app/src/main/java/org/briarproject/hotspot/StringUtils.java

+package org.briarproject.hotspot;
+
+import java.security.SecureRandom;
+import java.util.Random;
+
+class StringUtils {
+
+	private static final Random random = new SecureRandom();
+
+	private static String digits = "123456789"; // avoid 0
+	private static String letters = "abcdefghijkmnopqrstuvwxyz"; // avoid l
+	private static String LETTERS = "ABCDEFGHJKLMNPQRSTUVWXYZ"; // avoid I, O
+
+	public static String getRandomString(int length) {
+		char[] c = new char[length];
+		for (int i = 0; i < length; i++) {
+			if (random.nextBoolean()) {
+				c[i] = random(digits);
+			} else if (random.nextBoolean()) {
+				c[i] = random(letters);
+			} else {
+				c[i] = random(LETTERS);
+			}
+		}
+		return new String(c);
+	}
+
+	private static char random(String universe) {
+		return universe.charAt(random.nextInt(universe.length()));
+	}
+
+}

app/src/main/java/org/briarproject/hotspot/UiUtils.java

+package org.briarproject.hotspot;
+
+import android.content.Context;
+import android.content.DialogInterface;
+import android.content.Intent;
+import android.net.Uri;
+
+import androidx.annotation.StringRes;
+import androidx.appcompat.app.AlertDialog;
+import androidx.fragment.app.FragmentActivity;
+
+import static android.content.Intent.CATEGORY_DEFAULT;
+import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
+import static org.briarproject.hotspot.BuildConfig.APPLICATION_ID;
+
+class UiUtils {
+
+	static DialogInterface.OnClickListener getGoToSettingsListener(
+			Context context) {
+		return (dialog, which) -> {
+			Intent i = new Intent();
+			i.setAction("android.settings.APPLICATION_DETAILS_SETTINGS");
+			i.addCategory(CATEGORY_DEFAULT);
+			i.setData(Uri.parse("package:" + APPLICATION_ID));
+			i.addFlags(FLAG_ACTIVITY_NEW_TASK);
+			context.startActivity(i);
+		};
+	}
+
+	static void showDenialDialog(FragmentActivity ctx, @StringRes int title,
+			@StringRes int body, DialogInterface.OnClickListener onOkClicked,
+			Runnable onDismiss) {
+		AlertDialog.Builder builder = new AlertDialog.Builder(ctx);
+		builder.setTitle(title);
+		builder.setMessage(body);
+		builder.setPositiveButton(R.string.ok, onOkClicked);
+		builder.setNegativeButton(R.string.cancel,
+				(dialog, which) -> ctx.supportFinishAfterTransition());
+		builder.setOnDismissListener(dialog -> onDismiss.run());
+		builder.show();
+	}
+
+	static void showRationale(Context ctx, @StringRes int title,
+			@StringRes int body,
+			Runnable onContinueClicked, Runnable onDismiss) {
+		AlertDialog.Builder builder = new AlertDialog.Builder(ctx);
+		builder.setTitle(title);
+		builder.setMessage(body);
+		builder.setNeutralButton(R.string.continue_button,
+				(dialog, which) -> onContinueClicked.run());
+		builder.setOnDismissListener(dialog -> onDismiss.run());
+		builder.show();
+	}
+
+}

app/src/main/java/org/briarproject/hotspot/WebServer.java

+package org.briarproject.hotspot;
+
+import android.content.Context;
+
+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.hotspot.BuildConfig.VERSION_NAME;
+import static org.briarproject.hotspot.LogUtils.logException;
+
+public 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;
+
+	public WebServer(Context ctx) {
+		super(PORT);
+		this.ctx = ctx;
+	}
+
+	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,
+					INTERNAL_ERROR.getDescription());
+		}
+		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;
+		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("#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(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,
+					"Error 404, file not found.");
+		}
+		return res;
+	}
+}

app/src/main/java/org/briarproject/hotspot/WebServerManager.java

+package org.briarproject.hotspot;
+
+import android.content.Context;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.util.logging.Logger;
+
+import androidx.annotation.WorkerThread;
+
+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.hotspot.LogUtils.logException;
+import static org.briarproject.hotspot.NetworkUtils.getAccessPointAddress;
+import static org.briarproject.hotspot.WebServer.PORT;
+
+class WebServerManager {
+
+	interface WebServerListener {
+		@WorkerThread
+		void onWebServerStarted(String url);
+
+		@WorkerThread
+		void onWebServerError();
+	}
+
+	private static final Logger LOG =
+			getLogger(WebServerManager.class.getName());
+
+	private final WebServer webServer;
+	private final WebServerListener listener;
+
+	WebServerManager(Context ctx, WebServerListener listener) {
+		this.listener = listener;
+		webServer = new WebServer(ctx);
+	}
+
+	@WorkerThread
+	void startWebServer() {
+		try {
+			webServer.start();
+			onWebServerStarted();
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			listener.onWebServerError();
+		}
+	}
+
+	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;
+		}
+		listener.onWebServerStarted(url);
+	}
+
+	/**
+	 * It is safe to call this more than once and it won't throw.
+	 */
+	void stopWebServer() {
+		webServer.stop();
+	}
+
+}

app/src/main/res/layout/activity_main.xml

 <?xml version="1.0" encoding="utf-8"?>
-<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<androidx.fragment.app.FragmentContainerView xmlns:android="http://schemas.android.com/apk/res/android"
 	xmlns:tools="http://schemas.android.com/tools"
+	android:id="@+id/fragment_container"
+	android:name="org.briarproject.hotspot.HotspotFragment"
 	android:layout_width="match_parent"
 	android:layout_height="match_parent"
 	android:background="@android:color/white"
-	android:gravity="center"
-	android:orientation="vertical"
-	tools:context=".MainActivity">
-
-	<ImageView
-		android:id="@+id/qr_code"
-		android:layout_width="wrap_content"
-		android:layout_height="wrap_content"
-		android:contentDescription="@string/qr_code_description"
-		android:visibility="gone" />
-
-	<TextView
-		android:id="@+id/ssid"
-		android:layout_width="wrap_content"
-		android:layout_height="wrap_content"
-		android:textSize="16sp" />
-
-	<TextView
-		android:id="@+id/password"
-		android:layout_width="wrap_content"
-		android:layout_height="wrap_content"
-		android:textSize="16sp" />
-
-	<Button
-		android:id="@+id/button"
-		android:layout_width="wrap_content"
-		android:layout_height="wrap_content"
-		android:layout_margin="16dp"
-		android:onClick="onButtonClick"
-		android:text="@string/start_hotspot" />
-
-	<TextView
-		android:id="@+id/status"
-		android:layout_width="wrap_content"
-		android:layout_height="wrap_content"
-		android:textSize="16sp" />
-
-</LinearLayout>
\ No newline at end of file
+	tools:context=".MainActivity" />
\ No newline at end of file

app/src/main/res/layout/fragment_hotspot.xml

+<?xml version="1.0" encoding="utf-8"?>
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:background="@android:color/white"
+	android:fillViewport="true"
+	android:orientation="vertical"
+	tools:context=".HotspotFragment">
+
+	<LinearLayout
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:gravity="center"
+		android:orientation="vertical"
+		tools:context=".HotspotFragment">
+
+		<ImageView
+			android:id="@+id/qr_code"
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:contentDescription="@string/qr_code_description"
+			android:visibility="gone" />
+
+		<TextView
+			android:id="@+id/ssid"
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:textSize="16sp" />
+
+		<TextView
+			android:id="@+id/password"
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:textSize="16sp" />
+
+		<Button
+			android:id="@+id/button"
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:layout_margin="16dp"
+			android:text="@string/start_hotspot" />
+
+		<TextView
+			android:id="@+id/status"
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:layout_margin="16dp"
+			android:textSize="16sp"
+			tools:text="@string/stop_framework_busy" />
+
+		<Button
+			android:id="@+id/serverButton"
+			android:layout_width="wrap_content"
+			android:layout_height="wrap_content"
+			android:layout_margin="16dp"
+			android:text="@string/connected"
+			android:visibility="gone"
+			tools:visibility="visible" />
+
+	</LinearLayout>
+
+</ScrollView>

app/src/main/res/layout/fragment_interfaces.xml

+<?xml version="1.0" encoding="utf-8"?>
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:layout_width="match_parent"
+	android:layout_height="wrap_content">
+
+	<TextView
+		android:id="@+id/text"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:fontFamily="monospace"
+		android:padding="16dp"
+		tools:text="@tools:sample/lorem/random" />
+</ScrollView>
\ No newline at end of file

app/src/main/res/layout/fragment_server.xml

+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:background="@android:color/white"
+	android:gravity="center"
+	android:orientation="vertical"
+	tools:context=".ServerFragment">
+
+	<ImageView
+		android:id="@+id/qr_code"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:contentDescription="@string/qr_code_description"
+		android:visibility="gone"
+		tools:src="@tools:sample/avatars"
+		tools:visibility="visible" />
+
+	<TextView
+		android:id="@+id/info"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:padding="8dp"
+		android:gravity="center"
+		android:textSize="18sp"
+		android:text="@string/server_info" />
+
+	<TextView
+		android:id="@+id/url"
+		android:layout_width="wrap_content"
+		android:layout_height="wrap_content"
+		android:padding="8dp"
+		android:textSize="18sp"
+		tools:text="http://192.168.49.1:9999" />
+
+</LinearLayout>
\ No newline at end of file

app/src/main/res/menu/main.xml

+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto">
+	<item
+		android:id="@+id/interfaces"
+		android:title="@string/menu_interfaces"
+		app:showAsAction="never" />
+</menu>

app/src/main/res/values/ic_launcher_background.xml

 <?xml version="1.0" encoding="utf-8"?>
 <resources>
-    <color name="ic_launcher_background">#FFFFFF</color>
+	<color name="ic_launcher_background">#FFFFFF</color>
 </resources>
\ No newline at end of file

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

 <resources>
 	<string name="app_name">Offline Hotspot</string>
+
+	<string name="ok">OK</string>
+	<string name="cancel">Cancel</string>
+	<string name="continue_button">Continue</string>
+
+	<string name="permission_location_title">Location permission</string>
+	<string name="permission_hotspot_location_request_body">To create a Wi-Fi hotspot, Briar needs permission to access your location.\n\nBriar does not store your location or share it with anyone.</string>
+	<string name="permission_hotspot_location_denied_body">You have denied access to your location, but Briar needs this permission to create a Wi-Fi hotspot.\n\nPlease consider granting access.</string>
+	<string name="wifi_settings_title">Wi-Fi setting</string>
+	<string name="wifi_settings_request_enable_body">To create a Wi-Fi hotspot, Briar needs to use Wi-Fi. Please enable it.</string>
+	<string name="wifi_settings_request_denied_body">You have denied to enable Wi-Fi, but Briar needs to use Wi-Fi.\n\nPlease consider enabling it.</string>
+
+	<string name="menu_interfaces">Network interfaces</string>
 	<string name="start_hotspot">Start hotspot</string>
 	<string name="stop_hotspot">Stop hotspot</string>
 	<string name="ssid">Name: %s</string>
 	<string name="password">Password: %s</string>
 	<string name="starting_hotspot">Starting hotspot</string>
-	<string name="callback_started">Hotspot started</string>
-	<string name="callback_failed">Hotspot failed to start: error code %d</string>
-	<string name="callback_waiting">Waiting for hotspot to start</string>
-	<string name="callback_no_group_info">Hotspot failed to start: no group info</string>
+	<string name="start_callback_started">Hotspot started</string>
+	<string name="start_callback_started_freq">Hotspot started (%1$.2f GHz)</string>
+	<string name="start_callback_failed">Hotspot failed to start: error %s</string>
+	<string name="start_callback_failed_unknown">Hotspot failed to start with an unknown error, reason %d</string>
+	<string name="start_callback_no_group_info">Hotspot failed to start: no group info</string>
+	<string name="start_no_attempts_left">Hotspot failed to start with an unknown error</string>
+	<string name="stop_callback_failed">Unknown error while stopping hotspot (reason %d)</string>
+	<string name="stop_framework_busy">Unable to start the hotspot. If you have another hotspot running or are sharing your internet connection via Wifi, try stopping that and try again afterwards.</string>
 	<string name="hotspot_stopped">Hotspot stopped</string>
 	<string name="qr_code_description">QR code with Wi-Fi login details</string>
 	<string name="no_wifi_manager">Device does not support Wi-Fi</string>
 	<string name="no_wifi_direct">Device does not support Wi-Fi Direct</string>
-	<string name="callback_permission_denied">Location permission was denied</string>
+	<string name="wifi_5ghz_supported">5Ghz Wi-Fi is supported</string>
+	<string name="connected">Peer has connected</string>
+	<string name="connected_toast">Peer has connected, press button for download info</string>
+	<string name="web_server_error">Error starting web server!</string>
+	<string name="server_info">Visit this site on the other phone either by scanning the QR code or by typing this link manually.</string>
+
+	<!-- e.g. Download Briar 1.2.20 -->
+	<string name="website_download_title">Download %s</string>
+	<string name="website_download_intro">Someone nearby shared %s with you.</string>
+	<string name="website_download_outro">After the download is complete, open the downloaded file and install it.</string>
+	<string name="website_troubleshooting_title">Troubleshooting</string>
+	<string name="website_troubleshooting_1">If you cannot download the app, try it with a different web browser app.</string>
+	<string name="website_troubleshooting_2_old">To install the downloaded app, you might need to allow installation of apps from \"Unknown sources\" in system settings. Afterwards, you may need to download the app again.</string>
+	<string name="website_troubleshooting_2_new">To install the downloaded app, you might need to allow your browser to install unknown apps.</string>
+
 </resources>

app/src/main/res/values/styles.xml

 <resources>
 
-	<!-- Base application theme. -->
-	<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
-		<!-- Customize your theme here. -->
+	<style name="AppTheme" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
 		<item name="colorPrimary">@color/colorPrimary</item>
 		<item name="colorPrimaryDark">@color/colorPrimaryDark</item>
 		<item name="colorAccent">@color/colorAccent</item>
 	</style>
 
+	<style name="AppTheme.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />
+
+	<style name="AppTheme.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />
+
 </resources>

build.gradle

@@ -4,7 +4,7 @@ buildscript {
 		jcenter()
 	}
 	dependencies {
-		classpath 'com.android.tools.build:gradle:4.1.0'
+		classpath 'com.android.tools.build:gradle:4.1.3'
 	}
 }
 

gradle.properties

@@ -18,3 +18,5 @@ android.useAndroidX=true
 # Automatically convert third-party libraries to use AndroidX
 android.enableJetifier=true
 
+# Set testOnly to false, so debug app can be installed on recipient phones
+android.injected.testOnly=false