Add migration that drops offers table.

Add adaptive icon for API 26+ and Play Store icon

Closes #1456

See merge request briar/briar!1293

.idea/codeStyles/Project.xml

@@ -1,8 +1,5 @@
 <component name="ProjectCodeStyleConfiguration">
   <code_scheme name="Project" version="173">
-    <AndroidXmlCodeStyleSettings>
-      <option name="ARRANGEMENT_SETTINGS_MIGRATED_TO_191" value="true" />
-    </AndroidXmlCodeStyleSettings>
     <JavaCodeStyleSettings>
       <option name="ANNOTATION_PARAMETER_WRAP" value="1" />
       <option name="IMPORT_LAYOUT_TABLE">
@@ -31,6 +28,11 @@
       <option name="JD_ALIGN_EXCEPTION_COMMENTS" value="false" />
     </JavaCodeStyleSettings>
     <JetCodeStyleSettings>
+      <option name="PACKAGES_TO_USE_STAR_IMPORTS">
+        <value />
+      </option>
+      <option name="NAME_COUNT_TO_USE_STAR_IMPORT" value="2147483647" />
+      <option name="NAME_COUNT_TO_USE_STAR_IMPORT_FOR_MEMBERS" value="2147483647" />
       <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
     </JetCodeStyleSettings>
     <XML>

TRANSLATION.md

@@ -0,0 +1,9 @@
+Translations for this project are managed through Transifex:
+
+https://transifex.com/otf/briar
+
+If you'd like to volunteer as a translator, please create a Transifex account and request to be
+added to the project's translation team. The Localization Lab has some instructions and advice for
+translators here:
+
+https://wiki.localizationlab.org/index.php/Briar

bramble-android/.gitignore

@@ -3,3 +3,4 @@ gen
 build
 .settings
 src/main/res/raw/*.zip
+src/main/jniLibs

bramble-android/build.gradle

@@ -5,14 +5,14 @@ apply plugin: 'witness'
 apply from: 'witness.gradle'
 
 android {
-	compileSdkVersion 29
-	buildToolsVersion '29.0.2'
+	compileSdkVersion rootProject.ext.compileSdkVersion
+	buildToolsVersion rootProject.ext.buildToolsVersion
 
 	defaultConfig {
-		minSdkVersion 16
-		targetSdkVersion 28
-		versionCode 10207
-		versionName "1.2.7"
+		minSdkVersion rootProject.ext.minSdkVersion
+		targetSdkVersion rootProject.ext.targetSdkVersion
+		versionCode rootProject.ext.versionCode
+		versionName rootProject.ext.versionName
 		consumerProguardFiles 'proguard-rules.txt'
 
 		testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
@@ -53,10 +53,12 @@ dependencies {
 }
 
 def torBinariesDir = 'src/main/res/raw'
+def torLibsDir = 'src/main/jniLibs'
 
 task cleanTorBinaries {
 	doLast {
 		delete fileTree(torBinariesDir) { include '*.zip' }
+		delete fileTree(torLibsDir) { include '**/*.so' }
 	}
 }
 
@@ -67,8 +69,36 @@ task unpackTorBinaries {
 		copy {
 			from configurations.tor.collect { zipTree(it) }
 			into torBinariesDir
-			// TODO: Remove after next Tor upgrade, which won't include non-PIE binaries
-			include 'geoip.zip', '*_pie.zip'
+			include 'geoip.zip'
+		}
+		configurations.tor.each { outer ->
+			zipTree(outer).each { inner ->
+				if (inner.name.endsWith('_arm_pie.zip')) {
+					copy {
+						from zipTree(inner)
+						into torLibsDir
+						rename '(.*)', 'armeabi-v7a/lib$1.so'
+					}
+				} else if (inner.name.endsWith('_arm64_pie.zip')) {
+					copy {
+						from zipTree(inner)
+						into torLibsDir
+						rename '(.*)', 'arm64-v8a/lib$1.so'
+					}
+				} else if (inner.name.endsWith('_x86_pie.zip')) {
+					copy {
+						from zipTree(inner)
+						into torLibsDir
+						rename '(.*)', 'x86/lib$1.so'
+					}
+				} else if (inner.name.endsWith('_x86_64_pie.zip')) {
+					copy {
+						from zipTree(inner)
+						into torLibsDir
+						rename '(.*)', 'x86_64/lib$1.so'
+					}
+				}
+			}
 		}
 	}
 	dependsOn cleanTorBinaries
@@ -76,5 +106,6 @@ task unpackTorBinaries {
 
 tasks.withType(MergeResources) {
 	inputs.dir torBinariesDir
+	inputs.dir torLibsDir
 	dependsOn unpackTorBinaries
 }

bramble-android/src/main/AndroidManifest.xml

@@ -16,6 +16,8 @@
 		android:label="@string/app_name"
 		android:supportsRtl="true">
 
+		<receiver android:name=".system.AlarmReceiver" />
+
 	</application>
 
 </manifest>

bramble-android/src/main/java/org/briarproject/bramble/BrambleAndroidModule.java

@@ -6,6 +6,8 @@ import org.briarproject.bramble.plugin.tor.CircumventionModule;
 import org.briarproject.bramble.reporting.ReportingModule;
 import org.briarproject.bramble.socks.SocksModule;
 import org.briarproject.bramble.system.AndroidSystemModule;
+import org.briarproject.bramble.system.AndroidTaskSchedulerModule;
+import org.briarproject.bramble.system.AndroidWakefulIoExecutorModule;
 
 import dagger.Module;
 
@@ -13,6 +15,8 @@ import dagger.Module;
 		AndroidBatteryModule.class,
 		AndroidNetworkModule.class,
 		AndroidSystemModule.class,
+		AndroidTaskSchedulerModule.class,
+		AndroidWakefulIoExecutorModule.class,
 		CircumventionModule.class,
 		ReportingModule.class,
 		SocksModule.class

bramble-android/src/main/java/org/briarproject/bramble/BrambleAppComponent.java

@@ -0,0 +1,8 @@
+package org.briarproject.bramble;
+
+import org.briarproject.bramble.api.system.AlarmListener;
+
+public interface BrambleAppComponent {
+
+	AlarmListener alarmListener();
+}

bramble-android/src/main/java/org/briarproject/bramble/BrambleApplication.java

@@ -0,0 +1,6 @@
+package org.briarproject.bramble;
+
+public interface BrambleApplication {
+
+	BrambleAppComponent getBrambleAppComponent();
+}

bramble-android/src/main/java/org/briarproject/bramble/api/system/AlarmListener.java

@@ -0,0 +1,11 @@
+package org.briarproject.bramble.api.system;
+
+import android.content.Intent;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public interface AlarmListener {
+
+	void onAlarm(Intent intent);
+}

bramble-android/src/main/java/org/briarproject/bramble/api/system/AndroidWakeLock.java

@@ -0,0 +1,19 @@
+package org.briarproject.bramble.api.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public interface AndroidWakeLock {
+
+	/**
+	 * Acquires the wake lock. This has no effect if the wake lock has already
+	 * been acquired.
+	 */
+	void acquire();
+
+	/**
+	 * Releases the wake lock. This has no effect if the wake lock has already
+	 * been released.
+	 */
+	void release();
+}

bramble-android/src/main/java/org/briarproject/bramble/api/system/AndroidWakeLockManager.java

@@ -0,0 +1,38 @@
+package org.briarproject.bramble.api.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.concurrent.Executor;
+
+@NotNullByDefault
+public interface AndroidWakeLockManager {
+
+	/**
+	 * Creates a wake lock with the given tag. The tag is only used for
+	 * logging; the underlying OS wake lock will use its own tag.
+	 */
+	AndroidWakeLock createWakeLock(String tag);
+
+	/**
+	 * Runs the given task while holding a wake lock.
+	 */
+	void runWakefully(Runnable r, String tag);
+
+	/**
+	 * Submits the given task to the given executor while holding a wake lock.
+	 * The lock is released when the task completes, or if an exception is
+	 * thrown while submitting or running the task.
+	 */
+	void executeWakefully(Runnable r, Executor executor, String tag);
+
+	/**
+	 * Starts a dedicated thread to run the given task asynchronously. A wake
+	 * lock is acquired before starting the thread and released when the task
+	 * completes, or if an exception is thrown while starting the thread or
+	 * running the task.
+	 * <p>
+	 * This method should only be used for lifecycle management tasks that
+	 * can't be run on an executor.
+	 */
+	void executeWakefully(Runnable r, String tag);
+}

bramble-android/src/main/java/org/briarproject/bramble/network/AndroidNetworkManager.java

@@ -9,16 +9,17 @@ import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.network.NetworkManager;
 import org.briarproject.bramble.api.network.NetworkStatus;
 import org.briarproject.bramble.api.network.event.NetworkStatusEvent;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
+import org.briarproject.bramble.api.system.TaskScheduler.Cancellable;
 
-import java.util.concurrent.Future;
-import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.Executor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
@@ -50,20 +51,22 @@ class AndroidNetworkManager implements NetworkManager, Service {
 	private static final String WIFI_AP_STATE_CHANGED_ACTION =
 			"android.net.wifi.WIFI_AP_STATE_CHANGED";
 
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final EventBus eventBus;
+	private final Executor eventExecutor;
 	private final Context appContext;
-	private final AtomicReference<Future<?>> connectivityCheck =
+	private final AtomicReference<Cancellable> connectivityCheck =
 			new AtomicReference<>();
 	private final AtomicBoolean used = new AtomicBoolean(false);
 
 	private volatile BroadcastReceiver networkStateReceiver = null;
 
 	@Inject
-	AndroidNetworkManager(@Scheduler ScheduledExecutorService scheduler,
-			EventBus eventBus, Application app) {
+	AndroidNetworkManager(TaskScheduler scheduler, EventBus eventBus,
+			@EventExecutor Executor eventExecutor, Application app) {
 		this.scheduler = scheduler;
 		this.eventBus = eventBus;
+		this.eventExecutor = eventExecutor;
 		this.appContext = app.getApplicationContext();
 	}
 
@@ -104,11 +107,12 @@ class AndroidNetworkManager implements NetworkManager, Service {
 	}
 
 	private void scheduleConnectionStatusUpdate(int delay, TimeUnit unit) {
-		Future<?> newConnectivityCheck =
-				scheduler.schedule(this::updateConnectionStatus, delay, unit);
-		Future<?> oldConnectivityCheck =
+		Cancellable newConnectivityCheck =
+				scheduler.schedule(this::updateConnectionStatus, eventExecutor,
+						delay, unit);
+		Cancellable oldConnectivityCheck =
 				connectivityCheck.getAndSet(newConnectivityCheck);
-		if (oldConnectivityCheck != null) oldConnectivityCheck.cancel(false);
+		if (oldConnectivityCheck != null) oldConnectivityCheck.cancel();
 	}
 
 	private class NetworkStateReceiver extends BroadcastReceiver {

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothConnectionFactory.java

@@ -0,0 +1,36 @@
+package org.briarproject.bramble.plugin.bluetooth;
+
+import android.bluetooth.BluetoothSocket;
+
+import org.briarproject.bramble.api.io.TimeoutMonitor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
+
+import java.io.IOException;
+
+@NotNullByDefault
+class AndroidBluetoothConnectionFactory
+		implements BluetoothConnectionFactory<BluetoothSocket> {
+
+	private final BluetoothConnectionLimiter connectionLimiter;
+	private final AndroidWakeLockManager wakeLockManager;
+	private final TimeoutMonitor timeoutMonitor;
+
+	AndroidBluetoothConnectionFactory(
+			BluetoothConnectionLimiter connectionLimiter,
+			AndroidWakeLockManager wakeLockManager,
+			TimeoutMonitor timeoutMonitor) {
+		this.connectionLimiter = connectionLimiter;
+		this.wakeLockManager = wakeLockManager;
+		this.timeoutMonitor = timeoutMonitor;
+	}
+
+	@Override
+	public DuplexTransportConnection wrapSocket(DuplexPlugin plugin,
+			BluetoothSocket s) throws IOException {
+		return new AndroidBluetoothTransportConnection(plugin,
+				connectionLimiter, wakeLockManager, timeoutMonitor, s);
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothPlugin.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.plugin.bluetooth;
 
+import android.app.Application;
 import android.bluetooth.BluetoothAdapter;
 import android.bluetooth.BluetoothDevice;
 import android.bluetooth.BluetoothServerSocket;
@@ -9,7 +10,6 @@ import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
 
-import org.briarproject.bramble.api.io.TimeoutMonitor;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
@@ -59,7 +59,8 @@ import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
-class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
+class AndroidBluetoothPlugin
+		extends BluetoothPlugin<BluetoothSocket, BluetoothServerSocket> {
 
 	private static final Logger LOG =
 			getLogger(AndroidBluetoothPlugin.class.getName());
@@ -67,24 +68,31 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 	private static final int MAX_DISCOVERY_MS = 10_000;
 
 	private final AndroidExecutor androidExecutor;
-	private final Context appContext;
+	private final Application app;
 	private final Clock clock;
 
-	private volatile boolean wasEnabledByUs = false;
 	private volatile BluetoothStateReceiver receiver = null;
 
 	// Non-null if the plugin started successfully
 	private volatile BluetoothAdapter adapter = null;
 
 	AndroidBluetoothPlugin(BluetoothConnectionLimiter connectionLimiter,
-			TimeoutMonitor timeoutMonitor, Executor ioExecutor,
-			SecureRandom secureRandom, AndroidExecutor androidExecutor,
-			Context appContext, Clock clock, Backoff backoff,
-			PluginCallback callback, int maxLatency, int maxIdleTime) {
-		super(connectionLimiter, timeoutMonitor, ioExecutor, secureRandom,
-				backoff, callback, maxLatency, maxIdleTime);
+			BluetoothConnectionFactory<BluetoothSocket> connectionFactory,
+			Executor ioExecutor,
+			Executor wakefulIoExecutor,
+			SecureRandom secureRandom,
+			AndroidExecutor androidExecutor,
+			Application app,
+			Clock clock,
+			Backoff backoff,
+			PluginCallback callback,
+			int maxLatency,
+			int maxIdleTime) {
+		super(connectionLimiter, connectionFactory, ioExecutor,
+				wakefulIoExecutor, secureRandom, backoff, callback,
+				maxLatency, maxIdleTime);
 		this.androidExecutor = androidExecutor;
-		this.appContext = appContext;
+		this.app = app;
 		this.clock = clock;
 	}
 
@@ -96,13 +104,13 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 		filter.addAction(ACTION_STATE_CHANGED);
 		filter.addAction(ACTION_SCAN_MODE_CHANGED);
 		receiver = new BluetoothStateReceiver();
-		appContext.registerReceiver(receiver, filter);
+		app.registerReceiver(receiver, filter);
 	}
 
 	@Override
 	public void stop() {
 		super.stop();
-		if (receiver != null) appContext.unregisterReceiver(receiver);
+		if (receiver != null) app.unregisterReceiver(receiver);
 	}
 
 	@Override
@@ -124,36 +132,11 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 		return adapter != null && adapter.isEnabled();
 	}
 
-	@Override
-	void enableAdapter() {
-		if (adapter != null && !adapter.isEnabled()) {
-			if (adapter.enable()) {
-				LOG.info("Enabling Bluetooth");
-				wasEnabledByUs = true;
-			} else {
-				LOG.info("Could not enable Bluetooth");
-			}
-		}
-	}
-
-	@Override
-	void disableAdapterIfEnabledByUs() {
-		if (isAdapterEnabled() && wasEnabledByUs) {
-			if (adapter.disable()) LOG.info("Disabling Bluetooth");
-			else LOG.info("Could not disable Bluetooth");
-			wasEnabledByUs = false;
-		}
-	}
-
-	@Override
-	void setEnabledByUs() {
-		wasEnabledByUs = true;
-	}
-
 	@Override
 	@Nullable
 	String getBluetoothAddress() {
-		String address = AndroidUtils.getBluetoothAddress(appContext, adapter);
+		if (adapter == null) return null;
+		String address = AndroidUtils.getBluetoothAddress(app, adapter);
 		return address.isEmpty() ? null : address;
 	}
 
@@ -171,13 +154,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 	@Override
 	DuplexTransportConnection acceptConnection(BluetoothServerSocket ss)
 			throws IOException {
-		return wrapSocket(ss.accept());
-	}
-
-	private DuplexTransportConnection wrapSocket(BluetoothSocket s)
-			throws IOException {
-		return new AndroidBluetoothTransportConnection(this, connectionLimiter,
-				timeoutMonitor, s);
+		return connectionFactory.wrapSocket(this, ss.accept());
 	}
 
 	@Override
@@ -194,7 +171,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 		try {
 			s = d.createInsecureRfcommSocketToServiceRecord(u);
 			s.connect();
-			return wrapSocket(s);
+			return connectionFactory.wrapSocket(this, s);
 		} catch (IOException e) {
 			IoUtils.tryToClose(s, LOG, WARNING);
 			throw e;
@@ -229,7 +206,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 		filter.addAction(ACTION_DISCOVERY_STARTED);
 		filter.addAction(ACTION_DISCOVERY_FINISHED);
 		filter.addAction(ACTION_FOUND);
-		appContext.registerReceiver(receiver, filter);
+		app.registerReceiver(receiver, filter);
 		try {
 			if (adapter.startDiscovery()) {
 				long now = clock.currentTimeMillis();
@@ -266,7 +243,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 		} finally {
 			LOG.info("Cancelling discovery");
 			adapter.cancelDiscovery();
-			appContext.unregisterReceiver(receiver);
+			app.unregisterReceiver(receiver);
 		}
 		// Shuffle the addresses so we don't always try the same one first
 		shuffle(addresses);

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothPluginFactory.java

@@ -1,9 +1,11 @@
 package org.briarproject.bramble.plugin.bluetooth;
 
-import android.content.Context;
+import android.app.Application;
+import android.bluetooth.BluetoothSocket;
 
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.io.TimeoutMonitor;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
@@ -12,12 +14,15 @@ import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.system.AndroidExecutor;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
 import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.WakefulIoExecutor;
 
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
 
 import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
 
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.ID;
 
@@ -31,22 +36,32 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	private static final int MAX_POLLING_INTERVAL = 10 * 60 * 1000; // 10 mins
 	private static final double BACKOFF_BASE = 1.2;
 
-	private final Executor ioExecutor;
+	private final Executor ioExecutor, wakefulIoExecutor;
 	private final AndroidExecutor androidExecutor;
-	private final Context appContext;
+	private final AndroidWakeLockManager wakeLockManager;
+	private final Application app;
 	private final SecureRandom secureRandom;
 	private final EventBus eventBus;
 	private final Clock clock;
 	private final TimeoutMonitor timeoutMonitor;
 	private final BackoffFactory backoffFactory;
 
-	public AndroidBluetoothPluginFactory(Executor ioExecutor,
-			AndroidExecutor androidExecutor, Context appContext,
-			SecureRandom secureRandom, EventBus eventBus, Clock clock,
-			TimeoutMonitor timeoutMonitor, BackoffFactory backoffFactory) {
+	@Inject
+	public AndroidBluetoothPluginFactory(@IoExecutor Executor ioExecutor,
+			@WakefulIoExecutor Executor wakefulIoExecutor,
+			AndroidExecutor androidExecutor,
+			AndroidWakeLockManager wakeLockManager,
+			Application app,
+			SecureRandom secureRandom,
+			EventBus eventBus,
+			Clock clock,
+			TimeoutMonitor timeoutMonitor,
+			BackoffFactory backoffFactory) {
 		this.ioExecutor = ioExecutor;
+		this.wakefulIoExecutor = wakefulIoExecutor;
 		this.androidExecutor = androidExecutor;
-		this.appContext = appContext;
+		this.wakeLockManager = wakeLockManager;
+		this.app = app;
 		this.secureRandom = secureRandom;
 		this.eventBus = eventBus;
 		this.clock = clock;
@@ -67,13 +82,16 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	@Override
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		BluetoothConnectionLimiter connectionLimiter =
-				new BluetoothConnectionLimiterImpl();
+				new BluetoothConnectionLimiterImpl(eventBus);
+		BluetoothConnectionFactory<BluetoothSocket> connectionFactory =
+				new AndroidBluetoothConnectionFactory(connectionLimiter,
+						wakeLockManager, timeoutMonitor);
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		AndroidBluetoothPlugin plugin = new AndroidBluetoothPlugin(
-				connectionLimiter, timeoutMonitor, ioExecutor, secureRandom,
-				androidExecutor, appContext, clock, backoff,
-				callback, MAX_LATENCY, MAX_IDLE_TIME);
+				connectionLimiter, connectionFactory, ioExecutor,
+				wakefulIoExecutor, secureRandom, androidExecutor, app,
+				clock, backoff, callback, MAX_LATENCY, MAX_IDLE_TIME);
 		eventBus.addListener(plugin);
 		return plugin;
 	}

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothTransportConnection.java

@@ -6,6 +6,8 @@ import org.briarproject.bramble.api.io.TimeoutMonitor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.duplex.AbstractDuplexTransportConnection;
+import org.briarproject.bramble.api.system.AndroidWakeLock;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -21,16 +23,20 @@ class AndroidBluetoothTransportConnection
 	private final BluetoothConnectionLimiter connectionLimiter;
 	private final BluetoothSocket socket;
 	private final InputStream in;
+	private final AndroidWakeLock wakeLock;
 
 	AndroidBluetoothTransportConnection(Plugin plugin,
 			BluetoothConnectionLimiter connectionLimiter,
-			TimeoutMonitor timeoutMonitor, BluetoothSocket socket)
-			throws IOException {
+			AndroidWakeLockManager wakeLockManager,
+			TimeoutMonitor timeoutMonitor,
+			BluetoothSocket socket) throws IOException {
 		super(plugin);
 		this.connectionLimiter = connectionLimiter;
 		this.socket = socket;
 		in = timeoutMonitor.createTimeoutInputStream(
 				socket.getInputStream(), plugin.getMaxIdleTime() * 2);
+		wakeLock = wakeLockManager.createWakeLock("BluetoothConnection");
+		wakeLock.acquire();
 		String address = socket.getRemoteDevice().getAddress();
 		if (isValidBluetoothAddress(address)) remote.put(PROP_ADDRESS, address);
 	}
@@ -49,7 +55,9 @@ class AndroidBluetoothTransportConnection
 	protected void closeConnection(boolean exception) throws IOException {
 		try {
 			socket.close();
+			in.close();
 		} finally {
+			wakeLock.release();
 			connectionLimiter.connectionClosed(this);
 		}
 	}

bramble-android/src/main/java/org/briarproject/bramble/plugin/tcp/AndroidLanTcpPlugin.java

@@ -1,23 +1,30 @@
 package org.briarproject.bramble.plugin.tcp;
 
-import android.content.Context;
+import android.annotation.TargetApi;
+import android.app.Application;
 import android.net.ConnectivityManager;
+import android.net.LinkAddress;
+import android.net.LinkProperties;
 import android.net.Network;
-import android.net.NetworkInfo;
+import android.net.NetworkCapabilities;
 import android.net.wifi.WifiInfo;
 import android.net.wifi.WifiManager;
 
 import org.briarproject.bramble.PoliteExecutor;
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.network.event.NetworkStatusEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.settings.Settings;
 
 import java.io.IOException;
 import java.net.InetAddress;
+import java.net.InterfaceAddress;
+import java.net.NetworkInterface;
 import java.net.Socket;
+import java.net.SocketException;
 import java.net.UnknownHostException;
 import java.util.List;
 import java.util.concurrent.Executor;
@@ -28,14 +35,22 @@ import javax.net.SocketFactory;
 
 import static android.content.Context.CONNECTIVITY_SERVICE;
 import static android.content.Context.WIFI_SERVICE;
-import static android.net.ConnectivityManager.TYPE_WIFI;
+import static android.net.NetworkCapabilities.TRANSPORT_WIFI;
 import static android.os.Build.VERSION.SDK_INT;
 import static java.util.Collections.emptyList;
+import static java.util.Collections.list;
 import static java.util.Collections.singletonList;
+import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.api.plugin.LanTcpConstants.DEFAULT_PREF_PLUGIN_ENABLE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.INACTIVE;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
+import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
-class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
+class AndroidLanTcpPlugin extends LanTcpPlugin {
 
 	private static final Logger LOG =
 			getLogger(AndroidLanTcpPlugin.class.getName());
@@ -47,20 +62,22 @@ class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
 
 	private volatile SocketFactory socketFactory;
 
-	AndroidLanTcpPlugin(Executor ioExecutor, Context appContext,
-			Backoff backoff, PluginCallback callback, int maxLatency,
-			int maxIdleTime, int connectionTimeout) {
-		super(ioExecutor, backoff, callback, maxLatency, maxIdleTime,
-				connectionTimeout);
+	AndroidLanTcpPlugin(Executor ioExecutor,
+			Executor wakefulIoExecutor,
+			Application app,
+			Backoff backoff,
+			PluginCallback callback,
+			int maxLatency,
+			int maxIdleTime,
+			int connectionTimeout) {
+		super(ioExecutor, wakefulIoExecutor, backoff, callback, maxLatency,
+				maxIdleTime, connectionTimeout);
 		// Don't execute more than one connection status check at a time
 		connectionStatusExecutor =
 				new PoliteExecutor("AndroidLanTcpPlugin", ioExecutor, 1);
-		ConnectivityManager connectivityManager = (ConnectivityManager)
-				appContext.getSystemService(CONNECTIVITY_SERVICE);
-		if (connectivityManager == null) throw new AssertionError();
-		this.connectivityManager = connectivityManager;
-		wifiManager = (WifiManager) appContext.getApplicationContext()
-				.getSystemService(WIFI_SERVICE);
+		connectivityManager = (ConnectivityManager)
+				requireNonNull(app.getSystemService(CONNECTIVITY_SERVICE));
+		wifiManager = (WifiManager) app.getSystemService(WIFI_SERVICE);
 		socketFactory = SocketFactory.getDefault();
 	}
 
@@ -68,37 +85,137 @@ class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
 	public void start() {
 		if (used.getAndSet(true)) throw new IllegalStateException();
 		initialisePortProperty();
-		running = true;
+		Settings settings = callback.getSettings();
+		state.setStarted(settings.getBoolean(PREF_PLUGIN_ENABLE,
+				DEFAULT_PREF_PLUGIN_ENABLE));
 		updateConnectionStatus();
 	}
 
-	@Override
-	public void stop() {
-		running = false;
-		tryToClose(socket);
-	}
-
 	@Override
 	protected Socket createSocket() throws IOException {
 		return socketFactory.createSocket();
 	}
 
 	@Override
-	protected List<InetAddress> getUsableLocalInetAddresses() {
-		// If the device doesn't have wifi, don't open any sockets
-		if (wifiManager == null) return emptyList();
+	protected List<InetAddress> getUsableLocalInetAddresses(boolean ipv4) {
+		InetAddress addr = getWifiAddress(ipv4);
+		return addr == null ? emptyList() : singletonList(addr);
+	}
+
+	@Nullable
+	private InetAddress getWifiAddress(boolean ipv4) {
+		Pair<InetAddress, Boolean> wifi = getWifiIpv4Address();
+		if (ipv4) return wifi == null ? null : wifi.getFirst();
+		// If there's no wifi IPv4 address, we might be a client on an
+		// IPv6-only wifi network. We can only detect this on API 21+
+		if (wifi == null) {
+			return SDK_INT >= 21 ? getWifiClientIpv6Address() : null;
+		}
+		// Use the wifi IPv4 address to determine which interface's IPv6
+		// address we should return (if the interface has a suitable address)
+		return getIpv6AddressForInterface(wifi.getFirst());
+	}
+
+	/**
+	 * Returns a {@link Pair} where the first element is the IPv4 address of
+	 * the wifi interface and the second element is true if this device is
+	 * providing an access point, or false if this device is a client. Returns
+	 * null if this device isn't connected to wifi as an access point or client.
+	 */
+	@Nullable
+	private Pair<InetAddress, Boolean> getWifiIpv4Address() {
+		if (wifiManager == null) return null;
 		// If we're connected to a wifi network, return its address
 		WifiInfo info = wifiManager.getConnectionInfo();
 		if (info != null && info.getIpAddress() != 0) {
-			return singletonList(intToInetAddress(info.getIpAddress()));
+			return new Pair<>(intToInetAddress(info.getIpAddress()), false);
 		}
-		// If we're running an access point, return its address
-		for (InetAddress addr : getLocalInetAddresses()) {
-			if (addr.equals(WIFI_AP_ADDRESS)) return singletonList(addr);
-			if (addr.equals(WIFI_DIRECT_AP_ADDRESS)) return singletonList(addr);
+		List<InterfaceAddress> ifAddrs = getLocalInterfaceAddresses();
+		// If we're providing a normal access point, return its address
+		for (InterfaceAddress ifAddr : ifAddrs) {
+			if (isAndroidWifiApAddress(ifAddr)) {
+				return new Pair<>(ifAddr.getAddress(), true);
+			}
+		}
+		// If we're providing a wifi direct access point, return its address
+		for (InterfaceAddress ifAddr : ifAddrs) {
+			if (isAndroidWifiDirectApAddress(ifAddr)) {
+				return new Pair<>(ifAddr.getAddress(), true);
+			}
+		}
+		// Not connected to wifi
+		return null;
+	}
+
+	/**
+	 * Returns true if the given address belongs to a network provided by an
+	 * Android access point (including the access point's own address).
+	 * <p>
+	 * The access point's address is usually 192.168.43.1, but at least one
+	 * device (Honor 8A) may use other addresses in the range 192.168.43.0/24.
+	 */
+	private boolean isAndroidWifiApAddress(InterfaceAddress ifAddr) {
+		if (ifAddr.getNetworkPrefixLength() != 24) return false;
+		byte[] ip = ifAddr.getAddress().getAddress();
+		return ip.length == 4
+				&& ip[0] == (byte) 192
+				&& ip[1] == (byte) 168
+				&& ip[2] == (byte) 43;
+	}
+
+	/**
+	 * Returns true if the given address belongs to a network provided by an
+	 * Android wifi direct legacy mode access point (including the access
+	 * point's own address).
+	 */
+	private boolean isAndroidWifiDirectApAddress(InterfaceAddress ifAddr) {
+		if (ifAddr.getNetworkPrefixLength() != 24) return false;
+		byte[] ip = ifAddr.getAddress().getAddress();
+		return ip.length == 4
+				&& ip[0] == (byte) 192
+				&& ip[1] == (byte) 168
+				&& ip[2] == (byte) 49;
+	}
+
+	/**
+	 * Returns a link-local IPv6 address for the wifi client interface, or null
+	 * if there's no such interface or it doesn't have a suitable address.
+	 */
+	@TargetApi(21)
+	@Nullable
+	private InetAddress getWifiClientIpv6Address() {
+		for (Network net : connectivityManager.getAllNetworks()) {
+			NetworkCapabilities caps =
+					connectivityManager.getNetworkCapabilities(net);
+			if (caps == null || !caps.hasTransport(TRANSPORT_WIFI)) continue;
+			LinkProperties props = connectivityManager.getLinkProperties(net);
+			if (props == null) continue;
+			for (LinkAddress linkAddress : props.getLinkAddresses()) {
+				InetAddress addr = linkAddress.getAddress();
+				if (isIpv6LinkLocalAddress(addr)) return addr;
+			}
+		}
+		return null;
+	}
+
+	/**
+	 * Returns a link-local IPv6 address for the interface with the given IPv4
+	 * address, or null if the interface doesn't have a suitable address.
+	 */
+	@Nullable
+	private InetAddress getIpv6AddressForInterface(InetAddress ipv4) {
+		try {
+			NetworkInterface iface = NetworkInterface.getByInetAddress(ipv4);
+			if (iface == null) return null;
+			for (InetAddress addr : list(iface.getInetAddresses())) {
+				if (isIpv6LinkLocalAddress(addr)) return addr;
+			}
+			// No suitable address
+			return null;
+		} catch (SocketException e) {
+			logException(LOG, WARNING, e);
+			return null;
 		}
-		// No suitable addresses
-		return emptyList();
 	}
 
 	private InetAddress intToInetAddress(int ip) {
@@ -120,9 +237,11 @@ class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
 	private SocketFactory getSocketFactory() {
 		if (SDK_INT < 21) return SocketFactory.getDefault();
 		for (Network net : connectivityManager.getAllNetworks()) {
-			NetworkInfo info = connectivityManager.getNetworkInfo(net);
-			if (info != null && info.getType() == TYPE_WIFI)
+			NetworkCapabilities caps =
+					connectivityManager.getNetworkCapabilities(net);
+			if (caps != null && caps.hasTransport(TRANSPORT_WIFI)) {
 				return net.getSocketFactory();
+			}
 		}
 		LOG.warning("Could not find suitable socket factory");
 		return SocketFactory.getDefault();
@@ -130,31 +249,59 @@ class AndroidLanTcpPlugin extends LanTcpPlugin implements EventListener {
 
 	@Override
 	public void eventOccurred(Event e) {
+		super.eventOccurred(e);
 		if (e instanceof NetworkStatusEvent) updateConnectionStatus();
 	}
 
 	private void updateConnectionStatus() {
 		connectionStatusExecutor.execute(() -> {
-			if (!running) return;
-			List<InetAddress> addrs = getUsableLocalInetAddresses();
-			if (addrs.contains(WIFI_AP_ADDRESS)
-					|| addrs.contains(WIFI_DIRECT_AP_ADDRESS)) {
+			State s = getState();
+			if (s != ACTIVE && s != INACTIVE) return;
+			Pair<InetAddress, Boolean> wifi = getPreferredWifiAddress();
+			if (wifi == null) {
+				LOG.info("Not connected to wifi");
+				socketFactory = SocketFactory.getDefault();
+				// Server sockets may not have been closed automatically when
+				// interface was taken down. If any sockets are open, closing
+				// them here will cause the sockets to be cleared and the state
+				// to be updated in acceptContactConnections()
+				if (s == ACTIVE) {
+					LOG.info("Closing server sockets");
+					tryToClose(state.getServerSocket(true), LOG, WARNING);
+					tryToClose(state.getServerSocket(false), LOG, WARNING);
+				}
+			} else if (wifi.getSecond()) {
 				LOG.info("Providing wifi hotspot");
 				// There's no corresponding Network object and thus no way
 				// to get a suitable socket factory, so we won't be able to
 				// make outgoing connections on API 21+ if another network
 				// has internet access
 				socketFactory = SocketFactory.getDefault();
-				if (socket == null || socket.isClosed()) bind();
-			} else if (addrs.isEmpty()) {
-				LOG.info("Not connected to wifi");
-				socketFactory = SocketFactory.getDefault();
-				tryToClose(socket);
+				bind();
 			} else {
 				LOG.info("Connected to wifi");
 				socketFactory = getSocketFactory();
-				if (socket == null || socket.isClosed()) bind();
+				bind();
 			}
 		});
 	}
+
+	/**
+	 * Returns a {@link Pair} where the first element is an IP address (IPv4 if
+	 * available, otherwise IPv6) of the wifi interface and the second element
+	 * is true if this device is providing an access point, or false if this
+	 * device is a client. Returns null if this device isn't connected to wifi
+	 * as an access point or client.
+	 */
+	@Nullable
+	private Pair<InetAddress, Boolean> getPreferredWifiAddress() {
+		Pair<InetAddress, Boolean> wifi = getWifiIpv4Address();
+		// If there's no wifi IPv4 address, we might be a client on an
+		// IPv6-only wifi network. We can only detect this on API 21+
+		if (wifi == null && SDK_INT >= 21) {
+			InetAddress ipv6 = getWifiClientIpv6Address();
+			if (ipv6 != null) return new Pair<>(ipv6, false);
+		}
+		return wifi;
+	}
 }

bramble-android/src/main/java/org/briarproject/bramble/plugin/tcp/AndroidLanTcpPluginFactory.java

@@ -1,8 +1,9 @@
 package org.briarproject.bramble.plugin.tcp;
 
-import android.content.Context;
+import android.app.Application;
 
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
@@ -10,10 +11,12 @@ import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
+import org.briarproject.bramble.api.system.WakefulIoExecutor;
 
 import java.util.concurrent.Executor;
 
 import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
 
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.ID;
 
@@ -28,17 +31,22 @@ public class AndroidLanTcpPluginFactory implements DuplexPluginFactory {
 	private static final int MAX_POLLING_INTERVAL = 600_000; // 10 mins
 	private static final double BACKOFF_BASE = 1.2;
 
-	private final Executor ioExecutor;
+	private final Executor ioExecutor, wakefulIoExecutor;
 	private final EventBus eventBus;
 	private final BackoffFactory backoffFactory;
-	private final Context appContext;
+	private final Application app;
 
-	public AndroidLanTcpPluginFactory(Executor ioExecutor, EventBus eventBus,
-			BackoffFactory backoffFactory, Context appContext) {
+	@Inject
+	public AndroidLanTcpPluginFactory(@IoExecutor Executor ioExecutor,
+			@WakefulIoExecutor Executor wakefulIoExecutor,
+			EventBus eventBus,
+			BackoffFactory backoffFactory,
+			Application app) {
 		this.ioExecutor = ioExecutor;
+		this.wakefulIoExecutor = wakefulIoExecutor;
 		this.eventBus = eventBus;
 		this.backoffFactory = backoffFactory;
-		this.appContext = appContext;
+		this.app = app;
 	}
 
 	@Override
@@ -56,8 +64,8 @@ public class AndroidLanTcpPluginFactory implements DuplexPluginFactory {
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		AndroidLanTcpPlugin plugin = new AndroidLanTcpPlugin(ioExecutor,
-				appContext, backoff, callback, MAX_LATENCY, MAX_IDLE_TIME,
-				CONNECTION_TIMEOUT);
+				wakefulIoExecutor, app, backoff, callback,
+				MAX_LATENCY, MAX_IDLE_TIME, CONNECTION_TIMEOUT);
 		eventBus.addListener(plugin);
 		return plugin;
 	}

bramble-android/src/main/java/org/briarproject/bramble/plugin/tor/AndroidTorPlugin.java

@@ -1,10 +1,9 @@
 package org.briarproject.bramble.plugin.tor;
 
-import android.content.Context;
+import android.app.Application;
 import android.content.pm.PackageInfo;
 import android.content.pm.PackageManager;
 import android.content.pm.PackageManager.NameNotFoundException;
-import android.os.PowerManager;
 
 import org.briarproject.bramble.api.battery.BatteryManager;
 import org.briarproject.bramble.api.network.NetworkManager;
@@ -12,48 +11,76 @@ import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.system.AndroidWakeLock;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
-import org.briarproject.bramble.util.RenewableWakeLock;
+import org.briarproject.bramble.util.AndroidUtils;
 
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
+import java.util.logging.Logger;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipInputStream;
 
 import javax.net.SocketFactory;
 
-import static android.content.Context.MODE_PRIVATE;
-import static android.content.Context.POWER_SERVICE;
-import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
-import static java.util.concurrent.TimeUnit.MINUTES;
+import static android.os.Build.VERSION.SDK_INT;
+import static java.util.Arrays.asList;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
 class AndroidTorPlugin extends TorPlugin {
 
-	private final Context appContext;
-	private final RenewableWakeLock wakeLock;
+	private static final List<String> LIBRARY_ARCHITECTURES =
+			asList("armeabi-v7a", "arm64-v8a", "x86", "x86_64");
 
-	AndroidTorPlugin(Executor ioExecutor, ScheduledExecutorService scheduler,
-			Context appContext, NetworkManager networkManager,
-			LocationUtils locationUtils, SocketFactory torSocketFactory,
-			Clock clock, ResourceProvider resourceProvider,
+	private static final String TOR_LIB_NAME = "libtor.so";
+	private static final String OBFS4_LIB_NAME = "libobfs4proxy.so";
+
+	private static final Logger LOG =
+			getLogger(AndroidTorPlugin.class.getName());
+
+	private final Application app;
+	private final AndroidWakeLock wakeLock;
+	private final File torLib, obfs4Lib;
+
+	AndroidTorPlugin(Executor ioExecutor,
+			Executor wakefulIoExecutor,
+			Application app,
+			NetworkManager networkManager,
+			LocationUtils locationUtils,
+			SocketFactory torSocketFactory,
+			Clock clock,
+			ResourceProvider resourceProvider,
 			CircumventionProvider circumventionProvider,
-			BatteryManager batteryManager, Backoff backoff,
+			BatteryManager batteryManager,
+			AndroidWakeLockManager wakeLockManager,
+			Backoff backoff,
 			TorRendezvousCrypto torRendezvousCrypto,
-			PluginCallback callback, String architecture, int maxLatency,
-			int maxIdleTime) {
-		super(ioExecutor, networkManager, locationUtils, torSocketFactory,
-				clock, resourceProvider, circumventionProvider, batteryManager,
-				backoff, torRendezvousCrypto, callback, architecture, maxLatency, maxIdleTime,
-				appContext.getDir("tor", MODE_PRIVATE));
-		this.appContext = appContext;
-		PowerManager pm = (PowerManager)
-				appContext.getSystemService(POWER_SERVICE);
-		if (pm == null) throw new AssertionError();
-		wakeLock = new RenewableWakeLock(pm, scheduler, PARTIAL_WAKE_LOCK,
-				getWakeLockTag(), 1, MINUTES);
+			PluginCallback callback,
+			String architecture,
+			int maxLatency,
+			int maxIdleTime,
+			File torDirectory) {
+		super(ioExecutor, wakefulIoExecutor, networkManager, locationUtils,
+				torSocketFactory, clock, resourceProvider,
+				circumventionProvider, batteryManager, backoff,
+				torRendezvousCrypto, callback, architecture, maxLatency,
+				maxIdleTime, torDirectory);
+		this.app = app;
+		wakeLock = wakeLockManager.createWakeLock("TorPlugin");
+		String nativeLibDir = app.getApplicationInfo().nativeLibraryDir;
+		torLib = new File(nativeLibDir, TOR_LIB_NAME);
+		obfs4Lib = new File(nativeLibDir, OBFS4_LIB_NAME);
 	}
 
 	@Override
@@ -64,8 +91,8 @@ class AndroidTorPlugin extends TorPlugin {
 	@Override
 	protected long getLastUpdateTime() {
 		try {
-			PackageManager pm = appContext.getPackageManager();
-			PackageInfo pi = pm.getPackageInfo(appContext.getPackageName(), 0);
+			PackageManager pm = app.getPackageManager();
+			PackageInfo pi = pm.getPackageInfo(app.getPackageName(), 0);
 			return pi.lastUpdateTime;
 		} catch (NameNotFoundException e) {
 			throw new AssertionError(e);
@@ -74,7 +101,6 @@ class AndroidTorPlugin extends TorPlugin {
 
 	@Override
 	protected void enableNetwork(boolean enable) throws IOException {
-		if (!running) return;
 		if (enable) wakeLock.acquire();
 		super.enableNetwork(enable);
 		if (!enable) wakeLock.release();
@@ -86,16 +112,111 @@ class AndroidTorPlugin extends TorPlugin {
 		wakeLock.release();
 	}
 
-	private String getWakeLockTag() {
-		PackageManager pm = appContext.getPackageManager();
-		for (PackageInfo info : pm.getInstalledPackages(0)) {
-			String name = info.packageName.toLowerCase();
-			if (name.startsWith("com.huawei.powergenie")) {
-				return "LocationManagerService";
-			} else if (name.startsWith("com.evenwell.powermonitor")) {
-				return "AudioIn";
+	@Override
+	protected File getTorExecutableFile() {
+		return torLib.exists() ? torLib : super.getTorExecutableFile();
+	}
+
+	@Override
+	protected File getObfs4ExecutableFile() {
+		return obfs4Lib.exists() ? obfs4Lib : super.getObfs4ExecutableFile();
+	}
+
+	@Override
+	protected void installTorExecutable() throws IOException {
+		File extracted = super.getTorExecutableFile();
+		if (torLib.exists()) {
+			// If an older version left behind a Tor binary, delete it
+			if (extracted.exists()) {
+				if (extracted.delete()) LOG.info("Deleted Tor binary");
+				else LOG.info("Failed to delete Tor binary");
+			}
+		} else if (SDK_INT < 29) {
+			// The binary wasn't extracted at install time. Try to extract it
+			extractLibraryFromApk(TOR_LIB_NAME, extracted);
+		} else {
+			// No point extracting the binary, we won't be allowed to execute it
+			throw new FileNotFoundException(torLib.getAbsolutePath());
+		}
+	}
+
+	@Override
+	protected void installObfs4Executable() throws IOException {
+		File extracted = super.getObfs4ExecutableFile();
+		if (obfs4Lib.exists()) {
+			// If an older version left behind an obfs4 binary, delete it
+			if (extracted.exists()) {
+				if (extracted.delete()) LOG.info("Deleted obfs4 binary");
+				else LOG.info("Failed to delete obfs4 binary");
+			}
+		} else if (SDK_INT < 29) {
+			// The binary wasn't extracted at install time. Try to extract it
+			extractLibraryFromApk(OBFS4_LIB_NAME, extracted);
+		} else {
+			// No point extracting the binary, we won't be allowed to execute it
+			throw new FileNotFoundException(obfs4Lib.getAbsolutePath());
+		}
+	}
+
+	private void extractLibraryFromApk(String libName, File dest)
+			throws IOException {
+		File sourceDir = new File(app.getApplicationInfo().sourceDir);
+		if (sourceDir.isFile()) {
+			// Look for other APK files in the same directory, if we're allowed
+			File parent = sourceDir.getParentFile();
+			if (parent != null) sourceDir = parent;
+		}
+		List<String> libPaths = getSupportedLibraryPaths(libName);
+		for (File apk : findApkFiles(sourceDir)) {
+			ZipInputStream zin = new ZipInputStream(new FileInputStream(apk));
+			for (ZipEntry e = zin.getNextEntry(); e != null;
+					e = zin.getNextEntry()) {
+				if (libPaths.contains(e.getName())) {
+					if (LOG.isLoggable(INFO)) {
+						LOG.info("Extracting " + e.getName()
+								+ " from " + apk.getAbsolutePath());
+					}
+					extract(zin, dest); // Zip input stream will be closed
+					return;
+				}
+			}
+			zin.close();
+		}
+		throw new FileNotFoundException(libName);
+	}
+
+	/**
+	 * Returns all files with the extension .apk or .APK under the given root.
+	 */
+	private List<File> findApkFiles(File root) {
+		List<File> files = new ArrayList<>();
+		findApkFiles(root, files);
+		return files;
+	}
+
+	private void findApkFiles(File f, List<File> files) {
+		if (f.isFile() && f.getName().toLowerCase().endsWith(".apk")) {
+			files.add(f);
+		} else if (f.isDirectory()) {
+			File[] children = f.listFiles();
+			if (children != null) {
+				for (File child : children) findApkFiles(child, files);
 			}
 		}
-		return getClass().getSimpleName();
+	}
+
+	/**
+	 * Returns the paths at which libraries with the given name would be found
+	 * inside an APK file, for all architectures supported by the device, in
+	 * order of preference.
+	 */
+	private List<String> getSupportedLibraryPaths(String libName) {
+		List<String> architectures = new ArrayList<>();
+		for (String abi : AndroidUtils.getSupportedArchitectures()) {
+			if (LIBRARY_ARCHITECTURES.contains(abi)) {
+				architectures.add("lib/" + abi + "/" + libName);
+			}
+		}
+		return architectures;
 	}
 }

bramble-android/src/main/java/org/briarproject/bramble/plugin/tor/AndroidTorPluginFactory.java

@@ -1,28 +1,33 @@
 package org.briarproject.bramble.plugin.tor;
 
-import android.content.Context;
+import android.app.Application;
 
 import org.briarproject.bramble.api.battery.BatteryManager;
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.network.NetworkManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
 import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.TorConstants;
+import org.briarproject.bramble.api.plugin.TorDirectory;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
+import org.briarproject.bramble.api.system.WakefulIoExecutor;
 import org.briarproject.bramble.util.AndroidUtils;
 
+import java.io.File;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
 import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
 import javax.net.SocketFactory;
 
 @Immutable
@@ -38,9 +43,8 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 	private static final int MAX_POLLING_INTERVAL = 10 * 60 * 1000; // 10 mins
 	private static final double BACKOFF_BASE = 1.2;
 
-	private final Executor ioExecutor;
-	private final ScheduledExecutorService scheduler;
-	private final Context appContext;
+	private final Executor ioExecutor, wakefulIoExecutor;
+	private final Application app;
 	private final NetworkManager networkManager;
 	private final LocationUtils locationUtils;
 	private final EventBus eventBus;
@@ -49,18 +53,28 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 	private final ResourceProvider resourceProvider;
 	private final CircumventionProvider circumventionProvider;
 	private final BatteryManager batteryManager;
+	private final AndroidWakeLockManager wakeLockManager;
 	private final Clock clock;
+	private final File torDirectory;
 
-	public AndroidTorPluginFactory(Executor ioExecutor,
-			ScheduledExecutorService scheduler, Context appContext,
-			NetworkManager networkManager, LocationUtils locationUtils,
-			EventBus eventBus, SocketFactory torSocketFactory,
-			BackoffFactory backoffFactory, ResourceProvider resourceProvider,
+	@Inject
+	public AndroidTorPluginFactory(@IoExecutor Executor ioExecutor,
+			@WakefulIoExecutor Executor wakefulIoExecutor,
+			Application app,
+			NetworkManager networkManager,
+			LocationUtils locationUtils,
+			EventBus eventBus,
+			SocketFactory torSocketFactory,
+			BackoffFactory backoffFactory,
+			ResourceProvider resourceProvider,
 			CircumventionProvider circumventionProvider,
-			BatteryManager batteryManager, Clock clock) {
+			BatteryManager batteryManager,
+			AndroidWakeLockManager wakeLockManager,
+			Clock clock,
+			@TorDirectory File torDirectory) {
 		this.ioExecutor = ioExecutor;
-		this.scheduler = scheduler;
-		this.appContext = appContext;
+		this.wakefulIoExecutor = wakefulIoExecutor;
+		this.app = app;
 		this.networkManager = networkManager;
 		this.locationUtils = locationUtils;
 		this.eventBus = eventBus;
@@ -69,7 +83,9 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 		this.resourceProvider = resourceProvider;
 		this.circumventionProvider = circumventionProvider;
 		this.batteryManager = batteryManager;
+		this.wakeLockManager = wakeLockManager;
 		this.clock = clock;
+		this.torDirectory = torDirectory;
 	}
 
 	@Override
@@ -112,11 +128,12 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		TorRendezvousCrypto torRendezvousCrypto = new TorRendezvousCryptoImpl();
-		AndroidTorPlugin plugin = new AndroidTorPlugin(ioExecutor, scheduler,
-				appContext, networkManager, locationUtils, torSocketFactory,
-				clock, resourceProvider, circumventionProvider, batteryManager,
+		AndroidTorPlugin plugin = new AndroidTorPlugin(ioExecutor,
+				wakefulIoExecutor, app, networkManager, locationUtils,
+				torSocketFactory, clock, resourceProvider,
+				circumventionProvider, batteryManager, wakeLockManager,
 				backoff, torRendezvousCrypto, callback, architecture,
-				MAX_LATENCY, MAX_IDLE_TIME);
+				MAX_LATENCY, MAX_IDLE_TIME, torDirectory);
 		eventBus.addListener(plugin);
 		return plugin;
 	}

bramble-android/src/main/java/org/briarproject/bramble/system/AlarmConstants.java

@@ -0,0 +1,18 @@
+package org.briarproject.bramble.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+interface AlarmConstants {
+
+	/**
+	 * Request code for the broadcast intent attached to the periodic alarm.
+	 */
+	int REQUEST_ALARM = 1;
+
+	/**
+	 * Key for storing the process ID in the extras of the periodic alarm's
+	 * intent. This allows us to ignore alarms scheduled by dead processes.
+	 */
+	String EXTRA_PID = "org.briarproject.bramble.EXTRA_PID";
+}

bramble-android/src/main/java/org/briarproject/bramble/system/AlarmReceiver.java

@@ -0,0 +1,17 @@
+package org.briarproject.bramble.system;
+
+import android.content.BroadcastReceiver;
+import android.content.Context;
+import android.content.Intent;
+
+import org.briarproject.bramble.BrambleApplication;
+
+public class AlarmReceiver extends BroadcastReceiver {
+
+	@Override
+	public void onReceive(Context ctx, Intent intent) {
+		BrambleApplication app =
+				(BrambleApplication) ctx.getApplicationContext();
+		app.getBrambleAppComponent().alarmListener().onAlarm(intent);
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidLocationUtils.java

@@ -61,12 +61,12 @@ class AndroidLocationUtils implements LocationUtils {
 	private String getCountryFromPhoneNetwork() {
 		Object o = appContext.getSystemService(TELEPHONY_SERVICE);
 		TelephonyManager tm = (TelephonyManager) o;
-		return tm.getNetworkCountryIso();
+		return tm == null ? "" : tm.getNetworkCountryIso();
 	}
 
 	private String getCountryFromSimCard() {
 		Object o = appContext.getSystemService(TELEPHONY_SERVICE);
 		TelephonyManager tm = (TelephonyManager) o;
-		return tm.getSimCountryIso();
+		return tm == null ? "" : tm.getSimCountryIso();
 	}
 }

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidSystemModule.java

@@ -1,12 +1,17 @@
 package org.briarproject.bramble.system;
 
 import org.briarproject.bramble.api.event.EventExecutor;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.system.AndroidExecutor;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
 import org.briarproject.bramble.api.system.SecureRandomProvider;
 
 import java.util.concurrent.Executor;
+import java.util.concurrent.RejectedExecutionHandler;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
 
 import javax.inject.Singleton;
 
@@ -16,6 +21,23 @@ import dagger.Provides;
 @Module
 public class AndroidSystemModule {
 
+	private final ScheduledExecutorService scheduledExecutorService;
+
+	public AndroidSystemModule() {
+		// Discard tasks that are submitted during shutdown
+		RejectedExecutionHandler policy =
+				new ScheduledThreadPoolExecutor.DiscardPolicy();
+		scheduledExecutorService = new ScheduledThreadPoolExecutor(1, policy);
+	}
+
+	@Provides
+	@Singleton
+	ScheduledExecutorService provideScheduledExecutorService(
+			LifecycleManager lifecycleManager) {
+		lifecycleManager.registerForShutdown(scheduledExecutorService);
+		return scheduledExecutorService;
+	}
+
 	@Provides
 	@Singleton
 	SecureRandomProvider provideSecureRandomProvider(
@@ -47,4 +69,11 @@ public class AndroidSystemModule {
 	ResourceProvider provideResourceProvider(AndroidResourceProvider provider) {
 		return provider;
 	}
+
+	@Provides
+	@Singleton
+	AndroidWakeLockManager provideWakeLockManager(
+			AndroidWakeLockManagerImpl wakeLockManager) {
+		return wakeLockManager;
+	}
 }

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidTaskScheduler.java

@@ -0,0 +1,242 @@
+package org.briarproject.bramble.system;
+
+import android.annotation.TargetApi;
+import android.app.AlarmManager;
+import android.app.Application;
+import android.app.PendingIntent;
+import android.content.Intent;
+import android.os.Process;
+import android.os.SystemClock;
+
+import org.briarproject.bramble.api.lifecycle.Service;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.AlarmListener;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
+import org.briarproject.bramble.api.system.TaskScheduler;
+import org.briarproject.bramble.api.system.Wakeful;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.PriorityQueue;
+import java.util.Queue;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Future;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.logging.Logger;
+
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
+import static android.app.AlarmManager.ELAPSED_REALTIME_WAKEUP;
+import static android.app.AlarmManager.INTERVAL_FIFTEEN_MINUTES;
+import static android.app.PendingIntent.FLAG_CANCEL_CURRENT;
+import static android.content.Context.ALARM_SERVICE;
+import static android.os.Build.VERSION.SDK_INT;
+import static java.util.Objects.requireNonNull;
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.system.AlarmConstants.EXTRA_PID;
+import static org.briarproject.bramble.system.AlarmConstants.REQUEST_ALARM;
+
+@ThreadSafe
+@NotNullByDefault
+class AndroidTaskScheduler implements TaskScheduler, Service, AlarmListener {
+
+	private static final Logger LOG =
+			getLogger(AndroidTaskScheduler.class.getName());
+
+	private static final long ALARM_MS = INTERVAL_FIFTEEN_MINUTES;
+
+	private final Application app;
+	private final AndroidWakeLockManager wakeLockManager;
+	private final ScheduledExecutorService scheduledExecutorService;
+	private final AlarmManager alarmManager;
+
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	private final Queue<ScheduledTask> tasks = new PriorityQueue<>();
+
+	AndroidTaskScheduler(Application app,
+			AndroidWakeLockManager wakeLockManager,
+			ScheduledExecutorService scheduledExecutorService) {
+		this.app = app;
+		this.wakeLockManager = wakeLockManager;
+		this.scheduledExecutorService = scheduledExecutorService;
+		alarmManager = (AlarmManager)
+				requireNonNull(app.getSystemService(ALARM_SERVICE));
+	}
+
+	@Override
+	public void startService() {
+		scheduleAlarm();
+	}
+
+	@Override
+	public void stopService() {
+		cancelAlarm();
+	}
+
+	@Override
+	public Cancellable schedule(Runnable task, Executor executor, long delay,
+			TimeUnit unit) {
+		AtomicBoolean cancelled = new AtomicBoolean(false);
+		return schedule(task, executor, delay, unit, cancelled);
+	}
+
+	@Override
+	public Cancellable scheduleWithFixedDelay(Runnable task, Executor executor,
+			long delay, long interval, TimeUnit unit) {
+		AtomicBoolean cancelled = new AtomicBoolean(false);
+		return scheduleWithFixedDelay(task, executor, delay, interval, unit,
+				cancelled);
+	}
+
+	@Override
+	public void onAlarm(Intent intent) {
+		wakeLockManager.runWakefully(() -> {
+			int extraPid = intent.getIntExtra(EXTRA_PID, -1);
+			int currentPid = Process.myPid();
+			if (extraPid == currentPid) {
+				LOG.info("Alarm");
+				rescheduleAlarm();
+				runDueTasks();
+			} else if (LOG.isLoggable(INFO)) {
+				LOG.info("Ignoring alarm with PID " + extraPid
+						+ ", current PID is " + currentPid);
+			}
+		}, "TaskAlarm");
+	}
+
+	private Cancellable schedule(Runnable task, Executor executor, long delay,
+			TimeUnit unit, AtomicBoolean cancelled) {
+		long now = SystemClock.elapsedRealtime();
+		long dueMillis = now + MILLISECONDS.convert(delay, unit);
+		Runnable wakeful = () ->
+				wakeLockManager.executeWakefully(task, executor, "TaskHandoff");
+		Future<?> check = scheduleCheckForDueTasks(delay, unit);
+		ScheduledTask s = new ScheduledTask(wakeful, dueMillis, check,
+				cancelled);
+		synchronized (lock) {
+			tasks.add(s);
+		}
+		return s;
+	}
+
+	private Cancellable scheduleWithFixedDelay(Runnable task, Executor executor,
+			long delay, long interval, TimeUnit unit, AtomicBoolean cancelled) {
+		// All executions of this periodic task share a cancelled flag
+		Runnable wrapped = () -> {
+			task.run();
+			scheduleWithFixedDelay(task, executor, interval, interval, unit,
+					cancelled);
+		};
+		return schedule(wrapped, executor, delay, unit, cancelled);
+	}
+
+	private Future<?> scheduleCheckForDueTasks(long delay, TimeUnit unit) {
+		Runnable wakeful = () -> wakeLockManager.runWakefully(
+				this::runDueTasks, "TaskScheduler");
+		return scheduledExecutorService.schedule(wakeful, delay, unit);
+	}
+
+	@Wakeful
+	private void runDueTasks() {
+		long now = SystemClock.elapsedRealtime();
+		List<ScheduledTask> due = new ArrayList<>();
+		synchronized (lock) {
+			while (true) {
+				ScheduledTask s = tasks.peek();
+				if (s == null || s.dueMillis > now) break;
+				due.add(tasks.remove());
+			}
+		}
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("Running " + due.size() + " due tasks");
+		}
+		for (ScheduledTask s : due) {
+			if (LOG.isLoggable(INFO)) {
+				LOG.info("Task is " + (now - s.dueMillis) + " ms overdue");
+			}
+			s.run();
+		}
+	}
+
+	private void scheduleAlarm() {
+		if (SDK_INT >= 23) scheduleIdleAlarm();
+		else scheduleInexactRepeatingAlarm();
+	}
+
+	private void rescheduleAlarm() {
+		// If SDK_INT < 23 the alarm repeats automatically
+		if (SDK_INT >= 23) scheduleIdleAlarm();
+	}
+
+	private void cancelAlarm() {
+		alarmManager.cancel(getAlarmPendingIntent());
+	}
+
+	private void scheduleInexactRepeatingAlarm() {
+		alarmManager.setInexactRepeating(ELAPSED_REALTIME_WAKEUP,
+				SystemClock.elapsedRealtime() + ALARM_MS, ALARM_MS,
+				getAlarmPendingIntent());
+	}
+
+	@TargetApi(23)
+	private void scheduleIdleAlarm() {
+		alarmManager.setAndAllowWhileIdle(ELAPSED_REALTIME_WAKEUP,
+				SystemClock.elapsedRealtime() + ALARM_MS,
+				getAlarmPendingIntent());
+	}
+
+	private PendingIntent getAlarmPendingIntent() {
+		Intent i = new Intent(app, AlarmReceiver.class);
+		i.putExtra(EXTRA_PID, android.os.Process.myPid());
+		return PendingIntent.getBroadcast(app, REQUEST_ALARM, i,
+				FLAG_CANCEL_CURRENT);
+	}
+
+	private class ScheduledTask
+			implements Runnable, Cancellable, Comparable<ScheduledTask> {
+
+		private final Runnable task;
+		private final long dueMillis;
+		private final Future<?> check;
+		private final AtomicBoolean cancelled;
+
+		public ScheduledTask(Runnable task, long dueMillis,
+				Future<?> check, AtomicBoolean cancelled) {
+			this.task = task;
+			this.dueMillis = dueMillis;
+			this.check = check;
+			this.cancelled = cancelled;
+		}
+
+		@Override
+		public void run() {
+			if (!cancelled.get()) task.run();
+		}
+
+		@Override
+		public void cancel() {
+			// Cancel any future executions of this task
+			cancelled.set(true);
+			// Cancel the scheduled check for due tasks
+			check.cancel(false);
+			// Remove the task from the queue
+			synchronized (lock) {
+				tasks.remove(this);
+			}
+		}
+
+		@Override
+		public int compareTo(ScheduledTask s) {
+			//noinspection UseCompareMethod
+			if (dueMillis < s.dueMillis) return -1;
+			if (dueMillis > s.dueMillis) return 1;
+			return 0;
+		}
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidTaskSchedulerModule.java

@@ -0,0 +1,49 @@
+package org.briarproject.bramble.system;
+
+import android.app.Application;
+
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.system.AlarmListener;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
+import org.briarproject.bramble.api.system.TaskScheduler;
+
+import java.util.concurrent.ScheduledExecutorService;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class AndroidTaskSchedulerModule {
+
+	public static class EagerSingletons {
+		@Inject
+		AndroidTaskScheduler scheduler;
+	}
+
+	@Provides
+	@Singleton
+	AndroidTaskScheduler provideAndroidTaskScheduler(
+			LifecycleManager lifecycleManager, Application app,
+			AndroidWakeLockManager wakeLockManager,
+			ScheduledExecutorService scheduledExecutorService) {
+		AndroidTaskScheduler scheduler = new AndroidTaskScheduler(app,
+				wakeLockManager, scheduledExecutorService);
+		lifecycleManager.registerService(scheduler);
+		return scheduler;
+	}
+
+	@Provides
+	@Singleton
+	AlarmListener provideAlarmListener(AndroidTaskScheduler scheduler) {
+		return scheduler;
+	}
+
+	@Provides
+	@Singleton
+	TaskScheduler provideTaskScheduler(AndroidTaskScheduler scheduler) {
+		return scheduler;
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidWakeLockImpl.java

@@ -0,0 +1,74 @@
+package org.briarproject.bramble.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.AndroidWakeLock;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.logging.Logger;
+
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
+import static java.util.logging.Level.FINE;
+import static java.util.logging.Logger.getLogger;
+
+/**
+ * A wrapper around a {@link SharedWakeLock} that provides the more convenient
+ * semantics of {@link AndroidWakeLock} (i.e. calls to acquire() and release()
+ * don't need to be balanced).
+ */
+@ThreadSafe
+@NotNullByDefault
+class AndroidWakeLockImpl implements AndroidWakeLock {
+
+	private static final Logger LOG =
+			getLogger(AndroidWakeLockImpl.class.getName());
+
+	private static final AtomicInteger INSTANCE_ID = new AtomicInteger(0);
+
+	private final SharedWakeLock sharedWakeLock;
+	private final String tag;
+
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	private boolean held = false;
+
+	AndroidWakeLockImpl(SharedWakeLock sharedWakeLock, String tag) {
+		this.sharedWakeLock = sharedWakeLock;
+		this.tag = tag + "_" + INSTANCE_ID.getAndIncrement();
+	}
+
+	@Override
+	public void acquire() {
+		synchronized (lock) {
+			if (held) {
+				if (LOG.isLoggable(FINE)) {
+					LOG.fine(tag + " already acquired");
+				}
+			} else {
+				if (LOG.isLoggable(FINE)) {
+					LOG.fine(tag + " acquiring shared wake lock");
+				}
+				held = true;
+				sharedWakeLock.acquire();
+			}
+		}
+	}
+
+	@Override
+	public void release() {
+		synchronized (lock) {
+			if (held) {
+				if (LOG.isLoggable(FINE)) {
+					LOG.fine(tag + " releasing shared wake lock");
+				}
+				held = false;
+				sharedWakeLock.release();
+			} else {
+				if (LOG.isLoggable(FINE)) {
+					LOG.fine(tag + " already released");
+				}
+			}
+		}
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidWakeLockManagerImpl.java

@@ -0,0 +1,119 @@
+package org.briarproject.bramble.system;
+
+import android.app.Application;
+import android.content.Context;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
+import android.os.PowerManager;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.AndroidWakeLock;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
+
+import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
+
+import javax.inject.Inject;
+
+import static android.content.Context.POWER_SERVICE;
+import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
+import static java.util.concurrent.TimeUnit.MINUTES;
+import static java.util.concurrent.TimeUnit.SECONDS;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+
+@NotNullByDefault
+class AndroidWakeLockManagerImpl implements AndroidWakeLockManager {
+
+	/**
+	 * How often to replace the wake lock.
+	 */
+	private static final long LOCK_DURATION_MS = MINUTES.toMillis(1);
+
+	/**
+	 * Automatically release the lock this many milliseconds after it's due
+	 * to have been replaced and released.
+	 */
+	private static final long SAFETY_MARGIN_MS = SECONDS.toMillis(30);
+
+	private final SharedWakeLock sharedWakeLock;
+
+	@Inject
+	AndroidWakeLockManagerImpl(Application app,
+			ScheduledExecutorService scheduledExecutorService) {
+		PowerManager powerManager = (PowerManager)
+				requireNonNull(app.getSystemService(POWER_SERVICE));
+		String tag = getWakeLockTag(app);
+		sharedWakeLock = new RenewableWakeLock(powerManager,
+				scheduledExecutorService, PARTIAL_WAKE_LOCK, tag,
+				LOCK_DURATION_MS, SAFETY_MARGIN_MS);
+	}
+
+	@Override
+	public AndroidWakeLock createWakeLock(String tag) {
+		return new AndroidWakeLockImpl(sharedWakeLock, tag);
+	}
+
+	@Override
+	public void runWakefully(Runnable r, String tag) {
+		AndroidWakeLock wakeLock = createWakeLock(tag);
+		wakeLock.acquire();
+		try {
+			r.run();
+		} finally {
+			wakeLock.release();
+		}
+	}
+
+	@Override
+	public void executeWakefully(Runnable r, Executor executor, String tag) {
+		AndroidWakeLock wakeLock = createWakeLock(tag);
+		wakeLock.acquire();
+		try {
+			executor.execute(() -> {
+				try {
+					r.run();
+				} finally {
+					// Release the wake lock if the task throws an exception
+					wakeLock.release();
+				}
+			});
+		} catch (Exception e) {
+			// Release the wake lock if the executor throws an exception when
+			// we submit the task (in which case the release() call above won't
+			// happen)
+			wakeLock.release();
+			throw e;
+		}
+	}
+
+	@Override
+	public void executeWakefully(Runnable r, String tag) {
+		AndroidWakeLock wakeLock = createWakeLock(tag);
+		wakeLock.acquire();
+		try {
+			new Thread(() -> {
+				try {
+					r.run();
+				} finally {
+					wakeLock.release();
+				}
+			}).start();
+		} catch (Exception e) {
+			wakeLock.release();
+			throw e;
+		}
+	}
+
+	private String getWakeLockTag(Context ctx) {
+		PackageManager pm = ctx.getPackageManager();
+		for (PackageInfo info : pm.getInstalledPackages(0)) {
+			String name = info.packageName.toLowerCase();
+			if (name.startsWith("com.huawei.powergenie")) {
+				return "LocationManagerService";
+			} else if (name.startsWith("com.evenwell.powermonitor")) {
+				return "AudioIn";
+			}
+		}
+		return ctx.getPackageName();
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidWakefulIoExecutorModule.java

@@ -0,0 +1,23 @@
+package org.briarproject.bramble.system;
+
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.system.AndroidWakeLockManager;
+import org.briarproject.bramble.api.system.WakefulIoExecutor;
+
+import java.util.concurrent.Executor;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public
+class AndroidWakefulIoExecutorModule {
+
+	@Provides
+	@WakefulIoExecutor
+	Executor provideWakefulIoExecutor(@IoExecutor Executor ioExecutor,
+			AndroidWakeLockManager wakeLockManager) {
+		return r -> wakeLockManager.executeWakefully(r, ioExecutor,
+				"WakefulIoExecutor");
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/system/RenewableWakeLock.java

@@ -0,0 +1,130 @@
+package org.briarproject.bramble.system;
+
+import android.os.PowerManager;
+import android.os.PowerManager.WakeLock;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.concurrent.Future;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static java.util.logging.Level.FINE;
+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.api.nullsafety.NullSafety.requireNonNull;
+
+@ThreadSafe
+@NotNullByDefault
+class RenewableWakeLock implements SharedWakeLock {
+
+	private static final Logger LOG =
+			getLogger(RenewableWakeLock.class.getName());
+
+	private final PowerManager powerManager;
+	private final ScheduledExecutorService scheduledExecutorService;
+	private final int levelAndFlags;
+	private final String tag;
+	private final long durationMs, safetyMarginMs;
+
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	@Nullable
+	private WakeLock wakeLock;
+	@GuardedBy("lock")
+	@Nullable
+	private Future<?> future;
+	@GuardedBy("lock")
+	private int refCount = 0;
+	@GuardedBy("lock")
+	private long acquired = 0;
+
+	RenewableWakeLock(PowerManager powerManager,
+			ScheduledExecutorService scheduledExecutorService,
+			int levelAndFlags,
+			String tag,
+			long durationMs,
+			long safetyMarginMs) {
+		this.powerManager = powerManager;
+		this.scheduledExecutorService = scheduledExecutorService;
+		this.levelAndFlags = levelAndFlags;
+		this.tag = tag;
+		this.durationMs = durationMs;
+		this.safetyMarginMs = safetyMarginMs;
+	}
+
+	@Override
+	public void acquire() {
+		synchronized (lock) {
+			refCount++;
+			if (refCount == 1) {
+				if (LOG.isLoggable(INFO)) {
+					LOG.info("Acquiring wake lock " + tag);
+				}
+				wakeLock = powerManager.newWakeLock(levelAndFlags, tag);
+				// We do our own reference counting so we can replace the lock
+				// TODO: Check whether using a ref-counted wake lock affects
+				//  power management apps
+				wakeLock.setReferenceCounted(false);
+				wakeLock.acquire(durationMs + safetyMarginMs);
+				future = scheduledExecutorService.schedule(this::renew,
+						durationMs, MILLISECONDS);
+				acquired = android.os.SystemClock.elapsedRealtime();
+			} else if (LOG.isLoggable(FINE)) {
+				LOG.fine("Wake lock " + tag + " has " + refCount + " holders");
+			}
+		}
+	}
+
+	private void renew() {
+		if (LOG.isLoggable(INFO)) LOG.info("Renewing wake lock " + tag);
+		synchronized (lock) {
+			if (wakeLock == null) {
+				LOG.info("Already released");
+				return;
+			}
+			if (LOG.isLoggable(FINE)) {
+				LOG.fine("Wake lock " + tag + " has " + refCount + " holders");
+			}
+			long now = android.os.SystemClock.elapsedRealtime();
+			long expiry = acquired + durationMs + safetyMarginMs;
+			if (now > expiry && LOG.isLoggable(WARNING)) {
+				LOG.warning("Wake lock expired " + (now - expiry) + " ms ago");
+			}
+			WakeLock oldWakeLock = wakeLock;
+			wakeLock = powerManager.newWakeLock(levelAndFlags, tag);
+			wakeLock.setReferenceCounted(false);
+			wakeLock.acquire(durationMs + safetyMarginMs);
+			oldWakeLock.release();
+			future = scheduledExecutorService.schedule(this::renew, durationMs,
+					MILLISECONDS);
+			acquired = now;
+		}
+	}
+
+	@Override
+	public void release() {
+		synchronized (lock) {
+			refCount--;
+			if (refCount == 0) {
+				if (LOG.isLoggable(INFO)) {
+					LOG.info("Releasing wake lock " + tag);
+				}
+				requireNonNull(future).cancel(false);
+				future = null;
+				requireNonNull(wakeLock).release();
+				wakeLock = null;
+				acquired = 0;
+			} else if (LOG.isLoggable(FINE)) {
+				LOG.fine("Wake lock " + tag + " has " + refCount + " holders");
+			}
+		}
+	}
+}
+

bramble-android/src/main/java/org/briarproject/bramble/system/SharedWakeLock.java

@@ -0,0 +1,22 @@
+package org.briarproject.bramble.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.AndroidWakeLock;
+
+@NotNullByDefault
+interface SharedWakeLock {
+
+	/**
+	 * Acquires the wake lock. This increments the wake lock's reference count,
+	 * so unlike {@link AndroidWakeLock#acquire()} every call to this method
+	 * must be followed by a balancing call to {@link #release()}.
+	 */
+	void acquire();
+
+	/**
+	 * Releases the wake lock. This decrements the wake lock's reference count,
+	 * so unlike {@link AndroidWakeLock#release()} every call to this method
+	 * must follow a balancing call to {@link #acquire()}.
+	 */
+	void release();
+}

bramble-android/src/main/java/org/briarproject/bramble/util/RenewableWakeLock.java

@@ -1,100 +0,0 @@
-package org.briarproject.bramble.util;
-
-import android.os.PowerManager;
-
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import java.util.concurrent.ScheduledExecutorService;
-import java.util.concurrent.ScheduledFuture;
-import java.util.concurrent.TimeUnit;
-import java.util.logging.Logger;
-
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.ThreadSafe;
-
-import static java.util.concurrent.TimeUnit.MILLISECONDS;
-import static java.util.logging.Level.INFO;
-
-@ThreadSafe
-@NotNullByDefault
-public class RenewableWakeLock {
-
-	private static final Logger LOG =
-			Logger.getLogger(RenewableWakeLock.class.getName());
-
-	/**
-	 * Automatically release the lock this many milliseconds after it's due
-	 * to have been replaced and released.
-	 */
-	private static final int SAFETY_MARGIN_MS = 10_000;
-
-	private final PowerManager powerManager;
-	private final ScheduledExecutorService scheduler;
-	private final int levelAndFlags;
-	private final String tag;
-	private final long durationMs;
-	private final Runnable renewTask;
-
-	private final Object lock = new Object();
-	@Nullable
-	private PowerManager.WakeLock wakeLock; // Locking: lock
-	@Nullable
-	private ScheduledFuture future; // Locking: lock
-
-	public RenewableWakeLock(PowerManager powerManager,
-			ScheduledExecutorService scheduler, int levelAndFlags, String tag,
-			long duration, TimeUnit timeUnit) {
-		this.powerManager = powerManager;
-		this.scheduler = scheduler;
-		this.levelAndFlags = levelAndFlags;
-		this.tag = tag;
-		durationMs = MILLISECONDS.convert(duration, timeUnit);
-		renewTask = this::renew;
-	}
-
-	public void acquire() {
-		if (LOG.isLoggable(INFO)) LOG.info("Acquiring wake lock " + tag);
-		synchronized (lock) {
-			if (wakeLock != null) {
-				LOG.info("Already acquired");
-				return;
-			}
-			wakeLock = powerManager.newWakeLock(levelAndFlags, tag);
-			wakeLock.setReferenceCounted(false);
-			wakeLock.acquire(durationMs + SAFETY_MARGIN_MS);
-			future = scheduler.schedule(renewTask, durationMs, MILLISECONDS);
-		}
-	}
-
-	private void renew() {
-		if (LOG.isLoggable(INFO)) LOG.info("Renewing wake lock " + tag);
-		synchronized (lock) {
-			if (wakeLock == null) {
-				LOG.info("Already released");
-				return;
-			}
-			PowerManager.WakeLock oldWakeLock = wakeLock;
-			wakeLock = powerManager.newWakeLock(levelAndFlags, tag);
-			wakeLock.setReferenceCounted(false);
-			wakeLock.acquire(durationMs + SAFETY_MARGIN_MS);
-			oldWakeLock.release();
-			future = scheduler.schedule(renewTask, durationMs, MILLISECONDS);
-		}
-	}
-
-	public void release() {
-		if (LOG.isLoggable(INFO)) LOG.info("Releasing wake lock " + tag);
-		synchronized (lock) {
-			if (wakeLock == null) {
-				LOG.info("Already released");
-				return;
-			}
-			if (future == null) throw new AssertionError();
-			future.cancel(false);
-			future = null;
-			wakeLock.release();
-			wakeLock = null;
-		}
-	}
-}
-

bramble-api/src/main/java/org/briarproject/bramble/api/Consumable.java

@@ -0,0 +1,25 @@
+package org.briarproject.bramble.api;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+import javax.annotation.Nullable;
+
+/**
+ * An item that can be consumed once.
+ */
+@NotNullByDefault
+public class Consumable<T> {
+
+	private final AtomicReference<T> reference;
+
+	public Consumable(T item) {
+		reference = new AtomicReference<>(item);
+	}
+
+	@Nullable
+	public T consume() {
+		return reference.getAndSet(null);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/client/ClientHelper.java

@@ -35,24 +35,24 @@ public interface ClientHelper {
 
 	Message createMessageForStoringMetadata(GroupId g);
 
-	Message getMessage(MessageId m) throws DbException;
+	Message getSmallMessage(MessageId m) throws DbException;
 
-	Message getMessage(Transaction txn, MessageId m) throws DbException;
+	Message getSmallMessage(Transaction txn, MessageId m) throws DbException;
 
-	BdfList getMessageAsList(MessageId m) throws DbException, FormatException;
+	BdfList getSmallMessageAsList(MessageId m)
+			throws DbException, FormatException;
 
-	BdfList getMessageAsList(Transaction txn, MessageId m) throws DbException,
-			FormatException;
+	BdfList getSmallMessageAsList(Transaction txn, MessageId m)
+			throws DbException, FormatException;
 
-	BdfDictionary getGroupMetadataAsDictionary(GroupId g) throws DbException,
-			FormatException;
+	BdfDictionary getGroupMetadataAsDictionary(GroupId g)
+			throws DbException, FormatException;
 
 	BdfDictionary getGroupMetadataAsDictionary(Transaction txn, GroupId g)
 			throws DbException, FormatException;
 
 	BdfDictionary getMessageMetadataAsDictionary(MessageId m)
-			throws DbException,
-			FormatException;
+			throws DbException, FormatException;
 
 	BdfDictionary getMessageMetadataAsDictionary(Transaction txn, MessageId m)
 			throws DbException, FormatException;
@@ -67,8 +67,8 @@ public interface ClientHelper {
 			BdfDictionary query) throws DbException, FormatException;
 
 	Map<MessageId, BdfDictionary> getMessageMetadataAsDictionary(
-			Transaction txn, GroupId g, BdfDictionary query) throws DbException,
-			FormatException;
+			Transaction txn, GroupId g, BdfDictionary query)
+			throws DbException, FormatException;
 
 	void mergeGroupMetadata(GroupId g, BdfDictionary metadata)
 			throws DbException, FormatException;

bramble-api/src/main/java/org/briarproject/bramble/api/connection/ConnectionRegistry.java

@@ -22,14 +22,42 @@ import java.util.Collection;
 public interface ConnectionRegistry {
 
 	/**
-	 * Registers a connection with the given contact over the given transport.
+	 * Registers an incoming connection from the given contact over the given
+	 * transport. The connection's {@link Priority priority} can be set later
+	 * via {@link #setPriority(ContactId, TransportId, InterruptibleConnection,
+	 * Priority)} if a priority record is received from the contact.
 	 * <p>
 	 * Broadcasts {@link ConnectionOpenedEvent}. Also broadcasts
 	 * {@link ContactConnectedEvent} if this is the only connection with the
 	 * contact.
 	 */
-	void registerConnection(ContactId c, TransportId t,
-			InterruptibleConnection conn, boolean incoming);
+	void registerIncomingConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn);
+
+	/**
+	 * Registers an outgoing connection to the given contact over the given
+	 * transport.
+	 * <p>
+	 * Broadcasts {@link ConnectionOpenedEvent}. Also broadcasts
+	 * {@link ContactConnectedEvent} if this is the only connection with the
+	 * contact.
+	 * <p>
+	 * If the registry has any "better" connections with the given contact, the
+	 * given connection will be interrupted. If the registry has any "worse"
+	 * connections with the given contact, those connections will be
+	 * interrupted.
+	 * <p>
+	 * Connection A is considered "better" than connection B if both
+	 * connections have had their priorities set, and either A's transport is
+	 * {@link PluginConfig#getTransportPreferences() preferred} to B's, or
+	 * they use the same transport and A has higher {@link Priority priority}
+	 * than B.
+	 * <p>
+	 * For backward compatibility, connections without priorities are not
+	 * considered better or worse than other connections.
+	 */
+	void registerOutgoingConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, Priority priority);
 
 	/**
 	 * Unregisters a connection with the given contact over the given transport.
@@ -43,8 +71,8 @@ public interface ConnectionRegistry {
 
 	/**
 	 * Sets the {@link Priority priority} of a connection that was previously
-	 * registered via {@link #registerConnection(ContactId, TransportId,
-	 * InterruptibleConnection, boolean)}.
+	 * registered via {@link #registerIncomingConnection(ContactId, TransportId,
+	 * InterruptibleConnection)}.
 	 * <p>
 	 * If the registry has any "better" connections with the given contact, the
 	 * given connection will be interrupted. If the registry has any "worse"

bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseComponent.java

@@ -163,27 +163,23 @@ public interface DatabaseComponent extends TransactionManager {
 	 * less than or equal to the given length, for transmission over a
 	 * transport with the given maximum latency. Returns null if there are no
 	 * sendable messages that fit in the given length.
+	 *
+	 * @param small True if only single-block messages should be sent
 	 */
 	@Nullable
 	Collection<Message> generateBatch(Transaction txn, ContactId c,
-			int maxLength, int maxLatency) throws DbException;
+			int maxLength, int maxLatency, boolean small) throws DbException;
 
 	/**
 	 * Returns an offer for the given contact for transmission over a
 	 * transport with the given maximum latency, or null if there are no
 	 * messages to offer.
+	 *
+	 * @param small True if only single-block messages should be offered
 	 */
 	@Nullable
 	Offer generateOffer(Transaction txn, ContactId c, int maxMessages,
-			int maxLatency) throws DbException;
-
-	/**
-	 * Returns a request for the given contact, or null if there are no
-	 * messages to request.
-	 */
-	@Nullable
-	Request generateRequest(Transaction txn, ContactId c, int maxMessages)
-			throws DbException;
+			int maxLatency, boolean small) throws DbException;
 
 	/**
 	 * Returns a batch of messages for the given contact, with a total length
@@ -272,13 +268,14 @@ public interface DatabaseComponent extends TransactionManager {
 	Collection<Identity> getIdentities(Transaction txn) throws DbException;
 
 	/**
-	 * Returns the message with the given ID.
+	 * Returns the single-block message with the given ID.
 	 * <p/>
 	 * Read-only.
 	 *
 	 * @throws MessageDeletedException if the message has been deleted
+	 * @throws MessageTooLargeException if the message has more than one block
 	 */
-	Message getMessage(Transaction txn, MessageId m) throws DbException;
+	Message getSmallMessage(Transaction txn, MessageId m) throws DbException;
 
 	/**
 	 * Returns the IDs of all delivered messages in the given group.

bramble-api/src/main/java/org/briarproject/bramble/api/db/MessageTooLargeException.java

@@ -0,0 +1,8 @@
+package org.briarproject.bramble.api.db;
+
+/**
+ * Thrown when a multi-block message is requested from the database via a
+ * method that is only suitable for requesting single-block messages.
+ */
+public class MessageTooLargeException extends DbException {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/event/EventBus.java

@@ -18,6 +18,8 @@ public interface EventBus {
 	/**
 	 * Asynchronously notifies all listeners of an event. Listeners are
 	 * notified on the {@link EventExecutor}.
+	 * <p>
+	 * This method can safely be called while holding a lock.
 	 */
 	void broadcast(Event e);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/io/TimeoutMonitor.java

@@ -7,6 +7,10 @@ public interface TimeoutMonitor {
 	/**
 	 * Returns an {@link InputStream} that wraps the given stream and allows
 	 * read timeouts to be detected.
+	 * <p>
+	 * The returned stream must be {@link InputStream#close() closed} when it's
+	 * no longer needed to ensure that resources held by the timeout monitor
+	 * are released.
 	 *
 	 * @param timeoutMs The read timeout in milliseconds. Timeouts will be
 	 * detected eventually but are not guaranteed to be detected immediately.

bramble-api/src/main/java/org/briarproject/bramble/api/lifecycle/LifecycleManager.java

@@ -5,6 +5,7 @@ import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.Wakeful;
 
 import java.util.concurrent.ExecutorService;
 
@@ -65,6 +66,7 @@ public interface LifecycleManager {
 	 * Opens the {@link DatabaseComponent} using the given key and starts any
 	 * registered {@link Service Services}.
 	 */
+	@Wakeful
 	StartResult startServices(SecretKey dbKey);
 
 	/**
@@ -72,6 +74,7 @@ public interface LifecycleManager {
 	 * registered {@link ExecutorService ExecutorServices}, and closes the
 	 * {@link DatabaseComponent}.
 	 */
+	@Wakeful
 	void stopServices();
 
 	/**
@@ -104,6 +107,7 @@ public interface LifecycleManager {
 		 *
 		 * @param txn A read-write transaction
 		 */
+		@Wakeful
 		void onDatabaseOpened(Transaction txn) throws DbException;
 	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/lifecycle/Service.java

@@ -1,16 +1,20 @@
 package org.briarproject.bramble.api.lifecycle;
 
+import org.briarproject.bramble.api.system.Wakeful;
+
 public interface Service {
 
 	/**
-	 * Starts the service.This method must not be called concurrently with
+	 * Starts the service. This method must not be called concurrently with
 	 * {@link #stopService()}.
 	 */
+	@Wakeful
 	void startService() throws ServiceException;
 
 	/**
 	 * Stops the service. This method must not be called concurrently with
 	 * {@link #startService()}.
 	 */
+	@Wakeful
 	void stopService() throws ServiceException;
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/BluetoothConstants.java

@@ -6,8 +6,16 @@ public interface BluetoothConstants {
 
 	int UUID_BYTES = 16;
 
+	// Transport properties
 	String PROP_ADDRESS = "address";
 	String PROP_UUID = "uuid";
 
-	String PREF_BT_ENABLE = "enable";
+	// Local settings (not shared with contacts)
+	String PREF_ADDRESS_IS_REFLECTED = "addressIsReflected";
+	String PREF_EVER_CONNECTED = "everConnected";
+
+	// Default values for local settings
+	boolean DEFAULT_PREF_PLUGIN_ENABLE = false;
+	boolean DEFAULT_PREF_ADDRESS_IS_REFLECTED = false;
+	boolean DEFAULT_PREF_EVER_CONNECTED = false;
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/LanTcpConstants.java

@@ -7,7 +7,12 @@ public interface LanTcpConstants {
 	// Transport properties (shared with contacts)
 	String PROP_IP_PORTS = "ipPorts";
 	String PROP_PORT = "port";
+	String PROP_IPV6 = "ipv6";
 
-	// A local setting
+	// Local settings (not shared with contacts)
 	String PREF_LAN_IP_PORTS = "ipPorts";
+	String PREF_IPV6 = "ipv6";
+
+	// Default value for PREF_PLUGIN_ENABLE
+	boolean DEFAULT_PREF_PLUGIN_ENABLE = true;
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/Plugin.java

@@ -3,12 +3,56 @@ package org.briarproject.bramble.api.plugin;
 import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.api.settings.SettingsManager;
+import org.briarproject.bramble.api.system.Wakeful;
 
 import java.util.Collection;
 
 @NotNullByDefault
 public interface Plugin {
 
+	enum State {
+
+		/**
+		 * The plugin has not finished starting or has been stopped.
+		 */
+		STARTING_STOPPING,
+
+		/**
+		 * The plugin is disabled by settings. Use {@link #getReasonsDisabled()}
+		 * to find out which settings are responsible.
+		 */
+		DISABLED,
+
+		/**
+		 * The plugin is being enabled and can't yet make or receive
+		 * connections.
+		 */
+		ENABLING,
+
+		/**
+		 * The plugin is enabled and can make or receive connections.
+		 */
+		ACTIVE,
+
+		/**
+		 * The plugin is enabled but can't make or receive connections
+		 */
+		INACTIVE
+	}
+
+	/**
+	 * The string for the boolean preference
+	 * to use with the {@link SettingsManager} to enable or disable the plugin.
+	 */
+	String PREF_PLUGIN_ENABLE = "enable";
+
+	/**
+	 * Reason flag returned by {@link #getReasonsDisabled()} to indicate that
+	 * the plugin has been disabled by the user.
+	 */
+	int REASON_USER = 1;
+
 	/**
 	 * Returns the plugin's transport identifier.
 	 */
@@ -27,17 +71,28 @@ public interface Plugin {
 	/**
 	 * Starts the plugin.
 	 */
+	@Wakeful
 	void start() throws PluginException;
 
 	/**
 	 * Stops the plugin.
 	 */
+	@Wakeful
 	void stop() throws PluginException;
 
 	/**
-	 * Returns true if the plugin is running.
+	 * Returns the current state of the plugin.
 	 */
-	boolean isRunning();
+	State getState();
+
+	/**
+	 * Returns a set of flags indicating why the plugin is
+	 * {@link State#DISABLED disabled}, or 0 if the plugin is not disabled.
+	 * <p>
+	 * The flags used are plugin-specific, except the generic flag
+	 * {@link #REASON_USER}, which may be used by any plugin.
+	 */
+	int getReasonsDisabled();
 
 	/**
 	 * Returns true if the plugin should be polled periodically to attempt to
@@ -54,6 +109,7 @@ public interface Plugin {
 	 * Attempts to create connections using the given transport properties,
 	 * passing any created connections to the corresponding handlers.
 	 */
+	@Wakeful
 	void poll(Collection<Pair<TransportProperties, ConnectionHandler>>
 			properties);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/PluginCallback.java

@@ -1,9 +1,15 @@
 package org.briarproject.bramble.api.plugin;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.Plugin.State;
+import org.briarproject.bramble.api.plugin.event.TransportActiveEvent;
+import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
+import org.briarproject.bramble.api.plugin.event.TransportStateEvent;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.settings.Settings;
 
+import java.util.Collection;
+
 /**
  * An interface through which a transport plugin interacts with the rest of
  * the application.
@@ -21,6 +27,11 @@ public interface PluginCallback extends ConnectionHandler {
 	 */
 	TransportProperties getLocalProperties();
 
+	/**
+	 * Returns the plugin's remote transport properties.
+	 */
+	Collection<TransportProperties> getRemoteProperties();
+
 	/**
 	 * Merges the given settings with the plugin's settings
 	 */
@@ -32,12 +43,17 @@ public interface PluginCallback extends ConnectionHandler {
 	void mergeLocalProperties(TransportProperties p);
 
 	/**
-	 * Signals that the transport is enabled.
+	 * Informs the callback of the plugin's current state.
+	 * <p>
+	 * If the current state is different from the previous state, the callback
+	 * will broadcast a {@link TransportStateEvent}. If the current state is
+	 * {@link State#ACTIVE} and the previous state was not
+	 * {@link State#ACTIVE}, the callback will broadcast a
+	 * {@link TransportActiveEvent}. If the current state is not
+	 * {@link State#ACTIVE} and the previous state was {@link State#ACTIVE},
+	 * the callback will broadcast a {@link TransportInactiveEvent}.
+	 * <p>
+	 * This method can safely be called while holding a lock.
 	 */
-	void transportEnabled();
-
-	/**
-	 * Signals that the transport is disabled.
-	 */
-	void transportDisabled();
+	void pluginStateChanged(State state);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/PluginManager.java

@@ -41,4 +41,17 @@ public interface PluginManager {
 	 * Returns any duplex plugins that support rendezvous.
 	 */
 	Collection<DuplexPlugin> getRendezvousPlugins();
+
+	/**
+	 * Enables or disables the plugin
+	 * identified by the given {@link TransportId}.
+	 * <p>
+	 * Note that this applies the change asynchronously
+	 * and there are no order guarantees.
+	 * <p>
+	 * If no plugin with the given {@link TransportId} is registered,
+	 * this is a no-op.
+	 */
+	void setPluginEnabled(TransportId t, boolean enabled);
+
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/TorConstants.java

@@ -1,9 +1,12 @@
 package org.briarproject.bramble.api.plugin;
 
+import static java.util.concurrent.TimeUnit.DAYS;
+
 public interface TorConstants {
 
 	TransportId ID = new TransportId("org.briarproject.bramble.tor");
 
+	// Transport properties
 	String PROP_ONION_V2 = "onion";
 	String PROP_ONION_V3 = "onion3";
 
@@ -13,14 +16,45 @@ public interface TorConstants {
 	int CONNECT_TO_PROXY_TIMEOUT = 5000; // Milliseconds
 	int EXTRA_SOCKET_TIMEOUT = 30000; // Milliseconds
 
+	// Local settings (not shared with contacts)
 	String PREF_TOR_NETWORK = "network2";
 	String PREF_TOR_PORT = "port";
 	String PREF_TOR_MOBILE = "useMobileData";
 	String PREF_TOR_ONLY_WHEN_CHARGING = "onlyWhenCharging";
+	String HS_PRIVATE_KEY_V2 = "onionPrivKey";
+	String HS_PRIVATE_KEY_V3 = "onionPrivKey3";
+	String HS_V3_CREATED = "onionPrivKey3Created";
 
+	/**
+	 * How long to publish a v3 hidden service before retiring the v2 service.
+	 */
+	long V3_MIGRATION_PERIOD_MS = DAYS.toMillis(180);
+
+	// Values for PREF_TOR_NETWORK
 	int PREF_TOR_NETWORK_AUTOMATIC = 0;
 	int PREF_TOR_NETWORK_WITHOUT_BRIDGES = 1;
 	int PREF_TOR_NETWORK_WITH_BRIDGES = 2;
+	// TODO: Remove when settings migration code is removed
 	int PREF_TOR_NETWORK_NEVER = 3;
 
+	// Default values for local settings
+	boolean DEFAULT_PREF_PLUGIN_ENABLE = true;
+	int DEFAULT_PREF_TOR_NETWORK = PREF_TOR_NETWORK_AUTOMATIC;
+	boolean DEFAULT_PREF_TOR_MOBILE = true;
+	boolean DEFAULT_PREF_TOR_ONLY_WHEN_CHARGING = false;
+
+	/**
+	 * Reason flag returned by {@link Plugin#getReasonsDisabled()}.
+	 */
+	int REASON_BATTERY = 2;
+
+	/**
+	 * Reason flag returned by {@link Plugin#getReasonsDisabled()}.
+	 */
+	int REASON_MOBILE_DATA = 4;
+
+	/**
+	 * Reason flag returned by {@link Plugin#getReasonsDisabled()}.
+	 */
+	int REASON_COUNTRY_BLOCKED = 8;
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/TorDirectory.java

@@ -1,5 +1,6 @@
-package org.briarproject.bramble.api.system;
+package org.briarproject.bramble.api.plugin;
 
+import java.io.File;
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;
 
@@ -11,15 +12,11 @@ import static java.lang.annotation.ElementType.PARAMETER;
 import static java.lang.annotation.RetentionPolicy.RUNTIME;
 
 /**
- * Annotation for injecting a scheduled executor service
- * that can be used to schedule the execution of tasks.
- * <p>
- * The service should <b>only</b> be used for running tasks on other executors
- * at scheduled times.
- * No significant work should be run by the service itself!
+ * Annotation for injecting the {@link File directory} where the Tor plugin
+ * should store its state.
  */
 @Qualifier
 @Target({FIELD, METHOD, PARAMETER})
 @Retention(RUNTIME)
-public @interface Scheduler {
-}
+public @interface TorDirectory {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/WanTcpConstants.java

@@ -4,4 +4,7 @@ public interface WanTcpConstants {
 
 	TransportId ID = new TransportId("org.briarproject.bramble.wan");
 
+	// Default value for PREF_PLUGIN_ENABLE
+	boolean DEFAULT_PREF_PLUGIN_ENABLE = false;
 }
+

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/duplex/DuplexPlugin.java

@@ -8,6 +8,7 @@ import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.rendezvous.KeyMaterialSource;
 import org.briarproject.bramble.api.rendezvous.RendezvousEndpoint;
+import org.briarproject.bramble.api.system.Wakeful;
 
 import javax.annotation.Nullable;
 
@@ -21,6 +22,7 @@ public interface DuplexPlugin extends Plugin {
 	 * Attempts to create and return a connection using the given transport
 	 * properties. Returns null if a connection cannot be created.
 	 */
+	@Wakeful
 	@Nullable
 	DuplexTransportConnection createConnection(TransportProperties p);
 

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/event/BluetoothEnabledEvent.java

@@ -1,15 +0,0 @@
-package org.briarproject.bramble.api.plugin.event;
-
-import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import javax.annotation.concurrent.Immutable;
-
-/**
- * An event that informs the Bluetooth plugin that we have enabled the
- * Bluetooth adapter.
- */
-@Immutable
-@NotNullByDefault
-public class BluetoothEnabledEvent extends Event {
-}

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/event/DisableBluetoothEvent.java

@@ -1,15 +0,0 @@
-package org.briarproject.bramble.api.plugin.event;
-
-import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import javax.annotation.concurrent.Immutable;
-
-/**
- * An event that asks the Bluetooth plugin to disable the Bluetooth adapter if
- * we previously enabled it.
- */
-@Immutable
-@NotNullByDefault
-public class DisableBluetoothEvent extends Event {
-}

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/event/EnableBluetoothEvent.java

@@ -1,14 +0,0 @@
-package org.briarproject.bramble.api.plugin.event;
-
-import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import javax.annotation.concurrent.Immutable;
-
-/**
- * An event that asks the Bluetooth plugin to enable the Bluetooth adapter.
- */
-@Immutable
-@NotNullByDefault
-public class EnableBluetoothEvent extends Event {
-}

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/event/TransportActiveEvent.java

@@ -2,20 +2,22 @@ package org.briarproject.bramble.api.plugin.event;
 
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.Plugin.State;
 import org.briarproject.bramble.api.plugin.TransportId;
 
 import javax.annotation.concurrent.Immutable;
 
 /**
- * An event that is broadcast when a transport is disabled.
+ * An event that is broadcast when a plugin enters the {@link State#ACTIVE}
+ * state.
  */
 @Immutable
 @NotNullByDefault
-public class TransportDisabledEvent extends Event {
+public class TransportActiveEvent extends Event {
 
 	private final TransportId transportId;
 
-	public TransportDisabledEvent(TransportId transportId) {
+	public TransportActiveEvent(TransportId transportId) {
 		this.transportId = transportId;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/event/TransportInactiveEvent.java

@@ -2,20 +2,22 @@ package org.briarproject.bramble.api.plugin.event;
 
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.Plugin.State;
 import org.briarproject.bramble.api.plugin.TransportId;
 
 import javax.annotation.concurrent.Immutable;
 
 /**
- * An event that is broadcast when a transport is enabled.
+ * An event that is broadcast when a plugin leaves the {@link State#ACTIVE}
+ * state.
  */
 @Immutable
 @NotNullByDefault
-public class TransportEnabledEvent extends Event {
+public class TransportInactiveEvent extends Event {
 
 	private final TransportId transportId;
 
-	public TransportEnabledEvent(TransportId transportId) {
+	public TransportInactiveEvent(TransportId transportId) {
 		this.transportId = transportId;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/event/TransportStateEvent.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.api.plugin.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.Plugin.State;
+import org.briarproject.bramble.api.plugin.TransportId;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when the {@link State state} of a plugin changes.
+ */
+@Immutable
+@NotNullByDefault
+public class TransportStateEvent extends Event {
+
+	private final TransportId transportId;
+	private final State state;
+
+	public TransportStateEvent(TransportId transportId, State state) {
+		this.transportId = transportId;
+		this.state = state;
+	}
+
+	public TransportId getTransportId() {
+		return transportId;
+	}
+
+	public State getState() {
+		return state;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/simplex/SimplexPlugin.java

@@ -5,6 +5,7 @@ import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
 import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
 import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.api.system.Wakeful;
 
 import javax.annotation.Nullable;
 
@@ -18,6 +19,7 @@ public interface SimplexPlugin extends Plugin {
 	 * Attempts to create and return a reader for the given transport
 	 * properties. Returns null if a reader cannot be created.
 	 */
+	@Wakeful
 	@Nullable
 	TransportConnectionReader createReader(TransportProperties p);
 
@@ -25,6 +27,7 @@ public interface SimplexPlugin extends Plugin {
 	 * Attempts to create and return a writer for the given transport
 	 * properties. Returns null if a writer cannot be created.
 	 */
+	@Wakeful
 	@Nullable
 	TransportConnectionWriter createWriter(TransportProperties p);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/properties/TransportPropertyConstants.java

@@ -12,6 +12,11 @@ public interface TransportPropertyConstants {
 	 */
 	int MAX_PROPERTY_LENGTH = 100;
 
+	/**
+	 * Prefix for keys that represent reflected properties.
+	 */
+	String REFLECTED_PROPERTY_PREFIX = "u:";
+
 	/**
 	 * Message metadata key for the transport ID of a local or remote update,
 	 * as a BDF string.

bramble-api/src/main/java/org/briarproject/bramble/api/properties/event/RemoteTransportPropertiesUpdatedEvent.java

@@ -0,0 +1,27 @@
+package org.briarproject.bramble.api.properties.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when {@link TransportProperties} are received
+ * from a contact.
+ */
+@Immutable
+@NotNullByDefault
+public class RemoteTransportPropertiesUpdatedEvent extends Event {
+
+	private final TransportId transportId;
+
+	public RemoteTransportPropertiesUpdatedEvent(TransportId transportId) {
+		this.transportId = transportId;
+	}
+
+	public TransportId getTransportId() {
+		return transportId;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/SyncConstants.java

@@ -29,10 +29,15 @@ public interface SyncConstants {
 	 */
 	int MESSAGE_HEADER_LENGTH = UniqueId.LENGTH + 8;
 
+	/**
+	 * The maximum length of a block in bytes.
+	 */
+	int MAX_BLOCK_LENGTH = 32 * 1024; // 32 KiB
+
 	/**
 	 * The maximum length of a message body in bytes.
 	 */
-	int MAX_MESSAGE_BODY_LENGTH = 32 * 1024; // 32 KiB
+	int MAX_MESSAGE_BODY_LENGTH = MAX_BLOCK_LENGTH;
 
 	/**
 	 * The maximum length of a message in bytes.

bramble-api/src/main/java/org/briarproject/bramble/api/sync/SyncSessionFactory.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.api.sync;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.transport.StreamWriter;
 
 import java.io.InputStream;
@@ -14,10 +15,10 @@ public interface SyncSessionFactory {
 	SyncSession createIncomingSession(ContactId c, InputStream in,
 			PriorityHandler handler);
 
-	SyncSession createSimplexOutgoingSession(ContactId c, int maxLatency,
-			StreamWriter streamWriter);
+	SyncSession createSimplexOutgoingSession(ContactId c, TransportId t,
+			int maxLatency, StreamWriter streamWriter);
 
-	SyncSession createDuplexOutgoingSession(ContactId c, int maxLatency,
-			int maxIdleTime, StreamWriter streamWriter,
+	SyncSession createDuplexOutgoingSession(ContactId c, TransportId t,
+			int maxLatency, int maxIdleTime, StreamWriter streamWriter,
 			@Nullable Priority priority);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/sync/event/CloseSyncConnectionsEvent.java

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.api.sync.event;
+
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when all sync connections using a given
+ * transport should be closed.
+ */
+@Immutable
+@NotNullByDefault
+public class CloseSyncConnectionsEvent extends Event {
+
+	private final TransportId transportId;
+
+	public CloseSyncConnectionsEvent(TransportId transportId) {
+		this.transportId = transportId;
+	}
+
+	public TransportId getTransportId() {
+		return transportId;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/event/MessageToRequestEvent.java

@@ -1,26 +0,0 @@
-package org.briarproject.bramble.api.sync.event;
-
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import javax.annotation.concurrent.Immutable;
-
-/**
- * An event that is broadcast when a message is offered by a contact and needs
- * to be requested.
- */
-@Immutable
-@NotNullByDefault
-public class MessageToRequestEvent extends Event {
-
-	private final ContactId contactId;
-
-	public MessageToRequestEvent(ContactId contactId) {
-		this.contactId = contactId;
-	}
-
-	public ContactId getContactId() {
-		return contactId;
-	}
-}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/event/MessagesToAckEvent.java

@@ -7,16 +7,16 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import javax.annotation.concurrent.Immutable;
 
 /**
- * An event that is broadcast when a message is received from, or offered by, a
- * contact and needs to be acknowledged.
+ * An event that is broadcast when one or more messages are received from, or
+ * offered by, a contact and need to be acknowledged.
  */
 @Immutable
 @NotNullByDefault
-public class MessageToAckEvent extends Event {
+public class MessagesToAckEvent extends Event {
 
 	private final ContactId contactId;
 
-	public MessageToAckEvent(ContactId contactId) {
+	public MessagesToAckEvent(ContactId contactId) {
 		this.contactId = contactId;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/sync/event/MessagesToRequestEvent.java

@@ -0,0 +1,39 @@
+package org.briarproject.bramble.api.sync.event;
+
+import org.briarproject.bramble.api.Consumable;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import java.util.Collection;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when one or more messages are offered by a
+ * contact and need to be requested.
+ */
+@Immutable
+@NotNullByDefault
+public class MessagesToRequestEvent extends Event {
+
+	private final ContactId contactId;
+	private final Consumable<Collection<MessageId>> ids;
+
+	public MessagesToRequestEvent(ContactId contactId,
+			Collection<MessageId> ids) {
+		this.contactId = contactId;
+		this.ids = new Consumable<>(ids);
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	@Nullable
+	public Collection<MessageId> consumeIds() {
+		return ids.consume();
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/system/TaskScheduler.java

@@ -0,0 +1,43 @@
+package org.briarproject.bramble.api.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.concurrent.Executor;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * A service that can be used to schedule the execution of tasks.
+ */
+@NotNullByDefault
+public interface TaskScheduler {
+
+	/**
+	 * Submits the given task to the given executor after the given delay.
+	 * <p>
+	 * If the platform supports wake locks, a wake lock will be held while
+	 * submitting and running the task.
+	 */
+	Cancellable schedule(Runnable task, Executor executor, long delay,
+			TimeUnit unit);
+
+	/**
+	 * Submits the given task to the given executor after the given delay,
+	 * and then repeatedly with the given interval between executions
+	 * (measured from the end of one execution to the beginning of the next).
+	 * <p>
+	 * If the platform supports wake locks, a wake lock will be held while
+	 * submitting and running the task.
+	 */
+	Cancellable scheduleWithFixedDelay(Runnable task, Executor executor,
+			long delay, long interval, TimeUnit unit);
+
+	interface Cancellable {
+
+		/**
+		 * Cancels the task if it has not already started running. If the task
+		 * is {@link #scheduleWithFixedDelay(Runnable, Executor, long, long, TimeUnit) periodic},
+		 * all future executions of the task are cancelled.
+		 */
+		void cancel();
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/system/Wakeful.java

@@ -0,0 +1,19 @@
+package org.briarproject.bramble.api.system;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+/**
+ * Annotation for methods that must be called while holding a wake lock, if
+ * the platform supports wake locks.
+ */
+@Qualifier
+@Target(METHOD)
+@Retention(RUNTIME)
+public @interface Wakeful {
+}

bramble-api/src/main/java/org/briarproject/bramble/api/system/WakefulIoExecutor.java

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.api.system;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.METHOD;
+import static java.lang.annotation.ElementType.PARAMETER;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+/**
+ * Annotation for injecting the executor for long-running IO tasks that should
+ * run without sleeping. Also used for annotating methods that should run on
+ * this executor.
+ * <p>
+ * The contract of this executor is that tasks may be run concurrently, and
+ * submitting a task will never block. Tasks must not run indefinitely. Tasks
+ * submitted during shutdown are discarded.
+ */
+@Qualifier
+@Target({FIELD, METHOD, PARAMETER})
+@Retention(RUNTIME)
+public @interface WakefulIoExecutor {
+}

bramble-api/src/main/java/org/briarproject/bramble/util/PrivacyUtils.java

@@ -2,13 +2,17 @@ package org.briarproject.bramble.util;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
-import java.net.Inet6Address;
+import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.SocketAddress;
 
 import javax.annotation.Nullable;
 
+import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
+import static org.briarproject.bramble.util.StringUtils.isValidMac;
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+
 @NotNullByDefault
 public class PrivacyUtils {
 
@@ -19,7 +23,7 @@ public class PrivacyUtils {
 
 	@Nullable
 	public static String scrubMacAddress(@Nullable String address) {
-		if (address == null || address.length() == 0) return null;
+		if (isNullOrEmpty(address) || !isValidMac(address)) return address;
 		// this is a fake address we need to know about
 		if (address.equals("02:00:00:00:00:00")) return address;
 		// keep first and last octet of MAC address
@@ -27,39 +31,37 @@ public class PrivacyUtils {
 				+ address.substring(14, 17);
 	}
 
-	@Nullable
 	public static String scrubInetAddress(InetAddress address) {
-		// don't scrub link and site local addresses
-		if (address.isLinkLocalAddress() || address.isSiteLocalAddress())
-			return address.toString();
-		// completely scrub IPv6 addresses
-		if (address instanceof Inet6Address) return "[scrubbed]";
-		// keep first and last octet of IPv4 addresses
-		return scrubInetAddress(address.toString());
+		if (address instanceof Inet4Address) {
+			// Don't scrub local IPv4 addresses
+			if (address.isLoopbackAddress() || address.isLinkLocalAddress() ||
+					address.isSiteLocalAddress()) {
+				return address.getHostAddress();
+			}
+			// Keep first and last octet of non-local IPv4 addresses
+			return scrubIpv4Address(address.getAddress());
+		} else {
+			// Keep first and last octet of IPv6 addresses
+			return scrubIpv6Address(address.getAddress());
+		}
 	}
 
-	@Nullable
-	public static String scrubInetAddress(@Nullable String address) {
-		if (address == null) return null;
-
-		int firstDot = address.indexOf(".");
-		if (firstDot == -1) return "[scrubbed]";
-		String prefix = address.substring(0, firstDot + 1);
-		int lastDot = address.lastIndexOf(".");
-		String suffix = address.substring(lastDot, address.length());
-		return prefix + "[scrubbed]" + suffix;
+	private static String scrubIpv4Address(byte[] ipv4) {
+		return (ipv4[0] & 0xFF) + ".[scrubbed]." + (ipv4[3] & 0xFF);
+	}
+
+	private static String scrubIpv6Address(byte[] ipv6) {
+		String hex = toHexString(ipv6).toLowerCase();
+		return hex.substring(0, 2) + "[scrubbed]" + hex.substring(30);
 	}
 
-	@Nullable
 	public static String scrubSocketAddress(InetSocketAddress address) {
-		InetAddress inetAddress = address.getAddress();
-		return scrubInetAddress(inetAddress);
+		return scrubInetAddress(address.getAddress());
 	}
 
-	@Nullable
 	public static String scrubSocketAddress(SocketAddress address) {
 		if (address instanceof InetSocketAddress)
 			return scrubSocketAddress((InetSocketAddress) address);
-		return scrubInetAddress(address.toString());
+		return "[scrubbed]";
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreEagerSingletons.java

@@ -9,7 +9,6 @@ import org.briarproject.bramble.plugin.PluginModule;
 import org.briarproject.bramble.properties.PropertiesModule;
 import org.briarproject.bramble.rendezvous.RendezvousModule;
 import org.briarproject.bramble.sync.validation.ValidationModule;
-import org.briarproject.bramble.system.SystemModule;
 import org.briarproject.bramble.transport.TransportModule;
 import org.briarproject.bramble.versioning.VersioningModule;
 
@@ -31,8 +30,6 @@ public interface BrambleCoreEagerSingletons {
 
 	void inject(RendezvousModule.EagerSingletons init);
 
-	void inject(SystemModule.EagerSingletons init);
-
 	void inject(TransportModule.EagerSingletons init);
 
 	void inject(ValidationModule.EagerSingletons init);
@@ -50,7 +47,6 @@ public interface BrambleCoreEagerSingletons {
 			c.inject(new RendezvousModule.EagerSingletons());
 			c.inject(new PluginModule.EagerSingletons());
 			c.inject(new PropertiesModule.EagerSingletons());
-			c.inject(new SystemModule.EagerSingletons());
 			c.inject(new TransportModule.EagerSingletons());
 			c.inject(new ValidationModule.EagerSingletons());
 			c.inject(new VersioningModule.EagerSingletons());

bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreModule.java

@@ -21,7 +21,7 @@ import org.briarproject.bramble.rendezvous.RendezvousModule;
 import org.briarproject.bramble.settings.SettingsModule;
 import org.briarproject.bramble.sync.SyncModule;
 import org.briarproject.bramble.sync.validation.ValidationModule;
-import org.briarproject.bramble.system.SystemModule;
+import org.briarproject.bramble.system.ClockModule;
 import org.briarproject.bramble.transport.TransportModule;
 import org.briarproject.bramble.versioning.VersioningModule;
 
@@ -29,6 +29,7 @@ import dagger.Module;
 
 @Module(includes = {
 		ClientModule.class,
+		ClockModule.class,
 		ConnectionModule.class,
 		ContactModule.class,
 		CryptoModule.class,
@@ -48,7 +49,6 @@ import dagger.Module;
 		RendezvousModule.class,
 		SettingsModule.class,
 		SyncModule.class,
-		SystemModule.class,
 		TransportModule.class,
 		ValidationModule.class,
 		VersioningModule.class

bramble-core/src/main/java/org/briarproject/bramble/client/ClientHelperImpl.java

@@ -116,25 +116,27 @@ class ClientHelperImpl implements ClientHelper {
 	}
 
 	@Override
-	public Message getMessage(MessageId m) throws DbException {
-		return db.transactionWithResult(true, txn -> getMessage(txn, m));
+	public Message getSmallMessage(MessageId m) throws DbException {
+		return db.transactionWithResult(true, txn -> getSmallMessage(txn, m));
 	}
 
 	@Override
-	public Message getMessage(Transaction txn, MessageId m) throws DbException {
-		return db.getMessage(txn, m);
+	public Message getSmallMessage(Transaction txn, MessageId m)
+			throws DbException {
+		return db.getSmallMessage(txn, m);
 	}
 
 	@Override
-	public BdfList getMessageAsList(MessageId m) throws DbException,
-			FormatException {
-		return db.transactionWithResult(true, txn -> getMessageAsList(txn, m));
-	}
-
-	@Override
-	public BdfList getMessageAsList(Transaction txn, MessageId m)
+	public BdfList getSmallMessageAsList(MessageId m)
 			throws DbException, FormatException {
-		return toList(db.getMessage(txn, m).getBody());
+		return db.transactionWithResult(true, txn ->
+				getSmallMessageAsList(txn, m));
+	}
+
+	@Override
+	public BdfList getSmallMessageAsList(Transaction txn, MessageId m)
+			throws DbException, FormatException {
+		return toList(db.getSmallMessage(txn, m).getBody());
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/connection/ConnectionRegistryImpl.java

@@ -61,7 +61,19 @@ class ConnectionRegistryImpl implements ConnectionRegistry {
 	}
 
 	@Override
-	public void registerConnection(ContactId c, TransportId t,
+	public void registerIncomingConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn) {
+		registerConnection(c, t, conn, true);
+	}
+
+	@Override
+	public void registerOutgoingConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, Priority priority) {
+		registerConnection(c, t, conn, false);
+		setPriority(c, t, conn, priority);
+	}
+
+	private void registerConnection(ContactId c, TransportId t,
 			InterruptibleConnection conn, boolean incoming) {
 		if (LOG.isLoggable(INFO)) {
 			if (incoming) LOG.info("Incoming connection registered: " + t);
@@ -214,7 +226,8 @@ class ConnectionRegistryImpl implements ConnectionRegistry {
 	@Override
 	public boolean isConnected(ContactId c) {
 		synchronized (lock) {
-			return contactConnections.containsKey(c);
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			return recs != null && !recs.isEmpty();
 		}
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/connection/DuplexSyncConnection.java

@@ -47,20 +47,24 @@ abstract class DuplexSyncConnection extends SyncConnection
 
 	@Override
 	public void interruptOutgoingSession() {
+		SyncSession out = null;
 		synchronized (interruptLock) {
 			if (outgoingSession == null) interruptWaiting = true;
-			else outgoingSession.interrupt();
+			else out = outgoingSession;
 		}
+		if (out != null) out.interrupt();
 	}
 
 	void setOutgoingSession(SyncSession outgoingSession) {
+		boolean interruptWasWaiting = false;
 		synchronized (interruptLock) {
 			this.outgoingSession = outgoingSession;
 			if (interruptWaiting) {
-				outgoingSession.interrupt();
+				interruptWasWaiting = true;
 				interruptWaiting = false;
 			}
 		}
+		if (interruptWasWaiting) outgoingSession.interrupt();
 	}
 
 	DuplexSyncConnection(KeyManager keyManager,
@@ -99,6 +103,7 @@ abstract class DuplexSyncConnection extends SyncConnection
 				w.getOutputStream(), ctx);
 		ContactId c = requireNonNull(ctx.getContactId());
 		return syncSessionFactory.createDuplexOutgoingSession(c,
-				w.getMaxLatency(), w.getMaxIdleTime(), streamWriter, priority);
+				ctx.getTransportId(), w.getMaxLatency(), w.getMaxIdleTime(),
+				streamWriter, priority);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/connection/IncomingDuplexSyncConnection.java

@@ -59,8 +59,8 @@ class IncomingDuplexSyncConnection extends DuplexSyncConnection
 			onReadError(true);
 			return;
 		}
-		connectionRegistry.registerConnection(contactId, transportId,
-				this, true);
+		connectionRegistry.registerIncomingConnection(contactId, transportId,
+				this);
 		// Start the outgoing session on another thread
 		ioExecutor.execute(() -> runOutgoingSession(contactId));
 		try {

bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingDuplexSyncConnection.java

@@ -104,9 +104,8 @@ class OutgoingDuplexSyncConnection extends DuplexSyncConnection
 			onReadError();
 			return;
 		}
-		connectionRegistry.registerConnection(contactId, transportId,
-				this, false);
-		connectionRegistry.setPriority(contactId, transportId, this, priority);
+		connectionRegistry.registerOutgoingConnection(contactId, transportId,
+				this, priority);
 		try {
 			// Store any transport properties discovered from the connection
 			transportPropertyManager.addRemotePropertiesFromConnection(

bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingSimplexSyncConnection.java

@@ -72,7 +72,7 @@ class OutgoingSimplexSyncConnection extends SyncConnection implements Runnable {
 				w.getOutputStream(), ctx);
 		ContactId c = requireNonNull(ctx.getContactId());
 		return syncSessionFactory.createSimplexOutgoingSession(c,
-				w.getMaxLatency(), streamWriter);
+				ctx.getTransportId(), w.getMaxLatency(), streamWriter);
 	}
 }
 

bramble-core/src/main/java/org/briarproject/bramble/db/Database.java

@@ -12,6 +12,7 @@ import org.briarproject.bramble.api.db.DataTooOldException;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.MessageDeletedException;
+import org.briarproject.bramble.api.db.MessageTooLargeException;
 import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.identity.Author;
@@ -125,11 +126,6 @@ interface Database<T> {
 	void addMessageDependency(T txn, Message dependent, MessageId dependency,
 			MessageState dependentState) throws DbException;
 
-	/**
-	 * Records that a message has been offered by the given contact.
-	 */
-	void addOfferedMessage(T txn, ContactId c, MessageId m) throws DbException;
-
 	/**
 	 * Stores a pending contact.
 	 */
@@ -218,13 +214,6 @@ interface Database<T> {
 	boolean containsVisibleMessage(T txn, ContactId c, MessageId m)
 			throws DbException;
 
-	/**
-	 * Returns the number of messages offered by the given contact.
-	 * <p/>
-	 * Read-only.
-	 */
-	int countOfferedMessages(T txn, ContactId c) throws DbException;
-
 	/**
 	 * Deletes the message with the given ID. Unlike
 	 * {@link #removeMessage(Object, MessageId)}, the message ID and any other
@@ -332,13 +321,14 @@ interface Database<T> {
 	Collection<Identity> getIdentities(T txn) throws DbException;
 
 	/**
-	 * Returns the message with the given ID.
+	 * Returns the single-block message with the given ID.
 	 * <p/>
 	 * Read-only.
 	 *
 	 * @throws MessageDeletedException if the message has been deleted
+	 * @throws MessageTooLargeException if the message has more than one block
 	 */
-	Message getMessage(T txn, MessageId m) throws DbException;
+	Message getSmallMessage(T txn, MessageId m) throws DbException;
 
 	/**
 	 * Returns the IDs and states of all dependencies of the given message.
@@ -457,13 +447,13 @@ interface Database<T> {
 			int maxMessages, int maxLatency) throws DbException;
 
 	/**
-	 * Returns the IDs of some messages that are eligible to be requested from
-	 * the given contact, up to the given number of messages.
+	 * Returns the IDs of some single-block messages that are eligible to be
+	 * offered to the given contact, up to the given number of messages.
 	 * <p/>
 	 * Read-only.
 	 */
-	Collection<MessageId> getMessagesToRequest(T txn, ContactId c,
-			int maxMessages) throws DbException;
+	Collection<MessageId> getSmallMessagesToOffer(T txn, ContactId c,
+			int maxMessages, int maxLatency) throws DbException;
 
 	/**
 	 * Returns the IDs of some messages that are eligible to be sent to the
@@ -474,6 +464,15 @@ interface Database<T> {
 	Collection<MessageId> getMessagesToSend(T txn, ContactId c, int maxLength,
 			int maxLatency) throws DbException;
 
+	/**
+	 * Returns the IDs of some single-block messages that are eligible to be
+	 * sent to the given contact, up to the given total length.
+	 * <p/>
+	 * Read-only.
+	 */
+	Collection<MessageId> getSmallMessagesToSend(T txn, ContactId c,
+			int maxLength, int maxLatency) throws DbException;
+
 	/**
 	 * Returns the IDs of any messages that need to be validated.
 	 * <p/>
@@ -636,13 +635,6 @@ interface Database<T> {
 	 */
 	void removeMessage(T txn, MessageId m) throws DbException;
 
-	/**
-	 * Removes the given offered messages that were offered by the given
-	 * contact.
-	 */
-	void removeOfferedMessages(T txn, ContactId c,
-			Collection<MessageId> requested) throws DbException;
-
 	/**
 	 * Removes a pending contact (and all associated state) from the database.
 	 */

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseComponentImpl.java

@@ -61,10 +61,10 @@ import org.briarproject.bramble.api.sync.event.MessageAddedEvent;
 import org.briarproject.bramble.api.sync.event.MessageRequestedEvent;
 import org.briarproject.bramble.api.sync.event.MessageSharedEvent;
 import org.briarproject.bramble.api.sync.event.MessageStateChangedEvent;
-import org.briarproject.bramble.api.sync.event.MessageToAckEvent;
-import org.briarproject.bramble.api.sync.event.MessageToRequestEvent;
 import org.briarproject.bramble.api.sync.event.MessagesAckedEvent;
 import org.briarproject.bramble.api.sync.event.MessagesSentEvent;
+import org.briarproject.bramble.api.sync.event.MessagesToAckEvent;
+import org.briarproject.bramble.api.sync.event.MessagesToRequestEvent;
 import org.briarproject.bramble.api.sync.event.SyncVersionsUpdatedEvent;
 import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.transport.KeySetId;
@@ -91,7 +91,6 @@ import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
 import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
 import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
-import static org.briarproject.bramble.db.DatabaseConstants.MAX_OFFERED_MESSAGES;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
@@ -406,19 +405,22 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	@Nullable
 	@Override
 	public Collection<Message> generateBatch(Transaction transaction,
-			ContactId c, int maxLength, int maxLatency) throws DbException {
+			ContactId c, int maxLength, int maxLatency, boolean small)
+			throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
 			throw new NoSuchContactException();
-		Collection<MessageId> ids =
-				db.getMessagesToSend(txn, c, maxLength, maxLatency);
+		Collection<MessageId> ids;
+		if (small)
+			ids = db.getSmallMessagesToSend(txn, c, maxLength, maxLatency);
+		else ids = db.getMessagesToSend(txn, c, maxLength, maxLatency);
+		if (ids.isEmpty()) return null;
 		List<Message> messages = new ArrayList<>(ids.size());
 		for (MessageId m : ids) {
-			messages.add(db.getMessage(txn, m));
+			messages.add(db.getSmallMessage(txn, m));
 			db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
 		}
-		if (ids.isEmpty()) return null;
 		db.lowerRequestedFlag(txn, c, ids);
 		transaction.attach(new MessagesSentEvent(c, ids));
 		return messages;
@@ -427,34 +429,21 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	@Nullable
 	@Override
 	public Offer generateOffer(Transaction transaction, ContactId c,
-			int maxMessages, int maxLatency) throws DbException {
+			int maxMessages, int maxLatency, boolean small) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
 			throw new NoSuchContactException();
-		Collection<MessageId> ids =
-				db.getMessagesToOffer(txn, c, maxMessages, maxLatency);
+		Collection<MessageId> ids;
+		if (small)
+			ids = db.getSmallMessagesToOffer(txn, c, maxMessages, maxLatency);
+		else ids = db.getMessagesToOffer(txn, c, maxMessages, maxLatency);
 		if (ids.isEmpty()) return null;
 		for (MessageId m : ids)
 			db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
 		return new Offer(ids);
 	}
 
-	@Nullable
-	@Override
-	public Request generateRequest(Transaction transaction, ContactId c,
-			int maxMessages) throws DbException {
-		if (transaction.isReadOnly()) throw new IllegalArgumentException();
-		T txn = unbox(transaction);
-		if (!db.containsContact(txn, c))
-			throw new NoSuchContactException();
-		Collection<MessageId> ids = db.getMessagesToRequest(txn, c,
-				maxMessages);
-		if (ids.isEmpty()) return null;
-		db.removeOfferedMessages(txn, c, ids);
-		return new Request(ids);
-	}
-
 	@Nullable
 	@Override
 	public Collection<Message> generateRequestedBatch(Transaction transaction,
@@ -465,12 +454,12 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 			throw new NoSuchContactException();
 		Collection<MessageId> ids =
 				db.getRequestedMessagesToSend(txn, c, maxLength, maxLatency);
+		if (ids.isEmpty()) return null;
 		List<Message> messages = new ArrayList<>(ids.size());
 		for (MessageId m : ids) {
-			messages.add(db.getMessage(txn, m));
+			messages.add(db.getSmallMessage(txn, m));
 			db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
 		}
-		if (ids.isEmpty()) return null;
 		db.lowerRequestedFlag(txn, c, ids);
 		transaction.attach(new MessagesSentEvent(c, ids));
 		return messages;
@@ -559,12 +548,12 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Message getMessage(Transaction transaction, MessageId m)
+	public Message getSmallMessage(Transaction transaction, MessageId m)
 			throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
 			throw new NoSuchMessageException();
-		return db.getMessage(txn, m);
+		return db.getSmallMessage(txn, m);
 	}
 
 	@Override
@@ -819,7 +808,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 				db.addMessage(txn, m, UNKNOWN, false, false, c);
 				transaction.attach(new MessageAddedEvent(m, c));
 			}
-			transaction.attach(new MessageToAckEvent(c));
+			transaction.attach(new MessagesToAckEvent(c));
 		}
 	}
 
@@ -830,21 +819,20 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		T txn = unbox(transaction);
 		if (!db.containsContact(txn, c))
 			throw new NoSuchContactException();
-		boolean ack = false, request = false;
-		int count = db.countOfferedMessages(txn, c);
+		boolean ack = false;
+		List<MessageId> request = new ArrayList<>(o.getMessageIds().size());
 		for (MessageId m : o.getMessageIds()) {
 			if (db.containsVisibleMessage(txn, c, m)) {
 				db.raiseSeenFlag(txn, c, m);
 				db.raiseAckFlag(txn, c, m);
 				ack = true;
-			} else if (count < MAX_OFFERED_MESSAGES) {
-				db.addOfferedMessage(txn, c, m);
-				request = true;
-				count++;
+			} else {
+				request.add(m);
 			}
 		}
-		if (ack) transaction.attach(new MessageToAckEvent(c));
-		if (request) transaction.attach(new MessageToRequestEvent(c));
+		if (ack) transaction.attach(new MessagesToAckEvent(c));
+		if (!request.isEmpty())
+			transaction.attach(new MessagesToRequestEvent(c, request));
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseConstants.java

@@ -6,13 +6,6 @@ import static java.util.concurrent.TimeUnit.DAYS;
 
 interface DatabaseConstants {
 
-	/**
-	 * The maximum number of offered messages from each contact that will be
-	 * stored. If offers arrive more quickly than requests can be sent and this
-	 * limit is reached, additional offers will not be stored.
-	 */
-	int MAX_OFFERED_MESSAGES = 1000;
-
 	/**
 	 * The namespace of the {@link Settings} where the database schema version
 	 * is stored.

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseModule.java

@@ -6,7 +6,6 @@ import org.briarproject.bramble.api.db.TransactionManager;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.event.EventExecutor;
 import org.briarproject.bramble.api.lifecycle.ShutdownManager;
-import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.system.Clock;
 
 import java.sql.Connection;
@@ -22,9 +21,8 @@ public class DatabaseModule {
 
 	@Provides
 	@Singleton
-	Database<Connection> provideDatabase(DatabaseConfig config,
-			MessageFactory messageFactory, Clock clock) {
-		return new H2Database(config, messageFactory, clock);
+	Database<Connection> provideDatabase(DatabaseConfig config, Clock clock) {
+		return new H2Database(config, clock);
 	}
 
 	@Provides

bramble-core/src/main/java/org/briarproject/bramble/db/H2Database.java

@@ -6,7 +6,6 @@ import org.briarproject.bramble.api.db.DbClosedException;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.util.StringUtils;
 
@@ -51,9 +50,8 @@ class H2Database extends JdbcDatabase {
 	private volatile SecretKey key = null;
 
 	@Inject
-	H2Database(DatabaseConfig config, MessageFactory messageFactory,
-			Clock clock) {
-		super(dbTypes, messageFactory, clock);
+	H2Database(DatabaseConfig config, Clock clock) {
+		super(dbTypes, clock);
 		this.config = config;
 		File dir = config.getDatabaseDirectory();
 		String path = new File(dir, "db").getAbsolutePath();

bramble-core/src/main/java/org/briarproject/bramble/db/HyperSqlDatabase.java

@@ -6,7 +6,6 @@ import org.briarproject.bramble.api.db.DbClosedException;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.util.StringUtils;
 
@@ -51,9 +50,8 @@ class HyperSqlDatabase extends JdbcDatabase {
 	private volatile SecretKey key = null;
 
 	@Inject
-	HyperSqlDatabase(DatabaseConfig config, MessageFactory messageFactory,
-			Clock clock) {
-		super(dbTypes, messageFactory, clock);
+	HyperSqlDatabase(DatabaseConfig config, Clock clock) {
+		super(dbTypes, clock);
 		this.config = config;
 		File dir = config.getDatabaseDirectory();
 		String path = new File(dir, "db").getAbsolutePath();

bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java

@@ -16,6 +16,7 @@ import org.briarproject.bramble.api.db.DataTooOldException;
 import org.briarproject.bramble.api.db.DbClosedException;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.MessageDeletedException;
+import org.briarproject.bramble.api.db.MessageTooLargeException;
 import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.db.MigrationListener;
 import org.briarproject.bramble.api.identity.Author;
@@ -30,7 +31,6 @@ import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.Group.Visibility;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
-import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.validation.MessageState;
@@ -76,6 +76,7 @@ import static org.briarproject.bramble.api.db.Metadata.REMOVE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
 import static org.briarproject.bramble.api.sync.Group.Visibility.VISIBLE;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_BLOCK_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
 import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
 import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
@@ -98,7 +99,7 @@ import static org.briarproject.bramble.util.LogUtils.now;
 abstract class JdbcDatabase implements Database<Connection> {
 
 	// Package access for testing
-	static final int CODE_SCHEMA_VERSION = 47;
+	static final int CODE_SCHEMA_VERSION = 49;
 
 	// Time period offsets for incoming transport keys
 	private static final int OFFSET_PREV = -1;
@@ -180,8 +181,9 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " state INT NOT NULL,"
 					+ " shared BOOLEAN NOT NULL,"
 					+ " temporary BOOLEAN NOT NULL,"
-					+ " length INT NOT NULL,"
-					+ " raw BLOB," // Null if message has been deleted
+					+ " length INT NOT NULL," // Includes message header
+					+ " deleted BOOLEAN NOT NULL,"
+					+ " blockCount INT NOT NULL,"
 					+ " PRIMARY KEY (messageId),"
 					+ " FOREIGN KEY (groupId)"
 					+ " REFERENCES groups (groupId)"
@@ -218,13 +220,15 @@ abstract class JdbcDatabase implements Database<Connection> {
 					+ " REFERENCES messages (messageId)"
 					+ " ON DELETE CASCADE)";
 
-	private static final String CREATE_OFFERS =
-			"CREATE TABLE offers"
-					+ " (messageId _HASH NOT NULL," // Not a foreign key
-					+ " contactId INT NOT NULL,"
-					+ " PRIMARY KEY (messageId, contactId),"
-					+ " FOREIGN KEY (contactId)"
-					+ " REFERENCES contacts (contactId)"
+	private static final String CREATE_BLOCKS =
+			"CREATE TABLE blocks"
+					+ " (messageId _HASH NOT NULL,"
+					+ " blockNumber INT NOT NULL,"
+					+ " blockLength INT NOT NULL," // Excludes block header
+					+ " data BLOB," // Null if message has been deleted
+					+ " PRIMARY KEY (messageId, blockNumber),"
+					+ " FOREIGN KEY (messageId)"
+					+ " REFERENCES messages (messageId)"
 					+ " ON DELETE CASCADE)";
 
 	private static final String CREATE_STATUSES =
@@ -339,7 +343,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 	private static final Logger LOG =
 			getLogger(JdbcDatabase.class.getName());
 
-	private final MessageFactory messageFactory;
 	private final Clock clock;
 	private final DatabaseTypes dbTypes;
 
@@ -359,10 +362,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 
 	protected abstract void compactAndClose() throws DbException;
 
-	JdbcDatabase(DatabaseTypes databaseTypes, MessageFactory messageFactory,
-			Clock clock) {
+	JdbcDatabase(DatabaseTypes databaseTypes, Clock clock) {
 		this.dbTypes = databaseTypes;
-		this.messageFactory = messageFactory;
 		this.clock = clock;
 	}
 
@@ -440,10 +441,12 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (LOG.isLoggable(INFO))
 					LOG.info("Migrating from schema " + start + " to " + end);
 				if (listener != null) listener.onDatabaseMigration();
+				long startTime = now();
 				// Apply the migration
 				m.migrate(txn);
 				// Store the new schema version
 				storeSchemaVersion(txn, end);
+				logDuration(LOG, "Migration", startTime);
 				dataSchemaVersion = end;
 			}
 		}
@@ -463,7 +466,9 @@ abstract class JdbcDatabase implements Database<Connection> {
 				new Migration43_44(dbTypes),
 				new Migration44_45(),
 				new Migration45_46(),
-				new Migration46_47(dbTypes)
+				new Migration46_47(dbTypes),
+				new Migration47_48(dbTypes),
+				new Migration48_49()
 		);
 	}
 
@@ -508,7 +513,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_MESSAGES));
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_MESSAGE_METADATA));
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_MESSAGE_DEPENDENCIES));
-			s.executeUpdate(dbTypes.replaceTypes(CREATE_OFFERS));
+			s.executeUpdate(dbTypes.replaceTypes(CREATE_BLOCKS));
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_STATUSES));
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_TRANSPORTS));
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_PENDING_CONTACTS));
@@ -726,7 +731,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 		ResultSet rs = null;
 		try {
 			String sql = "SELECT messageId, timestamp, state, shared,"
-					+ " length, raw IS NULL"
+					+ " length, deleted"
 					+ " FROM messages"
 					+ " WHERE groupId = ?";
 			ps = txn.prepareStatement(sql);
@@ -739,9 +744,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 				boolean messageShared = rs.getBoolean(4);
 				int length = rs.getInt(5);
 				boolean deleted = rs.getBoolean(6);
-				boolean seen = removeOfferedMessage(txn, c, id);
 				addStatus(txn, id, c, g, timestamp, length, state, groupShared,
-						messageShared, deleted, seen);
+						messageShared, deleted, false);
 			}
 			rs.close();
 			ps.close();
@@ -788,8 +792,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 		PreparedStatement ps = null;
 		try {
 			String sql = "INSERT INTO messages (messageId, groupId, timestamp,"
-					+ " state, shared, temporary, length, raw)"
-					+ " VALUES (?, ?, ?, ?, ?, ?, ?, ?)";
+					+ " state, shared, temporary, length, deleted, blockCount)"
+					+ " VALUES (?, ?, ?, ?, ?, ?, ?, FALSE, 1)";
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, m.getId().getBytes());
 			ps.setBytes(2, m.getGroupId().getBytes());
@@ -797,21 +801,29 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.setInt(4, state.getValue());
 			ps.setBoolean(5, shared);
 			ps.setBoolean(6, temporary);
-			byte[] raw = messageFactory.getRawMessage(m);
-			ps.setInt(7, raw.length);
-			ps.setBytes(8, raw);
+			ps.setInt(7, m.getRawLength());
 			int affected = ps.executeUpdate();
 			if (affected != 1) throw new DbStateException();
 			ps.close();
+			sql = "INSERT INTO blocks (messageId, blockNumber, blockLength,"
+					+ " data)"
+					+ " VALUES (?, 0, ?, ?)";
+			ps = txn.prepareStatement(sql);
+			ps.setBytes(1, m.getId().getBytes());
+			ps.setInt(2, m.getBody().length);
+			ps.setBytes(3, m.getBody());
+			affected = ps.executeUpdate();
+			if (affected != 1) throw new DbStateException();
+			ps.close();
 			// Create a status row for each contact that can see the group
 			Map<ContactId, Boolean> visibility =
 					getGroupVisibility(txn, m.getGroupId());
 			for (Entry<ContactId, Boolean> e : visibility.entrySet()) {
 				ContactId c = e.getKey();
-				boolean offered = removeOfferedMessage(txn, c, m.getId());
-				boolean seen = offered || c.equals(sender);
+				boolean seen = c.equals(sender);
 				addStatus(txn, m.getId(), c, m.getGroupId(), m.getTimestamp(),
-						raw.length, state, e.getValue(), shared, false, seen);
+						m.getRawLength(), state, e.getValue(), shared, false,
+						seen);
 			}
 			// Update denormalised column in messageDependencies if dependency
 			// is in same group as dependent
@@ -830,37 +842,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
-	@Override
-	public void addOfferedMessage(Connection txn, ContactId c, MessageId m)
-			throws DbException {
-		PreparedStatement ps = null;
-		ResultSet rs = null;
-		try {
-			String sql = "SELECT NULL FROM offers"
-					+ " WHERE messageId = ? AND contactId = ?";
-			ps = txn.prepareStatement(sql);
-			ps.setBytes(1, m.getBytes());
-			ps.setInt(2, c.getInt());
-			rs = ps.executeQuery();
-			boolean found = rs.next();
-			if (rs.next()) throw new DbStateException();
-			rs.close();
-			ps.close();
-			if (found) return;
-			sql = "INSERT INTO offers (messageId, contactId) VALUES (?, ?)";
-			ps = txn.prepareStatement(sql);
-			ps.setBytes(1, m.getBytes());
-			ps.setInt(2, c.getInt());
-			int affected = ps.executeUpdate();
-			if (affected != 1) throw new DbStateException();
-			ps.close();
-		} catch (SQLException e) {
-			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps, LOG, WARNING);
-			throw new DbException(e);
-		}
-	}
-
 	private void addStatus(Connection txn, MessageId m, ContactId c, GroupId g,
 			long timestamp, int length, MessageState state, boolean groupShared,
 			boolean messageShared, boolean deleted, boolean seen)
@@ -1262,40 +1243,22 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
-	@Override
-	public int countOfferedMessages(Connection txn, ContactId c)
-			throws DbException {
-		PreparedStatement ps = null;
-		ResultSet rs = null;
-		try {
-			String sql = "SELECT COUNT (messageId) FROM offers "
-					+ " WHERE contactId = ?";
-			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
-			rs = ps.executeQuery();
-			if (!rs.next()) throw new DbException();
-			int count = rs.getInt(1);
-			if (rs.next()) throw new DbException();
-			rs.close();
-			ps.close();
-			return count;
-		} catch (SQLException e) {
-			tryToClose(rs, LOG, WARNING);
-			tryToClose(ps, LOG, WARNING);
-			throw new DbException(e);
-		}
-	}
-
 	@Override
 	public void deleteMessage(Connection txn, MessageId m) throws DbException {
 		PreparedStatement ps = null;
 		try {
-			String sql = "UPDATE messages SET raw = NULL WHERE messageId = ?";
+			String sql = "UPDATE messages SET deleted = TRUE"
+					+ " WHERE messageId = ?";
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, m.getBytes());
 			int affected = ps.executeUpdate();
+			if (affected < 0 || affected > 1) throw new DbStateException();
+			ps.close();
+			sql = "UPDATE blocks SET data = NULL WHERE messageId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setBytes(1, m.getBytes());
+			affected = ps.executeUpdate();
 			if (affected < 0) throw new DbStateException();
-			if (affected > 1) throw new DbStateException();
 			ps.close();
 			// Update denormalised column in statuses
 			sql = "UPDATE statuses SET deleted = TRUE WHERE messageId = ?";
@@ -1688,11 +1651,13 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public Message getMessage(Connection txn, MessageId m) throws DbException {
+	public Message getSmallMessage(Connection txn, MessageId m)
+			throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
-			String sql = "SELECT groupId, timestamp, raw FROM messages"
+			String sql = "SELECT groupId, timestamp, deleted, blockCount"
+					+ " FROM messages"
 					+ " WHERE messageId = ?";
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, m.getBytes());
@@ -1700,15 +1665,25 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (!rs.next()) throw new DbStateException();
 			GroupId g = new GroupId(rs.getBytes(1));
 			long timestamp = rs.getLong(2);
-			byte[] raw = rs.getBytes(3);
+			boolean deleted = rs.getBoolean(3);
+			int blockCount = rs.getInt(4);
 			if (rs.next()) throw new DbStateException();
 			rs.close();
 			ps.close();
-			if (raw == null) throw new MessageDeletedException();
-			if (raw.length <= MESSAGE_HEADER_LENGTH) throw new AssertionError();
-			byte[] body = new byte[raw.length - MESSAGE_HEADER_LENGTH];
-			System.arraycopy(raw, MESSAGE_HEADER_LENGTH, body, 0, body.length);
-			return new Message(m, g, timestamp, body);
+			if (deleted) throw new MessageDeletedException();
+			if (blockCount > 1) throw new MessageTooLargeException();
+			sql = "SELECT data FROM blocks"
+					+ " WHERE messageId = ? AND blockNumber = 0";
+			ps = txn.prepareStatement(sql);
+			ps.setBytes(1, m.getBytes());
+			rs = ps.executeQuery();
+			if (!rs.next()) throw new DbStateException();
+			byte[] data = rs.getBytes(1);
+			if (data == null) throw new DbStateException();
+			if (rs.next()) throw new DbStateException();
+			rs.close();
+			ps.close();
+			return new Message(m, g, timestamp, data);
 		} catch (SQLException e) {
 			tryToClose(rs, LOG, WARNING);
 			tryToClose(ps, LOG, WARNING);
@@ -2101,17 +2076,28 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	@Override
-	public Collection<MessageId> getMessagesToRequest(Connection txn,
-			ContactId c, int maxMessages) throws DbException {
+	public Collection<MessageId> getSmallMessagesToOffer(Connection txn,
+			ContactId c, int maxMessages, int maxLatency) throws DbException {
+		long now = clock.currentTimeMillis();
+		long eta = now + maxLatency;
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
-			String sql = "SELECT messageId FROM offers"
-					+ " WHERE contactId = ?"
-					+ " LIMIT ?";
+			String sql = "SELECT messageId FROM statuses"
+					+ " WHERE contactId = ? AND state = ?"
+					+ " AND length <= ?"
+					+ " AND groupShared = TRUE AND messageShared = TRUE"
+					+ " AND deleted = FALSE"
+					+ " AND seen = FALSE AND requested = FALSE"
+					+ " AND (expiry <= ? OR eta > ?)"
+					+ " ORDER BY timestamp LIMIT ?";
 			ps = txn.prepareStatement(sql);
 			ps.setInt(1, c.getInt());
-			ps.setInt(2, maxMessages);
+			ps.setInt(2, DELIVERED.getValue());
+			ps.setInt(3, MESSAGE_HEADER_LENGTH + MAX_BLOCK_LENGTH);
+			ps.setLong(4, now);
+			ps.setLong(5, eta);
+			ps.setInt(6, maxMessages);
 			rs = ps.executeQuery();
 			List<MessageId> ids = new ArrayList<>();
 			while (rs.next()) ids.add(new MessageId(rs.getBytes(1)));
@@ -2164,6 +2150,47 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public Collection<MessageId> getSmallMessagesToSend(Connection txn,
+			ContactId c, int maxLength, int maxLatency) throws DbException {
+		long now = clock.currentTimeMillis();
+		long eta = now + maxLatency;
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT length, messageId FROM statuses"
+					+ " WHERE contactId = ? AND state = ?"
+					+ " AND length <= ?"
+					+ " AND groupShared = TRUE AND messageShared = TRUE"
+					+ " AND deleted = FALSE"
+					+ " AND seen = FALSE"
+					+ " AND (expiry <= ? OR eta > ?)"
+					+ " ORDER BY timestamp";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setInt(2, DELIVERED.getValue());
+			ps.setInt(3, MESSAGE_HEADER_LENGTH + MAX_BLOCK_LENGTH);
+			ps.setLong(4, now);
+			ps.setLong(5, eta);
+			rs = ps.executeQuery();
+			List<MessageId> ids = new ArrayList<>();
+			int total = 0;
+			while (rs.next()) {
+				int length = rs.getInt(1);
+				if (total + length > maxLength) break;
+				ids.add(new MessageId(rs.getBytes(2)));
+				total += length;
+			}
+			rs.close();
+			ps.close();
+			return ids;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public Collection<MessageId> getMessagesToValidate(Connection txn)
 			throws DbException {
@@ -2182,7 +2209,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 		ResultSet rs = null;
 		try {
 			String sql = "SELECT messageId FROM messages"
-					+ " WHERE state = ? AND raw IS NOT NULL";
+					+ " WHERE state = ? AND deleted = FALSE";
 			ps = txn.prepareStatement(sql);
 			ps.setInt(1, state.getValue());
 			rs = ps.executeQuery();
@@ -2887,50 +2914,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
-	private boolean removeOfferedMessage(Connection txn, ContactId c,
-			MessageId m) throws DbException {
-		PreparedStatement ps = null;
-		try {
-			String sql = "DELETE FROM offers"
-					+ " WHERE contactId = ? AND messageId = ?";
-			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
-			ps.setBytes(2, m.getBytes());
-			int affected = ps.executeUpdate();
-			if (affected < 0 || affected > 1) throw new DbStateException();
-			ps.close();
-			return affected == 1;
-		} catch (SQLException e) {
-			tryToClose(ps, LOG, WARNING);
-			throw new DbException(e);
-		}
-	}
-
-	@Override
-	public void removeOfferedMessages(Connection txn, ContactId c,
-			Collection<MessageId> requested) throws DbException {
-		PreparedStatement ps = null;
-		try {
-			String sql = "DELETE FROM offers"
-					+ " WHERE contactId = ? AND messageId = ?";
-			ps = txn.prepareStatement(sql);
-			ps.setInt(1, c.getInt());
-			for (MessageId m : requested) {
-				ps.setBytes(2, m.getBytes());
-				ps.addBatch();
-			}
-			int[] batchAffected = ps.executeBatch();
-			if (batchAffected.length != requested.size())
-				throw new DbStateException();
-			for (int rows : batchAffected)
-				if (rows != 1) throw new DbStateException();
-			ps.close();
-		} catch (SQLException e) {
-			tryToClose(ps, LOG, WARNING);
-			throw new DbException(e);
-		}
-	}
-
 	@Override
 	public void removePendingContact(Connection txn, PendingContactId p)
 			throws DbException {

bramble-core/src/main/java/org/briarproject/bramble/db/Migration38_39.java

@@ -37,6 +37,7 @@ class Migration38_39 implements Migration<Connection> {
 			s.execute("ALTER TABLE incomingKeys"
 					+ " ALTER COLUMN contactId"
 					+ " SET NOT NULL");
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration39_40.java

@@ -36,6 +36,7 @@ class Migration39_40 implements Migration<Connection> {
 			s.execute("ALTER TABLE statuses"
 					+ " ALTER COLUMN eta"
 					+ " SET NOT NULL");
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration40_41.java

@@ -38,6 +38,7 @@ class Migration40_41 implements Migration<Connection> {
 			s = txn.createStatement();
 			s.execute("ALTER TABLE contacts"
 					+ dbTypes.replaceTypes(" ADD alias _STRING"));
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration41_42.java

@@ -89,6 +89,7 @@ class Migration41_42 implements Migration<Connection> {
 					+ " FOREIGN KEY (keySetId)"
 					+ " REFERENCES outgoingHandshakeKeys (keySetId)"
 					+ " ON DELETE CASCADE)"));
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration42_43.java

@@ -44,6 +44,7 @@ class Migration42_43 implements Migration<Connection> {
 					+ " ADD COLUMN handshakePublicKey _BINARY"));
 			s.execute("ALTER TABLE contacts"
 					+ " DROP COLUMN active");
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration43_44.java

@@ -50,6 +50,7 @@ class Migration43_44 implements Migration<Connection> {
 					+ " ADD COLUMN rootKey _SECRET"));
 			s.execute("ALTER TABLE outgoingKeys"
 					+ " ADD COLUMN alice BOOLEAN");
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration44_45.java

@@ -31,6 +31,7 @@ class Migration44_45 implements Migration<Connection> {
 		try {
 			s = txn.createStatement();
 			s.execute("ALTER TABLE pendingContacts DROP COLUMN state");
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration45_46.java

@@ -32,6 +32,7 @@ class Migration45_46 implements Migration<Connection> {
 			s = txn.createStatement();
 			s.execute("ALTER TABLE messages"
 					+ " ADD COLUMN temporary BOOLEAN DEFAULT FALSE NOT NULL");
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration46_47.java

@@ -39,6 +39,7 @@ class Migration46_47 implements Migration<Connection> {
 			s.execute(dbTypes.replaceTypes("ALTER TABLE contacts"
 					+ " ADD COLUMN syncVersions"
 					+ " _BINARY DEFAULT '00' NOT NULL"));
+			s.close();
 		} catch (SQLException e) {
 			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);

bramble-core/src/main/java/org/briarproject/bramble/db/Migration47_48.java

@@ -0,0 +1,95 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.db.DbException;
+
+import java.sql.Connection;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.logging.Logger;
+
+import static java.lang.System.arraycopy;
+import static java.sql.Types.BINARY;
+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.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
+class Migration47_48 implements Migration<Connection> {
+
+	private static final Logger LOG = getLogger(Migration47_48.class.getName());
+
+	private final DatabaseTypes dbTypes;
+
+	Migration47_48(DatabaseTypes dbTypes) {
+		this.dbTypes = dbTypes;
+	}
+
+	@Override
+	public int getStartVersion() {
+		return 47;
+	}
+
+	@Override
+	public int getEndVersion() {
+		return 48;
+	}
+
+	@Override
+	public void migrate(Connection txn) throws DbException {
+		Statement s = null;
+		ResultSet rs = null;
+		PreparedStatement ps = null;
+		try {
+			s = txn.createStatement();
+			s.execute("ALTER TABLE messages"
+					+ " ADD COLUMN deleted BOOLEAN DEFAULT FALSE NOT NULL");
+			s.execute("UPDATE messages SET deleted = TRUE WHERE raw IS NULL");
+			s.execute("ALTER TABLE messages"
+					+ " ADD COLUMN blockCount INT DEFAULT 1 NOT NULL");
+			s.execute(dbTypes.replaceTypes("CREATE TABLE blocks"
+					+ " (messageId _HASH NOT NULL,"
+					+ " blockNumber INT NOT NULL,"
+					+ " blockLength INT NOT NULL," // Excludes block header
+					+ " data BLOB," // Null if message has been deleted
+					+ " PRIMARY KEY (messageId, blockNumber),"
+					+ " FOREIGN KEY (messageId)"
+					+ " REFERENCES messages (messageId)"
+					+ " ON DELETE CASCADE)"));
+			rs = s.executeQuery("SELECT messageId, length, raw FROM messages");
+			ps = txn.prepareStatement("INSERT INTO blocks"
+					+ " (messageId, blockNumber, blockLength, data)"
+					+ " VALUES (?, 0, ?, ?)");
+			int migrated = 0;
+			while (rs.next()) {
+				byte[] id = rs.getBytes(1);
+				int length = rs.getInt(2);
+				byte[] raw = rs.getBytes(3);
+				ps.setBytes(1, id);
+				ps.setInt(2, length - MESSAGE_HEADER_LENGTH);
+				if (raw == null) {
+					ps.setNull(3, BINARY);
+				} else {
+					byte[] data = new byte[raw.length - MESSAGE_HEADER_LENGTH];
+					arraycopy(raw, MESSAGE_HEADER_LENGTH, data, 0, data.length);
+					ps.setBytes(3, data);
+				}
+				if (ps.executeUpdate() != 1) throw new DbStateException();
+				migrated++;
+			}
+			ps.close();
+			rs.close();
+			s.execute("ALTER TABLE messages DROP COLUMN raw");
+			s.close();
+			if (LOG.isLoggable(INFO))
+				LOG.info("Migrated " + migrated + " messages");
+		} catch (SQLException e) {
+			tryToClose(ps, LOG, WARNING);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(s, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/db/Migration48_49.java

@@ -0,0 +1,40 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.db.DbException;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.logging.Logger;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
+class Migration48_49 implements Migration<Connection> {
+
+	private static final Logger LOG = getLogger(Migration48_49.class.getName());
+
+	@Override
+	public int getStartVersion() {
+		return 48;
+	}
+
+	@Override
+	public int getEndVersion() {
+		return 49;
+	}
+
+	@Override
+	public void migrate(Connection txn) throws DbException {
+		Statement s = null;
+		try {
+			s = txn.createStatement();
+			s.execute("DROP TABLE offers");
+			s.close();
+		} catch (SQLException e) {
+			tryToClose(s, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/io/TimeoutMonitorImpl.java

@@ -3,15 +3,15 @@ package org.briarproject.bramble.io;
 import org.briarproject.bramble.api.io.TimeoutMonitor;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
+import org.briarproject.bramble.api.system.TaskScheduler.Cancellable;
+import org.briarproject.bramble.api.system.Wakeful;
 
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.Executor;
-import java.util.concurrent.Future;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
 import javax.annotation.concurrent.GuardedBy;
@@ -30,7 +30,7 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 
 	private static final long CHECK_INTERVAL_MS = SECONDS.toMillis(10);
 
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final Executor ioExecutor;
 	private final Clock clock;
 	private final Object lock = new Object();
@@ -38,10 +38,10 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 	private final List<TimeoutInputStream> streams = new ArrayList<>();
 
 	@GuardedBy("lock")
-	private Future<?> task = null;
+	private Cancellable cancellable = null;
 
 	@Inject
-	TimeoutMonitorImpl(@Scheduler ScheduledExecutorService scheduler,
+	TimeoutMonitorImpl(TaskScheduler scheduler,
 			@IoExecutor Executor ioExecutor, Clock clock) {
 		this.scheduler = scheduler;
 		this.ioExecutor = ioExecutor;
@@ -55,8 +55,9 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 				timeoutMs, this::removeStream);
 		synchronized (lock) {
 			if (streams.isEmpty()) {
-				task = scheduler.scheduleWithFixedDelay(this::checkTimeouts,
-						CHECK_INTERVAL_MS, CHECK_INTERVAL_MS, MILLISECONDS);
+				cancellable = scheduler.scheduleWithFixedDelay(
+						this::checkTimeouts, ioExecutor, CHECK_INTERVAL_MS,
+						CHECK_INTERVAL_MS, MILLISECONDS);
 			}
 			streams.add(stream);
 		}
@@ -64,33 +65,35 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 	}
 
 	private void removeStream(TimeoutInputStream stream) {
-		Future<?> toCancel = null;
+		Cancellable toCancel = null;
 		synchronized (lock) {
 			if (streams.remove(stream) && streams.isEmpty()) {
-				toCancel = task;
-				task = null;
+				toCancel = cancellable;
+				cancellable = null;
 			}
 		}
-		if (toCancel != null) toCancel.cancel(false);
+		if (toCancel != null) {
+			LOG.info("Cancelling timeout monitor task");
+			toCancel.cancel();
+		}
 	}
 
-	@Scheduler
+	@IoExecutor
+	@Wakeful
 	private void checkTimeouts() {
-		ioExecutor.execute(() -> {
-			List<TimeoutInputStream> snapshot;
-			synchronized (lock) {
-				snapshot = new ArrayList<>(streams);
-			}
-			for (TimeoutInputStream stream : snapshot) {
-				if (stream.hasTimedOut()) {
-					LOG.info("Input stream has timed out");
-					try {
-						stream.close();
-					} catch (IOException e) {
-						logException(LOG, INFO, e);
-					}
+		List<TimeoutInputStream> snapshot;
+		synchronized (lock) {
+			snapshot = new ArrayList<>(streams);
+		}
+		for (TimeoutInputStream stream : snapshot) {
+			if (stream.hasTimedOut()) {
+				LOG.info("Input stream has timed out");
+				try {
+					stream.close();
+				} catch (IOException e) {
+					logException(LOG, INFO, e);
 				}
 			}
-		});
+		}
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/keyagreement/KeyAgreementConnector.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.keyagreement;
 
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.crypto.KeyAgreementCrypto;
 import org.briarproject.bramble.api.crypto.KeyPair;
 import org.briarproject.bramble.api.data.BdfList;
@@ -8,6 +9,8 @@ import org.briarproject.bramble.api.keyagreement.KeyAgreementListener;
 import org.briarproject.bramble.api.keyagreement.Payload;
 import org.briarproject.bramble.api.keyagreement.TransportDescriptor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.BluetoothConstants;
+import org.briarproject.bramble.api.plugin.LanTcpConstants;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportId;
@@ -19,7 +22,9 @@ import org.briarproject.bramble.api.record.RecordWriterFactory;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.Callable;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.CountDownLatch;
@@ -28,8 +33,10 @@ import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 
+import static java.util.Arrays.asList;
 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.api.keyagreement.KeyAgreementConstants.CONNECTION_TIMEOUT;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
@@ -41,7 +48,10 @@ class KeyAgreementConnector {
 	}
 
 	private static final Logger LOG =
-			Logger.getLogger(KeyAgreementConnector.class.getName());
+			getLogger(KeyAgreementConnector.class.getName());
+
+	private static final List<TransportId> PREFERRED_TRANSPORTS =
+			asList(BluetoothConstants.ID, LanTcpConstants.ID);
 
 	private final Callbacks callbacks;
 	private final KeyAgreementCrypto keyAgreementCrypto;
@@ -105,24 +115,35 @@ class KeyAgreementConnector {
 		this.alice = alice;
 		aliceLatch.countDown();
 
-		// Start connecting over supported transports
+		// Start connecting over supported transports in order of preference
 		if (LOG.isLoggable(INFO)) {
 			LOG.info("Starting outgoing BQP connections as "
 					+ (alice ? "Alice" : "Bob"));
 		}
+		Map<TransportId, TransportDescriptor> descriptors = new HashMap<>();
 		for (TransportDescriptor d : remotePayload.getTransportDescriptors()) {
-			Plugin p = pluginManager.getPlugin(d.getId());
-			if (p instanceof DuplexPlugin) {
+			descriptors.put(d.getId(), d);
+		}
+		List<Pair<DuplexPlugin, BdfList>> transports = new ArrayList<>();
+		for (TransportId id : PREFERRED_TRANSPORTS) {
+			TransportDescriptor d = descriptors.get(id);
+			Plugin p = pluginManager.getPlugin(id);
+			if (d != null && p instanceof DuplexPlugin) {
 				if (LOG.isLoggable(INFO))
-					LOG.info("Connecting via " + d.getId());
-				DuplexPlugin plugin = (DuplexPlugin) p;
-				byte[] commitment = remotePayload.getCommitment();
-				BdfList descriptor = d.getDescriptor();
-				connectionChooser.submit(new ReadableTask(
-						new ConnectorTask(plugin, commitment, descriptor)));
+					LOG.info("Connecting via " + id);
+				transports.add(new Pair<>((DuplexPlugin) p, d.getDescriptor()));
 			}
 		}
 
+		// TODO: If we don't have any transports in common with the peer,
+		//  warn the user and give up (#1224)
+
+		if (!transports.isEmpty()) {
+			byte[] commitment = remotePayload.getCommitment();
+			connectionChooser.submit(new ReadableTask(new ConnectorTask(
+					transports, commitment)));
+		}
+
 		// Get chosen connection
 		try {
 			KeyAgreementConnection chosen =
@@ -148,15 +169,13 @@ class KeyAgreementConnector {
 
 	private class ConnectorTask implements Callable<KeyAgreementConnection> {
 
+		private final List<Pair<DuplexPlugin, BdfList>> transports;
 		private final byte[] commitment;
-		private final BdfList descriptor;
-		private final DuplexPlugin plugin;
 
-		private ConnectorTask(DuplexPlugin plugin, byte[] commitment,
-				BdfList descriptor) {
-			this.plugin = plugin;
+		private ConnectorTask(List<Pair<DuplexPlugin, BdfList>> transports,
+				byte[] commitment) {
+			this.transports = transports;
 			this.commitment = commitment;
-			this.descriptor = descriptor;
 		}
 
 		@Nullable
@@ -164,13 +183,18 @@ class KeyAgreementConnector {
 		public KeyAgreementConnection call() throws Exception {
 			// Repeat attempts until we connect, get stopped, or get interrupted
 			while (!stopped) {
-				DuplexTransportConnection conn =
-						plugin.createKeyAgreementConnection(commitment,
-								descriptor);
-				if (conn != null) {
-					if (LOG.isLoggable(INFO))
-						LOG.info(plugin.getId() + ": Outgoing connection");
-					return new KeyAgreementConnection(conn, plugin.getId());
+				for (Pair<DuplexPlugin, BdfList> pair : transports) {
+					if (stopped) return null;
+					DuplexPlugin plugin = pair.getFirst();
+					BdfList descriptor = pair.getSecond();
+					DuplexTransportConnection conn =
+							plugin.createKeyAgreementConnection(commitment,
+									descriptor);
+					if (conn != null) {
+						if (LOG.isLoggable(INFO))
+							LOG.info(plugin.getId() + ": Outgoing connection");
+						return new KeyAgreementConnection(conn, plugin.getId());
+					}
 				}
 				// Wait 2s before retry (to circumvent transient failures)
 				Thread.sleep(2000);

bramble-core/src/main/java/org/briarproject/bramble/plugin/PluginManagerImpl.java

@@ -1,6 +1,7 @@
 package org.briarproject.bramble.plugin;
 
 import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
@@ -8,6 +9,7 @@ import org.briarproject.bramble.api.lifecycle.Service;
 import org.briarproject.bramble.api.lifecycle.ServiceException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Plugin;
+import org.briarproject.bramble.api.plugin.Plugin.State;
 import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.PluginConfig;
 import org.briarproject.bramble.api.plugin.PluginException;
@@ -18,14 +20,16 @@ import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
-import org.briarproject.bramble.api.plugin.event.TransportDisabledEvent;
-import org.briarproject.bramble.api.plugin.event.TransportEnabledEvent;
+import org.briarproject.bramble.api.plugin.event.TransportActiveEvent;
+import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
+import org.briarproject.bramble.api.plugin.event.TransportStateEvent;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.properties.TransportPropertyManager;
 import org.briarproject.bramble.api.settings.Settings;
 import org.briarproject.bramble.api.settings.SettingsManager;
+import org.briarproject.bramble.api.system.WakefulIoExecutor;
 
 import java.util.ArrayList;
 import java.util.Collection;
@@ -36,15 +40,21 @@ import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.logging.Logger;
 
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static java.util.Collections.emptyList;
 import static java.util.logging.Level.FINE;
 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.api.plugin.Plugin.PREF_PLUGIN_ENABLE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.DISABLED;
+import static org.briarproject.bramble.api.plugin.Plugin.State.STARTING_STOPPING;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
@@ -56,7 +66,7 @@ class PluginManagerImpl implements PluginManager, Service {
 	private static final Logger LOG =
 			getLogger(PluginManagerImpl.class.getName());
 
-	private final Executor ioExecutor;
+	private final Executor ioExecutor, wakefulIoExecutor;
 	private final EventBus eventBus;
 	private final PluginConfig pluginConfig;
 	private final ConnectionManager connectionManager;
@@ -69,11 +79,15 @@ class PluginManagerImpl implements PluginManager, Service {
 	private final AtomicBoolean used = new AtomicBoolean(false);
 
 	@Inject
-	PluginManagerImpl(@IoExecutor Executor ioExecutor, EventBus eventBus,
-			PluginConfig pluginConfig, ConnectionManager connectionManager,
+	PluginManagerImpl(@IoExecutor Executor ioExecutor,
+			@WakefulIoExecutor Executor wakefulIoExecutor,
+			EventBus eventBus,
+			PluginConfig pluginConfig,
+			ConnectionManager connectionManager,
 			SettingsManager settingsManager,
 			TransportPropertyManager transportPropertyManager) {
 		this.ioExecutor = ioExecutor;
+		this.wakefulIoExecutor = wakefulIoExecutor;
 		this.eventBus = eventBus;
 		this.pluginConfig = pluginConfig;
 		this.connectionManager = connectionManager;
@@ -101,7 +115,7 @@ class PluginManagerImpl implements PluginManager, Service {
 				simplexPlugins.add(s);
 				CountDownLatch startLatch = new CountDownLatch(1);
 				startLatches.put(t, startLatch);
-				ioExecutor.execute(new PluginStarter(s, startLatch));
+				wakefulIoExecutor.execute(new PluginStarter(s, startLatch));
 			}
 		}
 		// Instantiate the duplex plugins and start them asynchronously
@@ -117,7 +131,7 @@ class PluginManagerImpl implements PluginManager, Service {
 				duplexPlugins.add(d);
 				CountDownLatch startLatch = new CountDownLatch(1);
 				startLatches.put(t, startLatch);
-				ioExecutor.execute(new PluginStarter(d, startLatch));
+				wakefulIoExecutor.execute(new PluginStarter(d, startLatch));
 			}
 		}
 	}
@@ -129,12 +143,16 @@ class PluginManagerImpl implements PluginManager, Service {
 		LOG.info("Stopping simplex plugins");
 		for (SimplexPlugin s : simplexPlugins) {
 			CountDownLatch startLatch = startLatches.get(s.getId());
+			// Don't need the wakeful executor here as we wait for the plugin
+			// to stop before returning
 			ioExecutor.execute(new PluginStopper(s, startLatch, stopLatch));
 		}
 		// Stop the duplex plugins
 		LOG.info("Stopping duplex plugins");
 		for (DuplexPlugin d : duplexPlugins) {
 			CountDownLatch startLatch = startLatches.get(d.getId());
+			// Don't need the wakeful executor here as we wait for the plugin
+			// to stop before returning
 			ioExecutor.execute(new PluginStopper(d, startLatch, stopLatch));
 		}
 		// Wait for all the plugins to stop
@@ -177,7 +195,27 @@ class PluginManagerImpl implements PluginManager, Service {
 		return supported;
 	}
 
-	private class PluginStarter implements Runnable {
+	@Override
+	public void setPluginEnabled(TransportId t, boolean enabled) {
+		Plugin plugin = plugins.get(t);
+		if (plugin == null) return;
+
+		Settings s = new Settings();
+		s.putBoolean(PREF_PLUGIN_ENABLE, enabled);
+		ioExecutor.execute(() -> mergeSettings(s, t.getString()));
+	}
+
+	private void mergeSettings(Settings s, String namespace) {
+		try {
+			long start = now();
+			settingsManager.mergeSettings(s, namespace);
+			logDuration(LOG, "Merging settings", start);
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+		}
+	}
+
+	private static class PluginStarter implements Runnable {
 
 		private final Plugin plugin;
 		private final CountDownLatch startLatch;
@@ -207,7 +245,7 @@ class PluginManagerImpl implements PluginManager, Service {
 		}
 	}
 
-	private class PluginStopper implements Runnable {
+	private static class PluginStopper implements Runnable {
 
 		private final Plugin plugin;
 		private final CountDownLatch startLatch, stopLatch;
@@ -250,7 +288,8 @@ class PluginManagerImpl implements PluginManager, Service {
 	private class Callback implements PluginCallback {
 
 		private final TransportId id;
-		private final AtomicBoolean enabled = new AtomicBoolean(false);
+		private final AtomicReference<State> state =
+				new AtomicReference<>(STARTING_STOPPING);
 
 		private Callback(TransportId id) {
 			this.id = id;
@@ -277,14 +316,22 @@ class PluginManagerImpl implements PluginManager, Service {
 		}
 
 		@Override
-		public void mergeSettings(Settings s) {
+		public Collection<TransportProperties> getRemoteProperties() {
 			try {
-				settingsManager.mergeSettings(s, id.getString());
+				Map<ContactId, TransportProperties> remote =
+						transportPropertyManager.getRemoteProperties(id);
+				return remote.values();
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
+				return emptyList();
 			}
 		}
 
+		@Override
+		public void mergeSettings(Settings s) {
+			PluginManagerImpl.this.mergeSettings(s, id.getString());
+		}
+
 		@Override
 		public void mergeLocalProperties(TransportProperties p) {
 			try {
@@ -295,15 +342,24 @@ class PluginManagerImpl implements PluginManager, Service {
 		}
 
 		@Override
-		public void transportEnabled() {
-			if (!enabled.getAndSet(true))
-				eventBus.broadcast(new TransportEnabledEvent(id));
-		}
-
-		@Override
-		public void transportDisabled() {
-			if (enabled.getAndSet(false))
-				eventBus.broadcast(new TransportDisabledEvent(id));
+		public void pluginStateChanged(State newState) {
+			State oldState = state.getAndSet(newState);
+			if (newState != oldState) {
+				if (LOG.isLoggable(INFO)) {
+					LOG.info(id + " changed from state " + oldState
+							+ " to " + newState);
+				}
+				eventBus.broadcast(new TransportStateEvent(id, newState));
+				if (newState == ACTIVE) {
+					eventBus.broadcast(new TransportActiveEvent(id));
+				} else if (oldState == ACTIVE) {
+					eventBus.broadcast(new TransportInactiveEvent(id));
+				}
+			} else if (newState == DISABLED) {
+				// Broadcast an event even though the state hasn't changed, as
+				// the reasons for the plugin being disabled may have changed
+				eventBus.broadcast(new TransportStateEvent(id, newState));
+			}
 		}
 
 		@Override

bramble-core/src/main/java/org/briarproject/bramble/plugin/PollerImpl.java

@@ -20,13 +20,16 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
 import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
-import org.briarproject.bramble.api.plugin.event.TransportDisabledEvent;
-import org.briarproject.bramble.api.plugin.event.TransportEnabledEvent;
+import org.briarproject.bramble.api.plugin.event.TransportActiveEvent;
+import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.properties.TransportPropertyManager;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
+import org.briarproject.bramble.api.system.TaskScheduler.Cancellable;
+import org.briarproject.bramble.api.system.Wakeful;
+import org.briarproject.bramble.api.system.WakefulIoExecutor;
 
 import java.security.SecureRandom;
 import java.util.ArrayList;
@@ -35,8 +38,6 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.concurrent.Executor;
-import java.util.concurrent.Future;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.logging.Logger;
@@ -57,8 +58,8 @@ class PollerImpl implements Poller, EventListener {
 
 	private static final Logger LOG = getLogger(PollerImpl.class.getName());
 
-	private final Executor ioExecutor;
-	private final ScheduledExecutorService scheduler;
+	private final Executor ioExecutor, wakefulIoExecutor;
+	private final TaskScheduler scheduler;
 	private final ConnectionManager connectionManager;
 	private final ConnectionRegistry connectionRegistry;
 	private final PluginManager pluginManager;
@@ -71,12 +72,16 @@ class PollerImpl implements Poller, EventListener {
 
 	@Inject
 	PollerImpl(@IoExecutor Executor ioExecutor,
-			@Scheduler ScheduledExecutorService scheduler,
+			@WakefulIoExecutor Executor wakefulIoExecutor,
+			TaskScheduler scheduler,
 			ConnectionManager connectionManager,
-			ConnectionRegistry connectionRegistry, PluginManager pluginManager,
+			ConnectionRegistry connectionRegistry,
+			PluginManager pluginManager,
 			TransportPropertyManager transportPropertyManager,
-			SecureRandom random, Clock clock) {
+			SecureRandom random,
+			Clock clock) {
 		this.ioExecutor = ioExecutor;
+		this.wakefulIoExecutor = wakefulIoExecutor;
 		this.scheduler = scheduler;
 		this.connectionManager = connectionManager;
 		this.connectionRegistry = connectionRegistry;
@@ -106,13 +111,13 @@ class PollerImpl implements Poller, EventListener {
 			ConnectionOpenedEvent c = (ConnectionOpenedEvent) e;
 			// Reschedule polling, the polling interval may have decreased
 			reschedule(c.getTransportId());
-		} else if (e instanceof TransportEnabledEvent) {
-			TransportEnabledEvent t = (TransportEnabledEvent) e;
-			// Poll the newly enabled transport
+		} else if (e instanceof TransportActiveEvent) {
+			TransportActiveEvent t = (TransportActiveEvent) e;
+			// Poll the newly activated transport
 			pollNow(t.getTransportId());
-		} else if (e instanceof TransportDisabledEvent) {
-			TransportDisabledEvent t = (TransportDisabledEvent) e;
-			// Cancel polling for the disabled transport
+		} else if (e instanceof TransportInactiveEvent) {
+			TransportInactiveEvent t = (TransportInactiveEvent) e;
+			// Cancel polling for the deactivated transport
 			cancel(t.getTransportId());
 		}
 	}
@@ -133,7 +138,7 @@ class PollerImpl implements Poller, EventListener {
 	}
 
 	private void connectToContact(ContactId c, SimplexPlugin p) {
-		ioExecutor.execute(() -> {
+		wakefulIoExecutor.execute(() -> {
 			TransportId t = p.getId();
 			if (connectionRegistry.isConnected(c, t)) return;
 			try {
@@ -149,7 +154,7 @@ class PollerImpl implements Poller, EventListener {
 	}
 
 	private void connectToContact(ContactId c, DuplexPlugin p) {
-		ioExecutor.execute(() -> {
+		wakefulIoExecutor.execute(() -> {
 			TransportId t = p.getId();
 			if (connectionRegistry.isConnected(c, t)) return;
 			try {
@@ -186,11 +191,11 @@ class PollerImpl implements Poller, EventListener {
 			if (scheduled == null || due < scheduled.task.due) {
 				// If a later task exists, cancel it. If it's already started
 				// it will abort safely when it finds it's been replaced
-				if (scheduled != null) scheduled.future.cancel(false);
+				if (scheduled != null) scheduled.cancellable.cancel();
 				PollTask task = new PollTask(p, due, randomiseNext);
-				Future future = scheduler.schedule(() ->
-						ioExecutor.execute(task), delay, MILLISECONDS);
-				tasks.put(t, new ScheduledPollTask(task, future));
+				Cancellable cancellable = scheduler.schedule(task, ioExecutor,
+						delay, MILLISECONDS);
+				tasks.put(t, new ScheduledPollTask(task, cancellable));
 			}
 		} finally {
 			lock.unlock();
@@ -201,7 +206,7 @@ class PollerImpl implements Poller, EventListener {
 		lock.lock();
 		try {
 			ScheduledPollTask scheduled = tasks.remove(t);
-			if (scheduled != null) scheduled.future.cancel(false);
+			if (scheduled != null) scheduled.cancellable.cancel();
 		} finally {
 			lock.unlock();
 		}
@@ -232,11 +237,11 @@ class PollerImpl implements Poller, EventListener {
 	private class ScheduledPollTask {
 
 		private final PollTask task;
-		private final Future future;
+		private final Cancellable cancellable;
 
-		private ScheduledPollTask(PollTask task, Future future) {
+		private ScheduledPollTask(PollTask task, Cancellable cancellable) {
 			this.task = task;
-			this.future = future;
+			this.cancellable = cancellable;
 		}
 	}
 
@@ -254,6 +259,7 @@ class PollerImpl implements Poller, EventListener {
 
 		@Override
 		@IoExecutor
+		@Wakeful
 		public void run() {
 			lock.lock();
 			try {

bramble-core/src/main/java/org/briarproject/bramble/plugin/bluetooth/BluetoothConnectionFactory.java

@@ -0,0 +1,14 @@
+package org.briarproject.bramble.plugin.bluetooth;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+
+import java.io.IOException;
+
+@NotNullByDefault
+interface BluetoothConnectionFactory<S> {
+
+	DuplexTransportConnection wrapSocket(DuplexPlugin plugin, S socket)
+			throws IOException;
+}