Merge branch '1081-share-app-via-wifi-hotspot' into 'master'

Share app via Wi-Fi hotspot

Closes #1081

See merge request briar/briar!1515

briar-android/src/main/java/org/briarproject/briar/android/AndroidComponent.java

@@ -36,6 +36,11 @@ import org.briarproject.briar.BriarCoreModule;
 import org.briarproject.briar.android.attachment.AttachmentModule;
 import org.briarproject.briar.android.attachment.media.MediaModule;
 import org.briarproject.briar.android.conversation.glide.BriarModelLoader;
+import org.briarproject.briar.android.hotspot.AbstractTabsFragment;
+import org.briarproject.briar.android.hotspot.FallbackFragment;
+import org.briarproject.briar.android.hotspot.HotspotIntroFragment;
+import org.briarproject.briar.android.hotspot.ManualHotspotFragment;
+import org.briarproject.briar.android.hotspot.QrHotspotFragment;
 import org.briarproject.briar.android.logging.CachingLogHandler;
 import org.briarproject.briar.android.login.SignInReminderReceiver;
 import org.briarproject.briar.android.removabledrive.ChooserFragment;
@@ -216,6 +221,16 @@ public interface AndroidComponent
 
 	void inject(NotificationsFragment notificationsFragment);
 
+	void inject(HotspotIntroFragment hotspotIntroFragment);
+
+	void inject(AbstractTabsFragment abstractTabsFragment);
+
+	void inject(QrHotspotFragment qrHotspotFragment);
+
+	void inject(ManualHotspotFragment manualHotspotFragment);
+
+	void inject(FallbackFragment fallbackFragment);
+
 	void inject(ChooserFragment chooserFragment);
 
 	void inject(SendFragment sendFragment);

briar-android/src/main/java/org/briarproject/briar/android/AndroidNotificationManagerImpl.java

@@ -30,6 +30,7 @@ import org.briarproject.bramble.util.StringUtils;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.conversation.ConversationActivity;
 import org.briarproject.briar.android.forum.ForumActivity;
+import org.briarproject.briar.android.hotspot.HotspotActivity;
 import org.briarproject.briar.android.login.SignInReminderReceiver;
 import org.briarproject.briar.android.navdrawer.NavDrawerActivity;
 import org.briarproject.briar.android.privategroup.conversation.GroupActivity;
@@ -63,9 +64,11 @@ import static android.app.Notification.DEFAULT_SOUND;
 import static android.app.Notification.DEFAULT_VIBRATE;
 import static android.app.NotificationManager.IMPORTANCE_DEFAULT;
 import static android.app.NotificationManager.IMPORTANCE_LOW;
+import static android.app.PendingIntent.getActivity;
 import static android.content.Context.NOTIFICATION_SERVICE;
 import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
 import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
+import static android.content.Intent.FLAG_ACTIVITY_SINGLE_TOP;
 import static android.os.Build.VERSION.SDK_INT;
 import static androidx.core.app.NotificationCompat.CATEGORY_MESSAGE;
 import static androidx.core.app.NotificationCompat.CATEGORY_SERVICE;
@@ -274,7 +277,7 @@ class AndroidNotificationManagerImpl implements AndroidNotificationManager,
 		b.setWhen(0); // Don't show the time
 		b.setOngoing(true);
 		Intent i = new Intent(appContext, SplashScreenActivity.class);
-		b.setContentIntent(PendingIntent.getActivity(appContext, 0, i, 0));
+		b.setContentIntent(getActivity(appContext, 0, i, 0));
 		if (SDK_INT >= 21) {
 			b.setCategory(CATEGORY_SERVICE);
 			b.setVisibility(VISIBILITY_SECRET);
@@ -619,13 +622,11 @@ class AndroidNotificationManagerImpl implements AndroidNotificationManager,
 	public void showSignInNotification() {
 		if (blockSignInReminder) return;
 		if (SDK_INT >= 26) {
-			NotificationChannel channel =
-					new NotificationChannel(REMINDER_CHANNEL_ID, appContext
-							.getString(
-									R.string.reminder_notification_channel_title),
-							IMPORTANCE_LOW);
-			channel.setLockscreenVisibility(
-					NotificationCompat.VISIBILITY_SECRET);
+			NotificationChannel channel = new NotificationChannel(
+					REMINDER_CHANNEL_ID, appContext
+					.getString(R.string.reminder_notification_channel_title),
+					IMPORTANCE_LOW);
+			channel.setLockscreenVisibility(VISIBILITY_SECRET);
 			notificationManager.createNotificationChannel(channel);
 		}
 
@@ -652,7 +653,7 @@ class AndroidNotificationManagerImpl implements AndroidNotificationManager,
 
 		Intent i = new Intent(appContext, SplashScreenActivity.class);
 		i.setFlags(FLAG_ACTIVITY_NEW_TASK | FLAG_ACTIVITY_CLEAR_TOP);
-		b.setContentIntent(PendingIntent.getActivity(appContext, 0, i, 0));
+		b.setContentIntent(getActivity(appContext, 0, i, 0));
 
 		notificationManager.notify(REMINDER_NOTIFICATION_ID, b.build());
 	}
@@ -720,4 +721,40 @@ class AndroidNotificationManagerImpl implements AndroidNotificationManager,
 	public void unblockAllBlogPostNotifications() {
 		androidExecutor.runOnUiThread((Runnable) () -> blockBlogs = false);
 	}
+
+	@Override
+	public void showHotspotNotification() {
+		if (SDK_INT >= 26) {
+			String channelTitle = appContext
+					.getString(R.string.hotspot_notification_channel_title);
+			NotificationChannel channel = new NotificationChannel(
+					HOTSPOT_CHANNEL_ID, channelTitle, IMPORTANCE_LOW);
+			channel.setLockscreenVisibility(VISIBILITY_SECRET);
+			notificationManager.createNotificationChannel(channel);
+		}
+		BriarNotificationBuilder b =
+				new BriarNotificationBuilder(appContext, HOTSPOT_CHANNEL_ID);
+		b.setSmallIcon(R.drawable.notification_hotspot);
+		b.setColorRes(R.color.briar_brand_green);
+		b.setContentTitle(
+				appContext.getText(R.string.hotspot_notification_title));
+		b.setNotificationCategory(CATEGORY_SERVICE);
+		b.setOngoing(true);
+		b.setShowWhen(true);
+
+		String actionTitle =
+				appContext.getString(R.string.hotspot_button_stop_sharing);
+		Intent i = new Intent(appContext, HotspotActivity.class);
+		i.addFlags(FLAG_ACTIVITY_SINGLE_TOP);
+		i.setAction(ACTION_STOP_HOTSPOT);
+		PendingIntent actionIntent = getActivity(appContext, 0, i, 0);
+		int icon = SDK_INT >= 21 ? R.drawable.ic_portable_wifi_off : 0;
+		b.addAction(icon, actionTitle, actionIntent);
+		notificationManager.notify(HOTSPOT_NOTIFICATION_ID, b.build());
+	}
+
+	@Override
+	public void clearHotspotNotification() {
+		notificationManager.cancel(HOTSPOT_NOTIFICATION_ID);
+	}
 }

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -36,6 +36,7 @@ import org.briarproject.briar.android.blog.BlogModule;
 import org.briarproject.briar.android.contact.ContactListModule;
 import org.briarproject.briar.android.contact.add.nearby.AddNearbyContactModule;
 import org.briarproject.briar.android.forum.ForumModule;
+import org.briarproject.briar.android.hotspot.HotspotModule;
 import org.briarproject.briar.android.introduction.IntroductionModule;
 import org.briarproject.briar.android.logging.LoggingModule;
 import org.briarproject.briar.android.login.LoginModule;
@@ -94,6 +95,7 @@ import static org.briarproject.briar.android.TestingConstants.IS_DEBUG_BUILD;
 		GroupListModule.class,
 		GroupConversationModule.class,
 		SharingModule.class,
+		HotspotModule.class,
 		TransferDataModule.class,
 })
 public class AppModule {
@@ -318,6 +320,11 @@ public class AppModule {
 			public boolean shouldEnableTransferData() {
 				return IS_DEBUG_BUILD;
 			}
+
+			@Override
+			public boolean shouldEnableShareAppViaOfflineHotspot() {
+				return IS_DEBUG_BUILD;
+			}
 		};
 	}
 }

briar-android/src/main/java/org/briarproject/briar/android/activity/ActivityComponent.java

@@ -38,6 +38,7 @@ import org.briarproject.briar.android.forum.CreateForumActivity;
 import org.briarproject.briar.android.forum.ForumActivity;
 import org.briarproject.briar.android.forum.ForumListFragment;
 import org.briarproject.briar.android.fragment.ScreenFilterDialogFragment;
+import org.briarproject.briar.android.hotspot.HotspotActivity;
 import org.briarproject.briar.android.introduction.ContactChooserFragment;
 import org.briarproject.briar.android.introduction.IntroductionActivity;
 import org.briarproject.briar.android.introduction.IntroductionMessageFragment;
@@ -177,6 +178,8 @@ public interface ActivityComponent {
 
 	void inject(CrashReportActivity crashReportActivity);
 
+	void inject(HotspotActivity hotspotActivity);
+
 	void inject(RemovableDriveActivity activity);
 
 	// Fragments

briar-android/src/main/java/org/briarproject/briar/android/activity/BaseActivity.java

@@ -46,6 +46,7 @@ import static java.util.logging.Level.INFO;
 import static java.util.logging.Logger.getLogger;
 import static org.briarproject.briar.android.TestingConstants.PREVENT_SCREENSHOTS;
 import static org.briarproject.briar.android.util.UiUtils.hideSoftKeyboard;
+import static org.briarproject.briar.android.util.UiUtils.showFragment;
 
 /**
  * Warning: Some activities don't extend {@link BaseActivity}.
@@ -177,13 +178,7 @@ public abstract class BaseActivity extends AppCompatActivity
 
 	public void showNextFragment(BaseFragment f) {
 		if (!getLifecycle().getCurrentState().isAtLeast(STARTED)) return;
-		getSupportFragmentManager().beginTransaction()
-				.setCustomAnimations(R.anim.step_next_in,
-						R.anim.step_previous_out, R.anim.step_previous_in,
-						R.anim.step_next_out)
-				.replace(R.id.fragmentContainer, f, f.getUniqueTag())
-				.addToBackStack(f.getUniqueTag())
-				.commit();
+		showFragment(getSupportFragmentManager(), f, f.getUniqueTag());
 	}
 
 	protected boolean isFragmentAdded(String fragmentTag) {

briar-android/src/main/java/org/briarproject/briar/android/contact/add/nearby/AddNearbyContactViewModel.java

@@ -53,6 +53,7 @@ import org.briarproject.briar.android.contact.add.nearby.AddContactState.Contact
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.KeyAgreementListening;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.KeyAgreementStarted;
 import org.briarproject.briar.android.contact.add.nearby.AddContactState.KeyAgreementWaiting;
+import org.briarproject.briar.android.util.QrCodeUtils;
 import org.briarproject.briar.android.viewmodel.LiveEvent;
 import org.briarproject.briar.android.viewmodel.MutableLiveEvent;
 

briar-android/src/main/java/org/briarproject/briar/android/fragment/ErrorFragment.java

@@ -17,7 +17,7 @@ import androidx.annotation.Nullable;
 @ParametersNotNullByDefault
 public class ErrorFragment extends BaseFragment {
 
-	private static final String TAG = ErrorFragment.class.getName();
+	public static final String TAG = ErrorFragment.class.getName();
 
 	private static final String ERROR_MSG = "errorMessage";
 
@@ -40,8 +40,7 @@ public class ErrorFragment extends BaseFragment {
 	public void onCreate(@Nullable Bundle savedInstanceState) {
 		super.onCreate(savedInstanceState);
 
-		Bundle args = getArguments();
-		if (args == null) throw new AssertionError();
+		Bundle args = requireArguments();
 		errorMessage = args.getString(ERROR_MSG);
 	}
 

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

@@ -0,0 +1,84 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Context;
+import android.content.DialogInterface;
+import android.net.wifi.WifiManager;
+
+import org.briarproject.briar.R;
+
+import androidx.annotation.StringRes;
+import androidx.appcompat.app.AlertDialog;
+import androidx.core.util.Consumer;
+import androidx.fragment.app.FragmentActivity;
+
+import static android.content.Context.WIFI_SERVICE;
+
+/**
+ * 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+.
+ */
+abstract class AbstractConditionManager {
+
+	enum Permission {
+		UNKNOWN, GRANTED, SHOW_RATIONALE, PERMANENTLY_DENIED
+	}
+
+	protected final Consumer<Boolean> permissionUpdateCallback;
+	protected FragmentActivity ctx;
+	WifiManager wifiManager;
+
+	AbstractConditionManager(Consumer<Boolean> permissionUpdateCallback) {
+		this.permissionUpdateCallback = permissionUpdateCallback;
+	}
+
+	/**
+	 * Pass a FragmentActivity context here during `onCreateView()`.
+	 */
+	void init(FragmentActivity ctx) {
+		this.ctx = ctx;
+		this.wifiManager = (WifiManager) ctx.getApplicationContext()
+				.getSystemService(WIFI_SERVICE);
+	}
+
+	/**
+	 * Call this during onStart() in the fragment where the ConditionManager
+	 * is used.
+	 */
+	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.
+	 */
+	abstract boolean checkAndRequestConditions();
+
+	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();
+	}
+
+	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/java/org/briarproject/briar/android/hotspot/AbstractTabsFragment.java

@@ -0,0 +1,129 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.Menu;
+import android.view.MenuInflater;
+import android.view.MenuItem;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+
+import com.google.android.material.tabs.TabLayout;
+import com.google.android.material.tabs.TabLayoutMediator;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+
+import javax.inject.Inject;
+
+import androidx.annotation.CallSuper;
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+import androidx.lifecycle.ViewModelProvider;
+import androidx.viewpager2.adapter.FragmentStateAdapter;
+import androidx.viewpager2.widget.ViewPager2;
+
+import static androidx.core.app.ActivityCompat.finishAfterTransition;
+import static org.briarproject.briar.android.AppModule.getAndroidComponent;
+import static org.briarproject.briar.android.util.UiUtils.showFragment;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public abstract class AbstractTabsFragment extends Fragment {
+
+	static String ARG_FOR_WIFI_CONNECT = "forWifiConnect";
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	protected HotspotViewModel viewModel;
+
+	protected Button stopButton;
+	protected Button connectedButton;
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		getAndroidComponent(requireContext()).inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(HotspotViewModel.class);
+	}
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		setHasOptionsMenu(true);
+		return inflater
+				.inflate(R.layout.fragment_hotspot_tabs, container, false);
+	}
+
+	@Override
+	@CallSuper
+	public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
+		TabAdapter tabAdapter = new TabAdapter(this);
+		ViewPager2 viewPager = view.findViewById(R.id.pager);
+		viewPager.setAdapter(tabAdapter);
+		TabLayout tabLayout = view.findViewById(R.id.tabLayout);
+		new TabLayoutMediator(tabLayout, viewPager, (tab, position) -> {
+			// tabs are set in XML, but are just dummies that don't get added
+			if (position == 0) {
+				tab.setText(R.string.hotspot_tab_manual);
+				tab.setIcon(R.drawable.forum_item_create_white);
+			} else if (position == 1) {
+				tab.setText(R.string.qr_code);
+				tab.setIcon(R.drawable.ic_qr_code);
+			} else throw new AssertionError();
+		}).attach();
+
+		stopButton = view.findViewById(R.id.stopButton);
+		stopButton.setOnClickListener(v -> {
+			// also clears hotspot
+			finishAfterTransition(requireActivity());
+		});
+		connectedButton = view.findViewById(R.id.connectedButton);
+	}
+
+	@Override
+	public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
+		inflater.inflate(R.menu.hotspot_help_action, menu);
+		super.onCreateOptionsMenu(menu, inflater);
+	}
+
+	@Override
+	public boolean onOptionsItemSelected(MenuItem item) {
+		if (item.getItemId() == R.id.action_help) {
+			Fragment f = new HotspotHelpFragment();
+			String tag = HotspotHelpFragment.TAG;
+			showFragment(getParentFragmentManager(), f, tag);
+			return true;
+		}
+		return super.onOptionsItemSelected(item);
+	}
+
+	protected abstract Fragment getFirstFragment();
+
+	protected abstract Fragment getSecondFragment();
+
+	private class TabAdapter extends FragmentStateAdapter {
+		private TabAdapter(Fragment fragment) {
+			super(fragment);
+		}
+
+		@Override
+		public Fragment createFragment(int position) {
+			if (position == 0) return getFirstFragment();
+			if (position == 1) return getSecondFragment();
+			throw new AssertionError();
+		}
+
+		@Override
+		public int getItemCount() {
+			return 2;
+		}
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/hotspot/ConditionManager.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;
+
+/**
+ * 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 ConditionManager extends AbstractConditionManager {
+
+	private static final Logger LOG =
+			getLogger(ConditionManager.class.getName());
+
+	private final ActivityResultLauncher<Intent> wifiRequest;
+
+	ConditionManager(ActivityResultCaller arc,
+			Consumer<Boolean> permissionUpdateCallback) {
+		super(permissionUpdateCallback);
+		wifiRequest = arc.registerForActivityResult(
+				new StartActivityForResult(),
+				result -> permissionUpdateCallback
+						.accept(wifiManager.isWifiEnabled()));
+	}
+
+	@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/ConditionManager29.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.lang.Boolean.TRUE;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.briar.android.util.UiUtils.getGoToSettingsListener;
+
+/**
+ * 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 ConditionManager29 extends AbstractConditionManager {
+
+	private static final Logger LOG =
+			getLogger(ConditionManager29.class.getName());
+
+	private Permission locationPermission = Permission.UNKNOWN;
+
+	private final ActivityResultLauncher<String> locationRequest;
+	private final ActivityResultLauncher<Intent> wifiRequest;
+
+	ConditionManager29(ActivityResultCaller arc,
+			Consumer<Boolean> permissionUpdateCallback) {
+		super(permissionUpdateCallback);
+		locationRequest = arc.registerForActivityResult(
+				new RequestPermission(), granted -> {
+					onRequestPermissionResult(granted);
+					permissionUpdateCallback.accept(TRUE.equals(granted));
+				});
+		wifiRequest = arc.registerForActivityResult(
+				new StartActivityForResult(),
+				result -> permissionUpdateCallback
+						.accept(wifiManager.isWifiEnabled())
+		);
+	}
+
+	@Override
+	void onStart() {
+		locationPermission = Permission.UNKNOWN;
+	}
+
+	private boolean areEssentialPermissionsGranted() {
+		boolean isWifiEnabled = wifiManager.isWifiEnabled();
+		if (LOG.isLoggable(INFO)) {
+			LOG.info(String.format("areEssentialPermissionsGranted(): " +
+							"locationPermission? %s, " +
+							"wifiManager.isWifiEnabled()? %b",
+					locationPermission, isWifiEnabled));
+		}
+		return locationPermission == Permission.GRANTED && 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/FallbackFragment.java

@@ -0,0 +1,127 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Context;
+import android.content.Intent;
+import android.content.pm.ResolveInfo;
+import android.net.Uri;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+import android.widget.ProgressBar;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.fragment.BaseFragment;
+import org.briarproject.briar.android.util.ActivityLaunchers.CreateDocumentAdvanced;
+
+import java.util.List;
+
+import javax.inject.Inject;
+
+import androidx.activity.result.ActivityResultLauncher;
+import androidx.annotation.Nullable;
+import androidx.fragment.app.FragmentActivity;
+import androidx.lifecycle.ViewModelProvider;
+
+import static android.content.Intent.ACTION_SEND;
+import static android.content.Intent.EXTRA_STREAM;
+import static android.content.Intent.FLAG_GRANT_READ_URI_PERMISSION;
+import static android.content.pm.PackageManager.MATCH_DEFAULT_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;
+import static org.briarproject.briar.android.AppModule.getAndroidComponent;
+import static org.briarproject.briar.android.hotspot.HotspotViewModel.getApkFileName;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class FallbackFragment extends BaseFragment {
+
+	public static final String TAG = FallbackFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private HotspotViewModel viewModel;
+	private final ActivityResultLauncher<String> launcher =
+			registerForActivityResult(new CreateDocumentAdvanced(),
+					this::onDocumentCreated);
+	private Button fallbackButton;
+	private ProgressBar progressBar;
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		FragmentActivity activity = requireActivity();
+		getAndroidComponent(activity).inject(this);
+		viewModel = new ViewModelProvider(activity, viewModelFactory)
+				.get(HotspotViewModel.class);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		return inflater
+				.inflate(R.layout.fragment_hotspot_fallback, container, false);
+	}
+
+	@Override
+	public void onViewCreated(View v, @Nullable Bundle savedInstanceState) {
+		super.onViewCreated(v, savedInstanceState);
+
+		fallbackButton = v.findViewById(R.id.fallbackButton);
+		progressBar = v.findViewById(R.id.progressBar);
+		fallbackButton.setOnClickListener(view -> {
+			beginDelayedTransition((ViewGroup) v);
+			fallbackButton.setVisibility(INVISIBLE);
+			progressBar.setVisibility(VISIBLE);
+
+			if (SDK_INT >= 19) launcher.launch(getApkFileName());
+			else viewModel.exportApk();
+		});
+		viewModel.getSavedApkToUri().observeEvent(this, this::shareUri);
+	}
+
+	private void onDocumentCreated(@Nullable Uri uri) {
+		showButton();
+		if (uri != null) viewModel.exportApk(uri);
+	}
+
+	private void showButton() {
+		beginDelayedTransition((ViewGroup) requireView());
+		fallbackButton.setVisibility(VISIBLE);
+		progressBar.setVisibility(INVISIBLE);
+	}
+
+	void shareUri(Uri uri) {
+		Intent i = new Intent(ACTION_SEND);
+		i.putExtra(EXTRA_STREAM, uri);
+		i.setType("*/*"); // gives us all sharing options
+		i.addFlags(FLAG_GRANT_READ_URI_PERMISSION);
+		Context ctx = requireContext();
+		if (SDK_INT <= 19) {
+			// Workaround for Android bug:
+			// ctx.grantUriPermission also needed for Android 4
+			List<ResolveInfo> resInfoList = ctx.getPackageManager()
+					.queryIntentActivities(i, MATCH_DEFAULT_ONLY);
+			for (ResolveInfo resolveInfo : resInfoList) {
+				String packageName = resolveInfo.activityInfo.packageName;
+				ctx.grantUriPermission(packageName, uri,
+						FLAG_GRANT_READ_URI_PERMISSION);
+			}
+		}
+		startActivity(Intent.createChooser(i, null));
+	}
+
+}

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

@@ -0,0 +1,143 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Intent;
+import android.os.Bundle;
+import android.view.MenuItem;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.activity.BriarActivity;
+import org.briarproject.briar.android.fragment.BaseFragment.BaseFragmentListener;
+import org.briarproject.briar.android.hotspot.HotspotState.HotspotError;
+import org.briarproject.briar.android.hotspot.HotspotState.HotspotStarted;
+
+import javax.annotation.Nullable;
+import javax.inject.Inject;
+
+import androidx.appcompat.app.ActionBar;
+import androidx.fragment.app.Fragment;
+import androidx.fragment.app.FragmentManager;
+import androidx.lifecycle.ViewModelProvider;
+
+import static org.briarproject.briar.android.util.UiUtils.showFragment;
+import static org.briarproject.briar.api.android.AndroidNotificationManager.ACTION_STOP_HOTSPOT;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class HotspotActivity extends BriarActivity
+		implements BaseFragmentListener {
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private HotspotViewModel viewModel;
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+		viewModel = new ViewModelProvider(this, viewModelFactory)
+				.get(HotspotViewModel.class);
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		setContentView(R.layout.activity_fragment_container);
+
+		ActionBar ab = getSupportActionBar();
+		if (ab != null) {
+			ab.setDisplayHomeAsUpEnabled(true);
+		}
+
+		FragmentManager fm = getSupportFragmentManager();
+		viewModel.getState().observe(this, hotspotState -> {
+			if (hotspotState instanceof HotspotStarted) {
+				HotspotStarted started = (HotspotStarted) hotspotState;
+				String tag = HotspotFragment.TAG;
+				// check if fragment is already added
+				// to not lose state on configuration changes
+				if (fm.findFragmentByTag(tag) == null) {
+					if (started.wasNotYetConsumed()) {
+						started.consume();
+						showFragment(fm, new HotspotFragment(), tag);
+					}
+				}
+			} else if (hotspotState instanceof HotspotError) {
+				HotspotError error = (HotspotError) hotspotState;
+				showErrorFragment(error.getError());
+			}
+		});
+
+		if (savedInstanceState == null) {
+			// If there is no saved instance state, just start with the intro fragment.
+			fm.beginTransaction()
+					.replace(R.id.fragmentContainer, new HotspotIntroFragment(),
+							HotspotIntroFragment.TAG)
+					.commit();
+		} else if (viewModel.getState().getValue() == null) {
+			// If there is saved instance state, then there's either been an
+			// configuration change like rotated device or the activity has been
+			// destroyed and is now being re-created.
+			// In the latter case, the view model will have been destroyed, too.
+			// The activity can only have been destroyed if the user navigated
+			// away from the HotspotActivity which is nothing we
+			// intend to support, so we want to detect that and start from scratch
+			// in this case. We need to clean up existing fragments in order not
+			// to stack new fragments on top of old ones.
+
+			// If it is a configuration change and we moved past the intro
+			// fragment already, then the view model state will be != null,
+			// hence we can use this check for null to determine the destroyed
+			// activity. It can also be null if the user has not pressed
+			// "start sharing" yet, but in that case it won't harm to start from
+			// scratch.
+
+			Fragment current = fm.findFragmentById(R.id.fragmentContainer);
+			if (current instanceof HotspotIntroFragment) {
+				// If the currently displayed fragment is the intro fragment,
+				// there's nothing we need to do.
+				return;
+			}
+
+			// Remove everything from the back stack.
+			fm.popBackStackImmediate(null,
+					FragmentManager.POP_BACK_STACK_INCLUSIVE);
+
+			// Start fresh with the intro fragment.
+			fm.beginTransaction()
+					.replace(R.id.fragmentContainer, new HotspotIntroFragment(),
+							HotspotIntroFragment.TAG)
+					.commit();
+		}
+	}
+
+	private void showErrorFragment(String error) {
+		FragmentManager fm = getSupportFragmentManager();
+		String tag = HotspotErrorFragment.TAG;
+		if (fm.findFragmentByTag(tag) == null) {
+			Fragment f = HotspotErrorFragment.newInstance(error);
+			showFragment(fm, f, tag, false);
+		}
+	}
+
+	@Override
+	public boolean onOptionsItemSelected(MenuItem item) {
+		if (item.getItemId() == android.R.id.home) {
+			onBackPressed();
+			return true;
+		}
+		return super.onOptionsItemSelected(item);
+	}
+
+	@Override
+	protected void onNewIntent(Intent intent) {
+		super.onNewIntent(intent);
+		if (ACTION_STOP_HOTSPOT.equals(intent.getAction())) {
+			// also closes hotspot
+			supportFinishAfterTransition();
+		}
+	}
+
+}

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

@@ -0,0 +1,78 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+import android.widget.TextView;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.fragment.BaseFragment;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+import androidx.lifecycle.ViewModelProvider;
+
+import static org.briarproject.briar.android.util.UiUtils.triggerFeedback;
+
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class HotspotErrorFragment extends BaseFragment {
+
+	public static final String TAG = HotspotErrorFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private static final String ERROR_MSG = "errorMessage";
+
+	public static HotspotErrorFragment newInstance(String message) {
+		HotspotErrorFragment f = new HotspotErrorFragment();
+		Bundle args = new Bundle();
+		args.putString(ERROR_MSG, message);
+		f.setArguments(args);
+		return f;
+	}
+
+	private String errorMessage;
+
+	@Override
+	public String getUniqueTag() {
+		return TAG;
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+
+		Bundle args = requireArguments();
+		errorMessage = args.getString(ERROR_MSG);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		requireActivity().setTitle(R.string.error);
+		return inflater
+				.inflate(R.layout.fragment_hotspot_error, container, false);
+	}
+
+	@Override
+	public void onViewCreated(View v, @Nullable Bundle savedInstanceState) {
+		super.onViewCreated(v, savedInstanceState);
+		TextView msg = v.findViewById(R.id.errorMessageDetail);
+		msg.setText(errorMessage);
+
+		Button feedbackButton = v.findViewById(R.id.feedbackButton);
+		feedbackButton.setOnClickListener(
+				button -> triggerFeedback(requireContext(), errorMessage));
+	}
+
+}

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

@@ -0,0 +1,52 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.os.Bundle;
+import android.view.View;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+
+import static org.briarproject.briar.android.util.UiUtils.showFragment;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class HotspotFragment extends AbstractTabsFragment {
+
+	public final static String TAG = HotspotFragment.class.getName();
+
+	@Override
+	public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
+		super.onViewCreated(view, savedInstanceState);
+		connectedButton.setOnClickListener(v -> showNextFragment());
+		viewModel.getPeerConnectedEvent().observeEvent(getViewLifecycleOwner(),
+				this::onPeerConnected);
+	}
+
+	@Override
+	protected Fragment getFirstFragment() {
+		return ManualHotspotFragment.newInstance(true);
+	}
+
+	@Override
+	protected Fragment getSecondFragment() {
+		return QrHotspotFragment.newInstance(true);
+	}
+
+	private void onPeerConnected(boolean connected) {
+		if (!connected) return;
+		Toast.makeText(requireContext(), R.string.hotspot_peer_connected,
+				Toast.LENGTH_LONG).show();
+	}
+
+	private void showNextFragment() {
+		Fragment f = new WebsiteFragment();
+		String tag = WebsiteFragment.TAG;
+		showFragment(getParentFragmentManager(), f, tag);
+	}
+
+}

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

@@ -0,0 +1,29 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class HotspotHelpFragment extends Fragment {
+
+	public final static String TAG = HotspotHelpFragment.class.getName();
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		return inflater
+				.inflate(R.layout.fragment_hotspot_help, container, false);
+	}
+
+}

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

@@ -0,0 +1,127 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Context;
+import android.content.pm.ApplicationInfo;
+import android.content.pm.PackageManager;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.Button;
+import android.widget.ProgressBar;
+import android.widget.TextView;
+
+import com.google.android.material.snackbar.Snackbar;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+
+import javax.inject.Inject;
+
+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;
+import static com.google.android.material.snackbar.BaseTransientBottomBar.LENGTH_LONG;
+import static org.briarproject.briar.android.AppModule.getAndroidComponent;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class HotspotIntroFragment extends Fragment {
+
+	public final static String TAG = HotspotIntroFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private HotspotViewModel viewModel;
+
+	private Button startButton;
+	private ProgressBar progressBar;
+	private TextView progressTextView;
+
+	private final AbstractConditionManager conditionManager = SDK_INT < 29 ?
+			new ConditionManager(this, this::onPermissionUpdate) :
+			new ConditionManager29(this, this::onPermissionUpdate);
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		FragmentActivity activity = requireActivity();
+		getAndroidComponent(activity).inject(this);
+		viewModel = new ViewModelProvider(activity, viewModelFactory)
+				.get(HotspotViewModel.class);
+	}
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View v = inflater
+				.inflate(R.layout.fragment_hotspot_intro, container, false);
+
+		startButton = v.findViewById(R.id.startButton);
+		progressBar = v.findViewById(R.id.progressBar);
+		progressTextView = v.findViewById(R.id.progressTextView);
+
+		startButton.setOnClickListener(this::onButtonClick);
+
+		conditionManager.init(requireActivity());
+
+		return v;
+	}
+
+	@Override
+	public void onStart() {
+		super.onStart();
+		conditionManager.onStart();
+	}
+
+	private void onButtonClick(View view) {
+		startButton.setEnabled(false);
+		startHotspotIfConditionsFulfilled();
+	}
+
+	private void startHotspotIfConditionsFulfilled() {
+		if (conditionManager.checkAndRequestConditions()) {
+			showInstallWarningIfNeeded();
+			beginDelayedTransition((ViewGroup) requireView());
+			startButton.setVisibility(INVISIBLE);
+			progressBar.setVisibility(VISIBLE);
+			progressTextView.setVisibility(VISIBLE);
+			viewModel.startHotspot();
+		}
+	}
+
+	private void onPermissionUpdate(boolean recheckPermissions) {
+		startButton.setEnabled(true);
+		if (recheckPermissions) {
+			startHotspotIfConditionsFulfilled();
+		}
+	}
+
+	private void showInstallWarningIfNeeded() {
+		Context ctx = requireContext();
+		ApplicationInfo applicationInfo;
+		try {
+			applicationInfo = ctx.getPackageManager()
+					.getApplicationInfo(ctx.getPackageName(), 0);
+		} catch (PackageManager.NameNotFoundException e) {
+			throw new AssertionError(e);
+		}
+		// test only apps can not be installed
+		if ((applicationInfo.flags & FLAG_TEST_ONLY) == FLAG_TEST_ONLY) {
+			int color = getResources().getColor(R.color.briar_red_500);
+			Snackbar.make(requireView(), R.string.hotspot_flag_test,
+					LENGTH_LONG).setBackgroundTint(color).show();
+		}
+	}
+
+}

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

@@ -0,0 +1,453 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.annotation.SuppressLint;
+import android.app.Application;
+import android.content.Context;
+import android.graphics.Bitmap;
+import android.net.wifi.WifiManager;
+import android.net.wifi.p2p.WifiP2pConfig;
+import android.net.wifi.p2p.WifiP2pGroup;
+import android.net.wifi.p2p.WifiP2pManager;
+import android.net.wifi.p2p.WifiP2pManager.ActionListener;
+import android.net.wifi.p2p.WifiP2pManager.GroupInfoListener;
+import android.os.Handler;
+import android.os.PowerManager;
+import android.util.DisplayMetrics;
+
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.bramble.api.settings.Settings;
+import org.briarproject.bramble.api.settings.SettingsManager;
+import org.briarproject.bramble.api.system.AndroidExecutor;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.hotspot.HotspotState.NetworkConfig;
+import org.briarproject.briar.android.util.QrCodeUtils;
+
+import java.security.SecureRandom;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+import androidx.annotation.RequiresApi;
+import androidx.annotation.UiThread;
+
+import static android.content.Context.POWER_SERVICE;
+import static android.content.Context.WIFI_P2P_SERVICE;
+import static android.content.Context.WIFI_SERVICE;
+import static android.net.wifi.WifiManager.WIFI_MODE_FULL;
+import static android.net.wifi.WifiManager.WIFI_MODE_FULL_HIGH_PERF;
+import static android.net.wifi.p2p.WifiP2pConfig.GROUP_OWNER_BAND_2GHZ;
+import static android.net.wifi.p2p.WifiP2pManager.BUSY;
+import static android.net.wifi.p2p.WifiP2pManager.ERROR;
+import static android.net.wifi.p2p.WifiP2pManager.NO_SERVICE_REQUESTS;
+import static android.net.wifi.p2p.WifiP2pManager.P2P_UNSUPPORTED;
+import static android.os.Build.VERSION.SDK_INT;
+import static android.os.PowerManager.FULL_WAKE_LOCK;
+import static java.util.Objects.requireNonNull;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.briar.android.util.UiUtils.handleException;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+class HotspotManager {
+
+	interface HotspotListener {
+		@UiThread
+		void onStartingHotspot();
+
+		@IoExecutor
+		void onHotspotStarted(NetworkConfig networkConfig);
+
+		@UiThread
+		void onDeviceConnected();
+
+		@UiThread
+		void onHotspotError(String error);
+	}
+
+	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";
+	private static final String HOTSPOT_KEY_SSID = "ssid";
+	private static final String HOTSPOT_KEY_PASS = "pass";
+
+	private final Context ctx;
+	@DatabaseExecutor
+	private final Executor dbExecutor;
+	@IoExecutor
+	private final Executor ioExecutor;
+	private final AndroidExecutor androidExecutor;
+	private final SettingsManager settingsManager;
+	private final SecureRandom random;
+	private final WifiManager wifiManager;
+	private final WifiP2pManager wifiP2pManager;
+	private final PowerManager powerManager;
+	private final Handler handler;
+	private final String lockTag;
+
+	private HotspotListener listener;
+	private WifiManager.WifiLock wifiLock;
+	private PowerManager.WakeLock wakeLock;
+	private WifiP2pManager.Channel channel;
+	@Nullable
+	@RequiresApi(29)
+	private volatile NetworkConfig savedNetworkConfig = null;
+
+	@Inject
+	HotspotManager(Application ctx,
+			@DatabaseExecutor Executor dbExecutor,
+			@IoExecutor Executor ioExecutor,
+			AndroidExecutor androidExecutor,
+			SettingsManager settingsManager,
+			SecureRandom random) {
+		this.ctx = ctx.getApplicationContext();
+		this.dbExecutor = dbExecutor;
+		this.ioExecutor = ioExecutor;
+		this.androidExecutor = androidExecutor;
+		this.settingsManager = settingsManager;
+		this.random = random;
+		wifiManager = (WifiManager) ctx.getApplicationContext()
+				.getSystemService(WIFI_SERVICE);
+		wifiP2pManager =
+				(WifiP2pManager) ctx.getSystemService(WIFI_P2P_SERVICE);
+		powerManager = (PowerManager) ctx.getSystemService(POWER_SERVICE);
+		handler = new Handler(ctx.getMainLooper());
+		lockTag = ctx.getPackageName() + ":app-sharing-hotspot";
+	}
+
+	void setHotspotListener(HotspotListener listener) {
+		this.listener = listener;
+	}
+
+	@UiThread
+	void startWifiP2pHotspot() {
+		if (wifiP2pManager == null) {
+			listener.onHotspotError(
+					ctx.getString(R.string.hotspot_error_no_wifi_direct));
+			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)
+	 */
+	@UiThread
+	private 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) {
+			releaseHotspotWithError(
+					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) {
+				if (LOG.isLoggable(INFO)) {
+					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) {
+				Runnable createGroup = () -> {
+					NetworkConfig c = requireNonNull(savedNetworkConfig);
+					WifiP2pConfig config = new WifiP2pConfig.Builder()
+							.setGroupOperatingBand(GROUP_OWNER_BAND_2GHZ)
+							.setNetworkName(c.ssid)
+							.setPassphrase(c.password)
+							.build();
+					wifiP2pManager.createGroup(channel, config, listener);
+				};
+				if (savedNetworkConfig == null) {
+					// load savedNetworkConfig before starting hotspot
+					dbExecutor.execute(() -> {
+						loadSavedNetworkConfig();
+						androidExecutor.runOnUiThread(createGroup);
+					});
+				} else {
+					// savedNetworkConfig was already loaded, create group now
+					createGroup.run();
+				}
+			} else {
+				wifiP2pManager.createGroup(channel, listener);
+			}
+		} catch (SecurityException e) {
+			// this should never happen, because we request permissions before
+			throw new AssertionError(e);
+		}
+	}
+
+	@UiThread
+	private void restartWifiP2pFramework(int attempt) {
+		LOG.info("retrying to start WifiP2p framework");
+		if (attempt < MAX_FRAMEWORK_ATTEMPTS) {
+			if (SDK_INT >= 27 && channel != null) channel.close();
+			channel = null;
+			handler.postDelayed(() -> startWifiP2pFramework(attempt + 1),
+					RETRY_DELAY_MILLIS);
+		} else {
+			releaseHotspotWithError(
+					ctx.getString(R.string.hotspot_error_framework_busy));
+		}
+	}
+
+	@UiThread
+	void stopWifiP2pHotspot() {
+		if (channel == null) return;
+		wifiP2pManager.removeGroup(channel, new ActionListener() {
+			@Override
+			public void onSuccess() {
+				closeChannelAndReleaseLocks();
+			}
+
+			@Override
+			public void onFailure(int reason) {
+				// not propagating back error
+				if (LOG.isLoggable(WARNING)) {
+					LOG.warning("Error removing Wifi P2P group: " + reason);
+				}
+				closeChannelAndReleaseLocks();
+			}
+		});
+	}
+
+	@SuppressLint("WakelockTimeout")
+	private void acquireLocks() {
+		// FLAG_KEEP_SCREEN_ON is not respected on some Huawei devices.
+		wakeLock = powerManager.newWakeLock(FULL_WAKE_LOCK, lockTag);
+		wakeLock.acquire();
+		// WIFI_MODE_FULL has no effect on API >= 29
+		int lockType =
+				SDK_INT >= 29 ? WIFI_MODE_FULL_HIGH_PERF : WIFI_MODE_FULL;
+		wifiLock = wifiManager.createWifiLock(lockType, lockTag);
+		wifiLock.acquire();
+	}
+
+	@UiThread
+	private void releaseHotspotWithError(String error) {
+		listener.onHotspotError(error);
+		closeChannelAndReleaseLocks();
+	}
+
+	@UiThread
+	private void closeChannelAndReleaseLocks() {
+		if (SDK_INT >= 27 && channel != null) channel.close();
+		channel = null;
+		if (wakeLock.isHeld()) wakeLock.release();
+		if (wifiLock.isHeld()) wifiLock.release();
+	}
+
+	@UiThread
+	private void requestGroupInfo(int attempt) {
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("requestGroupInfo attempt: " + attempt);
+		}
+		GroupInfoListener groupListener = group -> {
+			boolean valid = isGroupValid(group);
+			// If the group is valid, set the hotspot to started. If we don't
+			// have any attempts left, we try what we got
+			if (valid || attempt >= MAX_GROUP_INFO_ATTEMPTS) {
+				onHotspotStarted(group);
+			} else {
+				retryRequestingGroupInfo(attempt);
+			}
+		};
+		try {
+			if (channel == null) return;
+			wifiP2pManager.requestGroupInfo(channel, groupListener);
+		} catch (SecurityException e) {
+			// this should never happen, because we request permissions before
+			throw new AssertionError(e);
+		}
+	}
+
+	@UiThread
+	private void onHotspotStarted(WifiP2pGroup group) {
+		DisplayMetrics dm = ctx.getResources().getDisplayMetrics();
+		ioExecutor.execute(() -> {
+			String content = createWifiLoginString(group.getNetworkName(),
+					group.getPassphrase());
+			Bitmap qrCode = QrCodeUtils.createQrCode(dm, content);
+			NetworkConfig config = new NetworkConfig(group.getNetworkName(),
+					group.getPassphrase(), qrCode);
+			listener.onHotspotStarted(config);
+		});
+		requestGroupInfoForConnection();
+	}
+
+	private boolean isGroupValid(@Nullable WifiP2pGroup group) {
+		if (group == null) {
+			LOG.info("group is null");
+			return false;
+		} else if (!group.getNetworkName().startsWith("DIRECT-")) {
+			LOG.info("received networkName without prefix 'DIRECT-'");
+			return false;
+		} else if (SDK_INT >= 29) {
+			// if we get here, the savedNetworkConfig must have a value
+			String networkName = requireNonNull(savedNetworkConfig).ssid;
+			if (!networkName.equals(group.getNetworkName())) {
+				LOG.info("expected networkName does not match received one");
+				return false;
+			}
+		}
+		return true;
+	}
+
+	@UiThread
+	private void retryRequestingGroupInfo(int attempt) {
+		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),
+					RETRY_DELAY_MILLIS);
+		} else {
+			releaseHotspotWithError(ctx.getString(
+					R.string.hotspot_error_start_callback_no_group_info));
+		}
+	}
+
+	@UiThread
+	private void requestGroupInfoForConnection() {
+		LOG.info("requestGroupInfo for connection");
+		GroupInfoListener groupListener = group -> {
+			if (group == null || group.getClientList().isEmpty()) {
+				handler.postDelayed(this::requestGroupInfoForConnection,
+						RETRY_DELAY_MILLIS);
+			} else {
+				listener.onDeviceConnected();
+			}
+		};
+		try {
+			if (channel == null) return;
+			wifiP2pManager.requestGroupInfo(channel, groupListener);
+		} catch (SecurityException e) {
+			throw new AssertionError(e);
+		}
+	}
+
+	/**
+	 * Store persistent Wi-Fi SSID and passphrase in Settings to improve UX
+	 * so that users don't have to change them when attempting to connect.
+	 * Works only on API 29 and above.
+	 */
+	@RequiresApi(29)
+	@DatabaseExecutor
+	private void loadSavedNetworkConfig() {
+		try {
+			Settings settings = settingsManager.getSettings(HOTSPOT_NAMESPACE);
+			String ssid = settings.get(HOTSPOT_KEY_SSID);
+			String pass = settings.get(HOTSPOT_KEY_PASS);
+			if (ssid == null || pass == null) {
+				ssid = getSsid();
+				pass = getPassword();
+				settings.put(HOTSPOT_KEY_SSID, ssid);
+				settings.put(HOTSPOT_KEY_PASS, pass);
+				settingsManager.mergeSettings(settings, HOTSPOT_NAMESPACE);
+			}
+			savedNetworkConfig = new NetworkConfig(ssid, pass, null);
+		} catch (DbException e) {
+			handleException(ctx, androidExecutor, LOG, e);
+			// probably never happens, but if lets use non-persistent data
+			String ssid = getSsid();
+			String pass = getPassword();
+			savedNetworkConfig = new NetworkConfig(ssid, pass, null);
+		}
+	}
+
+	@RequiresApi(29)
+	private String getSsid() {
+		return "DIRECT-" + getRandomString(2) + "-" +
+				getRandomString(10);
+	}
+
+	@RequiresApi(29)
+	private String getPassword() {
+		return getRandomString(8);
+	}
+
+	private static String createWifiLoginString(String ssid, String password) {
+		// https://en.wikipedia.org/wiki/QR_code#WiFi_network_login
+		// do not remove the dangling ';', it can cause problems to omit it
+		return "WIFI:S:" + ssid + ";T:WPA;P:" + password + ";;";
+	}
+
+	// exclude chars that are easy to confuse: 0 O, 5 S, 1 l I
+	private static final String chars =
+			"2346789ABCDEFGHJKLMNPQRTUVWXYZabcdefghijkmnopqrstuvwxyz";
+
+	private String getRandomString(int length) {
+		char[] c = new char[length];
+		for (int i = 0; i < length; i++) {
+			c[i] = chars.charAt(random.nextInt(chars.length()));
+		}
+		return new String(c);
+	}
+
+}

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

@@ -0,0 +1,18 @@
+package org.briarproject.briar.android.hotspot;
+
+import org.briarproject.briar.android.viewmodel.ViewModelKey;
+
+import androidx.lifecycle.ViewModel;
+import dagger.Binds;
+import dagger.Module;
+import dagger.multibindings.IntoMap;
+
+@Module
+public interface HotspotModule {
+
+	@Binds
+	@IntoMap
+	@ViewModelKey(HotspotViewModel.class)
+	ViewModel bindHotspotViewModel(HotspotViewModel hotspotViewModel);
+
+}

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

@@ -0,0 +1,88 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.graphics.Bitmap;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import androidx.annotation.Nullable;
+import androidx.annotation.UiThread;
+
+@NotNullByDefault
+abstract class HotspotState {
+
+	static class StartingHotspot extends HotspotState {
+	}
+
+	static class NetworkConfig {
+		final String ssid, password;
+		@Nullable
+		final Bitmap qrCode;
+
+		NetworkConfig(String ssid, String password, @Nullable Bitmap qrCode) {
+			this.ssid = ssid;
+			this.password = password;
+			this.qrCode = qrCode;
+		}
+	}
+
+	static class WebsiteConfig {
+		final String url;
+		@Nullable
+		final Bitmap qrCode;
+
+		WebsiteConfig(String url, @Nullable Bitmap qrCode) {
+			this.url = url;
+			this.qrCode = qrCode;
+		}
+	}
+
+	static class HotspotStarted extends HotspotState {
+		private final NetworkConfig networkConfig;
+		private final WebsiteConfig websiteConfig;
+		// 'consumed' is set to true once this state triggered a UI change, i.e.
+		// moving to the next fragment.
+		private boolean consumed = false;
+
+		HotspotStarted(NetworkConfig networkConfig,
+				WebsiteConfig websiteConfig) {
+			this.networkConfig = networkConfig;
+			this.websiteConfig = websiteConfig;
+		}
+
+		NetworkConfig getNetworkConfig() {
+			return networkConfig;
+		}
+
+		WebsiteConfig getWebsiteConfig() {
+			return websiteConfig;
+		}
+
+		@UiThread
+		boolean wasNotYetConsumed() {
+			return !consumed;
+		}
+
+		/**
+		 * Mark this state as consumed, i.e. the UI has already done something
+		 * as a result of the state changing to this. This can be used in order
+		 * to not repeat actions such as showing fragments on rotation changes.
+		 */
+		@UiThread
+		void consume() {
+			consumed = true;
+		}
+	}
+
+	static class HotspotError extends HotspotState {
+		private final String error;
+
+		HotspotError(String error) {
+			this.error = error;
+		}
+
+		String getError() {
+			return error;
+		}
+	}
+
+}

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

@@ -0,0 +1,224 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.app.Application;
+import android.net.Uri;
+
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.TransactionManager;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.AndroidExecutor;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.hotspot.HotspotManager.HotspotListener;
+import org.briarproject.briar.android.hotspot.HotspotState.HotspotError;
+import org.briarproject.briar.android.hotspot.HotspotState.HotspotStarted;
+import org.briarproject.briar.android.hotspot.HotspotState.NetworkConfig;
+import org.briarproject.briar.android.hotspot.HotspotState.StartingHotspot;
+import org.briarproject.briar.android.hotspot.HotspotState.WebsiteConfig;
+import org.briarproject.briar.android.hotspot.WebServerManager.WebServerListener;
+import org.briarproject.briar.android.viewmodel.DbViewModel;
+import org.briarproject.briar.android.viewmodel.LiveEvent;
+import org.briarproject.briar.android.viewmodel.MutableLiveEvent;
+import org.briarproject.briar.api.android.AndroidNotificationManager;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+import androidx.annotation.UiThread;
+import androidx.lifecycle.LiveData;
+import androidx.lifecycle.MutableLiveData;
+
+import static android.os.Build.VERSION.SDK_INT;
+import static android.os.Environment.DIRECTORY_DOWNLOADS;
+import static android.os.Environment.getExternalStoragePublicDirectory;
+import static java.util.Objects.requireNonNull;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.copyAndClose;
+import static org.briarproject.briar.BuildConfig.DEBUG;
+import static org.briarproject.briar.BuildConfig.VERSION_NAME;
+
+@NotNullByDefault
+class HotspotViewModel extends DbViewModel
+		implements HotspotListener, WebServerListener {
+
+	private static final Logger LOG =
+			getLogger(HotspotViewModel.class.getName());
+
+	@IoExecutor
+	private final Executor ioExecutor;
+	private final AndroidNotificationManager notificationManager;
+	private final HotspotManager hotspotManager;
+	private final WebServerManager webServerManager;
+
+	private final MutableLiveData<HotspotState> state =
+			new MutableLiveData<>();
+	private final MutableLiveEvent<Boolean> peerConnected =
+			new MutableLiveEvent<>();
+	private final MutableLiveEvent<Uri> savedApkToUri =
+			new MutableLiveEvent<>();
+
+	@Nullable
+	// Field to temporarily store the network config received via onHotspotStarted()
+	// in order to post it along with a HotspotStarted status
+	private volatile NetworkConfig networkConfig;
+
+	@Inject
+	HotspotViewModel(Application app,
+			@DatabaseExecutor Executor dbExecutor,
+			LifecycleManager lifecycleManager,
+			TransactionManager db,
+			AndroidExecutor androidExecutor,
+			@IoExecutor Executor ioExecutor,
+			HotspotManager hotspotManager,
+			WebServerManager webServerManager,
+			AndroidNotificationManager notificationManager) {
+		super(app, dbExecutor, lifecycleManager, db, androidExecutor);
+		this.ioExecutor = ioExecutor;
+		this.notificationManager = notificationManager;
+		this.hotspotManager = hotspotManager;
+		this.hotspotManager.setHotspotListener(this);
+		this.webServerManager = webServerManager;
+		this.webServerManager.setListener(this);
+	}
+
+	@UiThread
+	void startHotspot() {
+		HotspotState s = state.getValue();
+		if (s instanceof HotspotStarted) {
+			// This can happen if the user navigates back to intro fragment and
+			// taps 'start sharing' again. In this case, don't try to start the
+			// hotspot again. Instead, just create a new, unconsumed HotspotStarted
+			// event with the same config.
+			HotspotStarted old = (HotspotStarted) s;
+			state.setValue(new HotspotStarted(old.getNetworkConfig(),
+					old.getWebsiteConfig()));
+		} else {
+			hotspotManager.startWifiP2pHotspot();
+			notificationManager.showHotspotNotification();
+		}
+	}
+
+	@UiThread
+	private void stopHotspot() {
+		ioExecutor.execute(webServerManager::stopWebServer);
+		hotspotManager.stopWifiP2pHotspot();
+		notificationManager.clearHotspotNotification();
+	}
+
+	@Override
+	protected void onCleared() {
+		super.onCleared();
+		stopHotspot();
+	}
+
+	@Override
+	public void onStartingHotspot() {
+		state.setValue(new StartingHotspot());
+	}
+
+	@Override
+	@IoExecutor
+	public void onHotspotStarted(NetworkConfig networkConfig) {
+		this.networkConfig = networkConfig;
+		LOG.info("starting webserver");
+		webServerManager.startWebServer();
+	}
+
+	@UiThread
+	@Override
+	public void onDeviceConnected() {
+		peerConnected.setEvent(true);
+	}
+
+	@Override
+	public void onHotspotError(String error) {
+		if (LOG.isLoggable(WARNING)) {
+			LOG.warning("Hotspot error: " + error);
+		}
+		state.postValue(new HotspotError(error));
+		ioExecutor.execute(webServerManager::stopWebServer);
+		notificationManager.clearHotspotNotification();
+	}
+
+	@Override
+	@IoExecutor
+	public void onWebServerStarted(WebsiteConfig websiteConfig) {
+		NetworkConfig nc = requireNonNull(networkConfig);
+		state.postValue(new HotspotStarted(nc, websiteConfig));
+		networkConfig = null;
+	}
+
+	@Override
+	@IoExecutor
+	public void onWebServerError() {
+		state.postValue(new HotspotError(getApplication()
+				.getString(R.string.hotspot_error_web_server_start)));
+		stopHotspot();
+	}
+
+	void exportApk(Uri uri) {
+		if (SDK_INT < 19) throw new IllegalStateException();
+		try {
+			OutputStream out = getApplication().getContentResolver()
+					.openOutputStream(uri, "wt");
+			writeApk(out, uri);
+		} catch (FileNotFoundException e) {
+			handleException(e);
+		}
+	}
+
+	void exportApk() {
+		if (SDK_INT >= 19) throw new IllegalStateException();
+		File path = getExternalStoragePublicDirectory(DIRECTORY_DOWNLOADS);
+		//noinspection ResultOfMethodCallIgnored
+		path.mkdirs();
+		File file = new File(path, getApkFileName());
+		try {
+			OutputStream out = new FileOutputStream(file);
+			writeApk(out, Uri.fromFile(file));
+		} catch (FileNotFoundException e) {
+			handleException(e);
+		}
+	}
+
+	static String getApkFileName() {
+		return "briar" + (DEBUG ? "-debug-" : "-") + VERSION_NAME + ".apk";
+	}
+
+	private void writeApk(OutputStream out, Uri uriToShare) {
+		File apk = new File(getApplication().getPackageCodePath());
+		ioExecutor.execute(() -> {
+			try {
+				FileInputStream in = new FileInputStream(apk);
+				copyAndClose(in, out);
+				savedApkToUri.postEvent(uriToShare);
+			} catch (IOException e) {
+				handleException(e);
+			}
+		});
+	}
+
+	LiveData<HotspotState> getState() {
+		return state;
+	}
+
+	LiveEvent<Boolean> getPeerConnectedEvent() {
+		return peerConnected;
+	}
+
+	LiveEvent<Uri> getSavedApkToUri() {
+		return savedApkToUri;
+	}
+
+}

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

@@ -0,0 +1,119 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.text.SpannableString;
+import android.text.method.LinkMovementMethod;
+import android.text.style.ClickableSpan;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.TextView;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+import androidx.core.util.Consumer;
+import androidx.fragment.app.Fragment;
+import androidx.lifecycle.ViewModelProvider;
+import androidx.viewpager2.widget.ViewPager2;
+
+import static android.text.Spanned.SPAN_EXCLUSIVE_EXCLUSIVE;
+import static android.view.View.GONE;
+import static org.briarproject.briar.android.AppModule.getAndroidComponent;
+import static org.briarproject.briar.android.hotspot.AbstractTabsFragment.ARG_FOR_WIFI_CONNECT;
+import static org.briarproject.briar.android.hotspot.HotspotState.HotspotStarted;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class ManualHotspotFragment extends Fragment {
+
+	public final static String TAG = ManualHotspotFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private HotspotViewModel viewModel;
+
+	static ManualHotspotFragment newInstance(boolean forWifiConnect) {
+		ManualHotspotFragment f = new ManualHotspotFragment();
+		Bundle bundle = new Bundle();
+		bundle.putBoolean(ARG_FOR_WIFI_CONNECT, forWifiConnect);
+		f.setArguments(bundle);
+		return f;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		getAndroidComponent(requireContext()).inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(HotspotViewModel.class);
+	}
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		return inflater
+				.inflate(R.layout.fragment_hotspot_manual, container, false);
+	}
+
+	@Override
+	public void onViewCreated(View v, @Nullable Bundle savedInstanceState) {
+		super.onViewCreated(v, savedInstanceState);
+
+		TextView manualIntroView = v.findViewById(R.id.manualIntroView);
+		TextView ssidLabelView = v.findViewById(R.id.ssidLabelView);
+		TextView ssidView = v.findViewById(R.id.ssidView);
+		TextView passwordView = v.findViewById(R.id.passwordView);
+
+		Consumer<HotspotStarted> consumer;
+		if (requireArguments().getBoolean(ARG_FOR_WIFI_CONNECT)) {
+			linkify(manualIntroView, R.string.hotspot_manual_wifi);
+			ssidLabelView.setText(R.string.hotspot_manual_wifi_ssid);
+			consumer = state -> {
+				ssidView.setText(state.getNetworkConfig().ssid);
+				passwordView.setText(state.getNetworkConfig().password);
+			};
+		} else {
+			linkify(manualIntroView, R.string.hotspot_manual_site);
+			ssidLabelView.setText(R.string.hotspot_manual_site_address);
+			consumer = state -> ssidView.setText(state.getWebsiteConfig().url);
+			v.findViewById(R.id.passwordLabelView).setVisibility(GONE);
+			passwordView.setVisibility(GONE);
+		}
+		viewModel.getState().observe(getViewLifecycleOwner(), state -> {
+			// we only expect to be in this state here
+			if (state instanceof HotspotStarted) {
+				consumer.accept((HotspotStarted) state);
+			}
+		});
+	}
+
+	private void linkify(TextView textView, int resPattern) {
+		String pattern = getString(resPattern);
+		String replacement = getString(R.string.hotspot_scanning_a_qr_code);
+		String text = String.format(pattern, replacement);
+		int start = pattern.indexOf("%s");
+		int end = start + replacement.length();
+		SpannableString spannable = new SpannableString(text);
+		ClickableSpan clickable = new ClickableSpan() {
+
+			@Override
+			public void onClick(View textView) {
+				ViewPager2 pager = requireActivity().findViewById(R.id.pager);
+				pager.setCurrentItem(1);
+			}
+
+		};
+		spannable.setSpan(clickable, start, end, SPAN_EXCLUSIVE_EXCLUSIVE);
+
+		textView.setText(spannable);
+		textView.setMovementMethod(LinkMovementMethod.getInstance());
+	}
+}

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

@@ -0,0 +1,86 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Context;
+import android.graphics.Bitmap;
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.ImageView;
+import android.widget.TextView;
+import android.widget.Toast;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.hotspot.HotspotState.HotspotStarted;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+import androidx.lifecycle.ViewModelProvider;
+
+import static org.briarproject.briar.android.AppModule.getAndroidComponent;
+import static org.briarproject.briar.android.hotspot.AbstractTabsFragment.ARG_FOR_WIFI_CONNECT;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class QrHotspotFragment extends Fragment {
+
+	public final static String TAG = QrHotspotFragment.class.getName();
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private HotspotViewModel viewModel;
+
+	static QrHotspotFragment newInstance(boolean forWifiConnect) {
+		QrHotspotFragment f = new QrHotspotFragment();
+		Bundle bundle = new Bundle();
+		bundle.putBoolean(ARG_FOR_WIFI_CONNECT, forWifiConnect);
+		f.setArguments(bundle);
+		return f;
+	}
+
+	@Override
+	public void onAttach(Context context) {
+		super.onAttach(context);
+		getAndroidComponent(requireContext()).inject(this);
+		viewModel = new ViewModelProvider(requireActivity(), viewModelFactory)
+				.get(HotspotViewModel.class);
+	}
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View v = inflater
+				.inflate(R.layout.fragment_hotspot_qr, container, false);
+
+		TextView qrIntroView = v.findViewById(R.id.qrIntroView);
+		ImageView qrCodeView = v.findViewById(R.id.qrCodeView);
+
+		boolean forWifi = requireArguments().getBoolean(ARG_FOR_WIFI_CONNECT);
+
+		qrIntroView.setText(forWifi ? R.string.hotspot_qr_wifi :
+				R.string.hotspot_qr_site);
+
+		viewModel.getState().observe(getViewLifecycleOwner(), state -> {
+			if (state instanceof HotspotStarted) {
+				HotspotStarted s = (HotspotStarted) state;
+				Bitmap qrCode = forWifi ? s.getNetworkConfig().qrCode :
+						s.getWebsiteConfig().qrCode;
+				if (qrCode == null) {
+					Toast.makeText(requireContext(), R.string.error,
+							Toast.LENGTH_SHORT).show();
+					qrCodeView.setImageResource(R.drawable.ic_image_broken);
+				} else {
+					qrCodeView.setImageBitmap(qrCode);
+				}
+			}
+		});
+		return v;
+	}
+
+}

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

@@ -0,0 +1,135 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.content.Context;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.R;
+import org.jsoup.Jsoup;
+import org.jsoup.nodes.Document;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.logging.Logger;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import androidx.annotation.Nullable;
+import fi.iki.elonen.NanoHTTPD;
+
+import static android.util.Xml.Encoding.UTF_8;
+import static fi.iki.elonen.NanoHTTPD.Response.Status.INTERNAL_ERROR;
+import static fi.iki.elonen.NanoHTTPD.Response.Status.NOT_FOUND;
+import static fi.iki.elonen.NanoHTTPD.Response.Status.OK;
+import static java.util.Objects.requireNonNull;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.briar.BuildConfig.VERSION_NAME;
+import static org.briarproject.briar.android.hotspot.HotspotViewModel.getApkFileName;
+
+@NotNullByDefault
+class WebServer extends NanoHTTPD {
+
+	final static int PORT = 9999;
+
+	private static final Logger LOG = getLogger(WebServer.class.getName());
+	private static final String FILE_HTML = "hotspot.html";
+	private static final Pattern REGEX_AGENT =
+			Pattern.compile("Android ([0-9]+)");
+
+	private final Context ctx;
+
+	WebServer(Context ctx) {
+		super(PORT);
+		this.ctx = ctx;
+	}
+
+	@Override
+	public void start() throws IOException {
+		start(NanoHTTPD.SOCKET_READ_TIMEOUT, false);
+	}
+
+	@Override
+	public Response serve(IHTTPSession session) {
+		if (session.getUri().endsWith("favicon.ico")) {
+			return newFixedLengthResponse(NOT_FOUND, MIME_PLAINTEXT,
+					NOT_FOUND.getDescription());
+		}
+		if (session.getUri().endsWith(".apk")) {
+			return serveApk();
+		}
+		Response res;
+		try {
+			String html = getHtml(session.getHeaders().get("user-agent"));
+			res = newFixedLengthResponse(OK, MIME_HTML, html);
+		} catch (Exception e) {
+			logException(LOG, WARNING, e);
+			res = newFixedLengthResponse(INTERNAL_ERROR, MIME_PLAINTEXT,
+					ctx.getString(R.string.hotspot_error_web_server_serve));
+		}
+		return res;
+	}
+
+	private String getHtml(@Nullable String userAgent) throws Exception {
+		Document doc;
+		try (InputStream is = ctx.getAssets().open(FILE_HTML)) {
+			doc = Jsoup.parse(is, UTF_8.name(), "");
+		}
+		String app = ctx.getString(R.string.app_name);
+		String appV = app + " " + VERSION_NAME;
+		String filename = getApkFileName();
+		doc.select("#download_title").first()
+				.text(ctx.getString(R.string.website_download_title, appV));
+		doc.select("#download_intro").first()
+				.text(ctx.getString(R.string.website_download_intro, app));
+		doc.select(".button").first().attr("href", filename);
+		doc.select("#download_button").first()
+				.text(ctx.getString(R.string.website_download_title, app));
+		doc.select("#download_outro").first()
+				.text(ctx.getString(R.string.website_download_outro));
+		doc.select("#troubleshooting_title").first()
+				.text(ctx.getString(R.string.website_troubleshooting_title));
+		doc.select("#troubleshooting_1").first()
+				.text(ctx.getString(R.string.website_troubleshooting_1));
+		doc.select("#troubleshooting_2").first()
+				.text(getUnknownSourcesString(userAgent));
+		return doc.outerHtml();
+	}
+
+	private String getUnknownSourcesString(@Nullable String userAgent) {
+		boolean is8OrHigher = false;
+		if (userAgent != null) {
+			Matcher matcher = REGEX_AGENT.matcher(userAgent);
+			if (matcher.find()) {
+				int androidMajorVersion =
+						Integer.parseInt(requireNonNull(matcher.group(1)));
+				is8OrHigher = androidMajorVersion >= 8;
+			}
+		}
+		return is8OrHigher ?
+				ctx.getString(R.string.website_troubleshooting_2_new) :
+				ctx.getString(R.string.website_troubleshooting_2_old);
+	}
+
+	private Response serveApk() {
+		String mime = "application/vnd.android.package-archive";
+
+		File file = new File(ctx.getPackageCodePath());
+		long fileLen = file.length();
+
+		Response res;
+		try {
+			FileInputStream fis = new FileInputStream(file);
+			res = newFixedLengthResponse(OK, mime, fis, fileLen);
+			res.addHeader("Content-Length", "" + fileLen);
+		} catch (FileNotFoundException e) {
+			logException(LOG, WARNING, e);
+			res = newFixedLengthResponse(NOT_FOUND, MIME_PLAINTEXT,
+					ctx.getString(R.string.hotspot_error_web_server_serve));
+		}
+		return res;
+	}
+}

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

@@ -0,0 +1,127 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.app.Application;
+import android.graphics.Bitmap;
+import android.util.DisplayMetrics;
+
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+import org.briarproject.briar.android.hotspot.HotspotState.WebsiteConfig;
+import org.briarproject.briar.android.util.QrCodeUtils;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.InterfaceAddress;
+import java.net.NetworkInterface;
+import java.net.SocketException;
+import java.util.Enumeration;
+import java.util.List;
+import java.util.logging.Logger;
+
+import javax.inject.Inject;
+
+import androidx.annotation.Nullable;
+import androidx.annotation.UiThread;
+
+import static java.util.Collections.emptyList;
+import static java.util.Collections.list;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.briar.android.hotspot.WebServer.PORT;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+class WebServerManager {
+
+	interface WebServerListener {
+		@IoExecutor
+		void onWebServerStarted(WebsiteConfig websiteConfig);
+
+		@IoExecutor
+		void onWebServerError();
+	}
+
+	private static final Logger LOG =
+			getLogger(WebServerManager.class.getName());
+
+	private final WebServer webServer;
+	private final DisplayMetrics dm;
+
+	private volatile WebServerListener listener;
+
+	@Inject
+	WebServerManager(Application ctx) {
+		webServer = new WebServer(ctx);
+		dm = ctx.getResources().getDisplayMetrics();
+	}
+
+	@UiThread
+	void setListener(WebServerListener listener) {
+		this.listener = listener;
+	}
+
+	@IoExecutor
+	void startWebServer() {
+		try {
+			webServer.start();
+			onWebServerStarted();
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			listener.onWebServerError();
+		}
+	}
+
+	@IoExecutor
+	private void onWebServerStarted() {
+		String url = "http://192.168.49.1:" + PORT;
+		InetAddress address = getAccessPointAddress();
+		if (address == null) {
+			LOG.info(
+					"Could not find access point address, assuming 192.168.49.1");
+		} else {
+			if (LOG.isLoggable(INFO)) {
+				LOG.info("Access point address " + address.getHostAddress());
+			}
+			url = "http://" + address.getHostAddress() + ":" + PORT;
+		}
+		Bitmap qrCode = QrCodeUtils.createQrCode(dm, url);
+		listener.onWebServerStarted(new WebsiteConfig(url, qrCode));
+	}
+
+	/**
+	 * It is safe to call this more than once and it won't throw.
+	 */
+	@IoExecutor
+	void stopWebServer() {
+		webServer.stop();
+	}
+
+	@Nullable
+	private static InetAddress getAccessPointAddress() {
+		for (NetworkInterface i : getNetworkInterfaces()) {
+			if (i.getName().startsWith("p2p")) {
+				for (InterfaceAddress a : i.getInterfaceAddresses()) {
+					// we consider only IPv4 addresses
+					if (a.getAddress().getAddress().length == 4)
+						return a.getAddress();
+				}
+			}
+		}
+		return null;
+	}
+
+	private static List<NetworkInterface> getNetworkInterfaces() {
+		try {
+			Enumeration<NetworkInterface> ifaces =
+					NetworkInterface.getNetworkInterfaces();
+			return ifaces == null ? emptyList() : list(ifaces);
+		} catch (SocketException e) {
+			logException(LOG, WARNING, e);
+			return emptyList();
+		}
+	}
+
+}

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

@@ -0,0 +1,36 @@
+package org.briarproject.briar.android.hotspot;
+
+import android.os.Bundle;
+import android.view.View;
+
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
+
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+
+import static android.view.View.GONE;
+
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
+public class WebsiteFragment extends AbstractTabsFragment {
+
+	public final static String TAG = WebsiteFragment.class.getName();
+
+	@Override
+	public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
+		super.onViewCreated(view, savedInstanceState);
+		connectedButton.setVisibility(GONE);
+	}
+
+	@Override
+	protected Fragment getFirstFragment() {
+		return ManualHotspotFragment.newInstance(false);
+	}
+
+	@Override
+	protected Fragment getSecondFragment() {
+		return QrHotspotFragment.newInstance(false);
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/reporting/BriarExceptionHandler.java

@@ -38,7 +38,7 @@ class BriarExceptionHandler implements UncaughtExceptionHandler {
 
 		// activity runs in its own process, so we can kill the old one
 		startDevReportActivity(app.getApplicationContext(),
-				CrashReportActivity.class, e, appStartTime, logKey);
+				CrashReportActivity.class, e, appStartTime, logKey, null);
 		Process.killProcess(Process.myPid());
 		System.exit(10);
 	}

briar-android/src/main/java/org/briarproject/briar/android/reporting/CrashReportActivity.java

@@ -33,6 +33,7 @@ import static java.util.Objects.requireNonNull;
 public class CrashReportActivity extends BaseActivity
 		implements BaseFragmentListener {
 
+	public static final String EXTRA_INITIAL_COMMENT = "initialComment";
 	public static final String EXTRA_THROWABLE = "throwable";
 	public static final String EXTRA_APP_START_TIME = "appStartTime";
 	public static final String EXTRA_APP_LOGCAT = "logcat";
@@ -55,10 +56,11 @@ public class CrashReportActivity extends BaseActivity
 		setContentView(R.layout.activity_dev_report);
 
 		Intent intent = getIntent();
+		String initialComment = intent.getStringExtra(EXTRA_INITIAL_COMMENT);
 		Throwable t = (Throwable) intent.getSerializableExtra(EXTRA_THROWABLE);
 		long appStartTime = intent.getLongExtra(EXTRA_APP_START_TIME, -1);
 		byte[] logKey = intent.getByteArrayExtra(EXTRA_APP_LOGCAT);
-		viewModel.init(t, appStartTime, logKey);
+		viewModel.init(t, appStartTime, logKey, initialComment);
 		viewModel.getShowReport().observeEvent(this, show -> {
 			if (show) displayFragment(true);
 		});

briar-android/src/main/java/org/briarproject/briar/android/reporting/ReportFormFragment.java

@@ -78,6 +78,9 @@ public class ReportFormFragment extends BaseFragment {
 		list = v.findViewById(R.id.list);
 		progress = v.findViewById(R.id.progress_wheel);
 
+		if (viewModel.getInitialComment() != null)
+			userCommentView.setText(viewModel.getInitialComment());
+
 		if (viewModel.isFeedback()) {
 			includeDebugReport
 					.setText(getString(R.string.include_debug_report_feedback));

briar-android/src/main/java/org/briarproject/briar/android/reporting/ReportViewModel.java

@@ -64,6 +64,8 @@ class ReportViewModel extends AndroidViewModel {
 	private final MutableLiveEvent<Integer> closeReport =
 			new MutableLiveEvent<>();
 	private boolean isFeedback;
+	@Nullable
+	private String initialComment;
 
 	@Inject
 	ReportViewModel(@NonNull Application application,
@@ -80,7 +82,8 @@ class ReportViewModel extends AndroidViewModel {
 	}
 
 	void init(@Nullable Throwable t, long appStartTime,
-			@Nullable byte[] logKey) {
+			@Nullable byte[] logKey, @Nullable String initialComment) {
+		this.initialComment = initialComment;
 		isFeedback = t == null;
 		if (reportData.getValue() == null) new SingleShotAndroidExecutor(() -> {
 			String decryptedLogs;
@@ -103,6 +106,11 @@ class ReportViewModel extends AndroidViewModel {
 		}).start();
 	}
 
+	@Nullable
+	String getInitialComment() {
+		return initialComment;
+	}
+
 	boolean isFeedback() {
 		return isFeedback;
 	}
@@ -140,7 +148,7 @@ class ReportViewModel extends AndroidViewModel {
 
 	/**
 	 * The content of the report that will be loaded after
-	 * {@link #init(Throwable, long, byte[])} was called.
+	 * {@link #init(Throwable, long, byte[], String)} was called.
 	 */
 	LiveData<ReportData> getReportData() {
 		return reportData;

briar-android/src/main/java/org/briarproject/briar/android/settings/SettingsFragment.java

@@ -36,6 +36,7 @@ public class SettingsFragment extends PreferenceFragmentCompat {
 	private static final String PREF_KEY_FEEDBACK = "pref_key_send_feedback";
 	private static final String PREF_KEY_DEV = "pref_key_dev";
 	private static final String PREF_KEY_EXPLODE = "pref_key_explode";
+	private static final String PREF_KEY_SHARE_APP = "pref_key_share_app";
 
 	@Inject
 	ViewModelProvider.Factory viewModelFactory;
@@ -85,6 +86,12 @@ public class SettingsFragment extends PreferenceFragmentCompat {
 			PreferenceGroup dev = requireNonNull(findPreference(PREF_KEY_DEV));
 			dev.setVisible(false);
 		}
+
+		if (!viewModel.shouldEnableShareAppViaOfflineHotspot()) {
+			Preference shareApp =
+					requireNonNull(findPreference(PREF_KEY_SHARE_APP));
+			shareApp.setVisible(false);
+		}
 	}
 
 	@Override

briar-android/src/main/java/org/briarproject/briar/android/settings/SettingsViewModel.java

@@ -262,4 +262,8 @@ class SettingsViewModel extends DbViewModel implements EventListener {
 		return screenLockTimeout;
 	}
 
+	boolean shouldEnableShareAppViaOfflineHotspot() {
+		return featureFlags.shouldEnableShareAppViaOfflineHotspot();
+	}
+
 }

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

@@ -1,4 +1,4 @@
-package org.briarproject.briar.android.contact.add.nearby;
+package org.briarproject.briar.android.util;
 
 import android.graphics.Bitmap;
 import android.util.DisplayMetrics;
@@ -22,12 +22,12 @@ import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
-class QrCodeUtils {
+public class QrCodeUtils {
 
 	private static final Logger LOG = getLogger(QrCodeUtils.class.getName());
 
 	@Nullable
-	static Bitmap createQrCode(DisplayMetrics dm, String input) {
+	public static Bitmap createQrCode(DisplayMetrics dm, String input) {
 		int smallestDimen = Math.min(dm.widthPixels, dm.heightPixels);
 		try {
 			// Generate QR code

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

@@ -61,6 +61,7 @@ import androidx.core.util.Consumer;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentActivity;
 import androidx.fragment.app.FragmentManager;
+import androidx.fragment.app.FragmentTransaction;
 import androidx.lifecycle.LifecycleOwner;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.Observer;
@@ -111,6 +112,7 @@ import static org.briarproject.briar.BuildConfig.APPLICATION_ID;
 import static org.briarproject.briar.android.TestingConstants.EXPIRY_DATE;
 import static org.briarproject.briar.android.reporting.CrashReportActivity.EXTRA_APP_LOGCAT;
 import static org.briarproject.briar.android.reporting.CrashReportActivity.EXTRA_APP_START_TIME;
+import static org.briarproject.briar.android.reporting.CrashReportActivity.EXTRA_INITIAL_COMMENT;
 import static org.briarproject.briar.android.reporting.CrashReportActivity.EXTRA_THROWABLE;
 
 @MethodsNotNullByDefault
@@ -137,13 +139,18 @@ public class UiUtils {
 
 	public static void showFragment(FragmentManager fm, Fragment f,
 			@Nullable String tag) {
-		fm.beginTransaction()
+		showFragment(fm, f, tag, true);
+	}
+
+	public static void showFragment(FragmentManager fm, Fragment f,
+			@Nullable String tag, boolean addToBackStack) {
+		FragmentTransaction ta = fm.beginTransaction()
 				.setCustomAnimations(R.anim.step_next_in,
 						R.anim.step_previous_out, R.anim.step_previous_in,
 						R.anim.step_next_out)
-				.replace(R.id.fragmentContainer, f, tag)
-				.addToBackStack(tag)
-				.commit();
+				.replace(R.id.fragmentContainer, f, tag);
+		if (addToBackStack) ta.addToBackStack(tag);
+		ta.commit();
 	}
 
 	public static String getContactDisplayName(Author author,
@@ -410,17 +417,25 @@ public class UiUtils {
 	}
 
 	public static void triggerFeedback(Context ctx) {
-		startDevReportActivity(ctx, FeedbackActivity.class, null, null, null);
+		triggerFeedback(ctx, null);
+	}
+
+	public static void triggerFeedback(Context ctx,
+			@Nullable String initialComment) {
+		startDevReportActivity(ctx, FeedbackActivity.class, null, null, null,
+				initialComment);
 	}
 
 	public static void startDevReportActivity(Context ctx,
 			Class<? extends FragmentActivity> activity, @Nullable Throwable t,
-			@Nullable Long appStartTime, @Nullable byte[] logKey) {
+			@Nullable Long appStartTime, @Nullable byte[] logKey, @Nullable
+			String initialComment) {
 		final Intent dialogIntent = new Intent(ctx, activity);
 		dialogIntent.setFlags(FLAG_ACTIVITY_NEW_TASK);
 		dialogIntent.putExtra(EXTRA_THROWABLE, t);
 		dialogIntent.putExtra(EXTRA_APP_START_TIME, appStartTime);
 		dialogIntent.putExtra(EXTRA_APP_LOGCAT, logKey);
+		dialogIntent.putExtra(EXTRA_INITIAL_COMMENT, initialComment);
 		ctx.startActivity(dialogIntent);
 	}
 
@@ -546,4 +561,5 @@ public class UiUtils {
 		activity.getWindow().setSoftInputMode(SOFT_INPUT_ADJUST_RESIZE |
 				SOFT_INPUT_STATE_HIDDEN);
 	}
+
 }

briar-android/src/main/java/org/briarproject/briar/api/android/AndroidNotificationManager.java

@@ -31,6 +31,7 @@ public interface AndroidNotificationManager {
 	int FORUM_POST_NOTIFICATION_ID = 6;
 	int BLOG_POST_NOTIFICATION_ID = 7;
 	int CONTACT_ADDED_NOTIFICATION_ID = 8;
+	int HOTSPOT_NOTIFICATION_ID = 9;
 
 	// Channel IDs
 	String CONTACT_CHANNEL_ID = "contacts";
@@ -42,12 +43,15 @@ public interface AndroidNotificationManager {
 	String ONGOING_CHANNEL_OLD_ID = "zForegroundService";
 	String ONGOING_CHANNEL_ID = "zForegroundService2";
 	String REMINDER_CHANNEL_ID = "zSignInReminder";
+	String HOTSPOT_CHANNEL_ID = "zHotspot";
+
 	// This channel is no longer used - keep the ID so we can remove the
 	// channel from existing installations
 	String FAILURE_CHANNEL_ID = "zStartupFailure";
 
 	// Actions for pending intents
 	String ACTION_DISMISS_REMINDER = "dismissReminder";
+	String ACTION_STOP_HOTSPOT = "stopHotspot";
 
 	Notification getForegroundNotification();
 
@@ -96,4 +100,8 @@ public interface AndroidNotificationManager {
 	void blockAllBlogPostNotifications();
 
 	void unblockAllBlogPostNotifications();
+
+	void showHotspotNotification();
+
+	void clearHotspotNotification();
 }