Start a web server after starting the hotspot

that serves its own app as a download

app/build.gradle

@@ -27,4 +27,5 @@ dependencies {
 	implementation 'androidx.appcompat:appcompat:1.2.0'
 	implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'
 	implementation 'com.google.zxing:core:3.4.0'
+    implementation 'org.nanohttpd:nanohttpd:2.3.1'
 }

app/src/main/AndroidManifest.xml

@@ -3,6 +3,7 @@
 	xmlns:tools="http://schemas.android.com/tools"
 	package="org.briarproject.hotspot">
 
+    <uses-permission android:name="android.permission.INTERNET" />
 	<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
 	<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
 	<uses-permission android:name="android.permission.CHANGE_WIFI_STATE" />

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

@@ -14,6 +14,8 @@ import androidx.annotation.Nullable;
 import androidx.fragment.app.Fragment;
 import androidx.lifecycle.ViewModelProvider;
 
+import org.briarproject.hotspot.MainViewModel.WebServerState;
+
 import static android.Manifest.permission.ACCESS_FINE_LOCATION;
 import static android.content.pm.PackageManager.PERMISSION_GRANTED;
 import static android.os.Build.VERSION.SDK_INT;
@@ -59,7 +61,6 @@ public class HotspotFragment extends Fragment {
                 passwordView.setText("");
                 button.setText(R.string.start_hotspot);
                 button.setEnabled(true);
-                serverButton.setVisibility(GONE);
                 hotspotStarted = false;
             } else {
                 String qrCodeText = createWifiLoginString(config.ssid, config.password,
@@ -75,7 +76,6 @@ public class HotspotFragment extends Fragment {
                 passwordView.setText(getString(R.string.password, config.password));
                 button.setText(R.string.stop_hotspot);
                 button.setEnabled(true);
-                serverButton.setVisibility(VISIBLE);
                 hotspotStarted = true;
             }
         });
@@ -84,6 +84,16 @@ public class HotspotFragment extends Fragment {
         if (SDK_INT >= 29 && (checkSelfPermission(requireContext(), ACCESS_FINE_LOCATION) != PERMISSION_GRANTED)) {
             requestPermissions(new String[]{ACCESS_FINE_LOCATION}, 0);
         }
+
+        viewModel.getWebServerState().observe(getViewLifecycleOwner(), state -> {
+            if (state == WebServerState.STOPPED) {
+                serverButton.setVisibility(GONE);
+            } else if (state == WebServerState.STARTED) {
+                serverButton.setVisibility(VISIBLE);
+            } else if (state == WebServerState.ERROR) {
+                statusView.setText(R.string.web_server_error);
+            }
+        });
     }
 
     public void onButtonClick(View view) {

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

@@ -15,6 +15,8 @@ import androidx.lifecycle.AndroidViewModel;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.MutableLiveData;
 
+import java.io.IOException;
+
 import static android.content.Context.WIFI_P2P_SERVICE;
 import static android.content.Context.WIFI_SERVICE;
 import static android.net.wifi.WifiManager.WIFI_MODE_FULL;
@@ -27,12 +29,15 @@ public class MainViewModel extends AndroidViewModel {
 
 	private final MutableLiveData<NetworkConfig> config = new MutableLiveData<>();
 	private final MutableLiveData<String> status = new MutableLiveData<>();
+	private final MutableLiveData<WebServerState> webServerState =
+            new MutableLiveData<>(WebServerState.STOPPED);
 
 	private final Application app;
 	private final String lockTag;
 	private final WifiManager wifiManager;
 	private final WifiP2pManager wifiP2pManager;
 	private final Handler handler;
+	private final WebServer webServer;
 
 	private WifiLock wifiLock;
 	private Channel channel;
@@ -44,6 +49,7 @@ public class MainViewModel extends AndroidViewModel {
         wifiManager = (WifiManager) app.getSystemService(WIFI_SERVICE);
         wifiP2pManager = (WifiP2pManager) app.getSystemService(WIFI_P2P_SERVICE);
         handler = new Handler(app.getMainLooper());
+        webServer = new WebServer(app);
     }
 
 	LiveData<NetworkConfig> getWifiConfiguration() {
@@ -54,6 +60,10 @@ public class MainViewModel extends AndroidViewModel {
 		return status;
 	}
 
+	LiveData<WebServerState> getWebServerState() {
+		return webServerState;
+	}
+
 	void startWifiP2pHotspot() {
 		if (wifiP2pManager == null) {
 			status.setValue(app.getString(R.string.no_wifi_direct));
@@ -100,6 +110,7 @@ public class MainViewModel extends AndroidViewModel {
 				config.setValue(new NetworkConfig(group.getNetworkName(), group.getPassphrase(),
 						true));
 				status.setValue(app.getString(R.string.callback_started));
+                startWebServer();
 			}
 		};
 		try {
@@ -110,7 +121,8 @@ public class MainViewModel extends AndroidViewModel {
 	}
 
 	private void releaseWifiP2pHotspot(String statusMessage) {
-		if (SDK_INT >= 27) channel.close();
+        stopWebServer();
+        if (SDK_INT >= 27) channel.close();
 		channel = null;
 		releaseLock();
 		config.setValue(null);
@@ -150,6 +162,23 @@ public class MainViewModel extends AndroidViewModel {
 		wifiLock.release();
 	}
 
+	private void startWebServer() {
+        try {
+            webServer.start();
+            webServerState.postValue(WebServerState.STARTED);
+        } catch (IOException e) {
+            e.printStackTrace();
+            webServerState.postValue(WebServerState.ERROR);
+        }
+    }
+
+    private void stopWebServer() {
+        webServer.stop();
+        webServerState.postValue(WebServerState.STOPPED);
+    }
+
+    enum WebServerState { STOPPED, STARTED, ERROR }
+
 	static class NetworkConfig {
 
 		final String ssid, password;

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

+package org.briarproject.hotspot;
+
+import android.app.Application;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+import fi.iki.elonen.NanoHTTPD;
+
+import static fi.iki.elonen.NanoHTTPD.Response.Status.NOT_FOUND;
+import static fi.iki.elonen.NanoHTTPD.Response.Status.OK;
+
+public class WebServer extends NanoHTTPD {
+
+    private final Application ctx;
+
+    public WebServer(Application ctx) {
+        super(9999);
+        this.ctx = ctx;
+    }
+
+    public void start() throws IOException {
+        start(NanoHTTPD.SOCKET_READ_TIMEOUT, false);
+    }
+
+    @Override
+    public Response serve(IHTTPSession session) {
+        if (session.getUri().endsWith("app.apk")) {
+            return serveApk();
+        } else {
+            String msg = "<html><body><h1>Download Offline Hotspot App</h1>\n";
+            msg += "<h2><a href=\"/app.apk\">Click here to download</a></h2>";
+            msg += "After download is complete, open the downloaded file and install it.";
+            return newFixedLengthResponse(msg + "</body></html>\n");
+        }
+    }
+
+    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) {
+            e.printStackTrace();
+            res = newFixedLengthResponse(NOT_FOUND, MIME_PLAINTEXT, "Error 404, file not found.");
+        }
+        return res;
+    }
+}

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

@@ -15,4 +15,5 @@
 	<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="connected">Peer connected</string>
+    <string name="web_server_error">Error starting web server!</string>
 </resources>

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