Avoid using the deprecated NetworkInfo API.

Merge plugin-toggles feature branch

See merge request briar/briar!1255

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

@@ -6,6 +6,8 @@ import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
 import android.net.ConnectivityManager;
+import android.net.Network;
+import android.net.NetworkCapabilities;
 import android.net.NetworkInfo;
 
 import org.briarproject.bramble.api.event.EventBus;
@@ -32,12 +34,15 @@ import static android.content.Intent.ACTION_SCREEN_OFF;
 import static android.content.Intent.ACTION_SCREEN_ON;
 import static android.net.ConnectivityManager.CONNECTIVITY_ACTION;
 import static android.net.ConnectivityManager.TYPE_WIFI;
+import static android.net.NetworkCapabilities.NET_CAPABILITY_INTERNET;
+import static android.net.NetworkCapabilities.TRANSPORT_WIFI;
 import static android.net.wifi.p2p.WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION;
 import static android.os.Build.VERSION.SDK_INT;
 import static android.os.PowerManager.ACTION_DEVICE_IDLE_MODE_CHANGED;
 import static java.util.concurrent.TimeUnit.MINUTES;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static java.util.logging.Level.INFO;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
@@ -52,7 +57,8 @@ class AndroidNetworkManager implements NetworkManager, Service {
 
 	private final ScheduledExecutorService scheduler;
 	private final EventBus eventBus;
-	private final Context appContext;
+	private final Application app;
+	private final ConnectivityManager connectivityManager;
 	private final AtomicReference<Future<?>> connectivityCheck =
 			new AtomicReference<>();
 	private final AtomicBoolean used = new AtomicBoolean(false);
@@ -64,7 +70,9 @@ class AndroidNetworkManager implements NetworkManager, Service {
 			EventBus eventBus, Application app) {
 		this.scheduler = scheduler;
 		this.eventBus = eventBus;
-		this.appContext = app.getApplicationContext();
+		this.app = app;
+		connectivityManager = (ConnectivityManager)
+				requireNonNull(app.getSystemService(CONNECTIVITY_SERVICE));
 	}
 
 	@Override
@@ -79,24 +87,33 @@ class AndroidNetworkManager implements NetworkManager, Service {
 		filter.addAction(WIFI_AP_STATE_CHANGED_ACTION);
 		filter.addAction(WIFI_P2P_THIS_DEVICE_CHANGED_ACTION);
 		if (SDK_INT >= 23) filter.addAction(ACTION_DEVICE_IDLE_MODE_CHANGED);
-		appContext.registerReceiver(networkStateReceiver, filter);
+		app.registerReceiver(networkStateReceiver, filter);
 	}
 
 	@Override
 	public void stopService() {
-		if (networkStateReceiver != null)
-			appContext.unregisterReceiver(networkStateReceiver);
+		if (networkStateReceiver != null) {
+			app.unregisterReceiver(networkStateReceiver);
+		}
 	}
 
 	@Override
 	public NetworkStatus getNetworkStatus() {
-		ConnectivityManager cm = (ConnectivityManager)
-				appContext.getSystemService(CONNECTIVITY_SERVICE);
-		if (cm == null) throw new AssertionError();
-		NetworkInfo net = cm.getActiveNetworkInfo();
-		boolean connected = net != null && net.isConnected();
-		boolean wifi = connected && net.getType() == TYPE_WIFI;
-		return new NetworkStatus(connected, wifi);
+		if (SDK_INT >= 23) {
+			Network net = connectivityManager.getActiveNetwork();
+			if (net == null) return new NetworkStatus(false, false);
+			NetworkCapabilities caps =
+					connectivityManager.getNetworkCapabilities(net);
+			if (caps == null) return new NetworkStatus(false, false);
+			boolean connected = caps.hasCapability(NET_CAPABILITY_INTERNET);
+			boolean wifi = caps.hasTransport(TRANSPORT_WIFI);
+			return new NetworkStatus(connected, wifi);
+		} else {
+			NetworkInfo net = connectivityManager.getActiveNetworkInfo();
+			boolean connected = net != null && net.isConnected();
+			boolean wifi = connected && net.getType() == TYPE_WIFI;
+			return new NetworkStatus(connected, wifi);
+		}
 	}
 
 	private void updateConnectionStatus() {

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

@@ -67,6 +67,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	private static final int MAX_DISCOVERY_MS = 10_000;
 
+	private final ScheduledExecutorService scheduler;
 	private final AndroidExecutor androidExecutor;
 	private final Context appContext;
 	private final Clock clock;
@@ -79,12 +80,13 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	AndroidBluetoothPlugin(BluetoothConnectionLimiter connectionLimiter,
 			TimeoutMonitor timeoutMonitor, Executor ioExecutor,
-			ScheduledExecutorService scheduler, SecureRandom secureRandom,
+			SecureRandom secureRandom, ScheduledExecutorService scheduler,
 			AndroidExecutor androidExecutor, Context appContext, Clock clock,
 			Backoff backoff, PluginCallback callback, int maxLatency,
 			int maxIdleTime) {
-		super(connectionLimiter, timeoutMonitor, ioExecutor, scheduler,
-				secureRandom, backoff, callback, maxLatency, maxIdleTime);
+		super(connectionLimiter, timeoutMonitor, ioExecutor, secureRandom,
+				backoff, callback, maxLatency, maxIdleTime);
+		this.scheduler = scheduler;
 		this.androidExecutor = androidExecutor;
 		this.appContext = appContext;
 		this.clock = clock;
@@ -152,6 +154,12 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 		wasEnabledByUs = true;
 	}
 
+	@Override
+	void onAdapterDisabled() {
+		super.onAdapterDisabled();
+		wasEnabledByUs = false;
+	}
+
 	@Override
 	@Nullable
 	String getBluetoothAddress() {
@@ -179,7 +187,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 	private DuplexTransportConnection wrapSocket(BluetoothSocket s)
 			throws IOException {
 		return new AndroidBluetoothTransportConnection(this, connectionLimiter,
-				timeoutMonitor, s);
+				timeoutMonitor, appContext, scheduler, s);
 	}
 
 	@Override

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

@@ -43,10 +43,10 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	private final BackoffFactory backoffFactory;
 
 	public AndroidBluetoothPluginFactory(Executor ioExecutor,
-			ScheduledExecutorService scheduler, AndroidExecutor androidExecutor,
-			Context appContext, SecureRandom secureRandom, EventBus eventBus,
-			Clock clock, TimeoutMonitor timeoutMonitor,
-			BackoffFactory backoffFactory) {
+			ScheduledExecutorService scheduler,
+			AndroidExecutor androidExecutor, Context appContext,
+			SecureRandom secureRandom, EventBus eventBus, Clock clock,
+			TimeoutMonitor timeoutMonitor, BackoffFactory backoffFactory) {
 		this.ioExecutor = ioExecutor;
 		this.scheduler = scheduler;
 		this.androidExecutor = androidExecutor;
@@ -71,12 +71,12 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	@Override
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		BluetoothConnectionLimiter connectionLimiter =
-				new BluetoothConnectionLimiterImpl();
+				new BluetoothConnectionLimiterImpl(eventBus);
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		AndroidBluetoothPlugin plugin = new AndroidBluetoothPlugin(
-				connectionLimiter, timeoutMonitor, ioExecutor, scheduler,
-				secureRandom, androidExecutor, appContext, clock, backoff,
+				connectionLimiter, timeoutMonitor, ioExecutor, secureRandom,
+				scheduler, androidExecutor, appContext, 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

@@ -1,17 +1,26 @@
 package org.briarproject.bramble.plugin.bluetooth;
 
 import android.bluetooth.BluetoothSocket;
+import android.content.Context;
+import android.os.PowerManager;
 
 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.util.RenewableWakeLock;
 
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.util.concurrent.ScheduledExecutorService;
 
+import static android.content.Context.POWER_SERVICE;
+import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
+import static java.util.concurrent.TimeUnit.MINUTES;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.PROP_ADDRESS;
+import static org.briarproject.bramble.util.AndroidUtils.getWakeLockTag;
 import static org.briarproject.bramble.util.AndroidUtils.isValidBluetoothAddress;
 
 @NotNullByDefault
@@ -19,18 +28,26 @@ class AndroidBluetoothTransportConnection
 		extends AbstractDuplexTransportConnection {
 
 	private final BluetoothConnectionLimiter connectionLimiter;
+	private final RenewableWakeLock wakeLock;
 	private final BluetoothSocket socket;
 	private final InputStream in;
 
 	AndroidBluetoothTransportConnection(Plugin plugin,
 			BluetoothConnectionLimiter connectionLimiter,
-			TimeoutMonitor timeoutMonitor, BluetoothSocket socket)
+			TimeoutMonitor timeoutMonitor, Context appContext,
+			ScheduledExecutorService scheduler, BluetoothSocket socket)
 			throws IOException {
 		super(plugin);
 		this.connectionLimiter = connectionLimiter;
 		this.socket = socket;
 		in = timeoutMonitor.createTimeoutInputStream(
 				socket.getInputStream(), plugin.getMaxIdleTime() * 2);
+		PowerManager powerManager = (PowerManager)
+				requireNonNull(appContext.getSystemService(POWER_SERVICE));
+		String tag = getWakeLockTag(appContext);
+		wakeLock = new RenewableWakeLock(powerManager, scheduler,
+				PARTIAL_WAKE_LOCK, tag, 1, MINUTES);
+		wakeLock.acquire();
 		String address = socket.getRemoteDevice().getAddress();
 		if (isValidBluetoothAddress(address)) remote.put(PROP_ADDRESS, address);
 	}
@@ -50,6 +67,7 @@ class AndroidBluetoothTransportConnection
 		try {
 			socket.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.annotation.TargetApi;
 import android.content.Context;
 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 +35,20 @@ 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.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());
@@ -68,37 +81,136 @@ 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, false));
 		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 +232,11 @@ 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 +244,59 @@ 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);
+				if (s == INACTIVE) bind();
 			} else {
 				LOG.info("Connected to wifi");
 				socketFactory = getSocketFactory();
-				if (socket == null || socket.isClosed()) bind();
+				if (s == INACTIVE) 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/tor/AndroidTorPlugin.java

@@ -27,6 +27,7 @@ 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 org.briarproject.bramble.util.AndroidUtils.getWakeLockTag;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
@@ -53,7 +54,7 @@ class AndroidTorPlugin extends TorPlugin {
 				appContext.getSystemService(POWER_SERVICE);
 		if (pm == null) throw new AssertionError();
 		wakeLock = new RenewableWakeLock(pm, scheduler, PARTIAL_WAKE_LOCK,
-				getWakeLockTag(), 1, MINUTES);
+				getWakeLockTag(appContext), 1, MINUTES);
 	}
 
 	@Override
@@ -74,7 +75,6 @@ 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();
@@ -85,17 +85,4 @@ class AndroidTorPlugin extends TorPlugin {
 		super.stop();
 		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";
-			}
-		}
-		return getClass().getSimpleName();
-	}
 }

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/util/AndroidUtils.java

@@ -3,6 +3,8 @@ package org.briarproject.bramble.util;
 import android.annotation.SuppressLint;
 import android.bluetooth.BluetoothAdapter;
 import android.content.Context;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
 import android.os.Build;
 import android.provider.Settings;
 
@@ -117,4 +119,17 @@ public class AndroidUtils {
 		if (SDK_INT < 24) return new String[] {"image/jpeg", "image/png"};
 		else return new String[] {"image/jpeg", "image/png", "image/gif"};
 	}
+
+	public static 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-api/src/main/java/org/briarproject/bramble/api/connection/ConnectionManager.java

@@ -1,8 +1,11 @@
-package org.briarproject.bramble.api.plugin;
+package org.briarproject.bramble.api.connection;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 
 @NotNullByDefault

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

@@ -0,0 +1,130 @@
+package org.briarproject.bramble.api.connection;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
+import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
+import org.briarproject.bramble.api.sync.Priority;
+
+import java.util.Collection;
+
+/**
+ * Keeps track of which contacts are currently connected by which transports.
+ */
+@NotNullByDefault
+public interface ConnectionRegistry {
+
+	/**
+	 * 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 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.
+	 * <p>
+	 * Broadcasts {@link ConnectionClosedEvent}. Also broadcasts
+	 * {@link ContactDisconnectedEvent} if this is the only connection with
+	 * the contact.
+	 */
+	void unregisterConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, boolean incoming, boolean exception);
+
+	/**
+	 * Sets the {@link Priority priority} of a connection that was previously
+	 * 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"
+	 * 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 setPriority(ContactId c, TransportId t, InterruptibleConnection conn,
+			Priority priority);
+
+	/**
+	 * Returns any contacts that are connected via the given transport.
+	 */
+	Collection<ContactId> getConnectedContacts(TransportId t);
+
+	/**
+	 * Returns any contacts that are connected via the given transport or any
+	 * {@link PluginConfig#getTransportPreferences() better} transport.
+	 */
+	Collection<ContactId> getConnectedOrBetterContacts(TransportId t);
+
+	/**
+	 * Returns true if the given contact is connected via the given transport.
+	 */
+	boolean isConnected(ContactId c, TransportId t);
+
+	/**
+	 * Returns true if the given contact is connected via any transport.
+	 */
+	boolean isConnected(ContactId c);
+
+	/**
+	 * Registers a connection with the given pending contact. Broadcasts
+	 * {@link RendezvousConnectionOpenedEvent} if this is the only connection
+	 * with the pending contact.
+	 *
+	 * @return True if this is the only connection with the pending contact,
+	 * false if it is redundant and should be closed
+	 */
+	boolean registerConnection(PendingContactId p);
+
+	/**
+	 * Unregisters a connection with the given pending contact. Broadcasts
+	 * {@link RendezvousConnectionClosedEvent}.
+	 */
+	void unregisterConnection(PendingContactId p, boolean success);
+}

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

@@ -0,0 +1,19 @@
+package org.briarproject.bramble.api.connection;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+/**
+ * A duplex sync connection that can be closed by interrupting its outgoing
+ * sync session.
+ */
+@NotNullByDefault
+public interface InterruptibleConnection {
+
+	/**
+	 * Interrupts the connection's outgoing sync session. If the underlying
+	 * transport connection is alive and the remote peer is cooperative, this
+	 * should result in both sync sessions ending and the connection being
+	 * cleanly closed.
+	 */
+	void interruptOutgoingSession();
+}

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/plugin/BluetoothConstants.java

@@ -8,6 +8,4 @@ public interface BluetoothConstants {
 
 	String PROP_ADDRESS = "address";
 	String PROP_UUID = "uuid";
-
-	String PREF_BT_ENABLE = "enable";
 }

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

@@ -1,67 +0,0 @@
-package org.briarproject.bramble.api.plugin;
-
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.contact.PendingContactId;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
-import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
-
-import java.util.Collection;
-
-/**
- * Keeps track of which contacts are currently connected by which transports.
- */
-@NotNullByDefault
-public interface ConnectionRegistry {
-
-	/**
-	 * Registers a connection with the given contact over the given transport.
-	 * Broadcasts {@link ConnectionOpenedEvent}. Also broadcasts
-	 * {@link ContactConnectedEvent} if this is the only connection with the
-	 * contact.
-	 */
-	void registerConnection(ContactId c, TransportId t, boolean incoming);
-
-	/**
-	 * Unregisters a connection with the given contact over the given transport.
-	 * Broadcasts {@link ConnectionClosedEvent}. Also broadcasts
-	 * {@link ContactDisconnectedEvent} if this is the only connection with
-	 * the contact.
-	 */
-	void unregisterConnection(ContactId c, TransportId t, boolean incoming);
-
-	/**
-	 * Returns any contacts that are connected via the given transport.
-	 */
-	Collection<ContactId> getConnectedContacts(TransportId t);
-
-	/**
-	 * Returns true if the given contact is connected via the given transport.
-	 */
-	boolean isConnected(ContactId c, TransportId t);
-
-	/**
-	 * Returns true if the given contact is connected via any transport.
-	 */
-	boolean isConnected(ContactId c);
-
-	/**
-	 * Registers a connection with the given pending contact. Broadcasts
-	 * {@link RendezvousConnectionOpenedEvent} if this is the only connection
-	 * with the pending contact.
-	 *
-	 * @return True if this is the only connection with the pending contact,
-	 * false if it is redundant and should be closed
-	 */
-	boolean registerConnection(PendingContactId p);
-
-	/**
-	 * Unregisters a connection with the given pending contact. Broadcasts
-	 * {@link RendezvousConnectionClosedEvent}.
-	 */
-	void unregisterConnection(PendingContactId p, boolean success);
-}

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

@@ -7,7 +7,9 @@ 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";
 }

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

@@ -3,12 +3,55 @@ 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 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.
 	 */
@@ -35,9 +78,18 @@ public interface Plugin {
 	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

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

@@ -1,6 +1,10 @@
 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;
 
@@ -32,12 +36,17 @@ 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/PluginConfig.java

@@ -5,6 +5,8 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 
 import java.util.Collection;
+import java.util.List;
+import java.util.Map;
 
 @NotNullByDefault
 public interface PluginConfig {
@@ -14,4 +16,11 @@ public interface PluginConfig {
 	Collection<SimplexPluginFactory> getSimplexFactories();
 
 	boolean shouldPoll();
+
+	/**
+	 * Returns a map representing transport preferences. For each entry in the
+	 * map, connections via the transports identified by the value are
+	 * preferred to connections via the transport identified by the key.
+	 */
+	Map<TransportId, List<TransportId>> getTransportPreferences();
 }

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

@@ -21,6 +21,21 @@ public interface TorConstants {
 	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;
 
+	/**
+	 * 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/event/ConnectionClosedEvent.java

@@ -13,13 +13,14 @@ public class ConnectionClosedEvent extends Event {
 
 	private final ContactId contactId;
 	private final TransportId transportId;
-	private final boolean incoming;
+	private final boolean incoming, exception;
 
 	public ConnectionClosedEvent(ContactId contactId, TransportId transportId,
-			boolean incoming) {
+			boolean incoming, boolean exception) {
 		this.contactId = contactId;
 		this.transportId = transportId;
 		this.incoming = incoming;
+		this.exception = exception;
 	}
 
 	public ContactId getContactId() {
@@ -33,4 +34,8 @@ public class ConnectionClosedEvent extends Event {
 	public boolean isIncoming() {
 		return incoming;
 	}
+
+	public boolean isException() {
+		return exception;
+	}
 }

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/sync/Priority.java

@@ -0,0 +1,23 @@
+package org.briarproject.bramble.api.sync;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * A record containing a nonce for choosing between redundant sessions.
+ */
+@Immutable
+@NotNullByDefault
+public class Priority {
+
+	private final byte[] nonce;
+
+	public Priority(byte[] nonce) {
+		this.nonce = nonce;
+	}
+
+	public byte[] getNonce() {
+		return nonce;
+	}
+}

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

@@ -0,0 +1,13 @@
+package org.briarproject.bramble.api.sync;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+/**
+ * An interface for handling a {@link Priority} record received by an
+ * incoming {@link SyncSession}.
+ */
+@NotNullByDefault
+public interface PriorityHandler {
+
+	void handle(Priority p);
+}

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

@@ -10,4 +10,5 @@ public interface RecordTypes {
 	byte OFFER = 2;
 	byte REQUEST = 3;
 	byte VERSIONS = 4;
+	byte PRIORITY = 5;
 }

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

@@ -49,4 +49,10 @@ public interface SyncConstants {
 	 * simultaneously.
 	 */
 	int MAX_SUPPORTED_VERSIONS = 10;
+
+	/**
+	 * The length of the priority nonce used for choosing between redundant
+	 * connections.
+	 */
+	int PRIORITY_NONCE_BYTES = 16;
 }

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

@@ -28,4 +28,8 @@ public interface SyncRecordReader {
 	boolean hasVersions() throws IOException;
 
 	Versions readVersions() throws IOException;
+
+	boolean hasPriority() throws IOException;
+
+	Priority readPriority() throws IOException;
 }

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

@@ -17,5 +17,7 @@ public interface SyncRecordWriter {
 
 	void writeVersions(Versions v) throws IOException;
 
+	void writePriority(Priority p) throws IOException;
+
 	void flush() throws IOException;
 }

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

@@ -2,18 +2,23 @@ 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;
 
+import javax.annotation.Nullable;
+
 @NotNullByDefault
 public interface SyncSessionFactory {
 
-	SyncSession createIncomingSession(ContactId c, InputStream in);
+	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/system/Clock.java

@@ -11,11 +11,6 @@ public interface Clock {
 	 */
 	long currentTimeMillis();
 
-	/**
-	 * @see System#nanoTime()
-	 */
-	long nanoTime();
-
 	/**
 	 * @see Thread#sleep(long)
 	 */

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-api/src/test/java/org/briarproject/bramble/test/ArrayClock.java

@@ -16,11 +16,6 @@ public class ArrayClock implements Clock {
 		return times[index++];
 	}
 
-	@Override
-	public long nanoTime() {
-		return times[index++] * 1_000_000;
-	}
-
 	@Override
 	public void sleep(long milliseconds) throws InterruptedException {
 		Thread.sleep(milliseconds);

bramble-api/src/test/java/org/briarproject/bramble/test/SettableClock.java

@@ -17,11 +17,6 @@ public class SettableClock implements Clock {
 		return time.get();
 	}
 
-	@Override
-	public long nanoTime() {
-		return time.get() * 1_000_000;
-	}
-
 	@Override
 	public void sleep(long milliseconds) throws InterruptedException {
 		Thread.sleep(milliseconds);

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

@@ -1,6 +1,7 @@
 package org.briarproject.bramble;
 
 import org.briarproject.bramble.client.ClientModule;
+import org.briarproject.bramble.connection.ConnectionModule;
 import org.briarproject.bramble.contact.ContactModule;
 import org.briarproject.bramble.crypto.CryptoExecutorModule;
 import org.briarproject.bramble.crypto.CryptoModule;
@@ -28,6 +29,7 @@ import dagger.Module;
 
 @Module(includes = {
 		ClientModule.class,
+		ConnectionModule.class,
 		ContactModule.class,
 		CryptoModule.class,
 		CryptoExecutorModule.class,

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

@@ -0,0 +1,79 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.transport.TransportConstants.TAG_LENGTH;
+import static org.briarproject.bramble.util.IoUtils.read;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+abstract class Connection {
+
+	protected static final Logger LOG = getLogger(Connection.class.getName());
+
+	final KeyManager keyManager;
+	final ConnectionRegistry connectionRegistry;
+	final StreamReaderFactory streamReaderFactory;
+	final StreamWriterFactory streamWriterFactory;
+
+	Connection(KeyManager keyManager, ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory) {
+		this.keyManager = keyManager;
+		this.connectionRegistry = connectionRegistry;
+		this.streamReaderFactory = streamReaderFactory;
+		this.streamWriterFactory = streamWriterFactory;
+	}
+
+	@Nullable
+	StreamContext recogniseTag(TransportConnectionReader reader,
+			TransportId transportId) {
+		StreamContext ctx;
+		try {
+			byte[] tag = readTag(reader.getInputStream());
+			return keyManager.getStreamContext(transportId, tag);
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		}
+	}
+
+	private byte[] readTag(InputStream in) throws IOException {
+		byte[] tag = new byte[TAG_LENGTH];
+		read(in, tag);
+		return tag;
+	}
+
+	void disposeOnError(TransportConnectionReader reader, boolean recognised) {
+		try {
+			reader.dispose(true, recognised);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+	}
+
+	void disposeOnError(TransportConnectionWriter writer) {
+		try {
+			writer.dispose(true);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+	}
+}

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

@@ -0,0 +1,114 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactExchangeManager;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.HandshakeManager;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.security.SecureRandom;
+import java.util.concurrent.Executor;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+@Immutable
+@NotNullByDefault
+class ConnectionManagerImpl implements ConnectionManager {
+
+	private final Executor ioExecutor;
+	private final KeyManager keyManager;
+	private final StreamReaderFactory streamReaderFactory;
+	private final StreamWriterFactory streamWriterFactory;
+	private final SyncSessionFactory syncSessionFactory;
+	private final HandshakeManager handshakeManager;
+	private final ContactExchangeManager contactExchangeManager;
+	private final ConnectionRegistry connectionRegistry;
+	private final TransportPropertyManager transportPropertyManager;
+	private final SecureRandom secureRandom;
+
+	@Inject
+	ConnectionManagerImpl(@IoExecutor Executor ioExecutor,
+			KeyManager keyManager, StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			HandshakeManager handshakeManager,
+			ContactExchangeManager contactExchangeManager,
+			ConnectionRegistry connectionRegistry,
+			TransportPropertyManager transportPropertyManager,
+			SecureRandom secureRandom) {
+		this.ioExecutor = ioExecutor;
+		this.keyManager = keyManager;
+		this.streamReaderFactory = streamReaderFactory;
+		this.streamWriterFactory = streamWriterFactory;
+		this.syncSessionFactory = syncSessionFactory;
+		this.handshakeManager = handshakeManager;
+		this.contactExchangeManager = contactExchangeManager;
+		this.connectionRegistry = connectionRegistry;
+		this.transportPropertyManager = transportPropertyManager;
+		this.secureRandom = secureRandom;
+	}
+
+
+	@Override
+	public void manageIncomingConnection(TransportId t,
+			TransportConnectionReader r) {
+		ioExecutor.execute(new IncomingSimplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, t, r));
+	}
+
+	@Override
+	public void manageIncomingConnection(TransportId t,
+			DuplexTransportConnection d) {
+		ioExecutor.execute(new IncomingDuplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, ioExecutor,
+				t, d));
+	}
+
+	@Override
+	public void manageIncomingConnection(PendingContactId p, TransportId t,
+			DuplexTransportConnection d) {
+		ioExecutor.execute(new IncomingHandshakeConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				handshakeManager, contactExchangeManager, this, p, t, d));
+	}
+
+	@Override
+	public void manageOutgoingConnection(ContactId c, TransportId t,
+			TransportConnectionWriter w) {
+		ioExecutor.execute(new OutgoingSimplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, c, t, w));
+	}
+
+	@Override
+	public void manageOutgoingConnection(ContactId c, TransportId t,
+			DuplexTransportConnection d) {
+		ioExecutor.execute(new OutgoingDuplexSyncConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				syncSessionFactory, transportPropertyManager, ioExecutor,
+				secureRandom, c, t, d));
+	}
+
+	@Override
+	public void manageOutgoingConnection(PendingContactId p, TransportId t,
+			DuplexTransportConnection d) {
+		ioExecutor.execute(new OutgoingHandshakeConnection(keyManager,
+				connectionRegistry, streamReaderFactory, streamWriterFactory,
+				handshakeManager, contactExchangeManager, this, p, t, d));
+	}
+}

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

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class ConnectionModule {
+
+	@Provides
+	ConnectionManager provideConnectionManager(
+			ConnectionManagerImpl connectionManager) {
+		return connectionManager;
+	}
+
+	@Provides
+	@Singleton
+	ConnectionRegistry provideConnectionRegistry(
+			ConnectionRegistryImpl connectionRegistry) {
+		return connectionRegistry;
+	}
+}

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

@@ -0,0 +1,283 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.Bytes;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.connection.InterruptibleConnection;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
+import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
+import org.briarproject.bramble.api.sync.Priority;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+import javax.inject.Inject;
+
+import static java.util.Collections.emptyList;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+
+@ThreadSafe
+@NotNullByDefault
+class ConnectionRegistryImpl implements ConnectionRegistry {
+
+	private static final Logger LOG =
+			getLogger(ConnectionRegistryImpl.class.getName());
+
+	private final EventBus eventBus;
+	private final Map<TransportId, List<TransportId>> transportPrefs;
+
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	private final Map<ContactId, List<ConnectionRecord>> contactConnections;
+	@GuardedBy("lock")
+	private final Set<PendingContactId> connectedPendingContacts;
+
+	@Inject
+	ConnectionRegistryImpl(EventBus eventBus, PluginConfig pluginConfig) {
+		this.eventBus = eventBus;
+		transportPrefs = pluginConfig.getTransportPreferences();
+		contactConnections = new HashMap<>();
+		connectedPendingContacts = new HashSet<>();
+	}
+
+	@Override
+	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);
+			else LOG.info("Outgoing connection registered: " + t);
+		}
+		boolean firstConnection;
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			if (recs == null) {
+				recs = new ArrayList<>();
+				contactConnections.put(c, recs);
+			}
+			firstConnection = recs.isEmpty();
+			recs.add(new ConnectionRecord(t, conn));
+		}
+		eventBus.broadcast(new ConnectionOpenedEvent(c, t, incoming));
+		if (firstConnection) {
+			LOG.info("Contact connected");
+			eventBus.broadcast(new ContactConnectedEvent(c));
+		}
+	}
+
+	@Override
+	public void setPriority(ContactId c, TransportId t,
+			InterruptibleConnection conn, Priority priority) {
+		if (LOG.isLoggable(INFO)) LOG.info("Setting connection priority: " + t);
+		List<InterruptibleConnection> toInterrupt;
+		boolean interruptNewConnection = false;
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			if (recs == null) throw new IllegalArgumentException();
+			toInterrupt = new ArrayList<>(recs.size());
+			for (ConnectionRecord rec : recs) {
+				if (rec.conn == conn) {
+					// Store the priority of this connection
+					rec.priority = priority;
+				} else if (rec.priority != null) {
+					int compare = compareConnections(t, priority,
+							rec.transportId, rec.priority);
+					if (compare == -1) {
+						// The old connection is better than the new one
+						interruptNewConnection = true;
+					} else if (compare == 1 && !rec.interrupted) {
+						// The new connection is better than the old one
+						toInterrupt.add(rec.conn);
+						rec.interrupted = true;
+					}
+				}
+			}
+		}
+		if (interruptNewConnection) {
+			LOG.info("Interrupting new connection");
+			conn.interruptOutgoingSession();
+		}
+		for (InterruptibleConnection old : toInterrupt) {
+			LOG.info("Interrupting old connection");
+			old.interruptOutgoingSession();
+		}
+	}
+
+	private int compareConnections(TransportId tA, Priority pA, TransportId tB,
+			Priority pB) {
+		if (getBetterTransports(tA).contains(tB)) return -1;
+		if (getBetterTransports(tB).contains(tA)) return 1;
+		return tA.equals(tB) ? Bytes.compare(pA.getNonce(), pB.getNonce()) : 0;
+	}
+
+	private List<TransportId> getBetterTransports(TransportId t) {
+		List<TransportId> better = transportPrefs.get(t);
+		return better == null ? emptyList() : better;
+	}
+
+	@Override
+	public void unregisterConnection(ContactId c, TransportId t,
+			InterruptibleConnection conn, boolean incoming, boolean exception) {
+		if (LOG.isLoggable(INFO)) {
+			if (incoming) LOG.info("Incoming connection unregistered: " + t);
+			else LOG.info("Outgoing connection unregistered: " + t);
+		}
+		boolean lastConnection;
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			if (recs == null || !recs.remove(new ConnectionRecord(t, conn)))
+				throw new IllegalArgumentException();
+			lastConnection = recs.isEmpty();
+		}
+		eventBus.broadcast(
+				new ConnectionClosedEvent(c, t, incoming, exception));
+		if (lastConnection) {
+			LOG.info("Contact disconnected");
+			eventBus.broadcast(new ContactDisconnectedEvent(c));
+		}
+	}
+
+	@Override
+	public Collection<ContactId> getConnectedContacts(TransportId t) {
+		synchronized (lock) {
+			List<ContactId> contactIds = new ArrayList<>();
+			for (Entry<ContactId, List<ConnectionRecord>> e :
+					contactConnections.entrySet()) {
+				for (ConnectionRecord rec : e.getValue()) {
+					if (rec.transportId.equals(t)) {
+						contactIds.add(e.getKey());
+						break;
+					}
+				}
+			}
+			if (LOG.isLoggable(INFO)) {
+				LOG.info(contactIds.size() + " contacts connected: " + t);
+			}
+			return contactIds;
+		}
+	}
+
+	@Override
+	public Collection<ContactId> getConnectedOrBetterContacts(TransportId t) {
+		synchronized (lock) {
+			List<TransportId> better = getBetterTransports(t);
+			List<ContactId> contactIds = new ArrayList<>();
+			for (Entry<ContactId, List<ConnectionRecord>> e :
+					contactConnections.entrySet()) {
+				for (ConnectionRecord rec : e.getValue()) {
+					if (rec.transportId.equals(t) ||
+							better.contains(rec.transportId)) {
+						contactIds.add(e.getKey());
+						break;
+					}
+				}
+			}
+			if (LOG.isLoggable(INFO)) {
+				LOG.info(contactIds.size()
+						+ " contacts connected or better: " + t);
+			}
+			return contactIds;
+		}
+	}
+
+	@Override
+	public boolean isConnected(ContactId c, TransportId t) {
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			if (recs == null) return false;
+			for (ConnectionRecord rec : recs) {
+				if (rec.transportId.equals(t)) return true;
+			}
+			return false;
+		}
+	}
+
+	@Override
+	public boolean isConnected(ContactId c) {
+		synchronized (lock) {
+			List<ConnectionRecord> recs = contactConnections.get(c);
+			return recs != null && !recs.isEmpty();
+		}
+	}
+
+	@Override
+	public boolean registerConnection(PendingContactId p) {
+		boolean added;
+		synchronized (lock) {
+			added = connectedPendingContacts.add(p);
+		}
+		if (added) eventBus.broadcast(new RendezvousConnectionOpenedEvent(p));
+		return added;
+	}
+
+	@Override
+	public void unregisterConnection(PendingContactId p, boolean success) {
+		synchronized (lock) {
+			if (!connectedPendingContacts.remove(p))
+				throw new IllegalArgumentException();
+		}
+		eventBus.broadcast(new RendezvousConnectionClosedEvent(p, success));
+	}
+
+	private static class ConnectionRecord {
+
+		private final TransportId transportId;
+		private final InterruptibleConnection conn;
+		@GuardedBy("lock")
+		@Nullable
+		private Priority priority = null;
+		@GuardedBy("lock")
+		private boolean interrupted = false;
+
+		private ConnectionRecord(TransportId transportId,
+				InterruptibleConnection conn) {
+			this.transportId = transportId;
+			this.conn = conn;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (o instanceof ConnectionRecord) {
+				return conn == ((ConnectionRecord) o).conn;
+			} else {
+				return false;
+			}
+		}
+
+		@Override
+		public int hashCode() {
+			return conn.hashCode();
+		}
+	}
+}

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

@@ -0,0 +1,109 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.connection.InterruptibleConnection;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.util.concurrent.Executor;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+
+@NotNullByDefault
+abstract class DuplexSyncConnection extends SyncConnection
+		implements InterruptibleConnection {
+
+	final Executor ioExecutor;
+	final TransportId transportId;
+	final TransportConnectionReader reader;
+	final TransportConnectionWriter writer;
+	final TransportProperties remote;
+
+	private final Object interruptLock = new Object();
+
+	@GuardedBy("interruptLock")
+	@Nullable
+	private SyncSession outgoingSession = null;
+	@GuardedBy("interruptLock")
+	private boolean interruptWaiting = false;
+
+	@Override
+	public void interruptOutgoingSession() {
+		SyncSession out = null;
+		synchronized (interruptLock) {
+			if (outgoingSession == null) interruptWaiting = true;
+			else out = outgoingSession;
+		}
+		if (out != null) out.interrupt();
+	}
+
+	void setOutgoingSession(SyncSession outgoingSession) {
+		boolean interruptWasWaiting = false;
+		synchronized (interruptLock) {
+			this.outgoingSession = outgoingSession;
+			if (interruptWaiting) {
+				interruptWasWaiting = true;
+				interruptWaiting = false;
+			}
+		}
+		if (interruptWasWaiting) outgoingSession.interrupt();
+	}
+
+	DuplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			Executor ioExecutor, TransportId transportId,
+			DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager);
+		this.ioExecutor = ioExecutor;
+		this.transportId = transportId;
+		reader = connection.getReader();
+		writer = connection.getWriter();
+		remote = connection.getRemoteProperties();
+	}
+
+	void onReadError(boolean recognised) {
+		disposeOnError(reader, recognised);
+		disposeOnError(writer);
+		interruptOutgoingSession();
+	}
+
+	void onWriteError() {
+		disposeOnError(reader, true);
+		disposeOnError(writer);
+	}
+
+	SyncSession createDuplexOutgoingSession(StreamContext ctx,
+			TransportConnectionWriter w, @Nullable Priority priority)
+			throws IOException {
+		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
+				w.getOutputStream(), ctx);
+		ContactId c = requireNonNull(ctx.getContactId());
+		return syncSessionFactory.createDuplexOutgoingSession(c,
+				ctx.getTransportId(), w.getMaxLatency(), w.getMaxIdleTime(),
+				streamWriter, priority);
+	}
+}

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

@@ -0,0 +1,72 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactExchangeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import javax.annotation.Nullable;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+abstract class HandshakeConnection extends Connection {
+
+	final HandshakeManager handshakeManager;
+	final ContactExchangeManager contactExchangeManager;
+	final ConnectionManager connectionManager;
+	final PendingContactId pendingContactId;
+	final TransportId transportId;
+	final DuplexTransportConnection connection;
+	final TransportConnectionReader reader;
+	final TransportConnectionWriter writer;
+
+	HandshakeConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			HandshakeManager handshakeManager,
+			ContactExchangeManager contactExchangeManager,
+			ConnectionManager connectionManager,
+			PendingContactId pendingContactId,
+			TransportId transportId, DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory);
+		this.handshakeManager = handshakeManager;
+		this.contactExchangeManager = contactExchangeManager;
+		this.connectionManager = connectionManager;
+		this.pendingContactId = pendingContactId;
+		this.transportId = transportId;
+		this.connection = connection;
+		reader = connection.getReader();
+		writer = connection.getWriter();
+	}
+
+	@Nullable
+	StreamContext allocateStreamContext(PendingContactId pendingContactId,
+			TransportId transportId) {
+		try {
+			return keyManager.getStreamContext(pendingContactId, transportId);
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		}
+	}
+
+	void onError(boolean recognised) {
+		disposeOnError(reader, recognised);
+		disposeOnError(writer);
+	}
+}

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

@@ -0,0 +1,107 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.PriorityHandler;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.util.concurrent.Executor;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class IncomingDuplexSyncConnection extends DuplexSyncConnection
+		implements Runnable {
+
+	IncomingDuplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			Executor ioExecutor, TransportId transportId,
+			DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager, ioExecutor, transportId, connection);
+	}
+
+	@Override
+	public void run() {
+		// Read and recognise the tag
+		StreamContext ctx = recogniseTag(reader, transportId);
+		if (ctx == null) {
+			LOG.info("Unrecognised tag");
+			onReadError(false);
+			return;
+		}
+		ContactId contactId = ctx.getContactId();
+		if (contactId == null) {
+			LOG.warning("Expected contact tag, got rendezvous tag");
+			onReadError(true);
+			return;
+		}
+		if (ctx.isHandshakeMode()) {
+			// TODO: Support handshake mode for contacts
+			LOG.warning("Received handshake tag, expected rotation mode");
+			onReadError(true);
+			return;
+		}
+		connectionRegistry.registerIncomingConnection(contactId, transportId,
+				this);
+		// Start the outgoing session on another thread
+		ioExecutor.execute(() -> runOutgoingSession(contactId));
+		try {
+			// Store any transport properties discovered from the connection
+			transportPropertyManager.addRemotePropertiesFromConnection(
+					contactId, transportId, remote);
+			// Update the connection registry when we receive our priority
+			PriorityHandler handler = p -> connectionRegistry.setPriority(
+					contactId, transportId, this, p);
+			// Create and run the incoming session
+			createIncomingSession(ctx, reader, handler).run();
+			reader.dispose(false, true);
+			interruptOutgoingSession();
+			connectionRegistry.unregisterConnection(contactId, transportId,
+					this, true, false);
+		} catch (DbException | IOException e) {
+			logException(LOG, WARNING, e);
+			onReadError(true);
+			connectionRegistry.unregisterConnection(contactId, transportId,
+					this, true, true);
+		}
+	}
+
+	private void runOutgoingSession(ContactId contactId) {
+		// Allocate a stream context
+		StreamContext ctx = allocateStreamContext(contactId, transportId);
+		if (ctx == null) {
+			LOG.warning("Could not allocate stream context");
+			onWriteError();
+			return;
+		}
+		try {
+			// Create and run the outgoing session
+			SyncSession out = createDuplexOutgoingSession(ctx, writer, null);
+			setOutgoingSession(out);
+			out.run();
+			writer.dispose(false);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onWriteError();
+		}
+	}
+}
+

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

@@ -0,0 +1,93 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactExchangeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager.HandshakeResult;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class IncomingHandshakeConnection extends HandshakeConnection
+		implements Runnable {
+
+	IncomingHandshakeConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			HandshakeManager handshakeManager,
+			ContactExchangeManager contactExchangeManager,
+			ConnectionManager connectionManager,
+			PendingContactId pendingContactId,
+			TransportId transportId, DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, handshakeManager, contactExchangeManager,
+				connectionManager, pendingContactId, transportId, connection);
+	}
+
+	@Override
+	public void run() {
+		// Read and recognise the tag
+		StreamContext ctxIn = recogniseTag(reader, transportId);
+		if (ctxIn == null) {
+			LOG.info("Unrecognised tag");
+			onError(false);
+			return;
+		}
+		PendingContactId inPendingContactId = ctxIn.getPendingContactId();
+		if (inPendingContactId == null) {
+			LOG.warning("Expected rendezvous tag, got contact tag");
+			onError(true);
+			return;
+		}
+		// Allocate the outgoing stream context
+		StreamContext ctxOut =
+				allocateStreamContext(pendingContactId, transportId);
+		if (ctxOut == null) {
+			LOG.warning("Could not allocate stream context");
+			onError(true);
+			return;
+		}
+		// Close the connection if it's redundant
+		if (!connectionRegistry.registerConnection(pendingContactId)) {
+			LOG.info("Redundant rendezvous connection");
+			onError(true);
+			return;
+		}
+		// Handshake and exchange contacts
+		try {
+			InputStream in = streamReaderFactory.createStreamReader(
+					reader.getInputStream(), ctxIn);
+			// Flush the output stream to send the outgoing stream header
+			StreamWriter out = streamWriterFactory.createStreamWriter(
+					writer.getOutputStream(), ctxOut);
+			out.getOutputStream().flush();
+			HandshakeResult result =
+					handshakeManager.handshake(pendingContactId, in, out);
+			contactExchangeManager.exchangeContacts(pendingContactId,
+					connection, result.getMasterKey(), result.isAlice(), false);
+			connectionRegistry.unregisterConnection(pendingContactId, true);
+			// Reuse the connection as a transport connection
+			connectionManager.manageIncomingConnection(transportId, connection);
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			onError(true);
+			connectionRegistry.unregisterConnection(pendingContactId, false);
+		}
+	}
+}

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

@@ -0,0 +1,79 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.PriorityHandler;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class IncomingSimplexSyncConnection extends SyncConnection implements Runnable {
+
+	private final TransportId transportId;
+	private final TransportConnectionReader reader;
+
+	IncomingSimplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			TransportId transportId, TransportConnectionReader reader) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager);
+		this.transportId = transportId;
+		this.reader = reader;
+	}
+
+	@Override
+	public void run() {
+		// Read and recognise the tag
+		StreamContext ctx = recogniseTag(reader, transportId);
+		if (ctx == null) {
+			LOG.info("Unrecognised tag");
+			onError(false);
+			return;
+		}
+		ContactId contactId = ctx.getContactId();
+		if (contactId == null) {
+			LOG.warning("Received rendezvous stream, expected contact");
+			onError(true);
+			return;
+		}
+		if (ctx.isHandshakeMode()) {
+			// TODO: Support handshake mode for contacts
+			LOG.warning("Received handshake tag, expected rotation mode");
+			onError(true);
+			return;
+		}
+		try {
+			// We don't expect to receive a priority for this connection
+			PriorityHandler handler = p ->
+					LOG.info("Ignoring priority for simplex connection");
+			// Create and run the incoming session
+			createIncomingSession(ctx, reader, handler).run();
+			reader.dispose(false, true);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onError(true);
+		}
+	}
+
+	private void onError(boolean recognised) {
+		disposeOnError(reader, recognised);
+	}
+}
+

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

@@ -0,0 +1,140 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.api.sync.PriorityHandler;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.security.SecureRandom;
+import java.util.concurrent.Executor;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.api.sync.SyncConstants.PRIORITY_NONCE_BYTES;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class OutgoingDuplexSyncConnection extends DuplexSyncConnection
+		implements Runnable {
+
+	private final SecureRandom secureRandom;
+	private final ContactId contactId;
+
+	OutgoingDuplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			Executor ioExecutor, SecureRandom secureRandom, ContactId contactId,
+			TransportId transportId, DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager, ioExecutor, transportId, connection);
+		this.secureRandom = secureRandom;
+		this.contactId = contactId;
+	}
+
+	@Override
+	public void run() {
+		// Allocate a stream context
+		StreamContext ctx = allocateStreamContext(contactId, transportId);
+		if (ctx == null) {
+			LOG.warning("Could not allocate stream context");
+			onWriteError();
+			return;
+		}
+		if (ctx.isHandshakeMode()) {
+			// TODO: Support handshake mode for contacts
+			LOG.warning("Cannot use handshake mode stream context");
+			onWriteError();
+			return;
+		}
+		// Start the incoming session on another thread
+		Priority priority = generatePriority();
+		ioExecutor.execute(() -> runIncomingSession(priority));
+		try {
+			// Create and run the outgoing session
+			SyncSession out =
+					createDuplexOutgoingSession(ctx, writer, priority);
+			setOutgoingSession(out);
+			out.run();
+			writer.dispose(false);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onWriteError();
+		}
+	}
+
+	private void runIncomingSession(Priority priority) {
+		// Read and recognise the tag
+		StreamContext ctx = recogniseTag(reader, transportId);
+		// Unrecognised tags are suspicious in this case
+		if (ctx == null) {
+			LOG.warning("Unrecognised tag for returning stream");
+			onReadError();
+			return;
+		}
+		// Check that the stream comes from the expected contact
+		ContactId inContactId = ctx.getContactId();
+		if (inContactId == null) {
+			LOG.warning("Expected contact tag, got rendezvous tag");
+			onReadError();
+			return;
+		}
+		if (!contactId.equals(inContactId)) {
+			LOG.warning("Wrong contact ID for returning stream");
+			onReadError();
+			return;
+		}
+		if (ctx.isHandshakeMode()) {
+			// TODO: Support handshake mode for contacts
+			LOG.warning("Received handshake tag, expected rotation mode");
+			onReadError();
+			return;
+		}
+		connectionRegistry.registerOutgoingConnection(contactId, transportId,
+				this, priority);
+		try {
+			// Store any transport properties discovered from the connection
+			transportPropertyManager.addRemotePropertiesFromConnection(
+					contactId, transportId, remote);
+			// We don't expect to receive a priority for this connection
+			PriorityHandler handler = p ->
+					LOG.info("Ignoring priority for outgoing connection");
+			// Create and run the incoming session
+			createIncomingSession(ctx, reader, handler).run();
+			reader.dispose(false, true);
+			interruptOutgoingSession();
+			connectionRegistry.unregisterConnection(contactId, transportId,
+					this, false, false);
+		} catch (DbException | IOException e) {
+			logException(LOG, WARNING, e);
+			onReadError();
+			connectionRegistry.unregisterConnection(contactId, transportId,
+					this, false, true);
+		}
+	}
+
+	private void onReadError() {
+		// 'Recognised' is always true for outgoing connections
+		onReadError(true);
+	}
+
+	private Priority generatePriority() {
+		byte[] nonce = new byte[PRIORITY_NONCE_BYTES];
+		secureRandom.nextBytes(nonce);
+		return new Priority(nonce);
+	}
+}

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

@@ -0,0 +1,115 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactExchangeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager;
+import org.briarproject.bramble.api.contact.HandshakeManager.HandshakeResult;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class OutgoingHandshakeConnection extends HandshakeConnection
+		implements Runnable {
+
+	OutgoingHandshakeConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			HandshakeManager handshakeManager,
+			ContactExchangeManager contactExchangeManager,
+			ConnectionManager connectionManager,
+			PendingContactId pendingContactId,
+			TransportId transportId, DuplexTransportConnection connection) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, handshakeManager, contactExchangeManager,
+				connectionManager, pendingContactId, transportId, connection);
+	}
+
+	@Override
+	public void run() {
+		// Allocate the outgoing stream context
+		StreamContext ctxOut =
+				allocateStreamContext(pendingContactId, transportId);
+		if (ctxOut == null) {
+			LOG.warning("Could not allocate stream context");
+			onError();
+			return;
+		}
+		// Flush the output stream to send the outgoing stream header
+		StreamWriter out;
+		try {
+			out = streamWriterFactory.createStreamWriter(
+					writer.getOutputStream(), ctxOut);
+			out.getOutputStream().flush();
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onError();
+			return;
+		}
+		// Read and recognise the tag
+		StreamContext ctxIn = recogniseTag(reader, transportId);
+		// Unrecognised tags are suspicious in this case
+		if (ctxIn == null) {
+			LOG.warning("Unrecognised tag for returning stream");
+			onError();
+			return;
+		}
+		// Check that the stream comes from the expected pending contact
+		PendingContactId inPendingContactId = ctxIn.getPendingContactId();
+		if (inPendingContactId == null) {
+			LOG.warning("Expected rendezvous tag, got contact tag");
+			onError();
+			return;
+		}
+		if (!inPendingContactId.equals(pendingContactId)) {
+			LOG.warning("Wrong pending contact ID for returning stream");
+			onError();
+			return;
+		}
+		// Close the connection if it's redundant
+		if (!connectionRegistry.registerConnection(pendingContactId)) {
+			LOG.info("Redundant rendezvous connection");
+			onError();
+			return;
+		}
+		// Handshake and exchange contacts
+		try {
+			InputStream in = streamReaderFactory.createStreamReader(
+					reader.getInputStream(), ctxIn);
+			HandshakeResult result =
+					handshakeManager.handshake(pendingContactId, in, out);
+			Contact contact = contactExchangeManager.exchangeContacts(
+					pendingContactId, connection, result.getMasterKey(),
+					result.isAlice(), false);
+			connectionRegistry.unregisterConnection(pendingContactId, true);
+			// Reuse the connection as a transport connection
+			connectionManager.manageOutgoingConnection(contact.getId(),
+					transportId, connection);
+		} catch (IOException | DbException e) {
+			logException(LOG, WARNING, e);
+			onError();
+			connectionRegistry.unregisterConnection(pendingContactId, false);
+		}
+	}
+
+	private void onError() {
+		// 'Recognised' is always true for outgoing connections
+		onError(true);
+	}
+}

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

@@ -0,0 +1,78 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriter;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class OutgoingSimplexSyncConnection extends SyncConnection implements Runnable {
+
+	private final ContactId contactId;
+	private final TransportId transportId;
+	private final TransportConnectionWriter writer;
+
+	OutgoingSimplexSyncConnection(KeyManager keyManager,
+			ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager,
+			ContactId contactId, TransportId transportId,
+			TransportConnectionWriter writer) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory, syncSessionFactory,
+				transportPropertyManager);
+		this.contactId = contactId;
+		this.transportId = transportId;
+		this.writer = writer;
+	}
+
+	@Override
+	public void run() {
+		// Allocate a stream context
+		StreamContext ctx = allocateStreamContext(contactId, transportId);
+		if (ctx == null) {
+			LOG.warning("Could not allocate stream context");
+			onError();
+			return;
+		}
+		try {
+			// Create and run the outgoing session
+			createSimplexOutgoingSession(ctx, writer).run();
+			writer.dispose(false);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			onError();
+		}
+	}
+
+	private void onError() {
+		disposeOnError(writer);
+	}
+
+	private SyncSession createSimplexOutgoingSession(StreamContext ctx,
+			TransportConnectionWriter w) throws IOException {
+		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
+				w.getOutputStream(), ctx);
+		ContactId c = requireNonNull(ctx.getContactId());
+		return syncSessionFactory.createSimplexOutgoingSession(c,
+				ctx.getTransportId(), w.getMaxLatency(), streamWriter);
+	}
+}
+

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

@@ -0,0 +1,64 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.properties.TransportPropertyManager;
+import org.briarproject.bramble.api.sync.PriorityHandler;
+import org.briarproject.bramble.api.sync.SyncSession;
+import org.briarproject.bramble.api.sync.SyncSessionFactory;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.StreamContext;
+import org.briarproject.bramble.api.transport.StreamReaderFactory;
+import org.briarproject.bramble.api.transport.StreamWriterFactory;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+import javax.annotation.Nullable;
+
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class SyncConnection extends Connection {
+
+	final SyncSessionFactory syncSessionFactory;
+	final TransportPropertyManager transportPropertyManager;
+
+	SyncConnection(KeyManager keyManager, ConnectionRegistry connectionRegistry,
+			StreamReaderFactory streamReaderFactory,
+			StreamWriterFactory streamWriterFactory,
+			SyncSessionFactory syncSessionFactory,
+			TransportPropertyManager transportPropertyManager) {
+		super(keyManager, connectionRegistry, streamReaderFactory,
+				streamWriterFactory);
+		this.syncSessionFactory = syncSessionFactory;
+		this.transportPropertyManager = transportPropertyManager;
+	}
+
+	@Nullable
+	StreamContext allocateStreamContext(ContactId contactId,
+			TransportId transportId) {
+		try {
+			return keyManager.getStreamContext(contactId, transportId);
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		}
+	}
+
+	SyncSession createIncomingSession(StreamContext ctx,
+			TransportConnectionReader r, PriorityHandler handler)
+			throws IOException {
+		InputStream streamReader = streamReaderFactory.createStreamReader(
+				r.getInputStream(), ctx);
+		ContactId c = requireNonNull(ctx.getContactId());
+		return syncSessionFactory
+				.createIncomingSession(c, streamReader, handler);
+	}
+}

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

@@ -13,28 +13,28 @@ class TimeoutInputStream extends InputStream {
 
 	private final Clock clock;
 	private final InputStream in;
-	private final long timeoutNs;
+	private final long timeoutMs;
 	private final CloseListener listener;
 	private final Object lock = new Object();
 	@GuardedBy("lock")
-	private long readStartedNs = -1;
+	private long readStartedMs = -1;
 
-	TimeoutInputStream(Clock clock, InputStream in, long timeoutNs,
+	TimeoutInputStream(Clock clock, InputStream in, long timeoutMs,
 			CloseListener listener) {
 		this.clock = clock;
 		this.in = in;
-		this.timeoutNs = timeoutNs;
+		this.timeoutMs = timeoutMs;
 		this.listener = listener;
 	}
 
 	@Override
 	public int read() throws IOException {
 		synchronized (lock) {
-			readStartedNs = clock.nanoTime();
+			readStartedMs = clock.currentTimeMillis();
 		}
 		int input = in.read();
 		synchronized (lock) {
-			readStartedNs = -1;
+			readStartedMs = -1;
 		}
 		return input;
 	}
@@ -47,11 +47,11 @@ class TimeoutInputStream extends InputStream {
 	@Override
 	public int read(byte[] b, int off, int len) throws IOException {
 		synchronized (lock) {
-			readStartedNs = clock.nanoTime();
+			readStartedMs = clock.currentTimeMillis();
 		}
 		int read = in.read(b, off, len);
 		synchronized (lock) {
-			readStartedNs = -1;
+			readStartedMs = -1;
 		}
 		return read;
 	}
@@ -92,8 +92,8 @@ class TimeoutInputStream extends InputStream {
 
 	boolean hasTimedOut() {
 		synchronized (lock) {
-			return readStartedNs != -1 &&
-					clock.nanoTime() - readStartedNs > timeoutNs;
+			return readStartedMs != -1 &&
+					clock.currentTimeMillis() - readStartedMs > timeoutMs;
 		}
 	}
 

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

@@ -52,7 +52,7 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 	public InputStream createTimeoutInputStream(InputStream in,
 			long timeoutMs) {
 		TimeoutInputStream stream = new TimeoutInputStream(clock, in,
-				timeoutMs * 1_000_000, this::removeStream);
+				timeoutMs, this::removeStream);
 		synchronized (lock) {
 			if (streams.isEmpty()) {
 				task = scheduler.scheduleWithFixedDelay(this::checkTimeouts,

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

@@ -1,709 +0,0 @@
-package org.briarproject.bramble.plugin;
-
-import org.briarproject.bramble.api.contact.Contact;
-import org.briarproject.bramble.api.contact.ContactExchangeManager;
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.contact.HandshakeManager;
-import org.briarproject.bramble.api.contact.HandshakeManager.HandshakeResult;
-import org.briarproject.bramble.api.contact.PendingContactId;
-import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.api.lifecycle.IoExecutor;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
-import org.briarproject.bramble.api.plugin.TransportConnectionReader;
-import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
-import org.briarproject.bramble.api.plugin.TransportId;
-import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
-import org.briarproject.bramble.api.properties.TransportProperties;
-import org.briarproject.bramble.api.properties.TransportPropertyManager;
-import org.briarproject.bramble.api.sync.SyncSession;
-import org.briarproject.bramble.api.sync.SyncSessionFactory;
-import org.briarproject.bramble.api.transport.KeyManager;
-import org.briarproject.bramble.api.transport.StreamContext;
-import org.briarproject.bramble.api.transport.StreamReaderFactory;
-import org.briarproject.bramble.api.transport.StreamWriter;
-import org.briarproject.bramble.api.transport.StreamWriterFactory;
-
-import java.io.IOException;
-import java.io.InputStream;
-import java.util.concurrent.Executor;
-import java.util.logging.Logger;
-
-import javax.annotation.Nullable;
-import javax.inject.Inject;
-
-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.transport.TransportConstants.TAG_LENGTH;
-import static org.briarproject.bramble.util.IoUtils.read;
-import static org.briarproject.bramble.util.LogUtils.logException;
-
-@NotNullByDefault
-class ConnectionManagerImpl implements ConnectionManager {
-
-	private static final Logger LOG =
-			getLogger(ConnectionManagerImpl.class.getName());
-
-	private final Executor ioExecutor;
-	private final KeyManager keyManager;
-	private final StreamReaderFactory streamReaderFactory;
-	private final StreamWriterFactory streamWriterFactory;
-	private final SyncSessionFactory syncSessionFactory;
-	private final HandshakeManager handshakeManager;
-	private final ContactExchangeManager contactExchangeManager;
-	private final ConnectionRegistry connectionRegistry;
-	private final TransportPropertyManager transportPropertyManager;
-
-	@Inject
-	ConnectionManagerImpl(@IoExecutor Executor ioExecutor,
-			KeyManager keyManager, StreamReaderFactory streamReaderFactory,
-			StreamWriterFactory streamWriterFactory,
-			SyncSessionFactory syncSessionFactory,
-			HandshakeManager handshakeManager,
-			ContactExchangeManager contactExchangeManager,
-			ConnectionRegistry connectionRegistry,
-			TransportPropertyManager transportPropertyManager) {
-		this.ioExecutor = ioExecutor;
-		this.keyManager = keyManager;
-		this.streamReaderFactory = streamReaderFactory;
-		this.streamWriterFactory = streamWriterFactory;
-		this.syncSessionFactory = syncSessionFactory;
-		this.handshakeManager = handshakeManager;
-		this.contactExchangeManager = contactExchangeManager;
-		this.connectionRegistry = connectionRegistry;
-		this.transportPropertyManager = transportPropertyManager;
-	}
-
-	@Override
-	public void manageIncomingConnection(TransportId t,
-			TransportConnectionReader r) {
-		ioExecutor.execute(new ManageIncomingSimplexConnection(t, r));
-	}
-
-	@Override
-	public void manageIncomingConnection(TransportId t,
-			DuplexTransportConnection d) {
-		ioExecutor.execute(new ManageIncomingDuplexConnection(t, d));
-	}
-
-	@Override
-	public void manageIncomingConnection(PendingContactId p, TransportId t,
-			DuplexTransportConnection d) {
-		ioExecutor.execute(new ManageIncomingHandshakeConnection(p, t, d));
-	}
-
-	@Override
-	public void manageOutgoingConnection(ContactId c, TransportId t,
-			TransportConnectionWriter w) {
-		ioExecutor.execute(new ManageOutgoingSimplexConnection(c, t, w));
-	}
-
-	@Override
-	public void manageOutgoingConnection(ContactId c, TransportId t,
-			DuplexTransportConnection d) {
-		ioExecutor.execute(new ManageOutgoingDuplexConnection(c, t, d));
-	}
-
-	@Override
-	public void manageOutgoingConnection(PendingContactId p, TransportId t,
-			DuplexTransportConnection d) {
-		ioExecutor.execute(new ManageOutgoingHandshakeConnection(p, t, d));
-	}
-
-	private byte[] readTag(InputStream in) throws IOException {
-		byte[] tag = new byte[TAG_LENGTH];
-		read(in, tag);
-		return tag;
-	}
-
-	private SyncSession createIncomingSession(StreamContext ctx,
-			TransportConnectionReader r) throws IOException {
-		InputStream streamReader = streamReaderFactory.createStreamReader(
-				r.getInputStream(), ctx);
-		ContactId c = requireNonNull(ctx.getContactId());
-		return syncSessionFactory.createIncomingSession(c, streamReader);
-	}
-
-	private SyncSession createSimplexOutgoingSession(StreamContext ctx,
-			TransportConnectionWriter w) throws IOException {
-		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
-				w.getOutputStream(), ctx);
-		ContactId c = requireNonNull(ctx.getContactId());
-		return syncSessionFactory.createSimplexOutgoingSession(c,
-				w.getMaxLatency(), streamWriter);
-	}
-
-	private SyncSession createDuplexOutgoingSession(StreamContext ctx,
-			TransportConnectionWriter w) throws IOException {
-		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
-				w.getOutputStream(), ctx);
-		ContactId c = requireNonNull(ctx.getContactId());
-		return syncSessionFactory.createDuplexOutgoingSession(c,
-				w.getMaxLatency(), w.getMaxIdleTime(), streamWriter);
-	}
-
-	private void disposeOnError(TransportConnectionReader reader,
-			boolean recognised) {
-		try {
-			reader.dispose(true, recognised);
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	private void disposeOnError(TransportConnectionWriter writer) {
-		try {
-			writer.dispose(true);
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	private class ManageIncomingSimplexConnection implements Runnable {
-
-		private final TransportId transportId;
-		private final TransportConnectionReader reader;
-
-		private ManageIncomingSimplexConnection(TransportId transportId,
-				TransportConnectionReader reader) {
-			this.transportId = transportId;
-			this.reader = reader;
-		}
-
-		@Override
-		public void run() {
-			// Read and recognise the tag
-			StreamContext ctx;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctx = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError(false);
-				return;
-			}
-			if (ctx == null) {
-				LOG.info("Unrecognised tag");
-				onError(false);
-				return;
-			}
-			ContactId contactId = ctx.getContactId();
-			if (contactId == null) {
-				LOG.warning("Received rendezvous stream, expected contact");
-				onError(true);
-				return;
-			}
-			if (ctx.isHandshakeMode()) {
-				// TODO: Support handshake mode for contacts
-				LOG.warning("Received handshake tag, expected rotation mode");
-				onError(true);
-				return;
-			}
-			connectionRegistry.registerConnection(contactId, transportId, true);
-			try {
-				// Create and run the incoming session
-				createIncomingSession(ctx, reader).run();
-				reader.dispose(false, true);
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onError(true);
-			} finally {
-				connectionRegistry.unregisterConnection(contactId, transportId,
-						true);
-			}
-		}
-
-		private void onError(boolean recognised) {
-			disposeOnError(reader, recognised);
-		}
-	}
-
-	private class ManageOutgoingSimplexConnection implements Runnable {
-
-		private final ContactId contactId;
-		private final TransportId transportId;
-		private final TransportConnectionWriter writer;
-
-		private ManageOutgoingSimplexConnection(ContactId contactId,
-				TransportId transportId, TransportConnectionWriter writer) {
-			this.contactId = contactId;
-			this.transportId = transportId;
-			this.writer = writer;
-		}
-
-		@Override
-		public void run() {
-			// Allocate a stream context
-			StreamContext ctx;
-			try {
-				ctx = keyManager.getStreamContext(contactId, transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				return;
-			}
-			if (ctx == null) {
-				LOG.warning("Could not allocate stream context");
-				onError();
-				return;
-			}
-			connectionRegistry.registerConnection(contactId, transportId,
-					false);
-			try {
-				// Create and run the outgoing session
-				createSimplexOutgoingSession(ctx, writer).run();
-				writer.dispose(false);
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onError();
-			} finally {
-				connectionRegistry.unregisterConnection(contactId, transportId,
-						false);
-			}
-		}
-
-		private void onError() {
-			disposeOnError(writer);
-		}
-	}
-
-	private class ManageIncomingDuplexConnection implements Runnable {
-
-		private final TransportId transportId;
-		private final TransportConnectionReader reader;
-		private final TransportConnectionWriter writer;
-		private final TransportProperties remote;
-
-		@Nullable
-		private volatile SyncSession outgoingSession = null;
-
-		private ManageIncomingDuplexConnection(TransportId transportId,
-				DuplexTransportConnection connection) {
-			this.transportId = transportId;
-			reader = connection.getReader();
-			writer = connection.getWriter();
-			remote = connection.getRemoteProperties();
-		}
-
-		@Override
-		public void run() {
-			// Read and recognise the tag
-			StreamContext ctx;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctx = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onReadError(false);
-				return;
-			}
-			if (ctx == null) {
-				LOG.info("Unrecognised tag");
-				onReadError(false);
-				return;
-			}
-			ContactId contactId = ctx.getContactId();
-			if (contactId == null) {
-				LOG.warning("Expected contact tag, got rendezvous tag");
-				onReadError(true);
-				return;
-			}
-			if (ctx.isHandshakeMode()) {
-				// TODO: Support handshake mode for contacts
-				LOG.warning("Received handshake tag, expected rotation mode");
-				onReadError(true);
-				return;
-			}
-			connectionRegistry.registerConnection(contactId, transportId, true);
-			// Start the outgoing session on another thread
-			ioExecutor.execute(() -> runOutgoingSession(contactId));
-			try {
-				// Store any transport properties discovered from the connection
-				transportPropertyManager.addRemotePropertiesFromConnection(
-						contactId, transportId, remote);
-				// Create and run the incoming session
-				createIncomingSession(ctx, reader).run();
-				reader.dispose(false, true);
-				// Interrupt the outgoing session so it finishes cleanly
-				SyncSession out = outgoingSession;
-				if (out != null) out.interrupt();
-			} catch (DbException | IOException e) {
-				logException(LOG, WARNING, e);
-				onReadError(true);
-			} finally {
-				connectionRegistry.unregisterConnection(contactId, transportId,
-						true);
-			}
-		}
-
-		private void runOutgoingSession(ContactId contactId) {
-			// Allocate a stream context
-			StreamContext ctx;
-			try {
-				ctx = keyManager.getStreamContext(contactId, transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onWriteError();
-				return;
-			}
-			if (ctx == null) {
-				LOG.warning("Could not allocate stream context");
-				onWriteError();
-				return;
-			}
-			try {
-				// Create and run the outgoing session
-				SyncSession out = createDuplexOutgoingSession(ctx, writer);
-				outgoingSession = out;
-				out.run();
-				writer.dispose(false);
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onWriteError();
-			}
-		}
-
-		private void onReadError(boolean recognised) {
-			disposeOnError(reader, recognised);
-			disposeOnError(writer);
-			// Interrupt the outgoing session so it finishes
-			SyncSession out = outgoingSession;
-			if (out != null) out.interrupt();
-		}
-
-		private void onWriteError() {
-			disposeOnError(reader, true);
-			disposeOnError(writer);
-		}
-	}
-
-	private class ManageOutgoingDuplexConnection implements Runnable {
-
-		private final ContactId contactId;
-		private final TransportId transportId;
-		private final TransportConnectionReader reader;
-		private final TransportConnectionWriter writer;
-		private final TransportProperties remote;
-
-		@Nullable
-		private volatile SyncSession outgoingSession = null;
-
-		private ManageOutgoingDuplexConnection(ContactId contactId,
-				TransportId transportId, DuplexTransportConnection connection) {
-			this.contactId = contactId;
-			this.transportId = transportId;
-			reader = connection.getReader();
-			writer = connection.getWriter();
-			remote = connection.getRemoteProperties();
-		}
-
-		@Override
-		public void run() {
-			// Allocate a stream context
-			StreamContext ctx;
-			try {
-				ctx = keyManager.getStreamContext(contactId, transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onWriteError();
-				return;
-			}
-			if (ctx == null) {
-				LOG.warning("Could not allocate stream context");
-				onWriteError();
-				return;
-			}
-			if (ctx.isHandshakeMode()) {
-				// TODO: Support handshake mode for contacts
-				LOG.warning("Cannot use handshake mode stream context");
-				onWriteError();
-				return;
-			}
-			// Start the incoming session on another thread
-			ioExecutor.execute(this::runIncomingSession);
-			try {
-				// Create and run the outgoing session
-				SyncSession out = createDuplexOutgoingSession(ctx, writer);
-				outgoingSession = out;
-				out.run();
-				writer.dispose(false);
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onWriteError();
-			}
-		}
-
-		private void runIncomingSession() {
-			// Read and recognise the tag
-			StreamContext ctx;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctx = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onReadError();
-				return;
-			}
-			// Unrecognised tags are suspicious in this case
-			if (ctx == null) {
-				LOG.warning("Unrecognised tag for returning stream");
-				onReadError();
-				return;
-			}
-			// Check that the stream comes from the expected contact
-			ContactId inContactId = ctx.getContactId();
-			if (inContactId == null) {
-				LOG.warning("Expected contact tag, got rendezvous tag");
-				onReadError();
-				return;
-			}
-			if (!contactId.equals(inContactId)) {
-				LOG.warning("Wrong contact ID for returning stream");
-				onReadError();
-				return;
-			}
-			if (ctx.isHandshakeMode()) {
-				// TODO: Support handshake mode for contacts
-				LOG.warning("Received handshake tag, expected rotation mode");
-				onReadError();
-				return;
-			}
-			connectionRegistry.registerConnection(contactId, transportId,
-					false);
-			try {
-				// Store any transport properties discovered from the connection
-				transportPropertyManager.addRemotePropertiesFromConnection(
-						contactId, transportId, remote);
-				// Create and run the incoming session
-				createIncomingSession(ctx, reader).run();
-				reader.dispose(false, true);
-				// Interrupt the outgoing session so it finishes cleanly
-				SyncSession out = outgoingSession;
-				if (out != null) out.interrupt();
-			} catch (DbException | IOException e) {
-				logException(LOG, WARNING, e);
-				onReadError();
-			} finally {
-				connectionRegistry.unregisterConnection(contactId, transportId,
-						false);
-			}
-		}
-
-		private void onReadError() {
-			// 'Recognised' is always true for outgoing connections
-			disposeOnError(reader, true);
-			disposeOnError(writer);
-			// Interrupt the outgoing session so it finishes
-			SyncSession out = outgoingSession;
-			if (out != null) out.interrupt();
-		}
-
-		private void onWriteError() {
-			disposeOnError(reader, true);
-			disposeOnError(writer);
-		}
-	}
-
-	private class ManageIncomingHandshakeConnection implements Runnable {
-
-		private final PendingContactId pendingContactId;
-		private final TransportId transportId;
-		private final DuplexTransportConnection connection;
-		private final TransportConnectionReader reader;
-		private final TransportConnectionWriter writer;
-
-		private ManageIncomingHandshakeConnection(
-				PendingContactId pendingContactId, TransportId transportId,
-				DuplexTransportConnection connection) {
-			this.pendingContactId = pendingContactId;
-			this.transportId = transportId;
-			this.connection = connection;
-			reader = connection.getReader();
-			writer = connection.getWriter();
-		}
-
-		@Override
-		public void run() {
-			// Read and recognise the tag
-			StreamContext ctxIn;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctxIn = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError(false);
-				return;
-			}
-			if (ctxIn == null) {
-				LOG.info("Unrecognised tag");
-				onError(false);
-				return;
-			}
-			PendingContactId inPendingContactId = ctxIn.getPendingContactId();
-			if (inPendingContactId == null) {
-				LOG.warning("Expected rendezvous tag, got contact tag");
-				onError(true);
-				return;
-			}
-			// Allocate the outgoing stream context
-			StreamContext ctxOut;
-			try {
-				ctxOut = keyManager.getStreamContext(pendingContactId,
-						transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onError(true);
-				return;
-			}
-			if (ctxOut == null) {
-				LOG.warning("Could not allocate stream context");
-				onError(true);
-				return;
-			}
-			// Close the connection if it's redundant
-			if (!connectionRegistry.registerConnection(pendingContactId)) {
-				LOG.info("Redundant rendezvous connection");
-				onError(true);
-				return;
-			}
-			// Handshake and exchange contacts
-			try {
-				InputStream in = streamReaderFactory.createStreamReader(
-						reader.getInputStream(), ctxIn);
-				// Flush the output stream to send the outgoing stream header
-				StreamWriter out = streamWriterFactory.createStreamWriter(
-						writer.getOutputStream(), ctxOut);
-				out.getOutputStream().flush();
-				HandshakeResult result = handshakeManager.handshake(
-						pendingContactId, in, out);
-				Contact contact = contactExchangeManager.exchangeContacts(
-						pendingContactId, connection, result.getMasterKey(),
-						result.isAlice(), false);
-				connectionRegistry.unregisterConnection(pendingContactId, true);
-				// Reuse the connection as a transport connection
-				manageOutgoingConnection(contact.getId(), transportId,
-						connection);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError(true);
-				connectionRegistry.unregisterConnection(pendingContactId,
-						false);
-			}
-		}
-
-		private void onError(boolean recognised) {
-			disposeOnError(reader, recognised);
-			disposeOnError(writer);
-		}
-	}
-
-	private class ManageOutgoingHandshakeConnection implements Runnable {
-
-		private final PendingContactId pendingContactId;
-		private final TransportId transportId;
-		private final DuplexTransportConnection connection;
-		private final TransportConnectionReader reader;
-		private final TransportConnectionWriter writer;
-
-		private ManageOutgoingHandshakeConnection(
-				PendingContactId pendingContactId, TransportId transportId,
-				DuplexTransportConnection connection) {
-			this.pendingContactId = pendingContactId;
-			this.transportId = transportId;
-			this.connection = connection;
-			reader = connection.getReader();
-			writer = connection.getWriter();
-		}
-
-		@Override
-		public void run() {
-			// Allocate the outgoing stream context
-			StreamContext ctxOut;
-			try {
-				ctxOut = keyManager.getStreamContext(pendingContactId,
-						transportId);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				return;
-			}
-			if (ctxOut == null) {
-				LOG.warning("Could not allocate stream context");
-				onError();
-				return;
-			}
-			// Flush the output stream to send the outgoing stream header
-			StreamWriter out;
-			try {
-				out = streamWriterFactory.createStreamWriter(
-						writer.getOutputStream(), ctxOut);
-				out.getOutputStream().flush();
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				return;
-			}
-			// Read and recognise the tag
-			StreamContext ctxIn;
-			try {
-				byte[] tag = readTag(reader.getInputStream());
-				ctxIn = keyManager.getStreamContext(transportId, tag);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				return;
-			}
-			// Unrecognised tags are suspicious in this case
-			if (ctxIn == null) {
-				LOG.warning("Unrecognised tag for returning stream");
-				onError();
-				return;
-			}
-			// Check that the stream comes from the expected pending contact
-			PendingContactId inPendingContactId = ctxIn.getPendingContactId();
-			if (inPendingContactId == null) {
-				LOG.warning("Expected rendezvous tag, got contact tag");
-				onError();
-				return;
-			}
-			if (!inPendingContactId.equals(pendingContactId)) {
-				LOG.warning("Wrong pending contact ID for returning stream");
-				onError();
-				return;
-			}
-			// Close the connection if it's redundant
-			if (!connectionRegistry.registerConnection(pendingContactId)) {
-				LOG.info("Redundant rendezvous connection");
-				onError();
-				return;
-			}
-			// Handshake and exchange contacts
-			try {
-				InputStream in = streamReaderFactory.createStreamReader(
-						reader.getInputStream(), ctxIn);
-				HandshakeResult result = handshakeManager.handshake(
-						pendingContactId, in, out);
-				Contact contact = contactExchangeManager.exchangeContacts(
-						pendingContactId, connection, result.getMasterKey(),
-						result.isAlice(), false);
-				connectionRegistry.unregisterConnection(pendingContactId, true);
-				// Reuse the connection as a transport connection
-				manageOutgoingConnection(contact.getId(), transportId,
-						connection);
-			} catch (IOException | DbException e) {
-				logException(LOG, WARNING, e);
-				onError();
-				connectionRegistry.unregisterConnection(pendingContactId,
-						false);
-			}
-		}
-
-		private void onError() {
-			// 'Recognised' is always true for outgoing connections
-			disposeOnError(reader, true);
-			disposeOnError(writer);
-		}
-	}
-}

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

@@ -1,150 +0,0 @@
-package org.briarproject.bramble.plugin;
-
-import org.briarproject.bramble.api.Multiset;
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.contact.PendingContactId;
-import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
-import org.briarproject.bramble.api.plugin.TransportId;
-import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
-import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
-
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
-import java.util.logging.Logger;
-
-import javax.annotation.concurrent.GuardedBy;
-import javax.annotation.concurrent.ThreadSafe;
-import javax.inject.Inject;
-
-import static java.util.logging.Level.INFO;
-import static java.util.logging.Logger.getLogger;
-
-@ThreadSafe
-@NotNullByDefault
-class ConnectionRegistryImpl implements ConnectionRegistry {
-
-	private static final Logger LOG =
-			getLogger(ConnectionRegistryImpl.class.getName());
-
-	private final EventBus eventBus;
-
-	private final Object lock = new Object();
-	@GuardedBy("lock")
-	private final Map<TransportId, Multiset<ContactId>> contactConnections;
-	@GuardedBy("lock")
-	private final Multiset<ContactId> contactCounts;
-	@GuardedBy("lock")
-	private final Set<PendingContactId> connectedPendingContacts;
-
-	@Inject
-	ConnectionRegistryImpl(EventBus eventBus) {
-		this.eventBus = eventBus;
-		contactConnections = new HashMap<>();
-		contactCounts = new Multiset<>();
-		connectedPendingContacts = new HashSet<>();
-	}
-
-	@Override
-	public void registerConnection(ContactId c, TransportId t,
-			boolean incoming) {
-		if (LOG.isLoggable(INFO)) {
-			if (incoming) LOG.info("Incoming connection registered: " + t);
-			else LOG.info("Outgoing connection registered: " + t);
-		}
-		boolean firstConnection = false;
-		synchronized (lock) {
-			Multiset<ContactId> m = contactConnections.get(t);
-			if (m == null) {
-				m = new Multiset<>();
-				contactConnections.put(t, m);
-			}
-			m.add(c);
-			if (contactCounts.add(c) == 1) firstConnection = true;
-		}
-		eventBus.broadcast(new ConnectionOpenedEvent(c, t, incoming));
-		if (firstConnection) {
-			LOG.info("Contact connected");
-			eventBus.broadcast(new ContactConnectedEvent(c));
-		}
-	}
-
-	@Override
-	public void unregisterConnection(ContactId c, TransportId t,
-			boolean incoming) {
-		if (LOG.isLoggable(INFO)) {
-			if (incoming) LOG.info("Incoming connection unregistered: " + t);
-			else LOG.info("Outgoing connection unregistered: " + t);
-		}
-		boolean lastConnection = false;
-		synchronized (lock) {
-			Multiset<ContactId> m = contactConnections.get(t);
-			if (m == null || !m.contains(c))
-				throw new IllegalArgumentException();
-			m.remove(c);
-			if (contactCounts.remove(c) == 0) lastConnection = true;
-		}
-		eventBus.broadcast(new ConnectionClosedEvent(c, t, incoming));
-		if (lastConnection) {
-			LOG.info("Contact disconnected");
-			eventBus.broadcast(new ContactDisconnectedEvent(c));
-		}
-	}
-
-	@Override
-	public Collection<ContactId> getConnectedContacts(TransportId t) {
-		synchronized (lock) {
-			Multiset<ContactId> m = contactConnections.get(t);
-			if (m == null) return Collections.emptyList();
-			List<ContactId> ids = new ArrayList<>(m.keySet());
-			if (LOG.isLoggable(INFO))
-				LOG.info(ids.size() + " contacts connected: " + t);
-			return ids;
-		}
-	}
-
-	@Override
-	public boolean isConnected(ContactId c, TransportId t) {
-		synchronized (lock) {
-			Multiset<ContactId> m = contactConnections.get(t);
-			return m != null && m.contains(c);
-		}
-	}
-
-	@Override
-	public boolean isConnected(ContactId c) {
-		synchronized (lock) {
-			return contactCounts.contains(c);
-		}
-	}
-
-	@Override
-	public boolean registerConnection(PendingContactId p) {
-		boolean added;
-		synchronized (lock) {
-			added = connectedPendingContacts.add(p);
-		}
-		if (added) eventBus.broadcast(new RendezvousConnectionOpenedEvent(p));
-		return added;
-	}
-
-	@Override
-	public void unregisterConnection(PendingContactId p, boolean success) {
-		synchronized (lock) {
-			if (!connectedPendingContacts.remove(p))
-				throw new IllegalArgumentException();
-		}
-		eventBus.broadcast(new RendezvousConnectionClosedEvent(p, success));
-	}
-}

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

@@ -1,13 +1,14 @@
 package org.briarproject.bramble.plugin;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 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.ConnectionManager;
 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;
@@ -18,8 +19,9 @@ 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;
@@ -36,6 +38,7 @@ 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;
@@ -45,6 +48,9 @@ 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.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;
@@ -177,6 +183,26 @@ class PluginManagerImpl implements PluginManager, Service {
 		return supported;
 	}
 
+	@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 class PluginStarter implements Runnable {
 
 		private final Plugin plugin;
@@ -250,7 +276,8 @@ 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;
@@ -278,11 +305,7 @@ class PluginManagerImpl implements PluginManager, Service {
 
 		@Override
 		public void mergeSettings(Settings s) {
-			try {
-				settingsManager.mergeSettings(s, id.getString());
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-			}
+			PluginManagerImpl.this.mergeSettings(s, id.getString());
 		}
 
 		@Override
@@ -295,15 +318,20 @@ 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));
+				}
+			}
 		}
 
 		@Override

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

@@ -3,8 +3,6 @@ package org.briarproject.bramble.plugin;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.PluginConfig;
 import org.briarproject.bramble.api.plugin.PluginManager;
 
@@ -29,20 +27,6 @@ public class PluginModule {
 		return new BackoffFactoryImpl();
 	}
 
-	@Provides
-	@Singleton
-	ConnectionManager provideConnectionManager(
-			ConnectionManagerImpl connectionManager) {
-		return connectionManager;
-	}
-
-	@Provides
-	@Singleton
-	ConnectionRegistry provideConnectionRegistry(
-			ConnectionRegistryImpl connectionRegistry) {
-		return connectionRegistry;
-	}
-
 	@Provides
 	@Singleton
 	PluginManager providePluginManager(LifecycleManager lifecycleManager,

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

@@ -1,6 +1,8 @@
 package org.briarproject.bramble.plugin;
 
 import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.event.ContactAddedEvent;
 import org.briarproject.bramble.api.db.DbException;
@@ -9,8 +11,6 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
@@ -20,8 +20,8 @@ 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;
@@ -98,21 +98,21 @@ class PollerImpl implements Poller, EventListener {
 			ConnectionClosedEvent c = (ConnectionClosedEvent) e;
 			// Reschedule polling, the polling interval may have decreased
 			reschedule(c.getTransportId());
-			if (!c.isIncoming()) {
-				// Connect to the disconnected contact
+			// If an outgoing connection failed, try to reconnect
+			if (!c.isIncoming() && c.isException()) {
 				connectToContact(c.getContactId(), c.getTransportId());
 			}
 		} else if (e instanceof ConnectionOpenedEvent) {
 			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());
 		}
 	}
@@ -215,7 +215,7 @@ class PollerImpl implements Poller, EventListener {
 			Map<ContactId, TransportProperties> remote =
 					transportPropertyManager.getRemoteProperties(t);
 			Collection<ContactId> connected =
-					connectionRegistry.getConnectedContacts(t);
+					connectionRegistry.getConnectedOrBetterContacts(t);
 			Collection<Pair<TransportProperties, ConnectionHandler>>
 					properties = new ArrayList<>();
 			for (Entry<ContactId, TransportProperties> e : remote.entrySet()) {

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

@@ -23,17 +23,9 @@ interface BluetoothConnectionLimiter {
 	boolean canOpenContactConnection();
 
 	/**
-	 * Informs the limiter that a contact connection has been opened. The
-	 * limiter may close the new connection if key agreement is in progress.
-	 * <p/>
-	 * Returns false if the limiter has closed the new connection.
+	 * Informs the limiter that the given connection has been opened.
 	 */
-	boolean contactConnectionOpened(DuplexTransportConnection conn);
-
-	/**
-	 * Informs the limiter that a key agreement connection has been opened.
-	 */
-	void keyAgreementConnectionOpened(DuplexTransportConnection conn);
+	void connectionOpened(DuplexTransportConnection conn);
 
 	/**
 	 * Informs the limiter that the given connection has been closed.

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

@@ -1,46 +1,48 @@
 package org.briarproject.bramble.plugin.bluetooth;
 
+import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
+import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
 
-import java.io.IOException;
-import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.logging.Logger;
 
+import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.logging.Level.INFO;
-import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.plugin.BluetoothConstants.ID;
 
 @NotNullByDefault
 @ThreadSafe
 class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 
 	private static final Logger LOG =
-			Logger.getLogger(BluetoothConnectionLimiterImpl.class.getName());
+			getLogger(BluetoothConnectionLimiterImpl.class.getName());
+
+	private final EventBus eventBus;
 
 	private final Object lock = new Object();
-	// The following are locking: lock
-	private final LinkedList<DuplexTransportConnection> connections =
+	@GuardedBy("lock")
+	private final List<DuplexTransportConnection> connections =
 			new LinkedList<>();
+	@GuardedBy("lock")
 	private boolean keyAgreementInProgress = false;
 
+	BluetoothConnectionLimiterImpl(EventBus eventBus) {
+		this.eventBus = eventBus;
+	}
+
 	@Override
 	public void keyAgreementStarted() {
-		List<DuplexTransportConnection> close;
 		synchronized (lock) {
 			keyAgreementInProgress = true;
-			close = new ArrayList<>(connections);
-			connections.clear();
 		}
-		if (LOG.isLoggable(INFO)) {
-			LOG.info("Key agreement started, closing " + close.size() +
-					" connections");
-		}
-		for (DuplexTransportConnection conn : close) tryToClose(conn);
+		LOG.info("Key agreement started");
+		eventBus.broadcast(new CloseSyncConnectionsEvent(ID));
 	}
 
 	@Override
@@ -65,35 +67,12 @@ class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 	}
 
 	@Override
-	public boolean contactConnectionOpened(DuplexTransportConnection conn) {
-		boolean accept = true;
+	public void connectionOpened(DuplexTransportConnection conn) {
 		synchronized (lock) {
-			if (keyAgreementInProgress) {
-				LOG.info("Refusing contact connection during key agreement");
-				accept = false;
-			} else {
-				LOG.info("Accepting contact connection");
-				connections.add(conn);
-			}
-		}
-		if (!accept) tryToClose(conn);
-		return accept;
-	}
-
-	@Override
-	public void keyAgreementConnectionOpened(DuplexTransportConnection conn) {
-		synchronized (lock) {
-			LOG.info("Accepting key agreement connection");
 			connections.add(conn);
-		}
-	}
-
-	private void tryToClose(DuplexTransportConnection conn) {
-		try {
-			conn.getWriter().dispose(false);
-			conn.getReader().dispose(false, false);
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
+			if (LOG.isLoggable(INFO)) {
+				LOG.info("Connection opened, " + connections.size() + " open");
+			}
 		}
 	}
 
@@ -101,8 +80,9 @@ class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 	public void connectionClosed(DuplexTransportConnection conn) {
 		synchronized (lock) {
 			connections.remove(conn);
-			if (LOG.isLoggable(INFO))
+			if (LOG.isLoggable(INFO)) {
 				LOG.info("Connection closed, " + connections.size() + " open");
+			}
 		}
 	}
 

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

@@ -10,7 +10,9 @@ import org.briarproject.bramble.api.keyagreement.KeyAgreementConnection;
 import org.briarproject.bramble.api.keyagreement.KeyAgreementListener;
 import org.briarproject.bramble.api.keyagreement.event.KeyAgreementListeningEvent;
 import org.briarproject.bramble.api.keyagreement.event.KeyAgreementStoppedListeningEvent;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
@@ -31,26 +33,27 @@ import org.briarproject.bramble.api.settings.event.SettingsUpdatedEvent;
 import java.io.IOException;
 import java.security.SecureRandom;
 import java.util.Collection;
-import java.util.LinkedList;
 import java.util.UUID;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicBoolean;
 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.concurrent.TimeUnit.SECONDS;
 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.TRANSPORT_ID_BLUETOOTH;
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.ID;
-import static org.briarproject.bramble.api.plugin.BluetoothConstants.PREF_BT_ENABLE;
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.PROP_ADDRESS;
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.PROP_UUID;
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.UUID_BYTES;
+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.INACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.STARTING_STOPPING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
@@ -64,27 +67,19 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 	private static final Logger LOG =
 			getLogger(BluetoothPlugin.class.getName());
 
-	/**
-	 * The delay between connection attempts when polling. This reduces
-	 * interference between Bluetooth and wifi.
-	 */
-	private static final long CONNECTION_ATTEMPT_INTERVAL_MS =
-			SECONDS.toMillis(5);
-
 	final BluetoothConnectionLimiter connectionLimiter;
 	final TimeoutMonitor timeoutMonitor;
 
 	private final Executor ioExecutor;
-	private final ScheduledExecutorService scheduler;
 	private final SecureRandom secureRandom;
 	private final Backoff backoff;
 	private final PluginCallback callback;
 	private final int maxLatency, maxIdleTime;
 	private final AtomicBoolean used = new AtomicBoolean(false);
 
-	private volatile boolean running = false, contactConnections = false;
+	protected final PluginState state = new PluginState();
+
 	private volatile String contactConnectionsUuid = null;
-	private volatile SS socket = null;
 
 	abstract void initialiseAdapter() throws IOException;
 
@@ -120,13 +115,11 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 
 	BluetoothPlugin(BluetoothConnectionLimiter connectionLimiter,
 			TimeoutMonitor timeoutMonitor, Executor ioExecutor,
-			ScheduledExecutorService scheduler, SecureRandom secureRandom,
-			Backoff backoff, PluginCallback callback, int maxLatency,
-			int maxIdleTime) {
+			SecureRandom secureRandom, Backoff backoff,
+			PluginCallback callback, int maxLatency, int maxIdleTime) {
 		this.connectionLimiter = connectionLimiter;
 		this.timeoutMonitor = timeoutMonitor;
 		this.ioExecutor = ioExecutor;
-		this.scheduler = scheduler;
 		this.secureRandom = secureRandom;
 		this.backoff = backoff;
 		this.callback = callback;
@@ -138,14 +131,18 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 		LOG.info("Bluetooth enabled");
 		// We may not have been able to get the local address before
 		ioExecutor.execute(this::updateProperties);
-		if (shouldAllowContactConnections()) bind();
+		if (getState() == INACTIVE) bind();
 	}
 
 	void onAdapterDisabled() {
 		LOG.info("Bluetooth disabled");
-		tryToClose(socket);
 		connectionLimiter.allConnectionsClosed();
-		callback.transportDisabled();
+		// The server socket may not have been closed automatically
+		SS ss = state.clearServerSocket();
+		if (ss != null) {
+			LOG.info("Closing server socket");
+			tryToClose(ss);
+		}
 	}
 
 	@Override
@@ -166,31 +163,24 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 	@Override
 	public void start() throws PluginException {
 		if (used.getAndSet(true)) throw new IllegalStateException();
+		Settings settings = callback.getSettings();
+		boolean enabledByUser = settings.getBoolean(PREF_PLUGIN_ENABLE, false);
+		state.setStarted(enabledByUser);
 		try {
 			initialiseAdapter();
 		} catch (IOException e) {
 			throw new PluginException(e);
 		}
 		updateProperties();
-		running = true;
-		loadSettings(callback.getSettings());
-		if (shouldAllowContactConnections()) {
+		if (enabledByUser) {
 			if (isAdapterEnabled()) bind();
 			else enableAdapter();
 		}
 	}
 
-	private void loadSettings(Settings settings) {
-		contactConnections = settings.getBoolean(PREF_BT_ENABLE, false);
-	}
-
-	private boolean shouldAllowContactConnections() {
-		return contactConnections;
-	}
-
 	private void bind() {
 		ioExecutor.execute(() -> {
-			if (!isRunning() || !shouldAllowContactConnections()) return;
+			if (getState() != INACTIVE) return;
 			// Bind a server socket to accept connections from contacts
 			SS ss;
 			try {
@@ -199,14 +189,13 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 				logException(LOG, WARNING, e);
 				return;
 			}
-			if (!isRunning() || !shouldAllowContactConnections()) {
+			if (!state.setServerSocket(ss)) {
+				LOG.info("Closing redundant server socket");
 				tryToClose(ss);
 				return;
 			}
-			socket = ss;
 			backoff.reset();
-			callback.transportEnabled();
-			acceptContactConnections();
+			acceptContactConnections(ss);
 		});
 	}
 
@@ -235,36 +224,39 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 		if (changed) callback.mergeLocalProperties(p);
 	}
 
-	private void acceptContactConnections() {
+	private void acceptContactConnections(SS ss) {
 		while (true) {
 			DuplexTransportConnection conn;
 			try {
-				conn = acceptConnection(socket);
+				conn = acceptConnection(ss);
 			} catch (IOException e) {
-				// This is expected when the socket is closed
-				if (LOG.isLoggable(INFO)) LOG.info(e.toString());
+				// This is expected when the server socket is closed
+				LOG.info("Server socket closed");
+				state.clearServerSocket();
 				return;
 			}
 			LOG.info("Connection received");
-			if (connectionLimiter.contactConnectionOpened(conn)) {
-				backoff.reset();
-				callback.handleConnection(conn);
-			}
-			if (!running) return;
+			connectionLimiter.connectionOpened(conn);
+			backoff.reset();
+			callback.handleConnection(conn);
 		}
 	}
 
 	@Override
 	public void stop() {
-		running = false;
-		tryToClose(socket);
-		callback.transportDisabled();
+		SS ss = state.setStopped();
+		tryToClose(ss);
 		disableAdapterIfEnabledByUs();
 	}
 
 	@Override
-	public boolean isRunning() {
-		return running && isAdapterEnabled();
+	public State getState() {
+		return state.getState();
+	}
+
+	@Override
+	public int getReasonsDisabled() {
+		return state.getReasonsDisabled();
 	}
 
 	@Override
@@ -280,33 +272,23 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 	@Override
 	public void poll(Collection<Pair<TransportProperties, ConnectionHandler>>
 			properties) {
-		if (!isRunning() || !shouldAllowContactConnections()) return;
+		if (getState() != ACTIVE) return;
 		backoff.increment();
-		LinkedList<Pair<TransportProperties, ConnectionHandler>> connectable =
-				new LinkedList<>();
-		for (Pair<TransportProperties, ConnectionHandler> pair : properties) {
-			TransportProperties p = pair.getFirst();
-			if (isNullOrEmpty(p.get(PROP_ADDRESS))) continue;
-			if (isNullOrEmpty(p.get(PROP_UUID))) continue;
-			connectable.add(pair);
+		for (Pair<TransportProperties, ConnectionHandler> p : properties) {
+			connect(p.getFirst(), p.getSecond());
 		}
-		if (!connectable.isEmpty()) poll(connectable);
 	}
 
-	private void poll(LinkedList<Pair<TransportProperties, ConnectionHandler>>
-			connectable) {
+	private void connect(TransportProperties p, ConnectionHandler h) {
+		String address = p.get(PROP_ADDRESS);
+		if (isNullOrEmpty(address)) return;
+		String uuid = p.get(PROP_UUID);
+		if (isNullOrEmpty(uuid)) return;
 		ioExecutor.execute(() -> {
-			if (!isRunning() || !shouldAllowContactConnections()) return;
-			Pair<TransportProperties, ConnectionHandler> pair =
-					connectable.removeFirst();
-			DuplexTransportConnection d = createConnection(pair.getFirst());
+			DuplexTransportConnection d = createConnection(p);
 			if (d != null) {
 				backoff.reset();
-				pair.getSecond().handleConnection(d);
-			}
-			if (!connectable.isEmpty()) {
-				scheduler.schedule(() -> poll(connectable),
-						CONNECTION_ATTEMPT_INTERVAL_MS, MILLISECONDS);
+				h.handleConnection(d);
 			}
 		});
 	}
@@ -344,15 +326,15 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 
 	@Override
 	public DuplexTransportConnection createConnection(TransportProperties p) {
-		if (!isRunning() || !shouldAllowContactConnections()) return null;
+		if (getState() != ACTIVE) return null;
 		if (!connectionLimiter.canOpenContactConnection()) return null;
 		String address = p.get(PROP_ADDRESS);
 		if (isNullOrEmpty(address)) return null;
 		String uuid = p.get(PROP_UUID);
 		if (isNullOrEmpty(uuid)) return null;
 		DuplexTransportConnection conn = connect(address, uuid);
-		if (conn == null) return null;
-		return connectionLimiter.contactConnectionOpened(conn) ? conn : null;
+		if (conn != null) connectionLimiter.connectionOpened(conn);
+		return conn;
 	}
 
 	@Override
@@ -362,7 +344,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 
 	@Override
 	public KeyAgreementListener createKeyAgreementListener(byte[] commitment) {
-		if (!isRunning()) return null;
+		if (getState() != ACTIVE) return null;
 		// No truncation necessary because COMMIT_LENGTH = 16
 		String uuid = UUID.nameUUIDFromBytes(commitment).toString();
 		if (LOG.isLoggable(INFO)) LOG.info("Key agreement UUID " + uuid);
@@ -374,7 +356,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 			logException(LOG, WARNING, e);
 			return null;
 		}
-		if (!isRunning()) {
+		if (getState() != ACTIVE) {
 			tryToClose(ss);
 			return null;
 		}
@@ -388,7 +370,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
 			byte[] commitment, BdfList descriptor) {
-		if (!isRunning()) return null;
+		if (getState() != ACTIVE) return null;
 		// No truncation necessary because COMMIT_LENGTH = 16
 		String uuid = UUID.nameUUIDFromBytes(commitment).toString();
 		DuplexTransportConnection conn;
@@ -408,7 +390,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 				LOG.info("Connecting to key agreement UUID " + uuid);
 			conn = connect(address, uuid);
 		}
-		if (conn != null) connectionLimiter.keyAgreementConnectionOpened(conn);
+		if (conn != null) connectionLimiter.connectionOpened(conn);
 		return conn;
 	}
 
@@ -448,17 +430,17 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 		}
 	}
 
+	@IoExecutor
 	private void onSettingsUpdated(Settings settings) {
-		boolean wasAllowed = shouldAllowContactConnections();
-		loadSettings(settings);
-		boolean isAllowed = shouldAllowContactConnections();
-		if (wasAllowed && !isAllowed) {
-			LOG.info("Contact connections disabled");
-			tryToClose(socket);
-			callback.transportDisabled();
+		boolean enabledByUser = settings.getBoolean(PREF_PLUGIN_ENABLE, false);
+		SS ss = state.setEnabledByUser(enabledByUser);
+		State s = getState();
+		if (ss != null) {
+			LOG.info("Disabled by user, closing server socket");
+			tryToClose(ss);
 			disableAdapterIfEnabledByUs();
-		} else if (!wasAllowed && isAllowed) {
-			LOG.info("Contact connections enabled");
+		} else if (s == INACTIVE) {
+			LOG.info("Enabled by user, opening server socket");
 			if (isAdapterEnabled()) bind();
 			else enableAdapter();
 		}
@@ -477,7 +459,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 		public KeyAgreementConnection accept() throws IOException {
 			DuplexTransportConnection conn = acceptConnection(ss);
 			if (LOG.isLoggable(INFO)) LOG.info(ID + ": Incoming connection");
-			connectionLimiter.keyAgreementConnectionOpened(conn);
+			connectionLimiter.connectionOpened(conn);
 			return new KeyAgreementConnection(conn, ID);
 		}
 
@@ -486,4 +468,70 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 			tryToClose(ss);
 		}
 	}
+
+	@ThreadSafe
+	@NotNullByDefault
+	protected class PluginState {
+
+		@GuardedBy("this")
+		private boolean started = false,
+				stopped = false,
+				enabledByUser = false;
+
+		@GuardedBy("this")
+		@Nullable
+		private SS serverSocket = null;
+
+		synchronized void setStarted(boolean enabledByUser) {
+			started = true;
+			this.enabledByUser = enabledByUser;
+			callback.pluginStateChanged(getState());
+		}
+
+		@Nullable
+		synchronized SS setStopped() {
+			stopped = true;
+			SS ss = serverSocket;
+			serverSocket = null;
+			callback.pluginStateChanged(getState());
+			return ss;
+		}
+
+		@Nullable
+		synchronized SS setEnabledByUser(boolean enabledByUser) {
+			this.enabledByUser = enabledByUser;
+			SS ss = null;
+			if (!enabledByUser) {
+				ss = serverSocket;
+				serverSocket = null;
+			}
+			callback.pluginStateChanged(getState());
+			return ss;
+		}
+
+		synchronized boolean setServerSocket(SS ss) {
+			if (stopped || serverSocket != null) return false;
+			serverSocket = ss;
+			callback.pluginStateChanged(getState());
+			return true;
+		}
+
+		@Nullable
+		synchronized SS clearServerSocket() {
+			SS ss = serverSocket;
+			serverSocket = null;
+			callback.pluginStateChanged(getState());
+			return ss;
+		}
+
+		synchronized State getState() {
+			if (!started || stopped) return STARTING_STOPPING;
+			if (!enabledByUser) return DISABLED;
+			return serverSocket == null ? INACTIVE : ACTIVE;
+		}
+
+		synchronized int getReasonsDisabled() {
+			return getState() == DISABLED ? REASON_USER : 0;
+		}
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/FilePlugin.java

@@ -16,6 +16,7 @@ import java.util.logging.Logger;
 import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.api.plugin.FileConstants.PROP_PATH;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
@@ -45,7 +46,7 @@ abstract class FilePlugin implements SimplexPlugin {
 
 	@Override
 	public TransportConnectionReader createReader(TransportProperties p) {
-		if (!isRunning()) return null;
+		if (getState() != ACTIVE) return null;
 		String path = p.get(PROP_PATH);
 		if (isNullOrEmpty(path)) return null;
 		try {
@@ -60,7 +61,7 @@ abstract class FilePlugin implements SimplexPlugin {
 
 	@Override
 	public TransportConnectionWriter createWriter(TransportProperties p) {
-		if (!isRunning()) return null;
+		if (getState() != ACTIVE) return null;
 		String path = p.get(PROP_PATH);
 		if (isNullOrEmpty(path)) return null;
 		try {

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/LanTcpPlugin.java

@@ -11,10 +11,10 @@ import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.settings.Settings;
-import org.briarproject.bramble.util.IoUtils;
 
 import java.io.IOException;
 import java.net.Inet4Address;
+import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.InterfaceAddress;
@@ -22,8 +22,9 @@ import java.net.ServerSocket;
 import java.net.Socket;
 import java.net.UnknownHostException;
 import java.util.ArrayList;
+import java.util.Deque;
+import java.util.LinkedList;
 import java.util.List;
-import java.util.Random;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
@@ -31,38 +32,48 @@ import javax.annotation.Nullable;
 
 import static java.lang.Integer.parseInt;
 import static java.util.Collections.addAll;
+import static java.util.Collections.emptyList;
 import static java.util.Collections.sort;
 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.TRANSPORT_ID_LAN;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.ID;
+import static org.briarproject.bramble.api.plugin.LanTcpConstants.PREF_IPV6;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.PREF_LAN_IP_PORTS;
+import static org.briarproject.bramble.api.plugin.LanTcpConstants.PROP_IPV6;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.PROP_IP_PORTS;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.PROP_PORT;
+import static org.briarproject.bramble.api.properties.TransportPropertyConstants.MAX_PROPERTY_LENGTH;
 import static org.briarproject.bramble.util.ByteUtils.MAX_16_BIT_UNSIGNED;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubSocketAddress;
+import static org.briarproject.bramble.util.StringUtils.fromHexString;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 import static org.briarproject.bramble.util.StringUtils.join;
+import static org.briarproject.bramble.util.StringUtils.toHexString;
+import static org.briarproject.bramble.util.StringUtils.utf8IsTooLong;
 
 @NotNullByDefault
 class LanTcpPlugin extends TcpPlugin {
 
 	private static final Logger LOG = getLogger(LanTcpPlugin.class.getName());
 
-	private static final int MAX_ADDRESSES = 4;
 	private static final String SEPARATOR = ",";
 
 	/**
 	 * The IP address of an Android device providing a wifi access point.
+	 * <p>
+	 * Most devices use this address, but at least one device (Honor 8A) may
+	 * use other addresses in the range 192.168.43.0/24.
 	 */
-	protected static final InetAddress WIFI_AP_ADDRESS;
+	private static final InetAddress WIFI_AP_ADDRESS;
 
 	/**
 	 * The IP address of an Android device providing a wifi direct
 	 * legacy mode access point.
 	 */
-	protected static final InetAddress WIFI_DIRECT_AP_ADDRESS;
+	private static final InetAddress WIFI_DIRECT_AP_ADDRESS;
 
 	static {
 		try {
@@ -91,29 +102,30 @@ class LanTcpPlugin extends TcpPlugin {
 	public void start() {
 		if (used.getAndSet(true)) throw new IllegalStateException();
 		initialisePortProperty();
-		running = true;
+		Settings settings = callback.getSettings();
+		state.setStarted(settings.getBoolean(PREF_PLUGIN_ENABLE, false));
 		bind();
 	}
 
 	protected void initialisePortProperty() {
 		TransportProperties p = callback.getLocalProperties();
 		if (isNullOrEmpty(p.get(PROP_PORT))) {
-			int port = new Random().nextInt(32768) + 32768;
+			int port = chooseEphemeralPort();
 			p.put(PROP_PORT, String.valueOf(port));
 			callback.mergeLocalProperties(p);
 		}
 	}
 
 	@Override
-	protected List<InetSocketAddress> getLocalSocketAddresses() {
+	protected List<InetSocketAddress> getLocalSocketAddresses(boolean ipv4) {
 		TransportProperties p = callback.getLocalProperties();
 		int preferredPort = parsePortProperty(p.get(PROP_PORT));
 		String oldIpPorts = p.get(PROP_IP_PORTS);
-		List<InetSocketAddress> olds = parseSocketAddresses(oldIpPorts);
+		List<InetSocketAddress> olds = parseIpv4SocketAddresses(oldIpPorts);
 
 		List<InetSocketAddress> locals = new ArrayList<>();
 		List<InetSocketAddress> fallbacks = new ArrayList<>();
-		for (InetAddress local : getUsableLocalInetAddresses()) {
+		for (InetAddress local : getUsableLocalInetAddresses(ipv4)) {
 			// If we've used this address before, try to use the same port
 			int port = preferredPort;
 			for (InetSocketAddress old : olds) {
@@ -139,17 +151,17 @@ class LanTcpPlugin extends TcpPlugin {
 		}
 	}
 
-	private List<InetSocketAddress> parseSocketAddresses(String ipPorts) {
+	private List<InetSocketAddress> parseIpv4SocketAddresses(String ipPorts) {
 		List<InetSocketAddress> addresses = new ArrayList<>();
 		if (isNullOrEmpty(ipPorts)) return addresses;
 		for (String ipPort : ipPorts.split(SEPARATOR)) {
-			InetSocketAddress a = parseSocketAddress(ipPort);
+			InetSocketAddress a = parseIpv4SocketAddress(ipPort);
 			if (a != null) addresses.add(a);
 		}
 		return addresses;
 	}
 
-	protected List<InetAddress> getUsableLocalInetAddresses() {
+	protected List<InetAddress> getUsableLocalInetAddresses(boolean ipv4) {
 		List<InterfaceAddress> ifAddrs =
 				new ArrayList<>(getLocalInterfaceAddresses());
 		// Prefer longer network prefixes
@@ -158,50 +170,74 @@ class LanTcpPlugin extends TcpPlugin {
 		List<InetAddress> addrs = new ArrayList<>();
 		for (InterfaceAddress ifAddr : ifAddrs) {
 			InetAddress addr = ifAddr.getAddress();
-			if (isAcceptableAddress(addr)) addrs.add(addr);
+			if (isAcceptableAddress(addr, ipv4)) addrs.add(addr);
 		}
 		return addrs;
 	}
 
 	@Override
-	protected void setLocalSocketAddress(InetSocketAddress a) {
+	protected void setLocalSocketAddress(InetSocketAddress a, boolean ipv4) {
+		if (ipv4) setLocalIpv4SocketAddress(a);
+		else setLocalIpv6SocketAddress(a);
+	}
+
+	private void setLocalIpv4SocketAddress(InetSocketAddress a) {
 		String ipPort = getIpPortString(a);
+		updateRecentAddresses(PREF_LAN_IP_PORTS, PROP_IP_PORTS, ipPort);
+	}
+
+	private void setLocalIpv6SocketAddress(InetSocketAddress a) {
+		String hex = toHexString(a.getAddress().getAddress());
+		updateRecentAddresses(PREF_IPV6, PROP_IPV6, hex);
+	}
+
+	private void updateRecentAddresses(String settingKey, String propertyKey,
+			String item) {
 		// Get the list of recently used addresses
-		String setting = callback.getSettings().get(PREF_LAN_IP_PORTS);
-		List<String> recent = new ArrayList<>();
-		if (!isNullOrEmpty(setting))
+		String setting = callback.getSettings().get(settingKey);
+		Deque<String> recent = new LinkedList<>();
+		if (!isNullOrEmpty(setting)) {
 			addAll(recent, setting.split(SEPARATOR));
-		// Is the address already in the list?
-		if (recent.remove(ipPort)) {
-			// Move the address to the start of the list
-			recent.add(0, ipPort);
+		}
+		if (recent.remove(item)) {
+			// Move the item to the start of the list
+			recent.addFirst(item);
 			setting = join(recent, SEPARATOR);
 		} else {
-			// Add the address to the start of the list
-			recent.add(0, ipPort);
-			// Drop the least recently used address if the list is full
-			if (recent.size() > MAX_ADDRESSES)
-				recent = recent.subList(0, MAX_ADDRESSES);
+			// Add the item to the start of the list
+			recent.addFirst(item);
+			// Drop items from the end of the list if it's too long to encode
 			setting = join(recent, SEPARATOR);
+			while (utf8IsTooLong(setting, MAX_PROPERTY_LENGTH)) {
+				recent.removeLast();
+				setting = join(recent, SEPARATOR);
+			}
 			// Update the list of addresses shared with contacts
-			List<String> shared = new ArrayList<>(recent);
-			sort(shared);
-			String property = join(shared, SEPARATOR);
 			TransportProperties properties = new TransportProperties();
-			properties.put(PROP_IP_PORTS, property);
+			properties.put(propertyKey, setting);
 			callback.mergeLocalProperties(properties);
 		}
 		// Save the setting
 		Settings settings = new Settings();
-		settings.put(PREF_LAN_IP_PORTS, setting);
+		settings.put(settingKey, setting);
 		callback.mergeSettings(settings);
 	}
 
+	protected boolean isIpv6LinkLocalAddress(InetAddress a) {
+		return a instanceof Inet6Address && a.isLinkLocalAddress();
+	}
+
 	@Override
 	protected List<InetSocketAddress> getRemoteSocketAddresses(
+			TransportProperties p, boolean ipv4) {
+		if (ipv4) return getRemoteIpv4SocketAddresses(p);
+		else return getRemoteIpv6SocketAddresses(p);
+	}
+
+	private List<InetSocketAddress> getRemoteIpv4SocketAddresses(
 			TransportProperties p) {
 		String ipPorts = p.get(PROP_IP_PORTS);
-		List<InetSocketAddress> remotes = parseSocketAddresses(ipPorts);
+		List<InetSocketAddress> remotes = parseIpv4SocketAddresses(ipPorts);
 		int port = parsePortProperty(p.get(PROP_PORT));
 		// If the contact has a preferred port, we can guess their IP:port when
 		// they're providing a wifi access point
@@ -216,20 +252,52 @@ class LanTcpPlugin extends TcpPlugin {
 		return remotes;
 	}
 
-	private boolean isAcceptableAddress(InetAddress a) {
-		// Accept link-local and site-local IPv4 addresses
-		boolean ipv4 = a instanceof Inet4Address;
-		boolean loop = a.isLoopbackAddress();
-		boolean link = a.isLinkLocalAddress();
-		boolean site = a.isSiteLocalAddress();
-		return ipv4 && !loop && (link || site);
+	private List<InetSocketAddress> getRemoteIpv6SocketAddresses(
+			TransportProperties p) {
+		List<InetAddress> addrs = parseIpv6Addresses(p.get(PROP_IPV6));
+		int port = parsePortProperty(p.get(PROP_PORT));
+		if (addrs.isEmpty() || port == 0) return emptyList();
+		List<InetSocketAddress> remotes = new ArrayList<>();
+		for (InetAddress addr : addrs) {
+			remotes.add(new InetSocketAddress(addr, port));
+		}
+		return remotes;
+	}
+
+	private List<InetAddress> parseIpv6Addresses(String property) {
+		if (isNullOrEmpty(property)) return emptyList();
+		try {
+			List<InetAddress> addrs = new ArrayList<>();
+			for (String hex : property.split(SEPARATOR)) {
+				byte[] ip = fromHexString(hex);
+				if (ip.length == 16) addrs.add(InetAddress.getByAddress(ip));
+			}
+			return addrs;
+		} catch (IllegalArgumentException | UnknownHostException e) {
+			return emptyList();
+		}
+	}
+
+	private boolean isAcceptableAddress(InetAddress a, boolean ipv4) {
+		if (ipv4) {
+			// Accept link-local and site-local IPv4 addresses
+			boolean isIpv4 = a instanceof Inet4Address;
+			boolean link = a.isLinkLocalAddress();
+			boolean site = a.isSiteLocalAddress();
+			return isIpv4 && (link || site);
+		} else {
+			// Accept link-local IPv6 addresses
+			return isIpv6LinkLocalAddress(a);
+		}
 	}
 
 	@Override
 	protected boolean isConnectable(InterfaceAddress local,
 			InetSocketAddress remote) {
 		if (remote.getPort() == 0) return false;
-		if (!isAcceptableAddress(remote.getAddress())) return false;
+		InetAddress remoteAddress = remote.getAddress();
+		boolean ipv4 = local.getAddress() instanceof Inet4Address;
+		if (!isAcceptableAddress(remoteAddress, ipv4)) return false;
 		// Try to determine whether the address is on the same LAN as us
 		byte[] localIp = local.getAddress().getAddress();
 		byte[] remoteIp = remote.getAddress().getAddress();
@@ -271,10 +339,10 @@ class LanTcpPlugin extends TcpPlugin {
 			} catch (IOException e) {
 				if (LOG.isLoggable(INFO))
 					LOG.info("Failed to bind " + scrubSocketAddress(addr));
-				tryToClose(ss);
+				tryToClose(ss, LOG, WARNING);
 			}
 		}
-		if (ss == null || !ss.isBound()) {
+		if (ss == null) {
 			LOG.info("Could not bind server socket for key agreement");
 			return null;
 		}
@@ -287,11 +355,18 @@ class LanTcpPlugin extends TcpPlugin {
 		return new LanKeyAgreementListener(descriptor, ss);
 	}
 
+	private List<InetSocketAddress> getLocalSocketAddresses() {
+		List<InetSocketAddress> addrs = new ArrayList<>();
+		addrs.addAll(getLocalSocketAddresses(true));
+		addrs.addAll(getLocalSocketAddresses(false));
+		return addrs;
+	}
+
 	@Override
 	public DuplexTransportConnection createKeyAgreementConnection(
 			byte[] commitment, BdfList descriptor) {
-		if (!isRunning()) return null;
-		ServerSocket ss = socket;
+		ServerSocket ss = state.getServerSocket(true);
+		if (ss == null) return null;
 		InterfaceAddress local = getLocalInterfaceAddress(ss.getInetAddress());
 		if (local == null) {
 			LOG.warning("No interface for key agreement server socket");
@@ -363,7 +438,7 @@ class LanTcpPlugin extends TcpPlugin {
 
 		@Override
 		public void close() {
-			IoUtils.tryToClose(ss, LOG, WARNING);
+			tryToClose(ss, LOG, WARNING);
 		}
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/LanTcpPluginFactory.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.plugin.tcp;
 
+import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
@@ -26,11 +27,13 @@ public class LanTcpPluginFactory implements DuplexPluginFactory {
 	private static final double BACKOFF_BASE = 1.2;
 
 	private final Executor ioExecutor;
+	private final EventBus eventBus;
 	private final BackoffFactory backoffFactory;
 
-	public LanTcpPluginFactory(Executor ioExecutor,
+	public LanTcpPluginFactory(Executor ioExecutor, EventBus eventBus,
 			BackoffFactory backoffFactory) {
 		this.ioExecutor = ioExecutor;
+		this.eventBus = eventBus;
 		this.backoffFactory = backoffFactory;
 	}
 
@@ -48,7 +51,9 @@ public class LanTcpPluginFactory implements DuplexPluginFactory {
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
-		return new LanTcpPlugin(ioExecutor, backoff, callback, MAX_LATENCY,
+		LanTcpPlugin plugin =  new LanTcpPlugin(ioExecutor, backoff, callback, MAX_LATENCY,
 				MAX_IDLE_TIME, CONNECTION_TIMEOUT);
+		eventBus.addListener(plugin);
+		return plugin;
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/PortMapperImpl.java

@@ -54,11 +54,13 @@ class PortMapperImpl implements PortMapper {
 				shutdownManager.addShutdownHook(() -> deleteMapping(port));
 			}
 			String externalString = gateway.getExternalIPAddress();
-			if (LOG.isLoggable(INFO))
-				LOG.info(
-						"External address " + scrubInetAddress(externalString));
-			if (externalString != null)
+			if (externalString == null) {
+				LOG.info("External address not available");
+			} else {
 				external = InetAddress.getByName(externalString);
+				if (LOG.isLoggable(INFO))
+					LOG.info("External address " + scrubInetAddress(external));
+			}
 		} catch (IOException | SAXException e) {
 			logException(LOG, WARNING, e);
 		}

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/TcpPlugin.java

@@ -3,8 +3,12 @@ package org.briarproject.bramble.plugin.tcp;
 import org.briarproject.bramble.PoliteExecutor;
 import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.keyagreement.KeyAgreementListener;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
@@ -14,7 +18,8 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 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.util.IoUtils;
+import org.briarproject.bramble.api.settings.Settings;
+import org.briarproject.bramble.api.settings.event.SettingsUpdatedEvent;
 
 import java.io.IOException;
 import java.net.InetAddress;
@@ -35,19 +40,26 @@ import java.util.logging.Logger;
 import java.util.regex.Pattern;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.Collections.emptyList;
 import static java.util.Collections.list;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.DISABLED;
+import static org.briarproject.bramble.api.plugin.Plugin.State.INACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.STARTING_STOPPING;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubSocketAddress;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
-abstract class TcpPlugin implements DuplexPlugin {
+abstract class TcpPlugin implements DuplexPlugin, EventListener {
 
 	private static final Logger LOG = getLogger(TcpPlugin.class.getName());
 
@@ -60,28 +72,28 @@ abstract class TcpPlugin implements DuplexPlugin {
 	protected final int maxLatency, maxIdleTime;
 	protected final int connectionTimeout, socketTimeout;
 	protected final AtomicBoolean used = new AtomicBoolean(false);
-
-	protected volatile boolean running = false;
-	protected volatile ServerSocket socket = null;
+	protected final PluginState state = new PluginState();
 
 	/**
 	 * Returns zero or more socket addresses on which the plugin should listen,
 	 * in order of preference. At most one of the addresses will be bound.
 	 */
-	protected abstract List<InetSocketAddress> getLocalSocketAddresses();
+	protected abstract List<InetSocketAddress> getLocalSocketAddresses(
+			boolean ipv4);
 
 	/**
 	 * Adds the address on which the plugin is listening to the transport
 	 * properties.
 	 */
-	protected abstract void setLocalSocketAddress(InetSocketAddress a);
+	protected abstract void setLocalSocketAddress(InetSocketAddress a,
+			boolean ipv4);
 
 	/**
 	 * Returns zero or more socket addresses for connecting to a contact with
 	 * the given transport properties.
 	 */
 	protected abstract List<InetSocketAddress> getRemoteSocketAddresses(
-			TransportProperties p);
+			TransportProperties p, boolean ipv4);
 
 	/**
 	 * Returns true if connections to the given address can be attempted.
@@ -118,49 +130,49 @@ abstract class TcpPlugin implements DuplexPlugin {
 	@Override
 	public void start() {
 		if (used.getAndSet(true)) throw new IllegalStateException();
-		running = true;
+		Settings settings = callback.getSettings();
+		state.setStarted(settings.getBoolean(PREF_PLUGIN_ENABLE, false));
 		bind();
 	}
 
 	protected void bind() {
 		bindExecutor.execute(() -> {
-			if (!running) return;
-			if (socket != null && !socket.isClosed()) return;
-			ServerSocket ss = null;
-			for (InetSocketAddress addr : getLocalSocketAddresses()) {
-				try {
-					ss = new ServerSocket();
-					ss.bind(addr);
-					break;
-				} catch (IOException e) {
-					if (LOG.isLoggable(INFO))
-						LOG.info("Failed to bind " + scrubSocketAddress(addr));
-					tryToClose(ss);
-				}
-			}
-			if (ss == null || !ss.isBound()) {
-				LOG.info("Could not bind server socket");
-				return;
-			}
-			if (!running) {
-				tryToClose(ss);
-				return;
-			}
-			socket = ss;
-			backoff.reset();
-			InetSocketAddress local =
-					(InetSocketAddress) ss.getLocalSocketAddress();
-			setLocalSocketAddress(local);
-			if (LOG.isLoggable(INFO))
-				LOG.info("Listening on " + scrubSocketAddress(local));
-			callback.transportEnabled();
-			acceptContactConnections();
+			if (getState() != INACTIVE) return;
+			bind(true);
+			bind(false);
 		});
 	}
 
-	protected void tryToClose(@Nullable ServerSocket ss) {
-		IoUtils.tryToClose(ss, LOG, WARNING);
-		callback.transportDisabled();
+	private void bind(boolean ipv4) {
+		ServerSocket ss = null;
+		for (InetSocketAddress addr : getLocalSocketAddresses(ipv4)) {
+			try {
+				ss = new ServerSocket();
+				ss.bind(addr);
+				break;
+			} catch (IOException e) {
+				if (LOG.isLoggable(INFO))
+					LOG.info("Failed to bind " + scrubSocketAddress(addr));
+				tryToClose(ss, LOG, WARNING);
+			}
+		}
+		if (ss == null) {
+			LOG.info("Could not bind server socket");
+			return;
+		}
+		if (!state.setServerSocket(ss, ipv4)) {
+			LOG.info("Closing redundant server socket");
+			tryToClose(ss, LOG, WARNING);
+			return;
+		}
+		backoff.reset();
+		InetSocketAddress local =
+				(InetSocketAddress) ss.getLocalSocketAddress();
+		setLocalSocketAddress(local, ipv4);
+		if (LOG.isLoggable(INFO))
+			LOG.info("Listening on " + scrubSocketAddress(local));
+		ServerSocket finalSocket = ss;
+		ioExecutor.execute(() -> acceptContactConnections(finalSocket, ipv4));
 	}
 
 	String getIpPortString(InetSocketAddress a) {
@@ -170,20 +182,22 @@ abstract class TcpPlugin implements DuplexPlugin {
 		return addr + ":" + a.getPort();
 	}
 
-	private void acceptContactConnections() {
-		while (isRunning()) {
+	private void acceptContactConnections(ServerSocket ss, boolean ipv4) {
+		while (true) {
 			Socket s;
 			try {
-				s = socket.accept();
+				s = ss.accept();
 				s.setSoTimeout(socketTimeout);
 			} catch (IOException e) {
-				// This is expected when the socket is closed
-				if (LOG.isLoggable(INFO)) LOG.info(e.toString());
+				// This is expected when the server socket is closed
+				LOG.info("Server socket closed");
+				state.clearServerSocket(ss, ipv4);
 				return;
 			}
-			if (LOG.isLoggable(INFO))
+			if (LOG.isLoggable(INFO)) {
 				LOG.info("Connection from " +
 						scrubSocketAddress(s.getRemoteSocketAddress()));
+			}
 			backoff.reset();
 			callback.handleConnection(new TcpTransportConnection(this, s));
 		}
@@ -191,13 +205,17 @@ abstract class TcpPlugin implements DuplexPlugin {
 
 	@Override
 	public void stop() {
-		running = false;
-		tryToClose(socket);
+		for (ServerSocket ss : state.setStopped()) tryToClose(ss, LOG, WARNING);
 	}
 
 	@Override
-	public boolean isRunning() {
-		return running && socket != null && !socket.isClosed();
+	public State getState() {
+		return state.getState();
+	}
+
+	@Override
+	public int getReasonsDisabled() {
+		return state.getReasonsDisabled();
 	}
 
 	@Override
@@ -213,7 +231,7 @@ abstract class TcpPlugin implements DuplexPlugin {
 	@Override
 	public void poll(Collection<Pair<TransportProperties, ConnectionHandler>>
 			properties) {
-		if (!isRunning()) return;
+		if (getState() != ACTIVE) return;
 		backoff.increment();
 		for (Pair<TransportProperties, ConnectionHandler> p : properties) {
 			connect(p.getFirst(), p.getSecond());
@@ -232,14 +250,22 @@ abstract class TcpPlugin implements DuplexPlugin {
 
 	@Override
 	public DuplexTransportConnection createConnection(TransportProperties p) {
-		if (!isRunning()) return null;
-		ServerSocket ss = socket;
+		DuplexTransportConnection c = createConnection(p, true);
+		if (c != null) return c;
+		return createConnection(p, false);
+	}
+
+	@Nullable
+	private DuplexTransportConnection createConnection(TransportProperties p,
+			boolean ipv4) {
+		ServerSocket ss = state.getServerSocket(ipv4);
+		if (ss == null) return null;
 		InterfaceAddress local = getLocalInterfaceAddress(ss.getInetAddress());
 		if (local == null) {
 			LOG.warning("No interface for server socket");
 			return null;
 		}
-		for (InetSocketAddress remote : getRemoteSocketAddresses(p)) {
+		for (InetSocketAddress remote : getRemoteSocketAddresses(p, ipv4)) {
 			// Don't try to connect to our own address
 			if (!canConnectToOwnAddress() &&
 					remote.getAddress().equals(ss.getInetAddress())) {
@@ -264,9 +290,10 @@ abstract class TcpPlugin implements DuplexPlugin {
 					LOG.info("Connected to " + scrubSocketAddress(remote));
 				return new TcpTransportConnection(this, s);
 			} catch (IOException e) {
-				if (LOG.isLoggable(INFO))
+				if (LOG.isLoggable(INFO)) {
 					LOG.info("Could not connect to " +
 							scrubSocketAddress(remote));
+				}
 			}
 		}
 		return null;
@@ -289,8 +316,12 @@ abstract class TcpPlugin implements DuplexPlugin {
 		return new Socket();
 	}
 
+	int chooseEphemeralPort() {
+		return 32768 + (int) (Math.random() * 32768);
+	}
+
 	@Nullable
-	InetSocketAddress parseSocketAddress(String ipPort) {
+	InetSocketAddress parseIpv4SocketAddress(String ipPort) {
 		if (isNullOrEmpty(ipPort)) return null;
 		String[] split = ipPort.split(":");
 		if (split.length != 2) return null;
@@ -301,14 +332,7 @@ abstract class TcpPlugin implements DuplexPlugin {
 			InetAddress a = InetAddress.getByName(addr);
 			int p = Integer.parseInt(port);
 			return new InetSocketAddress(a, p);
-		} catch (UnknownHostException e) {
-			if (LOG.isLoggable(WARNING))
-				// not scrubbing to enable us to find the problem
-				LOG.warning("Invalid address: " + addr);
-			return null;
-		} catch (NumberFormatException e) {
-			if (LOG.isLoggable(WARNING))
-				LOG.warning("Invalid port: " + port);
+		} catch (UnknownHostException | NumberFormatException e) {
 			return null;
 		}
 	}
@@ -366,4 +390,113 @@ abstract class TcpPlugin implements DuplexPlugin {
 			return emptyList();
 		}
 	}
+
+	@Override
+	public void eventOccurred(Event e) {
+		if (e instanceof SettingsUpdatedEvent) {
+			SettingsUpdatedEvent s = (SettingsUpdatedEvent) e;
+			if (s.getNamespace().equals(getId().getString()))
+				ioExecutor.execute(() -> onSettingsUpdated(s.getSettings()));
+		}
+	}
+
+	@IoExecutor
+	private void onSettingsUpdated(Settings settings) {
+		boolean enabledByUser = settings.getBoolean(PREF_PLUGIN_ENABLE, false);
+		List<ServerSocket> toClose = state.setEnabledByUser(enabledByUser);
+		State s = getState();
+		if (!toClose.isEmpty()) {
+			LOG.info("Disabled by user, closing server sockets");
+			for (ServerSocket ss : toClose) tryToClose(ss, LOG, WARNING);
+		} else if (s == INACTIVE) {
+			LOG.info("Enabled by user, opening server sockets");
+			bind();
+		}
+	}
+
+	@ThreadSafe
+	@NotNullByDefault
+	protected class PluginState {
+
+		@GuardedBy("this")
+		private boolean started = false, stopped = false, enabledByUser = false;
+
+		@GuardedBy("this")
+		@Nullable
+		private ServerSocket serverSocketV4 = null, serverSocketV6 = null;
+
+		synchronized void setStarted(boolean enabledByUser) {
+			started = true;
+			this.enabledByUser = enabledByUser;
+			callback.pluginStateChanged(getState());
+		}
+
+		synchronized List<ServerSocket> setStopped() {
+			stopped = true;
+			List<ServerSocket> toClose = clearServerSockets();
+			callback.pluginStateChanged(getState());
+			return toClose;
+		}
+
+		@GuardedBy("this")
+		private List<ServerSocket> clearServerSockets() {
+			List<ServerSocket> toClose = new ArrayList<>(2);
+			if (serverSocketV4 != null) {
+				toClose.add(serverSocketV4);
+				serverSocketV4 = null;
+			}
+			if (serverSocketV6 != null) {
+				toClose.add(serverSocketV6);
+				serverSocketV6 = null;
+			}
+			return toClose;
+		}
+
+		synchronized List<ServerSocket> setEnabledByUser(
+				boolean enabledByUser) {
+			this.enabledByUser = enabledByUser;
+			List<ServerSocket> toClose = enabledByUser
+					? emptyList() : clearServerSockets();
+			callback.pluginStateChanged(getState());
+			return toClose;
+		}
+
+		@Nullable
+		synchronized ServerSocket getServerSocket(boolean ipv4) {
+			return ipv4 ? serverSocketV4 : serverSocketV6;
+		}
+
+		synchronized boolean setServerSocket(ServerSocket ss, boolean ipv4) {
+			if (stopped) return false;
+			if (ipv4) {
+				if (serverSocketV4 != null) return false;
+				serverSocketV4 = ss;
+			} else {
+				if (serverSocketV6 != null) return false;
+				serverSocketV6 = ss;
+			}
+			callback.pluginStateChanged(getState());
+			return true;
+		}
+
+		synchronized void clearServerSocket(ServerSocket ss, boolean ipv4) {
+			if (ipv4) {
+				if (serverSocketV4 == ss) serverSocketV4 = null;
+			} else {
+				if (serverSocketV6 == ss) serverSocketV6 = null;
+			}
+			callback.pluginStateChanged(getState());
+		}
+
+		synchronized State getState() {
+			if (!started || stopped) return STARTING_STOPPING;
+			if (!enabledByUser) return DISABLED;
+			if (serverSocketV4 != null || serverSocketV6 != null) return ACTIVE;
+			return INACTIVE;
+		}
+
+		synchronized int getReasonsDisabled() {
+			return getState() == DISABLED ? REASON_USER : 0;
+		}
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/WanTcpPlugin.java

@@ -43,10 +43,11 @@ class WanTcpPlugin extends TcpPlugin {
 	}
 
 	@Override
-	protected List<InetSocketAddress> getLocalSocketAddresses() {
+	protected List<InetSocketAddress> getLocalSocketAddresses(boolean ipv4) {
+		if (!ipv4) return emptyList();
 		// Use the same address and port as last time if available
 		TransportProperties p = callback.getLocalProperties();
-		InetSocketAddress old = parseSocketAddress(p.get(PROP_IP_PORT));
+		InetSocketAddress old = parseIpv4SocketAddress(p.get(PROP_IP_PORT));
 		List<InetSocketAddress> addrs = new LinkedList<>();
 		for (InetAddress a : getLocalInetAddresses()) {
 			if (isAcceptableAddress(a)) {
@@ -76,14 +77,11 @@ class WanTcpPlugin extends TcpPlugin {
 		return ipv4 && !loop && !link && !site;
 	}
 
-	private int chooseEphemeralPort() {
-		return 32768 + (int) (Math.random() * 32768);
-	}
-
 	@Override
 	protected List<InetSocketAddress> getRemoteSocketAddresses(
-			TransportProperties p) {
-		InetSocketAddress parsed = parseSocketAddress(p.get(PROP_IP_PORT));
+			TransportProperties p, boolean ipv4) {
+		if (!ipv4) return emptyList();
+		InetSocketAddress parsed = parseIpv4SocketAddress(p.get(PROP_IP_PORT));
 		if (parsed == null) return emptyList();
 		return singletonList(parsed);
 	}
@@ -96,7 +94,8 @@ class WanTcpPlugin extends TcpPlugin {
 	}
 
 	@Override
-	protected void setLocalSocketAddress(InetSocketAddress a) {
+	protected void setLocalSocketAddress(InetSocketAddress a, boolean ipv4) {
+		if (!ipv4) throw new AssertionError();
 		if (mappingResult != null && mappingResult.isUsable()) {
 			// Advertise the external address to contacts
 			if (a.equals(mappingResult.getInternal())) {

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/WanTcpPluginFactory.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.plugin.tcp;
 
+import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.lifecycle.ShutdownManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
@@ -27,12 +28,14 @@ public class WanTcpPluginFactory implements DuplexPluginFactory {
 	private static final double BACKOFF_BASE = 1.2;
 
 	private final Executor ioExecutor;
+	private final EventBus eventBus;
 	private final BackoffFactory backoffFactory;
 	private final ShutdownManager shutdownManager;
 
-	public WanTcpPluginFactory(Executor ioExecutor,
+	public WanTcpPluginFactory(Executor ioExecutor, EventBus eventBus,
 			BackoffFactory backoffFactory, ShutdownManager shutdownManager) {
 		this.ioExecutor = ioExecutor;
+		this.eventBus = eventBus;
 		this.backoffFactory = backoffFactory;
 		this.shutdownManager = shutdownManager;
 	}
@@ -51,8 +54,10 @@ public class WanTcpPluginFactory implements DuplexPluginFactory {
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
-		return new WanTcpPlugin(ioExecutor, backoff,
+		WanTcpPlugin plugin = new WanTcpPlugin(ioExecutor, backoff,
 				new PortMapperImpl(shutdownManager), callback, MAX_LATENCY,
 				MAX_IDLE_TIME, CONNECTION_TIMEOUT);
+		eventBus.addListener(plugin);
+		return plugin;
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/tor/CircumventionProvider.java

@@ -17,7 +17,7 @@ public interface CircumventionProvider {
 	String[] BLOCKED = {"CN", "IR", "EG", "BY", "TR", "SY", "VE"};
 
 	/**
-	 * Countries where obfs4 bridge connection are likely to work.
+	 * Countries where obfs4 or meek bridge connections are likely to work.
 	 * Should be a subset of {@link #BLOCKED}.
 	 */
 	String[] BRIDGES = { "CN", "IR", "EG", "BY", "TR", "SY", "VE" };

bramble-core/src/main/java/org/briarproject/bramble/plugin/tor/TorPlugin.java

@@ -15,6 +15,7 @@ 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.NotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
@@ -54,6 +55,9 @@ import java.util.logging.Logger;
 import java.util.regex.Pattern;
 import java.util.zip.ZipInputStream;
 
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
 import javax.net.SocketFactory;
 
 import static java.util.Arrays.asList;
@@ -65,6 +69,11 @@ import static java.util.logging.Logger.getLogger;
 import static net.freehaven.tor.control.TorControlCommands.HS_ADDRESS;
 import static net.freehaven.tor.control.TorControlCommands.HS_PRIVKEY;
 import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+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.ENABLING;
+import static org.briarproject.bramble.api.plugin.Plugin.State.INACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.STARTING_STOPPING;
 import static org.briarproject.bramble.api.plugin.TorConstants.CONTROL_PORT;
 import static org.briarproject.bramble.api.plugin.TorConstants.ID;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_MOBILE;
@@ -76,6 +85,9 @@ import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_ONLY_WHE
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_PORT;
 import static org.briarproject.bramble.api.plugin.TorConstants.PROP_ONION_V2;
 import static org.briarproject.bramble.api.plugin.TorConstants.PROP_ONION_V3;
+import static org.briarproject.bramble.api.plugin.TorConstants.REASON_BATTERY;
+import static org.briarproject.bramble.api.plugin.TorConstants.REASON_COUNTRY_BLOCKED;
+import static org.briarproject.bramble.api.plugin.TorConstants.REASON_MOBILE_DATA;
 import static org.briarproject.bramble.plugin.tor.TorRendezvousCrypto.SEED_BYTES;
 import static org.briarproject.bramble.util.IoUtils.copyAndClose;
 import static org.briarproject.bramble.util.IoUtils.tryToClose;
@@ -113,16 +125,14 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	private final int maxLatency, maxIdleTime, socketTimeout;
 	private final File torDirectory, torFile, geoIpFile, obfs4File, configFile;
 	private final File doneFile, cookieFile;
-	private final ConnectionStatus connectionStatus;
 	private final AtomicBoolean used = new AtomicBoolean(false);
 
-	private volatile ServerSocket socket = null;
+	protected final PluginState state = new PluginState();
+
 	private volatile Socket controlSocket = null;
 	private volatile TorControlConnection controlConnection = null;
 	private volatile Settings settings = null;
 
-	protected volatile boolean running = false;
-
 	protected abstract int getProcessId();
 
 	protected abstract long getLastUpdateTime();
@@ -159,7 +169,6 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		configFile = new File(torDirectory, "torrc");
 		doneFile = new File(torDirectory, "done");
 		cookieFile = new File(torDirectory, ".tor/control_auth_cookie");
-		connectionStatus = new ConnectionStatus();
 		// Don't execute more than one connection status check at a time
 		connectionStatusExecutor =
 				new PoliteExecutor("TorPlugin", ioExecutor, 1);
@@ -190,7 +199,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			}
 		}
 		// Load the settings
-		settings = callback.getSettings();
+		settings = migrateSettings(callback.getSettings());
 		// Install or update the assets if necessary
 		if (!assetsAreUpToDate()) installAssets();
 		if (cookieFile.exists() && !cookieFile.delete())
@@ -258,7 +267,6 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			// Tell Tor to exit when the control connection is closed
 			controlConnection.takeOwnership();
 			controlConnection.resetConf(singletonList(OWNER));
-			running = true;
 			// Register to receive events from the Tor process
 			controlConnection.setEventHandler(this);
 			controlConnection.setEvents(asList(EVENTS));
@@ -266,11 +274,12 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			String phase = controlConnection.getInfo("status/bootstrap-phase");
 			if (phase != null && phase.contains("PROGRESS=100")) {
 				LOG.info("Tor has already bootstrapped");
-				connectionStatus.setBootstrapped();
+				state.setBootstrapped();
 			}
 		} catch (IOException e) {
 			throw new PluginException(e);
 		}
+		state.setStarted();
 		// Check whether we're online
 		updateConnectionStatus(networkManager.getNetworkStatus(),
 				batteryManager.isCharging());
@@ -278,6 +287,18 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		bind();
 	}
 
+	// TODO: Remove after a reasonable migration period (added 2020-06-25)
+	private Settings migrateSettings(Settings settings) {
+		int network = settings.getInt(PREF_TOR_NETWORK,
+				PREF_TOR_NETWORK_AUTOMATIC);
+		if (network == PREF_TOR_NETWORK_NEVER) {
+			settings.putInt(PREF_TOR_NETWORK, PREF_TOR_NETWORK_AUTOMATIC);
+			settings.putBoolean(PREF_PLUGIN_ENABLE, false);
+			callback.mergeSettings(settings);
+		}
+		return settings;
+	}
+
 	private boolean assetsAreUpToDate() {
 		return doneFile.lastModified() > getLastUpdateTime();
 	}
@@ -393,11 +414,11 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 				tryToClose(ss, LOG, WARNING);
 				return;
 			}
-			if (!running) {
+			if (!state.setServerSocket(ss)) {
+				LOG.info("Closing redundant server socket");
 				tryToClose(ss, LOG, WARNING);
 				return;
 			}
-			socket = ss;
 			// Store the port number
 			String localPort = String.valueOf(ss.getLocalPort());
 			Settings s = new Settings();
@@ -412,7 +433,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	private void publishHiddenService(String port) {
-		if (!running) return;
+		if (!state.isTorRunning()) return;
 		LOG.info("Creating hidden service");
 		String privKey = settings.get(HS_PRIVKEY);
 		Map<Integer, String> portLines = singletonMap(80, "127.0.0.1:" + port);
@@ -450,14 +471,15 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	private void acceptContactConnections(ServerSocket ss) {
-		while (running) {
+		while (true) {
 			Socket s;
 			try {
 				s = ss.accept();
 				s.setSoTimeout(socketTimeout);
 			} catch (IOException e) {
-				// This is expected when the socket is closed
-				if (LOG.isLoggable(INFO)) LOG.info(e.toString());
+				// This is expected when the server socket is closed
+				LOG.info("Server socket closed");
+				state.clearServerSocket(ss);
 				return;
 			}
 			LOG.info("Connection received");
@@ -467,10 +489,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	protected void enableNetwork(boolean enable) throws IOException {
-		if (!running) return;
-		connectionStatus.enableNetwork(enable);
+		state.enableNetwork(enable);
 		controlConnection.setConf("DisableNetwork", enable ? "0" : "1");
-		if (!enable) callback.transportDisabled();
 	}
 
 	private void enableBridges(boolean enable, boolean needsMeek)
@@ -494,9 +514,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 	@Override
 	public void stop() {
-		running = false;
-		tryToClose(socket, LOG, WARNING);
-		callback.transportDisabled();
+		ServerSocket ss = state.setStopped();
+		tryToClose(ss, LOG, WARNING);
 		if (controlSocket != null && controlConnection != null) {
 			try {
 				LOG.info("Stopping Tor");
@@ -510,8 +529,13 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	@Override
-	public boolean isRunning() {
-		return running && connectionStatus.isConnected();
+	public State getState() {
+		return state.getState();
+	}
+
+	@Override
+	public int getReasonsDisabled() {
+		return state.getReasonsDisabled();
 	}
 
 	@Override
@@ -527,7 +551,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	@Override
 	public void poll(Collection<Pair<TransportProperties, ConnectionHandler>>
 			properties) {
-		if (!isRunning()) return;
+		if (getState() != ACTIVE) return;
 		backoff.increment();
 		for (Pair<TransportProperties, ConnectionHandler> p : properties) {
 			connect(p.getFirst(), p.getSecond());
@@ -546,7 +570,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 	@Override
 	public DuplexTransportConnection createConnection(TransportProperties p) {
-		if (!isRunning()) return null;
+		if (getState() != ACTIVE) return null;
 		String bestOnion = null;
 		String onion2 = p.get(PROP_ONION_V2);
 		String onion3 = p.get(PROP_ONION_V3);
@@ -634,8 +658,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 								new TorTransportConnection(this, s));
 					}
 				} catch (IOException e) {
-					// This is expected when the socket is closed
-					if (LOG.isLoggable(INFO)) LOG.info(e.toString());
+					// This is expected when the server socket is closed
+					LOG.info("Rendezvous server socket closed");
 				}
 			});
 			Map<Integer, String> portLines =
@@ -663,10 +687,9 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	@Override
 	public void circuitStatus(String status, String id, String path) {
 		if (status.equals("BUILT") &&
-				connectionStatus.getAndSetCircuitBuilt()) {
+				state.getAndSetCircuitBuilt()) {
 			LOG.info("First circuit built");
 			backoff.reset();
-			if (isRunning()) callback.transportEnabled();
 		}
 	}
 
@@ -697,9 +720,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	public void message(String severity, String msg) {
 		if (LOG.isLoggable(INFO)) LOG.info(severity + " " + msg);
 		if (severity.equals("NOTICE") && msg.startsWith("Bootstrapped 100%")) {
-			connectionStatus.setBootstrapped();
+			state.setBootstrapped();
 			backoff.reset();
-			if (isRunning()) callback.transportEnabled();
 		}
 	}
 
@@ -736,7 +758,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	private void disableNetwork() {
 		connectionStatusExecutor.execute(() -> {
 			try {
-				enableNetwork(false);
+				if (state.isTorRunning()) enableNetwork(false);
 			} catch (IOException ex) {
 				logException(LOG, WARNING, ex);
 			}
@@ -746,12 +768,14 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	private void updateConnectionStatus(NetworkStatus status,
 			boolean charging) {
 		connectionStatusExecutor.execute(() -> {
-			if (!running) return;
+			if (!state.isTorRunning()) return;
 			boolean online = status.isConnected();
 			boolean wifi = status.isWifi();
 			String country = locationUtils.getCurrentCountry();
 			boolean blocked =
 					circumventionProvider.isTorProbablyBlocked(country);
+			boolean enabledByUser =
+					settings.getBoolean(PREF_PLUGIN_ENABLE, true);
 			int network = settings.getInt(PREF_TOR_NETWORK,
 					PREF_TOR_NETWORK_AUTOMATIC);
 			boolean useMobile = settings.getBoolean(PREF_TOR_MOBILE, true);
@@ -762,47 +786,70 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 
 			if (LOG.isLoggable(INFO)) {
 				LOG.info("Online: " + online + ", wifi: " + wifi);
-				if ("".equals(country)) LOG.info("Country code unknown");
+				if (country.isEmpty()) LOG.info("Country code unknown");
 				else LOG.info("Country code: " + country);
 				LOG.info("Charging: " + charging);
 			}
 
-			try {
-				if (!online) {
-					LOG.info("Disabling network, device is offline");
-					enableNetwork(false);
-				} else if (!charging && onlyWhenCharging) {
-					LOG.info("Disabling network, device is on battery");
-					enableNetwork(false);
-				} else if (network == PREF_TOR_NETWORK_NEVER ||
-						(!useMobile && !wifi)) {
-					LOG.info("Disabling network, device is using mobile data");
-					enableNetwork(false);
-				} else if (automatic && blocked && !bridgesWork) {
-					LOG.info("Disabling network, country is blocked");
-					enableNetwork(false);
-				} else if (network == PREF_TOR_NETWORK_WITH_BRIDGES ||
-						(automatic && bridgesWork)) {
-					if (circumventionProvider.needsMeek(country)) {
-						LOG.info("Enabling network, using meek bridges");
-						enableBridges(true, true);
+			int reasonsDisabled = 0;
+			boolean enableNetwork = false, enableBridges = false;
+			boolean useMeek = false, enableConnectionPadding = false;
+
+			if (!online) {
+				LOG.info("Disabling network, device is offline");
+			} else {
+				if (!enabledByUser) {
+					LOG.info("User has disabled Tor");
+					reasonsDisabled |= REASON_USER;
+				}
+				if (!charging && onlyWhenCharging) {
+					LOG.info("Configured not to use battery");
+					reasonsDisabled |= REASON_BATTERY;
+				}
+				if (!useMobile && !wifi) {
+					LOG.info("Configured not to use mobile data");
+					reasonsDisabled |= REASON_MOBILE_DATA;
+				}
+				if (automatic && blocked && !bridgesWork) {
+					LOG.info("Country is blocked");
+					reasonsDisabled |= REASON_COUNTRY_BLOCKED;
+				}
+
+				if (reasonsDisabled != 0) {
+					LOG.info("Disabling network due to settings");
+				} else {
+					LOG.info("Enabling network");
+					enableNetwork = true;
+					if (network == PREF_TOR_NETWORK_WITH_BRIDGES ||
+							(automatic && bridgesWork)) {
+						if (circumventionProvider.needsMeek(country)) {
+							LOG.info("Using meek bridges");
+							enableBridges = true;
+							useMeek = true;
+						} else {
+							LOG.info("Using obfs4 bridges");
+							enableBridges = true;
+						}
 					} else {
-						LOG.info("Enabling network, using obfs4 bridges");
-						enableBridges(true, false);
+						LOG.info("Not using bridges");
+					}
+					if (wifi && charging) {
+						LOG.info("Enabling connection padding");
+						enableConnectionPadding = true;
+					} else {
+						LOG.info("Disabling connection padding");
 					}
-					enableNetwork(true);
-				} else {
-					LOG.info("Enabling network, not using bridges");
-					enableBridges(false, false);
-					enableNetwork(true);
 				}
-				if (online && wifi && charging) {
-					LOG.info("Enabling connection padding");
-					enableConnectionPadding(true);
-				} else {
-					LOG.info("Disabling connection padding");
-					enableConnectionPadding(false);
+			}
+
+			state.setReasonsDisabled(reasonsDisabled);
+
+			try {
+				if (enableNetwork) {
+					enableBridges(enableBridges, useMeek);
+					enableConnectionPadding(enableConnectionPadding);
 				}
+				enableNetwork(enableNetwork);
 			} catch (IOException e) {
 				logException(LOG, WARNING, e);
 			}
@@ -810,33 +857,96 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	private void enableConnectionPadding(boolean enable) throws IOException {
-		if (!running) return;
 		controlConnection.setConf("ConnectionPadding", enable ? "1" : "0");
 	}
 
-	private static class ConnectionStatus {
+	@ThreadSafe
+	@NotNullByDefault
+	protected class PluginState {
 
-		// All of the following are locking: this
-		private boolean networkEnabled = false;
-		private boolean bootstrapped = false, circuitBuilt = false;
+		@GuardedBy("this")
+		private boolean started = false,
+				stopped = false,
+				networkInitialised = false,
+				networkEnabled = false,
+				bootstrapped = false,
+				circuitBuilt = false,
+				settingsChecked = false;
 
-		private synchronized void setBootstrapped() {
-			bootstrapped = true;
+		@GuardedBy("this")
+		private int reasonsDisabled = 0;
+
+		@GuardedBy("this")
+		@Nullable
+		private ServerSocket serverSocket = null;
+
+		synchronized void setStarted() {
+			started = true;
+			callback.pluginStateChanged(getState());
 		}
 
-		private synchronized boolean getAndSetCircuitBuilt() {
+		synchronized boolean isTorRunning() {
+			return started && !stopped;
+		}
+
+		@Nullable
+		synchronized ServerSocket setStopped() {
+			stopped = true;
+			ServerSocket ss = serverSocket;
+			serverSocket = null;
+			callback.pluginStateChanged(getState());
+			return ss;
+		}
+
+		synchronized void setBootstrapped() {
+			bootstrapped = true;
+			callback.pluginStateChanged(getState());
+		}
+
+		synchronized boolean getAndSetCircuitBuilt() {
 			boolean firstCircuit = !circuitBuilt;
 			circuitBuilt = true;
+			callback.pluginStateChanged(getState());
 			return firstCircuit;
 		}
 
-		private synchronized void enableNetwork(boolean enable) {
+		synchronized void enableNetwork(boolean enable) {
+			networkInitialised = true;
 			networkEnabled = enable;
 			if (!enable) circuitBuilt = false;
+			callback.pluginStateChanged(getState());
 		}
 
-		private synchronized boolean isConnected() {
-			return networkEnabled && bootstrapped && circuitBuilt;
+		synchronized void setReasonsDisabled(int reasonsDisabled) {
+			settingsChecked = true;
+			this.reasonsDisabled = reasonsDisabled;
+			callback.pluginStateChanged(getState());
+		}
+
+		// Doesn't affect getState()
+		synchronized boolean setServerSocket(ServerSocket ss) {
+			if (stopped || serverSocket != null) return false;
+			serverSocket = ss;
+			return true;
+		}
+
+		// Doesn't affect getState()
+		synchronized void clearServerSocket(ServerSocket ss) {
+			if (serverSocket == ss) serverSocket = null;
+		}
+
+		synchronized State getState() {
+			if (!started || stopped || !settingsChecked) {
+				return STARTING_STOPPING;
+			}
+			if (reasonsDisabled != 0) return DISABLED;
+			if (!networkInitialised) return ENABLING;
+			if (!networkEnabled) return INACTIVE;
+			return bootstrapped && circuitBuilt ? ACTIVE : ENABLING;
+		}
+
+		synchronized int getReasonsDisabled() {
+			return getState() == DISABLED ? reasonsDisabled : 0;
 		}
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/rendezvous/RendezvousPollerImpl.java

@@ -2,6 +2,7 @@ package org.briarproject.bramble.rendezvous;
 
 import org.briarproject.bramble.PoliteExecutor;
 import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.PendingContact;
 import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.contact.PendingContactState;
@@ -23,7 +24,6 @@ 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.ConnectionHandler;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
@@ -31,8 +31,8 @@ import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 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.properties.TransportProperties;
 import org.briarproject.bramble.api.rendezvous.KeyMaterialSource;
 import org.briarproject.bramble.api.rendezvous.RendezvousEndpoint;
@@ -269,11 +269,11 @@ class RendezvousPollerImpl implements RendezvousPoller, Service, EventListener {
 		} else if (e instanceof PendingContactRemovedEvent) {
 			PendingContactRemovedEvent p = (PendingContactRemovedEvent) e;
 			removePendingContactAsync(p.getId());
-		} else if (e instanceof TransportEnabledEvent) {
-			TransportEnabledEvent t = (TransportEnabledEvent) e;
+		} else if (e instanceof TransportActiveEvent) {
+			TransportActiveEvent t = (TransportActiveEvent) e;
 			addTransportAsync(t.getTransportId());
-		} else if (e instanceof TransportDisabledEvent) {
-			TransportDisabledEvent t = (TransportDisabledEvent) e;
+		} else if (e instanceof TransportInactiveEvent) {
+			TransportInactiveEvent t = (TransportInactiveEvent) e;
 			removeTransportAsync(t.getTransportId());
 		} else if (e instanceof RendezvousConnectionOpenedEvent) {
 			RendezvousConnectionOpenedEvent r =

bramble-core/src/main/java/org/briarproject/bramble/reporting/DevReporterImpl.java

@@ -6,7 +6,7 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TorConstants;
-import org.briarproject.bramble.api.plugin.event.TransportEnabledEvent;
+import org.briarproject.bramble.api.plugin.event.TransportActiveEvent;
 import org.briarproject.bramble.api.reporting.DevConfig;
 import org.briarproject.bramble.api.reporting.DevReporter;
 import org.briarproject.bramble.util.IoUtils;
@@ -92,8 +92,8 @@ class DevReporterImpl implements DevReporter, EventListener {
 
 	@Override
 	public void eventOccurred(Event e) {
-		if (e instanceof TransportEnabledEvent) {
-			TransportEnabledEvent t = (TransportEnabledEvent) e;
+		if (e instanceof TransportActiveEvent) {
+			TransportActiveEvent t = (TransportActiveEvent) e;
 			if (t.getTransportId().equals(TorConstants.ID))
 				ioExecutor.execute(this::sendReports);
 		}

bramble-core/src/main/java/org/briarproject/bramble/sync/DuplexOutgoingSession.java

@@ -11,13 +11,17 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.event.LifecycleEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.Offer;
+import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.SyncSession;
 import org.briarproject.bramble.api.sync.Versions;
+import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
 import org.briarproject.bramble.api.sync.event.GroupVisibilityUpdatedEvent;
 import org.briarproject.bramble.api.sync.event.MessageRequestedEvent;
 import org.briarproject.bramble.api.sync.event.MessageSharedEvent;
@@ -35,6 +39,7 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.logging.Logger;
 
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
@@ -71,9 +76,12 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 	private final EventBus eventBus;
 	private final Clock clock;
 	private final ContactId contactId;
+	private final TransportId transportId;
 	private final int maxLatency, maxIdleTime;
 	private final StreamWriter streamWriter;
 	private final SyncRecordWriter recordWriter;
+	@Nullable
+	private final Priority priority;
 	private final BlockingQueue<ThrowingRunnable<IOException>> writerTasks;
 
 	private final AtomicBoolean generateAckQueued = new AtomicBoolean(false);
@@ -86,18 +94,21 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 	private volatile boolean interrupted = false;
 
 	DuplexOutgoingSession(DatabaseComponent db, Executor dbExecutor,
-			EventBus eventBus, Clock clock, ContactId contactId, int maxLatency,
-			int maxIdleTime, StreamWriter streamWriter,
-			SyncRecordWriter recordWriter) {
+			EventBus eventBus, Clock clock, ContactId contactId,
+			TransportId transportId, int maxLatency, int maxIdleTime,
+			StreamWriter streamWriter, SyncRecordWriter recordWriter,
+			@Nullable Priority priority) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.eventBus = eventBus;
 		this.clock = clock;
 		this.contactId = contactId;
+		this.transportId = transportId;
 		this.maxLatency = maxLatency;
 		this.maxIdleTime = maxIdleTime;
 		this.streamWriter = streamWriter;
 		this.recordWriter = recordWriter;
+		this.priority = priority;
 		writerTasks = new LinkedBlockingQueue<>();
 	}
 
@@ -108,6 +119,8 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 		try {
 			// Send our supported protocol versions
 			recordWriter.writeVersions(new Versions(SUPPORTED_VERSIONS));
+			// Send our connection priority, if this is an outgoing connection
+			if (priority != null) recordWriter.writePriority(priority);
 			// Start a query for each type of record
 			generateAck();
 			generateBatch();
@@ -223,6 +236,12 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 		} else if (e instanceof LifecycleEvent) {
 			LifecycleEvent l = (LifecycleEvent) e;
 			if (l.getLifecycleState() == STOPPING) interrupt();
+		} else if (e instanceof CloseSyncConnectionsEvent) {
+			CloseSyncConnectionsEvent c = (CloseSyncConnectionsEvent) e;
+			if (c.getTransportId().equals(transportId)) interrupt();
+		} else if (e instanceof TransportInactiveEvent) {
+			TransportInactiveEvent t = (TransportInactiveEvent) e;
+			if (t.getTransportId().equals(transportId)) interrupt();
 		}
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/sync/IncomingSession.java

@@ -15,6 +15,8 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.Offer;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.api.sync.PriorityHandler;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.SyncSession;
@@ -47,17 +49,19 @@ class IncomingSession implements SyncSession, EventListener {
 	private final EventBus eventBus;
 	private final ContactId contactId;
 	private final SyncRecordReader recordReader;
+	private final PriorityHandler priorityHandler;
 
 	private volatile boolean interrupted = false;
 
 	IncomingSession(DatabaseComponent db, Executor dbExecutor,
 			EventBus eventBus, ContactId contactId,
-			SyncRecordReader recordReader) {
+			SyncRecordReader recordReader, PriorityHandler priorityHandler) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.eventBus = eventBus;
 		this.contactId = contactId;
 		this.recordReader = recordReader;
+		this.priorityHandler = priorityHandler;
 	}
 
 	@IoExecutor
@@ -86,6 +90,9 @@ class IncomingSession implements SyncSession, EventListener {
 				} else if (recordReader.hasVersions()) {
 					Versions v = recordReader.readVersions();
 					dbExecutor.execute(new ReceiveVersions(v));
+				} else if (recordReader.hasPriority()) {
+					Priority p = recordReader.readPriority();
+					priorityHandler.handle(p);
 				} else {
 					// unknown records are ignored in RecordReader#eof()
 					throw new FormatException();

bramble-core/src/main/java/org/briarproject/bramble/sync/SimplexOutgoingSession.java

@@ -11,11 +11,14 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.event.LifecycleEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.SyncSession;
 import org.briarproject.bramble.api.sync.Versions;
+import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
 import org.briarproject.bramble.api.transport.StreamWriter;
 
 import java.io.IOException;
@@ -56,6 +59,7 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private final Executor dbExecutor;
 	private final EventBus eventBus;
 	private final ContactId contactId;
+	private final TransportId transportId;
 	private final int maxLatency;
 	private final StreamWriter streamWriter;
 	private final SyncRecordWriter recordWriter;
@@ -65,12 +69,14 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private volatile boolean interrupted = false;
 
 	SimplexOutgoingSession(DatabaseComponent db, Executor dbExecutor,
-			EventBus eventBus, ContactId contactId, int maxLatency,
-			StreamWriter streamWriter, SyncRecordWriter recordWriter) {
+			EventBus eventBus, ContactId contactId, TransportId transportId,
+			int maxLatency, StreamWriter streamWriter,
+			SyncRecordWriter recordWriter) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.eventBus = eventBus;
 		this.contactId = contactId;
+		this.transportId = transportId;
 		this.maxLatency = maxLatency;
 		this.streamWriter = streamWriter;
 		this.recordWriter = recordWriter;
@@ -123,6 +129,12 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		} else if (e instanceof LifecycleEvent) {
 			LifecycleEvent l = (LifecycleEvent) e;
 			if (l.getLifecycleState() == STOPPING) interrupt();
+		} else if (e instanceof CloseSyncConnectionsEvent) {
+			CloseSyncConnectionsEvent c = (CloseSyncConnectionsEvent) e;
+			if (c.getTransportId().equals(transportId)) interrupt();
+		} else if (e instanceof TransportInactiveEvent) {
+			TransportInactiveEvent t = (TransportInactiveEvent) e;
+			if (t.getTransportId().equals(transportId)) interrupt();
 		}
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/sync/SyncRecordReaderImpl.java

@@ -11,6 +11,7 @@ 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.Offer;
+import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.Versions;
@@ -26,10 +27,12 @@ import javax.annotation.concurrent.NotThreadSafe;
 import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.MESSAGE;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
+import static org.briarproject.bramble.api.sync.RecordTypes.PRIORITY;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
 import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_SUPPORTED_VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
+import static org.briarproject.bramble.api.sync.SyncConstants.PRIORITY_NONCE_BYTES;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
 
 @NotThreadSafe
@@ -48,7 +51,7 @@ class SyncRecordReaderImpl implements SyncRecordReader {
 
 	private static boolean isKnownRecordType(byte type) {
 		return type == ACK || type == MESSAGE || type == OFFER ||
-				type == REQUEST || type == VERSIONS;
+				type == REQUEST || type == VERSIONS || type == PRIORITY;
 	}
 
 	private final MessageFactory messageFactory;
@@ -174,4 +177,23 @@ class SyncRecordReaderImpl implements SyncRecordReader {
 		nextRecord = null;
 		return supported;
 	}
+
+	@Override
+	public boolean hasPriority() throws IOException {
+		return !eof() && getNextRecordType() == PRIORITY;
+	}
+
+	@Override
+	public Priority readPriority() throws IOException {
+		if (!hasPriority()) throw new FormatException();
+		return new Priority(readNonce());
+	}
+
+	private byte[] readNonce() throws IOException {
+		if (nextRecord == null) throw new AssertionError();
+		byte[] payload = nextRecord.getPayload();
+		if (payload.length != PRIORITY_NONCE_BYTES) throw new FormatException();
+		nextRecord = null;
+		return payload;
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/sync/SyncRecordWriterImpl.java

@@ -8,6 +8,7 @@ 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.Offer;
+import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.Versions;
@@ -20,6 +21,7 @@ import javax.annotation.concurrent.NotThreadSafe;
 import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.MESSAGE;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
+import static org.briarproject.bramble.api.sync.RecordTypes.PRIORITY;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
 import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
@@ -73,6 +75,12 @@ class SyncRecordWriterImpl implements SyncRecordWriter {
 		writeRecord(VERSIONS);
 	}
 
+	@Override
+	public void writePriority(Priority p) throws IOException {
+		writer.writeRecord(
+				new Record(PROTOCOL_VERSION, PRIORITY, p.getNonce()));
+	}
+
 	@Override
 	public void flush() throws IOException {
 		writer.flush();

bramble-core/src/main/java/org/briarproject/bramble/sync/SyncSessionFactoryImpl.java

@@ -5,6 +5,9 @@ import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.api.sync.PriorityHandler;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.SyncRecordReaderFactory;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
@@ -18,6 +21,7 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.concurrent.Executor;
 
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
@@ -46,29 +50,32 @@ class SyncSessionFactoryImpl implements SyncSessionFactory {
 	}
 
 	@Override
-	public SyncSession createIncomingSession(ContactId c, InputStream in) {
+	public SyncSession createIncomingSession(ContactId c, InputStream in,
+			PriorityHandler handler) {
 		SyncRecordReader recordReader =
 				recordReaderFactory.createRecordReader(in);
-		return new IncomingSession(db, dbExecutor, eventBus, c, recordReader);
+		return new IncomingSession(db, dbExecutor, eventBus, c, recordReader,
+				handler);
 	}
 
 	@Override
-	public SyncSession createSimplexOutgoingSession(ContactId c,
+	public SyncSession createSimplexOutgoingSession(ContactId c, TransportId t,
 			int maxLatency, StreamWriter streamWriter) {
 		OutputStream out = streamWriter.getOutputStream();
 		SyncRecordWriter recordWriter =
 				recordWriterFactory.createRecordWriter(out);
-		return new SimplexOutgoingSession(db, dbExecutor, eventBus, c,
+		return new SimplexOutgoingSession(db, dbExecutor, eventBus, c, t,
 				maxLatency, streamWriter, recordWriter);
 	}
 
 	@Override
-	public SyncSession createDuplexOutgoingSession(ContactId c, int maxLatency,
-			int maxIdleTime, StreamWriter streamWriter) {
+	public SyncSession createDuplexOutgoingSession(ContactId c, TransportId t,
+			int maxLatency, int maxIdleTime, StreamWriter streamWriter,
+			@Nullable Priority priority) {
 		OutputStream out = streamWriter.getOutputStream();
 		SyncRecordWriter recordWriter =
 				recordWriterFactory.createRecordWriter(out);
-		return new DuplexOutgoingSession(db, dbExecutor, eventBus, clock, c,
-				maxLatency, maxIdleTime, streamWriter, recordWriter);
+		return new DuplexOutgoingSession(db, dbExecutor, eventBus, clock, c, t,
+				maxLatency, maxIdleTime, streamWriter, recordWriter, priority);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/system/SystemClock.java

@@ -12,11 +12,6 @@ public class SystemClock implements Clock {
 		return System.currentTimeMillis();
 	}
 
-	@Override
-	public long nanoTime() {
-		return System.nanoTime();
-	}
-
 	@Override
 	public void sleep(long milliseconds) throws InterruptedException {
 		Thread.sleep(milliseconds);

bramble-core/src/test/java/org/briarproject/bramble/connection/ConnectionRegistryImplTest.java

@@ -0,0 +1,611 @@
+package org.briarproject.bramble.connection;
+
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
+import org.briarproject.bramble.api.connection.InterruptibleConnection;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
+import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
+import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
+import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
+import org.briarproject.bramble.api.sync.Priority;
+import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.jmock.Expectations;
+import org.junit.Test;
+
+import java.util.Collection;
+
+import static java.util.Collections.emptyList;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
+import static org.briarproject.bramble.test.TestUtils.getContactId;
+import static org.briarproject.bramble.test.TestUtils.getRandomId;
+import static org.briarproject.bramble.test.TestUtils.getTransportId;
+import static org.briarproject.bramble.util.StringUtils.fromHexString;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+public class ConnectionRegistryImplTest extends BrambleMockTestCase {
+
+	private final EventBus eventBus = context.mock(EventBus.class);
+	private final PluginConfig pluginConfig = context.mock(PluginConfig.class);
+	private final InterruptibleConnection conn1 =
+			context.mock(InterruptibleConnection.class, "conn1");
+	private final InterruptibleConnection conn2 =
+			context.mock(InterruptibleConnection.class, "conn2");
+	private final InterruptibleConnection conn3 =
+			context.mock(InterruptibleConnection.class, "conn3");
+
+	private final ContactId contactId1 = getContactId();
+	private final ContactId contactId2 = getContactId();
+	private final TransportId transportId1 = getTransportId();
+	private final TransportId transportId2 = getTransportId();
+	private final TransportId transportId3 = getTransportId();
+	private final PendingContactId pendingContactId =
+			new PendingContactId(getRandomId());
+
+	private final Priority low =
+			new Priority(fromHexString("00000000000000000000000000000000"));
+	private final Priority high =
+			new Priority(fromHexString("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"));
+
+	@Test
+	public void testRegisterMultipleConnections() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// The registry should be empty
+		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId1));
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId2));
+		assertEquals(emptyList(), c.getConnectedContacts(transportId3));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId3));
+		assertFalse(c.isConnected(contactId1));
+		assertFalse(c.isConnected(contactId1, transportId1));
+		assertFalse(c.isConnected(contactId1, transportId2));
+		assertFalse(c.isConnected(contactId1, transportId3));
+
+		// Check that a registered connection shows up - this should
+		// broadcast a ConnectionOpenedEvent and a ContactConnectedEvent
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn1);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+		assertTrue(c.isConnected(contactId1));
+		assertTrue(c.isConnected(contactId1, transportId1));
+
+		// Register another connection with the same contact and transport -
+		// this should broadcast a ConnectionOpenedEvent and lookup should be
+		// unaffected
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn2);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+		assertTrue(c.isConnected(contactId1));
+		assertTrue(c.isConnected(contactId1, transportId1));
+
+		// Unregister one of the connections - this should broadcast a
+		// ConnectionClosedEvent and lookup should be unaffected
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
+		}});
+		c.unregisterConnection(contactId1, transportId1, conn1, true, false);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+		assertTrue(c.isConnected(contactId1));
+		assertTrue(c.isConnected(contactId1, transportId1));
+
+		// Unregister the other connection - this should broadcast a
+		// ConnectionClosedEvent and a ContactDisconnectedEvent
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(
+					ContactDisconnectedEvent.class)));
+		}});
+		c.unregisterConnection(contactId1, transportId1, conn2, true, false);
+		context.assertIsSatisfied();
+
+		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId1));
+		assertFalse(c.isConnected(contactId1));
+		assertFalse(c.isConnected(contactId1, transportId1));
+
+		// Try to unregister the connection again - exception should be thrown
+		try {
+			c.unregisterConnection(contactId1, transportId1, conn2,
+					true, false);
+			fail();
+		} catch (IllegalArgumentException expected) {
+			// Expected
+		}
+	}
+
+	@Test
+	public void testRegisterMultipleContacts() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Register two contacts with one transport, then one of the contacts
+		// with a second transport - this should broadcast three
+		// ConnectionOpenedEvents and two ContactConnectedEvents
+		context.checking(new Expectations() {{
+			exactly(3).of(eventBus).broadcast(with(any(
+					ConnectionOpenedEvent.class)));
+			exactly(2).of(eventBus).broadcast(with(any(
+					ContactConnectedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn1);
+		c.registerIncomingConnection(contactId2, transportId1, conn2);
+		c.registerIncomingConnection(contactId2, transportId2, conn3);
+		context.assertIsSatisfied();
+
+		assertTrue(c.isConnected(contactId1));
+		assertTrue(c.isConnected(contactId2));
+
+		assertTrue(c.isConnected(contactId1, transportId1));
+		assertFalse(c.isConnected(contactId1, transportId2));
+
+		assertTrue(c.isConnected(contactId2, transportId1));
+		assertTrue(c.isConnected(contactId2, transportId2));
+
+		Collection<ContactId> connected = c.getConnectedContacts(transportId1);
+		assertEquals(2, connected.size());
+		assertTrue(connected.contains(contactId1));
+		assertTrue(connected.contains(contactId2));
+
+		connected = c.getConnectedOrBetterContacts(transportId1);
+		assertEquals(2, connected.size());
+		assertTrue(connected.contains(contactId1));
+		assertTrue(connected.contains(contactId2));
+
+		assertEquals(singletonList(contactId2),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId2),
+				c.getConnectedOrBetterContacts(transportId2));
+	}
+
+	@Test
+	public void testConnectionsAreNotInterruptedUnlessPriorityIsSet() {
+		// Prefer transport 2 to transport 1
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(
+					singletonMap(transportId1, singletonList(transportId2))));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Connect via transport 1 (worse than 2) with no priority set
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn1);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 2 (better than 1) and set priority to high -
+		// the old connection should not be interrupted, despite using a worse
+		// transport, to remain compatible with old peers
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId2, conn2, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 3 (no preference) and set priority to high -
+		// again, no interruptions are expected
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId3, conn3, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+	}
+
+	@Test
+	public void testNewConnectionIsInterruptedIfOldConnectionUsesBetterTransport() {
+		// Prefer transport 1 to transport 2
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(
+					singletonMap(transportId2, singletonList(transportId1))));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Connect via transport 1 (better than 2) and set priority to low
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn1, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// The contact is not connected via transport 2 but is connected via a
+		// better transport
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 2 (worse than 1) and set priority to high -
+		// the new connection should be interrupted because it uses a worse
+		// transport
+		context.checking(new Expectations() {{
+			oneOf(conn2).interruptOutgoingSession();
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId2, conn2, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 3 (no preference) and set priority to low -
+		// no further interruptions
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId3, conn3, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+
+		// Unregister the interrupted connection (transport 2)
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
+		}});
+		c.unregisterConnection(contactId1, transportId2, conn2, true, false);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// The contact is not connected via transport 2 but is connected via a
+		// better transport
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+	}
+
+	@Test
+	public void testOldConnectionIsInterruptedIfNewConnectionUsesBetterTransport() {
+		// Prefer transport 2 to transport 1
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(
+					singletonMap(transportId1, singletonList(transportId2))));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Connect via transport 1 (worse than 2) and set priority to high
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn1, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(emptyList(), c.getConnectedContacts(transportId2));
+		assertEquals(emptyList(), c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 2 (better than 1) and set priority to low -
+		// the old connection should be interrupted because it uses a worse
+		// transport
+		context.checking(new Expectations() {{
+			oneOf(conn1).interruptOutgoingSession();
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId2, conn2, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		// Connect via transport 3 (no preference) and set priority to high -
+		// no further interruptions
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId3, conn3, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+
+		// Unregister the interrupted connection (transport 1)
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
+		}});
+		c.unregisterConnection(contactId1, transportId1, conn1, true, false);
+		context.assertIsSatisfied();
+
+		// The contact is not connected via transport 1 but is connected via a
+		// better transport
+		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId2));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId2));
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId3));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId3));
+	}
+
+	@Test
+	public void testNewConnectionIsInterruptedIfOldConnectionHasHigherPriority() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Register a connection with high priority
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn1, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Register another connection via the same transport (no priority yet)
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn2);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Set the priority of the second connection to low - the second
+		// connection should be interrupted
+		context.checking(new Expectations() {{
+			oneOf(conn2).interruptOutgoingSession();
+		}});
+		c.setPriority(contactId1, transportId1, conn2, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Register a third connection with low priority - it should also be
+		// interrupted
+		context.checking(new Expectations() {{
+			oneOf(conn3).interruptOutgoingSession();
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn3, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+	}
+
+	@Test
+	public void testOldConnectionIsInterruptedIfNewConnectionHasHigherPriority() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		// Register a connection with low priority
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
+		}});
+		c.registerOutgoingConnection(contactId1, transportId1, conn1, low);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Register another connection via the same transport (no priority yet)
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
+		}});
+		c.registerIncomingConnection(contactId1, transportId1, conn2);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+
+		// Set the priority of the second connection to high - the first
+		// connection should be interrupted
+		context.checking(new Expectations() {{
+			oneOf(conn1).interruptOutgoingSession();
+		}});
+		c.setPriority(contactId1, transportId1, conn2, high);
+		context.assertIsSatisfied();
+
+		assertEquals(singletonList(contactId1),
+				c.getConnectedContacts(transportId1));
+		assertEquals(singletonList(contactId1),
+				c.getConnectedOrBetterContacts(transportId1));
+	}
+
+	@Test
+	public void testRegisterAndUnregisterPendingContacts() {
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getTransportPreferences();
+			will(returnValue(emptyMap()));
+		}});
+
+		ConnectionRegistry c =
+				new ConnectionRegistryImpl(eventBus, pluginConfig);
+
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(
+					RendezvousConnectionOpenedEvent.class)));
+		}});
+		assertTrue(c.registerConnection(pendingContactId));
+		assertFalse(c.registerConnection(pendingContactId)); // Redundant
+		context.assertIsSatisfied();
+
+		context.checking(new Expectations() {{
+			oneOf(eventBus).broadcast(with(any(
+					RendezvousConnectionClosedEvent.class)));
+		}});
+		c.unregisterConnection(pendingContactId, true);
+		context.assertIsSatisfied();
+
+		try {
+			c.unregisterConnection(pendingContactId, true);
+			fail();
+		} catch (IllegalArgumentException expected) {
+			// Expected
+		}
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/contact/ContactExchangeIntegrationTestComponent.java

@@ -2,13 +2,13 @@ package org.briarproject.bramble.contact;
 
 import org.briarproject.bramble.BrambleCoreEagerSingletons;
 import org.briarproject.bramble.BrambleCoreModule;
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.test.BrambleCoreIntegrationTestModule;
 
 import java.util.concurrent.Executor;

bramble-core/src/test/java/org/briarproject/bramble/db/JdbcDatabaseTest.java

@@ -2420,11 +2420,6 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 			return time;
 		}
 
-		@Override
-		public long nanoTime() {
-			return time * 1_000_000;
-		}
-
 		@Override
 		public void sleep(long milliseconds) throws InterruptedException {
 			Thread.sleep(milliseconds);

bramble-core/src/test/java/org/briarproject/bramble/io/TimeoutInputStreamTest.java

@@ -36,7 +36,7 @@ public class TimeoutInputStreamTest extends BrambleTestCase {
 		in = new UnresponsiveInputStream();
 		listenerCalled = new AtomicBoolean(false);
 		stream = new TimeoutInputStream(new SettableClock(time), in,
-				TIMEOUT_MS * 1_000_000, stream -> listenerCalled.set(true));
+				TIMEOUT_MS, stream -> listenerCalled.set(true));
 		readReturned = new CountDownLatch(1);
 	}
 

bramble-core/src/test/java/org/briarproject/bramble/plugin/ConnectionRegistryImplTest.java

@@ -1,149 +0,0 @@
-package org.briarproject.bramble.plugin;
-
-import org.briarproject.bramble.api.contact.ContactId;
-import org.briarproject.bramble.api.contact.PendingContactId;
-import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
-import org.briarproject.bramble.api.plugin.TransportId;
-import org.briarproject.bramble.api.plugin.event.ConnectionClosedEvent;
-import org.briarproject.bramble.api.plugin.event.ConnectionOpenedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
-import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedEvent;
-import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
-import org.briarproject.bramble.test.BrambleMockTestCase;
-import org.jmock.Expectations;
-import org.junit.Test;
-
-import java.util.Collection;
-
-import static java.util.Collections.emptyList;
-import static java.util.Collections.singletonList;
-import static org.briarproject.bramble.test.TestUtils.getContactId;
-import static org.briarproject.bramble.test.TestUtils.getRandomId;
-import static org.briarproject.bramble.test.TestUtils.getTransportId;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
-
-public class ConnectionRegistryImplTest extends BrambleMockTestCase {
-
-	private final EventBus eventBus = context.mock(EventBus.class);
-
-	private final ContactId contactId = getContactId();
-	private final ContactId contactId1 = getContactId();
-	private final TransportId transportId = getTransportId();
-	private final TransportId transportId1 = getTransportId();
-	private final PendingContactId pendingContactId =
-			new PendingContactId(getRandomId());
-
-	@Test
-	public void testRegisterAndUnregister() {
-		ConnectionRegistry c = new ConnectionRegistryImpl(eventBus);
-
-		// The registry should be empty
-		assertEquals(emptyList(), c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-
-		// Check that a registered connection shows up - this should
-		// broadcast a ConnectionOpenedEvent and a ContactConnectedEvent
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
-			oneOf(eventBus).broadcast(with(any(ContactConnectedEvent.class)));
-		}});
-		c.registerConnection(contactId, transportId, true);
-		assertEquals(singletonList(contactId),
-				c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-		context.assertIsSatisfied();
-
-		// Register an identical connection - this should broadcast a
-		// ConnectionOpenedEvent and lookup should be unaffected
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(ConnectionOpenedEvent.class)));
-		}});
-		c.registerConnection(contactId, transportId, true);
-		assertEquals(singletonList(contactId),
-				c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-		context.assertIsSatisfied();
-
-		// Unregister one of the connections - this should broadcast a
-		// ConnectionClosedEvent and lookup should be unaffected
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
-		}});
-		c.unregisterConnection(contactId, transportId, true);
-		assertEquals(singletonList(contactId),
-				c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-		context.assertIsSatisfied();
-
-		// Unregister the other connection - this should broadcast a
-		// ConnectionClosedEvent and a ContactDisconnectedEvent
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(ConnectionClosedEvent.class)));
-			oneOf(eventBus).broadcast(with(any(
-					ContactDisconnectedEvent.class)));
-		}});
-		c.unregisterConnection(contactId, transportId, true);
-		assertEquals(emptyList(), c.getConnectedContacts(transportId));
-		assertEquals(emptyList(), c.getConnectedContacts(transportId1));
-		context.assertIsSatisfied();
-
-		// Try to unregister the connection again - exception should be thrown
-		try {
-			c.unregisterConnection(contactId, transportId, true);
-			fail();
-		} catch (IllegalArgumentException expected) {
-			// Expected
-		}
-
-		// Register both contacts with one transport, one contact with both -
-		// this should broadcast three ConnectionOpenedEvents and two
-		// ContactConnectedEvents
-		context.checking(new Expectations() {{
-			exactly(3).of(eventBus).broadcast(with(any(
-					ConnectionOpenedEvent.class)));
-			exactly(2).of(eventBus).broadcast(with(any(
-					ContactConnectedEvent.class)));
-		}});
-		c.registerConnection(contactId, transportId, true);
-		c.registerConnection(contactId1, transportId, true);
-		c.registerConnection(contactId1, transportId1, true);
-		Collection<ContactId> connected = c.getConnectedContacts(transportId);
-		assertEquals(2, connected.size());
-		assertTrue(connected.contains(contactId));
-		assertTrue(connected.contains(contactId1));
-		assertEquals(singletonList(contactId1),
-				c.getConnectedContacts(transportId1));
-	}
-
-	@Test
-	public void testRegisterAndUnregisterPendingContacts() {
-		ConnectionRegistry c = new ConnectionRegistryImpl(eventBus);
-
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(
-					RendezvousConnectionOpenedEvent.class)));
-		}});
-		assertTrue(c.registerConnection(pendingContactId));
-		assertFalse(c.registerConnection(pendingContactId)); // Redundant
-		context.assertIsSatisfied();
-
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(
-					RendezvousConnectionClosedEvent.class)));
-		}});
-		c.unregisterConnection(pendingContactId, true);
-		context.assertIsSatisfied();
-
-		try {
-			c.unregisterConnection(pendingContactId, true);
-			fail();
-		} catch (IllegalArgumentException expected) {
-			// Expected
-		}
-	}
-}

bramble-core/src/test/java/org/briarproject/bramble/plugin/PluginManagerImplTest.java

@@ -1,7 +1,7 @@
 package org.briarproject.bramble.plugin;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.PluginConfig;
 import org.briarproject.bramble.api.plugin.PluginException;

bramble-core/src/test/java/org/briarproject/bramble/plugin/PollerImplTest.java

@@ -1,10 +1,10 @@
 package org.briarproject.bramble.plugin;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.event.ContactAddedEvent;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
@@ -13,8 +13,8 @@ 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;
@@ -157,7 +157,21 @@ public class PollerImplTest extends BrambleMockTestCase {
 	}
 
 	@Test
-	public void testRescheduleAndReconnectOnConnectionClosed()
+	public void testRescheduleOnOutgoingConnectionClosed() {
+		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
+
+		context.checking(new Expectations() {{
+			allowing(plugin).getId();
+			will(returnValue(transportId));
+		}});
+		expectReschedule(plugin);
+
+		poller.eventOccurred(new ConnectionClosedEvent(contactId, transportId,
+				false, false));
+	}
+
+	@Test
+	public void testRescheduleAndReconnectOnOutgoingConnectionFailed()
 			throws Exception {
 		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
 		DuplexTransportConnection duplexConnection =
@@ -166,45 +180,40 @@ public class PollerImplTest extends BrambleMockTestCase {
 		context.checking(new Expectations() {{
 			allowing(plugin).getId();
 			will(returnValue(transportId));
-			// reschedule()
-			// Get the plugin
-			oneOf(pluginManager).getPlugin(transportId);
-			will(returnValue(plugin));
-			// The plugin supports polling
-			oneOf(plugin).shouldPoll();
-			will(returnValue(true));
-			// Get the plugin
-			oneOf(pluginManager).getPlugin(transportId);
-			will(returnValue(plugin));
-			// The plugin supports polling
-			oneOf(plugin).shouldPoll();
-			will(returnValue(true));
-			// Schedule the next poll
-			oneOf(plugin).getPollingInterval();
-			will(returnValue(pollingInterval));
-			oneOf(clock).currentTimeMillis();
-			will(returnValue(now));
-			oneOf(scheduler).schedule(with(any(Runnable.class)),
-					with((long) pollingInterval), with(MILLISECONDS));
-			will(returnValue(future));
-			// connectToContact()
-			// Check whether the contact is already connected
-			oneOf(connectionRegistry).isConnected(contactId, transportId);
-			will(returnValue(false));
-			// Get the transport properties
-			oneOf(transportPropertyManager).getRemoteProperties(contactId,
-					transportId);
-			will(returnValue(properties));
-			// Connect to the contact
-			oneOf(plugin).createConnection(properties);
-			will(returnValue(duplexConnection));
-			// Pass the connection to the connection manager
-			oneOf(connectionManager).manageOutgoingConnection(contactId,
-					transportId, duplexConnection);
 		}});
+		expectReschedule(plugin);
+		expectReconnect(plugin, duplexConnection);
 
 		poller.eventOccurred(new ConnectionClosedEvent(contactId, transportId,
-				false));
+				false, true));
+	}
+
+	@Test
+	public void testRescheduleOnIncomingConnectionClosed() {
+		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
+
+		context.checking(new Expectations() {{
+			allowing(plugin).getId();
+			will(returnValue(transportId));
+		}});
+		expectReschedule(plugin);
+
+		poller.eventOccurred(new ConnectionClosedEvent(contactId, transportId,
+				true, false));
+	}
+
+	@Test
+	public void testRescheduleOnIncomingConnectionFailed() {
+		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
+
+		context.checking(new Expectations() {{
+			allowing(plugin).getId();
+			will(returnValue(transportId));
+		}});
+		expectReschedule(plugin);
+
+		poller.eventOccurred(new ConnectionClosedEvent(contactId, transportId,
+				true, false));
 	}
 
 	@Test
@@ -322,7 +331,7 @@ public class PollerImplTest extends BrambleMockTestCase {
 	}
 
 	@Test
-	public void testPollsOnTransportEnabled() throws Exception {
+	public void testPollsOnTransportActivated() throws Exception {
 		DuplexPlugin plugin = context.mock(DuplexPlugin.class);
 
 		context.checking(new Expectations() {{
@@ -354,14 +363,14 @@ public class PollerImplTest extends BrambleMockTestCase {
 			// Get the transport properties and connected contacts
 			oneOf(transportPropertyManager).getRemoteProperties(transportId);
 			will(returnValue(singletonMap(contactId, properties)));
-			oneOf(connectionRegistry).getConnectedContacts(transportId);
+			oneOf(connectionRegistry).getConnectedOrBetterContacts(transportId);
 			will(returnValue(emptyList()));
 			// Poll the plugin
 			oneOf(plugin).poll(with(collectionOf(
 					pairOf(equal(properties), any(ConnectionHandler.class)))));
 		}});
 
-		poller.eventOccurred(new TransportEnabledEvent(transportId));
+		poller.eventOccurred(new TransportActiveEvent(transportId));
 	}
 
 	@Test
@@ -397,16 +406,16 @@ public class PollerImplTest extends BrambleMockTestCase {
 			// Get the transport properties and connected contacts
 			oneOf(transportPropertyManager).getRemoteProperties(transportId);
 			will(returnValue(singletonMap(contactId, properties)));
-			oneOf(connectionRegistry).getConnectedContacts(transportId);
+			oneOf(connectionRegistry).getConnectedOrBetterContacts(transportId);
 			will(returnValue(singletonList(contactId)));
 			// All contacts are connected, so don't poll the plugin
 		}});
 
-		poller.eventOccurred(new TransportEnabledEvent(transportId));
+		poller.eventOccurred(new TransportActiveEvent(transportId));
 	}
 
 	@Test
-	public void testCancelsPollingOnTransportDisabled() {
+	public void testCancelsPollingOnTransportDeactivated() {
 		Plugin plugin = context.mock(Plugin.class);
 
 		context.checking(new Expectations() {{
@@ -424,11 +433,55 @@ public class PollerImplTest extends BrambleMockTestCase {
 			oneOf(scheduler).schedule(with(any(Runnable.class)), with(0L),
 					with(MILLISECONDS));
 			will(returnValue(future));
-			// The plugin is disabled before the task runs - cancel the task
+			// The plugin is deactivated before the task runs - cancel the task
 			oneOf(future).cancel(false);
 		}});
 
-		poller.eventOccurred(new TransportEnabledEvent(transportId));
-		poller.eventOccurred(new TransportDisabledEvent(transportId));
+		poller.eventOccurred(new TransportActiveEvent(transportId));
+		poller.eventOccurred(new TransportInactiveEvent(transportId));
+	}
+
+	private void expectReschedule(Plugin plugin) {
+		context.checking(new Expectations() {{
+			// Get the plugin
+			oneOf(pluginManager).getPlugin(transportId);
+			will(returnValue(plugin));
+			// The plugin supports polling
+			oneOf(plugin).shouldPoll();
+			will(returnValue(true));
+			// Schedule the next poll
+			oneOf(plugin).getPollingInterval();
+			will(returnValue(pollingInterval));
+			oneOf(clock).currentTimeMillis();
+			will(returnValue(now));
+			oneOf(scheduler).schedule(with(any(Runnable.class)),
+					with((long) pollingInterval), with(MILLISECONDS));
+			will(returnValue(future));
+		}});
+	}
+
+	private void expectReconnect(DuplexPlugin plugin,
+			DuplexTransportConnection duplexConnection) throws Exception {
+		context.checking(new Expectations() {{
+			// Get the plugin
+			oneOf(pluginManager).getPlugin(transportId);
+			will(returnValue(plugin));
+			// The plugin supports polling
+			oneOf(plugin).shouldPoll();
+			will(returnValue(true));
+			// Check whether the contact is already connected
+			oneOf(connectionRegistry).isConnected(contactId, transportId);
+			will(returnValue(false));
+			// Get the transport properties
+			oneOf(transportPropertyManager).getRemoteProperties(contactId,
+					transportId);
+			will(returnValue(properties));
+			// Connect to the contact
+			oneOf(plugin).createConnection(properties);
+			will(returnValue(duplexConnection));
+			// Pass the connection to the connection manager
+			oneOf(connectionManager).manageOutgoingConnection(contactId,
+					transportId, duplexConnection);
+		}});
 	}
 }

bramble-core/src/test/java/org/briarproject/bramble/plugin/tcp/LanTcpPluginTest.java

@@ -4,6 +4,7 @@ import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.keyagreement.KeyAgreementListener;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Backoff;
+import org.briarproject.bramble.api.plugin.Plugin.State;
 import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
 import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
@@ -31,6 +32,7 @@ import static java.util.concurrent.Executors.newCachedThreadPool;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.COMMIT_LENGTH;
 import static org.briarproject.bramble.api.keyagreement.KeyAgreementConstants.TRANSPORT_ID_LAN;
+import static org.briarproject.bramble.api.plugin.Plugin.PREF_PLUGIN_ENABLE;
 import static org.briarproject.bramble.plugin.tcp.LanTcpPlugin.areAddressesInSameNetwork;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -302,10 +304,15 @@ public class LanTcpPluginTest extends BrambleTestCase {
 		private final CountDownLatch propertiesLatch = new CountDownLatch(2);
 		private final CountDownLatch connectionsLatch = new CountDownLatch(1);
 		private final TransportProperties local = new TransportProperties();
+		private final Settings settings = new Settings();
+
+		private Callback() {
+			settings.putBoolean(PREF_PLUGIN_ENABLE, true);
+		}
 
 		@Override
 		public Settings getSettings() {
-			return new Settings();
+			return settings;
 		}
 
 		@Override
@@ -324,11 +331,7 @@ public class LanTcpPluginTest extends BrambleTestCase {
 		}
 
 		@Override
-		public void transportEnabled() {
-		}
-
-		@Override
-		public void transportDisabled() {
+		public void pluginStateChanged(State newState) {
 		}
 
 		@Override

bramble-core/src/test/java/org/briarproject/bramble/rendezvous/RendezvousPollerImplTest.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.rendezvous;
 
+import org.briarproject.bramble.api.connection.ConnectionManager;
 import org.briarproject.bramble.api.contact.PendingContact;
 import org.briarproject.bramble.api.contact.PendingContactState;
 import org.briarproject.bramble.api.contact.event.PendingContactAddedEvent;
@@ -13,12 +14,11 @@ import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
-import org.briarproject.bramble.api.plugin.ConnectionManager;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
-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.properties.TransportProperties;
 import org.briarproject.bramble.api.rendezvous.KeyMaterialSource;
 import org.briarproject.bramble.api.rendezvous.RendezvousEndpoint;
@@ -178,10 +178,10 @@ public class RendezvousPollerImplTest extends BrambleMockTestCase {
 		rendezvousPoller.startService();
 		context.assertIsSatisfied();
 
-		// Enable the transport - no endpoints should be created yet
+		// Activate the transport - no endpoints should be created yet
 		expectGetPlugin();
 
-		rendezvousPoller.eventOccurred(new TransportEnabledEvent(transportId));
+		rendezvousPoller.eventOccurred(new TransportActiveEvent(transportId));
 		context.assertIsSatisfied();
 
 		// Add the pending contact - endpoint should be created and polled
@@ -212,8 +212,8 @@ public class RendezvousPollerImplTest extends BrambleMockTestCase {
 				new PendingContactRemovedEvent(pendingContact.getId()));
 		context.assertIsSatisfied();
 
-		// Disable the transport - endpoint is already closed
-		rendezvousPoller.eventOccurred(new TransportDisabledEvent(transportId));
+		// Deactivate the transport - endpoint is already closed
+		rendezvousPoller.eventOccurred(new TransportInactiveEvent(transportId));
 	}
 
 	@Test
@@ -230,10 +230,10 @@ public class RendezvousPollerImplTest extends BrambleMockTestCase {
 		rendezvousPoller.startService();
 		context.assertIsSatisfied();
 
-		// Enable the transport - no endpoints should be created yet
+		// Activate the transport - no endpoints should be created yet
 		expectGetPlugin();
 
-		rendezvousPoller.eventOccurred(new TransportEnabledEvent(transportId));
+		rendezvousPoller.eventOccurred(new TransportActiveEvent(transportId));
 		context.assertIsSatisfied();
 
 		// Add the pending contact - endpoint should be created and polled
@@ -269,12 +269,12 @@ public class RendezvousPollerImplTest extends BrambleMockTestCase {
 				new PendingContactRemovedEvent(pendingContact.getId()));
 		context.assertIsSatisfied();
 
-		// Disable the transport - endpoint is already closed
-		rendezvousPoller.eventOccurred(new TransportDisabledEvent(transportId));
+		// Deactivate the transport - endpoint is already closed
+		rendezvousPoller.eventOccurred(new TransportInactiveEvent(transportId));
 	}
 
 	@Test
-	public void testCreatesAndClosesEndpointsWhenTransportIsEnabledAndDisabled()
+	public void testCreatesAndClosesEndpointsWhenTransportIsActivatedAndDeactivated()
 			throws Exception {
 		long beforeExpiry = pendingContact.getTimestamp();
 
@@ -292,19 +292,19 @@ public class RendezvousPollerImplTest extends BrambleMockTestCase {
 				new PendingContactAddedEvent(pendingContact));
 		context.assertIsSatisfied();
 
-		// Enable the transport - endpoint should be created
+		// Activate the transport - endpoint should be created
 		expectGetPlugin();
 		expectCreateEndpoint();
 		expectStateChangedEvent(WAITING_FOR_CONNECTION);
 
-		rendezvousPoller.eventOccurred(new TransportEnabledEvent(transportId));
+		rendezvousPoller.eventOccurred(new TransportActiveEvent(transportId));
 		context.assertIsSatisfied();
 
-		// Disable the transport - endpoint should be closed
+		// Deactivate the transport - endpoint should be closed
 		expectCloseEndpoint();
 		expectStateChangedEvent(OFFLINE);
 
-		rendezvousPoller.eventOccurred(new TransportDisabledEvent(transportId));
+		rendezvousPoller.eventOccurred(new TransportInactiveEvent(transportId));
 		context.assertIsSatisfied();
 
 		// Remove the pending contact - endpoint is already closed

bramble-core/src/test/java/org/briarproject/bramble/sync/SimplexOutgoingSessionTest.java

@@ -4,6 +4,7 @@ import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
@@ -23,6 +24,7 @@ import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
 import static org.briarproject.bramble.test.TestUtils.getContactId;
 import static org.briarproject.bramble.test.TestUtils.getMessage;
 import static org.briarproject.bramble.test.TestUtils.getRandomId;
+import static org.briarproject.bramble.test.TestUtils.getTransportId;
 
 public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 
@@ -36,14 +38,15 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 
 	private final Executor dbExecutor = new ImmediateExecutor();
 	private final ContactId contactId = getContactId();
+	private final TransportId transportId = getTransportId();
 	private final Message message = getMessage(new GroupId(getRandomId()));
 	private final MessageId messageId = message.getId();
 
 	@Test
 	public void testNothingToSend() throws Exception {
 		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
-				dbExecutor, eventBus, contactId, MAX_LATENCY, streamWriter,
-				recordWriter);
+				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
+				streamWriter, recordWriter);
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction noMsgTxn = new Transaction(null, false);
 
@@ -76,8 +79,8 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 	public void testSomethingToSend() throws Exception {
 		Ack ack = new Ack(singletonList(messageId));
 		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
-				dbExecutor, eventBus, contactId, MAX_LATENCY, streamWriter,
-				recordWriter);
+				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
+				streamWriter, recordWriter);
 		Transaction ackTxn = new Transaction(null, false);
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction msgTxn = new Transaction(null, false);

bramble-core/src/test/java/org/briarproject/bramble/sync/SyncRecordReaderImplTest.java

@@ -8,6 +8,7 @@ import org.briarproject.bramble.api.record.RecordReader;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.Offer;
+import org.briarproject.bramble.api.sync.Priority;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.Versions;
@@ -24,11 +25,14 @@ import javax.annotation.Nullable;
 import static org.briarproject.bramble.api.record.Record.MAX_RECORD_PAYLOAD_BYTES;
 import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
+import static org.briarproject.bramble.api.sync.RecordTypes.PRIORITY;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
 import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_SUPPORTED_VERSIONS;
+import static org.briarproject.bramble.api.sync.SyncConstants.PRIORITY_NONCE_BYTES;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
+import static org.briarproject.bramble.test.TestUtils.getRandomBytes;
 import static org.briarproject.bramble.test.TestUtils.getRandomId;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
@@ -119,6 +123,31 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 		reader.readVersions();
 	}
 
+	@Test(expected = FormatException.class)
+	public void testFormatExceptionIfPriorityNonceIsTooSmall()
+			throws Exception {
+		expectReadRecord(createPriority(PRIORITY_NONCE_BYTES - 1));
+
+		reader.readPriority();
+	}
+
+	@Test(expected = FormatException.class)
+	public void testFormatExceptionIfPriorityNonceIsTooLarge()
+			throws Exception {
+		expectReadRecord(createPriority(PRIORITY_NONCE_BYTES + 1));
+
+		reader.readPriority();
+	}
+
+	@Test
+	public void testNoFormatExceptionIfPriorityNonceIsCorrectSize()
+			throws Exception {
+		expectReadRecord(createPriority(PRIORITY_NONCE_BYTES));
+
+		Priority priority = reader.readPriority();
+		assertEquals(PRIORITY_NONCE_BYTES, priority.getNonce().length);
+	}
+
 	@Test
 	public void testEofReturnsTrueWhenAtEndOfStream() throws Exception {
 		expectReadRecord(createAck());
@@ -173,6 +202,11 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 		return new Record(PROTOCOL_VERSION, VERSIONS, payload);
 	}
 
+	private Record createPriority(int nonceBytes) {
+		byte[] payload = getRandomBytes(nonceBytes);
+		return new Record(PROTOCOL_VERSION, PRIORITY, payload);
+	}
+
 	private byte[] createPayload() throws Exception {
 		ByteArrayOutputStream payload = new ByteArrayOutputStream();
 		while (payload.size() + UniqueId.LENGTH <= MAX_RECORD_PAYLOAD_BYTES) {

bramble-core/src/test/java/org/briarproject/bramble/test/TestPluginConfigModule.java

@@ -10,12 +10,15 @@ import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 
 import java.util.Collection;
+import java.util.List;
+import java.util.Map;
 
 import javax.annotation.Nullable;
 
 import dagger.Module;
 import dagger.Provides;
 
+import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonList;
 import static org.briarproject.bramble.test.TestUtils.getTransportId;
 
@@ -85,6 +88,12 @@ public class TestPluginConfigModule {
 			public boolean shouldPoll() {
 				return false;
 			}
+
+			@Override
+			public Map<TransportId, List<TransportId>> getTransportPreferences() {
+				return emptyMap();
+			}
+
 		};
 		return pluginConfig;
 	}

bramble-java/src/main/java/org/briarproject/bramble/plugin/DesktopPluginModule.java

@@ -6,11 +6,13 @@ import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.ShutdownManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.BackoffFactory;
+import org.briarproject.bramble.api.plugin.BluetoothConstants;
+import org.briarproject.bramble.api.plugin.LanTcpConstants;
 import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.reliability.ReliabilityLayerFactory;
-import org.briarproject.bramble.api.system.Scheduler;
 import org.briarproject.bramble.plugin.bluetooth.JavaBluetoothPluginFactory;
 import org.briarproject.bramble.plugin.modem.ModemPluginFactory;
 import org.briarproject.bramble.plugin.tcp.LanTcpPluginFactory;
@@ -18,33 +20,34 @@ import org.briarproject.bramble.plugin.tcp.WanTcpPluginFactory;
 
 import java.security.SecureRandom;
 import java.util.Collection;
+import java.util.List;
+import java.util.Map;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 
 import dagger.Module;
 import dagger.Provides;
 
 import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
+import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
 
 @Module
 public class DesktopPluginModule extends PluginModule {
 
 	@Provides
 	PluginConfig getPluginConfig(@IoExecutor Executor ioExecutor,
-			@Scheduler ScheduledExecutorService scheduler,
 			SecureRandom random, BackoffFactory backoffFactory,
 			ReliabilityLayerFactory reliabilityFactory,
 			ShutdownManager shutdownManager, EventBus eventBus,
 			TimeoutMonitor timeoutMonitor) {
 		DuplexPluginFactory bluetooth = new JavaBluetoothPluginFactory(
-				ioExecutor, scheduler, random, eventBus, timeoutMonitor,
-				backoffFactory);
+				ioExecutor, random, eventBus, timeoutMonitor, backoffFactory);
 		DuplexPluginFactory modem = new ModemPluginFactory(ioExecutor,
 				reliabilityFactory);
-		DuplexPluginFactory lan = new LanTcpPluginFactory(ioExecutor,
+		DuplexPluginFactory lan = new LanTcpPluginFactory(ioExecutor, eventBus,
 				backoffFactory);
-		DuplexPluginFactory wan = new WanTcpPluginFactory(ioExecutor,
+		DuplexPluginFactory wan = new WanTcpPluginFactory(ioExecutor, eventBus,
 				backoffFactory, shutdownManager);
 		Collection<DuplexPluginFactory> duplex =
 				asList(bluetooth, modem, lan, wan);
@@ -65,6 +68,13 @@ public class DesktopPluginModule extends PluginModule {
 			public boolean shouldPoll() {
 				return true;
 			}
+
+			@Override
+			public Map<TransportId, List<TransportId>> getTransportPreferences() {
+				// Prefer LAN to Bluetooth
+				return singletonMap(BluetoothConstants.ID,
+						singletonList(LanTcpConstants.ID));
+			}
 		};
 		return pluginConfig;
 	}

bramble-java/src/main/java/org/briarproject/bramble/plugin/bluetooth/JavaBluetoothPlugin.java

@@ -10,7 +10,6 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import java.io.IOException;
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
@@ -37,11 +36,10 @@ class JavaBluetoothPlugin extends BluetoothPlugin<StreamConnectionNotifier> {
 
 	JavaBluetoothPlugin(BluetoothConnectionLimiter connectionManager,
 			TimeoutMonitor timeoutMonitor, Executor ioExecutor,
-			ScheduledExecutorService scheduler, SecureRandom secureRandom,
-			Backoff backoff, PluginCallback callback, int maxLatency,
-			int maxIdleTime) {
-		super(connectionManager, timeoutMonitor, ioExecutor, scheduler,
-				secureRandom, backoff, callback, maxLatency, maxIdleTime);
+			SecureRandom secureRandom, Backoff backoff,
+			PluginCallback callback, int maxLatency, int maxIdleTime) {
+		super(connectionManager, timeoutMonitor, ioExecutor, secureRandom,
+				backoff, callback, maxLatency, maxIdleTime);
 	}
 
 	@Override

bramble-java/src/main/java/org/briarproject/bramble/plugin/bluetooth/JavaBluetoothPluginFactory.java

@@ -12,7 +12,6 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 
 import javax.annotation.concurrent.Immutable;
 
@@ -29,18 +28,15 @@ public class JavaBluetoothPluginFactory implements DuplexPluginFactory {
 	private static final double BACKOFF_BASE = 1.2;
 
 	private final Executor ioExecutor;
-	private final ScheduledExecutorService scheduler;
 	private final SecureRandom secureRandom;
 	private final EventBus eventBus;
 	private final TimeoutMonitor timeoutMonitor;
 	private final BackoffFactory backoffFactory;
 
 	public JavaBluetoothPluginFactory(Executor ioExecutor,
-			ScheduledExecutorService scheduler, SecureRandom secureRandom,
-			EventBus eventBus, TimeoutMonitor timeoutMonitor,
-			BackoffFactory backoffFactory) {
+			SecureRandom secureRandom, EventBus eventBus,
+			TimeoutMonitor timeoutMonitor, BackoffFactory backoffFactory) {
 		this.ioExecutor = ioExecutor;
-		this.scheduler = scheduler;
 		this.secureRandom = secureRandom;
 		this.eventBus = eventBus;
 		this.timeoutMonitor = timeoutMonitor;
@@ -60,12 +56,12 @@ public class JavaBluetoothPluginFactory implements DuplexPluginFactory {
 	@Override
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		BluetoothConnectionLimiter connectionLimiter =
-				new BluetoothConnectionLimiterImpl();
+				new BluetoothConnectionLimiterImpl(eventBus);
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		JavaBluetoothPlugin plugin = new JavaBluetoothPlugin(connectionLimiter,
-				timeoutMonitor, ioExecutor, scheduler, secureRandom, backoff,
-				callback, MAX_LATENCY, MAX_IDLE_TIME);
+				timeoutMonitor, ioExecutor, secureRandom, backoff, callback,
+				MAX_LATENCY, MAX_IDLE_TIME);
 		eventBus.addListener(plugin);
 		return plugin;
 	}

bramble-java/src/main/java/org/briarproject/bramble/plugin/modem/ModemPlugin.java

@@ -4,6 +4,7 @@ import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.keyagreement.KeyAgreementListener;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.ConnectionHandler;
 import org.briarproject.bramble.api.plugin.PluginCallback;
@@ -23,9 +24,16 @@ import java.util.Collection;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
 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.State.ACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ENABLING;
+import static org.briarproject.bramble.api.plugin.Plugin.State.INACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.STARTING_STOPPING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
@@ -44,8 +52,8 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 	private final PluginCallback callback;
 	private final int maxLatency;
 	private final AtomicBoolean used = new AtomicBoolean(false);
+	private final PluginState state = new PluginState();
 
-	private volatile boolean running = false;
 	private volatile Modem modem = null;
 
 	ModemPlugin(ModemFactory modemFactory, SerialPortList serialPortList,
@@ -75,6 +83,7 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 	@Override
 	public void start() throws PluginException {
 		if (used.getAndSet(true)) throw new IllegalStateException();
+		state.setStarted();
 		for (String portName : serialPortList.getPortNames()) {
 			if (LOG.isLoggable(INFO))
 				LOG.info("Trying to initialise modem on " + portName);
@@ -83,18 +92,20 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 				if (!modem.start()) continue;
 				if (LOG.isLoggable(INFO))
 					LOG.info("Initialised modem on " + portName);
-				running = true;
+				state.setInitialised();
 				return;
 			} catch (IOException e) {
 				logException(LOG, WARNING, e);
 			}
 		}
+		LOG.warning("Failed to initialised modem");
+		state.setFailed();
 		throw new PluginException();
 	}
 
 	@Override
 	public void stop() {
-		running = false;
+		state.setStopped();
 		if (modem != null) {
 			try {
 				modem.stop();
@@ -105,8 +116,13 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 	}
 
 	@Override
-	public boolean isRunning() {
-		return running;
+	public State getState() {
+		return state.getState();
+	}
+
+	@Override
+	public int getReasonsDisabled() {
+		return 0;
 	}
 
 	@Override
@@ -125,8 +141,8 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 		throw new UnsupportedOperationException();
 	}
 
-	private boolean resetModem() {
-		if (!running) return false;
+	private void resetModem() {
+		if (getState() != ACTIVE) return;
 		for (String portName : serialPortList.getPortNames()) {
 			if (LOG.isLoggable(INFO))
 				LOG.info("Trying to initialise modem on " + portName);
@@ -135,18 +151,18 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 				if (!modem.start()) continue;
 				if (LOG.isLoggable(INFO))
 					LOG.info("Initialised modem on " + portName);
-				return true;
+				return;
 			} catch (IOException e) {
 				logException(LOG, WARNING, e);
 			}
 		}
-		running = false;
-		return false;
+		LOG.warning("Failed to initialise modem");
+		state.setFailed();
 	}
 
 	@Override
 	public DuplexTransportConnection createConnection(TransportProperties p) {
-		if (!running) return null;
+		if (getState() != ACTIVE) return null;
 		// Get the ISO 3166 code for the caller's country
 		String fromIso = callback.getLocalProperties().get("iso3166");
 		if (isNullOrEmpty(fromIso)) return null;
@@ -232,4 +248,41 @@ class ModemPlugin implements DuplexPlugin, Modem.Callback {
 			if (exception) resetModem();
 		}
 	}
+
+	@ThreadSafe
+	@NotNullByDefault
+	private class PluginState {
+
+		@GuardedBy("this")
+		private boolean started = false,
+				stopped = false,
+				initialised = false,
+				failed = false;
+
+		private synchronized void setStarted() {
+			started = true;
+			callback.pluginStateChanged(getState());
+		}
+
+		private synchronized void setStopped() {
+			stopped = true;
+			callback.pluginStateChanged(getState());
+		}
+
+		private synchronized void setInitialised() {
+			initialised = true;
+			callback.pluginStateChanged(getState());
+		}
+
+		private synchronized void setFailed() {
+			failed = true;
+			callback.pluginStateChanged(getState());
+		}
+
+		private State getState() {
+			if (!started || stopped) return STARTING_STOPPING;
+			if (failed) return INACTIVE;
+			return initialised ? ACTIVE : ENABLING;
+		}
+	}
 }

bramble-java/src/test/java/org/briarproject/bramble/plugin/modem/ModemPluginTest.java

@@ -9,6 +9,8 @@ import org.junit.Test;
 
 import java.io.IOException;
 
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ENABLING;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 
@@ -33,6 +35,7 @@ public class ModemPluginTest extends BrambleMockTestCase {
 	@Test
 	public void testModemCreation() throws Exception {
 		context.checking(new Expectations() {{
+			oneOf(callback).pluginStateChanged(ENABLING);
 			oneOf(serialPortList).getPortNames();
 			will(returnValue(new String[] {"foo", "bar", "baz"}));
 			// First call to createModem() returns false
@@ -50,6 +53,7 @@ public class ModemPluginTest extends BrambleMockTestCase {
 			will(returnValue(modem));
 			oneOf(modem).start();
 			will(returnValue(true));
+			oneOf(callback).pluginStateChanged(ACTIVE);
 		}});
 
 		plugin.start();
@@ -65,12 +69,14 @@ public class ModemPluginTest extends BrambleMockTestCase {
 
 		context.checking(new Expectations() {{
 			// start()
+			oneOf(callback).pluginStateChanged(ENABLING);
 			oneOf(serialPortList).getPortNames();
 			will(returnValue(new String[] {"foo"}));
 			oneOf(modemFactory).createModem(plugin, "foo");
 			will(returnValue(modem));
 			oneOf(modem).start();
 			will(returnValue(true));
+			oneOf(callback).pluginStateChanged(ACTIVE);
 			// createConnection()
 			oneOf(callback).getLocalProperties();
 			will(returnValue(local));
@@ -93,12 +99,14 @@ public class ModemPluginTest extends BrambleMockTestCase {
 
 		context.checking(new Expectations() {{
 			// start()
+			oneOf(callback).pluginStateChanged(ENABLING);
 			oneOf(serialPortList).getPortNames();
 			will(returnValue(new String[] {"foo"}));
 			oneOf(modemFactory).createModem(plugin, "foo");
 			will(returnValue(modem));
 			oneOf(modem).start();
 			will(returnValue(true));
+			oneOf(callback).pluginStateChanged(ACTIVE);
 			// createConnection()
 			oneOf(callback).getLocalProperties();
 			will(returnValue(local));
@@ -121,12 +129,14 @@ public class ModemPluginTest extends BrambleMockTestCase {
 
 		context.checking(new Expectations() {{
 			// start()
+			oneOf(callback).pluginStateChanged(ENABLING);
 			oneOf(serialPortList).getPortNames();
 			will(returnValue(new String[] {"foo"}));
 			oneOf(modemFactory).createModem(plugin, "foo");
 			will(returnValue(modem));
 			oneOf(modem).start();
 			will(returnValue(true));
+			oneOf(callback).pluginStateChanged(ACTIVE);
 			// createConnection()
 			oneOf(callback).getLocalProperties();
 			will(returnValue(local));

bramble-java/src/test/java/org/briarproject/bramble/plugin/tor/BridgeTest.java

@@ -32,6 +32,7 @@ import javax.net.SocketFactory;
 import static java.util.Collections.singletonList;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
 import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
 import static org.briarproject.bramble.test.TestUtils.getTestDirectory;
 import static org.briarproject.bramble.test.TestUtils.isOptionalTestEnabled;
@@ -141,10 +142,10 @@ public class BridgeTest extends BrambleTestCase {
 			plugin.start();
 			long start = clock.currentTimeMillis();
 			while (clock.currentTimeMillis() - start < TIMEOUT) {
-				if (plugin.isRunning()) return;
+				if (plugin.getState() == ACTIVE) return;
 				clock.sleep(500);
 			}
-			if (!plugin.isRunning()) {
+			if (plugin.getState() != ACTIVE) {
 				fail("Could not connect to Tor within timeout.");
 			}
 		} finally {

bramble-java/src/test/java/org/briarproject/bramble/plugin/tor/TestPluginCallback.java

@@ -1,6 +1,7 @@
 package org.briarproject.bramble.plugin.tor;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.Plugin.State;
 import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
 import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
@@ -30,11 +31,7 @@ public class TestPluginCallback implements PluginCallback {
 	}
 
 	@Override
-	public void transportEnabled() {
-	}
-
-	@Override
-	public void transportDisabled() {
+	public void pluginStateChanged(State state) {
 	}
 
 	@Override

briar-android/src/androidTestScreenshot/java/org/briarproject/briar/android/ScreenshotTest.java

@@ -3,7 +3,7 @@ package org.briarproject.briar.android;
 import android.app.Activity;
 import android.util.Log;
 
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.briar.api.test.TestDataCreator;
 import org.junit.ClassRule;

briar-android/src/androidTestScreenshot/java/org/briarproject/briar/android/SetupDataTest.java

@@ -120,7 +120,8 @@ public class SetupDataTest extends ScreenshotTest {
 
 		// TODO add messages
 
-		connectionRegistry.registerConnection(bob.getId(), ID, true);
+		connectionRegistry.registerIncomingConnection(bob.getId(), ID, () -> {
+		});
 	}
 
 }

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

@@ -7,6 +7,7 @@ import org.briarproject.bramble.BrambleCoreModule;
 import org.briarproject.bramble.account.BriarAccountModule;
 import org.briarproject.bramble.api.FeatureFlags;
 import org.briarproject.bramble.api.account.AccountManager;
+import org.briarproject.bramble.api.connection.ConnectionRegistry;
 import org.briarproject.bramble.api.contact.ContactExchangeManager;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.crypto.CryptoExecutor;
@@ -19,7 +20,6 @@ import org.briarproject.bramble.api.keyagreement.PayloadEncoder;
 import org.briarproject.bramble.api.keyagreement.PayloadParser;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.PluginManager;
 import org.briarproject.bramble.api.settings.SettingsManager;
 import org.briarproject.bramble.api.system.AndroidExecutor;