.isWifiEnabled()) {
-				//noinspection deprecation
-				return wifiManager.setWifiEnabled(true);
-			}
-			return true;
-		} else {
-			return locationPermission == Permission.GRANTED
-					&& wifiManager.isWifiEnabled();
-		}
-	}
-
-	private void showDenialDialog(@StringRes int title, @StringRes int body,
-			OnClickListener onOkClicked) {
-		AlertDialog.Builder builder = new AlertDialog.Builder(ctx);
-		builder.setTitle(title);
-		builder.setMessage(body);
-		builder.setPositiveButton(R.string.ok, onOkClicked);
-		builder.setNegativeButton(R.string.cancel,
-				(dialog, which) -> ctx.supportFinishAfterTransition());
-		builder.show();
-	}
-
-	private void showRationale(@StringRes int title, @StringRes int body,
-			Runnable onContinueClicked) {
-		AlertDialog.Builder builder = new AlertDialog.Builder(ctx);
-		builder.setTitle(title);
-		builder.setMessage(body);
-		builder.setNeutralButton(R.string.continue_button,
-				(dialog, which) -> onContinueClicked.run());
-		builder.show();
-	}
-
-	private void requestPermissions() {
-		locationRequest.launch(ACCESS_FINE_LOCATION);
-	}
-
-	private void requestEnableWiFi() {
-		Intent i = SDK_INT < 29 ?
-				new Intent(Settings.ACTION_WIFI_SETTINGS) :
-				new Intent(Settings.Panel.ACTION_WIFI);
-		wifiRequest.launch(i);
-	}
+	abstract boolean checkAndRequestConditions();
 
 }

briar-android/src/main/java/org/briarproject/briar/android/hotspot/ConditionManager29Impl.java

@@ -0,0 +1,136 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Intent;
+import android.provider.Settings;
+
+import org.briarproject.briar.R;
+
+import java.util.logging.Logger;
+
+import androidx.activity.result.ActivityResultCaller;
+import androidx.activity.result.ActivityResultLauncher;
+import androidx.activity.result.contract.ActivityResultContracts.RequestPermission;
+import androidx.activity.result.contract.ActivityResultContracts.StartActivityForResult;
+import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
+import androidx.core.util.Consumer;
+
+import static android.Manifest.permission.ACCESS_FINE_LOCATION;
+import static androidx.core.app.ActivityCompat.shouldShowRequestPermissionRationale;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.briar.android.util.UiUtils.getGoToSettingsListener;
+import static org.briarproject.briar.android.util.UiUtils.showDenialDialog;
+import static org.briarproject.briar.android.util.UiUtils.showRationale;
+
+/**
+ * This class ensures that the conditions to open a hotspot are fulfilled on
+ * API levels >= 29.
+ * <p>
+ * As soon as {@link #checkAndRequestConditions()} returns true,
+ * all conditions are fulfilled.
+ */
+@RequiresApi(29)
+class ConditionManager29Impl extends ConditionManager {
+
+	private static final Logger LOG =
+			getLogger(ConditionManager29Impl.class.getName());
+
+	private Permission locationPermission = Permission.UNKNOWN;
+
+	private final ActivityResultLauncher<String> locationRequest;
+	private final ActivityResultLauncher<Intent> wifiRequest;
+
+	ConditionManager29Impl(ActivityResultCaller arc,
+			Consumer<Boolean> permissionUpdateCallback) {
+		super(permissionUpdateCallback);
+		locationRequest = arc.registerForActivityResult(
+				new RequestPermission(), granted -> {
+					onRequestPermissionResult(granted);
+					permissionUpdateCallback.accept(true);
+				});
+		wifiRequest = arc.registerForActivityResult(
+				new StartActivityForResult(),
+				result -> permissionUpdateCallback.accept(true));
+	}
+
+	@Override
+	void onStart() {
+		locationPermission = Permission.UNKNOWN;
+	}
+
+	private boolean areEssentialPermissionsGranted() {
+		if (LOG.isLoggable(INFO)) {
+			LOG.info(String.format("areEssentialPermissionsGranted(): " +
+							"locationPermission? %s, " +
+							"wifiManager.isWifiEnabled()? %b",
+					locationPermission,
+					wifiManager.isWifiEnabled()));
+		}
+		return locationPermission == Permission.GRANTED &&
+				wifiManager.isWifiEnabled();
+	}
+
+	@Override
+	boolean checkAndRequestConditions() {
+		if (areEssentialPermissionsGranted()) return true;
+
+		if (locationPermission == Permission.UNKNOWN) {
+			locationRequest.launch(ACCESS_FINE_LOCATION);
+			return false;
+		}
+
+		// If the location permission has been permanently denied, ask the
+		// user to change the setting
+		if (locationPermission == Permission.PERMANENTLY_DENIED) {
+			showDenialDialog(ctx, R.string.permission_location_title,
+					R.string.permission_hotspot_location_denied_body,
+					getGoToSettingsListener(ctx),
+					() -> permissionUpdateCallback.accept(false));
+			return false;
+		}
+
+		// Should we show the rationale for location permission?
+		if (locationPermission == Permission.SHOW_RATIONALE) {
+			showRationale(ctx, R.string.permission_location_title,
+					R.string.permission_hotspot_location_request_body,
+					this::requestPermissions,
+					() -> permissionUpdateCallback.accept(false));
+			return false;
+		}
+
+		// If Wifi is not enabled, we show the rationale for enabling Wifi?
+		if (!wifiManager.isWifiEnabled()) {
+			showRationale(ctx, R.string.wifi_settings_title,
+					R.string.wifi_settings_request_enable_body,
+					this::requestEnableWiFi,
+					() -> permissionUpdateCallback.accept(false));
+			return false;
+		}
+
+		// we shouldn't usually reach this point, but if we do, return false
+		// anyway to force a recheck. Maybe some condition changed in the
+		// meantime.
+		return false;
+	}
+
+	private void onRequestPermissionResult(@Nullable Boolean granted) {
+		if (granted != null && granted) {
+			locationPermission = Permission.GRANTED;
+		} else if (shouldShowRequestPermissionRationale(ctx,
+				ACCESS_FINE_LOCATION)) {
+			locationPermission = Permission.SHOW_RATIONALE;
+		} else {
+			locationPermission = Permission.PERMANENTLY_DENIED;
+		}
+	}
+
+	private void requestPermissions() {
+		locationRequest.launch(ACCESS_FINE_LOCATION);
+	}
+
+	private void requestEnableWiFi() {
+		wifiRequest.launch(new Intent(Settings.Panel.ACTION_WIFI));
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/hotspot/ConditionManagerImpl.java

@@ -0,0 +1,83 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Intent;
+import android.provider.Settings;
+
+import org.briarproject.briar.R;
+
+import java.util.logging.Logger;
+
+import androidx.activity.result.ActivityResultCaller;
+import androidx.activity.result.ActivityResultLauncher;
+import androidx.activity.result.contract.ActivityResultContracts.StartActivityForResult;
+import androidx.core.util.Consumer;
+
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.briar.android.util.UiUtils.showRationale;
+
+/**
+ * This class ensures that the conditions to open a hotspot are fulfilled on
+ * API levels < 29.
+ * <p>
+ * As soon as {@link #checkAndRequestConditions()} returns true,
+ * all conditions are fulfilled.
+ */
+class ConditionManagerImpl extends ConditionManager {
+
+	private static final Logger LOG =
+			getLogger(ConditionManagerImpl.class.getName());
+
+	private final ActivityResultLauncher<Intent> wifiRequest;
+
+	ConditionManagerImpl(ActivityResultCaller arc,
+			Consumer<Boolean> permissionUpdateCallback) {
+		super(permissionUpdateCallback);
+		wifiRequest = arc.registerForActivityResult(
+				new StartActivityForResult(),
+				result -> permissionUpdateCallback.accept(true));
+	}
+
+	@Override
+	void onStart() {
+		// nothing to do here
+	}
+
+	private boolean areEssentialPermissionsGranted() {
+		if (LOG.isLoggable(INFO)) {
+			LOG.info(String.format("areEssentialPermissionsGranted(): " +
+							"wifiManager.isWifiEnabled()? %b",
+					wifiManager.isWifiEnabled()));
+		}
+		return wifiManager.isWifiEnabled();
+	}
+
+	@Override
+	boolean checkAndRequestConditions() {
+		if (areEssentialPermissionsGranted()) return true;
+
+		if (!wifiManager.isWifiEnabled()) {
+			// Try enabling the Wifi and return true if that seems to have been
+			// successful, i.e. "Wifi is either already in the requested state, or
+			// in progress toward the requested state".
+			if (wifiManager.setWifiEnabled(true)) {
+				LOG.info("Enabled wifi");
+				return true;
+			}
+
+			// Wifi is not enabled and we can't seem to enable it, so ask the user
+			// to enable it for us.
+			showRationale(ctx, R.string.wifi_settings_title,
+					R.string.wifi_settings_request_enable_body,
+					this::requestEnableWiFi,
+					() -> permissionUpdateCallback.accept(false));
+		}
+
+		return false;
+	}
+
+	private void requestEnableWiFi() {
+		wifiRequest.launch(new Intent(Settings.ACTION_WIFI_SETTINGS));
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/hotspot/HotspotIntroFragment.java

@@ -1,7 +1,6 @@
 package org.briarproject.briar.android.hotspot;
 
 import android.content.Context;
-import android.content.Intent;
 import android.content.pm.ApplicationInfo;
 import android.content.pm.PackageManager;
 import android.os.Bundle;
@@ -20,15 +19,13 @@ import org.briarproject.briar.R;
 
 import javax.inject.Inject;
 
-import androidx.activity.result.ActivityResultLauncher;
-import androidx.activity.result.contract.ActivityResultContracts.RequestPermission;
-import androidx.activity.result.contract.ActivityResultContracts.StartActivityForResult;
 import androidx.annotation.Nullable;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentActivity;
 import androidx.lifecycle.ViewModelProvider;
 
 import static android.content.pm.ApplicationInfo.FLAG_TEST_ONLY;
+import static android.os.Build.VERSION.SDK_INT;
 import static android.view.View.INVISIBLE;
 import static android.view.View.VISIBLE;
 import static androidx.transition.TransitionManager.beginDelayedTransition;
@@ -45,22 +42,14 @@ public class HotspotIntroFragment extends Fragment {
 	ViewModelProvider.Factory viewModelFactory;
 
 	private HotspotViewModel viewModel;
-	private ConditionManager conditionManager;
 
 	private Button startButton;
 	private ProgressBar progressBar;
 	private TextView progressTextView;
 
-	private final ActivityResultLauncher<String> locationRequest =
-			registerForActivityResult(new RequestPermission(), granted -> {
-				conditionManager.onRequestPermissionResult(granted);
-				startHotspot();
-			});
-	private final ActivityResultLauncher<Intent> wifiRequest =
-			registerForActivityResult(new StartActivityForResult(), result -> {
-				conditionManager.onRequestWifiEnabledResult();
-				startHotspot();
-			});
+	private final ConditionManager conditionManager = SDK_INT < 29 ?
+			new ConditionManagerImpl(this, this::onPermissionUpdate) :
+			new ConditionManager29Impl(this, this::onPermissionUpdate);
 
 	@Override
 	public void onAttach(Context context) {
@@ -69,8 +58,6 @@ public class HotspotIntroFragment extends Fragment {
 		getAndroidComponent(activity).inject(this);
 		viewModel = new ViewModelProvider(activity, viewModelFactory)
 				.get(HotspotViewModel.class);
-		conditionManager =
-				new ConditionManager(activity, locationRequest, wifiRequest);
 	}
 
 	@Override
@@ -84,10 +71,9 @@ public class HotspotIntroFragment extends Fragment {
 		progressBar = v.findViewById(R.id.progressBar);
 		progressTextView = v.findViewById(R.id.progressTextView);
 
-		startButton.setOnClickListener(button -> {
-			startButton.setEnabled(false);
-			conditionManager.startConditionChecks();
-		});
+		startButton.setOnClickListener(this::onButtonClick);
+
+		conditionManager.init(requireActivity());
 
 		return v;
 	}
@@ -95,11 +81,15 @@ public class HotspotIntroFragment extends Fragment {
 	@Override
 	public void onStart() {
 		super.onStart();
-		conditionManager.resetPermissions();
+		conditionManager.onStart();
+	}
+
+	private void onButtonClick(View view) {
+		startButton.setEnabled(false);
+		startHotspot();
 	}
 
 	private void startHotspot() {
-		startButton.setEnabled(true);
 		if (conditionManager.checkAndRequestConditions()) {
 			showInstallWarningIfNeeded();
 			beginDelayedTransition((ViewGroup) requireView());
@@ -110,6 +100,13 @@ public class HotspotIntroFragment extends Fragment {
 		}
 	}
 
+	private void onPermissionUpdate(boolean recheckPermissions) {
+		startButton.setEnabled(true);
+		if (recheckPermissions) {
+			startHotspot();
+		}
+	}
+
 	private void showInstallWarningIfNeeded() {
 		Context ctx = requireContext();
 		ApplicationInfo applicationInfo;

briar-android/src/main/java/org/briarproject/briar/android/hotspot/HotspotManager.java

@@ -54,7 +54,7 @@ import static org.briarproject.briar.android.util.UiUtils.handleException;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
-class HotspotManager implements ActionListener {
+class HotspotManager {
 
 	interface HotspotListener {
 		void onStartingHotspot();
@@ -72,6 +72,7 @@ class HotspotManager implements ActionListener {
 
 	private static final Logger LOG = getLogger(HotspotManager.class.getName());
 
+	private static final int MAX_FRAMEWORK_ATTEMPTS = 5;
 	private static final int MAX_GROUP_INFO_ATTEMPTS = 5;
 	private static final int RETRY_DELAY_MILLIS = 1000;
 	private static final String HOTSPOT_NAMESPACE = "hotspot";
@@ -133,12 +134,80 @@ class HotspotManager implements ActionListener {
 			return;
 		}
 		listener.onStartingHotspot();
+		acquireLocks();
+		startWifiP2pFramework(1);
+	}
+
+	/**
+	 * As soon as Wifi is enabled, we try starting the WifiP2p framework.
+	 * If Wifi has just been enabled, it is possible that will fail. If that
+	 * happens we try again for MAX_FRAMEWORK_ATTEMPTS times after a delay of
+	 * RETRY_DELAY_MILLIS after each attempt.
+	 * <p>
+	 * Rationale: it can take a few milliseconds for WifiP2p to become available
+	 * after enabling Wifi. Depending on the API level it is possible to check this
+	 * using {@link WifiP2pManager#requestP2pState} or register a BroadcastReceiver
+	 * on the WIFI_P2P_STATE_CHANGED_ACTION to get notified when WifiP2p is really
+	 * available. Trying to implement a solution that works reliably using these
+	 * checks turned out to be a long rabbit-hole with lots of corner cases and
+	 * workarounds for specific situations.
+	 * Instead we now rely on this trial-and-error approach of just starting
+	 * the framework and retrying if it fails.
+	 * <p>
+	 * We'll realize that the framework is busy when the ActionListener passed
+	 * to {@link WifiP2pManager#createGroup} is called with onFailure(BUSY)
+	 */
+	void startWifiP2pFramework(int attempt) {
+		if (LOG.isLoggable(INFO))
+			LOG.info("startWifiP2pFramework attempt: " + attempt);
+		/*
+		 * It is important that we call WifiP2pManager#initialize again
+		 * for every attempt to starting the framework because otherwise,
+		 * createGroup() will continue to fail with a BUSY state.
+		 */
 		channel = wifiP2pManager.initialize(ctx, ctx.getMainLooper(), null);
 		if (channel == null) {
 			listener.onHotspotError(
 					ctx.getString(R.string.hotspot_error_no_wifi_direct));
 			return;
 		}
+
+		ActionListener listener = new ActionListener() {
+
+			@Override
+			// Callback for wifiP2pManager#createGroup() during startWifiP2pHotspot()
+			public void onSuccess() {
+				requestGroupInfo(1);
+			}
+
+			@Override
+			// Callback for wifiP2pManager#createGroup() during startWifiP2pHotspot()
+			public void onFailure(int reason) {
+				LOG.info("onFailure: " + reason);
+				if (reason == BUSY) {
+					// WifiP2p not ready yet or hotspot already running
+					restartWifiP2pFramework(attempt);
+				} else if (reason == P2P_UNSUPPORTED) {
+					releaseHotspotWithError(ctx.getString(
+							R.string.hotspot_error_start_callback_failed,
+							"p2p unsupported"));
+				} else if (reason == ERROR) {
+					releaseHotspotWithError(ctx.getString(
+							R.string.hotspot_error_start_callback_failed,
+							"p2p error"));
+				} else if (reason == NO_SERVICE_REQUESTS) {
+					releaseHotspotWithError(ctx.getString(
+							R.string.hotspot_error_start_callback_failed,
+							"no service requests"));
+				} else {
+					// all cases covered, in doubt set to error
+					releaseHotspotWithError(ctx.getString(
+							R.string.hotspot_error_start_callback_failed_unknown,
+							reason));
+				}
+			}
+		};
+
 		try {
 			if (SDK_INT >= 29) {
 				dbExecutor.execute(() -> {
@@ -151,12 +220,12 @@ class HotspotManager implements ActionListener {
 								.setPassphrase(savedNetworkConfig.password)
 								.build();
 						acquireLocks();
-						wifiP2pManager.createGroup(channel, config, this);
+						wifiP2pManager.createGroup(channel, config, listener);
 					});
 				});
 			} else {
 				acquireLocks();
-				wifiP2pManager.createGroup(channel, this);
+				wifiP2pManager.createGroup(channel, listener);
 			}
 		} catch (SecurityException e) {
 			// this should never happen, because we request permissions before
@@ -164,37 +233,18 @@ class HotspotManager implements ActionListener {
 		}
 	}
 
-	@Override
-	// Callback for wifiP2pManager#createGroup() during startWifiP2pHotspot()
-	public void onSuccess() {
-		requestGroupInfo(1);
-	}
-
-	@Override
-	// Callback for wifiP2pManager#createGroup() during startWifiP2pHotspot()
-	public void onFailure(int reason) {
-		if (reason == BUSY) {
-			// Hotspot already running
-			requestGroupInfo(1);
-		} else if (reason == P2P_UNSUPPORTED) {
-			releaseHotspotWithError(ctx.getString(
-					R.string.hotspot_error_start_callback_failed,
-					"p2p unsupported"));
-		} else if (reason == ERROR) {
-			releaseHotspotWithError(ctx.getString(
-					R.string.hotspot_error_start_callback_failed, "p2p error"));
-		} else if (reason == NO_SERVICE_REQUESTS) {
-			releaseHotspotWithError(ctx.getString(
-					R.string.hotspot_error_start_callback_failed,
-					"no service requests"));
+	private void restartWifiP2pFramework(int attempt) {
+		LOG.info("retrying to start WifiP2p framework");
+		if (attempt < MAX_FRAMEWORK_ATTEMPTS) {
+			handler.postDelayed(() -> startWifiP2pFramework(attempt + 1),
+					RETRY_DELAY_MILLIS);
 		} else {
-			// all cases covered, in doubt set to error
-			releaseHotspotWithError(ctx.getString(
-					R.string.hotspot_error_start_callback_failed_unknown,
-					reason));
+			releaseHotspotWithError(
+					ctx.getString(R.string.hotspot_error_framework_busy));
 		}
 	}
 
+	@UiThread
 	void stopWifiP2pHotspot() {
 		if (channel == null) return;
 		wifiP2pManager.removeGroup(channel, new ActionListener() {
@@ -301,7 +351,7 @@ class HotspotManager implements ActionListener {
 	}
 
 	private void retryRequestingGroupInfo(int attempt) {
-		LOG.info("retrying");
+		LOG.info("retrying to request group info");
 		// On some devices we need to wait for the group info to become available
 		if (attempt < MAX_GROUP_INFO_ATTEMPTS) {
 			handler.postDelayed(() -> requestGroupInfo(attempt + 1),

briar-android/src/main/java/org/briarproject/briar/android/hotspot/HotspotViewModel.java

@@ -110,7 +110,7 @@ class HotspotViewModel extends DbViewModel
 	}
 
 	@UiThread
-	private void stopHotspot() {
+	void stopHotspot() {
 		ioExecutor.execute(webServerManager::stopWebServer);
 		hotspotManager.stopWifiP2pHotspot();
 		notificationManager.clearHotspotNotification();

briar-android/src/main/java/org/briarproject/briar/android/util/UiUtils.java

@@ -6,6 +6,7 @@ import android.app.Activity;
 import android.app.KeyguardManager;
 import android.content.ActivityNotFoundException;
 import android.content.Context;
+import android.content.DialogInterface;
 import android.content.DialogInterface.OnClickListener;
 import android.content.Intent;
 import android.content.res.Resources;
@@ -52,6 +53,7 @@ import androidx.annotation.ColorRes;
 import androidx.annotation.DrawableRes;
 import androidx.annotation.Nullable;
 import androidx.annotation.RequiresApi;
+import androidx.annotation.StringRes;
 import androidx.annotation.UiThread;
 import androidx.appcompat.app.AlertDialog;
 import androidx.core.content.ContextCompat;
@@ -561,4 +563,31 @@ public class UiUtils {
 		activity.getWindow().setSoftInputMode(SOFT_INPUT_ADJUST_RESIZE |
 				SOFT_INPUT_STATE_HIDDEN);
 	}
+
+	public static void showDenialDialog(FragmentActivity ctx,
+			@StringRes int title,
+			@StringRes int body, DialogInterface.OnClickListener onOkClicked,
+			Runnable onDismiss) {
+		AlertDialog.Builder builder = new AlertDialog.Builder(ctx);
+		builder.setTitle(title);
+		builder.setMessage(body);
+		builder.setPositiveButton(R.string.ok, onOkClicked);
+		builder.setNegativeButton(R.string.cancel,
+				(dialog, which) -> ctx.supportFinishAfterTransition());
+		builder.setOnDismissListener(dialog -> onDismiss.run());
+		builder.show();
+	}
+
+	public static void showRationale(Context ctx, @StringRes int title,
+			@StringRes int body,
+			Runnable onContinueClicked, Runnable onDismiss) {
+		AlertDialog.Builder builder = new AlertDialog.Builder(ctx);
+		builder.setTitle(title);
+		builder.setMessage(body);
+		builder.setNeutralButton(R.string.continue_button,
+				(dialog, which) -> onContinueClicked.run());
+		builder.setOnDismissListener(dialog -> onDismiss.run());
+		builder.show();
+	}
+
 }

briar-android/src/main/res/values/strings.xml

@@ -757,6 +757,7 @@
 	<string name="hotspot_error_web_server_start">Error starting web server!</string>
 	<string name="hotspot_error_web_server_serve">Error presenting website.\n\nPlease send feedback (with anonymous data) via the Briar app if the issue persists.</string>
 	<string name="hotspot_flag_test">Warning: This app was installed with Android Studio and can NOT be installed on another device.</string>
+	<string name="hotspot_error_framework_busy">Unable to start the hotspot. If you have another hotspot running or are sharing your internet connection via Wifi, try stopping that and try again afterwards.</string>
 
 
 	<!-- Transfer Data via Removable Drives -->