Show an error message if Bluetooth isn't supported.

app/src/main/java/org/briarproject/interferometer/MainActivity.java

@@ -19,6 +19,7 @@ import static org.briarproject.interferometer.MainViewModel.ConnectionState.DISC
 import static org.briarproject.interferometer.MainViewModel.ConnectionState.DOWNLOADING;
 import static org.briarproject.interferometer.MainViewModel.ConnectionState.UPLOADING;
 import static org.briarproject.interferometer.MainViewModel.StartResult.INVALID_ADDRESS;
+import static org.briarproject.interferometer.MainViewModel.StartResult.NO_BLUETOOTH;
 import static org.briarproject.interferometer.MainViewModel.TestPhase.READY;
 
 public class MainActivity extends AppCompatActivity {
@@ -73,6 +74,8 @@ public class MainActivity extends AppCompatActivity {
 			StartResult result = viewModel.startTest(serverAddressEditText.getText().toString());
 			if (result == INVALID_ADDRESS) {
 				Toast.makeText(this, R.string.server_address_error, LENGTH_SHORT).show();
+			} else if (result == NO_BLUETOOTH) {
+				Toast.makeText(this, R.string.no_bluetooth_error, LENGTH_SHORT).show();
 			}
 		} else {
 			viewModel.stopTest();

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

 package org.briarproject.interferometer;
 
+import android.bluetooth.BluetoothAdapter;
 import android.util.Log;
 
 import java.io.IOException;
@@ -24,6 +25,7 @@ import static org.briarproject.interferometer.MainViewModel.ConnectionState.DISC
 import static org.briarproject.interferometer.MainViewModel.ConnectionState.DOWNLOADING;
 import static org.briarproject.interferometer.MainViewModel.ConnectionState.UPLOADING;
 import static org.briarproject.interferometer.MainViewModel.StartResult.INVALID_ADDRESS;
+import static org.briarproject.interferometer.MainViewModel.StartResult.NO_BLUETOOTH;
 import static org.briarproject.interferometer.MainViewModel.StartResult.STARTED;
 import static org.briarproject.interferometer.MainViewModel.TestPhase.DOWNLOAD;
 import static org.briarproject.interferometer.MainViewModel.TestPhase.READY;
@@ -35,7 +37,7 @@ public class MainViewModel extends ViewModel {
 
 	enum ConnectionState {DISCONNECTED, DOWNLOADING, UPLOADING}
 
-	enum StartResult {INVALID_ADDRESS, STARTED}
+	enum StartResult {INVALID_ADDRESS, NO_BLUETOOTH, STARTED}
 
 	private static final byte CONNECTION_TYPE_UPLOAD = 0;
 	private static final byte CONNECTION_TYPE_DOWNLOAD = 1;
@@ -69,6 +71,8 @@ public class MainViewModel extends ViewModel {
 	StartResult startTest(String serverAddress) {
 		HostPort hostPort = parseServerAddress(serverAddress);
 		if (hostPort == null) return INVALID_ADDRESS;
+		BluetoothAdapter adapter = BluetoothAdapter.getDefaultAdapter();
+		if (adapter == null) return NO_BLUETOOTH;
 		task = executorService.submit(() -> {
 			try {
 				testPhase.postValue(DOWNLOAD);

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

@@ -3,6 +3,7 @@
 
 	<string name="server_address">Server address</string>
 	<string name="server_address_error">Invalid address</string>
+	<string name="no_bluetooth_error">Device does not have Bluetooth</string>
 
 	<string name="start_test">Start test</string>
 	<string name="stop_test">Stop test</string>